DE102022214244A1 - MINIMIZING GLARE REFLECTIONS OF A HUD THROUGH TARGETED ANTI-REFLECTION - Google Patents

Abstract

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 take place and finally 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. In a further aspect, the invention relates to a correspondingly anti-reflective HUD.

Description

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 take place and finally applying at least one coating to the HUD which is designed to minimize the deflection of the incoming ambient light from the determined angular range.

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

Background and state of the art:

Head-up displays (HUD) are display systems in which the information to be displayed is projected into the user's field of vision, while at the same time allowing a view of the environment that is also in the field of vision. HUDs are known from motor vehicles or aircraft, for example. In vehicles, the information to be displayed can be projected via the vehicle's windshield into the user's eye area, into the so-called eyebox. HUDs can be implemented on the basis of a variety of different systems, most of which are already state of the art.

A HUD can usually comprise an imaging unit (PGU - picture generating unit) or a projector, as well as 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 a spatial area 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 be located behind the projection surface, for example.

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

In contrast to conventional images, holography stores not only the intensity of the imaged object but also phase relationships of the light coming from the object. These phase relationships contain additional spatial information, which can be used to create a three-dimensional impression of the image, for example. This is done with the help of interference of light rays while the object is being recorded. The object is illuminated with coherent light and reflected and scattered by the object. The resulting wave field, the so-called object wave, is superimposed with light that is 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 using a light-sensitive layer, for example, and the information contained in the phase is thus also stored. For reconstruction, the resulting hologram is illuminated with a light wave that is identical or similar to the reference wave, which is then diffracted by the recorded interference patterns. In this way, the original wave front of the object wave can 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, since these can have wavelength selectivity due to wavelength-selective interference.

Holograms can be transmission and reflection holograms, for example, which produce this reconstruction either in transmission or in reflection. If, for example, you are on the side of a transmission hologram opposite the light source and look at it, the object depicted appears three-dimensionally in front of you. With a reflection hologram, you preferably have to be on the same side as the light source. Reflection holograms preferably have a wavelength-selective efficiency to bend the light in a certain direction (along a certain 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 image produced, particularly the three-dimensional image. However, the person skilled in the art knows from the context what is meant by the term "hologram".

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

The use of these HOEs for beam shaping is particularly practical for HUDs. Since there is a great deal of freedom in the type of beam shaping required and little dependence on the dimensions of the HOE, the desired beam adjustment can be achieved without taking up a lot of installation space. This aspect is particularly interesting for motor vehicles, where installation space is often limited for a variety of reasons. In addition, aberrations can be reduced and/or corrected using HOEs. The 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 the content of which is hereby incorporated into this application.

With head-up displays, it is essential to redirect or even suppress interfering reflections from the sun, which are reflected by components of the HUD towards the driver and can blind them. This effect occurs not only in classic systems, but also in holographic HUDs. In comparison to classic HUDs, however, interfering reflections can also occur due to diffraction on the holograms. In particular, it can happen that 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.

So-called glaretraps for beam deflection are already known in the prior art, which enable ambient light to be deflected in the direction outside the eyebox. However, these are not suitable, for example, for specifically suppressing interference reflections caused by diffraction on a holographic component of the HUD. Also, 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, which can be applied to components of the HUD. These AR coatings typically work by including 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. If reflections are to be suppressed over a wide spectral range and/or for any angle of incidence, several such layer systems must be placed on top of one another. This is complex and expensive. It must also be ensured that the power of the additional rays introduced into the HUD (which are not reflected) does not cause any 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 of anti-reflective coating on HUDs is not yet known.

Object of the invention:

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 safe operability of the HUD. It is also an object of the invention to provide an improved, safer HUD that is at the same time cost-effective and easy to manufacture.

Summary of the invention:

The object is solved by the features of the independent claims. Preferred embodiments of the invention are described in the dependent claims.

• - Bereitstellung eines HUDs
• - Bestimmung von mindestens einem Winkelbereich von auf das HUD einstrahlenden Umgebungslichtes, für den eine kritische Umlenkung vom HUD in die Eyebox stattfinden kann
• - Aufbringen mindestens einer Beschichtung auf das HUD, welche eingerichtet ist, die Umlenkung vom einstrahlenden Umgebungslicht aus dem bestimmten Winkelbereich zu minimieren.

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:

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

An 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 in order to minimize stray light in the user's field of vision.

Redirection can refer to any physical effect, such as scattering, which can change the direction of light. Redirection includes, for example, reflection, refraction and/or diffraction.

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

Preferably, the terms electromagnetic radiation and light are used synonymously in this document and refer in particular to electromagnetic radiation comprising the visible spectral range. However, the ultraviolet spectral range and the near infrared range can also be included. Preferably, light in this sense comprises a spectral range (indicated 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.

The eyebox comprises in particular an area or a volume from which the HUD is to be viewed. The eyes of at least one viewer can/should be located in 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. This is why it is also preferably referred to as a defined eyebox. The eyebox can, for example, have dimensions of 150 mm x 150 mm in an area.

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 observation can also take place in exceptional cases.

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

Provision of a HUD describes in particular the provision of all or the essential components required for the operation of a HUD. These include, for example, imagers, optical components (in particular for beam adjustment), beam trap, cover glass and/or glaretrap.

Since a HUD can be provided before it is installed, for example in a vehicle, the projection surface, which is often contained in a window permanently installed in the vehicle (e.g. windshield), does not have to be included. However, the provision of the projection surface can also be included in the provision of the HUD.

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

It is important during provision that the components of the HUD are provided (whether before or after installation) which are essential for the anti-reflective coating, i.e. on which or through which a critical deflection takes place. These are in particular optical components for beam adjustment (e.g. wavefront manipulator) and/or cover glass.

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 value. These are different embodiments of the invention, which are explained in more detail below.

Since not all ambient light is critically redirected from all directions, a core of the invention is that the at least one angle range from which critical redirection occurs is determined. Thus, the at least one angle range preferably does not include all angles from all possible directions. The determination can be made, for example, by calculation or simulation. Determination of the angle range can also be understood as synonymous with calculation, specification and/or output of the angle range. A simulation can be computer-implemented or carried out using a simulation setup.

A calculation can typically be computer-implemented. 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 when installed. Furthermore, certain physical equations and/or models can be assumed which specifically define the deflection and which partly take into account physical properties of the HUD components.

A simulation setup can include lighting that is used 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, a HUD installed in a vehicle can be illuminated from different directions in a time-resolved manner, and the corresponding measurement can also be carried out in order to be able to assign measured light to the incident light. A simulation setup can preferably be carried out 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 smaller than the original.

The at least one angle range can of course comprise several angle ranges. These angle ranges can also relate to several, for example orthogonal planes, in which they are each defined. In the different planes, the specific angle range can be the same or different. The angle range is determined in such a way that it is clearly defined for a person skilled in the art. The reference axis/plane can be, for example, 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. Alternatively, several angle ranges can be determined for each normal at different points on the surface. The determination of the angle range preferably comprises information about the reference axis or plane and about the component of the HUD for which the angle range was determined.

Another core of the invention is the subsequent application of at least one coating to the HUD, which is designed to minimize the deflection of the incoming ambient light from the specific angular range. This can be, for example, an AR coating that is 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, i.e., 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 be present in the different planes for a given angle around the reference axis. This can advantageously work for a broad spectrum, but is specifically designed for the at least one specific angular range and is therefore less complex. For example, fewer layers need to be included.

To ensure that the non-reflected radiation does not re-enter the eyebox in another way and/or leads to 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.

The coating is preferably applied to the at least one component of the HUD that provides the critical deflection. If several components of the HUD are involved in the critical deflection, the coating is applied to at least the component that the ambient light hits first.

The coating can be applied, for example, by applying, gluing, depositing and/or spraying. The coating can, for example, be in the form of a film before application and then glued on (in the correct orientation according to the specific angle range).

The process allows a coating to be applied specifically to the angle ranges for which an undesirable 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 a simpler structure to be created that is suitable for mass production. At the same time, the angle ranges only need to be determined once and therefore do not require a great deal of additional effort.

• - Herstellen der Beschichtung.

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

• - Producing the coating.

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

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

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 of the invention and can, for example, comprise a wavefront manipulator and/or a waveguide, in particular for beam expansion.

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 in the direction of the projection surface.

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.

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 in the direction of the projection surface.

In HUDs, especially in vehicles, aberrations occur due to the curvature of the projection surface and/or due to compact arrangements in a small installation space with potentially strong tilting of individual components relative to one another and correspondingly complex folded beam paths. The aberrations that can typically occur are, for example, distortion, defocus, tilt, astigmatism, curvature of the image plane, spherical aberrations, higher astigmatism and coma.

A wavefront manipulator is advantageously used to at least partially correct and minimize imaging errors and to provide an improved head-up display that can also be particularly compact. To do this, as the name suggests, the wavefronts of the light rays of the HUD are manipulated in a suitable manner.

The wavefront manipulator preferably comprises a holographic arrangement (the wavefront manipulator is therefore 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. The at least two holographic elements are also designed to be reflective for at least the spectral range diffracted by the holographic component for beam adjustment and preferably a focal angle and an angular spectrum. The holographic elements are preferably otherwise designed to be 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. A first holographic element preferably 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 preferably is 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 in the interaction between the first and second elements.

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 generated more easily from the color channels. By connecting two reflection holograms in series, a transmission arrangement can still be realized and the manipulation can be distributed across two holograms.

The at least one holographic arrangement is preferably designed for the diffraction of light of 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 of which diffracts light of a spectral range, and/or each holographic element can include a so-called multiplex hologram, which diffracts light of several 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 which is 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 for the RGB color space or a CMY color space. C stands for cyan, M for magenta and Y for yellow.

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.

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 with the exception of the spectral range for which they are designed.

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, one for the green spectral range and one for the blue spectral range, which are arranged one on top of the other in the order mentioned. The second holographic element can also have a hologram designed for the red spectral range, one for the green spectral range and one for the blue spectral range, which are also arranged one on top of 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 on top of 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 immediately adjacent to the hologram of the second holographic element recorded for the red spectral range.

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 fixed direction. For example, both holographic elements may have holograms arranged with respect to a fixed direction in the order RGB (R - hologram recorded with red light, G - hologram recorded with green light, B - hologram recorded with blue light), which are arranged together such that the hologram R of one holographic element is adjacent to the hologram B of the other holographic element. Any other, different arrangements are also possible, for example RGB adjacent or adjacent to GBR, etc.

In the above description, the holographic arrangement can preferably be understood as comprising two holographic elements which are 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 which has already been diffracted by the first holographic element. For this purpose, the first holographic element is advantageously located along the beam path behind the second holographic element. Each holographic element (or the at least one hologram comprised by it) can be designed for one or more spectral ranges.

For the purpose of manipulating wavefronts for more than one spectral range, it may alternatively be preferred that more than one pair of holographic elements is included, with a pair each 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 include 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 another pair of holographic elements arranged directly next to one another for the blue spectral range. These respective pairs are preferably also arranged directly one behind the other in the beam path.

The holographic arrangement can be designed 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 under a surface of a cover glass or another optical component that is already present.

In this way, no 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 and which is designed to reflect sunlight in a specified direction so that it is not reflected via the head-up display in the direction of the eyebox. In this design variant, the holographic arrangement and the glare trap are preferably designed with the same curvature and arranged directly adjacent to each other.

The holographic arrangement is advantageously designed for a plurality of incident angles and/or for a plurality of incident angle ranges that do not overlap. For example, different image planes in a HUD can be realized through the different angles or angle 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 several incident angles or angle spectra, e.g. by comprising several holograms each designed for an incident angle or an incident angle spectrum.

In a preferred variant, the wavefront manipulator according to the invention comprises at least one optical element which has a free-form surface, i.e. an optically effective free-form surface, and is designed to be arranged in the beam path between the imaging unit and the holographic arrangement. The optical element comprising the free-form surface contributes to an improvement in resolution through a corresponding design of the free-form surface and allows a targeted correction of imaging errors. In addition, the optical element takes up very little installation space due to the free-form surface. It therefore also contributes significantly to an improvement in the imaging quality of a compactly designed head-up display.

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

The wavefront manipulator is therefore an essential component of the HUD and, due to its functionality, is often arranged in such a way that its surface is exposed to ambient light and this can generate undesirable deflections of ambient light in the direction of the eyebox either directly or, for example, via further deflection on the projection surface. Applying a coating to a surface of the wavefront manipulator and/or a surface of a cover of the wavefront manipulator is therefore particularly advantageous.

In a further preferred embodiment of the invention, the method further comprises the determination of sub-areas and/or components of the HUD for which the critical deflection from the HUD into the eyebox can take place, wherein the coating is applied to the sub-areas and/or components. This means that not only angular ranges are determined during the determination, but also the components and/or sub-areas of the HUD from which the critical deflection can take place. In this case, the determination of sub-areas and/or components of the HUD can also be referred to synonymously as the calculation, determination and/or output of sub-areas and/or components of the HUD for which the critical deflection from the HUD into the eyebox can take place. By only determining the essential components and/or sub-areas of the HUD that are relevant for a critical deflection and therefore have to be coated afterwards, a particularly efficient anti-reflective coating of the HUD can be carried out.

In a further preferred embodiment of the invention, the incident ambient ambient light radiation is assumed which is collimated from an origin region in the direction of the HUD, with each sub-region of a surface of a hemisphere centered around the HUD, which is divided into several sub-regions, being assumed to be the origin region of the collimated radiation, with a spectral distribution preferably corresponding to a spectral distribution of a black body (preferably at least partially) and/or at least partially to the spectral distribution of the sun. The person skilled in the art knows where to find corresponding information in the literature on the spectral distribution of a black body or the sun.

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%.

This embodiment is also available in 3 in the description of the invention. The assumptions described are particularly suitable for simulating direct sunlight on the HUD or its sub-areas and/or components.

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

Depending on the assumed size of the sub-areas, this can also be assumed to be quasi-point-shaped and there can only be a single beam per origin area, which runs from the respective origin area in the direction of the HUD. This is preferably also included if it is said that the radiation from the origin area in the direction of the HUD is collimated.

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

The radiation is preferably assumed to be blackbody radiation with regard to its spectral distribution, for example in a temperature range from 1000 Kelvin (K) to 10000 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 in particular in a temperature range from 5000 K to 6500 K, e.g. 6000 K. The person skilled in the art knows how to approximate or calculate the spectral distribution of a blackbody.

Such radiation is easy to simulate and yet realistically depicts real ambient light.

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.

This embodiment, in which critical deflection is already provided by the fact that ambient light is deflected into the eyebox regardless of the intensity, can reduce or prevent the deflection of ambient light of any intensity. This makes it particularly effective to anti-reflectively coat a HUD.

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).

The average radiation intensity may be a value that can be routinely determined by a person skilled in the art, for example the luminance of an average clear sky of 8000 cd/ ^m2 (candelas per square metre).

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.

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.

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

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.

The wavefront manipulator is preferably designed for one or more spectral ranges, see above. This is preferably 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 a critical deflection) of this ambient light can also occur. It is therefore 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.

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

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

Moth eye structures are, 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 as 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 described and are suitable for improved anti-reflective coating.

Nanostructures are, for example, in Ashok K. Sood et al.: Nanostructured AR coatings for optoelectronic applications, Nova Science Publishers, 2015 Nanostructures are particularly effective as AR coatings.

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

These are particularly simple, cost-effective and efficient.

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%.

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

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

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

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% 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%.

Such a coating is specially designed to attenuate a specific angle range compared to other angle ranges and is therefore particularly efficient and cost-effective.

In a further preferred embodiment of the invention, the coating comprises a plurality of individually effective layer elements, each of which is designed 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.

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

This makes it particularly easy to produce a suitable layer.

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.

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 of the holographic component, e.g. towards the vehicle interior.

On the cover glass preferably means on the side of the cover glass that is the side of the cover glass facing away from the wavefront manipulator. In a vehicle, this is preferably the side of the cover glass that is oriented towards the vehicle interior and is visible to a user, e.g. the driver of the vehicle.

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

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

• - Bereitstellen eines HUDs
• - Bestimmung von mindestens einem Winkelbereich von auf das HUD einstrahlenden Umgebungslichtes, für den eine kritische Umlenkung vom HUD in die Eyebox stattfinden kann (durch ein computerimplementiertes Verfahren)
• - Aufbringen mindestens einer Beschichtung auf das HUD, welche eingerichtet ist, die Umlenkung vom einstrahlenden Umgebungslicht aus dem bestimmten Winkelbereich zu minimieren.

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

• - Providing 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 (by a computer-implemented method)
• - Applying at least one coating to the HUD which is designed to minimize the deflection of incoming ambient light from the specific angular range.

It is apparent to the person 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.

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

The so-called glare trap can usually be arranged at a position between a projection surface and other components of the head-up display (e.g. 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 in the direction of 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 the wavefront manipulator (preferably between this component and the projection surface), with the manipulator or the component in particular having the same curvature as the glare trap.

The cover glass can 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.

The beam trap is designed, for example, as an absorbing element and is advantageously arranged in such a way that it directly blocks ambient light, so that it cannot enter the eyebox either directly or after being redirected. At the same time, due to the requirements for the HUD user's clear view, this beam trap can preferably only be installed in areas of the HUD or its surroundings where it does not obstruct the user's clear view through the projection surface.

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.

Therefore, a combination of the above-mentioned elements can be used for additional improved anti-reflective properties.

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 intended 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.

The bandpass filter can advantageously be placed directly on the coating of the HUD, either above or below.

The beam path includes in particular the volume occupied by the rays used to operate the HUD. Typically, the beam path extends from the light source across all optical components of the HUD (e.g. beam guidance) to an eyebox of the HUD.

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/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 several spectral ranges diffracted for beam adaptation within which the beam-adapting function is fulfilled. The above-mentioned holographic wavefront manipulator is preferably a holographic component.

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

Beam shaping preferably means influencing the shape of the beam. Beam shaping can in particular include manipulating the wave fronts. 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.

Beam guidance or deflection describes in particular a deviation of the beam path from an undisturbed electromagnetic (light) beam, forced by an optical component. Beam guidance can, for example, include beam folding in order 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.).

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 purpose of the holographic component.

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.

Typically, the holographic component will be set up to carry out beam adjustment 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 in accordance with the desired functionality. In addition, 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 hits the holographic component. This direction can preferably also be described by an angle or an angular spectrum around this angle if there is more than one direction, which is usually the case with the planar extent of the optical components, a desired field of view and a beam guidance that is not perfectly collimated. Therefore, the holographic component typically has a centroid angle and/or an angular spectrum that matches the angle or angular spectrum from which the light to be diffracted strikes the holographic component.

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 given 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 carries out 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 several cutting planes with the centroid angle (or parallel to these) 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.

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.

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 range 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).

A bandpass filter preferably refers to a filter which is largely permeable to electromagnetic radiation in a spectral range. The frequency or wavelength ranges below and above the passband are preferably not passed through or are significantly attenuated.

In the sense of the invention, it may also be preferred that the bandpass filter used here allows 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 blocks or attenuates the radiation between these spectral ranges. This is particularly desirable if the holographic component diffracts more than one spectral range for beam adaptation.

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 designed to suppress visible light outside the at least first spectral range.

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 directly from the holographic component or in interaction with other components of the HUD in the direction of the eyebox 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 and thus generate diffracted light in a variety of directions. This is an inherent property of the diffraction grating and cannot be completely prevented.

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 of the at least first spectral range, it can be essentially prevented or suppressed that light from 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.

Because the bandpass filter preferably works 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 works in the direction after diffraction, for example. The bandpass filter therefore works primarily to suppress light from unwanted spectral ranges in the direction of the holographic component and to suppress 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 greatly reduced or eliminated.

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 radiating onto 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 it that has passed through the filter). The attenuation can be different 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.

It has been found that an attenuation of a factor of 10 can already achieve sufficient interference removal with low requirements for the bandpass filter. This solution is therefore particularly simple and cost-effective.

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

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.

Description of the invention:

• 1a und 1b zeigen Komponenten eines HUDs, welches als Projektionsoberfläche eine Windschutzscheibe aufweist.
• 2a-d zeigen aus verschiedenen Perspektiven zwei durch das Verfahren bestimmte, beispielhafte Winkel eines exemplarischen HUDs, für die eine kritische Umlenkung in die Eyebox stattfindet.
• 3 zeigt eine bevorzugte Ausführungsform der bei der Simulation getroffenen Annahmen.
• 4 zeigt Reflektionseigenschaften einer Mottenaugen-Antifreflektionsschicht, welche beispielhaft optimiert ist.
• 5a und 5b zeigen ein HUD mit einer Windschutzscheibe, welches zusätzlich eine Glare-Trap und eine Strahlfalle aufweist.
• 6 zeigt ortsaufgelöst die Intensität von umgelenkten Lichtstrahlen in die Eyebox für ein simuliertes HUD.
• 7 stellt die wesentlichen Verfahrensschritte des erfindungsgemäßen Verfahrens dar.

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.

• 1a and 1b show components of a HUD, which has a windshield as a projection surface.
• 2a -d show from different perspectives two exemplary angles of an exemplary HUD determined by the method, for which a critical redirection into the eyebox takes place.
• 3 shows a preferred embodiment of the assumptions made in the simulation.
• 4 shows reflection properties of a moth eye anti-reflective coating, which is exemplary optimized.
• 5a and 5b show a HUD with a windshield, which also has a glare trap and a beam trap.
• 6 shows the spatially resolved intensity of redirected light rays into the eyebox for a simulated HUD.
• 7 represents the essential process steps of the process according to the invention.

1a shows components of a HUD 1 in a perspective view, which has a windshield 3 as a projection surface 2. In addition to this, the holographic component for beam adjustment 23 is shown, in this case a waveguide for beam expansion, which is covered by a cover glass 5. The designated eyebox 6 of the HUD 1 is also shown. In this case, this can include, for example, an eye position of a driver. Sun rays can now be redirected by the components of the HUD 1 shown, in particular reflected, so that they find their way into the eyebox 6. An 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 be used to achieve particularly efficient anti-reflective coating by determining only those angle ranges from which the critical deflection can occur. A coating is then applied to minimize the critical deflection, which works specifically for the specific angle ranges.

1b shows a to the in 1a shown similar HUD 1 in a perspective view, which allows a somewhat more frontal view of the windshield 3. In addition to the already shown 1a In addition to the components of the HUD 1 shown, the components 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.

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 takes place. Ambient light 9 from the first angle 8` is 2a and 2 B shown, ambient light 9 from the second angle 8" in the 2c and 2d shown. The 2a and 2c show the HUD 1 sideways, with the respective angle 8', 8" in the figure level. The 2 B and 2d show ambient light 9 from the 2a or c shown angles 8', 8" 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 ultimately ends up in the eyebox 6 due to further reflection on the windshield 3. 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. In addition, the essential deflection within the HUD 1 takes place at this component, which subsequently ends up in the eyebox 6. The angular range of the incident light 9 is preferably measured in relation to the normal 7 to the wavefront manipulator 4 or cover glass 5. The portions of the simulated sunlight that end up in the eyebox 6 due to reflection, In the examples shown, 0.00983% ( 2c and 2d ) or 1.52% ( 2a and 2 B) This may not sound like much, but since even a very small amount of reflected sunlight in the eyebox 6 is perceived as disruptive and hindering when reading the HUD 1, even such a small amount should preferably be further minimized. For the purposes of the method, it can 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 the same as the angular range determined in the image plane, but in some cases also different.

3 shows a preferred embodiment of the assumptions made in the simulation. This advantageously simulates the radiation of direct sunlight, the critical deflection of which is considered to be particularly disruptive and in some cases even dangerous, not so much because of the intensity itself, but above all because of the restricted view of the HUD 1 and/or the traffic, for example. Some exemplary beam paths are shown here, e.g. 9' and 9". The areas 10' and 10" are shown as the original areas 10, each shown as points in a graphical approximation. These areas 10`, 10" are in turn sub-areas of a hemisphere centered around the HUD 1, which is only shown in part here (reference number 11). Since the HUD 1 in turn has a finite extension 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 on the basis of empirical values, theoretical considerations and/or on the basis of (e.g. several upstream) simulations. A preferred point of the component can again be used for the centering, 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 12 of the hemisphere is in the HUD 1, e.g. at the mentioned preferred point. 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 an origin region 10 is collimated in the direction of the HUD 1 preferably means that the beams of rays from each origin region 10 form a collimated beam of rays and run in the direction of the HUD 1, with the direction of the HUD 1 mainly running 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 of rays is shown, but only one beam in each case. Radiation from different origin regions 10 is obviously collimated in different directions. Each origin region 10 and the associated beam of rays 9 can correspond to a possible position of the sun and the associated beam of rays from the sun at different orientations of the vehicle.

4 shows reflection properties of a moth eye anti-reflective coating, which is optimized to minimize the deflection (here: reflection) from a certain angle range between 10° and 40°.

On the left side, a color code with different shades of gray (see right y-axis or right ordinate axis) shows the reflectivity in % depending on the incident wavelength (see x-axis or abscissa axis) and the angle of incidence (see left y-axis or left ordinate axis). It is visible that the (undesirable) reflectivity increases at larger angles of incidence and wavelengths, reaching values of 1% or more or 5% or more, which are already too large depending on the design. However, since it is known from the simulation that the specific angle range for a critical deflection is between 10° and 40°, this circumstance is not critical if the layer is applied correctly. At the same time, such a layer, which is applied on optimized for a smaller angle range, much more cost-effective, simpler and lighter.

On the right-hand side, the reflectivity in % (y-axis) for the angle range between 10° and 40° is shown as an example for the three wavelengths 450 nm (marked with circles), 532 nm (marked with triangles) and 650 nm (marked with crosses). Only for 650 nm does the reflectivity for an angle range between 35° and 40° exceed the potentially critical value of 1%. These wavelengths are also marked in the left-hand image by the corresponding symbols.

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

5a and b show a HUD 1 with a windshield 3. The embodiment shown also includes 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. First of all, some of the incident light rays 16 are directly blocked by the beam trap 15, which can be designed as an absorbing element, for example. They cannot therefore get into the eyebox 6. At the same time, due to the requirements for the HUD user's clear view, the beam trap 15 can only be installed in areas of the HUD or its surroundings where it does not obstruct the user's clear view to the outside 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 in such a way 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 reach the safety eyebox 17.

In particular, in conjunction with the method described in this document for anti-reflective coating of a HUD 1 by calculating certain angle ranges and correspondingly coating the HUD 1, an eyebox 6 free of unwanted ambient light rays can be achieved.

5a shows a side view of the HUD 1, 5b shows a perspective view. In the perspective view according to 5b In addition, the intensity distribution of redirected ambient light around and into the Eyebox 6 is shown. The magnitude of the intensity increases from dark gray (practically no intensity) to light gray or white.

This is again in 6 illustrates the spatially resolved (in millimeters - mm) intensity (irradiance in watts per square millimeter - W/mm^2, 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 5 It is clear that only below the eyebox 6 some of the diverted intensity reaches the safety area 17". This could be improved by further optimization, e.g. of the HUD geometry.

7 shows the main process steps again. In a first step 18, a HUD is prepared. In a next step 19, the angular ranges of ambient light shining on the HUD are determined for which a critical deflection from the HUD into the eyebox can take place.

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.

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

LIST OF REFERENCE SYMBOLS

1

Head-Up Display (HUD)

2

Projection surface

3

Windshield

4

Wavefront manipulator

5

Cover glass

6

Eye box

7

Normal for determining the angle range

8th

Angle within the specified angle range

9

Incident ambient light

10

Areas of origin

11

Section of the hemisphere

12

Center of the hemisphere

13

(Freeform) mirror

14

Glare trap

15

Beam trap

16

Part of the incoming light rays which is blocked by the beam trap

17

Safety area around the eyebox

18

Deploy HUD

19

Determination of the angle ranges

20

Producing the coating

21

Applying the coating

22

Image provider

23

Holographic component for beam adjustment

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• EP2022055513 [0009]
• EP2022066787 [0009]

Cited non-patent literature

• T. Lohmüller, M. Helgert, M. Sundermann, R. Brunner, J. P. Spatz: Biomimetic Interfaces for High-Performance Optics in the Deep-UV light range, Nano Letters, June 2008 [0081]
• Guanjun Tan et al.: Broadband antireflection film with moth-eye-like structure for flexible display applications, Optica, Vol. 4, No. 7, 678, July 2017 [0081]
• Ashok K. Sood et al.: Nanostructured AR coatings for optoelectronic applications, Nova Science Publishers, 2015 [0082]

Claims (14)

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) - Determining 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 eyebox (6) can take place - 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. Procedure according to Claim 1 , further comprising the following intermediate step: - producing the coating (20). 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). Method according to one or more of the preceding claims, further comprising the determination of 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. Method according to one or more of the preceding claims, wherein the incident 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 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. Method according to one or more of the preceding claims, wherein the critical deflection is defined by the fact that a beam or radiation can be deflected into the eyebox (6) or wherein the critical deflection is defined by the fact 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. Procedure 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 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 designed to realize an attenuation of the deflection from the specific angular range by at least 95%, preferably by 99%. Procedure 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) - Determining 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 take place (19) - Applying at least one coating to the HUD (1) which is designed to minimize the deflection of the incoming ambient light (9) from the determined angular range (21). 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 adaptation (23), in particular a holographic wavefront manipulator (4), wherein in a beam path between holographic At least one bandpass filter is arranged between the holographic component and the eyebox (6) provided on the HUD (1), the bandpass filter being 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.

Images