WO2019238859A1

WO2019238859A1 - Optical waveguide for a head-up display

Info

Publication number: WO2019238859A1
Application number: PCT/EP2019/065564
Authority: WO
Inventors: Felicitas WILLE; Wolff VON SPIEGEL
Original assignee: Continental Automotive Gmbh
Priority date: 2018-06-15
Filing date: 2019-06-13
Publication date: 2019-12-19
Also published as: DE112019003032A5

Abstract

The invention relates to an optical waveguide for a head-up display. The optical waveguide has a substrate (54), a cover layer (55), and an optically active layer (56) located between the latter. The thickness (D_D) of the cover layer (55) is substantially smaller than the thickness (d_s) of the substrate (54).

Description

description

Optical fiber for a head-up display

The present invention relates to an optical waveguide for a head-up display, which has the optical waveguide for enlarging the exit pupil.

A head-up display with an optical waveguide is known from US 2016/0124223 A1. Grid structures for coupling and decoupling the image to be displayed are arranged on its surface. These are therefore insufficiently protected against environmental influences such as mechanical or chemical impairment. An improved optical waveguide is desirable.

According to the invention, the optical waveguide for

Head-up display on a substrate, a cover layer and an optically active layer located between them, preferably a hologram layer. The thickness of the cover layer is significantly less than the thickness of the substrate. This has the advantage that the substrate is more stable compared to the other two layers, which prevents or greatly reduces deformations, particularly during the manufacturing process. This fulfills the optical quality of the optical fiber. In particular, if one or more holograms are introduced into the optically active layer, a substrate that is stable against deformation makes sense, since its deformation would also result in deformations or stresses in the hologram and thus a deterioration in its optical properties.

The cover layer is advantageously a glass plate with a thickness of less than 1 mm, preferably less than 0.5 mm. This has the advantage that such a glass plate is flexible and can be rolled onto the optically active layer. In this way, air connections or stresses that occur when the substrate and cover layer are put together are avoided if these are both approximately the same thickness, in particular thicker than 1 mm. If the thickness of the substrate is less than 0.5 mm, it is even more flexible and can be rolled even more easily onto the optically active layer, which is preferably still liquid, and will only be written with a hologram after the top layer has been rolled off, for example by exposure using a laser scanner or from a negative, and fixed by curing. In order to set the exact distance between the substrate and the top layer, spaced elements are provided. According to a variant, their thickness is spatially varied. In this way, a two-dimensional curvature of the

Cover layer can be achieved, which is desired to achieve advantageous optical effects, such as compensating for distortions caused by the curvature of the windshield. The thinner the cover slip, the better it adapts to the desired two-dimensional curvature.

According to a variant of the invention, it is provided that the cover layer is a thin layer deposited on the optically active layer, the hologram layer, evaporated or separated from a liquid. This has the advantage that no unrolling is necessary. Evaporation or rolling is an even simpler manufacturing step. The thin layer advantageously has similar optical properties to the substrate, in particular with respect to the refractive index, in order to enable total internal reflection. If the thin layer is only a few molecular layers thick, the optical properties with regard to total internal reflection are less relevant. It then mainly serves to protect the hologram layer against mechanical and in particular chemical environmental influences.

The cover layer advantageously has a further optical functional layer. This is, for example, an anti-flex layer or a polarization adjustment layer.

A head-up display according to the invention has at least 2

Optical waveguide on whose respective top layer on the at least one other side facing the optical waveguide is arranged. This has the advantage of protection against mechanical influences from outside, since the thicker substrate is directed outwards.

Further variants and their advantages can also be found in the following description of exemplary embodiments.

Figure overview:

Fig.l head-up display according to the prior art

Fig. 2 schematic beam path

Fig. 3 schematic beam path with diffuser

Fig. 4 Beam path with a directed diffuser

Fig. 5 beam path with several imaging devices

Fig. 6 Beam path with an image in infinity

Fig. 7 Beam path with virtual doubling

Fig. 8 Beam path with optical fiber

Fig. 9 Beam path with optical fiber

Fig. 10 head-up display with fiber optic cable

Fig.ll optical fiber with two-dimensional magnification

Fig. 12 Head-up display with fiber optic cable

Fig. 13 Optical waveguide in longitudinal section

Fig. 14 optical fibers

figure description

Fig.l 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 display element 11 emits a beam of rays SB1, which is reflected by a folding mirror 21 onto a curved mirror 22, which is directed in the direction of the mirror unit 3, here as a windshield 31 of a vehicle is reflected. From there, the beam of rays SB2 reaches the eye 61 of an observer. This sees a virtual image VB, which is outside the vehicle above the hood or even in front of the vehicle located. 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 are symbolically a speed limit, the current vehicle speed and navigation instructions. As long as the eye 61 is 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 outside the eyebox 62, the virtual image VB is only partially or not at all visible to the viewer. The larger the eyebox 62, the less restricted the viewer is in choosing his seating position.

The curvature of the curved mirror 22 serves on the one hand to prepare the beam path and thus to provide 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 represented by the display element 11. The curved mirror 22 is rotatably supported by means of a bearing 221. The thereby possible rotation of the curved mirror 22 enables a displacement of the eyebox 62 and thus an adaptation of the position of the eyebox 62 to the position of the eye 61. The folding mirror 21 serves to ensure that the path covered by the beam SB1 between the display element 11 and the curved mirror 22 is long, and at the same time the optical unit 2 is still compact. The optical unit 2 is delimited from the surroundings by a transparent cover 23. The optical elements of the optical unit 2 are thus protected, for example, against dust located in the interior of the vehicle. On the cover 23 there is also an optical film 24 which is intended to prevent incident sunlight SL from reaching the display element 11 via the mirrors 21, 22. This can be temporarily or permanently damaged by the heat generated. To prevent this, for example, an infrared portion of the sunlight SL is filtered out by means of the optical film 24. A glare shield 25 is used to to shade falling light so that it is not reflected by the cover 23 towards the windshield 31, which would cause glare to the viewer. In addition to the sun light SL, the light from another interference light source 64 can reach the display element 11.

The same reference numerals are used in the following figures for the same or equivalent elements, and are not necessarily described again for each figure.

2-4 show a simplified schematic beam path in a head-up display. The different reflections are omitted for the sake of 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 imager 12, which is, for example, a spacial light modulator, also called SLM. Light is spatially modulated with an SLM. This can be done in different ways. A special type of SLM is a DMD projector, whereby 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 over an image area, or in which the image area is formed by a large number of micromirrors which are arranged next to one another and are illuminated by a light source. The eyebox 62 is identified in the viewing plane 63 by means of a reinforced line and limitation up and down.

2 shows points PI to P4 in the image plane 10. It can be seen that the point PI is only visible from parts of the eyebox 62 due to its position in the image plane 10 and the size of the aperture A. The point P4 is only visible outside the eyebox 62. Only the points P2 and P3 are visible in the eyebox 62; rays emanating from them also fall into the eye 61. Thus, only a small area 101 of the image plane 10 can be detected by the eye 61 in the position shown. 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 in points PI and P4 by means of diffusely scattered beams DS1-DS5, the direction of which indicates which direction is diffusely scattered, and the length of which indicates the intensity in the corresponding direction. It can be seen that the greatest intensity runs in the center of the corresponding beam shown in FIG. 2, illustrated here by the diffusely scattered beam DS3. The greater the angle of the other beams DS1, DS2, DS4, DS5 to the beam DS3, the lower their intensity. It can be seen that the beam DS5 entered the eye 61 from the point PI. The diffusely scattered rays DS3 and DS4 continue to fall into the eyebox 62, while the rays DS1 and DS2 lie outside and are therefore lost. The same applies to point P4.

4 shows the same arrangement as FIG. 3, but with a diffuser 131, which has a special diffusion characteristic. It can be seen that all the diffusely scattered rays DS1 to DS5 emanating from the point PI have approximately the same intensity and their angular distribution is such that they all reach the eyebox 62. There is therefore no loss of light at this point.

5 shows a similar arrangement to the previous figures, but here with several image generators 12. The image generators 12 are matched to one another in such a way that light rays are emitted in points PI and P4 in a larger angular range, which also means point P4 from the Eyebox 62 is visible out. By increasing the number of imagers 12, an effect similar to that of a diffuser 13 with regard to the visibility of the points PI to P4 in the entire eyebox 62 is achieved. 6 shows an arrangement similar to the previous figures, but here the imager 12 does not focus on one image plane, but collimates to infinity. The rays arriving in the observation plane 63 to a point each run parallel to one another. This makes it possible, instead of arranging several coordinated image generators 12, as shown in FIG. 5, to virtually double the one image generator 12. This is shown in the following figures.

FIG. 7 shows an arrangement similar to FIG. 6, but here with virtual doubling of the image generator 12. For this purpose, a beam splitter is arranged in the beam path of the image generator 12, which reflects part 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 of rays emanating from the imager 12, two of which are shown here, is doubled, and their intensity is halved in each case. Thus, both of the beams shown hit the eyebox 62. The virtual imager 12 'is indicated by dashed lines. By ge suitable arrangement of further beam splitters and suitable adjustment of their size can be achieved that beams can be viewed from a large angle range from any point of the eyebox 62 when the eye 61 is there.

Fig. 8 shows a similar arrangement as Fig. 7. However, the beam splitter 121 and the mirror 122 are replaced by an optical waveguide 5 here. 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 interfaces 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 part of the light impinging on them from the optical waveguide 5. For the sake of clarity, this is with the parallel beam at only one angle shown. One can see the principle of multiplication of the parallel beams. With a suitable arrangement, he can achieve a sufficiently uniform illumination of the eyebox 62. Instead of using mirror planes 522, 523, the coupling and uncoupling can also be carried out by means of diffraction gratings (not shown here) arranged on the surface of the optical waveguide 5 or in another manner known to the person skilled in the art.

FIG. 9 shows an arrangement similar to FIG. 8, but here the optical waveguide 5 has a coupling-in hologram 53 and a coupling-out 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 suitable selection of the holograms it can be achieved that the entire eyebox 62 is illuminated uniformly with parallel beams of rays at all desired angles.

Fig. 10 shows a head-up display similar to Fig.l, here al lerdings in spatial representation and with a Lichtwel lenleiter 5. One recognizes the schematically indicated imager 12, which generates a parallel beam SB1, which by means of the mirror plane 523 in the optical fiber 5 is coupled. Several mirror planes 522 each reflect part of the light impinging on them in the direction of the windshield 31, the mirror unit 3. From this, the light is reflected in the direction of the eye 61, which sees a virtual image VB above the bonnet or at a further distance in front of the vehicle.

Fig.ll shows a schematic spatial representation of an optical fiber 5 with two-dimensional magnification. In the lower left area, a coupling hologram 53 can be seen, by means of which light LI coming from an imager 12, not shown, is coupled into the optical waveguide 5. In it, it spreads to the top right in the drawing, according to arrow L2. In this area of light lenleiters 5 is a folding hologram 51, which acts similar to many partially arranged mirrors arranged one behind the other, and generates a widened in the Y direction, spreading in the X direction. This is indicated by three arrows L3. In the part of the optical waveguide 5 which extends to the right in the illustration, there is an out coupling hologram 52, which likewise acts similarly to many partially transparent mirrors arranged one behind the other, and couples out light indicated in the Z direction upwards from the optical waveguide 5 by arrows L4 , Here there is a widening in the X direction, so that the original incident light bundle LI leaves the optical waveguide 5 as an enlarged light bundle L4 in two dimensions. The optical waveguide 5 has a first optical waveguide 510 widening in the y-direction, which has the folding hologram 51, a second optical waveguide 520 widening in the x-direction, which has the coupling-out hologram 52, and a third optical waveguide 530, which has the coupling-in hologram 53.

Fig. 12 shows a spatial 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 waveguide 5. The holograms 51, 52, 53 present in the optical waveguides 5 are wavelength-dependent, so that one optical waveguide 5R, 5G, 5B is used for one of the elementary colors. An image generator 1 and an optical unit 2 are shown above the optical waveguide 5. Both together are often referred to as an imaging unit or PGU 100. The optics unit 2 has a mirror 20, by means of which the light generated by the image generator 1 and shaped by the optics unit 2 is deflected in the direction of the respective 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 low overall height compared to its light-emitting surface. 13 shows three optical fibers 5 in longitudinal section. The upper optical waveguide 5 has an ideally flat upper limiting surface 501 and an ideally flat lower limiting surface 502, both of which are arranged parallel to one another. It can be seen that a parallel light bundle LI, 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 'which are not completely flat and are not parallel to one another at least in sections. The optical waveguide 5 'thus has a thickness which varies in the direction of light propagation. It can be seen that the light bundle LI 'is no longer parallel after a few reflections and also has no homogeneous cross section. The lower optical waveguide 5 "has upper and lower limitation surfaces 501", 502 ", which deviate even more from the ideal shape than the upper two. The light beam LI" thus also deviates even more from the ideal shape.

14 shows in the lower right part an optical waveguide 5G, the example of which explains a solution according to the invention. The optical waveguide 5G consists of a substrate 54, here a glass substrate, a thin holographic layer, the hologram layer 56, and a further glass substrate as a cover layer 55. This is shown enlarged in a sectional view at the bottom left.

During the production of the optical waveguide 5G, there is initially an intermediate space 560 between the cover layer 55 with the thickness D _D and the substrate 54 with the thickness D _s , which are fixed at a distance D from one another. This is compared to the thickness DD of the cover layer and the thickness DS of the substrate exaggerated. A curable liquid material is filled into the intermediate space 560 during manufacture. This material is used to write a hologram 51,52,53 exposed and optionally cured in a further or simultaneous step.

In the upper part of the figure you can see the optical fiber 5G with dimensions according to the invention. The substrate 54 has a substantially greater thickness D _s than the thickness D _{D of} the cover layer 55. Here too, the thickness D of the hologram layer 56 is exaggerated.

In other words, the invention relates to the construction of optical waveguides 5,5R, 5G, 5B from substrates of different thicknesses. A conventional full-color fiber optic head-up display, also as

"Full-color waveguide head-up display", consists of three superimposed monochrome optical fibers 5R, 5G, 5B, one each for the color components red, green, and blue and each consisting of substrate 54, preferably made of glass, thin hologram layer 56 with spacer elements and a cover layer 55, which usually also consists of glass. By decoupling and overlaying the three colors, a mixed color image is obtained. The substrate 55 and the cover layer 55 of a monochrome optical waveguide 5, 5R, 5G, 5B usually have the same material thickness.

Glass substrates with a thickness greater than 1 mm are used. These are stiff, which makes bubble-free assembly of the two glasses very difficult. Controlled rolling of the glass substrate of the cover layer 55 on the substrate 54 coated with liquid material is therefore not possible. With the solution according to the invention, the rigidity of one of the glasses, here the cover layer 55, is lowered. This enables a controlled rolling of the glass of the cover layer 55 on the substrate 54 coated with material of the holographic layer without bubbles. The solution according to the invention describes a monochrome optical waveguide 5G consisting of two glasses, the substrate 54 and the cover layer 55, between which a thin holographic layer, the hologram layer 56, is arranged. Two glasses with a considerable difference in thickness are used. One of the glasses has a thickness of less than 1 mm, preferably less than 0.5 mm, in particular less than 0.1 mm, and thus has a reduced rigidity. The total thickness of the monochrome optical waveguide 5G remains constant in comparison with the current state of the art, so that the second glass, the substrate 54, is made stronger according to the reduction in the thickness of the first glass, the cover layer 55. In addition, the use of a flexible glass for producing monochrome 5G optical waveguides results in considerable advantages and simplifications in the course of production.

In the upper part of FIG. 14, a side view of a monochrome chrome optical waveguide 5G according to the invention is shown. The substrate 54 has a thickness greater than 1 mm. Separated by a thin hologram layer 56, a thin cover layer 56 made of glass with a thickness of substantially less than 1 mm is added to the structure. Both glasses usually have the same thickness. The solution according to the invention with different strengths does not change the overall thickness of the structure of the monochrome optical waveguide 5G. The thickness of the one glass, here the substrate 54, is increased by the amount by which the thickness of the other glass, here the cover layer 55, is reduced.

In an extreme case, the cover layer 55 is made extremely thin, so that it no longer necessarily has to be made as a disk material, but also, for example, as

Thin layer deposited, evaporated or applied in any other way. In extreme cases, it is also completely omitted. Then the hologram layer 56 forms the surface of the optical waveguide. The arrangement of the layer does not have to be that way take place that the thin layer or the cover layer 55 faces the driver. According to a variant, it is provided that it points into the interior of the device. In addition, it is advantageous to combine the function of the cover layer 55 or the applied thin layer with other functions, for example with anti-reflective properties for useful or stray light, polarization adjustments and the like.

Further details can be found in the claims or the introduction to the description. It is understood that the measures given can also be used according to the invention in a modification or in a combination other than that described here.

Reference character list

1 image generator

100 PGU (imaging unit)

10 image plane

101 area (the image plane)

11 display element

12 imagers

121 beam splitters

122 mirrors

123 mirror plane

13, 131 diffuser

14, 14R, 14G, 14B light source

2 optics unit

20 mirrors

21 folding mirrors

22 curved mirror

221 storage

23 transparent cover

24 optical film

25 glare protection

3 mirror unit

31 windshield

4 control unit

5 optical fibers

500 stacks (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 waveguide (widening in the y direction)

52 decoupling hologram

520 second optical waveguide (pointing in the x direction)

522 mirror plane

523 mirror plane

53 coupling hologram

530 third optical fiber (coupling)

54 substrate

55 top layer

551 thin film

56 hologram layer

560 space

61 eye

62 eyebox

63 Viewing level

64 Interference light source

A aperture

D distance

D _D Thick top layer

D _s thick substrate

DS1 DS5 diffuse scattered rays

LI L4 light

LSI, LS2 light rays

PI ... P4 point (on the image plane)

SB1, SB2 beams

SL sunlight

VB virtual image

Claims

claims

1) Optical fiber for a head-up display, having

- a substrate (54),

- a cover layer (55),

an optically active layer (56) located between them,

wherein the thickness (D _d ) of the cover layer (55) is substantially less than the thickness (D _s ) of the substrate (54).

2) Optical waveguide according to claim 1, wherein the cover layer (55) is a glass plate with a thickness (D _d ) less than 1 mm, preferably less than 0.5 mm.

3) Optical waveguide according to claim 1, wherein the cover layer (55) is a thin layer () vapor-deposited on the optically active layer (56) or deposited from a liquid.

4) Optical waveguide according to one of the preceding claims, wherein the cover layer (55) has a further optical function layer.

5) Head-up display with at least two optical fibers

(5R, 5G, 5B) according to one of the preceding claims, wherein the cover layer (55R, 55G, 55B) at least one of the optical waveguides (5R, 5G, 5B) on the at least one other optical waveguide (5R, 5G, 5B) facing of

Optical waveguide (5R, 5G, 5B) is arranged.