Multi-functional and multi-band reflective polarization converter based on an asymmetric metasurface in the terahertz band

In this study, we propose a multi-functional and multi-band polarization converter operating in the terahertz regime, based on an asymmetric metasurface. The polarization converter comprises a periodic array of unit cells, each consisting of a two-corner-cut square gold patch, a gold ground blocking sheet, and an intermediate polyimide dielectric substrate. The simulation results show that the proposed device functions as a cross-polarization converter (CPC) with over $\mathbf{9 0 \%}$ efficiency across three frequency bands of $0.43 \sim 0.51 \mathrm{THz}$, $0.66 \sim 0.89 \mathrm{THz}$, and $1.35 \sim 1.39 \mathrm{THz}$. Moreover, it serves as a linear-to-circular polarization (LP-to-CP) converter in four distinct frequency bands of $0.34 \sim 0.43 \mathrm{THz}, 0.51 \sim 0.66 \mathrm{THz}$, $0.89 \sim 1.35 \mathrm{THz}$, and $1.39 \sim 1.45 \mathrm{THz}$, maintaining an axial ratio (AR) below 3 dB. The normalized ellipticity of the reflected wave, indicative of circular polarization handedness, approaches ±1 within these operating bands. The converter’s multi-functionality and simple structure make it promising for biomedical applications, particularly in terahertz imaging.