Lens Design for Optical Head Compatible with Compact Disk and Digital Versatile Disk

This paper describes three approaches to lens design for reading different thickness disks with one optical system. In the case of an optical head using two different objectives with one actuator, the skew adjustments for both lenses are difficult. First we design objective lenses that are coma free against skew adjustment. The method that uses one objective lens with a liquid crystal shutter still results in a spherical aberration of 50 mλ for a 1.2 mm disk. Second, we design the inner area of the lens for a disk thickness of 0.9 mm, and then the spherical aberration becomes half. The third order spherical aberration of the entire aperture is made to be zero. Grating is integrated onto the surface of a dual focus lens, it causes stray light. We propose a grating profile that reduces stray light to one-fifth.