Patent ID: 7441416

Claim:
A method for manufacturing an optical preform by directing a flow of fine glass particles from a deposition burner onto a rotating elongated target preform, said method comprising the steps of: (a) feeding said burner with a flow of a glass precursor material via a first plurality of ducts and directing said flow of glass precursor material toward said target preform; (b) feeding said burner with a first flow of combustible gas and a first flow of combustion sustaining gas via said first plurality of ducts in order to generate an inner flame surrounding said flow of glass precursor material; (c) feeding said burner with a second flow of combustible gas and a second flow of combustion sustaining gas via a second plurality of ducts in order to generate an outer flame surrounding said inner flame; (d) reacting said glass precursor material in the presence of said flames, thus forming a flow of fine glass particles directed toward said target preform; and (e) confining and separating said inner flame from said outer flame with an elongated hollow separating element made of a heat resistant material that surrounds said inner flame and that does not form a part of a duct for the passage of any gas or glass precursor material.