Undoped-silica-core F-doped-silica-cladding optical fibers (“undoped fibers”) are an important fiber type for applications requiring resistance to ionizing radiation (e.g., the nuclear industry, space, and military applications), the most important fundamental radiation-induced color centers arising in such fibers being self-trapped holes (STH). Despite the previous in-depth STH investigations, there have remained a few not-fully understood issues, such as the relationship between the radiation-induced absorption (RIA) bands due to STH in undoped fibers, on the one hand, and in bulk silica samples, on the other, the role of strain in the silica network in the STH occurrence, and possible peculiarities of short-lived STH-like radiation-induced color centers at temperatures above RT. To address these issues, we investigate the RIA spectra in undoped fibers with different frozen-in strain in their silica network immediately in the process of γ-irradiation to a dose of 1 kGy, the irradiation temperature being in the range ±60 °C or liquid nitrogen temperature (LNT). Gaussian decomposition of the RIA spectra measured at LNT has yielded STH bands at 2.6 and 2.16 eV together with the “classical” STH bands at 1.88 and 1.63 eV observed in fibers more frequently than the former bands. Based on this observation, it is proposed that all the STH bands observable in fibers fall into two classes: those inherent in silica and those strain-assisted, which can adjoin each other in the fiber silica network. The inherent STH include the well-known low-temperature infrared absorption and the bands at 2.6 and 2.16 eV; the strain assisted STH, the 1.88- and 1.63-eV bands. The 1.88-eV band is argued to be due to STH1, the 1.63-eV one, due to STH2. Anomalously high RIA at T = 0 and +60 °C is revealed and explained for the first time. The former effect is found to be caused by extreme compression of silica at T ∼ 0 °C enhancing the strain-assisted STH bands. The anomaly at T = +60 °C is found to be due to a previously unknown broad RIA band at ∼1.08 eV, which is likely to be associated with STH or self-trapped electrons and to result from either large network strain at the compression phases of enhanced thermal oscillation, or large expansion at the opposite phases. The RIA enhancement at T = +60 °C observed in this paper for the first time can influence fiber applications in the nuclear industry associated with high temperatures and high dose rates.

No abstract

Radiation-induced attenuation (RIA) in undopedsilica-core optical fibers of which the preform cores are synthesized in high O 2 excess conditions in the vapor-gas mixture ("high oxygen excess fibers, HOE-fibers") is investigated in the spectral range 1.1-1.7 µm under γ-irradiation from a 60 Co-source. The O 2 excess degree, the F content in the cladding, the drawing speed and tension are varied among the fibers. RIA is found to strongly depend on the balance between the O 2 excess degree in the core and the F content in the cladding and also on the fiber drawing tension. RIA anticipated in HOE-fibers with optimized O 2 excess and a practicably low drawing tension at λ=1.55 µm is estimated to be a few times lower than that in the commercial radiation-resistant F-doped-silica-core fibers.Index Terms-Optical fiber radiation effects, optical fiber radiation resistance, radiation-induced attenuation (RIA).

No abstract