A method for manufacturing a security device comprising at least one first image visible from a first angle and a second image visible from a second angle, a security device obtained by the method, and an identity document bearing the security device.

Abstract

A method for manufacturing a security device (1) comprising: A step of providing a transparent window (2) having a front face and a rear face, and a microlens array formed on the front face; A step of defining an overall image having at least two interlaced frames, the first of the two frames being configured to represent a first image visible to an observer from a first viewing angle through the array, and the second of the two frames being configured to represent a second image visible to the observer from a second viewing angle through the array; A step of arranging the overall image with respect to the array; and A step of etching the overall image into the window through the rear face. A security device obtained by such a method and an identity document comprising such a device. Figure for the abstract: Fig. 4

Description

Title of the invention: Method for manufacturing a security device comprising at least a first image visible from a first angle and a second image visible from a second angle, security device obtained by the method and identity document comprising the security device

[0001] The invention relates to a method for manufacturing a security device, in particular a security device comprising a window provided with a lenticular network through which at least one image is visible according to a predefined viewing angle.

[0002] It also relates to a security device obtained by such a method, as well as an identity document comprising such a device.

[0003] The window of such a security device may constitute only a part of the security device, or the security device may consist entirely of such a window.

[0004] Customizing a lenticular array window to achieve a three-dimensional (3D) effect or animation is typically done through one side of the lenticular array lenses, and traditionally by laser engraving through the lenticular array.

[0005] However, the need to customize more and more images is growing, for example to create CLI / MI images (involving 2 or 3 images), SLI (generally 4 images), Lasink 3D (preferably 7 images), or even augmented Lasink 3D (for example 14 images).

[0006] Each image is for example engraved at its own angle, generally using a laser beam.

[0007] For each angle, the window is tilted at that angle relative to the laser beam to engrave the corresponding image.

[0008] Each image requires several tenths of a second to be engraved.

[0009] Thus, for example, to engrave fifteen images, therefore from fifteen different angles, fifteen movements are required, each taking about half a second and after each movement, several tenths of a second to engrave the corresponding image.

[0010] For a window considered, there is therefore a compromise to be made between the desired quality of visual effects and the time taken to produce all the desired images, which has an impact on the cost of customization.

[0011] For example, for a 3D Lasink image which preferably comprises seven images, for an angular amplitude of approximately -6° to +6°, it may be chosen to restrict the number of images to the four images of a classic SLI, which, in fact, reduces the quality of the visual rendering.

[0012] Another disadvantage of engraving through lenses involving tilting the window relative to the laser is that a laser, which is equipped with a galvanometer head provided with an F-theta lens to deflect the laser beam and thus reach different points in a marking field, is designed to focus the laser beam along a plane perpendicular to the axis of symmetry of the F-theta lens of the galvanometer head. However, when the surface of the window is no longer perpendicular to this axis, focusing is no longer ensured and the images may therefore lose sharpness.

[0013] The present invention aims to remedy, at least in part, the aforementioned drawbacks, while also leading to other advantages.

[0014] To this end, a first aspect proposes a method for manufacturing a security device comprising at least a first image visible to an observer at a first observation angle, and a second image visible to the observer at a second observation angle, the second observation angle being different from the first observation angle, the method comprising the following steps: - A step of providing a window which is transparent to at least a portion of visible light, the window having a front face and a back face, the back face being parallel to the front face, and the window having a microlens array formed on the front face; - A step of defining a global image comprising at least two interlaced frames, a first of the two frames being configured to represent the first image visible to the observer according to the first observation angle through the microlens array, and a second of the two frames being configured to represent the second image visible to the observer according to the second observation angle through the microlens array, once engraved; - A step of arranging the global image in relation to the microlens array; and - A step of engraving the overall image in the window through the rear face by a laser beam incident on the rear face, the laser forming an engraving point along an optical axis A, the optical axis A forming an angle of incidence a with the rear face of the window.

[0015] The overall engraved image is made up of the multiple frames necessary to produce the desired visual effect, for example to create a 3D effect image or an animation.

[0016] All the necessary frames are therefore engraved in one go, at the same angle of incidence a of the laser beam, by the rear face of the window, i.e. on the side opposite to that of microlenses.

[0017] The overall image therefore comprises an interlacing of at least two frames. Each image that will be observable according to a given observation angle is first compressed by the magnification factor of the microlenses in one direction, then cut into as many bands as there are microlenses. Then all the frames of all the images are interlaced so that this assembled image, i.e. the overall image, covers the entire surface opposite the lenticular zone, i.e. here the rear face of the window.

[0018] The saving in customization time is all the more considerable as the number of frames is large.

[0019] This facilitates the realization of sophisticated effects requiring a large number of images with large angular observation amplitudes.

[0020] Indeed, in a method according to the prior art, large amplitudes, by the relative inclination method, are not possible to achieve because one is then too far from the focal plane of the F-theta lens.

[0021] Advantageously, the window is kept perpendicular to the optical axis to ensure the best possible focusing in the engraving plane.

[0022] In an exemplary implementation, the angle of incidence a is between 80° and 100° relative to the rear face of the window, for example equal to 90°.

[0023] An angle of incidence a perpendicular to the rear face makes it possible, for example, to benefit from optimized focusing of the laser beam.

[0024] To do this, a laser engraving device comprises, for example, an F-Theta lens mounted on a galvanometric head, as described below.

[0025] In an exemplary implementation, the step of engraving the overall image is configured to produce the engraving point having a diameter at most equal to one half of a width of a strip of one of the frames of the image.

[0026] The diameter of the engraving point is preferably smaller than in a traditional process because the focusing of the microlenses is no longer used.

[0027] For example, the laser ideally has a sufficiently small spot size to be able to engrave each raster with at least two spots per raster band width. This allows for greater control over the level of engraving than if a single spot covered the width of a raster band because two spots are statistically much less sensitive to disturbances than a single spot. For example, with a 10 pm laser spot to produce 14 rasters with two spots per raster band width, the lenses have, for example, a pitch of 280 pm.

[0028] In an exemplary implementation, the laser is an ultraviolet laser.

[0029] Ultraviolet laser radiation here designates laser radiation with a wavelength less than or equal to 380 nm, for example between 300 nm and 380 nm.

[0030] In an exemplary implementation, the laser is a YAG laser that emits at a wavelength of 1064nm.

[0031] In an exemplary implementation, the laser is a CO2 laser that emits at a wavelength of 10640 nm.

[0032] However, there is a relationship between marking spot size and wavelength. To place a maximum number of frames under a microlens, a UV laser is advantageous because it can produce a smaller spot diameter than that of an infrared laser, for example.

[0033] In an exemplary implementation, the etching step is configured to form the overall image at a distance of less than 200 pm, for example between 0 pm and 200 pm, relative to the rear face.

[0034] In an exemplary implementation, the method comprises a step of frosting the rear face, the frosted rear face having a predefined roughness Ra configured to diffuse at least a portion of visible light.

[0035] A frosted coating made on the side opposite the lenses makes it possible to limit the risk of disturbance of the observation of the image due to a background environment which would be visible when looking through the window, in this case on the side of the microlenses.

[0036] This frosted glass diffuses visible light.

[0037] Visible light here refers to a light spectrum with a wavelength between approximately 380 nm and 780 nm.

[0038] In an exemplary implementation, the frosting step is implemented before the step of etching the overall image in the window, the step of etching the overall image in the window then being implemented through the frosted rear face.

[0039] The personalization made from the back of the window must however retain its precision as much as possible despite the frosting where applicable.

[0040] The frosting is then determined as a function of the engraving wavelength of the laser beam used, and vice versa.

[0041] For example, in practice, the method may include a step of determining the roughness as a function of the etching radiation.

[0042] Such a step may for example comprise sub-steps as follows: - A Nyquist test step, in which a Nyquist test is implemented, with a black / white alternation of bars according to a series of bars whose width decreases, for example down to approximately 10 pm; the bars being etched from the back of a window; the black / white alternation respecting a predefined visibility criterion; - A step of verifying that the visible spectrum is diffused according to a predefined diffusion criterion, by observing a scene through the frosted glass.

[0043] The scene must appear with a blur according to a predefined blur criterion, and the blur can be quantified by placing RGB Nyquist tests at a predefined distance from the frosted glass, and verifying that between a configuration without frosted glass and a configuration with frosted glass, several harmonics of blur are lost.

[0044] For example, without frosting, a pair of bars is observed while with frosting, the pair is no longer visible, nor a pair of double steps, nor even a pair of triple steps.

[0045] In an exemplary implementation, the step of frosting the rear face is configured to provide the roughness Ra of the frosted rear face at a value between 360 nm and 500 nm, for example at least about 380 nm and / or at most about 450 nm.

[0046] A minimum roughness is for example 360 ​​nm so that the roughness is greater than the wavelength of the available UV lasers, namely 355 nm (approximately a third of 1064 nm because in practice, UV lasers are produced from a frequency tripler crystal).

[0047] The roughness can however be at least equal to 380 nm (start of the visible spectrum).

[0048] If the back surface is not frosted, it is possible to engrave with a laser of any wavelength.

[0049] If, on the other hand, the surface is frosted (in particular to avoid being bothered by a background when observing the image in transmitted light) then the roughness diffuses visible light (wavelengths between approximately 380 nm and 780 nm). Any higher wavelength, and a fortiori all those in the infrared range, will also be diffused.

[0050] Therefore, UV laser radiation will then not be scattered.

[0051] In an exemplary implementation, the step of arranging the global image relative to the microlens array comprises: - A step of arranging a lighting source on one side of the window and a step of arranging a camera on the same side or on an opposite side of the window; - A step of illuminating the microlens array by the lighting source; - A stage of reception, by the camera, of a light beam having interfered with the window, i.e. having passed through it at least in part or being reflected at least in part by the window, depending on the arrangement of the camera and the lighting source relative to the window; - A step of determining a layout of the microlens array from the light beam received by the camera; and - A step of redefining the global image in relation to the determined arrangement of the microlens network.

[0052] In an exemplary implementation, the lighting source and the camera may for example be arranged on the same side of the window, for example on the microlens side. or back side.

[0053] Where appropriate, micro-singularities are preferably introduced into the lenticular network. The micro-singularities comprise, for example, small flats. Since these micro-singularities are produced at the same time as the lenticular network, their actual positions, i.e. their deviations from their theoretical positions, make it possible to deduce that at these locations, the lenticular network is displaced by the same deviations. An interpolation between these points makes it possible to determine where the actual lenticular network is located.

[0054] In another exemplary implementation, the lighting source and the camera can be arranged on either side of the window.

[0055] For example, the step of arranging the global image relative to the microlens array then comprises: - A step of arranging an illumination source on a front side of the window and a step of arranging a camera on a rear side of the window, the microlens array formed on the front face of the window being arranged between the illumination source and the rear face, and the rear face being arranged between the microlens array formed on the front face and the camera; - A step of illuminating the microlens array by the lighting source; - A stage of reception, by the camera, of a light beam having crossed the window; - A step of determining a layout of the microlens array from the light beam received by the camera; and - A step of redefining the global image in relation to the arrangement of the microlens network.

[0056] The precise arrangement of each real microlens, i.e. its position and its shape, in particular its width, can thus be identified and makes it possible to adapt each frame, or even each frame band, to each microlens.

[0057] The tolerance of the arrangement of the microlenses on the front face is severe (of the order of a micrometer) and a pitch of the microlenses can vary by a few microns.

[0058] The adjustment of the frames relative to the microlenses is preferably as precise as possible, i.e. in practice from 1 pm to 3 pm.

[0059] The best possible adaptation of the frames to the reality of the microlenses, for each window, makes it possible to promote better image quality, i.e. better rendering.

[0060] In an exemplary implementation, the illumination source provides a collimated spectrum.

[0061] In one exemplary implementation, the illumination source provides a spectrum of ultraviolet radiation.

[0062] In an exemplary implementation, the lighting source comprises a UV diode.

[0063] In an exemplary implementation, the camera comprises a camera sensitive to the UV radiation.

[0064] In an exemplary implementation, the method may comprise a step of creating at least one singular point configured to serve as a reference for the global image.

[0065] For example, the at least one singular point can be created by means of a rolling plate which, at certain locations in the microlens array, will impose a singularity like a micro-flat recognizable in image processing. Thus, these marks will serve as reference points from which the exact position of the lenses will be deduced.

[0066] It may be of interest that the personalization, that is to say the engraving of the overall image in the window, occurs when the security device is integrated into at least one part of an identity document.

[0067] At least one part of an identity document may, for example, consist of several layers assembled together by lamination.

[0068] For example, at least one of the layers may comprise the security device including the window, before etching the overall image.

[0069] In a method according to an embodiment of the invention, a single image is calculated, i.e. the global image which is made up of all the frames necessary to produce the desired effect, for example an animation or a 3D effect, said frames being interlaced.

[0070] This image can possibly be slightly geometrically modified to be adapted as best as possible to the reality of each microlens, and the personalization can thus be done in a single laser shot without the need to tilt the window relative to the incident laser beam to carry out the engraving of each image.

[0071] A method according to the invention makes it possible to provide personalized optical technologies with many images, and therefore more sophisticated effects, without requiring more operations.

[0072] According to an exemplary implementation, the step of defining the global image further includes at least a third frame and a fourth frame in the global image, the third frame being configured to represent a third image visible to the observer at a third viewing angle through the microlens array, and the fourth frame being configured to represent a fourth image visible to the observer at a fourth viewing angle through the microlens array, the third angle being different from the second angle and the first angle, and the fourth angle being different from the third angle, the second angle and the first angle.

[0073] Also provided, according to a second aspect, is a security device obtained by a method as described above.

[0074] For example, the device comprises: - a window which is transparent to at least a portion of visible light, the window having a front face and a back face, the back face being parallel to the front face, and the window having a microlens array formed on the front face, and - an overall image, engraved in the window, comprising at least two interlaced frames, a first of the two frames representing a first image visible to an observer at a first observation angle through the microlens array, and a second of the two frames representing a second image visible to the observer at a second observation angle through the microlens array, the second observation angle being different from the first observation angle.

[0075] In an exemplary embodiment, the rear face is frosted and has a predefined roughness (Ra) configured to diffuse at least a portion of visible light.

[0076] In an exemplary embodiment, the roughness (Ra) of the frosted rear face has a value between approximately 360 nm and 500 nm.

[0077] In an exemplary embodiment, the first image and the second image form a first stereoscopic image appearing to the observer in an observation direction orthogonal to the window as a first three-dimensional image.

[0078] In an exemplary embodiment, the image further includes at least a third frame and a fourth frame, the third frame representing a third image visible to the observer at a third viewing angle through the microlens array, and the fourth frame representing a fourth image visible to the observer at a fourth viewing angle through the microlens array, the third angle being different from the second angle and the first angle, and the fourth angle being different from the third angle, the second angle, and the first angle.

[0079] In an exemplary embodiment, the third image and the fourth image form a second stereoscopic image appearing to the observer in a direction of observation non-orthogonal to the window as a second three-dimensional image, and the second stereoscopic image being different from the first stereoscopic image.

[0080] For example, the second stereoscopic image represents the same object as the first stereoscopic image but seen from a different angle.

[0081] For example, the second stereoscopic image represents the same object as the first stereoscopic image, seen from the same angle, but one of the first and second stereoscopic images is in color, the other being in grayscale.

[0082] In an exemplary embodiment, the overall image is formed at a distance less than at 200 pm, for example between 0 pm and 200 pm, relative to the rear face.

[0083] Also proposed, according to a third aspect, is an identity document comprising a security device as described above.

[0084] For example, the identity document is an identity card, a passport, a bank card, an identification card (access badge type) or even a loyalty card, or other.

[0085] The invention, according to an exemplary embodiment, will be well understood and its advantages will appear better on reading the detailed description which follows, given for information purposes and in no way limiting, with reference to the appended drawings in which:

[0086] [Fig.l] represents a security device window provided with a microlens array on the front face;

[0087] [Fig.2] represents six frames, forming six images, serving as a basis for the definition of a global image;

[0088] [Fig.3] represents the device of [Fig.l] comprising a frosted surface formed on the rear face;

[0089] [Fig.4] represents the device of figures 1 or 3 in the window of which an overall image is engraved on the rear face;

[0090] [Fig.5] represents a block diagram schematizing a method according to an embodiment of the invention; and

[0091] [Fig.6] shows an identity document comprising a security device according to an exemplary embodiment.

[0092] The invention according to an exemplary embodiment aims to provide a method for manufacturing a security device comprising at least a first image visible to an observer according to a first observation angle, and a second image visible to the observer according to a second observation angle, the second observation angle being different from the first observation angle.

[0093] For this, the method, according to an exemplary implementation, comprises a step E01 of providing a window 2 of a security device 1, for example as shown diagrammatically in [Fig.l].

[0094] [Fig.l] shows a window 2 of a security device 1 according to an exemplary embodiment.

[0095] Window 2 is transparent to at least a portion of visible light.

[0096] In other words, it transmits at least 10%, or even 50%, or even 90%, or even 95% of a visible light spectrum passing through it.

[0097] Visible light here refers to a light spectrum with a wavelength between approximately 380 nm and 780 nm.

[0098] The window 2 comprises a front face 3 and a rear face 4 which are substantially parallel to each other and define between them a thickness denoted “e”.

[0099] The window 2 further comprises a microlens array 5, also referred to as a lenticular array, which is formed, by definition here, on the front face 3.

[0100] The microlenses 5 are all shown here as identical. They are, for example, cylindrical or spherical.

[0101] In the example representation of [Fig.l], each microlens 5 has a width “p”, also designated “p”.

[0102] This width is theoretically the same for all microlenses in a microlens array. However, in practice, this width may vary, within a tolerance zone, from one lens to another.

[0103] In order to produce a visual effect, for example a 3D image or an animation, at least two images are formed under the microlens array.

[0104] Each image is formed by a frame comprising a series of parallel bands, and one of the bands of the frame of each image is formed under each of the microlenses.

[0105] As illustrated in [Fig.4] for example, a band 6a of a frame of a first image and a band 6b of a frame of a second image are etched under the same microlens.

[0106] Each of the frames is thus configured to represent an image visible to an observer according to an observation angle, which is specific to the corresponding image, through the microlens array.

[0107] For purely illustrative purposes, [Fig.2] presents a complex case in which a visual effect is created from six images 60 (referenced 60a to 60f) making it possible, for example here, to create a 3D portrait in which the head of the portrait rotates according to an observation angle.

[0108] In the prior art, regardless of the number of images, each image is generally etched into the window through the microlens array at an angle specific to it, generally by means of a laser beam.

[0109] For each angle, the window is tilted at that angle relative to the laser beam to engrave the corresponding image.

[0110] Each image requires several tenths of a second to be engraved.

[0111] The invention according to an exemplary embodiment proposes in particular a step E02 of defining a global image comprising all of the frames to be engraved which are interlaced.

[0112] In this example, the overall image would comprise the six interlaced fields.

[0113] Once the overall image has been defined, the method according to an exemplary implementation can then comprise: - A step E04 of arranging the global image in relation to the microlens array; and - A step E05 of engraving the global image in the window.

[0114] In an exemplary implementation, illustrated for example [Fig.3], step E04 of arranging the global image with respect to the microlens array comprises for example sub-steps as follows: - A step of arranging a lighting source 7 on a front side of the window 2 and a step of arranging a camera 8 on a rear side of the window 2, the microlens array 5 formed on the front face 3 of the window 2 being arranged between the lighting source 7 and the rear face 4, and the rear face 4 being arranged between the microlens array 5 formed on the front face 3 and the camera 8; - A step of illuminating the microlens array 5 by the lighting source 7; - A step of reception, by the camera 8, of a light beam having passed through the window 2; - A step of determining an arrangement of the microlens array 5 from the light beam received by the camera 8; and - A step of redefining the global image in relation to the arrangement of the microlens network 5.

[0115] According to an alternative not shown, the camera and the lighting source can however be arranged on the same side of the window, and the processing of the image received by the camera is adapted.

[0116] The precise arrangement of each real microlens, i.e. its position and its shape, in particular its width p, can thus be identified and makes it possible to adapt each frame, or even each frame band, to each microlens 5.

[0117] In an exemplary implementation, the lighting source 7 provides a collimated ultraviolet radiation spectrum.

[0118] In an exemplary implementation, the camera 8 comprises a camera sensitive to UV radiation.

[0119] According to one embodiment of the invention, as illustrated [Fig.4] in particular, the etching step E05 is implemented through the rear face 4, here by a laser beam 9 with ultraviolet radiation, incident on the rear face 4.

[0120] The laser 9 forms for example an engraving point 10 along an optical axis A.

[0121] According to an interesting characteristic, the engraving point 10 has a diameter at most equal to half of a width of a strip of one of the frames of the image.

[0122] The optical axis A forms an angle of incidence a with the rear face 4 of the window 2.

[0123] The angle of incidence a is preferably between 80° and 100° relative to the rear face 4 of window 2. In this implementation example, the angle of incidence a is equal to 90°. In other words, the laser engraves perpendicular to the rear face 4. This has the advantage of obtaining optimized focusing throughout the marking plane.

[0124] In the present implementation example, [Fig.3] illustrates another interesting option.

[0125] Indeed, in [Fig.3], the rear face 4 also includes a frosted surface 11.

[0126] Such a frosted surface 11 is for example formed during a step E03 of frosting the rear face 4.

[0127] For example, the defined roughness is pre-made on a rolling back plate and is then replicated in the window.

[0128] The frosted rear face then has a predefined roughness Ra to diffuse at least part of the visible light.

[0129] For example, the roughness Ra of the frosted rear face 4 has a value between 360 nm and 500 nm,

[0130] A frosted glass 11 on the rear face 4 allows an observer to see the overall image sufficiently clearly once engraved in the window, limiting the risk of disturbance of the observation of the overall image due to a background environment which would be visible when looking through the window 2.

[0131] This may be the case if the security device is integrated into a passport in which a page following the one in which the security device would be arranged contains information which could interfere visually. Or this may be the case for an identity card or a bank card type card, or any other card, when they are arranged on any support.

[0132] The personalization made from the back of the window must however retain its precision as much as possible despite the frosting.

[0133] The frosting is then possibly determined as a function of the engraving wavelength of the laser beam 9 used, and vice versa.

[0134] For example, the roughness (Ra) has a value of about 400 nm for UV radiation of about 355 nm because such UV radiation will then not be scattered, which allows sufficiently precise engraving of the overall image through the frosted back face.

[0135] For example, in practice, the method may comprise a step of determining the roughness as a function of the etching radiation, for example comprising sub-steps as follows: - A Nyquist test step, in which a Nyquist test is implemented, with a black / white alternation of bars according to a series of bars whose width decreases to approximately 10 pm for example; the bars being engraved from the back of a window; the black / white alternation respecting a predefined visibility criterion; - A step of verifying that the visible spectrum is diffused according to a predefined diffusion criterion, by observing a scene through the frosted glass; the scene must appear with a blur according to a predefined blur criterion, and the blur can be quantified by placing RGB Nyquist tests at a predefined distance from the frosted glass, and by verifying that between a configuration without frosted glass and a configuration with frosted glass, several harmonics of blur are lost.

[0136] For example, without frosting, a pair of bars is observed while with frosting, the pair is no longer visible, nor a pair of double steps, nor even a pair of triple steps.

[0137] In the present implementation example, the frosting step E03 is implemented before the step of engraving the global image in window 2.

[0138] Therefore, the step of engraving the overall image in the window 2 is implemented through the rear face 4 with the frosted glass 11.

[0139] Thus, [Fig.4] illustrates a safety device 1 according to an exemplary embodiment, comprising: - Window 2, the rear face 4 of which is frosted and has a predefined roughness Ra configured to diffuse at least part of the visible light, - The overall image, engraved in window 2, comprising at least two interlaced frames (6a, 6b), but which may comprise all the frames of the images 60 depending on the desired visual effect.

[0140] As illustrated in [Fig.5], the method according to one embodiment of the invention can therefore take place as follows: - Step E01 of providing the window 2 transparent to at least a portion of visible light; - Step E02 of defining a global image comprising at least two interlaced frames, or even 4 frames, or even 6 or 7 frames depending on the desired visual effect, each frame being configured to represent an image visible to the observer according to a particular observation angle through the microlens array 5 once engraved; - Step E03 of frosting the rear face to produce a predefined roughness Ra configured to diffuse at least a portion of visible light; - Step E04 of arranging the overall image in relation to the microlens array; - Step E05 of engraving the overall image in window 2 through the rear face 4 by ultraviolet radiation laser beam, incident on the rear face.

[0141] Steps E03 of frosting and E04 of arrangement of the overall image may possibly be reversed.

[0142] [Fig.6] schematically shows an identity document 100 comprising such a safety device 1 according to an exemplary embodiment.

[0143] Here, the identity document 100 is an identity card, but it could be a passport or a bank card, an identification card (access badge type) or even a loyalty card, or other.

[0144] The identity document 100 comprises a main page comprising, for example, data relating to the holder of the document.

[0145] In the present exemplary embodiment, it comprises the security device 1 which may, for example, comprise a 3D portrait of the holder of the identity document 100.

Claims

Claims

1. A method of manufacturing a security device (1) comprising at least a first image visible to an observer at a first observation angle, and a second image visible to the observer at a second observation angle, the second observation angle being different from the first observation angle, the method comprising the following steps: - A step (E01) of providing a window (2) which is transparent to at least a portion of visible light, the window (2) comprising a front face and a rear face, the rear face being parallel to the front face, and the window (2) comprising a microlens array formed on the front face;- A step (E02) of defining a global image comprising at least two interlaced frames, a first of the two frames being configured to represent the first image visible to the observer according to the first angle of observation through the microlens array, and a second of the two frames being configured to represent the second image visible to the observer according to the second angle of observation through the microlens array; - A step (E04) of arranging the global image relative to the microlens array; and - A step (E05) of engraving the global image in the window (2) through the rear face by a laser beam incident on the rear face, the laser forming an engraving point along an optical axis A, the optical axis A forming an angle of incidence a with the rear face of the window (2).;

2. Method according to claim 1, in which the angle of incidence a is between 80° and 100° relative to the rear face of the window (2), for example equal to 90°.

3. A method according to any one of claims 1 or 2, wherein the step (E05) of engraving the overall image is configured to produce the engraving point having a diameter at most equal to half a width of a band of one of the frames of the image.

4. Method according to any one of claims 1 to 3, comprising a step (E03) of frosting the rear face, the frosted rear face having a predefined roughness Ra configured to diffuse at least a portion of visible light.

5. Method according to claim 4, in which the frosting step (E03) is implemented before the step of engraving the global image in the window (2), the step (E05) of engraving the global image in the window (2) being implemented through the frosted rear face (4).

6. Method according to any one of claims 4 or 5, comprising a step of determining the roughness as a function of the etching radiation, the step of determining the roughness comprising: - A Nyquist test step, in which a Nyquist test is implemented, with a black / white alternation of bars according to a series of bars whose width decreases; the bars being etched from the back of a window; the black / white alternation respecting a predefined visibility criterion; and - A step of verifying that the visible spectrum is diffused according to a predefined diffusion criterion, by observing a scene through the frosted glass.

7. Method according to any one of claims 1 to 6, in which the step (E04) of arranging the overall image with respect to the microlens array comprises: - A step of arranging a lighting source on one side of the window (2) and a step of arranging a camera on the same side or on an opposite side of the window (2); - A step of illuminating the microlens array by the lighting source; - A step of receiving, by the camera, a light beam having interfered with the window (2); - A step of determining a layout of the microlens array from the light beam received by the camera; and - A step of redefining the overall image with respect to the determined layout of the microlens array.

8. The method of any one of claims 1 to 7, wherein the step (E03) of defining the global image further includes at least a third frame and a fourth frame in the global image, the third frame being configured to represent a third image visible to the observer at a third viewing angle through the microlens array, and the fourth frame being configured to represent a fourth image visible to the observer at a fourth viewing angle through the microlens array, the third angle being different from the second angle and the first angle, and the fourth angle being different from the third angle, the second angle and the first angle.

9. A security device (1) obtained by a method according to any one of claims 1 to 8, the device (1) comprising: - a window (2) which is transparent to at least a portion of visible light, the window (2) comprising a front face (3) and a rear face (4), the rear face being parallel to the front face, and the window (2) comprising a microlens array (5) formed on the front face (3), and - an overall image, etched in the window (2), comprising at least two interlaced frames (6a, 6b), a first of the two frames representing a first image visible to an observer at a first viewing angle through the microlens array, and a second of the two frames representing a second image visible to the observer at a second viewing angle through the microlens array, the second viewing angle being different from the first viewing angle.

10. Device according to claim 9, wherein the rear face (4) is frosted and has a predefined roughness (Ra) configured to diffuse at least a portion of visible light.

11. Device according to claim 10, in which the roughness (Ra) of the frosted rear face (4) has a value between 360 nm and 500 nm.

12. Device according to any one of claims 9 to 11, in which the first image and the second image form a first stereoscopic image appearing to the observer in an observation direction orthogonal to the window (2) as a first image in three dimensions.

13. The device of any one of claims 9 to 12, wherein the image further includes at least a third frame and a fourth frame, the third frame representing a third image visible to the observer at a third viewing angle through the microlens array, and the fourth frame representing a fourth image visible to the observer at a fourth viewing angle through the microlens array, the third angle being different from the second angle and the first angle, and the fourth angle being different from the third angle, the second angle, and the first angle.

14. Device according to claim 13, in which the third image and the fourth image form a second stereoscopic image appearing to the observer in a direction of observation non-orthogonal to the window (2) as a second three-dimensional image, and the second stereoscopic image being different from the first stereoscopic image.

15. Identity document (100) comprising a security device (1) according to any one of claims 9 to 14, the identity document being an identity card, a passport, a bank card, an identification card or even a loyalty card, or other.

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