Transmissive Terahertz Tunable and Multifunctional Polarization Manipulation With Ge/VO₂ Hybrid Metasurface

To meet the growing demand for transmissive tunable multifunctional polarization manipulation devices, a tunable multifunctional polarization-manipulating metasurface (TMPMM) based on germanium dielectric pillars and $V{O}_2$ grating is proposed. When the $V{O}_2$ grating is in the insulating state, efficient cross-polarization conversion in the frequency range of 3.88-5.5 THz is achieved, with a maximum conversion efficiency exceeding 0.98. Within the frequency ranges of 2.31-2.61 THz and 6.42-6.68 THz, the linearly polarized (LP) wave is efficiently converted to a circularly polarized (CP) wave. When the $V{O}_2$ grating is in the metallic state, the function of asymmetric transmission (AT) is realized, where the TMPMM can be utilized as a broadband isolator and half-wave plate for an $x$ -polarized wave and can also be utilized as a narrowband isolator and polarization conversion switch for a $y$ -polarized wave. Under the forward incidence of CP waves, the TMPMM selectively transmits left- and right-circularly polarized waves near 2.25 THz and 6.37 THz, respectively, achieving significant spin-dependent polarization selection. Additionally, through simple temperature tuning, the proposed TMPMM enables dynamic control of AT, circular dichroism, and ellipticity. All these multifunctional and tunable properties are realized via temperature variation without altering the structural geometry parameters.