Research On Polarization Multiplexing Short Distance Optical Transmission Technology

With the application and popularization of high-speed,high-quality data services such as high-definition television and cloud computing,the demand for bandwidth in short-distance optical communication system has increased significantly.Therefore,the combination of advanced modulation formats,digital signal processing(DSP),polarization division multiplexing(PDM),intensity modulation(IM)and direct detection(DD)becomes one of the popular schemes for improving the transmission rate of the short-distance optical communication system.The scheme can double the transmission rate of the short-distance optical communication system,and the cost is low.Polarization multiplexing techniques utilize two orthogonal and independent polarization states in single fiber to transmit two signals.These two signals are affected by polarization mode dispersion(PMD)and polarization dependent loss(PDL)during transmission,which leads to mutual coupling and crosstalk between signals and seriously affects the transmission quality of communication system.Therefore,this paper focuses on how to apply the advanced modulation format,DSP and PDM techniques to double the transmission capacity and improve the system transmission performance under the premise of maintaining low cost and low complexity,and specific work of this paper is as follows:(1)In this paper,theories of DMT modulation technology are introduced firstly,and a cross-correlation symbol synchronization algorithm based on m sequence is applied to DMT IM/DD short-distance optical communication system.The proposed algorithm can accurately locate the starting position of the DMT symbol with only one training sequence.In this paper,the utilized and traditional synchronization algorithm are simulated from the aspects of cyclic prefix length and optical signal to noise ratio(OSNR).Simulation results show that the symbol synchronization algorithm based on m sequence has higher synchronization accuracy and yields about 0.5 dB OSNR improvement at a bit error ratio of 3.8×10-3 compared to other classical symbol synchronization algorithms.(2)Secondly,in order to estimate the channel of DMT IM/DD optical communication system,this paper adopts an expectation maximization(EM)algorithm.The EM algorithm,least mean square algorithm and channel estimation algorithm based on pilot are simulated and compared from the aspects of OSNR,received optical power(ROP)and constellation.Simulation results show that EM algorithm yields about 2 dB OSNR improvement at a bit error ratio of 3.8×10-3 compared to traditional channel estimation algorithm based on the same number of training sequences.(3)Finally,the paper focuses on the theory of PDM technology.And base on Optisystem 13.0 and MATLAB platform,200 Gbit/s DMT-PDM IM/DD short-distance optical communication system is set up.The feasibility of the demultiplexing scheme based on Stokes space is verified by the simulation system.Meanwhile,the influence of PMD and dispersion on the demultiplexing effect is also analyzed.Simulation results show that the performance of 200 Gbit/s dual polarization system transmitting 10 km yields 4 dB OSNR improvement at a bit error rate of 3.8×10-3 compared to that of 200 Gbit/s single polarization system transmitting 10 km.