Optical registration medium with dual information layer

Abstract

A read-only optical registration medium which successively includes: a transparent substrate; a first registration surface containing localized level variations representing binary data bits; a protective layer, whereby: between the substrate and the first registration surface, the medium further includes a dielectric trilayer which contains a first, second and third dielectric layer having respective refractive indices n.sub.1, n.sub.2 and n.sub.3, whereby, at both a first wavelength .lambda..sub.1 and a second wavelength .lambda..sub.2 : n.sub.2 <n.sub.1 and n.sub.2 <n.sub.3, the trilayer being constituted so as to be transparent at .lambda..sub.1 and to be semi-reflective at .lambda..sub.2 ; the surface of the trilayer nearest the substrate contains localized level variations representing binary data bits, thereby forming a second registration surface. An alternative registration medium according to the invention successively includes: a substrate (4); a first registration surface containing localized level variations representing binary data bits; a transparent protective layer, whereby: between the protective layer and the first registration surface, the medium further includes a dielectric trilayer which contains a first, second and third dielectric layer having respective refractive indices n.sub.1, n.sub.2 and n.sub.3, whereby, at both a first wavelength .lambda..sub.1 and a second wavelength .lambda..sub.2 : n.sub.2 <n.sub.1 and n.sub.2 <n.sub.3, the trilayer being constituted so as to be transparent at .lambda..sub.1 and to be semi-reflective at .lambda..sub.2 ; the surface of the trilayer nearest the protective layer contains Iocalized level variations representing binary data bits, thereby forming a second registration surface.

Dependencies are inferred from the claim text.