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A representation of waves of light moving in three dimensions
A representation of waves of light moving in three dimensions
A photonic crystal fibre with an air core at the centre
A photonic crystal fibre with an air core at the centre

Press Release - 07 July 2005

How does the photonic crystal fibre trap light?

Although light is made up of photons, it travels in waves. Imagine a flat pond into which you drop a pebble. A wave will spread out from the place where the pebble hits the water. If you drop a series of pebbles into the water, a series of waves will spread out.

Light also moves (though three-dimensionally) as a series of waves, and the gap between each wave is called a wavelength. We can’t see the actual wavelengths because they are too small for the eye to pick up – around one ten thousandth of a millimetre.

However, we perceive different wavelengths as different colours – blue light has a shorter wavelength than red light, for instance; white light is a mixture of all visible light.

Ultraviolet has a shorter wavelength than blue light (which our eyes cannot pick up) and infra-red has a longer wavelength (which again is invisible to our eyes). X-rays, gamma rays, microwaves and radio waves are all examples of light waves which we cannot see because the wavelength is either too long or short for our eyes. Together, these waves are all made up of electromagnetic radiation, part of which is visible light.

With the photonic crystal fibre, the central hole in the fibre is large enough to allow light of some wavelengths in, and once inside the larger central hole, the surrounding smaller holes prevent this light from leaking out.

This is because they are so small that their size is close to the wavelength of light. The laws of physics prevent light from entering such a small gap, and so it cannot escape out of the central hole. This traps light in the central hole and it can only travel one way – down the hole itself to the end of the fibre.


For more information on photonics, click the links on the left hand column of this page.

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