Performance degradation of multimode power-delivery optical fibers for harsh radiation environments

Background Power-delivery optical fibers are used to route high-power laser beams in radiation environments. Under high total ionizing dose(TID), radiation-induced point defects increase attenuation at the operating wavelength and enhance heat generation, leading to thermal buildup and reduced operating margins.

Purpose This study focuses on a pure-silica, step-index multimode power-delivery fiber and aims to evaluate the effects of ⁶⁰Co γ irradiation on its near-infrared transmission performance, the evolution of irradiation-induced point defects, and the temperature response under high-power operation, thereby elucidating the link between defect formation and macroscopic performance degradation.

Methods RIA spectra were measured for fiber samples irradiated to multiple total doses. Under high-power transmission, the output power and temperature rise of an unirradiated fiber and a 100 kGy-irradiated fiber were compared at identical pump settings to quantify irradiation-induced macroscopic degradation. Electron paramagnetic resonance (EPR) and photoluminescence (PL) measurements were performed to microscopically identify the generation and transformation of irradiation-induced point defects.

Results RIA increases overall with dose, and the additional attenuation at the 1080 nm operating wavelength rises markedly. The transmitted output power decreases by 0.5%-4.3% after irradiation and is accompanied by a pronounced temperature increase, indicating that irradiation-induced excess loss is more readily converted into thermal load during operation. EPR shows a monotonic accumulation of E′ paramagnetic centers, while PL exhibits oxygen-vacancy-related emission peaks that increase and then decrease with dose. Taken together, the results suggest that at high doses, oxygen-vacancy-related luminescent centers undergo charge-state redistribution and conversion toward non-radiative centers such as E′, leading to concomitant enhancement of excess loss and heat accumulation.

Conclusions These findings provide mechanistic interpretation and experimental evidence to support performance-degradation assessment and radiation-hardening design of power-delivery fibers for nuclear decommissioning, spent-fuel processing, and other radiation-intensive applications.