British and Chinese researchers have discovered a new family of 3D topological light-structured solitons: photonic hopfions. Their textures and topological numbers can be freely and independently configured. Such control of topological properties opens up the possibility of using these light quasi-particles for optical transmission of information. Imagine a smoke ring flying through the air. It can move in this way without losing its form, unless it encounters a disturbance. Such stable localized wave structures have been studied in various fields of research, including magnets, nuclear systems, and particle physics. However, these structures can resist perturbations through what scientists call “topological protection.” ” Topological solitons with a topologically protected spin texture are of fundamental interest for the study of fascinating physical phenomena and nonlinear field theories, ” the researchers note. A typical example is the hurricane-like texture at the nanolevel of a magnetic field in magnetic thin films that behave like particles (i.e. without changing their shape) called skyrmions. These complex topological structures are considered as promising information carriers. Similar donut-shaped (or toroidal) structures in three-dimensional space that visualize complex spatial distributions of various wave properties are called hopfions. However, it is very difficult to obtain such structures using light waves. A new family of 3D topological solitons Recent studies of structured light have revealed strong spatial variations in polarization, phase, and amplitude, opening up the possibility of creating topologically stable optical structures that behave like particles. Such quasiparticles of light, whose topological properties can be finely controlled, have great potential, especially for optical storage and transmission of information and for quantum technologies. To date, only a very limited number of Hopfions have been experimentally realized. For example, magnetic hopfions of the Bloch (vortex) and Neel (hedgehog) types can be excited and exist in a stable state in chiral magnets. In photonics, only fundamental-order Hopfions with a unit Hopf number have been reported, say the researchers, whose work is published in the journalAdvanced Photonics. It remains to study the generation and properties of higher order photon hopfions and their topological spin texture tuning. ” We present a new and highly unusual family of 3D topological solitons in structured light, photon hopfions, whose topological textures and topological numbers can be freely and independently tuned, far beyond the previously described fixed low-order topological textures ,” explains the first author of the study. Yijie Shen, from the University of Southampton. Shen and colleagues have demonstrated the generation of polarization patterns with topologically stable properties in three dimensions, which for the first time can be transformed and propagated in a controlled manner in free space. Three-dimensional topological solitons, such as Hopfions, are three-dimensional localized continuous field configurations with non-trivial particle structures that exhibit many important topological properties, they note. Principle applicable to other types of topological quasiparticles Experimental generation and characterization of this new hopfion family revealed “a rich structure of topologically protected polarization textures”. Unlike previous observations of hopfions localized in solid materials, the team found that an optical hopfion is able to propagate in free space with topological protection of the polarization distribution. It is this reliable topological structure that is of interest for the development of optical topological computing and communications. The researchers note that this newly developed model of optical topological hopfions can be easily extended to other higher order topological formations in other branches of physics. Higher order hopfions are difficult to observe in other areas, from high energy physics to magnetic materials. The optical approach proposed by Shen and co-workers may provide a better understanding of this complex field of structures in other branches of physics.