Automatic focusing system with dual diffraction gratings and converging means
Patent 4972075 Issued on November 20, 1990. Estimated Expiration Date: 
July 31, 2009. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
July 31, 2009. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent ReferencesFocus servo control system for automatically adjusting a relative distance between an objective lens unit and a recording surface of an optical recording medium Automatic focusing device Optical recording and reproducing equipment Optical scanning apparatus which detects scanning spot focus error Integrated optical disc pickup that allows variations in the wavelength of the laser beam Patent #: 4858215 InventorsAssigneeApplicationNo. 388013 filed on 07/31/1989US Classes:250/201.5, With optical storage medium; e.g., optical disc, etc.359/569, Including particular grating characteristic369/44.23Structure for shaping beam or causing astigmatic conditionExaminersPrimary: Nelms, David C.Attorney, Agent or FirmForeign Patent References
International ClassG01J 001/20Foreign Application Priority Data1988-08-02 JPAbstractAn automatic focusing system for forcusing on an optical disk, the system including a laser beam source, an objective lens, a photodetector for detecting a focusing error, a beam splitter disposed between the laser beam source and the objective lens and a pair of diffraction gratings disposed between the beam splitter and the photodetector means so as to form a moire pattern on the photodetector means. The laser beam produced from the laser beam source travels to the optical disk through the objective lens and then is reflected off the optical back through the objective lens travels to the photodetector. A converging lens may be disposed between the beam splitter and the gratings or between the two gratings. Further, a single optical member may be constituted so as to form a moire pattern on the photodetector. The optical member includes a transparent base plate for supporting the two gratings on the respective surfaces thereof. Also, in the case where a converging lens is disposed between the two gratings, the two gratings may be provided on the respective surfaces of the lens.Other References
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