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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、9.3和10.9dB。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。
Coherent optical Orthogonal Frequency Division Multiplexing (CO-OFDM) is more tolerant of chromatic dispersion (CD) and polarization mode dispersion (PMD) in optical fiber links, but the peak-to-average power ratio (PAPR) Features make it very sensitive to the nonlinear effect of optical fiber, seriously affecting the system transmission performance. In this paper, a method based on Constant Envelope (CE) modulation is proposed to reduce the PAPR of optical signals in the system to 0dB, which improves the nonlinear transmission performance of the CO-OFDM system. The simulation results show that the 40Gbit / s single-channel CE-modulated CO-OFDM system with 16QAM modulation on subcarriers can transmit data even after 800km dispersionless compensation, under dispersion compensation and periodic full dispersion compensation standard single-mode optical fiber (SSMF) Compared with the traditional CO-OFDM there is about 1.8dB cost, but the system maximum transmit optical power increased by 6.2, 9.3 and 10.9dB respectively. In addition, applying this scheme to CO-OFDM and 10Gbit / s NRZ-OOK hybrid transmission WDM system, the maximum transmitted optical power of the channel still achieves 5.2dB improvement. Therefore, the proposed CE modulation method proposed in this paper can effectively improve the non-linear optical fiber tolerance of CO-OFDM systems in different transmission environments.