For artists and romantics, the twinkling of stars is visual poetry; a dance of distant light as it twists and bends through a turbulent ocean of air above our heads.
Not everyone is so in love with the distortions of our atmosphere. For many scientists and engineers, a lot of research and ground-to-satellite communications would be much easier if the air simply weren’t there.
Losing our planet’s protective gas bubble is not exactly a popular option. But Australian and French researchers have teamed up to design the next best thing – a system that guides light through stormy currents of air that ripples with the flicker of a mirror.
The result is a laser link capable of being maintained in the atmosphere with unprecedented stability.
While astronomers have a few tricks up their sleeve to correct atmospheric distortions in the received light, it was a challenge to emit a coherent beam of photons from the ground to a distant receiver so that they stay together and on point.
Keeping transmissions on target and consistent – with their phases remaining perfectly in line – through hundreds of kilometers of moving air would allow us to connect highly accurate measuring instruments and communication systems.
Satellites could test ores or evaluate groundwater with improved accuracy. High-speed data transfer may require less power and contain more information.
Lead author Ben Dix-Matthews, an electrical engineer at the International Radio Astronomical Research Center in Australia, explained the technology to ScienceAlert.
“The active terminal essentially uses a small four-pixel camera that measures the lateral motion of the received beam,” says Dix-Matthews.
“This position measurement is then used to actively control an adjustable mirror that keeps the received beam centered and eliminates lateral movement caused by the atmosphere.”
In fact, the system can be used to compensate for the effects of moving air deformation in three dimensions – not just up and down, or left and right, but along the trajectory of the beam, keeping the connection centered and its phases in order. .
So far it has only been tested over a relatively short distance of 265 meters (about 870 feet). About 715 meters (just under half a mile) of fiber optic cable were run underground between the transmitter and receiver to carry a beam for comparison.
The results were so stable that they could be used to connect the types of optical atomic clocks used to test fundamental physics, such as Einstein’s theories of relativity.
Given the proven proof of the concept, there is no reason to believe that a similar technique will not one day target the sky and beyond. Although there are some obstacles that need to be overcome first.
“During this experiment we had to do the initial alignment manually, using a visible guide laser that was in line with the stabilized infrared beam,” Dix-Matthews told ScienceAlert.
“When making connections between optical atomic clocks, you’d better have a way to make this rough alignment easier.”
Fortunately, French Dix-Matthews employees are working on a device that will speed up the initial rough alignment process, promising a second generation of laser-bonded technology that will not require such a configuration involved.
The team found that temperature variations in the equipment affected the stability of the phase, limiting the signal duration to about 100 seconds. This obstacle will also be the focus of future improvements.
We may not need to wait long. Researchers are already making progress in modernizing their system.
“We started using a high-power laser amplifier that should help us cope with the larger expected power losses over longer distances, such as space,” says Dix-Matthews.
“We have also completely rebuilt our active terminal to make it more sensitive to the low power received and to make it more efficient in canceling the movement of the received beam.”
Given that orbiting technology is fast becoming a major goal for many data providers, potentially filling our skies with satellites, innovations that make the connections between communication systems in our atmosphere only more sought after.
As useful as our atmosphere is for, well, to keep us all alive, there are certainly some disadvantages to burying under a restless blanket of warm gas.
This research was published in Communications about nature.