Patent ID: 7151735

Claim:
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 different from the second wavelength; a converging optical system having an objective lens and a diffractive portion; and a photo detector for receiving light flux reflected from the first information recording plane or the second information recording plane; wherein first and second predetermined numerical apertures for the first light flux and the second light flux at an image side of the objective lens are provided for the first and second optical information recording media respectively, and the first predetermined numerical aperture for the first light flux is different from the second numerical aperture for the second light flux; wherein in case that the first light flux passes through the diffractive portion 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 the diffractive portion 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; and wherein a diffracting efficiency at the diffractive portion for the first nth ordered diffracted ray of the first light flux is A % and a diffracting efficiency for another ordered diffracted ray of the first light flux is B %, the diffracting efficiencies satisfy the following formula: A−B≧10, and a diffracting efficiency at the diffractive portion for the second n-th ordered diffracted ray of the second light flux is A′ % and a diffracting efficiency for another ordered diffracted ray of the first light flux is B′ %, the diffracting efficiencies satisfy the following formula: A′−B′≧10.