Tunable attenuation of light transmission artifacts in wearable displays

Abstract

Adjustable attenuation of light transmission artifacts in a wearable display is provided. A method for displaying an image using a wearable display system includes directing display light from a display toward a user through an eyepiece to project an image into the user's field of view, determining a relative location between an ambient light source and the eyepiece, and adjusting the attenuation of ambient light from the ambient light source through the eyepiece in response to the relative location between the ambient light source and the eyepiece.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit under 35 U.S.C. §119(e) of U.S. patent application Ser. No. 63 / 044,013, entitled “Tunable Attenuation of Light Transmission Artifacts in Wearable Displays,” filed June 25, 2020, which is incorporated by reference in its entirety herein.

[0002] The present disclosure relates to techniques for adjustable attenuation of light transmission artifacts in wearable displays. [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 eyepiece can be constructed using one or more thin layers of highly refractive materials. As an example, the eyepiece 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, collectively, the eyepieces can 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 in a wearable display system may also interact with ambient light, which is light from the environment the user is in. For example, diffractive structures in a wearable display system may diffract ambient light that is incident on the wearable display at high angles that would not normally enter 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 is described that includes an angularly selective film and reduces artifacts associated with ambient light incidence at high angles of incidence. For example, the angularly selective film can utilize a polarizer in combination with a polarization adjustment element, where the amount of adjustment varies depending on the angle of incidence of the light, to reduce the transmission of light at certain angles of incidence. In some embodiments, the angularly selective film can include a dynamic element in which the transmission properties can be varied in response to a stimulus, such as in response to an electric field.

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

[0008] In general, in a first aspect, the invention features a method for displaying an image using a wearable display system, the method including directing display light from a display toward a user through an eyepiece to project the image into the user's field of view, determining a relative location between an ambient light source and the eyepiece, and adjusting attenuation of ambient light from the ambient light source through the eyepiece in response to the relative location between the ambient light source and the eyepiece.

[0009]

[0013] Embodiments of a method for displaying an image using a wearable display system may include one or more of the following features. For example, determining the relative location includes determining an angle of incidence of ambient light from an ambient light source on the eyepiece, and an attenuation rate is adjusted based on the angle of incidence. The attenuation rate can be adjusted to reduce the transmittance of the ambient light at the angle of incidence compared to the attenuation rate at lower angles of incidence.

[0010] Attenuating the ambient light may include polarizing the ambient light to provide polarized light and modulating the polarization state of the polarized light as a function of the angle of incidence of the ambient light. The attenuation rate may be varied by varying the modulation rate of the polarization state of the polarized light. The modulation rate may be varied by varying the retardation rate provided by a layer of birefringent material in the path of the polarized light. The birefringent material may include liquid crystals. The retardation rate may be varied by varying an electric field applied to the liquid crystals. The liquid crystals may be blue phase liquid crystals or vertically aligned liquid crystals.

[0011] Attenuating the ambient light can further include directing the modulated polarized light through a second polarizer. The rate of attenuation can be varied using a liquid crystal element.

[0012] Determining the relative location between the ambient light source and the eyepiece can include monitoring an ambient light intensity and determining the relative location based on a change in the monitored ambient light intensity. The ambient light intensity can be monitored by obtaining an image of the surrounding environment, analyzing the obtained image, and determining a location of the ambient light source within the image.

[0013] In a second aspect, the invention features a wearable display system including an eyepiece stack having a world side and a user side facing the world side, the eyepiece stack being positioned on the user side during use, the user viewing displayed images delivered by the wearable display system through the eyepiece stack, which extends the user's field of view of the user's environment; an adjustable attenuator arranged on the world side of the eyepiece stack, the adjustable attenuator comprising an electro-optical cell arranged between a pair of linear polarizers; a camera module facing the world side; and an electronic processing module in communication with the adjustable attenuator and the camera module, the electronic processing module being programmed to determine information about a relative location of the eyepiece stack to an ambient light source based on images captured by the camera module, and to vary the attenuation rate of the adjustable attenuator based on the information about the relative location.

[0014] Embodiments of the wearable display system may include one or more of the following features: The adjustable attenuator may reduce the transmittance of visible light incident on the adjustable attenuator within a first range of angles of incidence without significantly reducing the transmittance of light incident on the adjustable attenuator at angles of incidence outside the first range.

[0015] The electro-optical cell may include a layer of liquid crystal material and the adjustable attenuator may further include a voltage source arranged to apply a variable voltage to the liquid crystal material. The liquid crystal material may be a blue phase liquid crystal material or a vertically aligned liquid crystal material. The adjustable attenuator may further include at least one layer of birefringent material in addition to the layer of liquid crystal material.

[0016] The at least one layer of birefringent material can include a pair of quarter wave plates disposed on opposite sides of the layer of liquid crystal material. Each quarter wave plate can be aligned with a corresponding one of the linear polarizers to form a circular polarizer. The at least one layer of birefringent material can further include a C-plate.

[0017] In some embodiments, the pass axes of the two linear polarizers can be crossed.

[0018] The electro-optic cell can rotate the polarization state of light transmitted by a first linear polarizer of a pair of linear polarizers on the world side of the adjustable attenuator. The amount of rotation of the polarization state can vary depending on the state of the electro-optic cell and the angle of incidence of the light transmitted by the first linear polarizer of the pair of linear polarizers. Light transmitted with a large angle of incidence can be rotated by less than light transmitted with a small angle of incidence.

[0019] The adjustable attenuator has an area greater than 50 mm x 50 mm.

[0020] The electro-optical cell may be a first electro-optical cell, and the adjustable attenuator may further include a second electro-optical cell and a third linear polarizer, the second electro-optical cell being arranged between the pair of linear polarizers and the third linear polarizer. Each of the first and second electro-optical cells may be comprised of a corresponding layer of liquid crystal material. The adjustable attenuator may further comprise one or more layers of birefringent material arranged on opposite sides of the corresponding layer of liquid crystal material.

[0021] The adjustable attenuator may include two or more stages, each stage comprising an electro-optical cell arranged between a pair of linear polarizers. Adjacent stages may share a linear polarizer.

[0022] 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) employing surface relief gratings can diffract stray ambient light into the display's eyebox, resulting in undesirable artifacts in 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.

[0023] Implementations can attenuate the transmittance of ambient light based on its angle of incidence. For example, a film 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.

[0024] 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, the eyepiece stack extending the user's field of view of the user's environment; an adjustable attenuator arranged on a world side of the eyepiece stack, the adjustable attenuator comprising an electro-optical cell arranged between a pair of linear polarizers; the world-facing camera module; an electronic processing module in communication with the adjustable attenuator and the camera module, the electronic processing module being programmed to determine information about a relative location of the eyepiece stack with respect to an ambient light source based on an image captured by the camera module, and to vary an attenuation ratio of the adjustable attenuator based on the information about the relative location; A wearable display system comprising: (Item 2) 2. The wearable display system of claim 1, wherein the adjustable attenuator reduces the transmittance of visible light incident on the adjustable attenuator within a first range of incidence angles without significantly reducing the transmittance of light incident on the adjustable attenuator at angles of incidence outside the first range. (Item 3) 3. The wearable display system of claim 1 or 2, wherein the electro-optical cell comprises a layer of liquid crystal material, and the adjustable attenuator further comprises a voltage source arranged to apply a variable voltage to the liquid crystal material. (Item 4) 4. The wearable display system of any one of items 1-3, wherein the liquid crystal material is a blue phase liquid crystal material or a vertically aligned liquid crystal material. (Item 5) 4. The wearable display system of any one of claims 1-3, wherein the adjustable attenuator further comprises at least one layer of birefringent material in addition to the layer of liquid crystal material. (Item 6) Item 6. The wearable display system of item 5, wherein at least one layer of birefringent material comprises a pair of quarter wave plates, the quarter wave plates being disposed on opposite sides of the layer of liquid crystal material. (Item 7) 7. The wearable display system of claim 6, wherein each of the pair of quarter-wave plates is aligned with a corresponding one of the linear polarizers to form a circular polarizer. (Item 8) 8. The wearable display system of claim 6 or 7, wherein the at least one layer of birefringent material further comprises a C-plate. (Item 9) 9. The wearable display system of any one of items 1-8, wherein the pass axes of the two linear polarizers are crossed. (Item 10) A wearable display system described in any one of items 1-9, wherein the electro-optical cell rotates the polarization state of light transmitted by a first linear polarizer of the pair of linear polarizers on the world side of the adjustable attenuator. (Item 11) Item 11. The wearable display system of item 10, wherein the amount of rotation of the polarization state varies depending on the state of the electro-optical cell and the angle of incidence of light transmitted by the first linear polarizer of the pair of linear polarizers. (Item 12) Item 12. The wearable display system of item 11, wherein light transmitted with a large angle of incidence is rotated less than light transmitted with a small angle of incidence. (Item 13) 13. The wearable display system of any one of claims 1-12, wherein the adjustable attenuator has an area greater than 50 mm x 50 mm. (Item 14) The wearable display system of any one of items 1-13, wherein the electro-optical cell is a first electro-optical cell, and the adjustable attenuator further comprises a second electro-optical cell and a third linear polarizer, and the second electro-optical cell is arranged between the pair of linear polarizers and the third linear polarizer. (Item 15) Item 15. The wearable display system of item 14, wherein the first and second electro-optical cells each comprise a corresponding layer of liquid crystal material. (Item 16) Item 16. The wearable display system of item 15, wherein the adjustable attenuator further comprises one or more layers of birefringent material arranged on opposite sides of the corresponding layer of liquid crystal material. (Item 17) 17. The wearable display system of any one of items 1-16, wherein the adjustable attenuator comprises two or more stages, each stage comprising an electro-optical cell arranged between a pair of linear polarizers. (Item 18) Item 18. The wearable display system of item 17, wherein adjacent stages share a linear polarizer. (Item 19) 1. A method for displaying an image using a wearable display system, comprising: directing display light from a display towards a user through an eyepiece to project an image into a field of view of said user; determining a relative location between an ambient light source and the eyepiece; adjusting an attenuation rate of ambient light from the ambient light source through the eyepiece in response to a relative location between the ambient light source and the eyepiece; A method comprising: (Item 20) 20. The method of claim 19, wherein determining the relative location includes determining an angle of incidence of the ambient light from the ambient light source on the eyepiece, and the attenuation rate is adjusted based on the angle of incidence. (Item 21) 21. The method of claim 20, wherein the attenuation rate is adjusted to reduce the transmittance of the ambient light at the angle of incidence compared to the attenuation rate at lower angles of incidence. (Item 22) 22. The method of any one of claims 19-21, wherein attenuating the ambient light comprises polarizing the ambient light to provide polarized light; and modulating a polarization state of the polarized light as a function of an angle of incidence of the ambient light. (Item 23) 23. The method of claim 22, wherein the rate of attenuation is varied by varying a rate of modulation of the polarization state of the polarized light. (Item 24) 24. The method of claim 23, wherein the modulation rate is varied by varying the retardation rate provided by a layer of birefringent material in the path of the polarized light. (Item 25) Item 25. The method of item 24, wherein the birefringent material comprises a liquid crystal. (Item 26) 26. The method of claim 25, wherein the retardation rate is varied by varying an electric field applied to the liquid crystal. (Item 27) 27. The method of claim 26, wherein the liquid crystal is a blue phase liquid crystal or a vertically aligned liquid crystal. (Item 28) 24. The method of claim 23, wherein attenuating the ambient light further comprises directing the modulated polarized light through a second polarizer. (Item 29) 29. The method of claim 28, wherein the attenuation rate is varied using a liquid crystal element. (Item 30) 30. The method of any one of items 19-29, wherein determining the relative location between the ambient light source and the eyepiece includes monitoring ambient light intensity and determining the relative location based on changes in the monitored ambient light intensity. (Item 31) Item 31. The method of item 30, wherein the ambient light intensity is monitored by obtaining an image of the surrounding environment, analyzing the obtained image, and determining a location of the ambient light source within the image. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 shows an embodiment of a wearable display system.

[0026] [Figure 2A] FIG. 2A shows a conventional display system for simulating three-dimensional image data for a user.

[0027] [Figure 2B] FIG. 2B illustrates aspects of an approach for simulating three-dimensional image data using multiple depth planes.

[0028] [Diagram 3] 3A-3C show the relationship between the radius of curvature and the radius of focus.

[0029] [Figure 4] FIG. 4 shows an embodiment of a waveguide stack for outputting image information to a user in an AR eyepiece.

[0030] [Diagram 5] 5 and 6 show examples of output beams output by waveguides.

[0031] [Figure 6] 5 and 6 show examples of output beams output by waveguides.

[0032] [Figure 7] 7A and 7B are schematic diagrams illustrating the light path through a display combiner having a surface relief grating.

[0033] [Figure 8] 8A and 8B are schematic diagrams of partitioning light transmission through a display combiner with and without an angle-selective film.

[0034] [Figure 9] FIG. 9 is a schematic diagram of an eyepiece with a display combiner and an embodiment of an adjustable attenuator.

[0035] [Figure 10] FIG. 10 is a plot showing the transmission for three different wavelengths as a function of incident light angle through an embodiment of an adjustable attenuator.

[0036] [Figure 11] 11A-11I are charts of different simulated rainbow artifacts corresponding to three different eyepiece embodiments at three different angles of incidence, respectively.

[0037] [Figure 12] Figures 12A, 12C, and 12E are charts showing the perceived color shift at three different retardation values, and Figures 12B, 12D, and 12F are charts showing the transmittance profiles for three different wavelengths at three different retardation values.

[0038] [Figure 13] FIG. 13 is a schematic diagram of an eyepiece with a display combiner and another embodiment of an adjustable attenuator.

[0039] [Figure 14] FIG. 14 is a plot showing transmission as a function of incident light angle through multiple adjustable attenuators for three different wavelengths.

[0040] [Figure 15] FIG. 15 is a schematic diagram of an eyepiece with a display combiner and yet a further example of an adjustable attenuator in combination with a static C-plate.

[0041] [Figure 16] FIG. 16 is a flow chart detailing an exemplary voltage control feedback mechanism for ambient light attenuation.

[0042] [Figure 17] 17A and 17B are schematic diagrams comparing light transmission through a display combiner at different angles of incidence.

[0043] [Figure 18] FIG. 18 is a schematic diagram comparing multiple light transmissions through a display combiner over time at multiple angles of incidence.

[0044] [Figure 19] 19A-19C are schematic diagrams of index ellipsoids comparing an isotropic medium and different blue phase LC materials.

[0045] [Figure 20] FIG. 20 is a schematic diagram of an exemplary electro-optical cell with a vertically aligned nematic liquid crystal layer.

[0046] [Figure 21]21A-21C are plots showing exemplary surface alignment patterns in a device using a vertically aligned nematic liquid crystal layer.

[0047] [Figure 22] FIG. 22 is a schematic diagram of an exemplary computer system useful in conjunction with a wearable display system.

[0048] In the drawings, like reference numbers indicate like elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] 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 in front of the user's 90 eye. The display 70 may be considered eyewear in some embodiments. A world-viewing (e.g., facing the user's environment and having a similar field of view) camera 81 is mounted within the frame 80. In some embodiments, a speaker 100 is coupled to the frame 80 and positioned adjacent the ear canal of the user 90. The display system may also include one or more microphones 110 to detect sound. The microphones 110 may enable a user to provide input or commands to the system 60 (e.g., voice menu command selections, natural language queries, etc.) and / or enable audio communication with other persons (e.g., other users of a similar display system). The microphone 110 may also collect audio data (e.g., sounds from the user and / or the environment) from around the user. 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 obtain data characterizing a physiological state of the user 90.

[0050] 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, built into headphones, or otherwise removably attached to the user 90 (e.g., in a backpack 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 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 the frame 80 or otherwise attached to the 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 the remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for passing to the display 70 after processing or retrieval. The local processing and data module 140 may be operatively coupled to the remote processing module 150 and the 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 the local processing and data module 140.In some embodiments, local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be attached to frame 80 or may be stand-alone devices that communicate with local processing and data module 140 by wired or wireless communication paths.

[0051] 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 configurations 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 modules.

[0052] The perception of an image as "three-dimensional" or "3-D" may 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 apart from the eyes 210, 220 by a distance 230 along an optical or z-axis parallel to the user's line of sight. The images 190, 200 are flat and the eyes 210, 220 may focus on the images by assuming a single accommodated state. Such a 3-D display system relies on the human visual system to combine the images 190, 200 and provide a perception of depth and / or scale of the combined image.

[0053] However, the human visual system is complex and it is 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 may be perceived as "three-dimensional" due to a combination of vergence-divergence and accommodation. The vergence-divergence movement of the two eyes relative to one another (e.g., the rotation of the pupils so that the pupils move toward or away from one another, converging the eyes' individual gazes and fixating on an object) is closely linked to the focusing (or "accommodation") of the eye's lenses. Under normal conditions, a change in the focus of the eye's lenses or accommodation of the eye to change focus from one object to another at a different distance will automatically produce a matching change in vergence-divergence at the same distance, a relationship known as the "accommodation-vergence-divergence 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 a slightly different presentation (and therefore a slightly different image) to each eye so that a three-dimensional perspective is perceived by the human visual system. However, such systems may be uncomfortable for some users because they merely 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.

[0054] FIG. 2B illustrates aspects of an approach for simulating three-dimensional image data using multiple depth planes. With reference to FIG. 2B, the eyes 210, 220 assume different accommodated states and focus objects at various distances along the z-axis. As a result, a particular accommodated 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 part of an object at a particular 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 presentations of images for each eye 210, 220 and by providing different presentations of images corresponding to multiple depth planes. Although 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, however, 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.

[0055] The distance between an object and the eye 210 or 220 may also change the amount of divergence of light from that object as viewed by that eye. Figures 3A-3C illustrate the relationship between distance and divergence of light rays. The distance between the object and the eye 210 is represented in the order of decreasing distances R1, R2, and R3. As shown in Figures 3A-3C, the light rays become more divergent as the distance to the object decreases. 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) may be said to have a spherical wavefront curvature that is a function of the distance the point is away from the user's eye. The curvature increases with decreasing distance between the object and the eye 210. As a result, at different depth planes, the divergence of the light rays is also different, and the divergence increases with decreasing distance between the depth plane and the user's eye 210. Although only a monocular 210 is illustrated in FIGS. 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.

[0056] A highly realistic simulation of perceived depth may be achieved by providing the eyes with different presentations of an image corresponding to each of a limited number of depth planes. The different presentations 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 the different depth planes that are out of focus.

[0057] FIG. 4 illustrates an example of a waveguide stack for outputting image information to a user in an AR eyepiece. Display system 250 includes a stack of waveguides or stacked waveguide assembly 260 that may 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, with FIG. 4 diagrammatically illustrating 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 be considered a light field display in some embodiments.

[0058] The waveguide assembly 260 may also include a number of features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or the number of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye with various levels of wavefront curvature or light beam divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. The image input devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to input image information into the waveguides 270, 280, 290, 300, 310, each of which may be configured to distribute incident light across each respective waveguide for output towards the eye 210, as described herein. Light exits an output surface 410, 420, 430, 440, 450 of each respective image input device 360, 370, 380, 390, 400 and is input into a corresponding input surface 460, 470, 480, 490, 500 of the respective waveguide 270, 280, 290, 300, 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or may be a portion of 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 towards 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.

[0059] 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, respectively. 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 different wavelengths or colors of light.

[0060] 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). The 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), including liquid crystal on silicon (LCOS) displays, and MEMS micromirror arrays, such as those used in digital light processing (DLP) displays. In some embodiments, the light projector system 520 may include a light emitting diode (LED) display, such as a micro LED display.

[0061] 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., ear piece 82) of frame 80 or disposed at an edge of display 70. In some embodiments, light module 530 may be separate from BS 550 and / or light modulator 540.

[0062] 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 represent diagrammatically 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 represent diagrammatically 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 the optical module 530 to one or more of the waveguides 270, 280, 290, 300, and 310. Additionally, one or more intervening optical structures may be provided between the scanning fiber or fibers and the one or more of the waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into the one or more of the waveguides 270, 280, 290, 300, 310.

[0063] The controller 560 controls the operation of the stacked waveguide assembly 260, including the operation of the image input devices 360, 370, 380, 390, 400, the light source 530, and the light modulator 540. In some embodiments, the controller 560 is part of the local data processing module 140. The controller 560 includes programming (e.g., instructions in a non-transitory medium) that coordinates the timing and provision of image information to the waveguides 270, 280, 290, 300, 310. In some embodiments, the controller may be a single integrated device or a distributed system connected by wired or wireless communication channels. The controller 560 may be part of the processing module 140 or 150 (FIG. 1) in some embodiments.

[0064] The waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each of the waveguides 270, 280, 290, 300, 310 may be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between their major top and bottom surfaces. In the illustrated configuration, each of the waveguides 270, 280, 290, 300, 310 may include out-coupling 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 the eye 210. The extracted light may also be referred to as out-coupled light, and the optical element that out-couples 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. Although the outcoupling optical elements 570, 580, 590, 600, 610 are illustrated disposed on the bottom major surface 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 waveguide 270, 280, 290, 300, 310. In some other embodiments, the waveguide 270, 280, 290, 300, 310 may be a monolithic piece of material and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within that piece of material.

[0065] 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 the 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 originating from that waveguide 280 as originating from the first focal plane, which is closer inward from optical infinity towards the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive power of the first lens 350 and the second lens 340 may add another incremental amount of wavefront curvature such that the eye / brain interprets the light originating from the third waveguide 290 as originating from a second focal plane that is closer inward from optical infinity than was the light from the second waveguide 280.

[0066] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power that represents the focal plane closest to the person. To compensate the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be placed on top of the stack to compensate for the aggregate refractive power of the lower lens stacks 320, 330, 340, 350. Such a configuration provides as many perceived focal planes as there are waveguide / lens pairs available. Both the outcoupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both may be dynamic using electroactive features.

[0067] 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.

[0068] 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 a particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 may be solid or surface features that may be configured to output light at specific angles. For example, the light extraction 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).

[0069] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features with a sufficiently low diffraction efficiency such that only a portion of the optical power of the light in the beam is redirected towards the eye 210 with each interaction, while the remainder continues to travel 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, 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.

[0070] 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 feature may include a layer of polymer dispersed liquid crystal in which microdroplets comprise a diffractive pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0071] 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 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.

[0072] FIG. 5 illustrates an example of an output beam output by a waveguide. Although one waveguide is shown (with a perspective view), other waveguides in the waveguide assembly 260 (FIG. 4) may 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 by TIR. Through interaction with diffractive features, the light exits the waveguide as an output beam 650. The 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 sub-portion of the total energy of the input light 640. Also, 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. The exit beam 650 is illustrated in FIG. 6 as being approximately parallel, but as discussed herein, a certain amount of refractive power may be imparted depending on the depth plane associated with the waveguide 270. A parallel exit beam may refer to a waveguide with an outcoupling optical element 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 sets of waveguides or outcoupling optical elements may output an exit beam pattern that is more divergent, as shown in FIG. 6, which would require the eye 210 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0073] 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 "EYEPIECES FOR AUGMENTED REALITY DISPLAY SYSTEM," the contents of which are incorporated by reference in their entirety.

[0074] 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, referring 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 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 light guide 710 toward a user of the display system.

[0075] 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 through the EPE by the user, the light diffracted from the world may appear as undesirable image artifacts. The angle of incidence that creates the artifacts in the user's field of view generally depends on the design on 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.

[0076] This effect is further illustrated in FIG. 8A, which shows a display combiner 800. Ambient light is incident at an angle of incidence θ inc , incident on the front surface of the display combiner 800. At least a portion of the incident light is transmitted through the grating and combiner as shown. However, the display combiner 800 supports a grating (not shown) that diffracts at least a portion of the incident light towards the user. This light, labeled stray light, is incident on the front surface of the display combiner 800 at an angle θ stray It diffracts at

[0077] 8B, an adjustable attenuator 810 can be applied to (e.g., cemented onto) the display combiner 800 to reduce stray light artifacts associated with ambient light. In general, the transmission of light through the attenuator 810 depends on both the angle of incidence of the light on the film and the optical state of one or more adjustable layers of the attenuator. As shown, the attenuator 810 is adapted to transmit light at a relatively high angle of incidence θ (e.g., 30° or more, 35° or more, 40° or more, 45° or more, such as a user might experience from overhead lighting in an indoor environment). inc , which attenuates (e.g., reduces or blocks) the transmission of light but at a lower incidence angle θ a 8. The attenuator 810 transmits light having a wavelength of 0.1 nm (e.g., "world light" as seen by the wearer in the core field of view of the device). As discussed in more detail below, the attenuator 810 can vary the attenuation angle at different angles of incidence in response to variations in ambient lighting conditions, such as, for example, varying relative orientation of the ambient light source with respect to the display. The attenuator 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.

[0078] For a given optical state, the transmission efficiency for incident light generally varies as a function of the angle of incidence from relatively high transmission efficiency (e.g., 40% or more, 45% or more) to relatively low transmission efficiency (e.g., less than 1%, less than 0.5%). Transmission 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 angle-selective film with an angle of incidence of 25° to 85° has a transmission efficiency of less than 0.5%. The exact angle of minimum transmission efficiency can be adjusted, such as within a certain angle range.

[0079] The adjustable attenuator may also only relatively slightly affect the color of the image viewed through the film. For example, for a D65 source, the adjustable attenuator may shift the 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 within a prescribed angular range (e.g., ±40°) (e.g., for a D65 source, the adjustable attenuator may shift the CIE 1931 white point by less than (+ / -0.02, + / -0.02) (e.g., (+ / -0.01, + / -0.01) or less).

[0080] The transmittance of an adjustable attenuator can also be characterized by attenuation, which may be high at least at some 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), may experience very low levels of attenuation (e.g., 2 dB or less, 1 dB or less).

[0081] In general, the adjustable attenuator 810 can be relatively thin. For example, the film 810 can have a total thickness in the range of 500 microns to 5,000 microns. Thus, the advantages of using an adjustable attenuator can be achieved without adding significant bulk to the wearable display system.

[0082] In some embodiments, the adjustable attenuator 810 is comprised of a multi-layer stack including an electro-optic cell (e.g., a liquid crystal electro-optic cell) arranged between a pair of polarizer films (e.g., linear polarizers). The polarizer films and the electro-optic cell significantly reduce the transmission of visible light incident on the adjustable attenuator 810 within a range of incidence angles without significantly reducing the transmission of light incident on the adjustable attenuator at angles of incidence outside that range.

[0083] In general, the configuration of the two polarizers and the electro-optic cell can be varied to provide a desired level of transmission variation over the angular incidence range of interest (e.g., −75° to +75°). In some embodiments, the polarizers are linear polarizers and the pass axes of the two linear polarizers can be crossed (e.g., at 90°).

[0084] In general, an electro-optical cell includes one or more variable birefringent layers that are designed to switch between different optical states such that, in at least one state, the layer rotates the polarization state of light transmitted by a first of a pair of linear polarizers, incident from the world side. The variable birefringent layers can include liquid crystal materials (e.g., nematic phase liquid crystal materials) that can be aligned such that, in at least one state, the extraordinary axis of the liquid crystal material is parallel to the plane of the layer (e.g., providing quarter-wave (QW) retardation) and / or, in a homeotropic alignment, the extraordinary axis of the liquid crystal material is perpendicular to the plane of the layer.

[0085] Typically, the amount by which an electro-optical cell rotates the polarization state varies depending on the composition and phase of the liquid crystal material and on the angle of incidence of the 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 transmission efficiency of the film. In such cases, a greater rotation is desired for on-axis light compared to light at a larger angle of incidence. Conversely, in some embodiments, the polarizer axes are parallel and the polarization adjusting film rotates on-axis light less than light at a larger angle of incidence.

[0086] In general, the adjustable attenuator is appropriately sized to cover at least a portion of the eyepiece of the wearable display system. For example, in some embodiments, the adjustable attenuator can have an area of ​​20 mm by 20 mm or greater (e.g., have an area whose shortest dimension is 20 mm).

[0087] Turning now to a specific embodiment of an adjustable attenuator, and referring to Figure 9, an eyepiece 900 of a wearable display system includes a display combiner 800 and a stack 910, which operates as an adjustable attenuator. The stack 910 includes a pair of linear polarizers 920a and 920b. Between the linear polarizers, the stack 910 includes a pair of quarter wave plates (QW) 930a and 930b on either side of an adjustable birefringent layer 940 (e.g., a liquid crystal layer).

[0088] In some implementations, the fast axes of waveplates 930a and 930b are oriented at approximately 45° to the pass axes of linear polarizers 920a and 920b, respectively, such that the combination of linear polarizer 920b and QW 930b converts unpolarized light incident from the world side to approximately circularly polarized light (i.e., the combination behaves as a circular polarizer). The combination of QW 930a and linear polarizer 920a behaves similarly. Note that the handedness of each circular polarizer is identical.

[0089] In at least one state, the tunable birefringent layer 940 has a zero retardation for normally incident light, but a non-zero retardation for obliquely incident light. Without wishing to be bound by theory, the retardation of the tunable birefringent layer as a function of incidence angle is [ka] where n o is the ordinary refractive index of the tunable birefringent layer, and n e is the extraordinary refractive index of the tunable birefringent layer, θ is the angle of incidence relative to the normal to the tunable birefringent layer interface, and k o = 2π / λ is the wave number of the incident light, λ is the wavelength of the incident light, and d is the thickness of the tunable birefringent layer. In addition, the effective refractive index of the tunable birefringent layer, n o and n ecan be modified by applying a non-zero voltage to the tunable birefringent layer. By using circularly polarized light, the excitation of the ordinary and extraordinary modes in the tunable birefringent layer for all angles of incidence is approximately equal. This is achieved by subtracting T=cos 2 This leads to the transmission of the same circular polarization state at the output of (Γ / 2).

[0090] In general, the transmission characteristics of stack 910 vary depending on the properties of tunable birefringent layer 940 (e.g., thickness and birefringence of the material forming the layer) and the applied voltage. An example of the transmission as a function of incidence angle for an exemplary implementation of stack 910 is shown in Figure 10, where the transmission as a function of incidence angle is shown for three different wavelengths, n o =1.5236, n e 10 is shown for a tunable attenuator configured as a C-plate with θ = 1.52 and thickness d = 153 μm. The tunable attenuator simulated to produce FIG. 10 has the same configuration as FIG. 9, e.g., with two linear polarizers, two quarter-wave plates, and a tunable birefringent layer. The transmittance is now normalized to 1 for on-axis light, remains at or close to 1 up to about 20°, and then falls monotonically to zero between 60° and 80°, depending on the wavelength. For shorter wavelengths (e.g., 460 nm to 525 nm), after a narrow peak attenuation window at 1010 and 1020, the transmittance increases as the angle of incidence increases up to 90°.

[0091] In the tunable birefringent layer, n o and n e The value for depends on the voltage applied to the tunable birefringent layer. This means that the transmittance as a function of the angle of incidence also depends on the voltage applied to the tunable birefringent layer. Furthermore, in 1010, 1020, and 1030, the minimum value associated with the transmittance at the variable wavelength can be adjusted to match the angle of incidence of a specific light source (e.g., overhead lighting or the sun), for example, as detected using a world-side sensor.

[0092] The effect of using an adjustable attenuator is illustrated in the plots shown in Figures 11A-I. These plots compare the rainbow artifacts formed by the eyepiece grating without an attenuator (Figures 11A,D,G), with a static attenuator (Figures 11B,E,H), and with an adjustable attenuator (Figures 11C,F,I) when light from an ambient light source is incident on the lens for three different non-zero angles of incidence. The rainbow artifacts are caused by the dispersion of the different wavelengths that make up the white light from the ambient source due to diffraction by the grating structure in the display combiner at non-zero angles of incidence (as illustrated in Figure 7B discussed above).

[0093] In Figures 11A-I, the optical rainbow artifact is shown for a white light source with a 5800K blackbody spectrum incident on the device from above at angles of incidence of 70° (Figures 11A-C), 60° (Figures 11D-F), and 50° (Figures 11G-I). A grating with a pitch of 390 nm was used to calculate the diffraction angle of the artifact. The images in column 1110 show the rainbow artifact perceived when no filter is present. The images in column 1120 show a reduction in the intensity of the rainbow artifact when a static C-plate filter with peak retardation at 550 nm is used. The images in column 1130 show a further reduction in artifact intensity over the images in column 1110 when the voltage controlling the retardation of the tunable birefringent layer in the film stack is selected relative to the angle of incidence of the light source. In FIG. 11C, the transmittance is modeled for an adjustable attenuator with a peak delay at 450 nm, in FIG. 11F, the transmittance is modeled for an adjustable attenuator with a peak delay at 660 nm, and in FIG. 11I, the transmittance is modeled for a peak delay at 900 nm.

[0094] When using an adjustable attenuator in a film stack (e.g., stack 910), there may be a tradeoff with color shift in the user's view of the world as seen through eyepiece 900. As the angle of incidence of light from ambient light sources is reduced, the peak delay of the adjustable attenuator should be adjusted to attenuate any artifacts as viewed by the user, as illustrated in Figures 11A-I.

[0095] However, as the peak delay of the adjustable attenuator is modified, there may be a perceptible color shift in the transmitted light. This effect is illustrated in Figures 12A-12F, which depict the transmission properties of adjustable attenuator sets at optimal peak delays of 550 nm (Figures 12A and 12B), 660 nm (Figures 12C and 12D), and 900 nm (Figures 12E and 12F). Figures 12A, 12C, and 12E depict simulated apertures for these three optical peak delays spanning a 100° field of view vertically and horizontally (-50° to 50°), respectively. The simulated apertures reduce transmission to zero for angles of incidence greater than 45°.

[0096] Figures 12B, 12D, and 12F show the transmittance curves of light transmitted at 460 nm, 525 nm, and 630 nm as a function of the angle of incidence. In Figures 12A, 12C, and 12E, dashed lines drawn at 45° angle of incidence are presented to show where the simulated aperture reduces the transmittance to zero. In Figures 12B, 12D, and 12F, at angles of incidence between 0° and 45°, the transmission curves of 630 nm (e.g., red) light are shown to have a higher transmittance than 460 nm (e.g., blue) light, indicating a lower attenuation of light at 630 nm wavelength. The relative ratio of red and blue light shifts the perceived color through the adjustable attenuator toward a red hue, depending on the angle of incidence. This effect can be seen in the simulated fields of view in Figures 12A, 12C, and 12E. For example, in Figure 12F, the transmittance curve for 460 nm light is approximately zero at a 45° angle of incidence, while light at 630 nm wavelength still has an approximate relative transmission value of approximately 0.2, as evidenced by the circumferential red hue around the edge of the field in Figure 12E.

[0097] Generally, FIG. 9 shows an example of an adjustable attenuator that includes a single adjustable birefringent layer 940 between two linear polarizers 920, although implementations with additional layers are also possible. For example, FIG. 13 shows an eyepiece 1300 that includes a film stack 1310 applied to the world side of a display combiner 800. The film stack 1310 includes three linear polarizers 1320a, 1320b, and 1320c. A first polarization adjustment stack is arranged between the polarizers 1320a and 1320b. The stack includes a pair of QWs 1330a and 1330b on either side of the adjustable birefringent layer 1340a. A second polarization adjustment stack is arranged between the polarizers 1320b and 1320c. The stack includes QWs 1330c and 1330d on either side of the adjustable birefringent layer 1340b. In effect, the stack 1310 performs like two stacks 910 placed together.

[0098] Stack 910 may be considered a "single stage" arrangement, and stack 1310 may be considered a two stage arrangement. In general, additional stages can be added. Without wishing to be bound by theory, several stages may be used in series to provide different transmission responses. [ka] wherein Γ n is the retardation factor of the nth stage, which varies as a function of the applied voltage.

[0099] The use of multiple stages in series can enable stronger attenuation of light from large angles of incidence. For example, referring to FIG. 14, the transmission for three different wavelengths as a function of angle of incidence for a two-stage adjustable attenuator arrangement such as stack 1310 is shown. In this example, for adjustable birefringent layers 1340a and 1340b, n o =1.5236, n e = 1.52, and the thickness of the tunable birefringent layer in the first stage 1340b is d 1 = 111 μm, and the thickness of the tunable birefringent layer in the second stage 1340a is d 2 = 111 μm. In comparison to the single-stage film depicted in FIG. 10, FIG. 14 demonstrates that the transmittances for all three wavelengths, normalized to 1 for on-axis light, remain at or near 1 up to about 20°, after which they decrease asymptotically for a wavelength of about 460 nm, but decrease monotonically at longer wavelengths (e.g., 525 nm to 630 nm) until they peak at a non-zero attenuation value at 90° incidence. At high incidence angles up to 90°, the transmittance remains low from 460 nm to 525 nm, rather than increasing from a minimum value at 60° to 80°. The transmittance no longer increases after the peak attenuation angle, unlike the transmittance at these wavelengths as depicted in FIG. 10.

[0100] When multiple stages are used in a film stack, the second layer may be a layer that is not an adjustable birefringent layer, i.e., it can be a static layer. Figure 15 shows an example adjustable attenuator 1510 that uses an adjustable birefringent layer 1550 in conjunction with a static C-plate 1540. The C-plate 1540 has zero retardation for normally incident light, but has a static non-zero retardation for obliquely incident light. When the adjustable birefringent layer 1550 is used in conjunction with the static C-plate 1540, the C-plate 1540 provides the initial retardation, and the adjustable birefringent layer provides an additional and variable amount of retardation to provide the total amount of retardation Γ required for the environment. The addition of the static C-plate layer 1540 can help reduce the driving voltage and the thickness of the adjustable birefringent layer.

[0101] In general, a wearable display system using an adjustable attenuator can detect and attenuate ambient light sources and eliminate optical artifacts (e.g., optical rainbow). The wearable display system can attenuate ambient light sources at different angles of incidence by controlling the adjustable attenuator and applying a differential voltage to the adjustable birefringent layer. An exemplary method for specific attenuation of light from ambient light sources is shown in FIG. 16. For example, image data from a frame-mounted camera can be sent to a local data processing module, which can be programmed to detect the presence of an ambient light source 1610. Areas of high brightness in the image data can be used by the local data processing module in some implementations to distinguish the ambient light source from a background image.

[0102] After the presence of an ambient light source in the field of view of the user of the wearable display system is detected, the angle of incidence of the ambient light source may be calculated by a local data processing module of the wearable display system 1620. The wearable display system may then send instructions to the display to control the voltage applied to the liquid crystal layer of the adjustable attenuator 1630. The modified voltage may modify the liquid crystal layer in a manner that attenuates the detected ambient light source. The system may then return to step 1610 and make a further determination whether the user field of view is changing (e.g., the user is moving, there is more than one ambient light source).

[0103] An example application for the detection and attenuation of ambient light sources described in FIG. 16 is depicted in FIGS. 17A and 17B. In FIG. 17A, an ambient light source 1710 emits light 1720 that hits an adjustable attenuator at a first angle of incidence 1730. By applying a voltage to the adjustable attenuator 1750, the ambient light can be attenuated 1770. In FIG. 17B, the ambient light source 1710 emits light 1720 that hits the adjustable attenuator at a different angle of incidence 1740. By applying a different voltage to the adjustable attenuator 1750, the ambient light can be attenuated 1770 for that specific angle of incidence 1740. In this manner, the transmission minima associated with different wavelengths of light (1010, 1020, and 1030) can be adjusted to attenuate a particular ambient light source at a unique angle of incidence.

[0104] Additionally, multiple ambient light sources at distinct angles of incidence and intensities may be attenuated within the user's field of view. FIG. 18 illustrates a first intensity S incident on an adjustable attenuator 1850. 1 1810, second strength S 2 1820, and the third strength S 3At 1830, three ambient light sources are shown. By operating in a time sequential mode of operation, these ambient light sources can be attenuated with respect to their individual intensities and angles of incidence. Some tunable birefringent layers have a time response (≦1 ms) that is faster than the frequency (< about 0.03 s) at which a new visual image frame is displayed to the user. The total time between frames displayed to the user is t total If the image is given as t, then this can be subdivided according to the n ambient light sources in the user's field of view. The total division is t total = Δt 1 +Δt 2 +...+Δt n After the intensity of each ambient light source is determined, the subframe time during which the particular light source will be primarily attenuated is calculated. 1 1810, S 2 1820, and S 3 The strength of 1830 is S 2 >S 3 >S 1 , the subframe time is Δt 2 1880>Δt 3 1890>Δt 1 1870. By implementing this function, each ambient light source at a distinct intensity level n is calculated for a distinct subframe time interval t n In this way, light from multiple ambient light sources can be attenuated based on their individual intensities and angles of incidence within a single frame displayed to a user.

[0105] In general, various applicable LC phases and modes can be used within the tunable birefringent layer. For example, in some embodiments, blue phase liquid crystals (BPLC) may be used as the tunable birefringent layer. BPLC displays are optically isotropic when no voltage is applied. In other words, the refractive index of the BPLC medium is equal in the three principal directions of the birefringent layer (e.g., n z =n x =n y). When a voltage is applied, for liquid crystal molecules with positive dielectric anisotropy, the liquid crystal molecules align with the resulting electric field, inducing birefringence in the layer. For the appropriate electrode geometry, the BPLC layer acts as a tunable C-plate and can induce positive or negative birefringence, depending on the birefringence of the LC material. For example, in a BPLC material with positive dielectric anisotropy and positive birefringence, the index ellipsoid, which describes the orientation of the refractive index, is n o =n x =n y , n z =n e , and n o <n e Then, n e are aligned along the electric field. In a BPLC material with negative birefringence, the index ellipsoid, which describes the orientation of the refractive index, is n o >n e is defined by n o is aligned orthogonally to the applied electric field. This effect is illustrated in Figures 19A-19C. In particular, Figure 19A shows the index ellipsoid of an isotropic optical medium, i.e., in the zero-voltage state of a BPLC layer. Figure 19B shows the index ellipsoid of a positive birefringent LC material with positive dielectric anisotropy when sufficient voltage is applied to the layer to align the LC molecules with a corresponding electric field E. Figure 19C shows the index ellipsoid of a negative birefringent LC material with positive dielectric anisotropy when sufficient voltage is applied to the layer to align the electric field E with the LC molecules.

[0106] In one embodiment, a vertically aligned nematic liquid crystal (VAN) material may be used between two circular polarizers in the film stack 910. A layer of vertically aligned liquid crystal (VALC) is the optical equivalent of a positive C-plate compensation film, with the added benefit that the retardation can be tuned by application of a voltage, much like is done with a conventional liquid crystal display (LCD).

[0107] A typical VALC device 2000 is shown in Figure 20 below. A typical VALC device comprises a layer 2040 of vertically aligned LC material between two substrates 2010. Each substrate 2010 supports a transparent electrode 2020 on the surface facing the LC layer 2040, and an alignment layer 2030 on the transparent electrode.

[0108] A voltage source (not shown) is connected to each electrode 2020 to apply a voltage across the LC layer 2040. The matching layer 2030 controls the alignment of the LC molecules at the boundaries of the LC layer 2040, thereby controlling the zero-voltage orientation of the LC molecules within the LC layer 2040. In general, the matching layer 2030 controls the alignment by introducing a pretilt angle 2050 (α), which ensures that the molecules are uniformly oriented when the applied voltage is removed, reducing the introduction of disclinations or other alignment defects into the LC layer. This pretilt angle is typically 1°-5° (e.g., 2°, 3°, 4°) relative to the surface normal of the substrate 2010 and can be established by physical rubbing of the polymer layer with a cloth or by exposure to linearly polarized UV light (the process is material dependent and known in the art).

[0109] In such devices, the retardation rate can be tuned uniformly across the active area of ​​the device when a single electrode 2020 is used. In some embodiments, the electrodes 2020 may be patterned such that the retardation rate can be tuned in a spatially variable manner. The electrodes may be roughly rectangular in shape and arranged in a Cartesian grid (as in a conventional LCD) to define an arbitrary retardation profile or a series of concentric circular shapes with fixed or variable widths, defining a rotationally symmetric retardation profile.

[0110] The pre-tilt angle 2050 is often uniform and unidirectional across the surface of the substrate 2010, as depicted in FIG. 21A, but in some cases may be spatially varied. Spatial variation of the pre-tilt can be used regardless of whether uniform or patterned electrodes are used. This can be used to implement delay profiles that are not achievable using patterned electrode structures, or without the need to pattern electrodes. While any suitable pattern of pre-tilt angles 2050 may be realized, in some embodiments the pre-tilt angles 2050 may be purely radial (e.g., pointing radially away from the central z-axis), as depicted in FIG. 21B, or purely azimuthal (e.g., progressing in a circular fashion around the central z-axis), as depicted in FIG. 21C.

[0111] A variety of suitable different materials can be used for each layer in the angularly selective film. The linear polarizer can be formed, for example, from a stretched polymer material (e.g., PVA) that is dyed with a chromophore (e.g., iodine). Commercially available linear polarizers, such as those available from SanritzCo. (Japan) or Nittto Denko (Japan), can be used. The QWs can be made, for example, from stretched polymer films or liquid crystal polymer films. The C-plate can be formed, for example, from a cast polymer film, such as cast cellulose triacetate. Liquid crystal polymer C-plates are also a possibility.

[0112] Generally, each layer is represented as a homogeneous layer, but composite layers are also possible. For example, a C-plate can be formed from multiple stacked layers, each with different optical properties than its neighbors. Similarly, multi-layer QWs can also be used.

[0113] 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 the transmitted light. In some embodiments, the stack includes one or more layers on the world side of the outermost linear polarizer. For example, anti-reflective films and / or hard coat layers can be included.

[0114] 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 combinations thereof.

[0115] 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 included in 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 them. Furthermore, a computer storage medium is not a propagating signal, but a computer storage medium can be a source or destination of computer program instructions encoded in an artificially generated propagating signal. A computer storage medium can also be or be included in one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

[0116] The term "data processing apparatus" encompasses all kinds of apparatus, devices, and machines for processing data, including, by way of example, a programmable processor, a computer, a system on a chip, or a plurality or combination of the above. The apparatus may include special purpose logic circuitry, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). In addition to hardware, the apparatus may also include code that creates an execution environment for the computer program, such as code that constitutes a 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.

[0117] 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 that store one or more modules, subprograms, or portions of code). A computer program can be deployed to run on one computer or on multiple computers located at one facility or distributed across multiple facilities and interconnected by a communication network.

[0118] Some of the processes and logic flows described herein can 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 can also be implemented by special purpose logic circuitry, such as an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit), and an apparatus can also be implemented as such.

[0119] Processors suitable for executing computer programs 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 according to 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 for receiving data therefrom, transferring 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 others), magnetic disks (e.g., internal hard disks, removable disks, and others), 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.

[0120] 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 interaction with the user as well, e.g., 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 the user by sending documents to and receiving documents from a device used by the user, e.g., 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.

[0121] 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.

[0122] 22 illustrates an exemplary computer system 2200 including a processor 2210, a memory 2220, a storage device 2230, and an input / output device 2240. Each of the components 2210, 2220, 2230, and 2240 may be interconnected, for example, by a system bus 2250. The processor 2210 may process instructions for execution within the system 2200. In some implementations, the processor 2210 is a single-threaded processor, a multi-threaded processor, or another type of processor. The processor 2210 may process instructions stored in the memory 2220 or on the storage device 2230. The memory 2220 and the storage device 2230 may store information within the system 2200.

[0123] The input / output device(s) 2240 provide input / output operations for the system 2200. In some implementations, the input / output device(s) 2240 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 device(s) may include a driver device configured to receive input data and send output data to another input / output device, e.g., the wearable display device 2260. In some implementations, mobile computing devices, mobile communication devices, and other devices may also be used.

[0124] Although the 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 that are described in the specification in the context of separate implementations can also be combined. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple embodiments separately or in any suitable subcombination.

[0125] Several implementations have been described. However, it is to 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. A wearable display system, comprising: a frame wearable by a user as eyewear, the frame housing an eyepiece stack, the eyepiece stack having a world side and a user side opposite the world side, wherein during use, the user positioned on the user side views displayed images delivered by the wearable display system through the eyepiece stack which extends the user's field of view of the user's environment; an adjustable attenuator arranged on the world side of the eyepiece stack, the adjustable attenuator comprising a first electro-optical cell and a second electro-optical cell separated from the first electro-optical cell by a first linear polarizer, the first electro-optical cell, the second electro-optical cell and the first linear polarizer being arranged between a pair of linear polarizers; a camera module mounted on the frame and facing the world; an electronic processing module in communication with the adjustable attenuator and the camera module, the electronic processing module being programmed to determine information about an angle of incidence of light from an ambient light source based on an image captured by the camera module, and to vary an attenuation factor of the adjustable attenuator based on the angle of incidence; Equipped with 13. A wearable display system, comprising: a) a first electro-optical cell and a second electro-optical cell, the first electro-optical cell and the second electro-optical cell arranged to receive light from the first electro-optical cell and the second electro-optical cell; and b) a second electro-optical cell arranged to receive light from the second electro-optical cell and the second electro-optical cell; and c) a first electro-optical cell arranged to receive light from the second electro-optical cell and the second electro-optical cell;

2. 2. The wearable display system of claim 1, wherein the electronic processing module is programmed to vary the attenuation ratio of the adjustable attenuator by controlling the optical states of the first electro-optical cell and the second electro-optical cell to reduce the transmittance of visible light incident on the adjustable attenuator by an amount dependent on the incidence angle within a first range of incidence angles.

3. 2. The wearable display system of claim 1 , wherein each of the first electro-optical cell and the second electro-optical cell comprises a layer of liquid crystal material, and the adjustable attenuator further comprises a voltage source arranged to apply a variable voltage to each of the liquid crystal materials.

4. The wearable display system of claim 3 , wherein the adjustable attenuator further comprises at least one layer of birefringent material in addition to the layers of liquid crystal material of the first electro-optical cell and the second electro-optical cell.

5. 5. The wearable display system of claim 4, wherein the at least one layer of birefringent material comprises a pair of quarter-wave plates disposed on opposite sides of the layer of liquid crystal material of the first electro-optical cell and the second electro-optical cell.

6. 6. The wearable display system of claim 5, wherein each of the pair of quarter-wave plates of the first and second electro-optical cells is arranged with respect to a corresponding one of the linear polarizers to form a circular polarizer.

7. The wearable display system of claim 5 , wherein the at least one layer of birefringent material further comprises a C-plate.

8. The wearable display system of claim 1 , wherein one of the first electro-optical cell or the second electro-optical cell rotates the polarization state of light transmitted by a first linear polarizer of the pair of linear polarizers on the world side of the adjustable attenuator.

9. The wearable display system of claim 8 , wherein the amount of rotation of the polarization state varies depending on the state of the first electro-optical cell or the second electro-optical cell and the angle of incidence of light transmitted by the first linear polarizer of the pair of linear polarizers.

10. 10. The wearable display system of claim 9, wherein transmitted light having a large angle of incidence is rotated less than transmitted light having a small angle of incidence.

11. The wearable display system of claim 1 , wherein the adjustable attenuator has an area greater than 50 mm by 50 mm.

12. The wearable display system of claim 1 , wherein each of the first and second electro-optical cells is comprised of a corresponding layer of liquid crystal material.

13. The wearable display system of claim 12 , wherein the adjustable attenuator further comprises one or more layers of birefringent material arranged on opposing sides of corresponding layers of the liquid crystal material of the first electro-optical cell and the second electro-optical cell.

14. 1. A method for displaying an image using a wearable display system, comprising: projecting an image into a field of view of a user by directing display light from a display through an eyepiece towards the user; determining a relative location between an ambient light source and the eyepiece; adjusting an attenuation rate of ambient light from the ambient light source through the eyepiece as a function of a relative location between the ambient light source and the eyepiece, such that (a) for angles of incidence less than 50°, ambient light having a wavelength within a wavelength range of 460 nm to 630 nm has a transmittance greater than 10% compared to the transmittance of normally incident light, and (b) for angles of incidence greater than 70°, ambient light having a wavelength within a wavelength range of 460 nm to 630 nm has a transmittance less than 10% compared to the transmittance of normally incident light, said adjusting being in turn polarizing the ambient light to provide polarized light; retarding the polarized light by a first amount to provide single retarded polarized light; polarizing the once retarded polarized light to provide twice polarized light; retarding the twice polarized light to provide twice retarded polarized light; polarizing the twice-retarded polarized light to provide thrice-polarized light, the intensity of the thrice-polarized light being attenuated relative to the ambient light; Including, A method comprising:

15. 3. The wearable display system of claim 2, wherein the electronic processing module is programmed to control the adjustable attenuator to reduce the transmittance of visible light incident on the adjustable attenuator within a first range of angles of incidence without significantly reducing the transmittance of light incident on the adjustable attenuator at angles of incidence outside the first range.

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