Numerical investigation of a microfiber-plane-grating composite optical waveguide for gas refractive index sensing

In this paper, we propose a microfiber-plane-grating composite optical waveguide (MPGCOW), which is formed by immobilizing a tapered microfiber on the surface of a plane grating with one defect, for gas refractive index (RI) sensing. Its optical properties and gas RI sensing properties are investigated by the finite difference time domain method. Results show that the MPGCOW has a photonic stop band and is very sensitive to the ambient gas RI variation. The largest gas RI sensing sensitivity of 486.67 nm/RIU and detection limit of 2×10^-6 are obtained by immersing the structure in the mixture gas of N₂ and He with various mixture ratios.