Offset Manchester coding for Rayleigh noise suppression in carrier-
distributed WDM-PONs
Jing Xu
a,
n
, Xiangyu Yu
a
, Weichao Lu
a
, Fengzhong Qu
a
, Ning Deng
b
a
Ocean College, Zhejiang University, Hangzhou 310058, China
b
Fixed Networks Research Department, Huawei Technologies Co., Ltd., Shenzhen 518129, China
article info
Article history:
Received 15 January 2015
Received in revised form
7 February 2015
Accepted 15 February 2015
Available online 16 February 2015
Keywords:
Differential phase-shift keying (DPSK)
Rayleigh noise
Wavelength-division-multiplexed passive
optical network (WDM-PON)
abstract
We propose a novel offset Manchester coding in upstream to simultaneously realize Rayleigh noise
suppression and differential detection in a carrier-distributed wavelength division multiplexed passive
optical network. Error-free transmission of 2.5-Gb/s upstream signals over 50-km standard single mode
fiber is experimentally demonstrated, with a 7-dB enhanced tolerance to Rayleigh noise.
& 2015 Elsevier B.V. All rights reserved.
1. Introduction
The wavelength-division-multiplexed passive optical network
(WDM-PON) is a promising candidate for the next generation
optical access network [1]. In a carrier-distributed WDM-PON, the
upstream carriers are remotely distributed from the optical line
terminal (OLT), thus eliminating wavelength-specific transmitters
and wavelength management at the cost-sensitive optical network
unit (ONU). To reduce the system cost, bidirectional transmission
over single feeder fiber is highly desirable. However, the intrinsic
Rayleigh backscattering (RBS) of the distributed optical carrier
induces severe interferometric crosstalk to the upstream signal.
The RBS, with a narrow spectrum, can be effectively suppressed by
an optical notch filter. However specially designed upstream
modulation formats are required to avoid the upstream signal it-
self being distorted by the notch filter [2,3]. Single-tone phase
modulation or optical carrier suppression can also be used to
suppress the RBS crosstalk [4,5]. The attention of the research
community has recently turned to the electrical high-pass filter
(HPF) based approach for RBS crosstalk suppression in WDM-PONs
[6–9]. In this approach only 8B10B coding, electronic equalization
or Manchester coding (MC) is required, thus resulting in only
minor modifications to the PON structure.
In this paper, we propose an offset-Manchester coding (OMC)
to suppress Rayleigh noise more effectively in the carrier-
distributed WDM-PON and to simultaneously realize upstream
differential detection, via a postdetection HPF. Compared with
prior schemes using 8B10B coding or electronic equalization [6,7],
albeit Manchester coding requires larger bandwidth it enables
much easier clock extraction. The unique self-clocking property of
Manchester coding together with differential detection enables
burst-mode upstream detection [10], which is desirable in hybrid
WDM/TDM-PONs. The Manchester encoder, an exclusive OR (XOR)
gate, is also simpler than the 8B10B encoder. Unlike the 8B10B
coding, no decoder is needed at the receiver side for Manchester
coding. In addition, by further using OMC that is generated by
offsetting data and clock signal before the XOR gate, the cutoff
frequency of the HPF used to remove Rayleigh noise can be much
higher than that using 8B10B coding, electronic equalization or MC
[6–9], leading to more effective Rayleigh noise suppression and
much relaxed requirement for the seed laser linewidth. The pro-
posed scheme is also simpler than the prior scheme employing
differential Manchester coding and self-homodyne coherent de-
tection [11].
2. System architecture and operation principles
Fig. 1 illustrates the proposed loopback architecture. After the
transmission in a 50-km standard single mode fiber (SMF), the
optical carriers from the OLT are wavelength routed toward dif-
ferent ONUs, by an arrayed waveguide grating (AWG) at the re-
mote node (RN). At the ONU, the CW light is modulated by a
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/optcom
Optics Communications
http://dx.doi.org/10.1016/j.optcom.2015.02.030
0030-4018/& 2015 Elsevier B.V. All rights reserved.
n
Corresponding author.
E-mail address: jxu-optics@zju.edu.cn (J. Xu).
Optics Communications 346 (2015) 106–109