Phase Estimation And XPM Effects In Coherent Optical WDM Systems

High-speed coherent optical communication and high-capacity wavelength division multiplexing(WDM)system are currently the main technologies in the field of fiber-optical transmission.In the coherent optical WDM system,the fiber nonlinear effect,represented by cross phase modulation(XPM),is the major factor to affect the system performance.This dissertation focuses on phase estimation and XPM effect of coherent optical communication WDM system.Moreover,it presents a comprehensive and in-depth study of system performance optimization from the aspects of theoretical analysis,systematic modeling,algorithm construction,and performance simulation.The dissertation proposes a flexible phase estimation(PE)algorithm for the single channel coherent optical communication system.It obtains the weighted factor via the maximum likelihood method.By so doing,it eliminates the influence of conventional PE receiver block length effect on the system.Through the theoretical analysis,the system performance could be predicted from the analytical expression of phase error variance of the flexible PE receiver.Moreover,based on the analytical method of small signal,the XPM intensity noise could be transformed to multiplicative noise by approximation.The dissertation comes up with an integrated XPM effect model to describe the influence of XPM intensity noise and XPM induced phase noise on the system.The XPM intensity noise shows the damage of signal noise ratio(SNR)form the aspects of theoretical analysis and performance simulation.Based on the autocorrelation function of XPM induced phase noise,the dissertation studies QPSK/OOK hybrid WDM system.The analytical expression of phase error variance is proposed to carry out the theoretical prediction of optimal block length in QPSK channel coherent receiver with M-th power and DA-ML algorithm.The weighted factor is introduced into the QPSK signal PE receiver to remove the block length effect in the QPSK/OOK combined WDM system.For the 16-QAM coherent optical WDM system,the dissertation starts from autocorrelation function of XPM induced phase noise and the statistical characteristics of 16-QAM signal power.It provides the analytical expression of phase error variance of conventional PE algorithm to predict the optimal block length.To overcome block length effect,weighted factors obtained based on the autocorrelation function of XPM induced phase noise are employed in PE receiver.Theory and simulation show that flexible 16-QAM PE receiver does not suffer from the block length effect.Finally,the dissertation proposes a method of reducing XPM effect by adjacent channel spectrum up-shifting.The variance of XPM intensity noise shows the stability of change with the increase of intermediate frequency(IF).And the variance of XPM phase noise presents the feature of monotonic decreasing along with the increase of IF.Under the action of XPM effect and the amplified spontaneous emission(ASE)noise,the CO-OFDM signal channel derives the analytical expression of Bit Error Ratio(BER),which validates the method of reducing XPM effect by adjacent channel spectrum up-shifting.