Optical pickup head wherein an error signal is produced by detec

Details Optical pickup head wherein an error signal is produced by detec Optical pickup head wherein an error signal is produced by detec

1991-03-14

1994-03-08

Psitos, Aristotelis

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4412, 369 4441, 369103, G11B 713

Patent

active

052933679

ABSTRACT:
A light source emits a light beam which is focused on an optical recording medium. The light beam is reflected and diffracted by the optical recording medium. A holographic optical element has divided regions formed with different holographic patterns. The divided regions of the holographic optical element diffract the light beam reflected and diffracted by the optical recording medium, and thereby generate diffraction light beams respectively. The divided regions of the holographic optical element lie in quadrants of an imaginary X-Y coordinate system respectively. An X axis of the coordinate system extends in a direction corresponding to a direction of a pit sequence on the optical recording medium, that is, a tangential direction of the optical recording medium. A Y axis of the coordinate system extends in a direction corresponding to a direction perpendicular to the direction of the pit sequence, that is, a radial direction of the optical recording medium. Photodetectors receive the diffraction light beams generated by the divided regions of the holographic optical element, and convert the received diffraction light beams into corresponding electric signals. Phases of the electric signals are compared, and a tracking error signal is generated on the basis of a result of the phase comparison.

REFERENCES:
patent: 4358200 (1982-11-01), Heemskerk et al.
patent: 4665310 (1987-05-01), Heemskerk
patent: 4731772 (1988-03-01), Lee
patent: 4929823 (1990-05-01), Kato et al.
"Patent Absracts Of Japan" vol. 13, No. 82 (P-833) Feb. 23, 1989, & JP-A-63 263636 (Matsushita Electric Ind Co Ltd) Oct. 31, 1988, * the whole document *.
"Applied Optics" vol. 27, No. 4, Feb. 1983, New York, NY, USA pp. 668-671; Yasuo Kimura et al: Compact optical head using a holographic optical element for CD players * p. 669, col. 1, lines 3-19; FIG. 1 *.

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