June 12 2025 -- The Hong Kong University of Science and Technology (HKUST)-led research team has adopted gyromagnetic double-zero-index metamaterials (GDZIMs) - a new optical extreme-parameter material – and developed a groundbreaking method to control light using GDZIMs. This discovery could revolutionize fields like optical communications, biomedical imaging, and nanotechnology, enabling advances in integrated photonic chips, high-fidelity optical communication, and quantum light sources.

Published in Nature, the study was co-led by Prof. CHAN Che-Ting, Interim Director of the HKUST Jockey Club Institute for Advanced Study and Chair Professor in the Department of Physics, and Dr. ZHANG Ruoyang, Visiting Scholar in the Department of Physics at HKUST.

Unlocking the Potential of GDZIMs and Optical Vortices

GDZIMs are a unique type of optical metamaterial with properties that reside precisely at the critical transition point between two different photonic topological phases and can manipulate light in ways previously thought impossible. Unlike conventional materials, GDZIMs exhibit zero electric permittivity and unique magneto-optic property that allow stable generation of optical spatiotemporal vortices—patterns of light that swirl in space and time. This makes them exceptionally effective for controlling light propagation, which is crucial for many advanced technologies.

Through constructing a magnetic photonic crystal and tuning the parameters to the critical phase transition point, the researchers realized this metamaterial for the first time. Using microwave real-time field-scanning systems, they further demonstrated that when a light pulse hits a GDZIM slab, it reflects as a spatiotemporal vortex—an exotic type of light wave-packet exhibiting a simultaneous swirling structure in space and time and carrying transverse orbital angular momentum. Their investigation revealed that the generation of this light vortex stems from GDZIM’s intrinsic topological properties, thereby ensuring exceptional stability regardless of the material’s size or surrounding environment. This breakthrough could lead to significant improvements in optical technologies, such as faster and more secure communication systems.

Prof. Chan explained, “This research bridges three important areas of physics: metamaterials, topological physics, and structured light fields. It establishes a conceptually new mechanism for manipulating light structures in space-time based on the nontrivial topological properties of metamaterials. These findings open doors to high-precision optical devices with a wide range of applications that we have only begun to explore.”

Dr. Zhang added, “The stability of these light vortices is remarkable. It provides a solid foundation for developing advanced materials and technologies that could transform industries like telecommunications and high-performance optical circuits.”

A Cross-Regional Effort to Transform Optical Technologies

GDZIMs have many potential applications in different fields. Not only can they help create small integrated photonic chips that improve communication by minimizing interference, but they can also lead to novel handedness-selective light sources for advanced technologies. Moreover, their unique mechanism for generating light vortices presents a promising approach toward long-distance, high-capacity spatial optical information transmission, potentially advancing both the speed and security of optical network communications. The study, titled “Bulk–spatiotemporal vortex correspondence in gyromagnetic zero-index media”, was conducted in collaboration with researchers from City University of Hong Kong, Shenzhen University,  Fudan University, Wuhan University, and University of Southampton.