Self-healing arrays of twisted light from a laser
- Wits Communications
Wits physicist part of team that develops novel laser.
Interacting twists and swirls occur in many natural systems, for instance, in clusters of cyclones encircling the poles of Jupiter and motile haploid cells of sea urchins swimming in vortex trajectories. But this type of interaction doesn’t naturally happen with light, until now.
An Italian-South African research collaboration featuring Professor Andrew Forbes from the School of Physics published in Nature Photonics a novel laser with 100 mini twisted laser beams that interact. Surprisingly, the interaction allowed the twists to self-heal if perturbed, ushering in a path to resilient arrays of light from lasers.
Inside the laser was a nano-structured “metasurface” made of an array of 10 x 10 mini metasurfaces, each capable of producing a twisted light beam. Twisted light is similar to the swirl we see in water draining from a sink, except in light the swirl is in its energy flow. By carefully designing the laser cavity, the team showed that the 100 twisted light beams could be coupled so that they shared common properties. As a consequence, when one was perturbed it could be self-healed by interacting with the others.
“Usually lasers give out one blob of light, like your laser pointer, but this laser gives out 100 exotic beams all coupled together and interacting,” explains Forbes, collaborator on the project and Distinguished Professor in the School of Physics where he heads up the Wits Structured Light Laboratory. “Lasers are often very sensitive to errors, but this laser can find the error and fix it!”
Link to the Nature Photonics article: https://www.nature.com/articles/s41566-022-00986-0
Geometric arrays of vortices can be found in various physics fields, owing their regular internal structure to mutual interactions within a spatially confined sys- tem. In optics, such vortex crystals may form spontaneously within a nonlinear resonator as the result of a complex energy minimization problem. Their crystallization is relevant in many areas of physics, though their usefulness in the framework of topological optics is limited by the lack of control over their topology. On the other hand, programmable devices used in free space, like spatial light modulators, allow the design of nearly arbitrary vortex distributions but without any intrinsic evolution. By combining non-Hermitian optics with on-demand topological transformations enabled by metasurfaces, we report a solid-state laser that generates optical vortices with mutual coupling and actively tunable topologies. We demonstrate 10×10 vortex laser arrays with nonlocal coupling networks that are not limited to nearest-neighbour coupling but rather dictated by the crystal’s topology. The vortex crystals exhibit sharp Bragg diffraction peaks, witnessing their coherence and high topological charge purity, which we resolve spatially over the whole lattice by introducing a parallelized analysis technique. By structuring light at the source, we enable complex transformations that allow to arbitrarily partition the orbital angular momentum inside the cavity and to heal topological charge defects, making these resonators a robust and versatile tool for advanced applications in topological optics.