Patent ID: 7957231

Claim:
An optical pick-up apparatus, comprising: a first light source for emitting a first light flux having a wavelength λ 1 ; a second light source for emitting a second light flux having a wavelength λ 2 (λ 2 >λ 1 ); a third light source for emitting a third light flux having a wavelength λ 3 (λ 3 >λ 2 ); and a light converging optical system for converging the first light flux on an information recording surface of a first optical information recording medium whose protective substrate thickness is t 1 , for converging the second light flux on an information recording surface of a second optical information recording medium whose protective substrate thickness is t 2 (t 1 <t 2 ), and for converging the third light flux on an information recording surface of a third optical information recording medium whose protective substrate thickness is t 3 (t 2 <t 3 ), so that the optical pick-up apparatus conducts recording and/or reproducing information by converging light flux from a light source on an information recording surface of an optical information recording medium through the light converging optical system; the light converging optical system comprising: an objective optical element commonly used for the first to the third optical information recording media and being a single lens which has a first phase structure, a second phase structure, and an aspheric surface on at least one surface thereof; a coupling lens independently or commonly used for each of the first to the third light sources such that a light flux emitted from at least the first light source enters as an infinite parallel light flux into the objective optical element and a light flux emitted from the second and third light sources enters as an infinite parallel light flux or a weak finite divergent light flux into the objective optical element; and a correcting element arranged in an optical path on which a light flux emitted from at least the first light source passes to arrive the objective optical element; wherein a light flux emitted from the first light source forms a converged spot on the information recording surface of the first optical information recording medium by only a refraction action of the aspheric surface, or by a combination of the refraction action and an optical action given by at least one of the first phase structure and the second phase structure, a light flux emitted from the second light source forms a converged spot on the information recording surface of the second optical information recording medium by a combination of a refraction action of the aspheric surface and an optical action given by at least one of the first phase structure and the second phase structure, and a light flux emitted from the third light source forms a converged spot on the information recording surface of the third optical information recording medium by a combination of a refraction action of the aspheric surface and an optical action given by at least one of the first phase structure and the second phase structure.