Geometric and spatial modulation of circular dichroism in terahertz metasurfaces

This study presents a chiral metasurface based on α-MoO₃, engineered to achieve strong and tunable circular dichroism (CD), the differential absorption of right- and left-circularly polarized (RCP and LCP) light, in the terahertz (THz) frequency range. By introducing anisotropic rectangular units with specific rotation angles, the design breaks in-plane structural symmetry, resulting in significant chiral optical responses. Through systematic optimization of geometric parameters, the metasurface demonstrates a high CD value of 0.92 at 10.92 THz. The physical origin of the observed CD is revealed by analyzing the electric field distributions under right- and left-circularly polarized light. The influence of key structural parameters-period, thickness, and rotation angle-on the CD response is thoroughly examined, establishing a clear correlation between geometry and optical performance. Furthermore, two structural variants, including elliptical unit arrays and hole-based designs, are explored to assess the role of unit shape and spatial arrangement in CD modulation. Results confirm that spatial and geometric modulation strategies effectively tailor terahertz circular dichroism, offering valuable insights for the development of high-performance chiral photonic devices.