Electric-magnetic-switchable free-space skyrmions in toroidal light pulses via a nonlinear metasurface

Recent advances reveal that light propagation in free space supports many exotic topological textures, such as skyrmions. Their unique space–time topologies make them promising candidates as next-generation robust information carriers. Hence, the ability of switching different texture modes to serve as a manner of data transfer is in high demand. However, previous studies focus on generation of one specific mode, lacking integrated devices with externally variable and stable mode generation capability. Here, we experimentally demonstrate the realization of switchable skyrmions between electric and magnetic modes in toroidal light pulses (TLPs) using a nonlinear metasurface platform in terms of broadband terahertz (THz) generation driven by a vectorial pulse. The spatial and temporal evolutions of them are also clearly observed. Our work establishes a new paradigm, to our knowledge, for manipulating and switching topologically structured light.