相干光正交频分复用系统(CO-OFDM)是未来高速光传输的重要解决方案,而偏振模色散(PMD)与偏振相关损耗(PDL)相互作用严重影响传输性能。分析了CO-OFDM系统中的偏振效应和数学模型,并通过仿真加以验证。结果表明,一阶PMD效应对正交频分复用(OFDM)信号子载波幅度附加余弦因子;二阶PMD效应中,去偏振项(DR)占主要因素,且一定程度上可缓解色度色散带来的相位噪声;另外,由于PMD带来OFDM子载波偏振度随频率变化加强,也对PDL带来的系统损伤有一定抑制作用,在不考虑色度色散,相对损耗因子α=0.5,单模光纤传输距离为720km条件下,系统Q值约有2dB提高。 Coherent optical Orthogonal Frequency Division Multiplexing (CO-OFDM) is an important solution for high-speed optical transmission in the future. The interaction between polarization mode dispersion (PMD) and polarization-dependent loss (PDL) seriously affects the transmission performance. The polarization effect and mathematical model in CO-OFDM system are analyzed and verified by simulation. The results show that the first-order PMD effect has an additional cosine factor for the subcarrier amplitude of the OFDM signal. In the second-order PMD effect, the depolarization term (DR) accounts for the main factor and to a certain extent can alleviate the chromatic dispersion In addition, the polarization degree of OFDM subcarriers brought by the PMD is strengthened with the change of frequency, and the system damage caused by PDL is also restrained. Without considering the chromatic dispersion, the relative loss factor α = 0.5, Mode fiber transmission distance of 720km conditions, the system Q value of about 2dB increase.