| 摘要 |
PURPOSE:To increase the capacity and density of recording as well as prevent crosstalk by forming light beam guide grooves respectively in the convex track and the concave track and performing tracking about the both tracks by said guide grooves. CONSTITUTION:When a laser light beam 4 is incident on a light beam guide groove 2 with a optical axis 4A normal to the center M of the groove, light is scattered by surfaces exactly mirror image with respect to the optical axis 4A, and each of the right and left halved light detector receives exactly equal amount of light, giving a mirror image curve with respect to the optical axis 4A as shown by curve QR. When the laser beam 4 is incident with its optical axis 4A at the bank A of the groove 2, scattered light is distributed asymmetric with respect to the optical axis 4A, and the right and left halved light detectors receive unequal amount of light, giving a curve PQ. This difference in amount of light received by the halved light detector due to misalignment of the optical axis with the center of the light beam guide groove 2 is fed as the tracking signal for the servo-control. |
