Apparatus for detecting focus error signal

Details Apparatus for detecting focus error signal Apparatus for detecting focus error signal

1990-03-01

1992-01-28

Envall, Jr., Roy N.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4423, 369124, G11B 700

Patent

active

050848500

ABSTRACT:
An apparatus for detecting a focus error signal in which reflected laser light is split into two optical paths by a polarized light beam splitter while astigmatisms are produced in the laser light by at least one astigmatism generating element, and the two split beams are led so as to be incident upon two quadrant photodetectors, respectively. A focus error signal is obtained as an electrical signal by subtracting the sum of the quantities of light received by one of the diagonal pairs of regions among the quadrant regions of the two photodetectors from the sum of the quantities of light received by the other diagonal pair. An offset component in a focus error signal is removed by, for example, a variable resistor. This arrangement enables cancelling of influence of double refraction in a magnetooptic disk or the like, thereby making the optical head free of the problem of such influence.

REFERENCES:
patent: 4123652 (1978-10-01), Bouwhuis
patent: 4546463 (1985-10-01), Opheij et al.
patent: 4695158 (1987-09-01), Kotaka et al.
patent: 4748610 (1988-05-01), Nakata et al.
Electronic Component and Application 6(1984), 4, 209-14.

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