Nonlinear Modeling And Simulation Study Of PCTW Optical Fiber Communication System

Dense Wavelength Division Multiplexing(DWDM),Coherent Optical Orthogonal Frequency Division Multiplexing(CO-OFDM)and Nyquist-WDM systems are important technologies to enhance the capacity of optical fiber communication.However,with the further expansion of capacity,the nonlinear effects of optical fiber limit the performance and capacity of the system in transmission.Phase-conjugated twin waves(PCTW),as an advanced digital nonlinear compensation technology,have some unique advantages compared with traditional nonlinear compensation technology.It is of great importance to research on how to effectively evaluate the nonlinear suppression of PCTW in large-capacity optical fiber communication systems for the optimization and upgrading of the systems.This paper theoretically analyzed and simulated the suppression degree of PCTW for nonlinear effects in large-capacity optical fiber communication systems.With regard to the influence of the inter-channel pulses walk-off effect,on the basis of the bandwidth-limited noise spectrum analysis theory,a semi-analytic calculation model for quadrature amplitude modulation(QAM)PCTW Nyquist-WDM system four-wave mixing(FWM)noise standard deviation was derived.And the semi-analytic model is used for the relevant calculation.The performances of central channel for two cases of 16 QAM PCTW Nyquist-WDM systems with same total spectral bandwidth and spectral efficiency,16-channel 32-Gbaud/ch and 32-channel 16-Gbaud/ch,are numerically compared.Numerical results by using our models show that the PCTW scheme is still greatly effective to suppress the impact of FWM noise on the performance of such systems even for optical fiber links with asymmetric power distribution.Also,the proposed theoretical model shows that the standard deviation of non-degenerate FWM noise is irrelevant to the system number of the QAM signal,as is different from the degenerate FWM case.OptiSystem and Matlab were used to construct a PCTW-based CO-OFDM DWDM superchannel system.Two PCTW implementation schemes were proposed for the particularity of OFDM modulation: time domain PCTW and frequency domain PCTW.The simulation results demonstrate that both PCTW schemes can effectively reduce the nonlinear damage of WDM system channels and improve the nonlinear tolerance of the system.In the meanwhile,the frequency domain PCTW scheme can suppress nonlinear crosstalk between subcarriers and has better performance.In this paper,a semi-analytic theoretical calculation model of FWM noise standard deviation of QAM PCTW Nyquist-WDM system and the simulation results of CO-OFDM DWDM system under different PCTW implementation schemes provide reference for the optimization design of large-capacity and long-distance backbone networks.