Numerical Simulations of Circular Dichroism and Polarization Conversion in VO2-Based Terahertz Metamaterials

Abstract

Metamaterials with actively tunable functionalities are highly desirable for applications of advanced optoelectronic devices. In this paper, we theoretically present a metamaterial with diversified functionalities by availing of the phase transition characteristics of vanadium dioxide (VO2) in terahertz frequency regions. The research results demonstrate that the function of the designed metamaterial can be switched from giant circular dichroism (CD) to a reflecting broadband half-wave plate (HWP) and a quarter-wave plate (QWP). When VO2 is in the isolating state, the metamaterial exhibits a quite distinct transmission efficiency for circularly polarized lights, thus resulting in a maximum CD value ~0.97 at the resonant frequency. When VO2 is operating in the metallic state, the metamaterial performs like a broadband HWP, in which the nearly perfect linear polarization conversion can be achieved at the frequency range from 3 to 7 THz. Moreover, the structure can play a role of a high-efficiency QWP that can simultaneously convert the incident linear polarized light to left-handed and right-handed circularly polarized light. The calculated ellipticity indicates a good polarization conversion at the frequency of 2.4 THz and 7.4 THz, respectively. The physical mechanism of the discussed features and effects can be explained by exploring the electric field distributions. Furthermore, the structural parameters also exert great influences for achieving giant CD and HWP as well as QWP. The proposed metamaterial may offer a new approach for designing metamaterial devices with multi-functions in THz regions.