Optical characteristics of aluminum coated fused silica core fibers under 14 MeV fusion neutron irradiation

The optical properties of Al-coated fused silica core optical fibers were observed under 14 MeV fast neutrons irradiation with samples pre-annealed at 150 and 300 °C. With the pre-annealing treatment, the optical absorption could be decreased except for the Si–OH (1390 nm). Under fast neutron irradiation, the radiation-induced transmission loss of pre-annealed fiber at 150 °C was over five times larger than that annealed at 300 °C. It is believed that the precursors of optical absorption were decreased by the annealing treatment. Under irradiation, the optical absorption at 1390 nm had characteristic changes. The absorption at 1390 nm was small during the irradiation and became large once the irradiation stopped. This behavior was only observed for the 1390 nm absorption. It is believed that the increase of the transmission loss under irradiation was caused by the atomic displacement by fast neutrons of Si–OHs and that the displaced Si–OHs recovered when the irradiation stopped.