Study of various cladding modes effective refractive indices behavior in long period fiber grating based refractive index sensor: Employing two layer and three layer geometry approach

Abstract

In this work, we have calculated various cladding modes effective refractive indices (ERI) by using two layer and three layer geometry in long period fiber grating (LPFG) and studied the variation of various cladding ERI due to variation in surrounding refractive index (SRI). Employing both two layer and three layer geometry approach, it is observed that in LPFG based refractive index sensor, sensitivity to SRI can be improved by using higher order cladding modes. Both two layer and three layer geometry results in nearly same values of ERIs for lower order cladding modes for any value of SRI but there is drastically increase in difference of results obtained by using two layer from three layer geometry as cladding mode order increases. Actually investigation of LPFG as refractive index sensor using two layer geometry is very simple and can be used for lower order cladding modes. But to achieve accurate results with enhanced sensitivity for higher order cladding modes, three layer geometry is best suited for studying LPFG as refractive index sensor. The response has been studied for surrounding refractive index variation from 1 to 1.45.