Abstract: Optical fibers are fixed to elongating tables by optical fiber fixing jigs. Coatings are removed from portions of the fibers and respective fibers of two different groups are placed into tight contact with one another. Rectifier rods, supported movably by rectifier rod supporting members, are disposed outside the optical fiber strands. The fibers are then heated by a gas burner 4A so as to be welded integrally with each other, and are then elongated. By using rectifier rods, the outside optical fiber strands of the groups being welded are not so strongly heated that uniform welding and elongation can be realized. In one preferred embodiment, the fibers are arranged such that there are gaps therebetween. These gaps are substantially 250 .mu.m. The gaps are sufficiently wide that heating gas flows in a manner such that all the optical fiber strands are heated uniformly to make it possible uniform welding and elongation.

Abstract: A method of manufacturing active optical fibers comprising preparing a preform and then drawing a fiber from the preform, wherein the method consists in using a preform having a doped peripheral outer zone, said zone being intended to constitute the outer cladding of the optical fiber, the doping of the peripheral zone giving it a refractive index greater than that of the optical cladding, and giving it a difference in softening temperature relative to that of the core of the optical fiber which is less than the difference that would exist if the outer zone were not doped.

Abstract: Bent sol-gel produced tubing is straightened by drawing, with tensile force and operating temperature to result in minimal plastic flow, so that size reduction is small. The method is usefully applied to reject recovery in the preparation of overclad tubes, which as encompassing closely-fitting core rods, form the composite preform from which optical fiber is drawn.

Abstract: In a method for making optical fiber preforms, the time taken for sintering and annealing the clad or jacket layer is significantly reduced by only partially sintering the jacket soot boule in an atmosphere of helium. For example, instead of using one hundred forty-three minutes to sinter completely the soot boule, the boule is only partially sintered by heating in a helium atmosphere for fifty-nine minutes. At this stage of course, the soot boule is still partially porous and is generally opaque. The completion of the sintering and the annealing is then done in a single step in an atmosphere of nitrogen. Surprisingly, we have found that this process does not entrap nitrogen in the soot jacket layer to any noticeable or harmful extent, and the total time for sintering and annealing is significantly reduced.

Abstract: A method for producing a silica glass optical fiber, which comprises coating carbon on the optical fiber with the use of the remaining heat of not less than 800.degree. C. possessed by the optical fiber just after heat wire drawing, for thermal decomposition of a carbon coat-forming gas comprised of one or more members selected from the group of halogenated hydrocarbons, hydrocarbons, and halogen molecules, which has 5 to 15 hydrogen atoms per 10 halogen atoms, and a reaction apparatus for coating carbon, wherein the area of the outer end of an exhaust region is greater than the transverse sectional area of a coating region, and the outer end is outwardly opened.

Abstract: There is provided an apparatus for the production of a hermetically coated optical fiber in which a glass preform for an optical fiber is melt drawn in a melt drawing furnace to produce a bare optical fiber which is passed to a reactor where a feed gas is supplied and the bare optical fiber is coated with a thin carbon coating made from the feed gas by the Chemical Vapor Deposition method characterized in that the reactor comprises an upper portion to which the feed gas is supplied, a middle portion in which the CVD method is substantially carried out and a lower portion from which an exhausted gas is withdrawn, and a cross sectional area of the middle portion perpendicular to a longitudinal direction of the optical fiber is larger than that of the upper portion.