Objective for optical disk, optical pickup, optical disk writer-reader, and optical disk reader

摘要

An objective for an optical disk is made of a single double-sided aspherical lens having a numerical aperture (NA) equal to or greater than 0.75 and capable of minimizing axial aberration, off-axis aberration, surface-to-surface eccentricity aberration, and chromatic aberration.The objective (11) has a first aspherical surface (1). The vertex of the first surface has a radius of curvature R1 defined as follows:where n is a refractive index of the lens, f is a focal length of the lens, t is a thickness along optical axis through the center of the lens and d is the thickness of a transmission layer of the optical disk.