Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1984-12-18
1987-03-31
Wan, Gene
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
369 44, H01J 516, G11B 712
Patent
active
046545190
ABSTRACT:
In an optical head, a laser beam emitted from a laser unit is collimated by a collimater lens and is transmitted through a polarized beam splitter and .lambda./4 plate. The collimated laser beam is converged onto a recording layer of an optical disk by an objective lens. A beam spot corresponding to the beam waist of the converged laser beam is formed on the recording layer in a just-in-focusing state and a beam spot larger than the beam spot corresponding to the beam waist is formed on the recording layer in a defocusing state. The laser beam reflected from the recording layer passes through the objective lens and is .lambda./4 plate and refrected by the polarized beam splitter. The polarized beam splitter has first and second beam emerging surfaces the first beam emerging surface being arranged perpendicularly to the optical axis and second beam emerging surface being arranged at a predetermined angle to the first beam emerging surface. Accordingly, the laser beam is separated into first and second laser beam components at the first and second beam emerging surfaces by the polarized beam splitter, which are directed in different directions. The first laser beam component is incident on a photodetector for detecting the focusing state of the objective lens.
REFERENCES:
patent: 3876841 (1975-04-01), Kramer et al.
patent: 3924063 (1975-12-01), Simons
patent: 4010317 (1977-03-01), Bouwhuis
patent: 4100577 (1978-07-01), Naruse et al.
patent: 4381557 (1983-04-01), Jebens
Kabushiki Kaisha Toshiba
Wan Gene
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