I. Introduction
There is a continuous growth of interest in passive fiber optic components for telecommunication, as well as for nontelecommunication applications. One of the basic passive component is the Fabry–Pérot (FP) filter. This component, requiring two spatially separated reflectors, may be realized using thin film multilayer reflectors [1], metallic mirrors [2], or fiber Bragg gratings (FBGs) [3]– [5]. For fiber optic applications, the use of coatings deposited directly on the fiber end-faces leads to devices with excellent performance, but is rather complex in terms of alignment and packaging. Bulk glass elements with dielectric coatings usually require use of collimation optics thus increasing the loss as well as the price of the component. However, photoinduced FBGs are all-fiber devices that have very low insertion loss. Especially convenient are chirped FBGs, which can easily cover a large spectral band and can be produced in a large volume using a chirped phase mask.