Abstract-Simulations of some physical parameters of homologous series of nBT and nCHBT at 0.3–20.0 THz

K. Sielezin,  Polan R. Kowerdziej,  J. Parka,

https://www.tandfonline.com/doi/abs/10.1080/02678292.2018.1563918?journalCode=tlct20

In this work, the terahertz (THz) absorption of homologous series of isothiocyanobiphenyls (nBT) and 4-(trans-4ʹ-n-alkylcyclohexyl)isothiocyanato-benzene (nCHBT) are simulated by using the density functional theory (DFT) method. Numerical results show that absorption of the tested nematic liquid crystals (NLCs) varies up to 0.04 in the broad range of 0.3–20.0 THz and takes maximum value in the range of 9–14 THz.

In addition, the values of molecular polarisabilities (αo, αe) increase with the increase in the number of carbon atoms in the alkyl chain, while refractive indices (no, ne) decreases. The calculated birefringence (Δn) values for nCHBT are approximately twice as large as the birefringence value for nBT. It is crucial to examine these series of nematic liquid crystals at THz frequencies due to the role of soft matter in various switchable THz components.

Abstract-Hypersensitive and tunable terahertz wave switch based on non-Bragg structures filled with liquid crystals

Lu Zhang,  Ya-Xian Fan, Huan Liu,  Lan-Lan Xu,  Jiu-Ling Xue,  Zhi-Yong Tao

http://ieeexplore.ieee.org/document/7933180/

We investigated a hypersensitive and tunable terahertz (THz) wave switch based on liquid-crystal-filled non-Bragg structures. Non-Bragg structures, which consist of periodically corrugated metallic tube walls, provide spectra with very sharp rising edges, making them usable for sensitive switching. Tunability can be achieved by dynamically shifting the rising edge of a THz spectrum by using an externally applied magnetic field to change the orientations of the nematic liquid crystal (E7) molecules. The simulated results revealed that the switch effects are hypersensitive and tunable in the THz frequency range and that such switches could be applicable in future THz systems.

Abstract-Electrically tunable terahertz polarization converter based on overcoupled metal-isolator-metal metamaterials infiltrated with liquid crystals

Borislav Vasić1, Dimitrios C Zografopoulos2, Goran Isić1, Romeo Beccherelli2  Radoš Gajić1

Published 21 February 2017 • © 2017 IOP Publishing Ltd 

http://iopscience.iop.org/article/10.1088/1361-6528/aa5bbd

Large birefringence and its electrical modulation by means of Fréedericksz transition makes nematic liquid crystals (LCs) a promising platform for tunable terahertz (THz) devices. The thickness of standard LC cells is in the order of the wavelength, requiring high driving voltages and allowing only a very slow modulation at THz frequencies. Here, we first present the concept of overcoupled metal-isolator-metal (MIM) cavities that allow for achieving simultaneously both very high phase difference between orthogonal electric field components and large reflectance. We then apply this concept to LC-infiltrated MIM-based metamaterials aiming at the design of electrically tunable THz polarization converters. The optimal operation in the overcoupled regime is provided by properly selecting the thickness of the LC cell. Instead of the LC natural birefringence, the polarization-dependent functionality stems from the optical anisotropy of ultrathin and deeply subwavelength MIM structures. The dynamic electro-optic control of the LC refractive index enables the spectral shift of the resonant mode and, consequently, the tuning of the phase difference between the two orthogonal field components. This tunability is further enhanced by the large confinement of the resonant electromagnetic fields within the MIM cavity. We show that for an appropriately chosen linearly polarized incident field, the polarization state of the reflected field at the target operation frequency can be continuously swept between the north and south pole of the Poincaré sphere. Using a rigorous Q-tensor model to simulate the LC electro-optic switching, we demonstrate that the enhanced light–matter interaction in the MIM resonant cavity allows the polarization converter to operate at driving voltages below 10 Volt and with millisecond switching times.

Abstract-Fast switching of nematic liquid crystals over a wide temperature range using a vertical bias electric field

Jung-Wook Kim, Tae-Hoon Choi, and Tae-Hoon Yoon  »View Author Affiliations

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-53-26-5856

Applied Optics, Vol. 53, Issue 26, pp. 5856-5859 (2014)
http://dx.doi.org/10.1364/AO.53.005856

We propose a drive scheme using a three-terminal electrode structure for submillisecond switching of nematic liquid crystals (LCs). A vertical bias electric field is continuously applied to the LCs, whereas an in-plane electric field controls the switching to the bright state. Applying the proposed scheme to a homogeneously aligned nematic LC cell yields a submillisecond response time of 0.7 ms at room temperature and 4.9 ms at −20°C.

© 2014 Optical Society of America