| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical pickup device which can properly record/reproduce information to/from an optical disk having a plurality of information recording layers, and to provide an objective lens unit. <P>SOLUTION: An opening limiting element AP can be moved by a driving mechanism DR in the direction of the optical axis of an objective lens OL. Then, NA1≈NA0≈NA2 can be attained by changing the optical axis direction position of the opening limiting element AP in accordance with magnification m, so that a change in a numerical aperture can be suppressed, when the numerical aperture is defined as NA0 when a parallel luminous flux indicated by a solid line is made incident on the object lens OL (m=0), the numerical aperture as NA1 when diverging light indicated by a dotted line is made incident (m>0), and the numerical aperture as NA2 when converging light indicated by a chain line is made incident (m<0). <P>COPYRIGHT: (C)2011,JPO&INPIT |
