The affection of fiber nonlinearity in coherent optical communication system

In this paper, we firstly analyzed the Gordon and Mollenauer (G-M) effect in dual polarization quaternary phase shift keying (DP-QPSK) system, whose simulation results indicate that the G-M is the main impairment which should be given a careful consideration. Secondly, a self-correlation technique was used to extract the cross phase modulation (XPM)-induced phase noise and XPM-induced polarization scattering for analyzing the characteristics of XPM in coherent optical orthogonal frequency division multiplexing (CO-OFDM) wavelength division multiplexed (WDM) transmission systems. The phase noise is verified as the dominant distortion in DP-OFDM systems while the XPM-induced polarization crosstalk is proved to be the decisive distortion in DP-QPSK coherent experiment. Thirdly, we discovered that the statistical characterization of the nonlinear noise in densely spaced 16QAM OFDM system deviate from Gauss distribution in the absence of amplified spontaneous emission (ASE) noise that cannot be regarded as the same in QPSK system.