Optoelectronics To Increase The Broadband Flow

"Consumers aresoon going to want data streams of 100 megabits per second in theirhomes and eventually 1 gigabit per second," says José Capmany, aresearcher at Valencia Technical University in Spain and thecoordinator of the IST programme-funded project. "There are two ways todo this: lay more cable, which involves public works and is expensiveand disruptive, or create technologies that allow existing cable to beused to its utmost potential, which is what we are doing."

LABELSis developing two key optoelectronic technologies to expand thecapacity and speed of fixed-line communications using fibre-opticcables and to improve the processing of radio frequency (RF) signals inwireless networks. Both techniques overcome bottlenecks in the flow ofdata and, though still in the experimental stage, are proving theirpotential to vastly improve data flow right along the chain.

"It'slike a river with many small streams running into it, if the flowbecomes too much the river will burst its banks," Capmany says. "It'sthe same with broadband communications which require a powerfulbackbone -- the river -- to handle ever increasing amounts of data."

Groundbreaking fibre-optic technique

Inthe case of fibre-optic networks, the LABELS project is developing agroundbreaking technique to transmit data faster while using fewerresources. The system is expected to play a role in a future generationof optical Internet Protocol (IP) routers, as opposed to the electronicones in use today. The major advantage of using light wavearchitectures for processing is that they can send and receive dataover multiple wavelengths as opposed to the single bandwidth thatelectronic systems are confined to, allowing the full potential ofoptical networks to be utilised.

The LABELS technique relies onsubcarrier multiplexing and label swapping in packet data transfer,allowing nodes at different stages along the network to change thewavelength at which the data is being carried. It is considerably moreflexible than existing Wavelength Division Multiplexing (WDM)techniques which, though increasing data transfer speeds, lock signalsto specific wavelengths.

"Existing WDM systems work like atelephone call: you first have to make a connection and then theinformation is transmitted, which is fine if it is being used for along duration of time. It is not optimally suited to sending data overthe Internet in packets, however, which is precisely what has made IPso successful and which is what we are applying in the optical domain,"Capmany says. "We are the only researchers in Europe currently workingon subcarrier multiplexing and label swapping in the optical domainthough other researchers here and in the United States are developingrelated technologies in the field."

Preliminary tests of theLABELS system, which will be fully evaluated later this year inValencia, have surpassed even the project's own goals regarding datatransfer rates. "We set out to achieve a rate of 10 Gbps but we sawthat we could actually reach 20 Gbps with the current system," thecoordinator notes. "With further development that could even beexpanded to 40 Gbps and beyond."

Enhanced performance in wireless radio frequency processing

Performanceincreases are also expected to result from LABELS' other application inradio frequency processing for wireless, where the partners are due totest the effects of replacing current electronic RF filters withoptical ones.

"The problem that has existed to date with theelectronic filters of radio antennas is that they are not flexiblebecause they are only made to send and receive over a specificwavelength which can cause bottlenecks and restricts the possibilityfor upgrades. By converting the filters to optical ones it's possibleto send and receive over more bandwidth, allowing the antennas to workat different wavelengths and allowing them to be used for differentapplications," Capmany explains.

The LABELS optical filters aredesigned to work between 130 MHz and 20 GHz and even open thepossibility to processing at very high frequencies -- up to 60GHz --where other techniques are less efficient.

Project partnerTelefónica I+D in Spain will test the system later this year forchannel switching in UMTS -- a particular challenge given the relativelylow 1.9 GHz frequency of the third generation mobile communicationstechnology.

"UMTS is not ideally suited to this technique, whichworks better at higher frequencies such as 5 or 10 GHz," Capmany says."However, mobile communications are continually moving up the radiospectrum and the fourth and fifth generation will probably operate atthose frequencies, giving our technology strong commercial potential inthe future."

Indeed, both the fixed-line and wireless systemsdeveloped by LABELS are not due to reach the market as commercialproducts for some time because of the need for further developments inrelated applications and services. However, Capmany expects to see thetechnologies in use by 2010, by which time today's stream of data willtruly be a fast-flowing river.