Metasurfaces with light-redirecting structures including multiple materials and methods for fabricating

Display devices include waveguides with metasurfaces as in-coupling and/or out-coupling optical elements. The metasurfaces may be formed on a surface of the waveguide and may include a plurality or an array of sub-wavelength-scale (e.g., nanometer-scale) protrusions. Individual protrusions may include horizontal and/or vertical layers of different materials which may have different refractive indices, allowing for enhanced manipulation of light redirecting properties of the metasurface. Some configurations and combinations of materials may advantageously allow for broadband metasurfaces. Manufacturing methods described herein provide for vertical and/or horizontal layers of different materials in a desired configuration or profile.

BACKGROUND

Field

The present disclosure relates to display systems and, more particularly, to augmented and virtual reality display systems.

Description of the Related Art

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 wherein they seem to be, or may be perceived as, real. A virtual reality, or “VR”, scenario typically involves the presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or “AR”, scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user. A mixed reality, or “MR”, scenario is a type of AR scenario and typically involves virtual objects that are integrated into, and responsive to, the natural world. For example, an MR scenario may include AR image content that appears to be blocked by or is otherwise perceived to interact with objects in the real world.

Referring toFIG.1, an augmented reality scene10is depicted. The user of an AR technology sees a real-world park-like setting20featuring people, trees, buildings in the background, and a concrete platform30. The user also perceives that he/she “sees” “virtual content” such as a robot statue40standing upon the real-world platform30, and a flying cartoon-like avatar character50which seems to be a personification of a bumble bee. These elements50,40are “virtual” in that they do not exist in the real world. Because the human visual perception system is complex, it is challenging to produce AR technology that facilitates a comfortable, natural-feeling, rich presentation of virtual image elements amongst other virtual or real-world imagery elements.

SUMMARY

Some aspects include an optical system. The optical system comprises a waveguide and an optical element on a surface of the waveguide. The optical element is configured to redirect light having a wavelength, and comprises a plurality of spaced-apart protrusions disposed on the waveguide. Each protrusion comprises a first vertical layer comprising a first material, and a second vertical layer comprising a second material different from the first material.

The optical element may be a metasurface. The first material and the second material may have different refractive indices. The first vertical layer may define a u-shaped cross-sectional profile, wherein the second material fills an interior volume of the u-shape. Each protrusion may further comprise an intermediate vertical layer disposed between the first vertical layer and the second vertical layer, the intermediate vertical layer comprising a third material different from the first material and the second material. The intermediate vertical layer and the second vertical layer may both have u-shaped cross-sectional profiles. The plurality of protrusions may comprise at least one of nanobeams and pillars. Protrusions of the plurality of protrusions may be separated from each other by a sub-wavelength spacing. As used herein, sub-wavelength dimensions are less than the wavelength of light, preferably visible light (e.g., the visible light which the metasurface is configured to receive and redirect in a display system, as disclosed herein). The wavelength may correspond to blue light, green light, or red light.

Some aspects include a method of manufacturing an optical element for redirecting light. The method includes providing a plurality of spaced-apart placeholders on a waveguide, conformally depositing a first blanket layer comprising a first material onto the placeholder and the waveguide, preferentially removing horizontally-oriented portions of the first blanket layer to expose at least a portion of the placeholders, and selectively etching the placeholders relative to the first blanket layer to form a plurality of vertically-oriented protrusions comprising the first material. The plurality of vertically-oriented protrusions are configured to redirect light.

The vertically-oriented protrusions may form a metasurface, the vertically-oriented protrusions having a spacing less than a wavelength of the light. The vertically-oriented protrusions may comprise at least one of nanobeams and pillars. The wavelength may correspond to blue light, green light, or red light. Providing the placeholders may comprise depositing a layer of a resist on the waveguide and patterning the resist to define the placeholders. Patterning the resist may comprise performing at least one of photolithography, electron beam lithography, and nanoimprint lithography. Conformally depositing the first layer may comprise depositing the first layer by atomic layer deposition. The method may further comprise conformally depositing a second blanket layer onto the first blanket layer, the second blanket layer comprising a second material different from the first material, wherein the second blanket layer is conformally deposited prior to preferentially removing the horizontally-oriented portions. Preferentially removing horizontally-oriented portions may remove horizontally-oriented portions of the second layer and the first layer. The first blanket layer may extend along sidewalls of the placeholders to define open volumes therebetween, further comprising filling the open volumes with a fill material before preferentially removing horizontally-oriented portions. Selectively etching the placeholders may comprise retaining the fill material. The fill material may have a different refractive index than the first material. Preferentially removing horizontally-oriented portions may comprise performing chemical mechanical polishing. The method may further comprise annealing remaining portions of the first blanket layer prior to selectively etching the placeholders. Selectively etching the placeholders may comprise at least one of wet etching and plasma etching.

Some aspects include an optical system. The optical system comprises a waveguide and an optical element on a surface of the waveguide. The optical element is configured to redirect light having a wavelength, and comprises a plurality of protrusions disposed on the waveguide. Each protrusion comprises a lower horizontal layer on the waveguide, the lower horizontal layer comprising a first material; and an upper layer on the lower horizontal layer, the upper horizontal layer comprising a second material different from the first material.

The optical element may comprise a metasurface. The first material and the second material may have different refractive indices. Each protrusion may further comprise an intermediate horizontal layer disposed between the upper layer and the lower layer, the intermediate layer comprising a third material different from the first material and the second material. The plurality of protrusions may comprise at least one of nanobeams and pillars. The plurality of protrusions may be separated from each other by a sub-wavelength spacing less than the wavelength of the light. The wavelength may correspond to blue light, green light, or red light. At least one of the first material and the second material may comprise a sulfur compound. The sulfur compound may be molybdenum sulfide.

Some aspects include a method of manufacturing an optical element. The method comprises forming a metasurface, wherein forming the metasurface comprises: depositing a lower blanket layer on a waveguide, the lower blanket layer comprising a first material; depositing an upper blanket layer on the lower blanket layer, the upper blanket layer comprising a second material different from the first material; forming an etch mask over the upper blanket layer, the etch mask exposing unmasked portions of the upper blanket layer; and removing unmasked portions of the upper blanket layer and the lower blanket layer to form a plurality of protrusions comprising remaining portions of the lower and upper layers, the protrusions configured to redirect light.

The vertically-oriented protrusions may form a metasurface, the vertically-oriented protrusions having a sub-wavelength spacing less than a wavelength of the light. The vertically-oriented protrusions may comprise at least one of nanobeams and pillars. The wavelength may correspond to blue light, green light, or red light. The method may further comprise converting at least one of the lower layer and the upper layer of each protrusion to a different material by exposing the plurality of protrusions to an atmosphere comprising a chemical species for incorporation into the at least one of the lower layer and the upper layer. Converting the lower layer or the upper layer may comprise at least one of sulfurization and selenization. The lower layer and the upper layer may be deposited by at least one of physical vapor deposition, chemical vapor deposition, and atomic layer deposition. At least one of the lower layer and the upper layer may have a thickness of 5 nanometers or less. The method may further comprise depositing a third layer onto the upper layer before forming the etch mask, the third layer comprising a third material different from the first material and the second material, wherein forming the etch mask comprises forming the etch mask over the third layer.

DETAILED DESCRIPTION

AR and/or VR systems may display virtual content to a user, or viewer. For example, this content may be displayed on a head-mounted display, e.g., as part of eyewear, that projects image information to the user's eyes. In addition, where the system is an AR system, the display may also transmit light from the surrounding environment to the user's eyes, to allow a view of that surrounding environment. As used herein, it will be appreciated that a “head-mounted” or “head mountable” display is a display that may be mounted on the head of a viewer or user.

In some display systems, one or more waveguides, such as a stack of waveguides, may be configured to form virtual images at a plurality of virtual depth planes (also referred to simply a “depth planes” herein) perceived to be at different distances away from the user. In some implementations, light containing image information may be in-coupled into a waveguide, propagate through the waveguide, and then be out-coupled (e.g., towards the eye of a viewer). Different waveguides of the stack of waveguides may have optical structures (e.g., out-coupling optical elements) that simulate the wavefront divergence of light propagating from objects to the user's eyes at different distances from the user's eye. In some implementations, as an alternative to, or in addition to waveguide optical structures for providing optical power, the display systems may also include one or more lenses that provide or additionally provide optical powers or desired amounts of wavefront divergence. Light with image information may be provided by an image source, and may be in-coupled into individual waveguides by an in-coupling optical element of each waveguide. The in-coupling and out-coupling optical elements may be a diffractive optical element, including a metasurface.

It will be appreciated that the in-coupling and out-coupling optical elements preferably meet various performance criteria to, e.g., provide good image quality and/or high power efficiency. For example, different waveguides may be configured to output light of different colors or wavelength. As result, in some implementations, the in-coupling and/or out-coupling optical elements may redirect light (in-couple or out-couple the light, respectively) with high selectivity and high efficiency for desired wavelengths, while redirecting light at low efficiency for other wavelengths. As another example, it may be desirable for the in-coupling and/or out-coupling optical elements to redirect light away from those optical elements at particular angles and/or receive incident light at particular angles for redirection. Preferably, the redirection of light of particular desired wavelengths and/or in or from particular desired directions is achieved with high-efficiency. These and various other performance parameters of meta-surfaces may be adjusting by appropriately designing the structures defining the meta-surfaces.

Advantageously, systems and methods described herein provide optical elements, such as in-coupling and/or out-coupling optical elements, which, in some implementations, allow a large amount of latitude in tuning the performance characteristics of the optical elements by allowing wide latitude in modifying properties related to the materials forming the optical elements. Metasurfaces are typically been formed of a single material. Some of the systems and methods described herein provide for individual constituent structures of a metasurface which include a plurality of materials at highly precise locations and proportions. For example, the protrusions forming a metasurface may have horizontal layers and/or vertical layers (e.g., concentric vertical layers) of different materials, e.g. materials having different refractive indices. Advantageously, the inclusion of multiple materials within individual protrusions of a metasurface may provide for greater customization in metasurface design, e.g., allowing for improved control of the scattering response (e.g., amplitude, phase shift, etc.) of metasurfaces. It will be appreciated that the meta-surfaces may form various structures providing controlled redirection or scattering of incident electromagnetic radiation, including light of visible wavelengths. In some implementations, multi-layered metasurface protrusions form broadband achromatic meta-lenses, broadband beam deflectors, broadband achromatic waveplates, broadband polarizers, and/or any other metasurface in which a similar scattering response is desired across a desired (e.g. broad) range of incident wavelengths.

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

Example Display Systems

FIG.2illustrates a conventional display system for simulating three-dimensional imagery for a user. It will be appreciated that a user's eyes are spaced apart and that, when looking at a real object in space, each eye will have a slightly different view of the object and may form an image of the object at different locations on the retina of each eye. This may be referred to as binocular disparity and may be utilized by the human visual system to provide a perception of depth. Conventional display systems simulate binocular disparity by presenting two distinct images190,200with slightly different views of the same virtual object—one for each eye210,220—corresponding to the views of the virtual object that would be seen by each eye were the virtual object a real object at a desired depth. These images provide binocular cues that the user's visual system may interpret to derive a perception of depth.

With continued reference toFIG.2, the images190,200are spaced from the eyes210,220by a distance230on a z-axis. The z-axis is parallel to the optical axis of the viewer with their eyes fixated on an object at optical infinity directly ahead of the viewer. The images190,200are flat and at a fixed distance from the eyes210,220. Based on the slightly different views of a virtual object in the images presented to the eyes210,220, respectively, the eyes may naturally rotate such that an image of the object falls on corresponding points on the retinas of each of the eyes, to maintain single binocular vision. This rotation may cause the lines of sight of each of the eyes210,220to converge onto a point in space at which the virtual object is perceived to be present. As a result, providing three-dimensional imagery conventionally involves providing binocular cues that may manipulate the vergence of the user's eyes210,220, and that the human visual system interprets to provide a perception of depth.

Generating a realistic and comfortable perception of depth is challenging, however. It will be appreciated that light from objects at different distances from the eyes have wavefronts with different amounts of divergence.FIGS.3A-3Cillustrate relationships between distance and the divergence of light rays. The distance between the object and the eye210is represented by, in order of decreasing distance, R1, R2, and R3. As shown inFIGS.3A-3C, the light rays become more divergent as distance to the object decreases. Conversely, as distance increases, the light rays become more collimated. Stated another way, it may be said that the light field produced by a point (the object or a part of the object) has a spherical wavefront curvature, which is a function of how far away the point is from the eye of the user. The curvature increases with decreasing distance between the object and the eye210. While only a single eye210is illustrated for clarity of illustration inFIGS.3A-3Cand other figures herein, the discussions regarding eye210may be applied to both eyes210and220of a viewer.

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

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

Without being limited by theory, it is believed that viewers of an object may perceive the object as being “three-dimensional” due to a combination of vergence and accommodation. As noted above, vergence movements (e.g., rotation of the eyes so that the pupils move toward or away from each other to converge the lines of sight of the eyes to fixate upon an object) of the two eyes relative to each other are closely associated with accommodation of the lenses of the eyes. Under normal conditions, changing the shapes of the lenses of the eyes to change focus from one object to another object at a different distance will automatically cause a matching change in vergence to the same distance, under a relationship known as the “accommodation-vergence reflex.” Likewise, a change in vergence will trigger a matching change in lens shape under normal conditions.

With reference now toFIG.4B, examples of different accommodative and vergence states of the eyes are illustrated. The pair of eyes222ais fixated on an object at optical infinity, while the pair eyes222bare fixated on an object221at less than optical infinity. Notably, the vergence states of each pair of eyes is different, with the pair of eyes222adirected straight ahead, while the pair of eyes222converge on the object221. The accommodative states of the eyes forming each pair of eyes222aand222bare also different, as represented by the different shapes of the lenses210a,220a.

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

Without being limited by theory, it is believed that the human eye typically may interpret a finite number of depth planes to provide depth perception. Consequently, a highly believable simulation of perceived depth may be achieved by providing, to the eye, different presentations of an image corresponding to each of these limited numbers of depth planes. In some implementations, the different presentations may provide both cues to vergence and matching cues to accommodation, thereby providing physiologically correct accommodation-vergence matching.

With continued reference toFIG.4B, two depth planes240, corresponding to different distances in space from the eyes210,220, are illustrated. For a given depth plane240, vergence cues may be provided by the displaying of images of appropriately different perspectives for each eye210,220. In addition, for a given depth plane240, light forming the images provided to each eye210,220may have a wavefront divergence corresponding to a light field produced by a point at the distance of that depth plane240.

In the illustrated implementation, the distance, along the z-axis, of the depth plane240containing the point221is 1 m. As used herein, distances or depths along the z-axis may be measured with a zero-point located at the exit pupils of the user's eyes. Thus, a depth plane240located at a depth of 1 m corresponds to a distance of 1 m away from the exit pupils of the user's eyes, on the optical axis of those eyes with the eyes directed towards optical infinity. As an approximation, the depth or distance along the z-axis may be measured from the display in front of the user's eyes (e.g., from the surface of a waveguide), plus a value for the distance between the device and the exit pupils of the user's eyes. That value may be called the eye relief and corresponds to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eye. In practice, the value for the eye relief may be a normalized value used generally for all viewers. For example, the eye relief may be assumed to be 20 mm and a depth plane that is at a depth of 1 m may be at a distance of 980 mm in front of the display.

With reference now toFIGS.4C and4D, examples of matched accommodation-vergence distances and mismatched accommodation-vergence distances are illustrated, respectively. As illustrated inFIG.4C, the display system may provide images of a virtual object to each eye210,220. The images may cause the eyes210,220to assume a vergence state in which the eyes converge on a point15on a depth plane240. In addition, the images may be formed by a light having a wavefront curvature corresponding to real objects at that depth plane240. As a result, the eyes210,220assume an accommodative state in which the images are in focus on the retinas of those eyes. Thus, the user may perceive the virtual object as being at the point15on the depth plane240.

It will be appreciated that each of the accommodative and vergence states of the eyes210,220are associated with a particular distance on the z-axis. For example, an object at a particular distance from the eyes210,220causes those eyes to assume particular accommodative states based upon the distances of the object. The distance associated with a particular accommodative state may be referred to as the accommodation distance, Ad. Similarly, there are particular vergence distances, Vd, associated with the eyes in particular vergence states, or positions relative to one another. Where the accommodation distance and the vergence distance match, the relationship between accommodation and vergence may be said to be physiologically correct. This is considered to be the most comfortable scenario for a viewer.

In stereoscopic displays, however, the accommodation distance and the vergence distance may not always match. For example, as illustrated inFIG.4D, images displayed to the eyes210,220may be displayed with wavefront divergence corresponding to depth plane240, and the eyes210,220may assume a particular accommodative state in which the points15a,15bon that depth plane are in focus. However, the images displayed to the eyes210,220may provide cues for vergence that cause the eyes210,220to converge on a point15that is not located on the depth plane240. As a result, the accommodation distance corresponds to the distance from the exit pupils of the eyes210,220to the depth plane240, while the vergence distance corresponds to the larger distance from the exit pupils of the eyes210,220to the point15, in some implementations. The accommodation distance is different from the vergence distance. Consequently, there is an accommodation-vergence mismatch. Such a mismatch is considered undesirable and may cause discomfort in the user. It will be appreciated that the mismatch corresponds to distance (e.g., Vd-Ad) and may be characterized using diopters.

In some implementations, it will be appreciated that a reference point other than exit pupils of the eyes210,220may be utilized for determining distance for determining accommodation-vergence mismatch, so long as the same reference point is utilized for the accommodation distance and the vergence distance. For example, the distances could be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., a waveguide of the display device) to the depth plane, and so on.

Without being limited by theory, it is believed that users may still perceive accommodation-vergence mismatches of up to about 0.25 diopter, up to about 0.33 diopter, and up to about 0.5 diopter as being physiologically correct, without the mismatch itself causing significant discomfort. In some implementations, display systems disclosed herein (e.g., the display system250,FIG.6) present images to the viewer having accommodation-vergence mismatch of about 0.5 diopter or less. In some other implementations, the accommodation-vergence mismatch of the images provided by the display system is about 0.33 diopter or less. In yet other implementations, the accommodation-vergence mismatch of the images provided by the display system is about 0.25 diopter or less, including about 0.1 diopter or less.

FIG.5illustrates aspects of an approach for simulating three-dimensional imagery by modifying wavefront divergence. The display system includes a waveguide270that is configured to receive light770that is encoded with image information, and to output that light to the user's eye210. The waveguide270may output the light650with a defined amount of wavefront divergence corresponding to the wavefront divergence of a light field produced by a point on a desired depth plane240. In some implementations, the same amount of wavefront divergence is provided for all objects presented on that depth plane. In addition, it will be illustrated that the other eye of the user may be provided with image information from a similar waveguide.

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

FIG.6illustrates an example of a waveguide stack for outputting image information to a user. A display system250includes a stack of waveguides, or stacked waveguide assembly,260that may be utilized to provide three-dimensional perception to the eye/brain using a plurality of waveguides270,280,290,300,310. It will be appreciated that the display system250may be considered a light field display in some implementations. In addition, the waveguide assembly260may also be referred to as an eyepiece.

In some implementations, the display system250may be configured to provide substantially continuous cues to vergence and multiple discrete cues to accommodation. The cues to vergence may be provided by displaying different images to each of the eyes of the user, and the cues to accommodation may be provided by outputting the light that forms the images with selectable discrete amounts of wavefront divergence. Stated another way, the display system250may be configured to output light with variable levels of wavefront divergence. In some implementations, each discrete level of wavefront divergence corresponds to a particular depth plane and may be provided by a particular one of the waveguides270,280,290,300,310.

With continued reference toFIG.6, the waveguide assembly260may also include a plurality of features320,330,340,350between the waveguides. In some implementations, the features320,330,340,350may be one or more lenses. The waveguides270,280,290,300,310and/or the plurality of lenses320,330,340,350may be configured to send image information to the eye with various levels of wavefront curvature or light ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image injection devices360,370,380,390,400may function as a source of light for the waveguides and may be utilized to inject image information into the waveguides270,280,290,300,310, each of which may be configured, as described herein, to distribute incoming light across each respective waveguide, for output toward the eye210. Light exits an output surface410,420,430,440,450of the image injection devices360,370,380,390,400and is injected into a corresponding input surface460,470,480,490,500of the waveguides270,280,290,300,310. In some implementations, each of the input surfaces460,470,480,490,500may be an edge of a corresponding waveguide, or may be part of a major surface of the corresponding waveguide (that is, one of the waveguide surfaces directly facing the world510or the viewer's eye210). In some implementations, a single beam of light (e.g. a collimated beam) may be injected into each waveguide to output an entire field of cloned collimated beams that are directed toward the eye210at particular angles (and amounts of divergence) corresponding to the depth plane associated with a particular waveguide. In some implementations, a single one of the image injection devices360,370,380,390,400may be associated with and inject light into a plurality (e.g., three) of the waveguides270,280,290,300,310.

In some implementations, the image injection devices360,370,380,390,400are discrete displays that each produce image information for injection into a corresponding waveguide270,280,290,300,310, respectively. In some other implementations, the image injection devices360,370,380,390,400are the output ends of a single multiplexed display which may, e.g., pipe image information via one or more optical conduits (such as fiber optic cables) to each of the image injection devices360,370,380,390,400. It will be appreciated that the image information provided by the image injection devices360,370,380,390,400may include light of different wavelengths, or colors (e.g., different component colors, as discussed herein).

In some implementations, the light injected into the waveguides270,280,290,300,310is provided by a light projector system520, which comprises a light module530, which may include a light emitter, such as a light emitting diode (LED). The light from the light module530may be directed to and modified by a light modulator540, e.g., a spatial light modulator, via a beam splitter550. The light modulator540may be configured to change the perceived intensity of the light injected into the waveguides270,280,290,300,310to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCD) including a liquid crystal on silicon (LCOS) displays. It will be appreciated that the image injection devices360,370,380,390,400are illustrated schematically and, in some implementations, these image injection devices may represent different light paths and locations in a common projection system configured to output light into associated ones of the waveguides270,280,290,300,310. In some implementations, the waveguides of the waveguide assembly260may function as ideal lens while relaying light injected into the waveguides out to the user's eyes. In this conception, the object may be the spatial light modulator540and the image may be the image on the depth plane.

In some implementations, the display system250may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous patterns, etc.) into one or more waveguides270,280,290,300,310and ultimately to the eye210of the viewer. In some implementations, the illustrated image injection devices360,370,380,390,400may schematically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or a plurality of the waveguides270,280,290,300,310. In some other implementations, the illustrated image injection devices360,370,380,390,400may schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each of which are configured to inject light into an associated one of the waveguides270,280,290,300,310. It will be appreciated that one or more optical fibers may be configured to transmit light from the light module530to the one or more waveguides270,280,290,300,310. It will be appreciated that one or more intervening optical structures may be provided between the scanning fiber, or fibers, and the one or more waveguides270,280,290,300,310to, e.g., redirect light exiting the scanning fiber into the one or more waveguides270,280,290,300,310.

A controller560controls the operation of one or more of the stacked waveguide assembly260, including operation of the image injection devices360,370,380,390,400, the light source530, and the light modulator540. In some implementations, the controller560is part of the local data processing module140. The controller560includes programming (e.g., instructions in a non-transitory medium) that regulates the timing and provision of image information to the waveguides270,280,290,300,310according to, e.g., any of the various schemes disclosed herein. In some implementations, the controller may be a single integral device, or a distributed system connected by wired or wireless communication channels. The controller560may be part of the processing modules140or150(FIG.9D) in some implementations.

With continued reference toFIG.6, the waveguides270,280,290,300,310may be configured to propagate light within each respective waveguide by total internal reflection (TIR). The waveguides270,280,290,300,310may each be planar or have another shape (e.g., curved), with major top and bottom surfaces and edges extending between those major top and bottom surfaces. In the illustrated configuration, the waveguides270,280,290,300,310may each include out-coupling optical elements570,580,590,600,610that are configured to extract light out of a waveguide by redirecting the light, propagating within each respective waveguide, out of the waveguide to output image information to the eye210. Extracted light may also be referred to as out-coupled light and the out-coupling optical elements light may also be referred to light extracting optical elements. An extracted beam of light may be outputted by the waveguide at locations at which the light propagating in the waveguide strikes a light extracting optical element. The out-coupling optical elements570,580,590,600,610may, for example, be gratings, including diffractive optical features, as discussed further herein. While illustrated disposed at the bottom major surfaces of the waveguides270,280,290,300,310, for ease of description and drawing clarity, in some implementations, the out-coupling optical elements570,580,590,600,610may be disposed at the top and/or bottom major surfaces, and/or may be disposed directly in the volume of the waveguides270,280,290,300,310, as discussed further herein. In some implementations, the out-coupling optical elements570,580,590,600,610may be formed in a layer of material that is attached to a transparent substrate to form the waveguides270,280,290,300,310. In some other implementations, the waveguides270,280,290,300,310may be a monolithic piece of material and the out-coupling optical elements570,580,590,600,610may be formed on a surface and/or in the interior of that piece of material.

With continued reference toFIG.6, as discussed herein, each waveguide270,280,290,300,310is configured to output light to form an image corresponding to a particular depth plane. For example, the waveguide270nearest the eye may be configured to deliver collimated light (which was injected into such waveguide270), to the eye210. The collimated light may be representative of the optical infinity focal plane. The next waveguide up280may be configured to send out collimated light which passes through the first lens350(e.g., a negative lens) before it may reach the eye210; such first lens350may be configured to create a slight convex wavefront curvature so that the eye/brain interprets light coming from that next waveguide up280as coming from a first focal plane closer inward toward the eye210from optical infinity. Similarly, the third up waveguide290passes its output light through both the first350and second340lenses before reaching the eye210; the combined optical power of the first350and second340lenses may be configured to create another incremental amount of wavefront curvature so that the eye/brain interprets light coming from the third waveguide290as coming from a second focal plane that is even closer inward toward the person from optical infinity than was light from the next waveguide up280.

The other waveguide layers300,310and lenses330,320are similarly configured, with the highest waveguide310in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power representative of the closest focal plane to the person. To compensate for the stack of lenses320,330,340,350when viewing/interpreting light coming from the world510on the other side of the stacked waveguide assembly260, a compensating lens layer620may be disposed at the top of the stack to compensate for the aggregate power of the lens stack320,330,340,350below. Such a configuration provides as many perceived focal planes as there are available waveguide/lens pairings. Both the out-coupling optical elements of the waveguides and the focusing aspects of the lenses may be static (i.e., not dynamic or electro-active). In some alternative implementations, either or both may be dynamic using electro-active features.

In some implementations, two or more of the waveguides270,280,290,300,310may have the same associated depth plane. For example, multiple waveguides270,280,290,300,310may be configured to output images set to the same depth plane, or multiple subsets of the waveguides270,280,290,300,310may be configured to output images set to the same plurality of depth planes, with one set for each depth plane. This may provide advantages for forming a tiled image to provide an expanded field of view at those depth planes.

With continued reference toFIG.6, the out-coupling optical elements570,580,590,600,610may be configured to both redirect light out of their respective waveguides and to output this light with the appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides having different associated depth planes may have different configurations of out-coupling optical elements570,580,590,600,610, which output light with a different amount of divergence depending on the associated depth plane. In some implementations, the light extracting optical elements570,580,590,600,610may be volumetric or surface features, which may be configured to output light at specific angles. For example, the light extracting optical elements570,580,590,600,610may be volume holograms, surface holograms, and/or diffraction gratings. In some implementations, the features320,330,340,350may not be lenses; rather, they may simply be spacers (e.g., cladding layers and/or structures for forming air gaps).

In some implementations, the out-coupling optical elements570,580,590,600,610are diffractive features that form a diffraction pattern, or “diffractive optical element” (also referred to herein as a “DOE”). Preferably, the DOE's have a sufficiently low diffraction efficiency so that only a portion of the light of the beam is deflected away toward the eye210with each intersection of the DOE, while the rest continues to move through a waveguide via TIR. The light carrying the image information is thus divided into a number of related exit beams that exit the waveguide at a multiplicity of locations and the result is a fairly uniform pattern of exit emission toward the eye210for this particular collimated beam bouncing around within a waveguide.

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

In some implementations, a camera assembly630(e.g., a digital camera, including visible light and infrared light cameras) may be provided to capture images of the eye210and/or tissue around the eye210to, e.g., detect user inputs and/or to monitor the physiological state of the user. As used herein, a camera may be any image capture device. In some implementations, the camera assembly630may include an image capture device and a light source to project light (e.g., infrared light) to the eye, which may then be reflected by the eye and detected by the image capture device. In some implementations, the camera assembly630may be attached to the frame80(FIG.9D) and may be in electrical communication with the processing modules140and/or150, which may process image information from the camera assembly630. In some implementations, one camera assembly630may be utilized for each eye, to separately monitor each eye.

With reference now toFIG.7, an example of exit beams outputted by a waveguide is shown. One waveguide is illustrated, but it will be appreciated that other waveguides in the waveguide assembly260(FIG.6) may function similarly, where the waveguide assembly260includes multiple waveguides. Light640is injected into the waveguide270at the input surface460of the waveguide270and propagates within the waveguide270by TIR. At points where the light640impinges on the DOE570, a portion of the light exits the waveguide as exit beams650. The exit beams650are illustrated as substantially parallel but, as discussed herein, they may also be redirected to propagate to the eye210at an angle (e.g., forming divergent exit beams), depending on the depth plane associated with the waveguide270. It will be appreciated that substantially parallel exit beams may be indicative of a waveguide with out-coupling optical elements that out-couple light to form images that appear to be set on a depth plane at a large distance (e.g., optical infinity) from the eye210. Other waveguides or other sets of out-coupling optical elements may output an exit beam pattern that is more divergent, which would require the eye210to accommodate to a closer distance to bring it into focus on the retina and would be interpreted by the brain as light from a distance closer to the eye210than optical infinity.

In some implementations, a full color image may be formed at each depth plane by overlaying images in each of the component colors, e.g., three or more component colors.FIG.8illustrates an example of a stacked waveguide assembly in which each depth plane includes images formed using multiple different component colors. The illustrated implementation shows depth planes240a-240f, although more or fewer depths are also contemplated. Each depth plane may have three or more component color images associated with it, including: a first image of a first color, G; a second image of a second color, R; and a third image of a third color, B. Different depth planes are indicated in the figure by different numbers for diopters (dpt) following the letters G, R, and B. Just as examples, the numbers following each of these letters indicate diopters (1/m), or inverse distance of the depth plane from a viewer, and each box in the figures represents an individual component color image. In some implementations, to account for differences in the eye's focusing of light of different wavelengths, the exact placement of the depth planes for different component colors may vary. For example, different component color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and/or may decrease chromatic aberrations.

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

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

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

In some implementations, the light source530(FIG.6) may be configured to emit light of one or more wavelengths outside the visual perception range of the viewer, for example, infrared and/or ultraviolet wavelengths. In addition, the in-coupling, out-coupling, and other light redirecting structures of the waveguides of the display250may be configured to direct and emit this light out of the display towards the user's eye210, e.g., for imaging and/or user stimulation applications.

With reference now toFIG.9A, in some implementations, light impinging on a waveguide may need to be redirected to in-couple that light into the waveguide. An in-coupling optical element may be used to redirect and in-couple the light into its corresponding waveguide.FIG.9Aillustrates a cross-sectional side view of an example of a plurality or set660of stacked waveguides that each includes an in-coupling optical element. The waveguides may each be configured to output light of one or more different wavelengths, or one or more different ranges of wavelengths. It will be appreciated that the stack660may correspond to the stack260(FIG.6) and the illustrated waveguides of the stack660may correspond to part of the plurality of waveguides270,280,290,300,310, except that light from one or more of the image injection devices360,370,380,390,400is injected into the waveguides from a position that requires light to be redirected for in-coupling.

The illustrated set660of stacked waveguides includes waveguides670,680, and690. Each waveguide includes an associated in-coupling optical element (which may also be referred to as a light input area on the waveguide), with, e.g., in-coupling optical element700disposed on a major surface (e.g., an upper major surface) of waveguide670, in-coupling optical element710disposed on a major surface (e.g., an upper major surface) of waveguide680, and in-coupling optical element720disposed on a major surface (e.g., an upper major surface) of waveguide690. In some implementations, one or more of the in-coupling optical elements700,710,720may be disposed on the bottom major surface of the respective waveguide670,680,690(particularly where the one or more in-coupling optical elements are reflective, deflecting optical elements). As illustrated, the in-coupling optical elements700,710,720may be disposed on the upper major surface of their respective waveguide670,680,690(or the top of the next lower waveguide), particularly where those in-coupling optical elements are transmissive, deflecting optical elements. In some implementations, the in-coupling optical elements700,710,720may be disposed in the body of the respective waveguide670,680,690. In some implementations, as discussed herein, the in-coupling optical elements700,710,720are wavelength selective, such that they selectively redirect one or more wavelengths of light, while transmitting other wavelengths of light. While illustrated on one side or corner of their respective waveguide670,680,690, it will be appreciated that the in-coupling optical elements700,710,720may be disposed in other areas of their respective waveguide670,680,690in some implementations.

As illustrated, the in-coupling optical elements700,710,720may be laterally offset from one another. In some implementations, each in-coupling optical element may be offset such that it receives light without that light passing through another in-coupling optical element. For example, each in-coupling optical element700,710,720may be configured to receive light from a different image injection device360,370,380,390, and400as shown inFIG.6, and may be separated (e.g., laterally spaced apart) from other in-coupling optical elements700,710,720such that it substantially does not receive light from the other ones of the in-coupling optical elements700,710,720.

Each waveguide also includes associated light distributing elements, with, e.g., light distributing elements730disposed on a major surface (e.g., a top major surface) of waveguide670, light distributing elements740disposed on a major surface (e.g., a top major surface) of waveguide680, and light distributing elements750disposed on a major surface (e.g., a top major surface) of waveguide690. In some other implementations, the light distributing elements730,740,750, may be disposed on a bottom major surface of associated waveguides670,680,690, respectively. In some other implementations, the light distributing elements730,740,750, may be disposed on both top and bottom major surface of associated waveguides670,680,690, respectively; or the light distributing elements730,740,750, may be disposed on different ones of the top and bottom major surfaces in different associated waveguides670,680,690, respectively.

The waveguides670,680,690may be spaced apart and separated by, e.g., gas, liquid, and/or solid layers of material. For example, as illustrated, layer760amay separate waveguides670and680; and layer760bmay separate waveguides680and690. In some implementations, the layers760aand760bare formed of low refractive index materials (that is, materials having a lower refractive index than the material forming the immediately adjacent one of waveguides670,680,690). Preferably, the refractive index of the material forming the layers760a,760bis 0.05 or more, or 0.10 or less than the refractive index of the material forming the waveguides670,680,690. Advantageously, the lower refractive index layers760a,760bmay function as cladding layers that facilitate total internal reflection (TIR) of light through the waveguides670,680,690(e.g., TIR between the top and bottom major surfaces of each waveguide). In some implementations, the layers760a,760bare formed of air. While not illustrated, it will be appreciated that the top and bottom of the illustrated set660of waveguides may include immediately neighboring cladding layers.

Preferably, for ease of manufacturing and other considerations, the material forming the waveguides670,680,690are similar or the same, and the material forming the layers760a,760bare similar or the same. In some implementations, the material forming the waveguides670,680,690may be different between one or more waveguides, and/or the material forming the layers760a,760bmay be different, while still holding to the various refractive index relationships noted above.

With continued reference toFIG.9A, light rays770,780,790are incident on the set660of waveguides. It will be appreciated that the light rays770,780,790may be injected into the waveguides670,680,690by one or more image injection devices360,370,380,390,400(FIG.6).

In some implementations, the light rays770,780,790have different properties, e.g., different wavelengths or different ranges of wavelengths, which may correspond to different colors. The in-coupling optical elements700,710,720each deflect the incident light such that the light propagates through a respective one of the waveguides670,680,690by TIR. In some implementations, the in-coupling optical elements700,710,720each selectively deflect one or more particular wavelengths of light, while transmitting other wavelengths to an underlying waveguide and associated in-coupling optical element.

For example, in-coupling optical element700may be configured to deflect ray770, which has a first wavelength or range of wavelengths, while transmitting rays780and790, which have different second and third wavelengths or ranges of wavelengths, respectively. The transmitted ray780impinges on and is deflected by the in-coupling optical element710, which is configured to deflect light of a second wavelength or range of wavelengths. The ray790is deflected by the in-coupling optical element720, which is configured to selectively deflect light of third wavelength or range of wavelengths.

With continued reference toFIG.9A, the deflected light rays770,780,790are deflected so that they propagate through a corresponding waveguide670,680,690; that is, the in-coupling optical elements700,710,720of each waveguide deflects light into that corresponding waveguide670,680,690to in-couple light into that corresponding waveguide. The light rays770,780,790are deflected at angles that cause the light to propagate through the respective waveguide670,680,690by TIR. The light rays770,780,790propagate through the respective waveguide670,680,690by TIR until impinging on the waveguide's corresponding light distributing elements730,740,750.

With reference now toFIG.9B, a perspective view of an example of the plurality of stacked waveguides ofFIG.9Ais illustrated. As noted above, the in-coupled light rays770,780,790, are deflected by the in-coupling optical elements700,710,720, respectively, and then propagate by TIR within the waveguides670,680,690, respectively. The light rays770,780,790then impinge on the light distributing elements730,740,750, respectively. The light distributing elements730,740,750deflect the light rays770,780,790so that they propagate towards the out-coupling optical elements800,810,820, respectively.

In some implementations, the light distributing elements730,740,750are orthogonal pupil expanders (OPE's). In some implementations, the OPE's deflect or distribute light to the out-coupling optical elements800,810,820and, in some implementations, may also increase the beam or spot size of this light as it propagates to the out-coupling optical elements. In some implementations, the light distributing elements730,740,750may be omitted and the in-coupling optical elements700,710,720may be configured to deflect light directly to the out-coupling optical elements800,810,820. For example, with reference toFIG.9A, the light distributing elements730,740,750may be replaced with out-coupling optical elements800,810,820, respectively. In some implementations, the out-coupling optical elements800,810,820are exit pupils (EP's) or exit pupil expanders (EPE's) that direct light in a viewer's eye210(FIG.7). It will be appreciated that the OPE's may be configured to increase the dimensions of the eye box in at least one axis and the EPE's may be to increase the eye box in an axis crossing, e.g., orthogonal to, the axis of the OPEs. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE of the same waveguide, while allowing the remaining portion of the light to continue to propagate down the waveguide. Upon impinging on the OPE again, another portion of the remaining light is redirected to the EPE, and the remaining portion of that portion continues to propagate further down the waveguide, and so on. Similarly, upon striking the EPE, a portion of the impinging light is directed out of the waveguide towards the user, and a remaining portion of that light continues to propagate through the waveguide until it strikes the EP again, at which time another portion of the impinging light is directed out of the waveguide, and so on. Consequently, a single beam of in-coupled light may be “replicated” each time a portion of that light is redirected by an OPE or EPE, thereby forming a field of cloned beams of light, as shown inFIG.6. In some implementations, the OPE and/or EPE may be configured to modify a size of the beams of light.

Accordingly, with reference toFIGS.9A and9B, in some implementations, the set660of waveguides includes waveguides670,680,690; in-coupling optical elements700,710,720; light distributing elements (e.g., OPE's)730,740,750; and out-coupling optical elements (e.g., EP's)800,810,820for each component color. The waveguides670,680,690may be stacked with an air gap/cladding layer between each one. The in-coupling optical elements700,710,720redirect or deflect incident light (with different in-coupling optical elements receiving light of different wavelengths) into its waveguide. The light then propagates at an angle which will result in TIR within the respective waveguide670,680,690. In the example shown, light ray770(e.g., blue light) is deflected by the first in-coupling optical element700, and then continues to bounce down the waveguide, interacting with the light distributing element (e.g., OPE's)730and then the out-coupling optical element (e.g., EPs)800, in a manner described earlier. The light rays780and790(e.g., green and red light, respectively) will pass through the waveguide670, with light ray780impinging on and being deflected by in-coupling optical element710. The light ray780then bounces down the waveguide680via TIR, proceeding on to its light distributing element (e.g., OPEs)740and then the out-coupling optical element (e.g., EP's)810. Finally, light ray790(e.g., red light) passes through the waveguide690to impinge on the light in-coupling optical elements720of the waveguide690. The light in-coupling optical elements720deflect the light ray790such that the light ray propagates to light distributing element (e.g., OPEs)750by TIR, and then to the out-coupling optical element (e.g., EPs)820by TIR. The out-coupling optical element820then finally out-couples the light ray790to the viewer, who also receives the out-coupled light from the other waveguides670,680.

FIG.9Cillustrates a top-down plan view of an example of the plurality of stacked waveguides ofFIGS.9A and9B. As illustrated, the waveguides670,680,690, along with each waveguide's associated light distributing element730,740,750and associated out-coupling optical element800,810,820, may be vertically aligned. However, as discussed herein, the in-coupling optical elements700,710,720are not vertically aligned; rather, the in-coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart as seen in the top-down view). As discussed further herein, this nonoverlapping spatial arrangement facilitates the injection of light from different resources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some implementations, arrangements including nonoverlapping spatially-separated in-coupling optical elements may be referred to as a shifted pupil system, and the in-coupling optical elements within these arrangements may correspond to sub pupils.

FIG.9Dillustrates an example of wearable display system60into which the various waveguides and related systems disclosed herein may be integrated. In some implementations, the display system60is the system250ofFIG.6, withFIG.6schematically showing some parts of that system60in greater detail. For example, the waveguide assembly260ofFIG.6may be part of the display70.

With continued reference toFIG.9D, the display system60includes a display70, and various mechanical and electronic modules and systems to support the functioning of that display70. The display70may be coupled to a frame80, which is wearable by a display system user or viewer90and which is configured to position the display70in front of the eyes of the user90. The display70may be considered eyewear in some implementations. In some implementations, a speaker100is coupled to the frame80and configured to be positioned adjacent the ear canal of the user90(in some implementations, another speaker, not shown, may optionally be positioned adjacent the other ear canal of the user to provide stereo/shapeable sound control). The display system60may also include one or more microphones110or other devices to detect sound. In some implementations, the microphone is configured to allow the user to provide inputs or commands to the system60(e.g., the selection of voice menu commands, natural language questions, etc.), and/or may allow audio communication with other persons (e.g., with other users of similar display systems. The microphone may further be configured as a peripheral sensor to collect audio data (e.g., sounds from the user and/or environment). In some implementations, the display system60may further include one or more outwardly-directed environmental sensors112configured to detect objects, stimuli, people, animals, locations, or other aspects of the world around the user. For example, environmental sensors112may include one or more cameras, which may be located, for example, facing outward so as to capture images similar to at least a portion of an ordinary field of view of the user90. In some implementations, the display system may also include a peripheral sensor120a, which may be separate from the frame80and attached to the body of the user90(e.g., on the head, torso, an extremity, etc. of the user90). The peripheral sensor120amay be configured to acquire data characterizing a physiological state of the user90in some implementations. For example, the sensor120amay be an electrode.

With continued reference toFIG.9D, the display70is operatively coupled by communications link130, such as by a wired lead or wireless connectivity, to a local data processing module140which may be mounted in a variety of configurations, such as fixedly attached to the frame80, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removably attached to the user90(e.g., in a backpack-style configuration, in a belt-coupling style configuration). Similarly, the sensor120amay be operatively coupled by communications link120b, e.g., a wired lead or wireless connectivity, to the local processor and data module140. The local processing and data module140may comprise a hardware processor, as well as digital memory, such as non-volatile memory (e.g., flash memory or hard disk drives), both of which may be utilized to assist in the processing, caching, and storage of data. Optionally, the local processor and data module140may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and so on. The data may include data a) captured from sensors (which may be, e.g., operatively coupled to the frame80or otherwise attached to the user90), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, gyros, and/or other sensors disclosed herein; and/or b) acquired and/or processed using remote processing module150and/or remote data repository160(including data relating to virtual content), possibly for passage to the display70after such processing or retrieval. The local processing and data module140may be operatively coupled by communication links170,180, such as via a wired or wireless communication links, to the remote processing module150and remote data repository160such that these remote modules150,160are operatively coupled to each other and available as resources to the local processing and data module140. In some implementations, the local processing and data module140may include one or more of the image capture devices, microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, and/or gyros. In some other implementations, one or more of these sensors may be attached to the frame80, or may be standalone structures that communicate with the local processing and data module140by wired or wireless communication pathways.

With continued reference toFIG.9D, in some implementations, the remote processing module150may comprise one or more processors configured to analyze and process data and/or image information, for instance including one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and so on. In some implementations, the remote data repository160may comprise a digital data storage facility, which may be available through the internet or other networking configuration in a “cloud” resource configuration. In some implementations, the remote data repository160may include one or more remote servers, which provide information, e.g., information for generating augmented reality content, to the local processing and data module140and/or the remote processing module150. In some implementations, all data is stored and all computations are performed in the local processing and data module, allowing fully autonomous use from a remote module. Optionally, an outside system (e.g., a system of one or more processors, one or more computers) that includes CPUs, GPUs, and so on, may perform at least a portion of processing (e.g., generating image information, processing data) and provide information to, and receive information from, modules140,150,160, for instance via wireless or wired connections.

FIGS.10A and10Billustrate examples of cross-sectional side and top down views, respectively, of a metasurface2002according to some implementations. A substrate2000has a surface2000aon which a metasurface2002comprising a plurality of metasurface unit cells2010is disposed. The unit cells2010each include one or more protrusions, comprising material extending upwards from the surface2000a. As illustrated, in some implementations, the unit cells2010include two protrusions2020a,2020b. In some implementations, the protrusions2020a,2020bmay take the form of free-standing pillars. In some other implementations, the protrusions2020a,2020bmay take the form of nanobeams that are laterally-elongated. Where the units cells2010include two or more protrusions, the protrusions2020a,2020bmay differ in size (e.g., one may be wider than the other), as illustrated. The protrusions2020a,2020bmay be formed of an optically transmissive material.

With continued reference toFIG.10A, the protrusions2020a,2020bmay be ridges (or nanobeams), which are laterally elongated into and out of the page and define trenches between neighboring protrusions. In some implementations, the protrusions2020a,2020bmay be linear. In some implementations, the protrusions2020a,2020bare continuous along their lengths, which may have benefits for providing a high diffraction efficiency. In some other implementations, the protrusions2020a,2020bmay be discontinuous along their lengths, e.g., the protrusions2020a,2020bmay each extend along a line, with gaps in the protrusions2020a,2020balong those lines.

The unit cells2010may repeat at regular intervals across the surface2000a, and may be parallel to one another such that the protrusions2020a,2020bare also parallel to one another. The unit cells2010may have a width P, which is the distance between identical points of directly neighboring unit cells2010. In some implementations, P may be in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 300 nm to 500 nm. It will be appreciated that P may be considered to be the pitch of the unit cells2010and may be substantially constant across a grating formed by those unit cells. In some other implementations, P may vary across the surface2000a.

Preferably, the refractive index of the material forming the protrusions2020a,2020bis different (e.g., higher) than the refractive index of the substrate2000. In some implementations, protrusions2020a,2020bor other structures (e.g., pillars or other shapes) may include a plurality of materials having different refractive indices, some of which may individually be higher or lower than the refractive index of the substrate2000. In some implementations, the substrate2000may be a waveguide, and may correspond to the waveguides270,280,290,300,310(FIG.6) and/or waveguides670,680, and690(FIG.9A). In such applications, the substrate preferably has a relatively high refractive index, e.g., 1.5, 1.6, 1.7, 1.8, 1.9, or higher, which can provide benefits for increasing the field of view of a display that forms an image by outputting light from that substrate2000. Examples of materials for forming the substrate2000include glass (e.g., doped glass), lithium niobate, plastic, a polymer, sapphire, or other optically transmissive material. In some implementations, the refractive index of the material forming the protrusions2020a,2020b(or an effective refractive index where the protrusions2020a,2020bor other nanostructures include a plurality of materials) may be 2.0 or higher, 2.5 or higher, 3.0 or higher, 3.3 or higher, or 3.5 or higher. Examples of materials for forming the protrusions2020a,2020binclude silicon-containing materials (e.g., amorphous or polysilicon, and silicon nitride), oxides, and gallium phosphide. Examples of oxides include titanium oxide, zirconium oxide, silicon dioxide, and zinc oxide. In some implementations, the material or combination of materials forming the protrusions2020a,2020bis the same, which has advantages for simplifying fabrication of the metasurface2002.

With continued reference toFIGS.10A and10B, in some implementations, one of the protrusions2020bhas a width NW2that is larger than the width NW1of the other of the illustrated protrusions2020a. In some implementations, the widths NW1and NW2are each in the range of 10 nm to 1 μm, including 10 nm to 300 nm, with NW1being greater than NW2as noted above. As illustrated, the protrusions2020a,2020bmay be separated by a gap in the range of 10 nm to 1 μm wide, including 10 nm to 300 nm wide. As also illustrated, the protrusions2020a,2020bhave a height hnw, which may be in the range of 10 nm to 1 μm, including 10 nm to 450 nm, in some implementations. Preferably, the heights of the protrusions2020a,2020bare substantially equal.

With continued reference toFIGS.10A and10B, the metasurface2002illustrated in these figures may work in the transmissive mode. Light rays2021a,2021bare redirected upon propagating through the metasurface2002formed by the protrusions2020a,2020b. As illustrated, the light ray2021ais incident on the metasurface2002at an angle α relative to the normal to the surface2000a. Preferably, the angle α is within the angular bandwidth for the metasurface2002such that the light ray2021ais redirected by the metasurface2002to propagate within the substrate2000at angles that facilitate total internal reflection within that substrate2000. As illustrated, the light ray2021bis redirected such that it makes out an angle θTIRwith the normal to the surface2000a. Preferably, the angle θTIRis within a range of angles that facilitate total internal reflection within the substrate2000. As disclosed herein, in some implementations, the metasurface2002may be utilized as an in-coupling optical element (e.g., as one or more of the in-coupling optical elements700,710,720(FIG.9A)) to in-couple incident light such that the light propagates through the substrate2000via total internal reflection.

The metasurface2002will also deflect light impinging on it from within the substrate2000. Taking advantage of this functionality, in some implementations, the metasurfaces disclosed herein may be applied to form out-coupling optical elements, such as one or more of the out-coupling optical elements570,580,590,600,610(FIG.6) or800,810,820(FIG.9B) instead of, or in addition to, forming an in-coupling optical element at different locations on the surface2000a. Where different waveguides have different associated component colors, it will be appreciated that the out-coupling optical elements and/or the in-coupling optical elements associated with each waveguide made have a geometric size and/or periodicity specific for the wavelengths or colors of light that the waveguide is configured to propagate. Thus, different waveguides may have metasurfaces with different geometric sizes and/or periodicities. As examples, the metasurfaces for in-coupling or out-coupling red, green, or blue light may be have geometric sizes and/or periodicities (pitches) configured to redirect or diffract light at wavelengths of, e.g., 638 nm, 520 nm, and 455 nm, respectively. In some implementations, the geometric size and periodicity of the protrusions2020a,2020band unit cells2010increases as wavelengths become longer, and/or the height or thickness of one or both of the protrusions2020a,2020bmay increase as wavelengths become longer.

In some implementations, where the metasurfaces2002are utilized as out-coupling optical elements, the metasurfaces2002may have geometric sizes and/or pitches that cause the metasurfaces to impart optical power onto the diffracted light. For example, the metasurfaces may be configured to cause light to exit the metasurface in diverging or converging directions. Different portions of the metasurface may have different pitches, which cause different light rays to deflect in different directions, e.g., so that the light rays diverge or converge.

In some other implementations, the metasurface2002may redirect light such that the light propagates away from the metasurface2002as collimated rays of light. For example, where collimated light impinges on the metasurface2002at similar angles, the metasurface2002may have consistent geometric sizes and a consistent pitch across the entirety of the metasurface2002to redirect the light at similar angles.

As noted above, while two protrusions2020a,2020bare illustrated for ease of discussion, the metasurface2002may include unit cells2010with one, or with more than two protrusions per unit cell2010. In addition, the protrusions may have various shapes. In some implementations, the protrusions may be pillars and/or rounded.

With reference toFIGS.11A-12B, additional metasurface design considerations will be discussed in greater detail.FIG.11Aillustrates a unit cell1110of an example metasurface1102with substantially cylindrical protrusions, or pillars1120, formed on a substrate1100, which may be similar to the substrate2000(FIGS.10A-10B). The metasurface1102may include a regular array of unit cells1110spaced equally along the x- and y-axes, and/or may include an array of unit cells1110having a first spacing along the x-axis and a different spacing along the y-axis. Each pillar1120of the metasurface in this example comprises a single material.

FIG.12Aillustrates a unit cell1210of an example metasurface1202that similarly includes substantially cylindrical structures, or pillar1220, formed on a substrate1200, which may be similar to the substrate2000(FIGS.10A-10B). However, the pillars1220of metasurface1202include an outer layer1222comprising a first material and an inner layer1224comprising a second material having a different refractive index.

FIGS.11B and12Bare phase maps illustrating optical properties of example configurations of the metasurfaces1102and1202, respectively. The phase map inFIG.11Bcorresponds to a metasurface having cylindrical pillars1120comprising titanium dioxide with a height of 600 nm and a unit cell pitch U of 200 nm. The phase map inFIG.12Bcorresponds to a metasurface having cylindrical pillars1220comprising an outer layer1222of titanium dioxide and an inner layer1224of air, with a height of 600 nm and a unit cell pitch U of 390 nm. As shown inFIG.11B, an array of pillars1120comprising a single material has relatively few degrees of design freedom, as modifications to the metasurface may be limited to changing the material, diameter, spacing, and height of the pillars1120, each of which may, e.g., change the resulting wavelength-dependent phase shift of the metasurface.

As shown inFIG.12B, the phase map corresponding to metasurface1202has a substantially different profile from the phase map corresponding to metasurface1102, due at least in part to the inclusion of an outer layer1222and an inner layer1224of a material different from the material of the outer layer1222. Thus, the ability to produce metasurfaces including a plurality of materials in nanostructure (e.g., pillars, nanobeams, etc.) introduces several more degrees of freedom to the metasurface design. For example, these additional degrees of freedom may include the number of layers, the material comprising each layer, and the thickness of each individual layer. Moreover, the layers may be formed by deposition processes which allow precise control of their thicknesses and location. Accordingly, metasurfaces with multi-layer structures as described herein advantageously allow for finer tuning of metasurface performance.

FIGS.13and14illustrate cross-sectional views of example configurations of multi-layer metasurfaces1302,1402.FIG.13illustrates a metasurface1302with protrusions1320formed by a plurality of vertically-oriented portions1322,1324,1326,1328. In some implementations, the vertically oriented layers1322,1324,1326,1328may have concentric u-shaped profiles as seen in a cross-sectional side view; the central portion1328may include one or more layers1322,1324,1326, which extend along opposing sidewalls and across a bottom surface of the central portion3028, such that each of the layers1322,1324,1326form a u-shaped profile. In some implementations, the protrusions1320may have a uniform size and each unit cell1310may include a single protrusion1320. As discussed above, and some other implementations, each unit cell1310may include multiple protrusions1320, with different protrusions within a unit cell having different physical dimensions (e.g., widths). For example, one protrusion1320of a unit cell1310may be larger than another protrusion of that unit cell (e.g., two protrusions1320of the unit cell may correspond to the protrusions2020a,2020b(FIGS.10A-10B)). The protrusions described herein may be formed from one, two, three, or more laminated layers.

FIG.14illustrates a metasurface1402with unit cells1410formed of protrusions1420, which each include a plurality of horizontally-oriented layers1422,1424,1426. As discussed herein, each unit cell may include one or more protrusions1420. In some implementations, each unit cell1310includes a plurality of protrusions1420. As illustrated, the unit cells1410may include two protrusions1420having different widths. The protrusions1420may each be formed of a plurality of horizontally-oriented layers1422,1424,1426, which may define a stack of such layers.

With reference to bothFIGS.13and14, the protrusions1320,1420may be, for example, nanobeams, pillars having rectangular, circular, or elliptical profiles when viewed from above, or may have other shapes. The spacing between adjacent protrusions1320or1420may be relatively small, for example, a sub-wavelength spacing (e.g., a nanometer-scale spacing) for visible light (e.g., blue light, green light, red light, etc.). In some implementations, the pitch of the unit cells may be in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 300 nm to 500 nm. Moreover, in some implementations, the thickness of some layers may be relatively small, such as approximately 5 nm or less. It will be understood that either horizontal or vertical layers may be implemented in a unit cell configuration, for example, unit cells comprising a single protrusion or a plurality of protrusions, unit cells comprising evenly sized or differently sized protrusions, unit cells comprising evenly spaced or differently spaced protrusions, etc.

With reference again toFIGS.13and14, the protrusions1320,1420may include a plurality of different materials such as one or more of silicon-containing materials (e.g., amorphous or polysilicon, and silicon nitride), oxides, gallium phosphide, or air (e.g., as the inner, central portion1328of protrusions1320). Examples of oxides include titanium oxide, zirconium oxide, silicon dioxide, and zinc oxide. In some implementations, all layers of each protrusion1320,1420may comprise different materials having different refractive indices. In some other implementations, one or more materials may be repeated or may have the same refractive indices. For example, in the metasurfaces1302and1402, layers1322and1326,1322and1328,1324and1328, or layers1422and1426may comprise the same material or may have the same refractive index. However, adjacent layers preferably have different refractive indices.

Example methods of manufacturing the metasurfaces1302and1402will now be described.

FIGS.15A-15Gillustrate an example process of manufacturing a metasurface1502including protrusions1520(FIG.15G) having vertically-oriented layers of material. In some implementations, the metasurface1502may be similar or identical to the metasurface1302ofFIG.13, and the protrusions1520may be similar or identical to the protrusions1320.

With reference toFIG.15A, a substrate1500may be provided to support the formation of the eventual protrusions. The substrate1500may be made of, for example, an optically transmissive material such as a glass, a polymer (e.g., a plastic), or the like, and may be similar or identical to the substrates2000(FIGS.10A-10B),1300(FIG.13), or1400(FIG.14). In some implementations, the substrate1500may be a waveguide.

With continued reference toFIG.15A, a plurality of placeholders1530are formed having a separation W and a height H. In some implementations, W corresponds to the width of an eventual protrusion1520(FIG.15G), and H is higher than the desired height of the protrusions1520. The placeholders1530may comprise a variety of materials, such as a resist material (e.g., a polymeric resist) or any other suitable material that is selectively etchable relative to the components of the protrusions. The placeholders may be linear structures (e.g., to form nanobeams therebetween), or may be a layer having openings with square, circular, elliptical or other profiles (e.g., to form pillars therebetween). In some implementations, the placeholders1530may be formed by depositing a layer of a resist onto the substrate1500, followed by patterning the resist to form the placeholders1530such as by photolithography, electron beam lithography, nanoimprint lithography, or the like.

With reference now toFIG.15B, a first blanket layer1522is deposited over the substrate1500and placeholders1530by a conformal deposition process. Preferably, the first blanket layer1522is deposited with a substantially uniform thickness T1. The thickness T1may be a sub-wavelength thickness, for example, a nanometer-scale thickness. The first blanket layer1522may comprise a material that will form the outer layer of the protrusions1520of the completed metasurface1502(FIG.15G).

With reference now toFIG.15C, a second blanket layer1524may be deposited over the first blanket layer1522(e.g., on and in contact with the first blanket layer1522). The second blanket layer1524may be a different material from the material making up the first blanket layer1522and may have a different refractive index. The second blanket layer1524may also be deposited by a conformal deposition process, such that the second blanket layer1524has a substantially uniform thickness T2. The thickness T2may similarly be a sub-wavelength thickness, for example, a nanometer-scale thickness.

With reference now toFIG.15D, a third blanket layer1526may be conformally deposited over the second blanket layer1524at a substantially uniform thickness T3. The third blanket layer1526preferably comprises a different material with a different refractive index relative than the material making up the second blanket layer1524. For example, the third blanket layer may comprise the same material or have the same refractive index as the first blanket layer1522, or may comprise a material having a different refractive index relative to both the first blanket layer1522and the second blanket layer1524. The thickness T3may similarly be a sub-wavelength thickness, for example, a nanometer-scale thickness. It will be appreciated that the third blanket layer1526may define open volumes1527.

With reference now toFIG.15E, the open volumes1527(FIG.15D) may be provided with a fill1528. In some implementations, the fill1528may effectively be a fourth layer that is deposited over the third blanket layer1526until that fourth layer occupies substantially the entireties of the volumes1527. In some implementations, the fill1528may be deposited by atomic layer deposition. In some other implementations, the fill1528is preferably deposited by a relatively fast deposition, e.g., a chemical vapor deposition (CVD) or physical vapor deposition (PVD). After the fill is deposited, the total thickness Ttof all deposited layers (e.g.,1522,1524,1526,1528) is preferably less than half of the width W between placeholders1530(e.g., Tt≤W/2). In some embodiments, the fill1528is air and no material is affirmatively deposited into the openings1527.

With reference now toFIG.15F, the horizontally-oriented portions of the layers1522,1524,1526,1528disposed above the placeholders1530may be removed, e.g., by a process such as chemical mechanical polishing (CMP), etching (e.g., liquid and/or plasma etching), milling, or any other suitable subtractive manufacturing process. In some implementations, a portion of the placeholders1530may be removed as well by the subtractive manufacturing process. Preferably, sufficient material is removed such that the entire width of each placeholder is exposed and not covered vertically by any of the layers1522,1524,1526,1528. In some implementations, the remaining structure may be annealed and/or modified, e.g., to increase its mechanical integrity.

After subtractive manufacturing exposes the placeholders1530, the placeholders1530may be removed to provide the metasurface1502depicted inFIG.15G. As discussed herein, the placeholders1530preferably comprise a material that is selectively etchable relative to the materials of the layers1522,1524,1526,1528. The placeholders1530may comprise a material that is removable by wet etching, plasma etching, or similar methods. For example, the placeholders1530may comprise a resist material that is soluble in a solvent that does not dissolve the materials of layers1522,1524,1526, and1528. Accordingly, the solvent may be used to remove the exposed placeholders ofFIG.15Fto form the metasurface1502ofFIG.15G. In some implementations, one or more layers (e.g., the first layer1522or the innermost layer1528) may be modified (e.g., converted to a different material) by processes such as sulfurization or other ion-exchange methods. In some implementations, it will be appreciated that the protrusions1520may substitute for the protrusions2020a,2020bof the metasurface2002(FIGS.10A-10B).

With reference again toFIGS.15B and15E, it will be appreciated that, in some implementations, the manufacturing method may proceed to filling the volumes1527(FIG.15E) directly after forming the structure ofFIG.15B, without forming additional intervening layers, e.g., the additional layers ofFIGS.15C-15D. In some other implementations, one or more of the additional blanket layers1524,1526(FIGS.15C and15D, respectively) may be formed before proceeding to filling the volumes1527. In yet other implementations, further blanket layers may be deposited after forming the additional blanket layers1524,1526and before proceeding toFIG.15E.

With reference again toFIGS.15B-15E, an example of a conformal deposition process for forming the various layers of the protrusions1520(e.g., the layer1522,1524,1526) is atomic layer deposition (ALD). Preferably, the layers are deposited with substantially uniform thicknesses, which are substantially uniform along sidewalls and top surfaces of the placeholders1530, and along the substrate surface between the placeholders1530. The thicknesses may be sub-wavelength thicknesses, for example, nanometer-scale thicknesses. In some implementations, the thickness may be less than 200 nm, including being in the range of 5 nm to 200 nm, less than 100 nm, 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 10 nm, 10 nm to 20 nm, 20 nm to 50 nm, 50 nm to 100 nm, or less than 5 nm. In some embodiments, the thicknesses of each of the constituent layers1520are substantially equal. In some other embodiments, the thicknesses of at least some of the layers may differ.

FIGS.16A-16Fillustrate an example process of manufacturing a metasurface1602or1602′ including horizontally layered protrusions1620(FIG.16F). In some implementations, the metasurface1602may be similar or identical to the metasurface1402ofFIG.14.

With reference toFIG.15A, a substrate1500may be provided to support the formation of the eventual protrusions1620(FIG.16F). The substrate1600may include, for example, an optically transmissive material such as a glass, a polymer (e.g., a plastic), or the like, and may be similar or identical to the substrates2000(FIGS.10A-10B),1300(FIG.13), or1400(FIG.14). In some implementations, the substrate1500may be a waveguide.

With reference now toFIG.16B, a plurality of blanket layers1622,1624,1626are sequentially deposited over the substrate1600. Because the layers may be formed on a flat substrate surface, requirements for conformality may be relaxed relative to the process ofFIGS.15A-15G, and the layers1622,1624,1626may be deposited by a conformal or non-conformal deposition method. For example, the layers1622,1624,1626may be deposited by methods such as physical vapor deposition, chemical vapor deposition, atomic layer deposition, or the like. In some implementations, for depositing thin layers (e.g., layers with a thickness of 5 nm to less) and/or where precise control over thickness is desired, the layers1622,1624,1626nay be deposited by ALD. Preferably, the layers1622,1624,1626blanket an area in which a plurality of protrusions1620(FIG.16F) will be formed.

Although three layers1622,1624,1626are depicted, it will be understood that the process ofFIGS.16A-16Fmay include the deposition of more or fewer than three layers. The layers1622,1624,1626may each be the same thickness or may have different thicknesses. Preferably, each individual blanket layer1622,1624,1626has substantially the same thickness across its full extent. The thickness of each layer may be a sub-wavelength thickness, for example, a nanometer-scale thickness. In some implementations, one or more blanket layers1622,1624,1626may each have a thickness of less than 200 nm, including a thickness in the range of 5 nm to 200 nm, less than 100 nm, including 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 10 nm, 10 nm to 20 nm, 20 nm to 50 nm, or 50 nm to 100 nm. In some implementations, one or more blanket layers1622,1624,1626may each have a thickness of approximately 5 nm or less. The thickness of each of the blanket layers1622,1624,1626is selected such that the total thickness of all blanket layers combined is equal to the desired height of protrusions1620of the finished metasurface1602or1602′ (FIGS.16E and16F, respectively). Each blanket layer1622,1624,1626preferably comprises a material having a different refractive index relative to an immediately adjacent one of the layers1622,1624,1626. In addition, the layer1622preferably has a different refractive index than the substrate1600. In some implementations, layers1622and1626(or other non-consecutive layers if more than three layers are included) may comprise the same material or may have the same refractive index.

After all desired layers1622,1624,1626have been deposited over the substrate1600, the deposited layers may be patterned. With reference now toFIG.16C, a etch mask may be formed over the top layer1626to define the protrusions1620(FIG.16E). It will be appreciated that the etch mask may include a plurality of mask features1630, which may be formed by depositing one or more layers of selectively-definable material and then patterning that material to define the mask features1630. The mask features1630may comprise any suitable material that is resistant to a subtractive manufacturing process for etching the blanket layers1622,1624,1626. For example, the mask features1630may include a resist, a hardmask, or other suitable etch mask material. In some implementations, a layer of resist material may be deposited on the layer1626and then patterned, e.g., by photolithography, imprinting, etc. Consequently, in some implementations, the mask features1630are resist features.

In some other implementations, a layer of etch mask material is deposited on the layer1626and a resist layer is subsequently deposited over the etch mask material. The resist layer is patterned in the pattern of subsequently transferred down to the layer of etch mask material to define the mask features1630in the layer of etch mask material.

It will be appreciated that, as seen in a top-down view, the mask features1630have a shape corresponding to the desired shape of the protrusions1620. For example, if the protrusions1620of the metasurface1602or1602′ will be nanobeams, the mask1630may include linear sections having the same width and length as the desired nanobeams in the plane parallel to the substrate1600. If the protrusions1620are pillars, the mask1630have the same two-dimensional shape as the desired nanobeams.

After forming the mask features1630, a subtractive manufacturing method may be applied to remove the portions of the blanket layers1622,1624,1626that are not covered by the mask1630, as shown inFIG.16D. The subtractive manufacturing method used to produce the configuration ofFIG.16Dmay include directional or non-directional etch processes, for example, wet etching, plasma etching, or the like. After etching the blanket layers1622,1624,1626, the mask features1630may be removed (e.g., by applying a solvent to dissolve those features, or by ashing) to form a metasurface1602including protrusions1620comprising horizontally-oriented layers1622,1624,1626, as shown inFIG.16E.

In some implementations, the metasurface1602ofFIG.16Emay be the desired configuration. In some other implementations, one or more of the layers1622,1624,1626may be modified (e.g., converted to a different material). The modification may include, for example, processes such as sulfurization or selenization, or other ion-exchange processes. For example, the protrusions1620may be exposed to an atmosphere comprising a concentration of a chemical that will be incorporated into the appropriate layer. In some implementations, ion-exchange processes may be desirable where the protrusions1620are to include a layer of a material that is difficult to deposit by typical deposition methods (and thus undesirable to form as one of layers1622,1624, and1626), but may be formed by ion-exchange from a material that is more easily deposited. In the example metasurface1602′ ofFIG.16F, the middle layer1624may be converted to a modified middle layer1624′ by ion-exchange. However, other layers (e.g., layers1622and/or1626) may be modified similarly if desired. For example, one of the layers1622,1624,1626may be deposited as a molybdenum compound (e.g., molybdenum oxides or the like) and exposed to a sulfurous atmosphere to convert the molybdenum compound to molybdenum sulfide. In some implementations, it will be appreciated that the protrusions1520may substitute for the protrusions2020a,2020bof the metasurface2002(FIGS.10A-10B).

Various example implementations of the invention are described herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate more broadly applicable aspects of the invention. Various changes may be made to the invention described and equivalents may be substituted without departing from the spirit and scope of the invention.

For example, while advantageously utilized with AR displays that provide images across multiple depth planes, the augmented reality content disclosed herein may also be displayed by systems that provide images on a single depth plane. In addition, while advantageously applied to metasurfaces, the multi-layer structures and related methods of manufacture disclosed herein may be applied to form other optical structures, including diffractive gratings formed of protrusions which are larger than the wavelengths of visible light.

In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act, or step(s) to the objective(s), spirit, or scope of the present invention. Further, as will be appreciated by those with skill in the art that each of the individual variations described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several implementations without departing from the scope or spirit of the present inventions. All such modifications are intended to be within the scope of claims associated with this disclosure.

Example aspects of the invention, together with details regarding material selection and manufacture have been set forth above. As for other details of the present invention, these may be appreciated in connection with the above-referenced patents and publications as well as generally known or appreciated by those with skill in the art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts as commonly or logically employed.

In addition, though the invention has been described in reference to several examples optionally incorporating various features, the invention is not to be limited to that which is described or indicated as contemplated with respect to each variation of the invention. Various changes may be made to the invention described and equivalents (whether recited herein or not included for the sake of some brevity) may be substituted without departing from the spirit and scope of the invention. In addition, where a range of values is provided, it is understood that every intervening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention.