Minimising glare reflections in a hud by means of targeted reflection reduction

Abstract

The invention relates to a method for reducing reflections in a head-up display (HUD) having a defined eyebox, comprising the steps of: providing a HUD; determining at least one range of angles of ambient light radiating onto the HUD, within which range critical deflection from the HUD into the eyebox can take place; and finally applying at least one coating to the HUD, which is designed to minimise the deflection of radiating ambient light from the determined range of angles. The invention also relates to a HUD in which reflections are correspondingly reduced. (Fig. 3)

Description

[0001] MINIMIZING GLARE REFLECTIONS ON A HUD THROUGH TARGETED ANTI-REFLECTION COATING

[0002] DESCRIPTION

[0003] In one aspect, the invention relates to a method for anti-reflective coating of a head-up display (HUD) with a defined eyebox, comprising the steps of providing a HUD, determining at least one angular range of ambient light radiating onto the HUD for which a critical deflection from the HUD into the eyebox can occur, and finally applying at least one coating to the HUD which is configured to minimize the deflection of the incoming ambient light from the determined angular range.

[0004] In a further aspect, the invention relates to a correspondingly anti-reflective HUD.

[0005] Background and state of the art:

[0006] 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.

[0007] 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 adaptation. 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.

[0008] In addition to “classic” projection systems with “classic” optical components, HUDs based on holographic components can be used.

[0009] 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.

[0010] Holograms can, for example, be transmission and reflection holograms, which each produce this reconstruction either in transmission or 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.

[0011] 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.

[0012] 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.

[0013] 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] So-called glaretraps for beam deflection are already known in the prior art; they allow the deflection of ambient light towards the outside of the eyebox. However, these are not suitable, for example, for specifically suppressing interference caused by diffraction on a holographic component of the HUD. Furthermore, not all reflections of ambient light into the eyebox can be prevented by glaretraps. Anti-reflection coatings (also called anti-reflective coatings or AR coatings for short) are known and can be applied to HUD components. These AR coatings typically work by comprising a layer system that generates destructive interference in the direction of reflection for at least one wavelength or wavelength range. The disadvantage of these AR coatings is that a layer system can only be optimized for one wavelength range and one direction of radiation.To suppress reflections across a broad spectral range and / or for any angle of incidence, several such coating systems are stacked on top of each other. This is complex and expensive. Furthermore, it must be ensured that the power of the additional rays introduced into the HUD (i.e., those for which the AR coating is effective and which are not reflected) does not cause problems. For example, these rays may be absorbed at one point in the HUD and cause significant heating. Unfortunately, an efficient, cost-effective, and safe method for anti-reflective coating of HUDs is not yet known.

[0015] Object of the invention:

[0016] It is an object of the invention to provide a method for anti-reflective coating of HUDs and an anti-reflective HUD that does not have the disadvantages of the prior art. In particular, it is an object of the invention to provide a simplified and cost-effective method for anti-reflective coating of a HUD that enables safe operation and usability of the HUD. It is also an object of the invention to provide an improved, safer HUD that is both cost-effective and easy to manufacture.

[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 method, preferably a computer-implemented method, for anti-reflective coating of a head-up display (HUD) with a defined eyebox, comprising the following steps:

[0020] Provision of a HUD Determination of at least one angular range of ambient light radiating onto the HUD for which a critical deflection from the HUD into the eyebox can occur

[0021] 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.

[0022] Anti-reflective coating of a HUD describes in particular a process in which the deflection of ambient light radiating onto the HUD into the eyebox of the HUD is minimized in order to minimize stray light in the user's field of vision.

[0023] Redirection can involve any physical effect, such as scattering, that can change the direction of light. Redirection includes, for example, reflection, refraction, and / or diffraction.

[0024] 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).

[0025] 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 may also be included. Light in this sense preferably encompasses a spectral range (specified as a wavelength in nanometers - nm) from 100 nm to 3000 nm, more preferably 280 nm to 1400 nm, and especially 380 nm to 780 nm.

[0026] The eyebox specifically comprises an area or volume from which the HUD is to be viewed. The eyes of at least one viewer can / should be located within this volume, hence the name eyebox. The eyebox is preferably a fixed size when designing a HUD, but this is only realized when the HUD is installed. Therefore, it is often referred to as a defined eyebox. The eyebox can, for example, have dimensions of 150 mm x 150 mm in one area.

[0027] 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.

[0028] The eyebox, as described in this document, may preferably include the safety eyebox.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] A critical deflection refers to a deflection into the 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.

[0034] Since not all ambient light is critically deflected from all directions, a core of the invention is that the at least one angular range from which the light is critically deflected is determined. Thus, the at least one angular range preferably does not include all angles from all possible directions. The determination can be made, for example, by calculation or simulation. Determining the angular range can also be understood as synonymous with calculating, specifying, and / or outputting the angular range. A simulation can be computer-implemented or performed using a simulation setup.

[0035] The angle range includes, for example, 60° or less, 50° or less, 40° or less, 30° or less, 20° or less, or 10° or less.

[0036] 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 that specifically define the deflection and that advantageously take into account the physical properties of the HUD components.

[0037] 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.

[0038] The at least one angular range can comprise a plurality of angular ranges. These angular ranges can also relate to a plurality of, for example, orthogonal planes in which they are each defined. The specific angular range can be the same or different in the different planes. 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, a plurality of angular ranges can be determined for respective normals at different points on the surface. The determination of the angular range preferably comprises information about the reference axis or-plane as well as the component of the HUD for which the angular range was determined.

[0039] A further core of the invention is the subsequent application of at least one coating to the HUD, which is designed to minimize the deflection of incoming ambient light from the specific angular range. This can be, for example, an AR coating specifically designed to suppress reflections for the specific angular range. The properties of the coating can be independent of the plane of the specific angular range, for example, they can be the same in all planes around a reference axis. However, they can also be different in different planes; for example, different reflection properties can exist in the different planes for a given angle around the reference axis.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 state-of-the-art coatings. For example, fewer layers are required.

[0040] To prevent the non-reflected radiation from re-entering the eyebox in other ways and / or causing heating through absorption within a component of the HUD, a suitable optical design that takes into account the further beam path of this non-reflected radiation and / or special, heat-dissipating, absorbing coatings can be used.

[0041] 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.

[0042] 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 glued on (in the correct orientation according to the specific angular range). This process allows a coating to be applied specifically to those angular ranges for which an undesired deflection into the eyebox would otherwise occur. There is no need to use a complex and expensive coating that works equally well in all directions. This saves costs and allows for a simpler structure suitable for mass production. At the same time, the angular ranges only need to be determined once, thus reducing the additional effort.

[0043] In a preferred embodiment of the invention, the method further comprises the following intermediate step:

[0044] Producing the coating.

[0045] After determining at least one angle range, a coating specifically designed for this range can be produced. This allows for particularly good adaptation and efficient anti-reflective coating.

[0046] Thin-film coating methods can be used for production (as well as application). Commonly used processes include physical vapor deposition, e.g., thermal evaporation and / or sputter deposition and / or chemical vapor deposition.

[0047] In a further preferred embodiment of the invention, the HUD comprises a holographic component for beam adjustment. A holographic component is described in more detail below with reference to a further aspect or embodiment of the invention and can, for example, comprise a wavefront manipulator and / or a waveguide, in particular for beam expansion.

[0048] Preferably, the coating is applied to a surface of the holographic component and / or a surface of a cover of the holographic component. The surface of the wavefront manipulator is, in particular, an outer surface of the holographic component facing the projection surface.

[0049] In a further preferred embodiment of the invention, the HUD comprises a projection surface, in particular a windshield, and a wavefront manipulator for arrangement in the beam path of the head-up display between an imaging unit and the projection surface, wherein the wavefront manipulator is in particular a holographic wavefront manipulator.

[0050] The imaging unit can be included, but it doesn't have to be. It can also be installed at a later date, for example. Nevertheless, the position of the wavefront manipulator is clearly defined for the expert, since the future positions of the components are already known or taken into account during the design of the HUD.

[0051] Preferably, the coating is applied to a surface of the wavefront manipulator and / or a surface of a cover of the wavefront manipulator. The surface of the wavefront manipulator is, in particular, an outer surface of the wavefront manipulator facing the projection surface. In HUDs, particularly in vehicles, aberrations arise, for example, due to the curvature of the projection surface and / or due to compact arrangements in a small installation space with potentially strong tilts of individual components relative to one another and correspondingly complex folded beam paths. The aberrations that can typically occur include distortion, defocus, tilt, astigmatism, curvature of the image plane, spherical aberrations, higher astigmatism, and coma.

[0052] A wavefront manipulator is advantageously used to at least partially correct and minimize image aberrations and provide an improved head-up display that can also be particularly compact. As the name suggests, this involves appropriately manipulating the wavefronts of the HUD's light rays.

[0053] 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.

[0054] By using reflection holograms, diffraction can be more wavelength-selective than with transmission holograms, resulting in fewer color aberrations and thus better generating a white image from the color channels. By connecting two reflection holograms in series, a transmission arrangement can still be advantageously realized, distributing the manipulation between two holograms.

[0055] 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 that diffractes light of multiple wavelengths. 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 on top of one another 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 defined color space, for example, the RGB color space or a CMY color space. Where C stands for cyan, M for magenta, and Y for yellow.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] In this way, no or hardly any additional installation space is required. For example, the wavefront manipulator can comprise a transmissive optical component which is 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 said transmissive optical component can, for example, be a so-called glare trap, which is usually arranged at a position between a windshield and a head-up display or another component of the head-up display (e.g.Wavefront manipulator and / or holographic component) and which is designed to reflect sunlight in a specified direction so that it is not reflected via the head-up display (or its other component) 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.

[0064] 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.

[0065] 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.

[0066] The optical element having the freeform surface can be reflective and / or transmissive. In particular, the optical element can be a freeform mirror.

[0067] The wavefront manipulator is therefore an essential component of the HUD and, due to its functionality, is often positioned so that its surface is exposed to ambient light, which can create unwanted deflections of ambient light toward the eyebox, either directly or, for example, via further deflection on the projection surface. Therefore, applying a coating to a surface of the wavefront manipulator and / or a surface of a cover of the wavefront manipulator is particularly advantageous.

[0068] In a further preferred embodiment of the invention, the method further comprises determining sub-regions and / or components of the HUD for which the critical deflection from the HUD into the eyebox can occur, wherein the coating is applied to the sub-regions and / or components. This means that not only angular ranges are determined during the determination, but also the components and / or sub-regions of the HUD from which the critical deflection can occur. A coating therefore does not have to take place for all components of the HUD, but only for those for which a critical deflection can actually occur. In this case, the determination of sub-regions and / or components of the HUD can also be referred to synonymously as calculating, defining and / or outputting sub-regions and / or components of the HUD for which the critical deflection from the HUD into the eyebox can occur.By identifying only the essential components and / or sub-areas of the HUD that are relevant for a critical deflection and therefore require subsequent coating, a particularly efficient anti-reflective coating of the HUD can be achieved. The specific sub-areas and / or components include, for example, optical components for beam adjustment (e.g., wavefront manipulators or holographic components for beam adjustment) and / or cover glass.

[0069] In a further preferred embodiment of the invention, the incoming ambient light is assumed to be radiation collimated from a source region toward the HUD. The source region of the collimated radiation is assumed to be each sub-region of a surface of a hemisphere centered around the HUD, which is divided into several sub-regions. A spectral distribution preferably corresponds to a spectral distribution of a blackbody (preferably at least partially) and / or at least partially to the spectral distribution of the sun. Those skilled in the art will know where to find corresponding information in the literature on the spectral distribution of a blackbody or the sun.

[0070] For centering, a preferred point of a component of the HUD can be used, e.g. a (preferably geometric) center of gravity of the component or of its surface

[0071] In this context, “at least partially” advantageously means a match (e.g. a spectral overlap) of at least 40%, more preferably at least 50%, even more preferably at least 60%, even more preferably at least 70% and in particular at least 80%.

[0072] This embodiment is also described in Figure 3 in the description of the invention. The described assumptions are particularly suitable for simulating direct sunlight irradiation onto the HUD or its sub-areas and / or components.

[0073] This simulation is not only suitable for determination by a computer-implemented method, but also for a simulation setup in a laboratory that has the properties mentioned above.

[0074] Depending on the assumed size of the sub-areas, the source area can also be assumed to be quasi-point-shaped, and there can be only a single ray per source area, which runs from the respective source area towards the HUD. A single ray is preferably considered a model for a narrow collimated beam. This is preferably also included when it is stated that the radiation from the source area towards the HUD is collimated.

[0075] The above assumptions are suitable for a particularly simple and resource-saving simulation, while at the same time achieving results that particularly well simulate real ambient light and its unwanted deflection.

[0076] The radiation is preferably assumed to be blackbody radiation with regard to its spectral distribution, e.g., in a temperature range from 1000 Kelvin (K) to 10,000 K, more preferably in a temperature range from 3000 K to 8000 K, even more preferably in a temperature range from 4000 K to 7000 K, and especially in a temperature range from 5000 K to 6500 K, e.g., 6000 K. Those skilled in the art know how to approximate or calculate the spectral distribution of a blackbody. Such radiation is easy to simulate and yet realistically reflects real ambient light.

[0077] In a further preferred embodiment of the invention, the critical deflection is defined by the fact that a beam or radiation can be deflected into the eyebox.

[0078] This design, in which critical deflection is already ensured by the fact that ambient light is redirected into the eyebox regardless of intensity, can reduce or prevent the deflection of ambient light of any intensity. This allows for a particularly effective anti-reflective coating on a HUD.

[0079] In a further preferred embodiment of the invention, the critical deflection is defined by a radiation intensity or a luminance (of deflected radiation within the eyebox) being above an average radiation intensity or luminance of non-deflected ambient light (preferably within the eyebox).

[0080] The average radiation intensity can be determined by a value that can be routinely determined by a person skilled in the art, e.g. the luminance of an average clear sky of 8000 cd / m 2 (Candela per square meter).

[0081] In this way, an efficiently anti-reflective HUD can be provided, where not all deflection of ambient light into the eyebox is to be minimized, but only when it produces intensities or luminances above a threshold value.

[0082] In a further preferred embodiment of the invention, a critical deflection is selected from the group comprising reflection, in particular Fresnel reflection, refraction, scattering and / or diffraction.

[0083] These types of redirection are particularly relevant for a HUD and its components.

[0084] In a further preferred embodiment of the invention, a critical deflection comprises the diffraction of the spectral range of the holographic wavefront manipulator diffracted for beam adaptation and preferably comprises a wavelength range selected from the group of red spectral range, in particular 640 nm, green spectral range, in particular 525 nm and / or 532 nm and / or blue spectral range, in particular 446 nm and / or 460 nm. The coating is preferably designed for this spectral or wavelength range, which means in particular that it is set up to minimize the deflection of the incoming ambient light from this spectral or wavelength range.

[0085] The fact that the critical deflection comprises the diffraction of the spectral range of the holographic wavefront manipulator diffracted for beam adaptation preferably means that it is undesired diffraction which merely lies in the same spectral range as the spectral range of the holographic wavefront manipulator diffracted for beam adaptation.

[0086] The wavefront manipulator is preferably designed for one or more spectral ranges, such as the (at least one) spectral range of the holographic wavefront manipulator that is diffracted for beam adaptation. Since ambient light can also be in this spectral range and / or adjacent to this spectral range, unwanted diffraction (i.e., in particular, critical deflection) of this ambient light can also occur. Therefore, it is advantageous if the coating is designed for this at least one spectral or wavelength range in order to minimize this form of critical deflection and thus provide an improved anti-reflective HUD.

[0087] This can be achieved, for example, by making the coating opaque or beam-deflecting in the respective spectral range for the specific angular range, but transparent for other angular ranges (particularly those required for the operation of the HUD).

[0088] In a further preferred embodiment of the invention, the coating comprises moth eye structures and / or nanostructures.

[0089] Moth-eye structures are described, for example, in T. Lohmüller, M. Helgert, M. Sundermann, R. Brunner, JP Spatz: Biomimetic Interfaces for High-Performance Optics in the Deep-UV Light Range, Nano Letters, June 2008, and in Guanjun Tan et al.: Broadband antireflection film with moth-eye-like structure for flexible display applications, Optica, Vol. 4, No. 7, 678, July 2017, the content of which is hereby deemed to be encompassed by this disclosure. Moth-eye structures are suitable for improved antireflection coating.

[0090] Nanostructures are described, for example, in Ashok K. Sood et al.: Nanostructured AR coatings for optoelectronic applications, Nova Science Publishers, 2015, the content of which is hereby incorporated by this disclosure. Nanostructures are particularly effective as AR coatings.

[0091] In a further preferred embodiment of the invention, the coating comprises an anti-reflection layer, in particular a dielectric layer.

[0092] These are particularly simple, cost-effective and efficient.

[0093] In a further preferred embodiment of the invention, the coating is designed to attenuate the deflection from the specific angular range by at least 95%, preferably by at least 99%.

[0094] The specialist knows how to find a suitable coating based on calculations, data sheets, etc. in order to achieve the required attenuation.

[0095] A reduction of at least 95% is sufficient for many cases and is therefore a particularly efficient solution.

[0096] By attenuating the light by at least 99%, a particularly improved anti-reflective HUD can be realized.

[0097] In a further preferred embodiment of the invention, the coating is configured to attenuate the deflection from the specific angular range by at least 95% and to attenuate a deflection from at least one other angular range, which preferably does not overlap with the specific angular range, by less than 95%, preferably by less than 80%, more preferably by less than 60%, and in particular by less than 40%. Such a coating is particularly designed to attenuate the specific angular range compared to other angular ranges and is therefore particularly efficient and cost-effective.

[0098] In a further preferred embodiment of the invention, the coating comprises a plurality of individually effective layer elements, each of which is configured to attenuate the deflection from an angular range partially overlapping with the specific angular range, wherein the respective partially overlapping angular ranges taken together overlap the specific angular range.

[0099] In principle, this is advantageously an AR layer which is composed of several AR layers, each designed for smaller angular ranges, and only when assembled does it acquire the functionality to minimize the deflection of light from the specific angular range.

[0100] This makes it particularly easy to produce a suitable layer.

[0101] In a further preferred embodiment of the invention, the coating is applied to the wavefront manipulator, in particular to a cover glass covering the wavefront manipulator.

[0102] The cover glass can preferably be an optically transparent cover for the spectral range used, which protects the wavefront manipulator from mechanical influences and contamination and at the same time represents an aesthetically pleasing cover for the holographic component, e.g. towards the vehicle interior.

[0103] On the cover glass preferably means on the side of the cover glass facing away from the wavefront manipulator. 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.

[0104] A coating on the cover glass is particularly easy to create (e.g., by coating the cover glass). This can also advantageously prevent unwanted reflections of ambient light on the cover glass.

[0105] The cover glass can be made of glass, polymethyl methacrylate (PMMA), polycarbonate (PC) or similar.

[0106] In a further aspect, the invention relates to an anti-reflective HUD manufactured by the following steps:

[0107] Providing a HUD

[0108] Determination of at least one angular range of ambient light incident on the HUD for which a critical deflection from the HUD into the eyebox can occur (by a computer-implemented method)

[0109] Applying at least one coating to the HUD, which is configured to minimize the deflection of incoming ambient light from the specific angular range. It will be apparent to those skilled in the art that advantages, definitions, and embodiments of the method according to the invention also apply to the claimed device according to the invention.

[0110] In a preferred embodiment of the invention, the HUD comprises a glare trap, a curved cover glass and / or a beam trap.

[0111] The so-called glare trap can usually be installed at a position between a projection surface and other components of the head-up display (e.g.

[0112] The glare trap can be arranged on a holographic component (wavefront manipulator and / or holographic component) and is preferably designed to reflect sunlight in a specified direction so that it is not reflected via the head-up display toward the eyebox. The glare trap preferably has a curvature for this purpose. The glare trap can, for example, be located directly adjacent to the holographic component or wavefront manipulator (preferably between this component and the projection surface), with the manipulator or component, in particular, having the same curvature as the glare trap.

[0113] The cover glass may preferably also have a curvature, wherein in particular the manipulator covered by it or the covered holographic component has the same curvature as the cover glass.

[0114] The beam trap is designed, for example, as an absorbing element and is advantageously positioned to directly block ambient light, preventing it from entering the eyebox either directly or after redirection. At the same time, due to the requirements for the HUD user's unobstructed view, this beam trap can preferably be installed only in areas of the HUD or its surroundings where it does not obstruct the user's clear view through the projection surface.

[0115] The glare trap and beam trap can be arranged and / or configured in such a way that the light reflected by the glare trap lands at least partially in the beam trap and is blocked by it.

[0116] Therefore, a combination of the above-mentioned elements can be used for additionally improved anti-reflection.

[0117] In a further preferred embodiment of the invention, the HUD further comprises a holographic component for beam adaptation, in particular a holographic wavefront manipulator, wherein at least one bandpass filter is arranged in a beam path between the holographic component and the provided eyebox of the HUD, wherein the bandpass filter 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, and wherein the spectral filter is preferably configured to suppress visible light outside the first spectral range.

[0118] This is also described in DE 102022214243, the content of which is hereby deemed to be encompassed by this disclosure. The bandpass filter can advantageously be positioned directly adjacent to the coating of the HUD, either above or below it.

[0119] 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.

[0120] 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 / guiding, and / or an optical (spectral, angle-selective, and / or polarization-selective) filter function. This 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. The aforementioned holographic wavefront manipulator is preferably a holographic component.

[0121] The spectral range is preferably a contiguous range, so that a plurality of spectral ranges preferably comprise a plurality of non-contiguous spectral ranges.

[0122] Beam shaping preferably means influencing the shape of the beam. Beam shaping can, in particular, involve 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, etc.

[0123] Beam guidance or deflection specifically describes 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, eyebox size, image size, image position, etc.).

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] Thus, the holographic component is preferably configured to diffract light from at least one spectral range and at least one angular spectrum 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 to create 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 from these spectral ranges, which originates 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).

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] Because the bandpass filter preferentially functions in different directions, 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, since the bandpass filter also functions, for example, in the direction that light has after diffraction by the holographic component. Thus, the bandpass filter preferentially suppresses light from unwanted spectral ranges in the direction of the holographic component as well as suppresses light from unwanted 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 significantly reduced or eliminated.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] With an attenuation factor of 100, a reduction in stray light can be achieved, which offers high safety and operability under all conditions, even in critical applications.

[0140] In particular, the combination of anti-reflective HUD through targeted coating and the use of a bandpass filter can realize an improved, anti-reflective HUD.

[0141] Description of the invention:

[0142] 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.

[0143] Figures 1a and 1b show components of a HUD that has a windshield as a projection surface.

[0144] Figures 2a-d show from different perspectives two exemplary angles of an exemplary HUD determined by the method, for which a critical deflection into the eyebox takes place.

[0145] Figure 3 shows a preferred embodiment of the assumptions made in the simulation.

[0146] Figure 4 shows the reflection properties of an optimized moth-eye anti-reflective coating. Figures 5a and 5b show a HUD with a windshield that additionally features a glare trap and a beam trap.

[0147] Figure 6 shows the spatially resolved intensity of deflected light rays into the eyebox for a simulated HUD.

[0148] Figure 7 shows the essential process steps of the process according to the invention.

[0149] Figure 1a shows components of a HUD 1 in a perspective view, which has a windshield 3 as its projection surface 2. In addition to this, the holographic component for beam adaptation 23 is shown, in this case a waveguide for beam expansion, which is covered by a cover glass 5. Also shown is the designated eyebox 6 of the HUD 1. In this case, this can, for example, include an eye position of a driver. Sun rays can now be redirected, in particular reflected, by the shown components of the HUD 1 in such a way that they find their way into the eyebox 6. One example reflection can take place directly from the cover glass 5 into the eyebox 6. Another example reflection is reflected from the cover glass 5 via the windshield 3 into the eyebox 6.Since such critical deflections into the eyebox 6 cannot occur from all possible angles, the method described here and the corresponding HUD 1 can achieve particularly efficient anti-reflective coating by determining only those angular ranges from which the critical deflection can occur. Subsequently, a coating is applied to minimize the critical deflection, which works specifically for the specific angular ranges.

[0150] Fig. 1b shows a HUD 1 similar to the one shown in Fig. 1a in a perspective view, which allows a somewhat more frontal view of the windshield 3. In addition to the components of the HUD 1 already shown in Fig. 1a, the freeform mirror 13 and imager 22 are also shown here. Instead of a holographic component 23 in the form of a waveguide, a wavefront manipulator 4 is included here.

[0151] Figures 2a-d show two exemplary angles 24 of an exemplary HUD 1, determined by the method, for which a critical deflection into the eyebox 6 occurs. Ambient light 9 from the first angle 8' is shown in Figures 2a and 2b, and ambient light 9 from the second angle 8" is shown in Figures 2c and 2d. Figures 2a and 2c show the HUD 1 from the side, with the respective angle 8', 8" lying in the plane of the figure. Figures 2b and 2d show ambient light 9 from the angles 8', 8" shown in Figures 2a and c, respectively, in a perspective view of the HUD 1. In all examples shown, incident light 9 causes a critical reflection on the wavefront manipulator 4 or its cover glass 5, which, through further reflection on the windshield 3, ultimately lands in the eyebox 6. In such a case, the angles 8 are preferably determined for the component of the HUD 1 to which the coating is subsequently to be applied.In the present case, for practical reasons (e.g., transparency of the projection surface), this is the wavefront manipulator 4 or its cover glass 5. Furthermore, the essential deflection within the HUD 1, which subsequently lands in the eyebox 6, takes place at this component. The angular range of the incident light 9 is preferably measured with respect to the normal 7 to the wavefront manipulator 4 or cover glass 5. The proportions of the simulated sunlight that land in the eyebox 6 due to reflection are, in the examples shown, 0.00983% (Figures 2c and 2d) and 1.52% (Figures 2a and 2b), respectively. This may not sound like much, but since even a very small proportion of reflected sunlight in the eyebox 6 is perceived as disruptive and obstructive when reading the HUD 1, even such a small proportion should preferably be further minimized.For the purposes of the method, it may therefore be advantageous to define any beam deflection into the eyebox 6 as "critical." The example angles 8 shown here lie within an angular range determined by a simulation for the HUDs shown, which ranges from 10° to 40° and lies within the image plane. The angular ranges can also lie in other planes and be equal to the angular range determined in the image plane, but in some cases also different.

[0152] Figure 3 shows a preferred embodiment of the assumptions made during the simulation. This advantageously simulates the irradiation of direct sunlight, the critical deflection of which is considered particularly disruptive and, under certain circumstances, even dangerous, not so much because of its intensity per se, but primarily because of the restricted view of the HUD 1 and / or, for example, the traffic. Some exemplary beam paths are shown here, for example, 9' and 9". The regions 10' and 10", each represented graphically as points, are depicted as the original regions 10. These regions 10' and 10", in turn, are subregions of a hemisphere centered around the HUD 1, which is only shown in part here (reference numeral 11).Since the HUD 1 in turn has a finite extent and consists of several components, the centering can advantageously be carried out around a component that plays a significant role in the critical deflection, in this case the wavefront manipulator 4 or its cover glass 5. This component can be determined based on empirical values, theoretical considerations and / or based on (e.g. several upstream) simulations. For the centering, a preferred point of the component can again be used, e.g. a (preferably geometric) center of gravity of the component or of its surface. As can be seen from the drawing, centering around the HUD 1 preferably means that the center point or starting point of the radius 12 of the hemisphere in the HUD 1 is located, e.g. at the aforementioned preferred point. This point, called the center point 12, is preferably the starting point of the radii of the hemisphere.The radius of the hemisphere can preferably be chosen based on practical considerations. The fact that the radiation (e.g., 9' and 9") from a source region 10 is collimated in the direction of the HUD 1 preferably means that the beams from each source region 10 form a collimated beam and run in the direction of the HUD 1, with the direction of the HUD 1 running primarily in the direction of the component of the HUD 1 or in the direction of its preferred point. In the example shown, this is a point on the surface of the wavefront manipulator 4 or the cover glass 5. In the example shown, no collimated beam is shown, but only one beam in each case. Radiation from different source regions 10 is obviously collimated in different directions towards point 12.Each origin region 10 and the associated beam 9 can correspond to a possible position of the sun and the associated beam of rays from the sun at different vehicle orientations. Figure 4 shows the reflective properties of a moth-eye anti-reflective coating, which is optimized to minimize deflection (here: reflection) from a specific angular range between 10° and 40°.

[0153] On the left, a color code with different grayscale levels (see right y-axis or right ordinate axis) shows the reflectivity in % as a function of the incident wavelength (see x-axis or abscissa axis) and the angle of incidence (see left y-axis or left ordinate axis). It is clear that the (unwanted) reflectivity increases at larger angles of incidence and wavelengths, reaching values ​​of 1% or greater, or 5% or greater, which are already too large depending on the design. However, since it is known from simulation that the specific angular range for critical deflection lies between 10° and 40°, this circumstance is uncritical if the layer is applied correctly. At the same time, such a layer, optimized for a smaller angular range, is significantly more cost-effective, simpler, and lighter.

[0154] On the right side, the reflectivity in % (y-axis) for the angular range between 10° and 40° is shown for the three wavelengths 450 nm (circled), 532 nm (triangled), and 650 nm (crossed). Only for 650 nm does the reflectivity exceed the potentially critical value of 1% for an angular range between 35° and 40°. These wavelengths are also marked with the corresponding symbols in the left image.

[0155] The assumption in both figures is that the incoming light is linearly polarized at 45°. One could also calculate a reflectivity averaged over all possible polarizations, but this would advantageously lead to the same result.

[0156] Figures 5a and b show a HUD 1 with a windshield 3. The illustrated embodiment further comprises a freeform mirror 13 as a further component of the HUD 1, a wavefront manipulator 4 designed as a glaretrap 14, and a beam trap 15. The mode of operation of these additional components will be explained below using the incident light rays 9 shown as an example. Firstly, a portion of the incident light rays 16 are directly blocked by the beam trap 15, which can be designed, for example, as an absorbing element. These rays cannot therefore reach the eyebox 6. At the same time, due to the requirements regarding the unobstructed view of the HUD user, the beam trap 15 can only be installed in areas of the HUD or its surroundings where it does not obstruct the user's unobstructed view through the windshield 3. The glaretrap 14 is provided for the remaining areas.This includes, in particular, a wavefront manipulator 4 curved around at least one axis such that, in interaction with the projection surface 2 in the form of the windshield 3, the rays reflected by the wavefront manipulator are redirected into areas outside the eyebox 6. Only a low intensity can still reach the safety eyebox 17.

[0157] In particular, in conjunction with the method described in this document for anti-reflective coating of a HUD 1 by calculating specific angular ranges and appropriately coating the HUD 1, an eyebox 6 free of unwanted ambient light rays can be achieved. Figure 5a shows a side view of the HUD 1, and Figure 5b shows a perspective view. The perspective view according to Figure 5b also shows the intensity distribution of redirected ambient light around and into the eyebox 6. The intensity increases from dark gray (virtually no intensity) to light gray or white.

[0158] This is illustrated again in Figure 6, which shows the spatially resolved (in millimeters - mm) intensity (irradiance in watts per square millimeter - W / mm A2, see right grayscale) of deflected light rays into the eyebox 6 and around the safety areas 17' and 17" surrounding the eyebox for a simulated HUD 1 according to Figure 5. It is evident that only below the eyebox 6 does some deflected intensity enter the safety area 17". This could be further improved through further optimization, e.g., of the HUD geometry.

[0159] Figure 7 illustrates the essential process steps once again. In a first step 18, a HUD is prepared. In a next step 19, the angular ranges of ambient light radiating onto the HUD are determined for which a critical deflection from the HUD into the eye box can occur.

[0160] In a further step 21, at least one coating is then applied to the HUD, which is designed to minimize the deflection of the incoming ambient light from the specific angular range.

[0161] It may further include the intermediate step 20 (shown in dashed lines), which comprises the production of the coating to be applied.

[0162] LIST OF REFERENCE SYMBOLS

[0163] 1 Head-Up Display (HUD)

[0164] 2 Projection surface

[0165] 3 Windshield

[0166] 4 Wavefront manipulator

[0167] 5 Coverglass

[0168] 6 Eye box

[0169] 7 Normals for determining the angular range

[0170] 8 angles within the specified angle range

[0171] 9 Incident ambient light

[0172] 10 areas of origin

[0173] 11 Section of the hemisphere

[0174] 12 Center of the hemisphere

[0175] 13 (freeform) mirrors

[0176] 14 Glaretrap

[0177] 15 Beam trap

[0178] 16 Part of the incoming light rays, which is blocked by the beam trap

[0179] 17 Safety area around the eyebox

[0180] 18 Deploy HUD

[0181] 19 Determination of the angular ranges

[0182] 20 Producing the coating

[0183] 21 Applying the coating

[0184] 22 imagers

[0185] 23 Holographic component for beam adjustment

Claims

PATENT CLAIMS 1 . Method for anti-reflective coating of a head-up display (HUD) (1) with a defined eyebox (6), comprising the following steps: Providing a HUD (18) Determination of at least one angular range (19) of ambient light (9) radiating onto the HUD (1) for which a critical deflection from the HUD (1) into the eye box (6) can occur Applying at least one coating (21) to the HUD (1) which is designed to minimize the deflection of the incoming ambient light (9) from the specific angular range.

2. The method according to claim 1, further comprising the following intermediate step: Producing the coating (20).

3. Method according to one of the preceding claims, wherein the HUD (1) comprises a projection surface (2), in particular a windshield (3), and a wavefront manipulator (4) for arrangement in the beam path of the head-up display (1) between an imaging unit and the projection surface (2), wherein the wavefront manipulator (4) is in particular a holographic wavefront manipulator (4).

4. Method according to one or more of the preceding claims, further comprising determining sub-regions and / or components of the HUD (1) for which the critical deflection from the HUD (1) into the eyebox (6) can take place, wherein the coating is applied to the sub-regions and / or components.

5. Method according to one or more of the preceding claims, wherein the incoming ambient light (9) is assumed to be radiation which is collimated from an origin region (10) in the direction of the HUD (1), wherein the origin region (10) of the collimated radiation is assumed to be each sub-region of a surface of a hemisphere (11) centered around the HUD, which surface is divided into several sub-regions, wherein preferably a spectral distribution corresponds at least partially to a spectral distribution of a black body and / or the sun.

6. Method according to one or more of the preceding claims, wherein the critical deflection is defined in that a beam or radiation can be deflected into the eyebox (6) or wherein the critical deflection is defined in that a radiation intensity is above an average radiation intensity of non-deflected ambient light. Method according to one or more of the preceding claims, wherein a critical deflection is selected from the group comprising reflection, in particular Fresnel reflection, refraction, scattering and / or diffraction. Method according to one or more of the preceding claims 3-7, wherein the critical deflection comprises the diffraction of the spectral range of the holographic wavefront manipulator (4) diffracted for beam adaptation and in particular comprises a wavelength range selected from the group of red spectral range, in particular 640 nm, green spectral range, in particular 525 nm and / or 532 nm and / or blue spectral range, in particular 446 nm and / or 460 nm. Method according to one or more of the preceding claims, wherein the coating comprises moth-eye structures and / or nanostructures and / or wherein the coating comprises an anti-reflection layer, in particular a dielectric layer.Method according to one or more of the preceding claims, wherein the coating is configured to attenuate the deflection from the specific angular range by at least 95%, preferably by 99%. Method according to one or more of the preceding claims 3-10, wherein the coating is applied to the wavefront manipulator, in particular to a cover glass (5) covering the wavefront manipulator. Anti-reflective HUD (1), manufactured by the following steps: Providing a HUD (18) Determination of at least one angular range of ambient light radiating onto the HUD (1), (9) for which a critical deflection from the HUD (1) into the eyebox (6) can occur (19) Applying at least one coating to the HUD (1) that is configured to minimize (21) the deflection of the incoming ambient light (9) from the specific angular range. Anti-reflective HUD (1) according to the preceding claim, comprising a glare trap (14), a curved cover glass (5), and / or a beam trap (15). Anti-reflective HUD (1) according to one of the preceding claims, further comprising a holographic component for beam adjustment (23), in particular a holographic wavefront manipulator (4), wherein at least one bandpass filter is arranged in a beam path between the holographic component and the provided eyebox (6) of the HUD (1). wherein the bandpass filter is transmissive to visible light in at least a first spectral range which includes at least one spectral range diffracted by the holographic beam-adapting component.

Images