EA020989B1 - Microoptic system for forming images in transmitted and reflected light - Google Patents

Abstract

The micro-optical system for forming dynamic visual images being claimed as the invention relates primarily to devices which can be used for certifying the authenticity of articles, and can be effectively used for protecting bank notes, securities, documents, plastic cards, bank payment cards, excise, identity and control marks, and also various popular goods from forgery. The micro-optical system according to the invention consists of elementary domains, in each flat phase elements of two types are recorded, the first of which represents a kinoform is liable for forming images in transmitted light, and the second represents diffraction gratings, forming an image in reflected light, wherein the depth microrelief of the kinoform exceeds the depth microrelief of the diffraction gratings. The claimed combination of the essential features of the invention ensures the achievement of the technical result that consists in increasing the reliability of the visual control of products protected using this invention by creating the easily checkable images in transmitted and reflected light. The realization of the micro-optical system for forming dynamic visual images can be implemented with the use of existing standard equipment.

Description

The inventive micro-optical system for visual authentication is related to the field of optical protective technologies, mainly to devices, the so-called security tags used to authenticate banknotes, plastic cards, securities, etc.

Currently, optical security technologies are widely used to authenticate banknotes, plastic cards, and securities. Most protective optical elements operate on reflection when the observer and the light source are on the same side of the optical element. The latter applies to both protective elements with a metallized microrelief and transparent optical elements (passport laminate).

Currently, progress in the field of technology for the production of banknotes and plastic cards has provided the opportunity to create so-called windows (\ ut <bo \ U5). This gives a practical opportunity to include transparent optical elements in banknotes and plastic cards that work both on the passage of light and its reflection. From the point of view of security against falsification, such optical elements are certainly promising.

The closest to the claimed invention, the technical solution for the totality of features is a micro-optical system described in patent I8 6417968 B1 (prototype).

The known micro-optical system is a surface structure that includes elements that are arranged in a mosaic order and are diffraction gratings with different profiles and strokes. In other words, the said patent describes a microscopic system consisting of elementary regions, in each of which a symmetric or asymmetric diffraction grating is recorded. All gratings have approximately the same depth, but different profiles and different orientations. The optical element described in the patent works on reflection and provides the effect of changing the intensity of reflected light from areas of the hologram when viewed from different angles. The optical element described in the patent can form the effect of changing images when the optical element is tilted or rotated, etc.

The disadvantages of the known micro-optical system include insufficient protection from fakes. In addition, the use of diffraction gratings as the basic optical element severely limits the possibilities of forming the directivity pattern of the optical element.

The objective of the present invention is to provide a micro-optical system with a higher degree of protection against fakes and imitations. In accordance with the invention, a micro-optical imaging system is described, the structure of which is a flat optical element, consisting of elementary regions, each of which is a rectangle, the size of which does not exceed 100 μm, while in each rectangle two-phase planar elements are recorded, the first of which is a kinoform, responsible for the formation of images in transmitted light, and the second - diffraction gratings, which form an image in reflection In this case, the depth of the microrelief of the kinoform is more than 3 times greater than the depth of the microrelief of diffraction gratings.

In the particular case of the implementation of the claimed microscopic system, a binary kinoform is used to form the image in transmitted light, while in transmitted light the observer sees two symmetric images with respect to the zero diffraction order at a point source.

In another particular case, multigradation kinoforms are used to form the image in transmitted light, while in transmitted light the observer sees two different images at a point source, which are not symmetrical with respect to the zero diffraction order.

The use in the claimed invention of optical elements with different depths of the microrelief is important, since this is what allows you to form an image in both transmitted and reflected light.

The central point of the claimed invention is the use of flat phase optical elements. Each flat phase optical element is characterized by its phase function, and vice versa, knowing the phase function, one can calculate the microrelief of a flat phase optical element.

The problem of synthesis of planar optical elements can be divided into two components: calculation of the phase function and synthesis of the microrelief of a planar phase optical element.

Currently, there are effective algorithms for solving inverse problems of the synthesis of plane optical elements. There are two approaches. The first makes it possible to calculate a smooth phase function (Sotrieg Orysk & Sotrieg Hoboduyu L.U. Oopsbatkku, A.A. In the second approach, the phase function is not smooth; it can oscillate rapidly. Such elements are called kinoforms.

Kinoform as an optical element was presented in the work of L.V. Leket, R.M. NYX, TATT. 1gbap. Thu kshoGott: but ne \ y \\ aeGgoSh hesopkyyysop beuyue, 1BM 1. Ke8. Yeah., 13 (1969), 105-155. There are two types of kinoforms: binary and multi-gradation. Unlike thin holograms recorded by

- 1,020,989 registration of the interference pattern, multi-gradation kinoform forms at a given wavelength image with high efficiency. Multi-gradation kinoform has the maximum theoretical efficiency in the formation of arbitrary images, close to 100%. Unlike volume phase holograms, which also have 100% diffraction efficiency, multi-gradation kinoforms can be mass-replicated from the original, while the energy efficiency of printed copies is also theoretically close to 100%. The effectiveness of binary kinoforms does not exceed 50%.

Existing algorithms make it possible to calculate the microrelief of a diffractive optical element - a kinoform, if geometric parameters, characteristics of light sources and the image to be formed are specified. If the microrelief depth of the diffraction gratings forming an image for visual inspection in reflected light is 0.1-0.2 μm, then the depth of the kinoform forming the image in transmitted light is 0.5-0.7 μm for binary elements, and for of multi-gradation kinoforms, the depth of the microrelief reaches 1-1.5 μm (SotryG Orysk & SotryG Nolodgaru LU A.U. Oopsbagku, A.A.

The basic technology for the formation of the microrelief of flat optical elements in the optical range is the technology of electron beam lithography. The specified technology allows you to form the microrelief of the microoptical system of the invention, with the necessary accuracy. Equipment for electronic lithography is very expensive, technology is knowledge-intensive and has limited distribution. All this creates a reliable barrier to protect the claimed system from fakes.

For mass replication of flat optical elements claimed in the invention, equipment for holographic technologies can be used: electroplating, installation of animation, equipment for rolling, application of adhesive coatings, etc. (Shocked Orosk & Shredded Hodgarduu A.U. Oopsbagku, A.A.

In the claimed micro-optical system, the image in reflected and transmitted light is observed visually. Manufacturing technology of originals is not publicly available. The technology of mass replication provides a low price for mass production.

In FIG. 1 shows a scheme for observing an image for passage; in FIG. 2 is a diagram for observing a reflection image;

in FIG. 3 is a diagram of dividing a region of an optical element into elementary regions;

in FIG. 4 - a variant of the location of the image forming region in transmitted light (kinoform) in the elementary region — the rectangle;

in FIG. 5 - a variant of the arrangement of the image forming region in reflected light (diffraction grating) in the elementary region - a rectangle; in FIG. 6 - fragment of the microrelief of the diffraction grating; in FIG. 7 is a fragment of a microrelief of a binary kinoform; in FIG. 8 is a fragment of the microrelief of a multi-gradation kinoform; in FIG. 9 is a fragment of the profile of the microrelief in the elementary rectangle; in FIG. 10 is an example of an image formed by passing a binary kinoform; in FIG. 11 is an example of an image formed on the passage of a multi-gradation kinoform;

in FIG. 12 is a fragment of a planar optical element forming the image shown in FIG. 10, and in reflected light, the image shown in FIG. thirteen;

in FIG. 13 is an example of an image formed for an observer in reflected light.

An optical transmission imaging scheme is shown in FIG. 1. A ray of light from a point source (1) falls on a transparent optical element (2) located in a transparent window. The radiation transmitted by the plane optical element forms an image for the observer (image in transmitted light). An optical reflection imaging circuit is shown in FIG. 2. A ray of light from a point source falls on the optical element. The reflected light scattered by the plane optical element forms an image for the observer. In FIG. Figure 3 shows a diagram of dividing the region of an optical element into elementary regions, each of which is an elementary rectangle with a size of not more than 100 μm. Each elementary rectangle contains two flat optical elements: kinoforms and diffraction gratings. In FIG. Figure 4 shows a conditional variant of placing a kinoform region in each elementary region — a rectangle (the kinoform region is shaded with dark color). Accordingly, in FIG. 5, the region filled with diffraction gratings is darkened. In FIG. 4 and 5, the region containing the diffraction gratings may not be round, but represent, for example, a square or a rectangle, or represent several rectangles filled with diffraction gratings. Accordingly, the entire remaining part of the elementary region is filled with kinoform. In FIG. Figure 6 shows a fragment of the microrelief of a planar optical element — a diffraction grating. In FIG. 7 shows an example of the microrelief of a flat optical element — a binary kinoform. In FIG. 6, 7, the depth of the microrelief is proportional to the darkening at each point in the figure. In FIG. 8 given

- 2 020989 fragment of the microrelief of a flat optical element - a multi-gradation kinoform. In FIG. Figure 9 shows an example of a fragment of a microrelief profile in an elementary rectangle (section along the line A-A in Fig. 5). It can be seen that the depth of the microrelief of the kinoform (1) differs from the depth of the microrelief of diffraction gratings (2) by more than three times. In FIG. 10 shows an example of an image formed by a binary kinoform for passage. In FIG. 11 shows an example of an image formed by a multi-gradation kinoform for passing. The image formed by the multi-gradation kinoform is fundamentally different from the image formed by the binary kinoform. Binary kinoform forms images that are identical in plus first and minus first diffraction orders. Multi-gradation kinoform allows you to create images that are different in plus the first and minus first diffraction orders.

The manufacture of the microrelief of multi-gradation kinoforms for the optical wavelength range is a difficult task, since the accuracy of the manufacture of the microrelief should be 20-30 nm (A. Goncharsky, On a Problem of the Synthesis of Nano-Optical Elements // Computational Methods and Programming, 2008, v. 9, No. 2). Formation of asymmetric visual images such as those shown in FIG. 11 is a guarantee of protection of the micro-optical system from fakes. It is the use of multi-gradation kinoforms (preferred option) that is the central point of the invention and distinguishes the claimed invention from the prototype. In FIG. 12 shows a fragment of a planar optical element forming the image shown in FIG. 10, at the same time, the optical element forms the image shown in FIG. 13. The fragment size of the optical element shown in FIG. 12 is 500x500 microns. A typical area of an optical element in a transparent window used to protect banknotes is a few square centimeters. The area of kinoform is indicated by the number 1.

An important point of the invention is the special structure of dividing a planar optical element into elementary regions. The size of the fragments of diffraction gratings forming a reflected image does not exceed 100 μm, while the distance between adjacent fragments of diffraction gratings is also not higher than 100 μm. This provides a raster structure of the image formed on reflection. The image is formed by separate disjoint pixels. However, the limited resolution of the human eye with the selected parameters of the partition (the size of the elementary region is less than 100 microns) does not allow the human eye to see individual elements of the raster in the generated image.

The special partitioning structure proposed in the application for an invention makes it possible to form an image for passage that is invariant (independent of) the source shift inside a transparent window. The calculation of the microrelief of the kinoform forming the image for passage is carried out in the entire region of the transparent window, with the exception of the regions of localization of diffraction gratings. In FIG. 12, this area is indicated by the number 1. An important characteristic of the kinoform is that each part of the kinoform forms the same image. The latter provides the possibility of small shifts of the source (or observer), at which the formed image does not change.

The main differences of the claimed microoptical system from the prototype.

1. In the present invention, for the formation of an image for passage, in contrast to the prototype, which operates only with diffraction gratings, kinoforms are used, which significantly expands the possibilities in image formation.

2. In the present invention, fragments of an optical element forming an image for transmission and reflection have a microrelief depth that differs by more than three times. It is the difference in depth in the elements that form the images in reflected light and in transmitted light that allows the micro-optical system to work at different positions of the source and observer relative to the controlled optical element. If the depth of the microrelief of the kinoform and diffraction gratings differs little from each other, then either one image or both images (in reflected or transmitted light) will have significantly lower brightness, which will complicate visual control.

3. The present invention proposes a special design of the optical element, in which the optical element is divided into elementary regions — rectangles no larger than 100 μm in size so that each elementary region contains fragments of the optical element, which work for transmission and reflection. This design ensures the invariance of the image formed during the passage under shifts of the light source. The image formed by the optical element in transmitted light does not change while the light source is visible through a transparent window.

The claimed micro-optical system allows for simple and reliable visual control for the observer. The manufacturing technology of the originals of flat optical elements, including multi-gradation kinoforms and diffraction gratings of different depths, is not publicly available, which provides reliable protection of the claimed micro-optical systems from fakes. The technology of mass replication is available and provides a low price for micro-optical systems for mass replication.

Currently proposed in the invention micro-optical systems can be implemented.

- 3,020,989

Moreover, mass replication of micro-optical systems is possible. For the manufacture of originals of micro-optical systems, electron beam technology can be used. Electron beam technology is unique in that it provides a very high resolution. Modern lithographs make it possible to form a microrelief with stamps of the order of 0.1 by 0.1 microns, the best of them have stamp sizes up to 20 by 20 nm. The accuracy of microrelief formation in height also amounts to about 20-30 nm. The microrelief depth of a flat optical element can be on the order of 1-1.5 microns. Such a depth is sufficient for the formation of optical elements operating on reflection and transmission. Electron beam technology makes it possible to fabricate with high accuracy a symmetric and asymmetric microrelief of micro-optical systems for imaging in transmitted and reflected light (Sotrieg OrOsk & Soter Sogloduyu A.U. .

UV-replication technologies can be used to replicate the original (81er-apy-Kerea1 UI 1trp1 Ljodgaryu Gog \ WaGeg-Leuye1 Satega MapiGasShypd Wu S. Kgesbck T. Sikpega, K. How! A, Ό. sa1e Keu1e№, 1i1u-Aidik1 2011). For mass replication, you can use UV-rolling machines (Ko11! Oh go11 uyuyuyuuuuuuuuuuuuuuuuuu, Tieuuuuuu Tzhek, Ouyuyuyu 2004), as well as standard equipment for the production of holograms (Oryuyu Eosyet Zesuyuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuyu , Ayes Noike, 2005).

The visual effect formed in the application for an invention is easily controlled. Micro-optical system is well protected from fakes.

The following example of a specific implementation of the invention confirms the possibility of its implementation, without limiting its scope.

Example.

As an example, a micro-optical system for calculating visual images in transmitted and reflected light is calculated and manufactured. In reflected light, the image shown in FIG. 13. In transmitted light on a point source, the observer sees the image shown in FIG. 10. The problem is solved using a flat optical element, a fragment of the microrelief of which is presented in FIG. 12. The size of the optical element was 10 by 10 mm. A flat optical element is divided into elementary regions — rectangles of 100 per 100 μm in size so that the number of elementary regions is 10000. In each elementary region, diffraction gratings are formed in a circle (see Fig. 5), whose area is 20% of the area of the elementary region. In the entire remaining region (see Fig. 4), binary kinoform is recorded, which forms the image shown in FIG. 10. The depth of the microrelief of the diffraction gratings is 0.15 μm. The depth of the microrelief of the kinoform is 0.7 μm. The original flat optical element is produced using electron beam lithography using an electron beam exposure apparatus ΖΒΛ21 manufactured by Karl Zeiss Jena with a minimum stamp size of 0.1 to 0.1 μm. Using electroforming, master matrices and work matrices are made. Using the installation of ultraviolet rolling, samples of the micro-optical system are made, which are claimed for patenting.

Studies have shown the high efficiency of the solutions proposed in the application.

Claims (3)

CLAIM 1. A micro-optical system for generating visual images in transmitted and reflected light, which is a flat optical element, characterized in that said element consists of elementary regions, which are rectangles, the size of which does not exceed 100 microns, with kinoforms recorded in each rectangle, responsible for the formation of images in transmitted light, and diffraction gratings that form the image in reflected light, and the depth of the microrelief of the kinoform is more than 3 times greater than The depth of the microrelief of the diffraction gratings is measured. 2. The microoptical system according to claim 1, in which a binary kinoform is used to form the image in transmitted light, while in transmitted light the observer sees two symmetric images with respect to the zero diffraction order at a point source. 3. The micro-optical system according to claim 1, in which a multi-radiation kinoform is used to form the image in transmitted light, while in transmitted light the observer sees two different images at a point source with respect to the zero diffraction order.