A novel technique for enhancing the photosensitivity of germanosilicate waveguides

Thermal treatment of GeO/sub 2/:SiO/sub 2/ waveguides, achieved by exposing the waveguides to CO/sub 2/ laser radiation before grating writing, increases the UV photosensitivity of optical fibres. Gratings written in treated fibres show a refractive index modulation two times greater and a Bragg wavelength shift 2 nm larger than those written in untreated fibres. The thermal treatment carried out on bulk samples showed a pronounced increase of the 242 nm absorption band, thus indicating that the increase of germanium oxygen deficient centres (GODC) is believed to be responsible for the higher photosensitivity.