Active Fiber Gas Sensor for Methane Detecting Based on a Laser Heated Fiber Bragg Grating

An active optical fiber gas sensor was developed in a cobalt-doped single mode fiber. This fiber can be heated up to a few hundred degrees Celsius by a heating laser, and a fiber Bragg grating (FBG) was fabricated inside this fiber as a thermometer. The Bragg wavelength of the FBG is sensitive to the thermal conductivity of the gas surrounding the fiber and can be used to monitor the concentration of a special gas once we know in advance the kind of gas. The proposed sensor is ideal for detecting explosive or corrosive gases in some practical application scenarios, such as gas pipeline, coal mine, flow meters, and so on. We have measured the methane concentration ranging from 0% to 4.8% (5% is its explosion limit) as a demonstration.