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

ABSTRACT Optical fibers with undoped silica core and fluorine doped silica cladding are known to be radiationresistant. Especially fibers with high OH—content core material show very low radiation inducedlosses which recover within a few hundred seconds after irradiations up to 100 krd dose. Even withthese promising properties radiation resistance is a limiting factor for some applications.Optical fibers with different grades of high Oil—content undoped silica core materials were pro-duced by using the same preform manufacturing and fiber drawing parameters. The UV—attenua-tion spectra of those fiber samples were measured. Then they were irradiated at a 60Co—source, andthe 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 radiationinduced 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 below100 krd. These precusor defects are transformed into color centers by ionizing radiation.1. INTRODUCTIONOptical fibers have become a reliable tool in telecommunication, laser power transmission, spectro-scopy, and other applications. Production parameters were optimized in order to achieve very smalllosses of the guided light. Optical fibers are used even in adverse environments e.g. under ionizingradiation. The excellent transmission values, however, can be degraded significantly under thoseconditions .