Measurement of Radiation-induced Attenuation in Visible-guiding Hollow Core Optical Fibres

Hollow core optical fibres (HCFs) have shown exceptional radiation hardness, characterised by low or negligible radiation-induced attenuation (RIA) [1], [2]. As such, HCFs are a promising candidate for fibre requirements in harsh environments such as future fusion facilities and space. The observed low RIA is due to the extremely low light-glass overlap, as the light guided in a HCF is >99.9% in gas (usually air), rather than glass. Yet, a recent study highlighted that the impact of irradiation on the gas within the fibre should not be neglected [1]; absorption signatures of radiolytically generated nitric acid were recorded in a HCF which had been subjected to high levels of gamma irradiation. As all studies on the effect of radiation on the performance of HCFs have so far almost exclusively focussed on the near-IR spectral range, but as it is known that considerable radiation induced loss can also occur in the UV and visible wavelength range [3], further investigation into the RIA of visible-guiding HCFs is needed. Measurements in the UV-visible are also important given that HCFs have shown great promise at these wavelengths, where they offer significantly improved optical performance as compared to standard all-solid optical fibres [4].