| Popis: |
Optical fibres have been developed to a high degree of sophistication for long-distance transmission. Compared with coaxial cables which have a bandwidth of 20MHz or so over distances of 3 to 5km, optical fibres can have almost infinite bandwidth and repeater spacings of several hundred kilometres. They are also small, light in weight, flexible and free from electromagnetic interference. It is not surprising, therefore, that optical fibres have already revolutionised telephone and data networks and are being rapidly installed in most countries of the world. Nevertheless, in normal communications terms optical fibre communications is in a very primitive stage of development. The only operation that can be performed is that of transmitting optical information from one point to another. In order to process the information it must be converted back to electrical form and operated on in complex electronic circuits. The information then has to be reconverted to the optical wavelength. Such methods of signal amplification are complex and expensive.The next stage of optical fibre communication will require fibre components in both passive and active form. Passive components such as couplers, switches and isolators are now becoming available commercially and research leading to active fibre devices is showing considerable promise. |
