Patent ID: 8477587
Filing Date: 2013-07-02
Classification: G11B

Abstract:
1. An objective optical element for use in an optical pickup apparatus which forms a converged spot on an information recording surface of a first optical information recording medium comprising a protective layer with a thickness of t1, by using a first light flux with a wavelength of λ1 emitted from a first light source, forms a converged spot on an information recording surface of a second optical information recording medium comprising a protective layer with a thickness of t2 (t1≦t2), by using a second light flux with a wavelength of λ2 (λ1<λ2) emitted from a second light source, and forms a converged spot on an information recording surface of a third optical information recording medium comprising a protective layer with a thickness of t3 (t2<t3), by using a third light flux with a wavelength of λ3 (1.9×λ1<λ3<2.1×λ1) emitted from a third light source, the objective optical element comprising: an optical functional surface, wherein the objective optical element is a single lens, an optical functional surface comprises: at least two areas of a central area comprising an optical axis and a peripheral area surrounding the central area, the central area being used for forming the converged spot on each of the information recording surfaces of the first optical information recording medium, the second optical information recording medium, and the third optical information recording medium, and the peripheral area is used for forming the converged spot on only the information recording surfaces of the first optical information recording medium and the second optical information recording medium out of the first optical information recording medium, the second optical information recording medium and the third optical information recording medium, the central area comprises a first central basic structure being a structure in a shape of ring-shaped zones divided by step differences and a second central basic structure being a structure in a shape of ring-shaped zones divided by step differences, where the first central basic structure and the second central basic structure are formed to be overlapped with each other, in the first central basic structure, an a-th order diffracted light flux has a higher light intensity than other order diffracted light fluxes when the first light flux passes through the first central basic structure, a b-th order diffracted light flux has a higher light intensity than other order diffracted light fluxes when the second light flux passes through the first central basic structure, and a c-th order diffracted light flux has a higher light intensity than other order diffracted light fluxes when the third light flux passes through the first central basic structure, and in the second central basic structure, a x-th order diffracted light flux has a higher light intensity than other order diffracted light fluxes when the first light flux passes through the second central basic structure, a y-th order diffracted light flux has a higher light intensity than other order diffracted light fluxes when the second light flux passes through the second central basic structure, and a z-th order diffracted light flux has a higher light intensity than other order diffracted light fluxes when the third light flux passes through the second central basic structure, the peripheral area comprises a first peripheral basic structure being a structure in a shape of ring-shaped zones divided by step differences and a second peripheral basic structure being a structure in a shape of ring-shaped zones divided by step differences, where the first peripheral basic structure and the second peripheral basic structure are formed to be overlapped with each other, in the first peripheral basic structure, an a-th order diffracted light flux has a higher light intensity than other order diffracted light fluxes when the first light flux passes through the first peripheral basic structure, and a b-th order diffracted light flux has a higher light intensity than other order diffracted light fluxes when the second light flux passes through the first peripheral basic structure, and in the second peripheral basic structure, a x-th order diffracted light flux has a higher light intensity than other order diffracted light fluxes when the first light flux passes through the second peripheral basic structure, and a y-th order diffracted light flux has a higher light intensity than other order diffracted light fluxes when the second light flux passes through the second peripheral basic structure, and the a of the a-th order diffracted light flux of the first central basic structure and the a of the a-th order diffracted light flux of the first peripheral basic structure are the same, the b of the b-th order diffracted light flux of the first central basic structure and the b of the b-th order diffracted light flux of the first peripheral basic structure are the same, the x of the x-th order diffracted light flux of the second central basic structure and the x of the x-th order diffracted light flux of the second peripheral basic structure are the same, and the y of the y-th order diffracted light flux of the second central basic structure and the y of the y-th order diffracted light flux of the second peripheral basic structure are the same, and values of the a is one of 1, 3 and 5, and values of the x is one of 2, 4 and 6.