dsp a disruptive technology for optical...
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Nortel Confidential Information
BUSINESS MADE SIMPLE
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DSPA Disruptive Technologyfor Optical Transceivers
Kim RobertsIan Roberts
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NoiseLimited
Transmission
> Early fibers had losses measured in dB/meter> Given the very finite amount of optical power that could be
coupled into the fibers, received powers quickly became very low.
> Thermal noise in the receiver limited the bandwidth and distance for optical transmission.• E.g. 1 Mb/s along 10 meters, experiments at Harlow Labs
FD-135 used Duobinary Coding in 1983to mitigate Modal Dispersion on
Multimode fiber
Proakis, Digital Communications
SuperDecoder
Decision Feedback
Winters et al, IEEE Communications Magazine, June 1993
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Forward Error Correction to Mitigate Noise
1 2 3 4 5 6 7 810
−15
10−10
10−5
100
Uncoded
Q
BE
R
Uncoded
1 2 3 4 5 6 7 810
−15
10−10
10−5
100
Uncoded
Q
BE
R
BCH−1BCH-1
Uncoded
1 2 3 4 5 6 7 810
−15
10−10
10−5
100
Uncoded
Q
BE
R
BCH−1
BCH−3BCH-3
BCH-1
Uncoded
1 2 3 4 5 6 7 810
−15
10−10
10−5
100
Uncoded
Q
BE
R
BCH−1
BCH−3RSG.975 BCH-3
BCH-1
Uncoded
1 2 3 4 5 6 7 810
−15
10−10
10−5
100
Uncoded
Q
BE
R
BCH−1
BCH−3RS
BCH−20
G.975
BCH-20
BCH-3
BCH-1
Uncoded
1 2 3 4 5 6 7 810
−15
10−10
10−5
100
Uncoded
Q
BE
R
BCH−1
BCH−3RS
BCH−20BCH−2⊗BCH−3
G.975
P-FECBCH-20
BCH-3
BCH-1
Uncoded
Peak Signal to RMS Noise Ratio
Log
Bit
Erro
r Rat
e af
ter F
EC
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Traditional Solution for Dispersion:Optical Compensation Modules
Maximum Likelihood Sequence EstimationMLSE
> M.Cavallari, C.R.S.Fludger, P.J.Anslow, Electronic signal processing for differential phase modulation formats, Optical Fiber Communication Conference, (Feb 2004)
Coherent to the E-Field
> Major sources of degradation are linear with respect to the optical E-field.• Linear and invertible functions• Linear functions are commutative
> Linear transducers can be built• Digital to E-field• E-field to digital
> Therefore, linear digital filtering can fully compensate
Linear Conversion from Digital to E-Field
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Dispersion Eliminator: WARP ASIC
0.13 μm BiCMOS
2.5 Mb High Speed Memory2.0 M Gates
6 T Ops per second
Two 20 Gs/s 6 bit DAC
17 Watts
Linear and nonlinear pre-compensation of 10 Gb/s±80,000 ps/nm (2 dB penalty point)
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Dispersion Precompensation
Signal Transmitted Signal after 1600 km of NDSFWith no optical compensation.
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10 Gb/swith no Traditional Dispersion Compensation
Eye diagrams after transmission over standard G.652 fiber with Nortel WARP processing.
0 Km 1600 km 3200 km 5120 km
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SPM Precompensation, 1280 km
5.0
7.0
9.0
11.0
13.0
15.0
-5.0 -3.0 -1.0 1.0 3.0 5.0
Average Launch Power dBm
Req
uire
d O
SNR
at 1
E-3 Linear Compensation Only
With SPM CompensationReference Line
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E-Field to Digital Transducer
> Two phases: Real and Imaginary (I and Q)• Best detected by mixing with a local oscillator
> Two polarizations
> Four dimensions fully span the E-field in a single mode fiber.
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Coherent Detection
QX Pol
I
I Y Pol
Q
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A/D and Filter ASIC
90 nm CMOS
20 M Gates
12 T Ops per second
Four 20 Gs/s 6 bit ADC
21 Watts
Linear and nonlinear post-compensation of 40 Gb/s±80,000 ps/nm, 25 ps mean PMD, 2 dB mean PDL
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40G/100G Agile Optical EngineBinary to dual polarization E-field
Full E-field to Digital Transducer
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40 Gb/s Coherent Dual Pol QPSK Modem
Real-time PMD tracking> 1000 km of NDSF
> 10G, 40G, and 100G at 50 GHz spacing
> JDS PMD emulator
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PMD Tracking
2323
100G Dual Carrier
10G10GeDCO eDCO
AgileAgile100G100G
AgileAgile40G40G
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100 Gb/sModem
200G, 400G, 1000G
>Lower cost per bit
>More bits per fiber
>Larger packet streams
(From here on are my personal speculations and not product delivery commitments.)
Lightpath Bit Rate
The bit rate is the product of three dimensions
More Symbols per Second
>Faster A/D•11, 28, 56, … GBaud
>More gates of DSP
>CMOS riding Moore’s Law• Bipolar is too hot and does not have the gate count
Electronics for Processing
More Bits per Symbol
-2 -1 0 1 2-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
DP 16-QAM
4 bits x 2 Pol=8 bits per Baud
x 28.5 Gbaud= 228 Gb/s
I
Q
● 40 G
Spectral Efficiency
20
0.2
2
6
0.8
● 10 G
● 100 G
Spectral Efficiency is ultimately determined by OSNR
“The Channel Capacity of a Multispan DWDM System Employing Dispersive Nonlinear Optical Fibers and an Ideal Coherent Optical Receiver”, Jau Tang, JLT, Vol. 20, No. 7, July 2002
Multiple Carriers
>Coherent Frequency Selection• Two carriers with 16-QAM = 400 Gb/s
>OFDM
>New ideas are needed
OFDM
> Jolley et al, OFC 2005
> First Optical OFDM: Multimode fiber in Nortel lab.
Spectral Efficiency
Year of Product Introduction
Tb/sinC Band
Bits/sperHz
1995 2000 2005 2010 Future…0
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2
3
4
0
5
10
15
20
● 10G10.7 Gb/s @ 50 GHz
●
● 46 Gb/s @ 50 GHz
112 Gb/s @ 50 GHz ●
224 Gb/s @ 50 GHz ●
448 Gb/s @ 80 GHz ●
525
1000 Gb/s @ 170 GHz ●6
100G Dual Carrier Real Time Data> 1000 km of NDSF
> 10G, 40G, and 100G at 50 GHz spacing
> JDS PMD emulator