Patent ID: 7034974
Filing Date: 2006-04-25
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 , 17 , 20 ) and an objective system ( 18 ) for converging the radiation beam on the information layer, the objective system ( 18 ) being characterised in that the ratio of the root mean square of the optical path difference's (OPD's) generated by the objective system at oblique beam entrance to the system satisfies the condition: within the field of the objective system ( 18 ), where OPD(A31) is the contribution of the third order Zernike coma to the root mean square wavefront aberration and OPD(A51) is the contribution of the fifth order Zernike coma to the root mean square wavefront aberration.