Radiation resistance of optical fibers: correlation between UV attenuation and radiation-induced loss

Optical fibers with undoped silica core and fluorine doped silica cladding are known to be radiation resistant. Especially fibers with high OH-content core material show very low radiation induced losses which recover within a few hundred seconds after irradiations up to 100 krd dose. Even with these promising properties radiation resistance is a limiting factor for some applications. Optical fibers with different grades of high OH-content undoped silica core materials were produced by using the same preform manufacturing and fiber drawing parameters. The UV-attenuation spectra of those fiber samples were measured. Then they were irradiated at a 60-Co-source, and the induced losses were recorded in the spectral range between 200 nm and 1600 nm wavelength. A correlation between the UV-attenuation characteristics of the unirradiated fiber and its radiation induced loss was found. The results indicate that defects already existing in the unirradiated fiber ('precursor defects') are responsible for the differences in radiation resistance at dose values below 100 krd. These precursor defects are transformed into color centers by ionizing radiation.