Patent ID: 7266070

Claim:
An objective lens for different optical recording media which, for a selected first optical recording medium, focuses at a first numerical aperture an incident light beam having a first wavelength onto a desired position of the first optical recording medium and, for a selected second optical recording medium, focuses at a second numerical aperture that is smaller than the first numerical aperture, an incident light beam having a second wavelength onto a desired position of the second optical recording medium, said objective lens comprising: at least one surface that is at least partially an aspheric surface that is defined using an equation for an aspheric surface wherein the surface height in the direction of the optical axis becomes discontinuous at a boundary line corresponding to the outer boundary of incident light of the second wavelength that is focused at the second numerical aperture onto a specified position of the second optical recording medium; at least one surface that is at least partially a diffraction optical surface that is defined using one phase difference function, said diffraction optical surface constructed so that a) the light flux of the first wavelength passing through a region of the diffraction optical surface corresponding to tho first numerical aperture is focused onto a specified position of the first optical recording medium by the refractive power of the objective lens and the light diffraction effect of the diffraction optical surface, b) the light flux of the second wavelength passing through the region of the diffraction optical surface that is outside the region that corresponds to the second numerical aperture is not focused onto the specified position of the second optical recording medium by the refractive power of the objective lens and the light diffraction effect of the diffraction optical surface, and c) the light flux of the second wavelength passing through the region of the diffraction optical surface corresponding to the second numerical aperture is focused onto the specified position of the second recording medium by the refractive power of the objective lens and the light diffraction effect of the diffraction optical surface; wherein: the diffraction optical surface and the aspheric surface are jointly formed so as to be superimposed on the same surface; and the phase difference defined by the one phase difference function of the diffraction optical surface is an integer multiple of 2·π where the aspheric surface becomes discontinuous on this same surface.