Patent ID: 7606120

Claim:
An objective lens for use in an optical head having a fixed distance between a first laser emitting a laser beam with a wavelength λ 1 and a second laser emitting a laser beam with a wavelength λ 2 being longer than the wavelength λ 1 , the objective lens focusing the laser beam emitted from the first laser on a first optical disk by a first numerical aperture and focusing the laser beam emitted from the second laser on a second optical disk by a second numerical aperture being smaller than the first numerical aperture, wherein wavefront aberration in design for the second optical disk is greater than wavefront aberration in design for the first optical disk, and a ratio t 1 /(t 1 +t 2 ) of a distance t 1 from an optical axis to the first laser and a distance (t 1 +t 2 ) between the first laser and the second laser is smaller than 0.80.