200-ghz and 50-ghz awg channelized linewidth dependent transmission of weak-resonant-cavity fpld...

200-GHz and 50-GHz AWG channelized

linewidth dependent transmission of

weak-resonant-cavity FPLD injection-locked by

spectrally sliced ASE

Gong-Ru Lin1, Tzu-Kang Cheng

1, Yu-Chieh Chi

1, Gong-Cheng Lin

2, Hai-Lin Wang

2, and

Yi-Hong Lin1

1Institute of Photonics and Optoelectronics, Department of Electrical Engineering, National Taiwan University,

No.1 Roosevelt Rd. Sec. 4, Taipei 106, Taiwan R.O.C. 2 Telecommunication Laboratories Advanced Technology, Chunghwa Telecom Co., Ltd., Taoyuan, Taiwan R.O.C.

*[email protected]

Abstract: In a weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD)

based DWDM-PON system with an array-waveguide-grating (AWG)

channelized amplified spontaneous emission (ASE) source located at remote

node, we study the effect of AWG filter bandwidth on the transmission

performances of the 1.25-Gbit/s directly modulated WRC-FPLD transmitter

under the AWG channelized ASE injection-locking. With AWG filters of two

different channel spacings at 50 and 200 GHz, several characteristic

parameters such as interfered reflection, relatively intensity noise, crosstalk

reduction, side-mode-suppressing ratio and power penalty of BER effect of

the WRC-FPLD transmitted data are compared. The 200-GHz AWG filtered

ASE injection minimizes the noises of WRC-FPLD based ONU transmitter,

improving the power penalty of upstream data by −1.6 dB at BER of 10−12

. In

contrast, the 50-GHz AWG channelized ASE injection fails to promote better

BER but increases the power penalty by + 1.5 dB under back-to-back

transmission. A theoretical modeling elucidates that the BER degradation up

to 4 orders of magnitude between two injection cases is mainly attributed to

the reduction on ASE injection linewidth, since which concurrently degrades

the signal-to-noise and extinction ratios of the transmitted data stream.

©2009 Optical Society of America

OCIS codes: (060.2330) Fiber optics communications; (140.3520) Lasers, injection-locked;

(250.5980) Semiconductor optical amplifiers; (140.5960) Semiconductor lasers.

References and links

1. D. J. Shin, Y. C. Keh, J. W. Kwon, E. H. Lee, J. K. Lee, M. K. Park, J. W. Park, Y. K. Oh, S. W. Kim, I. K. Yun, H.

C. Shin, D. Heo, J. S. Lee, H. S. Shin, H. S. Kim, S. B. Park, D. K. Jung, S. T. Hwang, Y. J. Oh, D. H. Jang, and C.

S. Shim, “Low-cost WDM-PON with colorless bidirectional transceivers,” J. Lightwave Technol. 24(1), 158–165

(2006).

2. P. Healey, P. Townsend, C. Ford, L. Johnston, P. Townley, I. Lealman, L. Rivers, S. Perrin, and R. Moore,

“Spectral slicing WDM-PON using wavelength-seeded reflective SOAs,” Electron. Lett. 37(19), 1181–1182

(2001).

3. H. Kim, S. Kim, S. Hwang, and Y. Oh, “Impact of dispersion, PMD, and PDL on the performance of

spectrum-sliced incoherent light sources using gain-saturated semiconductor optical amplifiers,” J. Lightwave

Technol. 24(2), 775–785 (2006).

4. S.-C. Lin, S.-L. Lee, and C.-K. Liu, “Simple approach for bidirectional performance enhancement on WDM-PONs

with directmodulation lasers and RSOAs,” Opt. Express 16(6), 3636–3643 (2008).

5. C. K. Chan, L. K. Chem, and C. Lin, “WDM PON for next-generation optical broadband access networks,” in Proc.

OECC, 2006.

6. P. Healey, P. Townsend, C. Ford, L. Johnston, P. Townley, I. Lealman, L. Rivers, S. Perrin, and R. Moore,

“Reflective SOAs for spectrally sliced WDM-PONs,” in Proc. OFC, Anaheim, CA, pp. 352–353, Feb. 2002.

#111727 - $15.00 USD Received 22 May 2009; revised 7 Aug 2009; accepted 11 Aug 2009; published 18 Sep 2009

(C) 2009 OSA 28 September 2009 / Vol. 17, No. 20 / OPTICS EXPRESS 17739

7. Z. Xu, Y. J. Wen, W.-D. Zhong, C.-J. Chae, X.-F. Cheng, Y. Wang, C. Lu, and J. Shankar, “High-speed

WDM-PON using CW injection-locked Fabry-Pérot laser diodes,” Opt. Express 15(6), 2953–2962 (2007).

8. H. D. Kim, S.-G. Kang, and C.-H. Lee, “A low-cost WDM source with an ASE injected Fabry-Perot semiconductor

laser,” IEEE Photon. Technol. Lett. 12(8), 1067–1069 (2000).

9. K.-Y. Park, and C.-H. Lee, “Intensity Noise in a Wavelength-Locked Fabry–Perot Laser Diode to a Spectrum

Sliced ASE,” IEEE J. Quantum Electron. 44(3), 209–215 (2008).

10. K.-M. Choi, J.-S. Baik, and C.-H. Lee, “Color-Free Operation of Dense WDM-PON Based on the

Wavelength-Locked Fabry–Pérot Laser Diodes Injecting a Low-Noise BLS,” IEEE Photon. Technol. Lett. 18(10),

1167–1169 (2006).

11. A. D. McCoy, B. C. Thomsen, M. Ibsen, and D. J. Richardson, “Filtering effects in a spectrum-sliced WDM system

using SOA-based noise reduction,” IEEE Photon. Technol. Lett. 16(2), 680–682 (2004).

12. H. Kim, H. C. Ji, and C. H. Kim, “Effects of Intraband Crosstalk on Incoherent Light Using SOA-Based Noise

Suppression Technique,” IEEE Photon. Technol. Lett. 18(14), 1542–1544 (2006).

13. G. P. Agrawal, “Fiber-Optic Communication Systems”, (Third Ed.), Willy Inter-Science, chapter 4–6, 2002.

14. J. S. Lee, Y. C. Chung, T. H. Wood, J. P. Meester, C. H. Joyner, C. A. Burrus, J. Stone, H. M. Presby, and D. J.

DiGiovanni, “Spectrum-sliced fiber amplifier light source with a polarization-insensitive electroabsorption

modulator,” IEEE Photon. Technol. Lett. 6(8), 1035–1038 (1994).

15. S.-G. Mun, J.-H. Moon, H.-K. Lee, J.-Y. Kim, and C.-H. Lee, “A WDM-PON with a 40 Gb/s (32 x 1.25 Gb/s)

capacity based on wavelength-locked Fabry-Perot laser diodes,” Opt. Express 16(15), 11361–11368 (2008).

1. Introduction

Amplified-spontaneous-emission (ASE) injection-locked semiconductor optical amplifiers or

laser diodes are promising sources for potential application in future wavelength division

multiplexed passive optical network (WDM-PON) technology. To construct the WDM-PON,

the user terminals or optical network units (ONUs) require the universal light source with

broadband gain spectrum which can be employed to all channels. The desired light source must

be remote-controlled or injection-locked at specific channel wavelength given by the central

office. Several cost-effective issues based on long-cavity Fabry-Perot laser diodes (FPLDs) and

reflective semiconductor optical amplifiers (RSOAs) [1–8] have been proposed to meet such a

colorless demand for being the universal light source, which can be applicable to each channel

under external injection-locking with amplified-spontaneous-emission (ASE) based incoherent

broadband light source (BLS). Later on, the ASE injection-locked RSOAs or FPLDs are rapidly

emerging to replace the distributed-feedback lasers at particularly selected wavelengths for

WDM-PON. To achieve wavelength independent operation and enhance the channel

compatibility in DWDM-PON, a new class of FPLD with weak-resonant-cavity (WRC) design

has been introduced recently [9,10]. The channelized ASE injection-locked WRC-FPLD with

front-facet reflectivity of only 1% exhibits intriguing features such as the much broader

spectrum when comparing with the conventional FPLDs, and the preserved longitudinal modes

to facilitate the SNR and ER. In fact, the conventional FPLD injected by ASE source filtered

with DWDM-PON at 50 GHz AWG channel spacing has ever been achieved, however, which

exhibits a difficulty in practical applications resulting from the increasing relative intensity

noise (RIN) with such narrow channel spacing [11]. Recently, a wavelength-locked FPLD

achieved by injecting the low-noise BLS instead of the erbium-doped fiber amplifier (EDFA) is

demonstrated for increasing channel capability of DWDM-PON [10]. Nonetheless, a major

reason leading to the constrain on using array waveguide grating (AWG) in such DWDM-PONs

is due to intra-band crosstalk, which occurs from the inevitable interference of ASE reflection

from AWG facet and the up-stream transmitted data under high-power injection case [12]. By

using an AWG filtered ASE as the injection-locking source in this work, we investigate the

up-stream transmission performances of the WRC-FPLD based DWDM-PON architecture with

AWG channel spacings of 200 GHz and 50 GHz. The error-free transmission at bit-rate of 1.25

Gbit/s can easily be achieved by using the spectrum-sliced ASE injecting-locked FPLD

transmitter in the DWDM-PON with AWG channel spacing of 50 GHz. The injection-locked

WRC-FPLD spectra within the AWG transmission window, the signal-to-noise ratio and the

on/off extinction ratio of the up-stream transmitted data, the receiving power penalty for the

back-to-back and the 25-km transmission BER performances at AWG of 200 GHz and 50 GHz

cases are compared. In addition, the correlation between the suppressed reflection of AWG



filtered ASE source and the corresponding BER performance in these DWDM-PON systems

are discussed.

2. Experimental setup

A typical DWDM-PON architecture with an EDFA based broadband ASE source for injection

locking the WRC-FPLD based up-stream transmitter at the localized optical network unit

(ONU) is shown in Fig. 1. The output power of the ASE source after passing through each

channel of the AWG based DWDM multiplexer must be sufficiently high for achieving better

injection-locking and up-stream transmission of the WRC-FPLD. Such a high-power

consumption inevitably raises an unexpected broadband reflection along the transmission path

in the DWDM-PON. In this case, the crosstalk between the broadband reflection of the injected

ASE and the up-stream transmitted data from the ASE injection-locked WRC-FPLD has left as

a serious problem to strongly affect the signal performance and network capacity.

Fig. 1. A conventional DWDM-PON with ASE based injection-locking source located at central

office.

Our previous study indicated that there is a power penalty up to 2 dB at BER of 10−9

occurred

for such a 1.25-Gbit/s directly modulated WRC-FPLD when injection-locking by a 200-GHz

AWG channelized ASE source. To promote the error-free transmission with a better sensitivity,

a mandatory solution relies strictly on removing such a broadband reflection from the

transmission path in the DWDM-PON system. In contrast, a modified DWDM-PON system in

Fig. 2 constructed by the WRC-FPLDs based ONUs and an AWG spectrally sliced ASE

injection-locker located prior to all ONUs is demonstrated. The EDFA based broadband ASE

source passes through an AWG with channel spacing of 50 GHz or 200 GHz to injection-lock

the WRC-FPLD via an optical circulator in each ONU.

Fig. 2. A modified DWDM-PON system with spectrally sliced ASE injection-locking source at

remote node.

Such an arrangement of the ASE source at remote node diminishes the broadband ASE

reflection as the optical circulator separate the injection and up-stream transmitting paths. In

each ONU, the WRC-FPLD exhibits a threshold current of about 25 mA, a longitudinal mode



spacing of 0.6 nm, the back and front facet reflectivity of 100% and 1%. The maximum

injection power of WRC-FPLD is limited at −3 dBm to avoid the damage on its end-face

anti-reflection coating. A long-cavity design enables the WRC-FPLD lasing at least one mode

within 50-GHz AWG channel during injection-locking condition. In experiment, the biased

current of FPLD directly modulated at 1.25 Gbit/s with pattern length of 223

-1 is maintained as

35 mA corresponding to 1.4 Ith for transmission performance diagnosis. I particular, we set the

WRC-FPLD temperature at 21°C, 23°C and 25°C to provide the different injection-locked

mode numbers within one AWG channel for optimizing the transmission performance.

3. Results and discussions

The spectral characteristics of the WRC-FPLD injected by AWG channelized ASE with

different 3dB spectral linewidths (∆λ = 0.35 nm for 50-GHz AWG and ∆λ = 1.1 nm for

200-GHz AWG) are also shown in Fig. 3. The conventional DWDM-PON is based on the ASE

injection-locked mode-extinction-free reflective semiconductor optical amplifier, which easily

causes transmission error by the ASE source dependent strong intensity noise. Alternatively, the

FPLD based transmitted without temperature control usually leads to an injection-locking

failure by its thermally drifting wavelength. In comparison, the long and weak resonant-cavity

design of the WRC-FPLD concurrently solves the drawbacks happened in conventional

DWDM-PON transmitters, which introduces a sufficiently broadband gain spectrum with

narrow longitudinal mode spacing, such that the injection-locking can always be maintained

and the weak-mode lasing scheme efficiently improves the stimulated to spontaneous power

ratio for better noise suppression.

1546.5 1547.0 1547.5 1548.0-70

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RF modulated Transmission spectrum

Po

wer(

dB

m)

Wavelength(nm)1546.5 1547.0 1547.5 1548.0

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Po

wer(

dB

m)

Wavelength(nm)1546.5 1547.0 1547.5 1548.0

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Free run


Po

wer(

dB

m)

Wavelength(nm)

1546.5 1547.0 1547.5 1548.0-70

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RF modulated

Transmission spectrum

Po

wer(

dB

m)

Wavelength(nm)

1546.5 1547.0 1547.5 1548.0-70

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RF modulated


Po

we

r(d

Bm

)

Wavelength(nm)1546.5 1547.0 1547.5 1548.0

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RF modulated


Po

wer(

dB

m)

Wavelength(nm)

Fig. 3. Upper: Spectra of 200-GHz AWG channelized ASE injection-locked WRC-FPLD at (a)

21°C, (b) 23°C, and (c) 25°C. Lower: Spectra of 50-GHz AWG channelized ASE

injection-locked WRC-FPLD at (a) 21°C, (b) 23°C, and (c) 25°C.

After passing through AWG channel, the filtered spectrum of the directly PRBS-modulated

WRC-FPLD differs significantly from that of a free-running WRC-FPLD, in which the

signal-to-noise ratio is greatly improved. At least two lasing WRC-FPLD modes can be ensured

within the spectral window when using the 200-GHz AWG and Mux/DeMux filters. The

injection-locking mode number periodically changes between 2 and 3 within a temperature

increment of 5°C, the corresponding mode spectra measured at temperature of 21°C, 23°C, and

25°C are shown in Figs. 3(a), 3(b) and 3(c), respectively [11]. Similar injection-locking

behaviour can also be observed if the channel spacing of the AWG changes from 200 GHz to 50



GHz, as shown from Fig. 3(e) to Fig. 3(f). In comparison, the side-mode suppressing ratio

(SMSR) of the WRC-FPLD injection-locked spectra also exhibits an inverse proportionality

with the spectral linewidth of the AWG channelized ASE source (see Fig. 4). At same injecting

power of −3 dBm, the WRC-FPLD injection-locked by the 50-GHz AWG-sliced ASE source

provides a better SMSR than that by the 200-GHz one (see Fig. 5). A maximum deviation on the

SMSR up to 3 dB for two different cases is observed, however, which seems to play a trivial

role on the transmission performance as compared to the influence by other parameters of the

WRC-FPLD as discussed below.

-15 -12 -9 -6 -315

20

25

30

35

50-GHz AWG

200-GHz AWG

SM

SR

(d

B)

ASE Injecting power (dBm)1542 1544 1546 1548 1550 1552

-70

-60

-50

-40

-30

-20

50-GHz AWG

200-GHz AWG

Po

we

r (d

Bm

)Wavelength (nm)

Fig. 4. SMSR of WRC-FPLD

injection-locked by 50-GHz

and 200-GHz AWG-sliced

ASE source.

Fig. 5. WRC-FPLD spectra

obtained injection-locked by

50-GHz and 200-GHz

AWG-sliced ASE sources.

The measured back-to-back optical eye diagrams are shown in Figs. 6 and 7. Increasing the

injection-locking ASE spectral linewidth from 0.35 to 1.1 nm (by changing the channel spacing

of the AWG filter from 50 GHz to 200 GHz) could effectively improve the signal-to-noise ratio

(SNR) of the WRC-FPLD up-transmitted data from 7.5 dB to 9.7 dB at same injecting power

level. The spectrally sliced ASE source increases its intensity noise when reducing the AWG

channels bandwidth, which eventually leads to the degradation on up-stream transmitted signal

quality by narrowing the injection-locked WRC-FPLD linewidth. In principle, the SNR of the

ASE injection-locked WRC-FPLD is inverse proportional to the spontaneous-spontaneous

beating noise given by 2I2ASEBe/m∆λ, where IASE is the ASE injecting power, Be is the electrical

bandwidth, m is the polarization ratio, and ∆λ is the spectral linewidth. This explains why the

SNR is degraded by shrinking the spectral linewidth of the AWG channelized ASE source.

Fig. 6. Eye-diagram of data

from WRC-FPLD


AWG-sliced ASE.

Fig. 7. Eye-diagram of data

from WRC-FPLD


AWG filtered ASE.

Lower SNR on the up-stream transmitted data from the WRC-FPLD injection-locked by the

AWG-sliced ASE with narrower channel spacing is observed, which reveals the difficulty in

raising the network capacities in ASE injection-locked WRC-FPLD based WDM-PON. In Figs.

8 and 9, the dynamic frequency chirps of the up-stream transmitted data from WRC-FPLD

injection-locked by 200-GHz and 50-GHz AWG-slice ASE sources at same power level of −3



dBm are compared. As shown in Fig. 8, a broader-linewidth injection (∆λ = 1.1 nm) could gives

rise to a larger dynamic chirp (varied from + 5.5 to −3 GHz), as the linewidth enhancement

factor (α) in the formula of dynamic frequency chirp (∆νc) is strongly inverse proportional to

∆λ,

( ) ( ) ( )ln1. (1)

2 4c

d P td tt

dt dt

φ αν

π π

∆ = − = −

With increasing power of the AWG-sliced ASE injection, the off-state power level of the

injection-locked WRC-FPLD transmitter is also enlarged due to the reduction on its threshold

current under external injecting operation. This inevitably causes a decreased on/off extinction

ratio (ER, as defined by Ion/Ioff) to dynamically suppress the negative frequency chirp of the

up-stream transmitted data, which could further contribute to different power penalty level with

replacing AWG channel bandwidth and with lengthening propagating distance. Apparently, the

shrinkage of ER on the WRC-FPLD under 50-GHz AWG-sliced ASE injection is more

significant than that under 200-GHz AWG-sliced ASE injection, since the injecting power is

more concentrated within a narrower linewidth for the former case. As a result, the dynamic

range of WRC-FPLD output power shrinks to result in a reduced ER as well as a small chirp, as

shown in Fig. 9. However, in the case of the ASE injection-locked WRC-FPLD transmitter,

there is an increasing power penalty on the BER receiving sensitivity with reducing AWG

channel bandwidth. Although the dynamic chirp of the WRC-FPLD transmitted data is slightly

reduced by decreasing ER, the effect of improving ER is more pronounced than the decreasing

chirp on the Q parameter as well as the BER of the WRC-FPLD transmitted up-stream data.

0 500 1000 1500 2000-6

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0

2

4

6

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0.2

0.4

0.6

0.8

1.0

Ch

irp

peak

to

peak (

GH

z)

Time (ps)

In

ten

sit

y (

a.u

.)

0 500 1000 1500 2000-6

-4

-2

0

2

4

6

0.0

0.2

0.4

0.6

0.8

1.0

Ch

irp

pe

ak t

o p

ea

k (

GH

z)

Time (ps)

In

ten

sit

y (

a.u

.)

Fig. 8. Transmitted data chirp

of WRC-FPLC


AWG-sliced ASE source.

Fig. 9. Transmitted data chirp

of WRC-FPLC


AWG-sliced ASE source.

To investigate the correlation between AWG-sliced ASE linewidth and transmission

performance in more detail, the BER analysis of the back-to-back and 25-km transmitted data

from the WRC-FPLD injection-locked by the AWG-channelized ASE source with changing

spectral linewidth are compared in Fig. 10. Under the injection power of −3 dBm, the 200-GHz

AWG-sliced ASE injection results in a WRC-FPLD data stream with a requested receiving

power as low as −31.6 dBm for BER of <10−9

. A receiving power penalty of about 1.3 dB is

obtained after 25-km propagation. In contrast, the 50-GHz AWG-sliced ASE injection provides

same BER performance at larger receiving power of −30.1 dBm. After 25-km SMF

transmission, the power penalty in the 50-GHz AWG based WDM-PON is approximately 1 dB,

however, changing the AWG to 200-GHz makes the power penalty increased to 1.5 dB. To

verify the nearly wavelength-independent operation of the WRC-FPLD, we detune the

operating temperature to make 50-GHz AWG-sliced ASE spectrum injected either on the peak

or on the valley between longitudinal modes. There is a negative power penalty of only 0.5 dB

observed between two conditions. The contribution of the injected ASE linewidth to the BER is



straightforward, since the 200-GHz AWG-sliced ASE with a broader linewidth leads to a BER

of only 4 × 10−11

at receiving power of −29.5 dBm even after 25-km propagation, which is at

least one order of magnitude lower than the BER of the back-to-back transmitted data generated

by the WRC-FPLD under 50-GHz AWG-sliced ASE injection. This result correlates well with

the positive contribution of ASE linewidth to the SNR as discussed in above section.

In addition to the SNR, there is another factor to affect the BER performance of the ASE

injection-locked WRC-FPLD is the on/off extinction. If we define the BER of WRC-FPLD

transmitted up-stream data as a function of Q parameter with optimum setting of the decision

threshold at the receiver part by [13]

( )

2

2

1exp 2

exp 2 11(2)

12 2 22

1

ERSNR

Q ERQBER erfc

ERQSNR

ER

π π

− − − + = ≈ ∝ − +

where the Q parameter is defined as Q = (Ion-Ioff)/[(σshot2 + σthermal

2)

1/2 + σthermal], in which the

numerator is the on/off level power deviation, and the denominator is the summation of the

root-mean-square shot and thermal noise currents. The Eq. (2) is obtained under the

thermal-noise limited condition with σshot<<σthermal, in which the effect of SNR is more

pronounced than that of ER on the BER performance unless the ER is too small. Our results

support the dominant effect of channel linewidth on the SNR of spectrum-sliced ASE source

[14], and the bandwidth of AWG is decisive to transmission performance in WDM-PON

transmitter [15]. Furthermore, only when the injection increases extremely high, which

inevitably causes a decreased on/off extinction ratio (ER, as defined by Ion/Ioff) to degrade the

BER performance of the up-stream transmitted data. When comparing with the SNR in general

case, the ER and chirp parameter are not the dominant factor to affect the back-to-back BER

performance of the injection-locked WRC-FPLD up-stream transmitter. Under the AWG-sliced

ASE injection, the WRC-FPLD transmitted data with relatively high ER exhibits Q = IASE/Isp-sp

= (SNR)0.5

= (m∆λ/2Be)0.5∝ (∆λ/Be)

0.5.

-33 -32 -31 -30 -29 -28 -2713

12

11

10

9

8

7

6

5

200G BTB

200G 25km SMF

50G BTB

50G 25km SMF

-Lo

g(B

ER

)

Receiving power (dBm)-14 -12 -10 -8 -6 -4 -22

4

6

8

10

12

7

8

9

10

11

12

200-GHz AWG

SN

R (

dB

)

Injection power (dBm)

50-GHz AWG

ER

(d

B)

Fig. 10. BER of WRC-FPLD


and 200-GHz AWG-sliced

ASE.

Fig. 11. SNR and ER versus

ASE injection power and

AWG channel bandwidth.

In Fig. 11, it is observed in experiment that the SNR of the WRC-FPDL transmitted data

linearly increases by 2 dB when enlarging ASE injecting power from −12 to −3 dBm, whereas

the ER oppositely degrades due to the reduction of threshold current associated with the shifted

power-current response at higher ASE injecting condition. In our case, the linewidths of the

WRC-FPLD injection-locked by 200-GHz and 50-GHz AWG-sliced ASE are 1.1 nm and 0.35

nm, respectively. The difference on Q parameters by a factor of 1.76 calculated from the



measured SNR is almost identical with that evaluated from the spectral linewidth deviation

(Q200GHz/Q50GHz = 1.77). By enlarging the 50-GHz and 200-GHz AWG-sliced ASE injecting

power from −12 to −3 dBm, the ER is oppositely decreased from 9 to 8 dB and from 11.5 to 9

dB, corresponding to the decreasing of the (ER-1)/(ER + 1) factor from 0.86 to 0.77 and from

0.77 to 0.72, respectively. A more significant degradation on ER by 2.5 dB at higher injecting

level has been observed when injection-locking the WRC-FPLD with ASE of larger linewidth.

Under high injection, the ER starts to play more important role on the BER than that under low

injection case. Even though, the ER of the WRC-FPLD transmitted data can still meet the

demand of data communication standards (ER >8 dB) no matter the injection ASE source is

sliced by 50-GHz or 200-GHz AWG. In summary, the 200-GHz AWG-sliced ASE injection

provides an increment on Q parameter by 1.75 times than the 50-GHz AWG-sliced ASE

injection case. This clearly elucidates the BER deviation between two injecting conditions up to

four orders of magnitude at same receiving power obtained.

5. Conclusion

In a weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) based DWDM-PON system

with channelized AWG DWDM multiplexer/de-multiplexer, the injecting-linewidth dependent

transmission performances of a channelized ASE injection-locked WRC-FPLD directly

modulated at 1.25Gbit/s is characterized. To effectively raise the network capacity of the

DWDM-PON system with injection-locked transmitter based ONU, the location of 50-GHz or

200-GHz AWG-sliced ASE source at remote-node for reducing the interfered crosstalk induced

by broadband ASE reflection at transmission path is proposed. With the DWDM AWG filters of

two different channel spacings at 50 and 200 GHz, several characteristic parameters such as

interfered reflection, relatively intensity noise, crosstalk reduction, side-mode-suppressing ratio

and power penalty of BER effect of the WRC-FPLD transmitted data are compared. The ideal

WDM-PON structure with 200-GHz channel bandwidth significantly improves the receiving

power of BER at 10−9

from −30 to −31.6 dBm. The 200-GHz AWG filtered ASE injection

minimizes the noises of WRC-FPLD based ONU transmitter, thus improving the power penalty

of upstream data by −1.6 dB even at BER of 10−12

. In contrast, there is a power penalty of 1.5 dB

if the AWG channel bandwidth 200-GHz is replaced by 50-GHz at same ASE injection power.

The 50-GHz AWG channelized ASE injection fails to promote better BER under back-to-back

transmission due to its narrow spectral linewidth. Nevertheless, the 50-GHz AWG exhibits a

lower negative frequency chirp as well as extinction ratio compared to 200-GHz in the

WDM-PON. Furthermore, the effects of signal-noise ratio and on/off extinction-ratio on the

BER and power penalty are experimentally demonstrated and theoretically elucidated. The

BER degradation up to 4 orders of magnitude is mainly attributed to the reduction of

injection-locked mode number and slightly increasing RIN noise, which concurrently degrade

the signal-to-noise and extinction ratios of the transmitted data stream.

Acknowledgment

This work is partially supported by the National Science Council of Republic of China under

grants NSC97-2221-E-002-055 and NSC98-2221-E-002-023-MY3.



200-ghz and 50-ghz awg channelized linewidth dependent transmission of weak-resonant-cavity fpld...

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