Regeneration of irradiated optical fibres by photobleaching?

Optical fibres that are permanently installed in nuclear reactors (fission or fusion) or at high energy physics accelerators can accumulate considerable long-lived radiation-induced loss. Four different fibre types were irradiated up to dose values from 10/sup 3/ to 10/sup 6/ Gy and an attempt was made to reduce the residual loss >or=28 h after the end of irradiation by injection of high intensity laser light (40-100 mW) of 672, 830 and 980 nm wavelength. The radiation-induced loss of undoped silica core fibres could not be reduced by photobleaching, whereas the loss of Ge-doped fibres could only be reduced after lower dose values and in the wavelength region of lowest loss increase (800-1200 nm) where it is tolerable anyhow.