Patent ID: 6807018
Filing Date: 2004-10-19
Classification: G02B,G11B

Abstract:
An objective lens of an optical pick-up which converges a shorter wavelength laser beam on a first optical disc having a thin cover layer and high data density and converges a longer wavelength laser beam on a second optical disc having a thick cover layer and low data density, wherein said objective lens is configured to provide axial astigmatism corresponding to wavefront aberration of 0.01&lgr; [rms] or more when the shorter wavelength laser beam is converged on the first optical disc, and to provide abaxial third order coma so that a sign thereof when the shorter wavelength laser beam is converged on the first optical disc will be opposite to the sign thereof when the longer wavelength laser beam is converged on the second optical disc, in a virtual state in which the optical axis of said objective lens coincides with the normal to the optical disc.