Patent ID: 7701832
Filing Date: 2010-04-20
Classification: G11B

Abstract:
1. An optical scanning device for scanning optical record carriers having information layers at different information layer depths within the carrier, the optical record carriers including a first optical record carrier having an information layer at a first information layer depth d 1 , a second optical record carrier having an information layer at a second information layer depth d 2 and a third optical record carrier having an information layer at a third information layer depth d 3 , wherein d 3 <d 2 <d 1 , the scanning device including a radiation source system for producing first, second and third radiation beams, for scanning said first, second and third record carriers, respectively, the device including a diffraction structure introducing first, second and third, different, wavefront modifications into at least part of the first, second and third, radiation beams, respectively, the diffraction structure being arranged to operate at selected diffraction orders m wherein at least one of the selected diffraction orders m wherein the diffraction structure is arranged such that the following relation holds: