Bidirectional display

Abstract

A first aspect of the invention relates a display device for bidirectional display, comprising a first, preferably diffractive, display element (AE1) for a display which is visible on a first side of the display device, and a second, preferably diffractive, display element (AE2) for a display which is visible on an opposite second side of the display device. The display device is designed for (preferably directed) scattering by AE1 of light directed onto the display device, which light strikes the first side of the display device with a first polarisation, wherein the scattering takes place counter to the direction of the light. At the same time, the display device is designed for (preferably directed) scattering by AE2 of light directed onto the display device, which light strikes the first side of the display device with a second polarisation different from the first polarisation, wherein the scattering takes place in the direction of the light. Further aspects of the invention relate to a display system comprising the display device and a PGU, to the PGU as such, and to a method for illuminating the display device.

Description

[0001] BIDIRECTIONAL DISPLAY

[0002] DESCRIPTION

[0003] In a first aspect, the invention relates to a display device for a bidirectional display, comprising a first, preferably diffractive display element (AE1) for a display visible on a first side of the display device, and a second, preferably diffractive, display element (AE2) for a display visible on an opposite second side of the display device. The display device is configured for (preferably directional) scattering by the AE1 of light directed onto the display device, which strikes the first side of the display device with a first polarization, wherein the scattering occurs opposite to the direction of the light.At the same time, the display device is set up for (preferably directed) scattering by the AE2 of light directed towards the display device, which strikes the first side of the display device with a second polarization different from the first, with the scattering taking place in the direction of the light.

[0004] In further aspects, the invention relates to a display system comprising the display device as well as a PGU, the PGU as such and a method for illuminating the display device.

[0005] Background and state of the art:

[0006] Classic displays that function in two directions, so-called bidirectional displays, are commonly found in trains, where they are installed on the ceiling of a train car above the aisle to show passengers the next stops. Typically, bidirectional displays require two separate screens, positioned with their respective backs facing each other. This makes the displays expensive and relatively bulky. Furthermore, such bidirectional displays cannot be made transparent, which precludes certain applications, such as mounting them on a window, especially a vehicle window. Therefore, there is a need for bidirectional displays without the drawbacks of the current technology.

[0007] Purpose of the invention:

[0008] It is therefore an object of the invention to provide a display device for a bidirectional display, a display system, a power distribution unit (PGU) for a display system, and a method for illuminating a display device, all of which avoid the disadvantages of the prior art. In particular, it is an object of the invention to provide a display device and a display system that are compact and simple in design, and in which the display device is essentially transparent to light. Furthermore, it is an object of the invention to provide a PGU and a method for implementing such a display system.

[0009] Summary of the invention:

[0010] The problem is solved by the features of the independent claims. Preferred embodiments of the invention are described in the dependent claims. In a first aspect, the invention relates to a display device for a bidirectional display, comprising a first, preferably diffractive display element (AE1) for a display visible on a first side of the display device, and a second, preferably diffractive, display element (AE2) for a display visible on an opposite second side of the display device. The display device is configured for (preferably directional) scattering by the AE1 of light directed onto the display device, which strikes the first side of the display device with a first polarization, wherein the scattering occurs opposite to the direction of the light.At the same time, the display device is set up for (preferably directed) scattering by the AE2 of light directed towards the display device, which strikes the first side of the display device with a second polarization different from the first, with the scattering taking place in the direction of the light.

[0011] Such a display has the advantage that a display can be provided on two different sides of the display device, although the light only needs to come from one side of the display device. This saves installation space. The light directed onto the display device only needs to have two different, preferably orthogonal, polarizations (first polarization and second polarization). The light directed onto the display device can be provided by at least one picture generating unit (PGU), for example, by two PGUs arranged directly next to each other. However, a single PGU can be used, which can provide the two polarizations, for example, using a time-division multiplexing method, as described below.

[0012] The statement that "the display is visible on a first side of the display device" can mean that the display is visible in a first half-space, or that the display is visible on a first side of the display device in a first half-space.

[0013] The statement that "the display is visible on a second side opposite the display device" can mean that the display is visible in a second half-space, or that the display is visible on a second side of the display device opposite the first side in a second half-space.

[0014] The first and second half-spaces can result, for example, from a division of the space into two spaces, which are called half-spaces because together they form the entire space in which the display device is located. This division can occur along a plane of arrangement of the display device, so that, for example, one half-space (the first half-space) adjoins the first side of the display device and extends from there in different directions away from the display device, and the other half-space adjoins the second side of the display device and extends from there in different directions away from the display device.

[0015] The statement that "the display device is designed for directed scattering by the AE1 of light directed onto the display device, which strikes the first side of the display device with a first polarization, with the scattering taking place opposite to the direction of the light" can alternatively or additionally be clarified as follows: the display device is designed for directed scattering by the AE1 of light directed from the first half-space onto the display device, which strikes the display device (in particular the first side) with a first polarization, with the scattering taking place in the direction of the first half-space.

[0016] The statement that "the display device is designed for directed scattering by the AE2 of light directed towards the display device, which strikes the first side of the display device with a second polarization different from the first, with the scattering taking place in the direction of the light" can alternatively or additionally be clarified as follows: the display device is designed for directed scattering by the AE2 of light directed from the first hemisphere towards the display device, which strikes the display device (in particular the first side) with a second polarization different from the first, with the scattering taking place in the direction of the second hemisphere.

[0017] The display device will now be explained using the exemplary display system shown in Figure 1. Figure 1 shows a display system 8 comprising a PGU 4 and a display device 1. The PGU 4 is arranged such that the light 5 emitted by it strikes a first side 9 of the display device 1. The first side 9 is shown here as the left side; however, it is also clear that the first side 9 and the PGU 4 illuminating the first side 9 can also be arranged on the right side.

[0018] The entirety of the light emitted by PGU 4 can also be referred to as the projection beam path. The emitted light contains light of a first polarization, for example, a so-called s-polarization (explanation of s- and p-polarization below), and light of a second polarization, different from the first. The second polarization can, for example, be perpendicular to the first polarization. If the first polarization is an s-polarization, then the second polarization can be a p-polarization. The light of the first and second polarizations can be emitted simultaneously, but it can also be time-division multiplexed. This can mean that the signal varies in polarization over time and, in particular, alternates between being s-polarized and p-polarized. This variation can occur at a fixed frequency, which, in particular, is so high that it is not relevant for human perception.The information to be displayed, which is contained in the light of the PGU 4, can differ between these two polarization states, even for directly successive light signals.

[0019] The display device 1 now comprises a first and a second display element (AE1 and AE2 – not explicitly shown in Fig. 1). AE1 and AE2 can be two separate physical elements encompassed by the display device 1, exhibiting the scattering properties described here. For example, the AEs can be diffractive scattering elements. In this case, AE1 scatters light in the opposite direction to the incident light 5 shown here, which strikes the first side 9 of the display device 1 from the PGU 4 and exhibits the first polarization. This scattered light is represented in the figure by the scattered light rays 3. The scattered light 3 is thus visible on the first side 9 of the display device 1 to the viewer s, who therefore receives the information displayed that strikes the first side of the display device 1 with the first polarization.The AE2, in turn, scatters light, which with the second polarization (first) strikes the first side 9 of the display device 1, in the direction of the incident light 5 shown in the image, represented by the scattered light rays 2. These scattered light rays 2 are thus visible to a viewer 7 who looks at the second side 10 of the display device 1. This viewer ? thus receives the information that is emitted by the PGU 4 with the second polarization.

[0020] In contrast to the above description regarding scattering directions, the operation of the display device can be described as follows: two half-spaces can exist, with the first half-space 12 located on or beyond the first side 9 of the display device, where the PGU 4 and the viewer 6 are located, and the second half-space 13 located on or beyond the second side 10 of the display device, where the viewer ? is located. The half-spaces 12 and 13 can be defined by a partition plane (additionally shown by the dashed line 11) between them. This partition plane 11 is at least partially formed or defined by the plane in which the display device 1 lies.The light coming from PGU 4 in the first hemisphere 12, which reaches the first side 9 of the display device with the first polarization, is scattered by AE1 (back) towards the first hemisphere 12, so that the information transmitted with the first polarization is visible to a viewer 6 in the first hemisphere 12. The light coming from PGU 4 in the first hemisphere 12, which reaches the first side 9 of the display device 1 with the second polarization, is scattered by AE2 towards the second hemisphere 13, so that it is visible there to a viewer 7.

[0021] A "bidirectional display" is preferably a display that can emit or display information in the form of light (e.g., an image) in two different directions. These two directions can be opposite to each other. Thus, the display is visible, for example, to two viewers looking at it from opposite directions.

[0022] "Display" preferably describes the function, i.e., the display of (image) information by means of light. The display device preferably describes the device which (among other things) enables such a display.

[0023] “Light” preferably describes electromagnetic radiation, e.g. in the form of electromagnetic waves, in the visible spectrum, especially at wavelengths between 360 nanometers (nm) and 830 nm.

[0024] A "display device for a bidirectional display" can describe a display device that enables such a bidirectional display. The display device can, for example, be "planar," which can mean that the display device essentially forms a surface, is flattened, and / or extends over a surface. It can also mean, for example, that the display device has a large extent along a plane or surface and a comparatively much smaller extent in a perpendicular direction, which can also be referred to as its thickness. The thickness can be essentially constant. The plane or surface can also be curved. A considerably smaller extent preferably means an extent that is at least twice as small as the smallest extent along the surface or plane.

[0025] Terms such as "essentially," "approximately," "about," "about," etc., preferably describe a tolerance range of less than ± 40%, preferably less than ± 20%, particularly preferably less than ± 10%, even more preferably less than ± 5%, and particularly less than ± 1%. Similarly, "similarly" preferably describes quantities that are approximately equal. "Partially" preferably describes at least 5%, particularly preferably at least 10%, and particularly at least 20%, and in some cases at least 40%. However, "partially" can also mean 5% or less, 2% or less, or 1% or less. Terms such as "essentially" preferably always include the exact value.

[0026] The first display element (AE1) or the second display element (AE2) is preferably a "diffractive display element". This can mean that it functions based on diffraction, thus enabling a diffraction-based display. Most importantly, it means that it includes a diffraction grating.

[0027] The description of AE1 as "first display element (AE1 ) for a display which is visible on a first side of the display device" can be synonymous with an AE1 which is set up for a display which is visible on the first side of the display device.

[0028] The description of AE1 as "AE2 for a display which is visible on an opposite second side of the display device" can be synonymous with an AE2 which is set up for a display which is visible on the second side of the display device.

[0029] The "second side" is the side of the display device opposite the first side. The "first side of the display device" is preferably the first flat side of the display device. The second side can then be the opposite flat side of the display device. The distance between the first and second sides can be described by the thickness of the display device.

[0030] The phrase "that the display is visible on the first side of the display device" preferably means that the display (i.e., the image, the information) is visible to a viewer located outside the display device who is looking at the first side of the display device.

[0031] The phrase "the display is visible on the second side of the display device" preferably means that the display (i.e., the image, the information) is visible to a viewer located outside the display device who is looking at the second side of the display device.

[0032] The display device is configured for (preferably directional) scattering by the AE1 of light directed towards the display device, which strikes the first side of the display device with a first polarization. The light directed towards the display device preferably strikes the first side of the display device first. This can mean that the light comes from outside the display device and is directed towards the display device in such a way that it strikes its first side first. The AE1 can also be located there. This can mean that the AE1 itself is configured for (preferably directional) scattering by the AE1 of light directed towards the display device, which strikes the first side of the display device with a first polarization.Simultaneously, the AE1 can then be essentially transparent to light with a second polarization striking the first side of the display device. The light directed at the display device can be spatially overlapping for the first and second polarizations. This can mean that light with the first and second polarizations has no distinguishable properties other than its polarization and, for example, strikes the display device at an identical angle or angular range. Regarding the angle-dependent diffraction properties of the AE1 / 2, suThe fact that the display device is configured for a (preferably directed) scattering by the AE1 of light directed towards the display device, which strikes the first side of the display device with a first polarization, can preferably mean that the AE1 is configured for a (preferably directed) scattering of light directed towards the display device, which strikes the first side of the display device with a first polarization.

[0033] The "first polarization" is a defined polarization, in particular a linear polarization, which is oriented along a (fixed) plane. More generally, the polarization of an electromagnetic wave preferably describes the plane in which the electric field vectors oscillate. This plane can be constant ("linear polarization") or constantly changing, e.g., rotating ("circular" or, more generally, "elliptical polarization").

[0034] "Scattering" or "diffusion" (used synonymously, if preferred) describes the deflection or redirection of light in various directions. The directions and / or intensities of the scattered light resulting from scattering or diffusion can, for example, follow Lambert's law. However, directions and / or intensities that deviate from Lambert's law can also occur. An important aspect of scattering or diffusion is that the light is not only deflected or redirected in a single direction, but in a multitude of directions, which can be described by an angular range. This allows an image to be viewed advantageously from different angles by the same observer.

[0035] The fact that the dispersion is "directional" can mean that it exhibits a preferred direction, i.e., that the intensity distribution deviates from Lambert's law. For example, the dispersion might be such that the display is essentially only visible within a well-defined eyebox. Furthermore, "directional" can mean that, in addition to dispersion, a deflection also occurs.

[0036] A "deflection" describes, in particular, a significant deviation of the principal beam direction of the light after scattering compared to the principal beam direction before scattering. A principal beam direction of light or a beam of light rays is preferably a direction in which the intensity of the light ray is maximum or averaged over all directions. The term principal beam or principal beam direction preferably refers to the central ray of a beam or its direction. The direction of the principal beam indicates, in particular, the direction of the beam. In the case of a collimated beam, the remaining rays of the beam run essentially parallel to the principal beam direction, so that the principal beam direction is preferably representative of the rays of a beam.In the case of a non-collimated beam, the rays of the beam define a solid angle, at the center of which lies the principal beam direction. Preferably, a deflection can mean that a significant change in the angle of the principal beam direction occurs, e.g., 10° or greater, 20° or greater, 30° or greater, 40° or greater, 50° or greater, 60° or greater, 70° or greater, or 80° or greater. In particular, a deflection (especially in the case of AE1) can mean that, generally speaking, an (approximate) reversal of direction occurs. This does not necessarily mean that the direction is reversed by exactly 180°; rather, it can mean that the direction is reversed from "in the direction of one half-space (e.g., the first half-space)" to "in the direction of another half-space (e.g., the second half-space)," as described herein. For example, a change in direction can mean that the change in angle is greater than "90° minus the main beam direction".The main beam direction is preferably specified as an angle, since the main beam direction includes a surface normal to AE1 (or AE2).

[0037] The fact that "scattering occurs opposite to the direction of the light" can mean that the AE1 does not transmit light striking the first side of the display device with a first polarization, but rather deflects this incident light in the direction of the side of the AE1 from which it struck the AE1. Thus, for example, the previously described reversal of direction can occur. Alternatively, one can imagine a surface normal vector pointing away from the display device, originating on the first side of the display device. If the light striking the first side of the display device with the first polarization exhibits at least a (preferably positive) projection component onto this surface normal vector, then the scattered part of the light preferably also exhibits a projection component onto this surface normal vector. One can also say, for example, that the AE1 scatters the light "reflexively."The "light" being referred to here is in particular the light directed at the display device, which is also at least partially transmitted into the display device and thus also has a direction within it.

[0038] Simultaneously, the display device is configured for (preferably directed) scattering by the AE2 of light directed towards the display device, which strikes the first side of the display device with a second polarization different from the first, with the scattering occurring in the direction of the light. The light directed towards the display device preferably strikes the first side of the display device first. This can mean that the light comes from outside the display device and is directed towards the display device in such a way that it strikes its first side first. The AE1 can be located there. This can mean that the AE1 itself is essentially transparent to light directed towards the display device, which strikes the first side of the display device with a second polarization different from the first, so that this light can transmit to the AE2, which, for example,The display device is arranged on or at the second side of the display device. The fact that the display device is configured for (preferably directional) scattering by the AE2 of light directed towards the display device, which strikes the first side of the display device with a first (or second) polarization, can preferably mean that the AE2 is configured for (preferably directional) scattering of light directed towards the display device, which strikes the first side of the display device with a first (or second) polarization.

[0039] The "second polarization" is a defined polarization, in particular a linear polarization, which is oriented along a (fixed) plane. This differs primarily from the first polarization. In particular, the second polarization can describe a polarization perpendicular to the first polarization.

[0040] The fact that "scattering occurs in the direction of the light" can mean that the AE2 light, which strikes the first side of the display device with a second polarization, scatters "transmissively," whereby a deflection may occur, but this does not lead to a reversal of direction. Alternatively, one can imagine, for example, a surface normal vector pointing away from the display device, which has its origin on the second side of the display device. Preferably, the light striking the first side of the display device with the second polarization has no (preferably positive) projection component onto this surface normal vector before scattering; however, the scattered part of the light preferably has a (preferably positive) projection component onto this surface normal vector after scattering.The light is preferably scattered by the AE2, whereby an additional angular change in the main beam direction of the incident light may preferably occur, but this change is not large enough to cause a reversal of direction as described herein. The "light" referred to here is, in particular, the light directed towards the display device, which is also at least partially transmitted into the display device and thus also has a direction within it.

[0041] AE1 and AE2 can, for example, scatter diffraction-based light, with the scattering being polarization-dependent. For instance, AE1 might only diffract light of the first polarization, and AE2 might only diffract light of the second polarization. However, it is also possible that both AEs diffract light of the same polarization, and that the display device additionally incorporates a suitable polarization modulator at an appropriate location (e.g., before AE2) to convert a second polarization into a first polarization. Thus, with suitable illumination by a PGU, for example using time-division multiplexing, light of the first and second polarizations can be alternately directed onto the first side of the display device. This allows, for example, the information contained in the respective polarized light to be displayed "simultaneously" on the respective sides of the display device, enabling a bidirectional display.

[0042] The terms "polarization modulator" and "polarization manipulator" are preferably used synonymously.

[0043] In a preferred embodiment of the invention, the elements or components of the layer stack are preferably substantially or partially transparent to (visible) light. The scattering of AE1 and / or AE2 can occur only for one or a few wavelengths or wavelength ranges, so that these are otherwise also substantially transparent. This makes it particularly easy to implement a double-sided display. Furthermore, a substantially or partially transparent display device enables interesting applications where it is possible to see through the display. Such a display device can, for example, be integrated into window panes of buildings or vehicles.

[0044] In a preferred embodiment, the AE1 and / or the AE2 comprises at least one holographic optical element (HOE), preferably a volume hologram and in particular a holographic diffuser.

[0045] In holography, unlike conventional imaging techniques such as photography, not only the intensity of an object being imaged is recorded, but also the phase relationships of the light emanating from the object. These phase relationships contain additional spatial information, allowing for the creation of a three-dimensional impression of the image. This is achieved through the interference of light rays during the recording or exposure. The object being exposed is illuminated with coherent light, which is reflected and scattered by the object. The resulting wave field, the so-called object wave, is superimposed with light coherent to the object wave (the so-called reference wave – typically from the same light source, e.g., a laser), and the wave fields interfere with each other as a function of their phase relationship. The resulting interference pattern is then used, for example, to create a three-dimensional image.The image is captured by a light-sensitive layer (also called exposure), thus storing the information contained in the phase. To reconstruct the image, the resulting hologram is illuminated with a light wave identical or similar to the reference wave, which is then diffracted by the recorded interference patterns. In this way, the original wavefront of the object wave can be reconstructed.

[0046] There are various types of holograms, such as volume holograms. Volume holograms preferably have a thickness sufficient to realize multiple Bragg planes. This allows volume holograms to be particularly wavelength- or angle-selective. Holograms can be, for example, transmission or reflection holograms, each generating this reconstruction either through transmission or reflection. For instance, if one is on the opposite side of a transmission hologram from the light source and views it, the depicted object appears three-dimensional. With a reflection hologram, one preferably needs to be on the same side as the light source. Reflection holograms preferably exhibit a particularly wavelength-selective efficiency in diffracting light in a specific direction (along a specific angle).The word hologram is used here primarily as a synonym for the holographic structure that generates light diffraction. Colloquially, "hologram" is sometimes used to refer to the generated, especially three-dimensional, image. However, an expert understands from the context what is meant by the term "hologram" in each case.

[0047] Besides three-dimensional representation, holograms can be used in the form of so-called holographic-optical (construction) elements (HOEs), whose holographic properties can be used for the optics of devices. For example, HOEs can replace conventional lenses, mirrors, and prisms. In other cases, HOEs are used as special diffraction gratings. HOEs exhibit, for example, spectral selectivity and / or angle-of-incidence selectivity. Simultaneously, they can be completely or partially transparent for other spectral ranges and / or angles of incidence. Holograms also enable a combination of representation and light shaping. Furthermore, HOEs can be used as diffusers with tailored scattering properties. Holograms, especially technical holograms, can be recorded directly using various holographic methods or with the aid of wavefront printers or similar technologies.Stereoholographic printers print from computer-generated data. While these manufacturing methods are suitable for the mass production of optical functions in the form of holograms, they are not practical due to the high time requirements. For this purpose, suitable methods, particularly optical replication, are available, in which a holographic "master" can be replicated many times using a suitable copying process.

[0048] A holographic optical element, in particular a volume hologram, enables a substantially or partially transparent AE1 and / or AE2 in a particularly simple manner. Holographic optical elements, and especially volume holograms, allow wavelength- and / or angle-selective diffraction, so that light scattering occurs only for suitable wavelengths and / or angles, while other wavelengths and / or angles are advantageously transmitted undiffracted. Thus, by appropriately matching the wavelength(s) and / or illumination angle of the PGU to the display device, a (partially) transparent display with the desired optical properties can be realized particularly easily. A holographic diffuser can be designed in such a way that the desired (preferably) directional scattering properties are achieved.

[0049] In another preferred embodiment of the invention, the AE1 is arranged on the first side of the display device and the AE2 is arranged on the second side of the display device.

[0050] The AE1 can, in particular, comprise a reflective surface diffuser arranged on or at the first side of the display device. A surface diffuser can, for example, include a relief hologram with the desired scattering properties. A surface diffuser is particularly suitable for the AE1 if the intended illumination angle through the PGU is approximately equal to or corresponds to the Brewster angle, since only s-polarized light is reflected at this angle. Because the diffuser is essentially formed by the surface of the display device on its first side, the light does not need to penetrate the display device for the AE1 to function, so the reflection of s-polarized light at the surface is not a problem. The first polarization can, for example, be an s-polarization.

[0051] In a further preferred embodiment of the invention, AE1 and / or AE2 comprise at least one reflection HOE (R-HOE) and / or at least one transmission HOE (T-HOE). The various possible variants are described, for example, in the description section below.

[0052] In a further preferred embodiment of the invention, the AE1 and / or the AE2 comprises a deflecting HOE and a holographic diffuser. The deflecting HOE and / or the holographic diffuser is preferably reflective. A possible variant of this embodiment is described, for example, below with reference to Fig. 4. Reflective holographic elements are particularly wavelength-selective and therefore cause fewer interference signals (e.g., rainbow effect). Even when used with broadband (PGU) light sources, a clear and sharp image can be achieved.

[0053] In a further preferred embodiment of the invention, the first polarization corresponds to an s-polarization and the second polarization to a p-polarization. s and p are preferably relative to the plane of incidence of the light beam on the (surface of the) display device. The s-polarization as the first polarization and the p-polarization as the second polarization is particularly advantageous if AE1 is located on the first side and AE2 on the second side, and at least AE1 diffracts s-polarization particularly efficiently.

[0054] In a further preferred embodiment of the invention, AE1 and AE2 are configured for the directed scattering of s-polarized light, wherein the display device further comprises a polarization manipulator arranged between AE1 and AE2, which is configured to convert p-polarized light into s-polarized light. It can be particularly advantageous if AE1 and AE2 are diffraction-based and, in particular, comprise holograms, that they are configured for the scattering of s-polarized light. Due to their manufacturing process, these often exhibit a significantly higher diffraction efficiency for s-polarization than for p-polarized light. The polarization manipulator is preferably configured to convert the second polarization into the first polarization and, in particular, the p-polarization into s-polarization in a single pass. The polarization manipulator can, for example, be...This is an A / 2 retardation plate (also called an A / 2 plate). This embodiment, comprising a polarization manipulator, is described, for example, in the description section in connection with Figures 2 and 3.

[0055] In a further preferred embodiment of the invention, a polarization filter is arranged between AE1 and AE2 for filtering light with the first polarization (preferably s-polarized light), which is preferably arranged upstream of the polarization manipulator along the direction of light (from the first hemisphere), preferably the direction of light coming from an illumination of a PGU. In other words, if AE1 is arranged on the first side of the display device and AE2 on the second side, then the polarization filter is preferably located closer to AE1 than the polarization manipulator. A polarization filter for filtering s-polarized light is preferably configured to filter s-polarized light. Filtering s-polarized light preferably means that the transmission of s-polarized light through the polarization filter is substantially suppressed or blocked (e.g., by reducing the polarization).Attenuation by at least a factor of 10, at least a factor of 100, or at least a factor of 1000). Preferably, the polarization filter has a transmission polarization perpendicular to the s-polarization (p-polarization), which is transmitted essentially unimpeded. The polarization filter can preferably also be referred to as a polarizer.

[0056] The polarization filter advantageously prevents, for example, non-scattered light with s-polarization (e.g., 0th diffraction order) from being transmitted through the display device by a display element (e.g., AE1) and thus becoming visible to a viewer on the second side of the display device. It also prevents light with s-polarization incident on the first side of the display device (if s-polarization is the primary polarization) from being transmitted to AE2 and thus diffracted by AE2. This prevents crosstalk.

[0057] Preferably, the polarization manipulator and / or the polarization filter is essentially achromatic or functions over a broad wavelength range of at least 100 nanometers (nm), more preferably at least 200nm, even more preferably at least 300nm and particularly at least 400nm.

[0058] In a further preferred embodiment of the invention, the polarization filter comprises a dichroic polarization filter. A dichroic polarization filter preferably absorbs the filtered polarization, in this case the s-polarization.

[0059] In a further preferred embodiment of the invention, the polarization filter comprises a polarization beam splitter (PBS), in particular a wiregrid polarization beam splitter (wiregrid PBS).

[0060] The polarization beam splitter is in particular a reflective polarization beam splitter which transmits the transmission polarization and reflects the filtered polarization.

[0061] Wire-grid polarizers, for example, comprise a multitude of thin wires arranged parallel to each other, whereby light polarized in the direction of the wires is reflected and light polarized perpendicular to the wires is transmitted.

[0062] It can also be a so-called "eighth-order grating", in which the grating structure is significantly smaller than the wavelength of the light, with the zeroth order being transmitted (typ. p) or reflected (typ. s) depending on the polarization.

[0063] Preferably, the polarization beam splitters mentioned are achromatic or function over a broad wavelength range of at least 100 nanometers (nm), more preferably at least 200nm, even more preferably at least 300nm and in particular at least 400nm.

[0064] In a further preferred embodiment of the invention, AE1 and AE2 are transmissive with respect to light split by the PBS. In other words, AE1 and AE2 are configured for diffusion in transmission with respect to light split by the PBS. This embodiment is described below for an exemplary variant in conjunction with Figure 4. For a particularly preferred embodiment, AE1 and AE2 each comprise two reflective holograms arranged one behind the other, wherein the hologram at which the light is first diffracted is preferably a deflecting hologram, and the hologram to which the light is diffracted after diffraction at the deflecting hologram is preferably a holographic diffuser (see also below, embodiment according to Figure 4). The use of reflective holograms, which are particularly wavelength-selective, has advantages with respect to the optical properties of the display.Broadband light sources can also be used for the PGU without loss of quality. In this embodiment, the AE1 is preferably configured to first transmit the s-polarized part of the light coming from the PGU.

[0065] In a preferred embodiment of the invention, the display device is configured for scattering light directed onto the display device by AE1 and AE2, with at least one wavelength. This single wavelength can comprise at least one wavelength range.

[0066] In a further preferred embodiment of the invention, the display device is suitable for (preferably directed) scattering of light from at least one first wavelength range and a second wavelength range different from the first. Preferably, the display device is suitable for scattering light in a first wavelength range, a second wavelength range different from the first, and a third wavelength range different from both the first and second. In particular, the first wavelength range can be assigned to the red color spectrum, the second wavelength range to the green color spectrum, and the third wavelength range to the blue color spectrum. In this way, an RGB display (RGB stands for a color mixture of "red," "green," and "blue") can be realized. If AE1 and / or AE2 comprises at least one hologram, this hologram can include several holograms that diffract the respective wavelength ranges.These holograms can be arranged one above the other, in particular stacked on top of the other, in a so-called stack. In an alternative embodiment, the hologram components assigned to the respective spectral ranges are contained in a single hologram. Such a hologram is preferably also referred to as a multiplex hologram.

[0067] In a further preferred embodiment of the invention, the display device comprises at least one substrate on which the AE1 and AE2 are preferably arranged. This substrate can, for example, comprise a substrate layer, which can be arranged in different layer planes within the device. It can also comprise more than one substrate, for example, two or more substrates. A substrate can advantageously provide the display device with mechanical stability without impairing its optical properties.

[0068] In a further preferred embodiment of the invention, at least one first HOE of AE1 is configured to deflect and scatter the light, provided it falls onto the first HOE (or onto the first side of the display device) with a suitable polarization within a first acceptance angle range of the first HOE, and / or at least one second HOE of AE2 is configured to scatter and preferably deflect the light, provided it falls onto the second HOE (or onto the first side of the display device) with a suitable polarization within a second acceptance angle range of the second HOE. Advantageously, the intrinsic diffraction properties of HOEs are utilized here, namely that they only efficiently diffract light from specific angles (acceptance angle range) (and specific wavelengths) and are therefore otherwise essentially transparent.The acceptance angle range (the first / second) is preferably selected to correspond to the angular range of the light that would be generated by the projection beam path of a PGU shining from a suitable position onto the first side of the display device. The suitable polarization preferably corresponds to s-polarization. Preferably, the first and second HOE correspond to the deflection hologram of the respective AE as described below with reference to Figure 4. In a further preferred embodiment of the invention, the first and second acceptance angle ranges are essentially identical. This is particularly advantageous when AE1 and AE2 are arranged in parallel and at a small distance from each other.

[0069] In a further aspect, the invention relates to a display system comprising the display device as described herein and an image generator unit (PGU) configured to illuminate the display device (in particular the first side of the display device) with light of the first and second polarizations, preferably from the first hemisphere. The PGU can be arranged, for example, as described below in Figures 1 and 2. Preferably, the PGU is arranged in the first hemisphere. The PGU is preferably configured to emit a first display content with light of a first polarization and a second display content with light of a second polarization. The first display content can be the same or different. Preferably, at least the second display content is mirror-inverted so that it is correctly oriented when viewing the second side of the display device.The PGU can preferably include a control unit, e.g. a (micro)processor and / or a memory unit.

[0070] It is evident to those skilled in the art that the advantages, definitions and embodiments of the display device according to the invention also apply to the claimed display system according to the invention and vice versa.

[0071] In a preferred embodiment of the invention, the illumination angle of the display system through the PGU differs from the main beam direction of the light deflected and / or scattered by the AE1 and / or AE2. The illumination angle through the PGU is advantageously also described by the main beam direction of the illumination through the PGU.

[0072] In a further preferred embodiment of the invention, the PGU is configured to direct light within the first acceptance angle range onto the first side of the display device (or onto the first HOE and / or AE1). Preferably, the first and second acceptance angle ranges are substantially identical, and the preferably parallel arrangement of AE1 and AE2 close to each other preferably ensures ideal illumination for both AEs.

[0073] In a further preferred embodiment of the invention, the PGU is configured to generate light in at least the first and second wavelength ranges. Preferably, the second wavelength range is different from the first and, in particular, does not overlap. Preferably, the PGU is configured to generate light in a first wavelength range, a second wavelength range different from the first, and a third wavelength range different from both the first and second. In particular, the first wavelength range can be assigned to the red color spectrum, the second wavelength range to the green color spectrum, and the third wavelength range to the blue color spectrum. Thus, especially in conjunction with a corresponding display device (so), an RGB display (RGB stands for a color mixture of "red," "green," and "blue") can be realized.

[0074] In another preferred embodiment, the PGU is configured to illuminate the display device (in particular the first side of the display device) with light of the first and second polarizations at respective intensities adapted to intensity losses due to Fresnel reflections on the first side of the display device. Depending on the illumination angle, Fresnel reflections may occur on the first side of the display device, differing for s- and p-polarization. For example, only s-polarized light is reflected when illuminated at the Brewster angle. The illumination intensity can compensate for these differing losses due to reflections. This can, for example, ensure that the brightness of the displays visible on the first and second sides of the display device is essentially the same.

[0075] In a third aspect, the invention relates to a power distribution unit (PGU) configured as a PGU for a display system as described herein. The PGU can be based, for example, on laser projection and / or on a liquid crystal display (LCD) or a micromirror array (DMD).

[0076] It is evident to the person skilled in the art that the advantages, definitions and embodiments of the PGU and the display system according to the invention also apply to the claimed PGU according to the invention and vice versa.

[0077] In a fourth aspect, the invention relates to a method for illuminating a display device of a display system as described herein, wherein the PGU emits light of the first polarization to visibly display first information on the first side of the display device and wherein the PGU emits light of the second polarization to visibly display second information on the second side of the display device.

[0078] It is evident to the person skilled in the art that the advantages, definitions and embodiments of the devices according to the invention (display device, display system, PGU) also apply to the claimed method according to the invention.

[0079] In some embodiments, the means for performing the steps of the method described herein may include a data processor and / or a storage device. In some implementations, the execution of the method may include one or more computers containing one or more data processors configured to execute one or more programs containing a variety of instructions for performing the method. Each data processor may contain one or more processor cores, and each processor core may contain logic circuits for processing data. For example, a data processor may contain an arithmetic and logical unit (ALU), a control unit, and various registers. Each data processor may contain a cache memory.Each data processor can contain a system-on-a-chip (SoC), which includes multiple processor cores, random-access memory, graphics processing units, one or more controllers, and one or more communication modules. Each data processor can contain millions or billions of transistors.

[0080] In a preferred embodiment of the invention, the light of the first and second polarizations is emitted in different time windows using a time-division multiplexing method. The time windows are preferably implemented at a sufficiently high frequency so that they are essentially imperceptible to humans. For example, the repetition frequency of the time windows can be at least 50 Hertz (Hz), at least 60 Hz, at least 70 Hz, at least 80 Hz, at least 90 Hz, or at least 100 Hz.

[0081] Description of the invention:

[0082] The invention will be explained below with reference to further figures and examples. The examples and figures serve to illustrate preferred embodiments of the invention without limiting them.

[0083] Figure 1 shows an example display system.

[0084] Figure 2 shows in detail an embodiment of the display device shown in Figure 1.

[0085] Figure 3 shows an embodiment of a layer stack for a display device.

[0086] Figure 4 shows an embodiment of the display device with a polarization beam splitter (PBS).

[0087] Figure 2 shows a detailed embodiment of the display device 1 shown in Figure 1. In particular, a possible layer structure of the display device is shown enlarged on the right. This comprises an AE1 14 on the first side 9 of the display device 1 (left), a polarizer 15, a substrate 16, a polarization manipulator 17, and an AE2 18 on the second side 10 of the display device 1.

[0088] The AE1 14, for example, is a first volume hologram (VHOE) that functions as a holographic diffuser. It is designed such that light from the PGU 4, which strikes the first side 9 of the display device 1 with the first polarization, is scattered by the first VHOE in the opposite direction to the light coming from the PGU 4, i.e., in the direction of the first hemisphere 12. This is shown by the arrows of the scattered light 3 on the left side of Figure 1. The arrows indicate the various directions in which the scattered light 3 propagates. The totality of these directions is also referred to as the scattering cone. For example, 80% of the scattered light may be located within this cone. In this case, the scattering can also be described as directional. This can mean, on the one hand, that the scattering has a different principal beam direction than the unscattered light coming from the PGU 4.In the present case, the scattering direction is even (approximately) opposite to the direction of the light coming from PGU 4. This could mean that, as shown, the light from PGU 4 is directed towards the second hemisphere 13, while the scattered light is directed towards the first hemisphere 12. Alternatively, directional scattering could mean that the scattering cone deviates significantly from scattering according to Lambert's law and that the radiant intensity cannot be described by a circle, but rather corresponds to an ellipse whose major axis points in the direction of a surface normal to the display device 1, or whose major axis is tilted relative to the surface normal to the display device 1. The scattering cone can vary depending on its position on the display device 1, for example, exhibiting a different tilt relative to the surface normal.This ensures that as much of the scattered light as possible is directed towards the expected viewing position, thus increasing the efficiency of the display. To fulfill the aforementioned properties and functions, the AE1 14 can, for example, be a reflective holographic diffuser.

[0089] Now, some of the light coming from the PGU 4 cannot be scattered by the AE1 14. This can occur, firstly, if the light does not have the first polarization, but, for example, the second polarization. This light is not scattered by the AE1 14, for example, because the AE1 14 has a diffraction efficiency of approximately zero for the second polarization. Secondly, the AE1 14 typically has a scattering efficiency of less than 1, so that some of the light of the first polarization can also be transmitted unscattered or undiffracted. If the AE1 14 is, for example, a VHOE, it has a diffraction efficiency of less than 1 and can transmit zeroth order light. To prevent this light from exiting unhindered on the second side 10 of the display device 1 or from causing interference in any other way, a polarization filter 15 can be included between the AE1 14 and the AE2 18, for example.A dichroic polarizing filter prevents the first polarization from transmitting. The second polarization, in turn, can transmit the polarizing filter 15 unimpeded. The AE2 18 on the second side scatters the transmitted light in the direction of the light coming from PGU 4, as indicated by the arrows of the scattered light 2. Both the light coming from PGU 4 and the scattered light 2 point towards the second hemisphere 13. This scattering can therefore also be described as directional. This can additionally or alternatively mean that, similar to what was described above for the scattered light 3, the scattered light 2, or rather its scattering cone, deviates significantly from scattering according to Lambert's law, and the radiant intensity cannot be described by a circle, but rather corresponds to an ellipse.Its main axis can, as described above, also point in the direction of a surface normal to the display device 1 or be tilted relative to it. The scattering cone can also vary depending on its position on the display device 1, for example, exhibiting a different tilt relative to the surface normal. To fulfill the aforementioned properties and functions, the AE2 18 can, for example, be a transmissive holographic diffuser.

[0090] It is possible that the AE2 18 is inherently capable of scattering light of the second polarization. However, it is also possible that the AE2 18 also scatters light of the first polarization. This can be due to technical reasons, for example, if the AE2 18 also includes a VHOE, which is particularly suitable for diffracting the first polarization. In that case, a polarization manipulator 17, such as a so-called lambda / 2 plate, can be included between AE1 14 and AE2 18. This can convert the second polarization into the first polarization, so that it can then be scattered by the AE2 18. If both a polarization filter 15 and a polarization manipulator 17 are included, the polarization manipulator 17 is arranged behind the polarization filter 15 in the direction of light coming from the PGU 4, as shown. A substrate 16 can also be included. This can, for example, ensure the mechanical stability of the layer stack shown.This can be arranged centrally in the layer stack, as shown, but also at any other location within the stack. The components of the layer stack included are preferably all substantially transparent to (visible) light. The scattering of AE1 14 and / or AE2 18 can occur only for one or a few wavelengths or wavelength ranges, so that these components are otherwise also substantially transparent.

[0091] Figure 3 shows an embodiment of a layer stack for a display device 1, in which the first polarization is s-polarization and the second polarization is p-polarization. s-polarization denotes the polarization direction of an electric field that oscillates perpendicular to the plane of incidence. The plane of incidence is defined by the incident vector, represented in the figure by the light beam coming from the PGU with s-polarization 19 or p-polarization 20, and the surface normal 21 to the first side 9 of the display device 1. p-polarization denotes an electric field oscillating parallel to the plane of incidence. In the embodiment shown, the light incident on the first side 9 of the display device 1 with s-polarization from the AE1 14 (here also a VHOE) is polarized as described above against the direction of the light beam 19 or p-polarization 20.Scattered towards the first hemisphere 12, s-polarized light, which is not scattered by the VHOE of AE1 14 due to a diffraction efficiency of less than 1, is now blocked by the polarization filter 15. This can be, for example, a dichroic polarization filter. Only p-polarized light passes through the polarization filter 15 unimpeded. This is then converted into s-polarization by the polarization manipulator 17 (in this case, a lambda / 2 plate) and can then also be scattered by the VHOE of AE2 18 with a high diffraction efficiency. This is because VHOEs have a significantly higher diffraction efficiency for s-polarized light than for p-polarized light.

[0092] Figure 4 shows an embodiment of the display device 1 in which the polarization filter 15 is a polarization beam splitter (PBS). The AE1 14 is configured to first transmit the s-polarized portion of the light 22 (dotted line) coming from the PGU 4. If the AE1 14 is, for example, at least one VHOE, this can be achieved through the angle-selective diffraction properties of the VHOE, which are then very small or essentially zero for the specific angle of incidence. This transmitted portion is then reflected by the PBS 15 (reference numeral 25) and passes through the AE1 14 again in the reverse direction, where it is now scattered in a specific direction, producing the scattered light beam that can now be seen by an observer (not shown) viewing the first side 9 of the display device. The AE1 14 is designed to scatter the light 25 reflected back from the PBS 15 into transmission.Several possible embodiments of the AE1 14 are conceivable.

[0093] In the case shown, the AE1 14 comprises two VHOEs 23 and 24. The VHOE 23, located on the outside of the first side 9 of the display device, is a reflection hologram, and the VHOE 24, located further towards the AE2 18, is a reflection holographic diffuser. The s-polarized light 25 reflected by the PBS 15 is initially transmitted undiffracted by the holographic diffuser 24 (again made possible by the angle-selective diffraction properties of the diffuser 24, which is implemented as a VHOE). Within the reflection hologram 23, the s-polarized light is then reflexively diffracted towards the holographic diffuser 24 (light beam 26). Such a reflection hologram 23, which roughly reverses the direction of the light in order to illuminate the holographic diffuser 24 at a suitable angle, is also called a deflection hologram.The diffraction angle can be larger than the critical angle of total internal reflection within the layer structure of the display device, so that after diffraction by the VHOE 23 through the diffuser 24, undiffracted light can no longer simply escape from the structure and produce stray light (a beam trap can be provided on one side of the display device 1, e.g., at the lower end 31 in the example shown, to absorb the undiffracted light). The light 26 diffracted by the reflection hologram 23 is in any case diffracted at an angle towards the diffuser 24 at which the latter exhibits a high diffraction efficiency. Therefore, the light is now reflectively scattered by the diffuser 24. The scattered light 3 then has an angular distribution such that it can pass through the reflection hologram 23 essentially unimpeded.However, if individual angles of the scattered light rays 3 are filtered due to an existing diffraction efficiency of the reflection hologram 23, this effect is advantageously negligible.

[0094] The light 22 coming from the PGU 4 also contains a p-polarized component, which the AE1 14 transmits unimpeded. This light is transmitted by the PBS 15 (transmitted light beam 27) and, in the illustrated embodiment, first reaches a polarization manipulator 17 (lambda / 2 plate), which converts the transmitted p-polarization into an s-polarization (indicated by the change from a dashed to a dotted line in the transmitted light beam 27). The now s-polarized light can then be scattered in a similar manner by a combination of a reflection hologram 28 (which can also be referred to as a deflection hologram) located on the outside of the second side 10 of the display device 1 and a holographic diffuser 29 (scattered light beam 2), so that the light 2 can be viewed by an observer of the second side 10 of the display device 1.Here too, the light beam 27 is initially transmitted undiffracted by the holographic diffuser 29 towards the reflection hologram 28 due to the unsuitable angle of incidence, and only then is it diffracted back to the diffuser 29 (diffracted light beam 30), preferably also at an angle greater than the critical angle of total internal reflection of the layer stack of the display device 1. The diffuser 29, in turn, has a high diffraction efficiency for the diffracted light 30 and diffractes it diffusely, so that the scattered beam 2 is generated. Similar to AE1 14, AE2 18 is thus configured to scatter the light 27 transmitted by the PBS 15 in transmission. Other possible embodiments of AE2 18 are also conceivable, as will be described below.

[0095] There may also be other, not shown, possible layered hologram configurations that can also achieve the desired functionality. For example, a single diffuser hologram can be used as AE1 14 or AE2 18, or a combination of a non-diffused hologram with a diffusely scattering hologram as shown. The respective holograms can be designed as transmission holograms or reflection holograms. The specific possibilities that can be realized depend, for example, on whether a PBS 15 is used or not and / or whether the light propagates within the display device 1 at an angle greater than the critical angle for total internal reflection. An advantage of using reflection holograms is their greater wavelength selectivity, which allows for better imaging and / or a more transparent display device 1 with fewer unwanted diffracted light rays.

[0096] For the AE2 18, the light path in the display device is essentially independent of whether a PBS 15 is used or not. However, when a PBS 15 is used, the light path of the AE1 14 changes, since then the light beam 22 coming from the PGU 4 is not to be diffracted directly by the AE1 14, but rather the light beam 25 reflected by the PBS 15, which is directed in the "opposite direction" or in the direction of the first hemisphere 12. Essentially, two cases can be distinguished: if a PBS 15 is used, the light 25 reflected by it is to be subsequently scattered by the AE1 14 in transmission; there should be no further "reversal" of the light direction. If no PBS 15 is used (see Figure 3), the light 22 coming from the PGU 4 should be scattered by reflection, i.e. there should be a “reversal” of the direction of light from a direction into the second half-space 13 to a direction into the first half-space 12.The AE2 18 should scatter in transmission in any case, without reversing the direction of light, regardless of whether a PBS 15 is used or not.

[0097] A transmission-operating AE (regardless of whether it is an AE1 or an AE2) can, for example, be a transmission-operating holographic diffuser exhibiting corresponding angle-dependent diffraction efficiencies, as described above in Figure 3 as a possible embodiment for AE2 18. Likewise, a transmission-operating hologram and a transmission-operating holographic diffuser can be combined, with the transmission-operating hologram coming first in the direction of light, followed by the transmission-operating holographic diffuser. The transmission-operating hologram, positioned first in the direction of light, allows, for example, the adjustment of the angle at which the light subsequently reaches the transmission-operating holographic diffuser. This can be adjusted, for example, so that a critical angle of total internal reflection in the diffuser is exceeded. This can have the advantage that light undiffracted by the diffuser (0.order) remains in the AE and does not generate any stray light. Similarly, a transmission hologram and a reflection holographic diffuser can be combined, with the transmission hologram coming first in the direction of light, followed by the reflection holographic diffuser. In this case, however, the transmission hologram must always diffract the light at an angle greater than the critical angle of total internal reflection in the reflection diffuser. The light is then first reflected at an outer surface of the display device 1 formed by an outer surface of the diffuser and can subsequently be scattered by reflection through the reflection diffuser.

[0098] A reflecting AE1 14 (e.g., when no PBS 15 is used) can be, for example, a reflecting holographic diffuser, as described above in connection with Figure 3 as a possible embodiment. Likewise, such an AE1 14 can be a combination of a reflecting deflecting hologram and a transmissive holographic diffuser. In this case, the light 22 coming from the PGU 4 advantageously first passes through the transmissive holographic diffuser undiffracted due to a diffraction efficiency that is essentially unsuitable for this angle. It is then reflected by the deflecting hologram and subsequently strikes the transmissive diffuser at the correct angle to be diffracted and scattered accordingly.

[0099] REFERENCE MARK LIST

[0100] 1 Display device

[0101] 2 Scattered light rays on the second side

[0102] 3 Scattered light rays on the first page

[0103] 4 PGU

[0104] 5 Projection beam path

[0105] 6 viewers of the first page

[0106] 7 viewers of the second page

[0107] 8 Display system

[0108] 9 First page of the display device

[0109] 10 Second side of the display device

[0110] 11. Division level of the two half-spaces

[0111] 12 First half-space

[0112] 13 Second half-space

[0113] 14 AE1

[0114] 15 Polarizer

[0115] 16 Substrat

[0116] 17 Polarization manipulator

[0117] 18 AE2

[0118] 19 s-polarized light beam from PGU

[0119] 20 p-polarized light beam from PGU

[0120] 21 Surface normal to the first side of the display device

[0121] 22 s- and p-polarized light beam from PGU

[0122] 23 Reflection hologram of AE1

[0123] 24 Holographic diffuser of the AE1

[0124] 25 Light reflected from the PBS

[0125] 26 Light diffracted by the reflection hologram of AE1

[0126] 27 Light transmitted by the PBS

[0127] 28 Reflection hologram of the AE2

[0128] 29 Holographic diffuser of the AE2

[0129] 30 Light diffracted by the reflection hologram of the AE2

[0130] 31 “Lower” end of the display device

Claims

PATENT CLAIMS 1. Display device (1) for a bidirectional display, comprising a first display element (AE1) (14) for a display which is visible on a first side (9) of the display device (1), a second display element (AE2) (18) for a display which is visible on an opposite second side (10) of the display device (1), wherein the display device (1) is configured for a scattering (3) by the AE1 (14) of light (5) directed onto the display device (1) which strikes the first side (9) of the display device (1) with a first polarization, opposite to the direction of the light (5), wherein the display device (1) is configured for a scattering (2) by the AE2 (18) of light (5) directed onto the display device (1) which strikes the first side (9) of the display device (1) with a second polarization different from the first, in the direction of the light (5).

2. Display device (1) according to claim 1, wherein the AE1 (14) and / or the AE2 (18) comprises at least one holographic optical element (HOE), preferably a volume hologram and in particular a holographic diffuser (24, 29), wherein the AE1 (14) and / or the AE2 (19) preferably comprise at least one reflection HOE (R-HOE) and / or at least one transmission HOE (T-HOE), wherein the AE1 and / or the AE2 in particular comprise a deflection HOE (23, 28) and a holographic diffuser (24, 29).

3. Display device (1) according to one of the preceding claims, wherein the AE1 (14) is arranged on the first side (9) of the display device (1) and the AE2 (18) is arranged on the second side (10) of the display device (1).

4. Display device (1) according to one or more of the preceding claims, wherein the first polarization corresponds to an s-polarization and wherein the second polarization corresponds to a p-polarization.

5. Display device (1) according to the previous claim, wherein AE1 (14) and AE2 (18) are configured for directed scattering (3, 2) of s-polarized light, wherein the display device (1) further comprises a polarization manipulator (17) arranged between AE1 (14) and AE2 (18), which is configured to convert p-polarized light into s-polarized light.

6. Display device (1) according to one or more of the preceding claims, comprising a polarization filter (15) arranged between AE1 (14) and AE2 (18) for filtering light with the first polarization, which is preferably arranged along the direction of light in front of the polarization manipulator (17).

7. Display device (1) according to the previous claim, wherein the polarization filter (15) comprises a dichroic polarization filter.

8. Display device (1) according to the preceding claim 6, wherein the polarization filter (15) comprises a polarization beam splitter (PBS), in particular a wiregrid polarization beam splitter (wiregrid PBS).

9. Display device (1) according to the previous claim, wherein the AE1 (14) and the AE2 (18) are configured for scattering in transmission with respect to light split by the PBS.

10. Display device (1) according to one or more of the preceding claims, wherein the display device (1) is suitable for scattering (3, 2), preferably directed scattering (3, 2) of light (5) of at least a first wavelength range and a second wavelength range different from the first.

11. Display system (8) comprising a display device (1) according to one or more of the preceding claims and an image generator unit (PGU) (4) which is configured to illuminate the display device (1) with light (5) with the first and second polarization.

12. Display system (8) according to one or more of the preceding claims, wherein the PGU (4) is configured to generate light (5) at least in the first and second wavelength ranges.

13. PGU (4), configured as PGU (4) for a display system (8) according to one or more of the preceding claims 11-12.

14. Method for illuminating a display device (1) of a display system (8) according to one or more of the preceding claims 11-12, wherein the PGU (4) emits light (5) of the first polarization to visibly display first information on the first side (9) of the display device (1) and wherein the PGU (4) emits light (5) of the second polarization to visibly display second information on the second side (10) of the display device (1), wherein preferably the light (5) of the first and the second polarization is emitted in different time windows in a time-division multiplexing method.

Images