Angle-selective attenuation of light transmission artifacts in wearable displays

Abstract

A wearable display system includes an eyepiece stack having a world side and a user side opposite the world side. During use, a user positioned at the user side views display images delivered by the wearable display system via the eyepiece stack that augment the user's view of the user's environment. The system also includes an optical attenuator arranged at the world side of the eyepiece stack, the optical attenuator having a layer of birefringent material with a plurality of domains each having a principal optical axis oriented in a corresponding direction different from the directions of the other domains. Each domain of the optical attenuator reduces transmission of visible light incident on the optical attenuator for a respective different range of incident angles.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to attenuation of light transmission artifacts in wearable displays.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Application No. 62 / 986,478, filed March 6, 2020, the contents of which are incorporated by reference herein in their entirety. BACKGROUND

[0004] Optical imaging systems, such as wearable display systems (e.g., wearable display headsets), can include one or more eyepieces that present a projected image to a user. The eyepieces can be constructed using thin layers of one or more high-refractive materials. As an example, the eyepieces can be constructed from one or more layers of high-refractive glass, silicon, metal, or polymer substrates.

[0005] Multiple eyepieces can be used in conjunction to project a simulated three- dimensional image. For example, multiple eyepieces— each having a different pattern— can be superimposed on top of one another, and each eyepiece can project a different depth layer of a stereoscopic image. Thus, the eyepieces can collectively present a volumetric image to a user across three dimensions. This can be useful, for example, in presenting a “virtual reality” environment to a user.

[0006] Optical elements in wearable display systems can also interact with ambient light, which is light from the environment in which the user is located. For example, diffractive structures in a wearable display system can diffract ambient light that is incident on the wearable display at high angles (which would not normally enter the user’s field of view) into the field of view, creating visible artifacts that degrade the user experience. SUMMARY

[0007] Wearable display systems (e.g., useful for augmented reality (AR) applications) are described that include an optical attenuator to mitigate artifacts related to ambient light that is incident on the display at high angles of incidence. The optical attenuator of examples can impart different degrees of attenuation to broadband light as a function of the angle of incidence. The optical attenuator is characterized by a spatial variation in the alignment of the optical axis of a birefringent medium in the attenuator between domains of the attenuator across a range of transmission angles of the clear aperture of the wearable display. For example, the director axis of a liquid crystal material used as a birefringent layer of the attenuator can vary spatially. This optical attenuator can further improve suppression of artifacts related to wearable displays and reduce color shift of the edge of the world seen by the user through the display compared to solutions that use a single-domain birefringent layer.

[0008] Various aspects of the present invention are summarized as follows.

[0009] Generally, in a first aspect, the invention features a wearable display system including: an eyepiece stack having a world side and a user side opposite the world side, where, during use, a user positioned at the user side views display images delivered by the wearable display system via the eyepiece stack that augment the user's view of the user's environment; and an optical attenuator disposed at the world side of the eyepiece stack, the optical attenuator having a layer of birefringent material with a plurality of domains each having a principal optical axis oriented in a corresponding direction different from the directions of the other domains. Each domain of the optical attenuator reduces transmission of visible light incident on the optical attenuator for a respective different range of incident angles.

[0010] Embodiments of the wearable display system can include one or more of the following features. For example, for an aperture of the eyepiece stack corresponding to an eyebox of the wearable display, a white point of an image viewed by the display at the user side with a D65 illuminant at the world side varies 0.01 Δu'v' or less in CIELUV color space across the aperture of the display defining the eyebox for incident angles of 40° or less. The aperture can have a diameter of 20 mm or more (e.g., 25 mm or more, 30 mm or more, 35 mm or more, 40 mm or more). The aperture can have a diameter of 50 mm or less.

[0011] The birefringent material can be a liquid crystal material, and the angle-selective film can further include a pair of orientation layers on opposite sides of the liquid crystal material, where at least one of the orientation layers is configured to provide different pre-tilts to the liquid crystal material in different domains of the angle-selective film. The polar pre-tilt at a domain intersecting the visual axis of the wearable display can be zero degrees, and the polar pre-tilt at at least one domain away from the visual axis is greater than zero. The at least two domains having non-zero polar pre-tilts can have different azimuthal pre-tilts.

[0012] The layer of birefringent material can be a spatially-varying o-plate.

[0013] The layer of birefringent material can include domains arranged in a one-dimensional pattern. Alternatively, the layer of birefringent material can include domains arranged in a two-dimensional pattern.

[0014] A layer of birefringent material can be disposed between a pair of linear polarizers. The pass axes of the two linear polarizers can cross. The birefringent film can rotate the polarization state of light transmitted through a first linear polarizer of the pair of linear polarizers on the world side of the polarization adjustment film. The amount of rotation of the polarization state varies depending on the angle of incidence of the light transmitted through the first linear polarizer of the pair of linear polarizers. Transmitted light having a large angle of incidence can be rotated less than transmitted light having a small angle of incidence. The optical attenuator can include a pair of quarter- wave plates disposed on opposite sides of the layer of birefringent material. Each quarter-wave plate can be arranged relative to a respective one of the linear polarizers to form a circular polarizer.

[0015] In some embodiments, the optical attenuator includes a second layer of birefringent material. The optical attenuator can further include three linear polarizers, each birefringent layer disposed between two linear polarizers of the three linear polarizers. Each layer of birefringent material can be a spatially varying o-plate. The optical attenuator can include a plurality of quarter-wave plates, a pair of quarter-wave plates disposed on opposite sides of each layer of birefringent material.

[0016] The optical attenuator can include two or more stages, each stage having a layer of birefringent material disposed between a pair of linear polarizers. Adjacent stages can share a linear polarizer.

[0017] The layer of birefringent material can be a switchable element having variable optical properties. The switchable element can include a liquid crystal layer between a pair of electrode layers.

[0018] Among other advantages, embodiments of the present invention can reduce unwanted optical artifacts (e.g., rainbow effects) in certain wearable displays related to stray ambient light that interacts with grating structures in the display. For example, waveguide-based wearable displays that employ surface relief gratings (e.g., for AR / MR applications) can diffract stray ambient light into the eyebox of the display, resulting in unwanted artifacts appearing in the user’s field of view, thereby degrading the user experience. Embodiments of the present invention can significantly reduce such artifacts without significantly impacting the user’s view of the world.

[0019] Embodiments can attenuate transmission of ambient light based on the angle of incidence and the location of incidence of the ambient light in the eyebox. For example, an attenuator that selectively attenuates light having an angle of incidence greater than the user’s field of view can mitigate the visibility of artifacts produced by a diffractive near-eye display without sacrificing transmission of the user’s view of the world.

[0020] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 An example of a wearable display system is shown.

[0022] Figure 2A A conventional display system for simulating three-dimensional image data to a user is shown.

[0023] Figure 2B Aspects of a method for simulating three-dimensional image data using multiple depth planes are shown.

[0024] Figures 3A-3C A relationship between a radius of curvature and a focal point radius is shown.

[0025] Figure 4 An example of a waveguide stack in an AR eyepiece for outputting image information to a user is shown.

[0026] Figure 5 And 6 An example of an exit beam output by a waveguide is shown.

[0027] Figure 7A And 7B is a schematic diagram of the optical path through a display combiner with a surface-relief grating.

[0028] Figure 8A And 8B is a schematic diagram comparing the transmission of light through a display combiner with an optical attenuator and without an optical attenuator.

[0029] Figure 9A And 9B is a diagram showing an eyebox and associated world transmission angles.

[0030] Figure 10 is a series of diagrams showing world transmission and artifact generation distributions.

[0031] Figure 11A And 11B is an example of an eyepiece with a single O-plate and a spatially varying O-plate.

[0032] Figure 12A And 12B is a further example of a spatially varying O-plate.

[0033] Figure 13 is an example of an eyepiece with multiple O-plates.

[0034] Figures 14A-14D is a diagram of the transmission distribution of an example O-plate calculated for three wavelengths.

[0035] Figures 15A-15C is an intensity diagram of the calculated transmission distribution of an example O-plate.

[0036] Figures 16A-16T is an image of the computed attenuation of optical rainbow artifacts.

[0037] Figures 17A-17D is an image of the computed color shift.

[0038] Figure 18 is a diagram of an example computer system that can be used for a wearable display system.

[0039] In the drawings, like reference numerals refer to like elements. DETAILED DESCRIPTION

[0040] Figure 1 An example wearable display system 60 is shown, which includes a display or eyepiece 70, and various mechanical and electronic modules and systems that support the functioning of the display 70. The display 70 is housed in a frame 80, which can be worn by a display system user 90, and is configured to position the display 70 in front of the eyes of the user 90. In some embodiments, the display 70 can be considered eyeglasses. In some embodiments, a speaker 100 is coupled to the frame 80 and positioned near the ear canal of the user 90. The display system can also include one or more microphones 110 to detect sound. The microphone 110 can allow the user to provide input or commands to the system 60 (e.g., selection of voice menu commands, natural language questions, etc.) and / or can allow for audio communication with other people (e.g., with other users of similar display systems). The microphone 100 can also collect audio data from the user’s surrounding environment (e.g., sound from the user and / or the environment). In some embodiments, the display system can also include a peripheral sensor 120a, which can be separate from the frame 80 and attached to the body of the user 90 (e.g., on the head, torso, limbs, etc.). In some embodiments, the peripheral sensor 120a can acquire data characterizing the physiological state of the user 90.

[0041] The display 70 is operatively coupled by a communication link 130 (e.g., by a wired or wireless connection) to a local data processing module 140, which can be mounted in various configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in an earpiece, or removably attached to the user 90 (e.g., in a backpack-style configuration or in a belt-coupling style configuration). Similarly, the sensors 120a are operatively coupled by a communication link 120b (e.g., by a wired lead or wireless connectivity) to the local processing and data module 140. The local processing and data module 140 can comprise a hardware processor, as well as digital memory, such as nonvolatile memory (e.g., flash memory or hard disk drive) that can be used to store data and / or instructions, such as software for controlling the operation of the local processing and data module 140. Such data can include instructions for processing data, for controlling the operation of the display 70, and / or for other purposes. These data can also include 1) data captured or generated by sensors, such as image capture devices (e.g., cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, gyros, and / or other sensors disclosed herein; and / or 2) data obtained and / or processed using the remote processing module 150 and / or the remote data repository 160 (including data about virtual content), which can be transferred to the display 70 after such processing or retrieval. The local processing and data module 140 can be operatively coupled by communication links 170, 180, such as via wired or wireless communication links, to the remote processing module 150 and the remote data repository 160, 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, the local processing and data module 140 can include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a radio device, and / or a gyro. In some other embodiments, one or more of these sensors can be attached to the frame 80 or can be standalone devices that communicate with the local processing and data module 140 through a wired or wireless communication pathway.

[0042] The remote processing module 150 can comprise one or more processors that analyze and process data, such as image or audio information. In some embodiments, the remote data repository 160 can be a digital data storage facility that is available through the Internet or other network configuration in a "cloud" resource configuration. In some embodiments, the remote data repository 160 can comprise one or more remote servers that provide information to the local processing and data module 140 and / or the remote processing module 150 (e.g., information for generating augmented reality content). In other embodiments, all data is stored, all computations are performed in the local processing and data module, allowing completely autonomous use from the remote modules.

[0043] An image can be perceived as "three-dimensional" or "3D" by providing slightly different presentations of the image to each of a user's eyes. Figure 2A A conventional display system for simulating three-dimensional image data to a user is shown. Two different images 190, 200 are output to the user, with each image intended for one eye 210, 220. The images 190, 200 are spaced apart from the eyes 210, 220 by a distance 230 along an optical or z-axis that is parallel to the user's line of sight. The images 190, 200 are flat, and the eyes 210, 220 can focus on the images by assuming a single accommodative state. Such 3D display systems rely on the human visual system to combine the images 190, 200 to provide a perception of depth and / or scale of the combined image.

[0044] However, the human visual system is complex, and providing a realistic perception of depth is challenging. For example, many users of conventional "3D" display systems find such systems uncomfortable or are unable to perceive depth at all. Objects can be perceived as "three-dimensional" due to a combination of vergence and accommodation. Vergence movements of the two eyes relative to each other (e.g., rotations of the eyes such that the pupils move toward or away from each other to cause the respective lines of sight of the eyes to converge in gazing at an object) are closely related to focusing (or "accommodation") of the lenses of the eyes. Under normal circumstances, changing the focus of the lenses of the eyes or accommodating the eyes to shift the focus from one object to another object at a different distance will automatically cause a matching change in vergence to the same distance, according to a relationship known as the "vergence-accommodation reflex," as well as pupil dilation or constriction. Likewise, under normal circumstances, a change in vergence will trigger a matching change in accommodation of the lens shape and pupil size. As described herein, many stereoscopic or "3D" display systems use slightly different presentations (and thus slightly different images) to display a scene to each eye, such that the human visual system perceives three-dimensional perspective. However, such systems can be uncomfortable for some users because they provide image information at a single accommodative state only, and work against the "vergence-accommodation reflex." Display systems that provide a better match between accommodation and vergence can form more realistic and comfortable simulations of three-dimensional image data.

[0045] Figure 2B Aspects of a method for simulating three-dimensional image data using multiple depth planes are shown. Reference is made to Figure 2BEyes 210 and 220 adopt different accommodation states to focus on objects at different distances along the z-axis. Therefore, a particular accommodation state can be considered associated with a specific one of the illustrated depth planes 240 (with an associated focal length) such that when the eye is in accommodation for a particular depth plane, an object or part of an object in that particular depth plane is in focus. In some embodiments, three-dimensional image data can be simulated by providing different presentations of the image for each eye 210, 220, and also by providing different presentations of the image corresponding to multiple depth planes. Although the respective fields of view of eyes 210 and 220 are shown as separate for clarity, they can overlap, for example, as the distance along the z-axis increases. Furthermore, although the depth planes are shown as flat for ease of illustration, it should be understood that the contours of the depth planes can be curved in physical space such that all features within the depth plane are in focus when the eye is in a particular accommodation state.

[0046] The distance between the object and the eye 210 or 220 can also change the amount of light scattering from the object as seen by that eye. Figures 3A to 3C The relationship between distance and light divergence is shown. The distances between the object and the eye 210 are represented by R1, R2, and R3 in decreasing order of distance. Figures 3A to 3C As shown, the light rays become more divergent as the distance to the object decreases. As the distance increases, the light rays become more collimated. In other words, the light field generated by a point (the object or part of the object) can be considered to have a spherical wavefront curvature, which is a function of the distance of that point from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. Therefore, the degree of divergence of the light rays varies at different depth planes, increasing as the distance between the depth plane and the user's eye 210 decreases. Although in order to... Figures 3A to 3C As clearly illustrated in other figures in this document, only a single eye 210 is shown; however, it should be understood that the discussion of eye 210 can be applied to both eyes 210 and 220 of the user.

[0047] Highly believable perceptual depth simulation can be achieved by providing the eye with different presentations of images corresponding to each of a finite number of depth planes. These different presentations can be individually focused by the user's eye, thus helping to provide depth cues based on the amount of eye accommodation required to bring different image features of the scene to focus on different depth planes and / or based on the observation of different image features out of focus on different depth planes.

[0048] Figure 4An example of a waveguide stack in an AR eyepiece for outputting image information to a user is shown. The display system 250 includes a waveguide stack or a stacked waveguide assembly 260, which can be used to provide three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. In some embodiments, the display system 250 is... Figure 1 System 60, Figure 4 Some parts of the system 60 are shown schematically in more detail. For example, the waveguide assembly 260 may be... Figure 1 The display 70 is a portion thereof. It should be understood that, in some embodiments, the display system 250 may be considered as a light field display.

[0049] Waveguide assembly 260 may also include multiple features 320, 330, 340, 350 between waveguides. In some embodiments, features 320, 330, 340, 350 may be one or more lenses. Waveguides 270, 280, 290, 300, 310 and / or multiple lenses 320, 330, 340, 350 may be configured to send image information to the eye at various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a specific depth plane and may be configured to output image information corresponding to that depth plane. Image injection devices 360, 370, 380, 390, 400 may serve as light sources for the waveguides and may be used to inject image information into waveguides 270, 280, 290, 300, 310, and as described herein, each waveguide may be configured to distribute incident light across each respective waveguide for output toward the eye 210. Light exits from the output surfaces 410, 420, 430, 440, and 450 of each respective image injection device 360, 370, 380, 390, and 400, and is injected into the corresponding input surfaces 460, 470, 480, 490, and 500 of the respective waveguides 270, 280, 290, 300, and 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, and 500 may be an edge of the corresponding waveguide or a portion of the main surface of the corresponding waveguide (i.e., one of the waveguide surfaces directly facing the world 510 or the user's eye 210). In some embodiments, a light beam (e.g., a collimated beam) may be injected into each waveguide and may be replicated in the waveguide (e.g., sampled into sub-beams by diffraction), and then guided to the eye 210 with an optical focal length corresponding to the depth plane associated with that particular waveguide. In some embodiments, a single image injection device among image injection devices 360, 370, 380, 390, 400 may be associated with multiple (e.g., three) waveguides 270, 280, 290, 300, 310 and inject light into these waveguides.

[0050] In some embodiments, the image injection devices 360, 370, 380, 390, 400 are discrete displays that each produce image information for injection into a respective waveguide 270, 280, 290, 300, 310. In some other embodiments, the image injection devices 360, 370, 380, 390, 400 are output ends of a single multiplexed display that can transmit image information to each of the image injection devices 360, 370, 380, 390, 400 via one or more optical conduits, such as fiber optic cables. It will be understood that the image information provided by the image injection devices 360, 370, 380, 390, 400 can include light of different wavelengths or colors.

[0051] 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, which can include a light source or light emitter such as a light-emitting diode (LED). Light from the light module 530 can be directed to a light modulator 540 (e.g., a spatial light modulator) via a beam splitter (BS) 550 and modulated by the light modulator. The light modulator 540 can spatially and / or temporally vary the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310. Examples of spatial light modulators include liquid crystal displays (LCDs) and digital light processing (DLP) displays, where liquid crystal displays include liquid crystal on silicon (LCOS) displays.

[0052] In some embodiments, the light projector system 520 or one or more components thereof can be attached to the frame 80 Figure 1 ). For example, the light projector system 520 can be part of the temple portion (e.g., ear stem 82) of the frame 80, or can be disposed at the edge of the display 70. In some embodiments, the light module 530 can be separate from the BS 550 and / or the light modulator 540.

[0053] In some embodiments, display system 250 can be a scanning fiber display including one or more scanning fibers to project light into one or more waveguides 270, 280, 290, 300, 310, and ultimately into eye 210 of a user in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.). In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 can schematically 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 can schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each of which is configured to inject light into an associated one of waveguides 270, 280, 290, 300, 310. One or more optical fibers can transmit light from light module 530 to one or more waveguides 270, 280, 290, 300, and 310. Further, one or more intermediate optical structures can be provided between the one or more scanning fibers and the one or more waveguides 270, 280, 290, 300, 310 to, for example, redirect light emerging from the scanning fibers into the one or more waveguides 270, 280, 290, 300, 310.

[0054] Controller 560 controls the operation of stacked waveguide assembly 260, including the image injection devices 360, 370, 380, 390, 400, light source 530, and light modulator 540. In some embodiments, controller 560 is part of local data processing module 140. Controller 560 includes programming (e.g., instructions in a non-transitory medium) that regulates timing and provides image information to waveguides 270, 280, 290, 300, 310. In some embodiments, the controller can be a single integral device, or a distributed system connected over wired or wireless communication channels. In some embodiments, controller 560 can be part of processing modules 140 or 150 Figure 1 ).

[0055] The waveguides 270, 280, 290, 300, 310 can be configured to propagate light within each respective waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 can each be planar or have another shape (e.g., curved), have a top major surface and a bottom major surface and edges extending between these top and bottom major surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 can each include an out-coupling optical element 570, 580, 590, 600, 610 configured to extract light from the waveguides to output image information to the eye 210 by redirecting light propagating inside the respective corresponding waveguide out of the waveguide. The extracted light can also be referred to as out-coupled light, and the out-coupling optical elements light can also be referred to as light extracting optical elements. The extracted light beams can be output by the waveguide at locations where light propagating in the waveguide strikes the light extracting optical elements. As discussed further herein, the out-coupling optical elements 570, 580, 590, 600, 610 can for example be diffractive optical features, including diffractive gratings. Although the out-coupling optical elements 570, 580, 590, 600, 610 are illustrated as being disposed at the bottom major surfaces of the waveguides 270, 280, 290, 300, 310, in some embodiments, as discussed further herein, the out-coupling optical elements 570, 580, 590, 600, 610 can be disposed at the top and / or bottom major surfaces, and / or can be disposed directly in the volume of the waveguides 270, 280, 290, 300, 310. In some embodiments, the out-coupling optical elements 570, 580, 590, 600, 610 can be formed in a layer of material attached to a transparent substrate to form the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 can be monolithic pieces of material, and the out-coupling optical elements 570, 580, 590, 600, 610 can be formed on surfaces and / or inside the piece of material.

[0056] Each waveguide 270, 280, 290, 300, 310 can output light to form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye can deliver collimated light beams to the eye 210. The collimated light beams can represent the optical infinity focal plane. The next waveguide 280 up can output collimated light beams that are transmitted through the first lens 350 (e.g., a negative lens) before reaching the eye 210. The first lens 350 can add a slight convex wavefront curvature to the collimated light beams such that the eye / brain interprets the light from this waveguide 280 as coming from a first focal plane closer inward from optical infinity towards the eye 210. Similarly, the third waveguide 290 has its output transmitted through the first and second lenses 350, 340 before reaching the eye 210. The combined optical power of the first and second lenses 350, 340 can add another increment of wavefront curvature, so that the eye / brain interprets light from this third waveguide 290 as coming from a second focal plane that is even closer inward from optical infinity than the focal plane of the second waveguide 280.

[0057] The other waveguide layers 300, 310 and lenses 330, 320 are configured similarly, with the highest waveguide 310 in the stack delivering its output through all the lenses between it and the eye to achieve the total optical power representing the closest focal plane to the person. To compensate for the stack of lenses 320, 330, 340, 350 when viewing / interpreting light from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 can be provided at the top of the stack to compensate for the total optical power of the underlying lens stack 320, 330, 340, 350. This configuration provides as many perceived focal planes as there are waveguide / lens pairs available. Both the outcoupling optics of the waveguides and the focusing aspects of the lenses can be static (i.e., not dynamic or electro-active). In some alternative embodiments, using electro-active features, one or both of the outcoupling optics of the waveguides and the focusing aspects of the lenses can be dynamic.

[0058] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 can have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 can output image sets to the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 can output image sets to the same multiple depth planes, one set per depth plane. This can provide advantages for forming tiled images to provide an expanded field of view at those depth planes.

[0059] The out-coupling optical elements 570, 580, 590, 600, 610 can be configured to both redirect light out of their respective waveguides and also output that light with the appropriate amount of divergence or collimation for the particular depth plane with which the waveguide is associated. As a result, waveguides having different associated depth planes can have out-coupling optical elements 570, 580, 590, 600, 610 of different configurations that output light with a different amount of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 can be volume features or surface features that can be configured to output light at particular angles. 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 can not be lenses; rather, they can simply be spacers (e.g., cladding layers and / or structures to form air gaps).

[0060] In some embodiments, the out-coupling optical elements 570, 580, 590, 600, 610 are diffractive features with a sufficiently low diffraction efficiency such that only a fraction of the power of the light beam is redirected to the eye 210 at each interaction, while the rest continues to move through the waveguide via TIR. Thus, the exit pupil of the replicated light module 530 is replicated across the entire waveguide to produce multiple output beams carrying image information from the light source 530, effectively expanding the number of locations at which the eye 210 can interpret the exit pupil of the replicated light source. These diffractive features can also have a diffraction efficiency that is variable across their geometry to improve the uniformity of the light output by the waveguide.

[0061] In some embodiments, one or more diffractive features can be switchable between an“on” state in which they actively diffract and an“off’ state in which they do not significantly diffract. For example, a switchable diffractive element can include a polymer dispersed liquid crystal layer in which the droplets form a diffractive pattern in a host medium, and the refractive index of the droplets can be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light) or the droplets can be switched to a refractive index that is mismatched from the refractive index of the host medium (in which case the pattern actively diffracts incident light).

[0062] In some embodiments, a camera assembly 630 (e.g., a digital camera, including visible and infrared light cameras) can be provided to capture images of the eye 210, portions of the eye 210, or at least portions of tissue surrounding the eye 210, to, for example, detect user input, extract biometric information from the eye, estimate and track gaze direction of the eye, monitor the physiological state of the user, etc. In some embodiments, the camera assembly 630 can include an image capture device and a light source to project light (e.g., infrared or near-infrared light) to the eye, which can then be reflected by the eye and detected by the image capture device. In some embodiments, the light source includes a light-emitting diode (“LED”) that emits infrared or near-infrared light. In some embodiments, the camera assembly 630 can be attached to the frame 80 Figure 1 ) and can be in electrical communication with the processing modules 140 or 150, which can process image information from the camera assembly 630 to make various determinations regarding, for example, the physiological state of the user, gaze direction of the wearer, iris recognition, etc. In some embodiments, one camera assembly 630 can be used for each eye to monitor each eye separately.

[0063] Figure 5 An example of an exit beam output by a waveguide is shown. One waveguide is shown (in perspective view), but other waveguides in the waveguide assembly 260 Figure 4 ) can function similarly. Light 640 is injected into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. Through interaction with the diffractive features, the light exits the waveguide as exit beams 650. Any of the exit beams 650 include a sub-portion of the total energy of the input light 640. In a reasonably efficient system, the sum of the energy of all exit beams 650 is equal to the energy of the input light 640. In Figure 6 , the exit beams 650 are shown as substantially parallel, but, as discussed herein, can be imparted with a certain amount of optical power depending on the depth plane associated with the waveguide 270. Parallel exit beams can indicate a waveguide with a coupling-out optical element that couples out light to form an image that appears to be set on a depth plane at a far distance (e.g., optical infinity) from the eye 210. Other waveguides or other coupling-out optical element sets can output a more divergent exit beam pattern, as shown in Figure 6 , which would require the eye 210 to accommodate for a closer distance to focus the more divergent exit beam pattern on the retina and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0064] Additional information regarding wearable display systems (e.g., including optical elements used in wearable display systems) can be found in U.S. Patent Publication No. US 2019 / 0187474 Al, entitled “EYEPIECES FOR AUGMENTED REALITY DISPLAY SYSTEM,” filed December 14, 2018, the contents of which are incorporated by reference in their entirety.

[0065] As described above, wearable display system 60 includes one or more optical elements having one or more grating structures that enhance the optical performance of the wearable display system. For example, with reference to Figure 7A and 7B , diffractive relief structure grating 710 functions as an exit pupil expander (EPE) in combination with near-eye display combiner 700 (e.g., a stacked waveguide assembly as described above), increasing the size of the exit pupil of the wearable display system. As Figure 7A shown, combiner 700 includes a waveguide 720 (e.g., a glass or polymer substrate) that guides edge-coupled light via total internal reflection (TIR) along its length, while grating 710 diffracts incident guided light such that at least some light is extracted from waveguide 720 toward a user of the display system.

[0066] With particular reference to Figure 7B , ambient light from the user’s environment also incides on display combiner 700 from the “world” side. This light interacts with grating 710, and at least some of this light can be diffracted into the user’s field of view. When viewed by the user through the EPE, the world-diffracted light can appear as an unwanted image artifact. The angle of incidence that produces an artifact in the user’s field of view is generally dependent on the design of the display combiner. For diffractive waveguide-based display combiners, large angles of incidence generally result in stray light paths that are closest to the center of the user’s world view.

[0067] This effect is further illustrated in Figure 8A , Figure 8A shows a display combiner 800. Ambient light incides on the front surface of display combiner 800 at an angle of incidence θ inc . As shown, at least some of the incident light transmits through the grating and combiner. However, display combiner 800 supports a grating (not shown) that diffracts at least some of the incident light toward the user. This light, labeled stray light, is diffracted at an angle θ stray .

[0068] With reference to Figure 8BAn optical attenuator (e.g., film 810) can be applied (e.g., laminated) to display combiner 800 to reduce stray light artifacts related to ambient light. Generally, the transmission of light through film 810 depends on the angle of incidence of the light on the film. As shown, film 810 reduces (e.g., blocks) the transmission of light with relatively high angles of incidence θ inc (e.g., 30° or more, 35° or more, 40° or more, 45° or more, such as a user would experience from overhead lighting in an indoor environment) but transmits light with lower angles of incidence θa(e.g., "world light" that a wearer sees in the core view of the device), film 810 can perform this function over a wide range of wavelengths, such as in the operating wavelength range of the display system, such as from 420 nm to 680 nm.

[0069] The transmission efficiency of incident light generally varies from a relatively high transmission efficiency (e.g., 40% or more, 45% or more) to a relatively low transmission efficiency (e.g., less than 1%, less than 0.5%) as a function of the angle of incidence. Transmission efficiency refers to the relative intensity of light transmitted at a particular wavelength. In some embodiments, unpolarized light at a wavelength in the range of 420 nm to 680 nm that is incident on the optical attenuator at an angle of incidence between 35° and 65° has a transmission efficiency of less than 0.5%. In certain embodiments, unpolarized light at a wavelength in the range of 420 nm to 680 nm that is incident on the optical attenuator at an angle of incidence between -32° and +32° has a transmission efficiency of greater than 45%.

[0070] The optical attenuator can also have a relatively small impact on the color of an image viewed through the film. For example, for a D65 source, the optical attenuator can shift the (0.33, 0.33) CIE 1931 white point for unpolarized light at angles of incidence between -32° and +32° by less than (+ / - 0.02, + / - 0.02) (e.g., (+ / - 0.01, + / - 0.01) or less) across the entire aperture of the display.

[0071] The transmission of the optical attenuator can also be characterized by an attenuation, which can be relatively high (e.g., 10 dB or more, 15 dB or more, 20 dB or more, 25 dB or more, 30 dB or more) for relatively high angles of incidence. Light at lower angles of incidence, such as 25° or less (e.g., 20° or less, 15° or less, 10° or less) can experience very low levels of attenuation (e.g., 2 dB or less, 1 dB or less).

[0072] Generally, film 810 can be relatively thin. For example, film 810 can have a total thickness in the range from 500 microns to 2,000 microns. Thus, the benefits of using an optical attenuator can be achieved without significantly increasing the volume of a wearable display system.

[0073] In some embodiments, the film 810 is a film stack including a polarization adjustment film (e.g., including one or more birefringent layers) disposed between a pair of polarizer films (e.g., linear polarizers). The polarizer films and the polarization adjustment film significantly reduce the transmission of visible light incident on the film 810 at large angles of incidence without significantly reducing the transmission of light incident on the optical attenuator at small angles of incidence.

[0074] In general, the configuration of the two polarizers and the polarization adjustment film can be varied to provide a desired level of transmission variation over the range of angles of incidence of interest (e.g., from -75° to +75°). In some embodiments, the polarizers are linear polarizers and the pass axes of the two linear polarizers can be crossed (e.g., by 90°).

[0075] In general, the polarization adjustment film includes one or more birefringent layers designed to rotate the polarization state of light incident from the world side that is transmitted by a first linear polarizer in the pair of linear polarizers. The birefringent layers can include A-plates, in which the extraordinary axis of the birefringent material is parallel to the plane of the layer (e.g., quarter waveplates (QW)), and / or C-plates, in which the extraordinary axis of the birefringent material is perpendicular to the plane of the layer, example arrangements are shown below. More generally, the birefringent layers can include uniaxial birefringent materials (e.g., as A-plates or C-plates) or biaxial birefringent materials.

[0076] In general, the amount by which the polarization adjustment layer rotates the polarization state depends on the configuration of the polarization adjustment layer and varies depending on the angle of incidence of the light transmitted by the first linear polarizer in the pair of linear polarizers. In some embodiments, the transmitted light with large angles of incidence (e.g., 35° or more) is rotated less than the transmitted light with small angles of incidence (e.g., less than 35°). For example, where the polarizers are crossed linear polarizers, the greater the amount of rotation up to 90°, the higher the transmission efficiency of the film. In this case, greater rotation of on-axis light is desirable compared to light at larger angles of incidence. Conversely, in some embodiments, the polarizer axes are parallel and the polarization adjustment film rotates on-axis light less than light at larger angles of incidence.

[0077] In general, the optical attenuator is suitably sized to cover at least a portion of the eyepiece of the wearable display system. For example, in some embodiments, the optical attenuator can have an area greater than 50 mm x 50 mm.

[0078] In general, ambient light diffracted into the user eyebox by the uniform grating will depend on where the light is incident in the clear aperture of the display. This effect is illustrated in Figure 9A and 9B is shown, Figure 9A and Figure 9BThe entrance plane of the netting eyepiece and the eyepiece including the grating element are depicted separately. The eyebox 920 refers to the spatial volume in which the effective viewable image formed by the display resides. The size of the eyebox is typically dependent on the pupil size and the eye relief 940. In Figure 9A , the vertical dimension of the eyebox for the user’s eye 910 is denoted as 920. Typically, this dimension can range from about 5 mm to about 25 mm. The eye relief distance 940 refers to the offset distance of the eye 910 from the eyepiece 930 and can typically range from 10 mm to 40 mm from the vertical center point 950. As Figure 9A indicated for the vertical entrance plane, the angle of incidence of the light transmitted by the eyepiece 930 into the eyebox 920 depends on the position at which the light is incident on the eyepiece. In particular, this illustrates three different points 950, 951, and 952. The range of angles of incidence at which light is transmitted at point 950 is denoted as a. This range is different for each point.

[0079] Referring to Figure 9B , the grating at each point 950, 951, and 952 also diffracts the incident ambient light into the eyebox 920. For each case, the range of angles of incidence at which ambient light is diffracted into the eyebox will be different. For example, at point 950, the eyepiece 930 diffracts incident light in a first range of angles b and a second range of angles g into the eyebox 920. The further points 951 and 952 will diffract incident light in respective ranges of angles into the eyebox.

[0080] This position dependence of the diffracted incident light is further illustrated by the diagram in Figure 10 , Figure 10 a series of simulation diagrams is shown, each diagram representing the transmission and diffraction characteristics of the eyepiece at a respective vertical position. In particular, the range of angles of incidence of the transmitted light incident on the world side is provided in black, and the range of angles of incidence of the diffracted light that produces a rainbow artifact at a particular wavelength is provided in red (625 nm), green (525 nm), and blue (460 nm), respectively.

[0081] The diagram on the left is calculated based on the entrance plane shown on the right in Figure 10 , Figure 10The right side of each plot includes an eyebox 1002 and an entrance pupil. Each plot is calculated (e.g., simulated) based on an 18 mm vertical dimension of the eyebox 1002, a 20 mm eye relief 1004, a 36.3 mm vertical dimension of the entrance pupil 1006. The entrance pupil 1006 is simulated to include a grating element with a 391 nm grating period, where the grating lines extend in the horizontal direction (e.g., perpendicular to the page plane). The title of each plot, located above each plot, indicates the vertical position of the calculated transmission and artifact windows, given as a vertical height 1010 from the center point 1020, in millimeters, with positive values above and negative values below the center point 1020. The vertical axis of each plot is a normalized value (e.g., from 0 to 1) representing high transmission (black) or high diffraction artifact generation (red, blue, green). The horizontal axis of each plot represents the angle of incidence of ambient light (Θ i ) relative to a ray 1030 normal to the face of the entrance pupil, where positive values of Θ i are measured clockwise from the normal 1030. For example, the shaded region 1040 is the world transmission window calculated at 16.6 mm above the center point 1020, and corresponds to a range of ~ -16° to -55°, as indicated by the topmost plot.

[0082] Thus, in this case, it can be desirable to use an optical attenuator that attenuates incident light from different angular ranges on the world side depending on where the light is incident on the eyepiece. This can improve the reduction of diffraction light artifacts across the eyepiece without significantly reducing the transmission of incident world light admitted to the eyebox.

[0083] Turning now to a particular example of such an optical attenuator and referring to Figure 11A The eyepiece 1100 for a wearable display system includes the display combiner 800 and a film stack 1110 that functions as an optical attenuator. The stack 1110 includes a pair of linear polarizers 1120a and 1120b. Between the linear polarizers, the stack 1110 includes a pair of quarter waveplates (QWs) 1130a and 1130b flanking a multi-domain birefringent film 1140.

[0084] The fast axes of the waveplates 1130a and 1130b are oriented at about 45° from the pass axes of the linear polarizers 1120a and 1120b, respectively, so that the combination of the linear polarizer 1120b and the QW 1130b converts unpolarized light incident from the world side into substantially circularly polarized light (i.e., the combination behaves as a circular polarizer). The combination of the QW 1130a and the linear polarizer 1120a behaves similarly. Note that the handedness of each circular polarizer is the same.

[0085] The multi-domain birefringent film 1140 includes different regions in which the principal optical axes of the birefringent material making up the film are oriented differently, such that the transmission properties of the film stack 1110 vary from domain to domain. For example, in some embodiments, the birefringent film 1140 is a liquid crystal birefringent film composed of domains of nematic liquid crystal material in which the director varies from domain to domain. Referring to Figure 11B An example of such a film is film 1141, which has three domains 1142, 1143, and 1144, each with its own unique director axis, such that θ c1 ≠ θ c2 ≠ θ c3 ≠ θ c , where θ is the azimuthal angle difference measured from the normal to the film plane. It is also possible for the director axis of one or more spatial regions to vary in orientation by a radial angle difference φ (e.g., θ c ). More generally, birefringent films with optical axes that are oriented non-perpendicularly and non-parallel to the film plane are generally referred to as O-plates and an O-plate with multiple domains, such as film 1141, can be considered a spatially varying O-plate.

[0086] The orientation of the nematic director in the film can be achieved by a variety of techniques. For example, the alignment is typically influenced by a pre-tilt angle (the angle of the director at the surface of the film) and / or the application of an external field, such as an electric field. The pre-tilt can be set in a variety of ways (e.g., mechanical polishing, exposure to linearly polarized light) to achieve a range of azimuthal and radial pre-tilt directions (e.g., θ c , φ c ). The range of azimuthal orientations θ c may range from -90° to 90° from the normal axis of the O-plate, and the range of radial orientations φ c may range from -180° to 180° from the x-axis. These techniques can be applied to different spatial domains on the O-plate such that each domain has a different pre-tilt.

[0087] In general, the spatial domains can take any form or size, or have any number. The director axes of the spatial regions can be aligned radially, concentrically, directionally, or any combination thereof between the spatial regions. Figure 12A and 12B show examples of such embodiments. Figure 12A An example spatially varying O-plate 1210 with nine different spatial domains 1220a-1220i separated by dashed lines is shown, each with a unique director axis whose axial direction is given by (θ c , φ c) value definitions. The eight pointing axes 1220a-1220h are arranged radially about a central axis normal to the face of the spatially-varying O-plate 1210, and one pointing axis 1220i is aligned normal to the face of the spatially-varying O-plate 1210, equivalent to a C-plate. The eight pointing axes of the spatial regions 1220a-1220h share a common azimuthal orientation θ c and a radial orientation φ c Bilaterally distributed from 0° to 180° in 45° increments from the x-direction (e.g., 0°, ±45°, ±90°, ±135°, 180°).

[0088] Figure 12B Another example of a spatially-varying O-plate 1211 is shown, having three distinct spatial domains 1221a-1221c separated by dashed lines. The spatial domains 1221a-1221c are aligned horizontally, without radial distribution. The pointing axes of the spatial regions 1221a and 1221c share a common azimuthal tilt θ c while the radial angle φ c are aligned parallel to the face of the spatially-varying O-plate 1211 at -90° and 90° in opposite polar directions. The pointing axes of the middle spatial region 1221b are aligned normal to the face of the spatially-varying O-plate 1210.

[0089] Figure 12A and 12B are specific examples of spatial region arrangements that can be implemented in a spatially-varying O-plate 1140 for an optical attenuator film stack 1110, although they are not limiting examples of further embodiments. More generally, other one- and two-dimensional domain arrangements can be employed. In general, strong ambient light sources occur more frequently overhead, and their reflection from below, as well as the simplified design of 12B can be a preferred embodiment for attenuating overhead artifacts. However, the radial design of 12A can be used to attenuate artifacts produced by light sources from any cone angle within the user’s field of view.

[0090] While Figure 11A An example of an optical attenuator including a spatially-varying O-plate 1140 between two linear polarizers 1120 is shown, implementations with additional layers are possible. For example, Figure 13An eyepiece 1300 is shown that includes a film stack 1310 applied to the world side of a display combiner 800. The film stack 1310 includes three linear polarizers 1320a, 1320b, and 1320c. A first polarization adjustment stack is arranged between polarizers 1320a and 1320b. This stack includes a pair of QWs 1330a and 130b flanking a spatially varying O-plate 1340a. A second polarization adjustment stack is arranged between polarizers 1320b and 1320c. This stack includes QWs 1330c and 1330d flanking a spatially varying O-plate 1340b. In effect, the performance of stack 1310 is similar to two stacks 1110 stacked together.

[0091] Stack 1110 can be considered a single stage arrangement, while stack 1310 is double stage. In general, additional stages can be added.

[0092] Turning now to the performance of single and double stage optical attenuators, in general, the transmission profiles achieved with double stage film stack 1310 can achieve more dramatic attenuation of artifacts produced by high incidence angle ambient light. Figures 14A-14D are computed transmission profile plots for three different wavelengths (e.g., 630 nm, 525 nm, 460 nm) of ambient light incident on the clear aperture. These plots compare the normalized log transmission of light versus incidence angle θ i . Figure 14A and Figure 14B Computed transmission profiles are shown for a single stage film stack (such as stack 1110) in which the birefringent film has a retardance (dΔn) of 550 nm. Figure 14A are computed using a single stage film stack (i.e., a C-plate) having an azimuthal orientation θ c of 0°, and show the bilateral symmetry about the peak transmission at 0° incidence angle θ i The three computed transmission profiles for light having respective wavelengths of 630 nm (red), 525 nm (green), and 460 nm (blue) monotonically decrease until incidence angle θ i is about ±60°, with the 460 nm transmission profile decreasing at the highest relative rate. Prior to an exponential drop-off to incidence angle θ i of ±90°, the transmission profiles then exhibit an inversion (e.g., 525 nm, 460 nm) or shoulder (630 nm) between incidence angle θ i ranges of ±60° to ±80° depending on wavelength.

[0093] In contrast, Figure 14B are shown for a single stage film stack having an azimuthal orientation θ cThe calculated transmission distribution of the single-stage film stack 1110. The three calculated transmission distributions for light with corresponding wavelengths of 630 nm (red), 525 nm (green), and 460 nm (blue) are no longer symmetrical, and the peak transmission has shifted to the incident angle θ. i A window centered at approximately 20° with an angle of ±20°. For incident angles θ greater than approximately 20°. i The transmission distribution extends to an incident angle θ of 90°. i The exponent drops to zero. However, as the incident angle θ... i As the wavelengths decrease, the transmission distribution decreases depending on their wavelengths (e.g., it decreases at the highest relative rate at 460 nm) until the incident angle θ is between approximately -40° and -50°. i Window. An incident angle θ between approximately -40° and -70°. i At that location, the transmission distribution is approximately 10 2 (630nm) and 10 3 The logarithmic factor between 460 nm and the peak increases to a secondary peak. This secondary peak is close to the primary peak calculated for the transmission distribution at a wavelength of 460 nm. After approximately -70°, the transmission distribution shifts to an incident angle θ of -90°. i It dropped to zero.

[0094] These incident angles θ, which increase the transmission distribution in 14A and 14B i Ranges of approximately ±60° to ±80° and approximately -40° to -70°, respectively, may result in unwanted color shifts in the user's field of view, where significant variations exist between wavelength transmission distributions. For example, in Figure 14B The incident angle θ is approximately -40°. i At this point, compared to 630nm light, the transmission distribution of 460nm (blue) light shows a >100-fold reduction in transmission. This could manifest as a noticeable red hue shift for the user, another undesirable optical artifact. To achieve strong light attenuation at all angles beyond the desired range of world transmission, the use of bilayer film stacking could be beneficial.

[0095] Figure 14C and 14D The calculated transmission distribution of an eyepiece using a bilayer film stack (such as 1310) is shown. Figure 14C It is calculated using a two-stage film stack, where the orientation θ is at the azimuth angle pointing to the axis. c Both stages have a delay of 480 nm (d1Δn, d2Δn) at 0°, and the results show the effect of the incident angle θ at 0°. i The bilateral symmetry of the peak transmission at that point is very similar to Figure 14A The single-stage membrane stack 1110. However, at bilateral incident angles θ ranging from ±60° to ±80°. i Within the range,Figure 14A The secondary peaks shown in FIG. 14D are no longer as pronounced, with an additional log factor of about 10 (630 nm) and 10 2 (460 nm) between the single-stage film stack 1110 and the dual-stage film stack 1310. Additionally, the peak transmission window remains the same over a range of incident angles θ i of about ±20° centered at 20° of incident angle θ

[0096] 14D is calculated using a dual-stage film stack with a birefringent film having a retardance of diAn 380 nm and d2An 270 nm and an orientation of the optic axis azimuthal angle orientation θ c at 20° of incident angle θ i of about ±20° centered at 20° of incident angle θ i The peak transmission window remains the same over a range of incident angles θ Figure 14B of about ±20° centered at 20° of incident angle θ Figure 15C Although the secondary peaks seen at incident angles θ i of about 10 2 .

[0097] The transmission profiles of Figure 14C and 14D demonstrate that using a dual-stage film stack can advantageously attenuate secondary peaks produced outside of the desired angular world transmission range, particularly when the optic axis is tilted, relative to a single-stage film stack. Furthermore, the wide variation in color shift (resulting in birefringent rainbow artifacts) at high incident angles is also significantly attenuated. Figure 14A and 14C may be a preferred embodiment of the orientation of the optic axis that can be used in spatially varying O-plate regions (such as 1220i) that are centrally located, where the field of view through the clear aperture is reduced to about ±20°, which corresponds to Figure 14A and 14C a specific world transmission window of Figure 14C and 14D may be an embodiment of the orientation of the optic axis in spatially varying O-plate regions (such as 1220a-1220h) because the world transmission window in these regions will be at incident angles θ i of greater than 0° and possibly less than 50°.

[0098] Figures 15A to 15C are examples of transmission profiles that can be achieved by O-plates with an optic axis having azimuthal and radial orientations. These figures are normalized heat map representations of the total transmittance through the clear aperture calculated using O-plates over an arbitrary y-axis range and an equal arbitrary x-axis range. Each figure is calculated using a different combination of the azimuthal and radial orientations of the optic axis of the O-plate (e.g., θc, φ c ). In Figure 15Cto the left is a reference coordinate system including the orientation of the angles Θ and φ. In Figure 15A the azimuthal orientation Θ c is 0° and the radial orientation φ c is 0°. The calculated transmission profile shows a radially symmetric transmission pattern with a peak 1410 at wave number ky= kx= 0 where the transmission is maximum. The transmission decreases as a function of the radial distance until it reaches 0 at a radial distance of 1.

[0099] Figure 15B The calculated transmission profile of an O-plate with an azimuthal orientation Θ c of 15° and a radial orientation φ c of 45° counterclockwise from the x-axis is shown. The calculated transmission profile is no longer radially symmetric but is bilaterally symmetric around the line that bisects the calculated transmission profile from (-1, -1) to (1, 1) in the (x, y) plane. The peak 1411 of the calculated transmission profile is near (~0.3, 0.3) allowing for a preferred transmission of light in the first quadrant of the plot.

[0100] Figure 15C The calculated transmission profile of an O-plate with an azimuthal orientation Θ c of 15° and a radial orientation φ c of 45° clockwise from the x-axis is shown. The calculated transmission profile is bilaterally symmetric around the line that bisects the calculated transmission profile from (-1, 1) to (1, -1) in the (x, y) plane. The peak 1412 of the calculated transmission profile is near (~0.3, -0.3) allowing for a preferred transmission of light in the fourth quadrant of the plot.

[0101] In general, while the foregoing examples illustrate calculations for specific O-plate arrangements, they are merely illustrative. More generally, the retardation of the film, the number and shape of the domains, and the director alignment within each region can be selected according to the eyebox size and grating structure to provide the desired attenuation of unwanted diffracted ambient light.

[0102] Figure 16A - T further illustrates possible amounts of attenuation using single stage, double stage, and spatially varying double stage O-plate optical attenuators. These images illustrate unwanted optical artifacts (e.g., optical rainbows) when an ambient light source is incident on the eyepiece at high angles of incidence. As Figure 7BAs shown, when white ambient light from a nearby source interacts with the grating 710 structure in the display combiner 700 from a high angle of incidence, the light becomes diffracted. The amount of diffraction depends on the wavelength of the incident light and the pitch or spacing of the grating 710. White light consists of many wavelengths, and each wavelength of the incident ambient light diffracted towards the user is diffracted to a different angle. This causes the white light to appear to be scattered like a rainbow as seen by the user, resulting in undesirable optical artifacts (e.g., optical rainbows).

[0103] exist Figures 16A-16T In the middle, for 70° ( Figures 16A-16D ), 60° Figures 16E-16H ) and 50° Figures 16I-16L ), 40° Figures 16M-16P ) and 30° Figures 16Q-16T An incident angle of 5700K blackbody spectrum white light source is incident on the eyepiece from above, showing optical rainbow artifacts. The diffraction angle of the artifacts is calculated using a 391nm grating with a 710-pitch. The black circles in each image correspond to light incident from the user through a white light source with a 5700K blackbody spectrum. Figure 16A The image shown on the right side of the -T shows a 4 mm eyebox, a 20 mm eyedropper distance, and a 36.3 mm aperture height, resulting in a viewing angle of ±42°. The first column 1610 of the image shows the calculated optical rainbow artifacts as seen by the user without a filter. The second column 1611 of the image shows the calculated optical rainbow artifacts as seen by the user using a single-stage film stack 1110. The third column 1612 of the image shows the calculated optical rainbow artifacts as seen by the user using a two-stage film stack 1310. The pointing axis of the O-plate used for calculating the second column 1611 and the third column 1612 has no azimuth or radial orientation (e.g., θ). c =φ c =0°). The fourth column 1613 of the image shows the calculated optical rainbow artifacts as seen by the user when using a stack of O-plate films with bilevel spatial variation. The bilevel spatial variation of the O-plates used to calculate the fourth column 1613 has Figure 12B The design shown.

[0104] Using the image in column 1610 as a reference, the largest and brightest optical rainbow artifacts are observed at larger incident angles (e.g., 60°, 70°). At larger incident angles (e.g., 60°, 70°), single-stage 1611 ( Figure 16B and 16F ) and dual-level 1612 ( Figure 16C and 16G ) has a significant impact on the attenuation of these optical rainbow artifacts, and uses a two-level spatially varied O-plate 1613 ( Figure 16D and 16H) than the single stage 1611 or dual stage 1612 film stack. This remains true for all other images and the remaining images shown in FIG. 16 for the angle of incidence. The single stage 1611 and dual stage 1612 film stacks have a significant impact on the attenuation of the noticeable optical rainbow artifacts, while the dual stage 1613 film stack using a spatially varying O-plate has the largest impact.

[0105] An optical attenuator using a spatially varying O-plate can further benefit in reducing the spatial color variation that can result from the use of an optical attenuator. Figures 17A-17D The color shift perceived by a user when viewing white light through ±45° viewing angles is shown for a filterless (1601), Figure 17A a single stage film stack (1602), Figure 17B a dual stage film stack (1603), Figure 17C and a dual stage film stack using a spatially varying O-plate (1604). Figure 17D The blue circles in the field of view represent increments of 15°. The film stacks used to calculate the white point shift for Figures 17A-17D are the same film stacks used to calculate the first through fourth columns (1601, 1602, 1603, 1604) in FIG. 16 (e.g., no filter, no director axis orientation, Figure 12B spatially varying O-plate of the design shown). In certain embodiments, the white point shift can be 0.01 u'v' or less (e.g., 0.005 or less, 0.002 or less, 0.001 or less, 0.0005 or less) from the D65 white point in at least one direction (e.g., over the entire range of 40° or less of the angle of incidence) at ±40° of the angle of incidence.

[0106] While the use of single and dual stage film stacks can provide significant attenuation of noticeable optical rainbow artifacts, as shown in the 1611 and 1612 columns of FIG. 16, they also produce perceptible color shifts within the 45° viewing angle. In Figure 17B there is a perceptible shift to the red frequency between the ±30° and ±45° viewing angles (e.g., between the second blue ring and the edge of the field of view). This same effect can be seen in Figure 14A At the ±45° angle of incidence θ i , the 630 nm transmission profile is higher than the 480 nm transmission profile. Longer wavelengths are associated with more red, and since the transmission is higher at these wavelengths, the perceived color shifts to a red hue.

[0107] The same effect is seen in Figure 17C but to a greater degree. In Figure 14C At the ±45° angle of incidence θ i , the 630 nm transmission profile is still higher than the 480 nm transmission profile, and the values of both transmission profiles at ±45° are lower thanFigure 14A The value in the figure represents the combined effect of total transmission loss at a viewing angle of ±45° when using a dual-layer film stack 1310 and a further reduction in the 480nm transmission distribution compared to 630nm.

[0108] Figure 17D This represents the same color shift perceived by the user through a bipolar film stack with spatially varying O-plates. Except for a lower redshift at extreme viewing angles approaching ±45°, the overall transmittance across the viewing window is higher. This can be attributed to... Figure 12B The three spatially varying regions. The pointing axis of the upper region 1221a has an azimuth angle θ of 15°. c and 90° radial orientation φ c (Vertical), the pointing axis of the middle region 1221b has an azimuth and radial orientation perpendicular to the surface of the O-plate, and the lower region 1221c has an azimuth orientation θ of 15°. c and a radial orientation of -90° φ c (Negative vertical). These directional orientations allow the peak world transmission window of each region 1221a-c to overlap with the ambient light incident angle of the observation window. From 14C (±20°), 14D (20°±20°), and with opposite radial orientations φ c The combination of a 14D world transmission window (-20°±20°) allows for a total near-peak world transmission window of approximately ±40°, such as Figure 17D What I saw in the video.

[0109] Typically, a variety of suitable materials can be used for each layer in an optical attenuator. For example, a linear polarizer can be formed from a stretched polymer material (e.g., PVA) stained with a chromophore (e.g., iodine). Commercially available linear polarizers can be used, such as those available from Sanritz Co. (Japan) or Nitto Denko (Japan). For example, the QW can be made from a stretched polymer film or a liquid crystal polymer film. The O-plate can be a liquid crystal material, including polymeric liquid crystal materials.

[0110] Typically, film stacks may include additional layers beyond those described above. For example, the stack may include extra layers to provide mechanical functions rather than optical functions. It may include adhesive layers and / or layers for mechanical strength and / or environmental protection. Such layers may be optically isotropic so as not to significantly affect the polarization of transmitted light. In some embodiments, the stack includes one or more layers on the world side of the outermost linear polarizer.

[0111] For example, an anti-reflective film and / or a hard coat layer can be included. While the foregoing examples of optical attenuators include optically passive elements, more generally, embodiments can also feature optically active elements. Such elements can change their optical properties, thereby changing the transmission properties of the optical attenuator in response to an electrical signal or some other physical stimulus. For example, the O-plate domains can be electro-optically tunable. For example, the O-plates can be formed as liquid crystal cells to which an electric field can be applied to change the LC director orientation between two or more different states, thereby changing the transmission properties of each domain.

[0112] Some embodiments described in this specification can be implemented as a set of one or more computer programs, that is, one or more modules of computer program instructions encoded on a computer storage medium for execution by, or to control the operation of, data processing apparatus. The computer storage medium can be a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination or set of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

[0113] Some embodiments described in this specification can be implemented as a set of one or more computer programs, that is, one or more modules of computer program instructions encoded on a computer storage medium for execution by, or to control the operation of, data processing apparatus. The computer storage medium can be a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination or set of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

[0114] The term“data processing apparatus” encompasses all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, a system on a chip, or multiple ones, or combinations, of the foregoing. The apparatus can include special purpose logic, for example, an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). The apparatus can also include, in addition to hardware, code that creates an execution environment for the computer programs in question, for example, code that constitutes processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them. The apparatus and execution environment can realize various different computing model infrastructures, such as web services, distributed computing and grid computing infrastructures.

[0115] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages. The computer program can be deployed in any form, including as a stand-alone program, as part of a file accessible by the operating system, as an applet, as a servlet, or as a server program, home page, home sheet, or other form of sequence of instructions executable by a processing device. The computer program can be deployed to be executed by one computer or by multiple computers in a location or in multiple locations, by a host of computers operating together or by a cloud of servers.

[0116] Some of the processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform actions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). Devices of this sort can include, in addition to circuits of the

[0117] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The computer includes a processor for executing instructions and one or more memory devices for storing instructions and data. The computer also includes, in some embodiments, one or more mass storage devices for storing data files; such devices are common, such as magnetic disks, magneto-optical disks, or optical disks. However, a computer need not have such devices. The computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program, as a subroutine, as an applet, or as a servlet. Furthermore, the computer program can be deployed to operate with a hosting service that provides infrastructure

[0118] To provide for interaction with a user, operations can be implemented on a computer having a display device, e.g., a monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse, trackball, tablet, touch-sensitive screen, or other type of pointing device, for interacting with a computer. Other kinds of devices can be used as well for providing interaction with a user as described above; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. In addition, a computer can interact with a user by sending documents to and receiving documents from a device that is used by the user; for example, by sending web pages to a web browser on a user’s client device in response to requests received from the web browser.

[0119] A computer system can include a single computing device, or multiple computers operating near one another or generally remote from one another and typically interacting through a communication network. Examples of communication networks include local area networks (“LANs”) and wide area networks (“WANs”), the Internet, networks that include satellite links, and peer-to-peer networks (e.g., ad hoc peer-to-peer networks). The relationship of client and server can arise by virtue of computer programs running on the respective computers and having a client-server relationship to one another.

[0120] Figure 18 An example computer system 1800 is shown including a processor 1810, a memory 1820, a storage device 1830, and an input / output device 1840. Each of the components 1810, 1820, 1830, and 1840 can be interconnected, for example, by a system bus 1850. The processor 1810 is capable of processing instructions for execution within the system 1800. In some implementations, the processor 1810 is a single-threaded processor, a multi-threaded processor, or another type of processor. The processor 1810 is capable of processing instructions stored by the memory 1820 or on the storage device 1830. The memory 1820 and the storage device 1830 can store information within the system 1800.

[0121] Input / output device 1840 provides input / output operations for system 1800. In some embodiments, input / output device 1840 can include one or more of a network interface device (e.g., an Ethernet card), a serial communication device (e.g., an RS-232 port), and / or a wireless interface device (e.g., an 802.11 card), a 3G modem, a 4G modem, and so forth. In some embodiments, input / output device can include driver devices configured to receive input data and send output data to other input / output devices, e.g., a wearable display system 1860. In some embodiments, mobile computing devices, mobile communication devices, and other devices can be used.

[0122] Although this description contains many specifics, these should not be construed as limiting the scope of the application but as merely describing a particular exemplification thereof. Certain features that are described in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination.

[0123] Many embodiments have been described. However, various modifications can be made without departing from their spirit and scope. Therefore, other embodiments are within the scope of the following claims.

Claims

1. A wearable display system, comprising: an eyepiece stack having a world side and a user side opposite the world side, wherein, during use, a user positioned at the user side views display images delivered by the wearable display system via the eyepiece stack that augment the user's view of the user's environment; and an optical attenuator disposed at the world side of the eyepiece stack, the optical attenuator comprising a layer of birefringent material having a plurality of domains each having a principal optical axis oriented in a corresponding direction different from the directions of the other domains, the layer of birefringent material disposed between a pair of linear polarizers, wherein each domain of the optical attenuator reduces the transmission of visible light incident on the optical attenuator for respective different ranges of incident angles.

2. The wearable display system of claim 1, wherein, For an aperture of the eyepiece stack corresponding to an eyebox of the wearable display system, a white point of an image viewed by the user side through the wearable display system with a D65 illuminant on the world side varies 0.01 Δu'v' or less in the CIELUV color space for incident angles of 40° or less across the aperture of the wearable display system defining the eyebox.

3. The wearable display system of claim 2, wherein, The aperture has a diameter of 20 mm or more.

4. The wearable display system of claim 3, wherein, The aperture has a diameter of 50 mm or less.

5. The wearable display system of claim 1, wherein, The birefringent material is a liquid crystal material and the optical attenuator further comprises a pair of alignment layers on opposite sides of the liquid crystal material, wherein at least one of the alignment layers is configured to provide different pre-tilts to the liquid crystal material in different domains of the optical attenuator.

6. The wearable display system of claim 5, wherein, The polar pre-tilt at a domain intersecting a visual axis of the wearable display system is zero degrees and the polar pre-tilt at at least one domain away from the visual axis is a greater non-zero.

7. The wearable display system of claim 5 or 6, wherein, At least two domains having a non-zero polar pre-tilt have different azimuthal pre-tilts.

8. The wearable display system of claim 1, wherein, The layer of birefringent material is a spatially varying o-plate.

9. The wearable display system of claim 1, wherein, The layer of birefringent material comprises domains arranged in a one-dimensional pattern.

10. The wearable display system of claim 1, wherein, The layer of birefringent material comprises domains arranged in a two-dimensional pattern.

11. The wearable display system of claim 1, wherein, Respective pass axes of the pair of linear polarizers cross.

12. The wearable display system of claim 1, wherein, The layer of birefringent material rotates a polarization state of light transmitted by a first linear polarizer of the pair of linear polarizers incident to the world side of the optical attenuator.

13. The wearable display system of claim 12, wherein, An amount of rotation of the polarization state varies depending on an incident angle of the light transmitted by the first linear polarizer of the pair of linear polarizers.

14. The wearable display system of claim 13, wherein, Transmitted light having a large incident angle is rotated less than transmitted light having a small incident angle.

15. The wearable display system of claim 1, wherein, The optical attenuator comprises a pair of quarter-wave plates disposed on opposite sides of the layer of birefringent material.

16. The wearable display system of claim 15, wherein, Each quarter-wave plate is arranged relative to a respective one of the linear polarizers to form a circular polarizer.

17. The wearable display system of claim 1, wherein, The optical attenuator comprises a second layer of birefringent material.

18. The wearable display system of claim 17, wherein, The optical attenuator further comprises three linear polarizers, each birefringent layer disposed between two of the three linear polarizers.

19. The wearable display system of claim 17, wherein each layer of birefringent material is a spatially varying o-plate.

20. The wearable display system of claim 19, wherein, The optical attenuator includes a plurality of quarter-wave plates, a pair of quarter-wave plates being arranged on opposite sides of the each layer of birefringent material.

21. The wearable display system of claim 1, wherein, The optical attenuator includes two or more stages, each stage including a layer of the birefringent material arranged between a pair of linear polarizers.

22. The wearable display system of claim 21, wherein, Adjacent stages share a linear polarizer.

23. The wearable display system of claim 1, wherein, The layer of birefringent material is a switchable element having variable optical properties.

24. The wearable display system of claim 23, wherein, The switchable element includes a liquid crystal layer between a pair of electrode layers.

25. A wearable display system comprising: an eyepiece stack having a world side and a user side opposite the world side, wherein, during use, a user positioned on the user side views display images delivered by the wearable display system via the eyepiece stack that augment the user’s view of a user environment; and an optical attenuator arranged on the world side of the eyepiece stack, the optical attenuator comprising: a layer of liquid crystal material having a plurality of domains, each domain having a director principal axis oriented in a corresponding direction that is different from the directions of other domains, the layer of liquid crystal material being arranged between a pair of linear polarizers; and a pair of orientation layers on opposite sides of the liquid crystal material, wherein at least one of the orientation layers is configured to provide a different pre-tilt angle to the liquid crystal material in different domains of the optical attenuator, wherein each domain of the optical attenuator reduces transmission of visible light incident on the optical attenuator for a respective different range of incident angles.

Images