弹光调制器是由各向同性的弹光晶体和压电晶体组成的热机电耦合器件,其谐振频率随温度变化存在严重漂移,导致弹光调制器工作不稳定。为了实现弹光调制干涉信号的相位延迟量沿正弦规律变化,有必要对影响弹光调制干涉仪的稳定因素进行分析与控制。针对此问题,在建立弹光调制器振动模型和频率温漂模型的基础上,提出了基于数字锁相技术的驱动电压自调节方法。在该方法中,根据弹光调制干涉信号的四倍频与二倍频的比值,基于FPGA调节DDS输出方波信号的占空比以稳定弹光调制干涉信号的相位延迟量。实验结果表明,驱动电压自调节时的相位延迟量变化幅度为0.6 %,电压一定时相位延迟量幅度下降了15.6 %,证明该方法有效的稳定了相位延迟量,从而提高了弹光调制器的稳定性和调制效率。
The photo-elastic modulator is a thermoelectric coupling instrument,which is composed of the isotropic photo-elastic crystal and a piezoelectric crystal. Its drifting resonant frequency as temperature varies results in unstable operation of the photo elastic modulator. In order to achieve the sine phase retardation of the photo-elastic modulation interference signal,it is necessary to analyze these factors,which affect the stability of photo-elastic modulation interferometer and control them. Aiming at the problem,the vibration model and frequency-drift model are established. A self-tuned method of driving voltage based on digital phase-lock technology is put forward. In the method,the duty ratio of the square wave output signal in DDS is adjusted according to the ratio of quadruple and double frequency for the photo-elastic modulation interference signal to stabilize the phase retardation. It is shown in the experiment that the changed amplitude of phase retardation in the self-adjusted drive voltage is 0.6 %,but the amplitude of phase retardation decreases by 15.6 % in the constant drive voltage. It proves that the method effectively stabilizes the phase retardation and improves the stability and modulation efficiency of the photo elastic modulator.