Abstract: An apparatus is described for writing and reading information tracks in an information surface of a record carrier by optical radiation. The apparatus comprises two diode lasers, one of which produces the write beam and the other a read beam. By means of polarization sensitive device the write spot and the read spot formed on the information layer are projected at a very small and stable distance from each other and the beams reflected by the information layer are spatially separated. The separated beams are routed to separate detectors with residual cross-talk between the beams being eliminated by wavelength-selective filters.

Abstract: The invention relates to an apparatus for reading a disc-shaped record carrier with a spiral information track in which an optically readable digitally coded information signal is recorded with a spatial bit frequency which is independent of the radius of the track turn. The scanning speed of the information track is selected to be a factor n higher than the scanning speed normally employed of the reproduction for the recorded information. By means of a memory device, information blocks being read and comprising a fixed number of data bits are time-expanded to restore the customary time relationship. A control unit determines the read-in cycles of the memory device for the storage of the information blocks being read and, via the radial positioning system for the read spot, it determines the scanning pattern of the record carrier so that the ultimately recorded information blocks are reproduced in the same sequence and at the desired rate.

Abstract: An apparatus for optically reading and/or recording information on a rotary optical disc (4), such as a video-disc player or an optical recorder, comprises an objective carrier (3) for an objective (2) which is radially moved to and fro over a frame (1) by a drive unit. Driving is effected by means of two electric motors (7) which rotate in opposite directions and which move the objective carrier (3) to and fro and, simultaneously but in an opposite direction, move two balancing masses (11) in paths on each side of the path of movement of the objective carrier, so that during accelerations and decelerations of the to-and-fro movements of the objective carrier no reactive forces or reaction moments are transmitted to the frame.

Abstract: In a radiation-sensitive semiconductor element which is divided into a number of sub-elements, the surface potential in the sub-elements varies with incident radiation as a result of charge carriers generated by the radiation. As soon as an adjustable threshold value of this potential is reached in one or more of the sub-elements, a current starts to flow which is signalled by means of a detector and a detection unit. Because the speed of reaching the threshold value depends on the intensity of the radiation, the time measured between the adjustment of the threshold value and the signalling of the current is a measure of the radiation intensity. By means of such a semiconductor element, the associated detection unit and extra electronics, if any, the energy or the cross-section of a beam can be determined and be readjusted, if necessary. Such a semiconductor device can also be used very readily for focusing, for example in VLP apparatus.

Abstract: A device is described for detecting the position of an object, which device comprises a radiation source, beam-splitting prism, and a detection system comprising a plurality of radiation-sensitive detectors. The object to whose position is to be measured carries only the prism, and each detector is divided into a plurality of subdetectors. The device enables changes in both position and inclination of the object to be measured.

Abstract: An apparatus for reading and/or writing an optically readable information structure, arranged in information tracks, on a record carrier, comprises a beam deflection element which is controlled by a control signal obtained from a tracking servo system. The apparatus is provided with a position detection system for detecting the position of the deflection element, and the signal from this detection system is applied to an input of the servo system for generating a control signal which is independent of the position of the deflecting element.

Abstract: To reduce the susceptibility of an electrodynamically controllable pivoting mirror device to stray magnetic fields, said device comprises a pivoting mirror which is mounted on a frame (4) so as to be pivotable by means of a suitable bearing arrangement (8, 9), on which mirror permanent-magnetic means (22-29) are arranged on which a pivoting torque can be exerted by means of control coils (20, 21) mounted on the frame. By providing the permanent-magnetic means, on the side where they are located, with two zones of north polarity (N) and two zones of south polarity (S), which are situated on diametrically opposed sides relative to the pivoting axis (7), and by moreover having the turns of the control coil extend over zones of north and of south polarity, a pivoting mirror device is obtained whose control coils dissipate a minimum amount of heat and which is less susceptible to external magnetic stray fields produced by components located in the vicinity, such as transformers and electric motors (FIG. 1).

Abstract: In order to improve the focussing of radiation from a source onto an object, in example for a "VLP" or "Compact Disk" system, a further control signal from an object-inclination detector is added to the focussing error signal, yielding improved control stability and smaller focussing errors.

Abstract: An optical read unit for reading radiation-reflecting video discs comprises a semiconductor laser which with the aid of a scan wobbler and a focussing wobbler is moved at high frequency in two directions relative to the video disc, a radial direction for tracking purposes and a direction normal to the disc for the purpose of automatic focussing. The semiconductor diode laser is mounted on a metal radiation source carrier which is connected to a heat sink for carrying off the heat with a low temperature gradient, and is driven by piezo-electric plates.

Abstract: An optical scanning device which scans a rotary video disc with the aid of a light beam comprises an objective which performs focussing movements, for focussing a light spot on a recording surface of the video disc, as well as tilting tracking movements and time-error correction movements. Near its lower end the objective is suspended in an impregnated corrugated loudspeaker diaphragm of fabric fibre which enables the various movements of the objective to be made without giving rise to annoying resonant effects. The tracking movements and the time-error correction movements are obtained with the aid of coils which are connected to the objective near the upper end and which are disposed in air gaps of associated permanent magnetic stators.

Abstract: A pivoting mirror device for pivoting a pivoting mirror about two mutually perpendicular pivoting axes under the influence of electric control signals, in particular for a video player which reads information from a video disk with the aid of a light beam using optical means, the mirror being journalled so as to be pivotable to all sides and the device comprising electro-dynamic drive means which include permanent magnets and control coils for controlling the pivoting movements. The mirror is supported near its center, while permanent magnetic positioning means which co-operate with permanent magnetic means which are connected to the mirror continually subject the bearing to pressure.

Abstract: An automatic optical focusing system suitable for an apparatus for reading an information track on a record carrier with the aid of a read spot which is focused in an imaginary focusing plane and which is formed by a radiation beam which is produced by a radiation source, more in particular suitable for a video disc player which employs optical reading, and serving for automatically keeping the read spot focused at the plane in which the information is disposed (information plane) during playing of a record carrier, comprising an optical focusing device, an oscillating optical element which cooperates with the radiation beam and which can effect high-frequency oscillations so that a high frequency oscillation of small amplitude about the coarse position of the focusing plane is obtained, an electromagnetic drive system for the high-frequency drive of the oscillating optical element, a radiation-sensitive detector which responds to the radiation beam which has been modulated by the information track, and a con