Patent ID: 7061691
Filing Date: 2006-06-13
Classification: G02B,G11B

Abstract:
1. A focus error signal production method for irradiating light upon an optical recording medium to obtain focus information of returning light from the optical recording medium, comprising the steps of: condensing light reflected from the optical recording medium using an optical lens; moving the optical lens relative to the optical recording medium, wherein said optical lens comprises: a substrate made of an optical material that has a continuous flat face on a first side through which an axis in a focus direction of said optical lens passes; and a convex element formed integrally with the substrate, configured such that a first focal length on a first cross section including the axis in the focus direction of the optical lens and a second focal length on a second cross section perpendicular to the first cross section and intersecting with the first cross section along the axis in the focus direction are different from each other; wherein said convex element has a convex curved face that protrudes from a second side of said substrate opposite from said first side so as to have a function as an optical lens, and wherein the first focal length is along the axis in the focus direction of the optical lens and the second focal length is along a second cross section that is perpendicular to the first cross section and intersects the first cross section along the axis in the focus direction of the optical lens.