Mol. Cryst. Liq. Cryst., Vol. 561: pp. 170–176, 2012 Copyright © Taylor & Francis Group, LLC ISSN: 1542-1406 print/1563-5287 online DOI: 10.1080/15421406.2012.687177 Optimizing of Control Signal Shape for Improving of Time Characteristics of Liquid Crystal Based Devices H. L. MARGARYAN, ∗ N. H. HAKOBYAN, D. L. HOVHANNISYAN, V. K. ABRAHAMYAN, D. K. POKHSRARYAN, AND S. R. MANUCHARYAN Yerevan State University, Yerevan, Armenia The dynamics of reorientation processes of planar oriented nematic liquid crystals can be controlled and improved by 1 kHz continuous, as well as pulsed, auxiliary electric fields. A device and a special software for forming a control signal of complex shape are created. We show that using a four-step control signal for optical switching allows fivefold reduction of switching time compared to conventional two-step signal. Keywords Electro-optical response; light valve; liquid crystal; transient nematic effect Introduction The operating speed is one of the main parameters of devices based on liquid crystals (LC)–displays, spatial light modulators, light valves, phase retarders, etc.). It is known that for improvement of operating speed the thickness of LC is reduced, special types of orienting coatings and liquid crystals are used, the control is carried out by pulse voltage. For example, the use of obliquely deposited orienting coatings reduces the orientation time, but the relaxation time increases in this case [1]. The increase in operating speed for both orientation processes is observed for the so-called π -cells, when obliquely deposited orienting coatings are placed opposite each other anti-parallel [2,3]. In this case, the transient processes take place in the presence of hydrodynamic flow, which contributes to operating speed. There are double-frequency liquid crystals, which change the sign of dielectric anisotropy at different frequencies of the control voltage [4,5]. Some studies are dedicated to the synthesis of quick-response LC or LC sensitization by means of nano-particles (fullerenes, nanotubes, ferroelectric particles, etc.) [6]. Recently polymer-stabilized LC found an application, in which the operating speed is provided with LC ordering not only by orientation at the boundaries, but also by LC stabilization in the volume between the long polymer molecules [7]. It is known that the degree of liquid crystal order is characterized by the order parameter S , which depends on the initial state of LC orientation, as well as on the external influences (temperature, electric and magnetic fields, etc.) [8]. When contacting of LC with specially treated surface of the substrate the order is changed: a near-surface polarity and short-range ∗ Address correspondence to H. L. Margaryan, Faculty of Radiophysics, Yerevan State University, 1 A. Manoogian Str., Yerevan 0025, Armenia. Tel./Fax: + 374 10 578373. E-mail: marhakob@ysu.am [602]/170