Patent ID: 6992838

Claim:
An objective lens for a DVD/CD compatible optical pickup, said objective lens being a refractive lens having a positive refractive power, said refractive lens including: a first lens surface on which an optical beam having a different wavelength for each of a plurality of optical recording media respectively including transparent substrates of different thicknesses is incident, said first lens surface having a positive refractive power for refracting the optical beam and thus focusing it onto an information recording surface formed on a transparent substrate of an optical recording medium, said first lens surface including a diffractive grating formed thereon over the entire surface thereof, said first lens surface being an aspherical surface satisfying the following condition: - 37 ≺ f Sr ≺ - 28 , where “f” denotes an effective focal distance of the objective lens, and “Sr” denotes a distance along an optical axis of the lens from one point at which an optical beam passing through the optical axis on the last surface of the objective lens meets the lens surface to another point at which an effective optical beam passing through the upper side meets the lens surface; and a second lens surface being an aspherical surface having a positive refractive power for refracting the optical beam and thus focusing it onto the information recording surface formed on the transparent substrate of the optical recording medium.