Patent ID: 7483358
Filing Date: 2009-01-27
Classification: G11B

Abstract:
1. An objective lens for use in an optical pickup apparatus which conducts reproducing and/or recording information for a first optical information recording medium having a first protective substrate with a first thickness t 1 by using a first light flux having a wavelength λ 1 from a first light source, conducts reproducing and/or recording information for a second optical information recording medium having a second protective substrate with a second thickness t 2 (t 1 ≦t 2 ) by using a second light flux having a wavelength λ 2 (λ 1 <λ 2 ) from a second light source, and conducts reproducing and/or recording information for a third optical information recording medium having a third protective substrate with a third thickness t 3 (t 2 ≦t 3 ) by using a third light flux having a wavelength λ 3 (λ 2 <λ 3 ) from a third light source, the objective lens comprising: at least one optical surface including at least two regions of a common region and a peripheral region located at a peripheral side than the common region in which the common region corresponds to a portion within a numerical aperture NA where NA NA NA wherein a diffractive structure constructed by plural coaxial ring-shaped zones is formed on the common region, and when n1 is a diffraction order of a diffracted ray having a maximum light amount among diffracted rays of the first light flux generated when the first light flux having the wavelength λ n2 is a diffraction order of a diffracted ray having a maximum light amount among diffracted rays of the second light flux generated when the second light flux having the wavelength λ n3 is a diffraction order of a diffracted ray having a maximum light amount among diffracted rays of the third light flux generated when the third light flux having the wavelength λ the following formulas are satisfied: the objective lens converges n1-th order diffracted ray of the first light flux generated at the common region onto an information recording plane of the first optical information recording medium to conduct reproducing and/or recording information for the first optical information recording medium, the objective lens converges n2-th order diffracted ray of the second light flux generated at the common region onto an information recording plane of the second optical information recording medium to conduct reproducing and/or recording information for the second optical information recording medium, and the objective lens converges n3-th order diffracted ray of the third light flux generated at the common region onto an information recording plane of the third optical information recording plane of the third optical information recording plane of the third optical information recording medium to conduct reproducing and/or recording information for the third optical information recording medium.