Abstract-High-speed efficient terahertz modulation based on tunable collective-individual state conversion within an active 3nm-two dimensional electron gas metasurface

Yuncheng Zhao, Lan Wang, Yaxin Zhang, Shen Qiao, Shixiong Liang, Xilin Zhang, Xiaoqing Guo, Zhihong Feng, Feng Lan, Zhi Chen, Xiaobo Yang, Ziqiang Yang,

https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.9b01273#

Terahertz (THz) modulators are always realized by dynamically manipulating the conversion between different resonant modes within a single unit cell of an active metasurface. In this paper, to achieve real high-speed THz modulation, we present a staggered netlike two-dimensional electron gas (2DEG) nanostructure composite metasurface that has two states: a collective state with massive surface resonant characteristics and an individual state with meta-atom resonant characteristics. By controlling the electron transport of the nanoscale 2DEG with an electrical grid, collective-individual state conversion can be realized in this composite metasurface. Unlike traditional resonant mode conversion confined in meta-units, this state conversion enables the resonant modes to be flexibly distributed throughout the metasurface, leading to a frequency shift of nearly 99% in both the simulated and experimental transmission spectra. Moreover, such a mechanism can effectively suppress parasitic modes and significantly reduce the capacitance of the metasurface. Thereby, this composite metasurface can efficiently control the transmission characteristics of THz waves with high-speed modulations. As a result, 93% modulation depth is observed in the static experiment and modulated sinusoidal signals up to 3 GHz are achieved in the dynamic experiment while the -3dB bandwidth can reach up to 1GHz. This tunable collective-individual state conversion may have great application potential in wireless communication and coded imaging.

Abstract-A Review of THz Modulators with Dynamic Tunable Metasurfaces

Lan Wang,  Yaxin Zhang , Xiaoqing Guo, Ting Chen, Huajie Liang,  Xiaolin Hao,  Xu Hou, Wei Kou,  Yuncheng Zhao,  Tianchi Zhou,  Shixiong Liang, Ziqiang Yang

https://www.mdpi.com/2079-4991/9/7/965/htm

Terahertz (THz) radiation has received much attention during the past few decades for its potential applications in various fields, such as spectroscopy, imaging, and wireless communications. To use terahertz waves for data transmission in different application systems, the efficient and rapid modulation of terahertz waves is required and has become an in-depth research topic. Since the turn of the century, research on metasurfaces has rapidly developed, and the scope of novel functions and operating frequency ranges has been substantially expanded, especially in the terahertz range. The combination of metasurfaces and semiconductors has facilitated both new opportunities for the development of dynamic THz functional devices and significant achievements in THz modulators. This paper provides an overview of THz modulators based on different kinds of dynamic tunable metasurfaces combined with semiconductors, two-dimensional electron gas heterostructures, superconductors, phase-transition materials, graphene, and other 2D material. Based on the overview, a brief discussion with perspectives will be presented. We hope that this review will help more researchers learn about the recent developments and challenges of THz modulators and contribute to this field.

Abstract-Dynamic Photoinduced Controlling of the Large Phase Shift of Terahertz Waves via Vanadium Dioxide Coupling Nanostructures

Yuncheng Zhao, Yaxin Zhang, Qiwu Shi, Shixiong Liang,  Wanxia Huang,  Wei Kou,  Ziqiang Yang,

https://pubs.acs.org/doi/10.1021/acsphotonics.8b00276

Utilizing terahertz (THz) waves to transmit data for communication and imaging places high demands on phase modulation. However, until now, it is difficult to realize a more than 100° phase shift in the transmission mode with one-layer structure. In this paper, a ring-dumbbell composite resonator nested with VO2 nanostructures is proposed to achieve the large phase shift. It is found that in this structure a hybrid mode with an enhanced resonant intensity, which is coupled by the L-C resonance and dipole resonance has been observed. Applying the photoinduced phase transition characteristics of VO2, the resonant intensity of the mode can be dynamically controlled, which leads to a large phase shift in the incident THz wave. The dynamic experimental results show that controlling the power of the external laser can achieve a phase shift of up to 138° near 0.6 THz using this one-layer VO2 nested composite structure. Moreover, within a 55 GHz (575–630 GHz) bandwidth, the phase shift exceeds 130°. This attractive phase shift modulation may provide prospective applications in THz imaging, communications, and so on.

Abstract-Linear polarization conversion of transmitted terahertz wave with double-layer meta-grating surfaces

Han Sun, Yaxin Zhang, Kailong Wang, Yuncheng Zhao, Wei Kou, Shixiong Liang, Jiaguang Han, and Ziqiang Yang

https://www.osapublishing.org/col/abstract.cfm?uri=col-16-8-081601

In this Letter, we demonstrate a linear polarization conversion of transmitted terahertz wave with double-layer meta-grating surfaces, which integrated the frequency selectivity of a split ring resonator metasurface and the polarization selectivity of a metallic grating surface. Since the double-layer can reduce the loss, and the Fabry–Perot like resonant effect between the two layers can improve the conversion efficiency, this converter can rotate the incident y-polarized terahertz wave into an x-polarized transmitted wave with relatively low loss and high efficiency. Experimental results show that an average conversion efficiency exceeding 75% from 0.25 to 0.65 THz with the highest efficiency of 90% at 0.43 THz with only −2  dB loss has been achieved.

© 2018 Chinese Laser Press

Abstract-Dynamic Photo-induced Controlling of the Large Phase Shift of Terahertz Waves via Vanadium Dioxide Coupling Nanostructures

Yuncheng Zhao, Yaxin Zhang, Qiwu Shi, Shixiong Liang, Wanxia Huang, Wei Kou, Ziqiang Yang,

https://pubs.acs.org/doi/abs/10.1021/acsphotonics.8b00276?mi=aayia761&af=R&AllField=nano&target=default&targetTab=std

Utilizing terahertz (THz) waves to transmit data for communication and imaging places high demands on phase modulation. However, until now, realizing a large phase shift using a one-layer structure in transmission mode has been difficult. In this paper, utilizing a composite unit cell by coupling the traditional metallic wire dipolar resonance and the split-ring capacitive inductance resonance results in an enhanced resonance coupling mode. Combined with a vanadium dioxide (VO2) nanostructure and applying the photo-induced phase transition, the resonant intensity of the mode can be dynamically controlled, which leads to an ultralarge phase shift in the incident THz wave. The dynamic experimental results show that controlling the power of the external laser can achieve a phase shift of up to 138 degrees near 0.6 THz using this one-layer VO2 nested composite structure. Moreover, within a 55 GHz (575 GHz-630 GHz) bandwidth, the phase shift exceeds 130 degrees. This attractive phase shift modulation may provide prospective applications in THz imaging, communications, etc.

Abstract-Mode coupling in terahertz metamaterials using sub-radiative and super-radiative resonators

Shen Qiao¹, Yaxin Zhang^1,a), Yuncheng Zhao¹, Shixiong Liang², Gaiqi Xu¹, Han Sun¹ and Ziqiang Yang¹
http://scitation.aip.org/content/aip/journal/jap/118/19/10.1063/1.4936169?TRACK=RSS
a) Author to whom correspondence should be addressed. Electronic mail:Zhangyaxin@uestc.edu.cn
J. Appl. Phys. 118, 193104 (2015); http://dx.doi.org/10.1063/1.4936169

We theoretically and experimentally explored the electromagnetically induced transparency (EIT) mode-coupling in terahertz (THz) metamaterialresonators, in which a dipole resonatorwith a super-radiative mode is coupled to an inductance-capacitance resonator with a sub-radiative mode. The interference between these two resonators depends on the relative spacing between them, resulting in a tunable transparency window in the absorptionspectrum.Mode coupling was experimentally demonstrated for three spacing dependent EITmetamaterials. Transmittance of the transparency windows could be either enhanced or suppressed, producing different spectral linewidths. These spacing dependent mode-couplingmetamaterials provide alternative ways to create THz devices, such as filters, absorbers, modulators, sensors, and slow-light devices.

Abstract-Gbps terahertz external modulator based on a composite metamaterial with a double-channel heterostructure

Yaxin Zhang , Shen Qiao , Shixiong Liang , Zhenhua Wu , Ziqiang Yang , Zhihong Feng , Han Sun , Yucong Zhou , Linlin Sun , Zhi Chen , Xianbing Zou , Bo Zhang , Jianhao Hu , Shaoqian Li ,Qin Chen , Ling Li , Gaiqi Xu , Yuncheng Zhao , and Shenggang Liu

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/acs.nanolett.5b00869

Publication Date (Web): April 28, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b00869

The past few decades have witnessed a substantial increase in terahertz (THz) research. Utilizing THz waves to transmit communication and imaging data has created a high demand for phase and amplitude modulation. However, current active THz devices, including modulators and switches, still cannot meet THz system demands. Double-channel heterostructures, an alternative semiconductor system, can support nano-scale two-dimensional electron gases (2DEGs) with high carrier concentration and mobility and provide a new way to develop active THz devices. In this article, we present a composite metamaterial structure that combines an equivalent collective dipolar array with a double-channel heterostructure to obtain an effective, ultra-fast and all-electronic grid-controlled THz modulator. Electrical control allows for resonant mode conversion between two different dipolar resonances in the active device, which significantly improves the modulation speed and depth. This THz modulator is the first to achieve a 1-GHz modulation speed and 85% modulation depth during real-time dynamic tests. Moreover, a 1.19-rad phase shift was realized. A wireless free-space-modulation THz communication system based on this external THz modulator was tested using 0.2-Gbps eye patterns. Therefore, this active composite metamaterial modulator provides a basis for the development of effective and ultra-fast dynamic devices for THz wireless communication and imaging systems.

Abstract-Controlling the transparency window in terahertz band using mode coupling metamaterials

Shen Qiao¹, Yaxin Zhang^1,a), Gaiqi Xu¹, Linlin Sun¹, Han Sun¹, Ling Li¹,Shixiong Liang², Yuncheng Zhao¹ and Ziqiang Yang¹
http://scitation.aip.org/content/aip/journal/jap/117/6/10.1063/1.4907870
1 Terahertz Science Cooperative Innovation Center, University of Electronic Science and Technology of China, Chengdu 610054, China
2 National Key Laboratory of Application Specific Integrated Circuit, Hebei Semiconductor Research Institute, Shijiazhuang 050051, China
a) Author to whom correspondence should be addressed. Electronic mail: Zhangyaxin@uestc.edu.cn
J. Appl. Phys. 117, 063103 (2015); http://dx.doi.org/10.1063/1.4907870

Mode-coupling metamaterials are typically composite structures with different resonance modes. Controlling couplings among these modes results in a sharp transparency window within the absorption spectrum of the metamaterials. Here, we present a composite structure of ring and split-ring resonators to constitute a new structure with entirely new mode. Experimental results show that the asymmetric combination of these resonators can result in a variation in transparency strength. The dimensions and relative positions of the split-ringresonator are discussed particularly with a series of experimental results. Simulation results show that the coupling intensity is the main reason for this behavior. Exploiting this aspect, a way to control the transparency window between composite structure metamaterials is proposed.