Abstract-Broadband diffusion of terahertz waves by multi-bit coding metasurfaces

Li-Hua Gao¹, Qiang Cheng^1,2, Jing Yang³, Shao-Jie Ma⁴, Jie Zhao¹, Shuo Liu¹, Hai-Bing Chen¹, Qiong He⁴, Wei-Xiang Jiang^1,2, Hui-Feng Ma^1,2, Qi-Ye Wen^2,5, Lan-Ju Liang^6,7, Biao-Bing Jin^2,6, Wei-Wei Liu^2,3, Lei Zhou⁴, Jian-Quan Yao⁷, Pei-Heng Wu⁶ and Tie-Jun Cui^1,2

1. ¹State Key Laboratory of Millimeter Waves, Department of Radio Engineering, Southeast University, Nanjing 210096, China
2. ²Cooperative Innovation Centre of Terahertz Science, No. 4, Section 2, North Jianshe Road, Chengdu 610054, China
3. ³Institute of Modern Optics, Key Laboratory of Optical Information Science and Technology (Ministry of Education), Nankai University, Tianjin 300071, China
4. ⁴State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Physics, Fudan University, Shanghai 200433, China
5. ⁵State Key Laboratory of Electronic Films and Integrated Devices, University of Electronic Science and Technology, Chengdu 610054, China
6. ⁶Research Institute of Superconductor Electronics (RISE), School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
7. ⁷Institute of Lasers and Optoelectronics, College of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China

Correspondence: Q Cheng, Email: qiangcheng@seu.edu.cn; TJ Cui, Email: tjcui@seu.edu.cn

Received 16 January 2015; Revised 23 April 2015; Accepted 26 April 2015

http://www.nature.com/lsa/journal/v4/n9/full/lsa201597a.html

The terahertz region is a special region of the electromagnetic spectrum that incorporates the advantages of both microwaves and infrared light waves. In the past decade, metamaterials with effective medium parameters or gradient phases have been studied to control terahertz waves and realize functional devices. Here, we present a new approach to manipulate terahertz waves by using coding metasurfaces that are composed of digital coding elements. We propose a general coding unit based on a Minkowski closed-loop particle that is capable of generating 1-bit coding (with two phase states of 0 and 180°), 2-bit coding (with four phase states of 0, 90°, 180°, and 270°), and multi-bit coding elements in the terahertz frequencies by using different geometric scales. We show that multi-bit coding metasurfaces have strong abilities to control terahertz waves by designing-specific coding sequences. As an application, we demonstrate a new scattering strategy of terahertz waves—broadband and wide-angle diffusion—using a 2-bit coding metasurface with a special coding design and verify it by both numerical simulations and experiments. The presented method opens a new route to reducing the scattering of terahertz waves.

Abstract-Broadband tunable liquid crystal terahertz waveplates driven with porous graphene electrodes

Lei Wang^1,*, Xiao-Wen Lin^1,*, Wei Hu¹, Guang-Hao Shao¹, Peng Chen¹, Lan-Ju Liang², Biao-Bing Jin², Pei-Heng Wu², Hao Qian³, Yi-Nong Lu³, Xiao Liang⁴, Zhi-Gang
 Zheng¹ and Yan-Qing Lu¹

http://www.nature.com/lsa/journal/v4/n2/full/lsa201526a.html

Versatile devices, especially tunable ones, for terahertz imaging, sensing and high-speed communication, are in high demand. Liquid crystal based components are perfect candidates in the optical range; however, they encounter significant challenges in the terahertz band, particularly the lack of highly transparent electrodes and the drawbacks induced by a thick cell. Here, a strategy to overcome all these challenges is proposed: Few-layer porous graphene is employed as an electrode with a transmittance of more than 98%. A subwavelength metal wire grid is utilized as an integrated high-efficiency electrode and polarizer. The homogeneous alignment of a high-birefringence liquid crystal is implemented on both frail electrodes via a non-contact photo-alignment technique. A tunable terahertz waveplate is thus obtained. Its polarization evolution is directly demonstrated. Furthermore, quarter-wave plates that are electrically controllable over the entire testing range are achieved by stacking two cells. The proposed solution may pave a simple and bright road toward the development of various liquid crystal terahertz apparatuses.