Can light spin like a whirlwind? Researchers have now shown that it will possibly. Scientists from the Faculty of Physics on the University of Warsaw, the Military University of Technology, and the Institut Pascal CNRS at Université Clermont Auvergne have created swirling “optical tornadoes” inside a particularly small structure. The advance points to a brand new way of constructing miniature light sources with complex shapes, which could support simpler and more scalable photonic devices for optical communication and quantum technologies.
“Our solution combines several fields of physics, from quantum mechanics, through materials engineering, to optics and solid-state physics,” explains Prof. Jacek Szczytko from the Faculty of Physics on the University of Warsaw, the leader of the research group. “The inspiration got here from systems known from atomic physics, where electrons can occupy different energy states. In photonics, an analogous role is played by optical traps, which confine light as an alternative of electrons.”
What Is an Optical Vortex?
“You’ll be able to consider it as an optical vortex,” says Dr. Marcin Muszyński from the Faculty of Physics on the University of Warsaw and Department of Physics City College of Latest York, the primary creator of the study. “The sunshine wave twists around its axis, and its phase changes in a spiral manner. Furthermore, even the polarization — the direction of oscillation of the electrical field — begins to rotate.”
These structured light states are attractive for applications reminiscent of quantum communication and controlling microscopic objects. Nevertheless, producing them has typically required complicated nanostructures or large experimental systems.
Liquid Crystals Offer a Simpler Path
The team selected a unique strategy. “As an alternative of constructing complex systems, we used a liquid crystal, a cloth with properties intermediate between a liquid and a solid. Although it will possibly flow like a liquid, its molecules arrange themselves in an ordered way, maintaining a hard and fast orientation and relative positions, very like in a crystal,” explains Joanna Mędrzycka, a nanotechnology student on the Faculty of Physics, University of Warsaw, who, along with Dr. Eva Oton from the Military University of Technology, prepared the liquid crystal samples.
Inside this material, special defects referred to as torons can form. “They may be imagined as tightly twisted spirals, just like DNA, along which the liquid crystal molecules are arranged. If such a spiral is closed by joining its ends right into a ring resembling a doughnut, we obtain a toron,” Mędrzycka explains. “These structures act as microscopic traps for light. A key step was creating an equivalent of a magnetic field for photons. Although light doesn’t reply to magnetic field like electrons do, an analogous behavior may be achieved for light by other means.”
A “Synthetic Magnetic Field” for Light
“Spatially variable birefringence, that’s, the difference within the propagation of various polarizations of sunshine, acts like an artificial magnetic field,” explains Dr. Piotr Kapuściński of the Faculty of Physics on the University of Warsaw. “We call it ‘synthetic’ because its mathematical description resembles the behavior of a magnetic field, although physically it’s not there. Because of this, light begins to ‘bend,’ very like electrons moving in cyclotron orbits.”
To strengthen the effect, the toron was placed inside an optical microcavity, a structure made from mirrors that repeatedly reflects light and keeps it confined for longer periods. “This makes the sphere much stronger,” says Dr. Muszyński. “Moreover, we will control the dimensions of the trap, and thus the properties of the sunshine, using an external electric voltage.”
Stable Light Vortices within the Ground State
Probably the most striking result got here next.
“In typical systems, light carrying orbital angular momentum appears in excited states,” explains Prof. Guillaume Malpuech from Université Clermont Auvergne and CNRS, who, along with Prof. Dmitry Solnyshkov and post-doc Daniil Bobylev, developed the theoretical model of the phenomenon. “For the primary time, we managed to acquire this effect in the bottom state, i.e., the lowest-energy state. This is important because the bottom state is essentially the most stable and the simplest for energy to build up in.”
“This makes it much easier to attain lasing,” emphasizes Prof. Szczytko. “Light naturally ‘chooses’ this state since it is related to the bottom losses.”
To verify this, the researchers introduced a laser dye into the system. “We obtained light that not only rotates but in addition behaves like laser light: it’s coherent and has a well-defined energy and emission direction,” says Dr. Marcin Muszyński.
Toward Simpler Photonic and Quantum Technologies
“It’s interesting that our approach draws inspiration from very advanced theories involving a so-called vectorial charge,” adds Prof. Dmitry Solnyshkov “So, in a way, we have managed to make photons behave not even like electrons, but like quarks, the charged particles which make up protons.
“This discovery opens a brand new pathway for creating miniature light sources with complex structures. “It shows that as an alternative of counting on complex nanotechnology, we will use self-organizing materials,” concludes Prof. Wiktor Piecek from the Military University of Technology. “In the long run, this may occasionally enable simpler and more scalable photonic devices, for instance for optical communication or quantum technologies.”