VERFAHREN ZUR HERSTELLUNG VON ROHLINGEN FUER LICHTLEITFASERN

摘要

In fabricating an optical fiber preform, a synthesizing torch (4) is inclined by 10 DEG to 60 DEG with respect to the rotation axis of a seed rod (2). Moving the rod while rotating it, a glass raw material gas and a flame forming gas are blown out individually from the torch to synthesize glass particles which are deposited onto one end of the rod, so that a cylindrical porous preform is grown in the direction of the rotation axis of the rod. Then the porous preform is heated at a high temperature to vitrify the porous preform into a transparent optical fibre preform. At least one exhaust port (9) is disposed with a distance of 1 mm to 50 mm from the periphery of the porous preform and in the vicinity of the growing surface of the porous preform. In fabricating the porous preform the outer diameter fluctuation is small, and the preform is formed stably without formation of crack on the periphery of the preform. The growing speed is improved easily. The synthesizing torch, e.g. Figure 15a (61) for core is so arranged to produce a glass particle stream deviated from the center area of flame stream. The diameter of a core may be narrowed to 10 mm or less, cladding-to-core-diameter ratio may be increased to be three or more. The mass-production of long-length and low-loss single-mode optical fibers is possible by VAD method.