Patent ID: 7733578
Filing Date: 2010-06-08
Classification: G02B,G11B

Abstract:
1. An object lens for plural types of optical storage medium having transparent substrates of different thickness, comprising: an incident surface sectioned into plural aspherical zones each having refractive power in a common use area for all monochromatic lights, so as to cancel out spherical aberration caused by a thickness difference between the transparent substrates with chromatic aberration caused by a difference in wavelength of each of the light beams substantially without using a diffractive lens structure, by which the objective lens condenses the light beam onto an information surface with a Root Mean Square (RMS) wavefront aberration ratio of 1<Wmax<Wmin≦1.8, where Wmax is a maximum RMS wavefront aberration among RMS wavefront aberrations of each of the light beams, and Wmin is a minimum RMS wavefront aberration among RMS wavefront aberrations of each of the light beams, for each of the plural types of optical storage medium.