System for illumination of a multipixel display device

Abstract

An optical homogenization plate (1) is used to illuminate a multipixel display device (10), e.g. a liquid crystal screen. A speckle noise suppression unit (3, 300) is provided for reducing speckle noise before the light is coupled into the homogenization plate (1). Components of this type can be used in a picture generating device of an HUD system.

Description

[0001] DESCRIPTION

[0002] SYSTEM FOR ILLUMINATION OF A MULTIPIXEL DISPLAY DEVICE

[0003] TECHNICAL FIELD

[0004] Various aspects of the disclosure relate to a system for illuminating a multi-pixel display device, for example, for a HUD system. In particular, various aspects of the disclosure relate to a system for illuminating a multi-pixel display device with a speckle noise suppression unit.

[0005] BACKGROUND

[0006] Transparent screen units are used in various application scenarios. For example, transparent screen units are used in HUD (Head-Up Display) systems in motor vehicles. A HUD system creates a virtual image so that the driver does not have to take their eyes off the road and can still perceive the displayed information. Unlike real images, which are displayed on a physical surface, such as a transparent area, the virtual image is created in a virtual image plane. In HUD systems, the virtual image plane is located outside the vehicle. The so-called eye box is the area within which the driver can perceive the virtual image.

[0007] Transparent display units have a picture generating unit (PGU). The PGU comprises a multi-pixel display device, such as a liquid crystal display or a micromirror array. The multi-pixel display device is illuminated by a light source.

[0008] Narrowband or monochromatic light sources are often used. This is especially the case when holographic optical elements (HOEs) are used. The reason for this lies in the wavelength-selective diffraction characteristics of an HOE. The diffraction efficiency of the HOE is a function of the wavelength.

[0009] Laser light sources are therefore often used as high-luminous flux light sources. Due to their coherence, these light sources cause considerable speckle noise in the image plane. This speckle noise impairs the visual image impression.

[0010] SUMMARY

[0011] There is a need for systems for illuminating multi-pixel displays (illumination systems) that reduce speckle noise. There is a need for compact lighting systems that can be integrated into limited space. There is a need for lighting systems that illuminate multi-pixel displays with a desired light distribution in the display plane.

[0012] This problem is solved by the features of the independent patent claims. The features of the dependent patent claims define embodiments.

[0013] The following describes optical systems and arrangements used to illuminate multi-pixel display devices. Speckle noise can be suppressed. The illumination intensity in a pixel plane of the multi-pixel display device can be specifically adjusted. A compact design can be enabled. Such systems and arrangements can be used together with the multi-pixel display device as the PGU of a head-up display (HUD) system. In various variants, several diffuser elements arranged in a cascade are used. These are arranged in front of the multi-pixel display device in the light beam path and enable customized illumination of a pixel plane of the multi-pixel display device.

[0014] According to various examples, the light is modified in stages by passing through multiple optical elements. For example, it can pass through two or more diffusers. This can ensure that the pixel plane of the multi-pixel display device is illuminated with a desired light distribution. The multi-pixel display device has a radiation characteristic that is adjusted by illuminating the pixel plane using the multiple optical elements.

[0015] For example, multiple diffusers can be arranged one after the other. A first diffuser can implement a speckle noise suppression unit. For this purpose, the diffuser can be moved, e.g., in the kHz range. A second diffuser can be configured to achieve suitable illumination of a third diffuser. The third diffuser can have a radiation characteristic that is adapted to an optical imaging system arranged in the light path behind the multi-pixel display device. For example, a corresponding entrance pupil of the optical imaging system can be suitably illuminated.

[0016] Individual sections of the light beam path can be guided within an optical block or implemented as a free beam. Typically, a more compact arrangement can be achieved by using an optical block to guide the light.

[0017] A system for illuminating a pixel plane of a multi-pixel display device is disclosed.

[0018] The system includes a laser light source. For example, the laser light source could comprise a single light emitter, such as a laser diode. A multicolor laser light source could also be used; such a multicolor laser light source could, for example, comprise three light emitters providing light of the red, green, and blue wavelengths.

[0019] The laser light source is generally designed to provide phase-coherent light, which can cause speckle noise.

[0020] The system also includes a speckle noise suppression unit. As a general rule, different types of speckle noise suppression units can be used. One implementation involves the use of a moving diffuser, which "averages out" the speckle pattern. However, other types of speckle noise suppression units also exist, for example, a liquid crystal light modulator element. Using the speckle noise suppression unit, the phase profile of the laser light can be changed, in particular, randomized. In general, an active device can be used as a speckle noise suppression unit, i.e., a device comprising a motor or actuator that moves one or more elements.

[0021] The speckle noise suppression unit can be designed, for example, as a diffuser that is moved in the kHz range.

[0022] The system also includes an optical waveguide that guides the coherent light emitted by the light source to the speckle noise suppression unit. An optical fiber can be used as the optical waveguide, for example, a multimode fiber. An output lens could be provided at one end of the optical waveguide facing the speckle noise suppression unit.

[0023] The system also includes an optical homogenization plate. This plate has a top surface, a bottom surface, and (at least) one side surface. The side surface is thus located at the edge between the top surface and the bottom surface. The thickness of the optical homogenization plate can be defined as the distance between the top surface and the bottom surface. The top surface can face a multi-pixel display device in a system integration into a PGU of a HUD system. The homogenization plate can be made of Plexiglas or glass. The homogenization plate has a plate-shaped, optically transparent substrate.

[0024] The system comprises a coupling structure. The coupling structure is configured adjacent to a speckle noise suppression unit on the side surface of the homogenization plate. The coupling structure is configured to couple light coming from the speckle noise suppression unit into the homogenization plate. The coupling structure can be glued or otherwise applied to the side surface of the homogenization plate as a separate component. However, the coupling structure could also be configured as a surface topography variation of the side surface of the homogenization plate.

[0025] The system further comprises a coupling-out structure. This is formed on the upper side of the homogenization plate. The coupling-out structure is configured to couple light out of the homogenization plate, distributed over the entire surface of the coupling-out structure, for illuminating the multi-pixel display device. This means that a specific light field, i.e., a specific intensity distribution as a function of the positions along the surface of the homogenization plate, can be achieved via the coupling-out structure. This makes it possible to achieve suitable illumination of the pixel plane of the multi-pixel display device. In particular, the pixel plane of the multi-pixel display device can be illuminated over its entire surface, i.e., all pixel elements are illuminated at one time, or there is no sequential illumination of different pixel elements.

[0026] By using the homogenization plate with coupling-out structure, a particularly compact illumination unit can be implemented, e.g. in particular in comparison to a free-beam beam path.

[0027] The output coupling structure can be implemented, in particular, as a diffuser. The diffuser scatters the light, thus achieving a specific radiation characteristic.

[0028] As a general rule, diffusers can be implemented in various ways, including microstructured diffusers, holographic diffusers, volumetric diffusers, and surface-relief-based diffusers. Diffusers can be made of various materials, including plastic, glass, and possibly coated.

[0029] As described above, it is possible to achieve a desired illumination of the pixel plane by using several diffusers (speckle noise suppression unit and output coupling structure).

[0030] Accordingly, a system for illuminating a pixel plane of a multi-pixel display device comprises a laser light source. The laser light source is configured to emit light along a beam path. The system also comprises a speckle noise suppression unit, implemented, for example, as a moving diffuser. This is arranged in the beam path. The system further comprises a diffuser. The diffuser is arranged in the beam path emanating from the laser light source behind the speckle noise suppression unit and is configured to emit the light with a radiation characteristic toward the multi-pixel display device.

[0031] The diffuser positioned first in the beam path thus enables the suppression of speckle noise. The diffuser positioned adjacent to the pixel plane of the multi-pixel display device in the beam path thus enables the desired radiation pattern for, first, the illumination of the pixel plane and, second, the illumination of an entrance pupil of an optical imaging system positioned behind the multi-pixel display device in the beam path.

[0032] Optionally, an additional diffuser could also be provided, arranged between the speckle noise suppression unit and the diffuser (near the display device). This diffuser is configured to emit the light with a further radiation characteristic toward the diffuser arranged adjacent to the display device. This further radiation characteristic can be configured to achieve full-surface illumination of the aperture of the diffuser arranged adjacent to the display device.

[0033] Such systems as described above can be part of a PGU of a HUD system. The HUD system can have one or more HOEs in the light beam path. The multi-pixel display device can be, for example, a liquid crystal display or a micromirror array.

[0034] The one or more HOEs can perform various functions. For example, it would be conceivable for the one or more HOEs to be part of or implement a wavefront manipulator, as described in WO 2022 / 189275 A1 (referred to therein as holographic elements), the corresponding disclosure content of which is incorporated herein by cross-reference.

[0035] For example, a corresponding wavefront manipulator can comprise two HOEs arranged directly one behind the other in the beam path. In other words, no further optical element or component is arranged between the two HOEs. The two HOEs are also designed to be reflective for at least one specified wavelength and a specified angle of incidence range. Light waves of the at least one specified wavelength and the specified angle of incidence range are thus efficiently diffracted. Preferably, the holographic elements are otherwise 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 range. The use of two at least partially reflective HOEs arranged directly one behind the other has various advantages. One advantage is, for example,that, particularly in connection with a head-up display, the image quality can be significantly improved through the individual design of the HOEs. The HOE requires almost no installation space, so that with the help of a corresponding wavefront manipulator in only limited available installation space, such as in a head-up display designed for a motor vehicle, a significant increase in image quality can be achieved (compared to implementations without HOEs). The holographic arrangement achieves, in particular, a high refractive power, comparable to the refractive power achieved, for example, by a transmissive optical component without chromatic aberration. Compared to transmission holograms, reflective HOEs offer a broader angular spectrum for a defined wavelength with high efficiency and higher wavelength selectivity.This allows the color channels to be separated from one another despite a wide spectrum of angles of incidence. The holographic arrangement thus enables a large field of view with simultaneous high efficiency and is therefore suitable for both VR head-up displays (VR - Virtual Reality) and augmented reality head-up displays (AR-HUD) with a large field of view and large numerical aperture. Further possible applications include head-up displays with curved projection surfaces, for example, head-up displays for vehicle windshields, particularly motor vehicles, aircraft, or ships, as well as for viewing windows in general. While various variants are described below in which one or more HOEs are used in the optical imaging system of a HUD system, the corresponding techniques for an image generation unit can also be used in conjunction with non-holographic HUD systems.

[0036] The features set forth above and features described below may be used not only in the corresponding explicitly set forth combinations, but also in further combinations or in isolation, without departing from the scope of the present invention.

[0037] SHORT DESCRIPTION OF THE CHARACTERS

[0038] FIG. 1 is a schematic view of an exemplary system for illuminating a multi-pixel display device. FIG. 2 is another side view of the exemplary system of FIG. 1.

[0039] FIG. 3 is a perspective view of the exemplary system of FIG. 1.

[0040] FIG. 4 shows the illumination intensity provided by the system along a pixel plane of the multi-pixel display device.

[0041] FIG. 5 illustrates a HUD system with the system for illuminating the multi-pixel display device and with the pixel display device according to various examples.

[0042] FIG. 6 is a polar plot (nominated) illustrating two possible angular distributions of the radiation pattern of the system for illuminating the multi-pixel display device.

[0043] FIG. 7 illustrates a local variation of the radiation characteristic by several polar plots of the corresponding angular distributions according to different examples.

[0044] FIG. 8 illustrates a local variation of the radiation characteristic by several polar plots of the corresponding angular distributions according to different examples.

[0045] FIG.9 schematically illustrates a speckle noise suppression unit according to various examples.

[0046] FIG. 10 schematically illustrates a HUD system according to various examples.

[0047] FIG. 11 is a schematic view of an exemplary system for illuminating a multi-pixel display device.

[0048] FIG. 12 is a perspective view of a structural implementation of the system of FIG. 11.

[0049] DETAILED DESCRIPTION

[0050] The properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings. FIG. 1 schematically illustrates a system 100 for illuminating a multi-pixel display device 10. Laser light (e.g., red-green-blue channels, or fewer or more channels) from a laser light source 19 is coupled into a speckle noise suppression unit 3—implemented here as a dynamically moving diffuser—by means of an optical fiber 4. For this purpose, a lens, e.g., a GRIN lens, can optionally be provided at the corresponding end of the optical fiber 4. The radiation characteristic of such a lens can be varied depending on the application. The lens can provide collimation.For example, a lens with a collimation characteristic can be provided that is adapted to the input angle range of the speckle noise suppression unit 3. In this case, particular attention should be paid to dispersion. Alternatively or additionally, a parabolic mirror can also be used for beam expansion and collimation between the end of the optical fiber 4 and the speckle noise suppression unit 3.

[0051] For example, the multi-pixel display device 10, together with the system 100, can be part of a PGU of a HUD system. It would also be conceivable for the multi-pixel display device 10, together with the system 100, to be part of a holo-diffuser. With such a holo-diffuser, an image is generated in an image plane arranged on a transparent surface. This can be used to implement, for example, transparent screens.

[0052] In such application scenarios, one or more HOEs may be present, which apply one or more optical effects to the light through diffraction. For example, the light can be redirected or collimated. These one or more HOEs require the light source to emit narrowband or monochromatic light. A laser is typically used as the light source for this purpose. The coherent light can be susceptible to speckle noise.

[0053] Speckle noise (also light granulation or laser granulation or speckle for short) refers to the granular interference phenomena that can be observed with sufficiently coherent illumination of optically rough object surfaces (unevenness in the order of the wavelength).

[0054] The diffuser implementing the speckle noise suppression unit 3 is moved randomly, for example, in both lateral directions perpendicular to the optical fiber axis, both relative to the optical fiber 4 and to the rest of the structure. For example, the movement frequency can be adjustable. This allows speckle noise to be effectively suppressed.

[0055] The light is then coupled into the transparent substrate of an optical homogenization plate 1 (e.g., made of glass or plastic) in a coupling structure 2 (also referred to as a light redistribution structure). The coupling structure 2 is arranged on a side surface 23 of the homogenization plate 1, directly adjacent to the speckle noise suppression unit 3. This enables a compact design; additional collimation lenses or similar devices are unnecessary.

[0056] A typical thickness of the homogenization plate 1 is in the range of 5 mm to 20 mm, preferably in the range of 10 mm to 20 mm.

[0057] The coupling structure 2 can be applied as a separate component to the homogenization plate 1. The coupling structure 2 can be designed, for example, as a lenticular array.

[0058] A lenticular array generally comprises a 1D or 2D array of lens-shaped elements (lenticules) configured to refract light in different directions. For example, a 1D array can be used in which the lenticules are spaced apart in a first direction and the lenticules are extended in a second direction perpendicular to the first direction.

[0059] The coupling structure 2 can be formed, for example, as a film, such as a lenticular array film. However, it would also be possible for the coupling structure 2 to be formed integrally with the homogenization plate 1, i.e., as a monolithic component. For example, the side surface 23 can be formed with a corresponding surface topography (e.g., as a lenticular array in the form of indentations on the side surface 23).

[0060] The light-conducting substrate of the optical homogenization plate 1 is provided on its underside 22 with a further transparent light redistribution structure 5, which redistributes the light field according to the desired design specifications, e.g. by multiple scattering and reflection 9.

[0061] The light redistribution structure 5 can be applied to the homogenization plate 1 as a separate component. The light redistribution structure 5 is realized, for example, in the form of (hemispherical) or ellipsoidal elevations or depressions directly in the substrate, but can also be achieved by gluing a structural film adapted to the refractive index. The light redistribution structure 5 can, for example, alternatively be designed as a film, for example a lenticular array film. However, it would also be possible for the light redistribution structure 5 to be formed integrally with the homogenization plate 1, i.e., as a monolithic component. For example, the underside 22 can be designed with a corresponding surface topography (e.g., as a lenticular array in the form of indentations).

[0062] The design specifications, such as lateral homogeneity and spatial orientation of the light field 8 emitted by the homogenization plate 1 (radiation characteristics of the homogenization plate 1) can be adjusted by the configuration, arrangement, size, and / or number of such light redistribution structures (the main radiation direction 205—perpendicular to the surface of the homogenization plate 1—is also provided with a reference symbol). Details relating to the light intensity of the light field 8 as a function of the position on the homogenization plate and the radiation characteristics of the light field 8 will be described later in connection with FIG. 4 and FIG. 6.

[0063] To reduce light losses on the underside 22 of the optical homogenization plate 1 below the light redistribution structure 5, a reflector structure 6 is provided, here embodied as a reflective layer. The reflector structure 6 redirects the light back toward the optical homogenization plate 1. The reflector structure 6 can, for example, be glued to the light redistribution structure 5 as a reflective foil. It would also be possible for the reflector structure 6 to be produced as a metallic vapor deposition (thin film), for example, with aluminum.

[0064] In order to specifically adjust the angular distribution of the light field leaving the homogenization plate, an optional output coupling structure 7 can be used on the upper side 21 of the homogenization plate 1. This can be designed as a diffractive diffuser. In such a scenario, several diffuser elements arranged in a cascade are used, namely the diffractive diffuser implementing the output coupling structure 7 and the diffuser implementing the speckle noise suppression unit 3. By means of a suitable design of the output coupling structure 7, a pixel plane 11 of the multi-pixel display device 10 can be illuminated in a customized manner. Pixels of a liquid crystal display, e.g., a thin-film liquid crystal display (TFT display), are arranged in the pixel plane 11.

[0065] The coupling-out structure 7 can be applied to the homogenization plate 1 as a separate component. The coupling-out structure 7 can be formed, for example, as a film. However, it would also be possible for the coupling-out structure 7 to be formed integrally with the homogenization plate 1, i.e., as a monolithic component. For example, the upper side 21 can be formed with a corresponding surface topography.

[0066] In particular, in various examples, it would be possible for the optical homogenization plate 1, together with the outcoupling structure 7, the incoupling structure 2, and the light redistribution structure 5, to be manufactured as a monolithic component. For example, this monolithic component could be made from a single plastic block. Possible manufacturing techniques include 3D printing or injection molding.

[0067] In order to suppress the visibility of the diffuser features of the output coupling structure 7 - for example a structured surface of the output coupling structure - for the human eye, it can be useful to decouple the pixel plane 11 from the exit plane or the output coupling structure 7, i.e. to distance it (cf. gap 12). For this purpose, the gap 12 preferably has an extent in the range of approximately 20 mm to 100 mm, optionally in the range of 25 mm to 25 mm, further optionally of 30 mm. The gap 12 is therefore typically larger than the thickness of the homogenization plate 1. The gap 1 has, for example, an extent of approximately 100% to 150% of a thickness of the homogenization plate 1, because the homogenization plate 1 is typically between 5 mm and 20 mm thick. However, the dimensioning of the gap 12 does not depend on the thickness of the homogenization plate 1, but rather on the positioning of the virtual image plane: This is explained below.

[0068] The human eye adapts – for example, in a HUD system – to the virtual image plane. This virtual image plane is mapped onto pixel plane 11. This means that structures – such as the diffuser features of the output structure – which are spaced from pixel plane 11 by a distance greater than the depth of field are only imaged very blurred and are therefore not perceived (or at least not perceived as disturbing). This is particularly advantageous for magnifying optical systems, such as the HUD system. There, pixel plane 11 is magnified and mapped onto the virtual image plane. Magnification factors of 10x or more, e.g. 15x or more, are conceivable. In augmented reality applications, the virtual image plane can be located virtually at infinity (the eye's long-distance accommodation is > 5 m) and have a large extent in the eye's field of vision.In general, distances between the eyebox and the virtual image plane of more than 5 m, more than 10 m, or more than 20 m are conceivable. If, in such a case, the gap 12 were dimensioned particularly small, so that the diffuser features of the output structure 7 lie within the depth of field, they would be particularly large and thus perceived as particularly disruptive in the viewer's field of vision. In general, it is possible to dimension the gap 12 as large as necessary (no significant diffuser features), but as small as possible (compact installation space).

[0069] Furthermore, it is possible to incline or tilt the pixel plane 11 relative to the homogenization plate 1.

[0070] FIG. 2 is a side view of the system 100 from FIG. 1. In FIG. 2 it can be seen that the lateral extent of the coupling structure 2 is smaller than the extent of the side surface 23 of the homogenization plate 1, i.e. along the z-axis in FIG. 2 along the long side of the side surface 23. For example, in the example of FIG. 2 the coupling structure 2 covers approximately 70% of the side surface 23. In general it would be conceivable for the lateral extent of the coupling structure 2 to be no greater than 80% or no greater than 70% of a side length of the side surface 23 or no greater than 50% of a side length of the side surface 23. In other examples it would also be conceivable for the coupling structure 2 to cover the entire side 23. The lateral extent of the coupling structure 2 can be equal to the side length of the side surface 23. The aperture of the speckle noise suppression unit 3 is also smaller than the lateral extent of the coupling structure 2.In general, the lateral extent of the speckle noise suppression unit 3, for example, cannot be greater than 20% of the area of ​​the coupling structure 2. By means of the coupling structure 2, a relatively large-area coupling of light into the homogenization plate 1 can take place, although the speckle noise suppression unit 3 typically has a relatively limited extent with respect to the side surface 23. The extent (width across the side surface) and texture (lenticular, prismatic) of the coupling structure 2 can be variably adapted (design degrees of freedom). For example, the coupling structure 2 can comprise one or more prismatic structures; these serve as scattering geometries for already coupled and internally reflected / scattered light. Thus, the radiation characteristics of the homogenization plate 1—i.e., the light distribution, e.g., homogeneity, of the light at the coupling structure 7—can be influenced at the location of the coupling structure 2.The light is also further redistributed within the homogenization plate 1, for example, by the light redistribution structure 5. For this reason, it is not absolutely necessary for the lateral extension of the coupling structure 2 to cover the entire length of the side surface 23. This is also evident in the perspective view of the system 100 in FIG. 3.

[0071] FIG. 4 shows the light intensity in the pixel plane 11 (the extent of the pixel plane 11 is indicated in FIG. 4 by the double arrow). The light intensity is determined by the emitted light field 8 (e.g., as an integral over all solid angles, as in FIG. 4, or also only for the main emission direction 205). From FIG. 4, it can be seen that a constant light intensity over the extent of the pixel area 11 can be achieved by appropriately shaping the light field 8 (e.g., by appropriately configuring the output coupling structure 7 and / or the light redistribution structure 5 and / or the input coupling structure 2). In other variants, other local dependencies of the light intensity would also be conceivable, for example, with a peak in the center of the pixel plane 11 or with several different maxima and minima of the light intensity.

[0072] FIG. 5 schematically illustrates a HUD system 200. The HUD system 200 comprises the system 100 (wherein FIG. 5 only shows the homogenization plate 1) for illuminating the multi-pixel display device 10. In FIG. 5, the pixel plane 11 is inclined relative to the homogenization plate 1. For this purpose, the main radiation direction 205 of the system 100 is shown. Furthermore, FIG. 5 shows further components of the HUD system 200 along the light beam path, for example, a mirror 206, a holographic optical element 202, the windshield 203, and the eyebox 204.

[0073] From the system level of the HUD system 200, as illustrated in FIG. 5 for a possible configuration, it can be seen that - in addition to the spatial dependence of the light intensity, compare FIG. 4 - the radiation characteristic of the homogenization plate 1 is also crucial for the quality of the image displayed by the HUD system 200. The radiation characteristic can be adjusted in particular by using a holographic diffuser as the output coupling structure 7. For example, in the polar plot of FIG. 6, two exemplary radiation characteristics 291, 292 (each normalized in amplitude to a common value for the main radiation direction 205, wherein in the example shown the main radiation direction is perpendicular to the surface of the output coupling structure 7, i.e. parallel to the y-axis) are shown with the solid and dashed lines.The polar plot shows the amplitude of the light emitted in the respective direction (in the xy plane). This amplitude distribution in the angular space specifies the radiation characteristic. In the example in FIG. 6 it is clear that the width of an angular spectrum of the light field 8 can be set using the output coupling structure 7: the respective width 295, 296 is shown in FIG. 6. In particular it is clear from FIG. 6 that the radiation characteristics have an angular spectrum that does not completely illuminate the half-space above the output coupling structure 7, i.e. the light is emitted in a more directed manner compared to a -90° - +90° reference radiation characteristic 299 (dotted line), which evenly illuminates the entire upper half-space. This allows the multi-pixel display device 10 to be illuminated in a targeted manner. It would also be conceivable for the radiation characteristic in the angular spectrum to be as shown in FIG.6, as a function of the lateral position (for example, along the X-axis plotted in FIG. 4) by changing the diffractive properties of the holographic diffuser as a function of this position. By selecting the appropriate radiation characteristic 291, 292 (angular spectrum and / or lateral variation), the image quality of the HUD system 200 can be increased.

[0074] FIG. 6 is only one example of a radiation pattern. Inhomogeneous radiation patterns are also conceivable. The illumination system and the imaging system (HUD) should be matched to each other. This means that the exit pupil of the illumination system and the entrance pupil of the HUD are coordinated to achieve the greatest possible luminous flux, while also preventing vignetting of the illumination system. This can also result in inhomogeneous or asymmetrical radiation patterns.

[0075] For example, FIGS. 7 and 8 show variants in which the radiation characteristic is changed by varying the respective angular spectrum 801 - 805 or 811 - 815 as a function of the lateral position along the x-axis (alternatively or additionally along the z-axis). The width of the angular spectrum is kept approximately the same, but the orientation of the main radiation direction 205 is tilted progressively away from the center 7' of the output structure 7 (FIG. 7) and progressively toward the center 7' of the output structure 7 (FIG. 8). This means that the main radiation direction 205 is changed by rotating the angular spectrum 801 - 805, 811 - 815 for different x-positions. In other words, the "radiation lobe" of the light is progressively tilted but retains approximately the same shape.In the illustrated examples, this is done symmetrically with respect to a center 7' of the output coupling structure 7, but in other examples, it could also be done asymmetrically with respect to the center 7'. By such a position-dependent variation of the main emission direction 205, the entrance pupil of the optical imaging system of the HUD system or the eyebox 204 can be illuminated to achieve a natural and uniform brightness impression.

[0076] FIG. 9 schematically shows a speckle noise suppression unit 300. This can, for example, implement the speckle noise suppression unit 3 from FIG. 1. The speckle noise suppression unit 300 comprises a diffuser 301 in an xy plane. To move the diffuser 301 in the xy plane, different drive types are conceivable. For example, an electrodynamic drive can be used. An electrodynamic drive, also referred to as an electromagnetic drive, uses, for example, a coil to generate an alternating magnetic field by moving a magnet. The magnet is connected to the diffuser 301. Corresponding actuators 303, which are mounted via a frame in a fixed reference system (mounting 304), are shown in FIG. 9. The drive frequency of the electrodynamic actuators 303 can be dynamically adjusted over a relatively wide frequency range, so that, for example,One or more eigenmodes of the mass-spring system (formed by the diffuser 301 and return springs 302) are resonantly excited. The best despeckle results can be achieved in such resonant states. This type of drive can be designed as a single- or dual-axis system (a dual-axis system is shown as an example in FIG. 9). Furthermore, it is also possible to initiate a non-deterministic movement via one or more vibration motors (e.g., a miniature motor with an eccentric flywheel on a motor shaft) connected to the support frame of the diffuser.

[0077] To achieve a suitable statistical averaging z, the motion frequency should not be less than 100 Hz. However, the optimal frequency range depends on the geometry and mass of the diffuser (natural frequency of the mass-spring system). Furthermore, psychoacoustic effects should also be considered during design, so there may be a trade-off between different target variables.

[0078] The scenario in FIG. 9 is just one example of a hardware implementation of a speckle noise suppression unit. In general, the light beam path can be varied over time. This can be achieved by mechanical movement (such as vibration or rotation) of an element in the beam path, such as a diffuse disk (see FIG. 9) or a fiber optic cable. The temporal variation of the beam path results in the speckles being "smeared" over time, which reduces the perceived noise. Alternatively, the phase of the incident light could also be varied, e.g., using spatial light modulators (SLMs).

[0079] FIG. 10 schematically illustrates a HUD system 600 according to various examples. The HUD system 600 includes a PGU 601. The PGU 601 includes a laser light source 605 configured to emit light along a beam path 606. The laser light source 605 corresponds to the laser light source 19 of FIG. 1.

[0080] The light strikes a speckle noise suppression unit 610. The speckle noise suppression unit 610 can be configured, for example, as described in FIG. 9 (speckle noise suppression unit 300).

[0081] Starting from the speckle noise suppression unit 610, the light propagates along the beam path 606 to an optical element 615. The optical element 615 is configured to uniformly illuminate the aperture of a diffuser 620. An example of the optical element 615 would be, for example, the homogenization plate 1 together with the light redistribution structure 5 (see FIG. 1). It is possible for the optical element 615 itself to be designed as a diffuser. A corresponding implementation will be discussed later in connection with FIG. 11.

[0082] The diffuser 620 (see FIG. 1: output structure 7) is then configured to emit the light along the beam path 606 with a radiation characteristic that illuminates the pixel plane of a multi-pixel display device 625 (corresponds to the multi-pixel display device 10 in FIG. 1). The units 605, 610, 615, 620 thus form a system 621, which corresponds, for example, to the system 100 in FIG. 1.

[0083] The light then leaves the PGU 601 along the beam path 606 and strikes an optical imaging system 630, which, for example, has one or more holographic optical elements. The optical imaging system 630 may alternatively or additionally have, for example, one or more deflection elements or lenses. The radiation characteristic of the diffuser 620 is configured so that the light illuminates the entrance pupil of the optical imaging system 630. The light then reaches an eyebox 645, from where a virtual image can be perceived. Corresponding techniques were described above in connection with FIGS. 6, 7, and 8.

[0084] For example, the section of the beam path 606 between the laser light source 605 and the speckle noise suppression unit 610 can be implemented at least partially via an optical waveguide, for example, a glass fiber. In connection with FIG. 1, aspects were described above in which the section of the beam path 606 between the speckle noise suppression unit 610 and the diffuser 620 runs in an optical block (homogenization plate 1). This enables a particularly compact design. However, free-beam implementations would also be conceivable. A corresponding variant is discussed below in FIG. 11.

[0085] FIG. 11 schematically illustrates a system 500. The system 500 provides functionality corresponding to the system 100 of FIG. 1. The system 500 can, for example, implement the system 621 of FIG. 10. In FIG. 11, however (unlike in FIG. 1), a free-beam beam path is used for the light to illuminate a multi-pixel plane 506 of a multi-pixel display device 507. The light is generated by a laser light source 501 (cf. laser light source 19 in FIG. 1 and laser light source 605 in FIG. 10). From the laser light source 501, the light propagates to a speckle noise suppression unit 502. This can be designed like the speckle noise suppression unit 3 in FIG. 1 or the speckle noise suppression unit 300 in FIG. 9.

[0086] The light can propagate as a free beam between the laser light source 501 and the speckle noise suppressor 502. It is also conceivable for the light to be guided by a fiber optic cable.

[0087] The speckle noise suppression unit 502 itself has a moving diffuser that implements a specific radiation characteristic 507. This illuminates another diffuser 504, which in turn has a radiation characteristic

[0088] 508. The radiation characteristic 508 is configured to achieve homogeneous illumination of a further diffuser 505. The diffuser 504 thus assumes the functionality of the homogenization plate 1 together with the light redistribution structure 5 in FIG. 1.

[0089] The light can propagate as a free beam between the speckle noise suppression unit and the diffuser 504 and between the diffuser 504 and the diffuser 505.

[0090] There is therefore an arrangement of several cascaded diffuser elements (speckle noise suppression unit 502 and diffuser 504 and diffuser 505).

[0091] The diffuser 505 has a radiation characteristic 509. This radiation characteristic 509 can be adjusted to illuminate an entrance pupil of an optical imaging system of a HUD system as desired. The radiation characteristic

[0092] 509 can be set according to the examples in FIG. 6, FIG. 7 and FIG. 8.

[0093] Then, the pixel plane 506 of the multi-pixel detector 507 is illuminated. This in turn has a radiation characteristic 510. Corresponding aspects have already been discussed in connection with FIG. 1 and the pixel plane 11 of the multi-pixel detector

[0094] 510 is discussed. For example, the main radiation direction of the multi-pixel display device 507 or, in general, the radiation characteristic 510 of the multi-pixel display device 507 can be adjusted by appropriately adjusting the diffuser 505 or by adapting the radiation characteristic 509.

[0095] In summary, techniques for illuminating a multi-pixel display device were described above. One or more narrowband and coherent light sources, for example lasers or laser diodes, can be used for the efficient illumination of the multi-pixel display device. For example, a PGU of a HUD system can be implemented in this way. Techniques are described for suppressing speckle noise. Techniques are described for achieving homogeneous illumination of large image fields. One or more diffusers are used for this purpose. The light distribution or the light field can be flexibly adjusted by appropriately configuring output coupling structures (e.g. implemented as a diffuser) or input coupling structures (e.g. implemented as a diffuser) or light redistribution structures. High luminance levels can be achieved.In particular, it is possible for the corresponding system for illuminating the multi-pixel display device to be arranged at a distance from a pixel plane of the multi-pixel display device (for example, translationally / parallel shifted and / or tilted). The light source can be arranged next to the optical elements for light redistribution, which allows flexibility with regard to the required installation space and reduces unwanted heat input. Overall, a compact design of the system for illuminating the multi-pixel display device can be achieved, for example, a small thickness perpendicular to the pixel plane of the multi-pixel display device.

[0096] FIG. 12 is a perspective view of a concrete implementation of the system 500 from FIG. 11. Two deflection mirrors 521, 522 are also shown.

[0097] Of course, the features of the previously described embodiments and aspects of the invention can be combined with one another. In particular, the features can be used not only in the described combinations, but also in other combinations or on their own, without departing from the scope of the invention.

Claims

PATENT CLAIMS 1 . A system (100, 621) for illuminating a pixel plane (11) of a multi-pixel display device (10, 625), the system (100, 621) comprising: - a laser light source (19, 601 , 605), - a speckle noise suppression unit (3, 300, 610), - an optical waveguide (4) which guides coherent light emitted by the laser light source (19, 601, 605) to the speckle noise suppression unit (3, 300, 610), - an optical homogenization plate (1) with a top side (21) and a bottom side (22) and a side surface (23), - a coupling structure (2) which is formed on the side surface (23) of the homogenization plate (1) adjacent to the speckle noise suppression unit (3, 300, 610) and which is configured to couple light coming from the speckle noise suppression unit (3, 300, 610) into the homogenization plate (1), and - a coupling-out structure (7) which is formed on the upper side (21) of the homogenization plate (1) and which is designed to couple out light from the homogenization plate (1) distributed over the entire surface of the coupling-out structure (7) for illuminating the multi-pixel display device (10, 625).

2. System (100, 621) according to claim 1, wherein an aperture of the speckle noise suppression unit (3, 300, 610) is smaller than a lateral extent of the coupling structure (2).

3. System (100, 621) according to claim 1 or 2, wherein a lateral extent of the coupling structure (2) is smaller than an extent of the side surface (23) of the homogenization plate (1).

4. System (100, 621) according to one of the preceding claims, wherein the speckle noise suppression unit (3, 300, 610) is arranged directly adjacent to the coupling structure (2).

5. System (100, 621) according to one of the preceding claims, wherein no collimating lenses are arranged between the speckle noise suppression unit (3, 300, 610) and the optical homogenization plate (1).

6. System (100, 621) according to one of the preceding claims, further comprising: - a light redistribution structure (5) formed on the underside (22) of the homogenization plate (1).

7. System (100, 621) according to claim 6, further comprising: - a reflector structure (6) extending along the light redistribution structure (5) on the underside (22) of the homogenization plate (1).

8. System (100, 621) according to one of the preceding claims, wherein the coupling structure (2) is designed as a lenticular array.

9. System (100, 621) according to one of the preceding claims, wherein the coupling-out structure (7) is designed as a diffuser, optionally as a holographic diffuser with an adjustable angular range.

10. System (100, 621) according to one of the preceding claims, wherein the coupling structure (2) is integral with the homogenization plate (1) as Surface structuring of the side surface (23) is formed.

11. System (100, 621) according to one of the preceding claims, wherein the coupling-out structure (7) is configured to couple the light out of the homogenization plate (1) with a locally variable radiation characteristic (8).

12. System (100, 621) according to one of the preceding claims, wherein the coupling-out structure (7) is configured to change a main radiation direction (205) depending on a position (x,z) on the coupling-out structure (7).

13. System (100, 621) according to claim 12, wherein the coupling-out structure (7) is configured to tilt the main radiation direction (205) along at least one axis (x, z) symmetrically with respect to a center (7') of the coupling-out structure (7).

14. System (100, 621) according to claim 12 or 13, wherein the coupling-out structure (7) is configured to change the main emission direction (205) as a function of the position by rotating an angular spectrum (801 - 805, 811-815) of the emitted light.

15. System (100, 621) according to one of the preceding claims, wherein the speckle noise suppression unit (3, 300, 610) is an active device.

16. System (100, 621) according to one of the preceding claims, wherein the speckle noise suppression unit (3, 300, 610) comprises a resonantly operated mass-spring system comprising a diffuser (301) suspended via one or more springs (302).

17. System (100, 621) according to claim 16, wherein a natural frequency of the mass-spring system of the speckle noise suppression unit (3, 300, 610) is not less than 100 Hz.

18. System (100, 621) according to one of the preceding claims, wherein the coupling-out structure (7) is arranged to illuminate a pixel plane of the multi-pixel display device (100, 625) over its entire area.

19. Image generating device (601) of a head-up display system (600), comprising: - the system (100) according to one of the preceding claims, and - the multi-pixel display device (10, 625).

20. Image forming device (601) according to claim 19, wherein the multi-pixel display device (10, 625) is arranged at a distance from the coupling-out structure (7) and the homogenization plate (1), wherein a distance (12) between the multi-pixel display device (10, 625) and the coupling-out structure (7) is in the range of 20 mm to 35 mm.

21. Image generating device (601) according to claim 19 or 20, wherein the pixel plane (11) of the multi-pixel display device (10, 625) is tilted relative to the homogenization plate (1).

22. Head-up display system, which includes: - the image forming device according to one of claims 19 to 21, and - an optical imaging system with a holographic optical element arranged in a beam path of the light emitted by the image generating device.

23. Head-up display system according to claim 22, wherein the coupling-out structure (7) is configured to couple the light out of the homogenization plate (1) with a radiation characteristic (8) configured to illuminate an entrance pupil of the optical imaging system.

24. A system (100, 500, 621) for illuminating a pixel plane (506) of a multi-pixel display device (10, 625, 507), the system comprising: - a laser light source (19, 601, 605) arranged to emit light along a beam path (606), - a speckle noise suppression unit (3, 300, 502, 610) arranged in the beam path (606), and - a diffuser (7, 505, 620) which is arranged in the beam path (606) emanating from the laser light source (19, 601, 605) behind the speckle noise suppression unit (3, 300, 502, 610) and which is configured to emit the light with an emission characteristic (8, 509) in the direction of the multi-pixel display device (10, 625, 507).

25. The system (100, 500, 621) of claim 24, further comprising - a further diffuser (615) which is arranged in the beam path (606) between the speckle noise suppression unit (3, 300, 502, 610) and the diffuser (7, 506, 620) and which is configured to emit the light with a further emission characteristic (508) in the direction of the diffuser (7, 505, 620), wherein the further emission characteristic (508) is configured to achieve full-surface illumination of an aperture of the diffuser (7, 505, 620).

26. System (500, 621) according to claim 24 or 25, wherein the beam path runs as a free beam between the speckle noise suppression unit and the diffuser.

27. Image generating device (601) of a head-up display system (600), comprising: - the system (100) according to any one of claims 24 to 26, and - the multi-pixel display device (10, 625).

28. Image generating device (601) according to claim 27, wherein the multi-pixel display device (10, 625) is arranged spaced and tilted relative to the diffuser (7, 505, 620).

29. Head-up display system, which includes: - the image forming device according to claim 27 or 28, and - an optical imaging system with a holographic optical element arranged in a beam path of the light emitted by the image generating device.

30. Image generating device for a head-up display system, comprising: - a multi-pixel display device (10, 625), - a light source (19, 601, 605), preferably a laser light source, which is arranged to emit light along a beam path towards the multi-pixel display device, and - a plurality of diffuser elements (7, 505, 615, 620) arranged in cascade along the beam path between the light source and the multi-pixel display device.

31. Head-up display system comprising: - the image forming device according to claim 30, - an optical imaging system with a holographic optical element arranged in a beam path of the light emitted by the image generating device.

32. Head-up display system according to claim 31, wherein the optical imaging system images a pixel plane of the multi-pixel display device onto a virtual image plane with a magnification factor of at least 10x, optionally at least 15x.

Images