Tailoring Low‐Dispersion Modes Through Transverse Brillouin Zone Folding

Abstract Lattice modulation‐induced Brillouin zone (BZ) folding has emerged as a powerful strategy for engineering diverse optical resonances. However, the low‐dispersion band structure along the Y‐M direction and the interactions between these folded bands remain largely unexplored. In this work, transverse periodic doubling is introduced in metasurfaces through geometric perturbations, leading to transverse BZ folding. This enables non‐radiative waveguide modes along the Y‐M direction, including a quasi‐flat band, to couple into the radiative continuum. This mechanism allows for the formation of a new class of guided mode resonances and even bound states in the continuum. By tuning the structural parameters to control the interactions between these folded bands, electromagnetically induced transparency is experimentally demonstrated with low dispersion and strong angular robustness. The proposed approach offers new insights into the design of low‐dispersion resonant modes and paves the way for high‐performance, angle‐insensitive optical devices.