| 摘要 |
PROBLEM TO BE SOLVED: To reproduce a CD and a DVD with one objective lens by changing polarization directions of a light beam, changing transmission/ interception of the light beam by a polarization plate and changing diameter of an entrance pupil of the objective lens. SOLUTION: The ring-like polarization plate 15 and a discoid thin plate 16 are set in shape to make a numerical aperture NA a comparatively large value, for example, 0.6 when an objective lens part 10 is used as the objective lens part for the DVD and to make the NA a comparatively small value, for example, 0.43 when the objective lens part 10 is used for the CD, and also an electromanget is on/off-controlled in accordance with a kind of the disk 4 as to whether it is the CD or the DVD. Then, a polarization plane of each light beam and return light beam to be incident on a Faraday element 8 is rotated at 90 deg. or transmitted at 0 deg. without rotation. Consequently, information can be read out of either of the disks. |
