Fiber gratings can be classified into short-period fiber Bragg gratings (FBGs) and long-period fiber gratings (LPFGs) based on the size of the refractive index modulation period. FBGs typically have a grating period ranging from hundreds of nanometers to microns. This periodic structure causes the fiber to reflect specific wavelengths of light, while transmitting others. The reflected wavelength, known as the Bragg wavelength, is determined by the period of. One of the most widespread in-fiber components are fiber Bragg gratings (FBGs). According to coupled-mode theory.
