A METHOD OF MAKING A HIGH PURITY GLASS ARTICLE SUCH AS A SOOT PREFORM, A SOOT PREFORM AND AN OPTICAL WAVEGUIDE FIBRE FORMED THEREFROM

摘要

A method of making solid glass articles by the flame hydrolysis technique. A thin stratum of low viscosity glass soot is applied to the surface of a mandrel. First and second coatings of glass soot are deposited on the surface of the thin stratum to form a porous preform. The refractive index of the soot particles of the first coating is greater than that of the soot of the second coating, and the soot of the first coating has a viscosity lower than that of the second coating. The mandrel is removed, and the soot preform is subjected to a high temperature whereby it is consolidated to form a dense glass blank. The glass surface tension and the relative viscosities of the inner and outer portions of the preform cause the aperture to close during the consolidation process. The thin stratum, which preferably includes P2O5, smoothes over the damage caused by removing the mandrel and reduces or even eliminates seed formation at the axis of the resultant glass blank. The blank may be heated and drawn into a filament, or it may be sliced into optical windows, lenses or the like.