Patent Publication Number: US-10761342-B2

Title: Floating hologram apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2016-0180820 filed on Dec. 28, 2016, in the Korean Intellectual Property Office, the entire disclosures of which are incorporated herein by reference for all purposes. 
     TECHNICAL FIELD 
     The present disclosure relates to a floating hologram apparatus. 
     BACKGROUND 
     A three-dimensional (3D) stereoscopic image display technology refers to a technology of reconstructing a two-dimensional (2D) image by adding predetermined depth information to the 2D image. 
     The 3D stereoscopic image display technology uses binocular disparity of human eyes to provide a 3D image. Methods for separating left and right images using the binocular disparity are classified into glasses type and glasses-free type. Examples of the glasses type method may include an anaglyph method, a polarized glasses method, and a shutter glasses method, and examples of the glasses-free type method may include a lenticular method, a parallax barrier method, and an optical plate method. Among these conventional methods, the polarized glasses method and the shutter glasses method are the oldest 3D display methods and have been widely used in 3D movies and 3D TVs. However, the polarized glasses method and the shutter glasses method require wearing special glasses for stereoscopic images and increase eye strain. Among the glasses-free type methods, the lenticular method and the parallax barrier method fix an observer&#39;s observation points to low-brightness and low-resolution images and cause headaches or dizziness when the observer constantly watches the images. 
     Meanwhile, examples of a complete stereoscopic method include a hologram method and a volumetric 3D display method. These complete stereoscopic methods implement only static stereoscopic images through a high-priced laser and precision optical apparatus but cannot provide real-time high-quality stereoscopic images. 
     Recently, methods for implementing real-time stereoscopic images at low costs by using a half mirror, a concave mirror, a Fresnel lens, a prism array, and the like have been suggested. However, the method using a half mirror reflects an image as a virtual image and requires a large physical size of the system, and the methods using a concave mirror, a Fresnel lens, and a prism array require high manufacturing costs and provide a narrow viewing angle. Particularly, in the case where a stereoscopic image is implemented using a prism array, the image quality may deteriorate. 
     SUMMARY 
     In view of the foregoing, the present disclosure provides a floating hologram apparatus capable of simultaneously projecting a first hologram image and a second hologram image. However, problems to be solved by the present disclosure are not limited to the above-described problems. There may be other problems to be solved by the present disclosure. 
     According to a first exemplary embodiment of the present disclosure, a floating hologram apparatus includes a display including a first output area to output a first hologram image and a second output area to output a second hologram image and a prism array positioned in front of the display and configured to refract rays of the first hologram image and the second hologram image. The prism array includes multiple prisms of which a first facet to which a ray of the second hologram image is incident and a second facet to which a ray of the first hologram image is incident have different angles. 
     According to an example, a projection position for a floating hologram of the first hologram image and a projection position for a floating hologram of the second hologram image are changed depending on a difference in angle between the first facet and the second facet. 
     According to an example, the first hologram image is an object image and the second hologram image is a background image. 
     According to an example, the first facet of each of the multiple prisms has an angle which is greater than an angle of the second facet. 
     According to an example, the first hologram image is a background image and the second hologram image is an object image. 
     According to an example, the second facet of each of the multiple prisms has an angle which is greater than an angle of the first facet. 
     According to an example, the floating hologram apparatus further includes between the display and the prism array, a first filter for controlling a field of view configured to block a ray incident at an angle within a first range among rays of the first hologram image and a second filter for controlling a field of view configured to block a ray incident at an angle within a second range among rays of the second hologram image. 
     According to an example, the first filter for controlling a field of view is attached to the front of the first output area and the second filter for controlling a field of view is attached to the front of the second output area. 
     According to an example, a first-type polarizing film is attached to the first output area and a second-type polarizing film having polarized light property orthogonal to the first-type polarizing film is attached to the second output area. 
     According to an example, the second-type polarizing film is attached to the first facet and the first-type polarizing film is attached to the second facet 
     According to an example, an input shutter to be turned on or off during each predetermined cycle is attached to the display, and an output shutter to be turned on or off is attached to the prism array. 
     According to an example, a first input shutter of the input shutter is attached to the first output area, a second input shutter of the input shutter is attached to the second output area, and a first output shutter of the output shutter is attached to an upper part of each of the prisms, and a second output shutter of the output shutter is attached to a lower part of each of the prisms. 
     According to an example, the first input shutter and the second output shutter are turned on while the second input shutter and the first output shutter are turned off during a first cycle. 
     According to an example, the first input shutter and the second output shutter are turned off while the second input shutter and the first output shutter are turned on during a second cycle different from the first cycle. 
     According to second exemplary embodiment of the present disclosure, a floating hologram apparatus includes a first display configured to output a first hologram image, a second display configured to output a second hologram image and a prism array configured to refract rays of the first hologram image and the second hologram image. The prism array includes multiple prisms of which a first facet to which a ray of the second hologram image is incident and a second facet to which a ray of the first hologram image is incident have different angles. 
     According to an example, the first display is positioned above the second display, and the prism array is positioned in front of the first display and the second display. 
     According to an example, a projection position for a floating hologram of the first hologram image and a projection position for a floating hologram of the second hologram image are controlled depending on a difference in angle between the first facet and the second facet. 
     According to an example, the first hologram image is an object image and the second hologram image is a background image. 
     According to an example, the first facet of each of the multiple prisms has an angle which is greater than an angle of the second facet. 
     According to an example, the first display is positioned in front of the second display. 
     According to an example, the first hologram image is a background image and the second hologram image is an object image. 
     According to an example, the second facet of each of the multiple prisms has an angle which is greater than an angle of the first facet 
     According to an example, the second display is positioned in front of the first display 
     According to any one of the above-described exemplary embodiments of the present disclosure, it is possible to provide a floating hologram apparatus capable of simultaneously projecting a first hologram image and a second hologram image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exemplary diagram illustrating a floating hologram apparatus according to an exemplary embodiment of the present disclosure. 
         FIG. 2  is an exemplary diagram illustrating a floating hologram apparatus according to another exemplary embodiment of the present disclosure. 
         FIG. 3  is an exemplary diagram illustrating a floating hologram apparatus according to another exemplary embodiment of the present disclosure. 
         FIG. 4  is an exemplary diagram illustrating a prism array according to an exemplary embodiment of the present disclosure. 
         FIG. 5  is an exemplary diagram illustrating a prism array according to another embodiment of the present disclosure. 
         FIGS. 6A-6E  are diagrams illustrating displays and output images according to exemplary embodiments of the present disclosure. 
         FIG. 7  is an exemplary diagram illustrating a floating hologram apparatus according to yet another exemplary embodiment of the present disclosure. 
         FIG. 8A  and  FIG. 8B  (shown collectively as  FIGS. 8B ( 1 ) to  8 B( 5 )) are diagrams respectively illustrating a filter for controlling a field of view according to an exemplary embodiment of the present disclosure. 
         FIG. 9  is an exemplary diagram illustrating a floating hologram apparatus according to still another exemplary embodiment of the present disclosure. 
         FIG. 10  is a diagram illustrating a filter for controlling a field of view according to another embodiment of the present disclosure. 
         FIG. 11  is an exemplary diagram illustrating a floating hologram apparatus according to still another exemplary embodiment of the present disclosure. 
         FIG. 12  is an exemplary diagram illustrating a floating hologram apparatus according to still another exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that the present disclosure may be readily implemented by those skilled in the art. However, it is to be noted that the present disclosure is not limited to the embodiments but can be embodied in various other ways. In drawings, parts irrelevant to the description are omitted for the simplicity of explanation, and like reference numerals denote like parts through the whole document. 
     Through the whole document, the term “connected to” or “coupled to” that is used to designate a connection or coupling of one element to another element includes both a case that an element is “directly connected or coupled to” another element and a case that an element is “electronically connected or coupled to” another element via still another element. Further, it is to be understood that the term “comprises or includes” and/or “comprising or including” used in the document means that one or more other components, steps, operation and/or existence or addition of elements are not excluded in addition to the described components, steps, operation and/or elements unless context dictates otherwise. 
     Through the whole document, the term “unit” includes a unit implemented by hardware, a unit implemented by software, and a unit implemented by both of them. One unit may be implemented by two or more pieces of hardware, and two or more units may be implemented by one piece of hardware. 
     Through the whole document, a part of an operation or function described as being carried out by a terminal or device may be carried out by a server connected to the terminal or device. Likewise, a part of an operation or function described as being carried out by a server may be carried out by a terminal or device connected to the server. 
     Hereinafter, an exemplary embodiment of the present disclosure will be described in detail with reference to the accompanying configuration views or process flowcharts. 
     First Embodiment 
       FIG. 1  is an exemplary diagram illustrating a floating hologram apparatus according to an exemplary embodiment of the present disclosure. Referring to  FIG. 1 , a floating hologram apparatus according to a first embodiment may include a prism array  100  configured to refract rays of a first hologram image and a second hologram image, a first display  110 - 1  configured to output the first hologram image, and a second display  110 - 2  configured to output the second hologram image. 
     The prism array  100  is positioned in front of the first display  110 - 1  and the second display  110 - 2 . In the prism array  100 , multiple prisms  120  configured to refract incident rays are arranged. 
     In this regard, the detailed configuration of the prism array  100  will be described with reference to  FIG. 4 . Referring to  FIG. 4 , the prism array  100  is configured such that the multiple prisms  120  configured to refract a first ray incident in a first direction and a second ray incident in a second direction different from the first direction toward an observer are consecutively arranged. 
     Each of the multiple prisms  120  may include an incident surface  200  which is an optical plane to which rays are incident, a first facet  130  which is an optical plane configured to refract a first ray incident from below the prism  120 , and a second facet  140  which is an optical plane configured to refract a second ray incident in a direction different from the direction of the first ray, i.e., from above the prism  120 . 
     Herein, refracted rays of the first ray and the second ray may proceed parallel to each other when viewed by the observer. 
     Referring to  FIG. 1  again, the first display  110 - 1  configured to output the first hologram image is distant as much as d w  from the prism array  100 . The second display  110 - 2  configured to output the second hologram image is distant as much as d sf  from the prism array  100 . Herein, the first hologram image may be a rear image, e.g., a background image. Further, the second hologram image may be a front image, e.g., an object image. 
     The first display  110 - 1  may be positioned above the second display  110 - 2 . Further, the first display  110 - 1  may be positioned behind the second display  110 - 2 . 
     A ray of the first hologram image output from the first display  110 - 1  is incident to the prism array  100  with a first incident angle θ r . The ray of the first hologram image incident to the prism array  100  may be refracted by the second facet  140  of the prism array  100 , and, thus, a floating hologram  160  of the first hologram image may be projected onto a first projection position behind the prism array  100 . 
     A ray of the second hologram image output from the second display  110 - 2  is incident to the prism array  100  with a second incident angle θ. The ray of the second hologram image incident to the prism array  100  may be refracted by the first facet  130  of the prism array  100 , and, thus, a floating hologram  150  of the second hologram image may be projected onto a second projection position behind the prism array  100 . 
     Herein, a distance d sr  from the prism array  100  to the first projection position and a distance d sf  from the prism array  100  to the second projection position can be calculated by the following Equations 1 and 2. 
     
       
         
           
             
               
                 
                   
                     D 
                     f 
                   
                   = 
                   
                     
                       d 
                       sf 
                     
                     
                       cos 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         θ 
                         f 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
             
               
                 
                   
                     D 
                     r 
                   
                   = 
                   
                     
                       d 
                       sr 
                     
                     
                       cos 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         θ 
                         r 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     As such, the ray of the first hologram image output from the first display  110 - 1  positioned relatively in the back is refracted by the prism array  100  and then proceeds toward the observer and the observer can see the floating hologram  160  (e.g., background image) of the first hologram image projected onto a position distant as much as D r . Further, the ray of the second hologram image output from the second display  110 - 2  positioned relatively in front is refracted by the prism array  100  and then proceeds toward the observer and the observer can see the floating hologram  150  (e.g., object) of the second hologram image projected onto a position distant as much as D f . 
     As such, a floating hologram of an object and a floating hologram of a background image can be respectively projected onto different projection positions using the two displays, i.e., the first display  110 - 1  and the second display  110 - 2 , which are arranged at different positions distant from the prism array  100 . 
     The observer can watch the floating hologram of the object and the floating hologram of the background image with a different sense of depths, respectively. 
     However, the floating hologram apparatus according to the first embodiment requires the two displays, i.e., the first display  110 - 1  and the second display  110 - 2 , and the two displays need to be positioned at different depths from each other, which causes an increase in size of the floating hologram apparatus. 
     Further, in the case where white rays are output from the first display  110 - 1  and the second display  110 - 2  and pass through the prism array  100 , rays of red, green, and blue components are output in different directions, respectively, due to a difference in refractive index depending on a wavelength. That is, even if a clear image is expressed through the first display  110 - 1  and the second display  110 - 2 , each color is separated through the prism array  100  and the image is projected on space, which is referred to as chromatic dispersion. 
     Such chromatic dispersion can be overcome by previously applying inverse distortion to colors of the first hologram image and the second hologram image. That is, if distances from the first display  110 - 1  and the second display  110 - 2  to the prism array  100  are determined, the amount of chromatic dispersion becomes uniform in the entire region. Therefore, if pixels are previously shifted and arranged depending on the amount of chromatic dispersion and watched through the prism array  100 , a floating hologram free of chromatic dispersion can be seen. 
     Meanwhile,  FIG. 1  illustrates that the first display  110 - 1  is positioned above the second display  110 - 2  and also positioned behind the second display  110 - 2 , but may not be limited thereto. 
     For example, the second display  110 - 2  may be positioned behind the first display  110 - 1 . In this case, desirably, the first hologram image may be an object image and the second hologram image may be a background image. 
     Second Embodiment 
       FIG. 2  is an exemplary diagram illustrating a floating hologram apparatus according to another exemplary embodiment of the present disclosure.  FIG. 2  is provided to solve the problem of the floating hologram apparatus according to the first embodiment, and a floating hologram apparatus according to a second embodiment may include the prism array  100  configured to refract rays of a first hologram image and a second hologram image and a single display  110 ′ configured to output the first hologram image and the second hologram image. 
     The display  110 ′ may include a first output area  110 - 3  to output the first hologram image and a second output area  110 - 4  to output the second hologram image.  FIG. 2  illustrates that the first output area  110 - 3  and the second output area  110 - 4  are arranged vertically, but may not be limited thereto. For example, the first output area  110 - 3  and the second output area  110 - 4  may be arranged horizontally. 
     In the case where the single display  110 ′ illustrated in  FIG. 2  and the prism array  100  including the first facet  130  and the second facet  140  having the same angle as illustrated in  FIG. 1  are used, floating holograms of the first hologram image and the second hologram image are projected onto positions equally distant from the prism array  100  according to Equations 1 and 2 (i.e., D r  and D f  are the same distance). 
     Therefore, in the second embodiment, an angle between the incident surface  200  of the prism array  100  and the first facet  130  is configured to be different from an angle between the incident surface  200  and the second facet  140 , and, thus, floating holograms of the first hologram image and the second hologram image can be projected onto different projection positions, respectively. 
     Referring to  FIG. 5 , the prism array  100  of the floating hologram apparatus according to the second embodiment may include the multiple prisms  120  of which the first facet  130  and the second facet  140  have different angles. 
     In general, as an angle between the incident surface  200  and a facet is increased, an incident angle of a ray is increased. For example, if an angle θ p1  between the incident surface  200  and the first facet  130  is greater than an angle θ p2  between the incident surface  200  and the second facet  140  as illustrated in  FIG. 4 , an incident angle θ i1  of a first ray is greater than an incident angle θ i2  of a second ray. 
     In this case, a floating hologram of the first ray is projected behind a floating hologram of the second ray according to Equations 1 and 2. Therefore, desirably, a hologram image incident to a facet having a greater angle with the incident surface  200  may serve as a background image and a hologram image incident to a facet having a smaller angle with the incident surface  200  may serve as an object image. 
     Referring to  FIG. 2  again, in the floating hologram apparatus according to the second embodiment, the first facet  130  of the prism array  100  may have an angle which is greater than an angle of the second facet  140 . 
     In this case, desirably, the first hologram image output from the first output area  110 - 3  may be an object image and the second hologram image output from the second output area  110 - 4  may be a background image. 
     As such, a ray of the first hologram image output from the first output area  110 - 3  is incident to the prism array  100  with a first incident angle θ f . The ray of the first hologram image incident to the prism array  100  may be refracted by the second facet  140  of the prism array  100 , and, thus, a floating hologram  150  of the first hologram image may be projected onto a first projection position behind the prism array  100 . 
     A ray of the second hologram image output from the second output area  110 - 4  is incident to the prism array  100  with a second incident angle θ r . The ray of the second hologram image incident to the prism array  100  may be refracted by the first facet  130  of the prism array  100 , and, thus, a floating hologram  160  of the second hologram image may be projected onto a second projection position behind the prism array  100 . 
     In this case, since the angle θ p1  of the first facet  130  is greater than the angle θ p2  of the second facet  140 , the incident angle θ r  of the ray of the second hologram image may be greater than the incident angle θ f  of the ray of the first hologram image. Thus, the ray of the first hologram image output from the first output area  110 - 3  is refracted by the prism array  100  and then proceeds toward the observer and the observer can see the floating hologram  150  (e.g., object) of the first hologram image projected onto a position distant as much as d sf . Further, the ray of the second hologram image output from the second output area  110 - 4  is refracted by the prism array  100  and then proceeds toward the observer and the observer can see the floating hologram  160  (e.g., background) of the second hologram image projected onto a position distant as much as d sr . 
     According to the second embodiment, the problem of the increase in size of the floating hologram apparatus according to the first embodiment can be solved using the single display  110 ′. Further, since the single display  110 ′ is used and the angle between the incident surface  200  of the prism array  100  and the first facet  130  is configured to be different from the angle between the incident surface  200  and the second facet  140 , floating holograms of the first hologram image and the second hologram image can be projected onto different projection positions, respectively. 
     Third Embodiment 
       FIG. 3  is an exemplary diagram illustrating a prism array according to another exemplary embodiment of the present disclosure. A floating hologram apparatus according to a third embodiment may include the prism array  100  configured to refract rays of a first hologram image and a second hologram image and the single display  110 ′ configured to output the first hologram image and the second hologram image like the floating hologram apparatus according to the second embodiment. 
     In the prism array  100  of the floating hologram apparatus according to the third embodiment, the second facet  140  has an angle which is greater than an angle of the first facet  130 . 
     In this case, desirably, the first hologram image output from the first output area  110 - 3  may be a background image and the second hologram output from the second output area  110 - 4  may be an object image. 
     Meanwhile, the floating hologram apparatus according to the first embodiment may have a different configuration. That is, referring to  FIG. 1 , the floating hologram apparatus according to the first embodiment may also be configured including the prism array  100  of which the first facet  130  and the second facet  140  have different angles. In this case, the first display  110 - 1  and the second display  110 - 2  may be equally distant from the prism array  100 . 
     For example, the first facet  130  may have an angle which is greater than an angle of the second facet  140 . In this case, desirably, the first hologram image may be an object image and the second hologram image may be a background image. 
     For another example, the second facet  140  may have an angle which is greater than an angle of the first facet  130 . In this case, desirably, the first hologram image may be a background image and the second hologram image may be an object image. 
     Accordingly, even if two displays are used, the size of the floating hologram apparatus can be reduced by arranging the two displays at the same position. 
       FIGS. 6A-6E  are diagrams illustrating displays and output images according to exemplary embodiments of the present disclosure.  FIG. 6A  illustrates that a first hologram image (object image) is output from the first output area  110 - 3  and a second hologram image (background image) is output from the second output area  110 - 4 . 
     Referring to  FIG. 6B , it can be seen that the first hologram image and the second hologram image are incident to the prism in different directions, respectively, and thus chromatic dispersion compensated in opposite directions. For example, in the first hologram image, a blue part faces upward and a red part faces downward and in the second hologram image, a blue part faces downward and a red part faces upward. 
     Referring to  FIG. 6C , it can be seen that if the first facet  130  and the second facet  140  of the prism array  100  have the same angle, a floating hologram of the first hologram image and a floating hologram of the second hologram image are seen as overlapped. 
     Referring to  FIG. 6D , it can be seen that if the first facet  130  of the prism array  100  has an angle which is greater than an angle of the second facet  140  (second embodiment), a floating hologram of the first hologram image is positioned in front of a floating hologram of the second hologram image. 
     Referring to  FIG. 6E , it can be seen that if the second facet  140  of the prism array  100  has an angle which is greater than an angle of the first facet  130  (third embodiment), a floating hologram of the second hologram image is positioned in front of a floating hologram of the first hologram image. 
     Referring to the floating hologram images in  FIG. 6C  to  FIG. 6E , it can be seen that the floating hologram (object image) of the first hologram image is seen as overlapped on the floating hologram (background image) of the second hologram image in a certain range (mainly in the vicinity of the center of the image). Since the two images are present on the single display  110 ′ and a distance between the two images is small, this problem occurs when the floating hologram apparatus is viewed from below or above or from a close distance. Therefore, in the following embodiments, methods capable of solving this problem will be suggested. 
     Fourth Embodiment 
       FIG. 7  is an exemplary diagram illustrating a floating hologram apparatus according to yet another exemplary embodiment of the present disclosure. Referring to  FIG. 7 , a ray output from a point A of the display  110 ′ is incident toward a lower part of the prism array  100  as a first hologram image and refracted by the prism array  100  and then proceeds toward the observer. A ray output from a point B of the display  110 ′ is incident toward an upper part of the prism array  100  as a second hologram image and refracted by the prism array  100  and then proceeds toward the observer. In this case, the observer may see the two hologram images as projected at different depths depending on a position of the observer due to a path difference between the two rays. 
     That is, each of the first hologram image and the second hologram image proceeds in a specific direction and is refracted by the prism array  100  and then proceeds toward the observer. However, in the general display  110 ′, an image is output from one point of the display  110 ′ at an angle of about 180° in order to secure a viewing angle. Therefore, some of rays output in other directions except the output directions of the first hologram image and the second hologram image may proceed toward the observer through the prism array  100 . That is, the observer may see an unwanted image that becomes noise of the image. 
     A floating hologram apparatus according to a fourth embodiment may include the display  110 ′, the prism array  100 , and filters  701  and  703  for controlling a field of view positioned between the display  110 ′ and the prism array  100 . 
     The display  110 ′ may include the first output area  110 - 3  configured to output a first hologram image and the second output area  110 - 4  configured to output a second hologram image. 
     The prism array  100  may include the multiple prisms  120  of which the first facet  130  and the second facet  140  have different angles (see  FIG. 1 ). 
     All the descriptions about the display  110 ′ and the prism array  100  in the first embodiment to the third embodiment can be applied to the floating hologram apparatus according to the fourth embodiment. 
     The filters for controlling a field of view  701  and  703  will be described in detail with reference to  FIG. 8A  and  FIG. 8B  (shown collectively as  FIGS. 8B ( 1 ) to  8 B( 5 )). Referring to  FIG. 8A , the filters for controlling a field of view  701  and  703  may include a bottom surface  801 , a top surface  803 , and multiple barriers  811  which are positioned between the bottom surface  801  and the top surface  803  and extended in a transverse direction when the observer watches the floating hologram apparatus. 
     The multiple barriers  811  are protruded from the bottom surface  801  toward the top surface  803  and may be arranged with space therebetween along a longitudinal direction when the observer watches the floating hologram apparatus. 
     If a height  805  of the multiple barriers  811  is P h  and a distance  807  between the multiple barriers  811  is P w , an angle  809  in which the rays pass the filters for controlling a field of view  701  and  703  is as shown in the following Equation 3. 
     
       
         
           
             
               
                 
                   ϕ 
                   = 
                   
                     2 
                     ⁢ 
                     
                       tan 
                       
                         - 
                         1 
                       
                     
                     ⁢ 
                     
                       
                         P 
                         w 
                       
                       
                         P 
                         h 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     Referring to  FIG. 8B  (shown collectively as  FIGS. 8B ( 1 ) to  8 B( 5 )), an angle in which the rays can be passed and an angle in which the rays can be blocked can be controlled by adjusting the height  805  and the distance  807  of the multiple barriers  811 . For example, in  FIG. 8B ( 3 ), a reference numeral  813  denotes a first arrangement of the barriers  811  which allows only the rays within a specific angle to pass through, and, thus, a stereoscopic image can be seen only from a specific direction. 
     Further, in  FIG. 8B ( 1 ), a reference numeral  815  denotes a second arrangement of the barriers  811  in which the barriers  811  are set to have a relatively great height, and, thus, an angle in which the rays can be passed can be controlled to be narrow. 
     Furthermore, in  FIG. 8B ( 5 ), a reference numeral  817  denotes a third arrangement of the barriers  811  in which the barriers  811  are set to have a small height, and, thus, an angle in which the rays can be passed can be controlled to be wide. Moreover, as indicated by reference numerals  819  and  821  in  FIG. 8(B) ( 2 ) and  FIG. 8(B) ( 4 ), the multiple barriers  811  may be set to have a great or small distance therebetween, and, thus, an angle in which the rays can be passed can be controlled to be wide or narrow. 
     Referring to  FIG. 7  again, in the floating hologram apparatus according to the fourth embodiment, the filters for controlling a field of view  701  and  703  are arranged between the display  110 ′ and the prism array  100 . For example, the filters for controlling a field of view  701  and  703  may include a first filter for controlling a field of view  701  that blocks a ray incident at an angle within a first range among rays of the first hologram image output from the first output area  110 - 3  and a second filter for controlling a field of view  703  that blocks a ray incident at an angle within a second range among rays of the second hologram image output from the second output area  110 - 4 . 
     In this case, the first filter for controlling a field of view  701  and the second filter for controlling a field of view  703  are provided slantly at a predetermined angle between the display  110 ′ and the prism array  100 . For example, the first filter for controlling a field of view  701  is provided such that its upper part is slanted toward the prism array  100  and the second filter for controlling a field of view  701  is provided such that its lower part is slanted toward the prism array  100 . 
     In the filters for controlling a field of view  701  and  703 , a predetermined angle to block the rays can be changed by adjusting at least one of the height and the distance of the multiple barriers  711 . For example, in the case where a first ray incident to the first filter for controlling a field of view  701  in a first direction is incident to the prism array  100  and refracted by the prism array  100 , a first stereoscopic image is generated behind the prism array  100 , but a second ray incident to the first filter for controlling a field of view  701  in a second direction is blocked by the first filter for controlling a field of view  701 , and, thus, a second stereoscopic image is not generated behind the prism array  100 . 
     For example, an upward ray among rays output in various directions from the point A of the display  110 ′ is incident to the first filter for controlling a field of view  701  at an angle of θ top  and blocked by the first filter for controlling a field of view  701 . On the other hand, a downward ray among the rays output in various directions from the point A is incident to the first filter for controlling a field of view  701  at an angle of θ bot  and passes through the first filter for controlling a field of view  701  and a stereoscopic image is generated behind the prism array  100 . 
     On the contrary, the second filter for controlling a field of view  703  may block the first ray incident in the first direction and allow the second ray incident in the second direction to pass through. 
     Therefore, since the filters for controlling a field of view  701  and  703  are provided slantly at a predetermined angle between the display  110 ′ and the prism array  100 , the pass angle  809  can be appropriately controlled. Therefore, the first filter for controlling a field of view  701  can block a ray which towards an upper part and the second filter for controlling a field of view  703  can block a ray which towards an lower part. 
     Thus, a large stereoscopic image can be seen in a wide field of view without any overlap between stereoscopic images. In this case, if an angle in which the rays pass is too small, angles of the rays incident to the prism array  100  become small, which results in a decrease of a vertical field of view of the entire system. Therefore, a pass angle for the filters for controlling a field of view  701  and  703  needs to be adjusted appropriately for characteristics of the system. 
     Fifth Embodiment 
     In the floating hologram apparatus according to the fourth embodiment, the filters for controlling a field of view  701  and  703  are provided slantly between the display  110 ′ and the prism array  100 , and, thus, a distance is formed between the display  110 ′ and the filters for controlling a field of view  701  and  703  and may cause deterioration in image quality. 
     A fifth embodiment is provided to solve the deterioration in image quality. 
       FIG. 9  is an exemplary diagram illustrating a floating hologram apparatus according to still another exemplary embodiment of the present disclosure. Referring to  FIG. 9 , a floating hologram apparatus according to the fifth embodiment may include the display  110 ′, the prism array  100 , and filters for controlling a field of view  901  and  902 . 
     The display  110 ′ may include the first output area  110 - 3  configured to output the first hologram image and the second output area  110 - 4  configured to output the second hologram image. 
     The prism array  100  may include the multiple prisms  120  of which the first facet  130  and the second facet  140  have different angles (see  FIG. 1 ). 
     All the descriptions about the display  110 ′ and the prism array  100  in the first embodiment to the third embodiment can be applied to the floating hologram apparatus according to the fifth embodiment. 
     The filters for controlling a field of view  901  and  902  are attached to the front of the display  110 ′. The filters for controlling a field of view  901  and  902  may include a first filter for controlling a field of view  901  that blocks a ray incident at an angle within a first range among rays of the first hologram image output from the first output area  110 - 3  and a second filter for controlling a field of view  902  that blocks a ray incident at an angle within a second range among rays of the second hologram image output from the second output area  110 - 4 . 
     The first filter for controlling a field of view  901  may be attached to the first output area  110 - 3  and the second filter for controlling a field of view  903  may be attached to the second output area  110 - 4 . 
     The filters for controlling a field of view  901  and  902  according to the fifth embodiment will be described with reference to  FIG. 10 . Referring to  FIG. 10 , the filters for controlling a field of view  901  and  902  may include a bottom surface  1001 , a top surface  1003 , and multiple barriers  1013  which are positioned between the bottom surface  1001  and the top surface  1003  and extended in a transverse direction when the observer watches the floating hologram apparatus. The multiple barriers  1013  are protruded slantly at a predetermined angle θ P  and may be arranged with space therebetween along a longitudinal direction when the observer watches the floating hologram apparatus. 
     Since the multiple barriers  1013  are arranged as slanted, only the rays approximately parallel to the respective barriers  1013  can pass through the filters for controlling a field of view  901  and  902 . 
     If a distance  1007  between the multiple barriers  1013  is P w  and a height  1005  of the multiple barriers  1013  is P h  and a slant angle  1011  of the barriers  1013  is θ P , an angle  809  in which the rays pass the filters for controlling a field of view  901  and  902  is as shown in the following Equation 4. 
     
       
         
           
             
               
                 
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                   [ 
                   
                     Equation 
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                     4 
                   
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     Therefore, an output direction and a pass angle of the rays can be controlled by adjusting the height, the distance, and the angle (the degree of slant of the barriers  1013 ) of the multiple barriers  1013 . 
     The filters for controlling a field of view  901  and  902  may be configured to control a predetermined angle in which the rays can be blocked by the filters for controlling a field of view  901  and  902  by changing at least one of the height, the distance, and the angle of the multiple barriers  1013 . 
     Referring to  FIG. 9  again, the multiple barriers  1013  of the first filter for controlling a field of view  901  are configured to be slanted toward a lower part of the display  110 ′. A first ray incident in a first direction (upward direction) among rays output from the point A of the first output area  110 - 3  cannot pass through the first filter for controlling a field of view  901  and thus is blocked, and a second ray incident in a second direction (downward direction) among the rays output from the point A can pass through the first filter for controlling a field of view  901 . 
     The multiple barriers  1013  of the second filter for controlling a field of view  902  are configured to be slanted toward an upper part of the display  110 ′. A first ray incident in a first direction (upward direction) among rays output from the point B of the second output area  110 - 4  can pass through the second filter for controlling a field of view  902 , and a second ray incident in a second direction (downward direction) among the rays output from the point B cannot pass through the second filter for controlling a field of view  902  and thus is blocked. 
     Therefore, only the ray which towards a lower part among the rays output from the first output area  110 - 3  of the display  110 ′ can be passed and only the ray which towards a upper part among the rays output from the second output area  110 - 4  of the display  110 ′ can be passed and proceed toward the observer. 
     An image can be seen as projected on space corresponding to a distance depending on a path difference between two rays. Thus, a large space image can be seen in a wide field of view without any image noise. In this case, if a pass angle of rays is too small, angles of the rays incident to the prism array  100  become small, which results in a decrease of a vertical field of view of the floating hologram apparatus. Therefore, a pass angle for the filters for controlling a field of view  901  and  902  needs to be adjusted appropriately for characteristics of the floating hologram apparatus. 
     Sixth Embodiment 
       FIG. 11  is an exemplary diagram illustrating a floating hologram apparatus according to still another exemplary embodiment of the present disclosure. Referring to  FIG. 11 , a floating hologram apparatus according to a sixth embodiment may include the display  110 ′ and the prism array  100 . 
     The display  110 ′ may include the first output area  110 - 3  configured to output the first hologram image and the second output area  110 - 4  configured to output the second hologram image. 
     The prism array  100  may include the multiple prisms  120  of which the first facet  130  and the second facet  140  have different angles (see  FIG. 1 ). 
     All the descriptions about the display  110 ′ and the prism array  100  in the first embodiment to the third embodiment can be applied to the floating hologram apparatus according to the sixth embodiment. 
     A first-type polarizing film  1101  may be attached to the first output area  110 - 3  of the display  110 ′ and a second-type polarizing film  1103  may be attached to the second output area  110 - 4 . Herein, the first-type polarizing film  1101  and the second-type polarizing film  1103  may have polarized light property orthogonal to each other. For example, the first-type polarizing film  1101  may have vertical polarized light property, and the second-type polarizing film  1103  may have horizontal polarized light property. 
     Otherwise, linearly polarized rays having angles orthogonal to each other may be used. Alternatively, a left circularly polarized ray and a right circularly polarized ray may be used using a quarter-wave plate with a circular polarizing filter or a linear polarizing filter at the same time. 
     The second-type polarizing film  1103  may be attached to the first facet  130  of the prism array  100  and the first-type polarizing film  1101  may be attached to the second facet  140 . 
     Therefore, rays of the first hologram image output from the first output area  110 - 3  may have the same polarized light property as the first-type polarizing film  1101  attached to the second facet  140  of the prism array  100 . Further, rays of the second hologram image output from the second output area  110 - 4  may have the same polarized light property as the second-type polarizing film  1103  attached to the first facet  130  of the prism array  100 . 
     Therefore, the first hologram image output from the first output area  110 - 3  of the display  110 ′ can be seen by the observer only through the second facet  140  of each prism of the prism array  100 . Meanwhile, the second hologram image output from the second output area  110 - 4  of the display  110 ′ can be seen by the observer only through the first facet  130  of each prism of the prism array  100 . 
     In the floating hologram apparatus using polarized light property according to the sixth embodiment, the polarized light property of the display  110 ′ needs to be considered in order to improve the light efficiency. If the display  110 ′ does not have polarized light property, the polarizing films  1101  and  1103  crossing to each other may be attached to the front of the display  110 ′ and the polarizing films  1101  and  1103  crossing to each other may also be attached to the prism array  100 . 
     If the display  110 ′ already has polarized light property, it is desirable to use its polarized light property in order not to reduce the light efficiency. That is, if the display  110 ′ has linear polarized light property in a specific direction, a polarizing film may not be attached to the first output area  110 - 3  of the display  110 ′ and a third-type polarizing film capable of rotating and changing the linear polarized light of the display  110 ′ in a specific direction may be attached to the second facet  140  of the prism array  100 . 
     A half wave plate may be attached to the second output area  110 - 4  of the display  110 ′ to turn a polarized light direction to 90° and a fourth-type polarizing film corresponding thereto may be attached to the first facet  130  of the prism array  100 . 
     Further, according to polarized light property, a quarter wave plate may be arranged in front of the display  110 ′ to show a left circularly polarized light and a right circularly polarized light, and a left circularly polarizing film and a right circularly polarizing film may be further attached to each prism surface of the prism array  100 . 
     If the display  110 ′ has circular polarized light property, the above descriptions may be applied after changing the circular polarized light to linear polarized light or reversing the direction of the circular polarized light. Further, the polarizing film attached to the prism array  100  may be attached to the back of the prism array  100 , i.e., a surface facing the display  110 ′, to separate the first hologram image and the second hologram image. Further, multiplexing using a liquid crystal or the like can also be employed for changing polarized light. 
     Seventh Embodiment 
       FIG. 12  is an exemplary diagram illustrating a floating hologram apparatus according to still another exemplary embodiment of the present disclosure. A floating hologram apparatus according to a seventh embodiment may include the display  110 ′ and the prism array  100 . 
     The display  110 ′ may include the first output area  110 - 3  configured to output the first hologram image and the second output area  110 - 4  configured to output the second hologram image. 
     The prism array  100  may include the multiple prisms  120  of which the first facet  130  and the second facet  140  have different angles (see  FIG. 1 ). 
     All the descriptions about the display  110 ′ and the prism array  100  in the first embodiment to the third embodiment can be applied to the floating hologram apparatus according to the seventh embodiment. 
     The display  110 ′ includes a first input shutter  1201  attached to the front of the first output area  110 - 3  and a second input shutter  1203  attached to the front of the second output area  110 - 4 . The prism array  100  includes a first output shutter  1205  attached to an upper part of each prism and a second output shutter  1207  attached to a lower part of each prism. The first output shutter  1205  and the second output shutter  1207  of the prism array may be provided on the front of the prism array  100 . 
     The first input shutter  1201  and the second input shutter  1203  are turned on/off alternately. Further, the first output shutter  1205  and the second output shutter  1207  are also turned on/off alternately. 
     The first input shutter  1201 , the second input shutter  1203 , the first output shutter  1205 , and the second output shutter  1207  may be synchronized with each other according to predetermined rules. 
     For example, the first input shutter  1201  and the second output shutter  1207  may be turned on simultaneously and the second input shutter  1203  and the first output shutter  1205  may be turned off during a first cycle. In this case, the first hologram image output from the first output area  110 - 3  of the display  110 ′ passes only through the second facet  140  of each prism and is refracted toward the observer. 
     During a second cycle, the second input shutter  1203  and the first output shutter  1205  may be turned on simultaneously and the first input shutter  1201  and the second output shutter  1207  may be turned off. In this case, the second hologram image output from the second output area  110 - 4  of the display  110 ′ passes only through the first facet  130  of each prism and is refracted toward the observer. 
     If turning on/off of the shutters during the first cycle and the second cycle are performed at 60 frames per second (30 frames each) or higher frames per second, the first hologram image can be provided with the second hologram image to the observer without the flicker of image. 
     The above description of the present disclosure is provided for the purpose of illustration, and it would be understood by those skilled in the art that various changes and modifications may be made without changing technical conception and essential features of the present disclosure. Thus, it is clear that the above-described embodiments are illustrative in all aspects and do not limit the present disclosure. For example, each component described to be of a single type can be implemented in a distributed manner. Likewise, components described to be distributed can be implemented in a combined manner. 
     The scope of the present disclosure is defined by the following claims rather than by the detailed description of the embodiment. It shall be understood that all modifications and embodiments conceived from the meaning and scope of the claims and their equivalents are included in the scope of the present disclosure.