Abstract:
The present invention provides a method for creating an optical feature, including: providing a substrate; creating one or more volumetric periodic/non-periodic structures on the substrate; and micromachining the one or more volumetric periodic/non-periodic structures on the substrate to create the optical feature. Optionally, the substrate is a photomaterial. The one or more volumetric periodic/non-periodic structures are aligned one or more of substantially perpendicular to, substantially parallel to, and substantially at an angle to the substrate. The one or more volumetric periodic/non-periodic structures have a predetermined frequency, orientation, and angle. Optionally, different portions of the one or more volumetric periodic/non-periodic structures are subjected to different degrees and/or shapes of micromachining.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present patent application/patent claims the benefit of priority of co-pending U.S. Provisional Patent Application No. 61/525,894, filed on Aug. 22, 2011, and entitled “VOLUME OPTICAL VARIABLE DEVICES AND METHODS FOR MAKING,” the contents of which are incorporated in full by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to volumetric optically variable devices (VOVDs) and methods for making the same. More specifically, the present invention relates to VOVDs and methods for making the same that include both volumetric periodic/non-periodic structure formation and surface micromachining steps. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventionally, a variety of techniques for producing holograms and other optically variable devices (OVDs) have been developed. These techniques generally involve utilizing the interference of two or more beams of coherent monochromatic light at the surface of a photosensitive material where the hologram or other OVD is produced. The monochromatic light is typically produced by a laser and, depending upon the desired result, the photosensitive material is chosen to produce a surface relief, gray scale, phase, or polarization holographic pattern. An OVD or VOVD is an iridescent image that exhibits various optical effects, such as movement and/or color changes. Advantageously, VOVDs cannot be photocopied or scanned, nor can they be accurately replicated or reproduced. Thus, VOVDs are often used as security devices and anti-counterfeiting measures on money, credit cards, government-issued identification cards, and the like. VOVDs are typically created through a combination of printing and embossing, and function via diffractive optical structures. Thus, different patterns, designs, and colors are created depending upon the amount of light striking a VOVD and the angle the VOVD is viewed at. Again, holograms are a type of VOVD. 
         [0004]    VOVDs, in general, are optical devices that diffract, refract, transmit, absorb, and/or scatter light, and whose optical properties can vary within. Examples of VOVDs include holographic films, holograms, diffraction gratings, embossed films, embossing rolls, original artwork, replicas, and the like. Optically variable media (OVM) are optical media that diffract, refract, transmit, absorb, and/or scatter light and whose optical properties can vary within. Examples of OVMs, which can be used to make VOVDs, include polymers, polymer films, multilayer films, films with inclusions, films with embossing layers, photoresist, epoxies, silicones, lacquers, cellulose triacetate, glasses, and other optical materials. 
         [0005]    Holograms of a variety of objects and patterns have been made using a single exposure to produce the desired final result. However, due to the expense and impracticality of the large optical systems needed, the size of these holograms is typically limited to about 1 square foot in size or smaller. Larger area holograms can be produced by a step-and-repeat procedure that tiles the object or pattern across the surface of the photosensitive material. This tiling, however, introduces seams or discontinuities between the adjacent areas, which are undesirable. To solve some of these problems, dot matrix holography was developed. In dot matrix holography, a larger holographic pattern is constructed by producing a large number of small holographic dots or pixels in a regular two-dimensional array. These holographic dots are on the order of 10&#39;s to 100&#39;s of microns in size, and there can be as few as 100 dots per linear inch or many as 2,000 or more dots per linear inch (i.e. 4,000,000 or more dots per square inch). 
         [0006]    The fundamental principle of current dot matrix holography involves the use of a laser beam, which is first split into two beams. These two beams are then recombined at the recording material to create an interference pattern in a small area (i.e. holographic dots). Changing the angle and orientation of the intersecting beams controls the period and orientation of the resultant gratings produced in the recording material. Writing many thousands of these dots with the desired properties, in a similar manner to how a dot matrix printer formerly created a printed image, produces complex dot matrix holographic designs. The system, which produces the dot matrix holograms, is typically computer controlled. In each dot, a grating is written with a desired grating period, grating depth, and/or grating orientation. In this manner, virtually any pattern can be produced. Because, each dot is controlled, the viewing angle, brightness, and/or color content of each dot can be adjusted. This allows a variety of visual effects to be produced. Brightness control, for example, allows gray scale or color images to be made. Kinetic effects can make an image appear to move or change as the hologram is tilted or the viewer shifts position. Three-dimensional effects can be made which make an image appear to come out of or be recessed into the surface of the hologram. 
         [0007]    Current dot matrix holography, however, has numerous important limitations with respect to viewing angle, number of lines on the OVM, color, and the like that may be achieved. Thus, what are still needed in the art are devices and methods that allow more robust and flexible holograms and other OVDs to be produced, in an efficient and practical manner. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    In various exemplary embodiments, the present invention provides VOVDs and methods for making the same that include both volumetric periodic/non-periodic structure formation and surface micromachining steps, such that more robust and flexible holograms and other OVDs are produced, in an efficient and practical manner. 
         [0009]    In one exemplary embodiment, the present invention provides a method for creating an optical feature, including: providing a substrate; creating one or more volumetric periodic/non-periodic structures on the substrate; and micromachining the one or more volumetric periodic/non-periodic structures on the substrate to create the optical feature. Optionally, the substrate is a photomaterial. The one or more volumetric periodic/non-periodic structures are aligned one or more of substantially perpendicular to, substantially parallel to, and substantially at an angle to the substrate. The one or more volumetric periodic/non-periodic structures have a predetermined frequency, orientation, and playback angle. Optionally, different portions of the one or more volumetric periodic/non-periodic structures are subjected to different degrees and/or shapes of micromachining. The one or more volumetric periodic/non-periodic structures are created on the substrate by, for example, a setup using the Denisiyk technique, which includes two beams interacting with a photomaterial from the opposite side—with beam structure, orientation, and angle being variable. The micromachining of the one or more volumetric periodic/non-periodic structures is performed by laser, mechanical, and/or chemical techniques, for example. 
         [0010]    In another exemplary embodiment, the present invention provides a method for creating an optical feature, including: providing a substrate; micromachining the substrate; and creating one or more volumetric periodic/non-periodic structures on the micromachined substrate to create the optical feature. Optionally, the substrate is a photomaterial. The one or more volumetric periodic/non-periodic structures are aligned one or more of substantially perpendicular to, substantially parallel to, and substantially at an angle to the micromachined substrate. The one or more volumetric periodic/non-periodic structures have a predetermined frequency, orientation, and playback angle. Optionally, different portions of the substrate are subjected to different degrees and/or shapes of micromachining. The one or more volumetric periodic/non-periodic structures are created on the micromachined substrate by, for example, a setup using the Denisiyk technique, which includes two beams interacting with a photomaterial from the opposite side—with beam structure, orientation, and angle being variable. The micromachining of the one or more volumetric periodic/non-periodic structures is performed by laser, mechanical, and/or chemical techniques, for example. 
         [0011]    In a further exemplary embodiment, the present invention provides a system for creating an optical feature, including: a substrate; a first device operable for creating one or more volumetric periodic/non-periodic structures on the substrate; and a second device operable for micromachining the one or more volumetric periodic/non-periodic structures on the substrate to create the optical feature. Optionally, the substrate is a photomaterial. The first device operable for creating one or more volumetric periodic/non-periodic structures on the substrate includes, for example, a setup using the Denisiyk technique, which includes two beams interacting with a photomaterial from the opposite side—with beam structure, orientation, and angle being variable. The second device operable for micromachining the one or more volumetric periodic/non-periodic structures includes a laser, mechanical, and/or chemical setup, for example. Optionally, the first device and the second device are the same device operated in different modes. 
         [0012]    In a still further exemplary embodiment, the present invention provides a system for creating an optical feature, including: a substrate; a first device operable for micromachining the substrate; and a second device operable for creating one or more volumetric periodic/non-periodic structures on the micromachined substrate to create the optical feature. Optionally, the substrate is a photomaterial. The second device operable for creating the one or more volumetric periodic/non-periodic structures on the micromachined substrate includes, for example, a setup using the Denisiyk technique, which includes two beams interacting with a photomaterial from the opposite side—with beam structure, orientation, and angle being variable. The first device operable for micromachining the substrate includes a laser, mechanical, and/or chemical setup, for example. Optionally, the first device and the second device are the same device operated in different modes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like device components/method steps, as appropriate, and in which: 
           [0014]      FIG. 1  is a schematic diagram illustrating one exemplary embodiment of the VOVD system of the present invention; 
           [0015]      FIG. 2  is a flowchart illustrating one exemplary embodiment of the VOVD method of the present invention; 
           [0016]      FIG. 3  is a series of schematic diagrams illustrating examples of volumetric periodic/non-periodic structures utilized in conjunction with the VOVD systems and methods of the present invention; 
           [0017]      FIG. 4  is a series of schematic diagrams illustrating examples of beam incident angles utilized in conjunction with the VOVD systems and methods of the present invention; 
           [0018]      FIG. 5  is a series of schematic diagrams illustrating examples of volumetric periodic/non-periodic structure creation and surface micromachining for different angled volumetric periodic/non-periodic structures utilizing the VOVD systems and methods of the present invention; and 
           [0019]      FIG. 6  is a series of schematic diagrams illustrating examples of volumetric periodic/non-periodic structure creation and surface micromachining for substantially parallel volumetric periodic/non-periodic structures utilizing the VOVD systems and methods of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    In various exemplary embodiments, the present invention relates to the creation of VOVDs utilizing a multi-step approach, including both volumetric periodic/non-periodic structure creation and surface micromachining. Thus, the present invention relates to a new type of VOVD structure, and a method for forming the same, based on a combination of dot matrix, volumetric holography, and laser selective micromachining concepts. The present invention introduces a method for originating a new class of VOVD micro/nanostructures by applying a two-step process—volumetric periodic/non-periodic structure recording and selective surface micromachining, both utilizing specific, controlled parameters. 
         [0021]    Referring to  FIG. 1 , in one exemplary embodiment of the present invention, the VOVD system  10  generally includes a computer  12 , a first VOVD creation device  14 , a second VOVD creation device  16 , and a material  18  for writing thereon. The computer  12  is communicatively coupled to the first VOVD creation device  14  and the second optical VOVD creation device  16  for the precise control thereof. The first VOVD creation device  14  and the second VOVD creation device  16  are collectively configured to create a VOVD on/in the material  18 . In an exemplary embodiment, the material  18  includes an OVM, such as, but not limited to, a polymer, a polymer film, a multilayer film, a films with inclusion, a films with embossing layers, a photoresist, an epoxy, a silicone, a lacquer, cellulose triacetate, a glass, and/or other optical material on which a two or three-dimensional image may be generated, such optical materials being well known to those of ordinary skill in the art. The display written on the material  18  can include, but is not limited to, a holographic film, a hologram, a diffraction grating, an embossed film, an embossing roll, an original artwork, a replica, and/or the like. 
         [0022]    The computer  12  is a digital computer that, in terms of hardware architecture, generally includes a processor  22 , input/output (I/O) interfaces  24 , a network interface  26 , a data store  28 , and a memory  30 . It will be appreciated by those of ordinary skill in the art that  FIG. 1  depicts the computer  12  in an oversimplified manner, and a practical embodiment of the computer  12  would include additional components and suitably configured processing logic to support conventional or known operating features that are not described in detail herein. The components  22 ,  24 ,  26 ,  28 , and  30  are communicatively coupled via a local interface  32 . The local interface  32  may be, for example, but is not limited to, one or more buses or other wired or wireless connections, well known to those of ordinary skill in the art. The processor  22  is a hardware device for executing software instructions. The processor  22  may be any custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the computer  12 , a semiconductor-based microprocessor (in the form of a microchip or chip set), or generally any device for executing software instructions. The I/O interfaces  24  are used to receive user input from and/or for providing system output to one or more other devices or components. In an exemplary embodiment, the optical VOVD creation devices  14  and  16  are communicatively coupled to the I/O interfaces  24 . 
         [0023]    The network interface  26  is used to enable the computer  12  to communicate on a network, such as the Internet, a wide area network (WAN), a local area network (LAN), and/or the like. In an exemplary embodiment, the optical VOVD creation devices  14  and  16  are communicatively coupled to the network interface  26 , either directly or indirectly, via intervening equipment. A data store  28  is used to store data. The data store  28  may include any of volatile memory elements, nonvolatile memory elements, and combinations thereof. The memory  30  may include any of volatile memory elements, nonvolatile memory elements, and combinations thereof. The software in the memory  30  may include one or more software programs, each of which includes an ordered listing of executable instructions for implementing logical functions. The software in the memory  30  includes, for example, a suitable operating system (OS)  34  and one or more other programs  36 . The OS  34  essentially controls the execution of other computer programs, such as the one or more other programs  36 , and provides scheduling, input-output control, file and data management, memory management, and communication control and related services. The one or more programs  36  may be configured to implement the various processes, algorithms, methods, techniques, etc. described herein associated with controlling the optical VOVD creation devices  14  and  16 . 
         [0024]    The first VOVD creation device  14  is configured to create volumetric periodic/non-periodic structures on the material  18  in a specific manner or pattern, as controlled by the computer  12 . The first VOVD creation device  14  includes, for example, a setup using the Denisiyk technique, which includes two beams interacting with a photomaterial from the opposite side—with beam structure, orientation, and angle being variable. The second VOVD creation device  16  is configured to micromachine the material  18  in a specific manner or pattern, as also controlled by the computer  12 . The second VOVD creation device  16  includes a laser, mechanical, and/or chemical setup, for example, such as a light source, a light intensity modulation device, and a beam positioning device. In an exemplary embodiment, the first VOVD creation device  14  is configured to create the volumetric periodic/non-periodic structures, and then the second VOVD creation device  16  is configured to micromachine the volumetric periodic/non-periodic structures. In another exemplary embodiment, the second VOVD creation device  16  is configured to micromachine the material  18 , and then the first VOVD creation device  14  in configured to create the volumetric periodic/non-periodic structures on the micromachined material. Micromachining can be based on a chemical reaction with or following the development of the material  18 , or by mechanical or laser ablation of the surface of the material  18 , for example. Note, while shown in  FIG. 1  as being separate devices, the first VOVD creation device  14  and the second VOVD creation device  16  may be a single device utilized for both creating volumetric periodic/non-periodic structures and micromachining. 
         [0025]    Referring to  FIG. 2 , in one exemplary embodiment of the present invention, VOVD method  40  includes two steps—creating a volumetric periodic/non-periodic structure on the material  18  ( FIG. 1 ) (step  42 ) and micromachining the volumetric periodic/non-periodic structure (step  44 ). The volumetric periodic/non-periodic structure on the material  18  is a VOVD device that includes a plurality of pixels tilted at specific angles. In an exemplary embodiment, the pixels may be formed using dot matrix techniques or the like. Each pixel has a high-frequency volumetric grating (HFVG), of around 3000 l/mm, for example. The playback angle for the HFVG is very high, and at some high (e.g. &gt;2000 l/mm) grating frequencies, a reflected beam lies on the surface plane where grating is recorded and, because of that, is not visible. To correct this issue, a surface with volumetric gratings has a tilt to a specific angle depending on the grating pitch. In the VOVD method  40  of the present invention, the tilted surface is created by optically micromachining the pixeled surface (step  44 ). After micromachining, the photo material may be developed (step  46 ). After developing, the surface of the material  18  has a complex structure, i.e. a volumetric grating written on tilted surface, for example. 
         [0026]    The VOVD method  40  of the present invention may be utilized to create new types of VOVDs based on the selective micromachining of individual pixels, or groups of pixels, recorded by dot matrix techniques or the like, with the goal to create a blazed grating profile for sending all light to one order, for example. The VOVD method  40  of the present invention may also be utilized to create new types of VOVDs based on a dot matrix blazed structure or the like, with an ability to create sharp channel separation for multichannel images, or color switch effects with sharp color separation. 
         [0027]    In general, the volumetric periodic/non-periodic structures are utilized to make an image and the color associated therewith. In particular, the volumetric periodic/non-periodic structures are formed over specific areas with selected individual optical characteristics such as, but not limited to, grating frequency, orientation, and playback angle. In an exemplary embodiment of the present invention, to adjust the playback angle and/pre-send different colors in the same direction, the second step  44  is applied, i.e. micromachining of the surface, with the goal of achieving a specific angle needed for color matching on an image or pattern appearance. 
         [0028]    Referring to  FIGS. 3 and 4 , in an exemplary embodiment, various examples are illustrated of a volumetric periodic/non-periodic structure  50  and beam incident angles  60  for the VOVDs of the present invention. In  FIG. 3 , four examples are illustrated of volumetric periodic/non-periodic structures  50  (labeled as  50   a,    50   b,    50   c,  and  50   d ). In an exemplary embodiment, the volumetric periodic/non-periodic structures  50   a,    50   b,    50   c , and  50   d  are recorded by applying light beams from the opposite side of or from the same side of a plate or other substrate with photoresist (e.g. photomaterial). The volumetric periodic/non-periodic structures  50   a,    50   b,    50   c,  and  50   d  are generated using the first VOVD creation device  14  ( FIG. 1 ). The volumetric periodic/non-periodic structure  50   a  illustrates two incident beams on the plate from approximately opposing angles on the same side. The volumeric periodic/non-periodic structure  50   b  illustrates two incident beams on the plate from different opposing angles on the same side. The volumetric periodic/non-periodic structure  50   c  illustrates two incident beams on the plate from opposing sides with different angles. The volumetric periodic/non-periodic structure  50   d  also illustrates two incident beams on the plate from opposing sides with different angles. The beams&#39; incident angles can be symmetric or asymmetric with reference to the plate in all cases. The beams&#39; incident angles can be changed together or separately for color selection. The color of pixels in the volumetric periodic/non-periodic structures  50  can be controlled in two ways. First, by changing the angle between beams, and, second, by changing the tilting angle of the pixel surface. By tilting the angle of the pixel surface it is possible to send different colors in specific directions. 
         [0029]    In an exemplary embodiment, the first VOVD creation device  14  may include a plurality of beams for projection onto the surface of the material  18 . The image or pattern or specific optical or non-optical structure is recorded into the material  18  in a pixel-by-pixel fashion. HFVGs can be recorded first, and second the pixel surface can micromachined, or the pixel surface can be micromachined first, and the volumetric periodic/non-periodic structures recorded second. Lastly, exposed and/or unexposed areas of the material  18  are removed, based upon the particular material, by developing it or by ablating it. 
         [0030]      FIG. 4  illustrates the result of the VOVD systems and methods  10  ( FIG. 1) and 40  ( FIG. 2 ) of the present invention where the control of the playback angles  60   a,    60   b  of the material  18  is enabled. For example, based upon the control of the optical VOVD creation  14  and  16 , the material  18  can have a symmetric or asymmetric playback angle. For example, the playback angle  60   a  illustrates a symmetric example, whereas the playback angle  60   b  illustrates an asymmetric example. 
         [0031]    Referring to  FIG. 5 , in another exemplary embodiment, the material  18  is illustrated after the two respective steps. The VOVD  70   a  includes periodic/non-periodic structures formed in a substantially vertical orientation, whereas the VOVD  70   b  includes periodic/non-periodic structures formed in an angled orientation. As will be readily apparent to those of ordinary skill in the art, any and all other suitable orientations are possible and may be utilized. The first step  72  illustrates the material  18  following the formation of the volumetric periodic/non-periodic structures. The second step  74  illustrates the material  18  with the formed volumetric periodic/non-periodic structures following micromachining. By tailoring and combining periodic/non-periodic structure frequency, periodic/non-periodic structure tilt angle, and micromachining angle(s), overall structures can be shaped in a blazed grating fashion for maximum efficiency and a specific manner and order of playback. Tilted surfaces can be flat or any desirable shape, for example. This includes, but is not limited to, micro-optics, such as lenses, prisms, and/or mirrors. By using this technique, it is possible to create colored optical and non-optical microelements of a wide variety. 
         [0032]    Referring to  FIG. 6 , in another exemplary embodiment, the material  18  is illustrated with the volumetric periodic/non-periodic structures substantially parallel to the material  18 , and with micromachining performed to selectively remove layers of the material  18  and the volumetric periodic/non-periodic structures. Similarly to  FIG. 5 , the material  18  is subjected to two steps  82  and  84 . In the first step  82 , volumetric periodic/non-periodic structures in the material  18  are created and exposed in such way that periodic/non-periodic structure plane is parallel to the photomaterial plate. In the second step  84 , by applying selected angular and tilting angle micromachining to the volumetric periodic/non-periodic structure, it is possible to create a wide variety of images. Here, the volumetric periodic/non-periodic structures can be recorded on an optical plate over all photomaterial volume at once from the opposite side of the photomaterial, for example, so that the volumetric periodic/non-periodic structures are parallel to the photomaterial surface, and then, by applying the second step  84 , selective micromachining, a color image can be created by assigning different tilting and orientation angles to individual pixels or groups of pixels, for example. In the case of a volumetric periodic/non-periodic structure recorded parallel to the underlying surface, planes of equal refraction index waveguides or optical channels can be created. 
         [0033]    Advantageously, the volumetric periodic/non-periodic structure VOVDs and methods of the present invention may be utilized in various applications to create high-frequency VOVDs (3-4,000 l/mm, for example) with tilted pixels, with an entire image being the same color, and/or the like. Using the systems and methods described herein, micro-optical elements and colored optical elements can be created—such as lenses, prisms, mirrors, etc. of specific colors, for example. Additionally, using the systems and methods described herein, waveguides with special functions, e.g. optical frequency separation, can be created. 
         [0034]    Although the present invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following claims.