Fig. 3. Experimental verification of the extrinsic planar chiral q-BIC with illumination symmetry breaking.

a Experimental setup for the Jones matrix spectra measurement under the circular polarization basis. P₁ and P₂ represent the polarizers, QWP is the quarter-wave plate, L₁, L₂, and L₃ are lenses. b Schematic of the metasurface with δ = 0 supporting chiral q-BICs through different incident angles along the φ = 90°direction. c Simulated and measured transmission Jones matrix spectra (T_lr, T_rl, T_rr and T_ll) for different incident angles (θ = 0°, 2°, 4°, 6°, 8°, 10°, 12°) along the φ = 90° direction. d Simulated and measured CD spectra for different incident angles extracted from the Jones matrix spectra in (c).