Two-photon excitation and bleaching of the 400 nm luminescence band in germanium-doped-silica optical fibres

The 400 nm luminescence band of germanium-doped-silica optical fibres was excited via two-photon absorption of an argon ion laser beam. It was observed that the photoluminescence decreased by as much as 25% during the exposure of the fibres to several hundred milliwatts of optical power for a few hours. Surprisingly, the amount of bleaching is not a given proportion of the initial intensity of the luminescence band. These luminescence measurements are qualitatively related to the photosensitivity of the optical fibres. The saturation of two-photon absorption at relatively low power is also observed.