Noncircular symmetric optical fiber waveguide having minimum modal dispersion

An optical fiber waveguide comprising a core surrounded by a layer of cladding material, the refractive index of said layer n.sub.c being less than n.sub.o the value of the index of refraction at the center of the core, and the index of refraction n in said core is graded in accordance with the following equation:

• n.sup.2 = n.sub.o.sup.2 (1-N)
• where N is the relative phase index equal to 0 at the center of said core and equal to 2.DELTA. at the core-cladding interface, .DELTA. being equal to 1/2(1-n.sub.c.sup.2 /n.sub.o.sup.2), characterized in that the relative index N has values at the coordinates x and y with respect to the core center given by the following equation:
• ##EQU12## where h(x,y) is any arbitrary homogeneous function of degree 2 in x and y other than a multiple of (x.sup.2 + y.sup.2), and N is a relative group index approximately given in terms of N by the following equation:
• N = [N + (S.sub.o -S)/n.sub.o.sup.2 ]/(1+S.sub.o /n.sub.o.sup.2),
• S being equal to [-(1/2)dn.sup.2 /d.lambda.] which is determined by measurements on the materials to be used to obtain the various values of n within the core, and S.sub.o is the value of S at the core center.