Patent Publication Number: US-2023152591-A1

Title: Augmented reality display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a bypass continuation application of International Patent Application PCT/KR2021/008733, filed on Jul. 8, 2021, which is based on and claims priority to Korean Patent Application No. 10-2020-0089160, filed on Jul. 17, 2020 in the Korean Intellectual Property Office, the disclosures of each of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     The disclosure relates to an augmented reality (AR) display device that displays augmented reality, and more particularly to an AR display device with a miniaturized display engine. 
     2. Description of Related Art 
     An augmented reality (AR) display device is a display device that enables a user to see AR, and may include, for example, AR glasses. An image optical system of the AR display device includes a display engine (a projector, etc.) that outputs an image, and a waveguide that transmits the output image to the eyes of a user. An image emitted from the display engine is transmitted to the eyes through the waveguide, allowing the user to see the image. 
     A wearable display device is a device that enables a user wearing the wearable display device to see a displayed screen. As such, wearable display devices are actively being studied, and various forms of wearable devices are currently or are expected to be released on the market. For example, a glasses-type display device (e.g., wearable glasses) or a head-mounted display device are examples of wearable display devices currently released or expected to be released on the market. To use the AR display device as a wearable display device, light weight and thinness are required for convenience of a user, and to this end, miniaturization of a high-resolution display engine is important. 
     SUMMARY 
     According to an embodiment of the disclosure, an augmented reality (AR) display device includes a display engine configured to project light of an image, a waveguide configured to receive and output light projected from the display engine, and a body on which the display engine and the waveguide are installed, in which the display engine includes a light source unit, a reflective display panel, and a projection optical system, the projection optical system includes an iris and a first projection lens group arranged between the iris and the display panel, the light source unit includes at least one of a light source and a light exit end positioned near the iris in a position deviating from an optical axis of the projection optical system such that an incident angle range of light incident to the display panel does not overlap with a reflection angle range of light reflected from the display panel, and the iris includes an effective opening through which light reflected from the reflective display panel passes. 
     In embodiments of the disclosure, the light source unit may include a plurality of light-emitting elements of different monochromatic colors, and the plurality of light-emitting elements may be arranged substantially adjacent to each other. 
     In embodiments of the disclosure, the light source unit may include a plurality of light-emitting elements arranged respectively at a plurality of positions spaced apart from one another. In embodiments of the disclosure, the plurality of light-emitting elements arranged spaced apart from one another may have different monochromatic colors. Alternatively, the plurality of light-emitting elements arranged spaced apart from one another may have a same monochromatic color. In embodiments of the disclosure, the plurality of light-emitting elements may be arranged at substantially regular spacing with respect to the optical axis of the projection optical system. 
     In embodiments of the disclosure, the effective opening may include a plurality of effective openings interspersed among the plurality of light-emitting elements. 
     In embodiments of the disclosure, the effective opening may include a plurality of effective openings corresponding to a plurality of light-emitting elements arranged spaced apart from one another. 
     In embodiments of the disclosure, a distance between a center of the effective opening and a center of the iris may be equal to a distance between the light source or the light exit end and the center of the iris. 
     In embodiments of the disclosure, the light source unit may include the light source and a light guide configured to guide the light emitted from the light source, and the light exit end may be an exit end of the light guide. 
     In embodiments of the disclosure, the light source unit may include the light source and a light pipe configured to transmit the light emitted from the light source, and the light exit end may be an exit end of the light pipe. 
     In embodiments of the disclosure, the light source may be a light-emitting diode (LED) or a laser diode (LD). 
     In embodiments of the disclosure, the first projection lens group may be configured to function as an illuminating optical system configured to uniformly illuminate the display panel with the light emitted from the light source unit. 
     In embodiments of the disclosure, the projection optical system may further include a second projection lens group arranged at a front end of the iris. 
     In embodiments of the disclosure, the projection optical system may further include a reflection member arranged at the front end of the iris to change a path of the light projected from the display engine. 
     In embodiments of the disclosure, the reflective display panel may be a liquid crystal on silicon (LCoS) panel. 
     In embodiments of the disclosure, at least a region of the waveguide may be formed of a transparent material to allow light of a real scene to pass therethrough. 
     In embodiments of the disclosure, the body may be configured to be wearable by a user. 
     In embodiments of the disclosure, the body may be any one of a body of a glass frame, a goggle frame, or a helmet and a body of a head mounted display (HMD). 
     According to the disclosure, an AR display device may innovatively reduce the volume of a display engine. 
     According to the disclosure, the AR display device may reduce weight and thickness thereof by reducing the volume of the display engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which identical or like reference numerals in the drawings denote identical or like elements, and wherein: 
         FIG.  1    illustrates the exterior of an augmented reality (AR) display device, according to an example embodiment of the disclosure; 
         FIG.  2    is a plan view illustrating the AR display device of  FIG.  1   ; 
         FIG.  3    is a block diagram of an AR display device, according to an example embodiment of the disclosure; 
         FIG.  4    illustrates an arrangement of a display engine and a waveguide, according to an example embodiment of the disclosure; 
         FIG.  5    illustrates an optical arrangement of a display engine, according to an example embodiment of the disclosure; 
         FIG.  6    illustrates a light source, according to an example embodiment of the disclosure; 
         FIG.  7    illustrates an arrangement of a light source and an iris, according to an example embodiment of the disclosure; 
         FIG.  8    illustrates an incident angle range and a reflection angle range in a display panel, according to an example embodiment of the disclosure; 
         FIG.  9    illustrates an optical arrangement of a display engine, according to an example embodiment of the disclosure; 
         FIGS.  10 - 16    illustrate various alternate arrangements of one or more light sources and an iris, according to example embodiments of the disclosure; 
         FIGS.  17  and  18    illustrate various alternate optical arrangements of a display engine, according to example embodiments of the disclosure; 
         FIG.  19    illustrates a light source unit, according to an example embodiment of the disclosure; and 
         FIG.  20    illustrates an additional optical arrangement of a display engine, according to an example embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, example embodiments of the disclosure will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals denote like components, and sizes of components in the drawings may be exaggerated for convenience of explanation. It is noted that embodiments of the disclosure to be described are merely examples, and various modifications may be made from such embodiments of the disclosure. 
     Although terms used in embodiments of the disclosure are selected with general terms popularly used at present under the consideration of functions in the disclosure, the terms may vary according to the intention of those of ordinary skill in the art, judicial precedents, or introduction of new technology. In addition, in certain cases, the applicant may voluntarily select terms, and in such cases, the meaning of the terms may be disclosed in a corresponding description part of an embodiment of the disclosure. Thus, the terms used in herein should be defined not by the simple names of the terms but by the meaning of the terms and the contents throughout the disclosure. 
     Singular forms include plural forms unless indicated otherwise contextually. When a portion is described as “comprising” or “including” a component, the portion does not necessarily exclude other components, but may further include other components unless stated otherwise. 
     In the disclosure, “augmented reality (AR)” means overlaying a virtual image generated on a computer onto a physical real-world environment or a real-world object to display one image. 
     In the disclosure, an “AR display device” refers to a device capable of expressing or producing AR, and may include but is not limited to AR glasses, a head-mounted display (HMD), an AR helmet, etc., worn by a user. The AR display device may be used in everyday applications such as information search, route guidance, camera photographing, etc. An AR glasses device, implementing the AR display device in the form of glasses, may be worn as a fashion item and used both in indoor and outdoor activities. 
     In the disclosure, a “real scene” refers to a scene of the real world an observer or the user sees through the AR display device, and may include real world object(s). In contrast, a “virtual image” is an image generated through a display engine. The virtual image may include both a static image and a dynamic image. The virtual image may be an image which is overlaid on the real scene to show information regarding a real object in the real scene or information or a control menu, etc., regarding an operation of the AR device. 
       FIG.  1    illustrates the exterior of an AR display device  100  according to an example embodiment of the disclosure, and  FIG.  2    is a plan view of the AR display device  100  of  FIG.  1   . 
     Referring to  FIGS.  1  and  2   , the AR display device  100  according to the illustrated embodiment of the disclosure may be a glasses-type display device configured to be worn by a user and may include a glasses-type body  110 . 
     The glasses-type body  110  may include, for example, a frame  111  and temples  119 . The frame  111  in which glass lenses  101 L and  101 R are positioned may have, for example, the shape of two rims connected by a bridge. The glass lenses  101 L and  101 R are examples, and may or may not have a refractive power (a power). The glass lenses  101 L and  101 R may be formed integrally, and in such case, the rims of the frame  111  may be integrated with the bridge  112 . The glass lenses  101 L and  101 R may be omitted. 
     The temples  119  may be connected to respective ends  113  of the frame  111  and extend in a direction. That is, a left temple  119 L may be connected to a left end  113 L, and likewise a right temple  119 R may be connected to a right end  113 R. The ends  113  of the frame  111  may be respectively connected to the temples  119  by a hinge  115 . The hinge  115  is an example, such that a known member connecting the ends  113  of the frame  111  with the temples  119 . In another example, the ends  113  of the frame  111  and the temples  119  may be integrally connected. 
     In the glasses-type body  110 , a display engine  120 , a waveguide  130 , and various electronic parts  190  may be arranged. The electronic parts  190  may be mounted in a part of the glasses-type body  110  or positioned distributed in a plurality of parts thereof, and may be mounted on a printed circuit board (PCB) substrate, a flexible PCB (FPCB) substrate, etc. 
     The display engine  120 , which may also be termed an optical engine, may be configured to generate light of a virtual image, and may include a left-eye display engine  120 L and a right-eye display engine  120 R. The left-eye display engine  120 L and the right-eye display engine  120 R may be positioned in the respective ends  113  of the frame  111  or in an upper portion of the frame  111 . In another example, the left-eye display engine  120 L and the right-eye display engine  120 R may be respectively positioned in a left temple  119 L and a right temple  119 R. In another example, the left-eye display engine  120 L and the right-eye display engine  120 R may be arranged at an upper end of the waveguide  130 . 
     More details of the display engine  120  will be described further herein. 
     The waveguide  130  may be configured to redirect or otherwise retransmit light of the virtual image generated in the display engine  120 , together with light of an external scene, to a pupil of the user. The waveguide  130  may include a left-eye waveguide  130 L and a right-eye waveguide  130 R. The left-eye waveguide  130 L and the right-eye waveguide  130 R may be respectively attached to the left glass lens  101 L and the right glass lens  101 R. Alternatively, the left-eye waveguide  130 L and the right-eye waveguide  130 R may be fixed on the frame  111  separately from the glass lenses  101 L and  101 R. 
       FIG.  3    is a block diagram of an AR display device  100 , according to an example embodiment of the disclosure. 
     Referring to  FIG.  3   , the AR display device  100  may include the display engine  120 , a processor  200 , an interface  210 , and a memory  220 . 
     The processor  200  may control the overall operation of the AR display device  100  including the display engine  120  by driving an operating system or an application, and perform various data processing and operations including image data. For example, the processor  200  may process image data including a left-eye virtual image and a right-eye virtual image that are rendered to have binocular disparity. The processor  200  may include, for example, at least one hardware among a central processing unit (CPU), a microprocessor, a graphic processing unit (GPU), application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), or field programmable gate arrays (FPGAs), without being limited thereto. 
     Data or a manipulation command is input to or output from an outside through the interface  210  which may include a user interface, for example, a touch pad, a controller, a manipulation button, etc., which may be manipulated by the user. In an embodiment, the interface  210  may include a wired communication module, such as a universal serial bus (USB) module, and a wireless communication module, such as Bluetooth, through which manipulation information of the user or data of a virtual image, transmitted from an interface included in an external device, may be received. 
     The memory  220  may include an internal memory such as volatile memory or nonvolatile memory. The memory  220  may store various data, programs, or applications for driving and controlling the AR display device  100  and input/output signals or data of a virtual image, under control of the processor  200 . 
     The display engine  120  may be configured to receive image data generated by the processor  200  and generate light of a virtual image, and may include the left-eye display engine  120 L and the right-eye display engine  120 R. Each of the left-eye display engine  120 L and the right-eye display engine  120 R may include a light source that outputs light and a display panel that forms a virtual image by using the light output from the light source, and may have a function such as a small projector. The light source may be implemented as, for example, a light-emitting diode (LED), and the display panel may be implemented as, for example, a liquid crystal on silicon (LCoS). 
     The display engine  120  and the waveguide  130  may be collectively termed optical parts herein. Although left-eye optical parts  120 L,  130 L will be described as an example below, a left-eye part and a right-eye part have structures symmetrical to each other, such that it would be understood by those of ordinary skill in the art that disclosed aspects of the left-eye optical parts  120 L,  130 L may be applied to right-eye optical parts  120 R,  130 R. 
       FIG.  4    illustrates an arrangement of the display engine  120  and the waveguide  130 , according to an example embodiment of the disclosure. Referring to  FIG.  4   , the waveguide  130  may be formed as a single layer or multiple layers of a transparent material in which the light may propagate while being internally reflected. The waveguide  130  may have the shape of a flat plate or a curved plate. Herein, the transparent material may refer to a material through which light in a visible light band passes. A transparency of the transparent material may be less than 100%, and the transparent material may have a certain color. The waveguide  130  may include a first region  131  facing the display engine  120  that receives light Li of a virtual image projected from the display engine  120 , a second region  132  to which the light of the virtual image incident to the first region  131  propagates, and a third region  133  that outputs light Lo of the virtual image propagating from the second region  132 . 
     The waveguide  130  may be mounted on the frame  111  of  FIG.  1    such that the third region  133  is positioned in front of the pupils of the user when the user wears the AR display device  100 . As the waveguide  130  is formed of a transparent material, the user may see the real scene as well as the virtual image through the AR display device  100 , and thus the AR display device  100  may implement AR. 
     In an embodiment of the disclosure, in the first region  131  of the waveguide  130 , an input diffraction grating may be formed to couple incident light. When the waveguide  130  is formed as a single layer, the input diffraction grating of the first region  131  may be formed on a surface facing the display engine  120 . Alternatively, when the waveguide  130  is formed as multiple layers, the input diffraction grating of the first region  131  may be formed on each layer or some layers. 
     The display engine  120  may be arranged such that emitted light is incident perpendicularly or inclinedly at a certain angle with respect to the first region  131 . 
     The second region  132  may be positioned in a first direction (for example, in  FIG.  4   , the direction indicated as X) with respect to the first region  131 . The second region  132  may overlap with the entire first region  131  or a part thereof. The second region  132  may be formed on the entire area of the waveguide  130 . In the second region  132 , a diffraction grating may be provided such that incident light of a virtual image propagates to the third region  133 . When the waveguide  130  is formed as a single layer, the diffraction grating of the second region  132  may be formed on the same surface as a surface where the diffraction grating of the first region  131  is formed or an opposite surface to the surface. When the waveguide  130  is formed as multiple layers, the diffraction grating of the second region  132  may be formed on the same surface as the surface where the diffraction grating of the first region  131  is formed, or on a different surface than the surface. Although it is described in the illustrated embodiment of the disclosure that the second region  132  is a single region, the second region  132  may be divided into a plurality of regions. When the waveguide  130  is formed as multiple layers, the second region  132  may include a plurality of regions formed on different layers. 
     The third region  133  may be positioned in a side of a surface facing eyes of the user when the user wears the AR display device  100 . For example, in  FIG.  4   , the third region  133  may be positioned in a second direction with respect to the first region  131 . The second direction may be the same as the first direction, as in the embodiment shown in  FIG.  4   , or it may be a different direction. The entire third region  133  or a part thereof may overlap with the second region  132 . In the third region  133 , an output grating array may be formed to output light propagating from the second region  132 . When the waveguide  130  is formed as a single layer, the output grating array of the third region  133  may be formed on a surface of the waveguide  130 , which faces the eyes of the user, or a back surface thereof. Alternatively, when the waveguide  130  is formed as multiple layers, the output grating array of the third region  133  may be formed on some or all of the multiple layers. 
       FIG.  5    illustrates an optical arrangement of the display engine  120 ,  FIG.  6    illustrates a light source  311 , and  FIG.  7    illustrates an arrangement of the light source  311  of a light source unit  310  and an iris  332 , each according to an example embodiment of the disclosure. 
     Referring to  FIGS.  5  to  7   , the display engine  120  may include the light source unit  310 , a display panel  320 , and a projection optical system  330 . 
     The light source unit  310  may include one light source  311  or a plurality of light sources  311 . The light source  311  may be arranged near the iris  332  of the projection optical system  330 . 
     The light source  311  may be, but not limited to, a light-emitting element such as a light-emitting diode (LED) or a laser diode (LD). For example, as shown in  FIG.  6   , the light source  311  may be an LED package on which light-emitting elements  311 R,  311 G, and  311 B of RGB are mounted. The light-emitting elements  311 R,  311 G, and  311 B of RGB may be arranged substantially adjacent to each other, such that they emit light from substantially the same position. 
       FIG.  6    illustrates an LED package on which one red LED chip  311 R, two green LED chips  311 G, and one blue LED chip  311 B are mounted, but the arrangement and composition of the LED chips is not limited to the configuration shown in  FIG.  6   . In another example, the light-emitting elements  311 R,  311 G, and  311 B of RGB may be provided one by one. In another example, a light-emitting element in white (W) may be further provided. In another example, two red light-emitting elements  311 R may be provided, and one green LED chip  311 G and one blue LED chip  311 B may be provided. The light-emitting elements  311 R,  311 G, and  311 B of RGB may be sequentially driven to sequentially illuminate red light, green light, and blue light. The light-emitting elements  311 R,  311 G, and  311 B of RGB may be driven in any suitable order. 
     A lens, for example in the form of a dome, may be provided on a top surface of the LED package such that the light-emission distribution of light emitted from the LED package may be suitable for the optical design of the projection optical system  330  described below. Alternatively, a condensing lens or collimating lens may be arranged attached to or spaced apart from an exit surface of the LED package. 
     The display panel  320  may be a device that forms an image by using the light emitted from the light source unit  310 , and include light modulation devices arranged two-dimensionally. The display panel  320  used in the illustrated embodiment of the disclosure may be a reflective display panel, e.g., a liquid crystal on silicon (LCoS) panel. In another example, the display panel  320  may be a digital micro-mirror device (DMD) panel or another known reflective panel, which is switchable from a state where micro mirrors are arranged selectively flat or tilted by an electrical signal. 
     In  FIG.  5   , cover glass  340  is arranged on a side of a panel surface  321  of the display panel  320 . The display panel  320  may implement a color image by chronologically forming two-dimensional images of red, green, and blue and reflecting red light, green light, and blue light, in correspondence to the red light, the green light, and the blue light chronologically illuminated from the light source unit  310 . 
     The projection optical system  330  may include a projection lens group  331  and the iris  332 . 
     The projection lens group  331  may be an optical member that projects an image generated from the display panel  320  to the first region  131  of the waveguide  130 , and may include one optical lens or a plurality of optical lenses. The projection lens group  331  may be arranged between the iris  332  and the display panel  320 . In other words, the iris  332  may be arranged on a front surface of the projection lens group  331 . The iris  332  may include an effective opening  333  that defines an effective diameter of the projection lens group  331 . The effective opening  333  may be formed of a transparent material or the air (i.e., a hole). While  FIG.  7    shows a case where the effective opening  333  is circular, the disclosure is not limited thereto. In another example, the effective opening  333  may have a polygonal shape. The iris  332  may further include an additional region  334  formed of an opaque material. 
     The light source  311  may be positioned on or in a side of the iris  332 . The light source  311  may be arranged spaced apart from a center C of the iris  332  by a distance d 1 . The center C of the iris  332  may be an optical axis (OA of  FIG.  5   ). 
     The light source  311  may be placed at substantially the same position as the iris  332 , when viewed in a longitudinal direction of the optical axis OA. Alternatively, the light source  311  may be arranged slightly apart toward a front side of the iris  332  (i.e., a far side from the display panel  320 ) or a rear side of the iris  332  (i.e., a near side to the display panel  320 ), when viewed in the longitudinal direction of the optical axis OA. 
     In an embodiment of the disclosure, in a position where the light source  311  of the iris  332  is arranged, a groove, etc., may be provided to allow the light source  311  to be mounted therein. 
     In an embodiment of the disclosure, a side of the iris  332  may be cut and the light source  311  may be arranged in a cut position. 
     The effective opening  333  may be provided in a position opposing the light source  311  with respect to the center C (i.e., the optical axis OA). A center of the effective opening may be spaced apart from a center C of the iris  332  by a distance d 2 . Light L emitted from the light source  311  may be illuminated to the display panel  320  through the projection lens group  331 . In this case, the projection lens group  331  may function as an illumination optical system for the light source  311 . The projection lens group  331  may allow the light emitted from the light source  311  to uniformly illuminate the entire panel surface  321  (i.e., an effective modulation surface) of the display panel  320 . Thereafter, the light of the 2D image reflected through modulation from the display panel  320  may pass through the projection lens group  331  and then through the effective opening  333  of the iris  332 , thus being projected to the waveguide  130 . 
       FIG.  8    illustrates an incident angle range and a reflection angle range in the display panel  320 , according to an example embodiment of the disclosure. Referring to  FIG.  8   , the incident light Li incident to the panel surface  321  may be positioned in a side with respect to a normal  329 , and the reflected light Lo reflected from the panel surface  321  may be positioned in the other side with respect to the normal  329 . As described above, the light source  311  is arranged spaced apart from the center C of the iris  332  (i.e., the optical axis OA), such that by appropriately selecting the distance d 1  of the light source  311  from the center C, the angle range of the incident light Li may be prevented from overlapping with the angle range of the reflected light Lo, and thus the effective opening  333  of the iris  332  may be separated from the light source  311 . 
     A diameter D 1  of the effective opening  333  may be equal to or less than a half of a diameter D 2  (i.e., a radius) of the iris  332 . The diameter D 1  of the effective opening  333  may differ according to an effective surface of the display panel  320  and an optical design of the projection lens group  331 . 
     The display engine  120  according to the illustrated embodiment of the disclosure may be used for an AR display device such as a glasses-type device, and thus may be required to be very small in size. Thus, in the illustrated embodiment of the disclosure, by arranging the light source unit  310  near the iris  332 , a member such as a prism arranged in front of a display panel in a conventional projection device may be removed, thereby reducing the size requirements of the display engine. 
     Although it is shown in  FIG.  5    that the light emitted from the light source  311  is focused on the effective opening  333  of the iris  332 , the disclosure is not limited thereto. 
     While it is described in the embodiment of the disclosure described with reference to  FIGS.  5  to  8    that the projection lens group  331  is arranged between the iris  332  and the display panel  320 , the disclosure is not limited thereto.  FIG.  9    illustrates an optical arrangement of a display engine, according to an example embodiment of the disclosure. Referring to  FIG.  9   , the display engine may include a light source unit  410 , a display panel  420 , and a projection optical system  430 . The illustrated embodiment of the disclosure is substantially the same as the display engine of the embodiment of the disclosure described with reference to  FIGS.  5  to  8   , except that the projection optical system  430  further includes a second projection lens group  433  as well as a first projection lens group  431  and an iris  432 . The second projection lens group  433  may be arranged in front of the iris  432  (i.e., a far side from the display panel  420 ) and project light passing through an effective opening of the iris  432  toward the first region  131  of the waveguide  130  of  FIG.  4   . 
     While an example where the light source unit  310  is structured such that one LED package having LED chips of RGB mounted thereon is arranged in a side of the iris  332  is described in the embodiment of the disclosure with reference to  FIGS.  5  to  8   , the disclosure is not limited thereto. Next, various alternate arrangements of one or more light sources and an iris will be described. 
       FIG.  10    illustrates another arrangement of a light source unit  510  and an iris  530 , according to an example embodiment of the disclosure. Referring to  FIG.  10   , the light source unit  510  may include four light sources  511  arranged substantially adjacent to each other, such that the four light sources  511  emit light from substantially the same position. The number of light sources  511  shown in  FIG.  10    is an example, and does not limit the scope of the disclosure. Each of the light sources  511  may be an LED package having LED chips of RGB mounted thereon. The plurality of light sources  511  are arranged in substantially the same position, such that one effective opening  531  corresponding thereto may be provided in the iris  530 . 
       FIG.  11    illustrates another arrangement of the light source unit  510  and the iris  530 , according to an example embodiment of the disclosure. Referring to  FIG.  11   , the light source unit  510  may include two light sources  511  and  512  arranged in two positions spaced apart from each other. Each of the light sources  511  and  512  may be an LED package having LED chips of RGB mounted thereon. The two light sources  511  and  512  are arranged in positions spaced apart from each other, such that two effective openings  531  and  532  corresponding thereto may be provided in the iris  530 . A distance d 1  between the light sources  511  and  512  and the center C of the iris  530  and a distance d 2  between centers of the effective openings  531  and  532  and the center C of the iris  530  may be substantially equal to each other. When a diameter of the two effective openings  531  and  532  is considered, an angle θ between the two light sources  511  and  512  with respect to the center C of the iris  530  may be limited and may be less than about 100 degrees. As shown in  FIG.  11   , the angle θ between the two light sources  511  and  512  may be about 90 degrees. An angle between the two effective openings  531  and  532  may be substantially equal to the angle θ between the two light sources  511  and  512 . 
       FIG.  12    illustrates another arrangement of the light source unit  510  and the iris  530  according to an example embodiment of the disclosure. Referring to  FIG.  12   , the light source unit  510  may include three light sources  511 ,  512 , and  513  arranged in three positions spaced apart from one another at substantially regular angular spacing with respect to the center C of the iris  530 . That is, the three light sources  511 ,  512 , and  513  may be arranged spaced apart from each other at an interval of substantially 120 degrees—one third of a circle defined with respect to the center C of the iris  530 . Each of the light sources  511 ,  512 , and  513  may be an LED package having LED chips of RGB mounted thereon. The three light sources  511 ,  512 , and  513  are arranged in positions spaced apart from each other, such that three effective openings  531 ,  532 , and  533  corresponding thereto may be provided in the iris  530 . The distance d 1  between the light sources  511 ,  512 , and  513  and the center C of the iris  530  and the distance d 2  between the effective openings  531 ,  532 , and  533  and the center C of the iris  530  may be substantially equal to each other. As can be seen in  FIG.  12   , such arrangement may alternatingly intersperse the effective openings  531 ,  532 , and  533  among the light sources  511 ,  512 , and  513 . 
       FIG.  13    illustrates another arrangement of the light source unit  510  and the iris  530 , according to an example embodiment of the disclosure. Referring to  FIG.  13   , a side  534  of the iris  530  where one light source  511  is arranged may be formed of an opaque material, and a half portion  535  may be removed in place of an effective opening. One light source  511  may be an LED package having LED chips of RGB mounted thereon. In the illustrated embodiment of the disclosure, the half portion  535  in which the opaque material of the iris  530  is removed may be understood as an effective opening. 
       FIG.  14    illustrates another arrangement of the light source unit  510  and the iris  530 , according to an example embodiment of the disclosure. The illustrated embodiment of the disclosure is substantially the same as the embodiment of the disclosure described with reference to  FIG.  13   , except that the light source unit  510  includes the two light sources  511  and  512 . Like in  FIG.  13   , a side of the iris  530  where the two light sources  511  and  512  are arranged may be formed of an opaque material, and a half portion  535  may be removed in place of an effective opening. The angle θ between the light sources  511  and  512  with respect to the center C of the iris  530  may be less than about 100 degrees, for example, substantially 90 degrees. 
       FIG.  15    illustrates another arrangement of the light source unit  510  and the iris  530 , according to an example embodiment of the disclosure. The illustrated embodiment of the disclosure is substantially the same as the embodiments of the disclosure described with reference to  FIGS.  13  and  14   , except that the light source unit  510  includes the three light sources  511 ,  512 , and  513 . Like in  FIGS.  13  and  14   , a side of the iris  530  where the light sources  511 ,  512 , and  513  are arranged may be formed of an opaque material, and the half portion  535  may be removed in place of an effective opening. The angle θ between the light sources  511  and  513  with respect to the center C of the iris  530  may be less than about 100 degrees, for example, substantially 90 degrees. The light sources  511 ,  512 , and  513  may be arranged at substantially regular angular spacing with respect to each other; for example, if the angle θ between the light sources  511  and  513  is substantially 90 degrees, the light source  512  between them may be arranged at substantially 45 degrees to each. 
     Although an example where light sources of the light source unit  510  include light-emitting elements of RGB is described in the above-described embodiments of the disclosure, the disclosure is not limited thereto.  FIG.  16    illustrates arrangement of a light source unit  610  and the iris  530  according to an embodiment of the disclosure. The illustrated embodiment of the disclosure is substantially the same as the embodiment of the disclosure described with reference to  FIG.  12   , except that the light source unit  610  includes different monochromatic light sources  611 ,  612 , and  613 . The different monochromatic light sources  611 ,  612 , and  613  may be, for example, a red LED chip, a green LED chip, and a blue LED chip. The iris  530  may include the three effective openings  531 ,  532 , and  533  corresponding to the three light sources  611 ,  612 , and  613 , like in  FIG.  12   . 
     Although an example where a light source of a light source unit is arranged directly in an iris is described in the above-described embodiments of the disclosure, the disclosure is not limited thereto.  FIG.  17    illustrates another optical arrangement of a display engine, according to an example embodiment of the disclosure. Referring to  FIG.  17   , the display engine may include a light source unit  710 , a display panel  720 , and a projection optical system  730 . The projection optical system  730  may include an iris  732 , a first projection lens group  731  arranged between the iris  732  and the display panel  720 , and a second projection lens group  733  arranged in front of the iris  732  (i.e., a far side from the display panel  720 ). In the illustrated embodiment of the disclosure, a light source  711  of the light source unit  710  may be arranged outside a projection optical system  730 , and light may be emitted toward the iris  732  of the projection optical system  730  through a separate light guide  712 . That is, the display engine according to the illustrated embodiment of the disclosure may be substantially the same as the display engine according to the above-described embodiments of the disclosure, except that a light exit end  714  of the light guide  712  is arranged near the iris  732 . The light guide  712  may be formed of a transparent material, and may transmit light emitted from the light source  711  through internal total reflection and allow light to be emitted to the light exit end  714  located at an end thereof. One or more mirrors  713  may be provided to change an optical path in the light guide  712 . An optical fiber may be used instead of the light guide  712 . 
       FIG.  18    illustrates another optical arrangement of a display engine, according to an example embodiment of the disclosure. Referring to  FIG.  18   , the display engine may include a light source unit  810 , a display panel  820 , and a projection optical system  830 . In the illustrated embodiment of the disclosure, a light source  811  of the light source unit  810  may be arranged inside a projection optical system  830 , and light may be emitted toward an iris  832  through a separate light pipe  812 . That is, the display engine according to the illustrated embodiment of the disclosure may be substantially the same as the display engine according to the above-described embodiments of the disclosure, except that a light exit end  814  of the light pipe  812  is arranged near the iris  832 . The light pipe  812  may be formed of a transparent material, and may transmit light emitted from the light source  811  through internal total reflection and allow light to be emitted to the light exit end  814  located at an end thereof. While  FIG.  18    shows an example where a cross-sectional size of the light pipe  812  is uniform in an optical-axis direction, the disclosure is not limited thereto. The cross-sectional size of the light pipe  812  may gradually increase in the optical-axis direction to adjust the light-emission distribution of light. 
     The projection optical system  830  may include the iris  832 , a first projection lens group  831  arranged between the iris  832  and the display panel  820 , and a second projection lens group  833  arranged in front of the iris  832  (i.e., a far side from the display panel  820 ). As the light source unit  810  includes the light source  811  and the light pipe  812 , a physical size of the light source unit  810  may increase, such that a part of the second projection lens group  833  may be removed to secure an installation space of the light source unit  810 . Like in the embodiment of the disclosure described with reference to  FIG.  5   , there may be no second projection lens group. 
     In another embodiment of the disclosure, an illuminating optical system lens may be arranged in place of the light pipe  812 . For example, the illuminating optical system lens may be a condensing lens or a collimating lens. 
       FIG.  19    illustrates a light source unit, according to an example embodiment of the disclosure. Referring to  FIG.  19   , a light source unit  910  may include different monochromatic first through third light sources  911 ,  912 , and  913  coupled by a first dichroic mirror  916  and a second dichroic mirror  917 . The first through third light sources  911 ,  912 , and  913  may be, for example, a red light source, a green light source, and a blue light source, respectively. The first dichroic mirror  916  may pass red light emitted from the first light source  911  and reflected off a mirror  915 , and reflect the green light emitted from the second light source  912 . Likewise, the second dichroic mirror  917  may pass the red light and the green light emitted from the first light source  911  and the second light source  912  and reflect the blue light emitted from the third light source  913 . Although not shown in the drawings, condensing lenses may be arranged on an optical path of the light source unit  910 . When the first to third light sources  911 ,  912 , and  913  are LDs, an optical member or a device for reducing a speckle due to coherency of laser may be additionally arranged. 
       FIG.  20    illustrates another optical arrangement of a display engine, according to an example embodiment of the disclosure. Referring to  FIG.  20   , the display engine may include a light source unit  1010 , a display panel  1020 , and a projection optical system  1030 . The projection optical system  1030  may include a projection lens group  1031  and an iris  1032 . A reflection member  1037  may be arranged in front of the iris  1032  to change a path of the projected light L away from the optical axis OA. The illustrated embodiment of the disclosure may be substantially the same as the display engine of the above-described embodiments of the disclosure, except that a reflection member  1037  for changing the path of the projected light L is further provided in the projection optical system  1030 . For example, when the AR display device is AR glasses, the size of the display engine may be limited, such that by arranging the reflection member  1037  at a front end of the projection optical system  1030 , more freedom may be given to designing of the exterior of the AR glasses. 
     While the AR display device according to the disclosure has been shown and described in connection with the embodiments of the disclosure to help understanding of the disclosure, it will be apparent to those of ordinary skill in the art that modifications and variations may be made. Therefore, the true technical scope of the disclosure should be defined by the appended claims.