Encapsulated, reflective input coupling grating, system including the same, and methods of making the same

Abstract

An article includes: a waveguide for guiding light at a wavelength, λ, the waveguide extending in a waveguide plane; an input coupling grating (ICG) optically coupled to a surface of the waveguide, the ICG comprising a plurality of metallic strips spaced apart from each other and extending parallel to each other in a first direction parallel to the waveguide plane, the ICG further comprising one or more dielectric materials encapsulating the metallic strips, each metallic strip having a first surface that is (i) oriented at an acute angle with respect to the waveguide plane, (ii) oriented perpendicularly with respect to the waveguide plane, or (iii) curvilinear in shape. The first surface of each metallic strip is configured to redirect incident light at the wavelength λ into the waveguide.

Description

[0001] Attorney Docket No. 40589-0348WO1; ML-5015WO

[0002] ENCAPSULATED, REFLECTIVE INPUT COUPLING GRATING, SYSTEM INCLUDING THE SAME, AND METHODS OF MAKING THE SAME

[0003] CROSS-REFERENCE TO RELATED APPLICATION

[0004]

[0001] This application claims the benefit of U. S. Patent Application No. 63 / 746,899 filed on January 17, 2025, which is incorporated by reference herein in its entirety.

[0005] TECHNICAL FIELD

[0006]

[0002] The present disclosure relates to display systems and, more particularly, to augmented and virtual reality display systems and input coupling gratings (ICGs) for use therewith.

[0007] BACKGROUND

[0008]

[0003] Modem computing and display technologies have facilitated the development of systems for so called “virtual reality” or “augmented reality” experiences, wherein digitally reproduced images or portions thereof are presented to a user in a manner wherein they seem to be, or may be perceived as, real. A virtual reality, or “VR”, scenario typically involves presentation of digital or virtual image information without transparency to other actual real-world visual input. An augmented reality, or “AR”, scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user. A mixed reality, or “MR”, scenario is a type of AR scenario and typically involves virtual objects that are integrated into, and responsive to, the natural world. For example, in an MR scenario, AR image content may be blocked by or otherwise be perceived as interacting with objects in the real world.

[0009]

[0004] Referring to FIG. 1, an augmented reality scene 10 is depicted wherein a user of an AR technology sees a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. In addition to these items, the user of the AR technology also perceives that he “sees” “virtual content” such as a robot statue 40 standing upon the real-world platform 30, and a cartoon-like avatar character 50 flying by, which seems to be a personification of a bumble bee, even though these elements 40, 50 do not exist in the real world. Because the human visual perception system is complex, it is challenging to produce an AR technology that facilitates a comfortable, natural -feeling, rich presentation of virtual image elements amongst other virtual or real-world imagery elements.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0010] SUMMARY

[0011]

[0005] Waveguides for AR and VR can include various types of gratings for coupling light from a projector into or out of a waveguide. Gratings used for coupling light into a waveguide, i.e., into guided modes in the waveguide, are generally referred to as "‘in-coupling gratings” or “input coupling gratings” (“ICGs). ICGs can be reflective, i.e., couple light into the waveguide by reflecting the light, or transmissive, i.e., transmit light to couple the light into the waveguide. Ideally, an ICG would couple all the light from the projector into the waveguide, but practically some of the light is lost because it is absorbed by the grating or not coupled into guided modes. For instance, some of the light can be transmitted or reflected by the grating, but not into a guided mode. Light that is reflected back to the projector, e.g., back-reflected light, can pose various problems, such as ghosting, stray light, and other undesirable effects. Large input ICGs, in particular, suffer more from back reflection due to multiple-bounce effects,

[0012]

[0006] The present disclosure provides ICGs that include metal or metal alloy strips encapsulated, e.g., embedded, in a dielectric material (or materials). This arrangement combines features of transmissive and reflective ICGs. For example, although the disclosed ICGs include a reflective layer, e.g,, provided by an array of metallic strips, this reflective layer is not the outermost layer of the ICG. Further, the metallic strips are discrete elements within the dielectric material, rather than one continuous grating, which allows light to be transmitted past the metallic strips. Although light being transmitted past the metallic strips (and potentially absorbed by the waveguide) can increase loss, this transmitted light will generally not back-reflect into the projector. When balancing competing adverse effects in AR technology, this additional loss can be preferred over back-reflection of light into the projector,

[0013]

[0007] Accordingly, by including metallic strips embedded within a dielectric material, the disclosed ICGs provide the advantages of reflective diffraction gratings, e.g., high in-coupling efficiency, while mitigating drawbacks of reflective diffraction gratings, such as back-reflection. In some implementations, the disclosed ICGs have low reflectivity for both polarized and unpolarized lights. In some implementations, the disclosed ICGs reduce back- reflection, e.g., to 10% or less of the incident light, and efficiently in-couple light into the waveguide, e.g., 40% or more of the incident light. Additionally, the disclosed ICGs can be relatively polarization insensitive, allowing use of unpolarized light without significant degradation in performance. These improvements can allow AR devices to deliver clearer, brighter, and more immersive visuals.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0014] BRIEF DESCRIPTION OF THE DRAWINGS

[0015]

[0008] FIG. 1 illustrates a user's view of augmented reality (AR) through an AR device.

[0016]

[0009] FIG. 2 illustrates a conventional display system for simulating three-dimensional imagery for a user.

[0017]

[0010] FIGS. 3A, 3B, and 3C illustrate relationships between radius of curvature and focal radius.

[0018]

[0011] FIG. 4A illustrates a representation of the accommodation-vergence response of the human visual system.

[0019]

[0012] FIG. 4B illustrates examples of different accommodative states and vergence states of a pair of eyes of the user.

[0020]

[0013] FIG, 4C illustrates an example of a representation of a top-down view of a user viewing content via a display system.

[0021]

[0014] FIG. 4D illustrates another example of a representation of a top-down view' of a user viewing content via a display system.

[0022]

[0015] FIG. 5 illustrates aspects of an approach for simulating three-dimensional imagery’ by modifying wavefront divergence.

[0023]

[0016] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user,

[0024]

[0017] FIG. 7 illustrates an example of exit beams outputted by a w aveguide.

[0025]

[0018] FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes images formed using multiple different component colors.

[0026]

[0019] FIG. 9A illustrates a cross-sectional side view' of an example of a set of stacked waveguides that each includes an in-coupling optical element.

[0027]

[0020] FIG. 9B illustrates a perspecti ve view' of an example of the plurality of stacked waveguides of FIG. 9A.

[0028]

[0021] FIG. 9C illustrates a top-down plan view' of an example of the plurality of stacked waveguides of FIGS. 9A and 9B.

[0029]

[0022] FIG. 9D illustrates an example of w earable display system.

[0030]

[0023] FIG. 10 is a cross-sectional view of an article including an example input coupling grating including metallic strips encapsulated by a dielectric material.

[0031]

[0024] FIGS. 11A and 1 IB are ray diagrams for reflected and transmitted diffracted light in a conventional reflective grating and in the input coupling grating of FIG. 10, respectively.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0032]

[0025] FIGS. 12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 121, 12J, and 12K depict cross- sectional views of various examples of shapes and arrangements of metallic strips.

[0033]

[0026] FIGS. 13A, 13B, and 13C depict cross-sectional views of various truncations of the input coupling grating of FIG. 10.

[0034]

[0027] FIG. 14 depicts a cross-sectional view of an example of an input coupling grating including additional layers above and below the encapsulated metallic strips.

[0035]

[0028] FIG. 15 A is a flow chart depicting a method of forming an input coupling grating.

[0036]

[0029] FIGS. 15B, 15C, 15D, and 15E depict cross-sectional views of various examples of a surface relief grating formed in tire method of FIG. 15A.

[0037]

[0030] FIGS. 16A, 16B, 16C, 16D, and 16E depict cross-sectional views of various stages of forming an input coupling grating.

[0038]

[0031] FIGS. 16F and 16G are scanning electron microscope (SEM) images of fabricated input coupling gratings.

[0039]

[0032] FIG. 17A and 17B are images of a blazed reflective input coupling grating and an input coupling grating including encapsulated metallic strips, respectively.

[0040]

[0033] FIGS. 18A-18R and 19A-19R depict plots of diffraction efficiencies for reflection and transmission diffractive orders for the grating of FIG. 17A.

[0041]

[0034] FIGS. 20A-20R and 21 A-21R depict plots of diffraction efficiencies for reflection and transmission diffractive orders for the grating of FIG. 17B.

[0042]

[0035] FIG, 22A is a schematic for how7light is launched into either a launch direction or an anti-launch direction, back -reflected, or transmitted into a w aveguide. FIG. 22B depicts a plot of the efficiencies for each of these outcomes.

[0043]

[0036] FIGS. 23A, 23B, and 23C are images of gratings including encapsulated metallic strips and additional layers. FIG. 23D depicts a plot of the efficiencies for the grating of FIG.

[0044] 23 A.

[0045]

[0037] Throughout the drawings, reference numbers may be re-used to indicate correspondence between referenced elements. Like reference numerals refer to like parts throughout. Unless indicated otherwise, the drawings are schematic not necessarily drawn to scale. The drawings are provided to illustrate example implementations described herein and are not intended to limit the scope of the disclosure.

[0046] DETAILED DESCRIPTION

[0047]

[0038] FIG. 2 illustrates a conventional display system for simulating three-dimensional imagery for a user. A user's eyes are spaced apart and that, when looking at a real object inAttorney Docket No. 40589-0348WO1; ML-5015WO

[0048] space, each eye will have a slightly different view' of the object and may form an image of the object at different locations on the retina of each eye. This may be referred to as binocular disparity and may be utilized by the human visual system to provide a perception of depth. Conventional display systems simulate binocular disparity by presenting two distinct images 190, 200 with slightly different view's of the same virtual object — one for each eye 210, 220 — corresponding to the view's of the virtual object that would be seen by each eye were the virtual object a real object at a desired depth. These images provide binocular cues that the user's visual system may interpret to derive a perception of depth.

[0049]

[0039] With continued reference to FIG. 2, the images 190, 200 are spaced from the eyes 210, 220 by a distance 230 on a z-axis. The z-axis is parallel to the optical axis of the viewer with the user’s eyes fixated on an object at optical infinity directly ahead of the view'er. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on the slightly different views of a virtual object in the images presented to the eyes 210, 220, respectively, the eyes may naturally rotate such that an image of the object falls on corresponding points on the retinas of each of the eyes, to maintain single binocular vision. This rotation may cause the lines of sight of each of the eyes 210, 220 to converge onto a point in space at which the virtual object is perceived to be present. As a result, providing three-dimensional imagery conventionally involves providing binocular cues that may manipulate the vergence of the user's eyes 210, 220, and that the human visual system interprets to provide a perception of depth.

[0050]

[0040] Generating a realistic and comfortable perception of depth is challenging, however. It will be appreciated that light from objects at different distances from the eyes have wavefronts with different amounts of divergence. FIGS. 3A-3C illustrate relationships between distance and the divergence of light rays. The distance between the object and the eye 210 is represented by, in order of decreasing distance, Rl, R2, and R3. As shown in FIGS. 3A-3C, the light rays become more divergent as distance to the object decreases. Conversely, as distance increases, the light rays become more collimated. Stated another way, it may be said that the light field produced by a point (the object or a part of the object) has a spherical wavefront curvature, which is a function of how' far away the point is from the eye of the user, The curvature increases with decreasing distance between the object and the eye 210. While only a single eye 210 is illustrated for clarity of illustration in FIGS. 3A-3C and other figures herein, the discussions regarding eye 210 may be applied to both eyes 210 and 220 of a viewer.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0051]

[0041] With continued reference to FIGS. 3A-3C, light from an object that the viewer's eyes are fixated on may have different degrees of wavefront divergence. Due to the different amounts of wavefront divergence, the light may be focused differently by the lens of the eye, which in turn may require the lens to assume different shapes to form a focused image on the retina of the eye. Where a focused image is not formed on the retina, the resulting retinal blur acts as a cue to accommodation that causes a change in the shape of the lens of the eye until a focused image is formed on the retina. For example, the cue to accommodation may trigger the ciliary muscles surrounding the lens of the eye to relax or contract, thereby modulating the force applied to the suspensory ligaments holding the lens, thus causing the shape of the lens of the eye to change until retinal blur of an object of fixation is eliminated or minimized, thereby forming a focused image of the object of fixation on the retina (e.g., fovea) of the eye. The process by which the lens of the eye changes shape may be referred to as accommodation, and the shape of the lens of the eye required to form a focused image of the object of fixation on the retina (e.g., fovea) of the eye may be referred to as an accommodative state.

[0052]

[0042] With reference now to FIG. 4A, a representation of the accommodation-vergence response of the human visual system is illustrated. The movement of the eyes to fixate on an object causes the eyes to receive light from the object, with the light forming an image on each of the retinas of the eyes. The presence of retinal blur in the image formed on the retina may provide a cue to accommodation, and the relati ve locations of the image on the retinas may provide a cue to vergence. The cue to accommodation causes accommodation to occur, resulting in the lenses of the eyes each assuming a particular accommodative state that forms a focused image of the object on the retina (e.g., fovea) of the eye. On the other hand, the cue to vergence causes vergence movements (rotation of the eyes) to occur such that the images formed on each retina of each eye are at corresponding retinal points that maintain single binocular vision. In these positions, the eyes may be said to have assumed a particular vergence state. With continued reference to FIG. 4, accommodation may be understood to be the process by which the eye achieves a particular accommodative state, and vergence may be understood to be the process by which the eye achieves a particular vergence state. As indicated in FIG. 4A, the accommodative and vergence states of the eyes may change if the user fixates on another object. For example, the accommodated state may change if the user fixates on a new object at a different depth on the z-axis.

[0053]

[0043] Without being limited by theory, it is belie ved that viewers of an object may perceive the object as being “three-dimensionaF’ due to a combination of vergence andAttorney Docket No. 40589-0348WO1; ML-5015WO

[0054] accommodation. As noted above, vergence movements (e.g., rotation of the eyes so that the pupils move toward or away from each other to converge the lines of sight of the eyes to fixate upon an object) of the two eyes relative to each other are closely associated wi th accommodation of the lenses of the eyes. Under normal conditions, changing the shapes of the lenses of the eyes to change focus from one object to another object at a different distance will automatically cause a matching change in vergence to the same distance, under a relationship known as tire “accommodation-vergence reflex.” Likewise, a change in vergence will trigger a matching change in lens shape under normal conditions.

[0055]

[0044] With reference now to FIG. 4B, examples of different accommodative and vergence states of the eyes are illustrated. The pair of eyes 222a is fixated on an object at optical infinity, while the pair eyes 222b are fixated on a point 221 at less than optical infinity. Notably, the vergence states of each pair of eyes is different, with the pair of eyes 222a directed straight ahead, wdiile the pair of eyes 222 converge on the point 221. The accommodative states of the eyes forming each pair of eyes 222a and 222b are also different, as represented by the different shapes of the lenses 210a, 220a.

[0056]

[0045] Undesirably, many users of conventional “3-D” display systems find such conventional sy stems to be uncomfortable or may not perceive a sense of depth at all due to a mismatch between accommodative and vergence states in these displays. As noted above, many stereoscopic or “3-D” display systems display a scene by providing slightly different images to each eye. Such systems are uncomfortable for many viewers, since they, among other things, simply provide different presentations of a scene and cause changes in the vergence states of the eyes, but without a corresponding change in the accommodative states of those eyes. Rather, the images are shown by a display at a fixed distance from the eyes, such that the eyes view all the image information at a single accommodative state. Such an arrangement works against the “accommodation-vergence reflex” by causing changes in the vergence state without a matching change in the accommodative state. This mismatch is believed to cause viewer discomfort. Display systems that provide a better match between accommodation and vergence may form more realistic and comfortable simulations of three- dimensional imagery.

[0057]

[0046] Without being limited by theory, it is believed that the human eye typically may interpret a finite number of depth planes to provide depth perception. Consequently, a highly believable simulation of perceived depth may be achieved by providing, to the eye, different presentations of an image corresponding to each of these limited numbers of depth planes. In some implementations, the different presentations may provide both cues to vergence andAttorney Docket No. 40589-0348WO1; ML-5015WO

[0058] matching cues to accommodation, thereby providing physiologically correct accommodation¬ vergence matching.

[0059]

[0047] With continued reference to FIG. 4B, two depth planes 240, corresponding to different distances in space from the eyes 210, 220, are illustrated. For a given depth plane 240, vergence cues may be provided by the displaying of images of appropriately different perspectives for each eye 210, 220. In addition, for a given depth plane 240, light forming the images provided to each eye 210, 220 may have a wavefront divergence corresponding to a light field produced by a point at the distance of that depth plane 240.

[0060]

[0048] In the illustrated implementation, the distance, along the z-axis, of the depth plane 240 containing the point 221 is 1 m. As used herein, distances or depths along the z-axis may be measured with a zero-point located at the exit pupils of the user's eyes. Thus, a depth plane 240 located at a depth of 1 m corresponds to a distance of 1 m away from the exit pupils of the user's eyes, on the optical axis of those eyes with the eyes directed towards optical infinity. As an approximation, the depth or distance along the z-axis may be measured from the display in front of the user's eyes (e.g., from tire surface of a waveguide), plus a value for the distance between the device and the exit pupils of the user's eyes. That value may be called the eye relief and corresponds to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eye. In practice, the value for the eye relief may be a normalized value used generally for all viewers. For example, the eye relief may be assumed to be 20 mm and a depth plane that is at a depth of 1 m may be at a distance of 980 mm in front of the display.

[0061]

[0049] With reference now to FIGS. 4C and 4D, examples of matched accommodation¬ vergence distances and mismatched accommodation-vergence distances are illustrated, respectively. As illustrated in FIG. 4C, the display system may provide images of a virtual object to each eye 210, 220. The images may cause the eyes 210, 220 to assume a vergence state in which the eyes converge on a point 15 on a depth plane 240. In addition, the images may be formed by a light having a wavefront curvature corresponding to real objects at that depth plane 240. As a result, the eyes 210, 220 assume an accommodative state in which the images are in focus on the retinas of those eyes. Thus, the user may perceive the virtual object as being at the point 15 on the depth plane 240.

[0062]

[0050] It will be appreci ated that each of the accommodative and vergence states of the eyes 210, 220 are associated with a particular distance on the z-axis. For example, an object at a particular distance from the eyes 210, 220 causes those eyes to assume particular accommodative states based upon the distances of the object, The distance associated with aAttorney Docket No. 40589-0348WO1; ML-5015WO

[0063] particular accommodative state may be referred to as the accommodation distance, Ad.

[0064] Similarly, there are particular vergence distances, Vd, associated with the eyes in particular vergence states, or positions relative to one another. Where the accommodation distance and the vergence distance match, the relationship between accommodation and vergence may be said to be physiologically correct. This is considered to be the most comfortable scenario for a viewer.

[0065]

[0051] In stereoscopic displays, however, the accommodation distance and the vergence distance may not always match. For example, as illustrated in FIG. 4D, images displayed to the eyes 210, 220 may be displayed with wavefront divergence corresponding to depth plane 240, and the eyes 210, 220 may assume a particular accommodative state in which the points 15a, 15b on that depth plane are in focus. However, the images displayed to the eyes 210, 220 may provide cues for vergence that cause the eyes 210, 220 to converge on a point 15 that is not located on the depth plane 240. As a result, the accommodation distance corresponds to the distance from the exit pupils of the eyes 210, 220 to the depth plane 240, while the vergence distance corresponds to the larger distance from the exit pupils of the eyes 210, 220 to the point 15, in some implementations. The accommodation distance is different from the vergence distance. Consequently, there is an accommodation-vergence mismatch. Such a mismatch is considered undesirable and may cause discomfort in the user. It will be appreciated that the mismatch corresponds to distance (e.g., Vd-Ad) and may be characterized using diopters.

[0066]

[0052] In some implementations, it will be appreciated that a reference point other than exit pupils of the eyes 210, 220 may be utilized for determining distance for determining accommodation-vergence mismatch, so long as the same reference point is utilized for the accommodation distance and the vergence distance. For example, the distances could be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., a waveguide of the display device) to the depth plane, and so on.

[0067]

[0053] Without being limited by theory', it is believed that users may still perceive accommodation-vergence mismatches of up to about 0.25 diopter, up to about 0.33 diopter, and up to about 0.5 diopter as being physiologically correct, without the mismatch itself causing significant discomfort. In some implementations, display systems disclosed herein (e.g., the display system 250, FIG. 6) present images to the viewer having accommodationvergence mismatch of about 0.5 diopter or less. In some other implementations, the accommodation-vergence mismatch of the images provided by the display system is about 0.33 diopter or less. In yet other implementations, the accommodation-vergence mismatch ofAttorney Docket No. 40589-0348WO1; ML-5015WO

[0068] the images provided by the display system is about 0.25 diopter or less, including about 0.1 diopter or less.

[0069]

[0054] FIG. 5 illustrates aspects of an approach for simulating three-dimensional imagery by modifying wavefront divergence. The display system includes a waveguide 270 that is configured to receive light rays 770 that is encoded with image information, and to output that light to the user's eye 210, The waveguide 270 may output the exit beam 650 with a defined amount of wavefront divergence corresponding to the wavefront divergence of a light field produced by a point on a desired depth plane 240. In some implementations, the same amount of wavefront divergence is provided for all objects presented on that depth plane. In addition, it will be illustrated that the other eye of the user may be provided with image information from a similar waveguide.

[0070]

[0055] In some cases, a single waveguide may be configured to output light with a set amount of wavefront divergence corresponding to a single or limited number of depth planes and / or the waveguide may be configured to output light of a limited range of wavelengths. Consequently, in some implementations, a plurality or stack of waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or to output light of different ranges of wavelengths. As used herein, it will be appreciated at a depth plane may be planar or may follow the contours of a curved surface.

[0071]

[0056] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user, A display system 250 includes a stack of waveguides, or stacked waveguide assembly, 260 that may be utilized to provide three-dimensional perception to the eye / brain using a plurality of waveguides 270, 280, 290, 300, 310. It will be appreciated that the display system 250 may be considered a light field display in some implementations. In addition, the waveguide assembly 260 may also be referred to as an eyepiece.

[0072]

[0057] In some implementations, the display system 250 is configured to provide substantially continuous cues to vergence and multiple discrete cues to accommodation. The cues to vergence can be provided by displaying different images to each of the eyes of the user, and the cues to accommodation may be provided by outputting the light that forms the images with selectable discrete amounts of wavefront divergence. Stated another way, the display system 250 may be configured to output light with variable levels of wavefront divergence. In some implementations, each discrete level of wavefront divergence corresponds to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, 310.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0073]

[0058] With continued reference to FIG. 6, the waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some implementations, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or the plurality of lenses 320, 330, 340, 350 may be configured to send image information to the eye with various levels of wavefront curvature or light ray divergence. Each waveguide level may be associated with a particular depth plane and can be configured to output image information corresponding to that depth plane. Image injection devices 360, 370, 380, 390, 400 may function as a source of light for the waveguides and may be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, each of which may be configured, as described herein, to distribute incoming light across each respective waveguide, for output toward the eye 210. Light exits an output surface 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into a corresponding input surface 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some implementations, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of a corresponding waveguide, or may be part of a major surface of the corresponding waveguide (that is, one of the waveguide surfaces directly facing the world 510 or the viewer's eye 210). In some implementations, a single beam of light (e.g., a collimated beam) may be injected into each waveguide to output an entire field of cloned collimated beams that are directed toward the eye 210 at particular angles (and amounts of divergence) corresponding to the depth plane associated with a particular waveguide. In some implementations, a single one of the image injection devices 360, 370, 380, 390, 400 may be associated with and inject light into a plurality (e.g., three) of the waveguides 270, 280, 290, 300, 310.

[0074]

[0059] In some implementations, the image injection devices 360, 370, 380, 390, 400 are discrete displays that each produce image information for injection into a corresponding waveguide 270, 280, 290, 300, 310, respectively. In some other implementations, the image injection devices 360, 370, 380, 390, 400 are the output ends of a single multiplexed display which may, e.g., pipe image information via one or more optical conduits (such as fiber optic cables) to each of the image injection devices 360, 370, 380, 390, 400. It will be appreciated that the image information provided by the image injection devices 360, 370, 380, 390, 400 may include light of different wavelengths, or colors (e.g., different component colors, as discussed herein).

[0075]

[0060] In some implementations, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light module 530, whichAttorney Docket No. 40589-0348WO1; ML-5015WO

[0076] may include a light emitter, such as a light emitting diode (LED). The light from the light module 530 may be directed to and modified by a light modulator 540, e.g., a spatial light modulator, via a beam splitter 550. The light modulator 540 may be configured to change the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCD) including a liquid crystal on silicon (LCOS) displays. It will be appreciated that the image injection devices 360, 370, 380, 390, 400 are illustrated schematically and, in some implementations, these image injection devices may represent different light paths and locations in a common projection system configured to output light into associated ones of the waveguides 270, 280, 290, 300, 310. In some implementations, the waveguides of the waveguide assembly 260 may function as ideal lens while relaying light injected into the waveguides out to the user's eyes. In this conception, the object may be the spatial light modulator 540 and the image may be the image on the depth plane.

[0077]

[0061] In some examples, μLED displays can be used in light projector system 520. μLED displays can unpolarized light over a large range of angles. Accordingly, μLED displays can beneficially provide imagery over wide fields of view with high efficiency.

[0078]

[0062] In some implementations, the display system 250 may be a scanning fiber display including one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous patterns, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the eye 210 of the viewer. In some implementations, the illustrated image injection devices 360, 370, 380, 390, 400 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or a plurality of the waveguides 270, 280, 290, 300, 310. In some other implementations, the illustrated image injection devices 360, 370, 380, 390, 400 may schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each of which are configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It will be appreciated that one or more optical fibers may be configured to transmit light from the light module 530 to the one or more waveguides 270, 280, 290, 300, 310. It will be appreciated that one or more intervening optical structures may be provided between the scanning fiber, or fibers, and the one or more waveguides 270, 280, 290, 300, 310 to, e.g., redirect light exiting the scanning fiber into the one or more waveguides 270, 280, 290, 300, 310.

[0079]

[0063] A controller 560 controls the operation of one or more of the stacked waveguide assembly 260, including operation of the image injection devices 360, 370, 380, 390, 400, theAttorney Docket No. 40589-0348WO1; ML-5015WO

[0080] light module 530, and the light modulator 540. In some implementations, the controller 560 is part of the local processing and data module 140. The controller 560 includes programming (e.g., instructions in a non-transitory medium) that regulates the timing and provision of image information to the waveguides 270, 280, 290, 300, 310 according to, e.g., any of the various schemes disclosed herein. In some implementations, the controller may be a single integral device, or a distributed system connected by wired or wireless communication channels. The controller 560 may be part of the local processing and data module 140 or remote processing module 150 (FIG. 9D) in some implementations.

[0081]

[0064] With continued reference to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each respective waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 may each be planar or have another shape (e.g., curved), with major top and bottom surfaces and edges extending between those major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 may each include out-coupling optical elements 570, 580, 590, 600, 610 that are configured to extract light out of a waveguide by redirecting the light, propagating within each respective waveguide, out of the waveguide to output image information to the eye 210. Extracted light may also be referred to as out-coupled light, and the out-coupling optical elements may also be referred to as light extracting optical elements. An extracted beam of light may be outputted by the waveguide at locations at which the light propagating in the waveguide strikes a light extracting optical element. The out-coupling optical elements 570, 580, 590, 600, 610 may, for example, be gratings, including diffractive optical features, as discussed further herein. While illustrated disposed at the bottom major surfaces of the waveguides 270, 280, 290, 300, 310, for ease of description and drawing clarity, in some implementations, the out-coupling optical elements 570, 580, 590, 600, 610 may be disposed at the top and / or bottom major surfaces, and / or may be disposed direc tly in the volume of the waveguides 270, 280, 290, 300, 310, as discussed further herein. In some implementations, the out-coupling optical elements 570, 580, 590, 600, 610 may be formed in a layer of material that is attached to a transparent substrate to form the waveguides 270, 280, 290, 300, 310. In some other implementations, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material and the out-coupling optical elements 570, 580, 590, 600, 610 may be formed on a surface and / or in the interior of that piece of material.

[0082]

[0065] With continued reference to FIG. 6, as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light to form an image corresponding to a particular depth plane. For example, the waveguide 270 nearest the eye may be configured to deliverAttorney Docket No. 40589-0348WO1; ML-5015WO

[0083] collimated light (which was injected into such waveguide 270), to the eye 210. The collimated light may be representative of the optical infinity focal plane. The next waveguide up 280 may be configured to send out collimated light which passes through the first lens 350 (e.g., a negative lens) before it may reach the eye 210; such first lens 350 may be configured to create a slight convex wavefront curvature so that the eye / brain interprets light coming from that next waveguide up 280 as coming from a first focal plane closer inward toward the eye 210 from optical infinity. Similarly, the third up waveguide 290 passes its output light through both the first and second lenses 350 and 340 before reaching the eye 210; the combined optical power of the first and second lenses 350 and 340 may be configured to create another incremental amount of wavefront curvature so that tire eye / brain interprets light coming from the third waveguide 290 as coming from a second focal plane that is even closer inward toward the person from optical infinity than was light from the next waveguide up 280.

[0084]

[0066] The other layers of waveguide 300, 310 and lenses 330, 320 are similarly configured, w ith the highest w aveguide 310 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power representative of the closest focal plane to the person. To compensate for the stack of lenses 320, 330, 340, 350 when viewing / interpreting light coming from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be disposed at the top of the stack to compensate for the aggregate power of the stack of lenses 320, 330, 340, 350 below. Such a configuration provides as many perceived focal planes as there are available w'aveguide / lens pairings. Both the out-coupling optical elements of the wav eguides and the focusing aspects of the lenses may be static (i.e., not dynamic or electro-active). In some alternative implementations, either or both may be dynamic using electro-active features.

[0085]

[0067] In some implementations, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same plurality of depth planes, with one set for each depth plane. This may provide advantages for forming a tiled image to provide an expanded field of view at those depth planes,

[0086]

[0068] With continued reference to FIG. 6, the out-coupling optical elements 570, 580, 590, 600, 610 may be configured to both redirect light out of their respective w aveguides and to output this light w ith the appropriate amount of divergence or collimation for a particularAttorney Docket No. 40589-0348WO1; ML-5015WO

[0087] depth plane associated with the waveguide. As a result, waveguides having different associated depth planes may have different configurations of out-coupling optical elements 570, 580, 590, 600, 610, which output light with a different amount of divergence depending on the associated depth plane. In some implementations, the out-coupling optical elements 570, 580, 590, 600, 610 may be volumetric or surface features, which may be configured to output light at specific angles. For example, the out-coupling optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some implementations, the features 320, 330, 340, 350 may not be lenses; rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0088]

[0069] In some implementations, the out-coupling optical elements 570, 580, 590, 600, 610 are diffractive features that form a diffraction pattern, or “diffractive optical element” (also referred to herein as a “DOE”). Preferably, the DOEs have a sufficiently low diffraction efficiency so that only a portion of the light of the beam is deflected away toward the eye 210 with each intersection of the DOE, while the rest continues to move through a waveguide via TIR. The light carry ing the image information is thus divided into a number of related exit beams that exit the waveguide at a multiplicity of locations and the result is a fairly uniform pattern of exit emission toward the eye 210 for this particular collimated beam bouncing around within a waveguide.

[0089]

[0070] In some implementations, one or more DOEs may be switchable between “on” states in which they actively diffract, and “off’ states in which they do not significantly diffract. For instance, a switchable DOE may include a layer of polymer dispersed liquid crystal, in which microdroplets include a diffraction pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not appreciably diffract incident light) or the microdroplet may be sw'itched to an index that does not match that of the host medium (in w hich case the pattern actively diffracts incident light).

[0090]

[0071] In some implementations, a camera assembly 630 (e.g,, a digital camera, including visible light and infrared light cameras) may be provided to capture images of the eye 210 and / or tissue around the eye 210 to, e.g., detect user inputs and / or to monitor the physiological state of the user. As used herein, a camera may be any image capture device. In some implementations, the camera assembly 630 may include an image capture device and a light source to project light (e.g., infrared light) to the eye, which may then be reflected by the eye and detected by the image capture device. In some implementations, the camera assembly 630 may be attached to the frame 80 (FIG. 9D) and may be in electricalAttorney Docket No. 40589-0348WO1; ML-5015WO

[0091] communication with the local processing and data module 140 and / or remote processing module 150, which may process image information from the camera assembly 630. In some implementations, one camera assembly 630 may be utilized for each eye, to separately monitor each eye.

[0092]

[0072] With reference now to FIG. 7, an example of exit beams outputted by a waveguide is shown. One waveguide is illustrated, but it will be appreciated that other waveguides in the waveguide assembly 260 (FIG. 6) may function similarly, where the waveguide assembly 260 includes multiple waveguides. Light 640 is injected into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At points where the light 640 impinges on the out-coupling optical element 570, e.g., a DOE, a portion of the light exits the waveguide as exit beams 650. The exit beams 650 are illustrated as substantially parallel but, as discussed herein, they may also be redirected to propagate to the eye 210 at an angle (e.g., forming divergent exit beams), depending on the depth plane associated with the waveguide 270. It will be appreciated that substantially parallel exit beams may be indicative of a waveguide with out-coupling optical elements that out-couple light to form images that appear to be set on a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of out-coupling optical elements may output an exit beam pattern that is more divergent, which would require the eye 210 to accommodate to a closer distance to bring it into focus on the retina and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity,

[0093]

[0073] In some implementations, a full color image may be formed at each depth plane by overlaying images in each of the component colors, e.g., three or more component colors. FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes images formed using multiple different component colors. The illustrated implementation shows depth planes 240a-240f, although more or fewer depths are also contemplated. Each depth plane may have three or more component color images associated with it, including: a first image of a first color, G; a second image of a second color, R; and a third image of a third color, B. Different depth planes are indicated in the figure by different numbers for diopters (dpt) following the letters G, R, and B. Just as examples, the numbers following each of these letters indicate diopters (1 / m), or inverse distance of the depth plane from a viewer, and each box in the figures represents an individual component color image. In some implementations, to account for differences in the eye's focusing of light of different wavelengths, the exact placement of the depth planes for different component colors may vary. For example, different component color images for a given depth plane may be placedAttorney Docket No. 40589-0348WO1; ML-5015WO

[0094] on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or may decrease chromatic aberrations.

[0095]

[0074] In some implementations, light of each component color may be outputted by a single dedicated waveguide and, consequently, each depth plane may have multiple waveguides associated with it. In such implementations, each box in the figures including the letters G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane where three component color images are provided per depth plane. While the waveguides associated with each depth plane are shown adjacent to one another in this drawing for ease of description, it will be appreciated that, in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other implementations, multiple component colors may be outputted by the same w aveguide, such that, e.g., only a single waveguide may be provided per depth plane.

[0096]

[0075] With continued reference to FIG. 8, in some implementations, G is the color green, R is the color red, and B is the color blue. In some other implementations, other colors associated with other wave lengths of light, including magenta and cyan, may be used in addition to or may replace one or more of red, green, or blue.

[0097]

[0076] It will be appreciated that references to a given color of light throughout this disclosure will be understood to encompass light of one or more wavelengths within a range of wavelengths of light that are perceived by a viewer as being of that given color. For example, red light may include light of one or more wavelengths in the range of about 620-780 nm, green light may include light of one or more wavelengths in the range of about 492-577 nm, and blue light may include light of one or more wavelengths in the range of about 435-493 nm.

[0098]

[0077] In some implementations, the light module 530 (FIG, 6) may be configured to emit light of one or more wavelengths outside the visual perception range of the viewer, for example, infrared and / or ultraviolet wavelengths. In addition, the in-coupling, out-coupling, and other light redirecting structures of the waveguides of the display system 250 may be configured to direct and emit this light out of the display towards the user's eye 210, e.g., for imaging and / or user stimulation applications.

[0099]

[0078] With reference now to FIG. 9A, in some implementations, light impinging on a waveguide may need to be redirected to in-couple that light into the waveguide. An incoupling optical element may be used to redirect and in-couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view' of an example of a plurality or set 660 of stacked waveguides that each includes an in-coupling optical element.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0100] The waveguides may each be configured to output light of one or more different wavelengths, or one or more different ranges of wavelengths. It will be appreciated that the set 660 of stacked waveguides may correspond to the waveguide assembly 260 (FIG. 6) and the illustrated waveguides of the set 660 of stacked waveguides may correspond to part of the plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more of the image injection devices 360, 370, 380, 390, 400 is injected into the waveguides from a position that requires light to be redirected for in-coupling.

[0101]

[0079] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated in-coupling optical element (which may also be referred to as a light input area on the waveguide), with, e.g., in-coupling optical element 700 disposed on a major surface (e.g., an upper major surface) of waveguide 670, in-coupling optical element 710 disposed on a major surface (e.g., an upper major surface) of waveguide 680, and in-coupling optical element 720 disposed on a major surface (e.g,, an upper major surface) of waveguide 690. In some implementations, one or more of tire in-coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the respective waveguide 670, 680, 690 (particularly where the one or more in-coupling optical elements are reflective, deflecting optical elements). As illustrated, the in-coupling optical elements 700, 710, 720 may be disposed on the upper major surface of their respective waveguide 670, 680, 690 (or the top of the next lower waveguide), particularly where those in-coupling optical elements are transmissive, deflecting optical elements. In some implementations, the in-coupling optical elements 700, 710, 720 may be disposed in the body of the respective waveguide 670, 680, 690. in some implementations, as discussed herein, the in-coupling optical elements 700, 710, 720 are wavelength selective, such that they selectively redirect one or more wavelengths of light, while transmitting other wavelengths of light. While illustrated on one side or comer of their respective waveguide 670, 680, 690, it will be appreciated that the in-coupling optical elements 700, 710, 720 may be disposed in other areas of their respective waveguide 670, 680, 690 in some implementations,

[0102]

[0080] As illustrated, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some implementations, each in-coupling optical element may be offset such that it receives light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from a different image injection device 360, 370, 380, 390, and 400 as shown in FIG. 6, and may be separated (e.g., laterally spaced apart) from other in-coupling opticalAttorney Docket No. 40589-0348WO1; ML-5015WO

[0103] elements 700, 710, 720 such that it substantially does not receive light from the other ones of the in-coupling optical elements 700, 710, 720.

[0104]

[0081] Each waveguide also includes associated light distributing elements, with, e.g., light distributing elements 730 disposed on a major surface (e.g., a top major surface) of waveguide 670, light distributing elements 740 disposed on a major surface (e.g., a top major surface) of waveguide 680, and light distributing elements 750 disposed on a major surface (e.g., a top major surface) of waveguide 690. In some other implementations, the light distributing elements 730, 740, 750, may be disposed on a bottom major surface of associated waveguides 670, 680, 690, respectively. In some other implementations, the light distributing elements 730, 740, 750, may be disposed on both top and bottom major surface of associated waveguides 670, 680, 690, respectively; or the light distributing elements 730, 740, 750, may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively,

[0105]

[0082] The waveguides 670, 680, 690 may be spaced apart and separated by, e.g., gas, liquid, and / or solid layers of material. For example, as illustrated, layer 760a may separate waveguides 670 and 680; and layer 760b may separate waveguides 680 and 690. In some implementations, the layers 760a and 760b are formed of low refractive index materials (that is, materials having a lower refractive index than the material forming the immediately adjacent one of waveguides 670, 680, 690). Preferably, the refractive index of the material forming the layers 760a, 760b is 0.05 or more, or 0.10 or less than the refractive index of the material forming the waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that facilitate total internal reflection (TIR) of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some implementations, the layers 760a, 760b are formed of air. While not illustrated, it will be appreciated that the top and bottom of the illustrated set 660 of waveguides may include immediately neighboring cladding layers.

[0106]

[0083] Preferably, for ease of manufacturing and other considerations, the material forming the waveguides 670, 680, 690 are similar or the same, and the material forming the layers 760a, 760b are similar or the same. In some implementations, the material forming the waveguides 670, 680, 690 may be different between one or more waveguides, and / or the material forming the layers 760a, 760b may be different, while still holding to the various refractive index relationships noted above.

[0107]

[0084] With continued reference to FIG. 9A, light rays 770, 780, 790 are incident on the set 660 of waveguides. It will be appreciated that the light rays 770, 780, 790 may be injectedAttorney Docket No. 40589-0348WO1; ML-5015WO

[0108] into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0109]

[0085] In some implementations, the light rays 770, 780, 790 have different properties, e.g., different wavelengths or different ranges of wavelengths, which may correspond to different colors. The in-coupling optical elements 700, 710, 720 each deflect the incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some implementations, the in-coupling optical elements 700, 710, 720 each selectively deflect one or more particular wavelengths of light, while transmitting other wavelengths to an underlying waveguide and associated in-coupling optical element.

[0110]

[0086] For example, in-coupling optical element 700 may be configured to deflect light rays 770, which has a first wavelength or range of wavelengths, while transmitting light rays 780 and 790, which have different second and third wavelengths or ranges of wavelengths, respectively. Tire transmitted light rays 780 impinge on and are deflected by the in-coupling optical element 710, which is configured to deflect light of a second w avelength or range of wavelengths. The light ray 790 is deflected by the in-coupling optical element 720, which is configured to selectively deflect light of third wavelength or range of wavelengths.

[0111]

[0087] With continued reference to FIG. 9A, the deflected light rays 770, 780, 790 are deflected so that they propagate through a corresponding waveguide 670, 680, 690; that is, the in-coupling optical elements 700, 710, 720 of each waveguide deflects light into that corresponding waveguide 670, 680, 690 to in-couple light into that corresponding waveguide. The light rays 770, 780, 790 are deflected at angles that cause the light to propagate through the respective waveguide 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguide 670, 680, 690 by TIR until impinging on the waveguide's corresponding light distributing elements 730, 740, 750.

[0112]

[0088] With reference now' to FIG. 9B, a perspective view of an example of the plurality of stacked waveguides of FIG. 9A is illustrated. As noted above, the in-coupled light rays 770, 780, 790, are deflected by the in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within the waveguides 670, 680, 690, respectively. Tire light rays 770, 780, 790 then impinge on the light distributing elements 730, 740, 750, respectively. The light distributing elements 730, 740, 750 deflect the light rays 770, 780, 790 so that they propagate towards the out-coupling optical elements 800, 810, 820, respectively.

[0113]

[0089] In some implementations, the light distributing elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some implementations, the OPEs deflect or distribute light to the out-coupling optical elements 800, 810, 820 and, in some implementations, may also increaseAttorney Docket No. 40589-0348WO1; ML-5015WO

[0114] the beam or spot size of this light as it propagates to the out-coupling optical elements, in some implementations, the light distributing elements 730, 740, 750 may be omitted and the in-coupling optical elements 700, 710, 720 may be configured to deflect light directly to the out-coupling optical elements 800, 810, 820. For example, with reference to FIG. 9A, the light distributing elements 730, 740, 750 may be replaced with out-coupling optical elements 800, 810, 820, respectively. In some implementations, the out-coupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light in a viewer's eye 210 (FIG. 7). It will be appreciated that the OPEs may be configured to increase the dimensions of the eye box in at least one axis and the EPEs may be to increase the eye box in an axis crossing, e.g., orthogonal to, the axis of the OPEs. For example, each OPE may be configured to redirect a portion of the light striking tlie OPE to an EPE of the same waveguide, w hile allowing the remaining portion of tire light to continue to propagate down the waveguide. Upon impinging on the OPE again, another portion of the remaining light is redirected to the EPE, and the remaining portion of that portion continues to propagate further down the waveguide, and so on. Similarly, upon striking the EPE, a portion of the impinging light is directed out of tire waveguide towards the user, and a remaining portion of that light continues to propagate through the waveguide until it strikes the EP again, at which time another portion of the impinging light is directed out of the waveguide, and so on. Consequently, a single beam of in-coupled light may be “replicated” each time a portion of that light is redirected by an OPE or EPE, thereby forming a field of cloned beams of light, as showm in FIG. 6. In some implementations, the OPE and / or EPE may be configured to modify a size of the beams of light.

[0115]

[0090] Accordingly, with reference to FIGS. 9A and 9B, in some implementations, the set 660 of waveguides includes waveguides 670, 680, 690; in-coupling optical elements 700, 710, 720; light distributing elements (e.g., OPEs) 730, 740, 750; and out-coupling optical elements (e.g., EPs) 800, 810, 820 for each component color. The waveguides 670, 680, 690 may be stacked with an air gap / cl adding layer between each one. The in-coupling optical elements 700, 710, 720 redirect or deflect incident light (with different in-coupling optical elements receiving light of different wavelengths) into its waveguide. The light then propagates at an angle which will result in HR within the respective waveguide 670, 680, 690. In the example show n, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700, and then continues to bounce down the waveguide, interacting w'ith the light distributing element (e.g., OPEs) 730 and then the out-coupling optical element (e.g., EPs) 800, in a manner described earlier. The light rays 780 and 790 (e.g., green and red light,Attorney Docket No. 40589-0348WO1; ML-5015WO

[0116] respectively) will pass through the waveguide 670, with light ray 780 impinging on and being deflected by in-coupling optical element 710. The light ray 780 then bounces down the waveguide 680 via TIR, proceeding on to its light distributing element (e.g., OPEs) 740 and then the out-coupling optical element (e.g., EPs) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 to impinge on the light in-coupling optical elements 720 of the waveguide 690, The light in-coupling optical elements 720 deflect the light ray 790 such that the light ray propagates to light distributing element (e.g., OPEs) 750 by TIR, and then to the out-coupling optical element (e.g., EPs) 820 by TIR. The out-coupling optical element 820 then finally out-couples tire light ray 790 to the viewer, who also receives the out-coupled light from the other -waveguides 670, 680.

[0117]

[0091] FIG. 9C illustrates a top-down plan view' of an example of the plurality of stacked waveguides of FIGS. 9 A and 9B. As illustrated, the waveguides 670, 680, 690, along with each waveguide's associated light distributing element 730, 740, 750 and associated out-coupling optical element 800, 810, 820, may be vertically aligned. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned; rather, the in-coupling optical elements are non-overlapping (e.g., laterally spaced apart as seen in the top-down view). As discussed further herein, this nonoverlapping spatial arrangement facilitates the injection of light from different resources into different w aveguides on a one- to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some implementations, arrangements including nonoverlapping spatially-separated in-coupling optical elements may be referred to as a shifted pupil system, and the in-coupling optical elements within these arrangements may correspond to sub pupils.

[0118]

[0092] Alternatively, in certain implementations, two or more of the in-coupling optical elements can be in an inline arrangement, in which they are vertically aligned. In such arrangements, light for waveguides further from the projection system is transmitted through the in-coupling optical elements for waveguides closer to the projection system, preferably with minimal scattering or diffraction.

[0119]

[0093] Inline configurations can advantageously reduce the size of and simplify the projector. Moreover, it can increase the field of view' of the eyepiece, e.g., by coupling of same color to several waveguides by making use of crosstalk. For example, green light can be coupled into blue and red active layers. Because of the pitch of each ICG can be different to provide improved (e.g., optimal) performance for a specific color, the allowed field of view' can be increased.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0120]

[0094] In inline configurations, except for the last layer in the optical path, the ICGs should be either at most partially reflective or otherwise transmissive to light having operative wavelengths of subsequent layers in the waveguide stack. In either case, the efficiency can be undesirably low unless the gratings are etched in a high-index layer (e.g., 1.8 or more for polymer based layers), or a high-index coating is deposited or growth on the grating.

[0121] However, this approach can increase the back-reflection into the projector lens, which thus can generate image artifacts such as image ghosting.

[0122]

[0095] FIG. 9D illustrates an example of w earable display system 60 into w hich the various waveguides and related systems disclosed herein may be integrated. In some implementations, the display system 60 is the display system 250 of FIG. 6, with FIG. 6 schematically show ing some parts of that display system 60 in greater detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0123]

[0096] With continued reference to FIG. 9D, the display system 60 includes a display 70, and various mechanical and electronic modules and systems to support the functioning of that display 70. The display 70 may be coupled to a frame 80, which is wearable by a display system user or user 90 and w hich is configured to position the display 70 in front of the eyes of the user 90. The display 70 may be considered eyewear in some implementations. In some implementations, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent the ear canal of the user 90 (in some implementations, another speaker, not shown, may optionally be positioned adjacent the other ear canal of the user to provide

[0124] stereo / shapeable sound control). The display system 60 may also include one or more microphones 110 or other devices to detect sound. In some implementations, the microphone is configured to allow the user to provide inputs or commands to the display system 60 (e.g., the selection of voice menu commands, natural language questions, etc.), and / or may allow audio communication with other persons (e.g., with other users of similar display systems. The microphone may further be configured as a peripheral sensor to collect audio data (e.g., sounds from the user and / or environment). In some implementations, the display system may also include a peripheral sensor 120a, which may be separate from the frame 80 and attached to the body of the user 90 (e.g., on the head, torso, an extremity, etc. of the user 90). The peripheral sensor 120a may be configured to acquire data characterizing a phy siological state of the user 90 in some implementations. For example, the sensor 120a may be an electrode.

[0125]

[0097] With continued reference to FIG. 9D, the display 70 is operatively coupled by communications link 130, such as by a wired lead or wireless connectivity, to a local processing and data module 140 which may be mounted in a variety of configurations, suchAttorney Docket No. 40589-0348WO1; ML-5015WO

[0126] as fixedly atached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removably attached to tire user 90 (e.g., in a backpack-style configuration, in a belt-coupling style configuration). Similarly, tire sensor 120a may be operatively coupled by communications link 120b, e.g., a wired lead or wireless connectivity, to the local processing and data module 140. lire local processing and data module 140 may include a hardware processor, as well as digital memory’, such as nonvolatile memory (e.g., flash memory or hard disk drives), both of which may be utilized to assist in the processing, caching, and storage of data. Optionally, the local processing and data module 140 may include one or more central processing units (CP U s), graphics processing units (GPUs), dedicated processing hardware, and so on. The data may include data a) captured from sensors (which may be, e.g., operatively coupled to the frame 80 or otherwise attached to the user 90), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, gyros, and / or other sensors disclosed herein; and / or b) acquired and / or processed using remote processing module 150 and / or remote data repository' 160 (including data relating to virtual content), possibly for passage to the display 70 after such processing or retrieval. Tire local processing and data module 140 may be operatively coupled by communication links 170, 180, such as via a wired or -wireless communication links, to the remote processing module 150 and remote data repository’ 160 such that the remote processing module 150 and remote data repository 160 are operatively coupled to each other and available as resources to the local processing and data module 140. In some implementations, the local processing and data module 140 may include one or more of the image capture devices, microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, and / or gyros. In some other implementations, one or more of these sensors may be attached to the frame 80, or may be standalone structures that communicate with the local processing and data module 140 by wired or wireless communication pathway s.

[0127]

[0098] With continued reference to FIG. 9D, in some implementations, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, for instance including one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and so on. In some implementations, the remote data repository' 160 may include a digital data storage facility, which may be available through the internet or other networking configuration in a “cloud” resource configuration. In some implementations, the remote data repository 160Attorney Docket No. 40589-0348WO1; ML-5015WO

[0128] may include one or more remote servers, which provide information, e.g., information for generating augmented reality content, to the local processing and data module 140 and / or the remote processing module 150. In some implementations, all data is stored, and all computations are performed in the local processing and data module, allowing fully autonomous use from a remote module. Optionally, an outside system (e.g., a system of one or more processors, one or more computers) that includes CPUs, GPUs, and so on, may perform at least a portion of processing (e.g., generating image information, processing data) and provide information to, and receive information from, local processing and data module 140, remote processing module 150, and remote data repository 160, for instance via wireless or wired connections.

[0129] Encapsulated, Reflective Input Coupling Gratings

[0130]

[0099] With reference to FIG. 10, an article 1000 includes a waveguide 1002 and an ICG 1004 optically coupled to the -waveguide 1002. Tire ICG 1004 includes metallic strips 1006 encapsulated by a dielectric material 1008, e.g., the metallic strips 1006 are embedded in the dielectric material 1008. The waveguide 1002 can correspond to one of waveguides 670, 680, or 690, described previously, and the ICG 1004 can correspond to one of input coupling gratings 700, 710, and 720, respectively.

[0131]

[0100] The waveguide 1002 extends in a waveguide plane, e.g., the XY plane, and generally extends beyond the ICG, The metallic strips 1006 are parallel to each other and spaced apart from each other along the Y direction, which is marked by dotted line 1010. In other words, the metallic strips 1006 possess translational symmetry with each other along the Y direction.

[0132]

[0101] Since the metallic strips 1006 form part of the ICG 1004, the metallic strips 1006 can be regularly spaced within the dielectric material 1008, For example, the grating pitch P of the metallic strips 1006 along the Y direction can depend on the operative wavelength of light coupled into the ICG 1004. In some implementations, the grating pitch P is λ or less. For example, the pitch can be from λ / 3 to λ, e.g., λ / 2.

[0133]

[0102] Each metallic strip 1006 is angled relative to the waveguide plane. For example, each metallic strip 1006 has a surface 1012 oriented at angle 0 relative to the Y direction. The surface 1013 opposite surface 1012 is also parallel to surface 1012. In this example, each metallic strip 1006 is a parallelogram defined by the angle 0 and a slant height and thickness, as will be discussed later on.

[0134] 5Attorney Docket No. 40589-0348WO1; ML-5015WO

[0135]

[0103] Between each pair of adjacent metallic strips 1006 is an opening 1019, such that the metallic strips 1006 form a louvered structure. For example, similar to a louvered structure, the metallic strips 1006, in the cross-sectional view, resemble an array of angled slats with openings therebetween.

[0136]

[0104] Various parameters of ICG 1004 can be varied to optimize coupling efficiency, reduce back-reflection, and to control into which diffraction orders light is reflected and transmitted. Tire thickness of the dielectric layer below and above the metallic strips 1006 can also vary. For example, a thickness DI of the dielectric layer below the metallic strips 1006 can be 10 nm to 200 nm, e.g., the thickness can be 200 nm, 150 nm, 100 nm, 50 nm, 40 nm, 30 nm, 20 nm, or 10 nm thick, or the metallic strip can contact the waveguide 1002 directly. The thickness D2 of the dielectric layer above the metallic strips can be a few microns or less, e.g., the layer can be 1 micron, 500 nm, 400 nm, 300 nm, 200 nm, or 100 nm thick, or the upper edge of the metallic strip can be coplanar with the upper surface of dielectric material 1008. The layer of dielectric material 1008 can have an overall thickness D3 in a range of 50 nm to 10 microns.

[0137]

[0105] The material choices of the metallic strips 1006, the dielectric material 1008, and the waveguide 1002 can vary. For example, the metallic strips 1006 can be pure metal, a metal alloy, or can include layers of different metals and / or alloys. Examples of pure metals are aluminum, silver, platinum, and gold. Examples of metal alloys are silver-platinum, aluminum-platinum, silver-copper, and aluminum-copper. Examples of multilayer structures include aluminum / chromium bilayers and silver / titanium bilayers.

[0138]

[0106] In some implementations, metalloid or dielectric strips, e.g., highly reflective silicon, replace the metallic strips 1006.

[0139]

[0107] In some implementations, the dielectric material 1008 includes an organic material. Tire dielectric material 1008 can include an inorganic material, such as silicon carbide (SiC), titanium dioxide (TiO2), lithium niobate (LiNbO3), tantalum pentoxide (Ta2O5), zirconium dioxide (ZrO2), silicon nitride (Si3N4), silicon oxynitride (SiOxNy), silicon oxide (SiO2), yttrium oxide (Y2O3), hafnium oxide (HfO2), aluminum oxide (Al2O3), and magnesium fluoride (MgF2). Additionally, optical organic polymers or inorganic-organic polymer composites, e.g., TiO2or ZrO2particles in polymer matrices, and porous inorganic polymers, can also be used. Other materials with similar optical, mechanical, or chemical properties may also be used, depending on the specific function of each layer.

[0140]

[0108] Tlie dielectric material 1008 can be a single dielectric material. In some implementations, the dielectric material 1008 can be a combination of multiple dielectricAttorney Docket No. 40589-0348WO1; ML-5015WO

[0141] materials. The waveguide 1002 can be composed of materials as described for waveguides 670, 680, and 690 above, e.g., glass.

[0142]

[0109] In operation, incoming light 1014 passes through the waveguide 1002, and at least part of incoming light 1014 in-couples into the waveguide 1002 by interacting with the reflective metallic strips 1006. In the example of FIG. 10, the incoming light 1014 is normally incident on the ICG 1004, but incoming light at other angles of incidence can be incoupled into the waveguide 1002. Incoming light 1014 can originate from a projector, e.g., light projector system 520. In some implementations, the projector is on a user side 1016 of the waveguide 1002, and the ICG 1004 is disposed on a world side 1018 of the waveguide 1002.

[0143]

[0110] Tlie mechanism of ICG 1004 differs in part from that of a conventional reflective ICG. In FIG. 11A, a conventional ICG 1001 includes a sawtooth diffraction grating 1003 covered by a conformal, metallic layer 1005 and disposed on a substrate 1007. Incoming light 1014a passes from the substrate 1007 into the ICG 1001. In this example, it is assumed that none of tlie light is absorbed by the ICG 1001.

[0144]

[0111] In the first bounce off of the ICG 1001, part of incoming light 1014a is back-reflected into the 0threflective diffractive order, e.g., “Ro,” while other parts are diffracted into the launch and anti-launch direction. The light reflected in the 0thorder has an angle of reflection equal to the angle of incidence, with both angles measured relative to the normal of tlie reflective surface, causing the light to bounce directly back toward the substrate 1007. In this case, the diffraction grating 1003 is angled, which leads to most of the incoming light 1014a being directed into the Fl8* reflective diffractive order, e.g., “R+i,” and the remaining light is directed into the - I'1reflective diffractive order “R-i.”

[0145]

[0112] Light diffracted into the +1streflective diffractive order direction travels in the launch direction, e.g., toward an out-coupling grating that will eventually direct light to a user’s eye. Light directed into the launch direction, e.g., the R+i light, follows a trajectory similar to total internal reflection (TIR) by bouncing off of the surface of the substrate 1007 opposite the surface on w hich the ICG 1001 is disposed. In the second bounce, most of the light is diffracted into the 0thorder, “R’o” light, while the remaining light is diffracted into the -1stand -2ndreflective diffractive orders, e.g., “R’-i” and “R’-2,” respectively.

[0146]

[0113] Light directed into the 0threflective diffractive order in the first bounce (Ro light) and into the -1streflective diffractive order in the second bounce (R’-i light) travels back towards tlie direction from which tlie incoming light originated. Consequently, the Ro and R’-i light is back-reflected into the projector, which can lead to ghosting issues.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0147] [1141 With reference to FIG. 1 IB, for ICG 1004, incoming light 1014 similarly diffracts into waveguide 1002, with light being directed into the 0th, +lst, and -1streflective diffractive orders in the first bounce and in the 0th, -1st, and -2ndreflective diffractive orders in the second bounce. In each of the first and second bounces, however, some of the light is transmitted into the 0thtransmissive diffractive order, e.g., “To” and “T’o,” respectively. Although not labeled, some light can also diffract into other transmissive orders, e.g,, +lstand -1sttransmissive diffractive orders. As a result, the amount of directed back toward the projector, e.g., R0 and R'-1 light, is less than that of ICG 1001. While the transmitted orders interact with the metallic strips, the amount of absorption is high, as well. Formulaically, and without wishing to be bound by theory’, this can be expressed in the following equations:

[0148]

[0115] Equation 1:

[0149] Reftotal= I0R0+ I0a1R+1R'-1+ I0a2R+1R'0R''-1+ I0R+1R'-2R+1+ ...

[0150]

[0116] Equation 2:

[0151] Launchtotal= I0A0R+1+ I0A1R+1R'0+ I0A2R+1R'0R''0...

[0152]

[0117] In Equation 2, L refers to the intensity of light that goes through n+1 bounces, Rn refers to the coefficient of the amplitude of light diffracted into the nthdiffractive order, where anis the ratio of (area going through n or more bounces and interacting with the grating):(the total ICG area). In a similar way, area coefficients An are defined as the ratio of (the effective area that gets launched after n bounces):(the total area of the ICG). Coefficients anand An can be calculated and generally depend on parameters, such as the size and shape of ICG, the operative wavelength X, the pitch, and the thickness of the waveguide.

[0153]

[0118] Reftotai is the total intensity of reflected light, which is to be minimized, and Launchtotal is the total intensity of launched light, which is to be maximized. Minimizing back-reflection corresponds to minimizing the orders Ro, R’-i, and R'-2. While reducing R+i also reduces back-reflection, having a high R+i indicates high launch efficiency, e.g., light effectively being directed into the launch direction, so reducing R+1is not a design goal. As an example, Table 1 shows the different reflective diffractive efficiency of diffractive orders of interest for normally incident light on each of the ICGs 1001 and 1004 having a pitch of 357 nm when the disposed on the waveguide having a refractive index of about 2.00.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0154] Table 1. Reflective diffractive efficiency of diffractive orders of interest

[0155] ICG 1001 ICG 1004

[0156] 620nm 530nm 460nm 620nm 530nm 460nm (Red) (Green) (Blue) (Red) (Green) (Blue) Ro 33% 26% 14% 5% 1 % 2% RH 40% 47% 57% 62% 66% 53% 1st

[0157] bounce R-i 7% 9% 12% 3% 1% 3%

[0158] R’-i 70 /

[0159] / / o 9% 12% 3% 1% 3% R’o 38% 38% 27% 12% 5% 8% 2nd

[0160] bounce R’-2 27% 24% 15% 19% 13% 6%

[0161]

[0162]

[0119] As indicated by Table 1, Ro, R-i, R’-i, and R'-2 are greater in ICG 1001 than these coefficients are in ICG 1004 for each of the operative wavelengths, e.g., red (620 nm), green (530 nm), and blue (460 nm). This advantage compounds in large ICGs, where multi -bounce effects are prevalent, e.g., more bounces occur for ICGs that extend for longer distances along the launch direction. Further R+1is greater in ICG 1004 for all three wavelengths compared to ICG 1001, meaning that more light is in-coupled into the launch direction at the first bounce. Additionally, R’-2 is lower in ICG 1004 for all three wavelengths compared to ICG 1001, so less power is wasted, e.g,, directed in the anti-launch direction, in ICG 1004,

[0163]

[0120] With reference to FIGS. 12A-12I, the shape of the metallic strips 1006 can vary. In cross-section, metallic strip 1006a has a parallelogram shape, defined by a full width Wl, a thickness Tl, a slant height S. and a slant angle 0 (where the angle (p is equal to 9O°-0). Hie full width Wl is measured along the direction in which the metallic strips are spaced apart from each other, e.g., along the Y direction. The thickness Tl is measured along a direction perpendicular to the slant angle 0 and parallel to the YZ plane. The slant height S is measured along a vertical direction, e.g,, the direction in which the waveguide 1002 and ICG 1004 are stacked, which is the Z direction in this example. Another parameter that can vary is the ratio of full width W1 to the pitch P.

[0164]

[0121] When viewed in cross-section, the outline of the metallic shape 1006a is a parallelogram that has two edges 1201 and 1202, which correspond to surfaces that extendAttorney Docket No. 40589-0348WO1; ML-5015WO

[0165] into the page (in the X direction) in FIG. 12A. Each surface is angled at an acute angle 0 relative to the waveguide plane. The outline of the metallic shape 1006a also includes two edges 1203 and 1204 that are angled perpendicularly relative to the waveguide below, e.g., an angle between the edges 1203 and 1204 and the waveguide plane is 90°.

[0166]

[0122] In some implementations, the thickness T1 is in a range of 5 to 100 nm, e.g., 40 nm. Tire full width Wl can be twice the pitch or less, e.g., / 10 to 2X. For example, the pitch can be 3X / 2,, X / 2, or X / 3. When the full width W 1 is greater than the pitch, adjacent metallic strips 1006 can overlap when viewed along a direction normal to the waveguide plane, e.g,, along the Z direction. Tire slant angle 0 can be 60° or less, e.g., 50°, 40°, 30°, 20°, or 10°.

[0167]

[0123] With reference to FIG. 12B, in cross-section, metallic strip 1006b has hockey stick shape, e.g., a parallelogram shape with an additional flat segment at the bottom. Similarly to the metallic strip 1006a, when viewed in cross-section, the outline of the metallic strip 1006b has two edges 1205 and 1206 that are acutely angled relative to the waveguide and two edges 1207 and 1208 that are perpendicularly angled relative to the waveguide. The edges 1207 and 1208 correspond to surfaces that extend into the page (in the X direction) in FIG. 12B. In addition, the outline of the metallic strip 1006b has two edges 1209 and 1210 that are angled parallel to the waveguide, e.g., an angle between the edges 1209 and 1210 and the waveguide plane is 0°.

[0168]

[0124] Metallic strip 1006b can have all tire same parameters as metallic strip 1006a, e.g., a full width Wl, a thickness Tl, a slant height S, and a slant angle 0. In addition, the metallic strip 1006b has a flat bottom segment width W2, a flat bottom segment height H1, and a ratio of flat bottom segment width W2 to full width Wl. Metallic strip 1006c has an upside down hockey stick shape, e.g., a parallelogram shape with an additional flat segment of the top. Similarly to metallic strip 1006b, metallic strip 1006c can have all the same parameters as metallic strip 1006a, as well as a flat top segment width W3, a flat top segment height H2, and a ratio of top bottom segment width W3 to full width Wl. Metallic strip 1006d has a double-sided hockey stick shape, e.g,, a parallelogram shape with flat segments at both the top and bottom. Metallic strip 1006d has all the parameters of both metallic strips 1006b and 1006c.

[0169]

[0125] In some implementations, width W2 is the same width of W l or less, width W3 is the same width of Wl or less. When widths W2 and W3 are zero, the shape of the metallic strip is a parallelogram as in FIG. 12A. The sum of W2 and W3 can be less than or equal to widthAttorney Docket No. 40589-0348WO1; ML-5015WO

[0170] Wl. In the example of FIG. 12D, the width Wl is equal to the pitch, width W2 is 0.1*W1, and W3 = 0.1*W1.

[0171]

[0126] The metallic strips can also have a staircase shape when viewed from cross-section. For example, metallic strip 1006e has a uniform staircase shape, e.g., the height H4 and width W4 of each “step” of the staircase is the same. The number of steps, the height H4 of each step, and the width W4 of each step determine the full width Wl and slant height S of metallic strip 1006e. For example, the full width Wl is (n+1 )W4, with n being the number of steps, and the slant height S is n(H4).

[0172]

[0127] Metallic strip 1006f has an irregular staircase shape, e.g., the heights and widths of each of tire steps are irregular. For example, metallic strip 1006f is composed of two steps. The first step has height H5 and width H5, and the second step has height H6 and width W6. Additionally, the flat bottom and top segments have different widths, e.g., width W6 is less than width W7. In the case of the staircase shape, the thickness T2 of the metallic strips can be measured as the shortest distance between parallel surfaces of the metallic strip.

[0173]

[0128] Like metallic strip 1006b, the outlines of each of metallic strips 1006c, 1006d, 1006e, and 1006f are composed of multiple edges, which can be oriented parallel, perpendicular, or at an acute angle relative to the waveguide.

[0174]

[0129] In some implementations, with reference to FIG. 12K, the metallic strips can have a curvilinear shape when viewed in parallel. In the cross section, the outline of the metallic strip 1006k has a concave edge 1211 and a convex edge 1212. Tire edges 1211 and 1212 correspond to surfaces that extend into the page (in the X direction) in FIG. 12K. In general, the shape of the metallic strips can depend on the shape of the structure that supports the metallic strips during fabrication.

[0175]

[0130] With reference to FIGS. 12G, 12H, and 121, each cycle of metallic strips can include two or more shapes, e.g., three or four different shapes. For example, each cycle of ICG 1204g includes two metallic strips 1206g1 and 1206g2 with the same shape, size, and orientation e.g., each of metallic strips 1206gl and 1206g2 are parallelograms with the same size parameters and angle of inclination. With reference to FIG. 12H, the size and orientation of metallic strips can vary. For example, metallic strips 1206h1 and 1206h2 of ICG 1204h are both parallelogram shaped, but the sizes and angles of orientation of metallic strips 1206h1 and 1206h2 differ. Further, each cycle can include metallic strips with varying shapes. With reference to FIG. 121, ICG 1204i includes metallic strips 1206i1 and 1206i2, where metallic strip 1206i2 has a double-ended hockey stick shape, and metallic strip 1206i1 has a parallelogram shape.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0176]

[0131] Other examples of combinations of multiple shapes in each cycle include a staircase shape, a curvilinear shape, and a parallelogram and multiple staircase shapes. In some implementations, the metallic strips of different shapes touch to form a new continuous shape. In some implementations, the metallic strips of different shapes are spaced apart from each other (i.e., the differently-shaped strips are discontinuous).

[0177]

[0132] FIG. 10 depicts an example in which the lateral spacing between adjacent metallic strips 1006 is zero, e g., one metallic strip ends where another begins (see dotted line 1020). In FIG. 10, the metallic strips 1006 neither overlap each other nor are spaced apart from each other when viewed along a direction normal to the waveguide plane, e.g., along the Z direction. However, other implementations are possible. With reference to FIG. 12J, when viewed along the Z direction, the metallic strips 1006g are spaced apart from each other due to there being a gap between the beginning and ends of adjacent metallic strips 1006g. For example, a gap G exists between the front of a metallic strip 1006g 1 and the end of metallic strip 1006g2. In this case, the pitch P is the sum of the full width W1 and the gap G. In some implementations, the gap G has a dimension of λ or less. For example, when the metallic strips have a high aspect ratio, the gap G can have a negative value such that the metallic strips overlap viewed along a direction normal to the waveguide plane.

[0178]

[0133] To further reduce undesired back-reflection, the disclosed eyepieces can include additional layers disposed on the dielectric material at the interface between the ICG 1004 and air. With reference to FIGS. 13A-13C, an additional layer can truncate the dielectric material 1008. Each of cross-sections 1300a, 1300b, and 1300c depicts an ICG including metallic strips 1006 embedded in a dielectric material 1008 and supported by waveguide 1002.

[0179]

[0134] On an upper surface 1302a of the dielectric material 1008, e.g., a surface opposite the surface of the dielectric material 1008 coupled to the waveguide 1002, is a blackening layer 1304. The blackening layer 1304 is so-called because the layer absorbs the majority of light in the operative wavelength range of the incoming light. In some implementations, the blackening layer 1304 includes black ink or inorganic materials, such as Si, Ge, C, and FeS2. Tire blackening layer 1304 can have a sufficient thickness T2 to effectively attenuate any light transmitted past the metallic strips 1006.

[0180]

[0135] In cross-section 1300b, one or more antireflective coatings 1306 are disposed on an upper surface 1302b of the dielectric material 1008. For example, the antireflective coatings 1306 can include silicon dioxide (SiO2), titanium dioxide (TiO2), magnesium fluorideAttorney Docket No. 40589-0348WO1; ML-5015WO

[0181] (MgF2), and / or hafnium dioxide (HfO2). in cross-section 1300c, a nano-structured antireflective coating 1308, e.g., a dielectric stack or moth eye structure, is disposed on an upper surface 1302c of the dielectric material.

[0182]

[0136] Tlie blackening layer 1304 can have an index of refraction substantially similar to that of the dielectric material 1008. For example, the indices can agree within 1% or less, e.g., 0%, to reduce back-reflection when light propagates from the dielectric material to the layers 1304. The antireflective coatings 1306 can have layers of alternating refractive index to reduce reflectivity via interference. The antireflective structure 1308 can have a smooth gradient of refractive index to reduce reflection caused by discrete refractive index steps. The increased complexity of the surface of nano-structured antireflective coating 1308 can also promote scattering in such a way that the light does not reflect back. In some implementations, the material used to truncate the dielectric material 1008 has a lower refractive index than that of the dielectric material 1008.

[0183]

[0137] In some implementations, additional layers within the ICG can further improve launch efficiency and mitigate back-reflection. With reference to FIG. 14, ICG 1004a includes a sawtooth dielectric grating 1402, a dielectric undercoat 1404 beneath metallic strip 1406, a coat 1408, and dielectric overcoat 1410. Tire coat 1408 can include either a metallic or dielectric material. Additionally, tire ICG 1004 includes a dielectric intermediate layer 1412 between the dielectric grating 1402 and the waveguide 1401. Although FIG. 14 depicts a parallelogram metallic strip 1406, other shapes are possible as discussed previously,

[0184]

[0138] Compared to the metallic layer 1005 conventional ICG 1001 of FIG. 11A, the metallic strip 1406 in ICG 1004a is not the outermost layer. Rather, the outermost layer of ICG 1004a is a conformal dielectric overcoat 1410. In other words, the metallic strip 1406 of ICG 1004a is sandwiched by dielectric layers,

[0185]

[0139] Each of the layers in the ICG 1004a can include one or more layers. For example, the dielectric intermediate layer 1412 can be a single layer of TiO2or a multilayer structure, such as TiO2 / HfO2 / SiO2 / MgF2. In some implementations, the dielectric intermediate layer 1412 reduces back-reflection by forming destructive interference between light reflected by the dielectric grating 1402 and the metallic strips 1406. In some implementations, the dielectric undercoat 1404 adjusts the spectral and angular distribution of diffraction efficiency of incoming light.

[0186]

[0140] Metallic strip 1406 can include highly reflective materials such as silver, platinum, aluminum, or gold. Tlie coat 1408 can include absorbing metals, e.g., titanium and chromium, or dielectric materials such as carbon. In some implementations, the coat 1408 modifies theAttorney Docket No. 40589-0348WO1; ML-5015WO

[0187] transmissive orders of diffracted light and loss. In some implementations, the material of the conformal dielectric overcoat 1410 is selected to allow light to exit for transmissive diffracted orders.

[0188]

[0141] A range of inorganic materials with varied refractive indices are suitable for dielectric materials in the ICG 1004a, such as silicon carbide (SiC), titanium dioxide (TiO2), lithium niobate (LiNbO3), tantalum pentoxide (Ta2O5), zirconium dioxide (ZrO2), silicon nitride (Si3N4), silicon oxynitride (SiOxNy), silicon oxide (SiO2), yttrium oxide (Y2O3), hafnium oxide (HfO2), aluminum oxide (Al2O3), and magnesium fluoride (MgF2). These materials can be selected based on refractive indices and low absorption characteristics in the visible spectrum. Additionally, optical organic polymers or inorganic-organic polymer composites, e.g., TiO2or ZrO2particles in polymer matrices, and porous inorganic polymers, can also be used. Other materials with similar optical, mechanical, or chemical properties may also be used, depending on the specific function of each layer,

[0189]

[0142] With reference to FIG. 15A, various methods may be used to form the disclosed ICGs. The method 1500 includes providing a waveguide that extends in a waveguide plane (1510). For example, the waveguide 1602 of FIG. 16A can be the waveguide. In some implementations, the waveguide is another waveguide described in the present disclosure.

[0190]

[0143] Tire method 1500 includes forming, using a first dielectric material and on a surface, e.g., surface 1602a, of the waveguide 1602, a surface relief grating, e.g., grating 1604 (1520). In the example of FIG. 16A, the grating 1604 is a blazed grating with an acute anti-blaze angle. In some implementations, the surface relief grating corresponds to dielectric grating 1402 of FIG. 14. In some implementations, the first dielectric material is an organic resist formed using nanoimprint lithography or inorganic dielectrics, such as TiOz.

[0191]

[0144] In some implementations, forming the surface relief grating includes forming a resist layer thickness (RLT) of less than amicron, e.g., 50 nm.

[0192]

[0145] Each ridge in the grating 1604 includes a surface 1604a that is oriented at an acute angle with respect to the waveguide plane. For example, the angle 0B between dotted line 1605a, which is parallel to the waveguide plane, and dotted line 1605b, which is parallel to the surface 1604a, is acute.

[0193]

[0146] With reference to FIGS. 15B-15E, the surface relief grating formed in step 1520 can have various shapes. For example, surface relief grating 1500b is a triangle grating, surface relief grating 1500c is a trapezoidal base grating, surface relief grating 1500d is an obtuse trapezoidal grating, and surface relief grating 1500e is a parallelogram grating.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0194]

[0147] The method 1500 includes depositing a metal 1607 or metal alloy on the surfaces 1604a to form multiple discrete metallic strips 1606 (1530). In some implementations, the metallic strips have a thickness in a range of 5 nm to 100 nm. For example, the metal can be silver, platinum, aluminum, or gold.

[0195]

[0148] Since the surface 1604a and dotted line 1605b along another surface of the metallic strips are parallel to each other, the metallic strips are also parallel to each other. In the example of FIG. 16B, the metallic strips 1606 have a double-sided hockey stick shape, as described in reference to FIG. 12D. in some implementations, depositing the metal 1607 includes depositing a metal alloy.

[0196]

[0149] Since the grating 1604 has an acute anti-blaze angle GAB, to keep the metallic strips 1606 discrete, e.g., separated by a gap d, the metal 1607 is deposited at an angle a relative to the vertical direction. When the metal is deposited at this angle, the upper portions of the grating can block lower portions of the grating from receiving deposited metal. The angle a can depend on the geometry of the grating and the desired shape of the metallic strips 1606. As a result, depositing the metal can include avoiding depositing metal on the exposed surfaces 1609.

[0197]

[0150] In some implementations, such as when forming a metallic strip with the shape shown in FIG. 121, depositing a metal on the surfaces to form multiple discrete metallic strips can include two separate metal deposition steps, with different deposition angles. For example and with reference to FIG. 16E, after the metal deposition of FIG. 16B, metal 1609 is deposited on the metallic strips 1606 and exposed portions of the surface relief grating at a different angle p. This second deposition forms metallic strips 1616, which contact both the surface relief grating 1604 and the metallic strips 1606. As a result, the overall width of the combined metallic strips, e.g,, width of metallic strips 1606 and 1616 combined, can vary.

[0198]

[0151] Tire method 1500 includes depositing more dielectric material 1608 over the metallic strips 1606 and the exposed surfaces 1609 of the surface relief grating between the metallic strips to encapsulate the metallic strips 1606 in dielectric material (1540). Hie layer of dielectric material 1608 can be up to tens of microns thick.

[0199]

[0152] In some implementations, the first dielectric material of the surface relief grating 1604 and the second dielectric material 1608 are the same. Each of the first and second dielectric materials can include one or more materials as disclosed herein. With reference to FIG. 16C, the metallic strip 1606 are completely encapsulated by dielectric material, e.g., every surface of each metallic strip 1606 is covered by a dielectric material. However, in some implementations, the metallic strips being encapsulated by a material can refer to partialAttorney Docket No. 40589-0348WO1; ML-5015WO

[0200] encapsulation, e.g., some portion of the surface of a metallic strip is not covered by the encapsulating material.

[0201]

[0153] In some implementations, the method 1500 can include additional steps or some of the steps can be divided into multiple steps. For example, with reference to FIG. 16D, method 1500 can further include depositing an absorptive material 1610 or antireflective structure, e.g., as discussed previously. In some implementations, depositing the absorptive material or antireflective structure can include sputtering, evaporation, chemical vapor deposition (CVD), e.g., plasma enhanced CVD (PECVD) and atomic layer deposition ALD.

[0202]

[0154] As depicted in FIG. 16D, the surface of the waveguide 1602 coupled to tire grating 1604, e.g., an ICG, is a projector-side of the waveguide.

[0203]

[0155] As another example, when forming the ICG 1004a of FIG. 14, the method 1500 can further include, before forming the surface relief grating, forming an intermediate dielectric layer. Between forming the surface relief grating and depositing the metal, the method 1500 can include depositing a dielectric undercoat on the exposed surfaces of the surface relief grating. Before depositing the second dielectric material, the method can include depositing either a metal or dielectric coat on top of the metallic strips 1606.

[0204]

[0156] In some implementations, multiple layers of metallic strips can be deposited directly onto each other by repeating step 1530 multiple times, e.g., with the same metallic material or different metallic materials, before proceeding to step 1540.

[0205]

[0157] In some implementations, depositing the dielectric material over the metallic strips 1606 includes forming a conformal coating and / or planarized coating. In other implementations, depositing the dielectric material over the metallic strips 1606 includes forming a non-conformal coating.

[0206]

[0158] In some implementations, the method 1500 further includes depositing, either directly on or above the metallic strips, lossy coatings to enhance loss of transmitted orders. These coatings will be discussed more with reference to FIGS. 22A-22D.

[0207]

[0159] In some implementations, there can be ICGs with encapsulated metallic strips for each wavelength of light, w here tire parameters vary betw een each ICG based on the wavelength. In this case, steps 1520, 1530, and 1540 repeat for each ICG. The parameters of each ICG can be selected to couple the light of a respective wavelength from the light projection system into the waveguide, the wavelengths corresponding to multiple differently colored pixels in a display.

[0208]

[0160] FIG. 16F is a scanning electron microscope (SEM) image of an example ICG fabricated according to the method 1500. A substrate 1620 including a waveguide wasAttorney Docket No. 40589-0348WO1; ML-5015WO

[0209] provided, as in step 1510. Then, a curvilinear surface relief grating 1622 was formed on a surface of the substrate 1620, as in step 1520. The grating 1622 was formed of TiCh.

[0210]

[0161] As disclosed above, in some implementations, the step 1530 of depositing a metallic strip layer is repeated multiple times. In this example, a layer 1624 of aluminum was deposited on the titanium dioxide before a titanium capping layer 1626 w as deposited on the aluminum. In this example, the aluminum layer was about 10 nm thick. The capping layer of titanium protects the underlying aluminum layer. Because the grating 1622 had a curvilinear shape, the metallic strips of aluminum and titanium also had a curvilinear shape, similarly to FIG. 12K. Then, a second dielectric layer 1628 of TiO2was deposited on the titanium layer. Tire second dielectric layer 1628 was formed through atomic layer deposition (ALD). Above the second dielectric layer 1628 is air.

[0211]

[0162] FIG. 16G is an SEM image of another example ICG fabricated according to the method 1500. Like the example shown in FIG, 16F, the fabricated ICG of FIG, 16G included a substrate 1630 supporting a curvilinear surface grating 1632 formed of TiO2. In this example, the tw o metallic layers were a lower layer 1634 of aluminum and an upper layer 1636 of chromium. The ICG of FIG. 16G also included a second dielectric 1638 layer of titanium dioxide,

[0212]

[0163] One difference between tire ICGs of FIGS. 16F and 16G was that the second dielectric layer 1628 was continuous, e.g., portions of the second dielectric layers 1628 above adjacent regions of the grating 1622 contact each other. In contrast, portions of the second dielectric layer 1638 above adjacent regions of the surface relief grating 1632 did not contact each other, e.g., the second dielectric layer 1638 w as made up of discrete portions. In this example, the discrete portions of the second dielectric layer 1638 were formed through sputtering titanium dioxide.

[0213] Simulation Results

[0214]

[0164] FIGS. 17A and 17B depict a comparative example. FIG. 17A depicts a blazed ICG 1700a, which is characterized by several parameters, such as blaze angle, anti-blaze angle, top width, bottom width, height, residual layer thickness (RLT), pitch, a gap w idth, and grating material. In this example, the top with is 50 nm, the gap width is 25 nm, the blaze angle is 27°, the anti-blaze angle is 85°, the pitch is 357 nm, the RLT is 20 nm, and the height is 140 nm. Generally, the parameters of diffraction gratings are selected to satisfy diffraction criteria. For example, the height is selected to satisfy the following equation:

[0215] [165 J Equation 3:Attorney Docket No. 40589-0348WO1; ML-5015WO

[0216] widthbottom+ widthtop+ height / tan(θblaze) + height / tan(θanti-blaze) = pitch

[0217]

[0218] ldn{Uhlaze) anti- blaze)

[0219] FIG. 17B depicts an ICG 1700b with embedded mirrors. Many of the same parameters that characterize blazed ICG 1700a also characterize ICG 1700b. In this example, the top width is 50 nm, the bottom width is 29 nm, the heights is 110 nm, the anti-blaze angle is 90°, the pitch is 357 nm, the RLT is 44 nm, the metal thickness is 20 nm, and the deposition thickness is 50 nm. ICG 1700b is part of a system including a 4 mm diameter ICG disposed on a waveguide having a thickness of 0.7 mm and a refractive index of 2,0. Each of the grating materials in ICGs 1700a and 1700b is titanium dioxide, and the metal in ICG 1700b is aluminum.

[0220]

[0166] ICG 1700b has a higher launch efficiency and reduces back-reflection compared to ICG 1700a. Similarly to the example of FIG. 1 IB, the performance can be evaluated as shown in Table 2, which lists coefficients of how much light is directed into each reflective order.

[0221] Table 2. Reflective coefficients for first and second bounces

[0222] Orders ICG 1700b ICG 1700a Red Green Blue Red Green Blue 1st R: 60% 66% 57% 39% 49% 50% Bounce

[0223] Ro 6% 1% 4% 29% 16% 11% R-i 5% 2% 2% 9% 14% 16% 2nd R’o 12% 5% 5% 42% 29% 22% Bounce

[0224] R’-i 5% 3% 2% 9% 14% 16%

[0225] R’-2 19% 12% 7% 17% 17% 25%

[0226]

[0227]

[0167] Comparing ICG 1700b to ICG 1700a, the coefficient Ro for back-reflected light is reduced by 79.31% for red light, by 93.75% for green light, and by 63.64% in blue light.

[0228] Further comparing ICG 1700b to ICG 1700a, the coefficient R’-i, which characterizes back-reflection after the second bounce, is reduced by 44.44% for red light, 78.75% for green light, and 87.5% for blue light. For blue light, which suffers more from higher-order bounceAttorney Docket No. 40589-0348WO1; ML-5015WO

[0229] effects, R -2, which also characterizes back-reflection, is reduced by 72% in ICG 1700b compared to ICG 1700a.

[0230]

[0168] Tire plots in FIG. 18A- 18R depict the coefficients for reflected and transmitted diffractive orders as a function of angle of incidence, e.g., +7° through -7° relative to normal incidence, for each of red, green, and blue w avelengths for the first bounce in ICG 1700a. The plots in FIG. 19A-19R depict the coefficients for reflected and transmitted diffractive orders as a function of angle of incidence for each of red, green, and blue wavelengths for the second bounce in ICG 1700a. The dashed lines correspond to transverse magnetic (TM) polarization, the dotted lines correspond to transverse electric (TE) polarization, and the solid lines correspond to an average of tire TM and TE values.

[0231]

[0169] As depicted in FIGS. 18H, 18 J, 18L, 18N, 18P, 18R, 19N, 19P, and I9R, the plots for transmissive orders, e.g., T+i, T-i, are flat lines at zero, since the coefficient is zero for these orders, as the ICG 1700a does not transmit light past the grating. Similarly, the plots of FIGS.

[0232] 19H, 19J, 19L, 19M, 19O, and 19Q for R+1and R+2in the second bounce also indicate that no light is directed into these orders.

[0233]

[0170] The plots in FIGS. 20A-20R depict the coefficients for reflected and transmitted diffractive orders as a function of angle of incidence for each of the red, green, and blue wavelengths in ICG 1700b in the first bounce. Tire plots in FIGS. 2IA-21R depict the coefficients for reflected and transmitted diffractive orders as a function of angle of incidence for each of the red, green, and blue wavelengths in ICG 1700b in the second bounce. As opposed to the plots in FIGS. 18A-18R and 19A-19R, the plots in FIGS. 20A-20R and 21A-21R for transmissive orders To, Ti, or T-i have nonzero values. It is noted that the sum of all the coefficients does not necessarily sum exactly to 1, since there is some loss due to higher-order effects.

[0234]

[0171] In ICG 1700a, the average value of tire first bounce coefficients (using the average of the TM and TE polarization and over the 14° range) is 71% for blue light, 79% for green light, and 77% for red light. The average value of the second bounce coefficients is 63% for blue light, 60% for green light, and 68% for red light. In ICG 1700b, the average value of the first bounce coefficients is 64% for blue light, 72% for green light, and 74% for a red light. Hie average value of the second bounce coefficients is 29 % for blue light, 31% for green light, and 46% for red light. In the first bounce, 2% of blue light is transmitted, 3.5% of green light is transmitted, and 3% of red light is transmitted. In the second bounce, 15% of blue light is transmitted, 11% of green light is transmitted, and 10% of red light is transmitted.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0235]

[0172] The transmission coefficients are higher for the second bounce because the second bounce interaction involves more angles of incidence along, e.g., parallel to the metallic strips, which can cause further attenuation of the light as it travels through the grating. This attenuation helps reduce undesirable effects caused by back-reflection. Blue light in particular experiences higher loss in ICG 1700b than in ICG 1700a, e.g., 0.36 for first bounce and 0.71 for the second bounce in ICG 1700b compared to 0.29 for the first bounce and 0.37 for the second bounce in ICG 1700a.

[0236]

[0173] With reference to FIG. 22A, generally, incoming light has four outcomes: being incoupled into the launch direction, being in-coupled into the anti-launch direction, being back- reflected, and being transmitted by an ICG. FIG. 22B depicts the launch efficiencies at a system level, e.g., in a 14° by 14° field of view (FOV), for each of these outcomes in ICGs 1700a and 1700b in red, green, and blue light. For example, “LaunchR” refers to the efficiency of in coupling red light into the launch direction, “backRefG” refers to the efficiency of back -reflecting green light, “AntiB” refers to the efficiency of launching blue light into the anti-launch direction, and “TransR” refers to the efficiency of transmitting red light. Data points with crosses refer to ICG 1700a, and data points with circles refer to ICG 1700b. In this example, each of ICGs 1700a and 1700b has a four-layer antireflective structure on the user-side to reduce total back-reflection.

[0237]

[0174] Generally, the efficiencies of back-reflection and in-coupling into the anti-launch direction is lower for ICG 1700b compared to ICG 1700a. In particular, back-reflection is less than 10% for all colors in ICG 1700b. As expected, the transmission efficiency for ICG 1700a is zero, and for ICG 1700b is nonzero. The system level loss for ICG 1700a is 19.66% for red light, 27.5% for green light, and 22.52% for blue light. The system level loss for ICG 1700b is 27.24% for red light, 40.24% for green light, and 50.89% for blue light. Although the loss of ICG 1700b is greater than that of ICG 1700a, back-reflection is greatly reduced, especially for blue light which suffers more severe bounce effects than red and green light due to its shorter wavelength.

[0238]

[0175] As visible in FIG. 22B, red light experiences a mean launch efficiency of 40% or more (e.g., 50%) and a mean back-reflection of 15% or less (e.g., 9%) over a field of view of 10° or more (e.g., 14° by 14°). Considering that the etendue conservation law suggests that the launch efficiency limit for a typical ICG is 20-60%, a launch efficiency of 50% is relatively high.

[0239]

[0176] Modulation transfer function (MTF) analysis is an indicator of contrast and sharpness, and Table 3 summarizes MTF results for ICGs 1700a and 1700b:Attorney Docket No. 40589-0348WO1; ML-5015WO

[0240] Table 3: MTF coefficients for ICGs 1700a and 1700b

[0241] Colors Orientation ICG 1700a ICG 1700b CPDs 8cpd 13 cpd 8 cpd 13 cpd (cycles per

[0242] degree)

[0243] Red X 0.725 0.610 0.701 0.575 y 0.707 0.557 0.684 0.523 Green X 0.688 0.582 0.636 0.512 y 0.659 0.522 0.605 0.453 Blue X 0.611 0.489 0.577 0.432 y 0.580 0.439 0.554 0.396

[0244]

[0245]

[0177] Overall, Table 3 indicates that using embedded metallic strips in ICG 1700b does not cause considerable phase discontinuity or a drop in MTF and sharpness.

[0246]

[0178] With reference to FIGS. 23A-23D, additional layers coated on or above the metallic strips can further enhance performance metrics. As discussed with reference to FIG. 14, additional lossy, lossless, and antireflective layers be disposed either above, below, or on the metallic strips. In FIG. 23A, an extra lossy / lossless coating is disposed directly on a reflective coating, e.g., the metallic strip. In FIG. 23B, an extra lossy / lossless coating is disposed above the reflective coating, with dielectric material being disposed between the lossy / lossless coating and the reflective coating. In FIG. 23C, an extra lossy / lossless coating is disposed both above and directly on the reflective coating, with dielectric material being disposed between the two lossy / lossless coatings.

[0247]

[0179] FIG. 23D depicts the launch efficiency results for the ICG in FIG, 23 A. By reducing the amount of light that travels past the metallic strips, then the amount of light that can be possibly directed back toward the projector is reduced. Thus, increasing the volume of the lossy material, e.g., Ti or Cr, mitigates the transmission powers while having minimal effect on the launch efficiency and back-reflection.

[0248] EMBODIMENTSAttorney Docket No. 40589-0348WO1; ML-5015WO

[0249]

[0180] Although the disclosed inventive concepts include those defined in the attached claims, it should be understood that the inventive concepts can also be defined in accordance with the following embodiments.

[0250]

[0181] Embodiment 1 is an article comprising:

[0251] a waveguide for guiding light at a wavelength, X, the waveguide extending in a waveguide plane; and

[0252] an input coupling grating (ICG) optically coupled to a surface of the waveguide, the ICG comprising a plurality of metallic strips spaced apart from each other and extending parallel to each other in a first direction parallel to the waveguide plane, the ICG further comprising one or more dielectric materials encapsulating tire metallic strips,

[0253] wherein each metallic strip has a first surface that is (i) oriented at an acute angle with respect to the waveguide plane, (ii) oriented perpendicularly with respect to the waveguide plane, or (iii) curvilinear in shape, and the first surface of each metallic strip is configured to redirect incident light at the wavelength X into the waveguide.

[0254]

[0182] Embodiment 2 is the article of embodiment 1, wherein the surface of the waveguide coupled to the ICG is a projector-side of the waveguide.

[0255]

[0183] Embodiment 3 is the article of embodiment 1 or embodiment 2, w herein all surfaces of each metallic strip are completely encapsulated by the one or more dielectric materials.

[0256]

[0184] Embodiment 4 is the article of any one of embodiments 1-3, wdierein the metallic strips form a grating w ith a pitch of X or less in a second direction parallel to tire w aveguide plane and perpendicular to the first direction.

[0257]

[0185] Embodiment 5 is the article of any one of embodiments 1-4, w herein the metallic strips have a width of 2X or less.

[0258]

[0186] Embodiment 6 is the article of any one of embodiments 1-5, wherein the metallic strips have a thickness 100 nm or less,

[0259]

[0187] Embodiment 7 is the article of any one of embodiments 1-6, w herein adjacent metallic strips are spaced apart by X or less.

[0260]

[0188] Embodiment 8 is the article of any one of embodiments 1-7, wherein the acute angle for each metallic strip is in a range from 10° to 60°.

[0261]

[0189] Embodiment 9 is the article of any one of embodiments 1-8, w herein the first surfaces of the metallic strips are parallel.

[0262]

[0190] Embodiment 10 is the article of any one of embodiments 1-9, w herein each metallic strip comprises a second surface opposite and parallel to the first surface.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0263]

[0191] Embodiment 11 is the article of any one of embodiments 1-10. when viewed normal to the waveguide plane, a first metallic strip begins where a second metallic strip begins.

[0264]

[0192] Embodiment 12 is the article of any one of embodiments 1-10, wherein, when viewed normal to the waveguide plane, adjacent metallic strips are spaced apart from each other.

[0265]

[0193] Embodiment 13 is the article of any one of embodiments 1-12, wherein the metallic strips transmit at least some light at X normally incident on the ICG on the side of the ICG facing the waveguide,

[0266]

[0194] Embodiment 14 is the article of any one of embodiments 1-13, wherein, in cross¬ section, each metallic strip has a parallelogram shape.

[0267]

[0195] Embodiment 15 is the article of any one of embodiments 1-13, wherein, in cross¬ section, each metallic strip has a staircase shape.

[0268]

[0196] Embodiment 16 is the article of any one of embodiments 1-13, wherein, in crosssection, each metallic strip has a shape of a parallelogram with at least one of a flat upper segment and a flat lower segment attached to the parallelogram,

[0269]

[0197] Embodiment 17 is the article of any one of embodiments 1-16, wherein the metallic strips comprise at least one of gold, silver, platinum, or aluminum.

[0270]

[0198] Embodiment 18 is the article of any one of embodiments 1-17, wherein the one or more dielectric materials comprise at least one of titanium oxide (TiO₂), silicon nitride (SiN), silicon carbide (SiC), or lithium niobate (LiNO₃)

[0271]

[0199] Embodiment 19 is the article of any one of embodiments 1-18, further comprising absorptive material for the wavelength. disposed on a surface of the dielectric material opposite the surface of tire dielectric material coupled to the waveguide.

[0272]

[0200] Embodiment 20 is the article of any one of embodiments 1-19, -wherein the absorptive material or the one or more antireflective coatings have an index of refraction that is substantially the same as the index of refraction of the dielectric material.

[0273]

[0201] Embodiment 21 is the article of any one of embodiments 1-18, further compri sing one or more an tireflective coatings disposed on a surface of tire dielectric material opposite the surface of the dielectric material coupled to the waveguide.

[0274]

[0202] Embodiment 22 is the article of any one of embodiments 1-21, wherein the one or more antireflective coatings comprise at least one of SiO₂, TiO₂, MgF₂, or HfO₂.

[0275]

[0203] Embodiment 23 is the article of any one of embodiments 1-18, further comprising a nano-structured antireflective coating disposed on a surface of the dielectric material opposite the surface of the dielectric material coupled to the waveguide.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0276]

[0204] Embodiment 24 is the article of any one of embodiments 1-23, wherein adjacent metallic strips overlap when viewed from a direction orthogonal to the waveguide plane.

[0277]

[0205] Embodiment 25 is the article of any one of embodiments 1-24, wherein the one or more dielectric materials encapsulating tire metallic strips comprise a first dielectric material forming a grating that supports the metallic strips.

[0278]

[0206] Embodiment 26 is the article of any one of embodiments 1-25, wherein the one or more dielectric materials encapsulating the metallic strips comprise a second dielectric material disposed between the grating that supports the metallic strips and tire waveguide.

[0279]

[0207] Embodiment 27 is the article of any one of embodiments 1-26, further comprising discrete strips of either a dielectric or metallic material, each discrete strip supported by a respective metallic strip.

[0280]

[0208] Embodiment 28 is the article of any one of embodiments 1-27, wherein the one or more dielectric materials encapsulating the metallic strips comprise a third dielectric material forming a conformal coating over tire metallic strips.

[0281]

[0209] Embodiment 29 is the article of any one of embodiments 1-28, wherein the ICG is configured to in-couple light incident on the ICG in a range of angles.

[0282]

[0210] Embodiment 30 is an article comprising:

[0283] a waveguide for guiding light at a wavelength,, the waveguide extending in a waveguide plane; and

[0284] an input coupling grating (ICG) optically coupled to a surface of the waveguide, the ICG comprising a plurality of metallic strips angled relative to the waveguide plane to form a louvered structure, the ICG further comprising one or more dielectric materials encapsulating the metallic strips,

[0285] the plurality of metallic strips being configured to reflect at least some light at X normally incident on the ICG on a side of the ICG facing the waveguide to couple the light into the waveguide.

[0286]

[0211] Embodiment 31 is a head-mounted display (HMD) system comprising:

[0287] a head-mountable frame;

[0288] a light projection system configured to output light to provide image content; a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light from the light projection system coupled into the waveguide; and

[0289] an in-coupling grating (ICG) optically coupled to a surface of the waveguide, the ICG comprising a plurality of metallic strips spaced apart from each other and extending parallelAttorney Docket No. 40589-0348WO1; ML-5015WO

[0290] to each other in a first direction parallel to a plane of the waveguide, each metallic strip having a first surface at an acute angle with respect to the plane of the waveguide, the ICG further comprising one or more dielectric materials encapsulating the metallic strips, wherein, for unpolarized incident light having at least one operative wavelength of the output light, the ICG has a mean launch efficiency of 40% or more and a mean back- reflection of 15% or less over a field of view of 10° or more in at least one direction,

[0291]

[0212] Embodiment 32 is the HMD system of embodiment 31, wherein the plurality of metallic strips of the ICG reflect tire unpolarized incident light.

[0292]

[0213] Embodiment 33 is the HMD system of embodiment 31 or embodiment 32, wherein the launch efficiency of the ICG corresponds to a first order diffraction efficiency of the ICG.

[0293]

[0214] Embodiment 34 is the HMD system of any one of embodiments 31-33, wherein, during operation, the ICG is configured to couple the light from the light projection system into the waveguide at operative wavelengths corresponding to multiple differently colored pixels in a display,

[0294]

[0215] Embodiment 35 is the HMD system of any one of embodiments 31-34, wherein the light from the light projection system is unpolarized light.

[0295]

[0216] Embodiment 36 is the HMD system of any one of embodiments 31-35, wherein the light projection system comprises a microLED display, an LCoS display, or a laser beam scanner display.

[0296]

[0217] Embodiment 37 is the HMD system of any one of embodiments 31-36, further comprising one or more additional waveguides and one or more additional ICGs each associated with a corresponding one of the additional waveguides.

[0297]

[0218] Embodiment 38 is a method comprising:

[0298] providing a waveguide extending in a waveguide plane;

[0299] forming, on a surface of the waveguide, a surface relief grating comprising a first dielectric material, the surface relief grating comprising a plurality of first surfaces each oriented at an acute angle with respect to the w aveguide plane;

[0300] depositing a metal on the first surfaces to form a plurality of discrete metallic strips; and

[0301] depositing a second dielectric material over the plurality of discrete metallic strips and exposed surfaces of the surface relief grating between the metallic strips to encapsulate the plurality of discrete metallic strips in dielectric material.

[0302]

[0219] Embodiment 39 is the method of embodiment 38, wherein the first and second dielectric materials are the same material.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0303]

[0220] Embodiment 40 is the method of embodiment 38 or embodiment 39, wherein a difference between a first refractive index of the first dielectric material is a second refractive index of the second dielectric material is less than 1 % for an operative wavelength of tire waveguide.

[0304]

[0221] Embodiment 41 is the method of any one of embodiments 38-40, further comprising depositing an absorptive layer for an operative wavelength on the second dielectric material.

[0305]

[0222] Embodiment 42 is the method of any one of embodiments 38-41, further comprising depositing one or more antireflective coatings on the second dielectric material.

[0306]

[0223] Embodiment 43 is the method of any one of embodiments 38-42, further comprising depositing an antireflective nanostructure on the second dielectric material.

[0307]

[0224] Embodiment 44 is the method of any one of embodiments 38-43, further comprising, before forming the surface relief grating, depositing a third dielectric material on the waveguide.

[0308]

[0225] Embodiment 45 is the method of any one of embodimen ts 38-44, further comprising, before depositing the metal on the first surfaces, depositing a fourth dielectric material on the first surfaces.

[0309]

[0226] Embodiment 46 is the method of any one of embodiments 38-45, further comprising, before encapsulating the plurality of discrete metallic strips in dielectric material, depositing a coat of either another metal or fifth dielectric material on the plurality' of discrete metallic strips,

[0310]

[0227] Embodiment 47 is the method of any one of embodimen ts 38-46, wherein the metal comprises at least one of gold, silver, platinum, and aluminum.

[0311]

[0228] Embodiment 48 is the method of any one of embodiments 38-47, wherein depositing the metal comprises depositing a metal alloy.

[0312]

[0229] Embodiment 49 is the method of any one of embodiments 38-48, wherein depositing the metal comprises depositing the metal at an angle relative to a vertical direction normal to the waveguide plane.

[0313]

[0230] Embodiment 50 is the method of embodiment 49, wherein depositing the metal further comprises depositing the metal at another angle relative to the vertical direction.

[0314]

[0231] Embodiment 51 is the method of embodiment 50, wherein the angle depends on a shape of the surface relief grating.

[0315]

[0232] Embodiment 52 is the method of any one of embodiments 38-51, wherein the metal is a first metal. The method further comprises depositing a second metal different from the first metal on the first metal.Attorney Docket No. 40589-0348WO1; ML-5015WO

[0316]

[0233] Embodiment 53 is the method of any one of embodiments 38-52, wherein depositing the second dielectric material comprises depositing discrete portions of the second dielectric material.

[0317]

[0234] Other implementations are in the following claims.

Claims

Attorney Docket No. 40589-0348WO1; ML-5015WOWhat is claimed is:

1. An article, comprising:a waveguide for guiding light at a wavelength, the waveguide extending in a waveguide plane; andan input coupling grating (ICG) optically coupled to a surface of the waveguide, the ICG comprising a plurality of metallic strips spaced apart from each other and extending parallel to each other in a first direction parallel to the waveguide plane, tire ICG further comprising one or more dielectric materials encapsulating the metallic strips,wherein each metallic strip has a first surface that is (i) oriented at an acute angle with respect to the waveguide plane, (ii) oriented perpendicularly with respect to the waveguide plane, or (iii) curvilinear in shape, and the first surface of each metallic strip is configured to redirect incident light at the wavelength A into the waveguide,2. The article of claim 1, wherein the surface of the waveguide coupled to the ICG is a projector-side of the waveguide.

3. The article of claim 1, w herein all surfaces of each metallic strip are completely encapsulated by the one or more dielectric materials.

4. The article of claim 1, wherein the metallic strips form a grating w ith a pitch of A or less in a second direction parallel to the waveguide plane and perpendicular to the first direction.

5. The article of claim 1, wherein the metallic strips have a width of 2A or less.

6. The article of claim 1, wherein the metallic strips have a thickness 100 nm or less.

7. The article of claim 1, wherein adjacent metallic strips are spaced apart by A or less.

8. The article of claim 1, wherein the acute angle for each metallic strip is in a range from 10° to 60°.Attorney Docket No. 40589-0348WO1; ML-5015WO9. The article of claim 1, wherein the first surfaces of the metallic strips are parallel.

10. Tire article of claim 1, wherein each metallic strip comprises a second surface opposite and parallel to the first surface.

11. The article of claim 1, wherein, when viewed normal to the waveguide plane, a first metallic strip begins where a second metallic strip begins.

12. The article of claim 1, wherein, when viewed normal to the waveguide plane, adjacent metallic strips are spaced apart from each other.

13. The article of claim 1, wherein the metallic strips transmit at least some light at normally incident on the ICG on the side of the ICG facing the waveguide.

14. Tire article of claim 1, wherein, in cross-section, each metallic strip has a parallelogram shape.

15. The article of claim 1, wherein, in cross-section, each metallic strip has a staircase shape.

16. The article of claim 1, wherein, in cross-section, each metallic strip has a shape of a parallelogram w ith at least one of a flat upper segment and a flat low er segment attached to the parallelogram.

17. Tlie article of claim 1, w herein the metallic strips comprise at least one of gold, silver, platinum, or aluminum.

18. The article of claim 1, wherein the one or more dielectric materials comprise at least one of titanium oxide (TiO₂), silicon nitride (SiN), silicon carbide (SiC), or lithium niobate (LiNO₃).

19. The article of claim 1, further comprising absorptive material for the w avelength X disposed on a surface of the dielectric material opposite the surface of the dielectric materialAttorney Docket No. 40589-0348WO1; ML-5015WOcoupled to the waveguide.

20. The article of claim 19, wherein the absorptive material or the one or more antireflective coatings have an index of refraction that is substantially the same as the index of refraction of the dielectric material.

21. The article of claim 1, further comprising one or more antireflective coatings disposed on a surface of the dielectric material opposite the surface of the dielectric material coupled to tire waveguide.

22. Tlie article of claim 21, wherein the one or more antireflective coatings comprise at least one of SiO₂, TiO₂, MgF₂, or HfO₂23. The article of claim 1, further comprising a nano-structured antireflective coating disposed on a surface of the dielectric material opposite tire surface of the dielectric material coupled to the waveguide.

24. Tire article of claim 1, wherein adjacent metallic strips overlap when viewed from a direction orthogonal to the waveguide plane.

25. The article of claim 1, wherein the one or more dielectric materials encapsulating the metallic strips comprise a first dielectric material forming a grating that supports the metallic strips.

26. Tire article of claim 25, wherein the one or more dielectric materials encapsulating the metallic strips comprise a second dielectric material disposed between the grating that supports the metallic strips and the waveguide.

27. The article of claim 1, further comprising discrete strips of either a dielectric or metallic material, each discrete strip supported by a respective metallic strip.

28. Tire article of claim 1, w herein the one or more dielectric materials encapsulating the metallic strips comprise a third dielectric material forming a conformal coating over theAttorney Docket No. 40589-0348WO1; ML-5015WOmetallic strips.

29. Tire article of claim 1, wherein the ICG is configured to in-couple light incident on the ICG in a range of angles.

30. The article of claim 1, wherein the plurality of metallic strips form a louvered structure.

31. A head-mounted display (HMD) system comprising:a head-mountable frame;a light projection system configured to output light to provide image content;a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light from the light projection system coupled into the waveguide; andan in-coupling grating (ICG) optically coupled to a surface of the waveguide, the ICG comprising a plurality of metallic strips spaced apart from each other and extending parallel to each other in a first direction parallel to a plane of the waveguide, each metallic strip having a first surface at an acute angle with respect to the plane of the waveguide, the ICG further comprising one or more dielectric materials encapsulating the metallic strips, wherein, for unpolarized incident light having at least one operative wavelength of the output light, the ICG has a mean launch efficiency of 40% or more and a mean back-reflection of 15% or less over a field of view of 10° or more in at least one direction.

32. A method comprising:providing a waveguide extending in a waveguide plane;forming, on a surface of the waveguide, a surface relief grating comprising a first dielectric material, the surface relief grating comprising a plurality of first surfaces each oriented at an acute angle with respect to the waveguide plane;depositing a metal on the first surfaces to form a plurality of discrete metallic strips; anddepositing a second dielectric material over the plurality of discrete metallic strips and exposed surfaces of the surface relief grating between the metallic strips to encapsulate the plurality of discrete metallic strips in dielectric material.

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