Review ArticleEnabling 4-Lane Based 400 G Client-Side Transmission Linkswith MultiCAP Modulation

Anna Tatarczak1 Miguel Iglesias Olmedo12 Tianjian Zuo3 Jose Estaran1

Jesper Bevensee Jensen1 Xiaogeng Xu3 and Idelfonso Tafur Monroy1

1DTU Fotonik Technical University of Denmark Building 343 2800 Kongens Lyngby Denmark2Optics Division Royal Institute of Technology Electrum 229 164 40 Kista Sweden3Transmission Technology Research Department Huawei Technologies Co Ltd Shenzhen 518129 China

Correspondence should be addressed to Anna Tatarczak atatfotonikdtudk

Received 9 May 2015 Revised 15 July 2015 Accepted 22 July 2015

Academic Editor Jose Luıs Santos

Copyright copy 2015 Anna Tatarczak et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

We propose a uniform solution for a future client-side 400G Ethernet standard based on MultiCAP advanced modulation formatintensity modulation and direct detection It employs 4 local area networks-wavelength division multiplexing (LAN-WDM) lanesin 1300 nmwavelength band andparallel optics links based on vertical cavity surface emitting lasers (VCSELs) in 850 nmwavelengthband Total bit rate of 432Gbps is transmitted over unamplified 20 km standard single mode fiber link and over 40 km link withsemiconductor optical amplifier 704Gbs transmission over 100m of OM3 multimode fiber using off-the-shelf 850 nm VCSELwith 101 GHz 3 dB bandwidth is demonstrated indicating the feasibility of achieving 100Gbs per lane with a single 25GHzVCSELIn this review paper we introduce and present in one place the benefits of MultiCAP as versatile scheme for use in a number ofclient-side scenarios short range long range and extended range

1 Introduction

Ever growing video-rich Ethernet traffic on the client-sideoptical networks calls for high-speed cost-effective opticaltransport data links Standardization of client-side opticaldata links is critical to ensure compatibility and interoper-ability of telecom and datacom equipment from differentvendors As depicted in Figure 1 the IEEE standardizationbody classifies the client-side links in three categories shortrange (SR) long range (LR) and extended range (ER) SRlinks which cover up to 100m are usually employed in datacenters and central offices LR links cover up to 20 km andare typically used to privately connect buildings of the samecompany or institution ER links cover up to 40 km and aretypically used to provide connectivity to customer-premisesequipment (CPE) and for metro applications The currentwork of the 400Gbps Ethernet Study Group [1] and the widerresearch community focuses on these three scenarios [2] Anoptical intensity modulationdirect detection (IMDD) linkoffering 400Gbps capacity with use of advanced modulationformats is an attractive and easily adaptable solution for

client-side links such as inter- and intradata center intercon-nects

The client-side links presented in this work are based onthe multiband and multilevel approach to carrierless ampli-tude phase (CAP) modulation MultiCAP [3] In this reviewpaper we demonstrate the flexibility of the IMDDMultiCAPbased solutions for a SR 100m link [4] a LR 20 km linkand an ER 40 km link [5] A SR client-side link that achieveserror-free 657Gbps over a 100m multimode fiber (MMF)OM3 using an 850 nm vertical cavity surface-emitting laser(VCSEL) is presented Furthermore two IMDDLAN-WDM432Gbps links are described an unamplified 20 km linkfor the LR scenario and semiconductor optical amplifier(SOA) based 40 km link for the ER scenario Four-lane LAN-WDM with 108Gbps per lane is obtained using 4 externallymodulated lasers (EMLs) in the O-band

Figure 2 summarizes the capacity per lane reported atthe considered transmission distances for several modulationformats The short range (SR) area of Figure 2 shows thehighest error-free bit rates achieved for 850 nm vertical cav-ity surface-emitting laser (VCSEL) based links Bit rate of

Hindawi Publishing CorporationAdvances in Optical TechnologiesVolume 2015 Article ID 935309 9 pageshttpdxdoiorg1011552015935309

2 Advances in Optical Technologies

Rack Rack

Data center 2

Short range Long range

Campus

Extended range

MetroaggregationData center 1

1mndash100m MMF 1kmndash20km SSMF 20kmndash40km SSMF

Figure 1 Scenario of client-side optical transmission links for shortrange (SR) long range (LR) and extended range (ER)

120

100

80

60

40

20

0

120

100

80

60

40

20

0

SR LR ER

[4][4]

[10]

[6][6]

[5] [5]

[7] [12][11]

[13]

[14]

[15][16]

0 10 15 20 25 30 35 4050 100

Capa

city

per

lane

(Gbp

s)

Transmission distance (m) Transmission distance (km)

NRZ4-PAM8-PAM

DMTCAP-64MultiCAP

WDM based 400Gbps demonstrated

Figure 2 State-of-the-art summary capacity per lane versus trans-mitted distance for the following modulation formats Nonreturnto Zero (NRZ) pulse amplitude modulation (PAM) discrete mul-titone (DMT) carrierless amplitude phase (CAP) and multibandcarrierless amplitude phase (MultiCAP) demonstrated in literatureapproaches to 400Gbps systems based on IMDD WDM areindicated by the black circle

70Gbps over 2m OM4 MMF was achieved using 4-levelpulse amplitude modulation (4-PAM) [6] 64Gbps over 57mOM2 using Nonreturn to Zero (NRZ) [7] and 56Gbps over50m OM4 using 8-PAM [6] All of these require very fastelectrical interfaces and suffer from low tolerance to modaldispersion compared to pass-band modulation formats [8]Using discrete multitone (DMT) at an 850 nm windowenabled a high transmission distance of 500m MMF with abit rate of 30-Gbps [9]

The MultiCAP solution presented in this paper achieveserror-free 657Gbps over 100m and 747Gbps over 1m usingan 850 nm VCSEL with a bandwidth of 101 GHz This solu-tion has the prospect of achieving 100Gbps over 100mMMFwith emerging 25GHz 850 nm VCSELs It overcomes bothelectrical and optical bandwidth limitations towards singlelane 100Gbps active optical cable (AOC) and employs costefficient 850 nm MMF technologies The 400 GE standardrequirement can thus be met by employing parallel opticallanes

The client-side links of long range (LR) and extendedrange (ER) are expected to meet the 400Gbps capacity byusing advanced modulation formats in combination withwavelength division multiplexing (WDM) [1]The higher thecapacity per lane the lower the number of WDM lanes and

therefore the number of transceivers The LR and ER areasin Figure 2 show the highest capacities per lane reported inO-band for different modulation formats In the LR of 10 kmNRZ coding enables 25Gbps [10] 4-PAM 50Gbps [11] CAP-64QAM 60Gbps [12] and DMT 106Gbps [13] MultiCAPachieves 108Gbps per lane with 20 km reach [5] In the ERof 40 km NRZ coding allows 40Gbps per lane [14] Beyond100Gbits per lane for ER is reached by DMT modulation[15] and MultiCAP [5] The DDIM WDM-based 400Gbpssystems were demonstrated as feasible in several of the citedworks (indicated in Figure 2) Eight lanes times 40Gbps [14] or16 lanes times 25-Gbps [10] were used to reach 400Gbps withNRZ coding A four-lane LAN-WDM 400Gbps solution wasdemonstrated using DMT over 30 km [16] and MultiCAPover 40 km standard single mode fiber (SSMF) [5] Both ofthem assume the 7 FEC overhead

The main contribution of this paper is the overview ofa uniform MultiCAP based solution for short long andextended range client-side links In all of these scenariosthe same implementation scheme can be used We reviewthe previously presented experimental results focusing onthe implementation similarities for different client-side sce-narios We include detailed description of the performedexperimentsMoreover we present the first full description ofthe used equalizer that was used in previous reported experi-mentsHaving a uniformmodulation format in different linkstypes lengths and different wavelength bands will not onlyallow for interoperability between kinds of equipment fromdifferent vendors but also reduce the cost and complexityfor the clients In this way a newly developed clientrsquos linkcan leverage the already existing implementation of differentlink typeWe show that using the same transceiverrsquos structureand equalization technique allows satisfying the 400 GEcapacity requirement in SR LR and ERMultiCAP advancedmodulation format is combined with parallel optics in SRand withWDM in LR and ERThis easily applicable solutionenables a simple upgrade from 100Gbps to 400Gbps in both850 nm MM links and 1310 nm SM links In the context of400Gbps Ethernet standardization we demonstrate that aMultiCAP based solution is feasible and worth consideringfor SR LR and ER

2 Methods

Figure 3 depicts the experimental setup for all of the con-sidered transmission scenarios At the transmitter side 5effective number of bits (ENOB) 64GSas digital-to-analogconverter (DAC) is used to generate MultiCAP signal Thetransmitter consists of a linear amplifier and a laser 850 nmVCSEL is used and in SR EMLs are used in LR and ERscenarios The channel consists of 100m MMF for SR and20 km of SSMF for LR ER scenario consists of 40 km SSMFand an SOA at the receiverThe receiver consists of a photodi-ode transimpedance amplifiers (TIAs) and a digital storageoscilloscope (DSO) The 400Gbps standard requirement inthe SR multimode scenario is expected to be fulfilled byparallel optics Therefore for the SR scenario we verify onlyone lane In the LR and ER scenarios the expected solutionto reach 400Gbps is WDM Hence in the experimental

Advances in Optical Technologies 3

DAC

VCSEL

PD

ADC

Short range TX Short range RX

Att

EML

ADC

Long and extended reach TX Long reach RX

B2BDAC MUX

SOA

DEMUX

PD

Extended reach RX

+

+

+

1m MMF

100m MMF

20km SSMF

40km SSMF+

Figure 3 Experimental setup of the short range (SR) scenario employs digital-to-analog converter (DAC) attenuator (Att) vertical cavitysurface-emitting laser (VCSEL) multimode fiber (MMF) photodiode (PD) and analog-to-digital converter (ADC) setups for long range(LR) and extended range (ER) additionally employ externallymodulated laser (EML)multiplexer (MUX) standard singlemode fiber (SSMF)semiconductor optical amplifier (SOA) and demultiplexer (DEMUX)

Table 1 Modulation order per band for different bit rates

Number Scenario Bit rate Baud rate per band B1 B2 B3 B4 B5 B61 SR 704Gbps 34Gbaud 32 32 16 8 8 42 SR 80Gbps 34Gbaud 64 32 32 16 8 43 LR and ER 108Gbps 4Gbaud 64 64 32 16 16 4

verification of the LR and ER setup four independentchannels ofDAC are used to drive four parallel lanes ofWDMtransmitter Additionally a WDM transmitter includes theWDMmultiplexer and the receiver a WDM demultiplexer

21 Signal Generation The signals are generated by a 4-output 64GSas digital-to-analog converter (DAC) with 5ENOB For signal generation we choose a 6-band configu-ration of MultiCAP [3] with different modulation orders perband which result in different bit rates Table 1 presents threeconfigurations and Figures 4(c)ndash4(e) depict the correspond-ing electrical spectra Each MultiCAP band is constructedfrom a pseudorandom bit sequence (PRBS) of 213 minus 1 bitsand delivers a baud rate as described in Table 1 The totalnumber of transmitted symbols is 49146 MultiCAP symbolsare generated by upsampling to 16 samples per symbol andsubsequent CAP filtering Upsampling factor is an integermultiple of baud rate of each subband The upsamplingprocedure is explained in detail in [3] The CAP filters arerealized as finite impulse response (FIR) with a length of20 symbols for SR scenario and 30 symbols for LR andER scenarios A roll-off coefficient of 005 was used atthe transmitter At the receiver time inverted versions ofthe CAP filters (roll off = 009) are used to recover thesymbol constellations We use the MultiCAP features ofpower and bit loading The constellation and power levelfor each band differs and is chosen empirically to best fit

the signal-to-noise ratio (SNR) of the specific frequencyband The bandsrsquo configuration and power choice depend onthe frequency response of the overall system

The frequency response of SR system is presented inFigure 4(a) A 3 dB bandwidth of 101 GHz a 10 dB bandwidthof 17GHz and a 20 dB bandwidth of 201 GHz are measuredThis frequency response allows for the first and the secondMultiCAP bands configurations presented in Table 1 Firstconfiguration shown in Table 1 and in Figure 4(c) enablesa total throughput of 704Gbps (657Gbps after 7 over-head forward error correction (FEC) decoding) whereas thesecond configuration shown in Figure 4(d) enables 80Gbps(747Gbps after 7 FEC) In these two cases 6 MultiCAPbands occupied the bandwidth of 21 GHz The frequencyresponse of optical back-to-back for both LR and ER systemsis presented in Figure 4(b) A 3-dB bandwidth of 890GHza 10-dB bandwidth of 1735GHz and a 20-dB bandwidth of24GHz are observedThe bandwidth in this case is effectivelylimited by the bandwidth of the DAC used This responseallowed for implementing the last band configuration fromTable 1 presented in Figure 4(e) This configuration enabledthroughput of 108Gbps (1009Gbps after 7 FEC) Band-width of 26GHz has been used for MultiCAP bands

22 Short Range A commercially available 850 nmVCSEL isused in the SR scenario Figure 5 shows the LIV curves andthe optical spectrum measured for the VCSEL The center

4 Advances in Optical Technologies

0 5 10 15 20 25 30

0Fr

eque

ncy

resp

onse

(dB)

Frequency (GHz)

Short range scenario

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

S21

(a)

0 5 10 15 20 25 30Frequency (GHz)

Long reach and extended reach scenario0

Freq

uenc

y re

spon

se (d

B)

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

S21

(b)

(dBm

)

20151050

minus20

minus40

minus60

(GHz)

(c)

(dBm

) minus20

minus40

minus602015

(GHz)1050

(d)

2520151050

(dBm

) minus20

minus40

minus60

minus80

(GHz)

(e)Figure 4 (a) Frequency response measured for short range (SR) scenario end-to-end link (b) frequency response measured for the opticalback-to-back of long range (LR) and extended range (ER) scenarios Received electricalMultiCAP spectrumand corresponding constellationstransmitted in each MultiCAP band for (c) short range (SR) scenario with total bit rate 704Gbps (d) short range (SR) scenario with total bitrate 80Gbps (e) long range (LR) and extended range (ER) scenarios with total bit rate 108Gbps

5

4

3

2

1

0

5

4

3

2

1

0

Pow

er (m

W)

Pow

er (m

W)

14 852 854 856 858 860121086420

Current (mA) Wavelength (nm)

Voltage

Volta

ge (m

V)

Power

012

010

008

006

004

002

000

Figure 5 Characterization of the VCSEL used in the short range scenario LIV curve measured at the room temperature optical spectrummeasured at bias current of 8mA

Advances in Optical Technologies 5

T = 30∘C

Vbias = minus15V

10

5

0

0

1304

1303

1302

130274

130272

130270

130268

minus5

minus3 minus2 minus1

minus10

minus15

minus20

Pow

er (d

Bm)

Lane 2 EML Lane 2 EML

Lane 2 EMLBias voltage (V)

Wav

eleng

th (n

m)

20 25 30 35 40 45

Temperature

Wav

eleng

th (n

m)

0minus2 minus1

Bias voltage (V)

T = 30∘C

(∘C)

Figure 6 Characterization of the EML of Lane 2 power versus bias current measured at 119879 = 30∘ wavelength versus temperature measuredat bias voltage of minus15 V wavelength versus bias voltage measured at 119879 = 30∘

frequency of the VCSELsrsquo spectrum at 8mA bias is 8572 nmTheDACoutput is amplified to a 12 Vp-p signal that is used todrive the VCSEL biased at 8mA An optical power of 6 dBmis launched into 100m of OM3 compliant MMF with a totallink loss of 05 dBThe signal is photodetectedwith an 850 nmphotodiode reverse biased at 4VThe signal is then amplifiedto a Vp-p of 1 V and digitally stored with an 80GSas DSOwith a resolution of 8 bits

23 Long Range and Extended Range The signals generatedby a 4-output DAC are decorrelated with delay lines Thelaser source used in these scenarios is EML The bias voltageand temperature characteristics of the EML employed in

Lane 2 are presented in Figure 6 The EMLrsquos bias voltage isminus15 V and the MultiCAP signal has a CMOS compatiblepeak-to-peak voltage of 25 Vp-p The center wavelengths ofthe EMLs in Lanes 0 to 3 are 1294 nm 1299 nm 1303 nm and1308 nm In order to keep thewavelengths stable temperaturecontrol is appliedThe output power of the EML in the testedlane is 6 dBmAverage output power of the EMLs ranges from4 dBm to 6 dBm

The optical signals are combined in a LAN-WDMmulti-plexer (MUX) with a channel spacing of 800GHz (G6941compliant) and transmitted over 20 km or 40 km (G652compliant) SSMF links MUX introduces 06 dB of insertionloss The span losses are 7 dB and 14 dB respectively For the

6 Advances in Optical Technologies

Table 2 Equalizerrsquos performance in terms of BER as comparedto the nonequalized system measured for three different signal-to-noise ratio (SNR) settings compared systems nonequalized systemwith a standard multimodulus algorithm (MMA) equalization andwith decision directed (DD)119870-means equalizer

SNR(dB)

BERnonequalized

system

BERMMA

equalizer

BERDD 119870-meansequalizer

206 189 sdot 10minus2 383 sdot 10minus3 867 sdot 10minus4

195 223 sdot 10minus2 766 sdot 10minus3 39 sdot 10minus3

182 367 sdot 10minus2 196 sdot 10minus2 148 sdot 10minus2

40 km transmission case a semiconductor optical amplifier(SOA) with a noise figure (NF) of 65 dB is employed atthe receiver before demultiplexing At the receiver sidethe signal is demultiplexed by a LAN-WDM demultiplexer(DEMUX) received by a photodiode (PD) and amplified by atransimpedance amplifier (TIA) DEMUX introduces 09 dBof insertion loss All of the components are 100GBASE-LR4and ER4 compatible

24 Demodulation and Equalization The receiver consistsof several digital signal processing (DSP) blocks which areimplemented in Matlab environment CAP filtering signaldownsampling phase offset removal and signal normal-ization are performed as explained in [3] Additionally weimplement an adaptive frequency domain equalization tomitigate linear impairmentsThe described adaptive decisiondirected (DD) equalization algorithmminimizes the receivedconstellation cluster size and quantization noise

We define the reference constellation by the centroidsfound using 119870-means algorithm which groups the receiveddata in the clusters [17]This reference constellation initializesthe describedDD equalization algorithm Clustersrsquo means arethe points of reference (starting decision)

We use an iterative equalizer where in every iteration thefollowing steps are performed first the error is calculatedbased on the Euclidean distance from the closest centroid asin a least mean square (LMS) equalizer

120576 (119899) = min 1003817100381710038171003817Cminus119910 (119899)

1003817100381710038171003817 (1)

where C denotes all centroids of the reference constellationand 119910(119899) is the received signal sample For equalization weuse 1198792 fractionally spaced FIR filter with 12 taps determinedempirically The taps coefficients of the DD equalizer areupdated according to the following equation

ℎ (119899 + 1) = ℎ (119899) + 120583 (119899) sdot 120576 (119899) sdot 119910 (119899)lowast (2)

where ℎ(119899) is the equalizer coefficient 120583(119899) is the step sizeinitialized as 75 sdot 10minus4 and 119910(119899)lowast is the complex conju-gate 119910(119899) Secondly the received signal is passed throughthe equalizer Finally the iterative process reestimates thecentroids of the equalized constellation and the describedsteps are repeated It was experimentally determined that2 iterations result in satisfactory equalization and furtheriterations do not show the performance improvement Toassure a faster convergence we implement the variable stepin DDThe step size is updated in the following manner [18]

120583 (119899 + 1) =120583 (119899)

1 + 120582120583 (119899) |120576 (119899)|2

120582 =

1 if 119899 = 0

0 if sgn (Re 120576 (119899)) = sgn (Re 120576 (119899 minus 1)) sgn (Im 120576 (119899)) = sgn (Im 120576 (119899 minus 1))

1 otherwise

(3)

where sgn denotes a sign functionIn order to quantify the improvement due to using an

equalizer we calculate BER for the equalized and nonequal-ized system for three different SNR values Moreover wepresent BER calculated for the system with a standard fre-quency domain equalizer namely multimodulus algorithm(MMA) Table 2 summarizes the BERs for all equalizationand SNR scenarios Decision directed (DD) 119870-means equal-izer improves the performance in terms of BER in all threeSNR scenarios At SNR of 206 dB using an equalizer allowsfor the improvement of 00181 in terms of BER In thefollowing sections all of the presented results are equalizedusing DD119870-means algorithm

After the signal is equalized the EVM is calculated andBER is computed In order to calculate bit error rate (BER)

the received demodulated signal is cross-correlated with thetransmitted signal and the errors are counted

3 Experimental Results

Figure 7 shows the measured BER curves for SR scenario Wedefine the sensitivity at a BER of the hard decision FEC codeat 7 overhead For the reported system it is 45 sdot 10minus3 [19]Thereby we can observe sensitivities of 21 47 and 54 dBmfor experimentally obtained 704Gbps over 1m 704Gbpsover 100m and 80Gbps over 1m respectivelyThemeasuredtransmission penalty after 100mMMF is 25 dB

For LR scenario per lane received bit error ratio (BER)back-to-back (B2B) and after 20 km SSMF transmission (noSOA) of the received signal is plotted in Figure 8(a) The

Advances in Optical Technologies 7

7 FEC limit

minus16

minus20

minus24

minus28

2 3 54 6

P (dBm)

70Gbps 1m80Gbps 1m

70Gbps 100m

log10(B

ER)

Figure 7 BER versus received optical power (ROP) for B2B and 100m transmission for 70GbpsMultiCAP configuration andB2B for 80Gbpsconfiguration

Received optical power per lane (dBm)

7 FEC limit

Lane 0 Lane 1

Lane 2 Lane 3

minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

minus9 minus8 minus7 minus6 minus5 minus4 minus3

log10(B

ER)

(a)

Received optical power per lane (dBm)

Single lane B2B

WDM center lane B2BWDM side lane B2B

7 FEC limit

minus14 minus13 minus12 minus11 minus10 minus9 minus8 minus7 minus6minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

Single lane 40kmWDM center lane 40km

WDM side lane 40km

log10(B

ER)

(b)Figure 8 (a) BER versus received optical power (ROP) for B2B and 20 km transmission for 4 lanes (b) BER versus ROP for the datatransmitted in the single lane (Lane 2) and for the data transmitted in all lines (BER curves for center lane Lane 2 and side lane Lane3) ROP measured before SOA the total bitrate of WDM system is 432Gbps

received optical power is measured before the MUX For allLAN-WDM lanes BERs are below the 7 hard decision FEClimit and no error floor is observed within the tested powerrange Receiver sensitivity at the FEC limit is minus60 dBm B2Band minus66 dBm after transmission No transmission powerpenalty is observedThe results for ER scenario are presentedin Figure 8(b) Received BER of a center lane and a side laneis plotted B2B and after 40 km SSMF transmission with all 4LAN-WDM lanes simultaneously amplified by a single SOAbefore demultiplexing Received optical power per channelis measured before the SOA For comparison the BER of asingle lane (remaining three lanes switched off) is includedin the graph All LAN-WDM lanes were received with a BERbelow the FEC limit after 40 km SSMF transmission with

a worst-case receiver sensitivity of minus99 dBm Presence ofneighboring channels in the link does not introduce penaltyin the 20 km scenario In case of 40 km scenario we observea 05 dB power penalty for the center lanes in the 4-lane casedue to interlanemodulation in the SOA In both scenarios nopenalty is observed in the side lanes

In the results presented BER is an average of the BERs inall MultiCAP bands

Finally the power budget calculation is evaluated inTable 3 For the SR scenario the optical output power mea-sured at the output of the VCSEL is 6 dBm The sensitivityat 7 FEC limit for 70Gbps 1m transmissions is equal to24 dBmTherefore power budget for this scenario is equal to36 dB In the LR and ER scenarios the optical output power

8 Advances in Optical Technologies

Table 3 System power budget

Transmissionlink type

Outputpower

Sensitivity FEC limit

Systempowerbudget

sr 70Gbps 6 dBm 24 dBm 36 dBLR 20 kmunamplified 54 dBm minus66 dBm 126 dB

ER 40 km SOAamplified 54 dBm minus99 dBm 159 dB

per lane is equal to 54 dBm It is measured after transmitterand hence after MUX The worst receiver sensitivity isminus66 dBm at FEC limit in case of 20 km transmission linkwith no amplification Therefore the power budget of thislink is 126 dB In case of 40 km transmission with SOA basedamplification the worst receiver sensitivity is minus99 dBm at theFEC limit Therefore for the amplified 40 km link the powerbudget is 159 dB The given receiver sensitivity is based onROP measured before receiver before PD in SR case beforeDEMUX in LR case and before SOA in ER case

The SR scenario represents a solution for an active opticalcable for data centers In terms of power budget themargin isnecessary only for the components heating up and aging Incase of LR and ER the calculated margin of 56 dB and 19 dBis sufficient for client-side links

4 Discussion

In the results presented for SR a steep roll-off of the VCSELrsquosfrequency response reduces the achievable capacity We usethe bit loading and power loading features of MultiCAP toovercome those limitations at the cost of worse sensitivityAs a consequence increasing the capacity from 70Gbpsto 80Gbps introduces the 31 dB penalty in sensitivity asshown in Figure 7 The bandwidth of the existing VCSELsis not sufficient to support 100Gbps per lane With theproposed MultiCAP scheme the emerging 25Gbps VCSELsare expected to satisfy the bandwidth requirement

The performance of the EMLs used in LR and ER issatisfactory to obtain 100Gbps after FEC per lane Moreoverthe local area network-wavelength division multiplexing(LAN-WDM) is proved to introduce negligible penalty bothfor 20 km and for 40 km link The power budget calculationindicates the maturity of the solution which allows for linklosses of 126 dB and 159 dB in LR and ER respectively

The clear difference in performance and achievablecapacity between SR and LR ER scenarios is attributedto the system bandwidth Even though the 3 dB and 10 dBbandwidths are similar for both systems the 20 dBbandwidthvaries by 5 dB For this reason the MultiCAP in SR isrecoverable when it occupies up to 21GHz while the LR andER signal is possible to recover when it occupies 26GHz(Figure 4) The last band in all three scenarios is highlysuppressed but thanks to the power loading and bit loadingfeatures of MultiCAP the information in the last band is alsopossible to recover if it carries QPSK

The proposed approach for 400Gbits client-side trans-mission links using MultiCAP modulation format representsan easily applicable solution that is robust simple and flexiblein upgrading from 100Gbits to 400Gbits while operating atthe O-band LAN-WDM wavelengths Moreover we presentapplicability of the MultiCAP solution in the SR multimode(MM) links We expect that with higher bandwidth of theupcoming 850 nmVCSELs this solution will enable 100Gbpsper lane and 400Gbps using parallel optics This technologypotentially provides a bridge for gray optics approach toclient-side inter- and intradata centers access and metrosegments

5 Conclusions

We present a uniform MultiCAP based solution for shortrange (SR) MM links long range (LR) 20 km single mode(SM) links and extended range (ER) 40 km SM links Theadvantageous feature of MultiCAP approach of being ableto assign parallel electrical interfaces of smaller bandwidthinto different frequency bands overcomes both electrical andoptical bandwidth limitations and eases the DSP pipeliningIts pass-band nature and multiband structure allow optimalusage of the available bandwidth maximizing obtainablecapacity In the SR scenario we have achieved record below-FEC bit rate transmission of 657 Gbps over 100m and747Gbps over 1m for 850 nmMMFdata links For upcoming400 GE standard long range and extended range criteria wepresent a MultiCAP LAN-WDM 400Gbps solution whichuses only commercial optical components from 100GBASE-LR4 and ER4 432Gbits MultiCAP signals are transmittedover 20 km SSMF without amplification and over 40 kmSSMF with SOA Interchannel mixing in the 40 km link andin SOA is proven to be negligible for a MultiCAP IMDDLAN-WDM system The proposed MultiCAP approach isa robust and flexible scheme which can cover most of theclient-side scenarios including inter- and intradata centersand up to 40 km client-side links

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] IEEE 400 Gbs Ethernet Study Group Meeting Materials 2014[2] J DrsquoAmbrosia and P Mooney ldquo400 Gbs ethernet why nowrdquo

Whitepaper of Ethernet Alliance 2013[3] M I Olmedo T Zuo J B Jensen et al ldquoMultiband carrierless

amplitude phase modulation for high capacity optical datalinksrdquo Journal of Lightwave Technology vol 32 no 4 pp 798ndash804 2014

[4] M I Olmedo A Tatarczak T Zuo J Estaran X Xu and I TMonroy ldquoTowards 100 Gbps over 100m MMF using a 850 nmVCSELrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash4 March 2014

[5] T Zuo A Tatarczak M Olmedo et al ldquoO-band 400 Gbitsclient side optical transmission linkrdquo in Proceedings of the

Advances in Optical Technologies 9

Optical Fiber Communications Conference and Exhibition (OFCrsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[6] K Szczerba PWestberghM Karlsson P A Andrekson andALarsson ldquo70Gbps 4-PAMand 56Gbps 8-PAMusing an 850 nmVCSELrdquo in Proceedings of the European Conference on OpticalCommunication (ECOC rsquo14) September 2014

[7] D Kuchta A V Rylyakov C L Schow et al ldquo64Gbs transmis-sion over 57mMMFusing anNRZmodulated 850 nmVCSELrdquoin Proceedings of the Optical Fiber Communications Conferenceand Exhibition (OFC rsquo14) pp 1ndash3 Optical Society of AmericaMarch 2014

[8] L Raddatz and I HWhite ldquoOvercoming themodal bandwidthlimitation of multimode fiber by using passband modulationrdquoIEEE Photonics Technology Letters vol 11 no 2 pp 266ndash2681999

[9] S Lee F Breyer S Randel D Cardenas H van den Boomand A Koonen ldquoDiscrete multitone modulation for high-speed data transmission over multimode fibers using 850-nmVCSELrdquo in Proceedings of the Conference on Optical FiberCommunicationmdashIncudes Post Deadline Papers (OFC rsquo09) pp1ndash3 IEEE San Diego Calif USA March 2009

[10] Y Doi T Ohyama T Yoshimatsu S Soma and M Ogumaldquo400GbE demonstration utilizing 100GbE optical sub-assem-blies and cyclic arrayed waveguide gratingsrdquo in Proceedings ofthe Optical Fiber Communications Conference and Exhibition(OFC rsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[11] W Kobayashi T Fujisawa S Kanazawa and H Sanjoh ldquo25Gbauds 4-PAM (50 Gbits) modulation and 10 km SMF trans-mission with 13 120583m InGaAlAs-based DMLrdquo Electronics Lettersvol 50 no 4 pp 299ndash300 2014

[12] J Zhang X Li Y Xia et al ldquo60-Gbs CAP-64QAM Transmis-sion using DML with direct detection and digital equalizationrdquoin Proceedings of the Optical Fiber Communication Conferenceand Exposition and the National Fiber Optic Engineers Confer-ence (OFCNFOEC rsquo14) IEEE March 2014

[13] T Chan I-C Lu J Chen W Way and T Chan ldquo400-Gbstransmission over 10-km SSMF using discrete multitone and13-mm EMLsrdquo IEEE Photonics Technology Letters vol 26 no16 pp 1657ndash1660 2014

[14] J P Turkiewicz and H de Waardt ldquoLow complexity up to 400-Gbs transmission in the 1310-nm wavelength domainrdquo IEEEPhotonics Technology Letters vol 24 no 11 pp 942ndash944 2012

[15] W Yan L Li B Liu et al ldquo80 km IMDD transmission for 100Gbs per lane enabled by DMT and nonlinearity managementrdquoin Proceedings of the Optical Fiber Communication ConferencepM2I4 Optical Society of America San Francisco Calif USAMarch 2014

[16] T Tanaka M Nishihara T Takahara et al ldquoExperimentaldemonstration of 448-Gbps+ DMT transmission over 30-kmSMFrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash3 March 2014

[17] N G Gonzalez D Zibar X Yu and I T Monroy ldquoOpticalphase-modulated radio-over-fiber links with K-means algo-rithm for digital demodulation of 8PSK subcarrier multiplexedsignalsrdquo in Proceedings of the Conference on Optical FiberCommunication CollocatedNational Fiber Optic Engineers Con-ference (OFCNFOEC rsquo10) pp 1ndash3 March 2010

[18] D Ashmawy K Banovic E Abdel-Raheem M Youssif HMansour and M Mohanna ldquoJoint MCMA and DD blindequalization algorithm with variable-step sizerdquo in Proceedingsof the IEEE International Conference on ElectroInformationTechnology (EIT rsquo09) pp 174ndash177 June 2009

[19] F Chang K Onohara and T Mizuochi ldquoForward error cor-rection for 100 G transport networksrdquo IEEE CommunicationsMagazine vol 48 no 3 pp S48ndashS55 2010

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DistributedSensor Networks

International Journal of

2 Advances in Optical Technologies

Rack Rack

Data center 2

Short range Long range

Campus

Extended range

MetroaggregationData center 1

1mndash100m MMF 1kmndash20km SSMF 20kmndash40km SSMF

Figure 1 Scenario of client-side optical transmission links for shortrange (SR) long range (LR) and extended range (ER)

120

100

80

60

40

20

0

120

100

80

60

40

20

0

SR LR ER

[4][4]

[10]

[6][6]

[5] [5]

[7] [12][11]

[13]

[14]

[15][16]

0 10 15 20 25 30 35 4050 100

Capa

city

per

lane

(Gbp

s)

Transmission distance (m) Transmission distance (km)

NRZ4-PAM8-PAM

DMTCAP-64MultiCAP

WDM based 400Gbps demonstrated

Figure 2 State-of-the-art summary capacity per lane versus trans-mitted distance for the following modulation formats Nonreturnto Zero (NRZ) pulse amplitude modulation (PAM) discrete mul-titone (DMT) carrierless amplitude phase (CAP) and multibandcarrierless amplitude phase (MultiCAP) demonstrated in literatureapproaches to 400Gbps systems based on IMDD WDM areindicated by the black circle

70Gbps over 2m OM4 MMF was achieved using 4-levelpulse amplitude modulation (4-PAM) [6] 64Gbps over 57mOM2 using Nonreturn to Zero (NRZ) [7] and 56Gbps over50m OM4 using 8-PAM [6] All of these require very fastelectrical interfaces and suffer from low tolerance to modaldispersion compared to pass-band modulation formats [8]Using discrete multitone (DMT) at an 850 nm windowenabled a high transmission distance of 500m MMF with abit rate of 30-Gbps [9]

The MultiCAP solution presented in this paper achieveserror-free 657Gbps over 100m and 747Gbps over 1m usingan 850 nm VCSEL with a bandwidth of 101 GHz This solu-tion has the prospect of achieving 100Gbps over 100mMMFwith emerging 25GHz 850 nm VCSELs It overcomes bothelectrical and optical bandwidth limitations towards singlelane 100Gbps active optical cable (AOC) and employs costefficient 850 nm MMF technologies The 400 GE standardrequirement can thus be met by employing parallel opticallanes

The client-side links of long range (LR) and extendedrange (ER) are expected to meet the 400Gbps capacity byusing advanced modulation formats in combination withwavelength division multiplexing (WDM) [1]The higher thecapacity per lane the lower the number of WDM lanes and

therefore the number of transceivers The LR and ER areasin Figure 2 show the highest capacities per lane reported inO-band for different modulation formats In the LR of 10 kmNRZ coding enables 25Gbps [10] 4-PAM 50Gbps [11] CAP-64QAM 60Gbps [12] and DMT 106Gbps [13] MultiCAPachieves 108Gbps per lane with 20 km reach [5] In the ERof 40 km NRZ coding allows 40Gbps per lane [14] Beyond100Gbits per lane for ER is reached by DMT modulation[15] and MultiCAP [5] The DDIM WDM-based 400Gbpssystems were demonstrated as feasible in several of the citedworks (indicated in Figure 2) Eight lanes times 40Gbps [14] or16 lanes times 25-Gbps [10] were used to reach 400Gbps withNRZ coding A four-lane LAN-WDM 400Gbps solution wasdemonstrated using DMT over 30 km [16] and MultiCAPover 40 km standard single mode fiber (SSMF) [5] Both ofthem assume the 7 FEC overhead

The main contribution of this paper is the overview ofa uniform MultiCAP based solution for short long andextended range client-side links In all of these scenariosthe same implementation scheme can be used We reviewthe previously presented experimental results focusing onthe implementation similarities for different client-side sce-narios We include detailed description of the performedexperimentsMoreover we present the first full description ofthe used equalizer that was used in previous reported experi-mentsHaving a uniformmodulation format in different linkstypes lengths and different wavelength bands will not onlyallow for interoperability between kinds of equipment fromdifferent vendors but also reduce the cost and complexityfor the clients In this way a newly developed clientrsquos linkcan leverage the already existing implementation of differentlink typeWe show that using the same transceiverrsquos structureand equalization technique allows satisfying the 400 GEcapacity requirement in SR LR and ERMultiCAP advancedmodulation format is combined with parallel optics in SRand withWDM in LR and ERThis easily applicable solutionenables a simple upgrade from 100Gbps to 400Gbps in both850 nm MM links and 1310 nm SM links In the context of400Gbps Ethernet standardization we demonstrate that aMultiCAP based solution is feasible and worth consideringfor SR LR and ER

2 Methods

Figure 3 depicts the experimental setup for all of the con-sidered transmission scenarios At the transmitter side 5effective number of bits (ENOB) 64GSas digital-to-analogconverter (DAC) is used to generate MultiCAP signal Thetransmitter consists of a linear amplifier and a laser 850 nmVCSEL is used and in SR EMLs are used in LR and ERscenarios The channel consists of 100m MMF for SR and20 km of SSMF for LR ER scenario consists of 40 km SSMFand an SOA at the receiverThe receiver consists of a photodi-ode transimpedance amplifiers (TIAs) and a digital storageoscilloscope (DSO) The 400Gbps standard requirement inthe SR multimode scenario is expected to be fulfilled byparallel optics Therefore for the SR scenario we verify onlyone lane In the LR and ER scenarios the expected solutionto reach 400Gbps is WDM Hence in the experimental

Advances in Optical Technologies 3

DAC

VCSEL

PD

ADC

Short range TX Short range RX

Att

EML

ADC

Long and extended reach TX Long reach RX

B2BDAC MUX

SOA

DEMUX

PD

Extended reach RX

+

+

+

1m MMF

100m MMF

20km SSMF

40km SSMF+

Figure 3 Experimental setup of the short range (SR) scenario employs digital-to-analog converter (DAC) attenuator (Att) vertical cavitysurface-emitting laser (VCSEL) multimode fiber (MMF) photodiode (PD) and analog-to-digital converter (ADC) setups for long range(LR) and extended range (ER) additionally employ externallymodulated laser (EML)multiplexer (MUX) standard singlemode fiber (SSMF)semiconductor optical amplifier (SOA) and demultiplexer (DEMUX)

Table 1 Modulation order per band for different bit rates

Number Scenario Bit rate Baud rate per band B1 B2 B3 B4 B5 B61 SR 704Gbps 34Gbaud 32 32 16 8 8 42 SR 80Gbps 34Gbaud 64 32 32 16 8 43 LR and ER 108Gbps 4Gbaud 64 64 32 16 16 4

verification of the LR and ER setup four independentchannels ofDAC are used to drive four parallel lanes ofWDMtransmitter Additionally a WDM transmitter includes theWDMmultiplexer and the receiver a WDM demultiplexer

21 Signal Generation The signals are generated by a 4-output 64GSas digital-to-analog converter (DAC) with 5ENOB For signal generation we choose a 6-band configu-ration of MultiCAP [3] with different modulation orders perband which result in different bit rates Table 1 presents threeconfigurations and Figures 4(c)ndash4(e) depict the correspond-ing electrical spectra Each MultiCAP band is constructedfrom a pseudorandom bit sequence (PRBS) of 213 minus 1 bitsand delivers a baud rate as described in Table 1 The totalnumber of transmitted symbols is 49146 MultiCAP symbolsare generated by upsampling to 16 samples per symbol andsubsequent CAP filtering Upsampling factor is an integermultiple of baud rate of each subband The upsamplingprocedure is explained in detail in [3] The CAP filters arerealized as finite impulse response (FIR) with a length of20 symbols for SR scenario and 30 symbols for LR andER scenarios A roll-off coefficient of 005 was used atthe transmitter At the receiver time inverted versions ofthe CAP filters (roll off = 009) are used to recover thesymbol constellations We use the MultiCAP features ofpower and bit loading The constellation and power levelfor each band differs and is chosen empirically to best fit

the signal-to-noise ratio (SNR) of the specific frequencyband The bandsrsquo configuration and power choice depend onthe frequency response of the overall system

The frequency response of SR system is presented inFigure 4(a) A 3 dB bandwidth of 101 GHz a 10 dB bandwidthof 17GHz and a 20 dB bandwidth of 201 GHz are measuredThis frequency response allows for the first and the secondMultiCAP bands configurations presented in Table 1 Firstconfiguration shown in Table 1 and in Figure 4(c) enablesa total throughput of 704Gbps (657Gbps after 7 over-head forward error correction (FEC) decoding) whereas thesecond configuration shown in Figure 4(d) enables 80Gbps(747Gbps after 7 FEC) In these two cases 6 MultiCAPbands occupied the bandwidth of 21 GHz The frequencyresponse of optical back-to-back for both LR and ER systemsis presented in Figure 4(b) A 3-dB bandwidth of 890GHza 10-dB bandwidth of 1735GHz and a 20-dB bandwidth of24GHz are observedThe bandwidth in this case is effectivelylimited by the bandwidth of the DAC used This responseallowed for implementing the last band configuration fromTable 1 presented in Figure 4(e) This configuration enabledthroughput of 108Gbps (1009Gbps after 7 FEC) Band-width of 26GHz has been used for MultiCAP bands

22 Short Range A commercially available 850 nmVCSEL isused in the SR scenario Figure 5 shows the LIV curves andthe optical spectrum measured for the VCSEL The center

4 Advances in Optical Technologies

0 5 10 15 20 25 30

0Fr

eque

ncy

resp

onse

(dB)

Frequency (GHz)

Short range scenario

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

S21

(a)

0 5 10 15 20 25 30Frequency (GHz)

Long reach and extended reach scenario0

Freq

uenc

y re

spon

se (d

B)

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

S21

(b)

(dBm

)

20151050

minus20

minus40

minus60

(GHz)

(c)

(dBm

) minus20

minus40

minus602015

(GHz)1050

(d)

2520151050

(dBm

) minus20

minus40

minus60

minus80

(GHz)

(e)Figure 4 (a) Frequency response measured for short range (SR) scenario end-to-end link (b) frequency response measured for the opticalback-to-back of long range (LR) and extended range (ER) scenarios Received electricalMultiCAP spectrumand corresponding constellationstransmitted in each MultiCAP band for (c) short range (SR) scenario with total bit rate 704Gbps (d) short range (SR) scenario with total bitrate 80Gbps (e) long range (LR) and extended range (ER) scenarios with total bit rate 108Gbps

5

4

3

2

1

0

5

4

3

2

1

0

Pow

er (m

W)

Pow

er (m

W)

14 852 854 856 858 860121086420

Current (mA) Wavelength (nm)

Voltage

Volta

ge (m

V)

Power

012

010

008

006

004

002

000

Figure 5 Characterization of the VCSEL used in the short range scenario LIV curve measured at the room temperature optical spectrummeasured at bias current of 8mA

Advances in Optical Technologies 5

T = 30∘C

Vbias = minus15V

10

5

0

0

1304

1303

1302

130274

130272

130270

130268

minus5

minus3 minus2 minus1

minus10

minus15

minus20

Pow

er (d

Bm)

Lane 2 EML Lane 2 EML

Lane 2 EMLBias voltage (V)

Wav

eleng

th (n

m)

20 25 30 35 40 45

Temperature

Wav

eleng

th (n

m)

0minus2 minus1

Bias voltage (V)

T = 30∘C

(∘C)

Figure 6 Characterization of the EML of Lane 2 power versus bias current measured at 119879 = 30∘ wavelength versus temperature measuredat bias voltage of minus15 V wavelength versus bias voltage measured at 119879 = 30∘

frequency of the VCSELsrsquo spectrum at 8mA bias is 8572 nmTheDACoutput is amplified to a 12 Vp-p signal that is used todrive the VCSEL biased at 8mA An optical power of 6 dBmis launched into 100m of OM3 compliant MMF with a totallink loss of 05 dBThe signal is photodetectedwith an 850 nmphotodiode reverse biased at 4VThe signal is then amplifiedto a Vp-p of 1 V and digitally stored with an 80GSas DSOwith a resolution of 8 bits

23 Long Range and Extended Range The signals generatedby a 4-output DAC are decorrelated with delay lines Thelaser source used in these scenarios is EML The bias voltageand temperature characteristics of the EML employed in

Lane 2 are presented in Figure 6 The EMLrsquos bias voltage isminus15 V and the MultiCAP signal has a CMOS compatiblepeak-to-peak voltage of 25 Vp-p The center wavelengths ofthe EMLs in Lanes 0 to 3 are 1294 nm 1299 nm 1303 nm and1308 nm In order to keep thewavelengths stable temperaturecontrol is appliedThe output power of the EML in the testedlane is 6 dBmAverage output power of the EMLs ranges from4 dBm to 6 dBm

The optical signals are combined in a LAN-WDMmulti-plexer (MUX) with a channel spacing of 800GHz (G6941compliant) and transmitted over 20 km or 40 km (G652compliant) SSMF links MUX introduces 06 dB of insertionloss The span losses are 7 dB and 14 dB respectively For the

6 Advances in Optical Technologies

Table 2 Equalizerrsquos performance in terms of BER as comparedto the nonequalized system measured for three different signal-to-noise ratio (SNR) settings compared systems nonequalized systemwith a standard multimodulus algorithm (MMA) equalization andwith decision directed (DD)119870-means equalizer

SNR(dB)

BERnonequalized

system

BERMMA

equalizer

BERDD 119870-meansequalizer

206 189 sdot 10minus2 383 sdot 10minus3 867 sdot 10minus4

195 223 sdot 10minus2 766 sdot 10minus3 39 sdot 10minus3

182 367 sdot 10minus2 196 sdot 10minus2 148 sdot 10minus2

40 km transmission case a semiconductor optical amplifier(SOA) with a noise figure (NF) of 65 dB is employed atthe receiver before demultiplexing At the receiver sidethe signal is demultiplexed by a LAN-WDM demultiplexer(DEMUX) received by a photodiode (PD) and amplified by atransimpedance amplifier (TIA) DEMUX introduces 09 dBof insertion loss All of the components are 100GBASE-LR4and ER4 compatible

24 Demodulation and Equalization The receiver consistsof several digital signal processing (DSP) blocks which areimplemented in Matlab environment CAP filtering signaldownsampling phase offset removal and signal normal-ization are performed as explained in [3] Additionally weimplement an adaptive frequency domain equalization tomitigate linear impairmentsThe described adaptive decisiondirected (DD) equalization algorithmminimizes the receivedconstellation cluster size and quantization noise

We define the reference constellation by the centroidsfound using 119870-means algorithm which groups the receiveddata in the clusters [17]This reference constellation initializesthe describedDD equalization algorithm Clustersrsquo means arethe points of reference (starting decision)

We use an iterative equalizer where in every iteration thefollowing steps are performed first the error is calculatedbased on the Euclidean distance from the closest centroid asin a least mean square (LMS) equalizer

120576 (119899) = min 1003817100381710038171003817Cminus119910 (119899)

1003817100381710038171003817 (1)

where C denotes all centroids of the reference constellationand 119910(119899) is the received signal sample For equalization weuse 1198792 fractionally spaced FIR filter with 12 taps determinedempirically The taps coefficients of the DD equalizer areupdated according to the following equation

ℎ (119899 + 1) = ℎ (119899) + 120583 (119899) sdot 120576 (119899) sdot 119910 (119899)lowast (2)

where ℎ(119899) is the equalizer coefficient 120583(119899) is the step sizeinitialized as 75 sdot 10minus4 and 119910(119899)lowast is the complex conju-gate 119910(119899) Secondly the received signal is passed throughthe equalizer Finally the iterative process reestimates thecentroids of the equalized constellation and the describedsteps are repeated It was experimentally determined that2 iterations result in satisfactory equalization and furtheriterations do not show the performance improvement Toassure a faster convergence we implement the variable stepin DDThe step size is updated in the following manner [18]

120583 (119899 + 1) =120583 (119899)

1 + 120582120583 (119899) |120576 (119899)|2

120582 =

1 if 119899 = 0

0 if sgn (Re 120576 (119899)) = sgn (Re 120576 (119899 minus 1)) sgn (Im 120576 (119899)) = sgn (Im 120576 (119899 minus 1))

1 otherwise

(3)

where sgn denotes a sign functionIn order to quantify the improvement due to using an

equalizer we calculate BER for the equalized and nonequal-ized system for three different SNR values Moreover wepresent BER calculated for the system with a standard fre-quency domain equalizer namely multimodulus algorithm(MMA) Table 2 summarizes the BERs for all equalizationand SNR scenarios Decision directed (DD) 119870-means equal-izer improves the performance in terms of BER in all threeSNR scenarios At SNR of 206 dB using an equalizer allowsfor the improvement of 00181 in terms of BER In thefollowing sections all of the presented results are equalizedusing DD119870-means algorithm

After the signal is equalized the EVM is calculated andBER is computed In order to calculate bit error rate (BER)

the received demodulated signal is cross-correlated with thetransmitted signal and the errors are counted

3 Experimental Results

Figure 7 shows the measured BER curves for SR scenario Wedefine the sensitivity at a BER of the hard decision FEC codeat 7 overhead For the reported system it is 45 sdot 10minus3 [19]Thereby we can observe sensitivities of 21 47 and 54 dBmfor experimentally obtained 704Gbps over 1m 704Gbpsover 100m and 80Gbps over 1m respectivelyThemeasuredtransmission penalty after 100mMMF is 25 dB

For LR scenario per lane received bit error ratio (BER)back-to-back (B2B) and after 20 km SSMF transmission (noSOA) of the received signal is plotted in Figure 8(a) The

Advances in Optical Technologies 7

7 FEC limit

minus16

minus20

minus24

minus28

2 3 54 6

P (dBm)

70Gbps 1m80Gbps 1m

70Gbps 100m

log10(B

ER)

Figure 7 BER versus received optical power (ROP) for B2B and 100m transmission for 70GbpsMultiCAP configuration andB2B for 80Gbpsconfiguration

Received optical power per lane (dBm)

7 FEC limit

Lane 0 Lane 1

Lane 2 Lane 3

minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

minus9 minus8 minus7 minus6 minus5 minus4 minus3

log10(B

ER)

(a)

Received optical power per lane (dBm)

Single lane B2B

WDM center lane B2BWDM side lane B2B

7 FEC limit

minus14 minus13 minus12 minus11 minus10 minus9 minus8 minus7 minus6minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

Single lane 40kmWDM center lane 40km

WDM side lane 40km

log10(B

ER)

(b)Figure 8 (a) BER versus received optical power (ROP) for B2B and 20 km transmission for 4 lanes (b) BER versus ROP for the datatransmitted in the single lane (Lane 2) and for the data transmitted in all lines (BER curves for center lane Lane 2 and side lane Lane3) ROP measured before SOA the total bitrate of WDM system is 432Gbps

received optical power is measured before the MUX For allLAN-WDM lanes BERs are below the 7 hard decision FEClimit and no error floor is observed within the tested powerrange Receiver sensitivity at the FEC limit is minus60 dBm B2Band minus66 dBm after transmission No transmission powerpenalty is observedThe results for ER scenario are presentedin Figure 8(b) Received BER of a center lane and a side laneis plotted B2B and after 40 km SSMF transmission with all 4LAN-WDM lanes simultaneously amplified by a single SOAbefore demultiplexing Received optical power per channelis measured before the SOA For comparison the BER of asingle lane (remaining three lanes switched off) is includedin the graph All LAN-WDM lanes were received with a BERbelow the FEC limit after 40 km SSMF transmission with

a worst-case receiver sensitivity of minus99 dBm Presence ofneighboring channels in the link does not introduce penaltyin the 20 km scenario In case of 40 km scenario we observea 05 dB power penalty for the center lanes in the 4-lane casedue to interlanemodulation in the SOA In both scenarios nopenalty is observed in the side lanes

In the results presented BER is an average of the BERs inall MultiCAP bands

Finally the power budget calculation is evaluated inTable 3 For the SR scenario the optical output power mea-sured at the output of the VCSEL is 6 dBm The sensitivityat 7 FEC limit for 70Gbps 1m transmissions is equal to24 dBmTherefore power budget for this scenario is equal to36 dB In the LR and ER scenarios the optical output power

8 Advances in Optical Technologies

Table 3 System power budget

Transmissionlink type

Outputpower

Sensitivity FEC limit

Systempowerbudget

sr 70Gbps 6 dBm 24 dBm 36 dBLR 20 kmunamplified 54 dBm minus66 dBm 126 dB

ER 40 km SOAamplified 54 dBm minus99 dBm 159 dB

per lane is equal to 54 dBm It is measured after transmitterand hence after MUX The worst receiver sensitivity isminus66 dBm at FEC limit in case of 20 km transmission linkwith no amplification Therefore the power budget of thislink is 126 dB In case of 40 km transmission with SOA basedamplification the worst receiver sensitivity is minus99 dBm at theFEC limit Therefore for the amplified 40 km link the powerbudget is 159 dB The given receiver sensitivity is based onROP measured before receiver before PD in SR case beforeDEMUX in LR case and before SOA in ER case

The SR scenario represents a solution for an active opticalcable for data centers In terms of power budget themargin isnecessary only for the components heating up and aging Incase of LR and ER the calculated margin of 56 dB and 19 dBis sufficient for client-side links

4 Discussion

In the results presented for SR a steep roll-off of the VCSELrsquosfrequency response reduces the achievable capacity We usethe bit loading and power loading features of MultiCAP toovercome those limitations at the cost of worse sensitivityAs a consequence increasing the capacity from 70Gbpsto 80Gbps introduces the 31 dB penalty in sensitivity asshown in Figure 7 The bandwidth of the existing VCSELsis not sufficient to support 100Gbps per lane With theproposed MultiCAP scheme the emerging 25Gbps VCSELsare expected to satisfy the bandwidth requirement

The performance of the EMLs used in LR and ER issatisfactory to obtain 100Gbps after FEC per lane Moreoverthe local area network-wavelength division multiplexing(LAN-WDM) is proved to introduce negligible penalty bothfor 20 km and for 40 km link The power budget calculationindicates the maturity of the solution which allows for linklosses of 126 dB and 159 dB in LR and ER respectively

The clear difference in performance and achievablecapacity between SR and LR ER scenarios is attributedto the system bandwidth Even though the 3 dB and 10 dBbandwidths are similar for both systems the 20 dBbandwidthvaries by 5 dB For this reason the MultiCAP in SR isrecoverable when it occupies up to 21GHz while the LR andER signal is possible to recover when it occupies 26GHz(Figure 4) The last band in all three scenarios is highlysuppressed but thanks to the power loading and bit loadingfeatures of MultiCAP the information in the last band is alsopossible to recover if it carries QPSK

The proposed approach for 400Gbits client-side trans-mission links using MultiCAP modulation format representsan easily applicable solution that is robust simple and flexiblein upgrading from 100Gbits to 400Gbits while operating atthe O-band LAN-WDM wavelengths Moreover we presentapplicability of the MultiCAP solution in the SR multimode(MM) links We expect that with higher bandwidth of theupcoming 850 nmVCSELs this solution will enable 100Gbpsper lane and 400Gbps using parallel optics This technologypotentially provides a bridge for gray optics approach toclient-side inter- and intradata centers access and metrosegments

5 Conclusions

We present a uniform MultiCAP based solution for shortrange (SR) MM links long range (LR) 20 km single mode(SM) links and extended range (ER) 40 km SM links Theadvantageous feature of MultiCAP approach of being ableto assign parallel electrical interfaces of smaller bandwidthinto different frequency bands overcomes both electrical andoptical bandwidth limitations and eases the DSP pipeliningIts pass-band nature and multiband structure allow optimalusage of the available bandwidth maximizing obtainablecapacity In the SR scenario we have achieved record below-FEC bit rate transmission of 657 Gbps over 100m and747Gbps over 1m for 850 nmMMFdata links For upcoming400 GE standard long range and extended range criteria wepresent a MultiCAP LAN-WDM 400Gbps solution whichuses only commercial optical components from 100GBASE-LR4 and ER4 432Gbits MultiCAP signals are transmittedover 20 km SSMF without amplification and over 40 kmSSMF with SOA Interchannel mixing in the 40 km link andin SOA is proven to be negligible for a MultiCAP IMDDLAN-WDM system The proposed MultiCAP approach isa robust and flexible scheme which can cover most of theclient-side scenarios including inter- and intradata centersand up to 40 km client-side links

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] IEEE 400 Gbs Ethernet Study Group Meeting Materials 2014[2] J DrsquoAmbrosia and P Mooney ldquo400 Gbs ethernet why nowrdquo

Whitepaper of Ethernet Alliance 2013[3] M I Olmedo T Zuo J B Jensen et al ldquoMultiband carrierless

amplitude phase modulation for high capacity optical datalinksrdquo Journal of Lightwave Technology vol 32 no 4 pp 798ndash804 2014

[4] M I Olmedo A Tatarczak T Zuo J Estaran X Xu and I TMonroy ldquoTowards 100 Gbps over 100m MMF using a 850 nmVCSELrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash4 March 2014

[5] T Zuo A Tatarczak M Olmedo et al ldquoO-band 400 Gbitsclient side optical transmission linkrdquo in Proceedings of the

Advances in Optical Technologies 9

Optical Fiber Communications Conference and Exhibition (OFCrsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[6] K Szczerba PWestberghM Karlsson P A Andrekson andALarsson ldquo70Gbps 4-PAMand 56Gbps 8-PAMusing an 850 nmVCSELrdquo in Proceedings of the European Conference on OpticalCommunication (ECOC rsquo14) September 2014

[7] D Kuchta A V Rylyakov C L Schow et al ldquo64Gbs transmis-sion over 57mMMFusing anNRZmodulated 850 nmVCSELrdquoin Proceedings of the Optical Fiber Communications Conferenceand Exhibition (OFC rsquo14) pp 1ndash3 Optical Society of AmericaMarch 2014

[8] L Raddatz and I HWhite ldquoOvercoming themodal bandwidthlimitation of multimode fiber by using passband modulationrdquoIEEE Photonics Technology Letters vol 11 no 2 pp 266ndash2681999

[9] S Lee F Breyer S Randel D Cardenas H van den Boomand A Koonen ldquoDiscrete multitone modulation for high-speed data transmission over multimode fibers using 850-nmVCSELrdquo in Proceedings of the Conference on Optical FiberCommunicationmdashIncudes Post Deadline Papers (OFC rsquo09) pp1ndash3 IEEE San Diego Calif USA March 2009

[10] Y Doi T Ohyama T Yoshimatsu S Soma and M Ogumaldquo400GbE demonstration utilizing 100GbE optical sub-assem-blies and cyclic arrayed waveguide gratingsrdquo in Proceedings ofthe Optical Fiber Communications Conference and Exhibition(OFC rsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[11] W Kobayashi T Fujisawa S Kanazawa and H Sanjoh ldquo25Gbauds 4-PAM (50 Gbits) modulation and 10 km SMF trans-mission with 13 120583m InGaAlAs-based DMLrdquo Electronics Lettersvol 50 no 4 pp 299ndash300 2014

[12] J Zhang X Li Y Xia et al ldquo60-Gbs CAP-64QAM Transmis-sion using DML with direct detection and digital equalizationrdquoin Proceedings of the Optical Fiber Communication Conferenceand Exposition and the National Fiber Optic Engineers Confer-ence (OFCNFOEC rsquo14) IEEE March 2014

[13] T Chan I-C Lu J Chen W Way and T Chan ldquo400-Gbstransmission over 10-km SSMF using discrete multitone and13-mm EMLsrdquo IEEE Photonics Technology Letters vol 26 no16 pp 1657ndash1660 2014

[14] J P Turkiewicz and H de Waardt ldquoLow complexity up to 400-Gbs transmission in the 1310-nm wavelength domainrdquo IEEEPhotonics Technology Letters vol 24 no 11 pp 942ndash944 2012

[15] W Yan L Li B Liu et al ldquo80 km IMDD transmission for 100Gbs per lane enabled by DMT and nonlinearity managementrdquoin Proceedings of the Optical Fiber Communication ConferencepM2I4 Optical Society of America San Francisco Calif USAMarch 2014

[16] T Tanaka M Nishihara T Takahara et al ldquoExperimentaldemonstration of 448-Gbps+ DMT transmission over 30-kmSMFrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash3 March 2014

[17] N G Gonzalez D Zibar X Yu and I T Monroy ldquoOpticalphase-modulated radio-over-fiber links with K-means algo-rithm for digital demodulation of 8PSK subcarrier multiplexedsignalsrdquo in Proceedings of the Conference on Optical FiberCommunication CollocatedNational Fiber Optic Engineers Con-ference (OFCNFOEC rsquo10) pp 1ndash3 March 2010

[18] D Ashmawy K Banovic E Abdel-Raheem M Youssif HMansour and M Mohanna ldquoJoint MCMA and DD blindequalization algorithm with variable-step sizerdquo in Proceedingsof the IEEE International Conference on ElectroInformationTechnology (EIT rsquo09) pp 174ndash177 June 2009

[19] F Chang K Onohara and T Mizuochi ldquoForward error cor-rection for 100 G transport networksrdquo IEEE CommunicationsMagazine vol 48 no 3 pp S48ndashS55 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Advances in Optical Technologies 3

DAC

VCSEL

PD

ADC

Short range TX Short range RX

Att

EML

ADC

Long and extended reach TX Long reach RX

B2BDAC MUX

SOA

DEMUX

PD

Extended reach RX

+

+

+

1m MMF

100m MMF

20km SSMF

40km SSMF+

Figure 3 Experimental setup of the short range (SR) scenario employs digital-to-analog converter (DAC) attenuator (Att) vertical cavitysurface-emitting laser (VCSEL) multimode fiber (MMF) photodiode (PD) and analog-to-digital converter (ADC) setups for long range(LR) and extended range (ER) additionally employ externallymodulated laser (EML)multiplexer (MUX) standard singlemode fiber (SSMF)semiconductor optical amplifier (SOA) and demultiplexer (DEMUX)

Table 1 Modulation order per band for different bit rates

Number Scenario Bit rate Baud rate per band B1 B2 B3 B4 B5 B61 SR 704Gbps 34Gbaud 32 32 16 8 8 42 SR 80Gbps 34Gbaud 64 32 32 16 8 43 LR and ER 108Gbps 4Gbaud 64 64 32 16 16 4

verification of the LR and ER setup four independentchannels ofDAC are used to drive four parallel lanes ofWDMtransmitter Additionally a WDM transmitter includes theWDMmultiplexer and the receiver a WDM demultiplexer

21 Signal Generation The signals are generated by a 4-output 64GSas digital-to-analog converter (DAC) with 5ENOB For signal generation we choose a 6-band configu-ration of MultiCAP [3] with different modulation orders perband which result in different bit rates Table 1 presents threeconfigurations and Figures 4(c)ndash4(e) depict the correspond-ing electrical spectra Each MultiCAP band is constructedfrom a pseudorandom bit sequence (PRBS) of 213 minus 1 bitsand delivers a baud rate as described in Table 1 The totalnumber of transmitted symbols is 49146 MultiCAP symbolsare generated by upsampling to 16 samples per symbol andsubsequent CAP filtering Upsampling factor is an integermultiple of baud rate of each subband The upsamplingprocedure is explained in detail in [3] The CAP filters arerealized as finite impulse response (FIR) with a length of20 symbols for SR scenario and 30 symbols for LR andER scenarios A roll-off coefficient of 005 was used atthe transmitter At the receiver time inverted versions ofthe CAP filters (roll off = 009) are used to recover thesymbol constellations We use the MultiCAP features ofpower and bit loading The constellation and power levelfor each band differs and is chosen empirically to best fit

the signal-to-noise ratio (SNR) of the specific frequencyband The bandsrsquo configuration and power choice depend onthe frequency response of the overall system

The frequency response of SR system is presented inFigure 4(a) A 3 dB bandwidth of 101 GHz a 10 dB bandwidthof 17GHz and a 20 dB bandwidth of 201 GHz are measuredThis frequency response allows for the first and the secondMultiCAP bands configurations presented in Table 1 Firstconfiguration shown in Table 1 and in Figure 4(c) enablesa total throughput of 704Gbps (657Gbps after 7 over-head forward error correction (FEC) decoding) whereas thesecond configuration shown in Figure 4(d) enables 80Gbps(747Gbps after 7 FEC) In these two cases 6 MultiCAPbands occupied the bandwidth of 21 GHz The frequencyresponse of optical back-to-back for both LR and ER systemsis presented in Figure 4(b) A 3-dB bandwidth of 890GHza 10-dB bandwidth of 1735GHz and a 20-dB bandwidth of24GHz are observedThe bandwidth in this case is effectivelylimited by the bandwidth of the DAC used This responseallowed for implementing the last band configuration fromTable 1 presented in Figure 4(e) This configuration enabledthroughput of 108Gbps (1009Gbps after 7 FEC) Band-width of 26GHz has been used for MultiCAP bands

22 Short Range A commercially available 850 nmVCSEL isused in the SR scenario Figure 5 shows the LIV curves andthe optical spectrum measured for the VCSEL The center

4 Advances in Optical Technologies

0 5 10 15 20 25 30

0Fr

eque

ncy

resp

onse

(dB)

Frequency (GHz)

Short range scenario

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

S21

(a)

0 5 10 15 20 25 30Frequency (GHz)

Long reach and extended reach scenario0

Freq

uenc

y re

spon

se (d

B)

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

S21

(b)

(dBm

)

20151050

minus20

minus40

minus60

(GHz)

(c)

(dBm

) minus20

minus40

minus602015

(GHz)1050

(d)

2520151050

(dBm

) minus20

minus40

minus60

minus80

(GHz)

(e)Figure 4 (a) Frequency response measured for short range (SR) scenario end-to-end link (b) frequency response measured for the opticalback-to-back of long range (LR) and extended range (ER) scenarios Received electricalMultiCAP spectrumand corresponding constellationstransmitted in each MultiCAP band for (c) short range (SR) scenario with total bit rate 704Gbps (d) short range (SR) scenario with total bitrate 80Gbps (e) long range (LR) and extended range (ER) scenarios with total bit rate 108Gbps

5

4

3

2

1

0

5

4

3

2

1

0

Pow

er (m

W)

Pow

er (m

W)

14 852 854 856 858 860121086420

Current (mA) Wavelength (nm)

Voltage

Volta

ge (m

V)

Power

012

010

008

006

004

002

000

Figure 5 Characterization of the VCSEL used in the short range scenario LIV curve measured at the room temperature optical spectrummeasured at bias current of 8mA

Advances in Optical Technologies 5

T = 30∘C

Vbias = minus15V

10

5

0

0

1304

1303

1302

130274

130272

130270

130268

minus5

minus3 minus2 minus1

minus10

minus15

minus20

Pow

er (d

Bm)

Lane 2 EML Lane 2 EML

Lane 2 EMLBias voltage (V)

Wav

eleng

th (n

m)

20 25 30 35 40 45

Temperature

Wav

eleng

th (n

m)

0minus2 minus1

Bias voltage (V)

T = 30∘C

(∘C)

Figure 6 Characterization of the EML of Lane 2 power versus bias current measured at 119879 = 30∘ wavelength versus temperature measuredat bias voltage of minus15 V wavelength versus bias voltage measured at 119879 = 30∘

frequency of the VCSELsrsquo spectrum at 8mA bias is 8572 nmTheDACoutput is amplified to a 12 Vp-p signal that is used todrive the VCSEL biased at 8mA An optical power of 6 dBmis launched into 100m of OM3 compliant MMF with a totallink loss of 05 dBThe signal is photodetectedwith an 850 nmphotodiode reverse biased at 4VThe signal is then amplifiedto a Vp-p of 1 V and digitally stored with an 80GSas DSOwith a resolution of 8 bits

23 Long Range and Extended Range The signals generatedby a 4-output DAC are decorrelated with delay lines Thelaser source used in these scenarios is EML The bias voltageand temperature characteristics of the EML employed in

Lane 2 are presented in Figure 6 The EMLrsquos bias voltage isminus15 V and the MultiCAP signal has a CMOS compatiblepeak-to-peak voltage of 25 Vp-p The center wavelengths ofthe EMLs in Lanes 0 to 3 are 1294 nm 1299 nm 1303 nm and1308 nm In order to keep thewavelengths stable temperaturecontrol is appliedThe output power of the EML in the testedlane is 6 dBmAverage output power of the EMLs ranges from4 dBm to 6 dBm

The optical signals are combined in a LAN-WDMmulti-plexer (MUX) with a channel spacing of 800GHz (G6941compliant) and transmitted over 20 km or 40 km (G652compliant) SSMF links MUX introduces 06 dB of insertionloss The span losses are 7 dB and 14 dB respectively For the

6 Advances in Optical Technologies

Table 2 Equalizerrsquos performance in terms of BER as comparedto the nonequalized system measured for three different signal-to-noise ratio (SNR) settings compared systems nonequalized systemwith a standard multimodulus algorithm (MMA) equalization andwith decision directed (DD)119870-means equalizer

SNR(dB)

BERnonequalized

system

BERMMA

equalizer

BERDD 119870-meansequalizer

206 189 sdot 10minus2 383 sdot 10minus3 867 sdot 10minus4

195 223 sdot 10minus2 766 sdot 10minus3 39 sdot 10minus3

182 367 sdot 10minus2 196 sdot 10minus2 148 sdot 10minus2

40 km transmission case a semiconductor optical amplifier(SOA) with a noise figure (NF) of 65 dB is employed atthe receiver before demultiplexing At the receiver sidethe signal is demultiplexed by a LAN-WDM demultiplexer(DEMUX) received by a photodiode (PD) and amplified by atransimpedance amplifier (TIA) DEMUX introduces 09 dBof insertion loss All of the components are 100GBASE-LR4and ER4 compatible

24 Demodulation and Equalization The receiver consistsof several digital signal processing (DSP) blocks which areimplemented in Matlab environment CAP filtering signaldownsampling phase offset removal and signal normal-ization are performed as explained in [3] Additionally weimplement an adaptive frequency domain equalization tomitigate linear impairmentsThe described adaptive decisiondirected (DD) equalization algorithmminimizes the receivedconstellation cluster size and quantization noise

We define the reference constellation by the centroidsfound using 119870-means algorithm which groups the receiveddata in the clusters [17]This reference constellation initializesthe describedDD equalization algorithm Clustersrsquo means arethe points of reference (starting decision)

We use an iterative equalizer where in every iteration thefollowing steps are performed first the error is calculatedbased on the Euclidean distance from the closest centroid asin a least mean square (LMS) equalizer

120576 (119899) = min 1003817100381710038171003817Cminus119910 (119899)

1003817100381710038171003817 (1)

where C denotes all centroids of the reference constellationand 119910(119899) is the received signal sample For equalization weuse 1198792 fractionally spaced FIR filter with 12 taps determinedempirically The taps coefficients of the DD equalizer areupdated according to the following equation

ℎ (119899 + 1) = ℎ (119899) + 120583 (119899) sdot 120576 (119899) sdot 119910 (119899)lowast (2)

where ℎ(119899) is the equalizer coefficient 120583(119899) is the step sizeinitialized as 75 sdot 10minus4 and 119910(119899)lowast is the complex conju-gate 119910(119899) Secondly the received signal is passed throughthe equalizer Finally the iterative process reestimates thecentroids of the equalized constellation and the describedsteps are repeated It was experimentally determined that2 iterations result in satisfactory equalization and furtheriterations do not show the performance improvement Toassure a faster convergence we implement the variable stepin DDThe step size is updated in the following manner [18]

120583 (119899 + 1) =120583 (119899)

1 + 120582120583 (119899) |120576 (119899)|2

120582 =

1 if 119899 = 0

0 if sgn (Re 120576 (119899)) = sgn (Re 120576 (119899 minus 1)) sgn (Im 120576 (119899)) = sgn (Im 120576 (119899 minus 1))

1 otherwise

(3)

where sgn denotes a sign functionIn order to quantify the improvement due to using an

equalizer we calculate BER for the equalized and nonequal-ized system for three different SNR values Moreover wepresent BER calculated for the system with a standard fre-quency domain equalizer namely multimodulus algorithm(MMA) Table 2 summarizes the BERs for all equalizationand SNR scenarios Decision directed (DD) 119870-means equal-izer improves the performance in terms of BER in all threeSNR scenarios At SNR of 206 dB using an equalizer allowsfor the improvement of 00181 in terms of BER In thefollowing sections all of the presented results are equalizedusing DD119870-means algorithm

After the signal is equalized the EVM is calculated andBER is computed In order to calculate bit error rate (BER)

the received demodulated signal is cross-correlated with thetransmitted signal and the errors are counted

3 Experimental Results

Figure 7 shows the measured BER curves for SR scenario Wedefine the sensitivity at a BER of the hard decision FEC codeat 7 overhead For the reported system it is 45 sdot 10minus3 [19]Thereby we can observe sensitivities of 21 47 and 54 dBmfor experimentally obtained 704Gbps over 1m 704Gbpsover 100m and 80Gbps over 1m respectivelyThemeasuredtransmission penalty after 100mMMF is 25 dB

For LR scenario per lane received bit error ratio (BER)back-to-back (B2B) and after 20 km SSMF transmission (noSOA) of the received signal is plotted in Figure 8(a) The

Advances in Optical Technologies 7

7 FEC limit

minus16

minus20

minus24

minus28

2 3 54 6

P (dBm)

70Gbps 1m80Gbps 1m

70Gbps 100m

log10(B

ER)

Figure 7 BER versus received optical power (ROP) for B2B and 100m transmission for 70GbpsMultiCAP configuration andB2B for 80Gbpsconfiguration

Received optical power per lane (dBm)

7 FEC limit

Lane 0 Lane 1

Lane 2 Lane 3

minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

minus9 minus8 minus7 minus6 minus5 minus4 minus3

log10(B

ER)

(a)

Received optical power per lane (dBm)

Single lane B2B

WDM center lane B2BWDM side lane B2B

7 FEC limit

minus14 minus13 minus12 minus11 minus10 minus9 minus8 minus7 minus6minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

Single lane 40kmWDM center lane 40km

WDM side lane 40km

log10(B

ER)

(b)Figure 8 (a) BER versus received optical power (ROP) for B2B and 20 km transmission for 4 lanes (b) BER versus ROP for the datatransmitted in the single lane (Lane 2) and for the data transmitted in all lines (BER curves for center lane Lane 2 and side lane Lane3) ROP measured before SOA the total bitrate of WDM system is 432Gbps

received optical power is measured before the MUX For allLAN-WDM lanes BERs are below the 7 hard decision FEClimit and no error floor is observed within the tested powerrange Receiver sensitivity at the FEC limit is minus60 dBm B2Band minus66 dBm after transmission No transmission powerpenalty is observedThe results for ER scenario are presentedin Figure 8(b) Received BER of a center lane and a side laneis plotted B2B and after 40 km SSMF transmission with all 4LAN-WDM lanes simultaneously amplified by a single SOAbefore demultiplexing Received optical power per channelis measured before the SOA For comparison the BER of asingle lane (remaining three lanes switched off) is includedin the graph All LAN-WDM lanes were received with a BERbelow the FEC limit after 40 km SSMF transmission with

a worst-case receiver sensitivity of minus99 dBm Presence ofneighboring channels in the link does not introduce penaltyin the 20 km scenario In case of 40 km scenario we observea 05 dB power penalty for the center lanes in the 4-lane casedue to interlanemodulation in the SOA In both scenarios nopenalty is observed in the side lanes

In the results presented BER is an average of the BERs inall MultiCAP bands

Finally the power budget calculation is evaluated inTable 3 For the SR scenario the optical output power mea-sured at the output of the VCSEL is 6 dBm The sensitivityat 7 FEC limit for 70Gbps 1m transmissions is equal to24 dBmTherefore power budget for this scenario is equal to36 dB In the LR and ER scenarios the optical output power

8 Advances in Optical Technologies

Table 3 System power budget

Transmissionlink type

Outputpower

Sensitivity FEC limit

Systempowerbudget

sr 70Gbps 6 dBm 24 dBm 36 dBLR 20 kmunamplified 54 dBm minus66 dBm 126 dB

ER 40 km SOAamplified 54 dBm minus99 dBm 159 dB

per lane is equal to 54 dBm It is measured after transmitterand hence after MUX The worst receiver sensitivity isminus66 dBm at FEC limit in case of 20 km transmission linkwith no amplification Therefore the power budget of thislink is 126 dB In case of 40 km transmission with SOA basedamplification the worst receiver sensitivity is minus99 dBm at theFEC limit Therefore for the amplified 40 km link the powerbudget is 159 dB The given receiver sensitivity is based onROP measured before receiver before PD in SR case beforeDEMUX in LR case and before SOA in ER case

The SR scenario represents a solution for an active opticalcable for data centers In terms of power budget themargin isnecessary only for the components heating up and aging Incase of LR and ER the calculated margin of 56 dB and 19 dBis sufficient for client-side links

4 Discussion

In the results presented for SR a steep roll-off of the VCSELrsquosfrequency response reduces the achievable capacity We usethe bit loading and power loading features of MultiCAP toovercome those limitations at the cost of worse sensitivityAs a consequence increasing the capacity from 70Gbpsto 80Gbps introduces the 31 dB penalty in sensitivity asshown in Figure 7 The bandwidth of the existing VCSELsis not sufficient to support 100Gbps per lane With theproposed MultiCAP scheme the emerging 25Gbps VCSELsare expected to satisfy the bandwidth requirement

The performance of the EMLs used in LR and ER issatisfactory to obtain 100Gbps after FEC per lane Moreoverthe local area network-wavelength division multiplexing(LAN-WDM) is proved to introduce negligible penalty bothfor 20 km and for 40 km link The power budget calculationindicates the maturity of the solution which allows for linklosses of 126 dB and 159 dB in LR and ER respectively

The clear difference in performance and achievablecapacity between SR and LR ER scenarios is attributedto the system bandwidth Even though the 3 dB and 10 dBbandwidths are similar for both systems the 20 dBbandwidthvaries by 5 dB For this reason the MultiCAP in SR isrecoverable when it occupies up to 21GHz while the LR andER signal is possible to recover when it occupies 26GHz(Figure 4) The last band in all three scenarios is highlysuppressed but thanks to the power loading and bit loadingfeatures of MultiCAP the information in the last band is alsopossible to recover if it carries QPSK

The proposed approach for 400Gbits client-side trans-mission links using MultiCAP modulation format representsan easily applicable solution that is robust simple and flexiblein upgrading from 100Gbits to 400Gbits while operating atthe O-band LAN-WDM wavelengths Moreover we presentapplicability of the MultiCAP solution in the SR multimode(MM) links We expect that with higher bandwidth of theupcoming 850 nmVCSELs this solution will enable 100Gbpsper lane and 400Gbps using parallel optics This technologypotentially provides a bridge for gray optics approach toclient-side inter- and intradata centers access and metrosegments

5 Conclusions

We present a uniform MultiCAP based solution for shortrange (SR) MM links long range (LR) 20 km single mode(SM) links and extended range (ER) 40 km SM links Theadvantageous feature of MultiCAP approach of being ableto assign parallel electrical interfaces of smaller bandwidthinto different frequency bands overcomes both electrical andoptical bandwidth limitations and eases the DSP pipeliningIts pass-band nature and multiband structure allow optimalusage of the available bandwidth maximizing obtainablecapacity In the SR scenario we have achieved record below-FEC bit rate transmission of 657 Gbps over 100m and747Gbps over 1m for 850 nmMMFdata links For upcoming400 GE standard long range and extended range criteria wepresent a MultiCAP LAN-WDM 400Gbps solution whichuses only commercial optical components from 100GBASE-LR4 and ER4 432Gbits MultiCAP signals are transmittedover 20 km SSMF without amplification and over 40 kmSSMF with SOA Interchannel mixing in the 40 km link andin SOA is proven to be negligible for a MultiCAP IMDDLAN-WDM system The proposed MultiCAP approach isa robust and flexible scheme which can cover most of theclient-side scenarios including inter- and intradata centersand up to 40 km client-side links

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] IEEE 400 Gbs Ethernet Study Group Meeting Materials 2014[2] J DrsquoAmbrosia and P Mooney ldquo400 Gbs ethernet why nowrdquo

Whitepaper of Ethernet Alliance 2013[3] M I Olmedo T Zuo J B Jensen et al ldquoMultiband carrierless

amplitude phase modulation for high capacity optical datalinksrdquo Journal of Lightwave Technology vol 32 no 4 pp 798ndash804 2014

[4] M I Olmedo A Tatarczak T Zuo J Estaran X Xu and I TMonroy ldquoTowards 100 Gbps over 100m MMF using a 850 nmVCSELrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash4 March 2014

[5] T Zuo A Tatarczak M Olmedo et al ldquoO-band 400 Gbitsclient side optical transmission linkrdquo in Proceedings of the

Advances in Optical Technologies 9

Optical Fiber Communications Conference and Exhibition (OFCrsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[6] K Szczerba PWestberghM Karlsson P A Andrekson andALarsson ldquo70Gbps 4-PAMand 56Gbps 8-PAMusing an 850 nmVCSELrdquo in Proceedings of the European Conference on OpticalCommunication (ECOC rsquo14) September 2014

[7] D Kuchta A V Rylyakov C L Schow et al ldquo64Gbs transmis-sion over 57mMMFusing anNRZmodulated 850 nmVCSELrdquoin Proceedings of the Optical Fiber Communications Conferenceand Exhibition (OFC rsquo14) pp 1ndash3 Optical Society of AmericaMarch 2014

[8] L Raddatz and I HWhite ldquoOvercoming themodal bandwidthlimitation of multimode fiber by using passband modulationrdquoIEEE Photonics Technology Letters vol 11 no 2 pp 266ndash2681999

[9] S Lee F Breyer S Randel D Cardenas H van den Boomand A Koonen ldquoDiscrete multitone modulation for high-speed data transmission over multimode fibers using 850-nmVCSELrdquo in Proceedings of the Conference on Optical FiberCommunicationmdashIncudes Post Deadline Papers (OFC rsquo09) pp1ndash3 IEEE San Diego Calif USA March 2009

[10] Y Doi T Ohyama T Yoshimatsu S Soma and M Ogumaldquo400GbE demonstration utilizing 100GbE optical sub-assem-blies and cyclic arrayed waveguide gratingsrdquo in Proceedings ofthe Optical Fiber Communications Conference and Exhibition(OFC rsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[11] W Kobayashi T Fujisawa S Kanazawa and H Sanjoh ldquo25Gbauds 4-PAM (50 Gbits) modulation and 10 km SMF trans-mission with 13 120583m InGaAlAs-based DMLrdquo Electronics Lettersvol 50 no 4 pp 299ndash300 2014

[12] J Zhang X Li Y Xia et al ldquo60-Gbs CAP-64QAM Transmis-sion using DML with direct detection and digital equalizationrdquoin Proceedings of the Optical Fiber Communication Conferenceand Exposition and the National Fiber Optic Engineers Confer-ence (OFCNFOEC rsquo14) IEEE March 2014

[13] T Chan I-C Lu J Chen W Way and T Chan ldquo400-Gbstransmission over 10-km SSMF using discrete multitone and13-mm EMLsrdquo IEEE Photonics Technology Letters vol 26 no16 pp 1657ndash1660 2014

[14] J P Turkiewicz and H de Waardt ldquoLow complexity up to 400-Gbs transmission in the 1310-nm wavelength domainrdquo IEEEPhotonics Technology Letters vol 24 no 11 pp 942ndash944 2012

[15] W Yan L Li B Liu et al ldquo80 km IMDD transmission for 100Gbs per lane enabled by DMT and nonlinearity managementrdquoin Proceedings of the Optical Fiber Communication ConferencepM2I4 Optical Society of America San Francisco Calif USAMarch 2014

[16] T Tanaka M Nishihara T Takahara et al ldquoExperimentaldemonstration of 448-Gbps+ DMT transmission over 30-kmSMFrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash3 March 2014

[17] N G Gonzalez D Zibar X Yu and I T Monroy ldquoOpticalphase-modulated radio-over-fiber links with K-means algo-rithm for digital demodulation of 8PSK subcarrier multiplexedsignalsrdquo in Proceedings of the Conference on Optical FiberCommunication CollocatedNational Fiber Optic Engineers Con-ference (OFCNFOEC rsquo10) pp 1ndash3 March 2010

[18] D Ashmawy K Banovic E Abdel-Raheem M Youssif HMansour and M Mohanna ldquoJoint MCMA and DD blindequalization algorithm with variable-step sizerdquo in Proceedingsof the IEEE International Conference on ElectroInformationTechnology (EIT rsquo09) pp 174ndash177 June 2009

[19] F Chang K Onohara and T Mizuochi ldquoForward error cor-rection for 100 G transport networksrdquo IEEE CommunicationsMagazine vol 48 no 3 pp S48ndashS55 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

4 Advances in Optical Technologies

0 5 10 15 20 25 30

0Fr

eque

ncy

resp

onse

(dB)

Frequency (GHz)

Short range scenario

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

S21

(a)

0 5 10 15 20 25 30Frequency (GHz)

Long reach and extended reach scenario0

Freq

uenc

y re

spon

se (d

B)

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

S21

(b)

(dBm

)

20151050

minus20

minus40

minus60

(GHz)

(c)

(dBm

) minus20

minus40

minus602015

(GHz)1050

(d)

2520151050

(dBm

) minus20

minus40

minus60

minus80

(GHz)

(e)Figure 4 (a) Frequency response measured for short range (SR) scenario end-to-end link (b) frequency response measured for the opticalback-to-back of long range (LR) and extended range (ER) scenarios Received electricalMultiCAP spectrumand corresponding constellationstransmitted in each MultiCAP band for (c) short range (SR) scenario with total bit rate 704Gbps (d) short range (SR) scenario with total bitrate 80Gbps (e) long range (LR) and extended range (ER) scenarios with total bit rate 108Gbps

5

4

3

2

1

0

5

4

3

2

1

0

Pow

er (m

W)

Pow

er (m

W)

14 852 854 856 858 860121086420

Current (mA) Wavelength (nm)

Voltage

Volta

ge (m

V)

Power

012

010

008

006

004

002

000

Figure 5 Characterization of the VCSEL used in the short range scenario LIV curve measured at the room temperature optical spectrummeasured at bias current of 8mA

Advances in Optical Technologies 5

T = 30∘C

Vbias = minus15V

10

5

0

0

1304

1303

1302

130274

130272

130270

130268

minus5

minus3 minus2 minus1

minus10

minus15

minus20

Pow

er (d

Bm)

Lane 2 EML Lane 2 EML

Lane 2 EMLBias voltage (V)

Wav

eleng

th (n

m)

20 25 30 35 40 45

Temperature

Wav

eleng

th (n

m)

0minus2 minus1

Bias voltage (V)

T = 30∘C

(∘C)

Figure 6 Characterization of the EML of Lane 2 power versus bias current measured at 119879 = 30∘ wavelength versus temperature measuredat bias voltage of minus15 V wavelength versus bias voltage measured at 119879 = 30∘

frequency of the VCSELsrsquo spectrum at 8mA bias is 8572 nmTheDACoutput is amplified to a 12 Vp-p signal that is used todrive the VCSEL biased at 8mA An optical power of 6 dBmis launched into 100m of OM3 compliant MMF with a totallink loss of 05 dBThe signal is photodetectedwith an 850 nmphotodiode reverse biased at 4VThe signal is then amplifiedto a Vp-p of 1 V and digitally stored with an 80GSas DSOwith a resolution of 8 bits

23 Long Range and Extended Range The signals generatedby a 4-output DAC are decorrelated with delay lines Thelaser source used in these scenarios is EML The bias voltageand temperature characteristics of the EML employed in

Lane 2 are presented in Figure 6 The EMLrsquos bias voltage isminus15 V and the MultiCAP signal has a CMOS compatiblepeak-to-peak voltage of 25 Vp-p The center wavelengths ofthe EMLs in Lanes 0 to 3 are 1294 nm 1299 nm 1303 nm and1308 nm In order to keep thewavelengths stable temperaturecontrol is appliedThe output power of the EML in the testedlane is 6 dBmAverage output power of the EMLs ranges from4 dBm to 6 dBm

The optical signals are combined in a LAN-WDMmulti-plexer (MUX) with a channel spacing of 800GHz (G6941compliant) and transmitted over 20 km or 40 km (G652compliant) SSMF links MUX introduces 06 dB of insertionloss The span losses are 7 dB and 14 dB respectively For the

6 Advances in Optical Technologies

Table 2 Equalizerrsquos performance in terms of BER as comparedto the nonequalized system measured for three different signal-to-noise ratio (SNR) settings compared systems nonequalized systemwith a standard multimodulus algorithm (MMA) equalization andwith decision directed (DD)119870-means equalizer

SNR(dB)

BERnonequalized

system

BERMMA

equalizer

BERDD 119870-meansequalizer

206 189 sdot 10minus2 383 sdot 10minus3 867 sdot 10minus4

195 223 sdot 10minus2 766 sdot 10minus3 39 sdot 10minus3

182 367 sdot 10minus2 196 sdot 10minus2 148 sdot 10minus2

40 km transmission case a semiconductor optical amplifier(SOA) with a noise figure (NF) of 65 dB is employed atthe receiver before demultiplexing At the receiver sidethe signal is demultiplexed by a LAN-WDM demultiplexer(DEMUX) received by a photodiode (PD) and amplified by atransimpedance amplifier (TIA) DEMUX introduces 09 dBof insertion loss All of the components are 100GBASE-LR4and ER4 compatible

24 Demodulation and Equalization The receiver consistsof several digital signal processing (DSP) blocks which areimplemented in Matlab environment CAP filtering signaldownsampling phase offset removal and signal normal-ization are performed as explained in [3] Additionally weimplement an adaptive frequency domain equalization tomitigate linear impairmentsThe described adaptive decisiondirected (DD) equalization algorithmminimizes the receivedconstellation cluster size and quantization noise

We define the reference constellation by the centroidsfound using 119870-means algorithm which groups the receiveddata in the clusters [17]This reference constellation initializesthe describedDD equalization algorithm Clustersrsquo means arethe points of reference (starting decision)

We use an iterative equalizer where in every iteration thefollowing steps are performed first the error is calculatedbased on the Euclidean distance from the closest centroid asin a least mean square (LMS) equalizer

120576 (119899) = min 1003817100381710038171003817Cminus119910 (119899)

1003817100381710038171003817 (1)

where C denotes all centroids of the reference constellationand 119910(119899) is the received signal sample For equalization weuse 1198792 fractionally spaced FIR filter with 12 taps determinedempirically The taps coefficients of the DD equalizer areupdated according to the following equation

ℎ (119899 + 1) = ℎ (119899) + 120583 (119899) sdot 120576 (119899) sdot 119910 (119899)lowast (2)

where ℎ(119899) is the equalizer coefficient 120583(119899) is the step sizeinitialized as 75 sdot 10minus4 and 119910(119899)lowast is the complex conju-gate 119910(119899) Secondly the received signal is passed throughthe equalizer Finally the iterative process reestimates thecentroids of the equalized constellation and the describedsteps are repeated It was experimentally determined that2 iterations result in satisfactory equalization and furtheriterations do not show the performance improvement Toassure a faster convergence we implement the variable stepin DDThe step size is updated in the following manner [18]

120583 (119899 + 1) =120583 (119899)

1 + 120582120583 (119899) |120576 (119899)|2

120582 =

1 if 119899 = 0

0 if sgn (Re 120576 (119899)) = sgn (Re 120576 (119899 minus 1)) sgn (Im 120576 (119899)) = sgn (Im 120576 (119899 minus 1))

1 otherwise

(3)

where sgn denotes a sign functionIn order to quantify the improvement due to using an

equalizer we calculate BER for the equalized and nonequal-ized system for three different SNR values Moreover wepresent BER calculated for the system with a standard fre-quency domain equalizer namely multimodulus algorithm(MMA) Table 2 summarizes the BERs for all equalizationand SNR scenarios Decision directed (DD) 119870-means equal-izer improves the performance in terms of BER in all threeSNR scenarios At SNR of 206 dB using an equalizer allowsfor the improvement of 00181 in terms of BER In thefollowing sections all of the presented results are equalizedusing DD119870-means algorithm

After the signal is equalized the EVM is calculated andBER is computed In order to calculate bit error rate (BER)

the received demodulated signal is cross-correlated with thetransmitted signal and the errors are counted

3 Experimental Results

Figure 7 shows the measured BER curves for SR scenario Wedefine the sensitivity at a BER of the hard decision FEC codeat 7 overhead For the reported system it is 45 sdot 10minus3 [19]Thereby we can observe sensitivities of 21 47 and 54 dBmfor experimentally obtained 704Gbps over 1m 704Gbpsover 100m and 80Gbps over 1m respectivelyThemeasuredtransmission penalty after 100mMMF is 25 dB

For LR scenario per lane received bit error ratio (BER)back-to-back (B2B) and after 20 km SSMF transmission (noSOA) of the received signal is plotted in Figure 8(a) The

Advances in Optical Technologies 7

7 FEC limit

minus16

minus20

minus24

minus28

2 3 54 6

P (dBm)

70Gbps 1m80Gbps 1m

70Gbps 100m

log10(B

ER)

Figure 7 BER versus received optical power (ROP) for B2B and 100m transmission for 70GbpsMultiCAP configuration andB2B for 80Gbpsconfiguration

Received optical power per lane (dBm)

7 FEC limit

Lane 0 Lane 1

Lane 2 Lane 3

minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

minus9 minus8 minus7 minus6 minus5 minus4 minus3

log10(B

ER)

(a)

Received optical power per lane (dBm)

Single lane B2B

WDM center lane B2BWDM side lane B2B

7 FEC limit

minus14 minus13 minus12 minus11 minus10 minus9 minus8 minus7 minus6minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

Single lane 40kmWDM center lane 40km

WDM side lane 40km

log10(B

ER)

(b)Figure 8 (a) BER versus received optical power (ROP) for B2B and 20 km transmission for 4 lanes (b) BER versus ROP for the datatransmitted in the single lane (Lane 2) and for the data transmitted in all lines (BER curves for center lane Lane 2 and side lane Lane3) ROP measured before SOA the total bitrate of WDM system is 432Gbps

received optical power is measured before the MUX For allLAN-WDM lanes BERs are below the 7 hard decision FEClimit and no error floor is observed within the tested powerrange Receiver sensitivity at the FEC limit is minus60 dBm B2Band minus66 dBm after transmission No transmission powerpenalty is observedThe results for ER scenario are presentedin Figure 8(b) Received BER of a center lane and a side laneis plotted B2B and after 40 km SSMF transmission with all 4LAN-WDM lanes simultaneously amplified by a single SOAbefore demultiplexing Received optical power per channelis measured before the SOA For comparison the BER of asingle lane (remaining three lanes switched off) is includedin the graph All LAN-WDM lanes were received with a BERbelow the FEC limit after 40 km SSMF transmission with

a worst-case receiver sensitivity of minus99 dBm Presence ofneighboring channels in the link does not introduce penaltyin the 20 km scenario In case of 40 km scenario we observea 05 dB power penalty for the center lanes in the 4-lane casedue to interlanemodulation in the SOA In both scenarios nopenalty is observed in the side lanes

In the results presented BER is an average of the BERs inall MultiCAP bands

Finally the power budget calculation is evaluated inTable 3 For the SR scenario the optical output power mea-sured at the output of the VCSEL is 6 dBm The sensitivityat 7 FEC limit for 70Gbps 1m transmissions is equal to24 dBmTherefore power budget for this scenario is equal to36 dB In the LR and ER scenarios the optical output power

8 Advances in Optical Technologies

Table 3 System power budget

Transmissionlink type

Outputpower

Sensitivity FEC limit

Systempowerbudget

sr 70Gbps 6 dBm 24 dBm 36 dBLR 20 kmunamplified 54 dBm minus66 dBm 126 dB

ER 40 km SOAamplified 54 dBm minus99 dBm 159 dB

per lane is equal to 54 dBm It is measured after transmitterand hence after MUX The worst receiver sensitivity isminus66 dBm at FEC limit in case of 20 km transmission linkwith no amplification Therefore the power budget of thislink is 126 dB In case of 40 km transmission with SOA basedamplification the worst receiver sensitivity is minus99 dBm at theFEC limit Therefore for the amplified 40 km link the powerbudget is 159 dB The given receiver sensitivity is based onROP measured before receiver before PD in SR case beforeDEMUX in LR case and before SOA in ER case

The SR scenario represents a solution for an active opticalcable for data centers In terms of power budget themargin isnecessary only for the components heating up and aging Incase of LR and ER the calculated margin of 56 dB and 19 dBis sufficient for client-side links

4 Discussion

In the results presented for SR a steep roll-off of the VCSELrsquosfrequency response reduces the achievable capacity We usethe bit loading and power loading features of MultiCAP toovercome those limitations at the cost of worse sensitivityAs a consequence increasing the capacity from 70Gbpsto 80Gbps introduces the 31 dB penalty in sensitivity asshown in Figure 7 The bandwidth of the existing VCSELsis not sufficient to support 100Gbps per lane With theproposed MultiCAP scheme the emerging 25Gbps VCSELsare expected to satisfy the bandwidth requirement

The performance of the EMLs used in LR and ER issatisfactory to obtain 100Gbps after FEC per lane Moreoverthe local area network-wavelength division multiplexing(LAN-WDM) is proved to introduce negligible penalty bothfor 20 km and for 40 km link The power budget calculationindicates the maturity of the solution which allows for linklosses of 126 dB and 159 dB in LR and ER respectively

The clear difference in performance and achievablecapacity between SR and LR ER scenarios is attributedto the system bandwidth Even though the 3 dB and 10 dBbandwidths are similar for both systems the 20 dBbandwidthvaries by 5 dB For this reason the MultiCAP in SR isrecoverable when it occupies up to 21GHz while the LR andER signal is possible to recover when it occupies 26GHz(Figure 4) The last band in all three scenarios is highlysuppressed but thanks to the power loading and bit loadingfeatures of MultiCAP the information in the last band is alsopossible to recover if it carries QPSK

The proposed approach for 400Gbits client-side trans-mission links using MultiCAP modulation format representsan easily applicable solution that is robust simple and flexiblein upgrading from 100Gbits to 400Gbits while operating atthe O-band LAN-WDM wavelengths Moreover we presentapplicability of the MultiCAP solution in the SR multimode(MM) links We expect that with higher bandwidth of theupcoming 850 nmVCSELs this solution will enable 100Gbpsper lane and 400Gbps using parallel optics This technologypotentially provides a bridge for gray optics approach toclient-side inter- and intradata centers access and metrosegments

5 Conclusions

We present a uniform MultiCAP based solution for shortrange (SR) MM links long range (LR) 20 km single mode(SM) links and extended range (ER) 40 km SM links Theadvantageous feature of MultiCAP approach of being ableto assign parallel electrical interfaces of smaller bandwidthinto different frequency bands overcomes both electrical andoptical bandwidth limitations and eases the DSP pipeliningIts pass-band nature and multiband structure allow optimalusage of the available bandwidth maximizing obtainablecapacity In the SR scenario we have achieved record below-FEC bit rate transmission of 657 Gbps over 100m and747Gbps over 1m for 850 nmMMFdata links For upcoming400 GE standard long range and extended range criteria wepresent a MultiCAP LAN-WDM 400Gbps solution whichuses only commercial optical components from 100GBASE-LR4 and ER4 432Gbits MultiCAP signals are transmittedover 20 km SSMF without amplification and over 40 kmSSMF with SOA Interchannel mixing in the 40 km link andin SOA is proven to be negligible for a MultiCAP IMDDLAN-WDM system The proposed MultiCAP approach isa robust and flexible scheme which can cover most of theclient-side scenarios including inter- and intradata centersand up to 40 km client-side links

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] IEEE 400 Gbs Ethernet Study Group Meeting Materials 2014[2] J DrsquoAmbrosia and P Mooney ldquo400 Gbs ethernet why nowrdquo

Whitepaper of Ethernet Alliance 2013[3] M I Olmedo T Zuo J B Jensen et al ldquoMultiband carrierless

amplitude phase modulation for high capacity optical datalinksrdquo Journal of Lightwave Technology vol 32 no 4 pp 798ndash804 2014

[4] M I Olmedo A Tatarczak T Zuo J Estaran X Xu and I TMonroy ldquoTowards 100 Gbps over 100m MMF using a 850 nmVCSELrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash4 March 2014

[5] T Zuo A Tatarczak M Olmedo et al ldquoO-band 400 Gbitsclient side optical transmission linkrdquo in Proceedings of the

Advances in Optical Technologies 9

Optical Fiber Communications Conference and Exhibition (OFCrsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[6] K Szczerba PWestberghM Karlsson P A Andrekson andALarsson ldquo70Gbps 4-PAMand 56Gbps 8-PAMusing an 850 nmVCSELrdquo in Proceedings of the European Conference on OpticalCommunication (ECOC rsquo14) September 2014

[7] D Kuchta A V Rylyakov C L Schow et al ldquo64Gbs transmis-sion over 57mMMFusing anNRZmodulated 850 nmVCSELrdquoin Proceedings of the Optical Fiber Communications Conferenceand Exhibition (OFC rsquo14) pp 1ndash3 Optical Society of AmericaMarch 2014

[8] L Raddatz and I HWhite ldquoOvercoming themodal bandwidthlimitation of multimode fiber by using passband modulationrdquoIEEE Photonics Technology Letters vol 11 no 2 pp 266ndash2681999

[9] S Lee F Breyer S Randel D Cardenas H van den Boomand A Koonen ldquoDiscrete multitone modulation for high-speed data transmission over multimode fibers using 850-nmVCSELrdquo in Proceedings of the Conference on Optical FiberCommunicationmdashIncudes Post Deadline Papers (OFC rsquo09) pp1ndash3 IEEE San Diego Calif USA March 2009

[10] Y Doi T Ohyama T Yoshimatsu S Soma and M Ogumaldquo400GbE demonstration utilizing 100GbE optical sub-assem-blies and cyclic arrayed waveguide gratingsrdquo in Proceedings ofthe Optical Fiber Communications Conference and Exhibition(OFC rsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[11] W Kobayashi T Fujisawa S Kanazawa and H Sanjoh ldquo25Gbauds 4-PAM (50 Gbits) modulation and 10 km SMF trans-mission with 13 120583m InGaAlAs-based DMLrdquo Electronics Lettersvol 50 no 4 pp 299ndash300 2014

[12] J Zhang X Li Y Xia et al ldquo60-Gbs CAP-64QAM Transmis-sion using DML with direct detection and digital equalizationrdquoin Proceedings of the Optical Fiber Communication Conferenceand Exposition and the National Fiber Optic Engineers Confer-ence (OFCNFOEC rsquo14) IEEE March 2014

[13] T Chan I-C Lu J Chen W Way and T Chan ldquo400-Gbstransmission over 10-km SSMF using discrete multitone and13-mm EMLsrdquo IEEE Photonics Technology Letters vol 26 no16 pp 1657ndash1660 2014

[14] J P Turkiewicz and H de Waardt ldquoLow complexity up to 400-Gbs transmission in the 1310-nm wavelength domainrdquo IEEEPhotonics Technology Letters vol 24 no 11 pp 942ndash944 2012

[15] W Yan L Li B Liu et al ldquo80 km IMDD transmission for 100Gbs per lane enabled by DMT and nonlinearity managementrdquoin Proceedings of the Optical Fiber Communication ConferencepM2I4 Optical Society of America San Francisco Calif USAMarch 2014

[16] T Tanaka M Nishihara T Takahara et al ldquoExperimentaldemonstration of 448-Gbps+ DMT transmission over 30-kmSMFrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash3 March 2014

[17] N G Gonzalez D Zibar X Yu and I T Monroy ldquoOpticalphase-modulated radio-over-fiber links with K-means algo-rithm for digital demodulation of 8PSK subcarrier multiplexedsignalsrdquo in Proceedings of the Conference on Optical FiberCommunication CollocatedNational Fiber Optic Engineers Con-ference (OFCNFOEC rsquo10) pp 1ndash3 March 2010

[18] D Ashmawy K Banovic E Abdel-Raheem M Youssif HMansour and M Mohanna ldquoJoint MCMA and DD blindequalization algorithm with variable-step sizerdquo in Proceedingsof the IEEE International Conference on ElectroInformationTechnology (EIT rsquo09) pp 174ndash177 June 2009

[19] F Chang K Onohara and T Mizuochi ldquoForward error cor-rection for 100 G transport networksrdquo IEEE CommunicationsMagazine vol 48 no 3 pp S48ndashS55 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

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RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Advances in Optical Technologies 5

T = 30∘C

Vbias = minus15V

10

5

0

0

1304

1303

1302

130274

130272

130270

130268

minus5

minus3 minus2 minus1

minus10

minus15

minus20

Pow

er (d

Bm)

Lane 2 EML Lane 2 EML

Lane 2 EMLBias voltage (V)

Wav

eleng

th (n

m)

20 25 30 35 40 45

Temperature

Wav

eleng

th (n

m)

0minus2 minus1

Bias voltage (V)

T = 30∘C

(∘C)

Figure 6 Characterization of the EML of Lane 2 power versus bias current measured at 119879 = 30∘ wavelength versus temperature measuredat bias voltage of minus15 V wavelength versus bias voltage measured at 119879 = 30∘

frequency of the VCSELsrsquo spectrum at 8mA bias is 8572 nmTheDACoutput is amplified to a 12 Vp-p signal that is used todrive the VCSEL biased at 8mA An optical power of 6 dBmis launched into 100m of OM3 compliant MMF with a totallink loss of 05 dBThe signal is photodetectedwith an 850 nmphotodiode reverse biased at 4VThe signal is then amplifiedto a Vp-p of 1 V and digitally stored with an 80GSas DSOwith a resolution of 8 bits

23 Long Range and Extended Range The signals generatedby a 4-output DAC are decorrelated with delay lines Thelaser source used in these scenarios is EML The bias voltageand temperature characteristics of the EML employed in

Lane 2 are presented in Figure 6 The EMLrsquos bias voltage isminus15 V and the MultiCAP signal has a CMOS compatiblepeak-to-peak voltage of 25 Vp-p The center wavelengths ofthe EMLs in Lanes 0 to 3 are 1294 nm 1299 nm 1303 nm and1308 nm In order to keep thewavelengths stable temperaturecontrol is appliedThe output power of the EML in the testedlane is 6 dBmAverage output power of the EMLs ranges from4 dBm to 6 dBm

The optical signals are combined in a LAN-WDMmulti-plexer (MUX) with a channel spacing of 800GHz (G6941compliant) and transmitted over 20 km or 40 km (G652compliant) SSMF links MUX introduces 06 dB of insertionloss The span losses are 7 dB and 14 dB respectively For the

6 Advances in Optical Technologies

Table 2 Equalizerrsquos performance in terms of BER as comparedto the nonequalized system measured for three different signal-to-noise ratio (SNR) settings compared systems nonequalized systemwith a standard multimodulus algorithm (MMA) equalization andwith decision directed (DD)119870-means equalizer

SNR(dB)

BERnonequalized

system

BERMMA

equalizer

BERDD 119870-meansequalizer

206 189 sdot 10minus2 383 sdot 10minus3 867 sdot 10minus4

195 223 sdot 10minus2 766 sdot 10minus3 39 sdot 10minus3

182 367 sdot 10minus2 196 sdot 10minus2 148 sdot 10minus2

40 km transmission case a semiconductor optical amplifier(SOA) with a noise figure (NF) of 65 dB is employed atthe receiver before demultiplexing At the receiver sidethe signal is demultiplexed by a LAN-WDM demultiplexer(DEMUX) received by a photodiode (PD) and amplified by atransimpedance amplifier (TIA) DEMUX introduces 09 dBof insertion loss All of the components are 100GBASE-LR4and ER4 compatible

24 Demodulation and Equalization The receiver consistsof several digital signal processing (DSP) blocks which areimplemented in Matlab environment CAP filtering signaldownsampling phase offset removal and signal normal-ization are performed as explained in [3] Additionally weimplement an adaptive frequency domain equalization tomitigate linear impairmentsThe described adaptive decisiondirected (DD) equalization algorithmminimizes the receivedconstellation cluster size and quantization noise

We define the reference constellation by the centroidsfound using 119870-means algorithm which groups the receiveddata in the clusters [17]This reference constellation initializesthe describedDD equalization algorithm Clustersrsquo means arethe points of reference (starting decision)

We use an iterative equalizer where in every iteration thefollowing steps are performed first the error is calculatedbased on the Euclidean distance from the closest centroid asin a least mean square (LMS) equalizer

120576 (119899) = min 1003817100381710038171003817Cminus119910 (119899)

1003817100381710038171003817 (1)

where C denotes all centroids of the reference constellationand 119910(119899) is the received signal sample For equalization weuse 1198792 fractionally spaced FIR filter with 12 taps determinedempirically The taps coefficients of the DD equalizer areupdated according to the following equation

ℎ (119899 + 1) = ℎ (119899) + 120583 (119899) sdot 120576 (119899) sdot 119910 (119899)lowast (2)

where ℎ(119899) is the equalizer coefficient 120583(119899) is the step sizeinitialized as 75 sdot 10minus4 and 119910(119899)lowast is the complex conju-gate 119910(119899) Secondly the received signal is passed throughthe equalizer Finally the iterative process reestimates thecentroids of the equalized constellation and the describedsteps are repeated It was experimentally determined that2 iterations result in satisfactory equalization and furtheriterations do not show the performance improvement Toassure a faster convergence we implement the variable stepin DDThe step size is updated in the following manner [18]

120583 (119899 + 1) =120583 (119899)

1 + 120582120583 (119899) |120576 (119899)|2

120582 =

1 if 119899 = 0

0 if sgn (Re 120576 (119899)) = sgn (Re 120576 (119899 minus 1)) sgn (Im 120576 (119899)) = sgn (Im 120576 (119899 minus 1))

1 otherwise

(3)

where sgn denotes a sign functionIn order to quantify the improvement due to using an

equalizer we calculate BER for the equalized and nonequal-ized system for three different SNR values Moreover wepresent BER calculated for the system with a standard fre-quency domain equalizer namely multimodulus algorithm(MMA) Table 2 summarizes the BERs for all equalizationand SNR scenarios Decision directed (DD) 119870-means equal-izer improves the performance in terms of BER in all threeSNR scenarios At SNR of 206 dB using an equalizer allowsfor the improvement of 00181 in terms of BER In thefollowing sections all of the presented results are equalizedusing DD119870-means algorithm

After the signal is equalized the EVM is calculated andBER is computed In order to calculate bit error rate (BER)

the received demodulated signal is cross-correlated with thetransmitted signal and the errors are counted

3 Experimental Results

Figure 7 shows the measured BER curves for SR scenario Wedefine the sensitivity at a BER of the hard decision FEC codeat 7 overhead For the reported system it is 45 sdot 10minus3 [19]Thereby we can observe sensitivities of 21 47 and 54 dBmfor experimentally obtained 704Gbps over 1m 704Gbpsover 100m and 80Gbps over 1m respectivelyThemeasuredtransmission penalty after 100mMMF is 25 dB

For LR scenario per lane received bit error ratio (BER)back-to-back (B2B) and after 20 km SSMF transmission (noSOA) of the received signal is plotted in Figure 8(a) The

Advances in Optical Technologies 7

7 FEC limit

minus16

minus20

minus24

minus28

2 3 54 6

P (dBm)

70Gbps 1m80Gbps 1m

70Gbps 100m

log10(B

ER)

Figure 7 BER versus received optical power (ROP) for B2B and 100m transmission for 70GbpsMultiCAP configuration andB2B for 80Gbpsconfiguration

Received optical power per lane (dBm)

7 FEC limit

Lane 0 Lane 1

Lane 2 Lane 3

minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

minus9 minus8 minus7 minus6 minus5 minus4 minus3

log10(B

ER)

(a)

Received optical power per lane (dBm)

Single lane B2B

WDM center lane B2BWDM side lane B2B

7 FEC limit

minus14 minus13 minus12 minus11 minus10 minus9 minus8 minus7 minus6minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

Single lane 40kmWDM center lane 40km

WDM side lane 40km

log10(B

ER)

(b)Figure 8 (a) BER versus received optical power (ROP) for B2B and 20 km transmission for 4 lanes (b) BER versus ROP for the datatransmitted in the single lane (Lane 2) and for the data transmitted in all lines (BER curves for center lane Lane 2 and side lane Lane3) ROP measured before SOA the total bitrate of WDM system is 432Gbps

received optical power is measured before the MUX For allLAN-WDM lanes BERs are below the 7 hard decision FEClimit and no error floor is observed within the tested powerrange Receiver sensitivity at the FEC limit is minus60 dBm B2Band minus66 dBm after transmission No transmission powerpenalty is observedThe results for ER scenario are presentedin Figure 8(b) Received BER of a center lane and a side laneis plotted B2B and after 40 km SSMF transmission with all 4LAN-WDM lanes simultaneously amplified by a single SOAbefore demultiplexing Received optical power per channelis measured before the SOA For comparison the BER of asingle lane (remaining three lanes switched off) is includedin the graph All LAN-WDM lanes were received with a BERbelow the FEC limit after 40 km SSMF transmission with

a worst-case receiver sensitivity of minus99 dBm Presence ofneighboring channels in the link does not introduce penaltyin the 20 km scenario In case of 40 km scenario we observea 05 dB power penalty for the center lanes in the 4-lane casedue to interlanemodulation in the SOA In both scenarios nopenalty is observed in the side lanes

In the results presented BER is an average of the BERs inall MultiCAP bands

Finally the power budget calculation is evaluated inTable 3 For the SR scenario the optical output power mea-sured at the output of the VCSEL is 6 dBm The sensitivityat 7 FEC limit for 70Gbps 1m transmissions is equal to24 dBmTherefore power budget for this scenario is equal to36 dB In the LR and ER scenarios the optical output power

8 Advances in Optical Technologies

Table 3 System power budget

Transmissionlink type

Outputpower

Sensitivity FEC limit

Systempowerbudget

sr 70Gbps 6 dBm 24 dBm 36 dBLR 20 kmunamplified 54 dBm minus66 dBm 126 dB

ER 40 km SOAamplified 54 dBm minus99 dBm 159 dB

per lane is equal to 54 dBm It is measured after transmitterand hence after MUX The worst receiver sensitivity isminus66 dBm at FEC limit in case of 20 km transmission linkwith no amplification Therefore the power budget of thislink is 126 dB In case of 40 km transmission with SOA basedamplification the worst receiver sensitivity is minus99 dBm at theFEC limit Therefore for the amplified 40 km link the powerbudget is 159 dB The given receiver sensitivity is based onROP measured before receiver before PD in SR case beforeDEMUX in LR case and before SOA in ER case

The SR scenario represents a solution for an active opticalcable for data centers In terms of power budget themargin isnecessary only for the components heating up and aging Incase of LR and ER the calculated margin of 56 dB and 19 dBis sufficient for client-side links

4 Discussion

In the results presented for SR a steep roll-off of the VCSELrsquosfrequency response reduces the achievable capacity We usethe bit loading and power loading features of MultiCAP toovercome those limitations at the cost of worse sensitivityAs a consequence increasing the capacity from 70Gbpsto 80Gbps introduces the 31 dB penalty in sensitivity asshown in Figure 7 The bandwidth of the existing VCSELsis not sufficient to support 100Gbps per lane With theproposed MultiCAP scheme the emerging 25Gbps VCSELsare expected to satisfy the bandwidth requirement

The performance of the EMLs used in LR and ER issatisfactory to obtain 100Gbps after FEC per lane Moreoverthe local area network-wavelength division multiplexing(LAN-WDM) is proved to introduce negligible penalty bothfor 20 km and for 40 km link The power budget calculationindicates the maturity of the solution which allows for linklosses of 126 dB and 159 dB in LR and ER respectively

The clear difference in performance and achievablecapacity between SR and LR ER scenarios is attributedto the system bandwidth Even though the 3 dB and 10 dBbandwidths are similar for both systems the 20 dBbandwidthvaries by 5 dB For this reason the MultiCAP in SR isrecoverable when it occupies up to 21GHz while the LR andER signal is possible to recover when it occupies 26GHz(Figure 4) The last band in all three scenarios is highlysuppressed but thanks to the power loading and bit loadingfeatures of MultiCAP the information in the last band is alsopossible to recover if it carries QPSK

The proposed approach for 400Gbits client-side trans-mission links using MultiCAP modulation format representsan easily applicable solution that is robust simple and flexiblein upgrading from 100Gbits to 400Gbits while operating atthe O-band LAN-WDM wavelengths Moreover we presentapplicability of the MultiCAP solution in the SR multimode(MM) links We expect that with higher bandwidth of theupcoming 850 nmVCSELs this solution will enable 100Gbpsper lane and 400Gbps using parallel optics This technologypotentially provides a bridge for gray optics approach toclient-side inter- and intradata centers access and metrosegments

5 Conclusions

We present a uniform MultiCAP based solution for shortrange (SR) MM links long range (LR) 20 km single mode(SM) links and extended range (ER) 40 km SM links Theadvantageous feature of MultiCAP approach of being ableto assign parallel electrical interfaces of smaller bandwidthinto different frequency bands overcomes both electrical andoptical bandwidth limitations and eases the DSP pipeliningIts pass-band nature and multiband structure allow optimalusage of the available bandwidth maximizing obtainablecapacity In the SR scenario we have achieved record below-FEC bit rate transmission of 657 Gbps over 100m and747Gbps over 1m for 850 nmMMFdata links For upcoming400 GE standard long range and extended range criteria wepresent a MultiCAP LAN-WDM 400Gbps solution whichuses only commercial optical components from 100GBASE-LR4 and ER4 432Gbits MultiCAP signals are transmittedover 20 km SSMF without amplification and over 40 kmSSMF with SOA Interchannel mixing in the 40 km link andin SOA is proven to be negligible for a MultiCAP IMDDLAN-WDM system The proposed MultiCAP approach isa robust and flexible scheme which can cover most of theclient-side scenarios including inter- and intradata centersand up to 40 km client-side links

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] IEEE 400 Gbs Ethernet Study Group Meeting Materials 2014[2] J DrsquoAmbrosia and P Mooney ldquo400 Gbs ethernet why nowrdquo

Whitepaper of Ethernet Alliance 2013[3] M I Olmedo T Zuo J B Jensen et al ldquoMultiband carrierless

amplitude phase modulation for high capacity optical datalinksrdquo Journal of Lightwave Technology vol 32 no 4 pp 798ndash804 2014

[4] M I Olmedo A Tatarczak T Zuo J Estaran X Xu and I TMonroy ldquoTowards 100 Gbps over 100m MMF using a 850 nmVCSELrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash4 March 2014

[5] T Zuo A Tatarczak M Olmedo et al ldquoO-band 400 Gbitsclient side optical transmission linkrdquo in Proceedings of the

Advances in Optical Technologies 9

Optical Fiber Communications Conference and Exhibition (OFCrsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[6] K Szczerba PWestberghM Karlsson P A Andrekson andALarsson ldquo70Gbps 4-PAMand 56Gbps 8-PAMusing an 850 nmVCSELrdquo in Proceedings of the European Conference on OpticalCommunication (ECOC rsquo14) September 2014

[7] D Kuchta A V Rylyakov C L Schow et al ldquo64Gbs transmis-sion over 57mMMFusing anNRZmodulated 850 nmVCSELrdquoin Proceedings of the Optical Fiber Communications Conferenceand Exhibition (OFC rsquo14) pp 1ndash3 Optical Society of AmericaMarch 2014

[8] L Raddatz and I HWhite ldquoOvercoming themodal bandwidthlimitation of multimode fiber by using passband modulationrdquoIEEE Photonics Technology Letters vol 11 no 2 pp 266ndash2681999

[9] S Lee F Breyer S Randel D Cardenas H van den Boomand A Koonen ldquoDiscrete multitone modulation for high-speed data transmission over multimode fibers using 850-nmVCSELrdquo in Proceedings of the Conference on Optical FiberCommunicationmdashIncudes Post Deadline Papers (OFC rsquo09) pp1ndash3 IEEE San Diego Calif USA March 2009

[10] Y Doi T Ohyama T Yoshimatsu S Soma and M Ogumaldquo400GbE demonstration utilizing 100GbE optical sub-assem-blies and cyclic arrayed waveguide gratingsrdquo in Proceedings ofthe Optical Fiber Communications Conference and Exhibition(OFC rsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[11] W Kobayashi T Fujisawa S Kanazawa and H Sanjoh ldquo25Gbauds 4-PAM (50 Gbits) modulation and 10 km SMF trans-mission with 13 120583m InGaAlAs-based DMLrdquo Electronics Lettersvol 50 no 4 pp 299ndash300 2014

[12] J Zhang X Li Y Xia et al ldquo60-Gbs CAP-64QAM Transmis-sion using DML with direct detection and digital equalizationrdquoin Proceedings of the Optical Fiber Communication Conferenceand Exposition and the National Fiber Optic Engineers Confer-ence (OFCNFOEC rsquo14) IEEE March 2014

[13] T Chan I-C Lu J Chen W Way and T Chan ldquo400-Gbstransmission over 10-km SSMF using discrete multitone and13-mm EMLsrdquo IEEE Photonics Technology Letters vol 26 no16 pp 1657ndash1660 2014

[14] J P Turkiewicz and H de Waardt ldquoLow complexity up to 400-Gbs transmission in the 1310-nm wavelength domainrdquo IEEEPhotonics Technology Letters vol 24 no 11 pp 942ndash944 2012

[15] W Yan L Li B Liu et al ldquo80 km IMDD transmission for 100Gbs per lane enabled by DMT and nonlinearity managementrdquoin Proceedings of the Optical Fiber Communication ConferencepM2I4 Optical Society of America San Francisco Calif USAMarch 2014

[16] T Tanaka M Nishihara T Takahara et al ldquoExperimentaldemonstration of 448-Gbps+ DMT transmission over 30-kmSMFrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash3 March 2014

[17] N G Gonzalez D Zibar X Yu and I T Monroy ldquoOpticalphase-modulated radio-over-fiber links with K-means algo-rithm for digital demodulation of 8PSK subcarrier multiplexedsignalsrdquo in Proceedings of the Conference on Optical FiberCommunication CollocatedNational Fiber Optic Engineers Con-ference (OFCNFOEC rsquo10) pp 1ndash3 March 2010

[18] D Ashmawy K Banovic E Abdel-Raheem M Youssif HMansour and M Mohanna ldquoJoint MCMA and DD blindequalization algorithm with variable-step sizerdquo in Proceedingsof the IEEE International Conference on ElectroInformationTechnology (EIT rsquo09) pp 174ndash177 June 2009

[19] F Chang K Onohara and T Mizuochi ldquoForward error cor-rection for 100 G transport networksrdquo IEEE CommunicationsMagazine vol 48 no 3 pp S48ndashS55 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

6 Advances in Optical Technologies

Table 2 Equalizerrsquos performance in terms of BER as comparedto the nonequalized system measured for three different signal-to-noise ratio (SNR) settings compared systems nonequalized systemwith a standard multimodulus algorithm (MMA) equalization andwith decision directed (DD)119870-means equalizer

SNR(dB)

BERnonequalized

system

BERMMA

equalizer

BERDD 119870-meansequalizer

206 189 sdot 10minus2 383 sdot 10minus3 867 sdot 10minus4

195 223 sdot 10minus2 766 sdot 10minus3 39 sdot 10minus3

182 367 sdot 10minus2 196 sdot 10minus2 148 sdot 10minus2

40 km transmission case a semiconductor optical amplifier(SOA) with a noise figure (NF) of 65 dB is employed atthe receiver before demultiplexing At the receiver sidethe signal is demultiplexed by a LAN-WDM demultiplexer(DEMUX) received by a photodiode (PD) and amplified by atransimpedance amplifier (TIA) DEMUX introduces 09 dBof insertion loss All of the components are 100GBASE-LR4and ER4 compatible

24 Demodulation and Equalization The receiver consistsof several digital signal processing (DSP) blocks which areimplemented in Matlab environment CAP filtering signaldownsampling phase offset removal and signal normal-ization are performed as explained in [3] Additionally weimplement an adaptive frequency domain equalization tomitigate linear impairmentsThe described adaptive decisiondirected (DD) equalization algorithmminimizes the receivedconstellation cluster size and quantization noise

We define the reference constellation by the centroidsfound using 119870-means algorithm which groups the receiveddata in the clusters [17]This reference constellation initializesthe describedDD equalization algorithm Clustersrsquo means arethe points of reference (starting decision)

We use an iterative equalizer where in every iteration thefollowing steps are performed first the error is calculatedbased on the Euclidean distance from the closest centroid asin a least mean square (LMS) equalizer

120576 (119899) = min 1003817100381710038171003817Cminus119910 (119899)

1003817100381710038171003817 (1)

where C denotes all centroids of the reference constellationand 119910(119899) is the received signal sample For equalization weuse 1198792 fractionally spaced FIR filter with 12 taps determinedempirically The taps coefficients of the DD equalizer areupdated according to the following equation

ℎ (119899 + 1) = ℎ (119899) + 120583 (119899) sdot 120576 (119899) sdot 119910 (119899)lowast (2)

where ℎ(119899) is the equalizer coefficient 120583(119899) is the step sizeinitialized as 75 sdot 10minus4 and 119910(119899)lowast is the complex conju-gate 119910(119899) Secondly the received signal is passed throughthe equalizer Finally the iterative process reestimates thecentroids of the equalized constellation and the describedsteps are repeated It was experimentally determined that2 iterations result in satisfactory equalization and furtheriterations do not show the performance improvement Toassure a faster convergence we implement the variable stepin DDThe step size is updated in the following manner [18]

120583 (119899 + 1) =120583 (119899)

1 + 120582120583 (119899) |120576 (119899)|2

120582 =

1 if 119899 = 0

0 if sgn (Re 120576 (119899)) = sgn (Re 120576 (119899 minus 1)) sgn (Im 120576 (119899)) = sgn (Im 120576 (119899 minus 1))

1 otherwise

(3)

where sgn denotes a sign functionIn order to quantify the improvement due to using an

equalizer we calculate BER for the equalized and nonequal-ized system for three different SNR values Moreover wepresent BER calculated for the system with a standard fre-quency domain equalizer namely multimodulus algorithm(MMA) Table 2 summarizes the BERs for all equalizationand SNR scenarios Decision directed (DD) 119870-means equal-izer improves the performance in terms of BER in all threeSNR scenarios At SNR of 206 dB using an equalizer allowsfor the improvement of 00181 in terms of BER In thefollowing sections all of the presented results are equalizedusing DD119870-means algorithm

After the signal is equalized the EVM is calculated andBER is computed In order to calculate bit error rate (BER)

the received demodulated signal is cross-correlated with thetransmitted signal and the errors are counted

3 Experimental Results

Figure 7 shows the measured BER curves for SR scenario Wedefine the sensitivity at a BER of the hard decision FEC codeat 7 overhead For the reported system it is 45 sdot 10minus3 [19]Thereby we can observe sensitivities of 21 47 and 54 dBmfor experimentally obtained 704Gbps over 1m 704Gbpsover 100m and 80Gbps over 1m respectivelyThemeasuredtransmission penalty after 100mMMF is 25 dB

For LR scenario per lane received bit error ratio (BER)back-to-back (B2B) and after 20 km SSMF transmission (noSOA) of the received signal is plotted in Figure 8(a) The

Advances in Optical Technologies 7

7 FEC limit

minus16

minus20

minus24

minus28

2 3 54 6

P (dBm)

70Gbps 1m80Gbps 1m

70Gbps 100m

log10(B

ER)

Figure 7 BER versus received optical power (ROP) for B2B and 100m transmission for 70GbpsMultiCAP configuration andB2B for 80Gbpsconfiguration

Received optical power per lane (dBm)

7 FEC limit

Lane 0 Lane 1

Lane 2 Lane 3

minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

minus9 minus8 minus7 minus6 minus5 minus4 minus3

log10(B

ER)

(a)

Received optical power per lane (dBm)

Single lane B2B

WDM center lane B2BWDM side lane B2B

7 FEC limit

minus14 minus13 minus12 minus11 minus10 minus9 minus8 minus7 minus6minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

Single lane 40kmWDM center lane 40km

WDM side lane 40km

log10(B

ER)

(b)Figure 8 (a) BER versus received optical power (ROP) for B2B and 20 km transmission for 4 lanes (b) BER versus ROP for the datatransmitted in the single lane (Lane 2) and for the data transmitted in all lines (BER curves for center lane Lane 2 and side lane Lane3) ROP measured before SOA the total bitrate of WDM system is 432Gbps

received optical power is measured before the MUX For allLAN-WDM lanes BERs are below the 7 hard decision FEClimit and no error floor is observed within the tested powerrange Receiver sensitivity at the FEC limit is minus60 dBm B2Band minus66 dBm after transmission No transmission powerpenalty is observedThe results for ER scenario are presentedin Figure 8(b) Received BER of a center lane and a side laneis plotted B2B and after 40 km SSMF transmission with all 4LAN-WDM lanes simultaneously amplified by a single SOAbefore demultiplexing Received optical power per channelis measured before the SOA For comparison the BER of asingle lane (remaining three lanes switched off) is includedin the graph All LAN-WDM lanes were received with a BERbelow the FEC limit after 40 km SSMF transmission with

a worst-case receiver sensitivity of minus99 dBm Presence ofneighboring channels in the link does not introduce penaltyin the 20 km scenario In case of 40 km scenario we observea 05 dB power penalty for the center lanes in the 4-lane casedue to interlanemodulation in the SOA In both scenarios nopenalty is observed in the side lanes

In the results presented BER is an average of the BERs inall MultiCAP bands

Finally the power budget calculation is evaluated inTable 3 For the SR scenario the optical output power mea-sured at the output of the VCSEL is 6 dBm The sensitivityat 7 FEC limit for 70Gbps 1m transmissions is equal to24 dBmTherefore power budget for this scenario is equal to36 dB In the LR and ER scenarios the optical output power

8 Advances in Optical Technologies

Table 3 System power budget

Transmissionlink type

Outputpower

Sensitivity FEC limit

Systempowerbudget

sr 70Gbps 6 dBm 24 dBm 36 dBLR 20 kmunamplified 54 dBm minus66 dBm 126 dB

ER 40 km SOAamplified 54 dBm minus99 dBm 159 dB

per lane is equal to 54 dBm It is measured after transmitterand hence after MUX The worst receiver sensitivity isminus66 dBm at FEC limit in case of 20 km transmission linkwith no amplification Therefore the power budget of thislink is 126 dB In case of 40 km transmission with SOA basedamplification the worst receiver sensitivity is minus99 dBm at theFEC limit Therefore for the amplified 40 km link the powerbudget is 159 dB The given receiver sensitivity is based onROP measured before receiver before PD in SR case beforeDEMUX in LR case and before SOA in ER case

The SR scenario represents a solution for an active opticalcable for data centers In terms of power budget themargin isnecessary only for the components heating up and aging Incase of LR and ER the calculated margin of 56 dB and 19 dBis sufficient for client-side links

4 Discussion

In the results presented for SR a steep roll-off of the VCSELrsquosfrequency response reduces the achievable capacity We usethe bit loading and power loading features of MultiCAP toovercome those limitations at the cost of worse sensitivityAs a consequence increasing the capacity from 70Gbpsto 80Gbps introduces the 31 dB penalty in sensitivity asshown in Figure 7 The bandwidth of the existing VCSELsis not sufficient to support 100Gbps per lane With theproposed MultiCAP scheme the emerging 25Gbps VCSELsare expected to satisfy the bandwidth requirement

The performance of the EMLs used in LR and ER issatisfactory to obtain 100Gbps after FEC per lane Moreoverthe local area network-wavelength division multiplexing(LAN-WDM) is proved to introduce negligible penalty bothfor 20 km and for 40 km link The power budget calculationindicates the maturity of the solution which allows for linklosses of 126 dB and 159 dB in LR and ER respectively

The clear difference in performance and achievablecapacity between SR and LR ER scenarios is attributedto the system bandwidth Even though the 3 dB and 10 dBbandwidths are similar for both systems the 20 dBbandwidthvaries by 5 dB For this reason the MultiCAP in SR isrecoverable when it occupies up to 21GHz while the LR andER signal is possible to recover when it occupies 26GHz(Figure 4) The last band in all three scenarios is highlysuppressed but thanks to the power loading and bit loadingfeatures of MultiCAP the information in the last band is alsopossible to recover if it carries QPSK

The proposed approach for 400Gbits client-side trans-mission links using MultiCAP modulation format representsan easily applicable solution that is robust simple and flexiblein upgrading from 100Gbits to 400Gbits while operating atthe O-band LAN-WDM wavelengths Moreover we presentapplicability of the MultiCAP solution in the SR multimode(MM) links We expect that with higher bandwidth of theupcoming 850 nmVCSELs this solution will enable 100Gbpsper lane and 400Gbps using parallel optics This technologypotentially provides a bridge for gray optics approach toclient-side inter- and intradata centers access and metrosegments

5 Conclusions

We present a uniform MultiCAP based solution for shortrange (SR) MM links long range (LR) 20 km single mode(SM) links and extended range (ER) 40 km SM links Theadvantageous feature of MultiCAP approach of being ableto assign parallel electrical interfaces of smaller bandwidthinto different frequency bands overcomes both electrical andoptical bandwidth limitations and eases the DSP pipeliningIts pass-band nature and multiband structure allow optimalusage of the available bandwidth maximizing obtainablecapacity In the SR scenario we have achieved record below-FEC bit rate transmission of 657 Gbps over 100m and747Gbps over 1m for 850 nmMMFdata links For upcoming400 GE standard long range and extended range criteria wepresent a MultiCAP LAN-WDM 400Gbps solution whichuses only commercial optical components from 100GBASE-LR4 and ER4 432Gbits MultiCAP signals are transmittedover 20 km SSMF without amplification and over 40 kmSSMF with SOA Interchannel mixing in the 40 km link andin SOA is proven to be negligible for a MultiCAP IMDDLAN-WDM system The proposed MultiCAP approach isa robust and flexible scheme which can cover most of theclient-side scenarios including inter- and intradata centersand up to 40 km client-side links

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] IEEE 400 Gbs Ethernet Study Group Meeting Materials 2014[2] J DrsquoAmbrosia and P Mooney ldquo400 Gbs ethernet why nowrdquo

Whitepaper of Ethernet Alliance 2013[3] M I Olmedo T Zuo J B Jensen et al ldquoMultiband carrierless

amplitude phase modulation for high capacity optical datalinksrdquo Journal of Lightwave Technology vol 32 no 4 pp 798ndash804 2014

[4] M I Olmedo A Tatarczak T Zuo J Estaran X Xu and I TMonroy ldquoTowards 100 Gbps over 100m MMF using a 850 nmVCSELrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash4 March 2014

[5] T Zuo A Tatarczak M Olmedo et al ldquoO-band 400 Gbitsclient side optical transmission linkrdquo in Proceedings of the

Advances in Optical Technologies 9

Optical Fiber Communications Conference and Exhibition (OFCrsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[6] K Szczerba PWestberghM Karlsson P A Andrekson andALarsson ldquo70Gbps 4-PAMand 56Gbps 8-PAMusing an 850 nmVCSELrdquo in Proceedings of the European Conference on OpticalCommunication (ECOC rsquo14) September 2014

[7] D Kuchta A V Rylyakov C L Schow et al ldquo64Gbs transmis-sion over 57mMMFusing anNRZmodulated 850 nmVCSELrdquoin Proceedings of the Optical Fiber Communications Conferenceand Exhibition (OFC rsquo14) pp 1ndash3 Optical Society of AmericaMarch 2014

[8] L Raddatz and I HWhite ldquoOvercoming themodal bandwidthlimitation of multimode fiber by using passband modulationrdquoIEEE Photonics Technology Letters vol 11 no 2 pp 266ndash2681999

[9] S Lee F Breyer S Randel D Cardenas H van den Boomand A Koonen ldquoDiscrete multitone modulation for high-speed data transmission over multimode fibers using 850-nmVCSELrdquo in Proceedings of the Conference on Optical FiberCommunicationmdashIncudes Post Deadline Papers (OFC rsquo09) pp1ndash3 IEEE San Diego Calif USA March 2009

[10] Y Doi T Ohyama T Yoshimatsu S Soma and M Ogumaldquo400GbE demonstration utilizing 100GbE optical sub-assem-blies and cyclic arrayed waveguide gratingsrdquo in Proceedings ofthe Optical Fiber Communications Conference and Exhibition(OFC rsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[11] W Kobayashi T Fujisawa S Kanazawa and H Sanjoh ldquo25Gbauds 4-PAM (50 Gbits) modulation and 10 km SMF trans-mission with 13 120583m InGaAlAs-based DMLrdquo Electronics Lettersvol 50 no 4 pp 299ndash300 2014

[12] J Zhang X Li Y Xia et al ldquo60-Gbs CAP-64QAM Transmis-sion using DML with direct detection and digital equalizationrdquoin Proceedings of the Optical Fiber Communication Conferenceand Exposition and the National Fiber Optic Engineers Confer-ence (OFCNFOEC rsquo14) IEEE March 2014

[13] T Chan I-C Lu J Chen W Way and T Chan ldquo400-Gbstransmission over 10-km SSMF using discrete multitone and13-mm EMLsrdquo IEEE Photonics Technology Letters vol 26 no16 pp 1657ndash1660 2014

[14] J P Turkiewicz and H de Waardt ldquoLow complexity up to 400-Gbs transmission in the 1310-nm wavelength domainrdquo IEEEPhotonics Technology Letters vol 24 no 11 pp 942ndash944 2012

[15] W Yan L Li B Liu et al ldquo80 km IMDD transmission for 100Gbs per lane enabled by DMT and nonlinearity managementrdquoin Proceedings of the Optical Fiber Communication ConferencepM2I4 Optical Society of America San Francisco Calif USAMarch 2014

[16] T Tanaka M Nishihara T Takahara et al ldquoExperimentaldemonstration of 448-Gbps+ DMT transmission over 30-kmSMFrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash3 March 2014

[17] N G Gonzalez D Zibar X Yu and I T Monroy ldquoOpticalphase-modulated radio-over-fiber links with K-means algo-rithm for digital demodulation of 8PSK subcarrier multiplexedsignalsrdquo in Proceedings of the Conference on Optical FiberCommunication CollocatedNational Fiber Optic Engineers Con-ference (OFCNFOEC rsquo10) pp 1ndash3 March 2010

[18] D Ashmawy K Banovic E Abdel-Raheem M Youssif HMansour and M Mohanna ldquoJoint MCMA and DD blindequalization algorithm with variable-step sizerdquo in Proceedingsof the IEEE International Conference on ElectroInformationTechnology (EIT rsquo09) pp 174ndash177 June 2009

[19] F Chang K Onohara and T Mizuochi ldquoForward error cor-rection for 100 G transport networksrdquo IEEE CommunicationsMagazine vol 48 no 3 pp S48ndashS55 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Advances in Optical Technologies 7

7 FEC limit

minus16

minus20

minus24

minus28

2 3 54 6

P (dBm)

70Gbps 1m80Gbps 1m

70Gbps 100m

log10(B

ER)

Figure 7 BER versus received optical power (ROP) for B2B and 100m transmission for 70GbpsMultiCAP configuration andB2B for 80Gbpsconfiguration

Received optical power per lane (dBm)

7 FEC limit

Lane 0 Lane 1

Lane 2 Lane 3

minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

minus9 minus8 minus7 minus6 minus5 minus4 minus3

log10(B

ER)

(a)

Received optical power per lane (dBm)

Single lane B2B

WDM center lane B2BWDM side lane B2B

7 FEC limit

minus14 minus13 minus12 minus11 minus10 minus9 minus8 minus7 minus6minus26

minus25

minus24

minus23

minus22

minus21

minus2

minus19

Single lane 40kmWDM center lane 40km

WDM side lane 40km

log10(B

ER)

(b)Figure 8 (a) BER versus received optical power (ROP) for B2B and 20 km transmission for 4 lanes (b) BER versus ROP for the datatransmitted in the single lane (Lane 2) and for the data transmitted in all lines (BER curves for center lane Lane 2 and side lane Lane3) ROP measured before SOA the total bitrate of WDM system is 432Gbps

received optical power is measured before the MUX For allLAN-WDM lanes BERs are below the 7 hard decision FEClimit and no error floor is observed within the tested powerrange Receiver sensitivity at the FEC limit is minus60 dBm B2Band minus66 dBm after transmission No transmission powerpenalty is observedThe results for ER scenario are presentedin Figure 8(b) Received BER of a center lane and a side laneis plotted B2B and after 40 km SSMF transmission with all 4LAN-WDM lanes simultaneously amplified by a single SOAbefore demultiplexing Received optical power per channelis measured before the SOA For comparison the BER of asingle lane (remaining three lanes switched off) is includedin the graph All LAN-WDM lanes were received with a BERbelow the FEC limit after 40 km SSMF transmission with

a worst-case receiver sensitivity of minus99 dBm Presence ofneighboring channels in the link does not introduce penaltyin the 20 km scenario In case of 40 km scenario we observea 05 dB power penalty for the center lanes in the 4-lane casedue to interlanemodulation in the SOA In both scenarios nopenalty is observed in the side lanes

In the results presented BER is an average of the BERs inall MultiCAP bands

Finally the power budget calculation is evaluated inTable 3 For the SR scenario the optical output power mea-sured at the output of the VCSEL is 6 dBm The sensitivityat 7 FEC limit for 70Gbps 1m transmissions is equal to24 dBmTherefore power budget for this scenario is equal to36 dB In the LR and ER scenarios the optical output power

8 Advances in Optical Technologies

Table 3 System power budget

Transmissionlink type

Outputpower

Sensitivity FEC limit

Systempowerbudget

sr 70Gbps 6 dBm 24 dBm 36 dBLR 20 kmunamplified 54 dBm minus66 dBm 126 dB

ER 40 km SOAamplified 54 dBm minus99 dBm 159 dB

per lane is equal to 54 dBm It is measured after transmitterand hence after MUX The worst receiver sensitivity isminus66 dBm at FEC limit in case of 20 km transmission linkwith no amplification Therefore the power budget of thislink is 126 dB In case of 40 km transmission with SOA basedamplification the worst receiver sensitivity is minus99 dBm at theFEC limit Therefore for the amplified 40 km link the powerbudget is 159 dB The given receiver sensitivity is based onROP measured before receiver before PD in SR case beforeDEMUX in LR case and before SOA in ER case

The SR scenario represents a solution for an active opticalcable for data centers In terms of power budget themargin isnecessary only for the components heating up and aging Incase of LR and ER the calculated margin of 56 dB and 19 dBis sufficient for client-side links

4 Discussion

In the results presented for SR a steep roll-off of the VCSELrsquosfrequency response reduces the achievable capacity We usethe bit loading and power loading features of MultiCAP toovercome those limitations at the cost of worse sensitivityAs a consequence increasing the capacity from 70Gbpsto 80Gbps introduces the 31 dB penalty in sensitivity asshown in Figure 7 The bandwidth of the existing VCSELsis not sufficient to support 100Gbps per lane With theproposed MultiCAP scheme the emerging 25Gbps VCSELsare expected to satisfy the bandwidth requirement

The performance of the EMLs used in LR and ER issatisfactory to obtain 100Gbps after FEC per lane Moreoverthe local area network-wavelength division multiplexing(LAN-WDM) is proved to introduce negligible penalty bothfor 20 km and for 40 km link The power budget calculationindicates the maturity of the solution which allows for linklosses of 126 dB and 159 dB in LR and ER respectively

The clear difference in performance and achievablecapacity between SR and LR ER scenarios is attributedto the system bandwidth Even though the 3 dB and 10 dBbandwidths are similar for both systems the 20 dBbandwidthvaries by 5 dB For this reason the MultiCAP in SR isrecoverable when it occupies up to 21GHz while the LR andER signal is possible to recover when it occupies 26GHz(Figure 4) The last band in all three scenarios is highlysuppressed but thanks to the power loading and bit loadingfeatures of MultiCAP the information in the last band is alsopossible to recover if it carries QPSK

The proposed approach for 400Gbits client-side trans-mission links using MultiCAP modulation format representsan easily applicable solution that is robust simple and flexiblein upgrading from 100Gbits to 400Gbits while operating atthe O-band LAN-WDM wavelengths Moreover we presentapplicability of the MultiCAP solution in the SR multimode(MM) links We expect that with higher bandwidth of theupcoming 850 nmVCSELs this solution will enable 100Gbpsper lane and 400Gbps using parallel optics This technologypotentially provides a bridge for gray optics approach toclient-side inter- and intradata centers access and metrosegments

5 Conclusions

We present a uniform MultiCAP based solution for shortrange (SR) MM links long range (LR) 20 km single mode(SM) links and extended range (ER) 40 km SM links Theadvantageous feature of MultiCAP approach of being ableto assign parallel electrical interfaces of smaller bandwidthinto different frequency bands overcomes both electrical andoptical bandwidth limitations and eases the DSP pipeliningIts pass-band nature and multiband structure allow optimalusage of the available bandwidth maximizing obtainablecapacity In the SR scenario we have achieved record below-FEC bit rate transmission of 657 Gbps over 100m and747Gbps over 1m for 850 nmMMFdata links For upcoming400 GE standard long range and extended range criteria wepresent a MultiCAP LAN-WDM 400Gbps solution whichuses only commercial optical components from 100GBASE-LR4 and ER4 432Gbits MultiCAP signals are transmittedover 20 km SSMF without amplification and over 40 kmSSMF with SOA Interchannel mixing in the 40 km link andin SOA is proven to be negligible for a MultiCAP IMDDLAN-WDM system The proposed MultiCAP approach isa robust and flexible scheme which can cover most of theclient-side scenarios including inter- and intradata centersand up to 40 km client-side links

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] IEEE 400 Gbs Ethernet Study Group Meeting Materials 2014[2] J DrsquoAmbrosia and P Mooney ldquo400 Gbs ethernet why nowrdquo

Whitepaper of Ethernet Alliance 2013[3] M I Olmedo T Zuo J B Jensen et al ldquoMultiband carrierless

amplitude phase modulation for high capacity optical datalinksrdquo Journal of Lightwave Technology vol 32 no 4 pp 798ndash804 2014

[4] M I Olmedo A Tatarczak T Zuo J Estaran X Xu and I TMonroy ldquoTowards 100 Gbps over 100m MMF using a 850 nmVCSELrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash4 March 2014

[5] T Zuo A Tatarczak M Olmedo et al ldquoO-band 400 Gbitsclient side optical transmission linkrdquo in Proceedings of the

Advances in Optical Technologies 9

Optical Fiber Communications Conference and Exhibition (OFCrsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[6] K Szczerba PWestberghM Karlsson P A Andrekson andALarsson ldquo70Gbps 4-PAMand 56Gbps 8-PAMusing an 850 nmVCSELrdquo in Proceedings of the European Conference on OpticalCommunication (ECOC rsquo14) September 2014

[7] D Kuchta A V Rylyakov C L Schow et al ldquo64Gbs transmis-sion over 57mMMFusing anNRZmodulated 850 nmVCSELrdquoin Proceedings of the Optical Fiber Communications Conferenceand Exhibition (OFC rsquo14) pp 1ndash3 Optical Society of AmericaMarch 2014

[8] L Raddatz and I HWhite ldquoOvercoming themodal bandwidthlimitation of multimode fiber by using passband modulationrdquoIEEE Photonics Technology Letters vol 11 no 2 pp 266ndash2681999

[9] S Lee F Breyer S Randel D Cardenas H van den Boomand A Koonen ldquoDiscrete multitone modulation for high-speed data transmission over multimode fibers using 850-nmVCSELrdquo in Proceedings of the Conference on Optical FiberCommunicationmdashIncudes Post Deadline Papers (OFC rsquo09) pp1ndash3 IEEE San Diego Calif USA March 2009

[10] Y Doi T Ohyama T Yoshimatsu S Soma and M Ogumaldquo400GbE demonstration utilizing 100GbE optical sub-assem-blies and cyclic arrayed waveguide gratingsrdquo in Proceedings ofthe Optical Fiber Communications Conference and Exhibition(OFC rsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[11] W Kobayashi T Fujisawa S Kanazawa and H Sanjoh ldquo25Gbauds 4-PAM (50 Gbits) modulation and 10 km SMF trans-mission with 13 120583m InGaAlAs-based DMLrdquo Electronics Lettersvol 50 no 4 pp 299ndash300 2014

[12] J Zhang X Li Y Xia et al ldquo60-Gbs CAP-64QAM Transmis-sion using DML with direct detection and digital equalizationrdquoin Proceedings of the Optical Fiber Communication Conferenceand Exposition and the National Fiber Optic Engineers Confer-ence (OFCNFOEC rsquo14) IEEE March 2014

[13] T Chan I-C Lu J Chen W Way and T Chan ldquo400-Gbstransmission over 10-km SSMF using discrete multitone and13-mm EMLsrdquo IEEE Photonics Technology Letters vol 26 no16 pp 1657ndash1660 2014

[14] J P Turkiewicz and H de Waardt ldquoLow complexity up to 400-Gbs transmission in the 1310-nm wavelength domainrdquo IEEEPhotonics Technology Letters vol 24 no 11 pp 942ndash944 2012

[15] W Yan L Li B Liu et al ldquo80 km IMDD transmission for 100Gbs per lane enabled by DMT and nonlinearity managementrdquoin Proceedings of the Optical Fiber Communication ConferencepM2I4 Optical Society of America San Francisco Calif USAMarch 2014

[16] T Tanaka M Nishihara T Takahara et al ldquoExperimentaldemonstration of 448-Gbps+ DMT transmission over 30-kmSMFrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash3 March 2014

[17] N G Gonzalez D Zibar X Yu and I T Monroy ldquoOpticalphase-modulated radio-over-fiber links with K-means algo-rithm for digital demodulation of 8PSK subcarrier multiplexedsignalsrdquo in Proceedings of the Conference on Optical FiberCommunication CollocatedNational Fiber Optic Engineers Con-ference (OFCNFOEC rsquo10) pp 1ndash3 March 2010

[18] D Ashmawy K Banovic E Abdel-Raheem M Youssif HMansour and M Mohanna ldquoJoint MCMA and DD blindequalization algorithm with variable-step sizerdquo in Proceedingsof the IEEE International Conference on ElectroInformationTechnology (EIT rsquo09) pp 174ndash177 June 2009

[19] F Chang K Onohara and T Mizuochi ldquoForward error cor-rection for 100 G transport networksrdquo IEEE CommunicationsMagazine vol 48 no 3 pp S48ndashS55 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

8 Advances in Optical Technologies

Table 3 System power budget

Transmissionlink type

Outputpower

Sensitivity FEC limit

Systempowerbudget

sr 70Gbps 6 dBm 24 dBm 36 dBLR 20 kmunamplified 54 dBm minus66 dBm 126 dB

ER 40 km SOAamplified 54 dBm minus99 dBm 159 dB

per lane is equal to 54 dBm It is measured after transmitterand hence after MUX The worst receiver sensitivity isminus66 dBm at FEC limit in case of 20 km transmission linkwith no amplification Therefore the power budget of thislink is 126 dB In case of 40 km transmission with SOA basedamplification the worst receiver sensitivity is minus99 dBm at theFEC limit Therefore for the amplified 40 km link the powerbudget is 159 dB The given receiver sensitivity is based onROP measured before receiver before PD in SR case beforeDEMUX in LR case and before SOA in ER case

The SR scenario represents a solution for an active opticalcable for data centers In terms of power budget themargin isnecessary only for the components heating up and aging Incase of LR and ER the calculated margin of 56 dB and 19 dBis sufficient for client-side links

4 Discussion

In the results presented for SR a steep roll-off of the VCSELrsquosfrequency response reduces the achievable capacity We usethe bit loading and power loading features of MultiCAP toovercome those limitations at the cost of worse sensitivityAs a consequence increasing the capacity from 70Gbpsto 80Gbps introduces the 31 dB penalty in sensitivity asshown in Figure 7 The bandwidth of the existing VCSELsis not sufficient to support 100Gbps per lane With theproposed MultiCAP scheme the emerging 25Gbps VCSELsare expected to satisfy the bandwidth requirement

The performance of the EMLs used in LR and ER issatisfactory to obtain 100Gbps after FEC per lane Moreoverthe local area network-wavelength division multiplexing(LAN-WDM) is proved to introduce negligible penalty bothfor 20 km and for 40 km link The power budget calculationindicates the maturity of the solution which allows for linklosses of 126 dB and 159 dB in LR and ER respectively

The clear difference in performance and achievablecapacity between SR and LR ER scenarios is attributedto the system bandwidth Even though the 3 dB and 10 dBbandwidths are similar for both systems the 20 dBbandwidthvaries by 5 dB For this reason the MultiCAP in SR isrecoverable when it occupies up to 21GHz while the LR andER signal is possible to recover when it occupies 26GHz(Figure 4) The last band in all three scenarios is highlysuppressed but thanks to the power loading and bit loadingfeatures of MultiCAP the information in the last band is alsopossible to recover if it carries QPSK

The proposed approach for 400Gbits client-side trans-mission links using MultiCAP modulation format representsan easily applicable solution that is robust simple and flexiblein upgrading from 100Gbits to 400Gbits while operating atthe O-band LAN-WDM wavelengths Moreover we presentapplicability of the MultiCAP solution in the SR multimode(MM) links We expect that with higher bandwidth of theupcoming 850 nmVCSELs this solution will enable 100Gbpsper lane and 400Gbps using parallel optics This technologypotentially provides a bridge for gray optics approach toclient-side inter- and intradata centers access and metrosegments

5 Conclusions

We present a uniform MultiCAP based solution for shortrange (SR) MM links long range (LR) 20 km single mode(SM) links and extended range (ER) 40 km SM links Theadvantageous feature of MultiCAP approach of being ableto assign parallel electrical interfaces of smaller bandwidthinto different frequency bands overcomes both electrical andoptical bandwidth limitations and eases the DSP pipeliningIts pass-band nature and multiband structure allow optimalusage of the available bandwidth maximizing obtainablecapacity In the SR scenario we have achieved record below-FEC bit rate transmission of 657 Gbps over 100m and747Gbps over 1m for 850 nmMMFdata links For upcoming400 GE standard long range and extended range criteria wepresent a MultiCAP LAN-WDM 400Gbps solution whichuses only commercial optical components from 100GBASE-LR4 and ER4 432Gbits MultiCAP signals are transmittedover 20 km SSMF without amplification and over 40 kmSSMF with SOA Interchannel mixing in the 40 km link andin SOA is proven to be negligible for a MultiCAP IMDDLAN-WDM system The proposed MultiCAP approach isa robust and flexible scheme which can cover most of theclient-side scenarios including inter- and intradata centersand up to 40 km client-side links

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] IEEE 400 Gbs Ethernet Study Group Meeting Materials 2014[2] J DrsquoAmbrosia and P Mooney ldquo400 Gbs ethernet why nowrdquo

Whitepaper of Ethernet Alliance 2013[3] M I Olmedo T Zuo J B Jensen et al ldquoMultiband carrierless

amplitude phase modulation for high capacity optical datalinksrdquo Journal of Lightwave Technology vol 32 no 4 pp 798ndash804 2014

[4] M I Olmedo A Tatarczak T Zuo J Estaran X Xu and I TMonroy ldquoTowards 100 Gbps over 100m MMF using a 850 nmVCSELrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash4 March 2014

[5] T Zuo A Tatarczak M Olmedo et al ldquoO-band 400 Gbitsclient side optical transmission linkrdquo in Proceedings of the

Advances in Optical Technologies 9

Optical Fiber Communications Conference and Exhibition (OFCrsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[6] K Szczerba PWestberghM Karlsson P A Andrekson andALarsson ldquo70Gbps 4-PAMand 56Gbps 8-PAMusing an 850 nmVCSELrdquo in Proceedings of the European Conference on OpticalCommunication (ECOC rsquo14) September 2014

[7] D Kuchta A V Rylyakov C L Schow et al ldquo64Gbs transmis-sion over 57mMMFusing anNRZmodulated 850 nmVCSELrdquoin Proceedings of the Optical Fiber Communications Conferenceand Exhibition (OFC rsquo14) pp 1ndash3 Optical Society of AmericaMarch 2014

[8] L Raddatz and I HWhite ldquoOvercoming themodal bandwidthlimitation of multimode fiber by using passband modulationrdquoIEEE Photonics Technology Letters vol 11 no 2 pp 266ndash2681999

[9] S Lee F Breyer S Randel D Cardenas H van den Boomand A Koonen ldquoDiscrete multitone modulation for high-speed data transmission over multimode fibers using 850-nmVCSELrdquo in Proceedings of the Conference on Optical FiberCommunicationmdashIncudes Post Deadline Papers (OFC rsquo09) pp1ndash3 IEEE San Diego Calif USA March 2009

[10] Y Doi T Ohyama T Yoshimatsu S Soma and M Ogumaldquo400GbE demonstration utilizing 100GbE optical sub-assem-blies and cyclic arrayed waveguide gratingsrdquo in Proceedings ofthe Optical Fiber Communications Conference and Exhibition(OFC rsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[11] W Kobayashi T Fujisawa S Kanazawa and H Sanjoh ldquo25Gbauds 4-PAM (50 Gbits) modulation and 10 km SMF trans-mission with 13 120583m InGaAlAs-based DMLrdquo Electronics Lettersvol 50 no 4 pp 299ndash300 2014

[12] J Zhang X Li Y Xia et al ldquo60-Gbs CAP-64QAM Transmis-sion using DML with direct detection and digital equalizationrdquoin Proceedings of the Optical Fiber Communication Conferenceand Exposition and the National Fiber Optic Engineers Confer-ence (OFCNFOEC rsquo14) IEEE March 2014

[13] T Chan I-C Lu J Chen W Way and T Chan ldquo400-Gbstransmission over 10-km SSMF using discrete multitone and13-mm EMLsrdquo IEEE Photonics Technology Letters vol 26 no16 pp 1657ndash1660 2014

[14] J P Turkiewicz and H de Waardt ldquoLow complexity up to 400-Gbs transmission in the 1310-nm wavelength domainrdquo IEEEPhotonics Technology Letters vol 24 no 11 pp 942ndash944 2012

[15] W Yan L Li B Liu et al ldquo80 km IMDD transmission for 100Gbs per lane enabled by DMT and nonlinearity managementrdquoin Proceedings of the Optical Fiber Communication ConferencepM2I4 Optical Society of America San Francisco Calif USAMarch 2014

[16] T Tanaka M Nishihara T Takahara et al ldquoExperimentaldemonstration of 448-Gbps+ DMT transmission over 30-kmSMFrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash3 March 2014

[17] N G Gonzalez D Zibar X Yu and I T Monroy ldquoOpticalphase-modulated radio-over-fiber links with K-means algo-rithm for digital demodulation of 8PSK subcarrier multiplexedsignalsrdquo in Proceedings of the Conference on Optical FiberCommunication CollocatedNational Fiber Optic Engineers Con-ference (OFCNFOEC rsquo10) pp 1ndash3 March 2010

[18] D Ashmawy K Banovic E Abdel-Raheem M Youssif HMansour and M Mohanna ldquoJoint MCMA and DD blindequalization algorithm with variable-step sizerdquo in Proceedingsof the IEEE International Conference on ElectroInformationTechnology (EIT rsquo09) pp 174ndash177 June 2009

[19] F Chang K Onohara and T Mizuochi ldquoForward error cor-rection for 100 G transport networksrdquo IEEE CommunicationsMagazine vol 48 no 3 pp S48ndashS55 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Advances in Optical Technologies 9

Optical Fiber Communications Conference and Exhibition (OFCrsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[6] K Szczerba PWestberghM Karlsson P A Andrekson andALarsson ldquo70Gbps 4-PAMand 56Gbps 8-PAMusing an 850 nmVCSELrdquo in Proceedings of the European Conference on OpticalCommunication (ECOC rsquo14) September 2014

[7] D Kuchta A V Rylyakov C L Schow et al ldquo64Gbs transmis-sion over 57mMMFusing anNRZmodulated 850 nmVCSELrdquoin Proceedings of the Optical Fiber Communications Conferenceand Exhibition (OFC rsquo14) pp 1ndash3 Optical Society of AmericaMarch 2014

[8] L Raddatz and I HWhite ldquoOvercoming themodal bandwidthlimitation of multimode fiber by using passband modulationrdquoIEEE Photonics Technology Letters vol 11 no 2 pp 266ndash2681999

[9] S Lee F Breyer S Randel D Cardenas H van den Boomand A Koonen ldquoDiscrete multitone modulation for high-speed data transmission over multimode fibers using 850-nmVCSELrdquo in Proceedings of the Conference on Optical FiberCommunicationmdashIncudes Post Deadline Papers (OFC rsquo09) pp1ndash3 IEEE San Diego Calif USA March 2009

[10] Y Doi T Ohyama T Yoshimatsu S Soma and M Ogumaldquo400GbE demonstration utilizing 100GbE optical sub-assem-blies and cyclic arrayed waveguide gratingsrdquo in Proceedings ofthe Optical Fiber Communications Conference and Exhibition(OFC rsquo14) pp 1ndash3 San Francisco Calif USA March 2014

[11] W Kobayashi T Fujisawa S Kanazawa and H Sanjoh ldquo25Gbauds 4-PAM (50 Gbits) modulation and 10 km SMF trans-mission with 13 120583m InGaAlAs-based DMLrdquo Electronics Lettersvol 50 no 4 pp 299ndash300 2014

[12] J Zhang X Li Y Xia et al ldquo60-Gbs CAP-64QAM Transmis-sion using DML with direct detection and digital equalizationrdquoin Proceedings of the Optical Fiber Communication Conferenceand Exposition and the National Fiber Optic Engineers Confer-ence (OFCNFOEC rsquo14) IEEE March 2014

[13] T Chan I-C Lu J Chen W Way and T Chan ldquo400-Gbstransmission over 10-km SSMF using discrete multitone and13-mm EMLsrdquo IEEE Photonics Technology Letters vol 26 no16 pp 1657ndash1660 2014

[14] J P Turkiewicz and H de Waardt ldquoLow complexity up to 400-Gbs transmission in the 1310-nm wavelength domainrdquo IEEEPhotonics Technology Letters vol 24 no 11 pp 942ndash944 2012

[15] W Yan L Li B Liu et al ldquo80 km IMDD transmission for 100Gbs per lane enabled by DMT and nonlinearity managementrdquoin Proceedings of the Optical Fiber Communication ConferencepM2I4 Optical Society of America San Francisco Calif USAMarch 2014

[16] T Tanaka M Nishihara T Takahara et al ldquoExperimentaldemonstration of 448-Gbps+ DMT transmission over 30-kmSMFrdquo in Proceedings of the Optical Fiber CommunicationsConference and Exhibition (OFC rsquo14) pp 1ndash3 March 2014

[17] N G Gonzalez D Zibar X Yu and I T Monroy ldquoOpticalphase-modulated radio-over-fiber links with K-means algo-rithm for digital demodulation of 8PSK subcarrier multiplexedsignalsrdquo in Proceedings of the Conference on Optical FiberCommunication CollocatedNational Fiber Optic Engineers Con-ference (OFCNFOEC rsquo10) pp 1ndash3 March 2010

[18] D Ashmawy K Banovic E Abdel-Raheem M Youssif HMansour and M Mohanna ldquoJoint MCMA and DD blindequalization algorithm with variable-step sizerdquo in Proceedingsof the IEEE International Conference on ElectroInformationTechnology (EIT rsquo09) pp 174ndash177 June 2009

[19] F Chang K Onohara and T Mizuochi ldquoForward error cor-rection for 100 G transport networksrdquo IEEE CommunicationsMagazine vol 48 no 3 pp S48ndashS55 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of