Patent ID: 7221492
Filing Date: 2007-05-22
Classification: G11B

Abstract:
1. An optical scanning device ( 1 ) for scanning an information layer ( 4 ) of an optical record carrier ( 2 ), the device ( 1 ) comprising a radiation source ( 11 ) for generating a radiation beam ( 12 , 15 , 20 ) and an objective system ( 18 ) for converging the radiation beam on the information layer, the information layer being covered by a transparent layer ( 3 ) of thickness t d and refractive index n d , the objective system being characterized in comprising a lens having a protection device projecting away from the lens towards the optical record carrier such that in use the distance between the protection device and the optical record carrier is less than the free working distance, the lens satisfying the condition: where t is the thickness of the lens, D is the entrance pupil diameter, FWD is the free working distance, and D, FWD, t and t