OPTICAL REGISTRATION MEDIUM WITH DUAL INFORMATION LAYER

摘要

A read-only optical registration medium (2) which sucessively comprises: a transparent substrate (4); a first registration surface (S1) containing localised level variations representing binary data bits; a protective layer (16), whereby: between the substrate (4) and the first registration surface (S1), the medium (2) further comprises a dielectric trilayer (8) which contains a first (81), second (82) and third (83) dielectric layer having respective refractive indices n1, n2 and n3, whereby, at both a first wavelength gamma 1 and a second wavelength gamma 2: n2 < n1 and n2 < n3, the trilayer (8) being constituted so as to be transparent at gamma 1 and to be semireflective at gamma 2; the surface of the trilayer (8) nearest the substrate (4) contains localised level variations representing binary data bits, thereby forming a second registration surface (S2). An alternative embodiment is also shown.