Study Of Hight-order QAM Signal Nonlinear Compensation And Carrier Phase Recovery

With the development of the internet technology in recent years, the bandwidth of the optical communication system can’t satisfy our need. Many researchers have focused on high- order Q AM modulation format. High-order QAM signal make full use of amplitude and p hase carrying information, which makes the transmission capacity improve greatly. But the high-order QAM signal have dense constellation points, and it’s affected by the nonlinear phase noise easily. Therefore, this thesis focuses on the study of high-order Q AM signal nonlinear compensation and carrier phase recovery technology.In this thesis, the optical communication system and its disadvantages are reviewed. We introduce the basic princip le and structure of optical communication system. We use the formula to explain how the optical signal to be modulated and demodulated. The differential coding and differential decoding technology are introduced. We use the simulation results to compare the advantages and disadvantages of direct phase detection and diffe rential decoding technology.In this thesis, the factors which lead to the optical signal distortion are discussed. We also discuss how to compensate the distortions. The d igital back-propagation algorithm is used to compensate nonlinearity and dispersion. At the same time, we discuss the influence of different algorithm parameters on the compensation result, and obtaine the optimum parameters of the algorithm.In this thesis, the blind phase search algorithm is used to compensate phase noise. In different laser linewidth, we compare the BER of the system. The sensitivity of receiver is calculated. The BER of the system are calculated with different OSN R and linewidth. Fina lly the optimal system parameters are obtained.In order to increase transmission capa city in the existing commercial systems, this paper puts forward the idea of different modulation format hybrid transmission. And then, we theoretical analyze how the different channel spacing and launched power affect the hybrid system. The channel which transmits 16 QAM modulation signal is researched with different channel spacing and launched power in the OOK-16 QAM and QPSK-16 Q AM hybrid system. We conclud that under the same condit ions, QPSK-16 Q AM hybrid system have a better transmission performance then OOK-16 Q AM hybrid system.