Nonlocal Coupling in Hybrid Bilayer Metasurfaces via Out‐of‐Plane Quadrupole Surface Lattice Resonance

A hybrid bilayer metasurface is prepared by placing a flexible metallic metasurface sticker onto another dielectric metasurface on solid substrate and the optical coupling between the two metasurfaces is investigated. The top layer supports a bright out‐of‐plane quadrupole surface lattice resonance (QSLR), while the bottom layer supports a dark quadrupole mode. When stacked together, they couple into two hybridized modes, symmetric and anti‐symmetric QSLRs. It is found that the splitting width, as well as the nature of these modes, depends on the spacer layer thickness t . The long decay length of the QSLR along the z ‐direction and its slow variation with t suggest that the interlayer coupling is mediated not by a local gap mode but by a nonlocal, extended mode. A key consequence of this nonlocal coupling is the insensitivity of the resonances to the lateral misalignment of the two layers. This alignment‐free property is highly advantageous for designing bilayer metasurfaces. Furthermore, it is demonstrated that photoluminescence enhancement from an emitter embedded in the spacer layer: The large field accumulation associated with the symmetric QSLR led to a remarkable photoluminescence enhancement up to 60 times compared to the bare spacer layer on the substrate. These findings pave the way toward quasi‐3D metasurfaces formed by stacking individual layers with precisely tuned interlayer distances, offering a promising approach for future photonic elements with integrated functionalities.