ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
Fibre optic communications. A cable containing optical fibres used to transmit telephone signals. The fibre optic filaments are seen at top right; the rest of the cable is shielding and protective layers. The fibres are made from a special glass which is flexible and has a high refractive index. Each filament is then coated with a protective layer with a low refractive index. A light beam entering the end of the fibre is completely internally reflected at the cylindrical surface of the core. The light may thus travel along the entire cable with little or no absorption. The telephone conversations are carried as pulsed, coded laser signals.
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