FWM mitigation based on serial correlation reduction by partial transmit sequence in coherent optical OFDM systems

Because of the narrow frequency interval among sub-carriers, FWM becomes one of the dominant nonlinearities in Coherent Optical OFDM systems. The dependence of the FWM noises on the serial correlation is investigated and the variance of FWM noises and SNR are derived theoretically in the case of independent distribution. The Partial Transmit Sequence (PTS) is introduced to reduce serial correlation approaching the independent distribution. The concept of average auto-correlation coefficient are employed to evaluate the reduction of the correlation. FWM noises are reduced efficiently without signal distortions and decreased spectral efficiency compared with the traditional algorithms.