Systems and methods for mixed reality

Abstract

To provide systems and methods for mixed reality.SOLUTION: A virtual image generation system comprises: a planar optical waveguide having opposing first and second faces; an in-coupling (IC) element configured for optically coupling a collimated light beam from an image projection assembly into the planar optical waveguide as an in-coupled light beam; a first orthogonal pupil expansion (OPE) element associated with the first face of the planar optical waveguide for splitting the in-coupled light beam into a first set of orthogonal light beamlets; a second orthogonal pupil expansion (OPE) element associated with the second face of the planar optical waveguide for splitting the in-coupled light beam into a second set of orthogonal light beamlets; and an exit pupil expansion (EPE) element associated with the planar optical waveguide for splitting the first and second sets of orthogonal light beamlets into an array of out-coupled light beamlets that exit the planar optical waveguide.SELECTED DRAWING: Figure 44

Description

[Technical Field]

[0001] The present disclosure relates to virtual reality, augmented reality, and mixed reality imaging and visualization systems. [Background technology]

[0002] Modern computing and display technologies have facilitated the development of "mixed reality" (MR) systems for so-called "virtual reality" (VR) or "augmented reality" (AR) experiences, in which digitally reproduced images, or portions thereof, are presented to a user in a manner that appears or can be perceived as real. VR scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual input. Augmented reality (AR) scenarios typically involve the presentation of digital or virtual image information as an extension to the visualization of the real world around the user (i.e., transparency to real-world visual input). Thus, AR scenarios involve the presentation of digital or virtual image information with transparency to real-world visual input.

[0003] MR systems typically generate and display color data, which increases the realism of the MR scenario. Many of these MR systems display color data by sequentially projecting sub-images in different (e.g., primary) colors or "fields" (e.g., red, green, and blue) corresponding to the color image in rapid succession. Projecting the color sub-images at a sufficiently high rate (e.g., 60 Hz, 120 Hz, etc.) can produce a smooth color MR scenario in the user's memory.

[0004] For example, referring to FIG. 1 , an augmented reality scene 4 is depicted in which a user of the AR / MR technology sees a real-world park-like setting 6 featuring people, trees, a building in the background, and a concrete platform 8. In addition to these items, the end user of the AR / MR technology also perceives as "seeing" a robot image 10 standing on the real-world platform 8 and a flying, cartoon-like avatar character 12 that appears to be an anthropomorphic bumblebee, although these elements 10, 12 do not exist in the real world. Consequently, the human visual perception system is highly complex, making it challenging to produce VR, AR, and / or MR technology that facilitates comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0005] Some VR, AR, and / or MR systems employ head-mounted displays (or helmet-mounted displays or smart glasses) that are at least loosely attached to the end user's head and therefore move as the user's head moves. When movement of the end user's head is detected by the display subsystem, the displayed data can be updated to account for changes in head pose (i.e., the orientation and / or location of the user's head). Head-mounted displays that enable AR / MR (i.e., simultaneous viewing of real and virtual objects) can have several different types of configurations. In one such configuration, often referred to as a "video see-through" display, a camera captures elements of a real scene, a computing system superimposes virtual elements on the captured real scene, and an opaque display presents the composite image to the eyes. Another configuration, often referred to as an "optical see-through" display, allows the end user to look through transparent (or translucent) elements in the display subsystem to directly view light from real objects in the environment. A transparent element, often referred to as a "combiner," overlaps the light from the display over the end user's viewpoint in the real world.

[0006] Some head-mounted VR / AR / MR systems employ a display screen within the field of view of the end user and an image projection assembly that projects images onto the display screen. As one example, the image projection assembly may take the form of a fiber optic scanning-based image projection assembly, and the display screen may take the form of an optical waveguide-based display, in which scanned and collimated light beams from the image projection assembly are injected via an internal coupling (IC) element and exit the surface of the optical waveguide-based display toward the user's eyes, thereby producing, for example, an image at a single optical viewing distance closer than infinity (e.g., arm's length), images at multiple discrete optical viewing distances or focal planes, and / or image layers stacked at multiple viewing distances or focal planes to represent a stereoscopic 3D object.

[0007] In head-mounted VR / AR / MR systems, given a fixed pupil distance (i.e., the distance from the final surface of the display screen and the user's eye or eyes), it is important that the entrance pupil of the user's eye (i.e., the image of the anatomical pupil as seen through the cornea) is aligned with and similar in size to the exit pupil of the display screen (i.e., the width of the cone of light available to the user's eye) in order to properly couple the instrument to one (in the case of a monocular arrangement) or both (in the case of a binocular arrangement) of the user's eye. A display screen exit pupil that is smaller than the user's eye entrance pupil will often result in a vignetted or vignetted image, while a display screen exit pupil that is larger than the user's eye entrance pupil will waste some light but allow for eye movement without vignetting or vignetting of the image.

[0008] To increase the wearability and comfort of head-mounted VR / AR / MR systems, it is desirable to miniaturize the image source and, in some cases, the image projection assembly, whenever possible. Without intervention, such an image projection assembly would result in an exit pupil much smaller than the entrance pupil of some eyes, assuming a reasonable pupil distance between the eye and the display screen. Therefore, optics are incorporated into the display subsystem to effectively expand the exit pupil of the display screen to match the entrance pupil of the user's eye. That is, the exit pupil of the display screen should create an "eyebox" that is slightly larger (e.g., 10 mm) than the entrance pupil of the user's eye (e.g., 5-7 mm), allowing eye movements within that eyebox to maintain a full view of the image presented by the display screen.

[0009] In addition to matching the exit pupil of the display screen with the entrance pupil of the user's eye, it is desirable to maximize angular resolution, minimize depth of field, and maximize the density of the wavefront density of the display screen in a VR / AR / MR system. Maximizing angular resolution results in a clearer and more lifelike virtual image, maximizing wavefront density mitigates image artifacts (such as the "screen door" effect (grid-like patterns and non-uniformities)), and minimizing depth of field allows the user to more easily accommodate to the virtual content on which the user is currently focused. That is, a smaller depth of field makes it easier for the eye to accommodate to the virtual content, providing a more natural visual real-world experience, while a larger depth of field makes it more difficult for the eye to accommodate to the virtual content, resulting in a less natural and possibly nauseating visual experience.

[0010] Therefore, there remains a need to provide a display screen for a VR / AR / MR system that is capable of producing a highly saturated optical beamlet array exit pupil that matches the entrance pupil of a user's eye without reducing the wearability of the VR / AR / MR system.

[0011] The brain's visual centers derive valuable perceptual information from the movement of the eyes and their components relative to one another. The vergence movement of the two eyes relative to one another (i.e., the rotational movement of the pupils toward or away from one another to converge and fixate the gaze of the eyes on an object) is closely linked to the focusing of the eye's lenses (or "accommodation"). Under normal conditions, changing the focus of the eye's lenses or accommodating the eyes to focus on objects at different distances will automatically result in a matching change in vergence to the same distance, a relationship known as the "accommodation-vergence reflex." Similarly, a change in vergence will, under normal conditions, induce a matching change in accommodation. Opposing this reflex, as in most conventional stereoscopic VR / AR / MR configurations, is known to cause eye strain, headaches, or other forms of discomfort to users.

[0012] Stereoscopic wearable glasses generally feature two displays for each eye configured to display images with slightly different element presentations so that a three-dimensional perspective is perceived by the human visual system. Such configurations have been found to be uncomfortable for many users due to a mismatch between vergence and accommodation (the "vergence-accommodation conflict"), which must be overcome to perceive images in three dimensions. In fact, some VR / AR / MR users are unable to tolerate stereoscopic configurations. Thus, most conventional VR / AR / MR systems are not optimally suited to presenting rich binocular three-dimensional experiences / scenarios in a manner that would be comfortable and maximally useful to users, in part because conventional systems are unable to address some of the fundamental aspects of the human perceptual system, including vergence-accommodation conflict.

[0013] One possible approach to addressing these issues (including vergence-divergence-accommodation conflict) is to project images onto multiple depth planes. To implement this type of system, one approach uses multiple light-guiding optical elements to direct light toward the user's eyes so that the light appears to originate from multiple depth planes. The light-guiding optical elements are designed to in-couple virtual light corresponding to a digital or virtual object, propagate it via total internal reflection (“TIR”), and then out-couple the virtual light and display the digital or virtual object to the user's eyes. In AR / MR systems, the light-guiding optical elements are also designed to be transparent to light from (e.g., reflected from) actual real-world objects. Thus, some of the light-guiding optical elements are designed to be transparent to real-world light from the real-world object while reflecting virtual light for propagation via TIR.

[0014] Various optical systems generate images at various depths to display VR / AR / MR scenarios. Some such optical systems are described in U.S. Utility Patent Application No. 14 / 555,585, the contents of which are previously incorporated by reference. Some VR / AR / MR systems employ wearable display devices (e.g., head-mounted displays, helmet-mounted displays, or smart glasses) that are at least loosely coupled to a user's head and therefore move as the user's head moves.

[0015] Some three-dimensional ("3-D") optical systems, such as those in VR / AR / MR systems, optically render virtual objects. The objects are "virtual" in that they are not actual physical objects located at discrete locations in 3-D space. Instead, the virtual objects exist only in the viewer's and / or listener's brain (e.g., visual centers) when stimulated by light beams directed at the audience's eyes.

[0016] VR / AR / MR systems must also be able to display virtual digital content at various perceived positions and distances relative to the user. Designing a VR / AR / MR system presents numerous other challenges, including the speed at which the system delivers the virtual digital content, the quality of the virtual digital content, the user's pupil distance (addressing vergence-accommodation conflicts), the size and portability of the system, and other system and optical challenges.

[0017] Furthermore, VR / AR / MR systems must be able to display virtual digital content in sharp focus to generate the realistic images required for a believable, immersive, and enjoyable VR / AR / MR experience / scenario. The lens of the eye must change shape (i.e., accommodate) to better focus the image or part of it.

[0018] The size limitations of head-mounted displays also result in image resolution limitations. Head-mounted VR / AR / MR display systems, such as those described in U.S. Utility Patent Application No. 14 / 555,585 (the contents of which are previously incorporated by reference), display images to users using light beams transmitted by TIR through light-guiding optical elements that preserve the light beam angle. The light beam diameter remains essentially the same throughout the light-guiding optical elements. The size limitations of head-mounted displays limit the sizes of various optical components (e.g., light sources, light-guiding optical elements, lenses, etc.), which in turn limit the diameter of the light beams generated by the head-mounted display. These light beam diameter limitations result in the resolution and FOV limitations described above.

[0019] The systems and methods described herein are designed to address these challenges. Summary of the Invention [Means for solving the problem]

[0020] According to a first aspect of the present disclosure, a virtual image generation system includes a planar optical waveguide (which may be a single integral substrate) having opposing first and second surfaces, and an incoupling (IC) element configured to optically couple a collimated light beam from an image projection assembly into the planar optical waveguide as an incoupling light beam. The image projection assembly may include a scanning device configured to scan the collimated light beam.

[0021] The virtual image generation system further comprises a first orthogonal pupil-expanding (OPE) element associated with the first face of the planar optical waveguide to split the incombined light beam into a first set of orthogonal light beamlets, and a second orthogonal pupil-expanding (OPE) element associated with the second face of the planar optical waveguide to split the incombined light beam into a second set of orthogonal light beamlets. In some embodiments, the first OPE element is disposed on the first face of the planar optical waveguide and the second OPE element is disposed on the second face of the planar optical waveguide. The IC element may be configured to optically couple, via total internal reflection (TIR), the collimated light beam from the image projection assembly as an internally coupled light beam within the planar optical waveguide along a first optical path that alternately intersects the first and second OPE elements, such that a portion of the internally coupled light beam is deflected, via TIR, as separate first and second sets of orthogonal light beamlets that propagate within the planar optical waveguide along second parallel optical paths, in which case the second parallel optical path may be orthogonal to the first optical path.

[0022] The virtual image generation system further comprises an exit pupil expansion (EPE) element associated with the planar optical waveguide to split the first and second sets of orthogonal light beamlets into an array of outcoupled light beamlets (e.g., a two-dimensional outcoupled light beamlet array) exiting the planar optical waveguide. The collimated light beam may define an entrance pupil, and the outcoupled light beamlet array may define an exit pupil that is larger than the entrance pupil, for example, at least 10 times larger than the entrance pupil, or even at least 100 times larger than the entrance pupil.

[0023] In some embodiments, the EPE element is disposed on one of the first and second surfaces of the planar optical waveguide. The first set of orthogonal optical beamlets and the second set of orthogonal optical beamlets may intersect with the EPE element such that a portion of the first set of orthogonal optical beamlets and the second set of orthogonal optical beamlets are deflected out of the planar optical waveguide as an outcoupled optical beamlet array. In some embodiments, the EPE element is configured to impart a convex wavefront profile onto the outcoupled optical beamlet array exiting the planar optical waveguide. In this case, the convex wavefront profile may have a center of radius at a focal point and produce an image at a given focal plane. In another embodiment, the IC element, the OPE element, and the EPE element are each diffractive.

[0024] According to a second aspect of the present disclosure, a virtual image generation system comprises a planar optical waveguide comprising a plurality of substrates, including a primary substrate having a first thickness and at least two secondary substrates having a second thickness, and at least two semi-reflective interfaces, each disposed between the substrates.

[0025] In some embodiments, each second thickness is less than the first thickness. For example, the first thickness may be at least twice the respective second thickness. In another embodiment, the second thicknesses are substantially equal to one another. In an alternative embodiment, two or more of the secondary substrates have second thicknesses that are unequal to one another. In this case, at least two of the unequal second thicknesses may be non-multiples of one another. In yet another embodiment, the first thickness may be a non-multiple of at least one of the second thicknesses and a non-multiple of each of the second thicknesses. In yet another embodiment, at least two of the plurality of secondary substrates have second thicknesses that are substantially unequal to one another.

[0026] In yet another embodiment, each semi-reflective interface may comprise a semi-reflective coating disposed between the substrates, for example, via one of physical vapor deposition (PVD), ion-assisted deposition (IAD), and ion beam sputtering (IBS), respectively. The coating may each be comprised of, for example, one or more of a metal (Au, Al, Ag, Ni-Cr, Cr, etc.), a dielectric (oxide, fluoride, and sulfide), and a semiconductor (Si, Ge). In yet another embodiment, adjacent ones of the substrates are comprised of materials having different refractive indices.

[0027] The virtual image generation system further includes an incoupling (IC) element configured to optically couple the collimated light beam from the image projection assembly as an incoupling light beam within the planar optical waveguide for propagation. The image projection assembly may include a scanning device configured to scan the collimated light beam. The semi-reflective interface is configured to split the incoupling light beam into multiple primary light beamlets that propagate within the primary substrate.

[0028] The virtual image generation system further comprises one or more diffractive optical elements (DOEs) associated with the planar optical waveguide to further split the plurality of primary light beamlets into an array of outcoupled light beamlets (e.g., a two-dimensional outcoupled beamlet array) that exit a face of the planar optical waveguide. The collimated light beam may define an entrance pupil, and the outcoupled light beamlet array may define an exit pupil larger than the entrance pupil, for example, at least 10 times larger than the entrance pupil, or even at least 100 times larger than the entrance pupil. In some embodiments, the first thickness of the primary substrate and the second thickness of the secondary substrate are selected such that the spacing between the centers of at least two adjacent ones of the outcoupled light beamlets is less than or equal to the width of the collimated light beam. In another embodiment, the first thickness and the second thickness are selected such that no gap greater than half of adjacent ones of the outcoupled light beamlets reside between their edges.

[0029] In some embodiments, the semi-reflective interface is configured to split the incoupling light beam into at least two incoupling light beamlets. In this case, the DOEs each comprise an orthogonal pupil expansion (OPE) element configured to split the at least two incoupling light beamlets into at least two sets of orthogonal light beamlets, the semi-reflective interface is configured to further split the at least two sets of orthogonal light beamlets into at least four sets of orthogonal light beamlets, and the DOEs comprise an exit pupil expansion (EPE) element configured to split the at least four sets of orthogonal light beamlets into a set of outcoupling light beamlets. The OPE element and the EPE element may be disposed on a face of the optical planar waveguide.

[0030] The at least two in-coupled optical beamlets may propagate within the planar optical waveguide along a first optical path that intersects with the OPE element via total internal reflection (TIR), such that a portion of the at least two in-coupled optical beamlets are diffracted via TIR into a set of at least two orthogonal optical beamlets that propagate within the planar optical waveguide along a second parallel optical path. The second parallel optical path may be orthogonal to the first optical path. The set of at least two orthogonal optical beamlets may intersect with the EPE element such that a portion of the set of at least two orthogonal optical beamlets is diffracted into a set of optical beamlets that are outcoupled out of the plane of the planar optical waveguide. In some embodiments, the EPE element may be configured to impart a convex wavefront profile onto the out-coupled optical beamlet array exiting the planar optical waveguide. In this case, the convex wavefront profile may have a radius centered at a focal point and produce an image at a given focal plane.

[0031] According to a third aspect of the present disclosure, a virtual image generation system comprises a planar optical waveguide comprising a plurality of substrates including a primary substrate having a first thickness and at least one secondary substrate each having at least one second thickness, and at least one semi-reflective interface disposed between the substrates.

[0032] The first thickness is at least twice the thickness of each of at least one second thickness. In some embodiments, the first thickness is a non-multiple of each of the second thicknesses. In other embodiments, the secondary substrate comprises a plurality of secondary substrates. In this case, the second thicknesses may be equal to one another, or two or more of the secondary substrates may have second thicknesses that are unequal to one another. The first thickness may be a non-multiple of at least one of the second thicknesses. At least two of the unequal second thicknesses may be non-multiples of one another.

[0033] In some embodiments, each semi-reflective interface comprises a semi-reflective coating, which may be disposed between the substrates, for example, via one of physical vapor deposition (PVD), ion-assisted deposition (IAD), and ion beam sputtering (IBS), respectively. The coating may each be comprised of, for example, one or more of a metal (Au, Al, Ag, Ni-Cr, Cr, etc.), a dielectric (oxide, fluoride, and sulfide), and a semiconductor (Si, Ge). In yet another embodiment, adjacent ones of the substrates are comprised of materials having different refractive indices.

[0034] The virtual image generation system further includes an incoupling (IC) element configured to optically couple the collimated light beam from the image projection assembly as an incoupling light beam within the planar optical waveguide for propagation. The image projection assembly may include a scanning device configured to scan the collimated light beam. The semi-reflective interface is configured to split the incoupling light beam into multiple primary light beamlets that propagate within the primary substrate.

[0035] The virtual image generation system further comprises one or more diffractive optical elements (DOEs) associated with the planar optical waveguide to further split the plurality of primary light beamlets into an array of outcoupled light beamlets (e.g., a two-dimensional outcoupled beamlet array) that exit a face of the planar optical waveguide. The collimated light beam may define an entrance pupil, and the outcoupled light beamlet array may define an exit pupil larger than the entrance pupil, for example, at least 10 times larger than the entrance pupil, or even at least 100 times larger than the entrance pupil. In some embodiments, the first thickness of the primary substrate and the second thickness of the secondary substrate are selected such that the spacing between the centers of at least two adjacent ones of the outcoupled light beamlets is less than or equal to the width of the collimated light beam. In another embodiment, the first thickness and the second thickness are selected such that no gap greater than half of adjacent ones of the outcoupled light beamlets reside between their edges.

[0036] In some embodiments, the semi-reflective interface is configured to split the incoupling light beam into at least two incoupling light beamlets. In this case, the DOEs each comprise an orthogonal pupil expansion (OPE) element configured to split the at least two incoupling light beamlets into at least two sets of orthogonal light beamlets, the semi-reflective interface is configured to further split the at least two sets of orthogonal light beamlets into at least four sets of orthogonal light beamlets, and the DOEs comprise an exit pupil expansion (EPE) element configured to split the at least four sets of orthogonal light beamlets into a set of outcoupling light beamlets. The OPE element and the EPE element may be disposed on a face of the optical planar waveguide.

[0037] The at least two in-coupled optical beamlets may propagate within the planar optical waveguide along a first optical path that intersects with the OPE element via total internal reflection (TIR), such that a portion of the at least two in-coupled optical beamlets are diffracted via TIR into a set of at least two orthogonal optical beamlets that propagate within the planar optical waveguide along a second parallel optical path. The second parallel optical path may be orthogonal to the first optical path. The set of at least two orthogonal optical beamlets may intersect with the EPE element such that a portion of the set of at least two orthogonal optical beamlets is diffracted into a set of optical beamlets that are outcoupled out of the plane of the planar optical waveguide. In some embodiments, the EPE element may be configured to impart a convex wavefront profile onto the out-coupled optical beamlet array exiting the planar optical waveguide. In this case, the convex wavefront profile may have a radius centered at a focal point and produce an image at a given focal plane.

[0038] According to a fourth aspect of the present disclosure, a virtual image generation system includes a pre-pupil expansion (PPE) element configured to receive a collimated light beam from an imaging element and split the collimated light beam into a set of initial outcoupled light beamlets. The virtual image generation system further includes a planar optical waveguide, an internal coupling (IC) element configured to optically couple the set of initial outcoupled light beamlets into the planar optical waveguide as a set of internally coupled light beamlets, and one or more diffractive elements associated with the planar optical waveguide to split the set of internally coupled light beamlets into a set of final outcoupled light beamlets that exit a face of the planar optical waveguide. The diffractive elements may include an orthogonal pupil expansion (OPE) element associated with the planar optical waveguide to further split the set of internally coupled light beamlets into a set of orthogonal light beamlets, and an exit pupil expansion (EPE) element associated with the planar optical waveguide to split the set of orthogonal light beamlets into a set of final outcoupled light beamlets.

[0039] In some embodiments, the collimated light beam defines an entrance pupil, the set of initially outcoupled light beamlets defines a pre-dilated pupil that is larger than the entrance pupil, and the set of final outcoupled light beamlets defines an exit pupil that is larger than the pre-dilated pupil. In one example, the pre-dilated pupil is at least 10 times larger than the entrance pupil, and the exit pupil is at least 10 times larger than the pre-dilated pupil. In some embodiments, the set of initially outcoupled light beamlets is optically coupled into a planar optical waveguide as a two-dimensional optical beamlet array, and the final outcoupled light beamlets exit a face of the planar optical waveguide as a two-dimensional optical beamlet array. In another embodiment, the set of initially outcoupled light beamlets is optically coupled into a planar optical waveguide as a one-dimensional optical beamlet array, and the final outcoupled light beamlets exit a face of the planar optical waveguide as a two-dimensional optical beamlet array.

[0040] In some embodiments, the PPE element comprises a compact planar optical waveguide, a compact OPE element associated with the compact planar optical waveguide for splitting the collimated light beam into a set of initial orthogonal light beamlets, and a compact EPE element associated with the compact planar optical waveguide for splitting the set of initial orthogonal light beamlets into a set of initial outcoupled light beamlets that exit a face of the compact planar optical waveguide. The PPE may further comprise a compact IC element configured to optically couple the collimated light beam into the planar optical waveguide.

[0041] In another embodiment, the PPE element comprises a diffractive beam splitter (e.g., a 1×N beam splitter or an M×N beam splitter) configured to split the collimated light beam into an initial set of diverging light beamlets, and a lens (e.g., a diffractive lens) configured to re-collimate the initial set of diverging light beamlets into a set of initial outcoupled light beamlets.

[0042] In yet another embodiment, the PPE element comprises a prism (e.g., a solid prism or a hollow prism) configured to split the collimated light beam into a set of incoupling light beamlets. The prism may comprise a semi-reflective prism plane configured to split the collimated light beam into a set of incoupling light beamlets. The prism may comprise a plurality of parallel prism planes configured to split the collimated light beam into a set of incoupling light beamlets. In this case, the parallel prism plane may comprise a semi-reflective prism plane. The plurality of parallel prism planes may comprise fully reflective prism planes, in which case a portion of the collimated light beam may be reflected in a first direction by at least one semi-reflective prism, and a portion of the collimated light beam may be transmitted to the fully reflective prism plane for reflection in the first direction. The prism may comprise a first set of parallel prism planes configured to split the collimated light beam into a set of initial orthogonal light beamlets that are reflected in a first direction, and a second set of parallel prism planes configured to split the initial orthogonal light beamlets into a set of in-combined light beamlets that are reflected in a second direction different from the first direction, and the first and second directivities may be orthogonal to each other.

[0043] In yet another embodiment, the PPE element comprises a first planar optical waveguide assembly configured to split the collimated light beam into a two-dimensional array of outcoupled light beamlets (e.g., an N×N light beamlet array) that exit a face of the first planar optical waveguide assembly, and a second planar optical waveguide assembly configured to split the two-dimensional outcoupled light beamlet array into a plurality of two-dimensional arrays of outcoupled light beamlets that exit a face of the second planar optical waveguide assembly as a set of incoupled light beamlets. The first and second planar optical waveguide assemblies may each have unequal thicknesses.

[0044] The two-dimensional outcoupling light beamlet array has an inter-beamlet spacing, and the multiple two-dimensional outcoupling light beamlet arrays are spatially offset from one another by an inter-array spacing that is different from the inter-beamlet spacing of the two-dimensional outcoupling light beamlet array. In some embodiments, the inter-array spacing of the multiple two-dimensional outcoupling light beamlet arrays and the inter-beamlet spacing of the two-dimensional outcoupling light beamlet array are non-multiples of one another. The inter-array spacing of the multiple two-dimensional outcoupling light beamlet arrays may be greater than the inter-beamlet spacing of the two-dimensional outcoupling light beamlet array.

[0045] In some embodiments, the first planar optical waveguide assembly includes a first planar optical waveguide having opposing first and second faces; a first internal coupling (IC) element configured to optically couple a collimated light beam within the first planar optical waveguide along a first optical path via total internal reflection (TIR) ​​for propagation; and a first exit pupil expander (E) associated with the first planar optical waveguide for splitting the collimated light beam into a one-dimensional array of optical beamlets that exit the second face of the first planar optical waveguide. a second IC element configured to optically couple the one-dimensional optical beamlet array into the second planar optical waveguide via TIR along a separate second optical path perpendicular to the first optical path for propagation therethrough; and a second exit pupil expander (EPE) element associated with the second planar optical waveguide for splitting the one-dimensional optical beamlet array into a two-dimensional optical beamlet array that exits the second face of the second planar optical waveguide. In this case, the first face of the second planar optical waveguide may be affixed to the second face of the first planar optical waveguide. The first and second planar optical waveguides may each have substantially equal thicknesses.

[0046] The second planar optical waveguide assembly includes a third planar optical waveguide having opposing first and second faces; a third IC element configured to optically couple the first two-dimensional optical beamlet array within the third planar optical waveguide via TIR along a separate third optical path for propagation; and a third EPE element associated with the third planar optical waveguide for splitting the two-dimensional optical beamlet array into a plurality of two-dimensional optical beamlet arrays that exit the second face of the third planar optical waveguide. The optical waveguide may include a fourth planar optical waveguide having two faces, a fourth IC element configured to optically couple the plurality of two-dimensional optical beamlet arrays for propagation within the fourth planar optical waveguide via TIR along a separate fourth optical path perpendicular to the third optical path, and a fourth EPE element associated with the fourth planar optical waveguide for splitting the plurality of two-dimensional optical beamlet arrays into a plurality of two-dimensional optical beamlet arrays that exit the second face of the fourth planar optical waveguide as input sets of optical beamlets. In this case, the first face of the fourth planar optical waveguide may be affixed to the second face of the third planar optical waveguide, and the first face of the third planar optical waveguide may be affixed to the second face of the second planar optical waveguide. The first and second planar optical waveguides may each have substantially equal thicknesses, and the third and fourth planar optical waveguides may each have substantially equal thicknesses. In this case, the substantially equal thickness of the first and second planar optical waveguides may be different from the substantially equal thickness of the third and fourth planar optical waveguides, and the equal thickness of the third and fourth planar optical waveguides may be greater than the equal thickness of the first and second planar optical waveguides.

[0047] In some embodiments, a mixed reality system includes a light source configured to generate a virtual light beam. The system also includes a light directing optical element having an input portion, an output portion, a first light directing optical sub-element, and a second light directing optical sub-element. The first light directing optical sub-element has a first thickness and the second light directing optical sub-element has a second thickness different from the first thickness.

[0048] In one or more embodiments, the light source and the light directing optical element are configured such that a virtual light beam enters the light directing optical element through the input portion, propagates through the light directing optical element by substantially total internal reflection, and splits into a plurality of virtual light beamlets. At least some of the plurality of virtual light beamlets may exit the light directing optical element through the output portion. The light directing optical element may be transmissive to the real-world light beam.

[0049] In one or more embodiments, neither the first ratio of the first and second thicknesses nor the second ratio of the second and first thicknesses is an integer. The input portion may include an internal coupling grating on the first light guiding optical subelement. The output portion may include an exit pupil expander on the first light guiding optical subelement. The second light guiding optical subelement may not overlie the exit pupil expander on the first light guiding optical subelement.

[0050] In one or more embodiments, the second thickness of the second light directing optical sub-element promotes substantially total internal reflection of light having a predetermined wavelength. The predetermined wavelength may be between 515 nm and 540 nm. The predetermined wavelength may be 520 nm or 532 nm. The predetermined wavelength may be 475 nm or 650 nm. The second thickness of the second light directing optical sub-element may promote substantially total internal reflection of a light beam generally parallel to the optical axis of the system more than a light beam oblique to the optical axis.

[0051] In one or more embodiments, the second light directing optical sub-element overlies substantially all of the first light directing optical sub-element. The second thickness may be substantially equal to an integer multiple of the wavelength of the virtual light beam. The second thickness may be an integer multiple of 475 nm, 520 nm, or 650 nm.

[0052] In one or more embodiments, the first and second light directing optical sub-elements each comprise a separate substantially flat sheet, such that the light directing optical element comprises a stack of substantially flat sheets. The light directing optical element may also have a refractive index gap between the first and second light directing optical sub-elements. The refractive index gap may be an air gap.

[0053] In one or more embodiments, the second light directing optical sub-element includes two reflective surfaces that reflect light in substantially the same direction. The second light directing optical sub-element may include two reflective surfaces that reflect light in substantially opposite directions. The system may also include a third light directing optical sub-element.

[0054] In another embodiment, a mixed reality system includes a light source configured to generate a virtual light beam. The system also includes a light directing optical element having an input portion, an output portion, a first light directing optical sub-element, and a second light directing optical sub-element. The first light directing optical sub-element has a first diffraction index. The second light directing optical sub-element has a second diffraction index different from the first diffraction index.

[0055] In one or more embodiments, the light source and the light directing optical element are configured such that a virtual light beam enters the light directing optical element through the input portion, propagates through the light directing optical element by substantially total internal reflection, and splits into a plurality of virtual light beamlets. At least some of the plurality of virtual light beamlets exit the light directing optical element through the output portion. The light directing optical element may be transparent to the real-world light beam.

[0056] In one or more embodiments, neither the first ratio of the first and second diffraction indices nor the second ratio of the second and first diffraction indices is an integer. The input portion may include an internal coupling grating on the first light guiding optical subelement. The output portion may include an exit pupil expander on the first light guiding optical subelement. The second light guiding optical subelement may not obscure the exit pupil expander on the first light guiding optical subelement.

[0057] In one or more embodiments, the second diffractive index of the second light directing optical sub-element promotes substantially total internal reflection of light having a predetermined wavelength. The predetermined wavelength may be between 515 nm and 540 nm. The predetermined wavelength may be 520 nm or 532 nm. The predetermined wavelength may be 475 nm or 650 nm.

[0058] In one or more embodiments, the second diffractive index of the second light directing optical sub-element promotes substantially total internal reflection of a light beam generally parallel to the optical axis of the system to a greater extent than a light beam oblique to the optical axis. The second light directing optical sub-element may overlie substantially all of the first light directing optical sub-element.

[0059] In one or more embodiments, the first and second light directing optical sub-elements each comprise a separate substantially flat sheet, such that the light directing optical element comprises a stack of substantially flat sheets. The light directing optical element may also have a refractive index gap between the first and second light directing optical sub-elements. The refractive index gap may be an air gap.

[0060] In one or more embodiments, the second light directing optical sub-element includes two reflective surfaces that reflect light in substantially the same direction. The second light directing optical sub-element may include two reflective surfaces that reflect light in substantially opposite directions. The system may also include a third light directing optical sub-element.

[0061] In yet another embodiment, a mixed reality system includes a light source configured to generate a virtual light beam. The system also includes a light directing optical element having an entrance portion, an orthogonal pupil expander, and multiple exit pupil expanders. The light source and light directing optical element are configured so that the virtual light beam enters the light directing optical element through the entrance portion, propagates through the light directing optical element by substantially total internal reflection, and splits into multiple first virtual light beamlets by interacting with the orthogonal pupil expander, and the multiple first virtual light beamlets enter respective ones of the multiple exit pupil expanders and split into multiple second virtual light beamlets by interacting with the multiple exit pupil expanders. At least some of the multiple second virtual light beamlets exit the light directing optical element through the exit pupil expander.

[0062] In one or more embodiments, the light directing optical element is transmissive to the real-world light beam. Each of the multiple exit pupil expanders may include a substantially planar sheet, such that the multiple exit pupil expanders include a stack of substantially planar sheets.

[0063] In one or more embodiments, the orthogonal pupil expander promotes substantially total internal reflection of light having a predetermined wavelength. The predetermined wavelength may be between 515 nm and 540 nm. The predetermined wavelength may be 520 nm or 532 nm. The predetermined wavelength may be 475 nm or 650 nm.

[0064] In one or more embodiments, the system also includes a plurality of light blockers that selectively block light to the plurality of exit pupil expanders. The plurality of light blockers may include LC shutters or PDLC outcoupling gratings. At least one of the plurality of light blockers may be positioned adjacent to an edge of the orthogonal pupil expander. At least one of the plurality of light blockers may be positioned adjacent to a central portion of the orthogonal pupil expander.

[0065] In yet another embodiment, a mixed reality system includes a light source configured to generate a virtual light beam. The system also includes a light directing optical element having an entrance portion, an orthogonal pupil expander, and an exit portion. The light source and light directing optical element are configured such that the virtual light beam enters the light directing optical element through the entrance portion, propagates through the light directing optical element by substantially total internal reflection, and splits into multiple virtual light beamlets by interacting with the orthogonal pupil expander. At least some of the multiple virtual light beamlets exit the light directing optical element through the exit portion.

[0066] In one or more embodiments, the orthogonal pupil expander includes a first orthogonal pupil sub-expander and a second orthogonal pupil sub-expander. The first and second orthogonal pupil sub-expanders split an incident light beam into the respective first and second orthogonal pupil sub-expanders. The first and second orthogonal pupil sub-expanders may each be a separate flat sheet. The first and second orthogonal pupil sub-expanders may be stacked on top of each other.

[0067] In one or more embodiments, the first orthogonal pupil sub-expander includes a first exit edge for directing the beamlet into the second orthogonal pupil sub-expander. The first exit edge may include a mirror. The first orthogonal pupil sub-expander may include a second exit edge for directing the beamlet into the second orthogonal pupil sub-expander. The first and second exit edges may each include a respective mirror.

[0068] In one or more embodiments, the orthogonal pupil expander includes first and second reflective edges. The first and second reflective edges may be orthogonal to one another. The orthogonal pupil expander may also include a third reflective edge.

[0069] In one or more embodiments, the orthogonal pupil expander includes an internal coupling grating and a highly diffractive region disposed opposite the internal coupling grating. The orthogonal pupil expander may include a first optical modifier configured to absorb light within a first wavelength range. The orthogonal pupil expander may also include a second optical modifier configured to absorb light within a second wavelength range. The first and second optical modifiers may be orthogonal to each other.

[0070] In one or more embodiments, the orthogonal pupil expander also includes a third light modifier configured to absorb light within a third wavelength range. The orthogonal pupil expander may include a diffractive optical element forming a "V" shape. The orthogonal pupil expander may include a plurality of PDLC switches.

[0071] In yet another embodiment, a mixed reality system includes a light source configured to generate a virtual light beam. The system also includes a light directing optical element having an input portion, an output portion, a first light directing optical sub-element, and a second light directing optical sub-element. The first light directing optical sub-element has a first light-modifying characteristic. The second light directing optical sub-element has a second light-modifying characteristic that is different from the first light-modifying characteristic.

[0072] The virtual image generation system comprises a plurality of substrates, including a primary substrate having a first thickness and at least two secondary substrates having a second thickness, and a planar optical waveguide, each substrate comprising at least two semi-reflective interfaces disposed between the substrates. The first thicknesses may be at least twice the respective second thicknesses. The system further comprises an internal coupling (IC) element configured to optically couple a collimated light beam within the planar optical waveguide as an internally coupled light beam for propagation. The semi-reflective interfaces are configured to split the internally coupled light beam into a plurality of first-order light beamlets propagating within the primary substrate. The system further comprises one or more diffractive optical elements (DOEs) associated with the planar optical waveguide for further splitting the plurality of first-order light beamlets into an array of externally coupled light beamlets exiting a face of the planar optical waveguide.

[0073] The virtual image generation system includes a pre-pupil expansion (PPE) element configured to receive a collimated light beam from the imaging element and split the collimated light beam into a set of initial outcoupled light beamlets, a planar optical waveguide, an internal coupling (IC) element configured to optically couple the set of initial outcoupled light beamlets into the planar optical waveguide as a set of internally coupled light beamlets, and one or more diffractive elements associated with the planar optical waveguide for splitting the set of internally coupled light beamlets into a set of final outcoupled light beamlets that exit a face of the planar optical waveguide.

[0074] The mixed reality system includes a light source configured to generate a virtual light beam. The system also includes a light directing optical element having an input portion, an output portion, a first light directing optical sub-element, and a second light directing optical sub-element. The first light directing optical sub-element has a first thickness and the second light directing optical sub-element has a second thickness different from the first thickness.

[0075] Additional and other objects, features, and advantages of the present disclosure are set forth in the detailed description, drawings, and claims. The present specification also provides, for example, the following items: (Item 1) 1. A virtual image generation system, comprising: a planar optical waveguide comprising a plurality of substrates, the plurality of substrates including primary substrates having a first thickness and at least secondary substrates each having at least one second thickness, and at least one semi-reflective interface disposed between the substrates, the first thickness being at least twice each of the at least one second thickness; an internal coupling (IC) element configured to optically couple a collimated light beam from an image projection assembly as an internally coupled light beam within the planar optical waveguide for propagation, the at least one semi-reflective interface configured to split the internally coupled light beam into a plurality of primary light beamlets propagating within the primary substrate; one or more diffractive optical elements (DOEs) associated with the planar optical waveguide for further splitting the plurality of primary light beamlets into an array of outcoupled light beamlets that exit a face of the planar optical waveguide; and A virtual image generation system comprising: (Item 2) Item 1. The virtual image generation system of item 1, wherein the first thickness is a non-multiple of each of the at least one second thickness. (Item 3) Item 10. The virtual image generation system of item 1, wherein the at least one secondary substrate comprises a plurality of secondary substrates. (Item 4) Item 4. The virtual image generation system of item 3, wherein at least two of the plurality of secondary substrates have second thicknesses that are substantially equal to one another. (Item 5) Item 4. The virtual image generation system of item 3, wherein at least two of the plurality of secondary substrates have second thicknesses that are substantially unequal to one another. (Item 6) 6. The virtual image generation system of claim 5, wherein the first thickness is a non-multiple of at least one of the second thicknesses. (Item 7) Item 6. The virtual image generation system of item 5, wherein at least two of the unequal second thicknesses are non-multiples of each other. (Item 8) Item 1. The virtual image generation system of item 1, wherein the first thickness and the second thickness are selected such that the spacing between the centers of at least two adjacent ones of the outcoupled light beamlets is less than or equal to the width of the collimated light beam. (Item 9) Item 1, a virtual image generating system, wherein the first thickness and the second thickness are selected such that no gap greater than half of adjacent ones of the outcoupled light beamlets reside between their edges. (Item 10) Item 10. The virtual image generating system of item 1, wherein each of the at least one semi-reflective interface comprises a semi-reflective coating. (Item 11) Item 11. The virtual image generating system of item 10, wherein the at least one semi-reflective coating is disposed between the substrates via one of physical vapor deposition (PVD), ion-assisted deposition (IAD), and ion beam sputtering (IBS), respectively. (Item 12) Item 11. The virtual image generating system of item 10, wherein each of the at least one semi-reflective coating is made of one or more of a metal (Au, Al, Ag, Ni—Cr, Cr, etc.), a dielectric (oxide, fluoride, and sulfide), and a semiconductor (Si, Ge). (Item 13) Item 10. The virtual image generating system of item 1, wherein adjacent ones of the plurality of substrates are made of materials having different refractive indices. (Item 14) Item 2. The virtual image generation system of item 1, wherein the at least one semi-reflective interface is configured to split the internally coupled light beam into at least two internally coupled light beamlets, and the one or more DOEs each comprise an orthogonal pupil expansion (OPE) element configured to split the at least two internally coupled light beamlets into a set of at least two orthogonal light beamlets, and the at least one semi-reflective interface is further configured to split the at least two sets of orthogonal light beamlets into a set of at least four orthogonal light beamlets, and the one or more DOEs comprise an exit pupil expansion (EPE) element configured to split the set of at least four orthogonal light beamlets into the set of externally coupled light beamlets. (Item 15) Item 15. The virtual image generating system of item 14, wherein the OPE element and EPE element are disposed on a surface of the optical planar waveguide. (Item 16) Item 15. The virtual image generation system of item 14, wherein the at least two internally coupled light beamlets propagate within the planar optical waveguide along a first optical path that intersects the OPE element via total internal reflection (TIR), such that a portion of the at least two internally coupled light beamlets are diffracted via TIR as a set of at least two orthogonal light beamlets that propagate within the planar optical waveguide along a second parallel optical path. (Item 17) Item 17. The virtual image generation system of item 16, wherein the second parallel optical path is orthogonal to the first optical path. (Item 18) Item 17. The virtual image generating system of item 16, wherein the set of at least two orthogonal optical beamlets intersects the EPE element such that a portion of the set of at least two orthogonal optical beamlets is diffracted as a set of optical beamlets that are outcoupled out of the plane of the planar optical waveguide. (Item 19) Item 15. The virtual image generation system of item 14, wherein the EPE element is configured to impart a convex wavefront profile onto the outcoupled optical beamlet array exiting the planar optical waveguide, the convex wavefront profile having a center of radius at a focal point and producing an image at a given focal plane. (Item 20) Item 1. The virtual image generation system of item 1, wherein the collimated light beam defines an entrance pupil and the outcoupling light beamlet array defines an exit pupil that is larger than the entrance pupil. (Item 21) 21. The virtual image generation system of claim 20, wherein the exit pupil is at least 10 times larger than the entrance pupil. (Item 22) 21. The virtual image generation system of item 20, wherein the exit pupil is at least 100 times larger than the entrance pupil. (Item 23) Item 1, a virtual image generation system, wherein the outcoupling optical beamlet array is a two-dimensional outcoupling optical beamlet array. (Item 24) Item 1. The virtual image generation system of item 1, further comprising a display subsystem having an image projection assembly configured to generate the collimated light beam. (Item 25) Item 25. The virtual image generation system of item 24, wherein the image projection assembly comprises a scanning device configured to scan the collimated light beam. (Item 26) 1. A virtual image generation system, comprising: a planar optical waveguide having opposing first and second surfaces; an incoupling (IC) element configured to optically couple a collimated light beam from an image projection assembly into the planar optical waveguide as an incoupling light beam; a first orthogonal pupil expansion (OPE) element associated with a first surface of the planar optical waveguide for splitting the incombined light beam into a first set of orthogonal light beamlets; a second orthogonal pupil expansion (OPE) element associated with a second surface of the planar optical waveguide for splitting the incombined light beam into a second set of orthogonal light beamlets; an exit pupil expansion (EPE) element associated with the planar optical waveguide for splitting the first and second sets of orthogonal optical beamlets into an array of outcoupled optical beamlets exiting the planar optical waveguide; A virtual image generation system comprising: (Item 27) Item 26. The virtual image generation system of item 25, wherein the planar optical waveguide is formed from a single, integral substrate. (Item 28) 26. The virtual image generation system of item 25, wherein the first OPE element is disposed on a first surface of the planar optical waveguide and the second OPE element is disposed on a second surface of the planar optical waveguide. (Item 29) Item 26. The virtual image generation system of item 25, wherein the EPE element is disposed on one of the first and second surfaces of the planar optical waveguide. (Item 30) Item 26. The virtual image generation system of item 25, wherein the IC element is configured to optically couple a collimated light beam from the image projection assembly as an internally coupled light beam within the planar optical waveguide via total internal reflection (TIR) ​​for propagation along a first optical path that alternately intersects the first OPE element and the second OPE element, such that a portion of the internally coupled light beam is deflected via TIR as the individual first set of orthogonal light beamlets and the second set of orthogonal light beamlets that propagate within the planar optical waveguide along second parallel optical paths. (Item 31) Item 31. The virtual image generation system of item 30, wherein the second parallel optical path is orthogonal to the first optical path. (Item 32) Item 26. The virtual image generating system of item 25, wherein the first set of orthogonal optical beamlets and the second set of orthogonal optical beamlets intersect with the EPE element such that a portion of the first set of orthogonal optical beamlets and the second set of orthogonal optical beamlets are deflected out of the planar optical waveguide as an outcoupled optical beamlet array. (Item 33) 26. The virtual image generation system of item 25, wherein the EPE element is configured to impart a convex wavefront profile onto the outcoupled optical beamlet array exiting the planar optical waveguide, the convex wavefront profile having a center of radius at a focal point and producing an image at a given focal plane. (Item 34) 26. The virtual image generation system of item 25, wherein the collimated light beam defines an entrance pupil and the outcoupling light beamlet array defines an exit pupil that is larger than the entrance pupil. (Item 35) Item 35. The virtual image generation system of item 34, wherein the exit pupil is at least 10 times larger than the entrance pupil. (Item 36) Item 35. The virtual image generation system of item 34, wherein the exit pupil is at least 100 times larger than the entrance pupil. (Item 37) 26. The virtual image generating system of item 25, wherein the IC element, the OPE element, and the EPE element are each diffractive. (Item 38) 26. The virtual image generation system of item 25, wherein the outcoupling optical beamlet array is a two-dimensional outcoupling optical beamlet array. (Item 39) Item 26. The virtual image generation system of item 25, further comprising the image projection assembly. (Item 40) 40. The virtual image generation system of claim 39, wherein the image projection assembly comprises a scanning device configured to scan the collimated light beam. (Item 41) 1. A virtual image generation system, comprising: a planar optical waveguide comprising a plurality of substrates, the plurality of substrates including a primary substrate having a first thickness and at least two secondary substrates having a second thickness, and at least two semi-reflective interfaces respectively disposed between the substrates; an internal coupling (IC) element configured to optically couple a collimated light beam from an image projection assembly as an internally coupled light beam within the planar optical waveguide for propagation, the at least two semi-reflective interfaces configured to split the internally coupled light beam into a plurality of primary light beamlets propagating within the primary substrate; one or more diffractive optical elements (DOEs) associated with the planar optical waveguide for further splitting the plurality of primary light beamlets into an array of outcoupled light beamlets that exit a face of the planar optical waveguide; and A virtual image generation system comprising: (Item 42) Item 42. The virtual image generation system of item 41, wherein each of the second thicknesses is less than the first thickness. (Item 43) Item 42. The virtual image generation system of item 41, wherein the first thickness is at least twice the respective second thickness. (Item 44) Item 42. The virtual image generation system of item 41, wherein the second thicknesses are substantially equal to each other. (Item 45) Item 42. The virtual image generation system of item 41, wherein the first thickness is a non-multiple of at least one of the second thicknesses. (Item 46) Item 42. The virtual image generation system of item 41, wherein two or more of the at least two secondary substrates have second thicknesses that are substantially unequal to one another. (Item 47) Item 47. The virtual image generation system of item 46, wherein the first thickness is a non-multiple of at least one of the second thicknesses. (Item 48) Item 47. The virtual image generation system of item 46, wherein at least two of the unequal second thicknesses are non-multiples of each other. (Item 49) Item 42. The virtual image generation system of item 41, wherein the first thickness and the second thickness are selected such that the spacing between the centers of at least two adjacent ones of the outcoupled light beamlets is less than or equal to the width of the collimated light beam. (Item 50) Item 42. The virtual image generating system of item 41, wherein the first thickness and the second thickness are selected such that no gap greater than half of adjacent ones of the outcoupled light beamlets resides between their edges. (Item 51) Item 42. The virtual image generating system of item 41, wherein each of the at least two semi-reflective interfaces comprises a semi-reflective coating. (Item 52) Item 52. The virtual image generating system of item 51, wherein the at least two semi-reflective coatings are each disposed between the substrates via one of physical vapor deposition (PVD), ion-assisted deposition (IAD), and ion beam sputtering (IBS). (Item 53) 52. The virtual image generating system of item 51, wherein each of the at least two semi-reflective coatings is made of one or more of a metal (Au, Al, Ag, Ni-Cr, Cr, etc.), a dielectric (oxide, fluoride, and sulfide), and a semiconductor (Si, Ge). (Item 54) Item 42. The virtual image generation system of item 41, wherein adjacent ones of the plurality of substrates are made of materials having different refractive indices. (Item 55) Item 42. The virtual image generation system of Item 41, wherein the at least two semi-reflective interfaces are configured to split the internally coupled light beam into at least two internally coupled light beamlets, the one or more DOEs each comprise an orthogonal pupil expansion (OPE) element configured to split the at least two internally coupled light beamlets into a set of at least two orthogonal light beamlets, the at least two semi-reflective interfaces are configured to further split the at least two sets of orthogonal light beamlets into a set of at least four orthogonal light beamlets, and the one or more DOEs comprise an exit pupil expansion (EPE) element configured to split the set of at least four orthogonal light beamlets into the set of externally coupled light beamlets. (Item 56) Item 56. The virtual image generation system of item 55, wherein the OPE element and EPE element are disposed on a surface of the optical planar waveguide. (Item 57) Item 56. The virtual image generation system of item 55, wherein the at least two internally coupled light beamlets propagate within the planar optical waveguide along a first optical path that intersects the OPE element via total internal reflection (TIR), such that a portion of the at least two internally coupled light beamlets are diffracted via TIR as a set of at least two orthogonal light beamlets that propagate within the planar optical waveguide along a second parallel optical path. (Item 58) Item 58. The virtual image generation system of item 57, wherein the second parallel optical path is orthogonal to the first optical path. (Item 59) Item 58. The virtual image generating system of item 57, wherein the set of at least two orthogonal optical beamlets intersects the EPE element such that a portion of the set of at least two orthogonal optical beamlets is diffracted as a set of optical beamlets that are outcoupled out of the plane of the planar optical waveguide. (Item 60) Item 56. The virtual image generation system of item 55, wherein the EPE element is configured to impart a convex wavefront profile onto the outcoupled optical beamlet array exiting the planar optical waveguide, the convex wavefront profile having a center of radius at a focal point and producing an image at a given focal plane. (Item 61) Item 42. The virtual image generation system of item 41, wherein the collimated light beam defines an entrance pupil and the outcoupling light beamlet array defines an exit pupil that is larger than the entrance pupil. (Item 62) Item 62. The virtual image generation system of item 61, wherein the exit pupil is at least 10 times larger than the entrance pupil. (Item 63) Item 62. The virtual image generation system of item 61, wherein the exit pupil is at least 100 times larger than the entrance pupil. (Item 64) Item 42. The virtual image generation system of item 41, wherein the outcoupling optical beamlet array is a two-dimensional outcoupling optical beamlet array. (Item 65) Item 42. The virtual image generation system of item 41, further comprising a display subsystem having an image projection assembly configured to generate the collimated light beam. (Item 66) Item 66. The virtual image generation system of item 65, wherein the image projection assembly comprises a scanning device configured to scan the collimated light beam. (Item 67) 1. A virtual image generation system, comprising: a pre-pupil expansion (PPE) element configured to receive a collimated light beam from the imaging element and split the collimated light beam into a set of initially outcoupled light beamlets; a planar optical waveguide; an internal coupling (IC) element configured to optically couple the set of initial outcoupled optical beamlets into the planar optical waveguide as a set of incoupled optical beamlets; one or more diffractive elements associated with the planar optical waveguide for splitting the set of in-coupled light beamlets into a set of final out-coupled light beamlets that exit a face of the planar optical waveguide; A virtual image generation system comprising: (Item 68) Item 68. The virtual image generation system of item 67, wherein the collimated light beam defines an entrance pupil, the set of initial outcoupled light beamlets defines a pre-dilated pupil that is larger than the entrance pupil, and the set of final outcoupled light beamlets defines an exit pupil that is larger than the pre-dilated pupil. (Item 69) Item 69. The virtual image generation system of item 68, wherein the pre-dilated pupil is at least 10 times larger than the entrance pupil and the exit pupil is at least 10 times larger than the pre-dilated pupil. (Item 70) Item 68. The virtual image generation system of item 67, wherein the set of initial outcoupled optical beamlets is optically coupled into the planar optical waveguide as a two-dimensional optical beamlet array, and the set of final outcoupled optical beamlets exits the face of the planar optical waveguide as a two-dimensional optical beamlet array. (Item 71) Item 68. The virtual image generation system of item 67, wherein the set of initially outcoupled optical beamlets is optically coupled into the planar optical waveguide as a one-dimensional optical beamlet array, and the set of final outcoupled optical beamlets exits the face of the planar optical waveguide as a two-dimensional optical beamlet array. (Item 72) Item 68. The virtual image generation system of item 67, wherein the one or more diffractive elements comprise an orthogonal pupil expansion (OPE) element associated with the planar optical waveguide to further split the set of internally coupled light beamlets into a set of orthogonal light beamlets, and an exit pupil expansion (EPE) element associated with the planar optical waveguide to split the set of orthogonal light beamlets into the final set of externally coupled light beamlets. (Item 73) The PPE element comprises: a compact planar optical waveguide; a compact OPE element associated with the compact planar optical waveguide for splitting the collimated light beam into a set of initial orthogonal light beamlets; a compact EPE element associated with the compact planar optical waveguide for splitting the set of initial orthogonal optical beamlets into a set of initial outcoupled optical beamlets emerging from a face of the compact planar optical waveguide; Item 73. The virtual image generation system of item 72, comprising: (Item 74) Item 74. The virtual image generation system of item 73, wherein the PPE element further comprises a miniature IC element configured to optically couple the collimated light beam into the planar optical waveguide. (Item 75) The PPE element comprises: a diffractive beam splitter configured to split the collimated light beam into an initial set of diverging light beamlets; a lens configured to recollimate the initial set of diverging light beamlets into the initial set of outcoupled light beamlets; Item 68. The virtual image generation system of item 67, comprising: (Item 76) Item 76. The virtual image generation system of item 75, wherein the diffractive beam splitter is a 1×N beam splitter. (Item 77) Item 76. The virtual image generation system of item 75, wherein the diffractive beam splitter is an M×N beam splitter. (Item 78) Item 76. The virtual image generation system of item 75, wherein the lens is a diffractive lens. (Item 79) Item 68. The virtual image generation system of item 67, wherein the PPE element comprises a prism configured to split the collimated light beam into the set of internally coupled light beamlets. (Item 80) 80. The virtual image generation system of item 79, wherein the prism is a solid prism. (Item 81) 80. The virtual image generation system of item 79, wherein the prism is a hollow prism. (Item 82) 80. The virtual image generation system of item 79, wherein the prism comprises a semi-reflective prism plane configured to split the collimated light beam into the set of internally coupled light beamlets. (Item 83) Item 83. The virtual image generation system of item 82, wherein the prism comprises a plurality of parallel prism planes configured to split the collimated light beam into the set of internally coupled light beamlets, and the two parallel prism planes comprise the semi-reflective prism planes. (Item 84) Item 84. The virtual image generation system of item 83, wherein the plurality of parallel prism planes comprise fully reflective prism planes, a portion of the collimated light beam is reflected in a first direction by the at least one semi-reflective prism, and a portion of the collimated light beam is transmitted to the fully reflective prism plane due to reflection in the first direction. (Item 85) Item 79. The virtual image generating system of item 79, wherein the prism comprises a first set of parallel prism planes configured to split the collimated light beam into a set of initial orthogonal light beamlets reflected in a first direction, and a second set of parallel prism planes configured to split the initial orthogonal light beamlets into a set of internally coupled light beamlets reflected in a second direction different from the first direction. (Item 86) Item 86. The virtual image generation system of item 85, wherein the first and second directions are mutually orthogonal. (Item 87) The PPE element comprises: a first planar optical waveguide assembly configured to split the collimated light beam into a two-dimensional array of outcoupled light beamlets exiting a face of the first planar optical waveguide assembly, the two-dimensional outcoupled light beamlet array having an inter-beamlet spacing; a second planar optical waveguide assembly configured to split the two-dimensional outcoupled optical beamlet array into a plurality of two-dimensional arrays of outcoupled optical beamlets that exit a face of the second planar optical waveguide assembly as the set of incoupled optical beamlets, the plurality of two-dimensional outcoupled optical beamlet arrays being spatially offset from one another by an inter-array spacing that is different from an inter-beamlet spacing of the two-dimensional outcoupled optical beamlet array; Item 68. The virtual image generation system of item 67, comprising: (Item 88) Item 88. The virtual image generation system of item 87, wherein the two-dimensional optical beamlet array is an N×N optical beamlet array. (Item 89) Item 88. The virtual image generation system of item 87, wherein the inter-array spacing of the plurality of two-dimensional outcoupling optical beamlet arrays and the inter-beamlet spacing of the two-dimensional outcoupling optical beamlet array are non-multiples of each other. (Item 90) Item 88. The virtual image generation system of item 87, wherein the inter-array spacing of the plurality of two-dimensional out-coupled light beamlet arrays exceeds the inter-beamlet spacing of the two-dimensional out-coupled light beamlet array. (Item 91) Item 88. The virtual image generation system of item 87, wherein the first and second planar optical waveguide assemblies each have unequal thicknesses. (Item 92) The first planar optical waveguide assembly comprises: a first planar optical waveguide having opposing first and second faces; a first internal coupling (IC) element configured to optically couple the collimated light beam within the first planar optical waveguide along a first optical path via total internal reflection (TIR) ​​for propagation; a first exit pupil expander (EPE) element associated with the first planar optical waveguide to split the collimated light beam into a one-dimensional array of light beamlets that exit a second surface of the first planar optical waveguide; and a second planar optical waveguide having opposing first and second faces; a second IC element configured to optically couple the one-dimensional optical beamlet array for propagation within the second planar optical waveguide via TIR along a separate second optical path perpendicular to the first optical path; and a second exit pupil expander (EPE) element associated with the second planar optical waveguide for splitting the one-dimensional optical beamlet array into a two-dimensional optical beamlet array exiting a second surface of the second planar optical waveguide; Item 88. The virtual image generation system of item 87, comprising: (Item 93) Item 93. The virtual image generation system of item 92, wherein the first surface of the second planar optical waveguide is affixed to the second surface of the first planar optical waveguide. (Item 94) Item 93. The virtual image generation system of item 92, wherein the first and second planar optical waveguides each have a substantially equal thickness. (Item 95) the second planar optical waveguide assembly comprising: a third planar optical waveguide having opposing first and second faces; a third IC element configured to optically couple the first two-dimensional optical beamlet array via TIR along a respective third optical path within the third planar optical waveguide for propagation; a third EPE element associated with the third planar optical waveguide to split the two-dimensional optical beamlet array into a plurality of two-dimensional optical beamlet arrays exiting a second surface of the third planar optical waveguide; a fourth planar optical waveguide having opposing first and second faces; a fourth IC element configured to optically couple the plurality of two-dimensional optical beamlet arrays for propagation within the fourth planar optical waveguide via TIR along a respective fourth optical path perpendicular to the third optical path; and a fourth EPE element associated with the fourth planar optical waveguide for splitting the plurality of two-dimensional optical beamlet arrays into a plurality of two-dimensional optical beamlet arrays that exit a second surface of the fourth planar optical waveguide as input sets of optical beamlets; Item 93. The virtual image generation system of item 92, comprising: (Item 96) Item 96. The virtual image generation system of item 95, wherein a first surface of the fourth planar optical waveguide is affixed to a second surface of the third planar optical waveguide. (Item 97) Item 97. The virtual image generation system of item 96, wherein a first surface of the third planar optical waveguide is affixed to a second surface of the second planar optical waveguide. (Item 98) Item 96. The virtual image generation system of item 95, wherein the first and second planar optical waveguides each have a substantially equal thickness, and the third and fourth planar optical waveguides each have a substantially equal thickness. (Item 99) Item 98. The virtual image generation system of item 97, wherein the substantially equal thicknesses of the first and second planar optical waveguides are different from the substantially equal thicknesses of the third and fourth planar optical waveguides. (Item 100) Item 100. The virtual image generation system of item 99, wherein the substantially equal thicknesses of the third and fourth planar optical waveguides exceed the substantially equal thicknesses of the first and second planar optical waveguides. (Item 101) 1. A mixed reality system, comprising: a light source configured to generate a virtual light beam; a light directing optical element having an input portion, an output portion, a first light directing optical sub-element, and a second light directing optical sub-element; Equipped with the first light directing optical sub-element has a first thickness; the second light directing optical sub-element has a second thickness different from the first thickness; Mixed reality system. (Item 102) The light source and the light directing optical element are configured such that the virtual light beam: (a) through the entrance portion into the light directing optical element; (b) propagating through the light directing optical element by substantially total internal reflection; (c) Splitting into multiple virtual light beamlets Item 102. The system of item 101, configured such that at least some of the plurality of virtual light beamlets exit the light directing optical element through the exit portion. (Item 103) Item 102. The system of item 101, wherein the light directing optical element is transparent to a real-world light beam. (Item 104) Item 102. The system of item 101, wherein neither the first ratio of the first and second thicknesses nor the second ratio of the second and first thicknesses is an integer. (Item 105) the entrance portion comprises an internal coupling grating on the first light directing optical sub-element; the output portion comprises an exit pupil expander on the first light directing optical sub-element; the second light directing optical sub-element is not overlaid by an exit pupil expander on the first light directing optical sub-element; Item 102. The system of item 101. (Item 106) Item 102. The system of item 101, wherein the second thickness of the second light directing optical sub-element promotes substantially total internal reflection of light having a predetermined wavelength. (Item 107) Item 107. The system according to item 106, wherein the predetermined wavelength is 515 nm to 540 nm. (Item 108) Item 108. The system of item 107, wherein the predetermined wavelength is 520 nm or 532 nm. (Item 109) Item 107. The system of item 106, wherein the predetermined wavelength is 475 nm or 650 nm. (Item 110) Item 102. The system of item 101, wherein the second thickness of the second light-guiding optical sub-element promotes substantially total internal reflection of a light beam that is approximately parallel to an optical axis of the system to a greater extent than a light beam that is oblique to the optical axis. (Item 111) Item 102. The system of item 101, wherein the second light directing optical sub-element overlies substantially all of the first light directing optical sub-element. (Item 112) Item 112. The system of item 111, wherein the second thickness is substantially equal to an integer multiple of the wavelength of the virtual light beam. (Item 113) Item 112. The system of item 111, wherein the second thickness is an integer multiple of 475 nm, 520 nm, or 650 nm. (Item 114) Item 102. The system of item 101, wherein the first and second light directing optical sub-elements each comprise a separate substantially flat sheet, such that the light directing optical element comprises a stack of substantially flat sheets. (Item 115) Item 115. The system of item 114, wherein the light directing optical element also has a refractive index gap between the first and second light directing optical sub-elements. (Item 116) Item 116. The system of item 115, wherein the refractive index gap is an air gap. (Item 117) Item 102. The system of item 101, wherein the second light directing optical sub-element comprises two reflective surfaces that reflect light in substantially the same direction. (Item 118) Item 102. The system of item 101, wherein the second light directing optical sub-element comprises two reflective surfaces that reflect light in substantially opposite directions. (Item 119) Item 102. The system of item 101, further comprising a third light directing optical sub-element. (Item 120) 1. A mixed reality system, comprising: a light source configured to generate a virtual light beam; a light directing optical element having an input portion, an output portion, a first light directing optical sub-element, and a second light directing optical sub-element; Equipped with the first light directing optical sub-element has a first diffraction index; the second light directing optical sub-element has a second diffraction index different from the first diffraction index; Mixed reality system. (Item 121) The light source and the light directing optical element are configured such that the virtual light beam: (a) through the entrance portion into the light directing optical element; (b) propagating through the light directing optical element by substantially total internal reflection; (c) Splitting into multiple virtual light beamlets Item 121. The system of item 120, configured such that at least some of the plurality of virtual light beamlets exit the light directing optical element through the exit portion. (Item 122) Item 121. The system of item 120, wherein the light directing optical element is transparent to a real-world light beam. (Item 123) Item 121. The system of item 120, wherein neither the first ratio of the first and second diffraction indices nor the second ratio of the second and first diffraction indices is an integer. (Item 124) the entrance portion comprises an internal coupling grating on the first light directing optical sub-element; the output portion comprises an exit pupil expander on the first light directing optical sub-element; the second light directing optical sub-element is not overlaid by an exit pupil expander on the first light directing optical sub-element; Item 121. The system of item 120. (Item 125) Item 121. The system of item 120, wherein the second diffraction index of the second light directing optical sub-element promotes substantially total internal reflection of light having a predetermined wavelength. (Item 126) Item 126. The system according to item 125, wherein the predetermined wavelength is 515 nm to 540 nm. (Item 127) Item 127. The system of item 126, wherein the predetermined wavelength is 520 nm or 532 nm. (Item 128) Item 126. The system of item 125, wherein the predetermined wavelength is 475 nm or 650 nm. (Item 129) Item 121. The system of item 120, wherein the second diffraction index of the second light directing optical sub-element promotes substantially total internal reflection of a light beam that is approximately parallel to an optical axis of the system to a greater extent than a light beam that is oblique to the optical axis. (Item 130) Item 121. The system of item 120, wherein the second light directing optical sub-element overlies substantially all of the first light directing optical sub-element. (Item 131) Item 121. The system of item 120, wherein the first and second light directing optical sub-elements each comprise a separate substantially flat sheet, such that the light directing optical element comprises a stack of substantially flat sheets. (Item 132) Item 132. The system of item 131, wherein the light directing optical element also has a refractive index gap between the first and second light directing optical sub-elements. (Item 133) Item 133. The system of item 132, wherein the refractive index gap is an air gap. (Item 134) Item 121. The system of item 120, wherein the second light directing optical sub-element comprises two reflective surfaces that reflect light in substantially the same direction. (Item 135) Item 121. The system of item 120, wherein the second light directing optical sub-element comprises two reflective surfaces that reflect light in substantially opposite directions. (Item 136) Item 121. The system of item 120, further comprising a third light-guiding optical sub-element. (Item 137) 1. A mixed reality system, comprising: a light source configured to generate a virtual light beam; a light directing optical element having an entrance portion, an orthogonal pupil expander, and a plurality of exit pupil expanders; Equipped with The light source and the light directing optical element are configured such that the virtual light beam: (a) through the entrance portion into the light directing optical element; (b) propagating through the light directing optical element by substantially total internal reflection; (c) splitting the first virtual light beamlets into a plurality of first virtual light beamlets by interacting with the orthogonal pupil expander, the plurality of first virtual light beamlets being incident on respective ones of the plurality of exit pupil expanders; (d) splitting the second virtual light beamlets into a plurality of second virtual light beamlets by interacting with the plurality of exit pupil expanders. wherein at least some of the plurality of second virtual light beamlets exit the light directing optical element through the exit pupil expander. (Item 138) Item 138. The system of item 137, wherein the light directing optical element is transparent to a real-world light beam. (Item 139) Item 138. The system of item 137, wherein each of the plurality of exit pupil expanders comprises a substantially flat sheet, such that the plurality of exit pupil expanders comprises a stack of substantially flat sheets. (Item 140) Item 138. The system of item 137, wherein the orthogonal pupil expander promotes substantially total internal reflection of light having a predetermined wavelength. (Item 141) Item 141. The system according to item 140, wherein the predetermined wavelength is 515 nm to 540 nm. (Item 142) Item 142. The system of item 141, wherein the predetermined wavelength is 520 nm or 532 nm. (Item 143) Item 141. The system of item 140, wherein the predetermined wavelength is 475 nm or 650 nm. (Item 144) Item 144. The system of item 143, further comprising a plurality of light blockers that selectively block light to the plurality of exit pupil expanders. (Item 145) Item 145. The system of item 144, wherein the plurality of optical isolators comprise LC shutters or PDLC outcoupling gratings. (Item 146) Item 145. The system of item 144, wherein at least one of the plurality of optical blockers is positioned adjacent to an edge of the orthogonal pupil expander. (Item 147) Item 145. The system of item 144, wherein at least one of the plurality of optical blockers is positioned adjacent to a central portion of the orthogonal pupil expander. (Item 148) 1. A mixed reality system, comprising: a light source configured to generate a virtual light beam; a light directing optical element having an entrance portion, an orthogonal pupil expander, and an exit portion; Equipped with The light source and the light directing optical element are configured such that the virtual light beam: (a) through the entrance portion into the light directing optical element; (b) propagating through the light directing optical element by substantially total internal reflection; (c) splitting the beam into a plurality of virtual light beamlets by interacting with the orthogonal pupil expander. wherein at least some of the plurality of virtual light beamlets exit the light directing optical element through the exit portion. (Item 149) the orthogonal pupil expander comprises a first orthogonal pupil sub-expander and a second orthogonal pupil sub-expander; the first and second orthogonal pupil sub-expanders each split a light beam incident on the respective first and second orthogonal pupil sub-expanders; Item 149. The system of item 148. (Item 150) the first and second orthogonal pupil sub-expanders are each individual flat sheets; and the first and second orthogonal pupil sub-expanders are stacked on top of each other; Item 149. The system of item 149. (Item 151) Item 151. The system of item 150, wherein the first orthogonal pupil sub-expander comprises a first exit edge for directing beamlets into the second orthogonal pupil sub-expander. (Item 152) Item 152. The system of item 151, wherein the first exit edge comprises a mirror. (Item 153) Item 152. The system of item 151, wherein the first orthogonal pupil sub-expander comprises a second exit edge for directing beamlets into the second orthogonal pupil sub-expander. (Item 154) Item 154. The system of item 153, wherein the first and second exit edges each comprise a respective mirror. (Item 155) Item 149. The system of item 148, wherein the orthogonal pupil expander comprises first and second reflective edges. (Item 156) Item 156. The system of item 155, wherein the first and second reflective edges are mutually orthogonal. (Item 157) Item 156. The system of item 155, wherein the orthogonal pupil expander further comprises a third reflective edge. (Item 158) Item 149. The system of item 148, wherein the orthogonal pupil expander comprises an internal coupling grating and a highly diffractive region positioned opposite the internal coupling grating. (Item 159) Item 149. The system of item 148, wherein the orthogonal pupil expander comprises a first light modifier configured to absorb light within a first wavelength range. (Item 160) Item 159. The system of item 159, wherein the orthogonal pupil expander further comprises a second light modifier configured to absorb light within a second wavelength range. (Item 161) Item 161. The system of item 160, wherein the first and second optical modifiers are mutually orthogonal. (Item 162) Item 161. The system of item 160, wherein the orthogonal pupil expander further comprises a third light modifier configured to absorb light within a third wavelength range. (Item 163) Item 149. The system of item 148, wherein the orthogonal pupil expander comprises a diffractive optical element that forms a "V" shape. (Item 164) Item 149. The system of item 148, wherein the orthogonal pupil expander comprises a plurality of PDLC switches. (Item 165) 1. A mixed reality system, comprising: a light source configured to generate a virtual light beam; a light directing optical element having an input portion, an output portion, a first light directing optical sub-element, and a second light directing optical sub-element; Equipped with the first light directing optical sub-element has a first light modifying property; the second light directing optical sub-element has a second light modifying characteristic that is different from the first light modifying characteristic. Mixed reality system. [Brief explanation of the drawings]

[0076] The drawings illustrate the design and utility of preferred embodiments of the present disclosure, where like elements are referred to by common reference numerals. In order to better understand how the foregoing and other advantages and objects of the present disclosure are obtained, a more particular description of the invention briefly described above will be given by reference to specific embodiments thereof which are illustrated in the accompanying drawings. With the understanding that these drawings depict only exemplary embodiments of the present disclosure and therefore should not be considered limiting of its scope, the present disclosure will be explained and described with additional specificity and detail through the use of the accompanying drawings.

[0077] [Figure 1]FIG. 1 is a photograph of a three-dimensional augmented reality scene that may be displayed to an end user by a prior art augmented reality generation device.

[0078] [Figure 2] FIG. 2 is a block diagram of a virtual image generation system constructed in accordance with some embodiments of the present disclosure.

[0079] [Figure 3A] FIG. 3A is a plan view of one technique that can be used to mount the virtual image generation system of FIG.

[0080] [Figure 3B] FIG. 3B is a plan view of another technique that can be used to mount the virtual image generation system of FIG.

[0081] [Figure 3C] FIG. 3C is a plan view of yet another technique that can be used to mount the virtual image generation system of FIG.

[0082] [Figure 3D] FIG. 3D is a plan view of yet another technique that can be used to mount the virtual image generation system of FIG.

[0083] [Figure 4] 4, 7 and 8 are detailed schematic diagrams of various mixed reality systems.

[0084] [Figure 5] 5 is a plan view of some embodiments of a display subsystem that may be used in the virtual image generation system of FIG. 2. FIG.

[0085] [Figure 6] FIG. 6 is a conceptual diagram of several embodiments of a primary waveguide device that may be used in the display subsystem of FIG. [Figure 7]4, 7 and 8 are detailed schematic diagrams of various mixed reality systems. [Figure 8] 4, 7 and 8 are detailed schematic diagrams of various mixed reality systems.

[0086] [Figure 9] FIG. 9 is a diagram depicting the focal plane of a mixed reality system.

[0087] [Figure 10] FIG. 10 is a detailed schematic diagram of the light directing optical elements of the mixed reality system.

[0088] [Figure 11] Figure 11A is a schematic diagram of a light beam entering the eye, according to various embodiments, and Figure 11B is the corresponding energy distribution pattern of the light beam in Figure 11A as focused by the lens onto the retina, according to various embodiments. [Figure 12] Figure 12A is a schematic diagram of a light beam entering the eye, according to various embodiments, and Figure 12B is the corresponding energy distribution pattern of the light beam in Figure 12A as focused by the lens onto the retina, according to various embodiments. [Figure 13] Figure 13A is a schematic diagram of a light beam entering the eye, according to various embodiments, and Figure 13B is the corresponding energy distribution pattern of the light beam in Figure 13A as focused by the lens onto the retina, according to various embodiments. [Figure 14] Figure 14A is a schematic diagram of a light beam entering the eye, according to various embodiments, and Figure 14B is the corresponding energy distribution pattern of the light beam in Figure 14A as focused by the lens onto the retina, according to various embodiments. [Figure 15] Figure 15A is a schematic diagram of a light beam entering the eye, according to various embodiments, and Figure 15B is the corresponding energy distribution pattern of the light beam in Figure 15A as focused by the lens onto the retina, according to various embodiments.

[0089] [Figure 16A] FIG. 16A is a schematic diagram of a light beamlet entering an eye, according to some embodiments.

[0090] [Figure 16B] FIG. 16B is an energy distribution pattern of the light beamlets in FIG. 16A as focused by the crystalline lens onto the retina, according to some embodiments.

[0091] [Figure 17A] FIG. 17A is a schematic diagram of a light directing optical element that generates an array of beamlets, according to some embodiments.

[0092] [Figure 17B] FIG. 17B is a schematic diagram of light beamlets associated with a pupil formed by an iris, according to some embodiments.

[0093] [Figure 18] 18A-18C are schematic diagrams showing light beamlets on the retina, according to various embodiments.

[0094] [Figure 19] FIG. 19 is a schematic diagram of a light beam and beamlets propagating through a beam multiplier tube according to some embodiments.

[0095] [Figure 20] FIG. 20 is a schematic diagram of a light beam and beamlets propagating through a beam multiplier tube into an eye, according to some embodiments.

[0096] [Figure 21] FIG. 21 is a schematic diagram of a light beam and beamlets propagating through two beam multipliers into an eye, according to some embodiments.

[0097] [Figure 22A]22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 22B] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 23] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 24] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 25] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 26] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 27] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 28] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 29] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 30] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 31] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 32] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 33-1]22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments. [Figure 33-2] 22A-33I are schematic diagrams of a light beam and beamlets propagating through a beam multiplier tube according to various embodiments.

[0098] [Figure 34] 34 is a plan view of some embodiments of the primary waveguide device of FIG.

[0099] [Figure 35] FIG. 35 is a cross-sectional view of the primary waveguide device of FIG. 34 taken along line 35-35.

[0100] [Figure 36] FIG. 36 is a cross-sectional view of the primary waveguide device of FIG. 34 taken along line 36-36.

[0101] [Figure 37] FIG. 37 is a plan view of another embodiment of the primary waveguide device of FIG.

[0102] [Figure 38] FIG. 38 is a plan view of yet another embodiment of the primary waveguide device of FIG.

[0103] [Figure 39] 39A-39C are perspective views of the primary waveguide device of FIG. 34, particularly illustrating the emission of outcoupled light beamlets at different focal planes.

[0104] [Figure 40A] FIG. 40A is a conceptual diagram of a relatively sparse exit pupil of a waveguide device for a display screen.

[0105] [Figure 40B] FIG. 40B is a conceptual diagram of a relatively dense exit pupil of a modified embodiment of the primary waveguide device of FIG.

[0106] [Figure 41] FIG. 41 is a plan view of some embodiments of the modified primary waveguide device of FIG. 40B.

[0107] [Figure 42] FIG. 42 is a cross-sectional view of the primary waveguide device of FIG. 41 taken along line 42-42.

[0108] [Figure 43] FIG. 43 is a cross-sectional view of the primary waveguide device of FIG. 41 taken along line 43-43.

[0109] [Figure 44] FIG. 44 is a plan view of another embodiment of the modified primary waveguide device of FIG. 40B.

[0110] [Figure 45] FIG. 45 is a cross-sectional view of a first variation of the primary waveguide device of FIG. 44 taken along line 45-45.

[0111] [Figure 46] FIG. 46 is a cross-sectional view of a first variation of the primary waveguide device of FIG. 44 taken along line 46-46.

[0112] [Figure 47] 47A-47D are profile diagrams illustrating the beam splitting technique employed in the modified primary waveguide device of FIG.

[0113] [Figure 48] FIG. 48 is a cross-sectional view of a first variant of the primary waveguide device of FIG. 44 taken along line 48-48, and particularly shows the overlap of the light beamlets.

[0114] [Figure 49] FIG. 49 is a cross-sectional view of a first variant of the primary waveguide device of FIG. 44 taken along line 49-49, and particularly shows the overlap of the light beamlets.

[0115] [Figure 50] FIG. 50 is a cross-sectional view of a second variation of the primary waveguide device of FIG. 44 taken along line 50-50.

[0116] [Figure 51] FIG. 51 is a cross-sectional view of a second variation of the primary waveguide device of FIG. 44 taken along line 51-51.

[0117] [Figure 52] FIG. 52 is a cross-sectional view of a second variation of the primary waveguide device of FIG. 44 taken along line 52-52, and particularly shows the overlap of the optical beamlets.

[0118] [Figure 53] FIG. 53 is a cross-sectional view of a second variant of the primary waveguide device of FIG. 44 taken along line 53-53, and particularly shows the overlap of the light beamlets.

[0119] [Figure 54] FIG. 54 is a cross-sectional view of a third variation of the primary waveguide device of FIG. 44 taken along line 54-54.

[0120] [Figure 55] FIG. 55 is a cross-sectional view of a third variation of the primary waveguide device of FIG. 44 taken along line 55-55.

[0121] [Figure 56] FIG. 56 is a cross-sectional view of a fourth variation of the primary waveguide device of FIG. 44 taken along line 56-56.

[0122] [Figure 57] FIG. 57 is a cross-sectional view of a fourth variation of the primary waveguide device of FIG. 44 taken along line 57-57.

[0123] [Figure 58]FIG. 58 is a plan view of another embodiment of a display subsystem used in the virtual image generation system of FIG.

[0124] [Figure 59A] 59A and 59B are conceptual diagrams of a relatively dense exit pupil of a primary waveguide arrangement of a display screen that has been pre-expanded with a pre-pupil expander (PPE). [Figure 59B] 59A and 59B are conceptual diagrams of a relatively dense exit pupil of a primary waveguide arrangement of a display screen that has been pre-expanded with a pre-pupil expander (PPE).

[0125] [Figure 60] FIG. 60 is a plan view of some embodiments of the PPE of FIGS. 59A and 59B used in conjunction with the primary waveguide device of FIG.

[0126] [Figure 61] FIG. 61 is a cross-sectional view of the primary waveguide device and PPE of FIG. 60 taken along line 61-61.

[0127] [Figure 62] FIG. 62 is a cross-sectional view of the primary waveguide device and PPE of FIG. 60 taken along line 62-62.

[0128] [Figure 63] FIG. 63 is a conceptual diagram of pre-expansion and conventional expansion of the entrance pupil of a collimated light beam to the exit pupil using the PPE of FIG.

[0129] [Figure 64] FIG. 64 is a plan view of another embodiment of the PPE of FIGS. 59A and 59B used in conjunction with the primary waveguide device of FIG.

[0130] [Figure 65] FIG. 65 is a cross-sectional view of the primary waveguide device and PPE of FIG. 64 taken along line 65-65.

[0131] [Figure 66] FIG. 66 is a cross-sectional view of the primary waveguide device and PPE of FIG. 64 taken along line 66-66.

[0132] [Figure 67] 67A and 67B are profile views of different variations of the PPE of FIG.

[0133] [Figure 68] FIG. 68 is a plan view of yet another embodiment of the PPE of FIGS. 59A and 59B used in conjunction with the primary waveguide device of FIG.

[0134] [Figure 69] FIG. 69 is a cross-sectional view of the primary waveguide device and PPE of FIG. 68 taken along line 69-69.

[0135] [Figure 70] FIG. 70 is a cross-sectional view of the primary waveguide device and PPE of FIG. 68 taken along line 70-70.

[0136] [Figure 71] FIG. 71 is a perspective view of the PPE of FIG.

[0137] [Figure 72] FIG. 72 is a cross-sectional view of a first variation of the PPE of FIG. 71 taken along line 72-72.

[0138] [Figure 73] FIG. 73 is a cross-sectional view of a first variation of the PPE of FIG. 71 taken along line 73-73.

[0139] [Figure 74] FIG. 74 is a cross-sectional view of a second variation of the PPE of FIG. 71 taken along line 74-74.

[0140] [Figure 75]FIG. 75 is a cross-sectional view of a second variation of the PPE of FIG. 71 taken along line 75-75.

[0141] [Figure 76] FIG. 76 is a plan view of yet another embodiment of the PPE of FIGS. 31A and 31B used in conjunction with the primary waveguide arrangement of FIG.

[0142] [Figure 77] FIG. 77 is a cross-sectional view of the primary waveguide device and PPE of FIG. 76 taken along line 77-77.

[0143] [Figure 78] FIG. 78 is a cross-sectional view of the primary waveguide device and PPE of FIG. 76 taken along line 78-78.

[0144] [Figure 79] FIG. 79 is a perspective view of the PPE of FIG.

[0145] [Figure 80] FIG. 80 is a plan view of yet another embodiment of the PPE of FIGS. 59A and 59B used in conjunction with the primary waveguide arrangement of FIG.

[0146] [Figure 81] FIG. 81 is a cross-sectional view of the primary waveguide device and PPE of FIG. 80 taken along line 81-81.

[0147] [Figure 82] FIG. 82 is a cross-sectional view of the primary waveguide device and PPE of FIG. 80 taken along line 82-82.

[0148] [Figure 83] FIG. 83 is a perspective exploded view of the PPE of FIG.

[0149] [Figure 84] 84 is a perspective view of several embodiments of planar waveguide assemblies used in the PPE of FIG. 83.

[0150] [Figure 85] 85A and 85B are perspective views of the top and bottom planar orthogonal waveguide units used in the planar waveguide assembly of FIG.

[0151] [Figure 86] 86A and 86B are cross-sectional views of the PPE of FIG.

[0152] [Figure 87A] 87A-87C are plan views of the transfer functions of the top and bottom planar orthogonal waveguide units of FIGS. 85A and 85B. [Figure 87B] 87A-87C are plan views of the transfer functions of the top and bottom planar orthogonal waveguide units of FIGS. 85A and 85B. [Figure 87C] 87A-87C are plan views of the transfer functions of the top and bottom planar orthogonal waveguide units of FIGS. 85A and 85B.

[0153] [Figure 88] Figure 88 is a schematic diagram illustrating various generation of beam splitting performed by the upper planar waveguide assembly used in the PPE of Figure 80 to split an array of two-dimensional beamlets into multiple arrays of two-dimensional beamlets that are accumulated to define a highly saturated exit pupil.

[0154] [Figure 89A] 89A-89H are plan views illustrating the generation of multiple two-dimensional arrays of optical beamlets from a single two-dimensional array of optical beamlets using the PPE of FIG. [Figure 89B] 89A-89H are plan views illustrating the generation of multiple two-dimensional arrays of optical beamlets from a single two-dimensional array of optical beamlets using the PPE of FIG. [Figure 89C]89A-89H are plan views illustrating the generation of multiple two-dimensional arrays of optical beamlets from a single two-dimensional array of optical beamlets using the PPE of FIG. [Figure 89D] 89A-89H are plan views illustrating the generation of multiple two-dimensional arrays of optical beamlets from a single two-dimensional array of optical beamlets using the PPE of FIG. [Figure 89E] 89A-89H are plan views illustrating the generation of multiple two-dimensional arrays of optical beamlets from a single two-dimensional array of optical beamlets using the PPE of FIG. [Figure 89F] 89A-89H are plan views illustrating the generation of multiple two-dimensional arrays of optical beamlets from a single two-dimensional array of optical beamlets using the PPE of FIG. [Figure 89G] 89A-89H are plan views illustrating the generation of multiple two-dimensional arrays of optical beamlets from a single two-dimensional array of optical beamlets using the PPE of FIG. [Figure 89H] 89A-89H are plan views illustrating the generation of multiple two-dimensional arrays of optical beamlets from a single two-dimensional array of optical beamlets using the PPE of FIG.

[0155] [Figure 90A] 90A-90D are plan views illustrating the correspondence of four different beamlet groups within the beam pattern of FIGS. 89A and 89B to four different initial beamlets within the single two-dimensional array of optical beamlets of FIG. 89A. [Figure 90B] 90A-90D are plan views illustrating the correspondence of four different beamlet groups within the beam pattern of FIGS. 89A and 89B to four different initial beamlets within the single two-dimensional array of optical beamlets of FIG. 89A. [Figure 90C] 90A-90D are plan views illustrating the correspondence of four different beamlet groups within the beam pattern of FIGS. 89A and 89B to four different initial beamlets within the single two-dimensional array of optical beamlets of FIG. 89A. [Figure 90D] 90A-90D are plan views illustrating the correspondence of four different beamlet groups within the beam pattern of FIGS. 89A and 89B to four different initial beamlets within the single two-dimensional array of optical beamlets of FIG. 89A. DETAILED DESCRIPTION OF THE INVENTION

[0156] The following description relates to display subsystems and methods to be used in augmented reality systems. However, it should be understood that while the present disclosure is well suited for use in augmented reality systems, the present disclosure, in its broadest aspects, may not be so limited and may apply to any waveguide-based imaging system. For example, the present disclosure may be applied to virtual reality systems. Thus, while often described herein in terms of augmented reality systems, the teachings should not be limited to such systems for such use.

[0157] Various embodiments of the present disclosure are directed to systems, methods, and articles of manufacture for implementing optical systems, in single or multiple embodiments. Other objects, features, and advantages of the present disclosure are set forth in the detailed description, drawings, and claims.

[0158] Various embodiments will now be described in detail with reference to the drawings, which are provided as illustrative examples of the present disclosure to enable those skilled in the art to practice the present disclosure. It should be noted that the drawings and the following examples are not intended to limit the scope of the present disclosure. Certain elements of the present disclosure may be implemented, partially or completely, using known components (or methods or processes), and only those portions of such known components (or methods or processes) necessary for understanding the present disclosure will be described, and detailed descriptions of other portions of such known components (or methods or processes) will be omitted so as not to obscure the present disclosure. Furthermore, various embodiments encompass currently known and future known equivalents of the components referenced herein by way of example.

[0159] Although the optical system may be implemented independently of the AR / MR system, many of the embodiments below are described in relation to an AR / MR system for illustrative purposes only.

[0160] With reference to FIG. 2 , several embodiments of a virtual image generation system 100 configured in accordance with the present disclosure will now be described. The virtual image generation system 100 may be operated as an augmented reality subsystem to provide images of virtual objects blended with physical objects within the field of view of the end user 50. There are two basic approaches to operating the virtual image generation system 100. The first approach employs one or more imagers (e.g., cameras) to capture images of the surrounding environment. The virtual image generation system 100 blends the virtual images into data representing the images of the surrounding environment. The second approach employs one or more at least partially transparent surfaces through which the surrounding environment is viewed and on which the virtual image generation system 100 generates images of the virtual objects.

[0161] The virtual image generation system 100 and the various techniques taught herein may be employed in applications other than augmented reality and virtual reality subsystems. For example, the various techniques may be applied to any projection or display subsystem, or to a pico-projector where movement may be performed by the end user's hands rather than their head. Thus, while often described herein in terms of an augmented reality or virtual reality subsystem, the present teachings should not be limited to such subsystems for such use.

[0162] For at least augmented reality applications, it may be desirable to spatially position various virtual objects relative to individual physical objects in the field of view of the end user 50. Virtual objects, also referred to herein as virtual tags or tags or callouts, may take a wide variety of forms, essentially any of a variety of data, information, concepts, or logical structures capable of being represented as an image. Non-limiting examples of virtual objects may include virtual text objects, virtual numeric objects, virtual alphanumeric objects, virtual tag objects, virtual field objects, virtual chart objects, virtual map objects, virtual instrumentation objects, or virtual visual representations of physical objects.

[0163] The virtual image generation system 100 comprises a frame structure 102 worn by an end user 50, a display subsystem 104 carried by the frame structure 102 such that the display subsystem 104 is positioned in front of the eyes 52 of the end user 50, and a speaker 106 carried by the frame structure 102 such that the speaker 106 is positioned adjacent to the ear canal of the end user 50 (optionally, another speaker (not shown) is positioned adjacent the other ear canal of the end user 50 to provide stereo / shapeable sound control). The display subsystem 104 is designed to present a light-based radiation pattern to the eyes 52 of the end user 50 with a high level of image quality and three-dimensional perception that is comfortably perceived as an augmentation to physical reality and may be capable of presenting two-dimensional content. The display subsystem 104 presents a sequence of frames at high frequencies, providing the perception of a single coherent scene.

[0164] In the illustrated embodiment, the display subsystem 104 employs an "optical see-through" display through which a user can view direct light from real objects through a transparent (or translucent) element. The transparent element, often referred to as a "combiner," superimposes the light from the display across the user's field of view in the real world. To this end, the display subsystem 104 includes a projection subsystem 108 and a partially transparent display screen 110 onto which the projection subsystem 108 projects images. The display screen 110 is positioned in the field of view of the end user 50 between the eyes 52 of the end user 50 and the surrounding environment such that direct light from the surrounding environment is transmitted through the display screen 110 to the eyes 52 of the end user 50.

[0165] In the illustrated embodiment, the image projection assembly 108 provides scanned light to a partially transparent display screen 110, where it is combined with direct light from the surrounding environment and transmitted from the display screen 110 to the eyes 52 of the user 50. In the illustrated embodiment, the projection subsystem 108 takes the form of a fiber optic scanning-based projection device, and the display screen 110 takes the form of a waveguide-based display into which the scanned light from the projection subsystem 108 is injected to generate, for example, an image at a single optical viewing distance closer to infinity (e.g., arm's length), images at multiple discrete optical viewing distances or focal planes, and / or image layers stacked at multiple viewing distances or focal planes to represent a stereoscopic 3D object. These layers in the light field may be stacked closely enough (i.e., one layer is within the scatter cone of an adjacent layer) to appear consecutively together to the human visual subsystem. Additionally or alternatively, photographic elements may be blended across two or more layers to increase the perceived continuity of the transition between layers in the light field, even when the layers are more sparsely stacked (i.e., one layer is outside the noise signal cone of an adjacent layer). Display subsystem 104 may be monocular or binocular.

[0166] The virtual image generation system 100 further comprises one or more sensors (not shown) mounted to the frame structure 102 for detecting the position and movement of the head 54 of the end user 50 and / or the position and interocular distance of the eyes of the end user 50. Such sensors may include image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, and / or gyroscopes).

[0167] The virtual image generation system 100 further comprises a user orientation detection module 112. The user orientation detection module 112 detects the instantaneous position of the end user's 50's head 54 and may predict the position of the end user's 50's head 54 based on position data received from the sensors. Detecting the instantaneous position of the end user's 50's head 54 facilitates determining the specific real object the end user 50 is looking at, thereby providing an indication of the specific text message to be generated for that real object, and further providing an indication of the text region to which the text message should be streamed. The user orientation module 112 also tracks the end user's 50's eyes 52 based on tracking data received from the sensors.

[0168] The virtual image generation system 100 further includes a control subsystem, which may take any of a wide variety of forms. The control subsystem includes several controllers, such as one or more microcontrollers, microprocessors or central processing units (CPUs), digital signal processors, graphics processing units (GPUs), other integrated circuit controllers, such as application specific integrated circuits (ASICs), programmable gate arrays (PGAs), such as field programmable gate arrays (FPGAs), and / or programmable logic controllers (PLUs).

[0169] The control subsystem of virtual image generation system 100 includes a central processing unit (CPU), a graphics processing unit (GPU) 116, one or more frame buffers 118, and a 3D database 120 for storing three-dimensional data. CPU 114 controls overall operation, while GPU 116 renders frames (i.e., converts three-dimensional scenes into two-dimensional images) from the three-dimensional data stored in 3D database 120 and stores these frames in frame buffer 116. Although not shown, one or more additional integrated circuits may control the loading of frames into and / or from frame buffer 116 and the operation of image projection assembly 108 of display subsystem 104.

[0170] The various processing components of the virtual image generation system 100 may be physically contained within a distributed subsystem. For example, as illustrated in Figures 3A-3D, the virtual image generation system 100 includes a local processing and data module 130 that is operably coupled to the display subsystem 104 and sensors, such as by wired leads or wireless connectivity 136. The local processing and data module 130 may be mounted in a variety of configurations, such as fixedly attached to the frame structure 102 (Figure 3A), fixedly attached to the helmet or hat 56 (Figure 3B), embedded within headphones, removably attached to the torso 58 of the end user 50 (Figure 3C), or removably attached to the waist 60 of the end user 50 in a belt-type configuration (Figure 3D). The virtual image generation system 100 further includes a remote processing module 132 and a remote data repository 134 operably coupled to the local processing and data module 130 by wired or wireless connectivity 138, 140, etc., such that these remote modules 132, 134 are operably coupled to each other and are available as resources to the local processing and data module 130.

[0171] The local processing and data module 130 may comprise a power-efficient processor or controller and digital memory, such as flash memory, both of which may be utilized to aid in processing, caching, and storing data captured from sensors and / or acquired and / or processed using the remote processing module 132 and / or the remote data repository 134, possibly for processing or readout and subsequent passage to the display subsystem 104. The remote processing module 132 may comprise one or more relatively powerful processors or controllers configured to analyze and process the data and / or image information. The remote data repository 134 may comprise a relatively large digital data storage facility, which may be available through the Internet or other networking configuration in a “cloud” resource configuration. In some embodiments, all data is stored and all calculations are performed in the local processing and data module 130, allowing for fully autonomous use from any remote module.

[0172] The couplings 136, 138, 140 between the various components described above may include one or more wired interfaces or ports for providing wired or optical communication, or one or more wireless interfaces or ports via RF, microwave, IR, and the like for providing wireless communication. In some implementations, all communication may be wired, while in other implementations, all communication may be wireless. In still further implementations, the wired and wireless communication options may differ from those illustrated in FIGS. 3A-3D . Thus, the particular wired or wireless communication options should not be considered limiting.

[0173] In the illustrated embodiment, the user orientation module 112 is contained within a local processing and data module 130, while the CPU 114 and GPU 116 are contained within a remote processing module 132, although in alternative embodiments, the CPU 114, GPU 124, or portions thereof, may be contained within the local processing and data module 130. The 3D database 120 may be associated with a remote data repository 134.

[0174] Before describing the details of embodiments of light directing optical elements, this disclosure will now provide a brief description of an illustrative MR system.

[0175] One possible approach to implementing an MR system uses multiple volume phase holograms, surface relief holograms, or light-directing optical elements incorporating depth plane information to generate images that appear to originate from distinct depth planes. In other words, a diffraction pattern or diffractive optical element ("DOE") may be incorporated into or imprinted / embossed onto a light-directing optical element ("LOE," e.g., a planar waveguide) such that collimated light (a light beam with a substantially planar wavefront) intersects the diffraction pattern at multiple locations as it undergoes substantially total internal reflection along the LOE and exits toward the user's eye. The DOE is configured such that light exiting the LOE through it is converged and appears to originate from a specific depth plane. The collimated light may be generated using an optical focusing lens ("concentrator").

[0176] For example, a first LOE may be configured to deliver collimated light to the eye that appears to originate from the optical infinity depth plane (0 diopters). Another LOE may be configured to deliver collimated light that appears to originate from a distance of 2 meters (½ diopters). Yet another LOE may be configured to deliver collimated light that appears to originate from a distance of 1 meter (1 diopter). It will be appreciated that by using stacked LOE assemblies, multiple depth planes can be created, with each LOE configured to display an image that appears to originate from a particular depth plane. It will be appreciated that a stack may include any number of LOEs. However, at least N stacked LOEs are required to generate N depth planes. Furthermore, N, 2N, or 3N stacked LOEs may be used to generate an RGB color image at N depth planes.

[0177] To present 3-D virtual content to a user, a mixed reality (MR) system projects images of the virtual content into the user's eye so that they appear to originate from different depth planes in the Z direction (i.e., orthogonal away from the user's eye). In other words, the virtual content can be thought of as varying not only in the X and Y directions (i.e., in a 2D plane orthogonal to the central visual axis of the user's eye), but also in the Z direction, so that the user may perceive objects as being very close, infinitely far away, or any distance in between. In other embodiments, the user may perceive multiple objects simultaneously in different depth planes. For example, the user may see a virtual dragon appearing from infinity and running toward the user. Alternatively, the user may simultaneously see a virtual bird at a distance of 3 meters from the user and a virtual coffee cup at arm's length (approximately 1 meter) from the user.

[0178] The multi-plane focusing system creates the perception of variable depth by projecting images onto some or all of multiple depth planes located at discrete fixed distances in the Z direction from the user's eyes. Referring now to FIG. 9 , it should be understood that the multi-plane focusing system may display frames at fixed depth planes 502 (e.g., the six depth planes 502 shown in FIG. 9 ). While an MR system can include any number of depth planes 502, one exemplary multi-plane focusing system has six fixed depth planes 502 in the Z direction. When generating virtual content in one or more of the six depth planes 502, a 3-D perception is created such that the user perceives one or more virtual objects at variable distances from the user's eyes. Given that the human eye is more sensitive to closer objects than to objects that appear farther away, more depth planes 502 are generated closer to the eyes, as shown in FIG. 9 . In other embodiments, the depth planes 502 may be positioned equidistant from each other.

[0179] Depth plane positions 502 may be measured in diopters, which are units of refractive power equal to the reciprocal of focal length measured in meters. For example, in some embodiments, depth plane 1 may be 1 / 3 diopters away, depth plane 2 may be 0.3 diopters away, depth plane 3 may be 0.2 diopters away, depth plane 4 may be 0.15 diopters away, depth plane 5 may be 0.1 diopters away, and depth plane 6 may represent infinity (i.e., 0 diopters away). It should be understood that other embodiments may generate depth planes 502 at other distances / diopters. Thus, when generating virtual content at strategically placed depth planes 502, a user may perceive virtual objects in three dimensions. For example, a user may perceive a first virtual object as being closer when displayed at depth plane 1 while another virtual object appears at infinity at depth plane 6. Alternatively, the virtual object may be first displayed at depth plane 6, then at depth plane 5, etc., until the virtual object appears very close to the user. It should be understood that the above example is significantly simplified for illustrative purposes. In another embodiment, all six depth planes may be centered on a particular focal distance away from the user. For example, if the virtual content to be displayed is a coffee cup 0.5 meters away from the user, all six depth planes may be generated at various cross sections of the coffee cup, giving the user a highly granular 3-D view of the coffee cup.

[0180] In some embodiments, the AR system may act as a multi-plane focusing system. In other words, all six LOEs may be simultaneously illuminated to generate images that appear to arise from six fixed depth planes in rapid succession, with the light source rapidly transmitting image information to LOE 1, then LOE 2, then LOE 3, etc. For example, a portion of a desired image, including an image of the sky at optical infinity, may be injected at time 1, and an LOE 1090 that retains light collimation (e.g., depth plane 6 from FIG. 9) may be utilized. An image of a closer tree branch may then be injected at time 2, and an LOE 1090 configured to create an image that appears to arise from a depth plane 10 meters away (e.g., depth plane 5 from FIG. 9) may be utilized. An image of a pen may then be injected at time 3, and an LOE 1090 configured to create an image that appears to arise from a depth plane 1 meter away may be utilized. This type of paradigm can be repeated in a rapid time series (eg, 360 Hz) manner so that the user's eyes and brain (eg, visual cortex) perceive the inputs as all being part of the same image.

[0181] The AR system is required to project images (i.e., by diverging or converging light beams) that appear to originate from various locations along the Z axis (i.e., depth planes) and generate images for the 3-D experience / scenario. As used herein, light beam includes, but is not limited to, the directional projection of light energy (including visible and invisible light energy) emitted from a light source. Generating images that appear to originate from various depth planes conforms to the vergence and accommodation of the user's eyes for the images, minimizing or eliminating vergence-accommodation conflicts.

[0182] FIG. 4 depicts a basic optical system 400 for projecting an image at a single depth plane. System 400 includes a light source 420 and an LOE 490 having an associated diffractive optical element (not shown) and an internal coupling grating 492 (ICG). The diffractive optical element may be of any type, including volume or surface relief. In some embodiments, ICG 492 is a reflective-mode aluminized portion of LOE 490. In other embodiments, ICG 492 is a transmissive diffractive portion of LOE 490. When system 400 is in use, a light beam from light source 420 enters LOE 490 through ICG 492 and propagates along LOE 490 by substantially total internal reflection (“TIR”) for display to a user's eye. While only one beam is illustrated in FIG. 4, it should be understood that multiple beams may enter LOE 490 from a wide range of angles through the same ICG 492. A light beam that is "incident" or "captured" into the LOE includes, but is not limited to, a light beam that interacts with the LOE to propagate along the LOE by substantial TIR. The system 400 depicted in FIG. 4 can include various light sources 420 (e.g., LEDs, OLEDs, lasers, and masked broad-area / broadband emitters). In other embodiments, light from the light sources 420 may be delivered to the LOE 490 via a fiber optic cable (not shown).

[0183] 5, the image projection assembly 108 includes one or more light sources 150 that generate light (e.g., emit different colored light in a defined pattern). The light sources 150 may take any of a wide variety of forms, such as a set of RGB lasers (e.g., laser diodes capable of outputting red, green, and blue light) operable to generate coherent collimated red, green, and blue light, respectively, according to a defined pixel pattern defined within individual frames of pixel information or data. Laser light provides high color saturation and is very energy efficient.

[0184] The image projection assembly 108 further includes a scanning device 152 that scans light in a predetermined scan pattern in response to a control signal. The scanning device 152 includes one or more optical fibers 154 (e.g., single-mode optical fibers), each having a proximal end 154a into which light is received from the light source 150 and a distal end 154b from which light is provided to the display screen 110. The scanning device 152 further includes a mechanical drive assembly 156 to which the optical fibers 154 are mounted. The drive assembly 156 is configured to displace the distal end 154b of each optical fiber 154 about a fulcrum 158 in accordance with the scan pattern.

[0185] To this end, drive assembly 156 includes a piezoelectric element 160 to which optical fiber 154 is mounted, and drive electronics 162 configured to transmit electrical signals to piezoelectric element 160, thereby vibrating distal end 154b of optical fiber 154 according to a scanning pattern. Operation of light source 150 and drive electronics 162 is thus coordinated in a manner to generate image data encoded in the form of spatially and / or temporally varying light. A description of optical fiber scanning techniques is provided in U.S. Patent Publication No. 2015 / 0309264, expressly incorporated herein by reference.

[0186] The projection assembly 108 further includes an optical coupling assembly 164 that couples light from the scanning device 152 into the display screen 110. The optical coupling assembly 164 includes a collimating element 166 that collimates the light emitted by the scanning device 152 into a collimated light beam 250. Although the collimating element 166 is illustrated in FIG. 5 as being physically separate from the optical fibers 154, the collimating element may be physically mounted to the distal end 154 b of each optical fiber 154 in a “microlens” arrangement, as described in U.S. patent application Ser. No. 15 / 286,215, entitled “Microlens Collimator for Scanning Optical Fiber in Virtual / Augmented Reality System,” which is expressly incorporated herein by reference. The optical coupling subsystem 164 further includes internal coupling (IC) elements 168, such as one or more reflective surfaces, diffraction gratings, mirrors, dichroic mirrors, or prisms, as will be described in more detail below, that optically couple the light into the edge of the display screen 110 at an angle that ensures the light propagates in the desired direction within the display screen 110.

[0187] As will be described in further detail below, the optical coupling subsystem 164 optically couples the collimated light beams 250 into the display screen 110, which will expand the pupil size of the collimated light beams 250 to be proportional to the entrance pupil size of the end user 50. In the embodiment described below, the display screen 110 employs a technique known as "beam doubling," which refers to a method of exit pupil expansion that expands the small diameter entrance pupil (e.g., approximately 50 microns to 1 mm) of each collimated light beam 250 from the image projection assembly 108 by doubling the individual light beams 250 into multiple light beamlets, resulting in a light beamlet array exit pupil that is specifically designed to substantially match the entrance pupil of one or both eyes of a user over a fixed pupil distance (e.g., approximately 5 mm to 7 mm). It should be noted that while the "beam doubling" technique is described herein as being implemented in the display screen 110, it should be understood that such "beam doubling" technique may be applied anywhere within the image generation system 100, including any similar substrate system / subsystem upstream from the display screen 110.

[0188] The degree to which the beam of collimated light 250 needs to be multiplied to achieve a given fill factor will depend on the original pupil size of the collimated light beam 250. For example, if the original pupil size of the collimated light beam 250 output by the image projection assembly 108 is 500 microns, such pupil size may need to be multiplied by a factor of 10 to achieve the desired fill factor, while if the original pupil size of the collimated light beam output by the image projection assembly 108 is 50 microns, such pupil may need to be multiplied by a factor of 100 to achieve the desired fill factor.

[0189] Preferably, the optical beamlet array exit pupil of the display screen is completely filled or saturated with optical beamlets to maximize wavefront density and minimize depth of field. If the filling of the optical beamlets in the exit pupil is too sparse, the wavefront density and depth of field of the display screen will be compromised, and if the diameter of the optical beamlets is too small, the angular resolution of the display screen will be compromised.

[0190] In theory, the thickness of the display screen 110 can be reduced to increase the number of light beamlets created from a single collimated light beam 250 input into the display screen 110, thereby increasing the fill-in-exit pupil with light beamlets. However, due to durability and manufacturing limitations, the display screen 110 can only be thinned to a limited extent, thereby limiting the fill-in-exit pupil. Also, while the entrance pupil of the collimated light beam 250 transmitted from the image projection assembly 108 into the display screen 110 could theoretically be increased to increase the fill-in-exit pupil with light beamlets, this would require a proportional increase in the size of the image projection assembly 108, thereby negatively affecting the wearability of the VR / AR system. Importantly, the embodiments described below increase the fill-in-exit pupil without requiring an increase in the size of the image projection assembly 108.

[0191] To this end, the display screen 110 acts as a pupil expander (PE), expanding the effective entrance pupil of a collimated light beam 250 (carrying image information) for display to one eye 52 (monocular) or both eyes 52 (binocular) of the end user 50. The display screen 110 takes the form of a waveguide device 170 including a planar optical waveguide 172 and one or more diffractive optical elements (DOEs) 174 optically coupled into and associated with the planar optical waveguide 172 for two-dimensionally expanding the effective entrance pupil of the collimated light beam 250. In an alternative embodiment, the waveguide device 170 may comprise multiple planar optical waveguides 172 and DOEs 174, each associated with a planar optical waveguide 172.

[0192] As best illustrated in FIG. 6 , the planar optical waveguide 172 has a first end 176 a and a second end 176 b, the second end 176 b opposing the first end 176 a along a length 178 of the planar optical waveguide 172. The planar optical waveguide 172 has a first face 180 a and a second face 180 b, where at least the first and second faces 180 a, 180 b (collectively, 180) form an internally reflected optical path (illustrated by solid arrow 182 a and dashed arrow 182 b, collectively, 182) at least partially along at least a portion of the length 178 of the planar optical waveguide 172. The planar optical waveguide 172 may take various forms that provide substantial total internal reflection (TIR) ​​for light striking face 180 at less than a defined critical angle.

[0193] The DOE 174 (illustrated in FIGS. 5 and 6 by a double-dashed line) interrupts the TIR optical path 182 and may take a wide variety of forms to provide multiple optical paths (illustrated by solid arrows 184a and dashed arrows 184b, collectively 184) between the interior 185a and exterior 185b of the planar optical waveguide 172 that extend along at least a portion of the length 178 of the planar optical waveguide 172. As will be explained in further detail below, light propagates within the planar optical waveguide 172 along internally reflected optical paths and, at various locations, intersects the DOE 174 to split the light into optical beamlets that are either diffracted along different internally reflected optical paths or out of the face 180b of the planar optical waveguide 172.

[0194] In the illustrated embodiment, the DOE 174 can be characterized as an optical component comprising one or more diffraction gratings, each with a periodic structure, such as a wavelength of light, that splits and diffracts light into several beams traveling in different directions. The diffraction gratings can be composed of surface nanobumps, nanopatterns, slits, etc., that can be photolithographically printed on a substrate. The DOE 174 can provide positioning of the apparent object and the focal plane of the apparent object. This can be achieved frame-by-frame, sub-frame-by-frame, or even pixel-by-pixel.

[0195] As illustrated in FIG. 6 , light propagates along the planar optical waveguide 172 with at least some reflections or “bounces” resulting from TIR propagation. Note that some implementations may employ one or more reflectors within the internal optical path, such as thin films, dielectric coatings, or metallic coatings, which may enhance reflection. The light propagates along the length 178 of the planar optical waveguide 172 and intersects with the DOE 174 at various locations along the length 178. The DOE 174 may be embedded within the planar optical waveguide 172 or may abut or be adjacent to one or more of the faces 180 of the planar optical waveguide 172. The DOE 174 performs at least two functions. The DOE 174 shifts the angle of the light, causing a portion of the light to escape TIR and emerge from the interior 185a, through the face 180 of the planar optical waveguide 172, and onto the exterior 185b surface. The DOE 174 focuses the outcoupled light to a viewing distance. Thus, when viewed through face 180 of planar optical waveguide 172, a digital image is visible at one or more viewing distances.

[0196] A collimated light beam 250 entering the waveguide 172 at one of two different angles will follow one of two TIR optical paths 182a, 182b and result in light beamlets 256 exiting the planar optical waveguide 172 along one of two sets of external optical paths 185a, 185b. That is, a collimated light beam 250a entering the waveguide 172 at an angle represented by TIR optical path 182a will result in light beamlet 256a exiting the planar optical waveguide 172 along the set of external optical paths 185a, and a collimated light beam 250b entering the waveguide 172 at an angle represented by TIR optical path 182b will result in light beamlet 256b exiting the planar optical waveguide 172 along the set of external optical paths 185b.

[0197] From the foregoing, it can be seen that display subsystem 104 generates a series of composite image frames of pixel information that present an image of one or more virtual objects to a user. Further details describing the display subsystem are provided in U.S. patent application Ser. No. 14 / 212,961, entitled "Display Subsystem and Method," and U.S. patent application Ser. No. 14 / 696,347, entitled "Planar Optical Waveguide Apparatus With Diffraction Elements(s) and Subsystem Employing Same," both of which are expressly incorporated herein by reference.

[0198] As explained above, FIG. 4 depicts a basic optical system 400 for projecting an image at a single depth plane. FIG. 7 depicts an alternative optical system 400′, which includes a light source 420, three LOEs 490, and three individual internal coupling gratings 492. The optical system 400′ also includes three beam splitters or dichroic mirrors 462 (to direct light to the individual LOEs) and three LC shutters 464 (to control when the LOEs are illuminated). When the system 400′ is in use, the light beam from the light source 420 is split into three sub-beams / beamlets by the three beam splitters 462. The three beam splitters also redirect the beamlets toward the individual internal coupling gratings 492. After the beamlets enter the LOEs 490 through their respective internal coupling gratings 492, they propagate along the LOEs 490 by substantial TIR, where they interact with additional optical structures to produce a display to the user's eyes. The surface of the internal coupling gratings 492 on the far side of the optical path can be coated with an opaque material (e.g., aluminum) to prevent light from passing through the internal coupling gratings 492 to the next LOE 490. In some embodiments, the beamsplitter 462 can be combined with wavelength filters to generate red, green, and blue beamlets. In such embodiments, three LOEs 490 are required to display a color image in a single depth plane. In another embodiment, the LOEs 490 may each present a portion of a larger single depth plane image area that is angularly displaced laterally within the user's field of view of either similar or different colors (a "tiled field of view").

[0199] FIG. 8 depicts yet another optical system 400″ having six beam splitters 462, six LC shutters 464, and six LOEs 490, each with its own ICG 492. As mentioned above in the discussion of FIG. 7, three LOEs 490 are required to display a color image in a single depth plane. Thus, the six LOEs 490 of this system 400″ are capable of displaying color images in two depth planes.

[0200] FIG. 10 depicts an LOE 490 having an ICG 492, an orthogonal pupil expander 494 (“OPE”), and an exit pupil expander 496 (“EPE”).

[0201] As shown in Figures 4-9, as the number of depth planes, field tiles, or generated colors increases (e.g., with increased MR scenario quality), the number of LOEs 490 and ICGs 492 also increases. For example, a single RGB color depth plane requires at least three LOEs 490, accompanied by three ICGs 492. As a result, any image defects (e.g., blur from limited beam diameter) are also multiplied, along with additional opportunities to impair MR scenario quality. Thus, increasing the number of optical elements required to generate an acceptable MR scenario exacerbates image quality issues.

[0202] The LOE 490 discussed above can additionally function as an exit pupil expander 496 (“EPE”) to increase the numerical aperture of the light source 420, thereby increasing the resolution of the system 400. Because the light source 420 produces light with a small diameter / spot size, the EPE 496 expands the apparent pupil size of the light exiting the LOE 490, increasing the system resolution. In other embodiments of the MR system 400, the system may further include an orthogonal pupil expander 494 (“OPE”) in addition to the EPE 496 to expand the light in both the X and Y directions. Further details regarding the EPE 496 and OPE 494 are described in the above-referenced U.S. Utility Patent Application No. 14 / 555,585 and U.S. Utility Patent Application No. 14 / 726,424, the contents of which are previously incorporated by reference.

[0203] 10 depicts LOE 490 having ICG 492, OPE 494, and EPE 496. FIG. 10 depicts LOE 490 from a top view, similar to the view from a user's eye. ICG 492, OPE 494, and EPE 496 may be any type of DOE, including volume or surface relief.

[0204] ICG 492 is a DOE (e.g., a linear grating) configured to capture light from light source 420 for propagation by TIR. In the embodiment depicted in Figure 10, light source 420 is positioned to the side of LOE 490.

[0205] OPE 494 is a DOE (e.g., a linear grating) that is tilted in the lateral plane (i.e., perpendicular to the light path) so that a light beam propagating through system 400 will be deflected 90 degrees to the side. OPE 494 is also partially transmissive and partially reflective along the light path so that the light beam passes partially through OPE 494 and forms multiple (e.g., 11) beamlets. In some embodiments, the light path is along the X-axis, and OPE 494 is configured to bend the beamlets about the Y-axis.

[0206] EPE 496 is a DOE (e.g., a linear grating) that is tilted in the axial plane (i.e., parallel to the optical path or in the Y direction) so that beamlets propagating through system 400 will be axially deflected by 90 degrees. EPE 496 is also partially transmissive and partially reflective along the optical path (Y axis) so that beamlets pass partially through EPE 496 and form multiple (e.g., seven) beamlets. EPE 496 is also tilted in the Z direction to direct some of the propagating beamlets toward the user's eyes.

[0207] Both OPE 494 and EPE 496 are also at least partially transmissive along the Z axis, allowing real-world light (e.g., reflected from real-world objects) to pass through OPE 494 and EPE 496 in the Z direction and reach the user's eyes. In some embodiments, ICG 492 is also at least partially transmissive along the Z axis to capture real-world light.

[0208] FIG. 11A shows a first light beam 610 entering the eye 600 and being focused by the lens 602 to a small spot 612 on the retina 604. Preferably, the small spot 612 is approximately the size of a photoreceptor on the retina 604. A first image or a first portion of an image corresponding to the first light beam 610 is focused, as shown by the energy distribution curve 614 corresponding to the first light beam 610 in the graph in FIG. 11B. FIG. 11A also depicts a second light beam 620 entering the eye 600 and being focused by the lens 602 to a larger spot 622 on the retina 604. A second image or a second portion of an image corresponding to the second light beam 620 (with the larger spot 622) is less focused (e.g., out of focus), as shown by the energy distribution curve 624 corresponding to the second light beam 620 in the graph in FIG. 11B. FIG. 11B depicts the energy distribution patterns of two real-world light beams as focused onto the retina by the crystalline lens.

[0209] FIG. 12A shows an eye 700 with a lens 702 that is accommodated such that a second light beam 720 is focused to a small spot 722 on the retina 704. As a result, a second image or a second portion of an image corresponding to the second light beam 710 is in focus, as shown by the energy distribution curve 724 corresponding to the second light beam 720 in the graph in FIG. 12B. However, in FIG. 12A, the first light beam 710 is focused to a larger spot 712 on the retina 704, resulting in a larger spot 712 on the retina 704. The first image or a first portion of an image corresponding to the first light beam 710 (with the larger spot 712) is less focused (e.g., out of focus), as shown by the energy distribution curve 714 corresponding to the first light beam 710 in the graph in FIG. 12B. FIG. 12B depicts the energy distribution patterns of two real-world light beams as focused by the lens onto the retina.

[0210] The size of the beam spot on the retina affects image resolution as follows: The function of the eye is to collect light information related to a "3-D" scene consisting of multiple point sources of light (e.g., emitted or reflected). For example, a tree may contain millions of point sources of light, reflecting light from the sun. The eye (e.g., the lens within it) bends the light beam into a spot on the retina. Ideally, the beam spot on the retina is the size of a photoreceptor. When well-focused on an object, the eye will converge the light beam from the object into the smallest possible spot on the retina. When the eye is out of focus on an object, the light beam is focused in front of or behind the retina, and the spot becomes more circular instead of a point. A wider, circular spot may impinge on several photoreceptors on the retina, resulting in a blurred image when interpreted by the viewer's occipital cortex. Furthermore, a smaller beam spot (e.g., a 2-3 mm diameter beam) will cause the spot size (i.e., blur or focus) to change more rapidly with lens accommodation. On the other hand, a larger beam spot (eg, a 0.5 mm diameter beam) will not cause the spot size (ie, blur or focus) to change with lens accommodation.

[0211] FIG. 13A shows an eye 800 with a lens 802 that is accommodated such that first and second light beams 810, 820 are focused to separate, larger spots 812, 822 on the retina 804. As a result, first and second images or first and second portions of one or more images corresponding to the first and second light beams 810, 820 are less focused (e.g., defocused) compared to a focused image, as shown by the energy distribution curves 814, 824 corresponding to the first and second light beams 810, 820 in the graph in FIG. 13B. FIG. 13B depicts the energy distribution patterns of two real-world light beams as focused onto the retina by the lens. As shown in FIGS. 11A-13B, the anatomical structure of a single lens makes it difficult to focus two light beams with different angles of incidence in parallel. When one beam is focused, the other beam will be defocused. 13A and 13B, attempting to accommodate the crystalline lens to an intermediate focus of two light beams can result in two out-of-focus images or portions of one or more images. As a result of anatomical limitations, when a single crystalline lens focuses one portion of the light beam or field of view ("FOV"), other light beams or portions of the FOV will be out of focus.

[0212] As this image focus limit increases, it introduces various other optical, anatomical, and technical limitations. Image resolution is a function of beam diameter and beam angle ("optical invariant"), which is linked to the number of resolvable spots (e.g., as in the laser scanner industry). The optical invariant is related to the numerical aperture collected by a pixel multiplied by the number of pixels. A larger light beam diameter results in higher image resolution. A smaller light beam diameter results in the ability to preserve increased light beam angle and maximize the FOV. These optical limitations make beam diameter optimization difficult because beam diameter affects both image resolution and light beam angle, resulting in a trade-off between image quality and FOV size.

[0213] 14A-14B demonstrate the relationship between light beam diameter and image resolution. As shown in FIG. 14A, a light beam 910 having a maximum-sized beam diameter 916 (e.g., sufficient to fill the entire pupil of the eye 900, or approximately 2-3 mm) produces a minimum spot size 912 for a given eye 900. The small spot size 912 results in a corresponding focused image, or portion thereof, as shown by the energy distribution curve 914 in FIG. 14B. FIG. 14B depicts the energy distribution pattern of a real-world light beam as focused onto the retina by the crystalline lens. The larger diameter of the light beam 910 allows the eye 900 to focus the light beam 900 by changing the shape of the crystalline lens 902. The ability to focus a maximum-sized light beam results in increased image resolution. However, a light beam 1010 having a smaller beam diameter 1016 (e.g., about 0.5 mm) produces a larger spot size 1012, as shown in Figure 15A. The larger spot size 1012 results in a corresponding out-of-focus image, or portion thereof, as shown by the energy distribution curve 1014 in Figure 15B. Figure 15B depicts the energy distribution pattern of a real-world light beam as focused onto the retina by the crystalline lens.

[0214] Furthermore, if the light beam diameter is approximately 0.5 mm, some eyes will experience open-loop accommodation, resulting in everything appearing at the same poor focus level. As in a pinhole camera, the entire FOV will be equally and poorly focused because the retinal space is too small to resolve larger spots displayed on it, as shown in Figures 15A and 15B. Furthermore, if the light beam diameter is approximately 0.5 mm, the pupil will be fully dilated, which can result in optical aberrations, such as a halo around the point source of light.

[0215] As explained above, various other optical, anatomical, and technical limitations result in performance limitations for head-mounted displays. For example, a light beam with a smaller diameter (e.g., approximately 0.5 mm) will result in lower image resolution and optical aberrations compared to a light beam with a larger diameter (e.g., approximately 2-3 mm). On the other hand, a light beam with a larger diameter (e.g., approximately 2-3 mm) will result in a narrower FOV compared to a light beam with a smaller diameter (e.g., approximately 0.5 mm). A balance between image resolution and FOV will result in suboptimal image resolution and FOV.

[0216] The following disclosure describes various embodiments of systems and methods for simulating a larger diameter light beam using multiple (e.g., an array) smaller diameter light beams. These beam doubling systems and methods generate a bundle of interrelated, interacting, and cloned beamlets 1116 that pass through the pupil and impinge on the retina 1104, as shown in FIG. 16A. The combination of the beam array, relative spacing, and beam diameters can produce a dense energy image at the retina 1104 (see FIG. 16B). FIG. 16B depicts the energy distribution pattern of an array of real-world light beams as focused onto the retina 1104 by the crystalline lens 1102, including the optical interactions of the light beams with each other. By eliminating energy in the side lobes (constant power) through interference and other optical properties of the beam array (e.g., coherence, phase uniformity, etc.), the optical energy (e.g., irradiance, peak intensity, etc.) is concentrated at the center of the graph, as shown by the energy distribution curve 1114 corresponding to beamlet 1116 in the graph in FIG. 16B. This concentrated optical energy, in turn, produces a more focused image with higher image resolution. For example, coherence and phase uniformity across beamlets 1116 may correspond to an energy distribution with a relatively high peak value and attenuated side lobes, and thus may contribute to a relatively focused and apparently sharp image. In fact, an array of cloned smaller diameter beamlets 1116 produces a smaller spot 1112 on the retina 1104 with a sharp point spread function 1114 that approximates the sharp point spread function 914 produced by the larger diameter beam 910 (see FIGS. 14A and 14B). The array of smaller diameter beamlets 1116 allows the system to overcome beam diameter limitations (arising from diffraction and / or device size limitations). At the same time, the system's use of smaller diameter light beams results in a wider FOV.

[0217] Multiple / array beamlets (each with a smaller diameter) simulate the light energy from a much larger diameter light beam, increasing image resolution while maintaining a wider FOV based on the smaller beam diameter.

[0218] Figure 17A diagrammatically depicts LOE 490 generating an array of beamlets 1216 from a single incident light beam 1210 (see beam multiplier, described below). Some of the beamlets 1216 that pass through the pupil 1206 formed by the iris 1208 are focused by the crystalline lens 1202. While Figure 17A depicts multiple beamlets 1216, Figure 17A does not depict a two-dimensional beamlet array, according to some embodiments. Figure 17B diagrammatically depicts a selected beamlet 1206 from the beamlet array passing through the pupil 1206 formed by the iris 1208.

[0219] The spacing of the beamlet spots can also affect image quality. As shown in FIG. 18A, the beamlet spots 1316 on the retina can overlap, with each beamlet spot 1316 covering more than one photoreceptor. When coherent and in phase, the beamlet spot 1316 distribution pattern depicted in FIG. 18A can result in a focused, sharp-appearing image. However, when each beamlet spot 1316 impinges on more than one photoreceptor, or when there is a phase difference between multiple beamlet spots impinging on a single photoreceptor, the resulting image can appear less sharp. FIGS. 18B and 18C depict other beamlet spot 1316 distribution patterns on the retina, with each beamlet spot 1316 covering approximately one photoreceptor. Generally, these distribution patterns can be less affected by coherence and phase uniformity than those in FIG. 18A and therefore can result in a highly focused, sharp-appearing image. Thus, beam array architecture, relative beam / beamlet spacing, and beam / beamlet diameter are factors that can affect the resolution / sharpness of the image at the retina.

[0220] FIG. 19 depicts a beam multiplier 1430 (i.e., a thin beam multiplier), which may be a light-guiding optical element such as the OPE 494 and / or EPE 496 of the LOE 490 (see FIG. 67). An input beam 1410 enters the beam multiplier 1430 (e.g., via an ICG or other input portion) and travels down the beam multiplier 1430 with substantial TIR. As the input beam 1410 travels down the beam multiplier 1430, each time the input beam 1410 interacts with an external coupling grating (“OCG”) 1498, a portion of the input beam 1410 exits the beam multiplier 1430 via the OCG 1498. The OCG 1498 is configured to allow a portion of the light beam to exit the beam multiplier 1430 while another portion of the light beam propagates along the beam multiplier 1430 with substantial TIR. The OCG 1498 may be any type of diffractive optical element, including volume or surface relief. The beam multiplier 1430 clones the single input beam 1410 into three output beamlets 1416, each encoding the same pixel information as the input beam 1410.

[0221] 19 is depicted in a side view, the beam multiplier tube 1430 may have a length and width like the OPE 494 and / or EPE 496 shown in FIG. 67. Furthermore, although the input beam 1410 is generally depicted as propagating in a left-to-right direction, the beam multiplier tube 1430 may be configured to direct the light beam in various patterns, including, but not limited to, a zigzag pattern, which produces an array of beamlets 1416 (see, e.g., FIG. 18B).

[0222] As shown in Figure 20, only a portion (i.e., one) of the beamlets 1516 exiting the beam multiplier 1530 pass through the pupil 1506 defined by the iris 1508 and are focused by the crystalline lens 1502. Thus, even with beam doubling, the spacing of the beamlets 1516 can affect the actual number of beams perceived by the user. Figure 20 also shows that the number of bounces of the input beam 1510 per length of the beam multiplier 1530 determines the number of beamlets 1516 exiting a given length of the beam multiplier 1530.

[0223] FIG. 21 depicts a thinner beam multiplier tube 1630′ according to some embodiments. A thicker beam multiplier tube 1630 is also depicted for comparison. Over approximately the same length, each input light beam 1610 (the angle of incidence is preserved between the two tubes) bounces more times in the thinner beam multiplier tube 1630′ compared to the thicker beam multiplier tube 1630. The input light beam 1610 bounces back and forth at a higher spatial frequency because the beam 1610 traverses a shorter distance before encountering each surface of the thinner beam multiplier tube 1630′. Therefore, a higher density of beamlets emerges from the thinner beam multiplier tube 1630′ compared to the thicker beam multiplier tube 1630. For example, each input light beam 1610 bounces 13 times within the thinner beam multiplier tube 1630′, while a similar input light beam 1610 bounces only three times within the thicker beam multiplier tube 1630. The thinner beam multiplier tube 1630′ provides more beam doubling (i.e., cloning) per length of the beam multiplier tube compared to the thicker beam multiplier tube 1630. Furthermore, when this linear increase in cloning efficiency is multiplied across two dimensions (e.g., length and width), the increase in cloning efficiency from reduced beam multiplier tube thickness becomes exponential. The individual spacing between doubled beamlets in two dimensions is not necessarily identical (although symmetry is preferred). Furthermore, the thinner beam multiplier tube 1630′ may reduce overlap through coherent interaction despite the increased beam size.

[0224] The beam multipliers depicted in Figures 19-21 include two opposing reflective surfaces that reflect light in substantially opposite directions, enabling substantial TIR. In other embodiments, the beam multipliers include more than two reflective surfaces. For example, the multi-surface beam multiplier 1730 depicted in Figure 22A includes first and second light directing optical sub-elements ("LOS") 1730A, 1730B. The first LOS 1730A is similar to the beam multiplier 1530 depicted in Figure 20 in that it has two (i.e., first and second) opposing reflective surfaces 1732, 1734. The second LOS 1730B depicted in Figure 22A has a third reflective surface 1736 that reflects light in substantially the same direction as the second reflective surface 1734 in the first LOS 1730A.

[0225] The second LOS 1730B is positioned across the first LOS 1730A such that the incident optical beam 1710 at least partially passes through the first LOS 1730A and enters the second LOS 1730B. As the incident optical beam 1710 passes through the first LOS 1730A, a portion of it is partially reflected by the second reflective surface 1734. The portion of the incident optical beam 1710 that passes through the second LOS 1730B is reflected by the third reflective surface 1736 in substantially the same direction as the portion of the incident optical beam 1710 reflected by the second reflective surface 1734. The addition of the second LOS 1730B and its third reflective surface 1736 results in a doubling of the number of beamlets 1716 propagating along the first and second LOS 1730A, 1730B due to substantial TIR.

[0226] The thickness of the second LOS 1730B depicted in FIG. 22A is such that some of the beamlets 1716 reflecting from the third reflective surface 1736 substantially overlap with the beamlets 1716 reflecting from the second reflective surface 1734. For situations in which some of the beamlets 1716 are out of phase with one another, such overlap can serve to amplify the effects of destructive interference between the out-of-phase beamlets. Additionally, the high level of overlap can serve to minimize the degree of doubling of the number of beamlets 1716. For example, the first bounce from the second and third reflective surfaces 1734, 1736 doubles the number of beams 1710 / beamlets 1716 from one to two, while the second bounce only doubles the number of beamlets 1716 from two to three. The degree to which at least a portion of the beamlets 1716 overlap can be controlled by adjusting the input beam 1710 diameter and / or the input beam 1710 separation, both of which are substantially preserved during substantial TIR. For example, the distance between the edges of two adjacent beamlets from among the number of beamlets 1716 can be increased by reducing the diameter of the input beam 1710.

[0227] The beam multiplier 1730 depicted in FIG. 22B includes first and second LOS 1730A, 1730B like the beam multiplier 1730 depicted in FIG. 22A. However, the thickness of the second LOS 1730B is adjusted / selected so that the beamlets 1716 reflecting from the third reflective surface 1736 do not overlap with the beamlets 1716 reflecting from the second reflective surface 1734. As a result, the beam multiplier 1730 depicted in FIG. 22B has a higher beamlet multiplication degree than the beam multiplier 1730 depicted in FIG. 22A. For example, the first bounce from the second and third reflective surfaces 1734, 1736 doubles the number of beams 1710 / beamlets 1716 from 1 to 2, while the second bounce doubles the number of beamlets 1716 from 2 to 4. Continuing this pattern, each bounce from the second and third reflective surfaces 1734, 1736 doubles the number of beamlets 1716 in a substantially exponential growth.

[0228] The beam multiplier tube 1830 depicted in Figure 23 includes first and second LOS 1830A, 1830B like the beam multiplier tube 1730 depicted in Figure 22A. The difference between the beam multiplier tubes 1730, 1830 is that the second LOS 1830B depicted in Figure 23 has a fourth reflective surface 1838 in addition to a third reflective surface 1836. The third and fourth reflective surfaces 1836, 1838 are located on opposite sides of the second LOS 1830B and reflect light in substantially opposite directions.

[0229] The second LOS 1830B is positioned across the first LOS 1830A such that the incident light beam 1810 at least partially passes through the first LOS 1830A and enters the second LOS 1830B. As the incident light beam 1810 passes through the first LOS 1830A, a portion of it is partially reflected by the second reflective surface 1834. The portion of the incident light beam 1810 that passes through the second LOS 1830B is reflected by the third reflective surface 1836 in substantially the same direction as the portion of the incident light beam 1810 reflected by the second reflective surface 1834. Before the reflected beamlet 1816 exits the second LOS 1830B, a portion of the reflected beamlet 1816 is reflected by the fourth reflective surface 1838 back toward the third reflective surface 1836. The addition of a fourth reflective surface 1838 in the second LOS 1830B results in a further doubling of the number of beamlets 1816 propagating along the first and second LOS 1830A, 1830B due to substantial TIR, even compared to the beam multiplier 1730 depicted in Figure 22A. As shown in Figure 23, the addition of the fourth reflective surface 1838 results in an additional bounce per optical beam 1810 / beamlet 1816, thereby doubling the number of beamlets produced in each interaction with the first and second LOS 1830A, 1830B (i.e., the light multiplier 1830).

[0230] The beam multiplier tube 1930 depicted in FIG. 24 includes first and second LOS 1930A, 1930B, like the beam multiplier tube 1830 depicted in FIG. 23. The difference between the beam multiplier tubes 1830, 1930 is that the beam multiplier tube 1930 depicted in FIG. 24 includes a third LOS 1930C. Like the second LOS 1930B, the third LOS 1930C includes opposing reflective surfaces (i.e., fifth and sixth reflective surfaces 1940, 1942) that reflect light in substantially opposite directions. The fifth and sixth reflective surfaces 1940, 1942 are disposed on opposite sides of the third LOS 1930C.

[0231] The third LOS 1930C is positioned across the second LOS 1930B (and thus the first LOS 1930A) such that the incident light beam 1910 passes at least partially through the first and second LOSs 1930A, 1930B and enters the third LOS 1930C. As the incident light beam 1910 passes through the first LOS 1930A, a portion of it is partially reflected by the second reflective surface 1934. Similarly, as the incident light beam 1910 passes through the second LOS 1930B, a portion of it is partially reflected by the third reflective surface 1936. The portion of the incident light beam 1910 that passes through the second LOS 1930B is reflected by the third reflective surface 1936 in substantially the same direction as the portion of the incident light beam 1910 that was reflected by the second reflective surface 1934. Similarly, a portion of the incident light beam 1910 that passes through the third LOS 1930C is reflected by the fifth reflective surface 1940 in substantially the same direction as the portion of the incident light beam 1910 that was reflected by the second and third reflective surfaces 1934, 1936, respectively.

[0232] Before the reflected beamlet 1916 exits the second LOS 1930B, a portion of the reflected beamlet 1916 is reflected by a fourth reflective surface 1938 back toward the third reflective surface 1936. Similarly, before the reflected beamlet 1916 exits the third LOS 1930C, a portion of the reflected beamlet 1916 is reflected by a sixth reflective surface 1942 back toward the fifth reflective surface 1940. The addition of the third LOS 1930C and its fifth and sixth reflective surfaces 1940, 1942 results in a further doubling of the number of beamlets 1916 propagating along the first, second, and third LOS 1930A, 1930B, 1930C due to substantial TIR. As shown in FIG. 24, the addition of the third LOS 1930C results in an additional pair of bounces per light beam 1910 / beamlet 1916, thereby doubling the number of beamlets produced in each interaction with the first, second, and third LOS 1930A, 1930B, 1930C (i.e., photomultiplier tube 1930).

[0233] Multi-surface beam multipliers can be fabricated using a lamination process. In some embodiments, a second substrate (e.g., a second LOS) having a second thickness is laminated onto a first substrate (e.g., a first LOS) having a first thickness. The interface between the two substrates may be partially reflective (e.g., a metal-coated / half-silvered mirror, a thin-film coating, a dichroic mirror, a dielectric interface, a diffraction grating, a diffractive element, etc.). In another embodiment, separate waveguides / LOEs can be laminated together with a partially reflective interface.

[0234] Additionally, the thickness ratio of the first and second LOS (and various subcombinations of any multiple LOS in the system) can also affect beamlet multiplication due to beamlet overlap. If the individual thicknesses are integer multiples or ratios (i.e., factors), cloned beamlets may overlap when they exit the first and second LOS, reducing beamlet multiplication. Thus, in some embodiments (see FIG. 22B), the first thickness of the first LOS may be a non-even factor of the second thickness of the second LOS. For example, the first thickness may be 0.3256 times the second thickness (e.g., instead of 0.2 or 0.5). Quasi-random beamlet arrays with multiple LOS may be angle-insensitive or subject to imperfections in LOS thickness.

[0235] Beam multipliers can also be tuned by varying the degree of reflectivity / transmission of various surfaces (e.g., other than 50 / 50). Using this and other techniques, multipliers can be tuned to have a uniform distribution of energy across the beamlets. For moderate beam multiplication amounts (e.g., sufficient to fill the eye's pupil), beam multipliers can be dual to ensure that beamlets (and groups) have the same amount of energy as the eye sweeps across different sets of beamlets. Equalizing the amount of energy across the beamlets minimizes intensity drops (artifacts; winking) as the user's eye sweeps the FOV. With an exponential increase in the number of beamlets, the beamlets will eventually randomly overlap, thereby reducing intensity artifacts.

[0236] FIG. 25 depicts a beam multiplier tube 2030 that is tuned / optimized to produce the most light (e.g., with an optimal beam diameter / energy distribution) for beamlets 2016 directed toward the center 2044 of the FOV. For example, the beam multiplier tube 2030 can be tuned to vary the light intensity / energy as a function of the angle of the beamlets 2016 that will emerge from the beam multiplier tube 2030. The beamlets 2016 are directed toward the center 2044 of the FOV so that they are more normal / orthogonal to the surface of the beam multiplier tube 2030 (i.e., have a smaller angle of incidence). This design minimizes artifacts in the center 2044 of the FOV, where some users' eyes will be directed most of the time, while at the same time controlling the amount of energy required to display an image. As a tradeoff, the beam multiplier tube 2030 is less tuned / optimized for the more eccentric beamlets 2016 in the peripheral portions of the FOV.

[0237] The FOV may be expanded using a kaleidoscopically adjusted beam multiplier. The relative reflectivity of the surfaces can be adjusted so that the beam multiplier has dense beam multiplication in optically important regions (e.g., the center of the FOV) and sparse beam multiplication in less optically important regions (e.g., the periphery of the FOV). The FOV can be determined for various types of eye tracking, including, but not limited to, interpupillary distance measurement and pupillary movement tracking.

[0238] The OPE 494 and EPE 496 depicted in FIG. 67 do not cover / obscure each other. However, if the OPE obscures the EPE or a portion thereof, there is an increased chance of multiple reflections of the beam (i.e., a reflected beam) that may exit the LOE 490 toward the user's eye. The reflected beam may be phase-shifted, resulting in artifacts (e.g., bull's-eye or Fresnel zone artifacts, "FZA"). One way to reduce FZA is by using an anti-reflective coating to reduce the reflected beam. Another way to reduce FZA is to separate the thin waveguide OPE from the EPE. The thickness of the thin waveguide OPE can also be adjusted to minimize FZA, since the thin waveguide OPE returns the beamlets in phase with respect to one wavelength (e.g., using a 2π thickness relationship). The relative phase difference between the beamlets is a function of wavelength and scan angle. The thickness of the thin waveguide OPE can be adjusted to minimize FZA with green light, to which the human eye is most sensitive. For example, a thin waveguide OPE can be tuned for 515 nm to 540 nm, 520 nm (green), or 532 nm (green). In other embodiments, a thin waveguide OPE can be tuned to minimize FZA with 475 nm (blue) light or 650 nm (red) light. Because the human eye is better able to discriminate blue light in the annular region around the fovea, some FZAs are more detrimental to blue light, and minimizing these FZAs for blue light can significantly improve image quality. Thus, a thin waveguide OPE can cover an EPE while reducing FZA if the thickness of the thin waveguide OPE is tuned to have a 2π thickness relationship.

[0239] 26A and 26B depict a beam multiplier tube 2600 having a refractive index gap (e.g., an air gap) 2602 that ensures that light will propagate by substantial TIR at the interface (with the refractive index gap) rather than being partially transmitted into adjacent layers. The light path beam through the multiplier tube starts at entry into OPE1 2604 (e.g., a thicker LOS), exits OPE1 2604 via OCG 2606, passes into OPE2 2608 via ICG 2610, and passes through OPE2 2608 (e.g., a thinner LOS). The refractive index gap 2602 controls the light flow through this beam multiplier tube 2600, allowing light to pass between OPE1 2604 and OPE2 2608 only via OCG 2606 and ICG 2610. By varying the thickness of OPE12604 and OPE22608, different periodic relationships can be achieved for OPE12604 and OPE22608. This can be adjusted to generate different spatial frequencies for beamlet cloning. The variable optical (light-modifying) property described above is LOE thickness, but other optical properties (such as diffraction index) can also be varied to achieve effects similar to those described herein.

[0240] There are two exit edges 2612, 2614 for OPE1 2604 (see FIG. 26B). In some embodiments, both exit edges are coupled to OPE2 2608. In another embodiment, the diffraction efficiency of OPE1 2604 can be varied in various portions of OPE1 2604 to direct most of the light to one exit edge (e.g., 2606), which is coupled into OPE2 2608.

[0241] Using such a system, the OPE (as a separate element) can be removed from the LOE 490 (see, e.g., FIG. 10) and extended into a separate layer 494 that covers the entire eyepiece or a significant portion thereof. Light is coupled into the LOE 490 and enters a separate large OPE 494 for multiplication as a controlled interface between two optical elements. The light beam travels stepwise through the OPE 494 and can be multiplied upon multiple interactions with the elements of the OPE 494. The exit beamlet from the OPE 494 is not a single beam, but rather multiple overlapping beamlets resulting from the beam splitting by the OPE 494.

[0242] The use of this design can also create large areas with smaller areas containing all or most of the information / light energy. Such a system can use a depth-switching mechanism to send light to different layers (e.g., multiple depth-plane layers). The layers can be polymer-dispersed liquid crystal ("PDLC") switchable layers. Alternatively, the layers can be waveguides with individual LC shutters. Such a system can use TIR-based structures from the main LOE to create multiple exit ports for redundant optical information that can be selected by LC shutters or PDLC switches. In some embodiments, a single OPE can feed light / optical information to multiple EPE layers (e.g., EPEs corresponding to red, green, and blue light).

[0243] FIG. 27 depicts a beam multiplier 2700 in which a single OPE 2702 feeds light / optical information to two EPE layers 2704, 2706 using two spatially displaced OCGs 2708, 2710. OCG1 2708 couples the OPE 2702 to EPE1 2704 through ICG1 2712. OCG2 2710 couples the OPE 2702 to EPE2 2706 through ICG2 2714. The OCGs 2708, 2710 can be PDLC, which can be turned on or off. Alternatively, an LC shutter layer (not shown) can be interposed between the OPE 2702 and the EPE layers 2704, 2706. In some embodiments, the number of EPE layers can be set to correspond to the number of depth layers for the MR system. In alternative embodiments, a single OCG can be divided into multiple windows with shutters or switches to selectively feed light / optical information to multiple EPE layers. In another embodiment 2800 (FIG. 28), OCGs 2808, 2810 can be formed at or from the two exit edges of the OPE 2802.

[0244] FIG. 29 depicts a beam multiplier tube 2900 with an OPE 2902 designed similarly to a "hall of mirrors." In this independent OPE module 2902, an input / primary beam 2904 is doubled by the OPE 2902, and the doubled beamlets exit the OPE 2902 via one or more OCGs 2906. Three of the four OPE edges 2908, 2910, 2912 may be polished and aluminum-coated to make them reflective. Two opposing mirrors 2908, 2912 reflect the beams and beamlets propagating through the OPE 2902, generating additional beamlets (with identical optical information) as the reflected beamlets interact with the OPE 2902. Such an OPE 2902 may be tuned to have a low diffraction efficiency toward the OCG 2906, but beam multiplication will be significantly increased with multiple passes through the OPE 2902. Optionally, the OPE 2902 may have one or more regions of relatively higher diffraction efficiency 2914 to facilitate beam doubling by increasing the beam length through the OPE 2902 before the beam / beamlet exits through the OCG 2906.

[0245] In a similar embodiment 3000 depicted in Figure 30, only two of the edges 3010, 3012 (the vertical edges) and a small portion of the third edge 3008 of the OPE 3002 are polished and coated with aluminum, making them reflective. This treatment results in reduced beamlet multiplication, but doubles the amount of area for output 3016 (e.g., for an OCG (not shown)). This design increases the surface area 3016 for outcoupling.

[0246] 29 and 30, the OPE 2902, 3002 can be optimized / tuned with variable diffraction efficiency. For example, the top left region in both of these embodiments can be tuned to diffract light in an up and down direction and minimize light reflected back towards the ICG 2918, 3018, which may unintentionally couple out of the OPE 2902, 3002.

[0247] The beam multiplier 3100 depicted in Figure 31 includes an OPE 3102 that is shared across wavelengths. A first OCG 3104 is tuned to outcouple green light with blue and red absorbers 3106 coupled to the OCG 3104. A second OCG 3108 is tuned to outcouple blue and red (i.e., magenta) light with a green absorber 3110 coupled to the OCG 3108.

[0248] 32 includes an OPE 3202 with three output regions 3204, 3206, 3208. The three output regions 3204, 3206, 3208 are tuned to outcouple red 3204, green 3206, and blue 3208 light, respectively, using OCGs 3204, 3206, 3208 along with matching absorbers 3210, 3212, 3214. The DOE 3216 in the OPE 3202 forms a "V" shape 3218 with an angle of approximately 90 degrees, although the DOE may form other shapes with different angles in other embodiments (e.g., to modify beamlet density (not shown)).

[0249] The beam doubler tube 3300 depicted in Figures 33A-33I illustrates various "quilts" of different OPE 3302 regions, allowing tuning of the OPE 3302 for various outcoupling patterns. In all of these OPEs 3302, a single input / primary beam 3304 is doubled, diffracted, and / or reflected by various components of the OPE 3302 to form various doubled beams / beamlets 3306 with various outcoupling patterns. For example, Figure 33A depicts an OPE 3302 including three sections 3308, 3310, and 3312 with different diffractive properties. The three sections may be independently switchable PDLC components (e.g., to vary the outcoupling pattern) or they may be static components. Figure 33C depicts an OPE 3302 with a diffractive section 3314 and first and second PDLC components 3316 and 3318 (e.g., to vary the outcoupling pattern). FIG. 33G depicts OPE 3302 causing DOE 3320 within OPE 3302 to form a "V" shape 3322 similar to OPE 3202 in FIG.

[0250] 34-36, one specific embodiment of display screen 110 will be described. As shown in FIG. 34, waveguide 172 is a single, integral substrate or plane of optically transparent material, such as, for example, glass, fused silica, acrylic, or polycarbonate; however, in alternative embodiments, waveguide 172 may be comprised of separate, distinct substrates or planes of optically transparent material bonded together at the same plane or at different planes. IC element 168 may be closely associated with (e.g., incorporated within) face 180b of waveguide 172 to receive collimated light beam 250 from image projection assembly 108 into waveguide 172 via face 180b; however, in alternative embodiments, IC element 168 may be associated with (e.g., incorporated within) other face 180a or even an edge of waveguide 172 to couple collimated light beam 250 into waveguide 172 as an internally coupled light beam. The DOE 174 is associated with the waveguide 172 (e.g., incorporated within the waveguide 172 or abutting or adjacent to one or more of the faces 180a, 180b of the waveguide 172) to expand the effective entrance pupil of the collimated light beam 250 in two dimensions, as briefly discussed above.

[0251] To this end, the DOE 174 comprises an orthogonal pupil expansion (OPE) element 186 closely associated with (e.g., incorporated within) the face 180b of the waveguide 172 to split the in-coupled light beam 252 into orthogonal light beamlets 254, and an exit pupil expansion (EPE) element 188 closely associated with (e.g., incorporated within) the face 180b of the waveguide 172 to split the orthogonal light beamlets 254 into a set of out-coupled light beamlets 256 that exit the face 180b of the waveguide 172 towards the eye 52 of the end user 50. In alternative embodiments in which the waveguide 172 is comprised of distinctly different planes, the OPE element 174 and the EPE element 188 may be incorporated into different planes of the waveguide 172.

[0252] OPE element 186 relays light along a first axis (the horizontal or x-axis in FIG. 34 ) and expands the effective pupil of the light along a second axis (the vertical or y-axis in FIG. 34 ). In particular, as best shown in FIG. 35 , IC element 168 optically incouples collimated light beam 250 as an incoupled light beam within waveguide 172 via TIR along an internally reflected optical path parallel to axis 262 (in this case, along the vertical or y-axis), and in doing so repeatedly intersects with OPE element 186. In the illustrated embodiment, the OPE element 186 has a relatively low diffraction efficiency (e.g., less than 50%) and comprises a series of diagonal diffraction elements (45 degrees to the x-axis) such that at each intersection with the OPE element 186, a portion (e.g., more than 90%) of the internally coupled light beam 252 continues to propagate within the waveguide 172 via TIR along an internally reflected optical path parallel to the axis 262 (y-axis), and the remaining portion (e.g., less than 10%) of the internally coupled light beam 252 is diffracted as an orthogonal light beamlet 254 (shown as a dashed line in FIG. 35 ) to propagate within the waveguide 172 via TIR along an internally reflected optical path parallel to the axis 264 (in this case, along the horizontal or x-axis) toward the EPE element 188. Although axis 264 is described as being perpendicular or orthogonal to axis 262 (y-axis), it should be understood that axis 264 may alternatively be oriented obliquely relative to axis 262 (y-axis).

[0253] In a similar manner, at each intersection with the OPE element 186, a portion (e.g., greater than 90%) of each orthogonal optical beamlet 254 continues to propagate within the waveguide 172 via TIR along individual internally reflected optical paths parallel to the axis 264 (x-axis), and the remaining portion (e.g., less than 10%) of the individual orthogonal optical beamlets 254 is diffracted as secondary optical beamlets 256 that propagate within the waveguide 172 via TIR along individual internally reflected optical paths (indicated by dashed lines) parallel to the axis 262 (y-axis). Thus, at each intersection with the OPE element 186, a portion (e.g., more than 90%) of each secondary light beamlet 256 continues to propagate within the waveguide 172 via TIR along an individual internally reflected optical path parallel to the axis 262 (y-axis), and the remaining portion (e.g., less than 10%) of the individual secondary light beamlets 256 is diffracted as a tertiary light beamlet 258 that combines in phase with the orthogonal light beamlet 254 and propagates within the waveguide 172 via TIR along an individual internally reflected optical path parallel to the axis 264 (x-axis).

[0254] Thus, by splitting the internally coupled light beam 252 via TIR into multiple orthogonal light beamlets 254 that propagate within the waveguide 172 along separate internally reflected optical paths parallel to the axis 264 (x-axis), the entrance pupil of the collimated light beam 250 that is internally coupled into the display screen 110 is expanded vertically along the y-axis by the OPE element 186.

[0255] The EPE element 188, and thus the effective exit pupil of the light along the first axis (the horizontal x-axis in FIG. 36 ), is further expanded. In particular, as best shown in FIG. 36 , the EPE element 188, like the OPE element 186, has a relatively low diffraction efficiency (e.g., less than 50%), and at each intersection with the EPE element 188, a portion (e.g., greater than 90%) of each orthogonal light beamlet 254 continues to propagate within the waveguide 172 along a respective internally reflected optical path parallel to the axis 264 (x-axis), while the remaining portion of each orthogonal light beamlet 254 is diffracted as an outcoupled light beamlet 256 that exits the face 180 b of the waveguide 172 (along the z-axis), as illustrated in FIG. That is, each time a light beamlet strikes the EPE element 188, a portion of it will be diffracted toward face 180b of the waveguide 172, while the remaining portion will continue to propagate within the waveguide 172 via TIR along an internal reflection optical path parallel to axis 264 (x-axis).

[0256] Therefore, by splitting each orthogonal light beamlet 254 into multiple outcoupled light beamlets 256, the entrance pupil of the collimated light beam 250 is further expanded horizontally along the x-axis by the EPE element 188, resulting in a two-dimensional array of outcoupled light beamlets 256 that resembles a larger version of the original incoupled light beam 252.

[0257] 34 as not overlapping in the xy-plane, it should be noted that the OPE element 186 and the EPE element 188 may completely overlap each other in the xy-plane, as illustrated in FIG. 39, or may partially overlap each other in the xy-plane, as illustrated in FIG. 38. In both cases, as in the embodiment illustrated in FIG. 34, the OPE element 186 will split the internally coupled light beam 252, which propagates within the waveguide 172 via TIR along an internally reflected optical path parallel to axis 262 (y-axis), into orthogonal light beamlets 254, which propagate within the waveguide 172 via TIR along separate internally reflected optical paths parallel to axis 264 (x-axis). In these cases, the OPE element 186 and the EPE element 188 will need to be disposed on opposite faces 180a, 180b of the waveguide 172, respectively.

[0258] In addition to outcoupling light beamlets 256 from face 180b of waveguide 172, EPE element 188 also serves to focus the output set of light beamlets 256 along a given focal plane so that the image or virtual object is seen by end user 50 at a viewing distance where a portion of the image or virtual object coincides with the focal plane. For example, if EPE element 188 had only a linear diffraction pattern, the outcoupled light rays 256 exiting face 180b of waveguide 172 toward end user's 50's eye 52 would be nearly parallel, as shown in FIG. 39A, which would be interpreted by end user's 50's brain as light from the viewing distance (focal plane) at optical infinity. However, if the EPE element 188 has both linear and radially symmetric diffraction pattern components, the outcoupled light beamlets 256 exiting the face 180b of the waveguide 172 will be rendered more divergent from the perspective of the eye 52 of the end user 50 (i.e., a convex curvature will be imparted to the optical wavefront), requiring the eye 52 to accommodate to a closer distance to bring the resulting image into focus on the retina, and will be interpreted by the brain of the end user 50 as light from a viewing distance (e.g., 4 meters) closer to the eye 52 than optical infinity, as shown in FIG. 39B. The out-coupled light beamlet 256 exiting face 180b of waveguide 172 will be rendered more divergent from the perspective of eye 52 of end user 50 (i.e., a more convex curvature will be imparted to the light wavefront), which may require eye 52 to accommodate to a closer distance to bring the resulting image into focus on the retina, and will be interpreted by the brain of end user 50 as light from a viewing distance closer to eye 52 (e.g., 0.5 meters), as shown in FIG. 39C.

[0259] Although the waveguide device 170 is described herein as having only one focal plane, it should be understood that multiple planar optical waveguides 172 with associated OPEs 176 and EPEs 178 can be used to generate images at multiple focal planes simultaneously or sequentially, as discussed in U.S. Patent Publication Nos. 2015 / 0309264 and 2015 / 0346490 (expressly incorporated herein by reference).

[0260] As previously mentioned, it is desirable to increase the saturation or fill of the exit pupil of the display screen 110. Without modification, the exit pupil of the display screen 110 may not be optimally saturated. For example, as illustrated in FIG. 40A , the pupil of the collimated light beam 250 may be expanded to an exit pupil 300 a of a 3×3 array of outcoupled light beamlets 256, which is relatively sparse in nature (i.e., the spacing between the outcoupled light beamlets 256 is relatively large). However, using a beam doubling feature in the display screen 110, the pupil of the collimated light beam 250 can be enhanced to be expanded to an exit pupil 300 b of a more saturated 9×9 array of outcoupled light beamlets 256, as illustrated in FIG. 40B .

[0261] For example, in some embodiments, two OPEs 186 are employed to double the number of orthogonal optical beamlets 254 obtained from the internally coupled optical beam 252, and therefore double the saturation of the two-dimensional array of externally coupled optical beamlets 256 emerging from face 180b of waveguide 172.

[0262] In particular, as shown in FIGS. 41-43, waveguide device 170a is similar to the described waveguide device 170, but waveguide device 170a includes a first face 180a adjacent to (e.g., on) a first face 180a of waveguide 172 to split an incoupled optical beam 252, which propagates within waveguide 172 via TIR along an internally reflected optical path parallel to axis 262 (y-axis), into a first set of orthogonal optical beamlets 254a for propagation within waveguide 172 via TIR along separate internally reflected optical paths parallel to axis 264 (x-axis). and a second OPE element 186b disposed adjacent to (e.g., on) the second face 180b of the waveguide 172 to split the incoupled optical beam 252, propagating within the waveguide 172 via TIR along internally reflected optical paths parallel to the axis 262 (y-axis), into a second set of orthogonal optical beamlets 254b for propagation within the waveguide 172 via TIR along separate internally reflected optical paths parallel to the axis 264 (x-axis). As best shown in FIG. 41 , the first and second sets of orthogonal optical beamlets 254a, 254b alternate with each other.

[0263] That is, as the incoupling light beam 252 propagating within the waveguide 172 along an internally reflected optical path parallel to the axis 262 (y-axis) via TIR alternately intersects the first and second OPE elements 186a, 186b on opposite faces 180a, 180b of the waveguide 172, a portion of the incoupling light beam 252 is diffracted as first and second primary sets of optical beamlets 254a, 254b, respectively, due to propagation within the waveguide 172 along alternating internally reflected optical paths parallel to the axis 264 (x-axis) via TIR. Secondary optical beamlets 256a, 256b (shown in FIGS. 41 and 42) are also generated from the beamlets 254a, 254b, respectively, which further create tertiary optical beamlets 258a, 258b (shown only in FIG. 41) that combine in phase with the orthogonal optical beamlets 254a, 254b, respectively. In turn, the first and second primary sets of optical beamlets 254a, 254b intersect the EPE element 188 on face 180b of the waveguide 172, and portions thereof are diffracted as first and second outcoupled optical beamlet sets 256a, 256b, respectively, that exit face 180b of the waveguide 172. Thus, doubling the orthogonal optical beamlets 254 correspondingly increases the saturation of the exit pupil 300a extended by the display screen 110 (shown in FIG. 40B).

[0264] In another embodiment, partially reflective interfaces are incorporated into the waveguide 172 to increase the number of optical beamlets propagating within the waveguide 172, thus increasing the saturation of the two-dimensional array of outcoupled optical beamlets 256 exiting the face 180b of the waveguide 172. In the embodiment illustrated below, the waveguide 172 comprises multiple layered substrates having at least one pair of adjacent substrates and a semi-reflective interface between each pair of adjacent substrates, such that an optical beam intersecting each semi-reflective interface is split into multiple beamlets propagating within the waveguide 172 via TIR, thereby increasing the density of outcoupled optical beamlets exiting the face 180b of the waveguide 172. Note that the adjacent substrates described below are not drawn to scale and are illustrated as multiples of each other for simplicity. However, adjacent substrates may be, and preferably are, non-multiples of one another so that the density of the internal packing of outcoupled light beamlets exiting the face of the waveguide is maximized.

[0265] 44-46, waveguide device 170b is similar to the previously described waveguide device 170, except that waveguide 172 is a composite substrate comprised of a primary waveguide 172a and a secondary waveguide 172b. Waveguide device 170b further comprises a semi-reflective interface 190 disposed between primary waveguide 172a and secondary waveguide 172b.

[0266] In some embodiments, semi-reflective interface 190 may take the form of a semi-reflective coating, such as one made of a metal, such as gold, aluminum, silver, nickel chromium, or chromium; a dielectric, such as an oxide, fluoride, or sulfide; a semiconductor, such as silicon or germanium; and / or a glue or adhesive with reflective properties, and may be disposed between primary waveguide 172a and secondary waveguide 172b via any suitable process, such as physical vapor deposition (PVD), ion-assisted deposition (IAD), ion beam sputtering (IBS), etc. The reflection-to-transmission ratio of semi-reflective coating 190 may be selected or determined, at least in part, based on the thickness of coating 190, or semi-reflective coating 190 may have a plurality of small perforations to control the reflection-to-transmission ratio. In an alternative embodiment, primary waveguide 172a and secondary waveguide 172b are made of materials with different refractive indices such that the interface between waveguides 172a, 172b is semi-reflective for light incident on the semi-reflective interface at less than a critical angle (i.e., the angle of incidence at which a portion of the light is transmitted through the semi-reflective interface and the remainder of the light is reflected by the semi-reflective interface). Semi-reflective interface 190 is preferably designed so that the angle of the light beam incident on semi-reflective interface 190 is preserved.

[0267] In either case, as best shown in Figure 45, IC element 168 couples collimated light beam 250 into planar optical waveguide 172 as incoupled light beam 252, which propagates within waveguide 172 via TIR along an internally reflected optical path parallel to axis 262 (y-axis). Semi-reflective interface 190 is configured to split incoupled light beam 252 into multiple incoupled light beamlets.

[0268] In particular, the semi-reflective interface 190 is configured to split the in-coupled light beam 252 into two primary in-coupled light beamlets (in this case, the first primary in-coupled light beamlet 252a (indicated by the solid line) and the second primary in-coupled light beamlet 252b (indicated by the dashed line) that propagate within the primary waveguide 172a along an internally reflective optical path parallel to the axis 262 (y-axis). As shown in FIG. 45, the semi-reflective interface 190 generates a secondary in-coupled light beamlet 252′ that propagates within the secondary waveguide 172b along an internally reflective optical path parallel to the axis 262 (y-axis) via TIR, from which the second primary in-coupled light beamlet 252b is created.

[0269] It should be understood that because the thickness of the primary waveguide 172 is a multiple (in this case, exactly twice the thickness) of the thickness of the secondary waveguide 172b, only two primary in-coupled light beamlets 252a, 252b are generated due to the recombination of the light beamlets. However, in the preferred case where the thickness of the primary waveguide 172a is not a multiple of the thickness of the secondary waveguide 172b, an additional primary in-coupled light beamlet 252 is generated at each intersection between a secondary in-coupled light beamlet 252' and the semi-reflective interface 190, and similarly, an additional secondary in-coupled light beamlet 252' is generated at each intersection between a primary in-coupled light beamlet 252 and the semi-reflective interface 190. In this way, the number of primary in-coupled light beamlets 252 increases geometrically along the axis 262 from the ICO 168.

[0270] The OPE elements 186 are configured to split the primary in-coupled light beamlets 252 a, 252 b into two sets of primary orthogonal light beamlets, respectively. In particular, the primary in-coupled light beamlets 252 a, 252 b intersect the OPE element 186 adjacent to the face 180 b of the waveguide 172 such that portions of the primary in-coupled light beamlets 252 a, 252 b are diffracted via TIR as two sets of primary orthogonal light beamlets 254 a, 254 b that propagate within the waveguide 172 along separate internally reflected optical paths parallel to the axis 264 (x-axis).

[0271] As best shown in Figure 46, the semi-reflective interface 190 is configured to split the two sets of orthogonal optical beamlets 254a, 254b into four sets of orthogonal optical beamlets. In particular, the semi-reflective interface 190 splits the set of primary orthogonal optical beamlets 254a into two sets of primary orthogonal optical beamlets 254a (in this case, a first set of primary orthogonal optical beamlets 254a(1) (indicated by solid lines) and a second set of primary orthogonal optical beamlets 254a(2) (indicated by dashed lines) that propagate within the primary waveguide 172a along separate internally reflected optical paths parallel to the axis 264 (x-axis) via TIR. As shown in Figure 46, the semi-reflective interface 190 splits the set of primary orthogonal optical beamlets 254a, 254b into two sets of primary orthogonal optical beamlets 254a (indicated by dashed lines) that propagate within the primary waveguide 172a along separate internally reflected optical paths parallel to the axis 264 (x-axis) via TIR. The semi-reflective interface 190 splits the set of orthogonal optical beamlets 254b via TIR into two more sets of primary orthogonal optical beamlets (not shown) that propagate within the primary waveguide 172a along separate internally reflective optical paths parallel to the axis 264' (x-axis), from which a second set of primary orthogonal optical beamlets 254a(2) is created. Similarly, the semi-reflective interface 190 splits the set of orthogonal optical beamlets 254b via TIR into two more sets of primary orthogonal optical beamlets (not shown) that propagate within the primary waveguide 172a along separate internally reflective optical paths parallel to the axis 264 (x-axis).

[0272] It should be understood that because the thickness of the primary waveguide 172a is a multiple (in this case, exactly twice the thickness) of the thickness of the secondary waveguide 172b, only two primary orthogonal optical beamlets 254 are generated from each orthogonal optical beamlet 254. However, in the preferred case where the thickness of the primary waveguide 172a is not a multiple of the thickness of the secondary waveguide 172b, an additional primary orthogonal optical beamlet 254 is generated at each intersection between a secondary orthogonal optical beamlet 254' and a semi-reflective interface 190, and similarly, an additional secondary orthogonal optical beamlet 254' is generated at each intersection between a primary in-coupled optical beamlet 254 and a semi-reflective interface 190. In this way, the number of primary orthogonal optical beamlets 254 increases geometrically from the ICO 168 along axis 264 (x-axis).

[0273] The EPE element 188 is configured to split each of the orthogonal optical beamlets into a set of outcoupled optical beamlets 256. For example, the set of primary orthogonal optical beamlets 254 (only sets of primary orthogonal optical beamlets 254a(1) and 254a(2) are shown) intersects with the EPE element 188 adjacent to the face 180b of the waveguide 172 such that a portion of the primary orthogonal optical beamlets 254 are diffracted as the set of outcoupled optical beamlets 256 that exit the face 180b of the waveguide 172. Thus, increasing the number of incoupled optical beamlets 252 and the number of orthogonal optical beamlets 254 correspondingly increases the saturation of the exit pupil 300a extended by the display screen 110 (shown in FIG. 40B).

[0274] 47A-47D, the manner in which a semi-reflective interface 190 doubles an optical beam (in this case, an in-coupled optical beam 252, although the same technique can be applied to an orthogonal beam 254 as well) into multiple beamlets 252 (in this case, two optical beamlets 252a and 252b) will now be described. In the embodiment of FIGS. 47A-47D, the primary waveguide 172a is a multiple of the secondary waveguide 172b, and therefore the primary optical beamlet 252 and the secondary optical beamlet 252′ may share some intersection points at the semi-reflective interface 190. However, as discussed briefly above, the primary waveguide 172a is preferably a non-multiple of the secondary waveguide 172b so that the number of common intersection points at the semi-reflective interface 190 is minimized, thereby generating additional optical beamlets 252 and maximizing internal filling of the out-coupled beamlets.

[0275] At the first intersection point P1 with the semi-reflective interface 190, a portion of the light beam 252 is transmitted through the semi-reflective interface 190 into the secondary waveguide 172b as secondary light beamlet 252', which is reflected by the face 180a of the waveguide 172 back to the second intersection point P2 of the semi-reflective interface 190, while a portion of the light beam 252 is reflected by the semi-reflective interface 190 back into the primary waveguide 172a as primary light beamlet 252a, which is reflected by the face 180b of the waveguide 172 back to the third intersection point P3 of the semi-reflective interface 190 (Figure 47A).

[0276] At the second intersection point P2 with the semi-reflective interface 190, a portion of the secondary light beamlet 252' is transmitted through the semi-reflective interface 190 into the primary waveguide 172b as primary light beamlet 252b, which is reflected by the face 180a of the waveguide 172 back to the fourth intersection point P4 of the semi-reflective interface 190, while a portion of the secondary light beamlet 252' is reflected by the semi-reflective interface 190 back into the secondary waveguide 172b as secondary light beamlet 252', which is reflected by the face 180a of the waveguide 172 back to the third intersection point P3 of the semi-reflective interface 190 (Figure 47B).

[0277] At a third intersection point P3 with semi-reflective interface 190, a portion of primary light beamlet 252a is transmitted through semi-reflective interface 190 into secondary waveguide 172b, and a portion of secondary light beamlet 252' is reflected by semi-reflective interface 190 back into secondary waveguide 172b, some of which incidentally combine together as secondary light beamlet 252' and are reflected by face 180b of waveguide 172 back to fourth intersection point P4 (FIG. 47C). Of course, primary light beamlet 252a and secondary light beamlet 252' may not have a common intersection point P3, in which case additional secondary light beamlets 252' may be generated. Further, at a third intersection point P3 with semi-reflective interface 190, a portion of secondary light beamlet 252′ is transmitted through semi-reflective interface 190 into primary waveguide 172a, and a portion of primary light beamlet 252a is reflected by semi-reflective interface 190 back into primary waveguide 172a, some of which may combine together as primary light beamlet 252a, which is reflected by face 180b of waveguide 172 back to a fifth intersection point P5 of semi-reflective interface 190 ( FIG. 47C ). Of course, secondary light beamlet 252′ and primary light beamlet 252a may not have a common intersection point P3, in which case additional primary light beamlets 252 may be generated.

[0278] At a fourth intersection point P4 with semi-reflective interface 190, a portion of primary light beamlet 252b is transmitted through semi-reflective interface 190 into secondary waveguide 172b, and a portion of secondary light beamlet 252' is reflected by semi-reflective interface 190 back into secondary waveguide 172b, some of which may combine together as secondary light beamlet 252' and are reflected by face 180b of waveguide 172 back to fifth intersection point P5 (FIG. 47D). Of course, primary light beamlet 252b and secondary light beamlet 252' may not have a common intersection point P4, in which case additional secondary light beamlets 252' may be generated. Furthermore, at a fourth intersection point P4 with semi-reflective interface 190, a portion of secondary light beamlet 252′ is transmitted through semi-reflective interface 190 into primary waveguide 172a, and a portion of primary light beamlet 252b is reflected by semi-reflective interface 190 back into primary waveguide 172a, some of which combine together as primary light beamlet 252b, which is reflected by face 180b of waveguide 172 back to a sixth intersection point P6 of semi-reflective interface 190 (FIG. 47D). Of course, secondary light beamlet 252′ and primary light beamlet 252b may not have a common intersection point P4, in which case additional primary light beamlets 252 may be generated.

[0279] Thus, from the foregoing, it can be seen that optical energy is transferred between the primary waveguide 172a and the secondary waveguide 172b to generate and propagate two optical beamlets 252a, 252b within the waveguide device 170.

[0280] Importantly, the thickness of the layered substrate is selected in conjunction with the expected angle of incidence of the light beam onto each semi-reflective interface so that there are no gaps between the edges of adjacent outcoupled beamlets 256.

[0281] 44-46, the thickness of secondary waveguide 172b is less than the thickness of primary waveguide 172a, and the thickness Δt of secondary waveguide 172b is selected so that the center-to-center spacing of adjacent resulting outcoupled optical beamlets 256 is less than or equal to the width w of collimated optical beamlet 250. Of course, if primary waveguide 172a is not a multiple of secondary waveguide 172b, the center-to-center spacing of adjacent resulting outcoupled optical beamlets 256 may be greater than the width w of collimated optical beamlet 250.

[0282] Note that the width w of the collimated light beam 250 relative to the size of the IC element 168 is exaggerated for illustrative purposes. In reality, the width w of the collimated light beam 250 would be much smaller than the size of the IC element 168, which would need to be large enough to accommodate all scan angles of the collimated light beam 250. In a preferred embodiment, the average spacing between adjacent outcoupled light beamlets 256 is minimized for the worst-case scan angle. For example, for the worst-case scan angle, there may be gaps between some of the adjacent outcoupled light beamlets 256, but there will be no gaps between the majority of the adjacent outcoupled light beamlets 256.

[0283] Therefore, the thickness Δt of the secondary waveguide 172b may be selected to minimize the spacing between adjacent outcoupled beamlets 256 based on the worst-case scan angle. Note that the worst-case scan angle is the one that results in the smallest angle of incidence of the incoupled light beam 252 on the semi-reflective interface 190. Of course, if the primary waveguide 172a were not a multiple of the secondary waveguide 172b, more outcoupled beamlets 256 would be generated, thereby necessarily reducing the average spacing between adjacent outcoupled beamlets 256. In this case, it may be beneficial to select thickness values ​​t and Δt that have a relatively high least common multiple. For example, when selecting thickness values ​​t and Δt, one may seek to maximize the least common multiple of the thickness values ​​t and Δt to maximize the amount of outcoupled beamlets 256 for the worst-case scan angle. Furthermore, the selection of thickness values ​​t and Δt may also result in a non-uniform / complex distribution of the outcoupled beamlets 256, which may minimize adverse effects created by coherent optical interactions between adjacent outcoupled beamlets 256.

[0284] For example, if the worst-case angle of incidence between the incoupled light beam 252 and the semi-reflective interface 190 is assumed to be 60 degrees, and the thickness t of the primary waveguide 172a is assumed to be exactly twice the thickness Δt of the secondary waveguide 172b, then the thickness Δt of the secondary waveguide 172b will be 1 / 2 times the width w of the incoupled light beam 252, such that adjacent primary incoupled light beamlets 252 will have no gaps between them, as illustrated in FIG. 48, adjacent primary orthogonal light beamlets 254 will have no gaps between them, and therefore adjacent outcoupled light beamlets 256 will have no gaps between them, as illustrated in FIG. 49. [ka] It should be.

[0285] It should be understood that for purposes of simplicity in the explanation, no refraction of light transmitted through semi-reflective interface 190 is assumed. However, if substantial refraction of light transmitted through semi-reflective interface 190 occurs, the angle of transmission of the light due to such refraction must be taken into consideration when selecting the thickness Δt of secondary waveguide 172b. For example, the greater the refraction of light, such that the angle of the transmitted light relative to semi-reflective interface 190 decreases, the more the thickness Δt of secondary waveguide 172b must be reduced to compensate for such refraction.

[0286] It should also be understood from the foregoing that the generation of primary in-coupled light beamlets 252 propagating within primary waveguide 172a along an internally reflective optical path parallel to axis 262 (y-axis) via TIR, followed by the generation of primary out-coupled light beamlets 256 propagating within primary waveguide 172a along an internally reflective optical path parallel to axis 264 (x-axis), will completely in-fill the exit pupil of display screen 110, assuming an appropriate thickness Δt of secondary waveguide 172b.

[0287] If it is desirable to reduce the thickness Δt of the secondary waveguide 172b and further reduce the average spacing between adjacent primary in-coupled optical beamlets 252, primary orthogonal optical beamlets 254, and out-coupled optical beamlets 256, the thickness t of the primary waveguide 172a may be much greater than the thickness Δt of the secondary waveguide 172b, for example, by three, four, five, or more times greater than the thickness Δt of the secondary waveguide 172b.

[0288] For example, as illustrated for waveguide device 170c in Figures 50 and 51, the thickness t of primary waveguide 172a is three times the thickness Δt of secondary waveguide 172b. As best shown in Figure 50, IC element 168 couples incoupling optical beam 252 into waveguide 172, which propagates within waveguide 172 via TIR along an internally reflected optical path parallel to axis 262 (y-axis). Semi-reflective interface 190 is configured to split incoupling optical beam 252 into three incoupling optical beamlets. In particular, the semi-reflective interface 190 splits the in-coupled light beam 252 into three primary in-coupled light beamlets 252 (a first primary in-coupled light beamlet 252a (indicated by a solid line) and two further primary in-coupled light beamlets 252b, 252c (indicated by dashed lines)) that propagate within the primary waveguide 172a along separate internally reflective optical paths parallel to the axis 262. As shown in FIG. 50, the semi-reflective interface 190 generates a secondary in-coupled light beamlet 252' that propagates within the secondary waveguide 172b along an internally reflective optical path parallel to the axis 264' (x-axis) via TIR, from which the two primary in-coupled light beamlets 252b, 252c are created.

[0289] It should be understood that because the thickness of the primary waveguide 172a is a multiple (in this case, exactly three times the thickness) of the thickness of the secondary waveguide 172b, only three primary in-coupled light beamlets 252a, 252b, 252c are generated due to the recombination of the light beamlets. However, in the preferred case where the thickness of the primary waveguide 172a is a non-multiple of the thickness of the secondary waveguide 172b, an additional primary in-coupled light beamlet 252 is generated at each intersection between a secondary in-coupled light beamlet 252' and the semi-reflective interface 190, and similarly, an additional secondary in-coupled light beamlet 252' is generated at each intersection between a primary in-coupled light beamlet 252 and the semi-reflective interface 190. In this way, the number of primary in-coupled light beamlets 252 increases geometrically from the ICO 168 along the axis 262 (y-axis).

[0290] The OPE elements 186 are configured to split the primary in-coupled light beamlets 252 a-252 c into a set of three primary orthogonal light beamlets, respectively. In particular, the primary in-coupled light beamlets 252 a-252 c intersect the OPE elements 186 adjacent to the face 180 b of the waveguide 172 such that portions of the primary in-coupled light beamlets 252 a-252 c are diffracted via TIR as a set of three primary orthogonal light beamlets 254 a-254 c that propagate within the waveguide 172 along separate internally reflected optical paths parallel to the axis 264 (x-axis).

[0291] As best shown in Figure 51, the semi-reflective interface 190 is configured to split the set of three orthogonal optical beamlets 254a-254c into nine orthogonal optical beamlet sets. In particular, the semi-reflective interface 190 splits the set of primary orthogonal optical beamlets 254a into three sets of primary orthogonal optical beamlets 254a (a first set of primary in-coupled optical beamlets 254a (indicated by solid lines) and two further sets of primary in-coupled optical beamlets 254b, 254c (indicated by dashed lines) that propagate within the primary waveguide 172a along separate internally reflective optical paths parallel to axis 262' (y-axis) via TIR. 2, generating a set of secondary in-coupled optical beamlets 252' that propagate within secondary waveguide 172b along axis 264 (x-axis), from which two sets of primary in-coupled optical beamlets 254b, 254c are created. Similarly, semi-reflective interface 190 splits set of orthogonal optical beamlets 254b via TIR into a set of three further primary orthogonal optical beamlets (not shown) that propagate within primary waveguide 172a along separate internally reflected optical paths parallel to axis 264 (x-axis).

[0292] It should be understood that because the thickness of primary waveguide 172a is a multiple (in this case, exactly three times the thickness) of the thickness of secondary waveguide 172b, only three sets of primary orthogonal optical beamlets 254a, 254b, 254c are generated due to the recombination of the optical beamlets. However, in the preferred case where the thickness of primary waveguide 172a is not a multiple of the thickness of secondary waveguide 172b, an additional set of primary orthogonal optical beamlets 254 is generated at each intersection between set of secondary orthogonal optical beamlets 254' and semi-reflective interface 190, and similarly, an additional set of secondary orthogonal optical beamlets 254' is generated at each intersection between set of primary orthogonal optical beamlets 254 and semi-reflective interface 190. In this way, the number of primary orthogonal optical beamlets 254 increases geometrically from ICO 168 along axis 264 (x-axis).

[0293] The EPE element 188 is configured to split the set of nine orthogonal optical beamlets into a set of outcoupled optical beamlets 256. In particular, as shown in FIG. 51 , the set of primary orthogonal optical beamlets 254 (only the sets of primary orthogonal optical beamlets 254a(1)-254a(3) are shown) intersect with the EPE element 188 adjacent to the face 180b of the waveguide 172 such that a portion of the primary orthogonal optical beamlets 254 are diffracted as the set of outcoupled optical beamlets 256 that exit the face 180b of the waveguide 172. Thus, increasing the number of incoupled optical beamlets 252 and the number of orthogonal optical beamlets 254 correspondingly increases the saturation of the exit pupil 300a extended by the display screen 110 (shown in FIG. 40B ).

[0294] It should be noted that such saturation of the exit pupil 300a by the waveguide device 170c of Figures 50-51 is comparable to the saturation of the exit pupil 300a by the waveguide device 170b of Figures 45-46 when the width w of the collimated light beam 250 incoupling in the waveguide device 170c is 2 / 3 smaller than the width of the collimated light beam 250 incoupling in the waveguide device 170b. That is, the thickness Δt of the secondary waveguide 172b needs to be scaled downward only proportionally to the reduction in the width w of the collimated light beam 250 incoupling in the waveguide device 170b. For example, assuming the same worst-case angle of incidence between the incoupled light beam 252 and the semi-reflective interface 190 is 60 degrees, the thickness Δt of the secondary waveguide 172b is 1 / 2 the width w of the incoupled light beam 252 such that the edges of adjacent primary incoupled light beamlets 252 will have no gaps between them, as illustrated in FIG. 52, the edges of the primary orthogonal light beamlets 254 will have no gaps between them, as illustrated in FIG. 53, and therefore the edges of adjacent outcoupled light beamlets 256 will have no gaps between them. [ka] can be scaled downward to

[0295] From the foregoing, it can be seen that the thickness t of the primary waveguide 172a can be much larger than the width w of the collimated light beam 250 that is incoupled into the waveguide devices 170b, 170c illustrated in FIGS. 44-53, while the thickness Δt of the secondary waveguide 172b can be smaller than the width w of the collimated light beam 250. However, if the thickness Δt of the secondary waveguide 172b required to eliminate center-to-center spacing of adjacent ones of the resulting outcoupled light beamlets 256 is too small for manufacturability purposes, given the worst-case scan angle, the thickness of the secondary waveguide 172b may alternatively be selected such that the thickness difference between the primary waveguide 172a and the secondary waveguide 172b is equal to the differential thickness Δt, as illustrated in the waveguide device 170d of FIGS. 54 and 55.

[0296] Thus, in this case, the thickness of secondary waveguide 172b may be selected to be slightly less than the thickness t of primary waveguide 172a, i.e., t-Δt. As best shown in Figure 54, IC element 168 couples incoupling light beam 252 into waveguide 172, which propagates within waveguide 172 via TIR along an internally reflected optical path parallel to axis 262 (y-axis). Semi-reflective interface 190 is configured to split incoupling light beam 252 into three incoupling light beamlets. In particular, the semi-reflective interface 190 splits the in-coupled light beam 252 into three primary in-coupled light beamlets 252 (the first primary in-coupled light beamlet 252a (indicated by a solid line) and two further primary in-coupled light beamlets 252b, 252c (indicated by dashed lines) that propagate within the primary waveguide 172a along separate internally reflective optical paths parallel to the axis 262. As shown in FIG. 54, the semi-reflective interface 190 generates two secondary in-coupled light beamlets 252(1)' and (2)' that propagate within the secondary waveguide 172b along separate internally reflective optical paths parallel to the axis 262' (y-axis) via TIR, from which the two primary in-coupled light beamlets 252b, 252c are created.

[0297] The OPE elements 186 are configured to split the primary in-coupled light beamlets 252 a-252 c into a set of three primary orthogonal light beamlets, respectively. In particular, the primary in-coupled light beamlets 252 a-252 c intersect the OPE elements 186 adjacent to the face 180 b of the waveguide 172 such that portions of the primary in-coupled light beamlets 252 a-252 c are diffracted via TIR as a set of three primary orthogonal light beamlets 254 a-254 c that propagate within the waveguide 172 along separate internally reflected optical paths parallel to the axis 264 (x-axis).

[0298] As best shown in Figure 55, the semi-reflective interface 190 is configured to split the set of three orthogonal optical beamlets 254a-254c into nine orthogonal optical beamlet sets. In particular, the semi-reflective interface 190 splits the set of primary orthogonal optical beamlets 254a into three sets of primary orthogonal optical beamlets 254a (a first set of primary in-coupled optical beamlets 254a (indicated by solid lines) and two further sets of primary in-coupled optical beamlets 254b, 254c (indicated by dashed lines) that propagate within the primary waveguide 172 along individual internally reflective optical paths parallel to the axis 264 (x-axis). As shown in Figure 55, the semi-reflective interface 190 propagates the set of primary orthogonal optical beamlets 254a-254c into the set of three orthogonal optical beamlets 254a-254c (indicated by dashed lines) that propagate within the primary waveguide 172 along individual internally reflective optical paths parallel to the axis 264' (x-axis) via TIR. 172b, from which two sets of primary in-coupled optical beamlets 254b, 254c are created. Similarly, semi-reflective interface 190 splits set of orthogonal optical beamlets 254b into a further set of three primary orthogonal optical beamlets (not shown) that propagate within primary waveguide 172a along separate internally reflective optical paths parallel to axis 264 (x-axis), and splits set of orthogonal optical beamlets 254c into a further set of three primary orthogonal optical beamlets (not shown).

[0299] The EPE element 188 is configured to split the set of nine orthogonal optical beamlets into a set of outcoupled optical beamlets 256. In particular, as shown in FIG. 55, the set of primary orthogonal optical beamlets 254 (only sets 254a(1)-254a(3) of primary orthogonal optical beamlets are shown) intersect with the EPE element 188 adjacent to the face 180b of the waveguide 172 such that a portion of the primary orthogonal optical beamlets 254 are diffracted as a set of outcoupled optical beamlets 256 that exit the face 180b of the waveguide 172. Thus, increasing the number of incoupled optical beamlets 252 and the number of orthogonal optical beamlets 254 correspondingly increases the saturation of the exit pupil 300a extended by the display screen 110 (shown in FIG. 40B).

[0300] The thickness Δt of the secondary waveguide 172b is selected in the same manner as above with respect to the waveguide devices 170b and 170c of FIGS. 44-53. The difference in thickness Δt between the primary waveguide 172a and the secondary waveguide 172b in the embodiment of FIGS. 54-55 is selected such that, assuming the same worst-case angle of incidence between the incoupled light beam 252 and the semi-reflective interface 190 is 60 degrees, the differential thickness Δt is equal to the width w of the incoupled light beam 252 such that the edges of adjacent primary incoupled light beamlets 252 and adjacent primary orthogonal light beamlets 254 will have no gaps therebetween, and therefore the edges of adjacent outcoupled light beamlets 256 will have no gaps therebetween. [ka] Thus, in this case, the thickness of the secondary waveguide 172b will exceed the width w of the incoupled light beam 252.

[0301] While the aforementioned waveguide devices 170a-170d illustrated in Figures 44-55 have been described as including only one secondary waveguide 172b, it should be understood that the waveguide device 170 may have multiple secondary waveguides 172b. For example, with reference to Figures 56 and 57, a waveguide device 170e includes two secondary waveguides 172b disposed on a primary waveguide 172a and four semi-reflective interfaces 190, one of which is disposed between the primary waveguide 172a and one of the secondary waveguides 172b, and one of which is disposed between each of the secondary waveguides 172b.

[0302] 56, IC element 168 couples incoupling optical beam 252 into waveguide 172, which propagates within waveguide 172 via TIR along an internally reflected optical path parallel to axis 262 (y-axis). Semi-reflective interface 190 is configured to split incoupling optical beam 252 into three incoupling optical beamlets. In particular, the semi-reflective interface 190 splits the in-coupled light beam 252 into three primary in-coupled light beamlets 252 (a first primary in-coupled light beamlet 252a (indicated by a solid line) and two further primary in-coupled light beamlets 252b, 252c (indicated by dashed lines) that propagate within the primary waveguide 172a along separate internally reflective optical paths parallel to the axis 262' (y-axis). As shown in FIG. 56, the semi-reflective interface 190 generates two secondary in-coupled light beamlets 252' that propagate within two separate secondary waveguides 172b along separate internally reflective optical paths parallel to the axis 262' (y-axis) via TIR, from which the two primary in-coupled light beamlets 252b, 252c are created.

[0303] The OPE elements 186 are configured to split the primary in-coupled light beamlets 252 a-252 c into a set of three primary orthogonal light beamlets, respectively. In particular, the primary in-coupled light beamlets 252 a-252 c intersect the OPE elements 186 adjacent to the face 180 b of the waveguide 172 such that portions of the primary in-coupled light beamlets 252 a-252 c are diffracted via TIR as a set of three primary orthogonal light beamlets 254 a-254 c that propagate within the waveguide 172 along internally reflected optical paths parallel to the axis 264 (x-axis).

[0304] As best shown in FIG. 57, the semi-reflective interface 190 is configured to split the set of three orthogonal optical beamlets 254a-254c into a set of nine orthogonal optical beamlets. In particular, the semi-reflective interface 190 splits the set of primary orthogonal optical beamlets 254a into three sets of primary orthogonal optical beamlets 254a (the first set of primary orthogonal optical beamlets 254a (indicated by solid lines) and two further sets of primary orthogonal optical beamlets 254b, 254c (indicated by dashed lines) that propagate within the primary waveguide 172a along respective internally reflective optical paths parallel to the axis 264 (x-axis) via TIR. As shown in FIG. 57, the semi-reflective interface 190 generates two sets of secondary in-coupled optical beamlets 252′ that propagate within two respective secondary waveguides 172b along respective internally reflective optical paths parallel to the axis 264′ (x-axis), from which the two primary orthogonal optical beamlets 252b, 252c are created. Similarly, the semi-reflective interface 190 splits the set of orthogonal optical beamlets 254b into a further set of three primary orthogonal optical beamlets (not shown) that propagate within the primary waveguide 172a along separate internally reflected optical paths parallel to the axis 264 (x-axis), and the set of orthogonal optical beamlets 254c into a further set of three primary orthogonal optical beamlets (not shown). In some embodiments, the two secondary waveguides 172b may have different thicknesses. Additionally, for reasons similar to those described above with reference to FIGS. 44-55, in some examples, these different thicknesses may be non-multiples of one another. It also follows that the thickness of the primary waveguide 172a may be a non-multiple of one or both of the two different thicknesses of the two secondary waveguides 172b. In other embodiments, the two secondary waveguides 172b may be equal in thickness.

[0305] The EPE element 188 is configured to split the set of nine orthogonal optical beamlets into a set of outcoupled optical beamlets 256. In particular, as shown in FIG. 57, the set of primary orthogonal optical beamlets 254 (only set 254a(1)-254a(3) of primary orthogonal optical beamlets are shown) intersect with the EPE element 188 adjacent to face 180b of the waveguide 172 such that a portion of the primary orthogonal optical beamlets 254 are diffracted as set 256 of outcoupled optical beamlets that exit face 180b of the waveguide 172. Thus, increasing the number of incoupled optical beamlets 252 and the number of orthogonal optical beamlets 254 correspondingly increases the saturation of the exit pupil 300a extended by the display screen 110 (shown in FIG. 40B). While the waveguide device 170e illustrated in Figures 56 and 57 has been described above as including two secondary waveguides 172b, it should be understood that the waveguide devices 170e and others described herein may have at least two (e.g., three, four, five, or more) secondary waveguides 172b.

[0306] In the aforementioned embodiment, the entrance pupil of the collimated light beam output by the collimation element 154 is expanded only by the combination of the OPE element 186 and the EPE element 188 of the display screen 110, and includes features closely associated with the OPE element 186 and the EPE element 188 for increasing saturation of the exit pupil of the display screen 110. Continuing, in the embodiments of the display subsystem 104′ described herein, the image projection assembly 108 further includes a pre-pupil expansion (PPE) 192, which, in the embodiment illustrated in FIG. 58 , is disposed between the collimation element 166 and the IC element 168 of the display screen 110.

[0307] The PPE 192 represents a first pupil expansion stage, designed to use one or more beam doubling techniques to pre-expand the entrance pupil of the collimated light beam 250 to an intermediate exit pupil 300a of a set of initial outcoupled light beamlets 256' (in this case a two-dimensional 3x3 array) prior to internal coupling into the waveguide device 170 of the display screen 110 (emulating the input of a conventional collimated light beam with a larger pupil size, as illustrated in Figure 59A), and the display screen 110 represents a second pupil expansion stage, which further expands the pupil size of the collimated light beam 250 in a conventional manner to a final exit pupil 300b of a set of final outcoupled light beamlets 256' (in this case a two-dimensional 9x9 array), as illustrated in Figure 59B.

[0308] In an alternative embodiment, the display screen 110 may further expand the pupil size of the collimated light beam 250 to an even more saturated exit pupil of the final outcoupled set of light beamlets 256 using the improved beam doubling techniques described above. However, it should be understood that the use of the PPE 192 is well suited to compact imaging devices that output a relatively small-pupil-sized light beam that can be expanded to a normal-pupil-sized light beam for input into a conventional PE due to the expansion to the exit pupil proportional to the entrance pupil size of the eye 52 of the end user 50. For example, the PPE 192 may expand the entrance pupil of the collimated beam to a pre-dilated pupil (e.g., at least a 0.5 mm pupil) that is at least 10 times larger than the entrance pupil (e.g., a 50 mil pupil size), and the waveguide device 170 of the display screen 110 may further expand the pre-dilated pupil of the collimated light beam 250 to an exit pupil (e.g., at least a 5 mm pupil) that is at least 10 times larger than the pre-dilated pupil of the collimated light beam 250. By utilizing a multi-stage pupil expansion system, the manufacturing constraints associated with expanding a relatively small pupil of a collimated beam into a relatively large and saturated exit pupil do not have to be imposed solely on one pupil expansion device, but rather are distributed among multiple expansion devices, thereby facilitating manufacturing of the overall system.

[0309] Referring now to Figures 60-63, some embodiments of the display subsystem 104' utilize a conventional PE comprising the aforementioned waveguide device 170 illustrated in Figures 34-36 and a PPE 192a, which in the illustrated embodiment takes the form of a miniaturized version of the waveguide device 170 mounted on the IC element 168.

[0310] To this end, PPE 192a takes the form of a waveguide device 170′ having a size proportional to the size of IC elements 168 of primary waveguide device 170. Similar to primary waveguide device 170 of display screen 110, miniature waveguide device 170′ comprises a planar optical waveguide 172′ taking the form of a single, integral substrate or plane of optically transparent material (as described above with respect to waveguide 172) and one or more DOEs 174′ associated with waveguide 172′ to pre-expand in two dimensions the effective exit pupil of a collimated light beam 250 optically coupled into waveguide 172′. PPE 192a further comprises an IC element 168' disposed on face 180b' of waveguide 172' to receive collimated light beam 250 from collimation element 166 into waveguide 172' via face 180b', although in alternative embodiments, IC element 168' may be disposed on the other face 180a' or even an edge of waveguide 172' to couple collimated light beam 250 into waveguide 172' as an internally coupled light beam. DOE 174' is associated with waveguide 172' (e.g., incorporated within waveguide 172' or abutting or adjacent to one or more of faces 180a', 180b' of waveguide 172') to pre-expand in two dimensions the effective entrance pupil of collimated light beam 250 optically coupled into waveguide 172', as discussed briefly above.

[0311] To this end, the DOE 174 comprises an orthogonal pupil expansion (OPE) element 186 for splitting the in-coupled light beam 252 into a set of initial orthogonal light beamlets 254', and an exit pupil expansion (EPE) element 188' for splitting each initial orthogonal light beamlet 254' into a set of initial out-coupled light beamlets 256' that exit the face 180b' of the waveguide 172'. In the particular embodiment illustrated in Figures 60-63, the OPE element 186' and the EPE element 188' completely overlap each other in the xy plane, and thus the OPE element 186' is disposed on the face 180a of the waveguide 172', and the EPE element 188' is disposed on the face 180b of the waveguide 172'. Alternatively, the OPE element 186' and the EPE element 188' may not overlap at all in the xy plane, in which case the OPE element 186' and the EPE element 188' may both be disposed on the same face 180b of the waveguide 172'.

[0312] OPE element 186′ relays light along a first axis (the horizontal or x-axis in FIG. 60) and pre-expands the effective exit pupil of the light along a second axis (the vertical or y-axis in FIG. 60). In particular, as best shown in FIG. 61, IC element 168′ optically incouples collimated light beam 250 as incoupled light beam 252′ for propagation within waveguide 172′ along internally reflected optical path 262 via TIR (in this case, along the vertical or y-axis), and in doing so repeatedly intersects with OPE element 186′. In the illustrated embodiment, the OPE element 186' has a relatively low diffraction efficiency (e.g., less than 50%) and comprises a series of diagonal diffraction elements (45 degrees to the x-axis) such that at each intersection with the OPE element 186', a portion (e.g., more than 90%) of the internally coupled light beam 252' continues to propagate within the waveguide 172' along an internally reflected optical path parallel to the axis 262 (y-axis) via TIR, and the remaining portion (e.g., less than 10%) of the internally coupled light beam 252' is diffracted as an initial orthogonal light beamlet 254' (shown as a dashed line in Figure 61) that propagates within the waveguide 172' towards the EPE element 188' along an internally reflected optical path parallel to the axis 264 (in this case, along the horizontal or x-axis) via TIR. Although axis 264 is described as being perpendicular or orthogonal to axis 262 (the y-axis), it should be understood that axis 264 may alternatively be oriented obliquely relative to axis 262 .

[0313] Thus, by splitting the internally coupled light beam 252′ into multiple initial orthogonal light beamlets 254′ propagating along parallel internal reflection optical paths 264, the entrance pupil of the collimated light beam 250 that is internally coupled into the compact waveguide device 170′ is pre-expanded vertically along the y-axis by the OPE element 186′.

[0314] The EPE element 188' thus further pre-expands the effective pupil of light along the first axis (the horizontal x-axis in FIG. 62 ). In particular, like the OPE element 186', the EPE element 188' has a relatively low diffraction efficiency (e.g., less than 50%) such that at each intersection with the EPE element 188', a portion (e.g., greater than 90%) of each initial orthogonal light beamlet 254' continues to propagate along a separate internally reflected optical path parallel to the axis 264 (x-axis), and the remaining portion of each initial orthogonal light beamlet 254' is diffracted as an initial outcoupled light beamlet 256' that exits the face 180b' of the waveguide 172' (along the z-axis) as shown in FIG. That is, each time a light beamlet strikes the EPE element 188', a portion of it will be diffracted toward face 180b of waveguide 172', while the remaining portion will continue to propagate along a separate internal reflection optical path parallel to axis 264 (x-axis).

[0315] Therefore, by splitting each initial orthogonal light beamlet 254' into multiple initial outcoupled light beamlets 256', the exit pupil of the internally coupled light beam 252 is further pre-expanded horizontally along the x-axis by the EPE element 188', resulting in a two-dimensional array of initial outcoupled light beamlets 256' that approximates a larger version of the original internally coupled light beam 252.

[0316] 34-36, the primary waveguide device 170 further expands the pupil of the collimated light beam 250 in two dimensions. That is, the initial outcoupled light beamlet 256′ is input into the IC element 168 of the primary waveguide device 170 as incoupled light beamlets 252(1)-252(4), which are then split by the OPE element 186 into a set of four orthogonal light beamlets 254(1)-254(4), which are further split by the EPE element 188 into the final outcoupled light beamlet 256, which exits the face 180b of the waveguide 172 toward the eye 52 of the end user 50.

[0317] 63, the single collimated light beam 250 is split by the OPE element 186′ into a one-dimensional array of four initial orthogonal light beamlets 254′, which are further split by the EPE element 188′ into a two-dimensional 4×4 array of initial outcoupled light beamlets 256′, which are further split by the OPE element 174′ into a two-dimensional 4×16 array of orthogonal light beamlets 254, which are further split into a 16×16 array of final outcoupled light beamlets 256. As can be appreciated, the use of the PPE 192a (i.e., the compact waveguide device 170′) increases the saturation of the exit pupil of the display screen 110 from the 4×4 array of final outcoupled light beamlets 256 to a 16×16 array of final outcoupled light beamlets 256. Of course, the PPE 192a can be designed to create smaller or larger arrays of initial outcoupled light beamlets 256′, e.g., a 2×2 array, a 3×3 array, a 5×5 array, etc., and can also be designed to create non-square matrices of initial outcoupled light beamlets 256′, e.g., a 2×3 array, a 3×2 array, a 3×4 array, a 4×3 array, etc. Importantly, the thickness of the waveguides 172 of the primary waveguide device 170 will exceed the thickness of the waveguides 172′ of the compact waveguide device 170′. In this case, for purposes of simplicity in illustration, the thickness of the primary waveguide 172 is four times the thickness of the secondary waveguide 172′. However, as discussed above with respect to the embodiments of Figures 44-57, it should be understood that it may be beneficial to maximize the least common multiple of the individual thickness values ​​of the waveguides 172, 172', thereby maximizing the amount of exit pupil provided for the widest scan angle, and further resulting in a non-uniform / complex distribution of the outcoupled beamlets 256, which may minimize adverse effects created by coherent optical interactions between adjacent outcoupled beamlets 256.

[0318] Referring now to Figures 64-66, another embodiment of a display subsystem 104' utilizes a conventional PE comprising the aforementioned waveguide device 170 illustrated in Figures 34-36 and PPE 192b, which, like PPE 192a, pre-expands in two dimensions the effective entrance pupil of a collimated light beam 250 optically coupled into PPE 192b, but unlike PPE 192a, takes the form of an adapter rather than a waveguide.

[0319] In particular, PPE 192b comprises a diffractive beam splitter 194 utilizing a single DOE that splits a collimated light beam 250 into a set of initially outcoupled light beamlets 256′. As best shown in FIGURES 65 and 66, diffractive beam splitter 194 comprises an optically planar substrate 196 having opposing first and second surfaces 196a, 196b and a diffraction grating 198 associated with one of the surfaces 196a, 196b, in this case, surface 196b of substrate 196. Diffraction grating 198 splits collimated light beam 250 incident on surface 196a of substrate 196 into a set of diverging light beamlets 254′ that exit surface 196b of substrate 196 at a divergence angle.

[0320] The diffraction grating 198 can be designed to generate an odd number of diverging light beamlets 254' from a single collimated light beam 250 or an even number of diverging light beamlets 254' from a single collimated light beam 250. Importantly, when the collimated light beam 250 intersects the diffraction grating 198, beamlets are created in different diffraction orders. For example, as shown in FIG. 67A, one diffraction grating 198' is designed to split the collimated light beam 250 into five diverging light beamlets 254', corresponding to five diffraction orders (-2, -1, 0, +1, +2), respectively, with each diverging light beamlet 254' separated by a separation angle θ sIt is separated only from the adjacent diverging optical beamlets 254'. As shown in FIG. 67B, another diffraction grating 198'' is designed to split the collimated optical beam 250 into four diverging optical beamlets 254' corresponding to four diffraction orders (-3, -1, +1, +3), respectively, and each diverging optical beamlet 256' is separated by a separation angle 2θ s It is separated only from the adjacent diverging optical beamlets 256'.

[0321] Diffraction grating 198 may split the collimated optical beam 250' into either a one-dimensional array of diverging optical beamlets 254' or a two-dimensional (M×N) array of diverging optical beamlets 254'. In the embodiments shown in FIGS. 64 - 66, the diffraction grating splits the collimated optical beam 250 into a 4×4 array of diverging optical beamlets 254'. Of course, PPE192b can be designed to create smaller or larger arrays of diverging optical beamlets 254', such as, for example, a 1×2 array, 2×1 array, 2×2 array, 3×3 array, 5×5 array, etc., and can further be designed to create non-square two-dimensional arrays of diverging optical beamlets 254', such as, for example, a 2×3 array, 3×2 array, 3×4 array, 4×3 array, etc.

[0322] Importantly, PPE192b applies an angle-preserving expansion to the collimated optical beam 250. That is, PPE192b bends the set of diverging optical beamlets 254' emerging from the surface 196b of the substrate 196 back to the original angle of the collimated optical beam 250'. To achieve this purpose, PPE192b includes a lens 200, in this embodiment, a diffraction lens that refocuses the diverging optical beamlets 254' as a set of initial external coupling optical beamlets 256' back to the original angle of the collimated optical beam 250'. Although the diffraction lens 200 is shown as being separate from the IC element 168, the function of the diffraction lens 200 can be incorporated into the IC element 168.

[0323] From the foregoing, it can be seen that PPE 192b pre-expands in two dimensions the effective entrance pupil of collimated light beam 250. In the same manner as described above with respect to Figures 34-36, primary waveguide device 170 also expands the pupil of collimated light beam 250 in two dimensions. That is, the 4×4 array of initial outcoupled optical beamlets 256′ enters the IC element 168 of the primary waveguide device 170 as a 4×4 array of incoupled optical beamlets 252 (only 252(1)-252(4) shown), as illustrated in FIGS. 64-66 , which are in turn split by the OPE element 186 into a 4×4 array of orthogonal optical beamlets 254 (only 254(1)-254(4) shown), which are further split by the EPE element 188 into final outcoupled optical beamlets 256 that exit the face 180b of the waveguide 172 towards the eye 52 of the end user 50. It is noteworthy that the separation angle θ in the embodiment of FIG. s or the separation angle 2θ in Figure 67B s will be selected such that the separation distance s between adjacent initial outcoupled light beamlets 256′ at their intersection with the lens 200 will be equal to the desired spacing of the final outcoupled light beamlets 256 emerging from the primary waveguide device 170.

[0324] Referring now to Figures 68-73, yet another embodiment of the display subsystem 104 utilizes a conventional PE comprising the aforementioned waveguide device 170 illustrated in Figures 34-36 and PPE 192c, which, like PPE 192a, pre-expands in two dimensions the effective exit pupil of a collimated light beam 250 optically coupled into PPE 192c, but unlike PPE 192a, takes the form of a prism rather than a waveguide.

[0325] As best shown in Figures 71-73, PPE 192c, in the illustrated embodiment, comprises an optically transparent prism body 202 in the form of a rectangular parallelepiped having a first face 202a and a second face 202b, and a plurality of prism planes 204 disposed within prism body 202. Plurality of prism planes 204 comprises a first set of parallel prism planes 204a disposed at an oblique angle (in this case, a 45 degree angle) to first face 202a, and a second set of parallel prism planes 204b at an oblique angle (in this case, a 45 degree angle) to second face 202b. In the illustrated embodiment, the first set of parallel prism planes 204a consists of two prism planes 202a(1) and 202a(2), and the second set of parallel prism planes 204b consists of two prism planes 202b(1) and 202b(2), although in alternative embodiments, each set of parallel prism planes 204 may consist of more than two prism planes.

[0326] Prism body 202 comprises prism sections 206a-202f that are joined together to create the entire prism body 202. Prism plane 204a(1) is formed at the interface between prism sections 206a and 206b, prism plane 204a(2) is formed at the interface between prism sections 206b and 206c, prism plane 204b(1) is formed at the interface between prism sections 206d and 206e, and prism plane 204b(2) is formed at the interface between prism sections 206e and 206f.

[0327] The prism plane 204 is configured to split the collimated light beam 250 entering the first face 202a of the prism body 202 into a set of initial out-coupled light beamlets 256' (in this case a 2x2 array of light beamlets 256') that exit the second face 202b of the prism body 202.

[0328] To this end, prism flat surfaces 204a(1) and 204b(1) may each be formed from a semi-reflective coating, such as gold, aluminum, silver, nickel chromium, chromium, or other gold; a dielectric material, such as an oxide, fluoride, or sulfide; a semiconductor, such as silicon or germanium; and / or a glue or adhesive with reflective properties, which may be disposed between adjacent prism sections 206 via any suitable process, such as physical vapor deposition (PVD), ion-assisted deposition (IAD), or ion beam sputtering (IBS). The reflection-to-transmission ratio of the semi-reflective coating may be selected or determined, at least in part, based on the thickness of the coating, or the semi-reflective coating may have a plurality of small perforations to control the reflection-to-transmission ratio. Thus, prism flat surfaces 204a(1) and 204b(1) may each split the light beam by reflecting a portion of the light beam and transmitting the remaining portion of the light beam. In contrast, prism planes 204a(2) and 204b(2) are each preferably formed from a fully reflective coating, which may be made of the same material as the semi-reflective coating, although the thickness of the coating may be selected such that prism planes 204a(2) and 204b(2) are fully reflective.

[0329] In alternative embodiments, adjacent prism sections 206 may be made of materials with different refractive indices such that prism planes 204 between individual prism sections 206 are semi-reflective (in the case of prism plane 204a(1) or 204b(1)) or fully reflective (in the case of prism planes 204a(2) and 204b(2)) for light incident on the semi-reflective interface at less than the critical angle. In either case, each prism plane 204 is preferably designed such that the angle of the light beam incident on prism plane 204 is preserved.

[0330] 72, the first set of prism planes 204a relay light along a first axis (the horizontal or x-axis) and pre-expand the effective exit pupil of the light along a second axis (the vertical or y-axis). In particular, the first set of prism planes 204a split the collimated light beam 250 incident on the first face 202a of the prism body 202 into two orthogonal light beamlets 254(1)' and 254(2)' and reflect these light beamlets 254' in a first direction toward the second set of prism planes 204b. That is, a portion of collimated light beam 250 is reflected by prism plane 204a(1) as orthogonal light beamlet 254(1)', and the remaining portion of collimated light beam 250 is transmitted by prism plane 204a(1) to prism plane 204a(2) for reflection as orthogonal light beamlet 254(2)'.

[0331] 73, the second set of prism planes 204b thus further pre-expand the effective exit pupil of the light along a second axis (the horizontal or x-axis). In particular, the second set of prism planes 204b split each of the orthogonal light beamlets 254′ into two initial outcoupled light beamlets 256′ and reflect these initial outcoupled light beamlets 256′ out of the second face 202b of the prism body 202 in a second direction that is orthogonal to the first direction, although the second direction may be non-orthogonal to the first direction. That is, a portion of orthogonal light beamlet 254(1)' is reflected by prism plane 204b(1) as initial outcoupled light beamlet 256(1)', and the remaining portion of orthogonal light beamlet 254(1)' is transmitted by prism plane 204b(1) to prism plane 204b(2) for reflection as initial outcoupled light beamlet 256(2)'. Similarly, a portion of orthogonal light beamlet 254(2)' is reflected by prism plane 204b(1) as initial outcoupled light beamlet 256(3)', and the remaining portion of orthogonal light beamlet 254(2)' is transmitted by prism plane 204b(1) to prism plane 204b(2) for reflection as initial outcoupled light beamlet 256(4)'. Thus, a 2 × 2 array of initial outcoupled light beamlets 256' emerges from the second face 202b of prism body 202.

[0332] From the foregoing, it can be seen that the PPE 192c two-dimensionally pre-expands the effective entrance pupil of the collimated light beam 250. In the same manner as described above with respect to Figures 34-36, the primary waveguide device 170 further two-dimensionally expands the pupil of the collimated light beam 250. That is, the initial outcoupled light beamlet 256' enters the IC element 168 of the primary waveguide device 170 as a 2 x 2 array of incoupled light beamlets (only 252(1)-252(2) are shown), as illustrated in Figures 68-70, which are then split by the OPE element 186 into a set of four orthogonal light beamlets (only 254(1)-254(2) are shown), which are further split by the EPE element 188 into the final outcoupled light beamlet 256 that exits the face 180b of the waveguide 172 towards the eye 52 of the end user 50.

[0333] The distance d between the prism planes 204 is preferably selected such that the distance s between adjacent initial outcoupled light beamlets 256′ will be equal to the desired spacing of the final outcoupled light beamlets 256 exiting the primary waveguide arrangement 170. In the illustrated embodiment, the prism planes 204 are oriented at a 45 degree angle with respect to the faces 202 a, 202 b of the prism body 202, and therefore the distance d is given by: d=s * It can be expressed as a function of distance s, such as sin 45°. The thickness of the waveguide 172 in the primary waveguide device 170 can be a multiple of the distance d between the prism planes 204 in each set of parallel prism planes 204 of the PPE 192c (in this case 2 × the distance d between the parallel prism planes 204) to facilitate internal filling of the final outcoupled light beamlets 256.

[0334] It should be understood that a larger array of initial out-coupled light beamlets 256' may be created by reducing the distance between the prism planes 204 within each set of parallel prism planes 204 of the PPE 192c relative to the size of the prism body 202, as illustrated in Figures 74 and 75.

[0335] For example, as illustrated in FIG. 74, a first set of prism planes 204a may split a collimated light beam 250 incident on a first face 202a of prism body 202 into three orthogonal light beamlets 254(1)'-254(3)' and reflect these light beamlets 254' toward a second set of prism planes 204b. That is, a portion of collimated light beam 250 is reflected by prism plane 204a(1) as orthogonal light beamlet 254(1)', and the remaining portion of collimated light beam 250 is transmitted by prism plane 204a(1) to prism plane 204a(2), which will be repeatedly reflected between prism planes 204a(1) and 204a(2), with a portion of it being transmitted back through prism plane 204a(1) as orthogonal light beamlets 254(2)' and 254(3)'.

[0336] 75, the second set of prism planes 204b split each of the orthogonal light beamlets 254′ into three initial outcoupled light beamlets 256′ and reflect these initial outcoupled light beamlets 256′ out from the second face 202b of the prism body 202. Thus, a 3×3 array of the initial outcoupled light beamlets 256′ exits the second face 202b of the prism body 202. That is, a portion of each orthogonal light beamlet 254 will be reflected by prism plane 204b(1) as initial outcoupled light beamlet 256(1)', and the remaining portion of this orthogonal light beamlet 254' will be transmitted by prism plane 204b(1) to prism plane 204b(2), which will be repeatedly reflected between prism planes 204b(1) and 204b(2), with a portion of it being transmitted back through prism plane 204b(1) as initial outcoupled light beamlets 256(2)' and 256(3)'.

[0337] Again, the distance d between the prism planes 204 is preferably selected so that the distance between adjacent initial outcoupled light beamlets 256′ will be equal to the desired spacing of the final outcoupled light beamlets 256 exiting the primary waveguide arrangement 170. In the illustrated embodiment, the prism planes 204 are oriented at a 45 degree angle relative to the faces 202 a, 202 b of the prism body 202, and therefore the distance d is given by: d=s * It can be expressed as a function of distance s, such as sin45°.

[0338] Thus, for each orthogonal light beamlet 254, three initial outcoupled light beamlets 256′ will be generated, thereby creating a 3×3 array of initial outcoupled light beamlets 256′ exiting the second face 202b of the prism body 202. Of course, the PPE 192c can be designed to create even larger arrays of initial outcoupled light beamlets 256′, e.g., a 4×4 array, a 5×5 array, etc., by further reducing the distance between the prism planes 204 within each set of parallel prism planes 204 of the PPE 192c relative to the size of the prism body 202.

[0339] Although PPE 192c has been described as generating a square array of initial outcoupled light beamlets 256′, PPE 192c can alternatively be designed to generate a non-square array of initial outcoupled light beamlets 256′, e.g., a 2×3 array, a 3×2 array, a 2×3 array, a 3×2 array, etc., by making the distance between prism planes 204a(1) and 204a(2) different from the distance between prism planes 204b(1) and 204b(2). Furthermore, although PPE 192c has been described as creating a two-dimensional array of initial outcoupled light beamlets 256′, PPE 192c can be designed to create a one-dimensional array of initial outcoupled light beamlets 256′, e.g., a 1×2 array, a 1×3 array, etc., by designing PPE 192c with only one set of parallel prism planes 204.

[0340] Furthermore, although PPE 192c has been described as generating an initial outcoupled light beamlet 256′ that exits prism body 202 at a perpendicular angle relative to face 202b of prism body 202, PPE 192c can be designed to cause initial outcoupled light beamlet 256′ to exit prism body 202 at an oblique angle relative to face 202b of prism body 202 by changing the orientation of one or both of the sets of prism planes 204 relative to face 202b of prism body 202.

[0341] 76-79, yet another embodiment of a display subsystem 104' utilizes a conventional PE comprising the aforementioned waveguide device 170 illustrated in FIGS. 34-36 and a PPE 192e which, like PPE 192c, takes the form of a prism, but unlike PPE 192c, utilizes a hollow prism as opposed to a solid prism to one-dimensionally pre-expand the effective entrance pupil of a collimated light beam 250 optically coupled into PPE 192e.

[0342] As best shown in FIG. 79 , the PPE 192e comprises an optically transparent hollow prism 208, which includes a first triangular prism section 210a and a second triangular prism section 210b. The prism sections 210a, 210b are spaced apart from one another to create an open space 212 therebetween, bounded on one side by a prism plane 212a of the prism section 210a and on the other side by a prism plane 212b of the prism section 210b, the prism planes 212a, 212b being parallel to one another. The first prism section 210a has a first face 214a opposite the prism plane 212a, and a second face 214b. The prism plane 212a is disposed at an oblique angle (in this case, a 45-degree angle) relative to the first and second faces 214a, 214b.

[0343] Prism plane 212 is configured to split collimated light beam 250 incident on first face 202a of prism section 210 into a set of initial light beamlets 256' (in this case, a 1 x 4 array of initial outcoupled light beamlets 256') that exit second face 214b of first prism section 210a. To achieve this goal, first prism plane 212a is designed to be partially reflective, while second prism plane 212b is designed to be fully reflective, in the same way that prism plane 204 of PPE 192c described above is designed to be partially reflective or fully reflective. Each prism plane 212 is preferably designed such that the angle of the light beam incident on prism plane 212 is preserved.

[0344] As best shown in Figure 79, the PPE 192c pre-expands the effective exit pupil of light one-dimensionally along a first axis (the horizontal or x-axis). In particular, the set of prism planes 212 splits the collimated light beam 250 into four initial outcoupled light beamlets 256' and reflects these initial outcoupled light beamlets 256' out from the second face 214b of the prism section 210b. Thus, a 1 x 4 array of the initial outcoupled light beamlets 256' exits the second face 214b of the prism body 210. That is, a portion of collimated light beam 250 will be reflected by prism plane 212a as initial outcoupled light beamlet 256(1)', and the remaining portion of collimated light beam 250 will be transmitted by prism plane 212b to prism plane 212a, which will be repeatedly reflected between prism planes 212a and 212b, a portion of which will be transmitted back through prism plane 212a as initial outcoupled light beamlets 256(2)'-256(4)'. Of course, PPE 192e can be designed to create smaller or larger one-dimensional arrays of initial outcoupled light beamlets 256', for example, a 1 x 2 array, a 1 x 3 array, a 1 x 5 array, etc., by decreasing or increasing the distance between prism planes 212 relative to the size of prism 208.

[0345] From the foregoing, it can be seen that the PPE 192e pre-expands in one dimension the effective entrance pupil of the collimated light beam 250. In the same manner as described above with respect to Figures 34-36, the primary waveguide device 170 further expands the pupil of the collimated light beam 250 in two dimensions. That is, the initial outcoupled light beamlet 256' is input into the IC element 168 of the primary waveguide device 170 as a 1 x 4 array of incoupled light beamlets 252(1)-252(4), as illustrated in Figures 76-78, which are in turn split by the OPE element 186 into a 1 x 4 array of orthogonal light beamlets 254(1)-254(4), which are further split by the EPE element 188 into the final outcoupled light beamlet 256 that exits the face 180b of the waveguide 172 towards the eye 52 of the end user 50.

[0346] The distance d between the prism planes 212 is preferably selected such that the distance s between adjacent initial outcoupled light beamlets 256′ will be equal to the desired spacing of the final outcoupled light beamlets 256 exiting the primary waveguide arrangement 170. In the illustrated embodiment, the prism planes 212 are oriented at a 45 degree angle with respect to the faces 214 a, 214 b of the prism body 202, and therefore the distance d is given by: d=s * It can be expressed as a function of distance s such as sin 45°. Importantly, the thickness of the waveguide 172 in the primary waveguide device 170 will be a multiple of the distance d between the prism planes 212 of the PPE 192e (in this case 2 × the distance d between the prism planes 212) to facilitate internal filling of the final outcoupled light beamlets 256.

[0347] It should be understood that because the distance d between the prism planes 212 is set simply by positioning the prism planes 212 relative to one another, the spacing between the final outcoupled light beamlets 256 can be set arbitrarily without concern for manufacturing limitations. That is, because the PPE 192e does not utilize optical substrates between the prism planes 212, but rather utilizes cavities between the prism planes 212, there is no need to be concerned about limitations associated with the minimum thickness of such optical substrates.

[0348] Referring now to Figures 80-89, some embodiments of the display subsystem 104 utilize a conventional PE comprising the aforementioned waveguide device 170 illustrated in Figures 34-36 and a PPE 192f, which in the illustrated embodiment takes the form of a multilayered miniature waveguide device 220 mounted on the IC element 168.

[0349] The compact waveguide device 220 has a size proportional to the size of the IC elements 168 of the primary waveguide device 170. The compact waveguide device 220 comprises a plurality of waveguide assemblies 222, in this case a top waveguide assembly 222 a and a bottom waveguide assembly 222 b. Each waveguide assembly 222 is configured to split each of one or more collimated beams or beamlets (collimated optical beam 250 in bottom waveguide assembly 222 b and outcoupled optical beamlet 256′ in top waveguide assembly 222 b) into a two-dimensional array (in this case a 4×4 array) of outcoupled optical beamlets 256′, as will be explained in further detail below.

[0350] In the particular miniature waveguide device 220 described herein, as illustrated in FIG. 83, the bottom waveguide assembly 222b functions to split a single collimated light beam 250 into a two-dimensional array of outcoupled light beamlets 256′, while the top waveguide assembly 222a functions to split the two-dimensional array of outcoupled light beamlets 256′ from the bottom waveguide assembly 222b into a two-dimensional array of multiple outcoupled light beamlets 256″. To achieve this goal, the top waveguide assembly 222a and the bottom waveguide assembly 222b are positioned relative to one another such that the top waveguide assembly 222a receives the outcoupled light beamlets 256′ from the bottom waveguide assembly 222b. For example, as will be illustrated below, the top surface 224a of the bottom waveguide assembly 222b is affixed to the bottom surface 224b of the top waveguide assembly 222a.

[0351] 84 and 85A-85B, each waveguide assembly 222 includes a pair of orthogonal waveguide units configured as a top orthogonal waveguide unit 226a and a bottom orthogonal waveguide unit 226b, with the bottom surface 228b of the top orthogonal waveguide unit 226a affixed to the top surface 228a of the bottom orthogonal waveguide unit 226b. The orthogonal waveguide units 226 are identical to one another, differing only in that they are oriented orthogonally relative to one another. Each orthogonal waveguide unit 226 includes a planar optical waveguide 230 (as described above with respect to waveguide 172) that takes the form of a single, integral substrate or plane of optically transparent material. The planar optical waveguides 230 of each orthogonal waveguide unit 226 are the same size and have top and bottom surfaces 230a, 230b, respectively. Each orthogonal waveguide unit 226 further comprises an IC element 232 associated with (e.g., disposed on) the bottom surface 230b of the respective planar optical waveguide 230, and an EPE 234 associated with (e.g., disposed on) the top surface 230a of the planar optical waveguide 230, respectively.

[0352] Each IC element 232 is configured to internally couple one or more optical beams or beamlets into a respective planar optical waveguide 230 (236a in the case of the top orthogonal waveguide unit 226a, or 236b in the case of the bottom orthogonal waveguide unit 226b) for propagation along an internally reflected optical path via TIR, and thereby repeatedly intersect with the EPE element 234. In the same manner as described above with respect to the EPE element 188 of the primary waveguide device 170, the EPE element 234 has a relatively low diffraction efficiency (e.g., less than 50%) such that at each intersection with the EPE element 234, a portion (e.g., greater than 90%) of each optical beam or beamlet continues to propagate along the respective internally reflected optical path 236, and the remaining portion of each optical beam or beamlet is diffracted as an initial outcoupled optical beamlet 256′ that exits the top surface 230a of the respective planar optical waveguide 230. In the illustrated embodiment, the sizes of the IC element 232 and the EPE element 234 are equal to each other and proportional to the size of the individual planar optical waveguides 230 with which they are associated, as will be explained in further detail below, so that the pupil expansion of the collimated light beam 250 is maximized while also facilitating internal coupling of a two-dimensional array of externally coupled light beamlets 256' from the bottom orthogonal waveguide unit 226b to the top orthogonal waveguide unit 226a.

[0353] The IC elements 232 of the orthogonal waveguide unit 226 are oriented orthogonally to each other so that each optical beam or beamlet (250 or 256') that is internally coupled into the bottom surface 224b of an individual waveguide assembly 222 is split into a two-dimensional array of initial externally coupled optical beamlets 256' (or 256'') that exit the top surface 224a of the waveguide assembly 222, as shown in FIG.

[0354] In particular, the IC elements 232 of each waveguide assembly 222 are oriented orthogonal to each other such that the IC element 232 associated with the bottom orthogonal waveguide unit 226b internally couples light for propagation along an internally reflected optical path parallel to a first axis 262 via TIR (in this case, along the y-axis), and the light is expanded along the first axis 262 by the corresponding EPE element 234 (see Figure 85B), while the IC element 232 associated with the top orthogonal waveguide unit 226a internally couples each light beam or beamlet for propagation along an internally reflected optical path parallel to a second axis 264 orthogonal to the first axis 264 via TIR (in this case, along the x-axis), and the light is expanded along its second axis 264 by the corresponding EPE element 234 (see Figure 85A).

[0355] As briefly discussed above with respect to FIG. 83, the bottom face 224b of the upper waveguide assembly 222a is affixed to the top surface 224a of the bottom waveguide assembly 222b such that the output of the bottom waveguide assembly 222a is provided as an input to the upper waveguide assembly 222a, thereby generating a plurality of arrays of outcoupled light beamlets 256'' from the single collimated light beam 250.

[0356] In particular, and with further reference to Figures 86A and 86B, the bottom waveguide assembly 222b receives the collimated light beam 250 from the collimation element 166 and splits the collimated light beam 250 into a two-dimensional array of initial outcoupled light beamlets 256', which exit the top surface 224a of the bottom waveguide assembly 222b.

[0357] That is, the IC element 224 associated with the bottom orthogonal waveguide unit 226b of the bottom waveguide assembly 222b optically couples the collimated light beam 250 as an initial inwardly coupled light beam 252' for propagation within the individual planar optical waveguide 230 along a first internally reflected optical path parallel to the axis 262 (y-axis) via TIR, and the EPE element 226 associated with the bottom orthogonal waveguide unit 226b of the bottom waveguide assembly 222b splits the collimated light beam 250 into a one-dimensional array of initial outwardly coupled light beamlets 256' that exit from the top surface 228a of the individual bottom orthogonal waveguide unit 226b.

[0358] In turn, the IC element 224 associated with the upper orthogonal waveguide unit 226a of the bottom waveguide assembly 222b optically couples the one-dimensional array of initial outcoupled optical beamlets 256' as initial orthogonal optical beamlets 254' for propagation within the individual planar optical waveguides 230 along second internally reflected optical paths parallel to the individual axes 264 (x-axis) orthogonal to the first internally reflected optical paths parallel to the axis 262 (y-axis) via TIR, and the EPE element 226 associated with the upper orthogonal waveguide unit 226a of the bottom waveguide assembly 222b splits the initial orthogonal optical beamlets 254' into a two-dimensional array of initial outcoupled optical beamlets 256' that exit the upper surface 228a of the individual upper orthogonal waveguide unit 226a.

[0359] The upper waveguide assembly 222a receives the two-dimensional array of initial outcoupled light beamlets 256' from the bottom waveguide assembly 222b and splits the two-dimensional array of initial outcoupled light beamlets 256' into multiple two-dimensional arrays of intermediate outcoupled light beamlets 256'', which exit from the top surface 224a of the upper waveguide assembly 222a.

[0360] That is, the IC element 224 associated with the bottom orthogonal waveguide unit 226b of the upper waveguide assembly 222a optically combines the two-dimensional array of initial outcoupled light beamlets 256' as an intermediate set of internally coupled light beams 252'' for propagation within the individual planar optical waveguides 230 along a first internally reflected optical path parallel to the axis 262 (y-axis) via TIR, and the EPE element 226 associated with the bottom orthogonal waveguide unit 226b of the upper waveguide assembly 222a splits the intermediate set of internally coupled light beamlets 252'' into a two-dimensional array of intermediate outcoupled light beamlets 256'' of the initial outcoupled light beamlets 256' that exit the top surface 228a of the individual bottom orthogonal waveguide unit 226b.

[0361] In turn, the IC element 224 associated with the upper orthogonal waveguide unit 226a of the upper waveguide assembly 222a optically couples the two-dimensional array of intermediate outcoupled optical beamlets 256'' as intermediate orthogonal optical beamlets 254'' for propagation within the individual planar optical waveguides 230 along individual second internally reflected optical paths 264 (x-axis) orthogonal to the first internally reflected optical path parallel to the axis 262 (y-axis) via TIR, and the EPE element 226 associated with the upper orthogonal waveguide unit 226a of the upper waveguide assembly 222a splits the intermediate orthogonal optical beamlets 254'' into a two-dimensional array of intermediate outcoupled optical beamlets 256'' that exit from the upper surface 228a of the individual upper orthogonal waveguide unit 226a.

[0362] Thus, the bottom waveguide assembly 222b splits the collimated light beam 250 into a two-dimensional array of initial outcoupled light beamlets 256′, and the top waveguide assembly 222a splits the two-dimensional array of outcoupled light beamlets 256′ into several two-dimensional arrays of intermediate outcoupled light beamlets 256″. The two-dimensional array of initial outcoupled light beamlets 256′ as well as the two-dimensional array of intermediate outcoupled light beamlets 256″ each have an inter-beamlet spacing s1, and the two-dimensional array of intermediate outcoupled light beamlets 256″ have an inter-array spacing s2 that is different from the inter-beamlet spacing s1 of the two-dimensional arrays of the initial outcoupled light beamlets 256′ and the intermediate outcoupled light beamlets 256″ (see, for example, Figures 89A and 89B). The inter-array spacing s2 and inter-beamlet spacing s1 are non-multiples of each other so that the light beamlets 256'' are dispersed in a manner that maximizes the density of the interior filling of the exit pupil of the PPE 192f and therefore the exit pupil of the display screen 110, as will be explained in further detail below.

[0363] Notably, inter-beamlet spacing s1 is dictated by the individual thicknesses of the waveguides 230 of the bottom waveguide assembly 222b. Similarly, inter-array spacing s2 is dictated by the individual thicknesses of the waveguides 240 of the top waveguide assembly 222a. The thicknesses of the waveguides 230 of the top and bottom waveguide assemblies 222 may be strategically selected based on the diameter of the collimated light beam 250. In some embodiments, inter-beamlet spacing s1 and inter-array spacing s2 may differ from one another but each be a multiple of the diameter of the collimated light beam 250 to maximize the interior filling of the exit pupil of the PPE 192f.

[0364] Thus, inter-beamlet spacing s1 can be a multiple (“m”) of the diameter (“d”) of collimated light beam 250, such that s1 = m × d. Using this value of s1, inter-array spacing s2 can be described by s2 = s1 + d. That is, s1 and s2 can be successive multiples of the diameter of collimated light beam 250, such that s2 = (m + 1) × d. For example, inter-beamlet spacing s1 can be three times the diameter of collimated light beam 250. Using this value of s1, inter-array spacing s2 can be four times the diameter of collimated light beam 250. As illustrated in the illustrated embodiment below, this results in inter-array spacing s2 being 1.33 × inter-beamlet spacing s1.

[0365] The first and second planar optical waveguide assemblies 222a, 222b have unequal thicknesses t1, t2, respectively, as illustrated in Figure 83, with such thicknesses being set by the thicknesses of the individual planar optical waveguides 230 incorporated into the individual orthogonal waveguide units 226a, 226b of the optical waveguide assemblies 222a, 222b. For example, as illustrated in Figures 86A and 86B, the thickness of the planar optical waveguide 230 incorporated into the top planar optical waveguide assembly 222a exceeds the thickness of the planar optical waveguide 230 incorporated into the bottom planar optical waveguide assembly 222b. Preferably, the first and second inter-beamlet spacings s1, s2, and therefore the thicknesses t1, t2 of the first and second planar optical waveguide assemblies 222a, 222b, are non-multiples of each other to ensure that multiple arrays of intermediate outcoupled light beamlets 252'' are generated from a single array of initial outcoupled light beamlets 252'.

[0366] As discussed briefly above, the bottom waveguide assembly 222b splits the collimated light beam 250 into a two-dimensional array of initial outcoupled light beamlets 256′, and the top waveguide assembly 222a splits the two-dimensional array of outcoupled light beamlets 256′ into several two-dimensional arrays of intermediate outcoupled light beamlets 256″. In other words, the bottom waveguide assembly 222b and the top waveguide assembly 222a each generate two transfer functions that are convolved to produce the desired pattern of intermediate outcoupled light beamlets 252″.

[0367] For example, as illustrated in FIG. 87A, the bottom waveguide assembly 222b (as the first expander) [ka] where x is the optical input into the bottom waveguide assembly 222b (light beam of diameter a) and y is the optical output from the bottom waveguide assembly 222b. In this example, the transfer function h1 results in a 4x4 array of light beamlets of diameter a, spaced apart from each other by a distance of 3a. Similarly, as shown in Figure 87B, the top waveguide assembly 222a (as the second expander) has a first transfer function h1 such that: [ka] where x is the optical input (optical beam of diameter a) into the top waveguide assembly 222a and y is the optical output from the bottom waveguide assembly 222a. In this example, the transfer function h2 results in a 4x4 array of optical beamlets of diameter a, spaced apart from each other by a distance of 4a. As illustrated in Figure 87C, the transfer functions h1 and h2 are [ka] 87A. Thus, a collimated light beam 250 (as optical input x) may be input into the bottom waveguide assembly 222b, which applies a transfer function h to the collimated light beam 250, thereby generating a two-dimensional array of intermediate outcoupled light beamlets 256′ having the beam pattern illustrated in FIG. 87A. The two-dimensional array of intermediate outcoupled light beamlets 256′ output by the bottom waveguide assembly 222b may be input into the top waveguide assembly 222a, which applies a transfer function h to the two-dimensional array of intermediate outcoupled light beamlets 256′, thereby generating a plurality of two-dimensional arrays of intermediate outcoupled light beamlets 256″, the combination of which creates the light beamlet pattern illustrated in FIG. 87C.

[0368] Referring now to Figures 88 and 89A-89H, multiple generations of intermediate outcoupled light beamlets 256'' rapidly increase as the two-dimensional array of initial outcoupled light beamlets 256' propagates through the upper optical waveguide assembly 222a. As a result, the density of intermediate outcoupled light beamlets 256'' gradually increases from left to right and top to bottom across the upper surface 224a of the upper planar optical waveguide assembly 222a through several generations of beam splitting until a completely filled N x N array of outcoupled light beamlets 258' is produced, in this case a 10 x 10 array of outcoupled light beamlets 258' (shown in Figure 89H). In the illustrated embodiment, seven generations of beam splitting, producing 16 two-dimensional arrays (in this case a 4 x 4 array) of intermediate outcoupled light beamlets 256(1)''-256(16)'', results in a densely saturated 10 x 10 array of outcoupled light beamlets 258'. As shown therein, the beamlet designated "0" is from the two-dimensional array of initial outcoupled optical beamlet 256', while the beamlets designated "1"-"16" are from the 16 two-dimensional array of intermediate outcoupled optical beamlets 256(1)"-256(16)", respectively. Notably, a letter scheme is used in FIGS. 89A-89H to make it easier to understand which initial outcoupled optical beamlet 256' corresponds to which intermediate outcoupled optical beamlet 256". Under this letter scheme, each beamlet in the 4x4 array of beamlets 256' output by the bottom waveguide assembly 222b (first expander) illustrated in FIG. 87A and input into the top waveguide assembly 222a (second expander) illustrated in FIG. 87B corresponds to a different alphabetic letter ("A"-"P"). In this manner, each beamlet 256'' output by the upper waveguide assembly 222a (second expander) can be considered to correspond to both a specific two-dimensional array of intermediate outcoupled optical beamlets 256(1)''-256(16)'' and an associated beamlet group ("A"-"P").

[0369] In particular, the two-dimensional array of intermediate outcoupled light beamlets 256(1)'' is generated directly from the two-dimensional array of initial outcoupled light beamlets 256' (see Figure 89A). In the first generation, the two-dimensional array of intermediate outcoupled light beamlets 256(1)'' produces a two-dimensional array of intermediate outcoupled light beamlets 256(2)'' and a two-dimensional array of intermediate outcoupled light beamlets 256(3)'' along the x-axis and y-axis, respectively (see Figure 89B).

[0370] In the second generation, the two-dimensional array of intermediate outcoupled light beamlets 256(2)'' produces a two-dimensional array of intermediate outcoupled light beamlets 256(4)'' along the x-axis, both the two-dimensional arrays of intermediate outcoupled light beamlets 256(2)'' and 256(3)'' are combined to produce a two-dimensional array of intermediate outcoupled light beamlets 256(5)'' along the x-axis and y-axis, respectively, and the two-dimensional array of intermediate outcoupled light beamlets 256(3)'' produces a two-dimensional array of intermediate outcoupled light beamlets 256(6)'' along the y-axis (see Figure 89C).

[0371] In the third generation, the two-dimensional array of intermediate outcoupled light beamlets 256(4)'' produces a two-dimensional array of intermediate outcoupled light beamlets 256(7)'' along the x-axis, both the two-dimensional arrays of intermediate outcoupled light beamlets 256(4)'' and 256(5)'' combine to produce a two-dimensional array of intermediate outcoupled light beamlets 256(8)'' along the x-axis and y-axis, respectively, both the two-dimensional arrays of intermediate outcoupled light beamlets 256(5)'' and 256(6)'' combine to produce a two-dimensional array of intermediate outcoupled light beamlets 256(9)'' along the x-axis and y-axis, respectively, and the two-dimensional array of intermediate outcoupled light beamlets 256(6)'' produces a two-dimensional array of intermediate outcoupled light beamlets 256(10)'' along the y-axis (see Figure 89D).

[0372] In the fourth generation, both two-dimensional arrays of intermediate outcoupled light beamlets 256(7)'' and 256(8)'' are combined to produce a two-dimensional array of intermediate outcoupled light beamlet 256(11)'' along the x-axis and y-axis, respectively; both two-dimensional arrays of intermediate outcoupled light beamlets 256(8)'' and 256(8)'' are combined to produce a two-dimensional array of intermediate outcoupled light beamlet 256(12)'' along the x-axis and y-axis, respectively; and both two-dimensional arrays of intermediate outcoupled light beamlets 256(9)'' and 256(10)'' are combined to produce a two-dimensional array of intermediate outcoupled light beamlet 256(13)'' along the x-axis and y-axis, respectively (see Figure 89E).

[0373] In the fifth generation, both two-dimensional arrays of intermediate outcoupled light beamlets 256(11)'' and 256(12)'' are combined to produce a two-dimensional array of intermediate outcoupled light beamlet 256(14)'' along the x-axis and y-axis, respectively, and both two-dimensional arrays of intermediate outcoupled light beamlets 256(12)'' and 256(13)'' are combined to produce a two-dimensional array of intermediate outcoupled light beamlet 256(15)'' along the x-axis and y-axis, respectively (see Figure 89F).

[0374] In the sixth generation, both two-dimensional arrays of intermediate outcoupled light beamlets 256(14)'' and 256(15)'' are combined to produce a two-dimensional array of intermediate outcoupled light beamlet 256(16)'' along the x-axis and y-axis, respectively (see Figure 89G).

[0375] It can be understood that all intermediate outcoupled light beamlets 256" designated with specific letters in the light beamlet pattern illustrated in FIG. 89H can follow corresponding initial outcoupled light beamlets with the same specific letter in the two-dimensional array of initial outcoupled light beamlets 256' illustrated in FIG. 89A. For example, in FIG. 90A, it can be seen that a 4×4 array of intermediate outcoupled light beamlets 256" designated with the letter "A" can be derived from a single initial outcoupled light beamlet 256a designated with the letter "A." As another example, it can be seen from FIG. 90B that a 4×4 array of intermediate outcoupled light beamlets 256" designated with the letter "D" can be derived from a single initial outcoupled light beamlet 256a designated with the letter "D." As yet another example, it can be seen from FIG. 90C that a 4×4 array of intermediate outcoupled light beamlets 256″ designated with the letter “M” can be derived from a single initial outcoupled light beamlet 256 a designated with the letter “M”. As yet another example, it can be seen from FIG. 90D that a 4×4 array of intermediate outcoupled light beamlets 256″ designated with the letter “P” can ...

Claims

1. A virtual image generation system, comprising: a planar optical waveguide having opposing first and second surfaces; an incoupling (IC) element configured to optically couple a collimated light beam from an image projection assembly into the planar optical waveguide as an incoupling light beam; a first orthogonal pupil expansion (OPE) element associated with the first surface of the planar optical waveguide, the first orthogonal pupil expansion (OPE) element for splitting the incombined light beam into a first set of orthogonal light beamlets; a second orthogonal pupil expansion (OPE) element associated with the second surface of the planar optical waveguide, the second orthogonal pupil expansion (OPE) element for splitting the incombined light beam into a second set of orthogonal light beamlets; an exit pupil expansion (EPE) element associated with the planar optical waveguide for splitting the first set of orthogonal optical beamlets and the second set of orthogonal optical beamlets into an array of outcoupled optical beamlets exiting the planar optical waveguide; A virtual image generation system comprising:

2. A virtual image generation system as described in claim 1, wherein the planar optical waveguide is formed from a single integrated substrate.

3. A virtual image generation system as described in claim 1, wherein the first OPE element is arranged on the first surface of the planar optical waveguide, and the second OPE element is arranged on the second surface of the planar optical waveguide.

4. A virtual image generation system as described in claim 1, wherein the EPE element is positioned on one of the first surface and the second surface of the planar optical waveguide.

5. The virtual image generation system of claim 1, wherein the IC element is configured to optically couple the collimated light beam from the image projection assembly as the internally coupled light beam for propagation within the planar optical waveguide along a first optical path that alternately intersects the first OPE element and the second OPE element via total internal reflection (TIR), whereby a portion of the internally coupled light beam is deflected as respective first set of orthogonal light beamlets and second set of orthogonal light beamlets that propagate within the planar optical waveguide along second parallel optical paths via TIR.

6. A virtual image generation system as described in claim 5, wherein the second parallel optical path is perpendicular to the first optical path.

7. The virtual image generation system of claim 1, wherein the first set of orthogonal optical beamlets and the second set of orthogonal optical beamlets intersect with the EPE element, thereby deflecting a portion of the first set of orthogonal optical beamlets and the second set of orthogonal optical beamlets as the array of externally coupled optical beamlets out of the planar optical waveguide.

8. The virtual image generation system of claim 1, wherein the EPE element is configured to impart a convex wavefront profile onto the array of externally coupled light beamlets exiting the planar optical waveguide, the convex wavefront profile having a center of radius at a focal point and generating an image at a given focal plane.

9. The virtual image generation system of claim 1, wherein the collimated light beam defines an entrance pupil and the array of externally coupled light beamlets defines an exit pupil that is larger than the entrance pupil.

10. A virtual image generation system as described in claim 9, wherein the exit pupil is at least 10 times larger than the entrance pupil.

11. A virtual image generation system as described in claim 9, wherein the exit pupil is at least 100 times larger than the entrance pupil.

12. A virtual image generation system as described in claim 1, wherein each of the IC element, the OPE element, and the EPE element is diffractive.

13. The virtual image generation system of claim 1, wherein the array of externally coupled light beamlets is a two-dimensional externally coupled light beamlet array.

14. The virtual image generation system of claim 1, further comprising the image projection assembly.

15. The virtual image generation system of claim 14, wherein the image projection assembly comprises a scanning device configured to scan the collimated light beam.

Images