Fig. 1. The characterization of the unit cell of the metasurface. (a) Schematic diagram of the original cell with two etching holes (rectangular hole 1 and rectangular hole 2), with a silicon cube array deposited on a quartz substrate; (b) top view of the unit cell with geometric parameters

Fig. 2. Transmission spectra, eigenmode, and Q factors of two A-BIC. (a) (d) The transmission spectra for x polarization and y polarization, respectively (triangle mark and star mark indicate the location of BIC); (b) (e) the simulated band structure (the eigenmode near the Γ point), corresponding to A-BIC1 and A-BIC2, respectively; (c) (f) the simulated Q factors of eigenmode, corresponding to A-BIC1 and A-BIC2 near the Γ point, respectively

Fig. 3. Two kinds of A-QBIC based on toroidal dipole with x polarization and y polarization. (a) (e) The transmittance of x polarization (d=250 nm) and y polarization (d=120 nm) and their coupling simulations, respectively, showing asymmetric Fano line shapes; (b) (f) the Cartesian multipole expansion of the A-QBIC scattering cross section in Fig.3 (a) and Fig.3 (d), respectively; (c) (g) the near-field distribution of the electric field on the metasurface in the x-y plane, the contours represent the near-field electric field distribution, and the white arrows and their lengths represent the direction and magnitude of the electric field respectively; (d) the near-field distribution of the magnetic field on the metasurface in the y-z plane, the contour plot represents the near-field magnetic field distribution, and the white arrows and their lengths represent the direction and magnitude of the magnetic field respectively; (h) the near-field distribution of the magnetic field of the metasurface in the x-z plane, the contours represent the near-field magnetic field distribution, and the white arrows and their lengths represent the direction and size of the magnetic field respectively

Fig. 4. Refractive index sensing applications. (a) (b) The change of transmission spectra of two resonant modes of the all-dielectric metasurface under different refractive indexes; (c) the difference of wavelength shift relative to refractive index and its M_FOM comparison between the two resonance modes

Fig. 5. Interaction of two quasi-BIC. (a) The presence of A-BIC1 (circular marker), A-BIC2(star marker) at 45° polarization, and their quasi-BIC interaction (dashed region); (b) enlarging of the dotted line area in Fig.5(a); (c)‒(e) the transmittance and MICMT fit for a fixed distance correspond to the three vertical dashed lines on the left, middle and right in Fig.5(b), respectively

Fig. 6. Design of slow light device. (a) Transmission spectrum as a function of polarization angle; (b) diagram of phase change due to polarization angle; (c) adjustable slow light with group delay due to polarization angle