Leaky Guided Mode-Induced Large-Angle Nonlocal Metasurfaces

Metasurfaces that can manipulate light in the spatial domain via local modes are an ultrathin alternative to conventional optical systems. However, achieving large-angle modulation with such metasurfaces presents significant challenges such as diminished efficiency. To address this, the concept of metagrating has been introduced, facilitating the development of devices with a high numerical aperture or wide field of view. Nonlocal metasurfaces, which possess nonlocal modes and control light in both the temporal and spatial domains, encounter even greater difficulties in achieving large-angle modulation due to mode degradation and wavelength-period dependency, but an effective solution has not been proposed yet. Here, we devised a method for realizing large-angle nonlocal metasurfaces by inducing multiple leaky guided modes (LGMs) using a minimally perturbed meta-atom array in conjunction with a waveguide slab. A system that achieves spatial and spectral modulation of light by leveraging the geometric phase with an additional grating vector and coupling between the LGMs is designed, and this system achieves a quality factor and diffraction efficiency of 2.2 × 103 and 29%, respectively, at an extreme deflection angle of 79°. This investigation holds significant potential for applications in systems requiring wavelength-selective large-angle modulation, such as augmented reality and nonlocal harmonic generation.