Radiation-induced absorption in high-purity silica fiber preforms

Abstract

The effect of the preform fabrication procedure on the radiation-induced absorption in KU-1 and KS-4V high-purity silica glasses was investigated (these glasses are used in fiber preform fabrication via outside fluorosilicate glass deposition on substrate rods and in the rod-in-tube process). The results demonstrate that the deposition of a reflective cladding onto KU-1 rods drastically increases the radiation-induced UV absorption of the rods. In particular, the concentrations of radiation-induced nonbridging oxygen hole centers and E′ centers in gamma-irradiated KU-1 rods with a fluorosilicate cladding are an order of magnitude higher than those in rods that were not heat-treated in plasma torch flames. At the same time, the deposition of a reflective cladding on KS-4V rods has little effect on the concentrations of these radiation-induced color centers. The radiation-induced absorption in KU-1 rods depends on the deposition temperature and duration but is insensitive to the composition of the gas mixture in the torch (in particular, to the presence of fluorination agents) and the presence of a fluorosilicate cladding. It is shown that, in preforms fabricated by the rod-in-tube process, the net concentration of radiation-induced color centers in the substrate rod is lower compared to the outside plasma deposition of fluorosilicate glass on the rod.