Erbium-doped silica optical fibers were irradiated by γ-rays, and their loss-increasing characteristics were analyzed. The loss is mainly induced by Er2+ created by the reduction of Er3+. It does not show a simple dependence on the Er3+ concentration. The loss increase is described by the sum of several saturating exponential terms and one linear term, which can be derived from the yield equation of E ′γ centers or other species induced from precursors by hole trapping. It is considered that hole trapping supplies electrons to induce the reduction and plays an important role in the loss increase.
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