Patent ID: 7299659

Claim:
A method for producing an optical preform which comprises: (a) feeding a flow of glass precursor material into a deposition burner and conferring to said flow a substantially circular cross-section; (b) feeding a flow of combustible gas and a flow of combustion sustaining gas into said burner, in order to create a flame for uniformly heating said flow of glass precursor material and causing said glass precursor material to react, thereby forming a flow of fine glass particles; (c) directing said flow of fine glass particles and said flame toward a target preform having an initial diameter; and (d) causing said flow of glass particles to impact onto said target preform, thus increasing the radial dimensions of said preform up to a final diameter; wherein the cross-section of at least the terminal portion of said flow impacting onto the target preform is modified into a cross-sectional shape having a major axis and a minor axis, said major axis being substantially orthogonal to the longitudinal axis of the target preform.