WDM coherent PDM-QPSK systems with and without inline optical dispersion compensation

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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) PDM-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.