Synopsis: The graded-index(GRIN)fiber has a core material whose reflective index varies with distance from the fiber axis. The light waves in a GRIN travel through the fiber in the ocillatory fashion of the above figure. The changing refractive index causes the rays to be continually redirected toward the fiber axis.

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Synopsis: The continuous change in the refractive index of the GRIN fiber can be illustrated by a series of small refractive step changes. The above figure demostrates this behavior. Many GRIN fibers resemble this step model because their cores are fabricated in layers. The bending of the rays at each small step follows Snell's law. A ray crossing the fiber axis strikes a series of boundaries,each time traveling into a region of lower refractive index,and thus bending farther toward the horizontal axis. At one of the boundaries away from the axis, the ray angle exceeds the critical angle and is totally reflected back toward the fiber axis. Now the ray goes from high to low refractive index media, thus bending toward the normal until it crosses the fiber axis. At this point, the procedure will repeat. In this manner, the fiber traps a ray, causing it to oscillate back and forth as it propogates down the fiber.

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GRIN Fiber

Synopsis: A chararacteristic of the GRIN fiber is the fact that the order of the wave is irrelevant to the distance it travels. In the above animation this phenomenon is shown, the ray that travels directly along the axis reaches the end of the fiber at the same time as the higher order ray .