Study Of Methane Gas Detection System Based On Optical Fiber Cavity Ring-Down

Compared to other gas sensing system, optical fiber cavity ring-down gas sensing system has obvious advantages. It costs little, work long-distance, and has a strong magnetic resistance. Particularly thanks for its networking capabilities,it can be composed of sensing network, optical transmission vast amount of information. With WDM, TDM and other technologies mature, fiber-optic cavity ring-down gas sensing system can be further simplified to reduce costs. These features make it be used on the livelihood of the people and the industry more and more widely.Absorption spectrum sensing technology is based on the theory of infrared absorption gas theory: for each gas has its specific group of absorption peaks and different absorption intensity corresponding to different gas concentration . It has obvious disadvantages: it is easily affected by light intensity and absorption spectra can be overwhelmed easily by the background light. By studying the optical fiber cavity ring-down gas sensing system ,we can know that this technology is not affected by the changes of light intensity, it is by measuring the different states of the ring-down time value to achieve the purpose of sensing,and because the input is narrow-band pulsed light, it is easy to filter out background light.Based on the traditional optical fiber cavity ring-down gas sensing system,this study desiged two optical fiber cavity ring-down gas sensing systems:one based on the fiber ring,and the other based on the NOLM. This study also analyzed each parameter of components of the system parameters, such as EDFA,coupler,isolator,gas-cell,pulsed laser. and pointed out the impact factors of the test results.This study carried out experiments on two systems, optimize the system by adjusting the device parameters, to further verify the feasibility of the system. Finally,pointed out the problems now exist on the system, proposed time-division multiplexing and wavelength- division multiplexing technology to improve system stability and sensitivity.