Abstract:
An identification card and a method for formation of the card are disclosed. The identification card comprises an optical identification element formed upon a surface of the identification card and an optical stripe formed on the optical identification element and having at least a portion formed substantially from a single material. The single material is configured to have a diffractive pattern formed thereon by exposure to a laser. The diffractive pattern is capable of retaining information that is, for example, unique to a cardholder and being readable by a light source external to the identification card.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 61/036,008 entitled “Authentication for a Data Card,” filed Mar. 12, 2008 which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to portable identity or transactional data storage cards, and more particularly, to producing secure data on the card through a computer-assisted diffractive or holographic writing process. 
       BACKGROUND 
       [0003]    Wireless electronic identification devices, such as radio frequency identification device (RFID) cards, are known in the art. RFID cards frequently include a unique serial number permanently and unalterably burned into an integrated circuit contained within the card. The integrated circuit typically has sufficient memory capacity for data (e.g., stored electronically) such as a card issuer identification (ID) number, user information (name, account number, signature image, etc.), the private key of a public-private key pair, a digital signature, and a personal identification number (PIN). 
         [0004]    Optical storage techniques may also be used with RFID cards. Optionally, optical storage techniques may be used separately as a primary or sole data storage means on an identification card. Such storage techniques are known in the art and utilize, for example, diffractive or holographic patterns embedded on the card. A common “rainbow transmission” hologram utilizes common white light (as opposed to monochromatic sources, such as lasers) as an illumination source on secured transaction cards (e.g., credit cards). The rainbow transmission hologram is fabricated as a surface relief pattern formed on a first side of a plastic film. A second side of the film is placed in contact with a reflective coating, such as a sputtered aluminum film region, which reflects light incident on the transmissive hologram thus allowing viewing from the first (i.e., front) side of the card. The holograms are commonly used as a security feature on a variety of transaction and identification cards. 
         [0005]    With reference to  FIG. 1 , a prior art identification card  100  includes an optically encoded stripe  101  holding, for example, user data. An enlarged section  103  of the optically encoded stripe  101  reveals a diffraction grating-based optical identification element  105 . The diffraction grating-based optical identification element  105  is comprised of an optical substrate  107 , an optical diffraction grating  109  formed over the optical substrate, and a protective top layer  111 . The optical diffraction grating  109  is frequently formed by photolithographic techniques known in the semiconductor fabrication art and is produced either over an uppermost surface or within a volume of the optical substrate  107 . 
         [0006]    The optical diffraction grating  109  is a periodic or aperiodic variation in the effective refractive index or effective optical absorption over at least a portion of the optical substrate  107 . A change in the effective refractive index or effective optical absorption produces diffractive elements. Diffractive elements are known in the optical arts. The optical diffraction grating  109  thus serves to either reflect or refract light in a certain way to produce diffracted patterns of light. The diffracted patterns may be observed optically or read with a specialized diffracted light viewer, described below. 
         [0007]    The optical diffraction grating  109  is frequently a photosensitive layer (e.g., such as photoresist) allowing patterning of the diffractive elements. The optical diffraction grating  109  may also be a hologram, as the diffraction grating  109  can transform, translate, or filter an optical input signal to produce a predetermined desired optical output pattern or signal. The use of holograms on identification and security transaction cards (e.g., credit cards) is well-known in the art. 
         [0008]    Referring now to  FIG. 2 , a specialized diffracted light viewer  200  is used for inspection of data contained on the prior art identification card  100 . The specialized diffracted light viewer  200  includes an incoming laser beam  201 A incident upon the diffraction grating-based optical identification element  105 , and an optical diffraction detector  203 . The optical diffraction detector  203  includes an optional biconvex collection lens element  205  and a charge-coupled device (CCD) detection element  207 . When the laser beam  201 A is incident on the diffraction grating-based optical identification element  105 , a plurality of diffracted light beams  201 B is produced. The plurality of diffracted light beams  201 B is collected either by the optional biconvex collection lens element  205  focusing the diffracted light beams  201 B onto the CCD detection element  207 , or onto the CCD detection element  207  directly. As shown in  FIG. 2  for clarity, the specialized diffracted light viewer  200  is being used in a transmission mode. However, the specialized diffracted light viewer  200  may be used in reflected light mode as well by selecting an optical substrate  107  ( FIG. 1 ) that is reflective. 
         [0009]    The CCD detection element  207  reads an optical signal contained within the plurality of diffracted light beams  201 B and determines a code based on diffractive elements present or the optical pattern produced. The CCD detection element  207  may be coupled to a computer (not shown) that verifies all information stored on the diffraction grating-based optical identification element  105 . Alternatively, the CCD detection element  207  may be a portion of a camera (not shown) allowing direct inspection of the data contained on the diffraction grating-based optical identification element  105 . 
         [0010]    With continued reference to  FIG. 2 , the incoming laser beam  201 A has a given wavelength, λ, at a given angle of incidence θ i . Any other input wavelength λ can be used as long as the wavelength is within an optical transmission range of the protective top layer  111 . Depending upon whether the specialized diffracted light viewer  200  is designed to be used in transmission or reflection mode will determine whether the optical substrate  107  should be optically transparent for a given wavelength and angle of incidence. 
         [0011]    While prior art identification cards having optically-embedded information have been produced and used successfully for many years, such cards tend to be expensive to manufacture and impossible to update since they rely upon photolithographically-produced diffraction elements containing user data. Manufacturing identification regions photolithographically is a time-consuming and expensive process requiring sophisticated fabrication facilities, expensive equipment, and caustic, dangerous chemicals. Therefore, what is needed is a safe and efficient system to produce an optically-based data storage region on an identification card. The card must be extremely difficult to copy while being easy for an end-user to read with a relatively inexpensive device. Ideally, the optically based data storage region will be incapable of being read either by a casual observer or surreptitiously without specialized equipment. 
       SUMMARY OF THE INVENTION 
       [0012]    In an exemplary embodiment, an optical media card forming at least a portion of an identification card is disclosed comprising an optical identification element formed upon a surface of the identification card and an optical stripe formed on the optical identification element having at least a portion formed substantially from a single material. The single material is configured to have a diffractive pattern formed thereupon by exposure to a laser. The diffractive pattern is capable of retaining information related to a cardholder and being readable by a light source external to the identification card. 
         [0013]    In another exemplary embodiment, a method of producing a diffractive pattern on an optical element is disclosed. The method comprises compiling data for an identification card, calculating a far-field diffraction pattern containing the data, and calculating the diffractive pattern that is substantially equivalent to the far-field diffraction pattern. 
         [0014]    In another exemplary embodiment, a processor-readable storage medium storing an instruction is disclosed. The processor-readable storage medium, when executed by a processor, causes the processor to perform a method for performing a diffraction pattern writing routine onto an optical element. The method comprises compiling data for an identification card, calculating a far-field diffraction pattern containing the data, and calculating the diffractive pattern that is substantially equivalent to the far-field diffraction pattern. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Various ones of the appended drawings merely illustrate exemplary embodiments of the present invention and must not be considered as limiting its scope. 
           [0016]      FIG. 1  is a top perspective view with cross-sectional detail of an identification card of the prior art having an optical stripe containing data. 
           [0017]      FIG. 2  is an optical diagram of a diffracted light viewer of the prior art used to read optically embedded data from an identification card such as the prior art identification card of  FIG. 1 . 
           [0018]      FIG. 3  is a top perspective view with detail of an exemplary embodiment of an identification card containing an optical stripe in accordance with aspects of the present invention. 
           [0019]      FIG. 4  is a simplified cross-sectional exemplary overview of light incident on the optical stripe of the identification card of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    As indicated above, a person of skill in the art recognizes that data and identification cards can be made more secure by utilizing an optical stripe on the card containing diffraction patterns produced by photolithography. Various embodiments of the present invention contemplate producing data cards using unique diffraction patterns produced by a laser using a holographic writing process. The diffraction pattern produced by the laser can be read either in transmission or reflection. No photolithography is required. In an exemplary embodiment, the diffraction pattern is not visible by a simple non-aided visual inspection of the card. 
         [0021]    With reference to  FIG. 3 , an exemplary embodiment of an identification card  300  includes a substrate  301  and an optical stripe  303 . In a specific exemplary embodiment, the optical stripe  303  is written with an optical head containing a laser (not shown). Optical heads for driving or scanning lasers in a plurality of directions with multiple degrees of freedom are known independently in the art. 
         [0022]    The optical stripe  303  may be comprised of, for example, a laser recording material such as Drexon®. Drexon® is made up of micrometer-sized silver particles in a gelatin matrix and having known optical reflectivity at various wavelengths. Drexon® is manufactured by LaserCard Corporation, 1875 N. Shoreline Blvd., Mountain View, Calif., USA. 
         [0023]    The laser used to write the optical stripe  303  may be, for example, a 780 nm wavelength solid state laser. Additionally, various other types and wavelengths of lasers, could be used as well. The laser writes a diffractive pattern  305  to the Drexon® media or any other media used to fabricate the optical stripe  303 . The diffractive pattern  305  may be one-dimensional (not shown) in that it varies in only one axis (for example, along a long axis of the identification card  300 ). Alternatively, as shown in  FIG. 3 , the diffractive pattern  305  may be two-dimensional in that the pattern varies both parallel to and normal to the long axis of the identification card  300 . The two-dimensional pattern may be best utilized where a viewer, such as the diffracted light viewer  200  of  FIG. 2 , is capable of scanning in two or more directions. Such scanning techniques are known independently in the art. 
         [0024]    In another embodiment (not shown), the diffractive pattern on the identification card  300  may be based on a patterned radial variation or some combination of Cartesian (e.g., one- or two-dimensional patterns) and radial variations. 
         [0025]    No matter the actual pattern produced, the diffractive pattern  305  is typically written by a laser or other coherent light source using a standard process of darkening (i.e., making an area of the final pattern non-reflective) a portion of a reflective material. Such processes are described in, for example, U.S. Patent No. to Richard M. Haddock, entitled “Method of Making Secure Personal Data Card,” which is commonly assigned to the assignee of the present invention and is hereby incorporated by reference in its entirety. Additionally, U.S. Pat. Nos. 4,680,459; 4,814,594; and 5,421,619, also assigned to the assignee of the present invention and hereby incorporated by reference, describe the creation of laser recorded data in optical memory cards. 
         [0026]    In a specific exemplary embodiment, a holographic writing process is used whereby two or more light beams (e.g., from a single laser in a system employing a beam splitter or, alternatively, a plurality of lasers) interfere with one another on a path to the reflective material resulting in interference patterns being written. 
         [0027]    In another specific exemplary embodiment, the diffractive pattern is established with a computer program causing the interference pattern to form in a particular way. The diffractive pattern is then converted either to a bitmap or vector pattern and a laser is instructed to write the pattern to a data storage medium to be viewed by a diffractive viewer. In this embodiment, the holographic process is thus simulated by a computer program which creates a bitmap or vector pattern that is written to the identification card  300  by darkening certain areas of the optical stripe  303  using a laser. A resulting diffractive pattern on the optical stripe  303  would not be visible on the identification card  300  without the use of an optical aid. The interference pattern would only be visible using an optical enhancement device such as, for example, a microscope. Even then, the diffractive pattern would be meaningless without a correct interpretive algorithm applied. 
         [0028]    In a specific exemplary embodiment, the diffractive pattern  305  is computed using a computer program that estimates a correct diffractive (i.e., input) pattern, calculates a corresponding output pattern, and then compares the resulting output patterns against a desired output pattern. The program keeps changing the diffractive pattern iteratively, keeping those changes that tend to produce a result that is closer to the desired output pattern. These changes are repeated until the output pattern is of sufficient quality (i.e., substantially equivalent to the desired pattern) to satisfy the need for the pattern to be identified. The software thus creates a diffractive pattern that instead of being recognized by people as a certain pattern, is recognized only by a specialized reader, described herein, as an encoded serial number. Two-dimensional bar codes and “micro-spot” technologies are independently known ways of encoding digital data (bits) onto an optical image. The image formed from the diffractive pattern  305  onto a CCD array of the reader contains light and dark areas that comprise the patterns. 
         [0029]    A modified version of the diffracted light viewer  200  may be utilized to read the identification card  300  in which the optional biconvex collection lens element  205  is unnecessary since an output light pattern coming from the identification card  300  is spreading out. Thus, a resulting image becomes larger at increasing distances from the CCD detection element  207  to the identification card  300 . Consequently, if the CCD detection element  207  is a certain distance from the identification card  300 , the optional biconvex collection lens element  205  is unnecessary. 
         [0030]    A normal reading/writing optical setup for typical optical memory cards of the prior art utilizes sharp angles for the light and therefore a very narrow depth-of-field. The narrow depth-of-field is required in order to maximize the size of the beam as it goes through the surface of a protective layer of a card. Maximizing the beam diameter allows optical setup to focus past any dirt or scratches on the surface layer. For example, a diameter of the spot on which the laser beam is focused may be 2.5 micrometers (μm), while the diameter of the area through which the beam passes on the surface of the card may be 2000 μm (i.e., 2 mm). 
         [0031]    Using the holographic process defined herein allows information on the identification card  300  to spread out, instead of merely spreading out the light as it passes the surface of the card. Thus, the viewing system can “look past” most dirt or scratches without tightly focusing the beam of light. Not having to tightly focus the light makes the reader for the hologram much less expensive than it might otherwise be since no complex optical trains are required. 
         [0032]    Thus, the identification card  300  may be read in a manner similar to how most short-range RFID cards are read today: by placing them in proximity to an inexpensive reader. However, the identification card  300  cannot be read unless the diffractive pattern  305  on the optical stripe  303  is exposed to an illuminating laser of the reader. Such a card cannot readily be read surreptitiously as can an RFID card. 
         [0033]    Thus, specific embodiments of the present invention employ a system that replaces an RFID card with an optical card that has advantages of an RFID card (e.g., an inexpensive reader, easy to scan) without accompanying disadvantages (e.g., susceptibility to electromagnetic fields, susceptibility to bending, and surreptitious reading). Prior art diffractive patterns on optical cards authenticate a type of card (using an image common to all cards of a given type) but cannot identify an individual card. Moreover, prior art optical cards are serialized using well-known techniques, but require a serial number reader that is relatively large and expensive. 
         [0034]    A diffractive serial number may be used as a replacement for a traditional RFID card. Alternatively, the optical stripe  303  with the diffractive pattern  305  may be used as a supplement to the traditional RFID card thus allowing certain data types to be encoded as RFID while the diffractive pattern  305  can carry more sensitive data. Since the diffractive pattern  305  produces a diffracted light pattern only discernible by a given system, a resulting embedded serial number (or any other types of embedded data) could not be surreptitiously read or cloned. 
         [0035]    A portion of the diffractive data storage reading system may consist of an optical diffractive viewer, currently available from LaserCard Corporation (Mountain View, Calif., USA). The viewer is a semiconductor laser that illuminates the medium (i.e., the optical stripe  303 ) coupled with a CCD detector. The viewer could be used to produce, for example, serial numbers for RFID or similar cards, where the serial numbers are written and read in diffraction. Such serial numbers help authenticate the cards. 
         [0036]    For example, one LaserCard Corporation diffractive viewer has no lenses. Only an inexpensive off-the-shelf solid-state 632.8 nm laser and a mirror are used to image a pattern from the diffractive pattern  305  onto a small screen (not shown) of approximately 1 cm in diameter. A skilled artisan will recognize that other types and wavelengths of reading lasers may be readily employed as well. A pattern corresponding to a serial number is written into the diffractive pattern  305 . The reader then replaces the small screen with a CCD array coupled to digital circuitry that interprets the pattern thus converting the pattern to a unique serial number. The reader might also have a lens, but the system will have a large depth of field, so a position of the lens, if used, will not be critical. 
         [0037]    As an overview of a reading process of the diffractive pattern  305 , reference is now made to a simplified exemplary process overview of  FIG. 4 , which includes a cross-section of the optical stripe  303  with a monochromatic incident beam at wavelength λ i  at an angle-of-incidence of θ i . The optical stripe  303  includes the diffractive pattern  305 , an optical substrate  401 , and a top protective layer  403 . 
         [0038]    In a specific alternative exemplary embodiment, the diffractive pattern  305  may not be surrounded by the optical substrate  401  or the top protective layer  403 . In this embodiment, the diffractive pattern may be interrogated by a laser directly in either a transmissive mode or a reflective mode (not shown) based upon a material selected on which the diffractive pattern  305  is produced. 
         [0039]    With continued reference to  FIG. 4 , to read the diffractive pattern  305  from the optical stripe  303 , the incident beam must be reflected, diffracted, or scattered by the diffractive pattern  305 . As is known to one of skill in the art, at least two conditions must be met for light to be reflected. First, a diffraction condition for the diffractive pattern  305  must be satisfied. This condition, as is known, is the diffraction (or reflection or scatter) relationship between the incident wavelength λ i , the input incidence angle θ i , an output incidence angle θ o , and a spatial period Λ of the diffractive pattern  305 . The governing equation is given as: 
         [0000]    
       
         
           
             
               
                 sin 
                  
                 
                   ( 
                   
                     θ 
                     i 
                   
                   ) 
                 
               
               + 
               
                 sin 
                  
                 
                   ( 
                   
                     θ 
                     o 
                   
                   ) 
                 
               
             
             = 
             
               
                 m 
                  
                 
                     
                 
                  
                 λ 
               
               
                 
                   n 
                   y 
                 
                  
                 Λ 
               
             
           
         
       
     
         [0000]    where m is the diffractive order being observed, n y  is the refractive index of a material through which incident and diffractive beams pass (e.g., n 1  is the refractive index of the optical substrate  401 ), and θ o  is an output angle of the diffracted beam (measured from an angle normal to a surface as indicated by a normal line  407 ). The spatial wavelength, Λ, of the diffractive pattern  305  is merely the inverse of the spatial frequency of the diffractive pattern, f. Thus, 
         [0000]    
       
         
           
             f 
             = 
             
               
                 1 
                 Λ 
               
               . 
             
           
         
       
     
         [0000]    The governing equation given above therefore provides a relationship between an incident beam and resulting diffracted beams. 
         [0040]    As a result, for a given input wavelength λ i , spatial wavelength Λ, and angle of incidence θ i , the output incidence angle θ o , may be readily determined. Rearranging the governing equation above to solve for θ o  and using m=1 for the first diffracted order, results in: 
         [0000]    
       
         
           
             
               θ 
               o 
             
             = 
             
               
                 sin 
                 
                   - 
                   1 
                 
               
               ( 
               
                 λ 
                 
                   Λ 
                   - 
                   
                     sin 
                      
                     
                       ( 
                       
                         θ 
                         i 
                       
                       ) 
                     
                   
                 
               
               ) 
             
           
         
       
     
         [0041]    The second condition for reading diffracted or scattered light is that the diffracted angle of the output beam θ o  must lie within an acceptable region of a Bragg envelope  409  to provide an acceptable intensity level of output light. The Bragg envelope  409  defines the diffracted or scattered efficiency of incident light. The Bragg envelope  409  has a center (or peak) on a center line  411  where refection efficiency is greatest when θ i =θ o . The Bragg envelope has a half-width θ B  from the center line  411  or a total width of 2θ B . For enhanced efficiency in light output, the diffracted angle of the output beam θ o  should be at the center of the Bragg envelope  409 . 
         [0042]    Thus, any code embedded into the diffractive pattern  305  of the optical stripe  303  may be readily discerned if all of the parameters given are known to devise a proper identification card reader. A skilled artisan would be able to extend the simplified parameters given above into designing a card reader capable of reading two-dimensional cards as defined herein. 
         [0043]    In the foregoing specification, the present invention has been described with reference to specific embodiments thereof. It will, however, be evident to a skilled artisan that various modifications and changes can be made thereto without departing from the broader spirit and scope of the present invention as set forth in the appended claims. For example, all embodiments described utilize a monochromatic light source in the form of a laser. However, a skilled artisan will recognize that other light sources, or combinations of sources, even at varying angles of incidence and polarization states, may be used as well. For instance, broadband sources with appropriate bandpass filters or monochromators may be used to form a diffractive pattern on the optical stripe. Further, other high-powered sources of electromagnetic radiation may also be adapted to form the diffractive pattern. Additionally, various combinations of embodiments described herein may be employed and both optical, magnetic, and other RFID structures may all be combined into a single identification card. Therefore, these and various other embodiments are all within a scope of the present invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.