Abstract-Anisotropic coding metamaterials and their powerful manipulation of differently polarized terahertz waves

Shuo Liu^1,2,*, Tie Jun Cui^1,3,*, Quan Xu⁴, Di Bao^1,2, Liangliang Du⁴, Xiang Wan^1,2, Wen Xuan Tang^1,2, Chunmei Ouyang⁴, Xiao Yang Zhou^1,2,5, Hao Yuan⁵, Hui Feng Ma^1,2, Wei Xiang Jiang^1,2, Jiaguang Han⁴, Weili Zhang^3,4 and Qiang Cheng^1,3

1. ¹State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China
2. ²Synergetic Innovation Center of Wireless Communication Technology, Southeast University, Nanjing 210096, China
3. ³Cooperative Innovation Centre of Terahertz Science, Chengdu 610054, China
4. ⁴Center for Terahertz Waves and College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China
5. ⁵Jiangsu Xuantu Technology Co., Ltd., Nanjing 211111, China

Correspondence: TJ Cui, Email: tjcui@seu.edu.cn

^*These authors contributed equally to this work.

Received 29 September 2015; Revised 19 January 2016; Accepted 20 January 2016
Accepted article preview online 26 January 2016

http://www.nature.com/lsa/journal/v5/n5/full/lsa201676a.html

Metamaterials based on effective media can be used to produce a number of unusual physical properties (for example, negative refraction and invisibility cloaking) because they can be tailored with effective medium parameters that do not occur in nature. Recently, the use of coding metamaterials has been suggested for the control of electromagnetic waves through the design of coding sequences using digital elements ‘0’ and ‘1,' which possess opposite phase responses. Here we propose the concept of an anisotropic coding metamaterial in which the coding behaviors in different directions are dependent on the polarization status of the electromagnetic waves. We experimentally demonstrate an ultrathin and flexible polarization-controlled anisotropic coding metasurface that functions in the terahertz regime using specially designed coding elements. By encoding the elements with elaborately designed coding sequences (both 1-bit and 2-bit sequences), the x- and y-polarized waves can be anomalously reflected or independently diffused in three dimensions. The simulated far-field scattering patterns and near-field distributions are presented to illustrate the dual-functional performance of the encoded metasurface, and the results are consistent with the measured results. We further demonstrate the ability of the anisotropic coding metasurfaces to generate a beam splitter and realize simultaneous anomalous reflections and polarization conversions, thus providing powerful control of differently polarized electromagnetic waves. The proposed method enables versatile beam behaviors under orthogonal polarizations using a single metasurface and has the potential for use in the development of interesting terahertz devices.

Abstract-Active graphene–silicon hybrid diode for terahertz waves

• 
  

• Quan Li,
• Zhen Tian,
• Xueqian Zhang,
• Ranjan Singh,
• Liangliang Du,
• Jianqiang Gu,
• Jiaguang Han
• & Weili Zhang

http://www.nature.com/ncomms/2015/150511/ncomms8082/full/ncomms8082.html

Controlling the propagation properties of the terahertz waves in graphene holds great promise in enabling novel technologies for the convergence of electronics and photonics. A diode is a fundamental electronic device that allows the passage of current in just one direction based on the polarity of the applied voltage. With simultaneous optical and electrical excitations, we experimentally demonstrate an active diode for the terahertz waves consisting of a graphene–silicon hybrid film. The diode transmits terahertz waves when biased with a positive voltage while attenuates the wave under a low negative voltage, which can be seen as an analogue of an electronic semiconductor diode. Here, we obtain a large transmission modulation of 83% in the graphene–silicon hybrid film, which exhibits tremendous potential for applications in designing broadband terahertz modulators and switchable terahertz plasmonic and metamaterial devices.