Facebook Patent | Fluid lens with output grating

Patent: Fluid lens with output grating

Drawings: Click to check drawins

Publication Number: 20210132387

Publication Date: 20210506

Applicant: Facebook

Abstract

In some examples, a device, such as an augmented reality or virtual reality device, may include one or more waveguide displays and one or more adjustable lenses, such as adjustable fluid lenses. In some examples, a device includes a waveguide display and a rear lens assembly that together provide a negative optical power for augmented reality light. A front lens assembly, the waveguide display, and the rear lens assembly may together provide an approximately zero optical power for real-world light. In some examples, an eye-side optical element having a negative optical power may defocus light from the waveguide display. Example devices may allow the adjustable lens (or lenses) to have a reduced mass and/or a faster response time.

Claims

1. A device comprising an optical configuration, wherein the optical configuration comprises: a front lens assembly comprising a front adjustable lens; a waveguide display assembly configured to provide augmented reality light; and a rear lens assembly comprising a rear adjustable lens, wherein: the waveguide display assembly is located between the front lens assembly and the rear lens assembly, a combination of the waveguide display assembly and the rear lens assembly provide a negative optical power for the augmented reality light, and the device is configured to provide an augmented reality image formed using the augmented reality light within a real-world image.

2. The device of claim 1, wherein the real-world image is formed by real-world light received by the front lens assembly, the real-world light then passing through at least a portion of the waveguide display assembly and the rear lens assembly.

3. The device of claim 1, wherein the device is configured so that, when worn by a user: the front lens assembly receives real-world light used to form the real-world image, and the rear lens assembly is located proximate an eye of the user.

4. The device of claim 1, wherein the device is configured so that the negative optical power corrects for vergence-accommodation conflict (VAC) between the real-world image and the augmented reality image.

5. The device of claim 1, wherein the waveguide display assembly provides at least a portion of the negative optical power for the augmented reality light.

6. The device of claim 1, wherein the waveguide display assembly comprises a waveguide display and a negative lens.

7. The device of claim 1, wherein the waveguide display assembly has a negative optical power of between approximately -1.5 D and -2.5 D, where D represents diopters.

8. The device of claim 1, wherein the waveguide display assembly comprises a waveguide display and the waveguide display provides the at least a portion of the negative optical power.

9. The device of claim 1, wherein the waveguide display assembly comprises a grating.

10. The device of claim 1, wherein the front adjustable lens comprises a front adjustable fluid lens having a front substrate, a front membrane, and a front lens fluid located between the front substrate and the front membrane.

11. The device of claim 1, wherein the rear adjustable lens comprises a rear adjustable fluid lens having a rear substrate, a rear membrane, and a rear lens fluid located between the rear substrate and the rear membrane.

12. The device of claim 1, wherein the rear lens assembly provides at least some of the negative optical power.

13. The device of claim 1, wherein the front lens assembly has a positive optical power.

14. The device of claim 13, wherein the positive optical power and the negative optical power are approximately equal in magnitude.

15. The device of claim 1, wherein the rear lens assembly comprises the rear adjustable lens and a supplemental negative lens.

16. The device of claim 1, wherein: the rear adjustable lens comprises a substrate; and the substrate has a concave exterior surface.

17. The device of claim 1, wherein: real-world light is received by the device through the front lens assembly and passes through the waveguide display assembly and the rear lens assembly to form the real-world image; the augmented reality light is provided by the waveguide display assembly and passes through the rear lens assembly to form the augmented reality image; and the negative optical power reduces vergence-accommodation conflict between the real-world image and the augmented reality image.

18. The device of claim 1, wherein the device is an augmented reality headset.

19. A method comprising: receiving real-world light through a front lens assembly and generating a real-world image by directing the real-world light through a waveguide display and a rear lens assembly; and directing augmented reality light from the waveguide display through the rear lens assembly to form an augmented reality image, wherein: the waveguide display and the rear lens assembly cooperatively provide a negative optical power for the augmented reality light, and the front lens assembly, waveguide display, and the rear lens assembly cooperatively provide an approximately zero optical power for the real-world light.

20. The method of claim 19, wherein the waveguide display receives the augmented reality light from an augmented reality light source and directs the augmented reality light out of the waveguide display using a grating.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 62/930,797, filed Nov. 5, 2019, the disclosure of which is incorporated, in its entirety, by this reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The accompanying drawings illustrate a number of exemplary embodiments and are a part of the specification. Together with the following description, these drawings demonstrate and explain various principles of the present disclosure.

[0003] FIGS. 1A-1C illustrate example fluid lenses.

[0004] FIGS. 2A-2G illustrate example fluid lenses and adjustment of the optical power of the fluid lenses.

[0005] FIG. 3 illustrates an example ophthalmic device.

[0006] FIGS. 4A-4B illustrate a fluid lens having a membrane assembly including a support ring.

[0007] FIG. 5 illustrates deformation of a non-circular fluid lens.

[0008] FIGS. 6, 7, and 8 illustrate vergence and accommodation distances, for example, within an augmented reality device including one or more adjustable lenses.

[0009] FIGS. 9A and 9B illustrate an optical configuration including a front lens assembly, a waveguide display, and a rear lens assembly.

[0010] FIG. 10 illustrates an eyeshape outline and a neutral circle.

[0011] FIGS. 11 and 12 illustrate optical powers associated with various surfaces of example optical configurations.

[0012] FIGS. 13A and 13B show lens thickness and fluid mass as a function of waveguide display optical power, for an example optical configuration.

[0013] FIGS. 14 and 15 illustrate optical powers associated with various surfaces of example optical configurations.

[0014] FIGS. 16A and 16B show lens thickness and fluid mass as a function of waveguide display optical power, for an example optical configuration.

[0015] FIG. 17 shows an example method of operating an augmented reality device.

[0016] FIG. 18 illustrates an example control system.

[0017] FIG. 19 illustrates an example display device.

[0018] FIG. 20 illustrates an example waveguide display.

[0019] FIG. 21 is an illustration of an exemplary artificial-reality headband that may be used in connection with some embodiments of this disclosure.

[0020] FIG. 22 is an illustration of exemplary augmented-reality glasses that may be used in connection with some embodiments of this disclosure.

[0021] FIG. 23 is an illustration of an exemplary virtual-reality headset that may be used in connection with some embodiments of this disclosure.

[0022] FIG. 24 is an illustration of exemplary haptic devices that may be used in connection with some embodiments of this disclosure.

[0023] FIG. 25 is an illustration of an exemplary virtual-reality environment according to some embodiments of this disclosure.

[0024] FIG. 26 is an illustration of an exemplary augmented-reality environment according to some embodiments of this disclosure.

[0025] Throughout the drawings, identical reference characters and descriptions indicate similar, but not necessarily identical, elements. While the exemplary embodiments described herein are susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail herein. However, the exemplary embodiments described herein are not intended to be limited to the particular forms disclosed. The present disclosure includes all modifications, equivalents, and alternatives falling within the scope of the appended claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0026] The present disclosure is generally directed to devices including fluid or liquid lenses, including adjustable liquid lenses. Fluid lenses are useful in a variety of applications. Improvements in the performance of such devices would, therefore, be of value in various applications. As is explained in greater detail below, embodiments of the present disclosure may be directed to devices and systems including fluid lenses, methods of device fabrication, and methods of device operation. In some examples, such devices may include eyewear devices, such as spectacles, sunglasses, goggles, visors, eye protection devices, augmented reality devices, virtual reality devices, and the like. Embodiments of the present disclosure may also include devices having one or more fluid lenses and a waveguide display assembly.

[0027] Adjustable fluid lenses are useful for ophthalmic, virtual reality (VR), and augmented reality (AR) devices. In some example AR and/or VR devices, one or more fluid lenses may be used for the correction of what is commonly known as the vergence accommodation conflict (VAC). Examples described herein may include such devices, including fluid lenses for the correction of VAC. Examples disclosed herein may also include fluid lenses, membrane assemblies (which may include a membrane and, e.g., a peripheral structure such as a support ring or a peripheral guide wire), and devices including one or more fluid lenses and waveguide display assemblies configured to provide augmented reality image elements.

[0028] Embodiments described herein may include adjustable fluid lenses including a substrate and a membrane, at least in part enclosing a lens enclosure. The lens enclosure may also be referred to hereinafter as an “enclosure” for conciseness. The enclosure may enclose a lens fluid (sometimes herein referred to a “fluid” for conciseness), and the interior surface of the enclosure may be proximate or adjacent the lens fluid.

[0029] The following provides, with reference to FIGS. 1-26, detailed descriptions of such devices, fluid lenses, optical configurations, methods, and the like. FIGS. 1-5 illustrate example fluid lenses. FIGS. 6-8 illustrate vergence and accommodation distances, for example, within an augmented reality device having adjustable lenses. FIGS. 9A and 9B illustrate an optical configuration including a front lens assembly, a waveguide display, and a rear lens assembly. FIG. 10 illustrates an eyeshape outline and a neutral circle. FIGS. 11-12 and 14-15 illustrate optical powers associated with various surfaces of example optical configurations. FIGS. 13A-13B and 16A-16B show example lens thickness and fluid mass as a function of waveguide display optical power. FIG. 17 shows an example method, for example, of operating an augmented reality device. FIG. 18 illustrates an example control system. FIG. 19 illustrates an example display device. FIG. 20 illustrates an example waveguide display. FIGS. 21-26 illustrate example augmented reality and/or virtual reality devices, which may include one or more fluid lenses according to embodiments of this disclosure.

[0030] Features from any of the embodiments described herein may be used in combination with one another in accordance with the general principles described herein. These and other embodiments, features, and advantages will be more fully understood upon reading the detailed description in conjunction with the accompanying drawings and claims.

[0031] FIG. 1A depicts a cross-section through a fluid lens, according to some examples. The fluid lens 100 illustrated in this example includes a substrate 102, a substrate coating 104, a membrane 106, a fluid 108 (denoted by dashed horizontal lines), an edge seal 110, a support structure 112 providing a guide surface 114, and a membrane attachment 116. In this example, the substrate 102 is a generally rigid, planar substrate having a lower (as illustrated) outer surface, and an interior surface on which the substrate coating 104 is supported. However, one or both surfaces of the substrate may be spherical, sphero-cylindrical, or formed with a more complex surface shape of the kind typically found in an ophthalmic lens (e.g., progressive, digressive, bifocal, and the like). In this example, the interior surface 120 of the substrate coating 104 is in contact with the fluid 108. The membrane 106 has an upper (as illustrated) outer surface and an interior surface 122 bounding the fluid 108. The substrate coating 104 is optional, and may be omitted.

[0032] The fluid 108 is enclosed within an enclosure 118, which is at least in part defined by the substrate 102 (along with the substrate coating 104), the membrane 106, and the edge seal 110, which here cooperatively define the enclosure 118 in which the fluid 108 is located. The edge seal 110 may extend around the periphery of the enclosure 118 and retain (in cooperation with the substrate and the membrane) the fluid within the enclosed fluid volume of the enclosure 118. In some examples, an enclosure may be referred to as a cavity or lens cavity.

[0033] In this example, the membrane 106 is shown with a curved profile so that the enclosure has a greater thickness in the center of the lens than at the periphery of the enclosure (e.g., adjacent the edge seal 110). The profile of the membrane may be adjustable to permit adjusting the optical power of the fluid lens 100. In some examples, the fluid lens may be a plano-convex lens, with the planar surface being provided by the substrate 102 and the convex surface being provided by the membrane 106. A plano-convex lens may have a thicker layer of lens fluid around the center of the lens. In some examples, the exterior surface of a membrane may provide the convex surface, with the interior surface being substantially adjacent the lens fluid.

[0034] The support structure 112 (which in this example may include a guide slot through which the membrane attachment 116 may extend) may extend around the periphery (or within a peripheral region) of the substrate 102, and may attach the membrane to the substrate. The support structure may provide a guide path, in this example a guide surface 114 along which a membrane attachment 116 (e.g., located within an edge portion of the membrane) may slide. The membrane attachment may provide a control point for the membrane, so that the guide path for the membrane attachment may provide a corresponding guide path for a respective control point.

[0035] The fluid lens 100 may include one or more actuators (not shown in FIG. 1A) that may be located around the periphery of the lens and may be part of or mechanically coupled to the support structure 112. The actuators may exert a controllable force on the membrane at one or more control points, such as provided by membrane attachment 116, that may be used to adjust the curvature of the membrane surface and hence at least one optical property of the lens, such as focal length, astigmatism correction, surface curvature, cylindricity, or any other controllable optical property. In some examples, the membrane attachment may be attached to an edge portion of the membrane, or to a peripheral structure extending around the periphery of the membrane (such as a peripheral guide wire, or a guide ring), and may be used to control the curvature of the membrane.

[0036] In some examples, FIG. 1A may represent a cross-section through a circular lens, though examples fluid lenses may also include non-circular lenses, as discussed further below.

[0037] FIG. 1B shows a fluid lens, of which FIG. 1A may be a cross-section. The figure shows the fluid lens 100, including the substrate 102, the membrane 106, and the support structure 112. In this example, the fluid lens 100 may be a circular fluid lens. The figure shows the membrane attachment 116 as moveable along a guide path defined by the guide slot 130 and the profile of the guide surface 114 (shown in FIG. 1A). The dashed lines forming a cross are visual guides indicating a general exterior surface profile of the membrane 106. In this example, the membrane profile may correspond to a plano-convex lens.

[0038] FIG. 1C shows a non-circular lens 150 that may otherwise be similar to the fluid lens 100 of FIG. 1B and may have a similar configuration. The non-circular lens 150 includes substrate 152, membrane 156, and support structure 162. The lens has a similar configuration of the membrane attachment 166, movable along a guide path defined by the guide slot 180. The profile of a guide path may be defined by the surface profile of the support structure 162, through which the guide slot is formed. The cross-section of the lens may be analogous to that of FIG. 1A. The dashed lines forming a cross on the membrane 156 are visual guides indicating a general exterior surface profile of the membrane 156. In this example, the membrane profile may correspond to a plano-convex lens.

[0039] FIGS. 2A-2D illustrate an ophthalmic device 200 including a fluid lens 202, according to some examples. FIG. 2A shows a portion of an ophthalmic device 200, which includes a portion of a peripheral structure 210 (which may include a guide wire or a support ring) supporting a fluid lens 202.

[0040] In some examples, the lens may be supported by a frame. An ophthalmic device (e.g., spectacles, goggles, eye protectors, visors, and the like) may include a pair of fluid lenses, and the frame may include components configured to support the ophthalmic device on the head of a user, for example, using components that interact with (e.g., rest on) the nose and/or ears of the user.

[0041] FIG. 2B shows a cross-section through the ophthalmic device 200, along A-A’ as shown in FIG. 2A. The figure shows the peripheral structure 210 and the fluid lens 202. The fluid lens 202 includes a membrane 220, lens fluid 230, an edge seal 240, and a substrate 250. In this example, the substrate 250 includes a generally planar, rigid layer. The figure shows that the fluid lens may have a planar-planar configuration, which in some examples may be adjusted to a plano-concave and/or plano-convex lens configuration. The substrate 250 may, in some examples, include a non-planar optical surface having fixed optical power(s).

[0042] In some examples disclosed herein, one or both surfaces of the substrate may include a concave or convex surface, and in some examples the substrate may have a non-spherical surface such as a toroidal or freeform optical progressive or digressive surface. In some examples, a substrate may have a concave or convex exterior substrate surface, and an interior surface substantially adjacent the fluid. In various examples, the substrate may include a plano-concave, plano-convex, biconcave, biconvex, or concave-convex (meniscus) lens, or any other suitable optical element. In some examples, one or both surfaces of the substrate may be curved. For example, a fluid lens may be a meniscus lens having a substrate (e.g., a generally rigid substrate having a concave exterior substrate surface and a convex interior substrate surface), a lens fluid, and a convex membrane exterior profile. The interior surface of a substrate may be adjacent to the fluid, or adjacent to a coating layer in contact with the fluid.

[0043] FIG. 2C shows an exploded schematic of the device shown in FIG. 2B, in which corresponding elements have the same numbering as discussed above in relation to FIG. 2A. In this example, the edge seal is joined with a central seal portion 242 extending over the substrate 250.

[0044] In some examples, the central seal portion 242 and the edge seal 240 may be a unitary element. In other examples, the edge seal may be a separate element, and the central seal portion 242 may be omitted or replaced by a coating formed on the substrate. In some examples, a coating may be deposited on the interior surface of the seal portion and/or edge seal. In some examples, the lens fluid may be enclosed in a flexible enclosure (sometimes referred to as a bag) that may include an edge seal, a membrane, and a central seal portion. In some examples, the central seal portion may be adhered to a rigid substrate component and may be considered as part of the substrate. In some examples, the coating may be deposited on at least a portion of the enclosure surface (e.g., the interior surface of the enclosure). The enclosure may be provided, at least in part, by one or more of the following: a substrate, an edge seal, a membrane, a bag, or other lens component. The coating may be applied to at least a portion of the enclosure surface at any suitable stage of lens fabrication, for example, to one or more lens components (e.g., the interior surface of a substrate, membrane, edge seal, bag, or the like) before, during, or after lens assembly. For example, a coating may be formed before lens assembly (e.g., during or after fabrication of lens components); during lens assembly; after assembly of lens components but before introduction of the fluid to the enclosure; or by introduction of a fluid including a coating material into the enclosure. In some examples, a coating material (such as a coating precursor) may be included within the fluid introduced into the enclosure. The coating material may form a coating on at least a portion of the enclosure surface adjacent the fluid.

[0045] FIG. 2D shows adjustment of the device configuration, for example, by adjustment of forces on the membrane using actuators (not shown). As shown, the device may be configured in a planar-convex fluid lens configuration. In an example plano-convex lens configuration, the membrane 220 tends to extend away from the substrate 250 in a central portion.

[0046] In some examples, the lens may also be configured in a planar-concave configuration, in which the membrane tends to curve inwardly towards the substrate in a central portion.

[0047] FIG. 2E illustrates a similar device to FIG. 2B, and element numbering is similar. However, in this example, the substrate 250 of the example of FIG. 2B is replaced by a second membrane 221, and there is a second peripheral structure (such as a second support ring) 211. In some examples disclosed herein, the membrane 220 and/or the second membrane 221 may be integrated with the edge seal 240.

[0048] FIG. 2F shows the dual membrane fluid lens of FIG. 2E in a biconcave configuration. For example, application of negative pressure to the lens fluid 230 may be used to induce the biconcave configuration. In some examples, the membrane 220 and second membrane 221 may have similar properties, and the lens configuration may be generally symmetrical, for example, with the membrane and second membrane having similar radii of curvature (e.g., as a symmetric biconvex or biconcave lens). In some examples, the lens may have rotational symmetry about the optical axis of the lens, at least within a central portion of the membrane, or within a circular lens. In some examples, the properties of the two membranes may differ (e.g., in one or more of thickness, composition, membrane tension, or in any other relevant membrane parameter), and/or the radii of curvature may differ. In these examples, the membrane profiles have a negative curvature that corresponds to a concave curvature. The membrane profile may relate to the external shape of the membrane. A negative curvature may have a central portion of the membrane closer to the optical center of the lens than a peripheral portion (e.g., as determined by radial distances from the center of the lens).

[0049] FIG. 2G shows the dual membrane fluid lens of FIG. 2E in a biconvex configuration, with corresponding element numbers.

[0050] In some examples, an ophthalmic device, such as an eyewear device, includes one or more fluid lenses. An example device includes at least one fluid lens supported by eyeglass frames. In some examples, an ophthalmic device may include an eyeglass frame, goggles, or any other frame or head-mounted structure to support one or more fluid lenses, such as a pair of fluid lenses.

[0051] FIG. 3 illustrates an ophthalmic device, in this example an eyewear device, including a pair of fluid lenses, according to some examples. The eyewear device 300 may include a pair of fluid lenses (306 and 308) supported by a frame 310 (which may also be referred to as an eyeglass frame). The pair of fluid lenses 306 and 308 may be referred to as left and right lenses, respectively (from the viewpoint of the user).

[0052] In some examples, an eyewear device (such as eyewear device 300 in FIG. 3) may include an ophthalmic device (such as eyeglasses or spectacles), smart glasses, a virtual reality headset, an augmented reality device, a head-up device, visor, goggles, other eyewear, other device, or the like. In such eyewear devices, the fluid lenses 306, 308 may form the primary vision-correcting or adjusting lenses which are positioned in a user’s field of view in use. An ophthalmic device may include fluid lenses that have an optical property (such as an optical power, astigmatism correction, cylindricity, or other optical property) corresponding to a prescription, for example, as determined by an eye examination. An optical property of the lens may be adjustable, for example, by a user or by an automated system. Adjustments to the optical property of a fluid lens may be based on the activity of a user, the distance to an observed article, or other parameter. In some examples, one or more optical properties of an eyewear device may be adjusted based on a user identity. For example, an optical property of one or more lenses within an AR and/or VR headset may be adjusted based on the identity of the user, which may be determined automatically (e.g., using a retinal scan) or by a user input.

[0053] In some examples, a device may include a frame (such as an eyeglass frame) that may include or otherwise support one or more of any of the following: a battery, a power supply or power supply connection, other refractive lenses (including additional fluid lenses), diffractive elements, displays, eye-tracking components and systems, motion tracking devices, gyroscopes, computing elements, health monitoring devices, cameras, and/or audio recording and/or playback devices (such as microphones and speakers). The frame may be configured to support the device on a head of the user.

[0054] FIG. 4A shows an example fluid lens 400 including a peripheral structure 410 that may generally surround a fluid lens 402. The peripheral structure 410 (in this example, a support ring) includes membrane attachments 412 that may correspond to the locations of control points for the membrane of the fluid lens 402. A membrane attachment may be an actuation point, where the lens may be actuated by displacement (e.g., by an actuator acting along the z-axis) or moved around a hinge point (e.g., where the position of the membrane attachment may be an approximately fixed distance “z” from the substrate). In some examples, the peripheral structure and hence the boundary of the membrane may flex freely between neighboring control points. Hinge points may be used in some examples to prevent bending of the peripheral structure (e.g., a support ring) into energetically favorable, but undesirable, shapes.

[0055] A rigid peripheral structure, such as a rigid support ring, may limit adjustment of the control points of the membrane. In some examples, such as a non-circular lens, a deformable or flexible peripheral structure, such as a guide wire or a flexible support ring, may be used.

[0056] FIG. 4B shows a cross-section of the example fluid lens 400 (e.g., along A-A’ as denoted in FIG. 4A). The fluid lens includes a membrane 420, fluid 430, edge seal 440, and substrate 450. The edge seal 440 may be flexible and/or collapsible. In some examples, the peripheral structure 410 may surround and be attached to the membrane 420 of the fluid lens 402. The peripheral structure may include membrane attachments 412 that may provide the control points for the membrane. The position of the membrane attachments (e.g., relative to a frame, substrate, or each other) may be adjusted using one or more actuators, and used to adjust, for example, the optical power of the lens. A membrane attachment having a position adjusted by an actuator may also be referred to as an actuation point, or a control point. Membrane attachments may also include non-actuation points, such as hinge points.

[0057] In some examples, an actuator 460 may be attached to actuator support 462, and the actuator may be used to vary the distance between the membrane attachment and the substrate, for example, by urging the membrane attachment along an associated guide path. In some examples, the actuator may be located on the opposite side of the membrane attachment from the substrate. In some examples, an actuator may be located so as to exert a generally radial force on the membrane attachment and/or support structure, for example, exerting a force to urge the membrane attachment towards or away from the center of the lens.

[0058] In some examples, one or more actuators may be attached to respective actuator supports. In some examples, an actuator support may be attached to one or more actuators. For example, an actuator support may include an arcuate, circular, or other shaped member along which actuators are located at intervals. Actuator supports may be attached to the substrate, or, in some examples, to another device component such as a frame. In some examples, the actuator may be located between the membrane attachment and the substrate, or may be located at another suitable location. In some examples, the force exerted by the actuator may be generally directed along a direction normal to the substrate, or along another direction, such as along a direction at a non-normal direction relative to the substrate. In some examples, at least a component of the force may be generally parallel to the substrate. The path of the membrane attachment may be based on the guide path, and in some examples the force applied by the actuator may have at least an appreciable component directed along the guide path.

[0059] FIG. 5 shows an example fluid lens 500 including a peripheral structure 510, here in the form of the support ring including a plurality of membrane attachments 512, and extending around the periphery of a membrane 520. Membrane attachments may include one or more actuation points and optionally one or more hinge points. The membrane attachments may include or interact with one or more support structures that each provide a guide path for an associated control point of the membrane 520. Actuation of the fluid lens may adjust the location of one or more control points of the membrane, for example, along the guide paths provided by the support structures. Actuation may be applied at discrete points on the peripheral structure, such as the membrane attachments shown. In some examples, the peripheral structure may be flexible, for example, so that the peripheral structure may not be constrained to lie within a single plane.

[0060] In some examples, a fluid lens includes a membrane, a support structure, a substrate, and an edge seal. The support structure may be configured to provide a guide path for an edge portion of the membrane (such as a control point provided by a membrane attachment). An example membrane attachment may function as an interface device, configured to mechanically interconnect the membrane and the support structure, and may allow the membrane to exert an elastic force on the support structure. A membrane attachment may be configured to allow the control point of the membrane (that may be located in an edge portion of the membrane) to move freely along the guide path.

[0061] An adjustable fluid lens may be configured so that adjustment of the membrane profile (e.g., an adjustment of the membrane curvature) may result in no appreciable change in the elastic energy of the membrane, while allowing modification of an optical property of the lens (e.g., a focal length adjustment). This configuration may be termed a “zero-strain” device configuration as, in some examples, adjustment of at least one membrane edge portion, such as at least one control point, along a respective guide path does not appreciably change the strain energy of the membrane. In some examples, a “zero-strain” device configuration may reduce the actuation force required by an order of magnitude when compared with a conventional support beam type configuration. A conventional fluid lens may, for example, require an actuation force that is greater than 1N for an actuation distance of 1 mm. Using a “zero-strain” device configuration, actuation forces may be 0.1N or less for an actuation of 1 mm, for quasi-static actuation. This substantial reduction of actuation forces may enable the use of smaller, more speed-efficient actuators in fluid lenses, resulting in a more compact and efficient form factor. In such examples, in a “zero-strain” device configuration, the membrane may actually be under appreciable strain, but the total strain energy in the membrane may not change appreciably as the lens is adjusted. This may advantageously greatly reduce the force used to adjust the fluid lens.

[0062] In some examples, a fluid lens may be configured to have one or both of the following features: in some examples, the strain energy in the membrane is approximately equal for all actuation states; and in some examples, the force reaction at the membrane edge is normal to the guide path. Hence, in some examples, the strain energy of the membrane may be approximately independent of the optical power of the lens. In some examples, the force reaction at the membrane edge may be normal to the guide path for some or all locations on the guide path.

[0063] In some examples, movement of the edge portion of the membrane along the guide path may not result in an appreciable change in the elastic energy of the membrane. This configuration may be termed a “zero-strain” guide path as, in some examples, adjustment of the membrane edge portion along the guide path does not appreciably change the strain energy of the membrane.

[0064] In some examples, the fluid lenses of the present disclosure may be used as principal lenses in eyewear. As described herein, such lenses may be positioned in front of a user’s eyes so the user looks through the lens at objects or images to be viewed, for example, when the user is wearing a head mounted device including one or more lenses. The lenses may be configured for vision correction or manipulation as described herein. Embodiments of the present disclosure may include fluid lenses including a lens fluid having a gas content, or reduced Henry law gas solubility, which may be controlled (e.g., reduced) to reduce the likelihood of bubble formation in the lens fluid.

[0065] FIG. 6 illustrates vergence-accommodation agreement in an eyewear device 600, such as a virtual reality device. The drawing is a horizontal-plane section view showing left and right waveguide displays, 610L and 610R respectively, and left and right adjustable fluid-filled lenses 602L and 602R, respectively. The element letter suffixes L and R are used to denote left and right elements, respectively. Each fluid lens, such as the right lens 602R, includes a membrane 620, a lens fluid 630, a side wall 640, and a substrate 650. The membrane, side wall, and substrate, at least in part, cooperatively provide an enclosure including the lens fluid 630. The waveguide displays 610L and 610R project stereoscopic virtual object 606 into the user’s eyes, such as right eye 604. Rays of light from the waveguide displays are shown as solid lines, extending from the waveguide displays to the eyes, while virtual rays (i.e. the apparent direction the rays came from) are denoted by dashed lines. The figure also shows the vergence angle .theta..sub.v, the corresponding vergence distance, the accommodation angle .theta..sub.a, and the accommodation distance.

[0066] The eyewear device 600 has properly adjusted fluid lenses 602L and 602R. The vergence distance and the accommodation distance to the virtual object 606 are approximately equal, and there is no vergence-accommodation conflict. In this example, the waveguide displays 610L, 610R output parallel rays of light that are defocused (diverged) by the corresponding negative power lenses 602L, 602R, respectively. The reduction of vergence-accommodation conflict (VAC) is very useful as this helps prevent possible VAC-related adverse effects on a user of the eyewear device, such as nausea, headaches, and the like. Examples of the present disclosure allow the reduction, substantial avoidance, or effective elimination of VAC, for example, using a negative optical power provided by the waveguide display assembly and/or the rear lens assembly.

[0067] FIG. 7 shows an eyewear device 700 with left and right fluid lenses 702L and 702R (respectively) that are incorrectly adjusted so that the accommodation distance of the virtual object 706 does not match the vergence distance from stereoscopy, and in this example the accommodation distance is appreciably less than the vergence distance. In this configuration, the user may experience VAC discomfort. Each fluid lens includes a membrane 720, a side wall 740, and a substrate 750. The membrane, side wall, and substrate, at least in part, cooperatively provide an enclosure including the lens fluid 730. The waveguide displays 710L and 710R project stereoscopic virtual object 706 (e.g., an augmented reality image element) into the user’s eyes, such as the right eye 704.

[0068] FIG. 8 shows a correctly adjusted eyewear device 800, for example, an augmented reality device. This device may be similar to the virtual reality device of FIG. 6. In addition to the eye-side adjustable lenses 870L and 870R for defocusing the light from waveguide displays 810L and 810R, the device includes front adjustable lenses 880L and 880R (e.g., front adjustable fluid lenses) to compensate for lenses 870L and 870R, for viewing real object 808 using the user’s eyes, such as eye 804. In some examples, the optical power of 880L and 880R are equal and opposite to that of 870L and 870R. The optical power of an example front lens may be equal in magnitude to the optical power of a rear lens assembly (or to the optical power of the rear lens assembly in combination with the waveguide display assembly 810). For example, if lens 870R has an optical power of -2D, then lens 880R may have an optical power +2D. Rays of light from the real object 808 are shown as solid lines, and the virtual rays to the apparent position of virtual object 806 are shown as dashed lines. Each front adjustable lens may include a front membrane 820, front lens fluid 830, and front substrate 850. Each rear adjustable lens may include a rear substrate 860, rear side wall 862, rear membrane 864, and rear lens fluid 866. Front and rear lens assemblies may include front and rear adjustable lenses, respectively, and any desired associated component, such as a frame or component thereof, actuator, and/or the like. The waveguide display assembly 810 is located between the front and rear lens assemblies.

[0069] FIG. 9A shows a schematic of an example optical configuration, for example, for an augmented reality device. The device includes waveguide display 900, rear adjustable lens 920, and front adjustable lens 930. An optional second rear lens 910 may be included, here denoted with the subscript hhr. In this example, the optical configuration includes, from left to right, a first lens or substrate 926 (which may include a non-adjustable lens, such as a hard lens or other non-adjustable lens, or a substrate), rear adjustable lens 920, optional second rear lens 910 (which may be a non-adjustable lens, such as a hard lens or other non-adjustable lens), a waveguide display 900 including a grating 904, a front substrate 932 (which may have a curved or planar surface), and a front adjustable lens 930 (which may include the front substrate 932). Adjustable lenses may include fluid lenses, such as those discussed herein, which may include a substrate, a lens fluid, and a membrane. The membrane may provide an adjustable curved surface, for example, as shown at 924 and 934. These examples are for illustrative purposes only, and may be used to define the various symbols. The illustration is not to scale, and may be shown expanded the in the thickness and separation of the optical elements for clarity.

[0070] In this example, the adjustable lenses may have an adjustable optical surface denoted with subscript m for membrane (or adjustable surface), and a non-adjustable optical surface denoted with a subscript h for hard (or non-adjustable surface). As discussed further below, the subscripts m (membrane) and h (hard) may be combined with the subscripts f (front) and r (rear), and in some cases with subscripts 1 or 2, referring to first or second actuation states respectively. These subscripts may be used to label the optical power of the respective surface. In this context, the term “hard” may refer to a generally non-adjustable surface, or a surface for which any change in curvature may be reasonably neglected in the analysis. The optical power may be denoted .PHI., and may be given in diopters, sometimes abbreviated to “D”. The subscripts f and r relate to the front (world side) and rear (eye side) of the device, respectively. The subscript v refers to virtual content, and the subscripts 1 and 2 refer to first and second actuation states. In some examples, for illustrative purposes, a hard surface may be shown as having a slight lateral displacement between two actuation states, but the optical power of the surface may be unchanged. The subscript g refers to the optical power of an output grating on the waveguide display, and the grating optical power is denoted .PHI..sub.g. Regarding the optical power associated with various curved surfaces, the rear non-adjustable surface 922 has an optical power .PHI..sub.hr, the rear adjustable surface 924 in a first actuation state has an optical power .PHI..sub.mr1, the non-adjustable surface 912 of the optional second rear lens 910 has an optical power .PHI..sub.hhr, the front non-adjustable surface of front substrate 932 has an optical power .PHI..sub.hf, and the front adjustable membrane surface 934 has an optical power .PHI..sub.mf1 in a first actuation state. In this example, the front substrate 932 may have a planar surface, but in some examples, one or both planar surfaces of the front substrate 932 may be replaced by a curved surface (e.g., a non-adjustable or adjustable curved surface). In some examples, one or more of the illustrated non-adjustable surfaces may be replaced by adjustable surfaces, such as adjustable curved surfaces.

[0071] FIG. 9B shows the same optical configuration as FIG. 9A, with the rear and front adjustable lenses in their second actuation states. In the second actuation states, the optical power of the rear adjustable lens 920 is denoted by .PHI..sub.mr2, and the optical power associated with the front adjustable membrane surface 934 (of front adjustable lens 930) is denoted by .PHI..sub.mf2. For conciseness, the front adjustable lens 930 may be referred to as the front lens, and the rear adjustable lens 920 may be referred to as the rear lens.

[0072] In some examples, the grating optical power may be non-adjustable, and may apply only to rays projected by the display; for example, .PHI..sub.g may only affect the user’s view of the virtual content, and not the real world.

[0073] The following equations may also be applied to the configuration illustrated in FIG. 9, or similar configurations, and may, for example, be adapted to other optical assemblies, including example optical assemblies with more, fewer, or different optical components.

[0074] In an example of zero net optical power, the real-world equations are:

.PHI..sub.hr+.PHI..sub.mr1+.PHI..sub.hhr+.PHI..sub.hf+.PHI..sub.mf1=0 (Equation 1)

.PHI..sub.hr+.PHI..sub.mr2+.PHI..sub.hhr+.PHI..sub.hf+.PHI..sub.mf2=0 (Equation 2)

[0075] Equations 1 and 2 do not include a term relating to grating power. Also, these equations may not apply in virtual reality devices, for example, in which there may be no real-world image.

[0076] The equivalent virtual-world equations are:

.PHI..sub.hr+.PHI..sub.mr1+.PHI..sub.hhr+.PHI..sub.g=.PHI..sub.v1 (Equation 3)

.PHI..sub.hr+.PHI..sub.mr2+.PHI..sub.hhr+.PHI..sub.g=.PHI..sub.v2 (Equation 4)

[0077] where .PHI..sub.v1 and .PHI..sub.v2 are the nearest and furthest virtual image projection powers, which may be predetermined, for example, by the optical design.

[0078] An example design may use .PHI..sub.v1=-3.5D and .PHI..sub.v2=-0.5D. This suggests that the virtual image may be in vergence-accommodation alignment between 29 cm and 2 m.

[0079] There are various possible design parameters, one or more of which may be used in the design of an optical configuration. An example design may include a minimum clearance between optical components (e.g., a minimum spacing between outside surfaces of adjacent components). For example, a design may include a condition that there is at least approximately 0.1 mm clearance between components. An example design may include a minimum thickness for any substrate, such as a non-adjustable substrate, or a non-adjustable lens. For example, a substrate may be at least approximately 0.5 mm thick. In some examples, a waveguide display may have a thickness of at least 1 mm, such as approximately 1.5 mm.

[0080] An example design may use spherical or non-spherical optics. In some examples, the lens fluid may include pentaphenyl trimethyl trisiloxane, which may have a refractive index of approximately 1.59, and a density of approximately 1.09 g/cc, under typical operating conditions.

[0081] FIG. 10 shows an example design eyeshape (in a solid line), with the optical center at the origin of the coordinate system shown. A consequence of the eyeshape and optical center is the size and location of the neutral circle (radius r.sub.n) shown as a dashed line in FIG. 10. For spherical optics, the neutral circle represents an intersection of the various membrane surface profiles for different actuation states, given the requirement of volume conservation from the incompressibility of the lens fluid. For example, with regard to the examples discussed above in relation to FIG. 9A, the membrane may intersect the neutral circle in the first and second actuation states 1 and 2, and between these locations at intermediate states.

[0082] In some examples, a device includes an optical configuration similar to that shown in FIG. 9A, but with the optional second rear lens 910 omitted. Equations 1-4, discussed above, may then be applied to this optical configuration, with .PHI..sub.hhr=0. Example design parameters may include a positive membrane curvature so that the pressure of the lens fluid is above atmospheric pressure. A minimum membrane curvature of +0.5D was chosen for evaluation. The positive pressure applied to the lens fluid may inhibit bubble formation. Also, having no curvature sign change during adjustment of a fluid lens may facilitate single-sided control of the membrane and may help reduce eye-obscuring specular reflections associated with a planar membrane state. For example, a planar membrane state may occur as a fluid lens is adjusted between positive (convex) and negative (concave) membrane configurations, for example, if the substrate is planar. In some examples, the fluid lens may not be integrated with the display.

[0083] In some examples, the grating optical power may be non-adjustable and may apply only to rays projected by the waveguide display. For example, the grating optical power (.PHI..sub.g) may only affect the user’s view of the virtual content (which may include augmented reality image elements) and not the real-world image.

[0084] FIG. 11 shows a surface plot of an augmented reality lens configuration, for example, using a configuration according to examples discussed above in relation to FIGS. 9A-10. The lens configuration may include a rear lens 920, waveguide display 900, and front lens 930. In this example, the front lens 930 may have a non-adjustable surface provided by substrate 932 and an adjustable surface provided by membrane 934. The lens configuration includes zero optical power for the waveguide display (.PHI..sub.g=0). Surface profiles are illustrated and denoted with the optical power labels discussed above in relation to FIGS. 9A and 9B. Regarding the membrane profiles of adjustable lenses having first and second states, these profiles intersect at the neutral circle. The surface optical power terms, as used in equations 1 to 4, are used to label the various surface profiles shown in the figure. In this example, the lens configuration thickness may be approximately 9 mm, and the fluid mass (e.g., of silicone oil) may be 5.4 g.

[0085] In FIG. 11, the optical power, .PHI., of the various surfaces is given in diopters, sometimes abbreviated to “D”, and the subscripts f and r related to the front (world side) and rear (eye side) of the device, respectively. The subscript v refers to virtual content, and the subscripts 1 and 2 refer to first and second actuation states, for example, of a fluid lens. The figure shows surface optical powers for the rear adjustable lens (920), waveguide display (900), and the front adjustable lens (930), sometimes referred to as the “front lens”, where the element numbers relate to an optical configuration similar to that shown in FIG. 9A. The illustrated optical powers relate to the rear non-adjustable surface of the rear fluid lens (.PHI..sub.hr), the membrane surface of the rear fluid lens in the first (.PHI..sub.mr1) and second (.PHI..sub.mr2) actuation states, the waveguide display (.PHI..sub.g), the non-adjustable surface of the front fluid lens (.PHI..sub.hf), and the membrane of the front fluid lens in the first (.PHI..sub.mf1) and the second (.PHI..sub.mf2) actuation states of the front fluid lens. In this example, the non-adjustable surface of the front fluid lens planar, but in some examples this may be replaced by a non-adjustable (or adjustable) curved surface. In some examples, one or more of the illustrated non-adjustable surfaces may be replaced by adjustable surfaces, such as adjustable curved surfaces. In some examples, the orientation of the front fluid lens may be reversed, so that the non-adjustable surface is the exterior surface.

[0086] FIG. 12 shows a similar lens system to that discussed above, in relation to FIG. 11. As discussed above in relation to FIG. 11, the lens system may include a rear lens 920, waveguide display 900, and front lens 930. The front lens 930 may have a non-adjustable surface provided by substrate 932 and an adjustable surface provided by membrane 934. However, in this example, the waveguide display has an output grating power of -2.0 D. The curvature of the rear substrate is changed (relative to the example of FIG. 11) from -4.0D to -2.0D, and the front substrate curvature is changed from 0D to -2.0D. In this example, the lens configuration thickness may be reduced to approximately 8 mm, and the fluid mass may be reduced to 3.2 g. The reductions in thickness and mass are in relation to the configuration discussed above in relation to FIG. 11.

[0087] The introduction of an optical power associated with the waveguide display (e.g., a grating optical power), in the example optical configuration of FIG. 12, allows one or more of various improvements, such as one or more of the following: an appreciable reduction in mass, an appreciable reduction in the thickness of the optical configuration, an appreciable increase in the response time of the fluid lens, and/or a reduction in complexity of manufacture (e.g., by allowing the substrates of the front and rear fluid lenses to be substantially identical). The example improvements determined for the modeled system of FIG. 12 include the following: the mass of the lens system decreased by 2.2 g (as the change in the mass of the substrates is negligible compared to the change in the mass due to reducing the fluid volume); the packaging thickness decreased by 1.1 mm; and the minimum center thickness of the rear adjustable lens increased, which may appreciably improve the response time. Also, in this example configuration, the front and rear lenses may be identical, which improves the efficiency of device manufacture. Hence, there are numerous various advantages available by introducing a grating optical power to the optical configuration.

[0088] FIGS. 13A and 13B show plots of overall optical assembly thickness (FIG. 13A) and fluid mass (FIG. 13B) as functions of grating power (.PHI..sub.g in diopters). The figures identify a range of grating powers over which thickness and weight are minimized or appreciably reduced. For example, the thickness and the fluid mass are at their lowest values for a grating optical power over a range of -1.6 D to -2.4 D. However, there are other grating optical power ranges over which improved device parameters may be obtained, compared with devices having a grating optical power outside of that range (e.g., in comparison with a zero grating power, .phi..sub.g=0). Example ranges (in diopters) include, without limitation, the ranges -1.5 to -2.5, -1.4 to -2.6, -1.3 to -2.7, -1.2 to -2.8. -1.1 to -2.9, -1 to -3, -0.5 to -3.5, and -0.1 to -3.9. Other possible ranges are apparent from the figures, such as -0.8 to -3.2. For example, the sum of the range limits may be approximately -4, and the range limits of the grating power may be in the form (-1.6+x) to (-2.4-x), where x may be a positive value, such as a multiple of 0.1, for example, up a value up to 1.5. In some examples, the grating optical power may be approximately -2, and the range limits and the range limits of the grating power may be in the form (-2+x) to (-2-x), where x may be a positive value, such as a multiple of 0.1 of 1.9 or less.

[0089] In some examples, such as using a different optical configuration, the grating optical power may be approximately -A and the range limits of the grating optical power may be in the form (-A+x) to (-A-x), where x may be a positive value, such as a multiple of 0.1, up to a value, such as (A-0.1).

[0090] In some examples, the membrane curvature (or the fluid pressure) may be negative or positive. In some examples, a device may be configured so that the membrane curvature does not pass through a planar state, which may also be termed a zero diopter (0 D) state. This may facilitate control of the membrane and may reduce specular reflections from the planar membrane surface. In some examples, the rear membrane curvature may be adjusted between +0.5D and +3.5D. In some examples, the grating optical power may be a negative value.

[0091] In some examples, the one or more membranes are not exposed, for example, to mechanical disturbances from outside the device. In some examples, a device may include a front element that also provides protection to the device, such as the non-adjustable substrate of a fluid lens, a non-adjustable lens (which may also be termed a fixed lens), or a window, or similar. One or more element surface of a device may have an antireflective surface and/or a scratch-resistant surface. In some examples, one or more fluid lenses (including, for example, a membrane and a substrate), may be configured so that the membrane faces inwards and the substrate faces outwards. For example, in relation to the optical configuration of FIG. 9A, the orientation of the front adjustable lens 930 may be reversed so that the membrane 934 is on the left (as illustrated), so that the membrane side of the lens faces the waveguide display 902, and the front substrate 932 is on the right (as illustrated). The substrate may provide an exterior surface for the device, such as an outer surface for an optical configuration of an eyewear device. The substrate may also be curved, having one or two curved surfaces, as discussed further below.

[0092] In some examples, the radius of curvature of the front element, such as the radius of curvature of the substrate of a fluid lens, or the outer surface of a fixed lens, may be fixed. The outer front surface may, for example, have a radius of curvature (sometimes referred to herein more concisely as “curvature”) in the range of 50 mm-250 mm, such as 100 mm-200 mm, for example, 125 mm-175 mm, for example, approximately 145 mm. This may be an aesthetic decision, for example, as a moving outer optical surface may be undesirable to consumers, and this curvature may be similar to the curvature of typical eyeglasses (e.g., approximately 3.5D for a refractive index of 1.5).

[0093] In some examples, an optical configuration may be similar to that shown in FIG. 9A, but the optional second rear (non-adjustable) lens 910 may be omitted.

[0094] In some examples, a fluid lens, such as the front fluid lens (e.g., front adjustable lens 930 of FIG. 9A), may be integrated with the waveguide display (e.g., waveguide display 900 of FIG. 9A). For example, the grating structure may provide a substrate for the fluid lens (e.g., the front substrate 932 of FIG. 9A may be omitted and the substrate of the front lens may be provided by the waveguide display 900). In some examples, the waveguide display may provide a substrate having a curved interface with the lens fluid. However, in some examples, the fluid lens and the waveguide display may be separate components.

[0095] FIG. 14 shows an optical configuration in which the waveguide display has zero optical power. The representations of curved surfaces are labeled with the associated optical powers, using the terminology introduced above in relation to the surfaces illustrated in FIG. 9A. The optical configuration may include a waveguide display 900, rear adjustable lens 920, and front adjustable lens 930 (e.g., as shown in FIG. 9A). FIG. 14 uses a similar labeling scheme to that of FIG. 9A. In this example, .PHI..sub.g=0, the lens thickness may be approximately 11 mm, and the fluid mass may be 5.4 g.

[0096] FIG. 15 shows an optical configuration having a grating optical power of .PHI..sub.g=-1.6 D. The representations of curved surfaces are labeled with the associated optical powers, using the terminology introduced in relation to FIG. 9A, and are similar to that of FIG. 14 discussed above. In this example, the thickness may be reduced to approximately 10 mm, and the fluid mass may be reduced to 3.2 g, relative to the configuration of FIG. 14. Hence, the inclusion of negative grating power allows the thickness and/or mass of the optical assembly to be reduced.

[0097] FIGS. 16A and 16B show plots of overall thickness (FIG. 16A) and fluid mass (FIG. 16B) as functions of grating power (.PHI..sub.g in diopters). The figures identify a range of grating powers over which thickness and weight are minimized, or appreciably reduced. For example, the thickness and the fluid mass are at their lowest values for a grating optical power over a range of -1.6 D to -2.4 D. However, there are other grating optical power ranges over which improved device parameters may be obtained, compared with devices having a grating optical power outside of that range, and these ranges may be similar to those discussed above in relation to FIGS. 13A and 13B.

[0098] FIG. 17 illustrates an example method 1700 of operating a device, such as a method of using an augmented reality device. The method may include: providing an optical configuration which includes a front lens assembly, a waveguide display assembly, and a rear lens assembly (1710); providing a real-world image (e.g., to a user) using real-world light that passes through the front lens assembly, the waveguide display assembly, and the rear lens assembly (1720); and generating an augmented reality image using augmented reality light provided (e.g., to the user) by the waveguide display assembly and which passes through the rear lens assembly (1730). In some examples, the grating assembly both provides the augmented reality image and provides a negative optical power for the real-world and/or augmented reality light.

[0099] In some examples, the front lens assembly may include a fluid lens having a membrane (having positive curvature) and a substrate (having negative curvature), the rear lens assembly may include a fluid lens having a membrane (e.g., having a positive or convex exterior surface curvature) and a substrate (having negative curvature), and the grating assembly may include a surface having a negative curvature. In some examples, the substrate of a fluid lens, such as a rear fluid lens, may have a concave exterior surface and the substrate may provide a negative optical power. In this context, an exterior surface may face outwards from the lens and may be substantially adjacent air. In some examples, the front lens assembly may have a positive optical power. In some examples, the positive optical power of the front lens assembly may be approximately equal to the negative optical power of the waveguide display assembly in combination with the rear lens assembly.

[0100] In some examples, a device may include an augmented or virtual reality device having a waveguide display in front of each of a user’s eyes and one or more adjustable lenses per eye. The adjustable lenses may be adjusted for one or more of the following purposes: providing improved focus for the eyes, distance or close viewing, or for correcting vergence accommodation conflict. One or more of the adjustable lenses may be a fluid filled lens. An additional eye-side optical element may be provided that defocuses light from the display so that the adjustable lens or lenses may be thinner and lighter and may have a faster response time. The additional eye-side optical element may include a refractive lens and/or may be provided as an optical power on the output grating of a waveguide type display.

[0101] Example embodiments of the present disclosure include devices with reduced or substantially eliminated vergence-accommodation conflict, including thin, light and low power devices. Device design may include reduction or minimization of thickness, weight, or response time. In some examples, the response time of a fluid lens may be traded for thickness and/or weight.

[0102] In some examples, a device includes an optical configuration including a front lens assembly, a waveguide display assembly, and a rear lens assembly. The waveguide display assembly may be configured to provide augmented reality image elements within a real-world image and may be located between the front lens assembly and the rear lens assembly. In some examples, the waveguide display assembly includes an element having a negative optical power for augmented reality light provided by the waveguide display assembly. The front lens assembly may receive real-world light used to form a real world image. Real-world light may enter and pass through the front lens assembly, pass through the waveguide display assembly, and then pass through the rear lens assembly to reach the eye of a user when the user wears the device.

[0103] In this context, the term “front” may refer to the word-side of the waveguide display assembly and the term “rear” may refer to the eye-side of the waveguide display, during normal use of a device. The front lens assembly may include a front adjustable lens, such as a front fluid lens. The rear lens assembly may include a rear adjustable lens, such as a rear fluid lens. The front and/or rear lens assemblies may further include lens control components, such as one or more actuators, eye ring, or other component. An arrangement of optical elements, such as distensible membranes, hard lenses, diffractive elements, waveguide displays, or other optical elements, may be termed a sequence of optical elements. A fluid lens with the membrane forward of the substrate (relative to a user’s eye) may represent a different sequence from a fluid lens with the lens at the front and the membrane rearwards, and both may have the same range of optical powers.

[0104] In some examples, the front adjustable lens includes a front fluid lens, which may include a front substrate, a front membrane, and a front lens fluid located between the front substrate and the front membrane. The rear adjustable lens may include a rear fluid lens, which may include a rear substrate, a rear membrane, and a rear lens fluid located between the rear substrate and the rear membrane. In some examples, the front substrate may have a front concave profile and an associated front negative optical power. In some examples, the rear substrate may have a rear concave profile, and an associated rear negative optical power. The front negative optical power may be approximately equal to the rear negative optical power.

[0105] In some examples, the real-world image may be formed by real-world light passing through the front lens assembly, at least a portion of the waveguide display assembly, and the rear lens assembly.

[0106] In some examples, augmented reality light may be provided by the waveguide display assembly. The waveguide display assembly may include a waveguide display. The waveguide display may include out-coupling components configured to couple light out of the waveguide display and towards the eye of the user. The out-coupling components may include a grating.

[0107] The waveguide display assembly may have a negative optical power, for example, for the augmented reality light. In some examples, the waveguide display assembly may include a waveguide display and a negative lens (the negative lens having a negative optical power). The negative lens may be located between the waveguide display and the rear lens assembly. The waveguide display assembly and/or the rear lens assembly may include a supplemental negative lens (e.g., a plano-concave lens, or a biconcave lens).

[0108] In some examples, the waveguide display may be configured to out-couple diverging light from the waveguide display. In some examples, the grating output surface may have a spatially variable blaze angle.

[0109] In some examples, the waveguide display may include one or more curved surfaces configured to diverge augmented reality light coupled out from the waveguide display by the grating. In some examples, the grating may be disposed on a curved surface, such as a parabolic or spherical surface. In some examples, one or more reflectors, for example, on an opposed surface of the waveguide display, may be either curved or arranged over a curved surface.

[0110] In some examples, a device may be (or include) an eyewear device configured to be worn by a user. The device may be configured to provide a real-world image, where real-world light forming the real-world image passes through the front lens assembly, the waveguide display assembly, and the rear lens assembly, and an augmented reality image, where the augmented reality image is provided by the waveguide display assembly and passes through the rear lens assembly. The rear lens assembly may include a rear adjustable fluid lens.

[0111] In some examples, the device may further include a support, such as a frame configured to support the lens configuration, one or more straps, or other suitable support (e.g., to support the device on the head of a user). The device may include an eyewear device. The device may include an augmented reality headset.

[0112] In some examples, the device is configured so that the waveguide display assembly has a negative optical power and the negative optical power corrects for vergence-accommodation conflict between the real-world image and the augmented reality image.

[0113] In some examples, a method includes providing an optical configuration, where the optical configuration includes a front lens assembly, a waveguide display assembly, and a rear lens assembly, providing a real-world image using real-world light that passes through the front lens assembly, the waveguide display assembly, and the rear lens assembly, and generating an augmented reality image using augmented reality light provided by the waveguide display assembly. The augmented reality light may pass through the rear lens assembly. The waveguide display assembly may provide the augmented reality image, and may also provide a negative optical power for the augmented reality light. The display assembly may provide the augmented reality image by receiving augmented reality light from an augmented reality light source and coupling the augmented reality light into the light path using a grating, where the waveguide display assembly provides a negative optical power for the augmented reality light. In some examples, the waveguide display assembly provides diverging augmented reality light. The method may also include a method of operating an augmented reality device.

[0114] Examples disclosed herein may include fluid lenses, membrane assemblies (that may include a membrane and, e.g., a peripheral structure such as a support ring or a peripheral wire), and devices including one or more fluid lenses. Example devices may include ophthalmic devices (e.g., spectacles), augmented reality devices, virtual reality devices, and the like. In some examples, a device may include a fluid lens configured as a primary lens of an optical device, for example, as the primary lens for light entering the user’s eye.

[0115] In some examples, a fluid lens may include a peripheral structure, such as a support ring, or a peripheral wire. A peripheral structure may include a support member affixed to the perimeter of a distensible membrane in a fluid lens. The peripheral structure may have generally the same shape as the lens periphery. In some examples, non-round fluid lens may include a peripheral structure that may bend normally to a plane, for example, a plane corresponding to the membrane periphery for a round lens. The peripheral structure may also bend tangentially to the membrane periphery.

[0116] A fluid lens may include a membrane, such as a distensible membrane. A membrane may include a thin sheet or film (having a thickness less than its width or height). The membrane may provide the deformable optical surface of an adjustable fluid lens. The membrane may be under a line tension, that may be the surface tension of the membrane. Membrane tension may be expressed in units of N/m.

[0117] In some examples, a device includes a membrane, a support structure configured to provide a guide path for an edge portion of the membrane, an interface device which connects the membrane, or a peripheral structure disposed around the periphery of the membrane, to the support structure and allows the membrane to move freely along the guide path, a substrate, and an edge seal. In some examples, the support structure may be rigid, or semi-rigid.

[0118] In some examples, an adjustable fluid lens may include a membrane assembly. A membrane assembly may include a membrane (e.g., having a line tension), and a wire or other structure extending around the membrane (e.g., a peripheral guide wire). A fluid lens may include a membrane assembly, a substrate, and an edge seal. In some examples, the membrane line tension may be supported by a support ring. This may be augmented by a static restraint and/or a hinge point at one or more locations on the support ring.

[0119] In some examples, a fluid lens may include a membrane, a support structure configured to provide a guide path for an edge portion of the membrane, and a substrate. The fluid lens may further include an interface device, configured to connect the membrane to the support structure and to allow the edge portion of the membrane to move freely along the guide path, a substrate, and an edge seal. In some examples, fluid lenses may include lenses having an elastomeric or otherwise deformable element (such as a membrane), a substrate, and a fluid. In some examples, movement of a control point of the membrane, for example, as determined by the movement of a membrane attachment along a guide path, may be used to adjust the optical properties of a fluid lens.

[0120] Example embodiments include apparatus, systems, and methods related to fluid lenses. In some examples, the term “fluid lens” may include adjustable fluid-filled lenses, such as adjustable liquid-filed lenses.

[0121] In some examples, a fluid lens, such as an adjustable fluid lens, may include a pre-strained flexible membrane which at least partially encloses a fluid volume, a fluid enclosed within the fluid volume, and a flexible edge seal which defines a periphery of the fluid volume, and an actuation system configured to control the edge of the membrane such that the optical power of the lens can be modified. The fluid volume may be referred to as an enclosure.

[0122] Controlling the edge of the membrane may require energy to deform the membrane, and/or energy to deform a peripheral structure such as a support ring, or a wire (e.g., in the case of a non-round lens). In some examples, a fluid lens configuration may be configured to reduce the energy required to change the power of the lens to a low value, for example, such that the change in elastic energy stored in the membrane as the lens properties change may be less than the energy required to overcome, for example, frictional forces.

[0123] In some examples, an adjustable focus fluid lens includes a substrate and an membrane (e.g., an elastic membrane), where a lens fluid is retained between the membrane and the substrate. The membrane may be under tension, and a mechanical system for applying or retaining the tension in the membrane at sections may be provided along the membrane edge or at portions thereof. The mechanical system may allow the position of the sections to be controllably changed in both height and radial distance. In this context, height may refer to a distance from the substrate, along a direction normal to the local substrate surface. In some examples, height may refer to the distance from a plane extending through the optical center of the lens and perpendicular to the optic axis. Radial distance may refer to a distance from a center of the lens, in some examples, a distance from the optical axis along a direction normal to the optical axis. In some examples, changing the height of at least one of the sections restraining the membrane may cause a change in the membrane’s curvature, and the radial distance of the restraint may be changed to reduce increases in the membrane tension.

[0124] In some examples, a mechanical system may include a sliding mechanism, a rolling mechanism, a flexure mechanism, or an active mechanical system, or a combination thereof. In some examples, a mechanical system may include one or more actuators, and the one or more actuators may be configured to control both (or either of) the height and/or radial distance of one or more of the sections.

[0125] An adjustable focus fluid lens may include a substrate, a membrane that is in tension, a fluid, and a peripheral structure restraining the membrane tension, where the peripheral structure extends around a periphery of the membrane, and where, in some examples, the length of the peripheral structure and/or the spatial configuration of the peripheral structure may be controlled. Controlling the circumference of the membrane may controllably maintain the membrane tension when the optical power of the fluid lens is changed.

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