Page 56 - Curriculum Visions Dynamic Book

(Above) Carbon fibre matting.
The sources of light are either light-emitting diodes (LEDs) or transistor lasers.
Optical fibres are immune to the interference that electrical signals suffer from, and so they are the preferred way of sending digital information. Optical cables are also thinner and lighter than the equivalent electric wires. Most of the main trunk communication links for a national telephone system are now optical rather than electrical. A standard optical cable can send 2.4 gigabits (thousand million) per second per fibre (but the data rate is increasing year by year). A booster is only needed to strengthen the light every 30 km or so. They are entirely optical amplifiers using the element erbium and no electronic components at all.
Visible light is only sent along fibre optic cables for short-distance work such as for medical examination of the body. In this case some of the fibres are used as an elongated lens, while others act as a way of getting illuminated light to the point to be investigated.
Carbon fibres
Although glass, like most synthetic fibres, is an insulator, carbon is a conductor of electricity. All natural and synthetic fibres contain carbon in their structure, but carbon fibres are made almost exclusively of carbon atoms.
When carbon atoms are made into fibres, they can
be very strong. The method of production is important in giving carbon fibres their distinctive qualities of flexibility and strength.
Carbon fibres are used like glass fibres to reinforce resins in composite materials. But they can also be made very flexible and given a soft feel so that they can be made into fabrics.
The qualities of a carbon fibre depend on the carbon content (even though all carbon fibres contain more than 90% carbon) and the way the carbon is made into layered sheets within the fibre.
Carbon fibres cannot be made directly from a carbon “solution.” Pure carbon is a solid. To make carbon fibres, therefore, the carbon is incorporated in some other fibre and extruded as a filament. The filament is then heated to cause it
56