FibreBragg Grating (FBG)

A Fibre Bragg Grating is a periodic or aperiodic perturbation of the effective refractive index in the core of an optical fibre. The perturbation is approximately periodic over a certain length of e.g. a few millimetres or centimetres, and the period is of the order of hundreds of nanometers. This leads to the reflection of light propagating along the fibre in a narrow range of wavelengths, for which a Bragg condition is satisfied.
A fibre Bragg grating reflects the selected wavelength and transmits others. A fibre Bragg grating can, therefore, be used as an inline optical filter to block certain wavelengths, or as a wavelength-specific reflector.