A display with stacked light guide elements providing different portions of the field of view

Abstract

A display for providing an image to a user's eye, the display having a composite light guide device, the composite light guide device being formed by a first slab waveguide (10) and a second slab waveguide (20) being juxtaposed. Image illumination from a projector (100) is partially introduced into each waveguide to propagate by internal reflection within the waveguide. The outcoupling configuration of the first waveguide (10) includes a first set of internal partially reflective surfaces (11) at an inclined angle, the first set of partially reflective surfaces being in a first region of the composite light guide device for outcoupling a first portion of a field of view, and the outcoupling configuration of the second waveguide (20) includes a second set of internal partially reflective surfaces (21) at an inclined angle, the second set of partially reflective surfaces being in a second region of the composite light guide device for outcoupling a second portion of the field of view, the second region at least partially not overlapping the first region.

Description

[0001] Technical field and background technology of the invention

[0002] The present invention relates to displays, and in particular, the present invention relates to displays with stacked light-guide optical elements that provide different portions of an image field of view. Certain head-up displays, particularly near-eye displays, employ a light-guide optical element (LOE) formed as a block of transparent material having parallel outer major surfaces that guide light by internal reflection, and having a set of partially reflective inner surfaces at oblique angles to the major surfaces. A collimated image is generated by an image projector and injected into the LOE (also referred to as a "waveguide" or "substrate") to propagate within the LOE by internal reflection until the collimated image is progressively coupled out by the partially reflective inner surfaces toward the user's eyes. An example of such a waveguide can be found in PCT Patent Application Publication No. WO 03081320 A1.

[0003] The angular size of the field of view that can be displayed by such an arrangement is limited by geometric optical considerations, such as the range of angles that can be captured within the waveguide to propagate by internal reflection and avoiding overlap between the image and its conjugate within the waveguide. Summary of the invention

[0004] The present invention is a display for providing an image to an eye of a user.

[0005] According to the teachings of an embodiment of the present invention, there is provided a display for providing an image to a user's eye, the display comprising: (a) a composite light guide device comprising: (i) a first light guide optical element, the first light guide optical element comprising a block of transparent material having a pair of mutually parallel major surfaces for guiding light by internal reflection at the major surfaces, and (ii) a second light guide optical element, the second light guide optical element comprising a block of transparent material having a pair of mutually parallel major surfaces for guiding light by internal reflection at the major surfaces, the first light guide optical element and the second light guide optical element being stacked in a manner where the major surfaces are juxtaposed; and (b) an image projector configured to project image illumination corresponding to a collimated image having an angular field of view, the image projector being optically coupled to the composite light guide device to introduce a first portion of the image illumination propagated within the first light guide optical element by internal reflection and a second portion of the image illumination propagated within the second light guide optical element by internal reflection, wherein the first light guide optical element comprises a first outcoupling configuration, the first outcoupling configuration comprising a first plurality of mutually parallel partially reflective surfaces, the first plurality of partially reflective surfaces being disposed between the major surfaces of the first light guide optical element and relative to each other. The main surface is angled obliquely, a first plurality of partially reflecting surfaces are located in a first region of the composite light guide device, and are used to couple out a first portion of a field of view of image illumination for viewing by eyes of a user, and wherein the second light guide optical element comprises a second coupling-out configuration, the second coupling-out configuration comprises a second plurality of mutually parallel partially reflecting surfaces, the second plurality of partially reflecting surfaces are disposed between the main surfaces of the second light guide optical element and are angled obliquely relative to the main surfaces, the second plurality of partially reflecting surfaces are not parallel to the first plurality of partially reflecting surfaces, and the second plurality of partially reflecting surfaces are located in a second region of the composite light guide device that does not at least partially overlap with the first region, and are used to couple out a second portion of a field of view of image illumination for viewing by eyes of a user, and wherein the optical coupling of the image projector to the composite light guide device and the deployment of the first plurality of partially reflecting surfaces and the second plurality of partially reflecting surfaces result in: first image illumination light and second image illumination light emitted in parallel from the image projector and coupled into the first light guide optical element and the second light guide optical element, respectively, propagate at different angles within the first light guide optical element and the second light guide optical element, but are coupled out by the first plurality of partially reflecting surfaces and the second plurality of partially reflecting surfaces, respectively, to become parallel light.

[0006] According to another feature of an embodiment of the present invention, an image projector injects image illumination into a composite light guide device via one of the main surfaces, and wherein a first portion of the image illumination is coupled into a first light guide optical element via a first reflector, and a second portion of the image illumination is coupled into a second light guide optical element via a second reflector.

[0007] According to another feature of an embodiment of the present invention, the first reflector and the second reflector are non-parallel.

[0008] According to another feature of an embodiment of the invention, the first reflector and the second reflector are total reflectors in a non-overlapping relationship.

[0009] According to another feature of an embodiment of the present invention, the second reflector is a partial reflector, and wherein the light reaches the first reflector after passing through the second reflector.

[0010] According to another feature of an embodiment of the invention, the second reflector is inside the second light-guiding optical element and wherein the first reflector is associated with a surface of a prism attached to a main surface of the first light-guiding optical element further from the image projector.

[0011] According to another feature of an embodiment of the present invention, an adjustment mechanism is provided to allow fine adjustment of the angle of the first reflector.

[0012] According to another feature of embodiments of the invention, the first light-guiding optical element and the second light-guiding optical element are separated by an air gap.

[0013] According to another feature of an embodiment of the present invention, the transparent material of the first light-guiding optical element and the second light-guiding optical element has a first refractive index, and wherein the first light-guiding optical element and the second light-guiding optical element are separated by a layer of material having a second refractive index, the second refractive index being lower than the first refractive index.

[0014] According to another feature of an embodiment of the invention, each of the juxtaposed main surfaces is provided with an antireflection coating.

[0015] According to another feature of an embodiment of the present invention, at least one of the juxtaposed major surfaces of the first light-guiding optical element and the second light-guiding optical element is provided with an angle-selective multilayer dielectric coating, which is configured to be completely reflective for incident angles greater than 60 degrees relative to the normal of the major surface, and to have a low reflectivity for incident angles less than 15 degrees relative to the normal.

[0016] According to another feature of an embodiment of the present invention, the first light-guiding optical element includes a first group of mutually parallel partially reflective deflection surfaces, the first group of deflection surfaces are arranged between the main surfaces of the first light-guiding optical element, the first group of deflection surfaces are arranged to gradually deflect a first portion of the image illumination propagating in the first light-guiding optical element toward the first plurality of partially reflective surfaces, and wherein the second light-guiding optical element includes a second group of mutually parallel partially reflective deflection surfaces, the second group of deflection surfaces are arranged between the main surfaces of the second light-guiding optical element, the second group of deflection surfaces are arranged to gradually deflect a second portion of the image illumination propagating in the second light-guiding optical element toward the second plurality of partially reflective surfaces.

[0017] According to another feature of an embodiment of the invention, the intersection line of the plane of the first set of deflection surfaces with the main surface is not parallel to the intersection line of the plane of the second set of deflection surfaces with the main surface.

[0018] According to another feature of an embodiment of the present invention, the first light-guiding optical element includes a first internal reflection surface, which is parallel to the first group of deflection surfaces and is arranged to deflect a first portion of the image illumination propagating in the first light-guiding optical element toward the first group of deflection surfaces, and wherein the second light-guiding optical element includes a second internal reflection surface, which is parallel to the second group of deflection surfaces and is arranged to deflect a second portion of the image illumination propagating in the second light-guiding optical element toward the second group of deflection surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention is herein described, by way of example only, with reference to the accompanying drawings, in which:

[0020] Figure 1 is a schematic side view of a display constructed and operative in accordance with the teachings of an embodiment of the present invention, the display employing a stack of light guide optical elements (LOEs) to deliver an image from a projector to a user's eye, wherein each LOE delivers a different portion of a field of view;

[0021] Figure 2 is similar to Figure 1 , showing an implementation in which the incoupled light rays are not parallel to the outcoupled light rays while the parallel image rays of the projected image remain parallel in the outcoupled image;

[0022] Figure 3 is similar to Figure 1 , showing a reduced size incoupling aperture achieved by using overlapping partially reflecting incoupling reflectors;

[0023] Figure 4A is similar to Figure 3 , showing the implementation of an in-coupling reflector on an external prism on a LOE;

[0024] Figure 4B is similar to Figure 4A A view in which an external prism is used with an external reflector surface;

[0025] Figure 4C is similar to Figure 4B A view of a device in which the outer reflector surface is made adjustable by using a Risley wedge prism pair;

[0026] FIG. 5A to FIG. 5C are front views of a second LOE for providing two-dimensional aperture expansion, a first LOE, and a stack assembled by the first LOE and the second LOE, respectively, according to another embodiment of a display according to the present invention; and

[0027] FIG. 6A to FIG. 6C They are respectively FIG. 5A to FIG. 5C Corresponding side view. DETAILED DESCRIPTION

[0028] The present invention is a display for providing an image to an eye of a user.

[0029] The principles and operations of a display according to the present invention may be better understood with reference to the drawings and accompanying description.

[0030] Referring now to the accompanying drawings, Figure 1 5 illustrate implementations of a display for providing an image to an eye of a user constructed and operated in accordance with the teachings of the present invention, wherein the eye is assumed to be located in an area designated by 101, referred to as an "eye motion box" (EMB), which represents the range of eye positions for which the display is designed to provide a complete image. Generally speaking, the display includes a composite light guide having a first light guide optical element ("LOE", interchangeably referred to as a "waveguide") 10 and a second light guide optical element 20, each formed as a block of transparent material having a pair of mutually parallel major surfaces (major surface 13 and major surface 14 for LOE 10, and major surface 23 and major surface 24 for LOE 20).

[0031] The two LOEs 10 and 20 are stacked with the major surface 14 and the major surface 23 juxtaposed so that the two waveguides maintain their properties as separate waveguides, thereby guiding the propagation of light within each LOE by internal reflection at the major surfaces. This can be achieved by maintaining an air gap between the juxtaposed surfaces, by providing an intermediate material layer with a lower refractive index (as a different material sheet or a low refractive index adhesive layer), or by providing a coating (usually in the form of a multilayer dielectric coating) that simulates TIR characteristics on one or both of the juxtaposed surfaces. The terms "juxtaposed" or "adjacent" are used to cover all of the above options, whether the major surfaces are separated by an air space, non-contact adjacent separated by an intermediate material layer, or in direct contact. In all cases, for light passing through the composite light guide device at an angle relatively close to vertical, a relatively high transmittance is preferably maintained, typically by applying an anti-reflective coating, to allow viewing of external scenes through the display.

[0032] An image projector 100 configured to project image illumination corresponding to a collimated image having an angular field of view is optically coupled to a composite light guide to introduce a first portion of the image illumination to propagate by internal reflection within a first LOE 10 and to introduce a second portion of the image illumination to propagate by internal reflection within a second LOE 20. Various implementations of coupling devices for optically coupling the image projector 100 to the composite light guide are discussed below.

[0033] The first LOE 10 includes a first out-coupling configuration having a first plurality of mutually parallel partially reflective surfaces 11 disposed between and obliquely angled relative to the major surfaces 13 and 14. The first plurality of partially reflective surfaces 11 are located in a first region of the composite light guide for coupling out a first portion of a field of view of image illumination for viewing by an eye of a user.

[0034] The second LOE 20 includes a second out-coupling configuration having a second plurality of mutually parallel partially reflective surfaces 21 disposed between the major surface 23 and the major surface 24 and obliquely angled relative to the major surface 23 and the major surface 24. The second plurality of partially reflective surfaces 21 are non-parallel to the first plurality of partially reflective surfaces 11 and are located in a second region of the composite light guide device that at least partially does not overlap with the first region for coupling out a second portion of the field of view of the image illumination for viewing by the user's eye.

[0035] The optical coupling of the image projector 100 to the composite light guide device and the deployment of the first plurality of partially reflecting surfaces 11 and the second plurality of partially reflecting surfaces 21 result in: the first light ray 15 of image illumination and the second light ray 25 of image illumination, which are emitted in parallel from the image projector 100 and coupled into the first light guide optical element 10 and the second light guide optical element 20 respectively, propagate at different angles within the first light guide optical element and the second light guide optical element, but are coupled out by the first plurality of partially reflecting surfaces 11 and the second plurality of partially reflecting surfaces 21 as parallel light rays 16 and light rays 26 respectively.

[0036] At this point, it is understood that the present invention provides a number of significant advantages. Specifically, since each waveguide only needs to transmit a sub-region of the angular field of view, the design requirements for the angle selective coatings and various other components used in the partially reflective surfaces of the outcoupling configuration are relaxed. Specifically, each outcoupling surface is preferably partially reflective to red, green and blue light in the angular range corresponding to the desired image, and highly transparent (anti-reflective) to red, green and blue light in the angular range corresponding to the conjugate image. If these characteristics are only required for a portion of the field of view of the image, the design requirements are significantly relaxed. Additionally or alternatively, due to the angular limitations of TIR and / or ghosting (formed by staggering portions of the image across the center plane of the waveguide and folding on itself, and / or by reflecting from an internal surface to reflect a portion of the image so that it overlaps with another portion (i.e., when a portion of the transmitted image portion propagates parallel to one of the partially reflective outcoupling surfaces)), the display can be implemented to transmit a larger field of view than a single waveguide can transmit. In each waveguide, the portion of the FOV that does not need to be delivered by that waveguide can be allowed to exceed these angular limits (either allowing that portion to escape TIR, or that portion of the image to be folded onto its conjugate) without affecting the quality of the image visible at the eye box.

[0037] At the same time, the fact that all parts of the image originate from a single image projector keeps manufacturing costs low and simplifies the task of maintaining alignment between different parts of the displayed image.These and other advantages of the invention will become more apparent from the examples detailed below.

[0038] Now go to Figure 1, which shows an implementation of the above display, wherein the display has two LOEs 10 and LOE 20, each of which is formed as a plate structure of a transparent material (e.g., glass or other material with a sufficient refractive index to support waveguide propagation). As described above, each LOE has two main parallel surfaces 13 and 14 (main parallel surfaces 23 and main parallel surfaces 24 for the second LOE 20), a set of internal parallel surfaces 11 with a partially reflective coating at an oblique angle relative to the main surfaces (inner parallel surfaces 21 for the second LOE). The LOE optionally also includes an inner surface 19 and an inner surface 29 parallel to the main surfaces, and the inner surface 19 and the inner surface 29 have partial reflections to make the output intensity distribution uniform. A particularly preferred implementation of the inner surface is a surface at the mid-plane of the waveguide, which has a reflectivity of about 50% for an angle range corresponding to the image illumination propagating in the waveguide, and has a low reflectivity (anti-reflection) at a viewing angle closer to perpendicular through the waveguide.

[0039] The image projector 100 (interchangeably referred to as a "POD") employed with the apparatus of the present invention is preferably configured to generate a collimated image, i.e., in a collimated image, the light of each image pixel is a parallel beam of light collimated to infinity with an angular direction corresponding to the pixel position. Thus, the image illumination spans an angular range corresponding to a two-dimensional angular field of view. The image projector 100 includes at least one light source, which is 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 device, typically implemented using one or more fast scanning mirrors, that scans illumination from a laser light source across the image plane of the projector while synchronously changing the intensity of the light beam on a pixel-by-pixel basis with the motion, thereby projecting a desired intensity for each pixel. In both cases, collimating optics are provided to generate an output projection image that is collimated to infinity. Some or all of the above components are typically arranged on the surface of one or more polarizing beam splitters (PBS) cubes or other prism devices known in the art.

[0040] In a particularly preferred implementation shown here, the image projector 100 injects image illumination into the composite light guide via one of the major surfaces 24. In this case, a first portion of the image illumination is coupled into the first light guide optical element 10 via the first reflector 12, and a second portion of the image illumination is coupled into the second light guide optical element 20 via the second reflector 22.

[0041] Even though surfaces 11 and 21 are not parallel and in-reflectors 12 and 22 are not parallel, if the absolute angles between these surfaces and the major surface of the LOE are equal (i.e., the absolute angles between surfaces 12 and 14 and between surfaces 11 and 14 are equal, and the angles between surfaces 22 and 24 and between surfaces 21 and 24 are also equal), then parallel rays 15 and 25 entering both LOEs will also leave the LOEs from the inner surface array in parallel (rays 16 and 26). This will occur even though the FOV directed by each LOE will be different due to the different angles of the tilted inner surfaces.

[0042] In addition, if Figure 2 As shown, even if the input coupling surface and the output coupling surface array are not parallel or at the same absolute angle to the main surface, as long as the angle difference is the same for the two LOEs, the parallel light rays 15 and 25 entering the two LOEs will also leave the LOEs (light rays 16 and 26) from the internal partially reflecting surface array in parallel, although at different angles than they entered (i.e., in this figure light rays 15 and 16 are not parallel).

[0043] exist Figure 1 and Figure 2 In an exemplary implementation of , the first reflector 12 and the second reflector 22 are total reflectors in a non-overlapping relationship. In this case, the input aperture widths of the two LOEs are approximately equal to the sum of the input apertures of the individual LOEs.

[0044] exist Figure 3 In the illustrated set of alternative implementations, the second reflector 22 is a partial reflector, and the light reaches the first reflector 12 after passing through the second reflector 22. Figure 3 In the case of , reflectors 12 and 22 are internal reflectors integrated within the LOE (i.e., between the planes of the corresponding major surfaces). The spatial overlap of the input apertures reduces the total input aperture width. For this implementation, the coupling surface reflectivity should be set to 50% for the LOE closer to the image projector. Therefore, in Figure 3 In the embodiment shown in FIG. 1 , surface 12 and surface 22 overlap, and surface 22 should have a reflectivity of about 50%.

[0045] exist FIG. 4A to FIG. 4C In a variant implementation shown, the second reflector 22 is internal to the second LOE 20 , while the first reflector is directly or indirectly associated with a surface of a prism 120 attached to a major surface 13 of the first LOE 120 that is farther from the image projector 100 .

[0046] Specifically, in Figure 4AIn this case, the prism 120 is glued to the LOE 10, and the light is reflected by the surface 121 of the prism 120 and coupled into the LOE.

[0047] exist Figure 4B In another option shown, instead of a reflective surface formed directly on the prism, the prism 120 can cooperate with an external reflective surface 122 that acts as a "first reflector" so that light exits the prism 120, reflects from the external surface 122, and re-enters the prism 120 to be guided inside the LOE, as shown in FIG. Figure 4B As shown, where light 15 is reflected by external surface 122 into LOE 10 via prism 120. In this case, surface 121 may be provided with an AR (anti-reflection) coating. Optionally, the positioning of external reflector surface 122 may be fixed by adhering some associated surfaces such as surface 123 and surface 124 to non-optically active areas of LOE 10 and / or prism 120 (i.e., light reaching the EMB from the image projector does not hit these surfaces as it propagates).

[0048] In some particularly preferred implementations, the display of the present invention may be provided with an adjustment mechanism for allowing fine adjustment of the angle of the first reflector. Figure 4B In an implementation of FIG. 1 , an active alignment system and process may be used to ensure parallelism of the light rays exiting the two LOEs. In such an alignment process, a single collimated beam is coupled into the two LOEs. The beam is also measured at the output as it is coupled out of the LOEs through the array of partially reflective internal surfaces 11 and 21. If the angular difference between surface 21 and surface 22 is not equal to the angular difference between surface 11 and surface 12, the light rays exiting LOE 10 will not be parallel to the light rays exiting LOE 20. If, for example, Figure 4B If an external mirror is used as in , the pitch and yaw of the mirror can be tilted using appropriate adjustment mechanisms until parallelism between rays 16 and 26 is achieved, and the position is then fixed by gluing surfaces 123 and 124 to maintain the orientation of reflector 122.

[0049] In addition, even in Figure 4A In the case of the prism 120 shown with an integrated reflective surface 121, a similar active alignment process can also be achieved by providing a set of interchangeable prisms with small angular differences that can be temporarily glued to the LOE 10, and selecting the prism with the closest angular difference between the light ray 16 and the light ray 26 to be permanently glued to the LOE 10.

[0050] Figure 4CAn alternative mechanism and corresponding method for adjusting the orientation of the first reflector input coupling surface of the LOE 10 is shown. In this case, on top of the prism 120, two wedge windows 130 and 140 are glued. The two wedge windows act as a Risley prism pair. A typical wedge value would be 1 degree and is indicated as α. In the drawings, the angles are exaggerated for clarity of illustration. If the two wedge windows have their wedges oriented relative to each other as shown in the figure, the reflective outer surface 141 is parallel to the outer surface of the prism 120. By rotating the window 140 relative to the window 130, the angle between the surface of the prism 120 and the reflective surface 141 can be varied by up to 2α. Therefore, by continuously rotating the prism 140, any polar angle within this range can be obtained. By rotating the window 130 (together with the window 140) relative to the surface of the prism 120, an adjustment of the azimuth angle can be obtained. Therefore, by appropriately rotating the two wedge windows, any desired orientation of the first reflector surface 141 can be obtained, thereby facilitating the active alignment process as described above. The two wedge-shaped windows are then fixed in their optimal positions by any suitable form of attachment, typically by using an optical adhesive.All intermediate surfaces are preferably provided with an AR coating to minimize undesired reflections that may cause ghosting.

[0051] Now go to FIG. 5A to FIG. 6C Although the present invention has been described so far in the context of an apparatus that performs expansion of the optical aperture of an image projector in one dimension, the present invention may also be implemented to benefit in the context of an LOE that performs aperture expansion in two dimensions. For such an implementation, the first light guide optical element 10 preferably includes a first set of mutually parallel partially reflective deflecting surfaces 17 disposed between the major surfaces 13 and 14 of the first light guide optical element 10. The first set of deflecting surfaces 17 is disposed to gradually deflect image illumination propagating within the first light guide optical element toward the first plurality of partially reflective surfaces 11. Similarly, the second light guide optical element 20 includes a second set of mutually parallel partially reflective deflecting surfaces 27 disposed between the major surfaces 23 and 24 of the second light guide optical element 20. The second set of deflecting surfaces 27 is disposed to gradually deflect portions of the image illumination propagating within the second light guide optical element toward the second plurality of partially reflective surfaces 21.

[0052] exist FIG. 5A to FIG. 6CIn a particularly preferred but non-limiting exemplary implementation of the first LOE 10, the first LOE 10 includes a first internal reflective surface 18 that is parallel to the first set of deflection surfaces 17 and is arranged to deflect a portion of the image illumination propagating within the first light-guiding optical element toward the first set of deflection surfaces. Similarly, the second LOE 20 includes a second internal reflective surface 28 that is parallel to the second set of deflection surfaces 27 and is arranged to deflect a portion of the image illumination propagating within the second light-guiding optical element toward the second set of deflection surfaces.

[0053] To simplify the presentation, Figure 5A and Fig. 6A 2 and 3 show a front view and a side view of the second LOE 20, respectively. Figure 5B and Figure 6B A similar view of the first LOE 10 is shown, and Figure 5C and Figure 6C Corresponding views of the assembled display are shown.Features of the second LOE 20 are shown in phantom to help distinguish the features when stacked.

[0054] Therefore, in addition to Figures 1 to 4C In addition to the aperture expansion of the LOE in the X direction achieved by the structure of , this embodiment also achieves an additional aperture expansion dimension along the Y direction. The deflection surface 17 and the deflection surface 27 are partially reflective surfaces, while the internal reflection surface 18 and the internal reflection surface 28 are parallel to their respective deflection surfaces but are preferably total reflectors. The light coupled from the image projector 100 through the surface 22 to be guided by the second LOE 20 is reflected by the surface 28 to be deflected toward the deflection surface 27, where the light is gradually deflected and reflected by the surface 27. Since the surface 27 and the surface 28 are both parallel, the final deflected light from the surface 27 of the array will be parallel to the light coupled into the LOE by the surface 22. The same applies to the light deflected by the surface 18 and the surface 17 within the LOE 10. Therefore, although the surface 27 and the surface 17 may not be parallel, the parallel light rays coupled into the first LOE 10 and the second LOE 20 can still be emitted in parallel.

[0055] In some implementations, the intersection line of the plane of the first set of deflection surfaces 17 with the major surfaces 13 , 14 is not parallel to the intersection line of the plane of the second set of deflection surfaces 27 with the major surfaces.

[0056] In some implementations, the first set of deflection surfaces 17 and / or the second set of deflection surfaces 27 are orthogonal to the main surface of the LOE. In this case, both the guided image and its conjugate are deflected by these surfaces and redirected towards the outcoupling region. In alternative implementations, the first set of deflection surfaces 17 and / or the second set of deflection surfaces 27 are inclined relative to the main surface of the LOE. In this case, only one image (the main image or its conjugate) is gradually deflected towards the outcoupling region, while the surface is preferably substantially transparent over a range of angles of incidence corresponding to the undesired image.

[0057] Implementation details – coating

[0058] To best implement the various embodiments described herein, it is most preferred to impart angle selective properties to the various surfaces and interfaces between elements. These properties can be conveniently generated using mature techniques for designing and implementing multilayer dielectric coatings, where a sequence of layers of specific thicknesses provides the desired properties.

[0059] With regard to the juxtaposed surfaces of the two LOEs as already mentioned, this may be performed so as to maintain the properties of the two LOEs as independent waveguides, thereby guiding the propagation of light within each LOE by internal reflection at the major surfaces. This may be achieved by maintaining an air gap between the juxtaposed surfaces, or by providing an intermediate material layer with a lower refractive index (as a different material sheet or a low refractive index adhesive layer). Alternatively, the functional separation of the LOEs may be ensured by providing a coating (typically in the form of a multilayer dielectric coating) simulating TIR properties on one or both of the juxtaposed surfaces. Thus, at least one of the juxtaposed major surfaces, and most preferably both major surfaces, is provided with an angularly selective multilayer dielectric coating, which is configured to be completely reflective (e.g., more than 95% reflectivity) for angles of incidence greater than 60 degrees, more preferably greater than 50 degrees, and in some cases from about 40 degrees upwards, relative to the normal to the major surfaces, while having a low reflectivity, preferably less than 5%, for angles of incidence less than 15 degrees, and more preferably up to about 30 degrees relative to the normal.

[0060] In each case, by including anti-reflective coatings on all surfaces and interfaces, visibility to a user looking through the composite waveguide at relatively low angles relative to the normal to the major surfaces is preferably maintained highly transparent.

[0061] Similarly, when used, uniformizing surfaces 19 and 29 preferably have a desired (typically approximately 50%) reflectance over the range of angles over which the image illumination propagates within the LOE, while being anti-reflective at small (nearly perpendicular) angles.

[0062] The outcoupling partially reflective surface is also preferably partially reflective at an angle of incidence corresponding to the desired portion of the image, while being anti-reflective for the conjugate image.The reflective proportion of the desired image may also increase sequentially between successive surfaces.

[0063] Most preferably, all of the above characteristics are substantially consistent for the different colors, thereby allowing the relevant portion of the field of view of the color image to be displayed via each LOE.

[0064] It should be understood that the above description is intended to be exemplary only and that many other embodiments are possible within the scope of the invention as defined by the appended claims.

Claims

1. A display for providing an image to an eye of a user, the display comprising: (a) A composite light guide device comprising: (i) a first light-guiding optical element comprising a block of transparent material having a pair of mutually parallel major surfaces for guiding light by internal reflection at said major surfaces, and (ii) a second light-guiding optical element, the second light-guiding optical element comprising a block of transparent material having a pair of mutually parallel major surfaces for guiding light by internal reflection at the major surfaces, the first light-guiding optical element and the second light-guiding optical element being stacked in such a manner that the major surfaces are juxtaposed; and (b) an image projector configured to project image illumination corresponding to a collimated image having an angular field of view, the image projector being optically coupled to the composite light guide to introduce a first portion of the image illumination propagating by internal reflection within the first light guide optical element and a second portion of the image illumination propagating by internal reflection within the second light guide optical element, wherein the first light guide optical element comprises a first out-coupling configuration, the first out-coupling configuration comprising a first plurality of mutually parallel partially reflective surfaces, the first plurality of partially reflective surfaces being disposed between and obliquely angled relative to the major surfaces of the first light guide optical element, the first plurality of partially reflective surfaces being located in a first region of the composite light guide device for coupling out a first portion of a field of view of the image illumination for viewing by an eye of the user, and wherein the second light guide optical element comprises a second out-coupling configuration, the second out-coupling configuration comprising a second plurality of partially reflective surfaces parallel to each other, the second plurality of partially reflective surfaces being disposed between the major surfaces of the second light guide optical element and obliquely angled relative to the major surfaces, the second plurality of partially reflective surfaces being non-parallel to the first plurality of partially reflective surfaces, and the second plurality of partially reflective surfaces being located in a second region of the composite light guide device that at least partially does not overlap the first region, for coupling out a second portion of the field of view of the image illumination for viewing by the user's eye, And wherein, the optical coupling of the image projector to the composite light guide device and the disposition of the first plurality of partially reflective surfaces and the second plurality of partially reflective surfaces are such that: the first image illumination light and the second image illumination light emitted in parallel from the image projector and respectively coupled into the first light guide optical element and the second light guide optical element propagate at different angles in the first light guide optical element and the second light guide optical element, but are respectively coupled out by the first plurality of partially reflective surfaces and the second plurality of partially reflective surfaces to become parallel light rays, wherein the image projector injects the image illumination into the composite light guide via one of the major surfaces, and wherein a first portion of the image illumination is coupled into the first light guide optical element via a first reflector, and a second portion of the image illumination is coupled into the second light guide optical element via a second reflector, wherein the second reflector is internal to the second light-guiding optical element, and wherein the first reflector is associated with a surface of a prism attached to a main surface of the first light-guiding optical element that is further away from the image projector, The display also includes an adjustment mechanism for allowing fine adjustment of the angle of the first reflector, wherein the adjustment mechanism includes two wedge-shaped windows, the two wedge-shaped windows having wedge shapes oriented relative to each other and fixed to the top of the prism, wherein the display is configured to perform the fine adjustment by appropriately rotating the two wedge-shaped windows before fixing them to the top of the prism to obtain the desired orientation of the surface of the first reflector.

2. The display according to claim 1, wherein: The first reflector and the second reflector are not parallel.

3. The display according to claim 1, wherein: The first reflector and the second reflector are total reflectors in a non-overlapping relationship.

4. The display according to claim 1, wherein: The second reflector is a partial reflector, and wherein light reaches the first reflector after passing through the second reflector.

5. The display according to claim 1, wherein: The first light-guiding optical element and the second light-guiding optical element are separated by an air gap.

6. The display according to claim 5, wherein: Each of the juxtaposed major surfaces is provided with an anti-reflective coating.

7. The display according to claim 1, wherein: The transparent material of the first and second light-guiding optical elements has a first refractive index, and wherein the first and second light-guiding optical elements are separated by a layer of material having a second refractive index, the second refractive index being lower than the first refractive index.

8. The display according to claim 7, wherein: Each of the juxtaposed major surfaces is provided with an anti-reflective coating.

9. The display according to claim 1, wherein: At least one of the juxtaposed major surfaces of the first light-guiding optical element and the second light-guiding optical element is provided with an angle-selective multilayer dielectric coating, which is configured to be completely reflective for incident angles greater than 60 degrees relative to the normal of the major surface, and to have low reflectivity for incident angles less than 15 degrees relative to the normal.

10. The display according to claim 1, wherein: the first light guide optical element comprising a first set of mutually parallel partially reflective deflecting surfaces, the first set of deflecting surfaces being disposed between the major surfaces of the first light guide optical element, the first set of deflecting surfaces being disposed to gradually deflect a first portion of the image illumination propagating within the first light guide optical element towards the first plurality of partially reflective surfaces, And wherein, the second light-guiding optical element includes a second group of mutually parallel partially reflective deflection surfaces, the second group of deflection surfaces being disposed between the main surfaces of the second light-guiding optical element, the second group of deflection surfaces being disposed to gradually deflect a second portion of the image illumination propagating within the second light-guiding optical element toward the second plurality of partially reflective surfaces.

11. The display according to claim 10, wherein: An intersection line of a plane of the first set of deflection surfaces with the major surface is not parallel to an intersection line of a plane of the second set of deflection surfaces with the major surface.

12. The display according to claim 10, wherein: the first light guide optical element comprising a first internal reflective surface parallel to the first set of deflecting surfaces and arranged to deflect a first portion of the image illumination propagating within the first light guide optical element towards the first set of deflecting surfaces, And wherein the second light guide optical element includes a second internal reflective surface parallel to the second set of deflecting surfaces and arranged to deflect a second portion of the image illumination propagating within the second light guide optical element toward the second set of deflecting surfaces.

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