Abstract: The invention provides an optical display device, utilizing a thermo-optical effect to inscribe a transmitted image in a film of a material exhibiting a smectic state. The crystal liquid layer is inserted between transparent electrodes and heated to be in the smectic mesophase. The image is recorded in the layer under the form of variations in the scattering coefficient thereof by applying the video signal transmitting the image between the electrodes, while an infra-red beam of constant intensity synchronously scans the layer at a constant rate to successively raise each point beyond the melting point of the liquid crystal material. A quick erasure of the recorded image is provided by applying between the electrodes a voltage pulse of suitable value.

Abstract: This invention relates to a projection device of which the optical device having a focal length is variable under the effect of an electrical signal and comprises a hollow transparent lens into which a liquid nematic crystal is introduced. Under the effect of the electrical signal applied between two transparent electrodes respectively arranged on the two inner surfaces of the lens, the index of the liquid crystal for the direction of incidence of the projected beam is capable of varying as a result of the oscillation of the molecules of the liquid crystal, the position of the focussing point of the projected beam varying in consequence.

Abstract: The invention concerns liquid-crystal display methods and their application to radar screens. The invention provides a method which consists in thermally writing on a layer of liquid-crystal two successive patterns which are combined in accordance with a law designated A .times. B in Boolean algebra by the way of a reorienting biasing voltage applied during the writing in of the second of said pattern.

Abstract: The invention relates to data display devices having a segmented structure. It provides a display device whose adjacent coplanar segments are divided up into complementary areas respectively connected to excitation units controlled simultaneously in such manner as to produce, in the absence of break down, a homogeneous display of the segments. The invention applies to display by elementary sources of light or by liquid crystals and other materials having electro-optical properties.