Abstract-Electrically tunable terahertz dual-band metamaterial absorber based on a liquid crystal

Zhiping Yin,  Yujiao Lu,  Tianyu Xia,  Weien Lai,  Jun Yang,  Hongbo Lua,  Guangsheng Deng,

http://pubs.rsc.org/en/content/articlelanding/2018/ra/c7ra13047c#!divAbstract

In this paper, a liquid crystal (LC) based tunable metamaterial absorber with dual-band absorption is presented. The proposed absorber is analysed both numerically and experimentally. The analysis shows that the two absorption peaks, originating from the new resonant structure, are experimentally detected at 269.8 GHz and 301.4 GHz when no bias voltage is applied to the LC layer. In order to understand the absorption mechanisms, simulation results for the surface current and power loss distributions are presented. Since liquid crystals are used as the dielectric layer to realize the electrically tunable absorber, a frequency tunability of 2.45% and 3.65% for the two absorption peaks is experimentally demonstrated by changing the bias voltage of the LC layer from 0 V to 12 V. Furthermore, the absorber is polarization independent and a high absorption for a wide range of oblique incidence is achieved. The designed absorber provides a way forward for the realization of tunable metamaterial devices that can be applied in multi-band detection and imaging.

Abstract-Triple-band tunable perfect terahertz metamaterial absorber with liquid crystal

Ruoxing Wang, Li Li, Jianlong Liu, Fei Yan, Fengjun Tian, Hao Tian, Jianzhong Zhang,  Weimin Sun,

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-26-32280

We report a compact triple-band tunable perfect terahertz metamaterial absorber (TMA) at the subwavelength scale of thickness, which is composed of a planar metallic disk resonator array above a conductive ground plane separated with liquid crystal (LC) mixture. The calculations of terahertz absorption spectra demonstrate triple near-unity absorption bands in the gap plasmonic resonance coupling regime. Three resonance frequencies of the absorber exhibit continuous linear-tunability as changing the refractive index of LC. Remarkably, each peak absorbance of the triple bands maintains at a level of beyond 99% in the whole tuning operation, and the absorbance can remain more than 90% over a wide range of incident angles. Our work suggests that the LC tunable absorber scheme has the potential to overcome the basic difficulty to perform simultaneously multiband spectral tuning and near-unity absorbance with wide angle of incidence and weak polarization dependence. The proposed LC-tunable multiband perfect TMA is promising in the application of biomolecular spectra-selective terahertz imaging and sensing.

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

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- A simulation study on terahertz absorption of liquid crystal mixture E7

Jian-qi Dong, Wen-qi Cheng, Meng-ge Li, Kai-li Wang, Ze-zhang Chen, Heng Ma,

http://iopscience.iop.org/article/10.1088/1361-6463/aa7d6c/meta

A simulation work on a broad THz absorption of liquid crystal mixture E7 consisting of 5CB, 7CB, 8OCB and 5CT is reported. Based on the density functional theory, the molecular structures of the monomers were optimized and calculated using the Gaussian package with base set B3LYP and 6-311g. The results indicate that the simulation of the characteristic absorption spectra is accurate compared to the experimental and literature report in the infrared band. By analyzing contribution of the benzene ring, C–O and alkyl bonds on THz absorption, it is found that there are no significant effects from the cyano group and the alkyl radical. The addition of a benzene ring leads to an increase in absorption intensity and redshift. By discussing the atomic mass distribution and the structural symmetry of the monomers, a reason for the strong THz absorption of 8OCB is proposed.