High Photosensitivity in SnO₂:SiO₂ Optical Fibers

Enhanced photosensitivity has been achieved in tin-doped silica optical fibers. Refractive index modulations (∼3^.10^-4) have been achieved by use of 248 nm UV radiation. Studies performed on preform slides proved that the refractive index change can be ascribed to structural rearrangements induced by photochemical reactions. The modified structure has shown extreme stability, and gratings written in this fiber start to be erased above 600°C. Exposure of the fiber to 255 nm laser radiation showed that, at high fluence, the refractive index modulation saturates and does not exhibit any sign of decrease.