Dong Yisi, Hu Pengcheng, Ran Ming, Le Zhitao, Fu Haijin, Yang Hongxing, Yang Ruitao
Opt Express. 2020 Oct 12;28(21):31700-31713. doi: 10.1364/OE.403448.
The phase modulation depth (PMD) in phase-generated-carrier demodulation is determined by the laser frequency modulation amplitude and working distance of a fiber-optic interferometer and must be set at a certain value. Active setting of the amplitude is unsuitable, especially for high-speed modulation, owing to variations in the laser source tuning coefficients. Existing calculation schemes for passive setting cannot work both owing to carrier phase delay (CPD) and the accompanied optical-intensity modulation (AOIM). Herein, a modified phase modulation depth calculation and setting technique is proposed. Double photoelectric detection and signal division are optimized to eliminate AOIM using a fiber delay chain and phase-locked amplifier module. Fast Fourier-transform and look-up table methods are used to calculate phase modulation depth without adding the carrier, which is unaffected by CPD. A fiber-optic Michelson interferometer is constructed to verify the feasibility of the proposed method. The experimental results show that AOIM can be eliminated; moreover, PMD can be calculated and set precisely. The displacement deviation is less than 1.03 nm. The resolution of measurement is considerably lesser than 1 nm and nanoscale accuracy is achieved in displacement measurement.
相位载波解调中的相位调制深度（PMD）由光纤干涉仪的激光频率调制幅度和工作距离决定，必须设置为特定值。由于激光源调谐系数的变化，主动设置幅度并不合适，尤其是对于高速调制。现有的被动设置计算方案由于载波相位延迟（CPD）和伴随的光强度调制（AOIM）而无法工作。在此，提出了一种改进的相位调制深度计算和设置技术。优化了双光电检测和信号分割，以使用光纤延迟链和锁相放大器模块消除AOIM。采用快速傅里叶变换和查找表方法来计算不添加载波的相位调制深度，该方法不受CPD影响。构建了光纤迈克尔逊干涉仪来验证所提方法的可行性。实验结果表明，可以消除AOIM；此外，可以精确计算和设置PMD。位移偏差小于1.03 nm。测量分辨率远小于1 nm，在位移测量中实现了纳米级精度。
