Orthogonal Flatbands-Enabled Robust Fano Resonances through Brillouin-Zone Folding

Yangsong Ye; Hanchuan Chen; Shijie Kang; Haitao Li; Ken Qin; Boyuan Ge; Xiexuan Zhang; Jingrong He; Jiusi Yu; Xiaoxiao Wu; Chunlei Yang

arXiv · 2609.25902

Orthogonal Flatbands-Enabled Robust Fano Resonances through Brillouin-Zone Folding

Yangsong Ye·Hanchuan Chen·Shijie Kang·Haitao Li·Ken Qin·Boyuan Ge·Xiexuan Zhang·Jingrong He·Jiusi Yu·Xiaoxiao Wu·Chunlei Yang

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Abstract

Fano resonances based on coherent interference between localized Lorentz modes and Fabry-Perot radiation continua have been widely explored for microwave metamaterial sensors, filters, and photonic devices. However, conventional Fano metasurfaces suffer from angular dispersion and polarization-dependent spectral variations, limiting robustness under dynamic illumination. Here, we propose a band-folding-enabled flatband engineering strategy to realize robust Fano resonances in a planar microwave metasurface with a 2x2 enlarged cell of orthogonally arranged H-shaped metallic resonators. The enlarged cell induces Brillouin-zone folding, generating a nearly dispersionless flatband near 15.3 GHz with suppressed momentum dependence and enhanced photonic confinement. This flatband state provides a high-Q localized resonance strongly coupled to the FP radiation continuum, producing a stable asymmetric Fano response. Furthermore, the orthogonal resonator configuration supports two polarization-decoupled dipole modes with comparable excitation efficiency, reducing polarization-induced spectral distortion. Near-field measurements and simulations verify localized flatband features, while far-field experiments demonstrate stable Fano responses under oblique incidence from 0° to 30° with minor resonance variation. A temporal coupled-mode theory model is developed to quantitatively describe Fano spectral evolution under different illumination conditions. This work establishes a flatband-mediated route toward robust microwave Fano metasurfaces and offers a general strategy for stable resonant photonic device design.

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Yangsong Ye, Hanchuan Chen, Shijie Kang, Haitao Li, Ken Qin, Boyuan Ge, Xiexuan Zhang, Jingrong He, Jiusi Yu, Xiaoxiao Wu, Chunlei Yang. 2026-09-22. Orthogonal Flatbands-Enabled Robust Fano Resonances through Brillouin-Zone Folding. https://arxiv.org/abs/2609.25902

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