Wavefront-Compatible Modal Reconfiguration in Phase-Change Nonlocal Metasurfaces

Abstract Nonlocal metasurfaces can provide narrow spectral responses and enhanced optical fields through coherent collective resonances. Introducing local phase encoding further enables wavefront control, but the associated perturbations can disrupt the coherent excitation of nonlocal resonances. This challenge becomes more severe in multimode systems, where the same phase-encoding scheme needs to accommodate distinct modal field distributions and coupling conditions. Here, we demonstrate wavefront-compatible modal reconfiguration in an Sb2Se3 nonlocal metasurface by introducing internal resonator coupling through integrated-resonant units (IRUs). By supporting multiple dipolar nonlocal resonant modes with isotropic field distributions, the IRUs preserve the collective resonances under in-plane rotation, enabling one nonlocal mode at 1558 nm in the amorphous state and two modes at 1500 and 1580 nm in the crystalline state. Across all three material-state-selected modes, the resonance wavelengths remain invariant within 1 nm over a 0°–180° rotation range, the geometric phase follows the ideal relation with root-mean-square errors below 2.5°, and the conversion efficiency fluctuations remain within 3%. As a proof of concept, a metalens based on this IRU switches from a single narrowband focusing channel to dual channels in the near-infrared region. These results show that state-selected nonlocal modes can be made compatible with geometric-phase encoding, providing a route to switchable narrowband metalenses and wavelength-multiplexed wavefront control.