Abstract: A scanning device for optical record carriers is provided with an objective lens (7) suitable for scanning record carriers (1, 21) having a transparent substrate (2, 23) of different thicknesses. The lens comprises an outer annular part (25) and an inner central part (26) within the annular part. Only the central part of the lens is used for forming a focus through a first substrate (2) having a first thickness. The central part is corrected for the spherical aberration of the first substrate. The annular and central part of the lens are used for forming a focus through a second substrate (23) having a different, second thickness. The annular part is corrected for the spherical aberration of the second substrate.

Abstract: An optical scanning device using one or more rows of scanning spots for simultaneously scanning a plurality of information tracks of an optical record carrier. The resulting radiation produced from the respective spots is imaged on respective photodetectors, and the detection signals from a plurality of the photodetectors are used to derive focus error and tracking error signals for the corresponding scanning spots. Error signals of the same type are then combined to derive servo control signals for respectively controlling focus and tracking of all scanning spots. The focus error signals can also be combined to derive further servo control signals for controlling tilt of the record carrier and tracking angle. Derivation of the servo control signals from error signals corresponding to a plurality of the scanning spots achieves improved immunity against the effects of dust or other artifacts on the surface of the record carrier.

Abstract: An optical unit includes a first holder with a radiation source, a second holder with a radiation-sensitive detector, a grating, and a mirror. The unit further includes a cylindrical mounting having a cylinder axis and a wall oriented transversely to the cylinder axis, the grating and the mirror being formed by optically transparent wall portions of the wall. The mounting has a first positioning surface to which the first holder with the radiation source is secured and a second positioning surface to which the second holder with the radiation-sensitive detector is secured.

Abstract: A device for optically scanning an information plane (2) having tracks (5). Radiation supplied by a radiation source (7) is focused on the information plane by an objective system (8). The beam reflected by the information plane is incident on a dividing element, for example, a grating (12), which divides the beam into two halves along a dividing line (17). Two sub-gratings (15, 16) at both sides of the dividing line, respectively, each form a sub-beam from one half of the beam, which sub-beams are detected by a detection system (10), which produces detection signals therefrom. A focus error signal is generated from the detector signals. According to the invention, modulation of the focus error signal by the track structure will be minimal if the dividing line (17) is located at an angle between 15.degree. and 80.degree. to the direction of the tracks.

Abstract: A polygonal scanning mirror for an optical recorder is magnetically suspended and rotated about a scanning axis. To control position of the scanning mirror, a curved surface mirror is fixed with respect to, and rotates with, the scanning mirror for receiving a radiation beam and reflecting it onto a detector array. The reflected radiation beam is preferably focused by an astigmatic imaging system. Output signals from the detector array are used to control electromagnets of the suspension system.

Abstract: A planar optical head is described with a corrected input grating for scanning a surface, for example, a recording surface (2) in an optical record carrier (1). A radiation source (5) supplies a beam (6) which is coupled into a waveguide (9) by an input grating (7) and is formed to a focused scanning beam (11) by an output grating (10). Deficiencies of the radiation beam such as the non-round cross-section of the beam, astigmatism and wavelength variations caused by the radiation source can be corrected by means of an adapted grating structure of the input grating.

Abstract: An optical system for determining the position and/or orientation of an object (10), for example, a freely suspended rotatable polygon mirror, comprises a convex mirror (24) on the rotation axis (11) of the polygon mirror and a plane mirror (25) perpendicular to the rotation axis. A convergent radiation beam is projected on the convex mirror (24). The reflected radiation is subsequently focused on a detection system (40, 45) via an astigmatic imaging system (75, 78, 51). A substantially parallel radiation beam is incident on the plane mirror (25), which beam, after reflection, is also focused to a radiation spot (34a) on the detection system (40, 46). The position and the shape of the radiation spots (34, 34a) are a measure of the position and the orientation of the polygon mirror (10). After processing, the output signals of the radiation detection system are applied to elements (91), for example electromagnets for stabilizing the polygon mirror (10).

Abstract: A planar optical head is described, which comprises a detector grating (15) for scanning a surface, for example, a recording layer (2) in an optical record carrier (1). A radiation source (5) supplies a beam (6) which is coupled into a waveguide (9) by an input grating (7) and is formed to a focused scanning beam (11) by an output grating (10). A scanning focus (13) having an optimum shape and a high intensity is obtained by arranging, in the path of the beam reflected by the record carrier, a special detector grating (15) which deflects this beam towards a detection system (17).

Abstract: An optical scanning device for scanning an information plane (2) having tracks is described, which device comprises a radiation source (4) supplying a scanning beam (3) and an objective system (5) for focusing the scanning beam to a scanning spot on the information plane (2). To obtain two tracking spots, two grating parts located at both sides of the scanning beam and capturing border rays from the radiation source are used.

Abstract: A grating objective comprises at least three gratings and in which an axial ray and a border ray of a radiation beam are interchanged at least two times so that the objective has a wavelength-independent behavior, a relatively large image field and a satifactorily uniform intensity distribution. A beam shaper and a grating objective with a built-in beam shaper are described based on the same principle.

Abstract: An optical scanning device is described with a mirror-objective (30) arranged between a radiation source (40) and an object (10) to be scanned, which mirror objective comprises two radiation windows (31, 34) and two reflectors (32, 33). By giving one of the windows (31, 34) an aspherical shape, the mirror objective is well corrected for spherical aberrations, while no stringent requirements need to be imposed on the accuracy of the shape of the aspherical surface (35).

Abstract: An optical scanning device which includes a radiation source, a mirror objective an a radiation-sensitive detection system, the mirror objective being a transparent body having a radiation window and a reflector symmetrical therewith on each of two opposed surfaces of such body. First diffraction elements are respectively arranged on the first and second radiation window and the second reflector, whereby radiation directed through the first window is focussed to a scanning spot on an information plane and radiation from such plane after a second passage through the mirror objective includes a number of diffracted beams directed on the radiation detection system. The diffracted beams enable detection of tracking errors and focussing errors of the scanning spot relative to tracks on the information plane.

Abstract: An optical scanning apparatus, which includes a radiation source (7) supplying a scaning beam (b.sub.1), an objective system (8) for focusing the scanning beam (b.sub.1) to a scanning spot (S.sub.1) in an information plane (2) to be scanned, and a first diffraction element (9) for deforming the beam reflected by the informatin plane (2) in such a way that a focus-error signal can be derived therefrom. The apparatus also includes a second diffraction element (10) for forming two auxiliary beams (b.sub.2, b.sub.3) by means of which a tracking-error signal can be derived, which second diffraction element has such a size and is arranged at such position that the beams originating from the first diffraction element (9) do not traverse the second diffraction element.

Abstract: An optical scanning device having a mirror-objective arranged between a radiation source and an object to be scanned, which mirror objective is a radiation-transparent body having a radiation window and concentric reflector on each of two opposite surfaces of such body. By providing at least one of the windows with an aspherical shape, the mirror objective is well corrected for spherical aberrations without imposing stringent requirements on the accuracy of such aspherical shape.

Abstract: Optical record carrier scanning apparatus including a source of radiation which is tunable to produce different wavelengths of a radiation beam and an optical assembly for forming the radiation beam into a spot for scanning information tracks on the record carrier. The optical assembly includes a diffraction grating which diffracts the beam so that only a selected diffraction order sub-beam thereof is formed into the scanning spot, the diffraction angle of such sub-beam and consequently the position of the scanning spot relative to the track being scanned being variable by variation of the wavelength of the radiation beam. A periodic transverse variation of spot position can thus be produced entirely optoelectronically, for producing a tracking error signal to control the scanning spot to remain centered on the information track.

Abstract: Apparatus for transferring data and other information between a data processing unit and a rectangular memory card which includes an optically readable data memory unit having a succession of substantially concentric data storage tracks thereon, the card also including at least one microelectronic component which stores further information. Such component is connected to connection points on the surface of the card. Data is read from the tracks of the memory unit by optical scanning during rotation of the card about the axis of symmetry of the memory unit, and information is transferred between the microelectronic component and the data processing unit by an information transfer unit which is coupled to the connection points on the card and to the data processing unit.

Abstract: A scanning unit for an optical disc record carrier includes a radiation-sensitive detection system having a plurality of detection elements on which is formed a reflected image of the scanning spot on the track structure of the record carrier. A tracking error signal is derived by combining the output signals of detection elements situated on respective sides of a boundary line between two halves of the detection system, and comparing with each other the combined signals from both halves. Several different such tracking error signals are derived, for boundary lines having different orietations with respect to the direction of the track instantaneously being scanned. The tracking error signal corresponding to a boundary line most nearly parallel to the direction of such track will be of greatest amplitude, and is selected as the tracking error signal used for controlling the scanning unit to follow the center line of such track.

Abstract: An optical record carrier having a surface layer which includes a substantially circular information track structure, such surface layer extending without interruption substantially up to the center of the track structure. When the record carrier is supported on a rotating turntable and scanned by a scanning beam producing a scanning spot having a width transverse to the track direction of at least a few times the period of the track structure, a diffracted beam is produced by the track structure in a direction transverse to the local track direction. A radiation-sensitive detection system in the path of the diffracted beam produces output signals indicating any centering error between the center of the track structure and the axis of rotation of the turntable. Such signals can be employed to control positioning means to position the record carrier on the turntable so as to eliminate such centering error.

Abstract: A scanning device for an optical recording and/or reproducing apparatus comprises a mirror objective in the form of a transparent body one surface of which forms an internally reflecting concave reflector and the opposite surface of which forms an internally reflecting convex reflector. A beam of radiation from a radiation source enters a window in the concave reflector, is divergently reflected by the convex reflector back to the concave reflector, and is consequently reflected thereby through a second window in the transparent body so as to form a scanning spot focussed on an information plane to be scanned by the device. The mirror objective includes a phase grating by which radiation reflected from the information surface is separated from the scanning beam and is directed to a radiation-detection system.

Abstract: An apparatus is described for optically scanning an information surface by moving said surface relative to a beam, which apparatus comprises a radiation source for supplying a beam, a collimator lens and an objective for focusing the beam to a spot in the information plane. The height of the apparatus can be reduced and/or a beam having an asymmetrical cross-section can be converted into a beam having a symmetrical cross-section by arranging a reflective diffraction grating with a suitable grating period between the collimator lens and the objective, while the angle of incidence between the normal on the grating and the chief ray of the scanning beam deviates considerably from 45.degree..