An optical fiber methane sensing system employing a two-step reference measuring method

An optical fiber methane sensing system utilizing a super-luminescent diode (SLD) in the 1.33-μm band and a fiber Fabry–Perot tunable filter (FFP-TF) is developed. A two-step reference measuring method, which is based on differential absorption technique, is employed; a reference channel is introduced to eliminate the fluctuation of the illuminant spectrum, and the reference wavelength acquired by tuning the FFP-TF is introduced to eliminate the environmental influence. The two-step reference measuring method has improved the reliability and stability of the system. A minimum detectable methane concentration of ∼0.3% has been experimentally achieved.