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Investigation of long term stability of arc-induced gratings heat treated at high temperatures

A long-period grating written in the SMF-28 fiber was heat treated at 1000 °C for 15 days. The spectrum of the grating shifted to longer wavelengths and the amplitude of the cladding mode resonances decreased as a result of structural relaxation. The background loss increased considerably for time longer than 200 h, and this loss is caused by devitrification of the fiber.