Optical Fiber Methane Gas Sensor Based On Evanescent Wave Field

In recent years, with the rapid development of optical fiber sensing technology, the research of optical fiber gas sensors has been seriously taken all over the world. The signal detected by optical fiber gas sensors, which is carried by light wave, has a small interference on surroundings and can be adapted to all kinds of surroundings.Nowadays the gas calamity occurs frequently, and it is the gas calamity that imperils the safety of mining industry in our country; furthermore, it has been the most serious matter that restricts the development of the mining industry. In mining exploitation, the ratio of gas calamity, especially the serious and extremely serious ones increase gradually, which causes serious economic losses and casualties and the hidden trouble in safety increases gradually. So, explicitly detecting the origin of the calamity counts for much for the whole coal-mining industry in China. Fiber sensing technology will just be one of the effective technical ways to solve the problems.By analysizing and contrasting the concentration of multi-gases, my paper gives careful consideration of optical fiber gas sensors on the basis of evanescent wave field. I designed a new gas sensor, self-developed the sensing part and micro-optic sensing cell. I mastered the technics of this part and the method of making the transformer's head in chamber. The ray of light source became parallel light after it passed optical collimator, then was coupled directly into multimode fibers which the diameter of fiber core is 800μm ( Two multimode fiber ends were polished to 45 and let them face to face). The total reflection happened when the light transfer to such fiber ends. According to the theory of the evanescent wave field happened in the total reflection, I adjusted the distance of the fiber ends to wavelength-scale and inspected the gases concentration in the evanescent wave field through the changes of light intensity. According to the conditions and equipment available in our lab, I did experiment on my designing system. The result proved this new system has high sensitivity, repeatability, and stability. Through the measurements, this system can effectively detecting multi-gases'concentration and will get a brighter application prospection.