Switchable holographic display

Abstract

In a first aspect, the invention relates to a holographic display device for the switchable display of images, wherein a light source, a light guide and at least two holographic diffraction gratings are configured for illumination of the at least two holographic diffraction gratings by light from the light source coupled into the light guide. Each holographic diffraction grating generates an image. Furthermore, a controllable light gate is allocated to each holographic diffraction grating. The light gate is configured to regulate the brightness of the generated image. In a further aspect, the invention relates to an operating device comprising a holographic display device as described and at least one operating element having at least one sensor. The sensor can detect an interaction with the operating element and output a detection signal. Furthermore, a control device is comprised which controls the light gate depending on the detection signal.

Description

[0001] SWITCHABLE HOLOGRAPHIC DISPLAY

[0002] DESCRIPTION

[0003] In a first aspect, the invention relates to a holographic display device for the switchable display of images, wherein a light source, a light guide, and at least two holographic diffraction gratings are configured to illuminate the at least two holographic diffraction gratings by light from the light source coupled into the light guide. Each holographic diffraction grating generates an image. Furthermore, each holographic diffraction grating is assigned a controllable light gate. The light gate is configured to regulate the brightness of the respectively generated image.

[0004] In a further aspect, the invention relates to an operating device comprising a holographic display device as described and at least one operating element with at least one sensor. The sensor can detect an interaction with the operating element and output a detection signal. Furthermore, a control device is included that controls the light gate depending on the detection signal.

[0005] Background and state of the art:

[0006] Illuminated displays, including holographic displays, are well known in the art. Often, such holographic displays utilize a light guide into which light is coupled and which includes a holographic structure for output and image generation. A so-called edge-lit arrangement is frequently employed, in which light is coupled into a light guide at an angle greater than the angle of total internal reflection and then output from the light guide through a holographic structure enclosed within the light guide to generate the display. If multiple images, particularly images of the same color, are to be generated in this way, they can be housed together in a light guide or a single edge-lit arrangement, or a separate light guide or edge-lit arrangement can be used for each image.In the first case, the images can only be controlled collectively in terms of brightness, and in particular, switched on and off, by adjusting the illumination light accordingly. Unfortunately, separate control of the brightness of individual images, which are created by holographic structures illuminated by a common light guide, and in particular by a single edge-lit arrangement, is not possible at all or only in a complicated and problematic way.

[0007] Object of the invention:

[0008] The object of the invention is to provide an improved holographic display device without the disadvantages of the prior art. In particular, the object of the invention is to provide a holographic display device that requires a single light guide to illuminate holographic structures and generate multiple images, wherein the brightness of the images can be individually controlled in a simple and effective manner. It is also an object of the invention to provide an improved operating device with a holographic display.

[0009] Summary of the invention: The object is achieved by the features of the independent claims. Preferred embodiments of the invention are described in the dependent claims.

[0010] In a first aspect, the invention relates to a holographic display device for the switchable display of images, comprising a light source, a light guide, and at least two holographic diffraction gratings. The light source, light guide, and the at least two holographic diffraction gratings are configured to illuminate the at least two holographic diffraction gratings by light from the light source coupled into the light guide. Each holographic diffraction grating is configured to couple light out of the light guide upon illumination by the light source in order to generate an image. Furthermore, each holographic diffraction grating is assigned a controllable light gate. The light gate is arranged and configured to regulate the brightness of the respectively generated image.

[0011] A holographic display device for the switchable display of images is preferably a device that generates images using holographic diffraction gratings, which are thus, as it were, displayed. These images are, in particular, switchable, meaning that properties of the images, in particular their brightness, can be influenced by a switching process. One could also speak of a controllability of the brightness of the images. Switchable image displays include, in particular, images that can be switched on and off.

[0012] A light guide is preferably a body that is transparent to electromagnetic radiation in a specific wavelength range. When coupled appropriately into the light guide, it allows this electromagnetic radiation to be guided, i.e., in particular, to be "transported" along a specific path within the light guide, e.g., directly and / or via so-called waveguiding through reflections, especially total internal reflection, at the boundary surfaces of the body. The electromagnetic radiation is preferably in the visible range, in particular between 380 nanometers (nm) and 780 nm.

[0013] Transparent preferably means that one can essentially see through the base body. Transparent specifically means that the base body has a transmittance, based on the light intensity (preferably in the specified wavelength range), of at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, and / or at least 95%.

[0014] Terms such as substantially, approximately, about, approx., etc. preferably describe a tolerance range of less than ±40%, preferably less than ±20%, particularly preferably less than ±10%, even more preferably less than ±5%, and especially less than ±1%. Similarly, preferably describes quantities that are approximately equal. Partially preferably describes at least 5%, particularly preferably at least 10%, and especially at least 20%, in some cases at least 40%. Terms such as substantially always preferably also include the exact value.

[0015] A holographic diffraction grating is preferably a grating based on holography for diffracting electromagnetic radiation, in particular light within the aforementioned spectrum, to produce an optical function. This optical function can in particular involve the production of an image. This image can have a three-dimensional depth effect, as is usual for holography, but it can also be a two-dimensional image. In contrast to conventional images, e.g. photography, in holography, in addition to the intensity of the imaged object, phase relationships of the light coming from the imaged object are also stored. These phase relationships contain additional spatial information, which can, for example, create a three-dimensional impression of the image. This happens with the help of interference of light rays during the recording of the object.The object is illuminated with coherent light, which is then reflected and scattered by the object. The resulting wave field, the so-called object wave, is superimposed with light coherent with the object wave (the so-called reference wave - typically from the same light source, e.g., a laser), and the wave fields interfere with each other as a function of their phase relationship. The resulting interference pattern is recorded, for example, using a light-sensitive layer, and the information contained in the phase is thus also stored. For reconstruction, the resulting hologram (the resulting diffraction grating) is illuminated with a light wave identical or similar to the reference wave, which is then diffracted by the recorded interference pattern. In this way, the original wavefront of the object wave can be reconstructed. There are various types of holograms, e.g., so-called volume holograms.Volume holograms preferably have a thickness that can also be used to store holographic image information. Volume holograms can, in particular, be white-light holograms, as these can exhibit wavelength selectivity due to wavelength-selective interference.

[0016] Holograms can, for example, be transmission and reflection holograms, which each produce this reconstruction either in transmission or in reflection. If, for example, one stands on the side of a transmission hologram opposite the light source and views it, the imaged object appears three-dimensional in front of one. With a reflection hologram, one must preferably be on the same side as the light source. Reflection holograms preferably have a wavelength-selective efficiency, diffracting light in a specific direction (or along a specific angle). The word hologram is preferably used here as a synonym for the holographic structure that produces the light diffraction. In common usage, the term "hologram" is sometimes used to refer to the generated image, particularly a three-dimensional image. However, a person skilled in the art knows from the context what the term "hologram" means in each case.

[0017] Holograms, especially technical holograms, can be recorded directly using various holographic processes or printed from computer-generated data using wavefront printers or stereo holographic printers. However, these manufacturing processes are not suitable for mass production of optical functions in the form of holograms due to the high time required. Suitable replication processes, particularly optical ones, are suitable for this purpose.

[0018] An "image" in the sense described here preferably refers to an optical image which transmits desired information ("the image") to a viewer, in particular without further transformation of the light and without the need for additional images. For example, the image can comprise a symbol. An image, even if it is a so-called partial image, is to be distinguished in particular from an individual pixel, which can create an image in interaction with a large number of other pixels. However, an individual pixel does not represent an image in the sense described here for a viewer; an individual pixel can rather be regarded as a pixel. This distinction can also arise from the dimensions of the diffraction grating or the image (see below), which can be significantly larger than the dimensions of a pixel.

[0019] At least two holographic diffraction gratings correspond to two or more holographic diffraction gratings, for example two, three, four, five, six, seven, eight, nine, ten, 15, 20 or even more diffraction gratings.

[0020] The light source, light guide, and the at least two holographic diffraction gratings are configured to illuminate the at least two holographic diffraction gratings by light from the light source coupled into the light guide. This preferably means that light from the light source, which is typically located outside the light guide, is first coupled into the light guide. For this purpose, the light guide and light source are preferably arranged sufficiently close to one another, specifically in such a way that a portion of the light from the light source, e.g. at least 10%, 20%, 30%, 40%, or at least 50% of the light source, is irradiated into the light guide through a (preferably transparent) outer surface of the light guide. This is preferably also referred to as coupling, wherein the coupling in, in particular, irradiation occurs in such a way that the light is guided in the light guide (see above).This light is guided, in particular, to the holographic diffraction gratings, so that they are illuminated. The illumination is preferably at an angle, angular range, or angular spectrum for which the holographic diffraction grating is designed to match the wavelength range of the light source.

[0021] The light source is preferably at least one light source, although it may also be multiple light sources. The one light source or multiple light sources advantageously jointly illuminate the multiple holographic diffraction gratings. This means, in particular, that the multiple holographic diffraction gratings are illuminated by the same light source or the same light sources. In the prior art, however, holographic diffraction gratings, whose generated images should be individually switchable, are illuminated by different light sources, so that the images are switched by switching the light sources.

[0022] Each holographic diffraction grating is configured to couple light out of the light guide upon illumination by the light source to create an image. For this purpose, the wavelength spectrum and angular spectrum of the illuminating light incident on the diffraction gratings are preferably first matched to these diffraction gratings, as described above. Then, the diffraction grating, preferably in accordance with its functionality, diffracts the light in such a way that a portion of the illuminating light is deflected and coupled out of the light guide, with the light further being deflected and coupled out in such a way that a desired image is created.

[0023] The surface of the light guide from which the light is coupled out by the holographic diffraction gratings is preferably called the output surface. A light gate, or synonymously a light valve, is preferably a component that can control the passage or transmission of light, especially for a previously mentioned spectrum of electromagnetic radiation.

[0024] Each holographic diffraction grating is assigned a controllable light gate. This means, for example, that there is (at least) one controllable light gate for each diffraction grating. To clarify, this primarily means that there is exactly one controllable light gate for each diffraction grating. This can mean that each diffraction grating has its own dedicated light gate, each of which is positioned in the beam path of the outcoupled light.

[0025] Furthermore, this preferably means that the light gate associated with a diffraction grating is “responsible” for controlling the brightness of the image produced by that diffraction grating.

[0026] The light gate is configured to regulate the brightness of the respective generated image. Regulating the brightness of the image preferably includes an adjustability of the brightness of the image, which includes at least two different adjustable values.

[0027] The fact that the light gate is configured to regulate the brightness of the respective generated image preferably means that it is arranged accordingly in a beam path of the light and can regulate its brightness, whereby this beam path is essential for the generation of the image. For example, the light gate, which is assigned to a diffraction grating, can be arranged in the beam path of the outcoupled light of this diffraction grating.

[0028] Such a display device allows the individual regulation of the brightness of images to be achieved in a particularly simple manner and with few components.

[0029] In a preferred embodiment of the invention, the light gate is arranged at least partially in a beam path of the outcoupled light of the associated diffraction grating. This also means that the image is already generated by the diffraction grating before passing through the entire light gate.

[0030] At least partially preferably means that at least some subcomponents of the light gate are arranged in the beam path. In particular, the entire light gate can also be arranged in the beam path of the outcoupled light.

[0031] In this way, the brightness of the image can be controlled particularly easily using the light gate.

[0032] In a further preferred embodiment of the invention, the light gate is configured to control the transmission of light depending on an applied control signal. The control of the light should advantageously not be arbitrary, but rather targeted. Applying a control signal to the light gate is particularly suitable for this purpose. The light gate can have a connection for this purpose. The control signal can then assume different values, to which different transmission values ​​then correspond, at least in part. In particular, the control signal can be an electrical control signal, the different values ​​of which can be realized, for example, in different, time-varying applied electrical voltages and / or current intensities. In a further preferred embodiment of the invention, the controllable transmission comprises at least two different transmission values.

[0033] In a further preferred embodiment of the invention, the light gate is configured to switch the image on and off. For this purpose, the intensity of the light must be adjustable so that in the first case (image on) the image is visible and in the second case (image off) the image is invisible. For "visible" and "invisible," the following definitions regarding an intensity difference can apply, for example.

[0034] In a further preferred embodiment of the invention, the transmission values ​​comprise a first and a second value, wherein the image is visible (or switched on) at the first transmission value and the image is invisible (or switched off) at the second transmission value. The difference between visible and invisible can, for example, correspond to an intensity difference of at least 1:100 or at least 1:1000. In the case of visible light, the transmission is preferably sufficiently high, for example 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0035] In a further preferred embodiment of the invention, the light gate comprises two (e.g., linear) polarization filters and a controllable polarization modulator (e.g., a liquid crystal cell) arranged between the polarization filters. This is described in more detail, for example, with reference to Figures 1 and 3.

[0036] In a further preferred embodiment of the invention, the first polarization filter, the second polarization filter, and the controllable polarization modulator are arranged in a beam path of the outcoupled light of the associated diffraction grating. This is described in more detail in Fig. 1, for example. In this case, the entire light gate is advantageously arranged in the beam path of the outcoupled light.

[0037] In a further preferred embodiment of the invention, the second polarization filter and the controllable polarization modulator are arranged in a beam path of the outcoupled light of the associated diffraction grating. The first polarization filter is a common first polarization filter for all light gates, arranged between the light source and the holographic diffraction gratings. This is described in more detail, for example, in Fig. 3.

[0038] The first polarization filter preferably has the function of giving the light a well-defined polarization, e.g., a linear polarization. The polarization filter is preferably configured to transmit this well-defined polarization and substantially block other polarizations. Advantageously, the well-defined polarization of the first polarization filter is matched to a preferred polarization of the diffraction grating. Typically, diffraction gratings essentially diffract a certain polarization (more efficiently than others), so that the well-defined polarization can, for example, correspond to the diffracted polarization of the diffraction grating. The polarization modulator can preferably modulate this well-defined polarization in a controllable manner. For this purpose, a control signal (e.g., electrical) can be applied, for example.The polarization modulator can be an electro-optical modulator, in particular a Pockels cell, a Kerr cell, or a liquid crystal cell. The first polarization filter preferably transmits a so-called s-polarization. s-polarization preferably refers to the polarization direction of an electric field that oscillates perpendicular to the plane of incidence. The plane of incidence is spanned, for example, by the incidence vector of the light beam incident on the diffraction grating and the surface normal to the diffraction grating. p-polarization refers to an electric field oscillating parallel to the plane of incidence. Holographic diffraction gratings are particularly efficient for s-polarized light.

[0039] The second polarization filter is configured, analogously to the first polarization filter, to essentially transmit a well-defined polarization (e.g., a linear polarization) and essentially block other polarizations. For example, in one embodiment, the second polarization filter can essentially transmit the same polarization as the first polarization filter or a polarization orthogonal thereto.

[0040] The second polarization filter can transmit different polarizations for different light gates (preferably different second polarization filters, one for each light gate). This can be useful, for example, if the light has undergone different polarization transformations on its way to the different light gates. This can be caused, for example, by a different number of total internal reflections occurring in the light guide.

[0041] In a further preferred embodiment, the light source is a light source for polarized light, wherein the light gate has a polarization modulator and a second polarization filter following it along the beam path (i.e. preferably located behind it).

[0042] The light source preferably emits linearly polarized light or light that can be converted into a linear polarization without loss, e.g., circularly polarized light. The polarization emitted by the light source is preferably matched to the polarization diffracted by the diffraction grating, so that as much emitted light as possible is diffracted by the respective diffraction grating. In this embodiment, the first polarization filter can be omitted, since the light is already well-definedly polarized by the light source. The light source can already emit polarized light due to its functionality (e.g., laser) and / or have a polarization filter incorporated into the light source. The light source preferably emits s-polarized light. This embodiment requires particularly few components.

[0043] In a further preferred embodiment of the invention, the generated image comprises a real and / or virtual image.

[0044] A so-called holographic structure is preferably a physical framework for the holographic diffraction gratings. It can, for example, also be defined by the following properties. The holographic structure can preferably comprise a material suitable for holography. For example, the holographic structure can comprise a photopolymer. It can also comprise a suitable carrier material, e.g. a polymer, for protection against chemical and / or mechanical influences. The diffraction grating can, for example, be introduced into the holographic structure by an embossing process and / or by exposure and is preferably contained within a partial volume of the holographic structure. The holographic structure and / or the carrier material can be in the form of a layer, in particular a film, or a layer system, in particular a film system.

[0045] In a further preferred embodiment of the invention, at least two of the holographic diffraction gratings are each comprised in a separate holographic structure.

[0046] In the aforementioned embodiment, each holographic structure always contains only one holographic diffraction grating, i.e., each diffraction grating contains a separate holographic structure. This enables particularly simple production of the holographic diffraction grating.

[0047] In a further preferred embodiment of the invention, at least two of the holographic diffraction gratings are included in a common holographic structure.

[0048] In the aforementioned embodiment, at least two, preferably all, holographic diffraction gratings are included in a holographic structure. Therefore, the holographic diffraction grating must be manufactured in such a way that multiple diffraction gratings can be incorporated into a single holographic structure. However, this simplifies the insertion of the diffraction gratings into the device, and the adjustment effort required to correctly position the at least two diffraction gratings relative to one another can be reduced.

[0049] In a further preferred embodiment of the invention, the holographic diffraction gratings are RGB diffraction gratings. RGB stands for red (R), green (G), and blue (B) and means that the diffraction gratings are suitable for diffracting red, green, and blue light. For this purpose, each diffraction grating can comprise (sub-)gratings for red, green, and blue light. Thus, with suitable illumination (e.g., by an RGB light source), an image in any color, especially white, can be generated by color mixing using suitable diffraction efficiencies for the respective colors.

[0050] In a further preferred embodiment, the holographic diffraction gratings are configured to generate monochrome images. For example, the diffraction grating can be designed to generate a red image through a corresponding diffraction efficiency for red illumination light. Advantageously, the light source emits correspondingly monochrome light, for example, in the red spectral range, to continue with the above example.

[0051] In a further preferred embodiment of the invention, the light guide, light source, and diffraction grating are configured to illuminate the holographic diffraction gratings without prior multiple reflections in the light guide. Thus, the light preferably impinges on the diffraction gratings directly from the coupling point into the light guide. This preferably also includes the case where the diffraction gratings are reflection holograms (see below) and a reflection occurs at an interface of the light guide before diffraction and coupling out by the diffraction gratings. Multiple reflections are, in particular, more than one reflection. This is a particularly simple illumination of the diffraction gratings, allowing particularly homogeneous illumination of all diffraction gratings and particularly homogeneous brightness of the generated images to be achieved.There can also be an embodiment of the device in which the light guide has a deflection surface for deflecting the coupled-in light. This is preferably a surface encompassed by the light guide at which a targeted deflection of the coupled-in light can take place in order to then guide it at a desired angle in the light guide towards the diffraction grating. The deflection can in particular be a reflection, but it can also be a diffraction. This deflection surface can, for example, be mirrored for this purpose, or the angle of the deflection surface with respect to the coupled-in light is such that total reflection takes place at the deflection surface. The deflection surface can also comprise a diffraction grating, in particular a hologram.In a variant of this embodiment, it may also be the case that no further multiple reflections occur for the illumination of the holographic diffraction gratings, even if the diffraction grating is, for example, a reflection hologram. This means that in this variant, the light guide has a deflection surface for deflecting the coupled-in light, whereby after reflection of the coupled-in light at the deflection surface, no multiple reflections occur in the light guide for the illumination of the holographic diffraction gratings.

[0052] In a further preferred embodiment of the invention, the light guide, light source, and diffraction grating are configured for illuminating the holographic diffraction gratings by waveguiding through multiple total reflections in the light guide. This allows light to be transported over long distances with virtually no loss, even in thin light guides. This also makes it easy to illuminate one or more diffraction gratings, which together occupy a large area. The coupled beam can preferably occupy a specific area at the location of the holographic diffraction grating along the plane of the holographic diffraction grating's extension. This area is preferably also referred to as a footprint. This area can be smaller than the extension of a single holographic diffraction grating or than the extension of all the holographic diffraction gratings combined (preferably including the spaces between the diffraction gratings).Then, several such footprints combined must illuminate the holographic diffraction gratings. Through multiple reflections in the light guide due to total internal reflection at the interfaces of the light guide, these footprints can be reproduced and thus also illuminate larger areas.

[0053] In a further preferred embodiment of the invention, the light guide, light source and diffraction grating are configured for the full-surface illumination of the holographic diffraction gratings by waveguiding through multiple total reflections in the light guide. Full-surface preferably means that the holographic diffraction gratings are illuminated over their entire surface, i.e. virtually without gaps. In this embodiment, the light guide, light source and diffraction grating are configured such that the footprints enable full-surface illumination of the holographic diffraction gratings. One possible way of achieving this is for the footprints to directly touch or even overlap one another. Geometric considerations play a particular role here, e.g.For direct contact of the footprints, it can be given that tan 0 = 0.5*F / d, where 0 is the angle that the coupled light beam makes with a normal of the interface (reflection surface) of the optical fiber (preferably in a plane along a longitudinal section of the optical fiber, i.e. a section along the light transmission direction or a longitudinal direction of the optical fiber). F is the extent of the footprint along this light transmission or longitudinal direction, and d is the thickness of the optical fiber. This applies in particular to optical fibers whose interfaces, where reflection occurs, are parallel. Another possibility is preferably that the footprints do not overlap, but that the footprints and diffraction gratings are arranged in such a way that each diffraction grating is fully illuminated by a footprint.

[0054] In the aforementioned embodiments, in which the diffraction gratings are illuminated by multiple reflections, it should be noted that each time the diffraction gratings are illuminated, a portion of the light is coupled out by them, and thus the light beam weakens in intensity with "each pass." Therefore, the diffraction gratings are preferably configured to couple out a largely constant intensity of light (where desired) when illuminated by multiple total reflections in the light guide. This can be achieved, for example, by appropriately varying the diffraction efficiency, for example by increasing it in certain sections the further the respective section of the diffraction grating is from the light source. This allows images with homogeneous brightness to be realized.

[0055] In a further preferred embodiment of the invention, the light guide comprises a substrate and the substrate material preferably comprises an optical plastic and / or an optical glass.

[0056] The substrate material preferably comprises an optical plastic, preferably selected from a group comprising polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymers (COP), cycloolefin copolymers (COC) and / or an optical glass, preferably selected from a group comprising borosilicate glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A, P-BK7, N-FK5, N-PK51, P-SK57, P-LAK35, P-LASF47, N-KZFS11, P-SF69 or SF57.

[0057] In a further preferred embodiment of the invention, the holographic diffraction gratings are enclosed in the light guide, wherein the holographic diffraction gratings are selected in particular from the group consisting of transmission holograms, reflection holograms, Z-holograms, and / or relief structures. The holographic diffraction grating can, for example, be incorporated into the substrate, e.g., inscribed by a laser.

[0058] It may also be preferred that the light guide comprises, in addition to the substrate, at least one layer applied to the transparent substrate, which layer has at least one holographic structure or at least one holographic diffraction grating.

[0059] The at least one layer comprises, for example, one or more of the following layers: a hologram layer, which preferably comprises the holographic structure, a layer comprising triacetate, a transparent adhesive layer or adhesive film (e.g., OCA), and / or a layer / film comprising polycarbonate (PC). The layer can, in particular, comprise a film, e.g., a hologram film, a triacetate film, an adhesive film, and / or a polycarbonate film. The layers / films in addition to the hologram layer / hologram film can, for example, comprise carrier layers / films or protective layers / films.

[0060] A so-called Z-hologram comprises two reflection holograms, preferably arranged directly one behind the other. The hologram following the light propagation path causes a first "reflection" (strictly speaking, this is, of course, a diffraction) of the light, followed by the hologram following the light propagation path. As a result, these two holograms thus advantageously act as transmissive holograms, allowing, for example, the advantages of a transmission hologram to be combined with those of a reflection hologram (higher wavelength and / or angular selectivity).

[0061] The relief structure or relief hologram is preferably a structure that has physical structures (e.g., elevations) on a material surface, which can include a corresponding diffraction grating. Due to the depressions or elevations, the light travels different path lengths in the material, causing a phase difference. This results in a phase grating, which is referred to as a diffraction grating. The relief holograms can also be produced as embossed holograms, for example, by introducing the depressions into the material using a stamp.

[0062] In a further preferred embodiment of the invention, the optical fiber has a planar extension. The optical fiber has an output surface for outputting the light from the optical fiber, which is arranged along the planar extension of the optical fiber. The holographic diffraction gratings are preferably arranged along the output surface.

[0063] "Flat" here means, in particular, forming a wider surface, being flattened, and / or extending across a surface. "Flat" can mean, for example, that the light guide has a large extension along a plane or surface and a relatively significantly smaller extension in a direction perpendicular to it. The plane or surface can also be a curved plane or surface. "Significantly smaller extension" preferably means an extension that is at least a factor of two smaller than the smallest extension along the plane or surface.

[0064] The output surface is preferably the surface of the light guide from or through which the light coupled out by the holographic diffraction grating is output. The output surface is, for example, the surface of the light guide that a user of the display device looks at.

[0065] The fact that the output coupling surface is arranged along the planar extent of the optical fiber can also mean that the output coupling surface is arranged parallel to it. The fact that the holographic diffraction gratings are preferably arranged along the output coupling surface means, in particular, that they are arranged parallel to the output coupling surface.

[0066] In a further preferred embodiment of the invention, the light gate is at least partially applied to the coupling-out surface.

[0067] On the output surface primarily means that the light gate is located outside the light guide, at least in the parts applied to the output surface. The light gate or its applied subcomponents can be applied directly to the output surface, preferably without any additional intermediate layer and / or components.

[0068] However, it may also be preferred that at least one further intermediate layer and / or additional component be present between the output surface and the parts of the light gate. In both cases, the viewer or user of the display device preferably directly observes the light gate and can directly recognize it when the image is "switched on."

[0069] It may be preferred that the light gates form a planar outer boundary surface of the device.

[0070] Preferably, gaps between light gates can also be filled with a filler material, which, together with the light gates, forms a flat outer interface of the device. This filler material can, for example, comprise a low-refractive-index layer (see below).

[0071] In a further preferred embodiment of the invention, a low-refractive-index layer is included on the coupling-out surface at least between the holographic diffraction grating and the parts of the light gate

[0072] The low-refractive-index layer is particularly designed for total reflection of illumination light at the low-refractive-index layer.

[0073] A low-refractive-index layer is preferably designed to ensure total reflection of the coupled-in light at the output surface even where the light gate or parts thereof are applied to the output surface, in particular regardless of the refractive index of the light gate.

[0074] For this purpose, the low-refractive layer advantageously has a lower refractive index than the light guide.

[0075] The fact that the low-refractive-index layer is enclosed at least between the holographic diffraction grating and the parts of the light gate preferably means that it is enclosed at least in the regions of the output surface where the light gate is present, namely on the output surface, between the diffraction grating and the light gate.

[0076] There may be free areas between the individual light gates on the output surface where there is no light gate; the low-refractive-index layer may be included there, but it does not have to be, since total reflection can advantageously take place there even without a low-refractive-index layer due to the different refractive indices between the light guide and the surrounding medium.

[0077] In a further preferred embodiment of the invention, the refractive index difference between the light guide (or holographic diffraction grating) and the low-refractive-index layer is at least 0.3. This advantageously ensures total internal reflection for preferred angles of the coupled light.

[0078] In a further preferred embodiment of the invention, the light guide (in particular the substrate and / or the holographic elements) has a refractive index between 1.45 and 2.0 and the low-refractive layer has a refractive index between 1.37 and 1.47.

[0079] In a further preferred embodiment of the invention, an air gap is provided between the optical fiber and the parts of the light gate, preferably between the output coupling surface and the parts of the light gate. The air gap advantageously has the same effect as the low-refractive-index layer, primarily the effect of ensuring total reflection of the coupled-in light at the output coupling surface or the outer surface of the optical fiber, even where the light gate or parts thereof are applied to the output coupling surface or the optical fiber, particularly regardless of the refractive index of the light gate.

[0080] The air gap can, for example, have a spacing between the light guide (in particular the coupling-out surface) and parts of the light gate which is one millimeter (mm) or less, preferably 0.5 mm or less.

[0081] For this purpose, particularly suitable materials with low costs and suitability for mass production can be found.

[0082] In a further preferred embodiment of the invention, the low-refractive-index layer comprises PVB.

[0083] In a further preferred embodiment of the invention, the light guide comprises a coupling surface for coupling in light from the light source.

[0084] The coupling surface is preferably an outer surface of the light guide, which is configured to couple light from the light source into the light guide. For this purpose, it has advantageous properties, such as transparency. The light from the light source is preferably coupled substantially or partially into the light guide through the coupling surface. The coupling surface can have further advantageous properties. It can, for example, be flat. However, it can also have particularly desired light-shaping properties, for example, it can be curved to achieve or support collimation of the coupled light.

[0085] Preferably, the light guide and light source are configured to couple light from the light source into the light guide. This may mean, for example, that the light source is positioned directly in front of the coupling surface and radiates toward the coupling surface.

[0086] In a further preferred embodiment of the invention, the optical fiber has a planar extension, with the coupling surface being located on a side surface of the optical fiber. The side surface preferably does not lie along the planar extension of the optical fiber, in particular perpendicular to it. However, the side surface can be beveled at an angle other than perpendicular to the planar extension, at least in the region of the coupling surface.

[0087] In particular, the holographic diffraction gratings form a so-called edge-lit hologram with the substrate of the light guide, in which the illumination light is coupled into a side surface of the light guide and illuminates the diffraction gratings through the light guide. The diffraction gratings, in turn, preferably diffract the light in such a way that the light is coupled out of the coupling-out surface, wherein the coupling-out surface is arranged along the planar extent. In particular, the coupled-in light that is not diffracted and coupled out (so-called zeroth order) remains in the light guide due to total internal reflection. In a further preferred embodiment of the invention, the light source is configured for irradiation into the coupling-in surface, in particular for coupling into the light guide, such that coupled-in light propagates at an angle greater than the critical angle of total internal reflection in the light guide.This preferably applies to at least one plane of the light guide, e.g., a longitudinal section of the light guide perpendicular to the output surface of the light guide (vertical plane). For this purpose, the input surface can be located in a beveled region of the side surface, for example, with the light source being arranged at an angle to the planar extent of the light guide. For example, the light source can be arranged such that it is aligned along a surface normal of the input surface. This allows for particularly simple input coupling while minimizing Fresnel reflections at the input surface, in particular at an angle greater than the critical angle of total internal reflection.

[0088] It may also be preferred for the coupling surface to be arranged along the planar extent of the optical fiber. The light source can also be arranged along a surface normal to the coupling surface. To ensure coupling at an angle greater than the angle of total internal reflection, the optical fiber can, for example, have a deflection surface configured to deflect the coupled light at an angle such that, after deflection, the light forms an angle with the boundary surfaces of the optical fiber (e.g., the coupling-out surface) that is greater than a critical angle of total internal reflection.

[0089] In a further preferred embodiment of the invention, the image is generated outside an extension of the light guide and thus preferably has a floating height relative to the light guide (or the coupling-out surface).

[0090] A flying height is preferably a distance of the image generated (preferably by the diffraction grating) from a reference plane, in particular measured in the vertical or perpendicular direction to this plane.

[0091] The reference plane here is in particular the coupling surface of the optical fiber.

[0092] A floating height can create a special visual effect. Even operating functions that don't rely on touching a surface can be implemented this way. The image can mark an operating area.

[0093] In a further preferred embodiment of the invention, the light source comprises at least one LED and / or one laser. It may comprise multiple LEDs and / or lasers.

[0094] The light source may, for example, comprise at least one LED and / or at least one laser. The light source preferably emits light in the visible spectrum, in particular between 380 nanometers (nm) and 780 nm in terms of wavelength.

[0095] The light source preferably does not include a separate beam-shaping component, e.g., a lens.

[0096] However, it may also be preferred that the light source comprises at least one beam-shaping component, for example at least one lens.

[0097] The light source is preferably arranged with a main radiation direction directed toward the coupling surface, especially if the light source has anisotropic radiation properties. LEDs are particularly simple, durable, and cost-effective, and they exhibit sufficient optical properties, particularly with regard to their coherence, for a variety of lighting functions, especially holographic lighting functions. LEDs are particularly efficient.

[0098] Preferably, LED emitters have dimensions between 0.5 x 0.5 mm 2 and 1 x 1 mm 2 In general, it can be said that smaller emitter areas are always advantageous for our application. The minimum distance of the coupling surface is independent of the emitter size.

[0099] In a further preferred embodiment of the invention, the emission spectrum of the LED can be assigned to a color.

[0100] In a further preferred embodiment of the invention, the emission spectrum of the LED cannot be assigned to one color, but comprises a multi-color spectrum.

[0101] In particular, it is an RGB LED (RGB = Red / Green / Blue), which has one or more emitters for R, G and B, which can preferably be controlled individually (in the case of several emitters).

[0102] For example, it could be an Osram MULTILED LRTB GVSG, which emits at 625 nm (red), 528 nm (true green), and 460 nm (blue). Intensities can range from 500 to 1000 millicandelas (mcd) for red, 1250 to 2010 mcd for green, and 180 to 560 mcd for blue.

[0103] In a further preferred embodiment of the invention, at least one collimation optic, preferably at least one lens, is included between the light source and the holographic diffraction gratings, preferably between the light source and the light guide.

[0104] The collimation optics are preferably configured to collimate the light from the light source in at least one plane. The collimation optics are preferably configured to collimate at least one plane along the planar extent of the optical fiber. However, it may also be preferred for the collimation optics to collimate the light from the light source in two mutually perpendicular planes.

[0105] This allows the beam properties of the illumination of the holographic diffraction grating to be improved and a better image to be produced.

[0106] In a further preferred embodiment of the invention, the holographic diffraction gratings are arranged side by side. This allows multiple images to be displayed side by side and their brightness to be controlled.

[0107] In a further preferred embodiment of the invention, several holographic diffraction gratings are arranged directly adjacent to one another. This allows images to be generated that are close to one another or adjacent to one another.

[0108] In a further preferred embodiment of the invention, a plurality of holographic diffraction gratings are arranged at a distance from one another, wherein the distance is preferably at least 1 mm, more preferably at least 2 mm, and in particular 3 mm or more. This allows, for example, images to be generated that are spaced apart from one another. This can, for example, improve the display or operability if the images indicate an operating area. In a further preferred embodiment, the light gates are arranged directly adjacent to one another. This can also be the case if the diffraction gratings are spaced apart from one another as described above.

[0109] In a further preferred embodiment, the light gates are also spaced apart, preferably at least 0.5 mm, more preferably at least 1.5 mm and in particular 2.5 mm or more.

[0110] In a further preferred embodiment of the invention, a plurality of holographic diffraction gratings are arranged in a matrix arrangement. A matrix arrangement preferably describes an arrangement of the diffraction gratings which can be described by the positioning of the diffraction gratings along two essentially vertical directions. For example, the arrangement can be described along a "row" and a "column" of a matrix. There is preferably a fixed number of diffraction gratings along each row, which corresponds to the number of columns. By specifying the number of columns and rows, the number of diffraction gratings can thus be determined. The number of rows and columns is preferably specified in the format A x B, where A is a natural number which specifies the number of rows and B is a natural number which specifies the number of columns.A 9 x 9 matrix comprises a total of nine rows with nine columns each, with a diffraction grating arranged in each column, thus comprising a total of 81 diffraction gratings. However, the number of columns does not necessarily have to correspond to the number of rows, as in the example.

[0111] In one variant, the matrix-like diffraction gratings generate images, each of which represents a symbol, e.g., a letter and / or a number and / or a special character. The images, taken together, display a PC keyboard, particularly a QWERTY keyboard. This allows individual keys or a luminous version of the keys to be switched on and off, e.g., to indicate that a specific key (e.g., the Caps Lock key) has been pressed or to enable operation in the dark.

[0112] In a further preferred embodiment of the invention, the holographic diffraction gratings and / or the generated images have an extension of at least 10 x 10 mm 2 This allows for particularly clearly recognizable images to be created.

[0113] Preferably, the light gates have substantially the same or larger dimensions, so that the light beams for displaying the generated images can be regulated by the light gate, in particular without parts of the light beams being cut off by excessively small dimensions of the light gates. Thus, the light gates or their switchable areas have dimensions or an extension of at least 10 x 10 mm. 2 preferably at least 11 x 11 mm 2 .

[0114] In a further preferred embodiment of the invention, at least two of the generated images have matching partial images which form an overall image.

[0115] In particular, the images created are directly adjacent to one another.

[0116] In a further preferred embodiment of the invention, a diaphragm layer is included, which is arranged on the coupling-out surface. The diaphragm layer can create an aesthetic effect, in particular through a specific coloring of the diaphragm layer. Furthermore, the diaphragm layer can form a mechanical and / or optical protective layer, which, for example, absorbs and / or reflects certain spectral components of electromagnetic radiation.

[0117] The aperture layer may in particular comprise a film.

[0118] In a further preferred embodiment of the invention, the low-refractive-index layer is arranged between the output coupling surface and the aperture layer. This reduces absorption of coupled-in / guided light in the aperture layer.

[0119] In a further preferred embodiment of the invention, the aperture layer has cutouts and / or transparent regions congruent with the holographic diffraction gratings. This allows the light diffracted by the diffraction gratings to be coupled out largely without absorption.

[0120] In a further preferred embodiment, at least one control device for controlling the light gates is included.

[0121] A control device or control unit is, in particular, at least one integrated circuit, e.g., at least one microprocessor, at least one processor or processor unit, at least one CPU, at least one computer, and / or at least one computer. A control device can, for example, comprise an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA). Furthermore, components known to those skilled in the art in this context, such as at least one electronic memory, an integrated circuit, at least one digital-to-analog converter, at least one analog-to-digital converter, and / or at least one amplifier, can be included.

[0122] In particular, the control device can generate at least one (electrical) signal for controlling at least one light gate.

[0123] In a further aspect, the invention relates to an operating device comprising a holographic display device as described above, at least one operating element with at least one sensor configured to detect an interaction with the operating element and output a detection signal, and a control device. The control device is configured to control the light gates depending on the detection signal.

[0124] The detection signal is preferably output from the sensor to the control device.

[0125] It will be apparent to the person skilled in the art that advantages, definitions and embodiments of the device according to the invention according to the first aspect also apply to the claimed device according to the invention according to the second aspect.

[0126] The operating device has a display device as described above, and also includes operating elements. The operating elements can be buttons, for example. An operating element preferably has appropriate symbols to identify the operating element. This can be provided, for example, by the images generated by the diffraction gratings. Secondly, the operating element advantageously includes an "operating mechanism" which, through interaction with the operating element, triggers an action that corresponds to the desired operability. For example, the action can be switching a lamp or a heater / ventilation system in a vehicle on and off. A corresponding sensor is included to detect the interaction. The sensor, for example, can be a proximity sensor, e.g., optical, a touch sensor, e.g., capacitive, or a pressure sensor, e.g., (piezo-)electric, or an electrical switch.In this way, various types of operating elements can be implemented, e.g. classic push buttons (in conjunction with a mechanically movable element of the operating device), but also touchscreen-like operating elements or operating elements in which a contactless interaction, e.g. within a display area of ​​the image with a floating height, triggers the operating mechanism. For this purpose, the sensor is configured to detect an interaction with the operating element and output a detection signal. This detection signal is passed on to a control device, wherein the control device is configured to control the light gates depending on the detection signal. For example, an image showing a lamp can be switched off after the lamp has been switched on by the operating element. Advantageously, the control device can also output a (e.g. electrical) signal that triggers the respective action, e.g.which turns the said lamp on or off.

[0127] In a preferred embodiment of the invention, at least two holographic diffraction gratings are provided with a control element associated with each holographic diffraction grating. The light gates associated with each diffraction grating are controlled depending on the detection signal of the control element associated with the diffraction grating.

[0128] For the previously described functionality of the control device, each holographic diffraction grating advantageously includes an associated control element with a respective sensor. The detection signal of the respective sensor then, in turn, controls the associated light gate.

[0129] In a third aspect, the invention relates to a method for an operating device as described above, comprising the following steps:

[0130] Output of a detection signal upon detection of an interaction with the control element by the sensor, preferably to the control device, control of the light gate in dependence on the detection signal by the control device.

[0131] It will be apparent to the person skilled in the art that advantages, definitions and embodiments of the device according to the invention according to the first aspect and the further aspect also apply to the claimed method according to the invention and vice versa.

[0132] Description of the invention: The invention will be explained below with reference to further figures and examples. The examples and figures serve to illustrate preferred embodiments of the invention without limiting it.

[0133] Figure 1 schematically shows an embodiment of the holographic display device.

[0134] Figure 2 schematically shows an embodiment of the holographic display device in which a low-refractive-index layer is included on the output surface.

[0135] Figure 3 shows an embodiment with varying structure of the light gates.

[0136] Figures 4a and b show an operating device according to a further aspect of the invention.

[0137] Figure 5 shows schematically the (process) steps involved in operating the control element.

[0138] Figure 1 schematically shows an embodiment of the holographic display device 1. With the display device 1, switchable images 6, 6', and 6" can be generated. By using appropriately configured or arranged, controllable light gates 7, 7', and 7", the brightness of the images 6, 6', and 6" can be controlled; in particular, the images 6, 6', and 6" can be switched on and off by controlling the transmission values ​​of the light gates 7, 7', and 7" accordingly.

[0139] The display device comprises a light source 4, e.g., an LED, a light guide 2, and, in the present case, three holographic diffraction gratings s, 3', and 3". The light guide 2 and the light source are arranged relative to one another in such a way that light from the light source 4 is coupled into the light guide 2, and this coupled light 5 subsequently illuminates the diffraction gratings s, 3', and 3". The diffraction gratings 3, 3', and 3" are thus illuminated jointly or by a common light source 4. The diffraction gratings s, 3', 3" at least partially decouple this illumination light from the light guide 2. The decoupled light 8 (see Fig. 2) subsequently generates an image 6, 6', and 6", in the present case, a real image 6, 6', and 6", with a floating height 18 above the light guide 2.The fact that the display of the images generated by the diffraction gratings 3, 3' and 3" can nevertheless be controlled separately is achieved in that each diffraction grating s, 3' and 3" has its own, associated light gate 7, 7' and 7", each of which is arranged in the beam path of the outcoupled light 8. This allows the transmission of the outcoupled light 8 in the light gate 7 to be controlled. If the transmission of the light gate 7 is set such that no outcoupled light 8 can pass through, then accordingly no image 6, 6' or 6" is generated. If the transmission of the light gate 7, 7' or 7" is set such that the outcoupled light of the respective diffraction grating 3, 3' or 3" can pass through essentially unhindered, an image 6, 6' or 6" visible to a viewer is generated.

[0140] Further details of the present embodiment according to Figure 1 of the display device 1 are explained below. First of all, the light guide 2 shown has a planar extension, i.e., it has a large extension along a plane or surface and a relatively much smaller extension in a direction perpendicular thereto. In the case shown, the planar extension extends along a horizontal line of the image, and the smaller extension along a vertical direction. The side surfaces of the light guide 2, for example, 17 and 17', extend along the smaller extension. In the example shown, the coupling surface 16 is arranged on the left side surface 17.Here, the coupling surface 17 is inclined at an angle relative to the image vertical in order to enable, in conjunction with the arrangement of the light source 4, an irradiation of the light into the light guide 2 at an angle greater than the critical angle of total reflection, as will be described below, among other things.

[0141] The light source 4 is configured to irradiate light into the light guide 2 through the coupling surface 16. For this purpose, the light source 4 is arranged in front of the coupling surface 16, essentially in such a way that the direction of irradiation into the coupling surface 16 essentially forms a right angle with it, in order to avoid, for example, light refraction and minimize Fresnel reflections. A collimating optic 19 (e.g. a lens) is arranged along the beam path between the light source 4 and the coupling surface 16. This collimates the light from the light source 4 at least in the image plane shown. Depending on the extent of the light source 4 perpendicular to the image plane, a cylindrical lens, for example, can be used for this purpose. However, a collimating optic 19 can also be used, which also effects collimation in the plane perpendicular to the image plane.

[0142] The variant shown represents a possible embodiment in which the arrangement and orientation of the coupling surface 16, together with the arrangement and, if applicable, orientation of the light source 4 as described, results in the light 5 coupled into the light guide 2 being guided at an angle greater than the critical angle of total internal reflection in the light guide 2. This means that the light radiated into the light guide 2 strikes the top and bottom of the light guide 2 within the image plane at an angle that is greater than said critical angle, whereby total internal reflection occurs at the top and bottom interfaces of the light guide 2. In this way, the light can be guided to the diffraction gratings 3, 3' and 3" without any significant losses by multiple reflections 13 in the light guide 2 (by waveguiding).On the other hand, the light not diffracted from the light guide 2 by the diffraction gratings 3, 3', and 3" (the so-called zeroth order) is transmitted further in the light guide 2 and does not reach the viewer, as can be the case with other holographic arrangements. Since an input light beam loses some radiant power through diffraction each time it passes through a diffraction grating 3, 3', and 3", the efficiencies of the diffraction gratings 3, 3', and 3" can be adjusted so that a part of a diffraction grating 3, 3', and 3" passed through later has a higher diffraction efficiency than a part passed through earlier, in order to generate homogeneously bright images overall.

[0143] It will be clear to those skilled in the art that there may be further embodiments in which the light source 4 and the coupling surface 17 are arranged and / or oriented differently, but which also allow irradiation at an angle greater than the angle of total internal reflection into the light guide 2. A suitable solution can be found depending on the given boundary conditions, such as installation space, efficiency requirements, etc.

[0144] In the embodiment shown, the holographic diffraction gratings 3, 3', and 3" are contained in a common holographic structure 12. This can, for example, be in the form of a foil applied to the substrate of the light guide 2. This simplifies the application of the diffraction gratings s, 3', and 3" and reduces any assembly effort. Depending on the overall size of the holographic structure 12, a corresponding exposure of several diffraction gratings s, 3', and 3" in a single structure 12 is also quite possible.

[0145] In the variant of the holographic illumination device 1 shown in Fig. 1, the light gates 7, 7', and 7" are arranged entirely in a beam path of the outcoupled light 8 of the respective associated diffraction gratings 3, 3', and 3", i.e., along the beam path of the light behind the respective diffraction grating 3, 3', and 3". Thus, the outcoupled light 8 of the respective diffraction grating 3, 3', and 3" passes through the respective associated light gates 7, 7', and 7". In the present case, each light gate 7, 7', and 7" comprises a first polarization filter 9 or first polarizer, a second polarization filter 10 or second polarizer, and an intermediate controllable polarization modulator 11. The first polarization filter 9 is arranged upstream of the beam path (i.e., closer to the light source) than the second polarization filter 10.The first polarization filter 9 essentially functions to impart a well-defined polarization to the light, e.g., a linear polarization. The polarization filter 9 is configured to transmit this well-defined polarization and essentially block other polarizations.

[0146] Advantageously, the well-defined polarization of the first polarization filter 9 is matched to the preferred polarization of the diffraction grating 3, so that the well-defined polarization essentially corresponds to the diffracted polarization of the diffraction grating 3 in order to maximize efficiency. The polarization modulator 11 can now modulate this well-defined polarization in a controllable manner. For this purpose, for example, a control signal (e.g., electrical) can be applied to the polarization modulator 11. The modulation can then be carried out depending on the control signal. For example, an existing linear polarization can be rotated to different degrees depending on the applied control signal. For example, with one control signal, a rotation can be approximately 0° (i.e., no rotation takes place), while with a second control signal, this can correspond to a rotation of 90°. The second polarization filter 10 is again configured like the first 9, a well-defined polarization (e.g.,a linear polarization) and to substantially block other polarizations. For example, in one embodiment the second polarization filter 10 can transmit substantially the same polarization as the first polarization filter 9. Then the maximum amount of outcoupled light 8 would be transmitted through the second polarization filter 10 if the polarization modulator 11 is controlled such that the rotation corresponds to 0° and substantially no light would be transmitted through the second polarization filter 10 if the polarization modulator 11 is controlled such that a rotation of the polarization by 90° takes place. Then in the first case the image 6 would be switched on and in the second case the image 6 would be switched off. In another embodiment the second polarization filter 10 can e.g.be configured to transmit a polarization that deviates essentially by 90° from the polarization transmitted by the first polarization filter 9 (so-called "crossed" polarization filters). A maximum of light is then transmitted through the second polarization filter 10 when the polarization modulator rotates the polarization by 90°, and essentially no light is transmitted when the rotation corresponds to 0°. Depending on the control and design of the light gate 7, intermediate values ​​of the polarization rotation can also be set, so that intermediate values ​​of the transmission can also be set and the brightness of the images 6, 6' and 6" can be regulated. The polarization modulator 11 can be implemented, for example, by a liquid crystal cell.

[0147] In addition to the embodiment shown, it is also conceivable that the light gate 7 is arranged only partially in a beam path of the outcoupled light 8, i.e., along the beam path of the light behind the diffraction grating s. For example, the first polarization filter 9 can already be arranged between the light source 4 and the coupling surface 17, preferably between the collimation optics 19 and the coupling surface 17, in particular on the coupling surface 17. Thus, only a single first polarization filter 9 would be required, which, as it were, establishes a well-defined polarization for all other light gate parts 7, 7', and 7". This would further simplify the structure of the display device 1.

[0148] Figure 2 schematically shows some details of an embodiment of the holographic display device 1. Some features of the device shown have already been described in Figure 1 and are therefore not presented in detail here. However, they are provided with the same reference numerals as in Figure 1 and can therefore be easily identified. Figure 2 shows a section of the light guide 2 and its structure and mode of operation in detail, without, for example, going into aspects of the coupling of the light into the light guide 2. Furthermore, elements applied to the light guide 2, such as the low-refractive index layer 15 and two light gates 7 and 7', are shown. The light guide 2 itself comprises, in the present exemplary embodiment, a substrate 20 ora substrate body and the holographic structure 12, here in the form of a hologram foil applied to the substrate 20, which comprises the diffraction gratings 3 and 3' as a common holographic structure 12. The hologram foil and substrate 20 have a very similar refractive index so that no unwanted reflections occur at their contact surface and an optically largely homogeneous light guide 2 is formed. The low-refractive-index layer 15 is included on the hologram foil, the function of which will be explained in more detail below. The respective associated light gates 7 and 7' are applied to the low-refractive-index layer 15 above the diffraction gratings 3, 3'. The light guide 2 is flat and has an output surface 14 at the interface between the hologram foil and the low-refractive-index layer 15. This output surface 14 is arranged along the flat extent of the light guide 2, i.e., in the example shown, along the image horizontal.The coupled-in light 5 is guided by total internal reflection at the upper and lower interfaces of the light guide 2, with the upper interface being the output surface 14. When the light strikes a diffraction grating 3, 3' and illuminates it, a portion of this coupled-in light 5 is diffracted by the respective holographic diffraction grating 3, 3' and deflected such that it is output from the output surface 14 of the light guide 2. The diffraction gratings 3, 3' shown are reflection holograms; the coupled-in light, coming from the lower interface of the light guide 2, initially transmits undiffracted, is then reflected at the output surface 14, and only subsequently is it diffracted by the diffraction gratings 3, 3' into the so-called first order and output from the output surface 14 of the light guide 2.The outcoupled light 8 is then transmitted through one of the light gates 7, 7', whereby the transmission can be controlled in the manner described above. The light gate 7 is also constructed as described above and comprises a first polarization filter 9, a second polarization filter 10, and an intermediate polarization modulator 11. The portion of the coupled-in light 5 not diffracted by the diffraction gratings 3 and 3' remains as zeroth order in the light guide 2. The function of the low-refractive-index layer 15 is to enable total reflection at the outcoupler surface 14 even where the light gates 7, 7' are located. Otherwise, without the low-refractive-index layer 15, the typically similar refractive indices between the light guide 2 and the light gate 7 would prevent total reflection at their contact surfaces, thus disrupting the total reflection or light conduction of the coupled-in light 5 in the light guide 2.For this purpose, the low-refractive-index layer 15 must have a correspondingly lower refractive index than the light guide 2, so that the critical angle of total internal reflection is smaller than the angle formed by the coupled-in light 5 with the surface normal of the output surface 14. A corresponding difference between the light guide 2 and the surrounding medium (usually air) must also naturally exist at the lower interface of the light guide 2. However, the light 8 diffracted and output by the holographic diffraction gratings 3, 3' can easily be transmitted by the low-refractive-index layer 15 in the direction of the light gates 7, 7', since it impinges on the interface between the light guide 2 and the low-refractive-index layer 15 at an angle smaller than the critical angle of total internal reflection (for example, as shown, at an angle of 0°, whereby the angle between the respective light beam and the surface normal to the interface is measured).The light guide 2 is therefore essentially defined by the fact that it has an approximately homogeneous refractive index and thus enables light transmission by total reflection on its outer surfaces (with a corresponding coupling angle).

[0149] Figure 3 shows an embodiment of the display device 1 that largely corresponds to the variant from Figure 1 (with identical reference numerals), but in which the structure of the light gates 7, 7', and 7" varies. Here, the second polarization filter 10 and the controllable polarization modulator 11 are still arranged in a beam path of the outcoupled light 8 of the associated diffraction grating 3, 3', 3", but the first polarization filter 9 is a common first polarization filter s for all light gates 7, 7', 7". In the example shown, it is arranged between the collimation optics 19 and the coupling surface 16, specifically directly on the coupling surface 16.As a result, advantageously only a single first polarization filter 9 is required, which defines a well-defined polarization for the entire illumination light, which then enables the transmission of the outcoupled light 8 through the individual light gates 7, 7' and 7" to be controlled as described above. However, it can happen that, for example, due to the different number of total reflections of the incoupled light 5 on the way to the various diffraction gratings 3, 3' and 3" or light gates 7, 7' and 7", different polarizations reach the respective modulators 11. It can therefore be useful for the respective second polarization filters 10 to be configured to transmit correspondingly different polarizations.Alternatively or additionally, it may be useful to control the respective polarization modulators 11 differently, so that known switching properties of the light gates 7, 7' and 7" are realized with known control signals.

[0150] Figures 4a and b show an operating device 26 according to a further aspect of the invention. The operating device 26 has a display device 1 as described above, and also includes operating elements 27, 27' and 27". The operating elements 27, 27' and 27" can be buttons, for example. Advantageous properties of an operating element 27 are, on the one hand, the identification of the operating element 27 by means of appropriate symbols, for example as an illuminated display or as a print. This identification can be provided, for example, by the images 6 generated by the diffraction gratings 3, 3' and 3". However, it can also be an additional functionality which is not described further here. Secondly, the operating element 27 must comprise an operating mechanism which, through interaction 22 with the operating element 27, triggers an action that corresponds to the desired operability. For example,The action may involve switching a lamp or heating / ventilation system in a vehicle on and off. A corresponding sensor 21 must be included to detect the interaction 22. The sensor 21 may be a proximity sensor, e.g., optical, a touch sensor, e.g., capacitive, or a pressure sensor, e.g., (piezo-)electric, or an electrical switch. Thus, various types of operating elements 27 can be implemented, e.g., classic push buttons (in conjunction with a mechanically movable element of the operating device), but also touchscreen-like operating elements 27 or operating elements 27 in which a contactless interaction 22, e.g., within a display area of ​​the image 6 with a hover height 18, triggers the operating mechanism. For this purpose, the sensor 21 is configured to detect an interaction 22 with the operating element 27 and to output a detection signal.This detection signal is forwarded to a control device (not shown), wherein the control device is configured to control the light gates 7, 7', 7" depending on the detection signal. For example, an image 6 showing a lamp can be turned off after the lamp has been turned on by the control element 27. Advantageously, the control device can also output a (e.g., electrical) signal that triggers the respective action, e.g., turns said lamp on or off. For this purpose, each holographic diffraction grating 5, 3', and 3" is advantageously assigned a control element 27, 27', and 27" with a respective sensor 21, 21. 1 and 21 ". The detection signal of the respective sensor 21 , 21 1 and 21“ then controls the respective assigned light gate 7, 7' and 7“.

[0151] A schematic snapshot of an ongoing interaction with the operating element 27' of the operating device 26 is shown in Figure 4a. A user's finger 22 approaches the operating element 27' to trigger the interaction 22 with the operating element 27'. For example, the light gate 7' can be touched, and a detection signal from the sensor 21 1 (shown purely schematically). The sensor 21 can, for example, be a capacitive sensor that detects contact with the surface of the light gate 7' (which is, for example, appropriately coated). It will be clear to a person skilled in the art that the representation of the light gate 7, which is shown significantly higher than the light guide 2, is purely schematic and that in reality, a flat upper surface of the device 1 or 26 can also be realized. The sensor 21 1can also be a proximity sensor that detects user interaction with the control element 27' in the area of ​​the indicated finger 22. The detection signal triggers the action desired by the interaction (e.g.: "lamp off") via the control device; moreover, the light gate 7' is controlled by the control device. For example, if image 6' (which, for example, shows a symbol of a lamp to indicate what is being controlled by the control element 27') was previously switched off because the lamp was switched on, to continue with the above example, image 6' can now be switched on by controlling the light gate 7' accordingly. This is shown in Figure 4b, where image 6' is symbolically represented simply as "B" here.

[0152] Figure 5 once again schematically shows the steps that occur when operating the control element: “detection of an interaction with the control element” 23 by the sensor 21, “output of a detection signal” 24 by the sensor 21 and “control of the light gate as a function of the detection signal” 25 by the control device.

[0153] LIST OF REFERENCE SYMBOLS

[0154] 1 Holographic display device

[0155] 2 light guides

[0156] 3 Holographic diffraction grating

[0157] 4 Light source

[0158] 5 Coupled light

[0159] 6 Generated image

[0160] 7 (Controllable) light gate

[0161] 8 Beam path of the outcoupled light

[0162] 9 First polarizing filter

[0163] 10 Second polarizing filter

[0164] 11 Controllable polarization modulator

[0165] 12 Holographic structure

[0166] 13 total reflections

[0167] 14 Decoupling area

[0168] 15 Low-refractive-index layer

[0169] 16 Coupling area

[0170] 17 Side surface of the light guide in flat design

[0171] 18 Hovering height

[0172] 19 Collimation optics

[0173] 20 Substrat

[0174] 21 Sensor

[0175] 22 Interaction (“finger”) of a user

[0176] 23 Detection of an interaction with the control element

[0177] 24 Output of a detection signal

[0178] 25 Control of the light gate depending on the detection signal

[0179] 26 Operating device

[0180] 27 Control element

Claims

PATENT CLAIMS 1. Holographic display device (1) for the switchable display of images (6), comprising a light source (4), a light guide (2) and at least two holographic diffraction gratings (3), which are configured to illuminate the at least two holographic diffraction gratings (3) by light (5) from the light source (4) coupled into the light guide (2), wherein each holographic diffraction grating (3) is configured to couple light out of the light guide when illuminated by the light source (4) in order to generate an image (6), wherein each holographic diffraction grating (3) is assigned a controllable light gate (7) which is configured to regulate a brightness of the respectively generated image (6).

2. Holographic display device (1) according to claim 1, wherein the light gate (7) is arranged at least in part in a beam path of the coupled-out light (8) of the associated diffraction grating (3).

3. Holographic display device (1) according to one or more of the preceding claims, wherein the light gate (7) is configured to control the transmission of light depending on an applied control signal, wherein the controllable transmission preferably comprises at least two different transmission values.

4. Holographic display device (1) according to the preceding claim, wherein the transmission values ​​comprise a first and a second value, wherein at the first transmission value the image (6) is visible and wherein at the second transmission value the image (6) is not visible.

5. Holographic display device (1) according to one or more of the preceding claims, wherein the light gate (7) comprises a first polarization filter (9) and a second polarization filter (10) and a controllable polarization modulator (11) arranged between the polarization filters (9, 10).

6. Holographic display device (1) according to the preceding claim, wherein the first polarization filter (9), the second polarization filter (10) and the controllable polarization modulator (11) are arranged in a beam path of the coupled-out light (8) of the associated diffraction grating (3).

7. Holographic display device (1) according to the preceding claim 5, wherein the second polarization filter (10) and the controllable polarization modulator (11) are arranged in a beam path of the outcoupled light (8) of the associated diffraction grating (3), wherein the first polarization filter (9) is a common first polarization filter (9) for all light gates (7, 7', 7"), which is arranged between the light source (4) and the holographic diffraction gratings (3, 3', 3").

8. Holographic display device (1) according to one or more of the preceding claims, wherein the light guide (2) has a planar extension, wherein the light guide (2) has an output surface (14) for coupling out the light from the light guide (2), which is arranged along the planar extension of the light guide (2), wherein the holographic diffraction gratings (3) are preferably arranged along the output surface (14).

9. Holographic display device (1) according to the preceding claim, wherein the light gate (7) is applied at least in part to the coupling-out surface (14).

10. Holographic display device (1) according to the preceding claim, wherein a low-refractive-index layer (15) is included on the coupling-out surface (14) at least between the holographic diffraction grating (3) and the parts of the light gate (7).

11. Holographic display device (1) according to the preceding claim, wherein a refractive index difference between the light guide (2) and the low-refractive-index layer (15) is at least 0.3, wherein preferably the light guide (2) has a refractive index between 1.45 and 2.0 and wherein preferably the low-refractive-index layer (15) has a refractive index between 1.37 and 1.

47.

12. Holographic display device (1) according to one or more of the preceding claims, wherein an air gap is included between the light guide and the parts of the light gate.

13. Holographic display device (1) according to one or more of the preceding claims, wherein the holographic diffraction gratings (3) are arranged next to one another, wherein preferably a plurality of holographic diffraction gratings (3) are arranged directly adjacent to one another or wherein preferably a plurality of holographic diffraction gratings are arranged at a distance from one another, wherein a distance is preferably at least 1 mm, more preferably at least 2 mm and in particular 3 mm or more.

14. Holographic display device (1) according to one or more of the preceding claims, wherein the holographic diffraction gratings (3) and / or the generated images (6) have an extent of at least 10 x 10 mm 2 .

15. Operating device (26) comprising a holographic display device (1) according to one or more of the preceding claims, wherein at least one operating element (27) is comprised with at least one sensor (21), wherein the sensor is configured to detect (23) an interaction (22) with the operating element (27) and to output a detection signal (24), and a control device, wherein the control device is configured to control (25) the light gates (7) in dependence on the detection signal.

16. Operating device (26) according to the preceding claim, wherein for at least two holographic diffraction gratings (3) an operating element (27) associated with the respective holographic diffraction grating (3) is included, wherein the light gates (7) associated with the respective holographic diffraction grating (3) are controlled as a function of the detection signal of the operating element (27) associated with the diffraction grating (3).

Images