Laser comms that cuts through clouds

It's a problem well known to drone pilots, people who work on satellite systems and anyone else who has ever used optical communications: At some point, the environment gets in the way. 

Using an optical communications system in certain atmospheric conditions, like haze, fog or other optical turbulence, can cause the light beam to break up and be misunderstood on the receiving end, jumbling the data.

“The further we go through the atmosphere, the more distortion we get,” said Tim Clark, director of Advanced Electrical-Optical at Raytheon Intelligence & Space, one of the four businesses that form Raytheon Technologies. “We get a lot of losses – particles in the air, water in the air.”

Thanks to a novel approach pioneered by RI&S engineers, the future of free-space optical, or FSO, communications is a unique receiver technology that provides a simple, compact, high-bandwidth data link capable of plowing through strong turbulence effects.

“We’re just scratching the surface of it,” Clark said. “There’s just a large number of potential uses for it.”

The issue is similar to the mirage effect one experiences when looking out across the desert. Refraction, or the bending of light from the temperature difference between the ground and the air, disrupts the image signal being transmitted to the eyes or cameras. Similarly, suspended particles such as haze, clouds, dust or fog, or simply layers within the atmosphere, can break up the optical laser signal and reduce signal in the beam.

“It sets certain limitations on how fast the data can be transmitted,” said Jae Kyung, RI&S principal investigator. “We need to undo all of those effects so that we can make these receivers work.”

The new RI&S receiver outperforms current free-space optical technologies, while providing scalability for future FSO systems. However, the advancement isn’t just a matter of performance. The new system also dramatically reduces the size of the receiver — from about the size of a toaster oven to something closer to a mobile phone.

The combination of better optical communications performance, higher bandwidth, and a lighter, smaller package could pay off big for systems such as satellites and unmanned aerial vehicles, enabling not just better communications, but also new strategies and tactics.

“We eliminate the effect of that turbulence,” Kyung said. “Under those conditions where most tech fails, we had no issues.”

RI&S recently demonstrated the technology’s ability to transmit high-definition video at the Navy’s research facility on the Chesapeake Bay in Maryland, broadcasting across a 16-kilometer path through rough atmospheric conditions at a rate of 1 gigabit per second. The plan is to push the rate to 10 gigabits per second in future tests — roughly 10 times as fast as the best residential Ethernet systems — and ultimately pressing to the 100 gigabits per second range desired for satellite missions.

“They want to pull data at very high rates,” Kyung said. “There is a tremendous amount of data that they want to send up to space, then send back down. To get to that 100-gigabit level, there’s still some research involved. But we have a good path now to that.”