Patent Publication Number: US-2022223824-A1

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0003423, filed on Jan. 11, 2021; the Korean Patent Application is incorporated by reference. 
     BACKGROUND 
     1. Field 
     The technical field relates to a display device. 
     2. Discussion of the Background 
     A display device may display images according to input signals. Modern display devices include liquid crystal display devices, organic light emitting display devices, and plasma display devices. 
     A display device may display an image to be viewed by multiple users at the same time. Accordingly, the display device is required to display the image with a wide viewing angle. 
     A display device may be used in a public space. For example, a display device of a mobile phone may be used in public transportation, and a display device of an automatic teller machine may be located outside a bank. In order to protect private information, the user of the display device may need to at least partially block a displayed image from being viewed by others. 
     The Background section is for understanding of the background of the patent application. The Background section may contain information that does not constitute prior art. 
     SUMMARY 
     Some embodiments may be related to a display device capable of selectively controlling a viewing angle. 
     An embodiment may be related to a display device. The display device may include a substrate, a first set of light emitting structures, a second set of light emitting structures, a diffraction layer, and a refraction pattern. The substrate may include a first region and a second region. The first set of light emitting structures may overlap the first region. The second set of light emitting structures may overlap the second region. The diffraction layer may overlap the first region without overlapping the second region. The refraction pattern may overlap the diffraction layer. The diffraction layer may include first-refractive-index members and second-refractive-index members that are alternately disposed. A refractive index of each of the first-refractive-index members is lower than a refractive index of each of the second-refractive-index members. 
     In a first viewing angle mode, each of the first set of light emitting structures and the second set of light emitting structures may brighten. In a second viewing angle mode, the first set of light emitting structures may emit light, and the second set of light emitting structures may emit no light. 
     The display device may include an intermediate layer disposed between the refraction pattern and the diffraction layer and overlapping at least the first region. 
     The display device may include a material member completely overlapping a face the second region. The material member may have only one refractive index. The refractive index of the material member may be equal to the refractive index of the second-refractive index members. A first face of the diffraction layer may be positioned between the substrate and a second face of the diffraction layer. A first face of the material member may be positioned between the substrate and a second face of the material member and may be positioned not farther from the substrate than the first face of the diffraction layer is. The second face of the material member may be positioned not closer to the substrate than the second face of the diffraction layer is. 
     The second-refractive-index members and the refraction pattern may be formed of a same material. 
     The refractive index of each of the second-refractive index members and a refractive index of the refraction pattern may be in a range of 1.5 to 1.8. 
     The display device may include a first medium layer disposed between the first set of light emitting structures and the diffraction layer. The first medium layer and the first-refractive-index members may be formed of a same material. 
     The display device may include a second medium layer disposed directly on the refraction pattern. The second medium layer and the first-refractive-index members may be formed of a same material. 
     A thickness of the diffraction layer in a direction perpendicular to the substrate may be 1 μm or less. 
     A cross section of each of the second-refractive-index members may have a quadrangle shape. 
     A pitch of the second-refractive-index members may be in a range of 0.25 μm to 1 μm. 
     Pitches of the second-refraction-index members may have different values. 
     The refraction pattern may include a refraction member. A cross section of the refraction member may have a triangle shape. 
     Widths of two faces of the refraction member may be unequal to each other. 
     The refraction pattern may include a refraction member. A cross section of the refraction member may have a lenticular shape. 
     The refraction pattern may include refraction members arranged in parallel. Two of the refraction members may directly contact each other. 
     An embodiment may be related to a display device. The display device may include the following elements: a first set of light emitting structures; a second set of light emitting structures neighboring the first set of light emitting structures; a diffraction layer disposed on the first set of light emitting structures and not on the second set of light emitting structures; and a refraction pattern disposed on the diffraction layer and refracting light that has passed through the diffraction layer toward a direction that is perpendicular to the diffraction layer. 
     A first set of discrete members of the diffraction layer and the refraction pattern may be formed of a same material. 
     The display device may include the following elements: a first medium layer disposed between the first set of light emitting structures and the diffraction layer; and a second medium layer disposed directly on the refraction pattern. Each of a refractive index of the diffraction layer and a refractive index of the refractive pattern may be greater than each of a refractive index of the first medium layer and a refractive index of the second medium layer. 
     In a first viewing angle mode, each of the first set of light emitting structures and the second set of light emitting structures may brighten. In a second viewing angle mode, the first set of light emitting structures may emit light, and the second set of light emitting structures may emit no light. 
     The diffraction layer diffracts light emitted by the light emitting structure and having a large incidence angle. The refraction pattern refracts the diffracted light toward the front direction, thereby reducing the viewing angle of the display device. 
     The diffraction layer and the refraction pattern may be selectively disposed on the first region of the display device and may not be disposed on the second region. In the first viewing angle mode, both the first light emitting structure disposed on the first region and the second light emitting structure disposed on the second region may emit light. In the second viewing angle mode, only the first light emitting structure disposed in the first region may emit light. Advantageously, the user of the display device may control the viewing angle of the display device by selecting one of the first viewing angle mode and the second viewing angle mode. The user may view an image having a wide viewing angle or a narrow viewing angle depending on the environment without a separate device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating a display device according to embodiments. 
         FIG. 2  is a cross-sectional view illustrating the display device of  FIG. 1  according to embodiments. 
         FIG. 3  is a diagram for describing the display device of  FIG. 2  in a first viewing angle mode according to embodiments. 
         FIG. 4  is a diagram for describing the display device of  FIG. 2  in a second viewing angle mode according to embodiments. 
         FIG. 5  is a cross-sectional view illustrating a display device according to embodiments. 
         FIG. 6  is a cross-sectional view illustrating a display device according to embodiments. 
         FIG. 7  is a cross-sectional view illustrating a display device according to embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Illustrative embodiments are described with reference to the accompanying drawings. 
     Although the terms “first,” “second,” etc. may be used to describe various elements, these elements should not be limited by these terms. These terms may be used to distinguish one element from another element. A first element may be termed a second element without departing from teachings of one or more embodiments. The description of an element as a “first” element may not require or imply the presence of a second element or other elements. The terms “first,” “second,” etc. may be used to differentiate different categories or sets of elements. For conciseness, the terms “first,” “second,” etc. may represent “first-category (or first-set),” “second-category (or second-set),” etc., respectively. 
     The term “connected” may mean “electrically connected” or “electrically connected through no intervening transistor.” The term “insulate” may mean “electrically insulate” or “electrically isolate.” The term “conductive” may mean “electrically conductive.” The term “include” may mean “be formed of” or “be made of.” The term “pattern” may mean “member” or “layer.” The term “the same as” may mean “equal to.” The term “different” may mean “unequal.” The term “drive” may mean “operate” or “control.” The term “on” may encompass “directly on” and/or “indirectly on.” 
       FIG. 1  is a plan view illustrating a display device  10  according to embodiments. 
     Referring to  FIG. 1 , the display device  10  may include a display area DA and a non-display area NDA. The display area DA may include pixels PX that are substantially arranged in a matrix form. Each of the pixels PX may display one predetermined basic color. One pixel may be a minimum unit capable of displaying a color independently of other pixels. Each of the pixels PX may display a first color, a second color, or a third color. For example, the first color, the second color, and the third color may be red, green, and blue, respectively. 
     Each first region A 1  of the display device  10  may include a predetermined number of pixels PX, e.g., four pixels PX adjacent to each other. For example, the four pixels may include one red pixel, two green pixels, and one blue pixel. Each second area A 2  of the display device  10  may be immediately adjacent to at least one first region A 1 . A predetermined number of pixels PX, e.g., four pixels PX, adjacent to each other may be disposed in each second region A 2 . First regions A 1  and second regions A 2  may be alternately disposed. First regions A 1  may be disposed in odd rows, and second regions A 2  may be disposed in even rows. First regions A 1  may be disposed in odd columns, and second regions A 2  may be disposed in even columns. First regions A 1  and second regions A 2  may be irregularly arranged. A first region A 1  and/or a second region A 2  may have a rectangular shape in the plan view. A first region A 1  and/or a second region A 2  may have one or more of various shapes, such as a rhombus. 
       FIG. 2  is a cross-sectional view illustrating the display device  10  of  FIG. 1  according to embodiments. 
     Referring to  FIG. 2 , the display device  10  may include a substrate  100 , a circuit layer  200 , light emitting structures  300 , a pixel-defining layer PDL, an encapsulation layer  400 , a material member  630 , a first medium layer  610 , a second medium layer  620 , and a viewing angle control structure  500 . 
     The substrate  100  may be a glass substrate, a quartz substrate, a plastic substrate, or the like. When the substrate  100  is a plastic substrate, the substrate  100  may be flexible, bendable, or rollable. When the substrate  100  is a plastic substrate, the substrate  100  may include at least one polymer resin; the substrate  100  may include two polymer resin layers and an inorganic material barrier layer disposed between the polymer resin layers. The substrate  100  may have a single layer structure or a multilayer structure. The substrate  100  may include regions A 1  and A 2  respectively corresponding to the regions A 1  and A 2  of the display device  10 . 
     The circuit layer  200  may be disposed on the substrate  100 . The circuit layer  200  may include at least one transistor and at least one capacitor. The circuit layer  200  may include at least one semiconductor layer, at least one conductive layer, and at least one insulating layer. The circuit layer  200  may provide signals and voltages to the light emitting structures  300 . 
     The pixel defining-layer PDL may be disposed on the circuit layer  200 . 
     The light emitting structures  300  may be disposed on the circuit layer  200 . Each of the light emitting structures  300  may include a first electrode  310  electrically connected to the circuit layer  200  and substantially exposed by the pixel-defining layer PDL, a light-emitting part  330  disposed on the exposed portion of the first electrode  310 , and a portion of a second electrode  350  disposed on the light-emitting part  330 . The first electrode  310  may be an anode electrode, and the second electrode  350  may be a cathode electrode. The light-emitting part  330  may be a single layer or may include functional layers. For example, the light-emitting part  330  may include a hole injection layer, a hole transport layer, an emission layer, an electron transport layer, and an electron injection layer. 
     The light emitting structures  300  may include a first light emitting structure LES 1  disposed in the first region A 1  and may include a second light emitting structure LES 2  disposed in the second region A 2 . The first light emitting structure LES 1  and the second light emitting structure LES 2  may receive different signals and different voltages according to the first region A 1  and the second region A 2 . Accordingly, the first light emitting structure LES 1  and the second light emitting structure LES 2  may emit light independently. Accordingly, a first viewing angle mode MOD 1  and a second viewing angle mode MOD 2  may be enabled. 
     The encapsulation layer  400  may be disposed on the light emitting structures  300 . The encapsulation layer  400  may include at least one inorganic layer (for blocking moisture and oxygen) and at least one organic layer (for providing desirably mechanical properties). For example, the encapsulation layer  400  may include a first inorganic layer, an organic layer disposed on the first inorganic layer, and a second inorganic layer disposed on the organic layer. 
     The first medium layer  610  may overlap the first region A 1  of the substrate  100  and may be disposed on the encapsulation layer  400 . The first medium layer  610  may not overlap the second region A 2  of the substrate  100  in a direction perpendicular to the substrate  100 . The first medium layer  610  may be disposed in the first region A 1  of the display device  10  and may not be disposed in the second region A 2  of the display device  10 . A refractive index of the first medium layer  610  may be about 1.5 or less. The first medium layer  610  may include acrylate. The refractive index of the first medium layer  610  may be less than one or more of a refractive index of a diffraction layer  510 , a refractive index of an intermediate layer  530 , and a refractive index of a refractive pattern  550 . 
     The viewing angle control structure  500  may be disposed on the first medium layer  610 . The viewing angle control structure  500  may overlap with the first region A 1  of the substrate  100  and may not overlap with the second region A 2  of the substrate  100  in a direction perpendicular to the substrate  100 . The viewing angle control structure  500  may be disposed in the first region A 1  of the display device  10  and may not be disposed in the second region A 2  of the display device  10 . The viewing angle control structure may include the diffraction layer  510 , the intermediate layer  530 , and the refraction pattern  550 . 
     The diffraction layer  510  may include a plurality of high refractive index patterns/members  511  and a plurality of low refractive index patterns/members  512 . The high refractive index patterns  511  and the low refractive index patterns  512  may be alternately disposed. The diffraction layer  510  may change a path of light received from the first light emitting structure LES 1  through diffraction. 
     A refractive index of each of the high refractive index patterns  511  may be greater than a refractive index of each of the low refractive index patterns  512 . The refractive index of each of the high refractive index patterns  511  may be in a range of about 1.5 to about 1.8, and the refractive index of each of the low refractive index patterns  512  may be about 1.5 or less. The high refractive index patterns  511  may include polyethylene naphthalate. The low refractive index patterns  512  may include acrylate. The first medium layer  610  and the low refractive index patterns  512  may include the same material. The first medium layer  610  and the low refractive index patterns  512  may have substantially the same refractive index. The high refractive index patterns  511  and the low refractive index patterns  512  may not significantly block light. 
     A thickness of the high refractive index patterns  511  in a direction perpendicular to the substrate  100  may be about 1 μm or less. A pitch P 1  of the high refractive index patterns  511  may be substantially constant. A width of each of the high refractive index patterns  511  may be substantially constant. A width of each of the low refractive index patterns  512  may be substantially constant. The pitch P 1  of the high refractive index patterns  511  may be in a range of about 0.25 μm to about 1 μm. The pitch P 1  of the high refractive index patterns  511  may be in a range of about 0.5 μml (or 500 nm) to about 0.8 μml (or 800 nm). A wavelength of visible light is about 400 nm to about 700 nm. A value obtained by dividing the wavelength of visible light by the pitch P 1  of the high refractive index patterns  511  may be in a range of about 0.75 to about 1.5. Accordingly, the diffraction layer  510  may effectively direct a path of light received from the first light emitting structure LES 1  to a front direction DF (shown in  FIG. 3 ) through diffraction. The front direction DF is perpendicular to the substrate  100 . 
     A cross section of each of the high refractive index patterns  511  may have a quadrangle shape. The cross section of each of the high refractive index patterns  511  may have one or more of various shapes. 
     The intermediate layer  530  may be disposed on the diffraction layer  510 . A refractive index of the intermediate layer  530  may be the same as a refractive index of the high refractive index patterns  511 . The refractive index of the intermediate layer  530  may be in a range of about 1.5 to about 1.8. The intermediate layer  530  and the high refractive index patterns  511  may include the same material. The intermediate layer  530  and the high refractive index patterns  511  may be directly connected to each other. The intermediate layer  530  may include polyethylene naphthalate. The refractive index of the intermediate layer  530  may be greater than the refractive index of the low refractive index patterns  512 . The diffraction layer  510  and the refraction patterns  550  may overlap the first region A 1  of the substrate  100  and may not overlap the second region A 2  of the substrate  100 . The intermediate layer  530  may or may not overlap the second region A 2 . The portion of the intermediate layer  530  overlapping the second region A 2  may be substantially flat. Light emitted from the second light emitting structure LES 2  may be insignificantly refracted at an entry interface of the intermediate layer  530  and may be insignificantly refracted at an exit interface of the intermediate later  530 . A viewing angle of light emitted by the second light emitting structure LES 2  may not be substantially changed. A thickness of the intermediate layer  530  may be configured according to embodiments. 
     The refraction pattern  550  may be disposed on the intermediate layer  530 . The refraction pattern/layer  550  may overlap the diffraction layer  510 . The refraction pattern  550  may include refraction parts/members  551  and  552  arranged in parallel. The refraction parts  551  and  552  may contact each other. A refractive index of the refraction pattern  550  may be the same as a refractive index of the high refractive index patterns  511 . The refractive index of the refraction pattern  550  may be in a range of about 1.5 to about 1.8. The refraction pattern  550  and the high refractive index patterns  511  may include the same material. The refractive index of the refraction pattern  550  may be greater than the refractive index of the low refractive index patterns  512 . The refraction pattern  550 , the intermediate layer  530 , and the high refractive index patterns  511  may include the same material. For example, the refraction pattern  550 , the intermediate layer  530 , and the high refractive index patterns  511  may all include polyethylene naphthalate. The refraction pattern  550  may change a path of light received from the diffraction layer  510  through refraction. 
     Cross sections of the refraction parts  551  and  552  may have triangle shapes/structures. For example, the cross section of each of the refraction parts  551  and  552  may have an isosceles triangle shape. The cross sections of the refraction parts  551  and  552  may have one or more of various shapes. Thicknesses of the refraction parts  551  and  552  and widths of the refraction parts  551  and  552  may be configured according to embodiments. Each of the refraction parts  551  and  552  may overlap about 5 or about 6 the high refractive index patterns  511 . 
     The second medium layer  620  may be disposed on the viewing angle control structure  500  in the first region A 1  of the display device  10 , and may be disposed on the encapsulation layer  400  in the second region A 2  of the display device  10 . The second medium layer  620  may overlap both the first region A 1  and the second region A 2  of the substrate  100 . The second medium layer  620  may overlap the first region A 1  but not the second region A 2  of the substrate  100 . A refractive index of the second medium layer  620  may be about 1.5 or less. The refractive index of the second medium layer  620  may be less than the refractive index of the viewing angle control structure  500 . The refractive index of the second medium layer  620  and the refractive index of the first medium layer  610  may be the same. The second medium layer  620  and the first medium layer  610  may include the same material. The second medium layer  620  may include acrylate. Each of the first medium layer  610 , the low refractive index patterns  512 , and the second medium layer  620  may include acrylate. Each of the high refractive index patterns  511 , the intermediate layer  530 , and the refraction pattern  550  may include polyethylene naphthalate. 
     The material member  630  may completely overlap a top/bottom face of the second region A 2  of the substrate  100  and may have only one refractive index. The bottom face of the material member  630  may not be positioned farther from the substrate  100  than the bottom face of the diffraction layer  510  is. The top face of the material member  630  may not be positioned closer to the substrate  100  than the top face of the diffraction layer  510  is. The refractive index of the material member  630  may be lower than the refractive index of the high refractive index patterns  511  and may be equal to the refractive index of the first medium layer  610 , the low refractive index patterns  512 , and the second medium layer  620 . The material member may include acrylate. 
     The display device  10  includes the viewing angle control structure  500  selectively disposed on the first region A 1 , so that an emission angle of light emitted from the first light emitting structure LES 1  may be reduced with reference the front direction DF (shown in  FIG. 3 ). A path of light emitted by the first light emitting structure LES 1  may be adjusted toward/to the front direction DF rather than a side direction. 
       FIG. 3  is a diagram for describing the display device of  FIG. 2  in a first viewing angle mode according to embodiments. The first viewing angle mode MOD 1  may be a wide viewing angle mode. 
     Referring to  FIG. 3 , both the first light emitting structure LES 1  disposed in the first region A 1  of the display device and the second light emitting structure LES 2  disposed in the second region A 2  of the display device may emit light in the first viewing angle mode MOD 1 . 
     Light emitted from the first light emitting structure LES 1  and input to the viewing angle control structure  500  may be called incident light IL. The light resulted from the incident light IL and outputted from the viewing angle control structure  500  may be called outgoing light OL. An acute angle formed by a direction D 1  of the incident light IL and the front direction DF may be called an incident angle IA. An acute angle formed by a direction D 2  of the outgoing light OL and the front direction DF may be called the emission angle. 
     When the pitch P 1  of the high refractive index patterns  511  is about 0.8 μm, due to the viewing angle control structure  500 , an incident light IL having the incident angle IA of about 20° may be changed to an outgoing light OL having an emission angle OA of about 9°. An incident light IL having the incident angle IA of about 30° may be changed to an outgoing light OL having the emission angle OA of about 25°. The emission angle OA may be smaller than the incident angle IA. Accordingly, an image displayed in the first region A 1  may provide a narrow viewing angle to a user of the display device  10 . 
     Since a path of light emitted by the second light emitting structure LES 2  is not substantially changed, the image displayed in the second region A 2  may provide a wide viewing angle to the user of the display device  10 . 
     The first viewing angle mode MOD 1  may be a normal mode, and in the first viewing angle mode MOD 1 , both the first light emitting structure LES 1  and the second light emitting structure LES 2  may display colors. 
     Accordingly, in the first viewing angle mode MOD 1 , the display device  10  may provide an image with a relatively wide viewing angle. In the first viewing angle mode MOD 1 , a user of the display device  10  may view an image provided by the display device  10  not only from the front of the display device  10  but also when not overlapping the display device  10 . 
       FIG. 4  is a diagram for describing the display device of  FIG. 2  in a second viewing angle mode according to embodiments. The second viewing angle mode MOD 2  may be a narrow viewing angle mode. 
     Referring to  FIG. 4 , the first light emitting structure LES 1  (disposed in the first region A 1  of the display device  10 ) may emit light in the second viewing angle mode MOD 2 . 
     Light emitted from the first light emitting structure LES 1  and inputted to the viewing angle control structure  500  may be called incident light IL. The light resulted from the incident light IL and outputted from the viewing angle control structure  500  may be called outgoing light OL. An acute angle formed by a direction D 1  of the incident light IL and the front direction DF may be called an incident angle IA. An acute angle formed by a direction D 2  of the outgoing light OL and the front direction DF may be called the emission angle. 
     When the pitch P 1  of the high refractive index patterns  511  is about 0.8 μm, due to the viewing angle control structure  500 , an incident light having the incident angle IA of about 20° may be changed to an outgoing light OL having an emission angle OA of about 9°. An incident light IL having the incident angle IA of about 30° may be changed to an outgoing light OL having the emission angle OA of about 25°. The emission angle OA may be smaller than the incident angle IA. Accordingly, an image displayed in the first region A 1  may provide a narrow viewing angle to a user of the display device  10 . 
     In the second viewing angle mode MOD 2 , only the first light emitting structure LES 1  disposed in the first region A 1  may emit light. The second light emitting structure LES 2  may not emit light. 
     The second viewing angle mode MOD 2  may be a private mode. In the second viewing angle mode MOD 2 , only the first light emitting structure LES 1  may display colors; the second light emitting structure LES 2  may not display colors. Accordingly, in the second viewing angle mode MOD 2 , the display device  10  may provide an image with a relatively narrow viewing angle. In the second viewing angle mode MOD 2 , a user of the display device  10  may view an image provided by the display device  10  from the front of the display device  10 . In the second viewing angle mode MOD 2 , the user of the display device  10  may not clearly see an image provided by the display device  10  when the user does not overlap the display device  10  and does not view the image in the front direction DF. 
     Referring to  FIGS. 3 and 4 , the display device  10  may be selectively driven in one of the first viewing angle mode MOD 1  and the second viewing angle mode MOD 2 . The user of the display device  10  may actively adjust the viewing angle according to the environment. For example, when being near no other persons, or when viewing an image that can be viewed by others, the user of the display device  10  may select the first viewing angle mode MOD 1  to view the image at a wide viewing angle. When there is another person around, or when viewing an image that should not be viewed by others, the user of the display device  10  may select the second viewing angle mode MOD 2  to view the image at a narrow viewing angle. 
       FIG. 5  is a cross-sectional view illustrating a display device  10  according to embodiments. 
     Referring to  FIG. 5 , lengths/widths of two (non-hypotenuse) sides/faces S 1  and S 1  of a refraction part  551 / 552  that are not parallel to the substrate  100  and/or to the layer  530  may be different. Lengths/widths of two sides/faces of a refraction part  551 / 552  at boundaries between the refraction pattern  550  and the second medium layer  620  may be different. Accordingly, among the light passing through the diffraction layer  510 , an emission angle of an outgoing light that is outputted from the first side/face S 1  may be different from an emission angle of an outgoing light that is outputted from the second side/face S 2 . The outgoing light that outputted from the first side/face S 1  and the outgoing light that is outputted from the second side/face S 2  may still be directed toward the front direction DF. The user may watch the image in the front direction DF, but may not clearly see the image when not viewing the image in the front direction DF. Although the lengths/widths of the two sides/faces S 1  and S 2  of the refraction pattern  550  are different, because of at least the diffraction performed by the diffraction layer  510  and the refraction performed by the refraction pattern  550 , the display device  10  may provide a narrow viewing angle. In the second viewing angle mode MOD 2 , nearby people who do not overlap the display device  10  and do not view the image in the front direction DF cannot clearly see the image. 
       FIG. 6  is a cross-sectional view illustrating a display device  10  according to embodiments. 
     Referring to  FIG. 6 , a cross section of the refraction pattern  550  may have a convex lenticular shape. The lenticular shape may be substantially semi-circular or semi-elliptical. Outgoing lights exiting the refraction pattern  550  be directed toward the front direction in many different angles. In the second mode MOD 2 , a user viewing the image displayed by the display device  10  in the front direction DF may smoothly recognize the image, and people not viewing the image in the front direction DF may not clearly see the image. 
       FIG. 7  is a cross-sectional view illustrating a display device  10  according to embodiments. 
     Referring to  FIG. 7 , pitches P 1 , P 2 , and P 3  of the high refraction index patterns  511  may have different values. For this reason, the degrees to which the diffraction layer  510  diffracts light may vary, such that outgoing lights having different degrees of diffraction may overlap each other. In the second viewing angle mode MOD 2 , a user viewing an image displayed by the display device  10  in the front direction DF can smoothly recognize the image, and people not viewing the image in the front direction DF may not clearly see the image. 
     Although illustrative embodiments have been described, various embodiments, arrangements, and modifications are practical. Practical embodiments are within the scope of the appended claims.