Patent ID: 7855944
Filing Date: 2010-12-21
Classification: G11B

Abstract:
1. An optical element for use in an optical pickup device to conduct reproducing and/or recording information for a first disk including a protective substrate having a thickness t 1 by the use of a first light flux having a wavelength λ 1 (nm) emitted from a first light source and to conduct reproducing and/or recording information for a second disk including a protective substrate having a thickness t 2 (t 2 ≧t 1 ) by the use of a second light flux having a wavelength λ 2 (λ 2 >λ 1 ) (nm) emitted from a second light source, the optical element comprising: an optical surface on which a first phase structure is formed to have a function to correct a spherical aberration caused by a difference in thickness of the protective substrate between the first optical disk and the second optical disk or a function to correct a spherical aberration caused by a difference in wavelength between the first light flux and the second light flux; an optical surface on which a second phase structure is formed such that when the wavelength of the first light flux changes, the second phase structure generates a spherical aberration in a direction reverse to a direction of a spherical aberration generated by the first phase structure, wherein the first phase structure is a diffractive structure that generates an n wherein when N wherein the first phase structure has a spherical aberration characteristic such that when a wavelength of an incident light flux shifts to a longer wavelength side, a spherical aberration changes to be under corrected.