Patent ID: 6172779
Filing Date: 2001-01-09
Classification: G02B,G11B

Abstract:
An optical pickup device for irradiating 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, comprises:a converging lens section coaxially disposed in an optical axis of the light beam to converge the light beam onto the recording surface; anda hologram lens section coaxially disposed in the optical axis of the light beam to diffract the light beam,wherein said 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 said hologram lens section and converged on said recording surface has a first numerical aperture existing in a direction intersecting a track extending direction and a second numerical aperture existing in the track extending directions,wherein the first numerical aperture is less than the second numerical aperture,wherein said diffraction grating pattern is an oval diffraction grating pattern consisting of a longitudinal parallel-line diffraction grating pattern and two semicircular diffraction grating patterns connected to both ends of the parallel-line diffraction grating pattern which are symmetrically formed with respect to the optical axis of the light beam, andwherein said oval diffraction grating pattern is symmetrically formed with respect to the optical axis of the light beam so as to have a longest width corresponding to the track extending direction which is greater than a shortest width of the pattern corresponding to the direction intersecting the track extending direction within a traverse cross-section of transmitting light beam.