对甲烷气体浓度的监测应用领域很多, 而目前绝大多数采用的是化学反应方法, 存在安全性低、 稳定性差等缺点, 而采用光学干涉法定性定量分析稳定性高、 抗干扰能力强。 设计了电光调制的干涉系统进一步提高其探测精度。 在干涉系统中, 利用可变折射率晶体LiNbO3的电光调制特性, 对晶体折射率进行调制, 增大静态光程扫描范围, 提高光谱分辨率。 系统对晶体两侧分别加载相位相反的调制信号, 使其在不改变干涉具尺寸的条件下提高光谱分辨率。 通过推导折射率调制度与光程差的函数关系, 仿真计算可知比同尺寸干涉系统光谱分辨率提高了近一个数量级。 实验采用SGT-3型声光调制器, 1 650 nm红外激光器对不同浓度的甲烷气体进行检测, 实验结果显示, 此方法比传统的热释电法精度好、 稳定性高, 更适合在矿井等复杂环境下应用。

Gas monitoring for methane concentration has been applied in many areas, while the vast majority of methods were based on the chemical reaction. There is a low security and poor stability shortcomings. In contrast, it is of high stability and strong anti-interference ability to monitor methane concentration using optical interferometry for quantitative analysis. As the system static interference limits the spectrcum resolution, we designed the electro-optical modulation interference system to further improve the detection accuracy for methane concentration. In the interferometer system, a variable refractive index crystal LiNbO3 was used for electro-optical modulation, and the static optical path length scan range was increased to improve the spectrum resolution. Both sides of the crystal were loaded with opposite phase modulated signal, so that it does not change the improved spectrum resolution interferometer size. By derivation of refractive index modulation as a function of optical path difference, the simulation found that the resolution was increased by nearly an order of magnitude than interference system spectrum resolution of the same size. The experiments used the SGT-3-type acousto-optical modulator and the 1 650 nm infrared lasers to detect different concentrations of methane gas. The experimental results show that the method is better than the traditional pyroelectric method in terms of accuracy and stability, and more suitable for application in the mine complex environment.