Abstract: Colors are generated in the display device by guiding light through three serially-arranged, electrically controlled color filters. Each filer attenuates one of three colors. The color filters incorporate two cholesteric filters, two .lambda./4 plates, and one electrically switchable liquid crystal display.

Abstract: Optically active compounds of the formula ##STR1## wherein n stands for the number 0 or 1; Z.sup.1 is a single covalent bond or --CH.sub.2 CH.sub.2 --; Z.sup.2 is a single covalent bond, --CH.sub.2 CH.sub.2 --, --CH.sub.2 O--, --OCH.sub.2 --, --COO-- or --OOC--; rings A.sup.1 and A.sup.2 each independently represent trans-1,4-cyclohexylene or optionally halogen-, cyano- and/or methyl-substituted 1,4-phenylene in which optionally 1 CH group or 2 CH groups is/are replaced by nitrogen; R.sup.2 is a group R.sup.4 or a group of the formula ##STR2## R.sup.4 is cyano, halogen, --OCY.sup.1 F.sub.2, --CY.sup.1 F.sub.2 or an alkyl group in which optionally one >CH--CH< is replaced by >C.dbd.C< and/or optionally one methylene group or two non-adjacent methylene groups is/are replaced by --O--, --COO-- and/or --OOC-- and/or optionally one methylene group is replaced by --CHY.sup.2 --; Y.sup.1 is hydrogen or fluorine; Y.sup.2 is halogen, cyano or methyl; R.sup.1 and R.sup.

Abstract: Compounds of the formula ##STR1## wherein R.sup.1 signifies a straight-chain alkyl group with 7 to 9 carbon atoms; and R.sup.2 represents a straight-chain alkyl group with 6 to 11 carbon atoms.their manufacture, liquid crystalline mixtures which contain these compounds and their use for electro-optical purposes.

Abstract: An optical frequency conversion element has a wave-guiding layer which consists of a .chi..sup.(2) -active ferroelectric liquid crystal. The monomeric or polymeric liquid crystal material has a periodic structure which permits the so-called quasi phase matching of a guided laser beam. The period length of the structure is equal to twice the coherence length l.sub.c =.pi./.DELTA..beta. of the material, whereby .DELTA..beta.=.beta..sub.o (2.omega.)-2.beta..sub.o (.omega.), with .omega.=angular frequency of the fundamental wave, 0=zero-order mode and .beta.=propagation constant of the mode.

Abstract: A bistable ferroelectric liquid crystal display cell utilizes two plates, a chiral ferroelectric smectic liquid crystal sandwiched between the plates, and an electrode for applying an electrical field to the plates. The chiral ferroelectric smectic liquid crystal has a structure which is influenced by the action of an electric field so that its optical anisotropy changes. By using a first polarizer connected to one of the plates and a second polarizer connected to the other plate, the unique bistable ferroelectric display produces dark parallel stripes when the polarizers are in a cross position relative to each other.

Abstract: A new mode of operation is proposed for light control systems consisting of a combination of liquid crystal cells and polarizers. The direct operation of liquid crystal cells with circularly-polarized light is advantageous in many respects. The circularly-polarized light is produced either with conventional circular polarizers or with monomeric or polymeric cholesteric liquid crystals. The new mode of operation is possible under certain conditions for all liquid crystal cells which hitherto had to be operated with linearly-polarized light.

Abstract: Small-pitch cholesteric liquid crystal mixtures are temperature compensated. They are particularly useful when no, or only a slight, temperature dependence of the selective reflection is permissible, because a considerable temperature dependence would interfere with or render wanted effects impossible. They are composed of a nematic liquid crystal doped with at least two chiral additives satisfying the following conditions:(1) a(c.sub.1 B.sub.1 +c.sub.2 B.sub.2)=b(c.sub.1 A.sub.1 +c.sub.2 A.sub.2)and(2) 1/.lambda..sub.o (T)=a(c.sub.1 A.sub.1 +c.sub.2 A.sub.2)+aT(c.sub.1 B.sub.1 +c.sub.2 B.sub.2)+bT(c.sub.1 A.sub.1 +c.sub.2 A.sub.2)where .lambda..sub.o denotes the mean value of the wavelength band of the selective reflection c.sub.1 c.sub.2, . . . denote the concentrations of the chiral dopants and A.sub.1,B.sub.1 are coefficients of a progression.

Abstract: The polarizer comprises a layer of cholesteric liquid crystal with Grandjean structure disposed in the path of the light and in which the light in a given wavelength range is reflected with selective and circular polarization or is transmitted with reversed direction of rotation, and a mirror which reversed the direction of rotation of the circular-polarized light. The component reflected by the mirror is also transmitted. If the liquid crystal layer is concentric with the source of natural light and the mirror is spherical, the result is a source of circular polarized light. A projection system is obtained by a combination of two of the aforementioned polarizers, one serving as a polarizer and one as an analyzer, and an interposed liquid crystal display cell for modulating the intensity of the polarized light.

Abstract: Compounds of the formula ##STR1## wherein R.sup.1 signifies a straight-chain alkyl group with 7 to 10 carbon atoms; R.sup.2 represents a straight-chain alkyl group with 1 to 8 carbon atoms; and n signifies either 1, 2 or 3, their preparation, liquid crystalline mixtures which contain these compounds and their use for electro-optical purposes.

Abstract: The polarizer comprises a layer of cholesteric liquid crystal with Grandjean structure disposed in the path of the light and in which the light in a given wavelength range is reflected with selective and circular polarization or is transmitted with reversed direction of rotation, and a mirror which reversed the direction of rotation of the circular- polarized light. The component reflected by the mirror is also transmitted. If the liquid crystal layer is concentric with the source of natural light and the mirror is spherical, the result is a source of circular polarized light. A projection system is obtained by a combination of two of the aforementioned polarizers, one serving as a polarizer and one as an analyzer, and an interposed liquid crystal display cell for modulating the intensity of the polarized light.