Design and analysis of a broadband terahertz polarization converter with significant asymmetric transmission enhancement

A tri-layered terahertz metamaterial based on the gratings-polarization converter-gratings (GPCG) structure is proposed, which is composed of a double L structure array sandwiched by two orthogonal metallic sub-wavelength gratings (SWGs). Simulation results show that two cascaded Fabry–Perot-like resonance cavities result in broadband polarization conversion with significant asymmetric transmission (AT) phenomenon. The improved polarization conversion rate (PCR) is over 0.99 from 0.20 THz to 1.97 THz with a relative bandwidth of 163.13%, almost 1.74 times that of other work, and the enhanced AT parameter is beyond 0.8 from 0.37 THz to 1.73 THz with a relative bandwidth of 129.52%. Moreover, in a wide range of incident angles, the proposed metamaterial maintains great AT performance, thus showing great potential applications in circulators, direction-dependent polarization converters and polarization-sensitive sensing and imaging.