Astigmatic method for detecting a focussing error in an optical

Details Astigmatic method for detecting a focussing error in an optical Astigmatic method for detecting a focussing error in an optical

1994-11-07

1997-06-03

Tran, Thang V.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369112, G11B 7095

Patent

active

056361890

ABSTRACT:
An optical pickup system for determining a focussing error by utilizing an improved astigmatic method, the system comprising: a light source; an optical detector, including a square light-reception surface formed by arranging four square photoelectric cells; a beam splitter provided with a reflection surface for reflecting the light beam from the light source and for transmitting the light beam reflected from the recording surface; a first and a second adders for adding outputs from each of two opposite corners of the square light-reception surface; an objective lens, disposed between the beam splitter and the optical disk; a graded index lens, located between the beam splitter and the optical detector, for making the light beam transmitted through the beam splitter astigmatic as it passes therethrough; and a differential amplifier for generating a focussing error signal.

REFERENCES:
patent: 4501493 (1985-02-01), Kubota
patent: 5161139 (1992-11-01), Inoue et al.
patent: 5195072 (1993-03-01), Fukui et al.

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