| 摘要 |
<p>A hologram (48) as an optical path branching means has two hologram areas (48b, 48c) for diffracting a return light beam to different directions respectively, with a boundary line (48a) between them formed inclined a preset angle to a direction corresponding to the radial direction of an optical disk (11). Light diffracted by one hologram area (48b) is received by the light receiving units (A1, A2) of a photodetector IC (44), and light diffracted by the other hologram area (48c) is received by light receiving units (A3, A4). With such a construction, a positional deviation of an objective (27) encountered upon access to a desired recording track on an optical disk (11) can be detected by determining the difference between a quantity of light received by the light receiving units (A1, A2) of the photodetector IC (44) and that received by the light receiving units (A3, A4).</p> |
