Photo-bleaching effect on gamma-ray and 14 MeV fast neutron induced transmission loss of fused silica core optical fiber

A photo-bleaching effect on radiation-induced transmission loss of fused silica core optical fibers was examined under Co-60 gamma-ray and 14 MeV fast neutron irradiation. In the visible wavelength range, radiation induced loss could be reduced by the photo-bleaching under the both irradiation. For using optical fibers in visible wavelength range such as a light guide and an image guide, the photo-bleaching is an effective technique to improve radiation resistance of optical fibers. In the meantime, a so-called microbending loss is generated by the radiations in the whole wavelength range. The microbending loss responded in a different way to the photo-bleaching between the both irradiation. The loss under the gamma-ray irradiation increased by the photo-bleaching, in contrast to its decrease under the fast neutron irradiation. It is considered that there will be multiple causes for the radiation enhanced microbending loss. Among the causes, that caused by modification of the reflection plane between the core/clad in optical fibers through the atomic displacement process can be reduced by the photo-bleaching. In general, it is concluded that the photo-bleaching technique is effective in improving radiation resistance of optical fibers under neutron associated and moderate flux radiation environments.