Method of and apparatus for overcladding an optical preform rod

Abstract From the Canadian patent

Methods and apparatus are provided for overcladding a preform rod. The preform rod is aligned with and inserted into an overcladding tube. The outer diameter of the preform rod and the inner diameter of the tube are such that the clearance between the tube and the rod does not exceed a predetermined value. Successive increments of length of the tube and rod therein are subjected to a controlled zone of heat while the pressure inside the tube is maintained at a value which is substantially less than that outside the tube. This causes the tube to be collapsed onto the preform rod to provide an overclad preform and subsequently is substantially concentric with respect to the optical fiber core.