Stray light filter for holographic huds

Abstract

The invention relates to a scattered-light-reduced HUD with a holographic component for beam adaptation. At least one band-pass filter is arranged in a beam path between the holographic component and a provided eyebox of the HUD. The band-pass filter is permeable for visible light in at least one first spectral range, which comprises at least one spectral range refracted by the holographic component for beam adaptation. The invention also relates to a corresponding holographic component for a scattered-light-reduced HUD. The invention also relates to a manufacturing method for the holographic component and to a holographic component produced by said method.

Description

[0001] LIGHT FILTER FOR HOLOGRAPHIC HUDS

[0002] DESCRIPTION

[0003] The invention relates to a scattered-light-reduced HUD with a holographic component for beam adjustment. At least one bandpass filter is arranged in a beam path between the holographic component and a designated eyebox of the HUD. The bandpass filter is transparent to visible light in at least a first spectral range, which includes at least one spectral range diffracted by the holographic component for beam adjustment.

[0004] The invention also relates to a corresponding holographic component for a scattered light reduced HUD.

[0005] The invention also relates to a manufacturing method for the holographic component and to a holographic component produced thereby.

[0006] Background and state of the art:

[0007] Head-up displays (HUDs) are display systems that project the information to be displayed into the user's field of vision, while simultaneously allowing a view of the surroundings within the field of vision. HUDs are familiar, for example, from cars or aircraft. In vehicles, the information to be displayed can be projected, for example, via the windshield of the vehicle into the user's eye area, the so-called eyebox. HUDs can be implemented using a variety of different systems, many of which are already state-of-the-art.

[0008] A HUD can typically comprise an imaging unit (PGU - picture generating unit) or a projector, a projection surface (often the windshield), and other optical components for beam adjustment. For example, an image can be generated using a PGU or projector. The image is projected (e.g., using the other optical components) onto the projection surface and from there into the so-called eyebox. This is preferably a plane or spatial region in which the projected image is perceptible to a viewer. The projected image can comprise a virtual and / or real image. The at least one virtual image plane, i.e., the plane on which the virtual image is generated, can, for example, be located behind the projection surface, i.e., on the other side of the projection surface than the eyebox.

[0009] In addition to “classic” projection systems with “classic” optical components, HUDs based on holographic components can be used.

[0010] In contrast to conventional imaging, holography stores not only the intensity of the imaged object but also the phase relationships of the light coming from the object. These phase relationships contain additional spatial information, which can, for example, create a three-dimensional impression of the image. This occurs through the interference of light rays during the recording of the object. The object is illuminated with coherent light and is reflected and scattered by the object. The resulting wave field, the so-called object wave, is superimposed with light coherent with the object wave (the so-called reference wave - typically from the same light source, e.g., a laser), and the wave fields interfere with each other as a function of their phase relationship. The resulting interference pattern is recorded, for example, using a light-sensitive layer, and thus the information contained in the phase is also stored.For reconstruction, the resulting hologram is illuminated with a light wave identical or similar to the reference wave, which is then diffracted by the recorded interference patterns. This allows the original wavefront of the object wave to be reconstructed. There are various types of holograms, e.g., so-called volume holograms. Volume holograms preferably have a thickness that can also be used to store holographic image information. Volume holograms can, in particular, be white-light holograms, as these can exhibit wavelength selectivity due to wavelength-selective interference.

[0011] Holograms can, for example, be transmission and reflection holograms, which each produce this reconstruction either in transmission or in reflection. If, for example, one stands on the side of a transmission hologram opposite the light source and views it, the imaged object appears three-dimensional in front of one. With a reflection hologram, one must preferably be on the same side as the light source. Reflection holograms preferably have a wavelength-selective efficiency, diffracting light in a specific direction (along a specific angle). The word hologram is preferably used here as a synonym for the holographic structure that produces the light diffraction. In common usage, the term "hologram" is sometimes used to refer to the generated image, particularly a three-dimensional image. However, a person skilled in the art knows from the context what the term "hologram" means in each case.

[0012] In addition to the three-dimensional representation of objects, holograms can also be used as so-called holographic optical devices (HOEs), whose holographic properties can be used in the optics of devices. For example, HOEs can replace conventional lenses, mirrors, and prisms. In other cases, HOEs are used as special diffraction gratings. HOEs exhibit, for example, spectral selectivity and / or selectivity with respect to the angle of incidence. At the same time, they can be completely or partially transparent to other spectral ranges and / or angles of incidence. Holograms also enable a combination of representation and light shaping.

[0013] The use of these HOEs for beam shaping is particularly practical for HUDs. Since there is considerable freedom in the type of desired beam shaping with little dependence on the dimensions of the HOE, the desired beam adaptation can be achieved without requiring a large amount of installation space. This aspect is particularly interesting for motor vehicles, where installation space is often limited for a variety of reasons. Furthermore, HOEs can reduce and / or correct aberrations. PCT applications PCT / EP2022 / 055513 and PCT / EP2022 / 066787 describe holographic-based wavefront manipulators, which are particularly preferably intended as holographic components for beam adaptation according to this document and whose content is hereby incorporated into this application.In head-up displays, it is essential to redirect or even suppress interfering reflections from the sun, which can be reflected by HUD components toward the driver and cause dazzling. This effect occurs not only in conventional systems but also in holographic HUDs. However, compared to conventional HUDs, additional interfering reflections can occur due to diffraction by the holograms. In particular, this can occur when, in addition to the illumination rays of the HUD, light rays from other spectral ranges and / or other directions are also directed into the eyebox.

[0014] While glaretraps for beam deflection are already known in the prior art, which allow the deflection of ambient light outside the eyebox, they are not suitable for specifically suppressing interference reflections caused by diffraction at a holographic component of the HUD. No known solution for this task is available in the prior art.

[0015] Object of the invention:

[0016] It is therefore an object of the invention to provide a HUD and a holographic component for a HUD without the disadvantages of the prior art. In particular, an object of the invention is to provide a HUD and a holographic component for a HUD that minimize interference from ambient light diffracted into the eyebox by the holographic component in a simple, compact, and effective manner. It is further an object of the invention to provide an improved HUD and an improved holographic component for a HUD that enables reliable and easy recognition of the displayed information without dazzling the user and improves the contrast of the HUD.

[0017] Summary of the invention:

[0018] The object is achieved by the features of the independent claims. Preferred embodiments of the invention are described in the dependent claims.

[0019] In a first aspect, the invention relates to a head-up display (HUD) with reduced scattered light, comprising a holographic component for beam adjustment, wherein at least one bandpass filter is arranged in a beam path between the holographic component and a provided eyebox of the HUD, in particular between the holographic component and a projection surface of the HUD. The bandpass filter is permeable to visible light in at least a first spectral range, which includes at least one spectral range diffracted by the holographic component for beam adjustment, and is preferably configured to suppress visible light outside the at least first spectral range.

[0020] The scattered light-reduced HUD is, in particular, a HUD of any kind which, thanks to the features of the invention, in particular the bandpass filter, advantageously redirects less ambient light into the eyebox or the safety eyebox compared to a HUD without these features. The term "scattered light" is to be understood here in the broadest sense of the term scattering, which encompasses any type of interaction between matter and electromagnetic radiation, in particular light. This scattering can, for example, include the phenomenon of diffraction and / or reflection. Preferably, the terms electromagnetic radiation and light are used synonymously in this document and refer, in particular, to electromagnetic radiation encompassing the visible spectral range. However, the ultraviolet spectral range and the near infrared range can also be included.Light in this sense preferably comprises a spectral range (specified as wavelength in nanometers - nm) from 100 nm to 3000 nm, more preferably 280 nm to 1400 nm and in particular 380 nm to 780 nm. It is apparent to the person skilled in the art that a spectral range can be specified not only as a frequency range in Hertz (Hz), but analogously (by appropriate conversion) also as a wavelength range in nm. Wavelength range and spectral range can preferably be used synonymously in this document.

[0021] The beam path specifically encompasses the volume occupied by the beams used to operate the HUD. Typically, the beam path extends from the light source through all optical components of the HUD (e.g., beam guidance) to the HUD's eyebox.

[0022] The eyebox specifically comprises an area or volume from which the HUD is to be viewed. This volume can / should contain, for example, the eyes of at least one viewer, hence the name eyebox. The eyebox can, for example, have dimensions of 150 mm x 150 mm.

[0023] The safety eyebox preferably comprises an area or volume that is larger than the eyebox, e.g. to 300mm x 300mm, in order to include a safety margin from which the observation can also take place in exceptional cases.

[0024] In this document, the term eyebox can also be used as eyebox including safety exebox.

[0025] HOEs have already been introduced above. A holographic component for beam adaptation can be a variant of a HOE. A holographic component for beam adaptation can comprise at least one hologram, in particular at least one HOE, which, as part of the HUD, fulfills an optical, preferably beam-adapting function, e.g., beam shaping, beam deflection / Z-guidance, and / or an optical (spectral, angle-selective, and / or polarization-selective) filter function. The function is preferably fulfilled in the spectral range diffracted for beam adaptation. There can also be multiple spectral ranges diffracted for beam adaptation, within which the beam-adapting function is fulfilled.

[0026] The spectral range is preferably a contiguous range, so that a plurality of spectral ranges preferably comprise a plurality of non-contiguous spectral ranges.

[0027] Beam shaping preferably means influencing the shape of the beam. Beam shaping can, in particular, include manipulating the wavefronts. Beam shaping includes, for example, collimating, focusing, defocusing, increasing the divergence, widening the beam diameter, reducing the beam diameter, generally changing the size and / or shape of the beam cross-section, or similar. Beam guidance or deflection describes, in particular, a deviation of the beam path from an undisturbed electromagnetic (light) beam, enforced by an optical component. Beam guidance can, for example, include beam folding to guide the beam from the light source to the eyebox under given boundary conditions (e.g., installation space, size of the eyebox, size of the image, position of the image, etc.).

[0028] The holographic component for beam adaptation is preferably configured to adapt the light beam (synonym: the light beam bundle, the light rays) of at least one spectral range (the spectral range diffracted for beam adaptation) according to the functional determination of the holographic component.

[0029] However, the holographic component for beam adaptation can preferably be configured to adapt the light beam (synonym: the light beam bundle, the light rays) of several (e.g. two or three) spectral ranges (i.e. several spectral ranges diffracted for beam adaptation) according to the functional purpose of the holographic component.

[0030] Typically, the holographic component will be configured to perform beam adaptation of the at least one spectral range emitted by the at least one light source of the HUD. Therefore, the at least one diffraction grating of the holographic component for beam guidance is preferably designed to diffract light in this spectral range according to the desired functionality. Furthermore, the spatial arrangement of the HUD components relative to one another is usually fixed, so that not only the diffracted spectral range is fixed, but also the direction from which the light to be diffracted strikes the holographic component. This direction can preferably also be described by an angle.An angular spectrum around this angle if more than one direction is involved, which is usually the case given the planar extent of the optical components, a desired field of view, and an imperfectly collimated beam path. Therefore, the holographic component typically has a centroid angle and / or an angular spectrum that corresponds to the angle or angular spectrum from which the light to be diffracted strikes the holographic component.

[0031] The centroid angle is preferably the angle for which the holographic component has the maximum diffraction efficiency. The angular spectrum of the holographic component is preferably an angular range that has an orientation determined by the centroid angle. The angular spectrum of the holographic component is in particular the (contiguous) range of angles around the centroid angle for which the holographic component also performs the (desired) diffraction. This angular spectrum can be defined, for example, by the diffraction efficiency there being at least 50% of the maximum diffraction efficiency. The angular spectrum can be defined along or parallel to a cutting plane with the centroid angle, if, for example, the holographic component only diffracts light whose direction lies within or parallel to this plane.However, the angular spectrum can also be defined along multiple cutting planes with the centroid angle (or parallel to them), and can also differ in each case. For example, the angular spectrum can be defined along or parallel to two mutually perpendicular cutting planes with the centroid angle.

[0032] Preferably, the centroid angle and / or angular spectrum of the holographic components are linked to the spectral range diffracted by them, so that a typical description of the holographic component consists in specifying the centroid angle and the angular spectrum distributed around it for a (at least one) specific diffracted spectral range.

[0033] Thus, the holographic component is preferably configured to diffract light of at least one spectral range and at least one angular spectrum in order to achieve the desired beam adaptation. For example, the light source can emit light in the red (R), green (G), and blue (B) spectral ranges in order to realize a colored or white light HUD. The light has a respective spectral distribution with a certain width in the respective spectral range. The holographic component is then preferably configured to diffract light of these spectral ranges that comes from the direction of the light source or another, upstream component of the HUD (thus light with a given angular spectrum and / or center angle).

[0034] A bandpass filter is preferably a filter that is largely permeable to electromagnetic radiation within a specific spectral range. The frequency or wavelength ranges below and above the passband are preferably either not passed through or significantly attenuated.

[0035] Within the meaning of the invention, it may also be preferred for the bandpass filter used here to allow electromagnetic radiation from more than a first spectral range to pass through, for example, from a second, a third, or even more spectral ranges, and to block or attenuate the radiation between these spectral ranges. This is particularly desirable if the holographic component diffracts more than one spectral range for beam adaptation.

[0036] The bandpass filter is permeable to visible light in at least a first spectral range (preferably also in a second and particularly preferably also in a third spectral range), which comprises at least one spectral range diffracted by the holographic component for beam adaptation, and is preferably configured to suppress visible light outside the at least first spectral range.

[0037] As discussed above, the holographic component is designed for at least one spectral range diffracted by the holographic component for beam adjustment and / or one angular spectrum diffracted by the holographic component for beam adjustment (and the corresponding centroid angle). Light from other spectral ranges, from other angles and / or with other angular spectra is advantageously either not diffracted at all by the holographic component or diffracted differently than the light for the HUD. Nevertheless, it is possible that light from other spectral ranges and / or other directions (thus other angles and / or angular spectra) is also diffracted by the holographic component in such a way that this light is directed towards the eyebox directly by the holographic component or in interaction with other components of the HUD and can thus generate stray light in the eyebox.This is particularly due to the fact that the diffraction grating encompassed by the holographic component can also generate constructive interference for other angles and / or wavelengths of incident light, thus diffracting light in a variety of directions. This is an inherent property of the diffraction grating and cannot be completely prevented.

[0038] Because the bandpass filter is now permeable to visible light in at least a first spectral range, which comprises at least one spectral range diffracted by the holographic component for beam adaptation, and is preferably designed to suppress visible light outside the at least first spectral range, it can be substantially prevented or suppressed that light of spectral ranges other than that of the at least first spectral range reaches the holographic component and can thus be diffracted by it in the direction of the eyebox.

[0039] Because the bandpass filter preferentially functions in different directions and / or has an at least partially suppressing effect, it can also prevent light from other spectral ranges that reach the holographic component despite the filter and are diffracted by it from passing through the bandpass filter. This is because the bandpass filter also functions, for example, in the direction determined after diffraction by the holographic component or at least has a partially suppressing effect. Partial can mean, for example, 40% suppression, 30% suppression, 20% suppression, or 10% or less suppression. Thus, the bandpass filter preferentially suppresses light from undesired spectral ranges in the direction of the holographic component as well as suppresses light from undesired spectral ranges after diffraction by the holographic component.By arranging the bandpass filter in the beam path between the holographic component and a designated eyebox of the HUD, stray light diffracted by the holographic component can be greatly reduced or eliminated.

[0040] In a preferred embodiment of the invention, the suppression comprises an attenuation by at least a factor of 10, preferably a factor of 20, and in particular a factor of 100. The intensity incident on the bandpass filter is used as a reference and compared with the intensity of the same light passing through the bandpass filter (or the portion of the light that has passed through the filter). The attenuation can vary for different angles of incidence and / or spectra, with the least attenuated angle or the least attenuated spectrum preferably being used to determine the attenuation.

[0041] It has been shown that even an attenuation of a factor of 10 can achieve sufficient interference suppression with low requirements for the bandpass filter. This solution is therefore particularly simple and cost-effective.

[0042] With an attenuation factor of 20, a particularly good compromise between bandpass filter quality and improved attenuation can be achieved. This solution is therefore particularly efficient. With an attenuation factor of 100, stray light reduction can be achieved, providing high levels of safety and operability under all conditions, even in critical applications.

[0043] In a further preferred embodiment of the invention, the first spectral range has a half-width of at most 20 nm, preferably at most 10 nm and in particular at most 5 nm.

[0044] These values ​​can each be combined with one of the aforementioned preferred values ​​for attenuation in a filter in order to have particularly advantageous filter properties.

[0045] Those skilled in the art know how to determine the half-width of a spectral range. The half-width is preferably the spectral range within the filter's passband that lies between the two spectral values ​​(lower and upper values) at which the bandpass filter's transmission has dropped to half its maximum.

[0046] It is clear to the person skilled in the art that the properties mentioned in this document for the first spectral range, such as the half-width here, should also apply to the second and any further spectral range, insofar as the bandpass filter is also permeable to these.

[0047] The half-widths can advantageously be selected depending on the spectral range diffracted by the holographic component for beam adaptation, so that this is not or only partially (partially can mean e.g. 40% or less, 30% or less, 20% or less or 10% or less) attenuated by the filter.

[0048] However, it may also be the case that the diffracted spectral range is significantly narrower than the mentioned half-widths and the half-width of the bandpass filter is chosen for other reasons (e.g. cost-benefit analysis).

[0049] It is obvious to the person skilled in the art that a narrower half-width is generally more advantageous in terms of suppressing stray light.

[0050] In a further preferred embodiment of the invention, an acceptance angle spectrum of the bandpass filter comprises the solid angle 2 TT sr.

[0051] The acceptance angle spectrum preferably refers to the angle range or angle ranges for which the filter has the desired or described here (i.e. defined) functionality.

[0052] The acceptance angle spectrum can in particular define the at least one angular range for which the filter allows light to pass at all, so that the light outside the acceptance angle spectrum is advantageously suppressed.

[0053] The acceptance angle spectrum can generally be defined along a single plane, but it can also be defined along multiple planes, each of which differs. In this embodiment, the acceptance angle spectrum comprises a solid angle and is therefore advantageously defined along three planes or in three-dimensional space. The solid angle is preferably the three-dimensional analogue to the frequently used two-dimensional angle, which lies within a plane. It preferably describes the portion of three-dimensional space that lies, for example, inside a volume that can be described by a partial area of ​​a sphere's surface and its connecting lines to the sphere's center. The solid angle is preferably defined as the area of ​​the partial area divided by the square of the sphere's radius. This dimensionless number is preferably denoted as a solid angle using the unit steradian (sr).

[0054] In the present case, the solid angle of a cone is preferably meant, wherein the partial area of ​​the spherical surface is in particular a circle.

[0055] Preferably, the cone is rotationally symmetric about the so-called reference axis, which is preferably a normal to the surface of the holographic component or a cover glass (see below), in particular a normal at the (geometric) center of gravity of the surface of the component or cover glass if the surface of the component or cover glass is curved. However, the solid angle can generally also be defined independently of a spatial axis of the filter.

[0056] The solid angle 2 TT sr (or 2 x TT sr) preferably describes the solid angle of a hemisphere, and thus in particular of a half-space. This hemisphere is also preferably rotationally symmetric about the aforementioned reference axis.

[0057] A half-space is preferably a subset of three-dimensional space bounded by a plane. The plane here preferably forms the surface of the holographic component or the cover glass if it is flat; more generally (also for curved surfaces), it is preferably the tangent of the surface at the intersection with the reference axis.

[0058] This ensures that the bandpass filter functions in the desired or defined manner over a wide angular range. Furthermore, the functionality of the HUD can remain unaffected by the filter for a wide range of possible angles of the HUD's beam path.

[0059] In a further preferred embodiment of the invention, the acceptance angle spectrum of the bandpass filter preferably comprises an angle spectrum of 10°, more preferably of 8°, even more preferably of 6° and in particular of 5°.

[0060] All these values ​​can also be meant as the upper limit of the angular spectrum, i.e. 10° or less, more preferably 8° or less, even more preferably 6° or less and in particular 5° or less.

[0061] In the most general case, the angular spectrum is preferably a contiguous range of angles which is defined in at least one plane, preferably in two planes (also different between the planes) and in particular is defined in three-dimensional space. This angular spectrum can preferably be defined as an angular range which is arranged symmetrically around an axis. This can be, for example, the above-mentioned reference axis. However, it can also be preferred for this angular range to be arranged symmetrically around an axis other than the reference axis described above. For example, the axis can be the centroid angle of the angular spectrum diffracted by the holographic component for beam adaptation. An example of an angular spectrum of 8° is an angular range of ±4° around the centroid angle in all planes rotated around the centroid angle, where the centroid angle can be, for example,forms an angle of 30° in a plane with the reference axis.

[0062] The preferred angles are suitable for generating a desired field of view (FoV) in an eyebox, while at the same time, the production of the bandpass filter is not too complex. Particularly with a bandpass filter comprising a layer system, it can be difficult to achieve a specific transmission and rejection spectrum over a broad spectral range. This FoV can, for example, be between 15° and 25° horizontally and 5° vertically, since the angles that determine the FoV in the eyebox can be considerably larger than at the bandpass filter if the latter is arranged on or near the cover glass, for example. This can depend, for example, on the installation position and shape of the filter or cover glass. It is therefore advantageous if the filter is mounted at a location where the angular spectrum of the HUD beam path is relatively small.Advantageously, this is the case within the HUD where it makes sense from a reflex avoidance perspective.

[0063] Due to the varying FoV depending on the direction, it may be useful for the acceptance angle spectrum to be different in one plane relative to the filter than in another. For example, there may be a first plane of diffracted light rays at the filter, with the light rays in this plane later generating the angular spectrum (and thus the FoV) in the horizontal plane of the eyebox, and a second plane of diffracted light rays at the filter, with the light rays in this second plane later generating the angular spectrum in the vertical plane of the eyebox. Then, for example, the acceptance angle spectrum in the first plane may be 25° and in the second plane 10°.

[0064] In a further embodiment, the acceptance angle spectrum of the bandpass filter is configured to generate a desired FoV of the HUD.

[0065] This FoV can, for example, be between 15° and 25° in the horizontal direction and 5° in the vertical direction.

[0066] In a further preferred embodiment of the invention, the acceptance angle spectrum comprises the center of gravity angle of the angle spectrum diffracted by the holographic component for beam adaptation.

[0067] This makes it particularly easy to ensure that the beam guidance for the HUD is not negatively influenced by the bandpass filter.

[0068] In a further preferred embodiment of the invention, the acceptance angle spectrum of the bandpass filter comprises an angular spectrum diffracted by the holographic component for beam adjustment and / or its centroid angle and is at most 10°, more preferably at most 5°, and in particular at most 2° larger than the diffracted angular spectrum. This embodiment ensures a high-quality HUD with a corresponding FoV, while the bandpass filter simultaneously and particularly effectively suppresses stray light that is blocked by the filter due to a deviating angular spectrum.

[0069] In a further preferred embodiment of the invention, the holographic component comprises a wavefront manipulator for arrangement in the beam path of the HUD between an imaging unit and a projection surface.

[0070] In HUDs, especially in vehicles, aberrations can occur due to the curvature of the projection surface and / or compact arrangements in a small installation space, with potentially significant tilts of individual components relative to each other and correspondingly complex folded beam paths. Typical aberrations include distortion, defocus, tilt, astigmatism, curvature of the image plane, spherical aberrations, higher astigmatism, and coma.

[0071] A wavefront manipulator is advantageously used to at least partially correct and minimize aberrations and provide an improved head-up display that can also be particularly compact. To achieve this, as the name suggests, the wavefronts of the HUD's light rays are appropriately manipulated.

[0072] The wavefront manipulator preferably comprises a holographic arrangement (therefore, the wavefront manipulator is to be regarded as a holographic component for beam guidance), which in turn has at least two holographic elements. The at least two holographic elements are arranged one behind the other in the beam path, preferably directly behind one another. It is particularly preferred that no further optical element or component is arranged between the at least two holographic elements. Furthermore, the at least two holographic elements are designed to be reflective for at least the spectral range diffracted by the holographic component for beam adjustment, and preferably for a centroid angle and an angular spectrum.Preferably, the holographic elements are otherwise transmissive, in other words transmissive for other spectral ranges, at least if they have the same angle of incidence and / or the same angular spectrum. Preferably, a first holographic element comprises at least one hologram for reflection, which is assigned to a hologram of a second holographic element for reflection. In other words, the at least two holographic elements are preferably designed such that light of the diffracted spectral range diffracted by a first holographic element in reflection, which light is preferably incident at the centroid angle and the angular spectrum of the holographic component, is then reflected in turn by the second holographic element, wherein the desired wavefront manipulation is achieved through the interaction between the first and second elements.

[0073] By using reflection holograms, diffraction can advantageously be more wavelength-selective than with transmission holograms, so that in particular fewer color aberrations occur and a white image can be better generated from the color channels. By connecting two reflection holograms in series, a transmission arrangement can nevertheless be advantageously realized and the manipulation can be distributed between two holograms. The at least one holographic arrangement is preferably designed for the diffraction of light from a plurality of spectral ranges diffracted for beam adaptation. For this purpose, several holograms can be included in each holographic element (so-called hologram stack), each diffracting light from a spectral range, and / or each holographic element can comprise a so-called multiplex hologram, which diffractes light of several wavelengths.

[0074] Preferably, each of the at least two holographic elements comprises a number, for example a plurality, of holograms. Each hologram is designed for at least one spectral range. A holographic element can, for example, comprise several holograms, which can be arranged one on top of the other as a stack. Alternatively, a holographic element can comprise at least one hologram designed for at least two spectral ranges. Preferably, the hologram or holograms are recorded for three different spectral ranges of a specified color space, for example, the RGB color space or a CMY color space. Here, C stands for cyan, M for magenta, and Y for yellow.

[0075] The individual, differing holograms of a holographic element can be arranged next to each other and / or one behind the other with respect to a center line or central axis, which can coincide with the optical axis, or with respect to another specified geometric parameter of the holographic element.

[0076] The holographic arrangement may comprise a first holographic element and a second holographic element, wherein several of the holograms or all of the holograms of the respective holographic element are identical or of the same design except for the spectral range for which they are designed.

[0077] Preferably, the first holographic element is arranged mirror-symmetrically to the second holographic element with respect to the arrangement of the individual holograms. For example, the first holographic element can comprise a hologram designed for the red spectral range, a hologram designed for the green spectral range, and a hologram designed for the blue spectral range, which are arranged one above the other in the stated order. The second holographic element can also have a hologram designed for the red spectral range, a hologram designed for the green spectral range, and a hologram designed for the blue spectral range, which are also arranged one above the other in this order.In the case of a mirror-symmetrical arrangement, the first holographic element and the second holographic element are arranged one upon the other or adjacent to one another in such a way that, for example, the hologram of the first holographic element recorded for the red spectral range is arranged directly adjacent to the hologram of the second holographic element recorded for the red spectral range.

[0078] Alternatively, the arrangement of the holograms of the first holographic element may be identical to the arrangement of the holograms of the second holographic element with respect to a specified direction. For example, both holographic elements may have holograms arranged in the RGB sequence (R - hologram recorded with red light, G - hologram recorded with green light, B - hologram recorded with blue light) with respect to a specified direction, arranged so that the R hologram of one holographic element is adjacent to the B hologram of the other holographic element. Any other, different arrangements are also possible, for example, RGB adjacent to or adjacent to GBR, etc.

[0079] In the above description, the holographic arrangement can preferably be understood as comprising two holographic elements arranged directly one behind the other along the beam path, with a first holographic element being designed for the first "reflective" diffraction and the second holographic element for the "reflective" diffraction of the light that has already been diffracted by the first holographic element. For this purpose, the first holographic element is advantageously located behind the second holographic element along the beam path. Each holographic element (or the at least one hologram comprised by it) can be designed for one or more spectral ranges.

[0080] For the purpose of manipulating wavefronts for more than one spectral range, it may alternatively be preferred to include more than one pair of holographic elements, with each pair designed for the same spectral range being arranged directly one behind the other along the beam path. In this case, not only is at least one hologram of the first or another holographic element assigned to at least one hologram of the second or another holographic element, but the pairs of holographic elements themselves, each designed for the same spectral range, are assigned to one another.For example, the holographic arrangement for this purpose can comprise a pair of holographic elements arranged directly one behind the other for the red spectral range, then a pair of holographic elements arranged directly one behind the other for the green spectral range, and then a pair of holographic elements arranged directly next to each other for the blue spectral range. These respective pairs are preferably also arranged directly one behind the other in the beam path.

[0081] The holographic arrangement can be configured in the form of at least one layer or at least one film or at least one substrate, for example, in the form of at least one volume hologram, or in the form of at least one plate. Additionally or alternatively, the holographic arrangement can have a flat surface or a curved surface. The holographic arrangement can, for example, be arranged on, on, or beneath a surface of a cover glass or another existing optical component.

[0082] This way, no additional installation space is required. For example, the wavefront manipulator can comprise a transmissive optical component designed to be arranged in the beam path between the holographic arrangement and the projection surface. In this case, the holographic arrangement can preferably be arranged on a surface of the transmissive optical component facing away from the projection surfaces. Both the transmissive optical component and the holographic arrangement can be curved, preferably with the same curvature.The aforementioned transmissive optical component can, for example, be a so-called glare trap, which is typically arranged between a windshield and a head-up display and is designed to reflect sunlight in a specific direction so that it is not reflected via the head-up display toward the eyebox. In this embodiment, the holographic arrangement and the glare trap are preferably designed with the same curvature and arranged directly adjacent to one another.

[0083] Advantageously, the holographic arrangement is designed for a plurality of incident angles and / or for a plurality of non-overlapping incident angle ranges. For example, different image planes in a HUD can be realized using different angles or angular spectra. For this purpose, the holographic arrangement can, for example, comprise separate pairs of holographic elements for each angle or for each incident angle spectrum. Alternatively, a single pair of holographic elements can also be designed for multiple incident angles or angular spectra, e.g., by comprising several holograms, each designed for an incident angle or an incident angle spectrum.

[0084] In a preferred variant, the wavefront manipulator according to the invention comprises at least one optical element that has a freeform surface, i.e., an optically effective freeform surface, and is designed for placement in the beam path between the imaging unit and the holographic arrangement. The optical element comprising the freeform surface contributes to an improvement in resolution through a corresponding design of the freeform surface and allows for targeted correction of imaging errors. Furthermore, due to the freeform surface, the optical element requires very little installation space. It therefore also contributes significantly to improving the imaging quality of a compact head-up display.

[0085] The optical element having the freeform surface can be reflective and / or transmissive. In particular, the optical element can be a freeform mirror.

[0086] In a further preferred embodiment of the invention, the at least one spectral range diffracted by the holographic component for beam adaptation comprises at least two, preferably three spectral ranges, in particular a red, a green and / or a blue spectral range, wherein the at least one bandpass filter is permeable to visible light in at least a first and a second, preferably also a third spectral range, wherein these each comprise the plurality of spectral ranges diffracted by the holographic component for beam adaptation and wherein the bandpass filter is preferably designed to suppress visible light outside the first, second and preferably third spectral range.

[0087] This makes it particularly easy to implement stray light suppression for an RGB HUD.

[0088] In a further preferred embodiment of the invention, the at least one spectral range diffracted by the holographic component for beam adaptation comprises at least a green spectral range and a red and / or blue spectral range, wherein the bandpass filter is transparent to visible light in the green spectral range, wherein the bandpass filter further comprises a shortpass filter which is transparent to visible light in the blue spectral range and is opaque to wavelengths above the blue spectral range and / or wherein the bandpass filter further comprises a longpass filter which is transparent to visible light in the red spectral range and is opaque to wavelengths below the red spectral range.

[0089] These additional filters have two separate spectral ranges or wavelength ranges, with the filters transmitting in a first range and being opaque in a second range. With a short-pass filter, the first range is that of the short-wavelength wavelengths and the second range is that of the long-wavelength wavelengths; with a long-pass filter, the opposite is true. In other words, the short-pass filter transmits light up to a maximum wavelength and is opaque above it, whereas the long-pass filter transmits from a minimum wavelength and is opaque below it.

[0090] The filters are preferably configured or coordinated so that they do not influence the functionality, particularly the transmission window, of the other filter. For example, a filter can be used that includes both the bandpass filter and the shortpass and longpass filters.

[0091] Preferably, the described embodiment is to be understood such that the bandpass filter further comprises a transmission window which is permeable to visible light in the blue spectral range (and preferably beyond that to shorter wavelengths - hence the preferred designation "short pass"). In this case, the transmission window is particularly designed such that the bandpass filter is opaque to wavelengths above the blue spectral range up to the transmission window of the bandpass filter in the green spectral range. Alternatively or additionally, the bandpass filter further comprises a transmission window which is permeable to visible light in the red spectral range (and preferably beyond that to longer wavelengths - hence the preferred designation "long pass").The transmission window is specifically designed so that the bandpass filter is opaque to wavelengths below the red spectral range up to the transmission window of the bandpass filter in the green spectral range. This results in multiple transmission windows: a narrow transmission window in the green spectral range combined with a wide transmission window in the blue spectral range and toward shorter wavelengths, and / or combined with a wide transmission window in the red spectral range and toward longer wavelengths. The resulting transmission behavior can then look, for example, as described in Fig. 9.

[0092] The embodiment described here takes advantage of the fact that light below the blue spectral range or above the red spectral range is barely or not at all visible to the human eye, and thus filtering these wavelength ranges is not absolutely necessary to avoid stray light. At the same time, short-pass and long-pass filters are cheaper to manufacture and simpler to construct than band-pass filters. In particular, if the filters are comprised in one or more layers, which are applied, for example, to the holographic component, considerable effort can be saved compared to applying multiple band-pass filters. In a further preferred embodiment of the invention, a red spectral range comprises a wavelength of 640 nm, a green spectral range a wavelength of 525 nm and / or 532 nm, and / or a blue spectral range a wavelength of 446 nm and / or 460 nm.

[0093] These wavelengths are particularly well-suited for standardized and readily available light sources. For example, they could be standard wavelengths of a laser light source.

[0094] In a further preferred embodiment of the invention, the spectral range diffracted by the holographic component for beam adaptation has a half-width of 5 nm, preferably 2 nm. Such narrow spectral ranges can achieve good imaging quality of the HUD, since for narrower spectral ranges, more precise and less smeared diffraction by the holographic component is possible and overall aberrations by the optical components of the HUD can be reduced. At the same time, the bandpass filter can have at least a narrow first spectral range, which is advantageously adapted to the diffracted spectral range and thus provide improved stray light suppression while simultaneously providing high imaging quality of the HUD.

[0095] In a further preferred embodiment of the invention, the bandpass filter is arranged on the holographic component.

[0096] In particular, the bandpass filter is applied to the carrier substrate, which is preferably encompassed by the holographic component. The holographic function of the holographic component can, for example, be encapsulated in a correspondingly exposed photopolymer layer. This, in turn, is preferably applied to a corresponding carrier substrate, which, for example, imparts mechanical stability. The structure can then be such that the bandpass filter is applied to one side of the carrier substrate and the photopolymer layer to the other side.

[0097] The carrier substrate can comprise, for example, glass, e.g., BK7, B270, or similar suitable materials known to those skilled in the art. By using one of these materials, a particularly good refractive index match of the filter to the substrate can be achieved, especially in the case of a coating.

[0098] This allows for a particularly compact and integrated component. At the same time, the bandpass filter is positioned directly where it is needed, allowing for particularly simple coordination between the holographic component and the bandpass filter.

[0099] In a further preferred embodiment of the invention, the holographic component is covered by a cover glass and the bandpass filter is arranged between the holographic component and the cover glass or on the cover glass.

[0100] The cover glass can preferably be an optically transparent cover for the spectral range used, which protects the holographic component from mechanical influences and contamination and at the same time represents an aesthetically pleasing cover for the holographic component, for example towards the vehicle interior.

[0101] The cover glass can be made of glass, polymethyl methacrylate (PMMA), and / or polycarbonate (PC), for example. "On the cover glass" preferably means on the side of the cover glass facing away from the holographic component. In a vehicle, this is preferably the side of the cover glass facing the vehicle interior and visible to a user, e.g., the driver of the vehicle.

[0102] A bandpass filter, which is arranged between the holographic component and the cover glass, is advantageously protected against mechanical influences and contamination just as the holographic component.

[0103] A bandpass filter arranged on the cover glass is particularly easy to manufacture (e.g., by coating the cover glass). Advantageously, the bandpass filter can also prevent reflections of ambient light on the cover glass.

[0104] In a further preferred embodiment of the invention, the HUD further comprises a glare trap and / or an angle filter, in particular a louvre grille.

[0105] An angle filter is preferably a filter that is transparent to light from one or more angular ranges and is preferably configured to suppress light from other angular ranges. This advantageously allows at least one angular spectrum to be selectively transmitted and ambient light from other angular ranges to be blocked, preventing it from being diffracted toward the eyebox by the holographic component.

[0106] A louvre grating as an embodiment of the angle filter is described, for example, in DE 10 2019 132 600 A1. It can be, for example, an optical grating designed to absorb light incident from the environment onto a first surface side of the grating at an angle of incidence within an angle of incidence range and to transmit projection light incident onto a second surface side of the grating at an angle of incidence within a projection angle range of the HUDS.

[0107] In a further preferred embodiment of the invention, the bandpass filter influences the luminance of the HUD by less than 5%.

[0108] Preferably, the bandpass filter otherwise does not influence the beam guidance or only negligibly.

[0109] This allows for an efficient HUD to be provided with reduced distracting light.

[0110] In a further preferred embodiment of the invention, at least one polarization filter is included in a beam path between the holographic component and a provided eyebox of the HUD, wherein the polarization filter is permeable to visible light of a first polarization, which comprises a polarization diffracted by the holographic component for beam adaptation.

[0111] A polarization filter is preferably a filter which is permeable to a well-defined polarization and preferably suppresses other, deviating polarizations.

[0112] Suppression can preferably be defined analogously, mutatis mutandis, to the bandpass filter above. The well-defined polarization can preferably be a linear polarization, i.e., a polarization along a plane. It can also be a circular polarization, i.e., a polarization that can be described over time by a rotating vector.

[0113] The fact that the first polarization includes the diffracted polarization preferably means that a projection of the diffracted polarization onto the first polarization is at least 50%, i.e., for example, that less than 50% of the intensity of the diffracted light is blocked by the polarization filter due to its polarization.

[0114] This value (the proportion of the projection of the diffracted polarization onto the first polarization) may also preferably be at least 60%, at least 70%, at least 80%, at least 90% and / or at least 95%.

[0115] The diffracted light preferably includes the useful light of the HUD.

[0116] By filtering the polarization in addition to the spectral filtering, stray light diffracted into the eyebox by the holographic component can be further reduced, because portions of the ambient light that do not have the first polarization are also suppressed by the polarization filter and thus cannot be diffracted.

[0117] In a further preferred embodiment of the invention, the polarization filter is comprised by the bandpass filter and / or the first polarization of the polarization filter deviates from a preferred polarization of the bandpass filter by less than 50%.

[0118] Because the polarization filter is enclosed by the bandpass filter, a particularly compact and efficient component can be realized.

[0119] It's possible that the bandpass filter already has a preferred polarization. This can mean that the bandpass filter is permeable to the preferred polarization and less permeable to, or suppresses, another polarization that differs from the second polarization.

[0120] The preferred position is preferably a well-defined polarization. This can preferably be linear polarization, i.e., polarization along a plane. It can also be circular polarization, i.e., a polarization that can be described over time by a rotating vector.

[0121] Suppression is preferably defined analogously to the polarization filter or bandpass filter mentioned above, mutatis mutandis.

[0122] Less transmissive preferably means an attenuation of light with a polarization other than the second by at least a factor of 2.

[0123] The fact that the preferred polarization deviates from the first polarization by less than 50% preferably means that the projection of the preferred projection onto the first polarization is proportionally at least 50%, i.e., less than 50% of the intensity of the diffracted light is blocked by the polarization filter due to its polarization. Preferably, the preferred polarization deviates from the first polarization by less than 40%, more preferably by less than 30%, even more preferably by less than 20%, and most preferably by less than 10%.

[0124] Through this coordination between polarization filter and bandpass filter, a particularly efficient HUD can be realized in which little of the HUD's useful light is filtered out and at the same time an improved suppression of stray light is achieved.

[0125] In a further preferred embodiment of the invention, the bandpass filter, the shortpass filter and / or the longpass filter is applied as at least one layer directly to the holographic component.

[0126] The at least one layer can, for example, be a dielectric layer system (preferably a system comprising multiple layers). This layer system can comprise, for example, 50-100 individual layers. These are preferably applied using physical vapor deposition (PVD). Particularly preferably, it can be an ion-assisted PVD process; in particular, at least one low-refractive-index and one high-refractive-index oxide are used to achieve the desired optical properties.

[0127] Preferably, the at least one layer, as already described above, is applied to the carrier substrate of the holographic component.

[0128] By applying it as a layer, a compact component can be provided which has essential functionalities for operating the HUD without disturbing light.

[0129] In a further preferred embodiment of the invention, the HUD has at least one coating which is designed to minimize the deflection of incoming ambient light into the eyebox.

[0130] In a further preferred embodiment of the invention, the HUD is produced by the following steps: preferably providing a HUD

[0131] Determination of angular ranges of ambient light incident on the HUD for which a critical deflection from the HUD into the eyebox can occur (preferably by a computer-implemented method)

[0132] Applying at least one coating to the HUD which is designed to minimize the deflection of the incoming ambient light from the specific angular range.

[0133] This embodiment is preferably also described in DE 102022214244, the content of which is hereby deemed to be encompassed by this disclosure.

[0134] Anti-reflective coating of a HUD specifically describes a process in which the redirection of ambient light radiating onto the HUD into the HUD's eyebox is minimized, thus minimizing stray light in the user's field of vision. Redirection can involve any physical effect, such as scattering, that can change the direction of the light. Redirection includes, for example, reflection, refraction, and / or diffraction.

[0135] Ambient light is, in particular, any light emitted by natural or artificial light sources that is not used to display information by the HUD (for example, the light from the HUD's imager is not ambient light).

[0136] The eyebox is preferably a fixed size in the design of a HUD, but is only realized when the HUD is installed. Therefore, it is often referred to as a defined eyebox.

[0137] Provision of a HUD specifically describes the provision of all or the essential components required for the operation of a HUD. These include, for example, imagers, optical components (especially for beam adjustment), beam traps, coverglass, and / or glaretrap.

[0138] Since the provision of a HUD can be made before its installation, e.g., in a vehicle, the projection surface, which is often contained within a permanently installed panel in the vehicle (e.g., windshield), does not necessarily have to be included. However, the provision of the projection surface can also be included in the provision of the HUD.

[0139] A HUD can also be provided after installation, for example, in a vehicle. In this case, in addition to the above-mentioned components, the projection surface can preferably already be included. Other components, such as electrical components, electrical power connections, etc., can also be included.

[0140] It is important during provision that the HUD components essential for anti-reflection are provided (whether before or after installation), i.e., those on which or through which critical deflection occurs. These include, in particular, optical components for beam adjustment (e.g., wavefront manipulators or holographic components for beam adjustment) and / or cover glass.

[0141] A critical deflection refers to a deflection into the eyebox and / or the safety eyebox that is undesirable. For example, any deflection can be undesirable, or deflection above a certain threshold can be undesirable. These are different embodiments of the invention, which are explained in more detail below.

[0142] Since not all ambient light is critically deflected from all directions, the idea is to determine at least one angular range from which critical deflection occurs. Thus, the at least one angular range preferably does not include all angles from all possible directions. This determination can be made, for example, by calculation or simulation. A simulation can be computer-implemented or performed using a simulation setup.

[0143] The angular range includes, for example, 60° or less, 50° or less, 40° or less, 30° or less, 20° or less, or 10° or less. A calculation can typically be computer-implemented. Computer-implemented can mean that a computer comprising at least one processor and at least one data memory is provided for suitable simulation methods. The calculation and / or the computer-implemented simulation can be based on certain assumptions about the incident ambient light, e.g. spectrum and / or direction, as well as specific geometric assumptions about the arrangement and dimensions of the HUD in the installed state. Furthermore, certain physical equations and / or models can be assumed which specifically define the deflection and which advantageously take physical properties of the HUD components into account.

[0144] A simulation setup can also or additionally include lighting that serves as a model for ambient light, as well as a measurement setup that can determine the deflection into the eyebox and the origin of the deflected light. For example, the illumination of a HUD installed in a vehicle can be performed from different directions in a time-resolved manner, and the corresponding measurement can also be performed to match the measured light to the incident light. A simulation setup can preferably be implemented on a true-to-original HUD and / or a true-to-original vehicle, or on a model that preferably only has partial components and / or is scaled down compared to the original.

[0145] The at least one angular range can comprise multiple angular ranges. These angular ranges can also relate to multiple, preferably orthogonal planes in which they are each defined. The angular range is determined in such a way that it is clearly defined for a person skilled in the art. The reference axis Z-plane can, for example, be a normal to the surface of the HUD or the respective component of the HUD, in particular a normal in the (geometric) center of gravity of the surface of the component if the surface of the component is curved. This can then, for example, be a normal to a tangent of the surface at the respective point. Alternatively, multiple angular ranges can be determined for each normal at different points on the surface. The determination of the angular range preferably includes information about the reference axis or plane as well as about the component of the HUD for which the angular range was determined.

[0146] Another key idea is the subsequent application of at least one coating to the HUD, designed to minimize the deflection of incoming ambient light from the specific angular range. This can, for example, be an AR coating specifically designed to suppress reflections within the specific angular range. This can advantageously function across a broad spectrum, but is specifically designed for at least one specific angular range and is therefore less complex than prior art coatings.

[0147] For example, fewer layers must be included.

[0148] The coating is preferably applied to at least one component of the HUD that provides the critical deflection. If multiple components of the HUD are involved in the critical deflection, the coating is applied to at least the component that is first impinged by the ambient light. The coating can be applied, for example, by application, gluing, deposition, and / or spraying. The coating can, for example, be in the form of a film prior to application and then adhered (in the correct orientation according to the specific angular range).

[0149] This process allows a coating to be applied specifically to the angular ranges where unwanted deflection into the eyebox would otherwise occur. There's no need to use a complex and expensive coating that works equally well in all directions. This saves costs and allows for a simpler design suitable for mass production. At the same time, determining the angular ranges only needs to be done once, thus reducing the additional effort.

[0150] In particular, the combination with the aforementioned aspect of the invention, which concerns a (bandpass) filter, can particularly effectively prevent stray light in the eyebox. Under certain conditions, the filter may be reflective in its stopband and therefore not contribute to suppressing critical reflections into the eyebox. The additional coating can nevertheless prevent critical deflection for specific angular ranges.

[0151] In a further aspect, the invention relates to a holographic component for beam adjustment, in particular a wavefront manipulator, for a scattered-light-reduced HUD, preferably as described above, comprising at least one bandpass filter arranged to lie in a beam path between the holographic component and a provided eyebox of the HUD. The bandpass filter is permeable to visible light in at least a first spectral range, which includes at least one spectral range diffracted by the holographic component for beam adjustment, and is preferably configured to suppress visible light above and below the first spectral range.

[0152] It will be apparent to the person skilled in the art that advantages, definitions and embodiments of the device according to the invention of the first aspect also apply to the claimed device according to the invention according to the further aspect.

[0153] In a further aspect, the invention relates to a method for producing a holographic component for beam adaptation, preferably as described herein, for a scattered light-reduced HUD, preferably as described herein, comprising the following steps: a. Providing the holographic component for beam adaptation, which is configured to carry out a beam adaptation of at least one spectral range by diffraction b. Coating the holographic component for beam adaptation with at least one first layer, wherein the at least one first layer is configured to comprise at least one bandpass filter in a beam path between the holographic component and a provided eyebox of the HUD, wherein the bandpass filter is permeable to visible light in at least a first spectral range, which comprises the spectral range diffracted by the holographic component for beam adaptation.It will be apparent to the person skilled in the art that advantages, definitions and embodiments of the device according to the invention of the first aspect or the further aspects also apply to the method according to the invention and vice versa.

[0154] The at least one first layer preferably comprises a plurality of layers and, in particular, a layer system. The layer system is preferably configured to form the at least one filter. For example, the layers can comprise partially reflective layers configured to achieve the preferred filter behavior through interference effects.

[0155] In a preferred embodiment of the invention, the at least one spectral range diffracted by the holographic component for beam adaptation comprises at least two, preferably three spectral ranges, in particular a red, a green and / or a blue spectral range, wherein the at least one bandpass filter is permeable to visible light in at least a first and a second, preferably also a third spectral range, wherein these each comprise the plurality of spectral ranges diffracted by the holographic component for beam adaptation (5).

[0156] In a further preferred embodiment of the invention, the at least one spectral range diffracted by the holographic component for beam adaptation comprises at least one green spectral range and one red and / or blue spectral range, wherein the bandpass filter is transparent to visible light in the green spectral range, further comprising a shortpass filter which is transparent to visible light in the blue spectral range and opaque to wavelengths above the blue spectral range and / or further comprising a longpass filter which is transparent to visible light in the red spectral range and opaque to wavelengths below the red spectral range.

[0157] In a further aspect, the invention relates to a holographic component for beam adaptation, in particular a wavefront manipulator, for a scattered light reduced HUD, preferably as described herein, manufactured by a method as described herein.

[0158] It will be apparent to the person skilled in the art that advantages, definitions and embodiments of the device according to the invention of the first aspect or the further aspects and of the method according to the invention also apply to this device according to the invention and vice versa.

[0159] Description of the invention:

[0160] The invention will be explained below with reference to further figures and examples. The examples and figures serve to illustrate preferred embodiments of the invention without limiting it.

[0161] Figure 1 shows various stray light components in a state-of-the-art HUD. Figure 2 examines stray light due to Fresnel reflections of ambient light on the surface of the wavefront manipulator.

[0162] Figure 3 shows stray light caused by ambient light diffracted by the holographic beam-adapting component.

[0163] Figure 4 shows the proportion of stray light caused by ambient light reflected by the mirror.

[0164] Figure 5 shows the proportion of stray light caused by ambient light reflected by the imager.

[0165] Figure 6 shows an exemplary HUD according to an embodiment of the invention.

[0166] Figure 7 shows components of a wavefront manipulator with bandpass filter.

[0167] Figure 8 shows the spectral transmission properties of an exemplary bandpass filter.

[0168] Figure 9 shows the spectral transmission properties of an exemplary combination of bandpass filter, longpass filter and shortpass filter.

[0169] Figure 10 shows the (undisturbed) beam path of a HUD with a bandpass filter.

[0170] Figure 11 shows the process steps of an embodiment of the process.

[0171] Figure 1 shows a HUD 1 and the stray light 2 (simulation) resulting from redirected ambient light 9, which is directed toward the (safety) eyebox, although no measures have been taken to suppress this. The HUD 1 shown comprises the components image generator (PGU) 3, (freeform) mirror 4, holographic component for beam adjustment 5, here in the form of a wavefront manipulator 6, and projection surface 7 in the form of a vehicle windshield 8. The wavefront manipulator can be covered by a cover glass (not explicitly shown). The (vertical extension of the) eyebox 10 lies to the left of the windshield in the beam field of stray light 2.

[0172] The following figures 2-5 show a decomposition of the stray light 2 into its individual components or according to its source component in the HUD 1.

[0173] Figure 2 considers stray light 2 due to Fresnel reflections of the ambient light 9 at the surface of the wavefront manipulator.

[0174] Figure 3 shows stray light 2, which is generated by ambient light 9 diffracted at the holographic component for beam adjustment 5 (here still wavefront manipulator 6).

[0175] Figure 4 shows the proportion of stray light 2 caused by ambient light 9 reflected by mirror 4.

[0176] Figure 5 shows the proportion of stray light 2 caused by ambient light 9 reflected by the imager 3.

[0177] If the portions of stray light that land in the eyebox due to various unwanted deflections are broken down (see Table 1 below), it becomes clear that the portion of Fresnel reflections from the components of the HUD 1, here the wavefront manipulator 6, is by far the largest. This portion can be greatly reduced by suitable measures, e.g., by applying suitable layers for the specific angular ranges of the deflected ambient light, as described in this document. Not shown in Table 1 is the portion of stray light that lands directly, i.e., without deflection, in the eyebox.

[0178] The next largest portion results from diffraction at the holographic component for beam adjustment 5. In the table, this is further broken down according to the different wavelengths for which the holographic subcomponents included in the calculated example are designed. Accordingly, the holographic interference deflections account for approximately one-third of the total interference light 2 and are therefore significant.

[0179] Table 1

[0180] Figure 6 shows an exemplary HUD 1 according to an embodiment of the invention. The components largely correspond to those of the HUD 1 shown in Figure 1 and are therefore not explained in detail again. Also shown here are the eyebox 10 and the beam path of the HUD 11 generated and deflected for the operation of the HUD 1. Key features of the invention are included in the holographic component for beam adjustment 5 (the wavefront manipulator 6).

[0181] This component is therefore shown again in an enlarged scale in Figure 7. The holographic component 5 shown for beam adaptation in the form of a wavefront manipulator 6 consists of a so-called hologram stack (or hologram stack) of reflection holograms 12, 13 and 14 (so-called Z-holograms) arranged in pairs, each of which is designed to diffract a specific spectral range. These reflection holograms arranged in pairs are preferably each associated holograms or holographic elements as described above in the summary of the invention for the wavefront manipulator. The lower pair 12 is designed to diffract blue light and could, for example, correspond to the blue HOE in Table 1, the middle pair 13 is designed for green light and could therefore correspond to the green HOE in Table 1, and the upper pair 14 diffracts red light and could therefore correspond to the red HOE in Table 1.1. By means of the respective pairs 13, 14, 15, the wavefronts of the HUD 1 coming from the imager 3 via the mirror 4 can be influenced in the respective spectral range as desired by introducing a desired diffraction function into the respective holograms. Example light rays are illustrated by the arrows. The spectral design of the respective pairs 12, 13, 14 advantageously corresponds to the spectral ranges in red, green, and blue emitted by the imager 3. Such RGB imaging methods (RGB stands for red, green, and blue) for generating a white or colored image are well known to those skilled in the art and need not be described in detail here. Ambient light 9, e.g.from the sun in the sky, which has been symbolically represented here (reference numeral 15), contains a broad spectrum and thus also the spectral ranges for which the respective pairs 12, 13, 14 are designed, but also spectral ranges adjacent to these spectral ranges. Those skilled in the art will know that a hologram which diffracts light of a specific wavelength from a specific direction in a specific direction diffracts light of a neighboring wavelength from the same direction in a neighboring direction and possibly light of other wavelengths from a different direction in the specific direction. Therefore, without further measures, this light may be undesirably deflected at the wavefront manipulator 6, which could lead to stray light in the eyebox 10.The penetration of ambient light 9 into the wavefront manipulator 6 is, however, largely prevented by a bandpass filter 16 located above the wavefront manipulator, which is only permeable to the respective spectral ranges for which the pairs 12, 13, and 14 are designed. Optionally, in addition to a bandpass filter 16 for green light, a shortpass filter for blue light and a longpass filter for red light can also be included. In this way, unwanted deflection of other spectral ranges from the ambient light 9 into the eyebox 10 can be significantly reduced, and stray light can be minimized. Figure 7 also shows a cover glass 17 covering the wavefront manipulator 6 and the bandpass filter 16. This can serve purely aesthetically as an optical cover, but it can also have other functionalities, such as a coating to minimize Fresnel reflections in the eyebox 10 or protection against contamination (e.g.Dust) of the manipulator 6. The bandpass filter 16 can itself be composed of several filter elements (e.g. bandpass filter, longpass filter and / or shortpass filter) in order to have the desired spectral properties.

[0182] Figure 8 shows the spectral transmission properties of an example bandpass filter. The bandpass filter was adapted to the RGB wavelengths used for HUD 1 and for which the holographic subcomponents are designed. Transmission is maximum at these wavelengths, with the spectral "transmission windows" each having a full width at half maximum (FWHM) of 5 nanometers (nm).

[0183] Figure 9 shows the spectral transmission properties of an embodiment which combines an exemplary bandpass filter with a shortpass filter and a longpass filter. Here, too, the filters were adapted to the RGB wavelengths used for the HUD 1 and for which the holographic components are designed. The shortpass filter is transparent to visible light in the blue spectral range of the HUD 1 and opaque to wavelengths above the blue spectral range. The longpass filter is transparent to visible light in the red spectral range of the HUD 1 and opaque to wavelengths below the red spectral range. The bandpass filter, in turn, is transparent to the green spectral range of the HUD 1. Thus, wavelengths below the blue and green spectral ranges are transmitted.Transmitted above the red spectral range, however, since these wavelengths are barely visible to the eye, stray light from this wavelength range can be tolerated under certain circumstances. At the same time, this design simplifies manufacturing.

[0184] Using such a filter, the above simulation for Table 1 was repeated and refined, see Table 2. The table shows, on the left, the stray light components without the use of a filter, and, on the right, the stray light components when using an embodiment as described in Fig. 8 and, on the far right, when using an embodiment as described in Fig. 9. The stray light components are again broken down by location and type of origin. The respective percentage of the total stray light that finds its way into the eyebox is shown, once in a radiometric evaluation and once in a photometric evaluation, which, in addition to the radiometric evaluation, also takes into account the sensitivity of the human eye for the respective wavelengths.The largest proportion is again Fresnel reflections from a HUD component, which cannot be reduced by using the filter. This proportion increases again when using the filter because less stray light is now generated by diffraction at the HOEs, thus shifting the relative proportion of stray light toward Fresnel reflections. In any case, it is clear that stray light from the holographic component can be significantly reduced when filters are used. As expected, the embodiment with short- and long-pass filters performs somewhat worse than the embodiment that uses bandpass filters for all spectral ranges. The simulation shown in Figure 10 shows that the beam path 11 of the HUD 1 is not affected by the use of the bandpass filter 16. The luminance distribution (not shown) is also not affected by the bandpass filter 16. Figure 9 shows the HUD with filter 16; the components of the HUD 1 shown are otherwise identical to, for example, Figure 1 and are therefore not described in detail here.

[0185] Figure 11 shows an exemplary embodiment of the method for producing the holographic component for beam adjustment. The method preferably comprises the steps of "providing the holographic component for beam adjustment" 18 and "coating the holographic component for beam adjustment with at least one first layer comprising the bandpass filter" 19.

[0186] LIST OF REFERENCE SYMBOLS

[0187] 1 HUD

[0188] 2 stray light

[0189] 3 image generators (PGU)

[0190] 4 (freeform) mirrors

[0191] 5 Holographic component for beam adjustment

[0192] 6 Wavefront manipulator

[0193] 7 Projection surface

[0194] 8 Windshield

[0195] 9 Ambient light

[0196] 10 Eye boxes

[0197] 11 HUD beam path

[0198] 12 hologram pair for blue spectral range

[0199] 13 Hologram pair for green spectral range

[0200] 14 hologram pairs for the red spectral range

[0201] 15 Sun

[0202] 16 bandpass filters

[0203] 17 Coverglass

[0204] 18 Providing the holographic component for beam adjustment

[0205] 19 Coating the holographic component for beam adaptation with at least a first layer comprising the bandpass filter

Claims

PATENT CLAIMS 1. A scattered light-reduced HUD (1) comprising a holographic component for beam adjustment (5), wherein at least one bandpass filter (16) is arranged in a beam path (11) between the holographic component (5) and a provided eyebox (10) of the HUD (1), wherein the bandpass filter (16) is permeable to visible light in at least a first spectral range, which comprises at least one spectral range diffracted by the holographic component for beam adjustment (5).

2. HUD (1) according to the preceding claim, wherein the first spectral range has a half-width of at most 20 nm, preferably at most 10 nm and in particular at most 5 nm.

3. HUD (1) according to one or more of the preceding claims, wherein an acceptance angle spectrum of the bandpass filter (16) preferably comprises an angular spectrum of 10°, more preferably of 8°, even more preferably 6° and in particular of 5°, wherein the acceptance angle spectrum preferably comprises the centroid angle of the angular spectrum diffracted by the holographic component for beam adaptation (5).

4. HUD (1) according to one or more of the preceding claims, wherein the acceptance angle spectrum of the bandpass filter (16) comprises an angle spectrum diffracted by the holographic component for beam adaptation (5) and / or its center of gravity angle and is at most 10°, more preferably at most 5° and in particular at most 2° greater than the diffracted angle spectrum.

5. HUD (1) according to one or more of the preceding claims, wherein the holographic component (5) comprises a wavefront manipulator (6) for arrangement in the beam path of the HUD (11) between an imaging unit (3) and a projection surface (7).

6. HUD (1) according to one or more of the preceding claims, wherein the at least one spectral range diffracted by the holographic component for beam adaptation (5) comprises at least two, preferably three spectral ranges, in particular a red, a green and / or a blue spectral range, wherein the at least one bandpass filter (16) is permeable to visible light in at least a first and a second, preferably also a third spectral range, these each comprising the plurality of spectral ranges diffracted by the holographic component for beam adaptation (5).

7. HUD (1) according to one or more of the preceding claims, wherein the at least one spectral range diffracted by the holographic component for beam adjustment (5) comprises at least one green spectral range and one red and / or blue spectral range, wherein the bandpass filter (16) is transparent to visible light in the green Spectral range, wherein the bandpass filter (16) further comprises a shortpass filter which is transparent to visible light in the blue spectral range and opaque to wavelengths above the blue spectral range and / or wherein the bandpass filter (16) further comprises a longpass filter which is transparent to visible light in the red spectral range and opaque to wavelengths below the red spectral range. HUD (1) according to the preceding claims 6 or 7, wherein a red spectral range comprises a wavelength of 640 nm, a green spectral range comprises a wavelength of 525 nm and / or 532 nm and / or a blue spectral range comprises a wavelength of 446 nm and / or 460 nm. HUD (1) according to one or more of the preceding claims, wherein the spectral range diffracted by the holographic component for beam adaptation (5) has a half-width of 5 nm, preferably 2 nm.HUD (1) according to one or more of the preceding claims, wherein the bandpass filter (16) is arranged on the holographic component (5), wherein the holographic component (5) is preferably covered by a cover glass (17) and the bandpass filter (16) is arranged between the holographic component (5) and the cover glass (17) or on the cover glass (17). HUD (1) according to one or more of the preceding claims, further comprising a glare trap and / or an angle filter, in particular a louvre grille.HUD (1) according to one or more of the preceding claims, wherein at least one polarization filter is included in a beam path (11) between the holographic component (5) and a provided eyebox (10) of the HUD (1), wherein the polarization filter is permeable to visible light of a first polarization, which comprises a polarization diffracted by the holographic component for beam adaptation (5), wherein the polarization filter is preferably included in the bandpass filter (16) and / or the first polarization of the polarization filter deviates from a preferred polarization of the bandpass filter (16) by less than 50%. HUD (1) according to one or more of the preceding claims, wherein the bandpass filter (16), the shortpass filter and / or the longpass filter is applied as at least one layer directly to the holographic component (5). HUD (1) according to one or more of the preceding claims, further comprising at least one coating which is configured to minimize the deflection of incoming ambient light (9) into the eyebox (10), wherein the HUD (1) is preferably produced by the following steps: determining angular ranges of ambient light (9) radiating onto the HUD (1) for which a critical deflection from the HUD (1) into the eyebox (10) can take place; applying at least one coating to the HUD (1) which is configured to minimize the deflection of incoming ambient light (9) from the determined angular range.Holographic component (5) for beam adaptation, in particular a wavefront manipulator (6), for a scattered-light-reduced HUD (1) according to one or more of the preceding claims, comprising at least one bandpass filter (16) which is arranged to lie in a beam path (11) between the holographic component (5) and a provided eyebox (10) of the HUD (1), wherein the bandpass filter (16) is permeable to visible light in at least a first spectral range, which comprises at least one spectral range diffracted by the holographic component for beam adaptation (5). Method for producing a holographic component for beam adaptation (5), preferably according to the preceding claim 15, for a scattered-light-reduced HUD (1), preferably according to one or more of the preceding claims 1-14, comprising the following steps: a.Providing the holographic component for beam adjustment (5), which is configured to perform beam adjustment of at least one spectral range by diffraction. b. Coating the holographic component for beam adjustment (5) with at least one first layer, wherein the at least one first layer is configured to comprise at least one bandpass filter (16) in a beam path (11) between the holographic component (5) and a provided eyebox (10) of the HUD (1), wherein the bandpass filter (16) is transmissive to visible light in at least a first spectral range, which comprises the spectral range diffracted by the holographic component for beam adjustment (5). Holographic component (5) for beam adjustment, in particular a wavefront manipulator (6), for a scattered-light-reduced HUD (1), preferably according to one or more of the preceding claims 1-14, produced by a method according to the preceding claim 16.

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