Much of modern life depends on the coding of information onto means of delivering it. A common method is to encode data in laser light and send it through optic cables. The increasing demand for more information capacity demands that we constantly find better ways of encoding it. Researchers at Aalto University’s Department of Applied Physics found a new way to create tiny hurricanes of light or vortices that can carry information. The method is based on manipulating metallic nanoparticles that interact with an electric field.

The design method, belonging to quasicrystals, was thought up by Kristian Arjas and experimentally realized by Jani Taskinen, both from Päivi Törmä’s Quantum Dynamics group. The discovery represents a funda­mental step forward in physics and carries the potential for entirely new ways of transmitting information. A vortex is in this case like a hurricane that occurs in a beam of light, where a calm and dark centre is surrounded by a ring of bright light. Just like the eye of a hurricane is calm due to the winds around it blowing in different directions, the eye of the vortex is dark due to the electric field of bright light pointing to different directions on different sides of the beam.

Previous physics research has connected what kind of vortices can appear with how much symmetry there is in the structure that produces them. For example, if particles in the nanoscale are arranged in squares the produced light has a single vortex; hexagons produce a double vortex and so on. More complex vortices require at least octagonal shapes. Now Arjas, Taskinen and the team unlocked a method for creating geometric shapes that theo­retically support any kind of vortex.

“This research is on the relationship between the symmetry and the rotationa­lity of the vortex, i.e. what kinds of vortices can we generate with what kinds of symmetries. Our quasi­crystal design is halfway between order and chaos,” Törmä says. In their study, the group manipulated 100,000 metallic nanoparticles to create their unique design. The key lay in finding where the particles interacted with the desired electric field the least instead of the most. “An electrical field has hotspots of high vibration and spots where it is essentially dead. We introduced particles into the dead spots, which shut down every­thing else and allowed us to select the field with the most interesting properties for appli­cations,” Taskinen says.

The discovery opens a wealth of future research in the very active field of topological study of light. It also represents the early steps for a powerful way of transmitting information in domains where light is needed to send encoded information, including telecommuni­cations. “We could, for example, send these vortices down optic fiber cables and unpack them at the destination. This would allow us to store our information into a much smaller space and transmit much more information at once. An optimistic guess for how much would be 8 to 16 times the information we can now deliver over optic fiber,” Arjas says. But practical appli­cations and scala­bility of the team’s design are likely to take years of engineering. (Source: Aalto U.)

Reference: K. Arjas et al.: High topological charge lasing in quasicrystals, Nat. Commun. 15, 9544 (2024); DOI: 10.1038/s41467-024-53952-5

Link: Quantum Dynamics, Dept. of Applied Physics, Aalto University School of Science, Espoo, Finland