甲烷探测系统中干涉噪声的研究

Research on interference noise in the methane detection system

甲烷在近红外波段的探测越来越多,为了补偿弱吸收缺点,使用灵敏度高的谐波检测技术。由于DFB激光器具有长相干的特点,在探测系统中容易产生干涉噪声。本文就气室所造成的干涉噪声进行理论分析,讨论了干涉噪声与正弦调制指数、气室长度的关系。基于这种关系,通过选择恰当的参数来减少干涉噪声。文中指出选用二次谐波来检测气体的原因及减少干涉噪声的方法。介绍了结构简单的聚焦气室,与传统的准直气室相比,具有插入损耗小,噪声低等优点,是多点光纤传感系统的理想选择。

In recent years there has been a great deal of interests in the development of optic gas sensors using the near - IR absorption lines of methane gas. To compensate for the weak line strengths, high sensitivity harmonic detection techniques are employed. Because of the very long coherence length of the DFB laser, muhi - reflections easily occur within the detection system. In the paper, we report the theoretical investigation into the interference noise and examine how the interference noises depend on factors such as the modulation index, cell length. Based on the factors, we can minimize the noise by judicious choice. We also indicate the reason of ehoasing the second harmonic to detect the gas and the ways to eliminate the noise. A type of focusing micro - optic cell has been presented ,with superior performance aver the traditional collimating cell, which can be the best choice of the multi - point optical fiber system because of the lower insertion loss and interference noise.