Optoelectronics to increase the broadband flow

The broadband boom is creating an ever-increasing demand for more capacity and higher rates of data transfer on both fixed-line and wireless networks. Helping to meet that demand, without the need to lay costly new infrastructure, is the LABELS project.

“Consumers are soon going to want data streams of 100 megabits per second in their homes and eventually 1 gigabit per second,” says José Capmany, a researcher at Valencia Technical University in Spain and the coordinator of the IST programme-funded project. “There are two ways to do this: lay more cable, which involves public works and is expensive and disruptive, or create technologies that allow existing cable to be used to its utmost potential, which is what we are doing.”

LABELS is developing two key optoelectronic technologies to expand the capacity and speed of fixed-line communications using fibre-optic cables and to improve the processing of radio frequency (RF) signals in wireless networks. Both techniques overcome bottlenecks in the flow of data and, though still in the experimental stage, are proving their potential to vastly improve data flow right along the chain.

“It’s like a river with many small streams running into it, if the flow becomes too much the river will burst its banks,” Capmany says. “It’s the same with broadband communications which require a powerful backbone – the river – to handle ever increasing amounts of data.”

In the case of fibre-optic networks, the LABELS project is developing a groundbreaking technique to transmit data faster while using fewer resources. The system is expected to play a role in a future generation of optical Internet Protocol (IP) routers, as opposed to the electronic ones in use today. The major advantage of using light wave architectures for processing is that they can send and receive data over multiple wavelengths as opposed to the single bandwidth that electronic systems are confined to, allowing the full potential of optical networks to be utilised.

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

“Existing WDM systems work like a telephone call: you first have to make a connection and then the information is transmitted, which is fine if it is being used for a long duration of time. It is not optimally suited to sending data over the Internet in packets, however, which is precisely what has made IP so successful and which is what we are applying in the optical domain,” Capmany says. “We are the only researchers in Europe currently working on subcarrier multiplexing and label swapping in the optical domain though other researchers here and in the United States are developing related technologies in the field.”

Preliminary tests of the LABELS system, which will be fully evaluated later this year in Valencia, have surpassed even the project’s own goals regarding data transfer rates.

“We set out to achieve a rate of 10 Gbps but we saw that we could actually reach 20 Gbps with the current system,” the coordinator notes. “With further development that could even be expanded to 40 Gbps and beyond.”

Performance increases are also expected to result from LABELS’ other application in radio frequency processing for wireless, where the partners are due to test the effects of replacing current electronic RF filters with optical ones.

“The problem that has existed to date with the electronic filters of radio antennas is that they are not flexible because they are only made to send and receive over a specific wavelength which can cause bottlenecks and restricts the possibility for upgrades. By converting the filters to optical ones it’s possible to send and receive over more bandwidth, allowing the antennas to work at different wavelengths and allowing them to be used for different applications,” Capmany explains.

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

Project partner Telefónica I+D in Spain will test the system later this year for channel switching in UMTS – a particular challenge given the relatively low 1.9 GHz frequency of the third generation mobile communications technology.

“UMTS is not ideally suited to this technique, which works better at higher frequencies such as 5 or 10 GHz,” Capmany says. “However, mobile communications are continually moving up the radio spectrum and the fourth and fifth generation will probably operate at those frequencies, giving our technology strong commercial potential in the future.”

Indeed, both the fixed-line and wireless systems developed by LABELS are not due to reach the market as commercial products for some time because of the need for further developments in related applications and services. However, Capmany expects to see the technologies in use by 2010, by which time today’s stream of data will truly be a fast-flowing river.