| 摘要 |
In an optical head apparatus, reflected light from the disk is diffracted by a hologram optical element, and received by an optical detector. A focusing error signal is detected from -1st-order diffracted light of the hologram optical element. A tracking error signal by the differential phase method, a tracking error signal by a push-pull method and the data signal recorded on the disk are detected from +1st-order diffracted light of the hologram optical element. A diffraction efficiency of the +1st-order diffracted light is higher than a diffraction efficiency of the -1st-order diffracted light.
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