Communicating with light – fibre optics
Glossary
ASCII. This acronym (pronounced asky) stands for American Standard Code for Information Interchange. It is an alphanumeric code commonly used in computers to represent letters, numerals and symbols.
ASCII uses a 7-bit code which produces 128 different combinations to represent different symbols. The decimal numbers 0 to 47 code for symbols and computer commands. Decimal numbers 48 to 57 code for the numerals (0-9), decimal numbers 65 to 90 code for capital letters (A-Z), and decimal numbers 97 to 122 code for lower case letters (a-z). For example, in a computer using the ASCII code, 'A' is represented by the decimal number 65. The computer 'reads' this as the binary number 01000001 and encodes the letter A.
Most computers use an 8-bit code (extended ASCII) which produces 256 different combinations to represent symbols. In addition to the regular character set represented by ASCII (in the decimal range from 0 to 127), extended ASCII has an additional 128 codes that can be used to represent additional symbols (eg, non-English characters or graphical symbols).
For more information see ASCII – What is it and why should I care? (Tela Communications, USA).
binary code. A digital coding system that uses a sequence of only two types of symbols (eg, 0 and 1) to represent data. The two symbols are called bits (an abreviation for binary digits). For more information see How bits and bytes work (How Stuff Works, USA).
bit. Binary digit. The smallest unit of information in a digital system. A bit can be 0 or 1. For more information see How bits and bytes work (How Stuff Works, USA).
digital codes (digital system of codes). Information that is represented as a series of discrete digits (numbers).
distortion. An undesired change in the shape of an electrical wave or signal. Distortion results in the loss of clarity in reception or reproduction, or even the loss of information in a digital system.
fibre optics (fibre optic communications). The transmission of information by the passage of light through flexible, glass fibres. Electrical impulses are converted into light which is then transmitted through the optical fibre. The light is then re-converted into electrical impulses at its destination.
inverse square law of radiation. States that illumination at a point varies inversely as the square of the distance from the light source.
If you halve the distance from a radiation source (such as a light, a fire, or a radio transmitter) you multiply by four the intensity of the radiation. This means that if you hold your hand 1 metre away from a light, then move your hand halfway towards the light (so it is just 50 centimetres away), there will be not double but four times as much light reaching your hand. If you halve the distance again to just 25 centimetres there will be sixteen times as much light reaching you hand compared to when it was 1 metre away. The same thing happens with radiated heat – which is why if you sit with your feet pointing at a camp fire, your feet can feel very hot while your chest is cool. Or, why a heat source strong enough to make metal glow red, may feel only pleasantly warm a short distance away.
laser. Light amplification by stimulated emission of radiation. A device that produces a high-intensity, directional, monochromatic beam of light.
light-sensitive cell. A device having a photoelectric property such as the ability to generate a current or change its electrical resistance when exposed to light.
modem. Modulator/demodulator. A device connected between a computer and a telephone line. It consists of a modulator that converts digital computer signals into audio signals for transmission over the telephone line and a corresponding demodulator to convert the incoming audio signals into digital form.
optical fibre. A glass thread that acts as a guide for lightwaves. Fibres used in telecommunications usually have a cladding of glass of a lower refractive index. In a communication system, several fibres are made up into a cable.
photoreceptor. A light-sensitive cell.
retina. The light-sensitive cell layers of the inner lining of the back of the eye.
telecommunications. The communication of information over a distance by means of radio waves, optical signals or along a transmission line.
trellis-coded modulation. A coding system used for high speed, reliable data transmission over telephone lines.
virtual reality. An artificial environment created by computers, in which people can immerse themselves and feel that this artificial reality really does exist. For more information see Virtual reality (Whatis.com, USA).
Page updated August 2006.