Patent ID: 8760990
Filing Date: 2014-06-24
Classification: G02B,G11B

Abstract:
1. An objective lens for use in an optical pickup apparatus which comprises a first light source for emitting a first light flux having a first wavelength λ 1 (390 nm≦λ 1 ≦415 nm), a second light source for emitting a second light flux having a second wavelength λ 2 (630 nm≦λ 2 ≦670 nm), and a third light source for emitting a third light flux having a third wavelength λ 3 (760 nm≦λ 3 ≦820 nm), and is configured to record and/or reproduce information for a BD including a protective substrate with a thickness t 1 by using the first light flux, to record and/or reproduce information for a DVD including a protective substrate with a thickness t 2 (t 1 <t 2 ) by using the second light flux, and to record and/or reproduce information for a CD including a protective substrate with a thickness t 3 (t 2 <t 3 ) by using the third light flux; the objective lens being a single lens made of plastic, comprising: an optical surface including at least a central region, an intermediate region surrounding the central region, and a peripheral region surrounding the intermediate region, wherein the central region includes a first optical path difference providing structure and the intermediate region includes a second optical path difference providing structure, wherein the objective lens is configured to converge the first light flux passing through the central region onto an information recording surface of the BD so as to enable to record and/or reproduce information, to converge the second light flux passing through the central region onto an information recording surface of the DVD so as to enable to record and/or reproduce information, and to converge the third light flux passing through the central region onto an information recording surface of the CD so as to enable to record and/or reproduce information; the objective lens is configured to converge the first light flux passing through the intermediate region onto the information recording surface of the BD so as to enable to record and/or reproduce information, to converge the second light flux passing through the intermediate region onto the information recording surface of the DVD so as to enable to record and/or reproduce information, and not to converge the third light flux passing through the intermediate region onto the information recording surface of the CD so as to enable to record and/or reproduce information; and the objective lens is configured to converge the first light flux passing through the peripheral region onto the information recording surface of the BD so as to enable to record and/or reproduce information, not to converge the second light flux passing through the peripheral region onto the information recording surface of the DVD so as to enable to record and/or reproduce information, and not to converge the third light flux passing through the peripheral region onto the information recording surface of the CD so as to enable to record and/or reproduce information, wherein the first optical path difference providing structure has a structure in which at least a first basic structure and a second basic structure are superimposed on each other, wherein the first basic structure is configured to make a light quantity of the first order diffracted light flux of the first light flux having passed through the first basic structure larger than a light quantity of any other order diffracted light flux, to make a light quantity of the first order diffracted light flux of the second light flux having passed through the first basic structure larger than a light quantity of any other order diffracted light flux, and to make a light quantity of the first order diffracted light flux of the third light flux having passed through the first basic structure larger than a light quantity of any other order diffracted light flux, and the first basic structure is a blaze type structure, wherein the second basic structure is configured to make a light quantity of the second order diffracted light flux of the first light flux having passed through the second basic structure larger than a light quantity of any other order diffracted light flux, to make a light quantity of the first order diffracted light flux of the second light flux having passed through the second basic structure larger than a light quantity of any other order diffracted light flux, and to make a light quantity of the first order diffracted light flux of the third light flux having passed through the second basic structure larger than a light quantity of any other order diffracted light flux, and the second basic structure is a blaze type structure, and wherein in the first basic structure, when a wavelength of an entering light flux changes to become longer, a spherical aberration changes in a deficient correction direction, and in the second basic structure, when a wavelength of an entering light flux changes to become longer, a spherical aberration changes in a deficient correction direction.