为了能够快速精确地测量波片相位延迟量和快轴方位角, 实现测量系统的集成化和自动化, 设计了基于弹光调制技术与数字锁相技术相结合的波片测量系统。采用弹光调制器对检测激光进行调制, 运用基于FPGA的数字锁相技术提取调制信号的一、二倍频项, 利用优化算法解调出波片相位延迟量和快轴方位角, 步进电机带动波片转动使快轴到达零度位置, 相位延迟量由LCD显示出来。搭建了实验系统, 并对1/4波片进行了测量。实验结果表明: 该系统对1/4波片快轴方位角的测量精度优于0.31°, 相位延迟量的测量精度和重复度分别优于99.47%和0.14°。测量系统的弹光调制器驱动信号、电机驱动信号、数据运算都由FPGA控制,实现了光机电一体化。

In order to efficiently and accurately measure the phase retardation of wave plate and the azimuth angle of fast axis at the same time, to realize the integration and automation of measuring system, a wave plate measuring system based on the combination of the photo-elastic modulation and the digital phase-locked technology was designed. The detecting laser was modulated by the photo-elastic modulator. By means of digital phase-locked technologies based on FPGA, the first harmonic term and the second harmonic term of the modulated signals were extracted. The phase retardation and the azimuth angle of fast axis of wave plate were demodulated by optimized algorithm. The stepper motor drives the wave plate to rotate to make the fast axis of wave plate reach the zero position. And the phase retardation was displayed by LCD. The experimental system was set up to measure the quarter-wave plate. The experimental results show that the measuring accuracy of azimuth angle of fast axis of quarter-wave plate is better than 0.31° and the measuring accuracy and repeatability of phase retardation of quarter wave plate are better than 99.47% and 0.14°, respectively. The driving signal of the photo-elastic modulator and stepper motor and the processing of the data were controlled by FPGA. The measuring system realized optical, mechanical and electronic integration and the automation of the measuring process.