Optic fibres and total internal reflection

1. Optic fibres and total internal reflection Senior Science Information Systems Elwell

2. OPTICAL FIBRES • Optical fibres are thin, transparent fibres of glass that transmit light throughout their length by internal reflection. • Fibre optic cables are made out of very pure glass, glass so pure that if it were kilometres thick, the glass would still appear perfectly transparent. • The fibre optic strand, although thin in diameter, is stretched to kilometres in length. Therefore only the purest of glass would be efficient and useful for sending light signals.

3. Inside an optical fibre

4. OPTICAL FIBRES – HOW LIGHT TRAVELS • The glass of these fibre optic cables is drawn into a very thin strand (as thin as human hair), then it is coated in two layers of plastic. By coating the glass in plastic (this is called the cladding), a “mirror” is created around the glass. • This creates a total internal reflection. In other words, when light is passed through the cable, the light will reflect off the interior surface of the cable, and continue to bounce off the reflective surface until it reaches the opening at the other end. • Light travels through the fibre optic cable and bounces off at shallow angles, and stays completely within the glass fibre.

5. outline the differences and the relative merits in the use of fibre optic cables and metal cables to transmit and receive information • Fibre optic cables have the following advantages when compared to wire based (or radio wave based) systems: • have a much greater bandwidth than metal cables. This means that they can carry more data per second, e.g. can transmit several gigabytes of data per second. • are not affected by radio waves, so there is no static • are much thinner and lighter than metal wires • are less susceptible to corrosion than metal cables • can handle digitally coded light (the natural form for computer data), as well as analog signals • can multiplex thousands of voice channels together over a single optical fibre • more secure as information cannot be intercepted easily. • The main disadvantage of fibre optics is that the cables are expensive to install. In addition, they are more fragile than wire and must be spliced together precisely and carefully. • Repeaters need to be added every 55-65 kilometres to boost the signal strength. • A fibre optic system is a particularly popular technology for local area networks. In addition, telephone companies are steadily replacing traditional metallic telephone lines with fibre optic cables. • http://www.abc.net.au/news/stories/2010/06/20/2931852.htm

6. Total internal Reflection

7. Total internal Reflection

8. Total internal reflection http://www.youtube.com/watch?v=PrEF9UN98cE