| 摘要 |
PURPOSE:To facilitate assembly and adjustment by achieving focusing by obtaining a focus error signal by placing detectors before and after an image formation position. CONSTITUTION:Laser light from a semiconductor laser 9 is passed through an objective lens 8, a beam splitter 4, a half-wavelength plate 3, and a condenser lens 2 and then reflected by a disk 10 to be focused through a detection system lens 5. When two small photodetectors are provided before and after an image-formation point along the optical axis, both the detectors have a difference in output due to a shaft in image-formation position and on the basis of this difference, feedback to a pickup driving coil is provided to exercise focus control without using any cylindrical lens. |
