Abstract-Thermally switchable terahertz wavefront metasurface modulators based on the insulator-to-metal transition of vanadium dioxide

Teng Wang, Jinwen He, Jinying Guo, Xinke Wang, Shengfei Feng, Florian Kuhl, Martin Becker, Angelika Polity, Peter J. Klar, and Yan Zhang

Fig. 1 Schematic image of the setup used for studying operational characteristics of the THz wavefront modulators as a function of temperature. (a) The device has no effect on the THz wave in its off-state (e.g., at T = 20 °C < TC). The THz device acts on the THz wave in its on-state (e.g., at T = 70 °C > TC) as (b) a multiple foci lens or (c) a Ariy beam generator. TTML: Temperature controlled THz multi-focus lens. TTAG: Temperature controlled THz Ariy beam gererator.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-15-20347

Active use of phase transition phenomena for reversibly tuning the properties of functional materials in devices currently is an attractive research area of materials science. We designed and fabricated two kinds of metasurface modulators for dynamically controlling the wavefront of terahertz (THz) radiation based on the temperature-induced insulator-to-metal phase transition of vanadium dioxide (VO2). The modulators designed are based on the C-shaped slot antenna array. The slot antennas are made of the VO2 films on c-sapphire substrates. The C-shaped slot antennas are active only when the VO2 is in its metallic phase, i.e. at temperatures T > TC ∼68 °C. At T > TC, the first kind acts as a THz multi-focus lens which converges an incident THz plane wave into four focal spots and the second kind as an Airy beam generator. We characterized the function of two THz wavefront modulators over a broad frequency range, i.e. from 0.3 to 1.2 THz. Such thermally switchable THz wavefront metasurface modulators with a capability of dynamically steering THz fields will be of great significance for the future development of THz active devices.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Reconfigurable Terahertz Metasurface Pure Phase Holograms

Jinying Guo, Teng Wang,  Huan Zhao, Xinke Wang,  Shengfei Feng, Peng Han, Wenfeng Sun,   Jiasheng Ye, Guohai Situ, Hou‐Tong Chen,Yan Zhang

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201801696?af=R

Terahertz (THz) radiation has many potential applications. However, comparing with the rapid development of THz sources and detectors, functional devices for THz modulation, especially the spatial modulation devices, are still insufficient. Here, a novel approach for generating arbitrary wavefronts of a THz beam is presented. By dynamically creating metasurface structures through illuminating a thin silicon wafer with femtosecond laser, which is spatially modulated, an array of reconfigurable subwavelength resonators is generated. The wavefront of the THz beam is then determined by forming spatial profiles of the Pancharatnam–Berry scattering phase by dynamically controlling the resonator orientation. Proof‐of‐concept experiments demonstrate that streaming holographic images and lenses of variable focal length can be realized in real time. The reconfigurable scheme demonstrated here is convenient and fast, and may lead to advances in a host of THz applications.

Abstract-High-efficiency terahertz devices based on cross-polarization converter

• Huan Zhao, 
• Xinke Wang, 
• Jingwen He, 
• Jinying Guo, 
• Jiasheng Ye, 
• Qiang Kan,  
• Yan Zhan

• https://www.nature.com/articles/s41598-017-18013-6#Sec2

Metasurface-based devices have been investigated intensively because of their attractive properties but these devices generally suffer from low efficiency. Here we demonstrate several high-efficiency terahertz (THz) devices based on cross-polarization converters that is composed of bilayer metasurface-based structures. The converter can transfer the polarization states of transmitted THz waves from the x-direction into the y-direction with an experimental conversion efficiency of 85%. This high-efficiency transfer mechanism is investigated in detail. Furthermore, this kind of devices can be fabricated easily. A THz metalens is designed and fabricated and its focusing and imaging properties are investigated experimentally. A pure phase THz hologram that can generate different images on different propagation planes is also designed and the image reconstruction capabilities of the phase holograms are demonstrated experimentally. The performance levels of all designed devices show excellent agreement between the theoretical expectations and the corresponding experimental results. This technology may pave the way towards practical applications of such metasurface devices.