High total dose irradiation experiments on fiber-optic components for fusion reactor environments

Optical fiber technology is seriously considered for communication and monitoring applications during the operation and maintenance of future thermonuclear fusion reactors. Their environment is characterized, in particular, by possibly high gamma dose-rates and total doses up to 100 MGy. The feasibility of applying photonic technology in such intense radiation fields therefore needs to be assessed. Whereas many reports deal with the radiation behavior of a variety of fiber-optic devices, only little information is available on the radiation tolerance at high total dose (e.g. >1 MGy). We describe our recent results obtained on fiber-optic components intended for ITER (International thermonuclear Experimental Reactor) remote-handling applications. We have conducted high total dose (up to 15 MGy) irradiation experiments on a variety of COTS fiber-optic devices, including edge-emitting laser diodes, vertical-cavity surface-emitting lasers, PIN photodiodes and single-mode optical fibers. A remarkably low radiation induced loss was obtained on a single-mode pure silica core optical fiber, whereas VCSELs confirmed their excellent radiation hardness. With the exception of photodiodes, the optical characteristics of selected fiber-optic devices seem to be able to cope with high total gamma doses. However, our results also indicate that radiation induced degradation of connector assemblies might limit their use in severe radiation environments.