Controllable Polarization Conversion Metasurfaces Based On Vanadium Dioxide

Terahertz technology is an international research hotspot,and the emergence of metasurface devices provides a new method for efficient manipulation of terahertz waves.Active metasurfaces capable of freely manipulating electromagnetic waves have become the research frontier.In this paper,active polarization converters in the terahertz regime are studied theoretically and experimentally by combining the insulation-to-metal phase transition characteristics of vanadium dioxide（VO₂）with artificial polarization metasurfaces.The details are as follows:1.Study on transmissive metasurfaces with switchable polarization conversion bandwidth.The designed metasurface with a multilayer structure can show an adjustable polarization conversion bandwidth at different temperatures.By designing the structural parameters and utilizing the phase transition of VO₂ and principle of current resonance,dynamic tunability of the polarization conversion from dual-broadband（0.45⁰.77 THz and 0.97¹.2 THz）to ultra-broadband（0.38¹.20 THz）can be realized with a high polarization conversion ratio.2.Study on transmissive metasurfaces with active controllable polarization conversion amplitude and polarization conversion ratio.The designed metasurface can adjust the polarization conversion amplitude under different electrical conductivity of VO₂.With the increase of the conductivity of VO₂,the amplitude of the cross-polarization increases gradually,and the polarization conversion efficiency near 1.1THz increases from 0%to 95%.The change process of the polarization conversion amplitude and polarization conversion efficiency fully reflects the dynamic control effect of VO₂ on polarization conversion.3.Study on reflective metasurfaces with controllable polarization conversion amplitude.The designed metasurface is a three-layer structure.With the gradual increase of the electrical conductivity of VO₂,the reflection amplitude of the co-polarization is basically unchanged,while the reflection amplitude of the orthogonal polarization is gradually reduced when maintaining the polarization conversion efficiency of 95%in the range of 0.8～1.8 THz.Thus,the dynamic adjustment of the polarization conversion amplitude is realized.