Research And Analyze Of Key Technologies On Mode-division Multiplexing Transmission System

With the rapid development of optical communication technology,demands of capacity have shown a trend of accelerated growth in the current times.The capacity of the traditional single-mode fiber communication system is approaching its nonlinear Shannon limit.So searching for high-speed and large-capacity optical transmission mechanism has become a major challenge.As a new and promising capacity expanding method,mode division multiplexing(MDM)technology can multiply the capacity of optical fiber communication system,and it has attracted more and more attention.MDM system uses multiple input multiple output(MIMO)structure,combining mode division multiplexing/demultiplexer,few-mode fiber,few-mode fiber amplifier,channel equalization technology,and it can realize transmitting signal steadily.In this paper,we analyze the transmission model,few-mode fiber and channel equalization algorithm of MDM system.The transmission system model is established to provide theoretical basis for system simulation and analysis.In view of few mode and crosstalk for MDM system,we design a kind of photonic crystal few-mode fiber with large Mode Differential Group Delay(MDGD),and it can effectively solve the problem of crosstalk between modes and realize transmitting four modes(LP01,LP11,LP21,LP02).Aiming at MDGD and mode coupling problems of the system,we analyze the existing constant modulus algorithm(CMA)structure and design a6×6 MIMO CMA algorithm to achieve mode demultiplexing.Based on mode theory,the design of photonic crystal few-mode fiber and improved CMA algorithm,we design 6×6 MIMO mode division multiplexing system on the VPItransmissionMaker simulation platform,and the transmission performance of the system is analyzed in the simulation.The simulation results show that the MDM system based on photonic crystal few-mode fiber can realize transmitting six modes(LP01,LP11 a,LP11b,LP21 a,LP21b,LP02).When signal to noise ratio is 22 dB,each mode carries transfer rate of 40 Gbps signal by 4QAM modulation,the MDM system succeeds in transmitting 34 km.Compared with the MDM system,which is based on traditional few-mode fiber,this system has large transmission capacity and excellent performance,it will have significant value in the high-speed and large-capacity optical transmission.