Display device and method for tracking virtual visible areas

Abstract

This invention relates to a display device for representing two-dimensional and / or three-dimensional scenes. The display device includes at least one illumination device for emitting sufficiently coherent light, at least one spatial light modulation device, at least one optical system, and a tracking device. A hologram is encoded into the at least one spatial light modulation device via monoparallax coding. The at least one optical system is configured to generate at least one virtual visible area at the position of an observer's eye. The encoded orientation of the hologram on the spatial light modulation device can be modified by the tracking device.

Description

[0001] This invention relates to a display device for representing two-dimensional and / or three-dimensional scenes. The invention is particularly intended to relate to a holographic display device, especially one provided close to the observer's eyes, such as a head-mounted display. The invention also relates to a method by which tracking of a virtual visible area (particularly a smaller area) can be achieved.

[0002] Compared to autostereoscopic displays or display devices, holographic displays or display devices generally present greater challenges in terms of the resolution of the spatial light modulation device present in the holographic display device and used for encoding the hologram, as well as in terms of the computational workload of the hologram.

[0003] WO 2006 / 066919 A1 describes, for example, how to reduce these requirements. For example, it describes there the generation of a virtual observer window, which is set within the diffraction order of the Fourier spectrum of a hologram encoded in a spatial light modulation apparatus, and through which an observer can view a reconstructed scene (preferably a three-dimensional scene) in a reconstructed space that may extend in front of and / or behind the spatial light modulation apparatus.

[0004] For the reconstruction of a single object point, this means that for any given object point in the scene, a sub-hologram is encoded into the spatial light modulation device. In one embodiment, the extension and position of the sub-hologram on the spatial light modulation device can be defined, for example, by projection of a visible area on the object point onto the spatial light modulation device via a virtual observer window or the object point itself. The overall hologram of a preferred 3D scene with multiple object points is represented as an overlap of sub-holograms of all object points in the 3D scene. The individual sub-holograms do not completely overlap each other, but rather are moved relative to each other according to the object point to which they will be reconstructed, so that only a portion of their surfaces is overlapped by one or more sub-holograms.

[0005] In other words, spatial image points can be generated in a holographic display device by encoding object points in sub-holograms. Encoding can be implemented in an external general-purpose computer system or in a control unit installed in the holographic display. It is known that the extension of any sub-hologram in a spatial light modulation device can be fixed (e.g., depending only on the depth position of the object point relative to the spatial light modulation device) or can be variable as required. It is further known that the geometric position of the sub-hologram on the spatial light modulation device and its extension can be changed according to technical requirements, such as the position of the observer's eye relative to the light modulation device for reconstructing the scene or the position of the voxels or pixels to be represented within the scene. The calculation of the encoded values ​​of the display points typically consists of the encoded values ​​of many object points. The calculation of the encoded values ​​is typically performed in a computing unit with a resolution higher than the actual panel bit depth. Normalization and mapping to pixel values ​​are performed only after the encoded values ​​are calculated, where, for example, nonlinearities of the gamma curve or other pixel-dependent calibration values ​​may be considered.

[0006] Multiple different or similar pixels or subpixels in a spatial light modulation device can be further combined into macropixels. However, spatial light modulation devices that do not do this can also exist. According to the present invention, this type of spatial light modulation device can be used similarly.

[0007] Figure 1 An apparatus is shown in which a sub-hologram SH is generated as a projection onto the spatial light modulation device SLM onto a plurality of object points having different depths relative to the object points. It is evident that the position of the sub-hologram on the SLM depends on the position of the object point relative to the visible region VW. The size, expansion, or magnitude of the sub-hologram also depends on the z-position of the encoded object point, where z is the distance between the object point and the SLM. In most cases, overlap of the sub-holograms occurs.

[0008] For holographic reconstruction of a scene (preferably a 3D scene), a sub-hologram is used in conjunction with a virtual visible region (also known as the observer region or observer window), through which the observer can observe the reconstructed scene.

[0009] For the purposes of head-mounted displays (HMDs), head-up displays (HUDs), or projection displays that have real or virtual images with a spatial light modulation device (also abbreviated as SLM), the term “SLM” as used herein is intended to refer to the image of the SLM that is visible from the virtual visible area.

[0010] Writing complex-valued holograms into a spatial light modulation device typically requires generating a 3D scene from the hologram. Here, multiple pixels of the spatial light modulation device can be combined by encoding to form macropixels, or they can be combined with a beam combiner to form macropixels.

[0011] Holographic display devices are particularly based on the diffraction effect at the aperture of the pixels in a spatial light modulation device and the interference of coherent light emitted by a light source. However, some important conditions for generating virtual visible areas in holographic display devices can be formulated and defined using geometric optics, and will be briefly mentioned here.

[0012] On the one hand, the path of the illumination beam in the display device is important here. This is especially important for generating a virtual visible region. The spatial light modulation device is illuminated by an illumination device containing at least one real or virtual light source. Then, light emitted from different pixels of the spatial light modulation device must be directed into the virtual visible region in each case. For this purpose, the illumination device typically images at least one light source of the spatial light modulation device onto an observer plane having the virtual visible region. This imaging of the light source is performed, for example, at the center of the virtual visible region. If the spatial light modulation device is illuminated with a plane wave corresponding to a light source at infinity, light from different pixels of the spatial light modulation device (e.g., light emitted perpendicular to these pixels) will be focused into the center of the virtual visible region. Light emitted not perpendicularly but rather at the same diffraction angle from different pixels of the spatial light modulation device in each case is then similarly focused at the same location in the virtual visible region in each case. However, the virtual visible region can also typically be moved laterally relative to the image of at least one light source; for example, the position of the image of at least one light source may coincide with the right or left edge of the visible region.

[0013] On the other hand, besides in direct-view displays, the imaging beam path is important in holographic display devices. Typically, head-mounted displays (HMDs) generate magnified images, such as spatial light modulation devices with smaller extensions. This is usually a virtual image seen by an observer at a greater distance than the spatial light modulation device itself is located at. The individual pixels of the spatial light modulation device are typically imaged in a magnified form.

[0014] The description of the present invention is primarily intended to refer to the case where a virtual visible region, comprising a virtual observer window and an optimal light spot, exists in the plane of the light source image. However, by corresponding transformations of the planes of the imaging beam path and the illumination beam path or the spatial light modulation device and the Fourier plane, the statements made are also accordingly applicable to embodiments of holographic display devices or displays having spatial light modulation devices imaged onto the virtual visible region. Therefore, the present invention is not intended to be limited to the case where a virtual visible region (i.e., a virtual observer window or an optimal light spot) exists in the plane of the light source image.

[0015] In principle, the possibility of using full disparity coding or single disparity coding to compute holograms or subholograms is known.

[0016] In the case of a holographic display device or display that generates a virtual visible region, total parallax encoding means that the virtual visible region has horizontal and vertical extensions, where these extensions are less than or equal to the generated diffraction order in their respective dimensions. The size of the diffraction order is determined by the individual horizontal or vertical pixel spacing of the spatial light modulation device used, the wavelength of the light used, and the distance between the spatial light modulation device and the virtual visible region. The virtual visible region is formed by a two-dimensional virtual observer window. Sub-holograms of object points in a three-dimensional (3D) scene also have horizontal and vertical extensions, typically comprising multiple pixels on the spatial light modulation device. The sub-hologram focuses light in the horizontal and vertical directions to reconstruct the object point. Both the virtual visible region and the sub-hologram can have, for example, rectangular shapes, but other shapes, such as circular or hexagonal shapes, are also possible in common use.

[0017] By comparison, when a hologram or subhologram is encoded with single disparity into a spatial light modulation device, the expansion of the generated virtual observer window is limited only by the expansion of the diffraction order in one dimension or direction (hereinafter referred to as the encoding direction of the hologram or subhologram). A subhologram typically occupies part of a single pixel row in the case of horizontal single disparity encoding, or part of a single pixel column in the case of vertical single disparity encoding on a spatial light modulation device, and thus has only one pixel in one dimension or direction, typically containing more than one. In this case, the subhologram essentially corresponds to a cylindrical lens that focuses light in one direction.

[0018] In other words, this situation can be explained in such a way that, in the case of single-parallax encoding, the virtual observer window exists only in one dimension or direction (i.e., the encoding direction of the hologram), and the optimal viewing range (also referred to as the optimal spot, similar to a stereoscopic display) exists in another dimension or direction (i.e., perpendicular to the encoding direction). Therefore, the term "optimal spot direction" is also used in this document if the encoding direction of the hologram is not referenced. The virtual observer window and the optimal spot then together form a virtual visible region in the observer plane, in which the observer is located to observe the generated scene. Furthermore, this name and meaning of the virtual visible region is used in the following disclosure according to the invention.

[0019] Full disparity coding of a hologram or subhologram requires sufficient coherent light equally in all directions or spatial directions, and this light must be emitted by a light source. In contrast, single disparity coding requires sufficient coherent light only in the coding direction of the hologram. In the optimal spot direction, i.e., the non-coding direction of the hologram, the coherence of the light can be less than that in the coding direction of the hologram.

[0020] The coherence of light can be set, for example, by the angular spectrum of the illumination from the spatial light modulation device. Different coherences of light can be set, for example, by using a slit light source, along the encoding direction of the hologram and in the optimal spot direction. Different angular spectra and different coherences of light are produced in the narrow side direction of the slit light source compared to its long side direction.

[0021] For example, diffusers can be used to achieve different coherence of light in the encoding direction and in the optimal spot direction. These diffusers can be positioned, for example, between the light source and the virtual visible area, or upstream or downstream of the spatial light modulation device in the light propagation direction, and have different scattering characteristics in the encoding direction and in the optimal spot direction of the hologram, particularly having a very narrow scattering angle in the encoding direction and a wide scattering angle in the optimal spot direction. This type of diffuser is also called a one-dimensional (1D) diffuser. A diffuser may exist, for example, as a product having a scattering angle of 40° in one direction and a scattering angle of 1° in the direction perpendicular to that direction.

[0022] However, in the case of single disparity coding, equally coherent illumination in the coding direction of the hologram and in the optimal spot direction can also be optionally used, wherein the expansion of the virtual observer window is the maximum value of a diffraction order in the coding direction, and the expansion of the optimal spot can be multiple diffraction orders in the optimal spot direction.

[0023] Horizontal or vertical monoparallax coding is generally known. Monoparallax coding can typically be used in conjunction with rectangular pixels of a spatial light modulation device, and / or with spatial color multiplexing and / or spatial multiplexing of the left / right eye on a spatial light modulation device, using color filters arranged in a stripe configuration. The size of the virtual observer window is proportional to the inverse of the pixel pitch. Therefore, in a display with rectangular pixels but no color filters, a smaller virtual observer window is disadvantageously produced in the direction of the long side of the pixel (i.e., in the direction of larger pixel pitch) than in the direction of the short side of the pixel (i.e., in the direction of smaller pixel pitch). Therefore, in a display without color filters, in the case of monoparallax coding with rectangular pixels, the direction of smaller pixel pitch is typically used as the coding direction of the hologram.

[0024] In displays with spatial color multiplexing, holograms can be written in an interleaved manner for different colors (typically red, green, and blue). When illuminated by a light source of one color (e.g., a red laser), color filters of other colors (e.g., green and blue) block the light. For this light source, the other color filters function in a similar way to the black areas that block light. Therefore, for a single color of light, the color pixels function in the same way as pixels with smaller apertures in the direction perpendicular to the color filter strips. Disadvantageously for the virtual observer window is that smaller apertures in this direction will result in more light at higher diffraction orders. In this case, the spacing perpendicular to the color filter strips that determines the size of the virtual observer window is the spacing to the nearest pixel with the same color filter.

[0025] For example, the direction parallel to the color filter strips will be used as the encoding direction of the hologram because a larger pixel aperture is typically present in this direction, and more light is present in the desired diffraction order. Conversely, the direction perpendicular to the color filter strips can be advantageously used because a smaller pixel aperture results in more light in higher diffraction orders, and multiple diffraction orders can also be used for the optimal spot size. Additional scattering elements used to generate the optimal spot size can potentially be omitted.

[0026] This also applies to the spatial multiplexing of the observer's left and right eyes. Here, the pixel spacing to the nearest pixel, perpendicular to the multiplexing strips of the observer's two eyes for the same eye and possibly for the same color, will determine the size of the virtual observer window. The multiplexing strips again effectively act as a smaller aperture in the direction perpendicular to the strips. The encoding direction parallel to the multiplexing strips will typically be chosen.

[0027] These examples demonstrate that single parallax coding is typically a fixed choice combined with specific parameters of the spatial light modulator or color or spatial multiplexing arrangement.

[0028] When the observer's eye position changes or moves, holographic display devices or displays using virtual visible areas typically need to track the virtual visible area.

[0029] Eye position is typically detected using a detection system (eye locator). As disclosed, for example, in WO 2010 / 149587 A2, optical elements (e.g., diffractive elements for light deflection) can also be used to move or track a virtual visible area to a newly detected eye position.

[0030] Solutions for coarse and fine tracking, combining virtual visible regions to new positions of the observer's eye following eye movements, have been disclosed in the prior art. Using a combination of different optical elements, one optical element tracks the virtual visible region to the newly detected eye position with a coarse or large step over a wide angular range; this is called coarse tracking. However, a second optical element tracks the virtual visible region to the newly detected eye position with a precise or small step over a narrow angular range; this is called fine tracking. However, using two different conventional optical elements to track the virtual visible region to different positions in the observer plane can be somewhat cumbersome.

[0031] Certain types of holographic display devices or displays (such as holographic head-mounted displays (HMDs)) require only a small eye-tracking area. For example, an HMD can be fixedly attached to an observer's head, similar to glasses or goggles, so that the entire device moves with the head. In this case, separate tracking is not required, or in particular, coarse tracking is not needed. Tracking the virtual visible area is only required when the position of the observer's pupil changes substantially within the eye or otherwise moves out of the virtual visible area. Here, using conventional optical elements to track the virtual visible area would be quite cumbersome, as this would particularly increase the overall size and weight of the HMD, which is especially disadvantageous in the case of a device attached to the observer's head. Furthermore, this could adversely affect light efficiency and energy consumption, which is particularly disadvantageous in the case of mobile (typically battery-operated) devices.

[0032] For example, WO 2018 / 037077 A2 describes the possibility of moving a virtual observer window over a small area by encoding via a prism function for fine tracking. However, this can only be done on a small number of diffraction orders due to the generally decreasing reconstruction intensity towards higher diffraction orders. The smaller the diffraction order, the smaller the area that can be moved, particularly by encoding via a prism function.

[0033] In principle, the virtual visible area can also be selected in such a way that its expansion is smaller than the expansion of the observer's pupil. For example, this can be accomplished by generating diffraction orders smaller than the observer's pupil expansion, by selecting the pixel spacing of the spatial light modulation device, the observer distance, and the wavelength of the light, and by using a filter device that filters out other diffraction orders so that only a single diffraction order can reach the observer's pupil.

[0034] If the size of the virtual visible area is, for example, about 1 mm, since the diffraction order is only about 1 mm in size, then the possible area of ​​movement within a small number of diffraction orders is limited to slightly smaller than, for example, ±1 mm to 2 mm by encoding, for example, a prism function. For example, in a head-mounted display, this is insufficient to cover the range of possible pupil movements within the eye.

[0035] Therefore, the object of the present invention is to provide a display device that can perform precise tracking or tracing of a virtual visible area in a small area in a simple manner.

[0036] In particular, one solution is intended to be provided for near-eye holographic display devices, such as holographic head-mounted displays, which generate a small virtual visible area, particularly smaller than the pupil of the observer's eye, in order to enable tracking of the virtual visible area in the event of pupil movement within the eye.

[0037] Furthermore, the object of this invention is to provide a corresponding method for precisely tracking virtual visible regions.

[0038] According to the present invention, this objective is achieved by a display device having the features of claim 1.

[0039] According to the present invention, a display device is provided that is particularly suitable for use as a near-eye display, and particularly suitable here for use as a head-mounted display, but such use is not intended to be limited to these displays or display devices. The display device can also be used, for example, as a future head-up display having a larger field of view than conventionally available head-up displays to date, or as a direct-view display in which coarse and fine tracking of the virtual visible area can be performed.

[0040] However, the present invention is intended to address only the fine tracking of virtual visible areas and to provide solutions in this regard. According to the present invention, fine tracking of virtual visible areas is intended to be understood as tracking that extends within a small range of a few millimeters (e.g., up to about 25 mm) in the horizontal and / or vertical directions in each case.

[0041] A display device of this type (particularly designed as a holographic display device) for representing two-dimensional and / or three-dimensional objects or scenes according to the invention comprises at least one illumination device emitting sufficiently coherent light, at least one spatial light modulation device for modulating the incident light, at least one optical system, and a tracking device. A hologram is encoded into the at least one spatial light modulation device via monoparallax coding. At least one optical system is provided to generate at least one virtual visible area at the position of the observer's eye. The encoded orientation of the hologram of the object points of the scene to be represented can be changed on the spatial light modulation device via the tracking device. The tracking device can be particularly provided for precisely tracking the at least one virtual visible area to the changing position of the observer's eye.

[0042] A hologram represents the sum of all sub-holograms, where each sub-hologram is assigned to each object point in the scene to be represented. A change in the encoding direction of the hologram means that the encoding direction also changes for each individual sub-hologram.

[0043] Due to the change in the encoding direction of the hologram on at least one spatial light modulation device, at least one virtual visible region can be advantageously moved to different positions depending on the new position of the observer's pupil. The hologram is encoded into at least one spatial light modulation device by single disparity encoding, i.e., it is then added together by one-dimensional sub-holograms. Therefore, different encoding directions of the hologram can be achieved by rotating the one-dimensional sub-hologram in different directions starting from the original center point on at least one spatial light modulation device. This means changing the encoding direction of the hologram for fine tracking, and due to the rotation of the hologram, at least one virtual visible region can also be moved, i.e. rotated, such that at least one virtual visible region is tracked accordingly or always overlapped with the pupil as it moves, so that the observer of the scene can always view the scene at a correspondingly high resolution.

[0044] Therefore, a change in the encoding direction of the hologram on the spatial light modulation apparatus means adjusting the hologram computation so that sub-holograms can be encoded in pixels set in a portion of a pixel row, a portion of a pixel column, or along the diagonal of the spatial light modulation apparatus, and then added together to form a hologram. Depending on the chosen encoding direction of the hologram, the hologram computation will thus change for the same represented scene (preferably a 3D scene).

[0045] The tracking device according to the invention is particularly suitable for fine tracking of at least one virtual visible area, i.e., only applicable to small movements of the pupil or eye, such as those that may occur when using a head-mounted display. For movements in which the observer also moves to different positions (e.g., in conjunction with a direct-view display device), such large tracking of at least one virtual visible area is achieved only through coarse tracking, wherein, according to the invention, fine tracking can then be used to accurately locate at least one virtual visible area relative to the eye region.

[0046] Coarse tracking will, for example, change the position of the virtual visible area in steps of approximately 25 mm horizontally and vertically. Fine tracking, however, will be used within an area of ​​approximately 25 mm horizontally × 25 mm vertically. However, the invention is not intended to be limited to this numerical example.

[0047] In this way, a tracking device that is no more complex than, for example, a diffraction device according to WO 2010 / 149587 A2 can be provided. Therefore, head-mounted displays can be designed to be more compact and cheaper in structure.

[0048] Other advantageous embodiments and improvements of the invention can be found in the other dependent claims.

[0049] At least one virtual visible area can be advantageously formed by a virtual observer window and an optimal spot, wherein the virtual observer window is provided in the encoding direction of the hologram and the optimal spot is provided in the non-encoding direction of the hologram.

[0050] In the case of single disparity coding, at least one virtual visible region is formed by a virtual observer window generated in the coding direction of the hologram and an optimal spot generated in the non-coding direction (i.e., in the optimal spot direction). In the optimal spot direction, light is distributed on an extended optimal spot that is narrower than the observer's eye distance. Furthermore, the extension of the optimal spot is greater than the extension of the virtual observer window in the coding direction.

[0051] In a particularly advantageous embodiment of the invention, the encoding direction of the hologram can be varied between at least two directions.

[0052] Four possible encoding directions can be preferably used, for example, horizontal, vertical, diagonal +45 degrees, or diagonal 135 degrees, relative to the pixel row or column of the spatial light modulation device into which the hologram is encoded, to adjust or track at least one virtual visible area to a new position of the eye or pupil. However, the invention is not intended to be limited to these four mentioned encoding directions of the hologram. Furthermore, different encoding directions (e.g., diagonal 30 degrees) are obviously also possible in addition to these four. Moreover, the invention is not intended to be limited to at least one rectangular pixel of the spatial light modulation device, which can be arranged in rows and columns. For example, the pixel can also be hexagonal, and six different encoding directions can be formed parallel to the sides of the hexagon.

[0053] In another advantageous embodiment of the invention, at least one position detection system may be provided, which can be used to determine the position of an observer's eyes (particularly the pupils) in the scene. Furthermore, the size of the pupils may optionally be detected.

[0054] To determine the appropriate encoding orientation of a hologram on at least one spatial light modulation device, a position detection system is used to detect the observer's eye position. The encoding orientation of the hologram to be encoded can be determined based on the detected eye position, so that at least one virtual visible region generated also coincides with the observer's eye. For this purpose, the encoding orientation from which at least one virtual visible region best or most appropriately overlaps with the eye or pupil can be selected for the observer's respective eye position from different encoding orientations (e.g., horizontal, vertical, diagonal, where other orientations are not intended to be excluded).

[0055] In a preferred embodiment, a spatial light modulation device can be used, which has similar or identical pixel spacing in both the horizontal and vertical directions. In another preferred embodiment, if macropixels, composed of multiple pixels of the spatial light modulation device, are used to represent the complex values ​​of object points in the scene, the spatial light modulation device can have the same macropixel spacing in both the horizontal and vertical directions.

[0056] The size or expansion of the virtual observer window, as well as the size or expansion of the optimal spot size in the observer plane, can be optionally changed depending on the encoding direction of the hologram on the spatial light modulation apparatus. In the embodiments of the spatial light modulation apparatus described above, where the pixel spacing in the horizontal direction and the pixel spacing in the vertical direction are the same or at least similar, for example, using the diagonal encoding direction of a hologram with two-dimensional pixels results in a pixel spacing in the diagonal direction that is √2 times (the square root of 2) larger than the pixel spacing in the horizontal or vertical direction, and therefore the expansion of the diffraction order generated in the observer plane is similarly not as large in the diagonal direction as in the horizontal or vertical direction. It may then be appropriate to select a diagonally generated virtual observer window that is also different from the virtual observer window generated horizontally or vertically. For example, due to the expansion of the tracking area, different size requirements are applied in the case of the optimal spot size in the observer plane. For example, if the horizontal tracking area used for fine tracking (or viewed as a whole in the case of a head-mounted display) is intended to be larger than the vertical tracking area, the expansion of the optimal horizontal spot can also be appropriately chosen to be larger than the expansion of the optimal vertical spot. For example, the size of the optimal spot can be set by the diffraction order used or by the scattering angle of the scattering element.

[0057] In a particularly preferred embodiment of the invention, the tracking device may include at least one controllable optical element disposed between at least one illumination device and the observer plane in which the observer of the scene is located.

[0058] For changes in the encoding direction of the hologram, the tracking device may include at least one controllable or switchable optical element in the beam path between at least one illumination device, which may contain at least one light source, and the observer plane, to generate an optimal light spot or virtual observer window in the changing direction. At least one controllable optical element may be positioned upstream or downstream of the spatial light modulation device in the light propagation direction. At least one controllable optical element may be designed as a scattering element that scatters incident light only in one direction. In this way, an optimal light spot can be generated in that defined direction or scattering direction.

[0059] In various advantageous embodiments of the invention, at least one controllable optical element of the tracking device can be designed as a polarization switch, wherein the tracking device comprises at least one passive deflection grating element (preferably a polarization grating element) and at least two passive scattering elements that scatter incident light in only one direction, wherein the passive deflection grating element and the at least two passive scattering elements operate in conjunction with the polarization switch.

[0060] At least one controllable optical element can be designed as a polarization switch, such as a non-pixelated liquid crystal cell or liquid crystal layer, which operates, functions, or is manipulated in conjunction with at least two passive scattering elements. One of the scattering elements can be selected to scatter the incident light accordingly, by means of a deflection grating element (e.g., a polarization grating element) whose deflection angle can be controlled in a polarization-selective manner, and a polarization switch that is controllable by an electric field and generates the polarization state of light according to the switching state, thus selecting the deflection angle within the deflection grating element. The polarization switch can be positioned upstream of the deflection grating element in the light propagation direction in the display device. Then, in each case, the scattering element generates an optimal light spot in the scattering direction in the observer plane. For this purpose, a one-dimensionally designed scattering element is also provided.

[0061] At least two passive scattering elements can be designed as a volume grating, wherein at least two passive scattering elements have different angular selectivity.

[0062] At least two passive scattering elements can be designed, for example, as a volume grating, which has a specific angular selectivity and thus effectively scatters only light incident within a specific angular range. Therefore, different angular selectivity can be set for each scattering element, for example. For each passive scattering element, the direction of the incident light it effectively scatters differs from the directions of the other passive scattering elements. For example, two passive scattering elements can be precisely provided, where one scattering element effectively scatters light incident at +30 degrees, and the other scattering element effectively scatters light incident at -30 degrees.

[0063] In the foregoing embodiments, at least two passive scattering elements may optionally also have different scattering characteristics, for example, they may generate different scattering angles. Therefore, the optimal spot size can then be set differently for each encoding direction of the hologram.

[0064] In an alternative embodiment, the tracking device may include at least one controllable optical element designed as a polarization switch. The tracking device may also include at least one redirection element (preferably a polarization beam splitter element) and at least two passive scattering elements that scatter incident light in only one direction in each case. One of the at least two different optical paths can be selected by the controllable optical element and the redirection element, and a scattering element is provided in each different optical path in each case. In other words, at least two passive scattering elements are positioned in different paths within the beam path and in one of these optical paths, and therefore one of the scattering elements can be selected by combining the redirection element with the polarization switch.

[0065] For example, the polarization of light incident on a polarizing beamsplitter element is set by a polarization switch. Depending on the polarization state, the light is emitted straight from the polarizing beamsplitter element or deflected at 90 degrees. Vertically scattering elements are, for example, set near one output of the polarizing beamsplitter element, while horizontally scattering elements are set near different outputs of the polarizing beamsplitter element. Depending on the polarization set by the polarization switch, the light reaches one scattering element or the other. In a further process, the light path can be combined by means of a combiner (e.g., a splitter cube) to further direct the light from the two scattering elements toward the observer plane.

[0066] Then, in each case, the scattering element generates an optimal spot size in the scattering direction within the observer plane. A one-dimensional scattering element design is also provided. Alternatively, scattering elements with different scattering angles can be used to generate optimal spots of different sizes, for example, for different scattering directions of light.

[0067] In another embodiment of the invention, it may be advantageously provided that the tracking device includes a passive scattering element designed to rotate.

[0068] The tracking device may also consist of a single passive scattering element, which is designed to be one-dimensional and mechanically rotated to change the scattering direction of the incident light. This means that the passive scattering element will rotate from a starting position to a final position to facilitate a change or switching process from one encoded direction of the hologram to a different encoded direction. When the final position is reached, the passive scattering element will remain in its final position during the display of the hologram on the SLM.

[0069] Multiple coding directions can be advantageously set using a single passive scattering element, for example, four different coding directions corresponding to different rotation angles of the passive scattering element (e.g., four different rotation angles).

[0070] However, in this embodiment, the scattering angle and therefore the optimal spot size are the same for all encoding directions.

[0071] Furthermore, it can be advantageously provided that the tracking device includes at least two controllable optical elements.

[0072] At least two controllable optical elements can also be used to change the encoding direction of the hologram. These at least two controllable optical elements can be designed as scattering elements that scatter incident light in only one direction in each case, effectively scattering it in different directions in each case. The first scattering element can, for example, scatter in a direction of approximately 20° vertical × 1° horizontal. Then, the second scattering element can, for example, scatter in a direction of approximately 1° vertical × 20° horizontal. By controlling or switching between one scattering element and the other, the encoding direction of the hologram can thus be rotated by 90° on the spatial light modulation device, wherein an optimal light spot of corresponding size can be generated perpendicular to the encoding direction of the hologram.

[0073] In other words, the first controllable optical element can advantageously scatter incident light in a predetermined first direction, while the second controllable optical element can scatter light in a predetermined second direction, wherein the first and second directions are different. The encoding direction of the hologram or sub-hologram can therefore be advantageously defined by the corresponding control of the first and second controllable optical elements. Thus, of the at least two controllable optical elements, one will be activated or controlled in each case to scatter light in the desired direction, while the other controllable optical element will be deactivated or uncontrolled so that it does not scatter light. The controllable optical elements can be accordingly designed such that they optionally also generate scattering angles of different sizes, in order to define the optimal spot size, for example, differently depending on the encoding direction of the hologram.

[0074] Furthermore, it can be provided that at least one controllable optical element comprises two substrates with a liquid crystal layer embedded between the two substrates. At least one of the two substrates of the at least one controllable optical element may preferably have a surface structure.

[0075] Two substrates are bonded together to create a controllable optical element, wherein the space between the two substrates is filled with a liquid crystal layer. Only one substrate of the controllable optical element preferably has a surface structure, while the other substrate can be designed to be flat. The surface structure of at least one substrate can be, in particular, a one-dimensional statistical surface structure, which can be pressed into a polymer layer forming part of the substrate. In this case, a “statistical surface structure” refers to a surface profile with an irregular repeating pattern, but with random fluctuations within predetermined limits, as described in detail below. The scattering characteristics of the controllable optical element can be predetermined by selecting the surface structure (i.e., its width, height, and statistical distribution). The surface structure can be designed, for example, similar to a surface relief grating or a blazed grating; however, compared to conventional grating elements, the grating period and / or blaze angle can be arbitrarily varied with position on the substrate so that instead of producing regular diffraction orders, light is scattered within a predetermined angular range. In other words, the surface structure can have a grating period that varies arbitrarily with position on the substrate.

[0076] The light scattering angle can then be set, for example, by predetermining minimum and maximum grating periods, and similarly by predetermining the frequency and / or range and distribution of different grating periods and blaze angles. The surface profile can be calculated, and a master can then be generated photolithographically for the surface structure having these predetermined features, for example, using a computer with a random number generator. An impression can then be created from this master. This surface structure can also typically be an irregular height profile, the width and height of which vary arbitrarily depending on the position of the controllable optical element on at least one substrate.

[0077] In another advantageous embodiment of the invention, it may be provided that the substrate of at least one controllable optical element includes an electrode system in each case, wherein each electrode system includes at least one electrode. The at least one electrode may be designed, for example, to be planar, i.e., unpixelated.

[0078] A substrate opposite to a substrate having a surface structure can be advantageously provided for aligning liquid crystals within a liquid crystal layer. This substrate, containing at least one controllable optical element, can be designed to be flat or planar and can be used for aligning liquid crystals within a liquid crystal layer. This can be accomplished, for example, by friction or photo-alignment.

[0079] The liquid crystal material of the liquid crystal layer may further have a first refractive index and a second refractive index, wherein the first refractive index is essentially corresponding to the refractive index of the surface structure, and the second refractive index is essentially different from the refractive index of the surface structure.

[0080] The birefringent liquid crystal material of the liquid crystal layer may have a first refractive index, such as a common refractive index, which is essentially the same as the refractive index of the surface structure. The common refractive index or first refractive index of the liquid crystal material and the refractive index of the surface structure of at least one controllable optical element are, for example, both n = 1.5. The birefringent liquid crystal material may further have a second refractive index, such as a superlative refractive index, which is different from the refractive index of the surface structure of at least one controllable optical element. The superlative refractive index or second refractive index of the liquid crystal material is, for example, n = 1.7, where the refractive index of the surface structure is n = 1.5.

[0081] If there are multiple controllable optical elements, wherein at least one substrate has a one-dimensional surface structure, it is advantageous to provide that these controllable optical elements are arranged in the optical path in such a way that the one-dimensional surface structure of each controllable optical element disposed on at least one substrate has a different orientation relative to each other in each case.

[0082] If multiple controllable optical elements are used in the optical path, i.e., at least two controllable optical elements, these controllable optical elements can be arranged relative to each other in such a way that the surface structures (preferably statistical surface structures) on the respective substrates of each controllable optical element have different orientations relative to each other in each case.

[0083] The surface structures of the two controllable optical elements can preferably be arranged at an angle of approximately 90° relative to each other. Similarly, the surface structures of individual controllable optical elements are similarly preferably arranged at 90° relative to each other. However, it is also possible, particularly in cases with more than two controllable optical elements, to arrange the individual controllable optical elements at different angles (e.g., 60° or 45°) relative to each other. For example, if one controllable optical element will be controlled or a voltage will be applied to it, and the other controllable optical element will not be controlled or no voltage will be applied to it, the incident light will be scattered in a first direction. Conversely, if one controllable optical element will not be controlled or no voltage will be applied to it, while the other controllable optical element will be controlled or a voltage will be applied to it, the incident light will be scattered in a second direction.

[0084] The scattering angles of each controllable optical element can be selectively designed to be different, thereby limiting the size of the optimal spot size in different ways along with the direction of the optimal spot.

[0085] At least one polarizing element may be provided upstream of at least one controllable optical element in the direction of light propagation.

[0086] At least one polarizing element can be designed as a polarizing grating element, and, for example, can deflect incident left-handed circularly polarized light to the positive first (+1st) diffraction order and right-handed circularly polarized light to the negative first (-1st) diffraction order. However, this is only intended to indicate that different polarized light can be deflected in different directions by means of at least one polarizing element.

[0087] In a particular embodiment of the invention, the tracking device may be designed as a filter device configured to eliminate diffraction levels.

[0088] As already explained, the present invention is not generally intended to be limited to the use of scattering elements or controllable optical elements for altering the encoding direction of a hologram or subhologram. Instead, the tracking device can also be designed as a filter device, which allows alteration of the encoding direction of a hologram or subhologram at at least one spatial light modulation device. For this purpose, coherent light can be used equally in all directions (i.e., in both the encoding and non-encoding directions of the hologram or subhologram). In the filter plane between at least one spatial light modulation device and the observer plane, particularly in the Fourier plane of the spatial light modulation device, unwanted diffraction orders can be filtered out for this purpose. In the encoding direction of the hologram or subhologram, only light from a single diffraction order should reach the observer's eye, as the observer will otherwise see unwanted multiple images of the reconstructed scene. Preferably, each object point in the three-dimensional scene will be reconstructed once for each diffraction order at different locations. However, perpendicular to the encoding direction of the hologram or subhologram, i.e., in the optimal spot direction, different diffraction orders will not cause interference to the observer's eye. In each case, the observer will see the same reconstructed scene in each diffraction order. The object point of the scene will be generated at the same location in each diffraction order in this optimal spot direction.

[0089] On the one hand, using multiple diffraction orders helps increase the area of ​​light reaching the observer's pupil. Therefore, an optimal light spot can also be generated using light from multiple diffraction orders in the observer's plane.

[0090] Then, for example, an optimal spot and virtual observer window can be generated by filtering in the Fourier plane of the SLM in a direction corresponding to the encoding direction of the hologram or sub-hologram, allowing only one diffraction order to pass and filtering out other generated diffraction orders, wherein multiple diffraction orders are allowed to pass in a direction perpendicular to the optimal spot direction. If the filter device is designed to be controllable, as a tracking device for filtering diffraction orders, it can, for example, switch from one state having a single diffraction order in the horizontal direction and multiple diffraction orders in the vertical direction to another state having a single diffraction order in the vertical direction and multiple diffraction orders in the horizontal direction. Therefore, it can be advantageous if the filter device is designed to be controllable. In other switching states of the filter device, diagonal diffraction orders, such as a diffraction order in the +45° direction and multiple diffraction orders in the -45° direction, and vice versa, can also be used.

[0091] This change or switching of the switching state of the filter device can be achieved by mechanical rotation of the aperture in the filter plane, or in different embodiments by an electrically switchable filter aperture that can switch back and forth between different orientations of the filter aperture.

[0092] The design of the rotating filter aperture only allows for setting the optimal spot size of the same size in different encoding directions of the hologram.

[0093] However, by using an electrically controllable filter aperture, different numbers of diffraction orders can be filtered according to the aperture setting in the optimal spot direction, thus generating optimal spots of different sizes according to the encoding direction of the hologram. For example, five diffraction orders in the horizontal direction, but seven diffraction orders in the vertical direction, can be used for optimal spots by selecting different sizes of apertures or openings in the filter plane for the horizontal and vertical optimal spots.

[0094] In various advantageous embodiments of the invention, at least one light source of at least one illumination device may be designed as a tracking device, wherein at least one light source is designed to be controllable in order to change the coherence characteristics of the light to be emitted.

[0095] In different embodiments, for example, the coherence characteristics of the light can be altered in such a way as to control or switch the light source of at least one illumination device, i.e., in each case, high coherence is used to generate the virtual observer window or low coherence is used to generate the optimal spot in different directions. High coherence in the encoding direction is understood here as coherence sufficient to cause light emitted from different pixels within a sub-hologram on the SLM to interfere with each other. Low coherence in the optimal spot direction means that light from adjacent pixels of the SLM does not need to interfere with each other in the optimal spot direction. For example, a slot-shaped light source with different coherence in the long and short sides of the slot can be used for SLM illumination. The coherence of the complexity of the radiation field generated by the extended quasi-monochromatic light source can be calculated in a known manner according to the van Cittert-Zernike theorem. In SLM illumination, such a slot-shaped light source can in particular generate different angular spectra in the short and long sides of the slot.

[0096] The SLM is preferably illuminated in the encoding direction of the hologram with an angular spectrum of 1 / 60° (i.e., one arcminute) or less, as this allows for hologram reconstruction with a resolution matching or exceeding that of the human eye. However, in the optimal spot direction, the SLM can be illuminated with a significantly larger angular spectrum (e.g., 1-2 degrees). The length and width of the slot-shaped light source and its distance from the SLM can be defined in such a way that these angular spectra are generated on the SLM. For example, if the imaging element (e.g., a lens) is located between the light source and the SLM, and the light source is within the focal length of the imaging element on the object side, then the light source is imaged to infinity by the imaging element. Light from one point of the light source is then incident parallel to the SLM. Light from another point of the light source is also incident parallel (but at a different angle than the first point) to the SLM. The angular spectrum is then determined by the extension of the light source and the focal length of the imaging element. Tanα = x / f, where x is the extension of the slit or slot, and f is the focal length. In the case of an imaging element with a focal length of 100mm, for example, the short side of the light source slot would be 29μm wide to generate an angular spectrum of 1 / 60 degree. The long side of the slot could be 3.5mm in length to generate an angular spectrum of 2 degrees.

[0097] It must also be considered that in display devices used for holographic reconstruction of objects or scenes, where a magnified image of the SLM visible from a virtual visible area is generated, the effective angular spectrum decreases with magnification. A numerical example of a slot light source here relates to an unmagnified SLM directly visible from the observer's angle. For an SLM imaged in magnified form, the light source can be proportionally larger with the magnification factor. For example, if the SLM image is magnified 10 times, the SLM can be illuminated with an angular spectrum of 1 / 6 degree × 20 degrees, so that an angular spectrum of 1 / 60 degree × 2 degrees is incident on the resulting image of the SLM. The slot light source can also be increased by 10 times.

[0098] In no way is the invention intended to be limited to slot-shaped light sources with precisely that size. Numerical notations are merely illustrative and for explanation purposes.

[0099] If the aim is to change the encoding orientation of a hologram or subhologram, a single slot-shaped light source can, for example, be controlled to rotate from one orientation to another along the short or long side of the slot. In different embodiments, multiple slot-shaped light sources with different orientations along the long side of the slot can also be used, with one light source turned on and another turned off if the aim is to change the encoding orientation of the hologram.

[0100] However, the coherence of the illumination from at least one spatial light modulation device can be adjusted using controllable optical elements to achieve high coherence in the encoding direction of the hologram in each case and reduced or low coherence in the direction of the optimal spot. For example, a one-dimensionally designed scattering element will reduce the coherence in the scattering direction.

[0101] The display device according to the invention can preferably be designed as a holographic display device. In particular, the display device can be designed as a head-mounted display, wherein the head-mounted display has the display device according to the invention for the observer's left eye and for the observer's right eye, respectively.

[0102] The objective of the invention is further achieved by a method for representing two-dimensional and / or three-dimensional scenes as described in claim 28.

[0103] The method for representing a two-dimensional and / or three-dimensional scene according to the present invention comprises at least one illumination device for emitting sufficiently coherent light, at least one spatial light modulation device, at least one optical system, a tracking device, and a position detection system. The position detection system determines the position of an observer's eye. The appropriate encoding orientation of a hologram of object points of the scene on the at least one spatial light modulation device is determined using the at least one optical system and the tracking device. The hologram represents the sum of all sub-holograms, wherein a hologram is assigned to each object point of the scene to be represented. A change in the encoding orientation of the hologram means that the encoding orientation also changes for each individual sub-hologram.

[0104] The hologram is encoded into at least one spatial light modulation device in a defined encoding direction using single-parallax coding. The at least one spatial light modulation device is illuminated by at least one illumination device, and the hologram is reconstructed by at least one optical system. At least one virtual visible area is generated at the observer's eye position.

[0105] In this way, by changing the encoding orientation of a hologram that will be encoded into at least one spatial light modulation device, the generated virtual visible area can be tracked by the observer's eye in a suitable, simple and low-cost manner.

[0106] For a hologram to be encoded, it is advantageous to choose an encoding direction that has the largest proportion of the virtual visible region that overlaps with the observer's pupil.

[0107] In each case, the encoding direction that provides the largest proportion of the virtual visible area within the observer's pupil is selected. If multiple possibilities exist for a suitable encoding direction with a region of equal size overlapping the pupil, one of these encoding directions can be selected.

[0108] What can be provided is that the observer's eye position, and in particular the position and possible size of the pupil, as well as the new eye position in the event of a change in the observer's eye position, can be determined by a position detection system. The virtual visible area rotates around its fixed center point in order to select a suitable encoding direction for the hologram to be encoded, and the direction of the virtual visible area having the largest proportion of overlap with the pupil area of ​​the observer's eye is determined.

[0109] The center point of the virtual visible region remains unchanged to define the appropriate encoding direction of the hologram, but always remains in the same position. This means that the virtual visible region does not move to different locations to track the virtual visible region to a new position of the eye (specifically the pupil), but always remains in the same position with its center point and only rotates around its center point. Furthermore, this means that the hologram on at least one spatial light modulation device also rotates around its center point, from which the appropriate encoding direction is selected, because the hologram is encoded using monoparallax coding. This is based on the fact that the sub-hologram or hologram to be encoded for the object point to be generated is determined by projection from the virtual visible region through the object point of the scene to be reconstructed onto at least one spatial light modulation device via a virtual observer window, such as... Figure 1 As shown.

[0110] There are now various possibilities for designing the teachings of the invention in an advantageous manner and / or for combining the described exemplary embodiments or configurations with each other. For this purpose, reference can be made, on the one hand, to the patent claims which are dependent on the independent patent claims, and on the other hand, to the following description of preferred exemplary embodiments of the invention with reference to the accompanying drawings, wherein the teaching embodiments are also generally described. The invention is described in summary based on the described exemplary embodiments, but is not intended to be limited thereto.

[0111] The attached diagram shows:

[0112] Figure 1: A schematic diagram of the holographic display device according to the present invention, in perspective view;

[0113] Figure 2 A schematic diagram of the virtual visible area relative to the observer's eye region, based on existing technology;

[0114] Figure 3 : A schematic diagram of an embodiment of the present invention for tracking virtual visible areas;

[0115] Figure 4 : A schematic diagram used to determine the appropriate encoding direction of a hologram;

[0116] Figure 5 A schematic diagram of a display device according to the present invention, wherein the encoding direction of the hologram can be changed by the display device;

[0117] Figure 6 :have Figure 5 A schematic diagram of a holographic display device according to the present invention, which is an alternative tracking device;

[0118] Figure 7 :have Figure 5 and 6 A schematic diagram of the holographic display device according to the present invention, showing an alternative tracking device;

[0119] Figure 8 : Schematic diagrams of sub-holograms with different coding orientations on a spatial light modulation device, as shown in figures a) to e);

[0120] Figure 9 : Schematic diagrams of sub-holograms with further different coding directions on a spatial light modulation device, as shown in figures a) to d); and

[0121] Figure 10 : A schematic diagram of the design of the controllable optical element of the tracking device according to the present invention.

[0122] It should be briefly mentioned that the same elements / parts / assemblies also have the same reference numerals in the accompanying drawings.

[0123] Figure 1A perspective view of the holographic display device is shown, and the device is simplified, omitting the illumination device and optical system. This display device is intended to illustrate and explain the invention, and will therefore be briefly described again. In this display device, for multiple object points in a scene at different depths, a sub-hologram is generated as a projection of a virtual observer window VW onto a spatial light modulation device SLM in the observer plane through the respective object points, relative to a spatial light modulation device. The observer is located in the observer plane, which is hereby represented by a representation of an eye with a pupil P. The spatial light modulation device SLM will be simply referred to as SLM below. It can be seen that the position of the sub-hologram on the SLM depends on the position of the object points relative to the virtual observer window VW. The size, expansion, or scale of the sub-hologram also depends on the z-position of the encoded object points, where z is the distance between the object point and the SLM. In most cases, overlap of the sub-holograms occurs.

[0124] Object points located at a distance from the observer's eye, near the entrance pupil (i.e., close to the SLM plane, or, in the case of a head-mounted display (HMD) or head-up display (HUD), close to the virtual plane of the SLM), have sub-holograms that are small in size or extent. For example, in the case of one-dimensional (1D) encoding of a hologram (also known as single disparity encoding), a small sub-hologram may have a lateral extent of 10 pixels, and in the case of two-dimensional (2D) encoding of a hologram (also known as full disparity encoding), it may have a lateral extent of 10 × 10 pixels.

[0125] For holographic reconstruction of a scene (preferably a 3D scene), a sub-hologram is used in conjunction with a virtual visible region. In the case of single disparity encoding of the hologram, the virtual visible region is formed by a virtual observer window in the encoding direction of the hologram and an optimal spot in the non-encoding direction of the hologram. Alternatively, in the case of full disparity encoding of the hologram, it is formed by a 2D virtual observer window through which the observer can view the reconstructed scene.

[0126] For example, according to Figure 1 The projection method can be used to calculate and generate holograms.

[0127] In the projection method, the outline of a virtual visible region in the observer plane is projected onto the SLM (Scanning Linear Modulation) through an object point, and a sub-hologram is generated on the SLM. In other words, the outline of the sub-hologram is formed or generated on the SLM through the projection of the outline of the virtual visible region. The phase function, intended to reconstruct the object point, is then encoded in the sub-hologram. In the simplest design, the amplitude function (or simply amplitude) in the sub-hologram is set to the same value for all pixels of the sub-hologram and is selected in such a way that the sub-hologram reconstructs the object point with a predetermined intensity. The size of the virtual visible region in the observer plane is limited to one diffraction order of the resulting diffraction pattern. Because the virtual visible region is limited to one diffraction order, other diffraction orders are invisible to the observer within the virtual visible region.

[0128] Therefore, holograms are generated that reconstruct two-dimensional and / or three-dimensional scenes visible from the virtual visible area.

[0129] For head-mounted displays (HMDs), head-up displays (HUDs), or projection displays with real or virtual SLM images, the term "SLM" as used herein is intended to refer to the image of the SLM visible from the virtual visible area.

[0130] In projection methods, in the simplest design, the amplitude of the sub-hologram is constant within its extension. However, it is also possible to provide a design in which this amplitude can be varied within the extension of the sub-hologram. This can be achieved, for example, by multiplying by the inverse of the Fourier transform of the pixel transmission, in order to obtain a more uniform brightness distribution in the virtual visible region.

[0131] It can be done by relying on Figure 1 The virtual observer window generated in the observer plane by the display device can have an expansion smaller than the observer's pupil or optionally larger than or equal to the pupil. However, the virtual observer window should generally not be larger than about 10 mm or at most about 15 mm, otherwise strict requirements must be imposed on the pixel pitch and pixel count of the SLM.

[0132] However, with the same SLM used to generate the virtual observer window—that is, with a specific or defined pixel pitch and a specific number of pixels in the SLM—an optimal spot can be generated in the observer plane, which can be significantly larger in terms of expansion than the virtual observer window. For example, the optimal spot can also have an expansion of approximately 20 mm or more. The observer's eye distance constitutes a limitation on the expansion of the optimal spot in a direct-view display. Therefore, the light from the optimal spot used for one eye should prevent impact on the observer's adjacent eyes. Since the observer's two eyes are horizontally adjacent to each other, this essentially relates only to the horizontal expansion of the optimal spot. Therefore, a vertically generated optimal spot can also be selected, for example, with an expansion greater than the eye distance. For head-mounted displays, it is advantageous to select the size of the optimal spot's expansion so that the area of ​​the optimal spot can cover the typical range of pupil movement within the eye.

[0133] The present invention will now refer to an example based on a holographic head-mounted display (HMD) as a display device according to the invention, in an exemplary embodiment. Figures 3 to 10 To explain further. Tracking of the virtual visible area previously implemented by the applicant will be referenced. Figure 2 The description is provided to provide a clearer understanding of the invention.

[0134] In the applicant's head-mounted display, each hologram or sub-hologram is encoded into an SLM for each object point in the scene via single parallax coding. Only a very small virtual observer window of approximately 1 mm and an optimal spot size of approximately 10 mm are primarily used, together forming a virtual visible region in the observer plane. Overall, this then produces a rectangular virtual visible region with substantially different edge lengths or extensions in two directions, where the reconstruction of the two-dimensional or three-dimensional scene is visible to the observer's pupil.

[0135] Figure 2 A virtual visible region, formed by a virtual observer window (VW) and an optimal spot (SS), according to prior art, is shown. This virtual visible region is generated in single disparity coding in hologram-to-SLM, where the coded hologram or sub-hologram has a fixed coding orientation, which in this case is a vertical coding orientation. An extended small virtual observer window (VW) is thus generated in the vertical direction. Figure 2 In this model, the expansion of the virtual observer window VW is smaller than the size of the observer's pupil P. It can be seen that the optimal spot SS, with an expansion significantly larger than the expansion of the virtual observer window VW, is generated in the horizontal direction.

[0136] exist Figure 2In illustration a), the position of the observer's pupil P is shown in the central region of the virtual visible area. This means that, in every case, the pupil P is located in the central region of the virtual observer window VW and the central region of the optimal spot SS. At this position of the pupil P relative to the virtual visible area, the observer's eye can perceive and observe the reconstructed scene, preferably a three-dimensional scene.

[0137] Figure 2 Illustration b) shows the case where the observer's pupil P moves horizontally relative to the center of the virtual visible area (specifically, relative to the center of the optimal light spot SS present in the horizontal direction). However, the pupil P remains within the optimal light spot SS of the virtual visible area. Similarly, in this case, the reconstruction of the preferred 3D scene can be seen and observed by the observer's eye.

[0138] exist Figure 2 In Figure c), compared to Figure b), it is shown that, in addition to horizontal movement, the observer's pupil P also moves vertically relative to the center of the virtual visible area. It can be seen that the pupil P is now outside the virtual visible area; that is, the virtual visible area and the pupil P no longer overlap or cover each other. The observer can no longer observe the reconstructed scene. In conventional display devices according to the prior art, the virtual visible area must now be moved by a suitable optical device (e.g., a diffraction device) and must be tracked to the new position of the pupil P. The virtual visible area moved to the new position of the pupil P in this manner is represented by the dashed line in Figure c).

[0139] and Figure 2 compared to, Figure 3 A virtual visible region generated in the observer plane where the observer's eye is located is shown, wherein the orientation of the virtual observer window and the orientation of the optimal spot can be changed according to the invention. Similarly, the hologram or sub-hologram is again encoded into the SLM via single disparity coding. Therefore, the encoding orientation of the hologram or sub-hologram on the SLM can be changed. (As in combination...) Figure 2 The virtual visible region is generated by encoding a hologram single disparity into an SLM, wherein the encoded hologram or sub-hologram has a fixed encoding direction, which in this case is a vertical encoding direction. As a result, a virtual observer window VW with a small expansion is generated in the vertical direction. Similarly, in this case... Figure 3 In the middle, for the sake of simplicity and to preserve Figure 2 In the example, the expansion of the virtual observer window VW is smaller than the size of the observer's pupil P. It can be seen that the optimal spot size, significantly larger than the expansion of the virtual observer window VW, is generated in the horizontal direction.

[0140] exist Figure 3 In illustration a), the position of the observer's pupil P is shown in the vertical encoding direction of the hologram or subhologram. The position of the observer's eye, and in particular the pupil, relative to the SLM is determined by means of a position detection system in order to determine the appropriate encoding direction of the hologram to be encoded into the SLM. Then, by means of, for example in Figure 5 The optical system and tracking device of the display device, shown in more detail, determine the appropriate encoding direction of the hologram, whereby the hologram is encoded into the SLM using simulated monoparallax coding, and a virtual visible region is generated in simulated form. It is then determined whether the virtual visible region covers the observer's pupil. If so, it can also be verified whether the simulated virtual visible region has the maximum proportional overlap with the observer's pupil in that encoding direction of the hologram. Similarly, if so, the hologram can now be encoded into the SLM in that determined encoding direction, and the object point can be reconstructed by illuminating the SLM using an illumination device and optical system, so that the observer can observe the object point through the actually generated virtual visible region.

[0141] If the eye or pupil moves while observing a point or scene, the virtual visible area must track the pupil so that the observer can continue observing the represented point or scene. Figure 3 Illustration b) shows the tracking of the virtual visible region. The changed position of the pupil P of the eye is shown here compared to illustration a). The eye or pupil P has been moved vertically so that the virtual visible region from illustration a) no longer covers the pupil P. The virtual visible region is now tracked to the new position of the pupil of the eye by rotating the virtual visible region around its center point M. Similarly, the encoding orientation of the hologram on the SLM is changed.

[0142] The encoding orientation of the hologram is therefore determined again through simulation (i.e., by rotating a virtual visible region generated in simulation form around its center point M). The encoding orientation of the hologram, in which the largest proportion of the virtual visible region overlaps or is covered by the pupil of the eye, is appropriately selected. If the encoding orientation of the hologram is appropriately selected, it can be encoded into the SLM using this selected and determined encoding orientation. In this way, a virtual visible region is now generated in the observer plane, which covers the new position of the pupil of the eye. By rotating the virtual visible region and therefore by rotating the encoding orientation, the virtual observer window and the optimal spot are again partially located within the pupil, allowing the observer to view the reconstructed scene without interference.

[0143] and Figure 2 In comparison, based on Figure 3During the tracking of the virtual visible area, even after the virtual visible area has been tracked to a new position of the eye or the pupil of the eye, the center point M of the rectangular area of ​​the virtual visible area formed by the virtual observer window and the optimal spot remains in the same position. Therefore, the center point M of the virtual visible area does not move during the tracking process.

[0144] Depending on the range of the desired pupil position, it is not necessary to select the rotation angle of the virtual visible area in any given small step size, and therefore it is also not necessary to select the rotation angle of the encoding direction, because in the case where the observer moves to different positions, the pupil cannot move over a large area during the observer's movement, for example, if the display device is used as a head-mounted display, as is the case for a direct-view display. There is no provision for tracking changes in the encoding direction of the virtual visible area in the hologram for large observer movements, but rather, it is particularly advantageous for fine tracking of the virtual visible area, as can be used, for example, in the case of a head-mounted display. Because the pupil of the eye can only move within a limited area, a small number of rotation angle settings will be sufficient, for example, four rotation angles, such as horizontal (0°), vertical (90°), and two diagonal rotation angle settings (+45° and -45°).

[0145] Figure 4 An arrangement is schematically presented, illustrating the virtual visible region at different rotation angle settings, which has an extended virtual observer window of approximately 1 mm and an extended optimal spot of approximately 10 mm. The virtual visible region is shown here with four possible rotation angle settings, namely, where the encoding direction of the hologram lies in the horizontal direction (B), the vertical direction (D), and the two diagonal directions (A and C). The rotation angle with the largest proportional area of ​​overlap between the virtual observer window VW and the optimal spot SS and the pupil P of the eye is selected to select and determine a suitable encoding direction for the hologram to be encoded into the SLM. If multiple possible encoding directions with an equal large area of ​​overlap between the virtual visible region and the pupil P of the eye emerge during the determination of a suitable encoding direction for the hologram, one of these encoding directions can be selected and used.

[0146] exist Figure 4In this design, the center or center point of the pupil P of the eye is set at an angle of approximately 22.5° relative to the horizontal line L or the center point M of the virtual visible area. It can be seen that the vertical encoding direction (D) and the diagonal encoding direction (-45°; C) have the same overlapping area with the pupil P of the eye, ensuring that when a hologram or sub-hologram is encoded into the SLM in the representation of the reconstructed object point or scene using these two encoding directions, the same amount of light enters the observer's eye through the pupil P. Therefore, one of these two encoding directions can be selected for the hologram or sub-hologram to be encoded into the SLM.

[0147] In principle, the change in the encoding direction of a hologram through rotation of a one-dimensional hologram can also be combined with the movement of a virtual observer window in the encoding direction through the encoding of prism terms in the hologram or sub-hologram, as disclosed in WO2018 / 037077A2, the disclosure of which is intended to be incorporated herein in its entirety. If a linear phase function (i.e., a prism function) is added to the phase of the hologram, the virtual observer window moves through segments of diffraction orders. A linear phase function with a difference of π between adjacent pixels would, for example, cause the virtual observer window to move by half (1 / 2) diffraction order, or a difference of 2π / x overall would cause a diffraction order to shift by 1 / x. However, due to the phase function in the hologram, the brightness distribution of the individual diffraction orders is not altered by this movement of the virtual observer window. The observer typically sees a preferred and correct reconstruction of the 3D scene, but if the observer moves from the central diffraction order to a higher diffraction order, the brightness of the scene decreases. Due to this brightness limitation, movement of the virtual observer window encoded by the prism term is typically limited to a small area of ​​only a few diffraction orders.

[0148] If the virtual observer window is smaller than the pupil, it should also be ensured that only light from one diffraction order reaches the eye by filtering the diffraction orders of the intermediate image with the virtual observer window in the optical system. For example, if the virtual observer window does not move, the filter will only allow light from the zeroth order diffraction order to pass through the eye. For example, if the virtual observer window moves half a diffraction order by means of a prism function, the filter should allow half of the zeroth order diffraction order and half of the first order diffraction order to pass through so that the light can reach the eye. This means that the filter aperture should be designed to be movable according to the prism function, for example, mechanically or by electronic control. This use of the filter aperture is possible in conjunction with all embodiments of the invention. In embodiments, if a rotatable filter aperture is used in any case in the Fourier plane to set or modify the encoding orientation of the hologram, it can be combined in the simplest way by designing the same filter aperture to be rotatable and movable.

[0149] However, if the virtual observer window is larger than the observer's pupil, filtering is not absolutely necessary, because this ensures that only light from a single diffraction order reaches the eye even without filtering. Figure 4 The example embodiment shown involves a virtual observer window smaller than the pupil of an eye. A virtual observer window of approximately 1 mm in size, along with an optimal spot size of approximately 10 mm, can still be shifted ±1 diffraction order, or ±1 nm, in the encoding direction of the hologram to cover a possible area of ​​approximately 3 mm × 10 mm.

[0150] Therefore, in addition to the rotation of the encoding orientation of the hologram or sub-hologram, the virtual visible area also undergoes small-scale movements, such as positive / negative diffraction orders, to better impact, cover, or overlap the pupil of the eye. Thus, a combination of rotation and small movements of the encoding orientation can also be considered when selecting the encoding orientation of the hologram that provides optimal overlap with the pupil P of the eye.

[0151] Here, as described above and relating only to rotation of the encoding direction, the assignment of the encoding direction for each eye position can be recalculated in each case, or it can be pre-calculated once for all relevant eye positions and stored, for example, in the form of a lookup table. In the latter case, based on the position of the pupil detected by the position detection system, the encoding direction of the hologram stored in the lookup table for that position will be selected. If necessary, the movement of the virtual observer window can be additionally implemented through prism entries similar to those stored in the lookup table.

[0152] Figure 5 A display device, particularly a holographic display device, is shown. This display device includes a tracking device 4, through which the encoding direction of the hologram can be modified.

[0153] If the scattering element is set close to the SLM or in the middle image plane of the SLM, the optimal spot can be generated in the observer plane by the scattering element.

[0154] It should be considered that in a display device for holographic reconstruction of objects or scenes, which generates a magnified image of the SLM visible from a virtual visible area, the scattering element similarly images in a magnified form, and the effective scattering angle decreases with magnification. In the case of imaging the SLM at 20x magnification, a scattering element with a scattering angle of approximately 20° × 1° generates, for example, an effective scattering angle of approximately 1° × 1 / 20°. If the image of the SLM is generated at a distance of 1m from the virtual visible area, an optimal spot size will be generated, for example, with an extension of approximately 17mm in the observer plane, where the effective scattering angle is 1° according to the formula tan 1° * 1000mm.

[0155] In this example, due to the 1 / 20° angle in the encoding direction, it is preferable that the resolution of the 3D scene is similarly limited to 20 pixels / degree in the encoding direction, and thus less than the maximum visible resolution of the eye. However, the values ​​are again just examples. A scattering element with a scattering angle of 20 degrees × 0.3 degrees can also be used.

[0156] In order to be based on Figure 3 and 4 Tracking the new position from the virtual visible region to the pupil of the eye is provided. For example, multiple controllable optical elements designed as scattering elements can be used to modify the encoding orientation of a hologram or subhologram, and thus also modify the optimal spot orientation. A first controllable optical element scatters light, for example, approximately 20° vertically × 1° horizontally, while a second controllable optical element scatters light approximately 1° vertically × 20° horizontally. By controlling one controllable optical element and then another, the encoding orientation of the hologram or subhologram can be rotated by 90°, and in each case, a correspondingly large optimal spot can be generated perpendicular to the encoding orientation.

[0157] This arrangement can optionally be extended as follows: a third controllable optical element will scatter the light, for example, approximately 1° in the diagonal +45° direction and approximately 20° in the diagonal -45° direction. A fourth controllable optical element will scatter the light, for example, approximately 1° in the diagonal -45° direction and approximately 20° in the diagonal +45° direction. In this case, with one of the controllable optical elements, selection from four coded directions can be achieved through control.

[0158] However, at least two passive scattering elements can also be provided in the tracking device to track the virtual visible area to a new position of the observer's pupil. These at least two passive scattering elements can be selected for light scattering by means of at least one controllable optical element of the tracking device.

[0159] At least two passive scattering elements can be designed, for example, as volume gratings, and can have specific angular selectivity for this purpose. In this case, different angular selectivity can be set for each scattering element designed as a volume grating.

[0160] Deflection grating elements and controllable optical elements can be provided to select or provide one of at least two passive scattering elements for light scattering. The deflection grating element has a controllable or switchable deflection angle, for example, for polarization selection purposes. The deflection grating element can be, for example, a polarization grating element that deflects left- or right-circularly polarized incident light to the +1st or -1st diffraction order, where each diffraction order corresponds to a different deflection angle. The controllable optical element can be designed as a polarization switch, such as an LC (liquid crystal) layer that can be controlled by an electric field. The controllable optical element in the form of a polarization switch generates a defined polarization state of light according to the switching state of the polarization switch, for example, left-handed circularly polarized light in one switching state and right-handed circularly polarized light in another switching state. In this way, the deflection angle can be selected within the deflection grating element, and one of the passive scattering elements of the tracking device can be selected based on the angular selectivity of the scattering element.

[0161] Figure 5 A display device with such a tracking device is shown. The display device comprises an illumination device 1 with at least one light source, an SLM 2, an optical system 3, and a tracking device 4. Other optical elements or devices in the display device are possible but unnecessary for explaining the invention. A hologram or sub-hologram is intended to be encoded in the SLM via single parallax coding to reconstruct or represent a scene for an observer. The SLM is illuminated by the illumination device 1 with sufficiently coherent light. The optical system 3, comprising, for example, at least one imaging element (e.g., a lens element), is disposed between the SLM 2 and the observer plane 5. The arrangement of the optical system 3 in the beam path is provided such that, without the tracking device 4, it will image the light from the illumination device 1 onto the observer plane 5 in a non-coding direction (i.e., the optimal spot direction). The optical system 3 also generates a magnified virtual image of the SLM 2 (not shown here) visible from the observer plane 5.

[0162] The tracking device 4 includes two passive one-dimensional scattering elements 6 and 7 positioned downstream of the SLM 2 in the direction of light propagation. The first scattering element 6 generates a scattering angle of 20° in the vertical direction and 1° in the horizontal direction. The second scattering element 7 generates a scattering angle of 1° in the vertical direction and 20° in the horizontal direction. The two passive one-dimensional scattering elements can be designed as volume gratings with the typical limited angular acceptance of a volume grating. The angular acceptance ranges of the two passive one-dimensional scattering elements differ from each other, allowing the selection of either the passive one-dimensional scattering element 6 or 7 based on the defined angle of incidence, through which the incident light is then scattered.

[0163] The tracking device 4 also includes a deflection grating element 8, which is disposed between the passive one-dimensional scattering element 6 and the SLM 2, in the form of a polarization grating element. The deflection grating element 8 deflects light polarized in a defined manner accordingly. For example, the deflection grating element 8 deflects incident left-handed circularly polarized light to the +1st diffraction order and incident right-handed circularly polarized light to the -1st diffraction order. Thus, a particular one-dimensional scattering element 6 or 7 can be selected, and light can be guided toward it, which is then scattered accordingly.

[0164] The tracking device 4 also includes a controllable optical element 9, which is designed as a polarization switch. The controllable optical element 9 is positioned in the optical path of the display device between the deflection grating element 8 and the SLM 2. The controllable optical element 9, in the form of a polarization switch, can be controlled to generate a defined polarization state of light. The controllable optical element 9 generates, for example, left-handed or right-handed circularly polarized light depending on its switching state. Therefore, selection is made by means of the controllable optical element 9 to determine whether the deflection grating element 8 deflects light to the +1st diffraction order or the -1st diffraction order. The passive one-dimensional scattering elements 6 and 7 are designed as volume gratings such that the deflection angle of the +1st diffraction order of the deflection grating element 8 is within the angular acceptable range of one of the passive one-dimensional scattering elements 6 or 7. The deflection angle of the -1st deflection order of the deflection grating element 8 is within the angular acceptable range of the other passive one-dimensional scattering element 6 or 7.

[0165] By means of the switching state of the controllable optical element 9 or the polarization switch and by means of the deflection grating element 8, one of the two passive one-dimensional scattering elements 6 or 7 that scatter the incident light in each case is selected, while the other passive one-dimensional unselected scattering element 6 or 7 has light passing through it at an angle beyond its acceptable range, so that the light is not scattered.

[0166] Figure 5 Figure a) illustrates the control or selection of the passive one-dimensional scattering element 6 in a first control state or switching state of the controllable optical element 9, while Figure b) illustrates the control or selection of the passive one-dimensional scattering element 6 in a second control state or switching state of the controllable optical element 9. To encode a hologram or subhologram into the SLM 2 with a suitable encoding orientation via single parallax encoding, the generation of the virtual visible region needs to be simulated beforehand to determine the suitable encoding orientation of the hologram to be encoded. The process shown in Figures a) and b) is then performed here, and the orientation of the virtual visible region having the maximum area overlapping with the observer's eye or pupil is determined by... Figure 3 and 4The virtual visible area is determined around its center point by means of tracking device 4. The hologram or sub-hologram is then encoded into the coding direction in SLM 2 so that the observer can observe the represented object or scene without interference even if the eye or the pupil of the eye moves to another position.

[0167] exist Figure 5 In the diagram a), the controllable optical element 9 is set to a first control state to simulate a virtual visible region and thus determine a suitable encoding direction. As a result, the passive one-dimensional scattering element 6 is initially selected for light scattering in the light direction. In this case, a virtual visible region is generated in the observer plane 5, wherein the virtual visible region is represented as shown in the diagram. Figure 5 The generated virtual observer window VW is produced in the drawing plane, and the optimal spot SS is generated perpendicular to the drawing plane.

[0168] exist Figure 5 In illustration b), the controllable optical element 9 is set to a second control state, resulting in the selection of a second passive one-dimensional scattering element 7, following the first passive two-dimensional scattering element 7, for light scattering. In this case, a virtual visible region is generated in the observer plane 5, where the region is now perpendicular to... Figure 5 The drawing plane generates the virtual observer window VW, and now the optimal spot SS is generated in the drawing plane. In this way, the orientation of the virtual observer window VW and the optimal spot SS in the observer plane 5 can be modified by rotation about their center point, so that the encoding orientation of the hologram is also changed due to the projection of the virtual observer window onto SLM 2, in order to determine the size or expansion of the hologram or subhologram.

[0169] By using another controllable optical element, another deflection grating element, and two additional passive one-dimensional scattering elements in the tracking device 4, this arrangement can be extended to four angular setting directions for the encoding direction of the hologram or sub-hologram: horizontal, vertical, and two diagonal angle settings. Then, depending on the control state of the first controllable optical element 9, the first controllable optical element 9 and the first deflection grating element 8 generate two possible deflection angles. The second controllable optical element can then set the polarization of the light, for example, such that the second deflection grating element, whose grating period differs from that of the first deflection grating element 8, deflects accordingly to the +1st diffraction order or the -1st diffraction order. This produces a total of four possible deflection angles, combinations of the +1st or -1st diffraction order of the first deflection grating element and the +1st or -1st diffraction order of the second deflection grating element. The four passive one-dimensional scattering elements can be designed as volume gratings in each case, with four different angular acceptance ranges corresponding to one of the four deflection angles of the arrangement of the controllable optical elements and deflection grating elements in each case.

[0170] If the hologram to be encoded requires other angular directions for encoding, other optical elements of this type can be provided in the tracking device.

[0171] The tracking device may also have at least one redirecting element instead of a deflection grating element, such as a polarization beamsplitter element, to select different paths in the optical path by changing the polarization of the light, wherein each path has a one-dimensional passive scattering element. For this purpose, the scattering elements in each path should be aligned differently. For example, a passive scattering element may scatter light in the horizontal direction in a first path at one output of the polarization beamsplitter element, while another passive scattering element may scatter light in the vertical direction in a second path at another output of the polarization beamsplitter element. In this case, the scattering elements need not be designed to be angle-selective. The number of paths and passive scattering elements can also be extended to four by means of a second controllable optical element and a second polarization beamsplitter element.

[0172] Replacing the deflection grating element, controllable optical element, and two passive scattering elements, according to Figure 5 The tracking device 4 of the display device may also include, for example, only a single passive scattering element, which is designed to be mechanically rotated to modify the scattering direction of the incident light. The passive scattering element is designed to be one-dimensional. The single passive scattering element scatters, for example, in one direction at 20° and in a direction perpendicular to it at 1°, wherein the 20° direction can be modified by rotating the passive scattering element, for example, from the horizontal direction to the vertical direction or a diagonal direction of +45° or -45°. This design advantageously reduces the number of required optical components because deflection grating elements and controllable optical elements are not required. However, conversely, a device for the mechanical rotation of the scattering element is needed.

[0173] However, in principle, the present invention is not limited to using a specific type of scattering element to change the scattering direction. It is also possible to consider using a single, electronically controllable one-dimensional scattering element whose scattering direction can be modified.

[0174] exist Figure 6Another example embodiment for tracing a virtual visible area to a new location of the observer's eye or the pupil of the eye is shown. The display device shown here includes an illumination device 10 with at least one light source, an SLM 20, and an optical system 30. The light source of the illumination device 10 is here designed as a slit or slot shape and illuminates the SLM 20 with sufficiently coherent light. The optical system 30 includes imaging elements, here two imaging elements 31 and 32, wherein no special arrangement of the imaging elements is provided. For example, only a single imaging element may be provided, which is positioned upstream or downstream of the SLM 20 in the direction of light propagation. Alternatively, more than two imaging elements may be provided.

[0175] Here, the SLM 20 is illuminated by light through an imaging element 31 disposed between the illumination device 10 and the SLM 20. The light is focused onto a virtual visible area in the observer plane 50, wherein another imaging element 32 of the optical system 30 is disposed downstream of the SLM 20 in the direction of light.

[0176] Figure 6 Illustration a) shows the generation of the virtual observer window VW in the observer plane 50 in the drawing plane. The light source of the illumination device 10 is moved or rotated in such a way that the narrow or short side of the slit-shaped or slot-shaped light source illuminates the SLM 20. For illustrative purposes, the light source is shown here in perspective so that its slot-shaped form is clearly visible. Strictly speaking, the long side of the slot of the light source will be perpendicular to the drawing plane and will not be visible in the side view. Due to the small extension of the light source in this light propagation direction, a very small angular spectrum is generated downstream of the subsequent imaging element 31. The SLM 20 is illuminated with essentially parallel light. Apart from the diffraction caused by the pixels of the SLM 20 (which is not shown here and generates the virtual observer window VW), the light emitted by the light source in the observer plane 50 in the direction corresponding to the encoding direction of the hologram encoded into the SLM 20 is again focused on a more or less point-shaped area.

[0177] like Figure 6 As shown in Figure b), the light source of the illumination device 10 is moved or rotated to trace the virtual visible area to a new or different position of the observer's eye or pupil. The light source is moved or rotated in such a way that the long side of the slit-shaped or slotted light source now illuminates the SLM 20. Light emitted from the light source from different positions and shown as continuous dotted or dashed lines strikes the SLM 20 at different angles, and thus is also imaged at different positions in the observer plane 50 by the imaging element 32. Therefore, the light is scattered in this direction. Therefore, an optimal spot SS is generated in the observer plane 50 by using the long side of the slit-shaped or slotted light source of the illumination device 10 to illuminate the SLM 20.

[0178] In this way, regardless of the diffraction at the pixels of SLM 20, a slit or slot-shaped image of a slit or slot-shaped light source is generated in the observer plane 50 in the short side direction of forming the virtual observer window VW and in the long side direction of forming the optimal light spot SS.

[0179] The slit or slot-shaped light source of the rotating illumination device 10 is used to determine the appropriate encoding orientation of the hologram on the SLM 20. The slit or slot of the light source can then be configured, for example, in such a way that the long side of the light source is relative to the orientation determined by… Figure 4 The horizontal line L exists in a horizontal or vertical direction, or at an angle of +45 degrees or -45 degrees, and the short or narrow side of the light source is provided perpendicular to that direction in each case.

[0180] exist Figure 7 Another example embodiment for tracking a virtual visible area to a new position of the observer's eye or the pupil of the eye is shown. The tracking device of the display device is designed here as a filter device. For this purpose, the display device includes an illumination device 100 having at least one light source, an SLM 200, an optical system 300, and a tracking device 400 designed as a filter device. The optical system 300 includes at least one imaging element, here three imaging elements 301, 302, and 303. The SLM 200 is illuminated by the light source of the illumination device 100 and by the imaging element 301 of the optical system 300 to generate a virtual visible area in the observer plane 500. Another imaging element 302 downstream of the SLM 200 in the direction of light propagation focuses the light into a filter plane 440, in which an intermediate image of the light source or a Fourier transform of the SLM 200 is generated. Therefore, the filter plane 440 can also be referred to as the intermediate image plane of the light source image or the Fourier plane of the SLM 200. An imaging element 303, positioned downstream of the filter plane 440 in the light direction, then images this intermediate image plane or Fourier plane 440 onto the observer plane 500, thereby generating a virtual visible region formed by a virtual observer window VW and an optimal spot SS. Diffraction orders, generated by the pixel structure of the SLM 200 and shown by dashed lines, are schematically drawn in the filter plane 440. The tracking device 400 includes an aperture or stop 401 that correspondingly filters out the incident light. This means that specific desired diffraction orders are allowed to pass through, while other diffraction orders are filtered out by the aperture 401 in the filter plane 440.

[0181] For illustrative purposes, the position of the diffraction order and the orientation of the filter aperture 401 are shown in perspective view in this figure. Strictly speaking, the horizontal diffraction order and the long side direction of the filter aperture 401 are located perpendicular to the direction of the filter aperture 401. Figure 7 The cross-sectional plane is drawn in the illustration a).

[0182] exist Figure 7 In Figure a), the aperture 401 of the tracking device 400 is configured in the display device such that it allows only one diffraction order to pass through in the vertical direction, but allows multiple diffraction orders to pass through in the horizontal direction. A virtual observer window VW is generated in the vertical direction in this manner. The aperture 401 configured in this way can be used for the vertical encoding direction of a hologram or sub-hologram to be encoded into the SLM 200.

[0183] exist Figure 7 In illustration b), the aperture 401 in the filter plane 440 is now positioned in the display device such that it now allows only one diffraction order to pass through in the horizontal direction and multiple diffraction orders to pass through in the vertical direction. This results in the generation of an optimal spot SS in the vertical direction. The aperture positioned in this way can be used for the horizontal encoding direction of a hologram or sub-hologram on the SLM 200.

[0184] Typically, it is not necessary to use the full number of diffraction orders in the optimal spot direction; instead, the size of aperture 401 can also include segments of diffraction orders. Aperture 401 can, for example, be the size of 4.4 diffraction orders. Aperture 401 should have the maximum size of one diffraction order in the encoding direction of the hologram or subhologram. However, the size of aperture 401 can also be smaller than one diffraction order. Furthermore, the center of aperture 401 need not coincide with the center of the diffraction order, but can be offset relative to it. Aperture 401 can also be configured to additionally filter out artifacts, such as zero-order spots. In its simplest case, the aperture 401 of the tracking device 400 can be a mechanically rotatable aperture stop. Aperture 401 can also be designed, for example, as an electrically controllable aperture, which is based on liquid crystal (LCD) and absorbs or transmits light depending on the switching state.

[0185] As already described, in certain embodiments of the invention, rotation of the encoding direction of the hologram can also be combined with small movements of the virtual observer window by encoding the prism function or prism terms in the hologram. If an aperture is used, this can be advantageously achieved by designing the aperture not only to be rotatable but also movable over small areas (e.g., moving one positive / negative diffraction order in the encoding direction). Therefore, in Figure 7 In diagram a), aperture 401 will further move in the vertical direction. Figure 7 In illustration b), aperture 401 will be further moved in the horizontal direction in each case to improve the overlap between the virtual visible area (i.e., the virtual observer window and the optimal spot) and the pupil of the eye.

[0186] exist Figure 8The image shows the pixel matrix of the SLM. As can be seen, in this case, the SLM has square pixels. Figure 8 In illustration a), only one SLM of this type is shown, while illustrations b) through e) show sub-holograms with different encoding orientations, which, according to the invention, can provide a way to trace a virtual visible region to a new position of the eye or the pupil of the eye. Illustration b) shows a sub-hologram with a vertical encoding orientation, where the sub-hologram is represented by gray shaded pixels. Illustration c) shows a sub-hologram with a horizontal encoding orientation. Illustration d) shows a sub-hologram with a diagonal encoding orientation (in this case, at -45 degrees). Illustration e) similarly shows a sub-hologram with a diagonal encoding orientation, but here the encoding orientation of the sub-hologram is +45 degrees. In each case, it is preferable that the hologram of the three-dimensional scene is calculated by summing the sub-holograms of the individual object points, where all sub-holograms have the same encoding orientation.

[0187] Figure 9 An alternative design for an SLM used to track virtual visible areas, which can be provided in a display device, is shown. Here, the SLM now has a pixel matrix with rectangular pixels. Figure 9 Illustration a) shows only this type of SLM with rectangular pixels, while illustrations b) to d) show sub-holograms with different encoding orientations, which can be provided according to the invention to trace a virtual visible region to a new location of the eye or the pupil of the eye. Illustration b) shows the encoding orientation of the sub-hologram, where the pixels are diagonally offset relative to each other in each case. Thus, the aspect ratio of the rectangular pixels produces an angle of approximately 25 degrees with the horizontal side of the SLM. This indicates that the invention is not intended to be limited to... Figure 8 The angles shown for the encoding directions are horizontal (0°), vertical (90°), and diagonal (+45°; -45°), but in this case, an encoding direction of, for example, 25° can also be used.

[0188] Figure 9 Illustrations c) and d) show the encoding directions for interpolating holograms based on the pixel matrix of the SLM. Illustration c) shows a sub-hologram with a 50-degree encoding direction. This can be achieved by always encoding two pixels upwards and one pixel to the right in the pixel matrix of the SLM. Illustration d) shows a sub-hologram with an approximately 12.5° encoding direction. This can be achieved by always encoding two pixels to the right and one pixel upwards in the SLM.

[0189] In this type of arrangement, more than four encoding directions can also be used for the hologram on the SLM, such as encoding directions of 0°, 90°, ±12.5°, ±25°, and ±50°. Therefore, in this case, there are eight encoding directions, where these values ​​are again only examples. Here, different possible encoding directions can be determined by... Figure 5 , 6 Alternatively, a tracking device 7 can be used, which allows for corresponding angle settings. This means that in the case of at least one optical element in the form of a scattering element, or in the case of at least one passive scattering element, or in the case of a filter device as a tracking device, or in the case of at least one light source as a tracking device, for example, according to Figure 9 The diagram in Figure b) shows that the 25° encoding direction angle should be adjustable so that it can be used according to... Figure 5 , 6 Or a specific tracking device (e.g., 7). The aforementioned angle is intended merely as an example and for explanation.

[0190] In the case of using a scattering element, the scattering direction of light, or in the case of using a slotted light source, the long side of the slotted light source, or in the case of using an aperture, the long side of the aperture, corresponds to the optimal spot direction in the filter plane of the display device in each case. The non-scattering direction, short side, or aperture of the slotted light source in the filter plane corresponds to the encoding direction.

[0191] Conversely, the sub-hologram has an extension of multiple pixels in the coding direction, but typically only an extension of one pixel perpendicular to the coding direction. Therefore, the long side of the sub-hologram points in the coding direction, and the short side points perpendicular to the coding direction.

[0192] In other words, the direction of light scattering, the long side of the light source, or the long side of the filter aperture is located perpendicular to the long side of the sub-hologram in each case.

[0193] according to Figure 10 The design of controllable optical elements for a tracking device is now described, which may, for example, include elements based on... Figure 5 The present invention is not intended to be limited to controllable optical elements designed in this manner. The controllable optical elements of the tracking device can therefore also have different designs that ensure controllability or switchability.

[0194] The controllable optical element 70 comprises two substrates 71 and 72. The two substrates 71 and 72 are bonded together, with a space between them filled with a liquid crystal layer 73 having a liquid crystal LC, or the liquid crystal layer 73 being embedded in the space. At least one substrate (in this case, substrate 71) also has a surface structure 74. The liquid crystal material is birefringent and has a first refractive index, such as a common refractive index, which is essentially the same as the refractive index of the surface structure 74. Both the liquid crystal LC and the surface structure 74 have a refractive index of n = 1.5. The birefringent liquid crystal LC also has a second refractive index, such as a superlative refractive index, which differs from the refractive index of the surface structure 74. For example, the liquid crystal LC has a superlative refractive index of n = 1.7, while the refractive index of the surface structure 74 is n = 1.5.

[0195] Surface structure 74 is, in particular, a one-dimensional statistical surface structure, which is, for example, imprinted into a polymer layer applied to substrate 71. Preferably, only one substrate has surface structure 74, while the other substrate is designed to be planar. Here, this means that substrate 71 has surface structure 74 and substrate 72 is designed to be planar or flat. Due to its planar design, substrate 72 is used for the alignment of the liquid crystal LC in the liquid crystal layer 73. This means that the liquid crystal LC is oriented on substrate 72. For example, the liquid crystal LC is aligned accordingly by rubbing or photo-orientation.

[0196] The light scattering characteristics of the controllable optical element 70 are predetermined by the selection of the surface structure 74, namely, the width, height, and statistical distribution of the surface structure 74. For example, the surface structure 74 can be designed to resemble a surface relief grating or a blazed grating; however, compared to conventional grating elements, the grating period and / or blaze angle can vary arbitrarily with position on the substrate 71, thus not producing regular diffraction orders, but instead scattering light within a predetermined angular range. The scattering angle can then be set, for example, within a certain range (i.e., within the minimum and maximum grating periods, and within the frequencies of different grating periods and / or within the range and distribution of blaze angles). The surface structure 74 can also be an irregular height profile, with its width and height varying arbitrarily with position on the substrate 71.

[0197] Furthermore, each of the two substrates 71 and 72 includes electrode systems 75 and 76. Substrate 71 has electrode system 75, which has at least one electrode. Substrate 72 has electrode system 76, which similarly has at least one electrode. The electrodes of electrode systems 75 and 76 can be designed to be planar, i.e., non-pixelated. In this case, at least one electrode of electrode system 75 is disposed behind the statistical surface structure 74 (i.e., between the surface structure 74 and the substrate 71) to generate a uniform field distribution.

[0198] By using a polarizing element upstream of the controllable optical element 70 in the light propagation direction of the display device, or by means of light that has been pre-polarized in the light path, such as a light source using radiatively polarized light, the light polarized on the input side impacts the controllable optical element 70. The liquid crystal LC of the liquid crystal layer 73 is oriented by the substrate 70, for example by friction or photo-guided orientation, such that, in the controlled state of the controllable optical element 70 or in the switching state when no electric field is applied to the electrode system 75 and 76, the refractive index of the liquid crystal LC, different from the refractive index of the surface structure 74, is effective for the incident light. In this state, the statistical surface structure 74 is optically visible. The surface structure 74 then causes a light scattering effect. This... Figure 10 The illustration in Figure a) is shown.

[0199] In different control or switching states of the controllable optical element 70, when a sufficiently strong electric field is applied to the electrode system 75 and 76, the refractive index of the liquid crystal LC corresponding to the refractive index of the surface structure 74 comes into play. This is in Figure 10 As shown in Figure b). Since the surface structure 74 and the liquid crystal LC have the same refractive index, the surface structure 74 is optically invisible in this controlled state of the controllable optical element 70. The surface structure 74 and the liquid crystal LC act as planar parallel plates. Therefore, no light is scattered downstream of the controllable optical element 70.

[0200] The alignment of the liquid crystal LC can correspond to, for example, the ECB (Electrically Controlled Birefringence) mode. When the applied voltage is turned off on the electrode system 75, 76 (i.e., in the absence of an electric field), the liquid crystal molecules are oriented in the plane of the substrate 72, as shown in Figure a). When the applied voltage is turned on (i.e., in the presence of an electric field between the electrodes of the electrode system 75, 76), the liquid crystal molecules are oriented perpendicular to the plane of the substrate 72, as shown in Figure b). However, the present invention is not intended to be limited to this arrangement of liquid crystal molecules. Other orientations of the liquid crystal molecules can also exist, such as the VA (Vertical Alignment) mode, in which the liquid crystal molecules are oriented perpendicular to the plane of the substrate 72 when no voltage is applied, and are oriented parallel to the plane of the substrate 72 when a voltage is applied (i.e., in the presence of an electric field between the electrodes of the electrode system 75, 76).

[0201] If multiple controllable optical elements exist in the tracking device of a display device, they can be arranged such that their statistical surface structures have different orientations in each case. For example, controllable optical elements of the same design can be rotated 90 degrees relative to each other. For example, if a voltage is applied in the light propagation direction to the first controllable optical element downstream of the SLM and no voltage is applied to the following second controllable optical element, the incident light will be scattered in the first direction. Conversely, if no voltage is applied to the first controllable optical element, but instead a voltage is applied to the second controllable optical element, the incident light will be scattered in a second direction different from the first direction.

[0202] Typically, a combination of multiple controllable optical elements (i.e., at least two controllable optical elements) can be used to switch between one-dimensional scattering and two-dimensional scattering, or to select between scattering and non-scattering states.

[0203] The present invention is not limited to the exemplary embodiments presented herein. Finally, it should be clearly stated that the above exemplary embodiments are merely for describing the claimed teachings, but the teachings are not intended to be limited to the exemplary embodiments.

Claims

1. A display device for representing two-dimensional and / or three-dimensional scenes, comprising: - At least one illumination device for emitting sufficiently coherent light. - At least one spatial light modulation device, wherein the hologram is encoded into the spatial light modulation device by single parallax coding in the coding direction. - At least one optical system, wherein the at least one optical system is configured to generate at least one virtual visible region at the observer's eye position, the at least one virtual visible region being formed by a virtual observer window and an optimal light spot, wherein the virtual observer window is provided in the encoding direction of the hologram, and the optimal light spot is provided in the non-encoding direction of the hologram, and - A tracking device, wherein the encoding direction of the single disparity hologram on the spatial light modulation device can be modified by the tracking device; and - The encoding direction of the single disparity hologram encoded into the spatial light modulation device can be changed between at least two directions.

2. The display device of claim 1, wherein at least one position detection system is provided, and the position of the observer's eyes, particularly the pupils, in the scene can be determined by the position detection system.

3. The display device of claim 1, wherein the tracking device includes at least one controllable optical element disposed between the at least one illumination device and the observer plane in which the observer of the scene is located.

4. The display device of claim 3, wherein the at least one controllable optical element is designed as a polarization switch, wherein the tracking device comprises at least one passive deflection grating element and at least two passive scattering elements that scatter incident light only in one direction, wherein the passive deflection grating element and the at least two passive scattering elements operate in conjunction with the polarization switch.

5. The display device of claim 4, wherein the at least one passive deflection grating element is a polarization grating element.

6. The display device of claim 4, wherein the at least two passive scattering elements are designed as volume gratings, wherein the at least two passive scattering elements have different angular selectivity.

7. The display device of claim 3, wherein the at least one controllable optical element is designed as a polarization switch, wherein the tracking device comprises at least one redirection element and at least two passive scattering elements that scatter incident light in only one direction in each case, wherein one of the at least two different optical paths can be selected by the controllable optical element and the redirection element, and the scattering element is provided in each of the different optical paths in each case.

8. The display device of claim 7, wherein the at least one redirection element is a polarization beam splitter element.

9. The display device of claim 1, wherein the tracking device comprises a passive scattering element designed to rotate.

10. The display device of claim 1, wherein the tracking device comprises at least two controllable optical elements.

11. The display device of claim 3 or 10, wherein the at least one controllable optical element or the at least two controllable optical elements are designed as scattering elements, wherein the at least one controllable optical element scatters incident light in only one direction, and wherein the at least two controllable optical elements scatter incident light in different directions in each case.

12. The display device of claim 10, wherein the first controllable optical element scatters incident light in a predetermined first direction, and wherein the second controllable optical element scatters light in a predetermined second direction, wherein the first direction is different from the second direction.

13. The display device of claim 12, wherein the encoding direction of the hologram can be determined by correspondingly controlling the first controllable optical element and the second controllable optical element.

14. The display device of claim 3, wherein the at least one controllable optical element comprises two substrates, and a liquid crystal layer is embedded between the two substrates.

15. The display device of claim 14, wherein at least one substrate of the at least one controllable optical element has a one-dimensional surface structure.

16. The display device of claim 15, wherein the surface structure has a grating period that varies arbitrarily with position on the substrate.

17. The display device according to any one of claims 14 to 16, wherein the substrate of the at least one controllable optical element comprises an electrode system in each case, wherein each of the electrode systems comprises at least one electrode.

18. The display device of claim 15, wherein the substrate located opposite the substrate having the surface structure is provided for alignment of liquid crystal in the liquid crystal layer.

19. The display device of claim 15, wherein the liquid crystal material of the liquid crystal layer has a first refractive index and a second refractive index, wherein the first refractive index substantially corresponds to the refractive index of the surface structure, and wherein the second refractive index is substantially different from the refractive index of the surface structure.

20. The display device of claim 15, wherein in the presence of a plurality of controllable optical elements having a one-dimensional surface structure in at least one substrate, the controllable optical elements are arranged in a beam path such that the one-dimensional surface structure of each of the controllable optical elements disposed on at least one substrate has a different orientation relative to each other in each case.

21. The display device of claim 20, wherein the surface structures of the controllable optical elements are arranged relative to each other at an angle of approximately 90°.

22. The display device of claim 1, wherein at least one polarizing element is provided upstream of the at least one controllable optical element in the direction of light propagation.

23. The display device of claim 1, wherein the tracking device is designed as a filter device, the filter device being configured to eliminate diffraction levels.

24. The display device of claim 23, wherein the filter device is designed to be controllable.

25. The display device of claim 1, wherein at least one light source of the at least one illumination device is designed as a tracking device, wherein the at least one light source is designed to be controllable in order to modify the coherence of the light to be emitted.

26. The display device of claim 1, wherein the display device is designed as a holographic display device.

27. A head-mounted display comprising a display device as described in any one of claims 1 to 26, respectively for the left eye and the right eye of an observer.

28. A method for representing a two-dimensional and / or three-dimensional scene by means of at least one illumination device emitting sufficiently coherent light, at least one spatial light modulation device, at least one optical system, a tracking device, and a position detection system, comprising: - The position detection system determines the position of the observer's eyes. - The appropriate encoding direction of the single disparity hologram on the at least one spatial light modulation device can be determined by the at least one optical system and the tracking device, wherein the encoding direction of the single disparity hologram can be changed between at least two directions; - The single disparity hologram is encoded into the at least one spatial light modulation device in a defined encoding direction via single disparity encoding, and - The at least one spatial light modulation device illuminates the hologram through the at least one illumination device, and the hologram is reconstructed by the at least one optical system, generating at least one virtual visible region at the location of the observer's eye, the at least one virtual visible region being formed by a virtual observer window and an optimal light spot, wherein the virtual observer window is provided in the encoding direction of the hologram, and the optimal light spot is provided in the non-encoding direction of the hologram.

29. The method of claim 28, wherein the encoding direction in which the virtual visible region of the hologram to be encoded has the largest proportion of overlap with the observer's pupil is selected.

30. The method of claim 29, wherein, in the event of a change in the observer's eye position, a new eye position is determined by the position detection system, the virtual visible region is rotated around its fixed center point to select a suitable encoding direction for the hologram to be encoded, and the direction in which the virtual visible region has the largest proportion of overlap with the region of the observer's pupil is determined.

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