The Online Library of Knowledge

Media and communications

Fibre optics

Bundles of optical fibresBundles of optical fibres 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.

Labels in an optical fibreLabels in an optical fibre

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.


Diagram of light travelling through a fibreDiagram of light travelling through a fibreAs 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.

The inventor of the telephone, Alexander Graham Bell, built a device called a Photophone, which could send a voice signal on a beam of light in 1880. It relied on sunlight being focused on to a mirror, but a cloudy day stopped it from working.

© 2019 Q-files Ltd. All rights reserved. Switch to Mobile