Optical waveguide structure and display device
By employing light guide structures with different refractive indices in AR display devices, the problem of image light deviation is corrected, increasing the amount of image light that can be received by the human eye and improving the brightness of the displayed image.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- INTERFACE ADVANCED TECH (CHENGDU) CO LTD
- Filing Date
- 2025-01-20
- Publication Date
- 2026-07-23
AI Technical Summary
In AR display devices, the image light deviates from the preset direction during its propagation within the optical waveguide, causing some of the image light to have difficulty escaping from the coupling grating, resulting in a reduction in the brightness of the displayed image seen by the user.
The optical waveguide structure includes a first light guide section and a second light guide section that are spliced together. The refractive index of the first light guide section is less than that of the second light guide section. When the image light is propagated in the first light guide section, the deviation from the edge is corrected. After being refracted by the second light guide section, the amount of image light that can be received by the human eye is increased.
It increases the amount of image light received by the human eye, thereby enhancing the brightness of the displayed image.
Smart Images
Figure CN2025073239_23072026_PF_FP_ABST
Abstract
Description
Optical waveguide structure and display device Technical Field
[0001] This application relates to an optical waveguide structure and a display device including the optical waveguide structure. Background Technology
[0002] Augmented Reality (AR) display devices combine virtual images with real-world scenes, allowing users to interact naturally with digital content, thus becoming a target for industry development. AR display devices include AR near-eye displays and AR head-up displays. Optical waveguides are increasingly seen as the mainstream solution to meet the imaging needs of AR display devices. This is mainly because optical waveguides can achieve total internal reflection. After the optical engine completes the imaging (generates image light), it couples the image light into the optical waveguide. The waveguide then transmits the image light to the eye (for near-eye displays) or the windshield (for head-up displays) through the principle of total internal reflection, before releasing it and being received by the human eye to form an image.
[0003] In current AR display devices, during the transmission of image light from the input grating to the output grating within the optical waveguide, some of the image light gradually shifts towards the edge of the optical waveguide. This makes it difficult for this portion of image light to exit from the area on the output grating corresponding to the eye box, resulting in a reduction in the amount of image light received by the human eye and a darkening of the displayed image seen by the user. Summary of the Invention
[0004] The first aspect of this application provides an optical waveguide structure, comprising:
[0005] An optical waveguide and an input grating and an output grating located on the same surface of the optical waveguide and spaced apart;
[0006] The optical waveguide includes a first light guide section and a second light guide section spliced together. The refractive index of the first light guide section is less than that of the second light guide section. The orthogonal projections of the coupling grating and the coupling grating on the optical waveguide along the thickness direction of the optical waveguide are located on the first light guide section.
[0007] The coupling grating is used to couple image light into the optical waveguide, so that the image light passes through the first light guide, the second light guide, and the first light guide in sequence and then exits the optical waveguide from the coupling grating.
[0008] In the optical waveguide structure provided in this application embodiment, when image light is coupled into the first light guide section from the coupling grating and propagated within the first light guide section, some of the image light deviates from the preset propagation direction and shifts towards the two sides of the optical waveguide. Since the refractive index of the first light guide section is less than that of the second light guide section, after the image light is refracted and transmitted through the second light guide section, the degree of deviation of the image light towards the edge of the optical waveguide is corrected, reducing the degree of deviation. This increases the amount of image light coupled out from the coupling grating and that can be received by the human eye, thereby improving the brightness of the displayed image seen by the human eye.
[0009] A second aspect of this application provides a display device, comprising:
[0010] A display used to emit light for images;
[0011] As described above, in the optical waveguide structure, the coupling grating of the optical waveguide structure is located in the optical path of the image light, and is used to couple the image light into the optical waveguide.
[0012] The aforementioned display device integrates the aforementioned optical waveguide structure, achieving all the beneficial effects of the aforementioned optical waveguide structure. Attached Figure Description
[0013] Figure 1 is a schematic diagram of the planar structure of the optical waveguide structure of the related technology.
[0014] Figure 2 is a three-dimensional structural diagram of the optical waveguide structure of the first embodiment of this application.
[0015] Figure 3 is a schematic diagram of the planar structure of the optical waveguide structure in Figure 2.
[0016] Figure 4 is a schematic diagram of the planar structure of an optical waveguide structure with the input grating and output grating set on different surfaces of the optical waveguide.
[0017] Figure 5 is a schematic diagram of the optical path when the image light is propagated in the optical waveguide structure in Figure 2.
[0018] Figure 6 is a schematic diagram of the planar structure of the optical waveguide structure according to the second embodiment of this application.
[0019] Figure 7 is a schematic diagram of the optical path when the image light is propagated in the optical waveguide structure in Figure 6.
[0020] Figure 8 is a schematic diagram of the planar structure of the optical waveguide structure according to the third embodiment of this application.
[0021] Figure 9 is a schematic diagram of the planar structure of the optical waveguide structure according to the fourth embodiment of this application.
[0022] Figure 10 is a three-dimensional structural diagram of the AR near-eye display device according to an embodiment of this application.
[0023] Figure 11 is a schematic diagram of the optical path of the image light emitted by the display in the AR near-eye display device of Figure 10.
[0024] Figure 12 is a schematic diagram of the optical path of image light in the AR head-up display device according to an embodiment of this application.
[0025] Key component symbols: AR near-eye display device 100 AR head-up display device 200 Optical waveguide structure 1a, 1 Optical waveguide 10a, 10 First surface 101 Second surface 102 First light guide 11 First part 111 Second part 112 Second light guide 12 First side 121 Second side 122 Third side 123 Fourth side 124 Coupled-in grating 20a, 20 Coupled-out grating 30a, 30 Receiving area 31a, 31 Display 2 Collimating lens 3 Imaging medium 4 Image light LSa, LS
[0026] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation
[0027] Figure 1 is a schematic diagram of the planar structure of the optical waveguide structure 1a in the related art. Referring to Figure 1, the optical waveguide structure 1a includes an optical waveguide 10a, a coupling grating 20a, and a coupling grating 30a. The coupling grating 20a and the coupling grating 30a are spaced apart on the same surface of the optical waveguide 10a. The coupling grating 20a is used to couple the image light LSA into the optical waveguide 10a, so that the image light LSA is propagated in the direction close to the coupling grating 30a within the optical waveguide 10a. The coupling grating 30a is used to couple the image light LSA out of the optical waveguide 10a.
[0028] When applying the optical waveguide structure 1a of the relevant technology to an AR display device, at least the following problems exist. Specifically, when a user uses an AR display device, the amount of image light coupled out of the coupling grating 30a that the human eye can receive is limited. That is, only a portion of the image light LSa coupled out of the coupling grating 30a can be received by the human eye. The emitting area corresponding to the image light LSa that can be received by the human eye on the coupling grating 30a is defined as the receiving area 31a. During the transmission of image light LSa from the input grating 20a to the output grating 30a, some image light LSa deviates from the preset propagation direction and shifts towards the edge of the optical waveguide 10a. This makes it difficult for this portion of image light LSa to be coupled out of the optical waveguide 10a from the receiving area 31a and ultimately received by the human eye, resulting in a decrease in the brightness of the displayed image seen by the human eye.
[0029] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.
[0030] It should be noted that when a component is referred to as being "fixed to" or "mounted to" another component, it can be directly on the other component or there may be an intervening component. When a component is considered to be "set on" another component, it can be directly set on the other component or there may be an intervening component. The term "and / or" as used herein includes all and any combination of one or more of the associated listed items. The terminology used in this application's specification is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.
[0031] To further illustrate the technical means and effects adopted by this application in achieving its intended purpose, the following detailed description of this application is provided in conjunction with the accompanying drawings and preferred embodiments.
[0032] Please refer to Figures 2 and 3 together. The optical waveguide structure 1 of the first embodiment of this application includes an optical waveguide 10 and a coupling grating 20 and a coupling grating 30 located on the same surface of the optical waveguide 10 and spaced apart. The coupling grating 20 is used to couple image light LS into the optical waveguide 10, and the coupling grating 30 is used to couple the image light LS from the coupling grating 20 out of the optical waveguide 10, so that the image light LS can be received by the human eye, thereby allowing the user to see the display image formed by the image light LS.
[0033] The optical waveguide 10 includes a first light guide section 11 and a second light guide section 12 spliced together. The refractive index of the first light guide section 11 is less than that of the second light guide section 12, and the refractive index of the second light guide section 12 ranges from 1.3 to 2.5 (inclusive). The orthographic projections of the coupling grating 20 and the coupling grating 30 along the thickness direction of the optical waveguide 10 onto the optical waveguide 10 are located on the first light guide section 11. Both the coupling grating 20 and the coupling grating 30 are disposed on the surface of the first light guide section 11. After the image light LS is coupled into the optical waveguide 10 from the coupling grating 20, it sequentially passes through the first light guide section 11, the second light guide section 12, and then exits the optical waveguide 10 from the coupling grating 30.
[0034] The optical waveguide 10 is generally a rectangular thin plate structure, including a first surface 101 and a second surface 102 that are spaced apart and opposite to each other. A coupling grating 20 and a coupling grating 30 are spaced apart on the first surface 101. The coupling grating 20 is a generally circular thin plate structure, and the coupling grating 30 is a generally rectangular thin plate structure. The line connecting the geometric centers of the coupling grating 20 and the coupling grating 30 is parallel to the long side of the first surface 101 and equidistant from the two long sides of the first surface 11. In other embodiments of this application, the coupling grating 20 and the coupling grating 30 may have other geometric structures, such as rhombuses or hexagons. In some implementations, as shown in FIG4, the coupling grating 20 and the coupling grating 30 are disposed on different surfaces of the optical waveguide 10, with the coupling grating 20 located on the first surface 101 and the coupling grating 30 located on the second surface 102.
[0035] The first light guide 11 includes a first part 111 and a second part 112 that are separated from each other. The first part 111 and the second part 112 are respectively connected to the two ends of the second light guide 12 and are flush with the second light guide 12 in the thickness direction. The first part 111, the second light guide 12, and the second part 112 are all rectangular thin plate structures, and the first part 111, the second light guide 12, and the second part 112 are sequentially spliced to form the optical waveguide 10. The thickness of the first part 111, the thickness of the second part 112, and the thickness of the second light guide 12 are the same. In the direction perpendicular to the thickness of the optical waveguide 10 (or, along the propagation direction of the image light LS in the optical waveguide 10, without considering the reflection direction of the image light LS in the optical waveguide 10), the width of the first part 111, the width of the second part 112, and the width of the second light guide 12 are the same. The coupling grating 20 is located on the surface of the first part 111, and the coupling grating 30 is located on the surface of the second part 112, so that the image light LS is coupled into the first part 111 from the coupling grating 20, and then sequentially transmitted through the first part 111, the second light guide 12, and the second part 112, and finally coupled out of the second part 112 from the coupling grating 30.
[0036] Referring to Figure 5, the first light guide portion 11 and the second light guide portion 12 are flush with each other in the thickness direction of the optical waveguide 10. The first surface 101 and the second surface 102 are both formed by the first light guide portion 11 and the second light guide portion 12, and the first surface 101 and the second surface 102 are basically smooth planes. The thickness of the first light guide portion 11 is equal to the thickness of the second light guide portion 12, so that the image light LS can be transmitted forward after being alternately reflected by the first surface 101 and the second surface 102 in the first light guide portion 11 and the second light guide portion 12, respectively.
[0037] The second light guide portion 12 includes a first side surface 121 and a second side surface 122 connected to the first light guide portion 11. The first side surface 121 and the second side surface 122 are located between the first surface 101 and the second surface 102, and are respectively connected to the first surface 101 and the second surface 102. In this embodiment, both the first side surface 121 and the second side surface 122 are planar. The first side surface 121 and the second side surface 122 are parallel to each other and both are perpendicular to the first surface 101. The first side surface 121 and the second side surface 122 are arranged sequentially at intervals in the direction from the coupling-in grating 20 to the coupling-out grating 30.
[0038] Both the first light guide portion 11 and the second light guide portion 12 are transparent solid structures. The material of the second light guide portion 12 can be glass, plastic, or a combination of both. In other embodiments, the first light guide portion 11 is a transparent solid structure, and the second light guide portion 12 is a transparent liquid structure. The material of the second light guide portion 12 includes water or oil. In this case, the second light guide portion 12 is located inside a solid container, and the refractive index of the solid container is the same as that of the first light guide portion 11.
[0039] Referring to Figures 6 and 7, in the optical waveguide structure 1 of the second embodiment of this application, unlike the first embodiment, both the first side surface 121 and the second side surface 122 are smooth curved surfaces. In some implementations, both the first side surface 121 and the second side surface 122 are spherical curved surfaces, and the curvature of the second side surface 122 is less than or equal to the curvature of the first side surface 121. The first side surface 121 and the second side surface 122 are curved toward the coupling grating 30. Since the two opposing first side surfaces 121 and the second side surface 122 of the second light guide portion 12 are both spherical curved surfaces, and the second light guide portion 12 is made of a transparent material. A lens is an optical element made of a transparent material (such as glass, crystal, etc.) and has two refractive surfaces. Therefore, the second light guide 12 can be considered as a lens structure. The first side surface 121 is the object side surface of the second light guide 12, and the second side surface 122 is the image side surface of the second light guide 12. The process of the image light LS being transmitted from the first part 111 through the second light guide 12 to the second part 112 is equivalent to an imaging process of the second light guide 12. The image light LS is a parallel beam, therefore, the object distance is infinite during the imaging process of the second light guide 12. In order to make the image light LS transmitted through the second light guide 12 also a parallel beam, that is, to make the image distance infinite during the imaging process of the second light guide 12, according to the lens imaging formula, the focal length of the second light guide 12 should be designed to be infinite. From the lens maker's equation, it can be deduced that the radius of curvature of the first side surface 121 and the radius of curvature of the second side surface 122 should satisfy the following relationship: n×(R2-R1+d)-d=0,
[0040] Where n is the refractive index of the first light guide 11, R1 is the radius of curvature of the first side 121, R2 is the radius of curvature of the second side 122, and neither the radius of curvature R1 nor the radius of curvature R2 is infinite, and d is the shortest distance between the first side 121 and the second side 122. In other words, d is the distance between the first side 121 and the second side 122 on the line connecting the center of the first side 121 and the center of the second side 122.
[0041] Since the first side surface 121 and the second side surface 122 of the second light guide 12 are smooth spherical surfaces convex in the same direction, and the curvature of the second side surface 122 is less than or equal to the curvature of the first side surface 121, when the curvature of the second side surface 122 is less than the curvature of the first side surface 121, the second light guide 12 is a concave lens structure. Concave lens structures generally diverge parallel light beams. Therefore, after the image light LS is transmitted through the second light guide 12, the beam radius of the image light LS expands, causing the beam radius of the image light LS emitted from the coupling grating 30 to also expand accordingly, thereby achieving a pupil dilation effect.
[0042] Referring to Figure 8, in the optical waveguide structure 1 of the third embodiment of this application, unlike the first and second embodiments, the first light guide portion 11 is arranged around the second light guide portion 12. In some implementations, the first light guide portion 11 is not separated by the second light guide portion 12, the first light guide portion 11 has a rectangular opening, and the second light guide portion 12 is a thin plate-like structure with a rectangular outline, with the first light guide portion 11 surrounding and connected to the outer edge of the second light guide portion 12. Along the propagation direction of the image light LS in the optical waveguide 10 (ignoring the reflection direction of the image light LS within the optical waveguide 10), the width of the second light guide portion 12 is smaller than the width of the outer outline of the first light guide portion 11. In this embodiment, both the first side surface 121 and the second side surface 122 are planar, parallel to each other, and both perpendicular to the first surface 101.
[0043] Please refer to Figure 9. In the optical waveguide structure 1 of the fourth embodiment of this application, unlike the third embodiment, the first side 121 and the second side 122 are both curved surfaces, and the curvature radii of the first side 121 and the second side 122 can satisfy the relationship in the second embodiment, so that the beam radius of the image light LS after being transmitted through the second light guide 12 is expanded to achieve the pupil expansion effect.
[0044] Please refer to Figures 3, 6, 8, and 9. In the four embodiments described above, the second light guide portion 12 further includes a third side surface 123 and a fourth side surface 124 arranged at intervals. The third side surface 123 and the fourth side surface 124 are located between the first surface 101 and the second surface 102, and are also located between the first side surface 121 and the second side surface 122. The first side surface 121, the third side surface 123, the second side surface 122, and the fourth side surface 124 are sequentially connected to form the sidewall of the second light guide portion 12. In the four embodiments described above, the third side surface 123 and the fourth side surface 124 are both planar. This application does not limit the shape of the third side surface 123 and the fourth side surface 124; in other embodiments, the third side surface 123 and the fourth side surface 124 may be curved surfaces.
[0045] Referring again to Figure 3, in order to allow more image light to exit from the area (receiving area 31) of the coupled-out grating 30 corresponding to the image light LS that can be received by the human eye, thereby improving the brightness of the displayed image seen by the human eye when using the display device, the optical waveguide 10 of the optical waveguide structure 1 of this embodiment includes a first light guide 11 and a second light guide 12, and the refractive index of the first light guide 11 is less than the refractive index of the second light guide 12. The second light guide 12 is used to refract and transmit the image light LS, causing the image light LS to deflect away from the edge of the optical waveguide 10, thereby reducing the degree of deflection of the image light LS towards the edge of the optical waveguide 10, increasing the number of image light LS emitted from the receiving area 31, so that the human eye can see more image light LS, thereby improving the brightness of the displayed image seen by the human eye.
[0046] The optical waveguide structure of this application embodiment can be applied to display devices using AR technology, such as AR near-eye display devices and AR head-up display devices.
[0047] This application also provides a display device using the above-described optical waveguide structure, including: a display for emitting image light; and an optical waveguide structure as described in any of the above embodiments, wherein a coupling grating is located in the optical path of the image light for coupling the image light into the optical waveguide.
[0048] The following explanations will take AR near-eye display devices and AR head-up display devices that utilize the aforementioned optical waveguide structure as examples.
[0049] Please refer to Figures 10 and 11 together, which are schematic diagrams of an AR near-eye display device 100 using the optical waveguide structure 1 according to an embodiment of this application.
[0050] The AR near-eye display device 100 of this application embodiment includes an optical waveguide structure 1, a display 2, and a collimating lens 3. The display 2 is used to emit image light LS, and the optical waveguide structure 1 is located in the optical path of the image light LS. The coupling grating 20 and the coupling grating 30 are both located on the first surface 101. The display 2 can be any one of a liquid crystal display, a fast-response liquid crystal display, a silicon-based liquid crystal display, a micro-light-emitting diode display, a digital light processing display, a laser beam scanning display, an active matrix organic light-emitting diode display, and a silicon-based organic light-emitting diode display; this application does not impose any limitation.
[0051] Collimating lens 3 is located between display 2 and coupling grating 20, and is spaced apart from display 2 and optical waveguide 10 respectively. The image light LS emitted by display 2 is a non-parallel beam. Collimating lens 3 is used to convert the image light LS from display 2 into a parallel beam before it exits to coupling grating 20. That is, coupling grating 20 is located in the optical path of image light LS emitted from collimating lens 3. Parallel light has a uniform intensity distribution and a small divergence angle, which allows the parallel light to be more uniformly distributed on the surface of optical waveguide 10 before entering optical waveguide 10, converting image light LS into a parallel beam. This helps to reduce scattering of image light LS when it is coupled into optical waveguide 10 through coupling grating 20, and improves optical coupling efficiency. The polarization state of image light LS can be circularly polarized or linearly polarized. The wavelength range of image light LS is generally 400nm-700nm (including the endpoint value). The color of image light LS can be formed by mixing red, green and blue in different proportions. This application does not limit the polarization state, color and wavelength of image light LS.
[0052] Please refer to Figure 12, which is a schematic diagram of an AR head-up display device 200 using the optical waveguide structure 1 according to an embodiment of this application.
[0053] The AR head-up display device 200 of this application embodiment includes an optical waveguide structure 1, a display 2, and a collimating lens 3, as well as an imaging medium 4. In the AR head-up display device 200, the coupling grating 20 and the coupling grating 30 are located on different surfaces of the optical waveguide 10, with the coupling grating 20 located on the first surface 101 and the coupling grating located on the second surface 102. The imaging medium 4 is located in the optical path of the image light LS emitted from the coupling grating 30, and is used to reflect the image light LS to the human eye, allowing the human eye to see the displayed image of the display 2. At the same time, the imaging medium 4 is also used to transmit external light, allowing the user to see the combination of the displayed image of the display 2 and the external scene, thereby achieving the purpose of augmented reality. The imaging medium 4 can be a plane mirror, a concave mirror, or a combination of multiple mirrors with different shapes. This application does not limit the shape and number of the imaging medium 4.
[0054] Those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of protection claimed in this application.
Claims
1. An optical waveguide structure, characterized in that, It includes an optical waveguide and an input grating and an output grating located on the same surface of the optical waveguide and spaced apart from each other; The optical waveguide includes a first light guide section and a second light guide section spliced together. The refractive index of the first light guide section is less than that of the second light guide section. The orthogonal projections of the coupling grating and the coupling grating on the optical waveguide along the thickness direction of the optical waveguide are located on the first light guide section. The coupling grating is used to couple image light into the optical waveguide, so that the image light passes through the first light guide, the second light guide, and the first light guide in sequence and then exits the optical waveguide from the coupling grating.
2. The optical waveguide structure as described in claim 1, characterized in that, The optical waveguide includes a first surface and a second surface that are spaced apart and opposite to each other. The first light guide portion and the second light guide portion are flush in the thickness direction of the optical waveguide. The first surface and the second surface are both formed by the first light guide portion and the second light guide portion.
3. The optical waveguide structure as described in claim 2, characterized in that, The second light guide portion includes a first side and a second side connected to the first light guide portion, and the first side and the second side are arranged sequentially at intervals in the direction from the coupled-in grating to the coupled-out grating.
4. The optical waveguide structure as described in claim 3, characterized in that, Both the first side and the second side are planes, and the first side and the second side are parallel to each other.
5. The optical waveguide structure as described in claim 4, characterized in that, The first side and the second side are perpendicular to the first surface.
6. The optical waveguide structure as described in claim 3, characterized in that, Both the first side and the second side are smooth curved surfaces, and both the first side and the second side are curved toward the coupling grating.
7. The optical waveguide structure as described in claim 6, characterized in that, Both the first side and the second side are spherical surfaces, and the curvature of the second side is less than or equal to the curvature of the first side.
8. The optical waveguide structure as described in claim 7, characterized in that, The optical waveguide structure satisfies the following relationship: n×(R2-R1+d)-d=0. Where n is the refractive index of the first light guide, R1 is the radius of curvature of the first side, R2 is the radius of curvature of the second side, and d is the shortest distance between the first side and the second side.
9. The optical waveguide structure as described in any one of claims 1-8, characterized in that, The refractive index of the second light guide portion ranges from 1.3 to 2.
5.
10. The optical waveguide structure as described in any one of claims 1-8, characterized in that, Both the first light guide and the second light guide are transparent solid structures.
11. The optical waveguide structure as described in any one of claims 1-8, characterized in that, The first light guide is a transparent solid structure, and the second light guide is a transparent liquid structure.
12. The optical waveguide structure as described in any one of claims 1-8, characterized in that, The first light guide includes a first part and a second part that are separated from each other. The first part and the second part are respectively connected to the two ends of the second light guide and are flush with the second light guide in the thickness direction. The coupling grating is located on the surface of the first part and the coupling grating is located on the surface of the second part. The coupling grating is used to couple the image light into the first part, so that the image light passes through the first part, the second light guide, and the second part in sequence and is coupled out of the second part from the coupling grating.
13. The optical waveguide structure as described in any one of claims 1-8, characterized in that, The first light guide portion is arranged around the second light guide portion.
14. A display device, characterized in that, include: A display used to emit light for images; as well as In any one of claims 1-13, the optical waveguide structure, wherein the coupling grating is located in the optical path of the image light and is used to couple the image light into the optical waveguide.
15. The display device as claimed in claim 14, characterized in that, The head-mounted display device also includes a collimating lens located between the display and the coupling grating, used to convert the image light from the display into a parallel beam before it is emitted to the coupling grating.
16. The display device as claimed in claim 14, characterized in that, The display device is an AR near-eye display device or an AR head-up display device.