Patent ID: 6646817
Filing Date: 2003-11-11
Classification: G11B

Abstract:
An objective lens, consisting of two lenses disposed in a luminous flux, for carrying out focusing on two optical recording media having different thicknesses from each other,wherein said two lenses are constituted by respective materials different from each other; wherein said two lenses satisfy the following conditional expressions (1) and (2) respectively with respect to wavelengths &lgr;1 and &lgr;2 of light: N1(&lgr;1)â‰…N2(&lgr;1)â€ƒâ€ƒ(1) N1(&lgr;2)â‰ N2(&lgr;2)â€ƒâ€ƒ(2) whereN1(&lgr;1) is the refractive index of the first lens with respect to wavelength &lgr;1 of light; N1(&lgr;2) is the refractive index of the first lens with respect to wavelength &lgr;2 of light; N2(&lgr;1) is the refractive index of the second lens with respect to wavelength &lgr;1 of light; and N2(&lgr;2) is the refractive index of the second lens with respect to wavelength &lgr;2 of light; wherein approximately equal to in equation (1) is defined as values equal to or less than 0.00057; wherein each lens surface has a form configured so as to suppress aberration in said objective lens as a whole, and wherein said wavelength &lgr;1 is used for one optical media and said wavelength &lgr;2 is used for another optical media.