Effect of low-earth orbit space on radiation-induced absorption in rare-earth-doped optical fibers

The implementation of optical systems, based on rare-earth doped fibers, in space environments adds a powerful new dimension of functionality to the design of space-based systems, particularly when high power and bandwidth, high fidelity, and low susceptibility to electromagnetic interference are desired. As these specialty fibers are often the most sensitive components of an optical system, extensive use requires considerable insight into the ionizing-radiation-induced changes experienced by the fibers during their operational lifetime. In this research, a suite of aluminosilicate fibers singly or co-doped with erbium and ytterbium ions was deployed into low-Earth orbit for approximately 18 months as part of the Materials International Space Station Experiment (MISSE) 7 mission. Optical spectroscopy performed on the retrieved fibers is compared to control data from pristine, unirradiated fibers, revealing colorcenter generation in the visible portion of the spectrum consistent with silica-related and aluminum-related absorption centers, with band-tailing into the near-infrared. Results suggest that visible to near infra-red (NIR) absorption experienced by the co-doped fiber is less-pronounced than in its singly-doped counterparts, likely a result of the lower aluminum concentration of this fiber. The data were also compared to data from terrestrial ⁶⁰Co irradiation of the same fiber types and it was found that the overall trends observed in the space-irradiated fibers in the near-infrared were accurately, although not identically, reproduced. The resultant information is important for the design and testing of radiation-hardened optical-fiber-based laser and amplifier systems.