Abstract:
There is a need for providing a finger vein image inputting device that can miniaturize and thin a finger vein authentication apparatus and provide high authentication accuracy. The finger vein image inputting device according to the present invention includes a body, a band pass filter for transmitting only light of a specific wavelength, a light source for applying light to a finger placed over the band pass filter, and an imaging means for imaging transmitted light from the finger. A gradient index lens is provided between the band pass filter and the imaging means and causes refractive-index distribution around an optical axis. A polarizing filter is provided at least one of between the light source and the finger and between the finger and an imaging device.

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese Patent Application No. 2007-260119 filed on Oct. 3, 2007, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a biometrics authentication technique and more particularly to a finger vein image inputting device used for a finger vein authentication apparatus. 
     (2) Description of the Related Art 
     Conventionally, passwords, keys, and seals have been used for personal identification. There is an increasing demand for improving a technique of personal identification as advancement of information society. Attention is focused on the biometrics using bodily characteristics specific to individuals. The biometrics has advantages of excellent convenience and improved security against theft, loss, invalid transfer, or oblivion for the secret data such as credit cards, etc. 
     The biometrics uses bodily characteristics such as fingerprint, palm, face, iris, voice pattern, and vein for personal authentication. Using finger veins, the finger vein authentication particularly causes less psychological resistance than fingerprints and is hardly falsified. 
     The finger vein authentication uses the fact that a hemoglobin in blood absorbs near infrared ray having a wavelength range of 700 to 1200 nm. The finger vein authentication applies the near infrared ray to a finger, images a vein pattern inside the finger, and collates the pattern with registered information for personal authentication. 
     The finger vein authentication provides a higher authentication accuracy than the finger print authentication and is used for cash dispenser or other products that require a high level of security. 
     Recently, mobile telephones equipped with an electronic money function are widely used. As a countermeasure against loss or theft of the mobile telephones, there is a demand for providing these mobile telephones with a function of authenticating an owner. Actually, some mobile telephones are equipped with finger print authentication devices. For an increased level of security, there is a demand for providing a mobile telephone with a finger vein authentication apparatus. However, the finger vein authentication apparatus needs to be miniaturized so as to be mounted on the mobile telephone. 
     JP-A No. 28872/2006 discloses an embodiment of using the gradient index lens array and the linear solid-state image sensor for miniaturizing the finger vein authentication apparatus. 
     The technique in JP-A No. 28872/2006 miniaturizes the finger vein authentication apparatus by using an optical system that applies light to the pad and the side of a finger. The light diffuses in the finger and is transmitted through the finger. The light is imaged under the finger pad to generate a vein image. Since the optical system makes a light source to be close to the finger surface, the light easily reflects on the finger surface, causing an unclear finger vein image due to the reflected light. When a mobile telephone is equipped with the optical system, it is necessary to consider the influence of outside light such as the sunlight because the mobile telephone may be used outdoors or in a bright room. 
     According to JP-A No. 28872/2006, the light is applied to the finger pad from a light emitting diode (LED) as a light source. JP-A No. 28872/2006 describes no means for decreasing the reflected light on the finger surface. In addition, JP-A No. 28872/2006 describes no means for decreasing the influence of outside light such as the sunlight. 
     It is therefore an object of the present invention to miniaturize and thin a finger vein authentication apparatus. It is another object of the present invention to provide a finger vein image inputting device capable of high authentication accuracy. 
     SUMMARY OF THE INVENTION 
     The finger vein image inputting device according to the present invention includes a body, a band pass filter for transmitting only light of a specific wavelength, a light source for applying light to a finger placed over the band pass filter, and an imaging means for imaging transmitted light from the finger. A gradient index lens (GRIN lens) is provided between the band pass filter and the imaging means and causes refractive-index distribution around an optical axis. A polarizing filter is provided at least one of between the light source and the finger and between the finger and an imaging device. 
     The invention can provide a finger vein image inputting device that can miniaturize and thin a finger vein authentication apparatus and provide high authentication accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the finger vein image inputting device of the invention according to first to fourth embodiments; 
         FIG. 2  is a sectional view showing the first embodiment of the finger vein image inputting device according to the invention; 
         FIG. 3  is a sectional view showing the second embodiment of the finger vein image inputting device according to the invention; 
         FIG. 4  is a sectional view showing the third embodiment of the finger vein image inputting device according to the invention; 
         FIG. 5  is a sectional view showing the fourth embodiment of the finger vein image inputting device according to the invention; 
         FIG. 6  is a perspective view showing the finger vein image inputting device of the invention according to fifth to eighth embodiments; 
         FIG. 7  is a sectional view showing the fifth embodiment of the finger vein image inputting device according to the invention; 
         FIG. 8  is a sectional view showing the sixth embodiment of the finger vein image inputting device according to the invention; 
         FIG. 9  is a sectional view showing the seventh embodiment of the finger vein image inputting device according to the invention; and 
         FIG. 10  is a sectional view showing the eighth embodiment of the finger vein image inputting device according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a perspective view showing the first to fourth embodiments of the finger vein image inputting device. The embodiments will be described below in detail. 
     With reference to  FIG. 1 , the following describes a construction of the finger vein image inputting device according to the invention. The finger vein image inputting device according to the embodiment includes a body  100 , a finger placing section  101 , a light source  102 , and an imaging section  103 . The finger placing section  101  is a recess formed on the body  100  and is shaped and sized so as to be capable of placing a finger. The light source  102  is provided at the side of an inner wall of the finger placing section  101 . The light source  102  generates near infrared ray having a specific wavelength suitable for imaging in a wavelength range of 700 to 1200 nm. 
     The embodiment in  FIG. 1  uses two light sources on each side, namely four light sources in total. An LED or a laser light source may be used for the light source  102 . The imaging section  103  is provided at the bottom of the finger placing section  101 . The imaging section  103  includes an imaging device (not shown) that images a vein pattern inside a finger  200 . The light from the light source  102  is applied to the finger  200 . The light is diffused in the finger  200 . Transmitted light is generated from the finger  200 . The imaging device captures the transmitted light. 
     According to the embodiment, the light source  102  is provided closely to the finger  200 . The light generated from the light source  102  may reflect on the surface of the finger  200  and the reflected light may enter the imaging device. As a result, a finger vein image may become unclear. Outside light such as the sunlight including the near infrared ray may cause the finger vein image to be unclear. As will be described later, the invention provides a mechanism for preventing the light from being reflected on the surface of the finger  200 , a mechanism for preventing the light reflected on the surface of the finger  200  from reaching the imaging device, and a mechanism for eliminating an effect of the outside light. 
     When the finger vein image inputting device is used for a mobile telephone, the body  100  complies with a body of the mobile telephone. 
     First Embodiment 
     With reference to  FIG. 2 , the following describes the first embodiment of the finger vein image inputting device according to the invention.  FIG. 2  shows a sectional view of the finger vein image inputting device according to the embodiment. 
     In the finger vein image inputting device according to the embodiment, the light source  102  is provided inside the body  100  or is embedded toward the inside from the side of the finger placing section  101 . The light source  102  is provided so that an optical axis thereof tilts with reference to the bottom surface of the finger placing section  101 . Optical axes of the two light sources  102  cross inside the finger  200 . A polarizing filter  121  is provided on the side of the finger placing section  101 . The polarizing filter  121  is provided in front of and closely to the light source  102 . 
     The bottom of the finger placing section  101  is provided with a band pass filter  110 , a polarizing filter  120 , a gradient index lens array  111 , and a solid-state image sensor  112 . These components constitute the imaging section  103  in  FIG. 1 . The band pass filter  110 , the polarizing filter  120 , the gradient index lens array  111 , and the solid-state image sensor  112  are provide for a recess formed in the body  100 . The band pass filter  110  and an upper part of the recess constitute the finger placing section  101 . 
     The band pass filter  110  is provided so as to be in contact with the pad of the finger  200  when the finger  200  is placed on the finger placing section  101 . The polarizing filter  120  is provided under the band pass filter  110  so as to be in contact with the band pass filter  110 . Similarly, the gradient index lens array  111  is arranged under the polarizing filter  120  so as to be in contact with the polarizing filter  120 . The solid-state image sensor  112  is arranged under the gradient index lens array  111  so as to be in contact with the gradient index lens array  111 . 
     The band pass filter  110  transmits the light of a specific wavelength from the light source  102  and does not transmit the other lights. The polarizing filters  120  and  121  transmit only the polarized light, namely the light vibrating in a specific direction (transmission axis). The gradient index lens array  111  includes multiple gradient index lenses (GRIN lenses). The shape of the gradient index lens is cylindrical. The gradient index lens has a refractive-index distribution toward the outside periphery around the optical axis as a normal line on a face including the optical axis. 
     The light from the light source  102  is transmitted through the polarizing filter  121  to become polarized light having an optimal vibration direction (transmission axis). The polarized light is applied to the finger  200 . Applying the polarized light to the finger  200  can reduce the reflection on the surface of the finger  200 . The light entering inside the finger  200  is diffused. The diffused light is partly absorbed and partly enters the band pass filter  110 . 
     The band pass filter  110  transmits only the light of the specific wavelength corresponding to the light source  102 . This makes it possible to prevent a finger vein image from being affected by outside light such as the sunlight entering the band pass filter  110 . When the wave length of light from the light source  102  approximately matches the wavelength of light transmitted through the band pass filter  110 , the recognition accuracy is greatly improved by sufficient light strength. 
     Only the polarized light transmitted through the band pass filter  110  is transmitted through the polarizing filter  120 . The light transmitted through the band pass filter  110  and the polarizing filter  120  is further transmitted through the gradient index lens array  11  and reaches the solid-state image sensor  112 . As mentioned above, a hemoglobin in blood absorbs near infrared ray having a wavelength range of 700 to 1200 nm. Accordingly, the solid-state image sensor  112  can clearly capture a vein silhouette of the finger  200 . The embodiment smoothly collates a vein image with the registered information and improves the recognition accuracy. 
     According to the embodiment, the polarizing filter  121  is provided in front of the light source  102 . The polarizing filter  120  is provided away from the solid-state image sensor  112  so as to be close to a finger. The polarizing filter  121  may not completely prevent the light from reflecting on the surface of the finger  200 . In such case, the polarizing filter  120  prevents the light reflected on the surface of the finger  200  from reaching the solid-state image sensor  112 . 
     The gradient index lens array  111  can generate an image at the same magnification and shorten a distance between a vein inside the finger  200  as an object surface and the solid-state image sensor as an imaging surface. Therefore, the finger vein image inputting device according to the embodiment can be miniaturized and thinned suitable for mounting on a mobile telephone. 
     Second Embodiment 
     With reference to  FIG. 3 , the following describes the second embodiment of the finger vein image inputting device according to the invention.  FIG. 3  shows a sectional view of the finger vein image inputting device according to the embodiment. The finger vein image inputting device according to the embodiment differs from the first embodiment in  FIG. 2  in that the polarizing filter  120  is not provided under the band pass filter  110 . The other parts of the construction may be the same as those of the first embodiment in  FIG. 2 . 
     According to this embodiment, the polarizing filter  120  is not provided under the band pass filter  110 . Similarly to the first embodiment, the polarizing filter  121  is provided in front of the light source  102 . This makes it possible to ensure a specified authentication accuracy. The number of polarizing filters in the second embodiment is smaller than that in the first embodiment, thus reducing the cost. 
     Elimination of the polarizing filter  120  increases the quantity of light reaching the solid-state image sensor  112  from the light source  102 . The effect is to increase the transmittance of an optical path from the light source  102  to the solid-state image sensor  112 . It is possible to decrease the light quantity of the light source  102  and save the power of the same. 
     It may be preferable to omit the polarizing filter  121  in front of the light source  102  and provide the polarizing filter  120  under the band pass filter  110  instead. In this case also, similar effects are produced. A radiating area of the light source  102  may be provided with a protective filter for transmitting the light of a specific wavelength. 
     Third Embodiment 
     With reference to  FIG. 4 , the following describes the third embodiment of the finger vein image inputting device according to the invention.  FIG. 4  shows a sectional view of the finger vein image inputting device according to the embodiment. The finger vein image inputting device according to the third embodiment differs from the first embodiment in  FIG. 2  in that single gradient index lens  150  is used as an imaging lens instead of the gradient index lens array  111 . 
     The third embodiment uses the smaller solid-state image sensor  112  than that used for the first embodiment in  FIG. 2 . The other parts of the construction may be the same as those of the first embodiment in  FIG. 2 . The first embodiment in  FIG. 2  uses the gradient index lens array  111  as an imaging lens and is capable of increasing areas for the gradient index lens array  111  and the solid-state image sensor  112 . The finger  200  can be imaged in a wider range. However, the gradient index lens array  111  is structured so as to arrange multiple cylindrical gradient index lenses adjacently to each other. An image captured by the solid-state image sensor  112  becomes discontinuous where the lenses are in contact with each other. 
     To solve this problem, single gradient index lens may be used when it is possible to ensure an imaging range needed for a specified authentication accuracy. The third embodiment uses single gradient index lens  150  instead of the gradient index lens array  111 . The structure of the finger vein image inputting device is simplified, making the assembly and adjustment easy and reducing costs. It is possible to solve the problem of a discontinuous image due to the use of multiple gradient index lenses. A clear finger vein image can be generated to improve the authentication accuracy. 
     In  FIGS. 2 and 4 , the finger  200 , the band pass filter  110 , and the polarizing filter  120  are vertically arranged in this order. Similar effects are also produced when the band pass filter  110  and the polarizing filter  120  are reversed. 
     Fourth Embodiment 
     With reference to  FIG. 5 , the following describes the fourth embodiment of the finger vein image inputting device according to the invention.  FIG. 5  shows a sectional view of the finger vein image inputting device according to the embodiment. The finger vein image inputting device according to the embodiment differs from the third embodiment in  FIG. 4  in that the polarizing filter  120  is not provided under the band pass filter  110 . The other parts of the construction may be the same as those of the third embodiment in  FIG. 4 . 
     The finger vein image inputting device according to the fourth embodiment differs from the second embodiment in  FIG. 3  in that single gradient index lens  150  is used as an imaging lens instead of the gradient index lens array  111 . The fourth embodiment uses the smaller solid-state image sensor  112  than that used for the second embodiment in  FIG. 3 . The other parts of the construction may be the same as those of the second embodiment in  FIG. 3 . 
     The embodiment uses single gradient index lens  150  and decreases the number of polarizing filters for cost reduction. Elimination of the polarizing filter  120  increases the quantity of light reaching the solid-state image sensor  112  from the light source  102 . The effect is to increase the transmittance of an optical path from the light source  102  to the solid-state image sensor  112 . It is possible to decrease the light quantity of the light source  102  and save the power of the same. It is possible to solve the problem of a discontinuous image due to the use of multiple gradient index lenses. A clear finger vein image can be generated to improve the authentication accuracy. 
     In the embodiment of  FIG. 5 , it may be preferable to omit the polarizing filter  121  in front of the light source  102  and provide the polarizing filter  120  under the band pass filter  110  instead. In this case also, similar effects are produced. A radiating area of the light source  102  may be provided with a protective filter for transmitting the light. 
       FIG. 6  is a perspective view showing the fifth to eighth embodiments of the finger vein image inputting device. The embodiments will be described below in detail. 
     With reference to  FIG. 6 , the following describes another construction of the finger vein image inputting device according to the invention. The finger vein image inputting device according to the embodiment includes the body  100 , the light source  102 , and the imaging section  103 . The embodiment provides no recess for placing a finger. A finger is placed on the imaging section  103 . That is, the imaging section  103  also functions as the finger placing section. 
     The embodiment provides the light sources  102  on both sides of the imaging section  103 . The light source  102  generates near infrared ray having a specific wavelength suitable for imaging in a wavelength range of 700 to 1200 nm. The embodiment in  FIG. 6  uses two light sources on each side, namely four light sources in total. An LED or a laser light source may be used for the light source  102 . 
     The imaging section  103  includes an imaging device (not shown) that images a vein pattern inside the finger  200 . The light from the light source  102  is applied to the finger  200 . The light is diffused in the finger  200 . Transmitted light is generated from the finger  200 . The imaging device captures the transmitted light. 
     According to the embodiment, the light source  102  is provided closely to the finger  200 . The light generated from the light source  102  may reflect on the surface of the finger  200  and the reflected light may enter the imaging device. As a result, a finger vein image may be come unclear. Out sidelight such as the sunlight including the near infrared ray may cause the finger vein image to be unclear. 
     As will be described later, the invention provides a mechanism for preventing the light from being reflected on the surface of the finger  200 , a mechanism for preventing the light reflected on the surface of the finger  200  from reaching the imaging device, and a mechanism for eliminating an effect of the outside light. 
     When the finger vein image inputting device is used for a mobile telephone, the body  100  complies with a body of the mobile telephone. 
     Fifth Embodiment 
     With reference to  FIG. 7 , the following describes the fifth embodiment of the finger vein image inputting device according to the invention.  FIG. 7  shows a sectional view of the finger vein image inputting device according to the embodiment. The finger vein image inputting device according to the embodiment uses the light source  102  so as to be embedded in the body  100 . The light source  102  is arranged so that its optical axis is orthogonal to the top surface of the body  100 . Optical axes of the two light sources  102  are parallel to each other. Similarly to the first embodiment in  FIG. 2 , the fifth embodiment may arrange the light source  102  so that its optical axis tilts with reference to the top surface of the body  100 . 
     The polarizing filter  121  is provided on the top surface of the body  100 . The polarizing filter  121  is provided in front of and closely to the light source  102 . 
     The bandpass filter  110  is also provided on the top surface of the body  100 . Below the band pass filter  110 , there are provided the polarizing filter  120 , the gradient index lens array  111 , and the solid-state image sensor  112 . These components constitute the imaging section  103  in  FIG. 6 . The band pass filter  110  is provided so as to be in contact with the pad of the finger  200  when the finger  200  is placed on the top surface of the body  100 . The polarizing filter  120  is provided under the band pass filter  110  so as to be in contact with the band pass filter  110 . Similarly, the gradient index lens array  111  is arranged under the polarizing filter  120  so as to be in contact with the polarizing filter  120 . The solid-state image sensor  112  is arranged under the gradient index lens array  111  so as to be in contact with the gradient index lens array  111 . 
     The band pass filter  110 , the polarizing filter  120 , the gradient index lens array  111 , and the solid-state image sensor  112  may be the same as those used for the first embodiment in  FIG. 2 . 
     The light from the light source  102  is transmitted through the polarizing filter  121  to become polarized light having an optimal vibration direction (transmission axis). The polarized light is applied to the finger  200 . Applying the polarized light to the finger  200  can reduce the reflection on the surface of the finger  200 . The light entering inside the finger  200  is diffused. The diffused light is partly absorbed and partly enters the band pass filter  110 . 
     The band pass filter  110  transmits only the light of the specific wavelength corresponding to the light source  102 . This makes it possible to prevent a finger vein image from being affected by outside light such as the sunlight entering the band pass filter  110 . Only the polarized light transmitted through the band pass filter  110  is transmitted through the polarizing filter  120 . The light transmitted through the band pass filter  110  and the polarizing filter  120  is further transmitted through the gradient index lens array  11  and reaches the solid-state image sensor  112 . 
     As mentioned above, a hemoglobin in blood absorbs near infrared ray having a wavelength range of 700 to 1200 nm. Accordingly, the solid-state image sensor  112  can clearly capture a vein silhouette of the finger  200 . The embodiment smoothly collates a vein image with the registered information and improves the recognition accuracy. 
     According to the embodiment, the polarizing filter  121  is provided in front of the light source  102 . The polarizing filter  120  is provided away from the solid-state image sensor  112  so as to be close to a finger. The polarizing filter  121  may not completely prevent the light from reflecting on the surface of the finger  200 . In such case, the polarizing filter  120  prevents the light reflected on the surface of the finger from reaching the solid-state image sensor  112 . 
     The gradient index lens array  111  can generate an image at the same magnification and shorten a distance between a vein inside the finger  200  as an object surface and the solid-state image sensor  112  as an imaging surface. The finger vein image inputting device can be miniaturized and thinned. The finger vein image inputting device according to the embodiment can be mounted on a mobile telephone. 
     Sixth Embodiment 
     With reference to  FIG. 8 , the following describes the sixth embodiment of the finger vein image inputting device according to the invention.  FIG. 8  shows a sectional view of the finger vein image inputting device according to the embodiment. The finger vein image inputting device according to the embodiment differs from the fifth embodiment in  FIG. 7  in that the polarizing filter  120  is not provided under the band pass filter  110 . The other parts of the construction may be the same as those of the fifth embodiment in  FIG. 7 . 
     According to this embodiment, the polarizing filter  120  is not provided under the band pass filter  110 . Similarly to the fifth embodiment, the polarizing filter  121  is provided in front of the light source  102 . This makes it possible to ensure a specified authentication accuracy. The number of polarizing filters in the sixth embodiment is smaller than that in the fifth embodiment, thus reducing the cost. Elimination of the polarizing filter  120  increases the quantity of light reaching the solid-state image sensor  112  from the light source  102 . The effect is to increase the transmittance of an optical path from the light source  102  to the solid-state image sensor  112 . It is possible to decrease the light quantity of the light source  102  and save the power of the same. 
     It may be preferable to omit the polarizing filter  121  in front of the light source  102  and provide the polarizing filter  120  under the band pass filter  110  instead. In this case also, similar effects are produced. A radiating area of the light source  102  may be provided with a protective filter for transmitting the light of a specific wavelength. 
     Seventh Embodiment 
     With reference to  FIG. 9 , the following describes the seventh embodiment of the finger vein image inputting device according to the invention.  FIG. 9  shows a sectional view of the finger vein image inputting device according to the embodiment. The finger vein image inputting device according to the seventh embodiment differs from the fifth embodiment in  FIG. 7  in that single gradient index lens  150  is used as an imaging lens instead of the gradient index lens array  111 . The seventh embodiment uses the smaller solid-state image sensor  112  than that used for the fifth embodiment in  FIG. 7 . The other parts of the construction may be the same as those of the fifth embodiment in  FIG. 7 . The fifth embodiment in  FIG. 7  uses the gradient index lens array  111  as an imaging lens and is capable of increasing areas for the gradient index lens array  111  and the solid-state image sensor  112 . The finger  200  can be imaged in a wider range. 
     However, the gradient index lens array  111  is structured so as to arrange multiple cylindrical gradient index lenses adjacently to each other. An image captured by the solid-state image sensor  112  becomes discontinuous where the lenses are in contact with each other. To solve this problem, single gradient index lens may be used when it is possible to ensure an imaging range needed for a specified authentication accuracy. 
     The seventh embodiment uses single gradient index lens  150  instead of the gradient index lens array  111 . The structure of the finger vein image inputting device is simplified, making the assembly and adjustment easy and reducing costs. It is possible to solve the problem of a discontinuous image due to the use of multiple gradient index lenses. A clear finger vein image can be generated to improve the authentication accuracy. In  FIGS. 7 and 9 , the finger  200 , the band pass filter  110 , and the polarizing filter  120  are vertically arranged in this order. Similar effects are also produced when the band pass filter  110  and the polarizing filter  120  are reversed. 
     Eighth Embodiment 
     With reference to  FIG. 10 , the following describes the eighth embodiment of the finger vein image inputting device according to the invention.  FIG. 10  shows a sectional view of the finger vein image inputting device according to the embodiment. The finger vein image inputting device according to the embodiment differs from the seventh embodiment in  FIG. 9  in that the polarizing filter  120  is not provided under the band pass filter  110 . The other parts of the construction may be the same as those of the seventh embodiment in  FIG. 9 . 
     The finger vein image inputting device according to the eighth embodiment differs from the sixth embodiment in  FIG. 8  in that single gradient index lens  150  is used as an imaging lens instead of the gradient index lens array  111 . The eighth embodiment uses the smaller solid-state image sensor  112  than that used for the sixth embodiment in  FIG. 8 . The other parts of the construction may be the same as those of the sixth embodiment in  FIG. 8 . 
     The embodiment uses single gradient index lens  150  and decreases the number of polarizing filters for cost reduction. Elimination of the polarizing filter  120  increases the quantity of light reaching the solid-state image sensor  112  from the light source  102 . The effect is to increase the transmittance of an optical path from the light source  102  to the solid-state image sensor  112 . It is possible to decrease the light quantity of the light source  102  and save the power of the same. It is possible to solve the problem of a discontinuous image due to the use of multiple gradient index lenses. A clear finger vein image can be generated to improve the authentication accuracy. 
     In the embodiment of  FIG. 10 , it may be preferable to omit the polarizing filter  121  in front of the light source  102  and provide the polarizing filter  120  under the band pass filter  110  instead. In this case also, similar effects are produced. A radiating area of the light source  102  may be provided with a protective filter for transmitting the light. 
     While there have been described specific preferred embodiments of the present invention, it is to be distinctly understood by those skilled in the art that the present invention is not limited thereto but may be otherwise variously embodied within the spirit and scope of the invention.