A Tunable Multi-Mode Dual-Band Terahertz Polarization Converter

The polarization conversion of electromagnetic waves plays a crucial role in practical application. Here, a tunable multi-mode dual-band high-efficiency and reflection-type polarization converter based on liquid crystal (LC) in the terahertz region is proposed. It is composed of periodic unit structures, each unit of which is constituted by the designed structure, LC mixture and fully reflected gold mirror. It numerically reveals that in the operating bandwidth 1.03–1.53 and 1.27–1.86 THz corresponding to the refractive index of LC mixture ñ o and ñ e , the converter can convert linear-polarized and circular-polarized waves to its corresponding cross-polarizations, whose polarization conversion ratio is larger than 90%. Meanwhile, the proposed converter can realize the conversion from linear-polarized wave to circular-polarized one in dual-band, 1.10–1.25 and 1.92–2.2 THz or 0.93–1.04 and 1.57–1.88 THz corresponding to ñ o and ñ e with axis ratio lower than 3 dB. The insensibility of incident angle is analyzed as well. In addition, the physical mechanism of the polarization conversion is disclosed. The ultra-thin and compactness characteristic of this designed polarization converter are very attractive for a variety of applications in EM measurement, sensing, terahertz technology and 6G communication.