Fig. 1. Schematic structure of the metasurface and energy band analysis. (a) Schematic of the supported chiral q-BIC structure of the silicon metasurface; (b) schematic representation of the unit cell structure of the metasurface; (c) energy band structure of the eigenmodes near the Γ point, with insets showing the magnetic field distributions of the three modes; (d) Q-factor of the eigenmode near the Γ point; (e) distribution of far-field polarization states corresponding to mode I

Fig. 2. Planar chiral analysis of the structural in-plane symmetry breaking endowed metasurface. (a) Schematic diagram of single cell of planar silicon metasurface under positive incidence when an in-plane asymmetric perturbation δ is introduced; (b) amplitude profiles and CD spectra of the transmittance components for the in-plane asymmetric perturbation δ=50 nm; (c) evolution plot of CD spectra with continuously varying asymmetry parameter δ; (d) Cartesian multipole expansion of the scattering cross section for chiral q-BIC modes; (e) magnetic dipole control of the electric field vector (arrow) and magnetic field （H） of the chiral q-BIC mode; (f) trend of the Q-factor of the mode with the in-plane asymmetry parameter δ

Fig. 3. Planar chiral analysis of the metasurface endowed with light asymmetry. (a) Schematic of a single cell of a planar silicon metasurface under oblique incidence; (b) CD spectra of the amplitude profiles of the transmittance components when θ=6° and φ=90°; (c) evolution plot of the CD spectra with successive changes in light incidence angle θ when φ=90°; (d) Cartesian multipole expansion of the scattering cross section for chiral q-BIC modes; (e) magnetic dipole control of the electric field vector (white arrow) and magnetic field of the chiral q-BIC mode; (f) trend of mode Q-factor with light incidence angle θ

Fig. 4. Evolution of CD and transmission spectra with incident light azimuth. (a) Evolution plot of CD with θ for φ=0°; (b)(c) evolution plots of TLR and TRL with φ for θ=6°; (d) evolution plot of CD with φ for fixed θ=6°

Fig. 5. Analysis of refractive index sensor performance. (a)(b) Evolution plots of the cross-polarized transmission components TRL and TLR concerning the refractive index of the substance to be measured; (c) linear redshift of the CD spectrum with the change of refractive index of the substance to be measured; (d) CD peak displacement versus the refractive index and FOM analysis; (e) evolution plots of the CD resonance wavelength and the CD peak as a function of the thickness d of the object to be measured