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-An ultrathin terahertz lens with axial long focal depth based on metasurfaces

Xiao-Yan Jiang,¹ Jia-Sheng Ye,^1,2,* Jing-Wen He,^1,3 Xin-Ke Wang,^1,2 Dan Hu,^1,3 Sheng-Fei Feng,^1,2 Qiang Kan,⁴ and Yan Zhang^1,2,3,5

¹Department of Physics, Capital Normal University and Beijing Key Lab for THz Spectroscopy and Imaging, Key Lab of THz Optoelectronics, Ministry of Education, Beijing 100048, China

²Beijing Center for Mathematics and Information Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150001, China

³Department of Physics, Harbin Institute of Technology, Harbin 150001, China

⁴State Key Laboratory for integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China

⁵yzhang@mail.cnu.edu.cn

^*Corresponding author: jiashengye@gmail.com

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-24-30030

The plasmonic resonance effect on metasurfaces generates an abrupt phase change. We employ this phase modulation mechanism to design the longitudinal field distribution of an ultrathin terahertz (THz) lens for achieving the axial long-focal-depth (LFD) property. Phase distributions of the designed lens are obtained by the Yang-Gu iterative amplitude-phase retrieval algorithm. By depositing a 100 nm gold film on a 500 μm silicon substrate and etching arrayed V-shaped air holes through the gold film, the designed ultrathin THz lens is fabricated by the micro photolithography technology. Experimental measurements have demonstrated its LFD property, which basically agree with the theoretical simulations. In addition, the designed THz lens possesses a good LFD property with a bandwidth of 200 GHz. It is expected that the designed ultrathin LFD THz lens should have wide potential applications in broadband THz imaging and THz communication systems.
© 2013 Optical Society of America