Recently, Prof. Cui Xiaohan from the Electromagnetic Metamaterials Team at the State Key Laboratory of Millimeter Waves, Southeast University, in collaboration with Associate Professor Zhang Ruoyang from Nanjing University and Prof. Chen Ziting's team from the Hong Kong University of Science and Technology, proposed and demonstrated a novel type of topological photonic waveguide — an insulator-free topological photonic multi-channel highway. The related findings have been published in the top-tier international journal Nature. This research offers a new solution to the long-standing challenge in traditional topological photonic waveguides of balancing topological protection with spatial utilization efficiency.
With the continuous advancement of optical communications and photonic computing, how to accommodate more channels within a limited area while reducing reflection and crosstalk has become a critical issue in integrated photonics. Although topological optical waveguides can help light navigate around defects and sharp bends, they require wide photonic insulator regions to provide topological protection and optical field confinement. These regions do not participate in transmission, thereby limiting the spatial utilization efficiency of the device.
One can think of a traditional topological waveguide as a dedicated road flanked by wide buffer zones: vehicles travel stably, but only a small portion of the space is actually used for traffic. The "photonic highway" constructed in this study, by contrast, is more like a multi-lane expressway with lanes tightly packed together — each channel not only transmits its own signal but also serves as a "guardrail" for its neighboring channels, eliminating the need for additional large-area isolation layers.
The underlying physical foundation lies in the team's design of four types of special photonic crystals — photonic valley semi-metals. In these structures, one of the two valley degrees of freedom behaves as a gapless Dirac semi-metal, while the other behaves as a topological insulator, allowing the material to simultaneously serve as both a waveguide and a topologicalphotonicinsulating layer. By arranging these four valley semi-metals in a specific sequence, four parallel one-way channels can be formed in space. Different channels cooperate mutually, achieving 100% spatial utilization while ensuring topologically protected unidirectional transmission in every region.
The team built an experimental platform in the microwave frequency band and verified the existence of four unidirectional guided-wave channels. They demonstrated that electromagnetic waves could still propagate unidirectionally along the predetermined channels even through sharp 60°, 90°, and 120° bends, with backscattering and inter-channel crosstalk effectively suppressed. In contrast to traditional topological waveguides, where light is mostly concentrated near narrow interfaces, the waves in this new structure can be distributed throughout the entire channel. Therefore, by adjusting the width and shape of the channels, the field distribution can be broadened, compressed, or laterally shifted, opening up new possibilities for simultaneously achieving signal transmission and wave-field profile control within a compact space.
At the fundamental research level, this breakthrough transcends the traditional framework in which topological optical transmission relies on material boundaries or interfaces, opening a new path toward parallel and unidirectional robust light guidance using the entire spatial region. At the application level, it is expected to provide a new solution for high-density photonic chips, with the potential to reduce inactive space, increase channel density, and enhance information capacity. According to the team, this technology can be extended to multiple practical frequency bands in the future, including communication-wavelength light and terahertz waves. However, before practical deployment, engineering challenges such as material loss, device coupling, and integration with functional components on photonic chips must still be addressed.
This cross-institutional collaborative effort represents a significant original advance in the fields of topological photonics and integrated photonics in China. It provides a new underlying physical scheme for reconciling "robust transmission" with "high-density integration," and builds a theoretical and technical foundation for independent innovation in next-generation high-speed optical communications and on-chip photonic computing.
Prof. Chen Ziting is the corresponding author of the paper. Professors Cui Xiaohan and Zhang Ruoyang are the co-first authors and co-corresponding authors.
Paper Link: https://www.nature.com/articles/s41586-026-10817-9
Source: SEU News Network
Translated by: Melody Zhang
Edited by: Leah Li
