Patent ID: 8488434
Filing Date: 2013-07-16
Classification: G11B

Abstract:
1. An objective lens configured to focus a first laser beam having a first wavelength on an information recording layer of a first optical disc, focus a second laser beam having a second wavelength longer than the first wavelength on an information recording layer of a second optical disc, and focus a third laser beam having a third wavelength longer than the first and second wavelengths on an information recording layer of a third optical disc, the objective lens comprising: a first shared region that is a region arranged in a center portion of the objective lens and configured to focus plural ones of the first laser beam, the second laser beam, and the third laser beam on the information recording layers of corresponding optical discs, the first shared region comprising a first annular zone step; and a second shared region that is a region arranged outside the first shared region and configured to focus plural ones of the first laser beam, the second laser beam, and the third laser beam on the information recording layers of corresponding optical discs, the second shared region comprising a second annular zone step, wherein a step amount of the first annular zone step of the first shared region is larger than a step amount of the second annular zone step of the second shared region, the second shared region is configured to focus the second laser beam and the third laser beam on the information recording layers of the corresponding optical discs, and the step amount of the second annular zone step is set such that aberrations occurring in the second laser beam and the third laser beam focused by the second shared region are smaller than 0.3λ.