Anatoli A. Muravski

Studies of the Anchoring Energy of Nematics on Grooved Surfaces

Abstract Previously we developed optical method enabling measurements of the liquid crystal twist angle in the cells with grooved surfaces. In this work azimuthal anchoring energy of a liquid crystal to a surface is estimated by measuring the deviation of the twist angle of the liquid crystal from the angle defined by direction of liquid crystal alignment on one rubbed and one grooved surfaces substrates. It was found that the twist angle in the cells depends not only on the parameters of the grooves, but also strongly depends on the material covering the grooves.

Achromatic phase retarders using double-layer liquid crystal cells

Achromatic phase retarders can be designed by combining two layers of birefringent materials with different dispersion of birefringence. We synthesized and studied several liquid crystalline structures in order to find combinations giving the best performance in achromatic phase retarders. We found that birefringence dispersion of liquid crystals is approximated well by the single band mode. The best achromatism is achieved with material having a very low resonance wavelength and birefringence. However the required thickness of the liquid crystal layers is large in these cases so that a compromise has to be found. Liquid crystal combinations with high and nearly equal clearing point should be used for devices in order to compensate the temperature drifts of birefringence against each other, thereby extending the operating temperature range. Achromatic phase retarders based on these measurements and calculations were constructed and tested. It was necessary to install an electrooptic regulation circuit for stabilizing the phase retardance at a target value. Device performance is reported and compared to achromatic retarders made of crystalline materials.

Fast-responding liquid crystal light-valve technology for color-sequential display applications

A color sequential projection system has some distinct advantages over conventional systems which make it uniquely suitable for consumer TV as well as high performance professional applications such as computer monitors and electronic cinema. A fast responding light-valve is, clearly, essential for a good performing system. Response speed of transmissive LC lightvalves has been marginal thus far for good color rendition. Recently, Sevchenko Institute has made some very fast reflective LC cells which were evaluated at Philips Labs. These devices showed sub millisecond-large signal-response times, even at room temperature, and produced good color in a projector emulation testbed. In our presentation we describe our highly efficient color sequential projector and demonstrate its operation on video tape. Next we discuss light-valve requirements and reflective light-valve test results.

SSFLC Polarization Switch for Zeeman Laser Stabilization Loop

Abstract Ferroeleciric liquid crystals (FLC) as light modulators in the stabilization system of a Zeeman laser increase the quality of stabilization due to the high switching speed and make the whole system very compact. We analyze the operation of the optical part of such a stabilization system and derive optimum values of the FLC cell parameters. Properties of available liquid crystals and their temperature dependence are considered as well as, in particular, the influence of a slight ellipticily of the laser radiation.

SSFLC for laser frequency stabilization

The paper describes the application of a Surface-Stabilized Ferroelectric Liquid Crystal (SSFLC) cell as a polarization switch in a frequency stabilization system of a Zeeman laser interferometer. The FLC cell is used as a field-controlled (lambda) /4 plate in which the optic axis can rapidly alternate between two positions, thereby alternatively switching either of two orthogonal radiations into the same measuring channel. The high switching speed of the FLC is here a key feature as it allows several thousand such calibration measurements to be performed in a second.

Analog gray-scale evaluation in ferroelectric LCD

The problems of analog gray scale in SSFLC are studied under different driving conditions with the aim to relate their behavior in real display devices. It is shown that electrooptic behavior of uniform chevron texture in transient levels is not stable enough under cross-talk free driving with random cross-talk data pulses. Non-uniform texture, obtained with low-frequency treatment of SSFLC, reproduces gray levels much better, but some kind of image sticking, which is not visible with conventional methods of studying electrooptic properties, is still observed. Special method of registration of sticking is proposed to make tests more reliable.

Optical properties of double OMI displays

Electrooptical and spectral properties of STN and OMI effects are compared with the aim to elucidate their capability of color devices. Special attention is paid to gray scale implementation for 3 basic colors and advantages of the OMI effect are shown for obtaining full-color gamut.

Comparative study of analog gray scale in various textures of SSFLC

Abstract The problems of analog gray scale in SSFLC are studied under different driving conditions with the aim to understand its behavior in real display devices. It is shown that electrooptic behavior of uniform chevron texture in transient levels is not stable enough with respect to random cross-talk data pulses even under cross-talk free driving. Non-uniform texture, obtained with low-frequency treatment of SSFLC, reproduces gray levels much better. The details of obtaining this texture are discussed.