The Research Of The DSP Compensation Algorithm In Coherent Optical Communication

With the ever-increasing communication bandwidth demand, coherent optical communication based on advanced modulation formats-coherent detection has been widely studied in the field of optical communication. The utilization of advanced modulation formats not only helps to high spectrum efficiency and high system capacity in a single fiber, but also increases the dynamic range and enables the offline compensation of link impairments in electric domain by digital signal processing (DSP). With the evolution of future system capacity to100Gb/s and more, advanced modulation format-coherent detection has become one of the key technologies in the future optical communication systems with long distance, high speed and high capacity.Based on the widely investigation of the key technologies and research hot topics for coherent optical communication, this paper focuses on the design and implementation of the receiving end DSP compensation algorithms in coherent optical communication system, which consists of the following parts:The introduction of research background for this topic, as well as the history and state-of-art research technologies domestic and outside;The research of coherent optical communication theory, system architecture and the impairments from the fiber link and transmitter; the analysis of algorithms for dispersion and nonlinearity compensation is made by considering the complexity and compensation effect; The impairments of polarization mode dispersion(PMD) and the constant modulus algorithm(CMA) for PMD compensation is discussed; Several updated CMA are introduced;The realization of offline DSP in coherent optical communication is detailed discussed, especially emphasis on the current varied algorithm for dispersion and nonlinearity elimination and the joint compensation for fiber dispersion and PMD; quadruplicate algorithm for carrier offset estimation and Viterbi-Viterbi for phase offset are also discussed in the paper;The digital backward propagation (DBP) algorithm is proposed and its application in the compensation of dispersion and nonlinearity is investigated. Ultra Wide Band over fiber (UWBoF) system is set to test the DBP algorithm. Results show that after compensation the distorted UWB signal after transmission of72km is well compensated and the correlation index with the original signal reaches to0.9. When the transmission distance is limited within200km, the correlation index after compensation remains above0.95;A high spectrum efficiency PM-QPSK coherent optical communication system is set up in Optisystem and DSP compensation algorithm simulated for link impairments. In the simulation,40Gbit/s PM-QPSK optical signals is transmitted in the standard single mode fiber, and by the utilization of DSP based on the DBP algorithm for dispersion and nonlinearity compensation and butterfly FIR for PMD remove, the constellation diagram of the recovered signal is demonstrated after transmission for200km.Finally, the conclusion is drawn for the thesis and the prospective of future research is presented.