| 摘要 |
PURPOSE:To detect a good tracking error signal even from an elliptic light spot, by providing a light selecting means which selects spatially a part of reflected light after passing through a diaphragm lens, and an optical detector. CONSTITUTION:A light beam (m) emitted from a semiconductor laser 13 is made incident on a deflection angle prism 4 through a condenser lens 14, and a reflecting mirror 22, and a light beam (m1) is made incident on an optical detector 19 through a deflecting beam splitter 10, etc. In this case, light made incident on the detector 19 become light spots M1' and M2', and through an optical mask 5, the M2' is shielded and only the incident beam of light M1' is made incident actually. In other words, only the reflected light M1' corresponding to the light spot M1 on an optical disk 1 is made incident on the detector 19. In this way, since it is possible to use only the reflected light of the light spot M1 having a strong light intensity, and a small spot diameter on an information track, out of light spot groups forming an elliptic light spot M, for the detection of the tracking error signal, a good tracking error signal can be obtained.
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