Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Patent
1994-11-07
1997-03-04
Tran, Thang V.
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
369 4414, 369103, 369112, 369 4423, G11B 709
Patent
active
056086954
ABSTRACT:
An optical pick-up apparatus for reading and/or writing information from and/or on an optical record medium including a semiconductor laser, an objective lens projecting a laser beam onto the optical record medium, a hologram optical element having a first hologram for diffracting the laser beam onto a first pair of photodetectors to derive a focusing error and a second hologram for diffracting the laser beam onto a second pair of photodetectors to derive a tracking error. Each of the photodetectors of the second pair has light receiving regions which are divided along a division line substantially parallel with a diffracting direction of the second hologram which introduces astigmatism into the diffracted beams. A large tracking error signal can be detected stably on the basis of a distribution of an amount of light in a far field by the push-pull method.
REFERENCES:
patent: 4945529 (1990-07-01), Ono et al.
patent: 5231620 (1993-07-01), Ohuchida
patent: 5391865 (1995-02-01), Kurata et al.
Olympus Optical Co,. Ltd.
Tran Thang V.
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