Optical pickup apparatus, objective lens, apparatus for reproducing and/or recording optical information recording medium

An optical pickup apparatus for conducting reproducing or recording information of at least two kinds of optical information recording media, comprising:

• a first light source to emit first light flux having a first wavelength to conduct reproducing or recording information of a first optical information recording medium having a first transparent base board;
• a second light source to emit second light flux having a second wavelength to conduct reproducing or recording information of a second optical information recording medium having a second transparent base board;
• an optical converging system having at least one optical element;
• and
• a photo detector to receive and detect light transmitting through or reflecting from a first information recording surface of the first optical information recording medium or light transmitting through or reflecting from a second information recording surface of the second optical information recording medium;
• wherein the first wavelength is different from the second wavelength and the thickness of the first transparent base board is different from that of the second transparent base board,
• wherein the optical element comprises a first region including an optical axis and a second region adjoining the first region and locating at the outside of the first region, the first region is a refractive surface and the second region is a diffractive surface,
• wherein when the first light flux passes through the second region of the optical element, the light amount of n-th order diffracted ray of the first light flux is larger than that of any other order diffracted ray of the first light flux, and when the second light flux passes through the second region of the optical element, the light amount of n-th order diffracted ray of the second light flux is larger than that of any other order diffracted ray of the second light flux, where n is an integer except 0,
• wherein the optical converging system converges the first light flux having passed through the first region and the n-th order diffracted ray of the first light flux having passed through the second region through the first transparent base board onto the first information recording surface so as to conduct reproducing or recording information of the first optical information recording medium, and the optical converging system converges the second light flux having passed through the first region through the second transparent base board onto the second information recording surface so as to conduct reproducing or recording information of the second optical information recording medium.