image: Figure | Experimental characterization for the on-chip meta-holography and AR demonstration. a, The on-chip metasurface is integrated onto the waveguide sitting on a transparent substrate to project LCP/RCP holographic images. The insets illustrate the phase distributions of the extracted LCP component for dielectric (Si) and metal (Al) materials. b, Optical setup to characterize the on-chip meta-holography. LP: linear polarizer. QWP: quarter-wave plate. Inset: SEM image of the metasurface sample. Scale bar: 500 nm. c, Measured LCP holographic image of “Key” and RCP holographic image of “Lock”. d, Actual experimental setup for the AR demonstration. The mobile phone camera captures virtual images floating on the background (green dashed frame) with no images present in the background picture (blue dashed frame). e, Experimentally captured AR images of a green “Key” and a green “Lock” floating on top of the background picture.
Credit: Cheng Yi et al.
Metasurfaces, as open optical systems, are widely regarded as ideal platforms for creating and exploiting topological exceptional points (EPs) due to their outstanding light-field manipulation capabilities. In previous studies, various functionalities have been demonstrated based on topological metasurfaces. However, these platforms often rely on metallic structures to introduce non-Hermitian properties, which inevitably lead to Ohmic losses. Such intrinsic dissipation limits overall optical efficiency and reduces compatibility with mainstream all-dielectric optical systems. Moreover, conventional free-space configurations hinder the integration of multiple devices into compact optical platforms, highlighting the urgent need for new design principles to overcome existing limitations in energy efficiency and device integration.
In a new paper published in Light: Science & Applications, a team of researchers, led by Professor Zhongyang Li from Wuhan University and Professor Qinghua Song from Tsinghua University reports a novel strategy for creating topological EPs by leveraging the precise extraction of guided wave optical fields via on-chip metasurfaces. This approach introduces non-Hermitian characteristics without the need for metals, enabling, for the first time, the creation of on-chip topological exceptional points within a fully all-dielectric environment. The resulting all-dielectric platform not only eliminates Ohmic losses but also suppresses zero-order diffraction background in projection-based augmented reality (AR) vector holography, thereby significantly enhancing image clarity and fidelity.
Specifically, the researchers engineered the shape and geometry of meta-atoms positioned atop the waveguide layer to realize topological EPs. For the extracted left-handed circularly polarized (LCP) component, a topological singularity appears in parameter space, exhibiting coinciding amplitude and phase singularities at the same spatial location. In contrast, no such topological features are observed for the right-handed circularly polarized (RCP) component. By combining Pancharatnam-Berry phase modulation with the topological phase accumulated around the EPs, the team successfully achieved polarization decoupling and independent encoding of dual-channel vector holography. A proof-of-concept demonstration of AR visualization showed vivid floating holographic images emerging from the background, confirming the practical potential of the platform.
In summary, this work represents an original attempt to integrate non-Hermitian features into an all-dielectric on-chip metasurface platform, aiming to achieve precise control of topological phases and significantly expand the degrees of freedom in optical encoding. The proposed on-chip all-dielectric topological metasurface enhances encoding capabilities through polarization decoupling, while maintaining excellent compatibility with integrated photonic systems. The researchers envision that this strategy could pave a promising path toward next-generation wearable AR devices, multiplexed information storage, and advanced optical display technologies.
Journal
Light Science & Applications
Article Title
Creating topological exceptional point by on-chip all-dielectric metasurface