Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Patent
1998-10-26
2000-12-12
Dinh, Tan
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
369274, 428 644, G11B 724, G11B 584
Patent
active
061607894
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an optical data storage disc.
Optical data storage discs, particularly compact discs (CD's or CD-ROM's), comprise a disc of transparent material formed over one side with a pattern of indentations (or "pits") defining digital data, and this indented side of the disc is provided with a thin coating of reflective material. The digital data is optically "read" from the opposite side of the disc.
In order to increase the density of the data stored on the disc, the indentations must be smaller and more closely packed. It has now been agreed by a major consortium that the thickness of the disc should be reduced in thickness from the usual 1.2 mm, to approximately 0.6 mm: this agreement is with a view to forming discs of very high data density, which require the reduced thickness in order that the indentations can be resolved and optically read. However, the strength and rigidity of the reduced-thickness disc then needs to be restored by adhering a reinforcing disc over its indented side.
We have previously developed techniques for applying holograms to conventional CD's and CD-ROM's, not only as a decoration but more importantly as a protection against counterfeiting. We have now devised techniques for providing high density optical data storage discs (e.g. DVD's--digital versatile discs) with holograms or other optically variable images.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided an optical data storage disc which comprises a first component disc formed over one side with a pattern of indentations defining digital data, the indented side of the first component disc being provided with a reflective coating, and a second component disc bonded to said indented side of the first component disc, said second component disc carrying a surface relief pattern which defines a holographic or other optically variable image.
The surface relief pattern of the second component disc may be formed directly into that side of the second component disc which faces the first component disc. This surface of the second component disc is preferably provided with a reflective coating.
The surface relief pattern may instead be formed into the surface of a coating applied to one side of the second component disc, for example by embossing or by a casting method such as a photo-polymerization process. The coated surface may face towards or away from the first component disc: in the latter case, the coating is further coated with an outer, protective layer. In some cases, the side of the second component disc facing the first component disc may be formed with a second pattern of indentations defining digital data. The two patterns of digital data may be read from opposite sides of the disc: the outer surface of either or both component discs may be formed with a surface relief defining a hologram or other optically variable image, or coated with a layer which is embossed or otherwise formed with such a relief and then coated with a semi-reflective layer.
The first and second component discs are preferably formed by injection moulding, the digital data pattern(s) thus being moulded directly.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:
FIG. 1 is a schematic sectional view, enlarged but not to scale, of an optical data storage disc in accordance with the invention;
FIG. 2 is a similar view of a second optical data storage disc in accordance with the invention;
FIG. 3 is a similar view of a third optical data storage disc in accordance with the invention;
FIG. 4 is a similar view of a fourth optical data storage disc in accordance with the invention;
FIG. 5 is a similar view of a fifth optical data storage disc in accordance with the invention; and
FIG. 6 is a similar view of a sixth optical data storage disc in accordance with the invention.
DETAILED DESCRIPTION OF THE DRAWING AND PREFERRED EMBODIM
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3dcd, L.L.C.
Dinh Tan
Schindler Edwin D.
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