WO2023111481A1

WO2023111481A1 - Security device which can be used to generate an enlarged projected image using microlenses and a perforated metal layer

Info

Publication number: WO2023111481A1
Application number: PCT/FR2022/052396
Authority: WO
Inventors: Paul AZUELOS; Marie MAZZOLINI
Original assignee: Idemia France
Priority date: 2021-12-17
Filing date: 2022-12-16
Publication date: 2023-06-22
Also published as: EP4448296A1; FR3130689B1; FR3130689A1

Abstract

The invention relates to a security device which can be used to generate an enlarged projected image on a surface spaced apart from the device when the device has a first face placed in front of the spaced surface and when a second face of the document opposite the first face is illuminated, the document comprising: a first layer (101) comprising an array of microlenses (102), and a second metal layer (103) arranged at a distance from the first layer that is greater than the focal length of each microlens, wherein the second metal layer includes a plurality of patterns (104), formed by one or more perforations in the metal layer (103), each pattern of the plurality of patterns being associated with a microlens so that when the second face of the document is illuminated, the enlarged projected image is formed on the spaced surface by the combination of the projections of each pattern.

Description

Title of the invention: Security device usable to generate an enlarged projected image using microlenses and a perforated metal layer

Technical area

The present invention relates to the field of security devices, and in particular optical security devices.

The invention applies in a non-exclusive manner to security documents, for example physical identity documents, such as a passport, an identity card, a driving licence, a residence permit, etc.

Prior technique

The identity market today requires increasingly secure identity documents (also known as identity documents). These documents must be easily authenticated and difficult to counterfeit (if possible tamper-proof). This market concerns a wide variety of documents, such as identity cards, passports, access badges, driving licenses, etc., which can be in different formats (cards, booklets, etc.).

Various types of security devices can be integrated into these documents to facilitate their authentication. For example, markings, printings, overlapping layers can be used so that, during authentication, there are no doubts about the authenticity of the document (and a fortiori about the identity of the bearer of this document). These devices are in fact intended to limit the risk of fraud, falsification or counterfeiting.

To be authenticated, these devices must be able to be observed by an operator or by a sensor of a camera which delivers automatically processed images (for example by a model obtained by automated learning). As can be seen, devices with fine and complex characteristics are sought after because they are difficult to reproduce, but they are on the other hand difficult to detect/process.

In particular, if the documents appear on a video stream, which is one of the possible document observation solutions, it can be difficult to observe the details of a security device well. As a result, documents that appear in a video stream are currently not authenticated in a satisfactory manner. There are other situations in which the observation is not always satisfactory for the authentication to be certain, in particular when the time dedicated to the authentication is limited.

Today there is a need for a security device that is difficult to reproduce, but which could be authenticated quickly, in various situations.

Disclosure of Invention

To solve at least some of the drawbacks mentioned above, the present invention relates to a security device that can be used to generate an enlarged projected image on a surface spaced a given distance from the device when the device has a first face placed opposite the spaced surface (for example, the first face and the spaced surface are spaced apart by the given distance and are substantially parallel in this configuration) and when a second face of the document opposite the first face is illuminated, the document comprising, on the first face to second face:

- a first layer comprising an array of microlenses, and

- a second layer of metal arranged at a distance from the first layer which is greater than the focal length of each microlens of the array of microlenses, in which the second layer of metal comprises a plurality of patterns, each pattern being formed by one or more perforations of the metal layer, each pattern of the plurality of patterns also being associated with a microlens of the network of microlenses (each pattern substantially faces a microlens), so that when the second face of the document is illuminated, the Magnified projected image is formed on the spaced surface by the combination of the projections of each pattern by their associated microlens.

The inventors of the present invention have observed that the very short focal lengths of microlenses allow them to be used to produce a magnified projection of an object placed at a very close distance from the microlens. This makes it possible to produce a compact device, which can then be integrated into a security document (having a thickness of the order of a millimeter).

It is thus possible to obtain an enlarged image having dimensions of the order of ten centimeters, for example, which facilitates the observation of a characteristic which can be used for the authentication of the device or of a document which comprises this device. Since the luminous flux passing through a microlens is low, it is proposed to use an array of microlenses and a plurality of perforated patterns in the metal layer: this allows each pattern (associated with a microlens) to contribute to the total luminous flux which will reach the spaced surface when using the device. Thus, there is a brighter projection, which can be observed in various conditions.

The metallic layer is substantially opaque, and it can be perforated by a material removal process (for example by application of a laser beam, or laser perforation) at the location of the perforations. The perforations pass through the metal layer, they are through, and form openings through which the luminous flux passes.

According to a particular embodiment, said one or more perforations of each pattern of the second layer of metal are obtained by applying a laser beam.

The use of a laser beam is particularly interesting because it makes it possible to easily deliver personalized security devices (this laser beam is used during a personalization step), because the application of the laser beam can be done according to different paths between two security devices to form different patterns.

For example, if the security devices are associated with a user, each pattern can indicate information relating to the user (date of birth, portrait, etc.)

According to a particular embodiment, all the patterns of the plurality of patterns have a maximum dimension which is smaller than the distance which separates the centers of two adjacent microlenses of the array of microlenses.

The maximum dimension of a pattern is for example the diameter of the circle in which this pattern is inscribed. The distance which separates the centers of two microlenses is generally designated by the Anglo-Saxon expression of pitch.

This particular embodiment makes it possible to prevent a pattern from being projected by a microlens with which it is not associated, because it overlaps a location dedicated to the pattern of this microlens. In fact, this embodiment makes it possible to have an enlarged projected image of better quality.

Preferably, the pattern is arranged inside a surface corresponding to the projection of the microlens associated with the pattern (the outline of the microlens, projected onto the second layer of metal which is parallel to the first layer, surrounds the pattern ). In fact, the person skilled in the art will be able to choose the position of the pattern and its position as a function in particular of the focal distance of the microlens, of the given distance, and of the desired size of the enlarged projected image.

According to a particular embodiment, the second layer of metal comprises a first pattern and a second pattern (spaced apart to each be associated with a lens specific to the pattern) both comprising a portion of identical pattern ( between the two patterns), and in which the first pattern and the second pattern are placed with respect to their respective associated microlenses so that: a light ray passing through a point of the identical pattern portion of the first pattern and the center of the microlens associated with the first pattern, and a light ray passing through the same point of the identical pattern portion of the second pattern and the center of the microlens associated with the second pattern, intersect at the same location of the spaced surface at the given distance.

The first pattern and the second pattern may be partly identical or totally identical.

With two portions of identical patterns, and the placement of the patterns defined here, a superposition of the projections is obtained in the enlarged projected image, and therefore an image obtained by a greater luminous flux, which facilitates its observation.

For example and without this being limiting, the light rays in this embodiment which pass, in a straight line, through a point of the identical pattern portion of the first pattern and the center of the microlens associated with the first pattern, the rays in this embodiment which pass, in a straight line, through the same point of the identical pattern portion of the second pattern and the center of the microlens associated with the second pattern, intersect, by propagating in a straight line, at the same location of the spaced surface at the given distance

Two portions of identical patterns are portions with the same shape, the same dimensions, but placed at different locations of the metal layer (since they are placed substantially opposite different microlenses).

For example and without this being limiting, the same point designates the same position in the pattern, for example in a frame of reference centered on each identical pattern portion. For example, if each portion of an identical pattern is shaped like the letter "A", the top of the A can be the same stitch on each pattern. A person skilled in the art knows how to place the patterns relative to the microlenses to obtain a crossing of the rays at the same point. In fact, it is possible to shift the patterns in the plane of the second layer of metal to obtain this property.

Also, in a non-limiting way, in this particular embodiment, there may not be any obstacle to the propagation of the rays between the lenses and the metal layer. For example, the document can be transparent between the metal layer and the lenses.

According to a particular embodiment, the array of microlenses has a center, and the first pattern is closer to the projection on the second metal layer of this center of the array of microlenses than the second pattern, and in which the identical portion of the first pattern is arranged within the second layer of metal with a first offset measured between a center of the identical portion of the first pattern and the projection of the center of the microlens associated with the first pattern, and the identical portion of the second pattern is arranged at the within the second layer of metal with a second offset measured between a center of the identical portion of the first pattern and the projection of the center of the microlens associated with the second pattern, the second offset being greater than the first offset (in absolute value) .

To obtain the property that a light ray passing through a point of the identical pattern portion of the first pattern and the center of the microlens associated with the first pattern, and a light ray passing through the same point of the identical pattern portion of the second pattern and the center of the microlens associated with the second pattern, intersect at the same location of the spaced surface at the given distance, the identical portions can be shifted in the plane of the second metal layer. This offset, measured relative to the projection of the center of the microlens associated with a pattern, is greater for the pairs of patterns and microlenses which are arranged on the periphery of the device, that is to say the pairs farthest from the center of the array of microlenses (or of its projection in the plane of the second layer of metal).

These offsets can be determined by a calculation.

As an indication, for microlenses of an array of microlenses arranged consecutively along an axis, with a central microlens arranged in the center of the array of microlenses, we will have:

- The central microlens associated with a pattern whose center coincides with the projection of the center of the first microlens (no offset), - The first microlens, moving away from the center of the grating along the axis, which has a shift between the projection of the center of this first microlens and the center of the pattern associated with the first microlens denoted Ap,

- The second microlens, moving away from the center of the grating along the axis, which has an offset between the projection of the center of this second microlens and the center of the pattern associated with the second microlens equal to 2 Ap,

- The N-th microlens, moving away from the center of the grating along the axis, which has an offset between the projection of the center of this N-th microlens and the center of the pattern associated with the N-th microlens equal to N from p.

The offset increases as one moves away from the projection of the center of the microlens array. The offset Ap can be calculated using the paraxial approximation:

With s ₀ the distance between the second layer of metal and the first layer (i.e. the microlenses, s, the given distance (between the spaced surface and the device), p _L the "pitch" (the gap or the period between the microlenses ) and f the focal length of the microlenses.

These offsets can be determined along different axes.

According to a particular embodiment, all the patterns of the plurality of patterns are identical, and in which all the light rays which pass through the same point of each pattern and through the center of the microlens associated with the pattern intersect at the same location of the spaced surface.

This particular embodiment has the advantage of forming a sharp image, with a maximum of luminous flux, which further facilitates its observation. Preferably, each microlens is associated with an identical pattern (there are as many patterns as there are microlenses).

In this particular embodiment, the pairs of microlenses and of identical pattern can each be associated with an offset, which increases when one moves away from the projection on the second layer of metal from this center of the network of microlenses. According to a particular embodiment, the device comprises, between the first layer and the second layer, a third layer comprising a plurality of colored filters, in which each colored filter is associated with a microlens.

Thus, the light which has passed the perforated patterns and the filters will be colored, which makes it possible to form an enlarged projected image with an additional property to facilitate the authentication of the security device.

According to a particular embodiment, the plurality of colored filters comprises a plurality of filters of a first color and a plurality of filters of a second color (different from the first color), and in which the patterns associated with the colored filters of the first color are all identical, and the patterns associated with colored filters of the second color are all identical.

This particular embodiment allows images to be formed in more than one color, with color variations visible in the projected image, as the patterns are different between the colors.

According to a particular embodiment, the plurality of colored filters comprises a plurality of red filters, a plurality of blue filters, and a plurality of green filters, and in which the patterns associated with the red filters are all identical, the patterns associated with the filters green filters are all identical, and the patterns associated with the blue filters are all identical.

Thus, we can form a colored image projected with many colors.

According to a particular embodiment, the device further comprises an opaque layer comprising a plurality of openings forming diaphragms arranged between the first and the second layer, in which each opening is associated with a microlens.

This particular embodiment makes it possible to prevent light rays which have passed a pattern from being directed towards a microlens associated with another pattern. A person skilled in the art will use the English expression “crosstalk” to designate this phenomenon.

According to a particular embodiment, the device further comprises, at the level of the second face, a surface having a roughness with a parameter Ra of between 0.5 μm and 10 μm, or a set of condensers, each condenser of the set of condensers cooperating with a microlens associated with the condenser and which is specific to it. These condensers can themselves be microlenses. They concentrate the luminous flux which arrives on the second face towards the patterns and the lenses, to cooperate with them.

According to a particular embodiment, the first layer and the second layer are buried between two transparent layers.

This particular embodiment makes it possible to protect the microlenses of the first layer and the perforated patterns of the second layer. Transparency also allows light to pass through.

According to a particular embodiment, the first layer and the second layer extend at least within a transparent window of a support.

The support, outside its window, may be opaque. By window, it is meant that only the metallic layer (and possibly the filters and the diaphragms) block the passage of light at the level of the window, between the first face and the second face.

According to a particular embodiment, the microlenses of the network of microlenses are arranged in a hexagonal pattern (that is to say in a honeycomb, or even in a hexagonal tiling).

This arrangement makes it possible to maximize the number of microlenses on a given surface.

The invention also proposes a security document comprising a security device as defined above, further comprising a marking of at least one item of information specific to the bearer of the document.

For example, this marking can be carried out on an opaque support.

The invention also proposes a method of manufacturing a security device that can be used to generate an enlarged projected image on a surface spaced a given distance from the device when the device has a first face placed facing the spaced surface and when a second face of the document opposite the first face is illuminated, the method comprising: obtaining a first layer comprising an array of microlenses, and assembling the first layer with a second layer of metal at a distance from the first layer which is greater than the focal length of each microlens of the array of microlenses, so that the first layer is on the side of the first face and the second layer on the side of the second face, a formation, in the second metal layer, of a plurality of patterns, each pattern being formed by one or more perforations of the metal layer, each pattern of the plurality of patterns being further associated with a microlens of the network of microlenses , so that when the second side of the document is illuminated, the enlarged projected image is formed on the spaced surface by the combination of the projections of each pattern by their associated microlens.

This method can be configured to manufacture devices according to all the embodiments of the security device defined above.

According to a particular mode of implementation, the method also comprises prior formation of the microlenses by application of a laser beam.

According to a particular mode of implementation, the perforation of the second layer of metal is implemented by applying a laser beam.

This perforation can be performed before or after the assembly step. For example, this perforation can be implemented during a personalization phase of a security document which incorporates the device.

The invention also proposes a method of using a security device as defined above or a security document as defined above, to generate an enlarged projected image on a surface separated by a given distance from the device (which may be included in a document), in which the first face of the device is placed facing the spaced surface and the second face of the device is illuminated.

The invention also proposes a system configured to implement the method of use defined above, comprising a lighting device and a surface arranged so that when a security device or a security document is between the device illuminator and the surface, with its second side illuminated by the illuminator, being spaced from the surface by the given distance, the enlarged projected image appears on the surface.

Brief description of the drawings

Other characteristics and advantages of the present invention will become apparent from the description given below, with reference to the appended drawings which illustrate examples of embodiments which are devoid of any limiting character. In the figures:

[Fig. 1A-1C] Figure IA shows a security device according to a first example, Figure IB shows its use, and Figure IC shows the projected image obtained; [Fig. 2A-2C] FIG. 2A represents a security device according to a second example, FIG. 2B shows its use, and FIG. 2C shows the projected image obtained;

[Fig. 3A-3C] FIG. 3A represents a security device according to a third example, FIG. 3B shows its use, and FIG. 3C shows the projected image obtained;

[Fig. 4A-4C] FIG. 4A represents a security device according to a fourth example, FIG. 4B shows its use, and FIG. 4C shows the projected image obtained;

[Fig. 5] Figure 5 shows a device according to a fifth example;

[Fig. 6] Figure 6 shows a device according to a sixth example;

[Fig. 7] Figure 7 shows a device according to a seventh example;

[Fig. 8] Figure 8 shows the paths of light rays;

[Fig. 9] Figure 9 shows more precisely two paths of light rays; And

[Fig. 10] Figure 10 shows the offset of the patterns relative to the microlenses.

Description of embodiments

A description will now be given of examples of security devices which use microlenses and a layer of metal with patterns obtained by perforation, which make it possible to project an enlarged image obtained by the combination of the images projected by the microlenses. We will also describe the method of manufacturing these security devices.

In Figure IA, there is shown in perspective and exploded view a security device 100, which will be used to generate an enlarged projected image, as described later with reference to Figures IB and IC.

The device 100 comprises a first layer 101 comprising an array of microlenses 102. This array of microlenses is produced with microlenses in the shape of half-spheres, arranged here according to a grid (other arrangements are possible, as will be described below). after with reference to Figure 5). The grid here is orthogonal, and the microlenses are arranged according to a periodic pattern with a given periodicity. For example, the microlenses 102 can be spaced apart by at least the focal distance of the microlenses, which implies a minimum spacing between two neighboring microlenses comprised between 50 micrometers and 300 micrometers. The spacing between the microlenses is preferably as small as possible to have a good covering factor of the surface within which the microlenses are arranged (for example according to a hexagonal pattern, which makes it possible to maximize this covering factor).

Although 16 microlenses have been represented here, it will be possible to produce devices with a hundred microlenses, for a device having dimensions less than 25 millimeters by 25 millimeters. Devices can be designed with more microlenses, for example 500×500 microlenses.

It will be noted that the term microlens is a lens having dimensions less than one millimeter, typically dimensions comprised between about ten micrometers and several hundreds of micrometers.

If we compare an array of microlenses to a single lens having the same dimensions as the array of microlenses, we note that the focal length of these microlenses is much lower than for the single lens, this makes it possible to produce a device very compact, of small dimensions, and therefore to allow its integration into a security document. Furthermore, the use of microlenses can increase the luminous flux which is transmitted (if we compare an array of microlenses to a single lens having dimensions comparable to that of the array of microlenses) and the homogeneity of the projected image (the microlenses making it possible to direct the rays preferentially in the direction of the projection - there is less distortion and spherical aberration for an array of microlenses than for a single lens having dimensions comparable to that of the array of microlenses). This allows to have a good depth of field for the projected image (which will be clear over a wide range of distances), and which finally allows to have a good magnification.

The microlenses can be manufactured during a phase well known to those skilled in the art under the name of personalization phases, that is to say the phase in which data specific to the bearer of the security document is entered on the security document. They can be produced by applying a laser beam which will cause thermal reflux (typically a carbon dioxide laser, in English “CO2 laser thermal reflow”).

Alternatively, it is possible to implement stamping to form the microlenses, for example during a rolling process. This process may be a thermoforming process which uses a microtextured metal lamination plate.

It will be noted that the first layer 101 can be a layer of a polymer (polycarbonate, polyethylene terephthalate, or even polyvinyl chloride) or another layer of glass, capable of allowing the formation of microlenses by application of a laser beam or by lamination. In fact, any transparent material in which the microlenses can be formed can be used. The following two documents present devices with arrays of microlenses:

- "Microlensed array based LCD projection display with software-only focal distance control" (Sieler et Al. (2013). Proceedings of SPIE - The International Society for Optical Engineering. 8643. 10.1117/12.2006198. DOI: 10.1117/12.2006198)

- "Ultraslim fixed pattern projectors with inherent homogenization of illumination" (Sieler et Al. (2012). Applied optics. 51. 64-74. 10.1364/A0.51.000064. DOI:

10.1364/AO.51.000064)

International application WO 2019/175514 also describes the formation of microlenses.

The device 100 also comprises a second layer 103 of metal. This layer is preferentially sufficiently opaque to block light, and it may comprise aluminum, for example over a thickness of between 20 nanometers and 5 micrometers.

The metal layer 103 comprises a plurality of patterns 104, all formed by perforations (or more precisely microperforations, with dimensions less than one micrometer) of the metal layer 103. Here, all the patterns 104 are identical, and they all have the shape of the letter "A". Also, there are as many patterns 104 as there are microlenses 102. In fact, each pattern 104 is associated with a microlens 102.

Preferably, the patterns of the plurality of patterns do not overlap (this property can apply to all the embodiments described here). Their dimensions are chosen according to the desired magnification, but also to prevent a microlens with which the pattern is not associated from receiving rays passed through this pattern.

By way of indication, the patterns may each be inscribed in a circle having a diameter smaller than the distance which separates the centers of two adjacent microlenses of the array of microlenses. The patterns may in fact each have a maximum dimension which is smaller than this distance between the centers of the microlenses.

The invention is nevertheless not limited to these limiting dimensions, the dimensions of the patterns being determined in particular by the focal lengths of the microlenses, the desired magnification, and the given distance. To form the patterns, any means of etching or removing material can be used. Preferably, a laser beam is applied to form the perforations which will form the patterns 104. The laser can be a YAG laser (for example at a wavelength of 1064 nm), a blue laser, a UV laser, etc. It is also possible to apply the beam at a pulse frequency of between 1 kHz and 100 kHz, although other configurations are possible.

The application of the laser beam to form the patterns can be implemented during the personalization phase, to mark a pattern specific to the device, or to the security document which incorporates this device, or even specific to the bearer of the security document ( for example a year of birth).

The manufacture of the device 100 includes the assembly of the first layer 101 with the second layer 103. As an indication, the layer 103 can be formed by deposition on the first layer 101 (on the face opposite that comprising the microlenses), or it can be assembled by gluing or in a hot stamping process.

The formation of the microlenses can be carried out before or after the assembly, and this is also the case for the formation of the patterns 104.

Preferably, the microlenses are formed after having formed the patterns, which will facilitate the alignment of the microlenses with respect to the patterns 104.

Figure IB shows the device 100 of figure IA according to a sectional view in a plane which passes through the patterns 104. In this figure, we can see the distance L1, due here to the thickness of the first layer 101, which spaces the microlenses 102 from the second layer 103. Here, the distance L1 is chosen to be greater than the focal length of all the microlenses (which are all identical). This configuration causes each microlens 102 to project an enlarged image of the pattern 104 associated with it.

For example, the distance L1 can be between 200 and 1000 micrometers, which allows the integration of the device 100 in a security document.

The device 100 is here transparent, except for the non-perforated portions of the second layer 103.

After being assembled, the device 100 comprises a first face F1, on the side of the microlenses, and a second face F2, on the side of the second layer 103. When the device is used, the second face F2 is illuminated, so that a image is projected from the Fl face side. Here, the lighting is performed by a lighting device of the smartphone type 1000, equipped with a flash 1001.

In the present description, when we speak of illuminating, this means providing a light flux greater than the ambient light intensity to obtain an image by projection. As can be seen, the ambient light intensity can vary, but those skilled in the art will be able to choose which light source is capable of causing the enlarged projected image to appear.

The enlarged projected image IMG appears on the surface S (spaced from the device 100 by a distance L2 that the person skilled in the art will know how to determine). It is visible from the front in figure IC. This is a single "A" having dimensions of the order of ten centimeters. This “A” is obtained by combining, and more precisely here by superimposing, the projections of the patterns 104 by the different microlenses.

Here, the flash 1001 produces a luminous flux F, which is divided between all the pairs formed by the patterns 104 and the microlenses 102.

As will be described below with reference to Figures 6 and 7, for identical patterns (or even portions of identical patterns), it is advantageous to ensure that all the light rays which pass through the same point of each pattern and through the center of the microlens associated with the pattern intersect at the same location of the spaced surface S. In fact, this condition makes it possible to have both a sharp image, but also a high luminous flux to obtain the image.

To verify this condition, the position of the patterns within the second layer 103 can be adapted.

Figure 2A is an exploded view of another device 100'. In the various figures, the same references designate identical elements.

The device 100′ comprises, analogously to the device 100, a first layer 101 with microlenses 102, and a second layer 103 with patterns 104.

It further comprises an opaque layer 105 comprising a plurality of openings forming diaphragms, this layer 105 being arranged between the first and the second layer, and each opening is associated with a microlens. Here, there are as many apertures as there are microlenses (and patterns). The opaque layer 105 with apertures can be printed on the first layer with black ink, with each aperture centered with respect to the lens associated with it.

The use of the opaque layer 105 and of the diagrams makes it possible to limit the propagation of light rays which have passed a pattern towards a microlens associated with another pattern. This makes it possible to properly control the angle in which the rays passed through a pattern which arrive on a microlens will be comprised.

FIG. 2B shows the use of device 100', to obtain an image IMG' visible in FIG. 2C, which has the same shape as the image IMG in FIG. IC, but which can be sharper due to the presence of the opaque layer 105.

Figure 3A is an exploded view of another device 100".

Device 100" comprises, similarly to device 100, a first layer 101 with microlenses 102, and a second layer 103 with patterns 104.

It further comprises a third layer 107 comprising a plurality of colored filters, here filters 108 of a first color, and filters 108' of a second color. Here, there are as many colored filters as there are microlenses (and patterns).

The third layer 107 can be printed.

In the device 100", all the patterns are not identical. In fact, the patterns associated with filters of the first color are all identical and are designated by the reference 104 (these are patterns in "A"), and the patterns associated with filters of the second color are all identical and are designated by the reference 104' (these are “B” patterns).

It is possible to design third layers with more than two colors, and in particular RGB (red-green-blue) matrices, with identical patterns for the red filters, identical patterns for the green filters, and identical patterns for the filters blue.

FIG. 3B shows the use of the device 100″ to obtain an image IMG″ visible in FIG. 3C. Due to the presence of the filters, a combination of patterns and colors is obtained, which makes it possible to form a more complex image: the superposition of an "A" of the first color and a "B" of the second color.

Figures 4A to 4B show a device 100'" and its use. This device 100'" differs from the device 100" of Figures 3A to 3B in that its second layer 103 comprises all identical patterns 104 (all of type "A" ).

On the IMG"' image, we see an enlarged "A" appear but of a color which is the additive combination of the first and the second color.

FIG. 5 shows a device 100"" comprising a first layer 101, a second layer of metal 103, and a layer 120 assembled against the layer of metal 103, opposite the first layer. The layer 120 is transparent, but it has a rough face at the level of the second face F2 of the device. This roughness will homogenize the luminous flux which passes through the patterns of the metal layer 103 by a diffusion effect. Any rough pattern can be used.

FIG. 6 shows a device 100'"" comprising a first layer 101, a second layer of metal 103, and a layer 130 assembled against the layer of metal 103, opposite the first layer. Layer 130 is transparent, and it is analogous to first layer 101 in that it comprises microlenses 131 which act as condensers, and each cooperate with a microlens 102. Obtaining microlenses 131 is analogous to obtaining microlenses 102. The microlenses 131 increase the intensity of the light flux which passes through the patterns.

Figure 7 shows a security document 200 which comprises a security device according to another example, which comprises a first layer 201, with microlenses 202, and a second layer of metal 203 with perforated patterns 204.

The first layer 201 differs from the first layer 101 described above in that the microlenses are arranged in a hexagonal pattern (a hexagonal tiling). This arrangement makes it possible to increase the number of microlenses on a given surface. Patterns 204 are therefore also arranged in a substantially hexagonal pattern.

The document 200 also comprises a first transparent protective layer 210, assembled on the side of the microlenses, and a second transparent protective layer 211, assembled on the side of the second layer 203, so that the first layer and the second layer are buried between these transparent layers that protect them. Here, document 200 also has a support SUP, in which an FNE window has been formed. The first layer 201 and the second layer 203 extend within this FNE window.

The use of transparent layers and of the window guarantee a good passage of light and therefore a good formation of the enlarged projected image.

The security document has been personalized here, it comprises information 212 specific to the bearer of the document marked on a surface.

Figure 8 shows the path of rays which have passed through the same point of identical patterns.

More specifically, the figure shows lenses 102 similar to those described above, patterns 104 represented by segments, and a luminous flux F which illuminates the patterns.

For each pattern, we have traced the light ray R which will pass through the center of the pattern and through the center of the microlens associated with this pattern (note that for reasons of simplicity, this is not visible in the figure) . All the rays R intersect at the same location E on the surface S (when the latter is at the distance L2 from the device).

To obtain this result, the patterns are offset, in the plane of the metal layer, with respect to their associated microlens.

This shift can be determined so that it is greater for the patterns furthest from the center of the array of microlenses (projected into the plane of the patterns).

In fact, for two identical patterns (or even for portions of identical patterns), a pattern further from the center (of the array of microlenses) will have a greater offset than a pattern closer to the center. It will be noted that an analytical calculation can provide these shifts.

In the figure, two axes A1 and A2 of two microlenses have been shown, these axes passing through the respective centers of the lenses.

The pattern associated with the lens with axis Al is substantially centered on the axis Al: there is no shift to apply for this pattern which is already well positioned.

The pattern associated with the lens of axis A2 is offset by an offset Ap in the plane of the metal layer so that the center of the pattern is placed so that the ray R which passes through the center of the pattern and through the center of the lens will arrive at location E. FIG. 9 shows in more detail the path of the rays and the offsets, for two microlenses 102A and 102B of the same array of microlenses, and two identical patterns 104A and 104B in the form of an A. It is sought to make the rays which pass through the same points of the patterns on the surface S, at a location E.

Lens 102A has an axis AA which does not coincide with the center CA of pattern 104A (which is shown in perspective). Here the center is offset by an offset pA which is determined as a function of the position of the lens 102A in the array of microlenses, in a manner known per se so that the rays coincide as explained above (an analytical calculation can provide these shifts).

Similarly, lens 102B has an axis AB that does not coincide with the center CB of pattern 104B (which is shown in perspective). Here the center is offset by an offset λpB which is determined as a function of the position of the lens 102B in the array of microlenses, in a manner known per se so that the rays coincide as explained above.

We consider here the point located in the inner corner of the upper triangle of the "A". For this point P1A within the pattern 104A, there is a ray RA which passes through this point, the center of the associated microlens 102A, and the location E. For the point PIB within the pattern 104B, there is a ray RB which passes through this point, the center of the associated microlens 102B, and location E. The rays RA and RB intersect at location E.

Figure 10 shows the offsets for an entire array of microlenses with all identical patterns (here in the shape of an “A”).

In this figure, it can be seen that the offsets are greater when moving away from the center of the array of microlenses.

A person skilled in the art will understand that the embodiments and variants described above only constitute non-limiting examples of implementation of the invention. In particular, the person skilled in the art may consider any adaptation or combination of the embodiments and variants described above, in order to meet a very specific need in accordance with the claims presented below.

Claims

[Claim 1] Security device usable to generate a projected image (IMG, IMG"'") enlarged on a surface (S) spaced a given distance (L2) from the device when the device has a first face (F1) placed facing the spaced surface and when a second face (F2) of the device opposite the first face is illuminated, the device comprising, from the first face towards the second face:

- a first layer (101) comprising an array of microlenses (102), and

- a second layer of metal (103) arranged at a distance (L1) from the first layer which is greater than the focal length of each microlens of the array of microlenses, in which the second layer of metal comprises a plurality of patterns (104, 1049, each pattern being formed by one or more perforations in the metal layer (103), each pattern of the plurality of patterns being further associated with a microlens of the array of microlenses, so that when the second side of the document is illuminated , the magnified projected image is formed on the spaced surface by the combination of the projections of each pattern by their associated microlens, wherein the second metal layer includes a first pattern (104A) and a second pattern (104B) both comprising a portion of an identical pattern, and in which the first pattern and the second pattern are placed with respect to their respective associated microlenses (102A, 102B) so that: a light ray (RA) passing through a point (P1A) of the portion of identical pattern of the first pattern and the center of the microlens associated with the first pattern, and a light ray (RB) passing through the same point (PIB) of the portion of identical pattern of the second pattern and the center of the microlens associated with the second pattern, intersect at the same location (E) of the spaced surface at the given distance.

[Claim 2] Device according to claim 1, wherein said one or more perforations of each pattern of the second layer of metal are obtained by application of a laser beam.

[Claim 3] Apparatus according to claim 1 or 2, wherein all of the plurality of patterns have a maximum dimension which is smaller than the distance between the centers of two adjacent microlenses of the array of microlenses.

[Claim 4] The device of claim 1, wherein the microlens array has a center, and the first pattern is closer to the projection on the second metal layer of that center of the microlens array than the second pattern, and in which the identical portion of the first pattern is arranged within the second layer of metal with a first offset measured between a center of the identical portion of the first pattern and the projection of the center of the microlens associated with the first pattern, and the identical portion of the second pattern is arranged within the second layer of metal with a second offset measured between a center of the identical portion of the first pattern and the projection of the center of the microlens associated with the second pattern, the second offset being greater than the first offset .

[Claim 5] Apparatus according to any one of claims 1 to

4, in which all the patterns of the plurality of patterns are identical, and in which all the light rays which pass through a same point of each pattern and through the center of the microlens associated with the pattern intersect at a same location on the surface spaced out.

[Claim 6] Apparatus according to any one of claims 1 to

5, comprising, between the first layer and the second layer, a third layer (107) comprising a plurality of color filters (108, 108'), in which each color filter is associated with a microlens.

[Claim 7] Apparatus according to claim 6, wherein the plurality of color filters includes a plurality of filters of a first color (108) and a plurality of filters of a second color (1089, and in which the patterns (104) associated with color filters of the first color are all identical, and the patterns (104') associated with color filters of the second color are all the same.

[Claim 8] Apparatus according to claim 6 or 7, wherein the plurality of color filters includes a plurality of red filters, a plurality of blue filters, and a plurality of green filters, and wherein the patterns associated with the red filters are all identical, the patterns associated with the green filters are all identical, and the patterns associated with the blue filters are all identical.

[Claim 9] Apparatus according to any one of claims 1 to

8, further comprising an opaque layer (105) comprising a plurality of apertures (106) forming diaphragms arranged between the first and the second layer, in which each aperture is associated with a microlens.

[Claim 10] Apparatus according to any one of claims 1 to

9, further comprising, at the level of the second face, a surface having a roughness with a parameter Ra of between 0.5 μm and 10 μm, or a set of condensers being microlenses, each condenser of the set of condensers cooperating with a microlens associated with the condenser and which is specific to it.

[Claim 11] Apparatus according to any one of claims 1 to

10, wherein the first layer and the second layer are buried between two transparent layers (210, 211).

[Claim 12] Apparatus according to any one of claims 1 to

11, in which the first layer and the second layer extend at least within a transparent window (FNE) of a support (SUP) of the device.

[Claim 13] Apparatus according to any one of claims 1 to

12, wherein the microlenses (202) of the microlens array are arranged in a hexagonal pattern. 22

[Claim 14] Security document comprising a device according to any one of claims 1 to 13, further comprising a marking (212) of at least one item of information specific to the bearer of the document.

[Claim 15] Method of manufacturing a security device which can be used to generate a projected image (IMG, ..., IMG""') enlarged on a surface (S) spaced by a given distance (L2) from the device when the device has a first face (F1) placed facing the spaced surface and when a second face (F2) of the device opposite the first face is illuminated, the method comprising: obtaining a first layer (101) comprising an array of microlenses (102), and an assembly of the first layer with a second layer of metal (103) at a distance (L1) from the first layer which is greater than the focal length of each microlens of the array of microlenses, of so that the first layer is on the side of the first face and the second layer on the side of the second face, a formation, in the second layer of metal, of a plurality of patterns (104, 1049, each pattern being formed by a or more perforations in the metal layer, each pattern of the plurality of patterns being further associated with a microlens of the array of microlenses, so that when the second side of the document is illuminated, the enlarged projected image is formed on the surface spaced apart by the combination of the projections of each pattern by their associated microlens, in which the second layer of metal comprises a first pattern (104A) and a second pattern (104B) both comprising a portion of an identical pattern, and in which the first pattern and the second pattern are placed relative to their respective associated microlenses (102A, 102B) such that: a light ray (RA) passing through a point (P1A) of the identical pattern portion of the first pattern and the center of the microlens associated with the first pattern, and a light ray (RB) passing through the same point (PIB) of the portion of 23 identical pattern of the second pattern and the center of the microlens associated with the second pattern, intersect at the same location (E) of the spaced surface at the given distance.

[Claim 16] A method according to claim 15, further comprising preforming the microlenses by applying a laser beam.

[Claim 17] A method according to claim 15 or 16, wherein the perforation of the second layer of metal is carried out by application of a laser beam.

[Claim 18] A method of using a security device according to any one of claims 1 to 13 or a security document according to claim 14, to generate an enlarged projected image on a surface spaced a given distance from the device, in which the first face of the device is placed facing the spaced surface (S) and the second face of the device is illuminated.

[Claim 19] A system configured to implement the method according to claim 18, comprising a security device according to any one of claims 1 to 14 or a security document according to claim 15, an illumination device (1000, 1001) and a surface (S) arranged so that when a security device or a security document is between the lighting device and the surface, with its second face illuminated by the lighting device, being spaced the surface by the given distance, the magnified projected image appears on the surface.