Abstract

Numerous advances have been made since the discovery of photosensitivity in optical fibers [1], but none perhaps more significant than fiber based gratings. Gratings are modulated refractive index patterns inscribed in the core of photosensitive optical fibers. In Bragg gratings, light propagating down the fiber length is selectively reflected at the wavelength which satisfies the Bragg condition. Long period gratings which involve coupling into forward propagating cladding modes are a second type of fiber based gratings. Gratings are most commonly written in fibers with germanium doped silica core. Photosensitivity has been also been demonstrated in germanosilicate fibers with codopants such as boron [2] and tin [3]. It has also been shown [4] that “loading” fibers with hydrogen or deuterium, greatly enhances their photosensitivity. This facilitates easy writing of gratings even in compositions that are otherwise minimally photosensitive, for instance, in phosphorus doped silica fiber [5].

© 1997 Optical Society of America