Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1986-01-08
1986-12-23
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
369 45, G11B 700
Patent
active
046313958
ABSTRACT:
Optical apparatus for controlling the focusing and positional accuracy of a light beam incident on an optical disk tracking guide in an optical read/write system. Laser beams are converged by an objective lens and directed onto the tracking guide to form a beam spot. Light reflected from the tracking guide is reconverged by the objective lens and directed toward a light shielding plate. The reflected light contains an image of the beam spot and diffraction patterns within the beam spot image which are caused by light reflected from the tracking guide. The plate allows only a portion of the reconverged light beam to pass, a portion which is displaced from the optical axis of the beam. The passed portion is converged by a projection lens and passed to a cylindrical lens. The beam spot image in the light passing through the cylindrical lens will become elongated. This light is directed to a photosensitive surface having a plurality of signal producing photosensitive regions. When the light beam is in focus and on track on the tracking guide, the elongated beam spot falls substantially equally between two of the photosensitive regions, and the diffraction patterns fall substantially in the center of the elongated beam spot image. If either the focusing or positional accuracy of the light beam is off, the photosensitive regions will generate signals which can be used to change the focus or position of the light beam with respect to the tracking guide.
REFERENCES:
patent: 4425636 (1984-01-01), Musha et al.
patent: 4455085 (1984-06-01), Kato et al.
Tokyo Shibaura Denki Kabushiki Denki
Westin Edward P.
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