Recirculating fiber delay-line filter with a fiber bragg grating

We propose a new recirculating fiber delay-line filter structure. In the proposed system a fiber Bragg grating (FBG) is used as a multireflection mirror in a fiber delay loop, and an erbium-doped fiber is used to provide gain in the loop. By adjusting parameters such as the coupling efficiency, the reflectivity of the FBG, and the gain, we can change the characteristics of the filter transfer function.