Abstract: An optical device for forming a stigmatic image of a laser source positioned at a predetermined point is intended to illuminate a reflecting surface while also providing a separation between the beam emerging from the source and the beam reflected from the surface. The device comprises a cube placed against a converging lens, the dimensions of the assembly thus formed being such that the cube face remote from the lens passes through a Weierstrass point of the spherical refracting surface formed by the lens. The laser source is positioned at the Weierstrass point. The cube is formed by two prisms cemented together, the interface being treated so as to have a polarization-separating effect.

Abstract: A device for recording and playing back information comprising an endless tape whereof one part has a translational movement in a direction x and n magnetic heads integral with one another whereof the gaps face that part and are aligned in a transverse direction y. The heads have a slow movement in the direction y and form n continuous tracks forming parallel and equidistant portions in the direction y.

Abstract: This disc has a layer of an inscribable and optically legible recording material deposited on a transparent plate traversed by the recording or reading beam and protected from the outside by a cover formed for example by a metal sheet, whose two surfaces are fixed to the layer so as to form a space in front of the latter.

Abstract: An integrated, multitrack, magnetic reading head in which a Hall effect or magneto-resistive material strip is deposited on a silicon substrate. The voltages produced in this strip are sampled by a group of amplifiers for the parallel-charging of a charge-coupled device, which is then read in series to obtain the output signal. Lateral tracks energize circuits making it possible by means of two resistive lines and a system of comparators to open the input gates of the charge-coupled device in order to correct the skew of the reading head.

Abstract: The invention relates to devices for optically recording information on a rotating carrier with a recording spot along a track. In accordance with the present invention, there is provided a reading spot kept at a constant distance, equal to an integral multiple of the pitch of the track, from said recording spot. The reading spot is made to follow an already recorded track element by means of a feedback loop. The simultaneous displacement of the two spots is controlled by a signal obtained by the detection of the reading beam.

Abstract: The present invention relates to the reading out of a track by means of a light spot which scans a track along which the information contained in a record is transcribed. The object of the invention is a read-out system which ensured focussing and tracking by the synchronous detection of positional errors with the help of a read-out beam one of the halves of which is intercepted by a half-wave plate; an oscillatory motion is imparted to the read-out spot in the plane containing the track.

Abstract: An optical system for recording n information signals on a photosensitive tape in the form of a discontinuous track made up of parallel track sections by means of n light beams having a two states modulated intensity, being simultaneously deflected by an acousto-optical deflector and focusing on the tape in the form of n equidistant spots aligned in a direction x. The combination of the deflection and a translation movement of the tape produces a scanning movement of said n spots in a direction perpendicular to x. The same system is made for the reading of the information transcribed on the tape, the beams being then not modulated, by means of photodetector means which receive the light emerging from the tape and provide information signals in relation with the physical modifications obtained on the tape during the recording.

Abstract: The present invention relates to data-carrier intended for the high-density recording of information by the use of an etching radiation beam. The data-carrier comprises a substrate upon which there are deposited a very thin film which is absorbent at the wavelength of the etching beam, and a film which is thermodegradable at a temperature lower than the degradation temperature of the absorbent film, the heat developed in the absorbent film being selectively diffused towards the adjacent thermodegradable film.

Abstract: The invention relates to a method and a device for the optical reading of information recorded on a support along a track in the form of diffracting elements. A diffraction pattern comprising a luminous central spot centered on the section of the track to be read and alternately dark and bright adjacent fringes is projected onto the support, the dark fringes adjacent to the central spot coinciding with the track sections in the neighborhood of the track section to be read. To that effect a pupil limited by two edges which are parallel to the direction of travel of the track is utilized, this pupil being placed against the reading objective.

Abstract: The present invention relates to the read-out of a data carrier having a track along which there is transcribed an angularly modulated carrier wave. In accordance with the present invention, there is provided a system for processing the read-out signal, which uses a feedback loop correcting the duty factor of a restored rectangular waveform when its value deviates from the value 0.5.

Abstract: The invention relates to an optical reading device, for the read out of data carried by a reflecting support, wherein the source is a non-polarized laser of which the exit surface is reflective; the optical noise due to the reflection of the incident wave at the support is partially suppressed by inserting between the last partially polarizing and/or birefractive element and the data carrier a quarter wavelength plate which optically decouples the incident wave and the return wave. The optical noise is thus limited to the beats between the incident wave and the return wave reflected a second time by the support.

Abstract: The optical reader, for information discs of which the items of information are locatable by addresses previously recorded on each of the grooves forming the track, comprises a device for counting the number of grooves traversed during search phases which simultaneously uses the envelope of the reading signal and the signal representing the radial error in the position of the head relative to the nearest track, for algebraically counting the number of tracks traversed. After comparison with the number of grooves to be traversed, the counting device controls the deceleration of the radial advance when the spot is at a predetermined distance from the groove to be reached and also its total stoppage and the closure of the radial servocontrol loop when the groove is reached.

Abstract: The invention relates to the focusing of an optical system by variation of the radius of curvature of a reflecting element, comprising two prepolarized thin plates of piezoelectric material which are joined together and each of which carries an electrode, the outer surface of one of the two thin plates being made reflective. An electrical signal characteristic of the correction to be made is applied between the two electrodes and produces a variation in the radius of curvature of the thin plates. This reflecting element is used in an optical system of the Cassegrin type or as a reflecting mirror.

Abstract: A device for focussing a read-out light beam on a moving data carrier. It comprises an objective lens which causes said read-out beam to converge on the data carrier; a cylindrical lens arranged in the path of a light beam reflected by the data carrier; and photo-electric means for detecting the reflected beam and arranged in such a fashion that the light spot obtained there, normally substantially circular in shape, is distorted by elongation if focussing of the read-out beam on the data carrier is incorrect.

Abstract: The invention relates to focussing sensors for measuring the deviation between the point of convergence of a beam of radiant energy and the surface of an object receiving this beam. According to the invention, a degree of asymmetry is first introduced into this beam, after which the image of this convergence point if formed on photoelectric sensors enabling the distortions of this image to be measured. These sensors supply signals which are dependent upon said deviation and enable it to be measured.This invention relates to optical focussing sensors by which it is possible to measure the focussing deviation of a beam of radiant energy of which the point of convergence has to be kept in coincidence with the surface of an object which it is desired to illuminate by a spot.

Abstract: The invention relates to the optical reading of a support comprising a track along which is arranged a series of information items which optically translate a carrier wave angularly modulated by the information. The read-out system uses a single lens for projecting a quasi-punctiform spot onto the support; a photodetector comprising four cells arranged in a square and asymmetrical illumination of the lens to ensure detection of the information and simultaneous supply of defocussing and tracking deviation signals.

Abstract: A flexible record disc engraved in the form of impressions along a track located in a ring-shaped zone is protected with a second flexible disc adhering at its central portion to the non-engraved part of the record disc. In the case where read-out is carried out on a stabilizing air cushion, the air remaining between the two discs is displaced by centrifugal force, so that good conditions of optical read-out are achieved.

Abstract: The present invention relates to the protecting against scratching and fouling of a data carrier which carries a relief impression readable optically by transmission. The data carrier in accordance with the invention is protected by a transparent protective layer with substantially smooth faces, which adheres to the peaks in the relief of the impression in such a way as to prevent the troughs in said relief from being filled up.

Abstract: The present invention relates to the protection of relief impressions formed in order to store information on a data carrier which can be optically read out by transmission. The invention relates to a data carrier the relief impression in which is protected by at least one layer transparent vis-a-vis the read-out radiation. The protective layer has an index of refraction that differs from that of the data carrier, per se. Thus, a refractive boundary at the relief impression is maintained and the information encoded in the diffractive relief pattern is preserved.

Abstract: A device for detecting the error in focussing a read-out beam on the impression. Two photodetector cells located respectively in front of and behind the optical axis of the system, in relation to the direction of transfer, produce two electrical signals the difference between which is the read-out signal, a control signal being obtained by a comparison of the phases of the two signals, one of which is phase-shifted so that the optimum focussing point corresponds to zero phase-shift.