Why optical fibres are used?

∆∆Optical fibre links are being increasingly used for both short-distance communications, such as for local area networks (LANs), and long-distance communications. This arises from the fundamental advantages of optical f ibre communications:

• They are low cost.

• They are robust when packaged.

• They can have very wide optical bandwidths (GHz) and long communication links (hundreds of kilometres).

• They are insensitive to electromagnetic interference.

∆∆This has led to the wide range of intercontinental communication links which are several thousand kilometres long, which distance considerably exceeds the maximum length of optical fibre that can be manufactured. It also exceeds the maximum link length over which an optical signal can be propagated without periodic amplification or regeneration. The environment is also somewhat harsh and remote, requiring high reliability and robust packaging.

∆∆The highest frequency was of the order of 1000 GHz. If the frequency is increased to about 1015 Hz, we would find that the signal would literally appear as visible light. Signals in the range 1012–1015 Hz appear as infra-red light, whereas those in the range 1015–1017 Hz appear as ultraviolet light. This raises the question, if we can transmit data using the lower frequency ranges, why should we not communicate at the higher light frequencies? In fact, there is no reason why we should not, but there are difficulties in taking the light from a source to some form of receiving unit within which the carrier could be separated from the basic information signal. There are plenty of materials, such as glass, through which we can pass light. A glass fibre would make a simple conductor of light. The problem is to retain the light within the glass, but it is possible by simple conductor of light. The problem is to retain the light within the glass, but it is possible by simply placing the f ibre within a cladding.

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