| US 7,548,383 B2 | ||
| Optical pickup and objective lens used therein | ||
| Katsuhiko Hayashi, Osaka (Japan); Yasuhiro Tanaka, Hyogo (Japan); Michihiro Yamagata, Osaka (Japan); and Kazuhiko Ishimaru, Osaka (Japan) | ||
| Assigned to Panasonic Corporation, Osaka (Japan) | ||
| Filed on Jun. 13, 2007, as Appl. No. 11/808,930. | ||
| Claims priority of provisional application 60/878400, filed on Jan. 04, 2007. | ||
| Claims priority of application No. 2006-163739 (JP), filed on Jun. 13, 2006. | ||
| Prior Publication US 2007/0291619 A1, Dec. 20, 2007 | ||
| Int. Cl. G02B 3/02 (2006.01); G11B 7/135 (2006.01) | ||
| U.S. Cl. 359—719 [369/112.01; 369/112.23] | 10 Claims |
| 1. An optical pickup for focusing a laser light onto a plurality of information recording faces provided in parallel with
each other in an information recording medium, comprising:
a light source which emits the laser light;
an objective lens for focusing the laser light entering the objective lens onto the information recording faces; and
an aberration correction element arranged at a base point located between the light source and the objective lens, a position
of the aberration correction element being configured to be movable on an optical axis from the base point, the aberration
correction element being configured to change a shape of the laser light by moving the position of the aberration correction
element on the optical axis from the base point so that the laser light is focused onto a target information recording face
out of the plurality of information recording faces,
wherein, when the aberration correction element is located at the base point, the objective lens forms a laser light spot
having minimum size at a point in the information recording medium, the point being apart from a light source side surface
of the information recording medium by a distance of Lc defined by an expression (1):
Lc=(L0+Ln)/2 (1),
wherein
L0 is a distance between the light source side surface of the information recoding medium and a nearest information recording
face nearest to the light source side surface; and
Ln is a distance between the light source side surface of the information recording medium and a farthest information recording
face farthest from the light source side surface.
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