Symmetry‐Assisted Spectral Line Shapes Manipulation in Dielectric Double‐Fano Metasurfaces

Abstract Spectral line shapes feature many essential resonant phenomena when diagnosing light–matter interactions. Particularly, tailoring spectral line shapes in photonics unveils a robust scheme to control electromagnetic waves and design functional optical devices. Here, the symmetry‐assisted manipulation of spectral line shapes in dielectric double‐Fano metasurfaces is theoretically proposed and experimentally demonstrated. Composed by a free‐standing silicon membrane with subwavelength aperture arrays, the metasurfaces simultaneously support two orthogonal localized modes (symmetric and antisymmetric) with high‐quality (high‐Q) factors and a propagating mode with a low‐Q factor. The symmetric and antisymmetric modes interfere with the propagating mode, resulting in the double‐Fano resonances with opposite signs of Fano parameters. The superposition of such double‐Fano resonances can produce multiple spectral line shapes, including double‐Fano resonances, a single Fano resonance, an electromagnetic‐induced‐transparency‐like (EIT‐like) window, and a complementary EIT‐like window, which have been analytically, numerically, and experimentally verified. Moreover, the EIT‐like window exhibits a steep dispersion, which is beneficial in slow light devices. Due to the anisotropy of the design, this EIT‐like window can transform into a complementary EIT‐like window when the incident polarization is rotated by 90°. Thus, such asymmetry‐assisted double‐Fano metasurfaces provide a new route to reveal photonic phenomena and construct multifunctional metadevices.