Patent ID: 7668065

Claim:
An optical pickup apparatus, comprising: a first light source far 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 and a first transparent substrate; 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 and a second transparent substrate, the first wavelength being different from 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 the 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 the 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 the second transparent substrate so as to reproduce or record information from or onto the second optical information recording medium, wherein the objective lens is made of polyolefin, and wherein following formulas are satisfied: −0.0002/° C.<Δ n/ΔT<− 0.00005/° C. 0.05 nm/° C.<Δλ1 /ΔT< 0.5 nm/° C., where ΔT is a temperature change, Δn is a change in refractive index of the objective lens at the time that the temperature change ΔT takes place, and Δλ1 is a change in wavelength of the first light source at the time that the temperature change ΔT takes place.