Abstract: This application discloses a technique for producing optical fibers with longitudinal variations in index of refraction. The deposition apparatus is arranged to allow for the formation of an intertwined double helix of two different materials. The technique does not require imposing any time dependent conditions on the fabrication apparatus.

Abstract: A light guide is produced by the out-diffusion of boron oxide through a free surface of a uniform borosilicate mass. The resulting structure consists of increased index silica rich regions near the surface in contact with lower index regions of a composition approaching that of the unmodified borosilicate. The out-diffusion process, generally carried out at a temperature approaching the softening point of the glass, may be applied to a borosilicate tube to result in a fiber preform. Fibers drawn from such a preform may be characterized by a silica core region, a borosilicate clad region, and a silica outer shell. Use of the procedure results in a graded index structure.