FR3130689A1 - Security device usable to generate an enlarged projected image using microlenses and a perforated metal layer - Google Patents

Abstract

A security device operable to generate an enlarged projected image using microlenses and a perforated metal layer A security device operable to generate an enlarged projected image on a surface spaced from the device when the device has a first face positioned facing 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 layer of metal (103) arranged at a distance of the first layer which is greater than the focal length of each microlens, wherein the second metal layer has a plurality of patterns (104), formed by one or more perforations in the metal layer (103), each pattern of the plurality pattern being associated with a microlens, 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. Figure for abstract: Fig. 1A

Description

Security device usable to generate an enlarged projected image using microlenses and a perforated metal layer

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

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

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 imagined, 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/treat.

In particular, if the documents appear on a video feed, 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 appearing in a video stream are currently not authenticated in a satisfactory manner.

There are other situations in which observation is not always satisfactory for authentication to be certain, in particular when the time dedicated to authentication is limited.

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

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 distance of each microlens of the array of microlenses,

wherein the second layer of metal comprises a plurality of patterns, each pattern being formed by one or more perforations of the layer of metal, each pattern of the plurality of patterns being further associated with a microlens of the array of microlenses (each pattern is substantially facing a microlens), 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.

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 usable for the authentication of the device or of a document which includes 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 that 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 wherein the first pattern and the second pattern are placed relative to their respective associated microlenses such 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 on the surface spaced 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, we obtain a superposition of the projections in the enlarged projected image, and therefore an image obtained by a greater luminous flux, which facilitates its observation.

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).

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.

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 an offset between the projection of the center of this first microlens and the center of the pattern associated with the first microlens noted ,
• 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 ,
• …
• 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 .

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

With the distance between the second layer of metal and the first layer (either the microlenses, the given distance (between the spaced surface and the device), the "pitch" (the gap or the period between the microlenses) and 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 that 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 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. The 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

an assembly of 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 that 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.

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate examples of embodiments without any limiting character. In the figures:

[Fig. 1A-1C] The represents a safety device according to a first example, the shows its use, and the shows the resulting projected image;

[Fig. 2A-2C] The represents a safety device according to a second example, the shows its use, and the shows the resulting projected image;

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

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

There represents a device according to a fifth example;

There represents a device according to a sixth example;

There represents a device according to a seventh example;

There shows the paths of light rays;

There more precisely shows two paths of light rays; And

There shows pattern offset from microlenses.

Claims (20)

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 opposite the spaced surface and when a second face (F2) of the document opposite the first face is illuminated, the document 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 distance of each microlens of the array of microlenses,
wherein the second layer of metal comprises a plurality of patterns (104, 104'), each pattern being formed by one or more perforations of the layer of metal (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. Device according to Claim 1, in which the said one or more perforations of each pattern of the second layer of metal are obtained by application of a laser beam. Device according to claim 1 or 2, in which 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. Device according to Claim 1 or 2, in which the second metal layer comprises a first pattern (104A) and a second pattern (104B) both comprising an identical pattern portion, 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 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 (P1B) 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 (E) of the spaced surface at the given distance. Device according to claim 4, in which 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 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. Device according to any one of Claims 1 to 5, 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 the same spaced surface location. Device according to any one of Claims 1 to 6, 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. Apparatus according to claim 7, wherein the plurality of color filters comprises a plurality of filters of a first color (108) and a plurality of filters of a second color (108'), and wherein the patterns (104) associated to color filters of the first color are all identical, and the patterns (104') associated with color filters of the second color are all identical. Device according to Claim 7 or 8, in which 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 green filters are all identical, and the patterns associated with the blue filters are all identical. Device according to any one of claims 1 to 9, further comprising an opaque layer (105) comprising a plurality of openings (106) forming diaphragms arranged between the first and the second layer, in which each opening is associated with a microlens. Device according to any one of Claims 1 to 10, 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, each condenser of the condenser assembly cooperating with a microlens associated with the condenser and which is specific to it. Device according to any one of claims 1 to 11, in which the first layer and the second layer are buried between two transparent layers (210, 211). Device according to any one of Claims 1 to 12, in which the first layer and the second layer extend at least within a transparent window (FNE) of a support (SUP). Apparatus according to any of claims 1 to 13, wherein the microlenses (202) of the array of microlenses are arranged in a hexagonal pattern. Security document comprising a device according to any one of claims 1 to 14, further comprising a marking (212) of at least one item of information specific to the bearer of the document. Method of manufacturing a security device that 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 opposite the spaced surface and when a second face (F2) of the document 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, 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 (104, 104'), 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 array of microlenses, such 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. A method according to claim 16, further comprising preforming the microlenses by applying a laser beam. Method according to claim 16 or 17, wherein the perforation of the second layer of metal is carried out by application of a laser beam. A method of using a security device according to any one of claims 1 to 14 or a security document according to claim 15, to generate an enlarged projected image on a surface spaced a given distance from the device, wherein the first face of the device is placed facing the spaced surface (S) and the second face of the device is illuminated. System configured to implement the method according to claim 19, comprising a lighting device (1000, 1001) and a surface (S) arranged so that when a security device or a security document is between the device of illumination and the surface, with its second face illuminated by the illumination device, being spaced from the surface by the given distance, the enlarged projected image appears on the surface.