HEAD-UP DISPLAY WITH PRECISELY ALIGNED OPTICAL FIBERS

Description

[0001] The present invention relates to a head-up display with precisely aligned optical fibers and a method for precise alignment.

[0002] US 2016 / 0124223 A1 discloses a head-up display with an optical fiber. To generate a color virtual image, at least two optical fibers for different colors are required. These should be aligned as precisely as possible to ensure a good color impression.

[0003] EP 3 226 063 A1 discloses a head-mounted display with an image generator and an optical unit. The optical unit can comprise several optical fibers with holograms. The optical fibers are aligned with each other in an alignment step. For this purpose, illuminated markings are provided in the optical fibers. The light coupled out of the optical fibers during illumination is detected by cameras and used for alignment.

[0004] The document is highly relevant to the present invention. What is not disclosed is that the light passing through a first marking subsequently passes through a second marking, and that the resulting pattern is evaluated.

[0005] US 2017 / 0299860 A1 discloses a waveguide-based display device. The display device comprises a projector unit that uses a beam scanner, an optical fiber, and an exit pupil expander optically coupled between the projector unit and the optical fiber. The optical fiber may comprise multiple optical fibers aligned with each other.

[0006] In a method for precisely aligning at least two holograms arranged in optical waveguides according to the invention, at least the following steps are performed: Writing a first hologram and a first marking into a first optical waveguide. Writing a second hologram and a second marking into a second optical waveguide. Positioning the first optical waveguide and the second optical waveguide relative to each other.Illuminating the first marking and the second marking with a light beam which successively passes through associated markings of the first optical waveguide and the second optical waveguide and is each influenced by the associated markings, wherein the markings of the individual optical waveguides are grating structures or holograms which influence the light used during illumination and are coordinated with one another such that correct alignment is detectable, and wherein the markings have a lens function whose associated focal lengths are selected such that a correct pattern only appears during illumination if the distance between the individual optical waveguides also assumes a predetermined value. Detecting a pattern which appears during illumination with the light beam after passing through the first marking and the second marking.Changing the position of one of the optical fibers until the detected pattern matches a given pattern.

[0007] According to the invention, the markings function as lenses. The focal lengths are selected such that a correct pattern only appears when the distance between the individual optical fibers also assumes a predetermined value. Precise positioning is thus possible not only in two dimensions, but also in three dimensions.

[0008] Advantageously, at least one of the markings is written into the same material into which the corresponding hologram is written. This is preferably done by exposing and fixing the hologram and the marking simultaneously. According to one variant, the hologram and the marking are exposed sequentially. The marking is created, for example, by burning in using a high energy input.

[0009] According to one variant, at least one of the markings is written into a different material than the one in which the corresponding hologram is written. Advantageously, the marking is applied as an opaque material next to the hologram in its plane or on the layer in which the hologram is located.

[0010] Advantageously, when correctly positioned, the markings of the individual optical fibers lie exactly on top of each other and produce a detectable pattern when illuminated.

[0011] According to one variant, the markings of the individual optical fibers, when correctly positioned, lie next to each other and, when illuminated, create a detectable pattern. In this pattern, the components resulting from the different markings are preferably located next to each other and can thus be detected separately.

[0012] Preferably, a central area of the marking allows light to pass through, while an outer area outside the central area strongly deflects light outward. The detected pattern is therefore only bright when the central areas of all superimposed markings are hit by the light beam, thus achieving precise positioning.

[0013] Advantageously, different markers are arranged at different positions on the optical fibers. This has the advantage of enabling even more precise positioning by combining different patterns to be evaluated.

[0014] According to the invention, a stack of optical waveguides is produced by means of a method according to the invention.

[0015] A head-up display according to the invention has such a stack of optical fibers.

[0016] Further variants and their advantages can also be found in the following description of exemplary embodiments. Figurenübersicht:

[0017] Fig.1Head-up display according to the prior art Fig.2Schematic beam path Fig.3Schematic beam path with diffuser Fig.4Beam path with directed diffuser Fig.5Beam path with multiple imagers Fig.6Beam path with image at infinity Fig.7Beam path with virtual doubling Fig.8Beam path with optical fiber Fig.9Beam path with optical fiber Fig.10Head-up display with optical fiber Fig.11Optical fiber with two-dimensional magnification Fig.12Head-up display with optical fiber Fig.13Optical fiber in longitudinal section Fig.14Stack of optical fibers and its production Fig.15Flow diagram of a method according to the invention. Character description

[0018] Fig.1 shows a schematic diagram of a head-up display according to the prior art. It has an image generator 1, an optical unit 2, and a mirror unit 3. A beam of rays SB1 emanates from a display element 11, is reflected by a folding mirror 21 onto a curved mirror 22, which reflects it towards the mirror unit 3, which is shown here as the windshield 31 of a vehicle. From there, the beam of rays SB2 reaches the eye 61 of a viewer. The viewer sees a virtual image VB, which is located outside the vehicle above the hood or even in front of the vehicle. Due to the interaction of the optical unit 2 and the mirror unit 3, the virtual image VB is an enlarged representation of the image displayed by the display element 11. Here, a speed limit, the current vehicle speed, and navigation instructions are symbolically shown.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 the eye 61. If the eye 61 is located outside the eyebox 62, the virtual image VB is only partially visible or not visible at all to the viewer. The larger the eyebox 62, the less restricted the viewer is in choosing their seating position.

[0019] The curvature of the curved mirror 22 serves, on the one hand, to prepare the beam path and thus ensure a larger image and a larger eyebox 62. On the other hand, the curvature compensates for a curvature of the windshield 31, so that the virtual image VB corresponds to an enlarged reproduction of the image displayed by the display element 11. The curved mirror 22 is rotatably mounted by means of a bearing 221. The resulting rotation of the curved mirror 22 enables the eyebox 62 to be moved and thus the position of the eyebox 62 to be adjusted to the position of the eye 61. The folding mirror 21 ensures that the path traveled by the beam SB1 between the display element 11 and the curved mirror 22 is long, while at the same time the optical unit 2 remains compact. The optical unit 2 is separated from the surroundings by a transparent cover 23.The optical elements of the optical unit 2 are thus protected, for example, against dust present in the interior of the vehicle. Furthermore, an optical film 24 is located on the cover 23, which is intended to prevent incoming sunlight SL from reaching the display element 11 via the mirrors 21, 22. The display element 11 can be temporarily or permanently damaged by the heat generated during this process. To prevent this, an infrared component of the sunlight SL, for example, is filtered out using the optical film 24. A glare shield 25 serves to shade light entering from the front so that it is not reflected by the cover 23 toward the windshield 31, which would dazzle the viewer. In addition to the sunlight SL, light from another interfering light source 64 can also reach the display element 11.

[0020] The same reference symbols are also used in the following figures for the same or equivalent elements and are not necessarily described again for each figure.

[0021] The Fig. 2-4 show a simplified schematic beam path in a head-up display. The various reflections have been omitted for clarity. On the left, you can see the eye 61, in the middle the image plane 10, which corresponds to both the display element 11 and the virtual image VB, and on the right the aperture A of an image generator 12, which is, for example, a spatial light modulator, also called an SLM. An SLM spatially modulates light. This can be done in different ways. A special type of SLM is a DMD projector, where DMD stands for "Digital Micromirror Device." This is a device in which either a single micromirror, movable in the X and Y directions, scans a laser beam across an image surface, or in which the image surface is formed by a plurality of micromirrors arranged side by side and illuminated by a light source.The eyebox 62 is marked in the viewing plane 63 by means of a reinforced line and upper and lower boundaries.

[0022] Fig.2 shows points P1 to P4 in the image plane 10. It can be seen that point P1, due to its position in the image plane 10 and the size of the aperture A, is only visible from parts of the eyebox 62. Point P4 is only visible outside the eyebox 62. Only points P2 and P3 are visible in the eyebox 62, and rays emanating from them also enter the eye 61. Thus, only a small area 101 of the image plane 10 can be captured by the eye 61 in its depicted position.

[0023] Fig.3 shows the same arrangement as Fig.2 , but with a diffuser 13 arranged in the image plane 10. This ensures that light coming from the imager 12 is diffusely scattered. This is indicated at points P1 and P4 by means of diffusely scattered rays DS1 - DS5, whose direction indicates the direction in which the scattering is more diffuse, and whose length indicates the intensity in the corresponding direction. It can be seen that the greatest intensity is in the center of the corresponding Fig.2 The direction of the beam shown is illustrated here by the diffusely scattered beam DS3. The larger the angle of the other beams DS1, DS2, DS4, and DS5 to beam DS3, the lower their intensity. It can be seen that beam DS5 entered eye 61 from point P1. The diffusely scattered beams DS3 and DS4 continue to fall into eyebox 62, while beams DS1 and DS2 lie outside and are thus lost. The same applies to point P4.

[0024] Fig.4 shows the same arrangement as Fig.3 , but with a diffuser 131 that has a special diffusion characteristic. It can be seen that all diffusely scattered rays DS1 to DS5 emanating from point P1 have approximately the same intensity, and their angular distribution is such that they all reach the eyebox 62. Therefore, no light loss occurs at this point.

[0025] Fig.5 shows a similar arrangement to the previous figures, but here with multiple imagers 12. The imagers 12 are coordinated so that light beams are emitted at points P1 and P4 over a larger angular range, whereby point P4 is also visible from the eyebox 62. By increasing the number of imagers 12, a similar effect is achieved as with a diffuser 13 with regard to the visibility of points P1 to P4 throughout the eyebox 62.

[0026] Fig.6 shows a similar arrangement to the previous figures, but here the imager 12 does not focus on one image plane, but rather collimates to infinity. The rays arriving at a point in the viewing plane 63 are parallel to each other. This makes it possible to arrange several coordinated imagers 12 instead of Fig.5 shown to virtually double the one imager 12. This is shown in the following figures.

[0027] Fig.7 shows a similar arrangement as Fig.6 , here, however, with virtual doubling of the imager 12. For this purpose, a beam splitter is arranged in the beam path of the imager 12, which reflects a portion of the radiation onto a mirror 122. The mirror plane 123 of the beam splitter 121 is aligned parallel to the mirror 122. The number of parallel beams emanating from the imager 12, two of which are shown here, is doubled, and their intensity is halved. Thus, both beams shown enter the eyebox 62. The virtual imager 12' is indicated by dashed lines. By suitably arranging additional beam splitters and suitably adjusting their size, it is possible to achieve that beams over a large angular range can be viewed from any point in the eyebox 62 when the eye 61 is located there.

[0028] Fig.8 shows a similar arrangement as Fig.7 However, here the beam splitter 121 and the mirror 122 are replaced by an optical waveguide 5. The optical waveguide 5 has a mirror plane 523, with which light coming from the imager 12 is coupled into the optical waveguide 5. The extension of the original beam direction is indicated by dashed lines. The light coupled into the optical waveguide 5 is totally reflected at its boundary surfaces and is thus guided within the optical waveguide 5. The optical waveguide 5 also has mirror planes 522, which are partially transparent and each couple a portion of the light incident on them out of the optical waveguide 5. For the sake of clarity, this is shown with the parallel beam at only one angle. The principle of multiplying the parallel beams can be seen. By suitable arrangement, a sufficiently uniform illumination of the eyebox 62 can be achieved.Instead of using mirror planes 522, 523, the coupling and decoupling can also be carried out using diffraction gratings (not shown here) arranged on the surface of the optical waveguide 5 or in another manner familiar to the person skilled in the art.

[0029] Fig.9 shows a similar arrangement as Fig.8 However, here the optical waveguide 5 has an input hologram 53 and an output hologram 52, which are arranged as volume holograms in the center of the optical waveguide 5. Here, too, only the principle is indicated. It is understood that by appropriately selecting the holograms, the entire eyebox 62 can be uniformly illuminated with parallel beams at all desired angles.

[0030] Fig.10 shows a head-up display similar to Fig.1 , but here in a spatial representation and with an optical fiber 5. The schematically indicated image generator 12 can be seen, which generates a parallel beam SB1, which is coupled into the optical fiber 5 by means of the mirror plane 523. Several mirror planes 522 each reflect a portion of the light incident on them towards the windshield 31, the mirror unit 3. From this, the light is reflected towards the eye 61, which sees a virtual image VB above the hood or at an even greater distance in front of the vehicle.

[0031] Fig.11 shows a schematic spatial representation of an optical waveguide 5 with two-dimensional magnification. In the lower left area, a coupling hologram 53 can be seen, by means of which light L1 coming from an image generator 12 (not shown) is coupled into the optical waveguide 5. In this area, it propagates to the top right in the drawing, according to arrow L2. In this area of the optical waveguide 5 is a folded hologram 51, which acts similarly to many partially transparent mirrors arranged one behind the other, and generates a light beam that is broadened in the Y direction and propagates in the X direction. This is indicated by three arrows L3.In the part of the optical waveguide 5 extending to the right in the figure, there is an output hologram 52, which also functions similarly to many partially transparent mirrors arranged one behind the other and, indicated by arrows L4, outputs light upwards in the Z direction from the optical waveguide 5. This widens in the X direction, so that the original incident light beam L1 leaves the optical waveguide 5 as a light beam L4 enlarged in two dimensions. The optical waveguide 5 has a first optical waveguide 510 that widens in the y direction and has the folded hologram 51, a second optical waveguide 520 that widens in the x direction and has the output hologram 52, and a third optical waveguide 530 that has the input hologram 53.

[0032] Fig.12 shows a three-dimensional representation of a head-up display with three optical fibers 5R, 5G, 5B, which are arranged one above the other and each represent an elementary color red, green, and blue. Together, they form the optical fiber 5. The holograms 51, 52, 53 present in the optical fibers 5 are wavelength-dependent, so that one optical fiber 5R, 5G, 5B is used for each of the elementary colors. Above the optical fiber 5, an image generator 1 and an optical unit 2 are shown. Both together are often referred to as an imaging unit or PGU 100. The optical unit 2 has a mirror 20, by means of which the light generated by the image generator 1 and shaped by the optical unit 2 is deflected in the direction of the respective input 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 low overall height compared to its light-emitting surface.

[0033] Fig 13 shows three optical waveguides 5 in longitudinal section. The upper optical waveguide 5 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 beam L1, which propagates 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 middle optical waveguide 5' has upper and lower boundary surfaces 501', 502' that are not completely flat and are not parallel to one another, at least in sections. The optical waveguide 5' thus has a thickness that varies in the direction of light propagation. It can be seen that the light beam L1' is no longer parallel after just a few reflections and also does not have a homogeneous cross-section.The lower optical fiber 5" has upper and lower boundary surfaces 501", 502", which deviate even more from the ideal shape than the upper two. The light beam L1" therefore also deviates even more from the ideal shape.

[0034] Fig. 14 shows a stack 500 of optical waveguides 5, 5R, 5G, 5B according to the invention for a head-up display and its manufacture. The input holograms 53R, 53G, 53B, the folded holograms 51R, 51G, 51B, and the output holograms 52R, 52G, 52B are each located on the upper boundary surface 501R, 501G, 501B. Also located there are markings 71R, 71G, 71B and 72R, 72G, 72B, which are arranged here in the corners located on the longest straight edge of the optical waveguide 5R, 5G, 5B. On the far left of the figure, a light source 73 can be seen, schematically depicted here as a light bulb. According to the invention, it is a laser that emits light beams LS1, LS2 that pass the markings 71R, 71G, 71B and 72R, 72G, 72B, respectively, and are detected by light detectors 74.These can be simple light detector cells, but preferably planar detector arrays with several rows and columns of light detectors are provided for detecting patterns.

[0035] In a stack 500 of optical waveguides 5, 5R, 5G, or 5B, each of the optical waveguides 5R, 5G, or 5B has at least one hologram 51R, 52R, 53R, 51G, 52G, 53G, or 51B, 52B, 53B, and each of the optical waveguides 5R, 5G, or 5B has at least one marking 71R, 72R, 721R, 71G, 72G, 721G, or 71B, 72B, 721B. Corresponding markings 71R, 71G, 71B, 72R, 72G, 72B, or 721R, 721G, 721B of the individual optical waveguides 5R, 5G, or 5B are arranged aligned with one another after production according to the invention.

[0036] Fig. 15shows a flowchart of a method according to the invention. The first holograms 51R, 52R, and 53R of a first optical waveguide 5R, as well as its two markings 71R, 72R, are written in a first step S1. This is preferably done by exposing a liquid material 76R, which forms the hologram layer 56R when cured. In a second step S2, the second optical waveguide 5G is written in a corresponding manner, and in a third step S3, the third optical waveguide 5B. In a fourth step S4, the optical waveguides 5R, 5G, 5B are roughly positioned relative to one another. In a further step S5, the markings 71R, 71G, 71B, 72R, 72G, 72B are illuminated by the light beams LS1, LS2. In a further step S6, the pattern M appearing after passing the markings is detected in the respective light detector 74 and fed to a control unit 75.This emits a signal SV to a positioning device (not shown here), which, in a further step S7, finely positions the position of the optical fibers 5R, 5G, 5B relative to one another until the detected pattern M matches a predetermined pattern. Additionally or alternatively, a marking 721R, 721G, 721B is applied using a material 761 that is different from the material 76, here black paint. The associated light source, detector, and light beam are not shown here for the sake of clarity. The markings 721R, 721G, 721B are shown arranged one above the other. A combination of one or two markings 71, 72 of the material 76 and two or one marking 721 of the different material 761 is also useful, but not shown here.

[0037] In other words, the invention relates to the correct alignment of the output hologram 52. For the folded hologram 51, and even more so for the input hologram 53, good alignment is desirable but not absolutely necessary. A full-color fiber optic head-up display, also referred to as a full-color waveguide head-up display, consists of three superimposed monochrome fiber optics 5R, 5G, 5B for the colors red, green, and blue. In order to fully utilize the optical compensation options, it is necessary to position the three individual fiber optics 5R, 5G, 5B precisely relative to one another. This is achieved, for example, by mechanical stops. Suitable measurement technology for alignment is not currently available. One problem is that if the three superimposed fiber optics 5R, 5G, 5B are not precisely aligned relative to one another, existing optical compensation options cannot be utilized.With the accuracies achievable to date, distortions or color shifts frequently occur. The invention proposes an alignment concept for the individual optical fibers 5R, 5G, and 5B arranged one above the other.

[0038] To ensure the most precise alignment possible of the individual monochrome optical fibers 5R, 5G, 5B to one another, markings 71, 72 are introduced during the exposure process to create the grating structures, the holograms 51, 52, and 53. These markings, in turn, are very precisely aligned with the holograms 51, 52, 53 present in the optical fibers 5R, 5G, 5B and are positioned so that they lie exactly one above the other when correctly aligned. During the alignment process, the optical fibers 5R, 5G, 5B are illuminated from below, and the markings are detected by the light detector 74, for example, a suitable camera. Once the optical fibers 5R, 5G, 5B are in the correct position, they are fixed in place.

[0039] By introducing the markings 71, 72 during and together with the generation of the grating structures, the holograms 51, 52, 53, in the individual optical waveguides 5R, 5G, 5B, the markings 71, 72 are positioned very easily and with high precision relative to the respective hologram 51, 52, 53. The subsequent alignment process of the various optical waveguides 5R, 5G, 5B to each other is also carried out very easily and precisely using camera recognition. The very precise alignment of the three individual optical waveguides 5R, 5G, 5B allows the full optical performance to be utilized in terms of optical compensation options for compensating for different curvatures of windshields 31.

[0040] Further details can be found in the claims or the introduction to the description. It is understood that the specified measures can also be used according to the invention in modifications or in combinations other than those described here. List of reference symbols

[0041] 1Image generator 100PGU (imaging unit) 10Image plane 101Area (of the image plane) 11Display element 12Image generator 121Beam splitter 122Mirror 123Mirror plane 13,131Diffuser 14, 14R, 14G, 14BLight source 2Optical unit 20Mirror 21Folding mirror 22Curved mirror 221Bearing 23Transparent cover 24Optical film 25Anti-glare screen 3Mirror unit 31Windshield 4Control unit 5 Optical fibers 500 Stack (of optical fibers) 501 Upper boundary surface 502 Lower boundary surface 503 Left boundary surface 504 Right boundary surface 505 Front boundary surface 506 Rear boundary surface 51 Folding hologram 510 First optical fiber (expanding in the y-direction) 52 Output hologram 520 Second optical fiber (expanding in the x-direction) 522 Mirror plane 523 Mirror plane 53 Input hologram 530 Third optical fiber (input) 56 Hologram layer 61Eye 62Eyebox 63Viewing plane 64Strobing light source 71, 71R, 71G, 71B Marking 72, 72R, 72G, 72B Marking 721, 721R, 721G, 721B Marking 73 Light source 74 Light detector 75 Control unit 76 Material, for hologram 76 1 Material, not for hologram A aperture DS1...DS5 diffusely scattered rays L1 ... L4 light LS1,LS2 light rays M pattern P1 ... P4 point (on the image plane) S1-S7 process steps SB1,SB2 beam SL sunlight SV signal, position change VB virtual image

Claims

1. Method for exactly aligning at least two holograms (52,52R,52G,52B, 53,53R,53G,53B) arranged in optical waveguides (5,5R,5G,5B) with respect to one another, with - writing (S1) a first hologram (51R,52R,53R) and a first mark (71R,72R,721R) in a first optical waveguide (5R), - writing (S2) a second hologram (51G,52G,53G) and a second mark (71G,72G,721G) in a second optical waveguide (5G), - positioning (S4) the first optical waveguide (5R) and the second optical waveguide (5G) with respect to one another, - illuminating (S5) the first mark (71R,72R,721R) and the second mark (71G,72G,721G) using a light beam (LS1,LS2) that successively passes mutually associated marks (71R,72R,721R,71G,72G,721G) of the first optical waveguide (5R) and of the second optical waveguide (5G) and that is in each case influenced by the mutually associated marks (71R,72R,721R, 71G,72G,721G), wherein the marks (71R,71G,72R,72G,721R,721G) of the individual optical waveguides (5R,5G) are grating structures or holograms that influence the light (LS1,LS2) used during the illumination (S5) and are adapted to one another in such a way that a correct alignment is detectable, and wherein the marks (71R,71G,72R,72G,721R,721G) have a lens function whose associated focal lengths are selected in such a way that a correct pattern only occurs during the illumination (S5) when the distance between the individual optical waveguides (5R,5G) also takes a specified value, - detecting (S6) a pattern (M) occurring during the illumination (S5) with the light beam (LS1,LS2) after passing the first mark (71R,72R,721R) and the second mark (71G,72G,721G), and - changing (S7) the position of one of the optical waveguides (5R,5G,5B) until the detected pattern (M) matches a specified pattern.

2. Method according to Claim 1, with - writing (S1,S2) at least one of the marks (71,72) in the same material (76) in which the associated hologram (5) is written.

3. Method according to Claim 1, with - writing (S1,S2) at least one of the marks (721) in a material (761) different from that in which the associated hologram (5) is written.

4. Method according to any of Claims 1-3, wherein the marks (71R,71G, 72R,72G, 721R,721G) of the individual optical waveguides (5,5R,5G,5B) are exactly on top of each other when correctly positioned and result in a detectable pattern (M) when illuminated (S5).

5. Method according to any of Claims 1-3, wherein the marks (71R,71G, 72R,72G, 721R,721G) of the individual optical waveguides (5,5R,5G,5B) lie next to one another when correctly positioned and result in a detectable pattern (M) when illuminated (S5).

6. Method according to Claim 1 or 2, wherein a central region of the mark allows light (LS1,LS2) to pass, while an outer region located outside the central region strongly deflects light (LS1,LS2) to the outside.

7. Stack (500) of optical waveguides (5R,5G) produced by means of a method according to any of the preceding claims.

8. Head-up display, having a stack (500) of optical waveguides (5R,5G) according to Claim 7.