Plastic fibres solve Facebook's airborne data problem

Back in 2014, Facebook and Google were fighting to buy a UK company called Ascenta that was developing a high altitude unmanned aircraft that could be used to provide Internet access around the world as aerial basestations. While Facebook won that battle (Google bought Titan Aerospace instead), both face the challenge of maintaining high speed data links at 60,000ft, both to other aircraft and to the ground.

Current 'free space optics' systems can be heavy and need to be steered to maintain a link. Now researchers at the Connectivity Lab have shown a new, passive approach that would work over long distances providing over 2Gbit/s of data, which is detailed at EETimes Europe.

Doped plastic fibres can capture free space laser signals

Instead of using optics to focus the light, the researchers have used plastic fibres doped with a fluorescent organic dye as the receptor. This can detect the light coming in from the free space link and convert it to a different frequency within the fibre. This signal can then be captured by a traditional high speed photomultiplier. 

This light collector features 126 sq cm of surface that can collect light from any direction, and, crucially, doesn’t need to be steered. This provides a lightweight, simpler receiver. 

“This approach has been used in luminescent concentrators for solar light harvesting, where the speed of the color conversion doesn’t matter. We showed that the same concept can be used for communication to circumvent pointing and tracking problems while accomplishing very high speeds," said Tobias Tiecke, who leads the research team. 

The initial system uses green and blue light, and the next challenge is to find materials that fluoresce in response to the near infra red light that would be coming from a laser on another aircraft or from the ground. Using ODFM modulation alongside near IR would boost the performance to 10Gbit/s, says Tiecke, which would be an elegant solution to the problem.

By Nick Flaherty www.flaherty.co.uk