Influence of the cladding thickness on the evolution of the NBOHC band in optical fibers exposed to gamma radiations

The gamma radiation induced loss spectra are recorded from 400 nm to 700 nm in high OH undoped silica core multimode step-index fibers having thin or thick cladding and polyimide or acrylate coating. For both coating materials, the better radiation resistance of thin-cladding fibers is observed. This behavior was reported in the past but not explained. A physical explanation is proposed on the basis of the assumed existence of peroxy-linkage precursors of the non-bridging oxygen hole centers (NBOHCS) and on the basis of a diffusion-limited radiation hardening due to radiolytic hydrogen released by the coating. Besides the radiation effects, an in-situ heating of the fibers performed after irradiation reveals a sensitivity of microbending losses to temperature.