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Fiber Bragg Grating (FBG) is a simple and low-cost filter built into the core of a wavelength-specific fiber cable. FBGs are used as inline optical filters to block certain wavelengths, or as wavelength-specific reflectors.
Implemented in the 1990s, FBGs improve optical signal quality and are key to fiber optic construction. FBGs also may be used to stabilize laser output.
A FBG is created by using an intense ultraviolet (UV) source to write a systematic (periodic or aperiodic) refractive index variations into an optical fiber core. As light moves along the fiber and encounters refractive index changes, a small amount of light is reflected at each boundary. When the grating and light wavelength period are the same, positive reinforcement is provided via power that is coupled from forward to backward directions. Light from other wavelengths cannot propagate, due to out-of-phase reflection interference.
The three most common FBG types are: