EP1668638A1

EP1668638A1 - An optical data carrier

Info

Publication number: EP1668638A1
Application number: EP04727936A
Authority: EP
Inventors: Martin John Richardson; Ronald Ashley Fisher; John David Wiltshire
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-04-16
Filing date: 2004-04-16
Publication date: 2006-06-14
Also published as: WO2004095447A1; GB0308877D0

Abstract

The invention relates to a playing surface (3) of a CD, DVD or the like, in which there are pit areas (1) and land area (2), the pit areas (1) being of reduced effective reflectivity as compared to the land area (2), which reflects substantially all of the light from an incident interrogating laser in a playing device. The depth of the pit area (1) is ideally one quarter of the wavelength of the interrogating laser, so reflected light is out of phase with light reflected from land area (2). By programming the signals and combining the digital and analogue signals, the authenticity of the disc can be checked as the combined signals, when correct act as a switch allowing the playing of the disc. If the combined signal is not correct, the disc will not play. Said analogue are derived from a hologram visible on the data carrying surface.

Description

AN OPTICAL DATA CARRIER

The invention relates to an optical data carrier, particularly compact discs (CDs), iϋgiial versatile discs (DVDs) -or CD-Rorns.

CDs and DVDs have become popular in terms not only of the entertainment industry for audiovisual amusement, but also in the computer industry where they are used to carry programs and other data in audio and audiovisual modes.

However, such products are relatively readily copied, which leads to piracy and counterfeiting, which have become major activities and are often controlled by organised crime.

It is accordingly necessary to protect legitimate producers of CDs and DVDs from unauthorised use of their copyright, and also to try to thwart the activities of criminals.

It is an object of the invention to seek to provide optical data carriers that are not susceptible of abuse as hereinbefore described.

According to a first aspect of the invention there is provided an optical data carrier having an active surface, comprising a holographic image and machine- readable data on the active surface, whereby to provide identification of a carrier as genuine.

Using the invention it is possible to provide a carrier such as a CD or DVD which can be identified as a genuine optical data carrying disc, particularly when the data may comprise a non- visual decryption key. The carrier may comprise pits and lands, and the decryption key may comprise data encryption of a digital mirror image of the holographic image in numerical form

Thus the holographic image may comprise both a hologram and a key which together may comprise a holographic switch device adapted to provide proof of genuineness of the optical data carrier.

The holographic switch device may extend radially of the data carrying surface of the carrier, and the radial extent may be across the full area of the data carrying surface.

Alternatively, the holographic switch device may comprise a discrete part of the area of the data carrying surface, or, again, may comprise part of a decorative or "branded" area of the carrier and being adapted to provide a light diffuser during reading of the carrier.

The total thickness of a structure comprising the holographic switch may be a fraction of the depths of the pits as compared to the area of the lands of the data carrying surface.

The carrier may comprise a holographic latent image exposed at a low level of energy into a photo-resist layer, which is subsequently exposed to a higher level of energy exposure of data (0/1) information of tracks of optically readable data of the carrier.

Suitably, the data pits may be cleared to the substrate of the carrier whilst the holographic data are confined to the limited modulation of the land surface. The carrier may include sequentially a layer of holograpically exposed hardened Silver Gelatine, or pure hardened Gelatine, and a layer of photoresist which has been dyed whereby to be responsive to a frequency of light .different to that of the frequency of light which either exposes the -digital information or the holographic information.

There may preferably be two image components with respective wavelengths, one for data recording, and one for holographic recording, said wavelengths being provided by a laser which is wavelength tunable to select said wavelengths.

This is particularly suitable where there may be photo-resist layers of differing spectral sensitivity adapted to separate the sensitivity of the two layers to that of the two laser frequency wavelengths.

There may be photo-resist coatings applied to a substrate, which may then be subjected to an imaging process in respect of the data track and being subjected to a holographic imaging state.

'Benton' holograms or micro-embossed computer generated holograms may be transferred into the resist, and the Benton holograms may suitably be of the 2D/3D and stereogram type and/or micro-embossed dot matrix diffraction fringes to create encryption for the holographic switch device.

There may also be a digitised dot-matrix grating polarised in a parallel vector providing alignment to that of the digital information (0/1) employed for holographic recording. Moreover, it is preferred that there may be direct imaging of plane gratings through masks which may be provided to expose the carrier with holographic information.

A holographic latent image may be created on the unexposed photo-resist by means of a micro-embosser from a separate pre-recorded medium, which suitably may comprise a shim which may carry the holographic image which on contact with the unexposed photo-resist is embossed into the resist under a predetermined pressure, thereby leaving behind the impression of a holographic image.

Following embossing of the holographic image into the resist, the resist may be receptive of digital encoding without interference from the holographic image. This is a particularly advantageous feature, particularly where masking may be provided by coating a high contrast silver halide emulsion directly onto the surface of the photo-resist prior to exposing the data track, the emulsion being exposed simultaneously during the data imaging step.

Subsequent to the data imaging step, or other negative masking, images can be exposed into the sensitised emulsion.

The layer of photo-resist may be developed, fixed and dried, and the underlying photo-resist areas may be protected from exposure from the holographic image exposure or images on other parts of the disc.

The emulsion may be washed away from the photo-resist before it is returned to the final stages of digital encoding, following production of the holographic image device. The holographic image device may be formed as a layer on a master prior to RMP.

TJheji!astejjrnayi;fjπιprise₌a _Bglass master and the holographic image may be on the bottom of the pit structure on the master.

The carrier may be produced in a single production step whereby both data and the holographic image are provided, and the holographic image may be a micro-embossed polarised holographic pattern on a land surface and in the same sector as the digital pit structure.

The carrier may be selected from the group comprising CDs, DVDs and CD- Roms.

According to a second aspect of the invention there is provided a method of making an optical data carrier using binary information to create a holographic three-dimensional graphic on the surface of the carrier and which uses the same information as binary code in the form of encryption within the digital information of the carrier, both acting in unison as a switch to activate or disallow play of the carrier.

A carrier embodying the invention is hereinafter described by way of example with reference to the accompanying drawings.

Fig. 1 is a detail of a data carrying or playing surface of an optical sub- wavelength carrier in the form of a CD, to magnification x 10,600;

Fig. 2 is a schematic view showing an electron micrograph of a land/pit structure of the surface of Fig. 1; Fig. 3 is a schematic cross-sectional view to a greatly enlarged scale of a carrier according to the invention;

Jjg- 4 is Ά schematic ,elevational view .of apparatus for reading a -carrier according to the invention;

Fig. 4 A is an enlargement of part of Fig. 4; and

Fig. 5 shows optically and graphically images of the land and pit areas on impact by an optical reader such as a laser beam.

The invention concerns improvements in or relating to data carriers and in particular has reference to Optical Data Carriers such as Compact Discs, Compact Disc Rom, Digital Versatile Discs and the like, i.e. "optical discs". Such discs have data stored in the form of, usually, spiral tracks which comprise 'pit' areas of reduced effective reflectivity in a surface of 'land' area which can reflect substantially all of the light from an incident laser beam which is directed to, and plays on the disc when in a player .

One advantage of a hologram is the difficulty of copying it and accordingly its use as a security device is important and will be well known in other fields such as secure labelling, credit and bank cards. These experiments with CD pressings date back to 1988 with an article published in Laser Focus/Electronic Imaging News, volume one pp; 149, titled "Injection-Moulded Holograms Use CD Technology" describing a technique for the placing of holograms on a CD surface by researchers Nils Abramson, Ea Jonsson and Hans I Bjelkhagen at the Laserlabbet, Linkoing in Sweden. The results obtained do not satisfy the rigorous requirements of play back as no data-pit structure was included and the tests were taken no further. Similarly, Patent publication number: WO 96/00446-G11B 23/40,23/38 filed in May 1994, suggests a method for the placing holograms over the data area of a Compact Disc. Unfortunately it is impossible to make a reflection, "Denisyuk" type (volume) hologram as suggested, using a photo-resist emulsion as used for mastering digital pit Jtoictxrres .on the surfae-e of compact discs. In contrast, the -invention =ef -the application results in a data carrier comprising a holographic image and machine readable data, suitably a decryption key, to provide identification of a genuine carrier suitably a CD, DVD or the like, otherwise "disc". This is achieved by combining both data-pit and a holographic micro-fringe grating onto a playable disc creating a unique signature or badge for the disc in question and to its originator, thereby providing a security emblem to identify the disc as a genuine product. Products not carrying the relevant badge, will not only thus be seen and identified as counterfeit, but will also not play without the suitable recognition hardware to identify the hologram and allow play. The image for this application originates from a computer generated holographic sequence using a numerical 'Bit-Map' to form of a micro- embossed fringe grating. This numerical sequence is also encoded onto the disc as standard binary data. Once the disc is placed into the computer, a message will appear on the monitor asking the operator to identify the subject of the hologram on the disc. If the answer given corresponds, then the disc will be authorised to play. If the two do not correspond, play will not be permitted. It is impossible to counterfeit the holographic image on the disc, or to transfer it to another disc. Only pressings made at the time of the original can carry the holographic image according to the invention.

Referring to the drawings, an optical data carries stores information in the form of a spiral track comprising of 'PIT' areas 1 of reduced effective reflectivity in a surface of 'LAND' areas 2, which reflect substantially all of the light from a laser in the playing device (Fig. 1). The reduced reflectivity of the pits 1 is achieved in one technique by arranging for their depth to coincide to one-quarter of the wavelength of the interrogating laser in the playing device. Thus although the bottom of the pit may be perfectly smooth and effectively comprise a plane mirror, light reflected out of it will be out-of- phase when compared with light reflected from land areas 2.

The kind of hologram to be recorded is restricted generally owing to certain physical laws governing the formation of the type of fringe structure used in the process of compact disc manufacturing. Accordingly, the hologram known as the 'Benton' hologram or 'Rainbow' hologram types form the base of the holographic exposure as their fringe structure is recorded as a plane sinusoidal wave onto the surface of a suitable proprietary silver gelatine emulsion. The holographic fringes are predominantly linear and relatively simple to define. The fringes recorded in a plane grating, and practically dot-matrix holograms are orderly and mathematically predictable in their structure making them ideally suited for the purpose of alignment - to run parallel to the pit structure 1 on the land surface 2 without interfering with the digital information as described by Fisher, Wiltshire and Richardson: GB Patent Number: WOO 120605.

Injection mouldings of the disc can be manifested in the form of a thickness variation in an embossed lacquer coated onto a carrier layer, which is relatively dimensionally stable. The surface structure of optical data carriers such as compact discs, and DVDs is an ideal carrier in terms of such dimensional stability.

The optical data carrier track 1, 2> is essentially a sub- wavelength structure of digital (0/1) information. Crosstalk or interference between signals can be avoided by virtue of the incompatibility of the sinusoidal signal of the hologram to the digital requirements of a reader system. The pit structure 1 of the data track provides a diffraction effect which is potentially destructive towards the optical effectiveness of the hologram, by virtue of its effective fringe, and the diffraction spacing can be arranged to be non-desirous toward the holographic design of the disc, since the diffraction fringe formation of the holographic image may appear at a pre-determined viewing angle. Using the invention it is ⁿossible o differentiate between the type -of structure capable -of carrying a digital optical signal, and the type of structure, which can effectively carry a holographic interference recording. Also it is possible to decorate the whole part of the active surface of optical discs with one or more holographic fringes that carry other information including signals directly relating to the activation of the digital information

Therefore a carrier can be produced by a method of production including the step of limiting the total thickness of the holographic structure as it is applied prior to digital encoding to a fraction of the depth of the data 'pits' 1 as compared to the 'land' areas 2 of the data recording structure of the optical disc 3. Advantageously this fraction is chosen to be within ordinary production limits of smoothness for a stamping master employed to produce the disc. Holographic fringes of acceptable commercial brightness can be made to conform to these limits using the flowing methods developed for this process.

Thus production of a disc according to the invention includes the steps of exposing a hologram at a low level of laser light energy into a photo resist layer which is later subsequently exposed to a high energy exposure of the data track (0/1) information. Modified solvent processing is then applied to the layer to obtain a suitable surface profile where the data pits are cleared to the glass substrate whilst the holographic fringe formation is confined to the limited modulation of the land surface. A still further process involves sequentially coating the photo-resist in two layers, one of which contains a dye, which inhibits the exposure of the hologram during the recording but will admit the light from the laser carrying the data by virtue of the differing wavelengths. Therefore there is additionally provided a method for the playback of optical discs using lasers of differing wavelengths to produce the two image components for data and hologram.

In a refinement of the .prpeess of using .two different frequencies / wavelengths, either photo-resist layers or a combination of photo-resist and silver halide of differing spectral sensitivity are used to separate the sensitivity of the two layers to the two laser wavelengths which can be emitted from one laser that is adapted to expose both hologram and data pit information simultaneously. An alternative process includes the step of first coating the glass plate with a pure, soft, gelatine layer. This gelatine layer is then 'cold micro-embossed' with a pre-existing, pre-designed, holographic image. This pure, soft, gelatine is then chemically treated with a suitable hardening agent. Once hardened, the gelatine is then over-coated with photo-resist, which in turn is exposed to laser light digital pit encoding. The final result leaves the pit structure 1 clean and un-affected by the hologram.

To prevent the second coating from gathering in the pre-cut 'pits', an aerosol method of coating may be used with the disc inverted relative to the ordinary coating regime. Dilution of the photo-resist solution with abnormal quantities of solvent for use in high-speed spin-coating equipment enables exceptionally thin layers to be successfully produced to within several nanometres of thickness. Use of abnormally dilute, cold, or brief solvent processing techniques can be used to treat these thin layers in an appropriate way during their development to obtain the most efficient hologram. The use of red iron oxide surface coating or other absorbent barrier layers to the glass substrate can be used to eliminate the unwanted effects of internal reflection of the holographic exposure within the substrate glass to improve the fidelity of both hologram and data recording. One method that encompasses the dual-layer process of coating optical discs also involves two types of processing described as follows. Step one involves the use of a glass master (1), sensitive to red. This master is placed into the digital mastering .recording machine -an -Α spiral of non-data track is formed. As this is a mathematical procedure it is possible to create a spiral of continuous exposure without the digital track (0/1) breaking the line of exposure. Processed the glass master (2) will have a spiral area of un-exposed resist made available by the blocking of light due to the glass master (1). Glass master (2) may now be placed back into the digital mastering machine where, with careful mathematical alignment, the digital data (0/1) may be exposed into the previously unexposed areas of photo-resist in the form of data pits. Both the data pit structure and holographic information are developed in a novel formula and a first generation metal father shim is grown from it. Unlike this described contact mask method critical registration of the mask is obtained sufficient to protect the track zone by coating fine grain silver halide («20nm. grains) high contrast emulsion directly onto the surface of the photoresist prior to exposing the data track. The resist is thus exposed simultaneously with the silver halide emulsion during the data-imaging step. Subsequently, other negative masking images, such as logo shaped window apertures, or the spiral mask to protect the critical outer extremity of the data spiral track, which is sometimes rendered corrupt by other process parameters or imperfections, can be exposed by red light into the sensitised silver halide emulsion. If the layer is developed, fixed and then dried the black silver can then selectively and accurately protect the underlying photo resist areas from exposure to the holographic image of images that cover other parts of the disc. After imaging the holographic information, the silver mask can be washed entirely away from the photo-resist before it is returned to be recorded with data pits. The un-exposed photo-resist is coated over the hardened gelatine, which carries the holographic emblem. This holographic emblem, which has been micro-embossed with a stamped pre-determined hologram which acts as a diffuser to the CD reader to scatter laser light onto, or away from, photosensitive cells which register the pattern of light to either be genuine or fake. These results leaving the data carrier unaffected by the combined efforts of holographic fringe and data pit structure.

Step three involves exposing the sandwich of plates (1) and (2) to the holographic recording exposure using the blue frequency of 488nm with the silver halide placed toward the laser emission. The holographic information may also be placed onto the unexposed photo-resist by means of micro embossing from a separate pre-recorded medium such as the first generation metal father shim.

This metal shim will carry the holographic pattern, which on contact with the un-exposed photo-resist will be impregnated into the resist using a predetermined pressure, leaving behind the impression of a holographic image without causing any detriment to the un-exposed photo-resist layer. This resist is then ready for digital encoding without interference from the holographic information. 'Micro embossing' refers to any process whereby a fringe structure or data structure is added to another structure by heat, pressure, or contact processes such as those recombination techniques using uv-cure polymers etc. or older conventional methods of any type.

I

Mechanical methods provide an ideal method of limiting fringe depth. The alignment of the micro-embossed pattern is polarised to the same vector as the digital data pit structure as seen in atomic force microscope image (Fig. 2). This is in order to reduce the crosstalk tendency of such well-defined fringes interfering with the data playback efficiency of the pit structure. Fig. 3 shows the structure referred to above, there being the glass substrate or master 4, hardened Gelatine layers 5, 6, exposed and developed photo-resist 7, and pit structure 1, the holographic fringes being represented by the lines 8 between 1, 4, 5. Thus the hologram appears at the bottom of the pits 1.

Optical sub-wavelengths structures have been mass-produced and sold commercially for many years in the form of compact discs. To protect the data pit layer of the CD, its surface is normally coated with a thin layer of plastic, whose refractive index is approximately 2. Given that the wavelength of light in a disc player is approximately 0.8 nu and that the pit depth is 0.1 lnm, the pit depth is one quarter of the operating wavelength in the plastic. Each pit imposes a half- wavelength phase delay between the field of incident on the CD and the one that is refracted. If the lateral of the pit are also sub- wavelength, then unique diffractive effects occur and may be used in the design of the holographic coded switch.

Digital versatile disc readers typically include in their optical hardware two or more photodiodes intended to monitor the lateral tracking and focus of the reading head. By altering the electronic, but not the optical systems of a reader, these photodiodes can be used additionally to read holographic information written on the disc. Holographic fringes can be used to create patterns of intensity at the photodiodes, which do not occur, in an ordinary (data - only) disc^' For example, a pattern of fringes equivalent to the fresnel diffraction pattern of a narrow slit will create the impression that the device is out of focus in the x - direction but not in the y - direction.

As shown in Figs. 4 and 4A, the disc 9, which can be a CD or a DVD, is read by a laser 10, the beam of which is polarised by a prism 11 after passing twice through a half-wave plate 12 (45° rotation) and objective 13 to a reader or sensor 14 via lens 15. Light detecting diodes 16, 17 receive reflected incident light from the pits and lands 2, and monitor whether the sequence of binary numbers is correct. Thus 010101.... could be a correct sequence, 10100100... could not be, and the CD/DVD ill not play. If the sequence is correct, and corresponds with the programme sequence, the CD/DVD will play. If not, the CD/DVD will not play.

The desired sequence of binary numbers is programmed as desired, and will be programmed for different regions, e.g. Europe and North /America/USA. Thus a DVD bought in, and programmed for, the USA cannot be played in Europe.

An optical readable disc is produced in a single production step, whereby the disc carries both data and a holographic image on the active surface in the absence of any compromise in the integrity of the data thereby enabling both data and the image to co-exist. The critical alignment of the micro-embossed polarised holographic pattern on the land surface, and in the same vector, as the digital data pit structure as seen in Figure 5, is also key to a method devised which enables the hologram to diffract light from its surface fringes onto a photo-diode light detector programmed to search and recognise a given pre-determined diffraction which will either activate, or not, play of the digital disc. Without the diffraction grating of the hologram being read in accordance to the pre-programmed instructions of the receiving machine it makes the copying of the said disc impossible with the data playback of the pit structure. In Fig. 5 there is shown formation of holographic fringes 18 running as parallel lines, the data pit 1 structure land area being shown as smaller, lighter dashes of light 19. Thus in Fig. 5, there is shown alignment of the micro-embossed polarised holographic pattern 19 on the land surface 3 and in the same vector as the digital pit structure 1. This enables the hologram to diffract light from its surface fringes onto a photo-diode light detector (16, 17), Figs. 4, 4A) programmed to search and recognise a given pre-determined diffraction which will either activate, or not, play of the CD or DVD 9. Without this diffraction grating of the hologram 18 being read in accordance to the pre-programmed instructions of the reading machine copying of the disc is impossible with the data nlaybaek of the pit structure. The respective graphics and shown at 20, at magnification of 5μm x 5μm.

It can thus be understood that rather than a random sequence of numbers as presently used for the encryption of digital information, a complementary approach of using the same digital information as was used in the production of the primary hologram is used in the invention . This verifies the product as authentic, and will in essence be a mirror image of the hologram but in a non- visual form. This is extremely useful to the product identifier as both the holographic image and digital information must tally for the disc to be authentic. Both the digital information for the data pit structure and the fringe formation of the image could both be holographically transferred during the primary mastering process. That is to say the hologram itself could eventually form the data pit structure utilizing the qualities of an e-beam laser to expose both fringe and data-pit simultaneously. It will be understood that while the present invention as described delimits a number of processes and methods of achieving the objectives set forth, the list of such methods is not exhaustive but the present invention embraces other procedures, which provides the same end result.

One of the advantageous aspects of a carrier embodying the invention is the preservation of the integrity of the data track and the differentiation of the digital data microstructure associated with it, from the holographic fringe structure based upon a cosine waveform. To this end means have been provided which not only to ensure control over the depth of the pit structure, but also, simultaneously, the spatial separation of the two structures on a microscopic basis by means described previously. Additionally, methods of providing a holographic microstructure have been provided , which result in the microstructure being compatible with the special needs of disc-,suriace imaging, Advantageously, the predominantly linear holographic fringe structure of the hologram is aligned, in the invention, with the data track in such a way that there is a lack of steeply ascending or descending relief detail transverse to the data track. This feature offers a significant reduction in the noise level associated with the electronic signal detected by the data reading system before filtration occurs. Thus, when using a 'dot-matrix' or other recording technique for the holographic component of the disc, it is relatively simple to implement general design rules which ensure that there are a minimal number of fringe features which provide relief changes in the disc surface that would tend to be difficult to distinguish from the digital data stream. In one embodiment the 'dot-matrix' or other digital imaging system can be programmed in its software to ensure that pixels in certain areas of the disc surface contain only structures which are compatible with the general principle of avoiding cross talk with the data track in that particular area of the surface e.g. the holographic fringe structure takes into account the rotational position of the image feature on the disc surface.

Thus using the invention described herein it is possible to provide an optical data carrier which includes on the data side of a CD or DVD the application of a holographic image, as a micro-embossed surface-relief structure, on the data carrying surface in order to inhibit play or fraudulent copying of the data. The

I

I hologram acts as a 'Holographic Switch' (H.S), without compromising the integrity of the optical data-carrying track. The 'Holographic Switch' can run either radially across the full surface of the disc or form a smaller, hidden section of the disc, may form part of a larger decorative or branded area and may act as a light-diffuser during reading of the disc. The holographic switch diffuses laser light either away, or toward, receptors inside the playing machine to activate play. This, combined with data encryption, whereby the encryption is a digital mirror image of the hologram in numerical form generated by computer, will form a secure optical data-carrier and is an improvement over e (j§t g e cryption techlήβries,

It will be understood that modifications are possible. Thus the holographic switch can be operable in the infra-red frequency range, making the whole switch process invisible to the naked human eye. Stated in another way, in all embodiments holographic information carried on the data structure of an optical disc 3 can simultaneously provide visible 'authentication' and a data 'side channel 1 ' carrying data such as cryptographic keys. The side-channel information can be read back by the optical pickup of a disc player but cannot be re-created by a 'burner' or drive. Thus the holographic structure provides a physical copy-protection feature. Access to the main channel data carried in the pits 1 of the disc 9 is unaffected, except to the extent that cryptographic keys in the side-channel are used to implement copy-control or DRM functions by which controlled access is delivered.

The holographic optical element in combination with digital data pit structures of discs 9, act as a digital authentication certificate of digital content. The element diffracts photons, at a given wavelength, for example 'red' or 'blue', toward a light reader and effectively acts as a switch.

The principle that light diffracts simultaneously from the surface of the pit structure and hologram offers encryption of this refracted light which, unlike other forms of digital encryption, comes from the analogue surface of the holographic optical element.

In terms of an optical disc technology, this optical switching technique may be used to carry information on the same master recording without the need for additional production processes. Combinations of this innovation will allow manufacturers to create products that will tackle counterfeiting in authentication systems added to DVD players and computers at little extra cost that only play authentic products,

A CD or DVD embodying the invention comprises a hologram or holographic pattern or a disc of reflective metal film, which is then attached to a plastic layer on which the data is normally held. A laser interrogating or reading the disc "sees" the signal reflected from the data as being stronger than that from the hologram, which scatters light in all directions. Viewed from a distance, however, the hologram is clearly visible. Thus the disc 9 carries both data and a holographic image on the active surface without compromise to the integrity of the data thereby enabling both data and image to coexist.

Claims

1. An optical data carrier having an active surface, comprising a holographic image and machine-readable data on the active surface, whereby to provide identification of a earner as genuine.

2. A carrier according to Claim 1, the data comprising a non- visual decryption key.

3. A carrier according to Claim 1 or Claim 2, comprising pits and lands, the decryption key comprises data encryption of a digital rriirror image of the holographic image in numerical form.

4. A carrier according to any preceding claim, the holographic image and machine readable data comprising a holographic switch device which is adapted to provide proof of genuineness of the optical data carrier.

5. A carrier according to Claim 4, the holographic switch device extending radially of the data carrying surface of the carrier.

6. A carrier according to Claim 5, the radial extent being across the full area of the data carrying surface.

7. A carrier according to Claim 5, the holographic switch device comprising a discrete part of the area of the data carrying surface.

8. A carrier according to Claim 5, the holographic switch device comprising part of a decorative or "branded" area of the carrier and being adapted to provide a light diffuser during reading of the carrier.

9. A carrier according to any of Claims 4 to 7, the total thickness of a structure comprising the holographic switch being a fraction of the depth of the pits as compared to the area of the lands of the data carrying surface.

10. A carrier according to Claim 9, comprising a holographic latent image exposed at a low level of energy into a photo-resist layer, which is subsequently exposed to a higher level of energy exposure of data (0/1) information of tracks of optically readable data of the carrier.

11. A carrier according to Claim 10, the data pits being cleared to the substrate of the carrier whilst the holographic data are confined to the limited modulation of the land surface.

12. A carrier according to Claim 11, including sequentially a layer of holographically exposed hardened Silver Gelatine, or pure hardened Gelatine, and a layer of photo-resist which has been dyed whereby to be responsive to a frequency of light different to that of the frequency of light which either exposes the digital information or the holographic information.

13. A carrier according to Claim 12, the use of a laser adapted to be wavelength tunable to select two differing wavelengths to produce two image components one for data recording, and one for holographic recording.

1 . A. to -Claim 13 , £om rising photo-resist layers of differing spectral sensitivity adapted to separate the sensitivity of the two layers to that of the two laser frequency wavelengths.

15. A carrier according to any one of Claims 11 to 14, comprising photo-resist coatings applied to a substrate, which is then subjected to an imaging process in respect of the data track and being subjected to a holographic imaging stage.

16. A carrier according to Claim 15, 'Benton' holograms or micro- embossed computer generated holograms being transferred into the resist.

17. A carrier according to Claim 16, the Benton holograms being of the 2D/3D and stereogram type and/or micro-embossed dot matrix diffraction fringes to create encryption for the holographic switch device.

18. A carrier according to Claim 16, a digitised dot-matrix grating polarised in a parallel vector providing alignment to that of the digital information (0/1) employed for holographic recording.

19. A carrier according to Claim 16, direct imaging of plane gratings through masks being provided to expose the carrier with holographic information.

20. A earner according to Claim 11, a holographic latent image being created on the unexposed photo-resist by means of a micro- embosser from a separate pre-recorded medium.

21. A carrier according to Claim 20, the pre-recorded medium comprising a shim carrying the holographic image which on contact with the unexposed photo-resist is embossed into the resist under a predetermined pressure, thereby leaving behind the impression of a holographic image.

22. A carrier according to Claim 21, whereby following embossing of the holographic image into the resist, the resist is receptive of digital encoding without interference from the holographic image.

23. A carrier according to Claim 19, masking being provided by coating a high contrast silver halide emulsion directly onto the surface of the photo-resist prior to exposing the data track, the emulsion being exposed simultaneously during the data imaging step.

24. A carrier according to Claim 23, wherein subsequent to the data imaging step, or other negative masking, images can be exposed into the sensitised emulsion.

25. A carrier according to Claim 24, the layer of photo-resist being developed, fixed and. dried, and the underlying photo-resist areas being protected from exposure from the holographic image exposure or images on other parts of the disc.

26. A carrier according to Claim 25, the emulsion being washed away from the photo-resist before it is returned to the final stages of digital encoding, following production of the holographic image device.

2.1.. carrier ₌accoχding ,to₌any of Claims 3 to 26-, the holographic image device being formed as a layer on a master prior to RMP.

28. A carrier according to Claim 27, the master comprising a glass master and the holographic image being on the bottom of the pit structure on the master.

29. A carrier according to any of Claims 3 to 28, produced in a single production step whereby both data and the holographic image are provided with the holographic image being a micro-embossed polarised holographic pattern on a land surface and in the same sector as the digital pit structure.

30. A carrier according to any preceding claim, selected from a group comprising CDs, DVDs and CD-Roms.

31. A method of making an optical data carrier using binary information to create a holographic three-dimensional graphic on the surface of the carrier and which uses the same information as binary code in the form of encryption within the digital information of the carrier, both acting in unison as a switch to activate or disallow play of the carrier.