提出了一种使用光学技术产生可调谐的四倍频相位编码信号的方案。利用一个马赫-曾德尔调制器(MZM),一个光滤波器(OBPF),一个布拉格光栅(FBG),一个环形器,两个偏振调制器(PolM)和光电探测器,结合波长复用技术、偏振调制技术和平衡探测技术,产生四倍频相位编码信号。仿真结果表明,此方法产生的相位编码信号具有大调谐范围,高倍频系数。仿真产生的20 GHz和40 GHz相位编码信号分别具有10.10 dB和9.79 dB的峰值旁瓣比,压缩比都是128。同时,从相位编码中恢复出来的相位信息分别具有200°和206°的变化。仿真结果验证了产生四倍频相位编码信号的可行性,所产生的相位编码信号具有20~40 GHz的调谐范围,同时还表现出很好的脉冲压缩性能。

针对外调制星间微波光子链路输出信噪比优化问题，建立了基于双电极马赫-曾德尔调制器的强度调制直接探测星间微波光子链路模型，通过优化调制器调制方式来提高链路性能。用数值模拟方法得到了单边带、双边带和推挽式3种调制方式下链路输出信噪比，利用曲面投影法求得了最优调制方式时一定信噪比要求下发射端所需最小光放大器增益和对应的调制器直流偏置相位。结果表明：相同输入射频信号功率和发射光功率情况下，双边带调制输出信噪比比单边带调制高3 dB，低直流偏置相位推挽调制可以进一步优化输出信噪比。输入射频信号功率为-20 dBm，输出信噪比为17.3 dB时，所需最小光放大器增益为43.9 dB，对应的直流偏置相位为0.87π。

为了实现对双电极马赫-曾德尔电光调制器任意直流偏置点的自动偏置控制，采用在闭环控制基础上，引入一个可调移相器使不同直流偏置点处误差信号相同的方法，理论分析了可调移相器相移量与直流偏置相位的关系，仿真得到对于不同偏置点，当调制器直流偏置相位漂移达-0.15rad ~0.08rad，移相器引入附加相位漂移-0.55rad~0.55rad时，经偏置控制后相位漂移被限制在-3.0×10-4rad~1.7×10-4rad范围内。结果表明，该方法有效实现了对电光调制器任意直流偏置点的自动偏置控制。

For the nonlinearity distortion problem of Mach-Zehnder modulator (MZM) applied in the on-board microwave photonics system, the situation for two input radio frequency (RF) signals with different frequencies and phases is discussed, and an exact analytical solution is derived with the method of expanding Bessel series and Graf addition theory. According to the analytical expression, the nonlinearity characteristics of the modulator can be precisely predicted, and the system performance can be optimized. The correctness of the analytical solution is approved by simulation results. Analytical results indicate that the nonlinearity distortion is suppressed as the decrease of modulation index, the increase of direct current bias phase shift and phase difference between two input RF signals. When the phase difference equals zero or π and the direct current bias phase shift is π/2, there are only odd-order distortion terms. When the phase difference equals zero or π and the direct current bias phase shift is π, there are only even-order distortion terms.

For the scheme of 80 GHz optical millimeter-wave (mm-wave) generation using two cascaded Mach-Zehnder modulators (MZMs), an exact analytical solution for the optical mm-wave affected by phase shift drift and splitting ratio is derived with the method of expanding Bessel series. The results show that for the carrier and the fourth-order sideband, the influence caused by phase shift drift is dominant, while the first-order, the second-order and the third-order sidebands are influenced by both phase shift drift and splitting ratio. It follows that the undesired sideband suppression ratio is at least 35.9 dB when the splitting ratio deviation is 0.001, and the phase shift drift is 1o. The performance of the system is perfect if the accuracy is achieved.