基于共轭干涉滤波的光学气体传感方法的研究

发布时间：2018-03-26 08:45

本文选题：气体传感　切入点：光谱吸收　出处：《武汉理工大学》2015年博士论文

【摘要】：光学气体检测在环境污染、工业过程控制、医疗诊断等领域应用较广。基于光谱吸收的气体检测技术是通过检测样气透射光强的变化来实现气体浓度的测量。与传统方式相比,该技术具有高精度、低交叉敏感、快速响应,易于成网等优点。其中窄带光谱吸收技术采用低成本的宽带光源,且可以利用滤波器选择不同的吸收峰实现不同气体的检测,具有非常好的工业应用潜质。本文提出了基于共轭干涉滤波的光学气体传感方法,该方法是利用光谱吸收和双光束干涉,实现了共轭干涉滤波器,该滤波器能通过对应吸收气体吸收光谱的光,而反射其他波长的光,从而获得与气体吸收谱线反转的梳状光谱。由于气体吸收谱线本质稳定的特性,滤波器将输出稳频的梳状光谱,并且通过更换滤波器中气体种类能输出对应气体的输出光谱。该方法能有效的压缩宽带光源的谱宽,大大提高气体检测灵敏度,且能解决气体检测中选择光源的问题。首先,以分子光谱理论、比尔朗伯定律为基础,分析了气体吸收线的谱线(线型、线宽、展宽)等理论,研究了基于光谱吸收的气体浓度检测技术。根据HITRAN数据库以及傅里叶红外光谱仪对气体吸收谱线的相关参数进行了确定。研究了温度、压力等因素对谱线展宽以及吸收系数的影响,为选择滤波器的物理参数提供了理论依据。其次,研究了共轭干涉式滤波器π相移实现方法的研究。通过对共轭干涉式滤波器结构的设计、比较以及讨论,确定其结构。并通过对输出光强的仿真、实验比较对滤波器参数进行确定,从而最终能输出稳定的π相移滤波输出。再次,研究了基于共轭干涉式滤波器的窄带稳定输出光源,包括线性腔单波长、多波长窄带光源,以及基于光纤环形腔的单波长、多波长窄带输出光源。该窄带光源的输出光能完全对应气体吸收峰的窄线宽以及中心波长,光强稳定,能有效的应用在(多)气体浓度检测上。最后,本文基于差分检测方案以及共轭干涉式滤波器的稳频输出光构建了单一气体检测系统以及多气体检测系统。对系统中的窄带光源、吸收气室、数据处理等关键器件以及关键技术进行分析。并设计了一种基于光纤空芯光子晶体光纤的气室结构,给低损耗、长光程气室提供方向。与此同时还采用了气体传感系统微弱信号的检测方法,能有效抑制噪声,实现输出信号的光谱重现,实验结果表明,气体检测的灵敏度和信噪比得到明显的提高。对单一气体和多气体共存情况下作了气体检测的实验,验证了该基于共轭干涉式滤波器的光纤气体传感系统,在多种气体混合环境下,可以完成对不同组分气体浓度的检测。
[Abstract]:Optical gas detection is widely used in the fields of environmental pollution, industrial process control, medical diagnosis and so on. The gas detection technology based on spectral absorption realizes the measurement of gas concentration by detecting the change of transmitted light intensity of sample gas. This technique has the advantages of high precision, low cross-sensitivity, fast response and easy netting. The narrow-band spectral absorption technology uses a low cost broadband light source, and the filter can be used to select different absorption peaks to realize the detection of different gases. In this paper, an optical gas sensing method based on conjugate interferometric filtering is proposed. The conjugate interferometer filter is realized by using spectral absorption and two-beam interference. The filter can reflect the light of other wavelengths by absorbing the absorption spectrum of the gas, thus obtaining the comb spectrum which is reversed from the absorption line of the gas, because of the intrinsic stability of the absorption line of the gas, The filter will output the comb spectrum of steady frequency and output spectrum of the corresponding gas by changing the kind of gas in the filter. This method can effectively compress the spectrum width of the broadband light source and greatly improve the sensitivity of gas detection. And it can solve the problem of choosing light source in gas detection. Firstly, based on the theory of molecular spectrum and Bill Lambert's law, the theory of spectrum line (line type, line width, broadening) of gas absorption line is analyzed. The technology of gas concentration detection based on spectral absorption is studied. The parameters of gas absorption spectrum line are determined by HITRAN database and Fourier transform infrared spectrometer. The temperature is studied. The influence of pressure and other factors on spectral line broadening and absorption coefficient provides a theoretical basis for selecting the physical parameters of the filter. The realization method of 蟺 phase shift of conjugate interferometric filter is studied. The structure of conjugate interferometric filter is determined by designing, comparing and discussing its structure. The parameters of the filter are determined experimentally, so that the stable 蟺 phase shift filter output can be output. Thirdly, the narrow band stable output light source based on conjugate interference filter is studied, including linear cavity single wavelength source and multi wavelength narrow band light source. And the single wavelength and multi wavelength narrow band output light source based on fiber ring cavity. The output energy of the narrow band light source completely corresponds to the narrow line width and center wavelength of the gas absorption peak, and the light intensity is stable. Can be used effectively in gas concentration detection. Finally, In this paper, a single gas detection system and a multi-gas detection system are constructed based on the differential detection scheme and the stable output light of the conjugate interferometric filter. The key devices such as data processing and key technologies are analyzed, and a kind of gas chamber structure based on optical fiber hollow photonic crystal fiber is designed to reduce the loss. At the same time, the weak signal detection method of the gas sensing system is adopted, which can effectively suppress the noise and realize the spectral reproduction of the output signal. The experimental results show that, The sensitivity and signal-to-noise ratio of gas detection have been improved obviously. The experiment of gas detection under the condition of the coexistence of single gas and multi-gas is carried out, which verifies the fiber optic gas sensing system based on conjugate interferometric filter. The concentration of different gas components can be detected in the environment of multiple gas mixtures.
【学位授予单位】：武汉理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TN713

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