The Secretary of State for Defence in Her Britannic Majesty's Government

Frances C Saunders

Edward P Raynes

Kenneth J Harrison

David J Thompson

Ian A Shanks

David F Newton

Anthony J Hughes

An electro-optic modulator consists of a Fabry-Perot etalon containing intra-cavity liquid crystal material between mirror layers. Each mirror bears a respective rubbed polyimide layer, which provides homogeneous alignment of the liquid crystal molecules. The mirror layers are connected to a bias voltage source, which provide an electrical bias variable between two values both above the threshold for refractive index sensitivity to applied voltage. For nematic materials, this is the Freedricks threshold or transition. The bias variation provides optical modulation of the etalon transmission with a time constant which is much shorter than devices switching between voltages either side of the threshold.

Liquid crystal electro-optic modulator in a fabry-perot interferometer

A liquid crystal display includes a liquid crystal cell formed by enclosing a thin layer of a cholesteric liquid crystal material between two slides. A set of electrode structures is formed on each slide so that voltages may be applied to the liquid crystal material causing an observable display effect. Voltages are supplied to the electrodes in sequence by driver electronics under the control of a logic unit which also controls a variable voltage source supplying voltages to the driver electronics. The logic unit controls the drive electronics to give an R.M.S. voltage V.sub.x at elements required to be at an OFF state and an R.M.S. voltage V.sub.c higher than V.sub.x at elements required to be in an ON state. The logic unit also controls the voltage source to reduce its voltage output to both OFF and ON elements simultaneously while maintaining the ratio of V.sub.x and V.sub.c for a period while information displayed is to be changed.

Liquid crystal displays

The reflectance of a mirror is variable to provide a dipping car mirror. The mirror comprises a liquid crystal cell formed by two transparent slides coated on their inner surfaces with electrodes. The front electrode is transparent while the rear one is a reflector or a separate reflecting surface is provided. Between the slides is a layer 8 to 12 .mu.m thick of a cholesteric liquid crystal material. The slides are surface treated to give a high tilt homogeneous boundary condition, i.e. the liquid crystal molecules at the slide wall incline at a high (20.degree.-75.degree.) tilt to the surface. A control unit applies either a high voltage (10 volts at 1 kHz) or a low voltage (1 to 2 volts at 1 kHz). The high voltage results in the liquid crystal adopting a light transmissive state. In this state light reflects off the rear of the cell. The low voltage state is a scattering state for the liquid crystal material. In the scattering state light reflects off the front slide and is about 1/10 that reflected off the rear electrode. A photocell controls the switching of the cell. With zero voltage across the cell the liquid crystal material adopts a light transmitter state.

Cholesteric liquid crystal mirror with safety features

A material suitable for a guest-host liquid crystal device comprises a solution of a liquid crystal material and a pleochroic dye characterized in that the dye comprises at least one anthraquinone compound free from water-solubilizing and ionic substituents and having the formula: ##STR1## wherein each of R and R.sup.1 independently represents an n-alkyl group having from 4 to 7 carbon atoms inclusive and wherein each of R.sup.2 and R.sup.3 is independently selected from hydrogen and alkyl groups having from 1 to 4 carbon atoms inclusive.

Liquid crystal materials containing pleochroic anthraquinone dyes

A material suitable for a guest-host liquid crystal device comprises a soion of a liquid crystal material and a pleochroic dye where in the pleochroic dye comprises at least one anthrquinone compound free from water solubilizing and ionic substituents and having the formula: ##STR1## wherein Q is NH.sub.2, OH, alkyl, aryl, NO.sub.2 or halo;

Liquid crystal compositions with pleochroic anthraquines dyes

A material suitable for a guest-host liquid crystal device comprises a solution of a liquid crystal material and a pleochroic dye wherein the pleochroic dye comprises at least one compound having a formula: ##STR1## wherein one of X and Y is OH and the other is NHR wherein R is H or lower alkyl; each of R.sub.1 and R.sub.2 independently represents alkyl, aryl, aralkyl, alkoxy or --NR.sub.3 R.sub.4 wherein each of R.sub.3 and R.sub.4 is independently H or lower alkyl, provided that R.sub.2 is always adjacent to an OH group.

A material suitable for a guest-host liquid crystal device comprises a solution of a liquid crystal material and a pleochroic dye wherein the pleochroic dye comprises at least one anthraquinone compound free from water solubilizing and ionic substituents and having the formula: ##STR1## wherein P is OH or NH.sub.2 ; each group X.sup.A is independently selected from OH, NO.sub.2, SR and NZ.sub.1 Z.sub.2 provided that one group X.sup.A is SR and the other group X.sup.A is OH, NO.sub.2 or NZ.sub.1 Z.sub.2 is 1 or 2; each group Q.sub.1 is independently alkyl having from 1 to 20 carbon atoms; each group R is independently selected from alkyl having from 1 to 20 carbon atoms, aryl having up to 15 carbon atoms and cycloalkyl having from 4 to 8 carbon atoms.

Organic materials

A material suitable for a guest-host liquid crystal device comprises a solution of a liquid crystal material and a pleochroic dye wherein the pleochroic dye comprises at least one compound having a formula: ##STR1## wherein: R represents a group selected from optionally substituted alkyl and optionally substituted monocyclic aryl;

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Malvern Wells, United Kingdom

Frances C Saunders