Eugene P. Pozhidaev

Orientational Kerr effect and phase modulation of light in deformed-helix ferroelectric liquid crystals with subwavelength pitch

We study both theoretically and experimentally the electro-optical properties of vertically aligned deformed helix ferroelectric liquid crystals (VADHFLC) with subwavelength pitch that are governed by the electrically induced optical biaxiality of the smectic helical structure. The key theoretical result is that the principal refractive indices of homogenized VADHFLC cells exhibit the quadratic nonlinearity and such behavior might be interpreted as an orientational Kerr effect caused by the electric-field-induced orientational distortions of the FLC helix. In our experiments, it has been observed that, for sufficiently weak electric fields, the magnitude of biaxiality is proportional to the square of electric field in good agreement with our theoretical results for the effective dielectric tensor of VADHFLCs. Under certain conditions, the 2π phase modulation of light, which is caused by one of the induced refractive indices, is observed without changes in ellipticity of incident light.

Switching dynamics of surface stabilized ferroelectric liquid crystal cells: effects of anchoring energy asymmetry.

We study both theoretically and experimentally switching dynamics in asymmetric surface stabilized ferroelectric liquid crystal cells where the bounding surfaces are treated differently to produce asymmetry in their anchoring properties. Our electro-optic measurements of the switching voltage thresholds, V+ and -V{-}, that are determined by the peaks of the reversal polarization current reveal the frequency dependent shift of the hysteresis loop, V{+}-V{-}. We examine the predictions of the uniform dynamic model with the anchoring energy taken into account. It is found that the asymmetry effects are dominated by the polar contribution to the anchoring energy. Frequency dependence of the voltage thresholds is studied by analyzing the properties of time-periodic solutions to the dynamic equation (cycles). For this purpose, we apply the method linking the cycles and the fixed points of the composition of two parametrized half-period mappings for the approximate model. It is found that the cycles are unstable and can only be formed if the driving frequency is lower than its critical value. The polar anchoring parameter is estimated by making a comparison between the results of modeling and the experimental data for the shift vs frequency curve.

Manifestation of chiral asymmetry of ferroelectric liquid crystals induced by optically active dipole dopants in a linear electrooptic effect

Abstract The existence of eight combinations of absolute spatial configuration, helix handedness and handedness of director tilt has been shown for ferroelectric liquid crystals induced by optically active dipole dopants (optically active diesters of 4,4″-terphenyl dicarboxylic acid). As in the case of individual ferroelectrics alternation of the helix handedness is observed depending on absolute configuration of the C*-atom and its position relative to the rigid core of the molecule. However for these induced ferroelectric liquid crystals the helix handedness does not depend on the inductive effect of the substituent adjacent to the C* atom, e.g. the helix handedness of all the (S)-2-chlorine substituted materials coincides with that of the (S)-2-methyl-butyl derivative. Substitution of a chlorine atom by a cyano group followed by conversion of absolute spatial configuration of the C* atom results in the opposite helical sense. Thus asymmetric parameters of the induced ferroelectric liquid crystals helix...

Multistable Electro-optical Modes in Ferroelectric Liquid Crystals

Multistable electro-optical modes exist under certain conditions in ferroelectric liquidcrystal (FLC) cells, which means that any light-transmission level can be memorized after the driving voltage is switched off. The multistability is responsible for three new electro-optical modes with different shapes of the gray-scale curve that can be either S-shaped (double or single dependent upon the applied-voltage pulse sequence and boundary conditions) or V-shaped dependent upon boundary conditions and FLC cell parameters. The origin of these modes will be described.

Fast Electro-optical Mode in Photo-aligned Reflective Deformed Helix Ferroelectric Liquid Crystal Cells

The electro-optical behavior of deformed helix ferroelectric liquid crystal in reflective mode is described in this paper. The electrically controlled reflectance has been measured at subkilohertz driving voltage frequency for different polarizations of the incident light and compared quite successfully with the simulation results.

V-shaped electro-optical mode based on deformed-helix ferroelectric liquid crystal with subwavelength pitch

— V-shaped electro-optical response is shown, both theoretically and experimentally, to be an inherent property of a deformed-helix ferroelectric liquid-crystal cell (DHFLC) under a special choice of the applied rectangular alternating-electric-field waveform, frequency, and cell geometry. In contrast to other known V-shaped ferroelectric liquid-crystal (FLC) modes, the discovered V-shaped switching is observed in a broadband frequency range including 1 kHz, and not at a certain characteristic frequency. This type of V-shaped switching allows for a drastic increase in the operating frequency of field-sequential-color (FSC) LCD cells in comparison with fast nematic liquid-crystal (NLC) modes.

Surface and volume bistability in ferroelectric liquid crystals

We call the bistabifity of ferroelectric liquid crystal (FLC) cells as the surface bistability (SB), if the dispersion part of anchoring energy is responsible for this type of bistabiity. SB was predicted theoretically [1] and investigated experimentally [2-4] .It was shown, that SB there exists in SSFLC cells possessing the bookshelf structure of smectic C layers [2] and SB there exists only in limited region of multidimensional space of cell and driving voltage parameters [3]. Anchoring energy of FLC with solid surface for SB structures is [4]: 102 iO erg / cm2 On the other hand there exists the volume bistability (VB), which have been observed by us recently in thick (15 mkm and more) layers of new FLC compositions [5].VB is a special phenomenon caused only with stereo chemical nature of the FLC composition and quite independent upon surfaces. In this work we would try: to found the physical principle for experimental measurement of an average free energy density of ferroelectrics, -to describe manifestations for both SB and VB, - to compare SB and VB from point of view their free energy parameters.

Electro-optical properties of deformed-helix ferroelectric liquid crystal display cells

General electrooptical properties of Deformed Helix Ferroelectric (DHF) liquid crystal effect have been analyzed. This promising effect opens the door to continuous gray scale of diode active matrix displays, the most low electric voltage amplitude in comparison with any other type of liquid crystal cells can drive DHF displays cells. On the contrary, high voltage and high frequency mode of DHF effect provides the response time about 1.5 micrometers in a very broad temperature range. The electrically controlled birefringence of DHF cells could be applied in adaptive optics.

Voltage sensor based on Deformed Helix Ferroelectric Liquid Crystal

In this paper we propose a new approach to fibre optic voltage sensors via voltage-controlled Liquid Crystals (LC), which would allow direct measurement of up to 400 kV/m electric fields at multiple points. In addition, a novel polarization independent fibre optic sensor configuration is presented that exhibits a linear electro-optic (EO) response to variations of the electrical field under test.

P-232L: Late-News Poster: New Results on Bistable Photoaligned Ferroelectric LCDs: Grey Scale Generation, Stabilization and Passive Driving Scheme

The principles for intrinsic greyscale generation and stabilization of bistable photoaligned FLCD are discussed and investigated. In order to realize these principles, the passive matrix driving scheme for FLCD is proposed and studied. Passive 160×160 matrix addressing photoaligned 5μm reflective FLC display (48mm×46mm) with high contrast and 4 memorized grey scale levels is demonstrated. Images can be saved for very long time without any power supply. 15V driving voltage is only needed to refresh information, which is impressive and desirable for low power consumption display such as PDA, e-paper etc.