Patent Number: 7,821,902

Title: Aberration detection device and optical pickup device provided with same

Abstract: An aberration detection device of the present invention is such that an absolute value of detection sensitivity of an aberration error signal is increased, and variation in detection sensitivity of the aberration error signal is little even when displacement between the center of light beam dividing means and the center of a bundle of light beams occurs due to a shift of a condensing optical system at the time of tracking control. A hologram element (2) divides light beams reflected from an information storage medium into at least two positive first order diffracted light beams. The hologram element (2) has a line (D1) extending in a radial direction and passing through an optical axis (OZ) and a division line (D2) having segments at least both ends thereof and a bulge in a center thereof, wherein the segments are substantially parallel to the line (D1), and the bulge (44) bulges toward the periphery of the hologram element (2) so that a top (D5) of the bulge (44) is substantially parallel to the line (D1).

Inventors: Ogata; Nobuo (Higashihiroshima, JP)

Assignee: Sharp Kabushiki Kaisha

International Classification: G11B 7/135 (20060101)

Expiration Date: 2018-10-26 0:00:00