Radiation Effects on Pure-Silica Multimode Optical Fibers in the Visible and Near-Infrared Domains: Influence of OH Groups

Abstract

Signal transmission over optical fibers in the ultraviolet to near-infrared domains remains very challenging due to their high intrinsic losses. In radiation-rich environments, this is made even more difficult due to the radiation-induced attenuation (RIA) phenomenon. We investigated here how the number of hydroxyl groups (OH) present in multi-mode (MM) pure-silica core (PSC) optical fibers influences the RIA levels and kinetics. For this, we tested three different fiber samples: one “wet”, one “dry” and one with an intermediate “medium” OH content. The RIA of the three samples was measured in the 400–900 nm (~3 eV to ~1.4 eV) spectral range during and after an X-ray irradiation at a dose rate of 6 Gy(SiO2) s−1 up to a total accumulated dose of 300 kGy(SiO2). Furthermore, we evaluated the H2-pre-loading efficiency in the medium OH sample to permanently improve both its intrinsic losses and radiation response in the visible domain. Finally, the spectral decomposition of the various RIA responses allows us to better understand the basic mechanisms related to the point defects causing the excess of optical losses. Particularly, it reveals the relationship between the initial OH groups content and the generation of non-bridging oxygen hole centers (NBOHCs). Moreover, the presence of hydroxyl groups also affects the contribution from other intrinsic defects such as the self-trapped holes (STHs) to the RIA in this spectral domain.

Intrinsic Point Defects in Silica for Fiber Optics Applications

“…These localized irregularities of the network are characterized by one or more energy levels lying in the band gap of the dielectric and are responsible for the shift in the optical absorption edge of the glass to lower energies. The phenomenon is known as photodarkening (or solarization) and is even more pronounced in silica optical fibers (OFs) which, due to their strained glass structure, exhibit a higher sensitivity to radiation as compared to the respective preforms [12][13][14][15][16][17][18][19][20][21][22].…”