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The effects of the drawing conditions, OH content and irradiation temperature on radiation-induced optical absorption bands in step-index fibers with pure silica cores clad with silicone or F-doped silica have been investigated. A loss peak was induced at 770 nm in silicone-clad fibers with both low and high OH-content silica cores, but the loss peak occurred at 630 nm in F-doped silica-clad fibers under γ-ray irradiation. The drawing conditions affected the growth of the loss peak in both silicone-clad and F-doped silica-clad fibers. The 770 nm band decreased under γ-ray irradiation exceeding 100 Gy at room temperature but did not decrease at 77 K. Radiation hardening was produced in the 770 nm band by γ-ray irradiation at room temperature or by room temperature annealing after irradiation at 77 K. The loss peaks at 770 nm and 630 nm in the two kinds of fiber are discussed in relation to the differences in the cladding materials.

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