A hydrolyzing flame technique is used to build up glass soots of at least two different compositions upon a rotating starting member. The process is repeated until the soots define at least one helically-oriented body of soot of one composition completely enveloped by a soot of a second composition. The soot-covered starting member is then subjected to heat to fuse it whereupon the soots are fused into compositions exhibiting different indices of refraction. The member can then be drawn into a elongate structure comprising an optical waveguide extending helically through the body of the structure.