| 摘要 |
A pick-up of an optical disc system without an angle control of the sub beam is provided to remove the necessity of controlling a diffraction lattice. In a process for generating the alternating current component as a tracking error signal, when a beam crosses a track, the beam is condensed/reflected at the specific positions, and then the reflected beam is diffracted. When a center beam is coincided with the land, a beam diffraction pattern is represented symmetrically. When the center beam is positioned between a groove and the land, the difference between the sub beam signals is generated and the left and right sides of the diffraction pattern are asymmetrical.
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