Waveguide for displaying an image, and holographic display having such a waveguide

Abstract

The invention relates to a waveguide for displaying an image, wherein: the waveguide (2) comprises a transparent base body (4) having a front face (5) and a rear face (6); the base body (4) has a coupling-in region (14) and a coupling-out region (15) which is spaced apart therefrom in a first direction, which coupling-out region has an image hologram (19) having an imprinted image; the coupling-in region (14) deflects at least some of the radiation (16) originating from a light source (3) such that the deflected part propagates as a coupled-in beam bundle (18) in the base body (4) by reflection as far as the coupling-out region (15) and impinges on the image hologram (19); the image hologram (19) deflecting at least part of the impinging beam bundle (18) in order to reconstruct the imprinted image such that the deflected part exits the base body (4) via the front face (5) or rear face (6) such that the imprinted image is perceptible for a viewer (B); the base body (4) has multiple layers, and at least one first layer (7) having a first refractive index and a second layer (9), formed on the first, having a second refractive index that is lower than the first refractive index; and the coupled-in beam bundle (18) in the first layer (7) propagates owing to internal total reflection at the boundary surface to the second layer (9).

Description

[0001] Waveguide for displaying an image and holographic display using such a waveguide

[0002] The present invention relates to a waveguide for displaying an image and a holographic display using such a waveguide.

[0003] Modern micro-optical processes make it possible to integrate complex tasks such as imaging or environmental monitoring, for example using holographic optical elements (HOE), discreetly or virtually invisibly into large-format glass surfaces. This makes it possible to implement, for example, transparent displays (e.g. in shop windows, refrigerated cabinets, car and truck side or front windows), lighting applications such as information and warning signals in any glass surface (e.g. in architecture, the automotive sector or even in designer glazing), and light-sensitive detection systems such as interior monitoring (e.g. eye tracking in vehicles and presence status of people in the interior). The disadvantage of this is that light conduction within the panes must always be achieved through total internal reflection at the outer interfaces or through very complex microstructures between the outer interfaces.Such microstructures are very expensive to manufacture, especially for large-format applications (costs increase quadratically with the size of the surface). Light transmission at the outer interfaces through total internal reflection is disadvantageously prone to interference, as dirt or water on the outer interfaces, for example, inhibits light transmission. Furthermore, the usable pane formats are severely limited if the surrounding pane substrates are tinted, as in the case of car windows. A tint of 30% means that even at a distance of 30 cm between the input and output surfaces, less than 1% of the light can propagate through the pane. The remainder is lost through absorption within the pane.

[0004] Based on this, it is therefore an object of the invention to provide a waveguide for displaying an image with which the difficulties mentioned above can be overcome as completely as possible. Furthermore, a holographic display using such a waveguide is to be provided.

[0005] The invention is defined in independent claims 1 and 12. Advantageous further developments are specified in the dependent claims. Since, according to the invention, the coupled beam is reflected by one or more reflections, in particular by one or more total internal reflections, at the interface between the first and second layers, the susceptibility to interference during light transmission can be significantly reduced.

[0006] The waveguide according to the invention can be designed such that the beam impinging on the image hologram covers the entire image hologram. However, it is also possible for the image hologram to have a first extent in the first direction that is greater than the extent of the beam cross-section of the coupled-in beam in the first direction, wherein the coupled-in beam propagates in the first direction such that it impinges on the image hologram multiple times at different locations that are offset from one another along the first direction. With each impact, a portion of the impinging beam is deflected to reconstruct the exposed image, and the remaining portion of the beam propagates further.

[0007] This makes it possible to illuminate even very large areas of the image hologram along the first direction and thus to reconstruct the desired image of the image hologram.

[0008] In particular, the image hologram can exhibit an efficiency gradient in which the deflection efficiency increases from the first to the last impact of the beam. This allows for a more homogeneous reconstructed image to be created.

[0009] The image hologram can in particular be designed as an image plane hologram, in which the reconstructed image is perceptible as a (substantially planar) image in the transparent base body.

[0010] The image hologram can be designed in such a way that the exposed image contains the image information, which is reconstructed by means of the incident beam of rays, so that the image is perceptible to a viewer.

[0011] The image hologram can further be designed such that the exposed image is a holographic diffuser or has one, which can generate the image using image information contained in the incident beam. Thus, with this design, the incident beam provides the image information, which is then perceivable by a viewer as an image, for example, in the plane of the image hologram. The waveguide can in particular be designed as laminated glass or as a laminated glass pane. The waveguide can be designed as a plane-parallel plate or curved, wherein the front and / or back can be curved. The waveguide can in particular be a window of a car or a truck or a part thereof.

[0012] Furthermore, the image hologram can be designed such that it has several exposed images designed for different wavelengths, so that depending on the selected wavelength of the coupled radiation, one of the images of the image hologram can be selectively reconstructed.

[0013] The waveguide and the coupling-out region can in particular be designed to be transparent.

[0014] The image hologram can be designed as a reflective hologram or as a transmissive hologram.

[0015] In particular, the image hologram can have one or more spaced-apart output regions, each of which deflects at least a portion of the coupled-in beam such that the deflected portion exits as diffuse or directed radiation. If the image hologram has several spaced-apart output regions, each of these can contain a portion of the exposed image.

[0016] The output regions can be formed as separate sub-holograms, so that no part of the image hologram is formed between the sub-holograms. In this case, the image hologram comprises the sub-holograms that are not spatially connected. However, it is also possible for the output regions to be spaced apart from one another, but all to be part of a single, spatially connected image hologram; thus, the image hologram does not have separate sub-holograms, but is formed as a single hologram with the spaced-apart output regions.

[0017] If the several spaced-apart output regions are designed in such a way that the output radiation emerges as diffuse radiation, the impression of a starry sky can be created, for example.

[0018] For example, each output region (e.g., each sub-hologram) can generate exactly one star of the starry sky to be created. However, it is also possible for at least one output region (e.g., each sub-hologram) to generate two or more stars of the starry sky to be created. Furthermore, the output regions can be spaced apart from each other but all be part of a single, interconnected image hologram that creates the starry sky to be created.

[0019] In particular, it is possible for the multiple output coupling regions to be designed to have two or more different output coupling efficiencies. This can be used to couple out radiation with different intensities at the individual output coupling regions. This allows, for example, brighter and less bright stars to be displayed for the desired starry sky.

[0020] Of course, the output coupling areas can also be designed so that they have identical output coupling efficiencies.

[0021] If the at least one coupling-out region is designed in such a way that the coupled-out radiation emerges as directed radiation, this can be used, for example, to realize a reading light or reading lighting.

[0022] The waveguide can be designed so that all output regions output the radiation as diffuse radiation or as directed radiation. It is also possible for one or more output regions to output the radiation as diffuse radiation, and one or more output regions to output the radiation as directed radiation.

[0023] The first layer can in particular be formed as a glass pane with a thickness greater than 2 mm. Preferably, the first layer is no thicker than 5 mm.

[0024] The image hologram may be formed on the first side and / or the second side of the first layer.

[0025] By forming the image hologram and / or arranging multiple output regions of the image hologram (e.g., a starry sky), a perceivable image can be generated when the image hologram is exposed to the coupled-in beam of light. Thus, the image information of the generated image is preferably contained (preferably completely) in the image hologram. In this case, one can say that the coupled-in radiation is free of image information. The coupled-in radiation can therefore also be referred to as illumination radiation.

[0026] The first layer can have a coupling region protruding from the first side. The coupling region can have a flat or curved entrance surface. Furthermore, the coupling region can have a deflection element that deflects at least a portion of the radiation coming from the light source such that the deflected portion of the coupled radiation is guided in the inner pane by reflections to the at least one coupling-out region.

[0027] The deflection element can be formed on the first side or second side of the first layer. If the deflection element is formed on the first side of the first layer, it is preferably designed as a transmissive deflection element. If the deflection element is formed on the second side of the first layer, it is particularly designed as a reflective deflection element.

[0028] The deflection element can be designed as a volume or surface grating and thus in particular as a hologram or relief grating.

[0029] The waveguide can have at least one further layer or disc, which is connected to the first layer, e.g., by means of a further adhesive layer. The refractive index of the further adhesive layer can be selected such that the light is reflected at the interface between the further disc and the further adhesive layer, as well as at the interface between the first layer and the further adhesive layer, in each case due to total internal reflection. The further disc can be designed in the same way as the first layer, so that the further disc and the first layer can each be referred to as a light guide.

[0030] Furthermore, two or more further discs with corresponding adhesive layers can be formed as a layer stack on the first layer, wherein the further discs can be formed in the same way as the first layer.

[0031] This means that two or more light guides can be integrated into the laminated glass pane, providing further design options for the desired lighting effects.

[0032] The image hologram can, for example, have essentially point-shaped output regions to create the starry sky described, for example. However, it is also possible for the at least one output region to have a larger surface area.

[0033] The waveguide according to the invention can be designed, for example, as a laminated glass pane, and in particular as a pane for a vehicle roof, through which a person inside the vehicle can, for example, see through. The laminated glass pane according to the invention can also be designed as another pane for a vehicle.

[0034] The vehicle can be a land, water and / or air vehicle.

[0035] In particular, it can be a car or a truck.

[0036] Furthermore, a hologram can be formed in the coupling region of the waveguide. The hologram of the coupling region can be designed as a transmissive hologram or a reflective hologram.

[0037] In the holographic display according to the invention, the light source can comprise one or more light-emitting diodes. In particular, the light-emitting diodes can emit light at different wavelengths.

[0038] The light source is preferably designed to emit radiation in the visible wavelength range. In particular, the radiation can be white light and / or colored light (such as red, green, and / or blue light). Furthermore, the light source can be designed to generate and emit several different colors. This is preferably controllable or adjustable. The light source can comprise one or more LEDs.

[0039] Furthermore, the holographic display can comprise a control unit for controlling the light source or the light-emitting diodes.

[0040] The holographic display can be designed such that the light from the light source directly hits and enters the base body without passing through additional optical elements. However, it is also possible for the holographic display to have at least one optical element (such as a lens) arranged between the light source and the waveguide, so that the light from the light source passes through this optical element and only then hits the base body.

[0041] It is understood that the features mentioned above and those to be explained below can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention. The invention is explained in more detail below using exemplary embodiments with reference to the accompanying drawings, which likewise disclose features essential to the invention. These exemplary embodiments are for illustrative purposes only and are not to be interpreted as restrictive. For example, a description of an exemplary embodiment with a large number of elements or components should not be interpreted to mean that all of these elements or components are necessary for implementation. Rather, other exemplary embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components.Elements or components of different embodiments may be combined with one another unless otherwise stated. Modifications and variations described for one of the embodiments may also be applicable to other embodiments. To avoid repetition, identical or corresponding elements in different figures are designated by the same reference numerals and are not explained more than once. The figures show:

[0042] Fig. 1 is a schematic sectional view of a first embodiment of the holographic display 1 according to the invention with the waveguide 2 according to the invention;

[0043] Fig. 2 is a plan view of the image hologram 19 of the waveguide 2 of Fig. 1;

[0044] Fig. 3 is a plan view of the light source 3 of Fig. 1,

[0045] Fig. 4 is a sectional view of another embodiment of the holographic display 1;

[0046] Fig. 5 is a sectional view of an embodiment of the laminated glass pane 1 according to the invention together with a light source 120;

[0047] Fig. 6 is a diagram of the wavelength-dependent refractive index profile of the inner pane 102 and the adhesive layer 104;

[0048] Fig. 7 is a diagram showing the wavelength dependence of the critical angle for total internal reflection at the boundary between inner pane 102 and adhesive layer 104;

[0049] Fig. 8 is a sectional view according to Fig. 1 of a further embodiment of the laminated glass pane 1 according to the invention; Fig. 9 is a sectional view according to Fig. 1 of a further embodiment of the laminated glass pane 1 according to the invention;

[0050] Fig. 10 is a sectional view according to Fig. 1 of a further embodiment of the laminated glass pane 1 according to the invention;

[0051] Fig. 11 is a sectional view according to Fig. 1 of a further embodiment of the laminated glass pane 1 according to the invention;

[0052] Fig. 12 is a sectional view according to Fig. 1 of a further embodiment of the laminated glass pane 1 according to the invention;

[0053] Fig. 13 is a sectional view according to Fig. 1 of a further embodiment of the laminated glass pane 1 according to the invention;

[0054] Fig. 14 is a sectional view according to Fig. 1 of a further embodiment of the laminated glass pane 1 according to the invention;

[0055] Fig. 15 is an enlarged detailed view of another embodiment of the laminated glass pane 1 according to the invention;

[0056] Fig. 16 is an enlarged detailed view of another embodiment of the laminated glass pane 1 according to the invention;

[0057] Fig. 17 is a plan view of the inner side 9 of the laminated glass pane 1 according to Fig. 1;

[0058] Fig. 18 is a view according to Fig. 17 of a further embodiment of the laminated glass pane according to the invention, and

[0059] Fig. 19 shows a further embodiment of the laminated glass pane 1 according to the invention.

[0060] In the embodiment shown in Fig. 1, the holgraphic display 1 comprises a waveguide 2 according to the invention for displaying an image and a light source 3.

[0061] The waveguide 2 has a transparent base body 4 with a front side 5 and a back side 6 and is plate-shaped. The base body 4 has a multilayer structure and comprises a first layer 7, on whose front side 8 a second layer 9 is applied, and on whose back side 10 a third layer 11 is applied, such that the first layer 7 is positioned between the second and third layers 9, 11. The first layer 7 has a first refractive index that is greater than a second refractive index of the second layer 9 and further greater than a third refractive index of the third layer 11.

[0062] On the side of the second layer 9 facing away from the first layer 7, a first glass layer 12 is formed, and on the side of the third layer 11 facing away from the first layer 7, a second glass layer 13 is formed. The side of the first glass layer 12 facing away from the first layer 7 can, for example, form the front side 5 of the base body 4. Furthermore, the side of the second glass layer 13 facing away from the first layer 7 can form the back side

[0063] 6 of the base body 4. The transparent base body can thus also be referred to as a laminated glass pane. The base body 4 can be designed, for example, as a vehicle pane, such as the windshield or a side window of a car or truck.

[0064] Furthermore, the waveguide 2 comprises a coupling region 14 and a coupling-out region 15 spaced from the coupling region 14 in a first direction (here the y-direction).

[0065] As can be seen from the schematic representation in Fig. 1, the light source 3 emits radiation 16, which enters the transparent base body 4 via the rear side 6 and strikes a coupling element 17 of the coupling region 14 arranged between the first layer 7 and the second layer 9, which deflects the radiation 16 in the direction of the coupling-out region 15 in such a way that it is guided as a coupled-in beam 18 due to total internal reflections at the interface between the first layer 7 and the second layer 9 as well as at the interface between the first layer 7 and the third layer 11 in the first layer 7 to the coupling-out region 15. In the coupling-out region 15, between the first layer

[0066] 7 and the second layer 9, an image hologram 19 with an exposed image is formed, onto which the guided beam 18 impinges. To reconstruct the exposed image, the beam 18 is at least partially deflected such that the deflected portion exits the base body 4 via the front side 5. This makes the exposed image perceptible to a viewer B.

[0067] In the embodiment described here, the image hologram is designed as an image plane hologram, so that the reconstructed image is perceptible to the observer as an image in the transparent base body 4.

[0068] As further schematically shown in Fig. 1, the coupled-in beam 18 strikes the image hologram 19 multiple times. For this purpose, the image hologram 19 is designed such that only a portion of the incident beam 18 is deflected for reconstruction by the image hologram 19. The remaining portion, after total internal reflection at the interface between the first layer 7 and the second layer 9 and subsequent total internal reflection at the interface between the first layer 7 and the third layer 11, will strike the image hologram 19 again, but in a position offset in the y-direction, wherein again only a portion of this is deflected by the image hologram 19 for reconstruction and coupled out via the front side 5 of the transparent base body 4.In this way, the image hologram 19 can be illuminated strip-by-strip by means of the coupled beam 18, wherein the strips along the first direction preferably strike the image hologram 19 in a manner adjacent to one another or partially overlapping.

[0069] In the illustration in Fig. 1, only one main beam is shown schematically for the radiation 16 and for the coupled beam 18. Of course, the radiation 16 has an extension in the first direction, which is predetermined, for example, by the light source 3, which also determines the strip height. The stripes can also be referred to as footprints of the coupled beam 18.

[0070] In the schematic top view of the image hologram 19 in Fig. 2, the strip-shaped illumination of the image hologram 19 with the coupled beam 18 is schematically illustrated by the five strips S1, S2, S3, S4, and S5, with the dashed lines indicating the main rays of each deflection and reconstruction. Strip S1 represents the first impact of the beam 18 on the image hologram 19, strip S2 represents the second impact, etc. In the embodiment described here, the adjacent illumination strips S1-S5 abut one another.

[0071] Since light is coupled out with each impact of the beam 18 on the image hologram 19 (strips S1-S5), the intensity of the reconstruction wave (the radiation deflected by the image hologram 19) decreases. As a result, the image reconstructed in this way can exhibit a perceptible decrease in brightness for an observer. To counteract this, the image hologram 19 can be provided with an efficiency curve designed such that the deflection efficiency increases with each subsequent impact. This means that the deflection efficiency for the first impact S1 is smaller than for the second impact S2, that the deflection efficiency for the second impact S2 is smaller than for the third impact S3, etc. This makes it possible to achieve a more homogeneous brightness in the reconstructed hologram image.

[0072] One or more light-emitting diodes can be used as the light source 3. If more than one light-emitting diode is used, they can be arranged next to one another, for example, in a direction transverse to the first direction (here along the x-direction (Fig. 3)). The light-emitting diodes L1, L2, L3 and L4 can, for example, emit light of the same color or light of different colors. Preferably, the light-emitting diodes L1-L4 are all arranged in one plane. In the embodiment described here, the light-emitting diodes L1 and L3 emit red light and the light-emitting diodes L2 and L4 emit green light. For this purpose, the image hologram 19 is designed such that it has an exposed first image for the radiation emitted by the light-emitting diodes L1, L3, and an exposed second image for the green radiation emitted by the light-emitting diodes L2 and L4.Preferably, the light source 3 is controlled by a control unit 20, which may or may not be part of the holographic display 1, such that none of the LEDs L1-L4 emit light, only the LEDs L1 and L3 emit light, or only the LEDs L2 and L4 emit light. This allows the first image or the second image in the transparent base body 4 to be selectively generated or switched on for a user.

[0073] In the described use with multiple colors, the image hologram 19 can comprise two holograms arranged one above the other (one for each corresponding color). However, it is also possible for the image hologram 19 to be a multiplex structure in which several gratings are written into a hologram foil.

[0074] The coupling element 17 can also be designed as a hologram. When using multiple colors, the coupling element 17 can be designed as a stack of holograms (one hologram for each color) or as a multiplex structure.

[0075] The holographic display 1 can be designed such that the radiation 16 from the light source 3 enters the base body 4 via the rear side 6 without passing through any additional optical components and, after passing through the second glass layer 13, the third layer 11, and the first layer 7, strikes the coupling element 17. The coupling element 17 can be designed such that it only deflects the radiation 16. However, it is possible for the coupling element 17 to additionally provide, for example, an optically imaging function, such as a lens function.

[0076] Of course, the radiation 16 can also be coupled into the transparent base body 4 via the front side 5 or via the lower end face 21. Furthermore, the coupling element 17 can be designed not only reflective, as shown in Fig. 1. It is also possible for the coupling element 17 to be transmissive, as schematically shown in Fig. 4.

[0077] Likewise, the image hologram 19 can be configured not only transmissively, as shown in Fig. 1. It is also possible for the image hologram 19 to be reflective (Fig. 4). Furthermore, the embodiment according to Fig. 1 can also be modified such that the image hologram 19 is configured as a reflection hologram. The light would then first pass through the hologram material of the image hologram 16, then be totally reflected at the interface between the hologram material and the second layer 9, and then be diffracted in reflection in the hologram material of the image hologram 19.

[0078] The image hologram 19 is in particular designed to be substantially transparent, so that a user B can look through the transparent base body 4 when viewing the image hologram 19 when the light source 3 is switched off.

[0079] Furthermore, it is possible to interpose one or more optical components, such as one or more lenses, between the light source 3 and the transparent base body 4. A cylindrical lens 22 is shown schematically in Fig. 1.

[0080] Since the image hologram 19 in the embodiment described here has a relatively large extent in the x-direction, a very large number of adjacent channels with LEDs and rotationally symmetrical collimation lenses would be necessary to illuminate the entire image hologram 19 in the x-direction. According to the invention, the described cylindrical lens 22 is used instead, which collimates the light from the LEDs in the y-direction (vertical direction) and performs no light shaping in the horizontal direction (x-direction). This allows for broad illumination in the horizontal direction, even though only a few LEDs are required.

[0081] The cylindrical lens 22 also has the advantage that only one optical element is required to shape the light for all LEDs L1-L4. This minimizes the adjustment effort compared to a design that would require a lens for each LED L1-L4.

[0082] In an advantageous further development, the coupling hologram 17 also includes a cylindrical function, which not only deflects the radiation 16 but also collimates it in the horizontal direction (x-direction) so that it can propagate under total internal reflection in the first layer 7. The combination of cylindrical lens and lens function of the coupling hologram 17 enables a geometrically broad plane wave (i.e., flat in two dimensions, so that the smallest possible angular spectrum is present), which can be used to reconstruct the image hologram 19. The coupling hologram 17 is particularly well suited for collimation in the x-direction because it can extend over the entire extent of the base body 4, while in the y-direction, due to the divergence of the light from the light source, the cylindrical lens 22 is more suitable, thus providing a particularly simple arrangement for collimation in all directions.

[0083] In the described embodiment, the transparent base body 4 is designed as a plane-parallel plate. Of course, it is also possible for the front side 5 and / or back side 6 to be curved. In this case, a deflection hologram 25 (dashed line in Fig. 1) can optionally be integrated along the propagation path between the coupling element 17 and the image hologram 19, which ensures that the angular spectrum of the coupled-in beam 18 is maintained and is not influenced by the curvature of the base body 4. Of course, several deflection holograms 25 can also be integrated along the propagation path. This can improve the homogeneity of the illumination of the image hologram 19.

[0084] Since the light guidance of the coupled beam 18 in the first layer 7 occurs by means of total internal reflection due to the lower refractive index second and third layers 9 and 11, the first glass layer 12 can, for example, be tinted or have an additional tinting layer, which, however, does not negatively influence the guidance of the coupled beam 18. For example, a tint of 30% would already mean that after a distance of 30 cm between the coupling element 17 and the image hologram 19, less than 1% of the coupled radiation 16 can propagate through the waveguide.

[0085] The refractive index of the first layer 7 is preferably at least 0.005 greater than the refractive index of the second layer 9 and preferably at least 0.005 greater than the refractive index of the third layer 11.

[0086] For example, PVB (polyvinyl butyral) with a refractive index in the range from 1.37 to 1.47 can be used for the second and third layers 9, 11, which are designed in particular as adhesive layers, and PC (polycarbonate) with a refractive index of 1.58 can be used for the first layer. Alternatively, it is possible, for example, to use EVA (ethylene-vinyl acetate copolymer) with a refractive index in the range from 1.37 to 1.47 for the second and third layers 9, 11, and PET (polyethylene terephthalate) with a refractive index of 1.56 for the first layer 7. In these examples, the coupled-in beam 18 can then be guided at an angle of greater than 61° to 71° in the first layer 7 (depending on the precise choice of the refractive index for the second and third layers 9, 11). The first layer 7 as well as the second and third layers 9, 11 preferably have an extinction coefficient which is each less than 0.001.It is also advantageous if the three layers 7, 9, and 11 exhibit very low scattering behavior. The haze values ​​should be less than 2 to minimize light loss due to scattering—similar to light loss due to absorption (detailed information on the haze value can be found, for example, in DIN EN ISO 13803:2015-02, DIN EN 2155-9:1989-11, DIN EN 62805-1:20018-06, DIN EN 1096-5:2016-06, and DIN ISO 15082:2018-02).

[0087] It is advantageous to use an amorphous material for the first layer 7 to avoid disruptive influences on light conduction, e.g., due to stress birefringence in the first layer 7. Examples of such an amorphous material are float glass and highly transparent thermoplastics such as PMMA, PC, PVC, COC, PET, etc. It is important that, particularly when using semi-crystalline plastics such as PMMA and PET, particular attention must be paid to the manufacturing conditions to ensure that the degree of crystallinity, and thus the stress birefringence of the final product, is as small as possible. For transparent materials obtained directly through polymerization (e.g., thermosets, epoxy resins, or 2-component acrylate systems), the manufacturing conditions also have a huge impact on the stress birefringence of the final product.Furthermore, it is advantageous to use a material that is as streak-free as possible for the first layer 7 in order to avoid the undesirable lens effect of the streaks and thus not influence the light transmission. Float glass and highly transparent thermoplastics such as PMMA, PC, PVC, COC, PET, etc. can also be used here. It is important that, particularly when using semi-crystalline plastics such as PMMA and PET, particular attention must be paid to the manufacturing conditions so that the degree of crystallinity and thus the stress birefringence of the end product is as small as possible. In the case of transparent materials obtained directly through polymerization (e.g., thermosets), the manufacturing conditions also have a huge influence on the stress birefringence of the end product.

[0088] The first layer 7 can have a layer thickness in the range of 50 μm to 2 mm (preferably up to 1 mm). Furthermore, the first layer can, for example, have a thickness of 70 to 500 μm if it is formed as a PC layer. The second and third layers 9, 11 can, for example, each have a thickness of 100 to 2000 μm if they are formed as a PVB layer or an EVA layer.

[0089] In the embodiment shown in Fig. 5, the waveguide 1 according to the invention is designed as a laminated glass pane 1 for a vehicle with an inner pane 102 and an outer pane 103, which is connected to the inner pane 102 via an adhesive layer 104. The inner pane 102 thus corresponds to the previously described first layer 7, and the outer pane 103 thus corresponds to the previously described second layer 9.

[0090] Although this and the other following embodiments each describe a laminated glass pane 1 for a vehicle, this is only an example of the waveguide according to the invention, which can be designed as a laminated glass pane for a vehicle but does not have to be designed as a laminated glass pane for a vehicle.

[0091] The laminated glass pane 1, shown schematically and not to scale in Fig. 5, can be designed in particular as a pane for a vehicle roof through which a person inside the vehicle can see. The outer pane 103 can be tinted. However, it can also be completely transparent.

[0092] The inner pane 102 is preferably completely transparent. The same applies to the adhesive layer 104.

[0093] The inner pane 102 has a first side 105 facing away from the outer pane 103 (or a first side 105 facing away from the outer pane 103) and a second side 106 facing the outer pane 103 (or a second side 106 facing the outer pane 103). The outer pane 103 has a third side 107 facing the inner pane 102 and a fourth side 108 facing away from the inner pane 102. The two panes 102, 103 are connected via the mutually facing sides 106, 107 by means of the adhesive layer 104.

[0094] When using the laminated glass pane 1 shown in Fig. 5 in a vehicle roof, the first side 105 of the inner pane 102 faces the interior of the vehicle and can therefore also be referred to as the inner side 109 of the laminated glass pane 1. The fourth side 108 of the outer pane 103 faces away from the interior of the vehicle and can therefore be referred to as the outer side 110 of the laminated glass pane 1.

[0095] The inner disc 102 further comprises a first edge 111 connecting the first and second sides 105, 106, which is curved (preferably convex). In particular, the edge has a so-called C-cut. A C-cut is understood here in particular to mean that the edge surface has a round cut. Viewed in cross section, the edge surface is thus round or C-shaped or, for example, has the shape of an arc of a circle or an elliptical arc. Similarly, the outer disc 103 has a second edge 112 connecting the third and fourth sides 107, 108, which is curved. The second edge 112 can also have a C-cut. The inner disc 102 further comprises a coupling region 115, on which a

[0096] A transmission grating 116 is provided. Furthermore, the inner pane 102 comprises a first, a second, and a third coupling-out region 117, 118, and 119, which are spaced apart from the coupling-in region 115 and spaced apart from one another. In the embodiment shown in Fig. 5, the coupling-out regions 117 to 119 are formed on the first side 105 of the inner pane 102.

[0097] Together with the light source 120 shown in Fig. 5, the laminated glass pane 1 forms a lighting system 121 for a vehicle.

[0098] The light source 120 emits radiation 122 (e.g., white light), which strikes the coupling region 115 with the transmission grating 116. The transmission grating 116 deflects the radiation 122 such that it propagates as coupled radiation 123 through reflections on the first and second sides 105, 106 of the inner pane 102 to the coupling-out regions 117 to 119. The reflections on the first and second sides 105, 106 are preferably total internal reflections. For this purpose, the refractive indices of the adhesive layer 104 and the inner pane 102 are selected accordingly. The refractive index of the adhesive layer 104 is therefore lower than the refractive index of the material of the inner pane 102. The adhesive layer 104 can, for example, be formed as a PVB layer (polyvinyl butyral layer). In this case, the refractive index profile of the adhesive layer 104 shown in Fig. 6 with the solid line K1 is present in a wavelength range of 400 to 1000 nm.

[0099] In Fig. 6, the wavelength A in nm is plotted along the abscissa, and the refractive index is plotted along the ordinate. A typical glass used for automotive windows exhibits the refractive index curve shown as a dashed line (curve K2) in Fig. 6. As can be seen from the diagram, there is a refractive index difference of approximately 0.03 (depending on the wavelength). This leads to a critical angle for total internal reflection, which is shown in Fig. 7 for wavelengths from 400 to 1000 nm. This critical angle is approximately 78.7° to 79.4° (depending on the wavelength).

[0100] In Fig. 7, the wavelength A in nm is plotted along the abscissa, and the critical angle θG in degrees is plotted along the ordinate (curve K3). This means that at angles of incidence greater than this critical angle on the second side 106, the coupled radiation 123 is totally reflected at the interface between the second side 106 and the adhesive layer 104.

[0101] The adjacent medium on the first side 105 is air with a refractive index of approximately 1, so that the corresponding critical angle for total internal reflection is smaller than that described for the second side 106. Thus, if total internal reflection for the coupled radiation occurs on the second side 106, this also applies to the reflection on the first side 105.

[0102] The coupled radiation 123 thus guided in the inner pane 102 then strikes the output coupling regions 117, 118, 119, which are designed here to output at least a portion of the radiation impinging on them as diffuse radiation, as indicated by the arrow bundles 124, 125, and 126 in Fig. 5. For a person inside the vehicle looking at the inner side 109, the output coupling regions 117, 118, and 119 are illuminated points. With appropriate distribution of the output coupling regions 117 to 119 on the inner side 109, the impression of a starry sky can be created, for example.

[0103] In particular, the output coupling regions 117 to 119 can be configured to have different output coupling efficiencies, so that the output light intensities at the individual output coupling regions 117, 118, and 119 are different. This allows brighter and dimmer stars to be displayed.

[0104] Of course, it is also possible to adjust the output efficiencies of the output regions 1 17-1 19 so that the output light intensities at two or more output regions 1 17-1 19 are the same.

[0105] In the illumination system 121 shown in Fig. 5, the propagation direction of the radiation 122 coming from the light source 120 is such that it strikes the first side 105 perpendicularly. However, it is also possible for the propagation direction of the radiation 122 to have an angle other than 90° to the first side 105, as shown in Fig. 8.

[0106] In the embodiments according to Figs. 5 and 8, the grating 1 16 is always designed as a transmission grating.

[0107] Furthermore, the grating 116 can be designed as a reflection grating. In this case, the preferred arrangement of the grating 116 is on the second side 106. This is shown in Figs. 9 and 10 for a perpendicular incidence of the radiation 122 on the first side 105 (Fig. 9) and for an angle of incidence of the radiation on the side 105 of other than 90° (Fig. 10).

[0108] Fig. 11 shows a modification of the laminated glass pane 1 from Fig. 9, in which the outcoupling regions 117-119 are designed such that the outcoupled radiation is emitted as directed radiation. This can be used to create, for example, a reading light or reading lighting for a person inside the vehicle. Fig. 12 shows a modification of the laminated glass pane from Fig. 10. In this modification, the second outcoupling region 118 is designed such that it couples out the radiation 123 as directed radiation, which in turn can be used to create a reading light. The first and third outcoupling regions 117 and 119 are designed such that the radiation 123 is emitted as diffuse radiation.

[0109] The grating 116 in Fig. 5 and 8 to 12 can be designed, for example, as a volume hologram or as a relief grating.

[0110] Fig. 13 shows a modification in which the inner pane 102 has a section 130 protruding from the first side 105 and having a flat entrance surface 131. The inner pane 102 therefore has a greater thickness in the region of the protruding section 130 than, for example, in the region in which the coupling-out regions 117-119 are located. Due to the protruding section 130, the inner pane 102 has a cross-sectional widening in this region compared, for example, to the region in which the coupling-out regions 117-119 are located. The inclination of the flat entrance surface 131 to the first side 105 is preferably selected such that radiation 122 entering perpendicularly via the flat entrance surface 131 has such an angle relative to the second side 106 that the desired total internal reflection takes place on the second side 106.

[0111] Fig. 14 shows a further development of the embodiment according to Fig. 13. In this further development, a lens 132 is arranged between the light source 120 and the entrance surface 131.

[0112] Fig. 15 shows a modification of the laminated glass pane 1 from Fig. 13, illustrating an enlarged detailed view. The inwardly projecting section 130 is designed as an inverted collector in such a way that the radiation 122 coming from the light source 120 is formed as a substantially parallel beam 123, which strikes the second side 106 at the necessary angle of incidence in order to be reflected by total internal reflection. For example, a parabolic light collecting lens (compound parabolic concentrator) can be used inverted as a collimating lens (compound parabolic collimator). Such a collimating lens is preferably reflective and non-imaging. It comprises at least one rotationally symmetrical parabolic surface, which collects or collects the light from a light source with a defined angular spectrum.The length of the collimation optics can be used to adjust which angular spectrum of the radiation 122 coming from the light source 120 can be formed as a substantially parallel beam 123. Fig. 16 shows a modification of the laminated glass pane of Fig. 15, in which, instead of the flat entrance surface 131, a lens-shaped entrance surface 135 with an annular projection 136 is formed. The portion of the radiation 122 that passes through the inner side 137 of the annular projection 136 is reflected by total internal reflection on the outer side 138 of the annular projection 136 and thus redirected toward the second side 106.

[0113] One could also say that the coupling area 115 has a TIR lens (TIR = total internal reflection). A TIR lens is an optical component that combines a reflector and a lens. At its center is a lens surrounded by a (possibly free-form) paraboloid. The transition area between the lens and the paraboloid is usually arranged concentrically around the light source. However, a deviation from the concentric shape can also occur in combination with a free-form paraboloid. The deflection across the parabolic surfaces occurs via total internal reflection.

[0114] Fig. 17 shows a schematic view of the inner side 109 of the laminated glass pane 1 of Fig. 5. The coupling-out regions are indicated by "x." Naturally, the coupling-out regions 117 to 119 are designed such that, when the light source 120 is not emitting radiation 122, they are not visible but transparent. The grating 116 is also preferably designed such that it is transparent to an observer.

[0115] Fig. 18 shows a modification of the laminated glass pane 1 according to Fig. 17 or of the illumination system 121 in the same manner as in Fig. 17. In this modification according to Fig. 18, a further light source 140, a further coupling grating 141, and further coupling-out regions 142, 143, and 144 are provided. Of course, more than two light sources can also be provided. It is also possible for the light from a further light source to travel not from left to right in the inner pane 102, as seen in Fig. 18, but from bottom to top or from top to bottom in the inner pane 102.

[0116] Fig. 19 shows a modification of the described embodiments in which a further pane 150 is bonded to the inner pane 102 by means of a further adhesive layer 151. This can be used to guide the light from a further light source 152, which is coupled into the further pane 150 via a coupling element 153, and to emit it as directed or non-directed radiation via corresponding coupling-out regions 155, 156, and 157. The remaining structure of the further pane 150 as well as the corresponding coupling-in region 153 and the further coupling-out regions 155-157 can be as described in connection with the inner pane 102. The inner pane 102 and the further pane 150 can thus also be referred to as the first and second light guides. The different light guides can also be used to guide and emit light of different wavelengths.The light sources 120 and 152 are designed accordingly.

[0117] Of course, not only two light guides can be provided. Three or more light guides can also be arranged in the same way, stacked on top of each other.

[0118] With two or more optical fibers, different output structures or different output areas can be present on the optical fibers. This allows for the creation of different light signatures or images, for example. In particular, these can be switched on and off individually.

[0119] The coupling-out regions described so far were based on essentially point-shaped coupling-out regions 117-119, 141-143, and 155-157, or on coupling-out regions 117-119, 141-143, and 155-157 with a small lateral extension compared to the distance between the coupling-out regions 117-119, 141-143, and 155-157. However, it is also possible to provide one planar coupling-out region or even several planar coupling-out regions.

[0120] If the decoupling region is flat, it can be designed such that it couples out the coupled-in radiation diffusely or directionally. In particular, it is possible for the flat decoupling region to be designed as a volume grating into which image information has been exposed. Upon illumination with the coupled-in radiation, the image can then be reconstructed so that a person in the vehicle can perceive the exposed image. In this case, the decoupling region can be designed as an image hologram. In particular, the image hologram can be designed such that it is designed as an image plane hologram so that it is perceivable by the person in the vehicle as an image in the inner pane 102.

[0121] In the described embodiments, the laminated glass pane 1 is shown with a flat outer side 100 and a flat inner side 109. Of course, the laminated glass pane 1 can be curved. In this case, the outer side 100 and / or the inner side 109 can be curved. In particular, the two panes 102, 103 can each have two curved sides 105-108, wherein the mutually facing second and third sides 106 and 107 of the inner pane 102 and the outer pane 103 preferably have complementary curvatures, so that the thinnest possible laminated glass pane 1 can be produced. The thickness of the inner pane 102 and the outer pane 103 can, in particular, range from greater than 2 mm up to 5 mm.

Claims

Carl Zeiss Jena GmbH Legal file: PAT 1250 / 347 Patent claims 1. Waveguide for displaying an image, wherein the waveguide (2) has a transparent base body (4) with a front (5) and a back (6), wherein the base body (4) comprises an input coupling area (14) and an output coupling area (15) spaced therefrom in a first direction, the output coupling area having an image hologram (19) with an exposed image, wherein the input coupling area (14) deflects at least a part of the radiation (16) coming from a light source (3) such that the deflected part propagates as an input beam (18) in the base body (4) by reflection to the output coupling area (15) and strikes the image hologram (19), wherein the image hologram (19) deflects at least a part of the incident beam (18) for the reconstruction of the exposed image such that the deflected part exits the base body (4) via the front (5) or back (6),so that the exposed image is perceptible to an observer (B), wherein the base body (4) is multilayered and has at least a first layer (7) with a first refractive index and a second layer (9) formed thereon with a second refractive index which is smaller than the first refractive index, and wherein the coupled beam of rays (18) propagates in the first layer (7) at the interface to the second layer (9) due to total internal reflection.

2. Waveguide according to claim 1, wherein a third layer (11) is formed on the side of the first layer (7) facing away from the second layer (9), wherein the third layer (11) has a third refractive index which is smaller than the first refractive index, and wherein the coupled beam of rays (18) propagates in the first layer (7) at the interface to the third layer (11) due to total internal reflection.

3. Waveguide according to claim 1 or 2, wherein the image hologram (19) has a first extent in the first direction which is larger than the extent of the beam cross-section of the coupled beam (18) in the first direction, wherein the coupled beam of rays (18) is propagated in the first layer (7) such that it repeatedly hits the image hologram (19) at different points which are offset from each other along the first direction and wherein at each point of impact a part of the incident beam of rays (18) is deflected to reconstruct the exposed image.

4. Waveguide according to claim 3, wherein the image hologram (19) has an efficiency profile in which the deflection efficiency increases from the first to the last impact of the beam of light (18).

5. Waveguide according to one of the above claims, wherein the image hologram (19) is designed as an image plane hologram, wherein the reconstructed image is perceptible as an image in the transparent base body (4).

6. Waveguide according to one of the above claims, wherein the first layer (7) is formed from an amorphous material.

7. Waveguide according to one of the above claims, wherein the first refractive index is at least 0.005 greater than the second refractive index.

8. Waveguide according to one of the above claims, wherein both the extinction coefficient of the first layer and the extinction coefficient of the second layer are each less than 0.

001.

9. Waveguide according to one of the above claims, wherein the coupling area (14) has a hologram (17) for deflecting the radiation (16) coming from the light source (3).

10. Waveguide according to one of the above claims, wherein the exposed image of the image hologram (19) represents a starry sky.

11. Waveguide according to claim 10, wherein the image hologram (19) comprises several spaced-apart has output coupling areas, each of which deflects at least a part of the incident beam (18) so that it exits as diffuse radiation to represent a starry sky.

12. Holographic display comprising a light source (3) and a waveguide according to one of the above claims.

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