Tailoring Photonic Dispersion via <i>Multiple</i> Brillouin Zone Foldings: A Route From Robust Ultrahigh‐ <i>Q</i> Resonances Toward Robust Giant Goos‐Hänchen Shifts

ABSTRACT Herein, the photonic dispersion of metasurfaces is tailored via multiple Brillouin zone foldings (BZFs) to achieve robust ultrahigh‐ Q resonances and giant Goos‐Hänchen shifts (GHSs) with geometry‐free and angle‐insensitive properties. By introducing the geometric perturbation into the lattice, the guided resonances (GRs) lying below the radiative continuum are folded into the radiative continuum and evolve into BZF‐induced guided mode resonances (BZF‐GMRs) with ultrahigh Q factors. Remarkably, the Q factors of the BZF‐GMRs maintain ultrahigh across a wide momentum space and exhibit ultralow sensitivity to the geometric shape of the scatterers, inherited from the intrinsic infinitely high Q factors of the GRs. More importantly, it is discovered that the Q factor of the BZF‐GMR scales with the fourth power of the order of BZF. Leveraging these robust ultrahigh‐ Q BZF‐GMRs, we realize giant geometry‐free and angle‐insensitive GHSs (on the scale of 10 3 λ ). Full‐wave simulations are performed to demonstrate the enhancement of GHSs. This work not only reveals the relationship between BZF and GHS, but also offers a general route to achieving robust ultrahigh‐ Q resonances and giant GHSs.