激光器电压调制驱动与锁相放大电路的研究

为解决光频漂移对气体浓度检测的影响,根据分布反馈式半导体激光器的波长可调制特性,设计了一种激光器电压调制驱动与锁相放大电路。该电路的电压调制驱动电路输出波形是2 Hz的锯齿波和2 kHz的方波的叠加,其中:2 Hz的锯齿波使激光器的中心波长缓慢扫过气体吸收中心线,确保气体吸收光强;2 kHz的方波一方面对激光器的波长进行二次微量调节,另一方面作为谐波检测的同步信号。锁相放大电路则对不受激光器波长漂移的激光调制信号3次谐波进行锁相放大。Matlab仿真结果表明,该电路的输出与模拟气体浓度吸收光强函数的幅值成比例,同时证实了检测3次谐波的可行性。

Research of Circuit of Voltage-modulated Driving and Phase-locked Amplifying of Laser

In order to eliminate influence of optical frequency drifting for detection of gas concentration,a circuit of voltage-modulated driving and phase-locked amplifying of laser was designed based on modulation characteristics of wavelength of DFB LD.The output waveform of the voltage-modulated driving circuit is superposition of 2 Hz sawtooth wave and 2 kHz square wave.The 2 Hz sawtooth wave makes central wavelength of DFB LD pass by central line of absorption of gas slowly,so as to ensure gas absorb light intensity.The 2 kHz square wave makes secondary micro-modulation of wavelength of DFB LD and it is used as synchronous signal of harmonic detection simultaneously.The phase-locked amplifying circuit selects and amplifies the third harmonic of modulation signal of DFB LD,which is not influenced by wavelength drifting of DFB LD.The result of Matlab simulation showed that the output of the circuit is proportional to the amplitude of absorption function of light intensity of gas concentration,and it verifies the feasibility of detection of the third harmonic wave.