Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2006-07-31
2011-10-11
Danielsen, Nathan A (Department: 2627)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S044410, C369S047450
Reexamination Certificate
active
08036092
ABSTRACT:
To provide an optical head device, which can detect an excellent focus error signal for a dual layer optical recording medium, and optical information recording/reproducing device. Reflected light from a dual layer optical recording medium is diffracted by a diffractive optical element divided into four regions, and is received by a photodetector. Optical spots are equivalent to negative first order diffracted light from the four regions of the diffractive optical element, and are received by four dual-divided light receiving sections, respectively, to be used for detection a focus error signal by a Foucault's method. The four dual-divided light receiving sections are provided with positive component light receiving sections for outputting the received light as a positive component of the focus error signal and negative component light receiving sections for outputting the received light as a negative component of the focus error signal, respectively. When a signal layer of the optical recording medium is far from an objective lens by a defocusing quantity equivalent to an interval between the first layer and the second layer from a just focus position, a diffraction direction of a diffracted light generated from the reflected light from the signal layer is set so as that the diffracted light spreads to the positive component light receiving section and the negative component light receiving section, and a plurality of the positive component light receiving sections and a plurality of negative component light receiving sections are arranged.
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Danielsen Nathan A
Foley & Lardner LLP
NEC Corporation
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