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Free-space laser communications promise fiber-like data rates without requiring a physical cable, making them attractive for satellites, remote locations and other environments where laying fiber is difficult. The atmosphere, however, creates a persistent problem. Changes in temperature and air density distort a laser beam as it travels, potentially scrambling the properties used to encode information.
Researchers from Wits University and the University of Bordeaux have demonstrated a different way to address that problem. Instead of trying to reconstruct a distorted beam at the receiver, they encoded information into topological properties of light designed to survive the distortion.
Topology deals with characteristics that remain unchanged even when something changes shape. A common analogy is a coffee mug and a doughnut: both contain one hole, so mathematically one can be continuously reshaped into the other without changing that defining property.
The researchers applied a similar principle to structured light by creating particle-like optical configurations known as skyrmions. Information was encoded into their topological structure rather than relying only on conventional properties such as intensity, color or polarization.
To test the approach outside the laboratory, the team transmitted skyrmion-encoded laser beams across a 270-meter open-air link between buildings on a university campus. Along the way, the beams encountered real atmospheric turbulence caused by wind and temperature variations.
According to Interesting Engineering, by the time the light reached the receiver, its physical appearance could be heavily distorted. Crucially, however, the underlying topology remained recognizable. The researchers reported more than 98% fidelity under most tested conditions, falling to around 86% during extreme turbulence.
That resilience could simplify free-space optical systems. Conventional approaches may use adaptive optics and real-time computation to measure atmospheric distortion and compensate for it. If the information itself is encoded in a property that remains stable through those disturbances, the receiver can potentially recover the payload without first reconstructing the original beam.
The technology could be particularly useful for satellite links and deep-space communications, where high data rates must be achieved while minimizing the weight, power consumption and computing requirements of communications hardware. It could also support terrestrial connections in locations where installing fiber is impractical.
There are potential defense applications as well. Free-space optical links can provide high-bandwidth communications between command posts, aircraft, satellites or other platforms. Reducing dependence on complex correction equipment could make such links more practical for mobile or constrained systems, although operational military environments would introduce additional challenges beyond atmospheric turbulence.
The experiment does not mean turbulence has been eliminated: under severe conditions, performance still declined. Instead, it demonstrates a different communications philosophy, rather than constantly fighting to preserve the shape of the light, preserve the information in a feature that remains meaningful even after the beam has been distorted.
The research was published here.
