Facebook is exploring ways of delivering internet connectivity via lasers, developing a new receiver technology that promises to be less complex and more affordable than current systems. Dubbed free-space laser communication, Facebook’s break-through is in an all-new optical detector that – unlike existing examples – would neither require mechanical stabilization, nor expensive micro-motors, sensing, or processing.
Whereas wireless internet systems like those we know as WiFi work for the most part on radio frequencies, free-space laser communication takes place in the visible or infrared spectrum. The advantages, there, are a reduction in interference from neighboring frequencies along with the potential for higher data rates.
In effect, a pulsed laser fires from a transmitter at one point and is picked up by a receiver elsewhere, with anything up to several miles in-between. The complexity arrives in the receiver: these need to use relatively small photo-diodes, around 1 square millimeter or smaller, if you want anything like gigabit per second data rates.
Problem is, the laser light spreads as a matter of course, meaning that by the time it hits the receiver, it’s broader than the photo-diode and thus data transmitted is lost. The solution so far has been to fit a lens in front, which re-focuses the laser to the photo-diode, but that requires real-time adjustment of its position.
“[Free-space optical] systems typically include automated mechanical tracking systems to maintain this alignment and correct for vibrations and beam variations due to atmospheric turbulence,” Facebook engineers Thibault Peyronel and Tobias Tiecke, who developed the new system, say, “which adds complexity and cost to the design.”
Their answer, detailed in a paper published by the journal Optica, is a new type of luminescent detector. Resembling a cricket bat, it actually consists of a bundle of plastic optical fibers, spread out at one end and then funneling down to the photo-diode at the other.
Each strand has been treated with an organic dye, absorbing blue light and in turn emitting green light. The blue laser light, therefore, hits the broad – 126 square centimeter – “paddle” section, whereupon it is converted to green light and fed to the electronic systems.
The engineers say that they’ve hit speeds greater than 2 Gbps with their prototype, with the larger design gathering up to 10 times the amount of light as comparable semiconductor photodetectors, despite having no moving parts.
Future iterations of the project will look to using higher-speed materials, which can use faster infrared wavelengths rather than visible light.
Assuming a commercial design proves cost-effective, actually deploying laser-based communications could take place much quicker than traditional WiFi. That’s because the visible and infrared frequencies aren’t regulated in the same way: there’d be no need for government or federal agency approval.
Eventual products could take the form of internet receivers that would not require professional installation, since their positioning would be less reliant on exact orientation. Facebook could supply such base-stations to the remote, currently-disconnected or poorly-connected locations it envisages benefiting from its Internet.org platform, which aims to get remote villages online, and then potentially communicate with those receivers using laser-equipped drones.