Abstract
The disclosure relates to an optical waveguide for a display device and to a method for producing such an optical waveguide. The optical waveguide has a substrate on which a hologram layer is arranged. A cover layer includes a light-transmissive material that has been subjected to a curing process is arranged on the hologram layer. The substrate can consist of glass. Alternatively, the substrate likewise consists of a light-transmissive material that has been subjected to a curing process.
Claims
1. An optical waveguide for a display device, the optical waveguide comprising: a substrate; a hologram layer arranged on the substrate; and a cover layer arranged on the hologram layer; wherein the cover layer includes a light-transmissive material that has been subjected to a curing process.
2. The optical waveguide as claimed in claim 1, wherein the substrate includes glass or also of a light-transmissive material that has been subjected to a curing process.
3. The optical waveguide as claimed in claim 1, wherein the light-transmissive material is a lacquer or an optically clear adhesive.
4. The optical waveguide as claimed in claim 3, wherein the light-transmissive material that has been subjected to a curing process has a refractive index of greater than or equal to 1.4.
5. The optical waveguide as claimed in claim 1, wherein the substrate or the cover layer has a structuring.
6. A method for producing an optical waveguide, the method comprising the steps of: applying a layer of a light-transmissive material onto a first mold plate; curing the applied light-transmissive material to form a cover layer; applying a hologram layer onto the cover layer; applying a substrate onto the hologram layer; and exposing the hologram layer to light and curing the hologram layer.
7. The method as claimed in claim 6, wherein a separating layer is arranged between the first mold plate and the layer of the light-transmissive material or between a second mold plate and the layer of the light-transmissive material.
8. The method as claimed in one of claims 6, wherein the first mold plate or a second mold plate has a structuring.
9. A method for producing an optical waveguide, the method comprising the steps of: applying a layer of a light-transmissive material onto a first mold plate; curing the applied light-transmissive material to form a cover layer; applying a hologram layer onto the cover layer; exposing the hologram layer to light and curing the hologram layer; applying a layer of a light-transmissive material onto the hologram layer; shaping the applied light-transmissive material by a second mold plate; and curing the applied light-transmissive material to form a substrate.
10. The method as claimed in claim 9, wherein a separating layer is arranged between the first mold plate and the layer of the light-transmissive material or between the second mold plate and the layer of the light-transmissive material.
11. The method as claimed in one of claim 7, wherein the first mold plate or the second mold plate has a structuring.
12. A device for generating a virtual image, the device comprising: an image-generating unit for producing an image; and an optics unit for projecting the image in the direction of a mirror unit for generating the virtual image; wherein the device has at least one optical waveguide as claimed in claim 1 for expanding an exit pupil.
Description
DESCRIPTION OF DRAWINGS
[0034] FIG. 1 schematically shows a head-up display according to the prior art for a motor vehicle;
[0035] FIG. 2 shows an optical waveguide with two-dimensional enlargement;
[0036] FIG. 3 schematically shows a head-up display with an optical waveguide;
[0037] FIG. 4 schematically shows a head-up display with an optical waveguide in a motor vehicle;
[0038] FIG. 5 shows three examples of an optical waveguide in longitudinal section;
[0039] FIG. 6 schematically shows a first embodiment of an optical waveguide according to the disclosure;
[0040] FIG. 7 schematically shows a second embodiment of an optical waveguide according to the disclosure;
[0041] FIG. 8 shows a production detail for the optical waveguide from FIG. 7;
[0042] FIG. 9 schematically shows a first production method for an optical waveguide according to the disclosure;
[0043] FIG. 10 shows a modification of the production method from FIG. 9; and
[0044] FIG. 11 schematically shows a second production method for an optical waveguide according to the disclosure.
[0045] Like reference symbols in the various drawings indicate like elements.
DETAILED DESCRIPTION
[0046] Initially, the basic concept of a head-up display with an optical waveguide will be explained with reference to FIGS. 1 to 4.
[0047] FIG. 1 shows a schematic diagram of a head-up display according to the prior art for a motor vehicle. The head-up display has an image generator 1, an optics unit 2, and a mirror unit 3. A beam bundle SB1 emanates from a display element 11 and is reflected by a folding mirror 21 onto a curved mirror 22 that reflects it in the direction of the mirror unit 3. The mirror unit 3 is illustrated here as a windshield 31 of a motor vehicle. From there, the beam bundle SB2 travels in the direction of an eye 61 of a viewer.
[0048] The viewer sees a virtual image VB that is located outside the motor vehicle above the engine hood or even in front of the motor vehicle. Due to the interaction of the optics unit 2 and the mirror unit 3, the virtual image VB is an enlarged representation of the image displayed by the display element 11. A speed limit, the current vehicle speed, and navigation instructions are symbolically represented here. As long as the eye 61 is located within the eyebox 62 indicated by a rectangle, all elements of the virtual image are visible to that eye 61. If the eye 61 is outside the eyebox 62, the virtual image VB is only partially visible to the viewer, or not at all. The larger the eyebox 62 is, the less restricted the viewer is when choosing their seating position.
[0049] The curvature of the curved mirror 22 is adapted to the curvature of the windshield 31 and ensures that the image distortion is stable over the entire eyebox 62. The curved mirror 22 is rotatably mounted by way of a bearing 221. The rotation of the curved mirror 22 that is made possible thereby makes it possible to displace the eyebox 62 and thus to adapt the position of the eyebox 62 to the position of the eye 61. The folding mirror 21 serves to ensure that the path traveled by the beam bundle SB1 between the display element 11 and the curved mirror 22 is long and, at the same time, that the optics unit 2 is nevertheless compact. The optics unit 2 is delimited with respect to the environment by a transparent cover 23. The optical elements of the optics unit 2 are thus protected for example against dust located in the interior of the vehicle. An optical film or a polarizer 24 is furthermore located on the cover 23. The display element 11 is typically polarized, and the mirror unit 3 acts like an analyzer. The purpose of the polarizer 24 is therefore to influence the polarization in order to achieve uniform visibility of the useful light. An anti-glare protection 25 serves to reliably absorb the light reflected via the interface of the cover 23 so that the observer is not dazzled. In addition to the sunlight SL, the light from another stray light source 64 can also reach the display element 11. In combination with a polarization filter, the polarizer 24 can additionally be used to block out incident sunlight SL.
[0050] FIG. 2 shows a schematic spatial illustration of an optical waveguide 5 with two-dimensional enlargement. In the lower left region, an input coupling hologram 53 can be seen, by way of which light L1 coming from an image-generating unit (not shown) is coupled into the optical waveguide 5. The light propagates therein in the drawing to the top right, according to the arrow L2. In this region of the optical waveguide 5, a folding hologram 51 that acts similarly to many partially transmissive mirrors arranged one behind the other and produces a light bundle that is expanded in the Y-direction and propagates in the X-direction is located. This is indicated by three arrows L3. In the part of the optical waveguide 5 that extends to the right in the figure, an output coupling hologram 52 is located, which likewise acts similarly to many partially transmissive mirrors arranged one behind the other and, indicated by arrows L4, couples light upward in the Z-direction out of the optical waveguide 5. In this case, an expansion takes place in the X-direction, so that the original incident light bundle L1 leaves the optical waveguide 5 as a light bundle L4 that is enlarged in two dimensions.
[0051] FIG. 3 shows a three-dimensional illustration of a head-up display with three optical waveguides 5R, 5G, 5B, which are arranged one above the other and each stand for an elementary color red, green, and blue. Together they form the optical waveguide 5. The holograms 51, 52, 53 present in the optical waveguide 5 are wavelength-dependent, meaning that one optical waveguide 5R, 5G, 5B in each case is used for one of the elementary colors. An image generator 1 and an optics unit 2 are shown above the optical waveguide 5. The optics unit 2 has a mirror 20, by way of which the light produced by the image generator 1 and shaped by the optics unit 2 is deflected in the direction of the respective input coupling hologram 53. The image generator 1 has three light sources 14R, 14G, 14B for the three elementary colors. It can be seen that the entire unit shown has a small overall structural height compared to its light-emitting surface.
[0052] FIG. 4 shows a head-up display in a motor vehicle similar to FIG. 1, except here in a three-dimensional illustration and with an optical waveguide 5. It shows the schematically indicated image generator 1, which produces a parallel beam bundle SB1 that is coupled into the optical waveguide 5 by way of the mirror plane 523. The optics unit is not shown for the sake of simplicity. A plurality of mirror planes 522 each reflect a portion of the light incident on them in the direction of the windshield 31, the mirror unit 3. The light is reflected thereby in the direction of the eye 61. The viewer sees a virtual image VB above the engine hood or at an even further distance in front of the motor vehicle. With this technology, too, the entire optics unit is incorporated in a housing that is separated with respect to the environment by a transparent cover. As with the head-up display from FIG. 1, a retarder can be arranged on this cover.
[0053] FIG. 5 shows three examples of an optical waveguide 5 in longitudinal section. The optical waveguide 5 in partial image (a) has an ideally flat upper boundary surface 501 and an ideally flat lower boundary surface 502, both of which are arranged parallel to one another. It can be seen that a parallel light bundle L1 propagating from left to right in the optical waveguide 5 remains unchanged and parallel in cross section due to the parallelism and flatness of the upper and lower boundary surfaces 501, 502. The optical waveguide 5 in partial image (b) has upper and lower boundary surfaces 501, 502 that are not completely flat and also not parallel to one another. The optical waveguide 5 thus has a thickness that varies in the light propagation direction. It can be seen that the light bundle L1 is no longer parallel after just a few reflections and also does not have a homogeneous cross section. The optical waveguide 5 in partial image (c) has upper and lower boundary surfaces 501, 502 that deviate even more from the ideal shape than those in partial image (b). The light bundle L1 therefore likewise deviates even more from the ideal shape. The flatness of the boundary surfaces 501, 502 is therefore of great importance for the quality of the light propagation in the optical waveguide.
[0054] FIG. 6 shows a first example of an optical waveguide 5 according to the disclosure. In this example, a substrate 54 made of glass is used. A thin hologram layer 56 is arranged on the substrate 54. A cover layer 55 consisting of a light-transmissive material that has been subjected to a curing process is arranged on the hologram layer 56. The light-transmissive material can be, for example, a lacquer or an optically clear adhesive. The refractive index of the material may be greater than or equal to 1.4. If necessary, the cover layer 55 can have a structuring.
[0055] FIG. 7 shows a second example of an optical waveguide 5 according to the disclosure. In this example, a substrate 54 that likewise consists of a light-transmissive material that has been subjected to a curing process is used. A thin hologram layer 56, onto which a cover layer 55 is applied, is in turn arranged on the substrate 54. As before, the cover layer 55 consists of a light-transmissive material that has been subjected to a curing process. The same light-transmissive material may be used for the substrate 54 and the cover layer 55, but different materials can also be used. In this example too, the light-transmissive material can be a lacquer or an optically clear adhesive. The refractive index may be greater than or equal to 1.4 here as well. If necessary, the substrate 54 or the cover layer 55 can have a structuring.
[0056] FIG. 8 shows a production detail for the optical waveguide 5 from FIG. 7. For the production of this construction, two mold plates 70, 71 having the desired surface properties are used. To remove the optical waveguide 5 from the manufacturing construction, the mold plates 70, 71 are separated, where the optical waveguide 5 becomes detached from the mold plates 70, 71.
[0057] FIG. 9 schematically shows a first production method for an optical waveguide according to the disclosure. First, a layer of a curable, light-transmissive material is applied S1 onto a first mold plate. This layer is cured S2 to form the cover layer. A hologram layer is then applied S3 onto the cover layer. A substrate is then applied S4 onto this hologram layer, and the hologram layer 56 is exposed S5 to light and cured S6.
[0058] FIG. 10 shows, in a schematic form, a production method for an optical waveguide according to the disclosure that is modified compared to FIG. 9. According to this advantageous variant, exposure S5 and curing S6 take place before the substrate is applied S4. The remaining steps correspond to those from FIG. 9.
[0059] FIG. 11 schematically shows a further production method for an optical waveguide according to the disclosure. First, a layer of a curable, light-transmissive material is applied S1 onto a lower mold plate. This layer is cured S2 to form the cover layer. This is followed by the application S3 of a hologram layer onto the cover layer and the exposure S5 and curing S6 of the hologram layer. This is followed by application S7 of a further layer of a curable, light-transmissive material onto the cured hologram layer. A second mold plate is used to shape S8 the material layer, which is followed by the curing S9 of the material layer to form the substrate. Finally, the mold plates are separated S10, where the optical waveguide becomes detached from the mold plates.
[0060] In all examples of the method, one or more further layers, which serve as separating layers for better detachability of the material layers from the respective mold plate, may be inserted between the mold plates and the respective adjoining material layers.
[0061] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.
LIST OF REFERENCE ELEMENTS
[0062] 1 Image generator/image-generating unit
[0063] 11 Display element
[0064] 14, 14R, 14G, 14B Light source
[0065] 2 Optics unit
[0066] 20 Mirror
[0067] 21 Folding mirror
[0068] 22 Curved mirror
[0069] 221 Bearing
[0070] 23 Transparent cover
[0071] 24 Optical film/polarizer
[0072] 25 Anti-glare protection
[0073] 3 Mirror unit
[0074] 31 Windshield
[0075] 5 Optical waveguide
[0076] 501 Upper boundary surface
[0077] 502 Lower boundary surface
[0078] 51 Folding hologram
[0079] 52 Output coupling hologram
[0080] 521 Output coupling region
[0081] 522 Mirror plane
[0082] 523 Mirror plane
[0083] 53 Input coupling hologram
[0084] 531 Input coupling region
[0085] 54 Substrate
[0086] 55 Cover layer
[0087] 56 Hologram layer
[0088] 61 Eye/viewer
[0089] 62 Eyebox
[0090] 64 Stray light source
[0091] 70 First mold plate
[0092] 71 Second mold plate
[0093] L1 . . . L4 Light
[0094] S1 Application of a material layer onto a first mold plate
[0095] S2 Curing the material layer to form a cover layer
[0096] S3 Applying a hologram layer onto the cover layer
[0097] S4 Applying a substrate onto the hologram layer
[0098] S5 Exposing the hologram layer to light
[0099] S6 Curing the hologram layer
[0100] S7 Applying a material layer onto the hologram layer
[0101] S8 Shaping the material layer
[0102] S9 Curing the material layer to form a substrate
[0103] S10 Separating the mold plates
[0104] SB1, SB2 Beam bundles
[0105] SL Sunlight
[0106] VB Virtual image
