Light ‘knots’ Survive 270-Metre Atmospheric Journey, Boosting Data Transmission Hopes

Researchers are increasingly investigating structured light as a means to enhance data transmission in optical networks, but practical implementation suffers from distortions such as atmospheric turbulence. Cade Peters (University of the Witwatersrand), Vagharshak Hakobyan (University of Bordeaux) and Alice Drozdov (University of the Witwatersrand) et al. now report the successful transmission of optical skyrmions, particle-like structures of light, across a 270m free-space link, demonstrating their remarkable resilience to these real-world atmospheric effects. This work is significant because it establishes, for the first time, the potential for utilising optical topologies as robust and reliable carriers of information in challenging environments, achieving greater than 98% fidelity in most conditions and opening avenues for advanced classical and quantum communications.

Robust topological light transmission through significant atmospheric turbulence is a challenging but achievable goal

Scientists have demonstrated the resilience of light-based topologies, specifically optical skyrmions, when transmitted through 270 metres of open air. This breakthrough addresses a critical limitation in modern optical networks, the susceptibility of structured light to distortions caused by atmospheric turbulence.

The research reveals that these particle-like light structures maintain their topological properties even when subjected to severe and rapidly changing atmospheric conditions, paving the way for more reliable data transmission. By utilising topology, information can be transmitted with almost perfect fidelity, exceeding 98% in most conditions and remaining above 86% even in the most turbulent environments tested.

Optical skyrmions, created and transmitted across the free-space link, exhibit a remarkable robustness against distortions affecting amplitude, phase, and polarisation. While the underlying characteristics of the light states are significantly altered by atmospheric turbulence, the fundamental topological numbers remain consistently preserved.

Researchers accounted for the dynamic nature of the atmospheric channel by analysing the state’s decoherence, revealing that even as polarisation decays, the core topology remains intact. This preservation of topology is crucial for maintaining signal integrity during transmission. This work represents the first successful demonstration of optical topologies as dependable information carriers in a real-world environment.

The study employed a spatially resolved Stokes polarimetry setup to measure the topology, enabling simultaneous assessment of all four Stokes parameters. Measurements were conducted under diverse atmospheric conditions, ranging from stable morning air to the intense distortions of midday heat, confirming the consistent preservation of the topological wrapping number.

The findings suggest potential applications extending beyond classical communication to encompass quantum communication protocols. Furthermore, the research highlights the potential for utilising topology to overcome limitations in complex channels beyond atmospheric turbulence. By performing measurements within the atmospheric coherence time, and extending to timescales exceeding it, the team demonstrated the continued robustness of the skyrmions. This resilience, achieved without any pre- or post-correction for channel distortion, underscores the inherent advantages of employing topological protection for optical data transmission and opens new avenues for robust, correction-free optical communication.

Optical skyrmion generation, polarisation mapping and free-space transmission characteristics were investigated

A spatial light modulator and a modified Mach, Zehnder interferometer generated optical skyrmions with topological charges of N = 1, 2 and 3 for transmission across a 270m free-space optical link. These beams were then projected onto a polarisation sensitive camera and 50:50 beam splitter to simultaneously measure horizontal, vertical, diagonal, antidiagonal, right-circular and left-circular polarisation intensity projections.

This single-shot measurement ensured full state of polarisation determination within the channel’s coherence time. Experimentally reconstructed states of polarisation and Stokes vector textures were mapped onto the spatial sphere for N = 1 and N = 2 skyrmions prior to free-space propagation, revealing distinct wrapping patterns around the Poincaré sphere corresponding to each topology.

The research team then assessed robustness through the real-world free-space link, initially characterising the skyrmions indoors to establish a baseline with no turbulence. Measurements were subsequently taken outdoors in the morning, midday and late afternoon to capture varying turbulence strengths.

Intensity profiles and states of polarisation were recorded at each time point, revealing distortions attributable to phase shifts induced by the channel and differing Gouy phases of component scalar beams. Each Laguerre-Gaussian beam component accumulated phase according to eiψ(z), where ψ(z) = (2p + |l| + 1) arctan(z/zR), influencing the polarisation structure but not the underlying skyrmion mapping.

Midday conditions produced the most severe distortions, manifesting as separate lobes in intensity profiles and rapid variations in polarisation, correlating with peak temperatures and strong turbulence. Conversely, morning conditions exhibited minimal distortion with roughly maintained cylindrical symmetry in the state of polarisation. Computed Stokes vector textures for morning data demonstrated that, despite noticeable differences from pre-propagation textures, the topological features remained intact, with vectors rotating once around for N = 1 and twice for N = 2, aligning with experimentally computed sphere coverage values of Nexp = 0.81±0.01 and 2.063±0.003 respectively.

Robust topological charge preservation in long-range free-space optical skyrmion propagation is experimentally demonstrated

Optical skyrmions exhibit remarkable resilience when transmitted through a 270-meter free-space optical link, maintaining information fidelity even under turbulent atmospheric conditions. Information transmission achieved greater than 98% fidelity in most cases, decreasing to 86% only in the most severe turbulence experienced during the study.

These particle-like topologies of light were successfully propagated, demonstrating preservation of topological numbers despite significant distortions to the underlying degrees of freedom. Researchers measured the topological wrapping number, a key characteristic of these skyrmions, and found it remained robust across a wide range of atmospheric conditions, from calm mornings to intense midday heat.

The study involved creating optical skyrmions using Laguerre-Gaussian beams, modulating the azimuthal index to tune the topological wrapping number and imbue the beam with orbital angular momentum. A spatially resolved Stokes polarimetry setup was employed, enabling simultaneous measurement of all four Stokes parameters in a single shot.

Measurements within the atmospheric coherence time revealed high robustness of the topological wrapping number, even when amplitude and phase distortions severely altered the beam’s appearance and polarisation. Averaging measurements over timescales exceeding the coherence time, to account for evolving distortions, showed preservation of the topological wrapping number despite a nearly 40% reduction in the beam’s degree of polarisation. These results demonstrate the potential for topological light to greatly improve the capacity of free-space optical communication, both classical and quantum, and motivate the development of new technologies for efficient generation and detection of these robust light states.

Turbulence-resistant propagation of topologically encoded information is crucial for robust quantum computation

Optical skyrmions demonstrate considerable resilience when transmitting data through turbulent atmospheric conditions. Researchers have successfully transmitted these complex light topologies over a 270-metre free-space optical link, revealing their stability despite significant distortions to amplitude, phase, and polarisation.

Crucially, the topological properties of the light remained preserved even as the underlying degrees of freedom were altered by turbulence and decoherence. Information encoded using these topologies was transmitted with high fidelity, exceeding 98% in most scenarios and remaining above 86% even under the most severe turbulence experienced during testing.

This work establishes the potential of optical skyrmions as robust carriers of information in real-world environments, offering a distinct advantage over methods requiring pre- or post-transmission compensation or channel measurement. The inherent invariance of topological structures allows them to propagate through distorting media without requiring knowledge of the channel characteristics, a benefit extending beyond the limitations of approaches reliant on channel unitarity.

The authors acknowledge that current measurement techniques, such as Stokes polarimetry, are susceptible to noise and fluctuations, potentially introducing errors in the determination of topological numbers. Future research may focus on developing dedicated topological detectors to improve measurement accuracy and explore the application of these principles to other complex communication channels, potentially benefiting both classical and quantum information transfer.