A Novel Bidirectional RSOA Based WDM-PON with Downstream
DPSK and Upstream Re-Modulated OOK Data
Jinnan Zhang1
, Xueguang Yuan1
, Yue Gu2
, Yongqing Huang1
, Minglun Zhang1
, Yangan Zhang1
1
Key Laboratory of Optical Communication and Light-wave Technologies, Ministry of Education
Beijing University of Posts and Telecommunications, Beijing 100876 China
e-mail:
[email protected] 2
Network Operation Supporting Center, China Mobile Group Beijing Co., Ltd., Beijing 100036
ABSTRACT
We propose a bidirectional reflective semiconductor optical amplifier (RSOA) based wavelength-division-
multiplexing passive optical network (WDM-PON) utilizing a differential phase shift keying (DPSK) signal for
down-link and an on-off keying (OOK) signal re-modulated for up-link with high extinction-ratio in both
directions. A 20 km range colorless WDM-PON without dispersion compensation was demonstrated within low
penalty for both 10 Gbit/s downstream and 5 Gbit/s upstream signals. We investigate the impacts of wavelength
and the injection power to the RSOA on upstream data. The BER performances of our scheme show that the
performance of our scheme is as good as those in case of continuous wave (CW) light injected RSOA. So our
scheme is a practical solution to meet the data rate and cost-efficient of the optical links simultaneously in
tomorrow’s WDM-PON access networks.
Keywords: WDM-PON, RSOA, DPSK, optical re-modulation.
1. INTRODUCTION
For optical access networks, wavelength-division-multiplexing passive optical networks (WDM-PON) are
considered as a promising solution for the next-generation of FTTx because of its almost-unlimited bandwidth,
security, and protocol transparency. But this requires expensive wavelength specified optical sources so that it
hasn’t been largely deployed. For this reason, an access network architecture utilizing a centralized light source
at central office (CO) and with data re-modulation using the downstream wavelength received at the optical
network unit (ONU) is an attractive solution for low-cost implementation of the upstream transmitter as it
requires no wavelength management and needs no expensive wavelength specified light source. Recently,
several schemes have been proposed based on semiconductor optical amplifier (SOA) [1, 2], and reflective
semiconductor optical amplifier (RSOA) because it can reuse the downstream signal received at the ONU for
upstream transmission. The downstream signal is amplified and re-modulated with upstream signal by the RSOA
and sent back to the CO. Thus, this technique does not require any additional broadband light sources at the CO
and can provide sufficient power budgets for the upstream signals. Some schemes have been proposed based on
RSOA with on-off keying (OOK) modulation as downstream signal [1]-[3]. However, those schemes required
high injection power and sacrificed the extinction ratio (ER) of the downstream data to reduce the crosstalk to
the upstream signal.
In this paper, a novel bidirectional WDM-PON architecture using differential phase shift keying (DPSK)
signal for downstream and using OOK signal re-modulated by RSOA for upstream is proposed. For downstream
transmission, the use of DPSK itself poses a number of advantages over the traditional OOK modulation format
[4]. For example, an optical phase modulator with a single LiNbO3 crystal usually costs less than a Mach–
Zehnder intensity modulator. In addition, the constant-intensity nature of the DPSK modulation format could
keep high ER and present higher tolerance to fiber nonlinear impairment and chromatic dispersion, thus
improving the system power budget. DPSK balanced detection also enables 3 dB receiver-sensitivity
enhancement. We experimentally demonstrated Low-penalty upstream data re-modulation and transmission at
5 Gb/s using RSOA to re-modulate a 10 Gb/s downstream optical DPSK wavelength.
2. PROPOSED ARCHITECTURE
Fig. 1 shows the proposed WDM-PON architecture. For down-link, a series of DFB lasers with various
wavelengths are modulated by phase modulators using 10 Gb/s pre-coding non-return to zero (NRZ)
downstream data to generate downstream DPSK signal. The generated DPSK signals are sent to a multiplexer
(MUX) normally made by Arrayed Waveguide Grating (AWG). A circulator is used before the downstream
signals are transmitted over the bidirectional single-mode fiber (SMF). While DPSK signals arrive at ONU
through bidirectional SMF via the AWG De-multiplexer (DEMUX) in remote node (RN). Various wavelength
lights are sent to different ONU. At the ONU, using optical splitter/coupler, portion of the DPSK signal is fed to
a DPSK balanced receiver, which get 3 dB receiver sensitivity enhancement.
For up-link, the other portion of the downstream DPSK signal from the splitter/coupler is re-modulated using
5 Gb/s non-return to zero (NRZ) upstream data by RSOA in the ONU. The re-modulated OOK signals re-pass
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