Transparent display

Abstract

The invention relates to a transparent display (600), comprising a holographic diffuser (611) extending substantially in a two-dimensional diffuser plane, and comprising an enlarging reflective element (612), wherein the holographic diffuser (611) and the reflective element (612) are part of a one-piece optical unit (610), and wherein image rays, reflected by the reflective element (612), are guided inside the optical unit (610) to the holographic diffuser (611).

Description

[0001] Description

[0002] Transparent display

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to transparent displays.

[0005] Many applications require very large-format displays. For example, lecture halls use displays that consist of a projector with an image generation unit and a screen. Short-throw projectors are increasingly being used, such as those disclosed in US 10 067 324 B2 and WO 2018 / 117210 A1. A short-throw projector can be positioned between the presenter and the screen even in smaller rooms, allowing the presenter to move freely around the room without being exposed to the light beams from the projector to the screen.

[0006] There is a growing demand for transparent displays. Transparent displays can offer viewers highly immersive augmented reality (AR) experiences. Transparent displays can be realized using transparent OLED displays embedded in glass substrates. The production of large, transparent displays based on OLED displays is very cost-intensive. Furthermore, they are generally not robust enough for use in harsh environments. Head-up displays are also known, in which images are projected onto transparent substrates so that the images are reflected on the substrate, allowing the viewer to visually perceive the images as well as the environment located behind the substrate. Head-mounted, transparent displays are described, for example, in the documents EP 3 320 384 B1, US 2011 / 0 164 294 A1, US 2010 / 0 066 926 A1 and US 2008 / 0 186 547 A1.DE 102019 206 025 A1 also describes head-up displays for use in vehicles.

[0007] Head-up displays typically have a limited field of view and a limited eyebox, i.e., the volume within which the viewer's eyes must be positioned to perceive the projected images. This is not a problem in vehicles, as the driver's lateral position relative to the head-up display is predetermined by the seat position. The vertical position of the eyes is also essentially fixed, as the driver adjusts the seat height to ensure the best possible all-round view.

[0008] The requirements for large-format displays are therefore fundamentally different from those for automotive head-up displays or head-mounted AR displays. In particular, uniform illumination with sufficient intensity poses a major challenge for large-format displays.

[0009] BRIEF SUMMARY OF THE INVENTION

[0010] Based on this, the present invention is based on the object of providing a cost-effective, in particular large-format, transparent display with a large field of view and a large eyebox.

[0011] According to the invention, this object was achieved with a transparent display according to the main claim and the method according to the secondary claim. Advantageous embodiments of the transparent display are specified in the subclaims.

[0012] A transparent display is proposed with a holographic diffuser extending substantially in a two-dimensional diffuser plane, and with a magnifying reflection element, wherein the holographic diffuser and the reflection element are part of a one-piece optical unit, wherein image rays reflected by the reflection element are guided within the optical unit to the holographic diffuser.

[0013] In exemplary embodiments, the proposed transparent display can achieve a transparency of more than 50 percent, which is typically unattainable with conventional transparent OLED displays. The proposed transparent display can be designed as a frameless transparent display. This is generally not possible with conventional transparent OLED displays.

[0014] Guiding the image rays in the optical unit from the reflection element to the holographic diffuser can reduce the risk of image degradation that can result from microparticles in the air in a free-beam display design.

[0015] The proposed transparent display can be configured to display images of very large dimensions while still having a particularly shallow depth. In particular, the optical unit, including the holographic diffuser and the reflection element, is adapted to the projector in such a way that a viewer perceives a very high-quality, evenly illuminated image.

[0016] BRIEF SUMMARY OF THE CHARACTERS

[0017] Examples are described below with reference to the following figures, where:

[0018] Fig. 1 shows a first transparent display;

[0019] Fig. 2 a second transparent display;

[0020] Fig. 3 a third transparent display;

[0021] Fig. 4 a fourth transparent display;

[0022] Fig. 5 a fifth transparent display; and

[0023] Fig. 6 a sixth transparent display.

[0024] DETAILED DESCRIPTION

[0025] Fig. 1 shows a large-format transparent display 100. The transparent display 100 has a holographic diffuser 111 extending substantially in a two-dimensional diffuser plane and a magnifying reflection unit 112. The holographic diffuser 111 and the reflection unit 112 are part of a one-piece optical unit 110, and image rays reflected by the reflection unit 112 are guided within the optical unit 110 to the holographic diffuser 111.

[0026] A width of the holographic diffuser 111 can be more than 150 mm, in particular more than 250 mm. A height of the holographic diffuser 111 can be more than 100 mm, in particular more than 150 mm. For example, the diagonal of the holographic diffuser 111 can be between 10 inches (25.4 cm) and 100 inches (254 cm). The thickness of the transparent display can be less than 10% of the diagonal of the holographic diffuser. In other words, the thickness of the transparent display 100 can be less than 10% of the image displayed by the holographic diffuser 111. The thickness of the transparent display 100 can in particular be less than 7%, preferably less than 6%, of the diagonal of the holographic diffuser 111.

[0027] The one-piece optical unit 110 can be connected to the top of the holographic diffuser

[0028] 111 and / or sides of the holographic diffuser 111 can be designed with decreasing thickness, without affecting the guidance of the image rays within the optical unit 110. The decreasing thickness towards the edges of the holographic diffuser 111 results in a further slimmer impression of the transparent display 100.

[0029] The reflection unit 112 can be designed as a mirror, in particular an aspherical mirror.

[0030] The transparent display 100 can further comprise a projector 120, wherein the projector 120 comprises an image generation unit, in particular a "Digital Micro-Mirror Device" (DMD). The optical unit 110 has a coupling element 113, which is configured to couple image beams generated by the image generation unit of the projector 120 into the optical unit 110.

[0031] The coupling element 113 is an optical surface of the optical unit 110. The coupling element 113 can be designed as an aspherical surface of the optical unit 110 or as an optical freeform surface.

[0032] The curvature of the coupling element 113 can be designed so that monochromatic aberrations of the projector 120 and / or the reflection element

[0033] 112 can be corrected.

[0034] The coupling element 113 can also be referred to as a coupling window. Chromatic aberrations generated due to the dispersion in the substrate of the optical unit 110 and the curvature of the coupling window 110 can be taken into account in the optical design of the projector 120 and thus compensated for in the overall system consisting of the projector 120 and the optical unit 110. The light source of the projector 120 can be light-emitting diodes (LEDs) or lasers.

[0035] The angle of incidence of the image rays onto the holographic diffuser 111 can be designed such that zero-order light diffracted by the holographic diffuser 111 cannot pass through the holographic diffuser 111 due to total internal reflection. This zero-order light can be reflected multiple times in the substrate of the optical unit 110 and exit at the upper end. A prism or curved surface can be provided there to guide this light to a light absorber. Preventing the passage of zero-order light can prove particularly advantageous when a laser is used as the light source of the projector 120 and special protection of the eyes of the viewer 101 from the laser light must be considered.

[0036] The holographic diffuser 111 may be laminated to the substrate of the optical unit 110.

[0037] In the transparent display 100 shown in Fig. 1, the viewer 101 is arranged on the same side of the substantially two-dimensional diffuser plane of the holographic diffuser 111 as the projector 120. The holographic diffuser 111 can be arranged on the same side of the optical unit 110 as the projector 120.

[0038] Figure 2 shows another transparent display 200. The transparent display 200 again comprises an optical unit 210 and a projector 220.

[0039] The optical unit 210 comprises a holographic diffuser 211, a reflection unit 212, and a coupling element 213. The coupling element 213 is provided on a side of the optical unit opposite the holographic diffuser 211. In contrast to the transparent display 100 shown in Fig. 1, the transparent display 200 is designed so that the projector 220 is arranged on a side opposite the viewer 201 with respect to the diffuser plane.

[0040] Image rays reflected by the reflection unit 212 are guided to the holographic diffuser 211 in the transparent display 200 by means of total internal reflection in the optical unit 210. This can serve to further reduce the thickness of the transparent display 200. The image rays are reflected by the reflection unit 212, which has a magnifying effect, and are totally reflected on the left side of the optical unit 210 before they strike the laminated holographic diffuser 211. The total internal reflection can cause a substantially lossless deflection of the image rays to the holographic diffuser 211. The holographic diffuser 211 then diffracts the image rays into the predetermined eyebox. Thus, the viewer 201 can perceive the image generated by an image generation unit in the projector 220.

[0041] The image rays reflected by the reflection element 212 are preferably only totally reflected once or not at all in the region of the holographic diffuser 211 in the optical unit 210. By eliminating total reflections in the region of the holographic diffuser 211, the risk of unwanted banding in the image perceived by the viewer can be reduced.

[0042] In particular, total internal reflection can reduce the thickness of the transparent display 200 by half. The components of the transparent display 200, which are shown in Fig.

[0043] 2 located below the holographic diffuser can be arranged in a base of the transparent display 200, invisible to the viewer 201. The viewer 201 therefore preferably sees only a borderless transparent disc on which color images are displayed.

[0044] If the projector 220 uses a laser as its light source, the polarization of the image beams emitted by the projector 220 can be adjusted so that, in combination with the design of the holographic diffuser 211, they produce a particularly high-quality image. In particular, the polarization of the light emitted by the projector 220 can be adapted to the holographic diffuser 211.

[0045] Figure 3 also shows a transparent display 300, which has an optical unit 310 and a projector 320. The optical unit 310 includes a holographic diffuser 311, a magnifying reflection element 312, and a coupling element 313.

[0046] In addition, the optical unit 310 has a deflection element 314. The deflection element 314 is configured to guide image rays coupled into the optical unit 310 by the coupling element 313 to the reflection unit 312. This makes it possible to arrange the projector 320 below the optical unit 310. This can lead to a further reduction in the thickness of the transparent display 300. The deflection element 314 can be designed as a total reflection prism, as shown in Fig. 3. However, it is also conceivable to provide a mirror as the deflection element.

[0047] The coupling elements 113, 213, 313 are designed as coupling windows of the respective optical unit 110, 210, 310.

[0048] Fig. 4 shows a transparent display 400 in which the coupling element 413 is designed as a holographic coupling element.

[0049] Image beams generated by projector 420 are coupled into optical unit 410 by means of coupling element 413, which is configured as a holographic coupling element. Coupling element 413 can, in particular, be a planar volume holographic element (v-HOE). As shown in Fig. 4, holographic coupling element 413 couples the image beams of projector 420 while maintaining their propagation direction.

[0050] The provision of a holographic coupling element 413 may have the advantage over a coupling window that it is easier to manufacture, especially when a large number of transparent displays are to be produced.

[0051] The coupling surface of the holographic coupling element 413 can be oriented such that the zeroth order of the light diffracted by the holographic coupling element 413, which is shown in dashed lines in Fig. 4, is guided to a first absorber element 415 and absorbed there. This can prevent it from causing unwanted scattered light in the optical unit.

[0052] The holographic coupling element 413 can comprise multiple layers of transmission holograms. Each layer can be used to couple the image beams in one color. For example, the holographic coupling element 413 can have a three-layer structure consisting of three transmission holograms, each transmission hologram being assigned to one of three colors, in particular red, green, and blue. It is also conceivable to provide a pair of reflection holograms for each color channel in order to increase the efficiency of the coupling element 413. In exemplary embodiments, it is provided that the incoming wavefront is also manipulated by means of the holographic coupling element 413, thus correcting aberrations of the transparent display 400.In particular, it may be possible to correct higher-order aberrations with the holographic coupling element by using optically fabricated holograms (OFH), which are obtained by constructing beams with freeform wavefronts.

[0053] Furthermore, it can be provided that the holographic coupling element 413 acts as a spectral filter, which only couples light of the desired wavelengths into the optical unit 410, while light with other wavelengths is filtered out and absorbed, for example, by the first absorber 415. This can ensure that the image rays incident on the holographic diffuser 411 have the narrowest possible bandwidth. This can ensure that the holographic diffuser 411 diffracts particularly little light into the zeroth order, so that little stray light is generated and eye safety is increased, particularly for the viewer 401. Such an approach can be particularly useful when using broadband light sources for the projector (e.g., LEDs).

[0054] Fig. 5 also shows a transparent display 500. The transparent display comprises an optical unit 510 and a projector 520. Image rays generated by the projector 520 are coupled into the optical unit 510 by means of a holographic coupling element 513. The holographic coupling element 513 directs the zeroth order of the diffracted light onto an absorber 515. The first order is directed to the reflection element 512.

[0055] In contrast to the reflection elements 112, 212, 312, and 412, the reflection element 512 is designed as a holographic reflection element. The holographic reflection element 512 can be essentially flat. Therefore, the complex manufacturing of a curved surface of the optical unit 510, as required for an aspherical mirror, can be eliminated.

[0056] The holographic reflection element 512 can, in particular, be a reflection hologram. The angular orientation of the essentially planar reflection element can be selected such that first-order Fresnel reflections, which are shown in Fig. 5 with dashed lines, are directed to a second absorber 516 and absorbed there. The desired image rays are diffracted by the reflection element 512 such that they strike the holographic diffuser 511 after total reflection.

[0057] In the transparent display 600 shown in Fig. 6, the zeroth diffraction order of the reflection element 612 is coupled out by means of an outcoupling prism 630 to the right side of the reflection element 612, which is designed as a reflection hologram, and absorbed by the second absorber 616. This can allow for a more flexible selection of the angle at which the reflection element 612 is arranged with respect to the input coupling element 613 and the holographic diffuser 611.

[0058] The holographic reflection element 612 can be constructed with light rays having wavefronts that can correct aberrations of other parts of the transparent display 600. In particular, distortion can be efficiently reduced by adjusting the diffraction angles of the main rays.

[0059] The transparent display 600 can have the particular advantage that the holographic coupling element 613, in combination with the holographic reflection element 612, can effect double spectral filtering of the image rays. As a result, the light incident on the holographic diffuser 611 becomes particularly monochromatic for each color channel, allowing the zero-order diffraction of light to be particularly efficiently suppressed by the holographic diffuser 611.

[0060] The various transparent displays proposed herein are characterized in particular by a beam guidance that enables more uniform illumination with higher intensity of the large-format displays with advantageously low aberrations.

[0061] In summary, the following examples are revealed:

[0062] Example 1. A transparent display comprising a holographic diffuser extending substantially in a two-dimensional diffuser plane and a magnifying reflection element, wherein the holographic diffuser and the reflection element are part of a one-piece optical unit, and wherein image rays reflected by the reflection element are guided within the optical unit to the holographic diffuser.

[0063] Example 2. Transparent display according to example 1, wherein a width of the holographic diffuser is greater than 150 mm, in particular 250 mm, and / or wherein a height of the holographic diffuser is greater than 100 mm, in particular 150 mm.

[0064] Example 3. Transparent display according to example 1 or 2, wherein image rays reflected by the reflection element are guided to the holographic diffuser by means of total reflection in the optical unit.

[0065] Example 4. Transparent display according to one of examples 1 to 3, wherein the reflection element comprises a mirror, in particular an aspherical mirror.

[0066] Example 5. The transparent display of any one of examples 1 to 4, wherein the reflective element comprises a holographic reflective element.

[0067] Example 6. Transparent display according to one of examples 1 to 3, wherein the transparent display comprises a projector, wherein the projector comprises an image generation unit, in particular a digital micromirror device, DMD, wherein the optical unit comprises a coupling element, wherein the coupling element is configured to couple image beams generated by the image generation unit into the optical unit.

[0068] Example 7. The transparent display according to example 6, wherein the coupling element is configured to guide the coupled image beams to the reflection element. Example 8. The transparent display according to one of examples 6 or 7, wherein the coupling element is configured to couple diverging image beams into the optical unit.

[0069] Example 9. Transparent display according to any one of examples 6 to 8, wherein the coupling element comprises a freeform surface of the optical unit.

[0070] Example 10. The transparent display according to any one of examples 6 to 8, wherein the coupling element comprises an aspherical surface of the optical unit.

[0071] Example 11. The transparent display of any one of examples 9 or 10, wherein the projector is configured to correct chromatic aberrations induced by the coupling element.

[0072] Example 12. The transparent display according to any one of examples 6 to 8, wherein the coupling element comprises a coupling grating and / or a holographic coupling element.

[0073] Example 13. The transparent display of any one of examples 6 to 12, wherein the coupling element is configured to correct monochromatic aberrations of the projector and / or the reflection element.

[0074] Example 14. Transparent display according to any one of examples 6 or 8 to 13, wherein the optical unit has a deflection element for guiding image rays coupled into the optical unit by the coupling element to the reflection element.

[0075] Example 15. The transparent display of example 14, wherein the deflecting element comprises a total reflection prism and / or a mirror.

[0076] Example 16. The transparent display according to any one of examples 6 to 15, wherein the optical unit comprises a first absorber element; wherein the first absorber element is configured to absorb zero-order image rays received from the coupling element. Example 17. The transparent display according to any one of examples 1 to 4 or 6 to 16, wherein the optical unit comprises a second absorber element, wherein the second absorber element is configured to absorb zero-order image rays received from the reflection element.

[0077] Example 18. The transparent display of any one of Examples 1 to 17, wherein the holographic diffuser is laminated to a substrate.

Claims

Patent claims 1. Large-format transparent display (100; 200; 300; 400; 500; 600), comprising a holographic diffuser (111; 211; 311; 411; 511; 611) extending substantially in a two-dimensional diffuser plane, and comprising a magnifying reflective element (112; 212; 312; 412; 512; 612), wherein the holographic diffuser (111; 211; 311; 411; 511; 611) and the reflective element (112; 212; 312; 412; 512; 612) are part of a one-piece optical unit (110; 210; 310; 410; 510; 610), and wherein image rays reflected from the reflection element (112; 212; 312; 412; 512; 612) are guided within the optical unit (110; 210; 310; 410; 510; 610) to the holographic diffuser (111 ; 211; 311; 411; 511 ; 611).

2. Large-format transparent display (100; 200; 300; 400; 500; 600) according to claim 1, wherein a width of the holographic diffuser (111; 211; 311; 411; 511; 611) is greater than 150 mm, in particular 250 mm, and / or wherein a height of the holographic diffuser (111; 211; 311; 411; 511; 611) is greater than 100 mm, in particular 150 mm.

3. Large-format transparent display (200; 300; 400; 500; 600) according to claim 1 or 2, wherein image rays reflected from the reflective element (212; 312; 412; 512; 612) are guided to the holographic diffuser (211; 311; 411; 511; 611) by means of total internal reflection in the optical unit (210; 310; 410; 510; 610).

4. Large-format transparent display (100; 200; 300; 400; 500; 600) according to claim 3, wherein the image rays reflected by the reflective element (212; 312; 412; 512; 612) in the area of ​​the holographic diffuser (211; 311; 411; 511; 611) in the optical unit (210; 310; 410; 510; 610) are reflected once or not totally.

5. Large-format transparent display (100; 200; 300; 400) according to one of claims 1 to 4, wherein the reflective element (112; 212; 312; 412) comprises a mirror, in particular an aspherical mirror. Large-format transparent display (500; 600) according to any one of claims 1 to 5, wherein the reflective element (512; 612) comprises a holographic reflective element. Large-format transparent display (100; 200; 300; 400; 500; 600) according to any one of claims 1 to 4, wherein the transparent display (100; 200; 300; 400; 500; 600) comprises a projector (120; 220; 320; 420; 520; 620), wherein the projector (120; 220; 320; 420; 520; 620) comprises an image generation unit, in particular a Digital Micromirror Device, DMD, wherein the optical unit (110; 210; 310; 410; 510; 610) comprises a coupling element (113; 213; 313; 413; 513; 613), wherein the coupling element (113; 213; 313; 413; 513; 613) is set up to couple image rays generated by the image generation unit into the optics unit (110; 210; 310; 410; 510; 610).Large-format transparent display (100; 200; 400; 500; 600) according to claim 7, wherein the coupling element (113; 213; 413; 513; 613) is configured to direct the coupled image rays to the reflection element (112; 212; 412; 512; 612). Large-format transparent display (100; 200; 300; 400; 500; 600) according to claim 7 or 8, wherein the coupling element (113; 213; 313; 413; 513; 613) is configured to couple diverging image rays into the optical unit (110; 210; 310; 410; 510; 610). Large format transparent display (100; 200; 300) according to one of claims 7 to 9, wherein the coupling element (113; 213; 313) comprises a freeform surface of the optical unit (110; 210; 310). Large-format transparent display (100; 200; 300) according to any one of claims 7 to 9, wherein the coupling element (113; 213; 313) comprises an aspherical surface of the optical unit (110; 210; 310). Large-format transparent display (100; 200; 300) according to any one of claims 10 or 11, wherein the projector (120; 220; 320) is configured to correct chromatic aberrations induced by the coupling element. Large-format transparent display (400; 500; 600) according to any one of claims 7 to 9, wherein the coupling element (413; 513; 613) comprises a coupling grating and / or a holographic coupling element (413; 513; 613).Large format transparent display (100; 200; 300; 400; 500; 600) according to one of claims 7 to 13, wherein the coupling element (113; 213; 313; 413; 513; 613) is configured to correct monochromatic aberrations of the projector (120; 220; 320; 420; 520; 620) and / or the reflection element (112; 212; 312; 412; 512; 612). Large-format transparent display (300) according to any one of claims 7 or 9 to 14, wherein the optical unit (310) comprises a deflecting element (314) for directing image rays coupled from the coupling element (313) into the optical unit (310) to the reflecting element (312). Large-format transparent display (300) according to claim 15, wherein the deflecting element (314) comprises a total internal reflection prism and / or a mirror. Large-format transparent display (400; 500; 600) according to any one of claims 7 to 16, wherein the optical unit (410; 510; 610) comprises a first absorber element (415; 515; 615). wherein the first absorber element (415; 515; 615) is configured to absorb zero-order image rays received from the coupling element (413; 513; 613).

18. Large-format transparent display (500; 600) according to any one of claims 1 to 5 or 7 to 17, wherein the optical unit (510; 610) comprises a second absorber element (516; 616), wherein the second absorber element (516, 616) is configured to absorb zero-order image rays received from the reflecting element (512; 612).

19. Large-format transparent display (100; 200; 300; 400; 500; 600) according to any one of claims 1 to 18, wherein the holographic diffuser (111 ; 211 ; 311 ; 411 ; 511 ; 611) is laminated onto a substrate.

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