Optical signals transmitted through cladded glass fibers are subject to delay distortion because of (1) dispersion in the material, (2) dispersion caused by the waveguide characteristic, and (3) delay differences between modes. We isolate these effects and evaluate their significance for cases of practical interest. These concern fibers in which the refractive index of the cladding is only slightly lower than that of the core.
D. Gloge, "Dispersion in Weakly Guiding Fibers," Appl. Opt. 10, 2442-2445 (1971)