Patent ID: 7239459
Filing Date: 2007-07-03
Classification: G11B

Abstract:
1. An optical scanning device for scanning an information layer of an optical record carrier, the device including a radiation source for generating a radiation beam having a wavelength λ and an objective system having a numerical aperture larger than 0.65 for converging the radiation beam on the information layer, the objective system including a first and a second lens both wade of plastic, characterized in that the first and second lens each have a temperature-dependence of the spherical aberration imposed on the radiation beam, the signs of the dependence of the first and second lens being different and the magnitudes of the dependence of the first and second lens being substantially equal such that the temperature-dependence of the spherical aberration of the objective system is reduced to less than 30 mλ OPDrms for a temperature change of 30 K.