Time multiplexes for correcting color aberrations in a transparent screen unit

Abstract

Several examples involve techniques for the synchronized control of a multi-color light source and a multi-pixel display device of an image generation unit for a transparent screen unit, e.g., a head-up display system. This can reduce color aberrations that arise, for example, from the use of holographic optical elements.

Description

TECHNICAL FIELD

[0001] Various examples of the invention relate to techniques for synchronously driving a multi-color light source and a multi-pixel display device of an image forming unit for a transparent display unit. BACKGROUND

[0002] Transparent display units are used in various application scenarios. For example, transparent display 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.

[0003] 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.

[0004] Narrowband or monochromatic light sources are often used. This is especially the case when one or more holographic optical elements (HOEs) are used in an optical imaging system of the HUD system. 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. HOEs are manufactured specifically for a specific wavelength.

[0005] It is known to use multiple monochromatic light sources to serve multiple color channels of the optical imaging system. For example, a red light source, a green light source, and a blue light source can be used to illuminate corresponding color channels of a liquid crystal display. Mixed-color images, in particular, can be generated this way.

[0006] It is observed that the images associated with the different color channels exhibit an undesirable offset from one another. This can occur due to color aberrations in the optical imaging system of the transparent display unit. To reduce or compensate for such undesirable offsets between the individual color images, it is known to apply pre-warping to the individual images. This pre-warping counteracts the observed offset.

[0007] However, it has been observed that in existing systems it is not possible to completely compensate for an offset between the individual color images by means of pre-distortion. BRIEF SUMMARY OF THE INVENTION

[0008] There is a need for improved image generation units with multiple color channels for transparent display units. In particular, there is a need for image generation units that address the above-mentioned limitations, i.e., better reduce or fully compensate for offsets between color frames.

[0009] This problem is solved by the features of the independent patent claims. The features of the dependent patent claims define embodiments.

[0010] A method for controlling an image generating unit for a transparent display unit is disclosed.

[0011] The transparent display unit can, for example, be a HUD system, for example, for projecting information into the field of vision of a car driver. The transparent display unit can also be a holographic display, for example, which displays information on a transparent surface.

[0012] The picture generating unit (PGU) comprises a multi-pixel display device and a multi-color light source. The multi-color light source is configured to emit coherent light in multiple source color channels. This illuminates the multi-pixel display device. Examples of source color channels include red, green, blue, or other complementary color systems.

[0013] For example, lasers or laser diodes can be used. Narrowband light-emitting diodes (LEDs) can also be used.

[0014] The method involves controlling the multicolor light source to emit the coherent light in time slots of a time-division multiplexing scheme. Each time slot is assigned to a single corresponding source color channel of the multiple source color channels. For example, time slot 1 <> red; time slot 2 <> green; time slot 3 <> blue; time slot 4 <> red; and so on.

[0015] The method also includes controlling the multi-pixel display device to display a corresponding display image in each of the time slots, which is associated with the respective wave color channel. The display images are thus each assigned to exactly one source color channel. For example, time slot 1 <> red display image; time slot 2 <> green display image; time slot 3 <> blue display image; time slot 4 <> red display image; and so on.

[0016] The display images exhibit a pre-distortion that reduces the color aberrations of an optical imaging system of the transparent screen unit for the source color channel associated with the respective display image. The optical imaging system can, for example, comprise one or more holographic optical elements and / or mirrors and / or lenses.

[0017] By applying the time-division multiplexing scheme, it is possible to correct color aberrations separately in time through digital preprocessing of the corresponding display images. Typically, color aberrations exhibit a wavelength dependence, meaning, for example, the direction or magnitude of an offset depends on the respective light of the source color channel. By applying the predistortions separately, a higher accuracy in correcting color aberrations can be achieved compared to reference implementations in which multiple source color channels are used simultaneously to illuminate the multi-pixel display device (which then also has multiple display color channels).

[0018] Various techniques are based on the realization that mixing of display color channels can occur in typical multi-pixel display devices. This means that pixels that primarily process light from a first source color channel also exhibit a certain sensitivity to light from a second source color channel. In reference implementations that do not use time-division multiplexing but instead pre-distort multiple source color channels in parallel with multiple display color channels, this results in a mixing of channel-specific pre-distortions; this reduces the quality of the color aberration correction. Activating the different source color channels separately avoids this mixing, and the color aberrations can be better compensated.

[0019] In particular, a translational offset between the images perceived by the user (e.g. virtual images in a HUD system) can be compensated for by shifting the display images in the multi-pixel display device in opposite directions. Such a translational offset is typically created by using a so-called HOE stack in the optical imaging system of the transparent screen unit. Several HOEs are used. The light of each source color channel is assigned a corresponding HOE element. Due to the diffractive properties of the holographic optical elements, they are highly wavelength-sensitive; accordingly, it is necessary to provide separate holographic optical elements for each color channel. The HOEs of the color channels are arranged in a stack structure. Each HOE has a certain thickness.This creates a corresponding offset of the light beam paths of the different channels. Different multi-pixel display devices can be used. In particular, it would be possible to use monochromatic multi-pixel display devices that have a single display color channel. This single display color channel can be broadband, i.e., configured to influence light from all source color channels in the relevant spectrum (e.g., to switch, redirect, or modulate it appropriately). An example would be a switchable digital micromirror array (DMD) without a color filter. By separating the color channels in time, a color image can still be reproduced by selecting a sufficiently fast repetition rate of the time slots. The time-division multiplexing scheme can, for example, have a switching frequency of time slots of no less than N × 25 Hz, where N is the number of color channels.Typically (for red-green-blue channels) N = 3. Color mixing is thus achieved in the viewer's eye by the rapid succession of different displayed color images (e.g. virtual images in the HUD system).

[0020] In other examples, however, a multi-pixel display device with multiple display color channels corresponding to the source color channels could also be used. For example, a liquid crystal display with red-green-blue display channels could be used. Appropriate color filters can be provided for this purpose. Despite any overlap between the display color channels, it is possible to achieve a good level of color aberration control due to the sequential activation of the corresponding source color channels according to the time-division multiplexing scheme.

[0021] In the various examples, the multi-pixel display device is illuminated with phase-coherent light. Accordingly, speckle noise may occur. A system for illuminating a pixel plane of a multi-pixel display device (illumination system) is disclosed, which allows the speckle noise to be suppressed or at least reduced.

[0022] 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 wavelengths red, green, and blue. Aspects related to a multicolor light source have already been described above. The laser light source is generally configured to provide phase-coherent light. This can then cause speckle noise.

[0023] The illumination 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 are also available, for example, a liquid crystal light modulator element. Using the speckle noise suppression unit, the phase profile of the laser light can be modified, in particular, randomized.

[0024] The speckle noise suppression unit can be designed, for example, as a diffuser that is moved in the kHz range.

[0025] The illumination system also includes an optical waveguide that guides the coherent light emitted by the light source to the speckle noise suppression unit. In particular, an optical fiber can be used as the optical waveguide. For example, a multimode fiber could be used. An output coupling lens could be provided at one end of the optical waveguide facing the speckle noise suppression unit.

[0026] The lighting system also includes an optical homogenization plate. This plate has a top side, a bottom side, and (at least) one side surface. The side surface is thus located at the edge between the top side and the bottom side. The thickness of the optical homogenization plate can be defined as the distance between the top side and the bottom side. In a system integration into a PGU of a HUD system, the top side can face a multi-pixel display device (corresponding aspects in connection with the control of a multi-pixel display device were described above). The homogenization plate can be made of Plexiglas or glass. The homogenization plate has a plate-shaped, optically transparent substrate.

[0027] The illumination 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.

[0028] The illumination system further comprises an output coupling structure. This is formed on the upper side of the homogenization plate. The output coupling structure is configured to output light from the homogenization plate, distributed over the entire surface of the output coupling structure, to illuminate 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 output coupling structure. This allows suitable illumination of the pixel plane of the multi-pixel display device to be achieved.

[0029] 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.

[0030] The output coupling structure can be implemented, in particular, as a diffuser. The diffuser scatters the light, thus achieving a specific radiation characteristic.

[0031] 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.

[0032] 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).

[0033] Accordingly, another illumination 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 illumination system also comprises a speckle noise suppression unit, implemented, for example, as a moving diffuser. This is arranged in the beam path. The illumination 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 beam pattern toward the multi-pixel display device.

[0034] 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.

[0035] Optionally, a further diffuser could also be provided, arranged between the speckle noise suppression unit and the diffuser (near the display device). This diffuser is configured to radiate 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.

[0036] Such lighting 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.

[0037] 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.

[0038] A control device for controlling an image generation unit for a transparent display unit is disclosed. The image generation unit comprises a multi-pixel display device and a multi-color light source. The multi-color light source is configured to emit coherent light in a plurality of source color channels to illuminate the multi-pixel display device. The control device is configured to control the multi-color light source to emit the coherent light in time slots of a time-division multiplexing scheme. Each time step is assigned to a single corresponding source color channel of the plurality of source color channels. The control device is further configured to control the multi-pixel display device to display a respective display image associated with the respective source color channel in each of the time slots.The display images have a pre-distortion that reduces color aberrations of an optical imaging system of the transparent screen unit for the source color channel associated with the respective display image.

[0039] It also describes program code that can be executed by a processor, whereby the processor can perform a method as described above.

[0040] 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. SHORT DESCRIPTION OF THE CHARACTERS Fig. 1 schematically illustrates a HUD system with an image generation unit according to various examples. Fig. Figure 2 illustrates a stacked arrangement of several HOEs assigned to different source color channels and forming part of an optical imaging system of the HUD system of Fig. 1 are. Fig. Figure 3 schematically illustrates a lateral displacement of virtual images corresponding to multiple color channels due to color aberrations induced by the stacked HOEs. Fig. Figure 4 schematically illustrates the spectra of several source color channels as well as the spectra of several display color channels. Fig. 5 schematically illustrates a sequence of time slots of a time-division multiplexing scheme for driving the multi-color light source of the multi-pixel display device according to various examples. Fig. 6 is a flowchart of an exemplary method. Fig. 7 is a schematic view of an exemplary illumination system for illuminating a multi-pixel display device. Fig. 8 is another side view of the exemplary system from Fig. 7. Fig. 9 is a perspective view of the exemplary system from Fig. 7. Fig. Figure 10 schematically illustrates a speckle noise suppression unit. Fig. 11 is a schematic view of an exemplary lighting system for illuminating a multi-pixel display device. Fig. 12 is a perspective view of the exemplary system of Fig. 11. DETAILED DESCRIPTION

[0041] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0042] The present invention is explained in more detail below using preferred embodiments with reference to the drawings. In the figures, identical reference numerals designate identical or similar elements. The figures are schematic representations of various embodiments of the invention. Elements shown in the figures are not necessarily drawn to scale. Rather, the various elements shown in the figures are depicted in such a way that their function and general purpose will be understood by those skilled in the art. Connections and couplings between functional units and elements shown in the figures can also be implemented as an indirect connection or coupling. A connection or coupling can be implemented wired or wirelessly. Functional units can be implemented as hardware, software, or a combination of hardware and software.

[0043] Fig. 1 schematically illustrates a HUD system 100 according to various examples. The system 100 includes an image generation unit 115. The image generation unit 115 includes a multicolor light source 111 configured to emit red light, blue light, and green light. In particular, coherent, narrowband light is emitted. The multicolor light source 111 is thus configured to emit narrowband, coherent light in three source color channels 301, 302, 303 (hereinafter simply referred to as color channels).

[0044] The corresponding beam paths of the three corresponding color channels 301, 302, 303 (red - green - blue) of the HUD system 100 are shown with solid, dotted and dashed arrows.

[0045] In addition, the image generation unit 115 also includes a multi-pixel display device 112. Generally, a monochromatic multi-pixel display device 112 or a multi-pixel display device with multiple display color channels can be used. An example implementation would be a liquid crystal display with a red display color channel, a green display color channel, and a blue display color channel. An alternative would be, for example, an implementation of the multi-pixel display device 112 using a DMD.

[0046] An illumination system 30 may optionally be provided between the multi-color light source 111 and the multi-pixel display device 112, which is configured to improve the illumination of the multi-pixel display device 112.

[0047] The multicolor light source 111 and the display device 112 are controlled by a control unit 119. The control unit 119 can be implemented, for example, as a processor with a memory, whereby the processor can load and execute program code from the memory. It would be possible for the control unit 119 to be implemented as an application-specific integrated circuit or as a field-programmable gate array (FPGA). A combination of corresponding logic circuits is also conceivable.

[0048] The control unit 119 can, for example, activate or deactivate different color channels of the multi-color light source 111. The control unit 119 can display different displays on the multi-pixel display device 112, e.g.—if the display device 112 is a multi-pixel display device with multiple color channels—on one or more color channels. The control unit 119 can deactivate individual color channels on the multi-pixel display device 112; in such a case, the corresponding pixels assigned to the respective deactivated color channel are controlled such that light is not transmitted.

[0049] The HUD system 100 also includes an optical imaging system 113. This is configured to generate a virtual image of the display images of the display device 112, which is visible from an eyebox 114. The optical imaging system 113 can comprise one or more lenses and / or mirrors. Alternatively or additionally, the optical imaging system 113 can comprise one or more HOEs, which are used, for example, for beam shaping. If particularly narrowband and coherent light is generated by the multi-color light source 111, the optical imaging system 113 and / or image generation unit 115 can comprise a speckle noise suppression unit. For example, a moving diffuser can be used to reduce speckle noise. For example, the speckle noise suppression unit could be part of the system 30 for illuminating the multi-pixel display device 112.

[0050] As described above, it is possible that the optical imaging system 113 comprises one or more HOEs. Details will be described in connection with Fig. 2 discussed.

[0051] Fig. 2 illustrates that the optical imaging system 113 can have a stack structure 150 comprising a plurality of HOEs 151, 152, 153. Each of the HOEs 151, 152, 153 can be configured, for example, as a volume hologram in which a transparent substrate is provided with a refractive index modulation. The spatial frequency of the respective refractive index modulation is tuned to the wavelength of a corresponding color channel 301, 302, 303, so that the light from the other color channels passes through the respective holographic optical element unaffected. The stack structure with a finite thickness of the holographic optical elements 151, 152, 153 results in a splitting of the beam paths of the color channels 301, 302, 303, as shown in Fig. 2. This shifts the virtual images 180 of the color channels 301, 302, 303 against each other, as shown in Fig. 3. This lateral offset is reduced in reference implementations by pre-distorting the respective display images of the multi-pixel display device 112, which are assigned to the different color channels 301, 302, 303. However, in conventional multi-pixel display devices, a mixture of the display color channels is present, so that the pre-distortion actually intended for the red color channel 301 would also affect the green color channel 302. This is shown in Fig. 4 shown.

[0052] In Fig. Figure 4 shows the spectra of the multicolor light source 111 for the color channels 301, 302, and 303 (dashed-dotted lines). These emission spectra are narrowband, meaning they typically have a width of no more than 5 nm.

[0053] Furthermore, Fig. 4 shows the spectra of the display color channels 391, 392, 393. Fig. 4, it can be seen that, for example, the spectrum of the display color channel 391 has a maximum approximately at the position of the maximum of the spectrum of the source color channel 301, but the spectrum of the source color channel 302 is located on a flank of the spectrum of the display color channel 391. As a result, a pre-distortion applied to the display image for the source color channel 301 also affects the source color channel 302 to a certain extent. Therefore, the lateral offset between the source color channels 301, 302, 303, which is perceived in the virtual images 180 (cf. Fig. 3), cannot be fully compensated. To solve or at least alleviate this problem, a time-division multiplexing scheme can be used. This is Fig. 5 illustrated.

[0054] Fig. 5 illustrates time slots 501-506 of a time-division multiplexing scheme 500. Time slot 501 and time slot 504 are assigned to color channel 301; time slot 502 and time slot 505 to color channel 302; and time slot 503 and time slot 506 to color channel 303.

[0055] During time slots 501 and 504, the multi-color light source 111 is controlled to emit only light according to the color channel 301. Simultaneously, the multi-pixel display device 112 is controlled to display a corresponding display image 511 associated with the color channel 301 during time slots 501, 504. During time slots 502, 505, the color channel 302 is then activated; furthermore, a display image 512 is activated, which has a predistortion appropriate for the color channel 302. During time slots 503, 506, the color channel 303 is activated. Furthermore, the multi-pixel display device 112 is controlled to display the display image 513, which has a predistortion associated with the color channel 303. In other words, a sequential and color-discrete multiplexing of the individual RGB color channels takes place.For each display image associated with a single color channel, the corresponding light emitter associated with the same color channel is also activated in the corresponding time slot. Thus, individual color channel images are displayed on the multi-pixel display device.

[0056] Fig. 6 is a flowchart of an exemplary method. The method of Fig. 6 is computer-implemented. The method from Fig. 6 can be applied by a control device of an image generation unit for a transparent display unit. For example, the method from Fig. 6 from the control unit 119 of the HUD system 100 Fig. 1 can be applied.

[0057] In box 905, it is checked whether the next time slot of a sequence of time slots of a time-division multiplexing scheme has started or is starting.

[0058] If this is the case, a signal is sent in box 910 to the respective time slot according to a predefined scheme (for example “round robin”, ie toggling through all color channels one after the other, cf. Fig. 5) assigned source color channel is selected as the current source color channel (see color channels 301, 302, 303 in Fig. 1)

[0059] In box 915, a current display image for the activated color channel is then obtained, and if necessary, in box 920, a specific predistortion is calculated for this current display image. The predistortion can also be precalculated. Techniques for determining the predistortion are known in the art. For example, a lateral offset due to a translational color aberration can be corrected by appropriately translating pixels in the display image.

[0060] In box 925, a multicolor light source is then controlled to activate one or more light emitters of the current source color channel (see box 910). In box 930, the current image with predistortion (see box 915, box 920) is displayed on the multi-pixel display device by controlling the multi-pixel display device accordingly. If the multi-pixel display device has multiple color channels, the current image is displayed on the display color channel associated with the current color channel, and the other display color channels are turned off. For a multi-pixel display device without multiple color channels, the current image is displayed on the single channel.

[0061] Box 905 is then executed again for the next time step. By executing the repeated iterations of box 905 quickly enough, i.e., by keeping the time slots short enough (switching frequency of the time slots), color mixing of the virtual images generated by the images displayed in box 930 occurs in the viewer's eye.

[0062] Fig. 7 schematically illustrates an illumination system 7030 for illuminating a multi-pixel display device 112 (cf. Fig. 1). The lighting system 7030 can, for example, be the lighting system 30 of Fig. 1. Laser light (e.g. red-green-blue channels or fewer or more channels; cf. Fig. 1: Channels 301, 302, 303) from a laser light source 111 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 an 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.

[0063] 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).

[0064] 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. The movement frequency can be adjusted, for example. This allows speckle noise to be effectively suppressed.

[0065] 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.

[0066] 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.

[0067] 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 may 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.

[0068] The coupling structure 2 can be designed, 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 designed with a corresponding surface topography (e.g., as a lenticular array in the form of indentations on the side surface 23).

[0069] 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.

[0070] 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).

[0071] The design specifications, such as lateral homogeneity and spatial orientation of the light field 8 emitted by the homogenization plate 1 (radiation characteristic of the homogenization plate 1) can be adjusted by the design, 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).

[0072] 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.

[0073] To specifically adjust the angular distribution of the light field leaving the homogenization plate, an optional coupling structure 7 can be used on the upper side 21 of the homogenization plate 1. This can be designed as a diffractive diffuser. By means of a suitable design of the coupling structure 7, a pixel plane 11 of the multi-pixel display device 112 can be illuminated in a customized manner. For example, OLED pixels or micromirrors are arranged in the pixel plane 11.

[0074] 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.

[0075] 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.

[0076] To suppress the visibility of the diffuser features of the output coupling structure 7 to the human eye, it may be useful to decouple, i.e., distance, the pixel plane 11 from the exit plane or the output coupling structure 7 (see gap 12). This depends on the system requirements. The gap 12 is preferably larger than 20% of the thickness 13 of the homogenization plate 1.

[0077] Furthermore, it is possible to incline or tilt the pixel plane 11 relative to the homogenization plate 1.

[0078] Fig. 8 is a side view of the lighting system 7030 of Fig. 7. In Fig. 8 it can be seen that the lateral extension of the coupling structure 2 is smaller than the extension of the side surface 23 of the homogenization plate 1, ie along the z-axis in Fig. 8 along the long side of the side surface 23. For example, the coupling structure 2 in the example of Fig. 8 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, however, 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 further smaller than the lateral extent of the coupling structure 2. In general, the lateral extent of the speckle noise suppression unit 3 can, for example, not 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 be achieved, 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 (lens-shaped, 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, at the output 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 shown in the perspective view of the illumination system 7030 in . Fig. 9 can be seen.

[0079] Fig. 10 schematically shows a speckle noise suppression unit 9300. This can, for example, be the speckle noise suppression unit 3 from Fig. 7. The speckle noise suppression unit 9300 comprises a diffuser 9301 in an xy-plane. To move the diffuser 9301 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 9301. Corresponding actuators 9303, which are mounted via a frame in a fixed reference system (mounting 9304), are in Fig. 9. The drive frequency of the electrodynamic actuators 9303 can be dynamically adjusted within a relatively wide frequency range, so that, for example, one or more eigenmodes of the mass-spring system (formed by the diffuser 9301 and return springs 9302) are resonantly excited. In such resonant states, the best despeckle results can be achieved. This type of drive can be designed as a single- or dual-axis system (in Fig. 10 shows an example of a two-axis system. Furthermore, it is also possible to initiate a non-deterministic movement via one or more vibration motors (e.g., miniature motors with eccentric flywheels on a motor shaft) connected to the support frame of the diffuser.

[0080] 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 the design, so there may be a trade-off between different target variables.

[0081] The scenario of Fig. Figure 10 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 Figure 10). Fig. 10) or a fiber optic cable. Temporarily changing the beam path causes the speckles to "smear" over time, reducing the perceived noise. Alternatively, the phase of the incident light could also be changed, e.g., using spatial light modulators (SLMs).

[0082] Fig. 11 schematically illustrates a lighting system 10500. The lighting system 10500 provides functionality similar to the lighting system 7030 on Fig. 7. In Fig. 11 is (unlike in Fig. 7) a free beam path for the light is used to illuminate a multi-pixel plane 10506 of a multi-pixel display device 112.

[0083] The light is generated by a laser light source 10501. From the laser light source 10501, the light propagates to a speckle noise suppression unit 10502. This can be implemented like the speckle noise suppression unit 9300 in Fig. 10 be trained.

[0084] The light can propagate as a free beam between the laser light source 10501 and the speckle noise suppressor of a 10502. It is also conceivable that the light is guided by a fiber optic cable.

[0085] The speckle noise suppression unit 10502 itself has a moving diffuser that implements a specific radiation characteristic 10507. This illuminates another diffuser 10504, which in turn provides a radiation characteristic 10508. The radiation characteristic 10508 is configured to achieve homogeneous illumination of another diffuser 10505. The diffuser 10504 thus assumes the functionality of the homogenization plate 1 together with the light redistribution structure 5 in Fig. 7.

[0086] The light can propagate as a free beam between the speckle noise suppression unit and the diffuser 10504 and between the diffuser 10504 and the diffuser 10505.

[0087] The diffuser 10505 has a radiation characteristic 10509. This radiation characteristic 10509 can be adjusted to illuminate an entrance pupil of an optical imaging system of a HUD system as desired.

[0088] Then, the pixel plane 10506 of the multi-pixel detector 112 is illuminated. This, in turn, has a radiation characteristic 10510.

[0089] Fig. 12 is a perspective view of a concrete implementation of the system 500 of Fig. 11. Two deflecting mirrors 521, 522 are also shown.

[0090] 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.

[0091] For example, various aspects related to a HUD system were discussed above. However, other transparent display units, such as holographic displays, can also benefit from the techniques described herein. Other optical imaging systems, such as those for projectors, can also benefit from the techniques described herein.

[0092] Furthermore, the above discussion primarily focused on color aberrations caused by a stack of HOEs, i.e., a translational offset from the images perceived by the user. However, other types of color aberrations can also be compensated. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2022 / 189275 A1

[0037]

Claims

[1] A method for controlling an image generation unit (115) for a transparent display unit (100), wherein the image generation unit (115) comprises a multi-pixel display device (112) and a multi-color light source (111), wherein the multi-color light source (111) is configured to emit coherent light in a plurality of source color channels (301, 302, 303) so as to illuminate the multi-pixel display device (112), the method comprising: - controlling (925) the multi-color light source (111) to emit the coherent light in time slots (501, 502, 503, 504, 505, 506) of a time-division multiplexing scheme (500), each time slot (501, 502, 503, 504, 505, 506) being assigned to a single corresponding source color channel (301, 302, 303) of the plurality of source color channels (301, 302, 303), and - controlling (930) the multi-pixel display device (112) to display a respective display image (511, 512, 513) in each of the time slots (501, 502, 503, 504, 505, 506) associated with the respective source color channel (301, 302, 303), wherein the display images (511, 512, 513) have a pre-distortion that reduces color aberrations of an optical imaging system (113) of the transparent screen unit (115) for the source color channel (301, 302, 303) associated with the respective display image (511, 512, 513). [2] Method according to claim 1, wherein the color aberrations are caused by a layer thickness of stacked holographic optical elements (151, 152, 153) of the optical imaging system (113), wherein different ones of the stacked holographic optical elements (151, 152, 153) are associated with different ones of the plurality of source color channels (301, 302, 303). [3] The method of claim 1 or 2, wherein the multi-pixel display device (111) comprises a single display color channel configured to affect light of all source color channels (301, 302, 303). [4] Method according to claim 1 or 2, wherein the multi-pixel display device (111) has an associated display color channel (391, 392, 393) for each source color channel (301, 302, 303), where spectra of the display color channels overlap with each other. [5] A method according to any one of the preceding claims, wherein the time division multiplexing scheme is a switching frequency of time slots of not less than N*25 Hz, where N is the number of source color channels. [6] Control device (119) of an image generation device (115) for a transparent screen unit (100), which is arranged to carry out the method according to one of the preceding claims. [7] System (100) comprising the control device (119) and the image generating device (115). [8] The system (100) of claim 7, wherein the system (100) further comprises an illumination system (30, 7030, 10500) for illuminating the multi-pixel display device (112). [9] The system (100) of claim 8, wherein the illumination system (30, 7030, 10500) further comprises a speckle noise suppression unit (3, 9300, 10502). [10] Program code that can be loaded and executed by a processor, wherein the processor, when executing the program code, carries out methods according to any one of claims 1 to 5.

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