| 摘要 |
A pick-up of an optical disc system without an angle control of the sub beam is provided to detect a stable DPP(Differential Push Pull) signal irrespective of position of the sub-beam. A diffraction device within an optical pickup performs defocusing of the sub beam. Two sub beams are used preferably, and an HOE(Holographic Optical Element) is used as a diffraction device. Phases of the main push full signal and the sub push full signal are opposite to each other so that a DPP signal detection is performed irrespective of a track pitch. When the sub push pull signal comprises the direct current component, the sub push pull signal is unrelated to a kind of the track pitch and the position of the sub beam. |
