Patent ID: 8169878
Filing Date: 2012-05-01
Classification: G02B,G11B

Abstract:
1. An objective optical element for use in an optical pickup apparatus, the optical pickup apparatus comprising: a first light source for emitting a first light flux having a first wavelength λ a second light source for emitting a second light flux having a second wavelength λ a third light source for emitting a third light flux having a third wavelength λ conducting recording and/or reproducing information using the first light flux for a first optical disk having a protective substrate with a thickness t1, conducting recording and/or reproducing information using the second light flux for a second optical disk having a protective substrate with a thickness t2 (t1≦t2), and conducting recording and/or reproducing information using the third light flux for a third optical disk having a protective substrate with a thickness t3 (t2>t3), the objective optical element comprising: a most peripheral area surround the peripheral area, wherein the central area comprises a first optical path difference providing structure, the peripheral area comprises a second optical path difference providing structure, wherein the objective optical element converges the first light flux which passes through the central area of the objective optical element onto the information recording surface of the first optical disk so that the optical pickup apparatus can record and/or reproduce information on the information recording surface of the first optical disk, the objective optical element converges the second light flux which passes through the central area of the objective optical element onto the information recording surface of the second optical disk so that the optical pickup apparatus can record and/or reproduce information on the information recording surface of the second optical disk, the objective optical element converges the third light flux which passes through the central area of the objective optical element onto the information recording surface of the third optical disk so that the optical pickup apparatus can record and/or reproduce information on the information recording surface of the third optical disk, the objective optical element converges the first light flux which passes through the peripheral area of the objective optical element onto the information recording surface of the first optical disk so that the optical pickup apparatus can record and/or reproduce information on the information recording surface of the first optical disk, and the objective optical element converges the second light flux which passes through the peripheral area of the objective optical element onto the information recording surface of the second optical disk so that the optical pickup apparatus can record and/or reproduce information on the information recording surface of the second optical disk, the objective optical element converges the first light flux passing through the most peripheral area of the objective optical element onto the information recording surface of the first optical disk so that the optical pickup apparatus can record and/or reproduce information for the first optical disk, and wherein the first optical path difference providing structure comprises a first basic structure and a second basic structure which overlap with each other, the first basic structure is an optical path difference providing structure which: wherein the third light flux which has passed through the first optical path difference providing structure forms a first best focus in which the third light flux forms a spot having a smallest diameter, and the third light flux which has passed through the first optical path difference providing structure forms a second best focus in which the third light flux forms a spot having a second smallest diameter, and the first best focus and the second best focus satisfy a following expression: where f (mm) is a focal length of the objective optical element for the third light flux which passes through the first optical path difference structure and forms the first best focus, and L (mm) is a distance between the first best focus and the second best focus.