光源振动实现激光自混合干涉外腔调制

External Cavity Modulation of Laser Self-mixing Interference by Light Source Vibration

从外腔长度高频调制的自混合干涉信号解调出外腔反射面低频振动信号的波形。为了实现外腔长度相对外腔反射面振动的高频调制,提出一个激光源振动方案,将激光二极管模块安装在长约23 mm,直径约13 mm的电磁激励振子上,用正弦信号激励电磁振子驱动激光源做振幅约四分之一波长,频率约7 kHz的正弦振动。采用傅里叶变换相位解包裹方法和数字信号处理从自混合干涉信号中解调出正弦波、三角波和方波激励外腔反射面振动的信号波形,最小可分辨振幅约0.02波长的振动波形。正弦振动的激光源的光束强度或偏振方向不随调制信号变化,优于外腔中插入相位调制器件的方法。实验测量表明,激光源正弦振动可以实现激光自混合干涉的外腔调制。

Signal waveforms of low frequency vibration of external cavity reflective surface were demodulated from self-mixing interference signals that external cavity length was modulated by a high frequency signal.In order to realize high frequency modulation of external cavity length against the low frequency vibration,a scheme of laser source sinusoidal vibration was proposed,in which a laser diode module was mounted on an electromagnetic vibrator with the length and diameter of 23 mm and 13 mm,respectively.The vibrator excited by a sinusoidal signal drives laser source vibration which amplitude and frequency was about a quarter wavelength and 7 kHz respectively.Using Fourier transform and phase unwrapped means,the low frequency vibration signal waveforms were demodulated from the self-mixing interference signals by digital signal process.The amplitude of the smallest waveform ably resolved was about 0.02 wavelengths.Light density or polarization direction of the laser source unchanged with modulation signal,which was superior to a phase modulator plugged in external cavity.From experimental measurement,it was sure that laser source of sinusoidal vibration can realize modulation of external cavity in self-mixing interference.