摘要
相干光正交频分复用系统(Coherent Optical Orthogonal Frequency Division Multiplexing,CO-OFDM)以其较好的色散抑制性能和简单有效的信号处理技术,是近年来光传输领域的研究热点.对于高速CO-OFDM传输系统,偏振模色散(Polarization-mode-dispersion,PMD)带来OFDM信号展宽及输出偏振态的不同,严重影响系统传输性能.文章对一阶PDM影响下CO-OFDM系统(PMD-CO-OFDM)的数学模型和作用机理进行分析,并通过仿真加以验证.结果表明,一阶PMD效应对OFDM信号附加与子载波频率相关的余弦因子,降低系统传输性能,通过信道均衡可有效去除此影响;另外,PMD效应一定程度上减弱子载波相关性,可抑制系统光纤非线性效应,在不考虑色散条件下PMD-CO-OFDM系统以10Gb/s的速率在单模光纤传输240km,差分群时延为50ps时较30ps系统Q值提高约0.2dB.
Abstract
Coherent optical orthogonal frequency division multiplexing system (CO-OFDM) is being considered as a promising technology for future high speed optical transmission with its resilience to fiber chromatic dispersion and ease of digital signal processing (DSP).Polarization Mode Dispersion (PMD) can influence system performance by bandwidth broadening and frequency-selective fading.With such a scheme,the mathematical model and effect of PMD to the transmission system is emphatically analyzed in CO-OFDM system based on first-order PDM (PMD-CO-OFDM).Analysis and simulation results show that,first-order PMD adds cosine factors for different OFDM subcarriers,which could be eliminated by channel equalization; meanwhile,PMD can reduce the fiber nonlinear penalty by decreasing the relativity of OFDM subcarriers.Without the consideration of chromatic dispersion,PMD-CO-OFDM system's Q value is improved by about 0.2dB with differential group delay (DGD) 50ps compared with 30ps,for speed of 10Gbit/s transmission through standard-single-mode fiber (SSMF) and with 240km distance transmission.
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维普
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