The Study Of Compensation Method Of Nonlinearity Impairment In CO-OFDM System

With the coming era of cloud computing, internet of things and big data, people’s requirements of data traffics increase rapidly. All these factors undoubtedly put forward higher requirement for the transmission performance of transmission system. Large capacity, high speed, and ultra-long haul transmission systems become the mainstream of the next generation broadband information network development. Orthogonal frequency division multiplexing (OFDM) is extensively investigated to be adopted into optical communications due to its superior performance like high spectral efficiency, robust against channel impairments. Together with coherent detection and digital signal processing (DSP), coherent optical OFDM (CO-OFDM) is popularly proposed as it can combat the linear impairments in fiber media efficiently. Polarization division multiplexing (PDM) is a technology that utilizes the polarization character of light to easily double the system capacity while keep the signal bandwidth to be the same at a moderate complexity level. Therefore, because of those benefits, PDM CO-OFDM system is regarded as the outstanding candidate for the optical transmission system with100G or even higher speed. However, the nonlinear effect impairment in OFDM system is a critical factor restricting its development, which should be resolved urgently. In this paper, the compensation method of nonlinearity impairments in CO-OFDM system will be studied. After having a understanding of the relevant technical backgrounds and theoretical supports, a series of simulation studies will be conducted based on112Gb/s PDM CO-OFDM system. The specific research contents and relevant outcomes are shown as follows: (1) The relevant principles of OFDM technology is studied firstly; the components and implementation of optical CO-OFDM system is then introduced; learn about the PDM technology; construct the112Gb/s PDM CO-OFDM system simulation platform with MATLAB and VPI.(2) Research the nonlinearity impairment and its compensation method in CO-OFDM system, and determined the mid-span optical phase conjugation (OPC) to compensate the nonlinearity impairments in optical domain as the research topic.(3) Implement the research of Eb/No algorithm based on112Gb/s PDM CO-OFDM system. Set up the theoretically model and make a series of simulations about OSNR, launch power, dispersion and nonlinearity. Make a comparison of the simulation results achieved by Monte Carlo algorithm and Eb/No algorithm and prove the efficiency of Eb/No method.(4) Theoretically analyze the working principles and the implementation mechanism of mid-span OPC; make research and simulation of the compensation by mid-span OPC in112Gb/s PDM CO-OFDM system. Meanwhile, compare the compensation efficiency of mid-span OPC in PDM CO-OFDM system and SC-PDM QPSK system. With the compensation of mid-span OPC, CO-OFDM system can achieve an improvement of launch power by2.5dBm and transmission distance by800km.