Abstract: A process is disclosed for making a preform from which optical fibers may be drawn, comprising forming a tubular glass body having a hollow center and concentric layers, at least one layer being a doped layer, and each layer having different indices of refraction. A partial vacuum is formed within the interior of the tubular glass body, at least part of the glass body is softened by heating, and the softened portions of the tubular glass body are collapsed to form a preform. The pressure of the partial vacuum is selected to effectively eliminate a dip in the index of refraction of any glass fiber drawn from the preform.

Abstract: A process is disclosed for producing an optical fiber comprising forming a tubular glass body having at least one doped layer, at least one concentric layer, each layer having a different index of refraction, and a hollow center. The glass body is heated until the softening point is reached, and is then drawn into a glass fiber. During drawing, a partial vacuum is maintained in the hollow center of the tubular glass body, the partial vacuum being of sufficient magnitude to reduce the evaporation of doping material from the interior of the tubular glass body and thereby effectively prevent a reduction in the index of refraction in the center of the optical fiber.

Abstract: In order to produce an optical cable core composed of a plurality of optical cable elements stranded together, each element is produced by longitudinally slitting a stable tube, inserting at least one optical fiber into the tube through the slit, and causing the slit to close behind the fiber so that the fiber lies loosely in the tube, and the resulting elements are then stranded together to form the core.

Abstract: A fiber light conductor housed in a hollow tubular sheath with the conductor being given an undulating configuration in order to minimize the adverse influence thereon of mechanical stresses and external forces.