  Optical fibres are fibres of glass, about a few tenths of a millimetre in diameter, which are used to carry signals in the form of pulses of light, over distances up to 50 km. These signals may be coded voice communications or computer data. 
The glass fibre is surrounded by plastic cladding, which has a lower index of refraction than the glass. Any light rays sent down the inner glass fibre will either reflect off the outer surface of the glass, or refract back into the glass when they try to escape into the cladding  Sending light signals this way has many uses. Wherever electrical signals are used in copper wire, fibre optics can be used instead. Many more signals can be sent at the same time this way, and there is less loss of energy. Light moving through glass fibres is also less subject to distortion from outside sources (like vehicle ignitions) than electrons moving through copper wire. Optical fibre cables are much lighter and thinner than copper cables. This means that much less space is required in underground cabling ducts. They are also easier to handle. Optical fibres are much more difficult to tap information from undetected ... a great advantage for banks and security installations. They can be used safely in explosive or flammable atmospheres.  Optical fibres are more expensive per metre than copper wire. However, one fibre can carry many more signals than a single copper cable, and the large transmission distances mean that fewer expensive power boosters are required. Optical fibres cannot be joined (spliced) together as a easily as copper cable, so people who work with them require special training and expensive precision splicing equipment. Optical fibres are commonly used in surgery to relay images from tiny cameras inserted in patients' bodies. They are used in communication cables for telephone and high-speed Internet connections, and for cable TV. |