LENS DESIGN FOR OPTICAL HEAD COMPATIBLE WITH COMPACT-DISK AND DIGITALVERSATILE DISK

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