Adaptive aberration compensation in high NA optics

Two approaches have been proposed for achieving 25-50 Gbyte capacity on one side of a 120 mm disc: using a two-element high numerical-aperture (NA) objective and using a dual-layered disc. One of the problems with these approaches is that an error in the cover-layer thickness of only a few microns can lead to serious spherical aberration. (SA). This is a particularly serious problem in dual-layered discs due to the distance between the two recording layers. Another problem is the narrow working distance (WD) of the two-element objective lens, which can result in the lens crashing onto the disc. To overcome these problems, we previously described accurate detection of and dynamic compensation for SA (Jpn. J. Appl. Phys., 40, 2001, and Proc. of SPIE, 4342, 2002) and a single-element high NA objective with a wide WD (Tech. Dig. of ISOM, 2001). In this paper, we review our related previous work and describe the latest advances.