The invention relates to a storage medium for the optical storage and retrieval of information.
In addition, the invention relates to a method of manufacturing a storage medium for the optical storage and retrieval of information and to a record carrier having information written thereon.
The information age has led to an explosion of information available to users. (Personal) computers are omnipresent and connected via a worldwide network of computer networks. The decreasing costs of storing data, and the increasing storage capacities of the same small device footprint, have been key enablers of this revolution. While current storage needs are being met, storage technologies continue to improve in order to keep pace with the rapidly increasing demand.
Media for optical storage of the kind mentioned in the opening paragraph are well known in the art. However, both magnetic and conventional optical data storage technologies, where individual bits are stored as distinct magnetic or optical changes on the surface of a recording medium, are approaching physical limits beyond which individual bits may be too small and/or too difficult to store and/or to distinguish. Inter-pixel or inter-symbol interference is a phenomenon in which intensity at one particular pixel contaminates data at nearby pixels. Physically, this interference arises from the band-limit of the (optical) channel, originating from optical diffraction or from time-varying aberrations in the lens system.
The invention has for its object to provide a storage medium with a higher data density. According to the invention, a medium for optical storage of the kind mentioned in the opening paragraph for this purpose comprises: a substrate, an active layer for retention of data and the active layer being provided with a pre-determined pattern of bit positions.
An active layer in the present description and claims is understood to be a layer in which information can be stored (coded) and changed.
In a conventional one-dimensional (optical) storage medium a single bit row is written along a spiral. In general, the track pitch is chosen large enough to reduce thermal cross talk between neighboring tracks to acceptable levels. In addition, a recording dye layer is or, alternatively, inorganic phase change layers are distributed homogeneously across the medium.
According to the invention the active layer in the storage medium is patterned beforehand such that recording or storing (coding) information in the active layer is possible only at pre-determined positions and with a certain shape. Because the active layer is not homogeneously distributed across the medium but only present at the pre-determined bit positions, (thermal) cross talk between adjacent bit positions is significantly reduced. As a consequence, the density of the bit positions can be increased as compared to the known storage media. When retrieving information from the storage medium, the size of the bit positions can even be smaller than the spot size of the retrieval means. When information is stored (recorded) in the storage medium, the spot size of the storage means, preferably, is such that only the active layer at the desired bit position is activated or de-activated and that the adjacent bit positions are (practically) not affected by the storing means. By employing a patterned recording medium, cross-talk between bit positions is significantly reduced.
Preferably, the substrate of the storage medium is provided with the pre-determined pattern of bit positions. This has the additional advantage that the active layer is provided at the bit positions in the substrate. Patterning the substrate of the storage medium largely facilitates the manufacturing of the storage medium according to the invention.
A method of manufacturing a storage medium for the optical storage and retrieval of information comprises the following steps. As a first step, a substrate is provided with a pre-determined pattern of bit positions. Subsequently, an active layer for retention of data is provided substantially at the location of the bit positions. In a favorable embodiment of the method, a pressing tool is used to generate the predetermined pattern of bit positions. In this manner the possible bit positions are known exactly beforehand. The method of manufacturing may, additionally, provide mirror layers and thermally insulating layers.
A preferred embodiment of the storage medium according to the invention is characterized in that the pre-determined pattern comprises a two-dimensional strip of bit positions. In a conventional one-dimensional (optical) storage medium, a single bit row is written along a spiral employing bit-length encoding as encoding concept. When a pre-determined pattern comprising a two-dimensional strip of bit positions is employed, the preferred encoding concept is bit-position encoding. Preferably, a strip is aligned horizontally and consists of a number of rows and columns. Preferably, code words do not cross boundaries of a strip.
A preferred embodiment of the storage medium according to the invention is characterized in that the pre-determined pattern comprises an at least partial quasi-hexagonal or quasi-square pattern. With a quasi-hexagonal or quasi-square pattern is meant a pattern of bit positions that may be ideally arranged hexagonally or square, respectively. However, small position distortions from the ideal pattern may be present. The number of nearest neighbors is six for the hexagonal pattern whereas it is four for a square pattern. The bit error rate is smaller for the quasi-hexagonal and quasi-square pattern as compared to the known storage medium. The higher packing density of the quasi-hexagonal pattern provides a higher storing efficiency than the quasi-square pattern. The quasi-hexagonal or quasi-square patterns are very suitably employed in a storage medium comprising a two-dimensional strip of bit positions.
The storage medium according to the invention can be a record carrier having information written thereon, e.g. an optical disc, a CD, a CD-Rom, a CD-R, a CD-RW, and a DVD, BD, optical memory cards, and similar products.
Other advantageous further developments are defined in the dependent claims.
The invention will now be explained in more detail with reference to a number of embodiments and accompanying drawing figures in which:
The Figures are purely diagrammatic and not drawn true to scale. Some dimensions are particularly strongly exaggerated for reasons of clarity. Equivalent components have been given the same reference numerals as much as possible in the Figures.
Preferably, the[0] active layer is a recording dye layer (typical for a WORM medium). Preferably, these layers are deposited by conventional techniques such as spin coating, embossing, molding, (photo)lithography, micro-contact printing or vapor deposition. Organic dye layers can be easily patterned. Alternatively, inorganic phase change layers may also be used as re-writable medium. Preferably, the latter layers are deposited by sputtering. Patterning organic dyes is preferred as compared to patterning re-writable rare earth recording layers.
Preferably, the storage medium is provided in the substrate 1 beforehand such that storing information is possible only at the pre-determined position and with a pre-determined shape. In this manner, a storage medium with a relatively high data density is obtained. Preferably, a pressing tool is employed to generate the pre-determined pattern 4 of bit positions 14, 14′, . . . . In this manner the possible bit positions are known exactly beforehand. The pressing tool imprints the pre-determined bit position structure as shown in
Preferably, the scaled distance dc* between centers of the bit positions 14, 14′, . . . is less than 0.84, preferably less than 0.63. The scaled distance dc* is a dimensionless distance. The distance dc (see
dc*=dc/(λ/2NA).
The expression λ/2NA is the so-called MTF cut-off, λ being the wavelength of (laser) light in nm and NA being the numerical aperture of the system. En this manner, dc* is independent from the nature of the readout system. If a system with a blue laser (λ=405 nm) and a NA=0.85 is used, dc is, preferably, less than 200 nm, preferably less than 150 nm.
Similarly, the scaled distance da1* between the active layer at a first bit position and the active layer at an adjacent bit position is less than 0.42, preferably less than 0.3. The scaled distance da1* is a dimensionless distance. The distance da1 (see
da1*=da1/(λ/2NA).
If a system with a blue laser (λ=405 nm) and a NA=0.85 is used, da1 is, preferably, less than 100 nm, preferably less than 70 nm. From experiments, it was found that a very suitable values for dc*≈0.59 and da1*≈0.17. For a system with a blue laser and a NA=0.85 the corresponding distances are dc≈140 nm and da1≈40 nm. The result is a significantly higher bit density for the storage medium according to the invention as compared to the known storage media. Compared to the so-called Blu-ray Disc standard, the physical bit density is increased roughly by a factor or two. By employing a recording medium with pre-determined pattern of bit positions provided with an active layer, writing cross-talk between bit positions is significantly reduced.
When a pre-determined pattern comprising a two-dimensional strip of bit positions as shown in
The sequence of thermal capping and mirror layers can be reversed. This improves the thermal insulation, but puts more stringent demands on the thermal shield layer with regard to its optical properties. In the embodiment of
An additional advantage of the embodiment of
A method of manufacturing the stack shown in
An alternative method of manufacturing the stack shown in
The land-pit contrast in the deposited dye thickness should be as large as possible, which is different from standard recording where the dye is deposited more or less homogeneously on and between the grooves. The patterned medium introduces one new factor into the recording system. In the (standard) case of a homogeneously recording layer, the data structure of the optical properties of the recording medium are selectively introduced during recording. Thereby, a large optical contrast between recorded an unrecorded areas can be easily achieved. In the pre-patterned case, care has to be taken to also achieve the required contrast between written and non-written bits. This can be done, e.g. by using a recording material that is largely transparent in its unwritten state such that the effective reflectivity of the stack is largely determined by the (homogenous) metal layer. Upon writing, the optical properties of the recording material are changed such that the effective reflectivity of the medium is now to a large extend determined by the active medium's properties.
The scope of the invention is not limited to the embodiments. The invention is embodied in each new characteristic and each combination of characteristics. Any reference sign do not limit the scope of the claims. The word “comprising” does not exclude the presence of other elements or steps than those listed in a claim. Use of the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.
Number | Date | Country | Kind |
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1022203 | Dec 2002 | NL | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB03/05445 | 11/20/2003 | WO | 6/16/2005 |