Photodarkening behaviour in Yb-doped aluminosilicate fibres at elevated temperatures is reported. The fibre was core-pumped at 977 nm and the transmitted powers were monitored at 633 (probe) and 977 nm (pump) simultaneously with ~47% of population inversion of Yb3+ ions. A saturated photodarkening loss was found, which is inversely proportional to temperature and, at ~573 K, the loss was negligible at the pump wavelength. From the decay curves at different temperatures, it was found that the photodarkening involves second-order kinetics to form colour centres.
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