For artists and romantics, the twinkling of stars is visual poetry; a dance of distant light as it spins 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 ground-to-satellite research and communication would be much easier if the air were simply not there.
Losing our planet’s protective gas bubble is not exactly a popular choice. 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 sway with the touch of a mirror.
The result is a laser link capable of being held by the atmosphere with unprecedented stability.
While astronomers have some tricks up their sleeve to correct atmospheric distortions in incoming light, it has been a challenge to emit a coherent beam of photons from the ground to a distant receiver so that they stay together and punctual.
Keeping transmissions objective and consistent (with their phases in perfect line) through hundreds of miles of changing air would allow us to link very accurate measurement tools and communications systems.
Satellites could probe minerals 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 Australia’s International Radio Astronomy Research Center, explained the technology to ScienceAlert.
“The active terminal basically uses a small four-pixel camera, which measures the lateral motion of the received beam,” says Dix-Matthews.
“This position measurement is used to actively control an adjustable mirror that keeps the received beam centered and eliminates lateral movement caused by the atmosphere.”
Indeed, the system can be used to compensate for the deformation effects of moving air in three dimensions, not only up and down, neither to the left nor to the right, but along the trajectory. of the beam, keeping the link centered and its phases in order.
So far it has only been tested at a relatively short distance of 265 meters (about 870 feet). About 715 meters (just under half a kilometer) of fiber optic cable was passed 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 that were used to test fundamental physics, such as Einstein’s theories of relativity.
With proven proof of concept, there is no reason to think that a similar technique will not one day point to 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 by hand, using a visible guide laser that was in line with the stabilized infrared beam,” Dix-Matthews told ScienceAlert.
“When making links between optical atomic clocks, it would be nice to have a way to make that thick alignment easier.”
Fortunately, Dix-Matthews ’French collaborators are working on a device that will speed up the initial coarse alignment process, promising a second generation of laser link technology that won’t require such an involved setup.
The team also found temperature variations in the equipment that affected the stability of the phase, limiting the signal duration to about 100 seconds. This obstacle will also be the focus of future improvements.
You may not have to wait long. Researchers are already making progress in upgrading their system.
“We’ve started using a high-power laser amplifier that 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 the low powers received and to make it more effective in canceling the movement of the received beam.”
With technology in orbit quickly becoming a major focus for many data providers, potentially filling our sky with satellites, innovations that make linking communications systems through our atmosphere only more sought after.
As useful as our atmosphere may be, well, to keep us all alive, there are certainly some drawbacks to being buried under a restless blanket of hot gas.
This research was published in Communications on Nature.