Photosensitivity in tantalum doped silica optical fibres

Photodarkening and photoinduced index changes are reported for the first time to our knowledge in tantalum-doped silica optical fibers exposed to KrF excimer laser emission at 248nm. The UV absorption of the tantalum-doped preform features the tail of a strong absorption band below 200nm. The 248nm-induced absorption in the UV also features the tail of a band below 200nm. Photodarkening at 900nm shows signs of saturation after several excimer pulses and some recovery after each pulse. Using an external holographic writing technique at 248nm, we also formed Bragg gratings at 1.55µm in these fibers. The grating growth saturated after several pulses and displayed a fast decay component when writing was performed with a higher pulse rate. The decay is well fitted by a stretched exponential with beta = 0.35.

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