Patent Publication Number: US-2020278548-A1

Title: Optical device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0023931 filed on Feb. 28, 2019, in the Korean Intellectual Property Office, the contents of which in their entirety are herein incorporated by reference. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to an optical device. 
     2. Description of the Related Art 
     Augmented reality is a technique of superimposing a virtual image on a real image viewed by a user&#39;s eyes and displaying the superimposed images as a single image. The virtual image may be an image in the form of text or graphics, and the real image may be information about an actual object observed in the field of view (FOV) of a device. 
     Augmented reality may be implemented using a head mounted display (HMD), a head-up display (HUD), or the like. When augmented reality is implemented using the head mounted display, it may be provided in the form of glasses so that the user can carry it easily, as well as put on or take off easily. 
     However, when augmented reality is implemented using an eye glass-type (or glasses-type) display device, a distance between a display device for displaying a virtual image and a reflector for reflecting an image from the display device and providing it to a user&#39;s eyes is small. A depth of field of the virtual image displayed by the display device may be proportional to an optical distance between the display device and the reflector. 
     SUMMARY 
     Aspects of embodiments of the present disclosure provide an optical device capable of increasing an optical distance between a display device, which displays a virtual image, and a reflector, which reflects an image from the display device, to provide the virtual image to a user&#39;s eye. 
     However, aspects of the present disclosure are not restricted to the one set forth herein. The above and other aspects of embodiments of the present disclosure will become more apparent to one of ordinary skill in the art to which the present disclosure pertains by referencing the detailed description of the present disclosure given below. 
     One or more example embodiments of the present disclosure provide an optical device including: a lens including a first surface and a plurality of side surfaces; a display device on a first side surface from among the plurality of side surfaces, the display device being configured to provide light to the first side surface; and a first reflector in the lens and configured to reflect the light provided by the display device after the light is reflected from a second side surface from among the plurality of side surfaces to the first surface. 
     The light provided by the display device may be reflected by a third side surface from among the plurality of side surfaces to travel toward a fourth side surface from among the plurality of side surfaces, and may be reflected by the fourth side surface to travel toward the second side surface. The third side surface may extend from a first side of the first side surface and the fourth side surface may be between the second side surface and the third side surface. 
     The optical device may further include an optical path changing member between the first side surface and the display device. The optical path changing member may be configured to change a path of the light provided by the display device such that the light provided by the display device travels toward the third side surface. 
     The optical path changing member may include: a base layer; a first light exit surface inclined at a first angle from the base layer; and a second light exit surface at a second angle from the base layer, wherein the first angle is less than the second angle. 
     The optical device may further include a polarizing film between the first side surface and the optical path changing member. 
     The optical device may further include a reflective sheet on the second side surface, the third side surface and the fourth side surface. 
     The first side surface may have a curved shape, and the display device may have a bent shape on the first side surface. 
     The optical device may further include a second reflector in the lens that is configured to reflect the light provided by the display device after the light is reflected from the second side surface to the first surface. 
     The first side surface and the second side surface may face away from each other. 
     The optical device may further include a reflective sheet on the second side surface of the lens. 
     The second side surface may be curved outwardly, and the reflective sheet may have a bent shape on the second side surface. 
     The second side surface may be curved toward a center of the lens, and the reflective sheet may have a bent shape on the second side surface. 
     The light provided by the display device may be incident on the first side surface, may be reflected by a second surface opposite to the first surface to travel toward the first surface, may be reflected by the first surface to travel toward the second side surface, may be reflected by the second side surface to travel toward the first surface, and may be reflected by the first surface to travel toward the first reflector. 
     The optical device may further include an optical path changing member between the first side surface and the display device. The optical path changing member may be configured to change a path of the light provided by the display device such that the light provided by the display device travels toward the second surface. 
     One or more example embodiments of the present disclosure provide an optical device including: a lens including a first lens portion, a second lens portion, and a third lens portion, the third lens portion being between the first lens portion and the second lens portion; a first display device on a first side surface of the first lens portion, the first display device being configured to provide a first light to the first side surface of the first lens portion; a second display device on a first side surface of the second lens portion, the second display device being configured to provide a second light to the first side surface of the second lens portion; a first reflector in the first lens portion and configured to reflect the second light reflected from a first side surface of the third lens portion to a first surface of the first lens portion; and a second reflector disposed in the second lens portion to reflect the first light reflected from the first side surface of the third lens portion to a first surface of the second lens portion. 
     The first light of the first display device may be incident on the first side surface of the first lens portion, may be reflected by a second side surface of the first lens portion to travel toward a second side surface of the third lens portion, may be reflected by the second side surface of the third lens portion to travel toward the first side surface of the third lens portion, and may be reflected by the first side surface of the third lens portion to travel toward the second reflector. 
     The first side surface of the third lens portion may be between the second side surface of the first lens portion and the second side surface of the second lens portion, and the second side surface of the third lens portion may be a surface opposite to the first side surface of the third lens portion. 
     The optical device may further include a first reflective sheet on the second side surface of the first lens portion, the second side surface of the second lens portion and the first side surface of the third lens portion; and a second reflective sheet on the second side surface of the third lens portion. 
     The optical device may further include a first optical path changing member between the first side surface of the first lens portion and the first display device. The first optical path changing member may be configured to change a path of the first light of the first display device such that the first light of the first display device travels toward the second side surface of the first lens portion. 
     The second light of the second display device may be incident on the first side surface of the second lens portion, may be reflected by the second side surface of the second lens portion to travel toward the second side surface of the third lens portion, may be reflected by the second side surface of the third lens portion to travel toward the first side surface of the third lens portion, and may be reflected by the first side surface of the third lens portion to travel toward the first reflector. 
     The optical device may further include a second optical path changing member between the first side surface of the second lens portion and the second display device. The second optical path changing member may be configured to change a path of the second light of the second display device such that the second light of the second display device travels toward the second side surface of the second lens portion. 
     The first side surface of the first lens portion may have a curved shape, and the first display device may have a bent shape on the first side surface of the first lens portion. 
     The first side surface of the second lens portion have a curved shape, and the second display device may have a bent shape on the first side surface of the second lens portion. 
     According to an embodiment of the present disclosure, after the light of the display device on the first side surface of the lens is totally reflected by at least one side surface of the lens, the light may be emitted to the first surface of the lens by the reflector and provided to the user&#39;s eye. Thus, the optical distance between the display device and the reflector can be increased. Therefore, the depth of field of the virtual image displayed on the display device can be deepened. 
     According to an embodiment of the present disclosure, because the optical device includes a plurality of reflectors, the luminance of the virtual image provided to the user&#39;s eye can be increased, and the area of the display device viewed by the user&#39;s eye, e.g., the field of view (FOV) of the user, can be enlarged. 
     According to an embodiment of the present disclosure, a reflective sheet may be disposed on the remaining side surfaces except the first side surface of the lens on which the display device is located, and the light of the device may be reflected by the reflective sheet. Therefore, the luminance of the virtual image of the display device provided to the user&#39;s eye can be increased. 
     According to an embodiment of the present disclosure, the display device may be a flexible display device having flexibility, and may have a bent shape on the first side surface of the lens formed as a curved surface (or may have a curved shape). Therefore, the light of the display device can travel toward the third side surface without the optical path changing layer and can be totally reflected by the third side surface. 
     According to an embodiment of the present disclosure, because the reflective sheet may be in a bent shape on one side surface of the lens that is formed as a curved surface, the reflective sheet may serve as a concave mirror. Accordingly, the light of the display device reflected by the reflective sheet on one side surface of the lens can be collected by the reflector. Therefore, the luminance of the virtual image of the display device provided to the user&#39;s eye can be increased by the reflector. 
     According to an embodiment of the present disclosure, because the reflective sheet may be in a bent shape on one side surface of the lens formed as a curved surface, the reflective sheet may serve as a convex mirror. Accordingly, the light of the display device reflected by the reflective sheet disposed on one side surface of the lens can be spread. Therefore, the virtual image of the display device provided to the user&#39;s eye by the reflector can be viewed in an enlarged manner by the user. 
     Aspects of embodiments of the present disclosure are not limited to the aforementioned aspects, and various other aspects are included in the present specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and features of the present disclosure will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
         FIG. 1  is a perspective view showing an optical device according to an embodiment; 
         FIGS. 2A-2B  are perspective views showing example embodiments of a lens of the optical device of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view showing a display device of the optical device of  FIG. 1 ; 
         FIGS. 4A-4C  show examples of an optical path changing layer of the optical device of  FIG. 1 ; 
         FIG. 5  is a perspective view showing an optical device according to an embodiment; 
         FIG. 6  is a perspective view showing an optical device according to an embodiment; 
         FIG. 7  is a perspective view showing an optical device according to an embodiment; 
         FIG. 8  is a perspective view showing an optical device according to an embodiment; 
         FIG. 9  is a perspective view showing an example embodiment of a lens of the optical device of  FIG. 8 ; 
         FIG. 10  is a side view showing an example of an optical path of the optical device of  FIG. 8 ; 
         FIG. 11  is a side view showing an example of an optical path of the optical device of  FIG. 8 ; 
         FIG. 12  is a perspective view showing an optical device according to an embodiment; 
         FIG. 13  is a perspective view showing an optical device according to an embodiment; 
         FIG. 14  is a perspective view showing an optical device according to an embodiment; 
         FIG. 15  is a perspective view showing an optical device according to an embodiment; 
         FIG. 16  is a perspective view showing an example of a lens of the optical device of  FIG. 15 ; 
         FIG. 17  is a perspective view showing an example of paths of a first light of a first display device and a second light of a second display device; 
         FIGS. 18A-18B  are perspective views showing an optical device according to an embodiment; 
         FIG. 19  is a perspective view showing an optical device according to an embodiment; 
         FIG. 20  is a perspective view showing an optical device according to an embodiment; and 
         FIG. 21  is an exemplary diagram illustrating an eye glass-type display including an optical device according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments of the present disclosure are shown. The present disclosure may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will filly convey the aspects and features of the disclosure to those skilled in the art. Accordingly, processes, elements, and techniques that are not necessary to those having ordinary skill in the art for a complete understanding of the aspects and features of the present disclosure may not be described. Unless otherwise noted, like reference numerals denote like elements throughout the attached drawings and the written description, and thus, descriptions thereof may not be repeated. In the drawings, the relative sizes of elements, layers, and regions may be exaggerated for clarity. 
     It will be understood that, although the terms “first,” “second,” “third,” etc., may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section described below could be termed a second element, component, region, layer or section, without departing from the spirit and scope of the present disclosure. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “under,” “above,” “upper,” and the like, may be used herein for ease of explanation to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or in operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” or “under” other elements or features would then be oriented “above” the other elements or features. Thus, the example terms “below” and “under” can encompass both an orientation of above and below. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein should be interpreted accordingly. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to,” or “coupled to” another element or layer, it can be directly on, connected to, or coupled to the other element or layer, or one or more intervening elements or layers may be present. In addition, it will also be understood that when an element or layer is referred to as being “between” two elements or layers, it can be the only element or layer between the two elements or layers, or one or more intervening elements or layers may also be present. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and “including,” when used in this specification, specify the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     As used herein, the terms “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent variations in measured or calculated values that would be recognized by those of ordinary skill in the art. Further, the use of “may” when describing embodiments of the present disclosure refers to “one or more embodiments of the present disclosure.” In addition, the use of alternative language, such as “or,” when describing embodiments of the present disclosure, refers to “one or more embodiments of the present disclosure” for each corresponding item listed. As used herein, the terms “use,” “using,” and “used” may be considered synonymous with the terms “utilize,” “utilizing,” and “utilized,” respectively. Also, the term “exemplary” is intended to refer to an example or illustration. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present specification, and should not be interpreted in an idealized or overly formal sense, unless expressly so defined herein. 
     Also, any numerical range disclosed and/or recited herein is intended to include all sub-ranges of the same numerical precision subsumed within the recited range. For example, a range of “1.0 to 10.0” is intended to include all subranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 10.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein, and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited herein. All such ranges are intended to be inherently described in this specification such that amending to expressly recite any such subranges would comply with the requirements of 35 U.S.C. § 112(a) and 35 U.S.C. § 132(a). 
     Hereinafter, embodiments of the present disclosure are described with reference to the attached drawings. 
       FIG. 1  is a perspective view showing an optical device  10  according to an embodiment.  FIGS. 2A-2B  are perspective views showing examples of a lens  100  of the optical device  10  of  FIG. 1 .  FIG. 3  is a cross-sectional view showing a display device  200  of the optical device  10  of  FIG. 1 .  FIGS. 4A-4C  show examples of an optical path changing layer  310  of the optical device  10  of  FIG. 1 . 
     Referring to  FIGS. 1, 2A-2B, 3, and 4A-4C , the optical device  10  according to an embodiment includes the lens  100 , the display device  200 , the optical path changing layer  310 , a polarizing film  320  and a first reflector  410 . The optical device  10  may be a device for providing an augmented reality or a virtual image. 
     The lens  100  may be formed, for example, of glass or plastic in a transparent or translucent manner. Accordingly, a user can view a real image through the lens  100 . The lens  100  may have a refractive power (e.g., a predetermined refractive power) in consideration of the visual acuity of the user. 
     The lens  100  may be formed as an octahedron having a first surface SF 1  and a second surface SF 2  which may be hexagonal, a first side surface SIF 1 , a second side surface SIF 2 , a third side surface SIF 3 , a fourth side surface SIF 4 , a fifth side surface SIF 5 , and a sixth side surface SIF 6 , as shown in  FIG. 2A . When the lens  100  is formed as an octahedron, as shown in  FIG. 2A , the second side surface SIF 2  may extend from one side (e.g., a first side) of the first side surface SIF 1 , and the third side surface SIF 3  may extend from the other side (e.g., a second side) opposite to the first side of the first side surface SIF 1 . The second side surface SIF 2  and the third side surface SIF 3  may face each other (e.g., may face away from each other), and a length of the second side surface SIF 2  in a first direction (X-axis direction) may be substantially the same as a length of the third side surface SIF 3  in the first direction (X-axis direction). The fourth side surface SIF 4  may be disposed between the second side surface SIF 2  and the third side surface SIF 3 . The fifth side surface SIF 5  may be disposed between the third side surface SIF 3  and the fourth side surface SIF 4 . The sixth side surface SIF 6  may be disposed between the second side surface SIF 2  and the fourth side surface SIF 6 . The first surface SF 1  may be a top surface, and the second surface SF 2  may be a bottom surface. The first surface SF 1 , which is a surface on which an eye E of a user (e.g., a user&#39;s eye) is located (or a surface near or adjacent the eye E of the user), may be an exit surface from which light of the display device  200  is emitted by the first reflector  410 . The second surface SF 2  may be an outer surface of the lens  100 . 
     Alternatively, according to embodiments, the lens  100  may be formed as a hexahedron having the first surface SF 1 , the second surface SF 2  and the first side surface SIF 1 , the second side surface SIF 2 , the third side surface SIF 3 , and the fourth side surface SIF 4 , as shown in  FIG. 2B . When the lens  100  is formed as a hexahedron as shown in  FIG. 2B , the second side surface SIF 2  may extend from one side (e.g., the first side) of the first side surface SIF 1 , the third side surface SIF 3  may extend from the other side (e.g., the second side) opposite to the first side of the first side surface SIF 1 , and the fourth side surface SIF 4  may face the first side surface SIF 1 . The first surface SF 1  may be a top surface, and the second surface SF 2  may be a bottom surface. The first surface SF 1 , which is a surface on which the user&#39;s eye E is located (or a surface near or adjacent the eye E of the user), may be an exit surface from which the light of the display device  200  is emitted by the first reflector  410 . The second surface SF 2  may be an outer surface of the lens  100 . 
     The lens  100  is not limited to the shapes shown in  FIGS. 2A-2B , and may be formed as a polyhedron having a first surface, a second surface and side surfaces, which are polygonal, for example. In addition, the lens  100  may be formed in other suitable shapes, such as a cylinder, an elliptic cylinder, a semicircular cylinder, a semi-elliptic cylinder, a distorted cylinder, or a distorted semicircular cylinder. The distorted cylinder and semicircular cylinder refer to a cylinder and a semicircular cylinder having a non-constant diameter. 
     The first reflector  410  is located (or disposed) in the lens  100 . The first reflector  410  may be a small mirror, such as a pin mirror. Although  FIG. 1  illustrates that the first reflector  410  has a circular cross section, the first reflector  410  may have any suitable shape, such as an elliptical or polygonal cross section. 
     The first reflector  410  may be formed to have a size that is smaller than a size of a pupil of the eye E. For example, a diameter of the first reflector  410  may range from about 500 μm to about 4 mm. According to embodiments, because the user focuses on a real image, it may be difficult for the user to recognize the first reflector  410 . However, as the size of the first reflector  410  decreases, the luminance of a virtual image provided to the user&#39;s eye E by the flexible display device  200  also decreases. Therefore the size of the first reflector  410  may be set in consideration of this fact. 
     The first reflector  410  may have a cylindrical shape, as shown in  FIG. 1 . In some embodiments, one of the two bottom surfaces may be a reflecting surface implemented as a mirror, and the other one of the two bottom surfaces and the side surfaces may not be implemented as mirrors. In order to emit light L totally reflected from the second side surface SIF 2  of the lens  100  to the first surface SF 1  of the lens  100 , a bottom surface of a lower portion of the first reflector  410  may be a reflecting surface, as shown in  FIG. 5 . 
     The first reflector  410  may reflect the virtual image displayed on the display device  200  and provide the virtual image to the user&#39;s eye E. Because the virtual image displayed on the display device  200  is reflected by the first reflector  410 , an optical distance between the display device  200  and the first reflector  410  can be increased. Accordingly, a depth of field of the virtual image displayed on the display device  200  may be deepened. 
     The display device  200  displays the virtual image for realizing the augmented reality. The display device  200  may be disposed on either of the side surfaces SIF 1  or SIF 2  of the lens  100 . For example, the display device  200  may be disposed on the first side surface SIF 1  of the lens  100 . 
     The display device  200  may be a flexible display device having flexibility, and may be configured to be bent. For example, the display device  200  may be an organic light emitting display device, as shown in  FIG. 3 , or an organic light emitting display device including a quantum dot. 
     Referring to  FIG. 3 , the display device  200  may include a substrate  1100 , a thin film transistor layer  1230 , a light emitting element layer  1240 , and a thin film encapsulation layer  1300 . 
     The thin film transistor layer  1230  is formed on the substrate  1100 . The thin film transistor layer  1230  includes thin film transistors  1235 , a gate insulating film  1236 , an interlayer insulating film  1237 , a protective film  1238 , and a planarization film  1239 . 
     A buffer film may be formed on the substrate  1100 . The buffer film may be formed on the substrate  1100  to protect the thin film transistors  1235  and light emitting elements from moisture penetrating through the substrate  1100  which can be susceptible to moisture permeation. The buffer film may include a plurality of alternately stacked inorganic films. For example, the buffer film may be formed of multiple films in which one or more inorganic films of a silicon oxide film (SiOx), a silicon nitride film (SiNx), and/or SiON are alternately stacked. In some embodiments, the buffer film may be omitted. 
     The thin film transistors  1235  may be formed on the buffer film. Each of the thin film transistors  1235  includes an active layer  1231 , a gate electrode  1232 , a source electrode  1233 , and a drain electrode  1234 . Although  FIG. 3  illustrates that each of the thin film transistors  1235  is formed by a top gate method in which the gate electrode  1232  is formed above the active layer  1231 , the present disclosure is not limited thereto. For example, each of the thin film transistors  1235  may be formed by a bottom gate method in which the gate electrode  1232  is located below the active layer  1231  or a double gate method in which the gate electrode  1232  is located both above and below the active layer  1231 . 
     The active layer  1231  may be formed on the buffer film. The active layer  1231  may be formed of a silicon-based semiconductor material or an oxide-based semiconductor material. A light shielding layer for shielding external light incident on the active layer  1231  may be formed between the buffer film and the active layer  1231 . 
     The gate insulating film  1236  may be formed on the active layer  1231 . The gate insulating film  1236  may be formed of an inorganic film, for example, a silicon oxide film (SiOx), a silicon nitride film (SiNx), or a multilayer film thereof. 
     The gate electrode  1232  and a gate line may be formed on the gate insulating film  1236 . The gate electrode  1232  and the gate line may be formed as a single layer or multiple layers made of molybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd), and copper (Cu), or an alloy thereof. 
     The interlayer insulating film  1237  may be formed on the gate electrode  1232  and the gate line. The interlayer insulating film  1237  may be formed of an inorganic film, for example, a silicon oxide film (SiOx), a silicon nitride film (SiNx), or a multilayer film thereof. 
     The source electrode  1233 , the drain electrode  1234  and a data line may be formed on the interlayer insulating film  1237 . Each of the source electrode  1233  and the drain electrode  1234  may be connected to the active layer  1231  via a contact opening (or a contact hole) passing through the gate insulating film  1236  and the interlayer insulating film  1237 . The source electrode  1233 , the drain electrode  1234  and the data line may be formed as a single layer or multiple layers made of molybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd), and copper (Cu), or an alloy thereof. 
     The protective film  1238  for insulating the thin film transistor  1235  may be formed on the source electrode  1233 , the drain electrode  1234  and the data line. The protective film  1238  may be formed of an inorganic film, for example, a silicon oxide film (SiOx), a silicon nitride film (SiNx), or a multilayer film thereof. 
     The planarization film  1239  may be formed on the protective film  1238  to flatten a step due to the thin film transistors  1235 . The planarization film  1239  may be formed of an organic film such as an acryl resin, an epoxy resin, a phenolic resin, a polyamide resin, and/or a polyimide resin. 
     The light emitting element layer  1240  is formed on the thin film transistor layer  1230 . The light emitting element layer  1240  includes light emitting elements and a pixel defining layer  1244 . 
     The light emitting elements and the pixel defining layer  1244  are formed on the planarization film  1239 . The light emitting elements may be organic light emitting diodes (or organic light emitting diode devices). For example, the light emitting elements may each include an anode electrode  1241 , light emitting layers  1242 , and a cathode electrode  1243 . 
     The anode electrode  1241  may be formed on the planarization film  1239 . The anode electrode  1241  may be connected to the source electrode  1233  of the thin film transistor  1235  via a contact opening (or a contact hole) passing through the protective film  1238  and the planarization film  1239 . 
     The pixel defining layer  1244  may be formed to cover an edge of the anode electrode  1241  on the planarization film  1239  to partition the pixels. For example, the pixel defining layer  1244  may serve as a pixel defining layer for defining pixels. Each of the pixels represents a region where the anode electrode  1241 , the light emitting layer  1242  and the cathode electrode  1243  are stacked sequentially and holes from the anode electrode  1241  and electrons from the cathode electrode  1243  are coupled to each other in the light emitting layer  1242  to emit light. 
     The light emitting layer  1242  is formed on the anode electrode  1241  and the pixel defining layer  1244 . The light emitting layer  1242  may be an organic light emitting layer. The light emitting layer  1242  may emit one of red light, green light and blue light. The peak wavelength range of red light may be about 620 nm to about 750 nm, and the peak wavelength range of green light may be about 495 nm to about 570 nm. Further, the peak wavelength range of blue light may be about 450 nm to about 495 nm. Alternatively, the light emitting layer  1242  may be a white light emitting layer that emits white light. In some embodiments, the red light emitting layer, the green light emitting layer, and the blue light emitting layer may have a laminated form, and may be a common layer formed commonly to the pixels. In some embodiments, the display device  200  may further include a separate color filter for displaying a red, green or blue color. 
     The light emitting layer  1242  may include a hole transporting layer, a light emitting layer, and an electron transporting layer. In addition, the light emitting layer  1242  may be formed in a tandem structure of two or more stacks, in which case a charge generating layer may be formed between the stacks. 
     The cathode electrode  1243  is formed on the light emitting layer  1242 . The cathode electrode  1243  may be formed to cover the light emitting layer  1242 . The cathode electrode  1243  may be a common layer formed commonly to the pixels. 
     When the light emitting element layer  1240  is formed by a top emission method in which light is emitted upwardly, the anode electrode  1241  may be formed of a metal material having high reflectivity to have a laminated structure of aluminum and titanium (Ti/Al/Ti), a laminated structure of aluminum and indium tin oxide (ITO) (ITO/AI/ITO), an APC alloy, and/or a laminated structure of an APC alloy and ITO (ITO/APC/ITO). The APC alloy is an alloy of silver (Ag), palladium (Pd) and copper (Cu). Further, the cathode electrode  1243  may be formed of a transparent conductive material (TCO), such as ITO or indium zinc oxide (IZO) that can transmit light or a semi-transmissive conductive material such as magnesium (Mg), silver (Ag), or an alloy of magnesium (Mg) and silver (Ag). When the cathode electrode  1243  is formed of a semi-transmissive conductive material, the light emission efficiency can be increased by microcavity. 
     When the light emitting element layer  1240  is formed by a bottom emission method in which light is emitted downwardly, the anode electrode  1241  may be formed of a transparent conductive material (TCO), such as ITO or IZO, or a semi-transmissive conductive material, such as magnesium (Mg), silver (Ag), or an alloy of magnesium (Mg) and silver (Ag). The cathode electrode  1243  may be formed of a metal material having high reflectivity to have a laminated structure of aluminum and titanium (Ti/Al/Ti), a laminated structure of aluminum and ITO (ITO/AI/ITO), an APC alloy, and/or a laminated structure of an APC alloy and ITO (ITO/APC/ITO). When the anode electrode  1241  is formed of a semi-transmissive conductive material, the light emission efficiency can be increased by microcavity. 
     The thin film encapsulation layer  1300  is formed on the light emitting element layer  1240 . The thin film encapsulation layer  1300  prevents oxygen or moisture from permeating the light emitting layer  1242  and the cathode electrode  1243 , or reduces the likelihood thereof. According to embodiments, the thin film encapsulation layer  1300  may comprise at least one inorganic film. The inorganic film may be formed of silicon nitride, aluminum nitride, zirconium nitride, titanium nitride, hafnium nitride, tantalum nitride, silicon oxide, aluminum oxide, and/or titanium oxide. Further, the thin film encapsulation layer  1300  may further include at least one organic film. The organic film may be formed to have a thickness sufficient to prevent particles from penetrating the thin film encapsulation layer  1300  and being injected into the light emitting layer  1242  and the cathode electrode  1243 , or to reduce the likelihood thereof. The organic film may include epoxy, acrylate and/or urethane acrylate. Instead of the thin film encapsulation layer  1300 , an encapsulation substrate may be disposed on the light emitting element layer  1240 . 
     A circuit board  210  is attached to one end (e.g., a first end) of the display device  200  (see, e.g.,  FIG. 1 ). Alternatively, the circuit board  210  may be attached to the other end (e.g., a second end) of the display device  200 . Alternatively, when there are many signal lines and voltage lines for driving the display device  200 , two flexible circuit boards  210  may be attached to the first end and the second end of the display device  200 , respectively. The circuit board  210  may be a flexible printed circuit board. 
     An integrated drive circuit  220  may be mounted on the circuit board  210 . The integrated drive circuit  220  may supply the display device  200  with data voltages, scan control signals, a source voltage, and the like for driving the display device  200 . The integrated drive circuit  220  may be an integrated circuit. 
     The optical path changing layer  310  may be disposed between the first side surface SIF 1  of the lens  100  and the display device  200 . The optical path changing layer  310  may change the path of the light L such that the light L of the display device  200  incident on the first side surface SIF 1  of the lens  100  travels toward the third side surface SIF 3  of the lens  100 , as shown in  FIG. 1 . 
     The optical path changing layer  310  may include a base layer  311   a  and an optical path changing pattern  311   b  disposed on the base layer  311   a , as shown in  FIGS. 4A-4C . The optical path changing pattern  311   b  may include a first light exit surface  3111  and a second light exit surface  3112 . 
     The optical path changing pattern  311   b  may have a triangular side surface (or a side surface with a triangular shape). For example, the optical path changing pattern  311   b  may have an isosceles triangular side surface such that a first angle θ 1  between an upper surface of the base layer  311   a  and the first light exit surface  3111  is substantially equal to a second angle θ 2  between the upper surface of the base layer  311   a  and the second light exit surface  3112 . Alternatively, the first angle θ 1  may be smaller than the second angle θ 2 , and a length of the first light exit surface  3111  may be greater than a length of the second light exit surface  3112 . For example, the optical path changing pattern  311   b  may have a right triangular side surface having the second angle θ 2  of 90° and the first angle θ 1  of 30°, as shown in  FIG. 4C . 
     An upper planarization layer  313  may be formed on the optical path changing pattern  311   b  as shown in  FIGS. 4B and 4C . The refractive index of the optical path changing pattern  311   b  may be different from the refractive index of the upper planarization layer  313 . 
     When the optical path changing pattern  311   b  has an isosceles triangular side surface having the first angle θ 1  and the second angle θ 2 , which are substantially equal to each other as shown in  FIGS. 4A and 4B , the light L incident on the optical path changing pattern  311   b  can be refracted by the first light exit surface  3111  and the second light exit surface  3112 . Accordingly, the light L incident on the optical path changing layer  310  can be diffused by the optical path changing layer  310 . 
     When the optical path changing pattern  311   b  is formed such that the first angle θ 1  is smaller than the second angle θ 2 , and the length of the first light exit surface  3111  is larger than the length of the second light exit surface  3112 , as shown in  FIG. 4C , the light L incident on the optical path changing pattern  311   b  can be refracted by the first light exit surface  3111 . Therefore, most of the light L incident on the optical path changing layer  310  can be refracted in an upper right direction of the optical path changing layer  310  by the optical path changing layer  310 , as shown in  FIG. 4C . 
     The light L of the display device  200  may travel toward the third side surface SIF 3  of the lens  100  by the optical path changing layer  310 . When the refractive index of the lens  100  is larger than the refractive index of air and an incident angle of the light L incident on the third side surface SIF 3  of the lens  100  is larger than a critical angle, the light L of the display device  200  may be totally reflected at the third side surface SIF 3  of the lens  100 . A part of the light L of the display device  200  that is totally reflected by the third side surface SIF 3  of the lens  100  may be totally reflected by the fourth side surface SIF 4  of the lens  100 . A part of the light L of the display device  200  totally reflected by the fourth side surface SIF 4  of the lens  100  may be totally reflected by the second side surface SIF 2  of the lens  100 . A part of the light L totally reflected by the second side surface SIF 2  of the lens  100  may be emitted to the first surface SF 1  of the lens  100  by the first reflector  410  and provided to the user&#39;s eye E. 
     Although  FIG. 1  illustrates that after the light L of the display device  200  is totally reflected by the three side surfaces of the lens  100 , the light L is reflected by the first reflector  410 , emitted to the first surface SF 1  of the lens  100 , and provided to the user&#39;s eye E, the present disclosure is not limited thereto. For example, after the light L of the display device  200  is totally reflected by the third side surface SIF 3  and the fourth side surface SIF 4  of the lens  100 , the light L may be emitted to the first surface SF 1  of the lens  100  by the first reflector  410  and provided to the user&#39;s eye E. Alternatively, after the light L of the display device  200  is totally reflected by the third side surface SIF 3  of the lens  100 , the light L may be emitted to the first surface SF 1  of the lens  100  by the first reflector  410  and provided to the user&#39;s eye E. Therefore, even when the user focuses on the real image through the lens  100 , the user can clearly view the virtual image displayed by the display device  200 . For example, even when the user does not move the focus adjusted to the real image, the user can clearly view the virtual image displayed by the display device  200 . 
     The greater the number of the side surfaces of the lens  100  where the light L of the display device  200  is totally reflected, the deeper the depth of field of the virtual image displayed on the display device  200 . However, because the loss of the light L of the display device  200  increases, the luminance of the virtual image of the display device  200  provided to the user&#39;s eye E may be reduced. Thus, the number of the side surfaces of the lens  100  where the light L of the display device  200  is totally reflected may be set in consideration of the depth of field of the virtual image displayed on the display device  200  and the luminance of the virtual image of the display device  200  provided on the user&#39;s eye E. 
     The polarizing film  320  may be disposed between the first side surface SIF 1  of the lens  100  and the optical path changing layer  310 . The polarizing film  320  may include a phase retardation film such as a linear polarizer plate and a quarter-wave (λ/4) plate. For example, a linear polarizer plate may be disposed on the first side surface SIF 1  of the lens  100 , and a phase retardation film may be disposed between the linear polarizer plate and the optical path changing layer  310 . Accordingly, the polarizing film  320  can prevent the light from the first side surface SIF 1  of the lens  100  from being reflected by the display device  200  and emitted to the first side surface SIF 1  of the lens  100 , while allowing the light L of the display device  200  to travel to the first side surface SIF 1  of the lens  100 . 
     According to the embodiment shown in  FIGS. 1-4 , after the light L of the display device  200  disposed on the first side surface SIF 1  of the lens  100  is totally reflected by least one side surface of the lens  100 , it may be emitted to the first surface SF 1  of the lens  100  by the first reflector  410  and provided to the user&#39;s eye E. Thus, the optical distance between the display device  200  and the first reflector  410  can be increased. Therefore, the depth of field of the virtual image displayed on the display device  200  can be deepened. 
       FIG. 5  is a perspective view showing an optical device  10 _ 1  according to an embodiment. 
     The embodiment shown in  FIG. 5  differs from the embodiment shown in  FIGS. 1-4  in that the optical device  10 _ 1  includes a plurality of reflectors  410  and  420 . A description overlapping with the embodiment discussed above with reference to  FIGS. 1-4  may be omitted, and differences from the embodiment(s) shown in  FIGS. 1-4  are mainly described below with reference to  FIG. 5 . 
     Referring to  FIG. 5 , the optical device  10 _ 1  includes a plurality of reflectors  410  and  420 . Although  FIG. 5  illustrates that the optical device  10 _ 1  includes two reflectors  410  and  420 , the present disclosure is not limited thereto. The optical device  10 _ 1  may include three or more reflectors, for example. As the number of reflectors increases, the luminance of the virtual image provided to the user&#39;s eye E may increase, and the area of the display device  200  viewed by the user&#39;s eye E, e.g., the field of view (FOV) of the user, may be enlarged. 
     The optical device  10 _ 1  may include a first reflector  410  and a second reflector  420 , as shown in  FIG. 5 . 
     The first reflector  410  and the second reflector  420  are disposed in the lens  100 . The first reflector  410  and the second reflector  420  may be small mirrors, such as pin mirrors. Although  FIG. 5  illustrates that the first reflector  410  and the second reflector  420  as having a circular cross section, the first reflector  410  and the second reflector  420  may have any suitable shape, such as an elliptical or polygonal cross section. 
     The first reflector  410  and the second reflector  420  are formed to be smaller in size than the pupil of the eye E. For example, each of the first reflector  410  and the second reflector  420  may be formed to have a diameter of about 500 μm to about 4 mm. According to embodiments, because the user focuses on the real image, it is difficult to recognize the first reflector  410  and the second reflector  420 . However, as the size of the first reflector  410  and the second reflector  420  decreases, the luminance of the virtual image provided to the user&#39;s eye E by the flexible display device  200  also decreases. Thus a size of the first reflector  410  and the second reflector  420  may be set or selected in consideration of this fact. 
     The first reflector  410  and the second reflector  420  may have a cylindrical shape, as shown in  FIG. 5 . According to embodiments, one of the two bottom surfaces may be a reflecting surface implemented as a mirror, and according to embodiments the other one of the two bottom surfaces and a side surface are not implemented as a mirror. In order to emit the light L totally reflected from the second side surface SIF 2  of the lens  100  to the first surface SF 1  of the lens  100 , the bottom surface of the first reflector  410  (e.g., a bottom surface of a lower portion of the first reflector  410 ) and the bottom surface of the second reflector  420  (e.g., a bottom surface of a lower portion of the second reflector  420 ) may be reflecting surfaces. 
     A part of the light L totally reflected by the second side surface SIF 2  of the lens  100  may be reflected by the first reflector  410  and the second reflector  420 , emitted to the first surface SF 1  of the lens  100 , and provided to the user&#39;s eye E. Because the virtual image displayed on the display device  200  is reflected by the first reflector  410  and the second reflector  420 , its depth of field is deepened. 
     Although  FIG. 5  illustrates that after the light L of the display device  200  is totally reflected by the three side surfaces of the lens  100 , the light L is emitted to the first surface SF 1  of the lens  100  by the first reflector  410  and the second reflector  402  and provided to the user&#39;s eye E, the present disclosure is not limited thereto. For example, after the light L of the display device  200  is totally reflected by the two side surfaces, e.g., the third side surface SIF 3  and the fourth side surface SIF 4  of the lens  100 , the light L may be emitted to the first surface SF 1  of the lens  100  by the first reflector  410  and the second reflector  402  and provided to the user&#39;s eye E. Alternatively, after the light L of the display device  200  is totally reflected by one side surface, e.g., the third side surface SIF 3 , of the lens  100 , the light L may be emitted to the first surface SF 1  of the lens  100  by the first reflector  410  and the second reflector  420  and provided to the user&#39;s eye E. 
     The greater the number of the side surfaces of the lens  100  where the light L of the display device  200  is totally reflected, the deeper the depth of field of the virtual image displayed on the display device  200 . However, because the loss of the light L of the display device  200  increases, the luminance of the virtual image of the display device  200  provided to the user&#39;s eye E may be reduced. Thus, the number of the side surfaces of the lens  100  where the light L of the display device  200  is totally reflected may be set (or selected) in consideration of the depth of field of the virtual image displayed on the display device  200  and the luminance of the virtual image of the display device  200  provided on the user&#39;s eye E. 
     According to the embodiment shown in  FIG. 5 , because the optical device  10 _ 1  includes the plurality of reflectors  410  and  420 , the luminance of the virtual image provided to the user&#39;s eye E can be increased as compared with embodiments where one reflector is provided, and the area of the display device  200  viewed by the user&#39;s eye E, (e.g., the field of view (FOV) of the user), can be enlarged. 
       FIG. 6  is a perspective view showing an optical device  10 _ 2  according to an embodiment. 
     The embodiment shown in  FIG. 6  differs from the embodiment shown in  FIGS. 1-4  in that a reflective sheet  330  is formed on the remaining side surfaces SIF 2  to SIF 6  except the first side surface SIF 1  of the lens  100 . A description overlapping with the embodiment described above with reference to  FIGS. 1-4  may be omitted, and differences from the embodiment shown in  FIGS. 1-4  are mainly described below with reference to  FIG. 6 . 
     Referring to  FIG. 6 , the optical device  10 _ 2  further includes the reflective sheet  330  disposed on the second side surface SIF 2 , the third side surface SIF 3 , the fourth side surface SIF 4 , the fifth side surface SIF 5 , and the sixth side surface SIF 6  of the lens  100 . One surface of the reflective sheet  330  facing the second side surface SIF 2 , the third side surface SIF 3 , the fourth side surface SIF 4 , the fifth side surface SIF 5 , and the sixth side surface SIF 6  of the lens  100  may be implemented as a mirror. 
     The light L of the display device  200  may travel toward the third side surface SIF 3  of the lens  100  by the optical path changing layer  310  and may be reflected by the reflective sheet  330  disposed on the third side surface SIF 3 . Further, a part of the light L of the display device  200  reflected by the reflective sheet  330  disposed on the third side surface SIF 3  of the lens  100  may be reflected by the reflective sheet  330  disposed on the fourth side surface SIF 4  of the lens  100 . Further, a part of the light L of the display device  200  reflected by the reflective sheet  330  disposed on the fourth side surface SIF 4  of the lens  100  may be reflected by the reflective sheet  330  disposed on the second side surface SIF 2  of the lens  100 . A part of the light L of the display device  200  reflected by the reflective sheet  330  disposed on the second side surface SIF 2  of the lens  100  may be emitted to the first surface SF 1  of the lens  100  by the first reflector  410  and provided to the user&#39;s eye E. Therefore, even when the user focuses on the real image through the lens  100 , the user can clearly view the virtual image displayed by the display device  200 . Thus, even when the user does not move the focus adjusted to the real image, the user can clearly view the virtual image displayed by the display device  200 . 
     In the embodiment shown in  FIGS. 1-4 , the light totally reflected by at least one side surface of the lens  100  is emitted to the first side surface SF 1  of the lens  100  by the first reflector  410 . On the other hand, in the embodiment shown in  FIG. 6 , the light reflected by the reflective sheet  330  disposed on at least one side surface of the lens  100  is emitted to the first surface SF 1  of the lens  100  by the first reflector  410 . The total reflection occurs only when the incident angle is larger than the critical angle, whereas the reflective sheet  330  reflects the incident light almost intact. Thus, when using the reflective sheet  330 , a ratio of the reflected light to the incident light can be increased as compared to embodiments when using the total reflection. 
     According to the embodiment shown in  FIG. 6 , the reflective sheet  330  is disposed on the remaining side surfaces SIF 2 , SIF 3 , SIF 4 , SIF 5 , and SIF 6  (except the first side surface SIF 1 ) of the lens  100 , and the light L of the display device  200  is reflected by the reflective sheet  330 . Therefore, the luminance of the virtual image of the display device  200  provided to the user&#39;s eye E can be increased. 
       FIG. 7  is a perspective view showing an optical device  10 _ 3  according to an embodiment. 
     The embodiment shown in  FIG. 7  differs from the embodiment shown in  FIGS. 1-4  in that the first side surface SIF 1  of the lens  100  is formed as a curved surface having a predetermined curvature. A description overlapping with the embodiment described above with reference to  FIGS. 1-4  may be omitted, and differences from the embodiment shown in  FIGS. 1-4  are mainly described with reference to  FIG. 7 . 
     Referring to  FIG. 7 , the first side surface SIF 1  of the lens  100  may be a curved surface, e.g., may have a curved shape having a predetermined curvature. The first side surface SIF 1  of the lens  100  may have a curved shape in an outward direction (e.g., the first direction (X-axis direction)) of the first side surface SIF 1 . Accordingly, a part of the first side surface SIF 1  of the lens  100  may face a part of the third side surface SIF 3 . 
     The display device  200  may be a flexible display device with flexibility, which can be bent. Thus, the display device  200  may be disposed in a bent shape on the first side surface SIF 1  of the lens  100  formed as a curved surface. Because a part of the first side surface SIF 1  of the lens  100  may face a part of the third side surface SIF 3  of the lens  100 , the light L of the display device  200  may travel toward the third side surface SIF 3  and may be totally reflected by the third side surface SIF 3 . Therefore, the optical path changing layer  310  may be omitted. 
     Although  FIG. 7  illustrates that first side surface SIF 1  of the lens  100  is formed as a curved surface, the present disclosure is not limited thereto. For example, when the length of the second side surface SIF 2  of the lens  100  in the first direction (X-axis direction) is shorter than the length of the third side surface SIF 3  of the lens  100  in the first direction (X-axis direction), the first side surface SIF 1  may be disposed obliquely such that a part of the first side surface SIF 1  of the lens  100  may face a part of the third side surface SIF 3 . According to embodiments, the first side surface SIF 1  may be formed as a flat surface rather than a curved surface. 
     According to the embodiment shown in  FIG. 7 , the display device  200  is a flexible display device having flexibility, and may be disposed in a bent shape on the first side surface SIF 1  of the lens  100  formed as a curved surface. Therefore, the light L of the display device  200  can travel toward the third side surface SIF 3  without the optical path changing layer  310  and can be totally reflected by the third side surface SIF 3 . 
       FIG. 8  is a perspective view showing an optical device  10 _ 4  according to an embodiment.  FIG. 9  is a perspective view showing an example of a lens  100  of the optical device  10 _ 4  of  FIG. 8 .  FIG. 10  is a side view showing an example of an optical path of the optical device  10 _ 4  of  FIG. 8 .  FIG. 11  is a side view showing an example of an optical path of the optical device  10 _ 4  of  FIG. 8 . 
     The embodiment shown in  FIGS. 8-11  differs from the embodiment shown in  FIGS. 1-4  in that after the light L of the display device  200  disposed on the first side surface SIF 1  of the lens  100  is reflected by the reflective sheet  330  disposed on the second side surface SIF 2  facing the first side surface SIF 1  of the lens  100 , the light L is reflected by the first reflector  410  and emitted to the first surface SF 1  of the lens  100 . A description overlapping with the embodiment described above with reference to  FIGS. 1-4  may be omitted, and differences from the embodiment shown in  FIGS. 1-4  are mainly described with reference to  FIGS. 8-11 . 
     Referring to  FIGS. 8-11 , the lens  100  may be formed in a decahedral shape including a first surface SF 1  and a second surface SF 2  which are octagonal and a first side surface SIF 1 , a second side surface SIF 2 , a third side surface SIF 3 , a fourth side surface SIF 4 , a fifth side surface SIF 5 , a sixth side surface SIF 6 , a seventh side surface SIF 7 , and an eighth side surface SIF 8 . When the lens  100  is formed in a decahedral shape, as shown in  FIG. 9 , the first side surface SIF 1  and the second side surface SIF 2  may face each other (e.g., may face away from each other), the third side surface SIF 3  may be disposed between one side of the first side surface SIF 1  and one side of the second side surface SIF 2 , and the fourth side surface SIF 4  may be disposed between the other side of the first side surface SIF 1  and the other side of the second side surface SIF 2 . The fifth side surface SIF 5  may be disposed between the first side surface SIF 1  and the third side surface SIF 3 , and the sixth side surface SIF 6  may be disposed between the second side surface SIF 2  and the third side surface SIF 3 . The seventh side surface SIF 7  may be disposed between the first side surface SIF 1  and the fourth side surface SIF 4 , and the eighth side surface SIF 8  may be disposed between the second side surface SIF 2  and the fourth side surface SIF 4 . The first surface SF 1 , which is a surface on which the user&#39;s eye E is located (or a surface near or adjacent the eye E of the user), may be an exit surface from which the light of the display device  200  is emitted by the first reflector  410 . The second surface SF 2  may be an outer surface of the lens  100 . 
     The lens  100  is not limited to that shown in  FIG. 9 , and may be formed as a polyhedron having a first surface, a second surface and side surfaces, which are polygonal, for example. In addition to the polyhedron, the lens  100  may be formed in other suitable shapes, such as a cylinder, an elliptic cylinder, a semicircular cylinder, a semi-elliptic cylinder, a distorted cylinder, or a distorted semicircular cylinder. The distorted cylinder and the distorted semicircular cylinder refer to a cylinder and a semicircular cylinder having a non-constant diameter. 
     The optical path changing layer  310  may change the path of the light L such that the light L of the display device  200  incident on the first side surface SIF 1  of the lens  100  travels toward the second surface SF 2  of the lens  100 , as shown in  FIG. 10 . 
     Alternatively, as shown in  FIG. 11 , instead of the optical path changing layer  310 , an inclination layer  340  for arranging the display device  200  to be inclined by a third angle θ 3  with respect to the first side surface SIF 1  of the lens  100  may be disposed between the first side surface SIF 1  of the lens  100  and the display device  200 . The third angle θ 3  indicates an angle that is inclined in a second direction (Y-axis direction) with respect to a direction opposite to a third direction (Z-axis direction). 
     The reflective sheet  330  may be disposed on the second side surface SIF 2  of the lens  100 . One surface of the reflective sheet  330  facing the second side surface SIF 2  of the lens  100  may be implemented as a mirror. The reflective sheet  330  may be formed flat in the first direction (X-axis direction) and the third direction (Z-axis direction). 
     As shown in  FIGS. 10-11 , the light L of the display device  200  may travel toward the second surface SF 2  of the lens  100 . When the refractive index of the lens  100  is larger than the refractive index of air and the incident angle of the light L incident on the second surface SF 2  of the lens  100  is larger than a critical angle, the light L of the display device  200  may be totally reflected at the second surface SF 2  of the lens  100 . A part of the light L totally reflected by the second surface SF 2  of the lens  100  may be totally reflected by the first surface SF 1  of the lens  100 . A part of the light L totally reflected by the first surface SF 1  of the lens  100  may be totally reflected again by the second surface SF 2  of the lens  100 . A part of the light L totally reflected again by the second surface SF 2  of the lens  100  may be reflected by the reflective sheet  330  disposed on the second side surface SIF 2  of the lens  100 . A part of the light L reflected by the reflective sheet  330  disposed on the second side surface SIF 2  of the lens  100  may be totally reflected again by the first surface SF 1  of the lens  100 . A part of the light L totally reflected again by the first surface SF 1  of the lens  100  may be emitted to the first surface SF 1  of the lens  100  by the first reflector  410  and provided to the user&#39;s eye E. Therefore, even when the user focuses on the real image through the lens  100 , the user can clearly view the virtual image displayed by the display device  200 . That is, even when the user does not move the focus adjusted to the real image, the user can clearly view the virtual image displayed by the display device  200 . 
     According to the embodiment shown in  FIGS. 8-11 , after the light of the display device  200  disposed on the first side surface SIF 1  of the lens  100  is totally reflected by least one side surface of the lens  100 , it may be emitted to the first surface SF 1  of the lens  100  by the first reflector  410  and provided to the user&#39;s eye E. Thus, the optical distance between the display device  200  and the first reflector  410  can be increased. Therefore, the depth of field of the virtual image displayed on the display device  200  can be deepened. 
       FIG. 12  is a perspective view showing an optical device  10 _ 5  according to an embodiment. 
     The embodiment shown in  FIG. 12  differs from the embodiment shown in  FIGS. 8-11  in that the optical device  10 _ 5  includes a plurality of reflectors  410  and  420 . A description overlapping with the embodiment described above with reference to  FIGS. 8-11  may be omitted, and differences from the embodiment shown in  FIGS. 8-11  are mainly described with reference to  FIG. 12 . 
     Referring to  FIG. 12 , the optical device  10 _ 5  includes a plurality of reflectors  410  and  420 . Although  FIG. 12  illustrates that the optical device  10 _ 5  includes two reflectors  410  and  420 , the present disclosure is not limited thereto. The optical device  10 _ 5  may include three or more reflectors, for example. As the number of reflectors increases, the luminance of the virtual image provided to the user&#39;s eye E may increase, and the area of the display device  200  viewed by the user&#39;s eye E, e.g., the field of view (FOV) of the user, may be enlarged. 
     The optical device  10  may include a first reflector  410  and a second reflector  420 , as shown in  FIG. 12 . 
     The first reflector  410  and the second reflector  420  are disposed in the lens  100 . The first reflector  410  and the second reflector  420  may be small mirrors, such as pin mirrors. Although  FIG. 12  illustrates that the first reflector  410  and the second reflector  420  have a circular cross section, they may have any suitable shape, such as an elliptical or polygonal cross section. 
     The first reflector  410  and the second reflector  420  are formed to be smaller in size than the pupil of the eye E. For example, each of the first reflector  410  and the second reflector  420  may be formed to have a diameter of about 500 μm to about 4 mm. In this case, since the user focuses on the real image, it is difficult to recognize the first reflector  410  and the second reflector  420 . However, as the size of the first reflector  410  and the second reflector  420  decreases, the luminance of the virtual image provided to the user&#39;s eye E by the flexible display device  200  also decreases. Thus, in consideration of this fact, the size of the first reflector  410  and the second reflector  420  may be set. 
     The first reflector  410  and the second reflector  420  may have a cylindrical shape, as shown in  FIG. 5 . In embodiments, one of the two bottom surfaces may be a reflecting surface implemented as a mirror, and the other one of the two bottom surfaces and the side surface may not be implemented as a mirror. In order to emit the light L totally reflected from the second side surface SIF 2  of the lens  100  to the first surface SF 1  of the lens  100 , the bottom surface of a lower portion of the first reflector  410  and the bottom surface of a lower portion of the second reflector  420  may be reflecting surfaces. 
     A part of the light L totally reflected by the second side surface SIF 2  of the lens  100  may be reflected by the first reflector  410  and the second reflector  420 , emitted to the first surface SF 1  of the lens  100 , and provided to the user&#39;s eye E. Because the virtual image displayed on the display device  200  is reflected by the first reflector  410  and the second reflector  420 , its depth of field is deepened. 
     According to the embodiment shown in  FIG. 12 , because the optical device  10 _ 5  includes the plurality of reflectors  410  and  420 , the luminance of the virtual image provided to the user&#39;s eye E can be increased as compared with embodiments where one reflector is provided, and the area of the display device  200  viewed by the user&#39;s eye E, e.g., the field of view (FOV) of the user, can be enlarged. 
       FIG. 13  is a perspective view showing an optical device  10 _ 6  according to an embodiment. 
     The embodiment shown in  FIG. 13  differs from the embodiment shown in  FIGS. 8-11  in that the second side surface SIF 2  of the lens  100  is formed as a curved surface, e.g., a curved surface having a predetermined curvature. A description overlapping with the embodiment described above with reference to  FIGS. 8-11  may be omitted, and differences from the embodiment shown in  FIGS. 8-11  is mainly described below with reference to  FIG. 13 . 
     Referring to  FIG. 13 , the second side surface SIF 2  of the lens  100  may be a curved surface having a predetermined curvature. The second side surface SIF 2  of the lens  100  may have a curved shape in an outward direction (e.g., a direction opposite to the second direction (Y-axis direction)) of the second side surface SIF 2 . 
     Because the reflective sheet  330  is disposed on the second side surface SIF 2  of the lens  100 , it may be arranged in a curved shape along the curvature of the second side surface SIF 2  of the lens  100 . Because the second side surface SIF 2  of the lens  100  is curved in the outward direction (e.g., a direction opposite to the second direction (Y-axis direction)) of the second side surface SIF 2 , the reflective sheet  330  may serve as a concave mirror. Accordingly, the light L of the display device  200  reflected by the reflective sheet  330  disposed on the second side surface SIF 2  of the lens  100  can be collected by the first reflector  410 . Therefore, the luminance of the virtual image of the display device  200  provided to the user&#39;s eye E can be increased by the first reflector  410 . 
     According to the embodiment shown in  FIG. 13 , because the reflective sheet  330  is arranged in a curved shape on the second side surface SIF 2  of the lens  100  which is formed as a curved surface, the reflective sheet  330  may serve as a concave mirror. Accordingly, the light L of the display device  200  reflected by the reflective sheet  330  disposed on the second side surface SIF 2  of the lens  100  can be collected by the first reflector  410 . Therefore, the luminance of the virtual image of the display device  200  provided to the user&#39;s eye E can be increased by the first reflector  410 . 
       FIG. 14  is a perspective view showing an optical device  10 _ 7  according to an embodiment. 
     The embodiment shown in  FIG. 14  differs from the embodiment shown in  FIGS. 8-11  in that the second side surface SIF 2  of the lens  100  is formed as a curved surface having a curvature, e.g., a predetermined curvature. A description overlapping with the embodiment described above with reference to  FIGS. 8-11  may be omitted, and differences from the embodiment shown in  FIGS. 8-11  are mainly described with reference to  FIG. 14 . 
     Referring to  FIG. 14 , the second side surface SIF 2  of the lens  100  may be a curved surface having a predetermined curvature. The second side surface SIF 2  of the lens  100  may have a curved shape toward the center of the lens  100  (e.g., in the second direction (Y-axis direction)). 
     Because the reflective sheet  330  is disposed on the second side surface SIF 2  of the lens  100 , it may be arranged in a curved shape along the curvature of the second side surface SIF 2  of the lens  100 . Because the second side surface SIF 2  of the lens  100  is curved toward the center of the lens  100  (e.g., in the second direction (Y-axis direction)), the reflective sheet  330  may serve as a convex mirror. Accordingly, the light L of the display device  200  reflected by the reflective sheet  330  disposed on the second side surface SIF 2  of the lens  100  is spread. Therefore, the virtual image of the display device  200  provided to the user&#39;s eye E by the first reflector  410  can be viewed in an enlarged manner by the user. 
     According to the embodiment shown in  FIG. 14 , because the reflective sheet  330  is arranged in a curved shape on the second side surface SIF 2  of the lens  100  which is formed as a curved surface, the reflective sheet  330  may serve as a convex mirror. Accordingly, the light L of the display device  200  reflected by the reflective sheet  330  disposed on the second side surface SIF 2  of the lens  100  can be spread. Therefore, the virtual image of the display device  200  provided to the user&#39;s eye E by the first reflector  410  can be viewed in an enlarged manner by the user. 
       FIG. 15  is a perspective view showing an optical device  10 _ 8  according to an embodiment.  FIG. 16  is a perspective view showing an example of a lens  100  of the optical device  10 _ 8  of  FIG. 15 .  FIG. 17  is a perspective view showing an example of paths of a first light of a first display device and a second light of a second display device. 
     Referring to  FIGS. 15-17 , the optical device  10 _ 8  according to an embodiment includes a lens  100 , a first display device  201 , a second display device  202 , a first optical path changing layer  311 , a second optical path changing layer  312 , a first polarizing film  321 , a second polarizing film  322 , a first reflector  410 , and a second reflector  420 . 
     The lens  100  may be formed of glass or plastic in a transparent or translucent manner. Accordingly, the user can view the real image through the lens  100 . The lens  100  may have a refractive power (e.g., a predetermined refractive power) in consideration of the visual acuity of the user. 
     As shown in  FIG. 16 , the lens  100  may include a first lens portion  101 , a second lens portion  102 , and a third lens portion  103  disposed between the first lens portion  101  and the second lens portion  102 . The first lens portion  101  may be formed as a hexahedron having an eleventh surface SF 11 , a twelfth surface SF 12 , an eleventh side surface SIF 11 , a twelfth side surface SIF 12 , a thirteenth side surface SIF 13 , and a fourteenth side surface SIF 14 , which each have a rectangular shape. The second lens portion  102  may be formed as a hexahedron having a twenty-first surface SF 21 , a twenty-second surface SF 22 , a twenty-first side surface SIF 21 , a twenty-second side surface SIF 22 , a twenty-third side surface SIF 23 , and a twenty-fourth side surface SIF 24 , which each have a rectangular shape. The third lens portion  103  may be formed as a hexahedron having a thirty-first surface SF 31 , a thirty-second surface SF 32 , a thirty-first side surface SIF 31 , a thirty-second side surface SIF 32 , a thirty-third side surface SIF 33 , an a thirty-fourth side surface SIF 34 , which each have a rectangular shape. 
     The twelfth side surface SIF 12  of the first lens portion  101  may extend from one side of the eleventh side surface SIF 11 , and the thirteenth side surface SIF 13  may extend from the other side opposite to the one side of the eleventh side surface SIF 11 . The fourteenth side surface SIF 14  may face the eleventh side surface SIF 11 . The eleventh surface SF 11  may be a top surface, and the twelfth surface SF 12  may be a bottom surface. The eleventh surface SF 11 , which is a surface on which a user&#39;s left eye LE is located (or a surface near or adjacent the left eye LE of the user), may be an exit surface from which the light of the second display device  202  is emitted by the first reflector  410 . The twelfth surface SF 12  may be an outer surface of the lens  100 . 
     The twenty-second side surface SIF 22  of the second lens portion  102  may extend from one side of the twenty-first side surface SIF 21 , and the twenty-third side surface SIF 23  may extend from the other side opposite to the one side of the twenty-first side surface SIF 21 . The twenty-fourth side surface SIF 24  may face the twenty-first side surface SIF 21 . The twenty-first surface SF 21  may be a top surface, and the twenty-second surface SF 22  may be a bottom surface. The twenty-first surface SF 21 , which is a surface on which a user&#39;s right eye RE is located (or a surface near or adjacent the right eye RE of the user), may be an exit surface from which the light of the first display device  201  is emitted by the second reflector  420 . The twenty-second surface SF 22  may be an outer surface of the lens  100 . 
     The thirty-second side surface SIF 32  of the third lens portion  103  may extend from one side of the thirty-first side surface SIF 31 , and the thirty-third side surface SIF 33  may extend from the other side opposite to the one side of the thirty-first side surface SIF 31 . The thirty-fourth side surface SIF 34  may face the thirty-first side surface SIF 31 . The thirty-first surface SF 31  may be a top surface, and the thirty-second surface SF 32  may be a bottom surface. 
     The fourteenth side surface SIF 14  of the first lens portion  101  may be in contact with the thirty-third side surface SIF 33  of the third lens portion  103 . The twenty-fourth side surface SIF 24  of the second lens portion  102  may be in contact with the thirty-fourth side surface SIF 34  of the third lens portion  103 . 
     Although  FIG. 16  illustrates that the first lens portion  101 , the second lens portion  102  and the third lens portion  103  of the lens  100  are formed as a hexahedron, the embodiments of the present disclosure are not limited thereto. For example, each of the first lens portion  101 , the second lens portion  102  and the third lens portion  103  of the lens  100  may be formed as a polyhedron having a first surface, a second surface and side surfaces, which are polygonal. In addition to the polyhedron, each of the first lens portion  101 , the second lens portion  102  and the third lens portion  103  of the lens  100  may be formed in other suitable shapes, such as a cylinder, an elliptic cylinder, a semicircular cylinder, a semi-elliptic cylinder, a distorted cylinder, or a distorted semicircular cylinder. The distorted cylinder and the distorted semicircular cylinder refer to a cylinder and a semicircular cylinder having a non-constant diameter. 
     The first reflector  410  is disposed in the first lens portion  101  of the lens  100 . The second reflector  420  is disposed in the second lens portion  102  of the lens  100 . The first reflector  410  and the second reflector  420  may be small mirrors, such as pin mirrors. Although  FIG. 15  illustrates that the first reflector  410  and the second reflector  420  have a circular cross section, they may have any suitable shape, such as an elliptical or polygonal cross section. 
     The first reflector  410  and the second reflector  420  are formed to be smaller in size than the pupil of the eye E. For example, each of the first reflector  410  and the second reflector  420  may be formed to have a diameter of about 500 μm to about 4 mm. In embodiments, because the user focuses on the real image, it is difficult to recognize the first reflector  410  and the second reflector  420 . However, as the size of the first reflector  410  and the second reflector  420  decreases, the luminance of the virtual image provided to the user&#39;s eye E by the flexible display device  200  also decreases. Thus, in consideration of this fact, the size of the first reflector  410  and the second reflector  420  may be set. 
     The first reflector  410  and the second reflector  420  may have a cylindrical shape, as shown in  FIG. 15 . In embodiments, one of the two bottom surfaces may be a reflecting surface implemented as a mirror, and the other one of the two bottom surfaces and the side surface are not implemented as a mirror. In order to emit the light L totally reflected from the thirty-first side surface SIF 31  of the third lens portion  103  of the lens  100  to the eleventh surface SF 11  of the first lens portion  101 , the bottom surface of an upper portion of the first reflector  410  may be a reflecting surface, as shown in  FIG. 15 . Further, in order to emit the light L totally reflected from the thirty-first side surface SIF 31  of the third lens portion  103  of the lens  100  to the twenty-first surface SF 21  of the second lens portion  102 , the bottom surface of an upper portion of the second reflector  420  may be a reflecting surface, as shown in  FIG. 15 . 
     The first reflector  410  may reflect the virtual image displayed on the second display device  202  and provide the virtual image to the user&#39;s left eye LE. The second reflector  420  may reflect the virtual image displayed on the first display device  201  and provide the virtual image to the user&#39;s right eye RE. Because the virtual image displayed on the first display device  201  is reflected by the second reflector  420 , its depth of field is deepened. Because the virtual image displayed on the second display device  202  is reflected by the first reflector  410 , its depth of field is deepened. 
     Each of the first display device  201  and the second display device  202  displays the virtual image for realizing the augmented reality. The first display device  201  may be disposed on one of the side surfaces of the first lens portion  101  and the second display device  202  may be disposed on one of the side surfaces of the second lens portion  102 . For example, the display device  200  may be disposed on the eleventh side surface SIF 11  of the first lens portion  101  and disposed on the twenty-first side surface SIF 21  of the second lens portion  102 . 
     A first circuit board  211  is attached to one end of the first display device  201 . Alternatively, the first circuit board  211  may be attached to the other end of the first display device  201 . Alternatively, when there are many signal lines and voltage lines for driving the first display device  201 , two first circuit boards  211  may be attached to one end and the other end of the first display device  201 , respectively. 
     A second circuit board  212  is attached to one end of the second display device  202 . Alternatively, the second circuit board  212  may be attached to the other end of the second display device  202 . Alternatively, when there are many signal lines and voltage lines for driving the second display device  202 , two second circuit boards  212  may be attached to one end and the other end of the second display device  202 , respectively. 
     Each of the first circuit board  211  and the second circuit board  212  may be a flexible printed circuit board. 
     A first integrated drive circuit  221  may be mounted on the first circuit board  211 . A second integrated drive circuit  222  may be mounted on the second circuit board  212 . The first integrated drive circuit  221  may supply the first display device  201  with data voltages, scan control signals, a source voltage, and the like for driving the first display device  201 . The second integrated drive circuit  222  may supply the second display device  202  with data voltages, scan control signals, a source voltage, and the like for driving the second display device  202 . The first integrated drive circuit  221  and the second integrated drive circuit  222  may be integrated circuits. 
     The first optical path changing layer  311  may be disposed between the eleventh side surface SIF 11  of the first lens portion  101  and the first display device  201 . The first optical path changing layer  311  may change the path of the first light L 1  such that the first light L 1  of the first display device  201  incident on the eleventh side surface SIF 11  of the first lens portion  101  travels toward the twelfth side surface SIF 12  of the first lens portion  101 , as shown in  FIG. 15 . 
     The second optical path changing layer  312  may be disposed between the twenty-first side surface SIF 21  of the second lens portion  102  and the second display device  202 . The second optical path changing layer  312  may change the path of the second light L 2  such that the second light L 2  of the second display device  202  incident on the twenty-first side surface SIF 21  of the second lens portion  102  travels toward the twenty-second side surface SIF 22  of the second lens portion  102 , as shown in  FIG. 15 . 
     The first optical path changing layer  311  and the second optical path changing layer  312  may be implemented as described above with reference to  FIGS. 4A-4C . 
     The first polarizing film  321  may be disposed between the eleventh side surface SIF 11  of the first lens portion  101  and the first optical path changing layer  311 . The second polarizing film  322  may be disposed between the twenty-first side surface SIF 21  of the second lens portion  102  and the second optical path changing layer  312 . 
     Each of the first polarizing film  321  and the second polarizing film  322  may include a phase retardation film such as a linear polarizer plate and a quarter-wave (λ/4) plate. In the case of the first polarizing film  321 , the linear polarizer plate may be disposed on the eleventh side surface SIF 11  of the first lens portion  101 , and the phase retardation film may be disposed between the linear polarizer plate and the first optical path changing layer  311 . Accordingly, the first polarizing film  321  can prevent the light from the eleventh side surface SIF 11  of the first lens portion  101  from being reflected by the first display device  201  and emitted to the eleventh side surface SIF 11  of the first lens portion  101 , or can reduce the likelihood thereof, while allowing the first light L 1  of the first display device  201  to travel to the eleventh side surface SIF 11  of the first lens portion  101 . 
     In embodiments including the second polarizing film  322 , the linear polarizer plate may be disposed on the twenty-first side surface SIF 21  of the second lens portion  102 , and the phase retardation film may be disposed between the linear polarizer plate and the second optical path changing layer  312 . Accordingly, the second polarizing film  322  can prevent the light from the twenty-first side surface SIF 21  of the second lens portion  102  from being reflected by the second display device  202  and emitted to the twenty-first side surface SIF 21  of the second lens portion  102 , or reduce the likelihood thereof, while allowing the second light L 2  of the second display device  202  to travel to the twenty-first side surface SIF 21  of the second lens portion  102 . 
     As shown in  FIG. 17 , the first light L 1  of the first display device  201  may travel toward the twelfth side surface SIF 12  of the first lens portion  101  by the first optical path changing layer  311 . When the refractive index of the lens  100  is larger than the refractive index of air and the incident angle of the first light L 1  incident on the twelfth side surface SIF 12  of the first lens portion  101  is larger than the critical angle, a part of the first light L 1  of the first display device  201  may be totally reflected by the twelfth side surface SIF 12  of the first lens portion  101 . A part of the first light L 1  totally reflected by the twelfth side surface SIF 12  of the first lens portion  101  may be totally reflected by the thirty-second side surface SIF 32  of the third lens portion  103 . A part of the first light L 1  totally reflected by the thirty-second side surface SIF 32  of the third lens portion  103  may be totally reflected by the thirty-first side surface SIF 31  of the third lens portion  103 . A part of the first light L 1  totally reflected by the thirty-first side surface SIF 31  of the third lens portion  103  may be emitted to the twenty-first surface SF 21  of the second lens portion  102  by the second reflector  420  and provided to the user&#39;s right eye RE. 
     Further, as shown in  FIG. 17 , the second light L 2  of the second display device  202  may travel toward the twenty-second side surface SIF 22  of the second lens portion  102  by the second optical path changing layer  312 . When the refractive index of the lens  100  is larger than the refractive index of air and the incident angle of the second light L 2  incident on the twenty-second side surface SIF 22  of the second lens portion  102  is larger than the critical angle, a part of the second light L 2  of the second display device  202  may be totally reflected by the twenty-second side surface SIF 22  of the second lens portion  102 . A part of the second light L 2  totally reflected by the twenty-second side surface SIF 22  of second lens portion  102  may be totally reflected by the thirty-second side surface SIF 32  of the third lens portion  103 . A part of the second light L 2  totally reflected by the thirty-second side surface SIF 32  of the third lens portion  103  may be totally reflected by the thirty-first side surface SIF 31  of the third lens portion  103 . A part of the second light L 2  totally reflected by the thirty-first side surface SIF 31  of the third lens portion  103  may be emitted to the eleventh surface SF 11  of the first lens portion  101  by the first reflector  410  and provided to the user&#39;s left eye LE. 
       FIG. 17  illustrates that after the first light L 1  of the first display device  201  is totally reflected three times, e.g., by the twelfth side surface SIF 12  of the first lens portion  101  and the thirty-first side surface SIF 31  and the thirty-second side surface SIF 32  of the third lens portion  103 , the first light L 1  is reflected by the second reflector  420 , emitted to the twenty-first surface SF 21  of the second lens portion  102 , and provided to the user&#39;s right eye RE. Further,  FIG. 17  illustrates that after the second light L 2  of the second display device  202  is totally reflected three times, e.g., by the twenty-second side surface SIF 22  of the second lens portion  102  and the thirty-first side surface SIF 31  and the thirty-second side surface SIF 32  of the third lens portion  103 , the second light L 2  is reflected by the first reflector  410 , emitted to the eleventh surface SF 11  of the first lens portion  101 , and provided to the user&#39;s left eye LE. However, the number of total reflections of the first light L 1  of the first display device  201  and the number of total reflections of the second light L 2  of the second display device  202  are not limited thereto. As the number of total reflections of the first light L 1  of the first display device  201  increases, the depth of the virtual image displayed on the first display device  201  may be deepened. However, because the loss of the first light L 1  of the first display device  201  increases, the luminance of the virtual image of the first display device  201  provided to the user&#39;s right eye RE may be reduced. As the number of total reflections of the second light L 2  of the second display device  202  increases, the depth of the virtual image displayed on the second display device  202  may be deepened. However, because the loss of the second light L 2  of the second display device  202  increases, the luminance of the virtual image of the second display device  202  provided to the user&#39;s left eye LE may be reduced. Thus, the number of total reflections of the first light L 1  of the first display device  201  and the number of total reflections of the second light L 2  of the second display device  202  may be set in consideration of the depths of field of the virtual images displayed on the first display device  201  and the second display device  202 , the luminance of the virtual image of the first display device  201  provided on the user&#39;s right eye RE and the luminance of the virtual image of the second display device  202  provided in the user&#39;s left eye LE. 
     Meanwhile, in order for the first light L 1  of the first display device  201  and the second light L 2  of the second display device  202  to be totally reflected at the first side surface SIF 1  and the second side surface SIF 2  of the third lens portion  103 , the length of the third lens portion  103  in the first direction (X-axis direction) may be longer than the length of the first lens portion  101  in the first direction (X-axis direction) and the length of the second lens portion  102  in the first direction (X-axis direction). 
     According to the embodiment shown in  FIGS. 15-17 , after the first light L 1  of the first display device  201  disposed on the eleventh side surface SIF 11  of the first lens portion  101  is totally reflected by at least one side surface of the third lens portion  103  connecting the first lens portion  101  and the second lens portion  102 , the first light L 1  may be emitted to the twenty-first surface SF 21  of the second lens portion  102  by the second reflector  420  disposed in the second lens portion  102 , and provided to the user&#39;s right eye RE. Further, after the second light L 2  of the second display device  202  disposed on the twenty-first side surface SIF 21  of the second lens portion  102  is totally reflected by at least one side surface of the third lens portion  103 , the second light L 2  may be emitted to the eleventh surface SF 11  of the first lens portion  101  by the first reflector  410  disposed in the first lens portion  101 , and provided to the user&#39;s left eye LE. Thus, the optical distance between the first display device  201  and the second reflector  420  and the optical distance between the second display device  202  and the first reflector  410  can be increased. Therefore, the depth of field of the virtual image displayed on the first display device  201  and the depth of field of the virtual image displayed on the second display device  202  can be deepened. 
       FIGS. 18A-18B  are perspective views showing an optical device  10 _ 9  according to an embodiment. 
     The embodiment shown in  FIGS. 18A-18B  differs from the embodiment shown in  FIGS. 15-17  in that the optical device  10 _ 9  further includes a third reflector  430  disposed adjacent to the first reflector  410  and a fourth reflector  440  disposed adjacent to the second reflector  420 . A description overlapping with the embodiment described above with reference to  FIGS. 15-17  may be omitted, and differences from the embodiment shown in  FIGS. 15-17  are mainly described with reference to  FIGS. 18A-18B . 
     Referring to  FIGS. 18A-18B , the optical device  10 _ 9  further includes the third reflector  430  disposed adjacent to the first reflector  410  and the fourth reflector  440  disposed adjacent to the second reflector  420 . Meanwhile, the number of reflectors of the optical device  10 _ 9  is not limited to that shown in  FIGS. 18A-18B . As the number of reflectors in the optical device  10 _ 9  increases, the luminance of the virtual image provided to the user&#39;s left eye LE and the user&#39;s right eye RE may increase, and the area of the display device  200  viewed by the user&#39;s left eye LE and the user&#39;s right eye RE, e.g., the field of view (FOV) of the user, may be enlarged. 
     The third reflector  430  is disposed in the first lens portion  101  of the lens  100 . The fourth reflector  440  is disposed in the second lens portion  102  of the lens  100 . The third reflector  430  and the fourth reflector  440  may be small mirrors, such as pin mirrors. Although  FIGS. 18A-18B  illustrate that the third reflector  430  and the fourth reflector  440  have a circular cross section, the third reflector  430  and the fourth reflector  440  may have any suitable shape, such as an elliptical or polygonal cross section. 
     The third reflector  430  and the fourth reflector  440  are formed to be smaller in size than the pupil of the eye E. For example, each of the third reflector  430  and the fourth reflector  440  may be formed to have a diameter of about 500 μm to about 4 mm. In embodiments, because the user focuses on the real image, it is difficult to recognize the third reflector  430  and the fourth reflector  440 . However, as the size of the third reflector  430  and the fourth reflector  440  decreases, the luminance of the virtual image provided to the user&#39;s eye E by the flexible display device  200  also decreases. Thus, in consideration of this fact, the size of the third reflector  430  and the fourth reflector  440  may be set. 
     The third reflector  430  and the fourth reflector  440  may have a cylindrical shape, as shown in  FIGS. 18A-18B . In embodiments, one of the two bottom surfaces may be a reflecting surface implemented as a mirror, and the other one of the two bottom surfaces and the side surface are not implemented as a mirror. In order to emit the light L totally reflected from the thirty-first side surface SIF 31  of the third lens portion  103  of the lens  100  to the eleventh surface SF 11  of the first lens portion  101 , the bottom surface of an upper portion of the third reflector  430  may be a reflecting surface, as shown in  FIGS. 18A-18B . Further, in order to emit the light L totally reflected from the thirty-first side surface SIF 31  of the third lens portion  103  of the lens  100  to the twenty-first surface SF 21  of the second lens portion  102 , the bottom surface of an upper portion of the fourth reflector  440  may be a reflecting surface, as shown in  FIGS. 18A-18B . 
     The third reflector  430  may reflect the virtual image displayed on the second display device  202  and provide it to the user&#39;s left eye LE. The fourth reflector  440  may reflect the virtual image displayed on the first display device  201  and provide it to the user&#39;s right eye RE. Because the virtual image displayed on the first display device  201  is reflected by the fourth reflector  440 , the depth of field is deepened. Because the virtual image displayed on the second display device  202  is reflected by the third reflector  430 , the depth of field is deepened. 
     As shown in  FIG. 18A , the first light L 1  of the first display device  201  may travel toward the twelfth side surface SIF 12  of the first lens portion  101  by the first optical path changing layer  311 . When the refractive index of the lens  100  is larger than the refractive index of air and the incident angle of the first light L 1  incident on the twelfth side surface SIF 12  of the first lens portion  101  is larger than the critical angle, a part of the first light L 1  of the first display device  201  may be totally reflected by the twelfth side surface SIF 12  of the first lens portion  101 . A part of the first light L 1  totally reflected by the twelfth side surface SIF 12  of the first lens portion  101  may be totally reflected by the thirty-second side surface SIF 32  of the third lens portion  103 . A part of the first light L 1  totally reflected by the thirty-second side surface SIF 32  of the third lens portion  103  may be totally reflected by the thirty-first side surface SIF 31  of the third lens portion  103 . A part of the first light L 1  totally reflected by the thirty-first side surface SIF 31  of the third lens portion  103  may be emitted to the twenty-first surface SF 21  of the second lens portion  102  by the second reflector  420  and the fourth reflector  440  and provided to the user&#39;s right eye RE. 
     Further, as shown in  FIG. 18B , the second light L 2  of the second display device  202  may travel toward the twenty-second side surface SIF 22  of the second lens portion  102  by the second optical path changing layer  312 . When the refractive index of the lens  100  is larger than the refractive index of air and the incident angle of the second light L 2  incident on the twenty-second side surface SIF 22  of the second lens portion  102  is larger than the critical angle, a part of the second light L 2  of the second display device  202  may be totally reflected by the twenty-second side surface SIF 22  of the second lens portion  102 . A part of the second light L 2  totally reflected by the twenty-second side surface SIF 22  of second lens portion  102  may be totally reflected by the thirty-second side surface SIF 32  of the third lens portion  103 . A part of the second light L 2  totally reflected by the thirty-second side surface SIF 32  of the third lens portion  103  may be totally reflected by the thirty-first side surface SIF 31  of the third lens portion  103 . A part of the second light L 2  totally reflected by the thirty-first side surface SIF 31  of the third lens portion  103  may be emitted to the eleventh surface SF 11  of the first lens portion  101  by the first reflector  410  and the third reflector  430  and provided to the user&#39;s left eye LE. 
     According to the embodiment shown in  FIGS. 18A-18B , because each of the first lens portion  101  and the second lens portion  102  includes the plurality of reflectors, the luminance of the virtual image provided to the user&#39;s left eye LE and the user&#39;s right eye RE can be increased as compared with embodiments where one reflector is provided, and the area of the display device  200  viewed by the user&#39;s left eye LE and the user&#39;s right eye RE, e.g., the field of view (FOV) of the user, can be enlarged. 
       FIG. 19  is a perspective view showing an optical device  10 _ 10  according to an embodiment. 
     The embodiment shown in  FIG. 19  differs from the embodiment shown in  FIGS. 15-17  in that a first reflective sheet  331  is disposed on the twelfth side surface SIF 12  of the first lens portion  101 , the twenty-second side surface SIF 22  of the second lens portion  102  and the thirty-first side surface SIF 31  of the third lens portion  103 , and a second reflective sheet  333  is disposed on the thirty-second side surface SIF 32  of the third lens portion  103 . A description overlapping with the embodiment described above with reference to  FIGS. 15-17  may be omitted, and differences from the embodiment shown in  FIGS. 15-17  are mainly described with reference to  FIG. 19 . 
     Referring to  FIG. 19 , the optical device  10 _ 10  further includes the first reflective sheet  331  disposed on the twelfth side surface SIF 12  of the first lens portion  101 , the twenty-second side surface SIF 22  of the second lens portion  102  and the thirty-first side surface SIF 31  of the third lens portion  103 , and the second reflective sheet  333  disposed on the thirty-second side surface SIF 32  of the third lens portion  103 . The twelfth side surface SIF 12  of the first lens portion  101 , the twenty-second side surface SIF 22  of the second lens portion  102 , and one surface of the first reflective sheet  331  facing the thirty-first side surface SIF 31  of the third lens portion  103  may be implemented as mirrors. One surface of the second reflective sheet  333  facing the thirty-second side surface SIF 32  of the third lens portion  103  may be implemented as a mirror. 
     The first light L 1  of the first display device  201  may travel toward the twelfth side surface SIF 12  of the first lens portion  101  by the first optical path changing layer  311 . The first light L 1  of the first display device  201  may be reflected by the first reflective sheet  331  disposed on the twelfth side surface SIF 12  of the first lens portion  101 . A part of the first light L 1  reflected by the first reflective sheet  331  disposed on the twelfth side surface SIF 12  of the first lens portion  101  may be reflected by the second reflective sheet  333  disposed on the thirty-second side surface SIF 32  of the third lens portion  103 . A part of the first light L 1  reflected by the second reflective sheet  333  disposed on the thirty-second side surface SIF 32  of the third lens portion  103  may be reflected by the first reflective sheet  331  disposed on the thirty-first side surface SIF 31  of the third lens portion  103 . A part of the first light L 1  reflected by the first reflective sheet  331  disposed on the thirty-first side surface SIF 31  of the third lens portion  103  may be emitted to the twenty-first surface SF 21  of the second lens portion  102  by the second reflector  420  and provided to the user&#39;s right eye RE. 
     Further, the second light L 2  of the second display device  202  may travel toward the twenty-second side surface SIF 22  of the second lens portion  102  by the second optical path changing layer  312 . A part of the second light L 2  of the second display device  202  may be reflected by the first reflective sheet  331  disposed on the twenty-second side surface SIF 22  of the second lens portion  102 . A part of the second light L 2  reflected by the first reflective sheet  331  disposed on the twenty-second side surface SIF 22  of the second lens portion  102  may be reflected by the second reflective sheet  333  disposed on the thirty-second side surface SIF 32  of the third lens portion  103 . A part of the second light L 2  reflected by the second reflective sheet  333  disposed on the thirty-second side surface SIF 32  of the third lens portion  103  may be reflected by the first reflective sheet  331  disposed on the thirty-first side surface SIF 31  of the third lens portion  103 . A part of the second light L 2  totally reflected by the thirty-first side surface SIF 31  of the third lens portion  103  may be emitted to the eleventh surface SF 11  of the first lens portion  101  by the first reflector  410  and provided to the user&#39;s left eye LE. 
     The total reflection occurs only when the incident angle is larger than the critical angle, whereas the first reflective sheet  331  and the second reflective sheet  333  reflect the incident light almost intact. Thus, in embodiments including the first reflective sheet  331  and the second reflective sheet  333 , a ratio of the reflected light to the incident light can be increased as compared with embodiments including total reflection. 
     According to the embodiment shown in  FIG. 19 , the first light L 1  of the first display device  201  and the second light L 2  of the second display device  202  are reflected by the first reflective sheet  331  disposed on the twelfth side surface SIF 12  of the first lens portion  101 , the twenty-second side surface SIF 22  of the second lens portion  102  and the thirty-first side surface SIF 31  of the third lens portion  103 , and the second reflective sheet  333  disposed on the thirty-second side surface SIF 32  of the third lens portion  103 . The luminance of the virtual images of the first display device  201  and the second display device  202  provided to the user&#39;s left eye LE and right eye RE can be increased. 
       FIG. 20  is a perspective view showing an optical device  10 _ 11  according to an embodiment. 
     The embodiment shown in  FIG. 20  differs from the embodiment shown in  FIGS. 15-17  in that the eleventh side surface SIF 11  of the first lens portion  101  and the twenty-first side surface SIF 21  of the second lens portion  102  are formed as a curved surface having a predetermined curvature. A description overlapping with the embodiment described above with reference to  FIGS. 15-17  may be omitted, and differences from the embodiment shown in  FIGS. 15-17  are mainly described with reference to  FIG. 20 . 
     Referring to  FIG. 20 , the eleventh side surface SIF 11  of the first lens portion  101  and the twenty-first side surface SIF 21  of the second lens portion  102  may be a curved surface, e.g., a curved surface having a predetermined curvature. The eleventh side surface SIF 11  of the first lens portion  101  may have a curved shape in an outward direction (e.g., the first direction (X-axis direction)) of the eleventh side surface SIF 11 . The twenty-first side surface SIF 21  of the second lens portion  102  may have a curved shape in an outward direction (e.g., a direction opposite to the first direction (X-axis direction)) of the twenty-first side surface SIF 21 . Accordingly, a part of the eleventh side surface SIF 11  of the first lens portion  101  may face a part of the twelfth side surface SIF 12 . A part of the twenty-first side surface SIF 21  of the second lens portion  102  may face a part of the twenty-second side surface SIF 22 . 
     The first display device  201  may be a flexible display device with flexibility, which can be bent. Thus, the first display device  201  may be disposed in a bent shape on the eleventh side surface SIF 11  of the first lens portion  101  formed as a curved surface. Further, because a part of the eleventh side surface SIF 11  of the first lens portion  101  may face a part of the twelfth side surface SIF 12 , the first light L 1  of the first display device  201  may travel toward the twelfth side surface SIF 12  without the first optical path changing layer  311  and may be totally reflected by the twelfth side surface SIF 12 . Therefore, the first optical path changing layer  311  may be omitted. 
     The second display device  202  may be a flexible display device with flexibility, which can be bent. Thus, the second display device  202  may be disposed in a bent shape on the twenty-first side surface SIF 21  of the second lens portion  102  formed as a curved surface. Further, because a part of the twenty-first side surface SIF 21  of the second lens portion  102  may face a part of the twenty-second side surface SIF 22 , the second light L 2  of the second display device  202  may travel toward the twenty-second side surface SIF 22  without the second optical path changing layer  312  and may be totally reflected by the twenty-second side surface SIF 22 . Therefore, the second optical path changing layer  312  may be omitted. 
     Although  FIG. 20  illustrates that the eleventh side surface SIF 1  of the first lens portion  101  and the twenty-first side surface SIF 21  of the second lens portion  102  are formed as curved surfaces, the present disclosure is not limited thereto. For example, when the length of the thirteenth side surface SIF 13  of the first lens portion  101  in the first direction (X-axis direction) is shorter than the length of the twelfth side surface SIF 12  in the first direction (X-axis direction), the eleventh side surface SIF 11  may be disposed obliquely such that a part of the eleventh side surface SIF 11  of the first lens portion  101  may face a part of the twelfth side surface SIF 12 . The first light L 1  of the first display device  201  may travel toward the twelfth side surface SIF 12  without the first optical path changing layer  311  and may be totally reflected by the twelfth side surface SIF 12 . In embodiments, the eleventh side surface SIF 11  of the first lens portion  101  may be formed as a flat surface rather than a curved surface. 
     Further, when the length of the twenty-third side surface SIF 23  of the second lens portion  102  in the first direction (X-axis direction) is shorter than the length of the twenty-second side surface SIF 22  in the first direction (X-axis direction), the twenty-first side surface SIF 21  may be disposed obliquely such that a part of the twenty-first side surface SIF 21  of the second lens portion  102  may face a part of the twenty-second side surface SIF 22 . The second light L 2  of the second display device  202  may travel toward the twenty-second side surface SIF 22  without the second optical path changing layer  312  and may be totally reflected by the twenty-second side surface SIF 22 . In embodiments, the twenty-first side surface SIF 21  of the second lens portion  102  may be formed as a flat surface rather than a curved surface. 
     According to the embodiment shown in  FIG. 20 , each of the first display device  201  and the second display device  202  is formed as a flexible display device with flexibility. The first display device  201  may be disposed in a bent shape on the eleventh side surface SIF 11  of the first lens portion  101  formed as a curved surface. The second display device  202  may be disposed in a bent shape on the twenty-first side surface SIF 21  of the second lens portion  102  formed as a curved surface. Thus, the first light L 1  of the first display device  201  may travel toward the twelfth side surface SIF 12  without the first optical path changing layer  311  and may be totally reflected by the twelfth side surface SIF 12 . Further, the second light L 2  of the second display device  202  may travel toward the twenty-second side surface SIF 22  without the second optical path changing layer  312  and may be totally reflected by the twenty-second side surface SIF 22 . 
       FIG. 21  is an exemplary diagram illustrating an eye glass-type display device  1  including an optical device according to various embodiments.  FIG. 21  shows that optical devices  10   a  and  10   b  according to the embodiments of the present disclosure can be applied to the eyeglass-type display device  1 . 
     Referring to  FIG. 21 , the eyeglass-type display device  1  may include a first optical device  10   a , a second optical device  10   b , a support frame  20 , and eyeglass legs  30   a  and  30   b . Although  FIG. 21  illustrates the eyeglass-type display  1  including the eyeglass legs  30   a  and  30   b , the optical devices  10   a  and  10   b  according to embodiments of the present disclosure may be applied to a head mounted display including a head mount band that can be mounted on the head instead of the eyeglass legs  30   a  and  30   b , for example. 
     The example to which the optical device is applied is not limited to that shown in  FIG. 21 , but it can be applied in various forms to various other electronic devices. 
     Although the preferred embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.