Functionalized diffuser element for head-up display

Abstract

An optical arrangement (91) for a head-up display system (90) on a deflection surface (190) comprises at least one projection unit (121), which is designed to project at least one image onto at least one functionalized diffuser element (122).

Description

[0001] DESCRIPTION

[0002] FUNCTIONALIZED DIFFUSER ELEMENT FOR HEAD-UP DISPLAY

[0003] TECHNICAL FIELD

[0004] Various examples of the disclosure relate to an optical arrangement for a head-up display. Various examples particularly relate to the use of a functionalized diffuser element.

[0005] BACKGROUND

[0006] Head-up displays (HUDs; also known as windshield display devices), for example, are used in vehicles to generate a virtual image so the driver doesn't have to take their eyes off the road. The HUD includes a projection unit and a wavefront manipulator.

[0007] The projection unit generates the visual information (e.g., speed, navigation instructions, warnings, etc.) used to create a virtual image. Typically, the projection unit is a compact projector mounted below the vehicle's dashboard. The projection unit uses either lasers, light-emitting diodes, or digital light processing (DLP) technology to generate the virtual images.

[0008] The wavefront manipulator is an optical component that manipulates the light beams generated by the projection unit to create a sharp and clearly visible virtual image. The wavefront manipulator can consist of lenses, mirrors, or one or more holographic optical elements (HOEs).

[0009] In contrast to a real image displayed on a physical surface (e.g., a screen), the virtual image is generated on a virtual image plane located behind the windshield (i.e., in the vehicle's surroundings) and extending from the eyebox. The eyebox is the area in which the driver can see the virtual image clearly. The following prior art is known: CN112946890A; DE 102012222421 A1;

[0010] DE102019131732A1 ; JPH08286139A; WO2023186627A1.

[0011] SUMMARY

[0012] An object of the present disclosure is to provide an optical arrangement for a HUD which has compact dimensions and good optical properties, in particular high brightness and good contrast of the virtual image in the eyebox.

[0013] This object is achieved by the features of the independent claims. The dependent claims define embodiments.

[0014] An optical arrangement for a HUD on a deflection surface, e.g. a windshield of a motor vehicle, is disclosed.

[0015] The optical arrangement comprises at least one projection unit. The at least one projection unit is configured to project at least one image onto at least one functionalized diffuser element. The at least one projection unit is configured to emit light along at least one beam path. The at least one projection unit can use, for example, DLP. A digital micromirror device (DMD) could also be used.

[0016] The optical arrangement also includes at least one functionalized diffuser element arranged along the at least one beam path. The at least one functionalized diffuser element is arranged to diffuse the at least one beam path. Thus, a virtual image of the at least one image projected onto the functionalized diffuser element becomes perceivable or visible in an eyebox of the HUD. The virtual image appears—as perceived from the eyebox—behind the deflection surface.

[0017] A diffuser element scatters light. It has a multitude of scattering centers. When parallel light rays strike a scattering center of 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 incident on the scattering element is scattered (scattering lobe). The diffuser element can therefore also redirect the light by appropriately orienting the scattering lobe. The diffuser element also makes it possible to reduce the divergence of the beam path by forming the scattering lobe with a width that is smaller than the divergence of the beam path before it strikes the diffuser element.

[0018] 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 equally frequently. For example, the scattering lobe shows no dependence on the lateral position within the aperture of the ground glass screen. The scattering characteristics also show no dependence on, for example, the wavelength or polarization of the incident light. For these reasons, the ground glass screen is not a functionalized diffuser element.

[0019] 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 and / or the polarization of the incident light. A functionalized diffuser element can alternatively or additionally have a non-uniform scattering characteristic. Thus, there is a macroscopic order to the scattering. In a functionalized diffuser element, the scattering centers can be 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., scatters light preferentially in certain directions; this is a deviation from an equally probable scattering in all directions within a spatial region. For example, it would be conceivable that in a functionalized diffuser element on a microscopic scale - i.e.,a length scale corresponding to the magnitude of the scattered light - a random scattering characteristic still exists; but due to a macroscopic ordering of the scattering centers on the macroscopic scale, certain scattering directions are favored. In other words, this means that with a functionalized diffuser element, the scattering characteristic, e.g., the scattering lobe, is specifically adjusted to certain properties that are required or advantageous for the optical system. By using at least one functionalized diffuser element, an eyebox, in particular, can be suitably designed. For example, a lateral dimension or the size of the eyebox can be suitably adjusted.

[0020] This prevents the eyebox from being too small or too large. By appropriately adjusting the scattering characteristics of the at least one functionalized diffuser element, the eyebox can be suitably positioned and / or dimensioned, for example. Stray light emitted by the at least one projection unit but not reaching the eyebox can be reduced. This allows the brightness of the virtual image, as perceived from the eyebox, to be increased compared to a reference implementation without functionalized diffuser elements, while maintaining the same light output of the at least one projection unit.

[0021] The at least one functionalized diffuser element can, for example, be at least one holographic diffuser element. Each of the at least one holographic diffuser element can be assigned to a corresponding beam path, thus scattering a respective beam path along which light is emitted by the at least one projection unit.

[0022] A holographic diffuser element has an HOE. The HOE forms the scattering surface. A holographic diffuser element achieves scattering of at least one beam path by diffracting the light at the HOE. This means that with the holographic diffuser element – ​​unlike with the classic diffuser element – ​​there are no microscopic scattering centers; instead, an effect comparable to scattering (see the above description of scattering) is achieved by diffracting the light. The HOE for this purpose 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 from 0.5 to 30 nm. In order to scatter light in multiple wavelength ranges, it would be possible to use multiple HOEs orto use multiple holographic diffuser elements, e.g., stacked. This allows light to be diffracted in multiple wavelength ranges, e.g., red (620-630nm), green (520-530nm), blue (420-430nm). 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 of a specific polarization, e.g., left or right circularly polarized. The HOE can optionally also act selectively on light that hits the HOE at a specific angle of incidence.

[0023] Examples of polarization-sensitive HOE designs are described in Weng, Yishi, et al., “Polarization volume grating with high efficiency and large diffraction angle.” Optics Express 24.16 (2016): 17746-17759. Similar techniques can also be used to create a holographic diffuser element that selectively scatters light with a specific polarization.

[0024] The use of holographic diffuser elements offers certain advantages. For example, holographic diffuser elements can be manufactured with particularly large areas. This enables large virtual images with relatively short projection lengths and large distances between the eyebox and the image plane of the virtual image, even up to a virtual image arranged at infinity (for example, in combination with a microlens array). For example, holographic diffuser elements can be manufactured in a replication process in which a holographic master is replicated (e.g., using a contact process). Holographic diffuser elements can be functionalized particularly flexibly. For example, variable wavelength 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 use of holographic diffuser elements, for example, enables an optical arrangement for a HUD that requires significantly less space than a reference arrangement using a freeform mirror. The eyebox can be defined by using holographic diffuser elements with a limited extension. The eyebox can be specially shaped, for example, with a curved design.

[0025] The at least one holographic diffuser element may comprise a plurality of holographic diffuser elements. These may be configured to diffract light with different wavelengths and / or different angles of incidence and / or different polarizations.

[0026] The multiple holographic diffuser elements can therefore be assigned to different optical channels. This allows for multiple beam paths to be dispersed differently. It would also be possible to create multicolored virtual images. It would be conceivable to operate multiple eyeboxes.

[0027] Due to the selectivity in the diffraction of light, it is possible, but not necessary, for the multiple holographic diffuser elements to be arranged in a stack. A first holographic diffuser element can thus extend along a second holographic diffuser element. This enables a particularly compact design of the optical arrangements.

[0028] If the plurality of holographic diffuser elements are arranged in a stack, a distance or gap can be provided between the holographic diffuser elements in the stack.

[0029] The virtual images of the multiple holographic diffuser elements can implement different color channels (e.g., red, green, and blue) of a common scene. Due to the offset in the depth direction, i.e., the gap, the image planes of the different virtual images of the multiple color channels can be offset from one another, creating an impression of depth in the common scene. This means that, for example, it is possible for the image plane of the blue color channel to appear closer or further away when viewed from the eyebox than the image plane of the red color channel, to give just one example. For a clear impression of depth, such a gap can, for example, be no smaller than 10% of the side lengths (this corresponds to the size of the aperture, which correlates with the lateral extent of the virtual images) of the multiple holographic diffuser elements.

[0030] Multiple holographic diffuser elements can be formed in a common substrate. For example, volume HOEs can be used in a common substrate. For example, multiple volume HOEs can be used in a common substrate, i.e., a large number of volume HOEs can be stacked or arranged laterally offset in a common substrate. This enables compact integration and simple manufacturing. The at least one holgraphic diffuser element can be arranged in the beam path, for example, in free-beam geometry or in edge-lit geometry. In edge-lit geometry, the light is coupled into the substrate via a side surface. The beam path then runs between the side surface and the scattering surface (which is tilted relative to the side surface) in the substrate.

[0031] Multiple holographic diffuser elements can serve different optical channels. For example, different projection units can be used for the different optical channels. Different optical channels can alternatively or additionally serve different eyeboxes. For example, it would be conceivable for a first eyebox, served by a first optical channel, to be provided for a driver of a motor vehicle; and a second eyebox, served by a second optical channel, to be provided for a passenger of the motor vehicle.

[0032] The multiple functionalized diffuser elements (e.g., holographic diffuser elements) can be configured to separate two or more beam paths. This means that the scattering lobes of the different diffuser elements can be oriented in such a way that the different beam paths are separated from each other. This allows, for example, multiple eyeboxes to be served. A separate beam splitter, etc., is not necessary, thus enabling a compact design.

[0033] However, it would generally also be conceivable for several beam paths to be combined by the diffuser elements.

[0034] The at least one functionalized diffuser element can be designed to better concentrate the light field into a limited solid angle. The scattering lobe can be particularly small. For example, a scattering lobe can be used that emits light only into a solid angle of 1° or no more than 5°. The divergence of a beam path scattered by a functionalized diffuser element can be greater upstream of the functionalized diffuser element than downstream of the functionalized diffuser element. In this way, the brightness of the virtual image can be increased while maintaining the same light output. Less scattered light is lost. By reducing scattered light, distractions to people in the surrounding area can also be reduced.

[0035] The at least one functionalized diffuser element is configured, for example, to deflect the at least one beam path to at least one eyebox of the HUD. This means that the at least one functionalized diffuser element can also have a deflection functionality. An angle of incidence of light onto the functionalized diffuser element can differ from an angle of reflection of the light. For example, the scattering lobe of the at least one functionalized diffuser element can not be oriented perpendicular to the scattering surface of the at least one functionalized diffuser element, but rather, for example, tilted relative to a corresponding plane normal. A corresponding angle of the scattering lobe can also vary as a function of the lateral position within the scattering surface. This can, for example, make it unnecessary to provide a separate mirror for deflecting the beam path.This allows the overall installation space required for the optical arrangement to be reduced.

[0036] At least one of the at least one diffuser element can be arranged in a transmission geometry. This means that the beam path passes through the scattering surface of the respective diffuser element. On the other hand, it would also be conceivable for at least one of the at least one functionalized diffuser element to be arranged in a reflection geometry in the beam path.

[0037] It is possible that the optical arrangement comprises one or more further optical elements in at least one beam path.

[0038] The optical arrangement can, for example, further comprise a deflecting element. This is arranged, for example, along the at least one beam path downstream of the at least one functionalized diffuser element (i.e., between at least one functionalized diffuser element and the deflecting surface). The deflecting element is configured to deflect the at least one beam path. The deflecting element can, for example, be a prism or a mirror. The deflecting element enables a particularly small installation space for the optical arrangement, which can be particularly helpful for system integration, for example, beneath a vehicle dashboard.

[0039] For example, it would be conceivable for the deflection element to be arranged such that the at least one beam path forms a loop. This means that a first section of a respective beam path is intersected by a second section of the respective beam path. This allows for a relatively long beam path, which can be helpful for enabling large projection distances, i.e., distances between the at least one functionalized diffuser element and the image plane of the virtual image.

[0040] The optical arrangement can, for example, comprise a microlens array. This can extend along the at least one functionalized diffuser element. A microlens array comprises a plurality of microlenses arranged side by side, each of which refracts light.

[0041] The microlens array can be arranged at a specific distance from the HOE of the functionalized holographic diffuser element. For example, the microlens array could be arranged at a distance from the HOE that corresponds to the "focal length" of the HOE. This causes the projected image to be projected onto the HOE to infinity. This results in a so-called "infinity display": the virtual image is perceived at infinity.

[0042] The microlens array can extend along a scattering surface of the diffuser element. The microlens array can, for example, be applied to a correspondingly functionalized diffuser element. For this purpose, a refractive index-matched adhesive can be used.

[0043] For example, each microlens of the microlens array can be assigned to a corresponding sub-area on the scattering surface of the functionalized diffuser element. The projection unit can be configured to project the entire image information of the virtual image into each sub-area. In other words, this means that each sub-area is assigned to multiple projection pixels of the projection unit. The same image information is projected into each sub-area. Such a projection mode is different from a projection mode used when no microlens array is present. If no microlens array is present, the virtual image is projected onto the functionalized diffuser element such that it fills the entire scattering surface. In other words, the virtual image is then projected onto the functionalized diffuser element such that it completely or predominantly fills the aperture of the functionalized diffuser element.

[0044] The at least one functionalized diffuser element can have a curved scattering surface. The curvature of the scattering surface can create an impression of depth for the virtual image. This is due to the fact that different areas of the scattering surface are located closer or further away from the eyebox. To convey a particularly pronounced impression of depth, the curvature can be comparatively pronounced. For example, it would be possible for the curvature to achieve an offset along the beam path of two points on the scattering surface that is no less than 10% of a side length of the scattering surface.

[0045] A curved scattering surface can be easily created, especially for holographic diffuser elements. This may be due to the manufacturing process of the holographic diffuser elements.

[0046] A HUD system is also disclosed. This includes the optical arrangement and the deflection surface.

[0047] The deflection surface can be transparent. The deflection surface can be a windshield of a motor vehicle.

[0048] The components of the HUD system are arranged and configured to provide the at least one eyebox.

[0049] A motor vehicle with such a HUD system is also disclosed.

[0050] For example, the system could have a back-darkening on a side of the deflection surface that is opposite the side of the deflection surface where the at least one beam path is reflected. This can increase the contrast of the virtual image.

[0051] 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.

[0052] SHORT DESCRIPTION OF THE CHARACTERS

[0053] FIG. 1 illustrates an exemplary variant of an optical arrangement for a HUD system according to various examples.

[0054] FIG. 2A illustrates an exemplary dependence of the scattering lobe of a functionalized diffuser element for different positions in the aperture of the functionalized diffuser element. FIG. 2B schematically illustrates the brightness for different pixels of the virtual image along a cross-section through the eyebox and at the edges of the eyebox according to various examples.

[0055] FIG. 3 illustrates an exemplary variant of an optical arrangement for a HUD system according to various examples.

[0056] FIG. 4A illustrates an exemplary variant of an optical arrangement for a HUD system according to various examples.

[0057] FIG. 4B illustrates an exemplary variant of an optical arrangement for a HUD system according to various examples.

[0058] FIG. 5 illustrates an exemplary variant of an optical arrangement for a HUD system according to various examples.

[0059] FIG. 6 illustrates an exemplary variant of an optical arrangement for a HUD system according to various examples.

[0060] FIG. 7 illustrates an exemplary variant of an optical arrangement for a HUD system according to various examples.

[0061] FIG. 8 illustrates an exemplary variant of an optical arrangement for a HUD system according to various examples.

[0062] FIG. 9 illustrates an exemplary variant of an optical arrangement for a HUD system according to various examples.

[0063] FIG. 10 illustrates an exemplary system integration of an optical arrangement for a HUD system according to various examples.

[0064] FIG. 11 illustrates an exemplary system integration of an optical arrangement for a HUD system according to various examples.

[0065] FIG. 12 schematically illustrates the dispersion of light (left) and the refraction of light (right).

[0066] DETAILED DESCRIPTION

[0067] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0068] FIG. 1 illustrates an exemplary HUD system 90. The HUD system 90 includes a windshield 190 of a motor vehicle having an inner side 191 (facing the interior) and an outer side 192 (facing the surroundings). The windshield 190 is shown in section. Furthermore, the HUD system 90 includes a backing 195 in an area of ​​the windshield 190 near its underside (facing the dashboard). The backing 195 (also referred to as "black backing") can be provided, for example, in the form of a black or gray coating or film. This is optional.

[0069] The HUD system 90 also includes an optical arrangement 91 with a projection unit 121. The projection unit 121 is configured to project an image onto a functionalized diffuser element 122 by emitting light along a beam path 130. The functionalized diffuser element 122 is configured to diffuse the beam path 130. In the example of FIG. 1, the functionalized diffuser element 122 is arranged in a transmission geometry in the beam path 130 (but could also be arranged in a reflection geometry in the beam path 130).

[0070] FIG. 1 shows how two light beams from beam path 130 strike two exemplary scattering centers 398, 399 of functionalized diffuser element 122. The two scattering centers 398, 399 are arranged at different positions on functionalized diffuser element 122. The light is scattered at scattering centers 398, 399. However, the scattering lobes at scattering centers 398, 399 are oriented differently. This ensures that functionalized diffuser element 122 reduces the divergence of beam path 130—viewed across the entire aperture of functionalized diffuser element 122. Between projection unit 121 and diffuser element 122, the width 395 of the light field along the beam path increases significantly (dashed arrow); Downstream of the diffuser element 122, the width 396 of the light field remains approximately constant (dotted arrow).By means of the windshield 190 - in cooperation with the location-dependent scattering characteristics of the functionalized diffuser element 122, ie the differently oriented scattering lobes of the scattering centers 398, 399 - a focusing is then achieved, ie the beam path 130 is convergent.

[0071] In addition, the functionalized diffuser element is configured to redirect the beam path 130 to an eyebox 95: the angle of incidence of the beam path 130 is different from the angle of reflection of the beam path 130. The virtual image 96 is also shown in FIG. 1.

[0072] The deflection of the beam path 130 takes place taking into account a variation in the angle of incidence of the beam path 130 onto the windshield 190 depending on the field position. For example, FIG. 2A illustrates different scattering lobes 311, 312 for the functionalized diffuser element 122 from the example of FIG. 1. It can be seen there that the scattering lobe 311 on one side of the aperture of the functionalized diffuser element 122 at the scattering centers 398 or on one side of the field is tilted more strongly relative to a plane normal 305 of a scattering plane 301 of the functionalized diffuser element 122 than the scattering lobe 312 on the other side of the aperture at the scattering centers 399. Furthermore, the scattering lobe 311 is wider than the scattering lobe 312.Generally speaking, a spatial dependence of the scattering characteristic of the functionalized diffuser element 122 can compensate for a different distance between the functionalized diffuser element 122 and the inner side 191 of the windshield 190, at which the beam path 130 is reflected. Different angles of incidence onto the windshield can be compensated. Furthermore, the perceptibility of the virtual image 96 or a beam path converging toward the eyebox 95 is enabled. The dependence of the scattering characteristic shown in FIG. 2A is only an example intended to illustrate qualitative and quantitative relationships, but should not be understood as limiting.

[0073] In particular, as already described above, the eyebox 95 can be formed by a suitable configuration of the scattering characteristics of the functionalized diffuser element 122. This is also shown in FIG. 2B. In FIG. 2B, center, the transverse extent of the eyebox 95 is shown (i.e., perpendicular to the beam path 130). The width of the eyebox perpendicular to the beam path 95 is defined by the width of the scattering lobes of the functionalized diffuser element 122. The scattering lobes converge in the eyebox. In FIG. 2B, top, the virtual image 96 is shown, with two pixels 611, 612 on different sides of the virtual image 96 being highlighted.

[0074] The eyebox 95 is formed by the scattering characteristic of the functionalized diffuser element 122 such that the brightness of the virtual image 96 for different pixels in the edge regions of the eyebox 95 increases or decreases uniformly, depending on whether one moves into the eyebox 95 or out of the eyebox 95. This is shown in FIG. 2B below, where the brightness for the two pixels 611, 612 is shown along the line AA'. In other words, the control characteristic of the functionalized diffuser element 122 - and in particular the location dependence of the control characteristic - ensures that the eyebox 95 has pixel-independent edges, as shown in FIG. 2B below. Pixel-independent edges can mean that a difference in the brightness decrease for different pixels of the virtual image 96 at the edge of the eyebox 95 is not greater than 10% (i.e.the ratio between the brightnesses of the different pixels does not vary by more than 10% in the edge area).

[0075] FIG. 2B also shows that the brightness for the two pixels 611, 612 within the eyebox 95 does not vary or varies only slightly. For example, a variation in brightness for the various pixels of the virtual image 96 may not be greater than 10% (e.g., relative to the average brightness value). This means that a pixel's brightness is essentially independent of position within the eyebox 95. This effect is also achieved by the appropriate control characteristics of the functionalized diffuser element 122 or the variable orientation of the scatter lobes. The eyebox 95 is illuminated in a targeted and uniform manner.

[0076] It should be understood that the specific scattering characteristics or the specific spatial dependence of the scattering lobes of the functionalized diffuser element 122 depend on various factors depending on the system integration, such as the tilt of the functionalized diffuser element 122 relative to the windshield 190, the size of the eyebox 95, etc. It would be possible for the windshield 190 and / or the diffuser element 122 to have a curvature; such a curvature can also be compensated for with regard to the two brightness characteristics (sharp edges of the eyebox 95 and homogeneous brightness within the eyebox 95). The specific scattering characteristics required to achieve such effects typically also depend on the spectrum width of the light source 121.

[0077] Referring again to FIG. 1: there, the functionalized diffuser element 122 is illuminated in free-beam geometry. However, this is only an example. Another variant is shown in FIG. 3. In the HUD system 90 in the variant of FIG. 3, the functionalized diffuser element 122 is integrated into an optical block (e.g., a flat plate) or a substrate 150. For example, the functionalized diffuser element 122 can be a holographic diffuser element which is implemented by a volume HOE on a side of the substrate 150 facing the windshield 190. The substrate 150 has two opposite side surfaces 151, 152. The beam path 130 is coupled into the substrate 150 via the side surface 151. The beam path 130 then runs in the substrate 150 from the side surface 151 to the functionalized diffuser element 122, but without being reflected on other outer surfaces of the substrate 150. In FIG.3, the functionalized diffuser element 122 is arranged in edge lit geometry in the beam path 130.

[0078] FIG. 4A schematically illustrates another variant of the HUD system 90 or the optical arrangement 91. The optical arrangement 91 in the variant of FIG. 4A comprises a plurality of optical channels. A first optical channel is associated with a first beam path 130-1, and a second optical channel is associated with a second beam path 130-2. The first optical channel has a first projection unit 121-1, and the second optical channel has a second projection unit 121-2. For example, it would be conceivable for the first projection unit 121-1 to emit light in a first wavelength range, while the second projection unit 121-2 to emit light in a second wavelength range, wherein the first wavelength range is different from the second wavelength range. For example, the first projection unit 121-1 could emit red light, and the second projection unit 121-2 could emit blue light, to give just one example.The first optical channel has a first functionalized diffuser element 122-1, and the second optical channel has a second functionalized diffuser element 122-2. In the example of FIG. 4A, the two diffuser elements 122-1, 122-2 (e.g., holographic diffuser elements) are each arranged in a free-beam geometry.

[0079] Beam paths 130-1, 130-2 are arranged, but other variants are also conceivable.

[0080] In FIG. 4A, the first beam path 130-1 passes twice through the functionalized diffuser element 122-2 assigned to the second optical channel. This is because the first functionalized diffuser element 122-1 is arranged in reflection geometry in the first beam path 130-1, while the second functionalized diffuser element 122-2 is arranged in transmission geometry in the second beam path 130-2. Furthermore, the first diffuser element 122-1 and the second diffuser element 122-2 form a stack. This means that the light traveling along the beam path 130-1 is not or only slightly scattered by the functionalized diffuser element 122-2, and the light traveling along the beam path 130-2 is not or only slightly scattered by the diffuser element 122-1.

[0081] In FIG. 4A, the two functionalized diffuser elements 122-1, 122-2 are illuminated in free-beam geometry. The functionalized diffuser element 122-1 is illuminated in reflection geometry by the beam path 130-1; the functionalized diffuser element 122-2 is illuminated in transmission geometry by the beam path 130-2. However, other variants are also conceivable, as illustrated, for example, in FIG. 4B. In the variant of FIG. 4B, the two functionalized diffuser elements 122-1, 122-2 (e.g. holographic diffuser elements) are illuminated in edge-illumination geometry and are formed in a common substrate 150. FIG. 5 shows yet another variant of the optical arrangement 91 with a plurality of diffuser elements 122-1, 122-2. In the variant of FIG. 5, both the first functionalized diffuser element 122-1 and the second functionalized diffuser element 122-2 are arranged in transmission geometry in the respective beam path 130-1, 130-2.It would be conceivable that the two diffuser elements 122-1, 122-2 are integrated in a common substrate (see FIG. 4B).

[0082] The light emitted by the first projection unit 121-1 along the first beam path 130-1 is not scattered by the second diffuser element 122-2. This is due to the functionalization of the second diffuser element 122-2. For example, the second functionalized diffuser element 122-2 can be designed to be wavelength-selective, so that the light emitted by the first projection unit 121-1 lies outside a wavelength range of light that is scattered by the second functionalized diffuser element 122-2. In addition to such multiplexing in the wavelength range, it would also be conceivable for the optical channels to be multiplexed based on the polarization and / or the angle of incidence of the respective light. Such multiplexing of light is made possible in particular by the use of holographic diffuser elements.

[0083] In the examples of FIG. 4A, FIG. 4B and FIG. 5, the two beam paths 130-1, 130-2 (from the separate projection units 121-1, 121-2) are combined by means of the diffuser elements 122-1, 122-2.

[0084] The two diffuser elements 122-1, 122-2 are stacked at a distance from one another in FIG. 4A, FIG. 4B, and FIG. 5; a corresponding gap 129 is illustrated in FIG. 4A. This gap 129 is dimensioned relative to the side length of the diffuser elements 122-1, 122-2, namely approximately 15% of the side length. The gap 129 creates a distance 99 between the virtual images 96-1, 96-2; this allows a scene with an impression of depth to be created. An impression of depth can also be achieved, however, by curving the scattering surface of a diffuser element.

[0085] FIGS. 6 and 7 illustrate variants of the HUD system 90 and the optical arrangement 91, respectively, in which the respective functionalized diffuser element 122 is convexly or concavely curved. Such a curvature imparts depth to the virtual image 96. In addition to a convex or concave curvature, other curvature shapes are also conceivable, particularly freeform curvatures.

[0086] FIG. 8 is a further variant of the HUD system 90. FIG. 8 is a plan view of the windshield 190 from the perspective of the interior of the motor vehicle, i.e. the inner side 191 of the windshield 190 extends in the plane of the drawing. In FIG. 8 it can be seen that the two functionalized diffuser elements 122-1, 122-2 separate the beam paths 130-1, 130-2, namely by deflecting the corresponding beam paths 130-1, 130-2 differently. This allows two different eyeboxes 95-1, 95-2 to be operated. For example, the eyebox 95-1 can be provided for a driver of the motor vehicle and the eyebox 95-2 for a passenger of the motor vehicle. Also in FIG.8, as already described above, light from the first optical channel can pass through the functionalized diffuser element 122-2 without being scattered because the light from the first optical channel has a wavelength and / or polarization to which the second holographic diffuser element 122-2 is not selective. This can be achieved in particular by using holographic diffuser elements.

[0087] Different eyeboxes can also be achieved with variants similar to FIG. 4A, FIG. 4B or FIG. 5, namely by having the different beam paths 130-1, 130-2 have sources spaced apart from one another.

[0088] FIG. 9 illustrates a variant of the HUD system 90 in which a microlens array 180 is provided. The microlens array 180 extends along the functionalized diffuser element 122. The microlens array 180 is arranged at a distance from the HOE of the functionalized diffuser element 122 that corresponds to a "focal length" of the HOE. In this case, the scattering characteristic of the HOE is configured to collect light. Using the microlens array 180, it is possible to shift the virtual image 96 to infinity. This is evident in FIG. 9 because the rays of the beam path 130 run parallel in front of the eyebox 95.

[0089] Such a variant with a microlens array can be combined with other variants disclosed herein; in particular, multiple optical channels could be implemented by a stack of holographic diffuser elements with a common microlens array. This means that - e.g., as shown in FIG. 4A - multiple holographic diffuser elements can be used, which are arranged offset from one another in the z-direction and extend along one another. Each of these holographic diffuser elements has a respective scattering characteristic, so that the correspondingly scattered light is collected. A type of "focal length" is thus defined. This focal length is different for the various holographic diffuser elements; in each case, it corresponds to a distance in the z-direction between the holographic diffuser elements.This ensures that the microlens array is positioned at the focal length of each of the holographic diffuser elements. This allows the virtual image planes of all channels to be at infinity.

[0090] FIG. 10 illustrates a further variant of the HUD system 90 or the optical arrangement 91. In the variant of FIG. 10, the optical arrangement 91 also includes a deflection element 181, here a mirror 181. This mirror 181 deflects the beam path 130. The mirror 181 is arranged between the functionalized diffuser element 122 and the windshield 190. In particular, the mirror 181 is arranged with respect to the functionalized diffuser element 122 or the projection unit 121 such that the beam path 130 forms a loop. This enables the optical arrangement 91 according to the variant of FIG. 10 to be integrated into a particularly small installation space. For example, it would be conceivable for the mirror 181 to be rotatable about an axis 182 (perpendicular to the plane of the drawing) (for example driven by a motor) in order to change or adjust the position of the eyebox 95.

[0091] FIG. 11 illustrates the optical arrangement 91 according to the variant from FIG. 10, showing the installation space 405. A beam trap 185 is also illustrated. The beam trap can trap stray light, which may be caused, for example, by unwanted Fresnel reflections or other reflections. Alternatively or additionally, ambient light—for example, from the vehicle interior—can be prevented from entering the optical arrangement 91. The beam trap 185 can be designed as a microlouvre grating. FIG. 11 also shows the projection distance 406 from the eyebox 95 to the virtual image 96. The projection distance 406 is particularly large due to the loop.

[0092] FIG. 12 (left) illustrates the scattering of an incident light beam at a scattering center; while FIG. 12 (right) shows the refraction of a light beam at an interface between two optical media with different refractive indices. In a holographic diffuser element, light is not scattered in a classical way, but rather diffracted. However, the diffraction is designed to simulate scattering centers in small areas (slightly larger than the wavelength of the light).

[0093] 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.

[0094] For example, techniques were disclosed above in which a functionalized diffuser element is used to define an eyebox for a HUD. In particular, it was explained how a HOE can be used to implement the functionalized diffuser element. In one variation, a projection unit projects multiple images onto a HOE, which simulates a microlens array. This means that the HOE each simulates the refraction of light rays at the microlenses of the microlens array. Each microlens simulated by the HOE is assigned a perspective of a 3D scene (also referred to as "elemental images"); this makes it possible to implement a light field projection of the 3D. This can enable a 3D display for a HUD, for example in a motor vehicle.

Claims

PATENT CLAIMS 1. Optical arrangement (91) for a head-up display system (90) on a deflection surface (190), the optical arrangement (91) comprising: - at least one projection unit (121, 121-1, 121-2) configured to project at least one image onto at least one functionalized diffuser element (122, 122-1, 122-2) by emitting light along at least one beam path (130, 130-1, 130-2), and - the at least one functionalized diffuser element (122, 122-1, 122-2) which is arranged along the at least one beam path (130, 130-1, 130-2) and which is configured to disperse the at least one beam path (130, 130-1, 130-2) in such a way that a virtual image (96) of the projected at least one image is perceivable in at least one eyebox (95) of the head-up display system (90).

2. Optical arrangement (91) according to claim 1, wherein a scattering characteristic of the functionalized diffuser element sets an extension of the eyebox perpendicular to the beam path (130).

3. Optical arrangement (91) according to claim 1 or 2, wherein a scattering characteristic of the functionalized diffuser element provides edges of the eyebox (91) which have no or only a slight dependence on the image position within the virtual image (96).

4. Optical arrangement (91) according to one of the preceding claims, wherein a scattering characteristic of the functionalized diffuser element provides a homogeneous brightness within the eyebox (91).

5. Optical arrangement (91) according to one of the preceding claims, wherein the at least one functionalized diffuser element (122, 122-1, 122- 2) comprises at least one holographic diffuser element (122, 122-1, 122-2).

6. Optical arrangement (91) according to claim 5, wherein the at least one holographic diffuser element (122, 122-1, 122-2) comprises a plurality of holographic diffuser elements (122, 122-1, 122-2) configured to diffract light having different wavelengths and / or different angles of incidence and / or different polarizations.

7. The optical assembly (91) of claim 6, wherein the plurality of holographic diffuser elements (122, 122-1, 122-2) are arranged in a stacked manner.

8. The optical assembly (91) of claim 7, wherein the plurality of holographic diffuser elements (122, 122-1, 122-2) are stacked spaced apart from one another.

9. The optical assembly (91) of claim 8, wherein a gap (129) between the plurality of holographic diffuser elements (122, 122-1, 122-2) is not less than 10% of a side length of the plurality of holographic elements (122, 122-1, 122-2).

10. Optical arrangement (91) according to one of claims 6 to 9, wherein the plurality of holographic diffuser elements (122, 122-1, 122-2) are formed in a common substrate (150).

11. Optical arrangement (91) according to one of claims 6 to 10, wherein the at least one holographic diffuser element (122, 122-1, 122-2) is arranged in edge illumination geometry in the at least one beam path (130, 130-1, 130-2).

12. Optical arrangement (91) according to one of the preceding claims, wherein the at least one functionalized diffuser element (122, 122-1, 122- 2) comprises a plurality of functionalized diffuser elements (122, 122-1, 122-2), wherein the plurality of functionalized diffuser elements (122, 122-1, 122-2) are configured to separate or combine two or more beam paths (130, 130-1, 130-2).

13. Optical arrangement (91) according to one of the preceding claims, wherein the at least one functionalized diffuser element (122, 122-1, 122- 2) is further configured to reduce a divergence of the at least one beam path.

14. Optical arrangement (91) according to one of the preceding claims, wherein the at least one functionalized diffuser element (122, 122-1, 122- 2) is further configured to deflect the at least one beam path (130, 130-1, 130-2).

15. Optical arrangement (91) according to one of the preceding claims, wherein at least one of the at least one diffuser element (122, 122-1, 122-2) is arranged in transmission geometry in the beam path (130, 130-1, 130-2).

16. Optical arrangement (91) according to one of the preceding claims, wherein at least one of the at least one diffuser element (122, 122-1, 122-2) is arranged in reflection geometry in the beam path (130, 130-1, 130-2).

17. Optical arrangement (91) according to one of the preceding claims, wherein the optical arrangement (91) further comprises: - a deflection element which is arranged along the at least one beam path downstream of the at least one diffuser element (122, 122-1, 122-2) and which is configured to deflect the at least one beam path.

18. Optical arrangement (91) according to claim 17, wherein the deflecting element is arranged such that the at least one beam path forms a loop.

19. Optical arrangement (91) according to one of the preceding claims, wherein the optical arrangement (91) further comprises: - a microlens array (180) extending along the at least one functionalized diffuser element (122, 122-1, 122-2).

20. The optical arrangement (91) of claim 19, wherein the at least one functionalized diffuser element (122, 122-1, 122-2) comprises at least one holographic diffuser element (122, 122-1, 122-2) having a holographic optical element defining a focal length for the light, wherein the microlens array (180) is arranged at a distance from the holographic optical element that corresponds to the focal length.

21. Optical arrangement (91) according to one of the preceding claims, wherein at least one of the at least one functionalized Diffuser element (122, 122-1, 122-2) has a curved diffuser surface.

22. Head-up display system (90), which includes: - the optical arrangement (91) according to one of the preceding claims, and - the deflection surface (190).

23. Head-up display system (90) according to claim 22, wherein the at least one beam path is reflected on a first side of the deflection surface (190), the head-up display system (90) further comprising a rear darkening (195) on a second side of the deflection surface (190).

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