Display element with optical elements arranged on a substrate to produce an image composed of light spots that appears to float above or below the substrate

Description

[0001] The invention relates to a display element comprising a substrate with a surface area in which a plurality of optical elements are arranged. The invention further relates to a data carrier comprising such a display element.

[0002] Data carriers, such as valuables or identification documents, but also other valuables, such as branded goods, are often equipped with security elements for protection, which allow verification of the authenticity of the data carrier and also serve as protection against unauthorized reproduction.

[0003] Particular attention is currently being paid to security elements with three-dimensional-looking images, since these are easily recognizable and verifiable even for laypersons, and cannot be faithfully reproduced using common copying methods.

[0004] Several techniques are known for creating a three-dimensional image impression when viewing flat images with both eyes. Anaglyph images, for example, consist of two superimposed stereoscopic half-images. When viewed with an aid such as red-green glasses or polarizing glasses, the two half-images are separated for each eye.

[0005] Another technique uses lens or mirror raster images consisting of a multi-layered structure with a motif layer and a lens or mirror layer spaced apart from the motif layer. An example of this technique is the 3D moiré magnifier described in publication WO 2009 / 000530 A2. US 7261417 B2 also uses a micromirror array together with a motif layer containing element images positioned at a specific distance from the micromirror array to produce an integrated image.

[0006] Another approach, as described for example in the publication WO 90 / 08338 A1, is to create the motif as a flat relief, whereby the surface of the motif is imitated and / or fragmented in the surface of the image.

[0007] Finally, holograms, holographic stereograms, and hologram-like gratings have long been used for security elements to create a three-dimensional image impression. Light diffraction and interference at the holographic structures and diffraction gratings play a crucial role in this technique.

[0008] In FR 2 943 800 A1, according to a first alternative, an image is also generated by means of a micromirror arrangement and a spaced image element layer, or according to a second alternative, by means of a micromirror arrangement with two different types of micromirrors, spherical micromirrors and pyramidal micromirrors.

[0009] Based on this, the invention aims to create a display element of the type mentioned above that has an attractive visual appearance. For security applications, the display element should also offer a high level of protection against counterfeiting and be easy for laypersons to verify for authenticity.

[0010] This problem is solved by the display element with the features of the main claim. A method for manufacturing such a display element, a data carrier equipped with such a display element, and a display device equipped with such a display element are specified in the dependent claims. Further developments of the invention are the subject of the sub-claims.

[0011] According to the invention, a generic display element comprises a substrate with a surface area in which a plurality of optical elements are arranged. The display element is designed and intended to generate, when illuminated with parallel light, a light spot image consisting of a plurality of light spots that appear to a viewer to be floating above or below the surface area and are arranged in the form of a predetermined motif. For this purpose, the aforementioned optical elements are formed by reflective optical elements, wherein each light spot of the light spot image is assigned at least one reflective optical element, which contributes to the generation of its assigned light spot when the display element is illuminated. The optical elements comprise curved mirrors. Each light spot of the light spot image is assigned a plurality of reflective optical elements.The majority of the associated reflective optical elements are spaced apart and distributed across the surface area. Reflective optical elements assigned to different light spots are nested within each other within the surface area.

[0012] The invention is thus based on the idea of ​​defining a three-dimensional motif consisting of light spots floating above or below the display element. To generate these light spots when illuminated, the display element comprises adjacent or nested sections of mirrors, lenses, or prisms designed to produce floating light reflections within a picture space under suitable illumination. These reflections, taken together, represent the desired three-dimensional motif. The floating light reflections are, in a physical sense, real images or virtual images of the illuminating light sources, as explained in more detail below. The visual effect is particularly good when the display element is illuminated with parallel light, for example, from a distant light source.

[0013] The three-dimensional light spot pattern created by the illumination offers the viewer an unusual and visually appealing three-dimensional image, giving the display element a high degree of attention-grabbing and recognizability. The presence or absence of the effect is easily determined by any user, making the display element readily verifiable. Nevertheless, the mirror arrangement is difficult for a potential counterfeiter to replicate due to the necessary expertise and technology.

[0014] For the sake of brevity, the reflective optical elements will subsequently be referred to simply as "optical elements." However, it is understood that, within the scope of the invention, this always refers to reflective optical elements. The optical elements can be purely reflective, such as a mirror or a micromirror, or both refractive and reflective, such as a lens or microprism with a semitransparent coating. In any case, diffraction and interference effects play no role in the reflective optical elements according to the invention and can always be neglected.

[0015] In a preferred embodiment, the optical elements and the elevation heights of the light spots are designed such that the condition f / d < 5 applies to both the light spots and the associated optical elements, where f denotes the elevation height of a light spot above or below the surface area and d indicates the diameter of the optical elements contributing to this light spot. This ensures that, at a normal viewing distance of approximately 30 cm, the light spots lie within the aperture of the associated optical element for both eyes of the viewer.

[0016] According to an advantageous embodiment of the invention, the light spots of the light spot image float at several different heights above or below the surface area to form a three-dimensional motif. According to an alternative, equally advantageous embodiment, the light spots of the light spot image float at the same height above or below the surface area in certain areas to form a backdrop motif. Advantageously, a three-dimensional motif can also be combined with a two-dimensional motif in the light spot image, since this allows the light spot image to be recognized even in poor lighting conditions, thus enabling authentication.

[0017] The optical elements include curved mirrors, in particular concave mirrors or convex mirrors. The curved mirrors can be spherical, elliptical, rotationally symmetric aspherical, non-rotationally symmetric aspherical, or trough-shaped, with the latter having straight or curved channels. Elliptical mirrors have different curvatures in the x and y directions, while the surface of aspherical mirrors deviates from a spherical shape. Aspherical mirrors can be rotationally symmetric or, in the most general case, non-rotationally symmetric. Straight, trough-shaped mirrors can be considered a special case of elliptical mirrors where the radius of curvature is infinitely large in one spatial direction. To achieve a low structural height, the curved mirrors can also be at least partially formed by Fresnel mirrors.

[0018] Additionally, the optical elements can also include lenses, in particular spherical, elliptical, rotationally symmetric aspherical, non-rotationally symmetric aspherical, or cylindrical lenses. Elliptical lenses have different curvatures in the x and y directions, while in aspherical lenses, the refractive lens surface deviates from a spherical shape. Aspherical lenses can be rotationally symmetric or, in the most general case, non-rotationally symmetric. Cylindrical lenses can be considered a special case of elliptical lenses in which the radius of curvature is infinitely large in one spatial direction. The lenses can also be formed, at least partially, by Fresnel lenses to achieve a lower structural height.

[0019] In this case, each light spot in the light spot image is assigned not just one, but a plurality of optical elements. Assignment means that the optical element contributes to the creation of that light spot through reflection and / or refraction when illuminated. The optical elements are spaced apart and distributed across the surface area. The resulting gaps between the individual optical elements allow several groups of optical elements, each assigned to different light spots, to be nested within the same surface area. In this way, a particularly high spatial resolution can be achieved in the light spot image, as explained in more detail below.

[0020] Another advantage of assigning multiple optical elements to a single light spot is that, due to the smaller dimensions of the individual optical elements that are then possible, elements with flat boundary surfaces can be used, which are easier to calculate and manufacture than a single curved optical element with the same optical effect.

[0021] To create a light spot image in which the light spots have different brightness levels, it is advantageous to assign each light spot in the image a number of optical elements corresponding to the brightness of that light spot within the motif formed by the light spots. If the optical elements are of different sizes, a total area of ​​optical elements corresponding to the brightness of that light spot within the motif formed by the light spots can also be assigned to each light spot.

[0022] The optical elements are particularly preferably formed by planar micromirrors or by small microprisms.

[0023] The predetermined motif can also be a changing image, showing different pictures depending on the viewing angle. A concrete example of how to create such a changing image is described below. It should be understood that the term "changing images" also includes images where only parts of the image are subject to change.

[0024] In reversible images, images or parts of images change when the viewing direction changes, especially when the image is tilted; which is why such images are also called reversible images. The change can occur when tilting horizontally or vertically, or when tilting in a direction between horizontal and vertical.

[0025] When the change in image content is abrupt, it is called a flip image. If the change occurs through intermediate stages, it is called a morphing image.

[0026] Furthermore, 2D-3D images can also be created as light spot images. In addition to areas that appear 3-dimensional (which are visible in front of or behind the plane of the representation element, or which seem to penetrate the plane of the representation element), there are also areas that appear 2-dimensional in or near the plane of the representation element (at or near height level 0).

[0027] In a 2D-3D image, 2D and 3D elements can lie side by side and / or appear alternately in the same location depending on the viewing direction. In such a 2D-3D alternating image, for example, two-dimensional image content (e.g., text or a logo) can be faded in and out of a 3D image depending on the viewing direction.

[0028] In an advantageous embodiment of the invention, the predetermined motif generated by the display arrangement is a fully three-dimensional body formed by the light spots.

[0029] According to a further development of the invention, the surface area in which the majority of optical elements are arranged can also be curved, for example cylindrically or spherically curved.

[0030] In a further embodiment of the invention, a subset of the optical elements generates hidden image information that is not visible without aids. This hidden image information contrasts with the overt image information formed by the light spot image described above, which is visible to the naked eye under normal illumination without any additional aids. The hidden image information, on the other hand, is not readily visible to the naked eye under normal illumination, but only becomes visible, for example, under directed laser illumination or requires a special viewing screen.

[0031] In an advantageous embodiment of the invention, the optical elements comprise a periodic arrangement of micromirrors, each with a distance to its nearest neighbor of 2 mm or less, in particular 1 mm or less. A viewer then no longer perceives the reflections of the mirrors, but sees only a single point of light per mirror, the shape of which depends on the ambient illumination. If the viewer tilts the display element, the points of light from the mirrors shift slightly to the side, specifically, depending on whether the mirrors are concave or convex, as if the points of light were located in front of, or preferably behind, the plane of the display element. Due to the periodic arrangement of the micromirrors, the viewer thus sees a regular grid of points of light which, when the display element is tilted, preferably appear to move as if they were located in a more distant plane.The light point grid can therefore form the background for another motif, for example for the warping effect described in the also pending German patent application DE 10 2009 056 934.0, or for a sawtooth representation with kinematic effect, such as the hologram structures of the publication EP 0 868 313 B1 (paragraph

[0034] therein). Fig. 8 with reflective sawtooth structures).

[0032] To protect the optical elements from contamination and abrasion, and to effectively prevent unauthorized modification by imprinting the surface structure, the optical elements are advantageously embedded in an environmental layer or a composite of environmental layers, particularly a protective layer. Such embedding generally alters the float height of the light spots, as a difference in refractive index between the embedding material and air, or between the embedding material and the lens material, changes the optical path. However, this change in the optical path can easily be taken into account during the design of the optical elements, so that the desired float heights are achieved after embedding.

[0033] In an advantageous design, the optical elements are formed as embossed structures in an embossed lacquer layer. If the display element is at least partially reflective, the embossed structures are preferably provided with a reflection-enhancing coating. Suitable reflection-enhancing coatings include, in particular, a full-surface or rasterized metallization, a high-refractive-index coating, a thin-film element with a color-shifting effect, or a cholesterol liquid crystal layer.

[0034] The structural heights of the embossed structures are preferably below 100 µm, preferably below 20 µm, and particularly preferably below 5 µm.

[0035] The display elements according to the invention can be combined with other security features, for example with diffractive structures, with hologram structures in all embodiments, metallized or non-metallized, with subwavelength structures, metallized or non-metallized, with subwavelength gratings, with layer systems that show a color change when tilted, semi-transparent or opaque, with diffractive optical elements, with refractive optical elements, such as prism beam shapers, with special hole shapes, with security features with specifically adjusted electrical conductivity, with incorporated materials with magnetic coding, with materials with phosphorescent, fluorescent or luminescent effects, with security features based on liquid crystals, with matte structures, with additional micromirror elements, with elements with a venetian blind effect or with sawtooth structures.Further security features with which the representation elements according to the invention can be combined are specified in publication WO 2005 / 052650 A2 on pages 71 to 73; these are included in the present description to that extent.

[0036] A method for producing a refractive display element of the described type, designed and intended to generate a light spot image from a plurality of light spots when illuminated, which appear to a viewer to be floating above or below the surface area and which are arranged in the form of a predetermined motif, is described. In the method, a substrate is provided and a plurality of reflective optical elements are arranged in a surface area of ​​the substrate, wherein each light spot of the light spot image is assigned at least one reflective optical element which, when the display element is illuminated, contributes to the generation of its assigned light spot.

[0037] According to an advantageous variant of the procedure, Given a desired three-dimensional motif with pixels Pj and height values ​​Zj above an xy-plane, where the pixels correspond to the light spots created by illumination, a brightness Ij between 0% and 100% is set for each pixel Pj, aperture cones with an aperture ratio > 0.2 are assigned to the pixels Pj, a coverage area Ej is determined for each pixel Pj by an intersection of the aperture cone emanating from the pixel with the xy-plane, the xy-plane is divided into a number of coarse fields and the coarse fields each into a number of fine fields, a number of fine fields to be filled are determined for each pixel Pj based on the specified height value Zj and the specified brightness value Ij, and the fine fields to be filled determined for pixel Pj are distributed substantially evenly among the coarse fields in the coverage area Ej of pixel Pj.The fine fields to be filled are covered with refractive and / or reflective optical elements which, when the representation element is illuminated, contribute to the generation of the light spot corresponding to the image point Pj.

[0038] According to another advantageous variant of the method, a fully three-dimensional body is represented by floating points of light. This preferably starts with a data set that describes the surface of the body to be represented by points in space, vertices of polygons, normal vectors, and absorption behavior (color, brightness).

[0039] Such data sets, suitable data formats and processing methods are generally known to the person skilled in the art; examples include VRML (Virtual Reality Modeling Language), STL (Surface Tesselation Language; Standard Triangulation Language) or 3D-CAD (3D- Computer Aided Design).

[0040] Data sets describing the surface of an object can be generated, for example, through computer-aided technical drawing or by 3D laser scanning of real three-dimensional objects. In the latter method, points in space are captured when a body is scanned with laser beams; these points describe the object. These points can then be stored on a computer, for example, in a so-called point cloud format.

[0041] To create a 3D light spot image of a fully three-dimensional body, such a data set must be processed as described below using steps a) to c) as an example: a) Lighting Concept: To make the surface of an object visible, light-dark contrasts are necessary. An object appears most natural when these light-dark contrasts are created using a lighting concept. To achieve this, one imagines one or more light sources positioned outside the object and, using Lambert's cosine law, the law of reflection, or other suitable physical laws, determines the surface brightness at all relevant points of the object from the directions of the imaginary light sources, the surface normals, and the absorption properties. b) Light Point Generation: As described above, each relevant point on the object is assigned a catchment area in an arrangement of micromirrors or microprisms. Within this catchment area, certain surface areas are covered with micromirrors or microprisms in the manner described above, so that the point on the object illuminates at the desired brightness.c) Occlusion Calculation Finally, a fully three-dimensional body, viewed from a certain direction, has a front and a back, meaning that some parts of the body are occluded and invisible. Therefore, for each microelement (or micromirror or microprism), it is essential to ensure that it is assigned only to the point on the body surface that lies closest or furthest away from it on the line connecting the microelement and the body point, depending on the viewing angle of the light spot image. This point on the body surface is determined using occlusion calculation methods familiar from 3D CAD, such as ray tracing or Z-buffering. If points that are actually occluded are also included in the light spot image, the body appears transparent, which, however, may be desirable in exceptional cases.

[0042] The invention also includes a data carrier with a display element of the type described, wherein the display element can be arranged, in particular, as a reflective security element in an opaque area of ​​the data carrier, or as an at least partially transparent security element in or above a transparent window area or a continuous opening of the data carrier. The data carrier can, in particular, be a valuable document such as a banknote, especially a paper banknote, a polymer banknote, or a foil-laminated banknote, but also an identification card, such as a credit card, a bank card, a payment card, an authorization card, an identity card, or a passport personalization page.

[0043] Further embodiments and advantages of the invention are explained below with reference to the figures, in the representation of which a scale and proportion-accurate reproduction has been omitted in order to increase clarity.

[0044] They show: Fig. 1 a schematic representation of a banknote with a security element according to the invention, Fig. 2 schematically a first embodiment with concave mirrors as reflective optical elements, Fig. 3 another embodiment with convex mirrors as reflective optical elements, Fig. 4 a predetermined light spot motif in the form of a three-dimensional light pyramid, Fig. 5 in (a) a convex mirror and in (b) the convex mirror of (a) replaced by a Fresnel mirror, Fig. 6 a top view of a plurality of convex mirrors, in (a) with mirrors with a square base and in (b) with trough-shaped mirrors of different orientations, Fig. 7 a further embodiment in which the refractive optical elements are formed by lenses, Fig. 8 in (a) to (d) four embodiments in which a curved concave mirror is decomposed into micro-optical elements with a square base and a flat mirror surface, Fig.9 the arrangement of a checkerboard-like layout according to . Fig. 8(b) with micromirrors, where (a) an intermediate step with only one micromirror group and (b) the complete coverage with two micromirror groups for two closely adjacent light spots is shown, Fig. 10 illustrates the calculation of the planar mirror surfaces of the micromirrors of the Figuren 8 and 9 , Fig. 11 illustrates the calculation of microprisms that arise from the dissection of a converging lens, Fig. 12 schematically shows a safety element with embedded micromirrors, and Fig. 13 shows in (a) to (c) three embodiments in which a light spot image according to the invention serves as a master for a volume hologram.

[0045] The invention will now be explained using the example of security features for banknotes. Figur 1 Figure 1 shows a schematic representation of a banknote 10 provided with a security element 12 according to the invention. The security element 12 can be designed as a reflective security element located in an opaque area of ​​the banknote 10, or it can be designed as a see-through security element, for example, arranged over a transparent window area of ​​the banknote 10.

[0046] When illuminated, for example by sunlight or a ceiling lamp, the security element 12 creates a three-dimensional image of light spots for the viewer, consisting of a plurality of light spots that appear to float either above or below the plane of the security element 12. Different light spots exhibit varying heights of suspension, so that together the light spots form a three-dimensional motif, for example, a pyramid of light protruding from the banknote.

[0047] These light spot images, created by the illumination and appearing to jump forward or backward from the banknote, offer the viewer an unusual, visually appealing three-dimensional image impression that is easy to check and memorize even for laypersons.

[0048] To explain the principle of the invention, it shows Fig. 2 A first embodiment of a security element 20, in which the three-dimensional motif 30 is simplified to three pixels 32. The security element 20 contains a substrate 22 which includes a plurality of small concave mirrors 24 in a surface area. Since only three pixels 32 of the motif are shown in the simplified figure, only three concave mirrors 24 are shown accordingly. However, it is understood that in practice a security element 20 will typically have a large number, for example, several tens, several hundred, or even several thousand refractive and / or reflective optical elements 24. Specific examples of security elements with a large number of optical elements are described below.

[0049] Returning to the presentation of the Fig. 2 The focal length f of the concave mirrors 24 arranged in the plane of the substrate 22 is each chosen such that, when illuminated by a distant light source 34, the concave mirrors 24 produce the specified image points as light spots 32. More precisely, the light spots 32 represent real images of the light source, as shown in the left part of the image. Fig. 2 indicated by the geometric ray path 36.

[0050] A three-dimensional image impression, that is, the viewer's perception 40 that the light spots 32 are floating at a certain height above the surface of the substrate 22, only arises through binocular vision. For this to occur, the design of the concave mirror arrangement must ensure that the real images 32 of the light source 34 lie within the opening of the relevant optical system, in this case a concave mirror 24, for each eye 42.

[0051] As shown in the right part of the image Fig. 2 To illustrate, a spot of light 32 lies within the opening of the concave mirror 24 for both eyes 42 if and only if, as seen from the spot of light 32, the opening angle ω of the concave mirror 24 is greater than the viewing angle α of the observer 40. The opening angle ω is given by the ratio of the mirror diameter d and the focal length f, ω = d / f, and the viewing angle α by the ratio of the interpupillary distance a and the viewing distance b, i.e., α = a / b. For a typical interpupillary distance a ≈ 6.5 cm and a typical viewing distance b ≈ 30 cm, the following condition is obtained: f / d < b / a ≈ 5 , That is, the condition that the ratio of the suspension height f of a light spot 32 to the diameter of the concave mirror 24 producing the light spot must be less than approximately 5. If the diameter of the concave mirror 24 is, as in the exemplary embodiment of the Fig. 2 For example, d = 0.5 mm, so floating heights of up to 2.5 mm with a three-dimensional image impression can be achieved.

[0052] The refractive and / or reflective optical elements can have dimensions of a few hundred micrometers or even a few millimeters, but can also be significantly smaller. For example, a concave mirror can be divided into a multitude of micromirrors, and these can be distributed over a specific area of ​​the substrate 22, as explained in more detail below. In any case, however, the dimension of an optical element used according to the invention is significantly larger than the wavelength of light, so that diffraction and interference effects can be neglected. In particular, the dimension of the optical elements is therefore advantageously larger than 2 µm, preferably even larger than 5 µm.

[0053] The light spots 32 of the given motif 30 can appear to the viewer 40 to float not only above, but also below the surface 22 of the substrate. With reference to Fig. 3 For this purpose, a plurality of small convex mirrors 26 are arranged in a surface area of ​​the substrate 22, the focal lengths of which are chosen such that, when illuminated by a distant light source 34, the convex mirrors 26 generate the specified image points as light spots 32. More precisely, in this case, the light spots 32 represent virtual images of the light source 34, which appear to the observer to float below the surface of the substrate, as shown in the right part of the image. Fig. 3 indicated by the geometric ray path 38.

[0054] Concave and convex mirrors can both be incorporated into the same safety element if parts of the design are to protrude while other parts are to be recessed behind the substrate surface. The illustration shows... Fig. 4 a predefined motif in the form of a three-dimensional pyramid of light 50 made up of a plurality of light spots 52, which float at different heights above or below the surface of the substrate 22.

[0055] In the exemplary embodiment of the Fig. 4 All convex mirrors have a diameter of 0.5 mm. The focal length f is specified positively for concave mirrors (floating height above the substrate surface) and negatively for convex mirrors (floating height below the substrate surface). Using this convention, the light spot 52-1 at the pyramid's apex has a floating height of f = + 2 mm, while the light spots 52-2 and 52-3 at the pyramid's edges float at heights of f = + 1.2 mm and f = + 0.4 mm, respectively. The light spots 52-1 to 52-3, with their positive floating heights, are generated by concave mirrors, as was already the case in the following example. Fig. 2 explained.

[0056] Moving further outwards in pyramid 50, the light spots 52-4 and 52-5 have a floating height of f = - 0.4 mm and f = - 1.2 mm respectively, thus appearing to the observer to float below the substrate surface 22. The base of the pyramid is finally formed from light spots 52-6, which have a floating height of f = - 2 mm and are therefore located 4 mm below the pyramid apex 52-1.

[0057] For all light spots 52, the condition |f| / d < 5 is satisfied, so that the pyramid 50 appears truly three-dimensional to the observer at a normal viewing distance and seems to pierce the substrate plane from bottom to top.

[0058] The floating height of the light spots is determined by the radius of curvature of the curved mirrors, as in Fig. 5(a) The following is an example of a convex mirror 60. With a diameter d and a radius of curvature r, the convex mirror 60 has a focal length of f = r / 2. For example, with a mirror diameter d = 0.5 mm, a radius of curvature of r = 4 mm is required for a focal length or levitation height of f = 2 mm. The structural height of the convex mirror in this case is calculated using the relationship h*(2r-h) = (d / 2) 2< , resulting in h = 7.8 µm.

[0059] Depending on the desired floating height, mirror structures can be created whose height h is too large for a given application, for example, because a maximum permissible embossing height or depth in an embossed layer is exceeded. In this case, the convex mirror 60 of the Fig. 5(a) can be replaced by a corresponding Fresnel mirror 62, which has a significantly lower structure height hf, as in Fig. 5(b) The zone widths z of the Fresnel zones 64 can be chosen arbitrarily, as long as they are large compared to the wavelength of light, in particular as long as z > 2 µm. Otherwise, the width z of the Fresnel zones 64 plays no role in the optical effectiveness of the Fresnel mirror 62.

[0060] If the convex mirrors of a security element have several different focal lengths, meaning the light spots of the resulting image have different elevations above and / or below the substrate surface, a truly three-dimensional motif is created. However, in some designs, it may be advantageous to use all convex mirrors with the same focal length, so that all light spots in the image have the same elevation. This creates a backdrop motif that appears to float at a specific height above or below the substrate surface.

[0061] The curved mirrors do not have to be spherically curved. For example, elliptical concave or convex mirrors with different curvatures in the x and y directions can also be used as optical elements according to the invention. Since, as explained above, the focal length f of a curved mirror is proportional to the radius of curvature r, the apparent height f of the corresponding light spot changes when an elliptically curved mirror is rotated.

[0062] If a given motif contains at least partially elliptical concave or convex mirrors, the light spots in the focal planes of the respective areas rise against the background or sink into the background when the arrangement is rotated. This effect is particularly noticeable when the light spots rising or sinking during rotation are combined with light spots that do not change during rotation and which represent a stationary reference point for the eye.

[0063] With regard to the supervision of the Fig. 6(a) The majority of curved mirrors 70, for example, with a rectangular or square base, can be arranged in a surface area 72 of the safety element.

[0064] For a three-dimensional image impression for a viewer, a lateral parallax is sufficient, i.e., a parallax along the line connecting the two eyes 42 of the viewer 40. The curved mirrors 74, 76, 78 can therefore also be shaped like troughs, as in the top view of the Fig. 6(b) shown. Trough-shaped convex mirrors exhibit a non-zero curvature only in one direction, namely perpendicular to the trough, while the curvature vanishes in the direction of the trough.

[0065] Attractive visual effects can also be achieved with an image constructed from trough-shaped curved mirrors 74, 76, 78. At a suitable viewing angle, the light spots appear to float above or below the substrate surface in the form of luminous lines suspended in the air.

[0066] Because of the adjacent position of the eyes, the strongest spatial effect in a 3D groove image is achieved when the grooves 74 run perpendicular to the line connecting the eyes 42. However, even diagonally running grooves 76 have a perpendicular component and thus also produce a light spot image with a three-dimensional effect.

[0067] If an image with grooves 76 lying at an angle in the image plane is rotated (80) so that the grooves are perpendicular, the three-dimensional effect is enhanced. If the viewer rotates the grooves 76 horizontally, the three-dimensional impression is reduced. In the case of a safety element, such as in Fig. 6(b) As shown, sub-areas with different orientations of the channels 74, 76, 78 contain, the light spots of the respective sub-areas rise up from the background or sink into the background when the arrangement is rotated (80).

[0068] The term "trough-shaped convex mirrors" refers to both concave and convex trough mirrors. Concave trough mirrors produce light spots that appear to float above the substrate surface, while convex trough mirrors produce light spots that appear to float below the substrate surface.

[0069] Furthermore, the trough-shaped curved mirrors do not have to run in a straight line, as in Fig. 6(b) They are not only shown, but can also be designed with curves. Attractive visual effects can also be achieved through such a design.

[0070] In another, in Fig. 7 In the illustrated embodiment of the invention, the optical elements are formed by refractive lenses instead of reflective mirrors. In this case, the refractive security element 90 is a see-through security element, which is checked for authenticity by the observer 40 by looking through it against an ideally distant light source 95.

[0071] Both converging lenses 92 and diverging lenses 96 are suitable as lenses, wherein, from the viewer 40's perspective, the convex converging lenses 92 produce light spots 94 as real images floating above the safety element 90, and the concave diverging lenses 96 produce light spots 98 as virtual images floating below the safety element 90.

[0072] The lenses can be spherical, elliptical, or cylindrical. Cylindrical lenses produce streak-like spots of light, while with elliptical lenses, the height at which the light spots are suspended changes when the safety element is rotated, as described above for elliptical mirrors. For the in Fig. 7 For the plano-convex and plano-concave lenses shown in Figures 92 and 96, the following applies to the diameter d, the radius of curvature r, the focal length f, and the lens height h for a refractive index of the lens material of n = 1.5 for lenses bordering air: f = 2 * r and h * 2 r − h = d / 2 2

[0073] Given a lens diameter d and a desired float height f, the radius of curvature r and the structure height h of the lens can be determined. If the structure height of a lens is too large for a desired application, the lenses can also be replaced by corresponding Fresnel lenses, as described in connection with Fig. 5 This is described for Fresnel mirrors. Here too, it is important to ensure that the zone widths of the Fresnel zones are large compared to the wavelength of light, but otherwise they can be chosen arbitrarily.

[0074] In the embodiments described so far, each light spot of the light spot image is assigned exactly one optical element which, when illuminated, produces this light spot, namely a concave mirror 24 ( Fig. 2 ), a convex mirror 26 ( Fig. 3 ), a converging lens 92 or a diverging lens 96 ( Fig. 7 The resolution achievable in the light spot image, i.e., the minimum distance between two light spots in the image, is limited to the diameter d of the curved mirrors or lenses in such a design. This diameter, in turn, is linked to the elevation height of the light spots via the aforementioned condition f / d < 5 for a three-dimensional image impression. High resolution in the light spot image is therefore only achievable for small elevation heights and thus a weak three-dimensional effect.

[0075] To achieve a higher resolution in the generated light spot image while maintaining the same high levitation height, the large mirrors or lenses used in the previous embodiments are each replaced by a plurality of smaller micromirrors or microprisms, which together have essentially the same optical effect as the original optical element. For the sake of simplicity, micromirrors and microprisms will subsequently be referred to collectively as micro-optical elements.

[0076] Each light spot in the image is then assigned a plurality of optical elements in the form of micro-optical elements. The higher resolution in the image is achieved by distributing the micro-optical elements not continuously next to each other, but at intervals across the surface. The spaces between the optical elements of one light spot can then be filled with optical elements assigned to other light spots. In this way, several groups of micro-optical elements, each assigned to different light spots, can be nested within each other in the same area.

[0077] The minimum distance between two light spots in the light spot image is then no longer given by the dimensions of the original large mirrors or lenses, but by the much smaller dimensions of the micro-optical elements into which the original mirrors or lenses are divided.

[0078] Furthermore, when a curved mirror or lens is decomposed into a plurality of micro-optical elements, the initially curved surfaces of these elements can generally be replaced by flat surfaces due to their small size. This replacement has no adverse effects on the resulting light spot image, especially when the dimensions of the micro-optical elements are smaller than the resolving power of the viewing situation. The advantage is that micro-optical elements with flat surfaces are easier to calculate and manufacture. From this perspective, it can even be advisable to decompose curved mirrors or lenses into small micro-optical elements with flat surfaces when nesting multiple groups of micro-optical elements is neither desired nor necessary.

[0079] To illustrate, Fig. 8 In (a) to (d) four embodiments in which a curved concave mirror is divided into micro-optical elements 100 with a square base and a flat mirror surface. In the embodiment of Fig. 8(a) A concave mirror used to generate a light spot is replaced by an arrangement of n x n micromirrors 100, which are arranged side by side without gaps within the area of ​​the safety element. The micromirrors 100 have, for example, dimensions of 50 µm x 50 µm and can be designed with a flat reflective surface without affecting the image quality. The number n x n of micromirrors is, for example, 10 x 10, so that the micromirrors occupy a total area of ​​0.5 mm x 0.5 mm. The calculation of the orientation of the flat reflective surfaces is described below with reference to Fig. 10 explained. As is evident to the expert, the calculation and manufacture of the planar micromirrors 100 is significantly simpler than the calculation and manufacture of a curved concave mirror with the same optical effect.

[0080] The exemplary embodiment of the Fig. 8(b) shows a design in which a curved concave mirror is initially arranged as in Fig. 8(a) The safety element is replaced by a plurality of micromirrors 102 with a flat reflective surface. However, the micromirrors 102 are arranged in a checkerboard pattern within the surface area of ​​the safety element, so that every second mirror position remains free. These initially unoccupied fields 104, shown in white in the figure, can then be occupied by micromirrors that are assigned to a different light spot.

[0081] The resolution of the light spot image can be significantly increased by such a nesting of micromirror groups: For example, if two light spots floating at a height of 5 mm are to be only 0.2 mm apart, curved mirrors or lenses with a focal length f = 5 mm are required. As described above, the diameter and focal length of the optical elements must satisfy the condition f / d < 5 for a three-dimensional effect, which, given the specifications, results in an optical diameter d > 1 mm. Adjacent curved mirrors or lenses would therefore have to be spaced more than 1 mm apart, so the required resolution of 0.2 mm cannot be achieved in this way.

[0082] If, on the other hand, a decomposition as in Fig. 8(b) In a configuration where only every second field is used with 50 µm x 50 µm micromirrors 102 to generate the first light spot, the intervening fields 104 can be occupied by micromirrors that generate a second light spot located 0.2 mm away. The condition f / d < 5 requires an optical diameter of more than 1 mm, which can be achieved, for example, by a checkerboard arrangement of 12 x 12 micromirrors 102 with 12 x 12 free fields 104, resulting in a diameter of d = 2*12*50 µm = 1.2 mm. The minimum distance between the light spot generated by the micromirror group 102 and the second light spot generated by the micromirrors arranged in the fields 104 is now 50 µm, so that the required resolution of 0.2 mm can easily be achieved.

[0083] The arrangement of a checkerboard pattern according to Fig. 8(b) with micromirrors is in Fig. 9 This is illustrated again in a cross-sectional view. With reference to Fig. 9(a) Every second field is covered with 50 µm x 50 µm micromirrors 102 to generate the first light spot 110. The micromirrors 102 form a group of micromirrors, all of which are assigned to the same light spot 110 and generate it together when illuminated.

[0084] The fields 104 located between the micromirrors 102 are available for the placement of micromirrors that are assigned to other light spots. In the extreme case, the fields 104 can be occupied by micromirrors 106 that serve to generate a light spot 112 which is only one micromirror diameter dm, i.e. 50 µm in the exemplary embodiment, away from the first light spot 110, as shown in Fig. 9(b) illustrated.

[0085] As from Fig. 9 As can be seen, the optical diameter d of the micromirror groups 102, 106 in the alternating mirror arrangement is given by d = 2*n*dm, where n represents the number of micromirrors of a group in a spatial direction. By appropriately choosing n, the optical diameter d can therefore always be made large enough to satisfy the condition f / d < 5, despite the high resolution dm.

[0086] Returning to the presentation of the Fig. 8 It is understood that the allocation of space within the safety element can be selected according to the desired number of nested groups of micro-optical elements. For example, only every fourth field can be occupied with micromirrors 102, each assigned to a specific light spot, as shown in Fig. 8(c) illustrated. The fields 104 shown in white in the figure, which are initially empty, can then be occupied by micromirrors that are assigned to up to three other light spots. In another design, every ninth field is occupied by micromirrors 102 assigned to a specific light spot, as in Fig. 8(d) shown. The fields 104 shown in white in the figure, which are initially still empty, can then be covered with micromirrors, which are assigned to up to eight other light spots.

[0087] The calculation of the planar mirror surfaces of the micromirrors is in Fig. 10 Illustrated. Shown in cross-section are some of the micromirrors 102 and the intervening, free fields 104 of a design according to the Figuren 8(b) and 9(a) .

[0088] For the calculation, (x 0 ,y 0 , z 0 ) denotes the position of the light spot 110 to be generated with z 0 > 0, (x,y,0) the position of the mirror element to be calculated. nis the normal vector of the mirror at the position (x,y,0), k the direction vector of the incident light ray and p the direction vector of the reflected light ray.

[0089] For each case, the position of the mirror surface, i.e., the normal vector, is required. n so that it comes from a predetermined direction k Incident light is reflected to the focal point (x0, y0, z0) for all micromirrors 102 assigned to the light spot 110. This is achieved according to the invention by n → = p → p → − k → k → p → p → − k → k → , p → = x 0 − x y 0 − y z 0 , p → = x 0 − x 2 + y 0 − y 2 + z 0 2

[0090] If the light source 120 is located at position (x L ,y L , z L ), then k ⇀ k ⇀ = x L − x y L − y z L x L − x 2 + y L − y 2 + z L 2

[0091] If the micromirror group 102 is designed for perpendicular light incidence, then k → k → = 0 0 − 1 , so that the normal vector n to n → = p → n p → n − k → k → p → n p → n − k → k → = x 0 − x y 0 − y z 0 + √ x 0 − x 2 + y 0 − y 2 + z 0 + 2 , results, where the abbreviation = x 0 − x 2 + y 0 − y 2 + z 0 2 was used.

[0092] Similarly, the normal vector nThe calculation is performed for micromirrors whose focal point (x₀, y₀, z₀) with z₀ < 0 lies below the plane of the safety element. According to the invention, this is done using the relationship... n → = − p → p → + k → k → p → p → + k → k → The calculation is then carried out as with concave mirrors.

[0093] Curved lenses can be simulated by small microprisms when decomposed into micro-optical elements. If the size of the microprisms is below the resolving power of the viewing situation, they can be used with the same optical effect but are easier to calculate and manufacture.

[0094] In Fig. 11 are used to illustrate a checkerboard-like partition as in Fig. 8(b) Some microprisms 122 are shown in cross-section. Analogous to the procedure for the micromirrors 102, the normal vector can also be determined for the microprisms 122. nThe calculation is such that the light incident from the light source 120 is refracted to the desired position of the light spot 110. The in Fig. 11 The remaining fields 124 can be occupied by microprisms that are assigned to a different light spot.

[0095] In all described variants, the refractive and / or reflective optical elements could also be embedded in an surrounding material or provided with a protective layer. Such embedding protects the optical elements from contamination and abrasion, and effectively prevents unauthorized modification by imprinting the surface structure.

[0096] The embedding is in Fig. 12 A safety element 130 with micromirrors 132 is shown schematically. By embedding the micromirrors 132 in the transparent protective layer 134 and the resulting change in the refractive index at the surface 136 of the protective layer 134, the position of the generated light spots 140 changes compared to the light spot position 142 in a non-embedded micromirror arrangement. More precisely, when the micromirrors 132 are embedded in a protective layer with refractive index n, the float height of a light spot 140 generated by the micromirrors 132 changes by a factor of approximately 1 / n. Typical protective coatings 134 have a refractive index of approximately n = 1.5, so the float heights of the light spots are reduced by about 2 / 3 compared to the float heights calculated for an open application.This change is of course usually already taken into account during the design of the micromirror arrangement so that the desired levitation heights are achieved after embedding.

[0097] In the case of embedded prisms or lenses, the difference in refractive index between the prism or lens material and the embedding material can be taken into account when calculating the deflection of the light rays.

[0098] To create a visually appealing three-dimensional image of light spots, the light spots should be able to exhibit different brightness levels. It may also be desirable for a light spot, i.e., a point of a motif floating in space, to appear differently bright from different directions. Such varying brightness levels of light spots can be generated in various ways within the scope of the invention. For example, the optical elements associated with a light spot can be dimmed depending on the desired fraction of the maximum brightness.

[0099] Currently, however, it is preferred to adjust the brightness of a light spot after its decomposition into micro-optical elements by the proportion of the area covered by micro-optical elements or by the number of fields per solid angle responsible for a light spot. This results in image areas that do not contain any mirrors or prisms directed at a light spot and that must therefore be kept dark.

[0100] Such image areas can be created in one of the following ways, for example. In a first approach, the darker areas in the specular light spot image are equipped with light traps, such as subwavelength structures like moth-eye structures, or with funnel-shaped, reflective structures with steep sides, where incident light is reflected back little or not at all. However, due to the steep sides, such light traps are not easy to produce. Therefore, it is advantageous to equip the dark areas in the specular light spot image with mirrors oriented so that they reflect areas of space that contain no light sources. The mirrors could, for example, be directed towards the viewer's body.

[0101] In the case of transparency safety elements, the dark areas are preferably equipped with prisms that direct light rays towards the viewer's eye from directions where there are no light sources, for example from the floor.

[0102] The surface area in which the optical elements are arranged does not have to be flat, but can be curved in any way. This is particularly easy to achieve if the optical elements are formed by small micro-optical elements. Since a normal vector is calculated for each micro-optical element anyway ( Figuren 10, 11 ), the local position and orientation of the surface of the safety element can be taken into account without much additional effort, as explained below using the example of a micromirror arrangement: As above, (x 0 ,y 0 , z 0 ) denotes the position of the desired light spot, (x,y,z) the position of a micromirror in space, where this position includes the curved surface of the safety element, further denotes n the normal vector of the micromirror at position (x,y,z), k the direction vector of the incident light ray and p the direction vector from the micromirror to the light spot, then according to the invention n → = ± p → p → ∓ k → k → p → p → ∓ k → k → , p → = x 0 − x y 0 − y z 0 − z , p → = x 0 − x 2 + y 0 − y 2 + z 0 − z 2 wobei das The upper sign applies to z 0 > 0, i.e., a real image floating above the substrate plane, and the lower sign applies to z 0 < 0, i.e., a virtual image floating below the substrate plane.

[0103] In a further development of the invention, the safety element can also generate a changing image of light spots when illuminated, in which different images become visible to the viewer from different directions. For example, the following procedure can be used for a reflective safety element; the procedure for a see-through safety element is analogous: When tilted sideways, the safety element should show a change from a light spot image A to a light spot image B. First, the necessary optical elements that generate the light spot images when illuminated are determined for both light spot images. In doing so, as in connection with the Figuren 8 bis 10 described, assigning a plurality of optical elements, in this case a plurality of micromirrors, to each spot of light.

[0104] When arranging the micromirrors in the surface area of ​​the security element, those micromirrors where the x-component nx of the normal vector is greater than zero are omitted for the light spot image A. This frees up half of the mirror positions, and the image is only visible within a limited angular range.

[0105] For the light spot image B, those micromirrors where the x-component nx of the normal vector is less than zero are omitted. The mirror positions freed up from light spot image A are then occupied by this reduced mirror arrangement. When the arrangement is tilted laterally, light spot image A and light spot image B are then alternately visible.

[0106] The safety element can also be designed for vertical tilting, for example by omitting, for light spot image A, those micromirrors where the y-component of the normal vector ny is greater than zero, and for light spot image B, those micromirrors where ny < 0. The reduced mirror arrangements with their limited visibility range are then blended across the surface area of ​​the safety element.

[0107] Instead of the conditions mentioned, other criteria can of course be used to separate the light spot images of a changing image. For example, the following conditions can be used: n y > c 1 für Bild A , c 1 < n y < c 2 für Bild B , n y < c 2 für Bild C Using two numerical values ​​c1 < c2, three light spot images A, B, C are alternated when tilting vertically. By selecting the numerical values ​​c1 and c2, the size of the visibility areas can be adjusted as desired.

[0108] In addition to switching between multiple 3D light spot images, switching between one or more 3D light spot images and one or more images generated in other ways is also possible.

[0109] It can also be advantageous to combine a three-dimensional motif with a two-dimensional motif in the light spot image, where all pixels are at the same height, preferably at or beyond the plane of the security element. Such two-dimensional light spot motifs remain clearly visible even under poor lighting conditions. For example, if a two-dimensional foreground motif is combined with a three-dimensional background motif, the light spot image does not disappear completely even in low light; instead, it is merely reduced to the more robust two-dimensional foreground motif. Therefore, authentication remains possible even in poor lighting conditions.

[0110] A light spot image can therefore contain not only floating 3D light spots, visible from certain viewing angles, but also 2D-appearing areas, visible from the same or different viewing angles. The 2D and 3D parts can thus lie side by side and / or appear alternately in the same location when the viewing direction changes.

[0111] In 2D-3D images, in addition to 3-dimensionally appearing parts (which are visible in front of or behind the plane of the security element or appear to penetrate the plane of the security element), there are also 2-dimensionally appearing parts at the level of the plane of the security element or near the plane of the security element (at height level 0 or near height level 0).

[0112] For an area at height zero, one can start with the mirror or prism configuration calculated for low-level light points (e.g., 0.5 mm) with the desired viewing angle. This includes all normal vectors that cover the intended solid angle. While for floating light points the micromirrors or microprisms in the plane of the safety element are arranged to illuminate specific points in space, the micromirrors calculated in this way, including their inclination, must be statistically distributed in the area intended for height zero. This ensures that instead of illuminating specific points in space, a solid angle is illuminated as desired. For lower intensities, this statistically mixed configuration must be made correspondingly incomplete, for example, by not utilizing all pixels or by not fully utilizing the pixels.

[0113] According to another advanced theory, the light spot image, in addition to the overtly visible image information, also contains hidden image information. For this purpose, the optical elements of the overt image information are arranged with spacing between them, and the gaps are at least partially filled with optical elements of the hidden image information.

[0114] Hidden image information can be created, for example, by assigning very small opening angles to the corresponding light spots, such as an opening angle of 0 for parallel light.

[0115] The light spots of the hidden image information can also be assigned different directions, which are so far apart that no coherent image is perceived when viewed without aids. For authentication purposes, the image can be projected onto a ground glass screen. The directions of the hidden image information preferably lie outside the directions from which the open 3D light spot image is viewed, so that the presence of hidden information is not readily apparent.

[0116] In an advantageous embodiment, the optical elements of the hidden image information are partially or completely housed in closely adjacent sub-areas of the security element and, if necessary, repeated multiple times across the surface of the security element. The hidden image information can then be successively or all at once illuminated with a narrow laser beam and projected onto a suitably positioned screen.

[0117] The following describes in more detail a particularly preferred procedure for producing a general three-dimensional light spot image.

[0118] First, a desired three-dimensional motif is defined with pixels Pj and height values ​​Zj above the xy-plane, where the pixels correspond to the light spots created by illumination. For a normal viewing distance of approximately 30 cm, the pixel spacing should be in the range of 0.1 to 0.5 mm. Next, a brightness Ij between 0% and 100% is assigned to each pixel Pj. Then, aperture cones with an aperture ratio > 0.2, for example, an aperture ratio of 0.4, are assigned to each pixel. For each pixel Pj, the intersection of the aperture cone emanating from the pixel with the xy-plane defines a catchment area Ej for that pixel Pj.

[0119] The xy-plane itself is divided into first, larger fields, for example, with dimensions of 0.1 mm × 0.1 mm. Each of these larger fields is further subdivided into second, smaller fields, for example, with dimensions of 10 µm × 10 µm. The larger fields are subsequently referred to as coarse fields, and the smaller fields as fine fields.

[0120] Within the area of ​​focus Ej of each pixel Pj, as many fine fields are reserved for this pixel as are determined based on the height value Zj and the brightness value Ij. For example, the number of fine fields can be chosen to be proportional to the brightness value and inversely proportional to (Zj) α< 1, with an exponent α ≤ 1, which is α = 1 for light spots formed by trough-shaped mirrors or cylindrical lenses and α = 2 for light spots formed by two-dimensionally focusing lenses or mirrors. The fine fields reserved for pixel Pj are then distributed essentially uniformly among the coarse fields within the area of ​​focus Ej of pixel Pj.

[0121] The number of fine fields per coarse field can also include a correction factor, which is determined, for example, as follows: First, without a correction factor, the number of fine fields to be filled within each coarse field, belonging to different pixels P j, is added. This results in a suggested allocation for the total number of filled fine fields in each coarse field.

[0122] If the number of occupied fine fields for all coarse fields is less than the maximum possible number, a correction factor greater than 1 can be chosen, and the occupancy multiplied by this correction factor so that the maximum occupancy is achieved in some coarse fields. Conversely, if the number of occupied fine fields exceeds the maximum occupancy, a correction factor less than 1 is chosen accordingly, which, after multiplication, results in an occupancy less than or equal to the maximum occupancy. If the maximum occupancy is exceeded in only a few coarse fields, instead of a uniform reduction, only the highest intensities can be capped at the maximum occupancy, or the fine fields of the exceeding coarse fields can be shifted to adjacent coarse fields.

[0123] The resulting pattern can now be implemented within the surface area of ​​the security element. Mirrors or prisms are positioned within the defined micro-areas to reflect or refract the incoming light onto the corresponding light spot. Additional security elements can be incorporated into the remaining unlit areas of the security element; for example, a hidden image of the type described above can be placed there.

[0124] A light spot image according to the invention can also serve as a master for a volume hologram, as now demonstrated by three embodiments with reference to Fig. 13 illustrated.

[0125] In the exemplary embodiment of the Fig. 13(a) A display arrangement 140 serves as a master, featuring a reflective 3D light spot image with micromirrors, designed for perpendicular incidence. A photopolymer plate 142 serves as a recording plate for the volume hologram. The photopolymer plate 142 is positioned in front of the display arrangement 140, so that the laser radiation from the recording laser 144, after beam expansion 146, is directed perpendicularly onto the photopolymer plate 142 as a reference wave 148. A portion of the laser radiation passes through the photopolymer plate 142, is directed perpendicularly onto the display arrangement 140, and, after reflection from the display arrangement 140, forms the object wave, which interferes with the reference wave 148 in the photopolymer plate 142. Bragg gratings are thereby exposed into the photopolymer plate 142, which as a volume grating image show the same 3D image as the 3D light spot image of the display arrangement 140 which serves as the master.

[0126] In the modification of the Fig. 13(b) The master display assembly 140 contains a reflective 3D light spot image calculated for light incidence at a specific angle to the perpendicular. Accordingly, the display assembly 140 and the photopolymer plate 142 positioned in front of the display assembly are illuminated with laser radiation at this angle. Interference between the reference wave 148 and the object wave reflected from the display assembly after passing through the photopolymer plate 142 generates a volume grid image in the photopolymer plate 142, which displays the same 3D image as the master 3D light spot image of the display assembly 140.

[0127] Finally, in this embodiment, the Fig. 13(c)A display arrangement 140 with a refracting 3D light spot image with microprisms, calculated for perpendicular light incidence, serves as the master. Here, the display arrangement 140 and the photopolymer plate 142 positioned in front of the display arrangement are illuminated from opposite sides by a beam splitter 150 and deflecting mirrors 152. In the photopolymer plate 142, the reference wave 148 and the object wave refracted by the display arrangement 142 interfere, thus generating a volume grating image that shows the same 3D image as the 3D light spot image of the display arrangement 140 serving as the master.

Claims

1. Display element (20) comprising a substrate (22) having a surface area in which a plurality of optical elements are arranged, wherein the display element (20) is designed and intended to generate, upon illumination (34) with parallel light, a light spot image (30) comprising a plurality of light spots (32) that appear to a viewer (40) to be floating above or below the surface area, wherein the optical elements are formed by reflective optical elements (24) and at least one reflective optical element is associated with each light spot of the light spot image (30), which, when the display element (20) is illuminated (34) by the parallel light, contributes to the generation of the light spot associated with it, and wherein the optical elements (24) comprise curved mirrors, characterized in that the light spots (32) are arranged in the form of a predetermined motif, each light spot (32) of the light spot image (30) is associated with a plurality of reflective optical elements (24), the plurality of associated reflective optical elements (24) are distributed at intervals across the surface area, and reflective optical elements (24) associated with different light spots (32) are arranged in an interlaced manner within the surface area.

2. Display element (20) according to claim 1, wherein the curved mirrors are elliptical or aspheric.

3. Display element (20) according to claim 1, wherein the curved mirrors are channel-shaped, wherein the channels of the channel-shaped curved mirrors extend in a straight or curvilinear manner.

4. Display element (20) according to claim 2, wherein the curved, elliptically shaped mirrors have different mirror curvatures in the x and y directions.

5. Display element (20) according to any one of claims 1 through 4, wherein the light spots (32) of the light spot image (30) float at several different heights above or below the surface area to form a three-dimensional motif.

6. Display element (20) according to any one of claims 1 to 4, wherein the light spots (32) of the light spot image (30) float in some areas all at the same floating height above or below the surface area to form a backdrop motif.

7. Display element (20) according to at least one of claims 1 to 6, wherein the light spots of the light spot image (30) have different brightnesses and each light spot (32) is assigned a number of optical elements (24) corresponding to the brightness of the light spot (32) within the motif formed by the light spots, or each light spot (32) is assigned a total area of optical elements corresponding to the brightness of the light spot within the motif formed by the light spots (32).

8. Display element (20) according to at least one of claims 1 through 7, wherein the predetermined motif is a lenticular image that displays different images when viewed from different directions.

9. Display element (20) according to at least one of claims 1 to 8, wherein the optical elements comprise a periodic array of micromirrors, each of which has a distance to its nearest neighbor of 2 mm or less.

10. Display element (20) according to at least one of claims 1 to 9, wherein the optical elements are embedded in a surrounding layer or a composite of surrounding layers.

11. Display element (20) according to at least one of claims 1 to 10, wherein the optical elements are formed as embossed structures in an embossing lacquer layer; wherein the embossed structures are provided with a reflection-enhancing coating.

12. Display element (20) according to at least one of claims 1 to 11, wherein the display element (20) is a security element for security papers, valuable documents, and other items requiring security.

13. A data carrier comprising a display element (20) according to at least one of claims 1 to 12.

14. A data carrier according to claim 13, wherein the display element (20) is a reflective security element arranged in an opaque region of the data carrier.

15. A data carrier according to at least one of claims 13 or 14, wherein the data carrier is a security document, such as a banknote, a certificate, a passport, or an ID card.