摘要：

The UV spectra of graded-index fiber-optic preforms have been studied using a technique in which annular masks of varying diameters are placed over the preforms. The collimated UV beam from a conventional absorption-spectrophotometer excites selected regions in the preform core, and the absorption spectra for the varying mask diameters are measured. With this technique and germania borosilicate and phosphosilicate (GeBSi and GePSi) preforms, a previously unresolved absorption band peaking at 330 nm was found and assigned to amorphous GeO(2). Measurements of the peak absorption coefficient were correlated with x-ray fluorescence measurements of GeO(2) concentrations. Absorption associated with P(2)O(5) overlaps the GeO(2) absorption below ~320 nm. That is, between 305 and 320 nm, GePSi preforms absorb strongly while GeBSi preforms absorb weakly. This difference in absorption behavior combined with weak filtering properties of the UV-cured coating at lambda > 305 nm explains why coated GePSi fibers are more sensitive to UV damage than coated GeBSi fibers.

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