EU project builds optical repeater for UWB

An EU funded project has developed an optical repeater for the ultra-wideband (UWB) signals.

The UWB signals used in these standards are broadcast at low power so have a range measured in metres or tens of metres.

Moshe Ran, co-ordinator of the UROOF project (photonic components for ultra-wideband radio over optical fibre), said: “You can’t extend the range over the air. So if you want to overcome the limitations of the short range, using optical fibre is a very elegant way of doing it.”

The researchers have built a hybrid system, in which UWB radio signals are turned into light, relayed over optical fibres, and then transformed back to radio again.

The team is using silicon-germanium (SiGe) phototransistors to drive vertical-cavity surface-emitting lasers (VCSELs), which emit a laser beam perpendicular to their top surface.

The researchers also had to build a gain control circuit to cope with varying input signal strengths.

They have demonstrated an integrated transceiver, dubbed Access Node 1, at several international forums, most recently at the International Conference on Ultra-wideband, which met in Hanover, Germany in September.

“We showed that with Access Node 1 we can transmit three streams of 480Mbit/s on the same fibre with negligible distortion,” says Ran. “That’s enough to transmit at least three streams of compressed high-definition television.”

The team has also built a second-generation access node using an electro-absorbtion transceiver (EAT) in which an optical signal is directly modulated by a radio signal.

The EAT based Access Node 2 has the potential to carry far more information than Access Node 1, but there is a catch. “With EAT you can approach 60GHz,” says Ran, “but it is expensive.”

The UROOF team is working to increase the bandwidth of Access Node 2 and reduce its cost.

Ran believes the work shows that it will be possible to redistribute UWB signals over long distances at relatively low cost.

“As ultra-wideband technology penetrates the mass market – within the next two years – it will be possible to manufacture an access node that will meet the demand very nicely,” says Ran.

The UROOF project received funding from ICT strand of the EU’s Sixth Framework Programme for research.

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