U.S. Philips Corporation

Adrianus J Duijvestijn

Peter Coops

Willem G Opheij

Peter De Zoeten

Andreas J Bressers

Dirk C Van Eck

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.

Apparatus for optically scanning an information plane

Optical scanning apparatus which includes a diode laser producing a radiation beam which is focussed by a lens system on a reflecting information plane to be scanned thereby. The reflected radiation is diffracted by a composite diffraction grating which includes a pair of sub-gratings, forming respective radiation spots on respective pairs of radiation detectors. The detectors in each pair are separated by a separating strip, the separating strips being substantially parallel to or co-linear with the bonding line between the sub-gratings. Such arrangement achieves correction for wavelength variations of the radiation beam, as well as fairly wide tolerances in the relative positioning of the various optical elements of the apparatus.

Apparatus for optically scanning a radiation-reflecting information plane

An apparatus for scanning the information plane of an optical record carrier with a radiation beam from a diode laser. The reflected radiation from the information plane is separated from the scanning beam and split into two sub-beams by a composite diffraction grating which also functions to focus the respective sub-beams on respective pairs of photodetectors. The composite grating consists of two sub-gratings which adjoin along a common bounding line, the sub-gratings having varying gratings periods and curved grating strips. Movement of the composite grating in the direction of the bounding line changes the axial imaging distance of the sub-beams from the grating, permitting adjustment of such distance to compensate for changes in the axial distance between the diode laser and the photodetector. The diode laser and photodetectors can therefore be assembled together as a single integrated unit.

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Eindhoven, Netherlands

Adrianus J Duijvestijn