Patent ID: 7821904
Filing Date: 2010-10-26
Classification: G11B

Abstract:
1. An objective optical element for use in an optical pickup apparatus which conducts reproducing and/or recording of the information by forming a converged spot on an information recording surface of a first optical information recording medium having a protective substrate thickness t 1 with a first light flux of a wavelength λ 1 emitted from a first light source, conducts reproducing and/or recording of the information by forming a converged spot on an information recording surface of a second optical information recording medium having a protective substrate thickness t 2 (t 1 ≦t 2 ) with a second light flux of a wavelength λ 2 (λ 1 <λ 2 ) emitted from a second light source, and conducts reproducing and/or recording of the information by forming a converged spot on an information recording surface of a third optical information recording medium having a protective substrate thickness t 3 (t 2 <t 3 ) with a third light flux of a wavelength λ 3 (λ 2 <λ 3 ) emitted from a third light source, the objective optical element consisting of a single lens which is commonly used for the first to the third optical information recording media, which has two phase structures of a first phase structure and a second phase structure, and whose at least one surface is an aspheric surface, wherein when the third light flux is incident on at least one of the first phase structure and the second phase structure, the third light flux is separated into two diffracted light fluxes, and the objective optical element is configured to converge a diffracted light flux of the two diffracted light fluxes whose focal position is far from the objective optical element on the information recording surface of the third optical information recording medium, and the third light flux has a light utilizing efficiency less than 50%.