| 摘要 |
PROBLEM TO BE SOLVED: To perform recording and reproducing by one pickup device with respect to optical disks having different recording densities and thickenesses by selectively diffracting beams according to polarization states to adjust the numerical aperture of an objective lens. SOLUTION: The recording and reproducing of optical disks having different recording densities and thicknesses are performed by applying a liquid crystal plate 15 performing the action converting the polarization states of beams and a polarizing hologram 16 and by changing the numerical aperture NA of an objective lens 17 properly. Besides, beams converted into parallel lights by a collimating lens 13 are focused on an optical disk D while being made to have a prescribed beam size. The beam size is made different according to the size of beams made incident on the objective lens 17. Consequently, the recording and reproducing of respective disks having different recording deinsities and thicknesses can be performed by changing the numerical aperture properly. |
