For this fiber the refractive index of the core is constant (see Fig 5). Since refractive index profile looks like a pulse or step, this kind of fiber is called the STEP INDEX FIBER. This structure is useful for analyzing propagation of light inside an optical fiber. Generally it is not used in practice because data transfer rate in this fiber is the lowest.
Just as a small exercise we can ask, what kind of pulse broadening occurs in a step index fiber if we do not use cladding?
Let us take 1Km of the optical fiber.
Since  and  ,
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