A dual-band transmissive polarization conversion metastructure based on the toroidal dipole-assisted EIT effect

Transmissive polarization manipulation devices find broad and consequential utility across domains such as satellite radar and wireless communication. This paper demonstrates a new design concept for a metastructure specifically engineered for polarization conversion (PC), based on the phenomenon of electromagnetically induced transparency (EIT) resulting from the assisted excitation of interference in toroidal dipoles. When subjected to normally incident x-polarized and y-polarized waves, the proposed metastructure can engender two distinct EIT windows of heightened transmission and low loss, achieving a maximum transmittance coefficient of 0.94. Then, under 45° linearly polarized wave incidence, leveraging the highly transmissive windows and introducing selective additional phase differences within different unit cells, the proposed metastructure can fulfill the requisite amplitude and phase conditions for achieving linear-to-circular PC in transmission mode. Numerical results substantiate that the proposed metastructure effectively retrieves the desired circularly polarized waves at 0.935 THz and 1.182 THz, yielding axial ratios of 1.22 dB and 1.18 dB, respectively, while maintaining robustness against wide-angle incidence. The proposed metastructure combines the three design concepts of toroidal dipoles, EIT, and linear-to-circular polarization conversion, enabling the realization of polarization-manipulating function with low loss and stability under large incident angles. This innovative design introduces fresh perspectives for transmissive polarization modulation devices, holding significant potential applications across diverse domains including polarization manipulation, optical filtering, multipole electromagnetics, and multifunctional integration.