Effect of cladding material on 2-eV optical absorption in pure-Silica core fibers and method to suppress the absorption

The growth of 2-eV optical absorption induced by γ-ray irradiation is larger in pure-silica core fibers with a dopedglass cladding than in the fibers with a silicone cladding, regardless of the manufacturing process. Precursors of nonbridging oxygen hole centers which abundantly exist at the core/cladding interface of the glass-cladding fibers are responsible for the difference in the absorption. A combined-treatment of hydrogen and γ-ray irradiation can remove these precursors and suppress the absorption.