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Crystals 2017, 7(10), 314; doi:10.3390/cryst7100314

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

1
National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures and College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China
2
Department of Chemistry, Tsinghua University, Beijing 100084, China
3
Department of Physics, Capital Normal University, Beijing Key Laboratory of Metamaterials and Devices, Key Laboratory of Terahertz Optoelectronics, Ministry of Education, and Beijing Advanced Innovation Center for Imaging Technology, Beijing 100048, China
*
Authors to whom correspondence should be addressed.
Academic Editor: Vladimir Chigrinov
Received: 20 September 2017 / Revised: 13 October 2017 / Accepted: 15 October 2017 / Published: 18 October 2017
(This article belongs to the Special Issue Micro and Nano Patterned Substrates for Liquid Crystal Alignment)
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Abstract

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. View Full-Text
Keywords: liquid crystals; patterned photoalignment; terahertz imaging; optical vortices; Pancharatnam-Berry phase liquid crystals; patterned photoalignment; terahertz imaging; optical vortices; Pancharatnam-Berry phase
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Ge, S.-J.; Shen, Z.-X.; Chen, P.; Liang, X.; Wang, X.-K.; Hu, W.; Zhang, Y.; Lu, Y.-Q. Generating, Separating and Polarizing Terahertz Vortex Beams via Liquid Crystals with Gradient-Rotation Directors. Crystals 2017, 7, 314.

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