中文摘要：

理论分析了直接检测光OFDM（DDO—OFDM）系统传输链路中光电器件所导致不理想的频率响应或者功率衰减现象，提出一种对O—OFDM信号子载波功率衰减进行预失真的技术来改善传输系统的性能。实验比较了常规的O-OFDM信号和进行预失真技术的O—OFDM信号在DDO—OFDM系统中传输后的性能，结果表明，在传输200km标准单模光纤（SSMF）后，常规的O-OFDM信号频谱的高频部分有一定程度的衰减，而通过预失真技术的O—OFDM信号频谱比较平坦，且在（BER）为10^-4时，其接收灵敏度比常规的O-OFDM信号显著地提高了3dB左右，说明使用该预失真技术可以有效地改善O-0FDM系统的性能。

英文摘要：

The non-ideal frequency response and power fading phenomenon caused by optic-electric device in the transmission link of a direct-detection optical orthogonal frequency-division multiplexing （DIX）- OFDM） system are theoretically analyzed. In order to reduce the influence of the non-ideal frequency re- sponse and power fading phenomenon,a digital pre-distortion technique for power fading of OFDM signal subcarriers is proposed. We compare regular OFDM signal with the pre-distorted OFDM signal in a DDO-OFDM system. The experimental results show that the power of high frequency subcarriers of the regular OFDM signal is attenuated severely after 200 km standard single-mode fiber （SMF） transmis- sion, but the spectrum is relatively flat by pre-distorting the power of the OFDM subcarriers at the high frequency. In addition, the received sensitivity of the pre-distorted OFDM signal is significantly improved by about 3 dB at a bit error rate of 1 × 10-4 compared with the regular one without this technique. It is demonstrated that this pre-distortion technique can improve the system＇s performance effectively.