Anti-lasers could give us perfect antennas, greater data capacity

Playing laser light backwards could adjust data transmission signals so that they perfectly match receiving antennas. The fine-tuning of signals like this, not achieved with such detail before, could create more capacity for ever-increasing data demand.

“Imagine, for example, that you could adjust a cell phone signal exactly the right way, so that it is perfectly absorbed by the antenna in your phone,” says Stefan Rotter of the Institute for Theoretical Physics of Technische Universität Wien (TU Wien) in a press release.

Rotter is talking about “Random Anti-Laser,” a project he has been a part of. The idea behind it is that if one could time-reverse a laser, then the laser (right now considered the best light source ever built) becomes the best available light absorber. Perfect absorption of a signal wave would mean that all of the data-carrying energy is absorbed by the receiving device, thus it becomes 100% efficient.

“The easiest way to think about this process is in terms of a movie showing a conventional laser sending out laser light, which is played backwards,” the TU Wein article says. The anti-laser is the exact opposite of the laser — instead of sending specific colors perfectly when energy is applied, it receives specific colors perfectly.

Counter-intuitively, it’s the random scattering of light in all directions that’s behind the engineering. However, the Vienna, Austria, university group performs precise calculations on those scattering, splitting signals. That lets the researchers harness the light.

How the anti-laser technology works 

The microwave-based, experimental device the researchers have built in the lab to prove the idea doesn’t just potentially apply to cell phones; wireless internet of things (IoT) devices would also get more data throughput. How it works: The device consists of an antenna-containing chamber encompassed by cylinders, all arranged haphazardly, the researchers explain. The cylinders distribute an elaborate, arbitrary wave pattern “similar to [throwing] stones in a puddle of water, at which water waves are deflected.”

Measurements then take place to identify exactly how the signals return. The team involved, which also includes collaborators from the University of Nice, France, then “characterize the random structure and calculate the wave front that is completely swallowed by the central antenna at the right absorption strength.” Ninety-nine point eight percent is absorbed, making it remarkably and virtually perfect. Data throughput, range, and other variables thus improve.

Achieving perfect antennas has been pretty much only theoretically possible for engineers to date. Reflected energy (RF back into the transmitter from antenna inefficiencies) has always been an issue in general. Reflections from surfaces, too, have been always been a problem.

“Think about a mobile phone signal that is reflected several times before it reaches your cell phone,” Rotter says. It’s not easy to get the tuning right — as the antennas’ physical locations move, reflected surfaces become different.

Scattering lasers

Scattering, similar to that used in this project, is becoming more important in communications overall. “Waves that are being scattered in a complex way are really all around us,” the group says.

An example is random-lasers (which the group’s anti-laser is based on) that unlike traditional lasers, do not use reflective surfaces but trap scattered light and then “emit a very complicated, system-specific laser field when supplied with energy.” The anti-random-laser developed by Rotter and his group simply reverses that in time:

“Instead of a light source that emits a specific wave depending on its random inner structure, it is also possible to build the perfect absorber.” The anti-random-laser.