Abstract-Bifunctional terahertz modulator for beam steering and broadband absorption based on a hybrid structure of graphene and vanadium dioxide

 

Wenwen Liu, Jiashuai Xu, Zhengyong Song

Schematic diagram of the proposed structure. (a) The whole 3D structure. (b) Schematic of 3D unit cell. (c) Top view of graphene patch.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-15-23331&id=453128

A bifunctional metamaterial is proposed based on a hybrid graphene and vanadium dioxide (VO2) configuration, which can realize a dynamic switch between beam steering and broadband absorption. The structure consists of a VO2 square, graphene patch, topas spacer, VO2 film, topas spacer, and metal substrate. When VO2 is in the metallic state, the structure serves as a coding metamaterial. By engineering different sizes of the top VO2 square and adjusting the Fermi energy level of graphene, the incident wave is scattered in different patterns. When VO2 is in the dielectric state, the structure serves as a broadband absorber. By changing the Fermi energy level of graphene from 0.0 eV to 0.9 eV, absorptance can be gradually changed and working bandwidth widens. There is an absorption band with near 100% absorptance from 0.9 THz to 1.35 THz when the Fermi energy level is 0.73 eV. And the designed broadband absorber is polarization-insensitive within the incident angle of 50°. Our work may show great potential in applications such as terahertz switching and modulation.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Switchable multifunctional terahertz metasurfaces employing vanadium dioxide

Xike Li, Shiwei Tang, Fei Ding, Shuomin Zhong, Yuanqing Yang, Tao Jiang,  Jun Zhou, 

https://www.nature.com/articles/s41598-019-41915-6?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+srep%2Frss%2Fcurrent+%28Scientific+Reports%29


In this paper, we design a type of switchable metasurfaces by employing vanadium dioxide (VO2), which possess tunable and diversified functionalities in the terahertz (THz) frequencies. The properly designed homogeneous metasurface can be dynamically tuned from a broadband absorber to a reflecting surface due to the insulator-to-metal transition of VO2. When VO2 is in its insulating state, the metasurface can efficiently absorb the normally incident THz wave in the frequency range of 0.535–1.3 THz with the average absorption of ~97.2%. Once the VO2 is heated up and switched to its fully metallic state, the designed metasurface exhibits broadband and efficient reflection (>80%) in the frequency range from 0.5 to 1.3 THz. Capitalizing on such meta-atom design, we further extend the functionalities by introducing phase-gradients when VO2 is in its fully metallic state and consequently achieve polarization-insensitive beam-steering and polarization-splitting, while maintaining broadband absorption when VO2 is in insulating state.

Abstract-Active Terahertz Chiral Metamaterials Based on Phase Transition of Vanadium Dioxide (VO2)

Shengxiang Wang, Lei Kang, Douglas H. Werner,

https://www.nature.com/articles/s41598-017-18472-x

Compared with natural materials, chiral metamaterials have been demonstrated with orders of magnitude stronger chiroptical response, which provides the basis for applications such as ultracompact polarization components and plasmonic-enhanced biosensing. Terahertz chiral metamaterials that allow dynamic polarization control of terahertz waves are of great practical interest, but remain extremely rare. Here, we show that hybrid metamaterials integrated with vanadium dioxide (VO2) exhibiting phase transition can enable dynamically tunable chiroptical responses at terahertz frequencies. In particular, a circular dichroism of ~40° and a maximum polarization rotation of ~200°/λ are observed around 0.7 THz. Furthermore, our study also reveals that the chiroptical response from the proposed metamaterials is strongly dependent on the phase transition of VO2, leading to actively controllable polarization states of the transmitted terahertz waves. This work paves the way for the development of terahertz metadevices capable of enabling active polarization manipulation.