光纤气体传感器解调方法的研究

利用可调谐激光光谱技术并结合二次谐波检测的波长调制方法对气体浓度进行检测，大大提高了检测灵敏度.然而光的传输和电路自身延时都会产生未知的相位延时，含有气体浓度信息的被测信号和二倍频参考信号的相位差变化严重影响二次谐波信号测量结果.本文设计出一种4路乘法锁相解调电路，设计中分别用正弦信号和余弦信号对被测信号进行解调，经积分电路后得到两路分别与相位差的正弦值和余弦值相关的解调信号.将两路解调信号平方，再通过加法器相加后消除相位差，得到完全与相位差无关的幅值信号.实验证明当被测信号相位在0°—90°变化时，解调 关键词： 可调谐半导体激光吸收光谱 波长调制 解调电路 相位差

Demodulation method for second harmonic signal in optical fiber gas sensor

The measurement sensitivity can be greatly improved when tunable laser spectroscopy together with the method of wavelength modulation of second harmonic detection is used to measure the gas density. However, light transfer and circuit delay will lead to unknown phase delay. The measurement results of second harmonic signal will be seriously influenced by the phase change of the frequency-doubled reference signal relative to the measured signals containing information of gas density. A four-channel multiplier demodulation circuit is designed here. Sinusoidal signals and cosine signals are used to demodulate measured signals. Then two demodulated signals appear relating to the phase difference of sinusoidal value and cosine values after the measured signals pass the integral circuit. The amplitude signals can be obtained, which have no relation with the phase difference when demodulated signals are squared through the adder and the phase difference is eliminated. Experiment shows that the stability of the measured results in the system has been improved greatly if the obtained second harmonic signal keeps stable when the phases change from 0° to 90°.