Sensitivity-optimized long-period fiber gratings for refractive index and temperature sensing

A long-period fiber grating sensor was fabricated by periodically changing the structure of single-mode fiber with an electric arc discharge technique. After the fabrication, the refractive index and temperature sensitivities were optimized by etching the cladding with hydrofluoric acid solution. The experimental results illustrate that the thinner cladding shows relatively higher refractive index and temperature sensitivities for the same order cladding mode, which are accordant with that of numerical simulation. After the long-period fiber grating was etched for 15min, average refractive index sensitivities of 214nm/refractive index unit (RIU) (1.3333-1.3931) and 1987nm/RIU (1.4115-1.4555) were achieved. An extremely higher refractive index sensitivity of 2731nm/RIU appears near 1.4555. By systematically studying the temperature sensing characteristic of cladding-etched long-period fiber grating in this work for the first time, the temperature sensitivity can reach as high as 144.23pm/degrees C when the ambient temperature changes from 30 to 80 degrees C. This work provides a theoretical reference for the fabrication of a high-sensitivity refractive index and temperature sensor based on arc-induced long-period fiber grating.