Waveguide-based projection display apparatus for vehicles with dynamic diffuse light absorber

Abstract

The invention relates to a waveguide-based projection display device, in particular for a vehicle, comprising an imaging unit and a planar waveguide comprising a light outcoupling facet constituted in a facet side of the waveguide for light beams generated by the imaging unit, an at least partially transparent reflective glass, in particular a windshield, which is arranged in a field of view of a user and constituted for reflecting the light beams outcoupled from the waveguide to an eye movement range predetermined for an eye of the user such that a virtual display image is generated in the field of view of the user, an eye tracking mechanism constituted for ascertaining an eye movement range window of a predetermined size within the eye movement range currently occupied by the eye of the user, and a dynamic stray light absorber constituted for obscuring the light outcoupling facet in a face section which is dynamically adjustable depending on a signal of the eye tracking mechanism, the face section extending from at least one of the edges of the light outcoupling facet, respectively, in order to at least partially limit the outcoupled light beams to the current eye movement range window.

Description

TECHNICAL FIELD

[0001] The invention relates to a waveguide-based projection display device, which can be used in particular in a motor vehicle or other type of vehicle. The projection display device is designed for producing a virtual display image which is inserted into the field of view of a user by reflection on an at least partially transparent reflection glass, in particular a windshield of a vehicle. The projection display device is based here on a waveguide in order to produce a comparatively large virtual display image with a small installation space. The invention also relates to a method for operating a projection display device and a vehicle equipped with the projection display device. BACKGROUND

[0002] Projection display devices are known in particular under the name head-up display (HUD). For example in a motor vehicle, it is possible in this way to superimpose a desired display content, for example an indication about a speed limit or other useful navigation and vehicle operation tips or entertainment content, in the form of a virtual display image on the real environment image in front of the vehicle which is observed by the driver or other passengers. To this end, the projection display device comprises in the classic construction type a display which is arranged underneath the upper side of the dashboard with suitable imaging and projection optics in order to produce a light beam with the desired display content and thus to project it onto the windshield of the motor vehicle or a combi-glass which is additionally arranged in front of the windshield, so that the light beam is reflected from the windshield or combi-glass towards the user in order to generate a virtual display image in front of or behind the reflection glass in the field of view of the user.

[0003] Alternative to this classic HUD construction type, which imaging and projection optics typically comprise a concave mirror in the light path behind the display, the size of which scales linearly with the HUD image, a HUD construction type with a planar waveguide (optical waveguide) of large area is known in particular for AR applications (Augmented Reality). By applying a planar waveguide, the installation space necessary for the HUD can be significantly reduced in relation to the classic HUD construction type in connection with the size of the virtual display image.

[0004] HUDs which make use of waveguides in order to display large HUD images in the case of small structural spaces - however will exhibit completely different stray light characteristics compared to classic HUDs. In the case of classic HUDs the stray light is mainly generated by the imaging unit in the form of an LCD (Liquid Crystal Display), DMD (Digital Micro-mirror Device) or LCOS (Liquid Crystal on Silicon), whereas in waveguide HUDs there are two sources of stray light: one is the imaging unit (Picture Generation Unit, PGU) which generates a usually collimated light beam with the display content, and the other is the waveguide itself in which the generated light beam is guided and outcoupled towards the windshield. This additional source of stray light is particularly pronounced in the state-of-the-art waveguide variants, because here a holographic structure is included in the waveguide which is used for light deflection and typically has a tendency towards increased scattering based on its material properties.

[0005] This mostly leads to the negative effect that the entire light outcoupling surface of the waveguide appears like a diffusely luminous surface. This diffusely luminous surface is reflected via the windshield into the driver's eyes and thus covers the road scene lying in front (see Figures 1 and 2).

[0006] During the day this stray light is usually not a problem. However at night it can lead to disturbing effects of the stray light especially in the case of long-distance driving in flat regions. The area below the horizon is illuminated by the vehicle's low beam, whereby the driver is more tolerant of the stray light of the HUD in this area. The area above the horizon is significantly more critical: because the driver has a particularly dark background here in which the stray light can be particularly easily seen by the driver. In the worst case the driver can even get the impression of driving through a thick fog. Especially for small and medium-sized drivers the area of stray light can be increased far above the horizon. SUMMARY

[0007] It is an object of the present application to propose a waveguide-based projection display device with which the described effects of stray light in the user's field of view, in particular in the area above the horizon, can be reduced or even eliminated. In particular the ability of the projection display device for the initially mentioned purposes for use in a motor vehicle or other land vehicle, air vehicle or water vehicle can thereby be improved.

[0008] This object is solved by a waveguide-based projection display device according to the present application, a corresponding method of operation, a corresponding control unit and a vehicle equipped with the projection display device. All further features and effects mentioned in the following description for the projection display device also apply to its method of operation, control unit and vehicle and vice versa.

[0009] According to a first aspect, a waveguide-based projection display device is provided, which in particular can be configured for use in a motor vehicle or any other ground vehicle, air vehicle or water vehicle. The projection display device in particular can relate to a head-up display (HUD).

[0010] The projection display device here comprises a planar, in particular flat, waveguide (optical waveguide). In one of its two face sides, the waveguide has a large-area light output coupling surface configured for one- or two-dimensional eyebox extension of light which is in the course of operation of the projection display device in- coupled into the waveguide on the side, in particular on the end side of the waveguide. The projection display device furthermore comprises an imaging unit (also referred to as PGU, picture generation unit) which is configured to generate a light beam having a desired display content and to in-couple it into the waveguide.

[0011] The projection display device furthermore comprises an at least partially transparent reflection glass which is arranged in the field of view of the user and configured for reflecting the light beam out-coupled from the waveguide to a predetermined eyebox for the eye thereof, such that a virtual display image is generated in the field of view of the user before or after the reflection glass.

[0012] The eyebox here can in particular be understood as a two-dimensional spatial range perpendicular to the light beam propagation direction. The eyebox position along the light beam propagation direction can for example be defined by a spacing to the reflection glass, wherein the user can also view the virtual display image with unimpaired quality in the case of a movement of the head towards or away from the reflection glass, for example by approximately 15 centimeters. The reflection glass can in particular be formed by a windshield of the vehicle.

[0013] Furthermore, the projection display device comprises an eye tracking mechanism which is configured to ascertain an eyebox window, i.e. a partial area, of a predetermined size within the eyebox which is currently occupied by the eye of the user. The total area of the eyebox can for example correspond to the total cross section of the light beam out-coupled from the light output coupling surface and reflected to the user, whereas the mentioned eyebox window only represents a partial region of the eyebox which for example can only cover a small fraction (e.g. less than a tenth, less than a quarter or less than a half) of the total area of the eyebox and whose position can furthermore be related to the height and the respective posture of the user. Depending on the accuracy of the eye tracking, the predetermined size of the eyebox window can vary and can for example in the case of a rectangular shape be determined by a height in the range of approximately 20 millimeters and a suitable width in the range of approximately 100 millimeters.

[0014] In order to solve the problem of stray light mentioned at the outset, a projection display device of the type described herein comprises a dynamic stray light absorber. The dynamic stray light absorber is designed to darken the light output coupling surface in a face section which can be dynamically adjusted in accordance with a signal of an eye tracking mechanism and in turn to darken stray light which in the operation of the projection display device emanates from the light output coupling surface. The face section extends from at least one of the edges of the light output coupling surface in order to at least partially limit the output-coupled light beam in its cross section to the sought eye movement range window.

[0015] To this end, the projection display device can comprise, for example, a suitable control unit which obtains an eye tracking signal of the eye tracking mechanism, processes this eye tracking signal if necessary in order to determine the eye movement range window currently occupied by the user's eye, and operates the dynamic stray light absorber in accordance with the eye movement range window in such a way that the cross section of the output-coupled light beam is at least partially reduced on the edge side, wherein the respective currently determined eye movement range window is always kept fully illuminated.

[0016] In this way, the undesired and particularly disturbing stray light mentioned at the outset, which can emanate from the light output coupling surface of the waveguide, can be at least partially blocked in the cross section area of the light beam which does not contribute to the image generation for the respective eye position of the user. Depending on the accuracy of the position detection of the eye and the design of the dynamic stray light absorber, the stray light area can be significantly reduced and in the best case completely eliminated in such a way that the light beam is reduced in the cross section in such a way that it only still illuminates the eye movement range window which is actually necessary for the display image generation. By this means, the edge produced by the disturbing stray light, which the user would see around the displayed virtual display image in the dark without the dynamic stray light absorber envisaged here, can be partially to completely eliminated.

[0017] The dynamic stray light absorber can in principle be arranged at any position in the light path of the light output-coupled from the waveguide, wherein it can be particularly advantageous in accordance with a specific embodiment to be arranged in or directly on the light output coupling surface only for spatial reasons. The dynamic stray light absorber can in this case cover the light output coupling surface in a dynamically adjustable range in order to block stray light in this area.

[0018] According to one embodiment form, the face section darkened by the dynamic stray light absorber extends from the edge of the light output coupling surface which is proximal to the user inwards along the light output coupling surface, whereby the upper eye movement range edge section above the eye movement range window can be darkened. With this embodiment form, the stray light problem mentioned at the outset can be solved above the horizontal line in the user's field of view. Additionally, the light output coupling surface can also be dynamically darkened in a face section which extends from the other edges here.

[0019] In a particular design variant, the dynamic stray light absorber comprises at least one curtain which can be automatically pulled inwards by at least one of its edges on or along the light output coupling surface in order to thereby darken a respective cross-sectional segment of the output-coupled light beam. Such a curtain can for example be provided or applied for other purposes as well, such as for protecting against misuse and / or for protecting the light output coupling surface if the projection display device is not in use, for example.

[0020] In a particular design variant, the dynamic stray light absorber is configured as a two-dimensional matrix of elements which can each be switched between a transmissive state and an absorptive state for the light output-coupled from the waveguide, i.e. not only for the useful light for image generation but also for interfering stray light. The matrix can extend along the entire light output coupling surface or at least in its edge region.

[0021] In this design variant, the dynamic stray light absorber can for example be configured as a liquid crystal matrix (LC matrix) which comprises at least one polarisation filter for switching its elements between a light transmissive state and a light blocking state. Thereby, in particular a fast switching time of the matrix elements can be achieved. For example, two polarisation filters can be provided here which have crossed, in particular mutually orthogonal, polarisation directions towards the two sides of the LC matrix. However, a single polarisation filter on the upper side of the matrix towards the reflecting glass can also be sufficient if the light output-coupled from the waveguide is already sufficiently polarised. Alternatively, the matrix can for example also be configured as an electrochromic matrix.

[0022] The individual switchable elements of the matrix can here in particular have a linear dimension of between approximately 1 mm and approximately 40 mm, for example be configured as squares or rectangles having a side length in this range.

[0023] The eye tracking mechanism can for example comprise at least one camera which is configured for optically detecting the eye movement range.

[0024] According to a further aspect, a method for operating a projection display device of the type described herein is provided. The method comprises here the following steps:

[0025] - generating a light beam by the imaging unit and input-coupling the light beam into the waveguide;

[0026] - obtaining an eye tracking signal by the eye tracking mechanism and therefrom deriving an eye movement range window currently occupied by the eye of the user within the eye movement range; and

[0027] - the dynamic stray light absorber is adjusted in accordance with the eye tracking signal or the determined eyebox window such that the light beam outcoupled from the waveguide is at least partially limited in its cross section to the determined eyebox window.

[0028] According to another aspect, a control unit for operating a projection display device of the type described herein is provided, which control unit is configured and arranged for automatically performing such a method.

[0029] According to another aspect, a vehicle, in particular a motor vehicle or any other land vehicle, an air vehicle or a water vehicle, is provided. The vehicle comprises a windshield and a dashboard arranged below it. Furthermore, the vehicle comprises a projection display device of the type described herein, which projection display device is formed by the windshield or a combined glass arranged in front of the windshield on the inside of the vehicle, and whose waveguide is configured with a face side of the light outcoupling face extending in or along the upper side of the dashboard, in particular flush with it. Furthermore, the vehicle comprises a control unit of the type described herein.

[0030] Brief summary: Stray light in a head-up display (HUD) of a motor vehicle often receives particular attention in the development of a HUD. Stray light can cause disturbances and fatigue precisely in the evening, since it reduces the contrast of the road scene. With waveguide-based AR-HUDs and the production of larger HUD images that go along with them, this topic is gaining increasing importance. The dynamic stray light absorber presented here makes it possible to eliminate stray light, in particular in the range above the horizon, which can be particularly disturbing in the dark; and furthermore to provide the user with a particularly good and safe driving experience. BRIEF DESCRIPTION OF DRAWINGS

[0031] The above-mentioned aspects and the particularly advantageous design of the application and its implementation forms are further elucidated below on the basis of examples shown in the drawings. The drawings are to be regarded as purely illustrative: they are therefore generally not to be interpreted as being true to scale. The drawings show:

[0032] Fig. 1 shows a side cross-sectional view of a vehicle comprising a waveguide-based projection display device according to the prior art, in which, in addition to the light path of the useful light, the light path of the stray light is also shown;

[0033] Fig. 2 shows the useful light range and the stray light area of the field of view of the driver of the vehicle in Fig. 1 ;

[0034] Figure 3 A side cross-sectional view of a vehicle comprising a waveguide-based projection display device of the type described herein is shown, in which the light path of the stray light is blocked by the edge of the waveguide close to the user by means of a dynamic stray light absorber;

[0035] Figure 4 a field of view of a driver of a vehicle in Figure 3 , wherein the range of useful light and the range of stray light above the horizon are eliminated by a dynamic stray light absorber;

[0036] Figure 5 a top view of a light output coupling surface of another waveguide-based projection display device of the type described herein, wherein the light path of stray light is blocked by a dynamic stray light absorber in the form of a matrix of switchable elements; and

[0037] Figure 6 a field of view of a driver of a vehicle in Figure 5 , wherein the range of useful light and the range of stray light around the HUD image are blocked by a dynamic stray light absorber from all sides.

[0038] The projection display device, the method, the control unit and the vehicle according to the above-mentioned aspects of the present application, as well as the different embodiments, variants and special design features mentioned in the description again above can be implemented in the examples shown in Figures 1 to 6. Therefore, all of their content is not repeated again in the following. The same applies accordingly to the term definitions and the effects already explained again above with respect to the individual features shown in Figures 1 to 6. DETAILED DESCRIPTION

[0039] Figure 1 shows in a strongly simplified schematic side cross-sectional view an example of a motor vehicle 17 with a waveguide-based projection display device 100 according to the prior art. Herein, in particular a head-up display (HUD) for augmented display applications (AR-HUD) is concerned.

[0040] The motor vehicle 17 comprises a windshield 2 and a dashboard arranged thereunder, in the upper side of which the projection display device 100 is arranged.

[0041] The projection display device 100 of Figure 1 comprises in a manner known per se a planar waveguide 3 (optical waveguide) which has a light output coupling surface 4 for light in its face side facing the windshield, the light being in-coupled into the waveguide 3 on the side, in particular on the end side of the waveguide 3. To this end, the projection display device 100 has an imaging unit (also referred to as PGU, picture generation unit) not shown additionally in Figure 1, which is configured to generate a light beam with the desired display content and to in-couple it into the waveguide 3.

[0042] The windscreen 2 serves as a reflecting glass in the projection display device 100, which reflects the light beams L output-coupled from the waveguide 3 on its light output-coupling face 4 to an eye-motion range 6 predetermined for the eyes of the user 5 (here: the driver of the motor vehicle), so that a virtual display image V (schematically indicated in Fig. 2) is generated in the field of view of the user 5 behind the windscreen 2. The eye-motion range 6 is to be understood here as a two-dimensional spatial range perpendicular to the light beam propagation direction. The user can well view the virtual display image V even in the case of a movement of the head of the user 5 by for example approximately 10-15 centimeters in the longitudinal direction of the vehicle from the depicted eye-motion range position. A corresponding three-dimensional spatial range 7 around the eye-motion range 6 is indicated in Fig. 1. This spatial range also includes different heights and different sitting positions of different users in the vertical direction.

[0043] As mentioned above, there are two scattering light sources in a conventional waveguide-HUD: one of them is the imaging unit, and the other one is the waveguide 3. This additional scattering light source can particularly strongly manifest itself in the waveguide 3 with a holographic structure for light deflection and typically with a tendency for increased scattering based on its material characteristics.

[0044] As shown in Fig. 1 and Fig. 2 according to the prior art, this leads to a negative effect in the case of a conventional projection display device 100, namely that the entire light output-coupling face 4 of the waveguide 3 appears like a diffusely luminous surface, which is reflected via the windscreen 2 into the eyes of the user 6 (here: the driver) and thus covers the road scene located in front with a luminous scattering light area 8 around a useful light range 9 in which the virtual display image V is shown.

[0045] Fig. 1 shows the light beam volume NL of the useful light for generating the virtual display image V for the user 5 according to the edge ray. Fig. 1 furthermore also shows the total light beam volume GL of the output-coupled light beams L, which illuminate the entire eye-motion range 6, and the upper edge ray SL of the scattering light, which here arrives from the light output-coupling face 4 of the waveguide 3 via the windscreen 2 to the eyes of the user 5 and leads to the generation of the scattering light area 8 around the useful light range 9 in which the virtual display image V is shown.

[0046] The scattered light is usually not a problem during the day. However, at night it can produce disturbing effects of scattered light precisely in the case of long-distance driving through plain areas. The scattered light region 8a below the horizon H is illuminated by the vehicle's dipped-beam, whereby the driver is more tolerant of scattered light in this region for the HUD. The scattered light region 8b above the horizon H is significantly more critical in comparison: here the driver often has a particularly dark background in which scattered light can be particularly easily seen by the driver. In the worst case, the driver can even get the impression of driving through thick fog. The scattered light region 8b can be raised far above the horizon H precisely for small and medium-sized drivers.

[0047] Figure 3 A side cross-sectional view of a vehicle is shown which comprises a waveguide-based projection display device 1 of the type described herein, wherein the light path of the scattered light is blocked by the dynamic scattered light absorber 10 from the user-approaching edge 11 of the light output coupling face 4. Here, the elements of the device 1 denoted by the same reference numerals can be designed analogously to Figures 1 and 2.

[0048] Figure 4 A side cross-sectional view of a vehicle is shown which comprises a waveguide-based projection display device 1 of the type described herein, wherein the light path of the scattered light is blocked by the dynamic scattered light absorber 10 from the user-approaching edge 11 of the light output coupling face 4. Here, the elements of the device 1 denoted by the same reference numerals can be designed analogously to Figures 1 and 2. Figure 3 The useful light range 9 and the scattered light region 8 in the field of view of the user 5 (driver of the vehicle) of the vehicle are shown, wherein the scattered light region 8b above the horizon H is eliminated by the dynamic scattered light absorber 10 by correspondingly darkening the light path of the scattered light.

[0049] Here, the scattered light problem (above the horizon H) is solved by the dynamically adjustable scattered light absorber 10, which is movable along the longitudinal axis of the vehicle as shown by the arrow in Figure 3 such a way that an optimized shading of the scattered light is always achieved, without the HUD image V being reduced here. The correct position of the front edge 12 of the dynamic scattered light absorber 10 is determined here by the position of the eyes of the user 5, which is detected by the camera 13 of a suitable eye tracking mechanism 14.

[0050] One possible embodiment of the dynamic scattered light absorber 10 is for example a curtain which is located on the user-approaching rear edge 15 of the projection display device 1 and on the light output coupling face and can be pulled inwards from its user-approaching edge 11 along the light output coupling face 4.

[0051] The upper eye movement range edge section 6b above the eye movement range window EF actually used by the user 5 is thereby darkened. At the same time, the light path of the scattered light with the edge light beam SL is thereby also blocked, which is indicated as a broken line (i.e. no longer present) in Figure 3 and 4 .

[0052] The scattered light beam is then blocked by the dynamic scattered light absorber 10 during operation of the device 1 in accordance with the respective current signal of the eye tracking mechanism 14. The camera 13 of the eye tracking mechanism provides the necessary data basis by eye tracking in order to correctly set the position of the front (further away from the user) absorber edge 12 in order not to reduce the eye movement range window EF currently used by the user 5. The automatic execution of this step can be implemented in a suitable control unit 18, which receives the signals of the eye tracking mechanism 14 in operation and accordingly actuates the dynamic scattered light absorber 10.

[0053] The positive influence on the scattered light can be seen here. Figure 4 The accuracy of the position detection of the eye can reduce the upper scattered light area 8b, in the best case up to the useful light range 9, in which the virtual display image V (HUD image range) is shown.

[0054] Figure 5 Another embodiment of the dynamic scattered light absorber 10 of a waveguide-based projection display device 1 of the type described here is shown. The dynamic scattered light absorber 10 here is a matrix of elements 16, which can be switched into a light-transmissive (16a) or light-absorbing (16b) state, for example an LC matrix with polarizers. The matrix in this example covers the entire light output coupling surface 4 of the waveguide 2, which is shown in a top view. The projection display device 1 can furthermore be constructed, for example, similar to the projection display device of Figure 3 .

[0055] This embodiment of the dynamic scattered light absorber 10 can have the advantage that, by means of it, not only the scattered light in the scattered light area 8b above the HUD image can be eliminated, but also the scattered light in the entire scattered light area 8, around the useful light range 9 respectively for the virtual display image V, as is shown in the field of view of the user 5 in Figure 3 . Figure 6

[0056] The LC-based embodiment with polarizers on the upper side also has the further advantage of a fast switching time or good transmission. Instead of an LC matrix, an electrochromic matrix can also be used. The individual switchable matrix elements 16 can have, for example, a linear dimension of approximately more than 1 mm to approximately less than 40 mm in Figure 5 .

[0057] List of reference signs

[0058] 1, 100 waveguide-based projection display device

[0059] 2 windshield

[0060] 3 waveguide

[0061] ​4 light output coupling surface

[0062] 5 user

[0063] 6 eye movement range (two-dimensional)

[0064] 7 three-dimensional spatial range from which a virtual display image is visible

[0065] 8 region of scattered light in the field of view of the user

[0066] 9 range of useful light in the field of view of the user

[0067] L output-coupled light beam

[0068] V virtual display image

[0069] NL light beam volume of useful light which contributes to the generation of the display image for the user

[0070] GL total light beam volume of the output-coupled light beam which illuminates the entire eye movement range

[0071] SL upper edge light beam of the scattered light

[0072] H horizontal line

[0073] EF eye movement range window currently occupied by the eye of the user

[0074] 8a region of scattered light below the horizontal line

[0075] 8b region of scattered light above the horizontal line

[0076] 10 dynamic scattered light absorber

[0077] 11 edge of the light output coupling surface close to the user

[0078] 12 front edge of the dynamic scattered light absorber in the longitudinal direction of the vehicle

[0079] 13 camera

[0080] 14 eye tracking mechanism

[0081] 15 rear edge of the projection display device close to the user

[0082] 16 matrix element

[0083] 16a light transmission

[0084] 16b light absorption

[0085] 17 motor vehicle

[0086] 18 control unit

Claims

1. Waveguide-based projection display device (1), comprising: - an imaging unit and a planar waveguide (3) comprising a light outcoupling facet (4) constituted in a facet side of the waveguide for light beams generated by the imaging unit, which light beams can be in-coupled into the waveguide (3) at the facet side; - an at least partially transparent reflective glass arranged in a field of view of a user (5) and constituted for reflecting light beams (L) outcoupled from the waveguide (3) to an eye movement range (6) predetermined for an eye of the user, so that a virtual display image (V) is generated behind the reflective glass in the field of view of the user (5); - an eye tracking mechanism (14) constituted for ascertaining an eye movement range window (EF) of a predetermined size within the eye movement range (6) currently occupied by the eye of the user (5); and - a dynamic stray light absorber (10) constituted for darkening the light outcoupling facet (4) in a face section dynamically adjustable in accordance with a signal of the eye tracking mechanism (14), which face section extends from at least one of the edges of the light outcoupling facet (4), respectively, so as to at least partially limit the outcoupled light beams (L) in their cross sections to the ascertained eye movement range window (EF).

2. The projection display device (1) according to claim 1, wherein The projection display device (1) is for use in a vehicle.

3. The projection display device (1) according to claim 1, wherein The planar waveguide (3) is a planar waveguide.

4. The projection display device (1) according to claim 1, wherein The light beams can be in-coupled into the waveguide (3) via an end side.

5. The projection display device (1) according to claim 1, wherein The reflective glass is a windshield (2) of the vehicle.

6. The projection display device (1) according to claim 1, wherein The face section darkened by the dynamic stray light absorber (10) extends at least from an edge (11) of the light outcoupling facet (4) proximate to the user inwardly along the light outcoupling facet, thereby darkening an upper eye movement range edge section above the eye movement range window (EF).

7. The projection display device (1) according to one of claims 1 to 6, wherein The dynamic stray light absorber comprises at least one curtain which can be pulled inwardly from at least one of its edges over and along the light outcoupling facet in order to thereby darkening a respective cross section of the outcoupled light beams.

8. The projection display device (1) according to one of claims 1 to 6, wherein The dynamic stray light absorber (10) is constituted as a matrix of elements (16) arranged along the light outcoupling facet (4) at least in its edge region, which elements can be switched between a transmissive state and an absorbing state, respectively, for light outcoupled from the waveguide (3).

9. The projection display device (1) according to claim 8, wherein The dynamic stray light absorber (10) is constituted - as a liquid crystal matrix comprising a polarizer on its upper side facing the reflective glass; or - as an electrochromic matrix.

10. The projection display device (1) according to claim 8, wherein The individually switchable elements (16) of the matrix have a linear dimension of between 1 mm and 40 mm.

11. The projection display device (1) according to one of claims 1 to 6, wherein The eye tracking mechanism (14) comprises at least one camera (13) constituted for optically detecting the eye movement range (6).

12. Method for operating a projection display device (1) according to one of claims 1 to 11, comprising the following steps: - generating light beams by an imaging unit and in-coupling the light beams into a waveguide (3); - obtaining eye tracking signals by an eye tracking device (14) and deriving therefrom an eye field (EF) currently occupied by the eye of the user (5) within the eye movement field (6); and - adjusting the dynamic scatter light absorber (10) in dependence on the eye tracking signals or the derived eye field (EF) such that the light beam (L) outcoupled from the waveguide (3) is at least partially limited in its cross section to the derived eye field (EF).

13. Control unit (18) for operating a projection display device (1) according to one of claims 1 to 11, which control unit is constituted and arranged for automatically carrying out the method according to claim 12.

14. Vehicle, comprising: - a windshield (4) and a dashboard arranged thereunder; - a projection display device (1) according to one of claims 1 to 11, the reflecting glass of which projection display device is formed by the windshield (2) or a combination glass arranged in front of the windshield on the inside of the vehicle, and the waveguide (3) of which projection display device extends in or along the upper side of the dashboard with the side of the waveguide on which the light outcoupling surface (4) is constituted; and - a control unit (18) according to claim 13.

15. The vehicle of claim 14, wherein, The vehicle is a motor vehicle (17).

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