Dynamic quarter-wave metasurface for efficient helicity inversion of polarization beyond the single-layer conversion limit

TL;DR

This paper introduces a dynamic multilayer metasurface device that achieves efficient helicity inversion of terahertz polarization beyond the fundamental limit of single-layer metasurfaces, using phase transition of vanadium dioxide.

Contribution

It presents a multilayer, tunable metasurface design that surpasses the efficiency limit of traditional single-layer transmissive metasurfaces for polarization conversion.

Findings

Achieved over 80% conversion efficiency at 0.90 THz.

Demonstrated dynamic helicity inversion beyond the 65% limit.

Implemented a practical fabrication method using room-temperature bonding.

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.