Optical pickup device including diffraction grating

Details Optical pickup device including diffraction grating Optical pickup device including diffraction grating

1991-04-18

1992-12-22

Young, Wayne R.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4441, 369112, G11B 709

Patent

active

051738902

ABSTRACT:
An optical pickup device having an optical system provided with at least a light source, a shaping prism, a diffracting element and a photodetector. The light source projects light whose intensity distribution has an elliptical shape in its cross section orthogonal to the optical axis. The shaping prism directs the light to a recording medium after shaping the intensity distribution thereof into a circular shape. The diffracting element has diffraction regions formed by at least one division line substantially parallel to a reference direction. The light reflected from the recording medium forms an elliptical bright portion on the diffracting element. The photodetector is divided by a plurality of division lines, at least one of which is substantially parallel to the reference direction. The diffracting element diffracts the reflected light so as to converge it on the photodetector. Have, a hypothetical line extending from a projecting point of the light source through the center of a light-receiving face of the photodetector is also set to be parallel to the reference direction. For example, when the shaping prism is to shape the intensity distribution having the elliptical shape with respect to its minor axis direction, the optical system is arranged so that the minor axis of the bright portion is parallel to the division line of the diffracting element. Thus, it is possible to always obtain an accurate focusing control signal.

REFERENCES:
patent: 4983017 (1991-01-01), Tsuji et al.
patent: 5066138 (1991-11-01), Toide et al.
patent: 5111448 (1992-05-01), Komma et al.
patent: 5111449 (1992-05-01), Kurata et al.

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