针对相干光正交频分复用系统中出现的高峰值平均功率比问题，提出分数阶傅里叶变换与高峰值平均功率比抑制算法相结合的方法.计算表明：随着分数阶傅里叶变换阶数的减小，信号的峰值平均功率比逐渐降低；与抑制算法结合后可进一步降低系统的峰值平均功率比，并解决抑制算法影响系统性能的问题.从结合的兼容性、抑制高峰值平均功率比效果及改善引入抑制算法后对系统的负面影响三方面进行仿真分析，结果表明：采用选择性映射算法与分数阶傅里叶变换结合后，旋转因子同为4时，峰值平均功率比高于6.6 dB的概率较单一选择性映射算法低104；选取高峰值平均功率比抑制情况相近时，结合算法的时间复杂度比单一选择性映射算法降低了8倍；采用限幅算法与分数阶傅里叶变换结合的仿真情况也较单一限幅算法有很大提高，表明该算法结合的兼容性良好.

Due to the high peak to average power ratio in coherent optical orthogonal frequency division multiplexing system, fractional Fourier transform combined with peak to average power ratio reduction algorithm was proposed. With the decrease of fractional Fourier transform order, the peak to average power ratio of signal is reduced. Fractional Fourier transform combined with the reduction algorithm can reduce the peak to average power ratio further, and improve the degradation of transmission performance caused by the reduction algorithm. The simulation analyses have three aspects including compatibility of the combination, inhibition effect of peak to average power ratio and improvement of the negative effects in the reduction algorithm. The results show that the probability of the selective mapping algorithm combined with fractional Fourier transform is 104 less than that of the single selective mapping algorithm when the rotation factor is 4 and the peak to average power ratio is higher than 6.6 dB. When the same degree of inhibition of peak to average power ratio is chosen, the time complexity of the combined algorithm decrease by 8 times than single algorithm. The simulation results using clipping algorithm combined with fractional Fourier transform have great improvement than single algorithm, which shows combined algorithm has good performance of compatibility.