Super-high-strength metal-coated low-hydroxyl low-chlorine all-silica optical fibers

High-purity KS-4V synthetic silica developed in the Silicate Chemistry Institute of the Russian Academy of Sciences is tested as the core material for radiation hardened optical fibers. Pure-silica-core fluorine-doped-silica-cladding optical fibers with polymer (acrylate) or metal (aluminum) coating are produced as the experimental samples. The light-reflecting fluorine-doped silica cladding is synthesized by the plasma outside deposition process. The aluminum coating technology used provides a very high strength of the fibers, unattainable for polymer coatings, and expands the fiber operating range up to 400°C. It is established that the metal coating application can result in the annealing of the drawing-induced color centers with an absorption peak at 630 nm. Post-γ-irradiation loss spectra in KS-4V-based fibers measured in 1-2 hours after 2 MGy irradiation at a dose rate of 8.3 Gy/s in the spectral range 350-700 nm are discussed. The 630 nm absorption peak is practically absent from the post-irradiation loss spectra of aluminum-coated KS-4V-based fibers