INDEPTH: NORTEL
What is Fibre Optics?
CBC News Online | April 28, 2004
First came the telegraph, then the telephone, then the computer, and with each new invention our hunger for information-at-the-blink-of-an-eye grew ten-fold. And we're still not satisfied.
Luckily, fibre optics promises to feed our need for information technology that's even faster than what we use today.
Fibre optics is the technique that uses optical fibres – transparent rods of glass or plastic that are stretched to be long, thin and flexible – to transmit data in the form of pulses of light.
Put simply, using fibre optics to communicate can be compared to writing a letter. To write a letter, you need three things: something to write (words), something to write with (a pen) and something to write on (paper). Fibre optics is the same except that the materials are different. Instead of using a pen to write words on paper, fiber optics uses lasers to pass coded light pulses along a network of optical fibres.
Transmitting data as light
Practically any light source, from a matchstick to a blowtorch, could be used to create the light pulses needed to make fibre optics work. However, lasers are used because they can produce many tightly-focused pulses of light per second.
These pulses are shot into one end of the optical fibres and travel down their length by internal reflections. In other words, the light bounces off the inside of the cladding – the lining that covers the fibres – until it reaches the other end.
The light travels incredibly fast – about 300,000 kilometres per second – which means information can go from one end of the Earth to the other almost instantly.
Testing 001 010 011
Like computers, fibre optics uses binary coding to translate data into light and vice versa. Binary codes are those series of "0's" and "1's" that sometimes pop up on your monitor when your computer goes haywire. They represent the letters, numbers and other symbols on your keyboard.
A single-digit binary code, consisting of only two combinations (1 and 0), could be used for responses to simple questions – 1 using the 1 to represent "yes" and the 0 represent "no." A code with two digts has twice as many combinations (00, 01, 10 and 11). In fact, every time another digit is added, the number of symbols the code can represent doubles. This is why computer programmers prefer codes with many digits.
The American Standard Code for Information Interchange, ASCII, for example, uses a code with seven digits. A 7-bit binary code has exactly 128 combinations. ASCII uses the first 48 combinations to represent symbols and computer commands, 10 more to code for the numerals 0-9, and another 52 to code for the letters of the alphabet (both upper and lower case). Six combinations are left unused. The letter A, for instance, is represented as the binary number 01000001, with the eighth digit acting as a check.
Writing in binary code using light works like Morse code, except that instead of having people at the other end deciphering the coded messages, there are receivers that convert the light back into electrical signals that are fed into a computer. Sound is tranmitted by first translating it into digital signals which are then encoded into light.
Two centuries of optical communications
Although what we consider today to be fibre optics has largely developed out of research done since the 1970s, the history of optical communications systems began more than 200 years ago.
In the 1790s, a French engineer named Claude Chappe built the first working optical telegraph – a column with a moveable crosswise beam that had two moveable arms. The devices were mounted on a network of towers so they could be seen from great distances. Operators relayed messages by changing the position of the arms, which represented letters, numbers and punctuation. The operators at the next tower read the message and passed it along. On a clear day, a message could be sent between Paris and Lille in less than ten minutes, a task that would take a courier 30 hours to complete.
With Napolean's support, the network grew to include more than 500 stations that connected 30 French cities with Paris. Russia, Australia, the U.S. and many eastern European countries constructed similar networks. In the 1840s, France replaced the optical telegraph with the electric telegraph.
In 1880, Alexander Graham Bell, already famous for inventing the telephone, patented a device he called the photophone, an optical telephone system that transmitted sound using a beam of light. But the photophone was no match for Bell's earlier invention because light signals became distorted after passing through the atmosphere.
About 40 years later, two inventors, British-born John Logie Baird and American Clarence W. Hansell, patented the idea of using arrays of transparent rods to transmit images. But it took Henrich Lamm, a medical student in Germany, to send the first image through a bundle of optical fibres. Because of the rise of the Nazi regime, Lamm had to flee to the U.S. and leave his work on optical communications behind.
Then in 1954, the study of fibre optics got its biggest boost ever when two groups of scientists announced they had made imaging bundles. Harold H. Hopkins and Narinder Kapany in London and Abraham van Heel in Holland published separate reports in the British science journal Nature. Their work was nothing compared to today's fibre optics, but the reports set the foundation for the explosion of work in the field since.
The ups and downs of fibre
Fibre optics is truly a step up from its predecessor, the metal wire traditionally used for phone lines and television cable.
The biggest difference is that optical fibres have a much greater bandwidth – the amount of information that a fibre can carry. The larger bandwidth means optical fibres can tranmit information over longer distances and in less time than copper cable. For instance all 32 volumes of the Encyclopedia Britannica can be sent through an optical connection in less than one second.
The large bandwidth also makes it possible to send more channels of information over the same line. The fastest fibre optics circuits are said to be able to transmit 250 television channels or thousands of telephone conversations at once. And fibre optics lines require fewer repeaters, the devices set along communications lines that are used to boost the light pulse in order to correct for signal distortions.
Optical fibres are lighter and thinner than copper cables with the same bandwidth. It takes more than 300 pounds of copper wire to carry the same amount of information as a single pound of optical fibre cable. They are also less susceptible to cross talk from other lines and electromagnetic interference from such things as lightning and nearby electric motors. And, unlike metal cable, optical fibres can transmit information digitally, the natural state of computer data, rather than analogically.
The major downfall of fibre optics technology remains its cost. Prices are dropping as demand for the technology grows, but the initial cost of switching to a fibre optics system is still high because of all the installation hardware required.
People are also hesistant to invest in optical-fibre-based networks because, like most quickly-evolving technologies, fibre optics will inevitably make old versions of itself obsolete.
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