为了减轻电光调制器的非线性效应以及光纤色度色散给直接检测光正交频分复用系统性能带来的损伤，对两者的损伤机理进行了理论分析.在此基础上提出了在发射中使用一种针对调制器的非线性采用预失真技术，而高频子载波功率衰减采用预增强的联合预处理技术来改善系统的性能.运用数值仿真法对所提出的方法进行了验证，结果表明在光背靠背传输系统中调制指数最优时，接收信号的误差矢量幅度值可以得到2 dB的改善.随着光纤传输距离的增长，正交频分复用信号高频子载波功率衰减程度加剧而使得信噪比恶化，从而导致系统误码性能急剧下降.使用所提出的预处理技术的计算复杂程度低，可以使接收机的灵敏度得到明显的改善.

In order to reduce the performance impairments of directdetection optical orthogonal frequencydivision multiplexing (DDOOFDM) system caused by the nonlinear effects of electroopitc modulator and fiber chromatic dispersion, the impairment mechanisms are analyzed theoretically. Based on the analysis results, a digital preprocessing technique which combined predistortion and preemphasis methods to combat the nonlinearity and power fading, respectively, is proposed to employ to OFDM transmitter to improve the system's performance. The proposed method is verified by numerical simulation. The simulation results show that error vector magnitude (EVM) of the received signal can obtain a 2 dB improvement when both modulation indexes are optimum, compared to without employing the predistortion technique at the optical backtoback transmission case. With the increasing of optical fiber transmission distance, the power of high freqency subcarriers of the received OFDM signal is attenuated severely, then the BER performace of the system is deteriorated dramatically. The sensitivity of OFDM receiver can be improved significantly with the proposed digital preprocessing technique with low computational complexity.