Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1984-06-28
1987-03-31
Wan, Gene
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
250204, 369 44, G01J 136, G11B 700
Patent
active
046545166
ABSTRACT:
In an optical head, a laser beam emitted from a laser unit is converged by an objective lens and is projected toward a light reflecting layer of an optical disk. The laser beam reflected by the light reflecting layer is directed toward a light shielding plate through the objective lens. One part of the laser beam is shielded by the light shielding plate, and the other part thereof is converged by the projection lens and is projected on the photo sensitive regions. When the objective lens is kept in the just in-focusing state, a differential signal between photo signals generated from the photo sensitive regions is maintained at zero level. The differential signal is set at zero level when the objective lens is located at a transition point corresponding to a distance .delta.tf within the defocusing range. The beam spot formed by the light beam when the objective lens is located in the transition point extends outside the photo sensitive regions. In this case, an area Sout of a beam spot portion outside the photo sensitive regions is set to be a value 3Sin which is three times an area of a beam spot portion Sin within the photo sensitive regions.
REFERENCES:
patent: 4079248 (1978-03-01), Lehureau
patent: 4521680 (1985-06-01), Ando
Kabushiki Kaisha Toshiba
Wan Gene
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