Patent Publication Number: US-2015069128-A1

Title: Optical reading device, optical reading method, and program

Description:
TECHNICAL FIELD 
     The present invention relates to techniques to determine the authenticity of passports, documents, kinds of cards, passes, paper money, cash vouchers, certificates, instruments, gift vouchers, paintings, tickets, public game voting cards, recording mediums having music or video, recording mediums having computer software, kinds of parts, kinds of products, and packages thereof and the like. 
     BACKGROUND ART 
     Japanese Patent No. 4714301 discloses a reading device, the device including a right circularly polarized light filter and a left circularly polarized light filter in order to detect circularly polarized light of a certain rotation direction which is selectively reflected by a cholesteric liquid crystal, and the device also has a structure in which one of the circularly polarized light filters is inserted in, or is removed from, an optical path. 
     In the structure disclosed in the Japanese Patent No. 4714301, a mechanism for moving the circularly polarized light filter is necessary in order to insert the circularly polarized light filter in the optical path or in order to remove the circularly polarized light filter from the optical path, and therefore the device should be larger and more complicated. Furthermore, it takes time to move the circularly polarized light filter, and therefore the rate of the authentication processing may be limited. 
     In view of such circumstances, an object of the present invention is to provide an optical reading device to authenticate an identification medium having a cholesteric liquid crystal, which has a structure in which a movable portion is not necessary to switch the circularly polarized light filter. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention is an optical reading device for reading an image from an identification medium that includes a cholesteric liquid crystal layer in which a hologram is processed, and an ink printed pattern layer, arranged in this order, from a reading surface. The optical reading device includes a primary light emitting means, a primary circularly polarized light filter which is arranged in front of the primary light emitting means and which selectively transmits circularly polarized light of a primary rotating direction, a secondary light emitting means, a secondary circularly polarized light filter which is arranged in front of the secondary light emitting means and which selectively transmits circularly polarized light in a secondary rotating direction that is opposite to the primary rotating direction, and a controlling means that controls selecting one of two kinds of irradiation, one is irradiation of the circularly polarized light of the primary rotating direction from the primary circularly polarized light filter to the identification medium, and the other is irradiation of the circularly polarized light of the secondary rotating direction from the secondary circularly polarized light filter to the identification medium. According to the first aspect of the present invention, by switching emission of the two light emitting means, the hologram image from the cholesteric liquid crystal layer and the image by the ink printed pattern can be read while switching them. 
     A second aspect of the present invention is an optical reading device in which the cholesteric liquid crystal layer displays a primary code information that is displayed by hologram, the ink printed pattern displays a secondary code information, the primary code information display and the secondary code information display overlap at least partially, if viewed from the reading side, the primary code information is selectively read by irradiation of the primary circularly polarized light, and the secondary code information is selectively read by irradiation of the secondary circularly polarized light, in the first aspect of the invention. According to the second aspect of the invention, in a case in which two code information are read at the same time, the codes cannot be decoded, thereby obtaining extremely sensitive authentication characteristics. 
     A third aspect of the present invention is an optical reading device in which a total reflection cholesteric liquid crystal layer that reflects circularly polarized light having the same rotating direction as circularly polarized light selectively reflected by the circularly polarized light filter layer or the cholesteric liquid crystal layer, is arranged between the cholesteric liquid crystal layer and the ink printed pattern layer; the circularly polarized light filter layer selectively interrupts circularly polarized light selectively reflected by the cholesteric liquid crystal layer; and the total reflection cholesteric liquid crystal layer has a property of reflecting circularly polarized light of all wavelengths of incident visible light band width, or has a reflection property equivalent to a case of reflecting circularly polarized light having all wavelengths of incident visible light band width, in the first or second aspect of the invention. 
     According to the third aspect of the invention, in a case in which circularly polarized light selectively reflected by the cholesteric liquid crystal layer is irradiated in order to selectively read a hologram image of the cholesteric liquid crystal layer, reflected light from the ink printed pattern can be further reduced. 
     A fourth aspect of the present invention is an optical reading device in which a color of irradiated light of the primary rotating direction is a primary color that is as the same as a color selectively reflected by the cholesteric liquid crystal layer, and the color of irradiated light of the secondary rotating direction is as the same as a color of the ink printed pattern, and is a secondary color which is different from the primary color, in one of the first to third aspects of the invention. 
     According to the fourth aspect of the invention, in a case in which circularly polarized light of a rotating direction selectively reflected by the cholesteric liquid crystal layer is irradiated, since a light component which reaches the ink printed pattern can be in principle nonexistent, a property in which reflect light from the cholesteric liquid crystal layer can be selectively observed can be further obtained. Furthermore, in a case in which circularly polarized light in a rotating direction not selectively reflected by the cholesteric liquid crystal layer is irradiated, since the cholesteric liquid crystal layer does not reflect any light, a property in which reflect light from the ink printed pattern can be selectively observed can be further obtained. 
     A fifth aspect of the present invention is a method for optically reading image data from an identification medium, the identification medium including: a cholesteric liquid crystal layer that is arranged at a side of a reading surface and which displays a hologram image indicating primary code information, and an ink printed pattern layer that is arranged at the side opposite to the reading surface of the cholesteric liquid crystal layer and which displays secondary code overlapping with the primary code display if viewed from the reading side, and in the method, the primary code information is selectively read by irradiation of primary circularly polarized light of a primary rotating direction, and the secondary code information is selectively read by irradiation of secondary circularly polarized light of a secondary rotating direction being opposite to the primary rotating direction. 
     A sixth aspect of the present invention is a program for controlling reading image data from an identification medium, the identification medium including: a cholesteric liquid crystal layer that is arranged at a side of reading surface and that displays a hologram image indicating primary code information, and an ink printed pattern layer that is arranged at the side opposite to the reading surface of the cholesteric liquid crystal layer and that displays secondary code overlapping with the primary code display if seen from the reading side, the program executes: a step of reading selectively the primary code information by irradiation of a primary circularly polarized light of a primary rotating direction, and a step of reading selectively the secondary code information by irradiation of a secondary circularly polarized light of a secondary rotating direction opposite to the primary rotating direction. 
     According to the present invention, in an optical reading device for authenticating an identification medium including a cholesteric liquid crystal, a structure is provided in which a movable portion for switching circularly polarized light filter is not necessary. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an oblique view showing the optical reading device of an Embodiment. 
         FIG. 2  is a block diagram showing the optical reading device of an Embodiment. 
         FIG. 3  is a cross sectional view showing an identification medium that can be read by the optical reading device of an Embodiment. 
         FIGS. 4A and 4B  are diagrams showing a two dimensional barcode. 
         FIG. 5  is a conceptual diagram showing a situation of optical reading in an Embodiment. 
         FIG. 6  is a conceptual diagram showing a situation of optical reading in a Comparative Example. 
         FIG. 7  is a cross sectional view showing another identification medium that can be read by the optical reading device of an Embodiment. 
         FIG. 8  is a cross sectional view showing another identification medium that can be read by the optical reading device of an Embodiment. 
         FIG. 9  is a cross sectional view showing another identification medium that can be read by the optical reading device of an Embodiment. 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS 
       10 : Optical reading device,  11 : light receiving part,  12 : light emitting part,  13 : light emitting part,  14 : right circularly polarized light filter,  15 : (¼) λ plate,  16 : linear polarized light filter,  17 : left circularly polarized light filter,  18 : (¼) λ plate,  19 : linear polarized light filter,  100 : identification medium,  101 : hard coat layer,  102 : cholesteric liquid crystal layer,  103 : hologram processing,  104 : printed pattern,  105 : adhesive layer,  200 : identification medium,  201 : circularly polarized light filter layer,  202 : (¼) λ plate,  203 : linear polarized light filter,  300 : identification medium,  301 : visible light all band reflecting cholesteric liquid crystal layer,  302 : red right circularly polarized light selective reflecting cholesteric liquid crystal layer,  303 : green right circularly polarized light selective reflecting cholesteric liquid crystal layer,  304 : blue right circularly polarized light selective reflecting cholesteric liquid crystal layer,  400 : identification medium,  401 : film substrate,  402 : letter printed pattern,  403 : primary code forming area, and  404 : secondary code forming area. 
     MODE FOR CARRYING OUT THE INVENTION 
     Structure of Optical Reading Device 
       FIG. 1  shows an oblique view of an optical reading device  10  of Embodiment, and  FIG. 2  shows a block view of the optical reading device  10 . The optical reading device  10  includes a light receiving part  11 , light emitting parts  12  and light emitting parts  13 . The light receiving part  11  includes an objective lens  22  and an imaging part  23 . The objective lens  22  is a lens constructing an optical system of the light receiving part  22 . In the figure, the objective lens is described as the optical system, and a more complicated optical system can be employed. The imaging part  23  is a camera constructed by a CCD camera or a CMOS image sensor, and transforms an image that is received by the light receiving part  11  into electronic data. 
     The optical reading device  10  includes an image identifying part  24  and a code reading part  25 . The image identifying part  24  identifies contents of an image that is photographed by the imaging part  23 . The code reading part  25  reads a code (bar code, hologram code, letter code or the like) that is contained in the image that is identified by the image identifying part  24 . This code contains an authenticity decision and product information or the like. The code information that is read at the code reading part  25  is output to the outside. It should be noted that a structure is also possible in which the optical reading device  10  includes therein a deciding means for making a decision of authenticity based on the contents of the code or a detecting means for detection of secondary information (product information such as product number, production history or the like, for example) based on the contents of the code. 
     As shown in  FIG. 1 , the light emitting part  12  is arranged in three parts vertically, if viewed from the front of the optical reading device  10 . The structure of one part of the light emitting part  12  among the three parts vertically arranged is explained as follows (the other two parts have the same structure). The light emitting part  12  includes a right circularly polarized light filter  14  and an LED  20 , which is a light emitting means. Here, one that emits white light is selected as the LED  20 . 
     The right circularly polarized light filter  14  transforms light that is emitted by the LED  20  into right circularly polarized light, and irradiates only the right circularly polarized light onto an object (upper direction in FIG.  2 ). The right circularly polarized light filter  14  has a structure in which a (¼) λ plate  15  and a linear polarized light filter  16  are layered. In this structure, linear polarized light that is polarized in a certain direction in the light that is emitted by the LED  20  is transmitted through the linear polarized light filter  16 , and then enters into the (¼) λ plate  15 . The direction of light polarization of the linear polarized light filter  16  and the direction of refractive index anisotropy of the (¼) λ plate  15  are set so that light that exits in the upper direction in  FIG. 2  from the (¼) λ plate  15  will be right circularly polarized light. Therefore, white light from the light source of LED  20  exits from the light emitting part  12  in the upper direction in the figure as right circularly polarized light. 
     The light emitting part  13  is arranged in three parts vertically. The structure of one part of the light emitting part  13  among the three parts vertically arranged is explained as follows (the other two parts have the same structure). The light emitting part  13  includes a left circularly polarized light filter  17  and an LED  21 , which is a light emitting means. The left circularly polarized light filter  17  transforms white light that is emitted by the LED  21  into left circularly polarized light, and irradiates only the left circularly polarized light to an object (upper direction in  FIG. 2 ). The left circularly polarized light filter  17  has a structure in which a (¼) λ plate  18  and a linear polarized light filter  19  are stacked. In this structure, linear polarized light that is polarized in a certain direction among white light that is emitted by the LED  21  is transmitted through the linear polarized light filter  19 , and then enters into the (¼) λ plate  18 . The direction of light polarization of the linear polarized light filter  19  and the direction of refractive index anisotropy of the (¼) λ plate  18  are set so that light that exits in the upper direction in  FIG. 2  from the (¼) λ plate  18  will be left circularly polarized light. Therefore, light from the light source of LED  21  exits from the light emitting part  13  as left circularly polarized light. 
     The timing of light emission of the LEDs  20  and  21  is determined by a controlling part  26 . The controlling part  26  switches a power source of the LEDs  20  and  21  ON and OFF, and controls switching light emission between the LED  20  and the LED  21 . The structure of the light emitting part  12  is not limited in the structure of three vertical parts, and a structure in which right circularly polarized light exits from one position, a structure in which multiple parts are arranged horizontally, a structure in which multiple parts are arranged along the circumference of the light receiving part  11 , or the like can be employed. Similar structures can be employed with respect to the light emitting part  13 . 
     Structure of Identification Medium 
       FIG. 3  shows an identification medium  100  that is read by the optical reading device  10  shown in  FIGS. 1 and 2 . The identification medium  100  has a layered structure in which a hard coat layer  101 , a cholesteric liquid crystal layer  102 , a printed pattern  104 , and an adhesive layer  105  are arranged from the observation side. The hard coat layer  101  is a protective layer that is constructed of a transparent material that does not disturb a light polarization condition of transmitted light. 
     A hologram processing  103  that is embossed is formed in the cholesteric liquid crystal layer  102 . In this example, the cholesteric liquid crystal layer  102  is set so as to selectively reflect red right circularly polarized light. Of course, a setting to selectively reflect the central wavelength of another color or a setting to selectively reflect left circularly polarized light can be employed. The hologram processing  103  forms the hologram image that displays a two dimensional barcode exemplified in  FIG. 4A . That is, the hologram processing  103  formed in the cholesteric liquid crystal layer  102  is one in which an embossed pattern is formed in the cholesteric liquid crystal layer  102  by embossing. In a case in which reflected light from the cholesteric liquid crystal layer  102  is observed, the two dimensional barcode shown in  FIG. 4A  is observed by optical interference due to this embossed pattern. It should be noted that the hologram processing  103  can be performed from any surface (upper surface or lower surface) of the cholesteric liquid crystal layer  102 , and similar optical function can be obtained in both cases. 
     The printed pattern  104  is constructed by printing ink on one surface of the cholesteric liquid crystal layer  102  (lower side surface in  FIG. 3  in the case of this example) at a predetermined pattern by an inkjet method. The printed pattern  104  has a pattern for displaying a two dimensional barcode shown in  FIG. 4B . The two dimensional barcode by the hologram image based on the hologram processing  103  shown in  FIG. 4A  and the two dimensional barcode based on the printed pattern  104  shown in  FIG. 4B  are different from each other, as shown in the design of  FIG. 4 , and they are set to show different contents of code from each other. Furthermore, the two dimensional barcode shown in  FIG. 4A  and the two dimensional barcode shown in.  FIG. 4B  overlap at least partially in the thickness direction of the identification medium  100 . 
     As the adhesive layer  105 , a transparent material is used. However, as long as reading of the two dimensional barcode of  FIG. 4B  is not adversely affected, pigment that is black, dark blue or the like, functioning as a light absorbing layer, can be mixed in. The adhesive layer  105  has a function of adhering the identification medium  100  onto an object, and it can have a function as a light absorbing layer in which a background of the cholesteric liquid crystal layer  103  and the printed pattern  104  is maintained to be dark, if necessary. It should be noted that in a condition in which it is not adhered to an object, a separator (release paper), which is not shown in the figure, is adhered on an exposed surface of the adhesive layer  105 . 
     Identifying Method 
     One example of authentication of the identification medium  100  of  FIG. 3  using the optical reading device of  FIG. 1  is explained below. The identification is performed in a condition in which the optical reading device  10  faces a surface of the hard coat layer  101  side of the identification medium  100 . First, a case in which the LED  20  emits light and the LED  21  does not emit light is explained. This situation is conceptually shown in  FIG. 5 . In this case, light that is emitted from the LED  20  is made into right circularly polarized light in the right circularly polarized light filter  14 , and is irradiated to the identification medium  100 . 
     Here, only light that enters into the cholesteric liquid crystal layer  102  from the LED  20  is right circularly polarized light. Left circularly polarized light and linear polarized light are not contained in light incident on the cholesteric liquid crystal layer  102  produced by the LED  20 . Therefore, reflection from the printed pattern  104  is weak, reflection from the cholesteric liquid crystal layer  102  is stronger, the two dimensional barcode (see  FIG. 4A ) caused by the hologram processing  103  that is arranged in the cholesteric liquid crystal layer  102  is identified at image identifying part  24  (see  FIG. 2 ), and furthermore, the code content is read by the code reading part  25 . During this process, the two dimensional barcode of  FIG. 4B  constructed by the printed pattern  104  is not read. 
     Next, a case in which the LED  21  emits light and the LED  20  does not emit light is explained. In this case, light that is emitted from the LED  21  is made into left circularly polarized light by the left circularly polarized light filter  17 , and it is irradiated on the identification medium  100 . Here, since only incident light from the LED  21  to the cholesteric liquid crystal layer  102  is left circularly polarized light, the incident light is transmitted through the cholesteric liquid crystal layer  102 , which is set to selectively reflect right circularly polarized light, and reaches the printed pattern  104 . Left circularly polarized light that reached the printed pattern  104  is reflected at the printed pattern  104 , the condition of light polarization is disturbed at this time, and a polarized light component which can be transmitted through the cholesteric liquid crystal layer  102  (hereinafter referred to as the “other polarized light component”) is reflected in the direction of the cholesteric liquid crystal layer  102  (upper direction in the figure). 
     Other polarized light components that are reflected at the printed pattern  104  are transmitted through the cholesteric liquid crystal and enter into the light receiving part  11 . This “other polarized light component” is light reflected from the printed pattern  104 , and contains an image of the two dimensional barcode shown in  FIG. 4B , and is transmitted through the cholesteric liquid crystal layer  102 . Therefore, the image of the two dimensional barcode shown in  FIG. 4B  is identified at the image identifying part  24  (see  FIG. 2 ), and the content of the code is read by the code reading part  25 . At this time, since the cholesteric liquid crystal layer  102  is optically transparent and therefore invisible, the two dimensional barcode in  FIG. 4A  cannot be read. 
     As explained so far, by turning on one of LED  20  and LED  21  and turning off the other, one of the two dimensional barcodes shown in  FIGS. 4A and 4B  can be selectively read. Furthermore, by turning on one of LED  20  and LED  21  and turning off the other, in a case in which a human observes reflected light from the identification medium of  FIG. 4A , a case in which a hologram reflected image from the cholesteric liquid crystal layer  102  is selectively viewed and a case in which an image of the printed pattern  104  is selectively viewed can be switched. 
     The steps to read information from the identification medium  100  that is explained so far can be executed by a software program. In this case, the controlling part  26  is made to function as a computer, and a program to execute the above steps is stored in a memory region that is owned by the controlling part  26  (or in a recording region arranged at another appropriate part). Then, by the controlling part  26  functioning as a computer, this program is read and executed, so that the above steps are performed by the optical reading device  10 . It should be noted that the program can be one that is stored in an appropriate recording medium and is then provided therefrom. Furthermore, a structure is possible in which the program is executed in a commercially available personal computer, a control signal is sent from this personal computer to the controlling part  26 , and then the operation of the optical reading device  10  is controlled. 
     Comparative Example 
     Hereinafter, a case is explained in which natural light is irradiated on the identification medium  100  and reflected light is observed via the circularly polarized light filter, without arranging the circularly polarized filter in front of the LED.  FIG. 6  shows a diagram that shows this situation conceptually.  FIG. 6  corresponds to  FIG. 5 , and the difference therebetween is that the circularly polarized light filter is arranged in front of the light source or in front of the detecting part. It should be noted that in the case of  FIG. 6 , the circularly polarized light filters  14  and  17  are removed, and therefore white light that is emitted from the light emitting parts  12  and  13  is not in a condition of specific light polarization. 
     In this case, red right circularly polarized light is reflected from the cholesteric liquid crystal layer  102 , and the other component (right circularly polarized light of other than red, left circularly polarized light, and linear polarized light) transmits the cholesteric liquid crystal layer  102  and reaches the printed pattern  104 . The red circularly polarized light that is reflected from the cholesteric liquid crystal layer  102  transmits the right circularly polarized light filter  601  and received at the light receiving part  11 . 
     On the other hand, the light component that reaches the printed pattern  104  is reflected there. In this case, conditions of light polarization are disturbed, and a polarized light component that can be transmitted through the cholesteric liquid crystal layer  102  (hereinafter referred to as the other polarized light component) is reflected from the printed pattern  104  in the direction of the cholesteric liquid crystal layer  102  (upper direction in the figure). This “other polarized light component” is transmitted through the cholesteric liquid crystal layer  102  from a lower part of the figure in the upward direction, is transmitted through the right circularly polarized light filter  601 , and is received at the light receiving part  11 . 
     That is, in the case of  FIG. 6 , despite that reflected light is detected from the identification medium  100  via the right circularly polarized light filter  601 , the two dimensional barcode of  FIG. 4A  and the two dimensional barcode of  FIG. 4B  are detected at the same time. Since the two dimensional barcode of  FIG. 4A  and the two dimensional barcode of  FIG. 4B  have their overlapped portion, in the case of the Comparative Example in  FIG. 6 , code information of the two dimensional barcodes cannot be detected individually. Furthermore, in a case in which reflected light from the identification medium  100  is detected directly not using the circularly polarized light filter  601 , the two dimensional barcode of  FIG. 4A  and the two dimensional barcode of  FIG. 4B  are detected at the same time, and thus the situation is the same. 
     Next, an example is explained in which the right circularly polarized light filter  601  is substituted with the left circularly polarized light filter  602  in  FIG. 6 . In this case, since red right circularly polarized light reflected from the cholesteric liquid crystal layer  102  is blocked by the circularly polarized light filter  602 , reflected light from the printed pattern  104  selectively reaches the light receiving part  11 , and the optical reading device  10  can selectively detect the two dimensional barcode of  FIG. 4B . 
     As explained so far with reference to  FIG. 6 , in the case in which reflected light from the identification medium  100  is detected via the circularly polarized light filter, two two-dimensional barcodes shown in  FIG. 4  cannot be switched and detected individually even if the left and right circularly polarized light filters are switched. 
     Other Aspects 
       FIG. 4  shows an example of the two dimensional barcode, but the structure of the code display is not limited only to this, and a one dimensional barcode, a micro letter code, an OCR code or combination thereof can be employed. Furthermore, a construction is possible in which one of the codes shown in  FIG. 4A  or  4 B is set as a picture display and one of the code or the picture is selectively read. In this case, identification is performed by identification by visual inspection or image analysis. It should be noted that as a picture other than a code display, a letter, diagram, pattern, kinds of design display, or combination thereof can be mentioned. 
     Modifications 
     A color that is emitted by the light emitting part  12  in the optical reading device  10  shown in  FIG. 1  and  FIG. 2  and a color that is selectively reflected by the cholesteric liquid crystal layer  102  in the identification medium  100  shown in  FIG. 3  are set to the same specific primary color. Furthermore, a color that is emitted by the light emitting part  13  and a color of the printed pattern  104  are set to the same specific secondary color that is different from the primary color. For example, setting is performed so that the light emitting part  12  emits red, and the cholesteric liquid crystal layer  102  selectively reflects red right circularly polarized light. Furthermore, setting is performed so that the light emitting part  13  emits green, and the printed pattern  104  is formed by green ink. It should be noted that as a method to specify emitting color of light emitting parts  12  and  13 , a method using a color filter or a method using an LED that emits a specific color can be mentioned. 
     In this case, in the operation construction shown in  FIG. 5 , red right circularly polarized light is irradiated from the optical reading device  10  onto the identification medium  100 , and all of it is reflected by the cholesteric liquid crystal layer  102 . Therefore, little light reaches the printed pattern  104 , and a situation is emphasized in which the printed pattern  104  is nearly invisible. That is, the situation is exhibited in which the two dimensional barcode of  FIG. 4A  can be seen and the two dimensional barcode of  FIG. 4B  cannot be seen (S/N ratio is increased more). 
     Furthermore, in the case in which the LED  21  emits light and the LED  21  does not emit light, green left circularly polarized light is irradiated to the identification medium  100 . During this time, there is no reflection from the cholesteric liquid crystal layer  102 , and green printed pattern  104  can be selectively seen. That is, the two dimensional barcode of  FIG. 4A  cannot be seen and the two dimensional barcode of  FIG. 4B  can be seen. For example, if right circularly polarized light is generated due to disturbance of light polarization conditions, since the red component is not contained (because green light is irradiated), there is no reflection generated from the cholesteric liquid crystal layer  102 , and there is an extremely low probability that the hologram image shown in  FIG. 4A  that is formed in the cholesteric liquid crystal layer  102  is visible. 
     It should be noted that another combination is possible, such as a case in which the light emitting part  12  emits green light, the cholesteric liquid crystal layer  102  selectively reflects green left circularly polarized light, the light emitting part  13  emits red light, and the printed pattern  104  is red. 
     Other Identification Medium 1 
       FIG. 7  shows an identification medium  200  which can be read by the optical reading device  10 . In the identification medium  200 , the technique disclosed in the above Japanese Patent No. 4714301 is used. The identification medium  200  further includes a circularly polarized light filter layer  201  in addition to the structure of the identification medium  100  shown in  FIG. 3 . It should be noted that the same explanation is applied to a part in  FIG. 7  having a reference numeral that is the same as that in  FIG. 3 . 
     The circularly polarized light filter layer  201  includes a structure in which a (¼) λ plate  202  and a linear polarized light filter layer  203  are layered seen from the reading side, selectively blocks circularly polarized light (right circularly polarized light in this case) which is selectively reflected by the cholesteric liquid crystal layer  102 , and selectively transmits circularly polarized light of the opposite rotating direction (left circularly polarized light in this case). Furthermore, in a case in which natural light enters from the surface of the circularly polarized light filter layer  201  opposite to the cholesteric liquid crystal layer  102  side, the circularly polarized light filter  201  selectively transmits circularly polarized light of the rotation direction opposite to the rotation direction of the circularly polarized light that is selectively reflected by the cholesteric liquid crystal layer  102  (left circularly polarized light in this case), against the cholesteric liquid crystal layer  102 . 
     In this structure, in a case in which right circularly polarized light is irradiated onto the identification medium  200 , right circularly polarized light other than red which transmitted through the cholesteric liquid crystal layer  102  is blocked at the circularly polarized light filter layer  201  and does not reach the printed pattern  104 . Therefore, in a case in which right circularly polarized light is irradiated onto the identification medium  200 , only the reflected light from the cholesteric liquid crystal layer  102  is preferentially read, and reflected light from the printed pattern  104  is rarely readable. That is, a situation is exhibited in which the two dimensional barcode of  FIG. 4A  is read and the two dimensional barcode of  FIG. 4B  cannot be read. 
     Furthermore, in this structure, since the only incident light that is reflected from the printed pattern  104  and enters in the cholesteric liquid crystal layer  102  is left circularly polarized light, the problem which is already explained in the Comparative Example in  FIG. 6  is solved, that is, the problem in which the printed pattern  104  is visible via the right circularly polarized light filter under natural ambient light. It should be noted that in a setting in which the cholesteric liquid crystal layer  102  selectively reflects left circularly polarized light, the circularly polarized light filter layer  201  is set so that left circularly polarized light is blocked and right circularly polarized light is selectively transmitted. 
     Other Identification Medium 2 
       FIG. 8  shows an identification medium  300  that can be read by the optical reading device  10 . The identification medium  300  includes a structure in which a visible light all-band reflecting cholesteric liquid crystal layer  301  is layered on a lower surface of the cholesteric liquid crystal layer  102 , in addition to the structure of the identification medium  100  shown in  FIG. 3 . 
     The visible light all-band reflecting cholesteric liquid crystal layer  301  has an optical property in which right circularly polarized light is selectively reflected, and under natural lighting, circularly polarized light that is selectively reflected is seen as light of all-band visible light. That is, its property is not a property in which a specific wavelength band range is selectively reflected; rather it is a property in which all the wavelengths of the incident visible light band range is reflected, or a reflection property equivalent to a case in which all the wavelengths of the incident visible light band range is reflected. 
     It should be noted that this is referred to as the “visible light all-band range” here as a matter of convenience, and this is not limited to a case containing all the components of the band range of visible light, and a case is also included which is a reflection property having a wavelength spectrum which is seen as light including visible light of the entire band if seen by a human due to combination of multiple wavelength peaks therein. Furthermore, hereinafter, a case is explained in which the visible light all-band range cholesteric liquid crystal layer  301  selectively reflects right circularly polarized light; however, it can be set so that left circularly polarized light is selectively reflected. 
     Hereinafter, the visible light all-band range reflecting cholesteric liquid crystal layer  301  is explained in detail. First, in an ordinary cholesteric liquid crystal layer, circularly polarized light having a specific rotation direction and specific central wavelength such as red or green is selectively reflected, and circularly polarized light of the opposite rotation direction, linear polarized light, and circularly polarized light having the above specific rotation direction and having wavelength component other than the above central wavelength are transmitted without being reflected. This is because the wavelength of light that is selectively reflected is decided based on the size of pitch of the cholesteric liquid crystal layer. On the other hand, the visible light all-band range reflecting cholesteric liquid crystal layer  301  selectively reflects circularly polarized light of all bands of visible light having specific rotation direction (or wavelength spectrum that can be so regarded). Of course, linear polarized light and circularly polarized light of opposite rotation direction is transmitted. This optical property can be obtained by complexing the cholesteric liquid crystal layer with multiple pitches. The visible light all-band range cholesteric liquid crystal layer is disclosed in Japanese Patent No. 3373374, for example. 
     The visible light all-band range reflecting cholesteric liquid crystal layer  301  is constructed of three layers: a primary cholesteric liquid crystal layer  302 , a secondary cholesteric liquid crystal layer  303 , and a tertiary cholesteric liquid crystal layer  304 . Here, the cholesteric liquid crystal layer  302  is set to selectively reflect red right circularly polarized light (wavelength 650±100 nm), the cholesteric liquid crystal layer  303  is set to selectively reflect green right circularly polarized light (wavelength 550±100 nm), and the cholesteric liquid crystal layer  304  is set to selectively reflect blue right circularly polarized light (wavelength 450±100 nm). Furthermore, the printed pattern  104  is formed at the tertiary cholesteric liquid crystal layer  304  of the adhesive layer  105  side. 
     A case is assumed in which natural light enters in this three-layer structure visible light all-band range reflecting cholesteric liquid crystal layer  301  from an upper direction of  FIG. 8 . In this case, red right circularly polarized light is selectively reflected from the primary cholesteric liquid crystal layer  302 , green right circularly polarized light is selectively reflected from the secondary cholesteric liquid crystal layer  303 , and blue right circularly polarized light is selectively reflected from the tertiary cholesteric liquid crystal layer  304 . During this time, since the primary cholesteric liquid crystal layer  302  transmits wavelength components of green and blue despite light polarization conditions and the secondary cholesteric liquid crystal layer  303  transmits wavelength components of blue despite light polarization conditions, right circularly polarized red, green, and blue light are reflected from the visible light all range reflecting cholesteric liquid crystal layer  301  in the upper direction of  FIG. 8 . 
     As the visible light all-band range reflection cholesteric liquid crystal layer  301 , in addition to the layered type shown in  FIG. 8 , a structure can be employed in which three kinds of cholesteric liquid crystals selectively reflecting circularly polarized light of the same rotation direction of red, green and blue is formed in stripes, grids, or dots having widths of about 50 μm. Furthermore, material in which the pitch of the cholesteric liquid crystal is continuously changed like gradation so as to have properties reflecting circularly polarized light of a wavelength band width having a width to some extent, can be used as the visible light all-band range reflection cholesteric liquid crystal layer  105 . 
     Furthermore, in addition to an RGB system, it is possible to produce conditions in which the human eye see it as if visible light of the entire range were reflected, by a combination of two colors or four colors or more. Of course, it is possible to obtain reflect light of a wavelength spectrum which covers as wide a visible light band range as possible, so as to have a property in which substantially the all-band range of visible light is reflected. It should be noted that the thickness of the visible light all-band range reflection cholesteric liquid crystal layer  301  may be in a range of 0.5 μm to 10 μm, and is desirably in a range of 1 μM to 5 μm. 
     The optical function of the identification medium  300  is basically the same as the identification medium  100 ; however, in a case in which right circularly polarized light from the LED  20  enters therein, since intensity of reflecting light from the cholesteric liquid crystal layer becomes weaker than in the case of reflection of a single color (for example, the case of the identification medium of  FIG. 3 ), reflection from the printed pattern  104  may be weaker, and therefore, reflected light of the hologram image based on the hologram processing  103  (for example, the image of the two dimensional barcode shown in  FIG. 4A ) can be detected (or observed) to be brighter. 
     Other Identification Medium 3 
       FIG. 9  shows an identification medium  400  which can be read by the optical reading device  10 . The identification medium  400  is an example in which the two dimensional barcode ( FIG. 4A ) of the hologram image and the two dimensional barcode ( FIG. 4B ) by printed patterns both shown in  FIG. 4  are arranged in a plane and another two dimensional barcode by printed pattern is further formed by a re-write printing using leuco dye or the like. It should be noted that the same explanation is applied to a part having a reference numeral the same as that in  FIG. 3 . 
     The identification medium  400  shown in  FIG. 9  includes a primary code forming region  403  and a secondary code forming region  404 . In the primary code forming region  403 , the two dimensional barcode display that is exemplified in  FIG. 4A  based on the hologram processing  103  is formed. In the secondary code forming region  404 , the two dimensional barcode display that is exemplified in  FIG. 4B  by printed pattern  402  of the re-write layer is formed. Here, reference numeral  401  is a film substrate such as PET, the re-write layer is arrange on the front surface side of the film substrate  401 , and the adhesive layer  105  is arranged on the back surface side. 
     The printed letter pattern  402  in the re-write layer can be re-written by using a dedicated printing and erasing device. Here, by combining code formed in the primary code forming region  403  and code information of the secondary code forming region  404 , it is set to obtain predetermined specific information. 
     Identification function of the identification medium  400  is explained below. Here, a case is explained in which the cholesteric liquid crystal layer  102  is set to selectively reflect right circularly polarized light, and optical reading is performed by using the optical reading device  10  shown in  FIG. 1 . 
     First, a case is explained in which reading is performed while the light emitting part  12  emits light and the light emitting part  13  does not emit light. In this case, reflected light from the printed pattern  402  and reflected light from the cholesteric liquid crystal layer  102  enters the light receiving part  11 . Therefore, the two dimensional barcodes shown in  FIGS. 4A and 4B  are read by the optical reading device  10 , and the content of the code displayed in the identification medium  400  can be read. 
     Next, in a case in which the light emitting part  12  does not emit light and the light emitting part  13  emits light, since left circularly polarized light is irradiated onto the cholesteric liquid crystal layer  102 , reflected light from the printed pattern  402  can be read; however, reflected light from the cholesteric liquid crystal layer  102  cannot be read. Therefore, the optical reading device  10  can only read one of the two dimensional barcodes shown in  FIGS. 4A and 4B , and the content of the code shown in the identification medium  400  cannot be read. In this way, authenticity can be determined depending on combination of light emitting pattern and reading data pattern. Furthermore, a type shown in  FIG. 7  or  FIG. 8  can be used in the primary code forming region  403 . 
     Since the content of the code can be re-written in a case in which re-write printing is used, the structure of the identification medium  400  can be applied to identification of an object for which it is necessary to re-write partially at a certain interval, such as for a commuting pass or a gate pass, for example. Furthermore, security can be further increased by encrypting the printed pattern code of  FIG. 4B  using the hologram code of the  FIG. 4A . 
     The present invention can be used as a technique to confirm authenticity.