Patent Description:
In order to prevent counterfeiting by means of scanning and copying, the holographic anti-counterfeiting technology is widely used as a solution for the optical anti-counterfeiting technology in various high-security or high value-added printed materials such as banknotes, identification cards, and product packaging, and has achieved an excellent effect.

At the end of the last century, with the development of computer science and image processing technologies, the holographic anti-counterfeiting technology has entered the era of digital development. One of the most important achievements is the successful application of the digital technology to the production of holograms. The comprehensive utilization of various technologies and devices such as a holography technology, a computer control system, a spatial light modulation device, and an image processing technology makes it possible to automatically photograph "dot matrix" holograms, so that digital composite holograms emerge as the times require. How to make digital holograms with large field of view and full parallax has become one of the hotspots of the holographic anti-counterfeiting technology all over the world. The specific effect of the full parallax image means that the human eye can see the content of the image within any observing angle range that is at an acute angle to the normal direction of the observed plane, and the content of the image corresponding to different angles is different, that is, binocular parallax within the full angle range. The full parallax anti-counterfeiting technology is one of the development directions of the current frontline public optical anti-counterfeiting technology.

Another type of the currently used holographic technology is to use the diffraction effect of patterned holographic micro-structures, to regulate and control a diffraction light field of the incident single-wavelength light (for example, blue corresponding to a single-wavelength laser with a wavelength of <NUM>), so as to realize the patterned reproduction pattern, so that the reproduction pattern is presented on a target carrier (surfaces such as a wall or a paper and the like) that can carry an image in a transmitted light direction or a reflected light direction. Such technology is one of the main means of the current second-line hidden optical anti-counterfeiting technology. However, such technology has the following limitations: (<NUM>) an incident light source must be monochromatic, otherwise no image can be reproduced; (<NUM>) a monochromatic laser light source is difficult to obtain, and as the laser is easy to cause irreversible burns of the fundus, an identification process of the light source has a high risk; (<NUM>) the technology is single in effect, and cannot implement a plurality of reproduction patterns in a same area; and (<NUM>) since diffractive micro-structures are easy to obtain, the technology lacks uniqueness, and an effectively anti-counterfeiting effect is hard to achieve.

Document <CIT> discloses an optical anti-counterfeiting element.

Some embodiments of the present invention provide an optical anti-counterfeiting element and an anti-counterfeiting product, to resolve or at least partially resolve the above technical problems.

In order to implement of the above objective, an embodiment of the present invention provides an optical anti-counterfeiting element. The optical anti-counterfeiting element includes: a substrate, comprising a first surface and a second surface that are opposite to each other; and a surface micro-structure layer, formed on at least a part of the first surface of the substrate. At least part of the surface micro-structure layer includes a first set of a micro-prism. The micro-prism has refractive and reflective functions simultaneously. Each pixel of a first pattern corresponds to refractive illumination spots of one or more micro-prisms in the first set of the micro-prism, so that: when the optical anti-counterfeiting element is irradiated on a first side of the optical anti-counterfeiting element, the refractive illumination spots of the first set of the micro-prism form the first pattern on a receiving carrier in a plane at a first distance from the second surface; when the optical anti-counterfeiting element is irradiated on a second side of the optical anti-counterfeiting element, the refractive illumination spots of the first set of the micro-prism form the first pattern on a receiving carrier in a plane at a second distance from the first surface; and a virtual image of the first pattern is observed when observed from the first side and from the second side of the optical anti-counterfeiting element, the first side is a side at which the first surface is located, and the second side is a side at which the second surface is located.

Another embodiment of the present invention provides an anti-counterfeiting product having the optical anti-counterfeiting element.

The optical anti-counterfeiting element provided in the embodiments of the present invention can provide various anti-counterfeiting effects and improve the anti-counterfeiting performance of the anti-counterfeiting element. Specifically, the optical anti-counterfeiting element provided in the embodiments of the present invention has the following advantages.

Other features and advantages of the embodiments of the present invention will be described in detail in the specific implementations below.

The accompanying drawings are used to provide a further understanding of the embodiments of the present invention, and constitute a part of the specification, which are used to explain the embodiments of the present invention with the following specific implementations, and do not constitute a limitation of the embodiments of the present invention. In the drawings:.

An optical anti-counterfeiting element and an anti-counterfeiting product having the optical anti-counterfeiting element according to the implementations of the present invention are described in detail below with reference to the drawings. It should be understood that, the drawings and detailed description are merely illustrative of preferred embodiments of the present invention, and are not intended to limit the scope of the present invention in any way. For ease of describing and explaining the embodiments of the present invention, the drawings are not drawn to true scale.

An implementation of the present invention provides an optical anti-counterfeiting element. The optical anti-counterfeiting element may include: a substrate, including a first surface and a second surface that are opposite to each other; and a surface micro-structure layer, formed on at least a part of the first surface of the substrate. At least part of the surface micro-structure layer may include a first set of a micro-prism. The micro-prism may have refractive and reflective functions simultaneously. Each pixel of a first pattern corresponds to refractive illumination spots of one or more micro-prisms in the first set of the micro-prism, so that: when the optical anti-counterfeiting element is irradiated on a first side of the optical anti-counterfeiting element, the refractive illumination spots of the first set of the micro-prism form the first pattern on a receiving carrier in a plane at a first distance from the second surface; when the optical anti-counterfeiting element is irradiated on a second side of the optical anti-counterfeiting element, the refractive illumination spots of the first set of the micro-prism form the first pattern on a receiving carrier in a plane at a second distance from the first surface; and a virtual image of the first pattern can be observed on the first side and the second side of the optical anti-counterfeiting element, the virtual image is a full parallax image, the first side is a side at which the first surface is located, and the second side is a side at which the second surface is located.

The patterns in the embodiments of the present invention may be words, letters, numbers, any specific signs, or a combination thereof. A pixel of the first pattern may be a very small point of the first pattern. Each pixel of the first pattern corresponds to the refractive illumination spots of one or more micro-prisms in the first set of the micro-prism. That is to say, through structures of the one or more micro-prisms, incident light can be refracted to a corresponding pixel point on the receiving carrier and forms a light spot. In this way, when the optical anti-counterfeiting element is irradiated on one side of the optical anti-counterfeiting element, a reproduced pattern can be observed by using the receiving carrier at a specific distance of the other side. A position of the receiving carrier configured to observe the reproduced pattern may be determined according to a focal length of the micro-prism. For the first set of the micro-prism forming the first pattern, during irradiation from the first side, each micro-prism can focus light beams on the receiving carrier in the plane at the first distance. During irradiation from the second side, each micro-prism can focus the light beams on the receiving carrier in the plane at the second distance. It may be understood that, if refracted light of the micro-prism can form the reproduced pattern on one side, a same reproduced pattern can be formed on the other side.

An incident light source for irradiating the optical anti-counterfeiting element may be white light (a light source at any visible wavelength band), such as phone flashlight, a D65 standard light source and the like. Alternatively, the incident light source may further be a single-wavelength light source, for example, a blue laser light source with a wavelength of <NUM>. The incident light source may be parallel light, and may vertically enter or obliquely enter (herein, the vertical or oblique incidence is relative to a plane parallel to a surface of the substrate) to the optical anti-counterfeiting element.

In addition, when the optical anti-counterfeiting element is irradiated or is under ambient light, the human eyes can directly observe floating or sunken full parallax images compared with a surface of the optical anti-counterfeiting element, and a relationship between the floating full parallax image and the sunken full parallax image observed on two sides of the optical anti-counterfeiting element is opposite. If the floating full parallax image is observed from the first side, the sunken full parallax image is observed from the second side, and vice versa. A pattern of the full parallax image formed by a set of a prism is consistent with a pattern formed by refracted light of the prism.

In an embodiment, a structure of the micro-prism may be one or more combinations of the following structures: a symmetrical or asymmetrical sawtooth structure, an arcuate structure, a sinusoidal structure or a hyperboloid structure.

In an embodiment, a height (may also be known as a depth) of the micro-prism may be less than <NUM> microns, specific, less than <NUM> microns.

In an embodiment, a width of the micro-prism on at least one dimension in a plane parallel to the surface of the substrate is less than <NUM> microns, specific, less than <NUM> microns.

In an embodiment, the surface micro-structure layer may be obtained by using micro-nano processing manners such as optical exposure and electron beam exposure, and duplicated in batch by using processing manners such as ultraviolet casting, molding, and nano-imprinting.

In an embodiment, at least part of the substrate may be at least translucent, or at least one side of the substrate is transparent. The substrate may be banknotes, passports, tickets, negotiable securities, and the like.

In some optional implementations, the optical anti-counterfeiting element may further reproduce a second pattern. A reproduced position of the second pattern may be at a distance different from a reproduced position of the first pattern from the optical anti-counterfeiting element. Likewise, the second pattern may also be divided into a plurality of pixels. Each pixel may correspond to refractive illumination spots of one or more micro-prisms in a second set of the micro-prism, so that: when the optical anti-counterfeiting element is irradiated on the first side of the optical anti-counterfeiting element, refracted light of the second set of the micro-prism forms the second pattern on a receiving carrier in a plane at a third distance from the second surface; when the optical anti-counterfeiting element is irradiated on the second side of the optical anti-counterfeiting element, the refracted light of the second set of the micro-prism forms the second pattern on a receiving carrier in a plane at a fourth distance from the first surface; and floating or sunken virtual images of the second pattern can be respectively observed on the first side and the second side of the optical anti-counterfeiting element, and the virtual images are full parallax images. The second pattern may be the same as or different from the first pattern.

In some optional implementations, the optical anti-counterfeiting element may further reproduce same or different patterns at continuously varying positions. Therefore, when the optical anti-counterfeiting element is irradiated on one side, a continuous switching effect or an animation effect of patterns is presented by changing a relative distance between the optical anti-counterfeiting element and the receiving carrier. Specifically, assuming that the continuous switching effect or the animation effect of N patterns is formed, each pattern of the N patterns may be the same or different. The surface micro-structure layer may be consist of N sets of the micro-prism. Each pixel of a reproduced pattern at an ith distance may correspond to refractive illumination spots of one or more micro-prisms of an ith set of N sets of the micro-prism, so that: when the optical anti-counterfeiting element is irradiated on the first side, the refractive illumination spots of the ith set of the N sets of the micro-prism form the ith pattern of the Nth pattern on a receiving carrier in a plane at an ith distance from the second surface; when the optical anti-counterfeiting element is irradiated on the second side, the refractive illumination spots of the jth set of the N sets of the micro-prism form a jth pattern of the Nth pattern on a receiving carrier in a plane at a jth distance from the first surface; and floating or sunken virtual images of the first pattern at different depths (different distances vertical to a plane of the substrate) can be respectively observed on the first side and the second side of the optical anti-counterfeiting element, the virtual images are full parallax images, where N is a positive integer greater than <NUM>, i is a positive integer from <NUM> to N, and j is a positive integer from <NUM> to N. N may be set as any proper value according to requirements.

In some optional implementations, the optical anti-counterfeiting element may reproduce a part of a three-dimensional image at continuously varying positions, so as to reproduce the three-dimensional image. For example, the three-dimensional image may be sliced and divided from height. Sliced portions with different heights may be formed by refracted light spots of the refracted light. Assuming that the three-dimensional image may be any three-dimensional image. The three-dimensional image may be divided into N patterns in depth. The surface micro-structure layer may be consist of N sets of the micro-prism. Each pixel of the ith pattern of the three-dimensional image corresponds to refractive illumination spots of one or more micro-prisms of the ith set of N sets of the micro-prism, so that: when the optical anti-counterfeiting element is irradiated on the first side, the refractive illumination spots of the ith set of the N sets of the micro-prism form the ith pattern of the three-dimensional image on a receiving carrier in a plane at the ith distance from the second surface, to cause the receiving carrier having receiving three-dimensional projection information to observe the three-dimensional image; when the optical anti-counterfeiting element is irradiated on the second side, the refractive illumination spots of the ith set of the N sets of the micro-prism form refractive illumination spots of the jth pattern of the three-dimensional image on a receiving carrier in a plane at the jth distance from the first surface, to cause the receiving carrier having the receiving three-dimensional projection information to observe the three-dimensional image; and floating or sunken virtual images of the three-dimensional image can be respectively observed on the first side and the second side of the optical anti-counterfeiting element, the virtual images are full parallax images, where N is a positive integer not less than <NUM>, i is a positive integer from <NUM> to N, and j is a positive integer from <NUM> to N. When the receiving carrier (such as space water mist) having the receiving three-dimensional projection information is used, the three-dimensional image of a third pattern can be directly seen in the space of the receiving carrier.

Based on the above any implementation, in some optional implementations, the optical anti-counterfeiting element may further include an adhesive layer covering the surface micro-structure layer. A refractive index difference between the adhesive layer and a material of the micro-prism may be greater than <NUM>, preferably, greater than <NUM>, and further specific, greater than <NUM>. Since the adhesive layer and the material of the micro-prism have different refractive indexes, refraction may occur at an interface between the adhesive layer and the micro-prism. In addition, the adhesive layer may play a role of protecting the micro-prism. It may be understood that, the adhesive layer may not exist, and there may be vacuum or air above a surface of the micro-prism.

The optical anti-counterfeiting element provided in the implementations of the present invention is further described below with reference to <FIG>.

<FIG> is a schematic cross-sectional view of an optical anti-counterfeiting element according to an implementation of the present invention. As shown in <FIG>, the optical anti-counterfeiting element according to the implementations of the present invention may include the substrate <NUM>. The substrate <NUM> has a first surface <NUM> and a second surface <NUM> that are opposite to each other. The first surface <NUM> is covered by the surface micro-structure layer <NUM>. The surface micro-structure layer <NUM> includes a plurality of micro-prisms <NUM> having refractive and reflective functions simultaneously. The micro-prisms <NUM> are covered by the adhesive layer <NUM>. Materials for manufacturing the adhesive layer <NUM> and the micro-prisms <NUM> have different refractive indexes.

The micro-prism <NUM> in <FIG> is of an asymmetrical sawtooth structure, and includes a steep surface and an inclined surface. A depth of the steep surface is in a range of <NUM> to <NUM> microns. An extending width on a plane determined by a normal direction of the inclined surface and a normal direction of the first surface <NUM> is in a range of <NUM> to <NUM> microns. An extending length in a direction perpendicular to the in-plane is not limited. A material forming the micro-prism <NUM> is a transparent ultraviolet radiation curing coating with a refractive index being <NUM>. The adhesive layer <NUM> covering a surface of the micro-prism is a transparent ultraviolet radiation curing coating with a refractive index being <NUM>.

A reproduction process of the surface micro-structure layer in the optical anti-counterfeiting element is explained below with reference to <FIG>. In <FIG>, when illumination light irradiates the optical anti-counterfeiting element on the side where the first surface <NUM>, a reproduced pattern-a hollow word "<IMG>" is presented on the receiving carrier on the side where the second surface <NUM> at a distance d from the optical anti-counterfeiting element. The illumination of a pixel position A' of the image is from one or more micro-prisms such as the micro-prism A in the surface micro-structure layer <NUM>. The one or more micro-prisms include at least one micro-prism that can refract light emitted by a light source S to A'. Subsets formed by the one or more micro-prisms act as a focusing lens, so that the light emitted by the light source S and partially projected to the first surface <NUM> is collected at the pixel position A'. Likewise, the illumination of a pixel position B' in the reproduced image is from one or more micro-prisms such as the micro-prism B in the surface micro-structure layer <NUM>. The one or more micro-prisms include at least one micro-prism that can refract the light emitted by the light source S to B'. The subsets formed by the one or more micro-prisms act as the focusing lens, so that the light emitted by the light source S and partially projected to the first surface <NUM> is collected at the pixel position B'. And so on, at any pixel position in the reproduced pattern (which is the hollow word "<IMG>" in this embodiment) on the receiving carrier at the distance d from the second surface <NUM>, equivalent focusing lenses formed by the corresponding one or more micro-prisms can be found in the surface micro-structure layer <NUM>.

In addition, materials of the adhesive layer <NUM> and the micro-prism <NUM> have different refractive indexes, so that reflection occurs at the interface between the adhesive layer <NUM> and the micro-prism <NUM>. As shown in <FIG>, in this embodiment, through the reflection effect, the human eye E on the illumination light side of the first surface <NUM> sees a floating virtual image-the hollow word "<IMG>". This process can be understood in this way. Each position of the floating virtual image is formed by the equivalent focusing lens set corresponding to <FIG> under a surface reflection effect. Each position of the floating virtual image may further be described as a bright spot on a surface of the equivalent focusing lens set (that is, each micro-prism may be equivalent to a part of a reflector). The plurality of bright spots form the complete floating virtual image. The virtual image is the full parallax image.

As shown in <FIG>, when illumination is performed from the second surface <NUM> of the substrate <NUM> of the optical anti-counterfeiting element in this embodiment, the hollow word "<IMG>" is reproduced on the receiving carrier on the side where the first surface <NUM> at the distance d' from the optical anti-counterfeiting element.

As shown in <FIG>, materials of the adhesive layer <NUM> and the micro-prism <NUM> have different refractive indexes, so that reflection occurs at the interface between the adhesive layer <NUM> and the micro-prism <NUM>. In this embodiment, through the reflection effect, the human eye E on the same side of the illumination light side and the second surface <NUM> sees a sunken virtual image-the hollow word "<IMG>". The virtual image is the full parallax image. The virtual image formed by reflected light may be observed without using the illumination light.

In <FIG>, an optional implementation is further given on the basis of the implementation in <FIG>. Under the illumination of the light source S on the side where the first surface <NUM>, a set of at least part of the micro-prisms in the surface micro-structure layer <NUM> is defined that a word "<IMG>" is reproduced on the receiving carrier on the side where the second surface <NUM> at the distance d" from the optical anti-counterfeiting element. The depth d" is different from d. Correspondingly, when the illumination light irradiates from the side where the second surface <NUM>, the word "<IMG>" is reproduced on the receiving carrier on the side where the first surface <NUM> at a specific distance from the optical anti-counterfeiting element. In addition, under the above cases, the human eye can respectively observe the virtual images of the words "<IMG>" and "<IMG>" presented in different depths on the side where the first surface <NUM> or the side where the second surface <NUM>. That is to say, when the illumination light source S irradiates from the side where the first surface <NUM>, the human eye can directly observe the words "<IMG>" and "<IMG>" in different depths on the side where the first surface <NUM> without using the receiving carrier. When the illumination light source S irradiates from the side where the second surface <NUM>, the human eye can directly observe the words "<IMG>" and "<IMG>" in different depths opposite to a depth of focus on the side where the second surface <NUM> without using the receiving carrier.

In <FIG>, an optional implementation is further given on the basis of the implementation in <FIG>. Under the illumination of the light source S on the side where the first surface <NUM>, the micro-prisms in the surface micro-structure layer <NUM> are further divided into a plurality of sets. Each set corresponds to a specific reproduced pattern on the receiving carrier under different depths, so that patterns (for example, a same pattern, or different patterns) are reproduced at continuously varying positions. In this embodiment, the content of the reproduced pattern is defined as a set of patterns according to the successive increasing of the reproduction depth. The set of images is the same (for example, five-ring patterns shown in <FIG>). When a relative distance between the optical anti-counterfeiting element and the receiving carrier is changed, a continuous switching effect or an animation effect of the set of images is presented. In this embodiment, the effect is the animation effect. In addition, when the illumination is performed from the side where the second surface <NUM>, the animation effect may be seen on the receiving carrier at different depths on the side where the first surface <NUM>. The virtual images at different depths can be directly and respectively observed by the human eye on two sides. The virtual images are full parallax images.

<FIG> shows a further optional implementation. In an example, the refracted light of the micro-prism may further reproduce a three-dimensional image. A part of the three-dimensional image may be reproduced at continuously varying positions. Under the illumination of the light source S on the side where the first surface <NUM>, the micro-prisms in the surface micro-structure layer <NUM> are further divided into a plurality of sets. Each set corresponds to slices of the three-dimensional image at different depths. Each slice is equivalent to a pattern. Each pixel of each pattern corresponds to refractive illumination spots of one or more micro-prisms. When the depth of the receiving carrier on the side where the second surface <NUM> is changed, slice information of the three-dimensional image at different depths can be seen. When the receiving carrier is a receiving carrier such as space water mist having the receiving three-dimensional projection information, the three-dimensional image may be directly seen in the space. In addition, when the illumination is performed from the side where the second surface <NUM>, slices of the three-dimensional image or the three-dimensional image itself may be seen on the receiving carrier on the side where the first surface <NUM>, and the human eye can directly observe the virtual images of the three-dimensional image on two sides without using the receiving carrier. The virtual images are full parallax images.

It may be understood that, a specific example of the optical anti-counterfeiting element provided in the embodiments of the present invention is not limited to structures shown in <FIG>.

In a further optional implementation of the present invention, the surface micro-structure layer may be covered by a single or multi-layer coating. The coating may be a single metal coating, a multi-layer metal coating, a coating formed by successively stacking an absorption layer, a low refractive index dielectric layer and a reflective layer, a multi-dielectric layer coating formed by successively stacking a high refractive index dielectric layer, a low refractive index dielectric layer and a high refractive index dielectric layer, and a coating formed by successively stacking an absorption layer, a high refractive index dielectric layer and a reflective layer. A structure of the coating may be called an interference multi-layer structure. The interference multi-layer structure may form a Fabry-Perot resonant cavity, and has a selection effect on incident white light, to cause emitting light to only include certain wave bands, so that a specific color is formed. When an incident angle is changed, an optical distance corresponding to the incident angle is changed, and an interference wave band is also changed, so that the color presented to an observer is changed as well, so as to form a light variation effect. In an implementation according to the present invention, the high refractive index dielectric layer refers to a dielectric layer of which refractive index is greater than or equal to <NUM>, and a material of the high refractive index dielectric layer may be ZnS, TiN, TiO<NUM>, TiO, Ti<NUM>O<NUM>, Ti<NUM>O<NUM>, Ta<NUM>O<NUM>, Nb<NUM>O<NUM>, CeO<NUM>, Bi<NUM>O<NUM>, Cr<NUM>O<NUM>, Fe<NUM>O<NUM>, HfO<NUM>, or ZnO and the like. The low refractive index dielectric layer refers to a dielectric layer of which refractive index is less than <NUM>, and a material of the low refractive index dielectric layer may be MgF2, SiO2 or the like. A material of the reflective layer may be a metal such as Al, Cu, Ni, Cr, Ag, Fe, Sn, Au, and Pt or a mixture thereof and an alloy. A material of the absorption layer may be a metal such as Al, Cr, Ni, Cu, Co, Ti, V, W, Sn, Si, and Ge or a mixture thereof and an alloy.

Physical and/or chemical deposition methods may be used to form the coating. For example, the methods include, but are not limited to, thermal evaporation, magnetron sputtering, MOCVD, molecular beam epitaxy and the like. In an embodiment, the coating may be form on the surface relief structure layer in the form of isomorphic covering. In an embodiment, at least one layer of the coating is patterned and hollowed out.

In a further optional implementation of the present invention, a diffractive holographic micro-structure or a non-diffractive surface micro-structure is added in the surface micro-structure layer.

In a further optional implementation of the present invention, the optical anti-counterfeiting element may be added with the following one or more of a conductive layer, a magnetic layer, or a layer composed of a material having an infrared characteristic, an ultraviolet characteristic or a polarization characteristic, which is equivalent to the corresponding addition of conductive anti-counterfeiting characteristics, magnetic machine-readable anti-counterfeiting characteristics, infrared characteristics, ultraviolet characteristics or polarization characteristics.

The optical anti-counterfeiting element according to the implementations of the present invention is applicable to various anti-counterfeiting products or tickets, and especially applicable to the manufacturing of windowed safety lines, labels, identifiers, wide strips, transparent windows, mulching films and the like. A thickness of the safety line is not greater than <NUM>. An anti-counterfeiting paper provided with the anti-counterfeiting element is applicable to the anti-counterfeiting of various high-safety products such as banknotes, passports, tickets, and negotiable securities.

Another aspect of the present invention provides an optical anti-counterfeiting product having the optical anti-counterfeiting element described in any implementation of the present invention. The product includes, but is not limited to, a high-safety product and a high-value-added product such as a banknote, a credit card, a passport, and a negotiable security, as well as various wrapping papers and wrapping boxes.

Claim 1:
An optical anti-counterfeiting element, comprising:
a substrate (<NUM>), comprising a first surface and a second surface that are opposite to each other;
a surface micro-structure layer (<NUM>), formed on at least a part of the first surface of the substrate,
wherein at least part of the surface micro-structure layer comprises a first set of a micro-prism (<NUM>),
the micro-prism has refractive and reflective functions simultaneously,
each pixel (A', B') of a first pattern corresponds to refractive illumination spots of one or more micro-prisms in the first set of the micro-prism, so that:
when the optical anti-counterfeiting element is irradiated on a first side of the optical anti-counterfeiting element, the refractive illumination spots of the first set of the micro-prism form the first pattern on a receiving carrier in a plane at a first distance from the second surface;
characterised in that
when the optical anti-counterfeiting element is irradiated on a second side of the optical anti-counterfeiting element, the refractive illumination spots of the first set of the micro-prism form the first pattern on a receiving carrier in a plane at a second distance from the first surface; and
a virtual image of the first pattern is observed when observed from the first side and from the second side of the optical anti-counterfeiting element, and
the first side is a side at which the first surface is located, and the second side is a side at which the second surface is located.