Patent ID: 7548383

Claim:
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): L c =( L 0 +L n )/2 (1), wherein L 0 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 L n 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.