LIGHTGUIDE TAMPER SEAL

Abstract

A tamper seal includes an optical waveguide arranged to guide a propagating light-beam along a propagation direction. First and second portions of the tamper seal are configured to be arranged on first and second parts, respectively, which are movable relative to each other. The first portion has an input coupler arranged to couple incident light into the optical waveguide, and the second portion has at least one output coupler arranged to couple out of the optical waveguide at least partially light guided in the optical waveguide. The input coupler, the optical waveguide, and the output coupler are configured to transmit light from the input coupler to the output coupler. The waveguide is configured to be disruptable and includes a layer having a distinctive appearance that is changed in response to an at least partial disruption of said optical waveguide.

Claims

1. A tamper seal comprising an optical waveguide comprising at least a first portion and a second portion configured to be respectively arranged on a first part and on a second part of an object, said first and second parts being movable relative to each other, wherein said optical waveguide is a flat and flexible multimode optical waveguide defining a plane and having, parallel to said plane, a first side and a second side opposite to said first side, said waveguide comprising at least a rectangular shaped waveguide core that has a smallest dimension, defined perpendicular to said propagation direction, greater than 10 ?m and smaller than 10 mm, said first portion comprising on one of said sides an input coupler arranged to couple incident light into said optical waveguide, said second portion comprising on one of said sides at least one output coupler arranged to couple out of said optical waveguide at least partially light guided in the optical waveguide, wherein said input coupler, said optical waveguide and said output coupler are configured to transmit light from said input coupler to said output coupler, said optical waveguide being further configured to be at least partially disruptable between said first portion and said second portion, said optical waveguide comprising a layer configured to produce at said outcoupling surface a visually distinctive appearance when light is incoupled in said incoupler, said layer being further configured so that said visually distinctive appearance is changed in response to a change of the optical guiding properties of said flat multimode waveguide in response to an at least partial disruption of said optical waveguide.

2. The tamper seal according to claim 1, wherein said visually distinctive appearance is the color of the outcoupled light by said outcoupling surface.

3. The tamper seal according to claim 1, wherein said visually distinctive appearance is the angular distribution of the outcoupled light by said outcoupling surface.

4. The tamper seal according to claim 1, wherein said visually distinctive appearance is the display of a logo or a symbol or a text and in that said change of appearance is the alteration of the display of said logo or symbol or text.

5. The tamper seal according to claim 4, wherein said change of said text comprises the substitution of at least one letter by another letter in said text.

6. The tamper seal according to claim 4, wherein said optical waveguide comprises a cladding and wherein said change of said visually distinctive appearance is produced by light leaking into said cladding.

7. The tamper seal according to claim 1, wherein the optical waveguide is made of polymer or glass or made in a water soluble polymer.

8. The tamper seal according to claim 1, wherein the optical waveguide comprises a portion of which the waveguiding properties are irreversibly altered by heat.

9. The tamper seal according to claim 1, wherein at least one of said input coupler or outcoupling surface comprises a water soluble polymer.

10. The tamper seal according to claim 1, wherein a second layer is arranged on at least a portion of said waveguide, said second layer being configured to enhance the sensitivity of the optical effect of the change of said visual distinctive appearance.

11. The tamper seal according to claim 10, wherein said second layer comprises at least one of an ink layer, a fluorescent layer, a phosphorescent layer, a colored layer comprising any type of pigment, an ultraviolet pigment, an infrared pigment, an optical scattering layer or a refractive optical element.

12. The tamper seal according to claim 10, wherein said second layer is incorporated into said optical waveguide.

13. The tamper seal according to claim 1, wherein at least one optical security element is arranged on at least a portion of said optical waveguide.

14. The tamper seal according to claim 13, wherein at least one optical security element is arranged on said output coupler.

15. The tamper seal according to claim 13, wherein the at least one optical security element comprises at least one of: a hologram, a zero order filter, a microlens array, a micro-prism array, a moir? effect device.

16. The tamper seal according to claim 1, wherein the input coupler and/or the output coupler is a diffractive coupler configured to diffract light according a first order of diffraction or a second order of diffraction.

17. The tamper seal according to claim 1, wherein said first and second portions are separated by a disruptable portion of the optical waveguide, a mechanical resistance of the disruptable portion being lower than a mechanical resistance of the first portion and a mechanical resistance of the second portion.

18. The tamper seal according to claim 1, wherein at least two outcoupling surfaces are arranged on the optical waveguide.

19. The tamper seal according to claim 1, wherein the optical waveguide comprises at least two separate optical waveguides arranged to an incoupling grating.

20. An object comprising a first part and a second part movable relative to each other, said first and second parts being sealed by the tamper seal according to claim 1, said first part and second parts being each integral with, respectively, first and second portions of the optical waveguide of said tamper seal, so that a displacement of the first and second parts of the object generates at least a partial disruption of the optical waveguide.

21. The object according to claim 20, wherein the object is a bottle and wherein said first part is a bottle and the second part is preferably the bottle cap, more preferably the cork, and further wherein the said first portion of the optical waveguide is arranged on said bottle and wherein the second portion of the optical waveguide is arranged on said bottle cap.

Description

DESCRIPTION OF THE DRAWINGS

[0034] The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

[0035] FIG. 1a illustrates a lateral view of the generic tamper seal comprising an optical waveguide with an input coupler and an outcoupling surface;

[0036] FIG. 1b illustrates a lateral view of the generic tamper seal comprising a first layer arranged on the outcoupling surface;

[0037] FIG. 1c illustrates a lateral view of the generic tamper seal comprising a wedged outcoupling surface where light is outcoupled;

[0038] FIG. 1d illustrates a lateral view of the generic tamper seal comprising an optical waveguide on which a cladding layer is arranged;

[0039] FIG. 1e illustrates a lateral view of the generic tamper seal comprising a first layer arranged on the optical waveguide;

[0040] FIG. 1f illustrates a lateral view of the generic tamper seal comprising a first layer arranged on the optical waveguide;

[0041] FIG. 2a Illustrates a lateral view of a tamper seal comprising an output coupler arranged on the outcoupling surface;

[0042] FIG. 2b Illustrates a top view of a tamper seal comprising an output coupler arranged on the outcoupling surface;

[0043] FIGS. 3-5 illustrate variants of a tamper seal with different arrangements of input and output couplers arranged as reflection or transmission couplers;

[0044] FIG. 6 illustrates a tamper seal comprising an output coupler and an optical waveguide comprising a cladding material;

[0045] FIG. 7 illustrates another tamper seal comprising a first layer arranged on the output coupler, both imbedded in the optical waveguide comprising a cladding;

[0046] FIG. 8a illustrates a tamper seal comprising a second layer arranged on the cladding arranged on the optical waveguide;

[0047] FIG. 8b illustrates a lateral view of tamper seal comprising a second layer and a security element arranged on the optical waveguide;

[0048] FIG. 9 illustrates a top view of tamper seal comprising a second layer and a security element arranged on the optical waveguide;

[0049] FIG. 10 illustrates a tamper seal comprising a plurality of waveguides and light outcoupling surfaces;

[0050] FIG. 11 illustrates a tamper seal comprising two curved portion of the optical waveguide;

[0051] FIG. 12 shows some exemplary objects according to the invention.

DETAILED DESCRIPTION

[0052] The following detailed description illustrates the principles and examples of embodiments according to the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the outlined principles of the invention and are included in its scope as defined in the claims. In the description and the figures, similar reference signs refer to the same or similar components or structural elements. Also, the term transparent as used herein the description encompasses an average visible transparency of a light beam of at least 70%, for light of the wavelength of interest. The term visible as used herein means light between the near-UV to the near-infra-red, i.e. between 300 nm-2 ?m as such wavelengths can be seen by human eye or can be easily converted to wavelengths visible to the human eye.

[0053] According to the invention, a tamper seal 1 comprises an optical waveguide 2 comprising at least two portions, a first portion 2A, called also the incoupling portion 2A, and a second portion 2B portion, called also the outcoupling portion 2B, of the optical waveguide 2. Said optical waveguide 2 is a multimode waveguide, the definition of which excludes monomode waveguides. Thus, monomode waveguides are not comprised in the present invention. Said optical waveguide 2 comprises at least a waveguide core, in which light is propagated by internal reflections. An example of such a core is a flat plastic sheet being surrounded by air. In such a flat plastic sheet light may propagate by total internal reflection at the interfaces of the plastic sheet and the air. Said core may have different cross section shapes and has a thickness greater than 10 ?m, preferably greater than 20 ?m, more preferably greater than 50 ?m, said thickness being defined perpendicular to the propagation direction of the guided light and in the thinnest part of the cross section of that core. Said thinnest part corresponds to the smallest dimension of the waveguide core. The shape of the cross section of the core may vary along the propagation direction of the propagating light beam. For example the core may be a tapered core. In another example the core has a rectangular cross section at one end and a different rectangular cross section at its other end. The thinnest part of the cross section of said waveguide core has a dimension smaller than 10 mm. For example a waveguide core may have a rectangular cross section dimension of 10 ?m?100 ?m, or 10 ?m?2 mm, or 10 mm?20 mm, or 10 mm?30 mm. In another example a waveguide core may have an elliptical cross section having dimensions of the smallest diameter x greatest diameter of 10 ?m?100 ?m, or 10 ?m?2 mm, or 10 mm?20 mm, or 10 mm?30 mm In another example a multimode waveguide having a circular shaped core may have a core diameter between 2 ?m and 10 mm. The dimension limitations are imposed only for the core of the multimode waveguide and do not apply to the external dimensions of the waveguide comprising a cladding or any other layer adapted to the core of the waveguide. Optical waveguides guiding UV, or visible or near IR light and having a core cross section dimension of at least 10 ?m are also called highly multimode waveguides as they guide a great number of modes. The core of an optical multimode waveguide and the propagation of light in the core of a multimode waveguide, as well as multimode waveguides that have no cladding layer is well described in the literature and will not be further commented here.

[0054] Said two portions are arranged, preferably by attachment elements 101-102, respectively to a first part 110 and a second part 120 of an object 100, said parts being movable to each other. The first and second parts 110,120 of the object 100 can be linked structurally together before being moved to each other, such as two parts of a foil, of a polymer sleeve or of a packaging element that will be partially disrupted and moved at a first opening. When said parts undergo a relative movement the optical waveguide 2 is at least partially disrupted and changes at least partially its optical guidance properties, usually losing this property. The arrangement of the optical waveguide 2 to the object parts 110,120 is not necessarily done below the optical waveguide 2 such as illustrated in the figures but can be done above it with a transparent medium for example laminated to the optical waveguide 2 or its cladding or by attachment elements which are not covering its whole surface.

[0055] According to a generic embodiment of the invention, illustrated in FIGS. 1a the incoupling portion 2A of the optical waveguide 2 comprises an incoupling surface 31 on which an input coupler 3 is arranged to the incident light 30 side of said optical waveguide 2, allowing to couple incident light 30 on that input coupler 3, inside the optical waveguide 2. The input coupler 3 may be a grating input coupler, comprising a plurality of grating elements. The input coupler 3 may comprise any type of incoupling structure, for example a refractive Fresnel microstructure. The optical waveguide 2 may be a ribbon optical waveguide 2 realized with a flexible material, transparent to visible light, arranged to transmit the incoupled light 32 in the optical waveguide 2 by total internal reflections through the optical waveguide 2 to the outcoupling surface 41 of the optical waveguide 2. In the generic embodiment of FIG. 1 the optical waveguide 2 has no cladding, and is preferably surrounded by air, and is substantially made of a single transparent material, preferably a flexible polymer, or thin glass or a fiber or fiber bundle, preferably at least partially, but not limited to water soluble polymer such as Polyvinylpolypyrrolidone or Polyvinyl alcohol, or any combination of these materials.

[0056] In the generic embodiment of FIG. 1a, said incoupling portion 2A and said outcoupling portion 2B of the tamper seal are intended to be attached to said parts 110,120 of the above mentioned object 100 by attachment means 100 which may comprise a gluing layer, a laminated adhesive or a mechanical attachment. It is obvious to the person skilled in the art that a wide variety of techniques exist that allow to arrange or to fix a tamper seal comprising a flexible optical waveguide 2 to any object 100 without damaging the tamper seal. Preferably the attachment of the said two portions 2A, 2B is realized substantially at the portions of the optical waveguide 2 where the incoupling surface 31 and the outcoupling surface 41 are arranged on the optical waveguide 2. The tamper seal 1 may also be attached to the object 100 at more than two attachment locations. For example, the tamper seal 1 may be additionally attached to the object 100 at a portion of the optical waveguide 2 located in between the incoupling surface 31 and the outcoupling surface 41 of the optical waveguide 2.

[0057] In a preferred variant of the generic embodiment of FIG. 1a the optical waveguide 2 has no cladding layer and has a cross section perpendicular to the propagation direction of the internal reflected light in the optical waveguide 2, which is substantially rectangular. Perpendicular to the propagating light direction in the optical waveguide, the optical waveguide 2 may have dimension (i.e. thickness?width) of 10 ?m?10 mm, preferably 20 ?m?500 ?m. The optical waveguide 2 may be a fiber optical waveguide having a substantially circular or elliptical core cross section and may have a diameter between 10 ?m-500 ?m, preferably 20 ?m-150 ?m.

[0058] In the generic embodiment of FIG. 1a, the light is transmitted and guided by the optical waveguide 2 from said incoupling surface 31 to said outcoupling surface 41, and said transmitted light will be outcoupled by said outcoupling surface 41 and leave the tamper seal as a substantially diverging light beam 40. The outcoupling surface 41 may be arranged at any side of the extremity of the optical waveguide 2 and may be for example a polished edge realized at the extremity of the optical waveguide 2, as illustrated in FIG. 1c, so that the outcoupled light beam 40 is a diverging light beam directed to a predetermined direction. The outcoupling surface 41 may be partially roughened to create a diffusing and diverging light beam leaving the optical waveguide 2. The outcoupling surface 41 is preferably arranged near perpendicular to the propagating light beam in the optical waveguide 2, at the extremity E of the second portion 2B of the optical waveguide as illustrated in FIG. 1a but may also be realized to the incident light side, or to the side opposite to it, of the optical waveguide 2, and located substantially near the extremity E of the optical waveguide 2, as illustrated in FIG. 2a. In a variant, at least two outcoupling surfaces 41 may be arranged at the outcoupling extremity E of the optical waveguide and at least one of the outcoupling surfaces 41 may comprise a metallic or dielectric reflecting structure.

[0059] In the generic embodiment illustrated in FIG. 1a, the optical waveguide 2 of the tamper seal 1 is designed to be disrupted, broken, partially destroyed or irreversibly deformed at a portion 200 of the optical waveguide 2 when said two parts of said object, to which the tamper seal 1 is arranged, undergo a relative displacement. It may also happen that the optical waveguide 2 of the tamper seal 1 is locally destroyed for instance by using a tool or by any other means. The mechanical resistance of the optical waveguide 2 may be designed by advantageously choosing the materials or also by incorporating a weak mechanical portion of the optical waveguide 2, for instance by partially scribing the optical waveguide or by arranging the optical waveguide 2 in different portions, which may have each different optical guidance properties comprising at least one portion having a weaker mechanical resistance. The optical waveguide 2 may also comprise at least one portion of which the optical guidance and transmission properties are changed by a heat sensitive portion. Upon heating this portion the transmitted colours, modes or intensity of the guided light is changed so that the intensity, colour and/or polarisation of the outcoupled light is altered. This may be an interesting feature in the tamper seal as heating is one of the methods used by counterfeiters in trying to remove the tamper seal, for example in situations wherein the tamper seal is protected by a plastic sleeve or in the case that the adhesives used to arranged in on the object can be more easily delaminated upon heating. The at least partial disruption, partial damage or breakage of the optical waveguide 2 will interrupt the light guided in the optical waveguide at the portion 200 and will be easily observed as it will lead to a change of the intensity and/or colour of the light decoupled by the outcoupling surface of the optical waveguide 2. An optical waveguide 2, in a similar way to an electrical waveguide or conductive wire, is sensitive to perturbations occurring over its whole propagation length, so that disruption or breakage of the optical waveguide 2 may occur at any place along the optical waveguide and produce substantially the same optical effects, detectable at said outcoupling surface of the optical waveguide.

[0060] It is generally admitted that re-establishing a good quality optical contact in a broken optical waveguide is very difficult. It usually requires specific equipment and the operation is very time-consuming, requiring also a highly skilled and trained person. The technology involved in the fabrication of the optical waveguide 2 and especially the input coupler requires a significant and expensive technological infrastructure and therefore the fabrication process is difficult to forge. These extremely high investment costs are a barrier for counterfeiters as the tamper seal such as described is very difficult to duplicate.

[0061] The irreversible loss of optical transmission quality in the optical waveguide 2 can be made very obviously by a specific design and engineering of the input coupler, the optical waveguide 2 and the combination of both. More precisely, the sensitivity of the detection of any disruption or perturbation of the optical waveguide 2 can be considerably enhanced by appropriate design of the input coupler 3 of the tamper seal. The applicant has filed an application PCT/EP2013/065631 describing the design, the method of realization and the obtained transmission and high efficient light coupling characteristics of an input coupler 3. The grating structures taught in PCT/EP2013/065631 can be adapted directly to the input coupler 3 of the tamper seal of the present invention. Examples of grating structures that can be adapted as an input coupler 3 structure are disclosed in the patents EP1767964 and EP1990661 and may be realized by any grating fabrication method adapted to plastic foils. In the application PCT/EP2013/065631, a rigorous simulation and optimization method is disclosed, proposing a grating coupler to which an enhancement layer is arranged. By advantageously choosing the profile of the grating elements and the appropriate enhancement layer of the input coupler, highly efficient input couplers can be devised and produced at low cost. According to the application PCT/EP2013/065631, incident light on the input coupler 3 can be coupled with high efficiency in a flexible foil or in a flexible ribbon. Moreover, laser beam can be transmitted by such couplers without losing their collimation. The manufacturing process costs of these input couplers are very low and allow manufacturing low cost tamper seals.

[0062] In a variant of the generic embodiment, intended to enhance the optical effect of an induced irreversible partial loss upon at least partial disruption of the optical waveguide, the input coupler 3 and the optical waveguide 2 are designed so that specific colours and/or guided modes are prevented from propagation in the optical waveguide, so that only specific colours or modes are transmitted by the optical waveguide. Upon at least partial rupture of the optical waveguide 2, light incident laterally on the breakage or disruption portion 200 of the optical waveguide 2 may incouple specific colours or modes, which can be easily detected by observing the light outcoupled at the edge of the optical waveguide 2. According to a variant, said specific colours and/or modes are attenuated by design in said optical waveguide. In still another variant, the tamper seal can be arranged so that unwanted guided light is outcoupled under an angle different than the outcoupling angle at the edge of an intact optical waveguide 2. According to another variant, the optical waveguide 2 may comprise at least two outcoupling surfaces 41 to couple light out of the optical waveguide. In yet another variant, at least two different edges may be arranged at the outcoupling surface of the optical waveguide, so that the light leaves the optical waveguide along two substantially different directions. When the optical waveguide is at least partially disrupted at least one of the outcoupled beams undergo a change in colour and/or intensity and/or polarisation.

[0063] In still another variant, illustrated in FIG. 1b at least a first layer 25 may be arranged on said outcoupling surface 41 of the optical waveguide 2, said first layer 25 being intended to interact with the transmitted light by the optical waveguide 2 incident on the outcoupling surface 41, said first layer 25 being further sensitive to any change of the transmitted lightbeam in the optical waveguide, for example a change of colour or a change of intensity and/or polarisation. Said at least first layer 25 may be an ink, a coloured layer, or any type of a fluorescent or phosphorescent material. Said first layer 25 may be arranged on only a portion of the outcoupling surface 31 of the waveguide. Said first layer 25 may comprise a security element, preferably a zero order filer or a hologram or any type of grating structure comprising grating elements, or any type of nanostructure. As an example, the first layer may show a logo, a symbol or a text, which may be altered by any disruption of the optical waveguide 2. Said first layer 25 may be arranged on different portions of the outcoupling surface 41 of the optical waveguide 2.

[0064] According to an embodiment illustrated in FIG. 1d, the optical waveguide 2 of the tamper seal 1 may comprise a cladding 20, also called cladding layer 20, arranged to at least one portion of the surface of the optical waveguide. The cladding may be arranged periodically on the optical waveguide 2 surface. The material of the cladding 20 is chosen to have a refractive index lower than the refractive index of the optical waveguide 2. In a variant the optical waveguide 2 may comprise at least two cladding layers 20, 22 arranged each on at least a portion of the optical waveguide 2.

[0065] According to an embodiment illustrated in FIG. 1e, at least a second layer 26 is arranged on at least a portion of the optical waveguide 2 and/or its out-coupling surface. This first layer 26 can change the light propagating property of the optical waveguide 2 by containing scattering elements, surface roughness or structures, absorbing elements or fluorescent or phosphorescent elements. These elements and/or surface features will change the light output of the waveguide by removing some modes or colours and/or adding some colours in the case of fluorescent or phosphorescent materials. Some of these elements or surface features may be incorporated into the optical waveguide 2, for example in the case of a polymer optical waveguide 2 by mixing the elements with the polymer matrix. These elements are preferably arranged in specific locations, such as after the input coupler 3, before the outcoupling surface 41, along the whole wavelength or periodically to select mode or colours that can propagate in the optical waveguide 2.

[0066] In a further embodiment of the invention, illustrated in FIG. 1f, at least a first layer 25 is arranged on at least a portion of the optical waveguide 2. This first layer is designed at enhancing the out-coupling of the light from the waveguide, or of changing its appearance, especially colour, angular distribution to make the out-coupling surface distinctive. This first layer can contain security elements creating a visually distinct appearance. The light transported in the optical waveguide 2 can be invisible to human eye, especially in the range of ultraviolet and infrared wavelengths and the first layer 25 can make the light visible to human eye, by comprising UV pigments such as fluorescent molecules or infrared pigments.

[0067] In a further embodiment, the input coupler 3 is designed to couple light at least partially into a cladding layer of the optical waveguide 2, and at least one second layer 26 comprising a security element 26 is arranged on the optical waveguide 2. In such an embodiment, any rupture of the cladding of the optical waveguide 2 will alter the luminosity or colour of said security element.

[0068] The optical waveguide 2 of the generic embodiment, illustrated in FIGS. 1a-f, may be any optical waveguide, for example a fiber ribbon comprising a plurality of multimode fibers, possibly arranged as a substantially flat multifiber ribbon. The fibers may also be arranged so that the arrangement has a substantially circular cross section. In the case of a multifiber arrangement, the ribbon may be fused at its extremities so as to allow arranging an input coupler to one of its fused extremities and an outcoupling surface on the other fused extremity E. For example, in the case wherein the optical waveguide 2 is an optical waveguide comprising a plurality of optical waveguides, such as a fiber bundle comprising a plurality of optical fibers, said first layer 25 may be arranged on the outcoupling surface of one of the fibers of said fiber bundle.

[0069] A great number of varieties can be devised to realize optical waveguides such as fiber bundles, in glass and/or plastic, as well as the techniques to align, assemble, polish and adapt the extremities of these optical waveguides 2 and/or bundles to specific shapes and geometries. These have been disclosed widely in the literature and will not be further explained herein. Some examples can be found in U.S. Pat. No. 3,514,351, U.S. Pat. No. 3,236,710, JP 19780126315.

[0070] In order to check the integrity of the tamper seal 1 according to the invention, at least one light source is necessary and the observation of the outcoupled light is required, preferably by a human eye, or by any light detection means sensitive to colour and/or intensity. The light source that directs light onto said input coupler may be any light source, for example a fixed light source or a mobile light source such as the light source from a pocket lamp, the light source from a smartphone duly equipped, a pocket lamp of some sort, a laser pointer, or any light source in the immediate environment of the object to which the tamper seal is arranged. Additional readout equipment may be useful for further control as the tamper seal of the invention may be designed advantageously to be combined with other security elements which may be optical, electronic or mechanical. Said readout equipment for example may comprise an analyser to detect the polarisation state of the outcoupled light beam.

[0071] In an exemplary realization, a white light LED providing a divergent white light beam may be directed on a 3 mm?3 mm sized incoupler arranged on a 4 mm?40 mm waveguide having a thickness of 50 um, on which a 3 mm?5 mm sized outcoupler is arranged. The angular alignment tolerance of said white light beam to the normal of the 3 mm?3 mm incoupler is typically 20?, the LED source is positioned preferably by the hand at 20 mm from said incoupler, and said incoupler, multimode waveguide and outcoupler are designed and arranged to project a green letter onto the retina of the eye or on a ccd chip of a camera facing said outcoupler. In the exemplary realization, upon at least partial disruption of the waveguide the color of the letter may not to be green any more, or may become invisible or a previously hidden texts or logo may appear showing the seal was manipulated and the protected object may not be genuine.

[0072] Another embodiment illustrated in FIG. 2a differs from the embodiment of FIG. 1 in that an output coupler 4 is arranged to the outcoupling surface 41 of the optical waveguide 2, and to the incident light 30 side of the optical waveguide 2. Preferably the output coupler 4 comprises a diffraction grating that couples the guided light out of the optical waveguide 2. FIG. 2b shows a top view of a tamper seal comprising an output coupler 4.

[0073] In another embodiment illustrated in FIG. 3, said input coupler 3 and said output coupler 4 are arranged to the side of the optical waveguide 2 opposite to the incident light beam on the optical waveguide 2. In such an embodiment the input and output couplers may comprise reflecting grating couplers.

[0074] In yet another embodiment, illustrated in FIG. 4 the output coupler 4 is arranged to the incident light side of the optical waveguide 2 and the input coupler 3 is arranged to the side of the optical waveguide 2 opposite to the incident light side. The input coupler 3 may also be arranged to the incident light side of the optical waveguide 2 while the output coupler 3 is arranged to the side of the optical waveguide 2 opposite to the incident light side.

[0075] In FIG. 5 is illustrated an embodiment wherein the input coupler 3 is arranged to the incident light side of the optical waveguide 2 and wherein the output coupler 4 is arranged to the side of the optical waveguide 2 of the incident light and is designed to outcouple light in reflection, to the opposite side of the incident light.

[0076] In FIG. 6, an embodiment is shown wherein the optical waveguide 2 comprises at least one cladding 20 and wherein an output coupler 4 is arranged on the outcoupling surface 41.

[0077] FIG. 7 shows an embodiment wherein the input coupler 3 and the output coupler 4 is imbedded in the cladding 20 of the optical waveguide 2, preferably close to the surface of the optical waveguide 2 and wherein the optical waveguide 2 comprises at least a second layer 26, substantially similar to the second layer 26 of FIG. 1e. In an embodiment similar to the one shown in FIG. 7 the input coupler and/or the output coupler may be imbedded in the optical guiding part, also called core, of the optical waveguide.

[0078] In another embodiment, a first layer 25, substantially similar to the first layer 25 of the preferred embodiment of FIG. 1f, is arranged on the output coupler 4. Said layer 25 may be arranged to the output coupler 4 in every embodiments of FIG. 2-FIG. 7.

[0079] In another embodiment, illustrated in FIG. 8a a second layer 26 is arranged on an optical waveguide 2 comprising a first cladding 20, and the input coupler 3 is designed to couple at least a portion of the light into the optical waveguide core. With most optical couplers and a light beam provided by a spectrally broad and non-collimated light source, some modes and/or wavelengths are expected to be incoupled into at least one of the optical waveguide claddings 20, 22. Said second layer 26 may be designed to remove specific portions or the whole light beam propagating in the optical waveguide cladding 20,22 by optical absorption or scattering or out-coupling. Especially stray light and non-desired colors or mode can be removed. According to the embodiment of FIG. 8a, the second layer 26 changes the intensity or the color of guided light into the cladding 20, 22 of the optical waveguide 2. Any damage to said second layer 26 will be detected by a change of the intensity or color of the out-coupled light from the waveguide core through at least one outcoupling surface 40.

[0080] In another embodiment illustrated in FIG. 8b, the said second layer 26 is arranged on the propagation axis of the waveguide after the light in-coupler 3. This allows removing non desired light propagation in the cladding of the optical waveguide 2. When the optical waveguide 2 is at least partially disrupted, attempts to re-establish an optical contact and a light-guiding property are expected not to rebuild a perfect core/cladding optical contact of the two partially separated optical waveguide 2 portions. After disruption and rebuild, a portion of the optical waveguide 2 is expected to let light leak out of the optical waveguide 2 core to the cladding arranged on the optical waveguide 2. This change of intensity or color of the light propagating in the wavelength core will change to some extent the intensity or color of the outcoupled light. This change will let light propagate in the cladding to the first layer 25. This first layer 25, substantially similar to the first layer 25 of the preferred embodiment of FIG. 1f will become visible when reached by light leaking out of the optical waveguide core. Such arrangements can be designed so that re-establishing poor optical contacts of at least partially disrupted optical waveguide 2 is very visible and lead to a distinctive appearance.

[0081] FIG. 9 illustrates the embodiment of the FIG. 8b from a top view. Upon disruption and poor quality rebuild of the optical guiding property of the optical waveguide 2, light is expected to be injected in the cladding and the text of first layer 25 to be visible. On the opposite, a genuine optical waveguide 2 is designed not to have light propagating in its cladding and the element 25 is not light-up. In this example a sign OK is visible as arranged on the output coupler 4 when the tamper seal is not damaged and a sign 45 NOT is visible when at least the optical waveguide 2 of the tamper seal 1 is at least partially damaged.

[0082] According to an embodiment at least two output couplers 4 are arranged on the optical waveguide 2. The at least two output couplers 4 and optical waveguides 2 may be arranged according to any combination of the embodiments of FIG. 1-10.

[0083] In another embodiment the tamper seal 1 according to the invention may comprise a plurality of input couplers 3 and output couplers 4 arranged along an optical waveguide, as illustrated in FIG. 10. Different optical waveguides 2 and different couplers may as well be integrated and a single seal for added complexity.

[0084] FIG. 11 shows an embodiment comprising a curved optical waveguide 2, comprising one input coupler 3 and two output couplers 4 arranged on the curved optical waveguide 2.

[0085] It will be obvious for the person skilled in the art that the tamper seal 1 may comprise a plurality of optical waveguides on which a plurality of input and output couplers may be arranged. Said plurality of input couplers may face each other or may be arranged so that they do not face each other. The same holds for the plurality of output couplers, i.e. output couplers may face each other or may be arranged so that they do not face each other. In an example of realization 3 multimode waveguides having each a different length are arranged parallel to each other and comprise each at a first end an input coupler and at their second end an output coupler. In such an arrangement the stack of 3 multimode waveguides comprise 3 input couplers arranged as a step and 3 output couplers arranged as another step. It will be obvious for the person skilled in the art that the at least one optical waveguide 2 of the tamper seal 1 may be further sensitive to its physical environment by engineering at least one of the couplers 3, 4 to delaminate easily from the at least one optical waveguide 2, or the at least one cladding 20, 22 from its optical waveguide 2, or the at least first 25 and second 26 layer from the optical waveguide 2 or cladding or outcoupling surface 41 where they are arranged.

[0086] The invention relates also to an object 100 comprising a first part 110 and a second part 120 movable relative to each other with said first 110 and second 120 parts being sealed by a tamper seal 1 according to the described embodiments. Some exemplary objects 100 are illustrated in FIG. 12. The object 100 to which the tamper seal 1 may be arranged may be any type of object 100 comprising at least two movable parts such as a bottle and a bottle cap. The object 100 to which the tamper seal 1 is arranged may be a container comprising a moveable cap or closure, a container box and its lid. The arrangement of the tamper seal 1 and its object 100 can be designed so that the outcoupled light 40 illuminates specific parts of the object 100 and/or can be incoupled into objects 100 at least partially transparent such as jar and bottle. Said object 100 may comprise laterally moving parts 110,120 such as doors or handles. The tamper seal 1 can also be integrated within a foil or be laminated on a foil which disruption is necessary to access or use the object 100, such as a polymer protection sheets or sleeves. In this case, the different parts of the foil or sleeve are moving relatively to each other upon disruption of the foil but can be structurally linked prior to this movement and or disruption. The person skilled in the art may devise other objects 100 to which the described tamper seal 1 may be arranged.