| 摘要 |
PURPOSE:To surely and accurately stop an objective lens at its focussing position, by stopping the displacement of the objective lens toward a recording medium when an output obtained by detecting the reflected light of a laser light for detection with a split detector exceeds another output obtained by detecting and amplifying the laser light with a detector and an amplifier. CONSTITUTION:A linear motor 3 and objective lens 10 approach a recording medium 2 through a vertical movement mechanism 19 under the control of a control circuit 21. An optical beam B coming out from a detection laser 11 is split into two parts by a half mirror 24 after passing through a lens 12 and one half of the optical beam B is made incident on a photodetector 25 and the other half of the beam B is converged onto the recording medium 2 of a disk 1 after passing through a polarization beam splitter (PBS)13, lambda/4 wave plate 14, mirror 9, and objective lens 10. The reflected light of the optical beam B advances in the reverse direction and is made incident on a split detector 15. The output of the split detector 15 is compared with the output of the detector amplified by an amplifier 27 at comparators 22 and 23 and, when the output of the split detector exceeds the output of the amplifier 27, the objective lens 10 is surely and accurately stopped at its focussing position through the controller 21. |
