EP4689483A1

EP4689483A1 - Augmented reality eyewear display using diffractive and reflective lightguides

Info

Publication number: EP4689483A1
Application number: EP23744275.1A
Authority: EP
Inventors: Alexander Koshelev; Christophe Peroz
Original assignee: Google LLC
Current assignee: Google LLC
Priority date: 2023-06-22
Filing date: 2023-06-22
Publication date: 2026-02-11
Also published as: WO2024263165A1

Abstract

Techniques for implementing an augmented reality (AR) eyewear display using a combination of diffractive and reflective lightguides are disclosed. An AR light combiner includes a reflective lightguide that expands the pupil of a light engine in one dimension. After the light is expanded through the reflective lightguide, the expanded pupil is coupled via a diffractive input grating into a diffractive lightguide acting as another pupil expander in another dimension, where the one-dimensional expansion of the reflective lightguide is substantially perpendicular to a one-dimensional expansion of the diffractive lightguide.

Description

AUGMENTED REALITY EYEWEAR DISPLAY USING DIFFRACTIVE AND REFLECTIVE LIGHTGUIDES

BACKGROUND

[0001] The present disclosure relates generally to an augmented reality (AR) eyewear display. In an AR eyewear display, light from an image source is coupled into a light guide substrate, generally referred to as a lightguide or waveguide, by an input optical coupling such as an in-coupling grating (i.e., an “incoupler”), which can be formed on a surface, or multiple surfaces, of the substrate or disposed within the substrate. Once the light beams have been coupled into the lightguide, the light beams are “guided” through the substrate, typically by multiple instances of total internal reflection, to then be directed out of the lightguide by an output optical coupling (i.e., an “outcoupler”), such as a reflective facet or an optical grating, to an eyebox (i.e., a volume where the eye receives an acceptable view of the image produced by a light engine with respect to a set of criteria and thresholds). The light beams projected from the lightguide overlap at an eye relief distance from the lightguide forming an exit pupil within which a virtual image generated by the image source can be viewed by the user of the eyewear display.

SUMMARY OF EMBODIMENTS

[0002] Techniques and systems described herein are directed in part to a lens element for an augmented reality (AR) eyewear display. In some embodiments, the lens element includes a diffractive incoupler configured to receive display light; a diffractive outcoupler configured to direct the display light toward an eye of a user; and a reflective lightguide configured to direct display light toward the diffractive incoupler. In some embodiments, the diffractive incoupler defines a first grating vector corresponding to a direction in which light is directed by the diffractive incoupler; the diffractive outcoupler defines a second grating vector corresponding to a direction in which light is directed by the diffractive outcoupler; and the first grating vector and the second grating vector are substantially aligned with a horizontal dimension of the lens element. In some embodiments, the diffractive incoupler is configured to compensate for spectral dispersion associated with the diffractive outcoupler by substantially matching a pitch and orientation of a grating of the diffractive incoupler with a pitch and orientation of a grating of the diffractive outcoupler. In some embodiments, the lens element includes a diffractive lightguide; and a recycling grating located and configured to direct light transmitted in the diffractive lightguide toward the diffractive outcoupler. In some embodiments, the reflective lightguide includes at least one surface at least partially shielded from external light sources. In some embodiments, light directed into the reflective lightguide by a light engine is substantially parallel to light directed into the diffractive incoupler by the reflective lightguide. In some embodiments, a prism is configured to direct light from the reflective lightguide toward the diffractive incoupler. In some embodiments, at least a portion of the reflective lightguide directs light away from the diffractive incoupler and into the prism. In some embodiments, the prism is at least partially located on a world side of the lens element. In some embodiments, the prism forms a portion of the reflective lightguide. In some embodiments, the reflective lightguide is positioned substantially parallel to the diffractive lightguide.

[0003] In other embodiments, a device is disclosed including a diffractive lightguide; and a reflective lightguide configured to: receive display light from a light engine; and direct the display light into the diffractive lightguide. In some embodiments, the reflective lightguide is configured to direct light toward an incoupler of the diffractive lightguide. In some embodiments, the device further includes a recycling grating configured to direct light transmitted in the diffractive lightguide toward a diffractive outcoupler. In some embodiments, the reflective lightguide includes at least one surface at least partially shielded from external light sources. In some embodiments, the reflective lightguide includes a prism configured to direct light from the reflective lightguide toward an incoupler of the diffractive lightguide. In some embodiments, the prism is at least partially located on a world side of the diffractive lightguide. In some embodiments, the device further includes a lens element including: a diffractive incoupler defining a first grating vector corresponding to a direction light is directed by the diffractive incoupler; and a diffractive outcoupler defining a second grating vector corresponding to a direction light is directed by the diffractive outcoupler, wherein the first grating vector and the second grating vector are substantially aligned with a horizontal dimension of the lens element. [0004] In other embodiments, a method is disclosed including: directing light from an edge of a reflective lightguide into a diffractive lightguide; and outcoupling the light from the diffractive lightguide. In some embodiments, the method includes redirecting at least a portion of the light directed into the diffractive lightguide using a recycling grating.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference symbols in different drawings indicates similar or identical items.

[0006] FIG. 1 is a diagram illustrating a rear perspective view of an example augmented reality (AR) display device using diffractive and reflective lightguides in accordance with some embodiments.

[0007] FIG. 2 is a diagram illustrating a cross-section view of an example implementation of a conventional AR display device.

[0008] FIG. 3 is a set of diagrams illustrating functional aspects of a conventional AR display device like that of FIG. 2.

[0009] FIG. 4 is a diagram illustrating an eye side view of a lens element in accordance with some embodiments.

[0010] FIG. 5 is a diagram illustrating an eye side view of an example AR display device incorporating a lens element like that of FIG. 4 in accordance with some embodiments.

[0011] FIG. 6 is a diagram illustrating a bottom view of the example AR display device of FIG. 5 in accordance with some embodiments.

[0012] FIG. 7 is a set of diagrams illustrating functional aspects of an AR display device like that of FIGS. 5 & 6. [0013] FIG. 8 is a diagram illustrating an eye side view of another example AR display device incorporating a lens element like that of FIG. 4 in accordance with some embodiments.

[0014] FIG. 9 is a diagram illustrating a side view of the example AR display device of FIG. 8 in accordance with some embodiments.

[0015] FIG. 10 is a diagram illustrating a bottom view of another example AR display device incorporating a lens element like that of FIG. 4 using optical adhesive in accordance with some embodiments.

[0016] FIG. 11 is a diagram illustrating a bottom view of another example AR display device incorporating a lens element like that of FIG. 4 using optical adhesive in accordance with some embodiments.

[0017] FIG. 12 is a diagram illustrating a bottom view of another example AR display device incorporating a lens element like that of FIG. 4 and a prism in accordance with some embodiments.

[0018] FIG. 13 is a diagram illustrating a bottom view of another example AR display device incorporating a lens element like that of FIG. 4 using co-planar diffractive and reflective lightguides in accordance with some embodiments.

[0019] FIG. 14 is a diagram illustrating an eye side view of a lens element incorporating a recycling grating in accordance with some embodiments.

[0020] FIG. 15 is a flow diagram illustrating a method of directing display light through an AR eyewear display with diffractive and reflective lightguides in accordance with some embodiments.

DETAILED DESCRIPTION

[0021] Diffractive and reflective lightguides are two types of lightguides conventionally used as augmented reality (AR) light combiners. While the two technologies have their advantages and disadvantages, both suffer from see-through artifacts. Diffractive lightguides utilize diffraction gratings (typically surface relief gratings) to couple light in and out of the lightguide as well as to expand the entrance pupil. Diffraction gratings often cause light from outside sources such as sunlight to diffract into the user’s eye, creating a well-known artifact typically referred to as “rainbow.” While there are a number of mitigation strategies aimed at reducing the brightness of this artifact, these strategies are only of practical use in indoor environments with fairly low brightness sources. Because the brightness of sunlight outdoors is very high, the only conventional way to completely mitigate this artifact is to remove the corresponding diffraction order altogether. In addition, the strong spectral dispersion associated with diffractive gratings resulting from different angles at which different wavelengths (e.g., colors) of light propagate after encountering such gratings often results in limited color uniformity performance.

[0022] Reflective lightguides typically use semi-transparent louver mirrors to achieve light coupling and expansion. Such mirrors introduce very limited spectral dispersion, resulting in high color uniformity performance. The highly directional nature of mirrors causes low world-side emission (i.e. , “eyeglow”) and no “rainbow” artifacts (although there can be limited world-source reflections). However, to achieve good image resolution, reflective lightguides need to be significantly thicker than a typical single plate diffractive lightguide. This results in fewer interactions between the light and optical elements (mirrors) compared to diffractive lightguides, which as a consequence requires that each interaction be relatively more efficient. However, this efficiency can result in significant see-through artifacts. For instance, the light from real-world objects could couple into the lightguide and outcouple with the same angle but in a different location in the eyebox. For objects that are not extremely far away (e.g., at infinity), this creates artifacts known as see-through ghosts. In addition, an orthogonal exit pupil expander of a reflective lightguide typically creates obstruction to the user’s view of the real world because the mirror coatings reflect light even for angular and spectral ranges outside of their primary design and intended purpose.

[0023] FIGS. 1 & 4-15 illustrate techniques for implementing an AR eyewear display using a combination of diffractive and reflective lightguides. Aspects of the present disclosure include an optical architecture for an AR light combiner in which the pupil of a light engine is first expanded in one dimension using a “one-dimensional” reflective lightguide (e.g., via an orthogonal pupil expander reflective lightguide 504 like that shown in FIG. 5, described further hereinbelow). Herein, a “onedimensional” lightguide refers to a lightguide that provides for pupil expansion (e.g., viewable image expansion) primarily along one dimension with little or no expansion along a perpendicular dimension. After the light is expanded in one dimension using such a one-dimensional reflective lightguide, the expanded pupil is coupled via a diffractive input grating into a diffractive lightguide acting as another one-dimensional output coupling expander (e.g., via an orthogonal pupil expander diffractive outcoupler 404 like that shown in FIG. 5, described further hereinbelow), where the one-dimensional expansion of the reflective lightguide is substantially perpendicular to (e.g., approximately 80-100 degrees offset from) the one-dimensional expansion of the diffractive lightguide.

[0024] In some embodiments, the reflective lightguide is located distal to or relatively far from the eyebox and may be folded out of plane or hidden in the glasses frame of an AR eyewear display system in order to limit see-through issues. In some embodiments, the diffractive lightguide is a thin one-dimensional expander with only one grating in the proximity of the eyebox (e.g., an outcoupler 404 like that shown in FIG. 5, described further hereinbelow) within the vicinity of the user eye. By only including a single visible grating (e.g., a single grating located in the proximity of the eyebox), see-through and “rainbow” artifacts are minimized. As is understood by those of ordinary skill in the art, a “k-vector” corresponds to or illustrates a direction in which light is directed by a diffractive grating. In some embodiments, the orientation of a k-vector of the outcoupler grating is selected to be aligned closely with a horizontal aspect or dimension of an optical combiner relative to an intended orientation during use, ensuring that overhead sources are effectively prevented from significantly interacting with the associated diffractive gratings and thus from creating “rainbow” artifacts. This would not be possible with a conventional diffractive lightguide, because traditional diffractive optical combiners typically require at least one diffractive grating with a significant vertical component, which is a primary source of “rainbow” effects. In addition, in some embodiments, the display light diffracts (i.e., is diffracted by diffractive gratings) only twice, as opposed to three times in the conventional diffractive lightguide (e.g., via an incoupler, an exit pupil expander, and an outcoupler). This reduces undesirable spectral dispersion effects and improves color uniformity compared to conventional diffractive lightguides.

[0025] FIG. 1 illustrates a rear perspective view of an example AR display system 100 using diffractive and reflective lightguides in accordance with some embodiments. The AR eyewear display system 100 includes a support structure 102 (e.g., a support frame) to mount to a head of a user and that includes an arm 104 that houses a laser projection system, micro-display (e.g., micro-light emitting diode (LED) display), or other light engine configured to project display light representative of images toward the eye of a user, such that the user perceives the projected display light as a sequence of images displayed in a field of view (FOV) area 106 at one or both of lens elements 108, 110 supported by the support structure 102. In some embodiments, one or both of lens elements 108, 110 include one or more diffractive lightguides, incouplers, and/or outcouplers, as discussed further hereinbelow. In some embodiments, the support structure 102 further includes a reflective lightguide, as discussed further hereinbelow, various sensors, such as one or more front-facing cameras, rear-facing cameras, other light sensors, motion sensors, accelerometers, and the like. The support structure 102 further can include one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth(TM) interface, a WiFi interface, and the like.

[0026] The support structure 102 further can include one or more batteries or other portable power sources for supplying power to the electrical components of the AR eyewear display system 100. In some embodiments, some or all of these components of the AR eyewear display system 100 are fully or partially contained within an inner volume of support structure 102, such as within the arm 104 in region 112 of the support structure 102. In the illustrated implementation, the AR eyewear display system 100 utilizes a spectacles or eyeglasses form factor. However, the AR eyewear display system 100 is not limited to this form factor and thus may have a different shape and appearance from the eyeglasses frame depicted in FIG. 1 .

[0027] One or both of the lens elements 108, 110 are used by the AR eyewear display system 100 to provide an AR display in which rendered graphical content can be superimposed over or otherwise provided in conjunction with a real-world view as perceived by the user through the lens elements 108, 110. For example, laser light or other display light is used to form a perceptible image or series of images that are projected onto the eye of the user via one or more optical elements, including a lightguide, formed at least partially in the corresponding lens element. One or both of the lens elements 108, 110 thus includes at least a portion of a lightguide that routes display light received by an incoupler (not shown in FIG. 1) of the lightguide to an outcoupler (not shown in FIG. 1) of the lightguide, which outputs the display light toward an eye of a user of the AR eyewear display system 100. Additionally, the lightguide employs two substantially orthogonal, one-dimensional exit pupil expanders (not shown in FIG. 1) in the light path between the incoupler and outcoupler, or in combination with the outcoupler, in order to increase the dimensions of the display exit pupil. Each of the lens elements 108, 110 is sufficiently transparent to allow a user to see through the lens elements to provide a field of view of the user’s real-world environment such that the image appears superimposed over at least a portion of the real-world environment.

[0028] FIG. 2 depicts a cross-section view 200 of a conventional implementation of a lens element 201 of an AR eyewear display system including a lightguide 202. Note that for purposes of illustration, at least some dimensions in the Z direction are exaggerated for improved visibility of the represented aspects. In this example, the lightguide 202 is a diffractive lightguide and implements diffractive gratings in a world side 207 at region 208 and/or diffractive gratings in an eye side 205 at region 210, and diffractive gratings of an incoupler 204 are implemented on an eye side 205 of the lens element 201 . The diffractive gratings of region 210 provide outcoupler functionality. Thus, display light 206 from a light source 209 is incoupled to the lightguide 202 via the incoupler 204 and propagated (through total internal reflection, for example) toward the region 208, whereupon the diffractive gratings of the region 208 diffract the incident display light for exit pupil expansion purposes, and the resulting light is propagated to the diffractive gratings of the region 210, which output the display light toward a user’s eye 212. In other examples, the regions 208 and 210 may switch sides, with the diffractive gratings of region 210 formed on the world side 207 and the diffractive gratings of region 208 formed on the eye side 205 of the lens element 201 , however, this may result in the regions 208 and 210 having different positions, dimensions, and shapes and also may require diffractive gratings in each region to have different characteristics. However, the exit pupil expander functionality in conventional diffractive lightguide lens elements such as the lens element 201 expands the light from the light source 209 both horizontally and vertically.

[0029] For example, as shown in FIG. 3, an x-space lightguide diagram 306, discussed further hereinbelow, illustrates an upper right-hand incoupler 310, a righthand exit pupil expander 312, and a central outcoupler 314 located in a lens element 316. The exit pupil expander 312 and outcoupler 314 expand (e.g., via sequential one-dimensional expansions resulting in a two-dimensional pupil expansion) light received from the incoupler 310 vertically and horizontally so that the light will properly interact with the outcoupler 314 and hence provide a desired display in the eyebox of the display. Accordingly, any diffractive gratings used for the exit pupil expander 312 or outcoupler 314 will include gratings that have a vertical component in a corresponding grating vector, which, as discussed further hereinbelow in the context of FIG. 3, can result in overhead light sources such as sunlight creating “rainbow” artifacts visible to a user of the device, as gratings with a vertical component include surfaces oriented such that they readily diffract and/or reflect overhead light into the lens element 316.

[0030] FIG. 3 is a set of diagrams illustrating functional aspects of a conventional lens element 201 like that of FIG. 2. As will be understood by those of ordinary skill in the art, diffractive grating lines are perpendicular to k-space lines. In the k-space diagram 302 of FIG. 3, the left-hand vertical k-space component 318 corresponds to the right-hand conventional exit pupil expander 312 in the x-space lightguide diagram 306. This vertical component of the corresponding left-hand vertical k-space component 318 in the k-space diagram 302 of FIG. 3 indicates that the grating lines in the conventional exit pupil expander include horizontal components (i.e. , the gratings are not oriented completely vertically relative to an intended orientation of the lens element 316 during use), which results in overhead light such as sunlight being able to create a “rainbow” effect in a conventional diffractive lightguide. Generally, if light encounters a grating along the direction of its k-vector (i.e. , perpendicular to the gratings), more diffraction results, while light perpendicular to a k-vector (i.e., parallel to the gratings) produces less diffraction. As shown in the incident ray diagram 304 and the diffracted ray diagram 308 of FIG. 3, light diffracted into a traditional diffractive lightguide like lightguide 202 of FIG. 2 from angles near the upper, left, and lower right sides of the eyebox (as shown in incident ray diagram 304) is diffracted into the eyebox and causes artifacts in the viewable image (as shown in diffracted ray diagram 308). For example, in traditional diffractive lightguide combiners, overhead lighting like sunlight will produce a refracted “rainbow” in the bottom-right quadrant of the eyebox.

[0031] FIG. 4 is a diagram illustrating an eye side view of a diffractive lightguide 400, which in some embodiments is incorporated into a lens element such as lens element 110 of FIG. 1 in accordance with some embodiments. As shown in FIG. 4, the diffractive lightguide 400 includes a diffractive incoupler 402 defining a first grating vector 406 corresponding to a first k-vector of the diffractive incoupler 402 and a diffractive outcoupler 404 defining a second grating vector 408 corresponding to a second k-vector of the diffractive outcoupler 404. In some embodiments, the first grating vector 406 and the second grating vector 408 are substantially aligned with (e.g., within 5-10 degrees of) a horizontal dimension of the lens element relative to the intended orientation of the lens element during use, are substantially parallel (e.g., within 5-10 degrees of one another), and are oriented in opposing directions. In this configuration, as described further hereinbelow in the context of FIG. 5, “rainbow” artifacts that would be produced by overhead lighting in a conventional diffractive lens element like lens element 201 of FIG. 2 are minimized.

[0032] FIG. 5 is a diagram illustrating an eye side view of an example AR display device 500 incorporating a diffractive lightguide 400 like that of FIG. 4 in accordance with some embodiments. In some embodiments, as shown in FIG. 5, a light engine 502 is coupled to the side of a one-dimensional expander reflective lightguide 504. The coupling may be achieved through the polished edge of the reflective lightguide (see, e.g., FIG. 5, described further hereinbelow), using a transmissive or reflective prism, and/or an embedded mirror, or a combination of these elements. In some embodiments, the input light is guided in the reflective lightguide 504 via total internal reflection. The light is partially reflected by a set of semi-transparent reflective louvers 506. This achieves pupil replication in one dimension, turning a relatively small projector pupil (e.g., about 1-5 mm radius) produced by the light engine 502 into a wide beam of light (e.g., about 10-30 mm length). In some embodiments, the expanded beam exits the reflective lightguide through a narrow edge forming an output facet proximal the diffractive lightguide 400 using either a polished edge or a prism and/or mirror attachment. In some embodiments, the angles of the input facet, louver mirror and output facet are selected such that chromatic aberration acquired at or resulting from the input facet in the light produced by the light engine 502 is fully compensated by the dispersion effect of the output facet, similar to the chromatic compensation applied to light as it travels through a flat glass window.

[0033] In some embodiments, the reflective louvers 506 in the reflective lightguide 504 further from the light engine 502 direct light toward the diffractive lightguide 400 slightly after reflective louvers 506 in the reflective lightguide 504 closer to the light engine 502. Although in some embodiments identical coatings are applied to the reflective louvers 506, in some embodiments, different coatings are applied to the reflective louvers 506 in order to enable light to transmit evenly through the reflective lightguide 504 rather than all being reflected into the diffractive lightguide by the first few louvers closest to the light engine 502. In some embodiments, the reflective lightguide includes louvers that operate at different optical power efficiencies for different angles and/or spectra of light to allow light to propagate through and be reflected more evenly through the length of the reflective lightguide 504 to ensure optimal image quality at the diffractive outcoupler 404. In some embodiments, light reflected by the reflective louvers 506 of the reflective lightguide 504 near to the light engine 502 needs to be redirected slightly downwards to be diffracted by the diffractive outcoupler 404 and produce a viewable image, while light further from the light engine 502 in the reflective lightguide 504 needs to be directed slightly upwards to be diffracted by the diffractive outcoupler 404 and produce a viewable image. As such, in some embodiments, the coatings of the reflective louvers 506 are optimized and/or distributed to ensure a substantially uniform or targeted distribution of light (e.g., in terms of opacity, brightness, and color) at the diffractive outcoupler 404. [0034] FIG. 6 is a diagram illustrating a bottom view of the example AR display device 500 of FIG. 5 in accordance with some embodiments. In some embodiments, the input facet 514 (FIG. 5), which in some embodiments is a polished facet, of the reflective lightguide 504 into which the light engine 502 couples and the output facet 606 from which light couples into the diffractive incoupler 402 of the diffractive lightguide 400 have characteristics similar to prisms. As such, this arrangement can cause chromatic aberration as light couples in and out of the reflective lightguide 504. However, by selecting an appropriate input angle 512 and output angle 604, chromatic aberrations at or resulting from the input facet can be effectively compensated by the chromatic aberration at the output facet. In some embodiments, the input and output facets are substantially parallel to provide for such chromatic aberration compensation.

[0035] In some embodiments, an output facet width 508 of the output facet 606 of a reflective lightguide is relatively narrow (1-5 mm) in a direction parallel to the grating vectors of the diffractive incoupler 402 (i.e., in a direction perpendicular to the longitudinal orientation of the gratings). The maximum coupling efficiency into the diffractive lightguide is partially determined by the ratio of the diffractive lightguide thickness to the input beam width along the direction of the incoupler grating vector. This limitation can be derived from the etendue conservation law. Thus, in some embodiments, the fact that the output beam from the reflective lightguide is relatively narrow along the incoupler grating vector (i.e., the output facet width 508 is relatively narrow compared to the thickness of the diffractive lightguide 400, e.g., only 3-8 times wider) improves overall system optical efficiency. The output of the reflective lightguide 504 is then coupled into the diffractive incoupler 402, and is outcoupled through the diffractive outcoupler 404 grating, which, together with the diffractive incoupler, forms a secondary orthogonal pupil expander using one-dimensional diffraction gratings. In some embodiments, the pitch and orientation of grating lines in the diffractive incoupler 402 and the diffractive outcoupler 404 are substantially identical in a matching configuration, ensuring that the spectral dispersion of the incoupler grating is fully compensated by the diffractive outcoupler 404. In some embodiments, the diffractive lightguide thickness 608 (e.g., 0.3-1.2 mm) is in the range of approximately 6% to 120% of the reflective lightguide thickness, which in some embodiments corresponds to the output facet width 508 (e.g., 1 .0-5 mm).

[0036] In some embodiments, after the reflective lightguide 504 expands light in one direction using reflective louvers 506, the light is outcoupled through a narrow edge output facet 606 into an air gap 602 rather than through a long, flat surface like in many conventional reflective lightguides, such that the beam at the edge is only about 2-4 mm wide. Such a small beam can then be efficiently coupled into the thin (e.g., 1 mm thickness) diffractive lightguide. If the beam were instead 10-12 mm, as is often the case in a conventional long, flat surface outcoupling from a reflective lightguide, then it would not be possible to couple into a thin diffractive lightguide due to conservation of etendue.

[0037] In some embodiments, the reflective lightguide 504 is co-optimized with the diffractive lightguide 400 to improve the efficiency and color uniformity of the system. For instance, as discussed above, in some embodiments, the louver mirror coatings are applied in such a way (e.g., using different coating materials or thicknesses) that the field angles comprising a lower portion of the eyebox are redirected towards the diffractive lightguide after field angles comprising higher portions of the eyebox. In this way, the reflective lightguide 504 evenly directs light between the top and the bottom of the one-dimensional outcoupler404 to produce a viewable image in the eyebox. In some embodiments, the relatively narrow beam produced by the reflective lightguide 504 results from the reflective lightguide 504 acting as a vertical one-dimensional pupil expander, while the diffractive lightguide 400 acts as a horizontal one-dimensional pupil expander. Because only the diffractive lightguide 400 is visible in the eyebox, and because it is one-dimensional, optical efficiency, performance, and see-through quality is improved relative to a traditional reflective or diffractive combiner.

[0038] FIG. 7 is a set of diagrams illustrating functional aspects of an AR display device 500 like that of FIGS. 5 & 6. As mentioned above, aspects of the disclosure provide for reduced production of rainbow artifacts. The k-space diagram 702 of FIG. 7 illustrates how light from a light engine propagates in a diffractive lightguide like the diffractive lightguide 400 of FIG. 4-6 as represented in the x-space lightguide diagram 706. As shown in the incident ray diagram 304 and diffracted ray diagram 308 of FIG. 3 and discussed above, in the case of conventional diffraction lightguide, a light source directly overhead, such as sunlight, could be diffracted towards the eye from the pupil expander. However, as shown in incident ray diagram 704 and diffracted ray diagram 708 of FIG. 7, by using a one-dimensional diffractive expander created by the diffractive incoupler 402 and/or the diffractive outcoupler 404, only light sources lower than about 20-30 degrees above the horizon are able to be diffracted towards the eye.

[0039] In some embodiments, as shown in the k-space diagram 702 of FIG. 7, the k-space diagram is closed due to the diffractive lightguide 400 resulting in an even number of diffractions (e.g., two). As noted above with reference to FIG. 3, if light encounters a grating along the direction of its k-vector (i.e., perpendicular to the grating lines), more diffraction results, while light perpendicular to a k-vector (i.e., parallel to the gratings) produces less diffraction. Because the k-vector corresponding to the diffractive lightguide 400 is a substantially horizontal line (e.g., within 5-10° of a pure horizontal line based on an intended orientation of the diffractive lightguide 400 during use), the grating lines are substantially vertical (e.g., within 5-10° of a pure vertical line based on an intended orientation of the diffractive lightguide 400 during use). Most overhead sources such as sunlight will be substantially perpendicular (e.g., within 5-10 degrees) to the k-vector and substantially parallel (e.g., within 5-10 degrees) with the grating lines, thus limiting the diffraction of those sources.

[0040] FIG. 8 is a diagram illustrating an eye side view of an example AR display device 800 incorporating a diffractive lightguide 400 similar to that of FIG. 4 in accordance with some embodiments. FIG. 9 is a diagram illustrating a side view of the example AR display device 800 of FIG. 8 in accordance with some embodiments. In some embodiments, as shown in FIG. 9 and represented by light beams 806, the reflective lightguide 804 is arranged such that the light beams output from the reflective lightguide 804 propagate along a direction approximately parallel to light beams output from the light engine 802 (e.g., within 3-5 degrees). In this case, the light interacts with louver mirrors 808 an even number of times, as it reflects off an upper louver (e.g., downward) into the reflective lightguide 804, and then reflects off other louvers toward the diffractive lightguide 400. In some embodiments, locating the light engine 802 back and away from the diffractive lightguide enables wider variation in AR device form factors.

[0041] FIG. 10 is a diagram illustrating a bottom view of an example AR display device 1000 incorporating a diffractive lightguide 1005 similar to the diffractive lightguide 400 of FIG. 4 using optical adhesive in accordance with some embodiments. FIG. 11 is a diagram illustrating a bottom view of an example AR display device 1100 incorporating a diffractive lightguide 1105 similar to the diffractive lightguide 400 of FIG. 4 using optical adhesive in accordance with some embodiments. Notably, some of the components in FIGS. 10 & 11 , such as the reflective lightguide 504, are located on an eye side 1010 of the diffractive lightguide 1005 and the diffractive lightguide 1105, and, in some embodiments, as shown in FIG. 10, a diffractive incoupler 1006 and a diffractive outcoupler 1008 are generally located on an eye side 1010 of the diffractive lightguide 1005. However, as shown in FIG. 11 , in some embodiments, a diffractive incoupler 1106 and a diffractive outcoupler 1108 are generally located on a world side 1012 of the diffractive lightguide 1105.

[0042] Although in some embodiments an air gap 602 is provided between the reflective lightguide 504 and the diffractive lightguide 400 (see, e.g., air gap 602 in FIG. 6), in some embodiments, no air gap is provided between the reflective and diffractive lightguide. Instead, in some embodiments, as shown in FIG. 10, a transparent optical adhesive 1004 physically joins the reflective lightguide 504 and the diffractive lightguide 1005. However, in some embodiments, the immersion created by the adhesive 1004, i.e., the changes light undergoes upon passing through the adhesive 1004, cannot be used to couple light such as light 1002 directly into the total internal reflection mode of the diffractive lightguide 1005 without the use of the diffractive incoupler 1006 due to the spectral dispersion of the diffractive incoupler 1006 being designed to compensate for the spectral dispersion of the diffractive outcoupler 1008 (and/or, likewise, the diffractive outcoupler 1008 being designed to compensate for the spectral dispersion of the diffractive incoupler 1006). [0043] FIG. 12 is a diagram illustrating a bottom view of an example AR display device 1200 incorporating a diffractive lightguide similar to the diffractive lightguide 400 of FIG. 4 and a prism 1202 in accordance with some embodiments. In some embodiments, a prism 1202 is incorporated with, attached to, collocated with, or located proximal to the reflective lightguide 504, as shown in FIG. 12, so that light directed from the eye side 1010 of the diffractive lightguide 1005 is coupled into the diffractive lightguide 1005 from the world side 1012 of the diffractive lightguide 1005. In this configuration, the diffractive lightguide 1005 acts as a periscope, i.e. , its angle relative to the input beam has minimal or no effect on the angle of the output beam. In some embodiments, using a prism such as prism 1202 to redirect light from the back (e.g., the eye side 1010) of the diffractive lightguide 1005 into the front (e.g., the world side 1012) of the diffractive lightguide 1005 helps ensure that a corresponding AR display device 1200 will be robust enough to withstand flexing of the diffractive lightguide or misalignment between the diffractive lightguide and the prism 1202 and/or reflective lightguide 504. If the light couples into the eye side 1010 and out through the eye side 1010, a flex in the diffractive lightguide 1005 will typically cause undesirable changes (e.g., resulting in image misalignment) in the angle of light exiting the diffractive outcoupler 1008 toward the eye because the diffractive lightguide 1005 acts like a mirror in such an implementation. However, when light is coupled into the world side 1012, it will exit at the same angle even if the lightguide is tilted or bent.

[0044] FIG. 13 is a diagram illustrating a bottom view of an example AR display device 1300 incorporating a diffractive lightguide similar to the diffractive lightguide 400 of FIG. 4 using co-planar diffractive and reflective lightguides in accordance with some embodiments. In the examples of FIGS. 5, 6, and 8-12, the reflective lightguide (e.g., reflective lightguide 504) is folded or angled out of the plane of the diffractive lightguide 400, e.g., towards the eye side 1010 of the diffractive lightguide 400. In such a configuration, the reflective lightguide 504 is easier to hide from the user’s view and enables placement of the reflective lightguide 504 inside, e.g., part of a frame of an AR device like AR eyewear display system 100 of FIG. 1 , such as in the support structure 102, a nose bridge of the support structure 102, or an arm 104 of the support structure, which enables one or more surfaces of the reflective lightguide 504 to be at least partially shielded from external light sources. However, as shown in FIG. 13, in some embodiments, the reflective lightguide 504 is located in-plane with (i.e. , substantially parallel to) the diffractive lightguide 1005, e.g., along their lengths. In some embodiments, in-plane alignment of the reflective lightguide 504 and the diffractive lightguide 1005 simplifies integration between the reflective lightguide 504 and the diffractive lightguide 1005 and/or optimizes manufacturability.

[0045] FIG. 14 is a diagram illustrating an eye side view of a diffractive lightguide 1400 incorporating a recycling grating 1402 in accordance with some embodiments. Due to the relatively large size of the input beam (e.g., length 510 of FIG. 5) relative to the height of the diffractive lightguide 400 (e.g., 40-90% of its height), in some embodiments, the diffractive lightguide 400 is afforded a significant performance advantage by incorporating a recycling grating 1402 into the lens element. In some embodiments, the recycling grating 1402 is a diffraction grating with a pitch of exactly or approximately one half that of (i.e., twice as many diffraction lines per unit length compared to) the diffractive outcoupler 404 grating. The recycling grating 1402 diffracts light back toward the diffractive outcoupler 404 in a way that is still consistent with the dispersion compensation associated with the diffractive incoupler 402 and the diffractive outcoupler 404. In some embodiments, the recycling grating 1402 reflects light back to the diffractive outcoupler 404 that was not outcoupled during a first pass. By using a recycling grating 1402, light is redirected in order to pass through the diffractive outcoupler 404 twice, which improves the efficiency and uniformity of the image produced by the diffractive lightguide 400. The wide input beam in the diffractive lightguide 400 ensures that a large portion of the diffractive outcoupler 404 receives the light from recycling grating and outcouples it, thus improving its utility.

[0046] FIG. 15 is a block diagram illustrating a method 1500 of using an AR eyewear display with diffractive and reflective lightguides in accordance with some embodiments. At block 1502, a light engine, such as the light engine 502 of FIG. 5 or the light engine 802 of FIG. 8, directs light for display into a reflective lightguide, such as the reflective lightguide 504 of FIG. 5 or the reflective lightguide 804 of FIG. 8. At block 1504, the reflective lightguide directs light for the display into a diffractive lightguide, such as the diffractive lightguide 400 of FIG. 4 or FIG. 8. In some embodiments, a recycling grating such as the recycling grating 1402 of FIG. 14 redirects at least a portion of the light directed into the diffractive lightguide using a recycling grating. At block 1506, the diffractive lightguide or a component thereof, such as diffractive outcoupler 404 of FIG. 4, outcouples and transmits the light for display out of the diffractive lightguide and, e.g., toward a user’s eye to provide the intended display.

[0047] In some embodiments, certain aspects of the techniques described above may be implemented by one or more processors of a processing system executing software. The software comprises one or more sets of executable instructions stored or otherwise tangibly embodied on a non-transitory computer readable storage medium. The software can include the instructions and certain data that, when executed by the one or more processors, manipulate the one or more processors to perform one or more aspects of the techniques described above. The non-transitory computer readable storage medium can include, for example, a magnetic or optical disk storage device, solid state storage devices such as Flash memory, a cache, random access memory (RAM) or other non-volatile memory device or devices, and the like. The executable instructions stored on the non-transitory computer readable storage medium may be in source code, assembly language code, object code, or other instruction format that is interpreted or otherwise executable by one or more processors.

[0048] A computer readable storage medium may include any storage medium, or combination of storage media, accessible by a computer system during use to provide instructions and/or data to the computer system. Such storage media can include, but is not limited to, optical media (e.g., compact disc (CD), digital versatile disc (DVD), Blu-Ray disc), magnetic media (e.g., floppy disk, magnetic tape, or magnetic hard drive), volatile memory (e.g., random access memory (RAM) or cache), non-volatile memory (e.g., read-only memory (ROM) or Flash memory), or microelectromechanical systems (MEMS)-based storage media. The computer readable storage medium may be embedded in the computing system (e.g., system RAM or ROM), fixedly attached to the computing system (e.g., a magnetic hard drive), removably attached to the computing system (e.g., an optical disc or Universal Serial Bus (USB)-based Flash memory) or coupled to the computer system via a wired or wireless network (e.g., network accessible storage (NAS)).

[0049] Note that not all of the activities or elements described above in the general description are required, that a portion of a specific activity or device may not be required, and that one or more further activities may be performed, or elements included, in addition to those described. Still further, the order in which activities are listed is not necessarily the order in which they are performed. Also, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure.

[0050] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. Moreover, the particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. No limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.

Claims

WHAT IS CLAIMED IS:

1 . A lens element for an augmented reality (AR) eyewear display, comprising: a diffractive incoupler configured to receive display light; a diffractive outcoupler configured to direct the display light toward an eye of a user; and a reflective lightguide configured to direct display light toward the diffractive incoupler.

2. The lens element of claim 1 , wherein the diffractive incoupler defines a first grating vector corresponding to a direction in which light is directed by the diffractive incoupler; the diffractive outcoupler defines a second grating vector corresponding to a direction in which light is directed by the diffractive outcoupler; and the first grating vector and the second grating vector are substantially aligned with a horizontal dimension of the lens element.

3. The lens element of claim 1 or claim 2, wherein the diffractive incoupler is configured to compensate for spectral dispersion associated with the diffractive outcoupler by substantially matching a pitch and orientation of a grating of the diffractive incoupler with a pitch and orientation of a grating of the diffractive outcoupler.

4. The lens element of any of claims 1 to 3, further comprising: a diffractive lightguide; and a recycling grating located and configured to direct light transmitted in the diffractive lightguide toward the diffractive outcoupler.

5. The lens element of any of claims 1 to 4, wherein the reflective lightguide includes at least one surface at least partially shielded from external light sources.

6. The lens element of any of claims 1 to 5, wherein light directed into the reflective lightguide by a light engine is substantially parallel to light directed into the diffractive incoupler by the reflective lightguide.

7. The lens element of any of claims 1 to 5, further comprising a prism configured to direct light from the reflective lightguide toward the diffractive incoupler.

8. The lens element of claim 7, wherein at least a portion of the reflective lightguide directs light away from the diffractive incoupler and into the prism.

9. The lens element of claim 8, wherein the prism is at least partially located on a world side of the lens element.

10. The lens element of claim 8 or claim 9, wherein the prism forms a portion of the reflective lightguide.

11 . The lens element of any of claims 1 to 5, wherein the reflective lightguide is positioned substantially parallel to the diffractive lightguide.

12. A device, comprising: a diffractive lightguide; and a reflective lightguide configured to: receive display light from a light engine; and direct the display light into the diffractive lightguide.

13. The device of claim 12, wherein the reflective lightguide is configured to direct light toward an incoupler of the diffractive lightguide.

14. The device of claim 12 or claim 13, further comprising a recycling grating configured to direct light transmitted in the diffractive lightguide toward a diffractive outcoupler.

15. The device of any of claims 12 to 14, wherein the reflective lightguide includes at least one surface at least partially shielded from external light sources.

16. The device of claim 12, wherein the reflective lightguide includes a prism configured to direct light from the reflective lightguide toward an incoupler of the diffractive lightguide.

17. The device of claim 16, wherein the prism is at least partially located on a world side of the diffractive lightguide.

18. The device of claim 12, further comprising a lens element comprising: a diffractive incoupler defining a first grating vector corresponding to a direction light is directed by the diffractive incoupler; and a diffractive outcoupler defining a second grating vector corresponding to a direction light is directed by the diffractive outcoupler, wherein the first grating vector and the second grating vector are substantially aligned with a horizontal dimension of the lens element.

19. A method, comprising: directing light from an edge of a reflective lightguide into a diffractive lightguide; and outcoupling the light from the diffractive lightguide.

20. The method of claim 19, further comprising redirecting at least a portion of the light directed into the diffractive lightguide using a recycling grating.