通过恒包络调制提高相干光OFDM系统的光纤非线性容限

相干光正交频分复用(CO-OFDM)对光纤链路中 的色度色散(CD)和偏振模色散(PMD)具有较强的容忍性,但 是OFDM信号高峰均功率比(PAPR)的特点使其对光纤非线性效应 非常敏感,严重影响了系统传输性能。 本文提出了基于恒包络(CE)调制的方法使得系统中光信号PAPR降低为0dB,从而提高了CO-OFDM系统的非 线性传输性能。仿真结果表明,子载波采用16QAM调制的40Gbit/s单信道CE调制CO -OFDM系统,在经800km无色散补偿、欠色散补偿和周期全色散补偿 标准单模光纤(SSMF)链 路传输后,虽然较传统CO-OFDM存在约1.8dB的代价,但是系统最大 发射光功率分别提高 了6.2、9.3dB。并且,将本文方案应 用 到CO-OFDM和10Gbit/s NRZ-OOK混合传输WDM系统中,信道最大发 射光功率仍获得了5.2dB的提高。因此,本文提出的CE调制方法能有 效地提高CO-OFDM系统在不同传输环境中的光纤非线性容限。

Improving the fiber nonlinear tolerance based on constant envelope modulation for CO-OFDM systems

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) can immun e to chromatic dispersion (CD) and polarization mode dispersion (PMD) in fi ber links.However, the large peak-to-average power ratio (PAPR) of OFDM signals makes it suscepti ble to fiber nonlinearities and consequently degrades the transmission performance.In this p aper,an approach based on constant envelope (CE) modulation,which can lower the PAPR of the opti cal signal to 0dB,is proposed to improve the fiber nonlinear performance for CO-OFDM systems.Simula tion results show that after 800km standard single-mode fiber (SSMF) transmission,the maximum launch power of the proposed 40Gbit/s CE-CO-OFDM system with 16-QAM subcarrier modulation is imp roved by 6.2dB, 9.3dB and 10.9dB compared with conventional CO-OFDM for the dispersion map w ithout dispersion compensation fiber (DCF),the 100ps/nm under-compensated and the fully periodi c compensation dispersion maps,respectively,although an optical signal-to-noise ratio (OSNR) penalty of ~1.8dB is observed in the linear region of transmissions.When the scheme is utilized in the hybrid wavelength division mult iplexing (WDM) transmission of the 40Gbit/s CO-OFDM channel with 10Gbit/s NRZ-OOK channels,a 5.2dB increase of the maximum launch power is also observed.Therefore,the proposed scheme can effectively improve the fiber nonli near tolerance for CO-OFDM systems in different transmission scenarios.