Analysis of Origin of Offset Seen in Astigma Method when We Read Land-Groove Disk

概要

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When we read a land-groove disk using the astigma method, we notice that the error signal has an offset. This offset makes the astigma method unavailable. We have simulated the focus-error signal using the diffraction theory and found the origin of the offset. The origin of the offset is attributed to the distorted reflected images from both land and groove. Similarly to the case of a dielectric multilayer, we can consider that the land-groove disk has an effective mirror surface which corresponds to the concept of an effective refractive index. The distorted reflected images from both land and groove are caused by the defocus from the effective mirror surface.
2007-01-15