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For artists and romantics, the twinkling of the stars is visual poetry; a distant dance of light that twists and curves through an ocean of turbulent air above our heads.
Not everyone is equally in love with the distortions in our atmosphere. For many scientists and engineers, a lot of ground-to-satellite research and communication would be a lot easier if the air just wasn’t there.
Losing our planet’s protective gas bubble isn’t 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 rippling air in the blink of an eye.
The result is a laser link capable of sustaining itself in the atmosphere with unprecedented stability.
While astronomers have a few tricks up their sleeve for correcting atmospheric distortions on incoming light, it has been a challenge to emit a coherent beam of photons from the ground to a distant receptor so that they stay together and at the same time. point.
Keeping the transmissions on target and consistent – with their phases perfectly aligned – over hundreds of kilometers of moving air would allow us to link very precise measurement tools and communication systems.
Satellites could search for minerals or assess groundwater tables 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, which measures the lateral movement of the received beam,” explains Dix-Matthews.
“This position measurement is then used to actively control a steerable mirror which keeps the received beam centered and suppresses lateral movement caused by the atmosphere.”
This is because the system can be used to compensate for the effects of warping air moving in three dimensions – not just up and down, or left and right, but along the beam path, maintaining the centered link and its phases in order.
So far, it has only been tested over a relatively short distance of 265 meters (around 870 feet). About 715 meters (just under half a mile) of fiber-optic cable was routed 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.
With the proof of concept demonstrated, there is no reason to believe that a similar technique will not one day target the sky and beyond. Although there are a few hurdles that need to be overcome first.
“During this experiment, we had to perform the initial alignment by hand, using a visible guide laser aligned with the stabilized infrared beam,” Dix-Matthews told ScienceAlert.
“When making connections between optical atomic clocks, it would be good to have a way to make this coarse alignment easier.”
Fortunately, Dix-Matthews French collaborators are working on a device that will speed up the initial rough alignment process, promising a second generation of laser bonding technology that won’t require such a complex setup.
The team also found that variations in equipment temperature affected phase stability, limiting the duration of the signal to around 100 seconds. This obstacle will also be the subject of future improvements.
We may not have to wait long. Researchers are already making progress in upgrading their system.
“We have started using a high power laser amplifier which should help us cope with the larger power losses expected over longer distances, such as in space,” says Dix-Matthews.
“We have also completely rebuilt our active terminal to make it more sensitive to low received powers and to make it more efficient at canceling the movement of the received beam.”
With in-orbit technology quickly becoming a major focus for many data providers, potentially filling our skies with satellites, innovations that link communication systems across our atmosphere will be further sought after.
As useful as our atmosphere is for, well, keeping us all alive, there are certainly downsides to being buried under a choppy blanket of hot gas.
This research was published in Nature communications.
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