Transmission of 100Gb/s Coherent PDM-QPSK over 16x100km of Standard Fiber with allerbium amplifiers J. Renaudier1, G. Charlet1, O. Bertran-Pardo1, H. Mardoyan1, P. Tran1, M. Salsi1, and S. Bigo1 1
Alcatel-Lucent, Bell Labs, Centre de Villarceaux, Route de Villejust, 91620 Nozay, France * Corresponding author:
[email protected]
Abstract: We report on the performance of 100Gb/s coherent non returnto-zero (NRZ-) polarization division multiplexed (PDM-) quadrature phase shift keying (QPSK) transmission over 16x100km of standard single mode fibre under constraints of typical transparent terrestrial networks, employing Erbium-Doped Fibre Amplifiers. We first evaluate the impact of cross non linear effects onto the performance of 100Gb/s coherent PDM-QPSK signals and we investigate the impact of shifting one of the polarization multiplexed tributaries by half a symbol duration with respect to the other one. Finally we show that this solution is robust against channel-to-channel cross-talk from transparent nodes and does not suffer from performance degradation stemming from co-propagating 40Gb/s channels. ©2008 Optical Society of America OCIS codes: (060.1660) coherent communication; (060.2330) fiber optics communication
References and links 1. 2. 3. 4.
5. 6.
7.
8. 9. 10. 11. 12.
13.
C. R. S. Fludger, et al., “Coherent Equalization and POLMUX-RZ-DQPSK for robust 100-GE transmission,” J. Lightwave Technol. 26, 64-72 (2008). G. Charlet et al, “Transmission of 16.4Tbit/s Capacity over 2,550km using PDM QPSK Modulation Format and Coherent Receiver ,” Proc. of OFC, paper PDP3, San Diego, USA (2008). P.J. Winzer et al, “10x107-Gb/s NRZ-DQPSK transmission at 1.0b/s/Hz over 12x100km including 6 optical routing nodes,” Proc. of OFC, paper PDP24, Anaheim, USA (2007). X. Zhou et al, “8x114-Gb/s, 25GHz spaced, Polmux-RZ-8PSK transmission over 640km of SSMF employing digital coherent detection and EDFA-only amplification,” Proc. of OFC, paper PDP1, San Diego, USA (2008). S.L. Jansen et al, “10x121.9-Gb/s PDM-OFDM transmission with 2b/s/Hz spectral efficiency over 1,000km of SSMF,” Proc. of OFC, paper PDP2, San Diego, USA (2008). D. van den Borne et al, “Coherent Equalization versus Direct Detection for 111-Gb/s Ethernet Transport,” Proc. of IEEE/LEOS Summer Topical Meeting on Advanced Digital Signal Processing in Next Generation Fiber, Portland, USA (2007). J. Renaudier et al, “Long-haul transmission systems involving coherent detection for linear impairments mitigation,” Proc. of IEEE/LEOS Summer Topical Meeting on Next Generation Transceiver Technologies for Long Haul Optical Communication, Acapulco, Mexico (2008). D. N. Godard, “Self-Recovering Equalization and Carrier Tracking in Two-Dimensional Data Communication Systems,” IEEE Trans. Commun. 28, 1867-1875 (1980). A. J. Viterbi et al, “Nonlinear estimation of PSK-modulated carrier phase with application to burst digital transmission,” IEEE Trans. Inf. Theory 29, 543-551 (1983). D. van den Borne et al, “1.6-b/s/Hz Spectrally Efficient Transmission Over1700 km of SSMF using 40x85.6Gb/s POLMUX-RZ-DQPSK,” J. Lightwave Technol. 25, 222-232 (2007). S. Chandrasekhar et al, “Experimental Investigation of System Impairments in Polarization Multiplexed 107-Gb/s RZ-DQPSK,” Proc. of OFC, paper OThU7, San Diego, USA (2008). J. Renaudier et al, “Impact of Temporal Interleaving of Polarization Tributaries onto 100Gb/s coherent transmission systems with RZ Pulse carving,” accepted for publication in IEEE Photonics Technology Letters. A. Carena et al, “Optical vs. electronic chromatic dispersion compensation in WDM coherent PM-QPSK systems at 111Gb/s,” Proc. of OFC, paper JThA57, San Diego, USA (2008).
#101528 - $15.00 USD
(C) 2009 OSA
Received 15 Sep 2008; revised 7 Nov 2008; accepted 8 Dec 2008; published 17 Mar 2009
30 March 2009 / Vol. 17, No. 7 / OPTICS EXPRESS 5112
1. Introduction In order to cope with the need for capacity, the development of 100Gb/s transponders for the next few years appears to be of interest for deployment plans of many carriers. As the move to 100Gbit/s channel rate in WDM systems is generally motivated by the need for an increase of the total system capacity, a technique fitting with the existing 50GHz-grid infrastructures is desirable. Among the different modulation formats and detection techniques recently proposed to meet the challenge of boosting the total system capacity [1-5], polarizationdivision multiplexing (PDM-) quadrature phase shift keying (QPSK) associated with coherent detection and digital signal processing (DSP) has attracted much attention. This approach is compatible with spectral efficiencies of at least 2bit/s/Hz, which is naturally advantageous for dense WDM systems, and has an excellent robustness to linear impairments. Indeed, chromatic dispersion (CD) can be fully compensated in the digital domain using dedicated finite impulse response (FIR) filters with appropriate length, and polarization mode dispersion (PMD) amounts greater than 20ps can be mitigated using blind equalization based on adaptive FIR filter [1,6,7]. Regarding the tolerance to non linear effects, which determines the maximum reach in long-haul WDM systems, transmission distances up to 2,500km have been reported in pioneering experiments [1,2] at 100Gbit/s. However, these experiments were realized using Raman amplification in order to improve the optical signal-to-noise ratio (OSNR) at the receiver. In this paper we focus on the performance of 100Gb/s coherent (NRZ-)PDM-QPSK transmission over 16x100km of standard single mode fibre (SSMF) under the constraints of typical transparent terrestrial networks, employing Erbium-Doped Fibre Amplifiers (EDFAs). After having assessed the impact of non linear effects in WDM systems using coherent detection, we investigate whether shifting one the polarization multiplexed tributaries by half a symbol duration with respect to the other one can be helpful to contain the impairments related to non linear effects. Then we evaluate the impact of channel-to-channel cross-talk from transparent nodes, as well as the impact of co-propagating a 100Gb/s channel together with 40Gb/s neighboring channels. 2. Set-up configuration As depicted in Fig. 1, our test-bed consists of 79 conventional DFB lasers, spaced by 50GHz and separated into two independently modulated, spectrally interleaved combs, plus one narrow linewidth (~100kHz) tunable external cavity laser (test channel), at 1545.72nm. The light from each set is sent to a distinct QPSK modulator operating at 28Gbaud (or 56Gb/s). The modulators are fed by 215-1-bit-long sequences at 28Gb/s, including forward error correction (FEC) and protocol overhead. Polarization multiplexing is then performed by dividing and recombining the QPSK data into a polarisation beam combiner (PBC) with an approximate 100 symbol delay, yielding PDM-QPSK data at 112Gb/s. Here, by choosing polarization maintaining fibres with appropriate lengths before the PBC, the two orthogonal polarization tributaries can be either temporally aligned or interleaved by half a symbol (~18ps). In the following, aligned-PDM-QSPK refers to signals with polarization tributaries pulse-to-pulse aligned, in contrast with interleaved-PDM-QSPK that refers to signals with polarization tributaries temporally interleaved by half a symbol. The corresponding eye diagrams observed on an Agilent digital communications analyzer are shown in the insets a) and b) of Fig. 1. When the tributaries are temporally aligned, the eye diagram exhibits a high extinction ratio and clearly defines the five transition states between symbols of PDM-QPSK format, as shown in the inset (a) of Fig. 1. On the contrary, when the tributaries are interleaved by half a symbol, a cw-like eye diagram is observed, as shown in the inset (b) of Fig. 1. For both cases of aligned- and interleaved-PDM-QPSK, the two combs are combined with a 50GHz interleaver. The resulting multiplex is boosted through a dual-stage EDFA incorporating -400ps/nm dispersion compensating fibre (DCF), passed into a low-speed (
