Patent ID: 7061834

Claim:
An optical head comprising a finite or pseudo-finite optical system comprising a light source having astigmatic difference and an objective lens that forms an optical spot on an information recording medium by a light flux emitted from the light source, and an objective lens driving device for driving the objective lens in a radial direction, wherein the optical system has optical properties in that the optical spot has an initial astigmatism on the design optical axis, the direction of the initial astigmatism is a direction in which a back-side line focus is substantially perpendicular to the radial direction of the information recording medium, and astigmatism is generated in the direction in which the initial astigmatism of the optical spot is reduced as the objective lens moves in the direction in which the objective lens is more distant from the design optical axis in the radial direction, and the direction of astigmatism of the optical spot farmed by the objective lens is a direction in which a back-side line focus is substantially perpendicular to the radial direction in the radial direction movement range of the objective lens.