Fibre Optics & Endoscopy

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Optical Fibres

Optical fibres transmit light by total internal reflection.

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  • Each fibre has a core of optically dense material that is covered by a layer of cladding with a much lower optical density.
  • This means that the boundary between the two materials has a very small critical angle.
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Small critical angle

  • Only light approaching the boundary at an angle that is very close to the normal (90 degrees to the boundary) will cross the boundary and be refracted (this light is lost).
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Long distances

  • Most of the light will be totally internally reflected and continue to travel through the core.
  • In this way, optical fibres can transmit light over very long distances.


When bundles of optical fibres are used together they can be used as a medical tool called an endoscope.

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  • Bundles of fibres can be used to transmit an image without a lens.
  • The output of this is called an endoscope.
  • Endoscopes are used to explore the body by insertion through the mouth, nose or small cuts.
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Medical use

  • Light is transmitted down one fibre bundle to illuminate internal parts, and the reflected light is transmitted back out through another to be observed.
  • Surgery can be performed by attaching cutting tools to an endoscope.
  • Internal bleeding can also be stopped by using the light from the endoscope to cauterize a bleed.

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