ADAPTIVE LENS ASSEMBLY INCLUDING POLARIZATION SELECTIVE LENS STACK FOR AUGMENTED REALITY DISPLAYS - Patent application

Abstract

To provide adaptive lens assemblies including polarization-selective lens stacks for nice augmented reality display.SOLUTION: The present disclosure relates to display systems and, more particularly, to augmented reality display systems. In one aspect, an adaptive lens assembly includes a lens stack configured to exert polarization-dependent refractive power to linearly polarized light. The lens stack includes a birefringent lens and an isotropic lens contacting each other to form a conformal interface therebetween. The adaptive lens assembly is configured to be selectively switched between a plurality of states having different refractive powers.SELECTED DRAWING: None

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 639,882, filed March 7, 2018, and entitled “ADAPTIVE LENS ASSEMBLIES INCLUDING POLARIZATION-SELECTIVE LENS STACKS FOR AUGMENTED REALITY DISPLAY,” the contents of which are incorporated herein by reference in their entirety.

[0002] (Cited by reference) This application incorporates by reference the entirety of each of the following patent applications: U.S. Patent Application No. 14 / 555,585, filed November 27, 2014, and published on July 23, 2015 as U.S. Patent Publication No. 2015 / 0205126; U.S. Patent Application No. 14 / 555,585, filed April 18, 2015, and published on October 22, 2015 as U.S. Patent Publication No. 2015 / 0302652; No. 14 / 690,401, U.S. Patent Application No. 14 / 212,961, now U.S. Patent No. 9,417,452, filed March 14, 2014 and issued August 16, 2016, and U.S. Patent Application No. 14 / 331,218, filed July 14, 2014 and published October 29, 2015 as U.S. Patent Publication No. 2015 / 0309263.

[0003] (Field) The present disclosure relates to display systems, and more particularly to augmented and virtual reality display systems. [Background technology]

[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 may be perceived as real. Virtual reality, or "VR", scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, and augmented reality, or "AR", scenarios typically involve the presentation of digital or virtual image information as an extension to the visualization of the real world around the user. Mixed reality, or "MR", scenarios are a type of AR scenario that typically involve virtual objects that are integrated into and respond to the natural world. For example, in MR scenarios, AR image content may be perceived as being blocked by or otherwise interacting with objects in the real world.

[0005] 1, an augmented reality scene 10 is depicted in which a user of the AR technology is viewing a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. In addition to these items, the user of the AR technology perceives that they are also "seeing" "virtual content," such as a robotic figure 40 standing on the real-world platform 30 and a flying, cartoon-like avatar character 50 that appears to be an anthropomorphic bumblebee, even though these elements 40, 50 do not exist in the real world. The human visual perception system is complex, and creating AR technology that facilitates a comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements is challenging.

[0006] The systems and methods disclosed herein address various challenges associated with AR or VR technology. Summary of the Invention [Means for solving the problem]

[0007] In a first aspect, an adaptive lens assembly includes a lens stack configured to exert a polarization-dependent refractive power on linearly polarized light. The lens stack includes a birefringent lens and an isotropic lens in contact with each other and forming a conformal interface therebetween. The adaptive lens assembly is configured to be selectively switched between a plurality of states having different refractive powers.

[0008] In a second aspect, a display device includes a waveguide assembly configured to guide light in a lateral direction parallel to an output surface of the waveguide assembly. The waveguide assembly is further configured to outcouple the guided light through the output surface. The display device additionally includes an adaptive lens assembly disposed on a first side of the waveguide assembly. The adaptive lens assembly is disposed to receive the outcoupled light from the waveguide assembly and to be selectively switched between a plurality of states having different refractive powers. The adaptive lens assembly includes a lens stack configured to exert a polarization-dependent refractive power on linearly polarized light. The lens stack includes a birefringent lens and an isotropic lens in contact with one another, the contacting surfaces of the birefringent lens and the isotropic lens forming a form-matching interface. The present specification also provides, for example, the following items: (Item 1) 1. An adaptive lens assembly comprising: a lens stack configured to exert a polarization-dependent refractive power on linearly polarized light; the lens stack comprises a birefringent lens and an isotropic lens, the birefringent lens and the isotropic lens contacting each other and forming a conformal interface therebetween; The adaptive lens assembly is configured to be selectively switched between a plurality of states having different optical powers. (Item 2) the birefringent lens has an optical axis and a birefringence (Δn) and is configured to exert a first refractive power on light having a polarization direction parallel to the optical axis and a second refractive power on light having a polarization direction perpendicular to the optical axis; Item 2. The adaptive lens assembly of item 1, wherein the isotropic lens has a refractive index and is configured to exert a third refractive power on light passing therethrough, the third refractive power having an opposite sign to the first and second refractive powers. (Item 3) The Δn is the extraordinary refractive index (n e ) and the normal refractive index (n o ) and the refractive index of the isotropic lens corresponds to the difference between the n o Item 3. The adaptive lens assembly of item 2, having substantially the same value as: (Item 4) 3. The adaptive lens assembly of claim 2, wherein the third refractive power is substantially the same in magnitude as the second refractive power, whereby the polarization selective lens stack is configured to exert substantially no refractive power on light having a polarization direction perpendicular to the optical axis. (Item 5) Item 3. The adaptive lens assembly of item 2, wherein the lens stack is configured to exert an optical power proportional to Δn on light having a polarization direction parallel to the optical axis. (Item 6) Item 1. The adaptive lens assembly of item 1, wherein the birefringent lens is a Fresnel lens comprising a plurality of grooves formed therein, adjacent ones of the grooves defining a Fresnel zone of the Fresnel lens. (Item 7) Item 7. The adaptive lens assembly of item 6, wherein the plurality of grooves comprises concentric circular grooves. (Item 8) 7. The adaptive lens assembly of claim 6, wherein the plurality of grooves comprise parallel grooves extending in a direction parallel to a major surface of the lens stack. (Item 9) Item 1. The adaptive lens assembly of item 1, wherein the birefringent lens comprises a liquid crystal (LC). (Item 10) 10. The adaptive lens assembly of claim 9, wherein the LC molecules of the birefringent lenses are substantially oriented in a lateral direction parallel to the major surfaces of the lens stack. (Item 11) 11. The adaptive lens assembly of any one of claims 1-10, further comprising a switchable half-wave plate comprising a twisted nematic (TN) liquid crystal (LC) optically coupled to the lens stack, the switchable half-wave plate being configured to preserve the polarization of linearly polarized light passing through it when activated and to alter the polarization of linearly polarized light passing through it when deactivated. (Item 12) The switchable half-wave plate is disposed on a first side of the polarization-selective lens stack, and the adaptive lens assembly is disposed on a second side of the polarization-selective lens stack. a second switchable half-wave plate comprising a TN LC optically coupled to the polarization selective lens stack; a second lens stack configured to exert a polarization-dependent optical power on linearly polarized light; Further equipped with the second lens stack comprises a second birefringent lens and a second isotropic lens, the second birefringent lens and the second isotropic lens contacting each other and forming a conformal interface therebetween; Item 12. The adaptive lens assembly of item 11, wherein the adaptive lens assembly is configured to be selectively switched between at least four states by electrically activating and / or deactivating the switchable wave plate and / or the second switchable half-wave plate. (Item 13) 11. The adaptive lens assembly of any one of items 1-10, wherein the birefringent lens comprises reactive mesogens and the lens stack comprises electrodes configured to apply an electric field across the birefringent lens such that the lens stack is configured to be electrically switchable between different refractive power states. (Item 14) A display device, comprising: a waveguide assembly configured to guide light in a lateral direction parallel to an output surface of the waveguide assembly, the waveguide assembly further configured to outcouple the guided light through the output surface; an adaptive lens assembly disposed on a first side of the waveguide assembly; Equipped with the adaptive lens assembly is positioned to receive light outcoupled from the waveguide assembly and to be selectively switched between a plurality of states having different optical powers; A display device, wherein the adaptive lens assembly comprises a lens stack configured to exert a polarization-dependent refractive power on linearly polarized light, the lens stack comprising a birefringent lens and an isotropic lens in contact with each other, the contact surfaces of the birefringent lens and the isotropic lens forming a conformal interface. (Item 15) the birefringent lens has an optical axis and a birefringence (Δn) and is configured to exert a first refractive power on light having a polarization direction parallel to the optical axis and a second refractive power on light having a polarization direction perpendicular to the optical axis; Item 15. The display device of item 14, wherein the isotropic lens has a refractive index and is configured to exert a third refractive power on light passing therethrough that is opposite in sign to at least one of the first refractive power and the second refractive power. (Item 16) Item 16. The display device of item 15, wherein the birefringent lens is a Fresnel lens having a plurality of grooves formed therein, adjacent ones of the grooves defining a Fresnel zone. (Item 17) Item 16. The display device of item 15, wherein the birefringent lens comprises a liquid crystal (LC). (Item 18) Item 16. The display device of item 15, wherein the LC molecules of the birefringent lenses are substantially oriented in the same direction parallel to a major surface of the polarization selective lens stack. (Item 19) a second adaptive lens assembly disposed on a second side of the waveguide assembly opposite the first side, the second adaptive lens assembly configured to be selectively switched between a plurality of states having different optical powers; Item 15. The display device of item 14, wherein the second adaptive lens assembly comprises a second lens stack configured to exert a polarization-dependent refractive power on linearly polarized light, the second lens stack comprising a second birefringent lens and a second isotropic lens, the second birefringent lens and the second isotropic lens contacting each other and forming a shape-matching interface therebetween. (Item 20) 20. The display device of item 19, wherein each of the first and second adaptive lens assemblies further comprises a switchable half-wave plate comprising twisted nematic (TN) liquid crystal (LC) optically coupled to a respective one of the lens stacks or the second lens stack, the switchable half-wave plate being configured to preserve the polarization of linearly polarized light passing through it when activated and to alter the polarization of linearly polarized light passing through it when deactivated. (Item 21) 21. The display device of claim 20, wherein each of the plurality of refractive powers exerted by the second adaptive lens assembly has substantially the same magnitude and has a corresponding one of the plurality of refractive powers exerted by the adaptive lens assembly having an opposite sign. (Item 22) 22. The display device of any one of items 14-21, wherein the adaptive lens assembly is formed on a first side of the waveguide assembly, and the display device further comprises a polarizing reflector interposed between the waveguide assembly and the adaptive lens assembly, the polarizing reflector configured to pass linearly polarized light having a first polarization therethrough and reflect linearly polarized light having a second polarization. (Item 23) 23. The display device of claim 22, further comprising a non-polarizing reflector on a second side of the waveguide assembly and a quarter-wave plate interposed between the non-polarizing reflector and the waveguide assembly, the non-polarizing reflector configured to reflect and modify the polarization of linearly polarized light having the first polarization incident thereon. (Item 24) 22. The display device of any one of items 14-21, wherein the adaptive lens assembly is formed on a first side of the waveguide, and the display device further comprises a polarizing reflector interposed between the adaptive lens assembly and the waveguide assembly, the polarizing reflector comprising cholesteric liquid crystals configured such that the polarizing notch reflector is configured to pass circularly polarized light having a first polarization therethrough and reflect circularly polarized light having a second polarization. (Item 25) 25. The display device of claim 24, further comprising a non-polarizing reflector on a second side of the waveguide assembly, the non-polarizing reflector configured to reflect and modify the polarization of circularly polarized light incident thereon having the second circular polarization. (Item 26) 20. The display device of claim 19, wherein each of the birefringent lens and the second birefringent lens comprises a reactive mesogen, and each of the lens stack and the second lens stack comprises an electrode configured to switch each of the lens stack and the second lens stack between different refractive power states. (Item 27) Item 15. The display device of item 14, wherein the birefringent lens comprises reactive mesogens and the polarization selective lens stack comprises electrodes for electrically switching the polarization selective lens stack between at least two refractive power states. (Item 28) on a second side of the waveguide assembly opposite the first side; A linear polarizer; a quarter-wave plate interposed between said waveguide assembly and said linear polarizer; 28. The display device of claim 27, further comprising: (Item 29) Item 23. The display device of item 22, wherein the polarizing reflector comprises a polarizing notch reflector. (Item 30) Item 23. The display device of item 22, wherein the non-polarizing reflector comprises a non-polarizing notch reflector. (Item 31) 22. A display device according to any one of items 14-21, wherein the display device is arranged in a head-mounted display. (Item 32) Item 32. The display device of item 31, further comprising a frame configured to be supported on a user's head. (Item 33) Item 32. The display device of item 31, wherein at least a portion of the display device is transparent and positioned in front of the user's eye when the user wears the display device, whereby the transparent portion transmits light from a portion of the environment in front of the user and the display device to the user's eye and provides a view of the portion of the environment in front of the user and the display device. (Item 34) Item 32. The display device of item 31, wherein the display device is configured to project light into a user's eye and display virtual image content in the user's field of view at different amounts of at least one of divergence and collimation, such that the displayed virtual image content appears to originate from different depths at different time periods. (Item 35) 22. The display device of any one of items 14-21, wherein the adaptive lens assembly comprises a Fresnel lens. (Item 36) Item 6. The adaptive lens assembly of any one of items 1-5, wherein the lens stack comprises a Fresnel lens. (Item 37) 11. The adaptive lens assembly of any one of items 6 and 8-10, wherein the grooves form an abrupt discontinuity in the thickness of the birefringent lens. (Item 38) 11. The adaptive lens assembly of any one of items 6 and 8-10, wherein the groove comprises a linear groove. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device. [Diagram 2] FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user. [Diagram 3] 3A-3C illustrate the relationship between the radius of curvature and the radius of focus. [Figure 4A] FIG. 4A illustrates a representation of the accommodation-vergence response of the human visual system. [Figure 4B] FIG. 4B illustrates examples of different accommodation and vergence states of a user's pair of eyes. [Figure 4C] FIG. 4C illustrates an example of a representation of a top-down view of a user viewing content through a display system. [Figure 4D] FIG. 4D illustrates another example of a representation of a top-down view of a user viewing content through a display system. [Diagram 5] FIG. 5 illustrates aspects of an approach for simulating a three-dimensional image by modifying wavefront divergence. [Figure 6] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide. [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly where each depth plane contains an image formed using multiple different primary colors. [Figure 9A]FIG. 9A illustrates a cross-sectional side view of an example set of stacked waveguides, each containing an internal coupling optical element. [Figure 9B] FIG. 9B illustrates a perspective view of the example of multiple stacked waveguides of FIG. 9A. [Figure 9C] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide example of FIGS. 9A and 9B. [Figure 9D] FIG. 9D illustrates an example of a wearable display system. [Figure 10] FIG. 10 illustrates an example of a display system including a pair of adaptive lens assemblies. [Figure 11] Figure 11A illustrates an example of the display system of Figure 10 that uses an adaptive lens to display virtual content to a user in a virtual depth plane, and Figure 11B illustrates an example of the display system of Figure 10 that provides a user with a view of real-world content through an adaptive lens. [Figure 12] Figure 12A illustrates a cross-sectional view of an exemplary polarization-selective lens stack comprising a birefringent lens and an isotropic lens. Figure 12B illustrates the polarization-selective lens stack of Figure 12A in operation to pass linearly polarized light having a first polarization therethrough. Figure 12C illustrates the polarization-selective lens stack of Figure 12A in operation to pass linearly polarized light having a second polarization therethrough. [Figure 13] Figure 13A illustrates the polarization-selective lens stack of Figure 12A with annotated parameters. Figure 13B illustrates a cross-sectional view and a top-down view of an example polarization-selective lens stack comprising a birefringent Fresnel lens and an isotropic lens. [Figure 14] Figure 14A illustrates a cross-sectional view of an example adaptive lens assembly comprising a polarization-selective lens stack combined with a switchable waveplate comprising twisted nematic liquid crystal. Figure 14B illustrates the switchable waveplate comprising twisted nematic liquid crystal of the adaptive lens assembly illustrated in Figure 14A. [Figure 15A]FIG. 15A illustrates a cross-sectional view of an example adaptive lens assembly comprising a first polarization-selective lens stack coupled to a first switchable waveplate comprising twisted nematic liquid crystal and a second polarization-selective lens stack coupled to a second switchable waveplate comprising twisted nematic liquid crystal. [Figure 15B] 15B-15E illustrate the example adaptive lens assembly of FIG. 15A in operation under different configurations configured to exert different optical powers. [Figure 15C] 15B-15E illustrate the example adaptive lens assembly of FIG. 15A in operation under different configurations configured to exert different optical powers. [Figure 15D] 15B-15E illustrate the example adaptive lens assembly of FIG. 15A in operation under different configurations configured to exert different optical powers. [Figure 15E] 15B-15E illustrate the example adaptive lens assembly of FIG. 15A in operation under different configurations configured to exert different optical powers. [Figure 16] FIG. 16 illustrates a cross-sectional view of an exemplary display device with a waveguide assembly interposed between a first adaptive lens assembly and a second adaptive assembly, each having a polarization-selective lens stack. [Figure 17] 17A and 17B illustrate cross-sectional views of an exemplary display device configured to display images using light coupled out from a waveguide assembly having different circular polarizations. [Figure 18] FIG. 18 illustrates a cross-sectional view of an exemplary switchable polarization-selective lens stack comprising a birefringent Fresnel lens and an isotropic lens. [Figure 19] FIG. 19 illustrates a cross-sectional view of an exemplary display device with a waveguide assembly interposed between a first adaptive lens assembly and a second adaptive assembly, each of which has a switchable polarization-selective lens stack. [Figure 20] FIG. 20 illustrates a cross-sectional view of an exemplary display device with a waveguide assembly inserted between a linear polarizer and a quarter-wave plate on a first side, and an adaptive assembly with a switchable polarization-selective lens stack on a second side. [Figure 21] 21A illustrates a plan view and a cross-sectional view of an exemplary one-dimensional (1D) Fresnel lens stack. FIG. 21B illustrates a cross-sectional view of an exemplary two-dimensional (2D) Fresnel lens stack. FIG. 21C illustrates a cross-sectional view of an exemplary two-dimensional (2D) Fresnel lens stack. [Figure 22] 22A-22D illustrate intermediate structures at different stages in the fabrication of an exemplary polarization-selective lens stack comprising a Fresnel birefringent lens and an isotropic lens. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Throughout the drawings, reference numbers may be reused to indicate correspondence between referenced elements. The drawings are provided to illustrate example embodiments described herein and are not intended to limit the scope of the present disclosure.

[0011] The AR system may display virtual content to a user or viewer while still allowing the user to see the world around them. Preferably, this content is displayed on a head-mounted display, for example as part of eyewear that projects image information to the user's eyes. In addition, the display may transmit light from the surrounding environment to the user's eyes, allowing a view of that environment as well. As used herein, it should be understood that a "head-mounted" or "head-mountable" display is a display that can be mounted on the viewer's or user's head.

[0012] In some AR systems, multiple waveguides may be configured to form virtual images at multiple virtual depth planes (also simply referred to herein as "depth planes"). Different ones of the multiple waveguides may have different refractive powers and may be formed at different distances from the user's eyes. The display system may also include multiple lenses that provide or additionally provide refractive power. The refractive power of the waveguides and / or lenses may provide images at different virtual depth planes. Undesirably, each of the waveguides and lenses may increase the overall thickness, weight, and cost of the display.

[0013] Advantageously, in various embodiments described herein, an adaptive lens assembly may be utilized to provide a variable refractive power, for example, to modify the wavefront divergence of light propagating through the lens assembly and provide a virtual depth plane at different perceived distances from the user. The adaptive lens assembly may include a polarization-selective lens stack with a birefringent lens and an isotropic lens in contact with each other, the contact surfaces of the birefringent lens and the isotropic lens forming a form-matching interface. The birefringent lens has an optical axis and a birefringence (Δn) and is configured to exert a first refractive power on light having a polarization direction parallel to the optical axis. The birefringent lens is configured to exert a second refractive power on light having a polarization direction perpendicular to the optical axis. The isotropic lens has a refractive index and is configured to exert a third refractive power on light passing therethrough, the third refractive power being opposite in sign to the first and second refractive powers. The adaptive lens assembly is configured to be selectively switched between a plurality of states having different refractive powers. The polarization selective lens stack is configured to exert a refractive force proportional to Δn on light having a polarization direction parallel to the optical axis. The third refractive power can be substantially the same or different in magnitude from the second refractive power. When the third refractive power and the second refractive power are substantially the same in magnitude, the polarization selective lens stack is configured to exert substantially no refractive force on light having a polarization direction perpendicular to the optical axis. When the third refractive power and the second refractive power are substantially different in magnitude, the polarization selective lens stack is configured to exert a refractive force that can be partially compensated, but not completely, on light having a polarization direction perpendicular to the optical axis, for example. In some applications, for example, when a user normally benefits from wearing corrective lenses such as prescription lenses or glasses, partial compensation may be desirable for the polarization selective lens stack to at least partially act as a corrective lens. Thus, when configured, the polarization selective lens stack is polarization selective.

[0014] The adaptive lens assembly can be configured to be selectively switched between a plurality of states having different refractive powers based on different configurations. In some embodiments, the adaptive lens assembly can be selectively switched by optically coupling a switchable half-wave plate comprising twisted nematic (TN) liquid crystal (LC) to the polarization-selective lens stack. In some embodiments, the birefringent lens comprises reactive mesogens, and the polarization-selective lens stack comprises electrodes configured to apply an electric field across the birefringent lens such that the polarization-selective lens stack can be electrically switchable between at least two refractive power states.

[0015] In some embodiments, the adaptive lens assembly forms part of a display device with a waveguide assembly to form images at different virtual depth planes. In various embodiments, the display device includes a pair of adaptive lens assemblies with a waveguide assembly interposed therebetween. The waveguide assembly includes a waveguide configured to propagate light (e.g., visible light) therein (e.g., via total internal reflection) and to outcouple the light. For example, the light may be outcoupled along an optical axis direction perpendicular to a major surface of the waveguide. One of the pair of adaptive lens assemblies may be formed on a first side of the waveguide assembly and may be configured to provide variable refractive power, modify the wavefront of the light passing through the adaptive lens assembly, and form images at each of a plurality of virtual depth planes. For example, the adaptive lens assembly may converge or diverge the outcoupled light received from the waveguide assembly. To compensate for modifications of the real world view due to convergence or divergence of the adaptive lens assembly and / or ambient light propagating through the waveguide assembly, the other of the pair of adaptive lens assemblies is additionally provided on a second side of the waveguide assembly opposite the first side. When the switchable waveplates of each adaptive lens assembly are in a corresponding state, the adaptive lens assemblies may have refractive powers with opposite signs, whereby the other of the adaptive lens assemblies corrects the distortion caused by the adaptive lens assembly on the first side of the waveguide assembly.

[0016] Advantageously, utilizing a switchable waveplate that is switchable between two states for a continuously variable adaptive lens having a continuously variable optical element simplifies driving the adaptive lens assembly and reduces the computational methods required to determine how to properly activate the adaptive lens assembly for a desired optical power. Additionally, by allowing the adaptive lens assembly to modify the wavefront divergence of the light output by the waveguides, the number of waveguides required to provide multiple depth planes is reduced for an arrangement in which each waveguide provides a particular amount of wavefront divergence.

[0017] Reference is now made to the drawings in which like reference numbers refer to like parts throughout, and in which, unless otherwise indicated, the drawings are schematic and are not necessarily drawn to scale.

[0018] (Exemplary Display System) FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user. It should be understood that the user's eyes are spaced apart and when viewing a real object in space, each eye may have a slightly different view of the object and form an image of the object at a different location on the retina of each eye. This may be referred to as binocular disparity and may be utilized by the human visual system to provide a perception of depth. Conventional display systems simulate binocular disparity by presenting two different images 190, 200 with slightly different views of the same virtual object (one for each eye 210, 220) that correspond to the view of the virtual object as it would appear by each eye as if the virtual object were a real object at a desired depth. These images provide binocular cues that the user's visual system may interpret to derive a perception of depth.

[0019] Continuing with reference to FIG. 2, the images 190, 200 are spaced 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 with the eyes 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 in the images presented to the eyes 210, 220 respectively, the eyes may naturally rotate so that the image of the object comes to a corresponding point on the retina of each eye to maintain single binocular vision. This rotation may cause the virtual object to converge to a point in space where it is perceived to be in the line of sight of each of the eyes 210, 220. As a result, the provision of three-dimensional images traditionally involves manipulating the vergence movement of the user's eyes 210, 220 to provide the perception of depth, providing binocular cues that the human visual system interprets.

[0020] However, creating a realistic and comfortable perception of depth is difficult. It should be understood that light from an object at different distances from the eye has a wavefront with different amounts of divergence. Figures 3A-3C illustrate the relationship between distance and divergence of light rays. The distance between the object and the eye 210 is represented in the order of decreasing distances R1, R2, and R3. As shown in Figures 3A-3C, the light rays become more divergent as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or part of an object) can be said to have a spherical wavefront curvature that is a function of the distance the point is away from the user's eye. As the curvature increases, the distance between the object and the eye 210 decreases. Although only a single eye 210 is illustrated in Figures 3A-3C and other figures herein for clarity of illustration, the discussion regarding the eye 210 may apply to both eyes 210 and 220 of a viewer.

[0021] 3A-3C, light from an object that a viewer's eye is fixating on may have different wavefront divergences. Due to the different wavefront divergences, the light may be focused differently by the eye's lens, which may then require the lens to assume a different shape and 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 an accommodation cue that causes a change in the shape of the eye's lens until a focused image is formed on the retina. For example, the accommodation cue may induce the ciliary muscle surrounding the eye's lens to relax or contract, thereby modulating the force applied to the suspensory ligament that holds the lens, thus changing the shape of the eye's lens, thereby forming a focused image of the fixated object on the eye's retina (e.g., fovea) until retinal blur of the fixated object is eliminated or minimized. The process by which the eye lens changes shape may be referred to as accommodation, and the shape of the eye lens required to form a focused image of a fixated object on the eye's retina (e.g., the fovea) may be referred to as the state of accommodation.

[0022] Referring now to FIG. 4A, a representation of the accommodation-vergence response of the human visual system is illustrated. A movement of the eye to fixate an object causes the eye to receive light from the object, which forms an image on each of the retinas of the eye. The presence of retinal blur in the image formed on the retina may provide a cue for accommodation, and the relative location of the image on the retina may provide a cue for vergence. The cue for accommodation causes accommodation to occur and each of the lenses of the eye to assume a particular accommodation state in which the lens forms a focused image of the object on the retina of the eye (e.g., the fovea). On the other hand, the cue for vergence causes a vergence movement (eye rotation) to occur such that the image formed on each retina of each eye is at a corresponding retinal point that maintains single binocular vision. In these positions, the eye may be said to assume a particular vergence state. Continuing with reference to FIG. 4A, accommodation can be understood to be the process by which the eye achieves a particular accommodation state, and vergence can be understood to be the process by which the eye achieves a particular vergence state. As shown in FIG. 4A, the accommodation and vergence state 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.

[0023] Without being limited by theory, it is believed that a viewer of an object may perceive the object as being "three-dimensional" due to a combination of vergence and accommodation. As noted above, vergence movement of the two eyes relative to one another (e.g., rotation of the eyes such that the pupils move toward or away from one another, converging the gaze of the eyes to fixate on an object) is closely associated with accommodation of the eye's lens. Under normal conditions, changing the shape of the eye's lens and changing focus from one object to another at a different distance will automatically result in a corresponding change in vergence to the same distance, under a relationship known as the "accommodation-vergence reflex." Similarly, a change in vergence will induce a corresponding change in lens shape under normal conditions.

[0024] 4B, examples of different accommodation and vergence states of the eyes are illustrated. The pair of eyes 222a fixates an object at optical infinity, while the pair of eyes 222b fixates an object 221 that is closer than optical infinity. Notably, the vergence states of each pair of eyes are different, with the pair of eyes 222a pointing straight ahead, while the pair of eyes 222 converge on 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.

[0025] Unfortunately, many users of conventional "3-D" display systems find such conventional systems uncomfortable or may not perceive any depth sensation at all due to the mismatch between accommodation and vergence states in these displays. As noted above, many stereoscopic or "3-D" display systems display a scene by providing a slightly different image to each eye. Such systems are uncomfortable for many viewers because, among other things, they simply provide different presentations of the scene, resulting in changes in the vergence states of the eyes, but without a corresponding change in the accommodation states of those eyes. Rather, images are presented by the display at a fixed distance from the eyes, such that the eyes view all image information in a single accommodation state. Such an arrangement counters the "accommodation-vergence reflex" by providing changes in the vergence states without a corresponding change in the accommodation state. It is believed that this mismatch results in viewer discomfort. Display systems that provide a better match between accommodation and vergence may produce a more realistic and comfortable simulation of a three-dimensional image.

[0026] Without being limited by theory, it is believed that the human eye can typically interpret a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth can be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. In some embodiments, the different presentations can provide both cues for vergence and matching cues for accommodation, thereby providing physiologically correct accommodation-vergence matching.

[0027] 4B, two depth planes 240 are illustrated that correspond to different distances in space from the eyes 210, 220. For a given depth plane 240, vergence cues may be provided by displaying appropriately different perspective images for each eye 210, 220. In addition, for a given depth plane 240, the light forming the image provided for each eye 210, 220 may have a wavefront divergence that corresponds to the light field produced by a point at the distance of that depth plane 240.

[0028] In the illustrated embodiment, the distance along the z-axis of the depth plane 240 containing the point 221 is 1 m. As used herein, the distance or depth along the z-axis may be measured with the zero point located at the exit pupil of the user's eye. Thus, the depth plane 240 located at a depth of 1 m corresponds to a distance of 1 m away from the exit pupil of the user's eye on the optical axis of those eyes with the eyes pointed at optical infinity. As an approximation, the depth or distance along the z-axis may be measured from the display (e.g., the surface of the waveguide) in front of the user's eye, and a value for the distance between the device and the exit pupil of the user's eye may be added. That value may be called the pupil distance and may correspond 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.

[0029] 4C and 4D, examples of matched accommodation-vergence distance and mismatched accommodation-vergence distance are illustrated, respectively. As illustrated in FIG. 4C, the display system may provide an image of a virtual object to each eye 210, 220. The image may cause the eyes 210, 220 to assume a vergence state in which the eyes converge on point 15 on the depth plane 240. In addition, the image may be formed by light having a wavefront curvature corresponding to a real object in that depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the image is focused on the retinas of those eyes. Thus, the user may perceive the virtual object as being at point 15 on the depth plane 240.

[0030] It should be appreciated that each of the accommodation and vergence states of the eyes 210, 220 is associated with a particular distance on the z-axis. For example, objects at particular distances from the eyes 210, 220 cause those eyes to assume a particular accommodation state based on the distance of the object. The distance associated with a particular accommodation state is referred to as the accommodation distance A. d Similarly, a particular vergence distance V associated with an eye during a particular vergence state may be referred to as d or positions relative to each other. When the accommodation distance and the vergence distance match, the relationship between accommodation and vergence is said to be physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0031] However, in a stereoscopic display, the accommodation distance and the vergence distance may not necessarily coincide. For example, as illustrated in FIG. 4D, the images displayed to the eyes 210, 220 may be displayed with a wavefront divergence corresponding to the depth plane 240, and the eyes 210, 220 may assume a particular accommodation state that focuses on points 15a, 15b on the depth plane. However, the images displayed to the eyes 210, 220 may provide a cue for vergence that causes the eyes 210, 220 to converge on a point 15 that is not located on the depth plane 240. As a result, the accommodation distance corresponds to the distance from the exit pupils of the eyes 210, 220 to the depth plane 240 in some embodiments, while the vergence distance corresponds to a larger distance from the exit pupils of the eyes 210, 220 to the point 15. The accommodation distance is different from the vergence distance. As a result, there is an accommodation-vergence mismatch. Such a mismatch may be considered undesirable and may cause discomfort to the user. d -A d ) and can be characterized in terms of diopters.

[0032] It should be understood that in some embodiments, reference points other than the exit pupils of the eyes 210, 220 may be utilized to determine distances for determining accommodation-vergence discrepancy, so long as the same reference points are utilized for accommodation distance and vergence distance. For example, distances may be measured from the cornea to the depth plane, from the retina to the depth plane, from the ocular lens (e.g., a waveguide of a display device) to the depth plane, etc.

[0033] Without being limited by theory, it is believed that a user may still perceive an accommodation-vergence mismatch of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as physiologically correct, without the mismatch itself causing significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250, FIG. 6) presents a viewer with an accommodation-vergence mismatch of about 0.5 diopters or less. In some other embodiments, the accommodation-vergence mismatch of an image provided by the display system is about 0.33 diopters or less. In still other embodiments, the accommodation-vergence mismatch of an image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0034] FIG. 5 illustrates aspects of an approach for simulating a three-dimensional image by modifying the wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to a user's eye 210. The waveguide 270 may output light 650 with a defined amount of wavefront divergence that corresponds to the wavefront divergence of a bright 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. In addition, it will be illustrated that the user's other eye may be provided with image information from a similar waveguide.

[0035] In some embodiments, a single waveguide may be configured to output light with a set wavefront divergence corresponding to a single or limited number of depth planes, and / or the waveguide may be configured to output light of a limited range of wavelengths. As a result, in some embodiments, multiple waveguides or stacks thereof may be utilized to provide different wavefront divergence for different depth planes and / or to output light of different ranges of wavelengths. It should be understood that as used herein, a depth plane may be a plane or may follow the contour of a curved surface.

[0036] 6 illustrates an example of a waveguide stack for outputting image information to a user. The display system 250 includes a stack of waveguides or a stacked waveguide assembly 260 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. It should be understood that the display system 250 can be considered a bright field display in some embodiments. Additionally, the waveguide assembly 260 can also be referred to as an eyepiece.

[0037] In some embodiments, the display system 250 may be configured to provide a substantially continuous cue for vergence and multiple separate cues for accommodation. The cue for vergence may be provided by displaying a different image to each of the user's eyes, and the cue for accommodation may be provided by outputting light forming images with selectable separate amounts of wavefront divergence. In other words, the display system 250 may be configured to output light with variable levels of wavefront divergence. In some embodiments, each separate level of wavefront divergence corresponds to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, 310.

[0038] Continuing with reference to FIG. 6, the waveguide assembly 260 may include a number of features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or the number of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye with various levels of wavefront curvature or light beam 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. The image input devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to input image information into the waveguides 270, 280, 290, 300, 310, each of which may be configured to distribute incident light across each respective waveguide for output towards the eye 210, as described herein. Light exits output surfaces 410, 420, 430, 440, 450 of the image input devices 360, 370, 380, 390, 400 and is input into corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or may be a portion of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 510 or the viewer's eye 210). In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide and output a total field of cloned collimated beams that are directed towards the eye 210 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 360, 370, 380, 390, 400 may be associated with and launch light into multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0039] In some embodiments, each of the image input devices 360, 370, 380, 390, 400 is a separate display that generates image information for input into the corresponding waveguide 270, 280, 290, 300, 310, respectively. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output of a single multiplexed display that may, for example, send image information via one or more optical conduits (such as fiber optic cables) to each of the image input devices 360, 370, 380, 390, 400. It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different primary colors as discussed herein).

[0040] In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520 that includes a light module 530 that may include light emitters such as light emitting diodes (LEDs). Light from the light module 530 may be directed through a beam splitter 550 to and modified by a light modulator 540, e.g., a spatial light modulator. The light modulator 540 may be configured to vary the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 and encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It should be understood that image injection devices 360, 370, 380, 390, 400 are illustrated diagrammatically and in some embodiments these image injection devices may represent different light paths and locations in a common projection system configured to output light into associated ones of waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of waveguide assembly 260 may act as ideal lenses, relaying light injected into the waveguides to the user's eye. In this concept, the object may be a spatial light modulator 540 and the image may be an image on a depth plane.

[0041] 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 to the viewer's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each of which is configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It is understood that one or more optical fibers may be configured to transmit light from the optical module 530 to one or more of the waveguides 270, 280, 290, 300, 310. It is understood that one or more intervening optical structures may be provided between the scanning fiber or fibers and one or more of the waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into one or more of the waveguides 270, 280, 290, 300, 310.

[0042] The 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, the controller 560 is part of the local data processing module 140. The controller 560 includes programming (e.g., instructions in a non-transient medium) that coordinates the timing and provision of image information to the 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 wired or wireless communication channels. The controller 560 may be part of the processing module 140 or 150 (FIG. 9D) in some embodiments.

[0043] Continuing with reference to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each respective waveguide by total internal reflection (TIR). Each of the waveguides 270, 280, 290, 300, 310 may be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between their major top and bottom surfaces. In the illustrated configuration, each of the waveguides 270, 280, 290, 300, 310 may include an outcoupling optical element 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting light propagating within each respective waveguide out of the waveguide and outputting image information to the eye 210. The extracted light may also be referred to as outcoupled light, and the outcoupling optical element light may also be referred to as a light extraction optical element. The extracted beam of light may be output by the waveguide at a location where the light propagating within the waveguide strikes the light extraction optical element. The outcoupling optical element 570, 580, 590, 600, 610 may be, for example, a grating including diffractive optical features as further discussed herein. Although shown disposed on the bottom major surface of the waveguide 270, 280, 290, 300, 310 for ease of explanation and clarity of the drawings, in some embodiments the outcoupling optical element 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguide 270, 280, 290, 300, 310 as further discussed herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be attached to a transparent substrate and formed within a layer of material forming the waveguide 270, 280, 290, 300, 310. In some other embodiments, the waveguide 270, 280, 290, 300, 310 may be a monolithic piece of material and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within that piece of material.

[0044] With continued reference to FIG. 6, as discussed herein, each waveguide 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 (injected into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next upper waveguide 280 may be configured to send collimated light that passes through a first lens 350 (e.g., a negative lens) before it can reach the eye 210. Such a first lens 350 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 closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first 350 and second 340 lenses before reaching the eye 210, and the combined refractive power of the first 350 and second 340 lenses may be configured to produce 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 closer inward toward the person from optical infinity, which was the light from the next upper waveguide 280.

[0045] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power that represents the focal plane closest to the person. To compensate the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be placed on top of the stack to compensate for the aggregate power of the lens stacks 320, 330, 340, 350 below. Such a configuration provides as many perceived focal planes as there are waveguide / lens pairs available. Both the outcoupling 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, either one or both may be dynamic using electroactive features.

[0046] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth planes, with one set per depth plane. This may provide an advantage for forming tiled images to provide an extended field of view at those depth planes.

[0047] Continuing with reference to FIG. 6, the out-coupling optical elements 570, 580, 590, 600, 610 can be configured to redirect light out of their respective waveguides and output this light with an appropriate amount of divergence or collimation for the particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes can have different configurations of out-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 can be volume or surface features that can be configured to output light at a particular angle. For example, the light extraction optical elements 570, 580, 590, 600, 610 can be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, the features 320, 330, 340, 350 may not be lenses; rather, they may simply be spacers (eg, cladding layers and / or structures for forming air gaps).

[0048] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features or "diffractive optical elements" (also referred to herein as "DOEs") that form a diffraction pattern. Preferably, the DOEs have a low enough diffraction efficiency so that only a portion of the light in the beam is deflected towards the eye 210 with 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 related exit beams that exit the waveguide at various locations, resulting in a very uniform pattern of exit emission towards the eye 210 for this particular collimated beam bouncing within the waveguide.

[0049] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not diffract significantly. For example, a switchable DOE may comprise a layer of polymer dispersed liquid crystal in which microdroplets comprise a diffractive pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not 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).

[0050] In some embodiments, a camera assembly 630 (e.g., a digital camera including visible and infrared light cameras) may be provided to capture images of the eye 210 and / or tissue surrounding the eye 210, for example, to detect user input and / or to monitor a physiological condition of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source for projecting light (e.g., infrared light) onto the eye that may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be mounted to the frame 80 (FIG. 9D) and may be in electrical communication with the processing modules 140 and / or 150 that may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized per eye to monitor each eye separately.

[0051] 7, an example of an exit beam output by a waveguide is shown. Although one waveguide is illustrated, it should be understood that other waveguides in the waveguide assembly 260 (FIG. 6) may function similarly and that the waveguide assembly 260 includes multiple waveguides. Light 640 is launched into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as an exit beam 650. The exit beam 650 is illustrated as substantially parallel, but may also be redirected to propagate to the eye 210 at an angle (e.g., forming a diverging exit beam) depending on the depth plane associated with the waveguide 270, as discussed herein. It should be understood that a substantially parallel exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set at a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other sets of waveguides or other outcoupling optics may output a more divergent exit beam pattern, which would require the eye 210 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0052] In some embodiments, a full color image may be formed at each depth plane by overlaying images in each of the primary colors, for example, 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 multiple different primary colors. The illustrated embodiment shows depth planes 240a-240f, but more or less depths are also envisioned. Each depth plane may have three or more primary color images associated with it, including a first image of a first color G, a second image of a second color R, and a third image of a third color B. The different depth planes are indicated in the diagram by different numbers for diopters (dpt) following the letters G, R, and B. By way of example only, the numbers following each of these letters indicate diopters (1 / m), i.e., the inverse of the distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact location of the depth planes for the different primary colors may vary to account for differences in the eye's focusing of different wavelengths of light. 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.

[0053] In some embodiments, the light of each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figure containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, with three primary color images provided per depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, but it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0054] 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or in place of one or more of red, green, or blue.

[0055] It should be understood that references to a given color of light throughout this disclosure will be understood to encompass one or more wavelengths of light within the range of wavelengths of light perceived by a viewer as being of that given color. For example, red light may include one or more wavelengths of light within the range of about 620-780 nm, green light may include one or more wavelengths of light within the range of about 492-577 nm, and blue light may include one or more wavelengths of light within the range of about 435-493 nm.

[0056] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light at one or more wavelengths outside the range of visual perception of a viewer, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide in-coupling, out-coupling, and other light redirecting structures of the display 250 may be configured to direct and emit this light away from the display toward the user's eye 210, e.g., for imaging and / or user stimulation applications.

[0057] 9A, in some embodiments, light impinging on a waveguide may need to be redirected to in-couple the light into the waveguide. An in-coupling optical element may be used to redirect and in-couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 660 of stacked waveguides, each including an in-coupling optical element. Each of the waveguides may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. It should be understood that the stack 660 may correspond to the stack 260 (FIG. 6), except that light from one or more of the image injection devices 360, 370, 380, 390, 400 is injected into the waveguide from a position that requires the light to be redirected for in-coupling, and the illustrated waveguides of the stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310.

[0058] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated incoupling optical element (which may also be referred to as the light input area on the waveguide), for example, incoupling optical element 700 is disposed on a major surface (e.g., the top major surface) of waveguide 670, incoupling optical element 710 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and incoupling optical element 720 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some embodiments, one or more of the incoupling optical elements 700, 710, 720 may be disposed on a bottom major surface of the respective waveguide 670, 680, 690 (particularly, one or more of the incoupling optical elements are reflective polarizing optical elements). As shown, the incoupling optical elements 700, 710, 720 may be disposed on the upper major surfaces of their respective waveguides 670, 680, 690 (or on top of the next lower waveguide), and in particular, the incoupling optical elements are transmissive polarizing optical elements. In some embodiments, the incoupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the incoupling 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 on one side or corner of their respective waveguides 670, 680, 690, it should be understood that the incoupling optical elements 700, 710, 720 may be disposed within other areas of their respective waveguides 670, 680, 690 in some embodiments.

[0059] As shown, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset such that it receives light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from a different image input device 360, 370, 380, 390, and 400, as shown in FIG. 6, and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 700, 710, 720 such that it does not receive substantially any light from others of the in-coupling optical elements 700, 710, 720.

[0060] Each waveguide also includes an associated light distribution element, for example, light distribution element 730 is disposed on a major surface (e.g., a top major surface) of waveguide 670, light distribution element 740 is disposed on a major surface (e.g., a top major surface) of waveguide 680, and light distribution element 750 is disposed on a major surface (e.g., a top major surface) of waveguide 690. In some other embodiments, light distribution elements 730, 740, 750 may be disposed on the bottom major surfaces of the associated waveguides 670, 680, 690, respectively. In some other embodiments, the light distribution elements 730, 740, 750 may be disposed on both the top and bottom major surfaces of the associated waveguides 670, 680, 690, respectively, or the light distribution elements 730, 740, 750 may be disposed on different ones of the top and bottom major surfaces of different associated waveguides 670, 680, 690, respectively.

[0061] The waveguides 670, 680, 690 may be spaced apart and separated, for example, by gas, liquid, and / or solid layers 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 index material (i.e., a material having a lower index of refraction than the material forming the immediately adjacent ones of the waveguides 670, 680, 690). Preferably, the index of refraction of the material forming layers 760a, 760b is 0.05 or greater, or 0.10 or less, than the index of refraction of the material forming the waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may act as cladding layers to promote total internal reflection (TIR) ​​of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 660 may include immediate cladding layers.

[0062] Preferably, for ease of manufacturing and other considerations, the materials forming the waveguides 670, 680, 690 are similar or the same, and the materials forming the layers 760a, 760b are similar or the same. In some embodiments, the materials forming the waveguides 670, 680, 690 may vary between one or more of the waveguides, and / or the materials forming the layers 760a, 760b may differ while still maintaining the various refractive index relationships described above.

[0063] 9A, light rays 770, 780, 790 are incident on the set of waveguides 660. It should be understood that light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0064] In some embodiments, the light beams 770, 780, 790 have different characteristics, e.g., different wavelengths or different ranges of wavelengths, that may correspond to different colors. Each of the incoupling optical elements 700, 710, 720 deflects incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optical elements 700, 710, 720 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

[0065] For example, incoupling optical element 700 may be configured to selectively deflect light beam 770 having a first wavelength or wavelength range while transmitting light beams 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. The transmitted light beam 780 impinges on and is deflected by incoupling optical element 710 configured to selectively deflect light of the second wavelength or wavelength range. Light beam 790 is deflected by incoupling optical element 720 configured to selectively deflect light of the third wavelength or wavelength range.

[0066] 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the incoupling optical elements 700, 710, 720 of each waveguide deflect the light into its corresponding waveguide 670, 680, 690 and incoupling the light into its corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguides 670, 680, 690 by TIR until they impinge on the corresponding light distribution elements 730, 740, 750 of the waveguides.

[0067]

[0046] Referring now to Figure 9B, a perspective view of the example of multiple stacked waveguides of Figure 9A is illustrated. As described above, the in-coupled light rays 770, 780, 790 are deflected by the in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within the waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then impinge on the light distribution elements 730, 740, 750, respectively. The light distribution elements 730, 740, 750 deflect the light rays 770, 780, 790 to propagate towards the out-coupling optical elements 800, 810, 820, respectively.

[0068] In some embodiments, the light distribution elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse the light to the out-coupling optical elements 800, 810, 820, and in some embodiments may also increase the beam or spot size of the light as it propagates to the out-coupling optical elements. In some embodiments, the light distribution elements 730, 740, 750 may be omitted and the in-coupling optical elements 700, 710, 720 may be configured to deflect the light directly to the out-coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the light distribution elements 730, 740, 750 may be replaced with the out-coupling optical elements 800, 810, 820, respectively. In some embodiments, the outcoupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light to the viewer's eye 210 (FIG. 7). It should be understood that an OPE may be configured to increase the size of the eyebox in at least one axis, and an EPE may be for increasing the eyebox in an axis that intersects (e.g., perpendicular to) the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE of the same waveguide, while allowing the remaining portion of the light to continue propagating along the waveguide. Upon striking the OPE again, another portion of the remaining light is redirected to the EPE, which continues to propagate further along the waveguide, etc. Similarly, upon striking the EPE, a portion of the striking 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 strikes the EP again, at which point another portion of the striking light is directed out of the waveguide, etc. As a result, a single beam of internally coupled light may be "replicated" each time a portion of that light is redirected by an OPE or EPE, thereby forming a cloned beam field of light, as shown in Figure 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0069] Thus, referring to Figures 9A and 9B, in some embodiments, a set of waveguides 660 includes, for each primary color, waveguides 670, 680, 690; in-coupling optical elements 700, 710, 720; light distribution elements (e.g., OPEs) 730, 740, 750; and out-coupling optical elements (e.g., EPs) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical elements 700, 710, 720 redirect or deflect the incoming light into that waveguide (with different in-coupling optical elements receiving different wavelengths of light). The light then propagates at an angle that will result in TIR within each waveguide 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 in the manner described above, then continues to bounce along the waveguide, interacting with the light distribution element (e.g., OPE) 730 and then the out-coupling optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, where light ray 780 strikes the in-coupling optical element 710 and is deflected thereby. Light ray 780 will then bounce along the waveguide 680, via TIR, to its light distribution element (e.g., OPE) 740 and then the out-coupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 and strikes the light in-coupling optical element 720 of the waveguide 690. The light in-coupling optical element 720 deflects the light beam 790 so that it propagates by TIR to the light distribution element (e.g., OPE) 750 and then by TIR to the out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the light beam 790 to a viewer that also receives the out-coupled light from the other waveguides 670, 680.

[0070] FIG. 9C illustrates a top-down plan view of the example of multiple stacked waveguides of FIGS. 9A and 9B. As shown, the waveguides 670, 680, 690 may be vertically aligned with each waveguide's associated light distribution element 730, 740, 750 and associated out-coupling optical elements 800, 810, 820. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the in-coupling optical elements are preferably non-overlapping (e.g., spaced apart laterally as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a particular light source to be uniquely coupled to a particular waveguide. In some embodiments, arrangements including non-overlapping, spatially separated in-coupling optical elements may be referred to as shifted pupil systems, and the in-coupling optical elements in these arrangements may correspond to sub-pupils.

[0071] 9D illustrates an example of a wearable display system 60 into which the various waveguide and associated systems disclosed herein may be integrated. In some embodiments, the display system 60 is the system 250 of FIG. 6, which diagrammatically shows some portions of the system 60 in greater detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0072] 9D , the display system 60 includes a display 70 and various mechanical and electronic modules and systems to support the functionality of the display 70. The display 70 may be coupled to a frame 80 that is wearable by a display system user or viewer 90 and configured to position the display 70 in front of the user's 90 eye. The display 70 may be considered eyewear in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the ear canal of the user 90 (in some embodiments, another speaker, not shown, may also be optionally positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). The display system 60 may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphones may be configured to allow the user to provide input or commands (e.g., voice menu command selections, natural language queries, etc.) to the system 60 and / or enable audio communication with other persons (e.g., other users of similar display systems). The microphone may further be configured as an ambient sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may also include ambient sensors 120a that are separate from the frame 80 and may be mounted on the body of the user 90 (e.g., the head, torso, limbs, etc. of the user 90). The ambient sensors 120a may, in some embodiments, be configured to obtain data that characterizes a physiological state of the user 90. For example, the sensors 120a may be electrodes.

[0073] 9D, the display 70 is operably coupled by a communication link 130, such as by wired leads or wireless connectivity, to a local data processing module 140, which may be mounted in a variety of configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in headphones or otherwise removably attached to the user 90 (e.g., in a backpack configuration, in a belt-connected configuration). Similarly, the sensor 120a may be operably coupled to the local processor and data module 140 by a communication link 120b, such as by wired leads or wireless connectivity. The local processing and data module 140 may comprise a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or hard disk drive), both of which may be utilized to aid in processing, caching, and storing 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 (which may be operatively coupled to the frame 80 or otherwise attached to the user 90), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein, and / or b) data obtained and / or processed using the remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for processing or readout and then passage to the display 70. The local processing and data module 140 may be operatively coupled to the remote processing module 150 and the remote data repository 160 by communications links 170, 180, such as via wired or wireless communication links, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to the local processing and data module 140.In some embodiments, local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be mounted on frame 80 or may be a stand-alone structure that communicates with local processing and data module 140 by a wired or wireless communication path.

[0074] 9D , in some embodiments, the remote processing module 150 may comprise one or more processors configured to analyze and process the data and / or image information, including, for example, one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. In some embodiments, the remote data repository 160 may comprise a digital data storage facility that 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 remote servers that provide information to the local processing and data module 140 and / or the remote processing module 150, for example, information for generating augmented reality content. In some embodiments, all data is stored and all calculations are performed within the local processing and data module, allowing for fully autonomous use from the remote modules. Optionally, an external system (e.g., one or more processors, one or more computer systems) including a CPU, GPU, etc. may perform at least a portion of the processing (e.g., processing the data to generate image information) and provide and receive information from the modules 140, 150, 160, for example, via a wireless or wired connection.

[0075] (Liquid crystal material for adaptive lens assembly) In general, liquid crystals possess physical properties that may be intermediate between traditional fluids and solids. Liquid crystals are fluid-like in some aspects, but unlike most fluids, the arrangement of molecules within liquid crystals exhibits some structural order. Different types of liquid crystals include thermotropic, lyotropic, and polymeric liquid crystals. The thermotropic liquid crystals disclosed herein can be implemented in a variety of physical states, e.g., phases, including nematic states / phases, smectic states / phases, chiral nematic states / phases, or chiral smectic states / phases.

[0076] As described herein, liquid crystals in a nematic state or phase can have relatively little positional order, but long-range directional order, with calamitic (rod-shaped) or discotic (disk-shaped) organic molecules whose long axes are substantially parallel. Thus, the organic molecules can flow freely, with their center of mass positions randomly distributed as in a liquid, while still maintaining their long-range directional order. In some implementations, liquid crystals in the nematic phase can be uniaxial, i.e., the liquid crystals have one axis that is longer and preferred, and the other two are approximately equal. In some implementations, the liquid crystal molecules are aligned along their long axes. In other implementations, the liquid crystals can be biaxial, i.e., in addition to aligning their long axes, the liquid crystals can also be aligned along secondary axes.

[0077] As described herein, liquid crystals in a smectic state or phase can have organic molecules that form relatively well-defined layers that can slide over one another. In some implementations, liquid crystals in a smectic phase can be positionally ordered along one direction. In some implementations, the long axes of the molecules can be oriented along a direction substantially perpendicular to the plane of the liquid crystal layer, while in other implementations, the long axes of the molecules can be tilted relative to the direction perpendicular to the plane of the layer.

[0078] Here, and throughout this disclosure, nematic liquid crystals consist of rod-shaped molecules with the long axes of neighboring molecules approximately aligned with each other. To describe this anisotropic structure, a dimensionless unit vector n, called the director, may be used to describe the direction of preferred orientation of the liquid crystal molecules.

[0079] Here, and throughout this disclosure, the azimuthal angle or rotation angle φ is used to describe the angle of rotation of liquid crystal molecules around an axis perpendicular to the layer normal direction or major surface of the liquid crystal layer, and is measured in a plane parallel to the major surfaces of the liquid crystal layer or substrate (e.g., the xy plane) and is measured between the alignment direction (e.g., the stretch direction or director direction) and a direction parallel to the major surfaces (e.g., the y-direction).

[0080] It should be understood that here, and throughout this disclosure, when angles, such as rotation angle φ, are referred to as being substantially the same or different between different regions, the average angles may be, for example, within about 1%, about 5%, or about 10% of each other, although the average angles may be greater in some cases.

[0081] As described herein, some liquid crystals in the nematic or smectic state can exhibit a twist in the layer normal direction. Such liquid crystals are referred to as twisted nematic (TN) or twisted smectic (SN) liquid crystals. TN or SN liquid crystals can exhibit molecular twisting around an axis perpendicular to the director, with the molecular axis parallel to the director. When the degree of twist is relatively large, the twisted liquid crystal can be referred to as a chiral or cholesteric phase.

[0082] As described herein, TN or SN liquid crystals may be described as having a twist angle or net twist angle (φ), which may refer to, for example, the relative azimuthal rotation between the top and bottom liquid crystal molecules across a defined length, e.g., the thickness of a liquid crystal layer.

[0083] As described herein, a "polymerizable liquid crystal" may refer to a liquid crystal material that can be polymerized (e.g., photopolymerized in situ), which may also be described herein as a reactive mesogen (RM).

[0084] The liquid crystal molecules, in some embodiments, may be polymerizable and, when polymerized, may form a large-scale network with other liquid crystal molecules. For example, the liquid crystal molecules may be linked by chemical bonds or by linking chemical species to other liquid crystal molecules. When joined together, the liquid crystal molecules may form liquid crystal domains that have substantially the same orientation and location as before they were linked together. The term "liquid crystal molecules" may refer to both the liquid crystal molecules before polymerization and the liquid crystal molecules formed by these molecules after polymerization. When polymerized, the polymerized network may be referred to as a liquid crystal polymer (LCP).

[0085] In some embodiments, prior to being polymerized, unpolymerized or polymerizable liquid crystal molecules may have at least a limited degree of rotational freedom. These unpolymerized liquid crystal molecules may, for example, rotate or tilt under electrical stimulation, which results in alteration of optical properties. For example, by applying an electric field, some liquid crystal layers containing unpolymerized liquid crystal molecules may be switched between one or more states with different diffraction or polarization alteration properties.

[0086] The inventors have recognized that the above-described properties of liquid crystals or reactive mesogens (RMs) can be advantageously applied to various components of the switchable waveplates and waveplate lenses disclosed herein. For example, in some unpolymerized RMs, the orientation of LC molecules can be modified after deposition, for example, by application of an external stimulus, such as an electric field. Based on this recognition, the inventors herein disclose waveplates and waveplate lenses that can be switched between multiple states by application of an external stimulus.

[0087] In addition, the inventors have recognized that the orientation of LC molecules at the surface or interface of some LC or RM when not polymerized can be aligned by controlling the surface or interface on which the LC molecules are formed. For example, a stack of multiple LC layers can be formed, and by controlling the orientation of the LC molecules closest to the surface of an LC layer, the orientation of the directly adjacent LC in the next LC layer can be controlled to have, for example, the same orientation as the LC molecules closest to the surface in the previous LC layer, or the same orientation as the elongated microstructures in the adjacent layer. In addition, the LC molecules between the LC molecules at the surface or interface can be controlled to have a predetermined amount of twist. Based on the recognition of these and other attributes, including birefringence, chirality, and ease for multiple coatings, the inventors herein disclose waveplates and waveplate lenses with tailored optical properties, such as useful properties such as broadband capability with diffraction efficiency, refractive power, and polarization, to name a few.

[0088] Display device having adaptive lens assembly As described above with reference to FIG. 6, some display systems according to embodiments include a waveguide assembly 260 configured to form images at multiple virtual depth planes. The waveguide assembly 260 includes waveguides 270, 280, 290, 300, 310, each configured to propagate light by total internal reflection (TIR), and includes out-coupling optical elements 570, 580, 590, 600, 610, each configured to extract light out of a respective one of the waveguides 270, 280, 290, 300, 310 by redirecting the light. Each of the waveguides 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. The waveguide assembly 260 may also optionally include multiple lenses 320, 330, 340, 350 between the waveguides to provide different refractive powers for forming images at different virtual depth planes.

[0089] In the illustrated embodiment of the waveguide assembly 260 in FIG. 6, the number of depth planes may be directly proportional to the number of waveguides and lenses. However, the inventors have recognized various challenges associated with implementing a waveguide assembly configured to display images at multiple depth planes by having a proportional number of waveguides and lenses. For example, a large number of waveguides 270, 280, 290, 300, 310 and a large number of corresponding lenses 320, 330, 340, 350 may undesirably increase the overall thickness, weight, cost, and manufacturing challenges for the waveguide assembly 260. For example, when formed from conventional lens materials, e.g., glass, each of the lenses 320, 330, 340, 350 may add several millimeters or tens of millimeters of thickness and corresponding weight to the display. In addition, a large number of waveguides and lenses may create undesirable optical effects for the user, e.g., relatively high absorption losses. Thus, in one aspect, the inventors have recognized potential advantages for display systems that may generate images at multiple depth planes using, in some cases, fewer waveguides, fewer lenses, thinner and lighter waveguides and lenses, and / or fewer lenses per waveguide.

[0090] As used herein, optical power (P, p, or φ), also referred to as refractive power, focusing power, or convergence power, refers to the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the inverse of the focal length of the device: P=1 / f. That is, high optical power corresponds to a short focal length. The SI unit for optical power is commonly the inverse meter (m -1 ).

[0091] As described herein, a converging lens that focuses light passing through it is described as having a positive refractive power, while a diverging lens that defocuses light passing through it is described as having a negative refractive power. Without being bound by theory, when light passes through two or more thin lenses that are relatively close to each other, the refractive power of the combined lenses can be approximated as the sum of the refractive powers of the individual lenses. Thus, when light passes through a first lens with a first refractive power P1 and further passes through a second lens with a second refractive power P2, the light can be understood to converge or diverge according to the sum of the refractive powers Pnet=P1+P2.

[0092] A medium that has an index of refraction that depends on the polarization and direction of propagation of light is said to be birefringent (or double refractive). As explained throughout this specification and understood in the relevant industry, light whose polarization is perpendicular to the optical axis of the birefringent medium experiences the ordinary index of refraction (n o ), and light whose polarization is parallel to the optical axis of the birefringent medium has an extraordinary refractive index (n e ), and the refractive index difference observed in a birefringent medium material is n e -n o is described as having a birefringence Δn. The phase delay of light in a material medium with birefringence Δn can be expressed as Γ=2πΔnd / λ at different λ, where d is the thickness of the medium.

[0093] As described herein, a "transmissive" or "transparent" structure, e.g., a transparent substrate, may allow at least a portion, e.g., at least 20, 30, 50, 70, or 90%, of incident light to pass therethrough. Thus, a transparent substrate may be a glass, sapphire, or polymer substrate in some embodiments. In contrast, a "reflective" structure, e.g., a reflective substrate, may reflect at least a portion, e.g., at least 20, 30, 50, 70, 90%, or more, of incident light therefrom.

[0094] FIG. 10 illustrates an example of a display device 1000 (e.g., a wearable display device) equipped with one or more adaptive lens assemblies, which include a polarization-selective lens stack, e.g., a pair of adaptive lens assemblies 1004, 1008 in an optical path 1016, with a waveguide assembly 1012 inserted between the pair of adaptive lens assemblies 1004, 1008. As described above, the waveguide assembly includes a waveguide configured to propagate light (e.g., visible light) under total internal reflection and to outcouple light in an optical axis extending from (e.g., perpendicular to) a light output surface (e.g., a major surface of the waveguide) of the waveguide. The light may be outcoupled by a diffraction grating in some embodiments. Each of the adaptive lens assemblies 1004, 1008 may be configured to at least partially transmit the light outcoupled therethrough. In the illustrated embodiment, each of the adaptive lens assemblies may be configured to receive outcoupled light from the waveguide assembly 1012 and to converge or diverge the outcoupled light along an optical axis. Each of the adaptive lens assemblies 1004, 1008 comprises a polarization-selective lens stack comprising a birefringent lens and an isotropic lens in contact with each other, the contact surfaces of the birefringent lens and the isotropic lens forming a form-matching interface therebetween. The adaptive lens assemblies are configured to be selectively switched between a plurality of states having different refractive powers. The adaptive lens assemblies are configured to modify the polarization state of the outcoupled light passing therethrough when activated (e.g., electrically activated).

[0095] As used herein, an adaptive lens assembly refers to a lens assembly having at least one optical property that can be adjusted (e.g., reversibly activated and deactivated using an external stimulus). Exemplary optical properties that can be reversibly activated and deactivated include refractive power (focal length), phase, polarization, polarization selectivity, transmittance, reflectance, birefringence, and diffraction properties, among other properties. In various embodiments, an adaptive lens assembly is capable of electrically varying the refractive power and polarization state of light passing through it.

[0096] In the illustrated embodiment, each of the pair of adaptive lens assemblies 1004, 1008 is configured to be selectively switched between at least two states, such that in a first state, each is configured to pass the outcoupled light through it without altering its polarization state, while in a second state, each is configured to alter the polarization state of the outcoupled light passing through it. For example, in the second state, each of the adaptive lens assemblies 1004, 1008 reverses the handedness of circularly polarized light, while in the first state, each of the broadband adaptive lens assemblies 1004, 1008 preserves the handedness of circularly polarized light.

[0097] Still referring to FIG. 10, the display device 1000 further comprises a waveguide assembly 1012 interposed between the pair of adaptive lens assemblies 1004, 1008. The waveguide assembly 1012 may be similar to the waveguide assembly 260 described above with respect to FIG. 6, which comprises one or more waveguides similar to one or more of the waveguides 270, 280, 290, 300, 310 in FIG. 6. For example, as described above with respect to FIGS. 6 and 7, the waveguide may be configured to propagate light in a lateral direction parallel to the major surfaces of the waveguide under total internal reflection. The waveguide may be further configured to outcouple light, for example, in a direction perpendicular to the major surfaces of the waveguide.

[0098] Still referring to FIG. 10 , a first adaptive lens assembly 1004 of the pair of adaptive lens assemblies is disposed on a first side of the waveguide assembly 1012, e.g., the side of the world 510 observed by the user, and a second adaptive lens assembly 1008 of the pair of lens assemblies is disposed on a second side of the waveguide assembly 1012, e.g., the side of the user's eye 210. The pair of adaptive lens assemblies as configured as described below provide the user with virtual content from the waveguide assembly 1012 in multiple virtual depth planes along with a view of the real world. In some embodiments, there is little or no distortion due to the presence of the pair of adaptive lens assemblies. The virtual content and the view of the real world are provided to the user upon activation of the first and second adaptive lens assemblies 1004, 1008, as described below with respect to FIGS. 11A and 11B.

[0099] 11A and 11B respectively illustrate examples of display devices 1100A / 1100B with adaptive lens assemblies and that, in operation, output image information to a user. In an unpowered state, the display devices 1100A and 1100B are structurally identical in some embodiments. The display device 1100A is used here to describe outputting a virtual image to a user, while the display device 1100B is used here to describe transmitting a real-world image to a user through the display device 1100B. The display devices 1100A / 1100B include a pair of switchable lens assemblies 1004, 1008 configured to be electrically activated, e.g., by application of a voltage or current. In some embodiments, in an inactive state, e.g., when no voltage or current is applied, each of the first and second switchable lens assemblies 1004, 1008 has a low, e.g., about zero, optical power. In some embodiments, for example, in an active state with a voltage or current applied, the first adaptive lens assembly 1004 on the world side may provide a first net refractive power (Pnet1) having a first sign, e.g., positive refractive power. When in the active state, the second adaptive lens assembly 1008 on the user side may provide a second net refractive power (Pnet2) having a second sign, e.g., negative refractive power. However, the embodiments are not so limited, and in other embodiments, the first and second adaptive lens assemblies may provide substantially zero refractive power when activated while providing a refractive power in the inactive state.

[0100] FIG. 11A illustrates an example of the display system of FIG. 10 displaying virtual content to a user in a virtual depth plane according to some embodiments. As described above, a waveguide assembly 1012 inserted between a pair of adaptive lens assemblies 1004, 1008 includes a waveguide configured to receive light containing virtual image information and propagate the light under total internal reflection. The waveguide assembly 1012 is further configured to outcouple the light toward the eye 210, for example, through a diffraction grating. The outcoupled light passes through the second adaptive lens assembly 1008 prior to entering the eye 210. When activated, the second adaptive lens assembly 1008 has a second net refractive power Pnet2, which may have a negative value, such that the user sees a virtual image in the virtual depth plane 1104.

[0101] In some embodiments, the second net refractive power Pnet2 may be electrically adjusted to adjust the second net refractive power (Pnet2) of the second adaptive lens assembly 1008, thereby adjusting the distance to the virtual depth plane 1104. For example, as a virtual object "moves" closer and farther relative to the eye 210 in the virtual three-dimensional space, the second net refractive power Pnet2 of the second adaptive lens assembly 1008 may be correspondingly adjusted such that the virtual depth plane 1104 is adjusted to track the virtual object. Thus, the user may experience relatively little or no accommodation / vergence mismatch beyond a tolerance threshold. In some embodiments, the magnitude of the distance to the virtual depth plane 1104 may be adjusted in discrete steps, while in some other embodiments, the magnitude of the distance to the virtual depth plane 1104 may be adjusted continuously.

[0102] FIG. 11B illustrates an example of the display system of FIG. 10 providing a user with a view of real-world content according to some embodiments. When the second adaptive lens assembly 1008 is activated to have a second net refractive power (Pnet2) for displaying virtual content in the virtual depth plane 1104, light from the real world passing through the second adaptive lens assembly 1008 may also be made to converge or diverge according to the Pnet2 of the activated second adaptive lens assembly 1008. Thus, objects in the real world may appear out of focus or distorted. To mitigate such distortion, according to an embodiment, when activated, the first and second adaptive lens assemblies 1004, 1008 may be configured to have refractive powers with opposite signs. In some embodiments, light passing through the first and second adaptive lens assemblies 1004, 1008 converges or diverges according to a combined refractive power having a magnitude that is approximately the difference between the magnitudes of the first and second net refractive powers Pnet1, Pnet2 of the first and second adaptive lens assemblies 1004, 1008, respectively. In some embodiments, the waveguide assembly 1012 may also have a refractive power, and the adaptive lens assembly 1008 may be configured to account for distortions caused by both the lens assembly 1004 and the waveguide assembly 1012. For example, the refractive power of the adaptive lens assembly 1008 may be opposite in sign to the sum of the refractive powers of the lens assembly 1004 and the waveguide assembly 1012.

[0103] In some embodiments, the first adaptive lens assembly 1004 is configured to have a first net refractive power Pnet1 having a magnitude that is close to or the same as the magnitude of a second net refractive power Pnet2, while having an opposite sign, of the second adaptive lens assembly 1008. As a result, when both the first and second adaptive lens assemblies 1004, 1008 are activated simultaneously, objects in the real world will appear relatively unaffected by the refractive power of the second adaptive lens assembly 1008, which is provided to display virtual content.

[0104] In some embodiments, the first adaptive lens assembly 1004 may be configured such that, when activated, the first net refractive power Pnet1 dynamically matches the second net refractive power Pnet2 of the second adaptive lens assembly 1008. For example, as the second net refractive power Pnet1 of the second switchable assembly 1008 is adjusted to track a virtual object moving in a virtual three-dimensional space, the first net refractive power Pnet1 of the first adaptive lens assembly 1004 may be dynamically adjusted such that the magnitude of the combined refractive power P=Pnet1+Pnet2 may be kept below a predetermined value. Thus, according to an embodiment, an object in the real world may be dynamically adjusted such that the magnitude of the combined refractive power P=Pnet1+Pnet2 is small, e.g., approximately 0 m. -1 By compensating the second net refractive power (Pnet2) of the second adaptive lens assembly 1008, which may have a negative value, with the first net refractive power (Pnet1) of the first adaptive lens assembly 1004 so that the second net refractive power (Pnet2) of the second adaptive lens assembly 1008 remains negative, unacceptable defocus can be prevented.

[0105] Polarization-selective lens stack with birefringent and isotropic lenses for an adaptive lens assembly Various embodiments described herein provide an adaptive lens assembly including a polarization-selective lens stack. In some implementations, the polarization-selective lens stack comprises birefringent lenses, e.g., a Fresnel birefringent lens and an isotropic lens, in contact with each other. Such assemblies may be compact (e.g., may have a reduced thickness) and / or lightweight. These assemblies may also potentially provide various advantageous optical functionalities, such as high bandwidth, increased switching speed, reduced chromatic aberration, increased ease of matching, and / or variable refractive power. In addition, various embodiments described herein may provide an adaptive lens assembly with a relatively low amount of leakage light that may otherwise lead to a "persistent" image. According to various embodiments, the adaptive assembly comprises a polarization-selective lens stack comprising a birefringent lens and an isotropic lens, as described herein.

[0106] 12A, to provide images at multiple depth planes with high efficiency over a wide range of the visible spectrum, an adaptive lens assembly according to various embodiments includes a polarization-selective lens stack 1200 configured to exert a polarization-dependent refractive power on linearly polarized light. The polarization-selective lens stack 1200 comprises a birefringent lens 1204 having an optical axis 1202 extending in a lateral direction, e.g., in an x-direction or y-direction perpendicular to the direction of light propagation (e.g., z-direction). The birefringent lens 1204 has a birefringent index (Δn). As explained above, Δn is determined by the extraordinary refractive index (n e ) and the normal refractive index (n o ) The birefringent lens 1204 can have a radius of curvature (R1) such that it is configured to exert a first refractive power (p1) on light passing through it and having a polarization direction parallel to the optical axis, and a second refractive power (p2) on light passing through it and having a polarization direction perpendicular to the optical axis.

[0107] The polarization-selective lens stack 1200 additionally has a refractive index (n c ) and an isotropic lens 1208 having a second radius of curvature (R2) such that it is configured to exert a third refractive power on light passing therethrough, the third refractive power being opposite in sign to the first refractive power (p1) and the second refractive power (p2).

[0108] In the illustrated embodiment, without limitation, n of the isotropic lens 1208 c is the n of the birefringent lens 1204 o However, n c In some other embodiments, n o It should be understood that the number of sigma-based filters may vary.

[0109] In the illustrated embodiment, without limitation, the first radius of curvature (R1) and the second radius of curvature (R2) are substantially the same in magnitude (R) but have opposite signs. Furthermore, because R1 and R2 are substantially the same in magnitude, the birefringent lens 1204 and the isotropic lens 1208 are in continuous contact along an interface having a radius of curvature R. That is, the contacting surfaces of the birefringent lens 1204 and the isotropic lens 1208 form a conformal interface therebetween.

[0110] 12B, the polarization-selective lens stack 1200 is illustrated in operation when the incident light 1212, e.g., linearly polarized light, has a direction of polarization that is parallel to the direction of the optical axis 1202. Under this condition, light passing through the birefringent lens 1204 is polarized as n e Light passing through the isotropic lens 1208 experiences a refractive index corresponding to n o Thus, the lens stack 1200 experiences a refractive index corresponding to

number

[0111] 12C, the polarization-selective lens stack 1200 is illustrated in operation when incident light 1216, e.g., linearly polarized light, has a direction of polarization that is perpendicular to the direction of the optical axis 1202. Under this condition, light passing through the birefringent lens 1204 experiences n o is the same as n e Thus, the lens stack 1200 experiences a refractive index corresponding to

number

[0112] 12A-12C, in some embodiments, the isotropic lens 1208 may be formed from an isotropic material, such as glass, acrylic, etc. On the other hand, the birefringent lens 1204 may be formed from or comprise a birefringent material, such as liquid crystal, according to various embodiments. For example, the birefringent lens 1204 may comprise a transparent substrate, such as a glass substrate, having liquid crystal (LC) molecules formed thereon that are elongated along a lateral direction (e.g., x-direction or y-direction) perpendicular to the light propagation direction (e.g., z-direction).

[0113] However, embodiments are not so limited and in other embodiments, the birefringent lens 1204 may be formed from or comprise a suitable birefringent material other than LC. For example, the birefringent lens 1204 may comprise, for example, BaB2O4, Be3Al2(SiO3)6, CaCO3LiNbO3TiO2SiC, tourmaline, and ZrSiO4, to name a few.

[0114] Polarization-selective lens stack with birefringent Fresnel and isotropic lenses for an adaptive lens assembly 12A-12C, a lens stack comprising a birefringent lens, e.g., an LC-based birefringent lens, and an isotropic lens, can provide a polarization-selective lens effect. In the following, a polarization-selective lens stack comprising a liquid crystal-based birefringent lens configured as a Fresnel lens is described.

[0115] A Fresnel lens may comprise a thin plate-type lens, for example a split prismatic structure formed by dividing a conventional curved (e.g., spherical) lens into a set of sections (e.g., concentric annular sections known as Fresnel zones). The Fresnel zones replace the continuous curvature of a continuous refractive lens with a set of identically shaped surfaces with discontinuities between them. Substantial reductions in thickness can be achieved by employing such split sections, and lenses with relatively large apertures can be manufactured using less material.

[0116] 13A illustrates a cross-sectional side view of the lens stack 1200 described above with respect to FIGS. 12A-12C annotated with relevant optical dimensions including the distance R from the focal point to a given location on the birefringent lens 1204, the radial distance A from a central axis (e.g., optical axis) of the lens stack 1200 to the given location, the angle θ defined by the distances R and A, and the thickness d of the curved portion of the birefringent lens 1204. As described above, in various implementations, the birefringent lens 1204 and the isotropic lens 1208 have substantially the same radii of curvature, such that the birefringent lens 1204 and the isotropic lens 1208 are in continuous contact along an interface formed therebetween having a radius of curvature R.

[0117] FIG. 13B illustrates a cross-sectional side view 1300A (top) and a top-down view 1300B (bottom) of a lens stack 1300 comprising a birefringent Fresnel lens 1304 and a corresponding lens, e.g., an isotropic Fresnel lens 1308. By employing the Fresnel lens 1304, the groove thickness d' of the curved portion of the birefringent lens 1304 can be substantially reduced. Despite the substantially reduced thickness d', the lens stack 1300 has a corresponding curvature, such as an effective radius of curvature R, which corresponds to the actual radius of curvature R of the conventional lens illustrated with respect to FIG. 13A. Thus, although not illustrated, the lens stack 1300A may additionally have a radial distance A of a given Fresnel zone or groove 1306 from the central axis of the lens stack 1300. k and distances R and A k 13B, despite grooves separating the Fresnel zones, the birefringent Fresnel lens 1304 and the isotropic lens 1308 are in continuous contact throughout the interface formed therebetween having an effective radius of curvature R. In some embodiments, successive Fresnel zones in the radially outward direction are spaced apart by different radial distances A kand different distances between adjacent grooves 1306. For example, in the illustrated embodiment, the distance between adjacent Fresnel zones is smaller in the radial outward direction of the birefringent Fresnel lens 1304. However, the embodiment is not so limited, and in other embodiments, the radial distance A of successive Fresnel zones may be smaller than k may increase linearly with a constant distance between adjacent Fresnel zones, while having different groove thicknesses within each zone, providing a similar or the same optical effect as the illustrated embodiment.

[0118] 13B (bottom), a birefringent Fresnel lens 1304 is shown with multiple concentric Fresnel zones according to an embodiment. The birefringent Fresnel lens 1304 has a radius A k According to various embodiments, the birefringent lens 1304 has a groove thickness d′ that defines a path length that is a multiple of the design wavelength λ (i.e., n e The kth Fresnel zone is designed such that d'=mλ). This arrangement can produce a phase jump of 2πm between the zones, leading to the same wavefront. The value of d' can be chosen (e.g., optimized) to balance processing tolerances and to reduce or minimize aberrations that may result from the sharp edges of the grooves 1316. In one example, the radius R of the kth Fresnel zone can be calculated by setting the thickness of the curved region to be kd', according to the following equation:

number

[0119] In some embodiments, the birefringent Fresnel lens 1304 includes LC. The LC molecules may be laterally oriented or have an elongation direction that extends substantially in the lateral direction 1320 (e.g., y direction) indicated by the arrow. In addition, the alignment direction of the LC molecules may be substantially uniform throughout the thickness of the birefringent Fresnel lens 1304 without undergoing rotation. That is, the local director n of the LC molecules may be substantially constant laterally across the area (e.g., in the z direction) and vertically across the thickness of the birefringent Fresnel lens 1304. The illustrated alignment may be suitable, for example, to provide polarization selectivity for linearly polarized light. In these embodiments, linearly polarized light having a polarization direction (e.g., y direction) that is parallel to the direction of the LC alignment is selected as n e or n o whereas linearly polarized light with a polarization direction perpendicular to the direction of LC alignment (e.g., x direction) experiences one of n e or n o As a result, lens stack 1300 exerts a refractive power of Δn / R on light having one linear polarization while exerting substantially zero refractive power on light having the other linear polarization, as described above.

[0120] In various embodiments herein and throughout the specification, the birefringent Fresnel lens 1304 can have an average, local, mean, central, maximum, or minimum birefringence (Δn) of 0.05-0.10, 0.15-0.20, 0.20-0.25, 0.25-0.30, 0.30-0.35, 0.35-0.40, 0.40-0.45, 0.45-0.50, 0.50-0.55, 0.55-0.60, 0.60-0.65, 0.65-0.70, or any value within any range defined by any of these values, e.g., 0.05-0.40. Additionally, the birefringent Fresnel lens 1304 can have an intralayer birefringence (Δn) range of 0.01-0.05, 0.05-0.10, 0.15-0.20, 0.20-0.25, 0.25-0.30, 0.30-0.35, 0.35-0.40, or any value within any range defined by any of these values.

[0121] In various embodiments herein and throughout the specification, the birefringent Fresnel lens 1304 has a thickness of about 0.1 μm to 200 μm, 0.1 to 5 μm, 5 to 50 μm, 50 to 100 μm, 100 to 150 μm, 150 to 200 μm, or any range value defined by these values, e.g., 5 to 200 μm.

[0122] (Adaptive Lens Assembly Comprising a Polarization-Selective Lens Stack Combined with a Switchable Waveplate) To provide images at multiple depth planes with high efficiency over a wide range of the visible spectrum, an adaptive lens assembly according to various embodiments includes a polarization-selective lens stack (e.g., 1200 in Figs. 12A-12C, 1300 in Fig. 13B) with birefringent and isotropic lenses. According to various embodiments, the adaptive lens assembly can be selectively switched between multiple states with different refractive powers. In the following, an adaptive lens assembly is disclosed in which selective switching is performed by activating or deactivating a switchable waveplate coupled to a polarization-selective lens included in the adaptive lens assembly according to an embodiment.

[0123] 14A, in some embodiments, an adaptive lens assembly 1400A is configured to be activated or deactivated by employing a switchable waveplate 1404 comprising LC in the same optical path as the above-described polarization-selective lens stack 1300 comprising a birefringent Fresnel lens 1304 and an isotropic lens 1308. The Fresnel lens 1304 may be formed using LC or other birefringent materials. The adaptive lens assembly 1400A may be selectively switched between different states by electrically activating and deactivating the switchable waveplate 1404 (or otherwise changing the state of the waveplate, e.g., by applying different voltages). An example of a switchable waveplate 1404 is illustrated with respect to FIG. 14B.

[0124] 14B, in some embodiments, the switchable waveplate 1402 can be a half-waveplate or polarization rotator comprising a layer 1402 of unpolymerized twisted nematic (TN) liquid crystal (LC) or reactive mesogen (RM) comprising TN LC molecules configured to be switched upon application of an electric field across the thickness of the layer 1402 of TN LC. The layer 1402 of TN LC is disposed between a pair of transparent substrates 1412. Each of the transparent substrates 1412 has conductive transparent electrodes 1416, 1420 formed on an inner surface. In some embodiments, the transparent electrodes 1416, 1420 can serve as substrates, and one or both of the substrates 1412 can be omitted.

[0125] The transparent electrodes 1416, 1420 and / or the surface of the substrate 1412 may be configured such that the TN LC molecules in contact with or directly adjacent to the upper electrode 1416 tend to orient with their long axes extending in a first lateral direction, while the TN LC molecules in contact with or directly adjacent to the lower electrode 1420 tend to orient with their long axes extending in a second lateral direction that is transverse to the first lateral direction, e.g., that may form an angle of about 90 degrees with respect to the first lateral direction. Thus, the TN LC molecules between the electrodes 1416, 1420 experience a twist.

[0126] Still referring to FIG. 14B (left), in operation, with no electric field across the TN LC layer 1402 (inactive state), the nematic director of the TN LC molecules undergoes a smooth 90 degree twist across the thickness of the TN LC layer 1402. As shown, incident light 1408 polarized in a first direction (the same direction as the LC molecules closest to the bottom electrode 1412) enters the TN LC layer 1402. The twisted arrangement of the TN LC molecules within the TN LC layer 1402 acts as an optical waveguide, rotating the plane of polarization by a quarter turn (90 degrees) before the light reaches the top electrode 1416. In this state, the TN LC layer 1402 acts to shift the polarization direction of linearly polarized light passing through it from one linear polarization direction to another. Thus, the transmitted light 1406A is polarized in a second direction opposite to the first direction (the same direction as the LC molecules proximate to the top electrode 1416).

[0127] On the other hand, when a voltage exceeding the threshold voltage (V>Vth) of the TN LC switchable waveplate 1404 is applied across the electrodes 1416, 1420 (right, active state), the TN LC molecules in the TN LC layer 1402 tend to align with the resulting electric field, and the optical waveguiding properties of the TN LC layer 1402 described above with respect to the inactive state are lost. In this state, the TN LC layer 1406 serves to preserve the polarization direction of the light passing through it. Thus, the incident light 1408 and the transmitted light 1406B are polarized in the same first direction (the same direction as the LC molecules closest to the bottom electrode 1420). When the electric field is turned off, the TN LC molecules relax back to their twisted state, and the TN LC molecules of the TN LC layer 1402 in the active state return to the configuration of the TN LC molecules of the TN LC layer 1402 in the inactive state (left).

[0128] Still referring to FIG. 14A , in operation, as described above, the polarization-selective lens stack 1300 applies a lens refractive power to the incident light 1420 passing therethrough, depending on the polarization direction of the incident light 1420. After applying or not applying a refractive power thereto, depending on the relative polarization direction of the incident light, the light is incident on the switchable waveplate 1404. As described above, the LC of the switchable waveplate 1404 is configured such that when activated, e.g., electrically activated, the polarization of linearly polarized light passing therethrough is preserved, while when deactivated, e.g., electrically deactivated, the polarization of linearly polarized light passing therethrough is altered, e.g., inverted or rotated. That is, depending on whether the switchable waveplate 1404 is activated or deactivated, a linearly vertically polarized (LVP) light beam is converted to a linearly horizontally polarized (LHP) light beam, or vice versa, or the polarization is preserved.

[0129] In operation, the LC of the birefringent Fresnel lens 1304 is configured such that when the polarization direction of the linearly polarized incident light 1420 is parallel to the optical axis of the birefringent Fresnel lens 1304, the polarization-selective lens stack 1300 exerts a refractive power thereon, as described above with respect to Fig. 12B, while when the polarization direction of the linearly polarized incident light 1420 is perpendicular to the optical axis, the polarization-selective lens stack 1300 exerts substantially zero refractive power thereon, as described above with respect to Fig. 12C. After passing through the birefringent lens stack 1300, when activated, e.g., electrically activated, the polarization of the linearly polarized light passing through the switchable waveplate 1404 is preserved, while when deactivated, e.g., electrically deactivated, the polarization of the linearly polarized light passing through the switchable waveplate 1404 is inverted or rotated due to rearrangement of the liquid crystal molecules.

[0130] With respect to Figures 14A-14B, an adaptive lens assembly is described that includes a passive polarization selective lens stack coupled with a waveplate (Figure 14A) for switchably applying lens power. The inventors recognize that by arranging multiple such elements, an adaptive lens assembly with multiple different lens powers can be formed. Thus, hereinafter, an embodiment of an adaptive waveplate lens assembly is disclosed that includes multiple passive polarization selective lens stacks coupled with a waveplate. Such an adaptive lens assembly can be integrated with a waveguide on either the user side or the world side to form, for example, the display device described with respect to Figures 11A and 11B.

[0131] 15A illustrates an example of an adaptive lens assembly 1500 comprising a plurality of passive polarization-selective lens stacks and a plurality of waveplates arranged in an alternating manner, the adaptive lens assembly 1500 exerting a plurality (e.g., at least four) possible refractive powers on light passing therethrough. The adaptive lens assembly 1500 comprises, in the order in which light passes therethrough, a first switchable waveplate (HWP1) 1404-1, e.g., a switchable half-waveplate, a first polarization-selective lens stack (L1) 1300-1, and a second switchable waveplate (HWP2) 1404-2, e.g., a switchable half-waveplate, and a second polarization-selective lens stack (L2) 1300-2. Each of HWP1 1404-1 and HWP2 1404-2 is configured in a manner similar to that described above with respect to FIGS. 14A and 14B. In addition, each of L1 1300-1 and L2 1300-2 is configured in a manner similar to that described above with respect to Figures 12A-12C and 13A-13B, however, the first polarization-selective lens stack 1300-1 and the second polarization-selective lens stack 1300-2 have different optical axes, different curvatures (e.g., effective radii of curvature), and / or different birefringence. That is, L1 1300-1 has a first optical axis (extending in the vertical or y-direction) and is configured to exert a first refractive power φ1 of Δn1 / R1, or a substantially zero first refractive power φ1, on light having a polarization direction parallel to the optical axis or a perpendicular polarization direction, respectively, incident thereon, while L2 1300-2 has a second optical axis (extending in the horizontal or x-axis) and is configured to exert a second refractive power φ2 of n2 / R2, or a substantially zero second refractive power φ2, on light having a polarization direction parallel to the optical axis or a perpendicular polarization direction, respectively, incident thereon.

[0132] 15B-15E illustrate the adaptive lens assembly 1500 in operation with respect to incident light 1420 having a polarization parallel to the optical axis of L1 1300-1 in four different states corresponding to HWP1 1404-1 / HWP 1404-2 being deactivated (off) / deactivated (off) (FIG. 15B), activated (on) / activated (on) (FIG. 15C), off / on (FIG. 15D), and on / off (FIG. 15E). As explained above, each of HWP1 1404-1 and HWP2 1404-2 has a TN It can be turned off and on, or deactivated and activated, by removing and applying a voltage across the LC layer. Each of HWP1 1404-1 and HWP2 1404-2 is configured to modify the polarization state of light passing through it (e.g., rotate or flip the polarization state) when electrically deactivated (off), while being configured to substantially pass light without modifying the polarization state of light passing through it when activated (on). An electrical signal, e.g., a current signal or a voltage signal, for switching each of HWP1 1404-1 and HWP2 1404-2 may be provided by a switching circuit (not shown) electrically connected thereto. For illustrative purposes, in the following, both HWP1 1404-1 and HWP2 1404-2 are TN LC cells with optical axes along the y and x directions in their two substrates, respectively, similar to FIG. 14B. In the illustrated embodiment, the incident light 1420 has a polarization parallel to the y-direction, i.e., linear vertical polarization (LVP). However, it should be understood that the polarization axis of the incident light 1420 may be polarized in a different direction, i.e., linear horizontal polarization (LHP), to achieve different optical power states.

[0133] 15B, each of HWP1 1404-1 and HWP2 1404-2 is in an off state and configured to rotate the polarization of linearly polarized light having one of the LVP and LHP to linearly polarized light having the other of the LVP and LHP. Thus, upon passing through HWP1 1404-1, the incident light 1420 having an LHP is converted to light 1424 that is incident on L1 1300-1 having an LHP, which exerts substantially zero refractive power (φ1=0) due to the relative orthogonal orientation between the polarization of the light 1424 and the optical axis of L1 1300-1. The light 1428 having an LHP that is then incident on HWP2 1404-2 is converted to light 1432 having an LVP. L2 1300-2 exerts substantially zero refractive power (φ=0) due to the relative orthogonal orientation between the polarization of L2 1300-2 and the optical axis of L2 1300-2. In essence, the adaptive lens assembly 1500 exerts a net refractive power φ+φ equal to approximately zero on the incoming light 1420 with LVP and does not modify its polarization to output light 1436 with LVP.

[0134] 15C, each of HWP1 1404-1 and HWP2 1404-2 is in an on state and configured to preserve the polarization of linearly polarized light passing through it. Thus, upon passing through HWP1 1404-1, the polarization of incident light 1420 with LVP is preserved in light 1424 incident on L1 1300-1, which exerts a refractive force (φ1) due to the relative parallel orientation between the polarization of light 1424 and the optical axis of L1 1300-1. The polarization of light 1428 with LVP incident on HWP2 1404-2 is then preserved in light 1432. L2 1300-2 exerts substantially zero refractive force (φ2=0) due to the relative orthogonal orientation between the polarization of light 1432 and the optical axis of L2 1300-2. In essence, the adaptive lens assembly 1500 exerts a net refractive power φ1+φ2 equal to approximately φ1 on the incident light 1420 having an LVP, and outputs light 1436 having an LVP.

[0135] 15D, HWP1 1404-1 is in an OFF state and configured to rotate the polarization of the linearly polarized light with one of the LVP and LHP to the linearly polarized light with the other of the LVP and LHP, while HWP2 1404-2 is in an ON state and configured to preserve the polarization of the linearly polarized light. Thus, upon passing through HWP1 1404-1, the incident light 1420 with the LVP is converted to light 1424 that is incident on L1 1300-1 with the LHP, which exerts substantially zero refractive power (φ1=0) due to the relative orthogonal orientation between the polarization of the light 1424 and the optical axis of L1 1300-1. The polarization of the light 1428 with the LHP that passes through HWP2 1404-2 is then preserved in light 1432. Light 1432 incident on L2 1300-2 has an LHP, and L2 1300-2 exerts a refractive power (φ2) due to the relative parallel orientation between the polarization of light 1424 and the optical axis of L2 1300-2. In essence, the adaptive lens assembly 1500 exerts a net refractive power φ1+φ2 equal to approximately φ2 on the incident light 1420 with an LHP, and outputs light 1436 with an LHP.

[0136] 15E, HWP1 1404-1 is in an on state and configured to preserve the polarization of linearly polarized light, while HWP2 1404-2 is in an off state and configured to rotate the polarization of linearly polarized light with one of the LVP and LHP to linearly polarized light with the other of the LVP and LHP. Thus, the polarization of the incident light 1420 with LVP is preserved in the light 1424 that is incident on L1 1300-1 with LVP upon passing through HWP1 1404-1, and L1 1300-1 exerts a refractive power (φ1) due to the relative parallel orientation between the polarization of the light 1424 and the optical axis of L1 1300-1. The light 1428 with LVP that passes through HWP2 1404-2 is then converted to light 1432 with LHP. L2 1300-2 exerts a refractive power (φ2) due to the relative parallel orientation between the polarization of light 1432 and the optical axis of L2 1300-2. In essence, the adaptive lens assembly 1500 exerts a net refractive power φ1+φ2 on the incoming light 1420 with LVP and outputs light 1436 with LHP.

[0137] 15A-15E, for light having linear polarization, four possible refractive powers (0, φ1, φ2, and 1+φ2) can be exerted on light passing through adaptive lens assembly 1500. As a numerical example, for design wavelengths of φ1=0.75D and φ2=1.5D, net refractive powers of 0, 0.75D, 1.5D, and 2.25D can be obtained using adaptive lens assembly 1500.

[0138] 15A-15E in conjunction with FIGs. 11A-11B, in the illustrated embodiment, incident light 1420 may represent a light beam incident on either the first adaptive lens assembly 1004 (world-side FIGs. 11A-11B) or the second adaptive lens assembly 1008 (user-side FIGs. 11A-11B). By installing an adaptive lens assembly 1500 on either or both sides, for example, the display system described above with respect to FIGs. 11A-11B can be implemented in accordance with various embodiments described herein.

[0139] Display device including an adaptive lens assembly having a polarization selective lens stack coupled to a non-polarizing waveguide assembly In the following example implementations, an adaptive lens assembly (e.g., adaptive lens assembly 1500, FIGS. 15A-15E) having multiple switchable polarization-selective lens stacks is integrated into a display device, such as the display devices described above with respect to FIGS. 10, 11A, and 11B.

[0140] 16 illustrates an example display device 1600 including a waveguide assembly 1012 inserted between a first or front adaptive lens assembly (FLA) 1004 and a second or rear adaptive lens assembly (BLA) 1008. The overall configuration of the display device 1600 may be similar to the display device 1100A / 1100B described above with respect to FIGS. 11A / 11B. In the illustrated embodiment, the BLA 1008 is configured similarly to the adaptive lens assembly 1500 described above with respect to FIGS. 15A-15E, including a first switchable waveplate (HWP1) 1404-1, a first polarization-selective lens stack (L1) 1300-1, a second switchable waveplate (HWP2) 1404-2, and a second polarization-selective lens stack (L2) 1300-2. The first and second polarization-selective lens stacks 1300-1, 1300-2 have, for example, different orthogonal optical axes, curvatures (e.g., effective radii of curvature), and / or different birefringence, such that L1 1300-1 is configured to exert a first refractive power φ1 of Δn1 / R1 or substantially zero on light incident thereon having a polarization direction parallel or perpendicular to the optical axis, respectively, while L2 1300-2 is configured to exert a second refractive power φ2 of Δn2 / R2 or substantially zero on light incident thereon having a polarization direction parallel or perpendicular to the optical axis, respectively.

[0141] The FLA 1004 includes a third switchable waveplate (HWP3) 1404-3, a third polarization-selective lens stack (L3) 1300-3, a fourth switchable waveplate (HWP4) 1404-4, and a fourth polarization-selective lens stack (L4) 1300-4. The third and fourth polarization-selective lens stacks 1300-3, 1300-4 have, for example, different orthogonal optical axes, effective radii of curvature, and / or different birefringence, such that L3 1300-3 is configured to exert a third refractive power φ of Δn / R or substantially zero on light incident thereon having a polarization direction parallel or perpendicular to the optical axis, respectively, while L4 1300-4 is configured to exert a fourth refractive power φ of Δn / R or substantially zero on light incident thereon having a polarization direction parallel or perpendicular to the optical axis, respectively.

[0142] In various embodiments, the effective radii of curvature of L1 1300-1 and L2 1300-2 are such that φ1 and φ2 have a first sign, e.g., a positive sign, while the effective radii of curvature of L3 1300-3 and L4 1300-4 are such that φ3 and φ4 have a second sign opposite to the first sign, e.g., a negative sign. That is, when the three possible net refractive powers of FLA 1004 (φ1, φ2, and φ1+φ2) can have one of a convergence or divergence effect (e.g., convergence), the three possible non-zero net refractive powers of BLA 1008 (φ3, φ4, and φ3+φ4) can have the other of a convergence or divergence effect (e.g., divergence). In the illustrated embodiment, the FLA 1004 and the BLA 1008 are configured to be substantially the same (e.g., one is concave and the other is convex, or vice versa), except for the curvature of the interface between the birefringent lens and the isotropic lens. In particular, the first adaptive lens assembly 1004 and the second adaptive lens assembly 1004 can be considered to form a mirror image with respect to the waveguide assembly 1012. Thus, when configured, L1 1404-1 and L3 1404-3 have refractive powers φ1 and φ3, respectively, that are substantially the same in magnitude but opposite in sign, and L2 1404-2 and L4 1404-4 have refractive powers φ2 and φ4, respectively, that are substantially the same in magnitude but opposite in sign. That is, φ1 is approximately equal to -φ3, and φ2 is approximately equal to -φ4.

[0143] 16, in the illustrated embodiment, the waveguide assembly 1012 is configured to outcouple totally internally reflected unpolarized light. In this configuration, the display device 1600 additionally includes a linear polarizer 1604 between the waveguide assembly 1012 and the BLA 1008, configured to reduce or eliminate (e.g., reflect or absorb) light having a polarization state that is not conducive to lensing by the BLA 1008. For example, in an arrangement where the light 1608 outcoupled from the waveguide assembly 1012, or the light 1620 transmitted unaffected through the FLA 1004 is not linearly polarized, e.g., not LVP, the linear polarizer 1604 serves to linearly polarize the transmitted light and deliver the incident light 1420 into the BLA 1008.

[0144] When configured, the BLA 1008 is responsible for providing variable refractive power (φ1, φ2, and φ1+φ2) and forming images at multiple depth planes for a virtual image emerging from the waveguide assembly 1012 towards the eye 210. While the BLA 1008 provides the virtual image by focusing images from the waveguide assembly 1012 at multiple depth planes, the world image may be distorted by the BLA 1008. The FLA 1004 is responsible for compensating for the distortion of the world image caused by the BLA 1008 by providing variable refractive power (e.g., -φ3=-φ1, φ4=-φ2, and φ3+φ4=-(φ1+φ2)) such that the world image is presented to the eye 210 without substantial distortion.

[0145] In various embodiments, for example, when deactivated, the FLA 1004 and the BLA 1008 each provide a net optical power (positive or negative) within the range of approximately ±5.0 diopters to 0 diopters, ±4.0 diopters to 0 diopters, ±3.0 diopters to 0 diopters, ±2.0 diopters to 0 diopters, ±1.0 diopters to 0 diopters, and may include any range defined by any of these values, for example, ±1.5 diopters. In some embodiments, the FLA 1004 between the waveguide assembly 1012 and the world may have a positive optical power, while the BLA 1008 between the waveguide assembly 1012 and the user may have a negative optical power, such that the optical powers of the FLA 1004 and the BLA 1008 compensate each other in viewing the world.

[0146] As described above, as the image of the virtual object generated by the light outcoupled by the waveguide assembly 1012 moves in 3D, the net refractive power of the BLA 1008 at the user side is adjusted to match the changing depth of the virtual depth plane. At the same time, according to an embodiment, the net refractive power of the FLA 1004 is correspondingly adjusted using a switching circuit so that the view of the real world is not undesirably defocused or distorted. To address this and other needs, in some embodiments, the display device 1600 includes a controller (not shown) configured such that when the net refractive power of one of the FLA 1004 and the BLA 1008 is electrically adjusted, the net refractive power of the other of the FLA 1004 and the BLA 1008 is correspondingly adjusted such that the combined net refractive power remains approximately constant, e.g., about 0. The controller circuit and the switchable wave plates are configured such that the time to switch between HWP1 1404-1, HWP2 1404-2, HWP3 1404-3, and HWP4 1404-4 to adjust the virtual depth plane using the second adaptive lens assembly 1008 and compensate for the real world view using the first adaptive lens assembly 1004 is less than about 100 milliseconds, less than about 50 milliseconds, less than about 10 milliseconds, less than about 5 milliseconds, less than about 1 millisecond, or a value within a range defined by any of these values.

[0147] Display device including an adaptive lens assembly having a polarization-selective lens stack configured to recycle light for improved optical efficiency As described above, adaptive lenses can be used to focus virtual images at multiple depth planes. However, an adaptive lens stack according to an embodiment includes a polarization-selective lens stack. As a result, some display devices with a polarization-selective lens stack may lose as much as 50% or even more in brightness due to loss of light with non-transmitted polarization. Therefore, there is a need for efficient conversion of virtual image polarization to create a compact / light-efficient variable-focus bright-field display. According to an embodiment, a display device with improved optical efficiency is described that employs a polarization-selective lens stack in combination with a notch reflector to recycle light with non-transmitted polarization.

[0148] As described herein, a notch reflector generally refers to a light reflector that reflects light within a particular range of wavelengths with relatively high efficiency while transmitting most wavelengths of light substantially unaltered. The particular range of wavelengths from which light is reflected is referred to as a "notch." A notch reflector can be formed from multiple dielectric layers (multilayers), liquid crystals, metamaterials, or metastructures, etc. A notch reflector can include diffractive optical elements, surface or volume holograms, etc. A notch reflector can be laminated onto a substrate material (e.g., polymer or glass). In some of the implementations described herein, to reflect RGB light, the reflector comprises multiple notch reflectors, and the notches in each reflector are tuned to one of the specific RGB colors (e.g., a reflector comprising an R-notch reflector, a G-notch reflector, and a B-notch reflector). Thus, the wavelength range of each notch can be matched to the wavelength range of light injected into the display (e.g., the R-notch is matched to the wavelength range of red light injected by a red LED or laser, and similarly for the G and B notches).

[0149] Various embodiments described herein include a notch reflector that includes a transmissive substrate, e.g., a polished glass or polymer substrate, having one or more optical layers formed thereon. The one or more optical layers are configured to notch reflect light having a wavelength range Δλ of about 40 nm, about 70 nm, about 100 nm, or about 150 nm, or any range between any of these values, the range being centered on red light, including one or more wavelengths of light in the range of about 620-780 nm, green light, including one or more wavelengths of light in the range of about 492-577 nm, or blue light, including one or more wavelengths of light in the range of about 435-493 nm. In some embodiments, the wavelength range Δλ may substantially cover a red light range of about 620-780 nm, a green light range of about 492-577 nm, or a blue light range of about 435-493 nm.

[0150] Various embodiments described herein include a notch reflector configured as a polarizing notch reflector. Within the notch reflection range, the polarizing notch reflector allows light having one polarization to pass through it substantially while substantially reflecting light having the opposite polarization. For example, when light having both left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) within the notch reflection range is incident on the polarizing notch reflector, the notch reflector can substantially reflect light having one of RHCP and LHCP while substantially passing light having the opposite of RHCP and LHCP. Similarly, when light having both linear vertical polarization (LVP) and linear horizontal polarization (LHP) is incident on the polarizing notch reflector, the notch reflector can substantially reflect light having one of LVP and LHP while substantially passing light having the opposite of LVP and LHP.

[0151] Various embodiments described herein additionally include a notch reflector configured as a non-polarizing notch reflector. Within the notch reflection range, the non-polarizing notch reflector substantially reflects light incident thereon, regardless of its polarization. For example, when light having both LHCP and RHCP within the notch reflection range is incident on the non-polarizing notch reflector, the notch reflector can substantially reflect the light having both RHCP and LHCP. Similarly, when light having both LVP and LHP is incident on a polarizing notch filter, the notch filter can substantially reflect the light having both LVP and LHP.

[0152] In various embodiments described herein, a notch reflector configured as a polarizing or non-polarizing notch reflector can also be configured as a polarization converting notch reflector. When reflecting light having a polarization within the notch reflection range, the polarization converting notch reflector converts the polarization of the reflected light to the opposite polarization. For example, when light having one of LHCP and RHCP within the notch reflection range is incident on the polarization converting notch reflector, the notch reflector converts one of RHCP and LHCP to the opposite of RHCP and LHCP. Similarly, when light having one of LVP and LHP is incident on the polarization converting notch reflector, the notch reflector converts one of LVP and LHP to the opposite of LVP and LHP.

[0153] As described herein, a notch reflector configured to reflect light having one or more polarizations within a notch reflection range (Δλ) can be configured to reflect substantially all of the light having one or more polarizations incident thereon. For example, when a notch reflector is configured to reflect light having one or both of an RHCP and an LHCP, the notch reflector may, for example, reflect more than 80%, more than 90%, more than 95%, more than 99%, more than 99.99%, more than 99.999%, or more than 99.9999% of the light having one of an RHCP and an LHCP incident thereon. On the other hand, when a notch reflector is configured to reflect light having one of an RHCP and an LHCP, the notch reflector may, for example, reflect more than 80%, more than 90%, more than 95%, more than 99%, more than 99.99%, more than 99.999%, or more than 99.9999% of the light having one of an RHCP and an LHCP incident thereon. Conversely, a notch reflector is configured such that light that is not reflected, e.g., light having a wavelength outside the notch reflection range (Δλ) or light having a polarization that the notch reflector is not configured to reflect, is substantially completely transmitted, e.g., greater than 80%, greater than 90%, greater than 95%, greater than 99%, greater than 99.99%, greater than 99.999%, or greater than 99.9999% of the light incident thereon is transmitted.

[0154] 17A illustrates a display device 1800A including an adaptive lens assembly configured to recycle light having a non-transmitted polarization according to an embodiment. The display device 1800A includes a waveguide assembly 1012, e.g., a non-polarizing waveguide assembly, inserted between the FLA 1004 and the BLA 1008 in a manner similar to that described above with respect to FIG. 16. The display device 1800A further includes a non-polarizing notch reflector 1808 inserted between the FLA 1004 and the waveguide assembly 1012, and a polarizing notch reflector 1812 inserted between the BLA 1008 and the waveguide assembly 1012.

[0155] Still referring to FIG. 17A, the non-polarizing notch reflector 1808 according to the embodiment is configured such that within the notch reflection range, the reflector 1808 substantially reflects light incident thereon, regardless of its polarization. Furthermore, in the illustrated embodiment, the non-polarizing reflector 1808 is configured as a polarization converting notch reflector configured such that upon reflecting light having a polarization within the notch reflection range, the polarization converting notch reflector converts the polarization of the reflected light to the opposite polarization. The non-polarizing notch reflector 1808 includes a transmissive substrate, such as a polished glass or polymer substrate, having one or more optical layers formed thereon. In some embodiments of the notch reflectors described herein, the one or more optical layers formed on the substrate can include one or more dielectric coatings whose combination results in the various notch reflection characteristics described above.

[0156] Still referring to FIG. 17A, the polarizing notch reflector 1812 according to the embodiment is configured such that within the notch reflection range, the polarizing notch reflector 1812 substantially reflects light incident thereon in a polarization selective manner. Furthermore, in the illustrated embodiment, the polarizing reflector 1812 is configured such that, unlike the non-polarizing notch reflector 1808, the notch reflector 1812 does not convert the polarization of the reflected light to the opposite polarization. The polarizing notch reflector 1812 includes a transmissive substrate, such as a polished glass or polymer substrate, having one or more optical layers formed thereon. In some embodiments, the one or more optical layers formed on the substrate can include one or more cholesteric liquid crystal (CLC) layers.

[0157] Still referring to FIG. 17A, the polarizing notch reflector 1812 comprises a CLC layer having LC molecules arranged in a plurality of chiral structures. In one implementation, each of the chiral structures extends in the layer depth direction by at least a helical pitch and comprises a plurality of LC molecules rotated in a rotation direction in succession. Without subscribing to any scientific theory, in various implementations, the CLC layer can be advantageously configured to substantially Bragg-reflect elliptically or circularly polarized light having a handedness of polarization that matches the rotation direction of the liquid crystal molecules, while substantially transmitting elliptically or circularly polarized light having a handedness of polarization that is opposite to the rotation direction of the liquid crystal molecules. When configured, when an incident light having a combination of light beams having LHCP and RHCP enters the polarizing notch reflector 1812 by Bragg reflection, light with one of the circular polarization handednesses is reflected by the polarizing notch reflector, while light with the opposite polarization handedness is transmitted therethrough without substantial interference. Here, and as explained throughout this disclosure, handedness is defined as being viewed in the direction of propagation.

[0158] In operation, light coupled out of the waveguide assembly 1012 includes a circularly polarized beam 1816-L with an LHCP and a circularly polarized beam 1816-R with an RHCP. The light beam 1816-L with an LHCP and the light beam 1816-R with an RHCP travel in, for example, a positive z-direction until the beams impinge on the polarizing notch reflector 1812. In the illustrated embodiment, the liquid crystal molecules in the chiral structure are continuously rotated in a clockwise direction in the same rotational direction as the light beam 1816-R. As a result, the light beam with an LHCP incident on the polarizing notch reflector 1812 is substantially reflected therefrom as 1816-L, while the light beam with an RHCP 1816-R is substantially transmitted through the polarizing notch reflector 1812.

[0159] The light beam 1816-R transmitted through the polarizing notch reflector 1812 passes through a quarter-wave plate (QWP) 1824, which converts the light beam 1816-R into a linearly polarized light 1824 having an LVP so as to be incident on the eye 210. On the other hand, the light beam 1816-L reflected by the polarizing notch reflector 1812 propagates towards the non-polarizing notch reflector 1808 and is then substantially reflected into a light beam 1820-R having the opposite polarization handedness, i.e., RHCP, due to the polarization conversion property of the non-polarizing notch reflector 1808. The resulting light beam 1820-R having RHCP is substantially transmitted through the waveguide assembly 1012 and the polarizing notch reflector 1812, followed by a quarter-wave plate (QWP) 1824, which converts the light beam 1820-R to linearly polarized light 1824 having LVP for incidence on the eye 210.

[0160] 17B illustrates a display device 1800B including an adaptive lens assembly configured to recycle light having a non-transmitted polarization according to some other embodiments. Similar to the display device described above with respect to FIG. 17A, the display device 1800B includes a waveguide assembly 1012, e.g., a non-polarizing waveguide assembly, inserted between the FLA 1004 and the BLA 1008, and a non-polarizing notch reflector 1808 and a quarter-wave plate (QWP) 1824 inserted between the FLA 1004 and the waveguide assembly 1012. The display device 1800B additionally includes a polarizing notch reflector 1814, e.g., a linear polarizing notch reflector, inserted between the waveguide assembly 1012 and the BLA 1812.

[0161] 17B, ​​similar to the polarizing notch reflector 1812 described above with respect to FIG. 17A, the polarizing notch reflector 1814 is configured such that within the notch reflection range, the notch reflector 1814 substantially reflects light incident on it in a polarization-selective manner. Furthermore, unlike the non-polarizing notch reflector 1808, the polarizing reflector 1814 does not convert the polarization of the reflected light to the opposite polarization.

[0162] In addition, unlike the polarizing notch reflector 1812 (FIG. 17A), the polarizing notch reflector 1814 does not include a CLC layer. Instead, the polarizing notch reflector 1814 includes a transmissive substrate, such as a polished glass or polymer substrate, having one or more optical layers formed thereon. In some embodiments of the notch reflectors described herein, the one or more optical layers formed on the substrate can include one or more dielectric coatings whose combination results in the various notch reflective properties described above.

[0163] 17B, ​​in operation, light coupled out of the waveguide assembly 1012 includes linearly polarized beam 1816-V having an LVP and 1816-H having an LHP. Light beams 1816-V and 1816-H travel in, for example, the positive z-direction until the beams impinge on the polarizing notch reflector 1814. Thereupon, light beam 1816-H is substantially reflected from the polarizing notch reflector 1814, while light beam 1816-V is substantially transmitted therethrough to enter the eye 210.

[0164] Light beam 1816-H is reflected by the polarizing notch reflector 1814, propagates towards and is transmitted through quarter-wave plate 1824, is reflected off of the non-polarizing notch reflector 1808, and is further transmitted through the quarter-wave plate 1824 as light beam 1820-V having the opposite polarization handedness, e.g., LVP, due to the polarization converting properties of the non-polarizing notch reflector 1808. The resulting light beam 1820-V is substantially transmitted through the polarizing notch reflector 1814 to be incident on the eye 210.

[0165] Although notch reflectors are discussed in the above examples where notch filters selectively modify the polarization state for one polarization of light, polarizing elements other than notch reflectors may also be used, such as those that may modify the polarization state over a wide range of wavelengths.

[0166] (Adaptive lens assembly with switchable polarization-selective lens stack) According to various embodiments disclosed herein, an adaptive lens assembly can generate images at multiple depth planes by selectively switching between multiple states with different refractive powers. Above, for example with respect to Figs. 14A-14B and 15A-15E, an adaptive lens assembly was described in which selective switching is performed by activating or deactivating a switchable waveplate coupled to a polarization-selective lens. In some embodiments, the polarization-selective lens itself can be configured to be directly switchable, thereby allowing for further simplification and / or compact integration of the adaptive lens assembly. In the following, according to an embodiment, an adaptive lens assembly is described in which selective switching is performed by activating or deactivating a switchable polarization-selective lens stack instead of switching a switchable waveplate coupled thereto.

[0167] As explained above, some LC molecules can, for example, alter their orientation (e.g., rotate and / or tilt) under electrical stimulation resulting in altered optical properties. In some embodiments, polarization-selective lens stacks can be configured to be switchable by employing reactive mesogens (RM) that comprise partially unpolymerized LC molecules.

[0168] FIG. 18 illustrates a switchable polarization-selective lens stack 1900 comprising a polarization-selective lens stack 1904 formed between transparent electrodes 1916, 1920. The polarization-selective lens stack 1904 comprises a birefringent Fresnel lens 1304 and an isotropic lens 1308. Thus, the polarization-selective lens stack 1904 is similar to that described above with respect to, for example, FIGS. 12A-12C and 13A-13B, except that instead of having a birefringent lens formed from polymerized LC, the birefringent lens 1304 of the polarization-selective lens stack 1904 comprises or is formed from an RM having unpolymerized LC molecules that can alter their orientation under an electric field. Once constructed, the switchable polarization-selective lens stack 1900 can perform functionality similar to the combination of a passive polarization-selective lens stack and a switchable waveplate, as described above with respect to, for example, FIG. 14A. That is, in operation, in the off state, e.g., when there is no voltage between the electrodes 1916, 1920, the LC molecules may be arranged in the same manner as described above with respect to Figures 12A-12C. Under this configuration, in operation, in a manner similar to that described above with respect to Figure 14A, the LCs of the polarization-selective lens stack 1904 are configured such that when the polarization direction of linearly polarized incident light 1420 incident thereon, e.g., LVP light, is parallel to the optical axis, the polarization-selective lens stack 1904 exerts a refractive power thereon and outputs light 1436 having LVP, while when the polarization direction of linearly polarized incident light incident thereon is perpendicular to the optical axis, the polarization-selective lens stack 1904 exerts substantially zero refractive power thereon. Thus, the switchable polarization-selective lens stack 1904 functions in a manner similar to the combination of a passive polarization-selective lens stack and a switchable waveplate, as described above. However, in the on state, for example, in the presence of a voltage between electrodes 1916, 1920, the polarization-selective lens stack 1904 can be configured to exert a different optical power on linearly polarized light having a polarization direction that is parallel to the optical axis.Various refractive powers can be produced by the LCs of the polarization-selective lens stack 1904 configured such that the birefringence is a function of the voltage applied across the electrodes 1916, 1920, e.g., due to the voltage-dependent tilt of the LC molecules (i.e., Δn=f(V)). On the other hand, for linearly polarized light having a polarization direction perpendicular to the optical axis, the polarization-selective lens stack 1904 exerts zero or near-zero refractive power. The latter (zero or near-zero refractive power) can be accomplished by matching the refractive index of the isotropic lens 1308 with that of the birefringent lens 1304. In this way, the refractive power of the polarization-selective lens stack 1904 can be controlled by an applied voltage, e.g., instead of stacking a combination of a passive polarization-selective lens stack and a switchable waveplate, as described above with respect to FIG. 14A. However, other refractive powers are possible, for example, by mismatching the refractive index of the isotropic lens 1308 with the refractive index of the birefringent lens 1304. Such implementations may be desirable, for example, when a user benefits from normally wearing corrective lenses, such as prescription lenses or glasses. For these users, partial compensation may be desirable for the polarization-selective lens stack to act at least in part as a corrective lens.

[0169] Display device including an adaptive lens assembly having a switchable polarization selective lens stack coupled to a non-polarizing waveguide assembly Below is an example display device as described above with respect to Figures 10, 11A, and 11B integrated with an adaptive lens assembly, which, according to some embodiments, includes a switchable polarization-selective lens stack as described above (e.g., polarization-selective lens stack 1904, Figure 18).

[0170] Figure 19 illustrates an example display device 2000 similar to the display device described above with respect to Figure 16 including a waveguide assembly 1012, e.g., a non-polarizing waveguide assembly, and a linear polarizer 1604, inserted between a first adaptive lens assembly (FLA) 2004 and a second adaptive assembly (BLA) 2008. However, unlike the FLA 1004 and BLA 1008 of the display device of Figure 16, the FLA 2004 and BLA 2008 each have a switchable polarization-selective lens stack similar to that described above with respect to Figure 18. That is, the combination of switchable waveplates and lens stacks included in the FLA 1004 and BLA 1008 of Figure 16 are replaced with first and second switchable polarization-selective lens stacks 1900A and 1900B, respectively.

[0171] In operation, the BLA 2008 is configured to focus a virtual image by exerting a refractive power φ on the linearly polarized light 1420 (e.g., with LVP) from the waveguide assembly 1012 using the first switchable polarization-selective lens stack 1900A in the off state, as described above with respect to Figure 18. Additionally, in a manner similar to that described above with respect to Figure 16, to prevent the world image from being distorted by the refractive power of the BLA 2008, the FLA 2004 serves to compensate by providing a compensating refractive power -φ (by having the switchable polarization-selective lens stack 1900B in the off state) such that the world image is presented to the eye 210 without substantial distortion.

[0172] FIG. 20 illustrates an exemplary display device 2100 similar to the display device described above with respect to FIG. 19 including a waveguide assembly and a second adaptive lens assembly (BLA) 2008. However, unlike the display device described above with respect to FIG. 19, the display device 2100 includes a polarizing waveguide assembly 1712 that couples polarized light, e.g., circularly polarized light 1708-R or 1708-L, into the BLA 2008. The polarizing waveguide assembly 1712 can comprise cholesteric liquid crystals, as described above with respect to FIG. 18A. Thus, the BLA 2008 additionally includes a first quarter-wave plate (QWP1) 1704, e.g., an achromatic quarter-wave plate, configured to convert the light 1708-R, 1708-L coupled out of the polarizing waveguide assembly 1712 into linearly polarized light 1420 incident on the BLA 2008. Thus, the BLA 1008 operates in a manner similar to that described above with respect to FIG.

[0173] However, unlike the display device 2000 of Figure 19, the display device 2000 does not have an FLA 2004 configured to cancel the undesired refractive power exerted by the BLA 2008 on the world-side light 1620 when the BLA 2008 exerts a refractive power on the light from the polarizing waveguide assembly 1712 containing the virtual image information. Instead, when displaying a virtual image, the display device 2100 is configured to selectively focus the light from the waveguide assembly 1712 while passing the world image substantially unaffected. This is accomplished by replacing the FLA 2004 (Figure 19) with a combination of a linear polarizer 1716 and a second quarter-wave plate (QWP2) 1714, e.g., an achromatic quarter-wave plate.

[0174] In some implementations, when displaying a world image, the display device 2100 exerts no substantial refractive power. Under this configuration, the unpolarized light 1620 from the world is linearly polarized, for example, by the linear polarizer 1716, into horizontal linear polarization (LHP), which is subsequently converted to circular polarization by the second quarter-wave plate (QWP2) 1714. Circularly polarized light incident on the polarizing waveguide assembly 1712 passes through it essentially unaffected and is converted by the QWP1 1704 into linearly polarized, e.g., LHP light. In the BLA 1008, the switchable polarization-selective lens stack 1900A is configured to exert substantially zero refractive power by orthogonally orthogonalizing its optical axis to the polarization direction of the incident LHP light, thereby passing the incident light essentially unaffected, as seen by the eye 210.

[0175] Still referring to FIG. 20, when displaying a virtual image, the BLA 2008 is configured to focus the virtual image from the waveguide assembly 1712 by exerting a refractive power φ on the linearly polarized light 1420 with LVP from the waveguide assembly 1712 using a switchable polarization-selective lens stack 1900A. Because there is only one lens element in the BLA stack, the polarization state of the virtual image remains unaltered, LVP, and parallel to the optical axis of the switchable lens, as described above with respect to FIG. 18. Thus, the world image is viewed by the user undistorted, while the virtual image is simultaneously subjected to a voltage-dependent refractive power φ(V).

[0176] (Polarization selective Fresnel lens stack, which comprises a stack of two one-dimensional Fresnel lenses) Fabrication of a polarization-selective Fresnel lens stack such as that described above with respect to FIG. 13B can have many challenges. For example, because the grooves in the isotropic lens are circular, it can be difficult and / or expensive to orient the LC molecules in a uniform horizontal direction. Below, alternative designs of polarization-selective Fresnel lens stacks are described that can be more easily manufactured by orienting the LC molecules along grooves that are linear instead of circular. For example, the grooves can be rotationally symmetric. The grooves can be non-rotationally symmetric (e.g., cylindrical).

[0177] FIG. 21A illustrates a simplified design of a polarization-selective Fresnel lens stack comprising a one-dimensional (1D) polarization-selective Fresnel lens stack 2200A according to some embodiments. Similar to the Fresnel lens stack described above with respect to FIG. 13B, the 1D polarization-selective Fresnel lens stack 2200A comprises a birefringent lens 2204 and an isotropic lens 2208. Additionally, similar to the birefringent lens described above with respect to FIG. 13B, the LC molecules are substantially oriented in a horizontal direction 2212, e.g., in the y-direction, along grooves 2216 that form the boundaries of the Fresnel zones 2212. However, unlike the polarization-selective Fresnel lens stacks having circular zones or grooves described above with respect to FIGS. 13A-13B, the 1D polarization-selective Fresnel lens stack 2200A is configured as a one-dimensional (1D) polarization-selective Fresnel lens stack in which the grooves 2212 extend substantially parallel to the horizontal direction 2212, e.g., in the y-direction.

[0178] FIG. 21B illustrates a simplified design of a polarization-selective Fresnel lens stack comprising a two-dimensional (2D) polarization-selective Fresnel lens stack 2200B according to some embodiments. The polarization-selective Fresnel lens stack 2200B comprises a pair of 1D polarization-selective Fresnel lens stacks 2200A-1, 2200A-2 as illustrated above with respect to FIG. 21A rotated 90 degrees relative to each other and with a half-wave plate (HWP) 2220, e.g., an achromatic HWP, inserted between them. Each of the pair of 1D polarization-selective Fresnel lens stacks 2200A-1, 2200A-2 comprises a birefringent lens 2204-1, 2204-2 and an isotropic lens 2208-1, 2208-2, respectively. In operation, the first 1D polarization-selective Fresnel lens stack 2200A-1 exerts a first lens refractive force in a first lateral direction (x-direction) on the linearly polarized incident light 1420 having a polarization direction parallel to the direction of the grooves 2212 formed therein. The HWP 2220 then rotates the linearly polarized light transmitted through the first 1D polarization-selective Fresnel lens stack 2200A-1 by 90 degrees to align the polarization direction with the groove extension direction of the second Fresnel lens stack 2200A-2, which exerts a second lens refractive force in a second lateral direction (y-direction) on the linearly polarized light transmitted through the HWP 2220 and having a polarization direction parallel to the direction of the grooves 2212 formed in the second Fresnel lens stack. Once constructed, the overall functionality of the two-dimensional (2D) polarization-selective Fresnel lens stack 2200B corresponds to that of the polarization-selective Fresnel lens stack described above with respect to FIG. 13B having circularly symmetric grooves, except for possible additional aberrations due to the increased number of grooves.

[0179] FIG. 21C illustrates a simplified design of a switchable polarization-selective Fresnel lens stack comprising a two-dimensional (2D) polarization-selective Fresnel lens stack 2200C according to some embodiments. The polarization-selective Fresnel lens stack 2200C comprises a pair of isotropic lenses 2208-1, 2208-2 rotated 90 degrees relative to each other such that their grooves cross each other. The pair of isotropic lenses 2208-1, 2208-2 has a birefringent lens 2204 interposed therebetween comprising RM or switchable unpolymerized liquid crystal molecules. The LC molecules of the birefringent lens 2204 are configured such that the LC molecules adjacent to the first isotropic lens 2208-1 are aligned in one lateral direction, e.g., the y-direction, while the LC molecules adjacent to the second isotropic lens 2208-1 are aligned in the other lateral direction, e.g., the x-direction. The two-dimensional (2D) polarization-selective Fresnel lens stack 2200C additionally comprises a pair of transparent electrodes 1916, 1920 interposed between which are isotropic lenses 2208-1, 2208-2 having an RM formed therebetween. In operation, the LC molecules of the birefringent lens 2204 act to provide a lensing effect, similar to the HWP 2220 of FIG. 21B, and also act as a half-wave plate. Once constructed, the overall function of the two-dimensional (2D) polarization-selective Fresnel lens stack 2200C is similar to that described above with respect to FIG. 21B.

[0180] (Method of making polarization selective Fresnel lens stacks) 22A-22D illustrate an example method for fabricating a polarization-selective Fresnel lens stack according to an embodiment.

[0181] 22A illustrates an intermediate structure 2300A comprising a template substrate 2304 formed by providing an isotropic material and forming grooves therein as described above with respect to FIG. 13B, via processes such as casting, molding, or diamond cutting, to name a few. Transparent electrodes such as ITO (also metal nanowires, polyethylenedioxythiophene (PEDOT), etc.) can be conformally deposited on the template substrate 2304 to fabricate a switchable polarization-selective Fresnel lens stack. A first LC alignment layer 2306 is then formed on the template substrate 2304, via any of spin, slot, blade, spray coating techniques, or combinations thereof, and then thermally baked (e.g., 100° C., 1 min) to remove excess solvent.

[0182] FIG. 22B illustrates an intermediate structure 2300B formed by providing a second substrate 2308 and forming a second LC alignment layer 2310 thereon, e.g., in a manner similar to that described above with respect to FIG. 22A.

[0183] Substrates 2304 and 2308 can be formed from a transparent material including, for example, acrylic, silicon dioxide, sapphire, or any suitable transparent material.

[0184] The alignment layers 2306, 2310 can include photo-alignment layers onto which the LC molecules, when deposited, can be oriented along a preferential direction due to, for example, anchoring energy exerted on the LC molecules by the photo-alignment layer. Examples of photo-alignment layers include polyimides, linearly polarized photopolymerizable polymers (LPPs), azo-containing polymers, coumarin-containing polymers, and cinnamate-containing polymers, to name a few.

[0185] The alignment layers 2306, 2310 may be formed by dissolving precursors, e.g., monomers, in a suitable solvent and coating the solution onto a substrate using a suitable process, e.g., spin coating, slot coating, doctor blade coating, spray coating, and jet (inkjet) coating, among other deposition processes. The solvent may then be removed from the coated solution. The alignment layers 2306, 2310 may also be cured, e.g., UV cured, e.g., with a polarizer, in preparation for subsequent alignment of the LC molecules thereon.

[0186] After coating, the alignment layers 2306, 2310 can be optically patterned or recorded. For example, optical patterning can be performed using linearly polarized light.

[0187] FIG. 22C illustrates an intermediate structure 2300C formed by bringing together intermediate structures 2300A (FIG. 22A) and 2300B (FIG. 22B) such that the first LC alignment layer 2306 and the second LC alignment layer 2310 face each other. In some embodiments, a plurality of spacers 2314 mixed with an adhesive can be disposed between the first LC alignment layer 2306 and the second LC alignment layer 2310 to form a cell gap 2318. The thus formed intermediate structure 2300C comprising a sandwich structure is exposed to linearly polarized ultraviolet (UV) light to simultaneously generate linear alignment patterns on both substrates 2304 and 2308. Alternatively, the alignment patterns can be formed using rubbed polyimide prior to generating the sandwich structure.

[0188] 22D illustrates an intermediate structure 2400D formed by filling the gap 2318 with an unpolymerized LC material or reactive mesogen (RM). The LC material may include a reactive mesogen mixture (including, for example, liquid crystal monomers, a solvent, a photoinitiator, and a surfactant).

[0189] Then, for example, a thermal anneal at 100° C. for 1 minute may be performed. For a switchable polarization-selective Fresnel lens stack, the process may end here. There are certain polymerizable LCs that can be filled in this way (e.g., UCL-001 from DIC Corporation Japan Ltd.). Subsequently, to form a passive polarization-selective Fresnel lens stack, the LC material or RM is exposed to UV light to polymerize the LC material and form the passive polarization-selective Fresnel lens stack.

[0190] Other embodiments are possible, for example, instead of the gap-fill process described above, an LC polymer (LCP) layer can be coated directly onto either or both of the substrates 2304, 2308 using a suitable process including, for example, spin coating, slot coating, doctor blade coating, spray coating, and inkjet coating, among other deposition processes. Additional Examples Example 1. An adaptive lens assembly, the adaptive lens assembly comprising a lens stack configured to exert a polarization-dependent refractive power on linearly polarized light; the lens stack comprises a birefringent lens and an isotropic lens in contact with one another forming a conformal interface therebetween; An adaptive lens assembly configured to be selectively switched between a plurality of states having different optical powers. Example 2 the birefringent lens has an optical axis and a birefringence (Δn) and is configured to exert a first refractive power on light having a polarization direction parallel to the optical axis and a second refractive power on light having a polarization direction perpendicular to the optical axis; 2. The adaptive lens assembly of example 1, wherein the isotropic lens has a refractive index and is configured to exert a third refractive power on light passing therethrough, the third refractive power having an opposite sign to the first and second refractive powers. (Example 3) Δn is the extraordinary refractive index (n e ) and the normal refractive index in the direction perpendicular to the optical axis of the birefringent lens (n o ) and the refractive index of an isotropic lens corresponds to the difference between the n o The adaptive lens assembly of example 2 having substantially the same value as Example 4: The adaptive lens assembly of any one of the preceding examples, wherein the third refractive power is substantially equal in magnitude to the second refractive power such that the polarization-selective lens stack is configured to exert substantially no refractive power on light having a polarization direction perpendicular to the optical axis. Example 5: The adaptive lens assembly of any one of the preceding examples, wherein the lens stack is configured to exert a refractive force proportional to Δn on light having a polarization direction parallel to the optical axis. (Example 6) An adaptive lens assembly described in any one of the preceding examples, wherein the birefringent lens is a Fresnel lens having a plurality of grooves formed therein, adjacent ones of the grooves defining a Fresnel zone of the Fresnel lens. (Example 7) An adaptive lens assembly as described in Example 6, wherein the plurality of grooves comprises concentric circular grooves. (Example 8) An adaptive lens assembly as described in Example 6, wherein the plurality of grooves comprises parallel grooves extending in a direction parallel to the major surface of the lens stack. (Example 9) An adaptive lens assembly according to any one of the preceding examples, wherein the birefringent lens comprises a liquid crystal (LC). (Example 10) An adaptive lens assembly as described in Example 9, wherein the LC molecules of the birefringent lenses are substantially oriented in a lateral direction parallel to the major surfaces of the lens stack. (Example 11) An adaptive lens assembly described in any one of the preceding examples, further comprising a switchable half-wave plate having a twisted nematic (TN) liquid crystal (LC) optically coupled to the lens stack, the switchable half-wave plate being configured to preserve the polarization of linearly polarized light passing through it when activated and to alter the polarization of linearly polarized light passing through it when deactivated. Example 12: A switchable half-wave plate is disposed on a first side of a polarization-selective lens stack, and an adaptive lens assembly is disposed on a second side of the polarization-selective lens stack. a second switchable half-wave plate comprising a TN LC optically coupled to the polarization selective lens stack; a second lens stack configured to exert a polarization-dependent refractive power on linearly polarized light, the second lens stack comprising a second birefringent lens and a second isotropic lens in contact with each other and forming a conformal interface therebetween; and and wherein the adaptive lens assembly is configured to be selectively switched between at least four states by electrically activating and / or deactivating the switchable waveplate and / or the second switchable half-waveplate. (Example 13) An adaptive lens assembly described in any one of Examples 1-10, wherein the birefringent lens comprises a reactive mesogen and the lens stack comprises electrodes configured to apply an electric field across the birefringent lens such that the lens stack is configured to be electrically switchable between different refractive power states. Example 14 A display device comprising: a waveguide assembly configured to guide light in a lateral direction parallel to an output surface of the waveguide assembly, the waveguide assembly further configured to outcouple the guided light through the output surface; an adaptive lens assembly disposed on a first side of the waveguide assembly, the adaptive lens assembly configured to receive light outcoupled from the waveguide assembly and to be selectively switched between a plurality of states having different optical powers; wherein the adaptive lens assembly comprises a lens stack configured to exert a polarization-dependent refractive power on linearly polarized light, the lens stack comprising a birefringent lens and an isotropic lens in contact with one another, the contacting surfaces of the birefringent lens and the isotropic lens forming a form-matching interface. Example 15 the birefringent lens has an optical axis and a birefringence (Δn) and is configured to exert a first refractive power on light having a polarization direction parallel to the optical axis and a second refractive power on light having a polarization direction perpendicular to the optical axis; The display device of Example 14, wherein the isotropic lens has a refractive index and is configured to exert a third refractive power on light passing therethrough, the third refractive power being opposite in sign to at least one of the first and second refractive powers. (Example 16) A display device as described in Example 15, wherein the birefringent lens is a Fresnel lens having a plurality of grooves formed therein, adjacent ones of the grooves defining a Fresnel zone. (Example 17) A display device as described in Example 15, wherein the birefringent lens comprises a liquid crystal (LC). (Example 18) A display device as described in Example 15, wherein the LC molecules of the birefringent lenses are substantially oriented in the same direction parallel to the major surfaces of the polarization selective lens stack. (Example 19) a second adaptive lens assembly disposed on a second side of the waveguide assembly opposite the first side, the second adaptive lens assembly configured to be selectively switched between a plurality of states having different optical powers, the second adaptive lens assembly comprising: The display device of Example 14, further comprising a second adaptive lens assembly comprising a second lens stack configured to exert a polarization-dependent refractive power on linearly polarized light, the second lens stack comprising a second birefringent lens and a second isotropic lens in contact with each other and forming a shape-matching interface therebetween. (Example 20) A display device as described in Example 19, wherein each of the first and second adaptive lens assemblies further comprises a switchable half-wave plate having a twisted nematic (TN) liquid crystal (LC) optically coupled to a respective one of the lens stacks or the second lens stack, the switchable half-wave plate being configured to preserve the polarization of linearly polarized light passing through it when activated and to alter the polarization of linearly polarized light passing through it when deactivated. (Example 21) A display device as described in Example 20, wherein each of the multiple refractive powers exerted by the second adaptive lens assembly has substantially the same magnitude and a corresponding one of the multiple refractive powers exerted by the adaptive lens assembly has an opposite sign. (Example 22) A display device described in any one of Examples 14-21, wherein the adaptive lens assembly is formed on a first side of the waveguide assembly, and the display device further comprises a polarizing reflector inserted between the waveguide assembly and the adaptive lens assembly, the polarizing reflector being configured to pass linearly polarized light having a first polarization therethrough and reflect linearly polarized light having a second polarization. (Example 23) A display device as described in Example 22, further comprising a non-polarizing reflector on the second side of the waveguide assembly and a quarter-wave plate inserted between the non-polarizing reflector and the waveguide assembly, the non-polarizing reflector being configured to reflect and modify the polarization of linearly polarized light having a first polarization incident thereon. (Example 24) A display device described in any one of Examples 14-21, wherein the adaptive lens assembly is formed on a first side of the waveguide, and the display device further comprises a polarizing reflector inserted between the adaptive lens assembly and the waveguide assembly, the polarizing reflector comprising a cholesteric liquid crystal configured such that the polarizing notch reflector is configured to pass circularly polarized light having a first polarization and to reflect circularly polarized light having a second polarization. (Example 25) A display device as described in Example 24, further comprising a non-polarizing reflector on a second side of the waveguide assembly, the non-polarizing reflector configured to reflect and modify the polarization of circularly polarized light incident thereon having a second circular polarization. (Example 26) A display device as described in Example 19, wherein each of the birefringent lens and the second birefringent lens comprises a reactive mesogen, and each of the lens stack and the second lens stack comprises an electrode configured to switch each of the lens stack and the second lens stack between different refractive power states. (Example 27) A display device as described in Example 14, wherein the birefringent lens comprises a reactive mesogen and the polarization selective lens stack comprises electrodes for electrically switching the polarization selective lens stack between at least two refractive power states. (Example 28) On a second side opposite to the first side of the waveguide assembly, A linear polarizer; A quarter-wave plate inserted between the waveguide assembly and the linear polarizer. The display device of Example 27, further comprising: (Example 29) A display device described in any one of Examples 22-25, wherein the polarizing reflector comprises a polarizing notch reflector. (Example 30) A display device described in any one of Examples 22-25 and 29, wherein the non-polarizing reflector comprises a non-polarizing notch reflector. (Example 31) A display device described in any one of Examples 14-30, arranged in a head-mounted display. (Example 32) A display device described in any one of Examples 14-31, further comprising a frame configured to be supported on a user's head. (Example 33) A display device described in any one of Examples 14-32, wherein at least a portion of the display device is transparent and positioned in a location in front of the user's eye when the user wears the display device so as to transmit light from a portion of the environment in front of the user and the display device to the user's eye and provide a view of a portion of the environment in front of the user and the display device. (Example 34) A display device described in any one of Examples 14-33, wherein the display device is configured to project light into the user's eye and display virtual image content in the user's field of view at different amounts of at least one of divergence and collimation, such that the displayed virtual image content appears to originate from different depths at different time periods. (Example 35) A display device described in any one of Examples 14-34, wherein the adaptive lens assembly comprises a Fresnel lens. (Example 36) A display device described in any one of Examples 1-13, wherein the lens stack comprises a Fresnel lens. (Example 37) A display device described in any one of Examples 6 and 8-10, wherein the grooves form an abrupt discontinuity in the thickness of the birefringent lens. (Example 38) A display device described in any one of Examples 6, 8-10, and 37, wherein the grooves have linear grooves.

[0191] It should be understood that any one of the above examples may be combined or used in the context of a wearable augmented reality head mountable display system and / or a method of making or using a wearable augmented reality head mountable display system. The head mountable display may comprise one or more of the following: a light modulation system configured to output light and form an image, a head mountable frame, and / or one or more waveguides attached to the frame and configured to receive light from the light modulation system.

[0192] (Additional Considerations) In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be apparent that various modifications and changes can be made thereto 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 restrictive sense.

[0193] Indeed, it should be understood that each of the systems and methods of the present disclosure have several innovative aspects, none of which is solely responsible for or required for the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of the present disclosure. For example, with reference to FIG. 15, it should be understood that one or more adaptive lens assemblies 1504-1-1504-3 may be disposed between individual ones of the waveguides 1012a, 1012b, and / or 1012c.

[0194] Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, although features may be described above as acting in a combination and may even be initially claimed as such, 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 subcombination or variation of the subcombination. No single feature or group of features is required or essential for every embodiment.

[0195] In particular, it should be understood that conditional terms used herein, such as "can," "could," "might," "may," "eg," and the like, are generally intended to convey that certain embodiments include certain features, elements, and / or steps, while other embodiments do not, unless specifically stated otherwise or understood otherwise within the context as used. Thus, such conditional terms are generally not intended to imply that features, elements, and / or steps are in any way required for one or more embodiments, or that one or more embodiments necessarily include logic for determining whether those features, elements, and / or steps are included or performed in any particular embodiment, with or without author input or prompting. The terms "comprising," "including," "having," and the like, are synonymous and used inclusively in a non-limiting manner and do not exclude additional elements, features, acts, operations, etc. The term "or", for example, when used to connect a list of elements, is used in its inclusive sense (and not its exclusive sense) so that the term "or" means one, some, or all of the elements in the list. In addition, the articles "a", "an", and "the" as used in this application and the appended claims are to be interpreted to mean "one or more" or "at least one" unless otherwise specified. Similarly, although operations may be depicted in the figures in a particular order, it should be recognized that such operations need not be performed in the particular order shown, or in sequential order, or that all of the illustrated operations need not be performed to achieve desirable results. Additionally, the figures may diagrammatically depict one or more exemplary processes in the form of a flow chart. However, other operations not depicted may also be incorporated within the diagrammatically illustrated exemplary methods and processes. For example, one or more additional operations may be performed before, after, simultaneously with, or during any of the illustrated operations.In addition, operations may be rearranged or reordered in other embodiments. In certain situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of 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.

[0196] Thus, the claims are not intended to be limited to the embodiments shown herein but are to be accorded the widest scope consistent with the present disclosure, the principles and novel features disclosed herein.

Claims

1. A method, the method comprising: focusing the virtual image at a plurality of depth planes within a view of the real world via an adaptive lens assembly of a head-mounted augmented reality display device; the adaptive lens assembly comprises a lens stack supported by the head-mounted augmented reality display device and is configured to exert a polarization-dependent refractive power on linearly polarized light; the lens stack comprises a birefringent lens and an isotropic lens, the birefringent lens and the isotropic lens contacting each other and forming a conformal interface therebetween; the focusing includes focusing the virtual image at the multiple depth planes in the real world view while simultaneously refocusing the real world view to appear without substantial distortion by selectively switching the adaptive lens assembly between multiple states having different optical powers.

2. The birefringent lens has an optical axis and a birefringence (Δn), and is configured to exert a first refractive power on light having a polarization direction parallel to the optical axis and to exert a second refractive power on light having a polarization direction perpendicular to the optical axis; 2. The method of claim 1, wherein the isotropic lens has a refractive index and is configured to exert a third refractive power on light passing therethrough, the third refractive power being opposite in sign to the first and second refractive powers.

3. The method of claim 2, wherein Δn corresponds to the difference between an extraordinary refractive index (n e ) of the birefringent lens in a direction parallel to the optical axis and an ordinary refractive index (n o ) of the birefringent lens in a direction perpendicular to the optical axis, and wherein the refractive index of the isotropic lens has substantially the same value as n o of the birefringent lens.

4. The method of claim 2, wherein the third refractive power is substantially the same in magnitude as the second refractive power, whereby the lens stack is configured to exert substantially no refractive power on light having a polarization direction perpendicular to the optical axis.

5. The method described in claim 2, wherein the lens stack is configured to exert an optical force proportional to Δn on light having a polarization direction parallel to the optical axis.

6. The method of claim 1, wherein the adaptive lens assembly further comprises a switchable half-wave plate comprising twisted nematic (TN) liquid crystal (LC) optically coupled to the lens stack, and the focusing comprises, when activated, preserving the polarization of linearly polarized light passing through the switchable half-wave plate, and when deactivated, modifying the polarization of linearly polarized light passing through the switchable half-wave plate.

7. The switchable half-wave plate is disposed on a first side of the lens stack, and the adaptive lens assembly is disposed on a second side of the lens stack. a second switchable half-wave plate comprising a TN LC optically coupled to the lens stack; a second lens stack configured to exert a polarization dependent optical power on linearly polarized light; and Further equipped with the second lens stack comprises a second birefringent lens and a second isotropic lens, the second birefringent lens and the second isotropic lens contacting each other and forming a conformal interface therebetween; 7. The method of claim 6, wherein the focusing comprises selectively switching the adaptive lens assembly between at least four states by electrically activating and / or deactivating the switchable half-wave plate and / or the second switchable half-wave plate.

8. The method of claim 1, wherein the birefringent lens comprises a reactive mesogen, and the lens stack comprises electrodes configured to apply an electric field across the birefringent lens such that the lens stack is configured to be electrically switchable between different refractive power states.

9. A method, comprising: and focusing the virtual image at a plurality of depth planes within a view of the real world via a head-mounted augmented reality display device, said focusing comprising: directing light through a waveguide assembly in a lateral direction parallel to an output surface of said waveguide assembly; outcoupling the guided light through the output surface via the waveguide assembly; receiving light outcoupled from the waveguide assembly via an adaptive lens assembly disposed on a first side of the waveguide assembly; selectively switching the adaptive lens assembly between a plurality of states having different optical powers to focus the virtual image at the plurality of depth planes in the real world view while simultaneously refocusing the real world view so that it appears without substantial distortion; A method comprising:

10. The method of claim 9, wherein the adaptive lens assembly comprises a lens stack configured to exert a polarization-dependent refractive power on linearly polarized light, the lens stack comprising a birefringent lens and an isotropic lens in contact with each other, the contact surfaces of the birefringent lens and the isotropic lens forming a shape-matching interface.

11. The birefringent lens has an optical axis and a birefringence (Δn), and is configured to exert a first refractive power on light having a polarization direction parallel to the optical axis and to exert a second refractive power on light having a polarization direction perpendicular to the optical axis; 11. The method of claim 10, wherein the isotropic lens has a refractive index and is configured to exert a third refractive power on light passing therethrough, the third refractive power being opposite in sign to at least one of the first and second refractive powers.

12. The adaptive lens assembly, wherein the adaptive lens assembly is a first adaptive lens assembly; The method comprises: selectively switching a second adaptive lens assembly disposed on a second side of the waveguide assembly opposite the first side between a plurality of states having different optical powers; 11. The method of claim 10, comprising exerting a polarization dependent refractive power on linearly polarized light by a second lens stack, the second lens stack comprising a second birefringent lens and a second isotropic lens, the second birefringent lens and the second isotropic lens contacting each other and forming a conformal interface therebetween.

13. The method of claim 12, wherein each of the first and second adaptive lens assemblies further comprises a switchable half-wave plate comprising twisted nematic (TN) liquid crystal (LC) optically coupled to a respective one of the lens stacks or the second lens stack, and wherein the focusing includes, when activated, preserving the polarization of linearly polarized light passing therethrough through the switchable half-wave plate, and when deactivated, modifying the polarization of linearly polarized light passing therethrough through the switchable half-wave plate.

14. The method described in claim 13, wherein each of the plurality of refractive powers exerted by the second adaptive lens assembly has a corresponding one of the plurality of refractive powers exerted by the adaptive lens assembly having substantially the same magnitude and opposite sign.

15. The method of claim 9, wherein the adaptive lens assembly is formed on a first side of the waveguide assembly, and the head-mounted augmented reality display device further comprises a polarizing reflector inserted between the waveguide assembly and the adaptive lens assembly, the polarizing reflector configured to pass linearly polarized light having a first polarization therethrough and reflect linearly polarized light having a second polarization.

16. The method of claim 15, further comprising reflecting and modifying the polarization of linearly polarized light having the first polarization incident thereon by a non-polarizing reflector on a second side of the waveguide assembly, wherein a quarter-wave plate is interposed between the non-polarizing reflector and the waveguide assembly.

17. The method of claim 9, further comprising passing circularly polarized light having a first polarization through a polarizing reflector interposed between the adaptive lens assembly and the waveguide assembly and comprising a cholesteric liquid crystal, and reflecting circularly polarized light having a second polarization through the polarizing reflector.

18. The method of claim 17, further comprising reflecting and modifying the polarization of the circularly polarized light incident thereon having the second circular polarization by a non-polarizing reflector on a second side of the waveguide assembly.

19. The method of claim 12, wherein each of the birefringent lens and the second birefringent lens comprises a reactive mesogen, and each of the lens stack and the second lens stack comprises an electrode configured to switch each of the lens stack and the second lens stack between different refractive power states.

20. The method of claim 10, wherein the birefringent lens comprises a reactive mesogen and the lens stack comprises electrodes for electrically switching the lens stack between at least two refractive power states.

Images