Abstract
The OH-ion distribution in preforms of high-silica optical fibers was investigated and related to the OH-contamination mechanism in the preform fabrication processes of the C.V.D method. The OH-ion distribution profiles were measured optically at 2.73 µm with a high spatial resolution of about 90 µm. It was confirmed from the OH-ion distribution profiles that one of the OH-contamination processes is the thermal diffusion of OH-ions from the supporting silica tube into the deposited glass layers during deposition. No significant difference was observed in the OH-ion diffusivity between nondoped silica glass and B2O3-doped silica glass. The OH-contamination in the center of the preform was attributed to the dissolution of the water vapor due to an accidental leak from the outlet of the deposited tube during the collapsing procedure. Based on this result, the OH-ion solubility in silica glass at a high temperature of 1900°C is estimated to be about 1.4×1020 OH/cm3·atm.1/2