Optical Data Storage in Photosensitive Fibres

Abstract

There is considerable interest in exploiting photosensitivity in germanosilicate optical fibres for application in the areas of optical communication and sensors. Hill et al [1] first observed permanent optically-induced changes of the refractive index of optical fibres in 1978. In their experiment coherent radiation at 514.5nm, reflected from the fibre ends, generated a standing wave in the fibre which induced a periodic refractive index change along its length. This formed a high reflectivity Bragg grating in the fibre which has a peak at the wavelength of the incident beam. Since then numerous studies into the grating growth mechanism and photosensitive fibres have been carried out [2],[3]. However, the mechanism which results in the perturbation to the refractive index of the fibre core is not fully understood. The spectral region where the fibre is photosensitive has been found to range from the uv to around 500nm.