WARSAW: Scientists have created tiny “optical tornadoes” using a surprisingly simple setup based on liquid crystals – swirling rays of light that spin like miniature tornadoes. Instead of relying on complex nanotechnology, the team used self-organized structures called taurons to trap and manipulate light, causing it to spiral and rotate in complex ways.Even more impressively, they achieved this effect in the most stable, lowest-energy state of light, making it much easier to generate laser-like beams with these unusual properties.Can light spin like a tornado? Researchers have now shown that this can happen. Scientists from the Faculty of Physics of the University of Warsaw, the University of Military Technology and the Institut Pascal CNRS of the University Clermont Auvergne have created an “optical tornado” spinning inside an extremely small structure.The advance points to a new way to fabricate miniature light sources with complex shapes, which could support simpler and more scalable photonic devices for optical communications and quantum technologies.“Our solution connects many areas of physics, from quantum mechanics through materials engineering to optics and solid-state physics,” explains the leader of the research group, Professor Jacek Szczytko of the Faculty of Physics at the University of Warsaw.“The inspiration came from systems known from nuclear physics, where electrons can occupy different energy states. In photonics, a similar role is played by optical traps, which confine light rather than electrons,” Szczytko said. What is an optical vortex?“You can think of it as an optical vortex,” says the study’s first author, Dr. Marcin Muszynski of the Physics Faculty of the University of Warsaw and the Physics Department of the City College of New York.“The light wave rotates around its axis, and its phase changes in a spiral manner. In addition, the polarization – the direction of oscillation of the electric field – also begins to rotate,” Marcin said.These structured light states are attractive for applications such as quantum communications and controlling microscopic objects. However, their production usually requires complex nanostructures or large experimental systems. Liquid crystals provide a simple wayThe team chose a different strategy. “Instead of building complex systems, we used a liquid crystal, a material that has properties intermediate between a liquid and a solid. Although it can flow like a liquid, its molecules arrange themselves in an ordered way, maintaining a fixed orientation and relative position, like crystals,” explains Joanna Medrzycka, a nanotechnology student at the Faculty of Physics of the University of Warsaw, who together with Dr. Eva Otten of the Military University of Technology prepared liquid crystal samples.Special defects called torsions can form within this material. “They can be imagined as tightly twisted spirals, similar to DNA, along which liquid crystal molecules are arranged. If such a spiral is closed by connecting its ends in a donut-like ring, we obtain a toron,” explains Medrzycka. “These structures act as microscopic traps for light. An important step was to create a magnetic field equivalent to that for photons. Although light does not respond to magnetic fields like electrons do, similar behavior can be achieved for light by other means.” A “synthetic magnetic field” for light.“Spatially variable birefringence, i.e. the difference in propagation of different polarizations of light, acts like a synthetic magnetic field,” explains Dr. Piotr Kapuscinski of the Faculty of Physics at the University of Warsaw. “We call it ‘synthetic’ because its mathematical description resembles the behavior of a magnetic field, even though physically it is not there. As a result, the light begins to ‘bend’, much like electrons rotating in cyclotron orbits.“To strengthen the effect, the toron was placed inside an optical microcavity, a structure made of mirrors that repeatedly reflect light and confine it for long periods of time. “It makes the field very strong,” says Dr. Muzynski. “Additionally, we can control the size of the trap and thus the properties of the light using an external electrical voltage.” Stable light vortex in the ground state. The most surprising result came next.“In typical systems, the orbital angular momentum carrying light appears in the excited state,” said Prof. of the Université Clermont Auvergne and CNRS. Guillaume Malpuech explains, who Prof. Together with Dmitry Solnyshkov and post-doc Daniil Bobilev developed a theoretical model of the phenomenon. “For the first time, we managed to achieve this effect in ground conditions, i.e., Lowest energy state. This is important because the ground state is the most stable and easiest to store energy.““This makes lasing much easier to achieve,” Professor Szczytko insists. “Light naturally ‘chooses’ this condition because it is associated with the least damage.”To confirm this, the researchers introduced a laser dye into the system. “We achieved light that not only rotates but also behaves like laser light: it is coherent and has a well-defined energy and emission direction,” says Dr. Marcin Muzynski.Towards simple photonic and quantum technologies“It is interesting that our approach draws inspiration from very advanced theories involving so-called vector charges,” says Professor Dmitry Solnyshkov.“This discovery opens a new path to creating miniature light sources with complex structures. “It shows that instead of relying on complex nanotechnology, we can use self-organized materials,” concludes Professor Victor Pasek of the University of Military Technology. “In the future, this could enable simpler and more scalable photonic devices, for example for optical communications or quantum technologies.“
