四波混频（FWM）效应是相干光正交频分复用（CO-OFDM）系统中最主要的非线性作用。分析基于小波变换的相干光正交频分（WT-OOFDM）系统原理，研究小波变换对FWM效应和光放大器自发辐射（ASE）引起的相位噪声的改善效果。数值结果表明，在采用常规G. 652光纤，100 Gbit/s的WT-OOFDM传输1500 km时，非线性相位噪声降低20%，总相位噪声降低15%。

Four-wave mixing (FWM) is the most important nonlinear effect in coherent optical orthogonal frequency-division multiplexing (CO-OFDM) system. The principle of CO-OFDM system based on wavelet transforms (WT-OOFDM) is analyzed, and effect of wavelet transforms on phase noise caused by FWM and amplified spontaneous emission (ASE) of optical amplifiers is discussed. For the conventional optical fiber G. 652, 100 Gbit/s WT-OOFDM system, the simulation results show that the variance of the total phase noise can be decreased by 15%, and the nonlinear phase noise has a 20% reduction while the transmission distance reaches 1500 km.