The Photorefractive Bragg Gratings in the Fibers for Telecommunications

(Received 13 March 1996, accepted 6 Septembre 1996)

Abstract
This revue article describes photorefractive Bragg gratings (elaboration, interest, performances) which are planned to be used in optical fibers for telecommunications. This application justifies the effort made presently to increase the photosensitivity of the fibers and the stability of the grating inscribed in them. Since Bragg gratings are based on UV induced refractive index change, underlied mechanisms are described as long as the change of UV absorption at the origin of photo transformation of the glass. Different models invoked to describe UV induced refractive index changes are extensively presented and criticized, leading to conclusions. The different directions of research undertaken to enhance the photosensitivity: H ₂ loading, other dopants, other glasses and other writing wavelengths are explicited. All this leads to a classification of Bragg gratings in terms of the UV induced mechanism involved.