Optical pickup apparatus, recording/reproducing apparatus provided with the optical pickup apparatus, optical element, and information recording/reproducing method

An optical pickup apparatus, comprising:

• a first light source for emitting a first light flux having a first wavelength for reproducing or recording information from or onto a first optical information recording medium having a first information recording plane;
• a second light source for emitting a second light flux having a second wavelength for reproducing or recording information from or onto a second optical information recording medium having a second information recording plane, the first wavelength being shorter than the second wavelength;
• a converging optical system comprising an objective lens and a diffraction surface;
• and
• a photo detector for receiving light flux reflected from the first information recording plane or the second information recording plane;
• wherein in case that the first light flux passes through at least a part of the diffraction surface to generate at least one diffracted ray, an amount of first n-th ordered diffracted ray of the first light flux is greater than that of any other ordered diffracted ray of the first light flux, and in case that the second light flux passes through at least a part of the diffraction surface to generate at least one diffracted ray, an amount of second n-th ordered diffracted ray of the second light flux is greater than that of any other ordered diffracted ray of the second light flux, where n stands for an integer other than zero;
• wherein the converging optical system converges the first n-th ordered diffracted ray of the first light flux on the first information recording plane of the first optical information recording medium through a first transparent substrate so as to reproduce or record information from or onto the first optical information recording medium;
• wherein the converging optical system converges the second n-th ordered diffracted ray of the second light flux on the second information recording plane of the second optical information recording medium through a second transparent substrate so as to reproduce or record information from or onto the second optical information recording medium, a thickness of the first transparent substrate being thinner than a thickness of the second transparent substrate;
• wherein in case that the converging optical system converges the first n-th ordered diffracted ray of the first light flux on the first information recording plane of the first optical information recording medium, a graph of a spherical aberration corresponding to the objective lens has no discontinuing section within NA1 which is a predetermined numerical aperture of the first optical information recording medium for the first light flux at an image side of the objective lens, and in case that the converging optical system converges the second n-th ordered diffracted ray of the second light flux on the second information recording plane of the second optical information recording medium, a graph of a spherical aberration corresponding to the objective lens has a discontinuing section within the NA1.