Application research of hollow-core photonic crystal fibers in methane sensing system

A novel optical fiber gas sensor based on cascade of hollow-core photonic crystal fibers (HC-PCF) is proposed. Using the comb filter characteristic of Fabry-Perot (F-P) interferometer, Near-infrared evenly-spaced multi methane absorption lines (R3, R4 and R5 lines in 2v3 overtone band around 1.66 µm) were detected simultaneously by tandem F-P interferometer and broadband SLED light source. Difference absorption detection based on equivalent absorption coefficient was used as signal processing method. Chirped fiber grating with its central wavelength around R4 was adopted as optical band-pass filter. The light power corresponding to three absorption lines and three reference wavelength was detected simultaneously by PIN PD. The diffusion of gas inside of the hollow core is analyzed and the optimal design of sensing head is completed. The feasibility of the system for methane detection is verified by experiments.