DE102023206165A1 - SWITCHABLE HOLOGRAPHIC DISPLAY - Google Patents

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 set up for illuminating 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. In addition, a controllable light gate is assigned to each holographic diffraction grating. The light gate is set up to regulate a brightness of the image generated in each case.
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 which controls the light gate depending on the detection signal.

Description

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 set up for illuminating 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. In addition, a controllable light gate is assigned to each holographic diffraction grating. The light gate is set up to regulate a brightness of the image generated in each case.

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 which controls the light gate depending on the detection signal.

Background and state of the art:

Illuminated displays, including holographic displays, are known from the state of the art. Often, such holographic illuminated displays use a light guide into which light is coupled and which includes a holographic structure for coupling out and image generation. Often, a so-called edge-lit arrangement is used, in which light is coupled into a light guide at an angle greater than the angle of total reflection and is then coupled out of the light guide by a holographic structure enclosed by the light guide in order to generate the display. If you want to generate several images, especially images of the same color, in this way, you can accommodate them together in a light guide or a single edge-lit arrangement, or you can use a separate light guide or edge-lit arrangement for each image. In the first case, the brightness of the images can only be controlled together and in particular switched on and off, namely by regulating the illumination light accordingly. Unfortunately, separate control of the brightness of individual images, which are generated by holographic structures illuminated with 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.

Object of the invention:

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 which uses a single light guide to illuminate holographic structures in order to generate several images, whereby the brightness of the images can be individually controlled in a simple and effective manner. It is also the object of the invention to provide an improved operating device with a holographic display.

Summary of the invention:

The object is solved by the features of the independent claims. Preferred embodiments of the invention are described in the dependent claims.

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 designed 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 designed to couple light out of the light guide when illuminated by the light source in order to generate an image. In addition, a controllable light gate is assigned to each holographic diffraction grating. The light gate is arranged and designed to regulate a brightness of the image generated in each case.

A holographic display device for the switchable display of images is preferably a device that generates images through holographic diffraction gratings, which are thus displayed as it were. These images are in particular switchable, which preferably means 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 displays of images include in particular images that can be switched on and off.

A light guide is preferably a body that is transparent to electromagnetic radiation in a certain wavelength range, which, when coupled into the light guide accordingly, makes it possible to guide this electromagnetic radiation, i.e. in particular to "transport" it along a certain path within the light guide. for example, directly and/or via so-called wave guidance through reflections, especially total internal reflections, 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.

Transparent preferably means that one can essentially see through the base body. Transparent means in particular that the base body has a transmittance based on the intensity of the light (preferably in the stated 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%.

Terms such as substantially, approximately, about, ca. 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 in particular less than ±1%. Similarly, preferably describes sizes that are approximately equal. Partially preferably describes at least 5%, particularly preferably at least 10%, and in particular at least 20%, in some cases at least 40%. Terms such as substantially preferably always include the exact value.

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. As is usual for holography, this can have a three-dimensional depth effect, but it can also be a two-dimensional image. In contrast to normal images, e.g. photography, in holography, in addition to the intensity of the object being imaged, phase relationships of the light coming from the object being imaged 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 while the object is being recorded. The object is illuminated with coherent light and is reflected and scattered by the object. The resulting wave field, the so-called object wave, is superimposed with light that is 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 that is identical or similar to the reference wave, which is then diffracted by the recorded interference patterns. In this way, the original wave front 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, since these can have wavelength selectivity due to wavelength-selective interference.

Holograms can be transmission and reflection holograms, for example, which produce this reconstruction either in transmission or in reflection. If, for example, you are on the side of a transmission hologram opposite the light source and look at it, the object depicted appears three-dimensionally in front of you. With a reflection hologram, you preferably have to be on the same side as the light source. Reflection holograms preferably have a wavelength-selective efficiency to diffract the light in a certain direction (or along a certain 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 describe the image produced, in particular the three-dimensional image. However, the person skilled in the art knows from the context what is meant by the term "hologram".

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. These manufacturing processes are suitable for mass production of optical functions in the form of holograms, but are not time-consuming. Suitable replication processes, particularly optical ones, are suitable for this.

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.

The light source, light guide and the at least two holographic diffraction gratings are designed 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 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, with the coupling in particular being irradiation in such a way that the light is guided in the light guide (see above). This light is guided in particular as far as the holographic diffraction gratings so that they are illuminated. The illumination preferably takes place at an angle or angle range or angle spectrum for which the holographic diffraction grating is designed to match the wavelength range of the light source.

The light source is preferably at least one light source, so it can also be several light sources. The one light source or the several light sources advantageously illuminate the several holographic diffraction gratings together. This means in particular that the several holographic diffraction gratings are illuminated by the same light source or the same light sources. In the prior art, however, holographic diffraction gratings, the images generated from which should be individually switchable, are illuminated by different light sources, so that the images are switched by switching the light sources.

Each holographic diffraction grating is designed to couple light out of the light guide when illuminated by the light source in order to create an image. To do this, the wavelength spectrum and angle spectrum of the illumination light striking the diffraction gratings are preferably initially matched to these diffraction gratings, as described above. The diffraction grating will then preferably diffract the light according to its functionality in such a way that part of the illumination light is deflected and coupled out of the light guide, with the light also being deflected and coupled out in such a way that a desired image is created.

The surface of the light guide from which the light is coupled out by the holographic diffraction gratings is preferably called the coupling-out surface.

A light gate, or synonymously a light valve, is preferably a component that can control the passage or transmission of light, especially for an aforementioned spectrum of electromagnetic radiation.

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. In addition, this preferably means that the light gate assigned to a diffraction grating is "responsible" for controlling the brightness of the image produced by this diffraction grating.

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

The fact that the light gate is designed to regulate the brightness of the respective image generated 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 coupled-out light of this diffraction grating.

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

In a preferred embodiment of the invention, the light gate is arranged at least in part in a beam path of the coupled-out light of the associated diffraction grating.

At least in part preferably means that at least some subcomponents of the light gate are arranged in the beam path. In particular, the complete light gate can also be arranged in the beam path of the coupled-out light.

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

In a further preferred embodiment of the invention, the light gate is arranged to, depending on an applied control signal, To control the transmission of light. The control of the light should advantageously not be arbitrary, but rather controlled in a targeted manner. Applying a control signal to the light gate is particularly suitable for this. The light gate can have a connection for this. The control signal can then take on different values, which then correspond at least partially to different transmission values. 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 strengths.

In a further preferred embodiment of the invention, the controllable transmission comprises at least two different transmission values.

In a further preferred embodiment of the invention, the light gate is designed to switch the image on and off. For this, for example, the intensity of the light must be adjustable so that in the first case (image switched on) the image is visible and in the second case (image switched off) the image is not visible. For "visible" and "not visible", for example, the following definitions with regard to an intensity difference can apply.

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 wherein the image is not visible (or switched off) at the second transmission value. The difference between visible and non-visible 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.

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. liquid crystal cell) arranged between the polarization filters. This is, for example, with reference to the 1 and 3 described in more detail.

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 coupled-out light of the associated diffraction grating. This is the case, for example, in 1 described in more detail. In this case, the complete light gate is advantageously arranged in the beam path of the coupled-out light.

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 coupled-out light of the associated diffraction grating. The first polarization filter is a common first polarization filter for all light gates, which is arranged between the light source and the holographic diffraction gratings. This is the case, for example, in 3 described in more detail.

The first polarization filter preferably has the function of giving the light a well-defined polarization, for example a linear polarization. The polarization filter is preferably set up to transmit this well-defined polarization and to essentially block other polarizations. The well-defined polarization of the first polarization filter is advantageously 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 correspond, for example, 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, for example, 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 second polarization filter is again configured analogously to the first polarization filter to essentially transmit a well-defined polarization (e.g. a linear polarization) and to 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.

The second polarization filter can transmit different polarizations for different light gates. This can be useful, for example, if the light has undergone different polarization transformations on the way to the different light gates. This can be caused, for example, by a different number of total reflections taking place in the light guide.

In a further preferred embodiment, the light source is a light source for polarized light, wherein the light gate comprises a polarization modulator and a subsequent (preferably behind) second polarization filter.

The light source preferably emits linearly polarized light or light that can be converted into a linear polarization without losses, 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 dispensed with, since the light is already polarized in a well-defined manner by the light source. The light source can already emit polarized light in terms of its functionality (e.g. laser) and/or have a polarization filter included in the light source. This embodiment requires particularly few components.

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

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 be introduced into the holographic structure, for example, 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.

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

In the aforementioned embodiment, each holographic structure always contains only one holographic diffraction grating, i.e. each diffraction grating contains its own holographic structure. This enables the holographic diffraction grating to be manufactured particularly easily.

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

In the aforementioned embodiment, at least two, preferably all, holographic diffraction gratings are in a holographic structure. Therefore, the holographic diffraction grating must be manufactured in such a way that several diffraction gratings can be incorporated into a holographic structure. However, the introduction of the diffraction gratings into the device is simplified and the adjustment effort for the correct arrangement of the at least two diffraction gratings relative to one another can be reduced.

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 diffraction of red, green and blue light. For this purpose, each diffraction grating can comprise (sub) gratings for red, green and blue light. As a result, with suitable lighting (e.g. by an RGB light source) and suitable diffraction efficiencies for the respective colors, an image in any color, in particular also in white, can be generated by color mixing.

In a further preferred embodiment, the holographic diffraction gratings are designed 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. The light source advantageously emits correspondingly monochrome light, for example in the red spectral range, to stay with the example mentioned.

In a further preferred embodiment of the invention, the light guide, light source and diffraction grating are designed to illuminate the holographic diffraction gratings without prior multiple reflections in the light guide. The light thus preferably hits the diffraction gratings directly from the coupling into the light guide. This preferably also includes the case where the diffraction gratings are reflection holograms (see below) and a reflection takes place 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, with which a particularly homogeneous illumination of all diffraction gratings and a particularly homogeneous brightness of the images generated can be achieved.

There may 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, on which a targeted deflection of the coupled-in light can take place in order to to then guide it at a desired angle in the light guide in the direction of the diffraction gratings. 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 in relation 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 can also be the case that no further multiple reflections take place 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 a reflection of the coupled-in light at the deflection surface, no multiple reflections take place in the light guide for the illumination of the holographic diffraction gratings.

In a further preferred embodiment of the invention, the light guide, light source and diffraction grating are set up for the illumination of the holographic diffraction gratings by wave guidance through multiple total reflections in the light guide. In this way, the light can be transported over a long distance with almost no loss, even in thin light guides. The illumination of one or more diffraction gratings, which together take up a large area, can also be easily enabled in this way. The coupled beam can preferably take up a certain area at the location of the holographic diffraction grating along the plane of the extension of the holographic diffraction grating. This area is preferably also referred to as a footprint. This can be smaller than the extension of a holographic diffraction grating or than the extension of the holographic diffraction gratings taken together (preferably including the spaces between the diffraction gratings). Then several such footprints taken together must result in illumination of 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.

In a further preferred embodiment of the invention, the light guide, light source and diffraction grating are set up for the full-surface illumination of the holographic diffraction gratings by wave guidance 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. almost without gaps. In this embodiment, the light guide, light source and diffraction grating are set up in such a way that the footprints enable full-surface illumination of the holographic diffraction gratings. One way of achieving this is for the footprints to directly touch one another or even overlap. Geometric considerations play a particularly important role here. For example, for direct contact of the footprints, tan Θ = 0.5*F/d can be given, where Θ is the angle that the coupled light beam forms with a normal of the interface (reflection surface) of the light guide (preferably in a plane along a longitudinal section of the light guide, i.e. a section along the light guide direction or a longitudinal direction of the light guide). F is the extent of the footprint along this light guide or longitudinal direction and d is the thickness of the light guide. This applies in particular to light guides whose interfaces, where the reflection takes place, are parallel. Another possibility is preferably that the footprints do not overlap, but footprints and diffraction gratings are positioned in such a way that each diffraction grating is fully illuminated by a footprint.

In the above-mentioned embodiments, in which the diffraction gratings are illuminated by multiple reflections, it should be noted that each time the diffraction gratings are illuminated, part of the light is coupled out by them, and thus the intensity of the light beam becomes weaker with "each pass". Therefore, the diffraction gratings are preferably designed to couple out a largely constant intensity of light (where desired) when illuminated by multiple total reflections in the light guide. This can be done, for example, by varying the diffraction efficiency accordingly, for example by making it larger in sections the further away the respective section of the diffraction grating is from the light source. In this way, images with a homogeneous brightness can be realized.

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.

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.

In a further preferred embodiment of the invention, the holographic diffraction gratings are included in the light guide, the holographic diffraction gratings being selected in particular from the group of transmission hologram, reflection hologram, Z-hologram and/or relief structure. The holographic diffraction grating can, for example, be introduced into the substrate, e.g. written in by a laser.

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.

The at least one layer comprises, for example, one or more of the following layers: hologram layer, which preferably comprises the holographic structure, layer comprising triacetate, transparent adhesive layer or adhesive film (e.g. OCA) and/or 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 comprise, for example, carrier layers/films or protective layers/films.

A so-called Z-hologram comprises two reflection holograms, preferably arranged directly one behind the other, whereby the hologram following along the light propagation causes a first "reflection" (strictly speaking, this is of course a diffraction) of the light and then the hologram first along the light propagation. As a result, these two holograms therefore have an advantageous transmissive effect, which means that, for example, the advantages of a transmission hologram can be combined with those of a reflection hologram (higher wavelength and/or angle selectivity).

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. The depressions or elevations cause the light to travel 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 by introducing the depressions into the material using a stamp, for example.

In a further preferred embodiment of the invention, the light guide has a planar extension. The light guide has an output surface for coupling the light out of the light guide, which is arranged along the planar extension of the light guide. The holographic diffraction gratings are preferably arranged along the output surface.

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

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

The fact that the coupling-out surface is arranged along the planar extension of the light guide can also mean that the coupling-out surface is arranged parallel to it. The fact that the holographic diffraction gratings are preferably arranged along the coupling-out surface means in particular that they are arranged parallel to the coupling-out surface.

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

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

However, it may also be preferred that at least one further intermediate layer and/or additional component is present between the coupling-out surface and the parts of the light gate.

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

Preferably, gaps between light gates can also be filled with a filling material which, together with the light gates, forms a flat outer boundary surface of the device. This filling material can, for example, comprise a low-refractive layer (see below).

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

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

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 independently of the refractive index of the light gate.

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

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 coupling-out surface where the light gate is present, namely on the coupling-out surface, between the diffraction grating and the light gate.

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.

In a further preferred embodiment of the invention, a refractive index difference between the light guide (or holographic diffraction grating) and the low-refractive layer is at least 0.3. In this way, total reflection can advantageously be ensured for preferred angles of the coupled-in light.

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.

In a further preferred embodiment of the invention, an air gap is included between the light guide and the parts of the light gate, preferably between the coupling-out surface and the parts of the light gate.

The air gap advantageously has the same effect as the low-refractive-index layer, in particular the effect of ensuring total reflection of the coupled-in light at the output surface or the outer surface of the light guide even where the light gate or parts thereof are applied to the output surface or the light guide, in particular regardless of the refractive index of the light gate.

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.

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

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

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

The coupling surface is preferably an outer surface of the light guide, which is designed 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 be flat, for example. However, it can also have particularly desired light-forming properties, for example it can be curved in order to achieve or support collimation of the coupled light.

Preferably, the light guide and the light source are designed to couple light from the light source into the light guide. This can mean, for example, that the light source is positioned directly in front of the coupling surface and radiates in the direction of the coupling surface.

In a further preferred embodiment of the invention, the light guide has a planar extension, with the coupling surface being present on a side surface of the light guide. The side surface is preferably not located along the planar extension of the light guide, in particular perpendicular to it. However, the side surface can be beveled at an angle other than a perpendicular angle to the planar extension, at least in the region of the coupling surface.

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 it is coupled out of the coupling-out surface, with the coupling-out surface being arranged along the planar extension. 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 reflection.

In a further preferred embodiment of the invention, the light source is designed to irradiate the coupling surface, in particular for coupling into the light guide, so that coupled light propagates at an angle greater than the critical angle of total reflection in the light guide. This preferably applies to at least one plane of the light guide, e.g. a longitudinal section plane of the light guide perpendicular to the coupling-out surface of the light guide (vertical plane). For this purpose, for example, the coupling surface can be located in a beveled region of the side surface, with the light source being arranged, for example, at an angle to the planar extent of the light guide. For example, the light source can be arranged such that it is arranged along a surface normal of the coupling surface. In this way, coupling can be carried out particularly easily and with a minimization of Fresnel reflections on the coupling surface, in particular at an angle greater than the critical angle of total reflection.

It may also be preferred that the coupling surface is arranged along the planar extent of the light guide. The light source can also be arranged along a surface normal of the coupling surface. In order to ensure coupling at an angle greater than the angle of total reflection, the light guide can, for example, have a deflection surface which is designed to deflect the coupled light at an angle so that after deflection the light forms an angle with the boundary surfaces of the light guide (e.g. coupling-out surface) which is greater than a critical angle of total reflection.

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).

A floating 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.

The reference plane here is in particular the output surface of the light guide.

A special optical effect can be achieved by setting the height of the screen. Operating functions that do not rely on touching a surface can also be implemented in this way. The image can mark an operating area.

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

The light source can comprise, for example, 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 relation to the wavelength of the light.

The light source preferably does not comprise a separate beam-forming component, e.g. a lens.

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

The light source is preferably arranged with a main radiation direction in the direction of the coupling surface, in particular if the light source has anisotropic radiation properties.

LEDs are particularly simple, long-lasting and cost-effective and have sufficient optical properties, particularly with regard to their coherence, for a variety of lighting functions, especially holographic lighting functions. LEDs are particularly efficient.

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 area is independent of the emitter size.

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

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

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).

For example, it could be an Osram MULTILED LRTB GVSG, which emits at 625 nm (red), 528 nm (true green), 460 nm (blue). Intensities can be, for example, 500 - 1000 milli-candelas (mcd) for red, 1250 - 2010 mcd for green and 180 - 560 mcd for blue.

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.

The collimation optics are preferably designed to realize a collimation of the light from the light source in at least one plane. The collimation optics are preferably designed to realize a collimation in at least one plane along the planar extent of the light guide. However, it may also be preferred that the collimation optics are designed to realize the light from the light source in two mutually perpendicular planes.

In this way, the beam properties of the illumination of the holographic diffraction grating can be improved and a better image can be produced.

In a further preferred embodiment of the invention, the holographic diffraction gratings are arranged next to one another. In this way, several images can be displayed next to one another and their brightness can be controlled.

In a further preferred embodiment of the invention, several holographic diffraction gratings are arranged directly adjacent to one another. In this way, images that are close to one another or adjacent to one another can be generated.

In a further preferred embodiment of the invention, several holographic diffraction gratings are arranged at a distance from one another, with a distance preferably being at least 1 mm, more preferably at least 2 mm and in particular 3 mm or more. In this way, for example, images can be generated which are spaced apart from one another. This can, for example, improve the representation or operability if the images show 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.

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.

In a further preferred embodiment of the invention, several 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 positioning the diffraction gratings along two directions that are essentially vertical to one another. 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. The number of diffraction gratings can thus be determined by specifying the number of columns and rows. The number of rows and columns is preferably specified in the format A x B, where A is a natural number that indicates the number of rows and B is a natural number that indicates 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 have to correspond to the number of rows, as in the example.

In one variant, the diffraction gratings arranged in a matrix form produce images, each of which represents a symbol, e.g. a letter and/or a number and/or a special character, whereby the images together show a PC keyboard, in particular a QWERTZ keyboard. In this way, individual keys or a luminous variant of the Keys can be switched on and off, for example to indicate that a certain key (e.g. the Caps Lock key) has been pressed or to enable operation in the dark.

In a further preferred embodiment of the invention, the holographic diffraction gratings and/or the images generated have an extent of at least 10 x 10 mm ² . In this way, particularly clearly recognizable images can be realized.

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

In particular, the images generated are directly adjacent to one another.

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 produce an aesthetic effect, in particular by a certain coloring of the diaphragm layer. In addition, 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.

The diaphragm layer may in particular comprise a film.

In a further preferred embodiment of the invention, the low-refractive index layer is arranged between the coupling-out surface and the diaphragm layer. In this way, absorption of coupled-in/guided light in the diaphragm layer can be reduced.

In a further preferred embodiment of the invention, the diaphragm layer has recesses and/or transparent areas congruent with the holographic diffraction gratings. In this way, the light diffracted by the diffraction gratings can be coupled out largely without absorption.

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

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 comprise, for example, an application-specific integrated circuit (ASIC), a programmable logic device (PLD) or a field programmable gate array (FPGA). Furthermore, components known to the person skilled in the art in this context, such as at least one electronic memory, an integrated circuit, at least one digital-analog converter, at least one analog-digital converter and/or at least one amplifier, can be included.

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

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 that is configured to detect an interaction with the operating element and to output a detection signal, and a control device. The control device is configured to control the light gates depending on the detection signal.

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

It will be apparent to those 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.

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 a corresponding symbol to identify the operating element. This can be provided, for example, by the images generated by the diffraction gratings. On the other hand, 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 heating/ventilation in a vehicle on and off. A corresponding sensor is included to determine 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, different 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. 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 set up to detect an interaction with the operating element and to output a detection signal. This detection signal is passed on to a control device, wherein the control device is set up 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 which triggers the respective action, e.g. switches the said lamp on or off.

In a preferred embodiment of the invention, a control element associated with the respective holographic diffraction grating is included for at least two holographic diffraction gratings. The light gates associated with the respective diffraction grating are controlled depending on the detection signal of the control element associated with the diffraction grating.

For the previously described functionality of the operating device, each holographic diffraction grating is advantageously provided with an associated operating element with a respective sensor. The detection signal of the respective sensor then in turn controls the respectively associated light gate.

• - Ausgabe eines Detektionssignal bei einer Detektion einer Interaktion mit dem Bedienelement durch den Sensor, vorzugsweise an die Steuerungsvorrichtung,
• - Steuerung des Lichtgatters in Abhängigkeit vom Detektionssignal durch die Steuerungsvorrichtung.

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

• - 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 depending on the detection signal by the control device.

It is 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.

Description of the invention:

• 1 zeigt schematisch eine Ausführungsform der holographischen Anzeigenvorrichtung.
• 2 zeigt schematisch eine Ausführungsform der holographischen Anzeigenvorrichtung, bei der eine niedrigbrechende Schicht auf der Auskoppelfläche umfasst ist.
• 3 zeigt eine Ausführungsform mit variierendem Aufbau der Lichtgatter.
• 4a und b zeigen eine Bedienvorrichtung gemäß einem weiteren Aspekt der Erfindung.
• 5 zeigt schematisch die bei der Bedienung des Bedienelementes ablaufenden (Verfahrens-) Schritte.

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.

• 1 schematically shows an embodiment of the holographic display device.
• 2 shows schematically an embodiment of the holographic display device in which a low-refractive layer is included on the coupling-out surface.
• 3 shows an embodiment with varying structure of the light gates.
• 4a and b show an operating device according to a further aspect of the invention.
• 5 shows schematically the (procedural) steps involved in operating the control element.

1 shows schematically 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 set up or arranged, controllable light gates 7, 7' and 7", the brightness of the images 6, 6', 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.

The display device has a light source 4, e.g. an LED, a light guide 2 and, in the present case, three holographic diffraction gratings 3, 3' and 3". The light guide 2 and the light source are arranged in relation to one another in such a way that the light from the light source 4 is coupled into the light guide 2 and this coupled light 5 then illuminates the diffraction gratings 3, 3' and 3". The diffraction gratings 3, 3' and 3" are therefore illuminated together or by a common light source 4. The diffraction gratings 3, 3', 3" at least partially decouple this illumination light from the light guide 2. The decoupled light 8 (see 2 ) then produces 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 produced by the diffraction gratings 3, 3' and 3" can nevertheless be controlled separately is achieved by the fact that each diffraction grating 3, 3' and 3" has its own, assigned light gate 7, 7' and 7", 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 in such a way that no outcoupled light 8 can pass through, no image 6, 6' or 6" is produced. If the transmission of the light gate 7, 7' or 7" is again adjusted so that the coupled-out light of the respective diffraction grating 3, 3' or 3" can pass essentially unhindered, an image 6, 6' or 6" visible to a viewer is produced.

In the following, further details of the present embodiment according to 1 the display device 1 is explained. 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 to this. In the case shown, the planar extension extends along a horizontal of the image and the smaller extension along a vertical direction. The side surfaces of the light guide 2 extend along the smaller extension, for example 17 and 17'. 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 to the image vertical in order to enable, in conjunction with the arrangement of the light source 4, the light to be irradiated into the light guide 2 at an angle greater than the critical angle of total reflection, as will be described below, among other things.

The light source 4 is designed 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 radiation into the coupling surface 16 essentially forms a right angle with it, for example to avoid light refraction and to 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. However, a collimating optic 19 can also be used, which also causes collimation in the plane perpendicular to the image plane.

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 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 reflection takes place at the upper and lower boundary surfaces of the light guide 2. On the one hand, the light can be guided to the diffraction gratings 3, 3' and 3" by multiple reflections 13 in the light guide 2 (through wave guidance) without significant losses. On the other hand, the light not diffracted out of the light guide 2 by the diffraction gratings 3, 3' and 3" (the so-called zeroth order) is guided further in the light guide 2 and does not reach the viewer, as can be the case with other holographic arrangements. Since a coupled 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" that passes through later has a higher diffraction efficiency than a part that passes through earlier, in order to generate homogeneously bright images overall.

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

In the embodiment shown, the holographic diffraction gratings 3, 3' and 3" are included in a common holographic structure 12. This can be in the form of a film, for example, which is applied to the substrate of the light guide 2. This simplifies the application of the diffraction gratings 3, 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 3, 3' and 3" in a single structure 12 is also quite possible.

In the 1 In the variant of the holographic lighting device 1 shown, the light gates 7, 7' and 7" are arranged entirely in a beam path of the coupled-out light 8 of the respective associated diffraction grating 3, 3' and 3", i.e. along the beam path of the light behind the respective diffraction grating 3, 3' and 3". The coupled-out light 8 of the respective diffraction grating 3, 3' and 3" thus passes through the respective associated light gate 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 a controllable polarization modulator 11 located between them. 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 has the function of giving the light to give a well-defined polarization, e.g. a linear polarization tion. The polarization filter 9 is set up accordingly to transmit this well-defined polarization and essentially block other polarizations. 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) and with a second control signal this can correspond to a rotation of 90°. The second polarization filter 10 is in turn designed, like the first 9, to essentially transmit a well-defined polarization (e.g. a linear polarization) and to essentially block other polarizations. For example, in one embodiment the second polarization filter 10 can transmit essentially the same polarization as the first polarization filter 9. Then the maximum amount of coupled-out 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 essentially 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, for example, be set up to transmit a polarization that deviates by essentially 90° from the polarization that the first polarization filter 9 transmits (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, for example, be implemented by a liquid crystal cell.

In addition to the embodiment shown, it is also conceivable that the light gate 7 is only partially arranged in a beam path of the coupled-out light 8, i.e. along the beam path of the light behind the diffraction grating 3. 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 at the same time 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.

2 shows schematically some details of an embodiment of the holographic display device 1. Some features of the device shown are already in 1 and are therefore not presented in detail here. However, they are marked with the same reference numerals as in 1 and can therefore be easily identified. 2 shows a section of the light guide 2 and its structure and function in detail, without, for example, going into aspects of coupling the light into the light guide 2. Furthermore, elements applied to the light guide 2 such as the low-refractive layer 15 and two light gates 7 and 7' are shown. The light guide 2 itself in the present embodiment comprises a substrate 20 or a substrate body and the holographic structure 12, here in the form of a hologram film applied to the substrate 20, which as a common holographic structure 12 comprises the diffraction gratings 3 and 3'. The hologram film and substrate 20 have a very similar refractive index so that no unwanted reflections occur on their contact surface and an optically largely homogeneous light guide 2 is formed. The low-refractive layer 15 is included on the hologram film, the function of which will be explained in more detail below. The associated light gates 7 and 7' are applied to the low-refractive 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 film and the low-refractive layer 15. This 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 reflections at the upper and lower interfaces of the light guide 2, with the upper interface being the output surface 14. When the light hits 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 in such a way that it is coupled out of the output surface 14 of the light guide 2. The diffraction gratings 3, 3' shown are reflection holograms, the coupled light transmits these from the lower boundary surface of the light guide 2 initially undiffracted, is then reflected at the output coupling surface 14 and only then diffracted by the diffraction gratings 3, 3' into the so-called first order and coupled out of the coupling-out surface 14 of the light guide 2. The coupled-out light 8 then transmits 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 part 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 layer 15 is now to enable total reflection at the coupling-out surface 14 even where the light gates 7, 7' are located. Otherwise, without the low-refractive 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 and thus disrupt the total reflection or light conduction of the coupled-in light 5 in the light guide 2. For this, the low-refractive layer 15 must have a correspondingly lower refractive index than the light guide 2, so that the critical angle of total reflection is smaller than the angle that the coupled-in light 5 forms with the surface normal of the output surface 14. Of course, a corresponding difference between the light guide 2 and the surrounding medium (usually air) must also exist at the lower interface of the light guide 2. However, the light 8 diffracted and coupled out by the holographic diffraction gratings 3, 3' can easily be transmitted by the low-refractive layer 15 in the direction of the light gates 7, 7', since it strikes the interface between the light guide 2 and the low-refractive layer 15 at an angle smaller than the critical angle of total reflection (for example, as shown, at an angle of 0°, the angle between the respective light beam and the surface normal to the interface being measured). The light guide 2 is therefore essentially defined by the fact that it has an approximately homogeneous refractive index and thus enables light to be guided by total reflection on its outer surfaces (with a corresponding coupling angle).

3 shows a variant that is largely similar to 1 corresponding embodiment (with corresponding reference numerals) of the display device 1, in which, however, 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 coupled-out light 8 of the associated diffraction grating 3, 3', 3", but the first polarization filter 9 is a common first polarization filter 9 for all light gates 7, 7', 7". In the example shown, this is arranged between the collimation optics 19 and the coupling surface 16, specifically directly on the coupling surface 16. This advantageously means that only a single first polarization filter 9 is required, which sets a well-defined polarization for the entire illumination light, which then makes it possible to control the transmission of the coupled-out light 8 through the individual light gates 7, 7' and 7" as described above. However, it can happen that, for example, due to the different number of total reflections of the coupled light 5 on the way to the different 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 set up to transmit different polarizations accordingly. Alternatively or additionally, it can 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.

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 a corresponding symbol, for example as a light 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. On the other hand, the control element 27 must comprise an operating mechanism which, through interaction 22 with the control element 27, triggers an action that corresponds to the desired operability. For example, the action can be switching a lamp or heating/ventilation in a vehicle on and off. To determine the interaction 22, a corresponding sensor 21 must be included. The sensor 21 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, different types of control elements 27 can be implemented, e.g. classic push buttons (in conjunction with a mechanically movable element of the control device), but also touchscreen-like control elements 27 or Control elements 27, in which a contactless interaction 22, e.g. within a display area of the image 6 with floating height 18, triggers the operating mechanism. the sensor 21 is set up to detect an interaction 22 with the control element 27 and to output a detection signal. This detection signal is passed on to a control device (not shown), wherein the control device is set up to control the light gates 7, 7', 7" depending on the detection signal. For example, an image 6 showing a lamp can be switched off after the lamp has been switched on by the control element 27. Advantageously, the control device can also output a (e.g. electrical) signal which triggers the respective action, e.g. switches the said lamp on or off. For this purpose, each holographic diffraction grating 3, 3' and 3" advantageously includes an associated control element 27, 27' and 27" with a respective sensor 21, 21' and 21". The detection signal of the respective sensor 21, 21' and 21" then controls the respective associated light gate 7, 7' and 7".

A schematic snapshot of an ongoing interaction with the control element 27' of the control device 26 is shown in 4a shown. A user's finger 22 approaches the operating element 27' in order to trigger the interaction 22 with the operating element 27'. In doing so, for example, the light gate 7' can be touched and trigger a detection signal from the sensor 21' (shown purely schematically). The sensor 21 can be, for example, a capacitive sensor that detects a touch on the surface of the light gate 7' (which is, for example, coated accordingly). It is also clear to the person skilled in the art that the representation of the light gate 7, which is shown greatly raised compared to 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' can also be a proximity sensor that detects an interaction of the user with the operating element 27' in the area of the finger 22 shown. The detection signal triggers the action desired by the interaction (e.g. "lamp off") via the control device, and the light gate 7' is also controlled by the control device. For example, if image 6' (which shows a symbol of a lamp to indicate what is controlled by the control element 27') was previously switched off because the lamp was switched on, to stay with the above example, image 6' can now be switched on by controlling the light gate 7' accordingly. This is in 4b shown, with Figure 6' being symbolically represented here simply as “B”.

5 shows once again schematically the steps involved in 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 depending on the detection signal” 25 by the control device.

REFERENCE SYMBOL LIST

1

holographic display device

2

light guide

3

Holographic diffraction grating

4

light source

5

Coupled light

6

generated image

7

(Controllable) light gate

8

beam path of the coupled-out light

9

First polarization filter

10

Second polarization filter

11

Controllable polarization modulator

12

Holographic structure

13

total reflections

14

output surface

15

low-refractive layer

16

coupling surface

17

Side surface of the light guide in flat design

18

hover height

19

collimation optics

20

substrate

21

sensor

22

interaction ("finger") of a user

23

detection of an interaction with the control element

24

output of a detection signal

25

Control of the light gate depending on the detection signal

26

control device

27

control element

Claims (16)

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 designed for illuminating the at least two holographic diffraction gratings (3) by means of light coupled into the light guide (2). Light (5) of the light source (4), wherein each holographic diffraction grating (3) is arranged to couple light out of the light guide when illuminated by the light source (4) in order to produce an image (6), wherein each holographic diffraction grating (3) is assigned a controllable light gate (7) which is arranged to regulate a brightness of the respectively produced image (6). 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). Holographic display device (1) according to one or more of the preceding claims, wherein the light gate (7) is designed to control the transmission of light depending on an applied control signal, wherein the controllable transmission preferably comprises at least two different transmission values. 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. 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). 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). Holographic display device (1) according to the previous claim 5 , wherein 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), 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"). 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 a coupling-out surface (14) for coupling the light out of 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 coupling-out surface (14). 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). Holographic display device (1) according to the preceding claim, wherein a low-refractive 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). 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 the light guide (2) preferably has a refractive index between 1.45 and 2.0 and wherein the low-refractive-index layer (15) preferably has a refractive index between 1.37 and 1.47. 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. 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 several holographic diffraction gratings (3) are arranged directly adjacent to one another or wherein preferably several 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. 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 . 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 the light gates (7) depending on the detection signal (25). Operating device (26) according to the previous claim, wherein for at least two holographic diffraction gratings (3) a control 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 depending on the detection signal of the control element (27) associated with the diffraction grating (3).

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