| 摘要 |
PURPOSE:To facilitate the position adjusting work of a photosensor by extracting an output based on the diameter change of a beam spot from a line-shaped photosensor as a focus error signal. CONSTITUTION:A beam emitted from a semiconductor laser 1 is supplied through a diffraction grating 2, a collimator lens 3 and a deflection beam splitter 4 to a disk D. A reflecting beam from a disk D, while a light path is changed by the splitter 4, is reflected by a mirror 7, and made spectral by a beam splitter 10. One side beam comes to RF and a photosensor 11 for tracking. Other side beam is supplied through an astigmatism optical means 12 to a photosensor 13 for focusing. The sensor 13 photodetects a central main beam out of 3 beams. The sensor 13 is made into a CCD line-shaped photosensor, and from the sensor 13, the output based on the diameter change of a beam spot is extracted as a focus error signal. Thus, the position adjustment of the sensor 13 can be facilitated. |
