Patent ID: 7773490
Filing Date: 2010-08-10
Classification: G02B,G11B

Abstract:
1. An optical compensator for use in an optical scanning device for scanning optical record carriers, there being at least two different information layer depths within two different ones of the carriers, the optical record carriers including a first optical record carrier, a second optical record carrier and a third optical record carrier, 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, said first, second and third radiation beams having different predetermined wavelengths, the optical compensator having a non-periodic phase structure through which each of said first, second and third radiation beams is arranged to pass, said non-periodic phase structure including a plurality of stepped annular zones separated by steps, the zones forming a non-periodic radial pattern, the stepped annular zones introducing first, second and third different wavefront modifications into at least part of the first, second and third radiation beams, respectively, wherein said optical compensator includes radial height variations corresponding to at least some of said plurality of stepped annular zones, said radial height variations being arranged such that non-zero contributions are provided to each of said first, second and third wavefront modifications by said optical compensator in parts of the wavefront corresponding to said at least some of said plurality of stepped annular zones.