Coatings Control Aberration in Optical Pickups

The demand for more-compact optical disk drives in laptops has created a problem: The shorter image-to-object distances result in astigmatism. The solution has been to introduce aberrations into the plastic lenses in the optical pickups, but this can be costly and time-consuming. Kai Man Hung of Sony Precision Engineering Center in Singapore has presented a simpler and more economical plan in the form of antireflection coatings.

Hung, who reported the findings in the Aug. 1 issue of Applied Optics, found that applying a strip of nonrotationally symmetrical coating to aspheric objective lenses of poly(methyl methacrylate) and Zeonex resin can reduce astigmatism by as much as 73 percent. The coatings had a negligible effect on third-order coma and spherical aberration.