Overview: Overview: Photoelastic modulator, a high-quality thermo-mechanical coupling device composed of isotropic elastic optical crystal and piezoelectric crystal, is widely used in polarization measurement, spectral measurement, and many other fields. A high-voltage resonant circuit is adopted to generate the periodically changing high voltage amplitude, which is applied to both ends of the piezoelectric crystal to drive the photoelastic modulator to perform forced telescopic vibration, thus generating periodic birefringence. Although the quality factor of the photoelastic modulator is as high as 10³, the photoelastic crystal in the photoelastic modulator will vibrate in length under the action of the piezoelectric crystal when driven by the high voltage. In addition, there will be thermal dissipation caused by dielectric loss and mechanical loss, some of which exchange heat with the environment, and the rest will raise the temperature of the photoelastic modulator itself. When the heat exchange between the photoelastic modulator and the external environment is happened before the heat balance, the resonant frequency will be changed, which will lead to the reduction of the modulator driving efficiency and the instability of the modulation amplitude. Standing from the perspective of mechanical point, the system can be equivalent to the vibration model of a damped spring-mass system. The system is an underdamped second-order system, and the modulator can also be equivalent to a RLC series resonant circuit from the electrical perspective. Therefore, when the temperature of the modulator changes, its electrical parameters and resonat will also vary. Therefore, this paper first analyzes the resonant frequency characteristics of the photoelastic modulator from the perspective of electricity, and establishes the equivalent circuit model of the photoelastic modulator and the composite resonant network model with the high-voltage resonant drive circuit. Meanwhile, the resonant network is analyzed, and the results show that when the phoyoelastic is in the resonant state, the modulator impedance and the inductance voltage amplitude of the high-voltage resonant circuit are both the smallest. Therefore, this paper designs a control and test system based on field programmable gate array (FPGA) by combining the above mentioned characteristic and applying the amplitude and frequency characteristics of the resonant network. FPGA completes the measurement of the inductance voltage amplitude and the demodulation of the photoelastic modulation signal through the digital phase-locked amplifier. After obtaining the inductance voltage amplitude, the real-time tracking of the minimum value of the inductance voltage amplitude can be obtained by FPGA, so that the tracking of the resonant frequency of the photoelastic modulator can be realized. By demodulating the modulated signal, the calibration optical path system of the photoelastic modulator is also capable of measuring the modulation amplitude of the modulator. Finally, this paper successfully builds the test system, and conducts the frequency sweep test to verify the feasibility of the resonance tracking system. The resonance tracking tests on the modulator are implemented at room temperature - 20℃ & 80℃ respectively. The results show that the test meets the requirements, and the maximum standard deviation of modulation amplitude is lower than 0.83% rad.

通过改变马赫-曾德干涉型幅度调制器的射频系数和偏置电压，调制光脉冲的强度。研究了幅度调制器对宽带低相干光时频特性影响的规律，分析调制后的光脉冲时域波形分布、光谱和复相干度模值曲线，结果表明，射频系数对光脉冲的光谱成分和时间相干性无明显的调制，射频系数存在最佳工作区间使得输出光脉冲的波形保真度最佳。当偏置电压处于半波电压时，光脉冲的时域波形保真度最好，时间相干性最低，但光谱成分会缺失。理论仿真了调制器的臂长差、偏置电压对宽带低相干光频域特性的影响，与由实测光谱计算出调制器的臂长差，实验结果进行了对比，结果基本符合。由于实际的电光重叠积分因子随加载电压值变化，因而模拟与实测结果存在误差，但研究得出的规律将为低相干脉冲精密整形系统提供更为明确的方向。

为了满足2.5 m大视场望远镜的跟踪要求，提出了望远镜主轴伺服三闭环控制设计方法。在整定好的电流环输入端注入正弦信号，扫频测试主轴伺服速度环的开环频率特性。根据谐振频率设计结构滤波器抑制机械谐振，从而达到更高的闭环带宽。最后，依据辨识得到的控制模型，设计速度环线性自抗扰控制器和位置环比例控制器。速度环基于线性扩张状态观测器估计扰动并补偿其影响，可以达到更高的低速跟踪精度。为解决快速搜索问题，根据设备允许的最大速度、加速度，基于离散最速跟踪微分器安排过渡过程。实验结果表明：线性自抗扰控制相比PI控制，2.5 m大视场望远镜进行1.24°视场角快速步进搜索的时间由1.6 s降低为1.0 s；以速度为2 （°）/s，加速度为1 （°）/s²作为等效正弦引导的误差均方根值由1.08″降低为0.60″；低速跟踪斜率为0.000 1 （°）/s的位置斜坡曲线时，位置跟踪稳态误差均方根值由0.015 8″降低为0.010 6″。线性自抗扰控制能够满足大视场角天文望远镜高效率快速搜索和低速精密跟踪的要求。

基于本征函数法对G波段交错栅慢波结构的高频特性建立了理论模型，考虑空间谐波级数项收敛后，计算得到了色散曲线和耦合阻抗以及损耗参量并采用仿真软件对计算结果进行了验证。对比发现理论模型计算的高频特性与仿真结果吻合较好，色散误差小于0.1%，耦合阻抗误差小于10%，损耗误差小于10%，可信度较高。研究结果表明，该模型对于拥有任意交错距离和上下栅高度的双栅结构具有普适性，在两种极限情况下可分别化为对齐双排矩形栅和矩形波导栅慢波结构。交错栅高频损耗主要发生在注通道区域，槽区底部损耗最小。