In brief: A group of researchers has demonstrated a compact optical device that switches between two distinct topological states of light, marking a key step toward terahertz communication systems that encode information using structured light. The system produces both electric and magnetic vortices – stable, ring-shaped patterns of terahertz radiation known as skyrmions – using a single, integrated platform.
The work, reported in Optica by scientists from Tianjin University and Nanyang Technological University, marks the first experimental realization of skyrmions that can be actively toggled between electric and magnetic configurations.
Unlike ordinary light pulses, these toroidal or "donut-shaped" electromagnetic fields curl back on themselves, creating resilient patterns that resist interference and distortion. That stability makes them attractive for encoding data in light-based or wireless channels, where signal integrity is critical.
The device is built around a nonlinear metasurface – an ultrathin sheet patterned with metallic nanostructures precisely arranged to manipulate light at the subwavelength scale. When struck by near-infrared femtosecond laser pulses with different polarization patterns, the metasurface converts the incoming light into tailored terahertz pulses.
Depending on the polarization, it generates either an electric-mode or magnetic-mode skyrmion, effectively switching between two distinct vortex states in free space.
According to the team, the architecture relies on simple optical components such as wave plates and vortex retarders to control input polarization. That setup enables rapid switching between modes without the need for bulky mechanical adjustments.
The resulting device functions as both a light generator and a programmable switch, bridging the gap between conventional optics and emerging terahertz technologies.
To validate performance, the researchers built an ultrafast terahertz measurement system that tracks each light pulse as it propagates. By scanning across multiple positions and time intervals, they reconstructed the evolving electromagnetic fields in fine detail. The measurements confirmed that the toroidal pulses maintained their topological signatures and that mode switching occurred reliably and with high signal fidelity.
Terahertz light lies between the microwave and infrared regions, making it uniquely suited for high-bandwidth communication and sensing. However, generating and modulating structured terahertz fields has long been a challenge due to the difficulty of precisely shaping electromagnetic wavefronts. This experiment demonstrates not only that such shaping is possible but that it can be controlled dynamically in real time.
The researchers describe their metasurface as a proof of concept for a future generation of optical components capable of encoding and routing information through topological photonics – the study of light structures defined by their geometric stability rather than intensity or frequency alone.
... continue reading