| 摘要 |
PURPOSE:To prevent focus dislocation from being generated and to stabilize the retrieval of an objective address by detecting a focus error signal with an optical detector arranged in the middle of the image forming position of second and third beams along the optical path of both beams, and detecting a tracking error signal with an optical detector to receive a first beam. CONSTITUTION:A reflected beam having a primary light generated in parallel to the track direction of a disk is transmitted by a first reflecting surface 19a and defined as a first beam and a beam to be samely reflected is transmitted by a send reflecting surface 19b and defined as a second beam. A beam to be reflected by the second reflected surface 19b is bent by 90 deg. to the channel direction of the disk on a third reflecting surface 19c and divided so as to be defined as a third beam reflected in the disk side. Then, an optical detector 13 is set in the middle of the image forming position of the second and third beams and the focus error signal is detected. Even when the centers of these second beam and third beam are dislocated from the center of the first beam, the focus error signal can be detected without being affected by a primary diffracting light. Thus, the retrieval of the purpose address can be made stable. |
