A LENS AND AN OPTICAL SYSTEM, AN OPTICAL HEAD AND AN OPTICAL DISK APPARATUS USING THE LENS AND OPTICAL PICKUP APPARATUS

摘要

The present invention is to make possible the thickness of the transparent substrate is a light beam condensed on the information recording surface with high light use efficiency with respect to each other a plurality of kinds of optical recording media. ; Of DVD substrate (2) having a thickness (t ₁₎ of a 0.6mm DVD is used as the light beam of the number NA = 0.63 beam 4 of the wavelength λ ₁ = 655nm, when the opening device is mounted on the optical disk, DVD substrate 2 It is focused on the information recording surface (2a). In addition, when the optical disk when the thickness (t ₂₎ of the CD substrate 3, the apparatus of the CD is mounted 1.2mm wavelength λ ₂ = 790nm light beam (5) being used effectively as a light flux of the numerical aperture of about 0.45 may, CD substrates ( and light-it converged on the information recording surface (3a) of the three). A wave front aberration due to the difference of the substrate between the DVD and the CD (2, 3) thickness occurs, this is offset by the generation of chromatic aberration due to a difference in wavelength of the light beam (4, 5), even if a difference in thickness of the transparent substrate, respectively It is of the well-converged on the information recording surface (2a, 3a).