Patent ID: 8432782

Claim:
An objective lens for converging a laser beam emitted from a laser light source on an information recording surface of an information recording medium, the objective lens comprising: a first area which has a diffraction structure which is formed on a surface on the laser light source side; a second area which has a diffraction structure which is formed outside the first area; and a third area which has a diffraction structure which is formed outside the second area, wherein the first area and the third area converge a laser beam having an order of diffraction with which diffraction efficiency is highest, out of laser beams having a wavelength λ 1 (390 nm≦λ 1 ≦430 nm) which are diffracted by the first area and the third area, on an information recording surface of a first information recording medium having a light transmission layer with a thickness t 1 , and the first area and the second area converge a laser beam having an order of diffraction with which diffraction efficiency is highest, out of laser beams having a wavelength λ 2 (630 nm≦λ 2 ≦680 nm) which are diffracted by the first area and the second area, on an information recording surface of a second information recording medium having a light transmission layer with the thickness t 2 , which is greater than the thickness t 1 , the diffraction efficiency of the laser beam having the wavelength λ 2 , which is diffracted by the second area and converges on the information recording surface of the second information recording medium, is greater than the diffraction efficiency of the laser beam having the wavelength λ 1 , which is diffracted by the second area, and converges on the information recording surface of the first information recording medium, and the second area does not converge a laser beam having an order of diffraction with which diffraction efficiency is highest, out of the laser beams having the wavelength λ 1 which are diffracted by the second area, on the information recording surface of the first information recording medium, and converges a laser beam having an order of diffraction which is different from the order of diffraction with which diffraction efficiency is highest, out of the laser beams having the wavelength λ 1 which are diffracted by the second area, on the information recording surface of the first information recording medium.