Abstract:
An optical waveguide  30  having a bending groove  34  parallel to two long sides of a rectangular shape thereof. The optical waveguide  30  is bent along the bending groove  34  so as to come into close contact with a frame of an optical touch panel. This makes it possible to attach the optical waveguide  30  to the frame without misalignment during assembly. Therefore, the optical waveguide  30  can emit light beams in a direction perpendicular to one side of a rectangular display screen opposed to one long side of the rectangular shape thereof. Further, the width of the frame of the optical touch panel  30  can be made smaller than that of the optical waveguide  30.  This makes it possible to achieve reduction in the width of the frame of the optical touch panel.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an optical waveguide and an optical touch panel using the same. 
         [0003]    2. Description of the Related Art 
         [0004]    An optical touch panel using optical waveguides each having a plurality of cores and a cladding surrounding the cores has been conventionally known (for example, U.S. Pat. No. 5,914,709). Such an optical touch panel determines the coordinates of position of a finger or a pen blocking a grid of light beams (infrared light beams), which is formed over a display screen with the use of optical waveguides, by detecting the intensity of light beams blocked by the finger or pen. Further, an optical touch panel using optical waveguides is thin and highly sensitive, and is therefore expected to have great potential. 
         [0005]    However, an optical touch panel using conventional optical waveguides has drawbacks in that it is difficult to perform the positioning of the optical waveguides and that it is also difficult to reduce the width of a frame thereof because the optical waveguides are arranged around a display screen. 
         [0006]      FIG. 1  shows plan and sectional views of a main part of an optical touch panel  10  using conventional optical waveguides  13 . In the optical touch panel  10  using the conventional optical waveguides  13 , the optical waveguides  13  are provided on a frame  12  surrounding a display screen  11 . 
         [0007]    The two long sides of the rectangular flat plate-shaped optical waveguide  13  have to be parallel to the corresponding long side of the frame  12 . However, actually, it is difficult to attach the optical waveguide  13  to the frame  12  so that the two long sides of the rectangular flat plate-shaped optical waveguide  13  becomes parallel to the corresponding long side of the frame  12  during assembly. Therefore, as shown in  FIG. 1 , misalignment (nonparallel) of the optical waveguide  13  is likely to occur. If such misalignment of the optical waveguide  13  occurs, as shown in  FIG. 1 , light beams  14  deviate from their normal emission direction, and are therefore not emitted in a direction perpendicular to one side of the rectangular display screen  11  opposed to one long side of the rectangular flat plate-shaped optical waveguide  13 , thereby lowering optical transmission efficiency. 
         [0008]    Further, in the optical touch panel  10  using the conventional optical waveguides  13 , the width of the frame  12  represented by W 1  needs to be equal to or larger than that of the optical waveguide  13  represented by W 3 . This makes it difficult to reduce the width “W 1 ” of the frame  12 . 
       SUMMARY OF THE INVENTION 
       [0009]    It is therefore an object of the present invention to provide an optical waveguide capable of accurately and easily performing the positioning thereof during assembly and reducing the width of a frame of an optical touch panel. 
         [0010]      FIG. 2  shows plan and sectional views of a main part of an optical touch panel  20  using an optical waveguide  23  of the present invention. In the optical touch panel  20  using the optical waveguide  23  of the present invention, the optical waveguide  23  is provided closely attaching to a frame  22  surrounding a display screen  21 . 
         [0011]    The optical waveguide  23  according to the present invention is a rectangular flat plate-shaped member, and has a bending groove  23   a  parallel to the two long sides of the rectangular shape thereof. The optical waveguide  23  is bent along the bending groove  23   a  so as to come into close contact with the frame  22 . This makes it possible to easily attach the optical waveguide  23  to the frame  22  without misalignment during assembly. The prevention of the occurrence of misalignment makes it possible to emit light beams  24  from the optical waveguide  23  in a direction perpendicular to one side of the rectangular display screen  21  opposed to one long side of the rectangular flat plate-shaped optical waveguide  23 . 
         [0012]    Further, the width of the frame  22  represented by W 2  can be made smaller than that of the optical waveguide  23 . This makes it easy to reduce the width of the frame  22  of the optical touch panel  20 . 
       SUMMARY OF THE PRESENT INVENTION IS AS FOLLOWS: 
       [0013]    In a first preferred embodiment, an optical waveguide of the present invention is a rectangular flat plate-shaped optical waveguide having a side surface corresponding to one long side of a rectangular shape thereof and a main surface, which comprises: a plurality of cores each having an end; a cladding surrounding the cores; and a bending groove, wherein the ends of the cores are arranged in parallel in the side surface, and the bending groove is provided in the main surface so as to be parallel to two long sides of the rectangular shape thereof. 
         [0014]    In a second preferred embodiment, the optical waveguide of the present invention is characterized by being bent along the bending groove so that a bent inside surface thereof comes into close contact with a peripheral portion of a display screen of an optical touch panel. 
         [0015]    In a third preferred embodiment, the optical touch panel of the present invention is characterized by comprising the above-described optical waveguide. 
       Advantages of the Invention 
       [0016]    When an optical touch panel is produced using the optical waveguides of the present invention, the positioning of the optical waveguides can be easily and accurately performed. For example, in the case of a 4.2-inch optical touch panel having four optical waveguides, it takes about 30 minutes to complete the positioning of optical waveguides when using conventional ones. However, the time required to complete the positioning of optical waveguides can be reduced to about 5 minutes by using the optical waveguides of the present invention. 
         [0017]    Further, when an optical touch panel is produced using the optical waveguides of the present invention, the width of a frame portion of the optical touch panel can be reduced to, for example, about ½ of that of an optical touch panel using conventional optical waveguides. 
         [0018]    For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  shows plan and sectional views of an optical touch panel using conventional optical waveguides; 
           [0020]      FIG. 2  shows plan and sectional views of an optical touch panel using optical waveguides of the present invention; 
           [0021]      FIG. 3  shows the three surfaces of the optical waveguide of the present invention; 
           [0022]      FIG. 4  is a perspective view of the optical waveguide of the present invention; and 
           [0023]      FIG. 5  shows plan and sectional views of an optical touch panel of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    The preferred embodiments of the present invention will now be described with reference to  FIGS. 1-5  of the drawings. Identical elements in the various figures are designated with the same reference numerals. 
       &lt;Optical Waveguide&gt; 
       [0025]    As shown in  FIG. 3 , an optical waveguide  30  of the present invention is a rectangular flat plate-shaped member, and has a plurality of cores  31  and a cladding  32  surrounding the cores  31 . The optical waveguide  30  of the present invention has a side surface  33  corresponding to one long side of the rectangular shape thereof (hereinafter, simply referred to as a “long side surface  33 ”) and a main surface  35 . In the long side surface  33 , ends  31   a  of the cores  31  are arranged in parallel. The main surface  35  has a bending groove  34  parallel to the two long sides of the rectangular shape of the optical waveguide  30 . 
         [0026]    The optical waveguide  30  of the present invention is suitable for use in an optical touch panel that determines the coordinates of a finger or a pen blocking a grid of light beams (infrared light beams) generally intersecting at right angles, which is formed over a display screen, by detecting the intensity of light beams blocked by the finger or pen. 
         [0027]    In such an optical touch panel, the optical waveguide  30  of the present invention emits or receives light beams through the ends  31   a  of the cores  31  arranged in parallel in the long side surface  33 . 
         [0028]    The bending groove  34  provided in the main surface  35  of the optical waveguide  30  of the present invention so as to be parallel to the two long sides of the rectangular shape of the optical waveguide  30  is used in the following manner. As shown in  FIG. 2 , an optical waveguide  23  of the present invention is bent along a bending groove  23   a  so as to come into close contact with a peripheral portion of a display screen  21  (typically, a frame  22 ) of an optical touch panel  20 . This makes it possible to accurately and easily perform the positioning of the optical waveguides  23  of the present invention when the optical waveguides  23  are mounted on the optical touch panel  20 . 
         [0029]    Each of the cores  31  of the optical waveguide  30  of the present invention has the other end  31   b.  The ends  31   b  of the cores  31  are preferably arranged in parallel in a side surface  36  of the optical waveguide  30  corresponding to one short side of the rectangular shape of the optical waveguide  30  (hereinafter, simply referred to as a “short side surface  36 ”). In a case where the optical waveguide  30  of the present invention emits light beams through the ends  31   a  of the cores  31  arranged in parallel in the long side surface  33 , the ends  31   b  of the cores  31  arranged in the short side surface  36  are optically connected to a light emitting element. On the other hand, in a case where the optical waveguide  30  of the present invention receives light beams through the ends  31   a  of the cores  31  arranged in the long side surface  33 , the ends  31   b  of the cores  31  arranged in the short side surface  36  are optically connected to a light receiving element. 
         [0030]    The thickness D of the optical waveguide  30  of the present invention is not particularly limited, but is usually in the range of 50 μm to 2 mm. 
         [0031]    The length L 1  of the long side of the rectangular shape of the optical waveguide  30  of the present invention is appropriately set depending on the size of a display screen of an optical touch panel to be produced. The length L 2  of the short side of the rectangular shape of the optical waveguide  30  (i.e., the width of the optical waveguide  30 ) of the present invention is preferably in the range of 1 to 15 mm. 
       &lt;Cores&gt; 
       [0032]    The cores  31  of the optical waveguide  30  of the present invention are formed from any material having a higher refractive index than the cladding  32  and high transparency at the wavelength of light traveling through the cores  31 . A material forming the cores  31  is preferably a UV curable resin having excellent patterning properties. Preferred examples of such a UV curable resin include UV curable acrylic resins, UV curable epoxy resins, UV curable siloxane resins, UV curable norbornene resins, and UV curable polyimide resins. 
         [0033]    The cross-sectional shape of each of the cores  31  is not particularly limited, but is preferably trapezoidal or rectangular from the viewpoint of patterning properties. The width of the cross section of each of the cores  31  is preferably in the range of 10 to 500 μm. The height of the cross section of each of the cores  31  is preferably in the range of 10 to 100 μm. 
       &lt;Cladding&gt; 
       [0034]    The cladding  32  of the optical waveguide  30  of the present invention is formed from any material having a lower refractive index than that of the core  31 . A material forming the cladding  32  is not particularly limited but is preferably a UV curable resin having excellent moldability. Preferred examples of such a UV curable resin include UV curable acrylic resins, UV curable epoxy resins, UV curable siloxane resins, UV curable norbornene resins, and UV curable polyimide resins. 
         [0035]    The maximum difference in refractive index between the core  31  and the cladding  32  is preferably 0.01 or more, more preferably 0.02 to 0.2. It is to be noted that the refractive index of a polymer resin for forming the cores  31  and the cladding  32  can be increased or decreased by introducing an organic group appropriately selected into the polymer resin or changing the organic group content of the polymer resin. The refractive index of the polymer resin can be increased by, for example, introducing a cyclic aromatic group (e.g., a phenyl group) into a resin molecule or increasing a cyclic aromatic group content per resin molecule. On the other hand, the refractive index of the polymer resin can be decreased by, for example, introducing a linear or aliphatic group (e.g., a methyl group or a norbornene group) into a resin molecule or increasing a linear or aliphatic group content per resin molecule. 
         [0036]      FIG. 4  shows an optical waveguide  40  of the present invention by way of example. The optical waveguide  40  has a cladding  41 , and the cladding  41  has a side surface  42  corresponding to one long side of the rectangular shape of the optical waveguide  40  (hereinafter, simply referred to as a “long side surface  42 ”), in which the ends of a plurality of cores are arranged in parallel. The long side surface  42  preferably has a long lens shape. The optical waveguide  40  having the cladding  41  whose long side surface  42  has a long lens shape can convert outgoing light, which usually tends to diffuse, into parallel light beams or can concentrate incident light, which usually tends to diffuse, to receive concentrated light. Therefore, when the optical waveguide  40  of the present invention is used for an optical touch panel, which will be described later, a wider tolerance for the positioning of the long side surface  42  of the cladding  41  in a height direction is achieved. The optical waveguide  40  of the present invention has a bending groove  43  parallel to the two long sides of the rectangular shape thereof. 
         [0037]    The long lens-shaped portion described above has preferably the shape of a convex lens, more preferably the shape of a convex lens having a cross-sectional shape of substantially a quarter of a circle, that is, the shape of a so-called half lenticular lens. In a case where the long lens-shaped portion has the shape of a convex lens, the curvature radius thereof is preferably in the range of 300 μm to 5 mm, more preferably in the range of 500 μm to 3 mm. 
       &lt;Bending Groove&gt; 
       [0038]    As shown in  FIG. 2 , the optical waveguide  23  of the present invention is bent along the bending groove  23   a  formed in the main surface thereof to bring the inside surface thereof into close contact with a peripheral portion of the display screen  21  (typically, the frame  22 ). This makes it easy to make a side surface  25  corresponding to one long side of the rectangular shape of the optical waveguide  23  parallel to one side of the rectangular display screen  21 . 
         [0039]    The bending groove  34  of the optical waveguide  30  of the present invention (see  FIG. 3 ) is formed in part of the cladding  32  not containing the cores  31  by pressing the edge of a knife against the cladding  32  so that the knife edge becomes parallel to the two long sides of the rectangular flat plate-shaped optical waveguide  30 . The bending groove  34  may be formed in only one of the two main surfaces of the optical waveguide  30 , that is, the main surface  35  or may be formed in both the two main surfaces. 
         [0040]    The cross-sectional shape of the bending groove  34  is not particularly limited. For example, the bending groove  34  may have a V-shaped cross section, a trapezoidal cross section, or a U-shaped cross section. 
         [0041]    The thickness of the optical waveguide  30  remaining under the bending groove  34  (i.e., the minimum thickness of the optical waveguide  30 ) is preferably in the range of 50 to 200 μm. This makes it possible to achieve both high optical transmission efficiency and bendability of the optical waveguide  30 . 
         [0042]    If the thickness of the optical waveguide  30  remaining under the bending groove  34  is less than 50 μm, it is too small to form the cores  31  or, even when the cores  31  can be formed, there is a fear that optical transmission efficiency may be lowered due to insufficient thickness of the cladding  32 . On the other hand, if the thickness of the optical waveguide  30  remaining under the bending groove  34  exceeds 200 μm, there is a fear that the bendability of the optical waveguide  30  may be deteriorated. 
       &lt;Touch Panel&gt; 
       [0043]    The optical waveguide of the present invention can be used in an optical touch panel suitable for use in, for example, display monitors for personal computers, ATMs, ticket vending machines, game machines, and tablet PCs. 
         [0044]      FIG. 5  shows plan and sectional views of one embodiment of an optical touch panel  50  using the optical waveguides of the present invention. The optical touch panel  50  includes two light emitting elements  51 , a coordinate input region  52 , two light emitting-side optical waveguides  53 , two light receiving-side optical waveguides  54 , and two light receiving elements  55 . The light emitting-side optical waveguide  53  transmits light emitted from the light emitting element  51  to generate light beams  56  crossing the coordinate input region  52 . The light receiving-side optical waveguide  54  receives the light beams  56  which have crossed the coordinate input region  52 . The light receiving element  55  detects the intensity of light received by the light receiving-side optical waveguide  54 . 
         [0045]    The light emitting element  51  is not particularly limited as long as it can generate light beams  56  that pass through the light emitting-side optical waveguide  53  and then cross the coordinate input region  52 . The light emitting element  51  preferably emits light having a wavelength in the near-infrared range (700 nm to 2500 nm). Examples of a light emitting element suitable as the light emitting element  51  include light emitting diodes and semiconductor lasers. 
         [0046]    The light receiving element  55  converts optical signals into electrical signals and detects the intensity of light received by the light receiving-side optical waveguide  54 . The light receiving element  55  preferably detects light having a wavelength in the near-infrared range (700 nm to 2500 nm). Examples of a light receiving element suitable as the light receiving element  55  include CMOS image sensors and CCD image sensors. 
         [0047]    The coordinate input region  52  refers to a region where the light beams  56  emitted from the light emitting-side optical waveguide  53  cross. The coordinate input region  52  is typified by, for example, a display screen such as a liquid crystal display panel or a plasma display panel. The coordinate input region  52  is preferably rectangular because it is easy to accurately adjust the position of the cores. An open space may be provided in front of the coordinate input region  52 . Alternatively, a glass panel or an acrylic panel may be provided on the surface of the coordinate input region  52  to improve scratching resistance. 
       EXAMPLES 
     &lt;Preparation of Varnish for Forming Cladding&gt; 
       [0048]    A varnish for forming cladding was prepared by mixing the following components: 
         [0049]    Component A: UV-curable epoxy-based resin having an alicyclic skeleton (EP 4080E manufactured by ADEKA CORPORATION) 100 parts by weight 
         [0050]    Component B: photo-acid-generation agent (CPI-200K manufactured by SAN-APRO Ltd.) 2 parts by weight 
       &lt;Preparation of Varnish for Forming Cores&gt; 
       [0051]    A varnish for forming cores was prepared by mixing the following components: 
         [0052]    Component C: UV-curable epoxy-based resin having a fluorene skeleton (OGSOL EG manufactured by Osaka Gas Chemicals Co., Ltd.) 40 parts by weight 
         [0053]    Component D: UV-curable epoxy-based resin having a fluorene skeleton (EX-1040 manufactured by Nagase ChemteX Corporation) 30 parts by weight 
         [0054]    Component E: 1,3,3-tris(4-(2-(3-oxetanyl))butoxyphenyl) butane 30 parts by weight (which was synthesized by the method described in Example 2 of Japanese Unexamined Patent Publication No. 2007-070320) 
         [0055]    Component B 1 part by weight 
         [0056]    Ethyl lactate 41 parts by weight 
       &lt;Formation of Optical Waveguide&gt; 
       [0057]    The varnish for forming cladding layer was applied onto the surface of a polyethylene naphthalate film having a thickness of 188 μm, irradiated with UV light at 1000 mJ/cm 2 , and thermally-treated at 80° C. for 5 minutes to form an under-cladding layer having a thickness of 20  82  m. The refractive index of the under-cladding layer as measured at a wavelength of 830 nm was 1.510. 
         [0058]    Then, the varnish for forming cores was applied onto the surface of the above described under-cladding layer and thermally-treated at 100° C. for 5 minutes to form a core layer. The core layer was then covered with a photo mask (gap: 100 μm), irradiated with UV light at 2500 mJ/cm 2 , and thermally-treated at 100° C. for 10 minutes. Then, a plurality of cores each having a width of 20 μm and a height of 50 μm were formed by dissolving away an unexposed portion of the core layer using an aqueous γ-butyrolactone solution and thermally treating the core layer at 120° C. for 5 minutes. The refractive index of each of the cores as measured at a wavelength of 830 nm was 1.592. 
         [0059]    Then, the entire cores were covered with the varnish for forming cladding to form a resin layer having a wet thickness of 60 μm. Then, the resin layer was heated at 80° C. for 5 minutes to remove air bubbles present around the cores. Then, a quartz concave-shaped mold was pressed against the resin layer, and the varnish for forming cladding was injected into the recess of the concave-shaped mold. Then, the varnish for forming cladding was irradiated with UV light at 2000 mJ/cm 2  through the concave-shaped mold and thermally treated at 80° C. for 5 minutes to form an over-cladding layer. Then, the concave-shaped mold was removed from the over-cladding layer. The thus obtained over-cladding layer had a thickness of 1 mm and was equipped with a convex lens having a cross-sectional shape of substantially a quarter of a circle (i.e., a half renticular lens having a radius of curvature of 1.5 mm) at its distal end. The refractive index of the over-cladding layer as measured at a wavelength of 830 nm was 1.510. 
         [0060]    The edge of a knife was pressed against the rectangular flat plate-shaped optical waveguide (length: 76 mm, width: 12 mm, thickness 1.02 mm) so as to be parallel to the two long sides of the rectangular flat plate-shaped optical waveguide to form a bending groove having a maximum depth of 900 μm. In this way, an optical waveguide having a bending groove was produced. 
       &lt;Production of Touch Panel&gt; 
       [0061]    The thus produced four optical waveguides were prepared and placed along the four sides of a rectangular glass plate (length: 88 mm, width: 88 mm) as a replacement for a display screen. Each of the optical waveguides was abutted against each side of the rectangular glass plate and bent along its bending groove so that the inside surface of the optical waveguide came into close contact with the glass plate. Then, the positioning of the optical waveguides was performed. 
         [0062]    The ends of cores of each of the two light emitting-side optical waveguides were optically connected via a UV curable adhesive to a light emitting element emitting light having a wavelength of 850 nm (VCSEL manufactured by OPTOWELL CO., Ltd.). The ends of cores of each of the other two light receiving-side optical waveguides were optically connected via a UV curable adhesive to a light receiving element (CMOS linear sensor array manufactured by TAOS Inc.). In this way, an optical touch panel was produced. When the intensity of light emitted from the light emitting element was defined as 100%, the optical touch panel was designed to allow the light receiving element to detect light having an intensity of 10% of that of light emitted from the light emitting element. The optical touch panel could accurately determine the coordinates of position of a finger blocking light beams crossing a coordinate input region thereof. 
         [0063]    Table 1 shows the frame width of the optical touch panel of the Example and the time required to complete the positioning of cores. The frame width refers to the width of an area covered with the optical waveguide placed on the surface of the glass plate along one side of the rectangular glass plate. The time required to complete the positioning of cores refers to the time required to complete the positioning of the optical waveguides to allow the light receiving element to detect light having an intensity of 10% of that of light emitted from the light emitting element. It is to be noted that in this example, the glass plate was used as a replacement for a display screen, but a highly-functional optical touch panel can be obtained by changing the glass plate to a display screen such as a liquid crystal display panel. 
       &lt;Comparative Example&gt; 
       [0064]    An optical touch panel using the optical waveguides obtained in the Example was produced in the same manner as in the Example except that the formation of a bending groove was omitted. Table 1 shows the frame width of the optical touch panel of the Comparative Example and the time required to complete the positioning of cores. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Time Required 
               
               
                   
                 Bending 
                 Frame Width 
                 for Positioning 
               
               
                   
                 Groove 
                 (mm) 
                 (min) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Example 
                 present 
                 6 
                 5 
               
               
                   
                 Comparative 
                 absent 
                 12 
                 30 
               
               
                   
                 Example 
               
               
                   
                   
               
             
          
         
       
     
       &lt;Method for Measuring Refractive Index&gt; 
       [0065]    The varnish for forming cladding layer was applied onto a silicon wafer by spin coating to form a film of the varnish, and the film of the varnish was used as a sample for measuring the refractive index of a cladding layer. The varnish for forming cores was applied onto another silicon wafer by spin coating to form a film of the varnish, and the film of the varnish was used as a sample for measuring the refractive index of a core. Measurement of refractive index was performed using a prism coupler (SPA-400 manufactured by Sairon Technology, Inc.). 
         [0066]    This application claims priority from Japanese Patent Application No. 2008-301135, which is incorporated herein by reference. 
         [0067]    There have thus been shown and described a novel optical waveguide and a novel optical touch panel which fulfill all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.