Simulation Research Of Nonlinear Compensation Scheme For Coherent Optic Communication System

With the continuous development of virtual reality,cloud computing,live video and other advanced technologies,people have higher and higher requirements for communication transmission rate and transmission bandwidth.Coherent optical communication system can achieve larger capacity of information transmission.A variety of optical fiber nonlinear effects limit the further capacity improvement of coherent optical communication system.In recent years,many nonlinear suppression schemes have been proposed.Phase Conjugate Twin Waves(PCTW)technology is an effective technology.PCTW can suppress linear and nonlinear damage.PCTW is simple in structure and easy to implement.Probabilistic shaping(PS)technology can also achieve a certain degree of nonlinear suppression and improve the performance of the optical fiber system.The main research contents and contributions of this paper are given as follows:(1)The traditional polarization domain of PCTW scheme can be extended to time and subcarrier domain.The signal and its conjugate propagate in two mutually orthogonal dimensions respectively.So,the nonlinear effect is compensated to a certain extent by coherent superposition at the receiving end.The relevant theoretical models of Huffman Coded Spherical Shaping(HCSS)are discussed in detail.Several PS coding schemes are analyzed,their average power and redundancy are calculated.The calculation formulas of symbol error rate and Bit Error Rate(BER)for high-order modulation format in optical fiber communication system with PS technique are derived.Based on the above research,a hybrid nonlinear effect suppression scheme which combines PS and PCTW techniques is further proposed in this paper.(2)For Orthogonal Frequency Division Multiplexing(OFDM)system based on multi-dimensional PCTW,the semi analytical model of Four Wave Mixing(FWM)noise for any signal constellation is derived.Based on the derived general models,example calculations are carried out to evaluate the performance of OFDM system with polarization-domain PCTW scheme for 16-ary signal with several kinds of signal constellations.Three types of 16-ary signal constellations are defined.Among all 16-ary signal constellations discussed here,the performance of(5,11)is best and that of the 16-ary Phase Shift Keying(PSK)is worst.The performance of(5,11)is close to that of(1,5,10)and 16-ary Quadrature Amplitude Modulation(QAM).(3)With co-simulation of Optisystem software and Matlab,a PCTW-PS optical fiber system for two modulation formats(16QAM and 64QAM)is built and simulated,which includes two PS codes(Huffman coding and sign inversion coding)and three PCTW dimensions(polarization domain,time domain and subcarrier domain).The simulation results show that both PS and PCTW can improve the system performance.Combination of PS and PCTW can better improve the system performance.Under the condition of the same capacity,16QAM-PCTW scheme in time domain has better performance.The simulation results also show that BERs for in-phase component I and its quadrature component Q of QAM are quite different for PCTW system.Therefore,the concept of PCTW-IQ imbalance is proposed in this paper and the imbalance is especially obvious for polarization domain PCTW scheme.