Effect of OH-group content on optical properties of silica core fiber waveguides during reactor irradiation

The transient optical loss (TOL) of silica core optical fiber waveguides of KU-1 grade (Russia, OH content 1000 ppm) and K-3 grade (Japan, OH content 10 ppm) have been measured during pulsed reactor irradiation (BARS-6 pulsed fission reactor (IPPE), pulse 80 μs, dose per pulse <5.5×1012 n/cm2 (9 Gy), dose rate <7×1016 n/cm2 s (1.1×105 Gy/s) in the visible range (fixed wavelengths 532 and 632 nm). Strong contribution from the light scattering induced by the irradiation in the silica fibers resulted in TOL. The light scattering is responsible for similarity of the spectral and temporal dependence of TOL of the optical fibers tested. The TOL of the unirradiated silica fibers is lower in the fiber with higher OH-group concentration (KU-1), whereas the difference in TOL of the KU-1 (high OH) and K-3 fiber (low OH) irradiated to a dose of ≈103 Gy is not so significant. The lower TOL of the KU-1 fiber is probably due to the effect of OH-groups on phase stability in the trap subsystem.