Radiation responses of ultra-low loss pure-silica-core optical fibers in the visible to infrared domains

-We investigated the origins of the steady state X-ray radiation-induced attenuation (RIA) in the visible to infrared spectral domains of an ultra-low loss Telecom-grade single-mode optical fiber. This pure-silica core optical fiber presents very high RIA in this spectral range, larger than so-called radiation sensitive optical fibers. The RIA is mainly caused by the appearance of two broad absorption features around 600 nm and 1200 nm, both leading to RIA levels of ∼2 dB/m at 2 kGy(SiO₂) at room temperature. While the infrared-RIA may be attributed to the absorption bands at 0.93 eV and 1.2 eV of possible variants of Self-Trapped Holes, the exact nature of the large 600 nm absorption around remains unclear. It could not be only related to a very efficient generation of Non-Bridging Oxygen Hole Centers but our analysis suggests the presence of another defect structure associated with an absorption band around 2.14 eV (FWHM = 0.52 eV), stable at room temperature, but that can be passivated by post irradiation hydrogen-loading treatment.