MEJORAS EN METODO PARA FORMAR UN ARTICULO DE VIRIO DE ALTA PUREZA

A glass optical waveguide preform is formed by depositing coatings (22, 28) of glass soot on a mandrel (20). The mandrel (20) ist removed and the porous preform (30) is consolidated. One end (44) of the preform aperture (42) is closed, the aperture is evacuated, and the remaining end (46) of the preform is heated, whereby it is caused to close. An intermediate fiber (56) is drawn from the resultant consolidated preform, the entire aperture (42) closing during drawing due to the low pressure within the aperture. The intermediate fiber (56) is severed into sections, each of which functions as a mandrel for the deposition of a further coating of cladding soot (70). The resultant composite article (74) is consolidated and drawn into an optical fiber. To prevent the formation of a devitrified layer at the aperture-forming surface during the consolidation step, the rate of soot deposition is initially reduced so that a stratum of fine soot is initially deposited on the mandrel. The stratum is initially discontinuous, but after a plurality of passes of the soot-producing burner, it becomes continuous. Thereafter, the formation of the remainder of the soot preform continues in a conventional manner.