Ultra-broadband and wide-angle reflective terahertz polarization conversion metasurface based on topological optimization

Terahertz polarization conversion devices have significant potential applications in various fields such as terahertz imaging and spectroscopy. In this paper, we utilize genetic algorithms to topologically optimize the metasurface unit cells and design a reflective linear polarization conversion metasurface with ultra-broadband and wide-angle characteristics. By partitioning the metallic pattern layer into quadrants, the encoding length is effectively reduced, resulting in a shorter optimization time. The research results indicate that the converter possesses a polarization conversion efficiency ratio higher than 90% and a relative bandwidth ratio of 125% in a range of 0.231-0.995 THz. Meanwhile, it can maintain excellent polarization conversion properties when the incident angle of terahertz waves is less than 45 degrees and the polarization angle is less than 15 degrees, demonstrating excellent practicality. New insights are provided for the design of terahertz wide-angle ultra-wideband polarization conversion devices, and the proposed metasurfce has potential applications in terahertz polarization imaging, spectroscopy and communication fields.