Research On Chromatic Dispersion Equalization In High-Speed Optical Fiber Communication Systems

As the increasing demand of ultra-long transmission length and ultra-high capacity for optical fiber communications,high-speed coherent optical fiber communication systems have become a hot research topic.However,chromatic dispersion(CD)is a critical factor limiting the transmission speed and length of an optical fiber communication system.Hence,the research on chromatic dispersion equalization technology in high-speed coherent optical fiber communication system is of great significance.This thesis studies the chromatic dispersion equalization methods in high-speed coherent optical fiber communication systems.The main work consists of the following parts:We first review the physical impairments and the equalization techniques in highspeed coherent optical fiber communication systems.The classic CD equalization methods are emphatically analyzed,especially the limitation caused by constant magnitudes of tap weights in classic methods.A time-domain CD equalization method using a weighted finite impulse response(FIR)filter is proposed.In this method,a weighted function is carefully selected in order to optimize the tap weights for FIR filters and to reduce the bit rate error(BER)after CD equalization.This thesis analyzes two kinds of weighted FIR filters,one uses a square-root raised cosine function as its weighted function(SRRC-FIR filter)and the other one uses a Gaussian function(GS-FIR filter).The high-speed coherent optical fiber communication systems in this thesis are established through co-simulation.Two kinds of softwares are used in this co-simulation: VPI transmission Maker(VPI)and MATLAB.The investigation and comparison of weighted FIR filters and two existing methods for CD equalization are successfully completed.Simulation results indicate that SRRC-FIR filters and GS-FIR filters are both able to reduce the BER after CD equalization for optical communication systems.This proves that time-domain CD equalization using a weighted FIR filter is an effective method to improve the performance of time-domain CD equalization.Through the application of weighted tap weights to frequency-domain CD equalization,a weighted overlap frequency domain equalization(OFDE)method is presented.In this method,the tap weights of OFDE are optimized by a weighted function,which should be appropriately chosen in order to enhance the performance of frequency-domain CD equalization.Two methods called SRRC-OFDE and RC-OFDE are investigated.The weighted functions employed in these two methods are a square-root raised cosine functionand a raised cosine function,respectively.The comparison between SRRC-OFDE,RC-OFDE and OFDE isconducted in our simulation systems.The simulation results suggest that weighted OFDE method can improve the performance for frequency-domain CD equalization.