Seal and sealing method

Abstract

The invention relates to a seal containing a substrate which can be applied to an object to be sealed, so that said seal is changed when it is removed without authorization, wherein the substrate contains or comprises a polymer and/or a glass and at least one optical waveguide is arranged in the substrate, at least one first Bragg grating being arranged in said optical waveguide, wherein the substrate has a thickness of less than 200 m. The invention further relates to a system having a seal of this kind and having an evaluation device, and also to a sealing method.

Claims

1. A seal, comprising a substrate, adapted to be applied to an object to be sealed, wherein the substrate comprises a polymer or a glass and the substrate accommodates at least one optical waveguide, said at least one optical waveguide comprising at least one first Bragg grating, the substrate having a thickness of less than 200 m, a length of more than 1 mm, and a width of more than 1 mm, and tampering with said seal results in a detectable change to the seal.

2. The seal of claim 1, wherein the substrate has a thickness of less than about 100 m or less than about 80 m or less than about 50 m.

3. The seal of claim 1, wherein said at least one optical waveguide includes a first optical waveguide and a second optical waveguide, said seal comprising at least one coupler arranged in the substrate, said at least one coupler connecting said first optical waveguide and said second optical waveguide to a connection waveguide or to a terminal for a connection waveguide.

4. The seal of claim 1, wherein the at least one optical waveguide is a single-mode optical waveguide.

5. The seal of claim 1, wherein the at least one first Bragg grating has a polarization-dependent reflection or a polarization-dependent transmission.

6. The seal of claim 1, wherein the substrate has at least one edge and said seal comprises a frame on said at least one edge.

7. The seal of claim 1, further comprising an optical fiber as a connection waveguide coupled to said at least one optical waveguide, said connection waveguide extending away from said seal.

8. The seal of claim 7, wherein at least one Bragg grating is arranged in the connection waveguide.

9. A system including the seal of claim 1, comprising an interrogation device, which includes a light source or a spectrometer or an evaluation unit or a reference signal memory.

10. A method for sealing, comprising: providing a seal having a substrate comprising a polymer or a glass, said substrate having a thickness of less than about 200 m, a length of more than 1 mm and a width of more than 1 mm, said substrate accommodating at least one optical waveguide, said at least one optical waveguide comprising at least one first Bragg grating; applying said substrate to an object to be sealed; coupling a first optical interrogation pulse into the at least one waveguide after said substrate is applied to the object; and detecting a first signal reflected by the at least one first Bragg grating as a signature of the seal, wherein tampering with said seal results in a detectable change in the signature of the seal.

11. The method of claim 10, wherein during the step of applying said substrate to an object to be sealed, the substrate is exposed to a mechanical stress which alters the signature of the seal.

12. The method of claim 10, comprising; storing the signature of the seal in a reference signal memory as a reference signal.

13. The method of claim 12, comprising: coupling a second optical interrogation signal into the at least one waveguide; detecting a second signal reflected by the at least one first Bragg grating; and comparing the second signal with the reference signal; and determining the integrity of the seal from a deviation between the second signal and the reference signal.

14. The method of claim 13, wherein said step of comparing said second signal with the reference signal comprises: comparing a first reflection spectrum of the reference signal to a second reflection spectrum of said second signal, said first and second reflection spectrum each including reflection peaks corresponding to the at least one first Bragg gratings, each of said reflection peaks having a spectral width, an amplitude, and a position corresponding to a reflection wavelength: and detecting differences in any of the spectral width, the amplitude, or the position of reflection peaks in the second signal with respect to the spectral width, the amplitude, or the position of the reflection peaks of the reference signal.

15. The method of claim 13, wherein the first or second optical interrogation signal comprises a plurality of light pulses, at least some light pulses of said plurality of light pulses differ from other light pulses of said plurality of light pulses with respect to a wavelength, or a propagation time, or a polarization.

16. The method of claim 13, comprising providing at least one second Bragg grating; measuring a temperature by means of said at least one second Bragg grating; and standardizing said reference signal and said second signal reflected by the at least one first Bragg gratings at the measured temperature.

17. The seal of claim 1, wherein said substrate is used as a cladding for the at least one optical waveguide, such that the waveguide can be produced by writing the core into the substrate.

18. The seal of claim 1, wherein said at least one optical waveguide forms a meandering pattern on said substrate.

19. The seal of claim 1, wherein the waveguide consists of a spatial region of the substrate which has a modified refractive index with respect to the surrounding material of the substrate, as a result of which total reflection occurs at a boundary between the spatial region and the surrounding material of the substrate.

20. The method for sealing of claim 10, wherein said step of providing a seal comprises: modifying a spatial region of the substrate to have a refractive index that is different from the refractive index of the surrounding material of the substrate so that total reflection occurs at a boundary between the special region and the surrounding material of the substrate, thereby forming the at least one waveguide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention shall be explained in more detail below by means of drawings without limiting the general inventive concept, wherein

(2) FIG. 1 shows a first embodiment of a seal according to the invention.

(3) FIG. 2 shows a second embodiment of the seal according to the invention.

(4) FIG. 3 shows, by way of example, a signature of a seal.

(5) FIG. 4 shows the change in the signature on the basis of the mechanical stress of the substrate.

(6) FIG. 5 shows an example of use of the seal according to the invention.

(7) FIG. 6 shows the change in the signature when the seal is damaged.

(8) FIG. 7 shows the block diagram of a reading device.

DETAILED DESCRIPTION

(9) FIG. 1 shows a first embodiment of a seal 1 according to the invention. The seal 1 contains a substrate 10, which is made e.g. from a polymer or thin glass or a composite material from at least one polymer and at least one thin glass. The substrate 10 has a thickness of less than about 200 m. In other embodiments of the invention, the substrate can have a lower thickness, e.g. less than about 100 m, less than about 80 m or less than about 50 m.

(10) In the illustrated embodiment, the substrate 10 is approximately square. However, in some embodiments of the invention, the substrate can also have another polygonal or round form. The areal extent of the substrate 10 can be selected between about 1 mm.sup.2 and about 40 mm.sup.2, wherein larger or smaller dimensions can also be chosen.

(11) At least one waveguide 3 is disposed in the substrate 10. The waveguide 3 consists of a core and a cladding, each having different refractive indices, such that light can be guided by total reflection on the boundary between core and cladding.

(12) According to the invention, the material of the substrate 10 is used as a cladding, such that the waveguide 3 can be produced by writing the core into the substrate. The waveguide 3 can be laid in straight or meandering fashion in the substrate. The illustrated geometry should therefore only be regarded as an example. The invention does not teach the use of a special course of the waveguide 3 as a solution principle.

(13) In the illustrated embodiment four first Bragg gratings 51, 52, 53 and 54 are arranged in the waveguide 3. Each Bragg grating contains a plurality of spatial regions, the refractive indices of which differ from the refractive index of the core. These spatial regions are arranged relative to one another at a predeterminable spacing which defines the grating constant of the Bragg grating. A single Bragg grating 51, 52, 53 or 54 can have a length within the waveguide 3 of between 1 mm and about 30 mm or between about 2 mm and about 10 mm.

(14) Like the first Bragg gratings 51, 52, 53 and 54, the waveguide 3 in the interior of the substrate 10 can also be produced by point-to-point exposure with a short-pulse laser. This makes it possible to produce each seal with an individual signature. In other embodiments of the invention, a mask can be used for the exposure to change the refractive index in the exposed spatial regions to such an extent that the desired structures are generated in the substrate 10. It is thus possible to produce identical seals with little effort. Nevertheless, seals which were reproduced with identical production parameters also show sufficient differences as regards the signatures so that they can still be distinguished and the replacement of a broken seal with an identical seal is impossible. As a result, the security can be increased.

(15) The waveguide 3 is brought into contact with a connection waveguide 4 on the outer edge of the substrate 10. The connection waveguide 4 can be or contain e.g. a polymer or glass fiber. In some embodiments of the invention, the two ends of the waveguide 3 can be connected to a connection waveguide 4. In this case, the signature of the seal can be determined as regards reflection and transmission to thus improve accuracy. In other embodiments of the invention, only a single connection waveguide 4 is attached to the seal 1, as illustrated in FIG. 1.

(16) The connection waveguide 4 has an optional second Bragg grating 41. The Bragg grating 41 serves to determine the temperature in the vicinity of the seal 1, such that the signature produced by the seal 1 can be corrected for temperature fluctuations.

(17) FIG. 2 shows a second embodiment of the present invention. The same constituents of the invention are provided with the same reference signs. Therefore, the below description is limited to the essential differences.

(18) According to FIG. 2, a coupler 35 is also arranged on the substrate 10 and is configured to divide light coupled in via the connection waveguide 4 into two waveguides 31 and 32. Each of the waveguides 31 and 32 contains a first Bragg grating 51 and 52 or 53 and 54. The light reflected by these Bragg gratings is reunited in the coupler 35 and can be supplied to the connection waveguide 4.

(19) In the same way as shown in FIG. 2 by means of a single coupler 35, waveguides can be split multiple times in tree-like fashion, such that the entire area of the substrate 10 is honeycombed with a network of waveguides with respectively associated Bragg gratings.

(20) The meandering course of the waveguide 3 that is outlined in FIG. 1 can also be combined with one or more couplers to cover a larger area of the substrate 10.

(21) FIG. 3 shows the spectral reply or the signature of an optical seal, as explained by way of example on the basis of FIGS. 1 and 2. What is shown is the intensity on the ordinate against the wavelength on the abscissa. FIG. 3 shows the intensity of reflected light depending on the wavelength in the case of an illumination with spectral broadband radiation, e.g. from a superluminescent diode.

(22) As is clear from FIG. 3, the reflection spectrum has 5 maximums. The first maximum at about 825 nm can be associated with the second Bragg grating 41 in the connection waveguide 4. This signal serves in a manner known per se to detect the temperature such that the signature of the first Bragg gratings 51, 52, 53 and 54 can be standardized to a standard temperature.

(23) The four reflection maximums 51, 52, 53 and 54 are also shown and can be associated with the four Bragg gratings 51, 52, 53 and 54 available in the seal with respectively different grating constant. They vary with respect to the spectral width, the position of the reflection maximum or the background when different seals are read out or a seal already applied to an object was either damaged or was applied to the object to be sealed with different mechanical stress. Therefore, a manipulation of the seal 1 can be proven when the signature explained by means of FIG. 3 as an example was detected and stored after the assembly of the seal and differs from a signature recorded at a later date. This correlation is explained e.g. by way of FIG. 4.

(24) FIG. 4 shows an enlarged illustration from FIG. 3 with the intensity maximum of the Bragg grating 53. Curve A illustrates the spectral reply of a Bragg grating in the case of a first mechanical stress of the substrate 10 and curve B shows the spectral reply of the Bragg grating 53 in the case of a second mechanical stress of the substrate 10. Since, as a rule, different mechanical stresses are induced in the substrate 10 by the assembly alone, even nominally identical seals can be distinguished from one another after the assembly on an object to be sealed on the basis of their signature. This applies all the more so when an already attached seal is damaged or replaced with a new seal without authorization. In this case, too, the manipulation attempts can be clearly proven on the basis of the different signature. Even the partial removal changes the mechanical stress in the substrate, thus changing the signature in the seal.

(25) FIGS. 3 and 4 show a comparatively simple signature which merely utilizes the spectrometrically determined intensity on the basis of the wavelength. Other embodiments of the invention can additionally consider the polarization or the signal propagation time to determine a more complex signature of the optical seal and thus prove manipulation attempts in an even more reliable way.

(26) FIG. 5 shows, by way of example, the assembly of an optical seal 1 on an object 2 to be protected. The object 2 comprises a microchip which is attached to a printed circuit board known per se. the microchip on the printed circuit board is surrounded by a frame 5, which is attached to the printed circuit board e.g. by adhesion.

(27) The frame 5 accommodates the seal 1, which is also connected to the frame by means of adhesion. This may be accompanied by mechanical stresses can thus be used to deform the seal 1 or the substrate 10 thereof in a defined way and to apply a unique mechanical stress to each seal 1 that influences the signature as explained above by means of FIGS. 3 and 4.

(28) As already explained above, the seal 1 is connected to a connection waveguide 4 which accommodates a second Bragg grating 41 to detect the temperature. The connection waveguide 4 is provided with a plug-in connector 45 to thus be connected to a reading device which is explained by means of FIG. 7.

(29) Since the frame 5 and the seal 1 enclose the underlying microchip and all its contacts, the microchip cannot be compromised, e.g. by unsoldering or by another manipulation.

(30) For this purpose, it is necessary to damage the seal 1 by violence. Such a manipulation can clearly be proven by means of the signature since other seals have either a different waveguide course, different grating constants of the Bragg gratings or other differences with respect to the original seal. Even if a nominally identical seal was attached to the frame 5, it would automatically be subjected to a different mechanical stress during the assembly on account of its low thickness, said stress also changing the signature as explained by means of FIG. 4.

(31) FIG. 6 shows again, by way of example, the change in the signature when the seal is damaged by a laser beam. This Figure shows the reflection maximums of two Bragg gratings in a seal which, as explained by means of FIG. 2, has two waveguides 31 and 32. In order to detect the signature, comparatively broad-band radiation, e.g. from a superluminescent diode, was introduced into the waveguide, and the light reflected by the Bragg gratings was detected.

(32) In order to carry out an exemplary manipulation of the seal, the substrate 10 was perforated by means of a laser.

(33) As also shown in FIG. 6, even this comparatively minor damage can clearly be proven by means of the signature. For example, the maximum at about 850 nm has fully disappeared. Even the maximum at 840 nm has a lower amplitude. In addition, the intensity of the substrate between the two maximums has increased.

(34) Therefore, even a minor damage by laser radiation can be clearly proven.

(35) FIG. 7 explains, by way of example, a reading device. The reading device 6 has a terminal to which the connection waveguide 4 can be connected in order to connect a seal 1 to the reading device 6.

(36) The reading device 6 also has a light source 61, the radiation of which can be supplied to the seal 1 via the connection waveguide 4. In the seal 1, this light propagates in the waveguides, as explained above by means of FIGS. 1 and 2.

(37) The light is reflected by the Bragg gratings of the seal 1. This reflected light again passes through the connection waveguide 4 and reaches a coupler in the interior of the reading device 6. It connects a spectrometer 62, e.g. an AWG or a micromirror array, to the seal 1.

(38) The reply signal determined in this way is referred to as the signature of the seal 1 for the purposes of the present invention. This signature can be processed by means of an evaluation unit 63 which contains e.g. a microprocessor or a DSP. Alternatively or additionally, such a signature can be stored in a reference signal memory 64. The reference signal memory 64 can comprise e.g. a semiconductor memory, a hard disk or also a cloud memory.

(39) The invention proposes to read out a signature after the assembly of the seal 1 with a first optical interrogation signal in the described way and to store this signature in the reference signal memory 64. If the integrity of the seal 1 shall be checked at a later date, a signature of the seal 1 is again detected in the described way by means of a second optical interrogation signal. This second signature can then be compared with the previously deposited reference signal from the reference signal memory 64 by means of the interrogation signal. In the case of deviations which can be recognized e.g. in automated fashion by pattern recognition, the reading device 6 can emit an acoustic and/or optical alarm which indicates that the seal 1 was compromised.

(40) The optical reading signal generated by the light source 1 can have a plurality of light pulses which differ as regards the time structure, by means of their spectral range or the polarization direction to thus be able to read out even complex seals 1.

(41) It goes without saying that the invention is not limited to the illustrated embodiments. Therefore, the above description should not be considered limiting but explanatory. The following claims should be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. If the claims and the above description define first and second embodiments, this designation serves to distinguish between two similar embodiments without determining a ranking order.