Abstract: A back projection device comprises an image generator (GI), an onward reflection mirror (MR) and at least one optical component (OM) capable of reflecting certain types of light beams almost entirely and reflecting certain other types of light beams almost entirely, said component being located in the proximity of a screen (E). The selection of optical behavior of the component (OM) may be done as a function of the polarization of the light beam, or else also as a function of its orientation with respect to said component (OM). Application: displays.

Abstract: Electrically piezoresistor produced by means of a piezoresistive element coupled to an electromechanical transducer, whose terminals are the input terminals of the piezoresistor. The piezoresistor comprises thermal drift compensating means.

Abstract: The invention provides an optical display device, utilizing a thermo-optical effect to inscribe a transmitted image in a layer of a material exhibiting a smectic state. Recording of the image with a full range of half tones without modulation of the recording beam and quick erasure of the recorded image without reheating of the film can be obtained by directly applying, simultaneously to the whole of the film either the video signal or an erasure voltage of suitable values. By associating this display device to a projection device utilizing a very bright source, the image thus recorded can be projected onto a large screen or a photosensitive substrate.

Abstract: The invention relates to switches which enable connections to be optically established between at least one incoming electrical circuit and one of several outgoing electrical circuits. It comprises associating at least one electrical light source, a thin magnetic layer forming a diffraction network and photoelectric receivers, the thin layer enabling the light beam issuing from the source to be directed onto the receivers selected.

Abstract: The present invention relates to holographic lenses.The wide field holographic lens in accordance with the invention is obtained by the superimposition of interference networks recorded within the volume of a thick material. These networks constitute a corresponding number of thick elementary holographic lenses, each of which satisfactorily covers a specific region of the field; the invention likewise describes a device for constructing said wide field holographic lens.

Abstract: The present invention relates to methods for protecting against drop-outs in a sound signal recorded on a video-disc. It consists in recording onto a video-disc the same sound signal through the sub-carriers with a constant delay from one to the other. On reading out this video-disc, the two sub-carriers are restored to synchronism and the sub-carrier not altered is chosen for playing the sound signal.

Abstract: The invention has for its object a reading arrangement which uses a source functioning by pulses and delay-action dividing optical means which successively ensure the illumination of M storage areas of the recording, each area comprising P bits 0 and 1. Thus, a single reading pulse makes possible the reading, with a mosaic of P photodetectors, of a block which comprises M words of P bits. The invention is particularly applicable to non-destructive optical reading stores, for instance holographic stores.

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 present invention relates to data carriers intended for optical read out. The data carrier in accordance with the invention comprises: a first transparent material at the surface of which the information is recorded in the form of an embossed pattern; a partially transparent metal layer covers said embossed pattern and a second, thick transparent material is deposited upon the metal layer for protection purposes.

Abstract: The present invention relates to the dissemination of binary digital data by analogue transmission or storage. The object of the invention is a communication system in which, prior to dissemination, the binary data are grouped into blocks forming vectors with N components, which are transformed into orthogonal vectors with N analogue components; after dissemination, the vectors experience a reverse transformation which makes it possible to reconstitute the binary digital data.

Abstract: The present invention relates to the dissemination of binary digital data by analogue transmission or storage. The object of the invention is a communication system in which, prior to dissemination, the binary data are grouped into blocks forming vectors with N components, which are transformed into orthogonal vectors with N analogue components; after dissemination, the vectors experience a reverse transformation which makes it possible to reconstitute the binary digital data.

Abstract: The present invention relates to a variable coupler for optical fibers, which can also operate as a mixer. This variable coupler comprises an optical system which concentrates the divergent radiation issuing from the output orifice of a transmitter fiber, on the input orifice of a first receiver fiber, and optical means (flat mirror, prism, plate with parallel faces, for example) capable of performing a translatory motion, which make it possible to intercept a variable fraction of said radiation and direct it on to the input orifice of a second receiver fiber.

Abstract: The invention relates to a device for recording a matrix of holographic lenses such that each lens, upon illumination by a monochromatic parallel beam produces a diffracted beam passing by a same common fixed aperture, which may be the pupil of a lens. In this device, an appropriate two-dimensional diffraction grating creates as many diffracted beams as there are lenses to be recorded, which beams interfer with a single parallel beam at the level of a photosensitive substrate. It is thus possible to carry out simultaneous recording of all the lenses of the matrix, which can afterwards be used in the recording of storage planes for optical stores.

Abstract: An optical system for the high density storage and retrieving of data, based upon the holographic recording technique, and incorporating two light deviating devices. The first of said devices enables the selection of an elementary area of the storage medium and the second of said device allows a plurality of superimposed holograms to be stored within said elementary area.