200-ghz and 50-ghz awg channelized linewidth dependent transmission of weak-resonant-cavity fpld...
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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.
*grlin@ntu.edu.tw
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
#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 17740
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
#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 17741
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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RF modulated Transmission spectrum
Po
wer(
dB
m)
Wavelength(nm)1546.5 1547.0 1547.5 1548.0
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Free run
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
Transmission spectrum
Po
wer(
dB
m)
Wavelength(nm)
1546.5 1547.0 1547.5 1548.0-70
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RF modulated
Transmission spectrum
Po
we
r(d
Bm
)
Wavelength(nm)1546.5 1547.0 1547.5 1548.0
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-60
-50
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-30 Free run
RF modulated
Transmission spectrum
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
#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 17742
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
injection-locked by 200-GHz
AWG-sliced ASE.
Fig. 7. Eye-diagram of data
from WRC-FPLD
injection-locked by 50-GHz
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
#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 17743
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
-4
-2
0
2
4
6
0.0
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
injection-locked by 200-GHz
AWG-sliced ASE source.
Fig. 9. Transmitted data chirp
of WRC-FPLC
injection-locked by 50-GHz
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
#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 17744
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
injection-locked by 50-GHz
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
#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 17745
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.
#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 17746
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