Research overview
This paper demonstrates a 2-bit terahertz “angle-tunable chiral encoder” based on quasi-bound states in the continuum (quasi-BICs), designed to detect both the polarization state and the incidence angle of THz waves with a compact, passive device. The structure consists of two layers of asymmetric dual split-ring resonators separated by a polyimide layer on silicon (54 × 54 unit cells, 171 µm period, 10 × 10 mm overall). Tilting the incidence angle between −30° and +30° switches the quasi-BIC resonances on and off in a complementary way and fully reverses the chiral response at 0.757 THz and 0.806 THz, giving the “0” and “1” encoding states. Multipole decomposition and coupled-mode theory attribute the strong extrinsic chirality to electric-quadrupole-dominated coupling. THz time-domain spectroscopy measurements, using wire-grid polarizers before and after the sample, agree well with simulation.
Key findings
- 2-bit THz chiral encoder based on quasi-bound states in the continuum
- Complete reversal of chiral response by tilting the incidence angle (±30°)
- Encoding states at 0.757 THz and 0.806 THz
- Passive detection of both THz incidence angle and polarization state
