Optical arrangement with holographic optical elements in z-configuration for a transparent display system

Abstract

Various aspects of the disclosure relate to an optical arrangement (100) comprising a plurality of holographic optical elements, HOEs, (91, 92). At least one HOE scatters the light. A deflection HOE (91) directs, for example, light onto a diffuser HOE (92), where the light is scattered by diffraction effects. By means of such a staggered arrangement of the two holographic optical elements (91, 92), the optical arrangement can be designed to be particularly compact, for example. Stray light can be reduced.

Description

[0001] DESCRIPTION

[0002] Optical arrangement with holographic optical elements in Z-configuration for a transparent display system

[0003] TECHNICAL FIELD

[0004] Various examples of the disclosure relate to an optical assembly for a transparent display system, wherein the optical assembly comprises a plurality of holographic optical elements in a stacked Z-configuration. In particular, various examples of the disclosure relate to the implementation of a diffuser functionality by at least one of the plurality of holographic optical elements.

[0005] BACKGROUND

[0006] Transparent display systems are known in which a transparent diffuser element is illuminated by a light source unit, so that when the diffuser element is viewed, the light projected onto it is perceived. The diffuser element thus acts as a display surface.

[0007] SUMMARY

[0008] There is a need for an optical arrangement for a transparent display system that allows for a large display area while maintaining a compact design. There is also a need for such an optical arrangement that reduces stray light.

[0009] This problem is solved by the features of the independent patent claims. The features of the dependent patent claims define embodiments.

[0010] The following describes aspects in which two holographic optical elements (HOEs) extend alongside each other. The light coming from a light source first passes through one of the two HOEs, but is not diffracted there (due to the appropriate angular selectivity of the diffraction structure). The light then strikes the other of the two HOEs and is diffracted there. Due to diffraction, the light is redirected back to one of the two HOEs and strikes this HOE in such a way that it is diffracted there. This is a so-called "Z-configuration." At least one of the HOEs is also used to scatter the light, i.e., acts as a diffuser element.

[0011] An optical arrangement for a transparent display system comprises a light source unit. The light source unit is configured to emit light along a beam path. The optical arrangement also comprises a first holographic optical element (HOE). This first HOE is configured to redirect the light if it falls onto the first HOE within a first acceptance angle of the first HOE. The optical arrangement further comprises a second HOE extending along the first HOE and configured to redirect the light if it falls onto the second HOE within a second acceptance angle of the second HOE.

[0012] In addition, the first HOE or the second HOE is also designed to disperse the light - provided it falls on this HOE within the respective acceptance angle.

[0013] The beam path impinges on the second HOE at a first position along the beam path such that the light impinges on the second HOE outside the second acceptance angle. Furthermore, the beam path impinges on the first HOE at a second position along the beam path, downstream of the first position, such that the light impinges on the first HOE within the first acceptance angle. The beam path impinges on the second HOE at a third position along the beam path, downstream of the second position, such that the light impinges on the second HOE within the second acceptance angle.

[0014] A system comprises a door for a motor vehicle. The door comprises a support structure, an outer panel attached to the support structure, an inner panel attached to the support structure, and a window frame supported by the support structure. The door also comprises a window pane mounted in the window frame. Furthermore, the door comprises an optical assembly as described above. The light source unit of the optical assembly is arranged in a space formed in the support structure between the outer panel and the inner panel. The first HOE and the second HOE are arranged on the window pane.

[0015] A motor vehicle includes such a system.

[0016] The motor vehicle may also include a control unit. This control unit is configured to control the light source unit of the optical arrangement, for example, depending on the driving situation of the motor vehicle.

[0017] A digital display window system comprises a support structure, a transparent pane held by the support structure, and an optical assembly as disclosed above. The light source unit is arranged, for example, in the support structure. The first HOE of the optical assembly and the second HOE of the optical assembly are arranged on the transparent pane.

[0018] A display system comprises such an optical arrangement as disclosed above and a control device configured to control the light source unit.

[0019] The features set forth above and features described below may be used not only in the corresponding explicitly set forth combinations, but also in further combinations or in isolation, without departing from the scope of the present invention.

[0020] SHORT DESCRIPTION OF THE CHARACTERS

[0021] FIG. 1A illustrates an optical arrangement according to various examples.

[0022] FIG. 1B illustrates an optical arrangement according to various examples.

[0023] FIG. 2 illustrates an optical arrangement according to various examples.

[0024] FIG. 3 illustrates an optical arrangement according to various examples.

[0025] FIG. 4 illustrates an optical arrangement according to various examples.

[0026] FIG. 5 illustrates an optical arrangement according to various examples.

[0027] FIG. 6 illustrates an optical arrangement according to various examples. FIG. 7 illustrates an optical arrangement according to various examples.

[0028] FIG. 8 illustrates an optical arrangement according to various examples.

[0029] FIG. 9 illustrates an optical arrangement according to various examples.

[0030] FIG. 10 illustrates an optical arrangement according to various examples.

[0031] FIG. 11 illustrates an optical arrangement according to various examples.

[0032] FIG. 12 illustrates a vehicle door according to various examples.

[0033] FIG. 13 schematically illustrates an angle-dependent scattering characteristic of a functionalized diffuser element according to various examples.

[0034] FIG. 14 schematically illustrates a digital display board system according to various examples.

[0035] FIG. 15 illustrates an optical arrangement according to various examples.

[0036] DETAILED DESCRIPTION

[0037] The present invention is explained in more detail below using preferred embodiments with reference to the drawings. In the figures, identical reference numerals designate identical or similar elements. The figures are schematic representations of various embodiments of the invention. Elements shown in the figures are not necessarily drawn to scale. Rather, the various elements shown in the figures are depicted in such a way that their function and general purpose will be understood by those skilled in the art. Connections and couplings between functional units and elements shown in the figures can also be implemented as an indirect connection or coupling. A connection or coupling can be implemented wired or wirelessly. Functional units can be implemented as hardware, software, or a combination of hardware and software.

[0038] Aspects related to transparent display systems are described below. Such a transparent display system has a diffuser element, i.e., an element designed to scatter light. A diffuser element scatters light. It has a plurality of scattering centers. If parallel light rays strike different points on a diffuser element, they are scattered in different directions, thus creating diffuse light. The type of scattering can also be referred to as scattering characteristics. The scattering characteristics describe, for example, a specific angular distribution under which the light striking the scattering element is scattered (scattering lobe). The diffuser element can therefore also be used to redirect the light by appropriately orienting the scattering lobe. The diffuser element also makes it possible to adjust the divergence of the beam path, for example,by forming the scatter lobe with a width that is smaller than the divergence of the beam path before it hits the diffuser element. However, it would also be conceivable to increase the divergence of the beam path. By appropriately adjusting the divergence of the beam path, a sharply defined eyebox can generally be created from which a display can be perceived.

[0039] A simple diffuser element is a ground glass screen. Such a screen exhibits the same scattering characteristics at different lateral positions within its aperture. This is achieved by a microscopically random orientation of the scattering centers, so that, on average, all scattering directions occur with equal frequency. For example, the scattering lobe shows no dependence on the lateral position within the aperture of the ground glass screen. The scattering characteristics typically show no selectivity with respect to the wavelength of the incident light. For these reasons, the ground glass screen is not a functionalized diffuser element.

[0040] A functionalized diffuser element, on the other hand, has a dependence of the scattering characteristic on the lateral position within the aperture and / or the wavelength of the incident light. A functionalized diffuser element can alternatively or additionally have a non-uniform scattering characteristic. A functionalized diffuser element therefore does not have randomly oriented scattering centers when viewed microscopically; rather, the scattering centers are generated in a defined manner in a special process. For example, a functionalized diffuser element can have a control characteristic that has several maxima, i.e., it preferentially scatters light in certain directions; this is a deviation from equally probable scattering in all directions within a spatial region. In other words, this means that with a functionalized diffuser element, the scattering characteristic, e.g.The scattering lobe is specifically adjusted to specific properties that are required or advantageous for the optical system. In some examples of the present disclosure, a functionalized diffuser element is used.

[0041] Generally speaking, a functionalized diffuser element can have a location-dependent control characteristic and / or an angle-dependent control characteristic. For example, it would be conceivable that a functionalized diffuser element could specifically enable the visibility of the display from certain viewing angles, while making the display invisible or imperceptible from other viewing angles. This would also enable privacy functionality, for example. Warnings can be issued specifically in specific areas where the warning is relevant. An example would be a display system in a motor vehicle door where a warning is to be issued in a blind spot of the vehicle.

[0042] In various examples of the disclosure, the diffuser element is implemented by a holographic optical element (HOE). The diffuser element is therefore a holographic diffuser element (diffuser-HOE). The HOE forms the scattering surface. A holographic diffuser element achieves scattering of the at least one beam path by diffracting the light at the HOE. For this purpose, the HOE has a spatial modulation of the refractive index. The HOE is therefore wavelength-selective, so that the scattering characteristics are different for different wavelengths of the incident light. For example, the HOE can selectively scatter light in a relatively limited wavelength range, for example, in a wavelength range with a width of 0.5 to 30 nm. To scatter light in multiple wavelength ranges, it would be possible to use multiple HOEs or multiple holographic diffuser elements, e.g., stacked.However, multiple HOEs can also be implemented in one film layer. For example, light can then be diffracted in multiple wavelength ranges, e.g. red (620-630 nm), green (520-530 nm), blue (455-465 nm). The wavelength range can be adjusted differently depending on the application. This affects the position of the wavelength range as well as the width of the wavelength range (selectivity). The HOE can optionally also act selectively on light that hits the HOE at a certain angle of incidence. The use of holographic diffuser elements has certain advantages. For example, holographic diffuser elements can be manufactured over a particularly large area. This enables large display surfaces for the display system. For example, holographic diffuser elements can be manufactured in a replication process in which a holographic master is replicated (e.g. in a contact process).Holographic diffuser elements can be functionalized with particular flexibility. For example, variable wavelength selectivity and / or angle selectivity can be achieved, depending on the system integration requirements. Furthermore, it is possible to integrate a corresponding system with a smaller installation space. The holographic diffuser elements can also be provided with a high degree of transparency. For example, holographic diffuser elements exhibit strong selectivity related to the incident wavelength or the angle of incidence of light. Light with a different wavelength or incident on the holographic diffuser element outside the acceptance angle range can be transmitted.

[0043] In various examples, the optical arrangement for the display system includes not only such a diffuser HOE, but also one or more additional HOEs. In particular, optical arrangements are disclosed in which light scattered by the diffuser HOE is first redirected by a redirection HOE toward the diffuser HOE. However, it would also be conceivable for the light to first be scattered by the diffuser HOE and then redirected by a redirection HOE.

[0044] In various examples, it is particularly possible for the light to initially pass through the diffuser HOE without being (significantly) diffracted. The light then hits the deflection HOE and is then directed back to the diffuser HOE. Similarly, it would also be conceivable for the light to initially pass through the deflection HOE without being (significantly) diffracted. The light then hits the diffuser HOE and is scattered by it, but also directed toward the deflection HOE.

[0045] Such an arrangement with two HOEs is referred to as a "z-configuration." Such an arrangement of the two HOEs in a HOE stack is also referred to as a z-configuration. Both HOEs extend in planes oriented parallel to the x-axis and y-axis of a corresponding coordinate system; the two HOEs can optionally be separated by a distance in the z-direction (the distance can also be zero).

[0046] The Z-configuration of the HOE allows the dimensions of the optical assembly to be relatively small. The beam path can be shaped by the deflection HOE before it hits the diffuser HOE. Accordingly, it would be conceivable for the beam path to first be shaped by the diffuser HOE before it hits the deflection HOE. The Z-configuration reduces stray light and improves the quality of the display.

[0047] In the following, one side of the HOE stack is referred to as the outside (for example, the side adjacent to the deflection HOE when it first diffracts the light); the opposite side is referred to as the inside. This is an arbitrary designation intended for ease of reading but is not intended to be limiting.

[0048] In various examples, two HOEs designed as volume reflection gratings are used in a "transmission geometry", with one of the two HOEs being the diffuser HOE. This means that the light originating from the light source unit passes through the stacked HOEs, even though the individual HOEs diffract the light in reflection geometry. The light is emitted by the light source, then propagates to the HOE stack; then initially passes through one of the HOEs (e.g. the diffuser HOE) undiffracted because the light hits this HOE outside of its acceptance angle (it is possible that some of the light is Fresnel-reflected at the surface of this HOE; however, this part is not considered here; such a portion can be reduced, for example, by an anti-reflective coating). The light then hits another HOE (e.g. the deflection HOE) within its acceptance angle.This HOE (also called the "first HOE" because it is the first HOE in the light beam path to actually diffract the light) then redirects the light towards the other HOE (also called the "second HOE"). This time, the light hits the second HOE within the acceptance angle, so that it is diffracted there as well. The second HOE is designed to redirect the light again using diffraction – in reflection geometry – so that the light then hits the first HOE again, but this time outside its acceptance angle. Therefore, the light passes through the first HOE this time and then leaves the optical arrangement.

[0049] The first HOE or the second HOE also provides a diffuser property, meaning the first HOE or the second HOE scatters the light. For example, the first HOE could be the "diffuser HOE"; however, it would also be conceivable for the second HOE to be the "diffuser HOE."

[0050] From the above, it can be seen that the light coming from the light source unit first strikes the second HOE and then leaves the optical arrangement on the other side, namely at the first HOE (i.e., on the side opposite the light source unit; this site is referred to below as the "outside"). This is the aforementioned transmission geometry of the HOE stack (this transmission geometry of the HOE stack will be illustrated later, particularly in connection with FIG. 1A). In addition to such a transmission geometry of the HOE stack, the HOE stack can also have a reflection geometry (discussed later in detail in connection with FIG. 1B).

[0051] The various HOEs disclosed herein can, as a general rule, be formed as bulk HOEs in a corresponding recording material, ie, the thickness of the recording material is much larger than the wavelength of light used for recording.

[0052] The optical arrangement disclosed herein can be used in various application scenarios. Different types of transparent display systems can be enabled.

[0053] For example, it would be conceivable for such an optical arrangement to be integrated into the door structure of a motor vehicle door. The HOE stack can then be attached to the door window. In this way, it would be conceivable for a display to be projected into the surroundings of the motor vehicle (corresponding to the exterior). Another application for such an optical arrangement would be digital display board systems, for example for offices, conference rooms, advertising boards, customer stoppers, information stands, etc. In such digital display board systems, the light source unit can then be integrated into a support structure of a frame, and a transparent pane of the digital display board system can carry the HOE stack.

[0054] Sometimes it may be desirable for the display to be projected not only onto the outside (HOE stack in transmission geometry) or only onto the inside (HOE stack in reflection geometry). Sometimes it may be desirable for projection to occur on both sides, i.e., the outside and the inside. In such a case, an additional diffuser HOE (also called a "third HOE") can be provided in the HOE stack, which scatters part of the light traveling along a partial beam path. The beam path then serves a first side (e.g., the inside) and the partial beam path then serves the other, second side (e.g., the outside).

[0055] FIG. 1A schematically illustrates an optical arrangement 100 for a transparent display system. The optical arrangement 100 has a light source unit 95. The light source unit 95 is configured to emit light along a beam path 70. The optical arrangement 100 further includes a deflection HOE 91 and a diffuser HOE 92, which together form a HOE stack 99. The diffuser HOE 92 extends along the deflection HOE 91; both HOEs 91, 92 extend in planes perpendicular to a z-axis. The two HOEs 91, 92 are arranged in a z-configuration.

[0056] From FIG. 1A, it can be seen that the beam path 70 exits the optical arrangement 100 on a side 61 (the outer side) opposite the side 62 on which the light source unit 95 is arranged. The beam path 70 thus "transmits" through the optical arrangement 100.

[0057] The deflection HOE 91 and the diffuser HOE 92 have approximately the same lateral extent in the respective plane parallel to the xy plane and thus form a display surface 60 for displaying information projected onto the two HOEs 91, 92 by the light source unit 95. A diffuser functionality provided by the diffuser HOE 92 allows the corresponding display to be viewed on this display surface 60.

[0058] To display variable information content, the light source unit 95 can be configured as a picture generating unit (PGU), DLP (digital light projector), or DMD (digital micromirror device). Another example would be a liquid crystal on silicon (LCOS)-based image generation unit. An LED light source could also be used. A laser diode or a laser could also be used as the light source.

[0059] In FIG. 1A, the distance 140 parallel to the z-axis between the deflection HOE

[0060] 91 and the diffuser HOE 92, whereby this distance 140 is not necessarily drawn to scale.

[0061] Both the deflection HOE 91 and the diffuser HOE 92 diffract the light in reflection geometry.

[0062] FIG. 1 A shows a scenario in which the light first hits the diffuser HOE

[0063] 92 and then the deflection HOE 91. An inverted arrangement is also possible and will be discussed later in connection with FIG. 15. Nevertheless, various concepts described below for the arrangement in which the light first strikes the diffuser HOE 92 are also applicable to the arrangement in which the light first strikes the deflection HOE 91.

[0064] In FIG. 1A, it can be seen that the beam path 70 initially impinges on the diffuser HOE 92 at a first position 71 along the beam path 70. The beam path 70 impinges on the diffuser HOE 92 at the first position 71 such that the light impinges on the diffuser HOE 92 outside an acceptance angle of the diffuser HOE 92. Therefore, the light is not diffracted by the diffuser HOE 92 and passes through it.

[0065] Optionally, it is possible for the acceptance angle of the diffuser HOE 92 to vary as a function of the position on the diffuser HOE 92. This ensures that the light is not diffracted across the width of the beam path 70 when the respective light rays first strike the diffuser HOE 92 at the respective first position 71.

[0066] The beam path 70 then impinges on the deflection HOE 91 at a second position 72, with the light incident on the deflection HOE 91 within the acceptance angle. Thus, the light is diffracted by the deflection HOE 91 (in reflection geometry). The deflection HOE 91 provides a deflection functionality. An angle 0 is shown in FIG. 1A, at which the light is reflected by the deflection HOE 91. Optionally, the deflection HOE 91 can also provide additional functionalities. For example, it would be conceivable for the deflection HOE 91 to also shape the beam path 70. For example, the divergence of the beam path 70 can be reduced. In other words, it would be conceivable for the deflection HOE 91 to also provide a collimation functionality.

[0067] Due to the deflection functionality provided by the deflection HOE 91, the beam path 70 re-enters the diffuser HOE 92 at a third position 73. This time, the light strikes the diffuser HOE 92 within the acceptance angle, so that the light is diffracted by the diffuser HOE 92 (in reflection geometry). For this purpose, it is particularly advantageous if the acceptance angle of the diffuser HOE 92 is location-dependent, i.e., if it varies as a position on the diffuser HOE 92 such that the light reflected by the deflection HOE 91 is diffracted everywhere on the diffuser HOE 92. The diffuser HOE 92 provides two optical functionalities, namely firstly to redirect the light (in the direction of the redirecting HOE 91, towards the outside 61) and secondly to scatter the light, i.e. a diffuser functionality.

[0068] The beam path 70 then strikes the deflection HOE 91 again at a fourth position 74; however, this time the light strikes the deflection HOE 91 outside the acceptance angle of the deflection HOE 91. Therefore, the light is not diffracted by the deflection HOE 91 this time, so that the light passes through the deflection HOE 91. The light then exits the optical arrangement 100 toward the outer side 61.

[0069] Such an optical arrangement 100, as discussed above in connection with FIG. 1A, has various advantages. Firstly, it is helpful for various system integration scenarios if the light source unit 95 can be arranged on the inner side 62. Secondly, it is also possible to use the two HOEs 91, 92 that diffract the light in reflection geometry (instead of in transmission geometry). Such HOEs diffract in reflection geometry typically have a lower wavelength selectivity than HOEs diffract in transmission geometry. In this way, spurious reflections are reduced. It is also advantageous that the display surface 60 is transparent when the light source unit 95 is switched off. This enables various applications, e.g., for display systems integrated into an information desk, etc. Furthermore, the vertical dimension 141 (perpendicular to the extent of the display surface 60) of the HOE stack orThe vertical dimension 142 of the entire optical arrangement 100 is small. This allows system integration in a small installation space. Due to the ability to shape the beam path 70 at the deflection HOE 91, a particularly large proportion of the light from the diffuser HOE 92 can be diffracted at the third position 73 along the beam path 70. Only a small amount of light is outside the acceptance angle of the diffuser HOE 92. Thus, little stray light occurs toward the inner side 62. To further reduce the stray light, a variant according to FIG. 2 can be used.

[0070] FIG. 1B schematically illustrates an optical arrangement 100A for a transparent display system. FIG. 1B shows a variant of FIG. 1A. In FIG. 1B, the diffuser HOE 92 is configured to diffract the light in a transmission geometry (this is different from FIG. 1A, where the light is diffracted by the diffuser HOE 92 in a reflection geometry). This achieves a display on the inner side 62. This means that in FIG. 1B, the light source unit 95 is arranged on the side on which the beam path 70 leaves the optical arrangement 100A. After being scattered and deflected at the third position 73, the light no longer travels to the deflection HOE 91.

[0071] FIG. 2 illustrates an optical arrangement 200 according to various examples. The optical arrangement 200 essentially corresponds to the optical arrangement 100. In the example of FIG. 2, the distance 240 between the deflection HOE 91 and the diffuser HOE 92 is dimensioned differently than the distance 140 between these elements in the scenario of FIG. 1A.

[0072] 2, the angle θ at which the light incident on the deflection HOE 91 travels away from the deflection HOE 91 is dimensioned differently than in FIG. 1A. This angle θ - which is predetermined by the deflection HOE 91 (by a suitable exposure process) - is dimensioned in the example of FIG. 2 such that a part of the light which is not diffracted by the diffuser HOE 92 at the third position 73 - due to a non-100% diffraction efficiency of the diffuser HOE 92 - is totally reflected within the recording material of the diffuser HOE 92 at the interface between this recording material and the environment (e.g. air or a substrate 90, see subsequent figures) and is then captured by a light trap 241 which is arranged adjacent to side surfaces of the HOE 91, 92. FIG. 3, FIG. 4 and 5 each show a corresponding optical arrangement 300, 400, 500.Each of the optical assemblies 300, 400, 500 can, for example, correspond to one of the optical assemblies 100, 200 as discussed above. In FIG. 3, FIG. 4 and FIG. 5, a substrate 90 is also shown. The substrate 90 can, for example, be a glass plate or a plastic film. The substrate 90 is not the recording material in which the HOEs 91, 92 are formed; but a substrate 90 that imparts a certain rigidity and strength to the HOE stack 99. The two HOEs 91, 92 are applied to the substrate 90. In the example of FIG. 3, the substrate 90 is arranged between the deflection HOE 91 and the diffuser HOE 92. In the example of FIG. 4, the substrate 90 extends along and adjacent to the diffuser HOE 92. In the example of FIG. 5, the substrate 90 extends along and adjacent to the deflection HOE 91.

[0073] In addition to the substrate 90, other elements may also be present. Examples include anti-reflective films, hard coatings for protection against external influences, encapsulation, etc.

[0074] FIG. 6 shows an optical arrangement 600 according to various examples. The optical arrangement 600 basically corresponds to the optical arrangement 100 or the optical arrangement 200 according to the examples in FIG. 1A and FIG. 2. However, the optical arrangement 600 includes an additional diffuser HOE 93. The additional diffuser HOE 93 serves an additional display for the inner side 62.

[0075] The further diffuser HOE 93 is also part of the HOE stack 90. ​​The further diffuser HOE 93 extends along the diffuser HOE 92 (in a plane parallel to the xy plane) and is configured to at least partially redirect and disperse the light, provided it falls on the further diffuser HOE 93 within a corresponding acceptance angle.

[0076] At the fifth position 75, which is located upstream of the first position 71, the beam path 70, originating from the light source unit 95, impinges on the further diffuser HOE 75 such that the light falls onto the further diffuser HOE 93 within the corresponding acceptance angle. The light is thus diffracted by the further diffuser HOE 75 in reflection geometry, so that the diffracted part of the light travels along a partial beam path 670, which is separated or split off from the beam path 70. The diffracted light is scattered and redirected. The partial beam path 670 and the beam path 70 exit the optical arrangement 600 in essentially opposite directions. The partial beam path 670 travels toward the inner side 62, while the beam path 70 travels toward the outer side 61. The further diffuser HOE 93 can thus be used to provide an indication for viewing angles from the inside 62.

[0077] In one example, it would be conceivable for the diffuser HOE 92 and the further diffuser HOE 93 to diffract light in the same wavelength range, meaning their acceptance wavelength ranges can overlap or even be identical. Then, a portion of the light that arrives at the fifth position 75 along the beam path 70 at the further diffuser HOE 93 is diffracted by the further diffuser HOE 93; the other portion continues along the beam path 70 toward the diffuser HOE 92. The diffraction efficiency of the further diffuser HOE 93 can be adjusted by a suitable exposure process, for example, to approximately 50%. In such a variant, the same display is enabled for the inner side 62 and for the outer side 61 by means of the partial beam path 670 and the beam path 70. Sometimes, however, it may also be desirable to enable different displays for the inner side 62 and for the outer side 61 by means of the partial beam path 670 and the beam path 70.For example, different images or different pictograms or symbols are to be displayed. In such a scenario, this can be achieved, for example, by multiplexing in wavelength space. For example, it would be conceivable for the diffuser HOE 92 and the further diffuser HOE 93 to diffract light in different wavelength ranges, meaning their acceptance wavelength ranges can be different. Different images can then be projected by the light source unit 95 in these different wavelength ranges, with these different images then being assigned to the inner side 62 or the outer side 61, respectively.

[0078] FIG. 7 illustrates an optical arrangement 700. The optical arrangement 700 corresponds to the principle of the optical arrangement 100A according to the example of FIG. 1B. In particular, a HOE stack 99 comprising the diffuser HOE 92 and the deflection HOE 91 is also present. The diffuser HOE 92 diffracts the light in the example of FIG. 7 in transmission geometry (as in FIG. 1B). The optical arrangement 700 includes a further diffuser HOE 93. The further diffuser HOE 93 serves a further display for the outer side 61. The HOE stack 99 also includes (as in FIG. 6) the further diffuser HOE 93. By selecting the diffraction efficiency of the deflection HOE 91 at the second position 72 to be significantly less than 100% - e.g., between 40% and 60% or preferably equal to 50% - the partial beam path 770 is split off from the beam path 70 at the second position 72.The light traveling along partial beam path 770 then falls at the corresponding fifth position 75 onto the further diffuser HOE 93, which diffracts this light into transmission geometry. As a result, the light traveling along partial beam path 770 is scattered at the fifth position 75. Partial beam path 770 then exits optical arrangement 700 toward the outer side 61. Beam path 70 exits optical arrangement 700 toward the inner side 62.

[0079] Instead of achieving the splitting of the partial beam path 770 by means of the reduced diffraction efficiency of the deflection HOE 91 at the second position 72, as explained above, it would also be possible for the light to be diffracted by the further diffuser HOE 93 to have a wavelength that differs from the wavelength of the light to be diffracted by the deflection HOE 91 and the diffuser HOE 92. This means that the wavelength of the light to be diffracted at the further diffuser HOE 93 lies outside an acceptance wavelength range of the deflection HOE 91, so that this light is not diffracted at the second position.

[0080] FIG. 8, FIG. 9, FIG. 10 and FIG. 11 each show an optical arrangement 800, 900, 1000, 1100. Each of the optical arrangements 800, 900, 1000, 1100 can be configured corresponding to the optical arrangement 600 from FIG. 6. FIG. 8, FIG. 9, FIG. 10 and FIG. 11 also show the arrangement of the substrate 90. The substrate 90, e.g., a plastic film or a glass substrate, can be arranged adjacent to each of the diffuser HOE 92, the deflection HOE 91 and the further diffuser HOE 93. The substrate 90 can also be arranged in different ways for the variant of the optical arrangement 700 from FIG. 7.

[0081] FIG. 12 illustrates a door 2000 for a motor vehicle. The door 2000 has a support structure 2100 to which an outer panel 2110 and an inner panel (not visible in FIG. 12) are attached. The support structure 2100 supports a window frame 2200 in which a window pane 2210 is mounted. The light source unit 95 is arranged in a space formed between the inner panel and the outer panel 2110, in the framework of the support structure 2100 (concealed by the outer panel 2110 in FIG. 12).

[0082] In the example of FIG. 12, the HOE stack 99 (comprising at least the deflection HOE 91 and the diffuser HOE 92) is mounted on the window pane 2210. The window pane 2210 can form the substrate 90.

[0083] For a viewer viewing door 2000 from outside the motor vehicle—that is, from the exterior side 61—a corresponding image is therefore visible on window 2210 as display 2500. This may, for example, be a warning, such as during a turning maneuver. For this purpose, a control unit can control light source unit 95 differently depending on the driving situation, e.g., by selectively switching it on or off or by displaying different images.

[0084] FIG. 13 illustrates aspects related to the use of the diffuser HOE 92 to provide a functionalized diffuser property. The diffuser HOE 92 provides a scattering characteristic that has two different scattering lobes 1301, 1302. The scattering characteristic is therefore angle-dependent. The scattering lobes have corresponding maxima 1308, 1309. This allows different displays to be provided in different spatial directions 1311, 1312. It would be possible for the two scattering lobes 1301, 1302 to be implemented for different wavelengths of light.

[0085] Generally speaking, by appropriately designing the scattering pattern, it may be possible to create one or more eyeboxes from which a display is visible. This can also provide privacy functionality, for example; this means that it is possible to create one or more spatially precisely defined eyeboxes outside of which the display can no longer be perceived. Furthermore, such a defined scattering pattern has the advantage that light is directed specifically into the eyebox. Less light is lost, so the display brightness (with the same light source brightness) is greater.

[0086] The scattering characteristic can also be configured depending on the location. Different lateral positions (xy plane) of the diffuser HOE 92 then provide, for example, one of the two scattering lobes 1301, 1302. FIG. 14 illustrates aspects related to a digital display board system 1400. The digital display board system 1400 comprises a support structure 1410 and a transparent pane 1470 supported by the support structure 1410. Feet 1415 are provided to hold the support structure 1410. Below the transparent pane 1470, in the area between the feet 1415, a space 1450 is provided in which the light source unit 95 can be arranged. This type of system integration is made possible because relatively steep angles of incidence of the beam path from the light source unit 95 to the deflection HOE 91 can be used in the z-configuration, as explained above in connection with FIG. 1 and the vertical dimension 142.The HOE stack 99 is mounted on the transparent pane 1470. The transparent pane 1470 thus implements the display surface 60. The digital display board system 1400 is particularly suitable in combination with an optical arrangement 600, 700 as shown in the examples of FIG. 6 or FIG. 7 to enable a display in both areas—in front of and behind the transparent pane 1470.

[0087] Various variations are conceivable. For example, the light source unit 95 could also be mounted above the transparent pane 1470.

[0088] In general, during system integration, the HOE stack 99 can be combined with other light-shaping elements. For example, it would be conceivable to use an optical filter to filter out certain light components of the light that has passed through the HOE stack 99.

[0089] For example, the filter could be implemented as a leaf filter. The leaf filter can be designed to only allow light within a specific angular range of the angle of incidence to pass through. Light incident on the leaf filter at angles outside this angular range can be filtered on the inner sides of the leaves. However, the filter could also be implemented using another HOE; such a filter could, for example, utilize total resection: For example, a corresponding HOE could be present that is designed to diffract light that was not diffracted by the HOE 91 and / or the HOE 92 of the HOE stack 99 (zeroth order of diffraction) in such a way that this then diffracted light is totally reflected at least once at an interface. The filter could, for example, comprise one or more light-absorbing elements (“beam dump”).For example, if another HOE is used, which, as described above, diffracts the zeroth diffraction order of HOEs 91, 92 in such a way that they are subsequently totally reflected, the totally reflected light could then be guided to the light-absorbing element. Filtering could also be achieved by exploiting the polarization of the light. Thus, a polarization filter could be used.

[0090] Various implementation variants for such a filter were described above. The various implementation variants can also be combined with one another. In general, such a filter can be formed, for example, on a flexible substrate, such as a film. It is conceivable that this filter substrate extends along the substrate 90 (see the preceding figures).

[0091] By using such a filter, stray light can be specifically reduced. For example, the eyebox can be defined more sharply than is possible using the HOE stack 99 alone. For example, it has been observed that the brightness of a corresponding image (compare, for example, display 2500 in FIG. 12) can drop in edge regions of the eyebox (without such a filter). To avoid such optical edge effects, appropriate filtering of such angular regions can be enabled using the additional filter. In such an example, components of the light that were diffracted by the HOE 91 and the HOE 92 after passing through the HOE stack 99 can be filtered out. Alternatively or additionally, non-diffracted components of the light could also be filtered out.

[0092] In general, during system integration, the HOE stack 99 can be combined with other light-shaping elements. For example, it would be conceivable to use an optical filter to filter out certain light components of the light that has passed through the HOE stack 99.

[0093] For example, the filter could be implemented as a louvre filter. The louvre filter can be designed to only allow light within a specific angular range of the angle of incidence to pass through. Light incident on the louvre filter at angles outside this angular range can be filtered on the inner sides of the louvres. However, the filter could also be implemented using another HOE; such a filter could, for example, utilize total internal reflection. For example, a corresponding HOE could be present that is designed to diffract light that was not diffracted by the HOE 91 and / or the HOE 92 of the HOE stack 99 (zeroth order of diffraction) in such a way that this then diffracted light is totally reflected at least once at an interface. The filter could, for example, comprise one or more light-absorbing elements (“beam dump”).For example, if another HOE is used, which, as described above, diffracts the zeroth order of HOEs 91, 92 in such a way that they are subsequently totally reflected, the totally reflected light could then be guided to the light-absorbing element. Filtering could also be achieved by exploiting the polarization of the light. Thus, a polarization filter could be used.

[0094] Various implementation variants for such a filter were described above. The various implementation variants can also be combined with one another. In general, such a filter can be formed, for example, on a flexible substrate, such as a film. It is conceivable that this filter substrate extends along the substrate 90 (see the preceding figures).

[0095] By using such a filter, stray light can be specifically reduced. For example, the eyebox can be defined more sharply than is possible using the HOE stack 99 alone. For example, it has been observed that the brightness of a corresponding image (compare, for example, display 2500 in FIG. 12) can drop in edge regions of the eyebox (without such a filter). To avoid such optical edge effects, appropriate filtering of such angular regions can be enabled using the additional filter. In such an example, components of the light that were diffracted by the HOE 91 and the HOE 92 after passing through the HOE stack 99 can be filtered out. Alternatively or additionally, non-diffracted components of the light could also be filtered out.

[0096] FIG. 15 schematically illustrates an optical arrangement 1500 for a transparent

[0097] Display system. The optical arrangement 1500 basically corresponds to the optical arrangement 100 from FIG. 1A. However, in the variant of FIG. 15, the diffuser HOE 92 and the deflection HOE 91 are interchanged. In other words, this means that the light first strikes the deflection HOE 91 – but passes through it undiffracted at the first position 71 because it strikes outside the corresponding acceptance angle. The light then strikes the diffuser HOE 92 at the second position 72, where it is scattered and deflected, so that it subsequently strikes the deflection HOE 91 again at the third position 73 along the beam path. There, it is then deflected again, to the outer side 61. Both HOEs 91, 92 thus diffract the light in reflection geometry.

[0098] The diffuser HOE 92 can, for example, diffuse a curved wavefront (e.g., a spherical wave). This can be particularly different from the variant of FIG. 1A, where the deflection HOE 91 (where the light coming from the light source 95 is first diffracted) can be configured to convert a curved wavefront into a flat wavefront.

[0099] The deflection HOE 91 can, for example, map the plane wavefront into a plane wavefront (so-called "plane-plane HOE"). The deflection HOE 91 can be designed as a grating. The deflection HOE 91 can be used, for example, to operate a defined eyebox.

[0100] For example, the acceptance angle of the deflection HOE 91 can be aligned with the maximum of the scattering lobe of the diffuser HOE 92 (cf. FIG. 13). The acceptance angle of the deflection HOE 91 can have a width corresponding to the width of the scattering lobe. If a location-dependent scattering lobe is used for the diffuser HOE 92, a location-dependent acceptance angle of the deflection HOE 91 can also be used. More generally, the acceptance angle of the deflection HOE 91 can be adapted to the scattering characteristics of the diffuser HOE 92.

[0101] Various variations of the optical arrangement 1500 are conceivable. For example, the deflection HOE 91 could diffract in transmission geometry (see also FIG. 1B). A substrate—e.g., "BK7" glass—can be provided, whereby the substrate can be arranged differently with respect to the two HOEs 91, 92 (as discussed in connection with FIG. 3, FIG. 4, and FIG. 5). The width of the gap 140 can vary (see FIG. 2).

[0102] There could also be another diffuser HOE (cf. diffuser HOE 93), which is arranged, for example, first in the beam path; there, a certain portion of the light can already be deflected and diffracted (cf. FIG. 6). It would also be conceivable for the additional diffuser HOE to diffract a partial beam path in transmission geometry, which is only split off from the beam path at the third position 73, as in FIG. 15 (by a diffraction efficiency that is significantly less than 1). Such an additional diffuser HOE could also be arranged as shown in FIG. 7, i.e., diffract a partial beam path in transmission geometry, which is split off from the beam path at the second position due to a reduced diffraction efficiency.

[0103] Of course, the features of the previously described embodiments and aspects of the invention can be combined with one another. In particular, the features can be used not only in the described combinations, but also in other combinations or on their own, without departing from the scope of the invention.

[0104] For example, techniques were described above in which the deflecting HOE 91 does not provide diffuser functionality. In other words, techniques were described in which only the diffuser HOE 92 (optionally together with another diffuser HOE 93) provides diffuser functionality. In various variants, it would be conceivable for the deflecting HOE 91 to also provide diffuser functionality. In other words, this means that two diffuser HOEs can be arranged in a Z configuration. If two diffuser HOEs are used in a Z configuration, they can have different scattering characteristics. For example, the diffuser HOE that scatters the light first could have a relatively narrow scattering lobe. This narrow scattering lobe could then be widened by the subsequent diffuser HOE, e.g., up to 180° wide.For example, the diffuser HOE that first scatters the light can convert a spherical wave into diffuse wavefronts; and the subsequent diffuser HOE can convert plane wavefronts into diffuse wavefronts with the desired scattering characteristics.

Claims

PATENT CLAIMS 1 . Optical arrangement (100, 1500, 100A, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) for a transparent display system, the optical arrangement comprising: - a light source unit (95) arranged to emit light along a beam path (70), - a first holographic optical element, HOE, (91 ), which is arranged to redirect the light, provided it falls on the first HOE (91 ) within a first acceptance angle of the first HOE (91 ), - a second HOE (92) extending along the first HOE (91) and configured to redirect the light incident on the second HOE (92) within a second acceptance angle of the second HOE (92), wherein at least one of the first HOE (91) and the second HOE (92) is further configured to disperse the light incident on the corresponding HOE (91, 92) within the corresponding acceptance angle, wherein the beam path (70) impinges on the second HOE (92) at a first position (71) along the beam path (70) such that the light impinges on the second HOE (92) outside the second acceptance angle, wherein the beam path (70) impinges on the first HOE (91) at a second position (72) along the beam path (70) downstream of the first position along the beam path (70) such that the Light falls on the first HOE (91 ) within the first acceptance angle,wherein the beam path (70) impinges on the second HOE (92) at a third position (73) along the beam path (70) downstream of the second position such that the light impinges on the second HOE (92) within the second acceptance angle.

2. Optical arrangement (100, 1500, 200, 300, 400, 500, 600, 800, 900, 1000, 1100) according to claim 1, wherein the beam path (70) impinges on the first HOE (91) at a fourth position (74) along the beam path (70), which is located downstream of the third position (73) along the beam path (70), such that the light impinges on the first HOE (91) outside the first acceptance angle.

3. Optical arrangement (100, 1500, 200, 300, 400, 500, 600, 800, 900, 1000, 1100) according to claim 1 or 2, wherein the beam path (70) leaves the optical arrangement towards a side (61) of the optical arrangement which is opposite a side (62) of the optical arrangement on which the light source unit (95) is arranged.

4. Optical arrangement (100A, 700) according to claim 1, wherein the beam path (70) leaves the optical arrangement towards the same side (62) downstream of the third position (73) on which the light source unit (95) is arranged.

5. Optical arrangement (600, 800, 900, 1000, 1100) according to one of claims 1 to 3, further comprising: - a third HOE (93) extending along the second HOE (92) and configured to redirect and disperse the light incident on the third HOE (93) within a third acceptance angle of the third HOE (93), wherein the beam path (70) impinges on the third HOE (93) at a fifth position (75) along the beam path (70) located upstream of the first position (71) along the beam path (70) in such a way that the light impinges on the third HOE (93) within the third acceptance angle, so that a partial beam path (670) is split off from the beam path (70) at the fifth position (75).

6. Optical arrangement (600, 800, 900, 1000, 1100) according to claim 5, wherein the third HOE (93) is arranged to detect the light beam propagated along the To diffract the light traveling along the partial beam path (670) in reflection geometry.

7. Optical arrangement (700) according to claim 1 or 4, further comprising: - a third HOE (93) extending along the first HOE (91) and configured to disperse the light, provided it falls (93) onto the third HOE within a third acceptance angle of the third HOE (93), wherein a partial beam path (770) is split off from the beam path (70) at the second position (72), wherein the partial beam path (770) impinges on the third HOE (93) at a fifth position (75) located downstream of the second position (72) along the partial beam path (770) such that the light impinges on the third HOE (93) within the third acceptance angle.

8. Optical arrangement (700) according to claim 7, wherein the third HOE (93) is configured to diffract the light traveling along the partial beam path (770) in transmission geometry.

9. Optical arrangement (600, 700, 800, 900, 1000, 1100) according to one of claims 5 to 8, wherein the partial beam path (670, 770) and the beam exit (70) leave the optical arrangement (600, 700) towards opposite sides (61, 62).

10. The optical assembly (600, 700, 800, 900, 1000, 1100) of any one of claims 5 to 9, wherein the second HOE (92) has a second acceptance wavelength range, wherein the third HOE (93) has a third acceptance wavelength range different from the second acceptance wavelength range.

11. Optical arrangement (200) according to one of the preceding claims, wherein a part of the light which is not reflected at the third position (73) by the second HOE (92) is diffracted, then undergoes total reflection within a recording material of the second HOE (92).

12. Optical arrangement (200) according to claim 10, further comprising: - a light trap (241) arranged adjacent to a side surface of at least the second HOE (92) and arranged to trap the part of the light not diffracted at the third position (73).

13. Optical arrangement (100, 1500, 100A, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) according to one of the preceding claims, wherein the first HOE (91) diffracts the light in reflection geometry, where the second HOE (92) diffracts the light in reflection geometry or in transmission geometry.

14. Optical arrangement (100, 1500, 100A, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) according to one of the preceding claims, wherein a first lateral extent of the first HOE (91) is in the range of 80% to 120% of a second lateral extent of the second HOE (92).

15. Optical arrangement (100, 1500, 100A, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) according to one of the preceding claims, wherein the first HOE (91) is further configured to shape the beam path (70) if the light is incident on the first HOE (91) within the first acceptance angle of the first HOE (91).

16. Optical arrangement (100, 1500, 100A, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) according to one of the preceding claims, wherein the light source unit (95) is an image generation unit.

17. Optical arrangement according to one of the preceding claims, wherein the one of the first HOE (91) and the second HOE (92) configured to diffuse the light implements a functionalized diffuser element with at least one of a location-dependent scattering characteristic or an angle-dependent scattering characteristic.

18. Optical arrangement (100, 1500, 100A, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) according to one of the preceding claims, wherein the first acceptance angle varies as a function of a position on the first HOE (91).

19. System that includes: - a door (2000) for a motor vehicle, comprising a support structure (2100), an outer panel (2110) attached to the support structure (2100), an inner panel attached to the support structure (2100), and a window frame carried by the support structure (2100), - a window pane (2210) mounted in the window frame (2200), and - the optical arrangement (100, 1500, 100A, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) according to one of the preceding claims, wherein the light source unit (95) is arranged in a space formed in the support structure (2100) between the outer panel (2110) and the inner panel, wherein the first HOE (91) and the second HOE (92) are arranged on the window pane (2210).

20. The system of claim 19, wherein the beam path (70) exits the optical assembly toward the outside of the door.

21. Motor vehicle which includes: - the system according to claim 19 or 20, - a control device which is arranged to control the light source unit (95) depending on the driving situation of the motor vehicle.

22. Digital display board system (1400), which includes: - a support structure (1410), - a transparent disc (1470) held by the support structure, and - the optical arrangement (100, 1500, 100A, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) according to one of claims 1 to 18, wherein the light source unit (95) is arranged in the support structure (1410), wherein the first HOE (91) and the second HOE (92) are arranged on the transparent disc (1470).

23. Display system that includes: - the optical arrangement according to one of claims 1 to 18, - a control device configured to control the light source unit.

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