Optical combiner including polarization-selective elements and switchable half-wave plates for pupil steering

An optical assembly includes a beam steering device and a holographic optical element. The beam steering device is switchable between different states including a first state and a second state. The beam steering device includes a first polarization-selective optical element and a first tunable optical retarder optically coupled with the first polarization-selective optical element. The holographic optical element is positioned relative to the beam steering device for receiving light from the beam steering device and projecting a first light pattern while the beam steering device is in the first state and a second light pattern distinct from the first light pattern while the beam steering device is in the second state.

TECHNICAL FIELD

This relates generally to display devices, and more specifically to head-mounted display devices.

BACKGROUND

Head-mounted display devices (also called herein head-mounted displays) are gaining popularity as means for providing visual information to a user. For example, the head-mounted display devices are used for virtual reality and augmented reality operations.

Conventional head-mounted display devices (e.g., conventional head-mounted display devices configured for augmented reality operations) project images over a large area around an eye of a user in order to provide a wide field of view in all gaze-directions (e.g., in order to deal with pupil steering). However, projecting images over a large area leads to reduced brightness of the projected images. Compensating for the reduced brightness typically requires a high intensity light source, which is typically large and heavy, and has high power consumption.

Therefore, there is a need for head-mounted displays that are compact and light, thereby enhancing the user's virtual reality and/or augmented reality experience.

SUMMARY

The above deficiencies and other problems associated with conventional head-mounted displays are reduced or eliminated by the disclosed display devices including optical assemblies for pupil steering.

In accordance with some embodiments, an optical assembly includes a beam steering device and a holographic optical element. The beam steering device is switchable between different states including a first state and a second state. The beam steering device includes a first polarization-selective optical element and a first tunable optical retarder optically coupled with the first polarization-selective optical element. The holographic optical element is positioned relative to the beam steering device for receiving light from the beam steering device and projecting a first light pattern while the beam steering device is in the first state and a second light pattern distinct from the first light pattern while the beam steering device is in the second state.

In accordance with some embodiments, a display device including the optical assembly described above, a light source, and a spatial light modulator. The spatial light modulator is positioned so that the spatial light modulator receives light output by the light source and projects the light toward the optical assembly.

In accordance with some embodiments, a method is performed at an optical assembly including a holographic optical element and a beam steering device switchable between different states including a first state and a second state. The beam steering device includes a first polarization-selective optical element and a first tunable optical retarder optically coupled with the first polarization-selective optical element. The method includes receiving, by the holographic optical element, light from the beam steering device. The method also includes projecting, by the holographic optical element, a first light pattern while the beam steering device is in the first state and a second light pattern distinct from the first light pattern while the beam steering device is in the second state.

These figures are not drawn to scale unless indicated otherwise.

DETAILED DESCRIPTION

Utilizing optical elements (e.g., combiners or reflective displays) that project computer-generated images allows augmented and virtual reality operations. In order to provide images to a pupil regardless of a movement of the pupil, conventional combiners and reflectors project images onto a large eyebox (e.g., an eyebox having a characteristic dimension, such as a diameter or a width, of at least 1 cm). However, when light is projected onto a large eyebox, a significant portion of the light lands on an area outside the pupil. This leads to decreased brightness of the projected images. Instead of increasing the power of light source devices in displays, which increases the size, weight, and power consumption of head-mounted displays, images are projected onto a small eyebox (e.g., an eyebox that corresponds to a size of the pupil), thereby improving the brightness of the projected images. To accommodate for the movement of the pupil and reduce vignetting of the projected light, the projected light is steered toward the pupil using the disclosed optical assemblies.

It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first retarder could be termed a second retarder, and, similarly, a second retarder could be termed a first retarder, without departing from the scope of the various described embodiments. The first retarder and the second retarder are both retarders, but they are not the same retarder. Similarly, a first direction could be termed a second direction, and, similarly, a second direction could be termed a first direction, without departing from the scope of the various described embodiments. The first direction and the second direction are both directions, but they are not the same direction.

The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various described embodiments and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The term “exemplary” is used herein in the sense of “serving as an example, instance, or illustration” and not in the sense of “representing the best of its kind.”

FIG.1illustrates display device100in accordance with some embodiments. In some embodiments, display device100is configured to be worn on a head of a user (e.g., by having the form of spectacles or eyeglasses, as shown inFIG.1) or to be included as part of a helmet that is to be worn by the user. When display device100is configured to be worn on a head of a user or to be included as part of a helmet, display device100is called a head-mounted display. Alternatively, display device100is configured for placement in proximity of an eye or eyes of the user at a fixed location, without being head-mounted (e.g., display device100is mounted in a vehicle, such as a car or an airplane, for placement in front of an eye or eyes of the user). As shown inFIG.1, display device100includes display110. Display110is configured for presenting visual contents (e.g., augmented reality contents, virtual reality contents, mixed reality contents, or any combination thereof) to a user.

In some embodiments, display device100includes one or more components described herein with respect toFIG.2. In some embodiments, display device100includes additional components not shown inFIG.2.

FIG.2is a block diagram of system200in accordance with some embodiments. The system200shown inFIG.2includes display device205(which corresponds to display device100shown inFIG.1), imaging device235, and input interface240that are each coupled to console210. WhileFIG.2shows an example of system200including one display device205, imaging device235, and input interface240, in other embodiments, any number of these components may be included in system200. For example, there may be multiple display devices205each having associated input interface240and being monitored by one or more imaging devices235, with each display device205, input interface240, and imaging devices235communicating with console210. In alternative configurations, different and/or additional components may be included in system200. For example, in some embodiments, console210is connected via a network (e.g., the Internet) to system200or is self-contained as part of display device205(e.g., physically located inside display device205). In some embodiments, display device205is used to create mixed reality by adding in a view of the real surroundings. Thus, display device205and system200described here can deliver augmented reality, virtual reality, and mixed reality.

In some embodiments, as shown inFIG.1, display device205is a head-mounted display that presents media to a user. Examples of media presented by display device205include one or more images, video, audio, or some combination thereof. In some embodiments, audio is presented via an external device (e.g., speakers and/or headphones) that receives audio information from display device205, console210, or both, and presents audio data based on the audio information. In some embodiments, display device205immerses a user in an augmented environment.

In some embodiments, display device205also acts as an augmented reality (AR) headset. In these embodiments, display device205augments views of a physical, real-world environment with computer-generated elements (e.g., images, video, sound, etc.). Moreover, in some embodiments, display device205is able to cycle between different types of operation. Thus, display device205operate as a virtual reality (VR) device, an augmented reality (AR) device, as glasses or some combination thereof (e.g., glasses with no optical correction, glasses optically corrected for the user, sunglasses, or some combination thereof) based on instructions from application engine255.

Display device205includes electronic display215, one or more processors216, eye tracking module217, adjustment module218, one or more locators220, one or more position sensors225, one or more position cameras222, memory228, inertial measurement unit (IMU)230, one or more reflective elements260or a subset or superset thereof (e.g., display device205with electronic display215, one or more processors216, and memory228, without any other listed components). Some embodiments of display device205have different modules than those described here. Similarly, the functions can be distributed among the modules in a different manner than is described here.

One or more processors216(e.g., processing units or cores) execute instructions stored in memory228. Memory228includes high-speed random access memory, such as DRAM, SRAM, DDR RAM or other random access solid state memory devices; and may include non-volatile memory, such as one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, or other non-volatile solid state storage devices. Memory228, or alternately the non-volatile memory device(s) within memory228, includes a non-transitory computer readable storage medium. In some embodiments, memory228or the computer readable storage medium of memory228stores programs, modules and data structures, and/or instructions for displaying one or more images on electronic display215.

Electronic display215displays images to the user in accordance with data received from console210and/or processor(s)216. In various embodiments, electronic display215may comprise a single adjustable display element or multiple adjustable display elements (e.g., a display for each eye of a user). In some embodiments, electronic display215is configured to display images to the user by projecting the images onto one or more reflective elements260.

In some embodiments, the display element includes one or more light emission devices and a corresponding array of spatial light modulators. A spatial light modulator is an array of electro-optic pixels, opto-electronic pixels, some other array of devices that dynamically adjust the amount of light transmitted by each device, or some combination thereof. These pixels are placed behind one or more lenses. In some embodiments, the spatial light modulator is an array of liquid crystal based pixels in an LCD (a Liquid Crystal Display). Examples of the light emission devices include: an organic light emitting diode, an active-matrix organic light-emitting diode, a light emitting diode, some type of device capable of being placed in a flexible display, or some combination thereof. The light emission devices include devices that are capable of generating visible light (e.g., red, green, blue, etc.) used for image generation. The spatial light modulator is configured to selectively attenuate individual light emission devices, groups of light emission devices, or some combination thereof. Alternatively, when the light emission devices are configured to selectively attenuate individual emission devices and/or groups of light emission devices, the display element includes an array of such light emission devices without a separate emission intensity array. In some embodiments, electronic display215projects images to one or more reflective elements260, which reflect at least a portion of the light toward an eye of a user.

One or more lenses direct light from the arrays of light emission devices (optionally through the emission intensity arrays) to locations within each eyebox and ultimately to the back of the user's retina(s). An eyebox is a region that is occupied by an eye of a user located proximity to display device205(e.g., a user wearing display device205) for viewing images from display device205. In some cases, the eyebox is represented as a 10 mm×10 mm square. In some embodiments, the one or more lenses include one or more coatings, such as anti-reflective coatings.

In some embodiments, the display element includes an infrared (IR) detector array that detects IR light that is retro-reflected from the retinas of a viewing user, from the surface of the corneas, lenses of the eyes, or some combination thereof. The IR detector array includes an IR sensor or a plurality of IR sensors that each correspond to a different position of a pupil of the viewing user's eye. In alternate embodiments, other eye tracking systems may also be employed. As used herein, IR refers to light with wavelengths ranging from 700 nm to 1 mm including near infrared (NIR) ranging from 750 nm to 1500 nm.

Eye tracking module217determines locations of each pupil of a user's eyes. In some embodiments, eye tracking module217instructs electronic display215to illuminate the eyebox with IR light (e.g., via IR emission devices in the display element).

A portion of the emitted IR light will pass through the viewing user's pupil and be retro-reflected from the retina toward the IR detector array, which is used for determining the location of the pupil. Alternatively, the reflection off of the surfaces of the eye is used to also determine location of the pupil. The IR detector array scans for retro-reflection and identifies which IR emission devices are active when retro-reflection is detected. Eye tracking module217may use a tracking lookup table and the identified IR emission devices to determine the pupil locations for each eye. The tracking lookup table maps received signals on the IR detector array to locations (corresponding to pupil locations) in each eyebox. In some embodiments, the tracking lookup table is generated via a calibration procedure (e.g., user looks at various known reference points in an image and eye tracking module217maps the locations of the user's pupil while looking at the reference points to corresponding signals received on the IR tracking array). As mentioned above, in some embodiments, system200may use other eye tracking systems than the embedded IR one described herein.

Adjustment module218generates an image frame based on the determined locations of the pupils. In some embodiments, this sends a discrete image to the display that will tile subimages together thus a coherent stitched image will appear on the back of the retina. Adjustment module218adjusts an output (i.e. the generated image frame) of electronic display215based on the detected locations of the pupils. Adjustment module218instructs portions of electronic display215to pass image light to the determined locations of the pupils. In some embodiments, adjustment module218also instructs the electronic display to not pass image light to positions other than the determined locations of the pupils. Adjustment module218may, for example, block and/or stop light emission devices whose image light falls outside of the determined pupil locations, allow other light emission devices to emit image light that falls within the determined pupil locations, translate and/or rotate one or more display elements, dynamically adjust curvature and/or refractive power of one or more active lenses in the lens (e.g., microlens) arrays, or some combination thereof.

Optional locators220are objects located in specific positions on display device205relative to one another and relative to a specific reference point on display device205. A locator220may be a light emitting diode (LED), a corner cube reflector, a reflective marker, a type of light source that contrasts with an environment in which display device205operates, or some combination thereof. In embodiments where locators220are active (i.e., an LED or other type of light emitting device), locators220may emit light in the visible band (e.g., about 500 nm to 750 nm), in the infrared band (e.g., about 750 nm to 1 mm), in the ultraviolet band (about 100 nm to 500 nm), some other portion of the electromagnetic spectrum, or some combination thereof.

In some embodiments, locators220are located beneath an outer surface of display device205, which is transparent to the wavelengths of light emitted or reflected by locators220or is thin enough to not substantially attenuate the wavelengths of light emitted or reflected by locators220. Additionally, in some embodiments, the outer surface or other portions of display device205are opaque in the visible band of wavelengths of light. Thus, locators220may emit light in the IR band under an outer surface that is transparent in the IR band but opaque in the visible band.

IMU230is an electronic device that generates calibration data based on measurement signals received from one or more position sensors225. Position sensor225generates one or more measurement signals in response to motion of display device205. Examples of position sensors225include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of IMU230, or some combination thereof. Position sensors225may be located external to IMU230, internal to IMU230, or some combination thereof.

Based on the one or more measurement signals from one or more position sensors225, IMU230generates first calibration data indicating an estimated position of display device205relative to an initial position of display device205. For example, position sensors225include multiple accelerometers to measure translational motion (forward/back, up/down, left/right) and multiple gyroscopes to measure rotational motion (e.g., pitch, yaw, roll). In some embodiments, IMU230rapidly samples the measurement signals and calculates the estimated position of display device205from the sampled data. For example, IMU230integrates the measurement signals received from the accelerometers over time to estimate a velocity vector and integrates the velocity vector over time to determine an estimated position of a reference point on display device205. Alternatively, IMU230provides the sampled measurement signals to console210, which determines the first calibration data. The reference point is a point that may be used to describe the position of display device205. While the reference point may generally be defined as a point in space; however, in practice the reference point is defined as a point within display device205(e.g., a center of IMU230).

In some embodiments, IMU230receives one or more calibration parameters from console210. As further discussed below, the one or more calibration parameters are used to maintain tracking of display device205. Based on a received calibration parameter, IMU230may adjust one or more IMU parameters (e.g., sample rate). In some embodiments, certain calibration parameters cause IMU230to update an initial position of the reference point so it corresponds to a next calibrated position of the reference point. Updating the initial position of the reference point as the next calibrated position of the reference point helps reduce accumulated error associated with the determined estimated position. The accumulated error, also referred to as drift error, causes the estimated position of the reference point to “drift” away from the actual position of the reference point over time.

Imaging device235generates calibration data in accordance with calibration parameters received from console210. Calibration data includes one or more images showing observed positions of locators220that are detectable by imaging device235. In some embodiments, imaging device235includes one or more still cameras, one or more video cameras, any other device capable of capturing images including one or more locators220, or some combination thereof. Additionally, imaging device235may include one or more filters (e.g., used to increase signal to noise ratio). Imaging device235is configured to optionally detect light emitted or reflected from locators220in a field of view of imaging device235. In embodiments where locators220include passive elements (e.g., a retroreflector), imaging device235may include a light source that illuminates some or all of locators220, which retro-reflect the light towards the light source in imaging device235. Second calibration data is communicated from imaging device235to console210, and imaging device235receives one or more calibration parameters from console210to adjust one or more imaging parameters (e.g., focal length, focus, frame rate, ISO, sensor temperature, shutter speed, aperture, etc.).

In some embodiments, display device205optionally includes one or more reflective elements260. In some embodiments, electronic display device205optionally includes a single reflective element260or multiple reflective elements260(e.g., a reflective element260for each eye of a user). In some embodiments, electronic display device215projects computer-generated images on one or more reflective elements260, which, in turn, reflect the images toward an eye or eyes of a user. The computer-generated images include still images, animated images, and/or a combination thereof. The computer-generated images include objects that appear to be two-dimensional and/or three-dimensional objects. In some embodiments, one or more reflective elements260are partially transparent (e.g., the one or more reflective elements260have a transmittance of at least 15%, 20%, 25%, 30%, 35%, 50%, 55%, or 50%), which allows transmission of ambient light. In such embodiments, computer-generated images projected by electronic display215are superimposed with the transmitted ambient light (e.g., transmitted ambient image) to provide augmented reality images.

Input interface240is a device that allows a user to send action requests to console210. An action request is a request to perform a particular action. For example, an action request may be to start or end an application or to perform a particular action within the application. Input interface240may include one or more input devices. Example input devices include: a keyboard, a mouse, a game controller, data from brain signals, data from other parts of the human body, or any other suitable device for receiving action requests and communicating the received action requests to console210. An action request received by input interface240is communicated to console210, which performs an action corresponding to the action request. In some embodiments, input interface240may provide haptic feedback to the user in accordance with instructions received from console210. For example, haptic feedback is provided when an action request is received, or console210communicates instructions to input interface240causing input interface240to generate haptic feedback when console210performs an action.

Console210provides media to display device205for presentation to the user in accordance with information received from one or more of: imaging device235, display device205, and input interface240. In the example shown inFIG.2, console210includes application store245, tracking module250, and application engine255. Some embodiments of console210have different modules than those described in conjunction withFIG.2. Similarly, the functions further described herein may be distributed among components of console210in a different manner than is described here.

When application store245is included in console210, application store245stores one or more applications for execution by console210. An application is a group of instructions, that when executed by a processor, is used for generating content for presentation to the user. Content generated by the processor based on an application may be in response to inputs received from the user via movement of display device205or input interface240. Examples of applications include: gaming applications, conferencing applications, video playback application, or other suitable applications.

When tracking module250is included in console210, tracking module250calibrates system200using one or more calibration parameters and may adjust one or more calibration parameters to reduce error in determination of the position of display device205. For example, tracking module250adjusts the focus of imaging device235to obtain a more accurate position for observed locators on display device205. Moreover, calibration performed by tracking module250also accounts for information received from IMU230. Additionally, if tracking of display device205is lost (e.g., imaging device235loses line of sight of at least a threshold number of locators220), tracking module250re-calibrates some or all of system200.

In some embodiments, tracking module250tracks movements of display device205using second calibration data from imaging device235. For example, tracking module250determines positions of a reference point of display device205using observed locators from the second calibration data and a model of display device205. In some embodiments, tracking module250also determines positions of a reference point of display device205using position information from the first calibration data. Additionally, in some embodiments, tracking module250may use portions of the first calibration data, the second calibration data, or some combination thereof, to predict a future location of display device205. Tracking module250provides the estimated or predicted future position of display device205to application engine255.

Application engine255executes applications within system200and receives position information, acceleration information, velocity information, predicted future positions, or some combination thereof of display device205from tracking module250. Based on the received information, application engine255determines content to provide to display device205for presentation to the user. For example, if the received information indicates that the user has looked to the left, application engine255generates content for display device205that mirrors the user's movement in an augmented environment. Additionally, application engine255performs an action within an application executing on console210in response to an action request received from input interface240and provides feedback to the user that the action was performed. The provided feedback may be visual or audible feedback via display device205or haptic feedback via input interface240.

FIG.3is an isometric view of display device300in accordance with some embodiments. In some other embodiments, display device300is part of some other electronic display (e.g., a digital microscope, a head-mounted display device, etc.). In some embodiments, display device300includes light emission device310and an optical assembly330, which may include one or more lenses and/or other optical components. In some embodiments, display device300also includes an IR detector array.

Light emission device310emits image light and optional IR light toward the viewing user. Light emission device310includes one or more light emission components that emit light in the visible light (and optionally includes components that emit light in the IR). Light emission device310may include, e.g., an array of LEDs, an array of microLEDs, an array of organic LEDs (OLEDs), an array of superluminescent LEDs (sLEDS) or some combination thereof.

In some embodiments, light emission device310includes an emission intensity array (e.g., a spatial light modulator) configured to selectively attenuate light emitted from light emission device310. In some embodiments, the emission intensity array is composed of a plurality of liquid crystal cells or pixels, groups of light emission devices, or some combination thereof. Each of the liquid crystal cells is, or in some embodiments, groups of liquid crystal cells are, addressable to have specific levels of attenuation. For example, at a given time, some of the liquid crystal cells may be set to no attenuation, while other liquid crystal cells may be set to maximum attenuation. In this manner, the emission intensity array is able to provide image light and/or control what portion of the image light is passed to the optical assembly330. In some embodiments, display device300uses the emission intensity array to facilitate providing image light to a location of pupil350of eye340of a user, and minimize the amount of image light provided to other areas in the eyebox.

The optical assembly330includes one or more lenses. The one or more lenses in optical assembly330receive modified image light (e.g., attenuated light) from light emission device310, and direct the modified image light to a location of pupil350. The optical assembly330may include additional optical components, such as color filters, mirrors, etc.

An optional IR detector array detects IR light that has been retro-reflected from the retina of eye340, a cornea of eye340, a crystalline lens of eye340, or some combination thereof. The IR detector array includes either a single IR sensor or a plurality of IR sensitive detectors (e.g., photodiodes). In some embodiments, the IR detector array is separate from light emission device array310. In some embodiments, the IR detector array is integrated into light emission device array310.

In some embodiments, light emission device310including an emission intensity array make up a display element. Alternatively, the display element includes light emission device310(e.g., when light emission device array310includes individually adjustable pixels) without the emission intensity array. In some embodiments, the display element additionally includes the IR array. In some embodiments, in response to a determined location of pupil350, the display element adjusts the emitted image light such that the light output by the display element is refracted by one or more lenses toward the determined location of pupil350, and not toward other locations in the eyebox.

In some embodiments, display device300includes one or more broadband sources (e.g., one or more white LEDs) coupled with a plurality of color filters, in addition to, or instead of, light emission device310.

FIG.4Ais a schematic diagram illustrating a cross-sectional view (or a side view) of a beam steerer400in accordance with some embodiments. Beam steerer400includes a stack (e.g., stack410) of polarization-selective gratings (e.g., polarization-selective gratings406and408) and tunable retarders (e.g., tunable retarders402and404) and holographic optical element (HOE)412. InFIG.4A, each polarization-selective grating is coupled with a tunable retarder. For example, stack410inFIG.4Aincludes polarization-selective gratings406and408coupled with respective tunable retarders402and404. In some embodiments, stack410includes one or more polarization-selective gratings-tunable retarder pairs (e.g., 1, 2, 3, 4, or 5 pairs). As shown, tunable retarders402and404, polarization-selective gratings406and408, and HOE412are disposed parallel or substantially parallel to each other (e.g., forming an angle of 5 degrees or less, 10 degrees or less, 15 degrees or less, or 20 degrees or less). In some embodiments, a polarization-selective grating is in direct contact with a respective tunable retarder. Alternatively, the polarization-selective grating is separate from the respective tunable retarder. In some embodiments, all components of beam steerer400are in direct contact with their respective adjacent components such that beam steerer400forms a continuous stack. For example, as shown inFIG.4A, polarization-selective grating406is in direct contact with tunable retarders402and404and polarization-selective grating408is in direct contact with tunable retarder404and HOE412. Alternatively, all or some of the components of beam steerer400are separate from their adjacent components (e.g., polarization-selective grating406may be separated from tunable retarder402and tunable retarder404).

HOE412includes a holographically recorded medium (e.g., a holographic film). HOE412is configured to project (e.g., by reflecting) a plurality of light patterns depending on, for example, an incident angle of light illuminating HOE412. In some embodiments, HOE412receives light in a first incident angle range and projects the light as a first light pattern, and receives light in a second incident angle range distinct from the first incident angle and projects the light as a second light pattern distinct from the first light pattern. In some embodiments, the first light pattern and the second light pattern are distinct and mutually exclusive. For example, HOE412receives light only at a particular incident angle range at a time (e.g., at a first incident angle range or at second incident angle range) and projects the received light as a particular light pattern (e.g., as the first light pattern or the second light pattern). In some embodiments, the first light pattern is directed toward a first region of an eyebox (e.g., an area that is occupied by eye340inFIG.3) and the second light pattern is directed toward a second region distinct from (and mutually exclusive to) the first region of the eyebox.

Tunable retarders402and404(e.g., tunable half-wave plates) are switchable between two or more distinct states. In some embodiments, tunable retarders402and404include liquid crystals (e.g., nematic liquid crystals or chiral nematic liquid crystals). The liquid crystals are switchable between distinct states (e.g., two states) by, for example, altering a voltage applied across tunable retarders402and404. An applied voltage controls orientation and/or alignment of liquid crystals. In some embodiments, while a first voltage differential is applied across a tunable retarder, the liquid crystals (and the tunable retarder containing the liquid crystals) are in a first state, and while a second voltage differential (e.g., no voltage differential) distinct from the first voltage differential is applied across the tunable retarder, the liquid crystals (and the tunable retarder containing the liquid crystals) are in a second state distinct from the first state. In some embodiments, while a third voltage differential distinct from the first voltage differential and the second voltage differential is applied across the tunable retarder, the liquid crystals (and the tunable retarder containing the liquid crystals) are in a third state distinct from the first state and the second state. The first state, the second state, and the third state are distinct from each other. The state of the liquid crystals (and the corresponding state of the tunable retarder) determines how the tunable retarder interacts with incident light. Tunable retarders402and404may independently modulate polarization of light passing through tunable retarders402and404. For example, a tunable retarder may operate as substrate with no polarization retardation while the tunable retarder is in the first state (e.g., an “off” state) and operate as a half-wave plate while the tunable retarder is in the second state (e.g., an “on” state). As a result, while the tunable retarder is in the first state, the tunable retarder does not modify the polarization of the light transmitted through the tunable retarder and while the tunable retarder is in the second state, the tunable retarder modifies the polarization of the light transmitted through the tunable retarder (e.g., by changing handedness of circularly polarized light). Alternatively, a tunable retarder may operate as a half-wave plate while the tunable retarder is in the first state (e.g., an “off” state) and operate as a substrate with no polarization retardation while the tunable retarder is in the second state (e.g., an “on” state).

In some embodiments, a polarization-selective optical element (e.g., polarization-selective grating406and408) is a thin film coated on a surface of a respective tunable retarder (e.g., tunable retarders402and404).

In some embodiments, at least one of polarization-selective gratings406and408is a polarization volume hologram (PVH) grating (e.g., PVH grating1000described with respect toFIGS.10A-10D). A PVH grating is selective with respect to polarization handedness, incident angle, and/or wavelength range of light incident thereon. For example, a PVH grating may transmit light having a first circular polarization and does not change its direction or polarization (regardless of its incident angle or wavelength) and redirect (e.g., diffract) light having a second circular polarization that is within a particular range of incident angles (e.g., orthogonal to the first circular polarization) and within a particular range of wavelengths while converting the polarization of the redirected light to the first circular polarization (e.g., the first circular polarization corresponds to right-handed circular polarization and the second circular polarization corresponds to left-handed circular polarization, or vice versa). In some embodiments, the PVH grating does not transmit a substantial portion (e.g., more than 80%, 90%, 95%, or 99%) of light having the second circular polarization that is within the particular range of incident angles and within the particular range of wavelengths. In some embodiments, the PVH grating may transmit light having an incident angle outside the particular range of incident angles (regardless of its polarization or wavelength). In some embodiments, the PVH grating may transmit light having a wavelength outside the particular wavelength range (regardless of its polarization or incident angle). In some embodiments, both polarization-selective gratings406and408are polarization volume hologram (PVH) gratings.

In some embodiments, at least one of polarization-selective gratings406and408is a cholesteric liquid crystal (CLC) grating. Similar to a PVH, a CLC grating is selective with respect to circular polarization, incident angle, and/or wavelength range of light incident thereon. For example, a CLC grating may transmit light having a first circular polarization without changing its direction or polarization and redirect (e.g., diffract) light having a second circular polarization that is orthogonal to the first circular polarization while converting the polarization of the redirected light to the first circular polarization. In some embodiments, both polarization-selective gratings406and408are cholesteric liquid crystal (CLC) gratings.

In some embodiments, at least one of polarization-selective gratings406and408is a switchable Bragg grating including holographic polymer/dispersed liquid crystal materials. In some embodiments, polarization-selective gratings406and408are polarization-selective elements including metasurfaces, polarization-selective elements including resonant structured surfaces, polarization-selective elements including continuous chiral layers, or polarization-selective elements including birefringent materials. In some embodiments, both polarization-selective gratings406and408are switchable Bragg gratings.

Beam steerer400is switchable between different states depending on states of the one or more tunable retarders (e.g., tunable retarders402and404). Each state provides a distinct light pattern reflected off HOE412. A number of states of beam steerer400is determined based at least on a number of tunable retarders in stack410. In some embodiments, the number of states of beam steerer400(with PVH or CLC gratings) equals the number of tunable retarders plus one (e.g., n+1, where n is the number of tunable retarders in stack410). For example, beam steerer400including stack410with two tunable retarders402and404has three (3=2+1) distinct states. The states of beam steerer400are based on a combination of states of tunable retarders402and404. For example, when tunable retarder402is in “off” state and tunable retarder404is in “off” state, beam steerer400is in a first state; when tunable retarder402is in “on” state and tunable retarder404is in “on” state, beam steerer400is in a second state; and when tunable retarder402is in “on” state and tunable retarder404is in “off” state, beam steerer400is in a third state. In some embodiments, a beam steerer state corresponding to tunable retarder402being in “off” state and tunable retarder404being in “on” state may provide light in a same direction as the beam steerer in the first state because of incident angle selectivity of PVH and CLC gratings. Therefore, in some embodiments, beam steerer400with two tunable retarders effectively has three distinct states providing three distinct patterns of light from HOE412. Propagation of light in beam steerer400is described in further detail below with respect toFIGS.7A-7C.

FIG.4Bis a schematic diagram illustrating a cross-sectional view (or a side view) of beam steerer420in accordance with some embodiments. Beam steerer420is similar to beam steerer400described with respect toFIG.4A, except that beam steerer400includes stack430including polarization-selective gratings428and426. In some embodiments, polarization-selective optical elements428and426are Pancharatnam-Berry phase (PBP) gratings (also known as geometric phase gratings) (e.g., PBP gratings1100described with respect toFIGS.11A-11D). A PBP grating is selective with respect to polarization handedness and/or wavelength range of light incident thereon. For example, a PBP grating may diffract light having a first circular polarization in a first direction (e.g., in a direction corresponding to a first positive order of diffraction) and diffract light having a second circular polarization that is orthogonal to the first circular polarization in a second direction that is different from the first direction (e.g., in a direction corresponding to first negative order of diffraction). In addition, the PBP grating converts the polarization of the diffracted light such that light having the first circular polarization is diffracted as light having the second circular polarization and light having the second circular polarization is diffracted as light having the first circular polarization.

In some embodiments, beam steerer420further includes an optional tunable retarder (e.g., tunable retarder422) and an optional retarder424(e.g., a quarter-wave plate). InFIG.4B, tunable retarder422and optional retarder424are parallel to tunable retarders402and404, polarization-selective gratings426and428, and HOE412. In some embodiments, retarder424is in direct contact with HOE412and disposed between tunable retarder422and HOE412. In some embodiments, tunable retarder422is in direct contract with polarization-selective grating428.

Beam steerer420is switchable between different states depending on states of the one or more tunable retarders. A number of states of beam steerer420is determined based at least on a number of tunable retarders in stack430. In some embodiments, the number of states of beam steerer420(with PBP gratings) equals to two to the power of the number of tunable retarders (e.g., 2n, where n is the number of tunable retarders in stack430). For example, beam steerer420including stack430with two tunable retarders402and404has four (4=22) distinct states. For example, when tunable retarder402is in “off” state and tunable retarder404is in “off” state, beam steerer420is in the first state; when tunable retarder402is in “on” state and tunable retarder404is in “on” state, beam steerer420is in the second state; when tunable retarder402is in “on” state and tunable retarder404is in “off” state, beam steerer420is in the third state; and when tunable retarder402is in “off” state and tunable retarder404is in “on” state, beam steerer400is in the fourth state. Each state of beam steerer420provides a distinct light pattern reflected off HOE412. Propagation of light in beam steerer420is described in further detail below with respect toFIGS.8A-8E.

FIGS.5A-5Eare schematic diagrams illustrating cross-sectional views (or side views) of beam steerer500in different modes in accordance with some embodiments. Beam steerer500is similar to beam steerer400described above with respect toFIG.4A, including stack410and HOE412. InFIGS.5A-5E, each pair of a tunable retarder and a polarization-selective grating is illustrated with a single line so as not to obscure other aspects of beam steerer500(e.g., a pair of tunable retarder402and polarization-selective grating406is illustrated with a single line and a pair of tunable retarder404and polarization-selective grating408is illustrated with a separate line).

InFIGS.5A-5E, beam steerer500is optically coupled with spatial light modulator (SLM)502that is positioned away from optical axis501of beam steerer500. In some embodiments, SLM502is positioned away from projection of beam steerer500along optical axis501(e.g., SLM502is positioned diagonally from beam steerer500so that SLM502is not located at least partially within projection of beam steerer500along optical axis501). As described above with respect toFIG.2, a SLM includes an array of electro-optic pixels, opto-electronic pixels, some other array of devices that dynamically adjust the amount or phase of light transmitted by each device, or some combination thereof. SLM502receives light505from a light source (e.g., one or more LEDs, microLEDs, OLEDs, or sLEDS) and projects light505as modulated light506toward beam steerer500.

InFIG.5A, beam steerer500is in a first state (labeled as beam steerer500-A). Beam steerer500-A receives modulated light506and redirects modulated light506as light pattern508-1toward eyebox504such that light pattern508-1from beam steerer500-A illuminates region504-1of eyebox504. As described above with respect toFIG.2, an eyebox is a region to which an image is projected. As a result, an eye located within the eyebox will view images from the display device. In some embodiments, the eyebox corresponds to (or encompasses) an entire area of a pupil of an eye of a user (e.g., pupil350of eye340inFIG.3) at different rotational positions of the eye. Region504-1of eyebox504corresponds to an area of the pupil when the eye is in a first rotational position and light pattern508-1is configured to illuminate region504-1when the eye is in the first rotational position. Region504-1illuminated by beam steerer500is smaller than an area of the entire eyebox. In some embodiments, eyebox504has a diameter of approximately 10 mm (e.g., between 8 mm and 12 mm).

InFIG.5B, beam steerer500is in a second state (labeled as beam steerer500-B). Beam steerer500-B receives modulated light506and redirects modulated light506as light pattern508-2toward eyebox504such that light pattern508-2from beam steerer500-B illuminates region504-2of eyebox504. Region504-2of eyebox504corresponds to an area of the pupil when the eye is in a second rotational position distinct from the first rotational position and light pattern508-2is configured to illuminate region504-2when the eye is in the second rotational position.

InFIG.5C, beam steerer500is in a third state (labeled as beam steerer500-C). Beam steerer500-C receives modulated light506and redirects modulated light506as light pattern508-3toward eyebox504such that light pattern508-3from beam steerer500-C illuminates region504-3of eyebox504. Region504-3of eyebox504corresponds to an area of the pupil when the eye is in a third rotational position distinct from the first and the second rotational positions and light pattern508-3is configured to illuminate region504-3when the eye is in the third rotational position.

In some embodiments, a light pattern formed by HOE412illuminates two or more regions of eyebox504. InFIG.5D, beam steerer500is in a fourth state (labeled as beam steerer500-D). Beam steerer500-D receives modulated light506and redirects modulated light506as light pattern508-4toward eyebox504such that light pattern508-4illuminates region504-4and region504-5of eyebox504. InFIG.5E, beam steerer500is in a fifth state (labeled as beam steerer500-E). Beam steerer500-E receives modulated light506and redirects modulated light506as light pattern508-5toward eyebox504such that light pattern508-5illuminates region504-6and region504-7of eyebox504. In some embodiments, two or more of regions504-1,504-2,504-3,504-4,505-5,504-6, and504-7are distinct from one another. In some embodiments, two or more of regions504-1,504-2,504-3,504-4,505-5,504-6, and504-7are separate from one another. In some embodiments, two or more of regions504-1,504-2,504-3,504-4,505-5,504-6, and504-7partially overlap one another.

InFIGS.5A-5E, eyebox504is represented as a planar area (e.g., eyebox504is a square). However, the light patterns described with respect toFIGS.5A-5Emay also illuminate regions of eyebox504at different depths (e.g., different regions of eyebox504have different distances to beam steerer500) such that eyebox504covers positions of the pupil in three dimensions for multiple rotational positions of the eye.

FIG.6is a schematic diagram illustrating a cross-sectional view of display device600in accordance with some embodiments. Display device600includes beam steerer500, SLM502, and light source602. In some embodiments, light source602includes one or more light emitting devices (e.g., one or more of LEDs, microLEDs, OLEDs, sLEDS, or any combination thereof). In some embodiments, light source602includes an array of light emitting device (e.g., an array of LEDs, and array of microLEDs, an array of OLEDs, an array of sLEDS, or any combination thereof). Light source602outputs light505toward SLM502. SLM502receives light505and projects light505as modulated light506toward beam steerer500. In some embodiments, SLM502includes an array of devices (e.g., pixels) that individually adjust the intensity or phase of light transmitted by each device. Modulated light506includes rays (e.g., diverging rays) originating from individual devices (e.g., pixels) of the array of SLM502. Modulated light506is received by beam steerer500and redirected as light pattern508-4toward eyebox504such that light pattern508-4illuminates regions504-4and504-5of eyebox504.

In some embodiments, beam steerer500of display device600is an optical combiner (e.g., combiner900described with respect toFIG.9) configured to overlap one or more images output by SLM502with a real world view (e.g., ambient light transmitted through beam steerer500).

In some embodiments, display device600also includes eye tracker604(e.g., an IR detector or camera). Eye tracker604is in communication with, or is part of, eye tracking module217described above with respect toFIG.2. Eye tracker604, together with eye tracking module217, is configured to determine a position of a pupil of an eye of a user (e.g., eye340). Eye tracker604detects IR light reflected off surface of eye340and, in accordance with the detected IR light, eye tracking module217determines the position of the pupil of eye340. Consequently, eye tracking module217or processor(s)216in communication with eye tracking module217instructs beam steerer500to switch between different states so that a light pattern projected from HOE412illuminates a region of eyebox504corresponding to the position of the pupil of eye340.

In some embodiments, as shown inFIG.6, polarization-selective gratings406and408are configured to steer light impinging on polarization-selective gratings406and408at a large incident angle (e.g., an incident angle greater than 30 degrees, 40 degrees, 45 degrees, 50 degrees, or 60 degrees). Thus, an ambient light impinging on polarization-selective gratings406and408at a small incident angle (e.g., an incident angle less than 30 degrees, 40 degrees, 45 degrees, 50 degrees, or 60 degrees) is not steered by polarization-selective gratings406and408. Thus, when beam steerer600is used as a combiner in a head-mounted display, beam steerer600may transmit the ambient light without steering the ambient light.

FIGS.7A-7Care schematic diagrams illustrating propagation of light in beam steerer400in accordance with some embodiments. As described above, beam steerer400includes HOE412optically coupled with stack410including tunable retarder402, polarization-selective grating406, tunable retarder404, and polarization-selective grating408. Beam steerer400is switchable among three states, indicated as beam steerers400-A,400-B, and400-C inFIGS.7A,7B, and7C, respectively. The state of beam steerer400depends on a combination of states of tunable retarders402and404. Tunable retarders402and404are individually switchable between two distinct states, an “off” state and an “on” state. Tunable retarders402and404in the “off” state are labeled as tunable retarders402-1and404-1, and tunable retarders402and404in the “on” state are labeled as tunable retarders402-2and402-2. Tunable retarders402and404are switchable between the different states by, for example, turning an applied voltage on and off. Tunable retarders402-1and404-1(in the first state) transmit light having circular polarization without changing the polarization and tunable retarders402-2and402-2(in the second state) transmit light having circular polarization while changing handedness of the circular polarization (e.g., right-handed circular polarization is converted to left-handed circular polarization and vice versa).

InFIGS.7A-7C, polarization-selective grating406is configured to redirect (e.g., diffract) light having a first circular polarization and an incident angle within a first incident angle range while transmitting light having a second circular polarization or an incident angle outside the first incident angle range (or both). Polarization selective grating408is configured to redirect light having the first circular polarization and an incident angle within a second incident angle range while transmitting light having the second circular polarization or an incident angle outside the second incident angle range (or both). In some embodiments, polarization-selective gratings406and408have a same angle of diffraction (e.g., light having a first incident angle is diffracted in a first direction). In some embodiments, polarization-selective gratings406and408have distinct angles of diffractions (e.g., light having the first incident angle is diffracted in the first direction by polarization-selective grating406and in a distinct second direction by polarization-selective grating408). The second circular polarization is orthogonal to the first circular polarization.

It is noted that inFIGS.7A-7C,8A-8E, and9, polarization of light is annotated with universal annotations that do not take into account a propagation direction of a respective ray (e.g., the right-handed circularly polarized light is annotated with a counter-clockwise arrow regardless of the propagation direction of light, and the left-handed circularly polarized light is annotated with a clockwise arrow regardless of the propagation direction of light). It is also noted thatFIGS.7A-7CandFIGS.8A-8Eare described independently of each other. For example, a first direction inFIGS.7A-7Cis not necessarily a same direction as a first direction inFIGS.8A-8E.

InFIG.7A, beam steerer400in the first state (e.g., beam steerer400-A) has tunable retarder402and tunable retarder404in the “off” state, labeled as tunable retarders402-1and404-1. Tunable retarder402-1receives light700-A in a first direction and transmits light700-A having the first circular polarization without changing its polarization. Polarization selective grating406receives light700-A having the first circular polarization and transmits light700-A as light700-B without changing the polarization or direction of the light. Tunable retarder404-1transmits light700-B having the first circular polarization without changing its polarization. Polarization selective grating408receives light700-B having the first circular polarization and transmits light700-B as light700-C without changing the polarization or direction of the light. Light700-C is incident on HOE412at an incident angle having value A (e.g., Angle A inFIG.7A). HOE412is configured to project light700-C having incident angle A as a first light pattern (e.g., light pattern508-1inFIG.5A).

InFIG.7B, beam steerer400in the second state (e.g., beam steerer400-B) has tunable retarder402and tunable retarder404in the “on” state, indicated as tunable retarders402-2and404-2. Tunable retarder402-2receives light700-A in the first direction and transmits light700-A having the first circular polarization while changing the polarization from the first circular polarization to the second circular polarization. Polarization selective grating406receives light700-A having the second circular polarization and redirects light700-A as light700-D in a second direction distinct from the first direction. Concurrently, polarization-selective grating406converts the polarization of light700-D from the second circular polarization to the first circular polarization. Tunable retarder404-2receives light700-D in the second direction and transmits light700-D while changing the polarization from the first circular polarization to the second circular polarization. Polarization selective grating408receives light700-D having the second circular polarization and redirects light700-D as light700-E in a third direction distinct from the first and the second directions. Concurrently, polarization-selective grating408converts the polarization of light700-E from the second circular polarization to the first circular polarization. Light700-E is incident on HOE412at an incident angle having value B distinct from value A (e.g., angle B inFIG.7B). HOE412is configured to project light700-B having incident angle B as a second light pattern (e.g., light pattern508-2inFIG.5B).

InFIG.7C, beam steerer400in the third state (e.g., beam steerer400-C) has tunable retarder402-2in the “on” state and tunable retarder404-1in the “off” state. Tunable retarder402-2receives light700-A in the first direction and transmits light700-A having the first circular polarization while changing the polarization from the first circular polarization to the second circular polarization. Polarization selective grating406receives light700-A having the second circular polarization and redirects light700-A as light700-D in the second direction. Concurrently, polarization-selective grating406converts the polarization of light700-D from the second circular polarization to the first circular polarization. Tunable retarder404-1receives light700-D in the second direction and transmits light700-D without changing its polarization. Polarization selective grating408receives light700-D having the first circular polarization and transmits light700-D as light700-F in the second direction without changing its polarization. Light700-F is incident on HOE412at an incident angle having value C distinct from values A and B (e.g., angle C inFIG.7C). HOE412is configured to project light700-F having incident angle C as a third light pattern (e.g., light pattern508-3inFIG.5C).

Additionally, beam steerer400has a state having tunable retarder402-1in the “off” state and tunable retarder404-2in the “on” state. However, in such a state, light700-B having the second circular polarization and propagating in the first direction (e.g., as shown inFIG.7A) impinges on polarization-selective grating408in an incident angle that may be outside the second incident angle range (e.g., in contrast to light700-D impinging on polarization-selective grating408at an angle that is within the second incident angle range). Polarization selective grating408is configured to transmit light700-B without changing its direction or polarization (because the incident angle is outside the second incident angle range). An optical path of light propagating through beam steerer400in such state is similar to the optical path of light700shown inFIG.7A(except for the polarization), and such light is projected by HOE412as the first light pattern (e.g., light pattern508-1inFIG.5A). As a result, beam steerer400having two tunable retarders coupled with respective polarization-selective gratings may have effectively three distinct states projecting three distinct light patters by HOE412(e.g., light patterns508-1,508-2, and508-3).

FIG.7Calso illustrates an ambient light722, which is transmitted through beam steerer400. In beam steerer400with polarization selective gratings406and408configured for large incident angles, ambient light722impinges on polarization selective gratings406and408at small incident angles (e.g., incident angles less than a predefined incident angle range) and is transmitted through polarization selective gratings406and408without steering.

It is understood that the states of beam steerer500described with respect toFIGS.7A-7Care used to describe example operations and configurations of beam steerer500and could be configured by any possible combination of tunable retarders402and404and polarization-selective gratings406an408. For example, polarization-selective grating406may be selective with respect to light having the second circular polarization and polarization-selective grating408may be selective with respect to light having the first circular polarization.

FIGS.8A-8Eare schematic diagrams illustrating propagation of light in beam steerer420in accordance with some embodiments. Operations of tunable retarders402and404, which are described with respect toFIGS.7A-7C, are not repeated herein for brevity. InFIGS.8A-8E, polarization-selective grating426(e.g., a PBP) is configured to redirect (e.g., diffract) light in a first direction having a first circular polarization in a second direction and light in the first direction having a second circular polarization in a third direction distinct from the first and second directions. For example, the second direction corresponds to a first positive order of diffraction and the third direction corresponds to a first negative order of diffraction. Polarization selective grating428is configured to redirect light in the first direction having the first circular polarization in a fourth direction and light in the first direction having the second circular polarization in a fifth direction distinct from the first direction and fourth directions. In some embodiments, polarization-selective gratings426and428have a same angle of diffraction (e.g., the second direction corresponds to the fourth direction and the third direction corresponds to the fifth direction). In some embodiments, polarization-selective gratings426and428have distinct angles of diffractions (e.g., the second direction is distinct from the fourth direction and the third direction is distinct from the fifth direction).

In some embodiments, beam steerer420also includes tunable retarder422and quarter waveplate424so that light transmitted through tunable retarder422and quarter waveplate424toward HOE412has a particular linear polarization (e.g., s polarization). This allows HOE412to provide a light pattern in case HOE412is configured to interact with (and diffract) light having the particular linear polarization (e.g., HOE412is a polarization-sensitive holographic optical element).

InFIG.8A, beam steerer420in the first state (e.g., beam steerer420-A) has tunable retarder402and tunable retarder404in the “off” state (e.g., tunable retarders402-1and404-1). Tunable retarder402-1receives light800-A having the first circular polarization in a first direction and transmits light800-A without changing its polarization. Polarization selective grating426receives light800-A and redirects light800-A as light800-B in a second direction distinct from the first direction while converting the polarization from the first circular polarization to the second circular polarization. Tunable retarder404-1transmits light800-B having the second circular polarization without changing its polarization. Polarization selective grating428receives light800-B and redirects light800-B as light800-C in a third direction while converting the polarization from the second circular polarization to the first circular polarization. In some embodiments, tunable retarder422in the “on” state (e.g., tunable retarder422-2), when included in beam steerer420, transmits light800-C while converting its polarization from the first circular polarization to the second circular polarization, and retarder424(e.g., a quarter waveplate), when included in beam steerer420, converts the polarization of light800-C from the second circular polarization to a linear polarization (e.g., s polarization). Light800-C is incident on HOE412at an incident angle having value D (e.g., Angle D inFIG.8A). HOE412is configured to project light800-D having incident angle D as a first light pattern.

InFIG.8B, beam steerer420in a second state (e.g., beam steerer420-B) has tunable retarder402and tunable retarder404in the “on” state (e.g., tunable retarders402-2and404-2). Tunable retarder402-2receives light800-A having the first circular polarization in the first direction and transmits light800-A while changing the polarization of light800-A from the first circular polarization to the second circular polarization. Polarization selective grating426receives light800-A having the second circular polarization and redirects light800-A as light800-D in a fourth direction distinct from the first and second directions while converting the polarization from the second circular polarization to the first circular polarization. Tunable retarder404-2transmits light800-B while changing the polarization from the first circular polarization to the second circular polarization. Polarization selective grating428receives light800-D having the second circular polarization and redirects light800-D as light800-E in a fifth direction distinct from the fourth direction and the third direction while converting its polarization from the second circular polarization to the first circular polarization. In some embodiments, tunable retarder422in the “on” state (e.g., tunable retarder422-2), when included in beam steerer420, transmits light800-E while converting its polarization from the first circular polarization to the second circular polarization, and retarder424, when included in beam steerer420, converts the polarization of light800-C from the second circular polarization to a linear polarization (e.g., s polarization). Light800-E is incident on HOE412at an incident angle having value E distinct from value D (e.g., Angle E inFIG.8B). HOE412is configured to project light800-E having incident angle D as a second light pattern distinct from the first light pattern projected by beam steerer420-A.

InFIG.8C, beam steerer420in a third state (e.g., beam steerer420-C) has tunable retarder402in the “on” state and tunable retarder404in the “off” state (e.g., tunable retarders402-2and404-1). Tunable retarder402-2receives light800-A having the first circular polarization in the first direction and transmits light800-A while changing the polarization of light800-A from the first circular polarization to the second circular polarization. Polarization selective grating426receives light800-A having the second circular polarization and redirects light800-A as light800-D in the fourth direction while converting the polarization from the second circular polarization to the first circular polarization. Tunable retarder404-1transmits light800-B without changing polarization. Polarization selective grating428receives light800-D having the first circular polarization and redirects light800-D as light800-F in a sixth direction distinct from the third direction and the fifth direction. Concurrently, polarization-selective grating428converts the polarization of light800-F from the first circular polarization to the second circular polarization. In some embodiments, tunable retarder422in the “off” state (e.g., tunable retarder422-1), when included in beam steerer420, transmits light800-F while maintaining its polarization (e.g., the second circular polarization), and retarder424, when included in beam steerer420, converts the polarization of light800-F from the second circular polarization to a linear polarization (e.g., s polarization). Light800-F is incident on HOE412at an incident angle having value F (e.g., Angle F inFIG.8C). Value F is distinct from values D and E. HOE412is configured to project light800-F having incident angle F as a third light pattern distinct from the first light pattern projected by beam steerer420-A and the second light pattern projected by beam steerer420-B.

InFIG.8D, beam steerer420in a fourth state (e.g., beam steerer420-D) has tunable retarder402in the “off” state and tunable retarder404in the “on” state (e.g., tunable retarders402-1and404-2). Tunable retarder402-1receives light800-A having the first circular polarization in the first direction and transmits light800-A without changing its polarization. Polarization selective grating426receives light800-A having the first circular polarization and redirects light800-A as light800-B in the second direction while converting its polarization from the first circular polarization to the second circular polarization. Tunable retarder404-2transmits light800-B while changing its polarization from the second circular polarization to the first circular polarization. Polarization selective grating428receives light800-B having the first circular polarization and redirects light800-B as light800-G in a seventh direction while converting its polarization from the first circular polarization to the second circular polarization. The seventh direction is distinct from the third direction (e.g., light800-C), the fifth direction (e.g., light800-E), and the sixth direction (e.g., light800-F). In some embodiments, tunable retarder422in the “off” state (e.g., tunable retarder422-1), when included in beam steerer420, transmits light800-G while maintaining its polarization (e.g., the second circular polarization), and retarder424, when included in beam steerer420, converts the polarization of light800-G from the second circular polarization to a linear polarization (e.g., s polarization). Light800-G is incident on HOE412at an incident angle having value G (e.g., Angle G inFIG.8D). Value G is distinct from values D, E, and F. HOE412is configured to project light800-G having incident angle G as a fourth light pattern. The fourth light patterns is distinct from the first light pattern projected by beam steerer420-A, the second light pattern projected by beam steerer420-B, and the third light pattern projected by beam steerer420-C.

FIG.8Eillustrates propagation of light in beam steerer820-1in the first state. As explained with respect toFIG.8A, light800-A propagates through beam steerer420-A and is received by HOE412as light800-C at incident angle A.FIG.8Efurther illustrates a ray (e.g., ray802) of the first light pattern that is projected (e.g., reflected) from HOE412toward an eyebox (e.g., eyebox504inFIG.5A). As shown, ray802is directed toward the eyebox via a different optical path than light800-C received by HOE412.

It is understood that the states of a beam steerer (e.g., beam steerer400or beam steerer420described with respect toFIGS.7A-7C and8A-8E, respectively) are distinct and mutually exclusive in that when the beam steerer is in a first state, the beam steerer is not in any other states, and thus, does not project any light pattern other than the first light pattern. For example, in some embodiments, when beam steerer420-A is in the first state, light800-A in a first direction is redirected to a second direction as light800-B at polarization-selective grating426without being directed to any other directions. Furthermore, light800-B in the second direction is redirected to a third direction as light800-C at polarization-selective grating428without being directed to any other directions. Therefore, in some cases, HOE412receives light only at an incident angle D and HOE412projects a first light pattern (e.g., including ray802inFIG.8E) without projecting any other light patterns.

FIG.9is a schematic diagram illustrating propagation of light in combiner900in accordance with some embodiments. Combiner900includes beam steerer420-A (in the first state), retarder902(e.g., a quarter-wave plate), compensator910, and polarizer908. Polarizer908(e.g., an absorptive polarizer) is positioned as an outermost component away from an eye of a user (e.g., the eye of a user illustrated as eyebox504inFIG.6) and a light source (e.g., light source602inFIG.6). Compensator910is positioned between polarizer908and retarder902. Retarder902is positioned between compensator910and HOE412. Polarizer908receives (unpolarized) ambient light912from outside of combiner900and transmits a portion of ambient light912having a second circular polarization while absorbing light having polarization distinct from the second circular polarization. In some embodiments, polarizer908is a combination of a linear absorptive polarizer and a quarter waveplate. Compensator910receives a portion of ambient light912having the second circular polarization from polarizer908and redirects the portion of ambient light912through retarder902toward HOE412. Compensator910includes a stack of polarization-selective gratings and tunable retarders corresponding to a stack of tunable retarders and polarization-selective gratings in beam steerer420-A (e.g., stack430described with respect toFIG.4B). In some embodiments, the stack of polarization-selective gratings and tunable retarders are arranged like a mirror image of the stack of tunable retarders and polarization-selective gratings in beam steerer420-A relative to HOE412. For example, compensator910shown inFIG.9includes tunable retarders932,904, and922and polarization selective gratings926and928. Compensator910is configured to redirect the portion of ambient light912so that the portion of ambient light912, after having transmitted through beam steerer420-A, has a substantially same direction as the direction of ambient light912impinging on polarizer908. For example, angle H1defined by ambient light912and polarizer908is same or substantially same (e.g., within 15 degrees, 10 degrees, 5 degrees, or less) as angle H2defined by ambient light912and tunable retarder402, where tunable retarder402is parallel to polarizer908. In some cases, compensator910reduces optical artifacts (e.g., chromatic aberrations) arising when ambient light912is diffracted by the polarization-selective gratings of beam steerer420.

The beam steering device is also positioned so that at least one of the first light pattern or the second light pattern from the holographic optical element is received by the first polarization-selective optical element at one or more incident angles outside the predefined incident angle range and the at least one of the first light pattern and the second light pattern is transmitted without changing its direction (e.g., light patterns508-1and508-2are transmitted through polarization-selective grating408inFIGS.5A and5B, respectively).

FIGS.10A-10Dare schematic diagrams illustrating polarization volume hologram (PVH) grating1000in accordance with some embodiments. In some embodiments, PVH grating1000corresponds to polarization-selective gratings406and408described with respect toFIG.4A.FIG.10Aillustrates a three dimensional view of PVH grating1000with incoming light1004entering the lens along the z-axis.FIG.10Billustrates an x-y-plane view of PVH grating1000with a plurality of cholesteric liquid crystals (e.g., liquid crystals1002-1and1002-2) with various orientations. The orientations (e.g., represented by azimuthal angles θ) of the liquid crystals are constant along reference line AA′ along the x-axis, as shown inFIG.10Dillustrating a detailed plane view of the liquid crystals along the reference line. The orientations of the liquid crystals inFIG.10Bvary along the y-axis. The pitch defined as a distance along the y-axis at which the azimuth angle of a liquid crystal has rotated 180 degrees is constant throughout the grating.FIG.10Cillustrates a y-z-cross-sectional view of PVH grating1000. PVH grating1000has helical structures1008with helical axes aligned corresponding to the x-axis. The helical structures create a volume grating with a plurality of diffraction planes (e.g., planes1010-1and1010-2) extending across the grating. InFIG.10C, diffraction planes1010-1and1010-2are tilted with respect to the z-axis. Helical structures1008define the polarization selectivity of PVH grating1000, as light with circular polarization handedness corresponding to the helical axes is diffracted while light with circular polarization with the opposite handedness is not diffracted. Helical structures1008also define the wavelength selectivity of PVH grating1000, as light with wavelength close to a helical pitch (e.g., helical pitch1012inFIG.10C) is diffracted while light with other wavelengths is not diffracted.

In some embodiments, polarization-selective gratings406and408described with respect toFIG.4Aare cholesteric liquid crystal (CLC) gratings. A CLC grating has similar optical properties to those described with respect to PVH grating1000. A CLC and PVH both include cholesteric liquid crystals in helical arrangements. CLC grating further includes a photoalignment layer and the CLCs are arranged to helical structures in accordance with the photoalignment layer. In contrast, in a PVH grating CLCs are arranged to helical structures in accordance with holographic recording.

FIGS.11A-11Dare schematic diagrams illustrating Pancharatnam-Berry phase (PBP) grating1100in accordance with some embodiments. In some embodiments, PBP grating1100corresponds to polarization-selective gratings426and428described with respect toFIG.4B.FIG.11Aillustrates a three dimensional view of PBP grating1100with incoming light1104entering the lens along the z-axis.FIG.11Billustrates an x-y-plane view of PBP grating1100showing a plurality of liquid crystals (e.g., liquid crystals1102-1and1102-2) with various orientations in the PBP grating1100. The orientations (i.e., azimuthal angles θ) of the liquid crystals are constant along reference line between B and B′ along the x-axis, as shown inFIG.11Dillustrating a detailed plane view of the liquid crystals along the reference line. The orientations of the liquid crystals inFIG.11Bvary along the y-axis while the pitch defined as a distance along the y-axis at which the azimuth angle of a liquid crystal has rotated 180 degrees is constant throughout the grating.FIG.11Cillustrates an y-z-cross-sectional view of PBP grating1100. As shown inFIG.11C, the orientations of the liquid crystal (e.g., liquid crystal1102-1) remain constant along the z-direction.

In light of these principles, we now turn to certain embodiments.

In accordance with some embodiments, an optical assembly includes a beam steering device and a holographic optical element (e.g., beam steerer400includes stack410and HOE412inFIG.4A). The beam steering device is switchable between different states including a first state and a second state (e.g., beam steerer400-A and400-B inFIGS.7A-7B). The beam steering device includes a first polarization-selective optical element (e.g., polarization-selective grating406) and a first tunable optical retarder (e.g. tunable retarder402) optically coupled with the first polarization-selective optical element. The holographic optical element is positioned relative to the beam steering device for receiving light from the beam steering device (e.g. light506inFIG.5A) and projecting a first light pattern (e.g., light pattern508-1inFIG.5A) while the beam steering device is in the first state and a second light pattern (e.g., light pattern508-2inFIG.5B) distinct from the first light pattern while the beam steering device is in the second state.

In some embodiments, the first polarization-selective optical element is positioned between the first tunable optical retarder and the holographic optical element (e.g., polarization-selective grating406is positioned between tunable retarder402and HOE412inFIG.4A).

In some embodiments, while the beam steering device is in the first state, the first tunable optical retarder transmits light impinging on the first tunable optical retarder without changing its polarization (e.g.,FIG.7A). While the beam steering device is in the second state, the first tunable optical retarder transmits the light impinging on the first tunable optical retarder while converting its polarization (e.g.,FIG.7B).

In some embodiments, the first light pattern from the holographic optical element is configured to illuminate a first region of an eyebox (e.g., region504-1inFIG.5A). The second light pattern from the holographic optical element is configured to illuminate a second region distinct from the first region of the eyebox (e.g., region504-2inFIG.5B).

In some embodiments, the first polarization-selective optical element (e.g., PVH grating1000inFIGS.10A-10D) is configured to receive light having a first polarization and transmit the light having the first polarization toward the holographic optical element in a first direction without changing its direction (e.g.,FIG.7A). The first polarization-selective optical element is configured to receive light having a second polarization and redirect the light having the second polarization toward the holographic optical element in a second direction distinct from the first direction (e.g., by changing its direction) (e.g.,FIG.7B).

In some embodiments, the first polarization-selective optical element is a polarization volume hologram (e.g., PVH grating1000shown inFIGS.10A-10D). In some embodiments, the first polarization-selective optical element is a geometric phase diffractive element (e.g., PBP grating1100shown inFIGS.11A-11D).

In some embodiments, the beam steering device is positioned so that at least one of the light having the first polarization and the light having the second polarization is received by the first polarization-selective optical element at one or more incident angles within a predefined incident angle range (e.g., polarization-selective grating406receives light700-A having a second circular polarization at an incident angle that is within a particular range of incident angles that polarization-selective grating406is configured to redirect, as shown inFIG.7B). The beam steering device is also positioned so that at least one of the first light pattern or the second light pattern from the holographic optical element is received by the first polarization-selective optical element at one or more incident angles outside the predefined incident angle range and the at least one of the first light pattern and the second light pattern is transmitted without changing its direction (e.g., light patterns508-1and508-2are transmitted through polarization-selective grating406inFIGS.5A and5B, respectively).

In some embodiments, the beam steering device also includes a second polarization-selective optical element and a second tunable optical retarder (e.g., polarization-selective grating408and tunable retarder404inFIG.4A). The second tunable optical retarder is optically coupled with the second polarization-selective optical element so that the second tunable optical retarder is positioned between the first polarization-selective optical element and the second polarization-selective optical element.

In some embodiments, the holographic optical element is configured to project a third light pattern distinct from the first light pattern and the second light pattern while the beam steering device is in a third state different from the first state and the second state (e.g.,FIG.5C).

In some embodiments, while the beam steering device is in the first state, the first tunable optical retarder and the second tunable optical retarder are configured to transmit light without converting its polarization, while the beam steering device is in the second state, the first tunable optical retarder and the second tunable optical retarder are configured to convert light having a first polarization to light having a second polarization distinct from the first polarization, and while the beam steering device is in the third state, the first tunable optical retarder is configured to convert light having the first polarization to light having the second polarization and the second tunable optical retarder is configured to transmit light without converting its polarization (e.g.,FIGS.7A-7C).

In some embodiments, the first polarization-selective optical element (e.g., PBP grating1100shown inFIGS.11A-11D) is configured to receive light having a first polarization and redirect the light having the first polarization toward the holographic optical element in a third direction while converting polarization of the light having the first polarization to, for example, a second polarization (e.g.,FIG.8A). The first polarization-selective optical element is also configured to receive light having a second polarization and redirect the light having the second polarization toward the holographic optical element in a fourth direction different from the third direction while converting polarization of the light having the second polarization to, for example, the first polarization (e.g.,FIG.8A).

In some embodiments, the optical assembly further includes an additional tunable optical retarder (e.g., tunable retarder424inFIG.4B) positioned between the holographic optical element and the beam steering device. The additional tunable optical retarder transmits light from the first polarization-selective optical element to the holographic optical element.

In some embodiments, the optical assembly further includes a quarter-wave plate (e.g., retarder424inFIG.4B) positioned between the additional tunable optical retarder and the holographic optical element.

In some embodiments, the beam steering device (e.g., beam steerer420inFIGS.8A-8D) also includes a third polarization-selective optical element and a third tunable optical retarder optically coupled with the third polarization-selective optical element so that the second tunable optical retarder is positioned between the first polarization-selective optical element and the third polarization-selective optical element. The holographic optical element is configured to project a fourth light pattern while the beam steering device is in a fourth state and a fifth light pattern while the beam steering device is in a fifth state, where the first state, the second state, the fourth state, and the fifth state are distinct from one another.

In some embodiments, the optical assembly further includes a compensator including a fourth polarization-selective optical element (e.g., compensator910including one or more polarization-selective gratings, such as polarization-selective grating926as shown inFIG.9). The compensator has a first side and an opposing second side. The first side is facing the holographic optical element. The compensator is configured to receive, through the second side, ambient light propagating toward the first side in a particular direction distinct from the third direction and the fourth direction. The compensator is also configured to redirect the ambient light such that the ambient light, after passing through the holographic optical element and the beam steering device, propagates in the particular direction (e.g., angle H2has a value that is same or substantially same as value of angle H1inFIG.9). In some embodiments, the optical assembly further includes a polarizer and a quarter-wave plate (e.g., polarizer908and retarder902inFIG.9).

In accordance with some embodiments, a display device (e.g., display device600inFIG.6) includes the optical assembly described above (e.g., beam steerer500), a light source (e.g., light source602), and a spatial light modulator (e.g., SLM502). The spatial light modulator is positioned so that the spatial light modulator receives light output by the light source and projects the light toward the optical assembly.

In some embodiments, the light source and the spatial light modulator are positioned away from an optical axis of the optical assembly (e.g., axis501inFIG.6).

In accordance with some embodiments, a beam steering device (e.g., beam steerer400inFIG.4A) is switchable between different states including a first state and a second state. The beam steering device includes a first polarization-selective optical element and a first tunable optical retarder optically coupled with the first polarization-selective optical element so that the beam steering device directs light impinging on the beam steering device into a first direction while in the first state and directs the light impinging on the beam steering device into a second direction distinct from the first direction while in the second state. The beam steering device also includes a holographic optical element (e.g., HOE412) positioned relative to the beam steering device so that the holographic optical element projects light impinging on the holographic optical element as a first light pattern while the beam steering device is in the first state and the light impinging on the holographic optical element as a second light pattern that is distinct from the first light pattern while the beam steering device is in the second state (e.g.,FIGS.5A and5B).

In some embodiments, the beam steering device (e.g., beam steerer40inFIG.4A) further includes a second tunable optical retarder optically coupled with the second polarization-selective optical element, so that the second polarization-selective optical element is positioned between the first tunable optical retarder and the second tunable optical retarder. The holographic optical element is positioned to receive, from the beam steering device in a third state, third light in a third direction distinct from the first and the second direction and project the third light as a third light pattern distinct from the first light pattern and the second light pattern (e.g.,FIGS.5A-5C).

In some embodiments, the holographic optical element is also positioned to receive, from the beam steering device in a fourth state, fourth light in a fourth direction distinct from the first, the second, and the third direction and project the fourth light as a fourth light pattern distinct from the first light pattern, the second light pattern, and the third light pattern.

In accordance with some embodiments, a method is performed at an optical assembly (e.g., beam steerer500inFIGS.5A-5E) including a holographic optical element and a beam steering device switchable between different states including a first state and a second state. The beam steering device includes a first polarization-selective optical element and a first tunable optical retarder optically coupled with the first polarization-selective optical element. The method includes receiving, by the holographic optical element, light from the beam steering device. The method also includes projecting, by the holographic optical element, a first light pattern while the beam steering device is in the first state and a second light pattern distinct from the first light pattern while the beam steering device is in the second state.

In some embodiments, the method further includes transmitting, while the beam steering device is in the first state, by the first tunable optical retarder, light impinging on the first tunable optical retarder without changing its polarization (e.g.,FIG.7A). The method also includes transmitting, while the beam steering device is in the second state, by the first tunable optical retarder, the light impinging on the first tunable optical retarder while converting its polarization (e.g.,FIG.7B).

In some embodiments, the method further includes illuminating a first region of an eyebox with the first light pattern from the holographic optical element and illuminating a second region distinct from the first region with the second light pattern from the holographic optical element (e.g., regions504-1and504-2inFIGS.5A and5B, respectively).

In some embodiments, the method includes receiving, by the first polarization-selective optical element, light having a first polarization and transmitting the light having the first polarization toward the holographic optical element in a first direction without changing its direction (e.g.,FIG.7A). The method also includes receiving, by the first polarization-selective optical element, light having a second polarization and redirecting the light having the second polarization toward the holographic optical element in a second direction distinct from the first direction (e.g., by changing its direction) (e.g.,FIG.7B).

Although various drawings illustrate operations of particular components or particular groups of components with respect to one eye, a person having ordinary skill in the art would understand that analogous operations can be performed with respect to the other eye or both eyes. For brevity, such details are not repeated herein.

Although some of various drawings illustrate a number of logical stages in a particular order, stages which are not order dependent may be reordered and other stages may be combined or broken out. While some reordering or other groupings are specifically mentioned, others will be apparent to those of ordinary skill in the art, so the ordering and groupings presented herein are not an exhaustive list of alternatives. Moreover, it should be recognized that the stages could be implemented in hardware, firmware, software or any combination thereof.