Optical spectra in pure-silica-core single mode optical fibers after high-fluence reactor irradiation

The paper describes the study of radiation-induced attenuation (RIA) spectra in reactor-irradiated single mode at lambda =1.55 mu m optical fibers (OFs) with differente high-temperature coatings (polyimyde, aluminum and copper). The OFs were previously irradiated up to fast neutron fluence 1.8 center dot 10(20) n/cm(2) and gamma dose 2.32 GGy. After three years of storage at room temperature (RT), the RIA spectra were examined in the range of 650-1700 nm. All RIA mechanisms acting in this spectral range were identified: a tail of non-bridging oxygen hole center, a long-wavelength RIA (LWRIA) band with a maximum at lambda > 1600 nm, unstructured "grey" loss due to coating microbendings or damage, and an absorption band peaking at 930 nm (E=1.33 eV). It was found out that the LWRIA can be significantly annealed at RT in polyimide-coated OFs. Grey loss were found to be more stable than those causing LWRIA. The LWRIA arising in reactor- and gamma-irradiated OFs have close thermal stability at RT and exhibit a similar shapes, which close to the absorption band of self-trapped holes (STH). This suggests a STH-like nature of the LWRIA.