FR3051565A1 - OPTICAL SECURITY COMPONENT AND METHOD FOR MANUFACTURING SUCH COMPONENT - Google Patents

Abstract

According to one aspect, the present disclosure relates to an optical security component (20) comprising a first layer (23) of dielectric material, at least partially structured on one side, a second layer (22), deposited on at least partially structured face of said first layer in at least a first region, and having a spectral band of reflection in the visible and a third layer (21) of dielectric material deposited on said second layer. The first layer (23) has in the first region at least a first structure formed by a first pattern modulated by a second pattern, such that the first pattern is adapted to form a first computer-synthesized hologram diffractive element calculated to generate under spatially coherent illumination at least a first recognizable image in at least a first reconstruction plane and the second motif is a subwavelength period periodic grating, determined to produce, after deposition of the second layer and encapsulation of said first structure by the third layer, a resonant filter in a first spectral band.

Description

OPTICAL SECURITY COMPONENT AND METHOD FOR MANUFACTURING A

TEL COMPONENT

Technical area

The present disclosure relates to an optical security component and a method of manufacturing such a component. The optical security component according to the present description applies in particular to the security marking for the securing and authentication of valuables.

State of the art

Many technologies are known for the authentication of valuables and especially for the authentication of valuable documents, such as banknotes or travel documents (passports, identity cards or other identification documents), or for the authentication of products by means of marking labels. These technologies aim at the production of optical safety components whose optical effects according to the observation parameters (orientation with respect to the axis of observation, position and dimensions of the light source, etc.) take on characteristic configurations and verifiable. The general purpose of these optical components is to provide new and differentiated visual effects, from physical configurations that are difficult to reproduce or imitated by a counterfeiter.

Among these components, the French patent application published under the number FR 2 983 318 describes a diflfractive optical element (or DOE according to the abbreviation "Diflfractive Optical Element"), also called computer-generated hologram (or HSO). A diflfracting optical element of this type comprises complex phase and amplitude data physically encoded in a DOE micro structure, these data being calculated so that when the DOE is illuminated by a substantially collimated light beam, a diagram of desired light intensity is generated in the far field or in a reconstruction plane. In practice, the data of the DOE can be determined by calculating an inverse Fast Fourier Transform (or FFT inverse, FFT being the abbreviation of "Fast Fourier Transform") of the desired reconstruction, that is to say of the desired intensity pattern in the far field or in the reconstruction plane. Such a diffractive optical element can operate in transmission (transmissive DOE) or in reflection (reflective DOE). In the case of a reflective DOE, a reflective layer may be applied to the microstructure encoding the complex phase and amplitude data.

FIGS. 1A and 1B thus represent a document of value 1, for example an identity document, comprising a security optical component 2 with a diffractive optical element of DOE type (respectively reflective and transmissive), as described in the art prior. In these figures, the beam 3 represents the lighting beam; it is for example derived from a point source or a laser. The beam 4 represents the reflected beam (FIG 1A) or transmitted (FIG IB) by the security optical component 2. In these examples, the data are calculated so that when the DOE is illuminated by a beam of light from a point source, a light intensity diagram 6 appears in a reconstruction plane 5.

A difficulty in using this type of optical security components, however, comes from the difficulty of producing elaborate color images. Indeed, when one illuminates this type of diffractive optical elements in polychromatic light, for example with a point white light, one generally obtains a white image with colored iridescence even if a DOE is calculated for a maximum efficiency with a length of d given wave.

This problem is solved in the patent application FR 2 983 318 of the prior art by interleaving in a diffractive optical element (DOE) diffracting structures calculated for specific wavelengths and illuminating the DOE with monochromatic light beams, at the wavelengths to which the diffracting structures are sensitive. Monochromatic beams at specific wavelengths are sent simultaneously, sequentially or cyclically.

However, for the authentication of a valuable object, this solution requires working with a set of monochromatic sources or with a set of spectral filters arranged in front of a monochromatic source. On the other hand, the quality of the color image is not entirely satisfactory because each dif & active structure of the DOE, even if it reacts mainly to a specific wavelength, is also sensitive to a lesser extent to the other lengths wave, resulting in unwanted color blends in the image.

The present description presents an optical security component with a hologram-synthesized computer element, enabling the reconstruction of high quality colored images under spatially coherent polychromatic lighting, of point or point-like white source type and thus without requiring a specific lighting device using multiple sources or filters. summary

According to a first aspect, the present description relates to an optical security component intended to be authenticated in the visible spectrum, in spatially coherent polychromatic light, comprising: a first layer of dielectric material, at least partially structured on one face, and having a first refractive index; a second layer, deposited on the at least partially structured face of said first layer in at least a first region, and having a spectral band of reflection in the visible; a third layer of dielectric material deposited on said second layer and having a third refractive index; and wherein said first layer has in the first region at least a first structure formed by a first pattern modulated by a second pattern, such that: the first pattern is adapted to form a first computer-synthesized hologram dififractive element (HSO ), calculated to generate, under spatially coherent illumination, at least a first recognizable image in at least one given reconstruction plane, O the second motif is a periodic network of subwavelength period, determined to produce, after the second layer and encapsulation of said first structure by the third layer, a resonant filter in a first spectral band.

The resonant filter is for example a resonant filter of DID (for "Dififactive identification Device) type which allows the excitation of guided modes within a region of the second layer of dielectric material, or a resonant filter of plasmonic type obtained through to a region of the second layer of metallic material which forms with the first and / or third layer of dielectric material a metal / dielectric interface or dielectric / metal / dielectric interfaces, or any other resonant filter having a resonance spectral band in the visible.

The "visible" in the sense of the present description, is understood as the spectral band between 380 nm and 780 nm.

According to one or more exemplary embodiments, one and / or the other of the first and third layers of dielectric material is transparent in the visible spectral band.

A layer is said to be transparent in a spectral band according to the present description if for each wavelength of said spectral band, at least 70% of a radiation at said wavelength is transmitted, preferably at least 80% and more preferably at least 90%.

In the present description, a thin layer is a layer of thickness between 10 nm and 200 nm.

The applicant has shown that the modulation of the dififractive optical element with a subwavelength grating adapted to form a resonant filter makes it possible to considerably increase the wavelength selectivity of the dififractive optical element.

According to one or more exemplary embodiments, the period of the sub-wavelength grating is between 100 nm and 700 nm, advantageously between 200 nm and 500 nm.

According to one or more exemplary embodiments, the subwavelength period periodic network is a one-dimensional network, defined by a network vector. This type of network makes it possible to show variable color effects as a function of the azimuth, for non-harmful incidence angles, and as a function of the angle of incidence for a given azimuth (for example in so-called "collinear" illumination ).

According to one or more exemplary embodiments, the subwavelength period periodic grating is a two-dimensional array, defined by two substantially perpendicular direction gratings. The periods in each of the directions may be identical, in which case the first image has a stable color in azimuth and a low variation depending on the incidence, or the periods may be different, in which case variable color effects may be observed depending on the the azimuth, for angles of incidence no harm.

According to one or more exemplary embodiments, the periodic network has a structure depth of between 10 nm and 350 nm.

According to one or more exemplary embodiments, the second layer comprises in at least a first region a thin layer of dielectric material, of thickness preferably between 20 nm and 200 nm and preferably between 60 nm and 150 nm, having a second index of refraction such that the second refractive index differs from the first refractive index and the third refractive index by at least 0.3. The second pattern of at least one structure of said first region is adapted to produce a DID type wavelength subtractive filter, forming a resonant bandpass filter in reflection.

According to one or more exemplary embodiments, the second layer comprises, in at least one second region, a thin layer of metallic material, continuous, advantageously greater than 40 nm in thickness, for example between 40 nm and 200 nm; the second pattern of at least one structure of said second region forms a resonant band-resonant filter in reflection, of plasmon filter type in reflection, called "R'plasmon" in the following description.

According to one or more embodiments, said thin layer of metallic material is sufficiently thick to present in the visible spectral band a residual maximum transmission as a function of the wavelength of 2%.

According to one or more exemplary embodiments, the second pattern forms a sinusoidal or quasi-sinusoidal profile network, that is to say continuously variable, this type of profile allowing a better propagation of the plasmonic modes while being compatible with photolithography manufacturing methods. Advantageously, the depth of the network is between 10% and 50% of the period, and preferably between 10% and 40% of the period. According to one or more exemplary embodiments, the second pattern forms a two-dimensional network.

According to one or more exemplary embodiments, the second layer comprises in at least a third region a thin layer of metallic material, preferably between 10 nm and 60 nm thick; the second pattern of at least one structure of said third region is adapted to produce a band-pass resonance filter in transmission, of plasmonic filter type in transmission, called "T'plasmon" in the following description.

According to one or more exemplary embodiments, the thin layer of metallic material is continuous; the second pattern forms a sinusoidal or quasi-sinusoidal profile network, that is to say continuously variable, this type of profile allowing a better propagation of plasmonic modes while being compatible with photolithography manufacturing methods. Advantageously, the depth of the network is between 10% and 53% of the period, which makes it possible to increase the efficiency of the plasmonic transmission. According to one or more exemplary embodiments, the second pattern forms a two-dimensional network.

According to one or more embodiments, the second layer is discontinuous; the second layer may also have, in one or more first regions, a thin layer of dielectric material, to form DID type filters, and / or in one or more second regions, a thin layer of metal material for example having a thickness greater than 40 nm to form R'Plasmon type filters (metal / dielectric interface) and / or in one or more third regions a thin layer of metal material for example with a thickness of between 10 nm and 60 nm to form filters of the type T'Plasmon (dielectric / metal / dielectric interface).

According to one or more exemplary embodiments, for at least one first structure, the first pattern is adapted to form a first refractive computer-synthesized hologram diflfractive element. The first pattern has a depth of between 100 nm and 500 nm, according to an example. .

According to one or more exemplary embodiments, for at least one second structure, the first pattern is adapted to form a first transmissive computer-synthesized hologram diflfractive element. The refractive indices of the first and third layers of dielectric material then differ from one to another. minus 0.1, according to one example, and the first pattern has a depth of between 100 nm and 1 μm, according to one example. The first layer of dielectric material is transparent.

According to one or more exemplary embodiments, the first computer-synthesized hologram diflfractive element is calculated to exhibit optimum efficiency at a wavelength within the resonance spectral resonant band.

According to one or more exemplary embodiments, the first computer-synthesized hologram diflfractive element is calculated to exhibit optimum efficiency at a wavelength located outside of said resonance spectral resonant band.

According to one or more embodiments, the first layer also has in the first region at least a second structure formed by a first pattern modulated by a second pattern, such that: the first pattern is adapted to form a second diflfractive element of computer-synthesized hologram type, calculated to generate, under spatially coherent illumination, at least one second recognizable image in a given second reconstruction plane, O the second motif is a periodic network of subwavelength period. determined to produce, after deposition of the second layer and encapsulation of said second structure by the third layer, a resonant filter in a second spectral band.

It is thus possible to simultaneously generate two difierent images of different colors, in reconstruction planes or not, when the component is illuminated in spatially coherent polychromatic light in the visible.

According to one or more exemplary embodiments, the at least first and second structures are arranged in zones that are interlaced with one another. This makes it possible to generate more complex images, and in particular multi-color images in the same reconstruction plane. According to one or more exemplary embodiments, the at least first and second structures are arranged in adjacent zones, the successive illumination of each zone making it possible to simulate a motion effect of an image and / or transformation. We can thus generate a colored animation.

According to one or more exemplary embodiments, the security optical component comprises other layers according to the needs required for the final application; for example, the security optical component may further comprise active layers for forming the HSO and the resonant filter, a support film carrying one of said layers of dielectric material and / or an adhesive layer disposed on one of said layers of dielectric material . These layers are neutral for the HSO and / or the resonant filter because they do not alter or influence the interfaces between the second layer and the first and third layers, respectively. They make it easier to adhere to the object to be secured and / or implemented industrially.

According to one or more exemplary embodiments, the first layer further comprises regions structured according to the present description, planar regions and / or other structured regions, encapsulated between the first and second layers of dielectric material, the other structured regions being adapted to form other visual effects.

According to a second aspect, the present description relates to a secure object comprising a support and a security optical component according to the first aspect, the security optical component being fixed on said support or integrated in the support. The secure object is for example a valuable document, such as a bank note, a travel document (passports, identity card or other identification document), a label for the authentication of a product . The secure object can be easily authenticated by observation in transmission or reflection, under coherent polychromatic lighting, thanks to the optical security component according to the present description; Moreover, its resistance to counterfeiting is high because of the technology implemented.

According to a third aspect, the present description relates to a method of manufacturing a security optical component according to the first aspect. The method comprises: - forming on a support film of said first layer of dielectric material; depositing the second layer on the first layer of dielectric material; the deposition on the second layer of the third layer of dielectric material.

According to one or more embodiments, the first layer of dielectric material, partially structured, is obtained by molding and UV curing a stamping varnish from a matrix carrying all of the structures.

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 1A and 1B (already described), two examples of secure objects integrating an optical component safety device with a diffractive element of HSO type according to the prior art; FIG. 2 a sectional view of an exemplary optical security component according to the present description; FIGS. 3A, 3B, 3C diagrams illustrating an example of a first pattern adapted to form a first diffractive element type HSO, an example of a second pattern adapted to form a resonant filter and an example of structure resulting from the modulation of the first pattern with the second pattern; FIG. 4A to 4E, diagrams showing different exemplary embodiments are a resonant filter associated with a reflective or transmissive HSO; FIGS. 5A-5D diagrams illustrating the dependence of the resonant filter resonant wavelength as a function of angle of incidence, collinear incidence (FIGS, 5A and 5C) and conical incidence (FIGS., 5B, 5D) ; FIGS. 6A and 6B examples of secure objects incorporating an exemplary security optical component according to the present description with an off-axis off-axis type diffractive element in reflection and a resonant filter ID, for a non-zero incidence angle and for two values azimuth; FIG. 7A, a first example of a security optical component comprising a matrix of pixels, a first portion of the pixels comprising a first structure formed of a first pattern adapted to form a first reflective type HSO diflfractive element, modulated by a second pattern, and a second portion of the pixels comprising a second structure formed of a first pattern adapted to form a second reflective HSO diflfractive element modulated by a second pattern; FIGS. 7B to 7D examples of secure objects incorporating a security optical component of the type of FIG. 7A for different incidence and azimuth values; FIG. 8, a second example of an optical security component comprising a matrix of pixels in the form of bands and images obtained by successive illumination of the different bands; FIG. 9, an example of a secure object integrating a first security optical component and a second security optical component, adapted for stereoscopic vision; FIGS. 10A-10B, 11A-11B, examples of secure objects incorporating examples of optical security components with structures adapted for the formation of diflfractive elements of the HSO type;

In the figures, shown for illustrative purposes, the scales are not respected for the sake of clarity in the representation.

detailed description

FIG. 2 is a sectional view of an exemplary security optical component 20 according to the present description.

The component 20 shown in FIG. 2 represents an example of an optical security component intended to be transferred to a document or a product for the purpose of securing it. It comprises alternatively a support film 24, for example a film of polymeric material, for example a film of polyethylene terephthalate (PET) of a few tens of microns, typically 5 to 50 pm, and an optional detachment layer 25, for example in natural or synthetic wax. The release layer makes it possible to remove the polymer support film 24 after attachment of the optical component to the product or document to be secured. The optical security component 20 furthermore comprises a set of layers 21-23 for carrying out the optical function of the component and which will be described in more detail below, as well as an adhesive layer 26, for example a layer of heat-reactive adhesive, for fixing the optical security component on the product or document. In practice, as will be detailed later, the security optical component can be manufactured by stacking the layers on the support film 24, then the component is fixed on a document / product to be secured by the adhesive layer 26. If necessary for the application, the support film 24 can then be detached, for example by means of the detachment layer 25. The set of layers 21-23 comprises in the example of FIG. 2, a first layer 23 of dielectric material, structured at least partially on one side, having a first refractive index ns; a second layer 22, comprising in at least a first region a layer of dielectric material or metal material, as will be detailed hereinafter, or comprising one or more regions with a layer of metallic material and one or more regions with a layer of dielectric material, deposited on the at least partially structured face of the first layer and having in each region a spectral band of reflection in the visible; a third layer 21 of dielectric material having a third refractive index and encapsulating the at least partially structured first layer coated with the second layer. As shown in FIG. 2, the first layer 23 has in at least a first region at least a first structure S.

FIG. 3C schematically shows an example of a first structure S, formed by a first pattern Si modulated by a second pattern Si.

The first pattern (FIG 3 A) is adapted to form a first reflective or transmissive computer-synthesized hologram (HSO) difactive element calculated to generate, under spatially coherent polychromatic illumination, at least a first recognizable image in a reconstruction plane. given, the second pattern (FIG 3B) is a periodic grating subwavelength period, determined to produce, after deposition of the second layer and encapsulation of said first structure, a resonant filter in a spectral band centered on a first wavelength in the visible.

More specifically, the first pattern codes according to the known prior art, complex phase and amplitude data calculated so that, when the diffractive element is illuminated by a beam of light, a desired light intensity diagram appears either in far field, either in a finite distance reconstruction plan.

The first pattern can form a multi-level (Si) structure, as shown in FIG. 3A or binary. A multi-level structure has at least 3 different height planes according to the z-axis perpendicular to the plane of the component, while a binary structure has only two level heights. A multi-level structure makes it possible to form non-symmetrical images with respect to the zero order, that is to say different on either side of the zero order, the zero order designating the specular reflection.

The depth of the first pattern determines the introduced phase and the "zero order" proportion, that is, the amount of incident light reflected in direct reflection or transmitted without deviation (near refraction). In practice, the depth of the first pattern chosen is between 80 nm and 2 μm, advantageously between 100 nm and 1 μm.

The first pattern can be calculated to form an image on the axis (diffracted order (s) centered on the zero or off-axis order (order (s) diffracted around the zero order ).

Moreover, the first pattern can be calculated in a known manner for a restitution of the image in a finite distance reconstruction plane, or in a far field, that is to say for a restitution of the image to the infinite.

We speak of Fourier HSO in the case of an HSO allowing a restitution of the image in far field when the HSO is illuminated by a beam of substantially collimated light. In practice, a Fourier HSO can be formed of a single element whose dimensions can be up to 30 mm x 30 mm, dimensions beyond which the computing times with current computers are very long, or from identical unitary elements, for example of dimensions between 2 pm x 2 pm and 2048 pm x 2048 pm which are subsequently repeated in X and Y either mechanically at the time of etching, or computerically before etching, to obtain a large HSO (or observation window) with dimensions up to 60 mm x 60 mm for example.

We speak of Fresnel HSO in the case of an HSO allowing a restitution of the image at a finite distance of the HSO when the HSO is illuminated by a substantially collimated light beam. Each point of the first pattern in the case of a Fresnel HSO contributes to forming the image in the reconstruction plane. Thus, in the case of a Fresnel HSO, an HSO of dimensions typically up to 30 mm × 30 mm is directly coded.

In either case, a suitable projection optical system makes it possible, for example, to project the image onto a screen.

In practice, we start from an image containing a recognizable information, we decide which functions we want to have (symmetrical or non-symmetrical image, restitution plan close to the HSO or far, etc.) to choose the type of HSO to make: binary or multilevel and Fourier or Fresnel, etc. Then, using HSO design software, for example IFTA (for "Iterative Fourier Transform Algorithm"), a first pattern or first HSO with dimensions in general of between 2 μm x 2 μm and 15 mm × 15 mm is calculated. . It is considered that an HSO can play the role of an observation window if it exceeds in its lateral dimensions the limit of the human eye opening namely 0.5 mm x 0.5 mm.

The design rules of the first pattern to form an HSO with the features described in the above paragraphs are described for example in "Applied Digital Optics: Front Micro-optics to Nanophotonics," Bernard C. Kress, Patrick Meyrueis, 2009.

In the remainder of the description, it will be understood that the set of examples described can be applied to all the known diffractive elements, HSO restoring a distant or far-field image of the HSO, HSO formed by a binary structure or multi-level, image restored symmetric or non-symmetrical with respect to the zero order, on the axis or off axis, HSO refiective or transmissive etc. unless explicitly stated otherwise.

FIGs. 4A to 4E illustrate diagrams showing nonlimiting examples of embodiment of a resonant filter associated with a refective or transmissive HSO, in order to increase the spectral selectivity thereof.

In these examples, there is shown symbolically a polychromatic source PS implemented for the authentication of the component. Spatially coherent polychromatic lighting can be obtained by a point or quasi-point polychromatic source, for example a white LED, the flash of a mobile phone, a luminous torch, and generally a non-extended light source. More precisely, it will be considered that a source is quasi-point or not extended if the ratio between the distance with the component and the largest dimension of the source is greater than 100.

By convention, there is 41 the lighting face of the component and 42 the face of the component opposite to the lighting face 4L

The layer of dielectric material 23 arranged on the side of the illumination face 41 is transparent and preferably colorless. The layer of dielectric material 21 arranged on the side of the face 42 opposite the lighting face may be transparent or not, depending on the applications.

The first pattern is calculated to form an HSO which generates in a reconstruction plane 5 a recognizable image, this image being visible by an observer, either directly, or by means of a projection device (not shown), or on the side of the illumination face (case of a reflective HSO), or the opposite side (case of transmissive HSO).

In the examples of FIGS. 4A and 4B, the second layer 22 comprises a layer of dielectric material and the resonant filter is a subtractive filter wavelength of DID type (for "Diffractive Identity Device"). The second pattern forms a subwavelength network, with one or two dimensions, adapted to allow the excitation of guided modes within the second layer 22, forming a band resonant filter in reflection, including the resonance spectral band Δλ is centered on a first wavelength λι. The second layer 22 comprises a thin layer, of thickness preferably between 20 nm and 200 nm and preferably between 60 nm and 150 nm, having a second refractive index n2 such that the second refractive index neither differs from the first refractive index and the third refractive index and at least 0.3, preferably at least 0.5. According to one or more exemplary embodiments, said thin layer of dielectric material is a so-called high refractive index ("HRI") material having a refractive index of between 1.8 and 2.9, advantageously between 2.0 and 2.4 and the first and third layers of dielectric material, on either side of the second layer, are so-called "low index" refractive index layers, having refractive indices between 1.3 and 1.8, advantageously between 1.4 and 1.7. The first layer of dielectric material 23 arranged on the side of the lighting face of the component is transparent in the visible.

In the example of FIG. 4A, the first pattern is adapted to form a first reflective HSO-type diflfractive element. For example, the first pattern is calculated to exhibit optimum efficiency at a wavelength in the spectral band Αλ of the resonant reflection filter, for example a wavelength close to λι. Thus the first image, observed by the observer located on the side of the illumination face 41 has an increased spectral selectivity at the wavelength λι for a given azimuth and angle of incidence and observation.

In the example of FIG. 4B, the first pattern is adapted to form a first transmissive HSO diffractive element. For example, the first pattern is calculated to exhibit optimum efficiency at a wavelength located outside the spectral band of the resonant reflection filter. DID. Indeed, in this example, the spectral band transmitted by the resonant filter corresponds to the spectral band of the illumination light Σλ to which the resonant spectral band Δλ is subtracted. In this example, the first and third refractive indices have a difference greater than 0.1, for the formation of the transmissive HSO. In this example, the first image observed by the observer on the side of the face 42 of the component opposite to the lighting face 41 has a lower selectivity than in the previous example; however, the color of the HSO is improved due to the rejection of a part of the spectral band.

In the example of FIG. 4C, the second layer 22 comprises a thin layer of metal material, preferably with a thickness greater than 40 nm. The second pattern forms a subwavelength network, with one or two dimensions, adapted to allow the formation of a reflection-band resonant filter, of the "R'plasmon" reflection plasmonic filter type, as described for example in the patent application FR 2982038Al. Advantageously, the second metal layer 22 is sufficiently thick to have a residual maximum transmission as a function of the wavelength of 2%. In this example, the first pattern is adapted to produce a first diffractive reflective HSO-type element calculated to exhibit optimal efficiency at a wavelength outside the spectral band of the resonant reflection filter for azimuth and angle. of incidence and observation given.

In the examples of FIGS. 4D and 4E, the layer 22 comprises a thin layer of metallic material, preferably between 10 nm and 60 nm thick, and the second pattern is adapted to produce a transmission band-pass resonance filter, of plasmonic filter type in transmission " T'Plasmon ", as described for example in the patent application FR 2973917 and having a resonance spectral band Δλ centered on a first wavelength λι for an azimuth and a given angle of incidence and observation.

In the example of FIG. 4D, the first pattern is adapted to form a first transmissive HSO-type diffractive element. For example, the first pattern is calculated to exhibit optimum efficiency at a wavelength in the spectral band Δλ of the resonant transmission filter, for example a wavelength close to λι; The first and second reduction indices advantageously have a difference greater than 0.1.

In this configuration, the user placed on the side of the face 42 can observe under a spatially coherent polychromatic illumination Σλ a colored image Δλ in transmission.

In the example of FIG. 4E, the first pattern is adapted to form a first reflective HSO-type diflfractive element. For example, the first pattern is calculated to exhibit optimum efficiency at a wavelength located outside the spectral band of the transmission-type resonant filter. T'Plasmon. Indeed, in this example, the spectral band Σλ - Δλ reflected by the resonant filter corresponds to the spectral band of the illumination light Σλ which is subtracted the resonant spectral band Δλ.

Whatever the nature of the resonant filter, the wavelengths of the excited resonances depend on the polarization and it can be shown that at non-zero incidence of the illumination beam, the reflected (or transmitted) spectral band will be modified by changing the the orientation of the component, obtained by azimuthal rotation thereof, except in the case of a two-dimensional network of equal periods.

FIGS. 5A-5D illustrate these effects in the case where the first pattern forms a one-dimensional network characterized by a grating vector kg, whose direction is perpendicular to the grating lines (symbolized by lines in FIGS., 5A and 5B) and the standard is inversely proportional to the period of the network. The plane Π corresponds to the plane in which the lighting beam is located.

FIG. 5C represents the spectra calculated in reflection for a so-called "collinear" incidence (configuration 5A: lighting beam in a plane Π perpendicular to the surface of the component and parallel to the direction of the grating vector) and an angle of incidence of the beam of The illumination measured relative to the component normal of 0 ° (curve 51) and 20 ° (curve 52).

FIG. 5D represents the spectra calculated in reflection for a so-called "conical" incidence (configuration 5B): lighting beam in a plane Π perpendicular to the surface of the component and perpendicular to the direction of the grating vector) and an angle of incidence of the beam of illumination measured with respect to the component normal of 0 ° (curve 53) and 20 ° (curve 54).

In both cases, the curves are calculated by assuming a DID with a pitch of 360 nm, a depth of 130 nm structuring a layer of zinc sulphate (ZnS) of 100 nm thick and encapsulated between two identical layers of polystyrene.

Collinear incidence is observed to rapidly change the spectral band of resonance with the angle of incidence while the modification is much slower in conical incidence. This eiFet makes it possible to further reinforce the authentication of the component by showing variable color effects as a function of the azimuth.

The reflection curves of FIGS. 5C and 5D are calculated in the case of a resonant filter of the DID type, but similar transmission curves would be observed in the case of a T'Plasmon type resonant filter. In the case of a R'Plasmon type resonant filter, absorption curves would show the same dependence with the azimuth and the angle of incidence.

Of course, in the case of a two-dimensional array (not shown in the figures), with substantially equal period in each direction, the color effect will be non-variable, or very slightly variable depending on the azimuth. We will find a variation of the colored effect with the azimuth, for angles of harmless incidence, if the periods in each direction are different.

FIGS. 6A and 6B schematically show a secure object 1, for example an identity document type document, comprising an example of a security optical component 60 according to the present description with an off-axis off-axis type diffractive element in reflection and a resonant filter ID, for a non-zero angle of incidence and for two azimuth values; in these figures, the beam 3 represents the lighting beam; it is for example derived from a point or quasi-point polychromatic source, for example a white LED source. The beam 4 represents the beam reflected by the optical security component 60. In these examples, the data are calculated so that, when the HSO is illuminated by a beam of divergent, convergent or collimated light, a light intensity diagram appears in FIG. a reconstruction plan 5 that can be infinite. In this example, the intensity diagram comprises an image 66 formed of two off-axis objects 61, 62. A residue 63 of the beam transmitted on the axis is also visible.

As shown in FIG. 6B, the rotation of the component in azimuth causes a color change of the image 66 with non-zero incidence of the illumination beam.

In addition to the increased spectral selectivity of the HSO obtained by the resonant filter, which results in a much better quality of the image 66, in this example an additional means of authentication of the security optical component is obtained thanks to a variable color effect. according to the azimuth.

FIG. 7A schematically represents a first example of a security optical component 70 comprising a pixel matrix. A first portion of the pixels 71 form a first zone. They comprise a first structure formed of a first pattern adapted to form a first reflective type HSO diffractive element, modulated by a second pattern. A second portion of the pixels 72 form a second zone. They comprise a second structure formed of a first pattern adapted to form a second diffractive element of HSO type in reflection, modulated by a second pattern. The first and second zones occupy, for example, a comparable surface.

More precisely in this example, the first pattern of the first structure arranged in the first zone (pixels 71) is a multi-level HSO making it possible to form the image "Ω" in far field off the axis. The second pattern of the first structure makes it possible to form a one-dimensional array adapted to form a resonant filter with a spectral resonance band. The grating is arranged so that, with an azimuth of 0 °, the variability of the resonant spectrum is small as a function of the angle of incidence of the illumination beam (as in FIG. 5B). By 90 ° azimuthal rotation of the component 70, the far-field variability of the resonance spectral band for the first region, as a function of the angle of incidence, becomes strong.

The first pattern of the second structure arranged in the second zone (pixels 72) is a multilevel HSO making it possible to form the "a" image in the far field off the axis. The second pattern of the second structure makes it possible to form a one-dimensional network similar to that of the second pattern of the first structure. But the grating is arranged substantially perpendicular to that of the second pattern of the first structure so that with an azimuth of 0 °, the variability of the resonant spectrum is high as a function of the angle of incidence of the beam of illumination and that by 90 ° azimuth rotation of the component 70, the far-field variability of the resonance spectral band for the second region, depending on the angle of incidence, is low.

FIG. 7B shows an illumination of a secure object 1 equipped with an optical security component 70 as shown in FIG. 7A at an incidence of 0 °. Thanks to the matrixing of the pixels, we obtain the two images "Ω" and "a" simultaneously. The incidence of 0 ° does not make it possible to differentiate in color the 2 images.

FIG. 7C illustrates a lighting of the secure object 1 with an angle of incidence of 20 °. In this case, the incidence of 20 ° makes it possible to differentiate in color the two images "Ω" and "a".

FIG. 7D shows illumination of the secure object 1 with an angle of incidence of 20 ° when the object 1 has undergone an azimuthal rotation of 90 °. In this case, we observe a color inversion of the two images "Ω" and "a".

Of course, the "colors" are presented here as examples. We could have second patterns for the first and second structures such that the initial colors of the first and second images are different for an incidence of 0 ° and have spectral variation behaviors as a function of the same or different incidence angle.

FIG. 8 schematically shows a second example of an optical security component 80 comprising a matrix of pixels in the form of bands (81 - 84) and images obtained by successive illumination of the different bands. Each band, of width L greater than 500 μm, for example, forms a region. In this example, the first patterns of each of the regions are adapted to form off-axis HSOs having the same object (an arrow) but at a different position and orientation in the observation plane (see Imi-Im4 images). The second pattern is for example identical for each of the regions so that the object (the arrow) is the same color on each image. The illumination in coherent polychromatic light on each band then makes it possible to reveal only one image separately from the other bands. The successive lighting of the different regions makes it possible to simulate the effects of movements.

Similarly, it will be possible to create morphing effects (deformation / transformation) by scanning. For example, the first image of the first zone may have a defined shape that evolves in each successive zone to simulate a movement and / or a transformation of the shape.

In addition, each zone of each first pattern may have a second pattern different in terms of period, network orientation and / or network depth to change the color of each of the areas.

FIG. 9 represents an example of a secure object integrating a first security optical component and a second security optical component, adapted for human stereoscopic vision or by video players or stereoscopic images;

In this example, two security optical components according to the present description 90l and 90r are arranged on a secure object 1 at a given distance from each other, so that for a given illumination 3, 3 'respectively on the 90l and 90r components, each eye / sensor sees an image independently. In this example, the left eye can only see the image 91, 92 from the security component 90l, while the right eye can see only the image 93, 94 from the security component 90r. Of course and as described above, each of the components 901 and 90r may have structures for generating HSOs with specific or identical colors related to resonant filtering. The mental reconstruction of the image allows the observation of the image on a virtual plane, the virtual plane can be positioned at a median distance of the two images from each of the components 90l and 90r.

FIGS. 10A and 10B and 11A-11B show other examples of secure objects integrating examples of optical security components with suitable structures for the formation of HSO-type diffractive elements, for example in the near field.

In the example of FIGS 10A and 10B, the optical security component 100 comprises a first structure arranged on an area 101 and a second structure arranged on an area 102, the areas 101 and 102 being formed of alternating pixels with each other to form a checkerboard (intertwined areas).

For example, the first structure 101 comprises a first pattern modulated with a second pattern, so as to form a Fresnel HSO, for generating a given color image 103 in a finite-distance reconstruction plane (HSO in the near field). ), the reconstruction plane 5 being behind the secure object 1 relative to the position of the lighting source. The second structure 102 comprises a first pattern modulated with a second pattern, so as to form a Fresnel HSO, making it possible to generate an image 104 of given color, for example different from the color of the object 103, in a plane of 5 'reconstruction at a finite distance (HSO in the near field), the reconstruction plane 5' being in front of the secure object 1 with respect to the position of the lighting source.

In non-zero incident lighting, for example at an incidence between 20 ° and 40 °, as shown in FIGS. 10A and 10B, it is possible to generate a color inversion of the images 103 and 104 by azimuthal rotation of the object 1, for example if the second patterns of each of the first and second structures are unidimensional, of the same period and oriented in directions substantially perpendicular.

In the example of FIGS. 11A and 11B, the security optical component 110 comprises a first structure arranged on an area 111, a second structure arranged on an area 112 and a third structure arranged on an area 113. The areas 111 - 113 are formed of pixels alternated with each other to form a checkerboard (intertwined areas).

For example, the first structure 111 includes a first pattern modulated with a second pattern, such as to form an HSO, for generating a given color image 114 in a finite distance reconstruction plane. The second structure 112 comprises a first pattern modulated with a second pattern, so as to form an HSO, for generating an image 115 of a given color, for example different from the color of the object 114, in the same reconstruction plane 5. The third structure 113 comprises a first pattern modulated with a second pattern, so as to form an HSO, making it possible to generate an image 116 of a given color, for example different from the color of the object 114 and the color of the object. object 115, in the same reconstruction plane 5. In this example, the images 114, 115, 116 complement each other to form a recognizable object, for example here a rectangular parallelepiped.

In non-zero incident lighting, for example at an incidence between 20 ° and 40 °, as shown in FIGS. IIA and 1IB, it is possible to generate a modification of one or the other of the colors of the images 114 - 116 by azimuthal rotation of the object 1 by selecting the appropriate resonant filters, as previously described.

The security components as described above can be implemented according to one or more exemplary embodiments as follows.

The different optical structures of the different regions are previously recorded by photolithography or electron beam lithography on a photosensitive medium or "photoresist" according to the Anglo-Saxon expression. An electroplating step makes it possible to postpone these optical structures in a resistant material, for example based on nickel, to produce the matrix or "master", see for example the reference work "diffraction handbook grating" and more particularly chapter 5 "Replicated Grating "(Christopher Plamer, Sixth Edition, Newport 2006). A stamping (or "embossing") can then be performed from the matrix thus produced to form the first layer of dielectric material at least partially structured. Typically, the first layer of dielectric material 23 (FIG 2) is a stamping varnish a few microns thick carried by a support film 24 from 5 pm to 50 pm of polymeric material, for example PET (polyethylene terephthalate) . The stamping can be done by hot pressing of the dielectric material ("hot embossing") or by molding and UV curing ("UV casting"), but preferably by UV molding and crosslinking due to the depth of the structures (typically between 80 nm and 1 μm). The refractive index of the layer formed by the stamping varnish is typically close to 1.5 for visible light.

Then comes the deposition of the second layer 22 on the layer and stamped or molded. The second layer may be a metal layer, deposited by thermal evaporation, for example under vacuum, in a perfectly controlled manner in thickness, with at least one for example of the following metals: silver, aluminum, gold, chromium, copper, nickel, etc. . The second layer may be a layer of dielectric material, for example zinc sulphide, titanium oxide. In one or more exemplary embodiments, the second layer may comprise metal regions and regions of dielectric material, as described below.

A closed layer of controlled refractive index is then applied, for example by evaporation in the case of a thin film or by a coating process. For some applications, such as rolling or hot stamping products, this layer may be the adhesive layer. The closure layer, which forms the third layer of dielectric material 21 may have, depending on the application, a refractive index substantially identical to that of the layer 23, around 1.5, or may have a refractive index different from that of the layer 23. The closure layer 21 may have a thickness greater than or equal to one micron, for example a few microns. Depending on the final destination of the product, an adhesive layer 26 may be applied to the closure layer.

According to one or more embodiments, the second layer 22 may comprise in one or more regions a dielectric material and / or may comprise in one or more regions a metallic material and / or may be discontinuous.

It is possible in either of these examples to deposit in a first step a metal layer on the first layer of dielectric material 23; then the metal layer is partially demetallized for the production of specific patterns or to facilitate the readability of the effect, or to generate other regions in which we can locally deposit a layer of dielectric material or another layer of metal material. For this, a first partial demetallization process consists in applying a protective varnish to the regions where it is desired that the metal layer be preserved. This varnish has for example a refractive index substantially identical to that of the first layer 23, for example around 1.5, with a thickness for example of the order of one micron. Subsequently, a chemical bathing step makes it possible to destroy the unprotected metal parts. Optionally, another metallic material or a dielectric material is deposited in one or more of the demetallized regions to form the second layer 22. Finally the third layer or closure layer 21 is applied to the entire component.

Another partial demetallization method consists in applying a soluble ink to the pattern on the stamped or UV-cured layer with a given pattern. When depositing the metal, it is applied uniformly on the layer but remains only on the areas where the ink is not located when the ink is removed.

According to one or more exemplary embodiments, it is possible to form a second layer 22 with one or more regions of dielectric material and one or more regions of metallic material by applying one or more dielectric materials before the metallization step. For this we can for example apply a soluble ink on the stamped layer or crosslinked with UV. A first thin layer deposition makes it possible to uniformly apply a dielectric material to the whole of the stamped or UV-cured layer and to the ink; the dielectric material remains only in the areas where the ink is not located when the ink is removed. Then a metallization step, which can be selective, is performed. If the metallization is selective, it will also include a preliminary step of printing soluble ink for selecting the application areas of the metal or the printing of a protective ink after deposition of the metal.

As can be seen from the example of manufacturing method described above, the inclusion of an optical security component according to the present description in a secure document is perfectly compatible with the presence in the same document of structures based on networks commonly used for the production of holographic components.

In particular, it will be possible to make a security optical component comprising one or more components as described above and one or more other types of optical security components, for example of the holographic type.

For this, a matrix is produced by recording the different patterns corresponding to the various optical security components on the photoresist support and then, as previously, an electroplating step makes it possible to transfer the optical structure of the photoresist to a solid support to form the matrix. The stamping or molding followed by the UV crosslinking can then be carried out from the matrix to transfer the different microstructures onto the film of polymer material.

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. In particular those skilled in the art will advantageously combine the optical properties of the many known optical security components with the properties of the optical security component according to the invention.

Claims (13)

claims An optical security component (20) for authentication in the visible spectrum, in spatially coherent polychromatic light, comprising: - a first layer (23) of dielectric material, at least partially structured on one side, and having a first index refraction (ns); - a second layer (22) deposited on the at least partially structured face of said first layer in at least a first region, and having a spectral band of reflection in the visible; a third layer (21) of dielectric material deposited on said second layer and having a third refractive index (ni); and wherein said first layer (23) has in the first region at least a first structure (S) formed by a first pattern (Si) modulated by a second pattern (Si), such that: O the first pattern (Si) is adapted to form a first computer-synthesized hologram-like difactive element calculated to generate, under spatially coherent illumination, at least a first recognizable image in at least a first reconstruction plane (5), O the second motif (S2) is a periodic network sub wavelength period, determined to produce, after deposition of the second layer and encapsulation of said first structure by the third layer, a resonant filter in a first spectral band. The optical security component of claim 1, wherein the second pattern of at least one first structure is a one-dimensional subwavelength array. 3. optical security component according to any preceding claim, wherein: - the first layer has in the first region at least a second structure formed by a first pattern modulated by a second pattern, such that: O the first pattern of the second structure is adapted to form a second computer-synthesized hologram type diifractive element. calculated to generate, under spatially coherent illumination, at least a second recognizable image in a second reconstruction plane (5 '), the second motif is a periodic network of subwavelength period, determined to produce, after deposition of the second layer and encapsulating said second structure by the third layer, a resonant filter in a second spectral band. An optical security component according to claim 3, wherein at least a first image and at least a second image are generated in the same reconstruction plane (5). An optical security component according to any one of claims 3 or 4, wherein the at least first and second structures are arranged in regions (71, 72) intertwined with one another. 6. Optical security component according to any one of claims 3 or 4, wherein the at least first and second structures are arranged in adjacent areas, the successive lighting of each zone to simulate a motion effect of a image and / or transformation. 7. optical security component according to any one of the preceding claims, wherein: in at least one region, the second layer is a thin layer of dielectric material, having a second refractive index (n2) such as the second index; (n) differs from the first refractive index (n3) and the third refractive index (n1) by at least 0.3; for at least one first structure of said region, the second pattern is adapted to produce a band resonant filter in reflection. 8. optical security component according to any one of the preceding claims, wherein: in at least one region, the second layer is a thin layer of metal material, greater than 40 nm thick; for at least one first structure of said region, the second pattern forms a band resonant reflection filter. 9. Security optical component according to any one of the preceding claims, wherein, for at least one first structure: in at least one region, the second layer is a thin layer of metal material, of thickness between 10 nm and 60 nm; for at least one first structure of said region, the second pattern is adapted to produce a transmission bandpass resonant filter. 10. optical security component according to any one of the preceding claims, wherein, for at least one structure: - the first pattern is adapted to form a first refractive computer synthesized hologram diflfractive element An optical security component according to any one of the preceding claims, wherein for at least one structure: the first pattern is adapted to form a first transmissive computer synthesized hologram diflfractive element; the first refractive indices (ns) and third refractive indices (ni) have a difference greater than 0.1. 12. Secure object comprising a support and an optical security component according to any one of the preceding claims, arranged on said support. 13. A method of manufacturing a security optical component according to any one of claims 1 to 11 comprising: - forming on a support film (24) of said first layer (23) of dielectric material; depositing the second layer (22) on at least a first region of the first layer of dielectric material; depositing on said second layer the third layer (21) of dielectric material.