Patent ID: 7414796
Filing Date: 2008-08-19
Classification: G02B,G11B

Abstract:
1. An objective lens for plural types of optical storage medium having transparent substrates of different thickness, the objective lens receiving light beams of different wavelengths, each corresponding to each of the plural types of optical storage medium and having a positive power to condense the light beam onto an information surface on each of the transparent substrates of the plural types of optical storage medium; wherein a lens surface of the objective lens is sectioned into plural aspherical zones having different refractive power radially from an optical axis in a common use region for all the light beams, the plural aspherical zones respectively have a single focal point corresponding to an inherent wavelength of each of the light beams, the focal point corresponding to the inherent wavelength of each of the light beams being arranged in a different position, and the objective lens substantially cancels out spherical aberration caused by a thickness difference between the transparent substrates with chromatic aberration caused by a difference in the wavelength of each of the light beams, by which the objective lens condenses the light beam onto the information surface with a Root Mean Square (RMS) wavefront aberration ratio of: where W