Liquid Crystal (LC) devices for Terahertz (THz) phase shifters have a thick cell gap, which inevitably results in a very slow response, particularly when they rely on the passive relaxation of LCs. To vastly improve the response characteristics of LCs for use in THz phase shifters, we virtually demonstrate a novel type of LC switching in which all processes are governed by an electric field between in-plane and out-of-plane tristable states, resulting in hexadirectional switching with three orthogonal orientation states and thereby attaining a broader range of phase shifts. This type of LC switching is achieved using a pair of substrates that mirror each other, each of which has two pairs of orthogonally arranged finger-shaped electrodes for in-plane switching. Further, the two substrates each have one grating-shaped electrode, thus forming a pair of electrodes for out-of-plane switching. Each hexadirectional switching process between the tristable states is driven by an electric field, thus maintaining a rapid response by avoiding long relaxation times.
THz time-domain spectroscopy is used to measure the frequency dependent (0.2-2.0 THz) complex refractive
index of a pure liquid crystal (LC), 4'-n-pentyl-4-cyanobiphenyl (5CB), and its LC colloids with SiO2 particles.
While the refractive index of the pure LC is found to vary markedly due to distinct spatial inhomogeneities
consisting of oriented domains within the sample, the LC colloids provide us with a spatially much more homogeneous
dielectric response which is very stable and reproducible, from which we can reliably deduce the optical
constants of pure 5CB using effective medium theory. While the absorption coefficient is found to be very small,
the refractive index of 5CB decreases considerably over our probe frequency range.
Electro-optical performances of in-plane switching mode active matrix addressed liquid crystal (LC) displays were analyzed by using device simulations. Practical combinations of 2D simulations to analyze precise electric and LC director fields and fast 1D simulations to grasp electro- optical characteristics were systematically utilized. Electrode geometries and tilt angle of the LC molecules at the substrate surface were identified as key points to optimize the electronic performance and optical performance, respectively.
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