Facebook’s Using Light to Wirelessly Transmit Internet Signals

Facebook Moves One Step Closer to Light-Based Wireless Communication

New York Times, July 21, 2016

Now, Facebook has published research on an unconventional solution: using light to wirelessly transmit internet signals. The work comes from a Facebook-led initiative called Internet.org, which, according to the initiative’s website, has so far brought internet access to more than 25 million people.

In a paper published Tuesday in Optica, researchers from Internet.org’s F Lab have outlined a new type of light detector that can be used for free-space optical communication, a communication technique that uses light to send data wirelessly.

Free-space optical communication works by encoding communication signals in laser beams. Transmitters on the ground or in satellites shoot that light through the air to receivers that can decode the data. (To understand this on simple terms, think of encoding and sending information through morse code using a flashlight.)

The Facebook researchers’ solution to this problem is a light detector that doesn’t need pointing and tracking, but still allows for fast transmission. To do this, they took advantage of fluorescence, the process of absorbing light and re-emitting it at a lower energy.

 Facebook’s detector contains a spherical bundle of special fluorescent fibers. The bundle, somewhere between the size of a golf ball and tennis ball, is able to absorb blue laser light from any direction and re-emit it as green light. Because that green light is diffuse, it can then be funneled to a small receiver that converts the light back to data.
 One longstanding obstacle to free-space optical communication is a trade-off between speed and size. To increase the number of laser signals hitting a receiver, one can increase the size of the receiver. But doing so makes the receiver slower.

Facebook’s new detector is able to achieve fast data rates of two gigabits per second — several orders of magnitude higher than those from radio frequencies — because light has a higher frequency than radio waves, and because the fluorescence process is fast. Free-space optical communication can also carry more information than radio communication, and is more secure because narrow laser beams are harder to intercept than wide radio waves.

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Image credit: Facebook Connectivity Lab