Research On Fiber-Optic Gas Sensor Based On The Fabry-Perot Cavity

The fiber gas detection technology carry the signal by the light and transfer signal by the fiber, so it is a high sensitivity gas detection technique. Methane concentration measurement is the paper's purpose. Fiber methane gas sensing technique is studied based on the principle of spectrum absorption. Different gas has its inherent absorptive spectrum because of its different molecu1e structure.If the spectrum of a 1ight covers with the absorption peak of a gas when a beam of the light passes through the gas,a strong absorption wil1 occur,and the absorptive intensity is related to the gas concentration.The gas, s species and concentration can be gotten by the detection of light absorptive intensity.Firstly, the primary methods of gas detection are introduced in the paper, by analyzing and comparing with these methods their advantages and disadvantages and the actualities and progress directions of the fiber gas sensor are reviewed at home or abroad,we select gas spectra1 absorption method as the theoretical foundation of this system.The basic principle of gas absorption measurement is given through the analysis of molecule spectrum theory. The near-infrared absorption spectrum of methane is chosen. And its absorption characteristic is analyzed. Thus, the basic principle of sensor's mathematical model is given.Secondly, the characteristics and influences on measurement of the section of light patch, photoelectric transformation and electric signal process system are analyzed.The method of using Fabry-Perot cavity and piezoelectric ceramic for filtering the broadband light source (SLD) and extracting the second harmonic for measuring gas concentrations.Finally, we report the investigation into the Fabry-Perot cavity of source by the methane system, modulate its spectrum by Matlab and analyze the relationship between the length of cavity and wavelength,peak transmittance and the parameters of cavity loss and so on.providing the guidance for the design of Fabry-Perot. Then analyze and simulate the optical properties of FBG, providing reference for the appropriate choice of FBG calibrated precisely the output wavelength of Fabry-Perot, Based on the current experimental device, the characteristics of the source spectrum and the near-infrared absorption of methane are tested. The methane concentration detection, the repeatability and stabilityof the system are studied.