弹光调制器谐振特性研究及其谐振频率自跟踪

Research on resonance characteristics of photoelastic modulators and self-tracking of resonant frequency

弹光调制器是一种由各向同性的弹光晶体和压电晶体组成的高品质因数热机电耦合器件,广泛用于偏振测量、光谱测量等诸多领域。但是在高压谐振状态下,其谐振频率会随着温度变化出现漂移,导致弹光调制器的相位调制幅值不稳定以及驱动效率降低。针对该问题,首先对弹光调制器谐振频率特性进行分析,建立了弹光调制器及其高压谐振驱动电路的复合谐振网络模型,提出了利用谐振网络的幅频特性进行频率跟踪的实现方法,并设计了基于现场可编程门阵列(field programmable gate array,FPGA)的控制测试系统,实现了谐振频率跟踪以及调制幅度的测量。通过测试验证了该方案可有效进行谐振频率跟踪,提高了弹光调制器的稳定性以及驱动效率,测试时长大于90 min,相位调制幅度的标准偏差为0.83%rad。

As a kind of high-quality factor thermo-electromechanical coupling device composed of isotropic elastic-optical crystal and piezoelectric crystal,photoelastic modulator(PEM)is widely applied for polarization measurement,spectrum measurement,and many other purposes.However,the resonant frequency tends to drift with temperature changes in the high-voltage resonant state,which destabilizes the phase modulation amplitude of the photoelastic modulator and reduces the driving efficiency.To solve this problem,the resonant frequency characteristics of the photoelastic modulator are analyzed at first.Then,a compound resonant network model of the photoelastic modulator and its high voltage resonant driving circuit is established,and a solution to frequency tracking based on the amplitude-frequency characteristics of the resonant network is proposed.Besides,a control test system based on field programmable gate array(FPGA)is developed to achieve resonant frequency tracking and modulation amplitude measurement.The test results show that this method is applicable to track the resonant frequency effectively and improve the stability and driving efficiency of the elastic light modulator.The duration of the test exceeds 90 min,and the standard deviation of the phase modulation amplitude is 0.83%rad.