Head-up display for an aircraft

Abstract

A head-up display (10) for an aircraft is disclosed, the head-up display (10) comprising an eyebox (1), a projection unit (8) which comprises a picture generator (5), and a combiner (2) located in the beam path (11) between the picture generator (5) and the eyebox (1). The combiner (2) has a front side (16) and a rear side (17), and the beam path (11) runs from the picture generator (5) to the eyebox (1) through the rear side (17) and the front side (16) of the combiner (2).

Description

[0001] Head-up display of an aircraft

[0002] The present invention relates to a head-up display, in particular a head-up display of an aircraft, e.g. an airplane.

[0003] Head-up displays (HUDs) are now used in a wide variety of applications, including in aircraft viewing windows. In aviation, head-up displays are used to project image data into the pilot's field of vision. The light waves used to create a virtual image are guided from an imager or projector across a projection surface to an eyebox.

[0004] A head-up display typically comprises a picture generating unit (PGU) or a projector, also called an image generator, a projection surface, an eyebox, and a virtual image plane. The image generator or projector generates an image. The image is projected onto the projection surface and from there into the eyebox. The eyebox is a spatial area in which the projected image is perceived by a user or viewer as a virtual image. The virtual image plane, i.e., the plane on which the virtual image is generated, is located on or behind the projection surface.

[0005] When a user looks through the projection surface of a head-up display, they see a coupled or mirrored "virtual image" superimposed on their image of the real world ("real image"). This allows the flight information displayed in the virtual image and the real world to be viewed simultaneously, without the pilot having to lower their gaze to look at a display on the instrument panel. Projected information on attitude and heading is displayed in a manner consistent with (i.e., correctly scaled and aligned with) the real world.

[0006] This superposition is achieved by a beam combiner, which is transparent to ambient light and also directs a beam of light generated by an external imager into an eyebox, which may contain the user's eye. The eye perceives this beam as a virtual image.

[0007] In the context of aircraft, a particular challenge is integrating HUD components into the available cockpit space without restricting or obstructing the pilot. One approach to this is to integrate HUD components in the space behind a given display and instrument panel of the aircraft.

[0008] Against this background, the object of the present invention is to provide a head-up display, in particular for a vehicle, e.g., an aircraft. This object is achieved by a head-up display for an aircraft according to claim 1. The dependent claims contain further advantageous embodiments of the invention.

[0009] The head-up display according to the invention, in particular for an aircraft, e.g., an airplane or helicopter, comprises an eyebox, a projection unit comprising an imager, and a combiner arranged in the beam path between the imager and the eyebox. An imager is understood to be a projector or an image-generating device. A combiner is understood to be a beam combiner as described above. The head-up display according to the invention is designed for aviation applications, in particular for installation in the cockpit of an aircraft, e.g., an airplane or helicopter. The head-up display according to the invention can also be designed for other applications.

[0010] The combiner has a front side, e.g., a front side located on the eyebox side, and a back side, e.g., a back side located on the imager side. The beam path runs from the imager to the eyebox through the back side and the front side of the combiner. In other words, the combiner is designed to be transmissive overall for light emitted from the imager to the eyebox. Furthermore, the combiner is preferably also designed to be transmissive, or at least predominantly transmissive, for ambient light.

[0011] The HUD according to the invention has the advantage that, thanks to the transmissive projection provided by the combiner, it can be integrated into the eyebox in the installation space behind a display and / or instrument panel. This reduces the required installation space and enables a spatially advantageous arrangement in otherwise rarely used areas of the instrument panel.

[0012] The distance between the center of the eyebox and the combiner is preferably between 150 mm and 450 mm. This is the preferred and most favorable range for aerospace applications.

[0013] Furthermore, the head-up display can be designed to project a virtual image from the center of the eyebox to a distance of at least 10 m. It is thus projected into a virtual image plane at a distance of 10 m or more from the center of the eyebox. Preferably, the projection is directed toward infinity with nearly parallel beams. This allows the perception of the projected image in a relaxed state for the eyes.

[0014] The head-up display can have a field of view (FOV) of at least 20 degrees in the horizontal direction, i.e. an azimuthal solid angle range of 20 degrees relative to the eyebox, and / or at least 15 degrees in the vertical direction, i.e. a meridional solid angle range of 15 degrees relative to the eyebox.

[0015] As mentioned above, the combiner is preferably designed to be transmissive in the line of sight or in a central viewing direction from the eyebox. It is therefore positioned in the line of sight relative to the eyebox and allows an unobstructed view of the surroundings.

[0016] The head-up display can be designed to project, for example, exclusively single-color or monochrome light into the eyebox. For aviation applications, it is advantageous if the head-up display is designed to project exclusively monochrome, preferably green, light into the eyebox.

[0017] For example, the combiner can have an optical effect, in particular a diffractive effect and / or a refractive power, in a spectral range with a full width at half maximum of 50 nm, in particular a maximum of 30 nm, preferably a maximum of 15 nm, e.g. a maximum of 2 nm. The combiner is preferably designed to be diffractive. The spectral range is preferably in the green spectral range, i.e. in the range between 500 and 565 nm. To optimally ensure unobstructed visibility through the combiner, it can have an optical effect, in particular a diffractive effect and / or a refractive power, exclusively in a green spectral range. Outside of this spectral range, the combiner allows an unobstructed view of the outside world or surroundings.

[0018] In an advantageous and presently preferred variant, a reflective deflecting element is arranged in the beam path between the projection unit and the combiner. In other words, the deflecting element is designed to reflect the beam path from the projection unit to the combiner. This has the advantage that the projection unit can be integrated in a geometrically very flexible manner into the installation space behind an instrument panel of an aircraft, i.e., it can also be arranged in a concealed manner, for example. As already mentioned, the projection unit can be designed to be integrated into the installation space behind a display or instrument panel of an aircraft, e.g., an airplane.Additionally or alternatively, the projection unit can have an optical axis or a radiation direction from the image generator to a projector cover, i.e. an optical axis within the projection unit, which is arranged at an angle of between 60 degrees and 90 degrees with respect to a viewing direction or a central viewing axis, in particular a straight-ahead direction, e.g. with respect to the aircraft, from the eyebox or with respect to a direction running perpendicular to a longitudinal center plane of the eyebox. In other words, the projection unit in this variant is designed to project vertically with respect to an upper side of an instrument panel cover. This enables an arrangement that is favorable from an installation space perspective, e.g. a hidden arrangement, of the projection unit behind a display or instrument panel.

[0019] The deflection element is preferably designed to be transmissive in the direction of view emanating from the eyebox. It can therefore be positioned in the direction of view relative to the eyebox, allowing an unobstructed view of the surroundings. This has the advantage and opens up the options of arranging the deflection element in front of or on a viewing window, e.g., an aircraft windshield, or integrating it into a viewing window, e.g., an aircraft windshield.

[0020] For example, the deflecting element can have an optical effect, for example reflective properties and / or optical refractive power, in a spectral range with a half-width of a maximum of 50 nm, in particular a maximum of 30 nm, preferably a maximum of 15 nm, e.g. a maximum of 2 nm. In one variant, the deflecting element is designed to be diffractive. The spectral range is preferably in the green spectral range, i.e. in the range between 500 and 565 nm. To optimally ensure unobstructed visibility through the deflecting element, it can have an optical effect, for example reflective properties and / or optical refractive power, exclusively in a green spectral range. Outside of this spectral range, the deflecting element allows an unobstructed view of the outside world or surroundings.

[0021] The deflection element may comprise a dielectric mirror and / or at least one hologram. For example, the deflection element may comprise a volume hologram and / or a relief hologram and / or a reflective relief hologram with a spectrally selective dielectric coating.

[0022] In a further variant, the projection unit comprises a projector cover, which is arranged in the beam path between the imager and the combiner, in particular between the imager and the deflection element, and which has an optical effect. The projector cover is preferably designed as a transmissive cover element. It has, for example, a front and a back, with the beam path passing through both. The optical effect can be refractive power or another imaging or beam-shaping or image-shaping or wavefront-shaping effect. The projector cover can be diffractive to achieve the optical effect. A refractive design is also possible.

[0023] The combiner and / or the deflecting element and / or the projector cover can be designed to deflect and / or focus the beam path. In other words, they can have an imaging, e.g. focusing, and / or beam-deflecting optical effect. In particular, the combiner and / or the projector cover and / or the deflecting element can be designed to deflect the beam in a horizontal and / or vertical direction or, in other words, in a radial direction with respect to a direction running perpendicular to a center plane of the eyebox. The described variants enable flexible positioning of the projection unit in the cockpit of an aircraft. In a further variant, the combiner and the deflecting element can be positioned with respect to a viewing direction, e.g.They can be arranged radially offset from one another, i.e., upwards or downwards and / or to the left or right, with a straight line in relation to the aircraft, or a central viewing axis extending from the eyebox or in a direction perpendicular to a center plane of the eyebox. In other words, they can be arranged horizontally and / or vertically offset from one another. These variants also allow for flexible positioning of the projection unit in the cockpit of an aircraft.

[0024] Furthermore, the projection unit can comprise an optical arrangement, such as optics or an optical system, which is arranged in the beam path between the imager and the combiner, in particular between the imager and the projector cover. The optical arrangement can have an optical effect. The optical effect can be, for example, refractive power or another imaging, beam-shaping, image-shaping, or wavefront-shaping effect. This allows the light beam to be directed in the desired direction and aberrations to be corrected. The optical arrangement can comprise reflective, refractive, and / or diffractive optical elements.

[0025] The combiner and / or the deflection element and / or the projector cover can be designed to deflect the beam in a horizontal and / or vertical direction, e.g. in relation to the eyebox or the direction of view. This allows the position of the individual components of the HUD to be very well adapted to the available installation space. Furthermore, the eyebox can have a longitudinal center plane. The longitudinal center plane is understood to be the center plane extending perpendicular to the direction of view or a central viewing axis, i.e. a plane bisecting the eyebox in the longitudinal direction. An image of the longitudinal center plane can be projected onto the projector cover. This projection can have an image scale between 2:1 and 1:3. The combiner and / or the projector cover preferably comprise a holographic optical arrangement.The holographic optical arrangement can comprise at least two holographic elements arranged directly one behind the other in the beam path, with a first holographic element being assigned to a second holographic element for reflection. In other words, no further optical element or component is arranged between the at least two holographic elements. For example, the first holographic element and the second holographic element can be spaced apart by a maximum of 15 mm.

[0026] The holographic elements of the holographic optical arrangement can be enclosed between two transparent supports or applied to the opposite outer surfaces of a transparent support. The supports can preferably be made of glass or comprise glass.

[0027] The combiner and / or the projector cover can be provided with an optically effective coating, for example an anti-reflective layer, on the outer surfaces.

[0028] The at least two holographic elements are designed to be reflective, for example, for at least one specified wavelength and a specified angle of incidence. Light waves of the at least one specified wavelength and the specified angle of incidence are thus efficiently diffracted. Furthermore, the holographic elements are preferably designed to be transmissive, in other words, transmissive for wavelengths that do not correspond to the at least one specified wavelength and have an angle of incidence outside the specified angle of incidence.

[0029] Preferably, a first holographic element comprises at least one hologram, which is assigned to a hologram of a second holographic element for reflection. In other words, the at least two holographic elements are configured such that light of at least one wavelength and at least one angle of incidence reflected by a first holographic element is reflected by the second holographic element.

[0030] The use of reflection holograms has the advantage that the intrinsic properties of reflection holograms can be utilized. These have efficiency curves that fundamentally differ from transmission holograms, whereby the efficiency curves of reflection holograms offer wavelength selectivity, which can, among other things, prevent the formation of double images. Due to the otherwise transmissive design and the use of reflection holograms, filter effects between the holograms are reduced or avoided. Preferably, the at least two holographic elements are arranged directly one behind the other in the beam path such that light entering the wavefront manipulator is reflected by a first of the holographic elements, and the light reflected by the first of the holographic elements is reflected by a second of the holographic elements.

[0031] The at least one holographic arrangement is preferably designed for the diffraction of light of only one wavelength or a narrow wavelength range.

[0032] The use of two at least partially reflective holographic elements arranged directly one behind the other has the advantage that, particularly in connection with a head-up display, the image quality can be significantly improved through the individual design of the holographic elements. The holographic elements take up almost no installation space, so that high image quality can be achieved even with only a small amount of available installation space. The holographic arrangement achieves, in particular, a high refractive power, comparable to the refractive power achieved, for example, by a transmissive optical component. The high refractive power allows the light to be deflected at a large angle, e.g. horizontally and / or vertically, which in turn opens up a wide variety of arrangement options.

[0033] Compared to transmission holograms, reflective holograms offer a wider angular spectrum for a defined wavelength with high efficiency and higher wavelength selectivity. The holographic arrangement thus enables a large field of view (FOV) with simultaneous high efficiency, making it suitable for applications with a large field of view and large numerical aperture. Further possible applications include head-up displays with curved projection surfaces, such as head-up displays for windshields and viewing windows in general.

[0034] A further advantage achieved by the holographic arrangement is that due to the high diffraction angle of the holographic arrangement, the proportion of light from unused diffraction orders that is reflected into the eyebox is reduced.

[0035] The holographic elements can be designed as volume holograms or relief holograms.

[0036] In a preferred variant, the first holographic element and / or the second holographic element are designed as volume holograms and have a refractive index modulation of at least 0.02, in particular at least 0.03 or 0.04, e.g., more than 0.05. In this way, a short distance, e.g., a distance between 150 mm and 450 mm, from the combiner to the eyebox and / or a large field of view (FOV) can be realized.

[0037] In a preferred variant, the first holographic element and / or the second holographic element are designed as freeform holograms. The respective holographic element can thus contribute to an improvement in resolution through a corresponding design of the freeform phase surface and allows for targeted correction of imaging errors. This also significantly contributes to improving the image quality of a compact head-up display.

[0038] In a hologram, the local beam deflection is determined by the spatial line density distribution. The line density distribution of the hologram results from the gradient of the local phase of the phase surface.

[0039] In the broader sense, a freeform phase surface is understood to be a non-trivial continuously differentiable function that can be represented, in particular, by means of a set of orthogonal basis functions or region-defined functions, in particular twice continuously differentiable region-defined functions. Examples of suitable orthogonal basis functions are polynomials, Zernike polynomials, or Chebyshev polynomials. Examples of suitable region-defined functions are piecewise polynomial functions (in particular, polynomial splines, such as bicubic splines, higher-order splines of fourth degree or higher, or polynomial non-uniform rational B-splines (NURBS)). In particular, a freeform phase surface does not need to exhibit axial symmetry or point symmetry.

[0040] A freeform hologram has been exposed to freeform wavefronts. Irradiation with a wavefront generates a defined freeform wavefront. This allows for manipulation of the wavefront with a high number of degrees of freedom. This is advantageous for correcting aberrations and for beam guidance and beam shaping. The holographic arrangement, in particular at least one of the holographic elements, can be designed, for example, to transform one freeform wavefront into another.

[0041] At least one hologram can be recorded or exposed with waves that have at least one freeform wavefront. This allows various aberrations to be corrected and the image quality to be improved. Because such a design allows light to be transformed with any wavefront, such as that generated using freeform surfaces, the number of components with freeform surfaces, such as lenses and / or mirrors, can be reduced. Plane waves and / or spherical waves can also be used to expose the holograms. By using the simplest possible wavefronts to expose the holograms, manufacturing costs can be reduced.

[0042] In another variant, the imager can include a diffuser with a location-dependent scattering function. The diffuser can be positioned close to the image plane of the imager, e.g., at a maximum distance of 10 mm. The diffuser provides a location-dependent illumination cone. The extent of the illumination cone is preferably designed to minimize the area illuminated by the HUD outside the volume of the eyebox.

[0043] In summary, the HUD according to the invention offers a powerful and optimally integrable system for aviation applications.

[0044] The invention will be explained in more detail below using exemplary embodiments with reference to the accompanying figures. Although the invention is illustrated and described in more detail by the preferred embodiments, the invention is not limited to the disclosed examples, and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention.

[0045] The figures are not necessarily detailed or to scale and may be enlarged or reduced in size for clarity of illustration. Therefore, functional details disclosed herein are not to be interpreted in a limiting sense, but merely as an illustrative basis for providing guidance to one skilled in the art to variously employ the present invention. As used herein, the term "and / or," when used in a series of two or more elements, means that any of the listed elements may be used alone, or any combination of two or more of the listed elements may be used. For example, if a composition is described that includes components A, B, and / or C, the composition may include A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

[0046] Fig. 1 shows schematically the beam path of a head-up display of an aircraft according to the invention in a side view.

[0047] Fig. 2 shows schematically the beam path of the head-up display shown in Figure 1 in a plan view.

[0048] Fig.3 shows schematically the beam path through a holographic arrangement of a combiner or a projector cover.

[0049] Figures 1 and 2 schematically show the beam path 11 of an aircraft head-up display 10 according to the invention. The beam path 11 is shown in a side view in Figure 1 and in a top view in Figure 2.

[0050] The head-up display 10 comprises a projection unit 8, a combiner 2 and an eyebox 1. The projection unit 8 comprises an image generator 5, a projector cover 3 and an optical arrangement 4, e.g. an optical system, arranged in the beam path 11 between the image generator 5 and the projector cover 3. The optical arrangement 4 can consist of conventional refractive or reflective optical elements or can comprise such elements. However, the optical arrangement 4 can also contain diffractive optical elements. Furthermore, the image generator 5 can comprise a diffuser (not explicitly shown), which is preferably arranged near the image plane of the image generator 5 and has a location-dependent scattering function. The diffuser can therefore provide a location-dependent illumination cone which limits the illuminated area to the eyebox 1.

[0051] The combiner 2 has a front side 16 and a rear side 17. The projector cover 3 has a front side 18 and a rear side 19. Both the projector cover 3 and the combiner 2 are designed to be transmissive. This means that light enters the respective component 2 or 3 through the rear side 17 or 19 and exits it through the respective front side 16 or 18.

[0052] A reflective deflecting element 20 is arranged in the beam path 11 between the projection unit 8, in particular the projector cover 3, and the combiner 2. The deflecting element 20 can have an optical effect, for example, a beam deflection relative to the specular direction and / or an imaging effect, e.g., a focusing effect.

[0053] The deflection element 20 can be configured to be diffractive. It can comprise at least one narrow-band (bandwidth less than 50 nm) dielectric mirror and / or a hologram, e.g., a volume hologram or a relief hologram. For example, the deflection element 20 can comprise a reflective volume hologram and / or a reflective relief hologram and / or a reflective relief hologram with a spectrally selective dielectric coating.

[0054] In the variant shown, the combiner 2 and the deflection element 20 are arranged horizontally and vertically offset from one another. In other words, the combiner 2 and the deflection element 20 are arranged radially offset from one another with respect to the viewing direction 9 or a direction or axis 13 running perpendicular to a center plane or center plane of the eyebox 1. A radial direction, which in the example shown runs horizontally, with respect to the direction or axis 13 is indicated in Figure 2 by an arrow 24. A direction not explicitly shown, running perpendicular to the direction 13 and the direction 24 would form a vertical direction. The offset between the combiner 2 and the deflection element 20 can be in this vertical direction and / or the horizontal direction 24.

[0055] Light emitted by the projection unit 8 via the projector cover 3 is reflected by the deflection element 20 to the combiner 2 and deflected by the combiner 2 towards the eyebox 1. If a user, preferably a pilot, looks from the eyebox 1 in the viewing direction 9 through the combiner 2, the user perceives an image projected by the projection unit 8 as a virtual image, for example at infinity. The field of view (FOV) provided by the head-up display 10 is indicated by arrows with the reference numbers 6 and 7. In the present case, a field of view 7 of at least 20° is achieved in the horizontal direction and a field of view 6 of at least 15° is achieved in the vertical direction. The distance between the center of the eyebox 1 and the combiner 2 is between 150 and 450 mm.

[0056] The combiner 2 is designed to be transmissive overall and has an optical effect, in particular refractive power, in a defined spectral range, preferably in the green spectral range, with a half-width of a maximum of 50 nm, in particular a maximum of 30 nm, preferably a maximum of 15 nm, e.g. a maximum of 2 nm.

[0057] The projection unit 8 shown can be integrated into an instrument panel of an aircraft. The combiner 2 can be suspended from the ceiling of a cockpit of the aircraft. The combiner 2 can have a rectangular base, for example, with beveled or rounded corners.

[0058] In the variant shown, the projection unit 8 is designed to project predominantly vertically. This means that an optical axis 12 of the projector unit 8, i.e., an optical axis 12 of the region of the beam path 11 between the imager 5 and the projector cover 3, runs essentially vertically. Thus, the optical axis 12 forms an angle 14 of at least 60°, preferably at least 70°, and 90° with a direction 13 running perpendicular to a longitudinal center plane of the eyebox 1.

[0059] By means of the combiner 2, the deflection element 20, and the projector cover 3, as shown in Figures 1 and 2, beam deflection is effected in both the horizontal and vertical directions. For this purpose, the combiner 2 and / or the projector cover 3 can comprise a holographic optical arrangement 15, which is preferably designed as a pair of reflective holograms 21, 22 arranged in a Z-arrangement, as a stack, or directly on top of one another. The beam path through such a holographic optical arrangement is shown schematically in Figure 3.

[0060] The holographic arrangement 15 shown as an example in Figure 3 comprises a first holographic element 21 and a second holographic element 22, which are arranged directly behind one another in the beam path, preferably adjacent to one another. For illustrative purposes, a distance 23 between the two holographic elements 21 and 22 is shown in Figure 3, which should actually be less than 15 mm, preferably less than 1 mm.

[0061] Light beams 11 radiated through the rear side 17, 19 initially transmit the first holographic element 21, are then reflected by the second holographic element 22, and radiated back to the first holographic element 21. The light reflected back by the second holographic element 22 toward the first holographic element 21 is reflected by the first holographic element 21 and then transmits the second holographic element 22 through the front side 16, 18.

[0062] The holographic elements 21 and 22 can be configured as volume holograms or relief holograms. When configured as a volume hologram, they can have a refractive index modulation of at least 0.02, preferably 0.04 or greater. The holographic elements 21 and 22 can have freeform holograms and can be designed, in particular, for correcting imaging errors and / or for beam guidance or beam deflection.

[0063] List of reference symbols:

[0064] 1 eye box

[0065] 2 combiners

[0066] 3 Projector cover

[0067] 4 optical arrangement

[0068] 5 imagers

[0069] 6 vertical field of view

[0070] 7 horizontal field of view

[0071] 8 Projection unit

[0072] 9 Viewing direction

[0073] 10 Head-up display

[0074] 11 Beam path

[0075] 12 optical axis

[0076] 13 Direction perpendicular to the center plane of the eyebox

[0077] 14 angles

[0078] 15 holographic arrangement

[0079] 16 Front

[0080] 17 Back

[0081] 18 Front

[0082] 19 Back

[0083] 20 deflection element

[0084] 21 first holographic element

[0085] 22 second holographic element

[0086] 23 Distance

[0087] 24 radial direction

Claims

Patent claims 1. Head-up display (10) of an aircraft, wherein the head-up display (10) comprises an eyebox (1), a projection unit (8) which comprises an image generator (5), and a combiner (2) arranged in the beam path (11) between the image generator (5) and the eyebox (1), characterized in that the combiner (2) has a front side (16) and a back side (17) and the beam path (11) runs from the image generator (5) to the eyebox (1) through the back side (17) and the front side (16) of the combiner (2).

2. Head-up display (10) according to claim 1, characterized in that a reflective deflection element (20) is arranged in the beam path (11) between the projection unit (8) and the combiner (2).

3. Head-up display (10) according to claim 1 or 2, characterized in that the projection unit (8) has an optical axis (12) within the projection unit (8), which is arranged at an angle (14) between 60 degrees and 90 degrees with respect to a viewing direction (9) from the eyebox (1) or with respect to a direction (13) running perpendicular to a longitudinal center plane of the eyebox (1).

4. Head-up display (10) according to one of claims 1 to 3, characterized in that the combiner (2) and / or the deflection element (20) are designed to be transmissive in the viewing direction (9) starting from the eyebox (1) and / or the combiner (2) and / or the deflection element (20) are designed to be diffractive.

5. Head-up display (10) according to one of claims 1 to 4, characterized in that the head-up display (10) is designed to project monochrome light into the eyebox (1).

6. Head-up display (10) according to one of claims 1 to 5, characterized in that the combiner (2) and / or the deflection element (20) have an optical effect in a spectral range with a half-width of maximum 50 nm.

7. Head-up display (10) according to one of claims 1 to 6, characterized in that the deflection element (20) comprises a dielectric mirror and / or at least one hologram.

8. Head-up display (10) according to claim 7, characterized in that the deflection element (20) comprises a volume hologram and / or a relief hologram and / or a reflective relief hologram with a spectrally selective dielectric coating.

9. Head-up display (10) according to one of claims 1 to 8, characterized in that the projection unit (8) comprises a projector cover (3) which is arranged in the beam path (11) between the image generator (5) and the combiner (2) or between the image generator (5) and deflection element (20) and which has an optical effect.

10. Head-up display (10) according to one of claims 1 to 9, characterized in that the combiner (2) and / or the deflection element (20) and / or the projector cover (3) are designed to deflect and / or focus the beam path (11).

11. Head-up display (10) according to one of claims 1 to 10, characterized in that the combiner (2) and the deflection element (20) are arranged radially offset from one another with respect to a viewing direction (9) starting from the eyebox (1) or with respect to a direction (13) running perpendicular to a center plane of the eyebox (1).

12. Head-up display (10) according to one of claims 1 to 11, characterized in that the distance between the center of the eyebox (1) and the combiner (2) is between 150 mm and 450 mm and / or the head-up display (10) is designed to project a virtual image from the eyebox (1) at a distance of more than 10 m and / or the head-up display (10) has a field of view of at least 20 degrees in the horizontal direction (7) and / or at least 15 degrees in the vertical direction (6).

13. Head-up display (10) according to claim 11 or 12, characterized in that the projection unit (8) comprises an optical arrangement (4) which is arranged in the beam path (11) between the image generator (5) and the combiner (2).

14. Head-up display (10) according to one of claims 1 to 13, characterized in that the combiner (2) and / or the projector cover (3) comprises a holographic optical arrangement (15) which comprises at least two holographic elements (21, 22) arranged directly one behind the other in the beam path (11), wherein a first holographic element (21) is assigned to a second holographic element (22) for reflection.

15. Head-up display (10) according to claim 14, characterized in that the first holographic element (21) and / or the second holographic element (22) are designed as a volume hologram and have a refractive index modulation of at least 0.02, and / or the first holographic element (21) and / or the second holographic element (22) are designed as a free-form hologram.

16. Head-up display (10) according to one of claims 1 to 15, characterized in that the image generator (5) comprises a diffuser with a location-dependent scattering function.

Images