Design of a coated thinly clad chalcogenide long-period fiber grating refractive index sensor based on dual-peak resonance near the phase matching turning point

Abstract

A novel design method of chalcogenide long-period fiber grating (LPFG) sensor based on the dual-peak resonance effect of LPFG near the phase matching turning point (PMTP) is presented. The refractive index sensing in high refractive index chalcogenide fiber was achieved by a coated thin-cladding film. The dual-peak resonant characteristics near PMTP and refractive index sensing properties of LPFG are analyzed first by the phase-matching condition of LPFG. The effects of film parameters and cladding radius on the sensitivity of refractive index are further discussed. The sensor is optimized by selecting appropriate film parameters and cladding radius. Simulation results show that the ambient refractive index sensitivity of dual-peak coated thin-cladding chalcogenide LPFG at the PMTP can be 2400 nm/RIU, which is significantly higher than that of non-optimized gratings. It has great application potential in the field of chemical and biosensor.