Diffraction Structure for Asymmetric Light Extraction and Augmented Reality Device Including the Same

Abstract

A head-mounted display system includes a head-mountable frame, an optical projection system configured to output light to provide image content, a waveguide supported by the frame and configured to guide at least a portion of the light from the optical projection system coupled therein, and a diffraction structure optically coupled to the waveguide and having a grating layer having a plurality of ridges each having a side surface inclined or stepped with respect to a plane of the waveguide and configured to couple the light guided by the waveguide from the waveguide toward a user side of the head-mounted display. The diffraction structure guides at least 25% more of the light guided by the waveguide to the user side than to the world side.

Description

Technical Field

[0001] Field The present disclosure relates to a display system, and more particularly, to an augmented reality display system and a virtual reality display system, and a diffraction structure for use therewith.

Background Art

[0002] Description of Related Art Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, where digitally reproduced images or portions thereof are presented to a user in a manner such that they appear to be real or can be perceived as such. Virtual reality, i.e., a "VR" scenario, typically involves presenting digital or virtual image information without transparency to other actual real-world visual inputs. Augmented reality, i.e., an "AR" scenario, typically involves presenting digital or virtual image information as an augmentation to the visualization of the actual world around the user. Mixed reality, i.e., an "MR" scenario, is a type of AR scenario and typically involves virtual objects integrated into and responsive to the natural world. For example, in an MR scenario, AR image content can be blocked or otherwise perceived when interacting with real-world objects.

[0003] Referring to FIG. 1, an augmented reality scene 10 is shown, where a user of AR technology views a setting 20 such as a real-world park featuring people, trees, buildings, and a concrete platform 30 in the background. In addition to these items, the user of AR technology also "sees" "virtual content" such as an image 40 of a robot standing on the real-world platform 30 and a flying, cartoon-like avatar character 50 that resembles an anthropomorphic bumblebee, although these elements 40, 50 do not even exist in the real world. Since the human visual perception system is complex, it is difficult to generate AR technology that facilitates a comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0004] The systems and methods disclosed herein address various challenges related to AR and VR technologies.

Summary of the Invention

Means for Solving the Problems

[0005] Overview Diffractive structures of an exit pupil expander (EPE) and / or a compound pupil expander (CPE) that can improve the optical efficiency of waveguide-based augmented reality (AR) devices by directing more light from the waveguide towards the user side rather than the world side of the device are described. Surface relief diffractive structures that can be implemented on one or both sides of an eyepiece lens are described.

[0006] Various aspects of the disclosed subject matter are summarized as follows.

[0007] Generally, in a first aspect, the present disclosure is a head-mounted display system, comprising a head-mountable frame, an optical projection system configured to output light to provide image content, a waveguide supported by the frame and configured to guide at least a portion of the light from the optical projection system coupled therein, and a diffraction structure optically coupled to the waveguide and configured to couple the light guided by the waveguide from the waveguide towards the user side of the head-mounted display, the diffraction structure having a grating layer having a plurality of ridges (e.g., grating lines) each having a side surface inclined or stepped with respect to the plane of the waveguide. The diffraction structure guides at least 25% more of the light guided by the waveguide towards the user side than towards the world side.

[0008] Examples of the head-mounted display system can include one or more of the following features. For example, the ridges can have a selected profile shape of trapezoid (e.g., inclined gratings such as shark fin gratings, truncated triangular gratings), parallelogram (e.g., inclined gratings), triangle (e.g., sawtooth and other blazed grating shapes), and stepped (e.g., each step having the same shape or different shapes).

[0009] The side surface can form an angle in the range of 20° to 80° (for example, greater than or equal to about 30°, greater than or equal to about 40°, greater than or equal to about 50°, greater than or equal to about 60°, less than or equal to about 80°, less than or equal to about 70°) with respect to the plane of the waveguide. The ridge can have a height in the range of 10 nm to 1,000 nm (for example, 50 nm to 500 nm, 100 nm to 400 nm, 200 nm to 400 nm, 250 nm to 350 nm). The ridge can have a pitch in the range of 100 nm to 5,000 nm (for example, 100 nm to 2,500 nm, 100 nm to 1,000 nm, 200 nm to 750 nm, 250 nm to 500 nm, 300 nm to 400 nm, 100 nm to 200 nm). The ridge can have a duty cycle in the range of 20% to 100% (for example, 10% to 75%, 20% to 50%, 30% to 40%).

[0010] The head-mounted display can include a layer of material having the same refractive index as the material forming the ridges of the diffraction structure, and the layer of material is arranged between the waveguide and the diffraction structure. The layer can have a thickness in the range of 5 nm to 50 nm (for example, 10 nm to 30 nm, 10 nm to 20 nm).

[0011] The grating layer can include a grating material having a refractive index of 1.5 or greater (for example, 1.6 or greater, 1.7 or greater, 1.8 or greater, 1.9 or greater) at the operating wavelength.

[0012] The head-mounted display can include an input coupling grating (ICG) arranged to couple light into the waveguide, and the ICG and the diffraction structure are arranged on the same side of the waveguide.

[0013] In some examples, the head-mounted display can include an input coupling grating (ICG) arranged to couple light into the waveguide, and the ICG and the diffraction structure are arranged on opposite sides of the waveguide.

[0014] The diffractive structure can be a component of an exit pupil expander (EPE) or a compound pupil expander (CPE) of a head-mounted display. The diffractive structure can be a first diffractive structure, and the EPE or CPE further includes a second diffractive structure on the side opposite to the first diffractive structure of the waveguide.

[0015] The diffractive structure can include a plurality of zones, and the structure of the grating layer in at least two of the zones is different. The grating structure of the grating layer can change abruptly from a first zone to a second zone adjacent to the first zone. In some examples, the grating structure of the grating layer changes continuously across the area of the diffractive structure.

[0016] At least some of the ridges can have a single-step shape.

[0017] Alternatively or additionally, at least some of the ridges have a multi-step geometry. The ridges having a multi-step geometry can include steps having a slope-like geometry.

[0018] The diffractive structure can direct at least 100% more light guided by the waveguide to the user side than to the world side.

[0019] The diffractive structure can direct at least 4% (e.g., 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 11% or more, 12% or more, 13% or more, 14% or more, 15% or more, up to 20% etc.) of the light from the waveguide to the user side.

[0020] The grating layer can be etched within the waveguide. Alternatively, the grating layer can be formed within a layer of material deposited on the waveguide (e.g., a layer of material having a refractive index in the range of 1.5 to 2.7).

[0021] The diffraction structure can include a layer of material deposited on the ridges of the grating layer. The layer of material can be deposited on fewer surfaces rather than all surfaces of the ridge. The layer of material can be deposited on all surfaces of the ridge. The layer of material can have a refractive index in the range of 1.7 to 2.7. The layer of material can have a refractive index in the range of 1.3 to 1.5.

[0022] Other features and advantages will become apparent from the drawings, the following description, and the claims.

Brief Description of the Drawings

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[0058] Throughout the drawings, reference numerals may be reused to indicate correspondence between referenced elements. The figures are provided to illustrate exemplary embodiments described herein and are not intended to limit the scope of the present disclosure. DETAILED DESCRIPTION

[0059] Detailed Description An AR system can display virtual content to a user or viewer while enabling the user to see the surrounding world. Preferably, this content is displayed on a head - mounted display that projects image information onto the user's eyes, for example as part of eyewear. Additionally, the display can also transmit light from the surrounding environment to the user's eyes to enable a view of its surrounding environment. As used herein, it will be understood that a “head - mounted” or “head - mountable” display is a display that can be worn on the head of a viewer or user.

[0060] In some AR systems, a virtual / augmented / mixed display having a relatively high field of view (FOV) can improve the viewing experience. The FOV of a display depends on the angle of the light output by the waveguide of the eyepiece through which the viewer sees the image projected onto their eye. Waveguides having a relatively high refractive index, such as a refractive index of 2.0 or greater, can provide a relatively high FOV. However, in order to efficiently couple light into a high refractive index waveguide, the diffractive optical coupling element must also correspondingly have a high refractive index. To achieve this goal, among other advantages, some displays for AR systems according to the embodiments described herein include waveguides having a material with a relatively high refractive index (e.g., 2.0 or greater) with respective diffraction gratings having a corresponding high refractive index, such as Li-based oxides, formed thereon. For example, the diffraction grating may be formed directly on the Li-based oxide waveguide by patterning a surface portion of the waveguide formed of the Li-based oxide.

[0061] Some high refractive index diffractive optical coupling elements, such as in-coupling or out-coupling optical elements, have strong polarization dependence. For example, an in-coupling grating (ICG) for in-coupling light into a waveguide in which the diffractive optical coupling element includes a high refractive index material can admit much more light of a given polarization than light of another polarization. Such an element can, for example, in-couple light having TM polarization into the waveguide at approximately three times the speed of light having TE polarization. Diffractive optical coupling elements having this type of polarization dependence can sometimes reduce efficiency (due to the low efficiency and overall elimination of one polarization), and can also create coherent artifacts and reduce the uniformity of the far-field image formed by the light coupled out of the waveguide. To obtain diffractive optical coupling elements that do not respond to polarization or at least reduce polarization sensitivity (e.g., couple light with relatively polarization-independent efficiency), some displays for AR systems according to various implementations described herein include waveguides having diffractive gratings formed in a blazed geometry. The diffractive grating may also be formed directly within the waveguide, which may include a high refractive index material (e.g., having a refractive index up to at least 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, or 2.7, or any range of values between any of these values). The diffractive grating may be formed, for example, by patterning a high refractive index material in a blazed geometry within a Li-based oxide such as lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), or within a high refractive index material such as zirconium dioxide (ZrO2), titanium dioxide (TiO2), or silicon carbide (SiC).

[0062] Reference is now made to the drawings, in which like reference numerals refer to like parts throughout. Unless otherwise indicated, the drawings are schematic diagrams and are not necessarily drawn to scale.

[0063] Figure 2 shows a conventional display system for simulating a three-dimensional image of a user. The user's eyes are separated, and when looking at an actual object in space, each eye has a slightly different view of the object and can form an image of the object at different positions on the retina of each eye. This can be called binocular disparity and can be utilized by the human visual system to provide a perception of depth. The conventional display system simulates binocular disparity by presenting two separate images 190, 200, each with a slightly different view of the same virtual object, to each eye 210, 220 corresponding to the views of the virtual object as seen by each eye 210, 220 when the virtual object is a real object at the desired depth. These images provide binocular cues that the user's visual system can interpret to derive a perception of depth.

[0064] Continuing to refer to Figure 2, the images 190, 200 are separated by a distance 230 along the z-axis from the eyes 210, 220. The z-axis is parallel to the viewer's optical axis, and at this time the viewer's eyes are fixated on an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on the slightly different views of the virtual object within the images presented to the eyes 210, 220 respectively, the eyes naturally rotate so that the images of the object fall on corresponding points on the retina of each eye in order to maintain a single binocular vision. This rotation can converge the lines of sight of each of the eyes 210, 220 to a point in the space where the virtual object is perceived to exist. As a result, providing a three-dimensional image has conventionally involved being able to manipulate the convergence / divergence movement of the user's eyes 210, 220 and providing binocular cues that the human visual system interprets to provide a perception of depth.

[0065] However, generating realistic and comfortable depth perception is difficult. It will be understood that light from objects at different distances from the eye has wavefronts with different amounts of divergence. FIGS. 3A-3C illustrate the relationship between the distance and divergence of light rays. The distances between the object and the eye 210 are represented by R1, R2, and R3 in decreasing order of distance. As shown in FIGS. 3A-3C, the light rays diverge more as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, it may be said that the light field produced by a point (an object or a part of an object) has a spherical wavefront curvature that is a function of how far that point is from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. Only a single eye 210 is shown in FIGS. 3A-3C and the other figures in this specification to clarify the explanation, but the discussion regarding the eye 210 may apply to both eyes 210 and 220 of the viewer.

[0066] Continuing to refer to FIGS. 3A-3C, light from the object at which the viewer's eye is gazing can have different degrees of wavefront divergence. Because of the different amounts of wavefront divergence, the light can be focused differently by the eye's lens, and the lens may need to take on different shapes in order to form a focused image on the eye's retina. If a focused image is not formed on the retina, the resulting retinal blur serves as a cue for accommodation to change the shape of the eye's lens until a focused image is formed on the retina. For example, the cue for accommodation triggers the ciliary muscle surrounding the eye's lens to relax or contract, thereby adjusting the force applied to the suspensory ligament that holds the lens, and thus changing the shape of the eye's lens until the blur of the retina of the gazing object is eliminated or minimized, thereby forming a focused image of the gazing object on the eye's retina (e.g., the fovea). The process by which the eye's lens changes shape may be referred to as accommodation, and the shape of the eye's lens required to form a focused image of the gazing object on the eye's retina (e.g., the fovea) may be referred to as the accommodative state.

[0067] Next, referring to FIG. 4A, the expression of the accommodation - convergence / divergence movement response of the human visual system is shown. The movement of the eyes to fixate on an object causes the eyes to receive light from the object, and the light forms 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 for accommodation, and the relative position of the image on the retina may provide a cue for convergence / divergence movement. The cue for accommodation causes accommodation to occur, and as a result, each lens of the eye assumes a specific accommodation state that forms a focused image of the object on the retina of the eye (e.g., the fovea). On the other hand, the cue for convergence / divergence movement causes the movement (rotation of the eyes) of convergence / divergence to occur such that the images formed on each retina of each eye are at corresponding retinal points that maintain a single binocular vision. At these positions, the eyes may be said to assume a specific convergence / divergence movement state. Continuing to refer to FIG. 4A, accommodation may be understood as the process by which the eyes achieve a specific accommodation state, and convergence / divergence movement may be understood as the process by which the eyes achieve a specific convergence / divergence movement state. As shown in FIG. 4A, when the user fixates on another object, the accommodation state and the convergence / divergence movement state of the eyes can change. For example, the accommodation state can change when the user fixates on a new object at a different depth on the z - axis.

[0068] Without being limited by theory, it is considered that the viewer of an object can perceive the object as "three - dimensional" by a combination of convergence / divergence movement and accommodation. As noted above, the movement of convergence / divergence of the two eyes relative to each other (e.g., the rotation of the eyes such that the pupils move closer to or away from each other to converge the line of sight of the eyes to fixate on an object) is closely associated with the accommodation of the lenses of the eyes. Under normal conditions, changing the shape of the lens of the eye to change the focus from one object to another object at a different distance automatically causes a corresponding change in the convergence / divergence movement for the same distance under the relationship known as the "accommodation - convergence / divergence reflex". Similarly, a change in convergence / divergence movement causes a corresponding change in the shape of the lens under normal conditions.

[0069] Referring now to FIG. 4B, examples of different focusing states and convergence / divergence movement states of the eyes are shown. The pair of eyes 222a is gazing at an object at optical infinity, and the pair of eyes 222b is gazing at an object 221 that is less than optical infinity. In particular, when the pair of eyes 222a is facing straight ahead and the pair of eyes 222 is converging on the object 221, the convergence / divergence movement states of each pair of eyes are different. The focusing states of the eyes forming each pair 222a and 222b of eyes are also different, as represented by the different shapes of the crystalline lenses 210a, 220a.

[0070] Unfortunately, many users of conventional "3D" display systems are uncomfortable with such conventional systems or may not perceive any sense of depth due to the mismatch between the focusing state and the convergence / divergence movement state in these displays. As noted above, many stereoscopic or "3D" display systems display a scene by providing slightly different images to each eye. Such systems merely provide different presentations of the scene, in particular, and cause a change in the convergence / divergence movement state of the eyes, but there is no corresponding change in the focusing state of those eyes, which is uncomfortable for many viewers. Rather, the images are presented by a display at a fixed distance from the eyes, whereby the eyes view all the image information in a single focusing state. Such an arrangement adversely affects the "accommodation-convergence / divergence reflex" by causing a change in the convergence / divergence movement state without a coordinated change in the focusing state. This mismatch is thought to cause discomfort to the viewer. A display system that provides better alignment between accommodation and convergence / divergence movement can create a more realistic and comfortable simulation of three-dimensional images.

[0071] Although not limited by theory, the human eye is generally thought to be able to interpret a finite number of depth planes to provide depth perception. As a result, a very realistic simulation of perceived depth can be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. In some embodiments, the different presentations may provide both cues to convergence / divergence motion and consistent cues to accommodation, thereby providing physiologically correct accommodation-convergence / divergence motion consistency.

[0072] Continuing to refer to FIG. 4B, two depth planes 240 corresponding to different distances in space from eyes 210, 220 are shown. For a given depth plane 240, the convergence / divergence motion cues can be provided by appropriately displaying images of different viewpoints for each eye 210, 220. Additionally, for a given depth plane 240, the light forming the images provided to each eye 210, 220 may have wavefront divergence corresponding to the light field generated by a point at the distance of that depth plane 240.

[0073] In the illustrated embodiment, the distance along the z-axis of depth plane 240 including point 221 is 1 m. As used herein, the distance or depth along the z-axis can be measured at a zero point located at the exit pupil of the user's eye. Thus, the depth plane 240 located at a depth of 1 m corresponds to a distance 1 m away from the exit pupil of the user's eye on the optical axis of these eyes when the eyes are directed at optical infinity. As an approximation, the depth or distance along the z-axis can be measured by adding the value of the distance between the device and the exit pupil of the user's eye from a display in front of the user's eye (e.g., from the surface of a waveguide). That value may be referred to as 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 of eye relief may be a normalized value commonly used for all viewers. For example, it may be assumed that the eye relief is 20 mm, and the depth plane at a depth of 1 m may be at a distance of 980 mm in front of the display.

[0074] Next, referring to FIGS. 4C and 4D, examples of the matched near - far adjustment - convergence / divergence movement distances and the mismatched near - far adjustment - convergence / divergence movement distances are shown respectively. As shown in FIG. 4C, the display system may provide an image of a virtual object to each of the eyes 210, 220. The image may cause the eyes 210, 220 to assume a convergence / divergence movement state in which the eyes converge on a point 15 on the depth plane 240. Additionally, the image may be formed by light having a wavefront curvature corresponding to the real object on the depth plane 240. As a result, both eyes 210, 220 assume a near - far adjustment state in which the image is in focus on the retinas of these eyes. Thus, the user may perceive the virtual object as being at the point 15 on the depth plane 240.

[0075] It will be appreciated that each of the near - far adjustment state and the convergence / divergence movement state of the eyes 210, 220 is associated with a specific distance on the z - axis. For example, an object at a specific distance from the eyes 210, 220 causes those eyes to assume a specific near - far adjustment state based on the distance of the object. The distance associated with a specific near - far adjustment state may be referred to as the accommodation distance Ad. Similarly, there is a specific convergence / divergence movement distance Vd, or a position relative to each other, associated with the eyes in a specific convergence / divergence movement state. When the accommodation distance and the convergence / divergence movement distance are matched, the relationship between accommodation and convergence / divergence movement can be said to be physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0076] However, in a stereoscopic display, the focus adjustment distance and the convergence / divergence movement distance may not always match. For example, as shown in FIG. 4D, the images displayed on eyes 210 and 220 can be displayed with wavefront divergence corresponding to depth plane 240, and eyes 210 and 220 can take a specific focus adjustment state focused on points 15a and 15b on that depth plane. However, the images displayed on eyes 210 and 220 can provide a cue for the convergence / divergence movement that converges eyes 210 and 220 on a point 15 that is not located on depth plane 240. As a result, in some embodiments, the focus adjustment distance corresponds to the distance from the exit pupils of eyes 210 and 220 to depth plane 240, while the convergence / divergence movement distance corresponds to a greater distance from the exit pupils of eyes 210 and 220 to point 15. The focus adjustment distance is different from the convergence / divergence movement distance. As a result, there is a focus adjustment - convergence / divergence movement mismatch. Such a mismatch is considered undesirable and may cause discomfort to the user. It will be understood that the mismatch corresponds to a distance (e.g., Vd - Ad) and can be characterized using diopters.

[0077] It will be understood that in some embodiments, a reference point other than the exit pupils of eyes 210 and 220 may be used to determine the distance for determining the focus adjustment - convergence / divergence movement mismatch as long as that reference point is used for the focus adjustment distance and the convergence / divergence movement distance. For example, the distance may be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., the waveguide of the display device) to the depth plane, etc.

[0078] Although not limited by theory, a user may still perceptually consider vergence-accommodation disparities of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters to be physiologically correct, and the disparities themselves are thought not to cause significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250 of FIG. 6) presents an image to a viewer having a vergence-accommodation disparity of about 0.5 diopters or less. In some other embodiments, the vergence-accommodation disparity of an image provided by the display system is about 0.33 diopters or less. In still other embodiments, the vergence-accommodation disparity of an image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0079] FIG. 5 shows aspects of a technique for simulating a three-dimensional image by modifying wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to the user's eye 210. The waveguide 270 may output light 650 with a prescribed amount of wavefront divergence corresponding to the wavefront divergence of the light field generated by a point on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on that depth plane. Additionally, it is shown that image information may be provided to the user's other eye from a similar waveguide.

[0080] In some embodiments, a single waveguide may be configured to output light having 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 within a limited wavelength range. As a result, in some embodiments, multiple waveguides or a stack of waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or to output light within different wavelength ranges. It will be appreciated that as used herein, a depth plane may be planar or may follow the contour of a curved surface.

[0081] FIG. 6 shows an example of a stack of waveguides for outputting image information to a user. The display system 250 includes a stack of waveguides or a stacked waveguide assembly 260 that can be utilized to provide a three-dimensional perception to the eye / brain using a plurality of waveguides 270, 280, 290, 300, 310. It will be appreciated that in some embodiments, the display system 250 may be considered a light field display. Additionally, the waveguide assembly 260 may also be referred to as an eyepiece.

[0082] In some embodiments, the display system 250 is configured to provide a substantially continuous cue to the convergence / divergence motion and a plurality of individual cues to the focus adjustment. The cue to the convergence / divergence motion can be provided by displaying different images to each of the user's eyes, and the cue to the focus adjustment may be provided by outputting light that forms an image with a selectable discrete amount of wavefront divergence. Stated another way, the display system 250 may be configured to output light having a variable level of wavefront divergence. In some embodiments, each discrete level of wavefront divergence may correspond to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, 310.

[0083] Continuing to refer to FIG. 6, waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some embodiments, features 320, 330, 340, 350 may be one or more lenses. 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 ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image input devices 360, 370, 380, 390, 400 may function as light sources for the waveguides and may be utilized to input image information into waveguides 270, 280, 290, 300, 310, and each of the waveguides may be configured to distribute incident light across each respective waveguide for output toward eye 210, as described herein. Light exits the output surfaces 410, 420, 430, 440, 450 of image input devices 360, 370, 380, 390, 400 and is input into the corresponding input surfaces 460, 470, 480, 490, 500 of waveguides 270, 280, 290, 300, 310. In some embodiments, each of input surfaces 460, 470, 480, 490, 500 may be at the edge of the corresponding waveguide or may be a portion of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces facing directly the world 510 or viewer's eye 210). In some embodiments, a single light beam (e.g., a collimated beam) may be input into each waveguide to output a full field of cloned collimated beams, and the cloned collimated beams are directed toward eye 210 at a particular angle (and divergence amount) corresponding to the depth plane associated with a particular waveguide. In some embodiments, a single one of image input devices 360, 370, 380, 390, 400 may be associated with and input light into a plurality (e.g., three) of waveguides 270, 280, 290, 300, 310.

[0084] In some embodiments, the image input devices 360, 370, 380, 390, 400 are individual displays each generating image information for input into the corresponding waveguides 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output ends of a single multiplexed display that can send image information, for example, via one or more light guides (such as an optical fiber cable), to each of the image input devices 360, 370, 380, 390, 400. It will be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different component colors as discussed herein).

[0085] In some embodiments, the light input into the waveguides 270, 280, 290, 300, 310 is provided by an optical projector system 520 comprising an optical module 530 that may include a light emitter such as a light emitting diode (LED). The light from the optical module 530 may be directed via a beam splitter 550 to a light modulator 540 such as, for example, a spatial light modulator, where it may be modified. The light modulator 540 may be configured to change the perceived intensity of the light input into the waveguides 270, 280, 290, 300, 310 in order to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs) including liquid crystal on silicon (LCOS) displays. The image input devices 360, 370, 380, 390, 400 are shown schematically and, in some embodiments, it will be understood that these image input devices may represent different optical paths and positions within a common projection system configured to output light to the relevant ones of the waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of the waveguide assembly 260 may function as an ideal lens while relaying the light input into the waveguide to the user's eye. In this concept, the object may be the spatial light modulator 540 and the image may be an image on a depth plane.

[0086] In some examples, the μLED display can be used in an optical projector system 520. The μLED display can be unpolarized over a wide range of angles. Thus, the μLED display can usefully provide an image over a wide field of view with high efficiency.

[0087] In some embodiments, the display system 250 may be a scanning fiber display having one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.) onto one or more waveguides 270, 280, 290, 300, 310 and ultimately to the viewer's eye 210. In some embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to input light into one or more of the waveguides 270, 280, 290, 300, 310. In some embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers each configured to input 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 optical module 530 to one or more of the 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, for example, to redirect the light exiting the scanning fiber into the one or more waveguides 270, 280, 290, 300, 310.

[0088] Controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of the image input devices 360, 370, 380, 390, 400, the light source 530, and the light modulator 540. In some embodiments, controller 560 is part of the local data processing module 140. Controller 560 includes programming (e.g., instructions in a non-transitory medium) that adjusts the timing and provision of image information to waveguides 270, 280, 290, 300, 310, for example, by any of the various methods disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by a wired or wireless communication channel. Controller 560 may be part of processing module 140 or 150 (FIG. 9D) in some embodiments.

[0089] Continuing to refer to FIG. 6, waveguides 270, 280, 290, 300, 310 can be configured to propagate light within each respective waveguide by total internal reflection (TIR). Waveguides 270, 280, 290, 300, 310 may each be planar or may have another shape (e.g., curved), and have a major top surface and a major bottom surface, and an edge extending between their major top surface and major bottom surface. In the illustrated configuration, waveguides 270, 280, 290, 300, 310 may each include outcoupling optical elements 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting light propagating within each respective waveguide out of the waveguide to output image information to the eye 210. The extracted light may be referred to as outcoupled light, and the outcoupling optical element light may be referred to as a light extraction optical element. The extracted light beam may be output by the waveguide at the location where the light propagating within the waveguide impinges on the light extraction optical element. Outcoupling optical elements 570, 580, 590, 600, 610 may be, for example, gratings including diffractive optical features, as further described herein. For ease of explanation and clarity of the drawings, outcoupling optical elements 570, 580, 590, 600, 610 are shown disposed on the bottom major surface of waveguides 270, 280, 290, 300, 310, but in some embodiments, as further discussed herein, they may be disposed on the upper and / or bottom major surfaces and / or may be disposed directly within the volume of waveguides 270, 280, 290, 300, 310. In some embodiments, outcoupling optical elements 570, 580, 590, 600, 610 may be formed within a layer of material attached to a transparent substrate to form waveguides 270, 280, 290, 300, 310. In some other embodiments, waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material, and outcoupling optical elements 570, 580, 590, 600, 610 may be formed on the surface and / or within the material piece.

[0090] Continuing to refer to FIG. 6, as discussed herein, each of the waveguides 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 closest to the eye may be configured to deliver collimated light (input to such waveguide 270) to the eye 210. The collimated light may represent an optically infinite focal plane. The waveguide 280 above that may be configured to output collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such a first lens 350 may be configured to create a slightly convex wavefront curvature such that the eye / brain interprets the light coming from the adjacent waveguide 280 above it as coming from a first focal plane closer inwardly toward the eye 210 from the optically infinite. Similarly, the third waveguide 290 above outputs its light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive power of the first lens 350 and the second lens 340 may be configured to generate another incremental amount of wavefront curvature such that the eye / brain interprets the light coming from the third waveguide 290 as coming from a second focal plane even closer inwardly toward the person from the optically infinite than the light from the waveguide 280 above it.

[0091] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, and the highest waveguide 310 in the stack sends its output through all the lenses between it and the eye for the aggregated focusing power representing the focal plane closest to that person. A compensation lens layer 620 may be disposed on top of the stack 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, to compensate for the aggregated power of the lower lens stack 320, 330, 340, 350. Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairings. Both the outcoupling optical element of the waveguide and the focusing aspect of the lens may be static (i.e., not dynamic or electrically active). In some alternative embodiments, either or both may be dynamic using electrically active features.

[0092] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, a plurality of waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same multiple depth planes, one set for each depth plane. This can provide an advantage for forming tiled images to provide an extended field of view at those depth planes.

[0093] Continuing to refer to FIG. 6, the outcoupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light from their respective waveguides and output this light with an appropriate amount of divergence or collimation with respect to a particular depth plane associated with the waveguide. As a result, waveguides having different associated depth planes may have different configurations of the outcoupling optical elements 570, 580, 590, 600, 610 that output light having different amounts of divergence according to the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 may be volume features or surface features that may be configured to output light at specific angles. For example, the light extraction optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, 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 voids).

[0094] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffraction features that form a diffraction pattern, i.e., a “diffractive optical element” (also referred to herein as “DOE”). Preferably, the DOE has a sufficiently low diffraction efficiency such that only a portion of the light of the beam is deflected towards the eye 210 at each intersection of the DOE, and the remainder continues to travel through the waveguide via TIR. Thus, the light carrying the image information is split into several associated emission beams that exit the waveguide at multiple locations, and the result is a fairly uniform pattern of emission radiation towards the eye 210 for this particular collimated beam that bounces back within the waveguide.

[0095] In some embodiments, one or more DOEs may be switchable between an “on” state where they actively diffract and an “off” state where they do not significantly diffract. For example, a switchable DOE may include a layer of polymer dispersed liquid crystal, in which the microdroplets contain 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 diffract enough to recognize the incident light), or the microdroplets may be switched to a refractive index that does not match the refractive index of the host medium (in which case the pattern actively diffracts the incident light).

[0096] In some embodiments, a camera assembly 630 (e.g., a digital camera including visible and infrared cameras) may be provided to capture an image of the eye 210 and / or the tissue surrounding the eye 210, for example, to detect user input and / or monitor the user's physiological state. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source for projecting light (e.g., infrared light) into the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be attached to the frame 80 (FIG. 9D) and may be in electrical communication with a processing module 140 and / or 150 that can process the image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized for each eye to monitor each eye separately.

[0097] Next, referring to FIG. 7, an example of an injection beam output by a waveguide is shown. Although one waveguide is shown, it will be understood that if the waveguide assembly 260 includes a plurality of waveguides, other waveguides (FIG. 6) within the waveguide assembly 260 may function similarly. Light 640 is input into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as the injection beam 650. The injection beam 650 is shown as being substantially parallel, but as discussed herein, it may be redirected to propagate at an angle (e.g., to form a diverging injection beam) to the eye 210 depending on the depth plane associated with the waveguide 270. A substantially parallel injection beam may be shown for a waveguide having an outcoupling optical element that outcouples light to form an image that appears 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 outcoupling optical elements may output an injection beam pattern that is more divergent, which requires the eye 210 to focus at a closer distance for focusing on the retina and is interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0098] In some embodiments, a full-color image may be formed on each depth plane by superimposing images of each of the component colors, e.g., three or more component colors. FIG. 8 shows an example of a stacked waveguide assembly in which each depth plane includes an image formed using a plurality of different component colors. The illustrated embodiment shows depth planes 240a-240f, although more or fewer depths are contemplated. Each depth plane may have three or more component color images associated therewith, which may include 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 shown in the figure by different numbers of diopters (dpt) following the letters G, R, and B. As an example, the number following each of these letters indicates the diopter (1 / m) or inverse distance of the depth plane from the viewer, and each box in the figure represents an individual component color image. In some embodiments, the exact arrangement of the depth planes of different component colors may vary to account for differences in the focus of the eye for light of different wavelengths. For example, the different component color images for a given depth plane may be arranged on the depth plane corresponding to different distances from the user. Such an arrangement may improve visual acuity and user comfort and / or reduce chromatic aberration.

[0099] In some embodiments, the light of each component color may be output by a single dedicated waveguide, and as a result, each depth plane may have a plurality of waveguides associated therewith. In such embodiments, it may be understood that each box in the figure containing the letter G, R, or B represents an individual waveguide, and three waveguides may be provided for each depth plane, in which case three component color images are provided for each depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this figure for ease of explanation, but it will be understood that in a physical device, all of the waveguides may be arranged in a stack having one waveguide per level. In some other embodiments, for example, a plurality of component colors may be output by the same waveguide such that only a single waveguide is provided for each depth plane.

[0100] Continuing to refer to FIG. 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with light of other wavelengths, including magenta and cyan, may be used in addition to, or in place of, red, green, or blue.

[0101] It will be understood that references throughout this disclosure to a given color of light are understood to encompass light of one or more wavelengths within the wavelength range of light that is 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.

[0102] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light of one or more wavelengths outside the viewer's visual range, such as infrared and / or ultraviolet wavelengths. Additionally, the waveguide in-coupling, out-coupling, and other light redirecting structures of the display 250 may be configured to direct and emit this light from the display towards the user's eye 210, for example, for imaging and / or user stimulation applications.

[0103] Next, referring to FIG. 9A, in some embodiments, light that impinges on a waveguide may need to be redirected to couple the light into the waveguide. An incoupling optical element may be used to redirect and incouple the light into its corresponding waveguide. FIG. 9A shows a cross-sectional side view of an example of a plurality or set 660 of stacked waveguides each including an incoupling optical element. The waveguides may each be configured to output light at one or more different wavelengths, or one or more different wavelength ranges. The stack 660 may correspond to the stack 260 (FIG. 6), except that light from one or more of the image input devices 360, 370, 380, 390, 400 is input into the waveguides from a location that requires the light to be redirected for incoupling. It will be appreciated that the illustrated waveguides of the stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310.

[0104] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes, for example, an in-coupling optical element 700 disposed on a major surface (e.g., the upper major surface) of waveguide 670, an in-coupling optical element 710 disposed on a major surface (e.g., the upper major surface) of waveguide 680, and an in-coupling optical element 720 disposed on a major surface (e.g., the upper major surface) of waveguide 690, including associated in-coupling optical elements (which may also be referred to as light input areas on the waveguide). In some embodiments, one or more of the in-coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of their respective waveguides 670, 680, 690 (particularly if one or more of the 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 (or the upper part of the next lower waveguide) of their respective waveguides 670, 680, 690, particularly if those in-coupling optical elements are transmissive deflecting optical elements. In some embodiments, the in-coupling optical elements 700, 710, 720 may be disposed within the body of their respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the in-coupling optical elements 700, 710, 720 are wavelength selective, whereby they selectively redirect one or more wavelengths of light while transmitting light of other wavelengths. Although shown on one side or corner of their respective waveguides 670, 680, 690, it will be understood that in some embodiments, the in-coupling optical elements 700, 710, 720 may be disposed within other areas of their respective waveguides 670, 680, 690.

[0105] As shown, the in-coupling optical elements 700, 710, 720 may be laterally offset from each other. In some embodiments, each in-coupling optical element may be offset such that light is received without passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from different image input devices 360, 370, 380, 390, and 400, as shown in FIG. 6, and may be separated (e.g., laterally spaced) from other in-coupling optical elements 700, 710, 720 such that light is not substantially received from another one of the other in-coupling optical elements 700, 710, 720.

[0106] Each waveguide may also include an associated optical distribution element having, for example, an optical distribution element 730 disposed on a major surface (e.g., an upper major surface) of waveguide 670, an optical distribution element 740 disposed on a major surface (e.g., an upper major surface) of waveguide 680, and an optical distribution element 750 disposed on a major surface (e.g., an upper major surface) of waveguide 690. In some other embodiments, the optical distribution elements 730, 740, 750 may be disposed on the bottom major surfaces of the associated waveguides 670, 680, 690, respectively. In some other embodiments, the optical distribution elements 730, 740, 750 may be disposed on both the upper and bottom major surfaces of the associated waveguides 670, 680, 690, respectively, or the optical distribution elements 730, 740, 750 may be disposed on different ones of the upper and bottom major surfaces of different associated waveguides 670, 680, 690.

[0107] Waveguides 670, 680, 690 may be separated and isolated, for example, by gas, liquid, and / or solid material layers. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the immediate adjacent of waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or more or 0.10 or less lower than the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the low refractive index layers 760a, 760b may function as cladding layers that facilitate total internal reflection (TIR) of light passing through waveguides 670, 680, 690 (e.g., TIR between the upper major surface and the lower major surface of each waveguide). In some embodiments, layers 760a, 760b are formed from air. Although not shown, it will be understood that the top and bottom of the illustrated set 660 of waveguides may include directly adjacent cladding layers.

[0108] Preferably, for ease of manufacture and other considerations, the materials forming waveguides 670, 680, 690 are similar or identical, and the materials forming layers 760a, 760b are similar or identical. In some embodiments, the materials forming waveguides 670, 680, 690 may be different between one or more waveguides, and / or the materials forming layers 760a, 760b may be different while still maintaining the various refractive index relationships noted above.

[0109] Continuing to refer to FIG. 9A, light rays 770, 780, 790 are incident on the set 660 of waveguides. It will be understood that light rays 770, 780, 790 may be input into waveguides 670, 680, 690 by one or more image input devices 360, 370, 380, 390, 400 (FIG. 6).

[0110] In some embodiments, the light rays 770, 780, 790 may have different characteristics, e.g., different wavelengths or different wavelength ranges corresponding to different colors. Each of the incoupling optical elements 700, 710, 720 deflects the incident light so that the light propagates through one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optical elements 700, 710, 720 selectively deflects one or more specific wavelengths of light while transmitting other wavelengths to the underlying waveguide and the associated incoupling optical element.

[0111] For example, the incoupling optical element 700 may be configured to deflect the light ray 770 having a first wavelength or wavelength range while transmitting the light rays 780 and 790 each having different second and third wavelengths or wavelength ranges. The transmitted light ray 780 impinges on the incoupling optical element 710 configured to deflect the light of the second wavelength or wavelength range and is thereby deflected. The light ray 790 is deflected by the incoupling optical element 720 configured to selectively deflect the light of the third wavelength or wavelength range.

[0112] Continuing to refer to FIG. 9A, the deflected light rays 770, 780, 790 are deflected so that they propagate through their corresponding waveguides 670, 680, 690. That is, the incoupling optical elements 700, 710, 720 of each waveguide deflect the light to their corresponding waveguides 670, 680, 690 to incouple the light into the corresponding waveguides. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through their respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through their respective waveguides 670, 680, 690 by TIR until they impinge on the corresponding optical distribution elements 730, 740, 750 of the waveguides.

[0113] FIG. 9B shows a perspective view of an example of the plurality of stacked waveguides of FIG. 9A. As noted above, the in-coupled light rays 770, 780, 790 are each deflected by the in-coupling optical elements 700, 710, 720 and then propagate by TIR within the waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then impinge on the optical splitting elements 730, 740, 750, respectively. The optical splitting elements 730, 740, 750 deflect the light rays 770, 780, 790 so as to propagate towards the out-coupling optical elements 800, 810, 820, respectively.

[0114] In some embodiments, the optical distribution elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or distribute light to the out-coupling optical elements 800, 810, 820, and in some embodiments, as this light propagates to the out-coupling optical elements, the beam or spot size of this light may be increased. In some embodiments, the optical distribution elements 730, 740, 750 may be omitted, and the in-coupling optical elements 700, 710, 720 may be configured to directly deflect light to the out-coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the optical distribution elements 730, 740, 750 may each be replaced by out-coupling optical elements 800, 810, 820. In some embodiments, the out-coupling optical elements 800, 810, 820 are an exit pupil (EP) or an exit pupil expander (EPE) that guides light to the viewer's eye 210 (FIG. 7). The OPE may be configured to increase the size of the eyebox in at least one axis, and it will be understood that the EPE may increase the eyebox in an axis that intersects, for example, is orthogonal to, the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light impinging on the OPE to the EPE of the same waveguide while allowing the remaining portion of the light to continue to propagate through the waveguide. When it hits 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 through the waveguide, and so on. Similarly, when it hits the EPE, a portion of the impinging light is directed from the waveguide to the user, and the remaining portion of that light continues to propagate through the waveguide until it hits the EP again, at which point another portion of the impinging light is derived from the waveguide, and so on. As a result, a single in-coupled light beam is "replicated" each time a portion of that light is redirected by the OPE or EPE, thereby forming a field of cloned light beams as shown in FIG. 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the light beam.

[0115] Thus, referring to FIGS. 9A and 9B, in some embodiments, the waveguide set 660 includes waveguides 670, 680, 690, in-coupling optical elements 700, 710, 720, optical distribution elements (e.g., OPE) 730, 740, 750, and out-coupling optical elements (e.g., EP) 800, 810, 820 for each component color. The waveguides 670, 680, 690 may be stacked with a gap / clad layer between each one. The in-coupling optical elements 700, 710, 720 direct or deflect the incident light into its waveguide (with different in-coupling optical elements receiving light of different wavelengths). The light then propagates at an angle within each of the waveguides 670, 680, 690 to provide TIR. In the illustrated example, the ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 and then bounces through the waveguide and interacts with the optical distribution element (e.g., OPE) 730 and then the out-coupling optical element (e.g., EP) 800 in the manner described previously. The rays 780 and 790 (e.g., green light and red light respectively) pass through the waveguide 670, where the ray 780 hits the in-coupling optical element 710 and is thereby deflected. The ray 780 then bounces down through the waveguide 680 via TIR and proceeds to its optical distribution element (e.g., OPE) 740 and then the out-coupling optical element (e.g., EP) 810. Finally, the ray 790 (e.g., red light) passes through the waveguide 690 and hits the in-coupling optical element 720 of the waveguide 690. The in-coupling optical element 720 deflects the ray 790 so that it propagates by TIR to the optical distribution element (e.g., OPE) 750 and then by TIR to the out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the ray 790 to the viewer, who also receives the out-coupled light from the other waveguides 670, 680.

[0116] FIG. 9C shows a top view of an example of a plurality of stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 can be vertically aligned with their associated optical splitting elements 730, 740, 750 and associated out-coupling optical elements 800, 810, 820. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the in-coupling optical elements do not overlap (e.g., are laterally spaced as seen in a top view). As further discussed herein, this non-overlapping spatial arrangement facilitates a one-to-one optical input from different resources to different waveguides, thereby enabling a unique light source to be uniquely coupled to a unique waveguide. In some embodiments, an array including non-overlapping spatially separated in-coupling optical elements may be referred to as a shifted pupil system, and the in-coupling optical elements within these arrays may correspond to sub-pupils.

[0117] Alternatively, in certain embodiments, two or more of the in-coupling optical elements can be in a vertically aligned in-line arrangement. In such an arrangement, light for a waveguide farther from the projection system is preferably transmitted through the in-coupling optical element for the waveguide closer to the projection system with minimal scattering or diffraction.

[0118] The in-line configuration can advantageously reduce and simplify the size of the projector. Further, this can increase the field of view of the eyepiece, for example, by coupling the same color to several waveguides, such as by utilizing crosstalk. For example, green light can be coupled to blue and red active layers. Since the pitch of each ICG can be different to provide improved (e.g., optimal) performance for a particular color, the acceptable field of view can be increased.

[0119] In an inline configuration, except for the last layer in the optical path, the ICG must be at most partially reflective or otherwise transmissive to light having the operating wavelength of subsequent layers in the waveguide stack. In either case, its efficiency can be undesirably low unless the grating is etched in a high refractive index layer (e.g., 1.8 or above in a polymer-based layer) or a high refractive index coating is deposited or grown on the grating. However, this approach can increase back reflection to the projector lens and thus may generate image artifacts such as image ghosts.

[0120] FIG. 9D shows an example of a wearable display system 60 in which various waveguides and related systems disclosed herein can be incorporated. In some embodiments, the display system 60 is the system 250 of FIG. 6, which schematically shows some parts of that system 60 in more detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0121] Continuing to refer to FIG. 9D, the display system 60 includes a display 70 and various mechanical and electronic modules and systems for supporting the functions of the display 70. The display 70 is wearable by a user 90 or viewer of the display system and is coupled to a frame 80 configured to position the display 70 in front of the eyes of the user 90. The display 70 may be considered eyewear in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the outer ear canal of the user 90 (in some embodiments, another speaker, not shown, may be positioned adjacent to the other outer ear canal of the user, if desired, to provide stereo / formable acoustic control). The display system 60 may also include one or more microphones 110 or other devices for detecting sound. In some embodiments, the microphone is configured to enable the user to provide an input or command to the system 60 (e.g., selection of a voice menu command, natural language question, etc.) and / or enable voice communication with other people (e.g., with other users of a similar display system). The microphone may also be further configured as a peripheral sensor for collecting audio data (e.g., sound from the user and / or the environment). In some embodiments, the display system may also include a peripheral sensor 120a that is separate from the frame 80 and can be attached to the body of the user 90 (e.g., on the head, torso, limbs, etc. of the user 90). The peripheral sensor 120a may be configured to obtain data characterizing the physiological state of the user 90 in some embodiments. For example, the sensor 120a may be an electrode.

[0122] Continuing to refer to FIG. 9D, the display 70 is operably coupled to a local data processing module 140 by a communication link 130 such as a wired lead or a wireless connection. The local data processing module can be fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or removably attached to the user 90 in other forms (e.g., a backpack-type configuration, a belt-coupled configuration), etc. Similarly, the sensor 120a can be operably coupled to the local processor and data module 140 by a communication link 120b such as a wired lead or a wireless connection. The local processing and data module 140 may include a hardware processor and digital memory such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which can be used to assist in data processing, caching, and storage. Optionally, the local processor and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. The data may include a) data captured from sensors such as an image capture device (e.g., a camera), a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, a gyro, and / or other sensors disclosed herein (e.g., operably coupled to the frame 80 or attached to the user 90 in another way), and / or b) data obtained and / or processed using the remote processing module 150 and / or the remote data repository 160 (including data related to virtual content), and passed to the display 70 after such processing or retrieval, if possible.The local processing and data module 140 may be operably coupled to the remote processing module 150 and the remote data repository 160 by communication links 170, 180, for example, via a wired or wireless communication link, whereby these remote modules 150, 160 are operably coupled to each other and are available as resources to the local processing and data module 140. In some embodiments, the local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyro. In some other embodiments, one or more of these sensors may be attached to the frame 80 or may be a stand-alone structure that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0123] Continuing to refer to FIG. 9D, in some embodiments, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, such as, for example, one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and the like. In some embodiments, the remote data repository 160 may be a digital data storage facility that may be available via the Internet or other networking configurations within a "cloud" resource configuration. In some embodiments, the remote data repository 160 may include one or more remote servers that provide information to the local processing and data module 140 and / or the remote processing module 150, such as information for generating augmented reality content. In some embodiments, all data is stored and all computations are performed within the local processing and data module to enable full autonomous use from the remote module. Optionally, an external system, such as one or more processors, one or more computer systems, including CPUs, GPUs, etc., may perform at least a portion of the processing (such as generation of image information, processing of data), and provide information to, and receive information from, modules 140, 150, 160, for example, via a wireless or wired connection.

[0124] Diffraction structure for asymmetric light extraction Providing a high-quality immersive experience to users of waveguide-based display systems, such as various display systems configured for virtual / augmented / mixed display applications as described above, depends in particular on various characteristics of the light entering and exiting the waveguide within the eyepiece of the display system. For example, a virtual / augmented / mixed display having high light in-coupling and out-coupling efficiencies can improve the viewing experience by increasing the luminance of the light directed to the user's eye. As discussed above, in-coupling optical elements, such as in-coupling diffraction gratings, can be used to couple light into the waveguide and guide it by total internal reflection. Similarly, out-coupling optical elements, such as out-coupling diffraction gratings, can be used to couple the light guided within the waveguide by total internal reflection from the waveguide.

[0125] As described above, for example, referring to FIGS. 6 and 7, the display systems described herein can include optical elements, such as in-coupling optical elements including diffraction gratings, out-coupling optical elements, light distribution elements, and / or a compound pupil expander-extractor (CPE). The CPE can operate both as a light distribution element that diffuses or distributes light within the waveguide and, in some cases, increases the beam size and / or eye box, and as an out-coupling optical element that couples light from the waveguide.

[0126] For example, as described above with reference to FIG. 7, the light 640 incident into the waveguide 270 at the input surface 460 of the waveguide 270 propagates and is guided within the waveguide 270 by total internal reflection (TIR). In various implementations, at the point where the light 640 impinges on the out-coupling optical element 570, a portion of the light guided within the waveguide can exit the waveguide as a beamlet 650. In some implementations, any of the optical elements 570, 580, 590, 600, 610, which can include one or more of an in-coupling optical element, an out-coupling optical element, a light distribution element, or a CPE, can be configured as a diffraction grating.

[0127] In order to achieve desirable characteristics of optical coupling into and / or outcoupling from waveguides 270, 280, 290, 300, 310, optical elements 570, 580, 590, 600, 610 configured as diffraction gratings can be formed of a suitable material and have a suitable structure for controlling various optical characteristics including diffraction characteristics such as diffraction efficiency as a function of polarization. Possible desirable diffraction characteristics may include, among other characteristics, any one or more of spectral selectivity, angular selectivity, polarization selectivity (or non-selectivity), high spectral bandwidth, high diffraction efficiency or wide field of view (FOV).

[0128] FIG. 10 shows a partial cross-sectional view of a display device 1000, such as an eyepiece lens, having a waveguide 1004 and a blazed diffraction grating 1008 formed on a substrate that is the waveguide 1004, according to some of the designs described herein. In the illustrated implementation, the blazed diffraction grating 1008 is formed within the substrate / waveguide 1004 (which is planar in this example). The surface of the substrate or waveguide 1004 has a surface topography that includes diffraction features that together form the diffraction grating 1008. The blazed diffraction grating 1008 is configured to diffract light having wavelengths in the visible spectrum such that light incident thereon is guided within the waveguide 1004 by TIR. The waveguide 1004 may be transparent and may form part of an eyepiece lens visible to a user's eye. Such a waveguide 1004 and eyepiece lens may be included within a head-mounted display, such as an augmented reality display. The waveguide 1004 can correspond, for example, to one of the waveguides 670, 680, 690 described above with respect to FIGS. 9A-9C. The blazed diffraction grating 1008 can correspond, for example, to one of the incoupling optical elements 700, 710, 720 described above with respect to FIGS. 9A-9C. The blazed diffraction grating 1008 configured to incouple light into the waveguide 1004 may be referred to herein as an incoupling grating (ICG). The display device 1000 may further include an optical element 1012 that can correspond, for example, to a light distribution element (e.g., one of the light distribution elements 730, 740, 750 shown in FIGS. 9A-9C) or an outcoupling optical element (e.g., one of the outcoupling optical elements 800, 810, 820 shown in FIGS. 9A-9C).

[0129] In operation, an incident light beam 1016, such as from an optical projection system providing image content, for example visible light, is incident on the blazed diffraction grating 1008 at an incident angle α measured with respect to the plane normal 1002 that is normal or orthogonal to the extending plane or plane of the blazed diffraction grating, or the surface 1004S of the substrate / waveguide and / or waveguide 1004, for example the major surface of the waveguide on which the grating is formed (shown in FIG. 10 as extending parallel to the y-x plane). The blazed diffraction grating diffracts the incident light beam 1016 at least partially as a diffracted light beam 1024 at a diffraction angle θ measured with respect to the plane normal 1002. When the diffracted light beam 1024 is diffracted at a diffraction angle θ that exceeds the critical angle θTIR for the occurrence of total internal reflection within the waveguide 1004, the diffracted light beam 1024 propagates and is guided within the waveguide 1004 via total internal reflection (TIR) in a direction generally parallel to the x-axis and along the length of the waveguide. A portion of this light guided within the waveguide 1004 can reach, for example, one of the optical distribution elements 730, 740, 750 or one of the outcoupling optical elements (800, 810, 820, FIGS. 9A - 9C) and be diffracted again.

[0130] As described herein, as in the illustrated implementation, a light beam incident at an angle in the clockwise direction with respect to the plane normal 1002 (i.e., on the right side of the plane normal 1002) is called to have a negative α (α < 0), while on the other hand, a light beam incident at an angle in the counterclockwise direction with respect to the plane normal 1002 (i.e., on the left side of the plane normal) is called to have a positive α (α > 0).

[0131] An appropriate combination of the high refractive index material and / or the structure of the diffraction grating 1008 can result in a specific range (Δα) of the incident angle α, which is referred to herein as the acceptance angle range or the field of view (FOV). One range Δα may be described by a range of angles extending to negative and / or positive values of α, outside of which the diffraction efficiency is reduced by 10%, 25%, more than 50%, or 75%, 80%, 90%, more than 95%, or any value within the range defined by any of these values with respect to the diffraction efficiency at α = 0 or in any other direction. In some implementations, it may be desirable to have a Δα within a range where the diffraction efficiency is relatively high and constant. For example, it is desired that the uniform intensity of the diffracted light be within Δα. Thus, in some implementations, Δα is associated with the angular bandwidth of the diffraction grating 1008, whereby the incident light beam 1016 within Δα is efficiently diffracted by the diffraction grating 1008 at a diffraction angle θ (e.g., in a direction parallel to the y - z plane) with respect to the surface normal 1002, where θ exceeds θTIR such that the diffracted light is guided within the waveguide 1004 under total internal reflection (TIR). In some implementations, this angular Δα range can affect the field of view seen by the user. In various implementations, it will be understood that light can be coupled into the incoupling grating (ICG) from either side. For example, light can be guided through the substrate or the waveguide 1004 and incident on a reflective incoupling grating (ICG) 1008 such as that shown in FIG. 10. The light may be subject to the same effect. For example, the light may be coupled to the substrate or the waveguide 1004 by the incoupling grating 1008 such that the light is guided within the substrate or the waveguide by total internal reflection. The range (Δα) of the incident angle α, referred to herein as the acceptance angle range or the field of view (FOV), can be brought about by the refractive index of the substrate or waveguide material. In FIG. 10, for example, a reduced range of angles (Δα’) shows the effect of the refraction of the high refractive index material on the light incident on the incoupling grating (ICG). However, the range of the angle (Δα) or the FOV is larger.

[0132] Both gratings 1008 and 1012 include grating features having peaks 1003 and grooves 1005. The blazed transmission grating 1008 includes a surface corresponding to the surface of the substrate or waveguide 1004S having a "sawtooth" pattern as seen from the illustrated cross-section. The patterned "sawteeth" are formed by the first slope portion 1007 of the surface 1004S. In the example shown in FIG. 10, the grating 1008 also includes a second (steeper) slope portion 1009. In the illustrated example, the first slope portion 1007 has a shallower slope than the second slope portion 1009 having a steeper slope. The first slope portion 1007 is wider than the second slope portion 1009 in this example.

[0133] When configured as an in-coupling optical element or an in-coupling diffraction grating, the diffraction grating 1008 can diffractively couple light incident on the substrate 1004, which can be a waveguide as described above. The diffraction grating 1012 is configured as an out-coupling optical element and diffractively couples light from the substrate 1004, which can also be a waveguide as described above.

[0134] The substrate 1004 can be formed of, for example, a high refractive index material having a refractive index of at least 1.7. The refractive index can be, for example, at least 1.8, at least 1.9, at least 2.0, at least 2.1, at least 2.2, or at least 2.3, and may be 2.4, 2.5, 2.6, 2.7, 2.8 or less, or may be within any range formed by any of these values, or may be outside of these ranges. In some implementations, for example, the substrate includes a Li-based oxide. In various examples disclosed herein, the diffraction features of the diffraction grating 1008 may be formed on the surface of the substrate 1004. The diffraction features may be formed in the substrate 1004, such as in a waveguide, or may be formed in a separate layer formed on the substrate 1004, such as on a waveguide, and may be optically communicated with the substrate 1004 and configured to couple light, for example, inside and outside the substrate 1004. In the illustrated example, the diffraction features of the diffraction grating 1008, such as lines, are formed in the substrate 1004, such as on the surface of the substrate. The diffraction features may be etched, for example, in the substrate 1004 having a high refractive index material such as a Li-based oxide. The substrate may include, for example, lithium niobate, and the diffraction grating may be formed in the lithium niobate substrate by etching or patterning the surface of the substrate. Other materials having a high refractive index may also be used. For example, other materials containing lithium, such as lithium oxide, for example lithium tantalate (LiTaO3), may be employed as the substrate. Silicon carbide (SiC) is another option for the substrate material. The examples are not so limited. In other examples, the diffraction features of the diffraction grating 1008 may be formed in a separate layer, for example, physically contacting, installed on the substrate 1004. For example, a thin film coating less than 200 nm thick, such as zinc oxide (ZnO), silicon nitride (Si3N4), zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), etc., may be installed on an existing high refractive index substrate. The thin film coating may be patterned to form the diffraction features. However, in some implementations, the diffraction features, such as the lines of the diffraction grating 1008, may be formed of a material different from that of the substrate.The substrate may include a high refractive index material such as, for example, a Li-based oxide (e.g., lithium niobate, LiNbO3, or lithium tantalate, LiTaO3), but the diffraction features may be formed from different materials such as a coating of zinc oxide (ZnO), zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), or other materials described herein. In some implementations, this other material formed on the substrate may have a lower refractive index. In some cases, the substrate 1004 may be, for example, silica glass (e.g., doped silica glass), silicon oxynitride, a transition metal oxide (e.g., hafnium oxide, tantalum oxide, zirconium dioxide, niobium oxide, aluminum oxide (e.g., sapphire)), plastic, a polymer-based material, or a material that is substantially optically transmissive to visible light having an appropriate refractive index different from that of the material of the Li-based oxide feature 1008, such as a material (including an amorphous high refractive index glass substrate) as described above.

[0135] In some examples, both the diffraction gratings 1008 and 1012 and the substrate 1004 or the waveguide include the same material, such as a Li-based oxide. In some implementations, the diffraction gratings 1008 and 1012 are directly patterned within the substrate 1004 such that the diffraction gratings and the substrate 1004 form a single component or a monolithic structure. For example, the substrate 1004 includes a waveguide having a diffraction grating 1008 formed directly within the surface of the waveguide or the substrate. In these implementations, the bulk Li-based oxide material may be patterned at the surface 1004S to form the diffraction grating 1008, and the Li-based oxide material below the diffraction grating 1008 may form the waveguide. In still some other implementations, the bulk or the substrate 1004 and the surface 1004S patterned to form the diffraction grating 1008 include different Li-based oxides. For example, the bulk Li-based oxide material patterned in the surface region to form the diffraction grating 1008 may be formed from a first Li-based oxide material, and the Li-based oxide material below the diffraction grating 1008 forming the substrate 1004 or the substrate region may be formed from a second Li-based oxide material different from the first Li-based oxide material. In a specific example, the diffraction gratings 1008 and 1012 are composed of different high refractive index materials such as zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), etc., and the material below the diffraction grating forming the substrate 1004 or the substrate region may be formed from a second material such as LiTaO3, LiNbO3, etc., and may be different from the first material coated as a thin film.

[0136] In the example shown in FIG. 10, the diffraction gratings 1008, 1012 include a plurality of blazed diffraction grating ridges (or lines) that are elongated in the first horizontal direction or the y direction and periodically repeat in the second horizontal direction or the x direction. The diffraction grating lines can be, for example, straight and continuous lines extending in the y direction. However, the embodiments are not limited thereto. In some implementations, the diffraction grating lines can be, for example, discontinuous lines in the y direction. In some other implementations, the discontinuous lines can form a plurality of pillars protruding from the surface of the grating substrate. In some implementations, at least some of the diffraction grating lines can have different widths in the x direction.

[0137] In the illustrated example, the diffraction grating lines of the diffraction grating 1008 have a profile with asymmetric opposing side surfaces that form different angles with respect to the plane of the substrate, such as a sawtooth profile. However, the embodiments are not limited thereto, and in other implementations, the diffraction grating lines can have symmetric opposing side surfaces that form similar angles with respect to the plane of the substrate.

[0138] Typically, when using one or more gratings with directional surface features in an EPE / CPE structure, it is considered that light can be preferentially extracted from the waveguide towards the user side rather than equally extracting light towards both the world side and the user side. Such a structure can improve the overall efficiency of the system by 25% or more (e.g., 50% or more, 75% or more, 100% or more, 150% or more, 200% or more, 300% or more, 400% or more, 500% or more, 600% or more, 700% or more, 800% or more, 900% or more, 1000% or more, e.g., 2000% or less, 1500% or less).

[0139] Referring to FIG. 11A, an exemplary EPE / CPE 1200 (shown in cross-section) includes an inclined grating 1210 on a resist RLT layer 1230 supported by a substrate 1220. The inclined grating 1210 is composed of inclined ridges 1211 separated by trenches 1212.

[0140] The height of the grating layer refers to the ridge dimension along the z-direction and is denoted by H. The ridge 1211 can have a height in the range of 10 nm to 1,000 nm (e.g., 50 nm to 500 nm, 100 nm to 400 nm, 200 nm to 400 nm, 250 nm to 350 nm).

[0141] The pitch P of the grating layer is the dimension along the x-direction between adjacent ridges or adjacent trenches. Usually, the pitch can be determined empirically and / or by simulation, similar to other parameters of the grating structure 1210. The pitch can be adjusted according to the operating wavelength of the grating. Usually, the pitch is in the range of 100 nm to 5,000 nm (e.g., 100 nm to 2,500 nm, 100 nm to 1,000 nm, 200 nm to 750 nm, 250 nm to 500 nm, 300 nm to 400 nm).

[0142] The ridge 1211 has a width W that refers to the ridge dimension along the x-direction. In the case of the grating structure 1210, since the opposing slopes of the ridge 1211 through the illustrated cross-section are parallel, the thickness of the ridge is constant with respect to the ridge through its height. However, in certain implementations, it is possible to vary (e.g., narrow) the width from the base to the top of the ridge. In embodiments where the width varies, the width can be determined at the midpoint of the height of the ridge.

[0143] The duty cycle refers to the ratio of the width to the pitch and is expressed as a percentage. In embodiments, the grating structure can have a duty cycle in the range of 5% to 95% (e.g., 10% to 75%, 20% to 50%, 30% to 40%).

[0144] The foregoing example is of a lattice structure having ridges in the shape of a parallelogram, but more generally, other blazed or inclined cross-sectional shapes are possible. For example, overall trapezoidal, triangular, and stepped shapes, including curved shapes, such as "shark fin", "serrated", and other diagonal or inclined (i.e., non-rectangular) geometric shapes are possible. Also, while the shapes are drawn with mathematical precision corresponding to the parallelogram shape, deviations from these shapes are inevitable due to manufacturing constraints and the like. Usually, as used herein, such ridges and other features are considered to have a particular shape in that their design defines such a shape and / or the structure has such a shape within the capabilities of the process used to manufacture such structures on a large scale. Examples of other possible shapes are described below.

[0145] While not wishing to be bound by theory, as an example, the optical performance of a structure such as EPE1200 was simulated to demonstrate the asymmetric light extraction characteristics of such a device. Referring to FIG. 11B, the viewing angle θ I simulated the optical characteristics of the first-order diffracted light resulting from light incident on the EPE from within the waveguide at θ I which was selected such that the first-order diffracted light propagated normal to the plane of the EPE (as shown). These rays represent the central portion of the user's field of view (FOV). As shown in FIG. 11B, the diffraction results in reflections of order -1 (RX-1) and transmissions of order -1 (TX-1).

[0146] Referring to FIGS. 12A to 12D, a parameter sweep of the EPE structure as shown in FIG. 11A was performed under the above-described incident conditions for light having a wavelength of 525 nm to identify a structure that provides directivity. In this simulation, the duty cycle was set to 50%, and the grating thickness H and the tilt angle θ were varied. For each plot, the grating thickness was the x-axis parameter and the tilt angle was the y-axis parameter. The grating thickness was varied from 60 nm to 200 nm and the tilt angle was varied from 10° to 80°. In all cases, the resist layer had a thickness of 10 nm. The four metrics used for the analysis were the average (over polarization S / P) RX-1 diffraction efficiency <rx-1>(Fig. 12A), average TX-1 diffraction efficiency <tx-1>(Fig. 12B), average reflectance (Fig. 12C), and d) for estimating directivity <tx-1> / <rx-1>It was a ratio (FIG. 12D).

[0147] <tx-1> / <rx-1>The value was observed to exceed a ratio of 10 for a thickness / tilt angle band that increases approximately linearly from about 100 nm and 20° to about 180 nm and about 50°. However, transmitted light ( <tx-1>) The maximum diffraction efficiency (e.g., 5% or higher) occurs at higher thickness values (e.g., 120 nm or higher) and higher tilt angles (e.g., 40° or higher). Usually, the diffraction efficiency of transmitted light must be high enough to guarantee the uniformity of the image across the FOV. The simulations reported here are merely examples and are not intended to be limiting, but they provide examples of specific empirical design tools that can be utilized to provide initial design points for the grating design. Further, although the structures described in FIG. 11A and simulated here are transmission gratings, as will become apparent below, the gratings for the EPE / CPE structures can also include reflection gratings.

[0148] To further investigate the design space of the tilted gratings, additional examples were simulated. In particular, four tilted structures as well as a baseline structure were simulated. The tilted structures are graphically shown in FIGS. 13A - 13D respectively. Table 1 below includes the parameter values for each example, and in each case, the thickness of the RLT layer was 10 nm and the simulation wavelength was 525 nm. In the figures, the arrows indicate the incident light direction. The grating ridges and the RLT layer had refractive indices of 2.0 - 2.5. The troughs had a refractive index of 1.0.

Table 1

[0149] The simulation results are shown in Table 2 below. RXD and TXD correspond to the diffraction efficiencies of RX - 1 and TX - 1. In columns 2 - 5, S and P correspond to the input polarization, and AV (columns 6 and 7) refers to the average of the S / P values. DTOT is the sum of the average efficiency values. This parameter is related to the uniformity across the FOV. TXRXAV and RXTXAV are the ratios TXAV / RXAV and RXAV / TXAV respectively, and are measures of the grating directivity.

Table 2

[0150] Columns 9 and 10 provide a sense of directivity. The values of the baseline grid are approximately 1 (specifically 0.93 and 1.08), indicating approximately equal amounts of light towards the user side and the world side. The inclined grid structures in FIGS. 13A and 13C show directivity towards the TX side (e.g., the user side of the EPE1200), while the inclined grid structures in FIGS. 13B and 13D show directivity towards the RX side (e.g., the world side of the EPE1200). Usually, different cases may be appropriately selected according to different eyepiece architectures, but in any case, the inclined grid structure can be designed to provide asymmetric light extraction from the waveguide.

[0151] The above simulation example was based on a grid with trapezoidal grid ridges, but other cross-sectional shapes of the grid ridges are also possible. For example, a blazed grid characterized by serrated ridges or stepped ridges is possible. An exemplary ridge shape is shown in FIG. 22 and will be discussed below.

[0152] For example, FIG. 22 shows an exemplary cross-sectional shape 2200 of a grid ridge. The cross-sectional shape 2210 includes a single slope-shaped geometry, and the cross-sectional shape 2220 includes a multi-step slope geometry, such as a stepped slope. The cross-sectional shapes 2230 and 2240 are characterized by other multi-step slope-shaped geometries, such as two different slope angles.

[0153] FIG. 14A shows in cross-section that a sawtooth grid 1410 is included on a resist RLT layer 1430 supported by a substrate 1420 with a part of the EPE / CPE1400. The sawtooth grid 1410 has a shallower blaze angle θ B and a steeper anti-blaze angle θ AB It is composed of ridges 1411, each characterized by []. For the grating 1410, the height, period, and duty cycle of the grating are defined as described above. The grating width is calculated at the base of each ridge 1411 (i.e., at the thickest part). Further, the ridges of the blazed grating can have a smooth surface or can be stepped. Each of these parameters can be determined / optimized using the methods disclosed herein.

[0154] Referring to FIGS. 14B to 14D, an example of a blazed grating was simulated as follows. In particular, a continuous blazed grating (FIG. 14B) and a four-step blazed grating (FIG. 14C) were simulated. The parameters of these structures are summarized in Table 3 below. [Table 3]

[0155] The simulation results are shown in Table 4 below. In each case, the ratio of transmitted light to reflected light is approximately 10:1. [Table 4]

[0156] Generally, as described above, the diffraction structure that provides asymmetric light extraction from a waveguide can be deployed on a waveguide in various configurations within an eyepiece lens, for example, in combination with an ICG. For example, gratings for EPE and / or CPE can be provided on one or both sides of the waveguide. Examples of one-sided deployment are shown in FIGS. 15A and 15B. In the eyepiece lens 1501 shown in FIG. 15A, the ICG 1510 and the EPE 1521 are formed on the same side of the waveguide 1530. The EPE 1521 is designed to preferentially extract light from the optical guide towards the user side 1540 using the design principle described above. In the eyepiece lens 1502 shown in FIG. 15B, the ICG 1510 and the EPE 1522 are formed on opposite sides of the same waveguide 1530. Similar to the eyepiece lens 1501, the EPE 1522 is designed to preferentially extract light from the optical guide towards the user side 1540.

[0157] FIG. 15C shows a bilateral configuration in which the CPE is composed of two gratings 1523 and 1524 formed on opposite sides of the waveguide 1530. In this design, both the gratings 1523 and 1524 are designed such that the eyepiece lens 1503 preferentially guides light to the user side 1540. FIG. 15D shows another bilateral configuration in which the CPE is composed of two gratings 1525 and 1526 formed on opposite sides of the eyepiece lens 1504 to preferentially direct light towards the world side 1550.

[0158] Typically, the structure of the grating for EPE or CPE can be uniform across the eyepiece lens or the grating structure can vary. The grating structure can vary abruptly or continuously. The structural characteristics that can vary include one or more of, for example, the blaze angle, anti-blaze angle, height, ridge width, period, duty cycle, etc. These characteristics can vary in the direction from the ICG towards the EPE / CPE side opposite the ICG or in other directions. In some examples, the structural characteristics can vary in two or more directions.

[0159] Referring to FIGS. 16A - 16D, in some examples, the eyepiece lens 1600 includes a CPE 1610 having four zones (1611 - 1614), each having a grating with a structure different from adjacent zones. The grating structures of each of the zones 1611 - 1614 are shown in cross - section in FIGS. 16B - 16D. Specifically, the zone closest to the ICG 1620, zone 1612, includes an RLT layer having a thickness of 10 nm and a grating height of 85 nm, as shown in FIG. 16D. The zone farthest from the ICG 1620, zone 1611, has an RLT layer having a thickness of 20 nm and a grating height of 225 nm, as shown in FIG. 16B. The other two zones, zones 1612 and 1614, both have an RLT layer having a thickness of 10 nm and a grating height of 175 nm. All the gratings have a blaze angle of 45° and an anti - blaze angle of 90°.

[0160] Simulations of such grating structures with blazed gratings on both sides of a substrate having a refractive index of 2.0 at a TTV of 400 nm and where the gratings and RLT layers have a refractive index of 1.65 demonstrated a user - side efficiency of 9.7% and a world - side efficiency of 1.6%.

[0161] Typically, the light extraction efficiency can vary across the area of the CPE and the use of different grating structures and / or zones of continuously varying grating structures, and can be used to reduce the variation in extraction efficiency across the CPE. For example, in some examples, the CPE has a user - side extraction efficiency that varies by 3 times or less (e.g., 2.5 times or less, 2 times or less, 1.5 times or less) across the entire area. In a particular example, the CPE can have a user - side extraction efficiency with a minimum value of 4% or more (e.g., 5% or more, 6% or more, 7% or more) and a maximum efficiency of 15% or less (e.g., 14% or less, 13% or less, 12% or less, 11% or less, 10% or less). In some examples, the user - side extraction efficiency is maximum at the center of the CPE.

[0162] Additional examples of a blazed sawtooth CPE structure having a stepwise change pattern are shown in FIGS. 17A - 18E. FIGS. 17A - 17B show cross - sectional profiles of the blazed sawtooth structure on the world side (FIG. 17A) and the user side (FIG. 17B) of the CPE. In this example, both structures have ridges with a blazed angle of 20° and an anti - blazed angle of 85°. Adjacent ridges are separated by a 20 nm gap.

[0163] FIG. 18A shows a plot indicating the lattice height variation across the lattice. Each lattice has 16 zones with the shortest lattice closest to the ICG. The lattice height monotonically increases from a minimum of 15 nm to a maximum of 90 nm for the zone farthest from the ICG. FIGS. 18B - 18C show the relative orientation of the lattice lines on the world side (FIG. 18B) and the user side (FIG. 18C), respectively.

[0164] The exemplary lattice structures described above are one - dimensional lattices, but other implementations are possible. For example, in some embodiments, an array of structures can be arranged in two directions to form a two - dimensional (2D) array of diffraction features. The 2D array of diffraction features can include undulations in two directions. In some examples, the undulations can be periodic, but in other examples, the pitch of the undulations can vary in at least one direction. According to the various examples described herein, the diffraction features have opposing sidewalls that are angled asymmetrically or obliquely. According to the various examples described herein, the diffraction mechanism can be tapered.

[0165] In some implementations, the diffractive feature can have opposing sidewalls that are substantially angled or skewed. In some implementations, the opposing sidewalls may be skewed in the same direction, and in other implementations, the opposing sidewalls may be skewed in opposite directions. In some other implementations, the diffractive feature can have one of the opposing sidewalls that is substantially skewed and that is substantially perpendicular or orthogonal to the horizontal axis or that is at least less skewed than the other sidewall of the other sidewall. In the various examples of 2D diffractive features described herein, the 2D diffractive features can be formed within or on a substrate below that can be a waveguide, as described above for the various examples of 1D diffractive features. For example, the 2D diffractive feature can be etched into the underlying substrate or can be formed by patterning a separate layer formed thereon. Thus, the 2D diffractive features can be formed from the same or different materials as the substrate material in a manner similar to that described above for the various 2D diffractive features. Other variations and configurations are possible.

[0166] Accordingly, any of the structures or devices described herein, such as a lattice structure, may include a 1D lattice. Similarly, any of the structures or devices described herein, such as a lattice structure, may include a 2D lattice. Such 2D lattices may be capable of diffusing light. These lattices may also include blazed lattices. Such blazed lattices may be capable of preferentially guiding light in a particular direction. In some implementations, a 2D lattice (e.g., having one angled facet on a diffraction feature) may preferentially guide light in one direction, and in other implementations, a 2D lattice (e.g., having two angled facets that are differently oriented on a diffraction feature) may preferentially guide light in multiple directions. Similarly, any of the methods or processes described herein may be used with a 1D lattice. Similarly, any of the methods or processes described herein may be used with a 2D lattice. These 1D or 2D lattices may be included within or on a substrate and / or waveguide, may be included in an eyepiece, and in some cases may be incorporated into a head-mounted display as disclosed herein. These lattices may be employed as an input lattice (e.g., ICG), an output lattice (EPE), an optical distribution lattice (OPE), or a combined optical distribution lattice / output lattice (e.g., CPE).

[0167] Typically, single-stage or multi-stage geometric-shaped blazed diffraction gratings are possible, and various techniques can be used to form the grating. In the example shown in FIGS. 19A-19B, the grating can be formed by depositing a blazed photoresist and then etching and patterning the photoresist.

[0168] Exemplary methods of forming blazed gratings and examples of various blazed grating geometries are described in U.S. Patent Application Publication No. 20210072437, titled "Display device with diffraction grating having reduced polarization sensitivity", the entire content of which is incorporated herein by reference.

[0169] FIG. 19A shows the formation of a single - stage blazed grating 1106 within a substrate 1104 that may be a waveguide 1004 (see, e.g., FIG. 10). A patternable material such as photoresist 1102 is deposited on the substrate 1104 that is or includes the waveguide 1104. The patternable material / photoresist 1102 is patterned to have the shape of a blazed grating. Forming a blazed shape within the photoresist 1102 may, in some implementations, involve imprinting a pattern such as a single - stage "sawtooth" pattern within the photoresist 1102 (e.g., depositing the photoresist on the substrate 1104 and then imprinting it with the blazed geometry). The photoresist 1102 may include a mask such as a hard mask. The patterned photoresist 1102 and the substrate 1104 may then be etched to form a blazed pattern within the substrate 1106. The etching of the photoresist 1102 and the substrate 1104 may include, for example, dry plasma or chemical etching and / or wet chemical etching. In some implementations, the etching shown in FIG. 19A may etch the material at a relatively constant rate, such that the portion of the patterned photoresist that is thickest results in a relatively small amount of material removal from the substrate, e.g., negligible or no removal, and the portion of the patterned photoresist that is thinnest (or non - existent) results in a relatively large amount of material removal from the substrate or the deepest etching into the substrate.

[0170] FIG. 19B is a scanning electron micrograph of a blazed photoresist grating 1112, and the blazed grating pattern is formed in the photoresist 1104, for example, by imprinting a patterned master into the photoresist. The diffraction grating 1112 shown has a single-stage blazed shape.

[0171] Referring to FIGS. 20A-20K, SEM micrographs of several grating structures that can be suitable for the EPE / CPE structure described above are shown. FIGS. 20A-20G show examples of one-dimensional gratings. FIGS. 20H-20J show examples of two-dimensional grating structures.

[0172] Furthermore, in some examples, the grating can include a single-sided or conformal coating having a different material on the grating ridges. For example, FIG. 20K shows an inclined shark fin grating imprinted with a resist having a refractive index of 1.53 and a thin RLT of less than 20 nm, and on which a blazed TiO2 coating having a refractive index of about 2.2 is deposited. It is believed that this can lead to the fact that an inclined structure with a low refractive index (for example, a refractive index of 1.3 to 1.5) has a higher diffraction directivity.

[0173] A further example of an eyepiece lens featuring EPE with double-sided gratings is shown in FIGS. 21A - 21D. Here, each structure is shown in cross-section and includes an ICG 212 on the side of the waveguide 2111 opposite the light projector. The direction of light from the projector is shown as arrow 2101. The eyepiece lens 2110 in FIG. 21A includes a pair of blazed gratings 2115 and 2116 whose ridge shape changes from the side closest to the ICG 2112 to the opposite side of the grating. In the grating 2115 on the same side of the waveguide 2111 as the ICG 2112, the blazed grating is inclined towards the ICG 2112. In other words, the side of each ridge having a blaze angle is on the opposite side of the side closest to the ICG. The grating 2116 is a blazed grating inclined from the ICG. In both cases, the blaze angle and the anti-blaze angle are the same across each grating and the same for both gratings 2115 and 2116, but the height and shape of the grating change. In particular, the height of the grating increases as the distance from the ICG 2112 increases, and the grating ridges include a flat upper surface whose size decreases as the distance from the ICG 2112 increases.

[0174] The eyepiece lens 2120 includes gratings 2125 and 2126 on the opposite side of the waveguide 2111. Here, the height of the grating changes in the same manner as the corresponding grating within the eyepiece lens 2110, but the blaze angle and the anti-blaze angle also change across the grating.

[0175] The eyepiece lens 2130 includes a pair of inclined gratings 2135 and 2136 with varying heights, and the height of the grating increases as the distance from the ICG 2112 increases. The grating 2135 is inclined towards the ICG 2112, and the grating 2136 is inclined outwards. The inclination angle is the same for both gratings and constant across the grating.

[0176] The eyepiece lens 2140 also includes two tilted gratings 2145 and 2146. In this example, the tilt angle varies across the grating. In the case of grating 2145, the ridges are tilted towards the ICG2112 closer to the ICG and outwards away from the ICG. In the case of grating 2146, the ridges are tilted outwards from the ICG closer to the ICG2112 and then tilted towards the ICG. Usually, the tilt angle can vary continuously across the grating or for each discrete zone.

[0177] Usually, the structure of each grating can be determined empirically and shaped to manipulate light differently to change the direction of light emitted from the display for different regions within the user's field of view.

[0178] Furthermore, referring to FIG. 21E, usually, each grating layer can include a single-layer grating or a multi-layer structure depending on the implementation. For example, in some examples, the grating layer 2150 includes ridges 2151 formed from a single material (e.g., resist). In some examples, the grating 2160 can include ridges where a portion of each ridge includes an additional layer, e.g., a high refractive index layer. In the case of grating 2160, one side of the ridge 2151 is coated with a layer 2161 of high refractive index material while the opposite side is exposed. The grating 2170 includes high refractive index layers 2171 on both sides of the ridge 2151. The grating 2180 includes an additional low refractive index layer 2171 on the ridge 2151 along with the partial layer 2161 on one side of the ridge. The grating 2190 includes a low refractive index layer 2171 on top of the layer 2171 covering both sides of the ridge 2151.

[0179] Other combinations of high refractive index and low refractive index layers are possible for both single-sided and double-sided diffraction gratings.

[0180] As described above, various grating ridge shapes can be considered, including those discussed above. Other exemplary ridge shapes are shown in cross-section in FIGS. 22A-22D. Each of these examples features a ridge formed from a single layer of grating material (e.g., resist) on top of a continuous layer 2221 of the same material supported by waveguide 2201. FIG. 22A shows a diffraction structure 2210 where ridge 2211 has a triangular profile, similar to the example discussed above. The diffraction structure 2220 shown in FIG. 22B features a ridge having a rectangular portion 2223 on top of a truncated triangular portion 2222. FIGS. 22C and 22D show examples having ridges that include two triangular portions. The diffraction structure 2230 in FIG. 22C includes two triangular portions 2231, 2232 that are inclined in the same direction. In other words, the blaze angles of both portions are on the same side of the ridge. However, the blaze angle and anti-blaze angle of portion 2232 are different from those of portion 2231. Portion 2231 is truncated. The diffraction structure 2240 in FIG. 22D includes two triangular portions where the triangles are inclined in opposite directions. Here, the lower triangular portion 2241 is truncated. Triangular portion 2241 has the same blaze angle and anti-blaze angle as portion 2242, although more generally, these can vary. Diffraction structures 0, 2230, and 2240 are thought to feature gratings having ridges with multi-step geometries that include slope steps.

[0181] Typically, the structure of the grating layer can be determined according to the specific performance requirements of a particular application. Accordingly, other embodiments are within the scope of the following claims. < / tx-1> < / tx-1>

Claims

Claim 1 A head-mounted display system comprising: a head-mountable frame; a light projection system configured to output light for providing image content; a waveguide supported by the frame, the waveguide being configured to guide at least a portion of the light from the light projection system coupled therein; a diffraction structure optically coupled to the waveguide, the diffraction structure being configured to couple light guided by the waveguide from the waveguide toward the user side of the head-mounted display, the diffraction structure comprising a grating layer having a plurality of ridges each having a side surface that is inclined or stepped with respect to a plane of the waveguide; and the diffraction structure guides at least 25% more light guided by the waveguide toward the user side than toward the world side, the head-mounted display system. Claim 2 The head-mounted display system according to claim 1, wherein the ridge has a profile shape selected from the group consisting of a trapezoid, a parallelogram, a triangle, and a step. Claim 3 The head-mounted display system according to claim 1, wherein the side surface forms an angle within a range of 20° to 80° with respect to the plane of the waveguide. Claim 4 The head-mounted display system according to any one of the preceding claims, wherein the ridge has a height within a range of 10 nm to 1,000 nm. Claim 5 The head-mounted display according to any one of the preceding claims, wherein the plurality of ridges have a pitch within a range of 100 nm to 5,000 nm. Claim 6 The head-mounted display system according to any one of the preceding claims, wherein the plurality of ridges have a duty cycle within a range of 20% to 100%. Claim 7 The head-mounted display according to any one of the preceding claims, further comprising a layer of a material having the same refractive index as the material forming the ridge of the diffraction structure, the layer of material being arranged between the waveguide and the diffraction structure. Claim 8 The head-mounted display according to claim 7, wherein the layer has a thickness within a range of 5 nm to 50 nm. Claim 9 The head-mounted display according to any one of the preceding claims, wherein the grating layer comprises a grating material having a refractive index of 1.5 or greater at an operating wavelength. Claim 10 The head-mounted display according to any of the preceding claims, further comprising an input coupling grating (ICG) arranged to couple light into the waveguide, wherein the ICG and the diffraction structure are arranged on the same side of the waveguide. **Claim 11** The head-mounted display according to any of claims 1 to 9, further comprising an input coupling grating (ICG) arranged to couple light into the waveguide, wherein the ICG and the diffraction structure are arranged on opposite sides of the waveguide. **Claim 12** The head-mounted display according to any of the preceding claims, wherein the diffraction structure is a component of an exit pupil expander (EPE) or a compound pupil expander (CPE) of the head-mounted display. **Claim 13** The head-mounted display according to claim 12, wherein the diffraction structure is a first diffraction structure, and the EPE or CPE further comprises a second diffraction structure on the side opposite to the first diffraction structure of the waveguide. **Claim 14** The head-mounted display according to any of the preceding claims, wherein the diffraction structure comprises zones, and the structure of the grating layer in at least two of the zones is different. **Claim 15** The head-mounted display according to claim 14, wherein the grating structure of the grating layer changes abruptly from a first zone to a second zone adjacent to the first zone. **Claim 16** The head-mounted display according to claim 14, wherein the grating structure of the grating layer changes continuously across the area of the diffraction structure. **Claim 17** The head-mounted display according to any of the preceding claims, wherein at least some of the ridges have a single-stage geometric shape. **Claim 18** The head-mounted display according to any of the preceding claims, wherein at least some of the ridges have a multi-stage geometric shape. **Claim 19** The head-mounted display according to claim 18, wherein the ridge having a multi-stage geometric shape includes a stage having a slope-like geometric shape. **Claim 20** The head-mounted display according to any of the preceding claims, wherein the diffraction structure guides at least 100% more light guided by the waveguide towards the user side than towards the world side. **Claim 21** The head-mounted display according to any of the preceding claims, wherein the diffraction structure guides at least 4% of the light from the waveguide towards the user side. **Claim 22** The grating layer is the head-mounted display according to any one of the preceding claims, which is etched in the waveguide.

23. The grating layer is formed in a layer of material deposited on the waveguide, and the layer of material has a refractive index in the range of 1.5 to 2.

7. The head-mounted display according to claims 1 to 21.

24. The diffraction structure includes a layer of material deposited on the ridge of the grating layer. The head-mounted display according to any one of the preceding claims.

25. The layer of material is deposited on less surfaces rather than all surfaces of the ridge surface. The head-mounted display according to claim 23.

26. The layer of material is deposited on all surfaces of the ridge surface. The head-mounted display according to claim 23.

27. The layer of material has a refractive index in the range of 1.7 to 2.

7. The head-mounted display according to claim 23.

28. The layer of material has a refractive index in the range of 1.3 to 1.

5. The head-mounted display according to claim 23.

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