Dual-band superposition induced broadband terahertz linear-to-circular polarization converter

A reflective broadband terahertz (THz) linear-to-circular (LTC) polarization converter based on a single-layer ultrathin metasurface is designed and experimentally demonstrated. Two different-size rectangular ultrathin metasurface micro-structures are proposed to realize such a broadband THz LTC polarization converter with bandwidth ranging from 0.832 to 1.036 THz. The phase delay between two orthogonal resonance modes is $-90°\pm 5°$. These qualities are realized mainly by combining two separated LTC polarization conversion frequencies and the benefit of the coupling between two different-size rectangles. The calculated results indicate that the bandwidth of the LTC polarization converter is controlled via the dimensions and period of the structure. This kind of ultrathin broadband THz polarization converter can be widely applied into wireless communication, imaging, and detection, and can widen the path to designing novel functional THz devices.