Radiation resistant optical fiber for visible region

Radiation resistance property of a series of optical preforms/fibers of different compositions including those available commercially has been investigated to find out a suitable fiber in the UV-visible wavelength range. The fibers drawn from commercial preforms exhibit feeble transmission in the UV zone prior to the radiation exposure and considerable darkening even with very low dose of radiation; although the preforms contain high OH in the core and it is claimed that higher OH content provides better transmission and radiation tolerance in the UV region. Radiation Induced Attenuation (RIA) dynamics for the wavelength range of 200 to 850 nm has been characterized `real-time' under γ radiation. Dependence of RIA on the OH concentration in the core has been analyzed for wavelength band of 400-500 nm and at 630 nm. The generation of E' and NBOH color centers is responsible for the absorption at the above two wavelength bands respectively and is strongly influenced by the fiber composition. The effect of dose rate up to the accumulated dose of 1MRad has been studied. This systematic study led to the fabrication of a fiber with better radiation resistance characteristics in the wavelength range of 400-700 nm with out any radiation induced absorption peak at 630 nm.