The invention relates to a medium comprising at least 60% of one or more compounds of formula I ##STR00001##
wherein R.sup.11, R.sup.12, MG.sup.11, MG.sup.12 and Sp.sup.1 have the meaning given herein below, to the use of such media in liquid crystal devices, in particular in flexoelectric liquid crystal devices, and to a flexoelectric liquid crystal device comprising a liquid crystal medium according to the present invention.

A liquid crystal (LC) mixture for a pitch variable optical element is provided. The LC mixture includes a host LC and one or more LC dimers dissolved as a guest in the host LC. The host LC and the one or more LC dimers have respective dielectric anisotropies of opposite signs in nematic phase. A net dielectric anisotropy of the LC mixture is substantially neutral.

An optical device is provided. The optical device includes an optical grating. The optical grating includes two electrodes arranged opposite to each other and a liquid crystal (LC) composition sandwiched between the electrodes. The two electrodes provide a driving voltage to the optical grating. The LC mixture includes a host LC and one or more LC dimers dissolved as a guest in the host LC. The host LC and the one or more LC dimers have respective dielectric anisotropies of opposite signs in nematic phase. A net dielectric anisotropy of the LC mixture is substantially neutral at a predetermined temperature.

A fast flexoelectro-optic switching device containing bimesogen-doped and polymer-stabilized vertical standing helix (PSVSH) in a cholesteric liquid crystal. The PSVSH device exhibits a response time of less than 0.7 millisecond, high contrast and negligible hysteresis which is suitable for applications including blur-free displays, field-sequential color displays and active optical elements.

The invention relates to a liquid crystal medium comprising one or more dielectrically negative compounds and one or more dielectrically positive compounds, characterized in that the medium as a whole exhibits a dielectrically anisotropy () in the range from 0.25 to +0.25. Furthermore, the invention relates to a method of production of such medium and to the use of such medium in a light modulation element utilizing flexoelectric switching.

Moreover, the invention relates to a light modulation element utilizing flexoelectric switching comprising the described medium, to a method of production of such light modulation element, to the use of such light modulation element in electro-optical devices and to these electro-optical devices as such.

A light modulation element comprising, preferably consisting of a cholesteric liquid crystalline medium sandwiched between two opposing substrates, an electrode arrangement, which is capable to allow the application of an electric field, which is substantially perpendicular to the main plane of substrate or the layer of the cholesteric liquid-crystalline medium, characterized in that one of the substrates is provided with a processed alignment layer adjacent to the cholesteric liquid crystalline medium and the other substrate is either provided with an unprocessed alignment layer adjacent to the cholesteric liquid crystalline medium or is not provided with an alignment layer. The invention is further related to a method of production of said light modulation element and to the use of said light modulation element in various types of optical and electro-optical devices, such as electro-optical displays, liquid crystal displays (LCDs), non-linear optic (NLO) devices, and optical information storage devices.

The invention relates to a medium comprising at least 60% of one or more compounds of formula I

##STR00001##

wherein R.sup.11, R.sup.12, MG.sup.11, MG.sup.12 and Sp.sup.1 have the meaning given herein below, to the use of such media in liquid crystal devices, in particular in flexoelectric liquid crystal devices, and to a flexoelectric liquid crystal device comprising a liquid crystal medium according to the present invention.

The invention relates to a medium comprising one or more compounds of formula I,

R.sup.11-A.sup.11-A.sup.12-(CH.sub.2).sub.s-A.sup.13-A.sup.14-R.sup.12I

in a concentration of up to 30% or less,
and one or more compounds of formula II,

R.sup.21-A.sup.21-A.sup.22-(A.sup.23).sub.u-Z.sup.21(CH.sub.2).sub.tZ.sup.22-A.sup.24-A.sup.25-A.sup.26-R.sup.22II

in a concentration of 10% or more,
wherein R.sup.11 to R.sup.22, A.sup.11 to A.sup.26, Z.sup.21, Z.sup.22, s, t, and u have one of the meanings as given in claim 1, to a method of production of such a media, to the use of such media in liquid crystal devices, in particular in flexoelectric liquid crystal devices, and to a flexoelectric liquid crystal device comprising a medium according to the present invention.

The present invention relates to a process of preparing a light modulation element of the PS-ULH (polymer stabilised ULH) type, which allows to reduce the operational voltage and allows to improve the switching time of the light modulation element.

The invention relates to bimesogenic compounds of formula I ##STR00001##
wherein R.sup.11, R.sup.12, MG.sup.11, MG.sup.12, X.sup.11, X.sup.12 and Sp.sup.1 have the meaning given in claim 1, to the use of bimesogenic compounds of formula l in liquid crystal media and particular to flexoelectric liquid crystal devices comprising a liquid crystal medium according to the present invention.