Chiral metasurface performing high-efficiency tunable chiroptical response in the near-infrared region

We propose and numerically demonstrate a tunable chiral metasurface based on bound states in the continuum (BICs), achieving synergistic control of a high quality factor (Q-factor) and strong chiral response through symmetry breaking. The metasurface employs meta-atoms with in-plane twofold rotational symmetry but no mirror symmetry, supporting BIC modes. By introducing a geometric asymmetry parameter (δ=W2−W1) or varying the illumination angle (θ,φ), the ideal BIC is transformed into a radiative quasi-BIC(Q-BIC),exciting significant chiral responses while retaining a high Q-factor. Simulation results show that under oblique incidence (θ=1°, φ=90°), the structure achieves a circular dichroism (CD) value exceeding 0.9 at 1335nm. Under normal incidence with δ=40nm (W1=191nm, W2=231nm), a CD peak of 0.9 is observed at 1462nm, demonstrating excellent intrinsic chirality. Parameter sweep analysis further reveals the evolution mechanism of the Q-BIC from a non-radiative state to a strongly chiral, high-Q state. Compared to traditional three-dimensional chiral structures, this planar metasurface offers both fabrication feasibility and high performance, providing a promising platform for applications such as chiral lasers, nonlinear filters, and chiral sensing.