Facebook designs light-bulb shaped detector to drive plans for drone internet access

Facebook has taken a step towards bringing internet access through laser

At Facebook's F8 Developer Conference this year, Mark Zuckerberg offered more details about his laser-firing drones that would encircle the globe to relay the internet to far-flung places, potentially the entire human population of the world.

The first solar-powered Aquila autonomous drones that would be deployed for the job are under flight testing. However, Facebook has published a paper in the journal Optica detailing how it would work.

Lasers would be a key component in the kind of  data linkage, but had some associated problems chiefly with the optical pickup to receive the signal. As lasers travel through the atmosphere they spread out and diffuse, which degrades signal quality reducing the maximum possible bandwidth of the system.

One solution to the problem could be to tightly focus the beam to mitigate the effect, but that is impractical on an ultra-light solar-powered drone.

The team had to therefore turn to fluorescent materials to catch the incoming light. Glow stick-looking fluorescent fibres collect and forward the received signal into a detector for conversion into electrical signals and ultimately network packets.

"We demonstrated the use of fluorescent optical fibres that absorb one colour of light and emit another colour," said Tobias Tiecke, who leads the research team.

"The optical fibres absorb light coming from any direction over a large area, and the emitted light travels inside the optical fibre, which funnels the light to a small, very fast photodetector."

With a surface area of 126 sq cm (19.5 sq in), the unique shape of the device allows it to collect light from any angle, which is then  concentrated onto a small photodetector. The fibres also contain organic dye molecules that absorb blue light but emit green.

"The fact that these fluorescent optical fibers emit a different color than they absorb makes it possible to increase the brightness of the light entering the system," says Tiecke. "This approach has been used in luminescent concentrators for solar light harvesting, where the speed of the colour 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."