利用光电振荡器(OEO)产生微波信号, 结合马赫-曾德尔调制器(MZM)的调制偏振敏感特性, 设计一种将微波三角波信号产生功能嵌入OEO系统的三角波和正弦信号发生器。MZM工作在最小传输点, 光场的偏振角通过偏振控制器调节后与调制器的最佳调制轴成一定夹角, 使平行于最佳调制轴的光场受载波抑制调制产生奇阶边带, 而正交分量的光场不被调制。两部分光场以符合三角波傅里叶关系的比例通过检偏器投影至同一方向, 并在光电探测器(PD)上拍频产生三角波信号。该三角波信号经过电带通滤波器后, 得到微波正弦信号输出并反馈完成OEO的振荡过程。理论上对三角波的产生原理进行分析和仿真, 实验上得到了质量良好的重复频率为5 GHz的三角波和正弦信号。本方案只需增加少量器件即可使OEO同时产生三角波、正弦信号, 结构简单, 具有实用性。

Using the capability that an optoelectronic oscillator (OEO) can generate microwave signals and modulation polarization sensitivity of Mach-Zehnder modulator (MZM), we design a triangular wave and sinusoidal signal generator which is an OEO system embedded by the triangular waveform generator. The bias of the MZM is set at the minimum transmission point, and the polarization angle of the light beam is controlled so that light enters the MZM with an angle for the best modulation axis. The component of the light field parallel to the best modulation axis is modulated by the optical carrier suppression in MZM to generate the odd-order sidebands, but the orthogonal component keeps unchanged. After filtering the negative sidebands and projecting the light field in the same direction by the analyzer, we generate a triangular waveform signal in the photodetector (PD). When the triangular waveform signal passes an electric bandpass filter, the corresponding sinusoidal microwave signal is obtained, which can also complete oscillation feedback for the OEO system. The principle of triangular waveform generation is theoretically analyzed and simulated. In the experiments, a clear and steady triangular waveform signal with a repetition frequency of 5 GHz is generated, meanwhile the sinusoidal microwave signal can be obtained simultaneously. With only a few devices added in OEO, the proposed scheme can generate both triangular waveform and sinusoidal signal simultaneously, which has the advantages of simple structure and practicability.