| Detection of gas is important in environmental, pollution monitoring and safety production.So it is of great importance to make real-time detection to those gases in order to get the information about the gas leakage, gas emission and gas distribution, thereby taking effective control measures. Spectrum absorption detects the gas concentration by measuring the intensity changes of transmitted or reflected light. Compared with orthodox method, it has the advantages of high precision, low-cross interference and fast-response time. It also has the best detection. And the narrowband spectrum technology which uses low-cost light source and filter to choose different absorption peak in order to detect different gases has great potential in industrial application.In this paper, the method of optical gas sensor on the basis of conjugate interference filter is put forward. The method is based on the principle of gas absorption and that of two-beam inference so as to accomplish the conjugate interference filter, which, with the corresponding gas absorbing corresponding spectrum of light and reflecting other irrelevant light, works out comb-shape spectrum which is opposite to the shape of the spectrum of gas absorption. Due to the stable nature of the spectrum of gas absorption, the filter will produce steady frequency of the comb-shape spectrum. Moreover, it will produce the output spectrum of the corresponding gases which need further measure. Firstly, the method can effectively contribute to compress the spectral width of broadband light source, greatly improve the sensibility of gas detection and solve the problems of selection of light source.First of all, basing on the theory of molecular spectroscopy and Beer-Lambert Law, the line profile, the line width and the line broadening of the gas absorption lines are analyzed. The method by using spectrum in order to measure the gas concentration is investigated. By the means of HITRAN database and Fourier infrared spectrometer, the absorption parameters are confirmed. The relationship between factors like temperature, pressure and so on and line broadening and absorption coefficient is studied in order to provide a basis of how to select parameters of the filter.Secondly, the author studies the methods of accomplishing the ?-phase shifting of conjugate interference filter by designing, comparing and discussing the construction of conjugate interference filter so as to confirm its structure. Through the output light intensity simulation, experimental comparison of filter parameters determined. As a result, the stable ?-shape shifting filtering is worked out.Once more, frequency stabilized lasers based on conjugate interference filter including linear lasers and ring lasers are analyzed. The output light of frequency stabilized lasers is directly correlated to the narrow line-width of the gas absorption and the central wavelength. And the output light is stable and it can be effectively applied to the gas concentration detection.Finally, according to the differential detection scheme and the conjugate interference filter, a single detection and multiple gas system are designed. The key devices like laser, test gas cell, data processing and the key technology are analyzed. The structure of a gas based on hollow-core fiber and photogenic crystal fiber is designed, which also elucidates the direction of the low-loss and low-path air chamber. And the method about how to detect a small-signal in the gas sensing system is put forward. The method can help suppress noise effectively and achieve high fidelity spectrum reproduction. The experiment result indicates that the sensitivity and the SNR of the gas detection have been significantly improved. In terms of the coexistence of pure gas and multiple gases, the gas detection is analyzed. Experiments prove that this optical fiber sensor based on conjugate interference filter can detect different levels of gas concentration in a multiple component gas environment. |
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