Abstract-Achieving broadband absorption and polarization conversion with a vanadium dioxide metasurface in the same terahertz frequencies

Zhengyong Song and Jiahe Zhang

Schematic of the designed switchable metasurface, consisting of periodic square-shaped VO2, SiO2 spacer, gold strip, VO2 film, and SiO2 spacer, and the bottom gold film.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-8-12487

We present the bifunctional design of a broadband absorber and a broadband polarization converter based on a switchable metasurface through the insulator-to-metal phase transition of vanadium dioxide. When vanadium dioxide is metal, the designed switchable metasurface behaves as a broadband absorber. This absorber is composed of a vanadium dioxide square, silica spacer, and vanadium dioxide film. Calculated results show that in the frequency range of 0.52-1.2 THz, the designed system can absorb more than 90% of the energy, and the bandwidth ratio is 79%. It is insensitive to polarization due to the symmetry, and can still work well even at large incident angles. When vanadium dioxide is an insulator, a terahertz polarizer is realized by a simple anisotropic metasurface. Numerical calculation shows that efficient conversion between two orthogonal linear polarizations can be achieved. Reflectance of a cross-polarized wave can reach 90% from 0.42 THz to 1.04 THz, and the corresponding bandwidth ratio is 85%. This cross-polarized converter has the advantages of wide angle, broad bandwidth, and high efficiency. So our design can realize bifunctionality of broadband absorption and polarization conversion between 0.52 THz and 1.04 THz. This architecture could provide one new way to develop switchable photonic devices and functional components in phase change materials.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz switching between broadband absorption and narrowband absorption

Zhengyong Song, Apeng Chen, and Jiahe Zhang, 

The calculated absorptances with different conductivities of VO2.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-2-2037

A multilayer metamaterial with switchable functionalities is presented based on the phase-transition property of vanadium dioxide. When vanadium dioxide is in the metallic state, a broadband absorber is formed. Calculated results show that the combination of two absorption peaks enables absorptance more than 90% in the wide spectral range from 0.393 THz to 0.897 THz. Absorption performance is insensitive to polarization at the small incident angle and work well even at the larger incident angle. When vanadium dioxide is in the insulating state, the designed system behaves as a narrowband absorber at the frequency of 0.677 THz. This narrowband absorber shows the advantages of wide angle and polarization insensitivity due to the localized magnetic resonance. Furthermore, the influences of geometrical parameters on the performance of absorptance are discussed. The proposed switchable absorber can be used in various applications, such as selective heat emitter and solar photovoltaic field.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement