Angle-selective attenuation of light transmission artifact in wearable display

Abstract

To provide angle-selective attenuation of light transmission artifacts in suitable wearable displays.SOLUTION: A wearable display system includes an eyepiece stack having a world side and a user side opposing the world side. During use, a user positioned on the user side views displayed images delivered by the wearable display system via the eyepiece stack which enhances a visual field of the user of the user's environment. In addition, the system includes an optical attenuator arranged on the world side of the eyepiece stack. The optical attenuator includes a layer of a birefringent material with a plurality of domains each having a main optical axis oriented in a corresponding direction different from directions of the other domains. Each domain of the optical attenuator reduces transmission of visible light incident on the optical attenuator, across a corresponding different range of incidence angles.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to techniques for attenuation of light transmittance artifacts in wearable displays. (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 986,478, filed March 6, 2020, the contents of which are incorporated herein by reference in their entirety. [Background technology]

[0003] An optical imaging system, such as a wearable display system (e.g., a wearable display headset), can include one or more eyepieces that present a projected image to a user. The eyepieces can be constructed using one or more thin layers of highly refractive materials. As an example, the eyepieces can be constructed from one or more layers of highly refractive glass, silicon, metal, or polymer substrates.

[0004] Multiple eyepieces can be used together to project a simulated three-dimensional image. For example, multiple eyepieces (each with a different pattern) can be layered on top of each other, with each eyepiece projecting a different depth layer of the stereoscopic image. Thus, the eyepieces can collectively present a stereoscopic image to a user across three dimensions. This can be useful, for example, in presenting a "virtual reality" environment to a user.

[0005] Optical elements within a wearable display system may also interact with ambient light, which is light from the environment the user is in. For example, diffractive structures within a wearable display system may diffract ambient light that is incident on the wearable display at high angles that would not normally be incident on the user's field of view into the field of view creating visible artifacts that diminish the user's experience. Summary of the Invention [Means for solving the problem]

[0006] A wearable display system (e.g., useful for augmented reality (AR) applications) is described that includes an optical attenuator for reducing artifacts associated with ambient light incident on the display at high angles of incidence. An exemplary optical attenuator can impart different levels of attenuation to broadband light as a function of angle of incidence. The optical attenuator features spatial variation in transmission angle range across the clear aperture of the wearable display by varying the alignment of the optical axis of a birefringent medium within the attenuator for each domain of the attenuator. For example, the director axis of a liquid crystal material used as a birefringent layer of the attenuator can be spatially varied. The optical attenuator can further improve suppression of artifacts associated with wearable displays and reduce color shifts at the edges of a user's view of the world through the display compared to solutions that utilize single-domain birefringent layers.

[0007] Various aspects of the present invention are summarized as follows.

[0008] In general, 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, the eyepiece stack being positioned on the user side during use, where a user views displayed images delivered by the wearable display system through the eyepiece stack, which increases the user's view of the user's environment, and an optical attenuator arranged on the world side of the eyepiece stack, the optical attenuator having a layer of birefringent material having multiple domains, each domain having a major optical axis oriented in a corresponding direction different from the directions of the other domains, each domain of the optical attenuator reducing the transmission of visible light incident on the optical attenuator over a corresponding range of different angles of incidence.

[0009] Embodiments of the wearable display system may include one or more of the following features: For example, for an aperture in the eyepiece stack corresponding to the eyebox of the wearable display, the white point of an image viewed through a display on the user side with a D65 illuminant on the world side varies by 0.01 Δu'v' or less in the CIELUV color space over an angle of incidence of 40° or less across the aperture of the display that defines the eyebox. The aperture has 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 has a diameter of 50 mm or less.

[0010] The birefringent material can be a liquid crystal material, and the angle-selective film can further include a pair of matching layers on opposite sides of the liquid crystal material, at least one of which is configured to provide different pretilt angles to the liquid crystal material in different domains of the angle-selective film. The polar pretilt angle in the domain intersecting the viewing axis of the wearable display can be zero degrees, and the polar pretilt angle in at least one domain away from the viewing axis can be greater than zero. At least two domains with non-zero polar pretilt angles can have different azimuthal pretilt angles.

[0011] The layer of birefringent material can be a spatially varying O-plate.

[0012] The layer of birefringent material may include domains arranged in a one-dimensional pattern. Alternatively, the layer of birefringent material may include domains arranged in a two-dimensional pattern.

[0013] The layer of birefringent material can be arranged between a pair of linear polarizers. The pass axes of the two linear polarizers can be crossed. The birefringent film can rotate the polarization state of light transmitted by the first linear polarizer of the pair on the world side of the polarization adjustment film. The amount of polarization state rotation varies depending on the angle of incidence of the light transmitted by the first linear polarizer of the pair. Light transmitted with a large angle of incidence can be rotated less than light transmitted with a small angle of incidence. The optical attenuator can include a pair of quarter-wave plates, which are positioned on opposite sides of the layer of birefringent material. Each quarter-wave plate can be aligned with a corresponding linear polarizer to form a circular polarizer.

[0014] In some embodiments, the optical attenuator includes a second layer of birefringent material. The optical attenuator can further include three linear polarizers, with each birefringent layer being arranged between two of the three linear polarizers. Each layer of birefringent material can be a spatially varying O-plate. The optical attenuator can include multiple quarter-wave plates, with a pair of quarter-wave plates arranged on opposite sides of each layer of birefringent material.

[0015] The optical attenuator can include two or more stages, each having a layer of birefringent material arranged between a pair of linear polarizers. Adjacent stages can share a linear polarizer.

[0016] The layer of birefringent material may be a switchable element having variable optical properties. The switchable element may comprise a liquid crystal layer between a pair of electrode layers.

[0017] Among other advantages, implementations of the present invention can reduce undesirable optical artifacts (e.g., rainbow effects) in certain wearable displays associated with stray ambient light interacting with grating structures in the display. For example, waveguide-based wearable displays (e.g., for AR / MR applications) that employ surface relief gratings can diffract stray ambient light into the display's eyebox, introducing undesirable artifacts into the user's field of view and diminishing the user's experience. Implementations of the present invention can significantly reduce such artifacts without significantly affecting the user's field of view.

[0018] Implementations can attenuate the transmittance of ambient light based on its angle of incidence and its location within the eyebox. For example, an attenuator that selectively attenuates light for angles of incidence greater than the user's field of view can reduce the visibility of artifacts produced by a diffractive eyepiece display without sacrificing transmittance of the user's view of the world.

[0019] 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. The present invention provides, for example, the following. (Item 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 on the user side views a displayed image delivered by the wearable display system through the eyepiece stack, which increases the user's field of view of the user's environment; an optical attenuator arranged on the world side of the eyepiece stack, the optical attenuator comprising a layer of birefringent material having a plurality of domains, each domain having a major optical axis oriented in a corresponding direction different from the directions of the other domains; Equipped with A wearable display system, wherein each domain of the optical attenuator reduces the transmission of visible light incident on the optical attenuator over a corresponding different range of angles of incidence. (Item 2) Item 1. A wearable display as described in item 1, wherein, for an aperture of the eyepiece stack corresponding to the eyebox of the wearable display, the white point of an image viewed through the display on the user side with a D65 illuminant on the world side varies by 0.01 Δu'v' or less in the CIELUV color space over an angle of incidence of 40° or less across the display aperture that defines the eyebox. (Item 3) 3. The wearable display of claim 1, wherein the opening has a diameter of 20 mm or more. (Item 4) 2. The wearable display of claim 1, wherein the opening has a diameter of 50 mm or less. (Item 5) A wearable display described in any one of the preceding items, wherein the birefringent material is a liquid crystal material, and the optical attenuator further comprises a pair of matching layers on opposite sides of the liquid crystal material, at least one of the matching layers configured to provide different pretilt angles to the liquid crystal material in different domains of the optical attenuator. (Item 6) Item 6. The wearable display of item 5, wherein the polar pretilt angle in a domain that intersects the viewing axis of the wearable display is zero degrees, and the polar pretilt angle in at least one domain that is away from the viewing axis is greater than non-zero. (Item 7) 7. The wearable display of item 5 or 6, wherein at least two domains with a non-zero polar pretilt angle have different azimuthal pretilt angles. (Item 8) 10. The wearable display of claim 1, wherein the layer of birefringent material is a spatially varying O-plate. (Item 9) 10. The wearable display of claim 1, wherein the layer of birefringent material has domains arranged in a one-dimensional pattern. (Item 10) 9. The wearable display of any one of items 1-8, wherein the layer of birefringent material comprises domains arranged in a two-dimensional pattern. (Item 11) 2. The wearable display system of claim 1, wherein the layer of birefringent material is arranged between a pair of linear polarizers. (Item 12) Item 12. The wearable display system of item 11, wherein the respective pass axes of the pair of linear polarizers are crossed. (Item 13) A wearable display system described in any one of items 1-11, wherein the layer of birefringent material rotates the polarization state of light transmitted by a first linear polarizer of the pair of linear polarizers incident on the world side of the optical attenuator. (Item 14) Item 14. The wearable display system of item 13, wherein the amount of rotation of the polarization state varies depending on the angle of incidence of light transmitted by the first linear polarizer of the pair of linear polarizers. (Item 15) Item 15. The wearable display system of item 14, wherein the light transmitted with a large angle of incidence is rotated less than the light transmitted with a small angle of incidence. (Item 16) Item 12. The wearable display system of any one of items 1-11, wherein the optical attenuator comprises a pair of quarter-wave plates, the quarter-wave plates being positioned on opposite sides of the layer of birefringent material. (Item 17) Item 17. The wearable display system of item 16, wherein each quarter-wave plate is aligned with a corresponding one of the linear polarizers to form a circular polarizer. (Item 18) 10. The wearable display system of claim 1, wherein the optical attenuator comprises a second layer of birefringent material. (Item 19) Item 19. The wearable display system of item 18, wherein the optical attenuator further comprises three linear polarizers, and each birefringent layer is arranged between two of the three linear polarizers. (Item 20) Item 19. The wearable display of item 18, wherein each layer of birefringent material is a spatially varying O-plate. (Item 21) 21. The wearable display system of item 20, wherein the optical attenuator comprises a plurality of quarter-wave plates, a pair of the quarter-wave plates arranged on opposite sides of each layer of the birefringent material. (Item 22) Item 18. A wearable display system as described in any one of items 1-17, wherein the optical attenuator comprises two or more stages, each stage comprising a layer of the birefringent material arranged between a pair of linear polarizers. (Item 23) Item 23. The wearable display system of item 22, wherein adjacent stages share a linear polarizer. (Item 24) Item 10. The wearable display system of item 1, wherein the layer of birefringent material is a switchable element having variable optical properties. (Item 25) Item 25. The wearable display system of item 24, wherein the switchable element comprises a liquid crystal layer between a pair of electrode layers. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 shows an embodiment of a wearable display system.

[0021] [Figure 2A] FIG. 2A shows a conventional display system for simulating a three-dimensional image for a user.

[0022] [Figure 2B] FIG. 2B illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes.

[0023] [Figure 3] 3A-3C show the relationship between the radius of curvature and the radius of focus.

[0024] [Figure 4] FIG. 4 shows an embodiment of a waveguide stack for outputting image information to a user within an AR eyepiece.

[0025] [Figure 5] 5 and 6 show examples of output beams output by waveguides. [Figure 6] 5 and 6 show examples of output beams output by waveguides.

[0026] [Figure 7] 7A and 7B are schematic diagrams illustrating the light path through a display combiner having a surface relief grating.

[0027] [Figure 8] 8A and 8B are schematic diagrams partitioning light transmission through a display combiner with and without an optical attenuator.

[0028] [Figure 9] 9A and 9B are diagrams displaying the eyebox and associated world transmission angles.

[0029] [Figure 10-1] FIG. 10 is a series of plots showing global transmittance and artifact incidence profiles. [Figure 10-2] FIG. 10 is a series of plots showing global transmittance and artifact incidence profiles.

[0030] [Figure 11A] 11A and 11B are examples of eyepieces with a single O-plate and a spatially varying O-plate. [Figure 11B] 11A and 11B are examples of eyepieces with a single O-plate and a spatially varying O-plate.

[0031] [Figure 12A] 12A and 12B are further examples of spatially varying O-plates. [Figure 12B] 12A and 12B are further examples of spatially varying O-plates.

[0032] [Figure 13] FIG. 13 is an example of an eyepiece with multiple O-plates.

[0033] [Figure 14] 14A-14D are plots of the calculated transmittance profile of an exemplary O-plate for three wavelengths.

[0034] [Figure 15] 15A-15C are intensity plots of the calculated transmittance profile of an exemplary O-plate.

[0035] [Figure 16] 16A-16T are images of the calculated attenuation of the optical rainbow artifact.

[0036] [Figure 17] Figures 17A-17D are images of the calculated color shifts.

[0037] [Figure 18] FIG. 18 is a schematic diagram of an exemplary computer system useful in conjunction with a wearable display system.

[0038] In the drawings, like labels indicate like elements. DETAILED DESCRIPTION OF THE INVENTION

[0039] Detailed Description FIG. 1 illustrates an exemplary wearable display system 60 including a display or eyepiece 70 and various mechanical and electronic modules and systems to support the functionality of the display 70. The display 70 may be housed within a frame 80, which is wearable by a display system user 90 and configured to position the display 70 directly in front of the user's 90's eyes. The display 70 may, in some embodiments, be considered eyewear. In some embodiments, a speaker 100 is coupled to the frame 80 and positioned adjacent the user's 90's ear canal. The display system may also include one or more microphones 110 to detect sound. The microphone 110 may enable a user to provide input or commands to the system 60 (e.g., voice menu command selections, natural language questions, etc.) and / or enable audio communication with other persons (e.g., other users of similar display systems). The microphone 110 may also collect audio data (e.g., sounds from the user and / or the environment) from the user's surroundings. In some embodiments, the display system may also include an ambient sensor 120a, which may be separate from the frame 80 and attached to the body of the user 90 (e.g., on the head, torso, limbs, etc.). The ambient sensor 120a, in some embodiments, may acquire data characterizing the physiological state of the user 90.

[0040] The display 70 is operably coupled by a communication link 130, such as wired or wireless connectivity, to a local data processing module 140, which may be mounted in a variety of configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, integrated into headphones, or otherwise removably attached to the user 90 (e.g., in a backpack-style configuration or in a belt-connected configuration). Similarly, the sensor 120a may be operably coupled to the local processor and data module 140 by a communication link 120b (e.g., wired or wireless connectivity). The local processing and data module 140 may include a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. The data may include 1) data captured from sensors (e.g., which may be operatively coupled to frame 80 or otherwise attached to user 90), such as image capture devices (e.g., cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein, and / or 2) data acquired and / or processed using remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for processing or retrieval and then passing to display 70. Local processing and data module 140 may be operatively coupled to remote processing module 150 and remote data repository 160 by communication links 170, 180, such as via wired or wireless communication links, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to local processing and data module 140.In some embodiments, local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be attached to frame 80 or may be stand-alone devices that communicate with local processing and data module 140 by a wired or wireless communication path.

[0041] Remote processing module 150 may include one or more processors for analyzing and processing data such as image and audio information. In some embodiments, remote data repository 160 may be a digital data storage facility, which may be available through the Internet or other networking configuration in a "cloud" resource configuration. In some embodiments, remote data repository 160 may include one or more remote servers that provide information (e.g., information for generating augmented reality content) to local processing and data module 140 and / or remote processing module 150. In other embodiments, all data is stored and all calculations are performed in the local processing and data module, allowing for fully autonomous use from the remote module.

[0042] The perception of an image as "three-dimensional" or "3-D" can be achieved by providing a slightly different presentation of the image to each eye of a user. FIG. 2A illustrates a conventional display system for simulating three-dimensional image data for a user. Two distinct images 190, 200, one for each eye 210, 220, are output to the user. The images 190, 200 are spaced from the eyes 210, 220 by a distance 230 along the optical or z-axis 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 a 3-D display system relies on the human visual system to combine the images 190, 200 and provide the perception of depth and / or scale of the combined image.

[0043] However, the human visual system is complex, making it difficult to provide a realistic perception of depth. For example, many users of conventional "3-D" display systems find such systems uncomfortable or may not perceive any sense of depth at all. Objects can be perceived as "three-dimensional" due to a combination of vergence and accommodation. Vergence movement of the two eyes relative to one another (e.g., pupil rotation so that the pupils move toward or away from one another, converging the eyes' individual lines of sight and fixating on an object) is closely linked to the focusing (or "accommodation") of the eye's lens. Under normal conditions, a change in the focus of the eye's lens or accommodation of the eye to change focus from one object to another at a different distance will automatically produce a coordinated change in vergence at the same distance, a relationship known as the "accommodation-vergence reflex" and pupil dilation or constriction. Similarly, under normal conditions, changes in vergence-divergence will induce matching changes in accommodation in lens shape and pupil size. As described herein, many stereoscopic or "3-D" display systems display a scene using slightly different presentations (and therefore slightly different images) to each eye so that a three-dimensional perspective is perceived by the human visual system. However, such systems can be uncomfortable for many users because they simply provide image information in a single accommodated state and work against the "accommodation-vergence-divergence reflex." Display systems that provide a better match between accommodation and vergence-divergence may produce a more realistic and comfortable simulation of three-dimensional image data.

[0044] FIG. 2B illustrates aspects of an approach for simulating three-dimensional image data using multiple depth planes. Referring to FIG. 2B, the eyes 210, 220 assume different accommodation states and focus objects at various distances along the z-axis. Consequently, a particular accommodation state may be said to be associated with a particular one of the illustrated depth planes 240, having an associated focal length such that an object or portion of an object at that depth plane is in focus when the eye is in an accommodated state relative to that depth plane. In some embodiments, three-dimensional image data may be simulated by providing different representations of images for each eye 210, 220, and by providing different representations of images corresponding to multiple depth planes. While the individual fields of view of the eyes 210, 220 are shown as separate for clarity of illustration, they may overlap, for example, as the distance along the z-axis increases. Additionally, for ease of illustration, the depth plane is shown as being flat, but it should be understood that the contours of the depth plane may be curved in physical space such that all features within the depth plane are in focus with the eye in a particular accommodated state.

[0045] The distance between an object and the eye 210 or 220 can also change the amount of divergence of light from the object as viewed by that eye. Figures 3A-3C illustrate the relationship between distance and divergence of light rays. The distance between an object and the eye 210 is represented by decreasing distances R1, R2, and R3. As shown in Figures 3A-3C, 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 (an object or part of an object) can be said to have a spherical wavefront curvature that is a function of the distance the point is from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. As a result, the divergence of light rays at different depth planes also differs, and the divergence increases as the distance between the depth plane and the user's eye 210 decreases. While only a single eye 210 is illustrated in Figures 3A-3C and other figures herein for clarity of illustration, it should be understood that the discussion regarding eye 210 may apply to both eyes 210 and 220 of a user.

[0046] A highly realistic simulation of perceived depth can be achieved by providing the eyes with different representations of an image corresponding to each of a limited number of depth planes. The different representations may be focused separately by the user's eyes, thereby serving to provide depth cues to the user based on the amount of ocular accommodation required to focus on different image features for a scene located on the different depth planes and / or based on the observation of different image features on different depth planes that are out of focus.

[0047] FIG. 4 illustrates an example of a waveguide stack for outputting image information to a user within an AR eyepiece. Display system 250 includes a stack of waveguides or stacked waveguide assembly 260 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. In some embodiments, display system 250 is system 60 of FIG. 1 , and FIG. 4 diagrammatically illustrates some portions of system 60 in greater detail. For example, waveguide assembly 260 may be part of display 70 of FIG. 1 . It should be understood that display system 250 may, in some embodiments, be considered a light field display.

[0048] The waveguide assembly 260 may also include multiple features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or multiple lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and configured to output image information corresponding to that depth plane. The image injection devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, each configured to distribute incident light across each respective waveguide for output toward the eye 210, as described herein. Light exits an output surface 410, 420, 430, 440, 450 of each respective image injection device 360, 370, 380, 390, 400 and is injected into a corresponding input surface 460, 470, 480, 490, 500 of the respective waveguide 270, 280, 290, 300, 310. In some embodiments, each input surface 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or a portion of a major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 510 or the user's eye 210). In some embodiments, a beam of light (e.g., a collimated beam) may be launched into each waveguide, replicated by refraction within the waveguide, such as by sampling into beamlets, and then directed toward the eye 210 with an amount of refractive power corresponding to the depth plane associated with that particular waveguide. In some embodiments, a single one of the image launch devices 360, 370, 380, 390, 400 may be associated with and launch light into multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0049] In some embodiments, each of the image input devices 360, 370, 380, 390, 400 is a discrete display that generates image information for input into a corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output of a single multiplexed display that may transmit image information via one or more optical conduits (such as fiber optic cables) to each of the image input devices 360, 370, 380, 390, 400. It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors.

[0050] In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light module 530, which may include a light source or light emitter, such as a light emitting diode (LED). Light from the light module 530 may be directed and modulated by a light modulator 540 (e.g., a spatial light modulator) via a beam splitter (BS) 550. The light modulator 540 may 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, including liquid crystal on silicon (LCOS) displays.

[0051] In some embodiments, light projector system 520 or one or more components thereof may be attached to frame 80 (FIG. 1). For example, light projector system 520 may be part of an temple portion (e.g., earpiece 82) of frame 80 or may be located on an edge of display 70. In some embodiments, light module 530 may be separate from BS 550 and / or light modulator 540.

[0052] In some embodiments, the display system 250 may be a scanning fiber display comprising one or more scanning fibers for projecting light in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately into the user's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. One or more optical fibers may transmit light from optical module 530 to one or more of waveguides 270, 280, 290, 300, and 310. Additionally, one or more intervening optical structures may be provided between the scanning fiber or fibers and one or more of waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into one or more of waveguides 270, 280, 290, 300, 310.

[0053] Controller 560 controls the operation of stacked waveguide assembly 260, including the operation of image input 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 contains programming (e.g., instructions in a non-transitory medium) that coordinates the timing and provision of image information to waveguides 270, 280, 290, 300, 310. In some embodiments, controller 560 may be a single integrated device or a distributed system connected by a wired or wireless communication channel. Controller 560, in some embodiments, may be part of processing module 140 or 150 (FIG. 1).

[0054] Waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Waveguides 270, 280, 290, 300, 310 may each be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between the major top and bottom surfaces. In the illustrated configuration, waveguides 270, 280, 290, 300, 310 may each include outcoupling optical elements 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting light propagating within each individual waveguide out of the waveguide and outputting image information to eye 210. The extracted light may also be referred to as outcoupled light, and the optical element that outcouples light may also be referred to as a light extraction optical element. The extracted beam of light may be output by the waveguide at a location where light propagating within the waveguide strikes the light extraction optical element. The outcoupling optical elements 570, 580, 590, 600, 610 may be diffractive optical features, including, for example, diffraction gratings, as discussed further herein. While the outcoupling optical elements 570, 580, 590, 600, 610 are illustrated disposed on the bottom major surfaces of the waveguides 270, 280, 290, 300, 310, in some embodiments, they may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 270, 280, 290, 300, 310, as discussed further herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be formed within a layer of material that is attached to a transparent substrate and forms the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material, and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within that piece of material.

[0055] Each waveguide 270, 280, 290, 300, 310 may output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may deliver a collimated beam of light to the eye 210. The collimated beam of light may represent an optical infinity focal plane. The next upper waveguide 280 may output a collimated beam of light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. The first lens 350 may add a slight convex wavefront curvature to the collimated beam so that the eye / brain interprets the light emerging from that waveguide 280 as emerging from a first focal plane closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive power of the first lens 350 and the second lens 340 may add another incremental amount of wavefront curvature such that the eye / brain interprets the light emerging from the third waveguide 290 as originating from a second focal plane that is closer inward from optical infinity than was the light from the second waveguide 280.

[0056] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for a collective focal power representing the focal plane closest to the person. To compensate for the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensatory lens layer 620 may be placed on top of the stack to compensate for the collective refractive power of the lower lens stacks 320, 330, 340, 350. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the waveguide outcoupling optical elements and the focusing sides of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, one or both may be dynamic using electro-active features.

[0057] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may output images set at the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may output images set at the same depth planes, with one set per depth plane. This may provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0058] The outcoupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light from its respective waveguide and output the light with an appropriate amount of divergence or collimation for the particular depth plane associated with that waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling optical elements 570, 580, 590, 600, 610, which output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light-extracting optical elements 570, 580, 590, 600, 610 may be solid or surface features, which may be configured to output light at specific angles. For example, the light-extracting optical elements 570, 580, 590, 600, 610 may be solid holograms, surface holograms, and / or diffraction gratings. In some embodiments, the features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (eg, cladding layers and / or structures to form an air gap).

[0059] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features with sufficiently low diffraction efficiency so that only a portion of the optical power of the light in the beam is redirected toward the eye 210 with each interaction, while the remainder continues traveling through the waveguide via TIR. Thus, the exit pupil of the optical module 530 is replicated across the waveguide, creating multiple output beams carrying image information from the light source 530 and effectively expanding the number of locations where the eye 210 can see the replicated light source exit pupil. These diffractive features may also have variable diffraction efficiency across their geometry, improving the uniformity of the light output by the waveguide.

[0060] In some embodiments, one or more diffractive features may 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 may include a layer of polymer-dispersed liquid crystal in which microdroplets form a diffractive pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0061] In some embodiments, a camera assembly 630 (e.g., a digital camera, including a visible light and IR light camera) is provided to capture images of the eye 210, a portion of the eye 210, or at least a portion of the tissue surrounding the eye 210, and may, for example, detect user input, extract biometric information from the eye, estimate and track the eye's gaze direction, monitor the user's physiological condition, etc. In some embodiments, the camera assembly 630 may include an image capture device and a light source for projecting light (e.g., IR or near-IR light) onto the eye, which may 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 IR or near-IR. In some embodiments, the camera assembly 630 may be mounted on the frame 80 ( FIG. 1 ) and may be in electrical communication with a processing module 140 or 150, which may process image information from the camera assembly 630 and make various determinations, for example, regarding the user's physiological condition, the wearer's gaze direction, iris identification, etc. In some embodiments, one camera assembly 630 may be utilized per eye to monitor each eye separately.

[0062] FIG. 5 illustrates an example of an output beam output by a waveguide. While one waveguide is shown (using a perspective view), other waveguides in the waveguide assembly 260 (FIG. 4) can function similarly. Light 640 is launched into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 via TIR. Through interaction with diffractive features, the light exits the waveguide as output beam 650. Output beam 650 replicates the exit pupil from a projector device that projects an image into the waveguide. Any one of the output beams 650 contains a subportion of the total energy of the input light 640. Furthermore, in a perfectly efficient system, the sum of the energies in all output beams 650 would be equal to the energy of the input light 640. Although the exit beam 650 is shown in FIG. 6 as being approximately parallel, as discussed herein, a certain amount of optical power may be imparted depending on the depth plane associated with the waveguide 270. A parallel exit beam may refer to a waveguide with outcoupling optics that outcouples light and forms an image that appears to be set on a depth plane at a long distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of outcoupling optics may output a more divergent exit beam pattern, as shown in FIG. 6, which would require the eye 210 to accommodate to a closer distance to focus on the retina and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0063] Additional information regarding wearable display systems (including, for example, optical elements used within wearable display systems) can be found in U.S. Patent Publication No. US2019 / 0187474A1, filed December 14, 2018, and entitled "EYE PIECES FOR AUGMENTED REALITY DISPLAY SYSTEM," the contents of which are incorporated by reference in their entirety.

[0064] As mentioned above, the wearable display system 60 includes one or more optical elements having one or more grating structures that improve the optical performance of the wearable display system. For example, with reference to Figures 7A and 7B, a diffractive relief structure, a grating 710, is used in conjunction with an eyepiece display combiner 700 (e.g., a stacked waveguide assembly as described above) as an exit pupil expander (EPE) to increase the size of the exit pupil of the wearable display system. As illustrated in Figure 7A, the combiner 700 includes a waveguide 720 (e.g., a glass or polymer substrate) that guides edge-coupled light along its length via total internal reflection (TIR) ​​while the grating 710 diffracts incident guided light such that at least a portion of the light is extracted from the waveguide 720 toward a user of the display system.

[0065] With specific reference to FIG. 7B , ambient light from the user's environment also enters the display combiner 700 from the “world” side. This light interacts with the grating 710, and at least a portion of this light may be diffracted into the user's field of view. When viewed by a user through the EPE, the light diffracted from the world may appear as undesirable image artifacts. The angle of incidence that produces the artifacts in the user's field of view generally depends on the design of the display combiner. For diffractive waveguide-based display combiners, large angles of incidence often result in stray light paths closest to the center of the user's world view.

[0066] This effect is further illustrated in Figure 8A, which shows a display combiner 800. Ambient light is incident at an angle θ inc , incident on the front surface of display combiner 800. At least a portion of the incident light is transmitted through the grating and combiner as shown. However, display combiner 800 supports a grating (not shown) that diffracts at least a portion of the incident light toward the user. This light, labeled stray light, is diffracted at an angle θ stray It diffracts at

[0067] 8B, an optical attenuator, e.g., film 810, can be applied to (e.g., laminated onto) display combiner 800 to reduce stray light artifacts associated with ambient light. Generally, the transmittance of light through film 810 depends on the angle of incidence of the light on the film. As shown, film 810 is designed to be transparent to the light emitted from a display combiner 800 at a relatively high angle of incidence θ (e.g., 30° or greater, 35° or greater, 40° or greater, 45° or greater, such as a user might experience from overhead lighting in an indoor environment). inc , but at a lower incidence angle θ a (e.g., "world light" as seen by the wearer within the device's core field of view). Film 810 can perform this function over a wide wavelength range, for example, over the operating wavelength range of the display system, such as 420 nm to 680 nm.

[0068] The transmittance efficiency for incident light generally varies as a function of the angle of incidence from relatively high (e.g., 40% or more, 45% or more) to relatively low (e.g., less than 1%, less than 0.5%). The transmittance efficiency refers to the relative intensity of light transmitted at a particular wavelength. In some embodiments, unpolarized light with a wavelength in the range of 420 nm to 680 nm incident on the optical attenuator with an angle of incidence between 35° and 65° has a transmittance efficiency of less than 0.5%. In certain embodiments, unpolarized light with a wavelength in the range of 420 nm to 680 nm incident on the optical attenuator with an angle of incidence between −32° and +32° has a transmittance efficiency of greater than 45%.

[0069] The optical attenuator may also have a relatively small effect on the color of the image viewed through the film. For example, for a D65 source, the optical attenuator may shift the (0.33, 0.33) CIE 1931 white point by less than (+ / -0.02, + / -0.02) (e.g., (+ / -0.01, + / -0.01) or less) for unpolarized light with angles of incidence from -32° to +32° across the display aperture.

[0070] The transmittance of an optical attenuator can also be characterized by attenuation, which can be high at relatively high angles of incidence (e.g., 10 dB or more, 15 dB or more, 20 dB or more, 25 dB or more, 30 dB or more). 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).

[0071] Generally, film 810 can be relatively thin. For example, film 810 can have a total thickness in the range of 500 microns to 2,000 microns. Thus, the benefits of using an optical attenuator can be achieved without adding significant bulk to the wearable display system.

[0072] In some embodiments, film 810 is a film stack that includes a polarization-modulating film (e.g., composed of one or more birefringent layers) arranged between a pair of polarizer films (e.g., linear polarizers). The polarizer and polarization-modulating films significantly reduce the transmittance of visible light incident on film 810 at large angles of incidence without significantly reducing the transmittance of light incident on the optical attenuator at small angles of incidence.

[0073] In general, the configuration of the two polarizers and polarization adjusting films can be varied to provide a desired level of transmittance variation over the angular incidence range of interest (e.g., −75° to +75°). In some embodiments, the polarizers can be linear polarizers and the pass axes of the two linear polarizers can be crossed (e.g., at 90°).

[0074] Generally, a polarization-modulating film includes one or more birefringent layers designed to rotate the polarization state of light transmitted by the first of a pair of linear polarizers incident from the world side. The birefringent layers can include A-plates (e.g., quarter-wave plates (QW)), in which the extraordinary axis of the birefringent material is parallel to the plane of the layer, and / or C-plates, in which the extraordinary axis of the birefringent material is perpendicular to the plane of the layer; exemplary arrangements are shown below. More generally, the birefringent layers can include uniaxial (e.g., as an A-plate or C-plate) or biaxial birefringent materials.

[0075] Typically, the amount by which a polarization-modulating layer rotates the polarization state varies depending on the configuration of the polarization-modulating layer and on the angle of incidence of light transmitted by the first of a pair of linear polarizers. In some embodiments, light transmitted with a large angle of incidence (e.g., 35° or greater) is rotated less than light transmitted with a small angle of incidence (e.g., less than 35°). For example, when a polarizer is crossed with a linear polarizer, the greater the amount of rotation up to 90°, the greater the transmittance efficiency of the film. In such cases, a greater rotation is desired for on-axis light compared to light at larger angles of incidence. Conversely, in some embodiments, the polarizer axes are parallel and the polarization-modulating film rotates on-axis light less than light at larger angles of incidence.

[0076] Generally, the optical attenuator is appropriately 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 by 50 mm.

[0077] In general, the ambient light diffracted by a uniform grating into a user's eyebox will depend on the location within the display's clear aperture upon which the light is incident. This effect is illustrated in FIGS. 9A and 9B, which depict the plane of incidence of a clear eyepiece and an eyepiece containing grating elements, respectively. Eyebox 920 refers to the volume of space within which a virtually visible image is formed by the display. The dimensions of the eyebox generally depend on pupil size and pupil distance 940. In FIG. 9A, the vertical dimension of the eyebox relative to the user's eye 910 is shown as 920. Generally, this dimension can be in the range of about 5 mm to about 25 mm. Pupil distance 940 refers to the offset distance of eye 910 from eyepiece 930 and can generally be in the range of 10 mm to 40 mm from the vertical center point 950. As shown, with respect to the normal plane of incidence in Figure 9A, the angle of incidence of light transmitted by eyepiece 930 into eyebox 920 depends on where the light is incident on the eyepiece. In particular, this is illustrated for three different points 950, 951, and 952. The range of incidence angles over which light is transmitted at point 950 is indicated by α. This range varies from point to point.

[0078] 9B, the gratings at each of points 950, 951, and 952 also diffract incident ambient light into eyebox 920. In each case, the incident angle range over which ambient light is diffracted into the eyebox will be different. For example, at point 950, eyepiece 930 diffracts incident light within a first angle range β and a second angle range γ into eyebox 920. Additional points 951 and 952 will diffract incident light within their respective angle ranges into the eyebox.

[0079] The location dependence of diffracted incident light is further illustrated by the plots in Figure 10, which shows a series of simulated plots, each plot being a representation of the transmission and diffraction properties of the eyepiece at a corresponding vertical location. In particular, the angular range of incidence of transmitted light incident on the world side is provided in black, and the angular range of incidence of diffracted light that produces rainbow artifacts at specific wavelengths is provided in red (625 nm), green (525 nm), and blue (460 nm), respectively.

[0080] The plots on the left were calculated based on the plane of incidence shown on the right side of FIG. 10 , which includes a clear aperture and an eyebox 1002. Each plot was calculated (e.g., simulated) based on an eyebox 1002 vertical size of 18 mm, a pupil distance 1004 of 20 mm, and a clear aperture 1006 vertical size of 36.3 mm. The clear aperture 1006 was simulated to include grating elements with a grating period of 391 nm, with the grating lines extending horizontally (e.g., perpendicular to the plane of the page). The title of each plot, located above each plot, indicates the vertical location at which the transmittance and artifact window were calculated, given as the vertical height 1010 from the center point 1020, expressed in mm; positive values ​​are above the center point 1020, and negative values ​​are below. The vertical axis for each graph is a normalized value (e.g., 0 to 1) representing high transmittance (black) or a high incidence of diffraction artifacts (red, blue, green). The horizontal axis for each graph is the ratio of ambient light (θ i ) represents the angle of incidence, and θ i Positive values ​​of θ are measured clockwise from the normal ray 1030. For example, the shaded area 1040 is the global transmittance window calculated at a point 16.6 mm above the center point 1020, which corresponds to a range of approximately −16° to −55°, as shown in the top graph.

[0081] Therefore, in such situations, it may be desirable to use an optical attenuator that attenuates different angular ranges of incident light from the world side depending on the location on the eyepiece where the light enters. This can improve the reduction of diffracted light artifacts across the entire eyepiece without substantially reducing the transmittance of incident world light that enters the eyebox.

[0082] Turning now to a specific example of such an optical attenuator, and referring to FIG. 11A, an eyepiece 1100 of a wearable display system includes a display combiner 800 and a film stack 1110, which operates 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-wave plates (QW) 1130a and 1130b on either side of a multidomain birefringent film 1140.

[0083] The fast axes of waveplates 1130a and 1130b are oriented at approximately 45° to the pass axes of linear polarizers 1120a and 1120b, respectively, so that the combination of linear polarizer 1120b and QW 1130b converts unpolarized light incident from the world side into approximately circularly polarized light (i.e., the combination behaves as a circular polarizer). The combination of QW 1130a and linear polarizer 1120a behaves similarly. Note that the handedness of each circular polarizer is identical.

[0084] The multidomain birefringent film 1140 includes different areas in which the major optic axes of the birefringent materials comprising the film are oriented differently so 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, consisting 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 oriented at θ c1 ≠θ c2 ≠θ c3θ is the azimuthal angle difference measured from the normal to the plane of the film. Orientations in which the director axes of one or more spatial regions vary by a radial angle difference φ are also possible (e.g., θ c , φ c ). More generally, birefringent films with their optic axes oriented non-perpendicular and non-parallel to the plane of the film are commonly referred to as O-plates, and O-plates with multiple domains, such as film 1141, can be considered spatially varying O-plates.

[0085] The alignment of the nematic director within the film can be achieved through several techniques. For example, alignment is generally influenced by the pretilt 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 pretilt can be adjusted to a range of azimuthal and radial pretilt angle directions (e.g., θ c , φ c ) can be set in various ways (e.g., mechanical buffing, exposure to linearly polarized light). c may range from -90° to about 90° from the normal axis of the O-plate, and the radial orientation φ c The range of the pretilt may range from -180° to 180° from the x-axis. These techniques may be applied to distinct spatial domains on the O-plate, such that each domain has a different pretilt.

[0086] In general, the spatial domains may take any shape or size or any number. The director axes of the spatial domains may be aligned radially, concentrically, directionally, or any combination thereof between the spatial domains. Figures 12A and 12B show examples of such embodiments. Figure 12A shows a diagram of a spatial domain with its axial orientation (θ c , φ c1 shows an example spatially varying O-plate 1210 with nine distinct spatial domains 1220a-1220i with unique director axes defined by θ ) values. Eight director axes 1220a-1220h are arranged to project radially around a central axis normal to the plane of the spatially varying O-plate 1210, with one director axis 1220i aligned normal to the plane of the spatially varying O-plate 1210, equivalent to a C-plate. The eight director axes of spatial domains 1220a-1220h are aligned at a common azimuthal orientation θ of 15°. c and share a radial orientation φ c are distributed on both sides from 0° to 180° in increments of 45° from the x-direction (e.g., 0°, ±45°, ±90°, ±135°, 180°).

[0087] 12B shows a further example of a spatially varying O-plate 1211 with three distinct spatial domains 1221a-1221c separated by dashed lines. The spatial domains 1221a-1221c are horizontally aligned with no radial distribution. The director axes of spatial domains 1221a and 1221c are aligned at a common azimuthal tilt θ of 15°. c While sharing the radial angle φ c are aligned in polar opposite directions parallel to the plane of spatially varying O-plate 1211 at -90° and 90°. The director axes of central spatial region 1221b are aligned normal to the plane of spatially varying O-plate 1210.

[0088] While Figures 12A and 12B are specific examples of spatial domain arrangements that can be achieved in the spatially varying O-plate 1140 used in the optical attenuator film stack 1110, they are not intended to limit further exemplary embodiments. More generally, other one-dimensional and two-dimensional domain arrangements can also be employed. Generally, strong ambient light sources arise more frequently from their reflections from above and below, and the simplified design of Figure 12B may be a preferred embodiment for attenuation of overhead artifacts. However, the radial design of Figure 12A may be used to attenuate artifacts produced by light sources from any cone angle within the user's view.

[0089] While FIG. 11A shows an example of an optical attenuator including a spatially varying O-plate 1140 between two linear polarizers 1120, implementations with additional layers are also possible. For example, FIG. 13 shows an eyepiece 1300 including 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 1330b on either side of 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 on either side of a spatially varying O-plate 1340b. In effect, stack 1310 performs like two stacks 1110 stacked together.

[0090] Stack 1110 may be considered a single stage arrangement, and stack 1310 may be considered a two stage. In general, additional stages may be added.

[0091] Turning now to the performance of single-stage and two-stage optical attenuators, in general, the transmittance profile achieved with the two-stage film stack 1310 can achieve more significant attenuation of artifacts produced from high-angle ambient light. Figures 14A-14D are plots of calculated transmittance profiles for three different wavelengths (e.g., 630 nm, 525 nm, 460 nm) of ambient light incident on a clear aperture. The plots show the transmittance profile for three different wavelengths (e.g., 630 nm, 525 nm, 460 nm) of ambient light incident on a clear aperture. i 14A and 14B show calculated transmittance profiles for a single-stage film stack, such as stack 1110, in which the birefringent film has a retardation (dΔn) of 550 nm. c , calculated using a single-stage film stack (i.e., a C-plate) with an incidence angle of 0° θ i The three calculated transmittance profiles for light with individual wavelengths of 630 nm (red), 525 nm (green), and 460 nm (blue) show bilateral symmetry around the peak transmittance at θ = 1.0°. The 460 nm transmittance profile exhibits a bilateral symmetry around the peak transmittance at θ = 1.0°. i The transmittance profile then decreases monotonically at ±90° angles of incidence θ i for incident angles θ of ±60° to ±80° before exponentially decreasing to i The ranges exhibit inversion (eg, 525 nm, 460 nm) or shoulder peaks (630 nm).

[0092] In contrast, Figure 14B shows the calculated transmittance profile for the single-stage film stack 1110 with an azimuthal orientation θ of 15°. The three calculated transmittance profiles for light with individual wavelengths of 630 nm (red), 525 nm (green), and 460 nm (blue) are no longer symmetrical, and the peak transmittance increases with the incidence angle θ. i Shifted to a ±20° window centered around about 20°. i The transmittance profile is given by the angle of incidence θ of 90°. iHowever, the incident angle θ i With the decrease of , the transmittance profile changes with the incidence angle θ of about -40° to -50°. i The window drops depending on the wavelength (for example, the maximum relative efficiency decreases at 460 nm). i Then, the transmittance profile is about 10 2 (630nm)~10 3 The transmittance profile increases by a logarithmic factor of (460 nm) to a secondary peak. This secondary peak approaches the value of the primary peak as calculated for the 460 nm wavelength transmittance profile. After about -70°, the transmittance profile decreases at an incidence angle θ of -90°. i will drop to zero.

[0093] 14A and 14B show the transmittance profiles for incident angles θ that increase from about ±60° to ±80° and from about −40° to −70°, respectively. i These ranges of wavelength transmittance can lead to undesirable color shifts in the user's field of view, with significant variations between wavelength transmittance profiles. For example, an incident angle θ of approximately −40° in FIG. 14B i In this example, the transmittance profile for light at 460 nm (blue) shows a >100-fold reduction in transmittance compared to light at 630 nm. This can appear to the user as a significant red phase shift, another undesirable optical artifact. To achieve strong attenuation of light over all angles outside the range required for global transmittance, it can be beneficial to use a two-stage film stack.

[0094] 14C and 14D show calculated transmittance profiles for an eyepiece using a two-stage film stack such as 1310. FIG. 14C shows the calculated transmittance profile for an eyepiece in which both stages are aligned at a 0° director axis azimuthal orientation θ c Δn, dΔn) of 480 nm, with a 0° angle of incidence θ similar to the single-stage film stack 1110 of FIG. 14A. iHowever, the transmittance is symmetrical around the peak transmittance at ±60° to ±80° incident angles θ i In the range from about 10 (630 nm) to 10 2 (460 nm). In addition, the peak transmittance window is reduced by an additional logarithmic factor of about ±20° of incident angle θ i The range remains the same between the single stage film stack 1110 and the two stage film stack 1310.

[0095] FIG. 14D shows a retardation of d1Δn 380 nm to d2Δn 270 nm and a director axis azimuthal orientation θ of 15°. c The peak transmittance window is calculated using a two-stage film stack with birefringent films, with a 20° incident angle θ as in FIG. i Centered on the top, incident angle θ of approximately ±20° i However, as in FIG. 15C, the incident angle θ is approximately −40° to −70°. i The secondary peak seen at 10 2 is significantly attenuated by a logarithmic factor greater than

[0096] The calculated transmittance profiles in Figures 14C and 14D demonstrate that the use of a two-stage film stack, rather than a single-stage film stack, can advantageously attenuate secondary peaks generated outside the desired angular world transmission range, particularly when the director axis is distorted. In addition, the wide variation in color shift at high incidence angles that leads to birefringence rainbow artifacts is also significantly attenuated. Figures 14A and 14C may be preferred embodiments of director axis orientation for use in centrally located, spatially varying O-plate regions such as 1220i, where the viewing angle through the clear aperture is reduced to approximately ±20°, which corresponds to the particular world transmittance window of Figures 14A and 14C. Figures 14C and 14D illustrate the use of a two-stage film stack, rather than a single-stage film stack, for incident angles θ where the world transmittance window in those regions is above 0° and potentially less than 50°. i1220a-1220h, it can be an embodiment of the director axis orientation within the spatially varying O-plate regions.

[0097] 15A-15C are examples of transmittance profiles that can be achieved through an O-plate with director axes oriented azimuthally and radially. The graphs are normalized heat map representations of the calculated total transmittance through a clear aperture using an O-plate across an arbitrary y-axis range and an equal arbitrary x-axis range. Each graph shows the transmittance profile for the azimuthal and radial orientations of the director axes of the O-plate (e.g., θ c , φ c ) are calculated using different combinations of θ and φ. On the left of FIG. 15C is a reference coordinate system, including the orientation of angles θ and φ. In FIG. 15A, the azimuthal orientation θ c is normal to the O-plate and has a radial orientation φ c is 0. The calculated transmittance profile shows a radially symmetric transmittance pattern with a peak 1410 at wavenumber ky = kx = 0, where the transmittance is maximum. The transmittance decreases as a function of radial distance until it reaches 0 at a radial distance of 1.

[0098] FIG. 15B shows the calculated transmittance profile of the O-plate, whose director axis is aligned at an azimuthal orientation θ of 15°. c and a radial orientation φ of 45° counterclockwise around the x-axis c The calculated transmittance profile is no longer radially symmetric, but is bilaterally symmetric about a line that bisects the calculated transmittance profile from (-1,-1) to (1,1) in the (x,y) plane. The peak of the calculated transmittance profile 1411 is around (approximately 0.3,0.3), allowing for favorable transmission of light in the first quadrant of the graph.

[0099] FIG. 15C shows the calculated transmittance profile of the O-plate, whose director axis is aligned at an azimuthal orientation θ of 15°. c and a radial orientation φ of −45° clockwise from the x-axis cThe calculated transmittance profile is symmetrical about a line that bisects the calculated transmittance profile from (-1,1) to (1,-1) in the (x,y) plane. The peak of the calculated transmittance profile 1412 is around (approximately 0.3,-0.3), allowing for favorable transmission of light in the fourth quadrant of the graph.

[0100] Generally, while the foregoing examples show calculations for specific O-plate arrangements, they are merely illustrative. More generally, the film retardation, the number and shape of domains, and the director alignment within each domain can be selected according to the eyebox size and grating structure to provide the desired attenuation of unwanted diffracted ambient light.

[0101] 16A-T further illustrate the amount of attenuation possible using single-stage, two-stage, and spatially-varying two-stage O-plate optical attenuators. These images illustrate undesirable optical artifacts (e.g., optical rainbows) when ambient light sources are incident on the eyepiece at high angles of incidence. As white ambient light from a nearby source interacts with the grating 710 structure in the display combiner 700 from high angles of incidence, the light becomes diffracted, as shown in FIG. 7B. The amount of diffraction depends on the wavelength of the incident light and the grating 710 pitch or spacing. White light is composed of many wavelengths, and each wavelength of incident ambient light diffracted toward the user is diffracted to a different angle. This causes the white light to appear diffused in a rainbow pattern as seen by the user, causing undesirable optical artifacts (e.g., optical rainbows).

[0102] In Figures 16A-16T, the optical rainbow artifact is shown for a white light source with a 5700 K blackbody spectrum incident on the eyepiece from above at angles of incidence of 70° (Figures 16A-16D), 60° (Figures 16E-16H), and 50° (Figures 16I-16L), 40° (Figures 16M-16P), and 30° (Figures 16Q-16T). A grating 710 pitch of 391 nm was used to calculate the diffraction angle of the artifact. The black circles in each image correspond to ±42° viewing angles as seen by a user with a 4 mm eyebox, 20 mm pupil distance, and a 36.3 mm clear aperture height, as shown on the right of Figures 16A-T. The first column of images 1610 shows the calculated optical rainbow artifact as seen by a user with no filters present. The second column of images 1611 shows the calculated optical rainbow artifact as it would appear to a user if a single-stage film stack 1110 were used. The third column of images 1612 shows the calculated optical rainbow artifact as it would appear to a user if a two-stage film stack 1310 were used. The director axes of the O-plates used to calculate the second column 1611 and the third column 1612 have no azimuthal or radial orientation (e.g., θ c =φ c =0°). The fourth column of images 1613 shows the calculated optical rainbow artifact as seen by a user when a two-stage spatially varying O-plate film stack is used. The two-stage spatially varying O-plate used to calculate the fourth column 1613 is of the design shown in FIG. 12B.

[0103] Using the images in column 1610 as a reference, the largest and brightest optical rainbow artifacts are seen at larger angles of incidence (e.g., 60°, 70°). At larger angles of incidence (e.g., 60°, 70°), the single-stage 1611 (FIGS. 16B and 16F) and two-stage 1612 (FIGS. 16C and 16G) have a significant effect on attenuating these optical rainbow artifacts, and the use of a two-stage spatially varying O-plate 1613 (FIGS. 16D and 16H) has a greater effect on attenuation than either the single 1611 or two-stage 1612 film stacks. This is also true for all other images and angles of incidence in the remaining images shown in FIG. 16. The single-stage 1611 and two-stage 1612 film stacks have a significant effect on attenuating the apparent optical rainbow artifacts, while the two-stage 1613 film stack, using a spatially varying O-plate, has the greatest effect.

[0104] Optical attenuators using spatially varying O-plates can be further beneficial in reducing spatial color variations that can result from the use of optical attenuators. Figures 17A-17D show the color shift as perceived by a user when white light is viewed through a viewing angle of ±45° using no filter (Figure 17A), a single-stage film stack (Figure 17B), a two-stage film stack (Figure 17C), and a two-stage film stack using a spatially varying O-plate (Figure 17D). Blue circles within the field of view represent 15° increments. The film stack used to calculate the white shift in Figures 17A-17D is the same film stack used to calculate columns 1-4 in Figure 16 (1610, 1611, 1612, 1613) (e.g., no filter, no director axis orientation, spatially varying O-plate design shown in Figure 12B). In some embodiments, the white point shift may be 0.01 Δu'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 over an incidence angle of ±40° (e.g., over the entire range of incidence angles of 40° or less) in at least one direction.

[0105] While the use of single-stage and dual-stage film stacks can provide significant attenuation of the apparent optical rainbow artifact, as shown in columns 1611 and 1612 of FIG. 16, they also create a perceptible color shift within a 45° viewing angle. In FIG. 17B, at viewing angles of ±30° to ±45° (e.g., between the second blue ring and the edge of the field of view), there is a perceptible shift for red frequencies. This same effect can also be seen in FIG. 14A. At ±45° angles of incidence θ i In this case, the 630 nm transmittance profile is higher than the 480 nm transmittance profile. Longer wavelengths are associated with more red, and because the transmittance at those wavelengths is higher, the perceived color is shifted toward the red hue.

[0106] The same effect is seen in Figure 17C, but to a greater extent. i 14A, the 630 nm transmittance profile is still higher than the 480 nm transmittance profile, and both transmittance profiles are at lower values ​​at ±45° than in Figure 14A. This is the combined effect of the loss in total transmittance at ±45° viewing angles and the further reduced 480 nm transmittance profile compared to 630 nm when using the two-stage film stack 1310.

[0107] Figure 17D shows the same color shift as perceived by a user through a two-stage film stack using a spatially varying O-plate. In addition to a lower red shift at the extreme viewing angles of about ±45°, the overall transmittance is higher across the entire viewing window. This can be attributed to the three spatially varying regions in Figure 12B. The director axis of the upper region 1221a is aligned with an azimuthal orientation θ of 15°. c and a radial orientation φ of 90° (positive perpendicular). c and the director axis of the central region 1221b has an azimuthal and radial orientation normal to the plane of the O-plate, and the lower region 1221c has an azimuthal orientation θ of 15°. c and a radial orientation φ of −90° (negative perpendicular). cThese director axis orientations allow the peak global transmittance window of each region 1221a-c to overlap with the ambient light incidence angle of the viewing window. The global transmittance windows and opposing radial orientations φ from Figures 14C (±20°), 14D (20°±20°), and 14D c The (-20° ± 20°) combination allows for a total near-peak global transmittance window of approximately ±40°, as seen in Figure 17D.

[0108] In general, a variety of suitable different materials can be used for each layer in the optical attenuator. The linear polarizer can be formed, for example, from a stretched polymer material (e.g., PVA) dyed with a chromophore (e.g., iodine). Commercially available linear polarizers, such as those available from Sanritz Co. (Japan) or Nittto Denko (Japan), can be used. The QW can be made, for example, from a stretched polymer film or a liquid crystal polymer film. The O-plate can be formed, for example, from a liquid crystal material, including a polymer liquid crystal material.

[0109] In general, the film stack can include additional layers other than those described above. For example, the stack can include additional layers to provide a mechanical function rather than an optical function. Adhesive layers and / or layers for mechanical strength and / or environmental protection can be included. Such layers can 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.

[0110] For example, anti-reflection films and / or hard coat layers can be included. While the above-described examples of optical attenuators include optically passive elements, more commonly, implementations can also feature optically active elements. Such elements can change their optical properties, and thus the transmissivity 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 adjustable. For example, the O-plate can be formed as a liquid crystal cell to which an electric field can be applied to vary the LC director orientation between two or more different states, thereby changing the transmissivity properties of each domain.

[0111] Some implementations described herein can be implemented as one or more groups or modules of digital electronic circuitry, computer software, firmware, or hardware, or in a combination of one or more of them. Although different modules can be used, each module need not be distinct, and multiple modules can be implemented on the same digital electronic circuitry, computer software, firmware, or hardware, or a combination thereof.

[0112] Some implementations described herein can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a computer storage medium for execution by or to control the operation of a data processing apparatus. The computer storage medium can be or be contained within a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of these. Furthermore, a computer storage medium is not a propagating signal, although a computer storage medium can be a source or destination of computer program instructions encoded within an artificially generated propagating signal. The computer storage medium can also be or be contained within one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

[0113] The term "data processing apparatus" encompasses all types of apparatus, devices, and machines for processing data, including, by way of example, a programmable processor, a computer, a system-on-chip, or a plurality or combination of the foregoing. An apparatus may include special-purpose logic circuitry, such as an FPGA (field-programmable gate array) or an ASIC (application-specific integrated circuit). In addition to hardware, an apparatus may also include code that creates an execution environment for the computer program, such as code constituting 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 these. The apparatus and execution environment may implement a variety of different computing model infrastructures, such as web services, distributed computing, and grid computing infrastructures.

[0114] 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. A computer program may, but need not, correspond to a file in a file system. A program can be stored within a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), within a single file dedicated to the program, or within multiple cooperating files (e.g., files storing one or more modules, subprograms, or portions of code). A computer program can be deployed to run on one computer or on multiple computers that are located at one facility or distributed across multiple facilities and interconnected by a communications network.

[0115] Some of the processes and logic flows described herein may be implemented by one or more programmable processors that execute one or more computer programs and perform actions by operating on input data and generating output. The processes and logic flows may also be implemented by, and apparatus may also be implemented as, special purpose logic circuitry, such as an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

[0116] Processors suitable for executing a computer program include, by way of example, both general-purpose and special-purpose microprocessors and 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. A computer includes a processor for performing actions in accordance with the instructions and one or more memory devices for storing instructions and data. A computer may also include one or more mass storage devices, such as magnetic, magneto-optical, or optical disks, for storing data, or be operatively coupled thereto to receive data therefrom, transfer data thereto, or both. However, a computer need not have such devices. Devices suitable for storing computer program instructions and data include all forms of non-volatile memory, media, and memory devices, including, by way of example, semiconductor memory devices (e.g., EPROM, EEPROM, flash memory devices, and the like), magnetic disks (e.g., internal hard disks, removable disks, and the like), magneto-optical disks, and CD-ROM and DVD-ROM disks. The processor and memory may be supplemented by, or incorporated in, special-purpose logic circuitry.

[0117] To provide for interaction with a user, the operations can be implemented on a computer having a display device (e.g., a monitor or another type of display device) for displaying information to the user, and a keyboard and pointing device (e.g., a mouse, trackball, tablet, touch-sensitive screen, or another type of pointing device) by which the user may provide input to the computer. Other types of devices can be used to provide for interaction with a user as well; 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. Additionally, the computer can interact with a user by sending documents to and receiving documents from devices used by the user, for example, by sending a web page to a web browser on the user's client device in response to a request received from the web browser.

[0118] A computer system may include a single computing device or multiple computers operating in close proximity to each other or generally remotely and typically interacting through a communications network. Examples of communications networks include local area networks ("LANs") and wide area networks ("WANs"), networks between networks (e.g., the Internet), networks with satellite links, and peer-to-peer networks (e.g., ad hoc peer-to-peer networks). The relationship of client and server may arise by virtue of computer programs running on separate computers and having a client-server relationship to each other.

[0119] 18 shows an exemplary computer system 1800 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 may 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 in the memory 1820 or on the storage device 1830. The memory 1820 and the storage device 1830 may store information within the system 1800.

[0120] The input / output devices 1840 provide input / output operations for the system 1800. In some implementations, the input / output devices 1840 may 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 wireless modem, a 4G wireless modem, etc. In some implementations, the input / output devices may include a driver device configured to receive input data and send output data to another input / output device, e.g., a wearable display device 1860. In some implementations, mobile computing devices, mobile communication devices, and other devices may also be used.

[0121] While this specification contains many details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular implementations. Certain features described herein in the context of separate implementations can also be combined. Conversely, various features described in the context of a single implementation can also be implemented in multiple embodiments separately or in any suitable subcombination.

[0122] Several implementations have been described. However, it should be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.

Claims

1. 1. A method comprising: displaying an image to the user via an eyepiece stack of a wearable display that augments the user's field of view of the user's environment; attenuating transmission of ambient light from the user's environment through the eyepiece stack to the user while displaying the image, wherein the attenuating includes: polarizing the ambient light incident on the eyepiece stack, thereby providing polarized ambient light; using a layer of liquid crystal material having a plurality of domains to rotate the polarization state of the polarized ambient light by an amount related to the domain into which the polarized ambient light is incident and the angle of incidence of the polarized ambient light, the liquid crystal material in each domain having a major optic axis oriented in a corresponding direction different from that of other domains of the liquid crystal material, the rotating providing polarization-rotated ambient light; and providing attenuated ambient light by absorbing at least a portion of the polarization-rotated ambient light, the amount of absorption varying depending on the domain into which the corresponding polarized ambient light is incident and the angle of incidence of the polarization-rotated polarized ambient light; and providing the increased view of the user's environment by combining the attenuated ambient light with the light forming the displayed image; Including A method comprising:

2. The method described in claim 1, wherein rotating the polarization state of the polarized ambient light includes applying a pretilt to different domains of the layer of the liquid crystal material.

3. The method of claim 2, wherein applying the pretilt includes using a pair of alignment layers on opposing sides of the liquid crystal material.

4. The method described in claim 2, wherein the polar pretilt angle in a domain that intersects with the viewing axis of the wearable display is zero degrees, and the polar pretilt angle in at least one domain that is away from the viewing axis is greater than zero.

5. The method described in claim 4, wherein at least two domains with non-zero polar pretilt angles have different azimuthal pretilt angles.

6. 10. The method of claim 1, wherein in domains that intersect a viewing axis of the wearable display, the polarization state of the polarized ambient light is rotated by zero degrees, and in at least one domain away from the viewing axis, the polarization state of the polarized ambient light is rotated by an amount greater than zero.

7. 7. The method of claim 6, wherein rotating the polarization state of the polarized ambient light comprises rotating the polarization state by an amount in a polar direction and rotating the polarization state by an amount in an azimuthal direction.

8. 8. The method of claim 7, wherein for at least two domains in which the polarization state of the polarized ambient light is rotated by a non-zero amount, the amount by which the polarization state is rotated in the polar direction is different from the amount by which the polarization state is rotated in the azimuthal direction.

9. The method of claim 1 , wherein the plurality of domains comprises domains arranged in a one-dimensional pattern or a two-dimensional pattern.

10. The method of claim 1 , wherein polarizing the ambient light comprises linearly polarizing the ambient light along a first pass axis.

11. 11. The method of claim 10, wherein absorbing at least the portion of the polarization-rotated ambient light comprises using a linear polarizer having a pass axis crossed from the first pass axis.

12. The method of claim 10, wherein polarizing the ambient light further comprises circularly polarizing the ambient light and circularly polarizing the polarization-rotated ambient light before absorbing it.

13. The method of claim 12 , wherein the amount by which the polarization state of the ambient light is rotated varies depending on the angle of incidence of the light incident on the eyepiece lens stack.

14. 14. The method of claim 13, wherein light having a large angle of incidence is rotated by a smaller angle than light having a small angle of incidence.

15. 10. The method of claim 1, further comprising: rotating the polarization state of the polarization-rotated ambient light by an amount related to the domain into which the polarization-rotated ambient light is incident and the angle of incidence of the polarization-rotated ambient light using a second layer of birefringent material having a second plurality of domains, each having a major optical axis oriented in a corresponding direction different from that of the other domains, wherein the rotating provides twice-polarized rotated ambient light; and providing the attenuated ambient light by absorbing at least a portion of the twice-polarized rotated ambient light.

16. 16. The method of claim 15, further comprising linearly polarizing the polarization-rotated ambient light between rotating the ambient light a first time and rotating the polarization-rotated ambient light a second time.

17. 2. The method of claim 1, wherein, for an aperture of the eyepiece stack corresponding to the eyebox of the wearable display, the white point of an image viewed through the eyepiece stack on the user side with a D65 illumination source on the world side varies by 0.1 Δu'v' or less in CIELUV color space over an angle of incidence of 40° or less across the aperture of the eyepiece stack that defines the eyebox.

18. The method of claim 17, wherein the opening has a diameter in the range of 20 mm to 50 mm.

19. The method of claim 1, wherein rotating the polarization state of the polarized ambient light includes changing the principal optical axis of the liquid crystal material in at least one of the plurality of domains so that the polarized ambient light is rotated by an amount related to the angle of incidence of the polarized ambient light.

20. The method described in claim 19, wherein at least one domain of the plurality of domains includes a domain into which the polarized ambient light is incident.

Images