The detection of gas concentration in coal, chemical, oil and other industries, especially in the mining of minerals is very important. Gas is a combustible, explosive gas, the upper limit of the 15Vol%, the lower limit of 5Vol%. The accident caused by the accident has caused great harm in the history of mining. Scientists have made unremitting efforts to measure the gas concentration in the scientific workers of all countries for a long time. Dry type, wet gas sensor, gas sensor and semiconductor gas sensor have been developed, which have good effect on the gas concentration detection, which greatly reduce the incidence of gas accidents.

In recent years, optical fiber sensing technology is emerging in the world. Optical fiber sensor has some conventional sensor incomparable advantages, such as high sensitivity, fast response speed, dynamic range is big, anti electromagnetic interference, ultra high insulation, passive, anti explosion, suitable for long-distance telemetry, small volume, flexible deflection, etc., very suitable for applications in harsh and dangerous environment, thus obtains the widespread attention. Fiber optic gas sensor research started late, until the last century eighty's before it was reported that the fiber optic gas detection experiment. Now there are two methods of gas detection, one is the use of gas spectral absorption detection concentration; two is the use of gas concentration and refractive index of the relationship between the refractive index measured by the interferometric method.

Single wavelength absorption comparison

The basic principle of the absorption method is based on the spectrum absorption, and the different material has different characteristic absorption spectrum. Single wavelength absorption comparison is a type of absorption spectral sensor, according to Lambert's law: