Theoretical investigation of a terahertz plasmonic reflective linear polarization converter based on orthogonal silver nanorods

Efficient manipulation of electromagnetic wave polarization in the terahertz (THz) regime remains challenging because many existing polarization converters rely on complex geometries, multilayer configurations, or provide limited physical insight into their operating mechanisms. Although numerous terahertz metasurface polarization converters have been reported, achieving high polarization conversion efficiency using structurally simple and fabrication-friendly architectures while maintaining a clear physical understanding of the conversion mechanism remains challenging. To address this challenge, a compact reflective terahertz polarization converter composed of two orthogonally oriented silver nanorods separated by a quartz substrate is theoretically investigated using full-wave electromagnetic simulations. Full-wave electromagnetic simulations demonstrate a maximum cross-polarized reflection coefficient of approximately 97% at 1.87 THz, while both the co-polarized reflected component and all transmitted components remain strongly suppressed. The polarization conversion mechanism is interpreted in terms of the excitation of orthogonal plasmonic currents within the nanorods, which produce destructive interference of the co-polarized reflected field and a corresponding enhancement of the cross-polarized component. A systematic parametric investigation is performed to quantify the influence of the rod length, width, thickness, and substrate thickness on the resonance characteristics and polarization conversion efficiency, providing practical design guidelines for performance optimization. Compared with representative THz reflective polarization converters reported in the literature, the proposed metasurface achieves comparable or higher conversion efficiency while preserving a remarkably simple and fabrication-friendly architecture. These characteristics make the proposed design a promising candidate for polarization control in terahertz imaging, wireless communication, and spectroscopic systems.