Optical system including a two-dimensional extension optical guide element with a retarder element

Abstract

One known problem with 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. [Solution] An optical system for directing image illumination incident in a coupled input region to an eye movement box for viewing by the user's eye, comprising a light guide optical element (LOE) formed of a transparent material, the LOE comprising: a first region having a first orientation and a planar shape including a first set of mutually parallel partial reflective surfaces; a second region having a second orientation non-parallel to the first orientation and a planar shape including a second set of mutually parallel partial reflective surfaces; a set of mutually parallel main outer surfaces extending across the first and second regions; and an optical retarder positioned between the first and second regions to rotate the polarization of light deflected by the first set of partial reflective surfaces before it reaches the second set of partial reflective surfaces.

Description

Technical Field

[0001] The presently disclosed subject matter relates to optical systems, and more particularly to an optical system 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. Thus, 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 the image along a substrate in which one or more sets of partially reflective inner surfaces ("facets") are embedded. One known problem with 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 subject matter currently disclosed, an optical system is provided for directing image illumination incident in a coupled input region to an eye movement box for viewing by the user's eye, the optical system comprising a light guide optical element (LOE) formed from a transparent material, the LOE comprising a first region having a first orientation and including a first set of mutually parallel partial reflective surfaces in a planar configuration, a second region having a second orientation non-parallel to the first orientation and including a second set of mutually parallel partial reflective surfaces in a planar configuration, and a set of mutually parallel main outer surfaces, the main outer surfaces extending 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 main outer surfaces. The LOE comprises a set of primary outer surfaces, wherein the partial reflective surfaces of the second set are oblique to the primary outer surface such that a portion of the image illumination propagating from the first region to the second region within the LOE by internal reflection at the primary outer surface is coupled out toward the eye movement box, and the partial reflective surfaces of the first set are oriented such that a portion of the image illumination propagating from the coupled input region within the LOE by internal reflection at the primary outer surface is deflected toward the second region, and the LOE further includes an optical retarder positioned between the first region and the second region to rotate the polarization of the light deflected by the partial reflective surfaces of the first set before it reaches the partial reflective surfaces of the second set.

[0005] According to some embodiments, the optical system includes a miniature image projector (POD) optically coupled to the LOE such that the image illumination is incident on the coupled input region of the LOE, so that the image illumination is confined in one dimension by internal reflections on a set of main outer surfaces.

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

[0007] According to some embodiments, the first set of partial reflective surfaces are oriented perpendicular to the main outer surface of the LOE.

[0008] In some embodiments, both the image illumination and its conjugate are biased towards a second region.

[0009] According to some embodiments, the first set of partial reflective surfaces are oriented obliquely with respect to the main outer surface of the LOE.

[0010] In some embodiments, either the image illumination or its conjugate is deflected to a second region.

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

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

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

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

[0015] According to some embodiments, the retarder is positioned within the LOE so as to extend between the main outer surfaces substantially perpendicular to the main outer surface.

[0016] According to some embodiments, the retarder is positioned within the LOE so as to extend between the main outer surfaces at an oblique angle to the main outer surface.

[0017] In some embodiments, the retarder is positioned within the LOE so as to be oriented substantially parallel to the main outer surface.

[0018] According to some embodiments, the retarder is oriented substantially adjacent to one of the main outer surfaces. [Brief explanation of the drawing]

[0019] To understand the present invention and to see how it can be put into practice, embodiments will be described as non-limiting examples with reference to the accompanying drawings: [Figure 1A] Figures 1A-1D show an example of a near-eye display system using LOE for 2D image magnification according to prior art. [Figure 1B] Figures 1A-1D show an example of a near-eye display system using LOE for 2D image magnification according to prior art. [Figure 1C] Figures 1A-1D show an example of a near-eye display system using LOE for 2D image magnification according to prior art. [Figure 1D] Figures 1A-1D show an example of a near-eye display system using LOE for 2D image magnification according to prior art. [Figure 2A] Figures 2A-2B show enlarged views of the LOE in Figures 1A-1B according to the prior art. [Figure 2B] Figures 2A-2B show enlarged views of the LOE in Figures 1A-1B according to the prior art. [Figure 3] Figure 3 shows the reflectivity characteristics of a ray of light at a certain incident angle in the S-polarized and P-polarized states. [Figure 4] Figure 4 shows a retarder embedded in an LOE according to one embodiment of the disclosed subject matter. [Figure 5A] Figures 5A-5E show various configurations of the retarder 40 having LOE according to embodiments of the disclosed subject matter. [Figure 5B]Figures 5A-5E show various configurations of retarder 40 with LOE according to embodiments of the disclosed subject matter, [Figure 5C] Figures 5A-5E show various configurations of retarder 40 with LOE according to embodiments of the disclosed subject matter, [Figure 5D] Figures 5A-5E show various configurations of retarder 40 with LOE according to embodiments of the disclosed subject matter, [Figure 5E] Figures 5A-5E show various configurations of retarder 40 with LOE according to embodiments of the disclosed subject matter, [Figure 6A] Figures 6A-6C show a known manufacturing method of an optical polarization retarder, [Figure 6B] Figures 6A-6C show a known manufacturing method of an optical polarization retarder, [Figure 6C] Figures 6A-6C show a known manufacturing method of an optical polarization retarder, [Figure 7A] Figures 7A-7D show an example of a manufacturing method of an LOE with an embedded retarder according to embodiments of the disclosed subject matter, [Figure 7B] Figures 7A-7D show an example of a manufacturing method of an LOE with an embedded retarder according to embodiments of the disclosed subject matter, [Figure 7C] Figures 7A-7D show an example of a manufacturing method of an LOE with an embedded retarder according to embodiments of the disclosed subject matter, [Figure 7D] Figures 7A-7D show an example of a manufacturing method of an LOE with an embedded retarder according to embodiments of the disclosed subject matter, [Figure 8A] Figures 8A-8E show an example of a manufacturing method of an LOE with an embedded retarder according to another embodiment of the disclosed subject matter, and [Figure 8B] Figures 8A-8E show an example of a manufacturing method of an LOE with an embedded retarder according to another embodiment of the disclosed subject matter, and [Figure 8C]Figures 8A-8E show an example of a method for manufacturing an LOE having an embedded retarder, according to another embodiment of the disclosed subject, and [Figure 8D] Figures 8A-8E show an example of a method for manufacturing an LOE having an embedded retarder, according to another embodiment of the disclosed subject, and [Figure 8E] Figures 8A-8E show an example of a method for manufacturing an LOE having an embedded retarder, according to another embodiment of the disclosed subject, and [Figure 9A] Figures 9A and 9B show an example of a diffraction LOE with an embedded retarder. [Figure 9B] Figures 9A and 9B show an example of a diffraction LOE with an embedded retarder. [Modes for carrying out the invention]

[0020] In the following detailed description, numerous specific examples are described in detail to provide a complete understanding of the present invention. However, those skilled in the art will understand that the subject matter currently disclosed can be carried out without these specific details. In other embodiments, known methods, procedures, and components are not 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 incidents an image onto a waveguide consisting of a transparent substrate that propagates the image by total internal reflection (TIR) ​​between the parallel outer surfaces of the waveguide. Optical elements embedded within the waveguide, such as partially reflective inner surfaces, redirect the image 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 propagates the image again along an axis perpendicular to the first waveguide via TIR, thereby magnifying the image into two dimensions. Facets embedded in the second waveguide cause the magnified image to be coupled and output toward the viewer.

[0022] While this disclosure primarily relates to partial reflectors as a coupled output method, it should be noted that the techniques described herein can also be applied to waveguides employing other optically coupled output elements (e.g., diffraction elements or combinations of reflection and diffraction elements) with appropriate modifications, as will be detailed below with reference to Figures 9A-9B. Similarly, while this disclosure primarily relates to waveguides configured mainly for two-dimensional image augmentation, the techniques disclosed herein can also be applied to one-dimensional waveguides with appropriate modifications that will be known to those skilled in the art.

[0023] Figures 1A and 1B schematically illustrate exemplary implementations of known devices in the form of a near-eye display, generally designated 10, in which the LOE 12 may be deployed. The near-eye display 10 uses a miniature image projector (or "POD") 14 optically coupled to the LOE 12 so that an image (also referred herein as "image illumination") is incident on the LOE 12 and the image light is confined in one dimension by internal reflections on a series of mutually parallel planar outer surfaces of the LOE 12. The light collides with one set of facets that are mutually parallel and inclined obliquely with respect to the propagation direction of the image light, each continuous facet deflecting a certain proportion of the image light in the deflection direction, which is also confined within the substrate / induced by internal reflections. The facets of this first set are located in a first region of the LOE, indicated as region 16, although they are not individually shown in Figures 1A and 1B. The partial reflections in this continuous facet achieve a first-dimensional optical aperture expansion.

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

[0025] The first set of facets deflects the image illumination from a first propagation direction, which is confined within the substrate by total internal reflection (TIR), to a second propagation direction, which is also confined within the substrate by TIR. The deflected image illumination then enters a second substrate region 18, which can be implemented as an adjacent separate substrate or as an extension of a single substrate, where a coupled output configuration (an additional set of partial reflection facets or a diffractive optical element) gradually coupled and output a certain proportion of the image illumination toward the observer's eye, which is located within a region defined as an eye movement box, thereby achieving a second dimension of optical aperture expansion.

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

[0027] In this specification, in the drawings and claims, the X-axis extends horizontally (Figure 1A) or vertically (Figure 1B) in the general extending direction of the first region of the LOE, and the Y-axis extends perpendicularly thereto, i.e., vertically in Figure 1A and horizontally in Figure 1B.

[0028] Very broadly speaking, the first region 16 of LOE12 can be considered to achieve aperture expansion in the X direction, while the second region 18 of LOE12 achieves aperture expansion in the Y direction. Note that the orientation shown in Figure 1A can be considered a "top-down" mounting configuration in which the image illumination entering the main part (second region) of the LOE enters from the upper edge, while the orientation shown in Figure 1B can be considered a "side-incidence" mounting configuration in which the axis, here referred to as the Y-axis, is deployed horizontally. In the remaining drawings, various features of a particular embodiment of the present invention are illustrated in either a top-down or side-incidence context, but it should be understood that all of these features are equally applicable to both embodiments.

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

[0030] The image projector 14 includes at least one light source, typically deployed to illuminate a spatial light modulator, such as an LCOS chip. The spatial light modulator modulates the projection intensity of each pixel in the image, thereby generating an image. Alternatively, the image projector may 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), where the illumination from the laser light source scans across the image plane of the projector, causing the beam intensity to change pixel by pixel in synchronization with the motion, thereby projecting the desired intensity onto each pixel. In either case, a collimating optical system is provided to produce an output projected 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] Optical coupling of the image projector 14 to the LOE 12 can be achieved by any suitable optical coupling, such as via a coupling prism having an obliquely angled input surface or via a reflective coupling configuration, via one of the side edges and / or main outer surfaces of the LOE. Details of the coupling input configuration are not important to the present invention and are schematically shown here as a wedge prism 15, which is a non-limiting embodiment applied to one of the main outer surfaces of the LOE.

[0032] It will be understood that the near-eye display 10 includes various additional components, typically including a controller 22 for operating an image projector 14, which typically employs power from a small onboard battery (not shown) or some other suitable power source. It will be understood that the controller 22 includes 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 show another embodiment of the existing near-eye display system 10 with three types of embedded elements. Similar to Figures 1A-1B, the projector (POD) 14 incidents an image onto the LOE 12, at which point the light is confined one-dimensionally by the TIR to a region between the two parallel main outer surfaces of the LOE. The image rays propagate through the waveguide in a certain 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 rays to different angular orientations and are also confined one-dimensionally by the TIR to a region between the two parallel main surfaces of the LOE. The rays are then reflected a second time by the facets of regions 16a and 16b, respectively, so that they return to their original orientations when incident on the LOE. Finally, the ray is reflected by a third set of mutually parallel facets of region 18 that redirect the ray so that the incident image is combined and output from the LOE and propagates toward the eye movement box where the observer's eye is positioned.

[0034] Referring here to Figure 2A, the optical properties of an embodiment of a near-eye display are illustrated in more detail. Specifically, a more detailed diagram of a light guide optical element (LOE) 12 formed from a transparent material is shown, comprising a first region 16 which is planar and has a first orientation and includes a first set of mutually parallel partial reflective surfaces 17, and a second region 18 which is planar and has a second orientation that is non-parallel to the first orientation and includes a second set of mutually parallel partial reflective surfaces 19. A set of mutually parallel main outer surfaces 24 extends across the first and second regions 16 and 18 such that both the first set of partial reflective surfaces 17 and the second set of partial reflective surfaces 19 are located between the main outer surfaces 24. Most preferably, the set of main outer surfaces 24 is a pair of surfaces that are continuous across the entirety of the first and second regions 16 and 18, respectively, but options having a set-down or increasing thickness between regions 16 and 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, there may be one or more additional LOE regions interposed between them to provide various additional optical or mechanical functions. The present invention is not limited to any particular manufacturing technique, but in certain particularly preferred implementations, a particularly high-quality main outer surface is achieved by employing a continuous outer plate in which separately formed regions 16 and 18 are sandwiched between them to form a composite LOE structure.

[0035] The optical properties of the LOE can be understood by tracing the image illumination path in reverse. The second set of partial reflective surfaces 19 are oblique to the main outer surface 24 such that, due to internal reflection from the main outer surface, a portion of the image illumination propagating within the LOE 12 from the first region 16 to the second region 18 is coupled and output from the LOE toward the eye movement box 26. The first set of partial reflective surfaces 17 are oriented such that, due to internal reflection from the main outer surface, a portion of the image illumination propagating within the LOE 12 from the coupled input region (coupled prism 15) is deflected toward the second region 18.

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

[0037] The near-eye display is designed to provide the full field of view (FOV) of a projected image to a user's eye located at a certain position within a permitted positional range, specified by an eye movement box (EMB) 26 (i.e., a shape typically represented as a rectangle, located away from the plane of the line of eye (LOE) from which the pupil of the eye will view the projected image). To reach the eye movement box, light must be combined and output from a second region 18 toward the EMB 26 by a second set of partial reflective surfaces 19. To provide the full image field of view, each point within the EMB must receive the image from the LOE across the entire angular range. Tracing the field of view backward from the EMB suggests a larger rectangle 28 from which the relevant illumination is combined and output from the LOE toward the EMB.

[0038] Figure 2A shows the first end 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 upward to the left and be partially reflected by a series of partial reflecting surfaces 17. As shown here, only a subset of facets generate reflections useful for providing the corresponding pixel in the image viewed by the user, and only sub-regions of those facets contribute to the observed image of this pixel. The relevant region is indicated by a thick black line, showing the ray corresponding to this pixel in the redirected image, reflected from facet 17 and then combined and output by facet 19 to reach the four corners of the EMB 26.

[0039] Here, and throughout the explanation, only the in-plane propagation direction of the ray is shown, here in the case of propagation within the LOE. However, it should be noted that the ray actually follows a zigzag path of repeated internal reflections from the two main outer surfaces, and the entire image field of view in one dimension is encoded by the angle of inclination of the ray relative to the main outer surfaces, corresponding to the pixel positions in the Y dimension. As one additional example, deflected and combined output rays, corresponding to the upper left corner of the image, as seen in the upper left corner of the EMB, are shown by dashed lines. Figure 2B schematically shows the LOE of Figure 2A rotated 90 degrees and with the ray and eye movement box removed from Figure 2A to aid in the visualization of 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 impacting the surface over a given angular range, where each angle is associated with a given field, and the angular range is thereby associated with the entire FOV of the projected image. It should be noted that the light impacting the facets includes light of different wavelengths over a relatively broad wavelength spectrum determined by the illuminating source. Furthermore, it should be noted that, generally speaking, the incident image may be polarized or unpolarized, and in each case the facet coating must be designed accordingly. For example, if the incident image is unpolarized (i.e., including both p-polarized and s-polarized light), the coating must be designed to take into account the effects of reflection of both p-polarized and s-polarized rays.

[0041] By definition, the polarization state of light is defined according to the angular orientation of a particular ray (i.e., the field k-vector, the orientation of a plane wave) with respect to the normal of the surface it collides with. Therefore, a polarized incident ray may have one polarization state when compared to one surface and another when compared to a different surface. Thus, when light propagates through an optical system with many surfaces, it is clear that the polarization state of the colliding rays is defined according to the direction of the incident ray and the angular orientation of the surface it collides with. As is clear from Figure 2A, when light propagates through a near-eye display, the light collides with parallel outer surfaces (also called "surfaces" here) 24, a first set of facets, and a second set of facets, each of which has a different angular orientation relative to one another. Therefore, a polarized ray associated with a certain field can be described as having a first polarization state relative to the LOE surface 24, a second polarization state relative to facet 17, and a third polarization state relative to facet 19. The polarization state of light rays relative to a surface affects the reflectivity of light rays from that surface. Therefore, ideally, the partial reflection coating for facet 17 should be designed differently from the partial reflection coating for facet 19 to achieve sufficiently high reflectivity in each set of facets. Furthermore, designing an optical coating with the required optical properties in a certain polarization and angular range is often extremely difficult. For example, designing a coating with high reflectivity for p-polarization near the Brewster angle is extremely difficult, if possible. Thus, polarization mismatch of the illumination light between the first and second sets of facets 17 and 19 may limit the feasibility of certain coating requirements and force compromises regarding the initial polarization state. Moreover, if the polarization state for the main outer surface 24 at any point along 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 to different fields, which can often lead to black lines in the output image.

[0042] As mentioned above, a drawback of existing LOEs is that the polarization of incoming light can differ in different regions of the LOE, for different sets of facets, and for the main outer surface of the LOE. This often leads to "impure" polarization of the incident image for the main surface. Because TIR induces different phases in s-polarization and p-polarization, the polarization of the incident image can rotate and change as light propagates through the LOE. This significantly complicates the design of thin optical coatings on facets, potentially leading to reduced output efficiency or local or global inhomogeneity in the projected output image.

[0043] Furthermore, as mentioned above, the reflectance when a light ray strikes a surface varies depending on the polarization state of that light ray relative to the surface. Figure 3 shows the reflectance as a function of the angle of incidence for exemplary coating designs for the first and second facets. As is clear, the reflectance for p-polarized light is zero near the Brewster angle. For this reason, it is generally preferable that the light propagating through the display is s-polarized, or at least mostly s-polarized, for facets 17 and 19 for maximum efficiency and simplification of coating design.

[0044] Therefore, the inventors have found that the efficiency and simplicity of a near-eye display system using LOE configured for two-dimensional extension can be improved by rotating the polarization of the light propagating between the first set of facets and the second set of facets so that both sets of facets are always s-polarized (or at least mostly s-polarized). "Efficiency" here refers to the fact that more projected light initially coupled into the near-eye display system is reflected back to the viewer, resulting in a brighter and / or more uniform output image.

[0045] Figure 4 schematically shows an embodiment of a waveguide similar to that shown in Figure 2B, but here it includes an optical retarder 40 positioned along the optical path between facet 17 (orthogonal to the outer surface in the shown embodiment) and facet 19, configured to rotate the polarization of the light after reflection from facet 17 and before reflection from facet 19. Therefore, assuming that the light input to the waveguide 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. The retarder 40 then rotates the polarization of the light so that it is s-polarized (or at least mostly s-polarized) with respect to facet 19. Now, since both facets 17 and 19 reflect s-polarized light to their respective surfaces in each set of facets, there is no need to consider the design of the coating separately. Furthermore, because the retarder ensures that the light propagating inside the waveguide is almost purely polarized compared to the main outer surface, the polarization of the light propagating inside the waveguide is not rotated by TIR. As will be further detailed below, the retarder 40 can be implemented in a variety of ways, including but not limited to half-wave plates.

[0046] As shown in Figures 5A–5E, the retarder 40 can be physically positioned in various possible locations within the LOE and oriented at various different angles. For example, as shown in Figure 5A, the retarder can extend between parallel planes across the thickness of the LOE (the z-axis in the drawing) and be oriented approximately perpendicular to the planes of the LOE. Figure 5B shows another configuration in which the retarder 40 is oriented obliquely to the planes of the LOE and non-parallel to the facets 19. Figure 5C shows a further configuration in which the retarder 40 is oriented parallel to the facets 19.

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

[0048] It should be noted 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, while the function of a retarder has so far been described as simply rotating the polarization of light, it should be noted that 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 may include a coating with a reflectivity of 50%. This allows the retarder 40 to additionally function as a "mixer," improving the intensity uniformity of the output image by mixing the propagated light rays. A near-eye display with an embedded mixer element was previously described in PCT Publication WO2021001841A1.

[0050] The retarder 40 can be implemented in various ways, including, but not limited to, a half-wave plate or a coated inner surface. Suitable coatings include, for example, dielectrics, birefringents, thin-film polymers, crystalline retarders, geometric phase lattice retarders, and the like. In some embodiments, as shown in the configuration 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 method for manufacturing a LOE with a retarder element will be described with reference to Figures 6A-8E.

[0052] Figures 6A-6C schematically illustrate known methods for fabricating optical retarders suitable for deployment within a LOE. In Figure 6A, the retarder is fabricated from a crystalline material such as quartz. A first transparent crystalline plate 42 made of a birefringent material is bonded to a transparent substrate 41. The substrate 41 is preferably made of the same material as the LOE. The bonded structure is then thinned, for example, by double-sided polishing, until the birefringent material reaches the required thickness. Figures 6B-6C show alternative methods for fabricating the retarder, either by coating the substrate 41 with a dielectric coating (homogeneous or heterogeneous) (Figure 6B), or by bonding a polycrystalline thin film to the substrate 41 (Figure 6C).

[0053] Next, LOE regions incorporating a second set of facets are formed according to a known method. Figure 7A schematically shows that a series of flat, transparent coated plates 38 are laminated and bonded together, and the LOE regions 18 are formed by slicing the laminate along oblique planes parallel to the flat surfaces of the plates (Figure 7A). The slices are then polished to form multiple LOE regions 18 (Figure 7B). Region 16 can be formed in a similar manner.

[0054] Two alternative methods have been proposed to form the final LOE structure including the retarder. Figures 7C-7D show a first method in which a single retarder element is bonded to a single LOE region 16 on one side and a single LOE region 18 on the opposite side (Figure 7C) to form the final LOE (Figure 7D).

[0055] The second method involves laminating and bonding multiple LOE regions 18 (Figure 8A), as shown in Figures 8A-8B, and bonding a retarder element spanning the thickness of the laminate 18' to the edge of the laminate (Figures 8B-8C). Next, as shown in Figures 8D-8E, blocks 16' of material representing multiple formed but unsliced ​​LOE regions 16 (i.e., those manufactured in an intermediate stage of the manufacturing of the LOE regions 16) are bonded to the opposite side of the retarder element, and the combined blocks are sliced ​​into multiple LOEs (Figure 8E), each containing a retarder embedded between two sets of facets.

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

[0057] While the present invention has been described herein primarily in the context of LOEs based on partially reflective internal surfaces, it will also be understood that the principles of the present invention can also be advantageously implemented in optical guide elements that use diffractive optical elements (DOEs) to achieve either or both an expansion of the optical aperture and / or a dimension of the combined output of image illumination directed from the waveguide to the observer.

[0058] As a non-limiting embodiment, Figures 9A–9B show an embodiment of an optical system implemented using a diffraction waveguide for directing image illumination incident in a coupled input region to an eye movement box for viewing by the user's eye. The optical system is formed from a transparent material and includes a first region containing a first DOE 27, a second region containing a second DOE 29, and a LOE 12 containing a set of mutually parallel main outer surfaces 24. The main outer surfaces extend across the first and second regions such that both the first DOE 27 and the second DOE 29 are located between the main outer surfaces 24. In the embodiment shown in Figure 9A, the image illumination is incident on one end of the first region and propagates in one direction along the length of the first region until it is deflected into the second region by one or more DOEs 27. In the embodiment shown in Figure 9B, image illumination is incident on the central part of the first region and propagated in the opposite direction until deflected to the second region by two or more DOEs 27a, 27b. In both cases, the image illumination is coupled and output from the second region to the eye movement box (not shown) by one or more DOEs 29.

[0059] As shown in Figures 9A and 9B, the LOE further includes an optical retarder 40 positioned 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 Figure 9A, and DOE 27a, 27b in the case of Figure 9B) before reaching the second DOE 29.

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

[0061] Non-limiting embodiments 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 a diffractive LOE can be fabricated by first fabricating a waveguide without an embedded retarder using one of the known methods described above, and then "writing" a holographic grating structure into the waveguide.

[0062] It should be understood that the embedded retarder described above with reference to Figure 4 in the context of an LOE having facets can also be used in other forms of LOE, such as an LOE having “partial” facets in region 16 or 18 (as described in more detail, for example, in WO2020 / 049542A1), with appropriate modifications as needed, as is known to those skilled in the art.

[0063] It is understood that the present invention is not limited in its applications to the details described herein or shown in the drawings. Other embodiments are possible and can be practiced and implemented in a variety of ways. Therefore, it is understood that the expressions and terminology used herein are for illustrative purposes only and should not be considered limiting. Thus, those skilled in the art will understand that the ideas upon which this disclosure is based can be readily used as a basis for designing other structures, methods, and systems to accomplish some of the purposes of the subject matter now disclosed.

Claims

1. An optical system for directing image illumination incident on a coupled input region to an eye movement box for viewing by the user's eye, comprising a light guide optical element (LOE) formed from a transparent material, wherein the LOE is A first region having a planar orientation and including a first set of mutually parallel partial reflecting surfaces, A second region having a planar orientation nonparallel to the first orientation, and including a second set of mutually parallel partial reflecting surfaces, A set of mutually parallel main outer surfaces, wherein the main outer surfaces extend across the first and second regions such that both the partial reflective surfaces of the first set and the partial reflective surfaces of the second set are located between the main outer surfaces without any gaps in between, The second set of partial reflective surfaces is at an oblique angle to the main outer surface such that a portion of the image illumination propagating within the LOE due to internal reflection from the main outer surface from the first region to the second region is coupled and output toward the eye movement box from the LOE, The first set of partial reflective surfaces is oriented such that, by internal reflection from the main outer surface, a portion of the image illumination propagating within the LOE from the coupled input region is deflected toward the second region. The optical system further includes an optical retarder positioned between the first region and the second region such that the LOE rotates the polarization of light deflected by the first set of partial reflectors before it reaches the second set of partial reflectors.

2. The optical system according to claim 1, further comprising a miniature image projector (POD) optically coupled to the LOE such that the image illumination is confined in one dimension by internal reflections on the main outer surface of the one set, and such that the image illumination is incident on the coupled input region of the LOE.

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 to an angular range corresponding to a two-dimensional angular field of view.

4. The optical system according to claim 1, wherein the partial reflective surfaces of the first set are oriented perpendicular to the main outer surface of the LOE.

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

6. The optical system according to claim 1, wherein the partial reflective surfaces of the first set are oriented obliquely with respect to the main outer surface of the LOE.

7. The optical system according to claim 6, wherein either the image illumination or its conjugate is deflected to the second region.

8. The optical system according to claim 1, wherein 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 undergoes expansion in a first dimension.

9. The optical system according to claim 1, wherein the second set of partial reflecting surfaces continuously reflects a proportion of the image illumination propagating within the second region such that the image illumination undergoes expansion in a second dimension.

10. The optical system according to claim 1, wherein the first region is configured to achieve aperture expansion in either the X-axis direction or the Y-axis direction, and the second region is configured to achieve aperture expansion in the other direction of the X-axis direction or the Y-axis direction.

11. The optical system according to claim 1, wherein the first and second sets of partial reflective surfaces are mounted as internal surfaces coated with a dielectric thin film coating configured to reflect light impacting the internal surface over a predetermined angular range.

12. The optical system according to claim 1, wherein the retarder is disposed within the LOE so as to extend substantially perpendicularly to the main outer surface and between the main outer surfaces.

13. The optical system according to claim 1, wherein the retarder is disposed within the LOE so as to extend between the main outer surfaces at an oblique angle with respect to the main outer surface.

14. The optical system according to claim 1, wherein the retarder is disposed within the LOE so as to be oriented substantially parallel to the main outer surface.

15. The optical system according to claim 14, wherein the retarder is oriented substantially adjacent to one of the main outer surfaces.

16. An optical system for directing image illumination incident on a coupled input region to an eye movement box for viewing by the user's eye, comprising a light guide optical element (LOE) formed from a transparent material, wherein the LOE is A first region having a planar orientation and including a first set of mutually parallel partial reflecting surfaces, A second region having a planar orientation nonparallel to the first orientation, and including a second set of mutually parallel partial reflective surfaces, A set of mutually parallel main outer surfaces, wherein the main outer surfaces extend across the first and second regions such that both the partial reflective surfaces of the first set and the partial reflective surfaces of the second set are located between the main outer surfaces without any gaps in between, The second set of partial reflective surfaces is at an oblique angle to the main outer surface such that a portion of the image illumination propagating within the LOE due to internal reflection from the main outer surface from the first region to the second region is coupled and output toward the eye movement box from the LOE, The first set of partial reflective surfaces is oriented such that, by internal reflection from the main outer surface, a portion of the image illumination propagating within the LOE from the coupled input region is deflected toward the second region, and the deflection is the only in-plane element change in the propagation direction of the image illumination occurring between the coupled input region and the second region of the LOE. The optical system further includes an optical retarder positioned between the first region and the second region such that the LOE rotates the polarization of light deflected by the first set of partial reflectors before it reaches the second set of partial reflectors.

Images