Virtual exceptional points in optical lossless bilayer metasurfaces
Phys. Rev. Applied 25, 044082 – Published 28 April, 2026
DOI: https://doi.org/10.1103/8bpn-t317
Abstract
Scattering exceptional points (EPs) in non-Hermitian metasurfaces present significant opportunities for asymmetric wave modulation, while traditional approaches rely on the precise engineering of material losses within metasurfaces. Here, we overcome this limitation by engineering the radiation loss in a lossless optical system and introduce the concept of virtual scattering EPs, which exhibit singularity characteristics analogous to those of traditional EPs. By leveraging both broken angular symmetry of a single-layer structure and momentum compensation inherent in its bilayer configuration, we propose an all-dielectric bilayer metasurface that manifests the virtual EP. In this configuration, incident waves from one side experience perfect retroreflection, while waves from the opposite side undergo complete disappearance of reflection. Furthermore, this unique architecture supports an interlayer resonance mechanism that facilitates the transition of the reflective subsystem from a non-Hermitian to a Hermitian state, enabling a dynamic switch between angularly asymmetric and symmetric retroreflections. Our findings open different avenues for realizing scattering EPs and exploring unique non-Hermitian physics, offering exciting prospects for multifunctional and reconfigurable optical devices.
