Abstract-Visible Measurement of Terahertz Power Based on Capsulized Cholesteric Liquid Crystal Film

Lei Wang,  Hongsong Qiu, Thanh Nhat Khoa Phan, Kosaku Kato, Boyoung Kang, Keisuke Takano, Yanqing Lu, Lujian Chen, Peng Lv, Kehan Yu, Wei Wei,  Biaobing Jin, Makoto Nakajima

file:///C:/Users/Randy/Downloads/applsci-08-02580.pdf

We demonstrate a new method to detect terahertz (THz) power using a temperature supersensitive capsulized cholesteric liquid crystal film based on the thermochromic and thermodiffusion effect, which is clearly observed. A quantitative visualization of the THz intensity up to 4.0 × 103 mW/cm2 is presented. The diameter of the color change area is linearly dependent on the THz radiation power above 0.07 mW in the steady state. Moreover, the THz power can be detected for 1 sec of radiation with a parabolic relation to the color change area. The THz power meter is robust, cost-effective, portable, and even flexible, and can be used in applications such as THz imaging, biological sensing, and inspection.

Abstract-Ultra-wideband high-efficiency reflective linear-to-circular polarization converter based on metasurface at terahertz frequencies

Yannan Jiang, Lei Wang, Jiao Wang, Charles Nwakanma Akwuruoha, and Weiping Cao

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-22-27616&origin=search

The polarization conversion of electromagnetic (EM) waves, especially linear-to-circular (LTC) polarization conversion, is of great significance in practical applications. In this study, we propose an ultra-wideband high-efficiency reflective LTC polarization converter based on a metasurface in the terahertz regime. It consists of periodic unit cells, each cell of which is formed by a double split resonant square ring, dielectric layer, and fully reflective gold mirror. In the frequency range of 0.60 – 1.41 THz, the magnitudes of the reflection coefficients reach approximately 0.7, and the phase difference between the two orthogonal electric field components of the reflected wave is close to 90° or –270°. The results indicate that the relative bandwidth reaches 80% and the efficiency is greater than 88%, thus, ultra-wideband high-efficiency LTC polarization conversion has been realized. Finally, the physical mechanism of the polarization conversion is revealed. This converter has potential applications in antenna design, EM measurement, and stealth technology.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing 

Abstract-Tunable reflective liquid crystal terahertz waveplates

Lei Wang, Shijun Ge, Wei Hu, Makoto Nakajima, and Yanqing Lu

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-7-6-2023&origin=search

Tunable liquid crystal devices that can change terahertz wave polarization continuously have many potential applications in terahertz optical systems. We present a reflective liquid crystal terahertz waveplate with sub-wavelength metal grating and metal ground plane electrodes. The thickness of the liquid crystal layer can be reduced to ~10% of that needed for the same phase shift at a given frequency in a transmissive waveplate. We experimentally demonstrate the same tunability as in the transmissive type just using half the thickness. We discuss the dependence on the angle of incidence for phase shift tunability, which can achieve beam steering and polarization conversion simultaneously. The proposed design can be applied in terahertz imaging, sensing, and communications.

© 2017 Optical Society of America

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.

Abstract-Graphene-based terahertz tunable plasmonic directional coupler

Meng-Dong He^1,a), Kai-Jun Wang¹, Lei Wang¹, Jian-Bo Li¹, Jian-Qiang Liu²,Zhen-Rong Huang³, Lingling Wang³, Lin Wang⁴, Wei-Da Hu⁴ and Xiaoshuang Chen⁴
http://scitation.aip.org/content/aip/journal/apl/105/8/10.1063/1.4894090
1 Institute of Mathematics and Physics, Central South University of Forestry and Technology, Changsha 410004, People's Republic of China
2 College of Science, Jiujiang University, Jiujiang 332005, People's Republic of China
3 Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education, Hunan University, Changsha 410082, People's Republic of China
4 National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, Shanghai 200083, People's Republic of China
a) Author to whom correspondence should be addressed. Electronic mail: hemendong@sohu.com
Appl. Phys. Lett. 105, 081903 (2014); http://dx.doi.org/10.1063/1.4894090

We propose and numerically analyze a terahertz tunable plasmonic directional coupler which is composed of a thin metal film with a nanoscale slit, dielectric grating, a graphene sheet, and adielectric substrate. The slit is employed to generate surface plasmon polaritons (SPPs), and the metal-dielectric grating-graphene-dielectric constructs a Bragg reflector, whose bandgap can be tuned over a wide frequency range by a small change in the Fermi energy level of graphene. As a graphene-based Bragg reflector is formed on one side of the slit, the structure enables SPP waves to be unidirectionally excited on the other side of the slit due to SPP interference, and the SPP waves in the Bragg reflector can be efficiently switched on and off by tuning the graphene'sFermi energy level. By introducing two optimized graphene-based Bragg reflectors into opposite sides of the slit, SPP waves can be guided to different Bragg reflectors at different Fermi energy levels, thus achieving a tunable bidirectional coupler.

Abstract-Artificial birefringent metallic planar structures for terahertz wave polarization manipulation

Lei Wang, Suhua Jiang, Haifeng Hu, Haomin Song, Wei Zeng, and Qiaoqiang Gan 
 »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-2-311

We propose an artificial birefringent terahertz (THz) device constructed by subwavelength L-shaped hole arrays on a single metallic layer. This structure is able to work as a polarizer when the incident frequency is between the cut-off frequencies of two eigenmodes. When the incident wave is beyond cut-off frequencies of these two modes, it can be designed as an efficient half- or quarter-wave plate with extraordinary transmission properties. A big effective index difference from 0.254 to 0.768 is obtained using a subwavelength-thick planar structure, which can reduce the thickness of the device to one tenth of conventional quartz birefringent crystals for THz waves.

© 2014 Optical Society of America

Abstract-Artificial Birefringent Metallic Planar Structures for Terahertz Wave Polarization Manipulation

• Lei Wang, haifeng Hu, Haomin Song, Wei Zeng, Suhua Jiang, and Qiaoqiang Gan
• http://www.opticsinfobase.org/ol/upcoming_pdf.cfm?id=197426

• Abstract: We propose an artificial birefringent terahertz (THz) device constructed by subwavelength L-shaped hole arrays on a single metallic layer. This structure is able to work as a polarizer when the incident frequency is between the cutoff frequencies of two eigenmodes. When the incident wave is beyond cutoff frequencies of these two modes, it can be designed as an efficient half- or quarter-wave plate with extraordinary transmission properties. A big effective index difference from 0.254 to 0.768 is obtained using a subwavelength-thick planar structure, which can reduce the thickness of the device to one tenth of conventional quartz birefringent crystals for THz waves.