Research Of Compensation Algorithms For Dispersion And Nonlinearities Of High-Level Modulated Coherent Optical Systems

Digital coherent optical communication technologies, which is consist of coherent detection and digital signal processing (DSP), provide internet service with potential solution to meet the growing demand of the bandwidth. As an effective way to improve the spectral efficiency of digital coherent optical systems, High-order modulation format has been favored by many studies. However, the signal distortion caused by the chromatic dispersion, fiber nonlinearitis and ASE noise becomes more notable, when increasing the capacity of systems by raising the order of modulation format and signal transmission rate. By processing received signal in the electronic domain, DSP technology opens up a flexible and low-cost ways to compensate transmission impairment.As the basis of this dissertation, the author set up the numerical simulation system for the digital coherent optical communication by the Matlab, firstly. The simulation model consists of transmitter, transmission link and receiver. Compensating the coherent dispersion and fiber nonlinearities by using the backward propagation (BP) algorithm, which is based on the split-step Fourier method (SSFM), has attracted much attention at present. Hence, the dissertation realizes the digital BP algorithm to compensate the chromatic dispersion and fiber nonlinearities, and the correlated BP algorithm to simplify the computation complexity. Moreover, comparing the performance of these two algorithms through simulation for the100Gb/s PDM16-QAM coherent optical system. In addition, the basic idea and performance of BP algorithm realized by symmetric SSFM, asymmetric SSFM and modified SSFM by shifting the nonlinear calculation point, respectively, and nonlinear compensation method for the WDM systems are also introduced. As the innovation points of this dissertation, the M-ary support vector machine (SVM) is introduced as a non-parameter nonlinear phase noise (NLPN) mitigation approach for the coherent optical systems. The NLPN tolerance of the system can be improved by using the M-ary SVM to conduct nonlinear detection. In this scheme, SVMs with different classification strategies are utilized to execute binary classification for signals impaired by fiber NLPN. Since the separating hyperplane of each SVM is constructed by training data, this scheme is independent from the knowledge of the transmission link. In numerical simulation, the M-ary SVM performs better than the existing schemes.