Patent ID: 7295508
Filing Date: 2007-11-13
Classification: G11B

Abstract:
1. An optical disc comprising at least: a substrate; a recording layer layered on the substrate and having a single-layer structure or multilayer structure; and a protection layer which is layered on the recording layer and thinner than the substrate and on which a recording or reproducing laser beam is incident, wherein the substrate and the recording layer are formed to satisfy conditions of expressions below: where y expresses displacement in a thickness direction of the optical disc, ni (i=1, 2, 3, . . . , m) expresses a thickness of each of the layers forming the optical disc, m (m≧2) expresses a total number of the layers forming the optical disc, Ei (i=1, 2, 3, . . . , m) expresses a Young's modulus of each of the layers forming the optical disc, e(y) expresses a distortion generated in the optical disc, eo expresses an initial distortion of the optical disc, αi (i=1, 2, 3, . . . , m) expresses an expansion coefficient depending on temperature and/or humidity in each of the layers forming the optical disc, T expresses an amount of change in temperature and/or humidity around the optical disc, θ expresses a warping amount of the optical disc, k expresses a curvature of the optical disc, and 1 expresses a width of an area where the layers forming the optical disc are layered.