We have fabricated a high numerical aperture objective lens that consists of only a single-element. This lens has a large working distance and no assembling procedures in comparison to a two-element objective lens already proposed. We have also developed aberration compensation methods for coma and spherical aberration. Especially, spherical aberration is compensated automatically by using a servo circuit. A signal read-out obtained from a high-density optical disk is demonstrated using this single-element objective lens.
