Fibre-optic communication is a way of sending information—data, telephone calls and television signals—with pulses of light through an optical fibre. The light forms a wave that is modulated (shaped) to carry information, just like a radio wave is modulated to make a signal that represents sound. The first live telephone calls to be sent through a fibre-optic system were made in 1977 in Chicago, USA.

Optical fibres

An optical fibre is a flexible thread of transparent silica (glass) or plastic. It is about the same thickness of a human hair. It consists of a central core, surrounded by cladding and, outside that, a protective outer coating called a buffer. The light travels through the core by being reflected backwards and forwards between the core and cladding. This process is called total internal reflection.
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As the light beam travels, its intensity, and thus the strength of its signal, becomes less and less. This is called attenuation, or transmission loss. This diagram shows beams of light travelling through the core of an optical fibre, reflecting backwards and forwards.

Advantages

Optical fibres have great advantages over copper wires because signals travelling along fibres lose their strength (attenuate) far more gradually. They also do not suffer from interference from other electromagnetic waves. Because of this, optical fibres are used in most long-distance and important communication networks, such as undersea communications cables. The fibres can also carry a very high amount of information: a single, broadband optical fibre cable can replace thousands of copper wires.