Optical system including a light guide optical element for two-dimensional expansion having a retarder element

Abstract

An optical system for directing image illumination incident at a coupling input region to an eye movement box for viewing by a user's eyes, comprising a light-directing optical element (LOE) formed from a transparent material, the LOE including a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation, a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation, a set of mutually parallel major outer surfaces extending across the first and second regions, and an optical retarder disposed between the first and second regions to rotate the polarization of light deflected by the first set of partially reflective surfaces before reaching the second set of partially reflective surfaces.

Description

Technical Field

[0001] The presently disclosed subject matter relates to optical systems, and more particularly, to optical systems including a light guiding optical element (LOE) configured for two-dimensional image expansion.

Background Art

[0002] In recent years, there has been an increasing demand among consumers for "smart" eyewear such as head-mounted displays (HMDs) and augmented reality (AR) glasses, collectively referred to as near-eye display systems. Therefore, in this rapidly evolving technical field, there is a growing need for optical systems that are smaller and lighter while providing a relatively large field of view (FOV) and generating bright and high-quality images.

[0003] Among known optical systems, there are those that use a waveguide (also referred to herein as a "light guide", "light guide optical element", or "LOE") to expand an input image by propagating an image along a substrate in which one or more sets of partially reflective inner surfaces ("facets") are embedded. One of the known problems of this type of optical system is that a small amount of light is lost due to polarization mismatch between partial reflections from non-parallel facets.

Summary of the Invention

Means for Solving the Problems

[0004] According to one aspect of the presently disclosed subject matter, there is provided an optical system for directing image illumination incident on a coupling input region towards an eye movement box for visual recognition by a user's eye, the optical system including a light guiding optical element (LOE) formed from a transparent material, the LOE having a first region that is planar with a first orientation and includes a first set of mutually parallel partial reflecting surfaces, a second region that is planar with a second orientation non-parallel to the first orientation and includes a second set of mutually parallel partial reflecting surfaces, and a set of mutually parallel major outer surfaces, the major outer surfaces extending across the first and second regions such that both the first set of partial reflecting surfaces and the second set of partial reflecting surfaces are located between the major outer surfaces, the second set of partial reflecting surfaces being at an oblique angle to the major outer surfaces such that a portion of the image illumination propagating from the first region into the second region within the LOE by internal reflection at the major outer surfaces is coupled out of the LOE towards the eye movement box, and the first set of partial reflecting surfaces being oriented such that a portion of the image illumination propagating from the coupling input region within the LOE by internal reflection at the major outer surfaces is deflected towards the second region, the LOE further including an optical retarder disposed between the first and second regions to rotate the polarization of the light deflected by the first set of partial reflecting surfaces before it reaches the second set of partial reflecting surfaces.

[0005] According to some aspects, the optical system includes a small image projector (POD) optically coupled to the LOE such that image illumination is incident on the coupling input region of the LOE such that the image illumination is confined in one dimension by internal reflection at a set of major outer surfaces.

[0006] According to some aspects, the POD is configured to generate a collimated image collimated to infinity such that the image illumination extends over an angular range corresponding to a two-dimensional angular field of view.

[0007] According to some aspects, the first set of partial reflecting surfaces is oriented perpendicular to the major outer surfaces of the LOE.

[0008] According to some aspects, both the image illumination and the conjugate of the image illumination are deflected to a second region.

[0009] According to some aspects, the first set of partial reflective surfaces is oriented obliquely with respect to the major outer surface of the LOE.

[0010] According to some aspects, either the image illumination or the conjugate of the image illumination is deflected to a second region.

[0011] According to some aspects, the first set of partial reflective surfaces continuously reflects a portion of the image illumination propagating within the first region such that the image illumination undergoes an expansion in a first dimension.

[0012] According to some aspects, the second set of partial reflective surfaces continuously reflects a portion of the image illumination propagating within the second region such that the image illumination undergoes an expansion in a second dimension.

[0013] According to some aspects, the first region is configured to achieve an aperture expansion in one of the X-axis direction or the Y-axis direction, and the second region is configured to achieve an aperture expansion in the other of the X-axis direction or the Y-axis direction.

[0014] According to some aspects, the first and second sets of partial reflective surfaces are implemented as an internal surface coated with a dielectric thin film coating configured to reflect light impinging on the internal surface over a predetermined angular range.

[0015] According to some aspects, the retarder is disposed within the LOE such that it extends between the major outer surfaces substantially perpendicular to the major outer surface.

[0016] According to some aspects, the retarder is disposed within the LOE such that it extends between the major outer surfaces at an oblique angle to the major outer surface.

[0017] According to some embodiments, the retarder is disposed within the LOE so as to be oriented substantially parallel to the major outer surface.

[0018] According to some embodiments, the retarder is oriented substantially adjacent to one of the major outer surfaces.

Brief Description of the Drawings

[0019] To understand the present invention and to see how it can be actually implemented, embodiments will be described by way of non-limiting examples with reference to the accompanying drawings:

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 2A

Figure 2B

Figure 3

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Figure 6A

Figure 6B

Figure 6C

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Figure 9

[0020] In the following detailed description, in order to provide a thorough understanding of the present invention, details of numerous specific examples are set forth. However, it will be understood by those skilled in the art that the presently disclosed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the disclosed subject matter.

[0021] As background, near-eye displays that use waveguides for image magnification typically include, or are coupled to, a projector that injects an image into a waveguide comprising a transparent substrate that propagates the image by total internal reflection (TIR) between parallel outer surfaces of the waveguide. Optical elements, such as partially reflective inner surfaces embedded within the waveguide, redirect the image either toward the viewer in the case of a one-dimensional waveguide or toward a second waveguide in the case of a two-dimensional waveguide. In the latter case, the second waveguide can propagate the image along an axis orthogonal to the first waveguide again via TIR, and the image can be magnified two-dimensionally. Facets embedded within the second waveguide couple the magnified image out toward the viewer.

[0022] Although the present disclosure is mainly related to a partial reflecting surface as a coupling output method, it should be noted that the techniques described herein can be similarly applied to waveguides employing other optical coupling output elements (such as diffraction elements or combinations of reflecting and diffraction elements, etc.) with appropriate modifications, as will be detailed below with reference to FIGS. 9A - 9B. Similarly, although the present disclosure is mainly related to waveguides configured mainly for two - dimensional image expansion, the techniques disclosed herein can also be applied to one - dimensional waveguides with appropriate modifications that would be known to those skilled in the art.

[0023] FIGS. 1A and 1B schematically show an exemplary implementation of a known device in the form of a near - eye display, generally designated 10, in which the LOE 12 can be deployed. The near - eye display 10 uses a small image projector (or "POD") 14 optically coupled to the LOE 12 such that an image (also referred to herein as "image illumination") is incident on the LOE 12 and the image light is confined in one dimension by internal reflection at a series of mutually parallel planar outer surfaces of the LOE 12. The light impinges on one set of facets that are parallel to each other and inclined obliquely with respect to the propagation direction of the image light, and each successive facet deflects a certain percentage of the image light, which is confined within the substrate / induced by internal reflection, in a deflection direction. This first set of facets is located in a first region of the LOE shown as region 16, although not individually shown in FIGS. 1A and 1B. The partial reflection in this successive set of facets achieves an optical aperture expansion in the first dimension.

[0024] In some embodiments, the set of facets described above is orthogonal to the major outer surface of the substrate. In this case, both the incident image and its conjugate that undergoes internal reflection when propagating within region 16 are deflected and become conjugate images propagating in the deflection direction. In other embodiments, the first set of facets is angled obliquely with respect to the major outer surface of the LOE. In the latter case, either the incident image or its conjugate forms the desired deflected image propagating within the LOE, while other reflections can be minimized by using, for example, an angle-selective coating on the facets that renders them relatively transparent to the range of incident angles presented by images for which reflection is not desired.

[0025] The first set of facets deflects the image illumination from a first propagation direction confined within the substrate by total internal reflection (TIR) to a second propagation direction also confined within the substrate by TIR. The deflected image illumination then enters a second substrate region 18 that can be implemented as an adjacent separate substrate or as an extension of a single substrate, within which a coupling output arrangement (a further set of partial reflection facets or a diffractive optical element) gradually couples out a portion of the image illumination towards the observer's eye located within the region defined as the eye movement box, thereby achieving a second dimension of optical aperture expansion.

[0026] The entire device 10 may be implemented separately for each eye and, preferably, each LOE 12 is supported relative to the user's head with the LOE facing the corresponding eye of the user. In one particularly preferred option as shown here, the support configuration is implemented as an eyeglass frame having side portions 20 for supporting the device relative to the user's ears. Other forms of support configurations may also be used, including but not limited to devices suspended from a headband, a visor, or a helmet.

[0027] In this specification, in the drawings and the claims, an X-axis extending horizontally (FIG. 1A) or vertically (FIG. 1B) in the general extending direction of the first region of the LOE, and a Y-axis extending perpendicular thereto, i.e., vertically in FIG. 1A and horizontally in FIG. 1B, are referred to.

[0028] Very roughly speaking, the first region 16 of the LOE 12 can be regarded as achieving an opening expansion in the X direction, while the second region 18 of the LOE 12 achieves an opening expansion in the Y direction. The orientation as shown in FIG. 1A can be regarded as a "top-down" implementation mode in which the image illumination entering the main part (the second region) of the LOE enters from the upper edge, and it should be noted that the orientation shown in FIG. 1B can be regarded as a "side-incidence" implementation mode in which the axis here referred to as the Y-axis is horizontally extended. In the remaining drawings, various features of the specific embodiments of the present invention are illustrated in the context of either the top-down orientation or the side-incidence, but it should be understood that all of those features are equally applicable to both embodiments.

[0029] The POD used in the device of the present invention is preferably configured to generate a collimated image, i.e., an image in which the light of each image pixel is a parallel beam collimated to infinity in the angular direction corresponding to the pixel position. Therefore, the image illumination extends over an angular range corresponding to the two-dimensional viewing angle.

[0030] The image projector 14 includes at least one light source typically provided for illuminating 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 the image. Alternatively, the image projector can include an array of LEDs (typically implemented using a micro-LED array or an OLED array) or a scanning arrangement (typically implemented using a high-speed scanning mirror), and while scanning the illumination from the laser light source across the image plane of the projector, the intensity of the beam varies pixel by pixel in synchronization with the movement, thereby projecting the desired intensity onto each pixel. In either case, a collimating optical system is 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 splitter (PBS) cubes or other prism configurations, as is well known in the art.

[0031] The optical coupling of the image projector 14 to the LOE 12 can be achieved by any suitable optical coupling, such as via one of the side edges and / or major outer surfaces of the LOE, for example via a coupling prism having an obliquely angled input surface or via a reflective coupling configuration. The details of the coupling input configuration are not important for the present invention and are schematically shown here as a wedge prism 15, which is a non-limiting example applied to one of the major outer surfaces of the LOE.

[0032] It will be understood that the near-eye display 10 includes various additional components, typically employing power from a small on-board battery (not shown) or some other suitable power source, and typically including a controller 22 for operating the image projector 14. The controller 22 will be understood to include all necessary electronic components, such as at least one processor or processing circuit for driving the image projector, as is all known in the art.

[0033] Figures 1C-1D schematically illustrate other embodiments of an existing near-eye display system 10 with three types of embedded elements. Similar to FIGS. 1A-1B, the projector (POD) 14 projects an image onto the LOE 12, whereupon the light is one-dimensionally confined by TIR in a region between two parallel major outer surfaces of the LOE. The light rays of the image propagate through the waveguide at an angular orientation until they are reflected by one of two sets of mutually parallel facets in regions 16a and 16b. These two mutually parallel facets redirect the light rays to different angular orientations and are one-dimensionally confined by TIR in a region between two parallel major surfaces of the LOE. Thereafter, the light rays are reflected a second time by the facets of regions 16a and 16b, respectively, so as to return to their original orientation when incident on the LOE. Finally, the light rays are reflected by a third set of mutually parallel facets in region 18 that redirect the light rays such that the incident image is coupled out of the LOE and propagates towards the eye movement box where the observer's eye is located.

[0034] Referring now to FIG. 2A, the optical characteristics of an embodiment of the near-eye display are illustrated in more detail. Specifically, a more detailed view of a light guiding optical element (LOE) 12 formed from a transparent material is shown, which includes a first region 16 having a planar first set of partially reflective surfaces 17 that are parallel to each other and have a first orientation, and a second region 18 having a planar second set of partially reflective surfaces 19 that are parallel to each other and have a second orientation that is non-parallel to the first orientation. A set of mutually parallel major outer surfaces 24 extends across the first and second regions 16 and 18 such that both the first set of partially reflective surfaces 17 and the second set of partially reflective surfaces 19 are located between the major outer surfaces 24. Most preferably, the set of major outer surfaces 24 is a pair of surfaces that are each continuous across the entirety of the first and second regions 16 and 18, although options having a step-down or step-up in thickness between region 16 and region 18 are also within the scope of the present invention. Regions 16 and 18 may be directly juxtaposed so as to meet at a boundary, which may be a straight boundary or some other form of boundary, or, depending on the particular application, one or more additional LOE regions may be interposed between those regions to provide various additional optical or mechanical functions. The present invention is not limited to any particular manufacturing technique, but in a particularly preferred implementation, a continuous outer plate is employed in which separately formed regions 16 and 18 are sandwiched therebetween to form a composite LOE structure, thereby achieving particularly high-quality major outer surfaces.

[0035] The optical characteristics of the LOE can be understood by tracing the image illumination path in reverse. The second set of partially reflective surfaces 19 is angled with respect to the major outer surface such that, by internal reflection at the major outer surface, a portion of the image illumination propagating within the LOE 12 from the first region 16 into the second region 18 is coupled out towards the eye movement box 26 from the LOE. The first set of partially reflective surfaces 17 is oriented such that, by internal reflection at the major outer surface, a portion of the image illumination propagating within the LOE 12 from the coupling input region (coupling prism 15) is deflected towards the second region 18.

[0036] One dimension of the angular spread of the projected image from the image projector 14 is represented, in FIG. 2A, by the illumination of a cone that spreads from the POD aperture on the right side of the LOE towards the left side of the LOE (projected onto the plane of the major outer surface 24). In the non-limiting example shown herein, the central optical axis of the POD defines the propagation direction within the LOE aligned with the X axis, and the angular spread (within the LOE) is approximately ±16°. (Note that the FOV angle is larger in air due to the change in refractive index.) The first set of partially reflective surfaces 17 is shown in the first region 16, and the second set of partially reflective surfaces 19 is shown in the second region 18.

[0037] The near-eye display is designed to provide the full FOV of the projected image to the user's eye located at a position within the permitted position range specified by the eye movement box (EMB) 26 (i.e., a shape typically represented as a rectangle that is away from the plane of the LOE where the pupil of the eye would view the projected image). To reach the eye movement box, light must be coupled out from the second region 18 towards the EMB 26 by the second set of partially reflective surfaces 19. To provide the full image field of view, each point within the EMB must receive an image over the full angular range from the LOE. Backtracking the field of view from the EMB suggests a larger rectangle 28 where the associated illumination is coupled out from the LOE towards the EMB.

[0038] FIG. 2A shows the first end portion of the field of view corresponding to the lower left pixel of the projected image. A beam of width corresponding to the optical aperture of the projector when coupled within the LOE is shown to propagate from the POD towards the upper left and be partially reflected from a series of partially reflective surfaces 17. As shown herein, only a subset of the facets produce reflections useful for providing the corresponding pixels in the image viewed by the user, and only a sub-region of those facets contribute to the observed image of this pixel. The relevant regions are indicated by thick black lines, and the light rays corresponding to this pixel in the redirected image that are reflected from the facet 17 and then coupled out by the facet 19 to reach the four corners of the EMB 26 are shown.

[0039] Here, throughout the description, only the in-plane propagation direction of the light rays, which is here during propagation within the LOE, is shown, but the light rays actually follow a zigzag path of multiple internal reflections repeated from two main outer surfaces, and it should be noted that the entire one-dimensional image field of view is encoded by the tilt angle of the light rays with respect to the main outer surface corresponding to the pixel positions in the Y dimension. As an additional example, the deflected and coupled output light rays corresponding to the upper left end of the image, as seen in the upper left corner of the EMB, are shown by the dashed lines. FIG. 2B schematically shows the state where the LOE of FIG. 2A is rotated by 90 degrees and the light rays and the eye movement box are removed from FIG. 2A to assist in visualizing the LOE.

[0040] Facets 17 and 19 are implemented as internal surfaces coated with a partially reflective coating, preferably a dielectric thin film coating, and are specifically designed to partially reflect light impinging on the surface over a predetermined angular range, each angle being associated with a predetermined field, and the angular range being thereby associated with the full FOV of the projected image. It should be noted that the light impinging on the facets includes light of different wavelengths over a relatively broad wavelength spectrum determined by the illumination source. Further, generally speaking, the incident image may be polarized or non-polarized, and in each case the facet coating must be designed accordingly. For example, if the incident image is non-polarized (i.e., includes both p-polarized and s-polarized light), a coating that takes into account the reflection of light rays of both p-polarized and s-polarized light needs to be designed.

[0041] By definition, the polarization state of light is defined according to the angular orientation of a particular light ray (i.e., the field k-vector, the orientation of a plane wave) with respect to the normal of the surface that the light ray impinges on. Thus, a polarized incident light ray may have one polarization state compared to one surface and a different polarization state compared to a different surface. Thus, when light propagates within an optical system having multiple surfaces, it is clear that the polarization state of the impinging light ray is defined according to the direction of the incident light ray and the angular orientation of the surface that the light ray impinges on. As is clear from FIG. 2A, when light propagates through a near-eye display, the light impinges on parallel outer surfaces (also referred to herein as "faces") 24, a first set of facets and a second set of facets, each of which has a different angular orientation relative to one another. Thus, a polarized light ray associated with a certain field can be expressed as having a first polarization state relative to the LOE face 24, a second polarization state relative to the facet 17, and a third polarization state relative to the facet 19. Since the polarization state of a light ray with respect to a surface affects the reflectivity of the light ray from that surface, ideally, the partial reflection coating of the facet 17 needs to be designed in a different way than the partial reflection coating of the facet 19 in order to achieve a sufficiently high reflectivity for each set of facets. Furthermore, it is often extremely difficult to design an optical coating that has the required optical properties in a certain polarization and angular range. For example, it is extremely difficult, if possible at all, to design a coating with a high reflectivity for p-polarization near the Brewster angle. Thus, the polarization mismatch of the illumination light between the first and second sets of facets 17 and 19 limits the feasibility of realizing certain coating requirements and may force a compromise with respect to the initial polarization state. Furthermore, if the polarization state with respect to the main outer surface 24 at any point along the LOE 12 is a combination of s-polarization and p-polarization, the polarization rotates during TIR, resulting in significant differences in the reflectivity of light from different facets for different fields, which may often result in black lines in the output image.

[0042] As described above, the drawback of the existing LOE is that the polarization of the incident light varies in different regions of the LOE and can be different for different sets of facets and for the major outer surface of the LOE. For this reason, the polarization with respect to the major surface of the incident image often leads to "impurity". Since TIR induces different phases for s-polarization and p-polarization, the polarization of the incident image may rotate and change when light propagates within the LOE. Therefore, the design of the thin optical coating of the facet becomes extremely complicated, and there is a possibility that the output efficiency decreases or local or overall non-uniformity occurs in the projected output image.

[0043] Also, as described above, the reflectance when a certain ray collides with the surface changes according to the polarization state of the ray with respect to the surface. FIG. 3 shows the reflectance as a function of the incident angle of an exemplary coating design for the first and second facets. As is clear, near the Brewster angle, the reflectance of p-polarization becomes zero. For this reason, usually, the light propagating through the display is preferably s-polarized, or at least mostly s-polarized, with respect to facets 17 and 19 for maximum efficiency and simplification of the coating design.

[0044] Therefore, the inventors have found that the efficiency and simplicity of a near-eye display system using an LOE configured for two-dimensional expansion can be improved by rotating the polarization of the light propagating between the first set of facets and the second set of facets to always be s-polarized (or at least mostly s-polarized) with respect to both sets of facets. Note that "efficiency" means that more projection light initially coupled and input into the near-eye display system is reflected towards the viewer, resulting in a brighter and / or more uniform output image.

[0045] Figure 4 schematically shows an embodiment of an LOE similar to that shown in Fig. 2B, where an optical retarder 40 is disposed along the optical path between facet 17 (which is orthogonal to the outer surface in the illustrated embodiment) and facet 19 and is configured to rotate the polarization of light after reflection from facet 17 and before reflection from facet 19. Thus, assuming that the light input to the LOE is s-polarized with respect to facet 17, after reflection from facet 17, the light will be mostly p-polarized with respect to facet 19. Thereafter, retarder 40 rotates the polarization so that the light is s-polarized (or at least mostly s-polarized) with respect to facet 19. Now, since both facet 17 and 19 reflect s-polarized light with respect to the respective surfaces of each set of facets, there is no need to separately consider the coating design. Further, due to the retarder, the light propagating inside the waveguide is almost pure polarized compared to the major outer surface, so that the polarization of the light propagating inside the waveguide does not rotate due to TIR. As will be described in more detail below, retarder 40 can be implemented in various ways including, but not limited to, including a half-wave plate.

[0046] As shown in FIGS. 5A-5E, retarder 40 can be physically disposed at various possible locations within the LOE and oriented at various different angles. For example, as shown in FIG. 5A, the retarder can extend between parallel planes across the thickness of the LOE (the z-axis in the drawing) and be oriented substantially perpendicular to the plane of the LOE. FIG. 5B shows another configuration where retarder 40 is oriented obliquely with respect to the plane of the LOE and non-parallel to facet 19. FIG. 5C shows a further configuration where retarder 40 is oriented parallel to facet 19.

[0047] FIG. 5D shows yet another configuration where retarder 40 is oriented parallel to the plane of the LOE and is physically located at a point between the planes, which may be the midpoint between the planes but is not necessarily so limited. Finally, FIG. 5E shows yet another configuration where retarder 40 is oriented parallel to the plane of the display and is physically located adjacent to one of the planes.

[0048] Note that in all cases, the size, position, and / or angle of the retarder should be determined such that all, or substantially all, of the light reflected from facet 17 passes through the retarder before being reflected by facet 19.

[0049] Furthermore, note that while the function that the retarder has been described as performing so far has only been to rotate the polarization of light, in some cases it may be desirable for the retarder to perform additional functions. For example, referring to the configuration shown in Figure 5D, the retarder 40 can include a coating having a reflectivity of 50%. Thereby, the retarder 40 additionally functions as a "mixer" and can improve the intensity uniformity of the output image by mixing the propagated light rays. Near-eye displays with embedded mixer elements have been previously described in PCT Publication WO2021001841A1.

[0050] The retarder 40 can be implemented in various ways including, but not limited to, as a half-wave plate or as a coated inner surface. Suitable coatings include, for example, dielectrics, birefringents, thin-film polymers, crystalline retarders, geometric phase grating retarders, etc. In some embodiments, as in the configuration shown in Figure 5C, the retarder can be implemented as a coating applied to the first facet in a second set of facets.

[0051] Next, an exemplary manufacturing method of an LOE having a retarder element will be described with reference to Figures 6A - 8E.

[0052] Figures 6A - 6C schematically show known methods for manufacturing an optical retarder suitable for deployment within an LOE. In Figure 6A, for example, a retarder is manufactured from a crystalline material such as quartz. A first transparent crystal plate 42 made of a birefringent material is adhered to a transparent substrate 41. The substrate 41 is preferably made of the same material as the LOE. Thereafter, the bonded structure is thinned, for example, by double-sided polishing until the birefringent material reaches the required thickness. Figures 6B - 6C show alternative methods by which the retarder can be manufactured, either by coating a dielectric coating (homogeneous or inhomogeneous) onto the substrate 41 (Figure 6B), or by adhering a polycrystalline thin film to the substrate 41 (Figure 6C).

[0053] Next, an LOE region incorporating a second set of facets is formed according to known methods. Figure 7A schematically shows forming an LOE region 18 by stacking and adhering a series of flat, transparent, coated plates 38 and slicing the stack along an oblique plane parallel to the flat surfaces of the plates (Figure 7A). Thereafter, the slices are polished to form a plurality of LOE regions 18 (Figure 7B). The region 16 can be formed in a similar manner.

[0054] Two alternative methods have been proposed for forming the final LOE structure including the retarder. Figures 7C - 7D show a first method of forming the final LOE (Figure 7D) by adhering a single retarder element to a single LOE region 16 on one side and a single LOE region 18 on the opposite side (Figure 7C).

[0055] The second method, as shown in FIGS. 8A - 8B, involves laminating and bonding a plurality of LOE regions 18 (FIG. 8A), and bonding a retarder element spanning the thickness of the laminate 18' to the end of the laminate (FIGS. 8B - 8C). Next, as shown in FIGS. 8D - 8E, a block 16' of material representing a plurality of LOE regions 16 that have been formed but not sliced (i.e., those produced at an intermediate stage in the manufacture of the LOE regions 16) is bonded to the opposite side of the retarder element, and the combined block is sliced into a plurality of LOEs (FIG. 8E), each containing a retarder embedded between two sets of facets.

[0056] In each of the above alternative methods, the final LOE may require shaping and polishing of both surfaces for accurate parallelism between the surfaces. In some embodiments, a transparent cover plate may be adhered to the surface, as is known in the art.

[0057] The present invention has thus far been described herein mainly in the context of LOEs based on partially reflective internal surfaces, but it will also be understood that the principles of the present invention can also be advantageously implemented in light guiding optical elements that use diffractive optical elements (DOEs) to achieve one or both of the expansion of the light aperture and / or the coupling output of image illumination from the waveguide towards the observer.

[0058] As a non-limiting example, FIGS. 9A-9B show an example of an embodiment of an optical system for directing image illumination incident in a coupling input region, which is implemented using a diffractive waveguide, toward an eye movement box for viewing by a user's eye. The optical system is formed from a transparent material and includes a first region including a first DOE 27, a second region including a second DOE 29, and an LOE 12 including one set of mutually parallel major outer surfaces 24. The major outer surfaces extend across the first and second regions such that both the first DOE 27 and the second DOE 29 are positioned between the major outer surfaces 24. In the embodiment shown in FIG. 9A, the image illumination is incident at one end of the first region and propagates in one direction along the length of the first region until it is deflected by one or more DOEs 27 into the second region. In the embodiment of FIG. 9B, the image illumination is incident at the center of the first region and propagates in the opposite direction until it is deflected by two or more DOEs 27a, 27b into the second region. In either case, the image illumination is coupled out from the second region to an eye movement box (not shown) by one or more DOEs 29.

[0059] As shown in FIGS. 9A-9B, the LOE further includes an optical retarder 40 disposed between the first and second regions to rotate the polarization of light deflected by the first DOE (i.e., DOE 27 in the case of FIG. 9A and DOEs 27a, 27b in the case of FIG. 9B) before it reaches the second DOE 29.

[0060] Note that in some embodiments, each of the first and second DOEs may actually be implemented as a set of DOEs. In that case, the "first DOE" should be understood to include the first set of DOEs, and the "second DOE" should be understood to include the second set of DOEs.

[0061] Non-limiting examples of the DOE include, for example, surface gratings and / or volume gratings (e.g., holographic gratings). In some embodiments (not shown), the LOE may include a DOE in one of the first and second regions and a facet in the other of the first and second regions. For example, the first region may include a DOE while the second region includes a facet, or the first region may include a facet while the second region includes a DOE. It should be understood that the diffractive LOE can be fabricated by first manufacturing a waveguide without an embedded retarder using any of the known methods described above, and then "writing" a holographic grating structure into the waveguide.

[0062] The embedded retarder described above with reference to FIG. 4 in the context of an LOE having a facet, as is known to those skilled in the art, can be used, with appropriate modifications as necessary, for other forms of LOE, such as an LOE having a "partial" facet in region 16 or 18 (as described in more detail in WO2020 / 049542A1).

[0063] It is understood that the present invention is not limited in its application to the details described in the description contained herein or shown in the drawings. The present invention is capable of other embodiments and can be practiced and carried out in various ways. Accordingly, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. Thus, those skilled in the art will understand that the concept on which this disclosure is based can be readily utilized as a basis for designing other structures, methods, and systems for accomplishing some of the objectives of the presently disclosed subject matter.

Claims

1. An optical system for directing image illumination incident on a coupling input region toward an eye movement box for visual recognition by a user's eye, comprising a light guiding optical element (LOE) formed of a transparent material, the LOE comprising: a first region that is planar with a first orientation and includes a first set of partially reflective surfaces that are parallel to each other; a second region that is planar with a second orientation non-parallel to the first orientation and includes a second set of partially reflective surfaces that are parallel to each other; a set of mutually parallel major outer surfaces, wherein both the first set of partially reflective surfaces and the second set of partially reflective surfaces are located between the major outer surfaces without an intervening gap, such that the major outer surfaces extend across the first and second regions, the set of mutually parallel major outer surfaces; such that a portion of the image illumination propagating within the LOE by internal reflection at the major outer surfaces from the first region to the second region is coupled and output from the LOE toward the eye movement box, the second set of partially reflective surfaces are at an oblique angle to the major outer surfaces; the first set of partially reflective surfaces are oriented such that a portion of the image illumination propagating within the LOE from the coupling input region by internal reflection at the major outer surfaces is deflected toward the second region; the LOE further includes an optical retarder disposed between the first region and the second region to rotate the polarization of the light deflected by the first set of partially reflective surfaces before reaching the second set of partially reflective surfaces; the first set of partially reflective surfaces are oriented perpendicular to the major outer surfaces of the LOE, the optical system.

2. The optical system according to claim 1, further comprising a small image projector (POD) optically coupled to the LOE such that the image illumination is incident on the coupling input region of the LOE so that the image illumination is confined in one dimension by internal reflection at the set of major outer surfaces.

3. The optical system according to claim 2, wherein the POD is configured to generate a collimated image collimated to infinity such that the image illumination extends over an angular range corresponding to a two-dimensional angular field of view.

4. The optical system according to claim 1, wherein both the image illumination and the conjugate of the image illumination are deflected to the second region.

5. An optical system for directing image illumination incident on a coupling input region towards an eye movement box for visual recognition by a user's eye, comprising a light guiding optical element (LOE) formed from a transparent material, the LOE comprising: a first region that is planar with a first orientation and includes a first set of mutually parallel partial reflecting surfaces; a second region that is planar with a second orientation non-parallel to the first orientation and includes a second set of mutually parallel partial reflecting surfaces; a set of mutually parallel major outer surfaces, wherein both the first set of partial reflecting surfaces and the second set of partial reflecting surfaces are positioned between the major outer surfaces without an intervening gap, and the major outer surfaces extend across the first and second regions; a part of the image illumination propagating within the LOE by internal reflection at the major outer surfaces from the first region to the second region is coupled and output from the LOE towards the eye movement box, and the second set of partial reflecting surfaces are at an oblique angle to the major outer surfaces; the first set of partial reflecting surfaces are oriented such that a part of the image illumination propagating within the LOE from the coupling input region by internal reflection at the major outer surfaces is deflected towards the second region; the LOE further includes an optical retarder disposed between the first region and the second region so as to rotate the polarization of the light deflected by the first set of partial reflecting surfaces before reaching the second set of partial reflecting surfaces; the first set of partial reflecting surfaces continuously reflect a proportion of the image illumination propagating within the first region such that the image illumination is expanded in a first dimension, the optical system.

6. An optical system for directing image illumination incident on a coupling input region towards an eye movement box for visual recognition by a user's eye, comprising a light guiding optical element (LOE) formed from a transparent material, the LOE comprising: a first region that is planar with a first orientation and includes a first set of mutually parallel partial reflecting surfaces; a second region that is planar with a second orientation non-parallel to the first orientation and includes a second set of mutually parallel partial reflecting surfaces; A set of mutually parallel major outer surfaces, wherein both the partial reflecting surfaces of the first set and the partial reflecting surfaces of the second set are located between the major outer surfaces without an intervening gap, such that the major outer surfaces extend across the first and second regions, a set of mutually parallel major outer surfaces, The partial reflecting surfaces of the second set are at an oblique angle to the major outer surfaces such that a portion of the image illumination propagating within the LOE by internal reflection at the major outer surfaces from the first region to the second region is coupled and output from the LOE towards the eye movement box, The partial reflecting surfaces of the first set are oriented such that a portion of the image illumination propagating within the LOE from the coupling input region by internal reflection at the major outer surfaces is deflected towards the second region, The LOE further includes an optical retarder disposed between the first region and the second region to rotate the polarization of the light deflected by the partial reflecting surfaces of the first set before reaching the partial reflecting surfaces of the second set, The partial reflecting surfaces of the second set are an optical system that continuously reflects a proportion of the image illumination propagating within the second region such that the image illumination undergoes an expansion in a second dimension. **Claim 7** The optical system according to claim 1, wherein the first region is configured to achieve an opening expansion in one of the X-axis direction or the Y-axis direction, and the second region is configured to achieve an opening expansion in the other of the X-axis direction or the Y-axis direction. **Claim 8** The optical system according to claim 1, wherein the partial reflecting surfaces of the first and second sets are implemented as internal surfaces coated with a dielectric thin film coating configured to reflect light impinging on the internal surface over a predetermined angular range. **Claim 9** The optical system according to claim 1, wherein the retarder is disposed within the LOE so as to extend substantially perpendicular to the major outer surfaces between the major outer surfaces. **Claim 10** An optical system for directing image illumination incident on a coupling input region towards an eye movement box for visual recognition by a user's eye, comprising a light guiding optical element (LOE) formed from a transparent material, the LOE A first region that is planar with a first orientation and includes a first set of mutually parallel partial reflecting surfaces, A second region that is planar with a second orientation non-parallel to the first orientation and includes a second set of mutually parallel partial reflecting surfaces, A set of mutually parallel major outer surfaces, wherein both the partial reflecting surfaces of the first set and the partial reflecting surfaces of the second set are located between the major outer surfaces without an intervening gap, and the major outer surfaces extend over the first and second regions, a set of mutually parallel major outer surfaces. The partial reflecting surfaces of the second set are at an oblique angle to the major outer surfaces such that a portion of the image illumination propagating within the LOE by internal reflection at the major outer surfaces from the first region to the second region is coupled and output from the LOE towards the eye movement box. The partial reflecting surfaces of the first set are oriented such that a portion of the image illumination propagating within the LOE from the coupling input region by internal reflection at the major outer surfaces is deflected towards the second region. The LOE further includes an optical retarder disposed between the first region and the second region to rotate the polarization of the light deflected by the partial reflecting surfaces of the first set before reaching the partial reflecting surfaces of the second set. The retarder is an optical system disposed within the LOE so as to extend between the major outer surfaces at an oblique angle to the major outer surfaces. **Claim 11**: An optical system for directing image illumination incident on a coupling input region towards an eye movement box for visual recognition by a user's eye, comprising a light guiding optical element (LOE) formed from a transparent material, the LOE comprising: A first region that is planar and has a first set of mutually parallel partial reflecting surfaces having a first orientation; A second region that is planar and has a second set of mutually parallel partial reflecting surfaces having a second orientation that is non-parallel to the first orientation; A set of mutually parallel major outer surfaces, wherein both the partial reflecting surfaces of the first set and the partial reflecting surfaces of the second set are located between the major outer surfaces without an intervening gap, and the major outer surfaces extend over the first and second regions, a set of mutually parallel major outer surfaces. The partial reflecting surfaces of the second set are at an oblique angle to the major outer surfaces such that a portion of the image illumination propagating within the LOE by internal reflection at the major outer surfaces from the first region to the second region is coupled and output from the LOE towards the eye movement box. The partial reflective surfaces of the first set are oriented such that, by internal reflection at the major outer surface, a portion of the image illumination propagating within the LOE from the coupling input region is deflected towards the second region. The LOE further includes an optical retarder disposed between the first region and the second region so as to rotate the polarization of the light deflected by the partial reflective surfaces of the first set before reaching the partial reflective surfaces of the second set. The retarder is an optical system disposed within the LOE so as to be oriented substantially parallel to the major outer surface. [

12. ] The optical system according to claim 11, wherein the retarder is oriented substantially adjacent to one of the major outer surfaces. [

13. ] An optical system for directing image illumination incident on a coupling input region towards an eye movement box for viewing by a user's eye, the optical system comprising a light guiding optical element (LOE) formed from a transparent material, the LOE comprising: a first region having a planar shape with a first set of mutually parallel partial reflective surfaces having a first orientation; a second region having a planar shape with a second set of mutually parallel partial reflective surfaces having a second orientation non-parallel to the first orientation; a set of mutually parallel major outer surfaces, wherein the major outer surfaces extend across the first and second regions such that both the first set of partial reflective surfaces and the second set of partial reflective surfaces are located between the major outer surfaces without an intervening gap; and the partial reflective surfaces of the second set are at an oblique angle to the major outer surface such that a portion of the image illumination propagating within the LOE by internal reflection at the major outer surface from the first region to the second region is coupled out from the LOE towards the eye movement box. The partial reflective surfaces of the first set are oriented such that, by internal reflection at the major outer surface, a portion of the image illumination propagating within the LOE from the coupling input region is deflected towards the second region, and the deflection is the only in-plane element direction change of the propagation direction of the image illumination occurring between the coupling input region and the second region of the LOE. The LOE is an optical system further including an optical retarder disposed between the first region and the second region so as to rotate the polarization of the light deflected by the partial reflective surfaces of the first set before reaching the partial reflective surfaces of the second set.

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