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Fibre optics. Experimental equipment used to investigate data communication using fibre optic cables (green). Optical fibres are made from flexible glass that has a high refractive index. Each fibre is then coated with an outer protective layer that has a low refractive index. The light beams that emerge from the end of each fibre have been completely internally reflected. The light may travel along the entire cable with little absorption. Bundles of optical fibres may be used to carry images, or high volumes of data such as telephone conversations. Photographed in Germany. (KEYSTONE/SCIENCE PHOTO LIBRARY/MAXIMILIAN STOCK LTD)