By Andrey Grishchenko, Ceram Optic SIA, Dmitrijs Saharovs and Mario Paredes, Armadillo SIA
This study examined the influence of the composition of the core material, preform production technology and posttreatment with hydrogen on the optical stability of the all-silica optical fibers to UV radiation. Elaborated fiber coating, consisting of carbon and polyimide layers, allows hydrogen saturation at 250 °C but shows excellent hermeticity at room temperature.
The comparative study of the optical fibers not saturated with hydrogen showed that silicas with both high and low content of hydroxyl groups are observed to have sufficient initial UV transparency and resistance to UV irradiation. More significantly is the occurrence of defects in the structure of silica causing absorption in the region of 200 - 400 nm as well as the presence of Si-H and Si-Cl groups, which act as precursors for defects with absorption peaks at 214 nm and 330 nm. The deposition method of a reflective cladding had a significant effect on the incidence of defects and Si-H groups in the fiber core. The most significant effect on induced loss was caused by hydrogen treatment of the fibers.
The findings of this study provide strategies to optimize the production of optically transparent all-silica fibers for various spectral regions and significantly improve their stability under UV and gamma irradiation.