Method for machining a mold for forming an eyepiece lens with an integrated spacer

Abstract

A method is disclosed for fabricating a mold for forming an eyepiece having a waveguide with an integrated spacer. The mold is formed by etching deep holes (e.g., 5 μm to 1,000 μm deep) into a substrate using wet or dry etching. An etching mask for defining the holes may be formed using a thick metal layer and / or multiple layers of different metals. A resist layer may be disposed over the etching mask. The resist layer may be patterned to form a pattern of holes, and the pattern may be transferred to the etching mask, which may be used to transfer the pattern into the underlying substrate. The patterned substrate may be utilized as a mold onto which a flowable polymer may be introduced and allowed to solidify.

Description

Technical Field

[0001] (Claims of Priority) This application claims the benefit of priority of U.S. Provisional Patent Application No. 62 / 983,518, filed on February 28, 2020, and entitled "METHOD OF FABRICATING MOLDS FOR FORMING EYEPIECES WITH INTEGRATED SPACERS", and U.S. Provisional Patent Application No. 63 / 043,039, filed on June 23, 2020, and entitled "METHOD OF FABRICATING MOLDS FOR FORMING EYEPIECES WITH INTEGRATED SPACERS". The above applications are hereby incorporated by reference in their entirety into this specification. (Cross - References to Related Applications)

[0002] This application incorporates by reference in their entirety the following patent applications: U.S. Application No. 14 / 555,585, filed on November 27, 2014, and published as U.S. Publication No. 2015 / 0205126 on July 23, 2015; U.S. Application No. 14 / 690,401, filed on April 18, 2015, and published as U.S. Publication No. 2015 / 0302652 on October 22, 2015; U.S. Application No. 14 / 212,961, filed on March 14, 2014, and issued as U.S. Patent No. 9,417,452 on August 16, 2016; U.S. Application No. 14 / 331,218, filed on July 14, 2014, and published as U.S. Publication No. 2015 / 0309263 on October 29, 2015; and U.S. Application No. 62 / 651,507, filed on April 2, 2018, and entitled "HYBRID POLYMER WAVEGUIDE AND METHODS FOR MAKING THE SAME".

[0003] This disclosure relates to display systems, and more particularly to augmented reality display systems.

Background Art

[0004] Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images or portions thereof are presented to a user in a manner that appears or can be perceived as being real. Virtual reality, i.e., the "VR" scenario, typically involves the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, and augmented reality, i.e., the "AR" scenario, typically involves the presentation of digital or virtual image information as an augmentation to the visualization of the actual world surrounding the user. Mixed reality, i.e., the "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, in an MR scenario, AR image content can be perceived as being blocked by or otherwise interacting with objects within the real world.

[0005] Referring to FIG. 1, an augmented reality scene 10 is depicted, and to a user of AR technology, a real-world park-like setting 20 characterized by people, trees, buildings in the background, and a concrete platform 30 is visible. In addition to these items, a user of AR technology also "sees" and perceives as "visible" "virtual content" such as a robot image 40 standing on the real-world platform 30 and an avatar character 50 in the form of a flying cartoon that appears anthropomorphic like a bumblebee, although these elements 40, 50 do not exist in the real world. The human visual perception system is complex, and it is difficult to produce AR technology that facilitates a comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0006] The systems and methods disclosed herein address various challenges associated with AR and VR technologies. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0007] In some embodiments, a method for forming a mold is provided. The mold may be utilized to form a waveguide having an integrated spacer. The method includes providing a substrate, depositing an etching mask layer over the substrate, defining an opening in the etching mask layer, and etching the substrate through the etching mask layer to define the opening in the substrate. The opening in the substrate has a depth of 5 μm to 1,000 μm.

[0008] In some embodiments, the method further includes depositing a photoresist layer over the etching mask layer and lithographically defining an opening in the photoresist layer. The step of defining an opening in the etching mask layer includes extending the opening in the photoresist layer into the etching mask layer. In some embodiments, the method further includes depositing an adhesion layer over the substrate prior to depositing the etching mask.

[0009] In some embodiments, the method further includes expanding the etching mask layer after stopping the step of depositing the etching mask. The step of expanding the etching mask layer includes depositing additional etching mask material directly on the etching mask layer. The step of depositing the additional etching mask material may include evaporation. The step of depositing the additional etching mask material may include electroplating. The additional etching mask material may be the same material as the material deposited during deposition of the etching mask layer.

[0010] In some embodiments, the etching mask layer has a thickness of 10 nm to 200 nm. In some embodiments, the step of etching the substrate through the etching mask layer includes wet etching. In some embodiments, the step of etching the substrate through the etching mask layer includes dry etching. In some embodiments, the substrate is formed from an optically transparent material, which may be selected from the group consisting of glass, quartz, and fused silica. In some embodiments, the etching mask layer is formed from a metal.

[0011] In some embodiments, the method further includes the step of defining an internal opening in the substrate. The ratio of the height of the internal opening to the height of the opening in the substrate may be 500:1 or greater. In some embodiments, the ratio is 100,000:1 or less. In some embodiments, the internal opening has a size and periodicity corresponding to a diffraction grating. In some embodiments, the method further includes the step of removing the etching mask layer. The present invention provides, for example, the following. (Item 1) A method for forming a mold, comprising: providing a substrate; depositing an etching mask layer over the substrate; defining an opening in the etching mask layer; etching the substrate through the etching mask layer to define an opening in the substrate; and the opening in the substrate has a depth of 5 μm to 1,000 μm. (Item 2) further comprising depositing a photoresist layer over the etching mask layer; lithographically defining an opening in the photoresist layer; and defining an opening in the etching mask layer includes extending the opening in the photoresist layer into the etching mask layer, the method according to Item 1. (Item 3) The method according to Item 1, further comprising depositing an adhesive layer over the substrate before depositing the etching mask. (Item 4) The method according to Item 1, further comprising expanding the etching mask layer after stopping the deposition of the etching mask. (Item 5) Expanding the etching mask layer includes depositing additional etching mask material directly on the etching mask layer, the method according to Item 4. (Item 6) Depositing the additional etching mask material includes evaporation, the method according to Item 5. (Item 7) Depositing the additional etching mask material includes electroplating, the method according to Item 5. (Item 8) The additional etching mask material is the same material as the material deposited during the deposition of the etching mask layer, the method according to Item 5. (Item 9) The etching mask layer has a thickness of 10 nm to 200 nm, the method according to Item 1. (Item 10) Etching the substrate through the etching mask layer includes wet etching, the method according to Item 1. (Item 11) Etching the substrate through the etching mask layer includes dry etching, the method according to Item 1. (Item 12) The substrate is formed of an optically transparent material, the method according to Item 1. (Item 13) The optically transparent material is selected from the group consisting of glass, quartz, and fused silica, the method according to Item 12. (Item 14) The method according to item 1, wherein the etching mask layer is formed of a metal. (Item 15) The method according to item 1, further comprising defining an internal opening in the substrate, wherein a ratio of a height of the internal opening to a height of the opening in the substrate is 500:1 or more. (Item 16) The method according to item 15, wherein the ratio is 100,000:1 or less. (Item 17) The method according to item 1, wherein the internal opening has a size and periodicity corresponding to the diffraction grating. (Item 18) The method according to item 1, further comprising removing the etching mask layer.

Brief Description of the Drawings

[0012]

Figure 1

[0013]

Figure 2

[0014]

Figure 3

[0015]

Figure 4A

[0016]

Figure 4B

[0017]

Figure 4C

[0018]

Figure 4D

[0019]

Figure 5

[0020]

Figure 6

[0021]

Figure 7

[0022]

Figure 8

[0023]

Figure 9A

[0024]

Figure 9B

[0025]

Figure 9C

[0026]

Figure 9D

[0027]

Figure 10A

[0028]

Figure 10B

[0029]

Figure 10C

[0030]

Figure 11A

[0031]

Figure 11B

[0032]

Figure 12

[0033]

Figure 13

[0034]

Figure 14

[0035]

Figure 15-1

Figure 15-2

[0036]

Figure 16

[0037]

Figure 17

Figure 18

[0038]

Figure 19

Figure 20

[0039]

Figure 21

[0040]

Figure 22A

[0041]

Figure 22B

Figure 22C

[0042]

Figure 23

[0043]

Figure 24

[0044]

Figure 25

[0045]

Figure 26

Figure 27

Figure 28

[0046]

Figure 29

[0047]

Figure 30

[0048]

Figure 31

[0049]

Figure 32

[0050]

Figure 33

[0051]

Figure 34

Best Mode for Carrying Out the Invention

[0052] Detailed Description An ocular expansion and virtual reality display system may include an ocular lens for directing image information into the viewer's eye. The ocular lens may be formed from a stack of waveguides that are separated by intervening beads of glue. It should be understood that the size of the beads and the size of the separation between waveguides provided by the beads can affect the optical performance of the ocular lens and the perceived image quality of the display system. For example, the beads may be formed in a specific location, then the upper waveguide may press the beads at a specific pressure, and then the beads may be solidified by curing. As a result, the formation of the spacers may require precise alignment and controlled pressure to maintain a constant separation distance between waveguides throughout the stack of waveguides. Providing such precise alignment and pressure control can be difficult. Additionally, when the waveguides are formed from a polymer, the polymer waveguides may be flexible, and using beads of material to separate the waveguides may not provide sufficient mechanical or structural stability to maintain the desired separation between waveguides.

[0053] In some embodiments, one or more waveguides that may be used to form a stack of waveguides may include integral spacers to provide a desired separation from an upper or lower structure such as another waveguide. Each waveguide may include surface relief features, such as diffractive optical elements, that are formed simultaneously with the spacers, for example, by imprinting. In some embodiments, the spacers and the main body of the waveguides form a monolithic structure. In some embodiments, the waveguide may be a hybrid waveguide comprising a plurality of layers, one of which may include a spacer and a diffractive optical element. In some embodiments, the spacer may extend laterally along the same axis as the diffractive optical element, which may facilitate the processing of the spacer and the diffractive optical element without deforming these features.

[0054] In some embodiments, the spacer and / or indentation may have a variable size, e.g., width, and / or a plurality of spacers and / or indentations may be formed as a group in the vicinity of the spacer and / or indentation. For example, both major surfaces of the waveguide may include spacers and indentations, thereby forming an interlocking system of the spacers and indentations with the underlying and / or overlying matching waveguides. Advantageously, the variable size and / or group in the vicinity of the spacer and / or indentation may increase the mechanical and structural stability of a single waveguide and / or a stack of waveguides.

[0055] In some embodiments, the spacer is disposed on one major surface of the waveguide, and the indentation is provided on the opposing major surface of the waveguide. The indentation is sized and positioned to align with the spacer of the adjacent waveguide, thereby forming a self-aligned stack of waveguides. The upper portion of the spacer may comprise light-scattering features and / or light-leakage prevention materials (e.g., an anti-reflective coating and / or an absorptive material) to prevent light leakage between waveguides.

[0056] In some embodiments, different waveguides of a stack of waveguides may be configured to internally couple and / or externally couple different colors, e.g., different primary colors of light for forming a full-color image. Additionally or alternatively, different waveguides of the waveguide may be configured to output light with different amounts of wavefront divergence to display image content at different apparent distances from a viewer.

[0057] Advantageously, the spacer, which is integral with the waveguide, provides a rigid structure to facilitate and reproducibly separate the spacers of the spacer stack. Additionally, providing mating recesses within the waveguide further facilitates the fabrication of a consistent stack of spacers by providing a self-aligning stack. Consistent separation between the spacers can provide consistent optical performance by promoting total internal reflection of light through the individual waveguides and consistently preventing light from leaking between the waveguides. Further, the manufacturing process can be simplified by eliminating separate steps of depositing beads of material, precisely applying pressure to the waveguide, and then curing the adhesive material. Rather, if the waveguide comprises a diffractive optical element, the spacer may be formed simultaneously with the diffractive optical element.

[0058] As discussed herein, the waveguide may form an eyepiece for an augmented and virtual reality display system. The waveguide may be configured to output light and display image content for a viewer. It should be understood that some light beams within the waveguide may travel through the waveguide without being externally coupled for the viewer. Such light may be referred to herein as "unused light." Unused light may, in some situations, reflect from the edge of the waveguide and propagate back through the waveguide, where the light may propagate out of the waveguide (e.g., be externally coupled by an external coupling element within the waveguide or escape from total internal reflection due to the angle at which the light reflects from the edge). Unfortunately, this propagation of unused light out of the waveguide can cause visual artifacts such as afterimages and / or a reduction in the contrast of the display system.

[0059] In some embodiments, one or more waveguides that can be used to form a stack of waveguides (which may include integral spacers for separating adjacent waveguides) may include edge treatments to reduce or mitigate unwanted reflections and propagation of unused light out of the waveguides, and thus may include edge treatments to improve image quality. Edge treatments may include, by way of example, light-absorbing materials applied to one or more edges of the waveguides and / or anti-reflection structures formed on those edges. In some embodiments, edge treatments may include black-dyeing materials, black ink, light-absorbing materials, edge roughening, external coupling gratings, light-trapping structures, absorbent polymers, and combinations of these with other treatments.

[0060] Advantageously, in some embodiments, various edge treatments may be formed simultaneously with the formation of the spacers and / or diffractive optical elements. For example, an imprint mold may include a pattern for defining an edge treatment (e.g., the pattern may define a rough texture, an external coupling optical element, and / or a light-trapping microstructure).

[0061] In some embodiments, waveguides with integral spacers as disclosed herein may be formed using an imprint or casting process. For example, the integral spacer and the waveguide may be formed simultaneously by a casting process in which a waveguide material in a liquid state is flowed onto or into a mold that contains a negative of the features desired to be formed on the surface of the waveguide (e.g., optical elements such as spacers and / or gratings). The material is then solidified, the mold is removed, leaving a waveguide with an integral spacer (and possibly other features such as optical elements).

[0062] An etching process may be utilized to define the desired negative features within the mold. However, the size of features such as spacers can be difficult and can cause surface defects for conventional machining processes, which, undesirably, can create optical artifacts. Advantageously, the machining processes, including wet or dry etching according to various embodiments, enable the formation of large openings for forming an integral spacer while providing a low level of defects on the front side and / or the back side of the substrate. In some embodiments, a multi-sided etching mask stack (e.g., including multiple layers of an etching mask and / or a metal etching mask within a stack with a photoresist layer) may be utilized to form an opening of a suitable size for forming an integral spacer while protecting the surface of the substrate from unwanted etching. In some embodiments, wet and / or dry etching may be utilized to etch the substrate through an etching mask. Advantageously, the selection of wet or dry etching may be made based on the desired cross-sectional profile of the opening to be formed. For example, wet etching may be utilized to form a wider opening with a more rounded corner than dry etching.

[0063] In some embodiments, the mold may be formed by etching deep holes or openings into the substrate using a multi - faceted etching mask stack. In some embodiments, the holes may be 5 μm to 1,000 μm in depth. The etching mask for defining the holes may be formed using a thick metal layer and / or multiple layers of different metals. A resist layer may be disposed over the etching mask. The resist layer may be patterned to form a pattern of the holes, the pattern may be transferred to the etching mask, and the etching mask may be used to transfer the pattern into the underlying substrate. The patterned substrate may be utilized as a mold onto which a flowable polymer can be introduced and allowed to solidify. The solidified polymer within the holes may form an integrated spacer. The solidified polymer may be removed (released) from the mold and form a waveguide with the integrated spacer.

[0064] It has been found that defects on the front surface of the substrate can be caused by pinholes in the deposited metal etching mask. Unfortunately, even when the metal etching mask appears to be retained after etching of the substrate, pinholes in the metal etching mask can allow some etching solution to leak through the metal etching mask, thereby causing unwanted etching of the substrate at locations separated across the substrate surface. In some embodiments, the pinholes can be reduced by, for example, increasing the thickness of the metal etching mask by deposition of an additional layer of the etching mask material, by use of a photoresist layer that is thick enough to be retained throughout the etching of the substrate, and / or by electroplating to increase the thickness of the earlier - deposited metal layer. Additionally, in some embodiments, the bottom surface of the substrate may be protected using a deposited metal layer and / or an adhered sacrificial substrate.

[0065] Reference is now made to the drawings, where like reference numerals refer to like parts throughout. Unless otherwise indicated, the drawings are schematic and are not necessarily drawn to scale. Exemplary display system

[0066] FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user. It should be understood that when the user's eyes are separated and looking at an actual object in space, each eye has a slightly different view of the object and can form an image of the object at different locations on the retina of each eye. This may be referred to as binocular disparity and can be utilized by the human visual system to provide a perception of depth. The conventional display system simulates binocular disparity by presenting two distinct images 190, 200 with slightly different views of one identical virtual object for each of the eyes 210, 220, corresponding to the views of the virtual object that would be seen by each eye as if the virtual object were an actual object at the desired depth. These images provide binocular cues that can be interpreted by the user's visual system to derive a perception of depth.

[0067] Continuing to refer to FIG. 2, the images 190, 200 are separated from the eyes 210, 220 by a distance 230 on the z-axis. The z-axis is parallel to the optical axis of the viewer in a state where the eye is fixating on an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on the slightly different views of the virtual object within the images presented to the eyes 210, 220 respectively, the eyes can necessarily rotate so that the image of the object comes to corresponding points on the respective retinas of the eyes and a single binocular vision is maintained. This rotation can converge the respective lines of sight of the eyes 210, 220 onto a point in the space where the virtual object is perceived to exist. As a result, the provision of a three-dimensional image has conventionally involved manipulating the convergence / divergence movement of the user's eyes 210, 220 and providing binocular cues that the human visual system interprets to provide a perception of depth.

[0068] However, generating realistic and comfortable perceptions of depth is difficult. It should be understood that light from objects at different distances from the eye has wavefronts with different amounts of divergence. FIGS. 3A-3C illustrate the relationship between distance and the divergence of light rays. The distances between the object and the eye 210 are represented in the order of decreasing distances R1, R2, and R3. As shown in FIGS. 3A-3C, the light rays diverge more as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, it can be said that the light field generated by a point (object or part of an object) has a spherical wavefront curvature that is a function of the distance the point is from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. Only the monocular eye 210 is illustrated in FIGS. 3A-3C and other figures in this specification for clarity of illustration, but the discussion regarding the eye 210 can be applied to both eyes 210 and 220 of the viewer.

[0069] Continuing to refer to FIGS. 3A-3C, light from an object that the viewer's eye is fixated on can have different degrees of wavefront divergence. Due to the different amounts of wavefront divergence, the light can be focused differently by the eye's lens, which in turn can require the lens to take on different shapes to form a focused image on the eye's retina. If a focused image is not formed on the retina, the resulting retinal blur acts as a cue for accommodation, causing a change in the shape of the eye's lens until a focused image is formed on the retina. For example, the cue for accommodation induces relaxation or contraction of the ciliary muscle that surrounds the eye's lens, thereby modulating the force applied to the zonular fibers that hold the lens, and thus changing the shape of the eye's lens until the retinal blur of the fixated object is eliminated or minimized, thereby forming a focused image of the fixated object on the eye's retina (e.g., the fovea). The process by which the eye's lens changes shape can be referred to as accommodation, and the shape of the eye's lens required to form a focused image of a fixated object on the eye's retina (e.g., the fovea) can be referred to as the accommodative state.

[0070] Referring now to FIG. 4A, the representation of the accommodation-convergence / divergence response of the human visual system is illustrated. Eye movements to fixate an object cause the eye to receive light from the object, and the light forms an image on each of the retinas of the eye. The presence of retinal blur in the image formed on the retina can provide a cue for accommodation, and the relative location of the image on the retina can provide a cue for convergence / divergence movement. The cue for accommodation causes accommodation and causes the lens of the eye to assume a particular accommodation state that forms a focused image of the object on the retina of the eye (e.g., the fovea). On the other hand, the cue for convergence / divergence movement causes a convergence / divergence movement (rotation of the eye) such that the images formed on each retina of each eye are at corresponding retinal points that maintain single binocular vision. At these positions, it can be said that the eye is in a particular convergence / divergence state. Continuing to refer to FIG. 4A, accommodation can be understood as the process by which the eye achieves a particular accommodation state, and convergence / divergence movement can be understood as the process by which the eye achieves a particular convergence / divergence state. As shown in FIG. 4A, the accommodation and convergence / divergence states of the eye can change when the user fixates on another object. For example, the accommodated state can change when the user fixates on a new object at a different depth on the z-axis.

[0071] Without being limited by theory, it is believed that an object viewer can perceive an object as "three-dimensional" due to the combination of convergence / divergence movement and accommodation. As described above, the convergence / divergence movement of the two eyes relative to each other (e.g., the movement of the pupils towards or away from each other, the rotation of the eyes that converges the lines of sight of the eyes to fixate on an object) is closely associated with the accommodation of the lens of the eye. Under normal conditions, a change in the shape of the lens of the eye to change focus from one object to another object at a different distance will automatically cause a corresponding change in convergence / divergence movement to the same distance under a relationship known as the "accommodation-convergence / divergence reflex". Similarly, a change in convergence / divergence movement will, under normal conditions, induce a corresponding change in the shape of the lens.

[0072] Referring now to FIG. 4B, examples of different accommodation and convergence / divergence states of the eyes are illustrated. A pair of eyes 222a fixates on an object at optical infinity, while a pair of eyes 222b fixates on an object 221 at less than optical infinity. It should be noted that the convergence / divergence states of each pair of eyes are different, with a pair of eyes 222a being directed straight ahead, while a pair of eyes 222 converge onto the object 221. The accommodation states of the eyes forming each pair of eyes 222a and 222b are also different, as represented by the different shapes of the lenses 210a, 220a.

[0073] Unfortunately, many users of conventional "3-D" display systems find such conventional systems uncomfortable or do not perceive any sense of depth at all due to the mismatch between accommodation and convergence / divergence states in these displays. As described 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 because they merely provide different presentations of the scene, causing a change in the convergence / divergence state of the eyes, but without a corresponding change in the accommodation state of those eyes. Rather, the images are presented at a fixed distance from the eyes by the display such that the eyes view all the image information in a single accommodation state. Such an arrangement goes against the "accommodation-convergence / divergence reflex" by causing a change in the convergence / divergence state without a corresponding change in the accommodation state. This mismatch is thought to cause discomfort to the viewer. A display system that provides a better match between accommodation and convergence / divergence can create a more realistic and comfortable simulation of a three-dimensional image.

[0074] Although not limited by theory, the human eye is typically thought to be able to interpret a finite number of depth planes and provide depth perception. As a result, a highly realistic simulation of the perceived depth can be achieved by providing different presentations of images corresponding to each of these limited number of depth planes to the eye. In some embodiments, the different presentations provide both cues for convergence / divergence motion and corresponding cues for accommodation, thereby providing a physiologically correct accommodation-convergence / divergence match.

[0075] Continuing to refer to FIG. 4B, two depth planes 240 corresponding to different distances in space from eyes 210, 220 are illustrated. For a given depth plane 240, convergence / divergence motion cues may be provided by appropriately displaying images of different viewpoints for each of eyes 210, 220. Additionally, for a given depth plane 240, the light forming the images provided to each eye 210, 220 may have a wavefront divergence corresponding to a light field generated by a point at the distance of that depth plane 240.

[0076] In the illustrated embodiment, the distance along the z-axis of depth plane 240 containing point 221 is 1 m. As used herein, the distance or depth along the z-axis may be measured using a zero point located at the exit pupil of the user's eye. Thus, a depth plane 240 located at a depth of 1 m corresponds to a distance 1 m away from the exit pupil of the user's eye on the optical axis of those eyes with the eyes directed towards optical infinity. As an approximation, the depth or distance along the z-axis is measured from the front of the display of the user's eye (e.g., from the surface of the waveguide), and a value related to the distance between the device and the exit pupil of the user's eye may be added. That value may be referred to as the pupil distance 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 pupil distance may generally be a normalized value used for all viewers. For example, the pupil distance may be assumed to be 20 mm, and the depth plane at a depth of 1 m may be at a distance of 980 mm in front of the display.

[0077] Referring now to FIGS. 4C and 4D, examples of consistent vergence-accommodation - convergence / divergence movement distances and inconsistent vergence-accommodation - convergence / divergence movement distances are illustrated, respectively. As shown in FIG. 4C, the display system may provide an image of a virtual object to each of the eyes 210, 220. The image may cause the eyes 210, 220 to assume a convergence / divergence movement state in which the eyes converge on a point 15 on the depth plane 240. In addition, the image may be formed by light having a wavefront curvature corresponding to the real object in the depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the image is in focus on their retinas. Thus, the user may perceive the virtual object as being at the point 15 on the depth plane 240.

[0078] It should be understood that the accommodation and convergence / divergence movement states of the eyes 210, 220 are each associated with a specific distance on the z-axis. For example, an object at a specific distance from the eyes 210, 220 causes those eyes to assume a specific accommodation state based on the distance of the object. The distance associated with a specific accommodation state may be referred to as the accommodation distance A d Similarly, there exists a specific convergence / divergence movement distance V d associated with a specific convergence / divergence movement state or the eyes in a particular position relative to each other. When the accommodation distance and the convergence / divergence movement distance are consistent, the relationship between accommodation and convergence / divergence movement can be said to be physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0079] However, in a stereoscopic display, the focusing adjustment distance and the convergence / divergence movement distance may not always match. For example, as shown in FIG. 4D, the images displayed on eyes 210, 220 may be displayed with wavefront divergence corresponding to depth plane 240, and eyes 210, 220 may take a specific focusing adjustment state in which points 15a, 15b on that depth plane are in focus. However, the images displayed on eyes 210, 220 may provide a cue for convergence / divergence movement that converges eyes 210, 220 on a point 15 that is not located on depth plane 240. As a result, the focusing adjustment distance corresponds to the distance from the exit pupils of eyes 210, 220 to depth plane 240 in some embodiments, while the convergence / divergence movement distance corresponds to a greater distance from the exit pupils of eyes 210, 220 to point 15. The focusing adjustment distance is different from the convergence / divergence movement distance. As a result, there is a focusing adjustment - convergence / divergence movement mismatch. Such a mismatch is considered undesirable and can cause discomfort to the user. The mismatch corresponds to a distance (e.g., V d -A d ) and it should be understood that it can be characterized using diopters.

[0080] In some embodiments, it should be understood that reference points other than the exit pupils of eyes 210, 220 can also be used to determine the distance for determining the focusing adjustment - convergence / divergence movement mismatch as long as the same reference point is used for the focusing adjustment distance and the convergence / divergence movement distance. For example, the distance can be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., the waveguide of the display device) to the depth plane, from the center of rotation of the eye, etc.

[0081] Although not limited by theory, it is believed that a user may physiologically perceive a vergence-accommodation disparity of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as being correct, without the disparity itself causing significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250, FIG. 6) presents an image to a viewer having a vergence-accommodation disparity of about 0.5 diopters or less. In some other embodiments, the vergence-accommodation disparity of the image provided by the display system is about 0.33 diopters or less. In still other embodiments, the vergence-accommodation disparity of the image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0082] FIG. 5 illustrates a side view of an approach for simulating a three-dimensional image by modifying wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to the user's eye 210. The waveguide 270 may output light 650 with a defined amount of wavefront divergence corresponding to the wavefront divergence of the light field generated by a point on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on that depth plane. Additionally, it will be shown that the user's other eye may be provided with image information from a similar waveguide.

[0083] In some embodiments, 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 within a limited range of wavelengths. As a result, in some embodiments, multiple or stacked waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or to output light within different ranges of wavelengths. It should be understood that, as used herein, a depth plane may follow the contour of a flat or curved surface. In some embodiments, advantageously, for simplicity, the depth plane may follow the contour of a flat surface.

[0084] FIG. 6 illustrates an example of a stack of waveguides for outputting image information to a user. The display system 250 includes a stack or stacked waveguide assembly 260 of waveguides that can be utilized to provide three-dimensional perception to the eye / brain using a plurality of waveguides 270, 280, 290, 300, 310. It should be understood that the display system 250 may be considered a light field display in some embodiments. Additionally, the waveguide assembly 260 may also be referred to as an eyepiece.

[0085] In some embodiments, the display system 250 may be configured to provide a substantially continuous cue for convergence / divergence movement and a plurality of discrete cues for depth adjustment. The cue for convergence / divergence movement may be provided by displaying different images to each of the user's eyes, and the cue for depth adjustment may be provided by outputting light that forms an image with a selectable discrete amount of wavefront divergence. In other words, the display system 250 may be configured to output light with a variable level of wavefront divergence. In some embodiments, each discrete level of wavefront divergence may correspond to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, 310.

[0086] Continuing to refer to FIG. 6, waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some embodiments, features 320, 330, 340, 350 may be one or more lenses. Waveguides 270, 280, 290, 300, 310, and / or a plurality of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image input devices 360, 370, 380, 390, 400 may function as light sources for the waveguides and may be utilized to input image information into waveguides 270, 280, 290, 300, 310, each configured to disperse incident light across an individual waveguide for output toward eye 210 as described herein. Light exits from output surfaces 410, 420, 430, 440, 450 of image input devices 360, 370, 380, 390, 400 and is input into corresponding input surfaces 460, 470, 480, 490, 500 of waveguides 270, 280, 290, 300, 310. In some embodiments, input surfaces 460, 470, 480, 490, 500 may each be an edge of the corresponding waveguide or a portion of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces facing directly toward world 510 or viewer's eye 210). It should be understood that the major surface of the waveguide corresponds to the surface of the waveguide across which the thickness of the waveguide extends. In some embodiments, a single beam of light (e.g., a collimated beam) may be input into each waveguide and output an entire field of cloned collimated beams directed toward eye 210 at a particular angle (and amount of divergence) corresponding to a depth plane associated with the particular waveguide. In some embodiments, a single one of image input devices 360, 370, 380, 390, 400 may be associated with and input light into a plurality (e.g., three) of waveguides 270, 280, 290, 300, 310.

[0087] In some embodiments, the image input devices 360, 370, 380, 390, 400 are discrete displays that each generate image information for input into their respective waveguides 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output ends of a single multiplexed display that can send image information to each of the image input devices 360, 370, 380, 390, 400, for example, via one or more optical waveguides (such as an optical fiber cable). It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 can include light of different wavelengths or colors (e.g., different primary colors as discussed herein).

[0088] In some embodiments, the light input into the waveguides 270, 280, 290, 300, 310 is provided by an optical projector system 520 that includes an optical module 530 that can include a light emitter such as a light emitting diode (LED). The light from the optical module 530 can be directed via a beam splitter 550 to a light modulator 540, such as a spatial light modulator, and thereby modified. The light modulator 540 can be configured to vary the perceived intensity of the light input into the waveguides 270, 280, 290, 300, 310 and to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs) including liquid crystal on silicon (LCOS) displays. The image input devices 360, 370, 380, 390, 400 are schematically illustrated and, in some embodiments, these image input devices can represent different optical paths and locations within a common projection system that are configured to output light into their associated waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of the waveguide assembly 260 can function as an ideal lens while relaying the light input into the waveguide to the user's eye. In this concept, the object can be the spatial light modulator 540 and the image can be an image on a depth plane.

[0089] In some embodiments, the display system 250 may 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 pattern, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately into the viewer's eye 210. In some embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to input light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each configured to input light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 530 to one or more waveguides 270, 280, 290, 300, 310. It should be understood that one or more intervening optical structures are provided between the scanning fiber or fibers and the one or more waveguides 270, 280, 290, 300, 310 and may, for example, redirect light exiting the scanning fiber into one or more of the waveguides 270, 280, 290, 300, 310.

[0090] Controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of the image input devices 360, 370, 380, 390, 400, the light source 530, and the light modulator 540. In some embodiments, controller 560 is part of local data processing module 140. Controller 560 includes programming (e.g., instructions in a non-transitory medium) that adjusts the timing and provision of image information to waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by a wired or wireless communication channel. Controller 560 may be part of processing module 140 or 150 (FIG. 9D) in some embodiments.

[0091] Continuing to refer to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 may each be planar or have another shape (e.g., curved), with major top and bottom surfaces and an edge extending between those major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 each include external coupling optical elements 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting the light propagating within each individual waveguide out of the waveguide and outputting the image information to the eye 210. The extracted light may also be referred to as external coupled light, and the external coupling optical elements may also be referred to as light extraction optical elements. The beam of the extracted light may be output by the waveguide at the location where the light propagating within the waveguide impinges on the light extraction optical element. The external coupling optical elements 570, 580, 590, 600, 610 may be gratings, for example, including diffractive optical features as further discussed herein. For ease of explanation and clarity of the drawings, the external coupling optical elements 570, 580, 590, 600, 610 are shown disposed on the bottom major surfaces of the waveguides 270, 280, 290, 300, 310, but in some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 270, 280, 290, 300, 310, as further discussed herein. In some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 may be attached to a transparent substrate and formed within a layer of material forming the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material, and the external coupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within the surface of that piece of material.

[0092] Continuing to refer to FIG. 6, as discussed herein, each of the waveguides 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (input into such waveguide 270) to the eye 210. The collimated light may represent an optically infinite focal plane. The next upper waveguide 280 may be configured to emit collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such a first lens 350 may be configured to generate a slight convex wavefront curvature such that the eye / brain interprets the light originating from the next upper waveguide 280 as originating from a first focal plane that is closer inwardly from the optically infinite towards the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive power of the first lens 350 and the second lens 340 may be configured to generate another incremental amount of wavefront curvature such that the eye / brain interprets the light originating from the third waveguide 290 as originating from a second focal plane that is even closer inwardly from the optically infinite towards the person than the light from the next upper waveguide 280.

[0093] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, and the top waveguide 310 in the stack sends its output through all of the lenses between it and the eye for the converging focusing power that represents the focal plane closest to the person. When viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensation lens layer 620 may be disposed on top of the stack to compensate for the stack of lenses 320, 330, 340, 350. Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairs. Both the external coupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both may be dynamic using electroactive features.

[0094] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, a plurality of waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same depth plane, or a plurality of subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same plurality of depth planes, using one set per depth plane. This can provide an advantage for forming tiled images to provide an expanded field of view at those depth planes.

[0095] Continuing to refer to FIG. 6, the external coupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light out of their respective waveguides for a particular depth plane associated with the waveguide and output this light with an appropriate amount of divergence or collimation. As a result, the waveguides having different associated depth planes may have different configurations of the external coupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 may be three-dimensional or surface features that are configured to output light at a specific angle. For example, the light extraction optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, the features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming voids).

[0096] In some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 are diffraction features or “diffractive optical elements” (also referred to herein as “DOEs”) that form a diffraction pattern. Preferably, the DOE has a sufficiently low diffraction efficiency such that only a portion of the light of the beam is deflected towards the eye 210 at each intersection of the DOE, while the remainder continues to travel through the waveguide via TIR. The light carrying the image information is thus split into several associated output beams that exit the waveguide at multiple locations, resulting in a very uniform pattern of output emission towards the eye 210 with respect to this particular collimated beam that bounces within the waveguide.

[0097] In some embodiments, one or more DOEs may be switchable between an “on” state where they actively diffract and an “off” state where they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer dispersed liquid crystal in which microdroplets have a diffraction pattern within a host medium, and the refractive index of the microdroplets may be switched to substantially match that of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0098] In some embodiments, a camera assembly 630 (e.g., a digital camera including visible and infrared light cameras) may be provided to capture an image of the eye 210 and / or the tissue surrounding the eye 210, e.g., to detect user input and / or monitor the user's physiological state. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source (e.g., infrared light) that projects light onto the eye and is then reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be attached to the frame 80 (FIG. 9D) and may communicate electrically with a processing module 140 and / or 150 that may process the image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized per eye to monitor each eye separately.

[0099] Referring now to FIG. 7, an example of an output beam output by a waveguide is shown. Although one waveguide is illustrated, it should be understood that other waveguides within the waveguide assembly 260 (FIG. 6) may function similarly, and the waveguide assembly 260 includes a plurality of waveguides. Light 640 is input into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates through the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as the output beam 650. The output beams 650 are illustrated as being substantially parallel, but as discussed herein, they may also be redirected at an angle to propagate to the eye 210 depending on the depth plane associated with the waveguide 270 (e.g., to form a diverging output beam). It should be understood that a waveguide with an external coupling optical element that externally couples light to form an image that appears to be set on a depth plane at a long distance (e.g., optical infinity) from the eye 210 may be shown. Other waveguides or other sets of external coupling optical elements may output a more divergent output beam pattern, which would require the eye 210 to focus at a closer distance and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0100] In some embodiments, a full-color image may be formed on each depth plane by overlaying the image on each of the primary colors, e.g., three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes an image formed using a plurality of different primary colors. The illustrated embodiment shows depth planes 240a-240f, although more or fewer depths may also be considered. Each depth plane may have three or more primary color images associated therewith, including a first image of a first color G, a second image of a second color R, and a third image of a third color B. Different depth planes are shown in the figure by different numbers associated with the diopters (dpt) following the letters G, R, and B. As a mere example, the numbers following each of these letters indicate the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the figure represents an individual primary color image. In some embodiments, the exact placement of the depth planes for different primary colors may vary to account for differences in the focusing of light of different wavelengths by the eye. For example, different primary 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 reduce chromatic aberration.

[0101] In some embodiments, the light of each primary color may be output by a single dedicated waveguide, and as a result, each depth plane may have a plurality of waveguides associated therewith. In such embodiments, it can be understood that each box in the figure, including those containing the letters G, R, or B, represents an individual waveguide, and three waveguides may be provided for each depth plane where three primary color images are provided for each depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of explanation, but it should be understood that in a physical device, all of the waveguides may be arranged in a stack with one waveguide per level. In some other embodiments, a plurality of primary colors may be output by the same waveguide, e.g., such that only a single waveguide is provided for each depth plane.

[0102] Continuing to refer to FIG. 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may also be used in addition to or instead of one or more of red, green, or blue.

[0103] It should be understood that references to the color of a given light throughout this disclosure are understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer as being that given color. For example, red light may include light of one or more wavelengths within the range of approximately 620 - 780 nm, green light may include light of one or more wavelengths within the range of approximately 492 - 577 nm, and blue light may include light of one or more wavelengths within the range of approximately 435 - 493 nm.

[0104] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light of one or more wavelengths outside the viewer's visual perception range, such as infrared and / or ultraviolet wavelengths. Additionally, the internal coupling, external coupling, and other light redirection structures of the waveguide of the display 250 may be configured to direct and emit this light from the display towards the user's eye 210, for example, for imaging and / or user stimulation applications.

[0105] Referring now to FIG. 9A, in some embodiments, light that impinges on a waveguide may need to be redirected to internally couple the light into the waveguide. An internal coupling optical element may be used to redirect and internally couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a stack 660 of a plurality or set of waveguides, each including an internal coupling optical element. Each waveguide may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. Stack 660 may correspond to stack 260 (FIG. 6), and it should be understood that the illustrated waveguides of stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more of image input devices 360, 370, 380, 390, 400 is input into the waveguides from a position that requires the light to be redirected for internal coupling.

[0106] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated internal coupling optical element (which may also be referred to as an optical input area on the waveguide). For example, internal coupling optical element 700 is disposed on a major surface (e.g., the upper major surface) of waveguide 670, internal coupling optical element 710 is disposed on a major surface (e.g., the upper major surface) of waveguide 680, and internal coupling optical element 720 is disposed on a major surface (e.g., the upper major surface) of waveguide 690. In some embodiments, one or more of internal coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the respective waveguides 670, 680, 690 (particularly, if one or more of the internal coupling optical elements are reflective deflecting optical elements). As illustrated, internal coupling optical elements 700, 710, 720 may be disposed on the upper major surface (or the top of the next lower waveguide) of their respective waveguides 670, 680, 690, particularly if those internal coupling optical elements are transmissive deflecting optical elements. In some embodiments, internal coupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, internal coupling optical elements 700, 710, 720 are wavelength selective such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated at one side or corner of their respective waveguides 670, 680, 690, it should be understood that internal coupling optical elements 700, 710, 720 may be disposed within other areas of their respective waveguides 670, 680, 690 in some embodiments.

[0107] As shown, the internally coupled optical elements 700, 710, 720 may be laterally offset from each other. In some embodiments, each internally coupled optical element may be offset such that its light is received without passing through another internally coupled optical element. For example, each internally coupled optical element 700, 710, 720 may be configured to receive light from different image input devices 360, 370, 380, 390, and 400, as shown in FIG. 6, and may be separated (e.g., laterally spaced) from other internally coupled optical elements 700, 710, 720 such that it substantially does not receive light from other internally coupled optical elements 700, 710, 720.

[0108] Each waveguide also includes an associated light dispersing element. For example, the light dispersing element 730 is disposed on a major surface (e.g., upper major surface) of the waveguide 670, the light dispersing element 740 is disposed on a major surface (e.g., upper major surface) of the waveguide 680, and the light dispersing element 750 is disposed on a major surface (e.g., upper major surface) of the waveguide 690. In some other embodiments, the light dispersing elements 730, 740, 750 may each be disposed on a bottom major surface of the associated waveguides 670, 680, 690. In some other embodiments, the light dispersing elements 730, 740, 750 may each be disposed on both the upper and bottom major surfaces of the associated waveguides 670, 680, 690, or the light dispersing elements 730, 740, 750 may each be disposed on different ones of the upper and bottom major surfaces within different associated waveguides 670, 680, 690.

[0109] Waveguides 670, 680, 690 may be separated and isolated, for example, by a gas, liquid, and / or solid layer of material. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the directly adjacent ones of waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or more above, or 0.10 or less below, the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that promote total internal reflection (TIR) of light (e.g., TIR between the upper and bottom major surfaces of each waveguide) through waveguides 670, 680, 690. In some embodiments, layers 760a, 760b are formed from air. It should be understood that, although not shown, the top and bottom of the illustrated set 660 of waveguides may include the nearest cladding layer.

[0110] Preferably, for ease of manufacturing and other considerations, the materials forming waveguides 670, 680, 690 are similar or identical, and the materials forming layers 760a, 760b are similar or identical. In some embodiments, the materials forming waveguides 670, 680, 690 may be different between one or more waveguides, and / or the materials forming layers 760a, 760b may still be different while maintaining the various refractive index relationships described above.

[0111] Continuing to refer to FIG. 9A, light rays 770, 780, 790 are incident on the set 660 of waveguides. It should be understood that light rays 770, 780, 790 may be input into waveguides 670, 680, 690 by one or more image input devices 360, 370, 380, 390, 400 (FIG. 6).

[0112] In some embodiments, the light rays 770, 780, 790 may have different properties, such as different wavelengths or different wavelength ranges, corresponding to different colors. The internal coupling optical elements 700, 710, 720 each deflect the incident light so that light propagates through an individual one of the waveguides 670, 680, 690 by TIR. In some embodiments, the internal coupling optical elements 700, 710, 720 each selectively deflect one or more specific wavelengths of light while transmitting other wavelengths to the underlying waveguide and the associated internal coupling optical element.

[0113] For example, the internal coupling optical element 700 may be configured to selectively deflect the light ray 770 having the first wavelength or wavelength range while transmitting the light rays 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. The transmitted light ray 780 impinges on the internal coupling optical element 710 configured to deflect light of the second wavelength or wavelength range, thereby being deflected. The light ray 790 is deflected by the internal coupling optical element 720 configured to selectively deflect light of the third wavelength or wavelength range.

[0114] Continuing to refer to FIG. 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the internal coupling optical elements 700, 710, 720 of each waveguide deflect light into its corresponding waveguide 670, 680, 690 and internally couple the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the individual waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the individual waveguides 670, 680, 690 by TIR until they impinge on the corresponding light dispersion elements 730, 740, 750 of the waveguide.

[0115] Referring now to FIG. 9B, a perspective view of an embodiment of the plurality of stacked waveguides of FIG. 9A is illustrated. As described above, the internally coupled light rays 770, 780, 790 are each deflected by the internally coupled optical elements 700, 710, 720 and then each propagate by TIR within waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then each impinge on the light dispersion elements 730, 740, 750. The light dispersion elements 730, 740, 750 each deflect the light rays 770, 780, 790 so as to propagate towards the external coupling optical elements 800, 810, 820, respectively.

[0116] In some embodiments, the light dispersing elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPE deflects or disperses light to the external coupling optical elements 800, 810, 820, and in some embodiments, also increases the beam or spot size of the present light as it propagates to the external coupling optical elements. In some embodiments, the light dispersing elements 730, 740, 750 may be omitted, and the internal coupling optical elements 700, 710, 720 may be configured to deflect light directly to the external coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the light dispersing elements 730, 740, 750 may each be replaced with the external coupling optical elements 800, 810, 820. In some embodiments, the external coupling optical elements 800, 810, 820 are an exit pupil (EP) or an exit pupil expander (EPE) that directs light within the viewer's eye 210 (FIG. 7). It should be understood that the OPE may be configured to increase the size of the eyebox in at least one axis, and the EPE may increase the eyebox in an axis that intersects, for example, is orthogonal to, the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light impinging on the OPE to the EPE of the same waveguide while allowing the remaining portion of the light to continue to propagate along the waveguide. Again, in response to a collision with the OPE, another portion of the remaining light is redirected to the EPE, and the remaining portion of that portion continues to propagate further along the waveguide and the like. Similarly, in response to a collision with the EPE, a portion of the colliding light is directed out of the waveguide towards the user, and the remaining portion of that light continues to propagate through the waveguide until it impinges on the EP again, at which point another portion of the colliding light is directed out of the waveguide, and so on. As a result, a single beam of internally coupled light is "replicated" each time a portion of that light is redirected by the OPE or the EPE, thereby forming a beam field of cloned light as shown in FIG. 6. In some embodiments, the OPE and / or the EPE may be configured to modify the size of the beam of light.

[0117] Thus, referring to FIGS. 9A and 9B, in some embodiments, the waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, internal coupling optical elements 700, 710, 720, light dispersion elements (e.g., OPEs) 730, 740, 750, and external coupling optical elements (e.g., EPs) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with a gap / cladding layer between each one. The internal coupling optical elements 700, 710, 720 redirect or deflect the incident light into their respective waveguides (using different internal coupling optical elements for receiving light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the illustrated example, the ray 770 (e.g., blue light) is polarized by the first internal coupling optical element 700 in the manner described above, then bounces along the waveguide and interacts with the light dispersion element (e.g., OPE) 730 and then the external coupling optical element (e.g., EP) 800. The rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670. The ray 780 impinges on the internal coupling optical element 710 and is thereby deflected. The ray 780 then bounces along the waveguide 680 via TIR and proceeds to its light dispersion element (e.g., OPE) 740 and then the external coupling optical element (e.g., EP) 810. Finally, the ray 790 (e.g., red light) passes through the waveguide 690 and impinges on the internal coupling optical element 720 of the waveguide 690. The internal coupling optical element 720 deflects the ray 790 such that the ray propagates to the light dispersion element (e.g., OPE) 750 via TIR and then to the external coupling optical element (e.g., EP) 820 via TIR. The external coupling optical element 820 then finally externally couples the ray 790 to the viewer, who also receives the light externally coupled from the other waveguides 670, 680.

[0118] FIG. 9C illustrates a top and bottom plan view of an embodiment of a plurality of stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned with associated optical dispersion elements 730, 740, 750 and associated external coupling optical elements 800, 810, 820 of each waveguide. However, as discussed herein, internal coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., laterally spaced as seen in the top and bottom views). As further discussed herein, this non-overlapping spatial arrangement facilitates the injection of light from different resources into different waveguides on a one-to-one basis, thereby enabling a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, an array including non-overlapping spatially separated internal coupling optical elements may be referred to as an offset pupil system, and the internal coupling optical elements within these arrays may correspond to sub-pupils.

[0119] FIG. 9D illustrates an embodiment of a wearable display system 60 in which various waveguides and related systems disclosed herein may be integrated. In some embodiments, display system 60 is the system 250 of FIG. 6, and FIG. 6 schematically shows some portions of that system 60 in more detail. For example, the waveguide assembly 260 of FIG. 6 may be part of display 70.

[0120] Continuing to refer to FIG. 9D, the display system 60 includes a display 70 and various mechanical and electronic modules and systems for supporting the functions of the display 70. The display 70 may be wearable by a display system user or viewer 90 and may be coupled to a frame 80 configured to position the display 70 in front of the user 90's eyes. In some embodiments, the display 70 may be regarded as an eyepiece. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the user 90's outer ear canal (in some embodiments, another speaker, not shown, may optionally be positioned adjacent to the user's other outer ear canal to provide stereo / formable sound control). The display system 60 may also include one or more microphones 110 or other devices that may detect sound. In some embodiments, the microphone is configured to enable the user to provide an input or command (e.g., selection of a voice menu command, natural language question, etc.) to the system 60 and / or to enable audio communication with other persons (e.g., other users of similar display systems). The microphone may further be configured as a peripheral sensor to collect audio data (e.g., sound from the user and / or the environment). In some embodiments, the display system 60 may further include one or more outwardly directed environmental sensors 112 configured to detect objects, stimuli, people, animals, locations, or other aspects of the world around the user. For example, the environmental sensor 112 may include one or more cameras that may be positioned facing outwardly to capture an image similar to at least a portion of the user 90's normal field of view. In some embodiments, the display system may also include a peripheral sensor 120a that is separate from the frame 80 and may be attached to the user 90's body (e.g., on the user 90's head, torso, limbs, etc.). In some embodiments, the peripheral sensor 120a may be configured to obtain data for characterizing the physiological state of the user 90.For example, the sensor 120a may be an electrode.

[0121] Continuing to refer to FIG. 9D, the display 70 is operably coupled to the local data processing module 140 by a communication link 130, such as a wired conductor or wireless connectivity, which may be mounted in various configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, built into headphones, or removably attached to the user 90 in some other way (e.g., in a backpack configuration, in a belt attachment configuration). Similarly, the sensor 120a may be operably coupled to the local processor and data module 140 by a communication link 120b, such as a wired conductor or wireless connectivity. The local processing and data module 140 may comprise a digital memory, such as a hardware processor and non-volatile memory (e.g., flash memory or hard disk drive), both of which may be utilized to assist in the processing, caching, and storage of data. Optionally, the local processor and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and the like. The data may include (a) data captured from sensors such as an image capture device (e.g., a camera), microphone, inertial measurement unit, accelerometer, compass, GPS unit, wireless device, gyroscope, and / or other sensors disclosed herein (e.g., operably coupled to the frame 80 or otherwise attachable to the user 90), and / or (b) potentially data obtained and / or processed using the remote processing module 150 and / or remote data repository 160 (including data related to virtual content) for passage to the display 70 after processing or retrieval. The local processing and data module 140 may operably couple the remote modules 150, 160 to the communication links 170, 180 via a wired or wireless communication link or the like, such that the remote modules 150, 160 are operably coupled to each other and available as resources to the local processing and data module 140.In some embodiments, the local processing and data module 140 may include one or more than one of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more than one of these sensors may be attached to the frame 80 or may be a stand-alone structure that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0122] Continuing to refer to FIG. 9D, in some embodiments, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, including, for example, one or more than one central processing unit (CPU), a graphics processing unit (GPU), dedicated processing hardware, etc. In some embodiments, the remote data repository 160 may include a digital data storage facility, which may be available through the Internet or other networking configurations in a "cloud" resource configuration. In some embodiments, the remote data repository 160 may include one or more than one remote server that provides information, such as information for generating augmented reality content, to the local processing and data module 140 and / or the remote processing module 150. In some embodiments, all data is stored and all calculations are performed in the local processing and data module, enabling fully autonomous use from the remote module. Optionally, an external system (e.g., one or more than one processor, one or more than one computer system) including a CPU, GPU, etc. may perform at least a portion of the processing (e.g., generating image information, processing data) and provide information to and receive information from modules 140, 150, 160, for example, via a wireless or wired connection. Exemplary waveguide structure

[0123] Referring now to FIG. 10A, an embodiment of a waveguide with a spacer is illustrated. The waveguide 1000 includes a main optically transmissive body 1010 and a spacer 1020 extending perpendicularly from a main surface 1022 of the main body 1010. Preferably, the spacer 1020 is integral with the waveguide 1000 and forms a monolithic structure with at least a portion of the waveguide that defines the main surface 1022. More preferably, the spacer 1020 forms a monolithic structure with the entire waveguide 1000, and the material of the waveguide 1000 extends vertically to form the spacer 1020. As a result, the spacer 1020 and the main body 1010 may be formed from the same material and may not have an intervening boundary.

[0124] In some embodiments, the spacer 1020 may be formed from a material different from the main body 1010 such that an intervening boundary is present at the interface of the spacer 1020 and the main body 1010. For example, the spacer 1020 may include a locally deposited material, which is then imprinted to form the spacer 1020.

[0125] In some embodiments, a recess 1030 is provided such that it extends into a main surface 1032 of the waveguide 1000. As shown, the main surface 1032, and thus the recess 1030, is disposed on the side opposite the main surface 1022 of the waveguide 1000. As further discussed herein, the recess 1030 is preferably positioned, shaped, and sized such that spacers of a lower waveguide (not shown) can be received within those recesses 1030. Similarly, the spacers 1020 are preferably positioned, shaped, and sized such that they can be received within recesses of an upper waveguide (not shown). In some embodiments, the waveguide 1000 may be provided without the recess 1030, and any lower spacers may simply contact the main surface 1032.

[0126] Continuing to refer to FIG. 10A, in some embodiments, the major surface 1022 may comprise surface relief features 1040. As shown, the spacer 1020 extends vertically to a height above the upper portion of the surface relief features 1040. Preferably, the spacer 1020 has a height sufficient to separate the waveguide 1000 from the upper waveguide by a desired separation distance, e.g., 30 μm or more. In some embodiments, the spacer 1020 has a height of 30 μm or more. As discussed herein, the spacer 1020 may, in some embodiments, fit within the recess 1030 of the upper waveguide. In such embodiments, the height of the spacer 1020 may be equal to the desired separation between waveguides (e.g., 30 μm) plus the height of the recess into which the spacer is inserted.

[0127] In addition to, or as an alternative to, the surface relief features 1040, in some embodiments, the opposing major surface 1032 may comprise surface relief features 1050. In some embodiments, one or both of the surface relief features 1040 and 1050 may include a pattern of protrusions and recesses sized and arranged to form a diffractive optical element, such as a diffraction grating. It should be understood that such a diffractive optical element may correspond to one or more of the internal coupling optical elements 700, 710, 720, the light dispersing elements 730, 740, 750, or the external coupling optical elements 800, 810, 820 of FIGS. 9A - 9C. In some embodiments, the waveguide 1000 may omit one or both of the surface relief features 1040, 1050 such that the major surfaces 1022, 1032 may be smooth, except for the spacers 1020, 1030, respectively.

[0128] In some embodiments, the surface relief features 1040, 1050 may advantageously increase or be the same across a given extent of the waveguide 1000 in terms of the density of the surface relief features. In some other embodiments, the surface relief features 1040, 1050 may be different. For example, the surface relief feature 1040 may be configured to diffract light of different wavelengths and / or different angles of incidence and / or output light at a different angle from the surface relief feature 1050.

[0129] Continuing to refer to FIG. 10A, the waveguide 1000 is formed from an optically transmissive material, such as a highly transparent material. Preferably, the material has a high refractive index, which may provide an advantage for providing a wide field of view. In some embodiments, the material has a refractive index greater than 1.5 or greater than 1.65. The material forming the waveguide 1000 may be a highly transparent polymer material, such as an organic polymer material. Examples of high refractive index materials include polyimide-based high refractive index resins, halogen-containing (e.g., bromine- or iodine-containing) polymers, phosphorus-containing polymers, thiol-ene-based polymers, and high refractive index resin materials. Examples of high refractive index resin materials include those commercially available from NTT-AT (Kawasaki-shi, Kanagawa, Japan) such as high refractive index resins sold under the names #565 and #566, and high refractive index resin materials commercially available from Akron Polymer System (Akron, Ohio, USA) sold under the names APS-1000, APS2004, APS-4001, and as part of the APS3000 series.

[0130] Referring now to FIG. 10B, an embodiment of a three-dimensional shape for the spacer and a recess for accommodating the spacer is illustrated. In some embodiments, the spacer 1020 and the corresponding recess 1030 may be laterally extended three-dimensional volumes. It should be understood that such laterally extended volumes may provide advantages for structural stability and mechanical strength, particularly when the waveguides are utilized to form a stack of similar waveguides. An example of such a laterally extended three-dimensional volume is a quadrangular prism of Shape A. In some embodiments, the spacer 1020 and the corresponding recess 1030 may have other shapes, including a quadrangular prism (Shape B), a cylindrical shape (Shape C), a quadrangular pyramid (Shape D), a triangular pyramid (Shape E), and a conical shape (Shape F). It should be understood that in some embodiments, a plurality of different shapes may be utilized within a single waveguide and / or a stack of waveguides. In some embodiments, the upper portion of the spacer 1020 having a sharp shape (e.g., a quadrangular pyramid (Shape D), a triangular pyramid (Shape E), or a conical shape (Shape F)) may be rounded or flattened to reduce stress at the contact point with an upper structure such as another waveguide. When the spacer 1020 is formed by imprinting, the desired rounding or flattening of the upper portion of the shape may be formed by a properly shaped mold or imprint reticle.

[0131] Referring now to FIG. 10C, an embodiment of a stack of waveguides with spacers is illustrated. The stack of waveguides 1100 has individual waveguides 1000a, 1000b, and 1000c, each having an optically transmissive body 1010a, 1010b, 1010c, respectively. Each waveguide includes a spacer 1020a, 1020b, 1020c, respectively. Preferably, each waveguide also includes recesses 1030a, 1030b, 1030c, respectively, for receiving the spacers of the directly underlying waveguide. It should be understood that once the spacer is received in the recess, it has a height that exceeds the depth of the recess such that the spacer separates the waveguides by a gap (e.g., an air gap). As shown, spacer 1020b fits into recess 1030a and spacer 1020c fits into recess 1030b.

[0132] In some embodiments, one or more of waveguides 1000a, 1000b, 1000c may include surface relief features on one or more of their major surfaces. For example, these waveguides may each include surface relief features 1040a, 1050b corresponding to surface relief features 1040, 1050 (FIG. 10A) of waveguide 1000. In some embodiments, different ones of waveguides 1000a, 1000b, 1000c may include diffractive optical elements configured to internally couple and / or externally couple light of different wavelengths, e.g., corresponding to different primary colors for forming a full-color image. For example, waveguides 1000a, 1000b, 1000c may correspond to waveguides 670, 680, 690 of FIGS. 9A-9C.

[0133] It should be understood that light can propagate, for example, from an internal coupling optical element to an external coupling optical element by total internal reflection through waveguides 1000a, 1000b, and 1000c. In addition, light leakage between waveguides can degrade image quality. In order to reduce the likelihood that spacers 1020, 1020a, 1020b, and 1020c can serve as conduits for light leakage between waveguides, spacers 1020, 1020a, 1020b, and 1020c are preferably disposed at locations outside the path of light propagation between the internal coupling optical element and the external coupling optical element.

[0134] In some embodiments, optical leakage between waveguides may be reduced using one or both of optical scattering features at the interface between the spacers 1020, 1020a, 1020b, 1020c and the directly adjacent waveguides and an optical leakage prevention material. Examples of the optical leakage prevention material include an absorbing material and a layer of a material forming an antireflective coating. FIG. 11A illustrates an example of a waveguide including a spacer 1020 with optical scattering features 1060 on the surface of the spacer configured to couple to an upper waveguide. In some embodiments, the optical scattering features 1060 may take the form of hills and valleys (e.g., irregularly oriented hills and valleys) on the surface of the spacer 1020. In some embodiments, the optical scattering features 1060 may be provided only on the upper surface of the spacer. In some other embodiments, the optical scattering features 1060 may also extend on the side surfaces of the spacer 1020. It should be understood that the optical scattering features 1060 may be formed, for example, by roughening the surface of the spacer 1020 by polishing. In some embodiments, the optical scattering features 1060 may be formed during the formation of the spacer 1020. For example, the spacer 1020 may be formed by imprinting, and the mold used to form the spacer 1020 includes a pattern for forming the optical scattering features 1060 on the upper portion of the spacer 1020, thereby advantageously enabling the simultaneous formation of waveguide features (e.g., diffractive optical element 1040), spacer 1020, and optical scattering features 1060. It should be understood that conventional waveguide materials such as glass are generally considered incompatible with such simultaneous formation due to concerns regarding breakage of discrete integral protrusions such as spacers and the inability to accurately reproduce the structural features forming the diffractive optical element 1040 and the optical scattering features 1060.

[0135] As described above, in some embodiments, one or more layers of material may be utilized to prevent light leakage between the spacer and the waveguide. FIG. 11B illustrates an example of a stack of waveguides 1100 that includes spacers 1020a, 1020b, 1020c and a light leakage prevention material 1070 at the interface between the spacers and the nearest of the waveguides 1000a, 1000b, 1000c. For example, the light leakage prevention material 1070 may be one or more layers of an absorptive material and / or a material that forms an antireflective coating. The light leakage prevention material 1070 may be provided between spacer 1020b and waveguide 1000a. The light leakage prevention material 1070 may also be provided between spacer 1020c and waveguide 1000b. In some embodiments, the light leakage prevention material 1070 may be applied to the spacer before attaching the spacer to another waveguide. For example, the light leakage prevention material 1070 may be deposited on the surface of the spacer before inserting the spacer into a matching recess in the upper layer waveguide. Examples of absorptive materials that serve as the light leakage prevention material 1070 include carbon black, mesoporous carbon, and carbon nanotubes (single and multi-layer nanotubes). Examples of carbon nanotubes include single atom carbon nanotubes such as VANTABLACK® available from Surrey NanoSystem (Newhaven, the United Kingdom). In some embodiments, the light leakage prevention material 1070 may be an absorptive adhesive, which may be used to adhere the spacer to the upper layer waveguide. In some embodiments, the spacer may include a light scattering feature and a light leakage prevention material at the interface between the spacer and the upper layer waveguide.

[0136] Continuing to refer to FIG. 11B, the light leakage prevention material 1070 may form an antireflective coating. Examples of antireflective coatings include single and multi-layer antireflective coatings formed from partially reflective and partially transmissive layers of material.

[0137] Referring now to FIGS. 12A - 12C, an embodiment of a method for forming a waveguide with a spacer is illustrated. Referring to FIG. 12A, a pair of molds 1200, 1202 are provided. Mold 1202 has a pattern of elevated features 1250, which may be a negative of the desired pattern to be defined in the waveguide to be formed. In some embodiments, mold 1202 includes a plurality of elevated features 1230 for forming indentations within the waveguide to be formed. A mass of material 1012 for forming the waveguide is deposited on mold 1202.

[0138] Referring to FIG. 12B, molds 1200, 1202 are brought together and compress material 1012 (FIG. 12A). The compressed material may undergo a curing process (e.g., exposure to UV light) to solidify the material and form waveguide 1010. As shown, the negative pattern 1250 defines a patterned structure 1050, which may be a diffractive optical element. It should be understood that additional negative patterns may be provided on mold 1202, if desired, to form additional structures, including diffractive optical elements.

[0139] Referring to FIG. 12C, molds 1200, 1202 are moved away from each other. Waveguide 1010 is released from the molds, thereby forming waveguide 1000.

[0140] Referring to FIGS. 12A - 12C, it should be understood that in some other embodiments, elevated features 1230 are omitted so that the resulting waveguide 1000 does not include indentations 1030. Instead, in some embodiments, the spacer of the lower waveguide simply rests on the bottom major surface of the upper waveguide.

[0141] As discussed herein, the spacer 1020 is preferably formed at a location remote from the path of light propagation between the internal coupling optical element and the external coupling optical element of the waveguide. FIGS. 13A - 13B illustrate an embodiment of a top plan view of a waveguide with a spacer. As shown in FIG. 13A, the spacer 1020 is preferably positioned along the periphery of the waveguide 1000. It should be understood that the spacer 1020 can thus surround an area in which diffractive optical elements such as internal coupling and external coupling optical elements are disposed therein.

[0142] In some embodiments, referring to FIG. 13B, the spacer 1020 may extend along the same axis 1042 as the surface relief feature 1040. In such embodiments, the spacer 1020 may include a spacer having a relatively long extension along the axis 1042 and a plurality of other spacers 1020' having relatively shorter extensions. For example, these other spacers 1020' may be spaced apart and arrayed within the group 1024, and the groups of spacers are spaced apart along an axis intersecting the axis 1042. Advantageously, having spacers 1020, 1020' extending along the same axis 1042 as the surface relief feature 1040 can facilitate consistent fabrication of the spacers and the surface relief features. For example, in some embodiments, the spacers and the surface relief features may be formed by imprinting using a mold that is subsequently removed by peeling the mold and the waveguide away from each other. This peeling can be performed along the axis 1042, and it should be understood that spacers or surface relief features extending along different axes may face an increased likelihood of breakage or deformation in response to the removal of the mold.

[0143] Referring now to FIG. 14, an embodiment of a waveguide is illustrated that includes a variable-dimension spacer 1020 and a recess 1030. It should be understood that some of the spacers 1020 may be wider than others. The width of the spacer 1020 can vary depending on its location on the waveguide 1000. For example, a spacer 1020 in a location where there is a low likelihood of interaction with light may be wider than a spacer 1020 in a location where there is a higher likelihood that the spacer 1020 will receive light and inadvertently leak that light into the neighboring waveguide.

[0144] Continuing to refer to FIG. 14, in some embodiments, a plurality of juxtaposed spacers 1020 and / or a plurality of juxtaposed recesses 1030 may be provided in place of the single spacer 1020 and recess 1030 illustrated in FIG. 10A. For example, as illustrated, two juxtaposed spacers 1020 and two corresponding juxtaposed recesses 1030 may be provided in place of the single spacer 1020 and 1030 of FIG. 10A. In some embodiments, the juxtaposed spacers and recesses may have different widths. In some embodiments, the spacers may be provided on both the top and bottom major surfaces of the waveguide 1000. In such embodiments, the spacers and recesses interlock when forming a stack, thereby advantageously increasing the stability and mechanical strength of a stack of waveguides formed using these waveguides. In some embodiments, individual ones of the spacers 1020 may include multiple layers, which decrease in width with distance from the major surface of the waveguide.

[0145] In some embodiments, the waveguide 1000 may be a hybrid waveguide formed by a plurality of layers of different materials. For example, the hybrid waveguide may include a core layer and at least one auxiliary layer. Preferably, the core layer is formed from a highly transparent material, and the auxiliary layer is formed from a thinner layer of material in which a surface relief structure such as a diffractive optical element is provided. In some embodiments, the material forming the core layer is, for example, a highly transparent polymer having a mid-transmittance of transparency greater than 85%, greater than 90%, or greater than 96% in the visible light spectrum across the thickness of the core layer. The material may be a flowable material (e.g., a flowable polymer) that can be flowed onto the surface and subsequently hardened, for example, by curing. The auxiliary layer may be thinner than the core layer and is preferably formed from a material different from the core layer. In some embodiments, the auxiliary layer is formed from a polymer (e.g., an organic polymer), an inorganic material, a hybrid organic / inorganic material, or a combination thereof. In some embodiments, for a given thickness, the auxiliary layer may have a lower transparency than the core layer in the visible spectrum and / or may have a lower homogeneity (in optical properties such as composition and / or transparency) than the core layer. However, this lower transparency and / or lower homogeneity may be improved by the relative thinness of the auxiliary layer compared to the core layer.

[0146] Preferably, the core layer is formed from a material with a high refractive index, which can advantageously provide a wide viewing angle for a display device that utilizes the core layer within the waveguide. In some embodiments, the material forming the core layer may have a refractive index of about 1.65 or greater, about 1.70 or greater, or about 1.80 or greater. Additionally, the auxiliary layer may be formed from a material with a refractive index different from that of the core layer. It should be understood that the difference in refractive index at the interface with the nanofabricated structure can facilitate the ability of the diffractive optical elements within that layer to redirect light. In some embodiments, the material forming the auxiliary layer has a refractive index that differs from that of the material forming the core layer by about 0.05 or greater, about 0.1 or greater, or about 0.2 or greater. In some embodiments, the waveguide may include an additional auxiliary layer in which depressions and / or additional surface relief features (e.g., diffractive optical elements) are formed. Additional details regarding hybrid waveguides are disclosed in U.S. Application No. 62 / 651,507, filed Apr. 2, 2018, entitled "HYBRID POLYMER WAVEGUIDE AND METHODS FOR MAKING THE SAME" (which is incorporated herein by reference in its entirety).

[0147] In some embodiments, the core and the auxiliary layer may be formed using a flowable material without vapor deposition. The core layer may be formed from a material having a relatively high refractive index as described above with respect to waveguide 1000, and the auxiliary layer may be formed from a material having a lower refractive index. Examples of low refractive index materials (e.g., having a refractive index lower than 1.65) include organic polymer materials, low refractive index resins, sol-gel based hybrid polymers (e.g., TiO2, ZrO2, and ITO sol-gel materials), polymers doped with nanoparticles (TiO2, ZrO2, etc.), and active materials (e.g., polymers doped with quantum dots). Examples of low refractive index organic polymer materials include those commercially available from Sigma-Aldrich (St. Louis, Missouri, USA) such as polymer materials sold under the names CPS1040UV, CPS1040UV-A, CPS1030, CPS1020UV, CPS1040UV-VIS, CPS1030UV-VIS, and CPS1020UV-VIS. Examples of low refractive index resins include those commercially available from Miwon (Nagase Group, Osaka, Japan).

[0148] In some embodiments, a pattern (e.g., a pattern defining a diffractive optical element) may be formed during the formation of the core and / or the auxiliary layer without separate patterning and etching processes. For example, the pattern may be imprinted and subsequently formed by solidifying or curing the imprinted material.

[0149] Figures 15A - 15G illustrate a method of forming a hybrid waveguide with a core layer and upper and lower auxiliary layers. Referring to FIG. 15A, a pair of molds 1201, 1202 are provided, and mold 1202 has a pattern of elevated features 1250 for forming surface relief features within the auxiliary layer to be formed. A mass of material 1300 for forming the auxiliary layer is subsequently deposited on mold 1202. Referring to FIG. 15B, molds 1201, 1202 are moved together closer, compressing the mass of material 1300 (FIG. 16A). The compressed material 1300 may undergo a curing process (e.g., by exposure to UV light), which solidifies the material and forms a solid auxiliary layer 1031. Referring to FIG. 15C, mold 1201 is separated from the auxiliary layer 1031, and a mass of core layer material 1310 is deposited on the auxiliary layer 1031. Referring to FIG. 15D, molds 1201, 1202 are moved together closer, compressing the mass of material 1310, thereby forming the core layer 1010. The compressed material may undergo a curing process (e.g., by exposure to UV light), which solidifies the material and forms a solid core layer 1010. Referring to FIG. 15E, mold 1201 is separated from the core layer 1010 and replaced with mold 1200. Mold 1200 includes a pattern of protrusions 1240 for defining surface relief features within an additional auxiliary layer. An additional mass of material 1320 for forming the additional auxiliary layer is deposited on the core layer 1010. Referring to FIG. 15F, molds 1200, 1202 are moved together closer, compressing the mass of material 1320 (FIG. 16E) and defining the auxiliary layer 1021. It should be understood that the pattern of features 1240 imprints the desired surface relief features 1040 within the auxiliary layer 1021. The compressed material forming the auxiliary layer 1021 may undergo a curing process to solidify the material and form a solid auxiliary layer 1020. Referring to FIG. 15G, molds 1200, 1202 are moved apart, and the hybrid waveguide comprising the core layer 1010 and auxiliary layers 1031, 1021 is released from the molds.

[0150] In some other embodiments, the core and the auxiliary layer may be formed from different flowable materials that are immiscible. These materials may be deposited on top of each other and then subsequently compressed and solidified. Further details regarding such processes can be found in U.S. Patent Application No. 62 / 651,507, filed on April 2, 2018, entitled "HYBRID POLYMER WAVEGUIDE AND METHODS FOR MAKING THE SAME".

[0151] Again, referring to FIGS. 12A - 12C and 15A - 15G, it should be understood that the molds 1200, 1201, 1202 may be patterned using a negative mold of the spacers and surface relief features to be formed. Additionally, the molds preferably have sufficient rigidity to imprint into the various flowable materials used to form the waveguide features. Examples of materials for forming the molds include glass, fused silica, quartz, silicon, and metals.

[0152] The negative mold of the spacers may be defined within these materials using various processes depending on whether the spacers have vertical or upwardly sloping sidewalls. For spacers with vertical sidewalls, spacers as seen in the top and bottom views may first be patterned by using lithography to pattern a photoresist deposited on, for example, the material to be patterned, and then etched through the patterned photoresist using directional etching. Examples of directional etching include dry etching such as RIE, ICP, sputter etching, etc. In some other embodiments, wet etching (e.g., including HF) may be utilized.

[0153] Regarding a spacer with an upward-sloping sidewall, the negative type of the spacer may be formed by patterning a three-dimensional shape as a mask within a resist layer using gray-scale lithography, and the geometry of the shape is transferred into the underlying substrate (mold material) by one or more dry etching techniques such as RIE, ICP, and sputter etching, or by wet etching. Regarding a silicon substrate, the upward-sloping sidewall surface may also be processed using wet chemical etching. In some embodiments, the top and bottom shapes / geometries may first be patterned within a resist layer using lithography, and then the substrate (mold) is etched using dry etching first and then wet etching. In the case of a silicon mold, the silicon wet etching may include KOH and TMAH. Exemplary waveguide structure for reducing the propagation of unused light out of the waveguide

[0154] As discussed herein, not all of the light propagating through the waveguide can be externally coupled as the light traverses the waveguide once transversely. The light that remains after propagating across the waveguide to the edge of the waveguide can be referred to as unused light. Also, as discussed herein, optical artifacts can occur when the unused light propagates out of the waveguide. The various embodiments disclosed herein provide an edge treatment that reduces the recirculation of light within the waveguide after contact with the edge or an area near the edge of the image, thereby reducing the likelihood that unused light will propagate out of the waveguide.

[0155] In some embodiments, the edge treatment may comprise an absorptive material that covers one or more images of the waveguide. Referring now to FIG. 16, an example of a waveguide 1602 having an edge covered with an absorptive material is illustrated. The waveguide 1602 has an upper major surface 1601, a bottom major surface 1603, and an edge 1605. The edge 1605 is covered with an absorptive material 1604. The absorptive material 1604 may, in some embodiments, be a layer of absorptive material applied over the edge of the waveguide 1602 and may absorb light beams 1606 and 1608 that are not utilized, and thus propagate toward the edge. The light beams that are not utilized may include light beams that are not externally coupled from the waveguide 1602 to an observer. The light beams that are not utilized may reflect from the edge 1605 of the waveguide 1602 and propagate back through the waveguide 1602 and then may be externally coupled from the waveguide 1602 (e.g., via external coupling elements such as the external coupling optical elements 800, 810, 820, etc. of FIG. 9B) as ghost images and / or stray light, which may reduce image quality.

[0156] Continuing to refer to FIG. 16, in the absence of the absorptive material 1604, light beams such as the light beam 1608 that impinge on the edge of the waveguide 1602 with a relatively large angle of incidence may reflect back from the edge and reduce contrast (e.g., by colliding on the upper major surface 1601 of the waveguide at an angle such that the light escapes from total internal reflection and propagates out of the waveguide 1602). Similarly, light beams such as the light beam 1606 that exit the waveguide 1602 with a relatively small angle of incidence may still, as an example, be reflected back into the waveguide by a portion such as the reflection 1607 due to the difference in the refractive index (Δn = n waveguide - n ink ) at the interface between the waveguides 1602 that form the interface with the edge of the waveguide.

[0157] Although not limited by theory, the refractive index (n) and extinction coefficient (k) of the light-absorbing material applied to the edge of the material 1604 etc. applied to the waveguide 1602 have been found to affect the degree to which the absorbing material extracts and absorbs light from the waveguide. Simulations were performed regarding absorption versus reflection of a light beam impinging on the light-absorbing material applied to the edge as a function of the extinction coefficient (k) of the light-absorbing material and as a function of the angle of incidence (e.g., measured with respect to the vector normal to the plane of the waveguide edge shown as Θ in FIG. 16, and the light beam 1606 has a larger angle of incidence than the light beam 1608). The simulations were performed regarding absorption of s-polarization (e.g., transverse electric TE polarization) and absorption of p-polarization (e.g., transverse magnetic TM polarization), and an average was obtained to determine the absorption average regarding s-polarization and p-polarization. The simulations assumed a waveguide having a refractive index of 1.73. Some of the simulations assumed a light-absorbing material having a refractive index of 1.55, while some of the simulations assumed a light-absorbing material having a refractive index of 1.65. The simulation results showed that a light beam with a higher angle of incidence (e.g., a light beam impinging relatively directly on the light-absorbing material 1604 instead of in an oblique pattern) may not be completely absorbed and may be reflected. In particular, as the angle of incidence increases beyond about 65 degrees, the absorption drops and the light begins to be reflected from the edge 1605 (e.g., due to the difference in refractive index between the waveguide 1602 and the light-absorbing material 1604). The simulation results also show that increasing the extinction coefficient k of the light-absorbing material 1604 increases the absorption of the higher angle of incidence light beam, but the increase is relatively limited (e.g., assuming all other factors are constant, the absorption at k = 0.05 is only about 50% higher than the absorption at k = 0.005).

[0158] Again, while not limited by theory, the simulation results indicate that an absorptive material having a refractive index of 1.65 is significantly superior to an absorptive material having a refractive index of 1.55. This is thought to be due to a lower difference in refractive index between the waveguide and the absorptive material. Thus, the simulation results illustrate that it is useful to reduce the difference in refractive index between the waveguide 1602 and the absorptive material 1604 in order to improve absorption by the absorptive material 1604, and also that it is useful, although to a lesser degree, to utilize an absorptive material 1604 with a high extinction coefficient (k). In some embodiments, the difference in refractive index between the waveguide 1602 and the absorptive material 1604 is 0.2 or less. Additionally, in some embodiments, the absorptive material 1604 has an extinction coefficient (k) of at least 0.02.

[0159] It should be understood that the above discussion pertains to a single interaction of the light beam with the edge 1605 and the absorptive material 1604. To further improve the absorption of the light beam into the absorptive material, the covered area of the absorptive material may be increased such that the absorptive material extends over a larger portion of the waveguide, as illustrated in FIGS. 17 and 18.

[0160] FIGS. 17-18 illustrate an example of a waveguide having an absorptive material extending over portions of the upper and bottom major surfaces 1801, 1803 of the waveguide 1802. As shown, the absorptive material 1804 covers at least one edge 1805 of the waveguide 1802 and also extends over portions adjacent to the edges of the upper and bottom major surfaces 1801, 1803 of the waveguide. In particular, the absorptive material 1804 may be formed on a portion of the waveguide 1802 that extends over a specific distance, illustrated as the length of the blackening treatment 1806 away from the edge 1805 of the waveguide 1802.

[0161] As shown in FIG. 18, extending the light absorbing material 1804 over a length 1806 can create multiple interactions between the propagating light beam and the light absorbing material 1804, and thus increase the absorption of the unused light beam. In particular, FIG. 18 illustrates how a particular light beam 1808 propagating within waveguide 1802 via total internal reflection (TIR) can interact with the light absorbing material 1804 at point 1810a and also at point 1810b.

[0162] In general, the length 1806 required to ensure that the propagating light interacts with the light absorbing material 1804 multiple times can vary depending on, among other possible factors, the difference in refractive index between the waveguide 1802 and the adjacent material (which may be air), the thickness of the waveguide 1802, the wavelength of the light passing through the waveguide 1802, the grating design (e.g., the design of the external coupling elements such as the external coupling optical elements 800, 810, 820, etc. of FIG. 9B), and the field of view of the waveguide 1802. FIG. 18 illustrates a particular example of blue light propagating via TIR inside a glass having a refractive index of 1.8 with air as the adjacent material, and a blackening length of at least about 1.87 mm of black ink (with n = 1.73) is sufficient to ensure multiple interactions. In some embodiments, the length 1806 may extend about 2 mm, about 5 mm, or about 2 - 5 mm from the waveguide edge to effectively absorb most of the propagating light that reaches the edge of the waveguide.

[0163] It has been determined that the thickness of the light absorbing material applied to the edges, such as the material 1604 applied to waveguide 1602 and the material 1804 applied to waveguide 1802, affects the degree to which the material extracts and absorbs light from the waveguide. Studies of light absorption by light absorbing materials such as black ink have been conducted for materials with three different refractive indices (n = 1.55, n = 1.65, and n = 1.73). Various simulations have been performed as a function of the angle of incidence and with an extinction coefficient of about 7×10 -3 ~ about 10×10 -3As the material thickness is varied, the potential thickness of the material that can be utilized to achieve a desired level of absorption (e.g., a minimum percentage of absorption that can be at least 95% absorption) is shown. Generally, materials with a greater thickness achieve the desired level of absorption when the angle of incidence is low (e.g., when light impinges on the material in a relatively perpendicular manner) compared to when the angle of incidence is high (e.g., when light impinges on the material in an oblique pattern). Additionally, materials with a greater thickness achieve the desired level of absorption when the extinction coefficient is lower. However, the absorption rate was not as dependent on the extinction coefficient as the angle of incidence. The simulation further showed that a material thickness of about 20 μm can advantageously be utilized to achieve a high level of absorption for a range of simulated angles of incidence (e.g., from about 20 degrees from perpendicular to about 70 degrees from perpendicular) and a desired range of simulated extinction coefficients (e.g., extinction coefficient from about 7×10 -3 ~ about 10×10 -3 ). In some embodiments, the light-absorbing material has a thickness of 20 μm or greater.

[0164] Any suitable material may be used as the light-absorbing or black-dyeing treatment material applied to the edge (e.g., material 1604 applied to waveguide 1602 and material 1804 applied to waveguide 1802). As an example, the light-absorbing or black-dyeing treatment material applied to the edge may be a thin-film material such as fullerene, graphene, amorphous silicon, germanium, etc. that can be deposited on the waveguide surface by physical or chemical vapor deposition or via other suitable treatment deposition processes, a black ink such as a low-viscosity black inkjet available from Nazdar (Shawnee, KS) that can be applied by inkjet printing or other suitable methods, and may include light-absorbing additives dispersed or dissolved in a polymer (e.g., a UV-curable polymer resin) such as carbon black, carbon nano powder, carbon nanotubes, metal nanoparticles, color dyes, pigments, phosphors, etc.

[0165] The simulation results of the reflectance of various different light-absorbing materials are shown in graph 2000 of FIG. 19 and graph 2050 of FIG. 20. The simulations of FIGS. 19 and 20 involve a single interaction of the light beam with the light-absorbing material.

[0166] The different light-absorbing materials simulated with respect to FIG. 19 include plot 2002 for black ink and plots 2004, 2006, 2008, 2010, 2012, 2014 for variable concentrations of carbon nanopowder dispersed or dissolved in resin. As shown by plot 2002 in FIG. 19, black ink has a low reflectance (e.g., a reflectance below 10%, and thus an absorption rate of at least 90%) for incident angles below about 55 degrees. However, the reflectance of black ink substantially increases when the incident angle exceeds 55 degrees. As shown by plots 2004, 2006, 2008, 2010, 2012, and 2014, increasing the concentration of carbon in the light-absorbing material tends to decrease the reflectance and thus increase the absorption rate of the light-absorbing material. However, once a certain concentration of carbon is reached, the performance of the light-absorbing material levels off, and further increases in carbon concentration do not further decrease the reflectance. In particular, FIG. 19 illustrates that concentrations of about 1.56% carbon (plot 2010), 6.25% carbon (plot 2012), and 25% carbon (plot 2014) have relatively similar reflection and absorption performance across the simulated incident angles.

[0167] The different light-absorbing materials simulated with respect to FIG. 20 include plot 2052 for etercure 6948.8B.28 (e.g., blue dye), plot 2054 for orange LPB (e.g., orange dye), plot 2056 for red LPB (e.g., red dye), and plot 2058 for RS1813 jet black (e.g., for black dye). As shown in FIG. 20, the orange and red dyes can maintain a reflectance below 10% over the entire range of simulated incident angles as seen in plots 2056 and 2058. In contrast, the blue dye has a reflectance below 10% only for simulated incident angles below about 53 degrees as seen in plot 2054, and the black dye has a reflectance below 10% only for simulated incident angles below about 63 degrees as seen in plot 2052.

[0168] Another technique for preventing absorption and / or reflection of a light beam at the edge of a waveguide is roughening of the waveguide edge, as shown in FIG. 21. Waveguide 2100 may be roughened to provide a rough texture at edge 2105. In some embodiments, edge 2105 is coated with light-absorbing material 2104. Waveguide 2102 may be roughened over upper and bottom major surfaces 2101, 2103 that extend away from the edge over a length of roughening 2110, which may be less than the length of blackening treatment 2112 over which light-absorbing material 2104 is applied along and across its edge. In some embodiments, the length of roughening 2110 may be from 2 mm to 5 mm from the edge of waveguide 2100, and the length of blackening treatment 2112 may extend from the waveguide edge by more than 2 mm to 5 mm beyond the roughened area. Roughening waveguide 2100 in this way can help to diffuse the propagating light, as indicated by the scattering of light beam 2106 when it impinges on the roughened area of waveguide 2100 where light-absorbing material 2104 is applied. Without being limited by theory, diffusion of a light beam such as light beam 2106 can increase the interaction between the light beam and light-absorbing material 2104 and can lead to an increase in the overall absorption rate.

[0169] (Extending inwardly from the edge of the waveguide 2100 (over the length of the roughening 2110), the edge and the adjacent surfaces of the waveguide may be roughened by grinding the waveguide, by forming the waveguide using a mold having a rough texture, or by other means. Different particle size sizes may be used when grinding the waveguide to different roughnesses. As an example, a particle size having P150 - 100μm particles or a particle size having P2500 - 8.4μm particles may be used when grinding the waveguide to the desired roughness. The waveguide may be formed, ground, or otherwise processed to have at least one surface roughness (Sa) in some embodiments. In some embodiments, the surface roughness (Sa) is in the range of 1 - 100. In some embodiments, the waveguide may be radially roughened such that less light is backscattered toward the active eyepiece lens area (e.g., away from the edge).

[0170] Additional techniques for improving the absorption of the light beam at the edge of the waveguide include forming a diffraction grating as shown in FIG. 22A or a light trapping structure as shown in FIGS. 22B and 22C along the edge of the waveguide.

[0171] FIG. 22A illustrates a waveguide 2200a with an edge 2205 coated with an absorptive material 2204, the absorptive material 2204 extending over the area of the blackening treatment 2212 on the upper and lower major surfaces 2201, 2203, and the waveguide 2202a includes an external coupling optical element 2220 over the area of a grating 2210a extending on the upper and lower major surfaces 2201, 2203 of the waveguide 2202a. In some embodiments, the external coupling optical element 2220 is a diffraction grating. In some embodiments, the waveguide 2202a may have such a grating on its edge in addition to or instead of having an external coupling optical element on the upper and lower major surfaces 2201, 2203 adjacent to the edge. In some embodiments, the absorptive material 2204 may be omitted.

[0172] The external coupling optical element 2220 may be, as an example, an external coupling diffraction grating configured to externally couple light propagating within the waveguide 2202a, such as the optical beams 2206 and 2208, into the light absorbing material 2204 where the light is absorbed. As an example, the area of the grating 2210a may extend 2 mm to 5 mm outward from the edge of the waveguide 2202a (e.g., to ensure that any optical beam propagating within the waveguide interacts with the grating), and the area of the blackening treatment 2212 may further extend 2 mm to 5 mm outward from the area of the grating 2210a (e.g., to facilitate absorption of the light scattered by the grating by the light absorbing material 2204). The design of the grating 2220 may vary depending on, among other possible factors, the refractive indices of the waveguide 2202a and the light absorbing material 2204, and the wavelength of the light propagating through the waveguide 2202a. In some embodiments, the diffraction grating 2220 may be formed within the waveguide 2202a by patterning a mold in which the waveguide 2202a is formed. The diffraction grating 2200 may, in some embodiments, be formed as part of and / or using the same processing techniques used to form other diffraction elements disclosed herein, such as the external coupling optical elements 800, 810, and 820 of FIG. 9B and the integrated spacers as disclosed herein.

[0173] FIG. 22B illustrates a waveguide 2202a coated with a light absorbing material 2204 where an edge 2205 extends across the area of a blackening treatment 2212 on upper and bottom major surfaces 2201, 2203. The upper and bottom major surfaces 2201, 2203 of the waveguide 2202a include light trapping structures 2230a and / or 2230b over a light trapping area 2210b extending from the edge 2205. In some embodiments, the waveguide 2202b may have light trapping structures on upper and bottom major surfaces 2201, 2203 adjacent to the edge, in addition to or instead of having such structures on its edge. In some embodiments, the light absorbing material 2204 may be omitted. The light trapping structures 2230a and 2230b may be, by way of example, microstructures. As shown in FIG. 22C, a simulated light beam 2232 incident on the edge region of the waveguide 2202b does not escape from the edge region without undergoing multiple interactions due to the shape and size of the light trapping structures 2230a and 2230b. As shown, during one of these interactions, light may escape from the waveguide and propagate into the light absorbing material 2204 (FIG. 22B) light absorbing material 2204. Without being limited by theory, the light trapping structures 2230a and 2230b may advantageously increase the absorption of light.

[0174] In some embodiments, the area of the light trapping 2210b may be from 2 mm to 5 mm from the edge of the waveguide 2202b (e.g., it can increase the likelihood that the optical beam propagating within the waveguide interacts with the light trapping structure), and the area of the blackening treatment 2212 may extend from 2 mm to 5 mm from the area of the light trapping 2210b (e.g., it can increase the likelihood that any light scattered by the light trapping structure is absorbed by the light absorbing material 2204). In some embodiments, light trapping structures such as structures 2230a and 2230b may be formed within the waveguide 2202b by patterning a mold in which the waveguide 2202b is formed. The light trapping structures 2230a and 2230b may, in some embodiments, be formed as part of and / or using the same processing techniques used to form diffractive elements disclosed herein, such as the external coupling optical elements 800, 810, and 820 of FIG. 9B and the integrated spacers as disclosed herein.

[0175] The design of the light trapping structures 2230a and 2230b can vary depending on, among other factors, the refractive indices of the waveguide 2202b and the light absorbing material 2204, and the wavelength of the light propagating through the waveguide 2202b. In some embodiments, the width and height of the light trapping structures 2230a and 2230b range from 0.5 μm to 100 μm. By way of example, the width and height of the light trapping structures 2230a and 2230b may be about 0.5 μm, about 1.0 μm, about 2.0 μm, about 4.0 μm, about 10.0 μm, about 20.0 μm, about 50 μm, about 75 μm, or about 100 μm, where "about" is understood to be within 0.4 μm.

[0176] It should be understood that any of the strategies for improving light absorption at the edge of the waveguide may be combined together. As an example, the waveguide may be made of a material having a sufficient thickness for a desired level of light absorption rate, which is on the edge and extends inwardly from the waveguide edge (as disclosed in FIGS. 17 and 18), and may include a light-absorbing material having any of surface roughening of the waveguide (as disclosed in FIG. 21), a diffraction grating (as disclosed in FIG. 22A), and / or a light trapping structure (as disclosed in FIGS. 22B and 22C).

[0177] FIG. 23 illustrates edges 2404a, 2404b of waveguide 2400 having a higher level of unused light. The strategies disclosed herein for improving light absorption at the edges of the waveguide may be applied to all of the edges of the waveguide, or in some embodiments, may be applied only to areas of the waveguide that are expected to have a higher level of unused light relative to other areas of the waveguide. For example, edges 2404a, 2404b of FIG. 23 may be considered to have a high level of unused light. The area with the high level of unused light may be an area of the waveguide in which a relatively large amount of light reaches the waveguide edge without being externally coupled. Such unused light, if not absorbed at the edge, may potentially be reflected back into the active display area, creating unwanted ghost images or stray light, and thus degrading the image quality. In some embodiments, the areas of waveguide 2400 with a high level of unused light include edge 2404a adjacent to internal coupling optical elements 700, 710, 720. Edge 2404a is on the side of internal coupling optical elements 700, 710, 720 that is opposite the direction in which light is directed by internal coupling optical elements 700, 710, 720 for final external coupling. Another area with a high level of unused light includes edge 2404b adjacent to external coupling optical elements 800, 810, 820. The light within this area includes light that has propagated across external coupling optical elements 800, 810, 820 without being externally coupled. It should be understood that the light incident on these edges is unused because it did not pass through these optical elements intended for external coupling and was not externally coupled. In contrast, the edges adjacent to light dispersing elements 730, 740, 750 may have a relatively low level of unused light and thus may not benefit much from the light absorption strategies described herein.

[0178] As described herein, it should be understood that the various waveguides 1602, 1802, 2102, 2202a, and 2202b of FIGS. 16 - 18 and 21 - 23 may include one or more integral spacers and / or recesses for receiving the spacers. Additionally, in some embodiments, the waveguides 1602, 1802, 2102, 2202a, and 2202b may be part of a stack of waveguides, each of which may include an integral spacer and a recess for receiving a lower spacer from a lower waveguide, which also includes an integral spacer.

[0179] FIG. 24 illustrates a stack of waveguides with an integrated spacer. The individual waveguides illustrated may be any of waveguides 1602, 1802, 2102, 2202a, 2202b, also illustrated in FIGS. 16 - 18 and 21 - 23. Only portions of waveguides 1602, 1802, 2102, 2202a, 2202b having integrated spacer 1020 and / or indentation 1030 are shown in this figure for clarity. The remainder of waveguides 1602, 1802, 2102, 2202a, and 2202b are shown in the corresponding ones of FIGS. 16 - 18 and 21 - 23 and may include various edge treatments (e.g., light absorbing material, rough texture, external coupling optical elements, light trapping microstructures) as disclosed herein. In some embodiments, waveguides 1602, 1802, 2102, 2202a, 2202b each have one or more integrated spacers 1020 configured to provide separation between the waveguide and the immediately upper layer waveguide. Thus, as illustrated, waveguides 1602, 1802, 2102, 2202a, 2202b with integrated spacers may form a waveguide stack (e.g., corresponding to waveguide stack 660 of FIGS. 9A - 9C). In some embodiments, waveguides 1602, 1802, 2102, 2202a, 2202b of the waveguide stack may each be similar (e.g., having similar edge treatments). In some other embodiments, the waveguides forming the waveguide stack may have different edge treatments (e.g., different ones of waveguides 1602, 1802, 2102, 2202a, 2202b from FIGS. 16 - 18 and 21 - 23 may be utilized at different positions within the waveguide stack).

[0180] It should be understood that the integrated spacers 1020 and / or indentations 1030 of the waveguides 1602, 1802, 2102, 2202a, and 2202b may be formed to have the shapes and orientations as described above with respect to FIGS. 10A - 15G. For example, in some embodiments, the waveguides 1602, 1802, 2102, 2202a, 2202b and the integrated spacer 1020 may be formed from a polymeric material that can be molded (e.g., using an imprint mold) to define the integrated spacer 1020. Additionally, as discussed herein, the mold may include relief features for defining one or more than one of the internal coupling optical element, the external coupling optical element, the edge and the adjacent rough surface texture 2105 (FIG. 21), the external coupling optical element 2220 (FIG. 22A), and the light trapping structures 2230a and / or 2230b (FIGS. 22B and 22C). Exemplary method for forming a mold

[0181] An example of the mold 1200 is shown in FIG. 25. The mold 1200 includes a pattern of features consisting of small features 1240a and large features 1240b, which may be openings on the surface of the mold 1200. The small features 1240a may have a height (or depth) h of about 10 nm to 250 nm a while the large features may have a height (or depth) h of about 5 μm to 1,000 μm bIt may have. In some embodiments, the small feature 1240a corresponds to a diffractive optical element, and the large feature 1240b corresponds to an integrated spacer. As shown, the small feature 1240a may be formed inside the mold 1200, while the large feature 1240b may be formed on the periphery of the mold 1200. As is clear from the above discussion, it should be understood that the small feature 1240a and the large feature 1240b are "small" and "large" in the sense that the feature 1240a is smaller than the feature 1240b. This difference in dimensions can apply to both the critical dimension of the feature and the height of the feature. In some embodiments, the ratio of the height of the large feature 1240b to the height of the small feature 1240a may be about 20:1 or greater, 500:1 or greater, 4,000:1 or greater. Additionally, the ratio of the height of the large feature 1240b to the height of the small feature 1240a may be about 100,000:1 or less.

[0182] Creating a mold with large features such as 1240b can present processing challenges. A long etching time is required to create the large feature, but prolonged exposure to the etching solution can damage or degrade portions of the substrate that are not intended to be etched. The methods described herein enable the processing of molds with large (e.g., micron or millimeter scale) features while maintaining low total thickness variation and surface roughness within the non-patterned area of the mold. As used herein, it should be understood that the substrate for forming the mold may be referred to as a wafer due to the physical similarity of some substrates to semiconductor wafers. However, it will be understood that in addition to semiconductor materials, the substrate may be formed from materials other than semiconductors. For example, in some embodiments, the substrate may be formed from a transparent material. Wet etching process

[0183] Referring to FIGS. 26 and 32, the mold machining may include the step of providing a substrate 2602, which will be formed in the mold as discussed herein. Preferably, the substrate 2602 has a flat and smooth surface and may have a thickness of about 0.3 mm to 20 mm. The substrate may comprise silicon or may be a glass, quartz, fused silica, or other transparent material substrate. Preferably, the substrate has a total thickness variation (TTV) of less than about 1 μm and a surface roughness (R q ).

[0184] An etching mask 2604 is applied to the substrate 2602 by a deposition process such as physical vapor deposition, sputtering, electron beam deposition, or thermal deposition. In some embodiments, the deposition process is chemical vapor deposition. Preferably, the etching mask 2604 is formed of a metal. Without being limited by theory, it is understood that the metal etching mask 2604 adheres better to the substrate 2602 than the polymer material of the photoresist layer 2606 when exposed to the etching solution over the duration required to etch large millimeter-scale features such as spacers. For example, if the photoresist layer 2606 is applied directly to the substrate 2602, the photoresist layer may peel off the substrate 2602 during the substrate etching process. In some embodiments, an adhesion layer 2610 may be applied before depositing the metal etching mask to facilitate adhesion between the metal etching mask 1604 and the substrate 2602. For example, the adhesion layer 2610 may be a layer of titanium or chromium material. In some embodiments, the adhesion layer 2610 may have a thickness of about 10 nm to 100 nm.

[0185] In some embodiments, the etching mask 2604 may be formed by one or more layers of a metal material that is removed by the chemicals of the substrate etchant at a rate lower than that of the material of the underlying substrate. In embodiments where hydrofluoric acid (HF) is used as the substrate etchant, a silver or copper mask may be used for low concentrations of HF, e.g., less than 30%. For higher concentrations of HF, e.g., greater than 50%, a gold or platinum mask may also be used. In some embodiments, the etching mask may include a gold layer having a thickness of about 10 nm to 200 nm. It should be understood that gold or platinum etching masks may also be used for etching chemicals having an HF concentration lower than 50%.

[0186] In some embodiments, the photoresist layer 2606 may be applied to the etching mask 2604, for example, by spin coating, and subsequently patterned using a lithography process such as electron beam, ultraviolet (UV), or nanoimprint lithography. The photoresist layer 2606 contains the pattern of the large features 2608 that will be transferred into the substrate 2602 and will form openings for forming spacers within the mold that will be formed by the substrate 2602.

[0187] The first etching step is performed to expose the substrate surface within the region of feature 2608, as shown in FIG. 27. In some embodiments, multiple layers of etching mask material may be disposed across the substrate surface to form an etching mask 2604. The layers of etching mask material may be removed by a single etching, if the various materials are etchable using a single etching, or by a sequence of etchings that are selective for the exposed materials of the layers. It should be understood that the etching may be wet and / or dry etching with appropriate chemistries for selectively removing the etching mask material relative to other exposed materials. If a sequence of etchings is performed, the first etching step may be performed to remove the metal mask material within the patterned region. In embodiments where the metal mask 2604 is gold, an etching solution chemistry that is selective for etching gold relative to other exposed materials is used in this step. If an adhesion layer 2610 is present, a second etching step may be performed to remove the adhesion layer within the patterned region. In embodiments where the adhesion layer 2610 is a chromium layer, an etching solution chemistry that is selective for etching chromium relative to other exposed materials is used in this step. The resulting structure is shown in FIG. 27.

[0188] The second etching step is performed to etch feature 2608 into substrate 2602, as shown in FIG. 28. In some embodiments, the substrate etching chemistry includes HF, which may have a concentration in the range of about 1% to about 50%. The HF may be mixed with a buffer such as ammonium fluoride (NH4F) to slow the etching rate and provide better control of the etching process. Examples of etching solutions and total wet etching times for forming a 10 μm high feature in fused silica are shown below.

Table 1

[0189] The second etching step preferably results in a selective removal of the substrate on the exposed substrate surface. The patterned photoresist layer 2606 may be etched away completely or partially, depending on the etchant, the duration of the etching, and the initial thickness of the photoresist layer. If the photoresist material is completely removed, the metal etching mask remains to protect a portion of the substrate surface.

[0190] Unfortunately, when the photoresist layer 2606 is very thin or completely removed and the metal etching mask 2604 is relied upon to protect a portion of the substrate 2602 from the substrate etching chemistry, in some cases, small defects may be seen within the substrate surface that were thought to be covered by the metal etching mask 2604. As shown in FIG. 29A, the metal etching mask 2604 can be understood to be formed by a metal etching mask layer 2604a of a metal material deposited by a single deposition process. Without being limited by theory, small gaps or pinholes 2900 within the metal mask 2604a are thought to allow the substrate etching solution to reach the surface of the substrate 2602 directly beneath the pinholes 2900 during some etching. As shown, the pinholes 2900 can be existing openings within the metal etching mask 2604a that are subsequently abraded by exposure to the etching solution and / or thinner portions of the metal etching mask 2604a. The etching solution (e.g., HF) can flow into these pinholes 2900 and etch the surface of the substrate 2602, as shown in FIG. 29B. For example, it has been observed that small spots or dots can be seen on the substrate surface after etching, as described above. These spots or dots are thought to be the result of etching of the substrate surface by the etching solution flowing through the pinholes 2900, which form recesses 2910 on the substrate surface.

[0191] In some embodiments, the thin areas that can be pinholes 2900 and / or in the etching mask 2604a are reduced. For example, the metal etching mask 2604a may be enlarged by deposition of another material across the metal etching mask 2604a and / or by depositing more of the same or different metals using another deposition process. Various strategies for preventing defects caused by pinholes, including deposition of a continuous layer of etching mask material to fill or block the pinholes, use of a photoresist to fill or block the pinholes, and electroplating to fill or block the pinholes, are shown in FIGS. 30A-C. It will be understood that each of these strategies may also increase the thickness of the more quickly deposited etching mask layer.

[0192] FIG. 30A shows a metal etching mask 2604 (FIGS. 26-28) formed by a plurality of overlapping metal mask layers 2604a, 2604b, 2604c, which may be deposited in succession in the deposition, one for each of the layers 2604a, 2604b, 2604c. In such a configuration, the locations of the pinholes within each of the layers 2604a, 2604b, 2604c will advantageously be different. This improves the substrate surface coverage and reduces the likelihood that the metal etching mask will be penetrated by the etchant used to etch the substrate 2602. The various metal mask layers 2604a, 2604b, 2604c may be formed from the same metal or different metals, and the deposition may be of the same type or different deposition processes including one or more deposition processes such as chemical vapor deposition (CVD) or physical vapor deposition (PVD). Preferably, in some embodiments, to simplify the formation of the etching mask 2604, the metal mask layers 2604a, 2604b, 2604c may each be formed from the same metal and deposited using the same deposition process. In some embodiments, two or more, three or more, or four or more layers may be deposited successively to form the integrated metal etching mask 2604. Additionally, in some embodiments, the total number of layers forming the integrated etching mask 2604 may be less than 10, less than 6, or less than 5.

[0193] Figure 30B shows an example where the photoresist layer is retained on the metal etching mask layer to reduce the diffusion of the substrate etching solution inside the pinholes. In some embodiments, the thickness of the photoresist layer 2606 may be increased to a level such that the photoresist will be retained throughout the expected duration of the substrate etching step. For example, in some embodiments, the thickness of the photoresist layer 2606 is selected such that after completion of the etching to define the opening 2608 in the substrate 2602, a portion of the photoresist layer 2606 still remains to cover the entire etching mask 2604. In some embodiments, the initial thickness of the photoresist layer 2606 is such that the remaining portion of the photoresist layer 2606 extends above the etching mask 2604 by 5% or more, 10% or more, 15% or more, 25% or more, or 30% or more of the height of the etching mask 2604 after completion of the etching of the substrate 2602.

[0194] FIG. 30C shows an electroplated layer 2604b grown over the metal etch mask layer 2604a, and both the electroplated layer 2604b and the metal etch mask layer 2604a together form the etch mask 2604. The electroplated layer may be of the same material as the metal etch mask material. In some embodiments, a different metal may be utilized for the electroplated layer. The thickening provided by the electroplated layer 2604b creates a very thick etch mask 2604, e.g., about 1 μm to 20 μm thick, with a consistent coverage rate and no pinholes. The electroplating step may be performed either before or after the photoresist patterning step. For example, after or as part of transferring the pattern of the openings in the photoresist layer 2606 into the etch mask 2604, the photoresist layer 2606 may be completely removed, thereby exposing the metal etch mask 2604a. Subsequently, the metal etch mask layer 2604a may be used as a seed layer, and subsequently, the electroplated layer 2604b may be selectively deposited over the metal etch mask layer 2604a before etching the substrate 2602.

[0195] In some embodiments, the deposition of additional metal layers (one or more successive metal etch mask layers 2604b, 2604c (FIG. 30A) formed by evaporation or electroplated metal etch mask layer 2604b (FIG. 30B), etc.) deposits the same metal over the existing metal etch mask layer 2604a, thereby simplifying the selection of the etching chemical for subsequent etching of the metal etch mask 2604. Reduction in substrate surface defects has been observed to be readily apparent to the naked eye when processing using the metal etch mask 2604 to which the thickening strategy as described above is applied.

[0196] In addition to protecting portions of the upper surface of the substrate 2602 from the etchant, it may also be advantageous to protect the bottom surface of the substrate to avoid changing the substrate thickness, flatness, and / or surface roughness during the substrate etching process. To protect the back side of the substrate, a substrate holder may be used, or the back side of the substrate may be shielded such that only one side of the substrate is in contact with the substrate etchant. In another configuration, a metal etch mask may be applied to the bottom side of the substrate to prevent contact with the substrate etchant. For example, a metal layer may be deposited on the bottom side of the substrate 2602. In some embodiments, the back side of the metal layer is formed from the same metal as that used to form the etch mask 2604, simplifying the number of precursors required for deposition and various depositions. In some other embodiments, the back side metal layer may be formed from a different metal, e.g., a metal having a higher resistance to the etchant chemistry used to etch the etch mask 2604 and / or the substrate 2602. In yet another configuration, a sacrificial substrate may be bonded to the bottom of the substrate. The sacrificial substrate may be bonded, for example, using a photoresist or other adhesive that can be easily dissolved, such as by immersion in an organic solution after the etching step so that the sacrificial substrate can be removed.

[0197] After etching the substrate 2602 and extending the opening 2608 into the substrate 2602, a third stage of etching may be performed. During this third stage, any remaining material forming the metal mask 2604 is removed, followed by a cleaning stage to wash away and remove any remaining etchant or debris.

[0198] FIG. 31 shows another diagram of the sequence of three etching steps corresponding to the three etching steps described above, and the resulting mold structure formed after mask material removal and cleaning. Structures 2) and 3) show the structures formed during the first etching step (as described above with respect to FIGS. 26 and 27). Structure 4) is formed during the second etching step (as described above with respect to FIG. 28), and structure 5) is formed during the third etching step after removal of the mask material.

[0199] Continuing to refer to FIG. 31, in the first illustrated intermediate structure 1), in some embodiments, an etching mask 2604, which may be formed from a metal, is deposited over a substrate 2602, which may be formed from a glass, in some embodiments. In the second illustrated intermediate structure 2), a resist layer 2606 is deposited over the etching mask 2604 and patterned to define an opening 2608 within the resist layer 2606. In the third illustrated intermediate structure 3), the etching mask 2604 is exposed to an etching chemical that is selective for the material of the etching mask 2604, and through the etching mask 2604, the opening 2608 is extended into the resist layer 2606. In the fourth illustrated intermediate structure 4), the underlying substrate 2602 is exposed to an etching solution (e.g., a wet etching solution such as an HF-containing etching solution) to remove the substrate material. In the fifth illustrated intermediate structure 5), the upper etching mask 2604 and any remaining photoresist material are removed, and the resulting structure is subjected to a cleaning process, thereby leaving a mold having an opening 2610 therein.

[0200] As shown, in some embodiments where the etching is wet etching, it should be understood that the wet etching can etch the substrate material both vertically (downward) and laterally, thereby forming the open volume 2610. Thus, the fifth illustrated intermediate structure 5) of FIG. 31 shows that the feature transferred into the substrate, i.e., the open volume 2610 formed from the opening 2608, has rounded walls or corners and is undercut in relation to the etching mask. Without being limited by theory, this is understood to occur because the wet etching is an isotropic process and the substrate etchant attacks both the exposed horizontal surface of the substrate and the vertical surfaces of the feature walls. Advantageously, the curved shape of the volume 2610 facilitates the release or removal of the spacer that can be formed within these volumes 2610.

[0201] FIG. 32 shows, in flowchart format, examples of various actions where wet etching is utilized to form an open volume within a substrate, and the substrate and open volume are used to form a mold that can be used to fabricate a waveguide with an integrated spacer formed within that open volume, as discussed above and illustrated in FIGS. 26 - 28 and 31. For example, it should be understood that the first, second, and third illustrated etching steps correspond to the first, second, and third etching steps discussed with reference to FIGS. 26 - 28 and 31. In the illustrated embodiment, the various etchings used to transfer the pattern from the photoresist layer to the etching mask and then to the substrate (or wafer) are wet etchings. Additionally, any mask material remaining after the third etching step may also be removed using wet etching. Dry etching process

[0202] As described above, wet etching tends to form a cross-sectional shape with rounded sidewalls and / or corners. If more vertical walls are desired for the features of the substrate being etched, a process involving dry etching may also be used. A flowchart of an exemplary dry etching method is shown in FIG. 33. The dry etching process may include, for example, a plasma-assisted etching process such as reactive ion etching (RIE), inductively coupled plasma RIE, or ion milling. In some embodiments, the dry etching process may be used to etch the substrate during a second etching stage. In some embodiments, the flowcharts of FIGS. 32 and 33 are otherwise the same. In some other embodiments, the first etching stage of FIGS. 32 and / or 33 and the first etching stage discussed above with respect to FIGS. 26-28 and 31 may utilize dry etching. In some embodiments, both the first and second etching stages of FIGS. 32 and / or 33 and both the first and second etching stages discussed above with respect to FIGS. 26-28 and 31 may utilize dry etching.

[0203] Dry etching, such as plasma etching, is directional and will result in less undercutting of the substrate under the etching mask, as shown in the comparative drawing of FIG. 34. However, plasma etching can also remove the etching mask over time and exacerbate the pinhole effect discussed above. It may be beneficial to use a very thick etching mask to reduce surface damage to the substrate directly under the etching mask. For example, the mask may be 1 μm thick for every 40 μm of the substrate to be etched if the substrate is made of a glass material. In some embodiments, multiple depositions of materials as described above with respect to FIGS. 30A and 30C may be utilized to provide a thick etching mask.

[0204] Examples of plasma etching parameters are provided below. As shown below, appropriate ranges for chamber pressure, gas composition and flux, RF power, temperature, and ICP power and / or VHF power may be selected based on the composition of the substrate to be etched and / or the final opening to be formed (e.g., the size and / or aspect ratio of the opening). In some embodiments, glass may be etched in a process with process parameters as provided below. 1) Chamber pressure (1 - 10 -4 Torr). 1. Including 1.20 millitorr to 5 millitorr 2. Including 100 millitorr to 20 millitorr 2) Gas composition and flux (as Ar, O2, N2, H2, C2F6, CF4, CHF3, CF3Cl, SF6, Cl2, BCl, HBr, and other halide gases). The flux ranges from 1 to 100 sccm. 1. Including SF6 / Ar 2. Including BCl3 / HBr / Ar 3. Including CF4 / CHF3 / Ar 3) RF power (10 - 500 W). 1. Including 200 - 100 W 2. Including 500 - 200 W 3. Including 100 - 10 W 4) Temperature (-150 - 100 °C). 1. Including -120 - -100 °C 2. Including -100 - 0 °C 3. Including 0 - 20 °C 4. Including 20 - 50 °C 5) ICP power, VHF power (10 - 2500 W).

[0205] Referring to both FIGS. 32 and 33, as discussed herein, the deposition of the etching mask may involve a single deposition or, more preferably, may involve multiple depositions of materials and / or the use of a thick resist layer, as discussed herein with respect to FIGS. 30A - 30C. Also, with respect to the first etching stage of FIGS. 32 and 33, the illustrated wet etching for the etching mask and optional adhesion layer may, in some embodiments, be replaced with dry etching.

[0206] It should be understood that the substrate or wafer and the open volumes formed within the substrate may constitute a mold, which may be used to fabricate waveguides with integrated spacers formed within those open volumes. It should be understood that, as discussed herein, waveguides may have multiple integrated spacers in various orientations and configurations. A single volume 2610 or only one or two openings 2608 are illustrated in FIGS. 26 - 28 and 31 for ease of discussion and illustration, but the number of volumes 2610 or openings 2608 may correspond to the number of desired spacers to be formed, and the orientation and configuration of those volumes 2610 or openings 2608 may correspond to the orientation and configuration of the desired spacers.

[0207] Furthermore, in the foregoing specification, the invention has been described with reference to its specific embodiments. However, it will become apparent that various modifications and changes can be made therein without departing from the broader spirit and scope of the invention. The specification and drawings are, therefore, to be regarded in an illustrative rather than a limiting sense.

[0208] In fact, it should be understood that the systems and methods of the present disclosure each have several innovative aspects, none of which alone contribute to or are required for the desirable attributes disclosed herein. The various features and processes described above can be used independently of each other or combined in various ways. All possible combinations and sub-combinations are intended to fall within the scope of the present disclosure.

[0209] Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, the various features described in the context of a single embodiment may also be implemented separately in multiple embodiments or in any suitable sub-combination. Further, a feature may be described above as acting in a certain combination and may further be claimed as such, but one or more features from the claimed combination may in some cases be deleted from the combination, and the claimed combination may be directed to a sub-combination or a variation of a sub-combination. No single feature or group of features is necessary or essential to every embodiment.

[0210] In particular, conditional clauses used in this specification such as "can", "could", "might", "may", "e.g.", and equivalents, generally convey that one embodiment includes certain features, elements, and / or steps while other embodiments do not, unless specifically stated otherwise or understood otherwise within the context in which they are used. Thus, such conditional clauses are not generally intended to imply that features, elements, and / or steps are required in any way for one or more embodiments, or that one or more embodiments necessarily include logic for determining whether these features, elements, and / or steps should be included or implemented in any particular embodiment, regardless of the author's input or prompting. The terms "comprising", "including", "having", and equivalents are synonyms and are used inclusively in a non-limiting manner, not excluding additional elements, features, acts, operations, etc. Also, the term "or", when used, for example, to connect a list of elements, is used in its inclusive sense (and not in its exclusive sense) such that the term "or" means one, some, or all of the elements in the list. Additionally, the articles "a", "an", and "the" as used in this application and the appended claims should be construed to mean "one or more than one" or "at least one" unless otherwise defined. Similarly, operations may be depicted in the drawings in a particular order, but it should be recognized that such operations need not be performed in the particular order shown or in a sequential order to achieve the desired result, nor is it necessary that all of the illustrated operations be performed. Further, the drawings may schematically depict one or more exemplary processes in the form of flowcharts. However, other operations not depicted may also be incorporated into the exemplary methods and processes schematically illustrated.For example, one or more additional operations may be performed before, after, at the same time as, or between any of the illustrated operations. Additionally, the operations may be rearranged or reordered in other embodiments. In certain situations, multitasking and parallel processing may be advantageous. Further, the separation of the various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the program components and systems described may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

[0211] Accordingly, the claims are not intended to be limited to the embodiments shown herein but are to be accorded the widest scope consistent with the disclosure, principles, and novel features disclosed herein.

Claims

1. A method for forming a mold, the method comprising: providing a substrate; forming an etching mask over the substrate, the forming of the etching mask comprising: depositing a first etching mask layer of a first metal by a first deposition process; depositing a second etching mask layer of a second metal by a second deposition process; wherein the first metal is different from the second metal and the first deposition process is different from the second deposition process; defining an opening in the etching mask; defining an opening in the substrate by etching the substrate through the etching mask; and the opening in the substrate has a depth of 5 μm to 1,000 μm.

2. The method further comprises: depositing a photoresist layer over the etching mask layer; lithographically defining an opening in the photoresist layer; and defining the opening in the etching mask includes extending the opening in the photoresist layer into the etching mask. The method according to claim 1.

3. The method according to claim 1, further comprising depositing an adhesive layer over the substrate before forming the etching mask.

4. Depositing the second etching mask layer includes vapor deposition. The method according to claim 1.

5. Depositing the second etching mask layer includes electroplating. The method according to claim 1.

6. The etching mask has a thickness of 10 nm to 200 nm. The method according to claim 1.

7. The method according to claim 1, wherein etching the substrate through the etching mask includes wet etching.

8. The method according to claim 1, wherein etching the substrate through the etching mask includes dry etching.

9. The method according to claim 1, wherein the substrate is formed of an optically transparent material.

10. The method according to claim 9, wherein the optically transparent material is selected from the group consisting of glass, quartz, and fused silica.

11. The method according to claim 1, further comprising defining an internal opening in the substrate, wherein a ratio of a height of the internal opening to a height of the opening in the substrate is 500:1 or greater.

12. The method according to claim 11, wherein the ratio is 100,000:1 or less.

13. The method according to claim 11, wherein the internal opening has a size and periodicity corresponding to a diffraction grating.

14. The method according to claim 1, further comprising removing the etching mask.

Images