Abstract: In an optical head apparatus for an optical information carrier comprising a semiconductor laser beam source, a condenser lens system and a beam splitter interposed therebetween in an optical system wherein the noise level may be beyond the allowable limit due to the excessive amount of the laser beam which is made incident on the laser beam source after being reflected by the information carrier, the reflected light attenuating means is provided between the optical information carrier and the semiconductor laser beam source, so that the noise level can be set to remain within the allowable limit.

Abstract: A polarization-rotator (22) and a polarization-sensitive beam combiner (30') are arranged in the radiation path between a phase-locked diode laser array (10) radiating in a stable supermode and a collimator lens (46). The two radiation lobes (11, 12) are superposed so that a single radiation spot (S) can be obtained. The quality of the spot can be improved by an arrangement of a prism system (40) and a spatial filter (45) in the lateral far field.

Abstract: A semiconductor laser device includes a semiconductor laser for emitting a laser beam, a coupling lens for collimating the laser beam as passing therethrough and a supporting member for supporting the laser and the coupling lens. As the ambient temperature changes, the supporting member either expands or contracts, thereby varying the distance between the laser and the coupling lens. However, it is so structured that the focal distance of the coupling lens varies in accordance with a change in the wavelength of the laser beam emitted from the laser which is caused by the change in the ambient temperature, so that the change in the distance between the laser and the coupling lens is effectively cancelled by the change in the focal distance of the coupling lens, whereby the laser beam passing through the coupling lens remains collimated even if the ambient temperature changes.

Abstract: An optical type head device comprises a laser beam source for emitting a laser beam, a light focussing means for converging the laser beam on a data storing surface of an optical type data storing medium, a laser beam detecting means which receives the laser beam reflected by the optical type data storing medium and modulated by data held by the same, and converts the data into electric signals, a driving current supplying means for supplying a driving current to the laser beam source. The driving current supplying means comprises a high frequency current generator which supplys to the laser beam source a high frequency current having a waveform ranging from the lower part of the threshold value at which the laser beam source starts emission of the laser beam to the higher part of the thresheld value, and the frequency of the high frequency current is at least twice as high as the maximum frequency component of information which is contained in the data storing medium.

Abstract: A laser light flux is divided and synthesized so that its light intensity distribution is changed from a Gaussian distribution to a non-Gaussian distribution. When a laser light flux having a Gaussian distribution is irradiated onto a dividing prism, it is divided into a left part and a right part which are refracted right and left inversely from each other. When the right and left parts are incident on a synthesizing prism, they are refracted again and travel to be overlapped with each other on a recording medium. The light intensity distribution on a segment at the apex of the synthesizing prism is weaker at the central part and stronger at the peripheral part. This is because the light fluxes resulting from the division are inverted in their position so that the central part of the Gaussian distribution is separated left and right while the peripheral part with a weaker light intensity is centered.

Abstract: A laser drum which can optically record and reproduce information on optical tapes. The laser drum comprises an upper drum which has two projection holes, rotates and is fitted with semiconductor lasers, a total reflective prism, stoppers, diffraction gratings, beam splitters, object lenses, condensing lenses and photodetectors.

Abstract: Apparatus for scanning the information surface of an optical disc record carrier with a radiation beam. Errors in beam focus on such surface are detected by providing two optical gratings in succession in the path of the radiation reflected from the record carrier. The gratings have a constant grating period, which may be equal or in a fixed ratio, the directions of the grating strips of the two gratings intersecting each other at a relatively small angle, thereby forming a Moire interference pattern in the radiation emergent from the two gratings which rotates due to changes in beam focus. This changes the relative amounts of radiation received by an assembly of radiation detecting elements adjacent the second grating, producing a focus error control signal which can be employed for correcting beam focus.

Abstract: A data recording and reproducing apparatus is disclosed in which an optical disc for recording, reproducing or erasing data is radiated with an erasing light beam and a recording-reproducing light beam sequentially to record or reproduce the data with the recording-reproducing light beam and erase the data with the erasing light beam. In rewriting the data, the erasing light beam is radiated in advance of the recording-reproducing light beam on a data section of the disc, and the old data is erased by temperature increase and annealing by the erasing light beam, while new data is recorded by temperature increase and quenching with the recording-reproducing light beam set to the recording light intensity. After recording the new data, the light intensity of the erasing light beam is gradually decreased and turned off.

Abstract: An optical pickup device comprises a light beam source, an objective lens system for causing a light beam emitted from the light beam source to impinge upon a record medium and for receiving a reflected light beam from the record medium, and intermediate lens system composed of a single lens element for causing the light beam emitted from the light beam source to be slightly converged and to enter into the objective lens system and for receiving the reflected light beam transmitted through the objective lens system. A beam splitter separates the reflected light beam transmitted through the objective lens system and the intermediate lens system from the light beam emitted from the light beam source, and a photodetector detects the reflected light beam separated by the beam splitter. Spherical aberration induced by the intermediate lens system in the light beam passing through the intermediate lens system and the objective lens system to the record medium is cancelled at the objective lens system.

Abstract: An optical head apparatus comprises a laser light source device emitting linearly polarized light, a converging lens for converging the light pencil emitted from the laser light source onto information recording tracks on a recording medium, and an optical system including a beam splitter for separating the light pencil reflected from the recording medium from the light pencil emitted from the laser light source. The converging lens is one formed by molding. The rotary position of the converging lens about the optical axis of the converging lens is so adjusted that the astigmatism of the optical system from the laser light source to the recording medium is minimum.

Abstract: In an optical data recording and reproducing system in which recording and reproducing data are carried out with a semiconductor laser, circuitry is provided to reduce the level of a high frequency current to be superposed on the laser during a data recording operation relative to the level during a data reproducing operation, to provide laser output only when necessary, to prolong laser life.

Abstract: A digital information recording and reproducing method for significantly improving the transfer rate of digital information, comprises the steps of: forming a plurality of light beam guide tracks on a recording medium capable of multiple light-wavelength recording, the tracks being spaced apart by a predetermined pitch and each of the tracks comprising a series of pre-pits disposed in a scan direction and spaced apart by an interval longer than the diameter of a spot of a light beam for use in recording and reproducing; and recording and reproducing an information bit by changing the light beam to have a different wavelength predetermined n times in a predetermined order while the light beam is scanned by one interval of the pre-pits.

Abstract: An optical IC-type head assembly for recording and for reading information on an optical disc, comprising a substrate, a light guiding layer comprising a dielectric thin film formed monolithically on the substrate, a laser oscillator for injecting the laser beam into the light guiding layer, a grating coupler for converging the laser beam on the optical disc, and a photo detector for receiving the beam reflected by the optical disc and coming out of the grating coupler. In one embodiment the substrate is made of material having cleavability. One side surface of the light guiding layer receiving the laser beam is a break surface formed by cleaving the substrate along the cleavage plane. The photo detector is disposed at the break surface of the light guiding layer. The substrate is preferably made of single crystal material.

Abstract: There is disclosed a light emitting device comprising at least a semiconductor laser and an optical modulating element for modulating the output light from the semiconductor laser. In accordance with the present invention, a capacitive element for suppressing noise of the semiconductor laser arising from reflected light is disposed in parallel relation to current injection terminals of the semiconductor laser.

Abstract: A write/read head comprises a laser whose resonator faces are formed by the storage medium and by a curved reflective surface which is positioned at a nominal distance from the medium and has a described residual radiant transmittance and a radius of curvature which is greater than the nominal distance. A mode diaphragm is provided between the active medium of the laser and the storage medium. Optical detector elements for the acquisition of position control signals and data read-out signals are arranged outside of the reflective surface and are symmetrically arranged with respect to the optical axis of the laser.

Abstract: A multi-beam optical recording system includes a semiconductor laser array. The laser beams are expanded via a prism beam expander to have generally circular cross-sections for optimum spot intensity on the recording medium. According to the teaching of the prior art, the average beam angle of incidence on the input prism of the beam expander is the Brewster angle. According to the present invention, means are provided for rotating the beam expander to minimize the variations in spacing between beams, these variations resulting from the magnification distortion of the prisms of the beam expander.

Abstract: The present invention is, in an optical head tracking error detecting apparatus in which a laser beam from a semiconductor laser element (1) is introduced into a diffraction grating (3), a 0-order beam and .+-.1st-order beams emitted from the diffraction grating (3) are introduced through a beam splitter (4) to an objective lens (5), a 0-order beam and .+-.1st-order beams of converged beams which are introduced into an optical recording medium (6) and reflected on the optical recording medium (6) are passed through the objective lens (5), reflected on the reflection surface of the beam splitter (4), and then introduced into a photodetector (7), a pair of photo-detection outputs corresponding to said .+-.

Abstract: An optical head for a laser memory disk in accordance with the present invention comprises: a substrate (1); a waveguide layer (3) formed over a main surface of the substrate; a semiconductor laser (4) for injecting laser beams into the waveguide layer, the semiconductor laser being set in a hollow (17) dug down at least into the waveguide layer; a focusing grating coupler (6) formed on the waveguide layer for focusing the injected laser beams on the memory disk and introducing beams reflected back from the disk into the waveguide; beam splitter means (5) formed on the waveguide layer between the semiconductor laser and the focusing grating coupler, for bisecting each of the reflected beams at a prescribed acute angle; and photodetector means (10) for converting the bisected beams into electrical signals, the photodetector means being provided along both the sides of the semiconductor laser and situated not nearer to the focusing grating coupler as compared with the semiconductor laser.

Abstract: A device for detecting the abnormality of an optical pick-up head has a laser diode for emitting a light beam through an optical system to a reference reflective region formed at a predetermined portion of an optical disk, a photosensor for receiving a reflected light from the reflective region through the optical system, and a photosensor for detecting directly the light amount of the laser diode. The difference or a ratio of the detection signals of the photosensors is obtained, and the difference or the ratio is compared with a predetermined value. When the compared result exceeds a predetermined value, the result is decided to be an abnormality of the pick-up head.

Abstract: A semiconductor laser drive device is adopted in an optical disk read/write unit for writing/reading data in/from an optical disk. The device has driver for modulating the laser beam of the intensity corresponding to a drive current value in accordance with write data WDATA, photodiode for detecting the light-emitting intensity of semiconductor laser, and APC circuit for comparing the detected light-emitting intensity of photodiode with a desired light-emitting intensity and changing the drive current value for semiconductor laser until the detected light-emitting intensity coincides with the desired light-emitting intensity. APC circuit has battery backup memory. A drive current value obtained at the start of the device is stored in memory. Thereafter, APC circuit starts APC from the stored drive current value.

Abstract: In a recording/reproducing optical system of the invention, which comprises a semiconductor laser causing single transverse mode oscillation and having beam radiation angles of .theta..perp. and .theta..parallel. in planes normal and parallel to an active layer, respectively; a collimator lens having a focal length f.sub.c ; an anamorphic optical element having a magnification ratio of 1:.beta. in two directions crossing each other at right angles; and an objective lens having a focal length f.sub.0, a numerical aperture NA.sub.0 and an aperture 2A.sub.0, and in which ratios A.sub.0 /W.perp. and A.sub.0 /W.parallel. of the apertures to diameters 2W.perp. and 2W.parallel., on the planes normal and parallel to the active layer, of beams which are emitted from the semiconductor laser, pass through the collimator lens and the anamorphic optical element and are incident to the objective lens have the following relations with predetermined values fi.perp. and fi.parallel.:A.sub.0 /W.perp..ltoreq.fi.perp.A.sub.0 /W.

Abstract: A device for processing optical data comprising:an optical waveguide formed on a substrate,a light source for the laser beam to be admitted into the waveguide,lens means provided on the waveguide for causing the beam propagating through the waveguide to emerge obliquely upward and focusing the emergent beam two-dimensionally,means for receiving the beam reflected obliquely from above,a base provided with the laser light source, the substrate and the light receiving means,a focusing drive mechanism for adjusting the position of the base upward or downward, anda tracking drive mechanism for adjusting the position of the base laterally.

Abstract: A self contained, replaceable diode laser module for providing a fully collimated, de-astigmatized, and circular cross-sectioned beam. In the preferred embodiment a first compound spherical lens partially collimates the beam. An in-line combined cross-section modifier system then de-astigmatizes and modifies the cross-section of the beam. The beam modifier system is comprised of first and second triangular prisms oriented at non-normal angles to the path of the beam. This allows both the cross-section and the astigmatism of the beam to be corrected. A planar mirror between the first and second prisms directs the beam from the first prism to the second prism, so that the beam can exit the second prism co-axial with the incident beam path. The beam then enters the second collimating subsystem.

Abstract: An optical head assembly for recording information on an optical disc or for taking out information already recorded, the optical head assembly including a semiconductor substrate and a dielectric light conducting layer formed on the substrate, the light conducting layer being internally formed with optical elements for converging laser beam from a laser beam source onto the optical disc and directing the reflected beam from the optical disc surface toward a photo detector. Output signal from the photo detector is used for reading information and also for allowing the optical head assembly to trace a track on the optical disc.

Abstract: An apparatus for recording data on a recording medium using an extended cavity laser in which the recording medium is an integral part of the laser cavity. The recording medium may be magnetic or nonmagnetic.

Abstract: An optical head for an optical signal recorder includes a nonpolarizing beam combiner for combining the light beams from two like-frequency, sic wavelength, lasers along one light path. The combined beams travel slightly diverging paths so that a first one of the beams can record signals on a disk while a second beam follows the first beam on the disk for direct reading-after-recording. Intermediate the combiner and the disk are a polarization type beam splitter and a focuser. One or more detectors receive reflected light from the disk via the beam splitter for detecting focus, sensed recorded signals and for tracking the beams to tracks of the disk. The combiner and splitter are preferably secured together as a single unit. The combiner uses refraction and internal reflection properties to combine the two like-frequency beams without polarization changes of either beam.

Abstract: In an optical recording system employing a semiconductor diode laser and having both read and write capabilities, the laser power must be carefully controlled at both the appropriate level for reading and at a different level for writing. Typically, a continuous read beam is emitted by the laser while pulses at the higher write power level are generated. The laser power control loop of the present disclosure maintains both the read and write output power of the laser within predetermined limits. A light sensing diode is used to determine laser output power, which is then used to operate the control circuit by adjusting the read and write current supplied to the laser. The output of the sensing diode voltage is passed through a read/write switch which is controlled by write pulses, which also control the laser. In read mode a DC signal is sent to a quad comparator circuit for read power control.

Abstract: Disclosed is an optical recording and reproducing apparatus having an erasing function. The invention aims at providing a practical apparatus which can effect recording, reproducing and erasing of signals in an erasable recording film by applying laser beams thereto. A substantially circular first fine beam spot is formed by a beam source such as a laser, and an elliptic second beam spot for erasing purposes is formed by another beam source such as a laser, with both beam spots are disposed in close proximity of each other on the same guide track. The erasing beam spot is elongated and has an axis which is tangent to the guide track on the recording medium. The power of intensity profile of the erasing beam spot is so controlled that the highest intensity is obtained at the leading end portion of the erasing beam spot as viewed in the direction of the scan, so that the signal can be erased stably and reliably with minimal erasing power.

Abstract: An optical information reading apparatus wherein the intensity distribution of a light beam projected onto a video disk through an objective optical system is so made that the intensity in the direction along an information track is larger than the intensity in the direction intersecting at right angles with the information track in order to improve S/N and to eliminate cross-talks.

Abstract: A servo tracking system for an optical record uses a pattern of preformed optically detectable uniform servo track marks disposed in parallel spaced apart columns in combination with a beam from a radiation source split by a diffraction grating into three beams having unequal power distribution. The placement of the beams across the pattern of preformed servo tracks on an optical recording material has one position for writing data by the center beam on an information track while the two outside beams intercept track marks on two adjacent tracks. For reading recorded data tracks, the beams shift to a second position in which the center beam intercepts marks on a servo track while the two outside beams read two adjacent data tracks. Because of the unequal power distribution, increasing the energy level of the radiation source causes the intensity of the middle beam during recording to reach a level sufficient to record while the two outside tracking beams remain below that threshold.

Abstract: Laser scan/electrophotographic non-impact printer is disclosed which comprises one or more laser diodes mounted on a rotating turntable, the angular scan of the laser diode being generated by rotation of the turntable. An optical system is provided for each beam emitted from the laser diode to shape and direct the beam toward the photosensitive surface. The information is carried on the beam by modulating the beam with the information output of the computer at the source of the beam. To increase the efficiency of the output of the device, the front and rear surfaces of the laser diodes may both be used.To overcome the difficulty of providing the necessary power to drive the laser diodes to the rotating turntable, a power source comprising a solar cell array illuminated by a lamp is provided. Preferably, this solar cell array is mounted on a surface above the surface of the laser diodes, so that it is easily carried by the rotating turntable. A rotating battery or power generator could also be used.

Abstract: This optical sensor has cylindrical symmetry and is comprised of a semiconductor light source/light detector combination and an optical element comprising a single lens, where the sensor is particularly suitable for uses in accurate position detection in data recording systems. In a preferred embodiment, the light source is a forward-biased p-n junction, while the light detector is a reverse-biased p-n junction located below the light source and coaxial therewith. Light from the source is directed to a point on a data recording medium and the light reflected therefrom passes through the light source to the light detecting junction. The ac signal corresponding to the reflected light is an indication of the position of the recording head with respect to the data storage medium.

Abstract: An optical and reversible recording and reproducing apparatus providing a practical apparatus in which information signals can be recorded, reproduced and erased by irradiating a laser beam and the like on the substrate to be optically recorded. More practically, there is provided such an apparatus wherein two light sources such as lasers having different wavelengths are used, and a first almost circular micro-lightspot is produced by one light source, while a second elliptic light spot having a longitudinal diameter in the tangential direction of a guide track on a disc is produced by the other light source. These first and second light spots are closely irradiated on one and the same guide track of an optical recording disc. The recording and reproducing of the signals are performed using the first light spot while the erasure of the recorded signals can be made by using the second light spot or using both first and second light spots in combination.

Abstract: An optical recording and reproducing head wherein light beams emitted from two light sources are combined and applied to a recording medium and the light beams reflected from the recording medium are drawn out in such a way that they are separated from each other. The wavelengths of the light beams from both light sources are different from each other, i.e., .lambda..sub.1, .lambda..sub.2, and the light beams from the light sources are combined by means of a polarization beam splitter, two quarter wave plates and optical filters, and are then simultaneously focussed by a single focussing lens substantially along the optical axis thereof, thereby allowing microspots of focussed light to be disposed on a disc close to each other. The light beams reflected from the disc are drawn out so as to be completely separated from each other by the polarization beam splitter owing to the difference in polarization direction.

Abstract: A two-segment contact buried heterostructure (BH) laser is pumped by a current applied to its absorber contact from a source of high impedance on the order of 100K.OMEGA. or more. The parasitic resistance between the absorber contact and the gain contact is high on the order of 10K.OMEGA.. For a given absorber (bias) current the laser exhibits a relatively wide hysteresis on the order of 1 mA or more in the light vs. gain contact current. Such a laser is highly useful as a bistable optical element. The laser is also bistable with selected pump gain and absorber currents to exhibit a wide hysteresis of voltage across the absorber contact vs. relative amounts of light which is reflected back to the laser as feedback. The laser serve both as a light source and as a detector for reading out binary information stored as light reflective spots on a medium, e.g. a video disk.

Abstract: Optical recording medium having a laser-recordable light-absorbing layer which is a carbide of iron or chromium has surprisingly high sensitivity. High carrier-to-noise ratios are attained using a laser-diode recording system at power levels below 10 mW.

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 optical head in a data carrier recording-reading device comprises a semiconductor laser source. A lens makes it possible to focus the beam from this source. A polarization beam splitter makes it possible to deflect the beam reflected by this carrier towards a group of photodetectors. According to the invention the splitter is an isosceles prism, which serves as an anamorphotic-splitting means. A quarter-wave plate is bonded to one of the faces of the prism. A planoconvex lens can also be bonded to the other face of the prism upstream of the photodetector.

Abstract: A method and apparatus is disclosed for reducing optical noise in an optical information processing system having a single longitudinal mode laser which is converged on a record medium for detecting information stored on the medium. A range from 1-10% of the total emitted light per facet of the laser is fed back to an emitting point of the laser to minimize the occurrence of optical noise present in the light emitted from the laser.

Abstract: An optical record and playback system is described for use in a multi-channel data processing system. An optical head which includes a laser diode array comprises a collection objective, an anamorphic beam expander and a focusing lens. The optical head collects the laser beams emitted by the diode array, expands the beam cross-section to form circular beams and focuses the beams to diffraction limited spots.

Abstract: An optical record and playback system is described for use in a multi-channel data processing system. An optical head which includes a laser diode array comprises a collection objective, an anamorphic beam expander, a relay lens and a focusing lens having a finite conjugate. The optical head collects the laser beams emitted by the diode array, expands the beam cross-section to form circular beams and focuses the beams to diffraction limited spots. In operation the relay lens is used to image the lasing spots from the laser diode array in the conjugate plane of the finite conjugate focusing lens.

Abstract: An optical disk system having direct read after write capabilities in which the write beam and the read beam are generated by a pair of integrated injection diode lasers. The integration can be achieved by mounting two separate injection diode lasers side by side in a common package or providing two side by side injection diode lasers formed on a common seminconductor substrate. The two lasers would be located in the same focal plane relative to a recording material, with one of the lasers pulse modulated to provide a data modulated write beam and the other laser driven in the continuous wave (CW) regime to provide a read beam of constant intensity. The plane containing the focused beams would be oriented relative to the recording material so that the focused beams impinge upon adacent portions of one data track of the recording material. Since the pair of lasers are closely spaced (1-1000 microns) a common optical path or train is used for both the write beam and the read beam.

Abstract: An optical disc device including a semiconductor laser as a light source and making the light output of the semiconductor laser different between an information recording operation and an information reproducing operation is disclosed in which the semiconductor laser is connected in parallel with protection circuit, and in which the protection circuit is put in a short-circuited state between two terminals thereof when a monitor signal corresponding to the light output of the semiconductor laser exceeds a predetermined value.

Abstract: An optical pickup wherein a semiconductor laser device for projecting a laser beam onto an optical disc is driven by a D.C. current and a high-frequency current superposed thereon, and the laser device oscillates in a multiple longitudinal mode.

Abstract: An optical scanning unit for scanning recording tracks of a record carrier with a radiation beam. The beam is emitted by a radiation source arranged at one end of a tubular member and is concentrated to a radiation spot by a lens system arranged at the other end of the tubular member. A double prism disposed between the source and lens system splits-off a reflected secondary radiation beam and directs it laterally towards an electronic output device through a lateral aperture in the tubular member. The output device converts the modulated reflected radiation into an electrical signal. The radiation source and the double prism are radially and axially aligned within the required tolerances on a metal prism support which, within an adjustment range, can be moved axially relative to the tubular member and which can be rotated to a limited extent.

Abstract: An optical system characterized in that a plano-convex lens for guiding onto a disk a light beam emitted from a semiconductor laser, and a prism for deriving reflected light from the disk are unitarily formed.

Abstract: An optical device for recording and reading on a data carrier is provided with first optical means forming a composite source of radiant energy comprising a first semiconductor-laser source for producing a polarized reading beam, a second semiconductor-laser source for producing a polarized recording beam, the two directions of polarization being at right angles to each other, and an optical element for combining the two beams followed by a polarizer. The device is also provided with second optical means comprising an optical separating element, a quarter-wave plate and an optical system for focusing the two reading and recording components after reflection from the tracks of the disk on two distinct zones of an optoelectronic detection device.

Abstract: A laser recording device adapted for use in a facsimile system in which a semiconductor laser is activated by a series of pulses the number of which is produced in accordance with an input signal. The input signal is sampled with a sampling pulse signal whereas the pulses applied to the semiconductor laser are produced at a frequency which is at least two orders of magnitude greater than the frequency of the pulses used to sample the input signal. The input signal is digitized and used to address a read-only memory which outputs a number of pulses in dependence upon the amplitude of the input signal. The output number of pulses may be logarithmically related to the magnitude of the input signal.

Abstract: A video disc record having a spiral video record track which can provide reproduced video signals with a desired frame rate such as thirty frames per second while the disc record is rotated at a very low speed such as two revolutions per minute. A preferred transducer machine uses a pulsed light source to supply successive light images to a video camera readout. Control signals are recorded on helical control tracks so that reproduction thereof facilitates the generation of a desired standard video signal from the video camera.

Abstract: An optical read unit is described for scanning a record carrier with a radiation-reflecting trackwise-arranged information structure. The read unit utilizes a diode laser which generates the read beam and also detects the information stored on the record carrier. The read unit is also provided with an opto-electronic system for detecting the position of the read spot relative to a track to be read and the position of the plane of focussing. The diode is mounted in a housing and the unit includes electromechanical apparatus for moving the housing in two perpendicular directions so as to correct the position of the read spot. The objective system for the formation of the read spot is of simple construction.