Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1982-05-05
1985-01-08
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
369 45, G01J 120
Patent
active
044928564
ABSTRACT:
An apparatus is disclosed for effecting a focus control of an objective lens with respect to a track having a crenellated pit construction recorded on an optical disc on which a light beam emitted from a laser light source is to be focused as a light spot by an objective lens. A light beam reflected by the disc is introduced via a reflection surface which is set substantially at a critical angle with respect to an optical axis onto a photodetector having four light receiving regions divided in orthogonal directions. A first focus signal is produced by deriving a difference between photoelectrically converted output signals from the light receiving regions in response to a variation in an average amount of the light projected on the photodetector. The output signals from the light receiving regions are further supplied to high pass filters and envelope detectors to derive two RF signal components modulated by the pit construction and a second focus signal is produced by deriving a difference between the RF signals. A very accurate focus control is effected in accordance with a composite focus signal obtained by mixing the first and second focus signals with each other.
REFERENCES:
patent: 4358774 (1982-11-01), Wilkinson
Austin II Ernest
Nelms David C.
Olympus Optical Co,. Ltd.
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