| 摘要 |
An optical scanning device (1) is for scanning two information layers (2, 2') with two radiation beams (4) in two operating modes. It comprises a radiation source (7) for emitting the two radiation beams, an objective lens system (8) for converging the two beams on the positions of the two information layers, and a phase structure (24) having an optical axis (19) and including a central part (P1) and at least one marginal part (P2) for forming a non-periodic stepped profile in the radial direction. One (P2) of said central and marginal parts (P1, P2) includes at least two segments (AS2,1, AS2,2) having two different step heights (h2,1, h2,2), respectively, for introducing in said first operating mode two wavefront modifications DeltaW2,1,1 and DeltaW2,2,1, respectively, and in said second operating mode two wavefront modifications DeltaW2,1, 2 and DeltaW2,2,2, respectively, where the difference (DeltaW2,1,2+ DeltaW2,2,2)-(DeltaW2,1,1+ DeltaW2,2,1) is asymmetric.
|
