A highly sensitive sensor of methane and hydrogen in tellurite photonic crystal fiber based on four-wave mixing

A tellurite photonic crystal fiber (PCF) sensor structure is proposed for simultaneous measurements of methane and hydrogen. The structure is a simple hexagonal three-cladding structure, and six air holes in the inner cladding are coated with methane sensitive film and hydrogen sensitive film respectively. Based on the degenerate four-wave mixing (DFWM) theory, the direct relationship between the wavelength shifts of the Stokes spectrum or anti-Stokes spectrum and the variations in gas concentration can be established to realize the accurate detection of gas concentration. The influences of the pump wavelength and gas-sensitive film thickness on the gas sensitivity are investigated, and the maximum sensitivities of methane and hydrogen after parameter optimization are − 2.052 nm/% and − 0.236 nm/%, respectively. The linearity of the fitting can reach up to 99.95%, and the low detection limit of methane is 450 ppm and hydrogen is 2500 ppm. The sensing method based on four-wave mixing in non-silica photonic crystal fiber can also be extended to other detections of gas mixtures in the mid-infrared field.