Optical fibres are used extensively in the field of telecommunications and medicine. In the telecommunication field they are used as an alternative signal carrier to copper wires in the telephone system. They are used to carrier digital signals in the form of light pulses over long distances.
An optical fibre consists of a very thin core of high purity glass. The core is covered by a second layer (cladding) also made from high purity glass. The cladding is less dense than the core and has a lower refractive index. Remember, for total internal reflection to occur the light rays must travel from a dense medium to a less dense medium. Thus light rays passing along the core at an angle greater than the critical angle are totally internally reflected. The surface of the high purity glass core acts like a perfect mirror and the light ray is continuously reflected along the length of the optical fibre core. The cladding is covered with a protective plastic buffer coating.
Advantages of Optical Fibres
Optical fibres are less expensive than copper wires.
Optical fibres are thinner than copper wires allowing more fibres to be bundled together in a given cable diameter. This allows for more information be it telephone conversations or television channels to be passed through the cable.
Electrical signals in copper wires interfere with other copper wires bundled in the same cable. As optical fibres carry light signals there is no interference between fibres bundled in the same cable resulting in a clearer signal.
Due to little degradation of the optical fibre signal the signal only needs to be boosted after long distances approximately 100km whereas for cooper cables this needs to be done a lot more often after approximately 8km. Thus optical fibres require less power for transmission.