Patent ID: 7460460
Filing Date: 2008-12-02
Classification: G11B

Abstract:
1. An objective optical system for use in an optical pickup apparatus for converging a first parallel light flux with a diameter φ 1 and a first wavelength λ 1 on an information recording surface of a first optical disk having a protective layer with a thickness t 1 within a numerical aperture NA 1 , and converging a second parallel light flux with a diameter φ 2 (φ 2 <φ 1 ) and a second wavelength λ 2 (λ 2 >λ 1 ) on an information recording surface of a second optical disk having a protective layer with a thickness t 2 (t 2 >t 1 ) within a numerical aperture NA 2 (NA 2 <NA 1 ), the objective optical system comprising: a first lens group having a phase structure; and a second lens group, wherein the first lens group and the second lens group are arranged in the objective optical system in this order from a longer conjugate distance side of the objective optical system, and the objective optical system satisfies following expressions: where W W M is a magnification of the second lens group when W W W wherein each of W W each of W wherein the objective optical system further satisfies where P P wherein the objective optical system further satisfies following expressions: where W W where W W W W