Patent ID: 8310909
Filing Date: 2012-11-13
Classification: 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 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 which records and/or reproduces information with the first light flux on an information recording surface of a first optical disc having a protective substrate with a thickness t an optical surface including a central area, an intermediate area surrounding the central area, and a peripheral area surrounding the intermediate area, wherein the central area includes a first optical path difference providing structure and the intermediate area includes a second optical path difference providing structure, wherein the objective lens converges the first light flux which passes through the central area, onto the information recording surface of the first optical disc so that information can be recorded and/or reproduced on the information recording surface of the first optical disc, the objective lens converges the second light flux which passes through the central area, onto the information recording surface of the second optical disc so that information can be recorded and/or reproduced on the information recording surface of the second optical disc, and the objective lens converges the third light flux which passes through the central area, onto the information recording surface of the third optical disc so that information can be recorded and/or reproduced on the information recording surface of the third optical disc, wherein the objective lens converges the first light flux which passes through the intermediate area, onto the information recording surface of the first optical disc so that information can be recorded and/or reproduced information on the information recording surface of the first optical disc, the objective lens converges the second light flux which passes through the intermediate area, onto the information recording surface of the second optical disc so that information can be record and/or reproduce information on the information recording surface of the second optical disc, and the objective lens does not converge the third light flux which passes through the intermediate area, onto the information recording surface of the third optical disc so that information can be recorded and/or reproduced on the information recording surface of the third optical disc, wherein the objective lens converges the first light flux which passes through the peripheral area, onto the information recording surface of the first optical disc so that information can be recorded and/or reproduced on the information recording surface of the first optical disc, the objective lens does not converge the second light flux which passes through the peripheral area, onto the information recording surface of the second optical disc so that information can be recorded and/or reproduced on the information recording surface of the second optical disc, and the objective lens does not converge the third light flux which passes through the peripheral area, onto the information recording surface of the third optical disc so that information can be recorded and/or reproduced on the information recording surface of the third optical disc, wherein the first optical path difference providing structure comprises a first basic structure and a second basic structure which are overlapped with each other, the first basic structure is ablaze-type structure, a value of X is an odd integer, the second basic structure is a blaze-type structure a value of L is an even integer, and the first basic structure has a paraxial power for the first light flux.