中文摘要：

分析了相干光正交频分复用（CO—OFDM）系统中四波混频（FWM，four—wavemixing）效应对系统性能的影响，提出了一种新的降低CO—OFDM系统中各个子载波序列相关性的方法——偏载波填充法（PCF，partialcarrierfilling）与部分序列传输（PTS，partialsequenceoftransmission）相结合。理论分析和仿真表明，这种方法能有效降低CO—OFDM系统的序列相关性，从而抑制信道内FWM效应对C0一OFDM系统带来的损伤。研究结果表明，本文提出的方法在传输距离达103km的情况下，误码率（BER）仍然低于10—3，与PTS方法相比，降低了将近1个数量级。

英文摘要：

Coherent optical orthogonal frequency division multiplexing （CO-OFDM） has attracted great research interests over the past few years due to the immunity to fiber chromatic dispersion （CD） and polarization mode dispersion （PMD）. However, CO-OFDM system is very sensitive to fiber nonlinear effects,especially to four-wave mixing （FWM） effects. In CO-OFDM system, the inner-band FWM effect is mainly dependent on serial correlation among the OFDM subcarriers. Therefore, inner-band FWM effect can be mitigated by reducing the serial correlation among the OFDM subcarriers. In this pa- per,we have investigated and theoretically analyzed the effects of inner-band FWM in the CO-OFDM system,and then introduced a novel method to reduce the serial correlation of OFDM subcarriers for mitigating the inner-band FWM effects. Our method combines the partial carrier filling （PCF） and par- tial sequence of transmission （PTS） together. Theoretical analysis and simulation results show that this method can effectively reduce the serial correlation of the CO-OFDM subcarriers, and mitigate the inner- band FWM effects in CO-OFDM system. In addition, simulation results also indicate that the bit-error- rate （BER） of the proposed system keeps lower than 10-3 （one order of magnitude lower than PTS） af- ter being transmitted over 1000 km fiber,which demonstrates the effectiveness of the proposed method.