Dynamic Quarter‐Wave Metasurface for Efficient Helicity Inversion of Polarization Beyond the Single‐Layer Conversion Limit

Abstract

Terahertz chiral sensing and polarization‐multiplexing communication demand subwavelength devices that dynamically invert polarization helicity. Metasurfaces can enhance anisotropy and fine tunability at subwavelength scales for this purpose. Although metasurfaces enabling deep modulation between orthogonal polarizations have been designed, they suffer from low conversion efficiencies. In this study, it is shown that the efficiency of conversion from linear to circular polarization by conventional single‐layer transmissive metasurfaces cannot exceed a fundamental limit. A dynamic reflective metasurface free from this limitation is then proposed. The device includes multilayer structures working as a terahertz quarter‐wave plate with switchable slow and fast axes. A phase transition of vanadium dioxide induces the necessary structural transformation of the metallic patterns. A practical fabrication method, based on the room‐temperature bonding technique of sapphires, is presented. Dynamic helicity inversion is demonstrated at 0.90 THz, with a conversion efficiency of over 80% that is beyond the fundamental limit of single‐layer transmissive metasurfaces (65%) and more than four times greater than that of previously reported devices.

Recent Advances in Reconfigurable Metasurfaces: Principle and Applications

“…For example, Vanadium dioxide (VO2) can be transformed from insulator to conductor by increasing the temperature; GST materials, which are composed of germanium (Ge), antimony (Sb), and tellurium (Te), can be heated and cooled to transfer between disordered amorphous states and the ordered crystal state. VO2 [ 106 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 , 148 , 149 ] and GST [ 105 , 150 , 151 , 152 , 153 , 154 , 155 , 156 , 157 , 158 , 159 , 160 , 161 , 162 , 163 ] provides abundant reconfiguration mechanisms for reconfigurable metasurfaces.…”

Tunable and switchable multi-functional terahertz metamaterials based on a hybrid vanadium dioxide–graphene integrated configuration

“…In contrast with the traditional wave plates made up of crystals or polymers, metamaterials to tailor the polarization state of the wave have attracted much attention due to their compact and flexible characteristics. 18,19 For practical applications, the actively tunable properties of metamaterials are highly desirable. The electromagnetic behaviors of conventional metamaterials composed of metal and dielectric are inconvenient to be altered once fabricated.…”

“…In contrast with the traditional wave plates made up of crystals or polymers, metamaterials to tailor the polarization state of the wave have attracted much attention due to their compact and flexible characteristics. 18,19…”

Nanolayered VO2-Based Switchable Terahertz Metasurfaces as Near-Perfect Absorbers and Antireflection Coatings

“…Graphene can support graphene surface plasmons from the mid-infrared to the THz region, which exhibit lower losses and considerably stronger subwavelength confinement in the EM field than those of noble metal plasmons . Meanwhile, the dynamic and continuous control of the graphene Fermi energy level makes it a promising material for designing actively tunable metasurfaces. − As a representative PCM, vanadium dioxide (VO 2 ) has been widely used on multifunctional nanoscale metasurfaces − because it can undergo an insulator–metal transition (IMT) under a threshold temperature of 340 K . The IMT of VO 2 triggers a drastic switching in the optical and electrical properties, leading to different responses to incident EM waves.…”