Patent ID: 6411594
Filing Date: 2002-06-25
Classification: G11B

Abstract:
An optical disc for reading and writing data using a laser beam applied via an objective lens provided in an optical disc recording and/or reproduction apparatus, said optical disc comprising:a transparent substrate; a recording layer formed on said transparent substrate; a clamp portion provided at a center portion of said transparent substrate, said clamp portion including a clamp portion surface at a top of said clamp portion and being integrated with said transparent substrate such that said clamp portion and said substrate form a one-piece unitary element; and a hub portion provided on said clamp portion coaxial with said clamp portion, and wherein said hub portion has a through hole into which a spindle shaft of a disc rotation device is inserted and has an outer diameter that is smaller than an outer diameter of said clamp portion; said clamp portion and said transparent substrate outside of said center portion having surfaces different in height so that said recording layer is positioned in the vicinity of a focus position of said objective lens which is at a neutral position.