An ultra-high sensitivity methane gas sensor based on the vernier effect with cryptophane- a film deposited in the photonic crystal fiber

Abstract Methane gas, due to its high flammability, is convenient for people’s daily lives, but its flammability poses safety hazards. Methane tends to explode when mixed with air. Therefore, it is particularly important to be able to effectively detect methane gas concentrations. A new methane gas sensor is presented in this paper. It is extremely sensitive to the reaction of methane gas. It consists of two fiber Sagnac interferometer (SI) loops, which utilize the vernier effect. The two fiber SI loops remain parallel. The optical fiber structure of the effective sensing in the sensing SI loop and the effective sensing in the reference SI loop are the same. Both of them adopt the polarization-maintaining photonic crystal fiber (PM-PCF) designed in this paper. However, the sensing SI loop uses a two-step filling technique to block small air holes and an immersion technique to deposit methane gas sensitive film on large air holes in PM-PCF. The sensing capability of the methane gas sensor was evaluated utilizing the finite element method (FEM). The numerical simulation results show that under the condition of the concentration of methane gas in the environment is 0–3.5%, the average sensitivity of two parallel Sagnac loops is 260.86 nm/%. Compared with other fiber optic methane gas sensors, the sensitivity of the sensor designed by this scheme is significantly improved, which provides a valuable reference and direction for the development of new methods and the design of ultra-sensitive methane gas sensors.