EP4643171A1

EP4643171A1 - Tunable grating for time multiplexed full color augmented reality waveguide

Info

Publication number: EP4643171A1
Application number: EP23712686.7A
Authority: EP
Inventors: Qinglan Huang
Original assignee: Google LLC
Current assignee: Google LLC
Priority date: 2023-03-02
Filing date: 2023-03-02
Publication date: 2025-11-05
Also published as: WO2024181982A1

Abstract

A display system includes a waveguide with tunable waveguide gratings having a pitch (i.e., a distance between adjacent grating features) that can be adjusted to optimize efficiency for each color of light and a light engine to time multiplex projection of each color of a frame synchronously with the grating adjustments. Light of each color of a frame is projected toward the waveguide while the gratings are tuned to the projected color, and the multiplexing frequency is higher than the human vision refresh rate, such that the discontinuity in projection of the different colors of light is not noticeable.

Description

TUNABLE GRATING FOR TIME MULTIPLEXED FULL COLOR AUGMENTED REALITY WAVEGUIDE

BACKGROUND

[0001] Wearable electronic eyewear devices include optical systems that magnify a display image and deliver a virtual image into the field of view (FOV) of a user. In some cases, wearable electronic eyewear devices also allow the user to see the outside world through a lens or see-through eyepiece. Some wearable electronic eyewear devices incorporate a near-to-eye optical system to display content to the user. For example, some eyewear display designs include a micro-display (“display”) positioned in a temple or rim region of a head wearable frame like a conventional pair of eyeglasses. The display generates images, such as computer-generated images (CGI), that are conveyed into the FOV of the user by optical elements such as waveguides deployed in the lens (or “optical combiner”) of the head wearable display frame. The wearable electronic eyewear device can therefore serve as a hardware platform for implementing augmented reality (AR) or mixed reality (MR). Different modes of augmented reality include optical see-through augmented reality, video see-through augmented reality, or opaque (VR) modes.

SUMMARY

[0002] In a first embodiment, a method includes tuning an incoupler grating and an outcoupler grating of a waveguide to a first range of wavelengths and, concurrently, projecting display light of the first range of wavelengths for a first frame from a light engine to the waveguide. In some aspects of the first embodiment, the method further includes tuning the incoupler grating and the outcoupler grating of the waveguide to a second range of wavelengths different from the first range of wavelengths and, concurrently, projecting from the light engine display light of the second range of wavelengths for the first frame. In some aspects of the first embodiment, the method also includes tuning the incoupler grating and the outcoupler grating of the waveguide to a third range of wavelengths different from the first and second ranges of wavelengths and, concurrently, projecting from the light engine display light of the third range of wavelengths for the first frame. [0003] In some aspects, a time between projecting display light of the first range of wavelengths for the first frame and projecting display light of the third range of wavelengths for the first frame is shorter than a human vision refresh rate. In other aspects, the method further includes signaling to initiate the tuning and the projecting with a clock signal.

[0004] In some aspects, at least one of the incoupler grating and the outcoupler grating is tunable via a microelectromechanical system. In other aspects, at least one of the incoupler grating and the outcoupler grating comprises a stretchable polymer that is tunable via stretching the polymer.

[0005] In another embodiment, a method includes tuning a pitch of an incoupler grating and an outcoupler grating of a waveguide to each of a plurality of colors at each of a plurality of time phases and projecting display light of a color of the plurality of colors for a first frame at each the plurality of time phases from a light engine to the waveguide.

[0006] In some aspects, tuning the pitch includes tuning the incoupler grating and the outcoupler grating to a first pitch tuned to a first color at a first time phase, tuning the incoupler grating and the outcoupler grating to a second pitch tuned to a second color at a second time phase, and tuning the incoupler grating and the outcoupler grating to a third pitch tuned to a third color at a third time phase.

[0007] In some aspects, projecting display light includes projecting display light of the first color for the first frame at the first time phase, projecting display light of the second color for the first frame at the second time phase, and projecting display light of the third color for the first frame at the third time phase.

[0008] In some aspects, a time between the first time phase, the second time phase, and the third time phase is shorter than a human vision refresh rate. In some aspects, the method further includes signaling to initiate the tuning and the projecting with a clock signal.

[0009] In some aspects, at least one of the incoupler grating and the outcoupler grating is tunable via a microelectromechanical system. In other aspects, at least one of the incoupler grating and the outcoupler grating comprises a stretchable polymer that is tunable via stretching the polymer.

[0010] In another embodiment, a display system includes a waveguide including a tunable incoupler grating and a tunable outcoupler grating. The display system further includes a controller to tune the tunable incoupler grating and the tunable outcoupler grating to each of a plurality of colors at each of a plurality of time phases and a light engine to project display light of one of the plurality of colors for a first frame to the waveguide at each the plurality of time phases.

[0011] In some aspects, the controller is configured to tune the tunable incoupler grating and the tunable outcoupler grating to a first pitch tuned to a first color at a first time phase, tune the tunable incoupler grating and the tunable outcoupler grating to a second pitch tuned to a second color at a second time phase, and tune the tunable incoupler grating and the tunable outcoupler grating to a third pitch tuned to a third color at a third time phase.

[0012] In some aspects, the light engine is configured to project display light of the first color for the first frame at the first time phase, project display light of the second color for the first frame at the second time phase, and project display light of the third color for the first frame at the third time phase.

[0013] In some aspects, a time from a beginning of the first time phase to an end of the third time phase is shorter than a human vision refresh rate. In some aspects, the display system further includes a clock signal to initiate the tuning and the projecting.

[0014] In some aspects, at least one of the tuanble incoupler grating and the tunable outcoupler grating comprises a stretchable polymer that is tunable via stretching the polymer or is tunable via a microelectromechanical system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference symbols in different drawings indicates similar or identical items.

[0016] FIG. 1 shows an example eyewear display system employing a light engine to project multiplexed colors for a frame and a waveguide with gratings that are tunable to each color in accordance with some embodiments.

[0017] FIG. 2 illustrates color non-uniformity of a single waveguide with static gratings.

[0018] FIG. 3 shows an example of a display system with a light engine to project multiplexed colors for a frame and a waveguide with gratings that are tunable to each color in accordance with some embodiments.

[0019] FIG. 4 illustrates a display system with a light engine projecting a different color for a frame at each of a plurality of time phases into a waveguide having gratings that are tuned to each color at each time phase in accordance with some embodiments.

[0020] FIG. 5 illustrates time multiplexing of projection of colors of a frame in accordance with some embodiments.

[0021] FIG. 6 is a flow diagram of a method of tuning incoupler and outcoupler gratings of a waveguide to match corresponding colors of time multiplexed projections of light in accordance with some embodiments.

DETAILED DESCRIPTION

[0022] Eyewear display devices potentially have multiple practical and leisure applications, but the development and adoption of wearable electronic display devices have been limited by constraints imposed by the optics, aesthetics, manufacturing process, thickness, field of view (FOV), and prescription lens limitations of the optical systems used to implement existing display devices. For example, the geometry and physical constraints of conventional designs result in displays having relatively small FOVs and relatively thick optical combiners. [0023] Wearable display devices for presenting AR content typically employ an optical combiner waveguide (also referred to as a “lightguide”) to convey and magnify display light emitted by a display to a user’s eye while also permitting light from the real-world scene to pass through the waveguide to the user’s eye, resulting in the imagery represented by the display light overlaying the real-world scene from the perspective of the user. Typically, the waveguide relies on total internal reflection (TIR) to convey light received from the display via incoupling features at one end of the waveguide to outcoupling features facing the user’s eye on the other end of the waveguide. The outcoupling features are configured to direct light beams from within the waveguide out of the waveguide such that the user perceives the projected light beams as images displayed in a field of view (FOV) area of a display component located in front of a user’s eye, such as a lens of an eyewear display device having the general shape and size of eyeglasses. The light beams exiting from the waveguide then overlap at an eye relief distance from the waveguide, forming a “pupil” within which a virtual image generated by the image source can be viewed.

[0024] A waveguide typically includes three sets of linear gratings - an incoupler grating, an exit pupil expander, and an outcoupler grating. Because diffractive gratings are dispersive, a grating with high efficiency for one part of the color frequency spectrum (e.g., blue light) often has low efficiency for another part of the color frequency spectrum (e.g., red light). To address the differences in efficiency, some designs employ a multi-waveguide architecture in which each color of light is separately guided into a different waveguide in a stack. For example, some designs include a separate waveguide for each of red, blue, and green wavelengths. Taken together, the stack of waveguides combines the light into a full color display. However, a waveguide stack is necessarily thicker than a single waveguide.

[0025] The optical performance of an eyewear display device is an important factor in its design; however, users also care significantly about aesthetics of wearable devices. Independent of their performance limitations, many of the conventional examples of wearable heads-up displays have struggled to find traction in consumer markets because, at least in part, they lack fashion appeal. Thus, it is desirable to integrate thin waveguides in eyewear display devices to achieve the form factor and fashion appeal expected of the eyeglass and sunglass frame industry. Not only are thinner waveguides more aesthetically appealing, they are also lighter.

[0026] Embodiments described herein provide tunable waveguide gratings having a pitch (i.e., a distance between adjacent grating features) that can be adjusted to optimize efficiency for each color of light and a light engine to time multiplex projection of each color of a frame synchronously with the grating adjustments. Light of each color of a frame is projected toward the waveguide while the gratings are tuned to the projected color, and the multiplexing frequency is higher than the human vision refresh rate, such that the discontinuity in projection of the different colors of light is not noticeable.

[0027] To illustrate, during a first time phase, the waveguide gratings are tuned to optimize coupling efficiency for blue light and the light engine projects blue light for a frame toward the waveguide. During a second time phase, the waveguide gratings are tuned to optimize coupling efficiency for green light, and the light engine projects green light for the frame toward the waveguide. During a third time phase, the waveguide gratings are tuned to optimize coupling efficiency for red light, and the light engine projects red light for the frame toward the waveguide. The sum of the durations of all three phases is shorter than the human vision refresh rate, such that the three phases are perceived as occurring simultaneously.

[0028] In some embodiments, the gratings are tunable using a microelectromechanical system (MEMS) or a stretchable polymer. In some embodiments, a clock signal is used to synchronize adjusting the pitch of the waveguide gratings with projecting light of each corresponding color of the frame. For example, the light engine and a controller for the waveguide gratings receive a clock signal that triggers initiation of adjusting the pitch of the waveguide gratings to optimize coupling efficiency for a color and projection light having the color by the light engine. By adjusting the pitch of the gratings to tune the incoupler and outcoupler to different ranges of wavelengths of projected display light, embodiments described herein facilitate higher coupling efficiency and color uniformity for a single waveguide, which has a thinner form factor for implementation in a lens of an eyewear display system. [0029] FIG. 1 illustrates an example eyewear display system 100 (also referred to as display system 100) employing a waveguide with tunable incoupler and outcoupler gratings and a time multiplexed light engine to project different colors of display light during time phases in which the gratings are tuned to couple the projected color into and out of the waveguide in accordance with some embodiments. The display system 100 has a support structure 102 that includes an arm 104, which houses a light engine (e.g., a laser projector, a micro-LED projector, a Liquid Crystal on Silicon (LCOS) projector, or the like), also referred to herein as a microdisplay. The light engine is configured to project images toward the eye of a user via a waveguide, such that the user perceives the projected images as being displayed in a field of view (FOV) area 106 of a display at one or both of spherical lens elements 108, 110. In the depicted embodiment, the display system 100 is a near-eye display system in the form of an eyewear display device in which the support structure 102 is configured to be worn on the head of a user and has a general shape and appearance (that is, form factor) of an eyeglasses (e.g., sunglasses) frame.

[0030] The support structure 102 contains or otherwise includes various components to facilitate the projection of such images toward the eye of the user, such as a light engine and a waveguide. In some embodiments, the support structure 102 further includes various sensors, such as one or more front-facing cameras, rearfacing cameras, other light sensors, motion sensors, accelerometers, and the like. In some embodiments, the support structure 102 includes one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth(TM) interface, a WiFi interface, and the like. Further, in some embodiments, the support structure 102 further includes one or more batteries or other portable power sources for supplying power to the electrical components of the display system 100. In some embodiments, some or all of these components of the display system 100 are fully or partially contained within an inner volume of support structure 102, such as within the arm 104 in region 112 of the support structure 102. It should be noted that while an example form factor is depicted, it will be appreciated that in other embodiments the display system 100 may have a different shape and appearance from the eyeglasses frame depicted in FIG. 1. It should be understood that instances of the term “or” herein refer to the non-exclusive definition of “or”, unless noted otherwise. For example, herein the phrase “X orY” means “either X, orY, or both”. [0031] One or both of the spherical lens elements 108, 110 are used by the display system 100 to provide an augmented reality (AR) display in which rendered graphical content can be superimposed over or otherwise provided in conjunction with a real- world view as perceived by the user through the spherical lens elements 108, 110. For example, a light engine of the display system 100 uses light to form a perceptible image or series of images by projecting the light onto the eye of the user via a projector of the light engine, a waveguide formed at least partially in the corresponding spherical lens element 108 or 110, and one or more optical elements (e.g., one or more scan mirrors, or one or more optical relays, that are disposed between the projector and the waveguide), according to various embodiments.

[0032] One or both of the spherical lens elements 108, 110 includes at least a portion of a waveguide that routes display light received by a tunable incoupler of the waveguide to a tunable outcoupler of the waveguide, which outputs the display light toward an eye of a user of the display system 100. The display light is modulated and projected onto the eye of the user such that the user perceives the display light as an image. In addition, each of the spherical lens elements 108, 110 is sufficiently transparent to allow a user to see through the spherical lens elements to provide a field of view of the user’s real-world environment such that the image appears superimposed over at least a portion of the real-world environment.

[0033] In some embodiments, the projector of the light engine of the display system 100 is a digital light processing-based projector, a scanning laser projector, or any combination of a modulative light source, such as a laser or one or more lightemitting diodes (LEDs), and a dynamic reflector mechanism such as one or more dynamic scanners, reflective panels, or digital light processors (DLRs). In some embodiments, the projector includes a micro-display panel, such as a micro-LED display panel (e.g., a micro-AMOLED display panel, or a micro inorganic LED (i-LED) display panel) or a micro-Liquid Crystal Display (LCD) display panel (e.g., a Low Temperature PolySilicon (LTPS) LCD display panel, a High Temperature PolySilicon (HTPS) LCD display panel, or an In-Plane Switching (IPS) LCD display panel). In some embodiments, the projector includes a Liquid Crystal on Silicon (LCOS) display panel. In some embodiments, a display panel of the projector is configured to output light (representing an image or portion of an image for display) into the waveguide of the display system. The waveguide expands the light and outputs the light toward the eye of the user via the tunable outcoupler.

[0034] The display system 100 may include a processor (not shown) that is communicatively coupled to each of the electrical components in the display system 100, including but not limited to the projector. The processor can be any suitable component which can execute instructions or logic, including but not limited to a micro-controller, microprocessor, multi-core processor, integrated-circuit, ASIC, FPGA, programmable logic device, or any appropriate combination of these components. The display system 100 can include a non-transitory processor- readable storage medium, which may store processor readable instructions thereon, which when executed by the processor can cause the processor to execute any number of functions, including causing the projector to output light representative of display content to be viewed by a user, receiving user input, managing user interfaces, generating display content to be presented to a user, receiving and managing data from any sensors carried by the display system 100, receiving and processing external data and messages, and any other functions as appropriate for a given application. The non-transitory processor-readable storage medium can be any suitable component, which can store instructions, logic, or programs, including but not limited to non-volatile or volatile memory, read only memory (ROM), random access memory (RAM), FLASH memory, registers, magnetic hard disk, optical disk, or any combination of these components. The projector outputs light toward the FOV area 106 of the display system 100 via the waveguide.

[0035] FIG. 2 illustrates color non-uniformity of a projection system 200 having a single waveguide 208 with an incoupler 204 and an outcoupler 206 having static gratings. In some embodiments, the projection system 200 is included in a display system, such as an embodiment of the eyewear display system 100 of FIG. 1. As shown, the projection system 200 includes a light engine 202 and the waveguide 208.

[0036] According to various embodiments, the light engine 202 includes a microdisplay panel that is configured to output display light corresponding to an image or a portion of an image to be displayed by the projection system 200. While the light engine 202 is used to generate light for images to be displayed, in some embodiments, the projection system 200 instead includes a different type of image source, such as a scanning laser projector. In some cases, the light engine 202 includes one or more discrete optical elements such as lenses, mirrors, or the like, configured to change the direction of the display light, to apply an optical function to the display light (e.g., collimation, focusing, or the like), or both. The light engine 202 is configured to project red light 210, green light 212, and blue light 214 for an image such as for a frame of video.

[0037] The term “waveguide,” as used herein, will be understood to mean a combiner using one or more of total internal reflection (TIR), specialized filters, or reflective surfaces, to transfer light from an incoupler (such as the incoupler 204) to an outcoupler (such as the outcoupler 206). In some display applications, the light is a collimated image, and the waveguide transfers and replicates the collimated image to the eye. In general, the terms “incoupler” and “outcoupler” will be understood to refer to any type of optical grating structure, including, but not limited to, diffraction gratings, holograms, holographic optical elements (e.g., optical elements using one or more holograms), volume diffraction gratings, volume holograms, surface relief diffraction gratings, or surface relief holograms. In some embodiments, a given incoupler or outcoupler is configured as a transmissive grating (e.g., a transmissive diffraction grating or a transmissive holographic grating) that causes the incoupler or outcoupler to transmit light and to apply designed optical function(s) to the light during the transmission. In some embodiments, a given incoupler or outcoupler is a reflective grating (e.g., a reflective diffraction grating or a reflective holographic grating) that causes the incoupler or outcoupler to reflect light and to apply designed optical function(s) to the light during the reflection.

[0038] In the illustrated example, each of the incoupler 204 and the outcoupler 206 are formed from diffraction gratings having elements (such as grooves) that are formed in or on material (e.g., silicon, glass, polymer, or the like) of the waveguide 208 via, for example, mechanical techniques (e.g., scoring) or chemical techniques (e.g., lithography). The gratings have a pitch, which is the lateral separation between adjacent grating elements. Light of different wavelengths interacts differently with the gratings. For example, red light 210, which has a relatively long wavelength, is diffracted at a larger angle with respect to a grating having a given pitch, whereas blue light 214, which has a relatively short wavelength, is diffracted at a smaller angle with respect to a grating having the same pitch. Thus, the fixed grating has higher diffraction efficiency for blue light 214 than for red light 210 or green light 212, and blue light 214 has higher pupil replication than red light 210 or green light 212. These effects contribute to low waveguide efficiency for red light 210 and color nonuniformity that negatively impacts the user experience. The low red light efficiency creates a bottleneck for overall waveguide brightness and the color non-uniformity results in a color drift from red at the left of the eyebox to blue at the right of the eye box.

[0039] During operation of the projection system 200, red, green, and blue display light 210, 212, 214 forming an image to be displayed is output by the light engine 202. The red, green, and blue display light 210, 212, 214 passes into the waveguide 208 via the incoupler 204. The incoupler 204 redirects the red, green, and blue display light 210, 212, 214 into the waveguide 208 and toward the outcoupler 206 via TIR. In some cases, an exit pupil expander (not shown) integrated within the waveguide 208 redirects the red, green, and blue display light 210, 212, 214 toward the outcoupler 206 of the waveguide 208, which projects the red, green, and blue display light 210, 212, 214 out of the waveguide 208 and, for example, toward an eye of a user.

[0040] However, due to the differences in the interactions between light of various wavelengths with the fixed pitch gratings of the incoupler 204 and outcoupler 206, light of different colors undergoes a different number of bounces within the waveguide 208, resulting in non-uniformity of colors exiting the waveguide 208 via the outcoupler 206. For example, as illustrated in FIG. 2, red light 210 undergoes six bounces within the waveguide 208, with two of the bounces against the outcoupler 206 at which the red light 210 is coupled out of the waveguide 208 toward the eye of a user. Green light 212, by contrast, undergoes ten bounces within the waveguide 208, with three of the bounces against the outcoupler 206 at which the green light 212 is coupled out of the waveguide 208 toward the eye of the user. Blue light 214, having the shortest wavelength, undergoes the most bounces (26) within the waveguide 208, of which six bounces are against the outcoupler 206, from which the blue light 214 is coupled out of the waveguide 208 toward the eye of the user. Thus, the ratio of red light 210 to green light 212 to blue light 214 exiting the waveguide 208 for the fixed pitch incoupler 204 and outcoupler 206 is approximately 2:3:6.

[0041] To enhance coupling efficiency and color uniformity for all colors in a single waveguide, the waveguide employs tunable gratings that have adjustable pitches to accommodate a range of colors and a light engine to project one color at a time for each frame synchronously with the grating pitch adjustments. For example, FIG. 3 illustrates a display system 300 with a light engine 202 to project multiplexed colors for a frame and a controller 310 to tune waveguide gratings to each color in accordance with some embodiments.

[0042] The display system includes a waveguide 208 having a tunable incoupler 304 and a tunable outcoupler 306. Each of the tunable incoupler 304 and the tunable outcoupler 306 is a diffraction grating that includes a number of features 320 separated by a pitch 322. The pitch 322 of the tunable incoupler 304 and the tunable outcoupler 306 is adjustable (i.e. , can be made smaller or larger) to couple light of different ranges of wavelengths (i.e., colors) into and out of the waveguide 208. For example, to tune the pitch 322 of the tunable incoupler 304 and the tunable outcoupler 306 to couple red light into and out of the waveguide 208, the pitch 322 is made larger, such that the lateral distance between adjacent grating features 320 is larger. To tune the pitch 322 of the tunable incoupler 304 and the tunable outcoupler 306 to couple blue light into and out of the waveguide 208, the pitch 322 is made smaller, such that the lateral distance between adjacent grating features 320 is smaller. For green light, the pitch 322 is set to an intermediate distance between the distance for red light and the distance for blue light.

[0043] In some embodiments, the tunable incoupler 304 and the tunable outcoupler 306 are tuned with a microelectromechanical system (MEMS). In the illustrated example, the tunable incoupler 304 is tuned with MEMS 316 and the tunable outcoupler 306 is tuned with MEMS 318. In some embodiments, the tunable incoupler 304 and the tunable outcoupler 306 are formed from dielectric and deformable viscoelastic material and are electrically tunable by applying different voltages to the dielectric material. In some embodiments, the tunable incoupler 304 and the tunable outcoupler 306 are formed from stretchable polymer that is tunable via stretching the polymer. [0044] The controller 310 sends a control signal 314 to each of the MEMS 316 and the MEMS 318 to initiate adjusting the pitch 322 of the tunable incoupler 304 and the tunable outcoupler 306. In some embodiments, the controller 310 is implemented as hard-coded or programmable logic, one or more processors executing software/firmware instructions, or any combination thereof.

[0045] In some embodiments, the light engine 202 is coupled to a driver or other controller (not shown), which controls the timing of emission of light from light sources (e.g., LEDs) of the light engine 202 in accordance with instructions received by the controller or driver from a computer processor (not shown) coupled thereto to modulate the output light to be perceived as images when output to the retina of the eye of the user. For example, during operation of the display system 300, the light sources of the light engine 202 output display light of selected wavelengths, and the display light is directed to the eye of the user via the waveguide 208. The light engine 202 modulates the respective intensities of each light source of the light engine 202, such that the output display light represents pixels of an image. For example, the intensity of a given light source or group of light sources of the light engine 202 corresponds to the brightness of a corresponding pixel of the image to be projected by the light engine 202.

[0046] In some embodiments, the controller 310 is coupled to the light engine 202, to synchronize projection of display light of selected wavelengths (colors) with adjustment of the pitch 322 of the tunable incoupler 304 and the tunable outcoupler 306. T o coordinate projection of display light of a given color for a frame with tuning of the tunable incoupler 304 and the tunable outcoupler 306 to enhance coupling efficiency of the display light of the color, a clock 312 provides a clock signal 324 to the controller 310 (and, in some embodiments, to the light engine 202). In response to the clock signal 324, the light engine 202 projects display light of a first color while the controller 310 sends a signal 314 to the MEMS 316 and the MEMS 318 to initiate tuning of the tunable incoupler 304 and the tunable outcoupler 306 to a pitch 322 to match the first color during a first time phase. In some embodiments, the controller 310 modulates the voltage of the signal 314 to vary the pitch 322 of the gratings of the tunable incoupler 304 and the tunable outcoupler 306. [0047] At the next clock signal 324, the light engine 202 projects display light of a second color for the frame while the controller 310 sends a signal 314 to the MEMS 316 and the MEMS 318 to initiate tuning of the tunable incoupler 304 and the tunable outcoupler 306 to a pitch 322 to match the second color during a second time phase. The clock 312 then sends another clock signal 324, prompting the light engine 202 to project display light of a third color for the frame while the controller 310 sends a signal 314 to the MEMS 316 and the MEMS 318 to initiate tuning of the tunable incoupler 304 and the tunable outcoupler 306 to a pitch 322 to match the third color during a third time phase. The first, second, and third time phases all occur within a span of time that is shorter than the human vision refresh rate, such that the three phases are perceived as occurring simultaneously.

[0048] FIG. 4 illustrates a display system with a light engine 202 projecting a different color for a frame at each of a plurality of time phases into a waveguide 208 having a tunable incoupler 304 and a tunable outcoupler 306 that are tuned to each color at each time phase in accordance with some embodiments. At a time TO, the clock 312 transmits a clock signal 324 to the controller 310 and to the light engine 202. In response to the clock signal 324, the light engine emits light having a first color (in the illustrated example, blue light 214), and the controller 310 sends a signal 314 to initiate adjusting the tunable incoupler 304 and the tunable outcoupler 306 to have a pitch 422 that is tuned to couple blue light 214 into and out of the waveguide 208.

[0049] At a time T1 , the clock 312 transmits a clock signal 324 to the controller 310 the light engine 202. In response to the clock signal 324, the light engine emits light having a second color (in the illustrated example, green light 212), and the controller 310 sends a signal 314 to initiate adjusting the tunable incoupler 304 and the tunable outcoupler 306 to have a pitch 424 that is tuned to couple green light 212 into and out of the waveguide 208.

[0050] At a time T2, the clock 312 transmits a clock signal 324 to the controller 310 the light engine 202. In response to the clock signal 324, the light engine emits light having a third color (in the illustrated example, red light 210), and the controller 310 sends a signal 314 to initiate adjusting the tunable incoupler 304 and the tunable outcoupler 306 to have a pitch 426 that is tuned to couple red light 210 into and out of the waveguide 208.

[0051] In the illustrated example, the pitch 422 that tunes the tunable incoupler 304 and the tunable outcoupler 306 to blue light 214 is smaller than the pitch 424 that tunes tunable incoupler 304 and the tunable outcoupler 306 to green light 212. In turn, the pitch 424 that tunes the tunable incoupler 304 and the tunable outcoupler 306 to green light 212 is smaller than the pitch 426 that tunes tunable incoupler 304 and the tunable outcoupler 306 to red light 210. By tuning the tunable incoupler 304 and the tunable outcoupler 306 to accommodate blue light 214, green light 212, and red light 210 at respective time phases, the display system achieves a same number of bounces for each of blue light 214, green light 212, and red light 210 within the waveguide 208 and a same number of bounces out of the outcoupler 306, resulting in more efficient coupling of all colors of display light and enhanced color uniformity at an eyebox of the waveguide 208.

[0052] FIG. 5 shows a timing diagram 500 illustrating time multiplexing of projection of colors of display light for a series of frames in accordance with some embodiments. In the illustrated example, at a time TO, the light engine 202 emits blue light 214 for a first frame 510 while the tunable incoupler 304 and the tunable outcoupler 306 have a pitch 422 that is tuned to blue light 214. At a time T1 , the light engine 202 emits green light 212 for the first frame 510 while the tunable incoupler 304 and the tunable outcoupler 306 have a pitch 424 that is tuned to green light 212. At a time T2, the light engine 202 emits red light 210 for the first frame 510 while the tunable incoupler 304 and the tunable outcoupler 306 have a pitch 426 that is tuned to red light 210. In other examples, the order of emission of the colors of display light and tuning of the gratings may be different.

[0053] At a time T3, the light engine 202 emits blue light 214 for a second frame 512 while the tunable incoupler 304 and the tunable outcoupler 306 have a pitch 422 that is tuned to blue light 214. At a time T4, the light engine 202 emits green light 212 for the second frame 512 while the tunable incoupler 304 and the tunable outcoupler 306 have a pitch 424 that is tuned to green light 212. At a time T5, the light engine 202 emits red light 210 for the second frame 512 while the tunable incoupler 304 and the tunable outcoupler 306 have a pitch 426 that is tuned to red light 210. [0054] At a time T6, the light engine 202 emits blue light 214 for a third frame 514 while the tunable incoupler 304 and the tunable outcoupler 306 have a pitch 422 that is tuned to blue light 214. At a time T7, the light engine 202 emits green light 212 for the third frame 514 while the tunable incoupler 304 and the tunable outcoupler 306 have a pitch 424 that is tuned to green light 212. At a time T5, the light engine 202 emits red light 210 for the third frame 514 while the tunable incoupler 304 and the tunable outcoupler 306 have a pitch 426 that is tuned to red light 210.

[0055] Thus, the light engine 202 multiplexes blue, green, and red display light for each frame during the time that the tunable incoupler 304 and the tunable outcoupler 306 are tuned to each respective color. The multiplexing of the colors for each frame occurs faster than the human eye can perceive the changes, such that the emission of light of the three colors appears to occur simultaneously. For example, for a frame rate of 60 frames per second, multiplexing of the three colors for each frame occurs at a rate of approximately 180 Hz.

[0056] FIG. 6 is a flow diagram of a method 600 of tuning incoupler and outcoupler gratings of a waveguide to match corresponding colors of time multiplexed projections of light in accordance with some embodiments. In some embodiments, the method 600 is performed by a display system such as the display system 300 illustrated in FIG. 3.

[0057] At block 602, the controller 310 receives a clock signal 324 from the clock 312. Concurrently, at block 612, the light engine 202 receives the clock signal 324 from the clock 312. At block 604, which marks the beginning of a first time phase TO, the controller 310 initiates adjusting the pitch 322 of the gratings of the tunable incoupler 304 and the tunable outcoupler 306 to accommodate display light of a first range of wavelengths (i.e, a first color). For example, in some embodiments, the tunable incoupler 304 and the tunable outcoupler 306 are adjusted using the MEMS 316, 318. In other embodiments, the gratings of the tunable incoupler 304 and the tunable outcoupler 306 are formed from stretchable polymer or a similar material, and the controller 310 applies a modulated voltage to stretch or contract the pitch of the gratings. [0058] In some embodiments, the controller 310 signals the light engine 202 to indicate that the tunable incoupler 304 and the tunable outcoupler 306 are set for the first color. At block 614, the light engine 202 emits display light of the first color for a current frame. In some embodiments, the light engine 202 emits display light of the first color in response to receiving the indication.

[0059] At block 606, which marks the beginning of a second time phase T1 , the controller 310 initiates adjusting the pitch 322 of the gratings of the tunable incoupler 304 and the tunable outcoupler 306 to accommodate display light of a second range of wavelengths (i.e., a second color). In some embodiments, the controller 310 signals the light engine 202 to indicate that the tunable incoupler 304 and the tunable outcoupler 306 are set for the second color. At block 616, the light engine 202 emits display light of the second color for the current frame. In some embodiments, the light engine 202 emits display light of the second color in response to receiving the indication.

[0060] At block 608, which marks the beginning of a third time phase T2, the controller 310 initiates adjusting the pitch 322 of the gratings of the tunable incoupler 304 and the tunable outcoupler 306 to accommodate display light of a range of wavelengths (i.e., a third color). In some embodiments, the controller 310 signals the light engine 202 to indicate that the tunable incoupler 304 and the tunable outcoupler 306 are set for the third color. At block 618, the light engine 202 emits display light of the third color for the current frame. In some embodiments, the light engine 202 emits display light of the third color in response to receiving the indication.

[0061] In some embodiments, certain aspects of the techniques described above may be implemented by one or more processors of a processing system executing software. The software comprises one or more sets of executable instructions stored or otherwise tangibly embodied on a non-transitory computer readable storage medium. The software can include the instructions and certain data that, when executed by the one or more processors, manipulate the one or more processors to perform one or more aspects of the techniques described above. The non-transitory computer readable storage medium can include, for example, a magnetic or optical disk storage device, solid state storage devices such as Flash memory, a cache, random access memory (RAM) or other non-volatile memory device or devices, and the like. The executable instructions stored on the non-transitory computer readable storage medium may be in source code, assembly language code, object code, or other instruction format that is interpreted or otherwise executable by one or more processors.

[0062] A computer readable storage medium may include any storage medium, or combination of storage media, accessible by a computer system during use to provide instructions and/or data to the computer system. Such storage media can include, but is not limited to, optical media (e.g., compact disc (CD), digital versatile disc (DVD), Blu-Ray disc), magnetic media (e.g., floppy disc, magnetic tape, or magnetic hard drive), volatile memory (e.g., random access memory (RAM) or cache), non-volatile memory (e.g., read-only memory (ROM) or Flash memory), or microelectromechanical systems (MEMS)-based storage media. The computer readable storage medium may be embedded in the computing system (e.g., system RAM or ROM), fixedly attached to the computing system (e.g., a magnetic hard drive), removably attached to the computing system (e.g., an optical disc or Universal Serial Bus (USB)-based Flash memory), or coupled to the computer system via a wired or wireless network (e.g., network accessible storage (NAS)).

[0063] Note that not all of the activities or elements described above in the general description are required, that a portion of a specific activity or device may not be required, and that one or more further activities may be performed, or elements included, in addition to those described. Still further, the order in which activities are listed are not necessarily the order in which they are performed. Also, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure.

[0064] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. Moreover, the particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. No limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.

Claims

WHAT IS CLAIMED IS:

1. A method comprising: tuning an incoupler grating and an outcoupler grating of a waveguide to a first range of wavelengths; and concurrently, projecting display light of the first range of wavelengths for a first frame from a light engine to the waveguide.

2. The method of claim 1 , further comprising: tuning the incoupler grating and the outcoupler grating of the waveguide to a second range of wavelengths different from the first range of wavelengths; and concurrently, projecting from the light engine display light of the second range of wavelengths for the first frame.

3. The method of claim 2, further comprising: tuning the incoupler grating and the outcoupler grating of the waveguide to a third range of wavelengths different from the first and second ranges of wavelengths; and concurrently, projecting from the light engine display light of the third range of wavelengths for the first frame.

4. The method of claim 3, wherein a time between projecting display light of the first range of wavelengths for the first frame and projecting display light of the third range of wavelengths for the first frame is shorter than a human vision refresh rate.

5. The method of any of claims 1 to 4, further comprising: signaling to initiate the tuning and the projecting with a clock signal.

6. The method of any of claims 1 to 5, wherein at least one of the incoupler grating and the outcoupler grating is tunable via a microelectromechanical system.

7. The method of any of claims 1 to 5, wherein at least one of the incoupler grating and the outcoupler grating comprises a stretchable polymer that is tunable via stretching the polymer.

8. A method, comprising: tuning a pitch of an incoupler grating and an outcoupler grating of a waveguide to each of a plurality of colors at each of a plurality of time phases; and projecting display light of a color of the plurality of colors for a first frame at each the plurality of time phases from a light engine to the waveguide.

9. The method of claim 8, wherein tuning the pitch comprises: tuning the incoupler grating and the outcoupler grating to a first pitch tuned to a first color at a first time phase; tuning the incoupler grating and the outcoupler grating to a second pitch tuned to a second color at a second time phase; and tuning the incoupler grating and the outcoupler grating to a third pitch tuned to a third color at a third time phase.

10. The method of claim 9, wherein projecting display light comprises: projecting display light of the first color for the first frame at the first time phase; projecting display light of the second color for the first frame at the second time phase; and projecting display light of the third color for the first frame at the third time phase.

11 . The method of claim 10, wherein a time between the first time phase, the second time phase, and the third time phase is shorter than a human vision refresh rate.

12. The method of any of claims 8 to 11 , further comprising: signaling to initiate the tuning and the projecting with a clock signal.

13. The method of any of claims 8 to 12, wherein at least one of the incoupler grating and the outcoupler grating is tunable via a microelectromechanical system.

14. The method of any of claims 8 to 12, wherein at least one of the incoupler grating and the outcoupler grating comprises a stretchable polymer that is tunable via stretching the polymer.

15. A display system comprising: a waveguide comprising a tunable incoupler grating and a tunable outcoupler grating; a controller to tune the tunable incoupler grating and the tunable outcoupler grating to each of a plurality of colors at each of a plurality of time phases; and a light engine to project display light of one of the plurality of colors for a first frame to the waveguide at each the plurality of time phases.

16. The display system of claim 15, wherein the controller is to: tune the tunable incoupler grating and the tunable outcoupler grating to a first pitch tuned to a first color at a first time phase; tune the tunable incoupler grating and the tunable outcoupler grating to a second pitch tuned to a second coIor at a second time phase; and tune the tunable incoupler grating and the tunable outcoupler grating to a third pitch tuned to a third color at a third time phase.

17. The display system of claim 16, wherein the light engine is to: project display light of the first color for the first frame at the first time phase; project display light of the second color for the first frame at the second time phase; and project display light of the third color for the first frame at the third time phase.

18. The display system of claim 17, wherein a time from a beginning of the first time phase to an end of the third time phase is shorter than a human vision refresh rate.

19. The display system of any of claims 15 to 18, further comprising: a clock signal to initiate the tuning and the projecting.

20. The display system of any of claims 15 to 19, wherein at least one of the tunable incoupler grating and the tunable outcoupler grating comprises a stretchable polymer that is tunable via stretching the stretchable polymer or is tunable via a microelectromechanical system.