Patent ID: 7286463

Claim:
An objective lens for focusing light from a light source onto optical recording media, the objective lens comprising, in order from the light source side along an optical axis: an objective lens element that includes a diffractive surface on at least one side; wherein the objective lens is configured to receive a collimated light beam of a first wavelength λ 1 on its light source side and to focus diffracted light of a particular order diffracted by the diffractive surface of the objective lens element with highest diffraction efficiency onto a desired portion of a first optical recording medium, to receive a collimated light beam of a second wavelength λ 2 on its light source side and to focus diffracted light of a particular order diffracted by the diffractive surface of the objective lens element with highest diffraction efficiency onto a desired portion of a second optical recording medium, and to receive a diverging light beam of a third wavelength λ 3 on its light source side and to focus diffracted light of a particular order diffracted by the diffractive surface of the objective lens element with highest diffraction efficiency onto a desired portion of a third optical recording medium; the particular order of highest diffraction efficiency of diffracted light is the same for light beams of two of the three wavelengths and different from the particular order of highest diffraction efficiency of the light beam of the other one of the three wavelengths; and the following conditions are satisfied: λ 1 <λ 2 <λ 3 WDs/f≧ 0.46 t/f≦ 0.70 where WDs is the shortest working distance from the recording medium side of the objective lens element to the objective lens side of the recording medium among the three working distances for the three wavelengths λ 1 , λ 2 , and λ 3 ; f is the focal length of the objective lens element for the wavelength λ 1 ; and t is the on-axis thickness of the objective lens element.