Objective lens for optical write/read head e.g. for optical memory/storage disc equipment, has lens surface divided into exclusion zone for light beam of first numerical aperture and a common zone for light beam of second numerical aperture

摘要

Objective lenses for optical memory disc systems can suffer from spherical aberration even though the objective lens is designed for the minimum spherical aberration with a digital versatile disc (DVD) but is used for information reproduction of a CD, then the spherical aberration can increase so much that information replay is impossible. The lens surface (11) must be divided into an exclusion zone (RE) designed for a high numerical aperture through which a light beam with a first numerical aperture enters, which is required for an optical memory disc with a first recording density, and a common zone (RC) through which enters a light beam having a second numerical aperture, which is smaller than the first.