Abstract-Terahertz beam switching by electrical control of graphene-enabled tunable metasurface

• 
  • 
    
• Yin Zhang, 
• Yijun Fen 
• Junming Zhao, 
• Tian Jiang & 
• Bo Zhu

https://www.nature.com/articles/s41598-017-14493-8

Controlling the terahertz wave, especially the dynamical and full control of terahertz wavefront, is highly demanded due to the increasing development of practical devices and application systems. Recently considerable efforts have been made to fill the ‘terahertz gap’ with the help of artificial metamaterial or metasurface incorporated with graphene material. Here, we propose a scheme to design tunable metasurface consisting of metallic patch array on a grounded polymer substrate embedded with graphene layers to electrically control the electromagnetic beam reflection at terahertz frequency. By adjusting geometric dimension of the patch elements, 360 degree reflection phase range may be achieved, thus abrupt phase shifts can be introduced along the metasurface for tailoring the reflected wavefront. Moreover, the reflective phase gradient over the metasurface can be switched between 90 and 360 degree by controlling the Fermi energy of the embedded graphene through voltage biasing, hence dynamically switching the reflective beam directions. Numerical simulations demonstrate that either single beam or dual beam dynamically switching between normal and oblique reflection angles can be well attained at working frequency. The proposed approach will bring much freedom in the design of beam manipulation devices and may be applied to terahertz radiation control.

Abstract-Backward spoof surface wave in plasmonic metamaterial of ultrathin metallic structure

• Xiaoyong Liu
• , Yijun Feng
• , Bo Zhu
• , Junming Zhao
•  & Tian Jiang

http://www.nature.com/articles/srep20448

Backward wave with anti-parallel phase and group velocities is one of the basic properties associated with negative refraction and sub-diffraction image that have attracted considerable interest in the context of photonic metamaterials. It has been predicted theoretically that some plasmonic structures can also support backward wave propagation of surface plasmon polaritons (SPPs), however direct experimental demonstration has not been reported, to the best of our knowledge. In this paper, a specially designed plasmonic metamaterial of corrugated metallic strip has been proposed that can support backward spoof SPP wave propagation. The dispersion analysis, the full electromagnetic field simulation and the transmission measurement of the plasmonic metamaterial waveguide have clearly validated the backward wave propagation with dispersion relation possessing negative slope and opposite directions of group and phase velocities. As a further verification and application, a contra-directional coupler is designed and tested that can route the microwave signal to opposite terminals at different operating frequencies, indicating new application opportunities of plasmonic metamaterial in integrated functional devices and circuits for microwave and terahertz radiation.

Abstract-Switchable quarter-wave plate with graphene based metamaterial for broadband terahertz wave manipulation

Yin Zhang, Yijun Feng, Bo Zhu, Junming Zhao, and Tian Jiang
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-21-27230

Graphene is a good candidate material in designing tunable terahertz devices due to its tunability of sheet conductivity. In this paper, we propose a scheme to design switchable quarter-wave plate for terahertz wave that is composed of graphene based grating and metallic grating structures. The proposed active device can dynamically switch the transmission wave among left-handed, right-handed circular polarization and linear polarization states by electrically controlling the Fermi energy of the graphene grating. The device is analyzed with grating circular polarizer theory and its performance is investigated through full wave simulations on practically realizable geometry. The proposed quarter-wave plate having a subwavelength thickness demonstrates a wide angle of incidence tolerance, and a broad bandwidth operation. This device concept offers a further step in developing tunable polarizers and polarization switchers, which may be applied in practical terahertz image and communication systems.

© 2015 Optical Society of America

Full Article  |  PDF Article

Abstract-Anomalous Terahertz Reflection and Scattering by Flexible and Conformal Coding Metamaterials

1. Lanju Liang¹, 
2. Meiqing Qi², 
3. Jing Yang³,
4. Xiaopeng Shen², 
5. Jiquan Zhai¹, 
6. Weizong Xu⁴, 
7. Biaobing Jin^1,5,*, 
8. Weiwei Liu^3,5,*,
9. Yijun Feng⁴, 
10. Caihong Zhang¹, 
11. Hai Lu⁴,
12. Hou-Tong Chen⁶, 
13. Lin Kang¹, 
14. Weiwei Xu¹,
15. Jian Chen^1,5, 
16. Tie Jun Cui^2,5,*, 
17. Peiheng Wu¹ and
18. Shenggang Liu^5,7

Article first published online: 30 JUN 2015

http://onlinelibrary.wiley.com/doi/10.1002/adom.201500206/abstract;jsessionid=75D9087BA4464D14DC4C0EA2F158CD85.f03t01?userIsAuthenticated=false&deniedAccessCustomisedMessage=

DOI: 10.1002/adom.201500206

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Arbitrary control of terahertz (THz) waves remains a significant challenge although it promises many important applications. Here, a method to tailor the reflection and scattering of THz waves in an anomalous manner by using 1-bit coding metamaterials is presented. Specific coding sequences result in various THz far-field reflection and scattering patterns, ranging from a single beam to two, three, and numerous beams, which depart obviously from the ordinary Snell's law of reflection. By optimizing the coding sequences, a wideband THz thin film metamaterial with extremely low specular reflection, due to the scattering of the incident wave into various directions, is demonstrated. As a result, the reflection from a flat and flexible metamaterial can be nearly uniformly distributed in the half space with small intensity at each specific direction, manifesting a diffuse reflection from a rough surface. Both simulation and experimental results show that a reflectivity less than −10 dB is achieved over a wide frequency range from 0.8 to 1.4 THz, and it is insensitive to the polarization of the incident wave. This work reveals new opportunities arising from coding metamaterials in effective manipulation of THz wave propagation and may offer widespread applications.

Abstract-Graphene based tunable metamaterial absorber and polarization modulation in terahertz frequency

Yin Zhang, Yijun Feng, Bo Zhu, Junming Zhao, and Tian Jiang  »View Author Affiliations

Optics Express, Vol. 22, Issue 19, pp. 22743-22752 (2014)
http://dx.doi.org/10.1364/OE.22.022743

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-19-22743

Graphene can be utilized in designing tunable terahertz devices due to its tunability of sheet conductivity. In this paper, we combine the metamaterial having unit cell of cross-shaped metallic resonator with the double layer graphene wires to realize polarization independent absorber with spectral tuning at terahertz frequency. The absorption performance with a peak frequency tuning range of 15% and almost perfect peak absorption has been demonstrated by controlling the Fermi energy of the graphene that can be conveniently achieved by adjusting the bias voltage on the graphene double layers. The mechanism of the proposed absorber has been explored by a transmission line model and the tuning is explained by the changing of the effective inductance of the graphene wires under gate voltage biasing. Further more, we also propose a polarization modulation scheme of terahertz wave by applying similar polarization dependent absorbers. Through the proposed polarization modulator, it is able to electrically control the reflected wave with a linear polarization of continuously tunable azimuth angle of the major axis from 0° to 90° at the working frequency. These design approaches enable us to electrically control the absorption spectrum and the polarization state of terahertz waves more flexibly.

© 2014 Optical Society of America