CHARACTERIZATION OF FLUORINE-DOPED SILICA GLASSES

Fluorine-doped silica glasses containing up to 2 wt% were prepared by the vapour-phase-axial-deposition (VAD) sintering process. The charact eristics of these glasses were investigated by Raman spectroscopy, vac uum-ultraviolet-ultraviolet (v.u.v-u.v.) spectroscopy, and viscosity m easurements. From the Raman spectroscopic investigation, it has been s hown that the Si-F bond structure in the fibres is the same as that in bulk glass and is not affected by codoped additives such as B2O3. Fro m the u.v.-v.u.v. spectroscopic investigation, it has been shown that the absorption band at 7.6 eV in high-purity silica glass is removed w ith the addition of fluorine. This addition produces a silica glass wi th most excellent transparency in u.v. and v.u.v. regions. Also it was observed that the optimum addition is around 1 wt%. This fact proves that fluorine incorporation in glass prevents the generation of defect s related to optical loss in fibres. From the viscosity study, it was found that the viscosity decreases with an increase of the fluorine co ntent in glass and the activation energy also decreases with increasin g fluorine content.