We present a bifunctional polarization converter based on Dirac semimetals (DSMs) and vanadium dioxide (VO2), which consists of two layers of DSMs on both sides, a metal grating and a VO2 board. The polarization converter frequency is dynamically tuned by changing the Fermi energy level of the DSMs. The result suggests that when VO2 is in an insulated state, the device behaves as a transmissive polarization converter. The dual-band transmissive polarization conversion and asymmetric transmission (AT) function of circularly polarized (CP) waves are realized at 1.99 THz and 3.46 THz, with the polarization converter ratio (PCR) reached 97.6% and 95.8%, respectively. In addition, when VO2 is in the metal state, the designed polarization converter is a reflective device, which can maintain the chirality of the reflected CP wave to the incident wave in a wide band. The polarization-maintaining ratio (PMR) in the range of 2 THz to 3.55 THz is higher than 88%. When the angle of incidence is less than 60°, the frequency band of the PMR is narrowed and the amplitude reaches more than 90%.

中文翻译：

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基于狄拉克半金属和二氧化钒的双功能可调太赫兹圆偏振转换器

我们提出了一种基于狄拉克半金属 (DSM) 和二氧化钒 (VO2) 的双功能偏振转换器，它由两侧的两层 DSM、金属光栅和 VO2 板组成。通过改变 DSM 的费米能​​级来动态调整极化转换器频率。结果表明，当 VO2 处于绝缘状态时，该器件表现为透射偏振转换器。在1.99 THz和3.46 THz频率下实现了圆偏振（CP）波的双波段透射偏振转换和非对称透射（AT）功能，偏振转换比（PCR）分别达到97.6%和95.8%。此外，当 VO2 处于金属态时，设计的偏振转换器为反射器件，可以在较宽的波段内保持反射 CP 波对入射波的手性。2 THz至3.55 THz范围内的保偏比(PMR)高于88%。当入射角小于60°时，PMR的频带变窄，幅度达到90%以上。