Fabrication of high-silica glass article

Claim 1

Method of producing an optical fiber comprising a core and a cladding surrounding the core, the core and the cladding consisting of high-silica glass, the method comprising making a high-silica glass body having a predetermined refractive index profile, with a center region of relatively high refractive index and a peripheral region of relatively low refractive index surrounding the center region, the glass body to be referred to as the preform, heating at least a part of the preform to a temperature above a sintering temperature, and drawing the optical fiber from the heated part of the preform, with the fiber core and cladding derived from the center region and peripheral region of the preform, respectively; wherein the preform is made by a process that comprises (a) making a porous high-silica body by a sol-gel process, the porous body having an inner portion and an outer portion; (b) drying the porous body including heat treatment in an atmosphere comprising chlorine to remove bound water; and (c) sintering the porous body at the sintering temperature such that the porous body is transformed into the preform, the center and peripheral regions of the preform derived, respectively, from the inner and outer portion of the porous body; the method further comprises (d) causing to be present, prior to completion of step (c), in both the inner and the outer portion of the porous body, a fluorine concentration that is effective to essentially prevent the evolution of bubbles in the heated part of the preform during the heating and fiber drawing, such that the core and the cladding of the optical fiber are essentially free of bubbles.