Diffractive structure for asymmetric light extraction and augmented reality device including same

Abstract

A head-mounted display system includes a head-mountable frame; a light projection system configured to output light to provide image content; a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light coupled into the waveguide from the light projection system; a diffractive structure optically coupled to the waveguide, the diffractive structure configured to couple light guided by the waveguide out of the waveguide toward a user side of the head mounted display, the diffractive structure having a grating layer with a plurality of ridges, each ridge having a side inclined or stepped relative to a plane of the waveguide. The diffractive structure directs the light guided by the waveguide towards the user side by at least 25% more than towards the world side.

Description

Technical Field

[0001] The present disclosure relates to display systems, and more particularly, to augmented and virtual reality display systems and diffractive structures for use therewith. Background Art

[0002] Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images, or portions thereof, are presented to a user in a manner that appears to be real or can be perceived as real. Virtual reality or "VR" scenes generally involve the presentation of digital or virtual image information without being transparent to other actual real-world visual input; augmented reality or "AR" scenes generally involve the presentation of digital or virtual image information as an enhancement to the visualization of the actual world around the user. Mixed reality or "MR" scenes are a type of AR scene, and generally involve virtual objects that are integrated into and responsive to the natural world. For example, in an MR scene, AR image content can be occluded by objects in the real world or perceived to interact with objects in the real world.

[0003] refer to Figure 1 , shows an augmented reality scene 10 in which a user of AR technology sees a real-world park-like setting 20 that features people, trees, buildings in the background, and a concrete platform 30. In addition to these items, the user of the AR technology also perceives that he "sees" "virtual content," such as a robot statue 40 standing on the real-world platform 30, and a cartoon-like avatar character 50 flying by that appears to be an avatar of a bumblebee, even though these elements 40, 50 do not exist in the real world. Because the human visual perception system is complex, it is extremely challenging to produce AR technology that facilitates comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0004] The systems and methods disclosed herein address various challenges associated with AR and VR technologies. Summary of the invention

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

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

[0007] In general, in a first aspect, the disclosure features a head-mounted display system, comprising: a head-mountable frame; a light projection system configured to output light to provide image content; a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light coupled into the waveguide from the light projection system; a diffractive structure optically coupled to the waveguide, the diffractive structure configured to couple light guided by the waveguide out of the waveguide toward a user side of the head-mounted display, the diffractive structure having a grating layer with a plurality of ridges (e.g., grating lines), the plurality of ridges each having a side that is inclined or stepped relative to a plane of the waveguide. The diffractive structure directs at least 25% more light guided by the waveguide toward the user side than toward the world side.

[0008] Examples of the head mounted display system may include one or more of the following features. For example, the ridges may have a profile shape selected from the group consisting of: trapezoidal (e.g., tilted gratings, such as Sharkfin gratings, truncated triangle gratings), parallelogram (e.g., tilted gratings), triangle (e.g., sawtooth and other blazed grating shapes), and stepped (e.g., where each step has the same shape, or steps with different shapes).

[0009] The angle of the side relative to the waveguide plane can be in the range of 20° to 80° (e.g., about 30° or more, about 40° or more, about 50° or more, about 60° or more, about 80° or less, about 70° or less). The ridges can have a height in the range of 10nm to 1,000nm (e.g., 50nm to 500nm, 100nm to 400nm, 200nm to 400nm, 250nm to 350nm). The ridges can have a pitch in the range of 100nm to 5,000nm (e.g., 100nm to 2,500nm, 100nm to 1,000nm, 200nm to 750nm, 250nm to 500nm, 300nm to 400nm, 100nm to 200nm). The ridges have a duty cycle in a range of 20% to 100% (eg, 10% to 75%, 20% to 50%, 30% to 40%).

[0010] The head mounted display may include a layer of material having the same refractive index as the material forming the ridges of the diffractive structure, the layer of material being arranged between the waveguide and the diffractive structure. The layer may have a thickness in the range of 5 nm to 50 nm (e.g., 10 nm to 30 nm, 10 nm to 20 nm).

[0011] The grating layer may include a grating material having a refractive index of 1.5 or greater (e.g., 1.6 or greater, 1.7 or greater, 1.8 or greater, 1.9 or greater) at an operating wavelength.

[0012] The head mounted display may comprise an input coupling grating (ICG) arranged to couple light into the waveguide, wherein the ICG and the diffractive structure are arranged on a same side of the waveguide.

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

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

[0015] The diffractive structure may include a plurality of regions, wherein the structure of the grating layer is different in at least two regions. The grating structure of the grating layer may change abruptly from a first region to a second region adjacent to the first region. In some examples, the grating structure of the grating layer changes continuously across the region of the diffractive structure.

[0016] At least some of the ridges may have a single step geometry.

[0017] Alternatively or additionally, at least some of the ridges have a multi-step geometry.The ridges having a multi-step geometry may comprise steps having an inclined geometry.

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

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

[0020] The grating layer may be etched into the waveguide. Alternatively, the grating layer may be formed in a layer of material deposited on the waveguide (eg a layer of material having a refractive index in the range from 1.5 to 2.7).

[0021] The diffractive structure may include a layer of material deposited on a ridge of the grating layer. The layer of material may be deposited on less than all faces of the ridge. The layer of material may be deposited on all faces of the ridge. The layer of material may have a refractive index in the range of 1.7 to 2.7. The layer of material may have a refractive index in the range of from 1.3 to 1.5.

[0022] Other features and advantages will be apparent from the accompanying drawings, the following description, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 An augmented reality (AR) view seen by a user through an AR device is shown.

[0024] Figure 2 A conventional display system for simulating a three-dimensional image for a user is shown.

[0025] Figures 3A to 3C The relationship between the radius of curvature and the focal radius is shown.

[0026] Figure 4A Shown is a representation of the accommodation-vergence response of the human visual system.

[0027] Figure 4B Examples of different accommodation and convergence states of a pair of eyes of a user are shown.

[0028] Figure 4C An example of a top view representation of a user viewing content via a display system is shown.

[0029] Figure 4D Another example of a top view representation of a user viewing content via a display system is shown.

[0030] Figure 5 Aspects of a method for simulating three-dimensional images by modifying wavefront divergence are shown.

[0031] Figure 6 An example of a waveguide stack for outputting image information to a user is shown.

[0032] Figure 7 An example of an outgoing light beam output by a waveguide is shown.

[0033] Figure 8 An example of a stacked waveguide assembly is shown where each depth plane includes an image formed using multiple different component colors.

[0034] Fig. 9A A cross-sectional side view of an example of a set of stacked waveguides each including an in-coupling optical element is shown.

[0035] Fig. 9B Shows Fig. 9A A perspective view of an example of multiple stacked waveguides.

[0036] Fig. 9C Shows Fig. 9A and 9B A top plan view of an example of multiple stacked waveguides.

[0037] Fig.9D An example of a wearable display system is shown.

[0038] Fig.10 Schematically shown is a cross-sectional view of a portion of a waveguide on which a diffraction grating is arranged, for example for coupling light into the waveguide.

[0039] Fig.11A is a cross-sectional view of an example diffractive structure including a tilted grating.

[0040] Fig. 11B is shown for a Fig.11A Schematic diagram of the light propagation direction of the EPE simulation performed for the diffractive structure shown.

[0041] Figures 12A-12D It shows Fig.11A Intensity plots of different performance parameters of a tilted grating as shown, swept over the tilt angle and grating thickness. These plots were generated by simulation.

[0042] Figures 13A-13D Shown are cross-sectional profiles of four different tilted grating designs investigated by simulation.

[0043] Fig.14A is a cross-sectional view of another example diffractive structure including a blazed grating.

[0044] Figures 14B-14D Shown are cross-sectional profiles of three different blazed grating designs studied by simulation.

[0045] Fig.15A and 15B is a schematic diagram showing an example single-sided arrangement for an eyepiece.

[0046] Fig. 15C and 15D is a schematic diagram showing an example bilateral arrangement for an eyepiece.

[0047] Fig.16A is a schematic diagram showing an example layout of a diffractive structure for an EPE and / or CPE, where different zones have different grating structures.

[0048] Figures 16B-16D It is shown Fig.16ACross-sectional view of the grating structure showing different regions of the diffractive structure shown in FIG.

[0049] Figures 17A-17B is a cross-sectional view showing an example diffractive structure of a CPE.

[0050] Fig.18A It is shown Figures 17A-17B Plot of grating thickness for different regions of an example diffractive structure shown.

[0051] Fig.18B and 18C It is shown Figures 17A-17B A plan view of the zone layout of an example diffractive structure is shown.

[0052] Fig.19A A cross-sectional view of a portion of a grating structure is shown, wherein the grating pattern is transferred from a resist layer to a substrate layer by dry etching.

[0053] Fig.19B So Fig.19A SEM micrograph of an example grating structure formed in the manner shown.

[0054] Figures 20A-20K are SEM micrographs of different examples of surface relief diffractive structures suitable for EPE and / or CPE.

[0055] Figures 21A-21D An example eyepiece including a double-sided grating is shown in cross-section.

[0056] Fig.21E Examples of grating structures comprising various combinations of coatings on the grating ridges are shown in cross-section.

[0057] Figures 22A-22D Example cross-sectional shapes of grating ridges including stepped ridges are shown.

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

[0059] AR systems can display virtual content to a user or viewer while still allowing the user to see the world around them. Preferably, the content is displayed on a head-mounted display, such as part of glasses, which projects image information into the user's eyes. In addition, the display can also transmit light from the surrounding environment to the user's eyes to allow viewing of the surrounding environment. As used herein, it should be understood that a "head-mounted" or "head-mountable" display is a display that can be worn on the head of a viewer or user.

[0060] In some AR systems, virtual / augmented / hybrid displays with relatively high fields of view (FOV) can improve the viewing experience. The FOV of the display depends on the angle of light output by the waveguide of the eyepiece, through which the viewer sees the image projected into his or her eye. Waveguides with relatively high refractive indices (e.g., 2.0 or higher) can provide relatively high FOVs. However, in order to effectively couple light into the high refractive index waveguide, the diffractive optical coupling element should also have a corresponding high refractive index. To achieve this goal, among other advantages, according to embodiments described herein, some displays for AR systems include a waveguide having a material with a relatively high refractive index (e.g., greater than or equal to 2.0) on which a corresponding diffraction grating with a corresponding high refractive index is formed, such as a lithium-based oxide. For example, a diffraction grating can be formed directly on the lithium-based oxide waveguide by patterning a surface portion of the waveguide formed by the lithium-based oxide.

[0061] Some high refractive index diffractive optical coupling elements (such as coupling-in or coupling-out optical elements) have strong polarization dependence. For example, an in-coupling grating (ICG) for coupling light into a waveguide, where the diffractive optical coupling element includes a high refractive index material that can accept light of a specific polarization significantly more than light of another polarization. For example, such an element can couple light with TM polarization into a waveguide at a ratio of approximately 3 times that of light with TE polarization. Diffractive optical coupling elements with such polarization dependence may have reduced efficiency (due to low efficiency and general rejection of one polarization), and may also produce coherence artifacts and reduce the uniformity of the far-field image formed by the light coupled out of the waveguide. In order to obtain a diffractive optical coupling element that is polarization-insensitive or at least has reduced polarization sensitivity (e.g., it couples light with efficiency that is relatively independent of polarization), according to various embodiments described herein, some displays for AR systems include a waveguide having a diffraction grating formed with a blazed geometry. The diffraction grating may also be formed directly in a waveguide, which may include a high refractive index material (e.g., having a refractive index of at least 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, or up to 2.7, or any range between the foregoing values). For example, a diffraction grating may be formed in a high refractive index material, such as lithium niobate (LiNbO), by patterning the high refractive index material with a blazed geometry. 3 ) or lithium tantalate (LiTaO 3 ) or lithium-based oxides such as zirconium oxide (ZrO 2 ), titanium dioxide (TiO 2 ) or silicon carbide (SiC).

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

[0063] Figure 2 A conventional display system for simulating a three-dimensional image for a user is shown. The user's eyes are spaced apart, and when viewing a real object in space, each eye will have a slightly different view of the object, and an image of the object may be formed at a different location on the retina of each eye. This may be referred to as binocular parallax, and may be used by the human visual system to provide a sense of depth. Conventional display systems simulate binocular parallax by presenting two different images 190, 200 (one for each eye 210, 220) with slightly different views of the same virtual object, corresponding to views of the virtual object that will be seen by each eye as a real object at the desired depth. These images provide binocular cues that the user's visual system may interpret to obtain a sense of depth.

[0064] Continue to refer Figure 2 , the images 190, 200 are spaced a distance 230 from the eyes 210, 220 on the z-axis. The z-axis is parallel to the optical axis of the viewer with the eyes looking at an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on the slightly different views of the virtual objects in the images presented to the eyes 210, 220, respectively, the eyes can naturally rotate so that the image of the object falls on the corresponding point on the retina of each eye to maintain a single binocular vision. The rotation can cause the line of sight of each eye 210, 220 to converge to the point in space where the virtual object is perceived to exist. Therefore, providing a three-dimensional image generally involves providing binocular cues that can manipulate the convergence of the user's eyes 210, 220 and be interpreted by the human visual system to provide a sense of depth.

[0065] However, producing a realistic and comfortable sense of depth is challenging. It should be understood that light from objects at different distances from the eye has wavefronts with different amounts of divergence. Figures 3A to 3C The relationship between distance and light divergence is shown in FIG. 2 . The distance between the object and the eye 210 is represented in the order of decreasing distance R1, R2, and R3. Figures 3A to 3C As shown, as the distance to the object decreases, the light becomes more divergent. Conversely, as the distance increases, the light becomes more collimated. In other words, it can be said that the light field generated by a point (object or part of an object) has a spherical wavefront curvature that is a function of how far the point is from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. Although for clarity in the description of Figures 3A to 3COnly a single eye 210 is shown in and other figures herein, but the discussion regarding eye 210 is applicable to both eyes 210 and 220 of a viewer.

[0066] Continue to refer Figures 3A to 3C , light from an object being looked at by a viewer's eye can have different degrees of wavefront divergence. Due to different amounts of wavefront divergence, light can be focused differently by the lens of the eye, which in turn may require the lens to assume different shapes to form a focused image on the retina of the eye. In the absence of a focused image formed on the retina, the resulting retinal blur acts as an accommodation cue that causes a change in the shape of the eye lens until a focused image is formed on the retina. For example, an accommodation cue can trigger the ciliary muscles surrounding the eye lens to relax or contract, thereby adjusting the force applied to the suspensory ligaments that hold the lens, thereby changing the shape of the eye lens until the retinal blur of the looked object is eliminated or minimized, thereby forming a focused image of the looked object on the retina of the eye (e.g., the fovea). The process by which the eye lens changes shape may be referred to as accommodation, and the shape of the eye lens required to form a focused image of the looked object on the retina of the eye (e.g., the fovea) may be referred to as an accommodation state.

[0067] Reference now Figure 4A , shows a representation of the accommodation-convergence response of the human visual system. Movement of the eyes to fixate on an object causes the eyes to receive light from the object, where the light forms an image on each retina of the eye. The presence of retinal blur in the image formed on the retina can provide accommodation cues, and the relative positions of the images on the retina can provide vergence cues. Accommodation cues cause accommodation to occur, so that the eye lenses respectively assume a specific accommodation state that forms a focused image of the object on the retinas of the eyes (e.g., the fovea). On the other hand, vergence cues cause vergence movements (eye rotations) to occur so that the images formed on each retina of each eye are at corresponding retinal points that maintain a single binocular vision. In these positions, it can be said that the eyes have assumed a specific vergence state. Continue with reference to Figure 4A , accommodation can be understood as the process by which the eye achieves a specific accommodation state, and vergence can be understood as the process by which the eye achieves a specific vergence state. Figure 4A As shown, if the user looks at another object, the accommodation and convergence states of the eyes can change. For example, if the user looks at a new object at a different depth on the z-axis, the accommodation state may change.

[0068] Without being limited by theory, it is believed that a viewer of an object may perceive the object as "three-dimensional" due to a combination of vergence and accommodation. As described above, the vergence movement of the two eyes relative to each other (e.g., the eyes rotate so that the pupils move toward or away from each other so that the eyes' line of sight converges to fixate on an object) is closely related to the accommodation of the eye lenses. Under normal circumstances, changing the shape of the eye lenses to change the focus from one object to another at a different distance will automatically cause a matching change in vergence to the same distance, under the relationship known as the "accommodation-convergence reflex." Likewise, under normal circumstances, a change in vergence will trigger a matching change in lens shape.

[0069] Reference now Figure 4B , examples of different accommodation states and convergence states of eyes are shown. A pair of eyes 222a is fixated on an object at optical infinity, while a pair of eyes 222b is fixated on an object 221 that is less than optical infinity. It is noteworthy that the convergence state of each pair of eyes is different, with one pair of eyes 222a looking straight ahead and one pair of eyes 222 converging on object 221. The accommodation state of the eyes forming each pair of eyes 222a and 222b is also different, as represented by the different shapes of the lenses 210a, 220a.

[0070] Unexpectedly, many users of conventional "3D" display systems find that such conventional systems are uncomfortable or may not perceive a sense of depth at all due to the mismatch between the accommodation and convergence states in these displays. As described above, many stereoscopic or "3D" display systems display a scene by providing slightly different images to each eye. Such systems are uncomfortable for many viewers because, among other things, such systems only provide different presentations of the scene and cause changes in the convergence state of the eyes, but there is no corresponding change in the accommodation state of these eyes. Instead, the image is displayed by a display at a fixed distance from the eyes so that the eyes view all image information in a single accommodation state. This arrangement violates the "accommodation-convergence reflex" by causing a change in the convergence state without a matching change in the accommodation state. This mismatch is believed to cause discomfort to the viewer. A display system that provides a better match between accommodation and convergence can form a more realistic and comfortable three-dimensional image simulation.

[0071] Without being limited by theory, it is believed that the human eye can generally interpret a limited number of depth planes to provide a sense of depth. Therefore, a highly credible simulation of perceived depth can be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. In some embodiments, the different presentations can provide both vergence cues and matching accommodation cues, thereby providing a physiologically correct accommodation-vergence match.

[0072] Continue to refer Figure 4B , two depth planes 240 are shown, corresponding to different distances in space from the eyes 210, 220. For a given depth plane 240, convergence cues may be provided by displaying images of appropriately different perspectives for each eye 210, 220. In addition, for a given depth plane 240, the light forming the image provided to each eye 210, 220 may have a wavefront divergence corresponding to the light field produced by a point at the distance of that depth plane 240.

[0073] In the illustrated embodiment, the distance along the z-axis of the depth plane 240 containing point 221 is 1 meter. As used herein, the distance or depth along the z-axis can be measured by locating the zero point at the exit pupil of the user's eye. Therefore, the depth plane 240 located at a depth of 1 meter corresponds to a distance of 1 meter from the exit pupil of the user's eye on the optical axis of the user's eye when the eye is pointed to optical infinity. As an approximation, the depth or distance along the z-axis can be measured from the display in front of the user's eye (e.g., from the surface of the waveguide), plus the value of the distance between the device and the exit pupil of the user's eye. This value can be called the eye relief and corresponds to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eye. In practice, the value of the eye relief can be a standardized value common to all viewers. For example, it can be assumed that the eye relief is 20 mm, and the depth plane at a depth of 1 meter can be at a distance of 980 mm in front of the display.

[0074] Reference now Figure 4C and 4D , respectively show examples of matched accommodation-convergence distances and mismatched accommodation-convergence distances. Figure 4C As shown, the display system can provide an image of a virtual object to each eye 210, 220. These images can cause the eyes 210, 220 to present a state of convergence, in which the eyes converge at a point 15 on the depth plane 240. In addition, the image can be formed by light having a wavefront curvature corresponding to a real object at the depth plane 240. As a result, the eyes 210, 220 present an accommodation state, in which the image is focused on the retinas of these eyes. Therefore, the user can perceive the virtual object as being located at a point 15 on the depth plane 240.

[0075] It should be understood that each of the accommodation and convergence states of the eyes 210, 220 is associated with a specific distance on the z-axis. For example, an object at a specific distance from the eyes 210, 220 causes these eyes to present a specific accommodation state based on the distance of the object. The distance associated with a specific accommodation state can be referred to as the accommodation distance Ad. Similarly, there is a specific convergence distance Vd associated with the eyes in a specific convergence state or relative to each other. When the accommodation distance and the convergence distance match, it can be said that the relationship between accommodation and convergence is physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0076] However, in stereoscopic displays, the accommodation distance and the convergence distance may not always match. Figure 4D As shown, the image displayed to the eyes 210, 220 can be displayed with a wavefront divergence corresponding to the depth plane 240, and the eyes 210, 220 can present a specific accommodation state in which the points 15a, 15b on the depth plane are in focus. However, the image displayed to the eyes 210, 220 can provide a convergence cue that causes the eyes 210, 220 to converge at a point 15 that is not located on the depth plane 240. As a result, in some embodiments, the accommodation distance corresponds to the distance from the exit pupil of the eyes 210, 220 to the depth plane 240, while the convergence distance corresponds to a greater distance from the exit pupil of the eyes 210, 220 to the point 15. The accommodation distance is different from the convergence distance. Therefore, there is an accommodation-convergence mismatch. This mismatch is considered to be undesirable and may cause discomfort to the user. It should be understood that the mismatch corresponds to a distance (e.g., Vd-Ad) and can be characterized using diopters.

[0077] In some embodiments, it should be appreciated that a reference point other than the exit pupil of the eye 210, 220 may be used to determine the distance used to determine the accommodation-vergence mismatch, as long as the same reference point is used for both the accommodation distance and the vergence distance. For example, the distance may be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., a waveguide of a display device) to the depth plane, and so forth.

[0078] Without being limited by theory, it is believed that the user may still perceive accommodation-convergence mismatches of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as physiologically correct without causing noticeable discomfort by itself. In some embodiments, the display systems disclosed herein (e.g., Figure 6The display system 250 in the embodiment of the present invention presents an image with an accommodation-convergence mismatch of about 0.5 diopters or less to a viewer. In some other embodiments, the accommodation-convergence mismatch of the image provided by the display system is about 0.33 diopters or less. In some other embodiments, the accommodation-convergence mismatch of the image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0079] Figure 5 Aspects of a method for simulating a three-dimensional image by modifying wavefront divergence are shown. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to the user's eye 210. The waveguide 270 can output light 650 with a defined amount of wavefront divergence that corresponds to the wavefront divergence of the light field produced by a point on the desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on the depth plane. In addition, it will be described that image information from a similar waveguide can be provided to the user's other eye.

[0080] In some embodiments, a single waveguide may be configured to output light having a set amount of wavefront divergence corresponding to a single depth plane or a finite number of depth planes, and / or the waveguide may be configured to output light of a finite wavelength range. Thus, in some embodiments, multiple waveguides or waveguide stacks may be utilized to provide different amounts of wavefront divergence for different depth planes and / or output light of different wavelength ranges. As used herein, it should be understood that a depth plane may be planar or may follow a curved profile.

[0081] Figure 6 An example of a waveguide stack for outputting image information to a user is shown. The display system 250 includes a waveguide stack or stacked waveguide assembly 260, which can be used to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. It should be understood that in some embodiments, the display system 250 can be considered a light field display. In addition, the waveguide assembly 260 can also be referred to as an eyepiece.

[0082] In some embodiments, the display system 250 is configured to provide a substantially continuous vergence cue and a plurality of discrete accommodation cues. The vergence cue can be provided by displaying a different image to each eye of the user, and the accommodation cue can be provided by outputting image-forming light having a selectable discrete amount of wavefront divergence. In other words, the display system 250 can be configured to output light having variable wavefront divergence levels. In some embodiments, each discrete level of wavefront divergence corresponds to a particular depth plane and can be provided by a particular one of the waveguides 270, 280, 290, 300, 310.

[0083] Continue to refer Figure 6 , the waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or the plurality of lenses 320, 330, 340, 350 may be configured to send image information to the eye at various levels of wavefront curvature or light divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to the depth plane. The image injection device 360, 370, 380, 390, 400 may be used as a light source for the waveguide and may be used to inject image information into the waveguides 270, 280, 290, 300, 310, each waveguide may be configured to distribute incident light across each respective waveguide for output toward the eye 210, as described herein. Light exits the output surfaces 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into the corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide, or may be part of a major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 510 or the viewer's eye 210). In some embodiments, a single beam (e.g., a collimated beam) may be injected into each waveguide to output an entire field of cloned collimated beams directed toward the eye 210 at a particular angle (and divergence) corresponding to a depth plane associated with a particular waveguide. In some embodiments, a single one of image injection devices 360, 370, 380, 390, 400 may be associated with and inject light into multiple (e.g., three) of waveguides 270, 280, 290, 300, 310.

[0084] In some embodiments, the image injection devices 360, 370, 380, 390, 400 are discrete displays that each generate image information for injection into a corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, the image injection devices 360, 370, 380, 390, 400 are outputs of a single multiplexed display, which may pipe the image information to each of the image injection devices 360, 370, 380, 390, 400 via one or more optical conduits (such as fiber optic cables), for example. It should be understood that the image information provided by the image injection devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different component colors as discussed herein).

[0085] In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light module 530, which may include a light emitter, such as a light emitting diode (LED). The light from the light module 530 may be directed to a light modulator 540 (e.g., a spatial light modulator) via a beam splitter 550 and modified by the light modulator 540. The light modulator 540 may be configured to change the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It should be understood that the image injection devices 360, 370, 380, 390, 400 are shown schematically, and in some embodiments, these image injection devices can represent different optical paths and positions in a common projection system that is configured to output light into associated waveguides in waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides in the waveguide assembly 260 can act as ideal lenses while relaying the light injected into the waveguides to the user's eyes. In this concept, the object can be the spatial light modulator 540, and the image can be an image on a depth plane.

[0086] In some examples, a μLED display can be used in the light projector system 520. The μLED display can not polarize light within a large range of angles. Therefore, the μLED display can advantageously provide images efficiently within a wide field of view.

[0087] In some embodiments, the display system 250 may be a scanning fiber display having one or more scanning fibers configured to project light into one or more waveguides 270, 280, 290, 300, 310 in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.), and ultimately to the viewer's eye 210. In some embodiments, the image injection devices 360, 370, 380, 390, 400 shown may schematically represent a single scanning fiber or a scanning fiber bundle configured to inject light into one or more of the waveguides 270, 280, 290, 300, 310. In some other embodiments, the image injection devices 360, 370, 380, 390, 400 shown may schematically represent a plurality of scanning optical fibers or a plurality of scanning optical fiber bundles, each of which is configured to inject light into an associated waveguide of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 530 to the one or more waveguides 270, 280, 290, 300, 310. It should be understood that one or more intermediate optical structures may be provided between the one or more scanning optical fibers and the one or more waveguides 270, 280, 290, 300, 310 to, for example, redirect light emitted from the scanning optical fibers into the one or more waveguides 270, 280, 290, 300, 310.

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

[0089] Continue to refer Figure 6, the waveguides 270, 280, 290, 300, 310 can be configured to propagate light within each respective waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 can each be planar or have another shape (e.g., curved) with a top major surface and a bottom major surface and an edge extending between these top major surfaces and bottom major surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 can each include an outcoupling optical element 570, 580, 590, 600, 610, which is configured to extract light from the waveguide by redirecting light propagating within the respective corresponding waveguide out of the waveguide to output image information to the eye 210. The extracted light can also be referred to as outcoupled light, and the outcoupling optical element light can also be referred to as a light extraction optical element. The extracted light beam can be output by the waveguide at the location where the light propagating in the waveguide is incident on the light extraction optical element. As further discussed herein, the coupling-out optical element 570, 580, 590, 600, 610 can be, for example, a grating of diffractive optical features. Although shown as being disposed at the bottom major surface of the waveguide 270, 280, 290, 300, 310, for ease of description and clarity of drawing, in some embodiments, as further discussed herein, the coupling-out optical element 570, 580, 590, 600, 610 can be disposed at the top and / or bottom major surface, and / or can be disposed directly within the volume of the waveguide 270, 280, 290, 300, 310. In some embodiments, the coupling-out optical element 570, 580, 590, 600, 610 can be formed in a material layer attached to a transparent substrate to form the waveguide 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be a single piece of material and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on a surface and / or within the interior of the piece of material.

[0090] Continue to refer Figure 6As discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light to form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye can be configured to deliver collimated light (which is injected into such a waveguide 270) to the eye 210. The collimated light can represent an optical infinity focal plane. The next upstream waveguide 280 can be configured to emit collimated light that passes through a first lens 350 (e.g., a negative lens) before it can reach the eye 210; such a first lens 350 can be configured to produce a slightly convex wavefront curvature so that the eye / brain interprets the light from the next upstream waveguide 280 as coming from a first focal plane that is closer to the eye 210 from optical infinity inward. Similarly, the third upstream waveguide 290 causes its output light to pass through both the first lens 350 and the second lens 340 before reaching the eye 210; the combined optical power of the first lens 350 and the second lens 340 can be configured to produce another increment of wavefront curvature so that the eye / brain interprets light from the third waveguide 290 as coming from a second focal plane that is further inward from optical infinity and closer to the person than light from the next upstream waveguide 280.

[0091] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all the lenses between it and the eye to obtain a total focal power that represents the focal plane closest to the person. In order to compensate for the stack of lenses 320, 330, 340, 350 when observing / interpreting light from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 can be provided on top of the stack to compensate for the total focal power of the lens stack 320, 330, 340, 350 below. This configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the outcoupling optics of the waveguide and the focusing aspects of the lens can be static (i.e., not dynamic or electro-active). In some alternative embodiments, one or both of them can be dynamic by using electro-active features.

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

[0093] Continue to refer Figure 6, the out-coupling optical elements 570, 580, 590, 600, 610 can be configured to both redirect light out of their respective waveguides and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes can have differently configured out-coupling optical elements 570, 580, 590, 600, 610, and the differently configured out-coupling optical elements 570, 580, 590, 600, 610 output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 can be volume features or surface features that can be configured to output light at a particular angle. For example, the light extraction optical elements 570, 580, 590, 600, 610 can be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, 350 may not be lenses; rather, they may simply be spacers (eg, cladding and / or structures used to form air gaps).

[0094] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features that form a diffraction pattern, or "diffractive optical elements" (also referred to herein as "DOEs"). Preferably, the DOE has a sufficiently low diffraction efficiency that only a portion of the beam is deflected away toward the eye 210 by each intersection with the DOE, while the remainder continues through the waveguide via TIR. Thus, the light carrying the image information is split into multiple related exit beams that exit the waveguide at multiple locations, and the result is a fairly uniform pattern of exit toward the eye 210 for this particular collimated beam bouncing within the waveguide.

[0095] In some embodiments, one or more DOEs can be switched between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE can include a polymer dispersed liquid crystal layer in which a droplet includes a diffraction pattern in a host medium, and the refractive index of the droplet can be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light) or the droplet can be switched to a refractive index that mismatches the refractive index of the host medium (in which case the pattern actively diffracts incident light).

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

[0097] Reference now Figure 7 , showing an example of an outgoing light beam output by a waveguide. One waveguide is shown, but it should be understood that in the case where the waveguide assembly 260 includes a plurality of waveguides, the waveguide assembly 260 ( Figure 6 ) may function similarly. Light 640 is injected into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light emerges from the waveguide as an exit beam 650. The exit beams 650 are shown as being substantially parallel, but as discussed herein, they may also be redirected to propagate to the eye 210 at an angle (e.g., to form diverging exit beams) that depends on the depth plane associated with the waveguide 270. It should be understood that substantially parallel exit beams may be indicative of a waveguide having an out-coupling optical element that out-couples light to form an image that appears to be disposed at a depth plane that is a long distance from the eye 210 (e.g., optical infinity). Other waveguides or other sets of outcoupling optical elements can output a more divergent exit beam pattern that will require the eye 210 to adjust to a closer distance in order to focus the more divergent exit beam pattern on the retina and will be interpreted by the brain as light coming from a distance closer to the eye 210 than optical infinity.

[0098] In some embodiments, a full color image can be formed at each depth plane by superimposing images in each of the component colors (eg, three or more component colors). Figure 8An example of a stacked waveguide assembly is shown, wherein each depth plane includes an image formed using a plurality of different component colors. The illustrated embodiment shows depth planes 240a-240f, but more or fewer depths are also contemplated. Each depth plane may have three or more component color images associated therewith, including: a first image of a first color G; a second image of a second color R; and a third image of a third color B. Different depth planes are represented in the figure by different numbers for the diopters (dpt) following the letters G, R, and B. By way of example only, the numbers following each of these letters represent the diopters (1 / m), or the inverse of the distance of the depth plane from the viewer, and each box in the figure represents a separate component color image. In some embodiments, the precise placement of the depth planes of different component colors may vary in order to account for differences in the eye's focus on light of different wavelengths. For example, different component color images of a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort, and / or may reduce chromatic aberration.

[0099] In some embodiments, light of each component color may be output by a single dedicated waveguide, and therefore, each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figure including the letters G, R, or B may be understood to represent a separate waveguide, and each depth plane may provide three waveguides, wherein each depth plane provides three component color images. Although for ease of description, the waveguides associated with each depth plane in this figure are shown as being adjacent to each other, it should be understood that in a physical device, the waveguides may all be arranged in a stacked form with one waveguide per layer. In some other embodiments, multiple component colors may be output by the same waveguide, so that, for example, each depth plane may provide only a single waveguide.

[0100] Continue to refer Figure 8 In some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light (including magenta and cyan) may be used in addition to red, green, or blue, or these other colors may replace one or more of red, green, or blue.

[0101] It should be understood that references throughout this disclosure to light of a given color will be understood to include light of one or more wavelengths within a range of wavelengths perceived by a viewer as light of the given color. For example, red light may include light of one or more wavelengths within a range of about 620-780 nm, green light may include light of one or more wavelengths within a range of about 492-577 nm, and blue light may include light of one or more wavelengths within a range of about 435-493 nm.

[0102] In some embodiments, the light source 530 ( Figure 6 ) can be configured to emit one or more wavelengths of light outside the visual perception range of a viewer, such as infrared and / or ultraviolet wavelengths of light. In addition, the incoupling, outcoupling, and other light redirecting structures of the waveguide of the display 250 can be configured to guide this light and direct it out of the display toward the user's eye 210, for example, for imaging and / or user stimulation applications.

[0103] Reference now Fig. 9A In some embodiments, it may be necessary to redirect light incident on a waveguide to couple the light into the waveguide. An incoupling optical element may be used to redirect and couple the light into its corresponding waveguide. Fig. 9A A cross-sectional side view of an example of a plurality of stacked waveguides or a stacked waveguide set 660 is shown, each waveguide including an incoupling optical element. The waveguides can each be configured to output light of one or more different wavelengths, or light of one or more different wavelength ranges. It should be understood that stack 660 can correspond to stack 260 ( Figure 6 ), and the waveguides shown in stack 660 may correspond to a portion of multiple waveguides 270, 280, 290, 300, 310, in addition to light from one or more image injection devices 360, 370, 380, 390, 400 being injected into the waveguide from a location where the light needs to be redirected for coupling.

[0104] The illustrated stacked waveguide set 660 includes waveguides 670, 680, and 690. Each waveguide includes an associated coupling optical element (which may also be referred to as a light input region on the waveguide), wherein, for example, coupling optical element 700 is disposed on a major surface (e.g., top major surface) of waveguide 670, coupling optical element 710 is disposed on a major surface (e.g., top major surface) of waveguide 680, and coupling optical element 720 is disposed on a major surface (e.g., top major surface) of waveguide 690. In some embodiments, one or more of the coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the corresponding waveguide 670, 680, 690 (particularly in the case where one or more coupling optical elements are reflective deflection optical elements). As shown, coupling optical elements 700, 710, 720 may be disposed on the top major surface (or the top of the next downstream waveguide) of their corresponding waveguides 670, 680, 690, particularly in the case where those coupling optical elements are transmissive deflection optical elements. In some embodiments, the coupling-in optical elements 700, 710, 720 can be disposed in the body of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the coupling-in optical elements 700, 710, 720 are wavelength selective such that they selectively redirect light of one or more wavelengths while transmitting light of other wavelengths. Although shown on one side or corner of their respective waveguides 670, 680, 690, it should be understood that in some embodiments, the coupling-in optical elements 700, 710, 720 can be disposed in other areas of their respective waveguides 670, 680, 690.

[0105] As shown, the coupling-in optical elements 700, 710, 720 can be laterally offset from each other. In some embodiments, each coupling-in optical element can be offset so that the coupling-in optical element receives light without the light passing through another coupling-in optical element. For example, each coupling-in optical element 700, 710, 720 can be configured to be offset from, for example, Figure 6 The different image injection devices 360, 370, 380, 390 and 400 shown receive light and can be separated from other coupling optical elements 700, 710, 720 (e.g., laterally spaced apart) so that the coupling optical element does not substantially receive light from other coupling optical elements in the coupling optical elements 700, 710, 720.

[0106] Each waveguide further includes an associated light distribution element, wherein, for example, the light distribution element 730 is disposed on a major surface (e.g., top major surface) of the waveguide 670, the light distribution element 740 is disposed on a major surface (e.g., top major surface) of the waveguide 680, and the light distribution element 750 is disposed on a major surface (e.g., top major surface) of the waveguide 690. In some other embodiments, the light distribution elements 730, 740, 750 may be disposed on the bottom major surface of the associated waveguides 670, 680, 690, respectively. In some other embodiments, the light distribution elements 730, 740, 750 may be disposed on the top major surface and the bottom major surface of the associated waveguides 670, 680, 690, respectively; or the light distribution elements 730, 740, 750 may be disposed on different major surfaces of the top major surface and the bottom major surface in different associated waveguides 670, 680, 690, respectively.

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

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

[0109] Continue to refer Fig. 9A, light rays 770, 780, 790 are incident on the waveguide set 660. It should be understood that light rays 770, 780, 790 may be injected through one or more image injection devices 360, 370, 380, 390, 400 ( Figure 6 ) are injected into waveguides 670, 680, and 690.

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

[0111] For example, the coupling-in optical element 700 can be configured to deflect light 770 having a first wavelength or a first wavelength range, while transmitting light 780 having a different second wavelength or a second wavelength range and light 790 having a third wavelength or a third wavelength range, respectively. The transmitted light 780 is incident on and deflected by the coupling-in optical element 710, which is configured to deflect light of the second wavelength or the second wavelength range. The light 790 is deflected by the coupling-in optical element 720, which is configured to selectively deflect light of the third wavelength or the third wavelength range.

[0112] Continue to refer Fig. 9A , the deflected light rays 770, 780, 790 are deflected so that the light rays 770, 780, 790 propagate through the corresponding waveguides 670, 680, 690; that is, the coupling optical element 700, 710, 720 of each waveguide deflects the light into the corresponding waveguide 670, 680, 690 to couple the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the corresponding waveguides 670, 680, 690 with TIR. The light rays 770, 780, 790 propagate through the corresponding waveguides 670, 680, 690 with TIR until they are incident on the corresponding light distribution elements 730, 740, 750 of the waveguides.

[0113] Reference now Fig. 9B , showing Fig. 9A6. As described above, the incoupled light rays 770, 780, 790 are deflected by the incoupling optical elements 700, 710, 720, respectively, and then propagate by TIR in the waveguides 670, 680, 690, respectively. Then, the light rays 770, 780, 790 are incident on the light distribution elements 730, 740, 750, respectively. The light distribution elements 730, 740, 750 deflect the light rays 770, 780, 790 so that the light rays 770, 780, 790 propagate toward the outcoupling optical elements 800, 810, 820, respectively.

[0114] In some embodiments, the light distribution elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or distribute light to the outcoupling optical elements 800, 810, 820, and in some embodiments, may also increase the beam size or spot size of the light as it propagates to the outcoupling optical elements. In some embodiments, the light distribution elements 730, 740, 750 may be omitted, and the coupling-in optical elements 700, 710, 720 may be configured to deflect light directly to the outcoupling optical elements 800, 810, 820. For example. Reference Fig. 9A , the light distribution elements 730, 740, 750 can be replaced by outcoupling optical elements 800, 810, 820, respectively. In some embodiments, the outcoupling optical elements 800, 810, 820 are exit pupils (EP) or exit pupil expanders (EPE) that direct light into the viewer's eye 210 ( Figure 7 ). It should be understood that the OPE can be configured to increase the size of the eye box in at least one axis, and the EPE can increase the eye box in an axis that intersects (e.g., is orthogonal) to the axis of the OPE. For example, each OPE can be configured to redirect a portion of the light that strikes the OPE to the EPE of the same waveguide, while allowing the remainder of the light to continue to propagate along the waveguide. Upon again impinging on the OPE, another portion of the remaining light is redirected to the EPE, and the remainder of that portion continues to propagate further along the waveguide, and so on. Similarly, upon striking the EPE, a portion of the incident light is directed out of the waveguide toward the user, and the remainder of the light continues to propagate through the waveguide until it strikes the EPE again, at which time another portion of the incident light is directed out of the waveguide, and so on. Therefore, whenever a portion of a single beam of coupled-in light is redirected by an OPE or EPE, that light can be "copied," thereby forming a field of cloned beams, such as Figure 6 As shown. In some embodiments, the OPE and / or EPE can be configured to modify the size of the light beam.

[0115] Therefore, reference Fig. 9A and Fig. 9BIn some embodiments, the waveguide set 660 includes: waveguides 670, 680, 690 for each component color; coupling optical elements 700, 710, 720; light distribution elements (e.g., OPE) 730, 740, 750; and outcoupling optical elements (e.g., EP) 800, 810, 820. The waveguides 670, 680, 690 can be stacked with air gaps / cladding between each waveguide. The coupling optical elements 700, 710, 720 redirect or deflect the incident light (light of different wavelengths received by different coupling optical elements) into its waveguide. The light then propagates at an angle that will cause TIR within the corresponding waveguide 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first coupling-in optical element 700 in the manner previously described, and then continues to bounce along the waveguide, interacting with the light distribution element (e.g., OPE) 730 and the coupling-out optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green light and red light, respectively) are transmitted through the waveguide 670, where light ray 780 is incident on and deflected by the coupling-in optical element 710. Light ray 780 then bounces along the waveguide 680 via TIR, proceeds to its light distribution element (e.g., OPE) 740, and then to the coupling-out optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) is transmitted through the waveguide 690 and is incident on the coupling-in optical element 720 of the waveguide 690. The light incoupling optical element 720 deflects the light 790 so that it propagates through TIR to the light distribution element (e.g., OPE) 750, and then propagates through TIR to the outcoupling optical element (e.g., EP) 820. The outcoupling optical element 820 then finally couples the light 790 out to the viewer, who also receives the outcoupled light from the other waveguides 670, 680.

[0116] Fig. 9C Shows Fig. 9A and Fig. 9B A top plan view of an example of multiple stacked waveguides. As illustrated, the waveguides 670, 680, 690 and the associated light distribution elements 730, 740, 750 and associated outcoupling optical elements 800, 810, 820 of each waveguide can be vertically aligned. However, as discussed herein, the coupling-in optical elements 700, 710, 720 are not vertically aligned; rather, the coupling-in optical elements do not overlap (e.g., are laterally spaced apart when viewed in a top view). As further discussed herein, this non-overlapping spatial arrangement facilitates one-to-one injection of light from different resources into different waveguides, thereby allowing a particular light source to be uniquely coupled to a particular waveguide. In some embodiments, arrangements including non-overlapping spatially separated coupling-in optical elements can be referred to as shifted pupil systems, and the coupling-in optical elements within these arrangements can correspond to sub-pupils.

[0117] Alternatively, in some embodiments, two or more coupling optical elements can be arranged in series, in which they are vertically aligned. In this arrangement, light for the waveguide farther from the projection system is transmitted through the coupling optical element for the waveguide closer to the projection system, preferably with minimal scattering or diffraction.

[0118] The in-line configuration can advantageously reduce the size of the projector and simplify the projector. In addition, it also increases the field of view of the eyepiece, for example, by coupling light of the same color to multiple waveguides using crosstalk. For example, green light can be coupled into the blue and red active layers. Since the pitch of each ICG can be different to provide improved (e.g., optimal) performance for a specific color, the allowed field of view can be increased.

[0119] In an in-line configuration, except for the last layer in the optical path, the ICG should at most partially reflect or otherwise transmit light at the operating wavelength of the subsequent layers in the waveguide stack. In each case, unless the grating is etched in a high refractive index layer (e.g., 1.8 or higher for polymer-based layers), or a high refractive index coating is deposited or grown on the grating, the efficiency will be very low. However, this approach will increase back reflections into the projector lens, which may therefore produce image artifacts, such as image ghosting.

[0120] Fig.9D An example of a wearable display system 60 is shown into which the various waveguides and related systems disclosed herein may be integrated. In some embodiments, the display system 60 is Figure 6 The system 250, wherein Figure 6 Some components of the system 60 are schematically shown in more detail. For example, Figure 6 The waveguide assembly 260 can be part of the display 70.

[0121] Continue to refer Fig.9D, the display system 60 includes a display 70, and various mechanical and electronic modules and systems that support the functions of the display 70. The display 70 can be coupled to a frame 80 that can be worn by a display system user or a user 90, and the frame 80 is configured to position the display 70 in front of the eyes of the viewer 90. In some embodiments, the display 70 can be regarded as glasses. In some embodiments, a speaker 100 is coupled to the frame 80 and is configured to be positioned adjacent to the ear canal of the user 90 (in some embodiments, another speaker (not shown) can be optionally positioned adjacent to the other ear canal of the user to provide stereo / shaped sound control). The display system 60 may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphone is configured to allow the user to provide input or commands to the system 60 (e.g., selection of voice menu commands, natural language questions, etc.), and / or may allow audio communication with other people (e.g., with other users of similar display systems). The microphone may be further configured as a peripheral sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may further include a peripheral sensor 120a, which may be separated from the frame 80 and attached to the body of the user 90 (e.g., on the head, torso, limbs, etc. of the user 90). In some embodiments, the peripheral sensor 120a may be configured to acquire data representing a physiological state of the user 90. For example, the sensor 120a may be an electrode.

[0122] Continue to refer Fig.9D, the display 70 is operably coupled to the local processing and data module 140 via a communication link 130 (such as, via a wired lead or a wireless connection), and the local data processing module 140 can be mounted in various configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or removably attached to the user 90 in other ways (e.g., in a backpack configuration, in a belt-coupled configuration). Similarly, the sensor 120a can be operably coupled to the local processing and data module 140 via a communication link 120b (e.g., a wired lead or a wireless connection). The local processor and data module 140 can include a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard drive), both of which can be used to assist in the processing, caching and storage of data. Optionally, the local processor and data module 140 can include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and the like. The data may include a) data captured from sensors (which may, for example, be operably coupled to the frame 80 or otherwise attached to the user 90), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radios, gyroscopes, and / or other sensors disclosed herein; and / or b) data acquired and / or processed using the remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for transmission to the display 70 after such processing or retrieval. The local processing and data module 140 may be operably coupled to the remote processing module 150 and the remote data repository 160 by communication links 170, 180 (such as via a wired or wireless communication link) so that these remote modules 150, 160 are operably coupled to each other and can be used as resources for the local processing and data module 140. In some embodiments, the local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a radio, and / or a gyroscope. In some other embodiments, one or more of these sensors may be attached to the frame 80, or may be an independent structure that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0123] Continue to refer Fig.9DIn some embodiments, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, for example, including one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. In some embodiments, the remote data repository 160 may include a digital data storage facility that may be obtained via the Internet or other network configurations in a "cloud" resource configuration. In some embodiments, the remote data repository 160 may include one or more remote servers that provide information to the local processing and data module 140 and / or the remote processing module 150, for example, information for generating augmented reality content. In some embodiments, all data is stored in the local processing and data module, and all calculations are performed, allowing for full autonomous use from the remote module. Optionally, an external system (e.g., a system of one or more processors, one or more computers) including a CPU, GPU, etc. may perform at least a portion of the processing (e.g., generating image information, processing data), and provide information to the modules 140, 150, 160, for example, via a wireless or wired connection, and receive information from these modules.

[0124] Diffractive structures for asymmetric light extraction

[0125] Providing a high-quality immersive experience to a user of a waveguide-based display system (such as, for example, the various display systems configured for the virtual / augmented / hybrid display applications described above) depends, among other things, on various characteristics of light coupled into and / or coupled out of a waveguide in an eyepiece of the display system. For example, a virtual / augmented / hybrid display with high light coupling-in and coupling-out efficiency can enhance the viewing experience by increasing the brightness of the light directed to the user's eyes. As discussed above, light can be coupled into a waveguide using an incoupling optical element (such as an incoupling diffraction grating) to be guided therein by total internal reflection. Similarly, light guided within a waveguide by total internal reflection can also be coupled out of the waveguide using an outcoupling optical element (such as an outcoupling diffraction grating).

[0126] As mentioned above, for example, reference Figure 6 and Figure 7 The display systems described herein may include optical elements, such as in-coupling optical elements including diffraction gratings, out-coupling optical elements, light distribution elements, and / or combined pupil expander-extractors (CPEs). The CPEs may function as light distribution elements to disperse or distribute light within the waveguide, thereby potentially increasing the beam size and / or eyebox, and may function as out-coupling optical elements to couple light out of the waveguide.

[0127] For example, as mentioned above Figure 7As described, light 640 injected into the waveguide 270 at the input surface 460 of the waveguide 270 propagates and is guided within the waveguide 270 by total internal reflection (TIR). In various embodiments, at the point where the light 640 is incident on the outcoupling optical element 570, a portion of the light guided within the waveguide may exit the waveguide as a small beam 650. In some embodiments, any optical element 570, 580, 590, 600, 610, which may include one or more of an incoupling optical element, an outcoupling optical element, a light distribution element, or a CPE, may be configured as a diffraction grating.

[0128] To achieve desired characteristics for coupling light into and / or out of the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings may be formed of suitable materials and have suitable structures for controlling various optical properties, including diffraction properties, such as diffraction efficiency that varies according to polarization. Possible desired diffraction properties may include any one or more of the following, among other properties: spectral selectivity, angular selectivity, polarization selectivity (or non-selectivity), high spectral bandwidth, high diffraction efficiency, or a wide field of view (FOV).

[0129] Fig.10 A cross-sectional view of a portion of a display device 1000 (such as an eyepiece) according to some designs described herein is shown, the display device having a waveguide 1004 and a blazed diffraction grating 1008 formed on a substrate that serves as the waveguide 1004. In the illustrated embodiment, the blazed diffraction grating 1008 is formed in the substrate / waveguide 1004 (in this example, the substrate / waveguide 1004 is planar). The surface of the substrate or waveguide 1004 has a surface topography including diffraction features that together form the diffraction grating 1008. The blazed diffraction grating 1008 is configured to diffract light having a wavelength within the visible spectrum so that light incident thereon is guided within the waveguide 1004 by TIR. The waveguide 1004 can be transparent and can form part of an eyepiece through which a user's eye can view. Such a waveguide 1004 and eyepiece can be included in a head-mounted display, such as an augmented reality display. For example, the waveguide 1004 can correspond to the above description of Figures 9A-9C For example, the blazed diffraction grating 1008 may correspond to the waveguides 670, 680, 690 described above. Figures 9A-9C The blazed diffraction grating 1008 configured to couple light into the waveguide 1004 may be referred to herein as an in-coupling grating (ICG). The display device 1000 may further include an optical element 1012, which may correspond to a light distribution element (e.g., Figures 9A-9C) or an outcoupling optical element (e.g., one of the light distribution elements 730, 740, 750 shown in Figures 9A-9C One of the outcoupling optical elements 800, 810, 820 shown in FIG. 8 ).

[0130] In operation, when an incident light beam 1016 (e.g., visible light, such as from a light projection system providing image content) is incident on a surface 1004S of the waveguide 1004 (e.g., a major surface of the waveguide on which the grating is formed (e.g., a major surface of the waveguide on which the grating is formed)) with respect to a plane perpendicular to or normal to the blazed diffraction grating or the substrate / waveguide, Fig.10 As shown, when the incident angle α of the plane normal 1002 of the major surface () extending parallel to the Y axis is incident on the blazed diffraction grating 1008, the blazed diffraction grating at least partially diffracts the incident light beam 1016 into a diffracted light beam 1024 at a diffraction angle θ measured relative to the plane normal 1002. When the diffracted light beam 1024 exceeds the critical angle θ for total internal reflection to occur in the waveguide 1004, the diffraction light beam 1024 is diffracted into the waveguide 1008 at least partially. TIR When diffracted at a diffraction angle θ of θ, the diffracted light beam 1024 propagates and is guided within the waveguide 1004 in a direction generally parallel to the x-axis and along the length of the waveguide via total internal reflection (TIR). For example, a portion of the light guided within the waveguide 1004 may reach one of the light distribution elements 730, 740, 750 or the outcoupling optical elements (800, 810, 820, Figures 9A-9C ) and diffracts again.

[0131] As described herein, as in the illustrated embodiment, a light beam incident at an angle clockwise relative to the plane normal 1002 (i.e., to the right of the plane normal 1002) is referred to as having a negative α (α<0), while a light beam incident at an angle counterclockwise relative to the plane normal 1002 (i.e., to the left of the plane normal) is referred to as having a positive α (α>0).

[0132] The appropriate combination of high refractive index materials and / or the structure of the diffraction grating 1008 can produce a specific range of incident angles α (Δα), referred to herein as the acceptance angle range or field of view (FOV). A range Δα can be described by an angular range spanning negative and / or positive values ​​of α, outside of which the diffraction efficiency drops by more than 10%, 25%, more than 50%, or more than 75%, 80%, 90%, 95%, or any value within a range defined by any of these values, relative to the diffraction efficiency at α=0 or some other direction. In some embodiments, it may be desirable to have a range of Δα where the diffraction efficiency is relatively high and constant, for example, a uniform diffracted light intensity within Δα is desired. Therefore, in some embodiments, Δα is associated with the angular bandwidth of the diffraction grating 1008 so that an incident light beam 1016 within Δα is effectively diffracted by the diffraction grating 1008 at a diffraction angle θ relative to the surface normal 1002 (e.g., a direction parallel to the yz plane), where θ exceeds θ TIR , so that the diffracted light is guided within the waveguide 1004 under total internal reflection (TIR). In some embodiments, the angle Δα range may affect the field of view seen by the user. It should be understood that in various embodiments, light can be guided to the incoupling grating (ICG) from either side. For example, light can be guided through the substrate or waveguide 1004 and incident on Fig.10 1008. The light may experience the same effects, for example, being coupled into the substrate or waveguide 1004 by the in-coupling grating 1008 so that the light is guided within the substrate or waveguide by total internal reflection. The range of incident angles α (Δα), referred to herein as the acceptance angle range or field of view (FOV), may be affected by the refractive index of the substrate or waveguide material. For example, Fig.10 In FIG. 5 , the reduced angular range (Δα′) shows the effect of the high refractive index material on the refraction of light incident on the incoupling grating (ICG). However, the angular range (Δα) or FOV is much larger.

[0133] Both gratings 1008 and 1012 include grating features with peaks 1003 and grooves 1005. Blazed transmission diffraction grating 1008 includes a surface corresponding to surface 1004S of a substrate or waveguide, which surface 1004S has a "sawtooth" shaped pattern when viewed in cross section as shown. The "sawtooth" pattern is formed by a first inclined portion 1007 of surface 1004S. Fig.10 In the example shown, the grating 1008 also includes a second (steeper) inclined portion 1009. In the example shown, the first inclined portion 1007 has a shallower inclination than the second inclined portion 1009, which has a steeper inclination. In this example, the first inclined portion 1007 is also wider than the second inclined portion 1009.

[0134] When configured as an in-coupling optical element or an in-coupling diffraction grating, the diffraction grating 1008 can diffractively couple light incident to the substrate 1004, which can be a waveguide as described above. The diffraction grating 1012 is configured as an out-coupling optical element and diffractively couples light from the substrate 1004, which can also be a waveguide as described above.

[0135] The substrate 1004 may be formed of a high refractive index material, for example, having a refractive index of at least 1.7. For example, the refractive index may be at least 1.8, at least 1.9, at least 2.0, at least 2.1, at least 2.2, or at least 2.3, and may be no more than 2.4, 2.5, 2.6, 2.7, 2.8, or may be within any range formed by any of these values, or may be outside these ranges. For example, in some embodiments, the substrate comprises a lithium-based oxide. In various examples disclosed herein, the diffraction features of the diffraction grating 1008 may be formed on a surface of the substrate 1004. The diffraction features may be formed in the substrate 1004 (e.g., a waveguide), or in a separate layer formed on the substrate 1004 (e.g., a waveguide), and are configured to be in optical communication with the substrate 1004, for example, coupling light into or out of the substrate 1004. In the illustrated example, the diffraction features (such as lines) of the diffraction grating 1008 are formed in the substrate 1004, such as on the surface of the substrate. For example, the diffractive features can be etched into the substrate 1004, which has a high refractive index material, such as a lithium-based oxide. For example, the substrate can include lithium niobate, and the diffraction grating can be formed in the lithium niobate substrate by etching or patterning the substrate surface. Other materials with a high refractive index can also be used. Other lithium-containing materials (such as lithium oxides, for example, lithium tantalate (LiTaO 3 )) can also be used as a substrate. Silicon carbide (SiC) is another option for the substrate material. Examples are not limited. In other examples, the diffraction features of the diffraction grating 1008 can be formed in a separate layer disposed on (e.g., in physical contact with) the substrate 1004. For example, zinc oxide (ZnO), silicon nitride (SiC) with a thickness of less than 200 nm can be disposed on an existing high refractive index substrate. 3 N 4 )、ZrO 2 ), titanium dioxide (TiO 2 ), silicon carbide (SiC), etc. The thin film coating can be patterned to form diffraction features. However, in some embodiments, the diffraction features (such as lines) of the diffraction grating 1008 can be formed of a material different from the substrate. For example, the substrate can include a high refractive index material, such as a lithium-based oxide (e.g., lithium niobate LiNbO 3 or LiTaO 3), however, the diffractive features can be formed from different materials, such as zinc oxide (ZnO), zirconium dioxide (ZrO 2 ), titanium dioxide (TiO 2 ), silicon carbide (SiC), or other materials described herein. In some embodiments, such other materials formed on the substrate may have a lower refractive index. In some cases, substrate 1004 may include materials (including amorphous high refractive index glass substrates): such as silicon-based glass (e.g., doped silicon glass), silicon oxynitride, transition metal oxides (e.g., hafnium oxide, tantalum oxide, zirconium oxide, niobium oxide, aluminum oxide (e.g., sapphire)), plastics, polymers, or other materials that are optically transmissive to visible light, such as having an appropriate refractive index as described above, which is different from the material of lithium-based oxide features 1008.

[0136] In some examples, the diffraction gratings 1008 and 1012 and the substrate 1004 or waveguide all include the same material, such as a lithium-based oxide. In some embodiments, the diffraction gratings 1008 and 1012 are directly patterned into the substrate 1004 so that the diffraction gratings and the substrate 1004 form a monolithic or monolithic structure. For example, the substrate 1004 includes a waveguide and the diffraction grating 1008 is directly formed on the surface of the waveguide or substrate. In these embodiments, the bulk lithium-based oxide material may be patterned at the surface 1004S to form the diffraction grating 1008, and the lithium-based oxide material below the diffraction grating 1008 may form the waveguide. In yet other embodiments, the bulk or substrate 1004 and the surface 1004S patterned to form the diffraction grating 1008 include different lithium-based oxides. For example, the main lithium-based oxide material patterned at the surface region to form the diffraction grating 1008 may be formed of a first lithium-based oxide material, while the lithium-based oxide material forming the substrate 1004 or the substrate region below the diffraction grating 1008 may be formed of a second lithium-based oxide material different from the first lithium-based oxide material. In some examples, the diffraction gratings 1008 and 1012 include different high refractive index materials, such as zirconium dioxide (ZrO 2 ), titanium dioxide (TiO 2 ), silicon carbide (SiC), etc., and the material forming the substrate 1004 or the substrate region below the diffraction grating may be formed of a second material, such as LiTaO 3 、LiNbO 3 etc., and is different from the first material coated as a thin film.

[0137] exist Fig.10In the example shown, the diffraction gratings 1008 and 1012 may include a plurality of blazed diffraction grating ridges (or lines) that are elongated in a first horizontal direction or y-direction and periodically repeated in a second horizontal direction or x-direction. For example, the diffraction grating lines may be straight and continuous lines extending in the y-direction. However, the embodiments are not limited thereto. In some embodiments, the diffraction grating lines may be discontinuous lines, for example in the y-direction. In some other embodiments, the discontinuous lines may form a plurality of columns protruding from the surface of the grating substrate. In some embodiments, at least some of the diffraction grating lines may have different widths in the x-direction.

[0138] In the illustrated example, the diffraction grating lines of the diffraction grating 1008 have a profile, such as a sawtooth profile, having asymmetric opposite side surfaces forming different angles relative to the substrate plane. However, the embodiment is not limited thereto, and in other implementations, the diffraction grating lines may have symmetric opposite side surfaces forming similar angles relative to the substrate plane.

[0139] In general, it is believed that the use of one or more gratings with directional surface features for EPE / CPE structures can preferentially extract light from the waveguide toward the user side, rather than extracting light equally toward the world side and the user side. Such a structure can increase the overall efficiency of the system by 25% or more (e.g., 50% or more, 75% or more, 100% or more, 150% or more, 200% or more, 300% or more, 400% or more, 500% or more, 600% or more, 700% or more, 800% or more, 900% or more, 1,000% or more, such as 2,000% or less, 1,500% or less).

[0140] refer to Fig.11A , an example EPE / CPE 1200 (shown in cross section) includes a tilted grating 1210 on a resist RLT layer 1230 supported by a substrate 1220. The tilted grating 1210 includes tilted ridges 1211 separated by grooves 1212.

[0141] The height of the grating layer refers to the ridge dimension along the Z direction and is denoted as H. The ridge 1211 may have a height ranging from 10 nm to 1,000 nm (eg, 50 nm to 500 nm, 100 nm to 400 nm, 200 nm to 400 nm, 250 nm to 350 nm).

[0142] The pitch P of the grating layer is the dimension between adjacent ridges or adjacent grooves along the X direction. In general, the pitch, like other parameters of the grating structure 1210, can be determined empirically and / or by simulation. The pitch can be adjusted according to the operating wavelength of the grating. In general, the pitch is in the range of from 100 nm to 5,000 nm (e.g., 100 nm to 2,500 nm, 100 nm to 1,000 nm, 200 nm to 750 nm, 250 nm to 500 nm, 300 nm to 400 nm).

[0143] The ridge 1211 has a width W, which refers to the ridge dimension along the X direction. For the grating structure 1210, the ridge 1211 is parallel across the relative slopes of the illustrated cross section, so the ridge thickness is constant throughout the entire height of the ridge. However, in some embodiments, the width may vary (e.g., narrow) from the bottom to the top of the ridge. In embodiments where the width varies, the width may be determined at the midpoint of the ridge height.

[0144] Duty cycle refers to the ratio of width to pitch, expressed as a percentage. In an embodiment, the grating structure may have a duty cycle in a range from 5% to 95% (eg, 10% to 75%, 20% to 50%, 30% to 40%).

[0145] Although the foregoing examples are of grating structures with parallelogram-shaped ridges, more generally, other blazed or tilted cross-sectional shapes are possible. For example, roughly trapezoidal, triangular, and stepped shapes are also possible, which may include concave shapes, such as "shark fins", "sawtooths", and other tilted or tilted (i.e., non-rectangular) geometries. In addition, although the shapes described correspond to parallelograms to mathematical precision, deviations from these shapes are inevitable due to manufacturing limitations, etc. In general, as used in this article, such ridges and other features are considered to have a specific shape, that is, their design dictates that such shape and / or structure have such a shape within the process capabilities used to mass-produce such structures. Examples of other possible shapes are described below.

[0146] Without wishing to be bound by theory, and by way of example, the optical performance of a structure like EPE 1200 was simulated to demonstrate the asymmetric light extraction properties of such a device. Fig. 11B , simulating the glancing angle θ I Optical properties of the first-order diffracted light generated by the light incident on the EPE from the waveguide. I is chosen so that the first order diffracted light propagates perpendicular to the plane of the EPE (as shown). These rays represent the central part of the user's field of view (FOV). Fig. 11B As shown, diffraction results in a reflection-1 (RX-1) order and a transmission-1 (TX-1) order.

[0147] refer to Figures 12A-12D For the above incident conditions, the following is performed for light with a wavelength of 525 nm: Fig.11A Parameters of the EPE structure shown were scanned to identify structures that provide directionality. For the simulations, the duty cycle was set to 50% and the grating thickness H and tilt angle θ were varied. For each figure, the grating thickness is the x-axis parameter and the tilt angle is the y-axis parameter. The grating thickness was varied from 60nm to 200nm and the tilt angle was varied from 10° to 80°. In each case, the resist layer had a thickness of 10nm. The four metrics used for the analysis are: Average (over polarization S / P) RX-1 diffraction efficiency <rx-1>(( Fig. 12A ); Average TX-1 diffraction efficiency <tx-1>( Fig. 12B ); Average reflectivity ( Fig. 12C ) and D) for estimating the directionality <tx-1> / <rx-1>ratio( Fig.12D ).

[0148] An approximately linear increase in thickness / tilt angle from about 100 nm and 20° to about 180 nm and about 50° was observed for the stripes. <tx-1> / <rx-1>The value of exceeds the ratio of 10. However, for transmitted light ( <tx-1>) occurs at higher thickness values ​​(e.g., 120 nm or more) and higher tilt angles (e.g., 40° or more). In general, the diffraction efficiency of the transmitted light should be high enough to ensure image uniformity across the FOV. While the simulations reported here are merely examples and are not intended to be limiting, they provide illustrations of certain empirical design tools that can be used to provide an initial design point for the grating design. In addition, while Fig.11A The structures described in and simulated here are transmission gratings, but as will become clear below, the gratings used in the EPE / CPE structures may also include reflection gratings.

[0149] To further investigate the design space of tilted gratings, additional examples were simulated. In particular, four tilted structures were simulated along with the baseline structure. Figures 13A-13D Table 1 below includes parameter values ​​for each example, and in each case, the thickness of the RLT layer is 10 nm and the simulated wavelength is 525 nm. In the figure, the arrow shows the direction of incident light. The grating ridges and the RLT layer have a refractive index of 2.0 to 2.5. The trough has a refractive index of 1.0.

[0150] picture structure Thickness(nm) Tilt angle (°) Duty cycle (%) N / A Baseline 90 90 35 Fig.13A Slanted 170 60 35 Fig. 13B Slanted 170 120 35 Fig. 13C Slanted 170 70 35 Fig.13D Slanted 170 110 35

[0151] Table 1

[0152] The results of the simulation are shown in Table 2 below. RXD and TXD correspond to the RX-1 and TX-1 diffraction efficiencies. In the second to fifth columns, S and P correspond to the input polarization, while AV (the sixth and seventh columns) refers to the average of the S / P values. DTOT is the sum of the average efficiency values. This parameter is related to the uniformity over the FOV. TXRXRXAV and RXTXAV are the ratios TXAV / RXAV and RXAV / TXAV, respectively, which are measures of the grating directivity.

[0153] Diagram / Structure RXDS TXDS RXDP TXDP RXAV TXAV DTOT TXRXAV RXTXAV Baseline 4.51 4.22 2.37 2.16 3.44 3.19 6.63 0.93 1.08 Fig.13A 1.2542 9.4454 0.4011 2.9514 0.8277 6.1984 7.0261 7.4891 0.1335 Fig. 13B 6.8454 3.0738 2.5102 0.8594 4.6778 1.9666 6.6444 0.4204 2.3786 Fig. 13C 2.0686 8.8536 0.6956 2.6511 1.3821 5.7524 7.1345 4.162 0.2403 Fig.13D 5.8281 4.4683 2.1394 1.204 3.9837 2.8361 6.8199 0.7119 1.4046

[0154] Table 2

[0155] The ninth and tenth columns provide a sense of directionality. The values ​​for the baseline grating are approximately 1 (specifically, 0.93 and 1.08), indicating approximately equal amounts of light towards the user side and the world side. Fig.13A and Fig. 13C The tilted grating structure of shows more directionality toward the TX side (e.g., the user side of the EPE 1200), while Fig. 13B and Fig.13D The tilted grating structure shows more directionality towards the RX side (e.g., the world side of the EPE 1200). In general, different cases can be selected as appropriate for different eyepiece architectures, but in either case, the tilted grating structure can be designed to provide asymmetric light extraction from the waveguide.

[0156] Although the foregoing simulation examples are based on gratings with trapezoidal grating ridges, other cross-sectional shapes of grating ridges are possible. For example, blazed gratings featuring sawtooth ridges or stepped ridges are possible. Example ridge shapes are shown in FIG. 22 described below.

[0157] For example, FIG22 shows an example cross-sectional shape 2200 of a grating ridge. Cross-sectional shape 2210 includes a single tilt geometry, and cross-sectional shape 2220 includes a multi-step tilt geometry, for example, a slope with steps. Cross-sectional shapes 2230 and 2240 feature other multi-step tilt geometries, for example, two different tilt angles.

[0158] Fig.14A A portion of an EPE / CPE 1400 is shown in cross section and includes a sawtooth grating 1410 on a resist RLT layer 1430 supported by a substrate 1420. The sawtooth grating 1410 includes ridges 1411, each ridge having a shallow blaze angle θ B and a steeper anti-blaze angle θ AB Characterization. For the grating 1410, the grating height, period, and duty cycle are defined as above. The grating width is calculated at the bottom of each ridge 1411 (i.e., at its thickest part). In addition, the ridges of the blazed grating can have smooth faces or can be stepped. Each of these parameters can be determined / optimized using the methods disclosed herein.

[0159] refer to Figures 14B-14D , an example of a blazed grating is simulated as follows. In particular, a continuous blazed grating ( Fig. 14B ) and the four-step blazed grating ( Fig. 14C ). The parameters of these structures are summarized in Table 3 below.

[0160] picture type Thickness(nm) Blaze Angle(°) Anti-blaze angle (°) Duty cycle (%) 14A Shine:Continuous 322 55 80 100 14B Shine: Four Steps 322 55 80 100 14C Shining: Second Step 322 55 80 100

[0161] Table 3

[0162] The simulation results are shown in Table 4. In each case, the ratio of transmitted light to reflected light is approximately 10:1.

[0163] picture RXDS TXDS RXDP TXDP RXAV TXAV DTOT TXRXAV RXTXAV 14B 7.37 0.2 5.53 1.2 6.45 0.7 7.15 0.11 9.24 14C 6.64 0.18 4.4 1.03 5.52 0.6 6.12 0.11 9.18

[0164] Table 4

[0165] In general, the diffractive structures providing asymmetric light extraction from the waveguide as described above can be deployed in the eyepiece in various configurations, for example, in combination with an ICG on the waveguide. For example, gratings for the EPE and / or CPE can be provided on one or both surfaces of the waveguide. Examples of single-sided deployments are shown in FIG. Fig.15A and 15B In the eyepiece 1501, as shown Fig.15A As shown, ICG 1510 and EPE 1521 are formed on the same side of waveguide 1530. EPE 1521 is designed to preferentially extract light from the light guide to the user side 1540 using the design principles described above. In eyepiece 1502, as shown Fig. 15B As shown, the ICG 1510 and the EPE 1522 are formed on opposite sides of the same waveguide 1530. Similar to the eyepiece 1501, the EPE 1522 is designed to preferentially extract light from the light guide to the user side 1540.

[0166] Fig. 15C A double-sided structure is shown, where the CPE includes two gratings 1523 and 1524 formed on opposite sides of a waveguide 1530. In this design, both gratings 1523 and 1524 are designed so that the eyepiece 1503 preferentially directs light to the user side 1540. Fig.15D Another double-sided structure is shown in which the CPE includes two gratings 1525 and 1526 formed on opposite sides of the eyepiece 1504 to preferentially direct light to the world side 1550.

[0167] Typically, the grating structure for the EPE or CPE can be uniform across the eyepiece, or the grating structure can vary. The grating structure can vary abruptly or continuously. The structural features that can vary include, for example, one or more of blaze angle, anti-blaze angle, height, ridge width, period, duty cycle, etc. These features can vary in the direction from the ICG to the EPE / CPE side opposite the ICG, or in other directions. In some examples, the structural features can vary in more than one direction.

[0168] refer to Figures 16A-16D In some examples, the eyepiece 1600 includes a CPE 1610 having four zones (1611-1614), each zone having a grating structure different from that of its adjacent zones. The grating structure for each zone 1611-1614 is shown in cross section at Figures 16B-16D Specifically, the region closest to ICG 1620, region 1612, includes an RLT layer having a thickness of 10 nm and a grating height of 85 nm, as shown in FIG. Fig.16D The region farthest from ICG 1620, region 1611, has an RLT layer with a thickness of 20 nm and a grating height of 225 nm, as shown in FIG. Fig. 16B The other two regions, regions 1612 and 1614, both have an RLT layer with a thickness of 10 nm and a grating height of 175 nm. All gratings have a blaze angle of 45° and an anti-blaze angle of 90°.

[0169] Simulations of such a grating structure with blazed gratings on either side of a substrate with a refractive index of 2.0 have demonstrated a user-side efficiency of 9.7% and a world-side efficiency of 1.6% at 400nm TTV, where the grating and RLT layers have a refractive index of 1.65.

[0170] Typically, the light extraction efficiency can vary over the area of ​​the CPE, and the use of zones of different grating structures and / or continuously varying grating structures is used to reduce the variation in extraction efficiency across the CPE. For example, in some examples, the CPE has a user-side extraction efficiency that varies by a factor of three or less (e.g., 2.5 or less, 2 or less, 1.5 or less) over the entire area. In certain examples, the CPE can have a user-side extraction efficiency that has a minimum value of 4% or greater (e.g., 5% or greater, 6% or greater, 7% or greater) and a maximum efficiency of 15% or less (e.g., 14% or less, 13% or less, 12% or less, 11% or less, 10% or less). In some examples, the user-side extraction efficiency is greatest at the center of the CPE.

[0171] Figure 17A-1 8E shows a further example of a blazed sawtooth CPE structure with a gradient pattern. Figures 17A-17B Shows the world side of CPE ( Fig.17A ) and user side ( Fig. 17B ) cross-sectional profile of a blazed sawtooth structure. In this example, both structures have ridges with a blaze angle of 20° and a reverse blaze angle of 85°. Adjacent ridges are separated by a gap of 20 nm.

[0172] Fig.18A A graph showing the variation in grating height across the gratings is shown. Each grating has 16 zones with the shortest grating being closest to the ICG. The grating height increases monotonically from a minimum of 15 nm to a maximum of 90 nm for the zone furthest from the ICG. Figures 18B-18C The world side ( Fig.18B ) and user side ( Fig.18C )'s relative orientation of the grating lines.

[0173] Although the grating structures of the aforementioned examples are one-dimensional gratings, other embodiments are possible. For example, in some embodiments, the array of structures can also be arranged in two directions to form a two-dimensional (2D) array of diffraction features. The 2D array of diffraction features can include undulations in two directions. In some cases, the undulations can be periodic, while in other cases, the pitch of the undulations can vary in at least one direction. According to various examples described herein, the diffraction features have relative sidewalls that are asymmetrically angled or inclined. According to various examples described herein, the diffraction features can be conical.

[0174] In some embodiments, the diffraction feature may have relative sidewalls that are substantially angled or tilted. In some embodiments, the relative sidewalls may be tilted in the same direction, while in other embodiments, the relative sidewalls may be tilted in opposite directions. In some other embodiments, one of the relative sidewalls of the diffraction feature may be substantially tilted, while the other sidewall of the sidewall is substantially perpendicular or orthogonal to the horizontal axis or at least less tilted than the other sidewall. In various examples of 2D diffraction features described herein, the 2D diffraction feature may be formed in or on an underlying substrate, which may be a waveguide, as described above for various examples of one-dimensional diffraction features. For example, the 2D diffraction feature may be etched into the underlying substrate, or formed by patterning a separate layer formed thereon. Therefore, the 2D diffraction feature may be formed by a material that is the same as or different from the substrate material in a manner similar to the various 2D diffraction features described above. Other variations and configurations are also possible.

[0175] Thus, any structure or device described herein, such as a grating structure, may include a one-dimensional grating. Similarly, any structure or device described herein, such as a grating structure, may also include a 2D grating. Such a 2D grating may scatter light. These gratings may also include a blazed grating. Such a blazed grating may preferably direct light into certain directions. In some embodiments, a 2D grating (e.g., having one tilted facet on a diffraction feature) preferably directs light into one direction, while in other embodiments, a 2D grating (e.g., having two tilted facets on a diffraction feature that are different) preferably directs light into multiple directions. Similarly, any method or process described herein may be used for a 1D grating. Similarly, any method or process described herein may be used for a 2D grating. These 1D or 2D gratings may be included in or on a substrate and / or waveguide, and may be included in an eyepiece, and may also be integrated into a head-mounted display disclosed herein. These gratings can be used as input gratings (eg, ICG), output gratings (EPE), light distribution gratings (OPE), or combined light distribution grating / output gratings (eg, CPE).

[0176] In general, blazed diffraction gratings of either single-step or multi-step geometries are possible, and a variety of techniques can be used to form the gratings. Figures 19A-19B In the example shown, the grating can be formed by depositing a blazed photoresist and then etching and patterning the photoresist.

[0177] Example methods of forming a blazed grating and examples of various blazed grating geometries are described in US20210072437A1, entitled “Display device with a diffraction grating having reduced polarization sensitivity,” the entire contents of which are incorporated herein by reference.

[0178] Fig.19A 1004 (see, for example, Fig.10 ) is formed in a single-step blazed grating 1106 in a substrate 1104 having a waveguide 1104. A patternable material such as a photoresist 1102 is deposited onto the substrate 1104, which may be or include a waveguide 1104. The patternable material / photoresist 1102 is patterned to have the shape of a blazed grating. In some embodiments, forming a blazed geometry in the photoresist 1102 may involve imprinting a pattern such as a single-step "sawtooth" pattern in the photoresist 1102 (e.g., depositing the photoresist on the substrate 1104 and then imprinting the blazed geometry). The photoresist 1102 may include a mask, such as a hard mask. The patterned photoresist 1102 and substrate 1104 may then be etched to form a blazed pattern in the substrate 1106. Etching the photoresist 1102 and substrate 1104 may involve, for example, dry plasma or chemical etching and / or wet chemical etching. In some embodiments, Fig.19A The etching shown in can etch away material at a relatively constant rate such that the thickest portions of the patterned photoresist result in relatively small amounts of material being removed from the substrate, e.g., negligible or no removal, while the thinnest (or non-existent) portions of the patterned photoresist result in relatively large amounts of material being removed from the substrate or the deepest etching into the substrate.

[0179] Fig.19B is a scanning electron micrograph of a blazed photoresist grating 1112, wherein the blazed grating pattern is formed in the photoresist 1104, for example, by imprinting the photoresist with a patterned master. The diffraction grating 1112 shown has a single-step blazed geometry.

[0180] refer to Figures 20A-20K , shows SEM micrographs of a number of grating structures suitable for the above-mentioned EPE / CPE structures. Figures 20A-20G An example of a one-dimensional grating is shown. Figures 20H-20J An example of a two-dimensional grating structure is shown.

[0181] Furthermore, in some examples, the grating may include a single-sided or conformal coating with a different material on the grating ridges. Figure 20K A tilted Shakfin grating is shown, which is imprinted with a 1.53 refractive index resist and a thin RLT of <20 nm, and on which a blazed TiO with a refractive index of ~2.2 is deposited. 2 It is believed that this can result in low refractive index (eg, refractive index of 1.3 to 1.5) tilted structures having even higher diffraction directivity.

[0182] Figures 21A-21D A further example of an eyepiece featuring an EPE with a double-sided grating is shown. Here, each structure is shown in cross-section and includes an ICG 212 on the side of the waveguide 2111 opposite the projector. The direction of light from the projector is shown as arrow 2101. Fig.21A The eyepiece 2110 in includes a pair of blazed gratings 2115 and 2116 whose ridge shapes vary from the side closest to the ICG 2112 to the opposite side of the grating. In the grating 2115 located on the same side of the waveguide 2111 as the ICG 2112, the blazed grating is tilted toward the ICG 2112. In other words, the side of each ridge having a blaze angle is opposite to the side closest to the ICG. The grating 2116 is a blazed grating tilted away from the ICG. In both cases, the blaze angle and anti-blaze angle are the same on each grating and are the same in gratings 2115 and 2116, but the grating height and shape vary. In particular, the height of the grating increases with increasing distance from the ICG 2112, and the grating ridges include a flat top surface whose size decreases with increasing distance from the ICG 2112.

[0183] Eyepiece 2120 includes gratings 2125 and 2126 on opposite sides of waveguide 2111. Here, the grating height varies similar to the corresponding gratings in eyepiece 2110, but the blaze angle and anti-blaze angle also vary across the grating.

[0184] The eyepiece 2130 includes a pair of tilted gratings 2135 and 2136 of varying height, with the grating height increasing with increasing distance from the ICG 2112. The grating 2135 is tilted toward the ICG 2112, while the grating 2136 is tilted away. The tilt angle of both gratings is the same and is constant across the gratings.

[0185] Eyepiece 2140 also includes two tilted gratings 2145 and 2146. In this example, the tilt angle varies across the gratings. For grating 2145, the ridges are tilted toward ICG 2112 at locations closer to the ICG, while ridges farther from the ICG are tilted away from the ICG. For grating 2146, the ridges are tilted away from ICG 2112 at locations closer to the ICG, and then tilted toward the ICG. In general, the tilt angle can vary continuously across the grating, or from discrete region to region.

[0186] Typically, the structure of each grating can be determined empirically and can be shaped to manipulate light differently to change the direction of light emitted from the display for different areas in the user's field of view.

[0187] In addition, reference Fig.21E , typically, each grating layer can include a single layer grating or a multi-layer structure, depending on the embodiment. For example, in some examples, the grating layer 2150 includes ridges 2151 formed of a single material (e.g., resist). In some examples, the grating 2160 can include ridges, wherein a portion of each ridge includes an additional layer, such as a high refractive index layer. For the grating 2160, one face of the ridge 2151 is coated with a layer 2161 of a high refractive index material, while the opposite face is bare. The grating 2170 includes a high refractive index layer 2171 on both faces of the ridge 2151. The grating 2180 includes an additional low refractive index layer 2171 on the ridge 2151 and a portion of the layer 2161 on one face of the ridge. The grating 2190 includes a low refractive index layer 2171 on top of the layer 2171, which covers both faces of the ridge 2151.

[0188] Other combinations of high and low refractive index layers are possible on both single-sided and double-sided diffraction gratings.

[0189] As previously mentioned, a variety of grating ridge shapes are contemplated, including those discussed above. Other example ridge shapes are Figures 22A-22D Each of these examples features a ridge formed by a single layer of grating material (e.g., resist) on top of a continuous layer 2221 of the same material supported by the waveguide 2201. Fig.22A A diffractive structure 2210 is shown in which the ridges 2211 have a triangular profile, similar to the examples discussed previously. Fig. 22B The diffractive structure 2220 shown in FIG. 2 is characterized by a ridge having a rectangular portion 2223 on top of a triangular portion 2222 with the top being truncated. Fig. 22C and 22D An example is shown having a ridge comprising two triangular portions. Fig. 22C The diffractive structure 2230 in FIG. 2 includes two triangular portions 2231 and 2232 tilted in the same direction. In other words, the blaze angles of the two portions are on the same side of the ridge. However, the blaze angle and anti-blaze angle of portion 2232 are different from the blaze angle and anti-blaze angle of portion 2231. Portion 2231 is truncated. Fig.22D The diffractive structure 2240 in 2240 comprises two triangular sections, where the triangles are tilted in opposite directions. Here, the lower triangular section 2241 is truncated. The triangular section 2241 has the same blaze angle and anti-blaze angle as section 2242, but more generally, these angles may vary. The diffractive structures 2230, 2240 are considered to be characterized by gratings with ridges having a multi-step geometry, the multi-step geometry including tilted steps.

[0190] In general, the structure of the grating layer can be determined based on the specific performance requirements of a particular application. Accordingly, other embodiments are within the following claims. < / tx-1> < / tx-1>

Claims

1. A head-mounted display system, comprising: Head-mountable frame; a light projection system configured to output light to provide image content; a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light coupled into the waveguide from the light projection system; a diffractive structure optically coupled to the waveguide, the diffractive structure configured to couple light guided by the waveguide out of the waveguide toward a user side of the head mounted display, the diffractive structure comprising a grating layer, the grating layer comprising a plurality of ridges, each ridge having sides that are inclined or stepped relative to a plane of the waveguide, wherein the diffractive structure directs at least 25% more light guided by the waveguide toward the user side than toward the world side.

2. The head mounted display system according to claim 1, wherein: The ridge has a profile shape selected from the group consisting of: a trapezoid, a parallelogram, a triangle, and a step shape.

3. The head mounted display system according to claim 1, wherein: The angle of the side surface relative to the plane of the waveguide is in the range of 20° to 80°.

4. A head mounted display system as claimed in any one of the preceding claims, wherein: The ridges have a height in the range of 10 nm to 1,000 nm.

5. A head mounted display as claimed in any one of the preceding claims, wherein: The plurality of ridges have a pitch in a range of 100 nm to 5,000 nm.

6. A head mounted display system as claimed in any preceding claim, wherein: The plurality of ridges have a duty cycle in a range of 20% to 100%.

7. A head-mounted display as described in any of the preceding claims, further comprising a layer of material having the same refractive index as the material forming the ridges of the diffractive structure, the layer of material being arranged between the waveguide and the diffractive structure.

8. The head mounted display according to claim 7, wherein: The layer has a thickness in the range from 5 nm to 50 nm.

9. A head mounted display as claimed in any preceding claim, wherein: The grating layer includes a grating material having a refractive index of 1.5 or greater at an operating wavelength.

10. A head mounted display as claimed in any preceding claim, further comprising an input coupling grating (ICG) arranged to couple light into the waveguide, wherein The ICG and the diffractive structure are arranged on the same side of the waveguide.

11. The head mounted display of any one of claims 1 to 9, further comprising an input coupling grating (ICG) arranged to couple light into the waveguide, wherein The ICG and the diffractive structure are arranged on opposite sides of the waveguide.

12. A head mounted display as claimed in any preceding claim, wherein: The diffractive structure is a component of an exit pupil expander (EPE) or a combined pupil expander (CPE) of the head mounted display.

13. The head mounted display according to claim 12, wherein: The diffractive structure is a first diffractive structure, and the EPE or CPE further comprises a second diffractive structure on a side of the waveguide opposite to the first diffractive structure.

14. A head mounted display as claimed in any preceding claim, wherein: The diffractive structure comprises zones, wherein the structure of the grating layer is different in at least two zones.

15. The head mounted display according to claim 14, wherein: The grating structure of the grating layer changes abruptly from a first region to a second region adjacent to the first region.

16. The head mounted display according to claim 14, wherein: The grating structure of the grating layer changes continuously across the area of ​​the diffractive structure.

17. A head mounted display as claimed in any preceding claim, wherein: At least some of the ridges have a single step geometry.

18. A head mounted display as claimed in any preceding claim, wherein: At least some of the ridges have a multi-step geometry.

19. The head mounted display according to claim 18, wherein: The ridge having a multi-step geometry includes steps having an inclined geometry.

20. A head mounted display as claimed in any preceding claim, wherein: The diffractive structure directs at least 100% more light guided by the waveguide toward the user side than toward the world side.

21. A head mounted display as claimed in any preceding claim, wherein: The diffractive structure guides at least 4% of the light from the waveguide to the user side.

22. A head mounted display as claimed in any preceding claim, wherein: The grating layer is etched into the waveguide.

23. The head mounted display according to claims 1 to 21, wherein: The grating layer is formed in a layer of material deposited on the waveguide, the layer of material having a refractive index in the range of 1.5 to 2.

7.

24. A head mounted display as claimed in any preceding claim, wherein: The diffractive structure comprises a layer of material deposited on ridges of the grating layer.

25. The head mounted display of claim 23, wherein: The layer of material is deposited on less than all sides of the ridge.

26. The head mounted display of claim 23, wherein: The layer of material is deposited on all sides of the ridge.

27. The head mounted display of claim 23, wherein: The material layer has a refractive index in the range of 1.7 to 2.

7.

28. The head mounted display of claim 23, wherein: The material layer has a refractive index in the range of 1.3 to 1.5.

Images