Radiation and temperature survivability of multimode step-index fluorine-doped silica fibers

In a search for optical fibers appropriate for long-term use in nuclear reactor instrumentation, effects of gamma radiation and high temperature on attenuation losses were investigated in three types of fiber. All of the fibers had silica cores with fluorine-doped silica cladding. Fibers with polyimide and aluminium coatings and uncoated fibers were tested. Samples were exposed to gamma radiation at dose rates ranging from 8.2 krad/h to 920 krad/h, with total doses up to 60 Mrad. The effects of heating the fibers, either concurrently with the radiation exposure or separately, were investigated. Heating irradiated fibers to 200°C generally reduced attenuation by annealing of radiation-induced defects. Higher temperatures caused rapid deterioration of fibers. A similar effect was observed when fibers were heated to above 200°C in the absence of radiation. Raising the temperature appears to suppress color centre formation, but beyond a threshold limit, higher temperatures result in jacket or cladding damage with net degradation