On the origin of the long-wavelength loss anomaly in H2-treated germano-phospho-silicate glass fibers.

We show, by isotopic substitution OH->OD, that the added loss beyond 1.3micron in optical fibers when treated in H2 at 200C is OH absorption. It consists of a peak around 1.4micron which is OH overtone absorption and a monotonic increase beyond 1. 5micron which is the wing of the OH fundamental absorption. The amount of OH fundamental absorption due to H2 at 200C is much smaller for a P-doped silica glass than for a Ge-P-doped glass.