Abstract-340-GHz 3-D Imaging Radar With 4Tx-16Rx MIMO Array

Binbin Cheng,  Zhenmao Cui, Bin Lu,  Yuliang Qin,  Qiao Liu,  Peng Chen,  Yue He,  Jun Jiang,   Xiaoyang He, Xianjin Deng, Jian Zhang, Liguo Zhu, 

https://ieeexplore.ieee.org/document/8404082/

A standoff 3-D imaging radar for security body scan at 340 GHz has been described. This terahertz imager incorporates a multiple input multiple output (MIMO) array as an electronic beam former in a horizontal dimension and an elliptic cylinder as a focusing reflector in elevation. Frequency-modulated continuous-wave (FMCW) emission with 16-GHz bandwidth caused a 10-mm-range resolution after calibration for nonlinearities of the distorted radar signals. The horizontal MIMO array contains 4 transmitters and 16 receivers (4Tx-16Rx) to generate a 64-Tx/Rx full virtual array corresponding to an antenna size of approximately 128 mm, which caused a horizontal resolution of about 14 mm at a distance of 3 m. FMCW signals were transmitted from the 4-Tx sequentially and focused as narrow beam lines by the elliptic reflector to get a 12-mm vertical resolution at 3 m. A fast-scanning mirror swings in the light path to make these beam lines screen in the vertical direction. A 4-Hz frame rate is now possible for a personal screen with a field of view of 2 m × 0.6 m.

Abstract-Generating, Separating and Polarizing Terahertz Vortex Beams via Liquid Crystals with Gradient-Rotation Directors

Shi-Jun Ge, Zhi-Xiong Shen, Peng Chen, Xiao Liang,  Xin-Ke Wang,  Wei Hu, OrcID, Yan Zhang, Yan-Qing Lu


http://www.mdpi.com/2073-4352/7/10/314

Liquid crystal (LC) is a promising candidate for terahertz (THz) devices. Recently, LC has been introduced to generate THz vortex beams. However, the efficiency is intensely dependent on the incident wavelength, and the transformed THz vortex beam is usually mixed with the residual component. Thus, a separating process is indispensable. Here, we introduce a gradient blazed phase, and propose a THz LC forked polarization grating that can simultaneously generate and separate pure THz vortices with opposite circular polarization. The specific LC gradient-rotation directors are implemented by a photoalignment technique. The generated THz vortex beams are characterized with a THz imaging system, verifying features of polarization controllability. This work may pave a practical road towards generating, separating and polarizing THz vortex beams, and may prompt applications in THz communications, sensing and imaging.

Abstract-Terahertz vortex beam generator based on a photopatterned large birefringence liquid crystal

Shijun Ge, Peng Chen, Zhixiong Shen, Wenfeng Sun, Xinke Wang, Wei Hu, Yan Zhang, and Yanqing Lu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-11-12349

A terahertz (THz) q-plate is proposed and demonstrated to generate THz vortex beams. It is composed of a large birefringence liquid crystal (LC) with spatially-varying director distribution sandwiched by two pieces of fused silica glass. A polarization-sensitive alignment agent is photopatterned to carry out the specific LC director distribution. THz vortex beams with different topological charges are characterized with a THz digital holographic imaging system. The intensity and phase distributions consistent with theoretical analyses are obtained. Besides, an eight-lobed intensity distribution is observed corresponding to the vertical polarization component of a cylindrical vector beam. This work may inspire novel THz applications.

© 2017 Optical Society of America

Abstract-Liquid crystal depolarizer based on photoalignment technology

Bing-Yan Wei, Peng Chen, Shi-Jun Ge, Li-Chao Zhang, Wei Hu, and Yan-Qing Lu

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-4-2-70

We propose a depolarizer based on the principle of a collection of half-wave plates with randomly distributed optic axes. The design is demonstrated by means of dynamically photopatterning liquid crystal into randomly aligned homogeneous domains. We characterize the liquid crystal depolarizer for 1550 nm and C-band (1520–1610 nm). A degree of polarization of less than 5% is obtained for any linearly polarized light. This study provides a practical candidate for high-performance depolarizers.

© 2016 Chinese Laser Press

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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.