Various characteristics of long-period fiber grating-based refractive index sensor

Abstract

In this paper, the response of long-period fiber grating (LPFG) as a refractive index sensor is theoretically investigated. The response has been checked for the surrounding refractive index (SRI) variation from 1 to 1.45. The sensitivity enhancement of LPFG as a refractive index sensor by employing higher-order cladding modes and by reducing the cladding radius is discussed. In the range of SRI from 1 to 1.45, HE13 mode has shown an overall wavelength shift of 0.0015μm and HE17 mode shows an overall wavelength shift of 0.0042μm, thus increasing the sensitivity of HE17 mode 2.8 times to that of HE13 mode. It was also found that reducing cladding radius by 10μm in case of HE17 mode results in an overall wavelength shift of 0.0066μm for SRI range from 1 to 1.45 and results in increased sensitivity up to 1.6 times. Also discussed is the variation of physical parameters such as grating length and peak-induced index change (PIIC) which influences the transmission spectrum of LPFG for its efficient use as a refractive index sensor.