Heart Of Laser Light Powers Next-Generation Radar

by Michael Keller

Not long ago, a little red Opel minivan rolled to a stop beside the port of Livorno, a seaside town in Italy's Tuscany region. A radar dish had been strapped to the vehicle's roof by the researchers within.

The team removed the dish from the roof, erected it on a tripod and pointed it toward the behemoth freighters lumbering in the nearby water. Then they popped the Opel's trunk to reveal boxes of electronics crammed inside. An umbilical soon connected the equipment to the dish.

When they turned on the system's power, they energized what might become the next generation of instruments for locating objects---a fully digital radar whose heart is powered by light.

"We are defining the position, speed and even the shape of big cargo ships in and outside the port," lead researcher Paolo Ghelfi, an electronics engineer with Italy's National Inter-University Consortium for Telecommunications (CNIT), tells Txchnologist. "Using a laser instead of traditional radar electronics means we can detect more accurate positions of objects. We can also detect smaller objects farther away because our system produces lower noise in the radar signal."

The CNIT team's Livorno port trial expanded their novel radar's portfolio of environments in which it can operate. They previously tested it at Pisa International Airport and compared their range and velocity data with that used for the facility's air traffic control. "Our data was very nice, very precise," Ghelfi says.

A heart of laser light

Their system, called Phodir, substitutes the electronics of traditional radar with one based on photonics, which uses a laser, optical filters and photodiodes to generate precise, high-quality radio frequency signals. While the photonic radar still uses radio waves to locate objects like conventional systems, the laser allows it to pulse highly tuned frequencies in a broad emission band from the tens of megahertz to possibly up to the hundreds of gigahertz. Current marine radar and air traffic control typically operate in the 1-12 gigahertz range, with higher frequencies typically meaning more precise detection of objects.

(The research team while testing the photonics-based coherent radar system on the roof of the laboratory in Pisa, Italy, detecting aerial traffic from the airport. Courtesy Antonella Bogoni.) 

Photonic radar's broad bandwidth means it should be considerably more flexible than contemporary systems, since its tuned frequencies could switch from low-resolution, fast scans of air or marine space to slower, high-resolution surveillance. Such functionality, Ghelfi says, requires more than one radar system today. And if their idea works out, the huge bandwidth boost could mean that tomorrow's photonic radar also does double duty as a communications system. "Imagine a radar system aboard an airplane that checks what's moving around outside but can also transmit data to the ground or other planes," he says.

Ghelfi says his team has been thinking about their work in light of the still unknown fate of Malaysia Airlines' flight 370, which disappeared on March 8 during a trip from Kuala Lumpur to Beijing. "We're thinking about this flight and about the radar system onboard. What if that system was also transmitting streaming video of what was going on in the cockpit to the ground," he says. "It could be like a second black box that streams data off the plane to somewhere else where it's recorded. Photonics allow huge bandwidths for something like this."

Their work was published on March 19 in the journal Nature. The authors say the next generation of radar needs to operate at higher bandwidths to increase resolution. This improvement is not possible with current systems, and if implemented, would "guarantee higher safety and speed in the control of air and marine traffic, even under non-optimal weather conditions." 

Need an integrated photonics revolution

There is still quite a bit of work to be done to see a photonics-based radar system come online. For one, Ghelfi says, integrated photonics components need to be created to unleash the full potential of light-based systems. He compares the possibilities to what happened with electronics after integrated circuits were invented---a technology revolution that swept across the world. Such integrated components would allow miniaturization and deployment of very small, very light photonic systems on moving objects.

"We're still some years away from integrated photonics," he says. "Nobody has yet produced the things we are developing, so it'll take time. But every problem can be solved and some affordable solution can be reached."

In commenting on the CNIT team's work, U.S. Naval Research Lab microwave photonics researcher Jason McKinney, who was not involved in the study, said, "Their work shows that such techniques may indeed provide capability for next-generation radar systems...The individual performances of the system's transmitter and [analog-to-digital converter] are world-class with respect to those of other photonics-based devices."

(CNIT’s Phodir photonic radar during a field test at Pisa International Airport. Courtesy CNIT.)

Top Image: The CNIT team perform a field trial of their photonic radar demonstrator system at the port in Livorno, Italy. Courtesy Antonella Bogoni.

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