Displays using dichroic combiners integrated with light guides

Abstract

The display includes a light guide (10, 110) with mutually parallel main surfaces and at least two image projectors (2a, 2b, 2c) outputting collimated light of at least a first and a second color, respectively. In one embodiment, the two image projectors introduce the collimated light to propagate in the light guide along the same in-plane direction. Interference of one of the coupling-in arrangements with internal reflection of the other color is avoided by providing a dichroic reflector (9a1, 9b1, 9a2, 9b2, 9a3) that is coplanar with the main surfaces of the light guide. Alternatively or additionally, the two colors can be introduced to propagate in two non-parallel directions and are combined by a dichroic reflector (12a, 12b) embedded in the light guide. A display is also disclosed having an optical relay (66a, 66b) for transferring images between two non-parallel light guides (110a and 110b, 10).

Description

[Technical field]

[0001] The present invention relates to displays, and in particular to displays that use dichroic combiners integrated with light guides and / or that use optical relays between rectangular light guides. [Background technology]

[0002] Several different projector technologies are used in augmented reality displays. Some of these, such as micro-LED arrays, are typically limited to generating monochrome images. To provide a color image to the user, typically three micro-LED arrays of three different colors are used. However, the combining optics required to combine the three colors can make the image projector bulky. This is particularly problematic for near-eye displays, whose components should be as compact as possible to minimize the size and weight of the display. Summary of the Invention

[0003] The present invention is a display that uses one or more dichroic combiners integrated with the light guides and / or uses an optical relay between rectangular light guides.

[0004] In accordance with the teachings of one embodiment of the present invention, a display includes: (a) a light guide having a pair of mutually parallel major surfaces, the pair of mutually parallel major surfaces supporting propagation of light within the light guide by internal reflection at the major surfaces; (b) a first image projector comprising a first monochrome image generator and a first collimating optic, the first image projector outputting collimated light of a first color corresponding to a first component of an image, the first image projector optically coupled to the light guide to introduce the collimated light of the first color into the light guide for propagation within the light guide in a first in-plane direction; and (c) a second image projector comprising a second monochrome image generator and a second collimating optic. a second image projector, the second image projector outputting collimated light of a second color corresponding to a second component of the image, the second image projector being optically coupled to the light guide to introduce the collimated light of the second color into the light guide to propagate within the light guide in a second in-plane direction non-parallel to the first in-plane direction; and (d) a dichroic reflector embedded within the light guide and oriented perpendicular to the major surface, the dichroic reflector bisecting an angle between the first in-plane direction and the second in-plane direction, the dichroic reflector being transmissive to the first color and reflective to the second color to redirect the light of the second color to be combined with the light of the first color and propagate within the light guide in the first direction.

[0005] According to a further feature of an embodiment of the invention, there is also provided a first set of mutually parallel partially reflective surfaces embedded within the light guide for gradually redirecting both the first color and the second color light to propagate in the polarized direction within the light guide, the first set of partially reflective surfaces being parallel to the dichroic reflector.

[0006] According to a further feature of an embodiment of the invention, the length of the optical path from the first image projector to the dichroic reflector is equal to or differs from the length of the optical path from the second image projector to the dichroic reflector by less than 20 percent.

[0007] According to a further feature of an embodiment of the invention, there is also provided: (a) a third image projector comprising a third monochrome image generator and a third collimating optic, the third image projector outputs collimated light of a third color corresponding to a third component of an image, the third image projector being optically coupled to the light guide to introduce the collimated light of the third color into the light guide for propagation within the light guide in a third in-plane direction; and (b) a second dichroic reflector embedded within the light guide and oriented perpendicular to the major surface and configured to redirect light of the third color to combine it with at least one of the light of the first and second colors, whereby the dichroic reflector and the second dichroic reflector together combine light of the first, second, and third colors.

[0008] According to a further feature of an embodiment of the invention, the third direction is parallel to the second direction and the second dichroic reflector is parallel to the dichroic reflector.

[0009] According to a further feature of an embodiment of the invention, the collimated light of at least one of the first and second colors propagates within the first region of the light guide, and the display includes: (a) a third image projector including a third monochrome image generator and a third collimating optics, the third image projector outputting collimated light of a third color corresponding to a third component of the image, the third image projector introducing the collimated light of the third color through a coupling-in area of ​​a first one of the major surfaces within the first region of the light guide such that the collimated light of the third color propagates within the light guide together with the light of the at least one of the first and second colors. and (b) an in-plane dichroic reflector associated with the coupling-in area and coplanar with the first major surface of the light guide, the in-plane dichroic reflector being reflective to at least one of the first and second colors to support light of at least one of the first and second colors propagating through the first region within the light guide by internal reflection, and being transmissive to the third color to enable coupling-in of light of the third color into the light guide.

[0010] According to a further feature of an embodiment of the invention there is also provided a rectangular light guide having a first pair of parallel surfaces and a second pair of parallel surfaces perpendicular to the first pair of parallel surfaces, the light guide being coupled to the rectangular light guide to introduce light of the first and second colors into the rectangular light guide for propagation within the rectangular light guide by four internal reflections.

[0011] In accordance with the teachings of one embodiment of the present invention, a display includes: (a) a light guide having first and second mutually parallel major surfaces, the first and second mutually parallel major surfaces supporting propagation of light within the light guide by internal reflection at the first and second major surfaces; (b) a first image projector comprising a first monochrome image generator and a first collimating optic, the first image projector outputs collimated light of a first color corresponding to a first component of an image, the first image projector being optically coupled to the light guide to introduce the collimated light of the first color into the light guide for propagation within a first region of the light guide in a first in-plane direction; and (c) a second image projector comprising a second monochrome image generator and a second collimating optic, the second image projector being optically coupled to the light guide such that the collimated light of the first color is introduced into the light guide for propagation within a first region of the light guide in a first in-plane direction. Also provided is a display comprising: (a) a second image projector that outputs collimated light of a second color corresponding to a second component of the image, the second image projector being optically coupled to the light guide to introduce the collimated light of the second color through a coupling-in area of ​​a first major surface in the first region of the light guide so as to propagate together with the light of the first color within the light guide in a first in-plane direction; and (d) a dichroic reflector associated with the coupling-in area and coplanar with the first major surface of the light guide, the dichroic reflector being reflective of the first color to support propagation of light of the first color through the first region within the light guide by internal reflection and being transmissive of light of the second color to enable coupling-in of light of the second color into the light guide.

[0012] According to a further feature of an embodiment of the invention, a second image projector is optically coupled to the light guide via a transmissive prism mounted in the coupling-in area.

[0013] According to a further feature of an embodiment of the invention, a second image projector is optically coupled to the light guide via a reflective surface that is integrated with a prism mounted in the coupling-in area.

[0014] According to a further feature of an embodiment of the invention, a second image projector is arranged to inject light of a second color through the second major surface such that light of the second color traverses the thickness of the light guide so as to be coupled into the light guide, transmitted by the dichroic reflector, reflected by the reflective surface and transmitted again by the dichroic reflector.

[0015] According to a further feature of an embodiment of the invention, the light of the first and second colors propagate together in a first in-plane direction in the second region of the light guide, and the display includes: (a) a third image projector including a third monochrome image generator and a third collimating optics, the third image projector outputs collimated light of a third color corresponding to a third component of the image, the third image projector coupling the collimated light of the third color through a second coupling-in area of ​​the first major surface or the second major surface in the second region of the light guide such that the collimated light of the third color propagates together with the light of the first and second colors in the first in-plane direction in the light guide. and (b) a second dichroic reflector associated with the second coupling-in area and substantially coplanar with the first major surface or the second major surface, the second dichroic reflector being reflective to the first and second colors to support light of the first and second colors propagating through the second region within the light guide by internal reflection, and being transmissive to the third color to enable coupling-in of light of the third color into the light guide.

[0016] According to a further feature of an embodiment of the invention the coupling-in area and the second coupling-in area are in overlapping relationship on opposite major surfaces of the light guide.

[0017] According to a further feature of an embodiment of the invention there is also provided a rectangular light guide having a first pair of parallel surfaces and a second pair of parallel surfaces perpendicular to the first pair of parallel surfaces, the light guide being coupled to the rectangular light guide to introduce light of the first and second colors into the rectangular light guide for propagation within the rectangular light guide by four internal reflections.

[0018] According to a further feature of an embodiment of the invention, an end of the rectangular light guide is optically coupled to a slab light guide having a coupling-out configuration for coupling out light propagating within the slab light guide towards a user's eye.

[0019] According to a further feature of an embodiment of the invention, there is also provided a set of mutually parallel partially reflective coupling-out surfaces embedded within the light guide at an oblique angle to the major surface to gradually reflect light propagating within the light guide so as to redirect both the first and second color light from the light guide towards the user's eye.

[0020] In accordance with the teachings of one embodiment of the present invention, there is also provided a light guide arrangement comprising: (a) a first rectangular light guide having a first pair of parallel surfaces and a second pair of parallel surfaces perpendicular to the first pair of parallel surfaces to support propagation of light by quadruple internal reflection, the first rectangular light guide having a first extension direction parallel to an intersection line between one of the first pair of parallel surfaces and one of the second pair of parallel surfaces; (b) a second light guide having at least the first pair of parallel surfaces to support propagation of light by internal reflection, the first pair of parallel surfaces being non-parallel to the first extension direction; and (c) an optical relay optically coupled between the first rectangular light guide and the second light guide, the optical relay relaying a collimated image propagating in the first rectangular light guide through a real image plane to a collimated image propagating in the second light guide.

[0021] According to a further feature of an embodiment of the invention, the optical relay is configured to image an output aperture plane of the first rectangular light guide onto an input aperture plane of the second light guide.

[0022] According to a further feature of an embodiment of the invention, the optical relay has unity magnification.

[0023] According to a further feature of an embodiment of the invention, the optical relay is optically symmetric with respect to the real image plane.

[0024] According to a further feature of an embodiment of the invention, the optical relay is optically coupled to each of the first rectangular light guide and the second light guide via a coupling prism.

[0025] According to a further feature of an embodiment of the invention, the optical relay includes a polarizing beam splitter prism having reflective lenses on two faces of the prism.

[0026] According to a further feature of an embodiment of the invention, the second light guide is a rectangular light guide having a second pair of mutually parallel major surfaces perpendicular to the first pair of major surfaces to support light propagation by quadruple internal reflection.

[0027] According to a further feature of an embodiment of the invention, the optical relay further comprises a beam spreading element disposed at the real image plane. [Brief description of the drawings]

[0028] The invention is herein described, by way of example only, with reference to the accompanying drawings. [Figure 1A] FIG. 13 is a schematic side view of a prism-based coupling-in arrangement used in certain implementations of the present invention for coupling a collimated image from an image projector into a light guide. [Figure 1B]FIG. 2 is a schematic side view of a reflective coupling-in arrangement employed in certain implementations of the present invention for coupling a collimated image from an image projector into a light guide. [Figure 1C] FIG. 1 is a schematic diagram of a collimated image projector suitable for use in certain embodiments of the present invention. [Figure 2A] FIG. 1 is a schematic front view of an operational display constructed in accordance with a first embodiment of the invention, using a dichroic combiner integrated with a light guide. [Figure 2B] FIG. 2B is a close-up view of selected elements from FIG. 2A showing the angular relationships between the components. [Diagram 3] FIG. 11 is a schematic front view of an operational display constructed in accordance with a second embodiment of the present invention, using a dichroic combiner integrated with a light guide. [Figure 4] FIG. 4 is a schematic partial side view of a coupling-in region of the light guide of FIG. [Diagram 5] FIG. 4 is a schematic front view of an operational display constructed in accordance with a further embodiment of the invention which combines features from the embodiments of FIGS. 2 and 3. [Figure 6] 6A and 6B are two additional schematic partial side views of displays according to further implementations of the present invention showing various combinations of prism-based and / or reflective coupling-in arrangements from both sides of the light guide. [Figure 7] 13 is a further schematic partial side view of a display according to a further implementation of the present invention, showing the combination of two monochrome images prior to coupling to a light guide. [Figure 8] FIG. 4 is a further schematic front view of a display according to a further implementation of the present invention, showing a coupling-in arrangement similar to that of FIG. 3 combined with a diffractive optical element for expanding the optical aperture of an injected image via a pair of diffractive redirections of light propagating within a light guide. [Figure 9]9A and 9B are schematic front and side views, respectively, of a display according to a further implementation of the invention in which image light is coupled into a rectangular light guide. [Figure 10A] FIG. 9B is a schematic partial front view of a coupling-in configuration for coupling multiple monochrome images into the rectangular light guide of FIG. 9A. [Figure 10B] FIG. 9B is an isometric view of a coupling-in configuration for coupling multiple monochrome images into the rectangular light guide of FIG. 9A. [Figure 10C] FIG. 10B is a front view of a variation of the coupling-in configuration of FIG. 10A. [Figure 11A] FIG. 10B is a schematic isometric view of a further variation of the coupling-in configuration of FIG. 10A, showing a double-sided coupling-in. [Figure 11B] FIG. 11B is a schematic partial isometric view of the coupling-in configuration of FIG. 11A shown integrated with adjacent light guide elements. [Figure 12A] FIG. 9B is a schematic partial front view of an alternative coupling-in configuration for coupling multiple monochrome images into the rectangular light guide of FIG. 9A. [Figure 12B] FIG. 9B is an isometric view of an alternative coupling-in configuration for coupling multiple monochrome images into the rectangular light guide of FIG. 9A. [Figure 12C] FIG. 12B is a front view of a variation of the coupling-in configuration of FIG. 12A. [Figure 13] 13A and 13B are schematic partial front and isometric views of a further alternative coupling-in force configuration for coupling multiple monochrome images into the rectangular light guide of FIG. 9A. [Figure 14A] FIG. 4 is a schematic top view of an alternative implementation of a display in which a rectangular light guide is used to couple an image into an aperture-extended light guide similar to those of FIGS. 2A and 3. [Figure 14B] FIG. 4 is a front view of an alternative implementation of a display in which a rectangular light guide is used to couple an image into an aperture-extended light guide similar to those of FIGS. 2A and 3. [Figure 14C] FIG. 14C is a schematic top view of a variation of the display of FIGS. 14A and 14B. [Figure 14D] FIG. 14C is a front view of an alternative implementation of the display of FIGS. 14A and 14B. [Figure 15A] FIG. 1 is a schematic top view of a display that uses an optical relay to transfer image light from a first rectangular light guide to a second light guide that is angled relative to the first light guide. [Figure 15B] FIG. 15B is a schematic top view similar to FIG. 15A, in which the optical relay is implemented using a PBS prism and reflective optics. [Figure 16] FIG. 15B is a schematic isometric view of an arrangement similar to FIG. 15A using right angle reflecting prisms for coupling in and out of a rectangular light guide. [Figure 17] FIG. 17 is a schematic isometric view similar to FIG. 16, but with the second light guide being a slab light guide. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention is a display that uses one or more dichroic combiners integrated with the light guides and / or uses an optical relay between rectangular light guides.

[0030] The principles and operation of a display according to the present invention may be better understood with reference to the drawings and accompanying description.

[0031] To begin with, various aspects of the invention relate to displays in which one or more dichroic combiners are integrated with a light guide to combine partial images from two or more monochrome image projectors. This provides a much more compact implementation than would typically be achievable by using a conventional dichroic prism arrangement that combines all colors before injecting the images into the light guide. Some of the light guide arrangements disclosed herein with reference to Figures 9A-14D also use rectangular light guides that direct image light by four internal reflections. A further aspect of the invention, useful in synergy with the arrangements of Figures 9A-14D or in other contexts using rectangular light guides, provides an optical relay between such a rectangular light guide and another slab-type or rectangular light guide to achieve coupling between non-parallel light guides, as will be described with reference to Figures 15A and 15B.

[0032] In the context of combining monochrome images, reference may be made herein to a "color display." The term "color display" is used herein to refer to any display that is not monochrome, even if it combines only two visible colors. The term "full color display" will be used specifically to refer to a display that can display a combination of three visible colors, typically red, green, and blue (RGB), that can be combined to produce the perception of white.

[0033] A particularly preferred, but non-limiting example of a monochrome image source for use in various implementations of the present invention is a micro LED (MLED) array, which provides a matrix of active illuminated pixels. FIG. 1C shows a typical monochrome image projector (or "display module") 2 based on an MLED array 4 combined with collimating optics 6 configured to collimate the light from each pixel of the MLED array 4 into a collimated beam. The collimating optics 6 are preferably configured to have a forward-projected aperture 7 through which the collimated beams corresponding to all of the pixels are projected. The MLED array is operated to generate the required image (or a color separation that is typically part of the final desired image) by a display driver 4a, which includes electronic circuitry for this purpose, as is well known in the art. Elsewhere in this specification, for ease of presentation, each image projector 2 is represented only diagrammatically, shown in side view as a single lens that diagrammatically represents the MLED array 4 as well as the collimating optics 6, and in plan view simply as a rectangular block. Color images are achieved by combining light from separate matrices, each of which produces a color separation of the desired image in a single color.

[0034] Collimated image light from the MLED can be coupled into a light guide to be transmitted to a near-eye display or for a head-up display. Figure 1A shows a module 2 in which light from an MLED 4 is collimated by collimating optics 6 and injected into a light guide 10 via a coupling prism 8 attached to a bounding surface 9. The arrows represent diagrammatically the beams propagating from the MLED into the light guide 10 and then propagating within the light guide 10 by internal reflection.

[0035] 1B shows an alternative configuration in which prism 8 provides the reflective surface. Throughout this specification, unless otherwise noted, these two options of coupling-in via a transmitting prism or a reflecting prism / surface are considered interchangeable, and where one is shown, additional variations using the alternative coupling-in configuration for some or all of the coupling-in positions are expressly envisaged.

[0036] In both the configurations of Figures 1A and 1B, corners 80 serve to trim the incoming light beam so that excess / unwanted light is not coupled into the light guide.

[0037] Reference is now made to Figures 2A and 2B, which show an operational display constructed according to a first aspect of the invention, where images from at least two, and preferably three, monochrome image projectors (modules 2a, 2b, and 2c) each project a different color image into a light guide 10, which are combined and expanded by dichroic reflectors 12a and 12b embedded within the light guide before being coupled out towards the user's eye. Each module has the same architecture as shown in either Figure 1A or Figure 1B, and the two module types can be mixed.

[0038] Light guide 10 has a pair of mutually parallel major surfaces (front and back in the front view shown here) that support the propagation of light within the light guide by internal reflection at the major surfaces. The arrows shown here represent guided light within light guide 10, i.e., guided light propagating by internal reflection from the front and back major surfaces of the light guide; only the "in-plane component" of the light rays, i.e., the component parallel to the major surfaces, are shown.

[0039] Thus, a first image projector 2a including a first monochrome image generator and a first collimating optic outputs collimated light of a first color corresponding to a first component of an image and is optically coupled to the light guide to introduce the collimated light of the first color into the light guide for propagation within the light guide in a first in-plane direction d1. The direction d1 referred to here corresponds to the representative central direction or "chief ray" of the collimated image, which also includes a range of other directions, as indicated by the arrows of the field edge rays on either side of d1.

[0040] A second image projector 2b, including a second monochrome image generator and a second collimating optic, outputs collimated light of a second color corresponding to a second component of the image. The second image projector 2b is optically coupled to the light guide to introduce the collimated light of the second color into the light guide to propagate within the light guide 10 in a second in-plane direction d2 non-parallel to the first in-plane direction d1. A dichroic reflector 12a embedded within the light guide 10 is oriented perpendicular to the major surface and bisects an angle α between the first and second in-plane directions. The dichroic reflector 12a is transparent to the first color and reflective to the second color to redirect the light of the second color to be combined with the light of the first color and propagate within the light guide in the first direction d1. This is most clearly shown in FIG. 2B.

[0041] In a preferred implementation of the three-color display shown here, a third image projector 2c including a third monochrome image generator and a third collimating optic outputs collimated light of a third color corresponding to a third component of the image. The third image projector 2c is optically coupled to the light guide to introduce the collimated light of the third color into the light guide to propagate in the light guide in a third in-plane direction d3 non-parallel to the first in-plane direction d1. A second dichroic reflector 12b embedded in the light guide is oriented perpendicular to the major surface and bisects the angle between the first in-plane direction d1 and the third in-plane direction d3. Most preferably, the third in-plane direction d3 is parallel to the second in-plane direction d2, and the second dichroic reflector 12b is parallel to the dichroic reflector 12a. The second dichroic reflector 12b is transparent to the first and second colors and reflective to a third color so as to redirect light of the third color to be combined with the light of the first and second colors and propagate within the light guide in the first direction d1.

[0042] In a particular preferred implementation, the coupling-in of light from at least the first and second image projectors, as well as the arrangement of the dichroic reflectors, is such that the optical path length from the first image projector 2a to the dichroic reflector 12a is equal to or differs by less than 20 percent from the optical path length from the second image projector 2b to the dichroic reflector 12a. This helps to maximize the overlapping area of ​​the images. Most preferably, the optical path lengths from all three image projectors to the second dichroic reflector 12b are also equal or differ by less than 20 percent. In this context, it should be noted that the front views of Figures 2A and 2B (in addition to being only schematic) cannot be used to evaluate the optical path length, since the optical path length also depends on the selected coupling-in geometry. For example, if modules 2a and 2b use prism coupling as in FIG. 1A while module 2c uses reflective coupling in as in FIG. 1B, the optical path of the image from module 2c may be longer than appears in the front view.

[0043] In one particularly preferred, but non-limiting implementation shown herein, the light guide 10 is part of a two-dimensional aperture-extended light guide arrangement that includes a first set 14 of mutually parallel partially reflective surfaces embedded within the light guide 10 to gradually redirect all color light to propagate in a polarized direction within the light guide such that the in-plane direction of propagation is generally downward in the drawing as shown, and a coupling-out arrangement, shown here as a second set 15 of mutually parallel partially reflective surfaces located within the second portion 20 of the light guide and disposed at an angle relative to the major surface, to gradually redirect a portion of the light propagating within the second portion 20 to be coupled out toward the user's eye. The partially reflective surfaces 15 are preferably implemented with an angle-selective partially reflective coating, typically implemented using multi-layer dielectric coatings known in the art, to selectively couple out the desired image light while being transparent to angles of incidence corresponding to the inverted form of the image produced during propagation within the light guide by internal reflection.

[0044] The partially reflective inner surfaces 14 and 15 are shown only diagrammatically and would generally need to be more closely spaced to provide continuous coverage of the image reaching the user's eye. These and other details of two-dimensional aperture-expanded light guides as well as shapes of alternative implementations may be found in previous documents such as U.S. Pat. No. 10,739,512 and in commercially available products from LUMUS Ltd. (Israel).

[0045] In such an embodiment, it is particularly advantageous for the dichroic reflectors 12a and / or 12b to be parallel to the first set of partially reflective surfaces 14. This allows the entire light guide region 10 to be manufactured as a stack of pre-coated parallel-faced plates, and preferably bonded into a block containing the coupling-out reflector 15, which can then be sliced ​​and polished to create multiple light guides simultaneously.

[0046] Reference is now made to figures 3 and 4, which show an alternative embodiment according to a further aspect of the invention, in which at least two, preferably three, monochrome image projectors of different colours are combined in tandem on a light guide 10 to introduce image light propagating in the same direction. Here, module 2b is placed behind 2a, while 2c is placed behind 2b. This tandem arrangement allows for a different arrangement of the modules. Assuming that the modules have the same angular divergence, there may be some mismatch in the beam distribution in the waveguide. This can be corrected by an appropriate length of the facets 14.

[0047] FIG. 4 shows a cross section of the tandem module of FIG. 3. A particular feature of this aspect of the invention is that for at least one of the coupling configurations, the boundary surface labeled 9 in either FIG. 1A or FIG. 1B is implemented with a dichroic coating that allows injection of a monochrome image from a corresponding image projector while maintaining the internal reflection condition of another previously injected color image propagating in the light guide. Thus, in the case of FIG. 4, interface 9a1 includes a dichroic coating that transmits light from 2a but reflects light from 2b and from 2c. Interface 9b1 includes a dichroic coating that transmits light from 2b and reflects light from 2c. Interface 9c1 may simply be transmissive. Now, every module has its own trimming corners 80a, 80b, and 80c.

[0048] At each of the interfaces 9a1 and 9b1, a dichroic coating is associated with a corresponding coupling-in area of ​​the image projector and provides a dichroic reflector that is coplanar with one of the major surfaces of the light guide 10. The coatings may most conveniently be applied to the coupling prisms 8a and 8b before bonding the prisms to the light guide.

[0049] Figure 5 shows a further implementation of the invention in which the principles described above with reference to Figures 2 and 3 are combined. Specifically, as shown in Figure 5, two modules 2a and 2b are deployed in tandem and inject their respective images along the same direction, while module 2c injects images in a non-parallel direction and uses an embedded dichroic combiner 12b to reflect the color from image projector 2c while transmitting light from projectors 2a and 2b. This allows for a simplification of the coating design of both boundary surfaces 9a1 and of dichroic combiner 12b, since each only needs to be reflective in a single narrow wavelength band. This configuration may also facilitate a more compact arrangement of the modules.

[0050] FIG. 6A shows a further configuration based on the principle of FIG. 3, but where the coupling-in area (interface 9a2) of module 2a and the coupling-in area (interface 9b2) of module 2b are in overlapping relationship on opposing main surfaces of the light guide 10. "Overlapping relationship" in this context refers to overlap of areas projected in a direction perpendicular to the main surface of the waveguide. In a particularly preferred implementation, the two modules are diametrically opposed (substantially complete overlap). This makes it easy to achieve the same optical path for the light from the two opposing modules, so that the beams along the light guide 10 will overlap. In this case, the dichroic coating of interface 9b2, in addition to reflecting light from module 2c, should also reflect light from module 2a, while interface 9a2 should reflect light from both modules 2b and 2c. This arrangement also allows the coupling of module 2c to be placed closer to other modules, thereby improving the overlap of the beam from module 2c with the beams from modules 2a and 2b. Alternatively, as shown in FIG. 5, the light from module 2c can be combined with other images by using an embedded dichroic combiner 12b, in which case the light paths of all three modules can be equal.

[0051] Referring to Fig. 6B, this shows a generally similar arrangement to Fig. 6A, but module 2b uses reflective coupling-in (corresponding to Fig. 1B), where the image light is transmitted through the thickness of the light guide 10 and reflected from a reflective surface 9b3 integrated with prism 8a. In this particular case, prism 8a also serves as a coupling prism for module 2a, so that reflective surface 9b3 is implemented as a dichroic reflector that reflects light from module 2b and transmits light from module 2a, embedded at the required angle within prism 8a. The dichroic coating at interface 9a3 is designed to transmit light from modules 2a and 2b, while reflecting light from module 2c.

[0052] As a result of this structure, light from module 2a is coupled in through prism 8a and is transmitted by both surfaces 9b3 and 9a3. Light from module 2b is injected by the second image projector through the lower major surface (as shown) to be coupled into light guide 10, traverses the thickness of light guide 10, is transmitted by the dichroic reflector at interface 9a3, is reflected by reflective surface 93b, and is transmitted again by the dichroic reflector at interface 9a3. Light from module 2c is coupled in as in FIG. 6A via coupling-in prism 8c (mounted at the edge of the light guide in this non-limiting case), then propagates along light guide 10 and is reflected by the dichroic reflector at interface 9a3 to continue in the light guide unaffected by the presence of prism 8a.

[0053] 7 shows a further alternative coupling-in arrangement, where the light from modules 2a and 2c is combined by using a dichroic cube having a dichroic reflector 9a4 that transmits the light from module 2a and reflects the light from module 2c. The dichroic cube is coupled to a surface of a light guide 10 to introduce the combined image into the light guide for propagation within the light guide.

[0054] Figures 4 and 6A-7 selectively show only the coupling-in region of a display system to clearly illustrate the exemplary coupling-in architecture options. Each of these configurations can be advantageously used with two-dimensional aperture-expanded light guides such as those shown in Figures 2A, 3, or 5, or with any of the alternative light guide arrangements that will be described below.

[0055] Reference is now made to Fig. 8, which shows a further preferred but non-limiting implementation that is generally similar to Fig. 3, but uses a diffractive arrangement 30 for aperture expansion in the light guide 10 instead of the partial reflector 14. The diffractive arrangement 30 deflects the light from modules a1, a2 and a3 at different angles afterwards, since the diffraction effect is highly wavelength-dependent. However, the diffractive arrangement 30 is arranged such that it subsequently diffracts a second time to return the light ray to its original (pre-diffraction) propagation direction in the light guide, thereby compensating for the spectral dependence of the diffraction angle. The position and configuration for the deployment of the diffractive arrangement 30 can vary and are only shown in this figure in a schematic manner. The coupling-out arrangement is preferably a set of partially reflective obliquely angled internal surfaces 15 as described above, which avoids introducing any chromatic aberrations.

[0056] 9A-13B, a particular display system uses a rectangular light guide having a first pair of parallel surfaces and a second pair of parallel surfaces that are perpendicular to the first pair of parallel surfaces to support the propagation of light within the rectangular light guide by four internal reflections. Rectangular light guides have the particular advantage that light rays at different angles corresponding to different parts of the image's field of view are contained within the light guide and therefore do not diverge in the same way as they do in the in-plane dimension of a slab-type light guide. An extensive example of a system using a rectangular light guide can be found in U.S. Patent No. 10,133,070 to LUMUS Ltd. Further aspects of the present invention provide various solutions for efficient and compact coupling-in of images from two or more monochrome image projectors into a rectangular light guide, as presented herein with reference to FIGS. 9A-13B.

[0057] For purposes of this description, light guides such as those described above (regions 10 and 20) defined by two reflective surfaces are referred to herein as "1D light guides" in the sense that they guide and confine light propagating within the light guide in one dimension, but the light diverges in the other (in-plane) dimension. Rectangular light guides defined by four reflective surfaces that create a rectangular cross section are referred to herein as "2D light guides" in the sense that they guide and confine the divergence of light in two dimensions as it propagates along the light guide. In Figures 9A and 9B and subsequent figures, these surfaces are marked 42U, 42D, 42L, and 42R.

[0058] 9A and 9B show an implementation of coupling MLEDs to a 2D light guide 110. Modules 2a, 2b, and 2c can be coupled to the 2D light guide in various ways. Light propagates in the 2D light guide in a 4-fold configuration, as shown in the light guide 110 in FIG. 9B. Partially reflective surfaces (interchangeably called "facets") 14 in the light guide 110 reflect the light so as to couple it from the light guide 110 to the 1D light guide 20, which guides the light until it is gradually redirected towards the observer's eye 30 by reflection from the partially reflective surfaces 15. Section 130 shown here is an inert block of glass or other material that serves to protect the light guide 110 and support section 50 to which the MLED projector module is coupled. Internal reflection at surfaces 42U and 42D is preferably maintained by leaving an air gap or, more preferably from a structural standpoint, by using a layer of low index adhesive or other low index material between the light guide 110 and the adjacent elements (light guide 20 and block 130).

[0059] A particular preferred configuration for coupling to a 2D light guide is based on two steps: first coupling to a 1D light guide in a manner similar to the previous figures, followed by coupling from the 1D light guide to a 2D light guide. Thus, the section 50 may be based on prism coupling to a 1D light guide as in FIG. 1A, or reflective coupling as in FIG. 1B, or a combination of both as in FIG. 6B. Combining the images from the MLED monochrome image projectors 2a, 2b, 2c, and possibly 2d (see below) in the 1D coupling section 50 can be performed as previously described for coupling to a 1D light guide, including tandem coupling as in FIG. 3 and FIG. 4, or embedded dichroic combiners as in FIG. 2, or a combination as in FIG. 5. The 1D section 50 is then coupled to a 2D light guide 110, as will be further detailed below.

[0060] 10A and 10B detail one possible embodiment of the coupling section 50. In this case, the modules 2a-2c couple to the 1D section 50 through a surface that is a continuation of the rectangular light guide surface 42R, using a coupling configuration corresponding to FIG. 4. The section 50 has two parallel main surfaces that are a continuation of the surfaces 42R and 42L of the light guide 110 and is combined in the 2D section 110 at a predefined angle such that the beams propagated in the section 50 by double internal reflection enter the light guide 110 so as to propagate in the light guide 110 via quadruple internal reflection. The virtual aperture of the coupling into 110 is represented as a dashed line 54 with a trimming edge 90abc that is perpendicular to the trimming (or aperture) 80a-80c that trims each individual coupling-in configuration into the section 50. Because aperture 54 (and its trimming edges 90abc) is common to all of the image projector modules 2a-2c, for optimum efficiency the collimating optics of each image projector preferably have a forward projected exit aperture that is in the same plane 54. This requires that the more remote projector modules have further forward projected exit apertures, as shown in Figure 10A, and therefore larger diameter optics.

[0061] Figure 10C shows an alternative implementation of a 1D light guide coupling section 50 including an embedded dichroic reflector 55 that combines image light from module 2c with image light from modules 2a and 2b. This configuration is the same as that of Figure 5 described above. The dichroic combiner can be introduced from the opposite orientation. Additionally, another dichroic surface can be introduced using a configuration equivalent to Figure 2.

[0062] FIG. 11 shows a further embodiment (similar to FIG. 6A) in which modules are coupled to both sides of the 1D light guide 50 to shorten the distance from the projector to the forward projected aperture 54. Here, four modules are used, 2d could be for another color or for projecting infrared illumination that may be required for eye tracking applications. FIG. 11B illustrates how an inactive section 130 can be used to protect the reflective surface 42U and to support (or be part of) the 1D section 50. This implementation is applicable to all 2D light guides presented here.

[0063] 12A-12C show another possibility of coupling an MLED array image projector to a 2D light guide 110. Here, the coupling of module 2c is done separately. There is a 1D light guide section 50ab (with trimming line 90ab) that couples modules 2a and 2b to the 2D light guide 110, and a separate 1D light guide part 50c (with trimming line 90c) that couples module 2c to the 2D light guide 110. In this case, a dichroic coating is implemented on surface 56 that is transparent to the color of light projected by module 2c, but reflective to the color of light projected by modules 2a and 2b. Light guide section 50c can be coupled to the 2D light guide 110 on any of the outer surfaces of the 2D light guide and is not limited to any particular orientation with respect to light guide section 50ab. Light guide section 50c may be coupled to surface 42U as shown in FIG. 12A, to surface 42D as shown in FIG. 12C, to surface 42R, or to surface 42L.

[0064] 13A and 13B show an alternative approach to coupling a monochrome image projector to a 2D light guide that uses dichroic facets in the 2D light guide. Here, module 2a is coupled from the end of the 2D light guide 110 as described above, while modules 2b and 2c are coupled from the side. First, they enter coupling prisms 8b and 8c, which have a back surface that is coplanar with or parallel to the back surface of the light guide 110, and the light enters the light guide 110. Then embedded dichroic combiners (facets) 58b and 58c reflect the light so that it co-propagates with the light from module 2a. In this example, facet 58c is implemented as a dichroic coating designed to reflect light from module 2c and transmit light from modules 2b and 2a. Facet 58b is implemented as a dichroic coating designed to reflect light from module 2b and transmit light from module 2a. Trimming of the incoming light from modules 2c and 2b occurs in one dimension at 80b and 80c (as before), while trimming in the other dimension is performed at the edges of the facets, namely edge 90b of facet 58b and edge 90c of facet 58c.

[0065] As an alternative to the configuration of FIG. 9A, where the light is laterally coupled out of the 2D light guide by an internal partial reflector, the light propagating in the 2D light guide 110 may instead exit the 2D light guide from an end, as shown in FIGS. 14A-14D. This configuration offers enhanced flexibility in making the system more ergonomic. In this case, the 2D light guide 110 is preferably coupled to a 1D light guide using a coupling prism 62. The light propagating with the light guide 110 by four internal reflections is converted to two internal reflections in the 1D light guide without loss of optical power. The orientation of the modules 2a-2d can be changed as required. FIGS. 14A and 14B show the modules 2a-2d in the same plane as the light guide (using a configuration like FIGS. 12A and 12B), while FIGS. 14C and 14D show an arrangement of the modules 2a-2d perpendicular to the plane of the 1D light guide. Orientations and / or combinations of the various coupling-in configurations described above are also possible.

[0066] In all of the above embodiments, the separate monochrome image projectors need to be carefully aligned to achieve the correct overlap of the partial images. In some cases, positioning the projector modules using a purpose-designed jig with properly positioned alignment surfaces may be sufficient to achieve the required image overlap. Alternatively, or additionally, a closed-loop alignment process may be implemented using a camera positioned to view the output of the light guide assembly during placement and fixation of the projector modules. In all cases, post-assembly fine-tuning is preferably done by adjusting a digital image offset implemented by the display driver 4a (FIG. 1C), which may be programmed as part of a factory calibration process and / or may be user-adjustable, all as known in the art.

[0067] 15A-17 show a further embodiment of the invention where the angle between a 2D (rectangular) light guide 110A (similar to 110 above) and another 2D (rectangular) light guide 110B or a 1D (slab) light guide 10 (which appear the same in top view) can be changed. This change in angle (or "folding") facilitates the ergonomic design of the projection system. FIG. 15A shows a top view of a light guide 110A with a coupled MLED array image projector that injects components of an image into the light guide, which are then coupled out through a coupling-out prism 64A (structurally equivalent to a coupling-in prism). A coupling-in prism 64B couples the light into the 2D light guide 110B or into the 1D light guide 10. According to one non-limiting exemplary implementation, the light guide 110A is shown with the projector configuration of FIGS. 12A and 12B, however, this aspect of the invention may also be advantageously used with any of the other coupling-in configurations described above, or any conventional image injection arrangement, for example a color image projector based on LCOS image generating chips sequentially illuminated by different colored illumination, or by a scanning intensity modulated laser beam image projector.

[0068] The coupling between the light guide 110A and the light guide 110B or 10 is via an optical relay optically coupled between the two light guides. The optical relay is represented here by two lenses 66A and 66B, each of which is typically implemented as a lens arrangement (e.g., similar to that shown in FIG. 1C). The optical relay relays a collimated image propagating in the rectangular light guide 110A through a real image plane (between the lenses) to a collimated image propagating in the second light guide. Furthermore, to maintain the efficiency of the light transfer between the light guides, the optical relay is preferably configured to image the output aperture plane 54A of the first rectangular light guide 110A to the input aperture plane 54B of the second light guide 110B or 10. Here, as an example, a point on the plane 54A is ray traced to a point on the plane 54B.

[0069] If the two light guides have similar dimensions, the optical relay advantageously has equal magnification, in which case the two lenses (or lens arrangements) 66A and 66B are advantageously identical and can be inverted, making the optical relay optically symmetric about the real image plane, thereby canceling most optical aberrations. As a result, no optical power is lost and the image is not distorted.

[0070] Figure 15B shows the same functionality as Figure 15A, but now the refractive optics have been replaced by reflective optics. The optical relay is now implemented using a polarizing beam splitter (PBS) prism 68, which has a diagonal PBS 69 with reflective lenses 66A and 66B on two faces of the prism. In this case, the polarization of the light at 110 is preferably controlled to minimize losses. As known in the art, quarter wave plates are used before each reflective lens to manage the reflection-transmission-reflection sequence at the PBS.

[0071] The diagrams in Figures 15A and 15B are schematic top views. In a particular preferred implementation, the coupling-out prism 64A can be designed to combine the quadruple beams / images propagating in the rectangular light guide 110A into a single output beam / image for coupling into a second light guide, thereby allowing smaller optics 66A and 66B and facilitating any orientation between the light guides 110A and 10 / 110B. Alternatively, the prism 64A may be designed to convert the quadruple propagating image into two output images (using a wedge similar to the coupling-in configuration of the 1D light guide). In this case, the two images are coupled between the light guides, the orientation must be maintained between the two light guides, and the relay optics 66A / B would be larger.

[0072] FIG. 16 shows a schematic arrangement similar to FIG. 15A, in which a corner-configured coupling-out prism 64A is used to output a single image from a first rectangular light guide 110A, and a similar coupling prism is used to couple the relayed image into a second rectangular light guide 110B. These prisms preferably include two vertical surfaces that support internal reflection, which are coplanar continuations of, or at least parallel to, the corresponding surfaces of the rectangular light guide 110A, as described in detail in the aforementioned U.S. Pat. No. 10,133,070, particularly in its FIGS. 6-9B. The non-limiting implementation shown here uses unity magnification (1:1), but transitions from a smaller aperture 54A in the first light guide to a larger aperture 54B in the second light guide. To aid in filling the entrance aperture of the second light guide, a beam spreading element 67 may be advantageously deployed at the real image plane. The beam spreading element is typically a microlens array (MLA) or may be a diffuser.

[0073] Figure 17 shows a similar arrangement in which the second light guide is a 1D (slab) light guide 10 and the coupling-in prism 64B is accordingly a simple prism similar to prism 8 above, with a single reflective surface parallel to one of the major surfaces of the light guide.

[0074] As mentioned above, the aspects of the invention shown in Figures 15A-17 are not limited to any particular type of light source or image generation technology. In addition to the main example of an MLED array monochrome projector, these configurations can also be advantageously used where the image introduced into the light guide 110A is formed by a modulated laser with a scanning arrangement, or by a liquid crystal on silicon (LCOS) chip display, DLP device, LCD, or any other image generator. The system may use separate image projectors for each color separately coupled to the light guide as shown, or a single projector generating a color image may be coupled to the light guide 110A. Optionally, the different injected colors can be generated by using different technologies, for example, a green scanning laser combined with red and blue micro LED arrays.

[0075] If the light guide 10 / 110B has an internal aperture extension (as exemplified above with reference to the light guides of FIGS. 2A-9B), the image from the exit aperture 54A projected onto the entrance aperture 54B may be smaller than the size of the entrance aperture 54B. Alternatively, if this image is the same size as or larger than the entrance aperture 54B, the light guide 10 / 110B will be uniformly illuminated.

[0076] Optionally, the optical system 66A / 66B can magnify the image at the exit aperture 54A that reaches the entrance aperture 54B, which means that for a collimated image the angular range covered by the field of view is reduced. Such magnification would also entail adjusting the angle between the light guide 110A and the light guide 10 / 110M, so that the angle between the exit aperture (plane) 54A and the entrance aperture (plane) 54B changes, since the longitudinal magnification is the square of the lateral magnification.

[0077] Note that the propagation angle of the image in light guide 110A (relative to the axis of the light guide) is not necessarily the same as the propagation angle of the image in light guide 10 or 110B, as long as the entire field of view of the image falls within the angular range for internal reflection and does not intersect the plane of symmetry of the light guide. The use of different propagation angles in the light guides provides further design flexibility by allowing adjustment of angles between the light guides.

[0078] In certain preferred implementations, light guides 110A and 10 / 110B may be implemented to be mechanically decoupled and allow for folding of light guide 110A relative to light guide 10 / 110B. Implementation of light guide 110A as part of a temple (or side) of an eyeglass frame, with a hinge or other folding mechanism, facilitates compact storage of the eyeglasses.

[0079] It will be understood that the above description is intended to serve as an example only, and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. A display, (a) a light guide having a pair of mutually parallel major surfaces, the pair of mutually parallel major surfaces supporting propagation of light within the light guide by internal reflection at the major surfaces; (b) a first image projector comprising a first monochrome image generator and a first collimating optic, the first image projector outputting collimated light of a first color corresponding to a first component of an image, the first image projector optically coupled to the light guide to introduce the collimated light of the first color into the light guide for propagation within the light guide in a first in-plane direction; (c) a second image projector comprising a second monochrome image generator and a second collimating optic, the second image projector outputting collimated light of a second color corresponding to a second component of the image, the second image projector optically coupled to the light guide such that the second image projector introduces the collimated light of the second color into the light guide for propagation within the light guide in a second in-plane direction non-parallel to the first in-plane direction; (d) a dichroic reflector embedded within the light guide and oriented perpendicular to the major surface, bisecting an angle between the first in-plane direction and the second in-plane direction, the dichroic reflector being transmissive to the first color and reflective to the second color to redirect the light of the second color to be combined with the light of the first color and propagate within the light guide in the first direction.

2. 2. The display of claim 1, further comprising a first set of mutually parallel partially reflective surfaces embedded within the light guide for gradually redirecting light of both the first color and the second color to propagate in a polarized direction within the light guide, the first set of partially reflective surfaces being parallel to the dichroic reflector.

3. 2. The display of claim 1, wherein an optical path length from the first image projector to the dichroic reflector is equal to or differs from an optical path length from the second image projector to the dichroic reflector by less than 20 percent.

4. (a) a third image projector comprising a third monochrome image generator and a third collimating optic, the third image projector outputting collimated light of a third color corresponding to a third component of the image, the third image projector optically coupled to the light guide to introduce the collimated light of the third color into the light guide for propagation within the light guide in a third in-plane direction; 13. The display of claim 1, further comprising: (b) a second dichroic reflector embedded within the light guide, oriented perpendicular to the major surface, and configured to redirect the light of the third color to combine it with the light of at least one of the first and second colors, such that the dichroic reflector and the second dichroic reflector together combine the light of the first, second, and third colors.

5. 5. The display of claim 4, wherein the third direction is parallel to the second direction and the second dichroic reflector is parallel to the dichroic reflector.

6. The collimated light of at least one of the first and second colors propagates within a first region of the light guide, and the display comprises: (a) a third image projector comprising a third monochrome image generator and a third collimating optic, the third image projector outputting collimated light of a third color corresponding to a third component of the image, the third image projector being optically coupled to the light guide such that the third image projector introduces the collimated light of the third color through a coupling-in area of ​​a first one of the major surfaces in the first region of the light guide for propagating within the light guide together with the light of the at least one of the first and second colors; 2. The display of claim 1, further comprising: (b) an in-plane dichroic reflector associated with the coupling-in area and coplanar with the first major surface of the light guide, the in-plane dichroic reflector being reflective to the at least one of the first and second colors to support the light of the at least one of the first and second colors propagating within the light guide through the first region by internal reflection, and being transmissive to the third color to enable coupling-in of the light of the third color into the light guide.

7. 10. The display of claim 1, further comprising a rectangular light guide having a first pair of parallel surfaces and a second pair of parallel surfaces perpendicular to the first pair of parallel surfaces, the light guide coupled to the rectangular light guide to introduce the light of the first and second colors into the rectangular light guide for propagation within the rectangular light guide by quadruple internal reflection.

8. A display, (a) a light guide having first and second mutually parallel major surfaces, the first and second mutually parallel major surfaces supporting propagation of light within the light guide by internal reflection at the first and second major surfaces; (b) a first image projector comprising a first monochrome image generator and a first collimating optic, the first image projector outputting collimated light of a first color corresponding to a first component of an image, the first image projector optically coupled to the light guide to introduce the collimated light of the first color into the light guide for propagation within a first region of the light guide in a first in-plane direction; (c) a second image projector comprising a second monochrome image generator and a second collimating optic, the second image projector outputting collimated light of a second color corresponding to a second component of the image, the second image projector optically coupled to the light guide such that the second image projector introduces the collimated light of the second color through a coupling-in area of ​​the first major surface in the first region of the light guide to propagate together with the light of the first color within the light guide in the first in-plane direction; (d) a dichroic reflector associated with the coupling-in area and coplanar with the first major surface of the light guide, the dichroic reflector being reflective to the first color to support the light of the first color propagating through the first region within the light guide by internal reflection, and being transmissive to the second color to enable coupling-in of the light of the second color into the light guide.

9. 9. The display of claim 8, wherein the second image projector is optically coupled to the light guide via a transmissive prism mounted in the coupling-in area.

10. 9. The display of claim 8, wherein the second image projector is optically coupled to the light guide via a reflective surface integral with a prism mounted in the coupling-in area.

11. 11. The display of claim 10, wherein the second image projector is arranged to inject the light of the second color through the second major surface such that the light of the second color traverses a thickness of the light guide so as to be coupled into the light guide, is transmitted by the dichroic reflector, is reflected by the reflective surface, and is transmitted again by the dichroic reflector.

12. the light of the first and second colors propagates together in the first in-plane direction within a second region of the light guide, and the display comprises: (a) a third image projector comprising a third monochrome image generator and a third collimating optics, the third image projector outputting collimated light of a third color corresponding to a third component of the image, the third image projector being optically coupled to the light guide such that the third image projector introduces the collimated light of the third color through a second coupling-in area of ​​the first major surface or the second major surface in the second region of the light guide such that the collimated light of the third color propagates in the first in-plane direction within the light guide together with the light of the first and second colors; 9. The display of claim 8, further comprising: (b) a second dichroic reflector associated with the second coupling-in area and substantially coplanar with the first major surface or the second major surface, the second dichroic reflector being reflective to the first and second colors to support the light of the first and second colors propagating within the light guide and through the second region by internal reflection, and being transmissive to the third color to enable coupling-in of the light of the third color into the light guide.

13. 13. A display as claimed in claim 12, wherein the coupling-in area and the second coupling-in area are in overlapping relationship on opposing major surfaces of the light guide.

14. 9. The display of claim 8, further comprising a rectangular light guide having a first pair of parallel surfaces and a second pair of parallel surfaces perpendicular to the first pair of parallel surfaces, the light guide coupled to the rectangular light guide to introduce the light of the first and second colors into the rectangular light guide for propagation within the rectangular light guide by quadruple internal reflection.

15. 15. The display of claim 7 or 14, wherein an end of the rectangular light guide is optically coupled to a slab light guide having a coupling-out configuration for coupling out light propagating in the slab light guide towards a user's eye.

16. 14. A display according to any one of claims 1 to 6 and 8 to 13, further comprising a set of mutually parallel partially reflective coupling-out surfaces embedded within the light guide at an oblique angle to the major surfaces so as to gradually reflect the light propagating within the light guide so as to redirect both the first and second color light from the light guide towards a user's eye.

17. A light guide arrangement, (a) a first rectangular light guide having a first pair of parallel surfaces and a second pair of parallel surfaces perpendicular to the first pair of parallel surfaces to support light propagation by quadruple internal reflection, the first rectangular light guide having a first extension direction parallel to a line of intersection between one of the first pair of parallel surfaces and one of the second pair of parallel surfaces; (b) a second light guide having at least a first pair of parallel surfaces for supporting propagation of light by internal reflection, the first pair of parallel surfaces being non-parallel to the first direction of extension; and (c) an optical relay optically coupled between the first rectangular light guide and the second light guide, the optical relay relaying a collimated image propagating in the first rectangular light guide through a real image plane to a collimated image propagating in the second light guide.

18. 20. The light guide arrangement of claim 17, wherein the optical relay is configured to image an output aperture plane of the first rectangular light guide onto an input aperture plane of the second light guide.

19. 20. The light guide arrangement of claim 17, wherein the optical relay has unity magnification.

20. The light guide arrangement of claim 17 , wherein the optical relay is optically symmetric about the real image plane.

21. 20. The light guide arrangement of claim 17, wherein the optical relay is optically coupled to each of the first rectangular light guide and the second light guide via a coupling prism.

22. 20. The light guide arrangement of claim 17, wherein the optical relay comprises a polarizing beam splitter prism having reflective lenses on two faces of the prism.

23. 20. The light guide arrangement of claim 17, wherein the second light guide is a rectangular light guide having a second pair of mutually parallel major surfaces perpendicular to the first pair of major surfaces to support light propagation by quadruple internal reflection.

24. 20. The light guide arrangement of claim 17, wherein the optical relay further comprises a beam spreading element disposed at the real image plane.

Images