Patent ID: 7675823

Claim:
An optical scanning device for scanning an optical record carrier ( 82 ) at a scanning position, the record carrier having an entrance surface ( 120 ) and at least one information layer, the device comprising: a radiation source ( 60 ) for generating a forward radiation beam ( 62 ), an objective system for focusing the radiation beam onto the at least one information layer, the objective system having an exit surface ( 122 ) being arranged in the part of the forward radiation beam between the radiation source and the scanning position and providing for evanescent coupling of the radiation with the optical record carrier across a gap between the exit surface and the entrance surface when the optical record carrier is located in the scanning position, a radiation detector ( 108 ) for detecting a reflected radiation beam coming from the objective system, said reflected radiation beam being a low frequency of and perpendicular polarized to said forward radiation beam, and providing a gap signal representing the width of the gap, characterized in that, the device comprise means ( 72 ) for adjusting the vergence of the forward radiation beam for correcting a focus offset in the device in dependence on the gap signal.