An optical fiber with a continually varying index of refraction. The index starts large along the center axis of the fiber and gradually decreases as light travels toward the perimeter of the fiber. This graded index smoothly guides light toward the center axis of the fiber. The fibers discussed in this module are of the simpler step-index construction.

An optics fiber whose core has a nonuniform index of refraction. The core is composed on concentric rings if glass whose refractive indices decrease from the center axis. The purpose is to reduce model dispersion and thereby increase fiber bandwidth.

Optical fibers have a cylindrical core and are surrounded by cladding. The refractive index of the core is always higher than that of the cladding to guide the light wave. If the refractive index of the core varies with the core radius (i.e., index gradually decreases from the center of the core to the outer radius) it is a graded-index (GRIN) fiber. Light travels along the fiber in a curved trajectory, always being refracted back towards the axis of the fiber.