Patent ID: 7224662

Claim:
An objective lens for an optical pickup, said optical pickup being capable of converging at least two beams having different wavelengths on data recording surfaces of at least two different optical discs at different numerical apertures, respectively, said objective lens comprising a refractive lens having a positive power, at least one surface of said refractive lens being divided into a central area having a necessary size for transmitting a lower NA beam, which is converged on an optical disc at a lower NA and a peripheral area having a size for transmitting a higher NA beam which is converged on an optical disc at a higher numerical aperture (NA), wherein, when a light beam having a wavelength corresponding to the optical disc requiring the higher NA is converged on the optical disc requiring the higher NA at the higher NA, the phase of light flux passed through said peripheral area is substantially the same as the phase of light flux passed through said central area, wherein, when a light beam having a wavelength corresponding to the optical disc requiring the lower NA is converged on the optical disc requiring the lower NA at the lower NA, the phase of light flux passed through a first annular region included in said peripheral area is different from the phase of light flux passed through said central area, and the phase of light flux passed through a second annular region, which is included in said peripheral area and outside said first region, is substantially the same as the phase of the light flux passed through said central area.