Optical safety components, manufacturing of such components and safety-critical objects equipped with such components

Abstract

The invention relates to a safety optical component (201) comprising a first layer (213) of dielectric material, at least one first diffractive structure (S) etched onto said first layer, and a second layer (214) at least partially covering said first diffractive structure and having a spectral band of reflection in the visible range. The first diffractive structure comprises an array of facets (220), each having a slope of fixed angular value and a crest line (225), the facets being designed to generate, for example, a surface appearing three-dimensional to an observer. Each facet of the array of facets is structured by a sub-wavelength diffraction grating (230) configured to produce, after deposition of the second layer, a colored effect.The diffraction gratings that structure the facets of the facet set include at least one property that varies depending on the orientation of the ridge line and / or the angular value of the slope of the facets. Fig. 2A.

Description

Title of the invention: Optical security components, manufacture of such components and secure objects equipped with such components Technical field of the invention

[0001] The present description relates to the field of security marking. More particularly, it relates to optical security components for verifying the authenticity of an object, for example a product or a valuable document, for example an identity document or a banknote, to a method for manufacturing such a component and to a secure object equipped with such a document. In particular, the present description relates to optical security components for verifying the authenticity of an object by observation in reflection, with the naked eye. State of the art

[0002] Many technologies are known for the authentication of documents or products, and in particular for the security of documents such as valuable documents, documents such as banknotes, passports or other identification documents. These technologies aim at the production of optical security components whose optical effects, depending on the observation parameters (orientation of the component relative to the positions of the source, the observer, the orientation of the component in tilt and / or in azimuth, etc.), take very characteristic and verifiable configurations. The general aim of these optical components is to provide new and differentiated optical effects, from physical configurations that are difficult to reproduce. Among these components, DOVID stands for "Diffractive Optical Variable Image Device", the optical components producing diffractive and variable images that are commonly called holograms.

[0003] Among these optical security components, components are known which are configured to generate an object which appears three-dimensionally to an observer.

[0004] Such an optical security component is described for example in patent application WO2011 / 138394 [Ref. 1]. An optical security component described in [Ref. 1] comprises a structure etched on a support with a given refractive index n0, a thin layer of a dielectric material with a refractive index n different from n0, the thin layer being deposited on the structure, and a layer of a material with an index n2 close to n0 which encapsulates the structure coated with the thin layer. The structure comprises a first pattern modulated by a second pattern. The first pattern is a bas-relief comprising a set of facets whose shapes are determined to simulate a relief image of a relief object and the second pattern is a periodic grating determined to modulate the first pattern in order to produce, after deposition of the thin layer and encapsulation of said structure, a first color according to a first observation orientation and a second different color according to a second observation orientation obtained by an azimuthal rotation of the component.

[0005] [Fig.lA] shows an optical security component 101 as described in [Ref. 1]. The bas-relief comprises in this example a set of facets whose shapes are determined to generate a compass rose surrounded by a texture, the whole appearing three-dimensionally to an observer. [Fig.lB] and [Fig.lC] illustrate partial views of the structure 110 of the optical security component 101 taken with an atomic force microscope (AFM), at two different resolutions of the microscope. The structure 110 comprises a first pattern 111 (bas-relief) modulated by a second pattern 121, in this example a one-dimensional periodic lattice. The bas-relief 111 of the structure 110, part of which is visible in [Fig.lB], comprises a set of facets 112 whose shapes have been calculated to simulate the relief of the object formed by the compass rose and the texture. The first pattern 111 is modulated by the second pattern 121, part of which is visible in [Fig.lC] obtained at higher resolution. [Fig.[Fig.lC] thus represents an image of a part of the structure visible in [Fig.lB] but enlarged to perceive the lines 122 forming the diffraction grating. After deposition of the thin layer and encapsulation of the structure, the object appears three-dimensionally to an observer with a first color during observation with a given azimuth angle and a second color after azimuthal rotation of the optical security component by an angle of approximately 90 degrees.

[0006] Thus, the optical security components as described in [Ref. 1] are known for the remarkable optical effects that they produce. They are easily controllable while being extremely difficult to falsify due to the technicality of the manufacturing process implemented. The optical security components as described in [Ref. 1] thus provide a very high level of security.

[0007] The present application describes an optical security component which makes it possible to generate an original polychrome visual effect visible in reflection by an observer, for example a recognizable polychrome surface appearing three-dimensionally for an observer. The original polychrome visual effect allows even more secure authentication compared to the visual effects of the state of the art. Summary of the invention

[0008] In the present description, the term "comprise" means the same as "include", "contain", and is inclusive or open and does not exclude other elements not described or shown. Furthermore, in the present description, the term "approximately" or "substantially" means the same as "having a margin less than and / or more than 10%, for example 5%", of the respective value.

[0009] According to a first aspect, the invention relates to an optical security component for the authentication by the naked eye of an object, for example a valuable document, for example an identity document or a banknote.

[0010] The component according to the first aspect comprises: - a first layer of dielectric material, transparent in the visible, having a first refractive index; - at least one first diffractive structure etched on said first layer; and - a second layer, at least partially covering said first diffractive structure, and having a spectral band of reflection in the visible; and in which: - said first diffractive structure comprises a set of facets, each facet having a slope of substantially fixed angular value and a crest line with an orientation defined according to an axis of the plane of the component, at least some of the facets having crest lines with different orientations and at least some of the facets having slopes with different angular values, in which: - each facet of the set of facets is structured by a subwavelength diffraction grating with one or more steps between approximately 150 nm and approximately 400 nm configured to produce, after deposition of the second layer, a colored effect; - the diffraction gratings that structure the facets of the facet set include at least one variable property depending on the orientation of the ridge line and / or the angular value of the slope of the facets.

[0011] In the present description, a layer transparent in the visible is defined as a layer having a transmission of at least 70%, preferably at least 80% for a wavelength included in the visible, that is to say a wavelength between approximately 400 nm and approximately 800 nm. A layer thus transparent makes it possible to observe with the naked eye the layers located under the transparent layer.

[0012] In the present description, an outline of the diffractive structure has, seen from above, a minimum dimension, defined by the smallest dimension of the outline which passes through a geometric center of the outline, greater than 500 μm, preferably greater than 1 mm, preferably greater than 2 mm. Such a minimum dimension makes it possible to generate a visual effect visible in reflection to the naked eye by an observer.

[0013] In the present description, the terms “gratings”, “diffraction gratings” and “sub-wavelength gratings” will be used interchangeably to designate the sub-wavelength diffraction gratings which structure the facets.

[0014] The optical component according to the first aspect is remarkable in particular in that it makes it possible to generate a polychrome visual effect, the color depending on the local slope and / or the orientation of the crest lines of the facets.

[0015] In exemplary embodiments, the facets are determined to generate a surface appearing, in reflection and according to a given observation angle, in a three-dimensional manner to an observer, that is to say a surface which appears curved or hollow relative to the plane of the component. This results for an observer in the appearance of a polychrome 3D surface, the colors of which vary according to the tilt and / or the azimuth. In exemplary embodiments, said surface has a recognizable shape, for example an alphanumeric sign or a geometric figure.

[0016] In other embodiments, the facets are determined to generate a recognizable shape or texture that is not necessarily perceived in relief by an observer but which presents another visual effect, for example a dynamic visual effect, for example an ortho parallax effect.

[0017] The original colored optical effect results from the structure of the security optical component according to the present description in which each subwavelength grating which structures a facet has a property which depends on the orientation of the crest line and / or the angular value of the slope of said facet. The security optical component is thus distinguished in particular from a security optical component as described in [ref. 1] in which the grating lines of the diffraction grating are all oriented in a single direction.

[0018] Said variable property of sub-wavelength diffraction gratings is for example: a direction of grating lines, a period, a depth.

[0019] In the present description, azimuthal rotation of the optical security component is a rotational movement of the component around an axis substantially perpendicular to a plane of the component.

[0020] A tilt is a rotational movement of the component about an axis included in a plane of the component. From a user's point of view, a plane of incidence of the light can be defined which includes an illumination axis of the component and an observation axis. A right / left tilt is a rotational movement about an axis included in the plane of the component and in the plane of incidence and an up / down tilt is a rotational movement about an axis included in the plane of the component and perpendicular to the plane of incidence.

[0021] Each facet is characterized by a ridge line, a slope with a given angular value, a height and a width. In exemplary embodiments, the plurality of facets is configured to form a microstructure for simulating the reflection properties of a three-dimensional surface of which a representation is to be given to an observer.

[0022] In the present description, the "height" of a facet is a distance between a lowest level of the facet and a highest level, the distance being measured along an axis perpendicular to a plane parallel to the plane of the component.

[0023] The ridge line of the facet is the locus of the highest level facet points. The ridge line of a facet is continuous and has a defined orientation relative to a reference axis of the component plane. The orientation of a ridge line may be fixed (straight line) or variable. In exemplary embodiments, the variation in the orientation of the ridge lines is continuous. In other exemplary embodiments, the variation in the orientation of the ridge lines is discontinuous.

[0024] The "width" of a facet is the width of the band resulting from the projection of the facet in a plane parallel to the plane of the component.

[0025] In exemplary embodiments, a minimum dimension of the width of the facets is equal to approximately 2 μm. According to one or more examples, the facets have a width of between approximately 2 μm and approximately 100 μm, advantageously between approximately 2 μm and approximately 80 μm, advantageously approximately 4 μm and approximately 40 μm.

[0026] According to one or more exemplary embodiments, all of the facets have a substantially identical height. The height of the facets is for example less than approximately 5 μm, advantageously less than approximately 2 μm, advantageously less than approximately 1 μm. According to one or more examples, the facets of all of the facets have different heights. In this case, however, the facets have a maximum height. Said maximum height is for example less than approximately 2 μm, advantageously less than approximately 1 μm.

[0027] According to one or more exemplary embodiments, all of the facets have a low level located in the same plane. In other exemplary embodiments, the low levels of the facets are not located in the same plane. In the case of facets of different heights, midpoints of the facets located between the low level and the high level may, for example, be located in the same plane.

[0028] By definition in the present description, a facet comprises a slope of substantially fixed angular value.

[0029] According to one or more exemplary embodiments, said minimum angular value of the slope of a facet (in absolute value) is equal to approximately 1°. According to one or more exemplary embodiments, said maximum angular value of the slope of a facet (in absolute value) is equal to approximately 45°. According to one or more examples, the angular value of the slope of a facet (in absolute value) is between approximately 1° and approximately 30°, advantageously between approximately 2° and approximately 15°.

[0030] The greater the number of facets with varying slope angular values ​​and / or ridge line orientations the set of facets comprises, the more complex the polychrome visual effect can be and therefore facilitate authentication. In particular, the reflection properties of a three-dimensional surface can be simulated with precision.

[0031] Thus, in exemplary embodiments, the set of facets comprises facets with at least 5 different slope angular values, advantageously at least 10, advantageously at least 50, or more depending on the dimension of the contour of the first diffractive structure.

[0032] In exemplary embodiments, the set of facets comprises facets with at least 5 different ridge line orientations, advantageously at least 10. Note that in exemplary embodiments, at least some of the facets have continuously variable ridge lines.

[0033] In exemplary embodiments, the set of facets results from a translation by zone of a three-dimensional surface whose reflection properties are to be simulated. For the determination of the set of facets, also called “bas-relief”, one can refer to the method of forming Fresnel lenses as described in [Ref. 2]. See also [Ref. 1].

[0034] According to one or more exemplary embodiments, at least a portion of the ridge lines of the facets of the set of facets are closed. Such sets of facets are, for example, bas-reliefs as described above.

[0035] According to one or more exemplary embodiments, said diffraction gratings comprise grating lines substantially parallel to each other and said at least one property is the orientation of said grating lines.

[0036] According to one or more exemplary embodiments, in which said at least one property is chosen from: a period of the networks, a depth of the networks.

[0037] Thus, in exemplary embodiments, the diffraction gratings which structure the facets comprise grating lines which are substantially parallel to each other, the other properties (pitch, depth, grating profile) being able to be substantially identical, and said at least one property is the orientation of said grating lines as a function of the orientation of the crest line of the structured facets.

[0038] For example, the network lines are chosen to be substantially parallel to the ridge lines. But in other embodiments, the network lines may have a non-zero angle relative to the ridge lines. For example, an angle of approximately 90° (network lines perpendicular to the ridge lines) or an angle strictly between 0° and 90°.

[0039] In exemplary embodiments, the angle is fixed and the orientation of the network lines follows the orientation of the ridge lines.

[0040] An observer will then be able to observe a polychrome visual effect, for example a surface appearing three-dimensional and polychrome, the colors depending on the orientation of the ridge lines relative to the observation axis. During a right / left and / or up / down tilt movement, the intensities of the colored effects can vary, which generates a dynamic visual effect, but whatever either the colored effect observed during a right / left and / or up / down tilt movement, this same colored effect will be observed after azimuthal rotation. This conservation of a dynamic colored effect by azimuthal rotation makes it even easier to control.

[0041] A method of authenticating such a security component with the naked eye may comprise: - observation of the optical safety component along an observation axis forming a given observation angle with the lighting axis; - a left / right and / or down / left tilt movement allowing you to observe a predetermined dynamic colored effect; - an azimuthal rotation movement of a predetermined angle allowing the conservation of the dynamic colored effect to be observed.

[0042] The azimuthal rotation angle is advantageously between approximately 30° and approximately 150°, for example between approximately 60° and approximately 120°.

[0043] Advantageously, the orientation of the grating lines of the diffraction gratings varies with the orientation of the crest line of the facets according to an identical function for all of the facets. This makes it easier to implement the diffractive structure.

[0044] For example, the function may be a predefined angle between the orientation of the ridge lines and the orientation of the network lines. However, in exemplary embodiments, the function may be a step function. Thus, the orientation of the network lines may be defined relative to a reference axis of the plane of the component, as a function of the orientation of the ridge lines relative to this same reference axis. For example, the orientation of the network lines relative to the reference axis may be fixed within predetermined ranges of values ​​of the orientation of the ridge lines.

[0045] In exemplary embodiments, the diffraction gratings are one-dimensional, that is to say that they only have a set of grating lines, parallel to each other.

[0046] In other embodiments, the diffraction gratings may be two-dimensional, that is to say they have a first set of grating lines, parallel to each other, and a second set of grating lines, also parallel to each other and generally perpendicular to the grating lines of the first set of grating lines.

[0047] In exemplary embodiments, the orientation of the grating lines of the diffraction gratings may be variable with the angular value of the slope of the facet.

[0048] In such a security optical component, regardless of the azimuth angle, the up / down and right / left tilts may have a color change, the color depending on the slope of the object locally. Thus, an observer will be able to observe a polychrome visual effect, for example a three-dimensional polychrome surface, all of whose regions of the same slope appear the same color.

[0049] The property of variable diffraction gratings with ridge line orientation and / or facet angular value is not limited to the orientation of the grating lines.

[0050] In particular, a property of the diffraction gratings that varies with the orientation of the ridge line and / or the angular value of the facet may also be a grating pitch, a grating depth, a grating profile, etc. Furthermore, several properties of the diffraction gratings may vary to generate other colored effects.

[0051] In exemplary embodiments, only one property of the diffraction gratings will be variable while the other properties will be identical for all the diffraction gratings.

[0052] Whatever the variable property of the diffraction gratings as a function of the orientation of the ridge line or the angular value of the slope of the facet, advantageously, said at least one property is variable according to an identical function for all the facets, which simplifies the manufacturing of the diffractive structure and possibly the authentication scenario.

[0053] According to one or more exemplary embodiments, a function is a step function. Thus, the property of the diffraction grating will be identical in ranges of orientation angle values ​​of the ridge lines measured relative to a reference axis or in ranges of angular values ​​of the slopes of the facets. Such a step definition can facilitate the manufacture of the diffractive structure.

[0054] In an optical security component according to the first aspect, the diffraction gratings which structure the facets are sub-wavelength. In practice, each diffraction grating comprises one or more pitches between approximately 150 nm and approximately 400 nm, advantageously between approximately 200 nm and approximately 400 nm.

[0055] The diffraction gratings are configured to produce, after deposition of the second layer, a colored effect. Generally, such a colored effect results from an optical resonance making it possible to generate band-stop or band-pass filters.

[0056] According to one or more exemplary embodiments, each subwavelength diffraction grating is configured to produce a guided mode optical resonance as described in [Ref. 1] - see also [Ref. 3] or [ref. 4].

[0057] In these exemplary embodiments, the second layer is a thin layer of transparent dielectric material having a second refractive index and encapsulated between said first layer of electrical material and a third layer of dielectric material having a third refractive index. The second refractive index has a difference with the first refractive index on the one hand, and with the third refractive index on the other hand, greater than or equal to approximately 0.3, advantageously greater than or equal to approximately 0.5 in absolute value.

[0058] According to one or more exemplary embodiments, said thin layer of dielectric material is a layer of so-called “high refractive index” (or “HRI”) material, having a refractive index of, for example, between 1.8 and 2.9, advantageously between 2.0 and 2.4, and the neighboring layers (first and third layers) are so-called “low refractive index” layers, having refractive indices of, for example, between 1.3 and 1.8, advantageously between 1.4 and 1.7. For example, said second layer comprises a material chosen from: zinc sulfide (ZnS), titanium dioxide (TiO2) and silicon nitride (Si3N4).

[0059] A thin layer within the meaning of the present description is a layer with a thickness of between approximately 5 nm and approximately 250 nm, preferably between approximately 10 nm and approximately 150 nm.

[0060] The thin layer of transparent dielectric material has a thickness of, for example, between approximately 20 nm and approximately 200 nm and preferably between approximately 60 nm and approximately 150 nm.

[0061] The subwavelength diffraction grating configured to produce a guided mode optical resonance is for example a one-dimensional grating, comprising grating lines substantially parallel to each other, and comprises one or more pitches between approximately 150 nm and approximately 400 nm, advantageously between approximately 200 nm and approximately 400 nm. The subwavelength diffraction grating may also be a two-dimensional grating, comprising first grating lines substantially parallel to each other and second grating lines substantially parallel to each other and perpendicular to the first grating lines.

[0062] The depth of the network is for example between approximately 30 nm and approximately 250 nm. The profile of the network is for example sinusoidal or pseudo-sinusoidal or rectangular.

[0063] In operation, such a diffraction grating is configured for the excitation of guided modes within said thin layer of transparent dielectric material, forming a band-pass resonant filter in reflection, the resonance spectral band of which is centered on a wavelength determined in a known manner as a function of the characteristics of the grating and the nature of the layers.

[0064] This results in a colored effect which depends in particular on the type of diffraction grating and the pitch(s) of the diffraction grating, or on the refractive index of the layers.

[0065] According to the present description, at least one property of the diffraction gratings is variable depending on the orientation of the ridge lines and / or the angular value of the slope of the facets. As explained previously, said at least one property (orientation of the network lines, network pitch, network depth, etc.) can be chosen depending on the desired color effect.

[0066] According to one or more exemplary embodiments, the subwavelength diffraction gratings are configured to produce a plasmonic resonance effect in reflection as described for example in [Ref. 5] or [Ref. 6].

[0067] In these examples, the second layer is metallic and comprises a thin layer of metallic material, for example silver, aluminum, gold, chromium, copper, advantageously with a thickness greater than approximately 40 nm. Advantageously, said metallic layer is sufficiently thick to have a maximum residual transmission as a function of the wavelength of 2%.

[0068] As in the previous examples, each subwavelength diffraction grating may comprise one or more pitches between approximately 150 nm and approximately 400 nm, advantageously between approximately 200 nm and approximately 400 nm; the subwavelength diffraction grating is for example a one-dimensional grating, and comprises a single set of grating lines substantially parallel to each other, or a two-dimensional grating which comprises a first set of grating lines substantially parallel to each other and a second set of grating lines substantially parallel to each other and perpendicular to the direction of the grating lines of the first set of grating lines.

[0069] The depth of the network is for example between 30 nm and 200 nm. The profile of the network is for example sinusoidal or pseudo-sinusoidal or rectangular.

[0070] In operation, such a diffraction grating is configured for the excitation of plasmonic modes at the metal-dielectric interface, forming a resonant notch filter in reflection, the resonance spectral band of which is centered on a wavelength determined in a known manner as a function of the characteristics of the grating and the nature of the layers.

[0071] This results in a colored effect which depends on the type of diffraction grating and the pitch(s) of the diffraction grating and the refractive indices of the layers.

[0072] According to the present description, at least one property of the diffraction gratings is variable depending on the orientation of the ridge lines and / or the angular value of the slope of the facets. As explained previously, said at least one property (orientation of the grating lines, pitch of the grating, depth of the grating, etc.) may be chosen depending on the desired colored effect.

[0073] According to one or more exemplary embodiments, the optical security component according to the first aspect comprises at least one second structure etched on said first layer, said second layer at least partially covering said second structure. The second structure is configured to form, for example and in a non-limiting manner, another structure according to the present description, a structure diffusing, a holographic structure, a diffractive structure, for example a structure making it possible to achieve an effect called Alphagram® developed by the applicant.

[0074] According to one or more exemplary embodiments, the optical security component according to the first aspect comprises one or more additional layers depending on the needs of the application, these additional layers being able or not to contribute to the desired visual effect.

[0075] Thus, according to one or more exemplary embodiments, the optical security component is configured for securing an object, for example a document or a product, and further comprises, on the face opposite the observation face, a layer suitable for transferring the component onto the document or the product, for example an adhesive layer or a reactivatable adhesive layer.

[0076] According to one or more exemplary embodiments, the optical security component further comprises, on the side of the first observation face, a support film intended to be detached after transfer of the component onto the document or product.

[0077] According to one or more exemplary embodiments, the optical security component is configured for the manufacture of a security track for securing banknotes, and comprises on the side of the first observation face and / or on the face opposite the first observation face, one or more protective layers.

[0078] According to a second aspect, the present description relates to a secure object, for example a secure valuable document, comprising a substrate and an optical security component according to the first aspect, deposited on said substrate or on one of the layers of said substrate in the case of a multilayer substrate.

[0079] Such a secure object is, for example, and in a non-limiting manner: a banknote, an identity or travel document, on a paper or polymer substrate.

[0080] According to a third aspect, the present description relates to methods of manufacturing optical security components according to the first aspect.

[0081] Thus, the present description relates to a method of manufacturing an optical security component for securing an object, for example a valuable document, for example an identity document or a banknote, the method comprising: - the deposition on a support film of a first layer of dielectric material, transparent in the visible; - the formation on said first layer of at least one first diffractive structure, - the deposition of a second layer at least partially covering said first diffractive structure, and having a spectral band of reflection in the visible, and in which: - said first diffractive structure comprises a set of facets, each facet having a slope of substantially fixed angular value and a ridge line with an orientation defined with respect to an axis of the plane of the component, at least a portion of the facets having ridge lines with different orientations and at least a portion of the facets having slopes with different angular values, wherein: - each facet of the set of facets is structured by a subwavelength diffraction grating with one or more steps between approximately 150 nm and approximately 400 nm configured to produce, after deposition of the second layer, a colored effect; - the diffraction gratings that structure the facets of the facet set include at least one variable property depending on the orientation of the ridge line and / or the angular value of the slope of the facets. Brief description of the figures

[0082] Other characteristics and advantages of the invention will appear on reading the description which follows, illustrated by the following figures:

[0083] [Fig. 1A] (already described) represents a simulation of a three-dimensional shape (wind rose) in a known state-of-the-art optical security component.

[0084] [Fig.lB] (already described) represents an image produced using an atomic force microscope of a region of the structure making it possible to generate the optical security component of [Fig.lA], with a first resolution.

[0085] [Fig.lC] (already described) represents an image produced using an atomic force microscope of a region of the structure making it possible to generate the optical security component of [Fig.lA], with a second resolution, higher than the first.

[0086] [Fig.2A] schematically illustrates a (partial) sectional view of an exemplary embodiment of a component according to the present description.

[0087] [Fig.2B] schematically illustrates a (partial) sectional view of another exemplary embodiment of a component according to the present description.

[0088] [Fig.3] illustrates the observation conventions of an optical security component according to the present description;

[0089] [Fig.4A] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart.

[0090] [Fig.4B] schematically illustrates grating lines of the diffraction gratings which structure the facets illustrated in [Fig.4A], the grating lines being parallel to each other and substantially parallel to the ridge lines.

[0091] [Fig.5A] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of the diffraction gratings which structure the facets, the network lines being parallel to each other and substantially parallel to the ridge lines.

[0092] [Fig.5B] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of the diffraction gratings which structure the facets, the grating lines being parallel to each other, substantially perpendicular to the ridge lines.

[0093] [Fig.5C] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of the diffraction gratings that structure the facets, the grating lines being parallel to each other, inclined relative to the ridge lines at a substantially constant angle.

[0094] [Fig.5D] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of two-dimensional diffraction gratings that structure the facets, first grating lines being parallel to each other, parallel to the ridge lines, and second grating lines being parallel to each other, perpendicular to the ridge lines.

[0095] [Fig.5E] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of the diffraction gratings which structure the facets, the grating lines being parallel to each other, of fixed orientation, the pitches of the gratings being variable, the pitch of each grating depending on the angular value of the slope of the facet which it structures.

[0096] [Fig.5F] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of the diffraction gratings which structure the facets, the grating lines being parallel to each other, of fixed orientation, the pitches of the gratings being variable, the pitch of each grating depending on the orientation of the ridge line of the facet which it structures.

[0097] [Fig.6] schematically illustrates a surface that we seek to represent in a three-dimensional way to an observer (here a character “5”), and regions illustrating the orientation of the network lines of the diffraction gratings relative to a given axis (vertical axis in the figure).

[0098] [Fig.7] schematically illustrates a surface that we seek to represent in a three-dimensional way to an observer (here a heart), and a gray level representation coding the orientation of the network lines of the diffraction gratings which structure the facets in relation to a given axis, between 0° and 360°.

[0099] [Fig.8A] illustrates the colored effects produced by an optical security component according to a first exemplary embodiment, before and after azimuthal rotation of 90°.

[0100] [Fig.8B] illustrates the colored effects produced by an optical security component according to a second exemplary embodiment, before and after azimuthal rotation of 90°.

[0101] [Fig.8C] illustrates the colored effects produced by an optical security component according to a third exemplary embodiment, before and after azimuthal rotation of 90°.

[0102] [Fig.9] illustrates the colored effects produced by an optical security component according to an exemplary embodiment, in an up / down and left / right tilt observation of the component. Detailed description

[0103] In the figures, the elements are not shown to scale for better visibility.

[0104] [Fig.2A] and [Fig.2B] schematically represent, in (partial) sectional views, two examples of optical security components according to the present description.

[0105] The optical security component 201 shown in [Fig.2A] represents, for example, an optical security component intended to be transferred in the form of a track or patch onto a document or product for the purpose of securing it. According to this example, it comprises a support film 211, for example a film made of polymer material, for example a polyethylene terephthalate (PET) film of a few tens of micrometers, typically 10 to 100 qm, as well as a detachment layer 212, for example made of natural or synthetic wax. The detachment layer makes it possible to remove the polymer support film 211 after transfer of the optical component onto the product or document to be secured.The optical security component 201 further comprises a first layer 213 of dielectric material, having a first refractive index ni and at least one first diffractive structure S comprising a set of facets 220 each structured by a sub-wavelength diffraction grating 230, and which will be described in more detail later.

[0106] In the example of [Fig.2A], the optical security component 201 also comprises a second reflective layer 214, at least partially covering said first structure S, and having a spectral band of reflection in the visible. The second layer 214 is for example a metallic layer (for example Aluminum, Silver, Chrome, Copper or a metal alloy). The second layer may also be a so-called refractive index variation layer having a refractive index n2 different from the neighboring layers (for example ZnS sulfide, TiO2, ...), the difference in refractive index with that of the neighboring layers having a value at least equal to 0.3, advantageously a value at least equal to 0.5.

[0107] As illustrated in [Fig.2A], each facet 220 of the facet set has a slope of angular value a, a height h and a width L. The facets of the facet set are determined to generate for example a surface appearing three-dimensionally to an observer, for example a figurative surface such as an alphanumeric sign, a geometric figure, a recognizable object (heart, shell, embossed silhouette, etc.). Each facet also has a ridge line 225. In exemplary embodiments, at least a portion of the ridge lines of the facets of the facet set are closed.

[0108] Each facet of the set of facets is structured by a subwavelength diffraction grating 230 with one or more pitches between approximately 150 nm and approximately 400 nm and configured to produce, after deposition of the second layer 214, a colored effect. As will be described in more detail below, the diffraction gratings that structure the facets have at least one variable property depending on the orientation of the ridge line and / or the angular value of the facets that they structure.

[0109] The subwavelength diffraction grating 230 is configured to produce, after deposition of the second layer 214, a colored effect. Examples of gratings will be described in more detail later. The colored effect may result from a resonance of guided modes, when the second layer 214 is made of dielectric material and has a refractive index difference at least equal to 0.3 with the neighboring layers, advantageously at least equal to approximately 0.5. In exemplary embodiments, the layer 214 made of dielectric material has a refractive index n2 greater than the refractive indices nB n3 of the neighboring layers and is referred to as a high index layer or HRI layer (for “High Refractive Index”). The colored effect may also result from a plasmonic resonance when the second layer 214 is metallic.

[0110] The optical security component may further comprise one or more additional layers, optically functional or non-functional, adapted to the application.

[0111] For example, in the example of [Fig.2A], the optical security component further comprises a layer of adhesive 217, for example a layer of heat-reactivatable adhesive, for transferring the optical security component onto the product or document.

[0112] In practice, as will be detailed later, the optical security component can be manufactured by stacking the layers on the support film 211, then the component is transferred onto a document / product to be secured using the adhesive layer 217. Optionally, the support film 211 can then be detached, for example by means of the detachment layer 212. The main observation face 200 of the optical security component is thus located on the side of the first layer 213 opposite the structured face of the layer 213.

[0113] The optical security component 202 shown in [Fig.2B] represents for example an optical security component intended for securing banknotes; it is for example a part of a security thread intended to be integrated into the paper during the manufacture of the note or a laminated track covering a window in the paper. In this example, the component 202 comprises as previously a support film 211 (12 to 50 pm) which will also serve as a protective film for the security thread, and, as in the example of [Fig.2A], a first layer 213 of dielectric material having a first refractive index ni at least one first diffractive structure S comprising a set of facets 220 each structured by a subwavelength diffraction grating 230, as described with reference to [Fig.2A].A second layer 214 at least partially covers said first diffractive structure S, and has a spectral band of reflection in the visible.

[0114] The optical security component 202 further comprises, in the example of [Fig.2B], a set of optional layers 215, 216, 218. The layer 215 (optional) is for example a layer of dielectric material, for example a transparent layer or an opaque colored layer which makes it possible to increase the contrast; the layer 216 (optional) is for example a security layer, for example a discontinuous layer with a specific pattern printed locally with a UV ink to produce a complementary marking which can be checked by eye or by machine; and the layer 218 (optional) is for example a protective layer, for example a second polymer film or a varnish. In the case of a laminated track, the layer 218 may be an adhesive layer. As in the previous example, the manufacturing can be carried out by stacking the layers on the support film 211. The dielectric layer 215 and the security layer 216 can form only one layer.The protective layer (or adhesive layer) 218 ​​and the layer 215 may also form a single layer.

[0115] It will be apparent to those skilled in the art that other optically or non-optically functional layers may be added depending on the needs of the application in each of the examples shown in [Fig.2A] and [Fig.2B] and that the embodiment variants shown in [Fig.2A] and [Fig.2B] may be combined.

[0116] The first structure is determined to simulate the reflection properties of the surface whose three-dimensional appearance is to be given to an observer.

[0117] As illustrated in [Fig.2A], the facets can result from a translation by zone of the surface whose reflection properties we seek to simulate. To determine it mination of facets, one can refer to known methods as described for example in [Ref. 1]. The ridge lines of the resulting facet set are at least partly closed ridge lines.

[0118] [Fig.3] illustrates the observation conventions of an optical security component according to the present description.

[0119] We can define a plane ir corresponding to the plane of the component.

[0120] From the point of view of a user (302, [Fig.3]), we can define a plane of incidence Pi of the light which comprises an axis of illumination of the component and an axis of observation. The axis of illumination corresponds to an incident beam coming from the source (301, [Fig.3]) and incident on the plane of the component at a point 0; the axis of observation corresponds to the beam reflected towards the observer. The observation is made in specular reflection with an angle of observation 0.

[0121] An up / down tilt 31 is a rotational movement around an axis x included in the plane of the component ir and perpendicular to the plane of incidence Pp. A right / left tilt 32 is a rotational movement around an axis included in the plane of the component and in the plane of incidence.

[0122] An azimuthal rotation 33 of the optical security component is a rotational movement of the component around an axis z substantially perpendicular to the plane of the component.

[0123] A reference position of the component can be defined as the angular position along the 2 tilt axes for which the specular reflection is observed with an angle of 30° between the normal to the z component and the observation axis of the component.

[0124] [Fig.4A] schematically illustrates, by way of example, ridge lines 225 formed by a set of facets configured to simulate a three-dimensional shape to an observer, in this example a heart.

[0125] [Fig.4B] schematically illustrates, by way of example, grating lines 235 of diffraction gratings 230 which structure the facets 220. In this example, the grating lines are parallel to each other and substantially parallel to the ridge lines.

[0126] Although few grating lines are represented, for each facet, the diffraction grating which structures the facet may comprise a minimum number of grating lines, for example at least 5 grating lines, advantageously at least 20 grating lines, or more depending on the width of the facets.

[0127] [Fig.5A] schematically illustrates ridge lines 225 formed by a set of facets 220 configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines 235 of the diffraction gratings that structure the facets. Inset 51 represents an enlargement of a region of the diffractive structure to schematically illustrate the arrangement of the network lines 235.

[0128] In this example, the network lines are parallel to each other and substantially parallel to the ridge lines.

[0129] The diffraction gratings which structure the facets 220 are in this example sub-wavelength diffraction gratings, of constant pitch, but whose orientation of the grating lines 235 varies with those of the ridge lines. In this example, the grating lines follow the ridge lines.

[0130] As will be illustrated later, in such an example, the observer perceives a polychrome object whose color depends locally on the azimuthal orientation of the ridge lines relative to the observation axis. Such an optical security component is further remarkable in that effects of higher light intensity are observed as a function of the up / down, right / left tilts. Furthermore, in this example there is a conservation of the colored effect during an azimuthal rotation of the component by the observer, which adds an additional level of security in the authentication. Indeed, whatever the azimuthal position of the optical security component, the same visual effect is observed in an up / down or right / left tilt.

[0131] [Fig.5B] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of the diffraction gratings that structure the facets, the grating lines being parallel to each other, substantially perpendicular to the ridge lines. Inset 52 represents an enlargement of a region of the diffractive structure to schematically illustrate the arrangement of the grating lines 235.

[0132] As in the previous example, the observer perceives a polychrome object whose color depends locally on the azimuthal orientation of the ridge lines relative to the observation axis. Such an optical security component is further remarkable in that effects of higher light intensity are observed as a function of the up / down, right / left tilts. Furthermore, in this example there is a conservation of the colored effect during an azimuthal rotation of the component by the observer, which adds an additional level of security in the authentication.

[0133] [Fig.5C] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of the diffraction gratings that structure the facets, the grating lines being parallel to each other, inclined with respect to the ridge lines at a substantially constant angle. Inset 53 represents an enlargement of a region of the diffractive structure to illustrate in a schematic of the arrangement of the network lines 235.

[0134] Here again, the observer perceives a polychrome object whose color depends locally on the azimuthal orientation of the ridge lines relative to the observation axis. Such an optical security component is further remarkable in that effects of higher light intensity are observed as a function of the up / down, right / left tilts. Furthermore, in this example there is a conservation of the colored effect during an azimuthal rotation of the component by the observer, which adds an additional level of security in the authentication.

[0135] [Fig.5D] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of two-dimensional diffraction gratings that structure the facets, first grating lines being parallel to each other, parallel to the ridge lines, and second grating lines being parallel to each other, perpendicular to the ridge lines. Inset 54 represents an enlargement of a region of the diffractive structure to schematically illustrate the arrangement of the grating lines 235. With such a security optical component, additional colored effects can be obtained, for example by choosing different periods for the grating lines in each of the directions.

[0136] [Fig.5E] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of the diffraction gratings that structure the facets, the grating lines being parallel to each other, of fixed orientation, the pitches of the gratings being variable, the pitch of each grating depending on the angular value of the slope of the facet that it structures. Inset 55 represents an enlargement of a region of the diffractive structure to schematically illustrate the arrangement of the grating lines 235.

[0137] In such a security optical component, regardless of the azimuth angle, the up / down and right / left tilts produce a color change, the color depending on the slope of the object locally.

[0138] [Fig.5F] schematically illustrates ridge lines formed by a set of facets configured to simulate a three-dimensional surface to an observer, in this example a heart, and grating lines of the diffraction gratings that structure the facets, the grating lines being parallel to each other, of fixed orientation, the pitches of the gratings being variable, the pitch of each grating depending on the orientation of the ridge line of the facet that it structures. Insets 56, 57 represent an enlargement of two regions of the diffractive structure to schematically illustrate the arrangement of the grating lines 235.

[0139] In this example, as will be described in more detail later with reference to [Fig.8C], an original colored effect can be observed compared to the colored effects of the optical security components. In particular, depending on the orientation of the ridge lines, there may or may not be a change of color by azimuthal rotation.

[0140] [Fig.6] schematically illustrates a surface that we seek to represent in a three-dimensional way to an observer (here a character “5”).

[0141] In this example, the diffraction gratings that structure the facets arranged to simulate the reflection behavior of the object “5” have grating lines whose orientation varies with the orientation of the ridge lines of the facets. In this example, however, the orientation of the grating lines varies in steps. The orientation of the ridge lines and the grating lines is defined relative to a reference axis, for example a vertical axis in the case of [Fig.6], in a rotation relative to an axis perpendicular to the plane of the component (axis perpendicular to the plane of the figure).

[0142] Thus, the region referenced 61 and more generally the regions in white, correspond to regions for which the orientation of the ridge lines is included in a first angular range, for example between 0 and 72 degrees from the reference axis. In these regions, the network lines are 36° to the reference axis. The region referenced 62 and more generally the regions with the same gray level, correspond to regions for which the orientation of the ridge lines is included in a second angular range, for example between 72 and 144. In these regions, the network lines are oriented at 108° from the reference axis. The region referenced 63 and more generally the regions with the same gray level, correspond to regions for which the orientation of the ridge lines is included in a third angular range, for example between 144 and 216. In these regions, the network lines are oriented at 180° from the reference axis.The region referenced 64 and more generally the regions with the same gray level, correspond to regions for which the orientation of the ridge lines is included in a fourth angular range, for example between 216 and 288. In these regions, the network lines are oriented at 252° from the reference axis. The region referenced 65 and more generally the regions with the same gray level, correspond to regions for which the orientation of the ridge lines is included in a fifth angular range, for example between 288 degrees and 360. In these regions, the network lines are oriented at 324° from the reference axis.

[0143] So in this example, the orientation of the network lines is defined according to a step function relative to the orientation of the ridge lines. In this example, there are ultimately only two orientations of the network lines and of course, we can look for a function with more steps for a more complex colored effect. Nevertheless, the variation of the network lines according to the ridge lines allows already to obtain an original colored 3D representation.

[0144] [Fig.7] schematically illustrates a surface that one seeks to represent in a three-dimensional way to an observer (here a heart), and as previously, the diffraction gratings that structure the facets arranged to simulate the reflection behavior of the “heart” object have grating lines whose orientation varies with the orientation of the crest lines of the facets. In this example, however, the orientation of the grating lines varies continuously with the orientation of the crest lines. The figure thus shows a grayscale representation conditioning the orientation of the grating lines of the diffraction gratings that structure the facets relative to a given reference axis, between 0° and 360°.

[0145] Thus the white regions correspond, for example, to the regions in which the grating lines are parallel to this reference axis. The more intense the gray, the greater the angle between the grating lines and the reference axis. The black regions correspond to the regions in which the grating lines make an angle of 360° with the reference axis, i.e. are again parallel. Such coding can be an intermediate step in calculating the diffractive structure.

[0146] [Fig.8A] illustrates the colored effects produced by an optical security component according to a first exemplary embodiment, before and after azimuthal rotation of 90°.

[0147] In this example, the set of facets of the first diffractive structure of the optical security component is configured to simulate to an observer a butterfly that appears in three dimensions. The diffraction gratings that structure the facets are in this example subwavelength diffraction gratings, of constant and identical pitch for all the gratings, with grating lines parallel to each other and parallel to the crest lines of the facets. Thus, the orientation of the grating lines varies with those of the crest lines and the grating lines are parallel, as illustrated for example in [Fig.5A] (insert 51).

[0148] When observing with a first azimuthal angle (diagram 81), the observer perceives a polychrome butterfly whose color depends locally on the azimuthal orientation of the ridge lines relative to the observation axis.

[0149] For example, for a pitch of the diffraction gratings equal to approximately 360 nm, the observer perceives with a green coloration (symbolized by the letter V in the figures) the regions with grating lines, and therefore ridge lines, substantially parallel to a direction of the plane of the component perpendicular to the plane of incidence (i.e. along the x axis, [Fig. 3]). On the contrary, the observer perceives with a red coloration (symbolized by the letter R in the figures) the regions with grating lines, and therefore ridge lines, substantially parallel to a direction of the plane of the component contained in the plane of incidence (i.e. along the y axis, [Fig. 3]). Between the two, the observer will be able to observe a mixture of these colors. A high / low tilt or left / right movement of the optical security component causes a variation in brightness, i.e. the intensity of each color, symbolized in this example by the size of the letters R and V.

[0150] Remarkably, in this example, we observe a conservation of the colored effect during an azimuthal rotation of 90° of the component by the observer (position 82) despite the rotation of the object of 90°.

[0151] Thus, the observer continues to perceive with a green coloring the regions with ridge lines substantially parallel to a direction of the plane of the component perpendicular to the plane of incidence, and continues to perceive with a red coloring the regions with ridge lines substantially parallel to a direction of the plane of the component contained in the plane of incidence.

[0152] This example thus allows an additional level of security in authentication compared to optical components known from the state of the art, in particular due to the original colored effect that it provides.

[0153] [Fig.8B] illustrates the colored effects produced by an optical security component according to a second exemplary embodiment, before and after azimuthal rotation of 90°.

[0154] In this example, the diffractive structure is similar to that shown with reference to [Fig.8A] but instead of having an identical diffraction grating pitch for all gratings, the diffraction grating pitch varies from one diffraction grating to another, depending on the orientation of the ridge lines.

[0155] Thus, according to the example chosen, the pitch of the diffraction gratings is equal to approximately 360 nm for an orientation of the ridge lines parallel to a first direction and is equal to approximately 420 nm for an orientation of the ridge lines parallel to a second direction, perpendicular to the first direction. For the facets whose ridge line is oriented between the first and second directions, the pitch of the gratings which structure the facets can vary continuously or in stages.

[0156] In a first position 83, it is assumed that the observer observes the optical security component along an observation axis included in a plane of incidence perpendicular to the first direction. As in the example of [Fig.8A], the observer perceives with a green coloring (symbolized by the letter V in the figures) the regions with grating lines, and therefore ridge lines, substantially parallel to the first direction (i.e. along the x axis, [Fig.3]). Unlike the previous example, as the pitch of the diffraction gratings which structure the facets whose ridge lines are oriented along the second direction, perpendicular to the first direction, is different (420 nm), the observer also perceives with a green coloring the regions with ridge lines substantially parallel to the second direction (i.e. along the y axis, [Fig.3]).Thus, as illustrated in diagram 83, the observer will observe a three-dimensional representation. butterfly, generally colored green, with local differences in brightness depending on the up / down or left / right tilts of the safety optical component.

[0157] After 90° azimuthal rotation of the component by the observer (position 84), the first direction is in the plane of incidence and the second direction is perpendicular to the plane of incidence. Thus, the facets whose crest lines are oriented in a direction perpendicular to the plane of incidence are structured by the diffraction gratings with a pitch of 420 nm and the facets whose crest lines are oriented in a direction contained in the plane of incidence are structured by the diffraction gratings with a pitch of 360 nm. Color changes then occur. In particular, the regions in which the crest lines are oriented in a direction perpendicular to the plane of incidence become blue (symbolized by the letter B) and the regions in which the crest lines are oriented in a direction contained in the plane of incidence become red.Between the two regions, the observer will be able to observe a mixture of these colors. An up / down or left / right tilt of the security optical component will cause a variation in the brightness, that is to say the intensity of each color, symbolized in this example by the size of the letters R and B.

[0158] Thus, in this example, there is no longer any conservation of the colored effect with the azimuthal rotation of the optical security component. Nevertheless, the colored effect provided is also original compared to the colored effects of the optical security components.

[0159] [Fig.8C] illustrates the colored effects produced by an optical security component according to a third exemplary embodiment, before and after azimuthal rotation of 90°.

[0160] In this example, the diffraction gratings comprise parallel grating lines but there is no variation in the orientation of the grating lines. In other words, the grating lines of all the diffraction gratings are substantially parallel to one direction. As illustrated for example in the example of [Fig.5F], only the pitch of the diffraction gratings varies with the orientation of the ridge lines.

[0161] Thus, according to the example chosen, the pitch of the diffraction gratings is equal to approximately 360 nm for an orientation of the ridge lines parallel to a first direction and is equal to approximately 420 nm for an orientation of the ridge lines parallel to a second direction, perpendicular to the first direction. For the facets whose ridge line is oriented between the first and second directions, the pitch of the gratings which structure the facets can vary continuously or in stages. It is assumed that the direction of the grating lines is the first direction.

[0162] In a first position 85, it is assumed that the observer observes the optical security component along an observation axis included in a plane of incidence perpendicular to the first direction (i.e. the direction of the grating lines in this example). As in the example of [Fig.8A], the observer then perceives with a green coloration the regions with ridge lines substantially parallel to the first direction (i.e. along the x axis, [Fig.3]). Since the pitch of the diffraction gratings that structure the facets whose ridge lines are oriented along the second direction, perpendicular to the first direction, is different (420 nm), the observer perceives with a different coloration the regions with ridge lines substantially parallel to the second direction (i.e. along the y axis, [Fig.3]). In this example a blue coloration (letter B) because the grating lines are always parallel to the first direction.

[0163] After 90° azimuthal rotation of the component by the observer (position 86), the first direction is in the plane of incidence and the second direction is perpendicular to the plane of incidence. Thus, the facets whose crest lines are oriented in a direction perpendicular to the plane of incidence are structured by the diffraction gratings with a pitch of 420 nm and the facets whose crest lines are oriented in a direction contained in the plane of incidence are structured by the diffraction gratings with a pitch of 360 nm. Color changes then occur. In particular, the regions in which the crest lines are oriented in a direction perpendicular to the plane of incidence remain green. Indeed, the change in pitch is accompanied by a variation in the orientation of the grating lines.Regions in which the ridge lines are oriented in a direction contained in the plane of incidence change from blue to red. Between the two regions, the observer may observe a mixture of these colors. An up / down or left / right tilt of the optical security component may cause a variation in brightness.

[0164] Thus, in this example, there is also no conservation of the colored effect with the azimuthal rotation of the optical security component. Nevertheless, the colored effect provided is also original compared to the colored effects of the optical security components. In particular, depending on the orientation of the ridge lines, there may or may not be a change of color by azimuthal rotation.

[0165] [Fig.9] illustrates the colored effects produced by an optical security component according to an exemplary embodiment, in an up / down and left / right tilt observation of the component.

[0166] In this example, the set of facets is configured to simulate the reflection of a three-dimensional surface of a heart (pattern 901).

[0167] The facets are structured by networks whose orientation of the network lines varies with the orientation of the ridge lines, for example as in the case of [Fig.7].

[0168] The colors are for example those illustrated in the example of [Fig.8A], in the case of a single grating pitch. The applicants have shown a stability of the colors in tilt which can go up to a few tens of degrees. However, a variation in the light intensity is observed.

[0169] In [Fig.9], the nuances of light intensity are represented, the lightest parts being the most intense.

[0170] Positions 921 and 922 correspond to an observation of pattern 901 during an up / down tilt.

[0171] Positions 923 and 924 correspond to an observation of pattern 901 during a right / left tilt.

[0172] Examples of methods for manufacturing optical security components according to the present description are now described.

[0173] A first step comprises the design of said at least one first diffractive structure according to the methods described above, and possible other structures.

[0174] Next comes a step of recording an original copy, also called an optical master. The optical master is, for example, an optical medium on which the structure(s) are formed.

[0175] The optical master can be formed by electronic or optical lithography methods known in the state of the art.

[0176] For example, according to a first embodiment, the optical master is produced by etching a resin sensitive to electromagnetic radiation using an electron beam. In this exemplary embodiment, the structure having all of the facets structured by the subwavelength diffraction gratings can be etched in a single step.

[0177] According to another embodiment, an optical lithography (or photolithography) technique can be used. The optical master is in this example a photosensitive resin plate and the origination step is carried out by one or more exposures of the plate by projections of masks, of the phase mask type and / or of the amplitude mask type, followed by development in an appropriate chemical solution. For example, a first exposure is carried out by projection of amplitude masks whose transmission coefficients are adapted so that, after development, a relief corresponding to the microstructures is formed, in the regions in which the microstructures are provided. Then, a second exposure is carried out, for example according to optical lithography methods known to those skilled in the art, for example two-photon lithography, to record the diffraction grating which structures each facet.Similar steps can be planned to generate other reliefs, such as a second diffraction grating in . other regions. The order of formation of the microstructures and diffraction gratings is arbitrary and can be modified. Subsequently, the development step is carried out. In this way, an optical master comprising a first diffractive structure in accordance with the present description is obtained after development.

[0178] The step of metallic copying of the optical master can then be carried out, for example by electroplating, as mentioned above, in order to obtain the replication matrix or metallic “master”. According to a variant, a step of matrix duplication of the metallic master can be carried out to obtain a large-scale production tool suitable for replicating the structure in industrial quantities.

[0179] The manufacture of the optical security component then comprises a replication step. For example, the replication can be carried out by stamping (by hot embossing of the dielectric material) the first layer 213 (FIGS. 2A, 2B) in dielectric material with a refractive index of nB, for example a low index layer, typically a stamping varnish a few microns thick. The layer 213 is advantageously carried by the support film 211, for example a film of 12 qm to 100 qm in polymer material, for example PET (polyethylene terephthalate). The replication can also be carried out by molding the stamping varnish layer before drying and then UV crosslinking ("UV casting"). Replication by UV crosslinking makes it possible in particular to reproduce structures having a large depth range and makes it possible to obtain better fidelity in the replication.Generally, any other high resolution replication method known from the prior art may be used in the replication step.

[0180] Next comes the deposition on the layer thus embossed of all the other layers, for example the reflective layer 214, the layer of dielectric material 215 (optional), the security layer 216 (optional) which can be deposited uniformly or selectively to represent a new pattern and the glue or varnish type layer (217, 218) by a coating process.

[0181] Optional steps known to those skilled in the art are possible, such as partial demetallization of the reflective layer 214. It is also possible to introduce a continuous or discontinuous opaque layer to enhance the contrast.

[0182] Although described through a certain number of exemplary embodiments, the optical security component according to the invention and the method of manufacturing said component comprise different variants, modifications and improvements which will be obvious to those skilled in the art, it being understood that these different variants, modifications and improvements are part of the scope of the invention as defined by the following claims. References

[0183] Ref. 1: WO2011 / 138394

[0184] Ref. 2: EP1782108A1

[0185] Ref. 3: EP 2264491

[0186] Ref. 4: MT Gale, “Zero-Order Grating Microstructures” in RL van Renesse, Optical Document Security, 2nd Ed., pp. 267 - 287

[0187] Ref. 5: WO2013060817

[0188] Ref. 6: WO2020229415

Claims

Claims

1. Optical security component (201, 202) for the authentication by the naked eye of an object, for example a valuable document, for example an identity document or a banknote, the component comprising: - a first layer (213) of dielectric material, transparent in the visible, having a first refractive index (ni); - at least one first diffractive structure (S) etched on said first layer; and - a second layer (214), at least partially covering said first diffractive structure, and having a spectral band of reflection in the visible;and wherein: - said first diffractive structure comprises a set of facets, each facet (220) having a slope of substantially fixed angular value (a) and a crest line (225) with an orientation defined as a function of an axis of the plane of the component, at least a portion of the facets having crest lines with different orientations and at least a portion of the facets having slopes with different angular values, wherein: - each facet of the set of facets is structured by a subwavelength diffraction grating (230) with one or more pitches between approximately 150 nm and approximately 400 nm configured to produce, after deposition of the second layer (214), a colored effect; - the diffraction gratings which structure the facets of the set of facets comprise at least one variable property as a function of the orientation of the crest line and / or the angular value of the slope of the facets.;

2. An optical security component according to claim 1, wherein said diffraction gratings comprise grating lines (235) substantially parallel to each other and said at least one property is the orientation of said grating lines.

3. Optical security component according to any one of the preceding claims, wherein said at least one property is chosen from: a period of the networks, a depth of the networks.

4. An optical security component according to any preceding claim, wherein said at least one property varies according to an identical function for all facets.

5. Optical security component according to any one of the claims- preceding indications, wherein said at least one property is variable in stages.

6. Optical security component according to any one of the preceding claims, in which the facets are determined to generate a surface appearing, in reflection and according to a given observation angle, in a three-dimensional manner to an observer, for example a surface having a recognizable shape, for example an alphanumeric sign or a geometric figure.

7. An optical security component according to any preceding claim, wherein at least a portion of the ridge lines of the facets are closed.

8. Optical security component according to any one of the preceding claims, wherein said second layer (114) is a layer of dielectric material having a second refractive index (n2), encapsulated between said first layer (113) of electrical material and a third layer of dielectric material (117, 115) having a third refractive index (n3), the second refractive index (n2) having a difference with the first refractive index (ni) on the one hand, and with the third refractive index (n3) on the other hand, greater than or equal to approximately 0.3, advantageously greater than or equal to approximately 0.5 in absolute value.

9. An optical security component according to any one of claims 1 to 7, wherein the second layer (114) comprises a metallic material.

10. Optical security component according to any one of the preceding claims, further comprising at least one second structure etched in said first layer, said second structure being chosen for example from: a diffusing structure, a holographic structure, a diffracting structure of the Alphagram® type.

11. Secure object, for example secure valuable document, comprising a substrate and an optical security component according to any one of the preceding claims, deposited on said substrate.

12. Method for manufacturing an optical security component for securing an object, for example a valuable document, for example an identity document or a banknote, the method comprising: - depositing on a support film a first layer of dielectric material (113), transparent in the visible; - forming on said first layer at least one first diffractive structure (S), - the deposition of a second layer (114) at least partially covering said first diffractive structure, and having a spectral band of reflection in the visible, and in which: - said first diffractive structure comprises a set of facets, each facet (220) having a slope of substantially fixed angular value (a) and a crest line (225) with an orientation defined as a function of an axis of the plane of the component, at least some of the facets having crest lines with different orientations and at least some of the facets having slopes with different angular values, in which: - each facet of the set of facets is structured by a subwavelength diffraction grating (230) with one or more steps between approximately 150 nm and approximately 400 nm configured to produce, after deposition of the second layer (214), a colored effect; - the diffraction gratings that structure the facets of the facet set include at least one variable property depending on the orientation of the ridge line and / or the slope of the facets.

Images