AU2016101590B4 - A 3d micromirror device - Google Patents

A 3d micromirror device Download PDF

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Publication number
AU2016101590B4
AU2016101590B4 AU2016101590A AU2016101590A AU2016101590B4 AU 2016101590 B4 AU2016101590 B4 AU 2016101590B4 AU 2016101590 A AU2016101590 A AU 2016101590A AU 2016101590 A AU2016101590 A AU 2016101590A AU 2016101590 B4 AU2016101590 B4 AU 2016101590B4
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Australia
Prior art keywords
device
floating image
optical
observer
pyramid
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AU2016101590A
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AU2016101590A4 (en
Inventor
Michael Hardwick
Robert Lee
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CCL Security Pty Ltd
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CCL Security Pty Ltd
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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/04Prisms
    • G02B5/045Prism arrays
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B42BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42DBOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30Identification or security features, e.g. for preventing forgery
    • B42D25/324Reliefs
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B42BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42DBOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30Identification or security features, e.g. for preventing forgery
    • B42D25/36Identification or security features, e.g. for preventing forgery comprising special materials
    • B42D25/373Metallic materials
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B44DECORATIVE ARTS
    • B44FSPECIAL DESIGNS OR PICTURES
    • B44F1/00Designs or pictures characterised by special or unusual light effects
    • B44F1/08Designs or pictures characterised by special or unusual light effects characterised by colour effects
    • B44F1/10Changing, amusing, or secret pictures
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B30/00Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images
    • G02B30/20Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes
    • G02B30/26Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes of the autostereoscopic type
    • G02B30/27Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images by providing first and second parallax images to an observer's left and right eyes of the autostereoscopic type involving lenticular arrays
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41MPRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M3/00Printing processes to produce particular kinds of printed work, e.g. patterns
    • B41M3/06Veined printings; Fluorescent printings; Stereoscopic images; Imitated patterns, e.g. tissues, textiles
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41MPRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M3/00Printing processes to produce particular kinds of printed work, e.g. patterns
    • B41M3/14Security printing
    • B41M3/148Transitory images, i.e. images only visible from certain viewing angles

Abstract

Abstract An optical device is disclosed comprising an array of reflecting surface relief structures projecting from or recessed into a base plane of the device. The structures generate an optical effect including a floating image at least when the device is viewed by an observer from a first position relative to an axis perpendicular to the base plane of the device. The floating image changes to another type of floating image or to a non-floating image when the device is rotated about the axis. A method of manufacturing an optical device is also disclosed.

Description

1 2016101590 08 Sep 2016

3D MICROMIRROR DEVICE CROSS REFERENCE TO RELATED APPLICATION

[0001] The present invention is related to the following international patent application, the disclosure of which is incorporated herein by cross reference. PCT/AU02/00551 entitled An Optical Device and Methods of Manufacture published under W002/091041.

FIELD OF THE INVENTION

[0002] The present invention relates to optical security devices and methods for their manufacture. In particular the present invention relates to optical security devices which include a reflecting surface relief structure or structures in their construction.

BACKGROUND TO THE INVENTION

[0003] Optical security devices are commonly used in security documents as a means of avoiding unauthorised duplication or forgery of such documents. Typically, such devices produce optical effects which may be difficult for a potential counterfeiter to replicate.

[0004] Counterfeiting of banknotes and other valuable documents has become an increasingly important issue in recent times due to ready availability of colour photocopiers and computer scanning equipment. This technology provides counterfeiters with a much easier route to copying of valuable documents issued using traditional security printing technologies. In response central banks and banknote printers have turned to technologies which produce images that vary with changing angle of view, and which therefore cannot be easily photographed.

[0005] Such devices known collectively as optically variable devices (OVDs) have proven to be very successful in reducing incidence of counterfeiting using computer scanning equipment. However, the counterfeiters have not been idle during this time and some groups have adopted alternative holographic approaches to counterfeiting or simulating diffractive optically variable devices produced by banknote printing groups. 2 2016101590 08 Sep 2016 [0006] Therefore there is a need for alternative OVD technologies which produce images well differentiated in their image characteristics from diffractive optically variable devices. The present invention may provide an alternative OVD technology based on reflective, rather than diffractive optical principles. The present invention may also provide a method for manufacturing optical security devices including such OVD technology.

SUMMARY OF THE INVENTION

[0007] The present invention may provide an optical device including a surface relief structure, or structures, which reflects incident light in a controlled manner to generate an optical effect having one or more images which appear to float above the surface of the device. The floating images may be due to a stereoscopic effect or perception of depth and/or 3-dimensional structure based on visual information derived by an observer with normally developed binocular vision.

[0008] Because the eyes of humans, and many animals, are located at different lateral positions on the head, binocular vision results in two slightly different images projected to the retinas of the eyes. The differences are due to different projection of objects as seen by each eye. These positional differences are referred to as horizontal disparities, or more generally, binocular disparities. Disparities are processed in the visual cortex of the brain to yield depth perception. While binocular disparities are naturally present when viewing a real 3-dimensional scene with two eyes, they can also be simulated by artificially presenting two different images separately to each eye using a method called stereoscopy. The perception of depth in such cases is also referred to as "stereoscopic depth".

[0009] Stereoscopic depth or a floating image effect may be generated more strongly for incident sources of light having a relatively narrow beam angle (i.e. not diffused light). The surface relief structure or structures of the present invention may also be arranged to produce a non-floating image when the device is rotated by 90 degrees about an axis perpendicular to the plane of the device. The non-floating image capability may include an image switching option wherein the non-floating 2016101590 27 Mar 2017 3 image may switch to a different type of non-floating image as the device is rocked back and forth about an axis within the plane of the device.

[0010] The non-floating images may be observable under a much greater range of light sources as these images do not involve a stereoscopic effect and therefore do not rely on binocular vision ability of the observer. By combining a floating image effect with a non-floating image effect, the optical device of the present invention may be authenticated under a much greater range of light sources as well as providing an increased level of security due to two different types of optical effects being utilized.

[0011] Since the operating mechanism of the optical device is based on reflection rather than diffraction, the optical effects produced by the device are achromatic and are therefore easily distinguishable from rainbow light optical effects produced by the more commonly available diffractive optically variable devices. This high level of differentiation from diffractive devices, some of which may be simulated or counterfeited using dot matrix hologram techniques, therefore promises a higher level of security when the device is used as an anti-counterfeiting feature on valuable documents.

[0012] According to one aspect of the present invention there is provided an optical device comprising an array of reflecting surface relief structures projecting from or recessed into a base plane of the device, which generate an optical effect including a floating image at least when the device is viewed by an observer from a first position relative to an axis perpendicular to the base plane of the device, and wherein the floating image changes to another type of floating image or to a nonfloating optical image when the device is rotated about said axis, wherein said array of reflecting structures includes at least a first group of reflecting surfaces oriented such that they reflect incident light into the left eye of the observer, but substantially do not reflect incident light into the right eye of the observer. 2016101590 27 Mar 2017 3a [0013] The non-floating image generated by the device may change to another non-floating image when the device is rotated, tilted or rocked back and forwards about an axis lying within the base plane of the device. In one form each reflecting surface relief structure may include a square based or rectangle based pyramid, wherein each of four sides associated with each pyramid forms a reflecting surface 4 2016101590 08 Sep 2016 or pixel. Each pyramid may have base dimensions of 500 microns or less and the height of the or each pyramid may be 250 microns or less.

[0014] In another form each reflecting surface relief structure may include a square based or rectangle based rectangular prism, wherein each of two inclined sides associated with each prism forms a reflecting surface, stripe or pixel.

[0015] At least a first group or array of reflecting surfaces associated with the reflecting surface relief structures may be inclined or oriented such that they reflect incident light into the left eye of the observer, but substantially do not reflect incident light into the right eye of the observer.

[0016] At least a second group or array of reflecting surfaces associated with the reflecting surface relief structures may be inclined or oriented such that they reflect incident light into the right eye of the observer but substantially do not reflect incident light into the left eye of the observer.

[0017] The above arrangement may generate an optical effect in the form of a stereoscopic or floating image at least when the surface relief structures are viewed from the first position relative to an axis perpendicular to the base plane of the device.

[0018] The floating image generated by the device may include a greyscale portrait of a face, scene, logo, alphanumeric character or any other graphic design wherein relative intensity of light reflected from the device is fixed or varies from point to point across the image.

[0019] The non-floating image generated by the device may include a greyscale portrait of a face, scene, logo, alphanumeric character or any other graphic design wherein relative intensity of light reflected from the device is fixed or varies from point to point across the image. The non-floating image may be generated by a diffractive or non-diffractive structure or by an ink that changes colour depending on viewing angle or position of the observer relative to the plane of the device. 2016101590 08 Sep 2016 5 [0020] Each projecting or recessed surface relief structure may be produced in any one of a number of ways. In one form the or each structure may be produced by applying a layer of embossable radiation curable ink to a substrate and embossing the layer prior to curing the ink via ultraviolet radiation.

[0021] Another way may be to use a vacuum metal deposition process. In this process, the surface to be coated may be placed in a vacuum, and the metal may be vaporised. When the vaporised metal contacts the surface, it may condense to form a metallic layer on the surface.

[0022] An alternative to a vacuum metal deposition process may be to utilise a metallic nanoparticle ink to coat the required surface. The application of such an ink may be achieved at substantially reduced cost compared to the vacuum deposition process, while still providing a thin coating that may be highly reflective, or semitransparent with a high refractive index, depending on the composition of the ink.

[0023] The optical security device may be embossed or attached to a valuable document such as a banknote, passport, credit card, cheque, etc. in order to prevent or inhibit counterfeiting of that document.

[0024] According to a further aspect of the invention, there is provided a method of manufacturing an optical device including forming an array of reflecting surface relief structures projecting from or recessed into a base plane of the device, to generate an optical effect in the form of a floating image at least when the device is viewed by an observer in a first position relative to an axis perpendicular to the base plane of the device, and wherein the floating image changes to another type of floating image or to a non-floating image when the device is rotated about said axis.

[0025] The method may include a step of applying a layer of embossable radiation curable ink to a substrate prior to being embossed while soft and curing the ink by radiation to form the array of reflecting surface relief structures. 6 2016101590 08 Sep 2016 [0026] The method may include a step of applying a coating of metallic nanoparticle ink to the relief structures to produce the reflective (or at least partially reflective) relief structures. The coating may be applied as a curable coating.

[0027] The ink may be applied as a silver nanoparticle ink. Where this is the case, the silver nanoparticle ink preferably has less than 40% silver. Alternatively, the method may include applying an aluminium nanoparticle ink or a gold nanoparticle ink.

[0028] The method may also include the step of providing at least one opacifying layer as an opacifying coating, preferably an opacifying ink layer.

[0029] Further aspects of the invention are directed to a security document, such as a banknote including the optical security device as described in any of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Specific embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which: [0031] Figure 1 shows an array of reflecting micro-pyramid structures according to one embodiment of the invention.

[0032] Figure 2 shows a cross sectional view of reflecting micro-pyramid structures.

[0033] Figure 3 shows observation geometry relative to a substrate plane.

[0034] Figures 4a to 4c show artwork comprising two interleaved tracks of micromirror pixels according to an embodiment of the invention.

[0035] Figures 5a and 5b show respective right and left eye micro-mirrors represented in 3D coordinate space. 2016101590 08 Sep 2016 7 [0036] Figure 6 shows right and left eye micro-mirrors represented in 2D coordinate space with grey scales representing depth into a resist. 2016101590 08 Sep 2016 8

DESCRIPTION OF PREFERRED EMBODIMENTS DEFINITIONS

Security document [0037] As used herein, the term security document includes all types of documents and tokens of value and identification documents including, but not limited to the following: items of currency such as banknotes and coins, credit cards, cheques, passports, identity cards, securities and share certificates, driver's licences, deeds of title, travel documents such as airline and train tickets, entrance cards and tickets, birth, death and marriage certificates, and academic transcripts.

[0038] The invention is particularly, but not exclusively, applicable to security documents or tokens such as banknotes or identification documents such as identity cards or passports formed from a substrate to which one or more layers of printing are applied. The diffraction gratings and optically variable devices described herein can also have application in other products, such as packaging.

Security Device or Feature [0039] As used herein the term security device or feature includes any one of a large number of security devices, elements or features intended to protect the security document or token from counterfeiting, copying, and alteration or tampering. Security devices or features can be provided in or on the substrate of the security document or in or on one or more layers applied to the base substrate, and can take a wide variety of forms, such as security threads embedded in layers of the security document; security inks such as fluorescent, luminescent and phosphorescent inks, metallic inks, iridescent inks, photochromic, thermochromic, hydrochromic or piezochromic inks; printed and embossed features, including relief structures; interference layers; liquid crystal devices; lenses and lenticular structures; optically variable devices (OVDs) comprising reflective optical structures including reflecting surface relief structures and diffractive devices including diffraction gratings, holograms and diffractive optical elements (DOEs). 9 2016101590 08 Sep 2016

Metallic Nanoparticle Ink [0040] As used herein, the term metallic nanoparticle ink refers to an ink having metallic particles of an average size of less than one micron.

Diffractive Optical Elements (DOEs) [0041] As used herein, the term diffractive optical element refers to a numericaltype diffractive optical element (DOE). Numerical-type diffractive optical elements (DOEs) rely on the mapping of complex data that reconstruct in the far field (or reconstruction plane) a two-dimensional intensity pattern. Thus, when substantially collimated light, e.g. from a point light source or a laser, is incident upon the DOE, an interference pattern is generated that produces a projected image in the reconstruction plane that is visible when a suitable viewing surface is located in the reconstruction plane, or when the DOE is viewed in transmission at the reconstruction plane. The transformation between the two planes can be approximated by a fast Fourier transform (FFT). Thus, complex data including amplitude and phase information has to be physically encoded in the micro-structure of the DOE. This DOE data can be calculated by performing an inverse FFT transformation of the desired reconstruction (i.e., the desired intensity pattern in the far field).

[0042] DOEs are sometimes referred to as computer-generated holograms, but they differ from other types of holograms, such as rainbow holograms.

Embossable Radiation Curable Ink [0043] The term embossable radiation curable ink used herein refers to any ink, lacquer or other coating which may be applied to the substrate in a printing process, and which can be embossed while soft to form a relief structure and cured by radiation to fix the embossed relief structure. The curing process does not take place before the radiation curable ink is embossed, but it is possible for the curing process to take place either after embossing or at substantially the same time as the embossing step. The radiation curable ink is preferably curable by ultraviolet (UV) radiation. Alternatively, the radiation curable ink may be cured by other forms of radiation, such as electron beams or X-rays. 10 2016101590 08 Sep 2016 [0044] The radiation curable ink is, preferably, a transparent or translucent ink formed from a clear resin material. Such a transparent or translucent ink is particularly suitable for printing light-transmissive security elements, such as subwavelength gratings, transmissive diffractive gratings and lens structures.

[0045] In one particularly preferred embodiment, the transparent or translucent ink preferably comprises an acrylic based UV curable clear embossable lacquer or coating.

[0046] Such UV curable lacquers can be obtained from various manufacturers, including Kingfisher Ink Limited, product ultraviolet type UVF-203 or similar. Alternatively, the radiation curable embossable coatings may be based on other compounds, eg. nitro-cellulose.

[0047] The radiation curable inks and lacquers used herein have been found to be particularly suitable for embossing microstructures, including diffractive structures such as diffraction gratings and holograms, and microlenses and lens arrays. However, they may also be embossed with larger relief structures, such as nondiffractive optically variable devices.

[0048] The ink is preferably embossed and cured by ultraviolet (UV) radiation at substantially the same time. In a particularly preferred embodiment, the radiation curable ink is applied and embossed at substantially the same time in a Gravure printing process.

[0049] Referring to the drawings, Figure 1 shows an optical device according to one embodiment of the present invention comprising array of reflecting micropyramid structures 10. Faces A and B on each micro-pyramid structure 10 correspond to floating image channels, while Faces C and D on each micro-pyramid structure 10 correspond to non-floating image switching channels.

[0050] While not shown in the drawings the number of faces on each pyramid structure may be other than 4 but greater than 3. 11 2016101590 08 Sep 2016 [0051] Referring to Figure 2, there is shown a cross section of an optical security device 20, wherein a layer of embossable radiation curable ink 22 is applied in an area of a surface of substrate 21 prior to being embossed while soft to form a micropyramid relief structure 23. The ink 22 may be cured by radiation to fix the embossed micro-pyramid relief structure 23. A metallic nanoparticle ink may be used to apply a thin reflective coating 24 to the relief structure 23 to produce a reflective or at least partially reflective relief structure such as micro-pyramid structure 10 shown in Figure 1.

[0052] Nanoparticle ink 24 may provide reflectivity which is equivalent to that achieved by vacuum metallisation, but may be provided more cheaply and efficiently as the ink may be applied by a printing method. In one embodiment of the present invention, the metallic nanoparticle ink includes a silver nanoparticle, having less than 40% silver. Flowever, a range of other metallic nanoparticle inks may also be suitable for use in accordance with the invention, for example, silver nanoparticle inks with greater than 40% silver, aluminium nanoparticle inks and gold nanoparticle inks.

[0053] A protective coating such as a transparent varnish 25 may be applied over the reflective or partially reflective relief structure 24. Protective coating 25 may be applied over metallic nanoparticle ink 24 and relief structure 23 as well as over other areas of substrate 21 in which relief structure 23 and metallic nanoparticle ink 24 is not present. The latter areas (not shown) may contain a non-floating image that may be visible at least when the device is rotated about an axis perpendicular to the plane of the device or is rocked back and forth about an axis within the plane of the device. The non-floating image(s) may comprise a diffractive or non-diffractive structure such as a colour changing ink.

[0054] Preferably, coating 25 includes a high refractive index (HRI) coating, as this may assist in ensuring that the optical effect produced by reflective relief structure 23/24 remains visible even if metallic nanoparticle ink 24 is applied in a very thin layer. Flowever, in other embodiments possible coatings may include a transparent, non-high refractive varnish. 12 2016101590 08 Sep 2016 [0055] It will be appreciated that a suitable coating should demonstrate one or all of the following attributes: good adhesion to the substrate, highly transparent, generally colourless, and robust. Possible coatings may include a transparent, non-high refractive varnish. Varnish may denote a material that results in a relatively durable and protective finish. Exemplary transparent varnishes may include, but are not limited to, nitrocellulose and cellulose acetyl butyrate. Alternatively, the coating may include a high refractive index coating, being a coating having a metal oxide component of small particle size and high refractive index dispersed in a carrier, binder or resin. Such a high refractive index coating may contain solvent as it is a dispersion. Where a high refractive index coating of this type is used, it may be air cured or UV cured.

[0056] Alternatively, a high refractive index coating utilising a non-metallic polymer, such as sulphur-containing or brominated organic polymers may also be used.

[0057] The metallic nanoparticle ink 24 is preferably applied to the surface of the relief structure 23 in a repeating pattern, such as a plurality of substantially parallel lines, or a plurality of substantially circular spots.

[0058] The metallic nanoparticle ink 24 may be applied by any one of several techniques that will be apparent to the person skilled in the art. Preferably, the ink is applied by gravure, however may also be applied by other suitable techniques such as flexography or offset printing.

[0059] Referring to Figure 3, the theory behind the stereoscopic or floating 3D image effect using a micro-mirror array may be illustrated with reference to a test image involving a simple piece of artwork in the form of a $ sign. The 3D effect required is for the image plane 30 which contains the $ sign to float above substrate plane 31 of the device at a height D of approximately 1 cm when viewed by an observer’s right and left eyes 32, 33 at a viewing distance H of 21 cm. The separation E between the observer’s eyes 32, 33 is assumed to be 8 cm and the area of the optical device is of dimensions less than 2cm x 2 cm. 13 2016101590 08 Sep 2016 [0060] The calculations in Figure 3 are based on micro-mirror pixels of dimensions 30 micron X 30 micron and inclined into substrate plane 31 at an angle of about 13 degrees for a surface depth of 7 microns (arctan(7/30)). For a resist depth of 7 microns, micro-mirror pixel size of 30x30 microns, observation distance of 21 cm and 8 cm eye to eye separation, there are two equations describing the two sets of micro-mirrors (note: the y axis here is directed out of the page).

[0061] Left eye micro-mirror set: z = 0.23 y-0.2 x (1) [0062] Right eye micro-mirror set: z = 0.23 y + 0.2 x (2) [0063] Note that for the 3D effect to be observed, the light rays reflected from the arrays of reflecting elements associated with eyes 32, 33 of the observer must appear to cross over each other in plane 30 between substrate plane 31 of the optical device and plane 34 containing eyes 32, 33 of the observer.

[0064] The artwork for the simple test image is shown in Figure 4a and consists of two interleaved tracks of micro-mirror pixels shown in figures 4b and 4c respectively. For an optical device of size 2cm x 2cm of 30 micron pixels, the overall size of the artwork is 667 pixels x 667 pixels. The pixel tracks of figure 4b correspond to micro-mirror pixels reflecting light into the left eye 33 of the observer and the pixel tracks of figure 4c correspond to micro-mirror pixels reflecting light into the right eye 32 of the observer.

[0065] The background pixels shown in black in figure 4a correspond to a flat background of the optical device. Note that in the artwork of Figures 4a-4c the x-axis is directed across the page and the y-axis is directed up the page. This is important and means that micro-mirror tracks associated with right and left eyes 32, 33 must be oriented in the y direction in order for the optical effect to be generated in accordance with the geometry shown in figure 3.

[0066] An illustration showing relative orientation based on equation (2) of micromirrors associated with the right eye 32 is shown in figure 5a. An illustration showing relative orientation based on equation (1) of micro-mirrors associated with the left eye 33 is shown in figure 5b. 2016101590 08 Sep 2016 14 [0067] An enlarged view of micro mirror orientations in the x-z plane is shown in figure 6. Micro-mirrors 61 associated with right eye 32 are defined by equation (2) and micro-mirrors 62 associated with left eye 33 are defined by equation (1).

[0068] In Figure 6 greys scale 63 represents micro mirrors associated with the right eye 32 and grey scale 64 represents micro mirrors associated with the left eye 33. The darker greyscales represent greater depth into the resist.

[0069] Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

Claims (5)

  1. The claims defining the invention are as follows:
    1. An optical device comprising an array of reflecting surface relief structures projecting from or recessed into a base plane of the device, which generate an optical effect including a floating image at least when the device is viewed by an observer from a first position relative to an axis perpendicular to the base plane of the device, and wherein the floating image changes to another type of floating image or to a non-floating image when the device is rotated about said axis, wherein said array of reflecting structures includes at least a first group of reflecting surfaces oriented such that they reflect incident light into the left eye of the observer, but substantially do not reflect incident light into the right eye of the observer.
  2. 2. An optical device according to claim 1, wherein the non-floating image generated by the device changes to another non-floating image when the device is rotated or rocked back and forwards about an axis lying within the base plane of the device.
  3. 3. An optical device according to claim 1 or 2, wherein each reflecting surface relief structure includes a square based or rectangle based pyramid, and wherein each of four sides associated with each pyramid forms a reflecting surface or pixel, and wherein each pyramid has base dimensions of 500 microns or less and the height of each pyramid is 250 microns or less.
  4. 4. An optical device according to any one of the preceding claims, wherein the image generated by the device includes a greyscale portrait of a face, scene, logo, alphanumeric character or other graphic design and wherein relative intensity of light reflected from the device is fixed or varies from point to point across the image.
  5. 5. An optical device according to any one of the preceding claims, wherein the device is embossed or attached to a valuable document such as a banknote, passport, credit card, cheque, etc in order to prevent or inhibit counterfeiting of that document.
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FR1758266A FR3055707A1 (en) 2016-09-08 2017-09-07 3d micro-mirrors device
PCT/AU2017/050979 WO2018045429A1 (en) 2016-09-08 2017-09-08 A 3d micromirror device

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US20120274998A1 (en) * 2009-10-30 2012-11-01 De La Rue International Limited Security device
US20130069360A1 (en) * 2010-03-24 2013-03-21 Securency International Pty Ltd. Security document with integrated security device and method of manufacture

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