| 摘要 |
<p>It is an object of the present invention to realize stable tracking control even in a structure including an objective lens (25) whose center is offset from a central line (21) extending from the central axis of an optical disk in the direction of the axis along which an optical pick-up is moved. An optical pick-up of the present invention includes a second optical system (2) having (i) a light source (21) for emitting a beam, (ii) a second diffraction grating (23) for splitting, into three beams MB, SB1, and SB2, the beam emitted from the light source, (iii) a second objective lens (25) for converging the three beams on an optical disk, and (iv) a photodetector (28) for detecting a push-pull signal from reflected light obtained by reflecting the three beams. The second objective lens is placed in an offset position offset from a central line. The second diffraction grating has a lattice structure plane that gives a phase difference to a light beam passing through the second diffraction grating, and the lattice structure plane is designed so that the amplitude of a push-pull signal detected from reflected light obtained by reflecting SB1 and SB2 is substantially 0.
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