Theoretical research of gas sensing method based on photonic crystal cavity and fiber loop ring-down technique

A high-sensitive gas sensing method is proposed, in which miniaturized photonic crystal (PC) cavity is utilized as the sensing element, and cryptophane E molecular is infiltrated in defected holes of PC cavity as the sensitive material to methane gas. Particularly, slow light in side-coupled PC waveguide is optimized to enhance refractive index sensitivity of the PC cavity and fiber loop ring-down technology is used to demodulate output resonant spectrum of the sensing system. Simulation results demonstrate that a refractive index sensitivity of 450 nm/RIU and a quality factor of 1105 can be obtained in the slow light engineered PC cavity. For measurement of methane concentration, the theoretical sensitivity can be up to 4.21 μs/% and the minimum detectable concentration can be as accurate as 2.37 ppm.