Optical head for generating a plurality of light beams and an op

Details Optical head for generating a plurality of light beams and an op Optical head for generating a plurality of light beams and an op

1994-11-08

1996-12-17

Ben, Loha

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

369110, 369121, 369 4437, 360114, G11B 700

Patent

active

055860974

ABSTRACT:
A recording/reproducing/erasing optical head for generating a plurality of light beams detects a defocused state by a method in which a light beam is caused to be nearly parallel to form optical spots on an opto-magnetic disk, the light beam from the optical spots on the opto-magnetic disk is condensed on a sensor by an objective lens and a condenser lens, and the size of the light spot on the sensor spaced by a predetermined distance in front of or behind the focal point of the condenser lens, and the size of the light spot on the sensor indicate the defocus state, wherein if the focal length of the objective lens is denoted as f.sub.o, the numerical aperture of the objective lens as NA, the focal length of the condenser lens as f.sub.con, the predetermined distance is .DELTA.d[mm], and (f.sub.con /f.sub.o).sup.2 =.gamma., the following relation is satisfied:

REFERENCES:
patent: 4517667 (1985-05-01), Sprague
patent: 5043960 (1991-08-01), Nakao et al.
patent: 5105407 (1992-04-01), Ishika
patent: 5144616 (1992-09-01), Yasukawa et al.
patent: 5353274 (1994-10-01), Nishikawa
patent: 5359588 (1994-10-01), Fujita et al.
patent: 5406542 (1995-04-01), Morimoto

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