Patent ID: 6636365
Filing Date: 2003-10-21
Classification: G11B

Abstract:
An optical pickup apparatus for conducting recording or reproducing, or both, information of a first optical information recording medium equipped with a first transparent plate having a thickness of t1 and a second optical information recording medium equipped with a second transparent plate having a thickness of t2, wherein t1 is less than t2, comprising:a first light source to emit a first light flux having a wavelength of &lgr;1 to the first optical information recording medium so as to conduct recording or reproducing, or both, information of the first optical information recording medium; a second light source to emit a second light flux having a wavelength of &lgr;2, wherein &lgr;1 is less than &lgr;2, to the second optical information recording medium so as to conduct recording or reproducing, or both, information of the second optical information recording medium; a converging optical system including a single objective lens made of a plastic material and converging the first light flux onto a recording surface of the first optical information recording medium or the second light flux onto a recording surface of the second optical information recording medium through the respective transparent plate; and a diaphragm having an aperture used for both of the first and second optical information recording medium; wherein a diffractive section including a plurality of ring-shaped zones is provided on at least one side surface of the objective lens within an effective diameter of the one side surface, the diffractive section has a continuous basic aspheric surface, the pitch of the plurality of ring-shaped zones becomes gradually small from the optical axis to a point h within the effective diameter and the pitch increases at the point h; wherein at the time of conducting recording or reproducing information of the first optical information recording medium, an aberration of the first light flux having passed through the diffractive section is corrected lower than a diffraction limit; wherein in a forward optical system from the second light source to the recording surface of the second information recording medium at the time of conducting recording or reproducing information of the second optical information recording medium, the second light flux has a spherical aberration discontinuous portion at the point h where a spherical aberration-stepped amount is 7 &mgr;m to 40 &mgr;m, an aberration of a partial light flux of the second light flux having passed through an inner part of the diffractive section inside of the point h is corrected lower than a diffraction limit, and a spherical aberration of a light ray of the second light flux having passed through the outermost portion of the aperture of the diaphragm is 7 &mgr;m to 40 &mgr;m.