Radiation resistance of fluorophosphate glasses for high performance optical fiber in the ultraviolet region

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Abstract
Transmission loss characteristics of a fluorophosphate fiber was investigated in 200–800 nm wavelength region. The transmission loss was found to be primarily dominated by extrinsic absorption due to transition metal impurities. The total scattering is the next most important loss factor which is in fact Rayleigh in character exhibiting a λ−4 dependence, and the ultraviolet absorption tail is the least significant loss factor. Radiation resistance characteristics of the bulk glasses corresponding to the core and cladding have also been investigated. Upon exposure to ultraviolet radiation from a 1 kW Hg-Xe lamp, the radiation-induced defect centers leading to additional absorption bands in the ultraviolet region result mainly from the photoionization processes of Fe2++hν=Fe3++e− and 2Cl−+hν=Cl2−+e− for the Cl− doped glasses, and the former one is also responsible for the glasses without doping of Cl−. The electron capture centers in the glasses are the [PO4] and/or [P2O7] groups. If the irradiation is carried out with a KrF excimer laser having high-energy density, the formation of radiation-induced defect centers is due not only to the photoionizable multivalent ions, but also to the photoionization of phosphate groups in the glasses. The latter process gives the purple color to the irradiated glasses.

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