Patent ID: 6775064
Filing Date: 2004-08-10
Classification: G02B,G11B

Abstract:
An objective lens for an optical pick-up configured for use with optical discs of a first format and a second format, the first format having higher information density than the second format, at least one surface of said objective lens being an aspherical surface, said at least one surface being divided into an effective area and an outer area outside said effective area, said effective area and said outer area being formed such that a predetermined gap is caused between a spherical aberration of a light beam passed through said effective area and a spherical aberration of a light beam passed through said outer area, a diffraction lens structure being formed on said at least one surface within said effective area, said outer area being connected with a base curve which is a macroscopic shape of said at least one surface within said effective area, the light beam passed through said effective area forming a beam spot on a predetermined surface of an optical disc, the light beam passed through said outer area being diffused on the predetermined surface in comparison with the beam spot, said effective area including a common area through which light passes for forming a beam spot on optical discs of either the first format or the second format, and an exclusive area through which light passes for forming a beam spot on optical discs of the first format but not the second format.