Patent Publication Number: US-11381804-B2

Title: Light projector using an acousto-optical control device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/262,547, filed Jan. 30, 2019 and entitled “LIGHT PROJECTOR USING AN ACOUSTO-OPTICAL CONTROL DEVICE”, which is a continuation of U.S. patent application Ser. No. 15/985,264, filed May 21, 2018 and entitled “LIGHT PROJECTOR USING AN ACOUSTO-OPTICAL CONTROL DEVICE”, which is a continuation of U.S. patent application Ser. No. 14/983,388, filed Dec. 29, 2015 and entitled “LIGHT PROJECTOR USING AN ACOUSTO-OPTICAL CONTROL DEVICE”, which claims the benefit of U.S. Provisional Application Ser. No. 62/097,563, filed on Dec. 29, 2014 and entitled “Acousto-Optical Control Devices for Near-Eye Displays”, the contents of the aforementioned applications are hereby incorporated by reference into the present application in their entirety. 
    
    
     BACKGROUND 
     Modern computing and display technologies have facilitated the development of systems for so-called “virtual reality” or “augmented reality” experiences, wherein digitally reproduced images or portions thereof are presented to a user and may be perceived as real. A virtual reality (“VR”) scenario typically involves presentation of digital or virtual image information without transparency to other actual real-world visual input. An augmented reality (“AR”) scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user. For example, referring to  FIG. 1 , an augmented reality scene  100  is depicted wherein a user of an AR technology device sees a real-world park-like setting  102  featuring people, trees, buildings in the background, and a concrete platform  104 . In addition to these items, the user of the AR technology also perceives that he/she “sees” a robot statue  106  standing upon the real-world platform  104 , and a cartoon-like avatar character  108  flying by, even though these elements ( 106 ,  108 ) do not exist in the real world. As it turns out, the human visual perception system is very complex, and producing a VR or AR technology that facilitates a comfortable, natural-feeling, rich presentation of virtual image elements amongst other virtual or real-world imagery elements is challenging. 
     Referring to  FIG. 2 , stereoscopic wearable glasses  200  type configurations have been developed which generally feature two displays (e.g.,  202 ,  204 ) that are configured to display images with slightly different element presentation such that a three-dimensional perspective is perceived by the human visual system. Such configurations have been found to be uncomfortable for many users due to a mismatch between vergence and accommodation that must be overcome to perceive the images in three dimensions. Indeed, some users are not able to tolerate stereoscopic configurations. 
     Referring to  FIG. 3 , a simplified cross-sectional view of a human eye  300  is depicted featuring a cornea  302 , iris  304 , lens—or “crystalline lens”  306 , sclera  308 , choroid layer  310 , macula  312 , retina  314 , and optic nerve pathway  316  to the brain. The macula is the center of the retina, which is utilized to see moderate detail. At the center of the macula is the “fovea”, which is used for seeing the finest details. The fovea contains more photoreceptors (approximately 120 cones per visual degree) than any other portion of the retina. 
     The human visual system is not a passive sensor type of system. It is configured to actively scan the environment. In a manner somewhat akin to scanning an image with a flatbed scanner or using a finger to read Braille from a paper, the photoreceptors of the eye fire in response to changes in stimulation, rather than constantly responding to a constant state of stimulation. Indeed, experiments with substances such as cobra venom, which is utilized to paralyze the muscles of the eye, have shown that a human subject will experience blindness if positioned with his/her eyes open, viewing a static scene with venom-induced paralysis of the eyes. In other words, without changes in stimulation, the photoreceptors don&#39;t provide input to the brain and blindness is experienced. It is believed that this is at least one reason that the eyes of normal humans have been observed to move back and forth, or dither, in side-to-side motion in what are called “microsaccades”. As noted above, the fovea of the retina contains the greatest density of photoreceptors, and while humans typically have the perception that they have high-resolution visualization capabilities throughout their field of view, they generally actually have only a small high-resolution center that they are mechanically sweeping around a lot, along with a persistent memory of the high-resolution information recently captured with the fovea. In a somewhat similar manner, the focal distance control mechanism of the eye (ciliary muscles operatively coupled to the crystalline lens in a manner wherein ciliary relaxation causes taut ciliary connective fibers to flatten out the lens for more distant focal lengths; ciliary contraction causes loose ciliary connective fibers, which allow the lens to assume a more rounded geometry for more close-in focal lengths) dithers back and forth by approximately ¼ to ½ diopter to cyclically induce a small amount of what is called “dioptric blur” on both the close side and far side of the targeted focal length. This is utilized by the accommodation control circuits of the brain as cyclical negative feedback that helps to constantly correct course and keep the retinal image of a fixated object approximately in focus. 
     The visualization center of the brain also gains valuable perception information from the motion of both eyes and components thereof relative to each other. Vergence movements (i.e., rolling movements of the pupils toward or away from each other to converge the lines of sight of the eyes to fixate upon an object) of the two eyes relative to each other are closely associated with focusing (or “accommodation”) of the lenses of the eyes. Under normal conditions, changing the focus of the lenses of the eyes, or accommodating the eyes, to focus upon an object at a different distance will automatically cause a matching change in vergence to the same distance, under a relationship known as the “accommodation-vergence reflex.” Likewise, a change in vergence will trigger a matching change in accommodation, under normal conditions. Working against this reflex, as do most conventional stereoscopic AR or VR configurations, is known to produce eye fatigue, headaches, or other forms of discomfort in users. 
     Movement of the head, which houses the eyes, also has a key impact upon visualization of objects. Humans move their heads to visualize the world around them. They often are in a fairly constant state of repositioning and reorienting the head relative to an object of interest. Further, most people prefer to move their heads when their eye gaze needs to move more than about 20 degrees off center to focus on a particular object (i.e., people don&#39;t typically like to look at things “from the corner of the eye”). Humans also typically scan or move their heads in relation to sounds—to improve audio signal capture and utilize the geometry of the ears relative to the head. The human visual system gains powerful depth cues from what is called “head motion parallax”, which is related to the relative motion of objects at different distances as a function of head motion and eye vergence distance (i.e., if a person moves his head from side to side and maintains fixation on an object, items farther out from that object will move in the same direction as the head; items in front of that object will move opposite the head motion. These are very salient cues for where things are spatially in the environment relative to the person—perhaps as powerful as stereopsis). Head motion also is utilized to look around objects, of course. 
     Further, head and eye motion are coordinated with the “vestibulo-ocular reflex”, which stabilizes image information relative to the retina during head rotations, thus keeping the object image information approximately centered on the retina. In response to a head rotation, the eyes are reflexively and proportionately rotated in the opposite direction to maintain stable fixation on an object. As a result of this compensatory relationship, many humans can read a book while shaking their head back and forth (interestingly, if the book is panned back and forth at the same speed with the head approximately stationary, the same generally is not true—the person is not likely to be able to read the moving book; the vestibulo-ocular reflex is one of head and eye motion coordination, generally not developed for hand motion). This paradigm may be important for augmented reality systems, because head motions of the user may be associated relatively directly with eye motions, and the system preferably will be ready to work with this relationship. 
     Indeed, given these various relationships, when placing digital content (e.g., 3-D content such as a virtual chandelier object presented to augment a real-world view of a room; or 2-D content such as a planar/flat virtual oil painting object presented to augment a real-world view of a room), design choices may be made to control behavior of the objects. For example, the 2-D oil painting object may be head-centric, in which case the object moves around along with the user&#39;s head (e.g., as in a GoogleGlass approach); or the object may be world-centric, in which case it may be presented as though it is part of the real world coordinate system, so that the user may move his head or eyes without moving the position of the object relative to the real world. 
     Thus when placing virtual content into the augmented reality world, how the content is presented must be given consideration. For example, in a world centric scheme the virtual object stays in position in the real world so that the user may move his/her ahead around it to see the object from different points of view. 
     The systems and techniques described herein are configured to work with the visual configuration of the typical human to address these challenges. 
     SUMMARY 
     In some embodiments, an approach for projecting light may be implemented using a acousto-optical depth switch that uses surface acoustic waves produced along a substrate to guide image light to different areas. The surface acoustic waves may be generated on a substrate using a transducer. Surface acoustic waves of different frequencies can guide image light onto different optical elements at different physical positions. The optical elements may be configured to show objects in an image at different distances from a viewer. 
     Further details of aspects, objects, and advantages of some embodiments are described below in the detailed description, drawings, and claims. Both the foregoing general description and the following detailed description are exemplary and explanatory, and are not intended to be limiting as to the scope of the embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The drawings illustrate the design and utility of some embodiments of the present invention. It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. In order to better appreciate how to obtain the above-recited and other advantages and objects of various embodiments of the invention, a more detailed description of the present inventions briefly described above will be rendered by reference to specific embodiments thereof, which are illustrated in the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  illustrates an example virtual or augmented reality environment, as according to some embodiments. 
         FIG. 2  illustrates a virtual or augmented reality headset, as according to some embodiments. 
         FIG. 3 . illustrates components of a human eye. 
         FIG. 4  illustrates a virtual or augmented reality headset and display modules, as according to some embodiments. 
         FIG. 5  illustrates an architecture for a virtual or augmented reality headset and display modules using a fiber scanning device, as according to some embodiments. 
         FIG. 6  illustrates an example of a virtual or augmented reality environment as a flat image, as according to some embodiments. 
         FIG. 7  illustrate an example of the a virtual or augmented reality environment of  FIG. 6  split into different depth planes, as according to some embodiments. 
         FIG. 8  illustrates an architecture for a virtual or augmented reality headset and display modules using a fiber scanning device and an acousto-optical depth switch, as according to some embodiments. 
         FIG. 9  illustrates internal architecture of the acousto-optical depth switch and a diffractive optical assembly, as according to some embodiments. 
         FIG. 10  illustrates an architecture for a virtual or augmented reality headset and display modules using a acousto-optical depth switch directly coupled to display circuitry comprising a light generator, as according to some embodiments. 
         FIG. 11  illustrates internal architecture of a diffractive optical assembly and acousto-optical depth switch having horizontal and vertical transducers, as according to some embodiments. 
         FIG. 12  illustrates internal architecture of a diffractive optical assembly and a horizontal orientated acousto-optical depth switch coupled to a vertical oriented acousto-optical depth switch, as according to some embodiments. 
         FIG. 13  illustrates internal architecture of a diffractive optical assembly and a horizontal orientated acousto-optical depth switch in parallel to a vertical oriented acousto-optical depth switch, as according to some embodiments. 
         FIG. 14  illustrates internal architecture of a diffractive optical assembly and a hybrid fiber scanning and acousto-optical depth switch device, as according to some embodiments. 
         FIG. 15  illustrates internal architecture of a diffractive optical assembly and a acousto-optical depth switch that covers resolutions that the fiber scanning device cannot reach, as according to some embodiments. 
         FIG. 16A-16C  shows flowcharts for methods for projecting light using an acousto-optical depth switch, as according to some embodiments. 
         FIG. 17  illustrates example system architecture. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments are directed to a method, system, and computer program product for acousto-optical control devices. Other objects, features, and advantages are described in the detailed description, figures, and claims. 
     Various embodiments of the methods, systems, and articles of manufacture will now be described in detail with reference to the drawings, which are provided as illustrative examples so as to enable those skilled in the art to practice the various embodiments. Notably, the figures and the examples below are not meant to limit the scope of the present invention. Where certain elements of the present invention can be partially or fully implemented using known components (or methods or processes), only those portions of such known components (or methods or processes) that are necessary for an understanding of the present invention will be described, and the detailed descriptions of other portions of such known components (or methods or processes) will be omitted so as not to obscure the invention. Further, the present invention encompasses present and future known equivalents to the components referred to herein by way of illustration 
       FIG. 4  illustrates an example system and operating environment in which the acousto-optical control devices may be implemented. As shown in  FIG. 4 , an AR system user  400  is depicted wearing a frame  404  structure coupled to a display system  402  positioned in front of the eyes of the user. A speaker  406  is coupled to the frame  404  in the depicted configuration and positioned adjacent the ear canal of the user (in one embodiment, another speaker, not shown, is positioned adjacent the other ear canal of the user to provide for stereo/shapeable sound control). The display  402  is operatively coupled  408 , such as by a wired lead or wireless connectivity, to a local processing and data module  410  which may be mounted in a variety of configurations, such as fixedly attached to the frame  404 , according to some embodiments. In additional embodiments, the local processing and data module  410  may be fixedly attached to a helmet or hat, embedded in headphones, removably attached to the torso of the user (in a backpack-style configuration, or removably attached to the hip of the user in a belt-coupling style configuration (not depicted). 
     The local processing and data module  410  may comprise a power-efficient processor or controller, as well as digital memory, such as flash memory, both of which may be utilized to assist in the processing, caching, and storage of data (a) captured from sensors which may be operatively coupled to the frame  404 , such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, and/or gyros; and/or (b) acquired and/or processed using the remote processing module  412  and/or remote data repository  414 , possibly for passage to the display  402  after such processing or retrieval. 
     The local processing and data module  410  may be operatively coupled ( 416 ,  418 ), such as via a wired or wireless communication links, to the remote processing module  412  and remote data repository  414  such that these remote modules ( 412 ,  414 ) are operatively coupled to each other and available as resources to the local processing and data module  410 . In some embodiments, the remote processing module  412  may comprise one or more relatively powerful processors or controllers configured to analyze and process data and/or image information. In some embodiments, the remote data repository  414  may comprise a relatively large-scale digital data storage facility, which may be available through the Internet or other networking configuration in a “cloud” resource configuration. In some embodiments, all data is stored and all computation is performed in the local processing and data module, allowing fully autonomous use from any remote modules. 
       FIG. 5  illustrates an example AR system that uses stacked waveguide assemblies (“EDGE”), according to some embodiments. The EDGE system  500  generally includes an image generating processor  502 , with a memory  512 , a CPU  516  and a GPU  514  and other circuitry for image generating and processing. The image generating processor  502  may be programmed with the desired virtual content for presentation to the AR system user. It should be appreciated that in some embodiments, the image generating processor  502  may be housed in the wearable AR system. In other embodiments, the image generating processor and other circuitry may be housed in a belt pack that is coupled to the wearable optics, or other configurations. 
     The virtual content or information generated by the image generating processor  502  may be transmitted to display circuitry  510 . The display circuitry  510  may comprise interface circuitry  532  that may be in communication with the image generation processor  502 , and may further interface with circuitry such as chip  534 , a temperature sensor  536 , a piezoelectric drive/transducer  538 , a red laser  540 , a blue laser  542 , and a green laser  544 , and a fiber combiner that combines the lasers (not depicted). Though lasers are illustrated here as an example of a light generator, other types of light generators (e.g., DLP, LCD, LEDs) can also be implemented in display circuitry  510 . 
     The display circuitry  510  may interface with a display or projective device, such as a fiber scanning device (FSD)  520 . Generally, an FSD  520  is a display device with one or more optical fibers that are vibrated rapidly to create various patterns to deliver the image. More details about the functioning of FSDs are described in U.S. patent application Ser. No. 14/555,585 filed on Nov. 27, 2014 and entitled “Virtual and augmented reality systems and methods”, the content of the aforementioned U.S. patent application is hereby expressly incorporated by reference for all purposes. Although the illustrated embodiment uses an FSD as a display device, one of ordinary skill in the art appreciates that other display devices known in the art, (e.g. DLP, OLED, LCDs, LCOS) may be similarly implemented. 
     The AR system may then use a coupling optic  522  to direct light from the FSD to a diffractive optical element (DOE) assembly  530  (e.g., diffractive optical elements). The coupling optics  522 , according to some embodiments, may refer to one more lenses that may be used to focus light to different depth planes in the DOE assembly. Briefly, according to some embodiments, a DOE assembly  530  is an apparatus comprised of one or more stacked planar waveguides with diffraction gratings that (1) deflect the image light along the span of the waveguide, (2) allow the image light to exit the waveguide at angles that mimic natural real-world diffractive effects. Each DOE layer may be customized to a specific focus depth, as described in further detail below. 
       FIG. 6  shows an illustrative example of a scene with objects at different distances shown in the same depth plane. There, a flat image  600  shows a man  602 , a tree  604  which is rooted in the ground  606 , and a moon  608  in the sky. In the real world, light diffracts or spreads out as it travels. Thus, light reflected from far away objects, such as the moon  608 , has spread out more than light reflected from closer objects, such as the man  602 . As explained above, the human vision system handles light coming from far and near objects in at least two ways (1) by line of sight adjustments (e.g. vergence movements), and (2) by focusing. For instance, when viewing the moon in the real world, the eyes adjust by converging each eye&#39;s line of sight to cross where the moon is located. Similarly, if one stares at the tip of his/her own nose, the eyes will again adjust converging each eye&#39;s line of sight to cross where the tip of the nose is located and the subject will outwardly appear “cross-eyed”. 
     In addition to adjusting lines of sight, each eye must focus its lensing system to account for the spreading out of light. For instance, the light reflected from the far-away moon  608  may appear more “blurry” than the light reflected from the man  602  if the light from the moon is not focused. Accordingly, to view the moon, each eye focuses its lens by flattening it out to refract the moonlight less and less, which will eventually bring the moon into focus. Similarly, to view the man each eye focuses its lens by making it more round to increasingly refract the incident light until the man comes into focus. As explained above, adjusting each eye&#39;s line of sight and focusing occur together automatically and is known as the “accommodation-vergence reflex.” 
     The issue with conventional/legacy stereoscopic AR or VR configurations is that they work against the accommodation-vergence reflex. For example, referring to the flat image  600  in  FIG. 6 , if a conventional/legacy stereoscopic AR or VR system displays the moon  608 , the tree  604 , and the man  602  at different perceived distances (e.g. the man appears closer and the moon appears farther), but all in-focus, then the eyes do not need to refocus when looking at the moon or the man. This causes a mismatch that works against the accommodation-vergence reflex. As mentioned, these sorts of legacy approaches are known to produce eye fatigue, headaches, or other forms of discomfort in users. 
     In contrast, the DOE assembly  530  (in  FIG. 5 ) works with the human accommodation-vergence reflex by displaying near and far away objects in different depth planes. For example,  FIG. 7  shows the same flat image  600  (e.g. the man, the tree, the ground, and the moon) broken up into three depth planes, DP 1 , DP 2 , DP 3 , to form a depth composite image  710 . The object that is intended to be closest, the man  620 , is displayed in depth plane  1  (DP 1 ), which has been tuned to mimic light spreading out from objects 1 meter away. The middle objects, the tree  604  and the ground  606 , are displayed in depth plane  2  (DP 2 ), which has been tuned to mimic light spreading out from objects 5 meters away. Finally, the farthest object, the moon  608 , is displayed in depth plane  3  (DP 3 ), which has been tuned to mimic light spreading out from objects 384,400,000 meters away. (384,400,000 meters is the approximate distance from the Earth to the Moon. However, for objects past a certain distance it is common to simply adjust the imaging system, such as a lensing system, to optical infinity, whereby the incident light rays are approximated as nearly parallel light rays.) In this way, a viewer of the depth-composite image  710  must adjust both his/her focusing and line of sight convergence when looking at the objects in the different depth planes, and no headaches or discomfort will occur. 
     Referring again to  FIG. 5 , the image generating processor  502  may be implemented as the device that “breaks-up” a flat image into a number of objects in a number of depth planes, according to some embodiments. In other embodiments, the image sequence is stored as separate depth plane specific image sequences, and the image processing generator transmits the pre-processed depth plane image sequences to the display circuitry ready for display. 
     In some embodiments, the DOEs are switchable between “on” states in which they actively diffract, and “off” states in which they do not significantly diffract. For instance, a switchable DOE may comprise a layer of polymer dispersed liquid crystal, in which microdroplets comprise a diffraction pattern in a host medium, and the refractive index of the microdroplets can be switched to substantially match the refractive index of the host material (in which case the pattern does not appreciably diffract incident light) or the microdroplet can be switched to an index that does not match that of the host medium (in which case the pattern actively diffracts incident light). More details about the volume phase holograms are described in U.S. patent application Ser. No. 14/555,585 filed on Nov. 27, 2014 and entitled “Virtual and augmented reality systems and methods”, the content of the aforementioned U.S. patent application is hereby expressly incorporated by reference for all purposes. 
     To conserve resources, such as battery power, in some embodiments it may be preferable to only display image information for a certain depth plane when the viewer is looking at objects in the depth plane. For instance, referring to  FIG. 7 , if the image consists only of the moon  608 , then DP 3  may be switched on, while the others depth planes, DP 1  and DP 2  switched off. Optionally, all three depth planes may be turned on and used to display objects in a sequenced fashion. For example, the FSD  520  may quickly switch between projecting images on DP 1 , DP 2 , DP 3  in rapid succession. Because the human vision system can only detect movements/changes up to a certain frequency (e.g. 30 Hz), the viewer will not perceive that the FSD  520  is switching between planes but will instead perceive a smooth multi-depth planed composite image stream. 
     Additionally, according to some embodiments, the system may also include an eye-tracking subsystem  550  ( FIG. 5 ). In this case, the eye-tracking subsystem can monitor the viewer&#39;s eye&#39;s (for instance by monitoring the eye&#39;s convergence angles) to determine whether the viewer is looking at a far object or a close object. If the system detects that the viewer is looking at the moon, for instance, then DP 3  can be switched on, and DP 1  and DP 2  switched off and/or attenuated. 
     A stacked configuration may use dynamic DOEs (rather than static waveguides and lenses) to provide multiplanar focusing simultaneously. For example, with three simultaneous focal planes, a primary focus plane (based upon measured eye accommodation, for example) could be presented to the user, and a + margin and − margin (one focal plane closer, one farther out) could be utilized to provide a large focal range in which the user can accommodate before the planes need be updated. This increased focal range can provide a temporal advantage if the user switches to a closer or farther focus (e.g., as determined by accommodation measurement). Then the new plane of focus could be made to be the middle depth of focus, with the + and − margins again ready for a fast switchover to either one while the system catches up. 
     However, this scenario assumes that the FSD is able to operate fast enough to rapidly generate different images/portions of the images to be injected into multiple DOEs. As explained, FSDs generally work by rastering back and forth over a given angle. The angle dictates the field of view (FOV) for the image that is displayed. In a system with six depth planes (e.g. DP 1 , DP 2  . . . DP 6 ), the FSD must be able to switch between depth planes six times per frame in a seamless manner. For example, if the frames per second (FPS) is 60 (typical in many video stream implementations), then for each frame the FSD must switch six times per frame. Additionally, in each depth plane there may be two target zones, one for green light and a second one for red and blue light. Accordingly, there may be 12 targets per frame that the FSD must be able to switch to. Thus, for 60 FPS and 12 targets the FSD must be able to switch approximately 714 times per second to raster a seamless image/video sequence. Because a FSD is a physical/mechanical device that actuates a fiber through an angle to raster images, it becomes increasingly difficult to actuate over larger angles fast enough, as the frames per second or number of depth planes increases. 
     Additionally, assuming FSD  520  can raster and switch fast enough, the coupling optics  522  (which direct light received from the FSD into the DOE assembly at nearly orthogonal angles) should be capable of matching the speed and FOV requirements of the FSD. Current approaches, such as using lenses to focus FSD light onto each depth plane, are limited at least with respect to the FOV requirements. Ideally, for realistic simulations, an FOV of 120 degrees is required to mimic natural real-world vision. However, current coupling optic approaches, such as using a variable focus lensing system, LC shutters, and/or grating systems, cannot product 120 degrees FOV, and cannot switch between depth planes fast enough to produce a seamless visual display. 
     Additionally, mechanically actuating an FSD and coupling optics, such as a lensing system, can drain power and resources, even if such approaches could switch fast enough over the required FOV. Thus, there is a need for an approach for quickly displaying images in multiple depth planes over a large field of view. 
       FIG. 8  illustrates an approach for quickly displaying images in multiple depth planes over a large field of view. There, the architecture  800  is similar to the architecture illustrated in  FIG. 5 , with exception to the acousto-optical depth switch (ADS)  802  that is capable of matching and/or exceeding the FSD&#39;s speed over a large FOV, such as 120 degrees. As illustrated in the example embodiment of  FIG. 8 , the ADS  802  is coupled to receive light from the FSD  520  and focus the light onto different DOE layers that are at different depths. 
       FIG. 9  illustrates internal architecture  900  showing aspects of the ADS and the DOE assembly, as according to some embodiments. There, the ADS  802  includes a logic module  950  and an acousto-optical (AO) modulator  952 . In the embodiment illustrated, the light input  902  from the FSD  520  enters the ADS  802  unit and is deflected (e.g. diffracted, refracted) at a number of angles into the DOE assembly  530 . Each DOE layer or diffractive element (e.g.  530   a ,  530   b ,  530   c ) corresponds to a depth plane (e.g. DP 1 , DP 2 , DP 3 ). For example, DOE layer  530   a  may correspond to DP 1 , and displays the man  620  ( FIG. 7 ) at a perceived distance of 1 meter away from the viewer. Likewise, DOE layer  530   b  may correspond to DP 2 , and displays the tree  604  rooted in the ground  606  at a perceived distance of 5 meters away from the viewer. Finally, DOE layer  530   c  may correspond to DP 3 , and displays the moon  608  at a perceived distance of 384,400,000 meters away (or at optical infinity). 
     In some embodiments, each DOE layer implements an in-coupling grating  960  to deflect the image light received form the ADS  802  along the span of the depth plane. The image may then exit the DOE layers towards the viewer  914  using a second set of diffraction gratings (not depicted). More details about the gratings are described in U.S. patent application Ser. No. 14/555,585, filed on Nov. 27, 2014 and entitled “Virtual and augmented reality systems and methods”, as well as U.S. patent application Ser. No. 14/726,424, filed on May 29, 2015 and entitled “Methods and systems for virtual and augmented reality”. The content of the aforementioned U.S. patent application is hereby expressly incorporated by reference for all purposes. 
     In some embodiments, the AO modulator receives the light through a coupling optic, guides the received light along a waveguide, uses a transducer to cause surface acoustic waves along a substrate (the surface acoustic waves change the index of refraction of the substrate), which causes the light to exit the substrate at an angle proportional to the surface acoustic wave period. In particular, as illustrated in  FIG. 9 , the input light  902  first interfaces with the AO modulator  952  through a coupler  904 , such as a prism. The coupler  904  directs the light into a waveguide  906  on a substrate  912 . In some embodiments, the substrate comprises a piezoelectric material such as quartz, or other piezoelectric transparent/translucent materials as are known in the art. In some embodiments, the substrate comprises a thin sheet of lithium niobate, which is also piezoelectric (i.e., generates electricity in response to pressure/stress). 
     In some embodiments, the lithium niobate substrate may be used as an electro-optical switch by applying high voltages (e.g. 30 volts) to change the index of refraction of the material and refract light in desired directions. However, running high voltages near the human face is typically not desired. Further, using high voltage switches, such as a 30-volt lithium niobate switch, may not be practical in wearable computer-vision systems where battery power is typically limited. 
     Alternatively, as illustrated in  FIG. 9 , instead of using the substrate as an electro-optical switch, the AO modulator uses the substrate  912  as an acousto-optical switch. For example, a transducer  908  may be supplied with very low voltages that causes the substrate to jiggle back and forth to produce waves along the surface of the substrate (e.g. “surface acoustic waves”). The surface acoustic waves may have a certain defined period (e.g. the distance from peak-to-peak) that is proportional to the frequency of waves produced by the transducer. That is, for example, if the transducer  908  receives 60 Hz AC, the period of the surface acoustic waves approximately matches 60 Hz (discounting, for example, the energy lost in the material itself, e.g., hysteresis). Likewise, if RF frequency power is supplied to the transducer, the surface acoustic waves will approximately match the RF frequencies. Thus, by changing the frequency of the transducer, the period of the induced surface waves can be controlled and/or tuned. Generally, in some embodiments, the logic module  950  may manage the AO modulator  952  to produce the required frequencies. For example, the logic module may receive a stream of data causes the transducer to change frequencies in a sequence to direct light to the DOE assemble layers. In other embodiments, other components, such as the image processing generator  502 , manage the AO modulator to produce the sequences of frequencies. 
     As mentioned, the surface acoustic waves change the index of refraction of the substrate and may also act as a type of diffraction grating. Initially, the waveguide and the substrate have two different indices of refraction, such that total internal reflection occurs for light inside the waveguide. Certain substrates, such as lithium niobate, have an index of refraction that changes in response to electrical energy or physical/mechanical energy (e.g. stresses). As such, by applying different surface acoustic waves to a lithium niobate substrate, the index refraction can be changed so as to breakdown the total internal reflection occurring within the waveguide and thus allow the light inside the waveguide to escape. 
     Further, the angle at which light of a given wavelength is deflected out of a grating is proportional to the wavelength of the light. For example, shining white light on a grating yields rainbows of “broken-up” colors that correspond to different wavelengths. In some embodiments, the surface acoustic waves act as a diffraction grating that diffracts the image light out of the waveguide/substrate interface (e.g. the interface between  912  and  906  in  FIG. 9 ) at angles proportional to the grating width (e.g. the distance from peak to peak for the surface acoustic wave). In this way, the input light  902  traveling through the waveguide  906  may be deflected by refraction (caused by the change in index of refraction of the substrate  912 ) and diffraction (caused by the surface acoustic waves inducing a diffraction grating effect proportional to the wave period). The combined effects can be used to guide the input light  902  onto a number of in-coupling grating targets, such as in-coupling grating  906 . Additionally, the speed at which light can be deflected from one target to the next can be adjusted by simply applying a different signal (e.g. different frequency) to the transducer  908 . In this way, the acousto-optical depth switch  802  can attain very high switching speeds over a large FOV. 
       FIG. 10  illustrates an approach that uses an acousto-optical device as a scanner and switch, without the need for a FSD and/or coupling optic. There, the architecture  1000  is similar to the architecture illustrated in  FIG. 8 , with exception to the acousto-optical scanner (AOS)  1002  and lack of FSD  520 . In operation, image signal from the display circuitry  510  is input directly into the AOS  1002 . The AOS  1002  may then modulate and deflect the light onto different depth planes using acousto-optical approaches like those discussed above. 
       FIG. 11 . illustrates internal architecture  1100  of the acousto-optical scanner (AOS)  1002  and DOE assembly  530 , as according to some embodiments. As illustrated, the input light/signal  902  from the display circuit  510  ( FIG. 5 ) may interface first with the coupler  1114 , which may be an optical coupler such as a prism. The coupler  1114  directs the light into a waveguide  1110  which uses total internal reflection to guide the light on a substrate  1108 . In contrast with the approaches discussed above, the AO modulator  1106  in  FIG. 11  has two transducers. The vertical transducer  1120  is discussed above, and generally produces vertical surface acoustic waves  1118  that cause the light to deflect at different angles towards the DOE assembly  530 . 
     The horizontal transducer  1116 , in some embodiments, may be aligned orthogonal to the vertical transducer  1120 . The horizontal transducer is implemented to produce horizontal surface acoustic waves  1112 . Like the vertical surface acoustic waves  1118 , which deflect the input light vertically (relative to the AO modulator), the horizontal surface acoustic waves may also deflect light in the waveguide but horizontally, using mechanisms such as Bragg diffraction. Thus as implemented, the AO modulator  1106  can control the input light in both the horizontal and vertical directions. For example, with reference to image output  1150 , in DP 2  the image to be displayed is the tree rooted in the ground. To direct the beam to scan the image horizontally  1152 , the horizontal transducer can modulate the horizontal surface acoustic waves by controlling the frequency and thus the horizontal deflection of the light. Likewise, to scan the image output vertically  1154 , the vertical transducer  1120  can modulate the vertical surface acoustic waves  1118  by controlling the frequency and thus the vertical deflection of light. 
       FIG. 12  shows an AOS architecture  1200  for deflecting the light using a horizontal AO modulator and a vertical AO modulator in a hybrid AOS unit  1202 , as according to some embodiments. There, the horizontal AO modulator  1204  may comprise the coupler, substrate, waveguide, and a horizontal transducer (e.g., horizontal transducer  1116 ), which may be used to produce horizontally deflected or shifted light  1222 . The horizontally deflected light may then be input into the vertical AO modulator  1206 . The vertical AO modulator may comprise a coupler, substrate, waveguide and a vertical transducer (e.g., vertical transducer  1120 ) which produces vertical surface acoustic waves that deflect the light vertically  1224 . Thus instead of one combined vertical/horizontal AO modulator (e.g.,  1106  in  FIG. 11 ), the two modulators ( 1204 ,  1206 ) are individual units and each may have their own substrate, coupler, and waveguide but with orthogonal transducers. 
       FIG. 13  shows an AOS architecture  1300  for deflecting the light using an upright modulator and an orthogonal modulator a hybrid AOS unit  1310 , as according to some embodiments. There, the upright modulator  1320  is constructed like the AO modulator  952  illustrated in  FIG. 9 . That is, it is capable of deflecting light in the up/down direction (relative to the modulator). When vertical input light  1304  is input into the upright modulator  1320  it is deflected in the vertical direction to scan an image, such as the image output  1150  in the vertical direction  1154 . 
     The orthogonal AO modulator  1322  is also constructed like the AO modulator  952  illustrated in  FIG. 9 . However, the orthogonal AO modulator may be rotated 90 degrees so that it is orthogonal to the upright modulator  1320 . In this way, the orthogonal AO modulator  1322  deflects horizontal input light  1302  to scan the image in the horizontal direction  1152 , without using Bragg diffraction. Though orthogonal modulators are illustrated here as an example, one of ordinary skill in the art appreciates that one or more AO modulators aligned at different angles may similarly be implemented to achieve full image scans. For example, in a three AO modulator implementation, a first AO modulator may be aligned at 0 degrees and input light into a second AO modulator which is oriented at 45 degrees (relative to the first AO modulator) which may input light into a third AO modulator oriented at 90 degrees (relative to the first AO modulator). In this way, the one or more in-between modulators can lessen slowly change the angles instead of going from 0 to 90 degrees in one step. 
     In some embodiments, it may be preferable to have one substrate, but with two of its orthogonal surfaces utilized. For instance, the top face of the substrate may implement a first coupler, waveguide, and transducer. While on the side face of the substrate, a second coupler, waveguide and transducer is implemented. In operation, this embodiment functions similar to the upright and orthogonal modulators illustrated in  FIG. 13  but without the need for a second substrate and/or AO modulator unit. 
       FIG. 14  illustrates an architecture  1400  for implementing a hybrid FSD/AOS module, as according to some embodiments. There, the hybrid FSD/AOS module  1402  is structurally similar to the FSD  520  and ADS  802  in  FIG. 8 . However, in the approach illustrated in  FIG. 14 , the AOS component is used as a complementary scanner/generator and switch.  FIG. 15  shows internal architecture  1500  of the AOS modulator  1550  as according to this embodiment. In this approach, an FSD (e.g., FSD  520 ) generates an image to be displayed at a certain resolution, the image is input from the FSD as illustrated at  1504 . For example, referring to the image output  1530 , FSDs generally have a limited resolution and can output light along a swirl at certain spacings. That is, the swirl  1510  in the image output  1530  represents points in which the FSD can project light. The circular points  1512  between the swirl are beyond the resolution of the FSD. However, though the FSD cannot reach the circular points between the swirl, the AO module can. In this approach, the hybrid FSD/AOS component features an AO modulator  1550  with both horizontal and vertical modulators, which can more finely generate image points that the FSD cannot target or reach. As according to some embodiments, the “primary” image points may first be generated by the FSD (e.g. the points along the FSD swirl  1510 ), whereas the secondary/complementary image points are then generated by the AO modulator  1550  so as to “fill-in” the points that lie beyond the resolution of the FSD. 
       FIG. 16A  shows a flowchart  1600  for an approach for projecting light using an acousto-optical depth switch, as according to some embodiments. At  1602 , an image generator, such as lasers, LEDs, or an LCD, generates image light comprising a series of images. The series of images may be a video sequence of images, where each image in the series depicts objects at different distances. For example, a first portion of the series could comprise all the objects in a first depth plane which is closed to viewer (e.g., viewer wearing a virtual reality or augmented reality headset). Likewise, other portions of the series may comprise objects at different distances. In an exemplary embodiment, six depth planes are implemented, each of which corresponding to six distances from the viewer. In some embodiments, the first depth plane of six corresponds to a distance of three meters or closer, and the sixth depth plane corresponds to optical infinity or an otherwise very large distance. 
     At  1604 , the image light generated by the light generator is input into an FSD, which actuates over an angle. As according to some embodiments, the FSD is used to project the light onto an acousto-optical depth switch coupling optic as shown at  1606 . The coupling optic, such as a prism, may direct the image light onto a wave guide, along a substrate. A transducer within the acousto-optical depth switch may vibrate at different frequencies to generate surface acoustic waves on the surface of the substrate. As explained above, surface acoustic waves of different frequencies deflect the image light at different angles. 
     At  1608 , the transducer may receive instructions from a logic module that instructs the transducer to produce SAWs at different frequencies to deflect the image light onto different optical elements, such as diffractive optical elements. 
       FIG. 16B  illustrates a flowchart  1609 , for using a acousto-optical depth switch to deflect light at different frequencies, as according to some embodiments. In some embodiments, the image light may be sequences into portions of light for different depth planes. For example, a first leading portion may comprise objects that are to be shown as closest to the viewer. The second portion may comprise objects that to be shown at an intermediate distance to the viewer. A third portion may comprise objects that are to be shown a farthest distance from the viewer. A logic module may direct the transducer to product SAWs of different frequencies in an alternating fashion to deflect the first portion to a first optical element using a first frequency as shown at  1610 , a second portion to a second optical element using a second frequency as shown at  1612 , and a third portion to a third optical element using a third frequency as shown at  1613 . Although only three depth planes and frequencies are discussed here as an example, other numbers of depth planes (e.g., six) and corresponding frequencies can likewise be implemented. 
       FIG. 16C  shows a flowchart  1614  for an approach for projecting light in orthogonal directions using orthogonally oriented transducers, as according to some embodiments. At  1616 , horizontal SAWs are generated using a horizontal transducer. The horizontal SAWs can deflect or raster light onto an optical element along a horizontal direction using Bragg diffraction. At  1618 , vertical SAWs are generated using a vertical transducer. The vertical SAWs can defect or raster light onto an optical element along a vertical direction using refraction and diffraction. 
       FIG. 17  is a block diagram of an illustrative computing system  1700  suitable for implementing a light projector and the logic module aspects, as according to some embodiments. Computer system  1700  includes a bus  1706  or other communication mechanism for communicating information, which interconnects subsystems and devices, such as processor  1707 , system memory  1708  (e.g., RAM), static storage device  1709  (e.g., ROM), disk drive  1710  (e.g., magnetic or optical), communication interface  1714  (e.g., modem or Ethernet card), display  1711  (e.g., CRT or LCD), input device  1712  (e.g., keyboard), and cursor control. 
     According to one embodiment of the invention, computer system  1700  performs specific operations by processor  1707  executing one or more sequences of one or more instructions contained in system memory  1708 . Such instructions may be read into system memory  1708  from another computer readable/usable medium, such as static storage device  1709  or disk drive  1710 . In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and/or software. In one embodiment, the term “logic” shall mean any combination of software or hardware that is used to implement all or part of the invention. 
     The term tentative embodiments, hard-wired circuitry may be used in place of refers to any medium that participates in providing instructions to processor  1707  for execution. Such a medium may take many forms, including but not limited to, non-volatile media and volatile media. Non-volatile media includes, for example, optical or magnetic disks, such as disk drive  1710 . Volatile media includes dynamic memory, such as system memory  1708 . According to some embodiments, a database  1732  may be accessed on a computer readable medium  1731  using a data interface  1733 ″ 
     Common forms of computer readable media includes, for example, floppy disk, flexible disk, hard disk, magnetic tape, any other magnetic medium, CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, RAM, PROM, EPROM, FLASH-EPROM, any other memory chip or cartridge, or any other medium from which a computer can read. 
     In an embodiment of the invention, execution of the sequences of instructions to practice the invention is performed by a single computer system  1700 . According to other embodiments of the invention, two or more computer systems  1700  coupled by communication link  1715  (e.g., LAN, PTSN, or wireless network) may perform the sequence of instructions required to practice the invention in coordination with one another. 
     Computer system  1700  may transmit and receive messages, data, and instructions, including program, i.e., application code, through communication link  1715  and communication interface  1714 . Received program code may be executed by processor  1707  as it is received, and/or stored in disk drive  1710 , or other non-volatile storage for later execution. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the above-described process flows are described with reference to a particular ordering of process actions. However, the ordering of many of the described process actions may be changed without affecting the scope or operation of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.