| With the development of the internet economy,coherent optical communication systems with ultra-long distance,ultra-large capacity,and ultra-high-speed have become a hot research direction in the field of optical communication.The chromatic dispersion(CD)and polarization mode dispersion(PMD)in the optical fiber channels lead to transmission signal distortion.Therefore,the implementation of efficient digital signal processing is the premise of effective signal reception.This paper main focuses on the research of adaptive equalization technology in ultra-high-speed optical signal acquisition systems.The research content of the paper includes:(1)The basic theory of adaptive equalization technology is studied,the signal modulation and coherent demodulation in coherent optical communication system,the signal damage in fiber link and the digital domain equalization are analyzed,and the common method of chromatic dispersion equalization(CDE)and PMD equalization are mainly studied,and the shortcomings of these methods are analyzed.A simulation platform for ultra-high speed polarization multiplexing coherent simulation system is built based on Optisystem 15 simulation software,which provide data support for the algorithm performance verification in this paper.(2)An algorithm of CDE based on singular value decomposition least square(SVDLS)method and an algorithm of CDE based on adaptive mutation particle swarm optimization algorithm(AMPSO)is proposed.The simulation results show that the algorithm based on singular value decomposition least square and adaptive mutation particle swarm optimization is suitable for higher-order modulation format and higher symbol rate,with better equalization performance and lower implementation complexity.When the signal bandwidth is limited by the Nyquist pulse shaping filter,the proposed equalization algorithms can be implemented in a narrower frequency range.The number of equalization filter taps is reduced by 37.5% and the equalization effect is better,which is suitable for low complexity and low delay hardware implementation.(3)A joint PMD equalization algorithm based on constant modulus algorithm and decision-directed least mean square(CMA-DDLMS)and a joint PMD equalization algorithm based on CMA and radius-directed algorithm(CMA-RDA)is proposed.The simulation results show that the CMA-DDLMS joint PMD equalization algorithm solves the large steady-state error of the CMA algorithm and weak “cold start” capability of the DDLMS algorithm;The CMA-RDA joint PMD equalization algorithm solves the problems of poor equalization performance of the CMA algorithm for non-constant mode modulation signal and the weak robustness of the RDA algorithm.Compared with CMA,MCMA and RDA,the two joint equalization algorithms proposed have a better equalization performance improvement for the damage equalization of polarization mode dispersion,polarization state rotation,polarization dependent loss and residual chromatic dispersion. |
