Research on the gas refractive index sensing based on microfiber double-knot resonator with a parallel structure

In this paper, we propose a method based on microfiber double-knot resonator with a parallel structure to detect the volume content of the hybrid gases of CO and CO2. The primary principle is that the mixed gases with different volume ratios have different refractive indexes (RIs). The transmission spectrum of the microfiber resonator immersing into the hybrid gases with different volume ratios will produce a spectral drift. The volume content of the mixed gases can be detected using the gas RI sensing method. We present a theoretical study on the influence of different parameters of the microfiber resonator on the gas sensing sensitivity. The observations indicate that the microfiber diameter has the largest impact on the gas sensing sensitivity, while other parameters have negligible effect on it. When the microfiber diameter is 1.0 mu m, the maximum sensitivity of 98.4 nm/RIU is obtained. Our results will provide some theoretical guidances for the application of the microfiber resonator in the gas sensing field.