Optical disc

Abstract

An optical disc comprises a disc substrate having a groove and a land, and a recording layer formed thereon through a transparent film. In such an optical disc, when a width of a land on a flat surface of the disc substrate is W.sub.L, a width of the groove is W.sub.G, an average angle of inclination of a side wall of the groove is .theta., and a film thickness of a transparent film on a flat surface of the disc substrate is D.sub.U, the average angle of inclination .theta. of a side wall of the groove is 50.degree. or more and, at the same time, a condition of D.sub.U (1-cos .theta.)/2 sin .theta..ltoreq.W.sub.G -W.sub.L .ltoreq.4D.sub.U (1-cos .theta.)/sin .theta. is satisfied. By satisfying such conditions, not on a flat surface of the disc substrate, but at a position of a recording layer, symmetry of a groove portion and a land portion can be enhanced. Therefore, in an optical disc of a land/groove recording/reproducing type, a recording condition of a mark row onto a land and reproducing signal quality and a recording condition of a mark row onto a groove and reproducing signal quality can be made uniform.

Dependencies are inferred from the claim text.