Abstract-Liquid crystal tunable terahertz lens with spin-selected focusing property

Zhixiong Shen, Shenghang Zhou, Shijun Ge, Wei Duan, Lingling Ma, Yanqing Lu, and Wei Hu

Fig. 1 (a) The schematic illustration of the spin-selected lens. (b) The photo of the sample under crossed polarizers (indicated by two yellow arrows). Scale bar: 1 mm. (c) The designed phase diagram. Inset shows a magnified 6 × 6 pixel array, which is divided into lattice I and II. The lattice periodicity p is 152 μm. (d) The focusing functions of lattice I and II.

We propose and demonstrate an active spin-selected lens with liquid crystal (LC) in the terahertz (THz) range. The lens is a superposition of two geometric phase lenses with separate centers and conjugated phase profiles. Its digitalized multidirectional LC orientations are realized via a dynamic micro-lithography-based photo-patterning technique and sandwiched by two graphene-electrode-covered silica substrates. The specific lens can separate the focusing spots of incident light with opposite circular polarizations. Its focusing performance from 0.8 to 1.2 THz is characterized using a scanning near-field THz microscope system. The polarization conversion efficiency varies from 32.1% to 70.2% in this band. The spin-selected focusing functions match well with numerical simulations. Such lens exhibits the merit of dynamic functions, low insertion loss and broadband applicability. It may inspire various practical THz apparatuses.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

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-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