<P> In fiber optics, a graded index is an optical fiber whose core has a refractive index that decreases with increasing radial distance from the optical axis of the fiber . </P> <P> Because parts of the core closer to the fiber axis have a higher refractive index than the parts near the cladding, light rays follow sinusoidal paths down the fiber . The most common refractive index profile for a graded - index fiber is very nearly parabolic . The parabolic profile results in continual refocusing of the rays in the core, and minimizes modal dispersion . </P> <P> Multi-mode optical fiber can be built with either graded index or step index . The advantage of the multi-mode graded index compared to the multi-mode step index is the considerable decrease in modal dispersion . Modal dispersion can be further decreased by selecting a smaller core size (less than 5 - 10μm) and forming a single mode step index fiber . </P>

The performance characteristics of multimode graded index fibers are