Photosensitive germanosilicate preforms and fibers

A detailed study of the ultraviolet loss spectra of germanosilicate preforms and fibers is reported. The fiber samples had peak losses of the order of 10 dB/cm, which was several orders of magnitude lower than in preform samples. All spectra could be described by a number of previously observed absorption bands, many of which had been associated with particular defects in germanosilicate glasses. The incorporation of phosphorous as a core codopant eliminated a loss band centered at 325 nm in as drawn fibers. The effect on the ultraviolet absorption spectra of increasing doses of irradiation from an ultraviolet fiber- coating curing-lamp source and also the change in fiber absorption before and after writing a 35% reflection grating are presented. The results are not consistent with the previously proposed model for photosensitivity based on the Kramers-Kronig mechanism.