Patent ID: 8040785
Filing Date: 2011-10-18
Classification: G11B

Abstract:
1. An optical disc, comprising: concave and convex marks synchronized with an integral multiple of a channel bit length in accordance with modulated main information; and a reflective film formed on the concave and the convex marks after the concave and convex marks are formed, wherein after the optical disc is produced, continuous or intermittent laser light synchronized with the integral multiple of the channel bit length is irradiated at intervals longer than a longest one of the concave and convex marks in accordance with a spiral track formed in a circumferential direction of the concave and convex marks to change an optical characteristic of the reflective film, thereby forming a recordable mark to record sub-information necessary to reproduce the main information in a superimposition manner, and the width of the recordable mark in a radial direction is narrower than that of the concave and convex marks in a radial direction.