Fiber Bragg Grating (FBG)

A Fiber Bragg Grating is a periodical variation of the refractive index  along the length (several millimeter or centimeter) of the fiber’s core. When the light passes through it just the part with a wavelength equal to Bragg’s wavelength is reflected. Any external disturbance (like variation in strain or temperature) can be the reason of a variation in grating period and consequently a shift in Bragg’s wavelength.