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.
In
our hypothetical example, imagine that instead of a water gun, you’re
pointing a blow dart gun at a water balloon attached to a funnel over
the potted plant. As soon as you hit the balloon, it pops and releases
water. With the addition of the balloon, you’ve eliminated the need to
move the pot around. You can shoot at the water balloon from any
direction, and the plant will get watered.
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.
Because
of all these benefits, building on Facebook’s proof of concept holds
tremendous potential not just for remote areas, but for meeting
increased data demand all over the world, said Kamran Kiasaleh, an optical communications scientist at the University of Texas at Dallas who was not involved in the study.
The technology fits in with Facebook’s plans
to beam internet access down from the skies using drones. With laser
transmitters and arrays of these light detectors, drones could exchange
data with one another and with ground stations. Indoors, these detectors
could provide high data rates to mobile devices.
For
now, the new light detector is still in early stages, said Tobias
Tiecke, a communication systems scientist at Facebook and a co-author of
the new paper. His team built their current device using off-the-shelf
materials that are used for harvesting solar light.
“The performance of our system can still be increased much further by developing materials tailored for communication,” he said.
