Unlocking closely spaced wavelength multiplexing by disrupting topological protection in non-Hermitian metasurfaces.

Wavelength-multiplexed metasurfaces enable precise, independent light control at multiple wavelengths within a single platform, demonstrating significant potential for compact applications in imaging, optical communications, and information processing. Exceptional points (EPs) in non-Hermitian systems have garnered considerable interest in optics and physics owing to their unique phase characteristics in parameter space. Prior approaches to wavelength-multiplexing metasurface design employ neural networks, polarization manipulation, or spatial division. In contrast, this work leverages the wavelength dependence of EPs to implement wavelength multiplexing with narrow channel spacing under a single polarization state. By adopting distinct paths in parameter space, we achieve customized wavelength-dependent phase manipulations. As a practical demonstration, we independently manipulate two wavelengths to generate orbital angular momentum (OAM) beams with distinct topological charges (with a wavelength spacing of 38 nm), and customized holographic patterns at shorter wavelength spacing (18 nm).