WO2008068700A1

WO2008068700A1 - Regenerable optical medium with limited viewing window

Info

Publication number: WO2008068700A1
Application number: PCT/IB2007/054886
Authority: WO
Inventors: Ronald J. A. Van Den Oetelaar; Antonius E. T. Kuiper; Donato Pasquariello
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-12-08
Filing date: 2007-12-03
Publication date: 2008-06-12
Also published as: TW200836188A

Abstract

An optical storage medium having a limited viewing window that is regenerable is disclosed. The optical storage medium comprises a data layer (22) wherein information is stored, access control means for controlling access to at least part of information stored in the data layer, the access control means (23) being enabled to switch from an initial state, the initial state allowing access to at least part of the stored information in the data layer, to a second state, the second state inhibiting said access, after a predetermined period of time from an activation moment, wherein the access control means are enabled to revert to the initial state allowing access. The optical storage medium is preferably used for renting content wherein the limited viewing window is replacing additional fees as an incentive for customer to return the disc in time.

Description

Regenerable optical medium with limited viewing window

FIELD OF THE INVENTION

The present invention relates generally to optical storage medium and use of such an optical storage medium for distributing content. The application also relates to a method of distributing content stored in a data layer of an optical storage medium and a method of distributing content.

BACKGROUND OF THE INVENTION

Use of optical storage media for distribution of content, such as video content music, games or software, is well known. It is noted that throughout this application, the word "content" is used to describe any intellectual creation that is copyrighted and that a copyright owner intends to distribute in certain markets, by itself or via third parties. It is assumed to comprise any of the following or combination thereof: video content, such as movies, audio content, such as music and audio books, games and/or software. It is further noted that, throughout this application, the word "distribution" is used to describe any means or methods of making content available to third parties, for example by means of direct sale, rental or licensing.

A known optical disc is the "limited lifetime" or "limited use" disc. An example of such a disc is the "ez-D" disc, known, for example, from US 6,790,501. An ez-D disc is supplied in a vacuum-sealed package, and when the package is opened the content on the disc can only be played for a limited time. The ez-D disc works on the principle that a reactive dye is mixed with the adhesive that bonds the DVD layer with a substrate (i.e. polycarbonate layer). The dye, which is sandwiched between the two polycarbonate layers, undergoes a transition from a reduced state to an oxidized state when exposed to air, as oxygen from the air diffuses through the polycarbonate layers. The dye is transparent in the reduced state whereas, in the oxidized state, the dye absorbs wavelengths used for optical writing and reading, thus making the data in the DVD layer unreadable. The governing degradation mechanism is that oxygen diffuses through the polycarbonate and reacts with the reactive dye. Limited lifetime discs are used for content distribution by means of rental, whereby a customer purchases the movie at a gas station, supermarket or wherever, and can then choose to watch the movie at a later time. However, once the vacuum seal is broken, the limited lifetime disc only has a predetermined play life. For example, the ez-D disc expires after a 48 hours play lifetime. This ensures a usage similar to that of rented DVD, with the difference that the customer is more attracted to use the service, as (s)he does of not facing the risk of being charged extra for not returning the rented disc on time. The above business model has the disadvantage that it is either environmentally non- friendly, if the limited lifetime optical disc are thrown away after a single use. It is noted that when limited lifetime disc are used, there is no incentive for consumer to return the disc for proper disposal. Providing such incentive for customers for collecting and recycling the used discs involves additional costs.

SUMMARY OF THE INVENTION It is an object of the invention to provide an optical media alleviating the above environmental concerns. The object of the inventions is reached when content is distributed onto an optical medium according to claim 1. An optical storage medium according to the invention comprises a data layer wherein information is stored and access control means for controlling access to at least part of the data layer, the access control means being enabled to switch from an initial state, the initial state allowing access to at least part of the stored information in the data layer, to a second state, the second state inhibiting said access, after a predetermined period of time from an activation moment, the access control means being enabled to revert to the state allowing access. As the access control means are enabled to revert to the state allowing access, if the optical storage medium is used for renting content to a customer and it is returned by the customer at any moment after the predetermined period of time, the state of the access control means can be reverted and the optical storage medium can be re-used for renting the content to another customer. Consequently, as an optical storage medium can be used several times, the total cost of producing the media is reduced. Part of this cost reduction may be used for providing an incentive to customers for returning the optical storage media, thereby alleviating said environmental concerns.

According to a first aspect of the invention the access control means comprise an access control layer, the access control layer covering at least part of the data layer, the data layer suitable to be scanned by means of a focused radiation beam in an optical scanning apparatus, the access control layer being enabled to switch from a state allowing saind scanning of the data layer to a state inhibiting said scanning. A possible solution to control the access to content stored on optical storage media involves use of suitable Digital Rights Management (DRM) methods. Typically, the rights of a user are obtained by means of interaction between an optical drive and media, and it may require a suitably adapted optical drive and connection to the Internet. This is disadvantageous, it limits the size of the distribution market by firstly, lack of compatibility with standard players by requiring a suitably adapted drive and secondly, as access to the Internet may not always be available. Use of an access control layer enabled to switch from a state allowing scanning of the data layer by means of a focused radiation beam a state inhibiting said scanning alleviates such problems, as the compatibility with standard players is maintained and access to internet is not required.

In an embodiment of the invention, the activation moment corresponds to an exposure of the access control layer to an activating substance, the access control layer being enabled to change an optical property after said exposure. This allows control of the start moment of the limited viewing window.

In an advantageous embodiment of the invention the access control layer is positioned with respect to other layers on a surface of the optical storage medium. It is noted that in the known, limited use disc from US 6,790,501, the reactive dye is sandwiched between the two polycarbonate substrate layers, the governing degradation mechanism is that oxygen diffuses through the substrate and reacts with the reactive dye. Thus as the lifetime is controlled by means of controlling the diffusion rate of oxygen through the substrate layers, such reactive dye is required to sandwiched between the two polycarbonate substrate layers. However, such placement between the two polycarbonate substrate layers inhibits access to said dye, therefore it is not possible to revert the dye to the original state after oxidation. In contrast, when the access control layer is positioned with respect to other layers on a surface of the optical storage medium, the access control layer is accessible for reagents and such reversal is possible. Furthermore, according to one aspect of the invention the access control layer further comprises means for controlling the length of the predetermined period of time. In an embodiment of the invention, a cover layer is provided on top of the access control layer, the cover layer having a high porosity. The cover layer may provide protection, for example against scratches, while the high porosity provides accessibility for reagents such that reversal of the state of the access control layer. According to an aspect of the invention, the activating substance is atmospheric oxygen, and the access control layer is enabled to switch from an oxidized state inhibiting scanning of the data layer to a reduced state allowing said scanning by exposure to a reducing agent. Preferably, the reducing agent is hydrogen or hydrogen sulphide gas. It is noted that this aspect is advantageously combined with the used of a porous cover layer, as the diffusion constant of a gas through such layer is much higher. It is further noted that hydrogen gas has a smaller molecule that O₂, therefore the diffusion of hydrogen is expected to be higher that that of atmospheric oxygen. Consequently, when hydrogen is used as reducing gas, the diffusion layer may advantageously be used for further controlling the predetermined period of time that the stored content in the data layer is accessible. The invention also related to use of an optical storage medium according to the invention for distributing content. According to an aspect of the invention, a method of distributing content comprising steps of: storing the content in a data layer wherein information, the data layer suitable to be read by means of a radiation beam in an optical scanning apparatus, providing access control means for controlling access to at least part of the data layer, the access control means being enabled to switch from a state allowing access to at least part of the stored information to a state blocking to said access at least part of the stored information after a predetermined period of time from an activation moment, distributing said optical storage media and receiving the optical storage media and after the predetermined period of time and reverting access control means to the state allowing access. This corresponds to distributing content via rental, wherein the financial penalties for returning content after the expiry of a rental period may be replaced to the fact that the content cannot be accessed anymore after the expiry of the rental period, thereby providing an incentive to return the content. According to an advantageous aspect of the invention, the data layer may be of the re-writable type, therefore allowing changing the content stored in the data layer prior to redistribution.

According to an advantageous aspect of the invention, a customer may be provided at any time with any number of optical storage media up to a predetermined number. In a rental business model, known for example from US 7,024,381, customers pay a monthly subscription fee. The subscription allows the customer to keep a revolving library of a preset number of optical media. The customer can exchange an old optical media for a new optical media in this library by sending the old media back to rental company, and receiving a new optical media by mail in return. The customer is allowed to exchange content as often as he/she likes. In this business model, there is no incentive for the customer to send a specific optical media back to rental company after a certain amount of time, other than that the customer is not interested anymore in watching the content stored thereon. The lack of such an incentive is a disadvantage for the rental company: popular (e.g. newly released) optical media may have a very low turnover rate, requiring the rental company to acquire a large initial stock of popular optical media from content providers, which may be expensive. When an optical media has a limited viewing window, the customer has an incentive to return the media after the predetermined period of time, as (s)he is not able to use the content after the predetermined period of time.

These and other aspects of the invention are apparent from and will be elucidated with reference to following more particular description of several embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will be appreciated upon reference to the following drawings, in which: Figure Ia illustrates a conventional optical storage medium while Figure Ib illustrated a cross section through a known optical storage medium having a limited viewing window;

Figure 2 illustrates a cross section through an optical storage medium according to an aspect of the invention; Figure 3 illustrates chemical reaction methylene blue to leuco methylene blue,

Figure 4a illustrates the measured absorption and transmission spectra of the disc comprising an access control layer comprising methylene blue in the oxidized state, while Figure 4b illustrates the time dependence of the absorbance and transmission a layer comprising methylene blue in the reduced state is exposed to air, while Figure 4c the time dependence of the absorbance and transmission a layer comprising methylene blue layer in the oxidized state while immersed in a 2% Sn(II) ethylhexanoate solution;

Figure 5 illustrates a cross section through an optical storage medium according to another aspect of the present invention;

Figure 6 illustrates an optical storage medium according to another aspect of the present invention;

Figure 7 illustrates a method of distributing entertainment content according to an aspect of the present invention.

Figure 8 illustrates a method of distributing content according to another aspect of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure Ia shows a conventional optical storage medium 11 having a track 12 and a central hole 10. The track 12, being the position of the series of (to be) recorded marks representing information, is arranged in accordance with a single spiral pattern constituting substantially parallel tracks on a data layer. Known examples of optical storage media suitable for distribution of content are CD-ROM, known from ECMA- 130 or DVD-ROM, known from ECMA-267 (also known as ISO IEC 16449). The track structure is constituted, for example, by a pre-groove, which enables a read/write head to follow the track during scanning. The track structure comprises position information, e.g. addresses, for indication the location of units of information, usually called information blocks. The position information includes specific synchronizing marks for locating the start of such information blocks. The position information is encoded in frames of modulated wobbles.

If viewed in cross-section, an optical storage medium usually comprises a transparent substrate, the data layer and a protective layer. For example, in DVD systems, the data layer is at a 0.6mm substrate and a further substrate of 0.6 mm is bonded to the backside thereof. The pregroove may be implemented as an indentation or elevation of the substrate material, or as a material property deviating form its surroundings.

The optical storage medium 11 is intended for carrying real-time information according to a standardized format, to be playable on standardized playback devices. The recording format includes the way information is recorded, encoded and logically mapped. The logical mapping may comprise a subdivision of the available area in a lead-in, a recording area for user data and a lead-out. Further, the mapping may comprise file management information for retrieving the user information, such as a Table of Contents or a file system, e.g. ISO 9660 for CD-ROM or UDF for DVD-ROM or high-density optical media such as Blu-ray (BD). Such file management information is mapped on a predefined location on the record carrier, usually in or directly after the lead-in area. However, this document does not relate to the application format, but to the physical structure of such optical storage medium. Figure Ib illustrates a cross section through a known type of optical disc, the so-called "limited lifetime" or "limited use" disc. An example of such a disc is the "ez-D" disc, as known, for example, from US 6,790,501. The ez-D disc comprises a bottom substrate layer 13 and a top substrate layer 17 that are bonded together, a data layer 14 and a reflective layer 15 being present at the interface thereof. Further, a reactive dye is mixed in the adhesive layer 23 that bonds the data layer 14 with the top substrate 17 (i.e. the top polycarbonate layer). An ez-D disc is a DVD type disc supplied in a vacuum-sealed package, and when the package is opened the content on the disc can only be played for a limited time. The dye goes from a reduced state to an oxidized state when exposed to air. The dye is transparent in the reduced state whereas, in the oxidized state, the dye absorbs wavelengths used for optical writing and reading, thus making the data in the DVD layer unreadable. The governing degradation mechanism is that oxygen diffuses through the substrate and reacts with the reactive dye. Thus, this type of disc provides a limited lifetime or limited use disc, which is achieved by superimposing the data layer with a layer that darkens when in contact with air. The lifetime is controlled by means of controlling the diffusion rate of oxygen through the substrate layers. Limited lifetime discs are exclusively used for content distribution by means of rental, whereby a customer purchases the movie at a gas-station, supermarket or wherever, and the customer can choose afterwards to watch the movie at a later time. However, once the vacuum seal is broken, the limited lifetime disc has only a predetermined playback life. For example, the ez-D only has a 48 hours playback lifetime.

An optical storage medium according to the invention is characterized by comprising access control means for controlling access to at least part of the data layer, the access control means being enabled to switch from a state allowing access to at least part of the stored information to a state blocking to said access at least part of the stored information after a predetermined period of time wherein the access control means are enabled to revert to the state allowing access. In the following, several embodiments for such access control means will be discussed.

Figure 2 illustrates a cross section through an optical storage medium according to an aspect of the invention. In the following, it will be appreciated that the term "topside" means the side that is located towards the laser source, whereas the term

"underside" means the side located away from the laser source. The optical storage medium comprises a stack of layers, including an underside substrate 21, a data layer 22, wherein the information may be stored, a topside substrate 24 and an access control layer 23. It is noted that, unlike the known ez-D disc, the access control layer 23 is placed on the topside surface of the topside substrate layer instead of being sandwiched between the two substrate layers.

With respect to the access control layer 23, it is chosen such that it has two states, a first state that allows readout access of the data layer and a second state that blocks readout access to the data layer. The access control layer 23 is further chosen such that a transition from the first state to the second state takes place automatically after a predetermined period from an activation event. Moreover, it is possible that to revert the state of the access control layer 23 from the second state to the first state.

In the following a detailed embodiment will be discussed for the case the readout of the data layer is performed by a red laser, i.e for DVD systems. LeucoMethylene blue is a known reactive dye that changes reversibly from a reduced transparent state to a blue oxidised state, known as methylene blue.

Fig. 3 a illustrates the reversible oxidation-reduction process of leuco methylene blue (transparent) into methylene blue (blue).

It is noted that, when (leuco)methylene blue is added to the access control layer 23, if the (leuco)methylene blue is in the transparent reduced state, readout of the data layer is possible. If the (leuco)methylene blue is in the blue oxidized state, readout of the data layer is inhibited, as the blue dye provides a high absorption in the red part of the spectra. Consequently, the presence of (leuco)methylene blue enables the two reversible states of the access control layer. It is further noted, that when an access control layer 23 comprising only

(leuco)methylene blue is placed on the topside surface of the topside substrate layer, it comes in direct contact with atmospheric oxygen, therefore accurate control of the viewing window is not possible. Consequently, the access control layer 23 according to the invention comprises a mixture of leuco methylene blue and Sn(II) 2-ethyl hexanoate. Sn(II) 2-ethyl hexanoate will transform into Sn(IV) 2-ethyl hexanoate in the present of an oxidizing agent. This latter conversion is not an equilibrium reaction, as opposed to that involving (leuco)methylene blue redox couple. The oxidation potential of Sn(II) 2-ethyl hexanoate is much lower than that of leuco methylene blue. Consequently, in the presence of an oxidant (oxygen from the ambient atmosphere, H₂O₂, etc.) Sn(II) 2-ethyl hexanoate oxidizes and forms Sn(IV) 2-ethyl hexanoate before the oxidation of leuco methylene blue starts. Only after all Sn(II) 2-ethyl hexanoate is consumed the oxidation and coloration of leuco methylene blue starts. Consequently, the concentration of Sn(II) 2-ethyl hexanoate in the access control layer 23 determines the incubation time before the access control layer 23 switches to the state inhibiting readout of the data layer, when the disc is exposed to ambient oxygen. Hence by adding or subtracting the Sn(II) 2-ethyl hexanoate content in the access control layer 23, the predetermined period of time that the stored content in the data layer is accessible may be increased or reduced.

Furthermore, it was verified experimentally that that the reaction of Leuco methylene blue (transparent) into methylene blue in the present of the Sn(II) ethyl hexanoate is reversible. The reduction of methylene blue back into Leuco methylene blue was obtained by using a solution of Sn(II) ethyl hexanoate.

The experiments were conducted as follows: A solution of 2% Sn(II) ethyl hexanoate in ethyl lactate was prepared. It is known that the rate of oxidation of methylene blue can be further controlled by the pH. A lower pH decreases the rate of oxidation and therefore favors the reduction reaction. The solution has been lowered slightly by adding 0.2 g ofadipic acid.

A disc comprising a 0.6 mm transparent polycarbonate substrate, an adhesive layer in the order of 25 micron comprising acrylate and Sn(II) ethyl hexanoate corresponding to 0.2% atomic Sn and a 100 nm thick layer comprising leuco methylene blue dye was exposed to air, so that the dye would oxidize to the blue state,

The absorption and transmission spectra of the disc during the oxidation process were monitored by means of UV- Vis spectroscopy. Figure 4a illustrates the measured absorption and transmission spectra of the disc comprising the oxidized methylene blue layer. A strong absorption peak in the red part of the spectrum is visible.

Figure 4b illustrates the time dependence of the absorbance and transmission a layer comprising methylene blue in the reduced state while exposed to air, as monitored with UV VIS spectroscopy at a wavelength of 588nm. The wavelength of 588 nm was chosen instead of 650 nm corresponding to a red laser as used in CD and DVDV systems in order to be able to monitor the start of the oxidation/reduction reaction. The absorbance of the layer at 650 nm of is too high when the methylene blue is in the oxidized state to be measured and, moreover, small changes in the transmission cannot be distinguished. Consequently, the absorbance and transmission at 588nm were measured, which resembles the behavior at 650 nm. One can see that in a time scale of several hours the layer changes from a transparent state to an absorbing state.

A cuvette with a path length of 1 mm was filled with the prepared solution of 2% Sn(II) ethyl hexanoate and the disc comprising the access control layer comprising methylene blue in the oxidized state as the active dye was place inside. When the layer comprising the dye is treated in the Sn(II) ethyl hexanoate solution, new Sn(II) salt is added to layer. The solution reverses the oxidation reaction, leading to the oxidized methylene blue being reduced back to leuco methylene blue (transparent). Figure 4c illustrates the time dependence of the absorbance and transmission a layer comprising methylene blue in the reduced state while immersed to the 2% Sn(II) ethyl hexanoate solution, as monitored with UV VIS spectroscopy at a wavelength of 588nm. One can see that in a time scale of several tens of minutes the layer changes from an absorbing state to a transparent state. It is noted that several other reducing agents may be used instead of the Sn(II) ethyl hexanoate solution for this purpose.

In addition, according to this aspect of the invention, there is provided a cover layer 55 on top of the access control layer 23, as shown in Fig 2. However, the time it takes for the regeneration, that is turning the reactive layer back to the transparent state using e.g. a Sn(II) ethyl hexanoate solution, is then governed by the permeability of said cover layer. It is noted that in principle the topside or the bottom side polycarbonate substrate may act as a cover layer, assuming these are further adapted with respect to their permeability, for example by using a porous layer. Compared to permeability of standard polycarbonate substrates used for DVD, it is advantageous to increase the permeability in order to increase the diffusion of liquids through the diffusion layer, e. g. Sn(II) ethyl hexanoate solution. In addition, according to another aspect of the invention, a reducing gas, such as, for example H₂ or H₂S may be used as a reducing agent instead of the Sn(II) ethyl hexanoate solution. It is noted that this aspect is advantageously combined with the use of a cover layer, as the diffusion constant of a gas through the cover layer is much higher. It is further noted that hydrogen gas has a smaller molecule that O₂, therefore the diffusion of hydrogen is expected to be higher that that of atmospheric oxygen. Consequently, when hydrogen is used as reducing gas, the cover layer may advantageously be used for further controlling the predetermined period of time that the stored content in the data layer is accessible.

In the following some further materials shall be explained which can be used according to the present invention to provide the effect of changing its optical reflectivity and/or transmittance over time, i.e. which can be used for the access control layer according to the present invention. With respect to the access control layer, it is sufficient to provide a reactive dye or indicator that, upon oxidation, gradually and reversibly transform from colorless to either blue (high absorption in the range of 600-700nm) or red, or upon oxidation, gradually and reversibly change color from red to blue or from blue to red. A dye or indicator having a high absorption in the range of 600-700nm in the oxidized state is suitable for use when the optical storage media requires a red laser for reading, such as DVD and CD media. A dye or indicator having a high absorption in the blue range in the oxidized state is suitable for use when the optical storage media requires a blue laser for reading, such as high-density discs such as Blu-ray (BD) or HD-DVD. For example, known dyes that are change from colorless to blue upon oxidation are Acridine Yellow (C₁₅H₁₆N₃Cl), which has a strong absorption peak centered around 41 lnm in the oxidized state and Triarlymethane dyes.

Particularly, oxazines (containing a N and an O atom in the second ring) and thiazines (containing a N and a S atom in the second ring) are suitable for this purpose. With respect to dyes compatible for use with DVD type media, another example is Nile-Blue. It is known that in a solution of water Nile-Blue gradually transforms in Nile Red: the NH2-group is replaced by =0. The absorption peak shifts from 650nm to 550nm. This also occurs when water is diffusing through the polycarbonate substrate to the dye layer, so that this molecule is a candidate for the aimed application. More details about such materials can be found in The Sigma- Aldrich

Handbook of Stains, Dyes and Indicators, F. J. Green, Aldrich Chemical Company, Milwaukee, Wisconsin (1990).

Advantageously, the predetermined period before the oxidation of the reactive dye or indicator, is controlled by the presence of a determined amount of a buffer substance having a lower oxidation potential. By adding or substrating the buffer substance in the access control layer the lifetime is increased or reduced, respectively. In this embodiment of the access control layer, its composition comprises at least two components, the first one is a dye or indicator which forms a redox couple with athmospheric oxygen, and the second component that has a lower oxidation potential that the first component and that is transparent both in reduced and oxidized state. The first component is responsible for the change in absorption parameters in the desired range as described above, while the second component is responsible for controlling the predetermined period of time.

Figure 6 illustrates an optical storage medium according to another aspect of the present invention; Region 62 comprises stored information, such as a main feature in a movie, that is protected by an access control layer as described with reference to Fig. 2 or 5. Region 61 comprises further information, such as special content features, and its structure correspond to a normal optical media, that is the information stored therein is directly accessible. Said regions are shown as annular regions around the hole 10, with Region 62 shown towards the outside. Such a physical arrangement provides the advantage of compatibility with standard player devices, which expect the lead-in region to be located at the inner part of a track. However, different arrangements are possible.

The disc structure presented in Figure 2, 5 and 6 referred to a read-only disc. It is noted that the idea is of course also applicable to write once disc and a rewritable disc, wherein the read only data layer is replaced accordingly with a layer comprising a suitable dye (write once) or with a phase change layer (rewritable).

Figure 7 illustrates a method of distributing content according to an aspect of the present invention. In step 71 (STORE) the content is stored onto the optical storage medium, and in step 72 (ACC CTRL) access control means as detailed above with respect to Figs 2 to 6 are provided. It is noted that the length of the predetermined period, i.e. the length of the viewing window, may be set in dependent on the content stored on disc. The optical storage medium may be stored in a protective atmosphere. In step 73 (EXP), the start of the viewing window is set, for example by exposing the optical storage medium to atmospheric oxygen. In step 74 the optical storage medium is distributed by a distributor, for example rented to a consumer by a rental company. It is noted that any of step 71-73 may be taken by a different party than the distributor, for example a producing company. In an alternative embodiment of the method, the distribution step 74 (DISTRIB) preceded the exposure step 73, wherein the exposure step 73 corresponds to the consumer opening a jewel case, therefore exposing the optical storage medium to atmospheric oxygen. After viewing the content and possibly after the expiry of the viewing window, the customer returns the optical storage medium to the distributor in step 75 (RETR). In step 76 (REG) the received the optical storage medium, having the access control means in state inhibiting scanning access to the data layer, are reverted to the initial state allowing access, as described above with respect to Figs 2 to 6. Optionally, in step 77 (CH/REDISTR), the regenerated optical media is redistributed. It is noted that if a rewritable optical media is used, it is also possible to change the stored content in this step before redistribution.

Figure 8 illustrates a method of distributing content according to another aspect of the present invention. This relates to renting content to customers, wherein the customers pay a monthly subscription fee for the right to keep a revolving library of a predefined number of optical media. The customer can exchange an old optical media for a new optical media in this library by sending the old media back to rental company, and receiving a new optical media by mail in return.

In step 81 (USR REQ), the distributor receives a request from the customer for receiving specific content. In step 82 (<N?), it is checked whether the number of optical storage media in the possession of the customer is below the predefined number. If yes, in step 83 (EXP) optical storage medium according to the invention, that is provided with access control means as detailed above with respect to Figs 2 to 6 is prepared and the start of the viewing window is set, for example by exposing the optical storage medium to atmospheric oxygen. It is noted that the length of the predetermined period, i.e. the length of the viewing window, may be set in dependent on the content stored on disc. For instance, popular DVDs may be given a shorter viewing window, in order to increase their turnover rate. In step 84 (DISTRIB), the optical storage media is sent to the customer. In step (84) an optical storage medium is received from the user and the access control means are reset to the initial state, so that said medium can be reused.

The present invention can be summarized as follows: An optical storage medium having a limited viewing window that is regenerable is disclosed. The optical storage medium comprises a data layer wherein information is stored, access control means for controlling access to at least part of information stored in the data layer, the access control means being enabled to switch from an initial state, the initial state allowing access to at least part of the stored information in the data layer, to a second state, the second state inhibiting said access, after a predetermined period of time from an activation moment, wherein the access control means are enabled to revert to the initial state allowing access. The optical storage medium is preferably used for renting content wherein the limited viewing window is replacing additional fees as an incentive for customer to return the disc in time.

It should be noted that the above-mentioned embodiments are meant to illustrate rather than limit the invention. And that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verbs "comprise" and "include" and their conjugations do not exclude the presence of elements or steps other than those stated in a claim. The article "a" or an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

CLAIMS:

1. An optical storage medium comprising: a data layer wherein information is stored; access control means for controlling access to at least part of information stored in the data layer, the access control means being enabled to switch from an initial state, the initial state allowing access to at least part of the stored information in the data layer, to a second state, the second state inhibiting said access, after a predetermined period of time from an activation moment; wherein the access control means are enabled to revert to the initial state allowing access.

2. An optical storage medium according to claims 1, characterized in that the access control means comprise an access control layer, the access control layer covering at least part of the data layer, the data layer suitable to be scanned by means of a focused radiation beam in an optical scanning apparatus; the access control layer being enabled to switch from a state allowing said scanning of the data layer to a state inhibiting said scanning.

3. An optical storage medium according to claim 2, characterized in that the activation moment corresponds to an exposure of the access control layer to an activating substance, the access control layer being enabled to change an optical property after said exposure.

4. An optical storage medium according to claim 3, characterized in that the access control layer is positioned with respect to other layers on a surface of the optical storage medium.

5. An optical storage medium according to claim 4, characterized in that the access control layer further comprises means for controlling a length of the predetermined period of time.

6. An optical storage medium according to claim 4 or 5, characterized in that a cover layer is provided on top of the access control layer, the cover layer having a high porosity.

7. An optical storage medium according to claims 5 or 6, characterized in that the activating substance is atmospheric oxygen, and the access control layer is enabled to switch from an oxidized state inhibiting scanning of the data layer to a reduced state allowing said scanning by exposure to a reducing agent.

8. An optical storage medium according to claims 7, characterized in that the reducing agent is hydrogen or hydrogen sulphide gas.

9. An optical storage medium according to claims 7 to 8, characterized in that the access control layer further comprises a buffer substance for controlling the predetermined period of time.

10. An optical storage medium according to claim 2, characterized in that the data layer is of the re-writable type.

11. Use of an optical storage medium according to any of the previous claims for distributing content.

12. A method of distributing content comprising steps of: storing the content in a data layer wherein information, the data layer suitable to be read by means of a radiation beam in an optical scanning apparatus; - providing access control means for controlling access to at least part of the data layer, the access control means being enabled to switch from a state allowing access to at least part of the stored information to a state blocking to said access at least part of the stored information after a predetermined period of time from an activation moment; distributing said optical storage media; receiving the optical storage media and after the predetermined period of time and reverting access control means to the state allowing access.

13. A method according to claim 12, characterized by setting a length of the predetermined period of time dependent on the content stored in the data layer.

14. A method according to any of claim 12 or 13, characterized by further comprising the step of re-distributing the media after the step of reverting access control means to the state allowing access.

15. A method according to claim 14, wherein the data layer is of the re-writable type, the method characterized by a step of changing the content stored in the data layer prior to the redistribution step.

16. A method according to any of claim 12-15, characterized by the media is distributed by means of rental.

17. A method according to claim 16, characterized by providing a customer up to a predetermined number of optical media.