Field of the Invention The present invention is related to the field of protection of optical media from being copied or otherwise used without authorization. Specifically the invention relates to a method of causing controlled changes in the properties of the media in order to detect unauthorized copies of optical media and to prevent their use and reproduction of unauthorized copies.

BACKGROUND of the Invention Illegal use and illegal copying of optical media of all types causes financial loses estimated on the order of tens of billions of dollars per year. As a result the producers of optical media have invested great effort and large amounts of money to prevent copying or unauthorized use of their property. Many technologies have been developed and many patents have been granted to prevent illegal copying of optical data. When the optical media is a CD, typical examples of these methods are disclosed in US 6,425,098, US 6,256,738, and US 6,031,815. The inventions described in these patents make use of manipulation and change of the standard formats and protocols for optical media by changing the impressed bits of information stored on the media. Recently there has been developed software such as CloneCD® , developed by Elaborate Bytes AG, which copies the original media bit-by-bit and thus makes any protection based on manipulation of the bits of data ineffective.

Copy protection of DVD -video is typically provided by encryption of the digital information on the media by use of the Content Scrambling System (CSS). The information can only be descrambled when encryption keys that have been placed on the DVD disc during the manufacturing process are used by a licensed DVD player. When a CSS protected disc is copied, the encryption keys aren't transferred to the copied DVD-E, and therefore the player will not recognize the copy. Unfortunately for copywrite owners, there are now available a wide variety of hardware and software that can be used with varying degrees of success to defeat the CSS system. Typical of the available software are Smart Ripper, for copying the contents of a DVD to the hard disc of a computer, and Clone DVD, for copying the contents to a DVD-R. The software of DVD X Copy™ XPress has a built in DVD ripper/decrypter and also burn engine. These and the many other programs available from the internet combined with the steady reduction in cost, ease of use, and versatility of media on which copies can be burned and burners, including dual-layer burners, are ever present reminders to the industry of the need to develop new methods of protecting the rights of the digital content owners.

In order to counter the developments described above, it has been realized that an effective defense against copying can be provided by causing physical changes to the medium itself. One such method is disclosed in US 6,589,626, which presents a method based on placing light-sensitive material at places capable of altering the data on the medium. The light- sensitive material undergoes a reversible change in its optical properties, typically a change in transmission as a result of irradiation by the reading laser. Two different data sets read from the same location at different times separated by the time it takes for the change to take place (or be reversed) verify the authenticity of the media and allow the media to be copied. In this patent is listed a wide variety of possible. materials that can be used in the invention. The inventors in fact claim all organic and all inorganic light- changeable materials. There is however no specific examples given or any description of any measurements or experiments that were carried out that show that any specific materials were particularly effective or, in fact that use of the method described will produce the desired results.

In International Patent Application WO2004/044911 by the same applicant, the description of which, including publications referenced therein, is incorporated herein by reference, are described optical media that are provided with movable mechanical elements and methods of using these media to verify the authenticity of the media and to prevent their unauthorized use and reproduction.

Chalcogenide materials are compounds possessing the common feature of comprising elements of the Group VIB of the periodic table, namely sulfur, selenium, and tellurium also referred to as chalcogens. Known chalcogenide compounds include combinations of these elements with other elements selected from arsenic, germanium, antimony, bismuth, halides, rare earth and transition metals, and some of the lanthanides as well, all with varying quantitative relations between them. Structural, optical, and photoelectronic properties of chalcogenide amorphous and non-amorphous materials have been the subject of interest for about 40 years. This interest has been stimulated both by basic scientific questions relating to the structure and properties of these materials, and the need to assess their potential technological applications.

Chalcogenides may appear and be processed in both crystalline and glass/amorphous phases, the latter being of most interest from a technological opto-electronic point of view. This is due to a number of interesting photo- and particularly laser-induced responses of chalcogenide glassy films (ChGF), two of which are known as photo-structural transformation and phase change. These phenomena, which may either be reversible or non-reversible, spread between amorphous-crystalline- amorphous (phase change) and amorphous-amorphous (structural) transformations; the physical interpretation of the latter phenomena is not that an actual structural change takes place but rather a change in the electronic energy states of the material.

In all cases, interaction of chalcogenides with light produces changes in their optical density and, as a result, in their transparency to light, a photoeffect known as photodarkening. Such an effect may either be transient or accumulative over time with repetitive operations, and in certain chalcogenides it may also be reversible or erasable. The reverse effects are known by the terms photobleaching and thermobleaching. For example, Ganjoo et al., Journal of Non- Crystalline Solids 299-302 (2002), pp. 917-923, report the results of laser-induced metastable and transient photodarkening effects in a-Se and a-As2Sβ3 exposed films in different temperatures.

Many publications in the field of opto-electronics report the employment of chalcogenides in various applications, inter alia, xerography, fiber optics, and in single-use or over-writable audio, visual, holographic, and software optical recording, utilizing their stable and, in rewritable applications, also their erasable phase-change response for storage of electro-magnetically transferred data, thereby enabling multi-use of the recording media. Some representative publications describing the application of these properties are: Paylock et al., Applied Physics A: Materials Science & Processing, (2002), 74(5), pp. 683-687, in which is described the potential of a-Se in holographic recording; US 2003/0064293, in which is disclosed the use of chalcogenides in photo-refractive holographic media; and US 5,136,677, in which the photo-induced refractive effect in glass chalcogenides is utilized in the production of optical fibers.

It is therefore an object of the present invention to provide a method based on changes of the optical properties of the media that allows authorized use of an optical media while preventing copying and/or use of unauthorized copies made of said media.

It is another object of this invention to provide an optical medium (disc) that comprises one or more optical implants.

It is yet another object of this invention to provide a system comprising an optical medium (disc) that comprises one or more optical implants and suitable control instructions which together provide means for detection and prevention of the use of unauthorized copies.

It is still another object of this invention to provide an optical medium (disc) that comprises one or more optical implants and suitable control instructions and on which unauthorized copies cannot be recorded.

It is a further object of this invention to provide specific alloys that are suitable for the optical implants and which allow all the other objectives of the invention to be efficiently and economically achieved.

Further purposes and advantages of this invention will appear as the description proceeds.

Summary of the Invention The present invention provides methods for preventing unauthorized copying from optical media and for detecting and preventing the use of optical media on which unauthorized copies have been made. The present invention also provides media, which are adapted for use with these methods. The methods of the invention consist of the addition to the discs, comprising the media on which the information is stored, one or more optical implants whose optical properties can be controllably and reversibly influenced by an external stimulus. In the preferred embodiments of the invention the optical implants are spots or areas coated with photochromic material and the external stimulus are the photons supplied by the beam of the reading laser, which impinges on the material. The implants of the invention can be incorporated within or on the surface of the optical discs and, together with suitable control instructions, allow the discs to be identified according to the method of the invention. The control instructions can be placed on the disc, on the reader, on a computer connected to the reader, or supplied from a remote location connected to the computer via the internet.

In this patent application: - The terms "disc" and "medium" or "discs", "media", "optical medium" and "optical media" are used interchangeably to refer to devices on which information is recorded and/or read optically. — The term "optical implant" refers to a material which is placed at specific localized positions on the media and whose optical properties can be changed under the influence of an external energy source. - The term "photochromic" refers to changes in the optical properties of a material that are caused by absorption of photons.

The invention is applicable to all forms of information including, but not limited to, music, movies, games, educational programs, data banks, and software. This information can be stored on and read optically from many types of media including, but not limited to, audio CD, CDR, CDRW, CDROM, DVD, DVDR, DVDRW, and magneto-optic discs.

In a first aspect, the present invention is an optical medium containing information optically readable by a beam of light and/or on which information can be written by a beam of light. The optical medium of the invention comprises one or more optical implants placed on the surface of or within the medium. These optical implants prevent, change, or otherwise influence the reading of a portion of the information at a particular location on the medium, by interfering with the beam of light as the result of controllable and reversible changes of the transmission of light through the material of which the optical implants are comprised. The changes of transmission are influenced by the reading beam of light. The material of which the optical implants are comprised is a thin film of chalcogenide material comprising an alloy of Selenium combined with lesser amounts of different elements. In preferred embodiments, the different elements are selected mainly from the group comprising: Te, Sb, As, and S.

The composition of the alloy is preferably selected from the group comprising: (a) Sβioo-xTβx, wherein 0<x<8.0; (b) Sbx Seioo-x, wherein 0 < x < 2.0; (c) AsySeioo-y, wherein 0 < y < 1.0; (d) Seioo-xTβx, wherein 0<x<8.0 with the addition of l%-2% Sb and/or As; (e) (Se95Te5)m x (SsSAs1S)n, wherein coefficients m and n are between m = 0.9, n = 0.1 and m = 0.7, n = 0.3; and (f) Sβioo-x-y SχTey, wherein 10<x<30, 0<y<5.

The optical implants can be located on the medium at one or more positions selected from the group comprised of: (a) on the surface of the substrate; (b) at the interface between the optically readable information on the medium and a reflecting or semi-reflecting layer; (c) at the bonding layer between pieces of the media; and (d) inside the polycarbonate layer. In a preferred embodiment the medium is a writable medium and comprises one or more optical implants at specific locations on the medium. In order to allow information downloaded from an internet site to be copied from the hard disc of a computer to the medium, the presence of the implants at the specific locations must be verified by control instructions that are downloaded from the internet site along with the information. In another embodiment, information cannot be downloaded from an internet site to the hard disc of a computer until the presence of a medium of the invention in one of the drives of the computer is verified by control instructions on the internet site. In another embodiment, the locations of the one or more optical implants on the medium can be selected from a large number of possibilities and the control instructions at an internet site scan all the possible locations to determine the exact locations of the implants. Once the exact locations of the implants on the medium is determined then they are included in a set of operating instructions that are downloaded from the internet site to the hard disc of the computer along with the information at the site. The medium can serve as a means of payment to the owner of an internet site for information downloaded from that site.

In another aspect the invention concerns a system comprising an optical medium of the invention and control instructions. The control instructions contain information suitable to control the mechanism employed for reading information contained on the medium and for verifying the authenticity of the medium by using the results of the readings. In a preferred embodiment of the system of the invention, the control instructions verify the authenticity of the medium by comparing the information read from the medium at one or more selected locations, corresponding to locations wherein the optical implants interfere with the beam of light. The control instructions can be comprised in software that can be provided on the optical medium, on the optical medium player, or on a separate application. In yet another aspect the invention presents a method of testing to determine if an unknown optical medium is an authorized optical medium of the invention or if it is an unauthorized copy of the original optical medium. The method of the invention prevents the use of the unknown optical medium if it is an unauthorized copy or allows the use of the unknown optical medium if it is an authorized optical medium. The method of the invention comprises the following steps: (a) place the medium on a suitable media player; (b) start the test; (c) read location A, obtaining reading A1; (d) instruct the drive of the player to repeatedly return to location A a predetermined number of times; (e) read location A, obtaining reading A2; (f) compare readings A1 and A2; (g) if A1 = A2, then the medium is not authentic and the control software is instructed to abort the reading of the remainder of the information on the medium and/or to prevent normal operation of the medium and/or the player and/or to execute other activities; and (h) if Ai ≠ A2, then the medium is authentic and the control software is instructed to continue reading of the remainder of the information on the medium and/or to execute other activities that are necessary to continue the application.

All the above and other characteristics and advantages of the invention will be further understood through the following illustrative and non-limitative description of preferred embodiments thereof, with reference to the appended drawings. Brief Description of the Drawings - Figs. IA and IB schematically show the principle of the operation of the invention; - Figs. 2A to 2E symbolically show cross-sectional views of the media showing a section of the spiral track for a CD and each of the DVD formats; - Fig. 3 presents typical plots showing photo-darkening and spontaneous bleaching as a function of irradiation time at room temperature for an amorphous Se film containing 1% Te; - Fig. 4 schematically shows some of the possible locations on a DVD 9 disc that can be chosen for placement of the optical implant; - Fig. 5 is a series of plots showing the change in transmission, during selected single pulses, through a SegsTes film irradiated by a series of lOμsec pulses; - Fig. 6 is a series of plots showing the change in transmission, during selected single pulses, through a (Se95Te5X85 x (Ss5Asi5)o.i5 film irradiated by a series of lOμsec pulses; and - Fig.7 is a series of plots showing the change in relative transmission, during selected single pulses, through a film of Seioo-χ-ySx Tey irradiated by a series of 10 μsec pulses.

Detailed Description of Preferred Embodiments The method of the invention can be used to identify and protect information that is stored on and can be read optically from any type of optical media. Such media include, but are not limited to: audio CD, CDR, CDROM, CDRW all of the DVD types and formats, including DVDR and DVDRW, and magneto-optic discs.

Figs. IA and IB show schematically the principle of the present invention. For purposes of illustration we consider a data disc 10 on which is created a spiral track 12, which contains all of the various types of information that are necessary for the data on the disc to be read. (It should be noted that all of the figures herein are merely schematic and do not attempt to show the actual relationship between the dimensions of the various film implants portrayed.) This information includes, for example, the table of contents, operation instructions, error correction codes, and the data itself. All of this information is arranged along the spiral according to standard formats proscribed by protocols, which are well known in the industry and have been developed for each type of information stored on the disk, for example music, movies, or data storage. In addition, instructions that are unique to the present invention and formulated in a manner similar to the exemplary algorithm described hereinbelow can be added at different locations on the data track of the disc and can be run at any selected time or in any predetermined order.

All of the information, both the data and, if supplied on the disc, the control instructions, is presented in digital form impressed into the substrate material of the disc (commonly polycarbonate plastic) forming a pattern of pits and lands which are then covered with a thin reflecting layer of metal, usually aluminum.

Figs. 2A to 2E symbolically are cross-sectional views of the media showing a section of the spiral track for a CD and each of the DVD formats. Fig. 2A shows a portion of the spiral track 12 of a CD. The thickness of the disk 10 is 1.2mm including the polycarbonate substrate 20, reflective aluminum layer 22, and a thin layer of acrylic plastic 24 deposited on top of the reflecting layer 22 to protect it. A label (not shown) is then placed on the top of the acrylic layer 24 to identify the contents of the disc. A laser 26, focused on the reflective layer covering the lands and pits, is used to read the information encoded in the spiral track 12. A DVD media disk is comprised of two polycarbonate substrate layers that are bonded together. The DVDs are produced in different formats that comprise either one layer (DVD 5) or two layers (DVD 9) that are read from one side of the media disc with a single laser or comprising either two layers (DVD 10) or four layers (DVD 18) that are read from both sides of the media disc by turning the media over. These four formats are schematically shown in Figs. 2B to 2E. For DVD 9 and DVD18, the laser 26 (or its focal point) must be able to be moved backwards and forwards in order to focus on the two spiral tracks 12 on the two layers that it must read. Also, the track 12 of the layer closest to the laser must be coated with a semi-reflective layer 28 in order to allow the track above it, which is covered by a fully reflective layer 22, to be read. The semi-reflective layer 28 is typically comprised of gold, silver alloy, or silicon. In Figs. 2C and 2E, the second position of laser 26 is schematically shown with broken lines. For all four of the formats, each of the polycarbonate substrates 20 has a thickness essentially equal to one half of the thickness "t" of a CD disk. The two substrates 20 are joined at bonding layer 30 to form the finished media disc 10.

In the case of both the CD and DVD, the light from a focused laser 26 shining orthogonally onto the track 12 through the polycarbonate substrate 20 is reflected from the pits and lands onto a detector (not shown in the figures). A tracking system moves the laser and detector back and forth along a line parallel to the radius of the disc in order to keep the laser focused on the spiral track on the disc as a drive circuit rotates the disc. The drive system varies the speed of rotation of the disc in order to cause the information in the spiral track on the media to pass the laser reading head at a constant linear velocity that is independent of the position on the disc of the information being read. All of the optical, mechanical, control elements, and software necessary to read the information recorded on the media discs are well known in the art and will not be further discussed herein. Referring to Fig. IA and Fig. 2A, numeral 14 designates an optical film implant, typically a spot or patch of photochromic material, placed in or on the media disk 10 at a position between the reading laser 26 and the location A on the spiral track 12. When it is exposed to radiation from the laser 26, the photochromic material of which the implant is comprised undergoes a change in its optical property. According to a preferred embodiment of the present invention, the implant comprises a photochromic material whose transparency changes from a clear state to a state that is sufficiently opaque to prevent correct reading of the information on the disc or to otherwise affect the reading of the information on the media. It is a further requirement of the invention that, in order to allow unlimited use of the media, the change in transparency is reversible, i.e. after a relaxation period the transparency of the photochromic material must return to a state that allows normal use of the media. When the original state of the material is essentially transparent, the photochromic effect is known as photo- darkening; and the reverse process is spontaneous bleaching, which takes place over a period of time tb after the source of light impinging on its surface is removed.

To verify the authenticity of the optical media the disc 10 is placed in the reader and instructions are given to read the information at predetermined location A on the spiral track 12. The information is read and will have a given value. At a time less than tb after the first reading the reader is instructed to read the information at location A second time and the two readings are compared. If, as a result of being illuminated by the laser beam, the optical transparency of the optical implant 14 is reduced below a value that is characteristic of the reader then the laser will be unable to read the information at location A the second time. For a typical computer DVD player checked by the inventors it was determined that reducing transmission of the media to about 30% to 50% of the intensity measured without the optical implant will prevent reading of the data. It is understood that, in order to be able to carry out the method described hereinabove, there must be a short time delay in the onset of the light-induced change after the beginning of the illumination by the laser light beam. This delay is necessary to permit correct reading of the information to be made before the material changes its optical properties.

If the intensity of the laser beam is not high enough to cause the required degree of change in optical density of the optical implant on a single reading, then various techniques can be used to cause the material of the implant to absorb enough photons to cause the required degree of photo- darkening to take place. In the preferred technique, the drive and tracking motors are instructed to rotate the disc such that the focused laser beam impinges on implant 14 a predetermined number of times during a period of time less than tb until the accumulative change in transparency is enough to interfere with reading of the information at location A. The properties of the photochromic material and the amount of radiation impinging on the optical implant each time that the laser beam passes over it are known; therefore the number of times the material must be exposed to the beam can be easily determined. Another technique is to alter the operating instructions of the drive system of the reader to reduce the speed of rotation of the disc to allow the photochromic material to absorb a sufficient number of photons.

If desired, a third reading, which should be the same as the original one, can be made after a period of time greater than tb. Optionally, the first reading can be made after the optical implant has absorbed enough photons to cause the required change in transparency and the second after tb. If the media behaves in accordance with the above, i.e. the readings at A are dependent on the amount of radiation from the laser that falls on the optical implant and the time after the initial irradiation at which the second reading is made, then this indicates that the photochromic material is present on the disc at location A, i.e. that the information is recorded on an authorized media.

Preferred photochromic materials for the optical implant 14 are amorphous chalcogenide materials, comprising selenium doped with different elements. The preferred method of working with these materials is to fabricate thin films by evaporation or high-frequency sputtering in vacuum. These films undergo photo-darkening under the influence of laser beam irradiation, followed, after a certain delay after irradiation ceases, by spontaneous bleaching at room temperature.

The essence of the photo-darkening process is the transition of the amorphous chalcogenide materials from a first stable state to an excited, metastable state, which is energetically separated from the stable state by a potential barrier, which in most cases cannot be overcome at room temperature. The main characteristic of the materials suitable for the present invention, i.e. reversible chalcogenide materials is a small value of the potential barrier separating those two states of the material. This fact permits the realization of reverse spontaneous transition of the material from metastable to stable state at room temperature, and it is the basis for the photo-optical effect i.e., dependence of the absorption coefficient on the illuminating light intensity.

A series of experiments have been carried out to test the suitability of different chalcogenide materials comprising selenium doped with different elements. The samples were prepared by evaporation of thin films on the surface of a substrate.

In Fig. 3 is presented typical characteristic plots showing photo-darkening (decrease of transmission T) and spontaneous bleaching (increase of transmission T) as a function of irradiation time at room temperature. The graph in Fig. 3 is for an amorphous Se film containing 1% Te with a thickness of 1.0 μm irradiated by a Nd: YAG laser beam, with wavelength λ= 532 nm and energy density ( J) of ~1.9 W/cm2. In Fig. 3, the downward pointing arrows mark the instant that the laser is switched on and the upward pointing arrows mark the instant at which the laser is switched off. In Fig. 3 time is shown on the horizontal axis and is measured in seconds.

The parameters of interest in determining the suitability of materials for use in the present invention is the ratio of the light transmission through the film in the non-irradiated and irradiated states (Tni/Ti), and the time of spontaneous bleaching at room temperature (tb).

Examples of films that have been found suitable for the invention are: 1) Films of Seioo-χTexO<x<8.O. Samples of thin films containing different amounts of Te were prepared. Table 1 shows some typical photo-darkening parameters for some of these films (at identical conditions of the He-Ne laser beam irradiation, λ = 632 nm, j~ 2.7 W/cm2).

Table 1

It can be seen from Table 1 that, at the intensity of the laser beam used in this experiment, the films with x = 0, 1.0, and 5.0 have TnZTi values in the range 1.14 — 1.48, and, according to the measurements of the inventors reported hereinabove, are thus suitable for the optical implants of the invention. The film with x=10.0 is characterized by appearance of non- erasing, i.e. not spontaneously reversible, photo-darkening, therefore films with this composition unsuitable for use with the invention. To supplement the data in Table 1, it is noted that the appearance of the phenomena of non-erasing was observed in all films with x>8.0.

The time of spontaneous bleaching at room temperature (tb) for films with x=0, 1.0, and 5.0 is relatively short, which also permits their use in the present invention. The conclusion drawn from Table 1 is that very suitable results are obtained using Se1OO xTex films with 1.0 < x < 5.0.

2) Films of Sbx Se1Oo-x, 0 < x < 2.0 and of AsySeioo-y, 0 < y < 1.0. The photo-darkening parameters for thin film samples of these materials (at identical conditions of the He-Ne laser beam irradiation, λ = 632 nm, j~ 2.7 W/cm2) are shown in Table 2. Table 2

It can be seen from Table 2 that the main parameters of the films of Sbx Seioo-x, where 0< x < 2.0, and of AsySeioo-y, where 0< y <1.0, are very close to those of pure Se films (x=0 and y=0). However, whereas pure Se films crystallize at temperatures greater than 40 degrees, the addition of small amounts of Sb and As, in the quantities mentionedτ above^ strongly suppressed the crystallization process and the films can be heated to much higher temperatures. This results in an increase of photosensitivity, particularly photo-darkening, and stability. In films with x >2.0 and y > 1.0 a non-erasing photo-darkening appears, and therefore, they are not suitable for use in the present invention.

It has also been shown that the introduction of small amounts of Sb and As (up to 1.0-2.0 %) into the Se+Te films has the same effect as in the case of Se films without Te; that is suppression of the crystallization process, which permits annealing of the films at much higher temperatures, resulting in an increase of photosensitivity and stability.

It can be seen from Fig. 3 that, under the conditions of the experiments described, the time required to achieve the maximum photo-darkening and spontaneous bleaching effects was on the order of tens of seconds. These times are very long compared to the time at which the laser beam will impinge on a given location on the medium during the operation of the DVD player. In a typical DVD player, the laser focuses the beam to a spot size on the order of one micron diameter and the medium rotates at such a rate that an area of this size on the disc will move across the laser beam in roughly 10"6sec. In a DVD reader the laser has an output of approximately 7 to 1OmW and the energy density at the focus is therefore about 0.25 to 1 xlO6 watts/cm2 as compared to the energy density of 2-3 watts/cm2 used to obtain the results described hereinabove. It is reasonable to assume that, although the effect may not be linear, the desired changes in optical properties of the thin films of chalcogenide materials comprising selenium doped with different elements described herein will take place in a much shorter period of time and will exhibit a greater degree of photo-darkening at the energy density supplied by the DVD player's laser. In order to confirm the validity of this assumption, the following measurements were made using a continuous laser having an output of ImW at 632nm to irradiate a sample comprised of a thin film comprised of Se+5%Te having lμm thickness. The sample was placed at a location where the spot size of the impinging beam was 0.7mm diameter resulting in an energy density of -2.7 watts/cm2 Over an interval of 5 sec the transmission of the sample was observed to be reduced by 10%. The sample was then moved relative to the laser to a position at which the spot size was reduced to 40microns resulting in an energy density of -27 watts/cm2. As a result of the increase of energy density by a factor of 10, a reduction in transmission by a factor of 3.5 was obtained in 0.5 sec, i.e. an interval of time 10% of the time period in the first measurement.

The results of this simple experiment clearly show the validity of the assumption that an increase in intensity of the laser will greatly reduce the amount of time of irradiation necessary to obtain a large increase in the amount of the photo-darkening effect obtainable with the selenium alloys and therefore confirm the correctness of the conclusions based on this assumption, i.e. that the alloys listed in Tables 1 and 2 are suitable materials for the optical implants of the invention.

Following the completion of the preliminary experiments described above, a special experimental installation was used, which allowed investigation of the transmission properties of developed chalcogenide films under conditions more closely approximating those in an actual optical media reader. Using this installation it was possible to irradiate the films with a focused beam from a pulsed laser having a wavelength of 650 nm and frequency 3Hz. The width of the pulses could be varied over the range of 10 - 100 μsec and the beam could be focused to produce a minimum spot size having a diameter of 7.0 microns.

In Fig. 5 is shown the change in transmission that occurs during selected single pulses when a O.βmicron thick SeθδTes film is irradiated by the series of 10 μsec pulses. The energy density is ~ 16kW/cm2. During the first lOμsec pulse (curve 1) the transparency of the film decreased from -0.35 to -0.2, i.e. by 43%. The laser continued to irradiate the sample and after one minute the 181st pulse was recorded (curve 2). For this pulse the initial transmission was -0.27 and photodarkening took place reducing the transmission to -0.15. The laser continued to irradiate the sample for four more minutes and the 905th pulse (curve 3) was sampled five minutes after the beginning of the irradiation period. In this pulse photodarkening is also observed with the transmission reduced from -0.22 to -0.12 during the duration of the pulse. Following the initial five minute period of irradiation, the laser beam was blocked and the film was kept in darkness for a three minute interval. Following the period of darkness, the sample was again irradiated by the laser and the change in transparency of the film during the first next 10 μsec pulse was recorded (curve 4). From this curve it can be seen that during the three minutes of darkness the transparency increased from -0.12 to -0.35 and then decreased to -0.2 by the end of the first pulse. The laser continued to irradiate the film and the pulse recorded one minute later (curve 5) again showed the essential photodarkening.

The results shown in Fig. 5 indicate that the SeθsTes film exhibits photodarkening during 10 μsec pulses of 16 kW/cm2 radiation and bleaching in darkness while retaining the photodarkening ability. Similar results were obtained for Seioo-χTex films having many different values of x as well as for Sbx Seioo-x (0 < x < 2.0) and AsySeioo-y (0 < y < 1.0) films. The results of the experiments showed that the initial transparency of the Seioo-χTex films having a thickness of 0.6 microns is not very large, i.e. 0.35 for SegδTβδ film, for the example shown in Fig. 5. The transparency can be increased by decreasing the thickness of the film. The inventors have found that higher initial transparency can be obtained by using four-component Se-Te-S-As chalcogenide films. Very positive results were obtained for (Se95Tβ5)m x (S8δAsi5)n films. The best results were observed in cases where coefficients m and n were between m = 0.9, n = 0.1 and m = 0.7, n = 0.3.

Fig. 6 shows the changes in transmission during the length of a pulse of a 0.75 micron thick (SegsTesKss x (SssAsisKiδ film irradiated by a series of 10 μsec pulses. The experiments were carried out as described hereinabove with reference to Fig. 5. We see here the changes of transparency during initial first pulse (curvel), after one minute of constant irradiation (curve 2), and after an additional four minutes of irradiation (curve 3). The film was then kept in darkness for three minutes and then irradiated again. The change in transparency of the first pulse (curve 1*) was then recorded and irradiation continued for five minutes with the pulse at one minute (curve 2*) and at five minutes (curve 3*) recorded. The experiment was repeated for two more cycles in which the sample irradiated for five minutes, followed by three minutes of darkness.

The general conclusion that can be reached from the results shown in Fig. 6 is that the sample exhibits good photodarkening and good reversibility after a period of darkness, as is the case for the SegsTes film. However, the initial transparency of the (SegsTesKss x (S85As].5)o.i5 film is much larger, i.e. -0.8. In Table 3 is displayed data showing the initial transparency for different (Se95Te5)m x (S85Asi5)n films. Table 3

It can be seen from Table 3 that in the films with m in the range 0.7-0.9 the initial transparency has a value in the range of 0.7-0.8; while in the films with m > 0.9 and m < 0.7 the initial transparency has a value in the range of 0.3 - 0.4.

Experiments similar to those described hereinabove with reference to Fig. 5 were also carried out using thin films of Seioo-χ-y Sx Tey, wherein 10<x<30, 0<y<5. Fig. 7 shows typical curves of the change in relative transmission through a 0.7 micron thick film of this material during the length of specific 10 μsec pulses selected from a series of pulses with which the film was irradiated. Shown in Fig. 7 is the change of relative transparency during initial first pulse (curve 1) and after one minute of constant irradiation (curve 2). The film was then kept in darkness for three minutes and then irradiated again. The change in transparency of the first pulse (curve 1*) was then recorded and irradiation continued for one minute with the pulse at one minute (curve 2*) recorded. The experiment was repeated for one more cycle in which the sample irradiated for one minute after three minutes of darkness. Curve 1** is the pulse recorded after keeping in darkness for three minutes after curve 2*. In the course of the experiments it was found that: if y >5, then the initial transparency is too small for working; if x<10, then there is no influence on the increase of transparency; and if x>30, then the cumulative effect seen after a series of pulses is very week. All the curves obtained for different films compositions, i.e. for different values x and y, have approximately similar form but the value of the real initial transparency could be changed by varying the x and y values.

The general conclusion that can be reached from the results shown in Fig. 7 is that the samples exhibit good photodarkening and good reversibility after a period of darkness, just as is the case for the SegβTes film and that initial transparency can be changed by the proper selection of the film composition (values of x and y).

In some of the experiments described herein a thin dielectric film comprised of a MgF2 film with thickness 100 — 200 nm was introduced between the chalcogenide film and the reflective layer of the DVD disc in order to prevent any possible interaction between the chalcogenide and metal layers that could influence the correct working of the media.

The method of the invention is capable of being carried out on existing optical playback devices, including blue laser DVDs, with no changes in the hardware necessary. For example, in the case of CDs, all that is necessary to execute the method of the invention is to make use of the ASPI code, or another library code, for DVDROM the ASPI code or another library code, and for DVD-Video navigation commands with SPRM and GPRM are used. In any case, the operating instructions are modified or new ones added to the media that instruct the tracking system is to move the laser to predetermined location A on the disc; or, if it is able, the drive is instructed to rotate the disc at the appropriate speed, and the rest of the procedure described hereinabove is carried out. If the disc is authorized, i.e. if it contains an optical element made of photochromic material, the two readings will be different and the system will be instructed to proceed with running the program or reading the information in the medium. If the disc does not contain the photochromic material at location A, then the two readings will be the same and the system will receive instructions either to not allow running the program or reading the information on the disk or to introduce errors that will prevent normal operation.

The invention described hereinabove can be carried out in many different ways. For example, in a preferred embodiment, the disc is provided with deposits of photochromic material at two or more locations. As discussed hereinabove, the source of the photons required to cause photo-darkening of the photochromic material is the laser used to optically read the information on the media. The amount of light falling on the photochromic material can be changed in a controllable way by, for example: changing the power output of the laser, which would, for some players, require modification of the hardware as well as the software; changing the speed at which the laser passes over the optical element; and increasing the number of times that the laser returns to the same location, i.e. making multiple readings at the location of the photochromic material. As described hereinabove, the degree of photo-darkening and time of spontaneous bleaching can be selected by proper choice of the constituents of the alloy. It is also possible to adjust the degree of photo- darkening by adjusting the thickness of the film.

The thin films of photochromic materials that are the optical implants can be created in/on the optical media by many different techniques including vacuum evaporation, vacuum sputtering, and injecting the material. Other techniques, such as spin coating, which is more suitable to covering large surface areas, can also be used in certain circumstances. All of these techniques are well known in the art and can be carried out using the standard equipment found in the optical media production lines. Skilled persons would have no difficulty in making the necessary changes in the production process of the optical media in order to create optical implants at predetermined locations.

In Fig. 4 are schematically shown some of the possible locations on a DVD 9 disc that can be chosen for placement of the optical element. These include (a) on the bonding layer 30 between the two halves of the disc, (b) in the lower polycarbonate substrate 20, (c) on the outside surface of the lower polycarbonate substrate 20, (d) between the second spiral track 12 and the reflective layer 22 and (e) between the first spiral track 12 and the semi- reflective layer 28. There are two different ways to place the deposit of photochromic material at location (b): in the first method the lower substrate is split into two pieces and implant 14 is deposited or sputtered on the surface of one of the pieces before they are bonded together; in the second method the photochromic material is injected along with the polycarbonate during the injection phase of the production of the media. The location (c) can only be used for very sensitive photochromic materials since it is so far from the focus of the laser 26. At location (d) and at location (e) the photochromic material is deposited or sputtered on top of track 12 stamped into the surface of the substrate 20 before reflective layer 22 or semi-reflective layer 28 is created.

The method of the invention will be further understood from the following algorithm that describes the control instructions that must be encoded as part of the control software supplied on the optical medium, on the optical medium player, or on a separate application according to the invention. These instructions instruct the optical player how to carry out a series of steps that will test the authenticity of the disc. The instructions outlined hereinbelow are for a medium containing one spot of photochromic material located at location A on the medium as described hereinabove. The data at specified location A is read once at the beginning and again at the end of the test period. It should be understood that the following algorithm is intended only as an example of the method of the invention and that many different sets of instructions, suitable for use with any of the embodiments described hereinabove, and other embodiments can be formulated. For example, algorithms could be written for cases in which two or more implants are present on the media or for a method in which readings are made at several locations, at some of which are known to be present implants and at others of which it is known that there are none. The necessary modifications needed to create sets of instructions for all of these as well as any other conceivable method of working with the optical implants of the invention will be apparent to the skilled person.

The steps of the algorithm for the simplified example are as follows: (a) place said medium on a suitable played; (b) start the test; (c) read location A, obtaining reading Ai; (d) instruct drive and tracking motors to repeatedly return to location A a predetermined number of times; (e) read location A, obtaining reading A2; (f) compare readings Ai and A2; (g) if Ai = A2, then an implant is not present and the medium is not authentic and the control software is instructed to abort the reading of the remainder of the information on the disc or to introduce errors that will prevent normal reading of the medium and/or to execute other activities, such as to "jump" to another location on the data track; and (h) if Ai ≠ A2, then an implant is present and the medium is authentic and the control software issues instructions to the reader to continue reading the remainder of the information on the disc and/or to execute other activities that are necessary to continue the application, such as to "jump" to another location on the data track or begin decryption of the data.

In addition to the use of the present invention to verify the authenticity of the information on optical media and preventing the unauthorized copying of the information or the reading of unauthorized copies, the present invention can be used to provide a solution to many other problems that prevent copywrite owners from retaining control over their property.

One such application of the method of the present invention is to provide recordable media on which the information which is recorded will be protected from copying. During the production process of CDR, CDRW, DVDR, and DVDRW discs, optical implants of the type described herein and can be placed at specific locations. It is possible to stamp information at these locations before creating the implant or to "burn" the information through the optical implants. The software to implement the method of the invention can be recorded on the media by means of a special compiler and after the compilation stage has been completed, the information can be "burned" onto the media. As a result of the presence of the optical implant and special software, the media is protected in the same way as the read¬ only media described hereinabove.

Writeable discs prepared as described hereinabove, can also be used to prevent illegal copying of information available on the internet. In one embodiment, along with the information that is downloaded from a site on the internet will be control instructions for checking the authenticity of the media according to the methods described herein. After the information is downloaded to the hard disc of the computer and before it can be burned onto a recordable media disc, the control instructions will search for the presence of the optical implant and, only if their presence on the media is confirmed, will they allow the downloaded information to be copied from the computer's hard disc to the media.

In a variation of the above method, special control instructions located at the internet site, can be activated to determine if a media of the invention has been loaded in the drive of the computer. These instructions will allow download of the information from the site only to the hard disk of a computer that contains a medium containing the optical implants.

In another embodiment, it is not necessary for to the control instructions located at the internet site to know in advance the exact locations of the optical implants on the medium. According to this embodiment the optical implants are located on the medium at one or more locations selected from a large number of possibilities. The control instructions at the internet site scan all the possible locations to determine the exact locations of the implants in the specific writeable medium that is placed in the computer. Once all the locations have been determined, they are included in a set of operating instructions that are downloaded from the internet site to the hard disc of the computer along with the information at the site. This embodiment has at least two advantages. Firstly, the information can be downloaded to a range of different media, instead of only to a single medium that is suitable to a particular internet site. Secondly, the control instructions need not be the same for the information downloaded from an internet site, but can vary depending on the medium on which the information is to be recorded. It is to be noted that in principle, the number of possible locations of the optical implants need not be limited and the control instructions on at the internet site can cause a search to be carried out on the entire data track of the medium before allowing the information from the site to be either downloaded or copied on the medium. The above methods can be used as a means of payment. Royalties or other payments that should be paid to the owner of the information on the internet site can be included in the price of the media and paid directly to the site owner by the manufacturer of the media, thereby ensuring that the owner of the original material is compensated when it is downloaded from the site. The locations at which the implants are placed on the media and the number of implants and the algorithms can be varied such that a specific medium can be used only to download information that has a particular price or from a particular site or group of sites.

Although embodiments of the invention have been described by way of illustration, it will be understood that the invention may be carried out with many variations, modifications, and adaptations, without departing from its spirit or exceeding the scope of the claims.