Overtone vibrations of OH groups in fused silica optical fibers

The OH-stretching fundamental, and the first, second, and third OH overtone vibrations have been examined using pure, GeO2-doped, graded index, fused silica optical fibers having OH contents from <1 ppm to ≳103 ppm. The previously reported component substructure of the fundamental OH-stretching contour was found to be repeated in the overtones, along with a set of involving fundamental vibrations of fused silica. Several new vibrations were uncovered and assigned. Examinations of deuterated OH samples helped to verify the assignments. The spectral broadening produced by GeO2 was interpreted in terms of a wider range of environments seen by the OH oscillators, compared to pure fused silica.