Fast Mode in the Electro-Optical Switching of a Liquid Crystal Cell with Interdigitated Electrodes
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TICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Fast Mode in the Electro-Optical Switching of a Liquid Crystal Cell with Interdigitated Electrodes I. V. Simdyankina, A. R. Geivandova,*, and S. P. Paltoa aShubnikov
Institute of Crystallography, “Crystallography and Photonics” Federal Research Center, Russian Academy of Sciences, Moscow, 119333 Russia *e-mail: [email protected] Received April 16, 2020; revised May 4, 2020; accepted May 4, 2020
Abstract—The conditions for the emergence of a fast electro-optical mode in a liquid crystal cell with a short period (p = 1.8 μm) of interdigitated electrodes have been investigated. The electro-optical switching in two liquid crystal mixtures differing in viscosity and dielectric and optical anisotropies has been studied through numerical simulations and experimentally. The fast mode switching times are shown to be in the submillisecond range and to be related to the switching of a near-electrode liquid crystal layer comparable in thickness to the period of the electrode structures. The inclusion of the entire liquid crystal volume in the switching process is characterized by a slow mode with considerably longer times. DOI: 10.1134/S1063776120090083
1. INTRODUCTION Modern photonic devices and displays based on liquid crystals (LCs) operate by changing the state of light polarization under the action of an electric field [1, 2]. The supramolecular structure in a LC layer is rearranged as a result of the orientational transition [3], which allows the light flux incident on the layer to be modulated. In the last two decades such technical characteristics of LC displays as contrast ratio, viewing angles, and electro-optical response time have been improved drastically. Nevertheless, increasing the electro-optical switching speed remains topical for extending applications of liquid crystals in new devices. The electro-optical response speed affects primarily the video information display quality. For example, a slow electro-optical response leads to moving image blurring, whereas a short switching time opens the possibilities for using the color sequential technology. The latter allows the color filters to be excluded from the design of LC displays, thereby increasing the light efficiency and image resolution. Thus, increasing the speed of LC modulators as a result of the search for new electro-optical effects and the development of LC materials is fundamentally important for the progress of the liquid crystal technology in both photonic and display devices. At first glance, it seems that the simplest way of increasing the speed is to create thin LC layers. As follows from Eqs. (1) and (2), the switch-on and switchoff times in the electro-optical effect are proportional to the square of the layer thickness d [1]. However, as
the layer thickness decreases, the optical anisotropy Δn of the LC material needs to be increased to provide the required phase delay for light modulation Δϕ (3):
τon ≈
4πγ d2 , Δε( f ) (U 2 − U th2 )
(1)
γd 2 (2) , 2 π Ki here, Uth is the threshold voltag
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