EP1875315A2 - Reseau de diffraction et procede de production associe - Google Patents

Reseau de diffraction et procede de production associe

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Publication number
EP1875315A2
EP1875315A2 EP06724031A EP06724031A EP1875315A2 EP 1875315 A2 EP1875315 A2 EP 1875315A2 EP 06724031 A EP06724031 A EP 06724031A EP 06724031 A EP06724031 A EP 06724031A EP 1875315 A2 EP1875315 A2 EP 1875315A2
Authority
EP
European Patent Office
Prior art keywords
diffraction grating
grating
radiation
diffraction
lattice
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP06724031A
Other languages
German (de)
English (en)
Inventor
Wittich Kaule
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Giesecke and Devrient GmbH
Original Assignee
Giesecke and Devrient GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Giesecke and Devrient GmbH filed Critical Giesecke and Devrient GmbH
Publication of EP1875315A2 publication Critical patent/EP1875315A2/fr
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
    • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
    • G07D7/06—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using wave or particle radiation
    • G07D7/12—Visible light, infrared or ultraviolet radiation
    • G07D7/128—Viewing devices
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1842—Gratings for image generation
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1847—Manufacturing methods
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
    • G03H1/0808—Methods of numerical synthesis, e.g. coherent ray tracing [CRT], diffraction specific
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/26—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
    • G03H1/30—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique discrete holograms only
    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
    • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
    • G07D7/003—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using security elements
    • G07D7/0032—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using security elements using holograms
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G03H1/2249—Holobject properties
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/0005—Adaptation of holography to specific applications
    • G03H1/0011—Adaptation of holography to specific applications for security or authentication
    • G03H2001/0016—Covert holograms or holobjects requiring additional knowledge to be perceived, e.g. holobject reconstructed only under IR illumination
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0402—Recording geometries or arrangements
    • G03H2001/043—Non planar recording surface, e.g. curved surface
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0476—Holographic printer
    • G03H2001/0482—Interference based printer
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2210/00—Object characteristics
    • G03H2210/20—2D object

Definitions

  • the invention relates to a method for producing a diffraction grating for a diffractive optical element having one or more subregions, each containing a lattice pattern defined by a lattice constant and an angular orientation.
  • the invention further relates to a diffraction grating which can be produced in this way and to a spectral apparatus or a diffractive optical element which is equipped with such a diffraction grating.
  • Spectral or diffractive optical element sensors often include diffraction gratings. There is a need to design the diffraction gratings as compact as possible and adapted to the particular application.
  • the present invention seeks to provide a method for producing a diffraction grating of the type mentioned, which avoids the disadvantages of the prior art.
  • the design of the diffraction grating for a given application situation should be able to be determined in a simple manner.
  • such diffraction gratings should be able to be found which have a simple overall geometry when the predetermined imaging and dispersion properties are achieved.
  • a step a the position of at least one source, from which radiation is incident on the diffraction grating, and in a step b), the position of at least one target, to which the diffraction grating is intended to deflect the radiation, are specified.
  • the spatial position and orientation of the subregions as well as the lattice constant and the angular orientation of the lattice patterns, which are required in order to deflect the radiation incident on the diffraction grating from the source to the target are then determined in a step c).
  • n (r), k x (F) and k 2 (F) are the normal vector, the incident wave vector and the fail wave vector at reference point F
  • m is the diffraction order
  • g ( r) represent the grid vector for the considered sub-area.
  • H (F) indicates the local normal vector of the diffraction grating which describes the orientation of the grating in three-dimensional space. Due to the generally curved overall geometry of the diffraction grating, the normal vector n (r) may vary along the curved grating area, emphasized in relation (1) by the explicitly written location dependence of the normal vector, g or g (f), if one wishes to emphasize location dependence , represents the grid vector of the respective sub-area.
  • the grating vector g also indicates the orientation of the grating lines.
  • the incident light is characterized in relation (1) by one or more illumination vectors Jc 1 (F), each representing a vector of length 2 ⁇ / ⁇ i pointing from the source to the reference point of the considered subregion of the diffraction grating, ⁇ i being the Wavelength of light so that monochromatic light passes through illumination vectors. rather length and white light is described by illumination vectors of different lengths.
  • the emergent beam is indicated by light-rejection vectors Jc 2 (r), each representing a vector of length 2 ⁇ / ⁇ 2, pointing from the considered sub-range to a target point on the receiver array, m represents the diffraction order, and is an integer.
  • the diffraction grating is subdivided into subregions within which the vector quantities occurring are taken to be constant. They are therefore related to a reference point with coordinates r ⁇ (x ⁇ , y 0 , z 0 ) within a subarea.
  • the shape and size of the subregions are advantageously chosen so that this simplification represents a sufficiently good approximation for the given application.
  • the size of the subregions can be selected depending on the curvature of the diffraction grating so that regions of greater curvature are divided into smaller subregions.
  • the distance between the source and the diffraction grating or between the diffraction grating and the receiver can affect the required size of the subregions.
  • the sub-regions are advantageously divided into different groups that divert the radiation incident from the source toward different points of the extended target region.
  • the target consists, for example, of n pixels
  • the vector formula (1) is independent of coordinate systems.
  • the vectors can be anywhere in space.
  • the relationship (1) can be represented in various ways. Further details are given in the international patent application PCT / EP2004 / 011497, the disclosure of which is incorporated in the present application in this respect.
  • the overall geometry of the diffraction grating will specify before the calculation.
  • the determination of the spatial position and orientation of the subregions in step c) then takes place taking into account this predetermined overall geometry.
  • a flat overall geometry or a cylindrically curved overall geometry can be specified for the diffraction grating. Both geometries allow a particularly simple realization of the calculated diffraction gratings in a substrate.
  • the overall geometry of the diffraction grating in step c) can also be determined together with the spatial position and the orientation of the subregions.
  • such a diffraction structure is advantageously selected as being optimal / having the simplest possible overall geometry.
  • additional optical elements such as concave mirrors, mirror systems, lenses, prisms or other optical gratings, can be provided, which are arranged in the beam path between the source and the diffraction grating or between the diffraction grating and the target.
  • the type and position of these optical elements can now be predefined according to a first variant of the invention prior to the calculation.
  • the subregions and the grid patterns are then determined in step c) taking into account the predetermined optical elements.
  • the type and position of the optical elements in step c) are determined together with the subregions and the lattice patterns.
  • the aim is to obtain as simple and as simple as possible optical elements as simple as possible producible geometry of the diffraction grating, the entire system should meet the given dispersion and imaging properties. It is understood that various solutions are possible, which prove to be optimal from different points of view. This can be taken into account by a weighting of the individual sub-goals (few optical elements, simple optical elements, simple geometry of the diffraction grating, etc.) and / or by specifying certain tolerance thresholds or maximum values. For example, the default may be to determine a diffraction grating having a flat or cylindrically curved overall geometry using at most two concave mirrors to be arbitrarily placed in the beam path.
  • optical elements can be done by conventional methods. However, at least one of the optical elements in the determination in step c) is preferred by the relationship
  • n oE , k l oE and k 2 oE represent the normal vector, the incident wave vector or the fail wave vector, rrioE the diffraction order and g oE a grating vector for the optical element.
  • the occurring Vectors may be location-dependent without this being explicitly written in relation (2).
  • the optical elements can thereby be described with the same formalism as the diffraction grating itself.
  • the general form of the relationship (2) not only refractive optical elements such as mirrors, prisms or lenses can be obtained, but also diffractive optical elements having a diffraction optical grating.
  • varying local vectors Jt 1 (r) and Jc 2 (F) are used to determine the lattice constants and angular orientations in step c) over the surface of the diffraction grating, their directions being determined by the connecting line between the source and the reference point of the respective subarea are given the connecting line of reference point and destination, and which are determined separately for each sub-area.
  • the source from which the radiation is incident on the diffraction grating may be given as a point light source or as a spatially extended source, for example as an entrance slit.
  • the target is given in an advantageous embodiment as a spatially extended target, in particular as a one-dimensionally extended target, such as a linear array of photodiodes, a CCD line or an exit slit.
  • the one-dimensionally extended target may be straight or curved.
  • the incident radiation is spectrally split by the diffraction grating to different positions of the target, so that the spectral composition of the incident radiation can be analyzed.
  • the target is predefined as a plurality of pixels, wherein each of the pixels is assigned at least one subregion of the diffraction grating which deflects the incident radiation toward this pixel. Through the entirety of the sub-areas, the entire destination is captured.
  • each of the pixels is even assigned a group of subregions containing a plurality of subregions. The subregions of a group may be distributed over the surface of the diffraction grating.
  • a homogeneous illumination of the target can be achieved even with only partial illumination of the diffraction grating.
  • the target can form hidden information that becomes clear only when using an implement.
  • At least one of the subregions contains, in addition to the first lattice pattern, at least one further res grid pattern which superimposes the first grid pattern.
  • the lattice constant and the angular orientation of the first and the at least one further lattice pattern are advantageously determined together in step c).
  • the first and the at least one further grid pattern can be assigned to different sources and / or to different destinations.
  • the superimposed grid patterns can be written on top of each other or exposed to one another in the further course of the production.
  • the subregions are each filled with grating patterns, whose lattice constants and angular orientations are given by the lattice constants and angular orientations determined in step c) for this subrange.
  • the diffraction grating can be inscribed in step d), in particular by means of an optical or electron beam lithography method, onto a radiation-sensitive material, in particular a resist layer applied to a substrate plate, in order to bring about a change in state therein.
  • a relief structure is generated by the change of state.
  • a metallization layer is advantageously applied to the radiation-sensitive material and a galvanic impression is produced.
  • the impression or a further Abf orm the same is advantageously used as an embossing die for embossing a lattice structure in a substrate.
  • the diffraction grating is produced by means of electron beam lithography, with which grating lines of the highest quality and finest resolutions up to the nanometer range can be produced.
  • the methods described in the publications DE 10226115 Al and DE 10243413 Al can be used, which are included in the present application in this respect.
  • the diffraction grating is generated holographically in step d) by superposition of two coherent monochromatic radiation beams in a radiation-sensitive substrate.
  • the required beam configuration is determined using the relationship
  • ⁇ 1 and k 2 are the wave vectors of the two beams used for exposure
  • n is the normal vector of the substrate surface
  • g is the grating vector of the grating pattern to be generated. Further details for determining the beam configuration using relationship (3) are shown below.
  • the invention also includes a diffraction grating for a diffractive optical element producible by a method of the type described, wherein the diffraction grating has one or more subregions each containing a grating pattern defined by a grating pitch and an angular orientation.
  • the invention also includes a diffraction grating manufacturable in the manner described with open and hidden image information / wherein the open image information is visible under ambient lighting conditions and the hidden image information is clearly recognizable only with an aid.
  • the hidden image information may be designed to illuminate the diffraction grating with divergent monochromatic radiation and to view the information on a catcher screen.
  • the hidden image information is formed by a plurality of pixels, wherein each of the pixels is associated with at least a subregion of the diffraction grating which deflects the incident radiation toward this pixel.
  • the invention further comprises a spectral apparatus equipped with a spectrally splitting diffraction grating of the type described above.
  • the spectral apparatus can contain, in addition to the diffraction grating, further optical elements, such as concave mirrors, mirror systems, lenses, prisms or additional optical gratings.
  • the diffraction grating of the spectral apparatus is designed with a simple overall geometry, in particular with a planar or a cylindrically curved overall geometry.
  • the invention also includes a diffractive optical element equipped with a diffraction grating of the type described.
  • Fig. 2 shows a detail of a subregion of the diffraction grating for
  • FIG. 3 shows another spectrometer configuration with a diffraction grating according to an embodiment of the invention
  • FIG. 4 shows a general spectrometer configuration with a diffraction grating according to the invention and two optical elements arranged between the source and the diffraction grating or between the diffraction grating and the detector.
  • Fig. 6 is a sketch for illustrating the generation after
  • FIG. 10 shows a diffraction grating according to the invention which, in addition to open image information, contains hidden image information (hidden image), and FIG
  • FIG. 11 shows a banknote with a self-verifying security feature comprising a diffraction grating according to the invention and an optical element.
  • Fig. 1 shows schematically a spectrometer configuration with a diffraction grating according to a first embodiment of the invention.
  • the spectrometer configuration 10 contains as a radiation source a window 12, in which the luminous medium is, whose spectrum is to be determined.
  • the core element of the spectrometer is the diffraction grating 20, which deflects the impinging light beams 14 in such a way that the emergent beams 16 strike the receiver diode array 18 spectrally dissected.
  • the vector relationship (1) specified above is achieved according to the invention.
  • n (f) x (£, (F) - k 2 (F)) m ⁇ g (f)
  • N (f) denotes the local normal vector of the diffraction grating 20, which determines its orientation in three-dimensional space. writes. As can be seen from Fig. 1, the normal vector n (f) varies along the curved grating surface.
  • FIG. 2 A section of the lower region 22 is shown again in FIG. 2 for the purpose of illustrating the variables occurring. Since the vector quantities n, k x , k 2 and g are assumed to be constant within the sub-area 22, their location-dependence is not indicated in FIG. 2. Incidentally, in the context of this description, for the sake of brevity, the explicit indication of the existing location dependencies of the vector quantities is often omitted.
  • g denotes the lattice vector of subregion 22, where ⁇ the lattice constant a, that is the distance of the grid lines 24 represents.
  • the grating vector g indicates the orientation of the grating lines, which is shown in Fig. 2 relative to a reference direction 26 mit Vietnamese e of the azimuth angle ⁇ .
  • the incident light is characterized by one or more illumination vectors Ar 1 (r), each pointing from the source 12 to the reference point of the considered sub-region 22 of the diffraction grating.
  • the spectral distribution of the incident light can be taken into account by a distribution of ⁇ vectors of different lengths.
  • the emergent rays are described by light-rejection vectors k 2 (F), each pointing from the considered subregion 22 to a target point on the receiver diode array 18.
  • n (f) Hy ⁇ X 0 ⁇ O ' Z 0)' • ⁇ " ä ⁇ ( x ⁇ 5> O 5 z o) * " ⁇ jy (, x o>ya> z oJ + ä? ( ⁇ : ⁇ '> O 5 Z o)
  • f (x, y, z) 0 defines an area that can be arbitrarily curved and describes the overall geometry of the diffraction grating 20
  • F (x o , y o , z o ) is the reference point for the considered subregion for which the calculation is currently performed
  • F 1 ( ⁇ 1 , y x , z ⁇ ) the position of the source 12
  • the direction of the grid vector is given by the arrow from the zero point to the point defined by the coordinates (g x , g y , g z ).
  • the overall geometry of the diffraction grating does not become too complicated, it may be advisable to use one or more further optical elements, for example concave mirrors, a mirror system, a lens system, prisms or another optical grating, in the beam path between source and diffraction grating or between diffraction gratings and receiver array.
  • one or more further optical elements for example concave mirrors, a mirror system, a lens system, prisms or another optical grating, in the beam path between source and diffraction grating or between diffraction gratings and receiver array.
  • a concave mirror 32 is arranged in the beam path between the source 12 and the diffraction grating 30. assigns.
  • the beam path 34, 35 via the concave mirror 32 can now be considered in the following manner.
  • the concave mirror can be described by the relation (1).
  • the vector relationship (1) is general enough to also describe other optical elements, such as the concave mirror 32. In order to avoid confusion of the occurring quantities, the quantities relating to an additional optical element are given the index "oE.” For the description of optical elements, the vector relationship (1) then becomes in the form
  • a refractive surface is an area separating homogeneous media with refractive indices m and n2. If ⁇ represents the vacuum wavelength, then a refracting surface can be chosen
  • a flat or curved surface with another optical lattice ie a surface which primarily diffracts light but can also reflect and possibly refract light (with different media above and below the lattice), is characterized by the general form of the relationship (2) described with moE ⁇ 0 and a corresponding grid vector.
  • the concave mirror 32 is now included by description according to point i) in the calculation of the diffraction grating 30 in order to achieve a simpler overall geometry of the diffraction grating 30. While the configuration of FIG. 1 requires a diffraction grating 20 of overall bowl-shaped geometry that is relatively expensive to manufacture, the additional free parameter introduced by use of the concave mirror 32 allows the use of a diffraction grating 30 of simpler geometry. In the exemplary embodiment, a cylindrically curved diffraction grating 30 can be used, which is relatively easy to produce, for example, by means of electron beam lithography. The shape and position of the concave mirror 32 is calculated in step c) in such a way that results for the diffraction grating 30 as simple as possible overall geometry.
  • optical elements 42 and 44 respectively. are ordered.
  • the optical elements 42 and 44 are shown in the figure for illustrative purposes only as a concave mirror, but may also represent more complex optical systems and even contain even optical diffraction gratings, as these too are correctly described by relationship (2).
  • the additional optical elements 42, 44 can often achieve a particularly simple overall geometry of the diffraction grating 40, in particular a cylindrically curved or planar overall geometry.
  • the optical elements 42 and 44 are preferably integrated into the calculation of the diffraction grating 40, as already explained above and in conjunction with FIG. 3.
  • the diffraction gratings thus calculated can then be produced, for example, by means of electron beam lithography, as described in document PCT / EP2004 / 011497, the disclosure of which is incorporated in the present description to this extent.
  • the calculated diffraction gratings can also be produced holographically, wherein the above-mentioned vector relationship (1) can then be used a second time for the calculation of the required beam configuration, as described in more detail below.
  • holographic grating generally refers to a diffraction grating which is produced by superposition of two coherent monochromatic radiation beams in a radiation-sensitive substrate.
  • nx (k ⁇ - k 2 ) g (3)
  • both the beams k x and k 2 are incident coherent beams, while the relation (1) is an incident beam and a dropout beam.
  • the vectors Hc 1 and k 2 are in relationship (3) vectors of length 2 ⁇ / ⁇ , which point in the beam direction, where ⁇ is the wavelength of the radiation used for the exposure.
  • the surface normal n is a unit vector that is perpendicular to the substrate surface in the impact area of the overlapping laser beams.
  • the lattice vector g is a vector of length 2 ⁇ / a which lies in the lattice plane and is parallel to the lattice lines, where a represents the lattice constant.
  • the vectors can be location-dependent, without this being expressed explicitly in the notation.
  • the area normal vector n can vary arbitrarily in space when using the vector relationship (3).
  • unparallel beams and uneven, ie curved collecting surfaces can be included in the calculation in a simple manner.
  • 5 schematically shows a structure 50 for producing a diffraction grating according to the invention with a radiation-sensitive layer 52 at a collecting surface 54.
  • the monochromatic light beam 60 of a laser source (not shown) is split via a half mirror 62 into two partial beams 64A and 64B, which coherently overlap in the lower region 56 after being deflected by the mirrors 66A and 66B.
  • the forming standing wave field by intersecting with the collection surface 54, creates a grid pattern with lines of maximum intensity and with minimum intensity gaps and exposes this grid structure into the radiation sensitive layer 52.
  • the illustration of Fig. 6 illustrates the most important calculation quantities:
  • the vectors k ⁇ and k 2 are the wave vectors of the rays emanating from the points Qi and Ch respectively and incident on a point P of the curved collection surface 54, n is the surface normal unit vector of area 54 at point P and g is the local grid vector of the line pattern generated at point P by interference.
  • the radiation-sensitive layer 52 at the collecting surface 54 is preferably no thicker than the light wavelength ⁇ . It may be formed, for example, by a silver halide emulsion. After development, a transparent light-dark line pattern then results, which is transparent as a diffraction grating.
  • the radiation-sensitive layer 52 may be formed on the collection surface 54 by, for example, a photoresist layer.
  • a photoresist layer results after the development of a mountain and valley wave profile, which is suitable for further processing by molding, so that the diffraction grating can be replicated and duplicated.
  • the superimposed coherent monochromatic waves are sine waves, the peak and valley intensity profile resulting from interference also has a sinusoidal character, so that grid structures 70 with a sinusoidal cross-section result in a conventional photoresist, as shown in FIG. a) is shown.
  • the reference numeral 72 designates the substrate, the exposed layer is denoted by 74.
  • the grating profile may be implemented both as a reflective profile 80 as shown in Fig. 8 (a) or as a transparent refractive profile 82 as shown in Fig. 8 (b).
  • the grid surface is metallized or the grid is made entirely in metal, for example as a galvanic impression.
  • the grid is embossed in a transparent plastic, for example a thermoplastic or a UV-curing lacquer. If the grating is to reflect as well as refractory, a coating of high refractive index material such as zinc sulfide may be used.
  • the remaining regions can be covered with an opaque mask.
  • the areas under the mask then remain unexposed.
  • the subregions 56 can be successively exposed to different grating patterns, thus obtaining the desired diffraction grating.
  • the superimposition of given beams produces a clearly defined grid, the inverse is ambiguous, so that there are several beam configurations that lead to the same given grid.
  • a ⁇ / 2.
  • opposite generating beams with an intermediate angle ⁇ 180 ° are required, as well as a collecting surface which is perpendicular to the wavefronts of the standing wave field.
  • Larger lattice constants are obtained by choosing the intermediate angle between the generating beams smaller than 180 °, and / or tilting the catching plane against the wave fronts of the wave field.
  • the relationship (3) describes the correct orientation of the beams involved for any collecting surfaces F in general form.
  • the positions of the mirrors 66A and 66B, the position of the laser source, and / or the position of the collecting surface 54 can be adjusted accordingly.
  • changes to the beam configuration are usually very complex, one generally prepares several beam configurations side by side in one setup, which are then activated or deactivated with shutters can be described, for example, in the document EP 0467601 A2 in connection with dot-matrix devices.
  • Laser beams are generally thin on their own accord, as illustrated in FIG. By inserting apertures and / or by focusing the rays, one can even reach area diameters of 0.1 mm or less.
  • FIG. 9 shows a schematic illustration of a "hidden image” sensor 90, ie a test device for hidden image information in holograms and other hologram-like diffraction structures so-called “hidden image”), which is not recognizable without special measures.
  • a hologram 92 to be tested is illuminated with a laser, for example a commercially available laser pointer 94.
  • the hidden image information contained in the sample hologram 92 is reconstructed by the laser radiation in a characteristic direction 96 and projected onto the generally curved surface of a screen 100.
  • the screen 100 now includes a diffraction grating calculated according to the present invention having a plurality of subregions 102 configured to direct radiation emanating from the sample hologram 92 to the viewer 98.
  • the location of the laser source, the sample, and the viewer are generally dictated by the design of such a sensor, so that the viewing geometry is determined for the calculation of the diffraction grating for the screen 100.
  • the contrast and the luminous intensity of the reconstructed image can be substantially increased by a screen thus calculated according to the invention.
  • FIG 10 shows a diffraction grating 110 according to the invention which, in addition to open image information, contains hidden image information (hidden image) 112, which is represented in the figure by the letter sequence "PL." While the open image information already appears under ordinary lighting conditions, FIG hidden image information only clearly recognizable when using an aid.
  • hidden image hidden image
  • the diffraction grating 110 is designed to illuminate the grating with the divergent light of a point monochromatic light source 114, such as a light emitting diode, and to view the information on a trapping screen 116.
  • a point monochromatic light source 114 such as a light emitting diode
  • the diffraction grating 110 for each displayed point (x 2 , y 2 , z 1) of the hidden information 112, there are provided small subregions 118 which are assigned to this point and which deflect the radiation 120 incident from the point light source 114 toward this point ( Beam 122).
  • the lattice parameters for these subregions 118 are determined by the vector relationship (1)
  • n (f) x ⁇ k x (F) - k 2 (F)) m ⁇ g (r)
  • the subareas 118 associated with a point ix 2 , y 2 ⁇ 2 ) may be arbitrarily distributed on the surface of the diffraction grating 110 because the determination of the lattice parameters with the vector relationship (1) ensures that the incident radiation 120 will be at the associated point of hidden information is distracted.
  • a plurality of groups of sub-regions 118 are distributed over the surface of the diffraction grating 110, each associated with one of the points of the hidden information 112.
  • the diffraction grating 110 is illuminated with the divergent radiation of the light emitting diode 114, all of these subareas 118 are illuminated together, so that the entire hidden information 112, in the exemplary embodiment the letter sequence "PL", appears on the screen 116.
  • the interpretation of the hidden information of the diffraction grating 110 on the illumination with the divergent light of a light emitting diode has several advantages over the design of the illumination with a laser.
  • light-emitting diodes as well as the electrical control of the LEDs are much cheaper than laser diodes and their electrical control.
  • laser diodes are often allowed only with low intensity, so that the brightness of the hidden internal f ormations when viewing with laser diodes is limited. Such a restriction does not apply to light-emitting diodes.
  • Another advantage for security applications is that it requires more know-how to interpret the hidden information of a diffraction grating on divergent light than on parallel light.
  • the security value of a lattice thus designed for value documents, such as banknotes and the like, is thus significantly higher.
  • optical elements in the beam path between light source 114 and diffraction grating 110 or between diffraction grating 110 and catching screen 116, which are included in the calculation of the lattice parameters for the hidden information.
  • the diffraction grating for example, can be calculated so that certain optical elements for the recognizability of the hidden information are additionally required.
  • FIG. 11 shows a banknote 130 which contains in a window area a transparent diffraction grating 132 with hidden image information.
  • an optical element 136 for example a converging lens, is provided in a further window area.
  • the diffraction grating 132 is now calculated using the vector relationship (1) and the relationship (2) for the optical element 136 such that the hidden information will be recognizable only in the intended lighting configuration, if the optical element 136 by folding the bill on the diffraction grating 132 is laid.
  • the diffraction grating 132 may be configured to absorb the incident radiation without deflects the optical element 136 in diverging directions while focusing the radiation in combination with the optical element 136 on the collecting screen.
  • the diffraction grating 132 and the optical element 136 thus form a hard-to-copy self-verifying security feature for the banknote 130.

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Abstract

L'invention concerne un procédé de production d'un réseau de diffraction (20) pour un élément optique à diffraction, lequel réseau comporte une ou plusieurs sous-zones (22) contenant chacune un motif de réseau défini par une constante du réseau et une orientation angulaire. Selon ledit procédé, la position d'au moins une source (12), de laquelle provient un rayonnement incident sur le réseau de diffraction (20), ainsi que la position d'au moins une cible (18), vers laquelle le réseau de diffraction (20) doit dévier ce rayonnement, sont spécifiées. La position spatiale et l'orientation des sous-zones (22) ainsi que la constante de réseau et l'orientation angulaire du motif de réseau, nécessaires pour dévier vers la cible (18) le rayonnement incident de la source (12) sur le réseau de diffraction (20), sont déterminées au moyen d'une relation vectorielle locale, qui relie l'orientation du réseau dans l'espace tridimensionnel, le rayonnement incident et émergent ainsi que la position et l'orientation du motif du réseau.
EP06724031A 2005-04-14 2006-04-05 Reseau de diffraction et procede de production associe Ceased EP1875315A2 (fr)

Applications Claiming Priority (2)

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DE102005017355A DE102005017355A1 (de) 2005-04-14 2005-04-14 Beugungsgitter und Verfahren zu seiner Herstellung
PCT/EP2006/003078 WO2006108539A2 (fr) 2005-04-14 2006-04-05 Reseau de diffraction et procede de production associe

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EP1875315A2 true EP1875315A2 (fr) 2008-01-09

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5075800A (en) * 1989-12-04 1991-12-24 Yeda Research And Development Co. Ltd. Method of optimizing holographic optical elements
EP1831736A1 (fr) * 2004-12-15 2007-09-12 Giesecke & Devrient GmbH Image quadrillee destinee a representer des images en couleurs reelles et procede de fabrication

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2508387B2 (ja) * 1989-10-16 1996-06-19 凸版印刷株式会社 回折格子パタ―ンを有するディスプレイの作製方法
US5291317A (en) 1990-07-12 1994-03-01 Applied Holographics Corporation Holographic diffraction grating patterns and methods for creating the same
DE10226115A1 (de) 2002-06-12 2003-12-24 Giesecke & Devrient Gmbh Verfahren zum Erzeugen eines Gitterbildes, Gitterbild und Sicherheitsdokument
DE10243413A1 (de) 2002-06-12 2003-12-24 Giesecke & Devrient Gmbh Verfahren zur Herstellung von Gitterbildern
EP1676157B9 (fr) * 2003-10-15 2011-09-07 Giesecke & Devrient GmbH Procédé pour génerer une image de réseau de diffraction plane ou courbe
DE10348623A1 (de) * 2003-10-15 2005-05-25 Giesecke & Devrient Gmbh Optisch variable Beugungsstruktur und Verfahren zu ihrer Herstellung

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5075800A (en) * 1989-12-04 1991-12-24 Yeda Research And Development Co. Ltd. Method of optimizing holographic optical elements
EP1831736A1 (fr) * 2004-12-15 2007-09-12 Giesecke & Devrient GmbH Image quadrillee destinee a representer des images en couleurs reelles et procede de fabrication

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO2006108539A2 *

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WO2006108539A2 (fr) 2006-10-19
DE102005017355A1 (de) 2006-10-19

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