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.

弹光调制器作为高Q值的谐振器件，在高压谐振下，其谐振频率将随着自身温度升高漂移，影响了弹光调制干涉仪的稳定性和重建光谱的准确性。在建立弹光调制器振动模型和频率温漂模型的基础上，提出了基于频率跟踪和幅值调节的弹光调制器双闭环自适应驱动控制方法。在该方法中，采用数字锁相技术的频率自扫描方法实现驱动频率对弹光调制器谐振频率的跟踪；基于检测参考激光干涉图的最大光程差的变化调节驱动信号的幅值，以实现重建光谱的稳定控制，同时基于参考激光的最大光程差参数实现重建光谱的定标。在实验中该驱动控制方法应用到弹光调制傅里叶变换光谱仪中，实现了驱动频率对弹光调制器谐振频率的实时跟踪和高压功放电路的幅值调节，使得干涉图的最大光程差稳定在0.236 nm左右，其精密度为3.3%；重建光谱的最大相对误差为2.5%。此实验验证了该方法能有效稳定弹光调制傅里叶变换光谱仪的光谱分辨率。