As the demand for data storage grows, better ways to encode large amounts of data for rapid transmission are required. One method of transmitting data is to encode the data in laser light and send it through optical fibers. A new design method from Aalto University provides a way to create light vortices for transmitting data in fiber optic telecommunications with quasicrystals. In theory, this method supports the creation of any type of light vortex. Previous research has connected vortex type with the symmetry of the structure used to produce the vortex. For example, nanoparticles arranged in a square were found to produce light with a single vortex, while nanoparticles arranged in a hexagon generated a double vortex. More complex vortices required at least an octagonal arrangement. A quasicrystal design method developed at Aalto University theoretically allows for the creation of any kind of vortex. Courtesy of Aalto University/Kristian Arjas. Lasing with topological charge 1 or 2 can be realized in periodic lattices of up to six-fold rotational symmetry. Higher order charges require symmetries not compatible with any 2D crystal structure. The Aalto team sought to design plasmonic structures with non-crystallographic symmetries. The team investigated the relationship between the rotationality of a light vortex and the symmetry of the structure used to create it. One of the team’s goals was to better understand what kinds of vortexes could be generated with various types of symmetries. The researchers manipulated about 100,000 metallic nanoparticles to observe where the particles had the least interaction with the desired electric field. They demonstrated control over the mode energies of the structures via the ohmic losses inherent to metallic nanoparticles. They realized lasing with very high values of the topological charge q. “An electrical field has hotspots of high vibration and spots where it is essentially dead,” researcher Jani Taskinen said. “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.” The team fabricated samples and experimentally measured lasing 8-, 10-, and 12-fold rotationally symmetric structures with topological charges q = -3, -4, and -5. The researchers experimentally demonstrated lasing high topological charges of up to -17 and +19. The quasicrystal lasing provided rich textures of multiple topological charges, matching theoretical coupled-dipole calculations. The momentum-resolved spectrum revealed lasing in an energetically narrow band that was nearly uniform over all the measured momentum values. The new quasicrystal design approach could be an initial step toward the use of light vortices for optical data transmission. “We could, for example, send these vortices down optic fiber cables and unpack them at the destination,” researcher Kristian Arjas said. “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.” Additionally, this design method for creating vortices could advance the topological study of light. Since the appearance of multiple, higher-order topological defects depends on the structure, it should be possible to optimize each quasicrystal to support only a single charge, the team believes. In this way, coherent, bright beams of almost arbitrarily high topological charge could be created. The research was published in Nature Communications (www.doi.org/10.1038/s41467-024-53952-5).
