| 摘要 |
PURPOSE:To ensure proper tracking despite a large displacement degree of an objective lens owing to a tracking drive, by unifying the objective lens and the incident luminous flux and making the reflected light beams passing through the optical axis of the objective lens incident to the center of a photodetecting part. CONSTITUTION:The light is reflected by the 1st polarized beam splitter 30 and transmits through the 2nd splitter 31 to be focused on a disk 6 via a 1/4 wavelength plate 4 and an objective lens 5. The reflected light is made incident to a splitter 31 via an objective lens 5 and the plate 4 and then reflected to be made incident to a photodetecting element 7. For tracking, splitters 30 and 31 and the lens 5 are unified together and then driven in a direction orthogonal to the optical axis of the lens 5. Therefore, no relative displacement is caused between the light made incident to the lens 5 from the right side and the lens 5. Thus the light beam which transmits through the lens 5 along its optical axis among the reflected beams from a disk 6 is always made incident at the center of the element 7. This process ensures the proper tracking although the lens 5 is shifted large by the tracking drive. |
