Abstract: A glass tube (31) from which optical fiber is to be drawn is heated by a torch assembly comprising a plurality of nozzles (54--54) disposed on a carriage. In order to avoid contamination of the tube by particles of the torch assembly resulting from thermal degradation,the nozzles are disposed in a plane which is normal to an axis (36) of the tube with each nozzle axis inclined so that flame fronts associated with the nozzles are substantially closer to the tube than to the torch assembly. Reaction of materials which are flowed into the tube is enhanced by including a second row of nozzles (91--91) which are inclined within a plane which is inclined to the longitudinal axis of the tube. In order to collapse the tube into a rod, a muffle member (100) preferably is caused to be disposed about the tube with an opening in the periphery of the muffle member to allow portions of the gas flows to converge and to allow heat energy to be transferred from the flame fronts to the tube.

Abstract: In one manufacture of a preform rod from which optical fiber is drawn, chemical materials are moved into a rotating preform tube to which is applied a moving zone of heat. Following a deposition mode, the tube is collapsed to provide the preform rod. Provisions must be made to supply the deposition materials from a rotating supply conduit into the rotating preform tube without leakage and without the ingress of contaminants while an end portion of the tube is gripped securely. This is accomplished by providing non-metallic ferrules about an end portion of the preform tube which are caused to be clamped against the end portion of the preform tube in sealing and gripping engagement therewith.

Abstract: Method and apparatus are provided for overcladding a preform rod (22). The preform rod is aligned with and inserted into an overcladding tube (30). 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 a drawn optical fiber in which the overcladding is substantially concentric with respect to the optical fiber core.