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    • 专利摘要:
    According to one aspect, the invention relates to a plasmon effect security optical component comprising two layers (2,4) of transparent dielectric material and a metal layer (3) arranged between said layers of transparent dielectric material to form two dielectric-metal interfaces. (31, 32). The metal layer is structured to form, on a first coupling zone, a first periodic two-dimensional coupling network (Ci) capable of coupling surface plasmon modes supported by said dielectric-metal interfaces with an incident light wave. , the first coupling network having an asymmetrical profile in each of its directions, and, on a second coupling zone, a second periodic two-dimensional coupling network (C2) able to couple surface plasmon modes supported by said dielectric-metal interfaces with an incident light wave, the second coupling network having an asymmetrical profile in each of its directions, different from that of the first coupling network.
    公开号:FR3017231A1
    申请号:FR1450766
    申请日:2014-01-31
    公开日:2015-08-07
    发明作者:Jean Sauvage-Vincent
    申请人:Hologram Industries SAS；
    IPC主号:
    专利说明:

    [0001] FIELD OF THE INVENTION The present invention relates to the field of security marking. More particularly, it relates to an optical security component having variable optical effects in reflection on its front and back faces, to a method of manufacturing such a component and to a secure document equipped with such a document. PRIOR ART Many technologies are known for authenticating documents or products, and especially for securing documents such as valuable documents such as banknotes, passports or other identification documents. These technologies aim to produce optical safety components whose optical effects according to the observation parameters (orientation with respect to the observation axis, position and dimensions of the light source, etc.) take very characteristic configurations. and verifiable. The general purpose of these optical components is to provide new and differentiated effects, from physical configurations that are difficult to reproduce. Among these components is called DOVID for "Diffractive Optical Variable Image Device", the optical components producing diffractive and variable images commonly called holograms. These components are usually observed in reflection.
    [0002] Other optical security components are known, which allow authentication by observation of the component in transmission. Thus, the French patent FR 2973917 in the name of the Applicant, describes a plasmon-effect optical security component comprising two layers of transparent dielectric material and a metal layer arranged between the layers of dielectric material to form two dielectric-metal interfaces, the layer metallic material being structured to form corrugations capable of coupling surface plasmon modes supported by the dielectric-metal interfaces with an incident light wave. Such a component has an extraordinary transmission effect in a spectral band centered on a centering wavelength, defined by the characteristics of the ripples of the coupling zones.
    [0003] In the present application, we are interested in optical security components having a plasmon effect, with variable reflection effects depending on the observation on the front face or on the back side of the component.
    [0004] SUMMARY OF THE INVENTION According to a first aspect, the invention relates to a plasmon effect security optical component, said optical component comprising two layers of transparent dielectric material and a metal layer arranged between said transparent dielectric material layers to form two dielectric interfaces. - metal and structured to form, on a first coupling zone, a first periodic two-dimensional coupling network capable of coupling surface plasmon modes supported by said dielectric-metal interfaces with an incident light wave, the first network with an asymmetrical profile in each of its directions, and on a second coupling zone, a second periodic two-dimensional coupling network capable of coupling surface plasmon modes supported by said dielectric-metal interfaces with a incident lightwave, the second network of c ouplage having an asymmetrical profile in each of its directions, different from that of the first coupling network when viewed from the same side of the component as the first coupling network.
    [0005] A two-dimensional network is a "crossed" network of two one-dimensional networks that intersect at right angles. It thus forms a structure whose shape is of the "egg box" type. Asymmetrical profile means in the present description a network whose profile in one direction does not have central symmetry (with respect to a point).
    [0006] Such a component has, at the first and second coupling regions, an extraordinary transmission effect in a spectral band centered on a given wavelength, defined by the characteristics of the metal-dielectric interfaces and the coupling network in this zone. Due to the asymmetric nature of the coupling network profiles and the difference between the asymmetrical profiles of the first and second coupling networks in the first and second coupling regions, the reflection observation on one side of the component has a variable color effect. according to each zone; indeed, the spectral band of the reflected light wave depends on the spectral band of the transmitted wave as well as the spectral band of the scattered wave which is modified according to the profile of the network.
    [0007] Moreover, the colored effect on each zone is variable in reflection as a function of the observation on one side or the other of the component; indeed the asymmetrical nature of the profile of each coupling network causes a variation of the spectral band of the reflected wave during the observation of one side or the other of the component which can also be translated by a variation of the reflected light intensity in a given spectral band.
    [0008] Each of the first and second coupling zones may take a different shape, be composed of contiguous parts or not, may according to a variant represent a recognizable pattern, the two coupling zones may alternatively have complementary shapes. According to a preferred embodiment of the invention, the periods are identical in both directions for each of the first and second coupling networks. Each two-dimensional network thus has a square mesh, which makes it possible to avoid color variations by azimuthal rotation of the component. According to one variant, the profile of each of the coupling networks in one direction is a pseudo-sinusoidal profile, that is to say which has a profile that is not perfectly sinusoidal, with a cyclic ratio other than 0.5. The duty ratio of the pseudo-sinusoid is defined as the ratio, measured for example over a period, between the smallest of the lengths between the length for which the value of the pseudo-sinusoid is greater than the median value of the pseudo-sinusoid. and the length for which the value of the pseudo-sinusoid is less than the median value of the pseudo-sinusoid, and the total length of the period. Advantageously, the duty cycle is strictly less than 40% (or 0.4), in order to generate sufficient dissymmetry and well-differentiated reflection effects, on one side or the other. According to a variant, the first and second coupling networks have identical periods, such that the spectral band of the transmitted wave is substantially identical in each of the zones. There is then a stability in transmission, during the observation of the component on each of its faces, while the effects in reflection vary because of the difference in the profiles of the networks seen on the same side of the component. According to one variant, the second coupling network is the negative of the first coupling network. This configuration makes it possible to observe a color inversion in the first and second zones, when the component is observed on each of its faces, the profile of a first coupling network seen on one side of the component being identical to the profile. the second coupling network seen on the other side of the component. According to one variant, the security optical component further comprises, on a region of at least one of the metal-dielectric interfaces, a layer of high-index or low-index dielectric material advantageously formed in a recognizable pattern. High or low index means materials whose refractive index has a difference An with the refractive index of the dielectric material with which it is in contact greater than 0.2 in absolute value. The presence of the high or low index layer causes a modification in the region in which it is deposited from the spectral band of the transmitted wave, making it possible to create new zones with variable color effects in transmission when the component is observed. one side. However, at the level of the region in which the high or low index layer is deposited, the color effects in transmission are identical during the observation on the front and the back of the component. The high or low index layer also causes a modification in the region where it is deposited and the side of the interface on which it is deposited, the spectral band of the reflected wave, due to diffusion phenomena. If the high or low index layer is selectively deposited on a metal-dielectric interface, the reflection effect is therefore variable during the observation of one side or the other of the component. It is thus possible to observe in transmission a pattern of a certain color on a background of another color, these colors being stable according to the observation recto or verso of the component. In reflection on the contrary, the colors of the pattern are variable according to an observation on one side or the other of the component. According to one variant, the metal layer may further comprise an unstructured zone. This area, of high optical density, makes it possible to further enhance the areas in which the coupling networks are arranged which have in a given spectral band an extraordinary transmission due to the plasmonic effect. Advantageously, the first and second coupling networks have a pitch of between 100 nm and 600 nm, and preferably between 200 nm and 500 nm. The depth is between 10% and 50% of the pitch, advantageously between 10% and 40% of the pitch, a reduced depth of the coupling network allowing a better propagation of the plasmonic modes. Advantageously, the difference in the refractive indices of said transparent dielectric materials in the targeted spectral band, preferably the visible one, forming each of said layers is less than 0.1, making coupling and thus plasmonic transmission maximized so as to obtain an effect of extraordinary extraordinary transmission at said centering wavelength. Advantageously, the metal layer is continuous over at least a portion, and chosen sufficiently thin to allow the coupling of the plasmonic modes propagating at the two metal-dielectric interfaces. According to a variant, at least part of the metal layer is continuous, formed of silver and its thickness is substantially between 20 and 60 nm, preferably between 35 nm and 45 nm. According to a variant, at least part of the metal layer is continuous, formed of aluminum and its thickness is substantially between 10 and 30 nm, preferably between 15 nm and 25 nm. According to an exemplary embodiment, the metal layer may be formed of a single metal. According to another embodiment, the metal layer comprises at least two parts each formed of a different metal. This may allow different visual effects, both in reflection and transmission in the spectral band of the plasmonic effect. According to a second aspect, the invention relates to a security optical element for securing a document and comprising at least one security optical component according to one of the first aspect. The security element may comprise other security components, for example holographic components. According to one variant, the security element comprises other layers according to the needs required for the final application; for example, the security element may comprise, in addition to active layers for the plasmonic effect, a support film carrying one of said layers of transparent dielectric material and / or an adhesive film disposed on one of said layers of transparent dielectric material. These films are neutral for the plasmonic effect because they do not alter or influence the dielectric-metal interface. They make it possible to facilitate the adhesion on the document to be secured and / or the implementation in an industrial way. According to a third aspect, the invention relates to a secure document comprising a support and an optical security element according to the second aspect, the security optical element being fixed on said support, said support comprising a transparency zone at which level is arranged said plasmonic optical security component. The secure document, for example a banknote type document of value or an authentication document, such as an identity card, can, thanks to the plasmon effect security optical component according to the invention, be easily controlled in reflection and in transmission by comparison of the colored effects on each of the faces, and its resistance to counterfeiting is high because of the technology used. According to one variant, the security optical component according to the first aspect or the security optical element according to the second aspect is encapsulated in the support of the secure document. Areas of transparency are provided on both sides of the optical security component, thus allowing control in reflection and transmission on each of the faces. According to a fourth aspect, the invention relates to a method of manufacturing a plasmon-effect security optical component comprising: depositing a metal layer on a first layer of structured transparent dielectric material, making it possible to obtain a first interface metal-dielectric structure, - encapsulation of said metal layer by a second layer of transparent dielectric material, to form a second dielectric interface - structured metal, and wherein: - the two dielectric-metal interfaces are structured to form, on a first coupling zone, a first periodic two-dimensional coupling network capable of coupling surface plasmon modes supported by said metal dielectric interfaces with an incident light wave, the first coupling network having an asymmetrical profile according to each of its directions, and on a second coupling zone, a second periodic two-dimensional coupling network, capable of coupling surface plasmon modes supported by said dielectric-metal interfaces with an incident light wave, the second coupling network having an asymmetrical profile in each of its directions, different from that of the first coupling network when viewed from the same side of the component as the first coupling network. The method of manufacturing a security optical component is fully compatible with the methods of manufacturing optical security components known in the prior art, including DOVID type components. According to a variant, the method also comprises the fabrication of a first matrix for structuring the metal-dielectric interfaces at the first coupling zone in order to form the first coupling network and the manufacture of a second matrix for the first coupling matrix. structuring the metal-dielectric interfaces at the second coupling zone to form the second coupling network, the second matrix being a negative replica of the first matrix. According to a variant, the method further comprises the deposition on a region of at least one of said metal-dielectric interfaces of a layer of low or high index dielectric material.
    [0009] BRIEF DESCRIPTION OF THE FIGURES Other features and advantages of the invention will appear on reading the description which follows, illustrated by the figures which represent: FIGS. 1 and 2, partial views, respectively according to a plane of section and from above of an optical security component according to the present description in two variants; FIG. 3, a diagram illustrating the effects of reflection, diffusion and transmission on both sides of the structured metal-dielectric interfaces in first and second coupling regions respectively comprising the first and second coupling networks; FIGS. 4A to 4D, the visual effects obtained by observation of the component in reflection and in transmission, on the front and the back of the component, in a configuration as described in FIG. 3; FIGS. 5A-5G, diagrams respectively illustrating a sinusoidal function and pseudo-sinusoidal functions, with different form factors, as well as other asymmetrical profiles; FIG. 6, a diagram illustrating the effects of reflection, diffusion and transmission on both sides of the structured metal-dielectric interfaces in a first zone, with a layer of high dielectric index deposited on a region of one of the interfaces; FIG. 7, a diagram illustrating the effects of reflection, diffusion and transmission of the two sides of the structured metal-dielectric interfaces in the first and second zones respectively comprising the first and second coupling networks, with a layer of high dielectric index deposited on a region of one of the interfaces; FIGS. 8A to 8D, the visual effects obtained by observation of the component in reflection and in transmission, on the front and the back of the component, in a configuration as described in FIG. 7; FIGS. 9A to 9F, diagrams illustrating the manufacturing of first and second matrices for the formation of the first and second coupling networks; FIGS. 10A to 10E, diagrams illustrating the manufacture of an optical security component according to an example; FIGS. 11A to 11F, diagrams illustrating the manufacture of an optical security component according to an example; FIGS. 12A and 12B, respectively front and back views of a secure document comprising an optical security component according to the present description. DETAILED DESCRIPTION FIGS. 1 and 2 show partial views of sectional views of safety components 10A and 10B according to exemplary embodiments. The security component according to the invention generally comprises a metal layer 3, for example a continuous layer of substantially constant thickness, typically a few tens of nanometers, arranged between two layers of transparent dielectric material 2, 4 to form two interfaces. dielectric - metal referenced respectively 32, 31 in Figures 1 and 2. The metal may be any metal capable of supporting a plasmon resonance, and preferably silver, aluminum, gold, chromium, copper. The dielectric materials may be any material allowing a "non-destructive association" with the metal, that is to say not likely to cause a physico-chemical reaction, for example of oxidation type, which would degrade the effect on control, regulate. The dielectric materials used for the layers 2 and 4 have substantially identical refractive indices, typically around 1.5, the difference of the indices being advantageously less than 0.1. For example, the layer 2 of dielectric material and of refractive index n1 is a layer of polymer material intended for embossing and layer 4 is a layer of encapsulation of polymer-type dielectric material of refractive index n2. substantially equal to n1. Layers 2 and 4 are transparent in the visible. In the example of FIG. 2, the security optical component 10B further comprises, on a region of at least one of said metal-dielectric interfaces, a layer 5 of high or low index dielectric material the effects of which will be detailed later. .
    [0010] Advantageously, all the layers are supported by a film 1 of 12 μm to 50 μm of polymer material, for example PET (polyethylene terephthalate). The support film 1 may have a support layer function of the optical layers during the manufacturing process, possibly mechanical protection; it can be removable after transfer of the optical layers on the final support, as will be detailed in more detail later. It is known that at the interface between a conductive material, for example a metal, and a dielectric material, can propagate a surface electromagnetic wave associated with a collective oscillation of electrons on the surface, called surface plasmon. This phenomenon is for example described in the basic work of H. Raether ("Surface plasmons", Springer-Verlag, Berlin Heidelberg). The coupling of an incident light wave to one or more plasmonic modes can be obtained in various ways, in particular by structuring the interface to form a coupling network with one or two dimensions. This basic principle is implemented in the security component according to the invention to obtain remarkable effects in transmission and reflection. In the safety component described by means of FIGS. 1 or 2, the metal layer 3 is structured so as to form, on a first coupling zone, a first two-dimensional coupling network (C1), capable of coupling plasmon modes of surface supported by the dielectric-metal interfaces 31 and 32 with an incident light wave, and, on a second coupling zone, a second two-dimensional coupling network (C2), also capable of coupling surface plasmon modes supported by said dielectric - metal interfaces with an incident light wave. The first coupling network Ci and the second coupling network C2 are periodic, asymmetrical profile in each direction, that is to say that for each network, the profile over a period has no symmetry. Different examples of asymmetric profiles in one direction will be detailed later. In each coupling zone, the metal layer is for example continuous, deformed so as to form said coupling networks. As illustrated in FIG. 1, each grating is characterized in each direction by a pitch A, the amplitude (or depth) h of the grating, defined as the height between the peak and the hollow, the thickness t of the metal layer at the coupling area and its asymmetry. Typically, the pitch of a grating in each of the directions is between 100 nm and 600 nm, advantageously between 200 nm and 500 nm and the height is between 10% and 50% of the pitch of the grating, advantageously between 10% and 40%. %. Advantageously, the grating pitches are identical in each direction, making it possible to limit the effects of color variations in reflection and / or transmission by azimuthal rotation of the component. The thickness t of the metal layer must also be sufficiently fine to allow excitation and coupling of surface plasmon modes to the two metal / dielectric interfaces, thus allowing a resonant transmission effect as will be described in more detail here. -Dessous. An incident polarization wave TM (magnetic transverse wave, that is to say, for which the magnetic field H is perpendicular to the plane of incidence xz which is the plane of the figure in FIG. 1) incident on the network is considered. with an azimuth of 0 ° with respect to the grating vector Kg and an angle of incidence 0 in the layer 4 with respect to the y axis normal to the plane of the network formed by the corrugations 104 and an azimuth (1). The network vector Kg, represented in FIG. 1, is the vector of direction perpendicular to the strokes of the network and of norm defined by Kg = 2; z-IA where A is the pitch of the network.
    [0011] For coupling, that is energy transfer between the incident wave in a dielectric medium of relative permittivity cd and the plasmonic mode, the following equality must be satisfied (1): j ( ko, ns, sin (0), sin (e)) 2 + (14 ris, sin (0), cos (e) + pK9) 2) (1) where: ka is the wave number defined by ko = 27z-12 ns is the refractive index of the dielectric material p is the diffractive order ksp is defined by ksi, = nspko, where nsp is the effective index of the propagating surface plasmon.
    [0012] When the metal layer is of finite thickness and, moreover, its thickness is of the order of magnitude of the penetration depth of the electromagnetic field of the plasmon mode in the metal (which is about 1 / (ko ( nsp2 + Re (s', 1)) 1/2)), the electromagnetic field of the plasmon mode at the upper interface of the metallic layer "sees" also the lower interface and must therefore also satisfy the boundary conditions fields at this lower interface. It follows that there are then two plasmon modes that can propagate along the metal layer, both of which have a maximum of field at the upper and lower interfaces of the metal layer: a plasmon mode whose magnetic field transverse H is even (thus the longitudinal electric field, responsible for the longitudinal oscillation of electrons, odd, with a zero crossing in the metal layer), called the "long range" plasmon mode, and a mode of plasmon whose H field is odd, more strongly absorbed by the metal, says the mode of plasmon "short range". Their effective indices are similar when the thickness of the metal layer is not too low (greater than 15 nm, for example) and these modes are both coupled in the presence of a grating when the incident wave emanates from a 2 0 source of light spatially and temporally inconsistent as a lighting lamp or natural sunlight. Thus, when the coupling condition is satisfied, the field of the two modes of coupled plasmons (or "excited") has a maximum at the lower interface of the metal layer too and can therefore, thanks to the presence of the network, radiate in the transmitted medium and thus allow the light energy to pass through the continuous metal layer and thus produce a transmission peak, hence the term resonant transmission. In this case, the effective plasmon index can be approximated by the following equation (2): (2 2 2 1 ko (ns sm) wns nn + nsp s 2ns 3 0 where cm the permittivity of the metal. (2) 2s' The effects of the asymmetry of the networks according to a first variant are illustrated in FIGS. 3 and 4. FIG. 3 represents a simplified sectional view of an example of an optical security component according to the present description and FIG. the visual effects obtained with this component in reflection and in transmission, on each of the faces A (recto) or B (verso). In FIG. 3, only the metal layer 3 is shown, the metal layer 3 being structured to present, as in FIG. 1, a first coupling network C1 in a first coupling zone ("zone 1") and a second coupling network C2 in a second coupling zone ("zone 4"). The first and second networks are asymmetrical , and in this example, one is the negative of the other As a result, the first coupling network Ci seen from a first face of the component (face A for example) is identical to the second coupling network C2 seen from the other side of the component (face B). and vice versa. The asymmetry of each of the networks Ci and C2 is reflected in particular by an extension of the electric field which is different to each of the dielectric-metal interfaces of the "long range" plasmon mode propagating along the two interfaces 31, 32, resulting in losses at the interfaces and extraordinary transmission at the coupling wavelength less effective than with a perfectly symmetrical network, such as for example a sinusoidal network. As in this example, the period of each of the networks seen from one side or the other of the component is identical, the coupling wavelength at which we observe an extraordinary transmission seen from one side or the other component will be identical; however, the losses at the interfaces on each side vary due to the asymmetry of the networks. As a result, the reflection of the incident light, whose luminous intensity is equal to the intensity of the incident wave to which the intensity of the transmitted wave is subtracted and the intensity of the luminous flux diffracted or diffused on interfaces, is variable depending on whether the component is observed on one side or on another. Thus, in the example of FIG. 3, if I0 denotes the light intensity of an incident wave, an extraordinary transmission T1 centered around a central coupling wavelength, identical, is observed on zone 1. depending on whether the component is observed on one side or the other. In zone 4, since the network C2 is the negative of the network C1, the periods are identical for the two networks and again, on this zone, the same transmission T1 is observed. Thus, during a transmission observation, the optical security component will have a uniform color over all the zones, the color being identical irrespective of the front or back observation of the component, as illustrated in FIGS. 4D. On the other hand, due to the asymmetry of the gratings Ci and C2, the diffraction and diffusion losses vary in intensity and in spectrum according to the observation of the component on either side. Thus, during the simplex observation of the component (face A) on zone 1, the diffraction and diffusion losses symbolized in FIG. 3 by the arrows Si will be different from the diffraction and diffusion losses symbolized in FIG. the arrows S2, observed on the back of the component (side B). This results in a spectral and intensity variation of the reflection observed on the front, and referenced Ri in Figure 3, and the reflection observed on the back, and referenced R2 in Figure 3. As in Zone 4 the C2 network is the negative of the grating Ci of the zone 1, the effects in reflection will be reversed between the zone 4 and the zone 1. In other words, on the zone 4 one will observe a reflection R2 on the front (face A) and a reflection Ri on the back (side B). This effect is shown diagrammatically in FIGS. 4A and 4C showing the front and the back of the security optical component during an observation in reflection. This observation is stable regardless of the azimuthal position of the component if the deformation of the profile is present in both directions. Such an optical security component thus has a first level of authentication resulting from a differentiated observation in reflection and in transmission of the component (observation in identical transmission between the two zones while the visual effect in reflection varies between the two zones) . The security optical component has a second level of authentication resulting from the reversal of the visual effects in reflection as a function of the observation zones (here zones 1 and 4) because of the particular structure of two networks with asymmetrical negative profiles. one of the other.
    [0013] An asymmetric profile network is one in which, in at least one direction, the profile is asymmetrical over a period; more precisely, it has no symmetry with respect to a point. When over a period, the profile has a concavity and a convexity, the concavity in an asymmetrical profile is different from the convexity. In other words, the concavity seen from the back is different from the concavity seen from the front. An example of these asymmetric profiles is made by pseudo-sinusoidal profiles.
    [0014] An example of pseudo-sinusoidal profiles is given by cycloidal profiles defined by: x = a * t-b * sint y = a-b * cos t where a and b real non-zero with 1 <la1 / 1b1 <5 and preferencel FIGS. 5A to 5C illustrate various network profiles including pseudo-sinusoidal profiles adapted to an optical security component according to the present description (FIGS. 5B, 5C, 5D) compared to a reference sinusoidal profile (FIG. 5A). ). The profiles presented are sectional views along one of the main directions of the 2D network, for example in the direction of the network vector. In the present description, a pseudo-sinusoidal profile is called a profile which is not perfectly sinusoidal, that is to say which has a duty cycle over a period other than 0.5, the duty cycle being the length of a half oscillation divided by the total period. Advantageously, to obtain a sufficient asymmetry effect, the duty cycle is chosen strictly less than 0.4 (or 40%). Thus, FIG. 5B illustrates a pseudo sinusoidal profile with a duty cycle equal to 0.4; FIG. 5C illustrates a pseudo sinusoidal profile with a duty cycle of 0.2 and at the extreme, FIG. 5D illustrates a pseudo sinusoidal profile with a cyclic ratio tending toward 0, that is to say a half oscillation. is very small in front of the other. The profile in the latter case tends to a profile in the form of "cuvettes" as illustrated in FIGS. 1, 2 or 3 2 0 for example. The asymmetric network profile, however, is not limited to a pseudo-sinusoidal profile, although the pseudo-sinusoidal profile is the easiest to manufacture. FIGS. 5E to 5G thus illustrate other types of possible profiles. In any case, over a period, there is a lack of symmetry. Figures 6 and 7 illustrate a second variant of an optical security component according to the present description (simplified sectional view) and Figure 8 illustrates the resulting visual effects. In this example, a layer of dielectric material 5 is present on a region of at least one of the metal-dielectric interfaces. FIGS. 6 and 7 illustrate a component of the type shown in FIG. 2, but again, to simplify the drawings, only the metal layer 3 and the layer of high index dielectric material 5 have been illustrated. As illustrated in FIG. 6, with respect to the effects shown in FIG. 3, the presence of a layer of high or low index dielectric material causes a variation of the transmission (T2) during the observation of the component on a face or on the other. It also results in a variation of the diffraction and scattering losses (S3) resulting in a reflection variation (R3), but only for the observation of the interface side which carries the high or low index layer (side A in Figures 6 and 7). The variation of the transmission is explained by the variation of the index of the dielectric which modifies the effective index of the plasmon and thus the transmitted wavelength. The variation of the diffraction and diffusion losses is explained by the modification of the dielectric index which modifies the conditions of diffractions, diffusions and coupling to the modes of plasmon.
    [0015] In FIG. 7, four zones can thus be distinguished. An area 1 with a first network C1; an area 2 with the same network C1 but which comprises on the metal-dielectric interface on the side of the side A (front side) a layer 5 of high or low index dielectric material; an area 3 with a second network C2 which, again, is the negative of the network C1 and on which extends the layer 5 of high or low index dielectric material; finally a zone 4 with the same network C2 but without the high or low index layer. In order to produce more characteristic visual effects, as illustrated in FIGS. 8A-8D, the zones 2 and 3 are formed in recognizable graphic forms. With regard to the zones 1 and 4, the visual effects are identical to those described by means of FIGS. 3 and 4. In particular, the phenomenon of extraordinary transmission (Ti) is of identical behavior in intensity and in spectrum whatever the face observation on these two areas. On the other hand, the reflection varies according to the observation of one side or the other of the component and is reversed between the two zones. With the presence of the high or low index dielectric layer (zones 2 and 3), the transmission changes with respect to zones 1 and 4, but remains the same behavior on zones 2 and 3 regardless of the observation face. Thus, as appears in FIGS. 8B and 8D, the behavior of the visual effect in transmission is again observed to be stable regardless of the observation face of the component, but in this example zones 2 and 3 form a recognizable graphic form ("HI") in transmission. Remarkably, as shown in FIG. 8A, in reflection, during the observation on the B side (back side) which corresponds to the side of the interface that does not carry the high or low index layer 5, the reflection is constant on each of the zones 1 and 2 on the one hand (reflection R2), 3 and 4 on the other hand (reflection Ri). So we do not see the symbol "HI" appear in reflection.
    [0016] On the other hand, on the front face, the presence of the high or low index dielectric layer 5 modifies the reflection due to the variation of the diffusion and diffraction losses (respectively S3 on zone 2 and S4 on zone 3). There are thus different reflections in intensity and spectrum on each of the zones and the appearance, in reflection on the front of the component, the graphic sign "HI". The component thus described has, with respect to the component described by means of FIGS. 3 and 4, an additional level of authentication, resulting from the appearance of a recognizable graphic sign, in reflection, on only one of the faces of the component. The security components as described above can be made for example according to manufacturing methods described by means of Figures 9 to 11. In a first step described for example by means of Figures 9A to 9F, matrices or "master" are obtained to create the microstructures that can then be reported on films for the realization of components. In an initial step illustrated in FIG. 9A, a recording of the optical microstructures intended to form a first two-dimensional coupling network is carried out by photolithography or electron beam lithography on a photosensitive medium 102 or "photoresist" according to FIG. Anglo-Saxon expression, carried by a substrate 101. The asymmetrical profile of the microstructures can be obtained by managing the linearity of the response of the photoresist used. The photoresist in question is used in its zone of non-linearity, the increase in the energy input to the photoresist will no longer correspond to the increase in the depth after chemical development. Highly asymmetrical profiles are obtained by this method. A chemical development step (FIG. 9B) makes it possible to reveal the optical microstructures thus obtained. Then an electroplating step (FIG. 9C) makes it possible to transfer these microstructures in a resistant material, for example based on nickel, to produce a first matrix 103 or "master" (FIG. 9D) forming in this example a first negative replica. A positive replica 105 (FIG. 9F), for example also based on nickel, can be obtained by a second electroplating step (FIG. 9E). A first matrix 103 and a second matrix 105 are thus obtained, each matrix forming the negative of one with respect to the other, these matrices being transferable on film to form optical security components as illustrated by FIG. FIGS. 10A to 10E thus illustrate a first example of manufacture of an optical security component as represented in FIGS. 1 or 2. In this first example, an assembly technique is obtained. , on the same matrix 106 based on nickel for example, a double positive and negative structure (Figure 10A). The transfer of the optical microstructures carried by the matrix 106 is made by stamping on a layer 2 of dielectric material, typically a stamping varnish of a few microns thick carried by a film 1 of 12 μm to 50 μm of polymer material, by example PET (polyethylene terephthalate). The refractive index of the layer formed of the stamping varnish is typically 1.5. Other technical layers, varnish type (not shown) may be present between the layer 2 and the film 1. The stamping (Figure 10B) is obtained by hot pressing of the dielectric material ("hot embossing") or by molding cold by UV crosslinking ("UV casting or UV curing"). Next comes the metallization of the layer thus embossed (FIG. 10C) making it possible to form a metal layer 3. The metallization is done under vacuum, in a perfectly controlled manner in thickness, with one of the following metals for example: silver, aluminum, gold , chrome, copper, etc. A controlled refractive index closure layer 4 is then applied (FIG. 10E), for example by a coating method. For some applications, such as rolling or hot stamping products, this layer may be the adhesive layer. The closure layer, which forms the layer 4 (FIG. 1) has a refractive index substantially identical to that of the embossed layer 2, around 1.5, with a thickness of about one micron (0.5 to 2 or more ) at several microns. Depending on the final destination of the product, an adhesive may be applied to the closure layer. According to a variant shown in FIG. 10D, it is possible to deposit a dielectric layer 5 of high or low index on a given region; the deposition of the dielectric layer 5 of high or low index can be done before or after metallization, preferably before metallization. A component of the type shown in FIG. 2 is then obtained. FIGS. 11A to 11F illustrate a second example of manufacturing an optical security component as represented in FIGS. 1 or 2. According to this example, only one of replicas of the matrix, for example the negative replica 103 of the matrix, is transferred to the layer of dielectric material 2 (FIG. 11A), making it possible to obtain a positive structure on the entire film (FIG. 11B). On a zone of the film 2 thus structured, a resin 6 is deposited (FIG. 11C) so as to partially cover the film, for example a UV-sensitive resin having a refractive index close to that of the film 2, thus permitting "Erase" the microstructures on the area of the film covered. The initial structure is, however, always present on part of the film 2. The other replica of the matrix is then transferred onto the resin 6, in this example the positive replica 105 of the matrix, for example by UV flash, in order to obtain a film 2 having both positive and negative structures (Figure 6). As before, a metallization is carried out (FIG. 11E) then the application of the closure layer 4 is carried out (FIG. 11F). Optionally, a layer of dielectric material is applied before or after the metallization, as in the example illustrated in FIG. 10D. According to a variant of the various methods of manufacturing an optical security component according to the present description, it is possible at the time of the metallization step to apply several different metals, for example to look for different visual effects. For this, we can for example apply with a given pattern a soluble ink on the embossed layer. When metallizing with the first metal, it is uniformly applied to the layer but remains only in areas where the ink is not present when the ink is removed. Then a second selective metallization is carried out also comprising a preliminary printing step of soluble ink for selecting the application areas of the second metal. It is possible during the application of the second metal that the metal layers are superimposed locally, forming zones of greater optical density, or on the contrary that results in non-metallized zones which, once closed by the closure layer , will form transparent areas in the component. According to one variant, the different metal zones may correspond to different coupling zones. In other words, the first metal is applied to a first coupling zone, while the second metal is applied to a second coupling zone, allowing different color effects in the different coupling zones. Alternatively, the different metals can be deposited in zones that do not correspond to the coupling zones. The methods of manufacturing a security optical component described above are compatible with the methods of manufacturing the security optical components known from the prior art, in particular the components of the DOVID type. In particular, it is possible to make a security optical element comprising one or more plasmon-type components as described above and one or more other types of optical security components, for example of the holographic type. For this purpose, a matrix can be made by recording the different patterns corresponding to the different optical security components on the photosensitive medium 102 or "photoresist". The stamping can then be performed from the matrix to transfer the different microstructures on the film of polymer material for embossing. The metallization whose thickness is controlled for the plasmon effect components can be made on the entire film, since it is perfectly compatible with the other components of the DOVID type operating in reflection. FIGS. 12A and 12B show a secure document 200, for example a bank note type document, thus equipped with a security element 210 comprising a plasmon-type security optical component 10 and other optical security components. 211, for example of the holographic type. Figure 12A is a top view of this component and Figure 12B is a bottom view. The security element 210 is in the form of a strip, typically of width 15 mm which is fixed on a support 212 of the document 200. The security element 210 is fixed to the support 212 by known means. For example, in the case of a document having a solid transparent zone, the security element can be attached by heat transfer reactivating a transparent adhesive layer previously applied to the closure layer 4 (see Figures 1 or 2). In this case, a detachment layer (for example a wax) can be applied between the stamping varnish 2 and the PET support film 1. It is possible, for example, to transfer the security element to the document by pressing hot or cold the security element on the document, the plasmonic component being in front of the transparent zone. During the transfer, the adhesive film sticks on the support 212 of the document and the release layer and the support film are removed. In the support 212 is provided a transparency window 213 at the level of the plasmonic type component 10. Seen from above, all the optical security components will be visible on the secure document 200 and controllable in reflection according to the various known methods of the invention. prior art. Viewed from below, only the plasmon-type component (s) will be visible; they can be controlled in reflection and transmission, as previously described. It is also possible to adapt this security component to any other document that can be authenticated by reflection and particularly to documents with an area of transparency such as plastic documents (polycarbonate) used in credit card format or even passport page. Although described through a number of exemplary embodiments, the security optical component according to the invention and the method of manufacturing said component comprise various variants, modifications and improvements which will be obvious to those skilled in the art. it being understood that these various variants, modifications and improvements fall within the scope of the invention as defined by the following claims.
    权利要求:
    Claims (12)
    [0001]
    REVENDICATIONS1. An optical security component (10A, 10B) having a plasmonic effect, comprising: - two layers (2,4) of transparent dielectric material; - a metal layer (3) arranged between said layers of transparent dielectric material to form two dielectric-metal interfaces (31, 32) and structured to form, on a first coupling zone, a first periodic two-dimensional coupling network (C1) capable of coupling surface plasmon modes supported by said dielectric-metal interfaces with a wave incident light, the first coupling network having an asymmetrical profile in each of its directions, and, on a second coupling area, a second periodic two-dimensional coupling network (C2) capable of coupling surface plasmon modes. supported by said dielectric-metal interfaces with an incident light wave, the second coupling network having an asymmetric profile according to one of its directions, different from that of the first coupling network when viewed from the same side of the component as the first coupling network.
    [0002]
    The optical security component of claim 1, wherein the periods are identical in both directions for each of the first and second coupling networks.
    [0003]
    3. Optical security component according to any one of the preceding claims, wherein the first and second coupling networks have identical periods.
    [0004]
    4. Optical security component according to claim 3, wherein the second coupling network is the negative of the first coupling network.
    [0005]
    5. Optical security component according to one of the preceding claims, wherein the profile in each of the directions of the first and second coupling network is a pseudo-sinusoidal profile having a duty cycle strictly less than 40%.
    [0006]
    6. optical security component according to one of the preceding claims, further comprising on a region of at least one of said metal-dielectric interfaces a layer of high or low index dielectric material.
    [0007]
    The optical security component of claim 6, wherein said layer of high or low index dielectric material is formed in a recognizable pattern.
    [0008]
    8. optical security element for securing a document and comprising at least one security optical component according to one of the preceding claims.
    [0009]
    A secure document (200) comprising a medium (212) and an optical security component according to any one of claims 1 to 7 or an optical security element (10) according to claim 8 attached to said medium, said medium comprising a region of transparency (213) at which said security optical component is arranged.
    [0010]
    10. A method of manufacturing a plasmon-effect optical safety component comprising: depositing a metal layer (3) on a first layer (2) made of transparent structured dielectric material, making it possible to obtain a first metal-metal interface; structured dielectric (32), - the encapsulation of said metal layer by a second layer (4) of transparent dielectric material, to form a second dielectric-metal interface (31) structured, and wherein: - the two dielectric interfaces - metal (31, 32) are structured to form, on a first coupling zone, a first periodic two-dimensional coupling network (Ci) capable of coupling surface plasmon modes supported by said dielectric-metal interfaces with a wave light incident, the first coupling network having an asymmetrical profile in each of its directions, and, on a second coupling zone, a second coupling network, two-dimensional coupling network (C2), periodic, capable of coupling surface plasmon modes supported by said dielectric-metal interfaces with an incident light wave, the second coupling network having an asymmetrical profile in each of its directions, different of that of the first coupling network when viewed from the same side of the component as the first coupling network.
    [0011]
    The method of claim 10, further comprising: - fabricating a first matrix for structuring the metal-dielectric interfaces at the first coupling area to form the first coupling network and manufacturing a second matrix for structuring the metal-dielectric interfaces at the second coupling zone to form the second coupling network, the second matrix being a negative replica of the first matrix.
    [0012]
    12. The method according to claim 10, further comprising: depositing on a region of at least one of said metal-dielectric interfaces a layer (5) of high or low index dielectric material.
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    同族专利:
    公开号 | 公开日
    AU2014380965A1|2016-08-25|
    CA2938326A1|2015-08-06|
    EP3099513B1|2018-02-07|
    US20170225502A1|2017-08-10|
    US10464366B2|2019-11-05|
    AU2014380965B2|2017-03-02|
    FR3017231B1|2020-07-24|
    WO2015113718A1|2015-08-06|
    CA2938326C|2021-03-02|
    EP3099513A1|2016-12-07|
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    法律状态:
    2015-12-22| PLFP| Fee payment|Year of fee payment: 3 |
    2016-09-23| CD| Change of name or company name|Owner name: HOLOGRAM.INDUSTRIES, FR Effective date: 20160823 |
    2016-12-21| PLFP| Fee payment|Year of fee payment: 4 |
    2017-12-21| PLFP| Fee payment|Year of fee payment: 5 |
    2019-12-19| PLFP| Fee payment|Year of fee payment: 7 |
    2020-12-17| PLFP| Fee payment|Year of fee payment: 8 |
    2021-12-15| PLFP| Fee payment|Year of fee payment: 9 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1450766A|FR3017231B1|2014-01-31|2014-01-31|OPTICAL SAFETY COMPONENT WITH A PLASMONIC EFFECT, MANUFACTURE OF SUCH COMPONENT AND SAFE DOCUMENT EQUIPPED WITH SUCH COMPONENT|FR1450766A| FR3017231B1|2014-01-31|2014-01-31|OPTICAL SAFETY COMPONENT WITH A PLASMONIC EFFECT, MANUFACTURE OF SUCH COMPONENT AND SAFE DOCUMENT EQUIPPED WITH SUCH COMPONENT|
    PCT/EP2014/079321| WO2015113718A1|2014-01-31|2014-12-24|Plasmonic optical security component, production of such a component and a secure document equipped with such a component|
    CA2938326A| CA2938326C|2014-01-31|2014-12-24|Plasmonic optical security component, production of such a component and a secure document equipped with such a component|
    AU2014380965A| AU2014380965B2|2014-01-31|2014-12-24|Plasmonic optical security component, production of such a component and a secure document equipped with such a component|
    US15/115,318| US10464366B2|2014-01-31|2014-12-24|Plasmonic optical security component, production of such a component and a secure document equipped with such a component|
    EP14830963.6A| EP3099513B1|2014-01-31|2014-12-24|Plasmonic optical security component, production of such a component and a secure document equipped with such a component|
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