Broadband Polarization-Independent Terahertz Multifunctional Liquid Crystal Coding Metasurface Based on Topological Optimization

Abstract In this paper, a broadband polarization-independent terahertz multifunctional coding metasurface based on topological optimization using liquid crystal (LC) is proposed. The metasurface can achieve reconfigurability for beam steering and vortex beam generation within the 0.68-0.72 THz frequency range. Firstly, the metasurface unit is topologically optimized using the Non-dominant sequencing genetic algorithms (NSGA-II) multi-objective optimization algorithm. By applying the LC's electrically tunable refractive index properties, the metasurface unit enables polarization-independent 2-bit coding within the 0.68-0.72 THz frequency range. Then, based on the designed metasurface unit, the array arrangement of the metasurface is reverse-designed to achieve beam steering and vortex beam generation. The results show that, for beam steering, not only can polarization-independent steering of both single- and multi-beam be achieved within the 35° elevation angle range, but also independent control of the target angle of each beam in the multi-beam steering. For vortex beam generation, the metasurfaces can achieve the generation of single- and multi-vortex beams with topological charges l =±1, ±2 within the 35° elevation angle range, and the generation angles of each vortex beam in the multi-vortex beam can be independently controlled. This provides flexibility and diversity in the generation of vortex beams. Therefore, the proposed terahertz LC metasurface can realize flexible control of reconfigurable functions and has certain application prospects in terahertz communication, phased array radar, and vortex radar.