Light guide device and display device for representing a scene

Abstract

The invention relates to a light guide device for guiding light. The light guide device has an optical fiber, a light coupling device and a light decoupling device. The light propagates in the light guide by reflection at the boundary surface of the light guide. After a predetermined number of light reflections at the boundary surface of the light guide, the light is decoupled from the light guide by the light decoupling device. A display device, in particular a near-eye display device, is also provided, which has an illumination device including at least one light source, at least one three-dimensional light modulation device, an optical system and a light guide device.

Description

[0001] This application is a divisional application of the application with application number 201880011482.7, international application number PCT / EP2018 / 053496, international application date February 13, 2018, the applicant is SeeRear Technologies Inc., and the invention name is “Light guide device and display device for representing scenes”. Technical Field

[0002] The present invention relates to a light guide device for guiding light and a display device for representing a scene (especially a three-dimensional scene), the display device comprising such a light guide device. In addition, the present invention also relates to a method for generating a reconstructed scene by means of a spatial light modulation device and a light guide device. Background Art

[0003] Light guides have a wide range of applications, especially in the field of optics. In particular, they are used in the field of lasers. Light guides generally have an internal core, which is surrounded by a coating or cladding. Light entering the light guide is usually propagated within the light guide by total reflection. This light guiding effect due to total reflection is caused by the refractive index of the core material being higher than the refractive index of the cladding material or, in the case where no cladding is provided, by the refractive index of the light guide material being higher than the refractive index of the surrounding environment, such as air.

[0004] However, the light guide device or light guide may also be used in other areas, for example in a device for representing a reconstructed scene, in particular for representing a preferably three-dimensional scene or object points. Such a device may be, for example, a display or display device located near the eyes of an observer of the scene, a so-called near-eye display. A near-eye display is, for example, a head mounted display (HMD).

[0005] For head mounted displays (HMDs) or similar near eye displays or display devices, it is desirable to use compact and light optical configurations. Since such display devices are generally fixed to the user's head, bulky and heavy arrangements can adversely affect the user's comfort.

[0006] In the case of an AR (Augmented Reality) HMD, it is additionally desirable that the user be able to perceive his natural environment as closely as possible without interference due to the HMD and, on the other hand, be able to perceive well the content displayed by the HMD itself.

[0007] If a spatial light modulation device and an optical device for imaging the spatial light modulation device are used, it is to be envisaged in this case that the optical device allows both light from the spatial light modulation device and light from the natural environment of the observer to reach the eye.

[0008] The visual range or field of view is also important for user comfort in an HMD. In this case, the largest feasible visual range is advantageous. However, in general, the representation of a large visual range in combination with high resolution requires a spatial light modulation device with a very high number of pixels.

[0009] Patent document US2013 / 0222384A1 discloses a holographic head mounted display (HMD) with an observer window. Figure 1 Such a head mounted display is schematically shown in FIG, and a large viewing range can be achieved by segmenting the viewing range. In this case, using a spatial light modulator 200 and a suitable optical system 400, 500, individual portions of the viewing range are generated in a temporal sequence, which are visible from the observer window. The advantage of this arrangement is that, due to the sequential representation, a large viewing range is achieved without requiring a large number of pixels of the spatial light modulator.

[0010] In the patent document US2013 / 0222384A1, various embodiments for generating multiple images of a spatial light modulator composed of segments or stitched together in this way are described. However, several of the described embodiments use optical components of relatively large size and are only compatible to a limited extent with the design requirements of compactness and / or lightness or usability in AR-HMDs.

[0011] For example, in Figure 2 The arrangement of patent document US2013 / 0222384A1 is shown in FIG. 1 , which has a plurality of lenses 800 immediately in front of the observer's eyes. This arrangement is particularly suitable for VR (virtual reality) HMDs. However, in AR-HMDs, these lenses 800 will have the following effect: since the observer can also perceive the natural environment through the lenses, the natural environment will be displayed in a distorted form.

[0012] Figure 3 Also from patent document US2013 / 0222384A1, an HMD device with a plurality of reflectors 950, 960, 970 is disclosed. By appropriate design of the reflectors as partially transmissive elements, this arrangement is in principle also suitable for an observer who perceives the surrounding environment. This means that the arrangement can be suitable for augmented reality (AR) applications. However, in order to produce a large visible range, larger reflectors will be required. This means that it may be difficult to obtain a compact, space-saving version of this arrangement.

[0013] An embodiment using a waveguide is also described in patent document US2013 / 0222384A1. Figure 4, and have one waveguide 1101 for the left eye of the observer and one waveguide 1102 for the right eye of the observer. In this arrangement, the spatial light modulators 201, 202 and the optical units 811, 812 are each arranged adjacent to the observer's head in the lateral direction, wherein the light for each eye is coupled into the thin waveguides 1101, 1102 by gratings 1111, 1112, respectively. The gratings used as coupling optical units are preferably designed as volume gratings, wherein they are used to couple light into the thin waveguide at a flat angle, so that light of all coupling angles propagates along the waveguide direction by total reflection at the two boundary surfaces of the waveguide, and the two boundary surfaces of the waveguide are arranged parallel to each other. In this case, the waveguide does not have to be completely flat, but can also have a curved surface. However, no quantitative specification on the surface curvature is provided in the patent document US2013 / 0222384A1. The light deflection device generates various angular spectra, which are coupled into the waveguide in a time sequence. In order to generate segmented multiple images, a different angular spectrum of each segment of the multiple images is coupled into the waveguide. Light of one of the angular spectra generated by the light deflection device is decoupled from the waveguide in the direction of the observer's eyes by a plurality of reflector gratings, each of which is designed to have a different angular range with respect to its angular selectivity and is arranged adjacent to each other.

[0014] according to Figure 4 The advantage of this arrangement over other designs described in patent document US2013 / 0222384A1 is that the waveguide is light and compact, and the observer can also perceive the environment around him when looking through the waveguide. Therefore, the use of waveguides is advantageous for AR arrangements. However, the use of waveguides is not limited to AR arrangements, but is also applicable to VR arrangements. In the description of patent document US2013 / 0222384A1, the waveguide is referred to as thin, but no numerical value of the thickness is set.

[0015] Here is also a quote from Keigo Iizuka's "Elements of Photonics", Vol. 2, Chapter 9 "A Guide to Planar Optics for Integrated Optical Devices" about light propagation in light guides: "The basis of integrated optical devices is planar light guides. Light is guided by a medium with a higher refractive index than the surrounding layers.... According to geometric optics, light will propagate with little loss by continuous total internal reflection (TIR) ​​as long as certain conditions are met. These conditions are that the layer supporting the propagation must have a higher refractive index than the surrounding medium and that the light must be emitted within angles that satisfy total internal reflection at the upper and lower boundaries. This simple theory of geometric optics breaks down when the size of the guiding medium is comparable to the wavelength of the light. In this case, the light guide supports propagation only at a discrete number of angles, called propagation modes". In the latter case, the light propagation is described by wave optics methods. The term "waveguide" is then often used. In such a waveguide there is no defined geometric beam profile.

[0016] In contrast, in this application the term "light guide" is used in such a way that it refers to a sufficiently thick arrangement for which light propagation can be described by geometrical optics. Such a light guide may have a thickness of, for example, a few millimeters, such as 2 mm or 3 mm.

[0017] Holographic displays or display devices are based inter alia on diffraction effects at the pixel aperture of a spatial light modulation device and interference of coherent light emitted by a light source. Nevertheless, several important conditions using geometrical optics can be formulated and defined for a holographic display generating a virtual observer window.

[0018] On the one hand, the illumination beam path in the display device is important for this purpose. It is used, among other things, to generate a virtual observer window. The spatial light modulator is illuminated by means of an illumination device comprising at least one real or virtual light source. Then, the light from different pixels of the spatial light modulator must be guided into the virtual observer window respectively. For this purpose, at least one light source of the illumination device illuminating the spatial light modulator is usually imaged in an observer plane with a virtual observer window. This imaging of the light source occurs, for example, in the center of the virtual observer window. When the spatial light modulator is illuminated with a plane wave corresponding to an infinitely distant light source, for example, different pixels of the spatial light modulator, light emitted vertically from these pixels, are focused in the center of the virtual observer window. Then, in the case of the same diffraction angle of each pixel of the spatial light modulator, the light generated non-vertically is also focused at the corresponding same position in the virtual observer window. However, in general, the virtual observer window can also be displaced laterally relative to the image of the at least one light source, for example, the position of the image of the at least one light source can coincide with the left edge or the right edge of the observer window.

[0019] On the other hand, imaging beam paths are important in holographic displays or display devices, in addition to direct-view displays. In HMDs, the spatial light modulator, which is small in size, produces an overall magnified image. This is usually a virtual image, which appears to be at a greater distance from the observer than the spatial light modulator itself. The individual pixels of the spatial light modulator are usually magnified and imaged.

[0020] However, patent document US2013 / 0222384A1 does not contain any teaching on how to design a waveguide to provide a well-defined imaging beam path and a well-defined illumination beam path and how to generate the image of the virtual observer window and the spatial light modulator in the desired manner. In particular, as pointed out, it is not possible to describe the beam paths geometrically in a waveguide in general. Various optical modes propagating in a waveguide may correspond to different light paths.

[0021] For example, an arrangement for a non-holographic HMD with a waveguide is described in patent document US2009 / 303212A1. A light modulator is imaged at infinity therein. Due to the infinite distance, the optical path of the light has no effect on the propagation in the waveguide. In simplified terms, even if the optical path components extending through the waveguide have different lengths, the entire optical path from the image of the pixel of the light modulator to the eye is always infinitely long.

[0022] However, in holographic displays, efforts are always made to achieve the ability to represent three-dimensional (3D) scenes with large depth areas. The purpose of such displays is generally not just to represent content at a great distance from the observer. Even if the image of the light modulator is located at infinity in the holographic display, the three-dimensional scene is generally represented at a finite distance. Using the arrangement described in patent document US2009 / 303212A1, in some cases, the light modulator itself can be properly imaged at infinity in the holographic display. However, it is not possible to properly reconstruct the object points of the scene at a finite distance (i.e. in front of the image of the light modulator).

[0023] A holographic direct-view display that generates a virtual observer window includes an illumination beam path. The display includes an illumination device having at least one light source. For example, the illumination device is designed as a backlight that generates a collimated plane wavefront that illuminates a spatial light modulator. The collimated wavefront corresponds to a virtual light source that illuminates the spatial light modulator from an infinite distance. However, a divergent or converging wavefront can also be used to illuminate the spatial light modulator, which corresponds to a real or virtual light source at a finite distance in front of or behind the spatial light modulator. The field lens focuses the light from the spatial light modulator at the position of the virtual observer window. If a hologram is not encoded in the spatial light modulator, the image of the light source thus forms the observer plane, and the periodic repetition of the image produces higher diffraction orders. If a suitable hologram is encoded in the spatial light modulator, the virtual observer window produces a diffraction order close to the zeroth order. This is referred to below by stating that the virtual observer window is located in the plane of the light source image. In a holographic direct-view display, the field lens that generates the light source image is usually located near the spatial light modulator. The observer views the spatial light modulator at its actual distance, and there is no image of the spatial light modulator. There is then no imaging beam path.

[0024] In other holographic display devices, such as head mounted displays (HMD), head up displays (HUD) or other projection displays, there may also be an imaging beam path, as already briefly mentioned. In these display devices viewed by an observer, a real or virtual image of the spatial light modulation device is generated, wherein the illumination beam path is still important for the generation of a virtual observer window. Therefore, the beam path, the illumination beam path and the imaging beam path are all important here.

[0025] In other display devices, such as stereoscopic display devices, the presence of an imaging beam path and an illumination beam path may also occur. A stereoscopic display device for producing an optimal light spot may have, for example, an optical arrangement similar to that of the holographic display, i.e., collimated illumination of a spatial light modulation device and a field lens, but may also have additional components, such as a scattering element with a limited scattering angle. If the scattering element is removed from the display device, the field lens will therefore produce an image of the light source in the plane of the optimal light spot. By using a scattering element, the light is distributed over an extended optimal light spot that is narrower than the interpupillary distance of the observer. However, the illumination beam path is important so that a complete stereoscopic image can be seen without vignetting effects. In this case, the three-dimensional stereoscopic display device may also have an imaging beam path, which is used by the spatial light modulation device to image at a specific distance from the observer.

[0026] In general, the display device may include lenses or other imaging elements that affect the beam path, the illumination beam path, and the imaging beam path. For example, a single imaging element may be arranged between the spatial light modulation device and the observer so that the imaging element generates both an image of the spatial light modulation device and an image of the light source in the observer plane.

[0027] In a holographic display device, the typical size of a sub-hologram of a hologram calculated from a three-dimensional scene depends on the position of the three-dimensional scene in space relative to the image plane of the spatial light modulator. For example, if the scene is located in front of the image plane of the spatial light modulator facing the observer, a sub-hologram with a large size is generated. However, large sub-holograms increase the computational workload during the calculation of the hologram. In the applicant's patent document WO2016 / 156287A1, a method is disclosed that reduces the computational workload by arithmetically introducing a virtual plane of the spatial light modulator. However, it is also desirable to select an optical system so that the image plane of the spatial light modulator is advantageously positioned so that a hologram with a sub-hologram of a small size can be calculated.

[0028] Due to limitations in the optical system and / or the imaging system, it may not be possible in all cases to generate an image of the spatial light modulator at a point that is advantageous for the calculation of the sub-hologram. For example, the requirement to produce a large field of view in a head-mounted display may necessitate the use of lenses with a short focal length immediately in front of the observer's eyes. On the other hand, if the spatial light modulator cannot be placed close enough to the lens, this makes it more difficult to produce an image plane of the spatial light modulator at a position that is advantageous for the calculation of the hologram.

[0029] Considering the overall situation, the optical elements required for the illumination beam path may have an adverse effect on the imaging beam path and vice versa.

[0030] In an optional design of a holographic display device that generates a virtual observer window, imaging of the spatial light modulation device can also be performed in the virtual observer window. If there is no physical screen, a screen or reference plane of the type used for the holographic representation of the three-dimensional scene is provided in the Fourier plane of the spatial light modulation device (and thus the image plane of the light source). Therefore, in such a display device, there is also an imaging beam path and an illumination beam path. But the importance of the hologram plane and the observer plane is exchanged. The virtual observer window is then located in the image plane of the spatial light modulation device and is therefore related to the imaging beam path. The hologram or reference plane used to calculate the hologram from the three-dimensional scene is located in the Fourier plane of the spatial light modulation device and is therefore related to the illumination beam path.

[0031] According to patent document WO2016 / 156287A1, a virtual plane for calculating the hologram of such a display device can be placed in the Fourier plane of the spatial light modulation device. The sub-holograms in the virtual plane are calculated and summed. Then, the hologram that can be written into the spatial light modulation device is determined by the Fourier transform of the summed hologram.

[0032] The display device with an image of a spatial light modulation device located in the observer plane can also be used in a modified form to produce a design of a stereoscopic three-dimensional display device with two planar views for the left and right eye.

[0033] If a suitably calculated hologram is written into the spatial light modulator and if the display device comprises an illumination device that produces sufficiently coherent light, a two-dimensional image is thus generated in the Fourier plane of the spatial light modulator with the Fourier transform of the hologram. Additional scattering elements can be located in this plane. If an image of the spatial light modulator is generated in the observer plane without a scattering element, an optimal light spot will thus be generated instead of using a scattering element. The size of the optimal light spot depends on the scattering angle of the scattering element. This arrangement can be used, for example, in a head-up display (HUD).

[0034] The following description mainly relates to the case where the virtual observer window or the optimal light spot is located in the plane of the light source image. The statements made also apply accordingly to embodiments with an image of the spatial light modulation device in the virtual observer window by corresponding exchange of the imaging beam path and the illumination beam path or the plane of the spatial light modulation device and the Fourier plane. Therefore, the present invention is not limited to the case with a virtual observer window or the optimal light spot located in the plane of the light source image.

[0035] As already briefly mentioned, the display device of patent document US 2013 / 0222384 A1 is a holographic display device, in which both the imaging beam path and the illumination beam path can cause difficulties. Depending on the selected optical system, in certain cases different beam paths are generated in different segments of the multiple images.

[0036] For the imaging beam path, this can mean that the image plane of the spatial light modulator is located at different depths in each segment. For a holographic display device, since the sub-holograms of each segment are calculated according to the corresponding image position of the spatial light modulator, in principle, different image planes of the spatial light modulator in different segments can be compensated. For example, for a segment with a very far image of the spatial light modulator, an object point at a specific distance from the observer can be encoded as a sub-hologram of an object point in front of the spatial light modulator, and an object point at a similar distance in a closer image of the spatial light modulator can be encoded as a sub-hologram of an object point behind the spatial light modulator. Although the image of the spatial light modulator is at different distances from the observer, a coherent three-dimensional scene can be represented. However, disadvantageously, the unfavorable image position for each segment of multiple images potentially increases the size of the sub-hologram, thereby increasing the amount of calculation. The potential displacement of the axial position of the virtual observer window caused by different optical paths in each segment can be more unfavorable than the displacement of the image of the spatial light modulator in each segment. The goal of segmentation or splicing is to generate a unified virtual observer window from which a large field of view can be seen. The position of the virtual observer window in which the individual segments of the multiple images are shifted in depth will in any case adversely affect the perception of the three-dimensional scene. Therefore, it is necessary to obtain a uniform light source image in the same observer plane in all segments. In addition, an image of the spatial light modulation device at an equal or at least similar distance from the observer is also generated for all segments. Typically, as disclosed in patent document US2013 / 0222384A1, a display device in which a light source image is generated in the observer plane will be used to generate segments of the multiple images. The segments are generated in the following manner, i.e., images of the spatial light modulation device offset relative to each other are generated in each individual segment.

[0037] However, for a display device with an image of a spatial light modulator located in the observer plane, segmentation or stitching can also be produced. For such a display device, an image of the spatial light modulator is generated at the same position in each segment to generate a uniform virtual observer window for all segments. In contrast, the Fourier planes of the spatial light modulator are shifted relative to each other in the individual segments to produce a large field of view. Since higher diffraction orders also result in the Fourier plane of the spatial light modulator as a whole, this arrangement can be produced, for example, in multiple stages, for example, by generating a non-shifted Fourier plane in the first stage, in which filtering is performed in such a way that only at most one diffraction order is transmitted and the other diffraction orders are filtered out. In the second stage, an image of this filtered diffraction order is generated, wherein the image is shifted relative to each other in the individual segments to produce a large field of view. An alternative is a single-stage system with a variable filter, in which all diffraction orders are shifted in the first stage, but the aperture of the filter is also shifted in such a way that the same diffraction order is transmitted in each case. Statements made about a display device with an image of a light source lying in the observer plane can also be correspondingly transferred to a display device with an image of a spatial light modulation device lying in the observer plane.

[0038] The optical systems used to generate the illumination beam path and the imaging beam path in the display device also generally have aberrations. For example, for a holographic display device with a light source image located in the observer plane, the following effects can occur. The aberrations of the imaging beam path affect the resolution of the image generated by the spatial light modulator and potentially also in the holographic display device the clarity and resolution of the three-dimensional scene whose hologram is encoded on the spatial light modulator.

[0039] Aberrations of the illumination beam path affect, for example, the imaging of a sharply defined virtual observer window. A virtual observer window blurred due to aberrations can lead to, for example, vignetting effects, such that the complete three-dimensional scene can no longer be seen from a specific position in the virtual observer window.

[0040] If an optical element has an influence on the illumination beam path as well as on the imaging beam path, its aberrations generally also have an influence on both beam paths. Summary of the invention

[0041] Therefore, the object of the present invention is to provide a device which can be used in a display device and with which a well-defined imaging beam path and a well-defined illumination beam path can be realized within the display device. In addition, a display device with such a device will be provided, in particular a display device arranged close to the eyes of a user, which enables a large visible range or field of view to be generated. This can preferably be achieved in combination with a segmented multiple image of a spatial light modulation device. Another object of the present invention is to provide a display device which has a compact and light structure and with which a virtual observer window at the same position can be generated for all segments of a plurality of images of a spatial light modulation device.

[0042] This object is achieved according to the invention by the features of claim 1 .

[0043] According to the present invention, a light guide device is proposed which is particularly suitable for use in near-eye displays, in particular for use in head mounted displays, but its use is not limited to these displays.

[0044] The light guide device for guiding light according to the present invention comprises a light guide, a light coupling device and a light decoupling device. The light entering the light guide by the light coupling device propagates inside the light guide by reflection at the boundary surface of the light guide, in particular by total reflection. The multiply reflected light is decoupled from the light guide by the light decoupling device. The decoupling of light is provided after a predetermined or preset number of light reflections at the boundary surface of the light guide.

[0045] This means that by means of the light guide device according to the invention, decoupling of the light occurs at different positions in the light guide after a corresponding predetermined or fixed defined number of reflections of the light at the boundary surface of the light. In this case, light of equal angular ranges can also each be decoupled at different positions in the light guide.

[0046] It is particularly advantageous if the light incident on the light guide is formed as a light column or light field having a plurality of or multiple light beams, so that all light beams of the light column or light field are decoupled from the light guide after each undergoing the same number of reflections at the boundary surfaces of the light guide.

[0047] According to the present invention, a light field is defined by a plurality of light beams within a specific area. Therefore, the light field is the entirety of the incident light beams.

[0048] For example, if the light guide device is used for a display device, such as a display device according to patent document US2013 / 0222384A1, for a single segment of multiple images of a spatial light modulator, light from each pixel of the spatial light modulator will be coupled into the light guide of the light guide device and decoupled after multiple reflections at the boundary surface of the light guide, and the respective number of reflections is equal for all pixels.

[0049] A defined geometric path exists in the light guide. Thus, the light path in the light guide and the number of reflections on its boundary surfaces can be specifically determined during the propagation of the light in the light guide. In this way, it is thus predetermined that the light is decoupled from the light guide after a previously defined number of reflections at the boundary surfaces of the light guide.

[0050] Therefore, it can be provided according to the invention that the incident position of the light on one boundary surface of the light guide, to which the light reaches after a predetermined number of reflections, can be determined based on the geometrical and optical properties of the light guide and the optical properties of the light coupling device. In this case, the thickness and / or possible curvature of the boundary surface of the light guide can preferably be used as the geometrical property of the light guide for determining the incident position of the light, wherein the refractive index of the light guide material can be used as the optical property of the light guide.

[0051] The geometry of the light guide is to be understood here as the thickness and possible curvature of the light guide, which may vary depending on the embodiment of the light guide. The optical properties of the light coupling device here relate to at least one element arranged in the light coupling device, for example a grating element. If the light coupling element is a grating element, then the optical property that influences the number of reflections of the light in the light guide is the grating period of the grating element. In order to determine the required number of reflections within the light guide, the thickness and any curvature of the light guide and the optical properties of the coupling element (in this case the grating period of the grating element) are therefore used and taken into account. The required or desired number of reflections of the light in the light guide is then determined and defined based on these values. The grating equation is usually called sinβ. 出射 =λ / g+sinβ 入射 , where g is the grating period, λ is the wavelength of light, and β 入射 is the incident angle of the light, β 出射 is the exit angle of the light. However, this equation only applies if the refractive index of the media in the light path before and after the grating element is equal. If a coupling element is used to couple light from air into the medium of the light guide, the refractive index n of the light guide must also be considered. 光导 :n 光导 sinβ 出射 =λ / g+n 空气 sinβ 入射 .

[0052] For example, if a light beam with a wavelength of λ=532nm is incident vertically on a coupling element from air, and the grating period of the coupling element is g=400nm and the refractive index of the light-conducting material is n 光导 =1.6, from which the angle β can be calculated 出射 =56.2°, at which angle the light beam propagates after being coupled into the light guide. In a planar light guide with a thickness of d=3 mm, the light beam travels a distance of 2dtanβ after, for example, reflection on the opposite side of the light guide. 出射(8.96 mm in this case) and then reaches the surface of the light guide on the side into which the light beam was coupled in. After five reflections, the light beam is decoupled from the light guide again at a distance of 5×8.96=44.8 mm from the coupling position.

[0053] Preferably, the determined values ​​can be saved or stored in a value table (lookup table). Saving or storing values ​​determined for the number of reflections of light in a value table is thus advantageous, since in this way these values ​​do not need to be determined again and the computational effort can therefore be reduced. The values ​​can then simply be retrieved from the value table and used accordingly.

[0054] The light guide device can also be advantageously used in a display device, which is used, for example, as an AR (augmented reality) display device, since it facilitates a good perception of the natural environment in AR applications. In this case, "augmented reality" is generally understood as a visual representation of an information item, which means that an additional information item / additional representation is generated by superposition and / or overlap to enhance the (moving) image or scene. Of course, the use of such a light guide device according to the invention is not limited to such an AR display device.

[0055] Further advantageous embodiments and developments of the invention can be found in the further dependent claims.

[0056] In an advantageous embodiment of the invention, provision can be made for the light decoupling device to be arranged on the light guide in such a way that the position of the light decoupling device corresponds to the light incidence position on one of the boundary surfaces, where the light reaches after a predetermined number of reflections. In this way it can be ensured that the light is also decoupled from the light guide at a predetermined position of the light guide. In this case, the dimensions of the light decoupling device include the dimensions of the light column incident on it, so that complete decoupling of the light is always ensured.

[0057] In a specific embodiment of the invention, it can be provided that the optical decoupling device is designed to be controllable, wherein the optical decoupling device can be controlled in such a way that, in a driving state of the optical decoupling device, the light is decoupled after a predetermined number of reflections, and in another driving state of the optical decoupling device, the light is further propagated in the light guide. Thus, it is possible to control how many times the light is reflected in the light guide before the light is decoupled. Thus, the number of reflections at the boundary surface of the light guide can be changed.

[0058] Furthermore, it can be advantageously provided that the optical decoupling device is divided into a plurality of parts, wherein the optical decoupling device is designed to be controllable in sections, wherein the optical decoupling device can be controlled in such a way that the number of reflections of the light at the boundary surface of the light guide is variable by means of one (e.g. a first) drive state of a part of the optical decoupling device, which corresponds to a light incident position at which the light arrives after a plurality of reflections, and by means of another (e.g. a second) drive state of another part of the optical decoupling device, which corresponds to a light incident position at which the light arrives after another number of reflections. Furthermore, by means of a further alternating control between different drive states of the parts of the optical decoupling device, the number of reflections of the light at the boundary surface of the light guide can be varied. By dividing the optical decoupling device into a plurality of parts, the number of reflections can be varied in a particularly advantageous manner.

[0059] It is particularly advantageous if the optical coupling device comprises at least one grating element, preferably a volume grating, or at least one mirror element, and if the optical decoupling device comprises at least one grating element, in particular a deflection grating element, preferably a volume grating, or at least one mirror element.

[0060] In a preferred embodiment of the invention, coupling and decoupling of light to a light guide can be achieved using grating elements, preferably controllable grating elements, for example using volume gratings. For example, if the light guide device is used in a display device, for example, the display device generates a segmented multiple image of a spatial light modulation device, the decoupling of the individual segments from the light guide can be controlled in the following way: at least one controllable grating element of the light decoupling device or individual parts of at least one controllable grating element are controlled to decouple, i.e., for example, are switched on or off. For example, the result of switching off a grating element of the decoupling device is that light incident on this grating element is not decoupled, but is reflected and propagated further in the light guide and is decoupled at another location of the light guide after a further reflection.

[0061] Instead of at least one controllable grating element, at least one mirror element can also be used in the light decoupling device for coupling and decoupling of light. For this purpose, the mirror element can have a mirror surface which is inclined relative to the light guide surface.

[0062] The grating constant of the grating element or the tilt angle of the mirror element relative to the light guide surface can be used as an optical property of the light coupling device for determining the light incidence position, which is the position where the light reaches after a predetermined number of reflections.

[0063] Particularly preferably, the optical decoupling device comprises at least one passive grating element in combination with a switching element, preferably a polarization selective grating element in combination with a polarization switch.

[0064] Instead of at least one switchable grating element, the optical decoupling device may also include a passive grating element combined with a switchable element. For example, the passive grating element may be designed as a polarization selective grating element, in particular a polarization selective Bragg grating element, which only deflects light in one polarization direction and does not deflect light in another polarization direction. In this case, the polarization selective grating element may be combined with a polarization switch as a switchable element. In this case, the passive grating element and the switch element may be arranged together on the outer surface or cladding of the light guide.

[0065] Compared to polarization gratings with large or larger grating periods, polarization-selective Bragg grating elements have a grating period of <2 μm and Bragg properties. Depending on the circular polarization direction of the incident light beam, the light beam is transmitted without diffraction or diffracted, wherein the maximum diffraction efficiency is achieved only at the right angle of incidence. The production of such polarization-selective Bragg grating elements is carried out in two steps. In the first step, holographic structuring of the layer is carried out at room temperature by a volume photoalignment technique of a liquid crystal polymer layer, the holographic structuring being initiated by a photoselective cycloaddition of cinnamate groups. Finally, thermal tempering (heating for a longer period of time) of the layer above the glass transition temperature Tg enhances the photoinduced optical anisotropy of the layer, thereby improving the diffraction efficiency of the grating element.

[0066] Circularly polarization selective Bragg grating elements with high diffraction efficiency (DE>95%), large diffraction angles (e.g., greater than 30°), wide angle and wavelength acceptance are formed on the basis of photo-crosslinkable liquid crystal polymers (LCP). These grating elements are produced by the specific properties of these photo-crosslinkable liquid crystal polymers and a two-step photochemical / thermal treatment. Holographic structuring enables high spatial resolution and arbitrary alignment of the liquid crystal directors as well as high optical quality and thermal and chemical stability of the final grating elements.

[0067] Such grating elements can be used in combination with polarization switches as binary switchable deflection elements and / or as switching elements for pre-deflection using field lenses. In addition, they can also be used as deflection polarization gratings or reflective polarization filters. The high available diffraction angle and high diffraction efficiency make this type of grating elements attractive for head-mounted displays in combination with AR (augmented reality) / VR (virtual reality) applications, where system-specified short focal lengths and large digital apertures are required. If two grating elements with opposite orientations are used, the deflection angle of the light can be doubled.

[0068] In the following description of the figures, a more comprehensive description of a polarization-selective Bragg grating element for use in a light decoupling arrangement of a light guiding arrangement may be given.

[0069] In a further embodiment of the invention, it can be provided that at least one controllable grating element of the light decoupling device extends over a predetermined area of ​​the light guide, wherein the grating element is divided into switchable parts.

[0070] In a feasible decoupling area of ​​the light guide, at least one switchable decoupling element in the form of a grating element is arranged. The grating element is divided into switchable parts. By switching on or off defined parts of the grating element, the decoupling position of the light from the light guide can be determined and defined. This also applies to passive grating elements combined with switching elements, i.e., for example, polarization-sensitive Bragg grating elements combined with polarization switches. The passive grating element will then extend over a predetermined area of ​​the light guide, wherein the switching element will be divided into individually switchable parts.

[0071] The decoupling element in the form of a switchable grating element may be, for example, a reflective grating element or a transmissive grating element.The reflective grating element may be arranged on the outside of the light guide, wherein the transmissive grating element may be arranged on the inside of the light guide.

[0072] In a particularly preferred embodiment of the invention, a light guide which is at least partially bent in at least one direction can be provided.

[0073] In certain embodiments, the light guide preferably has a straight or planar or flat geometry. This is the case, for example, for applications in which space saving is important, since a flat light guide takes up less installation space than a curved light guide. In other embodiments, in particular head-mounted displays, for example, the light guide may also have a curved geometry. In general, the light guide may also consist of straight and curved sections or also of a plurality of sections with different strengths of curvature. For example, the coupling region may be formed straight, but the decoupling region may be formed curved. For example, in the case of a head-mounted display designed similar to glasses, the straight section of the light guide may be arranged transversely to the head in the region of the temples and the curved section may be arranged in front of the eyes. A curved light guide makes it possible to use grating elements in the optical decoupling device, the decoupling angle of which is independent of the position of the grating element on / in the light guide.

[0074] According to the invention, in an advantageous embodiment of the invention it can be provided that the light guide at least partially has a hollow cylindrical shape, wherein the boundary surfaces of the portion form hollow cylindrical portions with different radii. The light guide can have a shape similar to a semicircle, for example.

[0075] The optical coupling device is arranged in the area where the light is coupled with the light guide of the light guide device according to the present invention. The optical coupling device has at least one coupling element, for example in the form of a grating element or a reflector element. The grating element can be designed to be controllable and / or switchable. Moreover, the coupling element can be arranged on the outer surface or the inner surface of the light guide. In one embodiment of the coupling element, it can be designed as a reflective grating element, which is arranged on the inner surface of the light guide. The light incident on the light guide initially passes through the light guide vertically, is deflected by the reflective grating element or the reflector element on the inner surface of the light guide, and then propagates through the light guide in a zigzag shape.

[0076] In an exemplary embodiment, in this case, the propagation angle can be selected so that reflection in the form of total reflection occurs at the boundary surface of the light guide and the surrounding medium (e.g. air). Optionally, an additional layer, such as a dielectric layer stack, can be arranged on the inner cladding surface or the outer cladding surface or the boundary surface of the light guide. The dielectric layer causes light incident at a specific or predetermined angle to be reflected. In this case, the dielectric layer can preferably be designed so that when the light guide device according to the present invention is used in a device for AR applications, ambient light can pass through the light guide during AR applications.

[0077] It can therefore further be advantageously provided that the light guide has a dielectric layer on its boundary surface.

[0078] In a particularly advantageous embodiment of the invention, the light deflection angle of the light coupling device and the light deflection angle of the light decoupling device can be selected to be opposite, so that a light beam incident vertically on the surface of the light guide can also leave the light guide vertically (i.e. at a right angle). In other words, the light deflection angle of the grating element of the light coupling device can be opposite to the light deflection angle of the grating element of the light decoupling device, so that a light beam entering the light guide vertically through the outer surface of the light guide also exits vertically from the inner surface of the light guide.

[0079] The light guide of the light guide arrangement may optionally consist of glass or optical plastic.

[0080] The grating elements of the light coupling device and / or the light decoupling device can be designed to be transmissive or reflective.

[0081] The size of the optical coupling device can advantageously be larger than the size of the light column incident on the light guide device, wherein the coupling position of the light column to the light guide can be shifted within the boundaries of the size of the optical coupling device. By shifting the coupling position of the light column, a predetermined or set number of reflections are performed in the light guide, and the position where the light beam is decoupled from the light guide is also shifted.

[0082] Furthermore, the object of the invention is also achieved by a display device according to claim 18 .

[0083] The display device according to the invention can be designed as a holographic display device or also as an autostereoscopic display device. The display device according to the invention can be designed particularly advantageously as a near-eye display device, such as a head-mounted display or a head-up display. In this case, the display device comprises an illumination device, at least one spatial light modulation device, an optical system and a light guide device according to the invention.

[0084] In order to illustrate the following description of the features of the display device according to the invention, it is first of all noted that in the case of a large field of view, the pupil of an observer of a scene generated using the display device generally rotates in different ways when the observer observes different parts of the field of view. A display device or display with a large field of view and a virtual observer window should generally also be understood in the present application as causing the virtual observer window to rotate together at its center point when the pupil of the observer's eye rotates. The requirement to generate a virtual observer window at the same position for all fragments of a plurality of images of a spatial light modulation device should generally be understood as causing the virtual observer windows for the individual fragments of the plurality of images to also be tilted relative to each other, but with a common center point.

[0085] If the observer observes different parts of the large field of view and rotates his eye at the same time, a rotation therefore occurs around the center point of the lens of the eye, which is located approximately 12 mm behind the pupil. Therefore, a lateral displacement of the pupil position also automatically occurs when the lens of the eye rotates. A rotation of 15° corresponds, for example, to a pupil displacement of approximately 3.2 mm. For display devices with a large field of view generated, for example, by segmented multiple images using a spatial light modulation device, an optional embodiment can therefore also intentionally take this change of the pupil position into account when the lens of the eye rotates, in such a way that the virtual observer windows of the individual segments of the multiple images are correspondingly shifted relative to each other. For example, for segments with a 15° spacing in the field of view, the center points of the virtual observer windows will also be shifted by 3.2 mm relative to each other, so that the center point of the virtual observer window corresponds to the center point of the pupil when the eye rotates. In this case, each segment therefore intentionally has a slightly shifted position and can additionally have a tilted alignment of the virtual observer window.

[0086] For example, the curvature of the light guide may be adjusted such that the displacement causes light to be decoupled perpendicularly to the light guide from the light guide surface at the observer distance.

[0087] In a display device according to the invention, decoupling of light takes place at different locations of the light guide device according to the invention after a corresponding predetermined number of light reflections at boundary surfaces of the light guide.

[0088] As already mentioned, there are defined geometric paths in the light guide. Therefore, during the propagation of light in the light guide, the light path in the light guide and the number of reflections at the boundary surfaces of the light guide can be defined. Therefore, the length of the light guide used can be predefined, the focal length of the imaging element of the optical system and the distance of the spatial light modulation device and the virtual observer window or the optimal spot from the light guide device can be set, in this way a specific imaging beam path and / or illumination beam path can be set. The term "observer area" used includes the virtual observer window or the optimal spot, depending on whether the display device according to the invention is designed as a holographic or stereoscopic display device.

[0089] In one embodiment of the display device according to the invention, it can be arranged that an image of the spatial light modulation device can be generated by the light guide device and the optical system. The image can define a field of view within which an information item of a scene encoded in the spatial light modulation device observed through the virtual observer area can be reconstructed.

[0090] It can advantageously be provided that a light source image of the at least one light source of the illumination device or an image of the spatial light modulation device can be generated by the light guide device and the optical system in the beam path after decoupling from the light guide device.

[0091] In this case, a virtual observer region may be generated in the image plane of the light source or in the image plane of the spatial light modulation device.

[0092] In another embodiment of the present invention, it can be provided that the light guide of the light guide device is at least partially bent into a part of a hollow cylinder, wherein the virtual observer area can be generated in the area of ​​the arc center point of the hollow cylinder.

[0093] In this case, it can be particularly preferably arranged that a plurality of images of the spatial light modulator consisting of fragments are generated by the light-guiding device and the optical system, wherein the plurality of images define a field of view within which scene information encoded in the spatial light modulator observed through a virtual observer area in the image plane of the light source is reconstructed.

[0094] In another embodiment, in this case it can be arranged that a plurality of images of diffraction orders consisting of fragments are generated by the light-guiding device and the optical system in the Fourier plane of the spatial light modulator, wherein the plurality of images define a field of view within which information of a scene encoded in the spatial light modulator observed through a virtual observer area in the image plane of the spatial light modulator is reconstructed.

[0095] An image of the spatial light modulation device can be generated by means of the light guide device and the optical system. The image defines the size of the field of view within which a scene or an object can be generated or reconstructed.

[0096] According to the invention, in order to generate a large field of view, at least one spatial light modulation device can be imaged multiple times next to each other and / or one above the other or laterally offset relative to each other. This is performed at a speed at which the observer does not perceive the time-sequential composition of the field of view. However, the images can also partially or completely overlap.

[0097] The scene or object can be generated in front of, behind or around the spatial light modulation device. In particular, in the holographic reconstruction of the scene, the area of ​​the scene generation depends on the depth encoding of the scene or object in the hologram.

[0098] The spatial light modulator can be generated so that it can be imaged magnified in the field of view. The plane of the spatial light modulator can be magnified in the field of view depending on the number of segments to be generated in the multiple images of the spatial light modulator, because the images of the spatial light modulator are generated magnified and thus define the size of the field of view.

[0099] For example, detailed disclosure of generating segmented multiple images of a spatial light modulation device can be found in patent document US 2013 / 0222384 A1, the disclosure of which is also fully incorporated herein.

[0100] In another embodiment, an optical system may be used to generate a Fourier plane of at least one spatial light modulation device. This may be performed, for example, using a 2f arrangement, where the SLM is arranged in the object-side focal plane of the imaging element and the Fourier plane forms the image-side focal plane of the imaging element. A filter aperture may be arranged in this Fourier plane, which transmits at most one diffraction order and filters out the other diffraction orders. Segmented multiple images of a portion or portions of the diffraction orders transmitted by the filter aperture may then be generated by the optical system. The multiple images of the diffraction orders define the size of the field of view within which a scene or object may be generated or reconstructed.

[0101] According to the invention, in order to generate a large field of view, the diffraction orders of at least one spatial light modulation device can be imaged multiple times next to each other and / or one on top of the other or laterally offset relative to each other. This is performed at a speed at which the observer does not perceive the time-sequential composition of the field of view. However, the images can also partially or completely overlap.

[0102] The scene or object can be generated in front of, behind or around the Fourier plane of the spatial light modulation device. In particular, in the holographic reconstruction of the scene, the area of ​​scene generation depends on the depth encoding of the scene or object in the hologram.

[0103] The diffraction orders of the spatial light modulator can be generated so that they can be imaged magnified in the field of view. The diffraction orders in the Fourier plane of the spatial light modulator can be magnified according to the number of segments to be generated by the spatial light modulator in the field of view, wherein the images of the diffraction orders are generated magnified in the Fourier plane of the spatial light modulator and thus define the size of the field of view.

[0104] An embodiment of a segmented multiple image with at least one spatial light modulation device is described in more detail below. However, these statements can also be transferred accordingly to the case of a segmented multiple image of diffraction orders in the Fourier plane of the spatial light modulation device.

[0105] According to the invention, with regard to the use of a light guide in an arrangement of segmented multiple images of at least one spatial light modulator, in particular for individual segments of multiple images of the spatial light modulator, light from various pixels of the spatial light modulator is coupled into the light guide and decoupled again after multiple reflections of the light at the boundary surfaces of the light guide, the number of reflections being equal in each case for all pixels of the spatial light modulator.

[0106] In other words, it can be arranged that, for a single segment of an image or multiple images, the light from each pixel of the spatial light modulation device is decoupled after entering the light guide device after multiple reflections at the boundary surface of the light guide, in each case the number of reflections being equal for all pixels.

[0107] Furthermore, it can be arranged that, for different fragments of the plurality of images, the number of reflections of light at the boundary surface of the light guide used to generate one fragment is different from the number of reflections of light at the boundary surface of the light guide used to generate another fragment. Different fragments of the plurality of images of the spatial light modulation device can be formed in the following manner, for example, for adjacent fragments of the plurality of images, different numbers of reflections are performed at the boundary surface of the light guide. However, other arrangements are also feasible, for example, for different fragments of the plurality of images, an equal number of light reflections are generated at the boundary surface of the light guide, but a shifted coupling position or a changed light coupling angle is used.

[0108] As already stated with respect to the light guide device according to the invention, the decoupling of the light for generating the individual segments of the plurality of images can be controlled, for example, in such a way that, for example, at least one grating element or individual parts of at least one grating element of the light coupling device are switched on or off to decouple the light. For example, as a result of switching off a grating element, light incident on this grating element is not decoupled, but is reflected and propagates further in the light guide and can be decoupled at another point in the light guide after a further reflection.

[0109] The light decoupling device and the light coupling device may also include reflector elements, in particular reflector elements with inclined mirror surfaces, instead of grating elements. These reflector elements may also be used to couple light into the light guide device or decouple light from the light guide device, respectively.

[0110] In one embodiment of the present invention, the number of reflections of light at the boundary surface of the light guide may be equal for different fragments of the plurality of images, and the locations where the light is coupled into the light guide may be different for the fragments.

[0111] The light deflecting device can advantageously be arranged in front of the light guiding device in the light guiding direction in order to shift the coupling position of the light in the light guide.

[0112] The displacement of the coupling position of the light on the light guide can preferably be achieved by a light deflection device. For this purpose, the light deflection device can include at least one grating element, whose grating period is settable. For example, the light deflection device can include two grating elements. Then, the first grating element deflects the incident light by a settable angle, wherein the second grating element deflects the light deflected by the first grating element in the opposite direction by an angle equal in absolute value but opposite in sign, so that substantially parallel shifted light is obtained or generated.

[0113] In another advantageous embodiment of the display device, it can be arranged that the optical system is designed as a two-stage optical system, wherein in a first stage, an intermediate image of at least one light source of the illumination device is generated by at least one first imaging element of the optical system, wherein in a second stage, the intermediate image of the light source is imaged in a virtual observer area by at least one second imaging element of the optical system, which virtual observer area is located in the optical path after the light is decoupled from the light guide.

[0114] According to the invention, a two-stage optical system can be used in a display device with a light guide. For this purpose, the display device comprises at least one spatial light modulation device and an illumination device, which illuminates the spatial light modulation device and comprises at least one light source. In the first stage, an intermediate image of the illumination device, i.e. an intermediate image of at least one light source comprised by the illumination device, and an intermediate image of an observer region, in particular a virtual observer window or an optimal light spot, are generated behind the spatial light modulation device in the direction of the light using at least one first imaging element, such as a lens. In the second stage, the intermediate image of the illumination device is then imaged in the observer plane, more precisely in the actual virtual observer window or the optimal light spot, using at least one further or second imaging element, which can also be a lens. For this purpose, in the display device, the light guide is positioned on the beam path behind the intermediate image of the illumination beam path and the second imaging element. The at least one first imaging element simultaneously generates an image of the spatial light modulation device. The second imaging element, which images the illumination device and the virtual observer window or the optimal light spot, also contributes to the imaging of the spatial light modulation device. By appropriately selecting the focal length of the imaging element of the optical system, another image of the spatial light modulator can be generated in the light guide (especially in the light guide). In one embodiment of the present invention, an intermediate image of the spatial light modulator in the light guide can also be generated only in the deflection direction of at least one grating element of the light coupling device, the light guide comprising a cylindrical imaging element, while in a direction perpendicular thereto, the intermediate image of the spatial light modulator can be located outside the light guide.

[0115] Furthermore, in a particularly advantageous embodiment of the display device, at least one variable imaging system can be provided which is arranged in front of the light-guiding device in the direction of the light.

[0116] The at least one variable imaging system can preferably be arranged adjacent to or as close as possible to the intermediate image plane or in the intermediate image plane of at least one light source of the illumination device and / or the variable imaging system can be arranged close to the spatial light modulation device or the image plane of the spatial light modulation device.

[0117] At least one variable imaging system may include at least one imaging element, which is designed as a grating element with a controllable variable period or a controllable liquid crystal element or at least two lens elements with a variable distance. At least one imaging element of the variable imaging system can be designed to be transmissive or reflective. For example, the variable imaging system may include two controllable liquid crystal elements as imaging elements, both of which can be designed to be reflective. Due to the reflective embodiment of the two liquid crystal elements, a certain distance is required between the two liquid crystal elements. Therefore, the two liquid crystal elements cannot be arranged precisely in the intermediate image plane of the irradiation device. Therefore, if the variable imaging system has such a liquid crystal element, it should generally be considered to be arranged as close as possible to the intermediate image plane of the irradiation device.

[0118] Thus, the variable imaging system can be arranged in or very close to the intermediate image plane of the illumination device, which plane simultaneously represents the intermediate image plane of the virtual observer window or the optimal spot. A variable imaging system is to be understood here as an imaging system, the focal length of which is variable. At least one first imaging element of the optical system also produces an image of the spatial light modulation device. At least one second imaging element of the optical system that images the virtual observer window or the optimal spot also contributes to the imaging of the spatial light modulation device. However, the variable imaging system can be advantageously used to shift the image of the spatial light modulation device in depth in or near the intermediate image plane of the illumination device or the virtual observer window or the optimal spot, without affecting the illumination beam path and the position and size of the virtual observer window or the optimal spot itself.

[0119] According to the invention, the image of the spatial light modulation device can therefore be shifted for each individual segment of the plurality of images of the spatial light modulation device by means of the variable imaging system in such a way that the different light paths of the light formed by the light guide of the light guide device for the respective different segments can be at least partially compensated for. Before the display device is put into operation, a calculation is performed of how much the image of the spatial light modulation device must be shifted for each individual segment.

[0120] Preferably, in this case, images visible to an observer are formed at an equal or at least similar depth from a virtual observer window or an optimal spot of the spatial light modulation device for all segments of the plurality of images. The variable imaging system comprises at least one imaging element, which can be designed, for example, as a grating element with a controllable variable period, such as a liquid crystal grating (LCG), or as an electrowetting lens or a liquid crystal lens. The variable imaging system can also comprise a system made of at least two imaging elements whose distance can be variably set relative to each other, for example in the form of at least two lenses, such as a zoom type objective.

[0121] The variable prism function or the variable lens function and / or the variable complex phase function can advantageously be written into at least one controllable imaging element of at least one variable imaging system.

[0122] The controllable imaging element of the variable imaging system can be arranged in the intermediate image plane of the illumination device to change the coupling position of the light with the light guide of the light guide device. By writing a variable prism function in the controllable imaging element, the coupling position of the light on the light guide can be shifted. In this way, the image of the spatial light modulation device can be shifted laterally in the field of view.

[0123] In such a controllable imaging element of a variable imaging system, such as a phase modulation element (e.g. a grating element with a controllable variable period (LCG)), instead of or in addition to a variable lens function or a prism function, a variable complex phase function can also be written, which thus deviates from a simple linear or spherical function. For example, the phase function used for aberration correction can be a polynomial. For example, the aberrations can be described by Zernike polynomials. This process is advantageously used to compensate for aberrations, especially in the case where the display device according to the invention is designed as a holographic display device. Therefore, it can be advantageously provided that the variable imaging system is arranged in the light source image plane of the illumination device or in the Fourier plane of the spatial light modulation device to correct aberrations in the imaging beam path.

[0124] If light is coupled into and decoupled from a light guide, for example by means of grating elements, aberrations are thus generated. For the imaging beam path, these aberrations can have an effect similar to astigmatism, for example resulting in an image of the spatial light modulation device at different distances relative to the observer in the horizontal and vertical directions. Furthermore, due to different path lengths between the coupling element and the decoupling element, different segments can also have different aberrations.

[0125] Aberration correction in the imaging beam path can be performed, for example, in conjunction with the amplitude and phase of the hologram determined during a back calculation from the virtual observer window through the light guide in the direction of the spatial light modulation device. However, the back calculation is initially performed only from the virtual observer window to the intermediate image plane of the illumination device. In particular, in exemplary embodiments in which there are substantial aberrations in the imaging beam path and there are no aberrations or only small phase aberrations in the illumination beam path, in the back calculation the beam in the intermediate image plane of the illumination device has essentially the correct position compared to the target position and angle of the beam directly in the virtual observer window, but due to the aberrations, has an incorrect angle. Therefore, for individual beams, the angle can be corrected by means of corresponding local imaging elements of the variable imaging system in the intermediate image plane of the illumination device, such as local deflection grating elements. For example, if β(x) is the beam at the desired angle of incidence at position x, and β'(x) is the beam at the actual angle of incidence at this position x, it can be determined that the current aberration is at least partially removed using the correction function Δβ(x)=β(x)-β'(x). The local grating period of the imaging element of the variable imaging system is then determined as g(x)=λ / tanΔβ(x), where λ is the wavelength of the light used. Therefore, taking into account the imaging ratio from the intermediate image plane of the illumination device to the virtual observer window, the grating period of the imaging element can be changed or adjusted in the following way so that the position and the required angle of incidence of each individual light beam correspond to those in the virtual observer window itself.

[0126] The advantage of correcting aberrations by means of a phase function in an intermediate image plane of the illumination device is that the correction is independent of the content of the preferred three-dimensional (3D) scene. Thus, for each segment of a plurality of images of the spatial light modulation device and for intermediate positions of the spatial light modulation device during successive displacements of the coupling position of the light in the light guide, the correction function can be calculated once respectively and stored in a value table and then repeatedly applied, and the corresponding grating period can be calculated.

[0127] A similarly designed second variable imaging system may also advantageously be arranged in the image plane of the spatial light modulation device to correct aberrations in the illumination beam path and to generate a virtual observer region at the same position for all segments of the plurality of images.

[0128] Using a variable imaging system in the image plane of the spatial light modulator rather than in the Fourier plane of the spatial light modulator makes it possible to correct aberrations in the illumination beam path, which phase differences are generated by at least one grating element of the light coupling device and / or the light decoupling device during the coupling and / or decoupling of light to and from the light guide, respectively.

[0129] In a further advantageous embodiment of the display device, it can be provided that at least one controllable grating element of the light decoupling device of the light-guiding device comprises at least one lens function.

[0130] In addition to the variable imaging system, the display device in the light decoupling device of the light guide device may also include a grating element having at least one lens function instead of a simple grating element. If multiple segments of the spatial light modulation device are generated to produce a large field of view, the lens functions for each different segment can be different. However, in another embodiment, the same lens function can be set for all segments of the multiple images. For example, in a light guide that only produces multiple segments adjacent to each other in the horizontal direction but only a single segment in the vertical direction, the light decoupling device may include a cylindrical lens function that is the same for all segments for producing vertical focus. This lens function contributes to the overall focal length of the variable imaging system. This reduces the setting range of the focal length of the variable imaging system that must be changed.

[0131] The display device according to the present invention can be advantageously designed as a head mounted display having two display devices, wherein each display device is designed according to the display device of any one of claims 18 to 38 and is respectively assigned to the left eye and the right eye of the observer.

[0132] Furthermore, the object of the invention is achieved by a method having the features of claim 40 .

[0133] The method according to the invention for generating a reconstructed scene by means of a spatial light modulation device and a light guide is carried out as follows:

[0134] – The spatial light modulation device modulates the incident light using the desired scene information,

[0135] – light modulated by the spatial light modulation device is coupled into the light guide by the optical coupling device and is decoupled from the light guide by the optical decoupling device, and

[0136] - decoupling the light from the light guide after a predetermined number of reflections at the boundary surfaces of the light guide.

[0137] Advantageously, an image of the spatial light modulation device or a plurality of images of the spatial light modulation device consisting of segments is generated.

[0138] An intermediate image of the spatial light modulation device may be generated within the light guide for at least partial segments of the plurality of images.

[0139] A first intermediate image of the spatial light modulation device is generated in the direction of the light in front of the light guide device or in front of the light guide. Another intermediate image of the spatial light modulation device can be generated so that the intermediate image for at least a partial segment of the plurality of images of the spatial light modulation device is located inside the light guide. For another partial segment of the plurality of images, the intermediate image can also be located outside the light guide.

[0140] The image of the spatial light modulation device is shifted for each individual segment of the plurality of images using at least one variable imaging system, the at least one variable imaging system being preferably arranged in a light source image plane of at least one light source of the illumination device, in the light path before the coupling of the light with the light guide, so that the different optical light paths generated in the light guide for each segment are at least partially compensated.

[0141] An aberration correction is performed for each individual segment of the plurality of images using the variable imaging system in such a way that at least one optical property of the variable imaging system is changed, wherein a correction function is calculated once for each segment and stored.

[0142] If the variable imaging system comprises, for example, a grating element with a controllable variable period (LCG), a phase function in polynomial form can be written therein for aberration correction.

[0143] Aberration correction for each individual segment of the plurality of images may be performed in an intermediate image plane of the illumination device and / or in the amplitude and phase curve of a hologram encoded in the spatial light modulation device.

[0144] The calculation of the correction function is achieved by reverse calculation of the light path and tracing back the light source image plane of at least one light source entering the illumination device from the virtual observer area through the light guide. BRIEF DESCRIPTION OF THE DRAWINGS

[0145] There are multiple options for configuring the teaching of the invention in an advantageous manner and / or combining the exemplary embodiments and / or configurations described above and below with one another. For this purpose, reference is made on the one hand to the patent claims according to the independent claims and on the other hand to the following description of preferred exemplary embodiments of the invention according to the drawings, in which generally preferred teaching configurations are also explained. In this case, the invention is explained in principle based on the described exemplary embodiments.

[0146] In the figure:

[0147] Figure 1 A schematic diagram of a holographic display device according to the prior art is shown;

[0148] Figure 2 Shown according to Figure 1 A schematic diagram of another embodiment of a display device;

[0149] Figure 3 Shown according to Figure 1 A schematic diagram of another embodiment of a display device;

[0150] Figure 4 Shown according to Figure 1 A schematic diagram of another embodiment of a display device, wherein the display device is designed as a head-mounted display;

[0151] Figure 5 A schematic diagram showing a simple display device without a light guide is shown;

[0152] Figure 6 A schematic diagram showing an enlarged virtual image of a spatial light modulation device;

[0153] Figure 7 Shows the position relative to Figure 6 A schematic diagram showing a change in the spatial light modulation device;

[0154] Figure 8 A schematic diagram showing a light guide device according to a first embodiment of the present invention;

[0155] Fig. 9 A schematic diagram showing a light guide device according to a second embodiment of the present invention;

[0156] Fig.10 A schematic diagram showing a light guide device according to a third embodiment of the present invention;

[0157] Fig.11 Shown according to Fig.10 Schematic diagram of a light guide device according to the present invention, wherein the light guide is cylindrical;

[0158] Fig.12 schematically illustrates an illumination beam path for a display device having a light guide;

[0159] Fig.13 schematically illustrates an imaging beam path of a display device, wherein each pixel forms a focus within a light guide;

[0160] Fig.14 schematically shows the displacement of the light coupling position of the light deflecting device;

[0161] Fig.15 Schematically illustrates the inverse calculation for determining the amplitude and phase of a hologram from a virtual observer window through a light guide to a spatial light modulation device;

[0162] Fig.16 It shows that due to Fig.15 a graphical representation of the intensity distribution in the plane of the spatial light modulator resulting from the inverse calculation of

[0163] Fig.17 Schematically illustrates the back calculation and aberration correction of the intermediate image plane of the illumination device;

[0164] Fig.18 The display device according to the present invention is schematically shown in the form of a head mounted display;

[0165] Fig.19 In conjunction with the propagation of light in the light guide, a straight light guide is shown in figure a) and a curved light guide is shown in figure b);

[0166] Fig. 20 A flat light guide is schematically shown, wherein different light beams are coupled into the light guide at different positions;

[0167] Fig.21 Schematically shows an embodiment of a light guide device having a light guide and a light decoupling device;

[0168] Fig. 22 A second embodiment of a light guide device having a light guide and a light decoupling device is schematically shown;

[0169] Fig.23 A third embodiment of a light guide device having a light guide and a light decoupling device is schematically shown;

[0170] Fig.24 A fourth embodiment of a light guide device having a light guide and a light decoupling device is schematically shown;

[0171] Fig.25 schematically shows a fifth embodiment of a light guide device having a light guide and a light decoupling device; and

[0172] Fig.26 A sixth embodiment of a light guide device having a light guide and a light decoupling device is schematically shown. DETAILED DESCRIPTION

[0173] Briefly, it is mentioned that identical elements / components / assemblies also have the same reference numerals in the figures.

[0174] In order to understand the exemplary embodiments now described, the relationship of the imaging beam path and the illumination beam path as well as the size of the observer area (i.e., the virtual observer window or optimal spot) to the field of view in the display device is first explained, especially on the basis of a simple holographic head-mounted display without the use of a light guide. When the term "observer window" is used hereinafter, this may also be understood as an "optimal spot" if the application may also be applied to a stereoscopic display device. The display device comprises an illumination device, a spatial light modulation device (hereinafter referred to as SLM) and an optical system comprising an ideal lens for illustration, i.e. a thin lens without imaging errors. Such a display device will have only a limited field of view and is therefore not suitable for augmented reality applications, which are referred to as AR applications hereinafter. In Figure 5 Such a display device is schematically shown in FIG.

[0175] A plane wave 1 with wavelength λ is used to irradiate the SLM. For example, an irradiation device including a point light source can be used to generate the plane wave 1, and the plane wave 1 is set at a position with a focal length from the lens of the optical system, and the lens of the optical system is located between the point light source and the SLM. Then a virtual image of the point light source is generated at infinity. The SLM has a pixel pitch p and is positioned at a distance d from a lens 2 with a focal length f1. When the SLM is irradiated with a plane wave, the irradiation device is located at infinity. Then, the irradiation device is imaged in the focal plane BE of the lens 2, that is, at a distance f1 from the lens 2, which can be clearly seen from Figure 5 the upper figure above.

[0176] If a hologram is written into the SLM, a virtual observer window VW with a size of f1λ / p is generated in the focal plane BE of the lens 2. This size can be taken into account in geometric optical modeling by observing the angularly diffracted light beams from the pixels of the SLM, as shown by Figure 5 the lower figure below. These light beams respectively originating from different pixels of the SLM are shown here in different gray shades.

[0177] In this case, the field of view is obtained from the arctangent of the spatial dimension of the SLM divided by the focal length f1 of the lens 2. This means that the horizontal field of view can be calculated as arctan(width of the SLM) / f1, and the vertical field of view is arctan(height of the SLM) / f1.

[0178] If the distance d between the SLM and the lens 2 < f1, then according to the imaging equation 1 / d' - 1 / d = 1 / f1, so a magnified virtual image 3 of the SLM is generated at a distance d' from the lens, and the magnification is β = d' / d. This is schematically shown in Figure 6 If the distance d between the SLM and the lens 2 > f1, then a real image will be generated instead of a virtual image.

[0179] If the distance between the SLM and the lens 2 is now changed, but its focal length remains unchanged, then the virtual observer window VW, the position and size of the virtual observer window VW, and the field of view 4 will thus remain unchanged, and only the position of the SLM image will change. This is schematically shown in Figure 7 However, for example, if the focal length of the lens 2 is changed, then the position of the image of the irradiation device, the position of the virtual observer window VW, the size of the virtual observer window VW, the size of the field of view 4, and the position of the SLM image will all change.

[0180] In particular, the field of view has a fixed relationship with the size of the virtual observer window, since both depend on the focal length f1 of the lens or the optical system of the display device. If the virtual observer window is enlarged, the field of view is therefore smaller in size, and vice versa. In general, the lens or optical system used influences both the illumination beam path and the imaging beam path within the display device.

[0181] The optical system of the display device as a whole may also include a plurality of lenses or imaging elements. The total focal length and the principal plane of the system can then be determined according to known methods of geometrical optics. The above statements then apply to the entire system.

[0182] If a light guide is introduced into such a display device having an optical system with multiple imaging elements and if initially only a single image of the SLM is used, the distances between the SLM, the imaging elements of the optical system, and the virtual observer in the imaging beam path and the illumination beam path must take into account the fixed coupling positions and the fixed decoupling positions of the light incident into the light guide, the propagation in the light guide, and the optical path between the coupling positions and the decoupling positions of the light on the light guide.

[0183] If, for example, a light guide is introduced between at least one imaging element and the virtual observer window, and the imaging element with a focal length of 60 mm is arranged near the position where the light is coupled into the light guide and the light path through the light guide is 40 mm, a virtual observer window can be created at a distance of 20 mm from the side decoupled from the light guide.

[0184] Figure 8 An illumination beam path of a display device according to the invention is shown, comprising a light guide 5. The light guide 5 comprises a light guide 6, a light coupling device 7 and a light decoupling device 8. In this case, the light coupling device 7 and the light decoupling device 8 comprise at least one mirror element 9, 10 respectively. Figure 8The reflector elements 9, 10 in the display device are designed as tilted reflector elements. Instead of the reflector elements, the optical coupling device 7 and the optical decoupling device 8 can also optionally include grating elements. The reflectors or grating elements of the optical coupling device 7 and the optical decoupling device 8 will be described in more detail below. The display device includes an SLM and an optical system having at least one imaging element. At least one imaging element is designed as a lens 11. The SLM and the lens 11 are located in front of the optical coupling device 7 in the direction of the light. For simplicity, only three pixels P1, P2 and P3 of the SLM are shown. The light from each pixel P1, P2 and P3 of the SLM is guided through the lens 11 to the light guide device 5 and incident therein. The number of times the light is reflected inside the light guide 6 can be determined according to the geometry of the light guide 6 (i.e., for example, the thickness or the possible curvature), and the optical properties of the optical coupling device 7 (in particular, the tilt angle of the tilted reflector element or, in the case of using a grating element, according to the grating period). Depending on the decoupling position of the light from the light guide, a certain number of light reflections in the light guide 6 is necessary, which can be defined in advance. These values ​​for the number of reflections for the various decoupling positions can then be stored in a value table and are therefore available during use and do not have to be calculated again. Therefore, they only need to be determined once. Figure 8 In the embodiment of the present invention, the light in the light guide 6 undergoes a fixed number of reflections at its boundary surfaces. In this case, an image of the illumination device is generated at a defined distance from the light guide device 5 after decoupling the light from the light guide device 5. A virtual observer window VW can be generated at this point of the image of the illumination device.

[0185] If a light guide 5 is introduced between the SLM and the optical system (here the lens 11), the light path through the light guide 6 will therefore affect the image position of the SLM. For example, if the distance between the SLM and the lens 11 is 50 mm, the SLM can be arranged at a distance of 10 mm from the light guide 5 if the light path in the light guide is 40 mm.

[0186] therefore, Figure 8 A light guide 5 in a display device is shown, wherein the light of all pixels of the SLM is decoupled from the light guide 5 again after a predetermined number of reflections in the light guide 6. Figure 8 The display device shown in generates only a single image of the SLM.

[0187] However, in order to be able to generate a large field of view, multiple images of segments of the SLM will be generated. In such a display device, the device can be used to generate a large field of view, and the light of the individual segments of the multiple images of the SLM are decoupled from the light guide at different locations.

[0188] For example, if light of different segments of a plurality of images of an SLM is coupled in a light guide at a fixed position, but decoupled from the light guide at different positions, a different light path through the light guide itself is thereby generated for each segment, such as Fig. 9 This relates in particular to the illumination beam path. In particular, this would mean a straight or planar light guide in the light guide, which is arranged between an imaging element with a fixed focal length and a virtual observer window, the distance of the virtual observer window of the light decoupled from the light guide varying for each fragment of the multiple images of the SLM. However, this is disadvantageous because observation of the entire scene generated using the display device cannot be from the same position. The observer has to move his head to see the part of the scene generated from each of the various positions. It is therefore important to generate a common virtual observer window in a common position for all fragments of the multiple images of the SLM at an equal distance from the light guide.

[0189] In order to compensate for this lack of virtual observer windows at different positions for individual fragments of the multiple images of the SLM, the display device includes a variable imaging system located in the beam path. The variable imaging system includes at least one imaging element, in particular at least one grating element with a controllable variable period or a controllable liquid crystal element or at least two lens elements with a variable distance. The imaging element can also be at least one lens with a variable focal length. The variable imaging system is arranged in front of an optical coupling device of a light guide device along the direction of light. The optical properties of the variable imaging system (i.e., for example, the focal length or the grating period) are adapted to each fragment of the multiple images of the SLM, so that in each case a virtual observer window is generated at a position at an equal distance from the decoupling side of the light guide device.

[0190] In addition, the light decoupling device comprises a lens term or a lens function that can replace a simple grating element, which is different for each segment of the multiple images of the SLM and contributes to the overall focal length. This facilitates settings within a set range, within which the optical properties of the variable imaging system must be changed for the individual segments. However, depending on the arrangement of the variable imaging system, this will generally affect the beam paths, i.e. both the imaging beam path and the illumination beam path. In order to only affect the illumination beam path, the variable imaging system will be arranged directly at the SLM or in the image plane of the SLM. For a display device with a variable imaging system that is arranged directly at the SLM and is located between the SLM and the position where the light is coupled into the light guide, a common virtual observer window at the same position can be generated overall by changing the optical properties of the variable imaging system for the individual segments of the multiple images of the SLM. However, as already mentioned, in particular these optical properties of the variable imaging system are related to the size of the virtual observer window and the field of view. Therefore, in accordance with Fig. 9In this design, a virtual observer window of different size is generated for each segment of the multiple images of the SLM, and the size of each portion of the field of view is also different for each segment. Therefore, each segment of the multiple images of the SLM contributes to the total field of view with different weights.

[0191] Regarding the virtual observer window, in this case also a minimum observer window which is effectively only generated for individual segments of the multiple images of the SLM is useful.

[0192] In particular, if the lens function is also used in the grating element of the light decoupling device for decoupling the light, and the decoupling device is different for each segment of the plurality of images of the SLM, further problems arise:

[0193] In general, adjacent segments of the multiple images of the SLM also overlap spatially when optically decoupled. Therefore, multiple layers of switchable grating elements must be generated one after another in the optical decoupling device to generate overlapping segments of the multiple images of the SLM. Therefore, in one configuration of the light guide device, adjacent segments of the multiple images of the SLM are alternately decoupled by grating elements on the surface / boundary surface of the front side and the rear side or both sides of the light guide of the light guide device.

[0194] Fig. 9 Three different illustrations of a display device with a light guide device 5 and with an illumination beam path are shown, in which three different fragments of a plurality of images of the SLM are generated. The light coupling device 7 here also comprises at least one mirror element 9, in particular a tilted mirror element. The light decoupling device 8 here comprises grating elements 12 instead of mirror elements, here there are three grating elements. The grating elements 12 are designed to be switchable or controllable. This means that the grating elements 12 can be switched into an on state and a off state. If the light propagating inside the light guide is to be decoupled at the grating element 12, this grating element 12 is controlled and switched from the off state to the on state. In this way, the light is no longer reflected at the grating element 12, but is decoupled from the light guide via the grating element 12. From Fig. 9 As can be clearly seen in Figure 1 , the grating elements 12 can be attached to the upper side or the lower side of the light guide. The lower side of the light guide is the side of the light guide that faces the virtual observer window VW. The upper side of the light guide is therefore the side of the light guide that is opposite to the lower side and is further away from the virtual observer window VW than the lower side. The grating elements 12 on the upper side of the light guide are designed as reflective grating elements and the grating elements 12 on the lower side of the light guide are designed as transmissive grating elements. In each case in all three illustrations Fig. 9 The SLM shown in is for simplicity to represent the SLM and the variable imaging system. Of course, this means that the SLM and the variable imaging system are two independent components that are not connected to each other.

[0195] according to Fig. 9 In the illustration a), light originating from an illumination device (not shown) is incident on the SLM and is thereby modulated with the information of the fragment or the image to be represented. The modulated light passes through the variable imaging system and is incident on the mirror element 9 of the optical coupling device 7 of the light guide device 5. The mirror element 9 reflects the light, wherein the light propagates in the light guide 6 with total reflection. The light propagating in this way in the light guide 6 is reflected at the boundary surfaces of the light guide until it is incident on the grating element 12, which is switched to the on state. In Fig. 9 After the illustration a), for the middle segment of the plurality of images of the SLM, the decoupling of the light takes place at the switchable reflective grating element 12 on the upper side of the light guide 6. This grating element 12 on the upper side of the light guide 6 not only deflects the light accordingly, but also has a lens function. The light decoupling of the left segment according to the illustration b) and the light decoupling according to the Fig. 9 The optical decoupling of the right-hand segments of the multiple images of the SLM of the illustration c) takes place in each case via a transmission switchable grating element 12 on the underside of the light guide. These transmission grating elements 12 on the underside of the light guide also have a lens function.

[0196] In addition, the focal length of the variable imaging system can be changed before the light of each segment is coupled into the light guide 6. In this way, for each segment according to Fig. 9 For all three segments of the multiple images of the SLM in illustrations a) to c) of FIG. 1 , a virtual observer window can be generated at the same position. However, in this example, compared with the virtual observer window VW and the field of view according to illustration a), the virtual observer window VW and the field of view according to FIG. Fig. 9 The size of the virtual observer window VW for the left segment of the multiple images of the SLM of illustration b) is slightly smaller and the field of view is therefore slightly larger. For the right segment of the multiple images of the SLM it is the opposite, the size of the virtual observer window VW is slightly larger and the field of view is slightly smaller. The reason for this is that the size of the virtual observer window depends on the optical path between the SLM and the virtual observer window according to λD / p, where D is the path between the SLM and the virtual observer window, which path length is different in each segment. The smaller angle of the field of view also results in an equal size of the SLM and a larger distance D from the virtual observer window.

[0197] The position of the decoupling point of the individual segments of the multiple images of the SLM of the light guide is fixed by the position of the lens function in the grating element used for decoupling, the position of the decoupling point being different for the individual segments. For example, since two different lens functions of the grating element are used to decouple the light, a continuous displacement of the individual segments is not possible, which is reasonable for specific applications, for example, for gaze tracking.

[0198] The light guide of the light guide device can be designed to be straight and / or planar or also curved.

[0199] Exemplary embodiments are explained below, each having a curved light guide. In a display device for generating at least one image of an SLM, a curved light guide instead of a planar light guide can have particular advantages. On the one hand, an illumination beam path can be enabled in which the use of a variable imaging system may not be required, so that with a fixed optical system a virtual observer window can be generated in each case at the same place or position for multiple fragments of the multiple images of the SLM. In addition, the virtual observer window can have the same size for multiple fragments of the multiple images of the SLM and, concomitantly, in each case also a partial field of view of the same size is generated for all fragments. As a result, all fragments of the multiple images of the SLM contribute equally to the entire field of view.

[0200] On the other hand, a light decoupling device can be used, the light decoupling angle of which is independent of the position on / in the light guide or the light guide device. In particular, the decoupling angle is equal in each case also for the decoupling of the individual segments of the plurality of images of the SLM. In particular, this also enables a continuous displacement of the decoupling position of the individual segments from the light guide, so that it is not necessary to provide a predetermined decoupling position of the individual segments.

[0201] In one exemplary embodiment, the curved light guide in the light guide arrangement forms a portion of a circular arc, wherein the virtual observer window represents a center point of the circle.

[0202] Therefore, both the inner and outer boundary surfaces of the light guide form arcs, wherein the inner boundary surface located closer to the virtual observer window has a smaller radius, and the outer boundary surface located farther from the virtual observer window has a larger radius. Therefore, the two boundary surfaces are also not parallel to each other.

[0203] For example, the inner boundary surface has a radius of 30 mm and is located 30 mm from the center of the virtual observer window. The outer boundary surface has a radius of 35 mm (corresponding to a light guide thickness of 5 mm) and is therefore located 35 mm from the center of the virtual observer window.

[0204] In a preferred exemplary embodiment, the light guide has a cylindrical shape, i.e., a curvature of the above-described form is present in one dimension and / or direction, and extends linearly in a dimension perpendicular thereto. For example, since in a display device in the form of an HMD, a large field of view in the horizontal direction is generally assigned greater importance than in the vertical direction, the light guide will preferably be arranged in the display device in the following manner, i.e., the curvature of the light guide extends in the horizontal direction, and the non-curved or straight embodiment of the light guide extends in the vertical direction.

[0205] The light guide may also be curved in two dimensions and / or directions. The inner and outer boundary surfaces of the light guide then have the shape of a portion of a spherical shell, wherein the center of the virtual observer window in each case represents the center point of the sphere.

[0206] A display device with a light guide comprises at least one SLM, an illumination device for illuminating the SLM, and an optical system, the light guide comprising a light guide bent in at least one direction, the illumination device having at least one light source, and the optical system having at least one imaging element. The illumination device, the SLM and the optical system are arranged relative to each other in such a way that, in the absence of the light guide with the light guide, the optical system images the illumination device in the center of a virtual observer window.

[0207] If a cylindrical light guide is used, the optical system preferably comprises a cylindrical imaging element.

[0208] The light guide device with the light guide is then introduced into the display device so that the image of the illumination device generated by the optical system is located in the center of the circular arc of the light guide. The illumination beam path extends through the display device in such a way that the beam is incident substantially perpendicularly on the outer surface of the light guide.

[0209] Using a cylindrical light guide, in the non-bending direction of the light guide, a cylindrical lens function is preferably arranged in the light decoupling device of the light guide device, or a cylindrical lens is arranged on or near the light decoupling side of the light guide, which focuses on the center of the virtual observer window in this direction.

[0210] However, if a single parallax hologram encoding is provided, the need for this vertical focusing can be omitted. Nevertheless, a lens can be provided on the decoupling side of the light guide, or a lens function can be provided in the light decoupling device, however, the focal length of the lens can also deviate from the distance to the virtual observer window.

[0211] The optical coupling device is arranged in a coupling region on the outer surface or the inner surface of the light guide. Then, the optical coupling device may have at least one grating element for decoupling the light from the light guide, and in one embodiment, the optical coupling device is a reflective grating element on the inner surface of the light guide. Then, the light first passes through the light guide vertically, is deflected by the reflective grating element on the inner surface, and then propagates through the light guide in a zigzag shape.

[0212] The propagation angle of light can be selected in the following way so that reflection occurs in the form of total reflection at the boundary surface between the light guide and the air. Optionally, the propagation angle of light can also be selected so that total reflection does not occur at its boundary surface with the air. For this case, an additional layer can be provided, such as a dielectric layer or a layer stack, which causes light incident on the layer or layer stack at a specific angle to be reflected, thereby causing the light to propagate further within the light guide due to reflection at the layer or layer stack. The layer or layer stack can preferably be designed so that ambient light can pass through the light guide in potential AR applications. The layer stack then selectively has a reflective effect only for a small angle range, where the angle range corresponds to the propagation angle of the light in the light guide. In this way, the display device can also be used in AR applications.

[0213] The light decoupling device is arranged in a potential light decoupling area in the light guide. The light decoupling device may comprise at least one passive or controllable or switchable grating element. By switching on or off the grating element or a defined part of the grating element, in case it is implemented as divided into switchable parts, a position where the light is decoupled from the light guide can be established. If a passive grating element is used, an additional switchable element is required, for example a polarization selective grating element that only deflects light of one polarization direction and does not deflect light of another polarization direction in combination with a polarization switch.

[0214] For example, in the case of light propagating by total reflection in the light guide, the angle is changed by the grating elements of the light decoupling device in such a way that the angle drops below the total reflection angle and the light emerges from the light guide.

[0215] During the propagation of the light in the light guide, the light beam is alternately reflected at the outer boundary surface with a larger radius and at the inner boundary surface with a smaller radius. As an illustration, this helps to focus at a position that is equal distance from the decoupling position of the light guide in each case, although the path lengths of the multiple light beams passing through the light guide after these light beams are decoupled are different.

[0216] In particular, the deflection angle of the grating element of the light decoupling device in the above-mentioned display device is independent of the position of the grating element in the light guide. For a cylindrical light guide, in which a cylindrical lens function is provided in the grating element, or a cylindrical lens is used near the decoupling position of the light in the non-curved direction of the light guide, the focal length of the lens or lens function is also independent of the decoupling position of the light. For example, this can be a rectangular grating element with a cylindrical lens function, which is laminated onto the inner curved surface of the cylindrical light guide, so that the focusing function acts perpendicular to the curvature direction.

[0217] By switching the light decoupling device to an on state or a off state, light of multiple fragments of multiple images of the SLM can be decoupled from the bent light guide after different numbers of reflections.

[0218] Fig.10 Such a curved light guide 15 is shown, which is arranged in a display device. In addition to the light guide 15 with the light guide 16, the display device also includes an SLM and an optical system. The optical system is shown here in the form of an imaging element 17. Light is coupled into the light guide 16 by an optical coupling device 18 and is decoupled from the light guide again by an optical decoupling device 19 after a predetermined number of reflections. Both the optical coupling device 18 and the optical decoupling device 19 include at least one grating element 20, 21. At least one grating element 20 of the optical decoupling device 19 is designed to be switchable or controllable and is divided into separate parts 20-1, 20-2 here. Here, part 20-1 of the grating element 19 is in a closed state, wherein part 20-2 is in an open state, so that the light propagating in the light guide is decoupled at part 20-2 of the grating. If part 20-1 of the grating element 19 is in an open state and part 20-2 is in a closed state, the light will be decoupled from the light guide after a smaller number of reflections. The light beams originating from the individual pixels P1, P2 and P3 of the SLM pass through the imaging element 17 and are incident on the light guide 16. The light beams are then incident on a light coupling device 18, which is arranged on the inner surface of the light guide 16. The light coupling device 18 comprises at least one grating element 21, which in this exemplary embodiment is designed to be reflective. The light beams incident on the grating element 21 are reflected and deflected in such a way that the light beams propagate in the light guide 16 via total reflection. The individual light beams are then decoupled from the light guide 16 of the light guide device 15 at the grating element 19, here at the portion 20-2 of the grating element, after a predetermined number of reflections. All light beams representing an image or fragments of a plurality of images of the SLM are decoupled after the same number of reflections.

[0219] However, instead of different numbers of reflections of different segments of the multiple images of the SLM, a continuous displacement of the light decoupling position on / in the light guide is also feasible. This can be achieved, for example, by a small displacement of the light coupling position and an equal number of light reflections at the boundary surfaces of the light guide.

[0220] A large field of view can then be generated, for example, by using a larger number of steps of generating individual fragments of the multiple images of the SLM using different numbers of reflections at the boundary surfaces of the light guide and a smaller number of steps of continuous displacement between the coupling positions of the light of the individual fragments of the multiple images of the SLM. For example, a field of view of size 60° can be generated by six fragments of 10° each that do not overlap. In this case, the light guide and the grating elements of the light coupling device can be designed to utilize additional reflections in the light guide so that the decoupling position of the light is offset by 20° from the viewing angle of the observer. In addition, by the displacement of the coupling position, the decoupling position can be shifted by 10° from the viewing angle of the observer at a fixed number of reflections.

[0221] For example, the light is then decoupled after one reflection to generate a first segment when the coupling position is not shifted. The light is decoupled after one reflection to generate a second segment when the coupling position is shifted by 10°. The light is decoupled after two reflections to generate a third segment when the coupling position is not shifted. The light is decoupled after two reflections to generate a fourth segment when the coupling position is shifted by 10°. The light is decoupled after three reflections to generate a fifth segment when the coupling position is not shifted. The light is decoupled after three reflections to generate a sixth segment when the coupling position is shifted by 10°.

[0222] Alternatively, small changes in the deflection angle of the light generated by the grating element 20 of the light coupling device 18 can also be used to generate a large field of view. However, for this purpose the grating element 20 must also be designed to be controllable or switchable.

[0223] The displacement of the coupling position of the light on the light guide is preferably performed by a light deflection device 29, which may comprise at least one grating element. Fig.14 Described in more detail. The grating element has a settable grating period. For example, a pair of two grating elements can be used in a light deflection device, wherein a first grating element deflects light from the SLM and then a second grating element deflects the light in the opposite direction, thereby substantially achieving a parallel offset result.

[0224] In a display device with a two-stage optical system or two-stage imaging of light, i.e., generating an intermediate image of the illumination device, the light deflection device can be arranged in the intermediate image plane of the illumination device. As an example, a field of view of approximately 60° in the curvature direction of the light guide is achieved by implementing a coarse step size of 20° after one additional reflection on the front and rear sides, and the coupling position is further moved by the light deflection device by up to ±10°.

[0225] With a cylindrical light guide, the displacement of the coupling position of the light on the light guide in the non-bending direction can also be implemented by means of a light deflection device. For example, a vertical field of view of size 20° can be composed of two segments of 10° each, where the light is coupled in the lower half or the upper half of the light guide by moving the vertical coupling position.

[0226] Fig.11A display device is shown in a perspective view, comprising an SLM, an optical system (here also in the form of an imaging element 17) and a light guide 22, which comprises a cylindrical light guide 23. It can be seen that in the non-bent direction of the light guide 23, light from different vertical positions V1, V2, V3 of the SLM is coupled into the light guide 23 by means of an optical coupling device 24. Thereafter, the light propagating in the light guide by total reflection is decoupled by means of an optical decoupling device 25 and focused in a virtual observer window VW on the decoupling side of the light guide 23 by means of a vertical cylindrical lens function incorporated in the optical decoupling device 25.

[0227] A continuous displacement of the segments is also reasonable, in particular if different parts of the field of view are to be represented depending on the content of the preferably three-dimensional (3D) scene to be represented or depending on the exact position at which the observer's eyes look during viewing of the scene.

[0228] Thus, for example, it may be possible to detect in the HMD exactly which parts of the scene the observer is looking at, and for example only these parts may be represented holographically.

[0229] A display device having a two-stage optical system or two-stage imaging will be described in more detail below.

[0230] In a holographic display device, such as an HMD, the SLM is imaged as a whole. In the case of segmented multiple images, one image of the SLM is generated for each segment. The image of the SLM at a predetermined distance sets the specific focal length of the imaging elements of the optical system used and the specific distance of the SLM from these imaging elements. In particular, the imaging beam path and the illumination beam path in the display device are generally not independent of each other. Potentially required settings of the illumination beam path can also potentially lead to changes in the imaging beam path.

[0231] In a configuration of a display device using a straight and / or planar light guide and at least one imaging element (e.g. a lens), before coupling into the light guide in the direction of the light, the focal length of the at least one imaging element must be changed, e.g. as described above, in order to set the virtual observer window of each segment of the multiple images of the SLM at the same position. If the distance of the SLM to the imaging element is fixed, the imaging position of the SLM is thereby changed in case of a change in the focal length of the imaging element. Thus, in the multiple images of the segment of the SLM, a different image plane of the SLM will be generated for each segment.

[0232] In another configuration of a display device using a light guide, which light guide only comprises at least one lens located between the light decoupling device of the light guide device and the eye of the observer or a lens function incorporated into the grating element of the light decoupling device, the focal length of the at least one lens between the light decoupling and the observer must be equal for all segments of the multiple images of the SLM. However, due to the different optical path lengths of the light of the individual segments of the multiple images of the SLM through the light guide, the distance between the SLM and the at least one lens or lens function in the grating element of the light decoupling device is different for the length of each segment. Therefore, in this case, the SLM image of each segment of the multiple images of the SLM is also at a different distance or at a different position overall.

[0233] In a holographic display device, it is not absolutely necessary for all segments of multiple images to have a common image plane. It is also possible to continuously represent a 3D scene on the boundaries of segments with different image planes of the SLM, for example, by adjusting the focal length of the sub-hologram of the hologram on the SLM in each segment. For example, if an object point is located in front of the SLM image plane of the segment, the object point of the scene can be represented in a segment of the multiple images of the SLM by a sub-hologram with a positive focal length (convex lens). For example, if an object point is located behind the SLM image of the segment, a neighboring object point in another segment at the same depth relative to the observer can be represented by a sub-hologram with a negative focal length (concave lens). However, on the other hand, if the image plane of the SLM is at least similar for all segments, for example it only differs by a few centimeters instead of meters, this simplifies the hologram calculation.

[0234] If grating elements are used for coupling light into a light guide and / or decoupling light out of the light guide, respectively, in particular grating elements with a small period (in the range of 1 μm or less), they therefore have large deflection angles of typically more than 30°, for example between 50° and 60°, thus generating aberrations in the beam path overall.

[0235] In order to keep the aberrations as small as possible, a pair of grating elements for coupling light into the light guide and decoupling light from the light guide is preferably used. This means that one grating element is arranged in the light coupling device and one grating element is arranged in the light decoupling device, wherein the two grating elements have substantially opposite and equal deflection angles. In the first grating element (i.e. the grating element of the light coupling device), for example, vertically incident light is deflected by an angle of 60° relative to the normal. In the second grating element (i.e. the grating element of the light decoupling device), the light incident at 60° is deflected in such a way that it emerges vertically from the grating element. After passing through the two grating elements, the angle at which the light emerges from the second grating element therefore corresponds to the angle of incidence of the light entering the first grating element. This arrangement of two grating elements in the light guide device, respectively for coupling light into the light guide or decoupling light from the light guide, is conducive to keeping the aberrations of the illumination beam path in the display device (e.g. HMD) small or reducing the aberrations. The remaining aberrations particularly affect the imaging beam path. Due to these aberrations, the position of the SLM image may be disadvantageously shifted compared to a light-guiding device that does not use a grating element in the light coupling device and / or the light decoupling device. In particular, this shift of the SLM image occurs mainly in the direction in which the grating element deflects the light, thereby also generating astigmatism of the SLM image. For example, for a horizontally deflected grating element, a horizontal pixel image of the SLM will be generated at a different depth than a vertical pixel image of the SLM.

[0236] In order to compensate or reduce the influence of grating elements in the light guide arrangement on the position of the SLM image, an intermediate image of the SLM may be generated inside the light guide and / or the light guide arrangement.

[0237] The display device can use a two-stage optical system to generate an intermediate image of the SLM. In this case, in addition to the two-stage optical system, the display device also includes at least one SLM and an illumination device having at least one light source that illuminates the SLM. In the first stage, an intermediate image of the illumination device is generated after the SLM in the direction of the light using at least one first imaging element (e.g., a lens) of the two-stage optical system and thus also an intermediate image of the virtual observer window to be generated. In the second stage, the intermediate image of the virtual observer window and the intermediate image of the illumination device are imaged in the actual virtual observer window or in the observer plane using at least one second imaging element (e.g., a lens) of the two-stage optical system. In this case, the light guide device in the display device is positioned in the light path after the intermediate image of the virtual observer window and the second imaging element. The arrangement with the first and second imaging elements also produces an image of the SLM. The second imaging element that images the intermediate image of the virtual observer window or the intermediate image of the illumination device, respectively, can also contribute to the imaging of the SLM. By appropriately selecting the focal length of the imaging element, another image of the SLM is generated inside the light guide of the light guide device. This intermediate image of the SLM inside the light guide can also be generated only in the deflection direction of the grating elements of the light coupling device and / or light decoupling device using, for example, cylindrical imaging elements, while the intermediate image of the SLM can be located outside the light guide in a direction perpendicular thereto.

[0238] exist Fig.12 2 shows a display device with a two-stage optical system. The display device further comprises at least one SLM and a light guide 26. In this case, the light guide 26 is arranged after the two-stage optical system in the direction of the light, which comprises at least two imaging elements 27 and 28. The first imaging element 27 is arranged after the SLM in the direction of the light, but in close proximity to the SLM. Fig.12 The illumination beam path for such a display device is schematically shown in this case, wherein the imaging element 27 generates an intermediate image ZB of an illumination device (not shown). The intermediate image ZB of the illumination device is then imaged in the virtual observer window VW by means of the imaging element 28, in which the image of the illumination device is again generated. However, the imaging system 30 can be arranged in the plane of the intermediate image ZB without having an influence on the illumination beam path. The function of the imaging system 30 on the imaging beam path will be explained below.

[0239] Fig.13 Shown according to Fig.12FIG. 1 is an imaging beam path of a display device of FIG. 1 , wherein an overview of the imaging beam path is shown in the upper figure and a detailed view of the circled area in the upper figure is shown in the lower figure. For the sake of clarity, the light originating from only one pixel of the SLM in the upper figure is shown. It can be seen that after passing through the imaging elements 27 and 28 and the imaging system 30, the light enters the light guide of the light guide device, propagates in the light guide by total reflection, and is then decoupled again by the light decoupling device.

[0240] The circled area of ​​the upper figure is shown in more detail in the lower figure, where however not only one beam is shown, but a plurality of beams originating from a plurality of pixels of the SLM. It can be seen from this detailed view that the individual pixels of the SLM are brought into focus in each case inside the light guide by means of the imaging elements 27 and 28 and the imaging system 30. This means that a further image ZS of the SLM is generated inside the light guide of the light guide arrangement 26. The imaging system 30 in the plane of the intermediate image ZB of the illumination arrangement has the advantageous property of influencing only the imaging beam path and not the illumination beam path.

[0241] If the imaging system 30 is, for example, a lens element, the image plane of the SLM can be moved by appropriate choice of the focal length of the lens element without the position of the virtual observer window being shifted unintentionally.

[0242] In the present example, the imaging element 28 is also a lens element. First, the focal length of this lens element is selected so that the light, after decoupling from the light guide 26, generates a virtual observer window. Taking into account the focal length of the imaging element 28, the focal length of the lens element of the imaging system 30 is then selected so that an image ZS of the SLM is generated inside the light guide of the light guide 26.

[0243] The magnitude of the aberrations in the imaging beam path caused by the grating elements used for light coupling and decoupling also depends on the distance of the grating elements, i.e. on the distance of at least one grating element of the light coupling device and at least one grating element of the light decoupling device. Therefore, individual segments of the multiple images of the SLM in the light guide will also result in different aberrations in the imaging beam path of each segment, wherein the light propagates different distances in the light guide and therefore has different distances between the grating element used for light coupling and the grating element of the light decoupling.

[0244] Regarding the solution for the different depth positions of the individual fragments of the multiple images of the SLM from the perspective of the virtual observer window, due to the different distances of the individual fragments of the multiple images of the SLM from the imaging elements of the optical system caused by different path lengths of the light in the light guide or also due to the aberrations generated by the grating elements used for coupling and decoupling, the following is proposed: As already disclosed, the display device comprises, in addition to a two-stage optical system, at least one SLM and an illumination device for illuminating the SLM. In a first stage, an intermediate image of the illumination device and thus also an intermediate image of the virtual observer window is generated behind the SLM in the direction of the light by at least one first imaging element. In a second stage, the intermediate image of the illumination device as well as the intermediate image of the virtual observer window are imaged in the actual virtual observer window by at least one second imaging element. Furthermore, the display device comprises a variable imaging system, see for example Fig.15 . This means that in this case the imaging system 30 in the intermediate image plane ZB is designed to be variable. The variable imaging system 30 is arranged in the intermediate image plane ZB of the virtual observer window or close to the intermediate image plane. The variable imaging system 30 includes at least one imaging element, which can be designed to be controllable. For example, the focal length of the imaging element can be variable. The arrangement with the first and second imaging elements 27, 28 also generates an image of the SLM. The second imaging element 28, which images the virtual observer window, also contributes to the imaging of the SLM. However, by using the imaging elements of the variable imaging system in the intermediate image plane of the virtual observer window or as close as possible to the intermediate image plane of the virtual observer window, the image of the SLM can also be advantageously shifted without affecting the illumination beam path and the position and size of the virtual observer window itself. The SLM image of each segment of the multiple images of the SLM is shifted in the following way by means of the imaging elements of the variable imaging system, that is, the different optical paths of the light through the light guide generated by the individual segments are at least partially compensated.

[0245] Due to the compensation, the visible image of the SLM that can be observed by the observer through the virtual observer window is at an equal or at least similar depth for all segments. The imaging element of the variable imaging system 30 can be, for example, a grating element with a controllable variable period (LCG-liquid crystal grating), an electrowetting lens, a liquid crystal lens, or also a system made of at least two imaging elements (e.g. lenses) whose distance is changed, similar to a zoom objective.

[0246] The intermediate image of the SLM can also be generated in such a way that the intermediate image of the SLM for a portion of the multiple images of the SLM is located inside the light guide. However, for another portion of the multiple images, the intermediate image of the SLM can also be located outside the light guide.

[0247] Due to this compensation, the intermediate images of all segment SLMs are preferably generated at a similar distance from the decoupled light leaving the light guide. For the case where the intermediate images of all segments are generated inside the light guide, the following is true, segments with a greater number of reflections in the light guide have intermediate images in the light guide further away from the coupling of the light than segments with a smaller number of reflections in the light guide.

[0248] Due to the use of grating elements which couple the light into the light guide or decouple it from the light guide, respectively, the astigmatism caused by only a single-stage optical system in the pixel imaging of the SLM can be at least partially compensated in the described two-stage system. This effect can be produced in a two-stage optical system of crossed, i.e. arranged perpendicularly relative to each other, cylindrical imaging elements (e.g. cylindrical lenses), each cylindrical imaging element with a variable focal length or a controllable grating element with a cylindrical lens function being used in an intermediate image plane of the virtual observer window, and for each segment of the multiple images of the SLM, the focal lengths of the two cylindrical imaging elements are each set in such a way that a horizontal and a vertical image of the SLM visible through the virtual observer window is produced in a similar depth plane.

[0249] Furthermore, a continuous displacement of the coupling position of the light on the light guide can be performed by means of a light deflection device 29 which is arranged in the virtual observer window and / or in the intermediate image plane ZB of the illumination device, in the direction of the light, immediately in front of the light guide or light guide device 26 and adjacent to the variable imaging system 30, e.g. Fig.14 As shown. The light deflection device 29 may comprise for this purpose at least one grating element, which is designed to be controllable or variable. Thus, light incident thereon can be deflected accordingly by the light deflection device 29, i.e. the grating elements of the light deflection device can be controlled in such a way that the incident light is deflected into a desired direction and thus coupled into the light guide, this coupling position on the light guide being different from the coupling position without such light deflection by the light deflection device 29. Fig.12 and Fig.14 The illumination beam paths are shown. Fig.12 , the undisplaced coupling position in the light guide without the use of a light deflecting device is shown in FIG. Fig.14 The displaced coupling position is shown in .

[0250] In this way, various coupling positions of the light can be generated on the light guide. The functions of the light deflection device 29 and the functions of the variable imaging system 30 can also be combined in one device or system, so that only one device is required for both functions. Both the lens function for variable imaging and the lens function for deflection can be written, for example, into the same controllable grating element.

[0251] The position of the image of the SLM relative to the preferred three-dimensional scene to be generated also affects, in particular, the calculation of the hologram to be encoded into the SLM. In particular, in the case where all sub-holograms form an overall hologram or hologram, the size of the sub-hologram depends on the distance at which the object points of the scene are located in front of or behind the SLM image plane, which also defines the field of view. If the image of the SLM is very close to the virtual observer window (through which the observer can observe the reconstructed or generated scene), the size of the sub-hologram is usually very large. Conversely, if the image of the SLM is located far away from the virtual observer window, this can also mean a sub-hologram of large size. If there is no image of the SLM at all between the virtual observer window and infinity, the three-dimensional scene can be represented, but it is a real image of the SLM located behind the virtual observer window. If the distance between the SLM and the imaging element is greater than the focal length of the imaging element, no virtual image is generated. The observer is then unable to see a clear image of the SLM. However, if the sub-hologram is encoded on the SLM itself, which has a sufficiently long focal length, i.e. not on its image, then an object point can be generated, the distance of which from the imaging element is less than the focal length of the imaging element, without generating a virtual image of the SLM, but of the object point. However, in this case, a sub-hologram of very large size is also provided.

[0252] In general, it may be advantageous to have the image plane of the SLM located within the three-dimensional scene so that a portion of the scene's object points are located in front and another portion of the object points are located behind the SLM image, e.g. the image plane is located about 1 meter or 1.5 meters from the virtual observer window. The computational effort for computing the hologram increases with the size of the sub-hologram.

[0253] For example, in a display device with a two-stage optical system and a variable imaging system, the position of the image plane of the SLM can be shifted in each segment of the plurality of images of the SLM in such a way that the typical or maximum size of the sub-hologram is minimized by adjusting the focal length of the imaging element of the variable imaging system. The workload of computing the hologram is then advantageously reduced.

[0254] In a display device not using a variable imaging system, the calculation of the hologram to be encoded into the SLM can be performed by a virtual SLM plane, which has a small average size of sub-holograms and is arithmetically transformed into a corresponding image plane of the SLM for each fragment of the multiple images of the SLM. This can also include a transformation to the real image plane of the SLM behind the virtual observer window. For example, the virtual image plane of the SLM will be the same for all fragments of the multiple images of the SLM, but the image plane of the SLM where the transformation is performed for each fragment according to the image plane generated by the optical system is different.

[0255] The following description relates to the inverse calculation of the determination of the amplitude and phase of the sub-holograms taking into account the aberrations of the optical system. As already described, aberrations are also produced in the imaging beam path, for example due to grating elements used for coupling light into the light guide or decoupling light from the light guide, respectively, which not only lead to undesired displacements of the pixel image of the SLM, but also have the consequence that a clear imaging pixel image of the SLM is completely absent.

[0256] In principle, a holographic display device can be used to clearly reconstruct three-dimensional object points of a scene in space even if the SLM is not clearly imaged. In some cases, however, the phase curve of the sub-hologram then has deviations from a simple spherical lens function, which usually forms a holographic direct-view display or display with clear imaging of the SLM. The amplitude curve of the sub-hologram may also have deviations from the typical curve, which in the simplest case is a constant amplitude across the sub-hologram.

[0257] A method will now be described for checking whether a sub-hologram can be correctly represented on the SLM and for determining the amplitude distribution and phase distribution in the sub-hologram, which is necessary for reconstructing an object point.

[0258] The method can preferably be performed using software for geometrical optics calculations, which simplifies the performance compared to wave optics calculations in more complex optical systems. First, a calculation of the light propagation from an object point of a preferably three-dimensional scene to a virtual observer window is performed, which would be the case if the object point actually existed in space and the optical system was not located between the object point and the virtual observer window. Thus, in the case of a wave optics calculation, the wavefront of the light originating from the object point is calculated in the virtual observer window. In a simplified geometric calculation, a light beam is calculated from the object point to various positions in the virtual observer window. Then, the calculation of the wavefront or light beam is performed in reverse from the virtual observer window through the optical system to the SLM.

[0259] This can be done as follows, for example: in the optical calculation, a beam splitting element is introduced in front of the virtual observer window in the direction of the light, and a mirror element is introduced at the position of the virtual observer window. The light from the object point of the three-dimensional scene is coupled at the surface of the beam splitting element, deflected toward the virtual observer window, reflected by the mirror element at the virtual observer window, enters the beam splitting element again and leaves through the other surface of the beam splitting element and thereby passes through the optical system in reverse to reach the SLM. In this way, the amplitude distribution and phase distribution in the sub-hologram can be determined for the object point.

[0260] Alternatively, for example, in optical calculations, a virtual observer window may be illuminated from behind, and a lens may be arranged in the virtual observer window, which will generate an object point without a remaining optical system. For example, in order to perform calculations of an object point 1 meter away from the virtual observer window, the virtual observer window may be illuminated from the back side using a plane wave, and a lens with a focal length of 1 m may be arranged in the virtual observer window. The amplitude distribution and phase distribution in the sub-hologram may also be calculated for the object point in this way.

[0261] For a display device having at least one SLM, a plurality of imaging elements of an optical system, and a light guide device, calculations can be performed, for example, so that light from a virtual observer window enters a light guide of the light guide device at a light decoupling position, and leaves the light guide again at a light coupling position, and then further propagates through the imaging elements of the optical system to the SLM. Then, the position and size of the sub-hologram are generated by the position at which the counter-propagating light beam is incident on the SLM.

[0262] Fig.15 A display device with an SLM, imaging elements 27 and 28 of an optical system, a variable imaging system 30 and a light guide 26 is schematically shown, wherein a back calculation for determining the amplitude distribution and the phase distribution of an object point is shown. In this case, a back calculation is performed from the virtual observer window VW through the light guide 26 to the SLM, and the values ​​are determined. The object point to be reconstructed can be correctly represented on the SLM, especially when the light beams at all positions within the virtual observer window VW are incident on the SLM in the back calculation. In addition, the light beams must be incident on the SLM at an angle less than or equal to half the diffraction angle of the SLM. The diffraction angle resulting from the wavelength λ used and the pixel pitch p of the SLM is λ / p. This condition is usually satisfied when the aberrations in the illumination beam path are small and the aberrations are essentially only present in the imaging beam path.

[0263] In the case of wave optics calculations, the amplitude and phase distributions of the object points in the sub-hologram can be directly defined by inverse calculations.

[0264] In geometric calculations, the amplitude distribution and phase distribution are defined as follows:

[0265] A geometric inverse calculation of the beams is performed using a very large number of beams (e.g. 100,000 beams). The relative intensity of a pixel in the sub-hologram of the SLM then results from the number of beams in the area of ​​the pixel incident on the SLM. The relative amplitude can be calculated as the square root of this intensity. For the absolute value of the amplitude, the sum of all intensities of the pixel in the sub-hologram is set equal to the intensity of the object point. Since the amplitude varies continuously overall in the sub-hologram, it does not have to be calculated separately for each pixel, but can also be interpolated based on the sample points in a simplified form.

[0266] Fig.16 The intensity distribution in the SLM plane is schematically shown, which is obtained according to Fig.15 The inverse calculation of the geometric calculation is obtained. It shows the intensity distribution in the sub-hologram. The sub-hologram shown in this example has a roughly triangular shape and has a roughly sickle-shaped narrow area with high intensity at the lower edge. It is significantly different from a conventional sub-hologram on an SLM, which has a rectangular shape with a constant amplitude over the entire area of ​​the sub-hologram. In particular, the calculation of the phase value can be performed when there is a unique association between the position on the SLM and the angle of incidence of the light beam entering the SLM. This means that the light beam cannot be incident on the same position in the SLM at significantly different angles. The lens function written into the sub-hologram can be considered as a diffraction grating with a grating period that varies with position. Therefore, for every two adjacent pixels of the SLM, the deflection angle of the light locally corresponds to the local grating period, whereby the difference in the phase values ​​of the two pixels can be defined. If a phase value is thus defined for the first pixel, a phase value corresponding to the desired difference can also be defined for each adjacent pixel. Therefore, the phase value can be defined step by step from one pixel to each adjacent pixel.

[0267] Therefore, first, the local grating period is determined in a geometric inverse calculation according to the incident angle of the light beam on the SLM. According to the equation tanα=λ / g, where α is the incident angle of the light beam and λ is the wavelength of the light, the local grating period g is defined as g=λ / tanα. Then, Where p is the pixel pitch of the complex-valued pixels of the SLM, representing the phase difference between two adjacent pixels, which is necessary to set the deflection angle. Therefore, if the first pixel has a phase value The second pixel therefore receives the phase value

[0268] With the two-dimensional pixel arrangement of the SLM, in this case, the incident angle is decomposed into a horizontal component and a vertical component. The above equations are then used to determine the local horizontal grating period and the vertical grating period, respectively. The phase difference of adjacent pixels is determined by the local grating period according to the ratio 2*π*p / g of the pixel pitch p with complex-valued pixels. For example, if the incident angle of the light beam on the SLM corresponds to half the diffraction angle, a phase difference of π is therefore generated between adjacent pixels. If the incident angle of the light beam on the SLM corresponds to, for example, one-quarter of the diffraction angle, a phase difference of π / 2 is therefore generated. The phase difference and the optional offset phase value are then used to define the phase curve in the sub-hologram. For example, the offset phase value can be defined so that the phase value of the pixel in the upper left corner of the sub-hologram is set to 0. Since the local grating period in the sub-hologram varies continuously overall, it does not have to be calculated separately for each pixel pair, but can be interpolated based on the sample points. The phase thus determined corresponds to the phase in the sub-hologram of the SLM illuminated with a plane wave. If the illumination wavefront deviates from a plane wave, it is therefore also subtracted from the phase value of the sub-hologram.

[0269] Similar to the description above, the phase distribution of the illumination wavefront can optionally be determined by geometrical optics calculations and the angle of incidence of the beam of the illumination device on the SLM. Such calculations can also be performed offline, and the determined values ​​can then be stored in a lookup table for hologram calculations.

[0270] As already explained, a two-stage optical system is preferably used in the display device, which generates an intermediate image plane of the illumination device. In an exemplary embodiment with such a two-stage optical system, a variable imaging system can be arranged in the intermediate image plane of the virtual observer window. In this case, the variable imaging system can include, for example, a grating element with a controllable variable period (LCG).

[0271] An exemplary embodiment is also described in which, in a two-stage optical system with an intermediate image of the illumination device, a light deflection device is arranged in the intermediate image plane of the illumination device to shift the light coupling position in the light guide by writing a lens function into at least one grating element of the light deflection device. The grating element can also be designed, for example, as a grating element with a controllable period. Both the variable imaging system and the light deflection device can also be combined here again in a single device.

[0272] Another exemplary embodiment of a display device with a two-stage optical system is described below. In this case, in at least one grating element of the variable imaging system and / or the light deflection device, wherein optionally or in addition to a simple lens function or prism function, the grating element is a phase modulation element, for example a grating element with a controllable variable period (LCG), a complex-valued phase characteristic can also be written to compensate for aberrations. For example, this can be performed in conjunction with the above-mentioned back calculation from the virtual observer window through the light guide in the direction of the SLM. However, first the back calculation is performed only from the virtual observer window to the intermediate image plane of the illumination device. Compared with the target position and the target angle in the actual virtual observer window, especially in the case where the aberrations are essentially only present in the imaging beam path and there are no or only small aberrations in the illumination beam path, in the back calculation, the light beam in the intermediate image plane of the illumination device has essentially the correct position, but due to the aberrations, there is an erroneous angle. Therefore, for each light beam, the angle can be corrected by the corresponding local grating element in the intermediate image plane of the illumination device. For example, if β(x) is the desired angle of incidence of the light beam at position x, β'(x) is the actual angle of incidence of the light beam at position x, then the correction value is Δβ(x) = β(x) - β'(x). Taking into account the imaging ratio from the intermediate image plane of the illumination device to the virtual observer window, the incident position of the light beam and the desired angle of incidence correspond to those in the actual virtual observer window. Similar to what has been described about the inverse calculation in the SLM, the local grating period is then defined as g(x) = λ / tanΔβ(x).

[0273] The advantage of correcting aberrations in the imaging beam path by means of a phase function in the intermediate image plane of the illumination device is that the correction is independent of the content of the three-dimensional scene. Thus, for each segment of a plurality of images of the SLM, the correction function and / or the correction value can be calculated once respectively, and in the case of a continuous shift of the coupling position of the light, feasible decoupling positions can also be selected and stored in a value table so that these values ​​can be reused when necessary.

[0274] By inverse calculation of the SLM, the aberration correction of the sub-hologram in the plane of the SLM described above means that with appropriate amplitude curves and phase curves in the sub-hologram, a sharp point can be generated for an object point in space even without a sharp image of the SLM pixel. The use of a variable imaging system in the intermediate image plane of the illumination device (also already described) does shift the image of the SLM, but a blurred image may exist.

[0275] In contrast, the image of the SLM itself is improved by the aberration correction in the intermediate image plane of the illumination device, which is now described. The image of the SLM pixel becomes sharper, so that the sub-hologram for reconstructing the object point can be more similar to a lens function with constant amplitude, as is also present in direct-view displays. The computational effort for calculating the hologram is therefore also reduced due to the smaller size of the sub-holograms. However, the two methods, namely the aberration correction in the intermediate image plane of the illumination device and the aberration correction in the amplitude curve and phase curve of the sub-hologram, can also be combined with one another.

[0276] For example, in the intermediate image plane of the illumination device Fig.17 The back calculation and aberration correction are performed in the following manner as shown, first the optical path of an object point is calculated, which is located at the center of the field of view portion of a single segment of the multiple images of the SLM and at a distance from the virtual observer window corresponding to the target distance of the SLM image from the virtual observer window to the intermediate image plane of the illumination device. With a sharply imaged SLM, the size of the sub-hologram will be only one pixel, since the object point is located in the display plane. The local grating period of the grating elements of the variable imaging system and / or the light deflection device in the intermediate image plane ZB of the illumination device is set so that during the further back calculation to the SLM, the light beams are transmitted together in one pixel in the center of the SLM. Fig.17 This is illustrated on the basis of an example of five light beams which propagate from different positions in a virtual observer window (not shown here) through a light guide or light guide arrangement 26 and an imaging element 28 to an intermediate image plane ZB of the illumination device and from there further through an imaging element 27 to the SLM after passing through a grating element arranged with a matching arrangement of the grating period arranged there. For object points which are at different distances from the virtual observer window but still in the central region of the field of view portion of the fragment of the plurality of images of the SLM, the sub-hologram forms a simple lens function whose focal length is the distance to the object point. However, for object points which are located at the edge of the partial field of view of the fragment, residual aberrations therefore still exist in the plane of the SLM if the same correction is used in the intermediate image plane ZB of the illumination device. For this purpose, the angle of incidence in the hologram plane is determined and the phase function of the sub-hologram is calculated from this, as already described for the further correction of the aberrations still present. In simplified form, in the middle region of the SLM sub-hologram the sub-hologram is used as a lens function without correction, since the pixel image there is sharp, but in the edge region of the SLM a sub-hologram with additional aberration correction in the SLM plane is used, since the pixel image there is not so sharp. Overall, however, in this case the required aberration correction for the sub-hologram in the SLM plane can also be significantly reduced by using a correction in the intermediate image plane of the illumination device.

[0277] As already described, the use of a variable imaging system in the intermediate image plane of the illumination device can be replaced by an optional embodiment, namely, the variable imaging system is replaced by the calculation of the conversion of the virtual SLM plane to the virtual observer window and back to the actual SLM plane (in this case, the real image plane of the SLM). During the conversion from the virtual SLM plane to the observer plane with the virtual observer window and thereby to the image plane of the SLM, the phase quadratic term is added to the phase value of the observer plane according to the distance from the two planes (SLM plane, observer plane). These phase quadratic terms are equivalent for the lens function. Using a variable imaging system in the intermediate image plane of the illumination device and therefore also using the intermediate image plane of the virtual observer window to move the SLM image as a method, or optionally for the purpose of the arithmetic displacement of the SLM image between the virtual plane of the SLM and the real image plane of the SLM, the arithmetic conversion of the object point to the observer plane and the addition of the quadratic term of the phase to the phase value in this plane, and the reverse calculation, is an optional option for aberration correction.

[0278] However, if, alternatively or additionally, a variable imaging system with a phase element is used in the intermediate image plane of the illumination device, the correction is also performed in the form of an arithmetic conversion, which is advantageous for aberration correction. Thus, sub-holograms are calculated in the almost aberration-free image plane of the SLM, from which they are mathematically converted into the intermediate image plane of the illumination device. In this intermediate image plane, a reciprocal aberration correction is performed and the corrected data are thus inversely transformed into the actual aberration-compromised image plane of the SLM. A combination of arithmetic correction and correction by means of a phase element is reasonable, for example, in the case of using grating elements with a one-dimensional electrode structure having a variable controllable period. For example, if two crossed grating elements are used in a variable imaging system or a light deflection device, a phase curve that depends only on the horizontal coordinate or only on the vertical coordinate can be corrected in each case by hardware in one grating element. In the additional arithmetic correction, other phase terms or phase functions that are independent of horizontal and vertical can be taken into account in the form of a two-dimensional matrix of phase values. To this end, a correction calculation is first performed for the phase curve, which is then decomposed into the individual components ph(x,y)=ph1(x)+ph2(y)+ph3(x,y).

[0279] In the case of mathematically taking into account the aberration correction, the correction values ​​can also be determined by back calculation from the virtual observer window via the angle and the local grating period, as if the correction element were physically present in the intermediate image plane of the illumination device.

[0280] Fig.18The head 31 of an observer is schematically shown, wherein a display device with a light guide 26 is arranged in front of the right eye RA and the left eye LA, respectively. The two display devices form a so-called head-mounted display (HMD), which is attached to the head 31 of the observer. For a better understanding, the beam paths of the respective display devices are unfolded. However, in order to provide a suitable HMD, the beam paths of the two display devices will in practice be folded beam paths. For this purpose, for example, a deflection mirror can be arranged between the SLM and the light guide 26, so that in each case the SLM and the imaging elements of the optical system are arranged laterally near the head 31 of the observer. In each case, light is coupled from the outside of the head 31 into the light guide 26 arranged in front of the respective eye LA, RA, propagates therein, and is decoupled from the light guide of the light guide 26 in the direction of the observer's eyes RA, LA by means of a light decoupling device 25. Then, a corresponding virtual observer window is generated on the pupils of the eyes RA, LA, so that the observer can observe the generated or reconstructed scene. In Fig.18 In the embodiment of the present invention, a curved light guide is used in the light guide 26. In principle, it is not necessary to track the virtual observer window in the HMD, since the HMD is fixedly connected to the head 31 of the user and therefore no major changes in the position of the user occur. This is because if the user moves, the HMD is also simultaneously shifted to this position. However, in certain cases it is reasonable to track the virtual observer window precisely if an observer tracking device is arranged after the light guide, preferably in the direction of the light, which observer tracking device for example comprises at least one liquid crystal grating element and is designed to track the virtual observer window in at least one direction, preferably in the horizontal direction.

[0281] The use of grating elements will be mentioned and described herein in various contexts. Display devices, such as HMDs, often require the use of multiple wavelengths, such as red, green and blue, for color reconstruction or representation of a scene. For this purpose, it can be provided, for example, that light of different wavelengths is applied sequentially in time to the grating element, in particular in the case of a grating element with a settable period, a grating is provided separately for each wavelength; or if grating elements are used, for example as coupling grating elements and decoupling grating elements for coupling light into or decoupling light from a light guide, respectively, grating elements with sufficient wavelength selectivity are used, for example so that they act only as grating elements for one wavelength. In general, a stack of multiple grating elements is also to be understood as a coupled grating element according to the invention, for example a stack of three grating elements, one grating element for one primary color red, green, blue (RGB) or one wavelength.

[0282] The above general description of the invention and the above description of exemplary embodiments firstly relate to a display device having a light guide and / or a light guide device. However, it should be noted here that for the sake of clarity, in particular the description parts relating to the two-stage optical system and the determination of the sub-holograms by back calculation are also generally applicable to holographic or stereoscopic display devices without a light guide or a light guide device.

[0283] In general, a display device with a two-stage optical system will be described, wherein the SLM is illuminated by an illumination device and an intermediate image of the virtual observer window is generated in an intermediate image plane of the illumination device by at least one first imaging element of the optical system. This intermediate image of the virtual observer window is imaged at the position of the actual virtual observer window by at least one second imaging element of the optical system. In this case, a variable imaging system comprising at least one imaging element is arranged in the intermediate image plane of the illumination device. Prism functions and / or lens functions and / or phase curves for aberration correction can be written into at least one imaging element.

[0284] The above-described arithmetic aberration correction in the intermediate image plane of the illumination device can generally be used for a two-stage optical system even if no light guide or light guiding device is used.

[0285] The display device as a whole may also be, for example, a holographic projection system, where a real image of the SLM is generated on a screen, or also a head-mounted display, which has other components like conventional lenses or mirrors instead of a light guide.

[0286] Such a display device can advantageously be used in conjunction with, for example, Figure 7 and Figure 8 The system combination described in the applicant's application PCT / EP2017 / 071328 in which a filter element is used in the intermediate image plane of the illumination device to perform filtering. For example, the filtering is used to filter out the zero-order spot or to filter out a specific diffraction order. The content disclosed in this application will be incorporated herein as a whole. Therefore, a passive or variable amplitude element used for filtering in the intermediate image plane of the illumination device can be combined with at least one phase element of the variable imaging system proposed here to realize a prism function or a lens function or for aberration correction. In addition, in addition to filtering, the amplitude element can also be used for aberration correction.

[0287] As described in the applicant's application PCT / EP2017 / 071328, the lateral displacement of the virtual observer window in one or two diffraction orders can also be combined with the two-stage optical system described here with a variable phase element in the intermediate image plane of the illumination device. For example, if the lens function for shifting the SLM image in depth is implemented as a phase element or grating element of a variable imaging system with a lateral displacement of the position of the virtual observer window, the phase element or grating element should have a size as large as the entire area considered, i.e. as large as a number of diffraction orders in the intermediate image plane of the illumination device. The position of the grating element where the lens function is written can also be shifted laterally on this grating element, and the size of the area on the grating element where the lens function is written must be as large as the area corresponding to the observer window, i.e. at most as large as one diffraction order. Other diffraction orders can be filtered out, for example, by filtering in the intermediate image plane of the illumination device. For example, it can be a controllable filtering device, with which various diffraction orders can be optionally filtered out or transmitted. In the case of a back calculation from the virtual observer window, for example for aberration corrections, only the correspondingly shifted partial size of at most one diffraction order is also used for the calculation of the correction. In the case of an arithmetic correction in a laterally shifted virtual observer window, this can be taken into account by the corresponding linear phase term in the hologram plane or SLM plane in the calculation.

[0288] In general, an additional grating element with a controllable variable grating period close to the SLM can also be used, with which the position of the intermediate image of the observer window is shifted in the intermediate image plane of the illumination device by a written lens function, and in this intermediate image plane a larger phase element or grating element of the variable imaging system can be used, the size of which is large enough to include the entire feasible area in which the intermediate image of the observer window can be shifted, wherein the phase function of the prism function or lens function or the phase function for aberration correction is written locally only in the area of ​​the current position of the intermediate image of the virtual observer window.

[0289] The back calculation from the virtual observer window through the optical system to the SLM is generally applicable not only to the combination of the optical system with a light guide and / or a light guide device and / or to a two-stage optical system. However, the back calculation method can be applied particularly advantageously in combination with a two-stage optical system, which contains a light guide (especially a curved light guide) in the second imaging stage and includes a controllable variable imaging system located in the intermediate image plane of the illumination device, and wherein the back calculation is used to determine the aberration correction in the form of a phase function written in the variable imaging system.

[0290] The following description discusses in general, and in particular, the calculation of angles in a light guide and decoupling positions on a light guide of a light guide arrangement.

[0291] The path that the light beam has covered after a defined number of reflections in the light guide can be calculated based on the geometry of the light guide and the optical properties of the light coupling means and the light decoupling means.

[0292] exist Fig.19 In FIG. 1 , an example of a straight or planar light guide LGA is shown in illustration (a), and an example of a curved light guide LGB is shown in illustration (b). Fig.19 In a), light L is coupled into the light guide LGA of thickness d in such a way that it propagates at an angle β relative to the normal of the light guide LGA. Then, light L reaches the surface opposite to the coupling side after a distance Δx=dtanβ from the coupling position, and reaches the surface of light coupling again after traveling twice the distance 2Δx=2dtanβ. If the light beam L is decoupled from the light guide LGA again after N reflections, the distance between the coupling side and the decoupling side is: 2Ndtanβ.

[0293] exist Fig.19 In b), the propagation of light in a curved light guide LGB is shown, which represents a cross section of a circular arc. The inner surface has a radius r1 around the center K, and the outer surface has a larger radius r2 around the center K. The thickness of the light guide LGB is d=r2-r1, i.e. the difference between the two radii r1 and r2. The coupled incoming light L is incident at an angle β relative to the normal on the inner surface of the light guide LGB, since the radius r2 on the outer side of the light guide LGB is different from r1, at a different angle β-γ / 2 relative to the normal. After reflection on the outer side of the light guide LGB, the light beam L reaches the inner side again after it covers an angular segment on the γ circular arc. The following relationship comes from the sine law:

[0294] γ=2*(β-asin(sin(β)r1 / r2)).

[0295] Numerical example: a light guide with an inner diameter of 32 mm, an outer diameter of 36 mm, an angle β of 51.9°, and an angle γ of 15° of the arc section may cause the light to be reflected on the outside of the light guide until it is incident on the inside of the light guide again. For four reflections of the light in the light guide, the light will propagate over an arc in the light guide of, for example, 60°. From the equation above, for the case of a bent light guide from a known coupling position on the light guide and an angle β, the decoupling position on the light guide after a defined number of reflections can therefore also be calculated.

[0296] To couple light into a light guide using a grating element, the known grating equation results: sinβ 出射 =λ / g+sinβ 入射 , where λ is the wavelength, g is the grating constant of the grating element, and β 入射 is the incident angle of the light, β 出射is the angle resulting from the subsequent propagation of the light in the light guide. If the incident and exit media are the same, the grating equation applies in this form. For the case where light is incident from air and propagates in a light guide with a refractive index of n, the refraction at the boundary surface of the two media must also be considered: sinβ 在介质中 =1 / nsinβ 在空气中 , where β 在介质中 is the incident angle of light on the grating element in a medium with a refractive index of n, β 在空气中 is the angle of incidence of light in air.

[0297] Fig. 20 A straight or planar light guide LG is shown, wherein now it is considered that different beams of the light column are coupled into the light guide LG at different locations or positions. In this case, these different coupling positions vary by a distance Δx. Fig. 20 It can be clearly seen that, for example, two light beams L1 and L2 with different angles α1 and α2 in air are incident on the coupling grating element G 入射 Therefore, these light beams L1 and L2 are also coupled to the coupling grating element G in the light guide LG. 入射 Deflection of different propagation angles β1 and β2.

[0298] In a display device, the angular spectrum for coupling light into the light guide can be generated, for example, by the diffraction angle of an SLM with a predetermined pixel pitch. By appropriately positioning the decoupling grating elements on the light guide, the light beams L1 and L2 can be decoupled from the light guide again after one, two or three reflections in the light guide in the present case. Fig. 20 The decoupling grating element G is shown 出射 , which is used for the case of two reflections (N=2) of light at the boundary surface of the light guide LG. Fig. 20 In the example shown, it becomes more difficult to decouple the light from the light guide LG after four reflections at the boundary surface of the light guide, since the light beam L1 extending at the smaller angle β1 arrives after four reflections at the same position P on the boundary surface of the light guide as the light beam L2 extending at the larger angle β2 after three reflections of the light at the boundary surface of the light guide LG. If a decoupling grating element is arranged at this position, it can happen that the light beam L2 extending at the angle β2 is unintentionally decoupled after three reflections in the light guide, and therefore too early. For a given size of the light column to be coupled and a given angular spectrum of the light to be coupled, this unfavorable overlap of the decoupling areas can be avoided, for example, by a suitable choice of the thickness of the light guide and the grating constant of the coupling grating element.

[0299] In the following description, grating elements in light coupling devices and light decoupling devices are discussed more broadly and explained in more detail.

[0300] As already mentioned, the light decoupling device for decoupling light from the light guide of the light guiding device may optionally comprise a controllable grating element or also a passive grating element combined with a polarization switch.However, the light decoupling device may also comprise only a passive grating element.

[0301] A switchable grating element or a combination of a passive grating element and a polarization switch is required for a display device, in which a plurality of images of the SLM consisting of segments are generated by the light guide device. The display device may also comprise only a passive grating element without an additional switching element in a specific configuration, in which display device only a single image of the SLM is generated by the light guide device, which image therefore does not consist of segments. Specific configurations of light decoupling devices of light guide devices that can be used for such a display device are described more extensively below.

[0302] The optical coupling device may also include grating elements. The specific arrangement of the grating elements may also be used in a similar form for the optical coupling device and the optical decoupling device. The controllable or passive grating elements may optionally be designed to be transmissive or reflective. They may optionally be arranged on an inner boundary surface, for example, between the optical waveguide core and an outer layer, such as a dielectric layer stack, or on the outer surface of the optical waveguide. The optical decoupling device may also include a combination of reflective and transmissive grating elements. In a display device having a light guide device, in the optical decoupling device, the transmissive grating elements are preferably arranged on the boundary surface or surface of the light guide facing the observer, and the reflective grating elements are preferably arranged on the boundary surface or surface of the light guide facing away from the observer.

[0303] In the display device, the light coupling device may also have a transmission grating element preferably located on a surface or boundary surface facing away from the observer, and a reflection grating element preferably located on a surface or boundary surface of the light guide facing the observer.

[0304] The deflection angle of the grating element is generally wavelength-dependent. The same grating element will typically deflect red light at a larger angle than green or blue light. For a display device with a light guide, light of different wavelengths, such as red, green and blue (RGB), is also advantageously decoupled at the same place or position of the light guide after the same predetermined number of light reflections within the light guide. In addition, light of different wavelengths then also propagates at the same angle from the decoupling position of the light guide to the observer area, i.e. the virtual observer window or the optimal light spot. This can be most easily achieved if the coupling angle and the decoupling angle of the light are equal for the wavelengths used (red, green, blue (RGB)). In order to couple the light into the light guide, for example, a reflector element can also be used, and the use of a reflector element instead of a grating element allows the coupling angle to be implemented independently of the wavelength.

[0305] The use of grating elements for coupling light into or decoupling light from a light guide and the implementation of equal angles for various colors or wavelengths requires the use of different grating elements for each wavelength or a single grating element whose grating period can be set for various colors. For example, it is known that volume gratings can have limited angular selectivity and wavelength selectivity. For example, volume gratings can be produced that advantageously deflect substantially only red light or only green light or only blue light, because they have very low diffraction efficiency at the corresponding other wavelengths.

[0306] The light coupling device or light decoupling device may comprise a stack of three grating elements, for example, a volume grating for red light, a volume grating for green light and a volume grating for blue light. The three volume gratings are designed so that they each also deflect the red light, green light and blue light incident on the volume grating at the same angle at the same angle. It is also known that a volume grating can reveal multiple grating functions in a single layer. As an alternative to a stack of grating elements, the light coupling device or light decoupling device can therefore also comprise a single grating element with multiple revealed grating functions for deflecting red light, green light and blue light. In the case of a stack of grating elements, all grating elements can optionally be designed to be switchable and / or controllable. However, a plurality of passive grating elements are then preferably used in combination with a single switching element, such as a polarization switch.

[0307] Another feasible way to achieve the same deflection angle in coupling and decoupling of light of different wavelengths is to use a grating element that deflects multiple wavelengths at different angles in combination with a correction grating element, each correction grating element respectively correcting the deflection angle of a single wavelength so that the deflection angle corresponds to the deflection angle of another wavelength. In such an optical coupling device or optical decoupling device, for example, the first grating element for deflecting multiple wavelengths can be designed as a surface relief grating or a polarization grating, and the other grating elements for correcting the deflection angle of one wavelength can each be designed as a volume grating. The first grating element deflects, for example, red light, green light and blue light, wherein the green light is deflected at a desired angle, but the red light is deflected at an angle that is too large and the blue light is deflected at an angle that is too small. Then, the further arranged grating element corrects the deflection angles of the blue light and the red light, so that the red light, green light and blue light are coupled into the light guide at the same deflection angle and decoupled again. In order to correct the deflection angle per wavelength, more than one grating element can also be used per wavelength, for example, a volume grating having two grating elements is arranged in each case per wavelength. The first volume grating for correcting the deflection angle can each be pre-deflected. The second volume grating can then deflect the pre-deflected light in such a way that the desired exit angle is achieved or generated. In this case, use is made of the fact that volume gratings with large deflection angles have overall narrower wavelength selectivity than volume gratings with small deflection angles. By means of the narrower wavelength selectivity, it is easier to achieve that the volume grating deflects light of only one wavelength.

[0308] In particular, the first grating element of the optical coupling device or optical decoupling device for deflecting multiple wavelengths can be designed to be switchable and / or controllable. The other grating elements for correcting the deflection angle of one wavelength can each be designed to be passive. However, all grating elements of the optical coupling device or optical decoupling device can also be designed to be passive. If the decoupling of light requires a switchable element or a switching element, the passive grating element can then be combined again with a polarization switch as a switching element. However, all grating elements can also be designed to be switchable and / or controllable.

[0309] In the configuration of the optical decoupling device, a passive grating element is used in combination with a switching element (e.g. a polarization switch), or at least one grating element itself is designed to be polarization selective, i.e., only deflects light of a predetermined polarization, or an additional polarization element is arranged between the polarization switch and the grating element.

[0310] However, in a configuration of the light decoupling device having only passive grating elements and no switching elements, in which only light of a defined polarization is decoupled, at least one grating element itself is designed to be polarization selective, or an additional polarization element is arranged between the polarization switch and the grating element.

[0311] A combination of polarization selectivity, wavelength selectivity and angle selectivity can be achieved, for example, using a specific type of volume grating. A volume grating having a grating structure made of a birefringent liquid crystal material and an isotropic material having a refractive index that is the same as the conventional or unconventional refractive index of the liquid crystal material can be used as a first linear polarization similar to the grating and a second linear polarization perpendicular to the first linear polarization similar to the isotropic material. Examples of such gratings are polymer dispersed liquid crystal (PDLC) gratings, polymer gratings or polymer liquid crystal polymer slices (POLICRYPS) gratings. These gratings are referred to as polarization selective volume gratings (PSVG) hereinafter. Liquid crystal-based polarization selective volume gratings can also be designed to be switchable, where the grating is arranged between two electrodes and the orientation of the liquid crystal is changed by an electric field. In the first switching state (hereinafter referred to as on), these gratings have a deflection effect on linearly polarized light (usually p-polarized light), but have a non-deflection effect on a linear polarization rotated 90° therefrom (usually s-polarization). In the second switching state (hereinafter referred to as off), these gratings have no effect on s-polarization or p-polarization. A specific type of switchable polarization-selective volume grating is sometimes also referred to in the literature as a "switchable Bragg grating (SBG)". In this article, the name PSVG is also used for this purpose. Another type of grating with high diffraction efficiency in a single diffraction order is a polarization grating (PG). Conventional polarization gratings deflect, for example, left-handed circularly polarized light in the +1 diffraction order and right-handed circularly polarized light in the -1 diffraction order, or vice versa, depending on the design of the grating. Compared to volume gratings, conventional polarization gratings have a wide-angle acceptance and high efficiency for a wide range of wavelengths.

[0312] However, special types of polarization gratings with small grating periods have the following properties: they deflect only light of defined circular polarization, but transmit without deflecting circularly polarized light with the opposite rotation direction. In order to distinguish them from polarization selective volume gratings (PSVG) and conventional polarization gratings (PG), they are referred to as Bragg polarization gratings (B-PG) hereinafter. These gratings will be described in more detail below.

[0313] In one configuration of the optical decoupling device with an additional polarization element, a wire grid polarizer (WGP) is arranged on the inner or outer cladding of the light guide. The wire grid polarizer can also be used as a thin film and can also be laminated, for example, onto a curved surface, such as the cladding of a curved light guide. A grating element is arranged or applied on the outer surface of the wire grid polarizer. The wire grid polarizer has the property of reflecting a first linear polarization light and transmitting a second linear polarization light perpendicular thereto. Therefore, the first polarization light is reflected by the wire grid polarizer on the light guide cladding and then propagates further in the light guide and therefore does not reach the grating element at all. The second linear polarization light perpendicular to the first linear polarization light passes through the wire grid polarizer and is incident on at least one grating element, for example a grating element stack consisting of three volume gratings, and can be deflected from the grating element or one of the grating elements in the case of a grating element stack being arranged and decoupled from the light guide.

[0314] As already mentioned, a switchable or controllable grating element or a polarization switch used in combination with a passive grating element can be divided into a plurality of parts, so that each part has a separate electrode, using which the switching of polarization can be performed in sections by applying an electric field. The term "part" also includes the approximate structure according to the invention. For example, a switchable or controllable grating element or a switching element (e.g. a polarization switch) can only be divided into three or four approximate parts, each of which has a separate electrode and has a width of several millimeters, e.g. 5mm-10mm. However, it can be divided more finely into a plurality of small parts, e.g. into strip-shaped parts with a width of 0.5mm.

[0315] A switchable or controllable grating element or a switching element divided into a plurality of segments can be arranged or used in a display device as follows, wherein a single image of the SLM or a plurality of images consisting of segments is generated by a light guide:

[0316] In one embodiment of the display device, the number of reflections of the light in the light guide to the decoupling is set by switching on and off a specific part of the switchable or controllable grating element or at least one switching element. For this purpose, it can also be provided that a specific part is set to one drive state and other parts are set to another drive state to change or vary or define the number of reflections of the light in the light guide.

[0317] In another embodiment of the display device, the decoupling position of the light is changed in fine steps by switching on and off specific parts of the switchable or controllable grating element or at least one switching element or also using different driving states of parts of a fixed number of reflections of the light at the boundary surface of the light guide. For example, this can be used to shift the position of a single segment of the multiple images of the SLM in fine steps. For example, this can be used in combination with gaze tracking to position a specific segment of the multiple images in the center of the observer's gaze direction.

[0318] Fig.21 A light guide device with a light guide LG and a light decoupling device is schematically shown, wherein a polarization switch PS is arranged on one side of the light decoupling device. The polarization switch PS itself can, for example, consist of a liquid crystal layer between electrodes to which an electric field can be applied. In this case, left-handed circularly polarized light CL initially propagates in the light guide LG, where, obviously, the left-handed circularly polarized light CL is Fig.21 The left side of the coupled into the light guide LG and propagates to the right via total reflection in the light guide LG. Fig.21 It can be further seen that the polarization switch PS is divided into two parts, which are referred to as the left part and the right part in the following for simplicity. Fig.21 In the left part of the left side, the polarization switch PS is controlled so that it does not change the polarization of the incident light. The left part is in the closed state. In the right part, the polarization switch is controlled so that it changes the polarization of the incident left-handed circular light CL to provide right-handed circular light CR after the light passes through the right part of the polarization switch PS. The right part of the polarization switch PS is in the open state.

[0319] On the outside of the light guide LG, i.e. after the polarization switch PS, a polarization grating element with volume grating properties is arranged, whereby a Bragg polarization grating B-PG is arranged. This Bragg polarization grating B-PG has the following properties: it deflects right-handed circularly polarized light CR by an angle defined by the grating period of the Bragg polarization grating B-PG, but does not deflect left-handed circularly polarized light CL. An additional carrier substrate, for example made of plastic, may be arranged between the polarization switch PS and the Bragg polarization grating B-PG and between the Bragg polarization grating B-PG and the outer surface of the light guide. Such a carrier substrate may be provided, for example, Fig.21 Shown but not required.

[0320] In operation of the light guide device, the left-handed circularly polarized light CL that passes through the left-hand portion of the polarization switch PS is then incident on the Bragg polarization grating B-PG, passes through it without deflection and is incident on the boundary surface of the light guide LG of the light guide device in such a way that total reflection TIR occurs. The light then propagates further in the light guide LG. The right-handed circularly polarized light CR that passes through the right-hand portion of the polarization switch PS is incident on the Bragg polarization grating B-PG, is deflected accordingly by the Bragg polarization grating B-PG, and is therefore perpendicularly incident on the boundary surface of the light guide LG into the surrounding dielectric air and is decoupled from the light guide LG. As already described, a correction grating element may also be present after the Bragg polarization grating B-PG, which is used in the light guide device to decouple light of multiple wavelengths from the light guide at the same angle.

[0321] Fig. 22 A light guide device is schematically shown, which includes a wire grid polarizer WGP in an optical decoupling device. Linear s-polarized light S propagates here in the light guide LG of the light guide device. The polarization switch PS provided is divided into two parts again here, into a right part and a left part. In the driven state or the on state of the left part of the polarization switch PS, it changes the incident s-polarized light S into p-polarized light P. As can be seen in the right part of the polarization switch PS, when in the closed state, the incident s-polarized light S passes through this part unchanged, so that the s-polarized light S still exists afterwards. Afterwards, the s-polarized light S is incident on the wire grid polarizer WGP. The wire grid polarizer WGP reflects the s-polarized light S, and then the s-polarized light S propagates further in the light guide LG, as shown by the arrow. In contrast, the p-polarized light P converted by the left part of the polarization switch PS passes through the wire grid polarizer WGP and is incident on the quarter wave plate QWP. The quarter wave plate QWP converts the incident p-polarized light P into right-handed circularly polarized light CR, which is then incident on the Bragg polarization grating B-PG. The right-handed circularly polarized light CR is deflected by the Bragg polarization grating B-PG, and then vertically incident on the boundary surface of the light guide LG, enters the surrounding dielectric air, and is decoupled from the light guide LG. The advantage of the light guide device constructed in this way is that the insufficient performance of the polarization switch PS and the quarter wave plate QWP can be compensated.

[0322] If less than 100% of the light is changed from s-polarized light to p-polarized light by the polarization switch PS, the light is reflected at the wire grid polarizer WPG. If less than 100% of the light is changed to circularly polarized light by the quarter wave plate QWP, the light is therefore reflected at the boundary surface by total reflection and also propagates further in the light guide LG. Thus, interference light with inappropriate polarization is prevented from being inadvertently decoupled from the light guide LG as well.

[0323] The light guide arrangement can also be used in combination with correction grating elements for other wavelengths of the primary colors RGB so that light of various wavelengths is decoupled from the light guide at equal angles.

[0324] Fig.23 The light guide device is schematically shown in FIG. 1 , which also includes a wire grid polarizer WGP located in the light decoupling device, similar to Fig. 22 The light guide LG and the light decoupling device now have a volume grating VG instead of a Bragg polarization grating B-PG. No quarter wave plate is provided here. The light propagation through the light guide LG and the light decoupling device is similar to Fig. 22 . Obviously, if a part of the polarization switch PS is in the closed state, the s-polarized light S is reflected at the wire grid polarizer WGP. If a part of the polarization switch PS is in the open state, the s-polarized light S incident thereon is converted into p-polarized light P, passes through the wire grid polarizer WGP, and is incident on the volume grating VG. In this exemplary embodiment, the volume grating VG itself is not designed to be polarization selective. It can be, for example, a volume grating made of a conventional photopolymer material. The p-polarized light P is deflected by the volume grating VP and then vertically incident on the boundary surface of the light guide LG, enters the surrounding dielectric air, and is decoupled from the light guide LG.

[0325] exist Fig.24 A light guide device with a light decoupling device is schematically shown in FIG. Fig.23 The only difference is that the volume grating VG is designed to be reflective. In the off state of the polarization switch PS, the incident s-polarized light S is reflected at the wire grid polarizer WGP and further propagates in the light guide LG. However, if a part of the polarization switch PS is in the on state, the incident s-polarized light is converted by the polarization switch PS into p-polarized light P, which passes through the wire grid polarizer WGP and is incident on the reflective volume grating VG. The p-polarized light P is deflected and reflected by the volume grating VG. Then, the reflected p-polarized light P passes through the optical decoupling device and the light guide LG vertically again, and is decoupled from the light guide LG on the opposite side.

[0326] exist Fig.25A light guide device is schematically shown in , wherein the light decoupling device comprises a switchable polarization selective volume grating PSVG, for example, based on liquid crystal. If the switchable polarization selective volume grating PSVG is in a certain driving state or in an off state, neither the s-polarized light S nor the p-polarized light P incident on the switchable polarization selective volume grating PSVG is deflected, but is reflected at the boundary surface of the light guide LG by total reflection and then propagates further in the light guide LG, as indicated by the leftmost arrow. However, if the switchable polarization selective volume grating PSVG is in another driving state or in an on state, the p-polarized light P is decoupled from the light guide LG. However, the s-polarized light S is reflected at the boundary surface of the light guide LG and propagates further in the light guide LG. The volume grating itself may be switchable or controllable here, wherein the switchable polarization selective volume grating PSVG is divided into two parts so as to Fig.25 The ability to control a switchable polarization selective volume grating PSVG can be better understood in conjunction with the optical path, thereby enabling a better description of the ability to control a switchable polarization selective volume grating PSVG. In a similar manner, such a light-guiding device can also be realized using a switchable Bragg polarization grating, using only circular light instead of linearly polarized light.

[0327] exist Fig.26 A light guide device is schematically shown in FIG. 1 , whose optical decoupling device includes a Bragg polarization grating B-PG and a plurality of volume gratings VG that deflect light of all wavelengths at different angles. The plurality of volume gratings VG form a volume grating stack, which, in this exemplary embodiment, has four volume gratings VG1, VG2, VG3 and VG4. The light R of a red wavelength, the light G of a green wavelength and the light B of a blue wavelength are now incident on the Bragg polarization grating B-PG at the same angle. In this case, the light G of a green wavelength is deflected so that it emerges from the Bragg polarization grating B-PG perpendicular to the surface or boundary surface of the light guide LG. However, the light R of a red wavelength and the light B of a blue wavelength emerge from the Bragg polarization grating B-PG at different angles, as shown based on FIG. Fig.26 As shown by the dotted arrows and solid arrows in .

[0328] The Bragg polarization grating B-PG is followed by a volume grating stack with four volume gratings VG1, VG2, VG3 and VG4. These volume gratings VG1, VG2, VG3 and VG4 of the volume grating stack are designed to be wavelength selective. In this exemplary embodiment, this means that the light G of the green wavelength passes through all four volume gratings VG1, VG2, VG3 and VG4 without deflection and is then decoupled from the light guide LG. The light R of the red wavelength passes through the first two volume gratings VG1 and VG2 without deflection and is only deflected by the last two volume gratings VG3 and VG4 so that it emerges from the light guide LG at the same angle as the light G of the green wavelength. The blue wavelength light B is deflected only by the first two volume gratings VG1 and VG2 and passes through the last two volume gratings VG3 and VG4 without being deflected, wherein the volume gratings VG1 and VG2 deflect the blue wavelength light in the following manner, that is, so that it emerges from the light guide LG at the same angle as the green wavelength light G or the red wavelength light.

[0329] In each case, a pair of volume gratings is used to correct the angle at which blue wavelength light and red wavelength light exit from the light guide, because the volume grating has a larger deflection angle and can more easily set a good wavelength selectivity. For example, before the volume grating VG2 deflects the blue wavelength light, the blue wavelength light B is first deflected to a larger angle by the volume grating VG1 so that it exits perpendicularly to the surface or boundary surface of the light guide LG.

[0330] The following description relates to the individual influencing of the imaging beam path and the illumination beam path in a display device having a diffractive element which is located in the Fourier plane of the SLM or in the light source plane of the illumination device or in the image plane of the SLM.

[0331] In a holographic display device or preferably another three-dimensional display device, such as a stereoscopic display device, at least one diffractive optical element is used in such a way that it substantially only influences the illumination beam path or only influences the imaging beam path. The at least one diffractive optical element is also referred to as a variable imaging system in the above description of the invention. Since the overall influence involving the illumination beam path and the imaging beam path is now mainly envisaged, the name "diffractive optical element" is used below.

[0332] The influencing of only the illumination beam path or only the imaging beam path is achieved in that at least one diffractive optical element is arranged in or near the image plane of the SLM to influence only the illumination beam path. Conversely, at least one diffractive optical element can be arranged in or near the Fourier plane of the SLM to influence only the imaging beam path. Fig.12 and Fig.13 In the embodiment, for example, at least one diffractive element, which is identified as a variable imaging system 30, is arranged in the light source plane of the illumination device so that it only affects the imaging beam path. Fig.12 and Fig.13 The first imaging element 27 shown in FIG. 2 , which is arranged in the plane of the SLM, may have at least one diffractive element which then only influences the illumination beam path.

[0333] In a three-dimensional display device, in which the light source image of at least one light source of the illumination device exists in the observer plane, the diffractive optical element in or near the Fourier plane of the SLM will affect the imaging beam path and thus affect the image plane of the SLM without changing the position and size of the observer area (especially the virtual observer window). However, the diffractive optical element in or near the image plane of the SLM will affect the position and size of the observer area without affecting the image distance of the SLM. In a three-dimensional display device, in which the image of the SLM is generated in the observer plane, and vice versa, the diffractive optical element in or near the image plane of the SLM affects the position of the reference plane used for hologram calculation (for example, it can be selected as the virtual image plane in the meaning of patent document WO2016 / 156287A1) without changing the position and size of the observer area. The contents of patent document WO2016 / 156287A1 are all incorporated herein. The diffractive optical element in or near the Fourier plane of the SLM affects the position and size of the observer area without affecting the distance of the reference plane.

[0334] The specific configuration is described in more detail below:

[0335] In particular, in a configuration for a display device which generates an image of a light source in an observer plane, a two-stage system is used which generates an intermediate image of the observer region or of the light source in the Fourier plane of the SLM, and wherein at least one diffractive optical element is arranged in the intermediate image plane or very close to the intermediate image plane in order to influence only the imaging beam path and to keep the position of the observer region unchanged. Fig.12 . In this case, at least one diffractive element or a variable imaging system 30 is arranged in the intermediate image plane of the illumination device. In general, such an arrangement with at least one diffractive element can also be used in devices without a light guide.

[0336] In particular, in a display device which generates an image of the light source in an observer plane, at least one diffractive optical element located in the Fourier plane of the SLM can have a lens function which influences the position of the image plane of the SLM.

[0337] In a display device that generates an image of a light source in an observer plane, the position of the image plane of the SLM can be preferably adjusted by at least one diffractive optical element in the Fourier plane of the SLM so that the average size of the sub-holograms used to calculate the preferred three-dimensional scene is reduced compared to a display device that does not use a diffractive optical element.

[0338] At least one diffractive optical element in the Fourier plane of the SLM can be designed in such a way as to correct aberrations in the imaging beam path. At least one diffractive optical element can be designed to be controllable. Furthermore, the diffractive optical element can be designed as a liquid crystal grating (LCG). Furthermore, two diffractive optical elements can also be used, wherein a horizontal cylindrical lens function is written into one diffractive optical element and a vertical cylindrical lens function is written into the other diffractive optical element.

[0339] In a display device that generates an image of a light source in an observer plane and generates segmented multiple images of an SLM to produce a large field of view, at least one controllable diffractive optical element is arranged in the Fourier plane of the SLM to write a lens function into the at least one diffractive optical element for each segment of the multiple images to generate an image plane of the SLM at a similar or equal distance from the observer for all segments.

[0340] In a display device, the display device generates an image of a light source in an observer plane and generates segmented multiple images of an SLM to produce a large field of view, and it includes a light guide having different numbers of reflections in the light guide to generate individual segments of the multiple images of the SLM, at least one controllable diffractive optical element is arranged in the Fourier plane of the SLM to equalize the different optical paths of the light of the individual segments in the light guide, and to generate an image plane of the SLM at a similar or equal distance from the observer for all segments.

[0341] In a display device, which generates an image of a light source in an observer plane and generates segmented multiple images of an SLM to produce a large field of view, and which includes a light guide having different numbers of reflections in the light guide to generate individual segments of the multiple images of the SLM and at least one grating element for coupling light into the light guide and / or decoupling light from the light guide, respectively, at least one controllable diffractive optical element can be arranged in the Fourier plane of the SLM to correct aberrations in the imaging beam path generated by the at least one grating element.

[0342] In a display device, which generates an image of a light source in an observer plane and generates segmented multiple images of an SLM to produce a large field of view, and which includes a light guide having different numbers of reflections in the light guide to generate individual segments of the multiple images of the SLM and at least one grating element for coupling light into the light guide and / or decoupling light from the light guide, respectively, at least one controllable diffractive optical element can be arranged in an image plane of the SLM to correct aberrations in the illumination beam path generated by the at least one grating element.

[0343] In a display device that generates a light source image in an observer plane and generates segmented multiple images of an SLM to generate a large field of view, and that includes a light guide having different numbers of reflections in the light guide to generate individual segments of the multiple images of the SLM, at least one controllable diffractive optical element may be arranged in the image plane of the SLM to equalize the different optical paths of light in the light guide for the individual segments of the multiple images of the SLM, and to generate an observer area at the same position for all the segments. The following will also be described with respect to this configuration of the display device:

[0344] If the curved light guide forms a circular arc cross section with the center of the observation area as the center point of the circle, and if, due to the use of a diffractive optical element in the image plane of the SLM, the light is decoupled from the light guide after a different number of reflections in the light guide for such a light guide, then an observer area at the same position is advantageously produced for all segments of the multiple images of the SLM, so that no additional correction is required in this respect. However, this does limit the geometry of the light guides that can be used.

[0345] The described embodiments with at least one diffractive optical element located in the image plane of the SLM can therefore also use other light guides, such as straight or planar light guides or curved light guides with a curvature deviating from a circular arc cross-section, but can generate observation areas for multiple segments at the same position.

[0346] In a display device that generates an image of a light source in an observer plane, the distance of the observer plane at which an observer's eye is focused can be detected in a holographic or stereoscopic system by gaze tracking. At least one controllable diffractive optical element located in the Fourier plane of the SLM can be used to change the position of the image plane of the SLM so that the image plane of the SLM is positioned at a distance from the observer that is similar or equal to the distance detected by gaze tracking.

[0347] However, the invention is not limited to the embodiments shown and described here. For example, the exemplary embodiments or embodiments mentioned here can also be transferred accordingly to a display device which generates an image of the SLM in the observer plane.

[0348] The following embodiments will be briefly described as examples: In a display device, which generates an image of the SLM in an observer plane and generates segmented multiple images of diffraction orders in the Fourier plane of the SLM to generate a large field of view, at least one controllable diffractive optical element can be arranged in the image plane of the SLM to write the lens function into the at least one diffractive optical element for each segment in the following manner, so that the Fourier plane of the SLM generates a reference plane for hologram calculation, which reference plane is at a similar or equal distance from the observer for all segments.

[0349] Polarization selective Bragg grating elements or Bragg polarization gratings in general, which will also be discussed below, can be advantageously used in a light decoupling device of a light guide to decouple light from the light guide. The light guide can then be advantageously used in a head mounted display.

[0350] The Bragg polarization grating can be fabricated by a bulk light alignment method, which ensures the independence of the molecular orientation of each pattern surface of the alignment layer and enables the formation of a tilted interference pattern. For this purpose, it is only necessary to rotate the pattern by an appropriate angle. In this case, it is envisaged that such tilted holographic polarization exposure can achieve complex 3D alignment of LC polymers without the use of additional chemical additives (chiral LC additives) or alignment layers. Advantageously, the LC directors are positioned perpendicular to the interference pattern in the plane. This means that the effective local birefringence does not depend on the tilt of the interference pattern. This is an advantage of photo-crosslinking LC polymers.

[0351] It can be determined by simulation that when a right-handed circularly polarized beam is incident on a Bragg polarization grating, diffraction occurs in the -1 diffraction order, where the Bragg polarization grating converts the incident right-handed circularly polarized light into left-handed circularly polarized light. In this case, the diffraction efficiency generated in the -1 diffraction order is about 98%. The other diffraction orders (zero diffraction order and +1 diffraction order) have negligible diffraction intensities. In contrast, if left-handed circularly polarized light incident on a Bragg polarization grating is used, diffraction hardly occurs in the -1 diffraction order and +1 diffraction order, but most of the light is in the zero diffraction order, where the diffraction efficiency is about 93%. The left-handed circularly polarized light passes through the Bragg polarization grating without being deflected and converted into another polarization state.

[0352] The Bragg polarization grating has a wide spectral acceptance and a wide angular acceptance due to its thin thickness. The spectral acceptance and angular acceptance of the Bragg polarization grating optimized for normal incident light with a wavelength of λ=532nm, for example, were measured using right-handed circularly polarized laser beams with wavelengths of 488nm, 532nm and 633nm, and corresponding results were obtained. In this case, the diffraction efficiency (η) of approximately more than 90% in the first diffraction order at the green wavelength was ±1 ) has almost the same diffraction efficiency for red and blue wavelengths. This in turn has the advantage that the grating element can be used over the entire visible spectral range.

[0353] The angular acceptance of the Bragg polarization grating is about 35°.

[0354] Due to the unique properties of such Bragg polarization gratings, such as the high optical quality of the film, high diffraction efficiency, wide angle or wide angle acceptance, and large spectral acceptance, such Bragg polarization gratings can be used in a wide range of applications. For example, they can be advantageously used in head-mounted displays (HMDs) or can also be used in devices for AR (augmented reality) applications or VR (virtual reality) applications. These grating elements, combined with polarization switches, achieve very efficient beam deflection of coherent light. In the case of using a wavelength of 532nm, a deflection angle of 42° in air (i.e., the angle between the two "effective" diffraction orders (i.e., the zeroth and first diffraction orders) of the Bragg polarization grating) was achieved in the simulation. The switching contrast (i.e., the ratio of the diffraction efficiency to the relative circular polarization) can be about 100. The specific polarization and diffraction properties of the Bragg polarization grating provide the option of combining multiple such grating elements in a stack. For example, a grating element stack may include two such grating elements, which are designed for normal incident light of green light. In operation, such a grating element stack will deflect the incident light beam in the +1st diffraction order or the -1st diffraction order, depending on the polarization state of the light (right-handed circularly polarized light or left-handed circularly polarized light). The two grating elements of the grating element stack have the same period Λ=0.77 μm and the same tilt angle, but opposite tilt angles of the interference pattern. By holographic exposure, the rotation angle It can be held at +28° or -28°. After holographic exposure and blending, the grating elements are fixed to each other using UV-curing glue.

[0355] A right-handed circularly polarized light beam incident on the grating element stack is diffracted by the first grating element in the -1 diffraction order and passes through the second grating element without diffraction due to its large angular deviation from the Bragg angle of the second grating element. A left-handed circularly polarized light beam incident on the grating element stack is not diffracted by the first grating element but is diffracted by the second grating element in its +1 diffraction order. The diffraction efficiency of the grating element stack in the ±1 diffraction order is about 85%. Such a grating element stack provides a diffraction angle of ±42° at a wavelength of 532 nm, which results in a total deflection angle of 84° in air. Such an efficient, large and symmetrical one-step polarization-dependent light deflection cannot be achieved using a single Bragg polarization grating.

[0356] In particular in a light-guiding device or a display device according to the invention, such a grating element stack can be used advantageously or else only a single Bragg polarization grating can be used.

[0357] Furthermore, combinations of embodiments and / or exemplary embodiments are possible. Finally, it should also be noted that the exemplary embodiments described above are only used to describe the claimed teachings, but do not limit the teachings to the exemplary embodiments.

Claims

1. A display device, comprising: A lighting device, comprising at least one light source, at least one spatial light modulation device, a light guide having different numbers of reflections therein to generate respective segments of a plurality of images of the spatial light modulation device; an optical system configured as a two-stage optical system, wherein a light source image of the at least one light source of the illumination device or an image of the at least one spatial light modulation device can be generated using the two-stage optical system; as well as At least one variable imaging system, the at least one variable imaging system being configured to correct aberrations using a phase curve and / or a prism function and / or a lens function, the at least one variable imaging system being arranged close to an intermediate image plane of at least one light source of the illumination device or an image plane of the at least one spatial light modulator, or the at least one variable imaging system being arranged in an intermediate image plane of at least one light source of the illumination device or in an image plane of the at least one spatial light modulator, wherein the display device generates an image of the light source in an observer plane and generates multiple images of segments of the spatial light modulator to generate a large field of view, and wherein at least one controllable diffractive optical element is arranged in a Fourier plane of the spatial light modulator to equalize different optical paths of light of each segment in the light guide and to generate an image plane of the spatial light modulator at a similar or equal distance from an observer for all segments, or wherein at least one controllable diffractive optical element is arranged in the image plane of the spatial light modulator to equalize different optical paths of light of each segment of the multiple images of the spatial light modulator in the light guide and to generate an observer area at the same position for all segments.

2. The display device according to claim 1, wherein the at least one variable imaging system is arranged in a middle plane of the light source image of the illumination device for correcting aberrations in the imaging optical path.

3. The display device according to claim 1, wherein the at least one variable imaging system is arranged in an image plane of the at least one spatial light modulation device for correcting aberrations in the illumination optical path. 4 . The display device according to claim 1 , wherein a virtual observation area can be generated within an image plane of the light source or within an image plane of the spatial light modulation device.

5. The display device of claim 1, wherein the imaging of the spatial light modulation device defines a field of view within which information of a scene encoded in the spatial light modulation device is reconstructed for observation through a virtual observation area.

6. A display device according to claim 1, wherein the optical system is configured to generate an intermediate image of the at least one light source of the illumination device in a first stage using at least one first imaging element of the optical system, wherein in a second stage, the intermediate image of the light source is imaged in a virtual observation area located after the spatial light modulation device in the optical path using at least one second imaging element of the optical system.

7. The display device according to claim 1, wherein the at least one variable imaging system is arranged behind the at least one spatial light modulation device in the direction of light.

8. A display device according to claim 1 or 7, wherein the at least one variable imaging system is arranged to be close to or located in an intermediate image plane of the at least one light source of the illumination device, and / or the at least one variable imaging system is arranged to be close to or located in an image plane of the at least one spatial light modulator device.

9. The display device of claim 1, wherein the at least one variable imaging system comprises at least one controllable imaging element.

10. The display device according to claim 9, wherein the controllable imaging element is designed as a grating element or a controllable liquid crystal element or at least two lens elements with a variable spacing. The display device according to claim 10 , wherein the grating elements have a controllable variable period.

12. The display device according to claim 1, wherein a variable prism function or a variable lens function and / or a variable complex phase function is written into at least one controllable imaging element of the at least one variable imaging system.

13. The display device according to claim 1 or 7, wherein the at least one variable imaging system comprises two controllable liquid crystal elements as imaging elements, and both of the two controllable liquid crystal elements can be designed to be reflective.

14. The display device of claim 1, wherein the at least one variable imaging system is configured to cause an image of the at least one spatial light modulation device to move in depth.

15. A display device according to claim 1, wherein during the reverse calculation of the direction from the virtual observation area toward the at least one spatial light modulator, the aberration correction in the imaging light path is combined with the determination of the amplitude and phase of the hologram to correct the incorrect angle of the light beam relative to its target position through a correction function.

16. A display device according to claim 1, wherein the optical system is used to generate multiple images composed of fragments of the at least one spatial light modulator, wherein the multiple images define a field of view, and information of the scene encoded in the at least one spatial light modulator is reconstructed within the field of view for observation through a virtual observation area in a light source image plane.

17. A display device according to claim 1, wherein the optical system is used to generate a plurality of images of diffraction orders consisting of fragments in the Fourier plane of the at least one spatial light modulator, wherein the plurality of images define a field of view, and information of the scene encoded in the at least one spatial light modulator is reconstructed within the field of view for observation through a virtual observation area in the image plane of the at least one spatial light modulator.

18. A display device according to claim 1, wherein the position of the image plane of the at least one spatial light modulator can be moved in each fragment of the multiple images of the at least one spatial light modulator by adjusting the focal length of the imaging element of the variable imaging system so as to minimize the maximum size of the sub-hologram.

19. The display device according to claim 15, wherein the correction function is calculated once for each segment of the plurality of images of the at least one spatial light modulation device and stored in a value table.

20. The display device of claim 1, wherein the two-stage optical system is configured to compensate for astigmatism.

21. A display device according to claim 20, wherein the two-stage optical system includes cross-cylindrical imaging elements, each of which has a variable focal length or a controllable grating element with cylindrical lens function, which is arranged in the intermediate image plane of the virtual observation window.

22. A display device according to claim 21, wherein for each segment of the multiple images of the at least one spatial light modulator, the focal length of the cylindrical imaging element or the grating element is set in the following manner, that is, horizontal and vertical images of the at least one spatial light modulator visible through the virtual observation window are produced in similar depth planes.

23. The display device according to claim 1, wherein the display device is configured as a head-up display device.

24. A head mounted display having two display devices, each of which is designed according to the display device according to any one of claims 1 to 22 and is respectively allocated to a left eye and a right eye of an observer.

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