Vehicle head-up display (HUD)

Abstract

This provides a head-up display that does not require a large projection optical system. [Solution] A vehicle head-up display (HUD) for displaying images to a user of a vehicle having a windshield 15 includes an image projector 14 that outputs a collimated image and an optical aperture expander. The optical aperture expander includes a light guide optical element (LOE) 10 having two main external surfaces 30a, 30b. The image projector 14 feeds a collimated image so that it propagates through the LOE by internal reflection at the main external surfaces. The LOE also has a set of parallel partially reflective inner surfaces 12 that gradually combine and output image illumination from the LOE. The optical aperture expander is positioned to follow a light path that includes reflection from surfaces associated with the vehicle's windshield 15 so that the image illumination combined and output from the partially reflective inner surfaces 12 is visible to the user while the user is looking at the scenery beyond the windshield.

Description

Technical Field

[0001] Field and Background of the Invention The present invention relates to a display, and more particularly to a head-up display for vehicles such as automobiles.

[0002] Many proposals and designs have been made for installing a HUD in front of a vehicle driver to assist in providing various visual functions, including but not limited to driving navigation, obtaining dashboard information without diverting the line of sight from the road, or projecting a thermal image onto the driver's eyes under poor visibility conditions.

[0003] Current solutions based on projecting an image onto the windshield have relatively limited eye motion boxes (EMBs) and fields of view (FOVs), or require relatively large projection optics to support wider EMBs and FOVs.

Summary of the Invention

[0004] The present invention is a vehicle head-up display (HUD) for displaying an image to a user of a vehicle.

[0005] As a preliminary, a light guide optical element (LOE) is a waveguide used for aperture expansion. The operating principle of the LOE and is presented in U.S. Patent No. 6,829,095 B2 entitled "Substrate-guided optical beam expander". LOE-based HUDs enable the realization of very compact and self-contained HUDs that can be easily installed in a narrow space. These allow the use of very small collimating optics without compromising on the field of view (FOV) or the eye motion box (EMB corresponding to the area where an image can be seen). Thus, the LOE-based aperture expansion arrangement simplifies the construction and manufacture of the optics associated with the HUD, and is thus suitable for a compact, inexpensive, consumer version of the HUD suitable for the automotive industry.

[0006] According to the teachings of embodiments of the present invention, a vehicle head-up display (HUD) for displaying an image to a user of a vehicle having a windshield, the HUD comprising: (a) an image projector comprising an image generator and a collimating optical system, the image projector outputting image illumination corresponding to a collimated image; and (b) an optical aperture expander comprising at least a first light guide optical element (LOE), the LOE having a pair of mutually parallel main outer surfaces, the image projector expanding the optical aperture so that the image illumination propagates within the LOE by internal reflection at the main outer surfaces. The present invention provides a vehicle head-up display (HUD) comprising an optical aperture expander, optically coupled to a tensioner, the LOE further includes at least one set of mutually parallel partial reflective surfaces located inside the LOE and inclined with respect to a main external surface, the set of partial reflective surfaces gradually coupled and output image illumination from the LOE, the optical aperture expander being positioned to follow a light path including reflections from surfaces associated with the vehicle's windshield, such that the image illumination coupled and output from the LOE is visible to the user while the user is looking at a scene beyond the windshield.

[0007] According to further features of embodiments of the present invention, the optical aperture expander further includes a second set of mutually parallel partial reflective surfaces arranged non-parallel to a first set of partial reflective surfaces, the second set of partial reflective surfaces being arranged to gradually redirect image illumination from the image projector toward the first set of partial reflective surfaces.

[0008] According to further features of embodiments of the present invention, the second set of partial reflective surfaces are located within the line of edge (LOE) between a pair of main external surfaces.

[0009] According to further features of embodiments of the present invention, the second set of partial reflective surfaces are located within a second LOE bounded by a second pair of principal outer surfaces.

[0010] According to further features of embodiments of the present invention, the second LOE is positioned adjacent to one of the main external surfaces of the first LOE, away from the vehicle's windshield.

[0011] According to further features of embodiments of the present invention, a set of partial reflective surfaces is positioned to combine and output image illumination from one of a pair of main external surfaces facing away from the windshield, and the HUD further comprises a reflective optical element having refractive power, which is configured to at least partially compensate for optical aberrations introduced into the image by reflection from surfaces associated with the windshield.

[0012] According to further features of embodiments of the present invention, the reflective optical element is further configured to define the apparent distance of the image seen by the user after reflection from a surface associated with the windshield.

[0013] According to further features of embodiments of the present invention, light reflected from the reflective optical element is transmitted through the LOE before reflection from the surface associated with the windshield.

[0014] According to further features of embodiments of the present invention, the combined image illumination output from the LOE follows an optical path that includes a first reflection at a high angle of incidence from a surface associated with the vehicle's windshield, an intermediate reflection from an additional reflective surface, and a second reflection from a surface associated with the windshield, so that it is visible to the user while the user is looking at a scene beyond the windshield.

[0015] According to further features of embodiments of the present invention, the surface associated with the windshield is an angle-selective reflector configured to have a first reflectance for light incident perpendicular to the surface and a second reflectance less than the first reflectance for light at an incident angle greater than 45 degrees.

[0016] According to further features of embodiments of the present invention, the additional reflective surface is a polarizing beam splitter, and a quarter-wave plate is interposed in the optical path between the surface associated with the windshield and the additional reflective surface.

[0017] According to further features of embodiments of the present invention, the surface and quarter-wave plate associated with the windshield are both incorporated into the windshield.

[0018] A further feature of the embodiments of the present invention also provides a second quarter-wave plate, which is integrated with the windshield and located on the side of the surface furthest from the user.

[0019] According to further features of embodiments of the present invention, the polarizing beam splitter is shaped to provide refractive power to at least partially compensate for optical aberrations introduced into the image by reflections from a surface associated with the windshield.

[0020] According to the teaching of embodiments of the present invention, there is also a system comprising a first HUD and a second HUD, wherein each of the first and second HUDs is implemented as described above, and each of the first and second HUDs provides a different field of view that is visible to the user and / or makes the field of view visible from different areas of the eye motion box.

[0021] According to further features of the embodiments of the present invention, the first HUD and the second HUD are arranged in an adjacent relationship.

[0022] According to further features of embodiments of the present invention, the first HUD and the second HUD are arranged in a partially overlapping relationship.

[0023] According to the teachings of embodiments of the present invention, the present invention also provides a vehicle door with a window-integrated display, the vehicle door comprising: (a) a door panel; (b) a window supported by the door panel, the window comprising a visible portion that provides a view of the scenery beyond the window and a concealed portion extending inward from the door panel, the window comprising a light guide optical element (LOE), the LOE having a pair of mutually parallel main external surfaces and at least a first set of mutually parallel partial reflective surfaces located inside the LOE and inclined with respect to the main external surfaces; and (c) an image projector comprising an image generator and a collimating optical system, the image projector being located inside the door panel and optically coupled to a region of the LOE within the concealed portion of the window to introduce image illumination corresponding to a collimated image into the LOE, the image illumination propagating through the LOE by internal reflection at the main external surfaces and gradually coupled out from the LOE from the visible portion of the window by the set of partial reflective surfaces.

[0024] According to further features of embodiments of the present invention, the optical coupling of the image projector to the LOE is via an air gap, and the vehicle door further includes a mechanism for raising and lowering the window, and the image projector is arranged to match to coupled input image illumination into the LOE via the air gap when the window is in the raised position.

[0025] According to further features of embodiments of the present invention, the LOE is sealed within a window material, and at least one layer of the sealing adjacent to the LOE is formed from a material having a lower refractive index than the material of the LOE in order to assist internal reflection at the main outer surface of the LOE. [Brief explanation of the drawing]

[0026] The invention is described herein only as an embodiment with reference to the accompanying drawings.

[0027] [Figure 1A]It is a schematic side view of a vehicle head-up display (HUD) for displaying an image to a user of a vehicle. [Figure 1B] It is a schematic front view of the HUD of FIG. 1A. [Figure 2] It is a schematic side view of a modified implementation example of the HUD of FIG. 1A. [Figure 3A] It is a schematic side view of a further modified implementation example of the HUD of FIG. 1A. [Figure 3B] It is an enlarged view of the area marked III in FIG. 3A. [Figure 4] It is a schematic front view of a system employing a plurality of HUD units according to FIG. 1A. [Figure 5A] It is a schematic side view of a system employing a plurality of HUD units similar to those in FIG. 1A stacked to provide an extended field of view. [Figure 5B] It is a schematic side view of a system employing a plurality of HUD units similar to those in FIG. 1A stacked to provide an extended eye motion box. [Figure 5C] It is a schematic front view of the systems of FIGS. 5A and 5B. [Figure 6A] They are schematic side and front views of a HUD according to a further aspect of the present invention, each suitable for an implementation example in a vertical window, particularly associated with a door panel. [Figure 6B] They are schematic side and front views of a HUD according to a further aspect of the present invention, each suitable for an implementation example in a vertical window, particularly associated with a door panel.

Mode for Carrying Out the Invention

[0028] The present invention is a vehicle head-up display (HUD) for displaying an image to a user of a vehicle.

[0029] The principle and operation of the head-up display according to the present invention can be better understood by referring to the drawings and the accompanying description.

[0030] Referring here to the drawings, Figures 1A to 5C illustrate various non-limiting embodiments of a first aspect of the present invention. This aspect of the present invention provides a vehicle HUD for displaying images to a user of a vehicle (not all shown) having a windshield 15. The user is represented in the drawings by images of the user's eyes 50 located in an area called the “eye motion box” (EMB) corresponding to a range of positions in which the display is designed. The “user” is typically the driver or operator of the vehicle, but may in some cases be a passenger in the vehicle other than the driver.

[0031] Generally speaking, a HUD according to this embodiment of the present invention includes an image projector or "POD" 14, which includes an image generator and a collimating optical system for outputting image illumination corresponding to a collimated image. To facilitate the use of image projectors having relatively small output optical apertures, the HUD further includes an optical aperture expander, which includes at least a first light guide optical element (LOE) 10. The LOE 10 has a pair of mutually parallel main external surfaces 30a, 30b. The image projector 14 is optically coupled to the optical aperture expander so that image illumination propagates within the LOE 10 by internal reflection at the main external surfaces 30a, 30b. The LOE 10 also includes at least one set of mutually parallel partial reflective surfaces (or "facets") 12 located inside the LOE and inclined toward the main external surfaces 30a, 30b. The set of partial reflective surfaces 12 gradually couples the image illumination away from the LOE 10.

[0032] According to this aspect of the present invention, the deployment of the optical aperture expander causes the image illumination coupled from the LOE to follow a light path that includes reflections from surfaces associated with the vehicle's windshield 15, so that it is visible to the user 50 while the user is looking at the scene beyond the windshield.

[0033] It will soon become clear that the present invention provides a highly advantageous HUD configuration. Specifically, by using one or more LOEs to expand the optical aperture of the POD, the use of a compact and lightweight POD is enabled, while the LOE expands the optical aperture to the required dimensions according to the required field of view and EMB dimensions. The LOE (not shown in the accurate scale) can be implemented as a thin, flat plate with small volume and weight. By using the windshield as a combiner, the user's real-world view is hardly obstructed.

[0034] In certain embodiments, the optical aperture expander also includes a second set of mutually parallel partial reflective surfaces 22, positioned non-parallel to the first set of partial reflective surfaces 12, so as to gradually redirect image illumination from the image projector 14 toward the first set of partial reflective surfaces 12. The partial reflective surfaces 22 thereby achieve optical aperture expansion of a first dimension, while the partial reflective surfaces 12 achieve optical aperture expansion of a second dimension. In the embodiments shown in Figures 1A and 1B, the second set of partial reflective surfaces 22 are located within a second LOE bounded by a second pair of main external surfaces 32a, 32b. In a preferred but non-limiting implementation example illustrated herein, the second LOE 20 is positioned adjacent to the main external surface 30b of the first LOE 10, i.e., on the side away from the vehicle's windshield 15. In this way, the two LOEs are effectively stacked one on top of the other, in a particularly compact configuration. The overall internal reflection conditions within each LOE can be maintained by either ensuring a small air gap between them, or, more simply, by interposing an "insulating layer" of a material having a relatively lower refractive index than the material of the LOE itself. The insulating layer material may be a low refractive index optical adhesive, or any other transparent low refractive index material having suitable mechanical properties. (This is true throughout the various embodiments discussed below, when two LOEs are shown with their surfaces adjacent to each other.)

[0035] The POD employed in the device of the present invention is preferably configured to produce a collimated image, that is, an image in which the light from each image pixel is a parallel beam collimated to infinity in the angular direction corresponding to the pixel position. Thus, the image illumination extends to an angular range corresponding to the two-dimensional field of view.

[0036] The image projector 14 includes at least one light source, typically deployed to illuminate a spatial light modulator, such as an LCOS chip. The spatial light modulator modulates the projection intensity of each pixel of the image, thereby generating an image. Alternatively, the image projector may include a scanning configuration, typically implemented using a high-speed scanning mirror, in which the intensity of the beam changes pixel by pixel in synchronization with the movement, while scanning illumination from a laser light source across the image plane of the projector, thereby projecting the desired intensity onto each pixel. In either case, a collimating optical system is provided to generate an output projected image that is collimated to infinity. Optionally, some or all of the above components may be arranged on the surface of one or more polarizing beam splitter (PBS) cubes or other prism configurations, as is well known in the art.

[0037] The optical coupling of the image projector 14 to the LOE at the beginning of the optical path (here, LOE 20) can be achieved by any suitable optical coupling, such as via a coupling prism with an inclined angle input surface, or via a reflective coupling configuration, via one of the side edges and / or main outer surfaces of the LOE. Details of the coupling input configuration are generally not important to the present invention and are selected according to preferred shape factors for a particular implementation example. In this exemplary embodiment, as best seen in Figure 1B, the coupled input of image illumination from the image projector 14 into the LOE 20 is achieved by an internal reflector 23 that deflects the image illumination so that it propagates along the LOE 20 by internal reflection from surfaces 32a, 32b until it reaches a partial reflective surface 22 that gradually coupled the image illumination toward the LOE 10. This achieves a first dimension of aperture enlargement with respect to the optical aperture of the image projector. Next, as best seen in Figure 1A, the coupled input of light from LOE20 into LOE10 is achieved by an internal reflector 13 that deflects the image illumination so that it propagates along LOE10 by internal reflections from surfaces 30a, 30b until it reaches a partial reflecting surface 12 that gradually coupled the image illumination toward the windshield 15, reflecting it toward the eyes of the user 50 located inside the eye motion box. This form of coupled input facilitates the compact stacked configuration of the HUD described above. Other options for the coupled input are also applicable, typically employing a coupling in prism. Such options are discussed in detail in the co-delegated PCT Patent Application Publication No. 2015 / 162611A1 and will not be described in detail here for the sake of brevity.

[0038] Numerous additional embodiments are presented below to illustrate additional aspects of the present invention. For the sake of simplicity of presentation, these embodiments are illustrated using a single LOE 10. However, it should be understood that each embodiment can also be implemented with two LOE configurations, similar to those in Figures 1A and 1B, as will be apparent to those skilled in the art.

[0039] In certain implementations, it is advantageous that the light reflected from the windshield is P-polarized (in the YZ plane), and the light induced in the LOE is typically S-polarized. To switch the polarization, an HWP (half-wave plate) 17 is advantageously introduced as shown. In addition, when two orthogonal LOEs are employed for two orthogonal extensions of the optical aperture, as illustrated here, an HWP 27 is advantageously introduced between the LOEs to rotate the polarization and convert the S-polarized light leaving LOE 20 to S-polarized light according to the orientation of the surface of LOE 10.

[0040] Although this specification exemplifies the use of a partial reflective surface 22 in a separate LOE from the partial reflective surface 12, alternative implementations may employ two non-parallel sets of partial reflective surfaces implemented within a single LOE, i.e., between the main external surfaces 30a and 30b. In this case, one set of partial reflective surfaces 22 is arranged to gradually deflect the image illumination within the LOE so that it propagates toward the partial reflective surface 12 by internal reflection. Such an LOE structure is discussed in detail in the co-delegated PCT Patent Application Publication No. 2020 / 049542A1.

[0041] In each embodiment described herein, the internal reflection of image illumination propagating along the LOE may be, for example, total internal reflection (TIR) ​​or Fresnel reflection. In addition, unlike transparent near-eye displays, the optical aperture expanders presented herein do not require the use of a transparent LOE. Therefore, the back (bottom) surface of the waveguide (30b) may be opaque, allowing the use of a specular reflective coating. This provides further design flexibility to the HUD, as the specular coating surface does not need to conform to TIR conditions, and therefore the waveguide can be mounted on or inside the vehicle dashboard without an air barrier between the waveguide and the dashboard.

[0042] In some embodiments, a relatively large distance between the observer's eye and the LOE increases the viewer's sensitivity to local non-uniformity of display brightness. In some cases, such effects are mitigated by providing a partial reflective coating on the upper surface 30a of the LOE 10 and a mirror coating on the lower surface 30b, which has the effect of mixing different parts of the aperture and improving the uniformity of the output.

[0043] Referring particularly to Figure 2, a specific feature of the HUD of the present invention is that the image illumination output by the projector 14 and propagated through the optical aperture expander is a collimated image. When this light is delivered to the user's eye without optical change, it provides the effect of an image located at infinity. In some cases, it is desirable to introduce additional optical elements (or a number of optical elements), such as (refractory or diffractory) lenses, into the optical path between the waveguide and the windshield to introduce additional refractive power in order to provide one or more of the following functions. 1. Shift of the focal plane observed by the occupant from infinity to an intermediate focal plane. Thus, some dashboard elements may appear closer than others, or all elements may appear at a preferred apparent distance. 2. Compensation for astigmatism, blurring, barrel distortion, pincushion distortion, or any other image distortion caused by the non-planarity of the windshield. (Certain types of distortion may be compensated for by digital image compositing adjustments to compensate for windshield or other induced image distortions.) 3. Lateral (X and / or Y) shift of the eyebox and / or field of view positioning. (Such shifts may also be made possible by mechanical shifting and / or reversing of the optical engine.)

[0044] One such implementation example is schematically shown in Figure 2, by introducing an optical element 199 (indicated by a dashed line) between the LOE 10 and the windshield 15. However, adding such an element can affect the compactness of the implementation. A particularly advantageous alternative implementation example is illustrated in Figure 2 (disregarding the dashed element 199), where, according to Figure 2, light is coupled and output downward from the LOE 10 and then reflected upward toward the windshield from the reflective optical element 19. The optical element 19 provides a similar function to that of element 199 described above. In some cases, element 19 may be integrated with a polarization rotation element, specifically a quarter-wave plate (QWP) 18, and the coating providing the reflective properties of the surface 12 may be implemented as a polarization-dependent coating. Thus, when S-polarized light is coupled and output by facet 12, the double pass of illumination through the QWP 18 before and after reflection at surface 19 converts the S-polarized light to P-polarized light, which then passes through facet 12 with minimal interruption. As shown in Figure 2, the orientation of facet 12 within LOE 10 is inverted here, so that the set of partial reflective surfaces 12 combines and outputs image illumination from the main external surface 30b (facing away from the windshield), where the image illumination is reflected by a reflective optical element 19 that modifies the image illumination according to its own refractive power. Element 19 can at least partially compensate for optical aberrations introduced into the image by reflection from surfaces associated with the windshield. Additionally or alternatively, element 19 may be configured to define the apparent distance of the image seen by the user after reflection from surfaces associated with the windshield.

[0045] In the preferred implementation shown here, light reflected from the reflective optical element 19 is transmitted through the LOE before reflection from the surface associated with the windshield. In alternative implementations, the LOE can be avoided in the return light path from element 19 to the windshield 15 by changing the orientation of the LOE and element 19.

[0046] Referring here to Figures 3A and 3B, in certain implementation examples, it may be useful to employ an optical path that includes two reflections from a surface associated with the windshield. In the embodiment shown here, the combined output image illumination from LOE 10 follows an optical path that includes a first reflection at a first incidence angle from a reflector surface associated with the vehicle's windshield, an intermediate reflection from an additional reflective surface 18, and a second reflection from a surface associated with the windshield, so that it is visible to the user's eye 50 while the user is viewing the scene beyond the windshield. Such a double-reflection architecture may be particularly advantageous in terms of discreet placement of the HUD system near the lower edge of the windshield. Although the features are not shown in combination, such an option is advantageously combined with the two-dimensional optical aperture expansion in Figures 1A and 1B, and / or the use of a reflective optical element 19 as in Figure 2.

[0047] Such an approach can be enhanced by employing an angle-selective reflector surface 21 associated with the windshield, having a first reflectance for light incident perpendicular to the surface and a second reflectance less than the first reflectance for light at incident angles greater than 45 degrees. This ensures that the first reflection is a relatively high proportion of reflection, thereby making it easier to ensure that sufficient display intensity remains after the second windshield reflection to easily provide a visible display. Such angle-selective reflectivity can be implemented using multilayer dielectric coatings, as is known in the art.

[0048] In particular optimized implementations of such an approach, various components are used to manage polarization and / or ensure sufficient image brightness. In one non-limiting specific embodiment, an additional reflective surface 18 is advantageously implemented as a polarization beam splitter, and a quarter-wave plate 17 is interposed in the optical path between the reflective surface associated with the windshield 15 and the additional reflective surface 18. A second quarter-wave plate 16 is advantageously included in the windshield and located on the user-away (outside) side of the surface. Most preferably, the first QWP 16 and the second QWP 17, as well as the partial reflector surface 21, are all incorporated into the windshield 15, for example, as shown in the enlarged partial view of Figure 3B.

[0049] Next, the operation of this configuration is as follows. Surface 18 preferably combines an HWP (half-wave plate) and a polarizing beam splitter (polarization-dependent mirror) that reflects only S-polarized light. The HWP converts the S-polarized light coupled from the LOE into P-polarized light, which then passes through the reflector 18. Inside the windshield, light reflected from the partial reflective layer 21 passes through the QWP 17 twice, which acts as a half-wave plate, converting the P-polarized light back into S-polarized light, which is then reflected by surface 18. The light reflected from surface 18, as S-polarized light, is incident on the windshield at a larger angle of incidence (i.e., a shallower angle), and the S-polarized light is converted back into P-polarized light by passing through the QWP 17 twice, before and after reflection at the partial reflector 21, before being delivered to the observer's eye 50.

[0050] In addition, the presence of QWP16 ensures that the light passing through the partial reflector 21 in the second reflection is also converted to P-polarization, incident on the outer surface of the windshield at an angle close to the Brewster angle, and does not reflect significantly, thereby avoiding the formation of ghost images. In such a highly efficient system, the dependence of the reflectivity of the surface 21 as a function of angle is significant, with high reflectivity at low angles of incidence (AOI) for the first reflection and low reflectivity at higher AOIs for the second reflection.

[0051] Optionally, the polarizing beam splitter on surface 18 is shaped in a manner similar to that of element 19 described above to provide refractive power to at least partially compensate for optical aberrations introduced into the image by reflections from surfaces associated with the windshield, and / or to provide a desired apparent range for the display.

[0052] Referring here to Figures 4 and 5A-5C, in certain cases it may be advantageous to integrate two or more HUDs into a combined system, each HUD providing the user with a different visible field of view and / or making the field of view visible from different areas of the eye motion box. These multiple HUDs may be arranged in an adjacent relationship, for example, aligned along the X direction as shown in Figure 4. Alternatively, in certain cases, the multiple HUDs may be arranged in a relationship that at least partially overlaps, as shown with reference to Figures 5A-5C.

[0053] Therefore, in some cases, two or more optical engines, each including an LOE and a POD, are mounted under the vehicle's windshield to reflect multiple images, each having its own eye-motion box and driver or passenger's field of view. The height, scale, and perceived focal plane of each of these images can be controlled independently, as detailed below. Figure 4 schematically shows multiple optical engines (OEs) projecting independent portions of an image without image stitching. “Image stitching” means that the projected and / or combined output images include image data in which portions overlap each other.

[0054] In some embodiments (even with a single HUD), the HUD system may include a controller configured to control one or more elements of the HUD. For example, the controller may be used to control the additional optical elements described above, which are implemented as electrically controllable optical elements, in order to achieve one of the above-mentioned objectives. The controller may control various HUD system elements independently of each other or in conjunction and cooperation with each other. For example, the controller may be used to adjust the depth of focus of an image separately and independently of each other. Preferably, the controller also includes all necessary electronic components, such as at least one processor or processing circuit, for driving an image projector, as is well known in the art.

[0055] Further options suggest that such adjustments / compensations may be performed independently for each of the multiple optical engines along any of the three axes. In the optimal embodiment, such adjustments may be performed using electronically tunable lenses, PZT actuators, or any other type of electrically variable optical element.

[0056] A particular preferred implementation of the present invention may offer one or more of the following advantages: 1. Expandable and adjustable eye motion box and field of view. 2. A focal plane that can be adjusted statically or dynamically for different image elements. 3. Compact shape factor for integration with the vehicle's dashboard. 4. Compact optical components enable cost-effectiveness and high optical performance.

[0057] Figures 5A to 5C illustrate further implementation examples in which two optical aperture expanders are arranged alternately in a relationship of at least partial overlap. The first HUD configuration includes an image projector 14, LOE 20, and LOE 10 in the same manner as the corresponding elements in Figures 1A and 1B. The second HUD configuration employs similar components, labeled 14', 20', and 10', respectively. These elements can be neatly nested with a suitable optical insulating layer between adjacent LOEs to maintain TIR conditions, as shown in the drawings. Various polarization schemes can be used to minimize interaction between the two HUDs in their overlapping regions. In one non-limiting embodiment, LOE 10' may operate on a partially reflective surface, implemented using a structural polarizer beam splitter (e.g., a wire grid beam splitter) that partially reflects P-polarized light, which is then transmitted by the partially reflective surface of LOE 10. In all other aspects, the structure and operation of LOE10' will be understood by applying them mutatis mutandis to LOE10.

[0058] Figure 5A illustrates a case where two HUD subsystems project different regions of the vertical field of view (FOV). Depending on the image content, these images may be sub-regions of a continuous image, “stitched” together to provide a single, continuous, enlarged field of view that is larger than what would be provided by a single HUD system of given dimensions. Figure 5B illustrates an alternative use where the same FOV is provided by both systems but complements each other to provide the required FOV over a larger eye-motion box region, represented by the vertical arrow EMB in Figure 5B.

[0059] In various embodiments disclosed herein, the desired parallelism of the optical surfaces and other optical properties of the HUD components may be affected by extreme temperature gradients. To avoid extreme temperature gradients, it may be preferable in some cases to implement thermal control of at least some of the HUD system. This can be implemented by mounting the various HUD components (POD and / or LOE) to a heating plate that tends to maintain a uniform temperature across the components. Most preferably, a thermoelectric temperature control component is associated with the heating plate to maintain the optical components within a target temperature range.

[0060] In certain implementation examples, it may be preferable to provide a UV-blocking layer incorporated into the windshield 15 to protect the optical components of the HUD from UV degradation. Additionally or alternatively, a UV-blocking layer may be provided on the uppermost surface of the HUD optical system, such as the HWP 17, PBS 18, or upper LOE surface 30a.

[0061] In certain cases, additional precautions may be necessary to prevent external radiation, and in particular direct sunlight, from reflecting off the surface of HUD optical components such as the LOE at angles that could cause “ghost” reflections that could reach the user’s eyes. Such precautions may include using a polarization strip across the lower edge of the windshield to allow only polarization that has not been transmitted to the user’s eyes (by one of the polarization schemes described above). This can be further enhanced by providing an anti-reflective coating on any exposed surface of the LOE to minimize surface reflection of sunlight glare. Additionally or alternatively, it may be possible to block certain directions of potential incident glare by carefully positioned mechanical baffles that protect the optical elements from incident sunlight glare at the relevant angles that carry a risk of ghost reflection.

[0062] In some embodiments, the HUD system may include an eye-tracking sensor configured to detect the position of the driver's pupil. A controller coupled to the eye-tracking sensor can be used to control optical elements positioned between the waveguide and the windshield based on the position of the eyeball or the direction of the field of view. For example, if the driver is looking into the distance, the optical elements may be adjusted to increase the depth of focus of one or more images. Similarly, if the driver's eyes are focused on a relatively close point, the optical elements may be adjusted to decrease the depth of focus of one or more images. Likewise, the controller may adjust the lateral position of one or more images based on the driver's direction of view, as detected by the eye-tracking sensor.

[0063] Further aspects of the present invention are schematically shown in Figures 6A and 6B. In this case, the waveguide (LOE) is introduced inside or adjacent to the side window of the car and is typically arranged substantially vertically. One preferred technique for this configuration is a composite LOE structure (such as described, for example, in "LOE with Two-Axis Internal Aperture Expansion"). Thus, the image can be expanded vertically and horizontally, providing a two-dimensional expansion of the image that further reduces the size and complexity of the imaging pod.

[0064] As shown in Figure 6A, the observer's eye 50 representing the EMB is positioned in front of the window 15a into which the LOE 10 is adjacent or integrated. The LOE ("waveguide") includes a set of mutually parallel partial reflective inner surfaces 12 that expand the optical aperture ("pupil") in one dimension, in this case along the Y direction, and another set of mutually parallel partial reflective inner surfaces 11 that expand the optical aperture in a perpendicular direction, here along the Z direction. In the non-limiting embodiment illustrated herein, light is introduced into the LOE from the POD 14 via a coupled prism 13. The structure can be implemented within the side window 15 in different sealing methods by optionally using an air gap, or a low refractive index adhesive, or another low refractive index insulating layer, to facilitate propagation by internal reflection. Therefore, the LOE is preferably sealed within the window material, and at least one layer of sealing adjacent to the LOE is formed from a material having a lower refractive index than the material of the LOE in order to assist internal reflection at the main outer surface of the LOE. Alternatively, angle-selective reflective coatings can be used to mimic TIR characteristics. In Figure 6B, the waveguide and POD are shown from a different viewpoint along the X direction.

[0065] According to one aspect of the present invention, the HUD window configuration is incorporated into the window of a vehicle door 155. In this case, the system according to the teachings of the present invention includes a door panel 155 and a window 15a supported by the door panel. The window 15a includes a visible portion 34a that provides a view of the scenery beyond the window and a concealed portion 34b that extends inward from the door panel 155. The LOE 10 integrated with the window 15a has a pair of mutually parallel main external surfaces 30a, 30b and at least a first set of mutually parallel partial reflective surfaces 12 that are inside the LOE and inclined with respect to the main external surfaces. The image projector 14, including the image generator and collimating optics, is located within the door panel 155 and is optically coupled to a region of the LOE 10 within the hidden portion 34b of the window to introduce image illumination corresponding to the collimated image into the LOE, the image illumination propagating within the LOE by internal reflection at the main external surface and gradually coupled out from the LOE from the visible portion of the window by a set of partial reflective surfaces. In certain particularly preferred cases, two-dimensional magnification is achieved by incorporating an additional set of mutually parallel internal partial reflective surfaces 11, similar to the configuration described in PCT Patent Application Publication No. 2020 / 049542A1. It is particularly advantageous that the image projector 14, and, if present, the facet 11, are located within the door panel 155, providing physical protection to the image projector and associated components, and preventing the facet 11 from generating problematic “ghost” reflections of ambient light from the sky and other light sources or bright objects.

[0066] Vehicle door windows typically include a mechanism for raising and lowering the window relative to the door panel, as indicated by arrow 40 in Figures 6A and 6B, which can add complexity to the implementation of the HUD. In certain cases, it may be preferable that the image projector does not move with the window. In this case, optical coupling of the image projector 14 to the LOE 10 can be advantageously achieved via an air gap 36. The implementation example described here employs an air gap along with a coupling in prism 13 integrated with the LOE. The image projector 14 is then positioned to match the air gap 36 and prism 13 to coupled input image illumination into the LOE 100, even when the window is in the raised position, without hindering the window's descent.

[0067] It will be understood that various HUDs of the present invention can be advantageously used to display a wide range of information relating to the operation of a vehicle. For example, in certain particularly preferred embodiments, the HUD system displays dashboard elements including two or more selected from the group consisting of a speedometer, turn signals, fuel gauge, and thermometer. Additionally or alternatively, the system may include a controller configured to receive data from multiple sensors and to generate multiple images corresponding to the data received from the multiple sensors for projection by the HUD for the user to view.

[0068] It will be understood that the above description is intended to serve only as an example, and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. A vehicle head-up display (HUD) for displaying images to the user of a vehicle having a windshield, (a) An image projector comprising an image generator and a collimating optical system, the image projector outputting image illumination corresponding to a collimated image, (b) An optical aperture expander comprising at least a first light guide optical element (LOE), wherein the LOE has a pair of mutually parallel main outer surfaces, and the image projector is optically coupled to the optical aperture expander such that the image illumination propagates within the LOE by internal reflection at the main outer surfaces, and the LOE further comprises at least one set of mutually parallel partial reflective surfaces located inside the LOE and inclined with respect to the main outer surfaces, the set of partial reflective surfaces gradually coupled and output the image illumination from the LOE, A vehicle head-up display (HUD) in which the optical aperture expander is positioned to follow a light path including reflections from surfaces associated with the windshield of the vehicle, such that the image illumination coupled and output from the LOE is visible to the user while the user is looking at a scene beyond the windshield.

2. The HUD according to claim 1, wherein the optical aperture expander further includes a second set of mutually parallel partial reflective surfaces arranged non-parallel to a first set of partial reflective surfaces, the second set of partial reflective surfaces being arranged to gradually redirect image illumination from the image projector toward the first set of partial reflective surfaces.

3. The HUD according to claim 2, wherein the second set of partial reflective surfaces is located within the LOE between the pair of main external surfaces.

4. The HUD according to claim 2, wherein the second set of partial reflective surfaces is located within a second LOE bounded by a second pair of main outer surfaces.

5. The HUD according to claim 4, wherein the second LOE is positioned adjacent to one of the main outer surfaces of the first LOE, which is separated from the windshield of the vehicle.

6. The HUD according to claim 1, wherein the set of partial reflective surfaces is arranged to combine and output the image illumination from one of the pair of main external surfaces facing away from the windshield, and the HUD further comprises a reflecting optical element having refractive power, the reflecting optical element being configured to at least partially compensate for optical aberrations introduced into the image by reflection from the surface associated with the windshield.

7. The HUD according to claim 6, wherein the reflective optical element is further configured to define the apparent distance of the image seen by the user after reflection from the surface associated with the windshield.

8. The HUD according to claim 6, wherein light reflected from the reflective optical element is transmitted through the LOE before reflection from the surface associated with the windshield.

9. The HUD according to claim 1, wherein the image illumination output from the LOE follows a light path including a first reflection at a high angle of incidence from a surface associated with the windshield of the vehicle, an intermediate reflection from an additional reflective surface, and a second reflection from the surface associated with the windshield, so that it is visible to the user while the user is looking at a scene beyond the windshield.

10. The HUD according to claim 9, wherein the surface associated with the windshield is an angle-selective reflector configured to have a first reflectance for light incident perpendicular to the surface and a second reflectance less than the first reflectance for light at an incident angle greater than 45 degrees.

11. The HUD according to claim 9, wherein the additional reflective surface is a polarizing beam splitter, and a quarter-wave plate is interposed in the optical path between the surface associated with the windshield and the additional reflective surface.

12. The HUD according to claim 11, wherein both the surface and the quarter-wave plate associated with the windshield are incorporated into the windshield.

13. The HUD according to claim 12, further comprising a second quarter-wave plate integrated with the windshield and located on the side of the surface furthest from the user.

14. The HUD according to claim 11, wherein the polarizing beam splitter is shaped to provide refractive power to at least partially compensate for optical aberrations introduced into the image by reflection from the surface associated with the windshield.

15. A system comprising a first HUD and a second HUD, wherein each of the first HUD and the second HUD is implemented in accordance with claim 1, and each of the first HUD and the second HUD provides different fields of view that are visible to the user and / or makes the field of view visible from different areas of the eye motion box.

16. The system according to claim 15, wherein the first HUD and the second HUD are arranged in an adjacent relationship.

17. The system according to claim 15, wherein the first HUD and the second HUD are arranged in a relationship that overlaps at least partially.

18. A vehicle door equipped with a window-integrated display, (a) Door panel and, (b) A window supported by the door panel, the window comprising a visible portion that provides a view of the scenery beyond the window and a concealed portion that extends inward from the door panel, wherein the window comprises a light guide optical element (LOE), the LOE having a pair of mutually parallel main external surfaces and at least a first set of mutually parallel partial reflective surfaces located inside the LOE and inclined with respect to the main external surfaces, (c) An image projector comprising an image generator and a collimating optical system, wherein the image projector is located within the door panel and is optically coupled to a region of the LOE within the concealed portion of the window in order to introduce image illumination corresponding to a collimated image into the LOE, the image illumination propagates through the LOE by internal reflection at the main outer surface, and is gradually coupled and output from the LOE from the visible portion of the window by the set of partial reflective surfaces.

19. The vehicle door according to claim 18, wherein the optical coupling of the image projector to the LOE is via an air gap, and the vehicle door further comprises a mechanism for raising and lowering the window, and the image projector is arranged to match input the image illumination into the LOE via the air gap when the window is in the raised position.

20. The vehicle door according to claim 18, wherein the LOE is sealed within a window material, and at least one layer of sealing adjacent to the LOE is formed from a material having a lower refractive index than the material of the LOE in order to assist internal reflection at the main outer surface of the LOE.

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