Interchannel Nonlinearities in Coherent Polarization-Division-Multiplexed Quadrature-Phase-Shift- Keying Systems
TL;DR: In this article, a 42.8-Gb/s coherent polarization-division-multiplexed quadrature-phase-shift-keying (PDM-QPSK) system with and without dispersion management is studied.
Abstract: We study with simulations interchannel nonlinear effects on a 42.8-Gb/s coherent polarization-division-multiplexed quadrature-phase-shift-keying (PDM-QPSK) system with and without dispersion management. We find that interchannel cross-phase-modulation induced nonlinear polarization scattering can severely degrade the performance of a dispersion-managed PDM-QPSK system. We demonstrate that the time-interleaved return-to-zero PDM-QPSK, where the symbols of the two polarizations are shifted by half a symbol in time, can significantly suppress the nonlinear polarization scattering in dispersion managed systems, and make systems with inline dispersion-compensation fiber (DCF) achieve better performance than those without DCF.
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TL;DR: A polarization-managed 8-dimensional modulation format that is time domain coded to reduce inter-channel nonlinearity and has negligible sensitivity to the polarization states of the neighboring WDM channels is demonstrated.
Abstract: We demonstrate a polarization-managed 8-dimensional modulation format that is time domain coded to reduce inter-channel nonlinearity. Simulation results show a 2.3 dB improvement in maximum net system margin (NSM) relative to polarization multiplexed (PM)-BPSK, and a 1.0 dB improvement relative to time interleaved return-to-zero (RZ)-PM-BPSK, for five WDM channels propagating over 1600 km ELEAF with 90% inline optical dispersion compensation. In contrast to the other modulations considered, the new 8-dimensional format has negligible sensitivity to the polarization states of the neighboring WDM channels. High-density WDM (HD-WDM) measurements on a 5000 km dispersion-managed link show a 1.0 dB improvement in net system margin relative to PM-BPSK.
96 citations
TL;DR: It is found that the LO phase noise to amplitude noise conversion can cause significant penalties in the 112-Gb/s system with only electronic dispersion compensation if distributed feedback lasers are used, but by using time-interleaved return-to-zero (RZ) P -QPSK, which can significantly suppress nonlinear polarization scattering.
Abstract: Using numerical simulations, we study and compare the performance of 42.8-Gb/s and 112-Gb/s intradyne coherent polarization-division- multiplexed quadrature-phase-shift-keying (PDM-QPSK) systems in wavelength-division-multiplexed (WDM) transmission with inline dispersion compensation fiber (DCF) and that with fully electronic dispersion compensation. Two effects are considered in the studies. One is fiber nonlinearities and the other is the local oscillator (LO) phase noise to amplitude noise conversion induced by electronic dispersion compensation. Results of 1000-km transmission employing standard single-mode fiber (SSMF) show that, for non-return-to-zero (NRZ) PDM-QPSK, both the 42.8-Gb/s and 112-Gb/s WDM systems with DCF have less tolerance to fiber nonlinearities than those with electronic dispersion compensation due to nonlinear polarization scattering. However, by using time-interleaved return-to-zero (RZ) P -QPSK, which can significantly suppress nonlinear polarization scattering in a system with inline DCF, the 42.8-Gb/s system with DCF can achieve better performance than that with electronic dispersion compensation, and comparable performance can be obtained for the 112-Gb/s system with DCF and that with electronic dispersion compensation. We find that the LO phase noise to amplitude noise conversion can cause significant penalties in the 112-Gb/s system with only electronic dispersion compensation if distributed feedback lasers are used.
93 citations
TL;DR: In this article, a simple fiber model is proposed to facilitate the determination of cross-phase modulation (XPM) effects and the phase noise and polarization scattering are calculated based on the system configurations and the time-consuming computation by the split step Fourier method is avoided.
Abstract: Previous investigations have revealed that the impairments of the cross-phase modulation (XPM) in dense wavelength-division multiplexing (DWDM) systems include two aspects: the XPM-induced phase noise and the XPM-induced polarization scattering. Such XPM phenomena are strongly dependent on the transmission system configurations and are nonintuitive. In this paper, a simple fiber model is proposed to facilitate the determination of XPM effects. By employing this model, the phase noise and polarization scattering are calculated based on the system configurations and the time-consuming computation by the split step Fourier method is avoided. The proposed model is verified by the dual polarization quadrature phase-shift keying coherent DWDM experiments and simulations in terms of the variance and autocorrelations of phase noise and polarization crosstalk as well as their dependence on relative polarization states and the overall Q-impairment. The proposed model helps deeper analysis of XPM phenomena, and eventually, leads to development of various XPM mitigation methods through transmission system design and coherent receiver DSP.
71 citations
TL;DR: In this paper, the authors demonstrate a polarization-managed 8-dimensional modulation format that is time domain coded to reduce inter-channel nonlinearity, and demonstrate a 2.33 dB improvement in maximum net system margin (NSM) relative to polarization multiplexed (PM)-BPSK, and a 1.0 dB improvement relative to time interleaved return to zero (RZ)-PBSK, for a five channel fill propagating on 20x80 km spans of 90% compensated ELEAF.
Abstract: We demonstrate a polarization-managed 8-dimensional modulation format that is time domain coded to reduce inter-channel nonlinearity. Simulation results show a 2.33 dB improvement in maximum net system margin (NSM) relative to polarization multiplexed (PM)-BPSK, and a 1.0 dB improvement relative to time interleaved return to zero (RZ)-PM-BPSK, for a five channel fill propagating on 20x80 km spans of 90% compensated ELEAF. In contrast to the other modulations considered, the new 8-dimentional (8D) format has negligible sensitivity to the polarization states of the neighboring channels. Laboratory results from High-density WDM (HD-WDM) propagation experiments on a 5000 km dispersion-managed link show a 1 dB improvement in net system margin relative to PM-BPSK.
51 citations
TL;DR: Recent advances in understanding the impact of fiber nonlinearities, polarization-mode dispersion, and polarization-dependent loss on PDM-QPSK coherent systems are reviewed.
Abstract: Coherent detection with digital signal processing (DSP) significantly changes the ways impairments are managed in optical communication systems. In this paper, we review the recent advances in understanding the impact of fiber nonlinearities, polarization-mode dispersion (PMD), and polarization-dependent loss (PDL) in coherent optical communication systems. We first discuss nonlinear transmission performance of three coherent optical communication systems, homogeneous polarization-division-multiplexed (PDM) quadrature-phase-shift-keying (QPSK), hybrid PDM-QPSK and on/off keying (OOK), and PDM 16-ary quadrature-amplitude modulation (QAM) systems. We show that while the dominant nonlinear effects in coherent optical communication systems without optical dispersion compensators (ODCs) are intra-channel nonlinearities, the dominant nonlinear effects in dispersion-managed (DM) systems with inline dispersion compensation fiber (DCF) are different when different modulation formats are used. In DM coherent optical communication systems using modulation formats of constant amplitude, the dominant nonlinear effect is nonlinear polarization scattering induced by cross-polarization modulation (XPolM), whereas when modulation formats of non-constant amplitude are used, the impact of inter-channel cross-phase modulation (XPM) is much larger than XPolM. We then describe the effects of PMD and PDL in coherent systems. We show that although in principle PMD can be completely compensated in a coherent optical receiver, a real coherent receiver has limited tolerance to PMD due to hardware limitations. Two PDL models used to evaluate PDL impairments are discussed. We find that a simple lumped model significantly over-estimates PDL impairments and show that a distributed model has to be used in order to accurately evaluate PDL impairments. Finally, we apply system outage considerations to coherent systems, taking into account the statistics of polarization effects in fiber.
48 citations
References
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IBM1
TL;DR: This paper solves the general problem of adaptive channel equalization without resorting to a known training sequence or to conditions of limited distortion.
Abstract: Conventional equalization and carrier recovery algorithms for minimizing mean-square error in digital communication systems generally require an initial training period during which a known data sequence is transmitted and properly synchronized at the receiver. This paper solves the general problem of adaptive channel equalization without resorting to a known training sequence or to conditions of limited distortion. The criterion for equalizer adaptation is the minimization of a new class of nonconvex cost functions which are shown to characterize intersymbol interference independently of carrier phase and of the data symbol constellation used in the transmission system. Equalizer convergence does not require carrier recovery, so that carrier phase tracking can be carried out at the equalizer output in a decision-directed mode. The convergence properties of the self-recovering algorithms are analyzed mathematically and confirmed by computer simulation.
2,645 citations
"Interchannel Nonlinearities in Cohe..." refers methods in this paper
...The DSP is comprised of four steps: 1) CD compensation with two 35-tap finite impulse response (FIR) filters [2]; 2) polarization demultiplxing with four seven-tap FIR filters employing the constant modulus algorithm [2], [ 7 ]; 3) carrier phase estimation using the block th-power scheme [1]; and 4) symbol identification [1]....
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TL;DR: In this paper, a coherent optical receiver for demodulating optical quadrature phase-shift keying (QPSK) signals is proposed. But the authors do not consider the phase-diversity homodyne detection at the receiver.
Abstract: This paper describes a coherent optical receiver for demodulating optical quadrature phase-shift keying (QPSK) signals. At the receiver, a phase-diversity homodyne detection scheme is employed without locking the phase of the local oscillator (LO). To handle the carrier phase drift, the carrier phase is estimated with digital signal processing (DSP) on the homodyne-detected signal. Such a scheme presents the following major advantages over the conventional optical differential detection. First, its bit error rate (BER) performance is better than that of differential detection. This higher sensitivity can extend the reach of unrepeated transmission systems and reduce crosstalk between multiwavelength channels. Second, the optoelectronic conversion process is linear, so that the whole optical signal information can be postprocessed in the electrical domain. Third, this scheme is applicable to multilevel modulation formats such as M-array PSK and quadrature amplitude modulation (QAM). The performance of the receiver is evaluated through various simulations and experiments. As a result, an unrepeated transmission over 210 km with a 20-Gb/s optical QPSK signal is achieved. Moreover, in wavelength-division multiplexing (WDM) environment, coherent detection allows the filtering of a desired wavelength channel to reside entirely in the electrical domain, taking advantage of the sharp cutoff characteristics of electrical filters. The experiments show the feasibility to transmit polarization-multiplexed 40-Gb/s QPSK signals over 200 km with channel spacing of 16 GHz, leading to a spectral efficiency as high as 2.5 b/s/Hz.
436 citations
"Interchannel Nonlinearities in Cohe..." refers background or methods in this paper
...The DSP is comprised of four steps: 1) CD compensation with two 35-tap finite impulse response (FIR) filters [2]; 2) polarization demultiplxing with four seven-tap FIR filters employing the constant modulus algorithm [2], [7]; 3) carrier phase estimation using the block th-power scheme [1]; and 4) symbol identification [ 1 ]....
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...ture-phase-shift-keying (PDM-QPSK) with coherent detection is a possible solution to upgrade existing 10-Gb/s dense wavelength-division-multiplexed (WDM) networks with 50-GHz channel spacing to 40 or 100 Gb/s [ 1 ]–[3]....
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...The QPSK signal is differentially encoded to avid phase ambiguity [ 1 ]....
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...The DSP is comprised of four steps: 1) CD compensation with two 35-tap finite impulse response (FIR) filters [2]; 2) polarization demultiplxing with four seven-tap FIR filters employing the constant modulus algorithm [2], [7]; 3) carrier phase estimation using the block th-power scheme [ 1 ]; and 4) symbol identification [1]....
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TL;DR: Results of a 42.8Gbit/s nonlinear transmission experiment, using polarization multiplexed QPSK data at 10.7GBaud, with 4 bits per symbol is presented, which allows the digital coherent receiver to be compensated digitally after transmission over 6400km of standard single mode fiber.
Abstract: Digital signal processing (DSP) combined with a phase and polarization diverse coherent receiver is a promising technology for future optical networks. Not only can the DSP be used to remove the need for dynamic polarization control, but also it may be utilized to compensate for nonlinear and linear transmission impairments. In this paper we present results of a 42.8Gbit/s nonlinear transmission experiment, using polarization multiplexed QPSK data at 10.7GBaud, with 4 bits per symbol. The digital coherent receiver allows 107,424 ps/nm of chromatic dispersion to be compensated digitally after transmission over 6400km of standard single mode fiber.
377 citations
"Interchannel Nonlinearities in Cohe..." refers methods in this paper
...The DSP is comprised of four steps: 1) CD compensation with two 35-tap finite impulse response (FIR) filters [2]; 2) polarization demultiplxing with four seven-tap FIR filters employing the constant modulus algorithm [ 2 ], [7]; 3) carrier phase estimation using the block th-power scheme [1]; and 4) symbol identification [1]....
[...]
...The DSP is comprised of four steps: 1) CD compensation with two 35-tap finite impulse response (FIR) filters [ 2 ]; 2) polarization demultiplxing with four seven-tap FIR filters employing the constant modulus algorithm [2], [7]; 3) carrier phase estimation using the block th-power scheme [1]; and 4) symbol identification [1]....
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TL;DR: In this article, the potential of electronic dispersion compensation (EDC) in amplified multispan 111-Gb/s wavelength division multiplexed systems based on polarization-multiplexed quadrature phase-shift keying modulation with coherent detection was investigated.
Abstract: We carried out an extensive simulative analysis to investigate in depth the potential of electronic dispersion compensation (EDC) in amplified multispan 111-Gb/s wavelength- division-multiplexed systems based on polarization-multiplexed quadrature phase-shift keying modulation with coherent detection, also in the presence of substantial fiber nonlinearity. For typical single-mode and nonzero dispersion-shifted fibers, our results show that the use of inline optical dispersion management is always suboptimal versus using EDC at the receiver.
89 citations
"Interchannel Nonlinearities in Cohe..." refers background or methods in this paper
...It shows that the PDM-QPSK system with inline DCF is limited to lower powers than the system without inline DCF [5], [ 6 ]....
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...It was shown that a PDM-QPSK coherent system with dispersion management could perform worse than that without dispersion management [5], [ 6 ], but the mechanism of signal degradation is not yet fully understood....
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TL;DR: In this paper, a dependence of nonlinear transmission penalty on bit sequence length in pseudolinear transmission is studied and it is shown that, for a realistic dispersion map, bit sequence lengths incorporating tens of thousands of bits or more may become necessary to accurately capture the nonlinear transmit penalty due to intrachannel nonlinear effects, especially at low bit-error ratio (<10/sup -5/).
Abstract: A dependence of nonlinear transmission penalty on bit sequence length in pseudolinear transmission is demonstrated and studied. It is shown that, for a realistic dispersion map, bit sequence lengths incorporating tens of thousands of bits or more may become necessary to accurately capture the nonlinear transmission penalty due to intrachannel nonlinear effects, especially at low bit-error ratio (<10/sup -5/).
68 citations
"Interchannel Nonlinearities in Cohe..." refers background in this paper
...The bit sequence length is sufficient to catch the nonlinear interaction for the system studied here [ 8 ]....
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