Optical pickup device including a hologram lens section with an ellipsoidal diffraction grating pattern concentrically and symmetrically formed with respect to an optical axis

摘要

A two-focal-point pickup device capable of suppressing the generation of glitch or bump in reproduced signal. The optical pickup device irradiates a light beam emitted from a light source onto an optical recording medium to form a light spot on a track of a recording surface of the optical recording medium to read the optical recording medium while controlling the position of the light spot relative to the track of the recording surface. The optical pickup device includes a converging lens section coaxially disposed in an optical axis of the light beam to converge the light beam onto the recording surface; and a hologram lens section coaxially disposed in the optical axis of the light beam to diffract the light beam. The hologram lens section has a diffraction grating pattern being formed in such a manner that a first-order diffraction light of the light beam caused by the hologram lens section and converged on the recording surface has a first numerical aperture existing in a direction intersecting the track extending direction and a second numerical aperture existing in the track extending direction. The first numerical aperture is less than the second numerical aperture.