Evgeny Pozhidaev

Structure of optically active compounds and ferroelectric properties of liquid crystals

Abstract A new series of optically active dipole dopants - diesters of 4,4″-terphenyl dicarboxylic acid - have been prepared. Most of the components are high melting substances. Some of 2-chlorine substituted compounds show a chiral smectic C* phase. The Ps value induced by optically active dipole dopants depends on several factors such as the magnitude of the dipole moment and the length of the alkyl tail at the C*-atom, the degree to which rotations of the molecule and the chiral center are hindered. In some cases the experimental PS value of the FLC-mixture induced by a pair of dopants with same Ps sign and opposite helix handedness is higher than the sum of the PS values induced by each dopant independently.

Photoaligned Ferroelectric Liquid Crystal Passive Matrix Display with Memorized Gray Scale

A new concept of a passive matrix ferroelectric liquid crystal display (FLCD) with a memorized gray scale is proposed. The physical origin of the gray scale in ferroelectric liquid crystal displays is considered. The criterion of reliable bistability is derived depending on the FLC hysteretic behavior in an electric field. The frequency and temperature dependences of the FLC hysteretic loop are discussed. A new approach for multiplex electronic addressing of the FLCD gray scale is given. A passively addressed 64×64 FLCD based on the photoalignment technique is developed. New applications of passively addressed FLCDs with a memorized gray scale are envisaged.

Optimization of alignment quality of ferroelectric liquid crystals by controlling anchoring energy

In this article, a method of measuring the anchoring energy by evaluating the relaxation time is proposed. The method is valid for both helical and helix-free structures. The results obtained using the proposed method are compared with published results 22) for the same photosensitive alignment material. The limitations of the proposed method are also discussed.

New Chiral Dopant Possessing High Twisting Power

We have synthesized and investigated a new chiral dopant. It belongs to the derivatives of p-terphenyldicarboxylic acid and has twisting power in the smectic C* mixture much higher than any chiral compound of this series known before. The ferroelectric liquid crystal mixtures on the base of achiral SmC matrix and the new chiral dopant have been elaborated and there optical and electro-optical properties were investigated.

Enhanced orientational Kerr effect in vertically aligned deformed helix ferroelectric liquid crystals

We disclose the vertically aligned deformed helix ferroelectric liquid crystal whose Kerr constant (Kkerr≈130  nm/V2 at λ=543  nm) is around one order of magnitude higher than any other value previously reported for liquid crystalline structures. Under certain conditions, the phase modulation with ellipticity less than 0.05 over the range of continuous and hysteresis-free electric adjustment of the phase shift from zero to 2π has been obtained at subkilohertz frequency.

Phase modulation and ellipticity of the light transmitted through a smectic C* layer with short helix pitch

A chiral ferroelectric smectic C* liquid crystal (FLC) with the helix pitch p 0 = 330 nm was developed to avoid any scattering of visible light when the helix is not unwound over a certain limit. Planar cells with different FLC layer thickness (16 and 44 μm) have been assembled with helix axis parallel to the glass plates and aligned along the rubbing direction. The ellipticity of the light passing through the cells vs. the electric field was investigated, and a method for evaluating the electrically controlled birefringence via ellipticity measurements has been established. We have found that the FLC cell is an optical retardation layer driven by the electric field, the effective birefringence being proportional to the square electric field. The physical origin of the electrically controlled phase shift of the light passing through the FLC layer has been analysed.

Sensors at Your Fibre Tips: A Novel Liquid Crystal- Based Photonic Transducer for Sensing Systems

Recent advances in both nano-fabrication and nano- materials open up rich new avenues in the optical sensing area. Using nano-grid electrodes, nanometer-scale photo-alignment layers and deformed helix ferro-electric liquid crystals with a sub-wavelength helix pitch of 150 nm, we have realised a fully integrated polarisation-based photonic transducer which exhibits fast response to an applied voltage/electric field, excellent linearity and allows multiplexing using standard, low cost telecom optical fibers.

Bistable and multistable states in ferroelectric liquid crystals

The effect of memorizing the structural states in a ferroelectric liquid crystal (FLC), known as biand multistability, is based on the existence of a domain structure that changes its properties under the action of an applied voltage. The criterion for the bistability steadiness of the optical-transmission states of FLC electrooptic cells is developed. This criterion is related to the hysteresis-loop parameters of the FLC layer. The conditions for the existence and steadiness of the hysteresis-free switching of the memorized optical-transmission states of multistable electrooptic cells are formulated.

Reflective mode of deformed-helix ferroelectric liquid crystal cells for sensing applications

We present a detailed theoretical and experimental study of the reflectance response of a deformed-helix ferroelectric (DHF) liquid crystal (LC) cell to an applied voltage under cross-polarisers. Using a model based on the effective dielectric tensor approximation, we derive simple analytical formulas to design a LC cell with maximum modulation depth and optimal linearity of the electro-optical response intensity versus the electric field. Our experimental results show that the cell works at frequencies up to 10 kHz and exhibits excellent linearity, with a total harmonic distortion as low as −70 dB. These findings suggest that DHF-LCs can be exploited to develop simple and accurate optical sensors.

Optimization of photo-aligned ferroelectric liquid-crystal display under passively addressed driving

A ferroelectric liquid-crystal (FLC) passively addressed 64 x 64 display based on the photo-alignment technique has been developed. The display matrix has dimensions of 33 x 33 mm 2 , and the FLC layer thickness is about 5 μm. Asymmetric boundary conditions, when only one of ITO surfaces of the display matrix is covered with the photo-aligning layer while another one is not, have been used for providing both high contrast ratio and steady multiplex operation. The electro-optical performance of the 5-μm FLC display is presented, including bistable switching in static operation, optimization in multiplexing operation, and gray-scale generation.