| 摘要 |
PROBLEM TO BE SOLVED: To enable reproducing an optical disk having different substrate thickness in one optical pickup device, and to make the optical pickup device, the convergent optical system, the objective lens, the reproducing method and the optical disk device simple and compact in structure. SOLUTION: This optical pickup device has the convergent optical system capable of reproducing a 1st optical information recording medium having a transparent substrate of t1 thickness and a 2nd optical information recording medium having a transparent substrate of t2 thickness, and when recording density of the 1st optical information recording medium is denoted as i1, and recording density of a 2nd optical information recording medium as i2 (<i1), while a numerical aperture on the side of the optical information recording medium of the optical system for converging a laser beam of a wavelength λ on the 1st optical information recording medium is denoted as NA0, and a numerical aperture on the side of the optical information recording medium of the optical system capable of reproducing the 2nd optical information recording medium by the laser beam as NA2, optimum wave front aberration in a range of the NA0 at the time of converging the laser beam via the substrate t1 thick is <=0.05λrms, while optimum wave front aberration in a range of the NA2 at the time of converging via the substrate t2 thick is <=0.07λrms. |
