Patent Publication Number: US-2020284971-A1

Title: Backlight module

Description:
RELATED APPLICATION 
     This application claims priority to Taiwan Application Serial Number 108107311, filed Mar. 5, 2019, and Taiwan Application Serial Number 108126223, filed Jul. 24, 2019, all of which are herein incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a backlight module. 
     Description of Related Art 
     In conventional handheld electronic devices, a variety of functional components are buried in the areas of the upper frame and the lower frame. In some electronic devices nowadays, the design of the upper frame is called off and the front camera is disposed in the center of the display area in order to pursue a higher screen-to-body ratio. However, as a result, an opening need to be formed in the display module and the backlight module in the display area, and such a design may cause a problem of nonuniform brightness near the opening of the display area. Therefore, how to solve the above problem is one of the important topics in the field. 
     SUMMARY 
     The present disclosure is related to a backlight module. The backlight module includes a light guide plate, a light emitting element, and a light guide element. The light guide plate has a first side and a second side. The light emitting element is adjacent to the first side of the light guide plate. The light guide element is disposed between the first side and the second side, and forms a first opening therein. The light guide element includes a first refractive part and a second refractive part. The first refractive part has a first refractive index, and the second refractive part has a second refractive index, in which the first refractive index and the second refractive index are different from a refractive index of the light guide plate. The orthogonal projections of the first refractive part and the second refractive part on the first side are non-overlapped with each other. 
     In summary, the backlight module provided in the present disclosure is able to guide the light emitted by the light emitting element on the first side to an end of the first opening close to the second side, thereby avoiding the problem that the light intensity cannot be uniformly distributed due to the first opening of the backlight module. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of an electronic device according to one embodiment of the present disclosure. 
         FIG. 2  is a cross-sectional view taken along line  2 - 2  shown in  FIG. 1 . 
         FIG. 3  is a front view of a backlight module in the electronic device according to the embodiment of  FIG. 1 . 
         FIG. 4  is a cross-sectional view taken along line  4 - 4  in  FIG. 3 . 
         FIG. 5  is a top view of a light guide element according to one embodiment of the present disclosure. 
         FIG. 6  is a top view of a light guide element according to another embodiment of the present disclosure. 
         FIG. 7  is a top view of a light guide element according to another embodiment of the present disclosure. 
         FIG. 8  is a top view of a light guide element according to another embodiment of the present disclosure. 
         FIG. 9  is a top view of a light guide element according to another embodiment of the present disclosure. 
         FIG. 10  is a top view of a light guide element according to another embodiment of the present disclosure. 
         FIG. 11  is a top view of a light guide element according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     For the embodiment below is described in detail with the accompanying drawings, embodiments are not provided to limit the scope of the present disclosure. Moreover, the operation of the described structure is not for limiting the order of implementation. Any device with equivalent functions that is produced from a structure formed by a recombination of elements is all covered by the scope of the present disclosure. Drawings are for the purpose of illustration only, and not plotted in accordance with the original size. 
     Referring to  FIG. 1 , which illustrates a front view of an electronic device  10  according to an embodiment of the present disclosure. Taking the present embodiment as an example, the electronic device  10  is a mobile phone having a display function and a photographing function. As shown in  FIG. 1 , the first surface  10   a  of the electronic device  10  has a display area DA and a frame area PA, in which the display area DA may display color images, and a first opening O 1  is formed in the display area DA. 
     As shown in  FIG. 1 , the electronic device  10  further includes a camera module  11 . The photographying module  11  is disposed in the first opening O 1 . In the present embodiment, the camera module  11  may include a charged coupled device (CCD), and the lens there of faces toward the first surface  10   a , thereby allowing the electronic device  10  to capture an external image facing the first surface  10   a.    
     Next, referring to  FIG. 2 , which illustrates a cross-sectional view taken along line  2 - 2  shown in  FIG. 1 . As shown in  FIG. 2 , the electronic device  10  further includes a cover glass  12 , a display module (including a filter layer  13 , a liquid crystal layer  14 , and a voltage control layer  15 ), a backlight module  16 , and a back cover module  17 . 
     As shown in  FIG. 2 , the cover glass  12  can be made of glass, acrylic or other types of transparent materials. The cover glass  12  forms the first surface  10   a  of the electronic device  10 . The cover glass  12  may protect components inside the electronic device  10  from the damage caused by the external environment. 
     As shown in  FIG. 2 , the display module in the present embodiment is a liquid crystal display (LCD) module, and the filter layer  13  includes a color filter therein. For example, in the present embodiment, the filter layer  13  includes a red filter layer, a blue filter layer, and a green filter layer. Different color filter layers allow light of different wavelengths to pass through. The filter layer with each color defines one sub-pixel, and multiple sub-pixels define one pixel unit. 
     As shown in  FIG. 2 , the liquid crystal layer  14  and the voltage control layer  15  are disposed between the filter layer  13  and the backlight module  16 . The liquid crystal layer  14  contains liquid crystal molecules. The voltage control layer  15  includes sub-pixel electrodes, thin film transistors (TFTs), data lines, and scan lines. Each of the sub-pixel electrodes corresponds to one thin film transistor, each thin film transistor corresponds to one sub-pixel, and each set of data lines and scan lines corresponds to one thin film transistor. The external controller can individually control the switching of each thin film transistor through the data line and the scan line. According to the switching of the thin film transistor, the sub-pixel electrode applies different degrees of voltage to the liquid crystal molecules in the liquid crystal layer  14 , and changes the tilt angles of the liquid crystal molecules, thereby controlling the light transmittance in each sub-pixel. 
     The backlight module  16  can provide light that is transmitted toward the first surface  10   a . The light sequentially passes through the voltage control layer  15 , the liquid crystal layer  14 , and the filter layer  13  that are located above the backlight module. As described above, the voltage control layer  15  and the liquid crystal layer  14  can control the light transmittance in different sub-pixels, and thereafter the light is converted into color light with different colors while passing through the filter layer  13 . As a result, the electronic device  10  can display color images by the filter layer  13 , the liquid crystal layer  14 , the voltage control layer  15 , and the backlight module  16 . 
     As shown in  FIG. 2 , the back cover module  17  can include a variety of different functional components, such as a processor, a battery, a radio or a playback device, and the like. The present disclosure is not limited thereto, and thus the above elements are not explicitly shown in  FIG. 2 . In the present embodiment, the camera module  11  is disposed on the back cover module  17  and protrudes toward the first surface  10   a.    
     As shown in  FIG. 2 , the first opening O 1  of the electronic device  10  is located within the filter layer  13 , the liquid crystal layer  14 , the voltage control layer  15 , and the backlight module  16 . The first opening O 1  extends through the filter layer  13 , the liquid crystal layer  14 , the voltage control layer  15 , and the backlight module  16 , so that the camera module  11  is able to be accommodated in the first opening O 1 . With the above design, the camera module  11  of the electronic device  10  can be located within the display area DA (see  FIG. 1 ), so that the display area DA can extend and surround the camera module  11  to increase the area of the display area DA. 
     Next, referring to  FIG. 3  and  FIG. 4 .  FIG. 3  illustrates a front view of the backlight module  16  in the electronic device  10  according to the embodiment of  FIG. 1 .  FIG. 4  is a cross-sectional view taken along line  4 - 4  shown in  FIG. 3 . The light guide plate  164  has a first side  16   a  and a second side  16   b  opposite the first side  16   a , and the first opening O 1  is disposed between the first side  16   a  and the second side  16   b.    
     As shown in  FIG. 4 , in the present embodiment, the backlight module  16  includes a light emitting element  161 , a light guide element  162 , a reflective film  163 , a light guide plate (LGP)  164 , and a diffusion film  165 . The light emitting element  161  is close to the first side  16   a  of the light guide plate  164 . The light guide element  162  is closer to the second side  16   b  of the light guide plate  164  and the first opening O 1  is formed therein. In other words, a distance between the light guide element  162  and the second side  16   b  is smaller than a distance between the light guide element  162  and the first side  16   a . The light guide plate  164  is disposed between the reflective film  163  and the diffusion film  165 , in which the diffusion film  165  is closer to the first surface  10   a  of the electronic device  10  (refer to  FIG. 1 ). 
     As shown in  FIG. 4 , the light emitting element  161  can be a light emitting diode (LED) or other light emitting elements. The light emitting element  161  is configured to emit light toward the second side  16   b  of the light guide plate  164 . The light is guided by the reflective film  163  and the light guide plate  164  to change its traveling direction, and finally passes through the diffusion film  165  and leaves the backlight module  16 . Specifically, the backlight module  16  in the present embodiment is side-light type, that is, the light emitting element  161  is located on one side of the display area DA of the electronic device  10  (refer to  FIG. 1  simultaneously). 
     As shown in  FIG. 4 , a portion of the light emitted by the light emitting element  161  reaches the first opening O 1 . The light guide element  162  is configured to guide the light to reach an end of the first opening O 1  close to the second side  16   b . As a result, it can be ensured that the light emitted by the light emitting element  161  can uniformly reach the space near the second side  16   b  of the light guide plate  164  without overflowing from the first opening O 1 . In the present embodiment, the light guide element  162  is detachably disposed in the backlight module  16 . In other words, as shown in  FIG. 4 , the backlight module  16  has a second opening O 2 , and the light guide element  162  is detachably disposed within the second opening O 2 . As shown in  FIG. 4 , the first opening O 1  has an inner diameter r1, and the second opening O 2  has an outer diameter r2, in which the inner diameter r1 is smaller than the outer diameter r2. Next, various embodiments of the detachable light guide element  162  will be described with reference to  FIG. 5  to  FIG. 11 . However, it should be understood that one skilled in the art can make changes according to actual needs, and thus it is not limited to those shown in  FIG. 5  to  FIG. 11 . 
     Referring to  FIG. 5 , which illustrates a top view of a light guide element  50  according to one embodiment of the present disclosure. In the present embodiment, the light guide element  50  is actually the light guide element  162  in  FIG. 3  and  FIG. 4 . Therefore, the following description of  FIG. 5  may also refer to  FIG. 3  and  FIG. 4  simultaneously. 
     As shown in  FIG. 5 , the light guide element  50  is ring-shaped entirely, and the first opening O 1  is formed in the center thereof. Specifically, the light guide element  50  has an inner diameter r1 and an outer diameter r2, in which the inner diameter r1 defines the size of the first opening O 1  and the outer diameter r2 defines the size of the second opening O 2  (refer to  FIG. 4  simultaneously). It should be understood that the dimensions of the elements in  FIG. 5  are not shown in actual scale. In some embodiments, a distance between an outer edge of the light guide element  50  and the first opening O 1  is d, and a radius of the first opening O 1  is R, which satisfy d≤R/10 to achieve better light transmission effect. 
     As shown in  FIG. 5 , the light guide element  50  includes a first refractive part  51  and a second refractive part  52 , in which the orthogonal projections of the first refractive part  51  and the second refractive part  52  on the first side  16   a  of the light guide plate  164  are non-overlapped with each other. The first refractive part  51  and the second refractive part  52  may be made of transparent refractive materials. For example, the first refractive part  51  and the second refractive part  52  may be made of a resin. The first refractive part  51  has a first refractive index n1, and the second refractive part  52  has a second refractive index n2. In the present embodiment, the first refractive part  51  and the second refractive part  52  are made of the same material, and thus the first refractive index n1 is equal to the second refractive index n2. 
     As shown in  FIG. 5 , the light guide element  50  further includes a third refractive part  53  and a fourth refractive part  54 . The third refractive part  53  and the fourth refractive part  54  are connected to the first refractive part  51  and the second refractive part  52 , and the third refractive part  53  is closer to the first side  16   a  than the fourth refractive part  54 . The third refractive part  53  and the fourth refractive part  54  may be made of transparent refractive materials. In the present embodiment, the third refractive part  53  has a third refractive index n3, and the fourth refractive part  54  has a fourth refractive index n4. In the present embodiment, the third refractive part  53  and the fourth refractive part  54  may be made of the same material, and thus the third refractive index n3 is equal to the fourth refractive index n4. More specifically, the third refractive index n3 and the fourth refractive index n4 are equal to the refractive index of the light guide plate  164  in  FIG. 4 . 
     Referring to  FIG. 3  and  FIG. 5  simultaneously, it should be understood that the third refractive part  53  is closer to the light emitting element  161 . Therefore, the light L emitted from the light emitting element  161  firstly passes through the light guide plate  164  and then enters the third refractive part  53 . In the present embodiment, since the refractive indices of the light guide plate  164  and the third refractive part  53  are the same, the light L does not deflect after passing through the interface  53   a  between the light guide plate  164  and the third refractive part  53 . 
     Thereafter, as shown in  FIG. 5 , the light L passes through the interface  51   a  between the third refractive part  53  and the first refractive part  51  (or the interface  52   a  between the third refractive part  53  and the second refractive part  52 ). In the present embodiment, the first refractive index n1 of the first refractive part  51  is greater than the third refractive index n3 of the third refractive part  53 . Due to the difference between the above refractive indices, the first refractive part  51  guides the light L to be deflected. 
     Next, as shown in  FIG. 5 , after leaving the interface  51   a  between the first refractive part  51  and the third refractive part  53 , the light L is incident on the interface  51   b  between the first refractive part  51  and the light guide plate  164 . Since the incident angle of the light L at the interface  51   b  is smaller than the total reflection angle of the interface  51   b , the light L is reflected and shifted in the direction toward the first opening O 1 . 
     Finally, as shown in  FIG. 5 , the light L shifted in the direction toward the first opening O 1  is incident on the interface  51   c  between the first refractive part  51  and the fourth refractive part  54 . In the present embodiment, the first refractive index n1 of the first refractive part  51  is greater than the fourth refractive index n4 of the fourth refractive part  54 . Due to the difference between the above refractive indices, the fourth refractive part  54  guides the light L away from the first opening O 1 . 
     As shown in  FIG. 5 , the light L incident on the light guide element  50  from the front of the first opening O 1  is guided to the rear of the first opening O 1  and is advanced toward the second side  16   b , and the emergent direction is close to the incident direction. In other words, the light guide element  50  enables the light L to be uniformly distributed to a region close to the second side  16   b  of the light guide plate  164  (refer to  FIG. 3 ). As a result, the brightness uniformity of the display area DA (see  FIG. 1 ) of the electronic device  10  can be ensured. 
     As shown in  FIG. 5 , the horizontal axis x1 at the intersection of the interface  51   a  and the first opening O 1  is parallel to the first side  16   a , and there is an angle a1 between the interface  51   a  and the horizontal axis x1. Similarly, the horizontal axis x2 at the intersection of the interface  51   c  and the first opening O 1  is parallel to the first side  16   a  and the second side  16   b , and there is an angle a2 between the interface  51   c  and the horizontal axis x2. In the present embodiment, the interface  51   a  is located below the horizontal axis x1 and the interface  51   c  is located above the horizontal axis x2. In other words, the directions of the angle a1 and the angle a2 are contrary, but the values of them are the same (the difference between them is a minus). 
     Different angle a1 and angle a2 may affect the degree of deflection of the light L. Specifically, the incident angle incident on the interface  51   b  should be smaller than the total reflection angle of the interface  51   b , so that the light L can reach the fourth refractive part  54 . The angle a1 of the interface  51   a  and the angle a2 of the interface  51   c  affect the degree of deflection of the light L. One skilled in the art can adjust the angle a1 and the angle a2 according to actual needs, so that the maximum proportion of the light L can be successfully reflected by the interface  51   c  to the fourth refractive part  54 . 
     For example, referring to  FIG. 6  herein, which illustrates a top view of a light guide element  60  according to another embodiment of the present disclosure. As shown in  FIG. 6 , the light guide element  60  is entirely the same as the light guide element  50 , and the difference is that the inclination angles of the interface  61   a  and the interface  61   c  of the light guide element  60  are different from that of the interfaces  51   a  and  51   c . Specifically, in  FIG. 6 , the interface  61   a  is parallel to the horizontal axis x1, and the interface  61   c  is parallel to the horizontal axis x2. In other words, in the present embodiment, the angle a1 and the angle a2 are both zero. 
     Alternatively, referring to  FIG. 7 , which illustrates a top view of a light guide element  70  according to another embodiment of the present disclosure. As shown in  FIG. 7 , the light guide element  70  is entirely the same as the light guide element  50 , and the difference is that the inclination angles of the interface  71   a  and the interface  71   c  of the light guide element  70  are different from that of the interfaces  51   a  and  51   c . In the present embodiment, the interface  71   a  is located above the horizontal axis x1, and the interface  71   c  is located below the horizontal axis x2. In other words, the signs of the angle a1 and the angle a2 in the present embodiment are opposite to that shown in  FIG. 5 . 
     Next, referring to  FIG. 8 , which illustrates a top view of a light guide element  80  according to another embodiment of the present disclosure. As shown in  FIG. 8 , the light guide element  80  is entirely the same as the light guide element  50 , and the difference is that the first refractive part  81 , the second refractive part  82 , and the fourth refractive part  84  of the light guide element  80  are combined with each other. In other words, in the present embodiment, the first refractive part  81 , the second refractive part  82 , and the fourth refractive part  84  are made of the same material, and the three are integrally formed such that the first refractive part  81 , the second refractive part  82 , and the fourth refractive parts  84  are combined into one C-shaped refractive part. In the present embodiment, the light can be guided through the interface  81   a  to the fourth refractive part  84  behind the first opening O 1 . In addition, the design in which the rear of the first opening O 1  is changed to the C-shape has an advantage of being easy to manufacture. 
     Next, referring to  FIG. 9 , which illustrates a top view of a light guide element  90  according to another embodiment of the present disclosure. The light guide element  90  is entirely the same as the light guide element  50 , and the difference is that the light guide element  90  further includes a reflective ring  95 . 
     As shown in  FIG. 9 , the reflective ring  95  is located at the center of the light guide element  90  and surrounds the first opening O 1 . The reflective ring  95  may be disposed on an inner surface of the first opening O 1 . Specifically, the reflective ring  95  can be a reflective metal ring, or a ring structure made of other total reflective materials. By disposing the reflective ring  95  around the first opening O 1 , it is able to prevent a portion of the light L that is not guided by the first refractive part  91  from directly entering the first opening O 1 . As a result, it is ensured that the camera module  11  (see  FIG. 2 ) located in the first opening O 1  is not disturbed by the light. In addition, the reflective ring  95  may also be disposed in the embodiment of  FIG. 7 , and the embodiment of  FIG. 7  needs the configuration of the reflective ring  95  more than that of  FIG. 5 . 
     Next, referring to  FIG. 10 , which illustrates a top view of a light guide element  100  according to another embodiment of the present disclosure. As shown in  FIG. 10 , the light guide element  100  is similar to the light guide element  90 , and the difference is that the light guide element  100  further includes a first reflective part  106  and a second reflective part  107 , and the angle a1 and the angle a2 are slightly different. In this embodiment, the reflective ring  105  may not exist, and may be omitted, such that the first reflective part  106  may be directly connected to the first opening O 1 . 
     As shown in  FIG. 10 , the first reflective part  106  and the second reflective part  107  may be made of metal or various reflective materials. The first reflective part  106  and the second reflective part  107  are respectively disposed in the third refractive part  103  and the fourth refractive part  104 , and each of the first reflective part  106  and the second reflective part  107  is disposed between the first refractive part  101  and the second refractive part  102 . In the present embodiment, the first reflective part  106  has a reflective surface  106   a  and a reflective surface  106   b . The reflective surface  106   a  is connected to the interface  101   a , and the reflective surface  106   b  is connected to the interface  102   a . Similarly, the second reflective part  107  has a reflective surface  107   a  and a reflective surface  107   b . The reflective surface  107   a  is connected to the interface  101   c , and the reflective surface  107   b  is connected to the interface  102   c.    
     As shown in  FIG. 10 , by disposing the first reflective part  106  in the third refractive part  103 , the emitted light L can be incident on the interface  101   a  and the interface  102   a  through the guiding of the reflective surface  106   a  and the reflective surface  106   b . The subsequent progression of the light L is similar to that shown in  FIG. 5 , and thus the description will not be repeated herein. 
     As shown in  FIG. 10 , the third refractive part  103  and the fourth refractive part  104  in the present embodiment are substantially the same. By disposing the second reflective part  107  in the fourth refractive part  104 , it enables the light L emergent from the interface  101   c  and the interface  102   c  can be guided through the reflective surface  107   a  and the reflective surface  107   b  to leave the light guide element  100  in the uniform direction. In summary, by designing the first reflective part  106  and the second reflective part  107  in the light guide element  100 , it further enables more light L to be guided to one side of the first opening O 1  close to the second side  16   b , and thus the brightness uniformity of the display area DA of the electronic device  10  is improved (refer to both  FIG. 1  and  FIG. 3 ). 
     As shown in  FIG. 10 , there is an angle a3 between the reflective surface  106   a  and the vertical axis y, and there is also an angle a3 between the reflective surface  106   b  and the vertical axis y with opposite direction. In the present embodiment, the following mathematical relation (1) between the angle a3, the first refractive index n 101  of the first refractive part  101  and the third refractive index n 103  of the third refractive part  103  is satisfied by: 
     
       
         
           
             
               
                 
                   
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     For example, in one embodiment, the first refractive index n 101  of the first refractive part  101  is between 1.51 and 2.10, the third refractive index n 103  of the third refractive part  103  is 1.5, and the angle a3 is between 12 and 83 degrees. As shown in  FIG. 10 , the angle between the reflective surface  106   a  and the reflective surface  106   b  is twice the angle a3, that is, the angle between the two reflective surfaces is between about 24 and 166 degrees. 
     As shown in  FIG. 11 , the second reflective part  107  and the first reflective part  106  in the present embodiment are disposed on two opposite sides of the first opening O 1 , and they are presented as symmetrically designed. It should be understood that the degrees of inclination of the reflective surface  106   a , the reflective surface  106   b , the reflective surface  107   a , and the reflective surface  107   b  can be adjusted according to actual needs, and thus it is not limited to those shown in  FIG. 10 . 
     Finally, referring to  FIG. 11 , which illustrates a top view of a light guide element  110  according to another embodiment of the present disclosure. As shown in  FIG. 11 , the light guide element  110  is similar to the light guide element  100 , and the difference is that the first refractive part  111  and the second refractive part  112  of the light guide element  110  respectively include a plurality of refractive layers. 
     As shown in  FIG. 11 , the first refractive part  111  includes a first refractive layer  1111 , a second refractive layer  1112 , and a third refractive layer  1113 . The first refractive layer  1111 , the second refractive layer  1112 , and the third refractive layer  1113  are sequentially arranged in a direction away from the first opening O 1 . The first refractive layer  1111  is adjacent to the reflective ring  115 . The second refractive layer  1112  surrounds the first refractive layer  1111 . The third refractive layer  1113  surrounds the second refractive layer  1112 . In the present embodiment, the first refractive layer  1111 , the second refractive layer  1112 , and the third refractive layer  1113  may be made of transparent refractive materials, such that the first refractive layer  1111  has the refractive index n11, the second refractive layer  1112  has the refractive index n12, and the third refractive layer  1113  has the refractive index n13. 
     Similarly, the second refractive part  112  includes a first refractive layer  1121 , a second refractive layer  1122 , and a third refractive layer  1123 . The first refractive layer  1121  is adjacent to the reflective ring  115 . The second refractive layer  1122  surrounds the first refractive layer  1121 . The third refractive layer  1123  surrounds the second refractive layer  1122 . In the present embodiment, the first refractive layer  1121 , the second refractive layer  1122 , and the third refractive layer  1123  may be made of transparent refractive materials, such that the first refractive layer  1121  has the refractive index n11, the second refractive layer  1122  has the refractive index n12, and the third refractive layer  1123  has the refractive index n13. In other words, in the present embodiment, the second refractive part  112  and the first refractive part  111  are mirror-symmetrical to each other. 
     In the present embodiment, the refractive index n12 is greater than the refractive index n13, and the refractive index n13 is greater than the refractive index n11. In other words, the refractive indices of the first refractive layer  1111 , the second refractive layer  1112 , and the third refractive layer  1113  are different from each other. In the present embodiment, the refractive index n11, the refractive index n12, and the refractive index n13 are all greater than the third refractive index n3 of the third refractive part  113 . Therefore, when the light L is incident on the first refractive part  111 , the deflection is occurred at the interface  111   a . The degree of the deflection is various according to the location where the light L enters. 
     Specifically, the greater the difference between the refractive indices of two adjacent media is, the greater the degree of deflection is. Therefore, by appropriately adjusting the refractive indices of the first refractive layer  1111 , the second refractive layer  1112 , and the third refractive layer  1113 , the amount of deflection of the light L incident with different angles can be more accurately adjusted, so that most of the light L can be transmitted to the fourth refractive part  114 . 
     Furthermore, as shown in  FIG. 11 , the refractive indices of the first refractive layer  1111 , the second refractive layer  1112 , and the third refractive layer  1113  are different from each other. Therefore, in addition to an interface  111   b  existed between the third refractive layer  1113  and the external medium, there is an interface  111   c  between the third refractive layer  1113  and the second refractive layer  1112  inside the first refractive part  111  and there is an interface  111   d  between the second refractive layer  1112  and the first refractive layer  1111 . The interface  111   b , the interface  111   c , and the interface  111   d  may have the same or different total reflection angles from each other. Since there are a plurality of interfaces in the first refractive part  111 , there is more chance of generating total reflection during the traveling of the light L in the first refractive part  111  to reach the fourth refractive part  114  behind the first opening O 1 . 
     In the present embodiment, since the first refractive part  111  has a plurality of interfaces, the light L can be effectively confined within the first refractive part  111 . Since the second refractive layer  1112  has the greater refractive index n12, furthermore, most of the light L is confined within the second refractive layer  1112 . As a result, after most of the light L enters the first refractive part  111  from the interface  111   a , it leaves the first refractive part  111  through the interface  111   e  rather than leaving the interface  111   b  through the interface  111   b  or entering the reflective ring  115 . Therefore, in some embodiments, it can remove the reflective ring  115  and still has a good light guiding effect. In the embodiment in which the reflective ring  115  is removed, the refractive index n11 of the first refractive layer  1111 , the refractive index n12 of the second refractive layer  1112 , and the refractive index n13 of the third refractive layer  1113  may be greater than the refractive index n air  (approximately equal to 1) of the air in the first opening O 1 , and thus it is further ensured that the light L is unable to enter the first opening O 1 . 
     In the present embodiment, the first refractive part  111  includes three refractive layers. However, in some embodiments, the first refractive part  111  may include two, four, or more refractive layers. For example, the first refractive part  111  in  FIG. 11  may include only the first refractive layer  1111  and the second refractive layer  1112  in which the refractive index n11 is smaller than the refractive index n12, so that it also can prevents the light L from entering the first opening O 1 . 
     As shown in  FIG. 11 , the vertical axis y at the connection of the reflective surface  116   a  and the reflective surface  116   b  is perpendicular to the first side  16   a  and the second side  16   b . There is an angle a4 between the reflective surface  116   a  and the vertical axis y, and there is also an angle a4 between the reflective surface  116   b  and the vertical axis y with opposite direction. In the present embodiment, the following mathematical relationship (2) between the angle a4, the refractive index n 1112  of the second refractive layer  1112  and the refractive index n 1113  of the third refractive layer  1113  is satisfied by: 
     
       
         
           
             
               
                 
                   
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     As shown in  FIG. 11 , the second reflective part  117  and the first reflective part  116  in the present embodiment are disposed on two opposite sides of the first opening O 1 , and they are presented as a symmetrical design. It should be understood that the degrees of inclination of the reflective surface  116   a , the reflective surface  116   b , the reflective surface  117   a , and the reflective surface  117   b  can be adjusted according to actual needs, and thus it is not limited to those shown in  FIG. 11 . 
     As shown in  FIG. 11 , in the present embodiment, the first refractive layer  1111 , the second refractive layer  1112 , and the third refractive layer  1113  are all circular arcs, and the three are concentric with each other. The first refractive layer  1111  has a thickness t1, the second refractive layer  1112  has a thickness t2, and the third refractive layer  1113  has a thickness t3. 
     Specifically, the thickness t1 refers to the difference between the radius of curvature of the surface of the first refractive layer  1111  close to the reflective ring  115  and the radius of curvature of the surface of the first refractive layer  1111  away from the reflective ring  115 . The thickness t2 refers to the difference between the radius of curvature of the surface of the second refractive layer  1112  close to the reflective ring  115  and the radius of curvature of the surface of the second refractive layer  1112  away from the reflective ring  115 . The thickness t3 refers to the difference between the radius of curvature of the surface of the third refractive layer  1113  close to the reflective ring  115  and the radius of curvature of the surface of the third refractive layer  1113  away from the reflective ring  115 . In the present embodiment, the sum of the thickness t1, the thickness t2, and the thickness t3 may be less than 5% of the inner diameter r1 of the first opening O 1 . It should be understood that the drawings are not shown in the actual scale for explanation. 
     Various embodiments of the light guide element  162  in  FIG. 4  have been described above with reference to  FIG. 5  to  FIG. 11 . In other words, the user can mount the light guide elements  50 - 110  shown in  FIG. 5  to  FIG. 11  in the backlight module  16  in  FIG. 4 . However, in some embodiments, the light guide element  162  can be integrally formed with the light guide plate  164 . 
     The light guide element  50  illustrated in  FIG. 5  is taken as an example herein. The refractive indices of the third refractive part  53  and the fourth refractive part  54  of the light guide element  50  are the same as the refractive index of the light guide plate  164 , so that the third refractive part  53 , the fourth refractive part  54 , and the light guide plate  164  can be integrally formed with the same material. In such an embodiment, the first refractive part  51  and the second refractive part  52  are disposed on the light guide plate  164 . Similarly, the first refractive parts  61 - 111  and/or the second refractive parts  62 - 112  of the light guide elements  60 - 110  in  FIG. 6  to  FIG. 11  may be integrally formed with the same material as the light guide plate  164 . 
     To sum up, the electronic device provided in the present disclosure has an opening located in the display area and the camera module is disposed in the opening, and such design reduces the area of the frame region required by the electronic device and increases the display area correspondingly. On the other hand, the electronic device provided in the present disclosure further includes a specially designed backlight module for guiding the light emitted by the light emitting element to be uniformly distributed in the display area of the camera module relative to one side of the light emitting element, so that the overall brightness of the display area is uniform. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalents.