Patent ID: 7106525

Claim:
An objective lens for an optical pick-up used for converging at least two light beams having different wavelengths on data recording surfaces of at least two optical discs having different recording densities, respectively, a wavelength of a light beam used for a first optical disc is longer than a wavelength of a light beam used for a second optical disc whose recording density is higher than that of the first optical disc, wherein said objective lens has at least one surface on which a plurality of annular zones are formed, wherein said at least one surface is divided into an inner area and an outer area outside the inner area, said inner area having a necessary size for providing a first NA required by the first optical disc, and said outer area having a necessary size for providing a second NA required by the second optical disc and higher than said first NA, wherein, with regard to the light beam used for the second optical disc, an optical path difference generated between at least one of steps formed between adjacent annular zones of said plurality of annular zones within said outer area is lower by a predetermined amount than an integral multiple of the wavelength of the light beam used for the second optical disc, wherein the optical path difference satisfies a condition: ( n− 0.4)≦ OPD/λ<n (1) where OPD is the optical oath difference, λ represents the wavelength of the light beam used for the second optical disc, and n represents a natural number.