Effect of Ionizing Radiation on Optical Transmission of Actively Pumped Yb- Doped Fiber Amplifiers

Fibers doped with Yb ³⁺ serve as optical amplification elements in many high-power amplification systems, and there is an interest in significantly extending the capabilities of rare-earth doped fiber amplifiers to space-based systems. We investigate the effects of gamma-radiation-induced photodarkening on the performance of such fibers, both for passive as well as active configurations. With an emphasis on low total ionizing doses, passive irradiations were found to show increased absorption across the visible and IR spectrum. Furthermore, continuous-pumping of an Yb ³⁺ -doped fiber amplifier in a gamma radiation environment was found to exhibit significantly greater degradation than a similar intermittently-pumped irradiated amplifier for low total ionizing doses of under 10 krad(Si) [100 Gy(Si)]. We discuss the implications of the data which provide insight into energy-transfer mechanisms in the fibers and the relationship of gamma-radiation-induced photodarkening and pump-radiation-induced photodarkening associated with the observed fiber degradation.