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Definition: graded-index fiber

A multimode optical fiber in which the refractive index of the core declines from its highest value at the center of the core to a value at the edge of the core that equals the refractive index of the cladding. This design compensates for modal dispersion by allowing light rays in the outer zones of the core to travel faster than those in the center of core. It is typically used for transmitting distances of a couple of kilometers. Standard graded-index fibers typically have a core diameter of 50 or 62.5 µm and a cladding diameter of 125 µm. See step-index fiber and dispersion-shifted fiber.