The internet is often called the “World Wide Web,” but it’s not actually accessible to residents of a large portion of the world. Today, four billion people are offline, and 1.6 billion of them live in sparsely populated areas around the world.
In recent years, a race to solve that problem has emerged among big tech companies like Google, SpaceX and Facebook. 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.
Most internet signals today are transmitted at high rates through wired optical fiber networks — which require expensive infrastructure — or at lower rates through wireless radio frequencies, which are limited in bandwidth, subject to regulations and vulnerable to interception.
In a paper published Tuesday in Optica, researchers from Internet.org’s Connectivity 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.
“It’s a completely new design,” said Julian Cheng, a communications engineer at the University of British Columbia who was not involved in the study. With a device that’s simpler than traditional light receivers, he said, the Facebook team was able to achieve wireless data rates on the order of wired systems.
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.)
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.
Instead, many free-space optical communication systems use smaller receivers with complex pointing and tracking systems. Because laser beams are narrow and travel in straight lines from point A to point B, these receivers have to continuously maneuver to catch laser beams head-on.
Imagine trying to water a small potted plant with a water gun from different angles, said Alan Willner, an optical communications scientist at the University of Southern California and president of the Optical Society, the professional society that published Internet.org’s paper. To maximize the amount of water you catch, you have to constantly move the pot around.
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.
