Abstract: In a method for producing optical glass fibers which comprises co-spinning glass melts of different kinds through coaxially disposed discharge nozzles of a multimember crucible composed of two or more crucible members having a discharge nozzle at their bottom, the improvement wherein the outermost nozzle has a length of at least 30 mm and is heated so that at least a part of it is maintained at a temperature equal to, or higher than, the temperature of the crucible thereby to increase the speed of spinning; and a high-speed spinning furnace used therefor.

Abstract: By heat treating a glass member containing at least one kind of cation to constitute a modifying oxide in contact with a source of another kind of cation to cause ion substitution, a light-conducting glass structure can be produced to have a refractive index distribution wherein the index varies progressively transversely to the intended light path, which is thereby bent toward the direction of increase of the index, such a light-conducting glass structure is not accompanied by differences or lagging of phase velocities of conducted light rays, spreading of the light flux width, and reflection losses.