The present invention relates to authentication and more specifically to optical devices and authentication methods.

BACKGROUND ART

Nowadays protection of intellectual properties and copyrights is a serious issue. A substantial number of world commerce constitutes fake, fraudulent or counterfeit products. This includes, among others, clothing items, pharmaceutical drugs and luxury items. In recent years, the prevalence of online shopping and e-commerce has proven a fertile ground for counterfeiters as it is more difficult to recognize an authentic product sold online. Furthermore, it is very difficult to identify and return robbed or missed items even after their localization as they are not associated with the rightful owner.

Current authentication and anti-counterfeit methods include overt, covert or forensic methods. Overt methods, such as by using holographic stripes, are visible to the naked eye and low cost to apply and detect but suffer from difficulty to detect a similar counterfeit overt structure and therefore have a low safety level. Overt features are intended to enable end users to verify the authenticity of a pack with the naked eye. Such features will normally be prominently visible, and difficult or expensive to reproduce. It should be noted that overt features may add significant cost, may restrict supply availability, and require education of end users to recognize them to be effective. Where overt features are used, experience is often that counterfeiters will apply a simple copy which mimics the genuine device, sufficiently well to confuse the average user.

Covert methods, such as, for example, by using holographic stripes with features that require a polarized lens to be identified, are invisible to the naked eye and generally more expensive to manufacture and detect, and have a medium level of difficulty to detect a similar counterfeit covert structure. Their safety level is accordingly considered average. The purpose of a covert feature is to enable the brand owner to identify a counterfeited product. The general public will not be aware of its presence nor have the means to verify it. A covert feature should not be easy to detect or copy without specialist knowledge, and their details may be controlled on a "need to know" basis. If compromised or publicized, most covert features may lose some if not all of their security value.

Finally, forensic methods, such as using chemical, biological or DNA taggants, include high-technology solutions which require laboratory testing or dedicated field test kits to scientifically prove authenticity. These are strictly a sub-set of covert technologies, but the difference lies in the scientific methodology required for authentication. Although they provide high level of security against copying, they have a high cost of manufacturing and detection.

The availability of diverse technologies enables misuse of protected designs and the identification of originality of products by the customer needs to be ensured. It is desirable to provide an authentication method that at least partially solves the above mentioned problems.

SUMMARY OF THE INVENTION It is an object of this disclosure to provide optical devices and authentication methods that at least partially solve the above mentioned problems.

In a first aspect of the invention an optical device is disclosed. The optical device may comprise a substrate layer and a waveguide layer. The waveguide layer may be arranged on a first surface of the substrate layer and may have a refractive index different to that of the substrate layer. The waveguide layer may comprise at least one grating layer patterned with a structure of nanoscale units along at least a first direction. The structure may be arranged to enable an optical waveguided mode resonance along at least the first direction in response to an illumination. The waveguide layer may further comprise at least one film layer that may act as an anti-reflective coating. The optical device may be arranged to produce an optical waveguide along at least the first direction that may generate a color in response to the illumination. The wavelength of the color may be defined by the pattern of the structure and the construction of the film layer. The waveguided modes may be invisible or nearly visible to the naked eye. It may require appropriate illumination to enable detection with the naked eye.

In some embodiments the at least one grating layer may be arranged on the first surface of the substrate and the at least one film layer may be deposited on the grating layer while in other embodiments the at least one film layer may be deposited on the substrate and the at least one grating layer may be arranged on top of the film layer.

In some embodiments the waveguide layer may comprise a plurality of film layers with alternating high and low refractive indices. As a result, it is possible to generate unique optical responses when the device is illuminated with white light as it may allow finetuning of the color generated by the illuminated waveguide. Additionally or alternatively the waveguide layer may comprise a plurality of overlaid grating layers. This may allow shapes and multicolor optical responses when the device is illuminated with white light.

In some embodiments the nanoscale units may be arranged in periodical unit cells in one, two or three dimensions. This may allow corresponding color patterns to be formed in one, two or three dimensions. In some embodiments the distance between the nanoscale units in the pattern may be at or below the wavelength of visible light. This means that the pattern may be visible only under predetermined waveguided mode resonances. In some embodiments the thickness of each film and/or grating layer may be between 1 nm and 500nm. The nanoscale units may be pillars, holes, lines, spheres, cubes, or the like or a combination thereof. Furthermore, when a plurality of grating layers is present, each grating layer may have nanoscale units that are of different shape or type. The size and shape of the layers and the units ensures that the optical device may not be easily copied.

In some embodiments the at least one grating layer may further comprise imperfections in the form of molecules, clusters or particles that may influence the color, such as pigments, or in the form of nanoparticles or quantum dots to enhance the optical effect of the generated color and/or to make copying difficult as the imperfections may generate unique optical responses.

In some embodiments the substrate layer may be transparent or semi- transparent. This may allow other machine readable code layers such as barcodes to be superimposed on the substrate without affecting the legibility of the code layer. The substrate layer may then be made of polymeric material, glass or quartz.

In some embodiments the optical device may comprise a code layer comprising at least a first machine readable code portion and the structure may comprise a second machine readable code portion that, when illuminated, complements the first machine readable code portion to generate a complete machine readable code, such as a barcode. In that case the optical device provides authentication via the nanostructured pattern and codification via the barcode layer. The barcode layer may not be readable unless the structure is illuminated. When the nanostructure of the optical device is illuminated, the barcode may be completed and may become readable by a barcode scanner. Therefore the optical device may have a dual function: authenticate with the nanostructure layer and codify by complementing the partial barcode layer. In some embodiments the optical device may be arranged as a label. This may allow attachment of the optical device to commercial products. Such an arrangement may include providing an adhesive layer so that the optical device may adhere to a product or sewing of the optical device to a product, such as a garment. One skilled in the art may appreciate that any type of attachment may be suitable so that the optical device is arranged as a label. The incorporation of the optical device in a label allows the label, and consequently the consumer product that the label is attached to, to be uniquely identifiable, as the differing property acts as a marker on the label. The property may be a size, distribution, type, patterning, material or thickness of the structure, although any other property that may affect the optical response should be anticipated.

In some embodiments the illuminated structure complements the barcode portion to generate a machine readable barcode.

In another aspect of the invention an authentication system is disclosed. The authentication system may be arranged to verify the authenticity of an optical device, as described with reference to previous aspects of the invention. The authentication system may further comprise a light source, such as a white light LED flashlight, to illuminate the optical device to produce a color along an optical waveguide of the optical device. The authentication system may further comprise a camera, such as a CCD camera, to capture an image of the optical device. Furthermore, the authentication system may comprise a memory having at least one reference image stored and a processor, adapted to compare the captured image with the stored reference image to generate an authentication message after comparing the two images. In some embodiments the authentication system may further comprise a communication device and a remote server. The white light source and the camera may be arranged with the communication device while the memory and the processor may be arranged with the server. The communication device may further comprise a first transceiver to transmit the captured image to the remote server and receive an authentication message from the server. The remote server may comprise a second transceiver, to receive the captured image and transmit the authentication message to the communication device.

By storing the reference image at a remote location, the level of security increases as the captured image is compared at the remote, and presumably safe, location with the reference image. The server may be arranged with the optical device manufacturer, with the product, where the optical device may be attached, manufacturer, or with a third trusted party that is entrusted with performing the authentication.

In other embodiments the white light source, the camera, the memory and the processor may be arranged with a communication device. The communication device may further comprise a display to display the authentication message generated by the processor. This arrangement may assure that an authentication can take place even in the absence of communication means or when an access to a remote location is not possible or practical. In some embodiments the light source may be a focused broadband light source such as a Light-Emitting Diode (LED) flashlight. This may ensure ubiquity of the white light source, as most modern day smartphones are equipped with such a light. In yet another aspect of the invention a method of fabricating an optical device is disclosed. The method may include the steps of providing a substrate; depositing a waveguide layer on a first surface of the substrate layer. The waveguide layer may comprise at least one film layer acting as antireflective coating, the method may further comprise the step of generating at least one grating layer on a surface of the waveguide layer patterned with a structure of nanoscale units along at least a first direction. The structure may be arranged to enable an optical waveguided mode resonance along at least the first direction in response to an illumination.

In some embodiments the step of generating at least one grating layer may comprise the steps of: providing a mould with a negative nanostructure pattern, the pattern comprising a structure of nanoscale units with distances at or below the wavelengths of visible light; and transferring the negative pattern by pressing the mould against the substrate to generate the grating layer. The pattern of the first surface of the substrate may have a structure of nanoscale features with distances at or below the wavelengths of visible light. The step of generating a pattern may be performed with one of an atomic layer deposition, chemical vapor deposition, physical vapor deposition, thermal evaporation or any other film deposition technique. The step of transferring the pattern may be performed by embossing or lithography. In the case of embossing, the master mould with the negative structure may be produced by lithographic methods.

In other embodiments the step of generating at least one grating layer may comprise depositing a nanostructure pattern on top of the waveguide layer. Said depositing a nanostructure pattern may be performed with any suitable deposition method and, in particular, (i) by evaporation of metals, metal compounds or polymers through a nanopatterned mask, (ii) by nanoxerography, (iii) by gluing a nanopatterned film on top of the waveguide layer, or (iv) by nanocontact lithography. In some embodiments the step of depositing a waveguide layer may comprise depositing a plurality of anti-reflective film layers on the substrate layer. The films may be deposited in such an order as to have alternating refractive indexes.

In another aspect of the invention, a method of authenticating an optical device is disclosed. The optical device may be similar to the optical devices described in the previous aspects of the invention. The method of authenticating may include the steps of: illuminating the optical device; detecting a waveguided mode; capturing an image of the waveguided mode;comparing said image with a reference image stored in a database; and recognizing authenticity of the optical device if a match is found in said images.

The step of capturing an image may also include recording of the image in a memory so that said comparing may be performed at a later time than when said capturing takes place.

In some embodiments the method of authenticating an optical device may further comprise the steps of: identifying at least one property of the image; comparing said at least one identified property with a reference property of the reference image stored in the database; and recognizing authenticity of the optical device if a match is found between said images and said property of the images.

In some embodiments said at least one property of the image may be a light propagation direction of the image or a color of the image. These two properties are effects produced by physical phenomena at nanometric scale and are virtually impossible to replicate without the original optical device at hand. In some embodiments the method may further comprise selecting a time sequence to illuminate the optical device, selecting a sweeping sequence to illuminate the optical device or both. In another aspect of the invention a computer implemented method of authenticating an optical device is disclosed. The optical device may be similar to the optical devices described in the previous aspects. The computer implemented method may comprise the steps of: activating a light source, such as a LED flashlight, to illuminate the optical device; activating a camera to record an image of a waveguided mode; identifying at least one property of the image; saving the recorded image and a first value corresponding to the identified property to a first memory; retrieving a reference image and a comparative value corresponding to a reference property from a database; comparing said recorded image and said first value with the reference image and the comparative value, respectively; and finally, displaying a message recognizing authenticity of product if a match is found. The computer implemented method may be realized by a programmed application installed in a communication device such as a smartphone or a tablet.

In yet another aspect of the invention a wireless communication device is disclosed. The device may comprise a light source; a camera; a processor; a memory; a transceiver; a display and a product authentication module. The memory and the processor may embody instructions stored in the memory and executable by the processor, wherein upon activation of the product authentication module the instructions may comprise functionality to activate the light source to illuminate an optical device to be authenticated; activate the camera to record an image of a waveguided mode of the optical device; identify a property of said image; save the recorded image and a first value corresponding to the identified property to the memory; transmit with the transceiver the recorded image and the saved value to a server, the server having a database with reference images and values; receive an authentication message from the server with the transceiver; acknowledge authenticity of the optical device if a match is found. In yet another aspect of the invention a code structure is disclosed. The code structure may comprise a first layer comprising a first portion of a machine readable code; a transparent layer on top of the first layer, said transparent layer comprising an optical device. The optical device may be according to the optical devices described in previous aspects of the invention. A pattern of a structure of nanoscale units of the first surface of said optical device may comprise a second portion of the code. The superposition of the first portion and the second portion may generate a code machine-readable by a scanning operation along a predetermined scanning line when the code structure is appropriately illuminated.

In yet another aspect of the invention a mobile payment system is disclosed. The system may comprise a credit card, a communication device for verifying the authenticity of the credit card and a remote server. The credit card may have a machine-readable code and an optical device on top of the machine- readable code. The optical device may be according to previous aspects of the invention. The communication device may comprise an illumination module for selectively illuminating the credit card; a camera for recording a waveguided mode image of the optical device and the barcode image; a transmitter for transmitting the recorded waveguided mode image and the code image to the remote server. The remote server may match the transmitted waveguided mode image and code to images stored in a database. The communication device may further comprise a receiver for receiving a verification message from the remote server if a match is found; and a payment module. Upon receipt of the verification message the payment module may be arranged to charge the authenticated credit card with a payment amount and issue an electronic receipt to be transmitted to the remote server. Additional objects, advantages and features of embodiments of the invention will become apparent to those skilled in the art upon examination of the description, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments of the present invention will be described in the following by way of non-limiting examples, with reference to the appended drawings, in which:

Fig. 1 shows an example of an optical device according to an embodiment. Fig. 1A is a schematic representation of a waveguide mode generation in optical devices according to embodiments of the invention.

Fig. 2 shows a cross section of an optical device according to an embodiment. Fig. 3 shows a cross section of an optical device according to another embodiment.

Fig. 3A shows a cross section of an optical device according to yet another embodiment.

Fig. 3B is a flow diagram of a method of manufacturing an optical device according to an embodiment.

Fig. 4 is a schematic representation of an authentication method and system according to an embodiment.

FIG. 4A is a flow diagram of an authentication method according to an embodiment. Fig. 5 is a flow diagram of an authentication method according to another embodiment. DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows an example of an optical device according to an embodiment. More specifically, Fig. 1 shows a lateral view of the optical device 1 10 and a plan view of a detail of optical device 1 10. In the lateral view of device 1 10, a first surface of the substrate is shown patterned with nanostructured units. In the example of Fig .1 , a square nanostructured area of 10mm has been created in the centre of a chip with oval-shaped holes arranged in a triangular or (hexagonal) pattern with a separation of about 300nm. The largest and smallest dimensions of the ovals are 200nm and 135nm, respectively, with a 5% tolerance. However, any distance between 100nm and 600nm is foreseen as part of the invention. The distance may be chosen such that a nanostructured pattern may be formed in a regular fashion and that the inter- feature spacing is at or below the wavelength of visible light. The depth of the holes is shown about 130nm. However, the depth of the holes may vary according to the thickness of the substrate. Therefore the relative depth of the structure should be such that the integrity of the substrate is not compromised. The area of the chip without the nanostructure is shown on the same level with the upper part of the nanostructure. The nanostructured area appears as teeth in the first surface of optical device 1 10.The chip may be transparent or semi-transparent. It may be, for example, of polymeric material, such as PET, PMMA, PDMS, PC, PE, PP, PS or similar, or it may be of glass or quartz.

One skilled in the art may appreciate that other shapes of holes may be possible, for example polygonal or circular shapes, and other patterns are possible, provided that the inter-feature distance remains at or below the wavelength of visible light and may extend throughout the whole surface area of the substrate or only in parts of it. Alternatively, other types of nanostructured units may be employed as part of the invention, such as pillars, pyramids, cones, lines, spheres, cubes or the like or a combination thereof. The nanostructured units may be placed in any ordered array such as an hexagonal, cubic, rectangular array or the like. Furthermore, the structure may be an overlay of multiple structures for multiple waveguiding resonance modes.

Fig. 1A is a schematic representation of a waveguide mode generation in optical devices according to embodiments of the invention. Example A shows snapshots A1 , A2 and A3 of an optical device 610 patterned with a regular pattern of horizontal parallel lines. That is, the nanostructure units are lines. Optical device 610 is first illuminated by a white light F as shown in snapshot A1 . An optical waveguide is generated along the direction of the parallel lines. This produces a color C1 all along the direction of the generated waveguide. Now, by moving or even rotating the illumination to different areas of the optical device, as shown in A2 and A3 snapshots, the colour remains the same and so does the direction of the waveguide. In the other example B of Fig. 1A, an optical device 610 ^' is grated with nanostructured units that generate a regular mesh in two dimensions. That is, the horizontal and vertical distance between consecutive nanostructured units may be the same. As a result, a waveguide is generated in a first direction and a similar waveguide, is generated in a second direction perpendicular to the first. The optical effect that results from this structure may be that of a cross having a center in the focal point of the illumination as may be seen from snapshots B1 -B3. The colour produced by the waveguide may be the same in the first and the second distance. However, if, for example, the distance between features in the one direction is not the same as the distance in the other direction, then the colours may be distinct.

Fig. 2 shows a cross section of an optical device according to an embodiment. Device 210 comprises nanostructured units 220 that appear as tapered protrusions from the substrate of device 210. The height of the protrusions may be between 50nm and 200nm, depending on the thickness of the substrate. Five nanostructured features are shown in Fig. 2. Features 220A- 220C belong to a first plane while features 220D and 220E belong to a second plane, parallel to the first and orthogonal to the substrate. All features have the shape of cone sections. However other shapes are possible provided that the inter-feature distance remains at or below the wavelength of visible light. In Fig. 1 and Fig. 2 the patterns shown are regular. That is, the pattern may comprise cells with repeating units that may result in a microscopic or macroscopic structure with repeating features, identical in size and inter- feature separations. The cells may be produced by any kind of lithography (nanoimprint, e-beam, microcontact printing, etc.) and may be repeated in one, two or three dimensions. Any regular pattern may induce such optical phenomena; however the detailed parameters may define the direction and the wavelength of the colour.

However, if an irregular pattern is used or if a partly irregular pattern is used, then the colours or the direction may vary even within the same waveguide. An irregular or partly irregular pattern may be formed with the introduction of imperfections in a regular pattern. Such imperfections may be molecules, clusters or particles that may influence the color, such as pigments, or they may be nanoparticles or quantum dots. Furthermore, said imperfections may be provoked by intentional scratches or defects on the grating layer. This may result in intentionally stopping a waveguided mode at an arbitrarily selected point or area that may appear as random to the untrained eye.

Fig. 3 shows a cross section of an optical device according to an embodiment. A substrate 310 may have a refractive index Ns. On top of the substrate, a waveguide layer may be deposited. The waveguide layer 330 may be formed of a film layer 330 having a refractive index Nw that is different from Ns. The film layer 330 may comprise one or more thin films each having its own refractive index. The films may have alternating high and low refractive indices so that the frequency range of the colour of the resulting waveguided mode is selectively narrow. On top of the film layer 330 a grating layer having a plurality of nanostructure units 315A-315D is shown. The nanostructure units are shown in the form of pillars.

Fig. 3A shows a cross section of an optical device with a plurality of film layers 330A-330D deposited on a grating layer represented here by nanostructured units 320 in the form of tapered protrusions of the substrate 31 OA. The layers are shown having a distance between them for clarity purposes. However, one skilled in the art may appreciate that each layer should be perceived deposited on top of another layer, the first layer being deposited on the nanostructured surface of the substrate. The layers may be made of different materials, thickness and refractive indices. The purpose of the different refractive indices is to generate unique waveguided resonance modes that will give unique optical responses once illuminated. The thickness of each layer may be between 1 nm and 100nm. The alternating thin films of high and low refractive index materials may functionalize the substrate structure and act as anti-reflective coating and as an enabler of waveguided mode resonances. In the example of Fig. 3, four layers 330A-330D are shown. However any number of layers may be used provided that at least one layer acts as anti- reflective coating and another layer as an enabler of a waveguided mode resonance. The design of the deposited thin films, their thicknesses and periodicity may define the waveguided mode of the resonances in terms of color. The repeating structure of the nanoscale features on the substrate may define the direction of propagation of the waveguided light along the structure upon illumination. Fig. 3B is a flow diagram of a method of manufacturing an optical device according to an embodiment. In a first step 355 a substrate is provided. In a next step 365 a waveguide layer may be deposited on the substrate. The waveguide layer may comprise a plurality of films with alternating refractive indices. The thin film layers may be deposited with atomic layer deposition (ALD), chemical vapour deposition (CVD) or with physical vapour deposition

(PVD) techniques such as sputtering, thermal evaporation or roll-to-roll technology or similar. Then, in step 375, a grating layer may be generated having a pattern with a structure of nanoscale units along at least a first direction. The structure may be arranged to enable an optical waveguided mode resonance along at least the first direction in response to an illumination. The generation of the grating layer depends on the order of the various layers of the optical device. In the case when the grating layer is below the waveguide layer, then the generation of the grating layer may follow the following steps: First, a mould may be provided having a negative nanostructure pattern. Then, the pattern may be transferred to the waveguide layer. The nanostructured features on the substrate may be transferred by embossing or structured directly by lithographic methods or with roll-to-roll technology. For embossing, the mould with the negative nanostructure may be produced by lithographic methods.

In the case where the waveguide layer is below the grating layer, then the grating layer may be generated by depositing a nanostructure pattern on top of the waveguide layer. This may be performed either by evaporation of metals, metal compounds or polymers through a nanopatterned mask, or by nanoxerography or by gluing a thin nanopatterned film on top of the waveguide layer or by nanocontact lithography, or by any other suitable technique.

Fig. 4 is a schematic representation of an authentication method and system according to an embodiment. Optical device 410 may be placed on product 415. A smartphone 430 equipped with an LED flashlight and a CCD camera may illuminate the optical device 410 and capture the illuminated image. The illuminated image 440 is a magnification of the image on the product 420. The illuminated image 440 may consist of a QR code (a two dimensional machine readable code) and a waveguide layer that comprises nanostructured units 420. The nanostructured units may only be visible when illuminated as the waveguided resonance mode of the waveguide layer is enabled with the white light of the LED flashlight. The illuminated image 440, i.e. the combination of the QR code and the illuminated nanostructured layer, may be unique for each particular item or product. The illuminated image may be used to provide two distinct services: an authentication service 470 or an ownership service 480. In case the user of the smartphone wants to verify authenticity of the product, a programmed application installed on the smartphone may be operated. The application may establish an online communication between the smartphone and a server that may reside in a cloud 460, containing the database of codes in order to enable an online verification of the authenticity of the product. Said application ("app") may read the code beneath the optical device, as well as the top authenticating optical response of the device in parallel. A response from the server may be an answer to the question: "Verified or Fake?", or similar, to indicate if a match between the captured image and a reference image has been found stored in a database of the server.

In the case of an ownership service the question may be "product missed or stolen?" therefore the answer may correspond to the presence or not of a reference image in a database of missing or stolen authentic products.

The coding itself may be done:

i) with the standard coding technologies, such as QR, barcodes, etc, as stand-alone;

ii) with the coding described in (i) in conjunction with the optical device. In that case, a portion of the QR code may be visible before illumination and the remaining portion of the QR code may become visible after illumination. Therefore, the QR code may only be read once the waveguided resonance modes have been enabled by the LED flashlight; or

iii) with the optical device as stand-alone. In that case, the whole QR code may be invisible before illumination and may become visible when the waveguided resonance modes are enabled by the LED flashlight.

The application may adapt the detection mode, depending onpre-programmed conditions, in order to create unique optical responses based on the time when the LED is switched on. For example, a unique time sequence may be initiated when the stored application is activated to authenticate an optical device or a product bearing the optical device. A pre-programmed time delay may be introduced between program activation and LED illumination. In that case, a video capture or a snapshot sequence may be unique in the sense that the nanostructured pattern may be "invisible" for a predetermined time period A and "visible" for a predetermined time period B. Time periods A and B may be unique to each particular optical device or product and may be associated to the time when the capture takes place. As a result, video recordings of captures may not be used to mimic authentication procedures as each video capture may be different from one time to another.

Furthermore, a video capture or snapshot sequence may be valid only if a unique movement sequence of the illumination takes place. For example, for one product this sequence may be first in one direction, then in another direction so that a unique "unlock" pattern may be generated that allows authentication of the illuminated optical device.

Fig. 4A is a flow diagram of an authentication method according to an embodiment. In a first step 480, an optical device may be illuminated. Then, in step 482, a waveguided resonance mode may be detected. A commercial smartphone equipped with a camera and a LED flashlight may be used for illumination of the device with light and for detecting the lateral waveguided modes. Then, in step 484, an image of the illuminated waveguide may be recorded. Next, in step 486, at least a property of the image may be identified.

Said property may be the light propagation direction, that is structure- dependent, or the color, which may be coating dependent or unit size dependent or unit type or order dependant, or a combination thereof. The propagation direction and the color may be recorded with the camera and compared with a database for recognition of authenticity of the product.Then, in step 488, said recorded image and identified property may be compared with a reference image and corresponding property. Finally, the authenticity of the optical device may be recognised.

Fig. 5 is a flow diagram of an authentication method according to another embodiment. In a first step 580, a time when an authentication function is requested may be identified. Then, in step 582 a detection mode based on the identified time may be selected. The detection mode may include a time sequence or delay of illumination or a sweeping direction sequence of illumination, distance of illumination, angle of rotation of focal point, light source power or brightness or a combination thereof. In a next step 584, an illumination device may be activated based on the selected detection mode. Then, in step 586, a camera may be activated. In step 588, a machine readable code such as a 1 D barcode or 2D QR code beneath an optical device may be identified. The optical device may be of the type described with reference to Fig. 1 - Fig. 3. In step 590, a nanostructured pattern may be identified on the optical device. In step 592 a response to said identified code, sequence and pattern may be generated. This response may be numerical and may correspond to a reference value, which would be the authentication value, stored in a database. In step 594, the response may be compared and matched with the authentication value stored in the database and, if a match is found, then the authentication may be considered successful.

The initiation of the waveguided optical modes may occur with direct illumination with the white light LED flashlight of a smartphone, tablet PC or any processor controlled portable or mounted device containing a LED flashlight, CCD camera and with optional internet connection. The system may operate with or without internet connection, in the latter case by preloading the correct match between code and optical device into the smartphone, tablet PC, or other device. The waveguided modes may only be detected by the CCD camera upon illumination with the LED light source. The waveguided modes may be invisible or nearly invisible to the naked eye before illumination. The direction of the propagating light may be controlled by the structure and may be influenced by intentional disturbance of the structural pattern. The color of the propagating light that, as mentioned before may be coating dependent or unit size dependent or unit type or order dependant, may be controlled by the multilayer stack and may also be influenced by intentional addition of imperfections, such as inorganic or organic particles or molecules, or by intentional scratching of the surface of the multilayer stack, in order to luminescence or fluorescence in the total area or in parts of it.

It should be noted that two or more optical devices may be overlayed, creating more complex optical patterns and features.

The proposed solution offers a number of advantages. First of all, it is very hard to forge. The optical effect provided by the nanostructured features is unique to the particular nanostructure. To accomplish the same optical response precise copying of the structure at nanolevel would be required which is nearly impossible with the current state of technology as the optical effects are driven by physical phenomena at nanometric scale. Furthermore, the optical and mathematical coding on top of the nano coding provides an extra level of security, at least partially independent to the structure per se. For example, the coding can change and include different parameters of the structure such as size, distribution, type, patterning, layer material, thickness, etc. Another advantage of the optical device is that the optical device with the nanostructure is cheap to manufacture and may, therefore, be used to authenticate either a manufacturer, a batch or even a single product. A further advantage of the invention is that the authentication process may be accomplished without special hardware or purpose-built devices but with an appropriately programmed common smartphone equipped with a flashlight and a camera. The smartphone may either access a remote database in a server or in a cloud based service via a communication network to perform the authentication operation, or it may have pre-stored reference images for comparing and authenticating an optical device. Providing the database in a remote server or over a cloud service may allow product authentication with high data security, ownership control at the consumer's request (e.g. missed, robbed or neutral status of the product may be adjustable by the consumer) as well as change of a product status at the manufacturer request (e.g. a defective batch may be traced or targeted campaigns and promotions may be directed to the end consumer). Additionally, ownership verification or counterfeit detection may be distributed in a social network. A new social network may be created to fight against counterfeiting and stolen goods. Rewards may be offered for the recovery of missed/robbed objects, e.g. as a percentage of their value, and the registering of original products as well as counterfeit detection and reporting may be encouraged.

Subsequently, a mobile payment system shall be described that is facilitated by the optical devices and authentication methods described above. A bank may issue a credit card labelled with an optical device as described above. The customer's data may be stored at the bank's payment system server. The data may be recorded in the credit card in a machine-readable code, such as a QR code. A verification nanolayer may be put on top of the QR code. A seller may have a mobile phone or tablet with a payment system app (no additional POS required). The customer may pay with his credit card. The authenticity of the credit card may be verified by the optical device with an authentication method as described above. Finally the data of the customer may be read by the QR code.

Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described before, but should be determined only by a fair reading of the claims that follow. Further, although the embodiments of the invention described with reference to the drawings comprise computer apparatus and processes performed in computer apparatus, the invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the processes according to the invention. The carrier may be any entity or device capable of carrying the program.

For example, the carrier may comprise a storage medium, such as a ROM, for example a CD ROM or a semiconductor ROM, or a magnetic recording medium, for example a floppy disc or hard disk. Further, the carrier may be a transmissible carrier such as an electrical or optical signal, which may be conveyed via electrical or optical cable or by radio or other means.

When the program is embodied in a signal that may be conveyed directly by a cable or other device or means, the carrier may be constituted by such cable or other device or means.

Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.