Optical assembly and head-up display having multiple image planes - Patents.com

Abstract

Disclosed is an optical assembly (11) for a head-up display (10) on a projection surface (5), the optical assembly (11) comprising an image generating device (22) including at least one imaging unit (26, 27) and at least one wavefront manipulator (23) arranged in a beam path between the image generating device (22) and the projection surface (5). The optical assembly (11) is configured to generate virtual representations (8, 18) in at least two different image planes, the image generating device (22) having at least a first region (26, 28) and a second region (27, 29), and the image generating device (22) and the wavefront manipulator (23) are configured in combination to generate the virtual representation (8) in the first image plane from an image generated in the first region (26, 28) of the image generating device (22) and to generate the virtual representation (18) in the second image plane from an image generated in the second region (27, 29) of the image generating device (22).

Description

[Technical Field]

[0001] The present invention relates to an optical arrangement for a head-up display (HUD) and to a head-up display. [Background technology]

[0002] Head-up displays are currently used in the context of a variety of applications, particularly in connection with vehicle viewing windows, such as automobile windshields, windscreens, or even aircraft viewing windows, which typically have a curved surface that is used as a projection surface for the head-up display.

[0003] A head-up display typically includes an image generation unit (PGU) or projector, a projection surface, an eyebox, and a virtual image plane. An image is generated in the image generation plane by the image generation unit or projector. The image is projected onto the projection surface and from the projection surface into the eyebox. The eyebox is a plane or spatial region in which the projected image is perceivable by a viewer as a virtual image. The virtual image plane, i.e., the plane on which the virtual image is generated, is located above or behind the projection surface.

[0004] Conventional HUD systems have only one image plane and one image generation plane (see FIG. 1). Considering the market demands for future HUD systems, it will be necessary to realize multiple image planes with different image distances in the HUD. To reduce costs and maintain system stability, the components in the HUD should be installed as fixedly as possible, and moving parts should be eliminated. At the same time, the installation space requirement should not be substantially increased.

[0005] Against this background, it is an object of the present invention to provide an advantageous optical arrangement for a head-up display on a projection surface and in particular an advantageous head-up display that allows the generation of virtual images in different image planes.

[0006] These objects are achieved by an optical arrangement for a head-up display according to claim 1 and by a head-up display according to claim 15. The dependent claims contain further advantageous configurations of the invention. Summary of the Invention [Means for solving the problem]

[0007] An optical arrangement according to the invention for a head-up display on a projection surface comprises an image generating device and at least one wavefront manipulator arranged in a beam path between the image generating device and the projection surface. The image generating device comprises at least one image generating unit. The optical arrangement according to the invention is designed to generate virtual images in at least two different image planes, i.e., image planes at different image distances. In this context, the image distance is the distance between the image plane of the virtual image and the eyebox.

[0008] To generate at least two different image planes, the image generating device has at least a first region and a second region. In combination with each other, the image generating device and the wavefront manipulator are designed to generate a virtual image in the first image plane from an image generated in the first region of the image generating device, and to generate a virtual image in the second image plane from an image generated in the second region of the image generating device. In other words, the at least two different or offset image planes are located at offset distances from the eyebox or from the projection plane along the optical axis.

[0009] The optical arrangement according to the invention is advantageous in that multiple image planes with different image distances can be realized in the head-up display. In the process, the components required for this purpose can be securely attached to the head-up display. Therefore, no moving parts are required. This allows for a robust optical arrangement and therefore a correspondingly robust head-up display. Furthermore, the optical arrangement according to the invention can be produced cost-effectively and can optionally be retrofitted to existing head-up displays with little expense.

[0010] The first and second regions of the image generating device may have a common image generating plane. In other words, the image generating device may thus have only a single image generating unit or component, with only one, for example segmented, image generating plane. Alternatively, the first region of the image generating device may have a first image generating plane, and the second region of the image generating device may have a second image generating plane. In this variant, the first and second image generating planes may be different from each other. In particular, there may be two different components or image generating units, for example, arranged at offset distances from the wavefront manipulator. This variant is particularly suitable for retrofitting an existing head-up display with further image generating devices or units, thus realizing multiple image planes with different image distances in the head-up display.

[0011] The at least one wavefront manipulator preferably includes at least one holographic arrangement. The at least one holographic arrangement is preferably designed to diffract light at multiple wavelengths. For this purpose, multiple holograms, each diffracting light at one wavelength, and / or multiple holograms diffracting light at multiple wavelengths, can be arranged as a hologram stack. Additionally or alternatively, the at least one wavefront manipulator includes at least one optical element with a free-form surface. Advantageously, the optical element with the free-form surface is arranged in the beam path between the image generating device and the holographic arrangement. Multiple free-form surfaces may be present, for example, in the form of multiple corresponding optical elements or one optical element with multiple free-form surfaces. Each individual free-form surface may be designed for beam shaping of light emitted from a specific region of the image generating device and / or a specific image generating unit. For example, there may be a first image generating unit or first region and a first free form surface arranged in the beam path of light emitted from such first image generating unit or first region, and a second image generating unit or second region and a second free form surface arranged in the beam path of light emitted from such second image generating unit or second region.

[0012] At least the holographic arrangement and / or the further free-form surface element can realize an advantageous wavefront manipulator within a small installation space, which in particular corrects occurring image errors or aberrations. In particular, imaging aberrations such as distortion, defocus, tilt, astigmatism, curvature of the image plane, spherical aberration, higher-order astigmatism, coma, etc. can be corrected with the help of the holographic element and / or the free-form surface. The optical element including the free-form surface contributes to an increase in resolution due to the corresponding configuration of the free-form surface and enables targeted correction of imaging aberrations. Furthermore, since the optical element is a free-form surface, it takes up little installation space. In other words, the optical element also significantly contributes to improving the imaging quality of head-up displays with a compact configuration.

[0013] A freeform surface should be understood in a broad sense to mean a complex surface that can be represented by a domain-defined function, especially a domain-defined function that is twice continuously differentiable. Suitable examples of domain-defined functions are (especially piecewise) polynomial functions (especially polynomial splines, such as bicubic splines, splines of degree 4 or higher, or polynomial non-uniform rational B-splines (NURBS)). These should be distinguished from simple surfaces that can be described as circles along at least their principal meridians, such as spherical, aspherical, cylindrical, and toric surfaces. In particular, a freeform surface need not have axial or point symmetry, and different regions of the surface may have different values ​​for the mean surface power value.

[0014] In an advantageous variant, the wavefront manipulator comprises at least a first holographic arrangement and a second holographic arrangement, the first holographic arrangement being designed to generate a virtual image in a first image plane from an image generated in a first region of the image generating device, and the second holographic arrangement being designed to generate a virtual image in a second image plane from an image generated in a second region of the image generating device. In this way, a head-up display with multiple image planes at different image distances can be realized purely by a suitable configuration of multiple holographic arrangements, without requiring additional installation space.

[0015] In particular, the first holographic arrangement can be designed to diffract light at at least a first wavelength. For example, the first holographic arrangement can be designed to diffract light at three different wavelengths in a defined color space. The second holographic arrangement can be designed to diffract light at at least a second wavelength. For example, the second holographic arrangement can be designed to diffract light at three wavelengths in a defined color space, but these wavelengths are different from the wavelengths for which the first holographic arrangement is designed. In this case, the difference between the first and second wavelengths must exceed a defined limit. For example, the first holographic arrangement can be designed to diffract red light at a first wavelength, and the second holographic arrangement can be designed to diffract red light at a second wavelength that is slightly different from the first wavelength. For example, the two wavelengths of red light can differ from each other by at least 10 nanometers or at least 20 nanometers. Similarly, the first holographic arrangement and the second holographic arrangement can be designed to diffract green light and blue light at defined wavelengths for which the holographic arrangements are designed, the wavelengths of the individual colors again differing by a defined absolute difference value.

[0016] The at least one optical element comprising the holographic arrangement and / or the freeform surface can each be configured to be reflective and / or transmissive, thereby enabling the implementation of variable beam paths, in particular folded beam paths, in a small installation space. The reflective configuration of the optical element with the freeform surface is particularly advantageous in connection with head-up display applications with a compact configuration, since in this way the optical element can simultaneously contribute to the required beam deflection even at high angles of incidence without inducing additional image errors, in particular chromatic aberrations, during processing.

[0017] Preferably, the free-form surface is designed to at least partially correct at least one aberration or one imaging aberration, which may be at least one of the aforementioned imaging aberrations. The imaging aberration may be caused by the projection surface, in particular in the case of a curved projection surface, and / or may be caused by the image generation unit and / or by the shape of the beam path, for example in the context of a head-up display. Furthermore, the free-form surface allows the resolution and therefore the imaging quality to be optimized.

[0018] Preferably, the freeform surface has a surface shape derived from an imaging function that depends on at least one defined parameter. The at least one defined parameter may result from the envisaged application of the wavefront manipulator. For example, the radius of curvature of the windshield may be used as a parameter influencing the shape of the freeform surface. The optical element may have several freeform surfaces, in particular to be able to perform aberration corrections that are adapted to the shape of the respective application. For example, in the context of an automotive application, a specific selection or arrangement of the freeform surfaces used makes it possible to use a uniform wavefront manipulator that can be adapted to the specific shape of the windshield.

[0019] Advantageous properties and characteristics of holographic arrangements that can be used within the scope of the present invention are described below.

[0020] The holographic arrangement may include at least two holographic elements. The at least two holographic elements are preferably arranged directly in succession in the beam path. In other words, no further optical elements or components are arranged between the at least two holographic elements. Furthermore, the at least two holographic elements may be configured to be reflective for at least a defined wavelength and a defined range of angles of incidence. Otherwise, the holographic elements preferably have a transmissive design.

[0021] The use of two holographic elements arranged directly adjacent to each other and configured to be at least partially reflective has the advantage, particularly in relation to head-up displays, that imaging quality can be significantly improved by the individual configuration of the holographic elements. To this end, the holographic elements take up very little installation space, allowing a significant improvement in imaging quality to be achieved by the wavefront manipulator when only limited installation space is available, such as in head-up displays designed for automobiles. This holographic arrangement achieves high refractive power, particularly refractive power comparable to that achieved by optical components configured to be transmissive without chromatic aberration. Compared to transmission holograms, reflection holograms for defined wavelengths offer a wider angular spectrum with high efficiency and greater wavelength selectivity. As a result, color channels can be separated from each other despite a wide incidence angle spectrum. This holographic arrangement therefore simultaneously enables a large field of view (FOV) with high efficiency and is therefore suitable for both VR head-up displays (VR-virtual reality) and augmented reality head-up displays (AR HUDs) with large fields of view and large numerical apertures. Further application possibilities are offered by head-up displays with curved projection surfaces, for example head-up displays for the windscreens of vehicles, in particular motor vehicles, rail vehicles, aircraft or ships, and generally for observation windows.

[0022] 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, and further, high quality multi-color image representations can be produced.

[0023] Preferably, each of the at least two holographic elements includes several holograms, each hologram being recorded or generated at at least one defined wavelength. The holographic element may, for example, include several holograms, which may be arranged one above the other as a stack. As an example, the holographic element may have several, preferably multiple, monochromatic holograms. Alternatively, the holographic element may include at least one hologram recorded or generated at at least two defined wavelengths. Preferably, such holograms are recorded at three different wavelengths in a defined color space, e.g., configured as an RGB hologram or a CMY hologram, or as a hologram formed from multiple individual wavelengths in different color spaces. In the examples mentioned, R stands for red, G stands for green, B stands for blue, C stands for cyan, M stands for magenta, and Y stands for yellow.

[0024] Thus, at least one, and preferably two, of the at least two holographic elements may include at least two, and preferably three, holograms configured to be reflective at mutually different wavelengths. Additionally or alternatively, at least one, and preferably two, of the at least two holographic elements may include at least one hologram configured to be reflective at at least two, and preferably three, mutually different wavelengths. In other words, the holograms mentioned are recorded at corresponding, mutually different wavelengths.

[0025] The placement of the individual holograms of the holographic element or the overall holograms of the hologram arrangement can be used as a degree of freedom to avoid filtering effects between the holograms. The individual, mutually distinct holograms of the holographic element can be placed next to and / or behind each other with respect to a center line or central axis, which may coincide with the optical axis, or with respect to some other defined shape parameter of the holographic element.

[0026] The holographic arrangement can include a first holographic element and a second holographic element, with the holograms or all of the holograms in each holographic element being identical or configured identically except for the wavelength for which they are designed. In other words, the holograms or all of the holograms in the first holographic element can be configured identically and differ from each other only with respect to the wavelength for which they are designed. Similarly, the holograms or all of the holograms in the second holographic element can be configured identically and differ from each other only with respect to the wavelength for which they are designed.

[0027] Preferably, the first holographic element is arranged mirror-symmetrically with respect to the second holographic element with respect to the arrangement of the individual holograms. For example, the first holographic element can include a hologram recorded with red light, a hologram recorded with green light, and a hologram recorded with blue light, with these holograms arranged one above the other in the aforementioned order. The second holographic element can similarly include a hologram recorded with red light, a hologram recorded with green light, and a hologram recorded with blue light, with these also arranged one above the other in the aforementioned order. In the case of a mirror-symmetric arrangement, the first and second holographic elements are arranged one above the other or adjacent to each other, for example, such that the hologram of the first holographic element recorded with red light is arranged directly adjacent to the hologram of the second holographic element recorded with red light. Alternatively, the arrangement of the holograms of the first holographic element can be identical to the arrangement of the holograms of the second holographic element with respect to the defined direction. For example, both holographic elements may have holograms arranged in the order RGB (R - hologram recorded with red light, G - hologram recorded with green light, B - hologram recorded with blue light) with respect to a defined direction, and they are arranged opposite each other so that hologram R of one holographic element is adjacent to hologram B of the other holographic element. Any other mutually different arrangement is possible as well, for example RGB adjacent or adjacent to GBR.

[0028] In a further advantageous variant, the holograms of at least one holographic element are recorded with two design wavefronts, where at least one design wavefront of at least one hologram of the latter is identical in terms of wavelength and angle of incidence to at least one design wavefront of another hologram of one of the holographic elements, in particular the first and / or second holographic element. Using identical design wavefronts for different wavelengths has the advantage that the required holograms can be produced inexpensively and with high precision.

[0029] The jointly used design wavefronts are preferably defined as plane waves, which minimize filtering effects between different wavelengths and have the advantage, compared to the use of non-plane waves, that the positioning tolerances of the color-assigned holograms relative to one another can be more leniently selected, i.e., it is possible to vary the distance between the holograms along the optical axis and / or laterally, i.e., perpendicular to the optical axis, without adversely affecting the imaging quality.

[0030] The holographic arrangement, particularly at least one of the holographic elements, is preferably configured to convert a spherical wave into a plane wave. As a result, the holographic arrangement, particularly the holographic element, has a high refractive power without increasing the volume and thus the required installation space. Furthermore, the beam cross-section on the mirror can be reduced, thereby reducing both the size and the refractive power of the mirror. This is advantageous because the refractive power is better distributed within the system and is less sensitive to the tolerances of the refractive power. Furthermore, at least one of the holographic elements can be configured to convert a free-form wavefront into a plane wavefront or a spherical wave into a free-form wavefront. At least one hologram can be recorded or exposed with at least one free-form wave. As a result, various aberrations can be corrected, improving performance. With such a configuration, the number of components with free-form surfaces, such as lens elements and / or mirrors, can be reduced due to the fact that it is possible to convert light with any wavefront, such as that generated by a free-form surface.

[0031] The direction of incidence of the design wavefront for at least two holographic elements of the holographic arrangement can be used as a degree of freedom to avoid filtering effects between different wavelengths. The direction of incidence can also be selected to be different for each wavelength. Preferably, the design wavefront for at least two wavelengths, preferably the three wavelengths, is the same design wavefront for each holographic element, differing only in the wavelengths used.

[0032] The distance between the holograms and their thickness are negligible compared to the dimensions or extent of the wavefront manipulator or the optical arrangement including the wavefront manipulator. Therefore, the holographic arrangement is free from aberrations potentially caused by the extent in the optical axis direction. The design wavefront of the holographic element can further be used as a degree of freedom to compensate for material tolerances, for example, material shrinkage. In this case, the typical design wavefronts differ slightly from each other.

[0033] Preferably, at least two holographic elements are arranged at a distance of less than 1 mm, in particular less than 0.5 mm, preferably less than 0.1 mm from each other. This distance is preferably zero or negligible. As a result, firstly, a high imaging quality is achieved, and furthermore, the individual holographic elements do not have to be subsequently adjusted in terms of their position relative to each other.

[0034] The holographic arrangement may be configured in the form of a layer, film, or substrate, for example, in the form of a volume hologram or plate. Additionally or alternatively, the holographic arrangement may have a flat or curved surface. The holographic arrangement may be, for example, arranged on or above the surface of a cover glass or some other optical component that is already present. In this way, no additional installation space is required. For example, the wavefront manipulator may include an optical component that is configured to be transparent and designed to be arranged in the beam path between the holographic arrangement and the projection surface. In this case, the holographic arrangement may preferably be arranged on the surface (facing away from the projection surface) of the optical component configured to be transparent. Both the optical component configured to be transparent and the holographic arrangement may preferably be configured to be curved with the same curvature. The aforementioned optical component configured to be transparent may, for example, be a so-called glare trap, which is usually arranged between the windshield and the head-up display and is designed to reflect sunlight in a defined direction so that sunlight is not reflected towards the eyebox via the head-up display. In this configuration variant, the holographic arrangement and the glare trap are preferably configured with the same curvature and are arranged directly adjacent to each other.

[0035] Overall, the holographic elements allow the wavefront manipulator to deflect the light used to a much greater or more extreme degree than is possible with conventional refractive optical components, and furthermore, to project high quality multicolor images.

[0036] The image generating device advantageously includes at least one plane, i.e., a spatially extended plane, designed to emit light in a defined emission angular range with a maximum bandwidth defined in relation to the wavelength of the emitted light. Preferably, each light-emitting point in the plane emits light in the form of a scattering lobe or in a defined angular range. This can be achieved, for example, by using a diffuser. Preferably, the image generating device is designed to emit laser light, in particular a laser beam. Advantageously, the image generating device is designed to emit laser light in at least two, preferably at least three, different wavelengths. This preferably involves three different wavelengths in a defined color space, for example, red, green, and blue, or cyan, magenta, and yellow. Because holographic elements are more sensitive in relation to wavelength than other optical components, such as mirrors and lens elements, it is advantageous if the image generating device is configured to have a maximum bandwidth defined in relation to the wavelength of the emitted light.

[0037] The optical arrangement according to the invention preferably has a volume of less than 10 liters, in other words occupies an installation space of less than 10 liters. This optical arrangement provides in particular a head-up display that is made very compact, i.e., occupies only a small installation space, while at the same time ensuring very high imaging quality in multiple image planes. The optical arrangement according to the invention is suitable for retrofitting, for example, automobiles, aircraft, or VR installations, such as VR glasses.

[0038] In a further variant, the wavefront manipulator, in particular the at least one holographic arrangement, is designed to spectrally separate images in different image planes or to separate such images by generating different polarization states for the various image planes.

[0039] The image generation device may include multiple image generation units. In particular, a first image generation unit may comprise a first region of the image generation device, and a second image generation unit may comprise a second region of the image generation device. In other words, each image generation unit may be designed to generate a virtual image in a defined image plane. Such a configuration allows, in particular, a simple and cost-effective retrofitting of an existing head-up display.

[0040] Furthermore, the wavefront manipulator may include multiple holographic arrangements, each designed to generate a virtual image in a defined image plane. Similarly, the wavefront manipulator may include multiple optical elements having a freeform surface and designed to generate a virtual image in at least a defined image plane. These variations also allow existing head-up display systems to be easily and cost-effectively retrofitted with suitable holographic arrangements and / or freeform elements in order to realize a head-up display with two or more image planes at different image distances.

[0041] The head-up display according to the present invention includes the optical arrangement according to the present invention as described above, thereby having the features and advantages already defined above. The projection surface can be the surface of a windshield or an observation window of a vehicle. The projection surface or the observation window can have a curved configuration. The vehicle can be a car, an airplane, a rail vehicle, or a ship. The observation window can be glasses, in particular smart glasses, a head-wearable transparent screen, AR glasses or an AR helmet, a visor, or an eyepiece of a microscope.

[0042] The head-up display according to the present invention allows for the generation of virtual images with a large field of view in multiple image planes. For example, it is possible to generate a rectangular virtual image with a field of view of at least 10°, preferably at least 15° x 5° (FOV: 15° x 5°), and observable at a certain distance from the eyebox, for example, a distance of 2 to 12 meters. The eyebox may have dimensions of up to 150 mm x 150 mm.

[0043] The brightness and uniformity of the virtual image can be optimized by the corresponding design wave of the holographic element. Furthermore, the uniformity of the degree of whiteness can be set by setting the coefficient of color mixing, for example, setting the RGB color space in the image generation unit. Hereinafter, the present invention will be described in more detail based on exemplary embodiments with reference to the accompanying drawings.

[0044] Although the present invention has been more particularly shown and described in detail by preferred exemplary embodiments, the invention is not limited to the disclosed examples, and those skilled in the art can derive other variations therefrom without departing from the scope of protection of the present invention.

[0045] The drawings are not necessarily accurate to scale in all details and may be expanded or reduced for purposes of clarity. As such, the functional details disclosed herein should not be understood as limiting, but merely as an illustrative basis to provide guidance to those skilled in the art for using the present invention in various ways.

[0046] As used herein, the term "and / or," when used in a series of two or more elements, means that any of the listed elements can be used alone, or any combination of two or more of the listed elements can be used. For example, if a composition containing components A, B, and / or C is recited, the composition can include A alone; B alone; C alone; a combination of A and B; a combination of A and C; a combination of B and C; or a combination of A, B, and C. [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 1 shows a schematic side view of the beam path of a head-up display with one image plane for a motor vehicle windshield. [Figure 2] 1 shows a schematic side view of the beam paths of a head-up display according to the invention with two image planes for a motor vehicle windshield; FIG. [Figure 3] 1A-1C show schematic diagrams of beam paths for different object planes with the same optical components. [Figure 4] 1A and 1B show schematic diagrams of beam paths for the same object plane with different optical components. [Figure 5] 1 shows a schematic representation of a first embodiment variant of a head-up display according to the invention, with an optical arrangement according to the invention; [Figure 6] 3 shows a schematic representation of a second embodiment variant of a head-up display according to the invention, with an optical arrangement according to the invention; [Figure 7] 3 shows a schematic representation of a third embodiment variant of a head-up display according to the invention, with an optical arrangement according to the invention; FIG. [Figure 8] 4 shows a schematic view of a fourth embodiment variant of a head-up display according to the invention, having an optical arrangement according to the invention; FIG. [Figure 9] FIG. 1 shows a schematic diagram of a first variant of a holographic arrangement. [Figure 10]FIG. 10 shows a schematic diagram of a second variant of the holographic arrangement. [Figure 11] FIG. 1 shows a schematic diagram of a beam path within a holographic arrangement. DETAILED DESCRIPTION OF THE INVENTION

[0048] 1 shows a schematic diagram of a beam path of a head-up display 10 having an image plane. The head-up display 10 comprises an image generation unit 1, a projection surface 5, for example in the form of a windshield of a motor vehicle, and a wavefront manipulator 7. The projection surface 5, for example the windshield, may be configured with a curved shape. For vehicular applications, the image generation unit 1 and the wavefront manipulator 7 are preferably arranged in an integrated manner in an attachment (not shown). The head-up display 10 is configured to generate a virtual image 8 on the projection surface 5, in particular on the surface of the windshield or in the external area of ​​the vehicle, for example in the direction of travel behind the surface of the windshield. The beam path is identified by the reference sign 6.

[0049] In the configuration variant shown, the wavefront manipulator 7 comprises a holographic arrangement 4 and an optical element 3 which is configured to be reflective, has a freeform surface and is arranged in the beam path 6 running from the image generating unit 1 between the image generating unit 1 and the holographic arrangement 4. The optical element 3 is preferably configured as a freeform surface mirror.

[0050] The image generation unit 1 emits light waves in the direction of a wavefront manipulator 7. The image information output by the image generation unit 1 or the image generated is identified by an arrow with reference sign 2, while its virtual image is identified by reference sign 8. The wavefront manipulator 7 is used to correct imaging aberrations and, optionally, to extend the beam path. The wavefront manipulator 7 guides the light waves in the direction of a projection plane 5, in particular a curved projection plane. At the projection plane 5, the light waves are reflected in the direction of an eyebox 9. In this case, the eyebox 9 forms an area in which the user must or can be positioned in order to be able to perceive the virtual image 8 generated by the head-up display 10. The image plane is defined by the image distance of the virtual image 8.

[0051] 2 shows schematically the beam paths of a head-up display 10 according to the invention having two image planes, the head-up display 10 comprising an optical arrangement 11 according to the invention. The first image plane corresponds to the image plane defined by the virtual image 8. The second image plane is defined by a further virtual image 18. The corresponding beam paths are identified by the reference sign 16. The first and second image planes have offset image distances. In this case, the beam paths 6 and 16 may have a spatial overlap.

[0052] 3 and 4 illustrate the optical principles underlying the present invention. Considering an optical system in a simplified manner as a single lens element 12 with a focal length f and an optical axis 13, an imaging situation arises between objects (image generators) 14, 17 and images (virtual images) 15, 19, as shown in FIG. 3. FIG. 3 shows the beam paths of the images 15, 19 for different object distances or object spacings s1, s2 with the same optical component 12. If the same system (only one focal length f) is used for either different object spacings (s1 and s2) or different image spacings (s1' and s2'), two different image planes arise. That is, it is not possible to realize two image spacings (s1' and s2') with sufficient quality by a single optical system with the same object spacing (PGU).

[0053] If the same image generation plane of the image generation unit 1 is used for both virtual images 15 and 19, two different imaging systems 12a and 12b are required. This means that the components 12a and 12b and the positions of the components 12a and 12b may be different, as shown in Figure 4. Figure 4 shows the beam paths of images for the same object plane with different optical components 12a and 12b.

[0054] Modified embodiments of the present invention will be described in more detail below with reference to Figures 5 to 8. Each of Figures 5 to 8 shows a head-up display 10 according to the present invention, which has an optical arrangement 11 according to the present invention and a projection surface 5. The projection surface 5 can be, for example, a windshield or an observation window.

[0055] The optical arrangement 11 comprises in each case an image generating device 22 and a wavefront manipulator 23 arranged in the beam path between the image generating device 22 and the projection plane 5. In the variant shown, the wavefront manipulator 23 comprises in each case a holographic arrangement 24 and at least one optical element 25 with a freeform surface.

[0056] In the variant shown in FIG. 5 , the various image planes are realized by two image generation units 26 and 27, where the first image generation unit 26 forms a first region of the image generation device 22 and the second image generation unit 27 forms a second region of the image generation device 22. The first image generation unit 26 and the second image generation unit 27 have respective image generation planes or object planes that are different from each other. In the variant shown, the image generation plane of the second image generation unit 27 is arranged closer to the freeform surface element 25 than the image generation plane of the first image generation unit 26. In the variant shown in FIG. 5 , the same holographic arrangement 24 and the same optical element 25 configured as a freeform surface mirror are used for the two generated virtual image planes. Furthermore, the wavelengths of the utilized color space, e.g., red, green, blue (RGB), are identical for the two generated image planes. In the example shown, the rays of the beam path emerging from the first region 26 of the image generating device 22 are identified by an arrow with the reference sign 31, and the rays of the beam path emerging from the second region 27 of the image generating device 22 are identified by an arrow with the reference sign 32. As an alternative to the RGB color space, three wavelengths in different color spaces can be used. Configurations with fewer than three different wavelengths, for example only one wavelength or only two wavelengths, are also possible. As is clear from FIG. 5, spatial overlapping of the beam paths is also possible.

[0057] 6 differs from the variant shown in FIG. 5 in that there is only one image generation unit instead of two. In this variant, the image generation device 22 has a first region 28 and a second region 29, where the first region 28 emits light rays for an image in a first image plane and the second region 29 emits light rays for an image in a second image plane different from the first image plane. The image generation device 22 configured in this way may, for example, include individual segments located in the same image generation plane but designed for the generation of virtual images in different image planes.

[0058] In the variant shown in Fig. 6, the various image planes within the wavefront manipulator 23 are separated from one another by the presence of two different optical elements with freeform surfaces. In particular, there is a first freeform surface mirror 20 and a second freeform surface mirror 30, the first freeform surface mirror 20 projecting the light rays transmitted by the first region 28 in the direction of the holographic arrangement 24, and the second freeform surface mirror 30 projecting the light rays emitted by the second region 29 in the direction of the holographic arrangement 24. As an alternative to the variant shown, it is also possible to provide only one freeform surface 25 with correspondingly configured areas. In Figs. 5 and 6, the three light rays of the first beam path 31, which are incident on the projection plane 5 to the left or further up in the drawing, are designed to generate a virtual image in the first image plane, and the three light rays of the second beam path 32, which are incident on the projection plane 5 to the right or further down in each case, are designed to generate a virtual image in a second image plane offset from the first image plane.

[0059] In the variant shown in Fig. 6, in order to separate the beam paths at the freeform surface mirror 25 or at the regions 20 and 30, the two virtual image planes must have a certain lateral distance from each other perpendicular to the optical axis. For example, this means that the look-down angle of the field of view (FOV) or the vertical image position relative to the image plane must be selected to be larger than in the variant shown in Fig. 5. In this case, the two beam paths can be compensated by different freeform surface mirrors 20, 30. In this way, two offset image planes can be realized. The image generation planes or object planes for the two virtual images can be located not only on the same image generation region, but also in different parts or regions, for example above or below each other, or laterally adjacent to each other.

[0060] The variant shown in Figure 7 differs from the variant shown in Figure 6 firstly in that the two regions 28 and 29 of the image generating device are designed to emit offset light waves and in that the wavefront manipulator 23 comprises a first holographic arrangement 34 and a second holographic arrangement 35. In this case, the first holographic arrangement 34 is designed to generate a virtual image in a first image plane from an image generated in the first region 28 of the image generating device 22, and the second holographic arrangement 35 is designed to generate a virtual image in a second image plane from an image generated in the second region 29 of the image generating device 22.

[0061] The first color light 31 emitted by the first region 28 has a wavelength that differs from the first color light 36 emitted by the second region 29 by more than a defined limit, for example, by more than 10 nanometers. The light 31 and 36 can be red light. The second color light 32 emitted by the first region 28 has a wavelength that differs from the second color light 37 emitted by the second region 29 by more than a defined limit, for example, by more than 10 nanometers. The light 32 and 37 can be green light. The third color light 33 emitted by the first region 28 has a wavelength that differs from the third color light 38 emitted by the second region 29 by more than a defined limit, for example, by more than 10 nanometers. The light 33 and 38 can be blue light. The first region 28 and the second region 29 can also be designed to emit light from offset color spaces, for example, the first region 28 can be designed to emit light from an RGB color space and the second region 29 can be designed to emit light from a CMY color space.

[0062] Preferably, the first holographic arrangement 34 is inefficient at diffracting the light emitted by the second region 29, and the second holographic arrangement 35 is inefficient at diffracting the light emitted by the first region 28. Therefore, the wavelengths emitted by the various regions are selected to be different for the two virtual image planes. Preferably, two wavelength triplets of a defined color space, e.g., red, green, and blue, are selected, and these wavelength triplets differ from each other depending on the region from which they are emitted. For example, the first region 28 can emit red light at a wavelength that differs from the red light emitted by the second region 29 by a defined absolute difference value. In the illustrated variant, the two holographic arrangements 34 and 35 are arranged consecutively in the beam path. In principle, adjacent arrangements are also possible. Alternatively, gratings for two wavelengths of related colors can be written into the same hologram, i.e., two blue holograms in two holographic arrangements 34 and 35 can be written or exposed to two holograms in a joint holographic arrangement (a blue multiplexed hologram). Similar to the example shown in Figure 10, there may be multiple multiplexed holograms, e.g., an RR' hologram, a GG' hologram, and a BB' hologram (i.e., six holograms as a stack), or any other suitable combination. This allows the number of hologram arrangements to be reduced without limiting functionality.

[0063] The embodiment variant shown in FIG. 8 combines the various variants already described with reference to FIGS. 5 to 7. Two different image generating units 26 and 27 are present, with their image generating planes positioned differently from one another. Furthermore, the wavelengths emitted by the two image generating units 26, 27 differ by a defined minimum absolute value. The light emitted by the first image generating unit 26 is reflected by the first freeform mirror 20 towards the holographic arrangement 24. The light emitted by the second image generating unit 27 is reflected by the second freeform surface mirror 30 towards the projection plane 5, either through the holographic arrangement 24 or the holographic arrangement 24. In the variant shown in FIG. 8, the holographic arrangement 24 is only efficient for diffracting the wavelength of the light emitted by the first image generating unit 26. The light emitted by the second image generating unit 27 has a wavelength that is not efficiently diffracted by the holographic arrangement 24. This means that only one freeform surface 30 is used for shaping the light 33 emitted by the second image generating unit 27. In contrast, a freeform surface 20 and a wavelength-matched holographic arrangement 24 are used for the beam path 31 of the light emitted by the image generating device 26 .

[0064] Preferred variations of the configuration of the holographic arrangement 24 will now be described with reference to FIGS.

[0065] The holographic arrangement 24 shown in FIG. 9 includes a first holographic element 41 and a second holographic element 42. In the illustrated embodiment variant, the first holographic element 41 and the second holographic element 42 each have three monochromatic holograms arranged one above the other, of which, by way of example, a hologram recorded with red light is identified by reference numeral 51, a hologram recorded with green light is identified by reference numeral 52, and a hologram recorded with blue light is identified by reference numeral 53. The first holographic element 41 and the second holographic element 42 are arranged relative to each other such that the individual holograms are arranged in mirror symmetry with respect to each other. In the illustrated variant, the holograms 51 recorded with red light are arranged directly adjacent to each other. The first holographic element 41 and the second holographic element 42 can be arranged directly adjacent to each other or at a negligible distance from each other, preferably less than 1 millimeter.

[0066] 9 and 10, an incoming light wave in the form of a beam is identified by an arrow carrying the reference numeral 49, and a beam path of light exiting holographic arrangement 24 is identified by an arrow carrying the reference numeral 50. In the variation shown in Figure 9, the individual, mutually different holograms 51, 52, and 53 of the individual holographic elements 41 and 42 are arranged behind one another with respect to a center line or central axis 43 along the latter, which may be the optical axis. The individual, mutually different holograms 51, 52, and 53 of the individual holographic elements 41 and 42 may also be arranged laterally with respect to one another with respect to the center line or central axis 43.

[0067] Figure 10 shows a further embodiment variant of the wavefront manipulator 24 according to the invention. In contrast to the variant shown in Figure 9, the first holographic element 41 and the second holographic element 42 each contain only one hologram, which hologram is, however, in each case recorded with light having several different wavelengths. The variant shown involves two RGB holograms by way of example. The holograms have, for example, a hologram grating structure generated with red light, a hologram grating structure recorded with green light, and a hologram grating structure recorded with blue light.

[0068] FIG. 11 shows a schematic diagram of the beam path within the holographic arrangement 24. For illustrative purposes, the first holographic element 41 and the second holographic element 42 are shown positioned at a distance from each other. However, this only serves to illustrate the beam path. In this case, incident light 49 is reflected wavelength-specifically at each hologram 51-53 or holographic grating structure 51-53 over a specific range of incident angles: blue light for a hologram 53 recorded in blue light, green light for a hologram 52 recorded in green light, and correspondingly red light for a hologram 51 recorded in red light. In the illustrated variant, incident light 49 first passes through the second holographic element 42 and is reflected at the first holographic element 41. Light 48 reflected by the first holographic element 41 is reflected at the second holographic element 42 to form a wavefront 50 exiting the holographic arrangement.

[0069] The first holographic element 41 is configured to convert a spherical wave into a plane wave. As a result, the holographic element 24 has high optical power without increasing its volume and thus the required installation space. Furthermore, the beam cross-section on the mirror can be reduced, thereby reducing both the mirror size and optical power. This is advantageous because the optical power is better distributed within the system and is less sensitive to optical power tolerances. The transmitted wavefront 48 is preferably planar. As a result, inter-wavelength filtering effects are minimized. This also reduces the precision with which the holographic elements 41 and 42 must be positioned relative to each other in the lateral direction. Compared to conventional components, the first holographic element 41 acts like a concave mirror, and the second holographic element 42 acts like a plane mirror. Overall, the holographic arrangement 24, and in particular the hologram stack including the first holographic element 41 and the second holographic element 42, has the functionality of a positive lens but with minimal volume. [Explanation of symbols]

[0070] 1 Image Generation Unit 2. Output image information 3 Optical elements with freeform surfaces 4 Holographic Configuration 5 Projection plane 6 Beam Path 7 Wavefront Manipulator 8 Virtual image, image plane 9 Eye Box 10 Head-up display 11 Optical arrangement 12 lens elements 13 Optical axis 14 Object 15 images 16 Beam Path 1 17 Object 18 Virtual Image, Image Plane 19 images 20 Freeform Mirror 22 Image generation devices 23 Wavefront Manipulator 24 Holographic Configuration 25 Optical element with freeform surface 26 Image Generation Unit 27 Image Generation Unit 28 First Area 29 Second Area 30 Freeform Mirror 31 Beam Path 32 Beam Path 33 Beam Path 34 First Holographic Configuration 35 Second Holographic Configuration 41 First Holographic Element 42 Second Holographic Element 43 Center line 48 Beam Path 49 Beam Path 50 Beam Path 51 Holograms recorded with red light 52 Holograms recorded with green light 53 Holograms recorded with blue light s1 object distance s2 object distance s1' image distance s2' image distance

Claims

Claim 1 An optical arrangement (11) for a head-up display (10) on a projection surface (5), comprising an image generation device (22) including at least one image generation unit (26, 27), and at least one wavefront manipulator (23) arranged in a beam path between the image generation device (22) and the projection surface (5). In the optical arrangement (11), the optical arrangement (11) is designed to generate virtual images (8, 18) in at least two different image planes. The image generation device (22) has at least a first region (26, 28) and a second region (27, 29). The image generation device (22) and the wavefront manipulator (23) are designed in combination with each other to generate a virtual image (8) in a first image plane from an image generated in the first region (26, 28) of the image generation device (22), and to generate a virtual image (18) in a second image plane from an image generated in the second region (27, 29) of the image generation device (22). Characterized in that, the optical arrangement (11). Claim 2 The first region (28) and the second region (29) of the image generation device (22) have a common image generation plane, or the first region (26) of the image generation device (22) has a first image generation plane, and the second region (27) of the image generation device (22) has a second image generation plane, and the first image generation plane and the second image generation plane are different from each other. Characterized in that, the optical arrangement (11) according to claim 1. Claim 3 The at least one wavefront manipulator (23) includes at least one holographic arrangement (24) and / or at least one optical element (25) having a free-form surface. Characterized in that, the optical arrangement (11) according to claim 1. Claim 4 The at least one holographic arrangement (24) is designed to diffract light at multiple wavelengths. Characterized in that, the optical arrangement (11) according to claim 3. Claim 5 The wavefront manipulator (23) comprises at least a first holographic arrangement (34) and a second holographic arrangement (35), the first holographic arrangement (34) being designed to generate a virtual image (8) in the first image plane from an image generated in the first region (28) of the image generation device (22), and the second holographic arrangement (35) being designed to generate a virtual image (18) in the second image plane from an image generated in the second region (29) of the image generation device, the optical arrangement (11) according to claim 3, characterized in that.

6. The first holographic arrangement (34) is designed to diffract light at least at a first wavelength, the second holographic arrangement (35) is designed to diffract light at least at a second wavelength, and the difference between the first wavelength and the second wavelength exceeds a defined limit value, the optical arrangement (11) according to claim 5, characterized in that.

7. The holographic arrangement (24) and / or the at least one optical element (25) are configured to be reflective and / or transmissive, the optical arrangement (11) according to claim 3, characterized in that.

8. The holographic arrangement (24) includes at least two holographic elements (41, 42) arranged directly in series in the beam path (48, 49, 50), the optical arrangement (11) according to claim 3, characterized in that.

9. The holographic arrangement (24) includes at least two holographic elements (41, 42) configured to be reflective for at least a defined wavelength and a defined range of incident angles, the optical arrangement (11) according to claim 3, characterized in that.

10. The holographic arrangement (24) includes at least two holographic elements (41, 42), where at least one holographic element (41, 42) includes a plurality of holograms (51, 52, 53) arranged vertically one above the other as a stack, or at least one holographic element (41, 42) includes at least one hologram (51, 52, 53) recorded using at least two defined wavelengths, characterized in that the optical arrangement (11) according to claim 3.

11. The wavefront manipulator (23) is designed to spectrally separate the images of the different image planes, or is designed to separate the images by generating different polarization states for the various image planes, characterized in that the optical arrangement (11) according to claim 1.

12. The image generation device (22) comprises a plurality of image generation units (26, 27), characterized in that the optical arrangement (11) according to claim 1.

13. The wavefront manipulator (23) includes a plurality of holographic arrangements (34, 35), each designed to generate a virtual image (8, 18) in a defined image plane, characterized in that the optical arrangement (11) according to claim 1.

14. The wavefront manipulator (23) has a freeform surface and includes a plurality of optical elements (20, 25, 30), each designed to generate a virtual image in at least a defined image plane, characterized in that the optical arrangement (11) according to claim 1.

15. A head-up display (10) including a projection surface (5), characterized in that it includes the optical arrangement (11) according to any one of claims 1 to 14.

16. The projection surface (5) is the surface of the front windshield or observation window of a vehicle, characterized in that the head-up display (10) according to claim 15.

Images