A Survivable WDM Passive Optical Network with Colorless Optical

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A Survivable WDM Passive Optical Network with Colorless Optical Powered By Docstoc
					OECC 2006 5E2-2-1




 A Survivable WDM Passive Optical Network with
         Colorless Optical Network Units
                                    Bo Zhang, Chun-Kit Chan and Chinlon Lin
                                    Center for Advanced Research in Photonics
       Department of Information Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong.
                   Tel: +852-2609-8479, Fax: +852-2603-5032, Email: bzhang4@ie.cuhk.edu.hk

Abstract                                                      and protection fiber feeders. Under normal operation, the
We propose and experimentally demonstrate a survivable        switch is connected to the working feeder fiber. The RN
network architecture for WDM-PONs with colorless              consists of two identical 2×N AWGs, one for the
ONUs. Fiber failure can be protected and the                  downstream wavelengths and the other for the upstream
bi-directional traffic can be restored promptly.              wavelengths. The AWG dedicated for the upstream traffic
                                                              at the RN connects to the receivers at the CO via another
1 Introduction                                                pair of working and protection feeder fibers. The spectral
Wavelength division multiplexed passive optical network       transmission peaks of the two AWG input ports are spaced
(WDM-PON) is a very promising approach for                    by half of the free-spectral range (FSR) of the AWG.
next-generation broadband access. In such network,            Wavelength assignment plan for upstream and
colorless (wavelength-independent) optical network units      downstream wavelengths is shown in Fig. 2.
(ONUs) are desirable to reduce the costs of operation,
administration, and maintenance (OA&M) functions [1].                                                                                          CO
Recently, a WDM-PON architecture using centralized                                              Data control circuit

light sources (CLS) at the central office (CO) has                   Centralized
                                                                                                                                                                                       Receivers
                                                                                                LD1
                                                                                                      LD2
                                                                                                            LD3
                                                                                                                    LD4

                                                                                                                          LD5
                                                                                                                                LD6
                                                                                                                                      LD7
                                                                                                                                            LD8
                                                                       BLS
emerged as an attractive solution for colorless ONU
implementation [2]-[3]. To assure network reliability,               1 x N AWG                              1 x N AWG

protection and restoration functionalities are highly                                      WDM                                                         Decision                       2 x N AWG
                                                                                                                                                        circuit
                                                                               Optical
desirable. In [4], a wavelength-shifted protection scheme                      Switch
was reported for a carrier distributed WDM-PON.
                                                                     WORKING                                PROTECTION                                        WORKING                                              PROTECTION
However, it duplicated a set of transmitters, receivers,              FIBER I                                 FIBER I                                          FIBER II                                              FIBER II
which largely increased both the network complexity and
                                                                                                                                              RN
the cost.                                                                       2 x N AWG                                                                                             x N AWG
                                                                                                                                                                                    2 2 x N AWG
    In this paper, we propose a survivable architecture to      λ1 λ5 λ2 λ6 λ3 λ7 λ4 λ8 λ5 λ1 λ6 λ2 λ7 λ3 λ8 λ4                                          λ9         λ10         λ11         λ12         λ13        λ14      λ15    λ16
                                                                                                                                                              λ13         λ14         λ15         λ16         λ9         λ10    λ11    λ12
                                                                λ9 λ13λ10 λ14 λ11 λ15 λ12 λ16 λ13 λ9 λ14 λ10 λ15 λ11 λ16 λ12
protect the fiber link between the CO and remote node
(RN) in a CLS WDM-PON. The protection switching is
performed at the CO, and the ONU is kept simple and             WDM             WDM              WDM                            WDM                     WDM                      WDM                          WDM               WDM
                                                                        Mod.




                                                                                         Mod.




                                                                                                                  Mod.




                                                                                                                                            Mod.




                                                                                                                                                                     Mod.




                                                                                                                                                                                              Mod.




                                                                                                                                                                                                                         Mod.




                                                                                                                                                                                                                                        Mod.



colorless.                                                      PD              PD                  PD                          PD                      PD                       PD                           PD                PD

                                                                ONU 1           ONU 2               ONU 3                       ONU 4                    ONU 5                   ONU 6                        ONU 7              ONU 8

2 Network topology and wavelength assignment
Fig. 1 illustrates our proposed WDM-PON architecture                      Fig. 1: Proposed network architecture with 8 ONUs
with N ONUs. Without loss of generality, 8 ONUs are
                                                                                                      Upstream                                                                   Downstream
considered as an example. WDM broadband light sources
(BLS), supplying un-modulated optical carriers in the                                    0.5FSR                               0.5FSR                                0.5FSR                               0.5FSR
C-band are centralized at the CO, and they are to be
modulated at the ONUs for the upstream traffic, thus no
wavelength-specific transmitter is incorporated at the
subscriber side. The downstream channels are assigned                                λ 1 λ2 λ3 λ4                        λ 5 λ6 λ7 λ8                         λ 9 λ10 λ11 λ12                      λ13 λ14 λ15 λ16
with L-band wavelengths. Both the L-band downstream            Normal: ONU 1 2                  3     4                   5      6      7          8            1         2     3      4                5 6 7 8

wavelengths and the C-band BLS wavelengths are               Protection: ONU 5 6                7     8                   1      2      3          4            5         6     7      8                1 2 3 4
combined by the L/C combiner, followed by a 1×2 optical                              Fig. 2: Proposed wavelength assignment plan
switch, which connects to the RN via a pair of working
OECC 2006 5E2-2-2




    There are two fibers connecting RN and each ONU.            was 8-km long. Two 16×16 AWG with 100 GHz channel
One distribution fiber delivers a downstream signal and         spacing and an FSR of 12.8 nm were used in the RN. At
an optical carrier to each ONU, while the modulated             the CO side, EDFAs were inserted in front of the AWG in
upstream signal is delivered back to RN through the other       order to compensate for the insertion loss. We have
fiber. Since there is no light source in the ONU, the           measured the bit-error-rate (BER) performance using 2.5
                                                                Gb/s 223-1 PRBS data for both the upstream and the
colorless ONU can support any wavelength channel.
                                                                downstream traffic under normal and protection modes,
                                                                respectively. Avalanche photo diode (APD) receiver was
3 Protection operation principles
                                                                used in our experiment. From the results depicted in Fig.
Under normal operation, the switch is connected to the
                                                                3, nearly no power penalty was observed for both normal
working fiber I. Both the downstream wavelength λi (i = 1,      and protection operations. We have also measured the
2, …, N) and upstream carrier λi+N are transmitted via          switching time in case of the simulated fiber cut. The
working fiber I to ONUi (i = 1, 2, …, N). At each ONU,          fiber link between the CO and the RN was intentionally
downstream wavelength λi was received by a                      disconnected to simulate the fiber cut scenario, with the
photodetector (PD), while the optical carrier λi+N is           result shown in the inset of Fig. 3. The switching time
modulated by upstream signal and sent back to the CO via        was measured to be about 5 ms.
working fiber II. In this case, only the working fibers are
used, and there is no traffic running on the protection
fibers.
   In case of any cut in the working feeder fiber, the CO
will detect the power loss of upstream signals. So, the
data control circuit will change the status of the
downstream signals. The downstream signal destined for
ONUi (i = 1, …, N/2) is changed to another wavelength
λi+N/2, while the downstream signal destined for ONUj (j =
N/2+1, …, N) is changed to wavelength λj-N/2. At the same
time, the decision circuit will trigger the optical switch to
connect to the protection fiber I. Thus, both the
downstream wavelength λi (i = 1, 2, …, N) and upstream           Fig. 3: BER characteristics under normal and protection states.
carriers λi+N are transmitted via the protection fiber I to         Inset shows the switching time during traffic restoration.
the RN. With the wrap-around spectral periodicity
property of the AWG, the downstream wavelength λi (i =          5 Summary
1, …, N/2) and the upstream carrier λi+N are routed and         We have proposed a simple protection architecture for
sent to ONUi+N/2, while the downstream wavelength λj (j         optical carrier distributed WDN-PONs, which can achieve
= N/2+1, …, N) and the upstream carrier λj+N are routed         fast protection and traffic restoration against feeder fiber
and sent to ONUj-N/2. At the ONU, the dedicated                 failure successfully. The ONUs are colorless. The
downstream signals are received, while the upstream             bi-directional transmission of the 2.5 Gb/s signal over the
carriers are modulated and sent back to CO via the              WDM-PON have been experimentally demonstrated and
protection fiber II. As the colorless ONU in such carrier       characterized. In the proposed protection scheme, only
distributed WDM-PONs can handle any wavelength,                 one set of transceivers are needed at the CO, and all
there is no protection equipment needed in any ONU.             monitoring and protection equipment is consolidated at
                                                                the CO. However, data switching between downstream
4 Experimental Results                                          signals is necessary when any feeder fiber failure occurs.
We have experimentally investigated the transmission            This project was partially supported by a research grant
performance and the protection switching of our proposed        from Hong Kong RGC (CUHK4216/03E).
network. ONU 1 with working downstream and upstream
                                                                References
wavelengths of 1546.52 nm and1581.36 nm, respectively;
                                                                1. K. Iwatsuki et al., J. Lightwave. Technol, pp. 2623-2630,
and protection downstream and upstream wavelengths of
                                                                    2004.
1549.72 nm and 1584.73 nm, respectively, was                    2. B. Zhang et al., OFC2006, OTuC6, 2006.
demonstrated. The data rate for both the upstream and the       3. H. Suzuki et al., ECOC2004, Tu4.6.3, 2004.
downstream channels was 2.5 Gb/s. The standard single           4. H. Suzuki et al., ECOC2005, Mo4.3.4, 2005
mode fiber (SMF) link between the CO and the RN was
20-km long, while that between the RN and each ONU

				
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