针对应用于毫米波光纤无线通信(ROF)系统的光学倍频毫米波生成方法, 探讨了光纤色散造成的毫米波幅度衰落问题。提出使用双电极马赫曾德尔光调制器(MZM)生成毫米波的方案: 光波进入双电极MZM的两臂后分别由同频反相的微波信号调相, 然后叠加完成相位强度转换。已调光波经光纤传输后再经光电转换产生调相微波的高次谐波, 实现所需毫米波的生成, 其幅度的最大化只需调整调相指数即可完成。就两种不同偏置状态的毫米波生成系统的色散衰落特性进行比较, 发现两臂直流偏置端都接地的双电极光调制器ROF系统的色散性能更好, 光纤色散不会导致奇次谐波的出现, 也不会出现偶次幅度衰落到0的情况。上述数学分析的结论通过仿真、实验得到了验证。

This paper focuses on discussing the millimeter-wave amplitude fading problems caused by fiber chromatic dispersion for the millimeter-wave generated by optical frequency multiplication in the millimeter-wave radio-over-fiber (ROF) system. A novel millimeter-wave generation technique using dual-electrode Mach-Zehnder modulator (MZM) is proposed. Light-wave injected into dual-electrode MZM is split into two optical carriers, which are phase modulated by two microwave signals respectively and then combined together to fulfill the phase-intensity conversion and is transmitted through the fiber, and finally photo-detected to generate electrical signal consisting of harmonics of the microwave signal. The desired millimeter-wave signal is one of the harmonics and can be maximized just by adjusting the phase modulation index. The chromatic dispersion affection on millimeter-wave fading for two different bias states of the dual-electrode MZM is analyzed and compared. This study finds that the tolerance of ROF system to fiber chromatic dispersion is better when the two direct current (DC) biases of dual-electrode MZM are earthed. Optical fiber chromatic dispersion does not cause the appearance of odd harmonics, in addition, the amplitudes of even harmonics do not decline to zero. The conclusion of mathematical analysis has been verified by computer simulation and experiment.