Patent Publication Number: US-2016240575-A1

Title: Optical device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefits of U.S. provisional application Ser. No. 62/115,646, filed on Feb. 13, 2015. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to an optical device. 
     2. Description of Related Art 
     Optical devices such as optical fingerprint collection devices are widely used for fingerprint collection and identification. The collection of fingerprints through optical devices is based on optical imaging the finger surface through optical sensors. Most conventional optical devices for fingerprint collection use a prism which is directly contacted by a finger of the user, and a light source and an image capture unit is installed at different side of the prism. Through total internal reflection and frustrated total internal reflection (FTIR), the ridge-valley patterns of a fingerprint may produce a high contrast fingerprint image. 
     However, through the use of a prism, the volume of the optical device is relatively large. In particular, the thickness of the optical device must be greater than the height of the prism. Since the prism must be large enough to contact an entire finger, the overall volume required of the prism limits how small the height of the prism may be. Therefore, since the thickness of the optical fingerprint collection device is limited to be greater than the height of the prism, the resulting overall volume of the optical device is relatively large. As a result, the optical device cannot be conveniently installed in electronic devices where installation space is limited. 
     Electronic devices have been trending to be slim. Installing a conventional large optical device will result in the electronic device unable to be thin. 
     SUMMARY OF THE INVENTION 
     The invention provides an optical device. The optical device includes an image capture unit, at least one light emitting device, and a light conductor. The light conductor defines a space above a substrate on which the image capture unit is disposed. The light conductor includes a central portion and a surrounding portion. The central portion is disposed above the space and has a first surface relatively far from the image capture unit and a second surface opposite to the first surface and relatively close to the image capture unit. The surrounding portion is connected to the central portion and surrounding the space. The surrounding portion includes a reflection surface connected to the first surface and tilted at an angle toward the image capture unit with respect to a plane of the first surface. The reflection surface is adapted to perform total reflection. 
     According to an embodiment of the invention, the surrounding portion includes an inner surrounding surface enclosing the space, connected to the second surface of the central portion, and an outer surrounding surface being the reflection surface. 
     According to an embodiment of the invention, the surrounding portion includes an inner surrounding surface enclosing the space, connected to the second surface of the central portion, and an outer surrounding surface having at least two surfaces forming an obtuse angle. One of the at least two surfaces is the reflection surface. 
     According to an embodiment of the invention, the surrounding portion includes an inner surrounding surface enclosing the space and having at least two surfaces forming an obtuse angle. One of the at least two surfaces is connected to the second surface of the central portion. The surrounding portion also includes an outer surrounding surface having at least two surfaces forming an obtuse angle, wherein one of the at least two surfaces is the reflection surface. 
     According to an embodiment of the invention, the reflection surface is adapted to totally reflect light beams emitted from the at least one light emitting device to the first surface of the central portion. 
     According to an embodiment of the invention, the reflection surface is tilted toward the image capture unit so as to form an obtuse angle with respect to the first surface. 
     According to an embodiment of the invention, the surrounding portion of the light conductor defines at least one containing space adapted to enclose the at least one light emitting device. 
     According to an embodiment of the invention, the surrounding portion of the light conductor further includes a surface being an incident surface for the light beams from the at least one light emitting device. 
     According to an embodiment of the invention, the reflection surface is coated with metal so as to totally reflect the light beams. 
     According to an embodiment of the invention, the surrounding portion includes an inner surrounding surface enclosing the space and connected to the second surface of the central portion, and the inner surrounding surface is coated with metal so as to totally reflect the light beams. 
     According to an embodiment of the invention, the image capture unit is configured to capture an image of an object by receiving scattered light beams when total internal reflection at the first surface is frustrated by the object touching the optical device. 
     According to an embodiment of the invention, the light conductor is light pervious to the light beam. 
     According to an embodiment of the invention, the optical device further includes a microstructure layer. The microstructure layer is disposed on the first surface. The microstructure layer is adapted to scatter light beams. 
     Based on the above, the light conductor surrounds the image capture unit, and reflects the light beam within the light conductor. Since the light conductor is thin, the optical device may be relatively thin, allowing convenient installation in devices with limited installation space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a three-dimensional schematic view of an optical device according to an embodiment of the invention. 
         FIG. 2  is a bottom view of the optical device of  FIG. 1 . 
         FIG. 3  is a schematic cross-sectional view of the optical device of  FIG. 1  taken along the line A-A′. 
         FIG. 4  is the schematic cross-sectional view of the optical device of  FIG. 3  contacting a finger. 
         FIG. 5  is a three-dimensional schematic view of an optical device according to an embodiment of the invention. 
         FIG. 6  is a bottom view of the optical device of  FIG. 5 . 
         FIG. 7  is a schematic cross-sectional view of the optical device of  FIG. 5  taken along the line B-B′. 
         FIG. 8  is a schematic cross-sectional view of an optical device according to yet another embodiment of the invention. 
         FIG. 9  is a schematic cross-sectional view of an optical device according to yet another embodiment of the invention. 
         FIG. 10  is a schematic cross-sectional view of an optical device according to yet another embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
       FIG. 1  is a three-dimensional schematic view of an optical device according to an embodiment of the invention.  FIG. 2  is a bottom view of the optical device of  FIG. 1 .  FIG. 3  is a schematic cross-sectional view of the optical device of  FIG. 1  taken along the line A-A′.  FIG. 4  is the schematic cross-sectional view of the optical device of  FIG. 3  contacting a finger. Referring to  FIG. 1  to  FIG. 4 , an optical device  100  includes an image capture unit  130 , at least one light emitting device  142 , and a light conductor  120 . The light conductor  120  defines a space S above a substrate  110  on which the image capture unit  130  is disposed. The light conductor  120  includes a central portion  180  and a surrounding portion  170 . The central portion  180  is disposed above the space S and includes a first surface S 1  relatively far from the image capture unit  130  and a second surface S 2  opposite to the first surface S 1  and relatively close to the image capture unit  130 . That is to say, relative to the first surface S 1 , the second surface S 2  is closer to the image capture unit  130 . The surrounding portion  170  is connected to the central portion  180  and surrounds the space S. The surrounding portion  170  includes an inner surrounding surface S 4  enclosing the space S and an outer surrounding surface S 5 . The outer surrounding surface S 5  includes at least two surfaces, a reflection surface S 3  and an outer surface S 6 . The reflection surface S 3  is connected to the first surface S 1  and tilted at an angle θ 1  toward the image capture unit  130  with respect to a plane P of the first surface S 1 . The reflection surface S 3  is adapted to perform total reflection. The reflection surface S 3  and the outer surface S 6  form an obtuse angle θ 2 , and the reflection surface S 3  also forms an obtuse angle with respect to the first surface S 1 . The outer surface S 6  may be substantially perpendicular to the substrate  110 . The inner surrounding surface S 4  is connected to the second surface S 2  of the central portion  180 . The angle at which the inner surrounding surface S 4  is connected to the second surface S 2  may be substantially perpendicular. That is to say, the cross-sectional shape of the space S that is defined by the light conductor  120  may be, for example, a rectangle. The three-dimensional shape of the space S is, for example, a cuboid. However, the invention is not limited thereto, and the angle may be adjusted according to design requirements and the shape of the space S may be different, and the three dimensional shape of the space S may be, for example, a dome, a trapezoidal prism, or any other suitable shape. 
     The surrounding portion  170  further includes at least one surface S 7  enclosing the at least one light emitting device  142 . That is to say, the surrounding portion  170  defines at least one containing space  140  with the substrate  110 . The containing space  140  is defined by the at least one surface S 7  and the substrate  110 . The containing space  140  is adapted to enclose the light emitting device  142 . The surface S 7  is adapted to be an incident surface for the light beams from the at least one light emitting device  142  to enter the light conductor  120 . 
     In the embodiment, two containing spaces  140  are shown in  FIG. 3 , and the containing space  140  has a square shaped cross-section. However, the invention is not limited thereto. The number of containing spaces  140  and number of light sources  142  can be adjusted according to user requirements. Furthermore, the cross-section of the containing space  140  can be any suitable shape such as a dome or a rectangle. In addition, the containing space  140  can also be shaped to closely fit and contact around the light source  142  so that the surface S 7  which is the incident surface is in contact with the light source  142 . 
     The light emitting device  142  is disposed on the substrate  110  and emits a plurality of light beams. The reflection surface S 3  is adapted to reflect or totally reflect light beams emitted from the at least one light emitting device  142  to the first surface S 1  of the central portion  180 . For example, the light beam L is reflected or totally reflected by the reflection surface S 3  to the first surface S 1  of the central portion  180 . Thus, the reflection surface S 3  may be a total reflection surface adapted to totally reflect the light beam L within the light conductor  120 . The reflection surface S 3  is tilted at the angle θ 1  toward the image capture unit  130  with respect to a plane P of the first surface S 1 . In the embodiment, the plane P of the first surface is parallel to an x-axis direction. This way, the light beam L may be totally reflected within the light conductor  120  as the total internal reflection, which is also called total reflection. The angle θ 1  is less than 90 degrees, and for example, between 40 degrees and 50 degrees such that the reflection surface S 3  is configured to be a surface where a total reflection occurs. However, the invention is not limited thereto. It should be noted that the light beams emitted from the light emitting device  142  can also be light beams that are not ideally parallel. The configuration of the angle θ 1  (or the configuration of an angle formed by the reflection surface S 3  and the first surface S 1  is for totally reflecting most of the incident light beams having different light paths to the first surface S 1  after traveling to the reflection surface S 3  (at the same time, a small portion of the incident light beams may be reflected to the first surface S 1  and refracted to outside the optical device). Or, the configuration of the angle θ 1  may not cause almost all of the light beams to be totally reflected to the first surface S 1 , but the proportion of the light beams that are totally reflected to the first surface S 1  may be greater than the proportion of the refracted light beams escaped from the optical device. The angle θ 1  can be adjusted according to the user requirements. The reflection surface S 3  may be coated with metal so as to increase the proportion of light beams emitted from the light emitting device  142  to be reflected off the reflection surface S 3  to the central portion  180  of the light conductor  120 . This increases the amount of light within the light conductor  120 , so as to increase the brightness and contrast of the image captured by the image capture unit  130 . 
     In the embodiment, a thickness H 1  (i.e., the thickness of the central portion  180 ) between the first surface S 1  and the second surface S 2  is, for example, between 0.2 mm and 0.8 mm. However, the invention is not limited there to. The thickness H 1  provided between the first surface S 1  and the second surface S 2  is likely desired to be as thin as possible so as to keep the optical device  100  thin. However, a greater thickness allows more light beams from the light emitting device  142  to enter the central portion  180  between the first surface S 1  and the second surface S 2 . In addition, the thickness H 1  must be thick enough so that when a user presses the first surface S 1 , the light conductor  120  does not break. Therefore, the thickness H 1  between the first surface S 1  and the second surface S 2  may be adjusted according to user requirements. 
     In the embodiment, the material usually surrounding the light conductor  120  is air. In detail, the space between the light conductor  120  and the image capture unit  130  is usually air. When the optical device  100  is not contacted, everything outside the first surface S 1  is usually air. The refractive index of air is around 1. In the embodiment, the refractive index of the material of the light conductor  120  is, for example, from 1.4 to 2 for glass, 1.49 for polymethylmethacrylate (PMMA), 1.58 for polycarbonate (PC), 1.65 for resin, or 1.77 for sapphire. However, the invention is not limited thereto. The light conductor  120  is also light pervious to the light beam L. That is to say, the light beams emitted from the light emitting device  142  are capable of passing through the light conductor  120 . When the first surface S 1  is not contacted by a finger, the material outside the first surface S 1  is air. At this point, the light emitted from the light emitting device  142  is reflected or totally reflected by the reflection surface S 3  to the first surface S 1  and total internal reflection may occur in the light conductor  120 . In detail, after the light is totally reflected from the first surface S 1  to the second surface S 2 , the light may be totally reflected from the second surface S 2  to the first surface S 1 . That is to say, the light will be totally reflected between the second surface S 2  and the first surface S 1 . On the other hand, light may have incident angles that do not cause total internal reflection at the first surface S 1  and the second surface S 2 , and may be refracted at the first surface S 1  to outside of the optical device  100 . Or, the light may be, for example, reflected from the first surface S 1  and refracted at the second surface S 2  to then enter the image capture unit  130 . 
     When the light travels to a boundary of two different mediums, for example, the light is incident from a medium of a greater refraction index to another medium of a smaller refraction index, there is more reflection and less refraction. For example, compared to the refraction index of the air (approximate to 1), the refraction index of a human finger is larger and closer to the refraction index of the light conductor  120 . Hence, there is more reflection light when the light travelling in the light conductor  120  to a boundary of the light conductor  120  and the air than to a boundary of the light conductor  120  and another medium which has a refraction index larger than the air has. Referring to  FIG. 4 , when the first surface S 1  is not contacted by a finger, most of the light beams entering the central portion  180  of the light conductor  120  may have total internal reflection between the first surface S 1  and the second surface S 2  (only a small portion of the light is refracted and escaped out of the optical device or to the image capture unit  130 ). When the finger F contacts the first surface S 1 , part of the light beam L in the contact portion (i.e. the ridges of the finger) is reflected and the other part of the light beam L in the contact portion is refracted. The part of the light beam L refracted and entering to the finger F is some absorbed by the finger and some scattered. Due to the refraction light entering the finger, the light energy reflected to the image capture unit  130  remains less. On the other hand, the valleys of the finger F do not substantially contact the first surface S 1 . Thus, there is an air gap between the valley of the finger F and the first surface S 1 . As a result, the valley positions may have total internal reflection and reflection, and the reflected light energy is more than in the ridge portion. Thus, the valley portions have more light to be reflected to the second surface S 2  then be refracted to enter the image capture unit  130 . The image capture unit  130  may then, for example, generate a fingerprint image having darker ridge portions and brighter valley portions. In the embodiment, the object that contacts the first surface S 1  of the optical device  100  is a finger F. The image of the object is the fingerprint of the finger F. However, the invention is not limited thereto. The object may be any object other than a finger F, and the image may be any image of any suitable object contacting the first surface S 1 . 
     Furthermore, the inner surrounding surface S 4  may be coated with metal so as to further increase the amount of light beams reflected to the central portion  180  of the light conductor  120 . As the amount of light beams reflected to the central portion  180  of the light conductor  120  is increased, the image capture unit  130  receives more light and generates a relatively clear image. In addition, the outer surface S 6  and the reflection surface S 3  of the outer surrounding surface S 5  may also be coated with metal so as to further increase the amount of light beams reflected to the central portion  180  of the light conductor  120 . 
     Furthermore, in the embodiment, the central portion  180  may be scratch resistant material as shown in  FIG. 3 . That is to say, the material of the central portion  180  may be a suitable scratch resistant material. In the embodiment, the central portion  180  and the surrounding portion  170  are separately formed in order to include the scratch resistant material as the material of the central portion  180 . This way, the light conductor  120  is protected from being scratched. The scratch resistant material is, for example, sapphire, but the invention is not limited thereto. The scratch resistant material that is used can be selected according to user requirements. The light beam L will still transmit through the scratch resistant material to the central portion  180  formed by the scratch resistant material. When the finger F contacts the first surface S 1 , part of the light beam L in the ridge portion is reflected and the other part is refracted. The part of the light beam L that is refracted and enters to the finger F are some absorbed by the finger and some scattered. Due to the refraction light entering the finger, the light energy reflected to the image capture unit  130  remains less. Regarding the valley portions that do not substantially contact the first surface S 1 , the light beam L may have total internal reflection and reflection at the valley positions, and the reflected light is more than in the ridge portion. The reflected light in the valley portion is refracted from the second surface S 2  to reach the image capture unit  130 . Thus, the image capture unit  130  receives the light beams so as to generate a fingerprint image including darker ridge portions and brighter valley portions.  FIG. 3  and  FIG. 4  show the material of the central portion  180  as a scratch resistant material different from the material of the surrounding portion  170 . This clearly shows the distinction between the central portion  180  and the surrounding portion  170 . However, the invention is not limited thereto. The material of the central portion  180  is not limited to a scratch resistant material, and may be the same material as the surrounding portion  170 . In addition, the surrounding portion  170  may also be composed of the same scratch resistant material as the central portion  180 . That is to say, the material of the central portion  180  and the surrounding portion  170  may be the same or different, and may be scratch resistant or not scratch resistant according to user requirements. In the embodiment, a height H 2  from the substrate to the second surface S 2  of the central portion  180  is greater than a height of the image capture unit  130  and a lens (not shown). 
       FIG. 2  is a bottom view of the optical device of  FIG. 1 . Referring to  FIG. 2 ,  FIG. 2  shows the bottom view of the optical device  100  without showing the substrate  110  and the image capture unit  130 .  FIG. 2  shows the arrangement of the light emitting devices  142  and the containing spaces  140 . In the embodiment, the number of light emitting devices  142  is twelve. However, the invention is not limited thereto. The number of light emitting devices  142  and the number of the containing spaces  140  may be adjusted according to the user. In addition, the spacing and arrangement of the light emitting devices  142  on each of the sides of the light conductor  120  may be adjusted according to the user. In the embodiment, the light emitting devices  142  are light emitting diodes. However, the invention is not limited thereto. 
     As seen in  FIG. 2 , the number of containing spaces  140  is equal to the number of light emitting devices  142 . However, the invention is not limited thereto. In another embodiment, the light conductor  120  may include only one containing space  140  extending through all sides of the light conductor  120 . That one containing space  140  may contain all the light emitting devices  142  of the optical device  100 . The number of containing spaces  140  may be adjusted according to design requirements. 
       FIG. 1  is a three-dimensional schematic view of the optical device. In the embodiment, the light conductor  120  is rotatably symmetrical about a center axis C of the first surface S 1  of the light conductor  120 , such as the light conductor  120  having a square shape depicted in  FIG. 2 , which has a rotational symmetry of 90 degrees. However, the invention is not limited thereto, and the light conductor can be any shape with or without rotational symmetry. 
       FIG. 5  is a three-dimensional schematic view of an optical device according to an embodiment of the invention.  FIG. 6  is a bottom view of the optical device of  FIG. 5 .  FIG. 7  is a schematic cross-sectional view of the optical device of  FIG. 5  taken along the line B-B′. Referring to  FIG. 5  to  FIG. 7 , the embodiment of  FIG. 5  to  FIG. 7  is similar to the embodiment of  FIG. 1  to  FIG. 4 . Similar elements will apply similar reference numerals as in the embodiment of  FIG. 1  to  FIG. 4 . Description of similar elements will not be repeated and can be referred to in the description of  FIG. 1  to  FIG. 4 . As seen in  FIG. 7 , the optical device  200  includes a substrate  210 , a light emitting device  242 , a light conductor  220 , and an image capture unit  230 . The light conductor  220  includes a central portion  280  and a surrounding portion  270 . A containing space  240  is defined by a surface S 7 , which is the incident surface for the light beams from the light emitting device  242 , of the surrounding portion  270  and the substrate  210 . The optical device  200  further includes a scratch resistant layer  290  disposed on the first surface S 1  of the central portion  280  for protecting the light conductor  220  from being scratched. A material of the scratch resistant layer  290  is, for example, sapphire. The scratch resistant layer  290  can also use any other kind of scratch resistant material. When the finger F (ridge portions) contacts the scratch resistant layer  290 , the light beam L will transmit through the central portion  280  and the scratch resistant layer  290  to the finger F. A portion of the light entering to the finger F is absorbed and scattered, and only a little light energy can be reflected to the image capture unit  230 . On the other hand, the valley positions may have more reflected light than the ridge portions and the light is reflected to the second surface S 2  then to the image capture unit  230 . Furthermore, a cross-sectional shape of the containing space  240  has a dome shape. However, the cross-sectional shape of the containing space  240  may be any other suitable shape such as a square or a rectangle. In addition, the containing space  240  can also be shaped to closely fit and contact around the light source  242  so that the light incident surface S 7  is in contact with the light source  242 . 
     Furthermore, in the embodiment shown in  FIG. 7 , the surrounding portion  270  includes an inner surrounding surface having at least two surfaces S 8 , S 9  that form an obtuse angle θ 3 . In the embodiment, the surface S 9  is connected to the second surface S 2  of the central portion  280 . That is to say, in the embodiment, the cross-sectional shape of the space S is a combination of a trapezoid and a rectangle. The description of the thicknesses and heights of the optical device  200  may be referred to in the description of  FIG. 1  to  FIG. 4 , and will not be repeated herein. In addition, the arrangement of the light emitting devices  242  and the containing spaces  240  may be referred to the description of  FIG. 1  to  FIG. 4 , as the number and configuration may be adjusted according to user requirements. 
     Referring to  FIG. 5 , in the embodiment, the light conductor  220  is rotatably symmetrical about a center axis C of the first surface S 1  of the light conductor  220 . In particular, the light conductor  220  has a cylindrical shape, and has a rotational symmetry of 360 degrees. In other embodiments, the shape of the light conductor  220  can be, for example, square shaped with a rotational symmetry of 90 degrees similar to  FIG. 1  and  FIG. 2 , or rectangular shaped with a rotational symmetry of 180 degrees. However, the invention is not limited thereto, and the light conductor can be any shape with or without rotational symmetry. 
     Referring to  FIG. 6 ,  FIG. 6  shows the bottom view of the optical device  200  without showing the substrate  210  and the image capture unit  230  of  FIG. 7 .  FIG. 6  shows the arrangement of the light emitting devices  242  and the containing spaces  240 . In the embodiment, the number of light emitting devices  242  is eight. However, the invention is not limited thereto. The number of light emitting devices  242  and the number of and the containing spaces  240  may be adjusted according to the user. In addition, the spacing and arrangement of the light emitting devices  242  on around the light conductor  220  may be adjusted according to the user. In the embodiment, the light emitting devices  242  are light emitting diodes. However, the invention is not limited thereto. 
     As seen in  FIG. 6 , the number of containing spaces  240  is one, and all the light emitting devices  242  are contained in the containing space  240 . However, the invention is not limited thereto. The containing spaces  240  may be increased and adjusted in size to contain one or more light emitting devices  242 . Similar to  FIG. 3 , the number of containing spaces  240  may also be the same number as the light emitting devices  242 . The number of containing spaces  240  may be adjusted according to design requirements. 
       FIG. 8  is a schematic cross-sectional view of an optical device according to yet another embodiment of the invention. Referring to  FIG. 8 , the embodiment of  FIG. 8  is similar to the embodiment of  FIG. 1 . Similar elements will apply similar reference numerals as in the embodiment of  FIG. 1 . Description of similar elements will not be repeated and can be referred to in the description of  FIG. 1 . As seen in  FIG. 8 , the optical device  300  includes a substrate  310 , a light emitting device  342 , a light conductor  320 , and an image capture unit  330 . The light conductor  320  includes a central portion  380  and a surrounding portion  370  connected to each other. A containing space  340  is defined by a surface S 7  of the surrounding portion  370  and the substrate  310 . The description of the cross-sectional shape of the containing space  340  is similar to the containing space  140 , and the same description will not be repeated herein. 
     Furthermore, in the embodiment, the surrounding portion  370  includes the inner surrounding surface S 4  connected to the second surface S 2  of the central portion  380  to define the space S. In the embodiment, the cross-sectional shape of the space S is defined as a dome. That is to say, the connection between the inner surrounding surface S 4  and the second surface S 2  form a dome shape to define the cross section of the space S. The three-dimensional shapes of the light conductor  320  may be similar to the three-dimensional shape as shown in  FIG. 1  or  FIG. 5 , but is not limited thereto. That is to say, the light conductor  320  may have different types of rotational symmetry or not. The three-dimensional shape of the light conductor  320  may be any suitable shape according to design requirements. 
       FIG. 9  is a schematic cross-sectional view of an optical device according to yet another embodiment of the invention. Referring to  FIG. 9 , the embodiment of  FIG. 9  is similar to the embodiment of  FIG. 1 . Similar elements will apply similar reference numerals as in the embodiment of  FIG. 1 . Description of similar elements will not be repeated and can be referred to in the description of  FIG. 1 . As seen in  FIG. 9 , the optical device  400  includes a substrate  410 , a light emitting device  442 , a light conductor  420 , and an image capture unit  430 . The light conductor  420  and the substrate  410  define a space S. The light conductor  420  includes a central portion  480  and a surrounding portion  470  connected to each other. 
     Furthermore, in the embodiment, the surrounding portion  470  includes the inner surrounding surface S 4  connected to the second surface S 2  of the central portion  480 . The surrounding portion  470  also includes an outer surrounding surface S 10  connected to the first surface S 1  of the central portion. In the embodiment, the outer surrounding surface S 10  is tilted towards the image capture unit  430  to form an angle θ 1  with the substrate  410 . Similarly, the inner surrounding surface S 4  tilts towards the image capture unit  430  to form an angle with the substrate. In the embodiment, the inner surrounding surface S 4  and the outer surrounding surface S 10  are parallel to each other so that the respective angles formed by the inner surrounding surface S 4  and the outer surrounding surface S 10  are equal to each other. However, the invention is not limited thereto, and the inner surrounding surface S 4  and the outer surrounding surface S 10  do not have to be parallel to each other. Furthermore, the outer surrounding surface S 10  is the reflection surface adapted to totally internally reflect the light beam L. 
     A containing space  440  is defined by a surface S 7  of the surrounding portion  470  and the substrate  410 . The description of the cross-sectional shape of the containing space  440  is similar to the containing space  240 , and the same description will not be repeated herein. 
     In the embodiment, the shape of the cross section of the space S is defined as a trapezoid. That is to say, the connection between the inner surrounding surface S 4  and the second surface S 2  form a trapezoid shape to define the cross section of the space S. The three-dimensional shapes of the light conductor  420  may be similar to the three-dimensional shape as shown in  FIG. 1  or  FIG. 5 , but is not limited thereto. The three-dimensional shape of the light conductor  420  may be any suitable shape according to design requirements. The three-dimensional shapes of the light conductor  420  may be similar to the three-dimensional shape as shown in  FIG. 4  or  FIG. 6 , but is not limited thereto. That is to say, the light conductor  420  may have different types of rotational symmetry or not. The three-dimensional shape of the light conductor  420  may be any suitable shape according to design requirements. 
     In the embodiment of  FIG. 8  and  FIG. 9 , part of the light beam L is reflected and the other part of the light beam L is refracted when the optical device is touched, so that the image capture unit may capture an image of an object by receiving reflected and refracted light beams. The same descriptions can be referred to in the description of  FIG. 1  to  FIG. 4 , and will not be repeated herein. 
     Referring to  FIG. 10 ,  FIG. 10  is a schematic cross-sectional view of an optical device  500  according to yet another embodiment of the invention.  FIG. 10  shows a finger contacting the optical device  500 . The embodiment of  FIG. 10  is similar to the embodiment of  FIG. 1  to  FIG. 4 . Similar elements will apply similar reference numerals as in the embodiment of  FIG. 1  to  FIG. 4 . As seen in  FIG. 10 , the optical device  500  includes a substrate  510 , a light emitting device  542 , a light conductor  520 , and an image capture unit  530 . The light conductor  520  and the substrate  510  define a space S. The light conductor  520  includes a central portion  580  and a surrounding portion  570  connected to each other. The difference between the embodiment of  FIG. 10  and the embodiment of  FIG. 1  to  FIG. 4  is that the optical device  500  further includes a microstructure layer  590  disposed on the first surface S  1 . The microstructure layer  590  is adapted to increase light scattering, and the microstructure layer  590  can be, but not limited to, made of materials with particles by which the light can be scattered. In another example, the microstructure layer  590  has a rough surface regardless of what the material it is used. The rough surface also helps light scattering. 
     When the first surface S 1  of the optical device  500  is not contacted by an object, the light enters the light conductor  520  and the microstructure layer  590 . The light beams are scattered by the microstructure layer  590  and enter the light conductor  520 . When the microstructure layer  590  of the first surface S 1  of the optical device  500  is contacted by the finger F, part of the light beam is refracted into the finger F and is absorbed by the finger F. On the other hand, the valleys of the finger do not substantially contact the microstructure layer  590 , and the light is still scattered by the microstructure layer  590  and refracted by the light conductor  120  to enter the image capture unit  530 . Benefit from the microstructure layer  590 , lights in the valley portions reflected to enter the image capture unit  530  are more than in the option device  100 . Accordingly, the fingerprint image generated by the image capture unit  530  has darker ridge portions and brighter valley portions. 
     In other embodiments, the optical device  500  of  FIG. 10  may be varied and modified as described in the embodiments of  FIG. 1  to  FIG. 9 . The same will not be repeated herein. 
     To sum up, the light conductor surrounds the image capture unit, and reflects the light beam within the light conductor. Since a light conductor is thin, the optical device may be relatively thin, allowing convenient installation in devices with limited installation space. Accordingly, an electronic device installing the optical device can be relatively thin because the optical device does not increase the thickness of the electronic device. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.