Abstract: A granular body, from which an article having a nonuniform refractive index may be formed, has grains of two substances which have different refractive indicies in a geometric distribution in the granular body corresponding to the geometric distribution of the substances required for the nonuniform refractive index of the article and a way of shape-stabilizing the granular body. A method of making the granular body comprises controllably feeding the grains into the geometric distribution in the granular body and shape-stabilizing it. Preferably the granular body is compressed into a porous compact which holds itself together and is treated with a gas to achieve desired optic properties in the article.

Abstract: Disclosed is a method for the axial building up, in a vertical arrangement, of a hollow cylindrical soot body having no internal support and consisting substantially of silicon dioxide by means of at least one flame hydrolysis build-up burner serving for the soot production. In this method the soot is deposited at the beginning of the build-up onto an auxiliary body, and during the build-up the build-up burner and the growing soot body are rotated relative to one another, and the burner is at the same time held at an unvarying distance from the growing end of the hollow cylinder and centrally above the predetermined cross section of the upwardly growing end of the cylinder wall. The penetration of soot into the interior of the cylinder is prevented by means of a directed gas stream.

Abstract: In an optical fiber having a core whose material consists essentially of vitreous silica, said core having a jacket of plastic which is optically effective at least on a length of 10 m reckoned from the light input end of the fiber and which has a refractive index n.sub.M which is smaller than that of the core, the improvement wherein the core has an outer layer whose refractive index n.sub.ext is smaller than the refractive index n.sub.K of the remaining inner core portion which is constant and greater than the refractive index n.sub.M of the jacket, and n.sub.ext lies in the range from n.sub.K -(n.sub.K -n.sub.M). (0.25 to 0.8) and whose thickness amounts to between 0.8 .mu.m and 8 .mu.m.