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<p>Nonlocal flat optics such as photonic crystal slabs, guided-resonance dielectric metasurfaces, and plasmonic lattices use collective Bloch modes and their radiation coupling to achieve sharp spectral selectivity, tailored dispersion, and wavefront control within subwavelength thicknesses. Yet in single-layer platforms, optical functionality is constrained by limited geometric degrees of freedom: in-plane symmetry and pre-patterned geometry largely determine mode structure, while radiation channels, linewidths, and polarization responses are often linked through fixed symmetry-imposed selection rules. Bilayer nonlocal flat-optics platforms break this bottleneck by introducing interlayer degrees of freedom that are independent of the in-plane lattice design, most importantly the interlayer separation (controlling near-field hybridization strength and far-field interference phase), as well as relative translation, twist, and lattice mismatch. This review organizes bilayer nonlocal flat optics by interlayer configurations and highlights the additional design space and reconfigurability uniquely enabled by two coupled flat-optical layers. For example, we connect aligned bilayers to mode hybridization, radiation interference, and high-<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(Q\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>Q</mi> </math></EquationSource> </InlineEquation> routes to bound states in the continuum. We then show how lateral misalignment unlocks symmetry breaking, off-Γ singularities, unidirectional guided resonances, and synthetic-dimensional non-Hermitian topology. Next, we discuss how lattice mismatch generates moiré superlattices with miniband flattening and localization into moiré cavities, and how twist-driven momentum mixing supports twist-tunable resonances, moiré quasi-BICs, structured radiation such as optical vortices, beam steering, and emergent chirality. Across these themes, bilayer systems unify band-structure engineering, radiation-channel topology, and post-fabrication tunability into a compact platform for reconfigurable flat-optical devices.</p>

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Bilayer nonlocal flat optics

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月9日

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  • Haoning Tang,
  • Shanhui Fan,
  • Yao Jie,
  • Hai Son Nguyen,
  • Eric Mazur,
  • Yuan Cao

摘要

Nonlocal flat optics such as photonic crystal slabs, guided-resonance dielectric metasurfaces, and plasmonic lattices use collective Bloch modes and their radiation coupling to achieve sharp spectral selectivity, tailored dispersion, and wavefront control within subwavelength thicknesses. Yet in single-layer platforms, optical functionality is constrained by limited geometric degrees of freedom: in-plane symmetry and pre-patterned geometry largely determine mode structure, while radiation channels, linewidths, and polarization responses are often linked through fixed symmetry-imposed selection rules. Bilayer nonlocal flat-optics platforms break this bottleneck by introducing interlayer degrees of freedom that are independent of the in-plane lattice design, most importantly the interlayer separation (controlling near-field hybridization strength and far-field interference phase), as well as relative translation, twist, and lattice mismatch. This review organizes bilayer nonlocal flat optics by interlayer configurations and highlights the additional design space and reconfigurability uniquely enabled by two coupled flat-optical layers. For example, we connect aligned bilayers to mode hybridization, radiation interference, and high- \(Q\) Q routes to bound states in the continuum. We then show how lateral misalignment unlocks symmetry breaking, off-Γ singularities, unidirectional guided resonances, and synthetic-dimensional non-Hermitian topology. Next, we discuss how lattice mismatch generates moiré superlattices with miniband flattening and localization into moiré cavities, and how twist-driven momentum mixing supports twist-tunable resonances, moiré quasi-BICs, structured radiation such as optical vortices, beam steering, and emergent chirality. Across these themes, bilayer systems unify band-structure engineering, radiation-channel topology, and post-fabrication tunability into a compact platform for reconfigurable flat-optical devices.