Optical head device and optical information recording or reproducing device

Abstract

[Problems] To provide an optical head and an optical information recorder/reproducer in which a high signal/noise ratio can be attained for an RF signal. [Means of Solving Problems] Reflected light beam from a disc (6) is divided into three light beams, a zero order light beam and ±first order diffraction light beams by a diffraction optical element (7a). Each light beam is further divided into four light beams by a diffraction optical element (8) which is divided into four regions by two lines passing the optical axis of incident light and respectively being parallel with the radial direction and the tangential direction of the disc (6) before being received by a photodetector (10a). Zero order light beam from the diffraction optical element (7a) is used for detecting a track error signal and an RF signal by a phase difference method or a push-pull method, and ±first order diffraction light beams from the diffraction optical element (7a) is used for detecting a focus error signal by a Foucault method.

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