Patent Publication Number: US-2009230183-A1

Title: Polarizing optical element and method of making the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-65515 filed on Mar. 14, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a polarizing optical element incorporated in an image capturing apparatus, for example. 
     2. Description of the Prior Art 
     A polarizing optical element is well known as disclosed in Japanese Laid-open Patent Publication Nos. 2004-271558 and 2006-201540. A resist film is formed on a glass substrate in the production of the polarizing optical element, for example. Nanoimprint is employed to transfer a predetermined pattern to the resist film. The resist film is patterned in a predetermined contour. The glass substrate is then subjected to dry etching. The glass substrate is carved out at a position outside the resist film. Parallel grooves are formed on the surface of the glass substrate, for example. An aluminum film is formed on the surface of the glass substrate so infill the grooves after the resist film has been removed. The aluminum film is thereafter removed from the surface of the glass substrate. Strips of film made of aluminum are thus formed in the grooves of the glass substrate. The polarizing optical element is in this manner produced. 
     In such a conventional method, expensive equipment is necessary for dry etching. It is not easy to utilize such equipment for dry etching. In addition, chlorine gas, which is harmful for people and the environment, is utilized for dry etching. If the thickness of the resist film is not constant, residue of the resist film remains on the surface of the glass substrate between the strips of resist film. The surface of the glass substrate cannot thus be subjected to dry etching. It is required to adjust the thickness of the resist film based on high technique to prevent generation of the residue. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part will be obvious from the description, or may be learned by practice of the present invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the present invention to provide a polarizing optical element and a method of making the same, allowing a simplified production process without dry etching. 
     According to a first aspect of the present invention, there is provided a method of making a polarizing optical element, comprising: forming a reactive resin thin film on the surface of a substrate; urging parallel bars, lying on the surface of the reactive resin thin film, against the surface of the substrate so as to establish strips of film made of a reactive resin between the adjacent ones of the parallel bars; curing the strips of film; forming an optically impermeable film on the surface of the substrate to cover over the strips of film; and applying polishing process along a plane parallel to the surface of the substrate so that the strips of film and strips of the optically impermeable film alternately arranged are exposed along the plane. 
     The parallel bars are urged against the surface of the substrate in the method. As a result, the strips of film made of a reactive resin are formed between the adjacent ones of the parallel bars. The thickness of the strips of film can be adjusted in a facilitated manner. The optically impermeable film is formed on the surface of the substrate to cover over the strips of film. The strips of film and the strips of optically impermeable film are thus alternately arranged. The polarizing optical element can be produced without dry etching, for example. The production process of the polarizing optical element can be simplified. The production cost of the polarizing optical element can be reduced. 
     The refractive index of the strips of film is set equal to the refractive index of the substrate after the cure of the strips of film in the method. Moreover, the method allows employment of a reactive resin thin film made of one of a light curable resin and a thermosetting resin. The polarizing optical element is incorporated in an authenticating unit, for example. The authenticating unit is incorporated in an automatic transaction machine, for example. 
     According to a second aspect of the present invention, there is provided a polarizing optical element comprising: a glass substrate having optical permeability; strips of resin film having optical permeability, the strips of resin film arranged on the surface of the substrate; and strips of optically impermeable film formed on the surface of the substrate at positions between the adjacent ones of the strips of resin film. The polarizing optical element of this type can be produced in a relatively facilitated manner based on the aforementioned method. The production process of the polarizing optical element can be simplified. The production cost of the polarizing optical element can be reduced. 
     The refractive index of the glass substrate is set equal to that of the strips of resin film in the polarizing optical element. The strips of resin film are made of one of a light curable resin and a thermosetting resin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiment in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view schematically illustrating an automatic teller machine as a specific example of an automatic transaction machine according to the present invention; 
         FIG. 2  is a sectional view schematically illustrating the structure of an image capturing apparatus incorporated in an authenticating unit according to the present invention; 
         FIG. 3  is an exploded view schematically illustrating the image capturing apparatus; 
         FIG. 4  is a perspective view schematically illustrating a polarizing optical element according to an embodiment of the present invention; 
         FIG. 5  is a perspective view schematically illustrating a substrate prepared for producing the polarizing optical element; 
         FIG. 6  is a perspective view schematically illustrating a process of forming a reactive resin thin film on the surface of the substrate; 
         FIG. 7  is a perspective view schematically illustrating a process of forming a reactive resin thin film on the surface of the substrate; 
         FIG. 8  is a perspective view schematically illustrating a process of urging parallel bars against the surface of the substrate; 
         FIG. 9  is a perspective view schematically illustrating a process of forming strips of films made of a reactive resin on the surface of the substrate; and 
         FIG. 10  is a perspective view schematically illustrating substrate covered with an aluminum film prior to application of polishing process. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  schematically illustrates an automatic teller machine (ATM)  11  as a specific example of an automatic transaction machine. The ATM  11  allows various kinds of transactions such as withdrawal of cash, deposit of cash to own account, deposit of cash to other&#39;s account, transfer, and the like. The ATM  11  includes a box-shaped enclosure  12 . A bill opening  13  and a coin opening  14  are formed in the front of the enclosure  12 . An opening/closing cover is attached to close each of the bill opening  13  and the coin opening  14 . A user puts/takes bills and coins in/out of the bill opening  13  and the coin opening  14 , respectively, for withdrawal/deposit of cash or transfer. 
     A card slot  15  and a passbook slot  16  are formed in the front of the enclosure  12 . The card slot  15  is designed to receive a plastic ATM card with a magnetic stripe or plastic smartcard with a chip for various kinds of transactions, for example. The passbook slot  16  is likewise designed to receive a passbook. Transactions are recorded in the received passbook. An input device, namely a touch screen panel  17 , is also incorporated in the enclosure  12  for various kinds of transactions. Key buttons for options, ten keys, character or alphabetical keys are displayed on the screen of the touch screen panel  17 , for example. When the key buttons, the ten keys and the character keys are touched on the surface of the touch screen panel  17 , corresponding processings, numerals and characters are input into the ATM  11 . 
     An authenticating unit  18  is incorporated in the front of the enclosure  12  at a position adjacent to the touch screen panel  17 . The authenticating unit  18  is utilized for personal authentication of a user of the ATM  11 . The authenticating unit  18  includes an image capturing apparatus. The image capturing apparatus will be described later. The image capturing apparatus is designed to capture the image of the veins of the user&#39;s palm. Biometric authentication software, incorporated in the ATM  11 , is executed for personal authentication. The biometric authentication software is stored in a storage apparatus, for example. In the biometric authentication software, the data of the captured image of the veins is compared with the data of the pre-registered image of the veins so as to detect similarity and difference in characteristics between these two images. 
       FIG. 2  schematically illustrates an image capturing apparatus  21  incorporated in the authenticating unit  18 . The image capturing apparatus  21  includes a box-shaped casing  22 . A first substrate  32  for a camera board is incorporated in the casing  22 . Referring also to  FIG. 3 , an image sensor  24  is mounted on the first substrate  23 . The image sensor  24  is a CMOS (complementary metal-oxide semiconductor) image sensor, for example. The image sensor  24  is designed to detect an image based on the amount of light received at each pixel. A polarizing optical element  25  is placed on the image sensor  24 . The polarizing optical element  25  is designed to convert light led to the image sensor  24  into a light beam having linear polarization. The polarizing optical element  25  will be described later in detail. 
     An optical unit  26  is placed on the image sensor  24  on the surface of the first substrate  23 . A lens optical system such as a collective lens is incorporated in the optical unit  26 . The optical unit  26  is opposed to an opening  27  formed in the top plate of the casing  22 . A visible light cut filter  28  is fitted in the opening  27 . The visible light cut filter  28  serves to prevent visible light or spectrum from entering the casing  22  through the opening  27  toward the optical unit  26 . A stepped cylindrical hood  29  is attached to the optical unit  26 , for example. The hood  29  serves to prevent unintended light from entering the optical unit  26  from the outside of a predetermined range. 
     Light-emitting elements  31  are mounted on the surface of the first substrate  23  at the periphery of the optical unit  26 . The light-emitting elements  31  output near-infrared light toward the opening  27 . Diffusers  32  and polarizing optical elements  33  are placed on the surface of the first substrate  23 . The polarizing optical elements  33  are designed to convert the near-infrared light output from the light-emitting elements  31  into a light beam having linear polarization. A cylindrical light guiding body  34  is placed on the polarizing optical elements  33 , for example. The cylindrical light guiding body  34  serves to lead the near-infrared light output from the light-emitting elements  31  to the outer space through the opening  27 . In this manner, the near-infrared light is radiated to a predetermined image capturing area A in the outer space at a uniform intensity through the opening  27 . Each of the polarizing optical elements  33  has the structure identical to the structure of the aforementioned polarizing element  25 . 
     A second substrate  35  for a controller circuit board is enclosed in the casing  22  at a position behind the first substrate  23 . The second substrate  35  is electrically connected to the first substrate  23  through a first connector  36 . A second connector  37  is mounted on the second substrate  35  for connection to external devices. The second substrate  35  is electrically connected to a motherboard, not shown, incorporated in the ATM  11  through the second connector  37 , for example. A cable  38  may be coupled to the second connector  37  on the second substrate  35  for connection to the motherboard, for example. The operation of the image capturing apparatus  21  can thus be controlled. Simultaneously, data specifying the image of veins, captured by the image capturing apparatus  21 , can be output to the motherboard. 
     Now, assume that personal authentication is executed in the authenticating unit  18  of the ATM  11 . The user&#39;s palm is set above the opening  27 . The light-emitting elements  31  output near-infrared light. The near-infrared light is radiated to the palm from the opening  27  through the light guiding body  34 . As conventionally known, near-infrared light is absorbed into hemoglobin in red blood cells flowing in veins. A distribution of intensity is thus generated in the near-infrared light reflected from the palm. The reflected near-infrared light is led into the image sensor  24  through the optical unit  26 . The image sensor  24  outputs image data of the veins to the motherboard. The captured image data of the veins is compared with the pre-registered image data. Personal authentication is in this manner executed. 
       FIG. 4  schematically illustrates the polarizing optical element  25 ,  33  according to an embodiment of the present invention. The polarizing optical element  25 ,  33  includes a substrate  41  in the shape of a flat rectangular parallelepiped, for example. The substrate  41  is a glass substrate having optical permeability. Strips  42  of resin film are arranged in parallel with one another on the surface of the substrate  41 . The individual strip  42  of resin film is formed in the shape of a bar having the rectangular cross-section set perpendicular to the longitudinal axis of the bar, for example. The bar is received on the surface of the substrate  41  at one of the parallel surfaces extending in parallel with the longitudinal axis. Light passes through the strips  42  of resin film. The refractive index of the strips  42  of resin film is set equal to that of the substrate  41 . The strips  42  of resin film may be made of a light curable resin, for example. Here, the light curable resin is an ultraviolet curable resin such as “PAK-01®” produced by Toyo Gosei Co., Ltd., for example. 
     Strips  43  of optically impermeable film are formed on the surface of the substrate  41  at positions between the adjacent ones of the strips  42  of resin film. The strips  42  of resin film and the strips  43  of optically impermeable film are alternately arranged on the surface of the substrate  41 . The individual strip  43  of optically impermeable film is formed in the shape of a rectangular bar in the same manner as the strip  42  of resin film, for example. Light cannot pass through the strips  43  of optically impermeable film. The strips  43  of optically impermeable film are made of a metal material such as aluminum, for example. Alternatively, the strips  43  of optically impermeable film may be made of one of metal materials such as tungsten, copper, gold, silver, nickel, titanium and chromium. The polarizing optical element  25 ,  33  allows the near-infrared light to pass through the strips  42  of resin film while the near-infrared light is absorbed in the strips  43  of optically impermeable film. The near-infrared light is thus converted into a light beam having linear polarization through the polarizing optical elements  25 ,  33 . 
     Each of the polarizing optical elements  25 ,  33  has the rectangular outline along the periphery of the substrate  41 . The outline has the dimension (long side×short side) 7 [mm]×5 [mm] or 10 [mm]×6 [mm], for example. A width W 1  of the individual strip  42  of resin film, defined along the long side of the substrate  41 , is set at 80 nm approximately, for example. Likewise, a width W 2  of the individual strip  43  of optically impermeable film, defined along the long side of the substrate  41 , is set at 60 nm approximately, for example. The thicknesses of the strips  42 ,  43  of resin film  42  and optically impermeable film, measured in the vertical direction perpendicular to the surface of the substrate  41 , are set at 150 nm approximately, for example. 
     Next, description will be made on a method of making the polarizing optical elements  25 ,  33 . As shown in  FIG. 5 , a substrate  51  of a flat rectangular parallelepiped is prepared, for example. The dimension of the substrate  51  is sufficiently large so that two or more substrates  41  are cut out of the substrate  51 , for example. The substrate  51  is made of glass. A light curable resin is applied to the front surface of the substrate  51 . A reactive or curable resin thin film  52  is in this manner formed on the front surface of the substrate  51 , as shown in  FIG. 6 . The light curable resin is the aforementioned ultraviolet curable resin such as “PAK-01®”. The thickness of the reactive resin thin film  52  is set at 150 nm approximately, for example. 
     As shown in  FIG. 7 , a stamper  53  is prepared. The stamper  53  includes a main body  54  of a flat rectangular parallelepiped, for example. The lower surface of the main body  54  is a flat surface. A transfer pattern, namely parallel bars  55 , is formed integral with the lower surface of the main body  54 . The individual parallel bar  55  has the rectangular cross-section set perpendicular to the longitudinal axis of the bar. The bar is received on the main body  54  at one of the parallel surfaces extending in parallel with the longitudinal axis. Grooves  56  are defined between the respective adjacent ones of the parallel bars  55 . The exposed or top surfaces of the parallel bars  55 , extending in parallel with the flat lower surface of the main body  54 , are defined within a plane. The outline of the parallel bar  55  corresponds to that of the strip  43  of optically impermeable film. The outline of the groove  56  corresponds to that of the strip  42  of resin film. The stamper  53  may be an electroformed stamper made of a metal material, for example. 
     As shown in  FIG. 8 , the stamper  53  is urged against the front surface of the substrate  51 . So-called nanoimprint is executed. The top surfaces of the parallel bars  55  are brought in close contact with the front surface of the substrate  51  after having laid on the surface of the reactive resin thin film  52 . The reactive resin thin film  52  is forced to run into the grooves  56  of the stamper  53 . The strips  42  of resin film, made of a reactive resin, are in this manner formed between the adjacent ones of the parallel bars  55 . Ultraviolet rays are then radiated to the substrate  51  from the backside of the substrate  51 , for example. The ultraviolet rays serve to cure the strips  42  of resin film between the adjacent ones of the parallel bars  55 . The stamper  53  is then removed from the substrate  51 . The strips  42  of resin film are in this manner formed on the front surface of the substrate  51 , as shown in  FIG. 9 . 
     Aluminum is sputtered onto the front surface of the substrate  51 , as shown in  FIG. 10 . An optically impermeable film  57  is thus formed on the front surface of the substrate  51 . The optically impermeable film  57  covers over the strips  42  of resin film. Spaced between the adjacent ones of the strips  42  of resin film are filled with a part of the optically impermeable film  57 . Polishing process is then applied to the optically impermeable film  57  along a plane parallel to the front surface of the substrate  51  from the upper or exposed widest surface thereof. The polishing process may be chemical-mechanical polishing (CMP), for example. The strips  42  of resin film and the strips  43  of optically impermeable film, which are alternately arranged, are thus exposed along the aforementioned plane, as shown in  FIG. 4 . Subsequently, the polarizing optical elements  25 ,  33  may be cut out. 
     In the polarizing optical elements  25 ,  33 , the strips  42  of resin film and the strips  43  of optically impermeable film are alternately arranged on the surface of the substrate  41 . The strips  42  of resin film are formed on the surface of the substrate  41  based on nanoimprint. The thickness of the strips  42  of resin film can be adjusted in a facilitated manner. In addition, sputtering is employed to form the strips  43  of optically impermeable film between the adjacent ones of the strips  42  of resin film, for example. The polarizing optical elements  25 ,  33  can be produced without dry etching. The production process of the polarizing optical elements  25 ,  33  can be simplified. The production cost of the polarizing optical elements  25 ,  33  can be reduced. 
     A laser beam such as an electron beam (EB), a focused ion beam (FIB), or the like, may be radiated to the reactive resin thin film  52 , in place of employment of the stamper  53 , for forming the strips  42  of resin film. The reactive resin thin film  52  is exposed to the laser beam within a restricted area. The reactive resin thin film  52  is thus cured or hardened based on the exposure. The reactive curable resin thin film  52  is uncured over the unexposed area around the exposed restricted area. The uncured portion of the reactive resin thin film  52  is removed. The strips  42  of resin film are in this manner formed out of the reactive resin thin film  52 . The stamper  53  may be made of a material having optical permeability. Ultraviolet rays may be radiated to the substrate  51  behind the stamper  53 . 
     In the polarizing optical elements  25 ,  33 , the strips  42  of resin film may be made of a reactive resin such as thermosetting resin in place of the aforementioned light curable resin. Here, the thermosetting resin may be a resin preferably utilized for an insulating interlayer in a printed circuit board or the like. Such a resin includes polymethylmethacrylate (PMMA) and “HSG-255®” produced by Hitachi Chemical Company, Ltd., for example. The strips  42  made of the thermosetting resin have optical permeability in the same manner as described above. Likewise, the refractive index of the strips  42  made of the thermosetting resin is set equal to that of the substrate  41 . 
     Thermosetting resin in liquid state is applied to the front surface of the substrate  51  for the production of the polarizing optical elements  25 ,  33 . The reactive resin thin film  52  is in this manner formed on the front surface of the substrate  51 . The stamper  53  is then urged against the front surface of the substrate  51  in the same manner as described above. Since the reactive resin thin film  52  is made of thermosetting resin, the thermosetting resin is cured or hardened between the adjacent ones of the parallel bars  55  in response to application of heat to the reactive resin thin film  52 . A so-called hot embossing is executed. Subsequently, the aforementioned process may be executed. 
     The turn of the embodiments isn&#39;t a showing the superiority and inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.