For decades, humans have used radio waves to remotely control drones. But this summer, British defense firm QinetiQ announced the successful control of a drone by laser. The communication and control method—between a flying robot and a human operator—suggests a new way to command drones in circumstances where traditional radio controls are susceptible to interference or interception. It is a promising technology, one that trades the existing known set of radio control limitations for a whole new set of laser-focused challenges.
The demonstration took place earlier this year at the Salisbury Plain Training Ground in southern England near Stonehenge. The drone was controlled, at least in part, by a system called “Free Space Optical Communications (FSOC),” in which information is turned into light, transmitted through the open sky, and picked up by a dedicated receiver.
“FSOC provide very high bandwidth, very low probability of detection communications, low logistical footprint and the potential to negate the considerable investment that adversaries may have made in denying the RF spectrum,” reads the July announcement from QinetiQ.
The demonstration took place in March of 2022, as part of a broader push by the United Kingdom’s Defence Science and Technology Laboratory effort to make drone communications more resilient. Communications that depend on sending and receiving laser signals can struggle in low-visibility weather, like fog or dust, which obscures the sky. The promise of this approach, though, is for the possibility of clear, high-bandwidth transmission of vast quantities of data rapidly with light, and done openly wherever the sender and receiver may be. This has already been realized in networks of fiber-optic cables, which are closed space optical communications, and require infrastructure investment to establish and connect.
Light years
Making this kind of communication work has been the subject of military research for decades. In 2004, the Air Force Research Laboratory and DARPA collaborated on the Optical and Radio Frequency Combined Link Experiment (ORCLE). The program aimed to combine the high data capacity of light communications with the signal fidelity of radio. ORCLE set out to integrate both methods into a network of communication nodes, with an understanding that radio would allow for persistent communication in difficult weather.
In 2008, DARPA awarded a contract to Northrop Grumman for the Optical RF Communications Adjunct (ORCA) project, aimed at providing “an all-weather, high connectivity, jam resistant, high bandwidth network,” according to Northrop Grumman’s release.
Because of the limits of optical communication alone, much of the research on free-space optical communication pairs it with radio communication for greater resiliency.
“Although FSOC systems can be inoperable through clouds or thick fog, employing them in a hybrid RF/optical link configuration can yield a system that can operate under most weather conditions and provide high-bandwidth, secure, jam-resistant communications under most conditions,” argued the authors of a 2011 paper on free-space optical networks, including members of DARPA.
More recently, DARPA has focused its research on optical communications in space between satellites, which is free from the atmospheric obstacles impeding light-based communication on earth.
Free space, narrow aperture
Radio signals are sent over known frequencies, understood and monitored for ever a century. The nature of radio transmission means the waves can be observed beyond where they are received, as the signals travel through open air and sometimes refract or diffuse across terrain and atmospheric phenomena. That trait is useful for transmitting information over distance, but is less useful for keeping that information secret. The promise of optical communication, specifically based on lasers, is that it will instead concentrate all its transmitted information in a narrow beam of light.
“Free Space Optical Communications is almost impossible to intercept or detect, as the laser beam travels directly from one platform to another over a very narrow path,” QinetiQ describes on its website. “Interception would require an adversary to be physically present in the path of the beam – something that is extremely difficult to achieve.”
If interception is difficult, maintaining a signal is likely not easy. While a drone would have the advantage of knowing where the directed beam is coming from, and automatically orienting its receiver to that point, it could become vulnerable to laser dazzlers, designed to disable the sensors on a flying robot.
The greatest promise of the technology, used at the shorter ranges of small drones, is that it would allow soldiers a way to command a scout without being detected along radio frequencies. QinetiQ’s announcement notes that the demonstration “included Free Space Optical Communications (FSOC) as a bi-directional link in its mission communication system.”
Other bi-diretional communication links may exist in the system tested by QinetiQ, serving as fail-safes or backups. A drone designed to only receive laser signals could be challenging to use. A drone that includes a laser signal alongside traditional methods would, in a fail-case, operate normally, while having the potential for extra utility.
For now, this technology appears focused on the command, control, and data transfer functions of a scouting drone. The challenge becomes more complex should it apply to a drone designed to carry weapons. But with just a scout, the faster data transfers of optical communication would let useful video arrive rapidly, or allow greater resolution cameras without bandwidth concerns. All with the promise, at least, that the drone would be useful even in the face of radio jammers and counter-drone technologies.
