直接检测光OFDM系统中的偏振相关损耗研究

对于高速光传输，直接检测的光正交频分复用系统（direct detection optical orthogonal frequency division multiplexing, DDO-OFDM）中的偏振相关损耗（polarization dependent loss, PDL）与偏振模色散相互作用，对系统传输带来较大影响。对DDO-OFDM系统中PDL与一阶PMD作用机理和数学模型进行了分析，并通过数字仿真加以验证。结果表明:在PDL与PMD联合作用下，对OFDM信号幅度及相位均产生影响，通过发送导频序列可有效实现信号均衡；由于输出偏振态随频率产生旋转，PMD效应一定程度上缓解PDL所致系统损伤，差分群时延为50 ps条件下，以10 Gb/s的速率在单模光纤传输480 km，DDO-OFDM系统Q值提高约0.8 dB。

Polarization dependent loss in direct detection optical OFDM systems

Polarization dependent loss (PDL) and polarization mode dispersion (PMD) in direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) system influence performance seriously in high speed transmission. The mathematical model and mechanism of transmission were analyzed in DDO-OFDM systems. Analysis and simulation results show that, PDL and PMD may bring amplitude and phase noise which could be eliminated by signal equalization. Meanwhile, PMD may mitigate the effect of PDL because of the rotation of the state of polarization（SOP）. The system Q value is improved by about 0.8 dB for 480 km distance and speed of 10 Gbit/s transmission through standard-single-mode fiber (SSMF) with the differential group delay (DGD) of 50 ps.