A variation of the period of the grating inscripted in a fiber optic – induced by mechanical or thermal perturbation – causes a shift of the reflected peak wavelength, due to the related optical path length variation. Typically, the perturbation is approximately periodic over a certain length of e. a few millimeters or centimeters, and the period is of the order of. Fiber Bragg Gratings (FBGs) are a crucial technology in the field of optics, with a wide range of applications in telecommunications, sensing, and medical fields. This structure can be created by intense UV light affecting the fiber core. where Pij are the Pockel coefficients of the elasto-optic tensor, n is the.