A Fiber Bragg Grating (FBG) consists of a periodic modulation of the refractive index along the core of an optical fiber. This modulation is typically achieved through exposure to ultraviolet (UV) light, which induces a permanent change in the germanium-doped silica core's refractive. 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. where Pij are the Pockel coefficients of the elasto-optic tensor, n is the. Fiber Bragg grating (FBG) optical sensors have emerged as a leading technology for distributed strain and temperature measurement.