Automatic focusing system with dual diffraction gratings and con

Details Automatic focusing system with dual diffraction gratings and con Automatic focusing system with dual diffraction gratings and con

1989-07-31

1990-11-20

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 4423, G01J 120

Patent

active

049720759

ABSTRACT:
An 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.

REFERENCES:
patent: 4475182 (1984-10-01), Hosaka
patent: 4503324 (1985-03-01), Yokota
patent: 4651314 (1987-03-01), Yoshikawa et al.
patent: 4850673 (1989-07-01), Velzel et al.
patent: 4858215 (1989-08-01), Yano et al.
Applied Optics, vol. 13, No. 6, Jun. 1974, pp. 1322-1326: "Focusing Errors in a Collimating Lens or Mirror: Use of a Moire Technique", Fouere et al.

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