Fig. 1. (a) Schematic diagram of liquid crystal (LC)-integrated quasi-BIC metasurface. Here LC is filled into the cell between two graphite electrodes, and a static magnetic field pre-anchors LC molecules along the u-axis. (b) Schematic diagram of LC orientation evolution with actuation between low and high voltages. (c) Active modulation of quasi-BIC from OFF to ON states due to polarization rotation enabled by LC layer.

Fig. 2. (a) Schematic diagram of DSRR as a building block of a metasurface array. (b) Experimental and (c) simulated transmission amplitude spectra of DSRR with different rotation angles of 0°, 15°, 30°, and 45° under y-polarization excitations. (d) Q-factors of quasi-BIC with α. Surface current distributions of (e) DSRR with α=0° at 0.8 THz, DSRR with α=30° located at (f) 0.56 THz and (g) 0.87 THz, and the arrows indicate the direction of the surface current.

Fig. 3. (a) Schematic diagram of LC birefringence measurement under electric (z-axis) and magnetic fields (y-axis). (b) Experimental time-domain signals when LC orients along the y-axis and z-axis, and double quartz layer without LC as the reference. (c) Experimental LC refractive indexes and phase difference. (d) Microscope image of quasi-BIC structure with an angle α=30°. (e) Experimental and (f) simulated transmission amplitude spectra of quasi-BIC structure at x-pol and y-pol excitations.

Fig. 4. (a) Schematic diagram of measurement setup for LC-integrated metasurface. The first polarizer (P1) ensures the incident light is linear polarization along the x-axis, and the transmitted parallel (Txx) and crossed (Tyx) polarization components are detected by rotating the second polarizer (P2). Schematic diagram of polarization state conversion and transmission spectra when LC is along the (b) z-axis and (c) u-axis. Experimentally measured (d) Txx and (e) Tyx polarization components under different voltages at forward incidence (+z direction). Experimentally measured (f) Txx and (g) Tyx polarization components at backward incidence (−z direction).

Fig. 5. Analysis of asymmetric transmission of LC-integrated metasurface. Polarization conversion and transmittance spectra at (a) forward incidence and (b) backward incidence. Amplitude transmission (dB) at forward and backward incidence under the voltage of (c) 0 V, (d) 70 V, (e) 110 V, and (f) 150 V.

Fig. 6. Band diagram and radiative Q of BIC mode in DSRR (α=0°).