X‐ray photoelectron imaging of germanosilicate optical fibre preforms

The germanosilicate glass core (GeO 2 –SiO 2 ) of an optical fibre preform has been analysed and imaged using small‐spot (∼450 μm) x‐ray photoelectron spectroscopy (XPS). The germanium oxide was most readily detected in the glass preform sample using the Al K α x‐ray‐induced Ge L 3 MM Auger feature. The observed Ge L 3 MM lineshape and estimated oxidation state shift of 8.8 eV with respect to pure germanium indicate that the germanium is predominantly in the form of GeO 2 (+4 oxidation state) within the germanosilicate core. Argon ion etching was found to sputter preferentially the oxygen from the glass, and the observed changes in Ge L 3 MM Auger lineshapes suggest that suboxide defects (GeO) are produced. Quantitative XPS images and linescans were used to map the spatial distribution of germanium within the preform and were in good agreement with measured refractive index profiles.