Optical pickup apparatus and objective optical element

An optical pick-up apparatus, comprising:

• a first light source for emitting a first light flux having a wavelength λ1;
• a second light source for emitting a second light flux having a wavelength λ2 (λ2>λ1);
• a third light source for emitting a third light flux having a wavelength λ3 (λ3>λ2);
• 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 t1, for converging the second light flux on an information recording surface of a second optical information recording medium whose protective substrate thickness is t2 (t1≦t2), and for converging the third light flux on an information recording surface of a third optical information recording medium whose protective substrate thickness is t3 (t2<t3), 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.