Design and analysis of a multi-band and dual-functional terahertz wave polarization converter based on asymmetric cross-shaped metasurface

In this paper, a reflective multi-band and dual-functional terahertz wave polarization converter based on a metasurface is proposed. The unit cell of the proposed metasurface consists of a periodic array of two asymmetric Jerusalem cross-shaped resonators. The proposed metasurface behaves as a linear-cross polarization (LCP) converter at dual frequency bands of 0.911 similar to 0.926 THz and 1.088 similar to 1.093 THz. The polarization conversion rate (PCR) of the converter is above 95%, and the ellipticity of the reflected wave is about 0 within these two operating bands. Moreover, the proposed metasurface behaves as a linear to circular polarization (LTCP) converter at dual bands of 0.461 similar to 0.862 THz and 0.968 similar to 1.068 THz. The ellipticity of reflected wave approaches +/- 1 within these two operating bands. Wide angular stability up to 50. oblique along with high efficiency reveals the good robustness of the converter. The root cause of the polarization conversion has been analyzed through surface current distribution and multiple interference theory as well. We also analyzed the effects of asymmetry and different size structures on polarization conversion, which can provide some reference experience for the design of metasurface polarization converters in the future. The dual-functional, angular stability and simple structure make this converter an outstanding applicant for terahertz detection, dual-link satellite communication, and terahertz imaging.