Transparent display

Abstract

The invention relates to a transparent display comprising a holographic diffuser that extends substantially in a two-dimensional diffuser plane and comprising a projector, the projector having an image generation unit, in particular a digital micromirror device (DMD), and a reflection unit, wherein the reflection unit is configured to reflect, in the direction of the holographic diffuser, images generated by the image generation unit, and the image generation unit is arranged on a side of the diffuser plane lying opposite the reflection unit. The invention also relates to a method for producing a holographic diffuser.

Description

[0001] Description

[0002] Transparent display

[0003] 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.

[0004] There is a growing need for transparent displays. Transparent displays can offer viewers highly immersive and 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 to be used 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 and the viewer can visually perceive the images as well as the environment located behind the substrate from their perspective. Head-up displays typically have a limited field of view and the so-called eyebox, i.e.The volume in which the viewer's eyes must be located in order to perceive the projected images is limited.

[0005] Based on this, the present invention is based on the object of providing a cost-effective transparent display with a large field of view and a large eyebox.

[0006] According to the invention, this object was achieved with a transparent display according to the main claim and the method according to the dependent claim. Advantageous embodiments of the transparent display are specified in the subclaims. A transparent display is proposed, comprising a holographic diffuser extending substantially in a two-dimensional diffuser plane, and comprising a projector, wherein the projector has an image generation unit, in particular a digital micromirror device (DMD), and a reflection unit, wherein the reflection unit is configured to reflect images generated by the image generation unit toward the holographic diffuser, and wherein the image generation unit is arranged on a side of the diffuser plane opposite the reflection unit.

[0007] A holographic diffuser can be understood in particular as an optical element which specifically scatters incident light from one or more specific directions so that it can be perceived by at least one viewer in an eyebox. In contrast, a conventional diffuser typically scatters the light in many different directions and not specifically in one specific direction. The holographic diffuser can be set up so that the eyebox is at a predetermined angle and / or distance from the holographic diffuser. The holographic diffuser can be designed to scatter incident light of one or more predetermined wavelengths and / or wavelength ranges. The holographic diffuser can also be configured so that the light is scattered so that it can be viewed by viewers in more than two eyeboxes.For this purpose, a holographic diffuser can comprise a volume or area hologram. A holographic diffuser can, in particular, comprise a holographic optical element.

[0008] In some embodiments, the diffuser may have a certain curvature, e.g., if it is mounted on a curved support such as a curved glass pane. In such a case, the diffuser does not lie exactly in one plane. In such cases, the diffuser plane is understood to be a plane that approximates the shape of the diffuser, e.g., has the smallest deviation from the diffuser according to a predetermined metric. The metric may, for example, be a sum of absolute values ​​of distances of the diffuser plane defined in this way from the diffuser, a sum of squared distances of the diffuser plane defined in this way from the diffuser, or another function of distances of the diffuser plane defined in this way from the diffuser. The distances may be measured in a predetermined grid, e.g., a square or rectangular grid.Furthermore, a method for producing a holographic diffuser, in particular a holographic diffuser for a transparent display as described above, is proposed, wherein different tile sections of a diffuser substrate are exposed using one or more master tiles, whereby a plurality of holographic diffuser tile sections are obtained, wherein the holographic diffuser tile sections form the holographic diffuser.

[0009] The proposed transparent display can be configured to reproduce images of very large dimensions while still having a particularly shallow depth. In particular, the holographic diffuser and the optical elements of the projector are adapted to each other in such a way that a viewer perceives a very high-quality, evenly illuminated image.

[0010] Examples are described below with reference to the following figures, where:

[0011] Fig. 1 a transparent display;

[0012] Fig. 2 shows part of a first projector of a transparent display; and

[0013] Fig. 3 shows part of a second projector of a transparent display.

[0014] Figure 1 shows a transparent display 1000. The transparent display 1000 has a holographic diffuser 1200 and a projector 1100. The holographic diffuser 1200 extends essentially in a two-dimensional diffuser plane 1201. The holographic diffuser 1200 and the projector 1100 are coordinated with one another such that a viewer 1300 can perceive not only objects on the side of the diffuser 1200 facing away from him, but also images generated by an image generation unit 1111. The image generation unit 1111 can, in particular, be a digital micromirror device (DMD).

[0015] The projector 1100 has a reflection unit 1150, which is configured to reflect images generated by the image generation unit 1111 toward the holographic diffuser 1200. For this purpose, the image generation unit is arranged on a side of the diffuser plane 1201 opposite the reflection unit.

[0016] According to the embodiment illustrated in Fig. 1, the reflection unit 1150 can be arranged, in particular, on a side of the diffuser plane 1201, which is provided for viewing the transparent display 1000 by a viewer 1300. The reflection unit 1150 can, in particular, be an aspherical mirror.

[0017] The transparent display 1000 can provide the viewer 1300 with highly immersive and AR experiences. Unlike conventional transparent displays, transparent displays of the type illustrated in Fig. 1 can enable very large eyeboxes and / or very large fields of view. At the same time, the transparent display 1000 can be designed to be very compact. In particular, a depth of the transparent display 1000 in a direction perpendicular to the diffuser plane 1201 can be significantly smaller than the dimensions of the transparent display 1000 in the diffuser plane 1021.

[0018] The transparent display 1000 can be a freestanding transparent display 1000. The transparent display 1000 can also be configured as an integrated transparent display. In this way, functional surfaces can be provided. For example, the transparent display 1000 can be integrated into furniture, household appliances, and / or entertainment devices. The transparent display 1000 can also be integrated into commercial devices, in particular machine tools. It is also conceivable to provide the transparent display as a display in a vehicle.

[0019] For example, the holographic diffuser 1200 can be mounted on or in a window of the vehicle, such as a windshield, a rear window, or a side window, for example, arranged between two individual panes of a laminated glass pane. Such panes typically have a certain curvature, which accordingly leads to a curved shape of the diffuser 1200. In this case, as explained above, the diffuser plane 1201 is a plane that approximates the shape of the diffuser 1200. In the case of a side window, the projector 1100 can then be arranged, for example, in a B-pillar of the vehicle.

[0020] In arrangements for vehicle windows, the image generation unit 1111 or the reflection unit 1150 can be located on an exterior side of the vehicle. To protect against mechanical influences (e.g., rain, wind, particles), this unit can then be protected by an encapsulation, for example, made of plastic, whereby the light can pass through transparent sections of the encapsulation and / or be guided into and / or out of the encapsulation by means of an optical fiber.

[0021] In the case of movable vehicle windows, as is often the case with side windows, the projector 1100 can be movable with the side window, for example in the above-mentioned B-pillar or underneath the side window. In this case, a projection can also take place when the side window is half open, as long as the area of ​​the vehicle window that has the diffuser 1200 is visible. In some embodiments, the reflection unit 1150 can also be adaptive, e.g. by tilting and / or variable optics, so that the projection can follow a movement of the vehicle window. In other cases, the projector 1100 is permanently installed. In such cases, for example, a projection can only take place when the side window is completely closed.

[0022] The holographic diffuser 1200 can, in particular, comprise a volume hologram. By designing the holographic diffuser 1200 as a volume hologram, a particularly small thickness of the diffuser 1200 can be achieved compared to other diffusers 1200. For example, the use of a volume hologram can enable a thickness of the holographic diffuser 12000 of less than one millimeter, whereas a thickness of approximately 12 millimeters is typically required for Fresnel screens.

[0023] Providing the transparent display 1000 in the form of a combination of the projector 1100 and the holographic diffuser 1200 can make it possible to provide a transparent display 1000 with a particularly high transparency for ambient light, so that a viewer 1300 can particularly well perceive the surroundings on the side of the holographic diffuser facing away from them. The transparency can, for example, be more than 90%. By providing the transparent display 1000 as a combination of the holographic diffuser 1200 and the projector 1100 with a correspondingly defined relative position, the rays 1400 generated by the image generation unit 1111 and reflected by the reflection unit 1150 can be adjusted in their direction and wavelength such that the very high sensitivity of a volume hologram for the angle of incidence and / or the wavelength of the incident rays 1400 can be optimally utilized. Even if in Fig.1 shows a free-beam optics between image generation unit 1111 and reflection unit 1150 as well as between reflection unit 1150 and diffuser 1200, the light can also be guided at least partially by means of optical fibers and / or in a medium.

[0024] Fig. 2 shows part of a first projector that can be used as projector 1100 of the transparent display 1000. The projector 1100 shown in Fig. 1 can, in particular, comprise a refraction unit. In the example shown in Fig. 2, the refraction unit can include a rear lens group 2120, a middle lens group 2130, and a front lens group 2140.

[0025] The refraction unit is arranged in the beam path between the image generation unit 1111 or 2111 and the reflection unit 1150. The image generation unit 2111 is arranged off-center of an optical axis of the refraction unit in an object plane. In this way, the surface of the image generation unit 2111 can be optimally utilized to project the images generated by the image generation unit 2111 onto the holographic diffuser.

[0026] The image generation unit 2111 is a DMD. However, the use of other image generation units is also conceivable. A cover glass 2112 can be provided between the image generation unit 2111 and the refraction unit 2111.

[0027] The rear lens group is configured to couple light with a telecentric beam path on the object side from the image generation unit 2111 into the refraction unit. This enables a more uniform illumination of a holographic diffuser 1200 compared to that which could be achieved with a projector according to WO 2018 / 117210 A1.

[0028] The rear lens group 2120 comprises a coupling block 2121. In an embodiment not shown, the coupling block can be designed as a total reflection prism. A total reflection prism can be understood, in particular, as an optical prism in which light is deflected by total internal reflection at an inner surface of the prism. The light can, in particular, enter or exit the total reflection prism essentially perpendicularly. The coupling block 2121 shown in Fig. 2 has a convex surface 2123 facing away from the image generation unit 2111. The convex surface 2123 acts as a field lens to diffract the chief ray such that object-side telecentricity is obtained.

[0029] The effect of the convex surface of the coupling block 2121 can also lead to a reduction in the numerical aperture of the object beam. This can improve the coupling of the light from the image generation unit 2111, so that the brightness of the image reproduced by the holographic diffuser can be increased with the same light output from the image generation unit 2111. This can, in particular, imply higher energy efficiency of the transparent display 1000. The object beam can, in particular, have a numerical aperture (NA) of 0.2. The rear lens group 2120 has a first positive lens 2122. The first positive lens 2122 can serve to further collimate the beam. In particular, the first positive lens 2122 can guide the beam to the middle lens group 2130 and its aperture stop 2133.

[0030] The middle lens group 2130 can be configured, in particular, to correct chromatic aberrations. The middle lens group 2130 has a negative lens 2131. The negative lens 2131 can be made, in particular, from flint glass. The middle lens group 2130 further comprises a second positive lens 2132. The second positive lens 2132 can be made, in particular, from crown glass. Starting from the image generation unit 2111, the second positive lens 2132 is arranged after the negative lens 2131 in the beam path. The negative lens 2131 is designed as a meniscus lens. This can enable the second positive lens 2132 to be arranged very close to the negative lens 2131. The second positive lens 2132 and the negative lens 2131 in combination act as a converging lens.In this way, the light beam can be focused even more before it passes through the aperture stop 2133 in order to achieve a high magnification for the largest possible image on the holographic diffuser.

[0031] The front lens group 2140 adjoins the aperture stop 2133 and has a first aspherical surface 2143 and a second aspherical surface 2144 arranged in front of the first aspherical surface 2143. The front lens group 2140 can have a low converging power. The first aspherical surface 2143 serves to correct field-dependent aberrations, in particular distortion and astigmatism. For this purpose, the first aspherical surface 2143 can be arranged in particular close to the reflection unit 1150.

[0032] The second aspherical surface 2144 is configured to correct aperture-dependent aberrations, in particular spherical aberrations. For this purpose, the second aspherical surface 2144 can be arranged, in particular, near the aperture stop 2133.

[0033] The first front lens group 2140 can, in particular, as shown in Fig. 2, consist of a single first aspherical lens 2141, which has the first aspherical surface 2143 and the second aspherical surface 2144. The first aspherical lens 2141 can be a meniscus lens. The first aspherical lens 2141 can, in particular, be made of polymethyl methacrylate (PMMA). This can enable particularly cost-effective production, in particular mass production by injection molding.

[0034] The first aspherical lens 2141 can have a large thickness. This allows for an extremely large, high-order field curvature to be achieved. The high field curvature can allow the field curvature induced by the reflection unit 1150 to be efficiently compensated to obtain a flat image plane. This is especially true if the reflection unit 1150 is an aspherical mirror. Thus, an intermediate image in the optical system can be omitted, which can consequently be designed more simply.

[0035] Fig. 3 shows part of a second projector of a transparent display. This also has an image forming unit 3111, a cover glass 3112, a rear lens group 3120, a middle lens group 3130 and a front lens group 3140. The coupling block 3121, the first positive lens 3122, the negative lens 3131, the second positive lens 3132, the aperture stop 3133, the first aspherical surface 3143 and the second aspherical surface 3144 correspond to the coupling block 2121, the first positive lens 2122, the negative lens 2131, the second positive lens 2132, the aperture stop 3133, the first aspherical surface 2143 and the second aspherical surface 2144, so that to avoid repetition with regard to their properties, reference is made to the explanations for Fig. 2. In contrast to the part of the first projector shown in Fig. 2, the part shown in Fig.The part of the second projector shown in Figure 3 has a first aspherical lens 3141 and additionally a second aspherical lens 3142. The first aspherical lens 3141 has the first aspherical surface 3143, and the second aspherical lens 3142 has the second aspherical surface 3144. The division into the two aspherical lenses 3141, 3142 can reduce the thermal load on the lenses of the front lens group 3140. In addition, the division into two aspherical lenses 3141, 3142 can provide two additional aspherical surfaces 3145, 3146, which enable further improved correction of field-dependent higher-order aberrations, in particular astigmatism and higher-order distortions.

[0036] As shown in Fig. 2, the refractive unit can consist of only five lenses. This allows manufacturing effort and the corresponding costs to be kept particularly low. The provision of two lenses in the front lens group as shown in Fig. 3 can further improve the quality of the reproduced image and further increase the numerical aperture. At the same time, the limitation to a total of six lenses results in substantial cost savings compared to conventional refractive units.

[0037] A transparent display according to Fig. 1 with a projector having a refractive unit according to Fig. 2 or 3 can allow images to be displayed on the holographic diffuser with a size of 1800 mm to 1050 mm at a resolution of 1920 x 1080 pixels (Full HD 1080P).

[0038] The refractive units formed by the rear lens group 2120 or 3120, the middle lens group 2130 or 3130, and the front lens group 2140, 3140, as shown in Fig. 2 and Fig. 3, respectively, can be designed to be rotationally symmetrical, in particular, eccentric freeform elements can be omitted. This can simplify the adjustment of the optical elements during manufacturing and significantly reduce waste during series production.

[0039] Despite the small dimensions and simple design of the projectors shown in Fig. 2 and Fig. 3, the reflection unit can be positioned at a distance of only 15 cm from the holographic diffuser. Furthermore, a throw ratio of less than 0.1, in particular less than 0.08, can be achieved.

[0040] The variants according to Fig. 2 and Fig. 3 can in particular have the following properties:

[0041] A large-format transparent display requires a large holographic diffuser. Manufacturing such a large holographic diffuser is challenging because the exposure of large holograms is limited by the power of the light sources and the size of the manufacturing equipment.

[0042] A method for producing a holographic diffuser, in particular a holographic diffuser for a transparent display as described above, is therefore proposed, wherein different tile sections of a diffuser substrate are exposed using a plurality of master tiles, whereby a plurality of holographic diffuser tile sections are obtained, wherein the holographic diffuser tile sections form the holographic diffuser.

[0043] To produce large-format holographic diffusers, several smaller holographic diffusers are combined. The holographic diffuser is conceptually divided into several tiles, and these tiles are manufactured using at least one master tile. For different diffuser tiles, separate master tiles can also be used for production. In series production, the individual diffuser tile sections are also produced separately. This reduces manufacturing difficulties and increases yield.

[0044] To generate the at least one master tile, a point light source arranged at the center of the aperture stop can be used to generate a construction beam with a freeform wavefront. In this way, aperture-related aberrations can be compensated.

[0045] In summary, the following examples are revealed:

[0046] Example 1. Transparent display (1000), with a holographic diffuser (1200) extending substantially in a two-dimensional diffuser plane (1201), and with a projector (1100), wherein the projector (1100) has an image generation unit (1111), in particular a digital micromirror device, DMD, and a reflection unit (1150), wherein the reflection unit (1150) is configured to reflect images generated by the image generation unit (1111) in the direction of the holographic diffuser (1200), wherein the image generation unit (1111) is arranged on a side of the diffuser plane (1201) opposite the reflection unit (1150).

[0047] Example 2. Transparent display (1000) according to example 1, wherein the holographic diffuser (1200) comprises a volume hologram.

[0048] Example 3. Transparent display (1000) according to example 1 or 2, wherein the holographic diffuser (1200) has a thickness of less than one millimeter.

[0049] Example 4. Transparent display (1000) according to one of examples 1 to 3, wherein the reflection unit (1150) is arranged on a side of the diffuser plane (1201) which is intended for viewing of the transparent display (1000) by a viewer (1300).

[0050] Example 5. Transparent display (1000) according to one of examples 1 to 4, wherein the projector has a refraction unit (2120, 2130, 2140; 3120, 3130, 3140), wherein the refraction unit (2120, 2130, 2140; 3120, 3130, 3140) is arranged in the beam path between the image generation unit (1111) and the reflection unit (1150).

[0051] Example 6. Transparent display (1000) according to example 5, wherein the image generation unit (1111; 2111; 3111) is arranged off-center of an optical axis of the refraction unit (2120, 2130, 2140; 3120, 3130, 3140).

[0052] Example 7. Transparent display (1000) according to one of examples 5 or 6, wherein the refraction unit (2120, 2130, 2140; 3120, 3130, 3140) comprises a rear lens group (2120; 3120), wherein the rear lens group (2120; 3120) is configured to couple light with an object-side telecentric beam path from the image generation unit (1111) into the refraction unit (2120, 2130, 2140; 3120, 3130, 3140).

[0053] Example 8. Transparent display (1000) according to example 7, wherein the rear lens group (2120; 3120) comprises a coupling block (2121; 3121) having a convex surface (2123, 3123) facing away from the image generation unit (1111).

[0054] Example 9. Transparent display (1000) according to example 7 or 8, wherein the coupling block (2121; 3121) has a planar surface (2124; 3124).

[0055] Example 10. Transparent display (1000) according to one of examples 7 to 9, wherein the coupling block is designed as a total reflection prism.

[0056] Example 11. The transparent display (1000) according to any one of examples 7 to 10, wherein the rear lens group (2120; 3120) comprises a first positive lens (2122; 3122).

[0057] Example 12. Transparent display (1000) according to one of examples 5 to 11, wherein the refraction unit (2120, 2130, 2140; 3120, 3130, 3140) comprises a middle lens group (2130, 3130) arranged, in particular starting from the image generation unit (1111), in the beam path after the rear lens group (2120; 3120), wherein the middle lens group (2130, 3130) is configured to correct chromatic aberrations.

[0058] Example 13. Transparent display (1000) according to example 12, wherein the middle lens group (2120; 3120) has a negative lens (2131; 3131), in particular a negative lens made of flint glass.

[0059] Example 14. Transparent display (1000) according to example 13, wherein the negative lens (2131) is a meniscus lens.

[0060] Example 15. Transparent display (1000) according to one of examples 12 to 14, wherein the middle lens group (2130; 3130) has a second positive lens (2132; 3132), in particular made of crown glass.

[0061] Example 16. Transparent display (1000) according to example 15, wherein the second positive lens (2132; 3132) is arranged after the negative lens (2131; 3131) in the beam path starting from the image generation unit (1111; 2111; 3111).

[0062] Example 17. Transparent display (1000) according to one of examples 12 to 16, wherein the middle lens group comprises a diaphragm (2133), in particular a diaphragm arranged starting from the image generation unit (1111) in the beam path after the second positive lens (2132).

[0063] Example 18. Transparent display (1000) according to one of examples 5 to 17, wherein the refraction unit (2120, 2130, 2140; 3120, 3130, 3140) comprises a front lens group (2140; 3140), in particular a front lens group arranged downstream of the middle lens group (2120; 3120) in the beam path from the image generation unit (1111), wherein the front lens group (2120; 3120) has a first aspherical surface (2143; 3143) and a second aspherical surface (2144; 3144), in particular a front lens group arranged downstream of the first aspherical surface (2143; 3143) in the beam path from the image generation unit (1111). Example 19. The transparent display (1000) according to example 18, wherein the first aspherical surface (2143; 3143) is configured to correct field-dependent aberrations.

[0064] Example 20. The transparent display (1000) of example 18 or 19, wherein the second aspherical surface (2144; 3144) is configured to correct aperture-dependent aberrations.

[0065] Example 21. The transparent display (1000) according to any one of examples 18 to 20, wherein the front lens group (2140; 3140) comprises a first aspherical lens (2141; 3141), the first aspherical lens (2141; 3141) having the first aspherical surface (2143; 3143).

[0066] Example 22. The transparent display (1000) of example 21, wherein the first aspherical lens (2141) has the second aspherical surface (2144).

[0067] Example 23. Transparent display (1000) according to example 21, wherein the front lens group (3140) comprises a second aspherical lens (3142), in particular a second aspherical lens (3142) arranged in the beam path in front of the first aspherical lens (3141) starting from the image generation unit (1111), wherein the second aspherical lens (3142) has the second aspherical surface (3143).

[0068] Example 24. Transparent display (1000) according to any one of examples 21 to 23, wherein the first aspherical lens (2141; 3141) and / or the second aspherical lens (3142) is made of polymethyl methacrylate, PMMA.

[0069] Example 25. The transparent display (1000) according to any one of examples 21 to 24, wherein the first aspherical lens (2141, 3141) and / or the second aspherical lens (3142) is a meniscus lens. Example 26. The transparent display (1000) according to any one of examples 1 to 25, wherein the holographic diffuser (1200) is arranged on or in a window of a vehicle.

[0070] Example 27. A method for producing a holographic diffuser, in particular a holographic diffuser for a transparent display (1000) according to any one of Examples 1 to 26, wherein different tile sections of a diffuser substrate are exposed using at least one master tile, thereby obtaining a plurality of holographic diffuser tile sections, wherein the holographic diffuser tile sections form the holographic diffuser. Example 28. A method for producing a holographic diffuser according to Example 27, wherein a point light source arranged in a center of the aperture is used to generate a design beam with a freeform wavefront to produce the master tile.

Claims

Claim T: Transparent display (1000) comprising a holographic diffuser (1200) extending substantially in a two-dimensional diffuser plane (1201), and a projector (1100), wherein the projector (1100) comprises an image generation unit (1111), in particular a digital micromirror device (DMD), and a reflection unit (1150), wherein the reflection unit (1150) is configured to reflect images generated by the image generation unit (1111) towards the holographic diffuser (1200), the image generation unit (1111) being arranged on a side of the diffuser plane (1201) opposite the reflection unit (1150). Transparent display (1000) according to claim 1, wherein the holographic diffuser (1200) comprises a volume hologram. Transparent display (1000) according to claim 1 or 2, wherein the holographic diffuser (1200) has a thickness of less than one millimeter.Transparent display (1000) according to any one of claims 1 to 3, wherein the reflection unit (1150) is arranged on one side of the diffuser plane (1201) which is intended for viewing the transparent display (1000) by a viewer (1300). Transparent display (1000) according to any one of claims 1 to 4, wherein the projector has a refraction unit (2120, 2130, 2140; 3120, 3130, 3140), wherein the refraction unit (2120, 2130, 2140; 3120, 3130, 3140) is in the beam path. between the image generation unit (1111) and the reflection unit (1150). Transparent display (1000) according to claim 5, wherein the image generation unit (1111; 2111; 3111) is arranged off-center from an optical axis of the refraction unit (2120, 2130, 2140; 3120, 3130, 3140). Transparent display (1000) according to one of claims 5 or 6, wherein the refraction unit (2120, 2130, 2140; 3120, 3130, 3140) comprises a rear lens group (2120; 3120), wherein the rear lens group (2120; 3120) is configured to couple light with an object-side telecentric beam path from the image-forming unit (1111) into the refraction unit (2120, 2130, 2140; 3120, 3130, 3140). Transparent display (1000) according to claim 7, wherein the rear lens group (2120; 3120) comprises a coupling block (2121; 3121) which has a convex surface (2123, 3123) facing away from the image generation unit (1111).Transparent display (1000) according to claim 7 or 8, wherein the coupling block (2121; 3121) has a planar surface (2124; 3124). Transparent display (1000) according to any one of claims 7 to 9, wherein the coupling block is configured as a total internal reflection prism. Transparent display (1000) according to any one of claims 7 to 10, wherein the rear lens group (2120; 3120) comprises a first positive lens (2122; 3122). Transparent display (1000) according to one of claims 5 to 11, wherein the refraction unit (2120, 2130, 2140; 3120, 3130, 3140) comprises a, in particular a, middle lens group (2130, 3130) arranged starting from the image generation unit (1111) in the beam path after the rear lens group (2120; 3120). wherein the middle lens group (2130, 3130) is configured to correct chromatic aberrations. Transparent display (1000) according to claim 12, wherein the middle lens group (2120; 3120) comprises a negative lens (2131; 3131), in particular one made of flint glass. Transparent display (1000) according to claim 13, wherein the negative lens (2131) is a meniscus lens. Transparent display (1000) according to any one of claims 12 to 14, wherein the middle lens group (2130; 3130) comprises a second positive lens (2132; 3132), in particular one made of crown glass. Transparent display (1000) according to claim 15, wherein the second positive lens (2132; 3132) is arranged in the beam path after the negative lens (2131; 3131) starting from the image generation unit (1111; 2111; 3111).Transparent display (1000) according to one of claims 12 to 16, wherein the middle lens group comprises an aperture (2133), in particular one arranged in the beam path after the second positive lens (2132) starting from the image generating unit (1111). Transparent display (1000) according to one of claims 5 to 17, wherein the refraction unit (2120, 2130, 2140; 3120, 3130, 3140) comprises a front lens group (2140; 3140) arranged in the beam path after the middle lens group (2120; 3120) starting from the image generation unit (1111), wherein the front lens group (2120; 3120) has a first aspherical surface (2143; 3143) and a second aspherical surface (2144; 3144) arranged in the beam path in front of the first aspherical surface (2143; 3143) starting from the image generation unit (1111). Transparent display (1000) according to claim 18, wherein the first aspherical surface (2143; 3143) is configured to correct field-dependent aberrations. Transparent display (1000) according to claim 18 or 19, wherein the second aspherical surface (2144; 3144) is configured to correct aperture-dependent aberrations. Transparent display (1000) according to any one of claims 18 to 20, wherein the front lens group (2140; 3140) comprises a first aspherical lens (2141; 3141), wherein the first aspherical lens (2141; 3141) has the first aspherical surface (2143; 3143). Transparent display (1000) according to claim 21, wherein the first aspherical lens (2141) has the second aspherical surface (2144).Transparent display (1000) according to claim 21, wherein the front lens group (3140) comprises a second aspherical lens (3142), in particular a second aspherical lens (3142) arranged in the beam path upstream of the first aspherical lens (3141) starting from the image-forming unit (1111), wherein the second aspherical lens (3142) has the second aspherical surface (3143). Transparent display (1000) according to any one of claims 21 to 23, wherein the first aspherical lens (2141; 3141) and / or the second aspherical lens (3142) is made of polymethyl methacrylate, PMMA. Transparent display (1000) according to any one of claims 21 to 24, wherein the first aspherical lens (2141, 3141) and / or the second aspherical lens (3142) is a meniscus lens. Transparent display (1000) according to any one of claims 1 to 25, wherein the holographic diffuser (1200) is arranged on or in a window of a vehicle. A method for producing a holographic diffuser, in particular a holographic diffuser for a transparent display (1000) according to any one of claims 1 to 26, wherein, using at least one master tile, different tile sections of a diffuser substrate are exposed, thereby obtaining several holographic diffuser tile sections, the holographic diffuser tile sections forming the holographic diffuser. A method for producing a holographic diffuser according to claim 27, wherein, for generating the master tile, a point light source arranged in a center of the aperture is used, with which a construction beam with a free-form wavefront is generated.

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