Optical layer for improving the performance of an eyepiece for use with virtual and augmented reality display systems

Abstract

An improved diffractive optical element for use in an eyepiece for an extended reality system. The diffractive optical element comprises a diffractive structure, the diffractive structure having a waveguide substrate, a surface grating positioned on a first side of the waveguide substrate, and one or more optical layer pairs disposed between the waveguide substrate and the surface grating. Each optical layer pair comprises a low refractive index layer and a high refractive index layer disposed directly on an outer side of the low refractive index layer. In one embodiment, the eyepiece further comprises one or more intermediate layers disposed between the optical layer pair and the waveguide substrate.

Description

Technical Field

[0001] The present disclosure relates to imaging and visualization systems for virtual reality and augmented reality, and more particularly to an improved eyepiece design for a display system for a virtual reality and / or augmented reality system.

Background Art

[0002] Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" (VR) or "augmented reality" (AR) and / or "mixed reality" (MR) experiences, where digitally reproduced images or portions thereof are presented to a user in a way that they can appear as if they are real, or can be recognized as such. Virtual reality, i.e., a "VR" scenario, typically involves the presentation of digital or virtual image information that is opaque to visual input from the actual real world. Augmented reality, i.e., an "AR" scenario, typically involves the presentation of digital or virtual image information as an augmentation to the visualization of the actual world around the user. A mixed reality scenario is a type of AR scenario in which physical objects and virtual objects in the real world coexist and can interact in real time, in addition to involving a broader integration of the real world and the virtual world. As used herein, the terms "extended reality" and "XR" are used to collectively refer to any of VR, AR, and / or MR. Further, the term "AR" means either or both of AR and MR.

[0003] For example, referring to FIG. 1, an extended reality scene (4) is shown, where a user of AR technology is viewing a situation (6) such as a real-world park characterized by people, trees, buildings, and a concrete platform (1120) in the background. In addition to these items, the user of AR technology can also "see" and perceive these elements (2, 1110), such as a robotic image (1110) standing on the real-world platform (1120) and a flying comic-like avatar character (2) that appears to be an anthropomorphic representation of a bumblebee, even though these elements do not exist in the real world. As a conclusion, the human visual perception system is very complex, and it is difficult to generate VR or AR technology that facilitates the presentation of virtual image elements with a comfortable and natural-rich feeling among other virtual or real-world image elements.

[0004] When it comes to presenting 3D virtual content to the user of an XR system, there are many challenges. A central prerequisite for presenting 3D content to the user involves creating the perception of multiple depths. In other words, it may be desirable for some virtual content to appear closer to the user, while other virtual content may appear to come from farther away. Therefore, to achieve 3D perception, the XR system should be configured to deliver virtual content to the user at different focal planes.

[0005] To generate a true sense of depth, and more specifically a simulated surface depth, for each point within the field of view of the display, it is desirable to generate an adaptive response corresponding to that virtual depth. If the adaptive response for a display point does not correspond to the virtual depth of that point such that it is determined by both the convergence and stereoscopic binocular depth cues, the human visual system will experience a conflict in adaptation, resulting in an unstable image, harmful eye fatigue, headaches, and a near-complete lack of surface depth without adaptation information.

[0006] Accordingly, there is a need for improved techniques for implementing 3D displays that solve these and other problems of conventional techniques. The systems and techniques described herein are configured to address these challenges in cooperation with typical human visual configurations. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEMS

[0007] Embodiments of the present invention relate to devices, systems, and methods for facilitating XR interactions for one or more users. More specifically, this document discloses an improved eyepiece design for virtual reality and / or augmented reality display systems having improved performance over previous eyepiece designs. The eyepiece design disclosed herein includes innovative coating layers of optical elements of a display system that improve the functional performance of the eyepiece, such as selectively adjusting diffraction efficiency for a particular color, increasing the magnitude and uniformity of the diffraction efficiency of the eyepiece, increasing the combined injection pupil expander (CPE) efficiency of the eyepiece, and / or increasing the input coupling grating (ICG) emission efficiency of the eyepiece.

[0008] Accordingly, one embodiment disclosed herein is an eyepiece for an XR display system for delivering XR content to a user. The eyepiece includes a diffractive optical element (DOE) that receives light associated with one or more frames of image data and directs the light towards the user's eye. The DOE includes a diffractive structure having a waveguide substrate, a surface grating positioned on a first side of the waveguide substrate, and one or more optical layer pairs disposed between the waveguide substrate and the surface grating. The optical layer pairs may be disposed directly on the first side of the waveguide substrate or there may be one or more intermediate layers (also referred to herein as "underlayers") disposed between the optical layer pairs and the waveguide substrate. Each optical layer pair includes a low refractive index layer and a high refractive index layer disposed directly on an outer side of the low refractive index layer. The terms "inner" and "outer" are with respect to a plane passing through the center of the thickness of the waveguide substrate, which plane is the most inner position. The high refractive index layer has a higher refractive index than the low refractive index layer. The use of the innovative optical layer pairs is adjusted to improve the uniformity of the display of a particular color by the eyepiece by better matching the diffraction efficiency of the DOE with the bounce interval (out-coupled beam density) and the ICG emission efficiency (both of which depend on the angle of incidence of the light incident on the eyepiece).

[0009] In another aspect, the DOE for the eyepiece may include a first optical layer pair on a first side of the waveguide substrate and a second optical layer pair on a second side of the waveguide substrate (i.e., the side opposite the first side). The DOE may also include a second surface grating on the second side of the waveguide substrate, and the second optical layer pair is between the waveguide substrate and the second surface grating. In yet another aspect, the eyepiece may further include an input coupling grating disposed on the waveguide substrate.

[0010] In yet another aspect, the DOE may include a first pair of optical layers on a first side of the waveguide substrate and a second pair of optical layers disposed directly outside the first pair of optical layers. In this way, the second pair of optical layers can amplify the performance improvement of the first optical pair. One or more additional pairs of optical layers can be stacked on top of the other optical layers to match the diffraction efficiency of the DOE to the bounce interval or to adjust any other desired optical parameter of the eyepiece.

[0011] In another aspect, the waveguide substrate has a refractive index higher than that of the low refractive index layer. In yet another aspect, the waveguide substrate is formed from TAFD55 glass having a refractive index (about 2.0) higher than that of the low refractive index layer. In yet another aspect, the surface grating has a high refractive index greater than about 1.7. As used herein, the term "about" means plus or minus 10%.

[0012] In an additional aspect of the eyepiece, the high refractive index layer can be formed from Si3N4, ZrO2, TiO2, SiC, ZnTe, GP, BP and / or similar materials having a high refractive index (greater than 1.7) and low absorption (k < 0.001). In another aspect, the high refractive index layer can be applied to the DOE by any suitable process such as spray deposition, applying a film. The high refractive index layer can also include an organic filler-based material such as an organic UV and / or thermosetting resin composite composed of sulfur, aromatic groups and high refractive index nanoparticles (e.g., ZrO2, TiO2). The low refractive index layer can be formed from inorganic materials such as MgF, SiO2, and organic materials having a refractive index of about 1.53 such as normal UV and thermosetting resins, and Teflon®-type materials having a refractive index of about 1.3. The low refractive index coating layer can be applied to the DOE by any suitable process such as spray deposition, applying a film.

[0013] On the other hand, the surface grating has a low refractive index (i.e., lower than the refractive index of the high refractive index layer) and can be applied to a DOE having a pattern of an organic material on the high refractive index layer of the optical coating layer using photolithography or imprint lithography using an ultra-thin RLT (about 20 nm). An upper surface layer having a higher refractive index than the low refractive index layer can also be installed on the upper surface grating. The upper surface layer can remove any air space gap and form a gap layer between a plurality of stacked diffractive structures that provide a support structure for the stacked diffractive component.

[0014] In another embodiment disclosed herein, an XR display system for delivering extended reality content to a user is related. The XR display system includes an image source for providing one or more frames of image data, a light modulator for transmitting light associated with the one or more frames of image data, and an eyepiece having a DOE for receiving the light associated with the one or more frames of image data and directing the light towards the user's eyes. The DOE can be any of the DOEs described herein, including the DOE described above for one embodiment disclosed herein. Here too, a DOE having an innovative pair of optical layers can be adjusted to improve the uniformity of the display of a particular color by the eyepiece by better matching the diffraction efficiency of the DOE with the bounce interval (the outcoupled beam density) and the ICG emission efficiency (both of which depend on the angle of incidence of the light incident on the eyepiece).

[0015] In an additional aspect, the XR display system can include any combination of one or more of the additional aspects and features of the eyepiece embodiment, as described herein.

[0016] In another embodiment disclosed herein, it relates to an XR system for generating XR content and displaying it to a user. The XR system comprises a computer having a computer processor, a memory, a storage device, and a software application executable to program the computer to perform operations enabling an augmented reality system. The XR system includes an XR display system. The XR display system can be any suitable display system, such as an XR headset having a display for displaying 3D virtual images (i.e., XR images). For example, the XR headset can include a frame structure configured to be worn on the user's head. The frame structure includes an image source for providing one or more frames of image data, a light modulator for transmitting light associated with one or more frames of image data, and an eyepiece having a DOE for receiving light associated with one or more frames of image data and directing the light towards the user's eyes. The DOE can be any of the DOEs described herein, including the DOE described above for one embodiment disclosed herein. Again, a DOE having an innovative optical layer pair can be adjusted to improve the uniformity of the display of a particular color by the eyepiece by better matching the diffraction efficiency of the DOE with the bounce interval (out-coupled beam density) and the ICG emission efficiency (both of which depend on the angle of incidence of the light incident on the eyepiece).

[0017] In an additional aspect, the XR headset can include one or more outward-facing image sensors (e.g., a camera, or other computer vision device) for capturing an image of the user's surrounding environment. The XR headset can also include one or more other sensors, such as an inward-facing camera (e.g., for gaze tracking, etc.) and one or more kinematic sensors (e.g., an inertial measurement unit (IMU), accelerometer, orientation sensor, compass, gyroscope, GPS sensor, camera, and / or computer vision, etc.).

[0018] In an additional aspect, the XR display system may include any combination of one or more of the additional aspects and features of the eyepiece embodiments, as described herein.

[0019] Additional and other objects, features, and advantages of the present invention are described in the detailed description, the drawings, and the claims.

Brief Description of the Drawings

[0020] The drawings illustrate the design and utility of various embodiments of the present disclosure. It should be noted that the drawings are not drawn to scale, and elements of similar structure or function are represented by like reference numerals throughout the drawings. To better understand how to obtain the above and other advantages and objects of various embodiments of the present disclosure, a more detailed description of the present disclosure briefly described above is provided by reference to the specific embodiments thereof shown in the accompanying drawings. It is understood that these drawings show only typical embodiments of the present disclosure and should not be considered as limiting its scope. The present disclosure is described and explained with additional specificity and detail by using the accompanying drawings.

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Mode for Carrying Out the Invention

[0042] The following describes various embodiments of an improved eyepiece design for an extended reality (XR) display system and an XR system for delivering extended reality content to a user. The improved eyepiece utilizes an additional optical layer on a diffractive optical element (DOE) of the XR display system's eyepiece to receive light associated with frames of image data displayed on the XR display system. The disclosed eyepiece improves the functional performance of the eyepiece, such as selectively adjusting diffraction efficiency for a particular color, increasing the magnitude and uniformity of the eyepiece's diffraction efficiency, increasing the combined collimated pupil expander (CPE) efficiency of the eyepiece, and / or increasing the input coupling grating (ICG) emission efficiency of the eyepiece.

[0043] According to some embodiments of the present invention, a DOE is used, and the DOE has a diffractive structure including one or more pairs of optical layers disposed between a waveguide substrate and an upper grating surface. Typically, the waveguide substrate has a high refractive index, and the upper grating surface also has a high refractive index. One or more pairs of optical layers are disposed between the waveguide substrate and the surface grating. Each pair of optical layers includes a low refractive index layer and a high refractive index layer directly disposed outside the low refractive index layer. As described herein, the pair of optical layers having a high refractive index layer and a low refractive index layer can be adjusted to improve the performance of the DOE, including improving diffraction efficiency and the uniformity of the display of discrete colors, increasing the magnitude and uniformity of the eyepiece's diffraction efficiency, increasing the CPE efficiency of the eyepiece, and / or increasing the ICG emission efficiency of the eyepiece. Improving diffraction efficiency has the advantage of enabling a "brighter" light output to the XR display. (Display system according to some embodiments)

[0044] This portion of the disclosure describes an exemplary display system that can be used in conjunction with the improved diffractive structure disclosed herein.

[0045] FIG. 2 shows a conventional stereoscopic 3D simulation display system for an XR system. The display system typically has separate displays 74 and 76 for each eye 4 and 6, respectively, at a fixed radial focal distance 10 from the eyes. This conventional approach does not take into account many of the valuable cues utilized by the human eye and brain to detect and interpret depth in three dimensions, including accommodation cues.

[0046] In fact, a typical human eye can interpret multiple depth layers based on radial distance; for example, a human eye can approximately interpret 12 depth layers. The near-distance limit of about 0.25 meters is approximately the closest depth of focus, and the far-distance limit of about 3 meters means that any item farther than about 3 meters from the human eye receives an infinite focus. The layers of focus become thinner as they approach the eye; in other words, the eye can perceive differences at very small focal distances relatively close to the eye, and this effect disappears as the object moves farther away from the eye. At the infinite object position, the depth of focus / refractive interval value is about 1 / 3 diopter.

[0047] Figure 3 shows an improved approach for implementing a stereoscopic 3D simulation display system for use in an AR system according to some embodiments of the present invention, where two complex images, one for each eye 4 and 6, are displayed, and different radial focal depths (12) for different sides (14) of each image are utilized to provide the perception of three-dimensional depth layer formation in the perceived image to each eye. Since there are multiple focal planes (e.g., 12 focal planes) between the user's eyes and infinity, these focal planes, and the data within the depicted relationships, are constantly moving around as the human eye uses the focal planes to perceive depth, and thus can be utilized to position virtual elements within an extended reality scenario for the user's observation. This figure shows a specific number of focal planes of different depths, but it should be noted that the implementation aspects of the present invention can use any number of focal planes required for a particular desired application, and thus the present invention is not limited to devices having only the specific number of focal planes shown in any of the figures of this disclosure.

[0048] Referring to FIGS. 4A - 4D, some general component options of an XR system according to some embodiments of the present invention are shown. In the detailed description section following the description of FIGS. 4A - 4D, various systems, subsystems, and components are presented to address the objective of providing a high-quality and comfortably perceivable display system for the human XR experience.

[0049] As shown in FIG. 4A, an XR system user (60) is shown wearing a frame (64) structure coupled to a display system (62) positioned in front of the user's eyes. A speaker (66) is coupled to the frame (64) in the illustrated configuration and is positioned adjacent to the user's external ear canal (in one embodiment, another speaker, not shown, is positioned adjacent to the user's other external ear canal to provide stereo / formable acoustic control). The display (62) is operably coupled (68) to a local processing and data module (70) by, for example, a wired lead or a wireless connection, and the local processing and data module (70) can be attached fixedly to the frame (64), attached fixedly to a helmet or hat (80) as shown in the embodiment of FIG. 4B, embedded in headphones, removably attached to the user's torso (82) in a backpack-type configuration as shown in the embodiment of FIG. 4C, or removably attached to the user's waist (84) in a belt-coupled configuration as shown in the embodiment of FIG. 4D, etc., and can be attached in various configurations.

[0050] The local processing and data module (70) may comprise a power - efficient processor or controller and a digital memory such as a flash memory, both of which can be utilized to assist in the processing, caching, and storing of data. The data can be captured from sensors (such as an image capture device (e.g., a camera), microphone, inertial measurement unit, accelerometer, compass, GPS unit, wireless device, and / or gyro) that can be operably coupled to the frame (64), and / or obtained and / or processed using the remote processing module (72) and / or the remote data repository (74), perhaps for passing to the display (62) after such processing or retrieval. The local processing and data module (70) can be operably coupled (76, 78) to the remote processing module (72) and the remote data repository (74), for example via a wired or wireless communication link, whereby these remote modules (72, 74) are operably coupled to each other and available as resources to the local processing and data module (70).

[0051] In one embodiment, the remote processing module (72) may comprise one or more relatively powerful processors or controllers configured to analyze and process data and / or image information. In one embodiment, the remote data repository (74) may comprise a relatively large - scale digital data storage facility, which may be available via other networking configurations in an Internet or “cloud” resource configuration. In one embodiment, all data is stored and all calculations are performed in the local processing and data module, enabling complete autonomous use from any remote module.

[0052] Perception of the Z - axis difference (i.e., the distance straight out from the eye along the optical axis) can be facilitated by using a waveguide in combination with a variable - focus optical element configuration. Image information from a display is collimated, incident on the waveguide, and can be distributed in a large - exit - pupil manner using any suitable substrate - guided - optical method known to those skilled in the art. Then, the variable - focus optical element capability can be utilized to change the focus of the wavefront of the light emerging from the waveguide, providing the eye with the perception that the light coming from the waveguide is from a particular focal distance. In other words, since the incident light is collimated to avoid issues in a total - internal - reflection waveguide configuration, it exits in a collimated form, requiring the observer's eye to accommodate to the far - point for focusing on the retina and being naturally interpreted as being from optical infinity - unless the light is re - focused by some other intervention and perceived as being from a different viewing distance: one such suitable intervention is a variable - focus lens.

[0053] In some embodiments, the collimated image information is incident on glass or other material at an angle such that it undergoes total internal reflection and is passed to an adjacent waveguide. The waveguide can be configured such that the collimated light from the display is distributed so that it exits somewhat uniformly over a distribution of mirrors or diffractive features along the length of the waveguide. As it exits towards the eye, the exiting light passes through a variable - focus lens element, and depending on the controlled focus of the variable - focus lens element, the light exiting the variable - focus lens element and incident on the eye has various levels of focus (a collimated flat wavefront representing optical infinity, an increasingly large beam divergence / wavefront curvature representing a closer viewing distance to the eye 58 (see FIGS. 5 - 12)).

[0054] In a "frame sequential" configuration, a stack of consecutive two-dimensional images can be sequentially supplied to a display in a manner similar to how a computed tomography system uses stacked image slices to represent a three-dimensional structure, in order to generate a three-dimensional perception over time. A series of two-dimensional image slices can each be presented to the eye at a different focal distance relative to the eye, and the eye / brain integrates such a stack into a perception of a coherent three-dimensional volume. Depending on the type of display, sequence processing on a line-by-line basis, or even pixel-by-pixel sequence processing, can be performed to generate the perception of three-dimensional viewing. For example, in a scanning light display (such as a scanning fiber display or a scanning mirror display), the display sequentially presents one line or one pixel at a time to the waveguide.

[0055] Referring to FIG. 6, the stacked waveguide assembly 178 can be utilized to provide a three-dimensional perception to the eye / brain by having a plurality of waveguides 182, 184, 186, 188, 190 and a plurality of weak lenses 198, 196, 194, 192, which are configured together to transmit image information to the eye with different levels of wavefront curvature for each waveguide level indicative of the focal distance to be perceived for that waveguide level. A plurality of displays (200, 202, 204, 206, 208), or in another embodiment a single multiplexed display, can be used to direct collimated image information into waveguides 182, 184, 186, 188, 190, each of which can be configured to substantially equally distribute the incident light over the length of each waveguide in order to exit downward toward the eye, as described above.

[0056] The waveguide 182 closest to the eye is configured to deliver collimated light that is incident on such a waveguide (182) to the eye, which may represent an optically infinite focal plane. The next higher waveguide (184) is configured to deliver collimated light that passes through a first weak lens (192, e.g., a weak negative lens) before reaching the eye (58). The first weak lens (192) may be configured to produce a slightly convex wavefront curvature, whereby the eye / brain interprets the light coming from its next higher waveguide (184) as coming from a first focal plane that is more inwardly directed towards the person from the optically infinite. Similarly, the third higher waveguide (186) passes its output light through both the first lens (192) and the second lens (194) before reaching the eye (58). The combined refractive power of the first lens (192) and the second lens (194) may be configured to create another incremental amount of wavefront divergence, whereby the eye / brain interprets the light coming from its third higher waveguide (186) as coming from a second focal plane that is more inwardly directed towards the person from the optically infinite than the light from the next higher waveguide (184).

[0057] Other waveguide layers (188, 190) and weak lenses (196, 198) are similarly configured, and the highest waveguide (190) in the stack delivers its output between the eye and through all the weak lenses for the total focal power representing the focal plane closest to the person. A compensation lens layer (180) is placed at the top of the stack to compensate for the stack of lenses (198, 196, 194, 192) when viewing / interpreting light coming from the world (144) on the other side of the stacked waveguide assembly (178). Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairs and also has a relatively large exit pupil configuration as described above. Both the reflective sides of the waveguides and the focusing sides of the lenses can be static (i.e., not dynamic or electrically active). In an alternative embodiment, they can be dynamic using electrically active features as described above, enabling a small number of waveguides to be multiplexed in time series to generate a greater number of effective focal planes.

[0058] Various diffraction configurations can be used to focus and / or redirect a collimated beam. For example, passing a collimated beam through a linear diffraction pattern such as a Bragg grating deflects or "steers" the beam. Passing a collimated beam through a radially symmetric diffraction pattern, i.e., a "Fresnel zone plate", changes the focus of the beam. A combined diffraction pattern having both linear and radial elements can be used to produce both deflection and focusing of a collimated input beam. These deflection and focusing effects can be produced not only in reflection mode but also in transmission mode.

[0059] These principles can be applied in waveguide configurations to enable additional optical system control. As shown in FIG. 7, a diffraction pattern (220) or "diffractive optical element" (or "DOE") is embedded within a planar waveguide (216) such that when a collimated beam is totally internally reflected along the planar waveguide (216), it intersects the diffraction pattern (220) at multiple locations. The structure can also include another waveguide (218) into which the beam can be incident (e.g., by a projector or display), and the DOE (221) is embedded within this other waveguide (218),

[0060] Preferably, the DOE (220) has a relatively low diffraction efficiency such that only a portion of the light of the beam is deflected towards the eye (58) at each intersection of the DOE (220), and the remainder continues to travel through the planar waveguide (216) via total internal reflection. Thus, the light carrying the image information is split into several associated light beams that exit the waveguide at a number of positions, and the result is a fairly uniform pattern of emitted radiation towards the eye (58) with respect to this particular collimated beam that travels through the planar waveguide (216) while being offset. In this case, the emitted beams directed towards the eye (58) are shown in FIG. 8 as being substantially parallel since the DOE (220) has only a linear diffraction pattern. However, a change in this linear diffraction pattern pitch can be used to controllably deflect the emitted parallel beams, thereby generating a scanning or tiling function.

[0061] Referring to FIG. 9, due to the change in the radially symmetric diffraction pattern component of the embedded DOE (220), the emitted beam pattern is more divergent, which requires the eye to accommodate to a closer distance in order to focus the eye on the retina and is interpreted by the brain as light from a viewing distance closer to the eye than optical infinity.

[0062] Referring to FIG. 10, the addition of another waveguide (218) into which the beam can be incident (e.g., by a projector or display), the DOE (221) embedded in this other waveguide (218), such as a linear diffraction pattern, can function to disperse the light over the larger planar waveguide (216), which, during operation, functions to provide the eye (58) with an incident field of very large incident light exiting from the larger planar waveguide (216), e.g., a large eyebox, according to a particular DOE configuration.

[0063] The DOE (220, 221) is shown bisecting the associated waveguides (216, 218), but this is not necessary and they can be placed near or on either side of either of the waveguides (216, 218) to have the same function. Thus, as shown in FIG. 11, by injecting a single collimated beam, the entire field of the replicated collimated beams can be directed towards the eye (58). Further, in the scenario of the combined linear diffraction pattern / radially symmetric diffraction pattern as described above, a beam distribution waveguide optical system with Z-axis focusing ability (for functions such as extended exit pupil function, and in the configuration such as that in FIG. 11, the exit pupil can be the same size as the optical element itself, which can be a very important advantage for user comfort and ergonomics) is presented, and both the divergence angle of the replicated beams and the wavefront curvature of each beam represent light coming from a point closer than optical infinity.

[0064] In one embodiment, one or more DOEs are switchable between an “on” state where the DOE actively diffracts and an “off” state where the DOE diffracts little. For example, a switchable DOE can comprise a layer of polymer dispersed liquid crystal, in which the microdroplets have a diffraction pattern in the host medium and the refractive index of the microdroplets can be switched to be substantially the same as the refractive index of the host material (in which case the pattern does not appreciably diffract the incident light), or the microdroplets can 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). Further, by dynamic changes to the diffraction period, a beam scanning or tiling function can be achieved. As described above, it is desirable to have a relatively low diffraction grating efficiency in each DOE (220, 221). This is because it facilitates the distribution of light and light coming through the waveguide that is preferably transmitted (e.g., in an augmented reality configuration, light coming from the world 144 towards the eye 58) is less affected when the diffraction efficiency of the DOE (220) where the light intersects is low, and thus a better view of the real world through such a configuration is achieved.

[0065] The configuration as shown in this specification is preferably driven by the incidence of image information in a time-series manner, and frame sequential driving is the simplest to implement. For example, an image of the sky at optical infinity can be incident at time1, and a diffraction grating that maintains the collimation of light can be utilized. Subsequently, an image of a closer tree branch can be incident at time2 while the DOE provides controllable focus change (e.g., 1 diopter or 1 meter away) to provide the eye / brain with the perception that the light information of the tree branch is coming from a closer focal range. This type of paradigm can be rapidly repeated in time series, whereby the eye / brain perceives that the input is all parts of the same image. This is just an example of two focal planes, and preferably, the system includes more focal planes to provide a smoother transition between objects and their focal distances. This type of configuration generally assumes that the DOE is switched relatively slowly (i.e., in the range of dozens to hundreds of cycles per second, synchronized with the frame rate of the display where the image is incident).

[0066] In stark contrast, there can be a configuration where the DOE element can shift the focus at dozens of MHz to hundreds of MHz or more, which facilitates switching the focus state of the DOE element on a per-pixel basis when the pixels are scanned into the eye (58) using a scanning light display type of approach. This is desirable because it means that it can keep the frame rate of the entire display very low: low enough (in the range of about 60 - 120 frames per second) to ensure that "flicker" is not a problem.

[0067] Between these ranges, if the DOE can be switched at a KHz rate, on a line-by-line basis, the focus at each scan line can be adjusted, which can provide a visible benefit to the user with respect to temporal artifacts, for example, during eye movement relative to the display. For example, different focal planes within a scene can be interleaved in this way (as will be described in more detail later in this disclosure) to minimize visible artifacts in response to head movement. A line-by-line focus modulator can be operably coupled to a line-scanning display (such as a grid light valve display) in which a linear array of pixels is swept to form an image; and can be operably coupled to a scanning light display (such as a fiber scanning display and a mirror scanning light display).

[0068] A stacked configuration similar to those in FIG. 6 can use a dynamic DOE to simultaneously provide multi-plane focusing. For example, with three simultaneous focal planes, the primary focal plane can be presented to the user (e.g., based on the measured eye accommodation), and the + margin and - margin (i.e., one focal plane is closer and one is farther away) can be utilized to provide a wide range of focus that the user can accommodate before the plane needs to be updated. This increased range of focus can provide a temporal advantage when the user switches to a closer or farther focus (i.e., as determined by the accommodation measurement): the new focal plane can be made to be at an intermediate depth of focus, and the + margin and - margin are reset to be ready for a quick switch to either one while the system catches up.

[0069] Referring to FIG. 12, a stack (222) of planar waveguides (244, 246, 248, 250, 252) is shown, each having a mirror (254, 256, 258, 260, 262) at an end, each configured such that collimated image information incident on one end by a display (224, 226, 228, 230, 232) travels while being deflected by total internal reflection to the mirror, where some or all of the light is reflected towards an eye or other target. Each of the mirrors may have a slightly different angle such that they all reflect the outgoing light towards a common destination such as the pupil. Lenses (234, 236, 238, 240, 242) may be inserted between the display and the waveguide for beam steering and / or focusing.

[0070] As described above, an object at optical infinity produces a substantially flat wavefront, while a closer object, such as one meter from the eye, produces a curved wavefront (having a convex radius of curvature of about one meter). The optical system of the eye needs to have sufficient refractive power to bend the incoming light rays such that the incoming light rays are ultimately focused onto the retina (the convex wavefront is changed to concave and then reaches a focus on the retina). These are the basic functions of the eye.

[0071] In many of the above-described embodiments, the light directed towards the eye is treated as part of one continuous wavefront, a portion of which strikes the pupil of a particular eye. In another approach, the light directed towards the eye can be effectively discretized or decomposed into a plurality of beamlets or individual light rays, each having a diameter of less than about 0.5 mm and a unique propagation path as part of a larger aggregated wavefront, and the larger aggregated wavefront can be functionally generated by the aggregation of the beamlets or light rays. For example, a curved wavefront can be approximated by aggregating a plurality of discrete adjacent collimated beams, each of which represents an origin that coincides with the center of the radius of curvature of the desired aggregated wavefront by approaching the eye at an appropriate angle.

[0072] When the beamlets have a diameter of about 0.5 mm or less, they appear to pass through a pinhole lens configuration, which means that each individual beamlet is always relatively focused on the retina regardless of the eye's accommodation state, but the trajectory of each beamlet is affected by the focusing state. For example, when the beamlets approach the eye parallel to represent a discrete and parallel converging wavefront, an eye correctly accommodated at infinity deflects the beamlets to converge on the same shared spot on the retina and appears in focus. When the eye is focused, for example, at 1 m, the beam converges on a spot in front of the retina, crosses the path, and falls on multiple adjacent or partially overlapping spots on the retina, appearing blurred.

[0073] When the beamlets approach the eye in a diverging configuration with a shared origin 1 meter from the observer, a 1 m focus steers the beam to a single spot on the retina and appears in focus, and when the observer is focused at infinity, the beamlets converge on a spot behind the retina, creating multiple adjacent or partially overlapping spots on the retina and producing a blurred image. More generally, the focusing of the eye determines the degree of overlap of the spots on the retina, and a given pixel is "in focus" when all of the spots are directed at the same spot on the retina and "out of focus" when the spots are displaced from each other. This concept that all beamlets with a diameter of 0.5 mm or less can always be focused and aggregated so that they are perceived by the eye / brain as being substantially the same as a coherent wavefront can be utilized in creating configurations for comfortable three-dimensional virtual reality or augmented reality perception.

[0074] In other words, a set of multiple thin beams can be used to emulate what is being done with a variable focus beam of larger diameter, and when the beamlet diameter is kept to a maximum of about 0.5 mm, they maintain a relatively static focus level and, if necessary, to create the perception of being out of focus, the beamlet angular trajectories can be selected to create an effect like that of a larger out-of-focus beam (such defocusing procedures may not be the same as Gaussian blurring for larger beams and can create a multimodal point spread function that can be interpreted similarly to Gaussian blurring).

[0075] In some embodiments, the beamlets are not mechanically deflected to form this intensive focusing effect; rather, the eye receives a subset of many beamlets, where the subset of beamlets includes both a number of angles of incidence and a number of positions where the beamlets intersect the pupil; to represent a given pixel from a particular viewing distance, a portion of the beamlets from the subset that includes the appropriate angle of incidence and intersection with the pupil is turned on with a color and intensity that match (as if they were emitted from the same shared origin in space) to represent its convergent wavefront, while beamlets within the subset that do not match the shared origin are not turned on with that color and intensity (however, some of them may be turned on at some other color and intensity level, for example, to represent different pixels).

[0076] Referring now to FIG. 5, an exemplary embodiment of an XR system 800 using an improved eyepiece having an improved diffraction structure will be described. The XR system generally includes an image generation processor 812, at least one FSD 808 (fiber scanning device), an FSD circuit 810, a coupling optics 832, and a pair of eyepieces 804 (one for each eye 58). Each eyepiece 804 includes an optical assembly 802 (also referred to as a “DOE assembly 802”). The DOE assembly 802 includes a plurality of stacked DOEs 1300 having a diffraction structure that includes a waveguide having an improved diffraction structure as described herein. The system 800 may also include a gaze tracking subsystem 806. As shown in FIG. 5, the FSD circuit may include a circuit 810 that communicates with the image generation processor 812, and the circuit 810 includes a maxim chip CPU 818, a temperature sensor 820, a piezoelectric drive / transducer 822, a red laser 826, a blue laser 828, and a green laser 830, and a fiber combiner that combines all three lasers 826, 828, and 830. Note that other types of imaging technologies may be used instead of the FSD device. For example, in some embodiments of the present invention, a high-resolution liquid crystal display (“LCD”) system, a ferroelectric panel display with a backlight, and / or a high-frequency DLP system may all be used.

[0077] The image generation processor 812 is responsible for generating the virtual content that is ultimately presented to the user. The image generation processor 812 can convert an image or video associated with the virtual content into a format that can project it in 3D to the user. For example, in generating 3D content, the virtual content may need to be formatted such that certain portions of the image are presented on certain depth planes and other portions are presented on other depth planes. Alternatively, all of the image can be generated on a particular depth plane. Alternatively, the image generation processor can be programmed to supply slightly different images to the left and right eyes such that the virtual content appears consistently comfortable to the user's eyes when viewed together. In one or more embodiments, the image generation processor 812 delivers the virtual content to the optical assembly in a time series. A first portion of the virtual scene can be delivered first such that the optical assembly projects the first portion on a first depth plane. Next, the image generation processor 812 can deliver another portion of the same virtual scene such that the optical assembly projects the second portion on a second depth plane, etc. Here, the alvarez lens assembly can be translated laterally quickly enough to generate multiple lateral translations (corresponding to multiple depth planes) on a per-frame basis.

[0078] The image generation processor 812 may further include a memory 814, a CPU 818, a GPU 816, and other circuitry for image generation and processing. The image generation processor 812 can be programmed with the desired virtual content to be presented to the user of the AR system. It should be understood that in some embodiments, the image generation processor can be housed in a wearable XR system. In other embodiments, the image generation processor and other circuitry can be housed in a belt pack coupled to a wearable optical element.

[0079] The XR system 800 also includes a coupling optical system 832 for directing light from the FSD towards the optical assembly 802. The coupling optical system 832 may refer to one or more conventional lenses used to direct light into the DOE assembly. The XR system 800 also includes a gaze tracking subsystem 806 configured to track the user's eye and determine the user's focus.

[0080] In one or more embodiments, software blurring may be used to induce blurring as part of a virtual scene. The blurring module may be part of the processing circuitry in one or more embodiments. The blurring module may blur portions of one or more frames of the image data being supplied to the DOE. In such embodiments, the blurring module may blur portions of frames not intended to be rendered at a particular depth frame. Exemplary techniques that can be used to implement the above-described image display system and components therein are described in U.S. Patent Application No. 14 / 555,585, filed November 27, 2014, which is hereby incorporated by reference in its entirety. (Improved Diffraction Structure)

[0081] As described above, the diffraction pattern can be formed on the planar waveguide such that when the collimated beam is totally internally reflected along the planar waveguide, the beam intersects the diffraction pattern at multiple positions. This arrangement can be stacked to provide image objects at multiple focal planes within a stereoscopic 3D simulation display system according to some embodiments of the present invention.

[0082] Figures 13A - 13H show some exemplary embodiments of a diffraction structure 1300 for a DOE 804 that utilizes an optical layer pair to improve the performance of the eyepiece of the XR display system 800. The different embodiments of Figures 13A - 13H have a surface grating 1304, an input coupling grating 1310 (also referred to herein as an "ICG" or "coupling grating"), a first mirror element 1308, and various configurations of an optical layer pair 1306 relative to each other, and a waveguide substrate 1302. For example, the embodiments of Figures 13A - 13D ("both sides") have a surface grating 1304 and an optical layer pair 1306 on both sides of the waveguide substrate 1302, while the embodiments of Figures 13E - 13H ("one side") have a surface grating 1304 and an optical layer pair 1306 on only the first side of the waveguide substrate 1302.

[0083] Figure 13A shows a diffraction structure 1300a (i.e., DOE 804) in which a surface grating 1304, an input coupling grating 1310, and a first mirror element 1308 are all disposed (e.g., formed, deposited, or arranged) on one surface of one of the optical layer pairs 1306. The diffraction structure 1300a includes a waveguide substrate 1302 (also referred to herein as a "light guide", "substrate", or "waveguide substrate"). The waveguide substrate 1302 has a high refractive index relative to the low refractive index elements of the diffraction structure 1300a. For example, the waveguide substrate 1302 can be formed of TAFD55 glass having a refractive index of about 2.0.

[0084] The upper optical layer pair 1306a (also referred to as the "first optical layer pair 1306a") is disposed on the first side of the waveguide substrate 1302 (the upper side in the orientation of the waveguide substrate 1302 shown in FIG. 13A), and the lower optical layer pair 1306b (also referred to as the "second optical layer pair 1306b") is disposed on the second side of the waveguide substrate 1302 (the lower side in the orientation of the waveguide substrate 1302 shown in FIG. 13A). As used herein, the terms "upper" and "lower" are used only to distinguish elements from each other and to refer to their relative positions, and do not refer to the vertical relationship or orientation of any element of the present invention. Only one upper optical layer pair 1306a is shown for the diffraction structure 1300a, but additional upper optical layer pairs 1306a, such as a second upper optical layer pair 1306a, may be stacked on the first optical layer pair 1306a. Similarly, only one lower optical layer pair 1306b is shown for the diffraction structure 1300a, but additional lower optical layer pairs 1306b, such as a second lower optical layer pair 1306b, may be stacked on the upper optical layer pair 1306b. For example, FIG. 13I shows a diffraction structure 1300i having two upper optical layer pairs 1306a stacked on each other and two lower optical layer pairs 1306b stacked on each other. In other embodiments, there may be a different number of stacked optical layer pairs 1306 (e.g., one upper optical layer pair 1306a and two lower optical layer pairs 1306b) on the upper and lower portions of the waveguide substrate 1302. In fact, any of the exemplary embodiments of the diffraction structure 1300 shown in FIGS. 13A-13G may have a plurality of optical layer pairs 1306 stacked on each other. As another example, FIG. 13J shows a one-sided diffraction structure 1300j having a plurality of optical layer pairs 1306a, in this case two optical layer pairs 1306a.

[0085] Each pair of optical layers 1306a, 1036b includes a low refractive index layer 1305a, 1035b and a high refractive index layer 1307a, 1307b directly disposed on the outer side of the low refractive index layer 1305. As defined above, the terms "inner" and "outer" are with respect to a plane 1311 passing through the center of the thickness of the waveguide substrate 1302, and that plane 1311 is the innermost position. In other words, if an element is close to the plane 1311, it is "inside" another element. The high refractive index layer 1307 has a higher refractive index than the low refractive index layer 1305. The ratio of the refractive index of the high refractive index layer 1307 to the low refractive index layer 1305 is adjusted to selectively improve the uniformity of a specific color of the diffraction efficiency for a specific color, increase the magnitude and uniformity of the diffraction efficiency of the eyepiece, increase the (CPE) efficiency of the eyepiece, and / or increase the input coupling grating (ICG) emission efficiency of the eyepiece. The pair of optical layers 1306 can be directly disposed on the surface of the waveguide substrate 1302, or there can be one or more intermediate layers (also referred to herein as "underlayers" as described herein) disposed between the pair of optical layers 1306 and the waveguide substrate 1302.

[0086] As shown in FIG. 13A, the input coupling grating 1306 is disposed on the outer surface of the first pair of optical layers 1306a. The diffraction structure 1300a has an upper surface grating 1304a disposed on the outer surface of the upper pair of optical layers 1306a on the first side of the waveguide substrate 1302 and a lower surface grating 1304b disposed on the outer surface of the lower pair of optical layers 1306b on the second side of the waveguide substrate 1302. Accordingly, the upper pair of optical layers 1306a is disposed between the waveguide substrate 1302 and the upper surface grating 1304a, and the lower pair of optical layers 1306b is disposed between the waveguide substrate 1302 and the lower surface grating 1304b. The upper surface grating 1304a and the lower surface grating 1304b have a lower refractive index with respect to the high refractive index element. As some non-limiting examples, the diffraction grating 1304 can be formed of a material such as KT21. KT21 has a refractive index of about 1.5.

[0087] The first mirror element 1308 is installed on the outer surface of the upper optical layer pair 1306a. The surface input coupling grating 1306 is installed on the outer surface of the second optical layer pair 1306a. The light beam 1310 shows an example of the path of the input light beam when the light is processed by the diffraction structure 1300a to provide image objects on a plurality of focal planes within the volumetric 3D simulation display system. The incident angle 1316 of the light beam as it travels through the diffraction structure 1300 is also shown in FIG. 13A.

[0088] Referring to FIG. 13B, the diffraction structure 1300b is the same as the diffraction structure 1300a, except that the first mirror element 1308 is installed on the surface of the first side (i.e., the upper surface) of the waveguide substrate 1302.

[0089] FIG. 13C shows a diffraction structure 1300c that is the same as the diffraction structure 1300b, except that the ICG 1310 is installed on the outer surface of the low refractive index layer 1305b of the lower optical layer pair 1306b.

[0090] The diffraction structure 1300d shown in FIG. 13D is the same as the diffraction structure 1300b, except that the ICG 1310 is installed directly on the lower surface of the waveguide substrate 1302. In fact, this configuration of the ICG 1310, which is installed directly on the surface of the waveguide substrate 1302 and has no optical layer pair of the optical layers between the ICG 1310 and the waveguide substrate 1302, can be used in all of the embodiments shown in FIGS. 13A - 13H because the intervening layer may degrade the performance of the DOE 1300.

[0091] Referring to FIG. 13E, the diffraction structure 1300e is similar to the diffraction structure 1300a, except that it has only the optical layer pair 1306 and the surface grating 1304 on the upper side of the waveguide substrate 1302. Thus, the ICG 1310 is installed directly on the lower surface of the waveguide substrate 1302. Further, the surface grating 1304 is formed by both a grating etched into the high refractive index layer 1307 of the upper optical layer pair 1306 and an overcoat 1312 (which may be a low refractive index layer).

[0092] Referring to FIG. 13F, the diffraction structure 1300f is the same as the diffraction structure 1300e, except that the surface grating 1304a is formed only by etching the high refractive index layer 1307a of the upper optical layer pair 1306a.

[0093] The diffraction structure 1300g shown in FIG. 13G is the same as the diffraction structure 1300a, except that the surface grating 1304a is formed only in the low refractive index overcoat 1312 on the upper side of the waveguide substrate 1302.

[0094] As shown in FIG. 13H, the diffraction structure 1300h is the same as the diffraction structure 1300g, except that the diffraction structure 1300g also includes a high refractive index layer 1314 (e.g., an upper surface layer or coating) on the surface grating 1304a. The high refractive index layer 1314 on the surface grating 1304 can be added to any of the embodiments 1300a-1300f.

[0095] As described herein, the addition of the optical layer pair 1306 between the surface grating 1304 and the waveguide substrate 1302 improves the performance of the eyepiece. The added optical layer pair 1306 provides additional degrees of freedom for adjusting the diffraction efficiency versus the angle of incidence and the wavelength behavior. This effect is likely the result of a combination of the thin film interference effect and the change in the direction of light by Snell's law when light is incident on the surface grating 1304. The ability to adjust the diffraction efficiency versus the angle of incidence and the wavelength potentially enables:

[0096] a. By sharing all colors (e.g., the three primary colors) in a single waveguide and selectively adjusting the diffraction efficiency for a particular color in a single substrate eyepiece that propagates in different angular ranges of the angle of incidence 1316, resulting in better color uniformity, and

[0097] b. By better matching the diffraction efficiency to the bounce interval (the outcoupled beam density) and the ICG emission efficiency (which also depends on the angle of incidence 1316), improving the uniformity across the field of view.

[0098] Referring to FIGS. 14A and 14B, each graph shows the diffraction efficiency versus the angle of incidence for a square diffraction structure having a surface grating of square grooves on glass without the optical layer pair 1306 (FIG. 14A) as compared to a diffraction structure having a single optical layer pair 1306 (FIG. 14B). The diffraction structure 1300 having a single optical layer pair 1306 is schematically shown in FIG. 14C. The diffraction structure of FIG. 14C includes an optical layer pair 1306 having a low refractive index layer 1305 with a coating / membrane of SiO2 and a high refractive index layer 1306 with a coating / membrane of TiO2. The graphs of FIGS. 14A and 14B show that the diffraction efficiency of the diffraction structure 1300 having the optical layer pair 1306 increases at a higher angle of incidence 1316, the bounce interval decreases, which helps to compensate for the lower out-coupled power.

[0099] FIGS. 15A and 15B show a comparison of the response of a single diffraction structure in the three primary colors (red, blue, green, RGB) with (FIG. 15B) and without (FIG. 15A) the use of the optical layer pair 1306. The diffraction structure used in the image of FIG. 15B included a double-sided surface grating imprint having a honeycomb structure and a waveguide substrate formed from TAFD55 glass and coated with the optical layer pair 1306 under the imprinted grating. The optical layer pair 1306 included a high refractive index layer 1307 with a 100 nm thick TiO2 layer and a low refractive index layer 1305 with a 10 nm thick SiO2 layer. As shown in FIG. 15A, the blue light has the brightest blue region 1502 and the less bright blue is 1504, the green light has the brightest green region 1506 and the less bright green region 1508, and the red light has the brightest red region 1510 and the less bright red region 1512. FIG. 15

[0100] The goal of color response is to obtain maximum overlap of all three colors. As shown in FIGS. 15A and 15B, this occurs near the center. Red and blue typically appear on opposite sides of the field of view. Expanding either of these colors towards the center helps to provide a larger area with appropriate color overlap and the potential to obtain an appropriate color image. As can be seen by comparing FIGS. 15A and 15B, the use of the optical layer pair 1306 expands red at the center of the image, and this particular optical layer pair 1306 is designed to enhance it. In FIG. 15B, red is present in more than 3 / 4 of the image within the eyepiece coated with the optical layer pair 1306, while in FIG. 15A without the optical layer pair 1306, red is present in only about 1 / 2 of the image. Generally, higher refractive index coatings, and combinations of coatings with multiple refractive indices, result in larger and more complex variations in diffraction efficiency. For a three-layer eyepiece stack where each layer is separately optimized for red, green, and blue wavelengths, the addition of the coating of the optical layer pair 1306 affects the diffraction efficiency as described above, which in turn affects the overall optical performance as further described below.

[0101] FIG. 16A schematically shows a substrate structure 1300 having an ICG 1310 and a CPE 1318. The CPE 1318 is a grating structure of various heights as shown in FIG. 16A. A display engine (e.g., a projector) couples light into the waveguide substrate 1302 via the ICG 1310. For example, the display engine can be a liquid crystal on silicon (LCOS) display. Each LCOS pixel is mapped to a specific angle of incidence at the location of the ICG 1310.

[0102] FIG. 16B is a momentum space diagram of the substrate structure 1300 of FIG. 16A. In the momentum space diagram, each incident angle is mapped to the momentum of the light indicated by the box 1320 on the right side. The light in the waveguide propagating towards the CPE 1318 consists of light rays, and the momentum of the light rays is shifted by the ICG lattice vector (2π / lattice period). The corresponding momentum of the in-coupled light is inside the box 1322 on the left side. All these light rays interact with the lattice region in the CPE 1318 that undergoes an appropriate shift in momentum space (upper box 1324 and lower box 1326). The CPE lattice 1318 is designed to disperse the light and out-couple it. FIG. 16C shows a typical example of the emission efficiency as a function of the incident angle of the substrate structure 1300. The diffraction efficiency for s-polarized light subject to CPE diffraction shown in FIG. 16B is shown in FIG. 16D. As is clear from FIGS. 16C and 16D, both the emission efficiency and the diffraction efficiency of the lattice are highly non-uniform as a function of the incident angle of the light, and thus the momentum of the display pixel. Another factor contributing to the non-uniformity is the non-uniformity in the amount of interaction between the light rays in the waveguide 1302 and the diffraction grating 1304. For the light rays in the waveguide within the momentum outline by the box 1322 on the left side of FIG. 16B, the number of hits with the surface grating 1304 for a propagation distance of 2 mm is shown in FIG. 16E. Thus, the light rays corresponding to the left part of the field of view interact more strongly compared to the light rays corresponding to the right part of the field of view. As a result, within the CPE 1318 region, the position of the strongest emission from a particular display pixel varies greatly, resulting in a non-uniform distribution of the emission at a given position. This is schematically shown in FIG. 16F together with the simulated light distribution at the center of the CPE 1318. Ideally, the distribution shown in the upper schematic should be uniform across all fields of view.

[0103] Ideally, the distribution shown in the upper schematic should be uniform across all fields of view.

[0104] To capture the role of diffraction efficiency, the CPE efficiency across the field of view is defined as the multiplication of the diffraction efficiency, the number of hits with the grating, and the ICG emission efficiency (normalized with an appropriate factor). This quantification is shown by the following equation:

[0105] CPE 効率(θx,θy) = Diffraction efficiency × (Number of hits within 2 mm) / 10 × ICG emission efficiency

[0106] Figures 17A and 17B show a comparison of the uniformity of diffraction efficiency for a diffraction structure without an optical layer pair 1306 (Figure 17A) compared to a diffraction structure with a single optical layer pair 1306 (Figure 17B). Figure 17A corresponds to a single-layer design consisting of a TAFD55 glass waveguide substrate 1302 and a surface grating 1304 of a 20 nm thick KT21 material layer. Figure 17B corresponds to the same design as in Figure 17B, but with the addition of a single optical pair 1306 having a high refractive index layer 1307 of 90 nm thick TiO2 and a low refractive index layer 1305 of 10 nm thick SiO2 inserted between the waveguide substrate 1302 and the surface grating layer 1304. In both Figures 17A and 17B, the left 2d plot shows the variation of the diffraction efficiency, the central 2d plot shows the CPE efficiency defined above, and the right 2d plot shows the normalized radiation distribution within a 4 mm square box centered on the CPE. The simulations were performed using in-house ray tracing software.

[0107] For ideal uniform emission near the CPE center (where the human eye is located), the CPE efficiency should be uniform across the field of view. Diffraction efficiency engineering by adding the optical layer pair 1306 reduces the non-uniformity of the CPE efficiency, as shown by the central 2d plots in FIGS. 17A and 17B. The uniformity gain is recognized by a full ray tracing simulation. The uniformity is characterized by a typical 8020 uniformity (the difference between the 80th percentile value and the 20th percentile value divided by the median 50th percentile value) across the inner 80% of the field of view. The lower the value of the 8020 uniformity score, the better the uniformity. This is an example, but additional optimizations based on different combinations of coatings and overcoatings can be implemented to optimize the uniformity of the CPE efficiency and, as a result, the extended reality (XR) waveguide display across the field of view.

[0108] In addition to the architectures presented above in FIGS. 13A - 13G, 14C, and 16 (possible with patterns of organic materials on the high refractive index layer 1305 using photolithography or imprint lithography with an ultra-thin RLT (about 20 nm such as ML's J-FILTM)), the architecture should function similarly for the angles considered in the following cases:

[0109] 1) The high refractive index grating can be etched (using reactive ion etching "RIE", inductively coupled plasma etching "ICP", ion beam etching "IBE", etc.) using pattern definition from the organic layer.

[0110] 2) The high refractive index layer can be further deposited on top of the organic pattern using a PVD (sputtering, evaporation) or "CVD" (low pressure plasma CVD "LPPECVD", atomic layer deposition "ALD", "atmospheric pressure plasma enhanced" APPECVD) process, and it defines the pattern for the overcoat high refractive index layer.

[0111] 3) The second low refractive index layer can be deposited on the first high refractive index layer (above the first low refractive index layer) that is etched (RIE, ICP, IBE) using a patterned resist.

[0112] 4) Similarly, the second low refractive index layer having a pattern can obtain a high refractive index overcoat using a PVD (sputtering, evaporation) or CVD (PPPECVD, ALD, APPECVD) process that defines a high refractive index pattern.

[0113] The high refractive index layer 1307 can be a film or coating applied as described herein. The high refractive index layer 1307 can include various inorganic materials such as Si3N4, ZrO2, TiO2, SiC, ZnTe, GP, BP and / or similar materials having a high refractive index (greater than 1.7), and low absorption (k < 0.001) type materials having a high refractive index greater than 1.7 and low absorption (k < 0.001). The high refractive index layer 1307 can also include any suitable organic filler-based material such as an organic UV and / or thermosetting resin composite composed of sulfur, aromatic groups (maintaining a high refractive index of the polymer substrate > 1.6), and high refractive index nanoparticles having a functional surface (e.g., ZrO2, TiO2), preventing particle aggregation and maintaining uniform particle dispersibility in the composite resin solution (which can lead to internal scattering of light in TIR across a uniformly homogeneous high refractive index film).

[0114] The low refractive index layer 1305 can also be a film or coating applied as described herein. The low refractive index layer 1305 can include, without limitation, any suitable inorganic materials such as MgF, SiO2, and organic materials having a refractive index in the vicinity of about 1.53 such as normal UV and thermosetting resins, and Teflon (registered trademark) type materials having a refractive index of about 1.3. Sol-gel type techniques can be used to create porous materials whose refractive index can reach 1.1 to 1.2 (which can cause internal scattering of light in TIR across a uniformly homogeneous low refractive index film). As shown in FIGS. 13A - 13G, the pattern of the surface grating 1304 and the optical layer pair 1306 of the diffraction structure 1300 can be on the same side, the opposite side, or both sides of the waveguide substrate 1302.

[0115] The diffraction structure 1300 disclosed herein can be manufactured using any suitable manufacturing technique. Certain high refractive index polymers such as those known as "MR174" can be directly embossed, printed, or etched to produce the desired patterned structure, but there can be issues regarding the curing shrinkage of such layers. Thus, in another embodiment, another material can be imprinted, embossed, or etched onto a high refractive index polymer layer (i.e., a layer of MR174, etc.) to produce functionally similar results. State-of-the-art printing, etching (which can include resist removal and patterning steps similar to those utilized in conventional semiconductor processes), and embossing techniques can be utilized and / or combined to achieve such printing, embossing, and / or etching steps. For example, molding techniques similar to those utilized in the manufacture of DVDs can also be utilized in certain replication processes. Additionally, certain jetting or deposition techniques utilized in printing and other deposition processes can be utilized to accurately deposit certain layers.

[0116] In the foregoing specification, the present invention has been described with reference to its specific embodiments. However, it will be apparent that various modifications and changes can be made without departing from the broader spirit and scope of the present invention. For example, the above process flow is described with reference to a specific order of process operations. However, many of the described orders of process operations can be changed without affecting the scope or operation of the present invention. Accordingly, the present specification and drawings should be regarded in an illustrative rather than a limiting sense.

[0117] Various exemplary embodiments of the present invention are described herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate more broadly applicable aspects of the present invention. Various changes can be made to the described invention, and equivalents can be substituted without departing from the true spirit and scope of the present invention. Further, many modifications can be made to adapt a particular situation, material, composition of matter, process, process act or step to the objectives, spirit or scope of the present invention. Further, as will be understood by those skilled in the art, each of the individual variations described and illustrated herein has separate components and features that can be readily separated from or combined with features of any of several other embodiments without departing from the scope or spirit of the present invention. All such modifications are intended to be within the scope of the claims related to this disclosure.

[0118] The present invention includes methods that can be carried out using the subject device. The methods can include the act of providing such a suitable device. Such provision can be done by an end user. In other words, the act of "providing" simply requires the end user to obtain, access, approach, position, set, activate, power on, or otherwise act to provide the device required in the method. The methods recited herein can be carried out in any order of the recited logically possible events, as well as in the order of the recited events.

[0119] Exemplary aspects of the present invention are described above along with details regarding the selection and manufacture of materials. Regarding other details of the present invention, these are related to the patents and publications referenced above, as well as those generally known or recognized by those skilled in the art. The same may apply to the method-based aspects of the present invention with respect to additional operations that are commonly or logically used.

[0120] Furthermore, the present invention is described with reference to several examples incorporating various features as necessary, but the present invention is not limited to what is described or shown as contemplated for each variation of the present invention. Without departing from the true spirit and scope of the present invention, various changes can be made to the described present invention, and equivalents (whether listed herein or not included for the sake of some brevity) can be substituted. Further, when a range of values is provided, it is understood that all intervening values between the upper and lower limits of that range, as well as any other described value or intervening value within the described range, are included in the present invention.

[0121] Any optional features of the described variations of the present invention are also contemplated to be described and claimed independently or in combination with any one or more of the features described herein. References to singular items include the possibility that there are multiple of the same item. More specifically, as used in this specification and the claims associated with this specification, the singular forms "a", "an", "the foregoing", and "the" include plural referents unless otherwise specified. In other words, the use of an article enables the subject item in the above description, as well as "at least one" of the claims associated with this disclosure. Further, note that such claims can be drafted to exclude any optional elements. Thus, this description is intended to serve as a preamble for using exclusive terms such as "alone", "only", etc. in relation to the listing of elements of the claims or the use of "negative" limitations.

[0122] Without using such exclusive terms, the term "comprising" in the claims related to the present disclosure shall allow for the inclusion of any additional elements, regardless of whether a given number of elements are recited in such claims or whether the addition of a feature can be regarded as transforming the nature of the elements recited in such claims. Unless specifically defined herein, all technical and scientific terms used herein shall be given the broadest commonly understood meaning possible while maintaining the validity of the claims.

[0123] The scope of the present invention is not limited by the examples and / or the designation of the subject matter provided, but rather is limited only by the language of the claims related to the present disclosure.

[0124] The above description of the illustrated embodiments is not intended to be exhaustive or to limit the embodiments to the exact forms disclosed. Embodiments and examples are described herein for illustrative purposes, but various equivalent modifications can be made without departing from the spirit and scope of the present disclosure, as will be recognized by those skilled in the art. The teachings provided herein for various embodiments can be applied not necessarily to the above-described exemplary AR systems, but to other devices implementing virtual or AR or hybrid systems and / or using a user interface.

[0125] For example, the foregoing detailed description has described various embodiments of devices and / or processes via the use of block diagrams, schematics, and examples. As long as such block diagrams, schematics, and examples include one or more functions and / or operations, it will be understood by those skilled in the art that each function and / or operation within such block diagrams, flowcharts, or examples can be implemented individually and / or collectively by a wide range of hardware, software, firmware, or substantially any combination thereof.

[0126] In one embodiment, the subject matter can be implemented via an application specific integrated circuit (ASIC). However, one of ordinary skill in the art will recognize that, in the embodiments disclosed herein, in whole or in part, as one or more computer programs executed by one or more computers (e.g., as one or more programs operating on one or more computer systems), as one or more programs executed on one or more controllers (e.g., microcontrollers), as one or more programs executed by one or more processors (e.g., microprocessors), as firmware, or as substantially any combination thereof, it can be implemented equivalently to a standard integrated circuit, and that designing the circuitry and / or writing code for software and / or firmware is within the skill of one of ordinary skill in the art in light of the teachings of this disclosure.

[0127] When logic is implemented as software and stored in a memory, the logic or information can be stored on any computer-readable medium for use by or in connection with any processor-related system or method. In the context of this disclosure, a memory is a computer-readable medium that is an electronic, magnetic, optical, or other physical device or means that includes or stores a computer and / or processor program. Logic and / or information can be embodied on any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device such as a computer-based system, a system including a processor, or another system that can fetch instructions from the instruction execution system, apparatus, or device and execute the instructions associated with the logic and / or information.

[0128] In the context of this specification, a "computer-readable medium" can be any element that can store logic and / or programs associated with information for use by or in connection with an instruction execution system, apparatus, and / or device. A computer-readable medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device. More specific examples (non-exhaustive list) of computer-readable media include portable computer disks (magnetic, compact flash (registered trademark) cards, secure digital, etc.), random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM, EEPROM, or flash memory), portable compact disk read-only memory (CDROM), digital tape, and other non-transitory media.

[0129] Any of the methods described herein can be executed using variations. For example, many of the methods can include additional operations, omit some operations, and / or execute operations in a different order than that illustrated or described.

[0130] Additional embodiments can be provided by combining the various embodiments described above. All U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, and non-patent publications mentioned herein and / or listed in the application data sheet, unless inconsistent with the specific teachings and definitions of this specification. Aspects of the embodiments can be modified, if necessary, to use the systems, circuits, and concepts of various patents, applications, and publications to provide further embodiments.

[0131] These and other modifications can be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be construed as limiting the claims to the specific embodiments disclosed in the specification and claims, but rather such claims should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the present disclosure.

[0132] Furthermore, various embodiments described above can be combined to provide additional embodiments. Aspects of the embodiments can be modified, as needed, to utilize concepts from various patents, applications, and publications to provide further embodiments.

[0133] These and other modifications can be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be construed as limiting the claims to the specific embodiments disclosed in the specification and claims, but rather such claims should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the present disclosure.

Claims

1. An eyepiece for an XR display system, wherein the eyepiece receives light associated with one or more frames of image data and includes a diffractive optical element (DOE) for directing the light towards a user's eye, the DOE includes a diffractive structure, the diffractive structure having a waveguide substrate having a first side and a second side opposite the first side, a surface grating positioned on the first side of the waveguide substrate, and one or more optical layer pairs disposed between the waveguide substrate and the surface grating, each optical layer pair includes a low refractive index layer and a high refractive index layer disposed directly outside the low refractive index layer, the high refractive index layer having a refractive index higher than that of the low refractive index layer, the eyepiece.

2. The eyepiece according to claim 1, wherein the one or more optical layer pairs are disposed directly on the first side of the waveguide substrate.

3. The eyepiece according to claim 1, further comprising one or more intermediate layers disposed between the optical layer pair and the waveguide substrate.

4. The one or more optical layer pairs, a first optical layer pair on the first side of the waveguide substrate, and a second optical layer pair on the second side of the waveguide substrate The eyepiece according to any one of claims 1 to 3.

5. The eyepiece according to any one of claims 1 to 4, further comprising a second surface grating on the second side of the waveguide substrate, the second optical layer pair being between the waveguide substrate and the second surface grating.

6. The eyepiece according to any one of claims 1 to 5, further comprising an input coupling grating disposed on the first side of the waveguide substrate and a first mirror disposed on the second side of the waveguide substrate.

7. The eyepiece according to any one of claims 1 to 6, wherein the waveguide substrate has a refractive index higher than that of the low refractive index layer.

8.

9. The eyepiece according to any one of claims 1 to 8, wherein the grating surface has a refractive index lower than that of the high refractive index layer. The high refractive index layer is Si ３ N ４ , ZrO ２ , TiO ２ , SiC, ZnTe, GP, and BP, and the high refractive index layer has a refractive index greater than about 1.7 The low refractive index layer is composed of a material selected from the group consisting of MgF, SiO ２ , a UV curable resin, and a thermosetting resin, and the low refractive index layer has a refractive index smaller than about 1.

53. The eyepiece according to any one of claims 1 to 7.

10. The eyepiece according to any one of claims 1 to 9, further comprising an upper surface layer disposed on an outer surface of the surface grating, the upper surface layer having a refractive index higher than that of the low refractive index layer.

11. An extended reality (XR) display system for delivering extended reality content to a user, the system comprising ​ ​ An image light source for providing one or more frames of image data, an optical modulator for transmitting light associated with the one or more frames of image data, and a diffractive optical element (DOE) that receives light associated with the one or more frames of image data and directs the light toward a user's eye comprising: The DOE includes a waveguide substrate having a first side and a second side opposite the first side, a surface grating positioned on the first side of the waveguide substrate, and a diffractive structure having one or more pairs of optical layers disposed between the waveguide substrate and the surface grating. Each pair of optical layers includes a low refractive index layer and a high refractive index layer directly disposed outside the low refractive index layer, and the high refractive index layer has a higher refractive index than the low refractive index layer, XR display system. **Claim 12** The system according to claim 11, wherein the one or more pairs of optical layers are directly disposed on the first side of the waveguide substrate. **Claim 13** The system according to claim 11, wherein the diffractive structure further comprises one or more intermediate layers disposed between the pair of optical layers and the waveguide substrate. **Claim 14** The one or more pairs of optical layers include a first pair of optical layers on the first side of the waveguide substrate, and a second pair of optical layers on the second side of the waveguide substrate. The system according to any one of claims 11 to 13. **Claim 15** The diffractive structure further comprises a second surface grating on the second side of the waveguide substrate, and the second pair of optical layers is between the waveguide substrate and the second surface grating. The system according to any one of claims 11 to 14. **Claim 16** an input coupling grating disposed on the first side of the waveguide substrate, and a first mirror disposed on the second side of the waveguide substrate The system according to any one of claims 11 to 15, further comprising. **Claim 17** The waveguide substrate has a refractive index higher than the refractive index of the low refractive index layer. The system according to any one of claims 11 to 16. **Claim 18** The high refractive index layer is Si ３ N ４ , ZrO ２ , TiO ２ , SiC, ZnTe, GP, and BP, and the high refractive index layer has a refractive index greater than about 1.7 The low refractive index layer is composed of a material selected from the group consisting of MgF, SiO ２ , a UV curable resin, and a thermosetting resin, and the low refractive index layer has a refractive index smaller than about 1.53, the system according to any one of claims 11 to 17. **Claim 19** The grating surface has a refractive index lower than the refractive index of the high refractive index layer. The system according to any one of claims 11 to 18. **Claim 20** The diffractive structure further comprises an upper surface layer disposed on an outer surface of the surface grating, and the upper surface layer has a refractive index higher than the refractive index of the low refractive index layer. The system according to any one of claims 11 to 19. **Claim 21** The DOE comprises a stacked waveguide assembly having a plurality of diffraction structures stacked together, and the plurality of diffraction structures includes the diffraction structure, and the system according to any one of claims 11 to 19.

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