An X-ray absorption study of doped silicate glass, fibre optic preforms

Optical fibre preforms, which have their germanosilicate core regions doped with small quantities of the rare-earth element erbium, have been studied using Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) at the germanium K absorption edge. These studies were performed using a circular X-ray beam of 100 mu m diameter, allowing information to be gathered as a radial function of position across the core region of the preform. This positioning was accomplished by means of a motorized pinhole collimator and sample stage developed for use on the focused X-ray beamline 8.1, at the SRS, Daresbury Laboratory, UK. The EXAFS results are consistent with the germanium sites coordinated to surrounding oxygen atoms at a mean distance of 0.17 nm. Absorption maps of the rare-earth and germanium distribution across the core region of the preforms have also been obtained, showing a correlation between the distributions of the two atom types.