Multimode fibers

FTTH >> Technology >> Principles of the transmission by optical fiber


They are fibers that allow the passage of several beams of light (ways) through the nucleus, which they are reflected with different angles within the nucleus. Its reach is limited constructions with little distance among them. This type of fibers has a nucleus (Core) with a diameter much greater than the one of fibers monoway. Within fibers multiway, two main types, those of stepped index and those of gradual index exist, that allows a superior reach slightly.

In fibers of staggered index, several different waves or ways through the fiber propagate.

Total internal reflection in the multimode fiber

Very intuitively one sees that the waves that are reflected, cross much greater distance than those than they propagate by the nucleus without being reflected. This gives rise to a phenomenon, known like dispersion that produces attenuation of the transmitted signal. This phenomenon is inevitable in the optical fiber multiway and is the ocasionante of which the length of these fibers cannot be as great as the one of fibers monoway.

In fibers of gradual index, the refractive index of the nucleus decreases from the center towards the coating. This causes that the dispersion is reduced, since the beams arrive almost at the same time, since near the coating, the rays propagate more quickly than in the nucleus.

Index graduated in the multimode fiber

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