Objective lens for an optical pickup

摘要

The present invention relates to an objective for an optical disk comprising a single lens, wherein the objective has first and second aspherical surfaces, a numerical aperture (NA) of the objective is equal to or greater than 0.75 and an angle u1' between a highest ray passing through the objective and an optical axis satisfies the following condition: 0.94.K < sin(u1') < 1.06.K and K = (0.60866-0.11.t/f-0.1272.d/f)(0.83+0.2.NA).NA/0.85 where f is a focal length of the objective, t is a thickness along optical axis through center of the objective and d is the thickness of a transmission layer of the optical disk. Further, it relates to an objective for an optical disk which comprises a single lens, wherein an angle between a normal to the first surface at a point where a highest ray enters the first surface and an optical axis is equal to or less than 57 degrees. It also relates to an objective for an optical disc which comprises a single lens, wherein an angle &thetas; between a normal to the surface at a point where a highest ray enters the first surface and an optical axis satisfies the following condition: &thetas; < 57-47.3.(0.85-NA)(degrees). It also relates to an optical pickup, an optical disk writer-reader and an optical disk reader comprising one of the previously described objectives.