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Fibre Optics

  Fibre optic cables are manufactured from glass or transparent plastic and used to transmit light and optical images. This medium of transmission may be used to transmit digital data over long distances avoiding the need for expensive copper electrical cables.

Fibre optic cable works on the principle of total internal reflection of light. This principle was first understood in the 1870s, but major developments in this field have occurred since the 1950s. Light enters at one end of the cable and has multiple reflections from one side of the cable to the other until the light appears at the far end. For transfer of sound or information the light is encoded in a series of binary pulses (1 or 0) and is then decoded at the receiving end. If the light is to travel long distances, repeaters are used to boost the signal at regular intervals.

The first experimentation with light with a transmission medium began with scientists trying to send light down long hollow pipes, which had mirrors and lenses to guide the light straight down the pipe. The pipes were then buried for protection. This method worked well as long as the pipes were not disturbed, but failed as soon as the pipes were bent. Fibre optic cables overcame this problem in allowing light to travel down its length without the need for mirrors or lenses. In fact, fibre optic cables can be bent into any shape required, even around sharp corners.

Fibre optics are used widely in medicine to transmit images of the internal organs to a camera outside, so eliminating the need for exploratory surgery. Even if surgery is required (for example, removal of cartilage), fibre optics can reduce the severity of the operation. Only small incisions need to be made and armed with a fibre optic cable attached to a camera and a laser or small shears or scalpels operated by slender cables passing down the tube, the surgeon may cut or sew cartilage together. Thus the patient may be remobilized in days instead of weeks.

The advantages of fibre optic transmission systems include, weight and cost reduction, much improved signal to noise ratio and the use of lower cost materials. AA

Further reading N.S. Kapany, Fibre Optics: Principles and Applications.



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