Explain The Term "Optical Fibres" And How They Work On Total Internal Reflection

Optical fiber (or "fiber optic") refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic strand or fiber. Optical fiber carries much more information than conventional copper wire and is in general not subject to electromagnetic interference and the need to retransmit signals. Most telephone company long-distance lines are now made of optical fiber.

Total Internal Reflection:

When light is incident from a denser to rarer medium the ray deviates away from the normal. For a certain angle of incidence (i = ic) the angle of refraction becomes 900. This angle of incidence is called the critical angle. Any ray with incident angle greater than this critical angle will be completely reflected back to the denser medium (see fig). This phenomenon is called Total Internal Reflection.

Optical fiber:

Optical fibers are made of glass. These are glass fibers. Now for fiber optic communication glass fibers are simply not enough they have to be specially built for total internal reflection (TIR). To achieve TIR the optical fiber is given an outer layer having a lower refractive index called cladding and the central part of the glass fibre is called core.

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It  is a flexible, transparent fiber made of glass (silica) or plastic, slightly thicker than a human hair.

How they work on "Total Internal Reflection" :-

When light traveling in an optically dense medium hits a boundary at a steep angle (larger than the critical angle for the boundary), the light will be completely reflected. This is called total internal reflection. This effect is used in optical fibers to confine light in the core. Light travels through the fiber core, bouncing back and forth off the boundary between the core and cladding. Because the light must strike the boundary with an angle greater than the critical angle, only light that enters the fiber within a certain range of angles can travel down the fiber without leaking out. This range of angles is called the acceptance cone of the fiber. The size of this acceptance cone is a function of the refractive index difference between the fiber's core and cladding.


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