This paper deals with mathematical modeling, design and application of Fiber Bragg Grating as temperature sensor. The temperature-dependent change of the refractive indices of the fiber, consequently the shift of its Bragg wavelength, is used as a measure of the temperature. The temperature sensitivity of FBGs originates from two intrinsic effects: the thermo-optic. GitHub - benfrey/FBG-SimPlus: Fiber Bragg grating (FBG) simulation tool for Finite Element Method (FEM) models. The FBG is constructed with an effective index of 1.