Near-Flatband Resonances in Bilayer Moire Superlattices for Visible-to-Infrared Meta-Optics

Abstract Flat photonic bands enable extreme light confinement, slow-light effects, and angle-robust resonances that are valuable for meta-optics and integrated photonics. Here we report the design, fabrication, and experimental characterization of 1D Moiré superlattices formed by two closely spaced dielectric gratings with slightly mismatched periodicities. Using temporal coupled-mode theory and numerical simulations, we demonstrate that the guided modes fold and hybridize into nearly flat bands across the entire Brillouin zone. We develop an atomic layer deposition-based process to fabricate multilayer TiO2/air metasurfaces with controlled interlayer gaps and a high refractive-index contrast from visible to near-infrared. Experimental transmission spectra confirm a resonance with a resonance shift Δλ of 3.5 nm around a center wavelength of 1538 nm over an incidence-angle range of ±24◦. We further numerically demonstrate a wide-angle, wavelength-selective waveguide coupler with 32° angular bandwidth and a 0.9 nm resonance shift around 1447 nm. Our results establish TiO2 Moiré superlattices as a versatile platform for angle-robust waveguide couplers and AR/VR photonic devices, combining light-confining resonances with scalable fabrication.