ANALYSIS OF OH ABSORPTION-BANDS IN SYNTHETIC SILICA

The presence of bound hydroxyl (SiOH) in silica is well known to produ ce an optical fundamental absorption band at about 2.7 mu m. For optic al fiber applications the influence of the corresponding overtones and combination modes on the absorption spectrum are of significant impor tance. A literature review is presented which reveals uncertainties re garding the correct absorption band intensities as well as their spect ral positions. We present precise data on spectral position and relati ve intensities of OH absorption bands in state of the art synthetic si lica. Our investigations cover the influence of different manufacturin g techniques, OH content, and a comparison of bulk and fiber data. Wit h the knowledge of the conversion factors between the intensities of d ifferent OH absorption bands it is possible to predict the entire OH r elated transmission performance of an optical component by measurement of a single absorption band, e.g.,, the fundamental mode at 2.7 mu m or the 1.38 mu-m band in the low loss range of optical fibers.