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Telecommunication
Optical fibres are now the standard point to point cable link between telephone substations.
Local Area Networks (LAN's)
Multimode fibre is commonly used as the "backbone" to carry signals between the hubs of LAN's from
where copper coaxial cable takes the data to the desktop. Fibre links to the desktop, however, are
also common.
Cable TV
As mentioned above domestic cable TV networks use optical fibre because of its very low power
consumption.
CCTV
Closed circuit television security systems use optical fibre because of its inherent security, as well as
the other advantages mentioned above.
Optical Fibre Sensors
Many advances have been made in recent years in the use of Optical Fibres as sensors. Gas
concentration, chemical concentration, pressure, temperature, and rate of rotation can all be sensed
using optical fibre. Much work in this field is being done at the University of Strathclyde [3].
2.3.2 Technology
An optical fibre is a cylindrical dielectric waveguide made of low-loss materials such as silica glass. It
has a central core, in which the light is guided, embedded in an outer cladding of slightly lower
refractive index. Light rays incident on the core-cladding boundary at angles greater than the critical
angle undergo total internal reflection and are guided through the core without refraction. Rays of
greater inclination to the fibre axis lose part of their power into the cladding at each reflection and are
not guided.
There are three main kinds of fibre optics, the most simple being the ‘step index’ where the light is
bounced along the length of the fibre from one side to the other. Two materials with different densities
are needed, the less dense being used as coating. In this method, the light travels in zig-zag motion
and thus transmission of information can take some time. Another way of producing fibre optics
involves the ‘graded index’ fibre which also relies on materials with different densities. The variation
occurs in the centre of the fibre causing the light to bounce, but in a smoother and more gradual curve.
The sharpest and most direct transmission of light travelling in a straight line is achieved by applying a
synthetic fibre possessing a very narrow inner core, almost in the width of the actual path of light. The
Japanese company Mitsubishi Rayon was one of the first companies that were active in developing
plastic fibre optics for illumination in the 1990ties [5].
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