Principles of the transmission by optical fiber

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Video: Optical fiber manufacture

The optical fiber is just a light conductor. The light is catched in this conduit and possible speed throughout the same one propagates to the Maxima. The speed of propagation of the light depends on the type of material used transparency, since the Maxima speed c = 299.792.458 m/s is only reached in the emptiness. In the rest of means the propagation takes place at smaller speed, the relation between the speed of the light in the emptiness and in another means, it is known as refractive index of means and is characteristic of each material.

The physical reason by which the light is catched within the conduit, is based on the reflection laws and refraction of the light, according to which, when a ray crosses the border from an average transparent physicist to another one also is transparent, but where the speed of propagation is smaller, the trajectory of the same one varies, following a well-known physical law like Law of Snell.

This it is the reason that when a wood in the water puts, this one seems to bend.

$Refraction of the light when happening form means to another one with different index of refraction: n2>n1$

More concretely the optical phenomenon on which the transmission of the light in the fiber glass conduit is based denominates TIR (Total Internal Reflection), according to which, when a light ray happens of means towards another one with smaller refractive index, if it affects the border of the materials with a determined angle, does not pass no light through the border of the material. The angle from which the light ray is catched totally denominates critical angle of incidence.

The scheme following sample the critical angle of incidence in red.

$The The more great it is the normal angle to, the more the small one is the fraction of transmitted light until it is arrived at ántgulo in that it happens total the internal reflection.The color of rays is for helping to distinguish rays and it does not stop to indicate no dependency of the color$

Reflection of the light in the optical fiber

The optical fiber cables are constructed being based on that principle. Let us see a graphical example:

n nucleus > n coating > n air
Ray 1 is reflected partially because also it is refracted
Ray 2 is reflected totally

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22-1-2008

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