UCD
sets standard for
fibre optic transission
Dublin
scientists have broken one barrier holding
back the information superhighway
Dick Ahlstrom, The Irish Times
Bell labs in the US is one of the world's leading research institutes, so if you can top its achievements you have done something special.
A team at University College Dublin's Optoelectronics Research Centre took a single optical fibre and "split" it electronically into 2,000 distinct data channels, topping the best Bell could do by a factor of five.
The centre's director, Prof Ronan O'Dowd, said: "This is really a 'hero' experiment we started doing last spring.
"A hero experiment is when you try to push the technical capabilities to their limits or explore the technical limits."
Achieving such a record is not just about kudos. It sets the "design floor" for a technology, a technical barrier used by designers to establish how far a device can be taken in actual use.
Splitting a single light-carrying fibre into 2,000 channels is a remarkable bit of work. By comparison, the latest installed fibre optic cable systems have 40 channels and there are trials under way to increase this to 80 channels.
The computer and communications industries are trying to find how to get more and more data down a single line, Prof O'Dowd said. Five years ago these players were intent on ramping up data transfer speeds as a way to achieve higher data volumes, going from millions of bits of information per second to one billion bits, then 10 billion and now 40 billion.
"And even that isn't enough to satisfy the world's hunger for information," Prof O'Dowd said.
If you start to hit problems at increasing speed, the next best thing is to create individual streams and then run separate data down each channel.
What the UCD team has done is to create the greatest number of individual channels technically possible in a single fibre using existing technology.
"It has been proven to be achievable, it is not theoretical," Prof O'Dowd said. Even so, it will be some time before commercial devices able to support so many channels will be on the market.
The technique used to create those extra channels is known as "wavelength multiplexing", Prof O'Dowd said. The fibre is not physically divided, but its carrying capacity is separated electronically, with each channel being assigned a different light wavelength.
Fibre optic cables are designed to carry light and the system uses a semiconductor laser to produce the light. The laser can be electronically tuned for sending data down any of the 2,000 channels. It can switch between channels like you would switch between stations on a radio, each of which has its own frequency.
There had been active wavelength multiplexing research for six or seven years and the International Telecommunications Union, the world governing body, standardised wavelength multiplexing for 20 channels per fibre in 1997. This has been pushed to 40 and the number keeps increasing as the equipment used improves. "We decided to take this and see what was the floor," Prof O'Dowd said.
The work was done last spring and the team included Prof O'Dowd, Mr Sean O'Duil, Mr Neal O'Gorman, Mr Gavin Mulvihill and Mr. Paddy Matthews. Advanced software had to be developed, able to process millions of bits of data at high speed without loss. The laser also had to be tuneable to the maximum 2,000 distinct channels to get the most out of each fibre and had to be able to switch between them quickly.
Frequency is measured in hertz or cycles per second and the team managed to get the separation between channels down to just two billionths of a hertz (two gigahertz). They pushed the transmissions speed up to one billion bits of information per second but found that it could not be increased without causing, "cross-talk" - information bleeding across from one channel into the next.
Researchers at the Optoelectronics Research centre, including Prof O'Dowd and Ms Yu Yonglin, also found that they could get the laser to "change stations" from one frequency to the next in just a few billionths of a second. "This is quite an achievement I think," Prof O'Dowd said.
He added that a working device would not have so many channels. "We are not saying you will have 2,000 channels routing down that fibre." Having so many means you limit the bits per second you can send. In practice, a network designer might use only one in 10 channels and then run the channels at much higher data transfer speeds.
Even so, having 200 working high-speed channels is miles ahead of the best existing technology and, given the Bell device must work under similar constraints, the UCD version would still be five times faster.
The great promise in the technology is that it will produce an "intelligent network", Prof O'Dowd said, a system that can route the data on the basis of its frequency. This makes for a more "agile" network and points the way for the future of telecommunications.
Prof O'Dowd also noted with pride that Ireland was playing its part in this advanced technology. "These future networks, some of the key developments are taking place right here in Dublin in UCD."
Copyright �, 2000 University College Dublin
UCD, Belfield, Dublin 4, Ireland.
Tel : +353-1-7067777
http://www.ucd.ie