Patent Publication Number: US-11397368-B1

Title: Ultra-wide field-of-view scanning devices for depth sensing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/960,045, filed Apr. 23, 2018, which claims benefit of U.S. Provisional Patent Application Ser. No. 62/513,286, filed May 31, 2017, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure generally relates to depth sensing, and specifically relates to ultra-wide field-of-view scanning devices for three-dimensional (3D) depth sensing. 
     To achieve a compelling user experience for depth sensing when using head-mounted displays (HMDs) and near-eye displays (NEDs), it is important to create a dynamic and all solid-state light scanning device with both ultrafast scanning speed (e.g., MHz) and large field-of-view. Usually, there are tradeoffs between speed, field-of-view and real-time reconfigurable illumination characteristics. Typically, a microelectromechanical system (MEM) having a mechanical-based mirror device can be used for scanning. However, the mechanical-based mirror device has stability issues and has a limited scanning speed. In addition, the mechanical-based mirror device is not reconfigurable in real time applications. 
     Most depth sensing methods rely on active illumination and detection. The conventional methods for depth sensing involve mechanical scanning or fixed diffractive-optics pattern projection, using structured light or time-of-flight techniques. Depth sensing based on time-of-flight uses a MEM with a mechanical-based mirror device (scanner) to send short pulses into an object space. The depth sensing based on time-of-flight further uses a high speed detector to time-gate back scattered light from the object to create high resolution depth maps. However, the mechanical-based scanner performs inadequately in relation to scanning speed, real-time reconfiguration and mechanical stability. The scanning speed is often limited to a few kHz along a fast axis and a few hundred Hertz along a slow axis. In addition, the mechanical-based scanner has stability and reliability issues. Depth sensing based on a fixed structured light pattern uses a diffractive optical element to generate a fixed structured light pattern projected into an object space. The depth sensing based on the fixed structured light pattern further uses a pre-stored look-up table to compute and extract depth maps. However, the depth sensing based on the fixed structured light pattern and the diffractive optical element is not robust enough for dynamic depth sensing. 
     SUMMARY 
     A depth camera assembly (DCA) determines depth information associated with one or more objects in a local area. The DCA comprises a light generator, an imaging device and a controller. The light generator is configured to illuminate the local area with structured light in accordance with emission instructions. The light generator comprises an illumination source, an acousto-optic deflector (AOD), a liquid crystal device (LCD), and a projection assembly. The illumination source is configured to emit one or more optical beams. The AOD generates diffracted scanning beams (in one or two dimensions) from the one or more optical beams emitted from the illumination source. The AOD is configured to function as at least one dynamic diffraction grating that diffracts the one or more optical beams by at least one diffraction angle to form the diffracted scanning beams based in part on the emission instructions. The LCD includes a plurality of liquid crystal gratings (LCGs). Each LCG in the LCD has an active state in which the LCG is configured to diffract the diffracted scanning beams by another diffraction angle larger than the at least one diffraction angle based in part on the emission instructions to generate the structured light. The projection assembly is configured to project the structured light into the local area. The imaging device is configured to capture one or more images of portions of the structured light reflected from one or more objects in the local area. The controller may be coupled to both the light generator and the imaging device. The controller generates the emission instructions and provides the emission instructions to the light generator. The controller is also configured to determine depth information for the one or more objects based at least in part on the captured one or more images. 
     An eyeglass-type platform representing a near-eye display (NED) can integrate the DCA. The NED further includes an electronic display and an optical assembly. The NED may be part of an artificial reality system. The electronic display of the NED is configured to emit image light. The optical assembly of the NED is configured to direct the image light to an eye-box of the NED corresponding to a location of a user&#39;s eye. The image light may comprise the depth information of the one or more objects in the local area determined by the DCA. 
     A head-mounted display (HMD) can further integrate the DCA. The HMD further includes an electronic display and an optical assembly. The HMD may be part of an artificial reality system. The electronic display is configured to emit image light. The optical assembly is configured to direct the image light to an eye-box of the HMD corresponding to a location of a user&#39;s eye. The image light may comprise the depth information of the one or more objects in the local area determined by the DCA. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a diagram of a near-eye-display (NED), in accordance with one or more embodiments. 
         FIG. 1B  is a cross-section of an eyewear of the NED in  FIG. 1A , in accordance with one or more embodiments. 
         FIG. 2A  is a diagram of a head-mounted display (HMD), in accordance with one or more embodiments. 
         FIG. 2B  is a cross section of a front rigid body of the HMD in  FIG. 2A , in accordance with one or more embodiments. 
         FIG. 3A  is an example depth camera assembly (DCA), in accordance with one or more embodiments. 
         FIG. 3B  illustrates a scanning field covered by the DCA in  FIG. 3A , in accordance with one or more embodiments. 
         FIG. 3C  illustrates different diffraction settings in the DCA in  FIG. 3A  to cover the scanning field in  FIG. 3B , in accordance with one or more embodiments. 
         FIG. 4  is a flow chart illustrating a process of determining depth information of objects in a local area based on ultra-wide field-of-view scanning, in accordance with one or more embodiments. 
         FIG. 5  is a block diagram of an artificial reality system in which a console operates, in accordance with one or more embodiments. 
     
    
    
     The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles, or benefits touted, of the disclosure described herein. 
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a near-eye display (NED), a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers. 
     A depth camera assembly (DCA) for determining depth information of objects in a local area surrounding some or all of the DCA is presented herein. The DCA includes a light source, one or more cameras and a controller. The light source includes a laser source and an acousto-optic deflector (AOD) that generates structured light using light emitted from the laser source. The AOD can be composed of one or more acousto-optic devices or plates. Each acousto-optic plate can be configured to diffract incident light by a specific diffraction angle controlled by, e.g., an electric field applied to the acousto-optic plate. The light source also includes a plurality of active liquid crystal gratings (LCGs). Adjustments to settings of the plurality of LCGs determine where the structured light is projected into the local area. The one or more cameras capture one or more images of portions of the structured light reflected from the objects in the local area. Note that the portions of the structured light can be also scattered from one or more objects in the local area, wherein scattering represents a form of diffuse reflection. The controller determines depth information based on the captured one or more images. 
     In some embodiments, the DCA is integrated into a NED that captures data describing depth information in a local area surrounding some or all of the NED. The NED further includes an electronic display and an optical assembly. The NED may be part of an artificial reality system, e.g., an AR system and/or VR system. The electronic display of the NED is configured to emit image light. The optical assembly of the NED is configured to direct the image light to an eye-box of the NED corresponding to a location of a user&#39;s eye, the image light comprising the depth information of the objects in the local area determined by the DCA. 
     In some embodiments, the DCA is integrated into a HMD that captures data describing depth information in a local area surrounding some or all of the HMD. The HMD may be part of an artificial reality system. The HMD further includes an electronic display and an optical assembly. The electronic display is configured to emit image light. The optical assembly is configured to direct the image light to an eye-box of the HMD corresponding to a location of a user&#39;s eye, the image light comprising the depth information of the objects in the local area determined by the DCA. 
       FIG. 1A  is a diagram of a NED  100 , in accordance with one or more embodiments. The NED  100  presents media to a user. Examples of media presented by the NED  100  include one or more images, video, audio, or some combination thereof. In some embodiments, audio is presented via an external device (e.g., speakers and/or headphones) that receives audio information from the NED  100 , a console (not shown), or both, and presents audio data based on the audio information. The NED  100  may be part of an artificial reality system (not shown). The NED  100  is generally configured to operate as an artificial reality NED. In some embodiments, the NED  100  may augment views of a physical, real-world environment with computer-generated elements (e.g., images, video, sound, etc.). 
     The NED  100  shown in  FIG. 1A  includes a frame  105  and a display  110 . The frame  105  includes one or more optical elements which together display media to users. The display  110  is configured for users to see the content presented by the NED  100 . The display  110  generates an image light to present media to an eye of the user. The NED  100  also includes a DCA (not shown in  FIG. 1A ) configured to determine depth information of a local area surrounding some or all of the NED  100 . The NED  100  also includes an illumination aperture  113 , and an illumination source of the DCA emits light (e.g., structured light) through the illumination aperture  113 . An imaging device of the DCA captures light from the illumination source that is reflected from the local area, e.g., through the imaging aperture  115 . Light emitted from the illumination source of the DCA through the illumination aperture  113  comprises structured light, as discussed in more detail in conjunction with  FIG. 3A . Light reflected from the local area through the imaging aperture  115  and captured by the imaging device of the DCA comprises portions of the reflected structured light. The NED  100  may also include an orientation detection device  120  that generates one or more measurement signals in response to motion of the NED  100  and generates information about orientation of the NED  100 . Examples of the orientation detection device  120  include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, or some combination thereof. 
       FIG. 1B  is a cross section  125  of an eyewear of the NED  100  illustrated in  FIG. 1A , in accordance with one or more embodiments. The cross section  125  includes at least one display assembly  130  integrated into the display  110 , an eye-box  140 , and a DCA  150 . The eye-box  140  is a location where an eye  145  is positioned when a user wears the NED  100 . In some embodiments, the frame  105  may represent a frame of eye-wear glasses. For purposes of illustration,  FIG. 1B  shows the cross section  125  associated with a single eye  145  and a single display assembly  130 , but in alternative embodiments not shown, another display assembly which is separate from the display assembly  130  shown in  FIG. 1B , provides image light to another eye  145  of the user. 
     The display assembly  130  is configured to direct the image light to the eye  145  through the eye-box  140 . In some embodiments, when the NED  100  is configured as an AR NED, the display assembly  130  also directs light from a local area surrounding the NED  100  to the eye  145  through the eye-box  140 . The display assembly  130  may be configured to emit image light at a particular focal distance in accordance with varifocal instructions, e.g., provided from a varifocal module (not shown in  FIG. 1B ). 
     The display assembly  130  may be composed of one or more materials (e.g., plastic, glass, etc.) with one or more refractive indices that effectively minimize the weight and present to the user a field of view of the NED  100 . In alternate configurations, the NED  100  includes an optical assembly with one or more optical elements between the display assembly  130  and the eye  145 . The optical elements may act to, e.g., correct aberrations in image light emitted from the display assembly  130 , magnify image light, perform some other optical adjustment of image light emitted from the display assembly  130 , or some combination thereof. The example for optical elements may include an aperture, a Fresnel lens, a convex lens, a concave lens, a liquid crystal lens, a diffractive element, a waveguide, a filter, a polarizer, a diffuser, a fiber taper, one or more reflective surfaces, a polarizing reflective surface, a birefringent element, or any other suitable optical element that affects image light emitted from the display assembly  130 . 
     The frame  105  further includes a DCA  150  configured to determine depth information of one or more objects in a local area surrounding some or all of the NED  100 . The DCA  150  includes an illumination source  155 , an imaging device  160 , and a controller  165  that may be coupled to at least one of the illumination source  155  and the imaging device  160 . In some embodiments (now shown in  FIG. 1B ), the illumination source  155  and the imaging device  160  each may include its own internal controller. In some embodiments (not shown in  FIG. 1B ), the illumination source  155  and the imaging device  160  can be widely separated, e.g., the illumination source  155  and the imaging device  160  can be located in different assemblies. 
     The illumination source  155  may be configured to illuminate the local area with structured light through the illumination aperture  113  in accordance with emission instructions generated by the controller  165 . The illumination source  155  may include a plurality of emitters that each emits light having certain characteristics (e.g., wavelength, polarization, coherence, temporal behavior, etc.). The characteristics may be the same or different between emitters, and the emitters can be operated simultaneously or individually. In one embodiment, the plurality of emitters could be, e.g., laser diodes (e.g., edge emitters), inorganic or organic LEDs, a vertical-cavity surface-emitting laser (VCSEL), or some other source. 
     The imaging device  160  includes one or more cameras configured to capture, through the imaging aperture  115 , one or more images of at least a portion of the structured light reflected from one or more objects in the local area. In one embodiment, the imaging device  160  is an infrared camera configured to capture images in the infrared spectrum. Additionally or alternatively, the imaging device  160  may be also configured to capture images of visible spectrum light. The imaging device  160  may include a charge-coupled device (CCD) detector, a complementary metal-oxide-semiconductor (CMOS) detector or some other types of detectors (not shown in  FIG. 1B ). The imaging device  160  may be configured to operate with a pre-determined frame rate for fast detection of objects in the local area. 
     The controller  165  may generate the emission instructions and provide the emission instructions to the illumination source  155  for controlling operation of the illumination source  155 . The controller  165  may control, based on the emission instructions, operation of the illumination source  155  to dynamically adjust a pattern of the structured light illuminating the local area, an intensity of the light pattern, a density of the light pattern, location of the light being projected at the local area, etc. The controller  165  may be also configured to determine depth information for the one or more objects in the local area based in part on the one or more images captured by the imaging device  160 . In some embodiments, the controller  165  provides the determined depth information to a console (not shown in  FIG. 1B ) and/or an appropriate module of the NED  100  (e.g., a varifocal module, not shown in  FIG. 1B ). The console and/or the NED  100  may utilize the depth information to, e.g., generate content for presentation on the display  110 . More details about the structure and operation of the DCA  150  are disclosed in conjunction with  FIGS. 3A-3C  and  FIG. 4 . 
       FIG. 2A  is a diagram of a HMD  200 , in accordance with one or more embodiments. The HMD  200  may be part of an artificial reality system. In embodiments that describe AR system and/or a MR system, portions of a front side  202  of the HMD  200  are at least partially transparent in the visible band (˜380 nm to 750 nm), and portions of the HMD  200  that are between the front side  202  of the HMD  200  and an eye of the user are at least partially transparent (e.g., a partially transparent electronic display). The HMD  200  includes a front rigid body  205 , a band  210 , and a reference point  215 . The HMD  200  also includes a DCA configured to determine depth information of a local area surrounding some or all of the HMD  200 . The HMD  200  also includes an imaging aperture  220  and an illumination aperture  225 , and an illumination source of the DCA emits light (e.g., structured light) through the illumination aperture  225 . An imaging device of the DCA captures light from the illumination source that is reflected from the local area through the imaging aperture  220 . Light emitted from the illumination source of the DCA through the illumination aperture  225  comprises structured light, as discussed in more detail in conjunction with  FIG. 3A  and  FIG. 4 . Light reflected from the local area through the imaging aperture  220  and captured by the imaging device of the DCA comprises portions of the reflected structured light. 
     The front rigid body  205  includes one or more electronic display elements (not shown in  FIG. 2A ), one or more integrated eye tracking systems (not shown in  FIG. 2A ), an Inertial Measurement Unit (IMU)  230 , one or more position sensors  235 , and the reference point  215 . In the embodiment shown by  FIG. 2A , the position sensors  235  are located within the IMU  230 , and neither the IMU  230  nor the position sensors  235  are visible to a user of the HMD  200 . The IMU  230  is an electronic device that generates fast calibration data based on measurement signals received from one or more of the position sensors  235 . A position sensor  235  generates one or more measurement signals in response to motion of the HMD  200 . Examples of position sensors  235  include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU  230 , or some combination thereof. The position sensors  235  may be located external to the IMU  230 , internal to the IMU  230 , or some combination thereof. 
       FIG. 2B  is a cross section  240  of the front rigid body  205  of the HMD  200  shown in  FIG. 2A . As shown in  FIG. 2B , the front rigid body  205  includes an electronic display  245  and an optical assembly  250  that together provide image light to an eye-box  255 . The eye-box  255  is the location of the front rigid body  205  where a user&#39;s eye  260  is positioned. For purposes of illustration,  FIG. 2B  shows a cross section  240  associated with a single eye  260 , but another optical assembly  250 , separate from the optical assembly  250 , provides altered image light to another eye of the user. The front rigid body  205  also has an optical axis corresponding to a path along which image light propagates through the front rigid body  205 . 
     The electronic display  245  generates image light. In some embodiments, the electronic display  245  includes an optical element that adjusts the focus of the generated image light. The electronic display  245  displays images to the user in accordance with data received from a console (not shown in  FIG. 2B ). In various embodiments, the electronic display  245  may comprise a single electronic display or multiple electronic displays (e.g., a display for each eye of a user). Examples of the electronic display  245  include: a liquid crystal display, an organic light emitting diode (OLED) display, an inorganic light emitting diode (ILED) display, an active-matrix organic light-emitting diode (AMOLED) display, a transparent organic light emitting diode (TOLED) display, some other display, a projector, or some combination thereof. The electronic display  245  may also include an aperture, a Fresnel lens, a convex lens, a concave lens, a diffractive element, a waveguide, a filter, a polarizer, a diffuser, a fiber taper, a reflective surface, a polarizing reflective surface, or any other suitable optical element that affects the image light emitted from the electronic display. In some embodiments, one or more of the display block optical elements may have one or more coatings, such as anti-reflective coatings. 
     The optical assembly  250  magnifies received light from the electronic display  245 , corrects optical aberrations associated with the image light, and the corrected image light is presented to a user of the HMD  200 . At least one optical element of the optical assembly  250  may be an aperture, a Fresnel lens, a refractive lens, a reflective surface, a diffractive element, a waveguide, a filter, or any other suitable optical element that affects the image light emitted from the electronic display  245 . Moreover, the optical assembly  250  may include combinations of different optical elements. In some embodiments, one or more of the optical elements in the optical assembly  250  may have one or more coatings, such as anti-reflective coatings, dichroic coatings, etc. Magnification of the image light by the optical assembly  250  allows elements of the electronic display  245  to be physically smaller, weigh less, and consume less power than larger displays. Additionally, magnification may increase a field-of-view of the displayed media. For example, the field-of-view of the displayed media is such that the displayed media is presented using almost all (e.g., 110 degrees diagonal), and in some cases all, of the user&#39;s field-of-view. In some embodiments, the optical assembly  250  is designed so its effective focal length is larger than the spacing to the electronic display  245 , which magnifies the image light projected by the electronic display  245 . Additionally, in some embodiments, the amount of magnification may be adjusted by adding or removing optical elements. 
     As shown in  FIG. 2B , the front rigid body  205  further includes a DCA  265  for determining depth information of one or more objects in a local area  270  surrounding some or all of the HMD  200 . The DCA  265  includes a light generator  275 , an imaging device  280 , and a controller  285  that may be coupled to both the light generator  275  and the imaging device  280 . The light generator  275  emits light through the illumination aperture  225 . In accordance with embodiments of the present disclosure, the light generator  275  is configured to illuminate the local area  270  with structured light  290  in accordance with emission instructions generated by the controller  285 . The controller  285  is configured to control operation of certain components of the light generator  275 , based on the emission instructions. The controller  285  provides the emission instructions to a plurality of diffractive optical elements of the light generator  275  to control a field-of-view of the local area  270  illuminated by the structured light  290 . More details about controlling the plurality of diffractive optical elements of the light generator  275  by the controller  285  are disclosed in conjunction with  FIGS. 3A-3C  and  FIG. 4 . 
     The light generator  275  may include a plurality of emitters that each emits light having certain characteristics (e.g., wavelength, polarization, coherence, temporal behavior, etc.). The characteristics may be the same or different between emitters, and the emitters can be operated simultaneously or individually. In one embodiment, the plurality of emitters could be, e.g., laser diodes (e.g., edge emitters), inorganic or organic LEDs, a vertical-cavity surface-emitting laser (VCSEL), or some other source. In some embodiments, a single emitter or a plurality of emitters in the light generator  275  can emit light having a structured light pattern. More details about the DCA  265  that includes the light generator  275  are disclosed in conjunction with  FIG. 3A . 
     The imaging device  280  includes one or more cameras configured to capture, through the imaging aperture  220 , portions of the structured light  290  reflected from the local area  270 . The imaging device  280  captures one or more images of one or more objects in the local area  270  illuminated with the structured light  290 . The controller  285  is also configured to determine depth information for the one or more objects based on the captured portions of the reflected structured light. In some embodiments, the controller  285  provides the determined depth information to a console (not shown in  FIG. 2B ) and/or an appropriate module of the HMD  200  (e.g., a varifocal module, not shown in  FIG. 2B ). The console and/or the HMD  200  may utilize the depth information to, e.g., generate content for presentation on the electronic display  245 . 
     In some embodiments, the front rigid body  205  further comprises an eye tracking system (not shown in  FIG. 2B ) that determines eye tracking information for the user&#39;s eye  260 . The determined eye tracking information may comprise information about an orientation of the user&#39;s eye  260  in the eye-box  255 , i.e., information about an angle of an eye-gaze. The eye-box  255  represents a three-dimensional volume at an output of a HMD in which the user&#39;s eye is located to receive image light. In one embodiment, the user&#39;s eye  260  is illuminated with a structured light. Then, the eye tracking system can use locations of the reflected structured light in a captured image to determine eye position and eye-gaze. In another embodiment, the eye tracking system determines eye position and eye-gaze based on magnitudes of image light captured over a plurality of time instants. 
     In some embodiments, the front rigid body  205  further comprises a varifocal module (not shown in  FIG. 2B ). The varifocal module may adjust focus of one or more images displayed on the electronic display  245 , based on the eye tracking information. In one embodiment, the varifocal module adjusts focus of the displayed images and mitigates vergence-accommodation conflict by adjusting a focal distance of the optical assembly  250  based on the determined eye tracking information. In another embodiment, the varifocal module adjusts focus of the displayed images by performing foveated rendering of the one or more images based on the determined eye tracking information. In yet another embodiment, the varifocal module utilizes the depth information from the controller  285  to generate content for presentation on the electronic display  245 . 
       FIG. 3A  is an example DCA  300  configured for depth sensing based on structured light with an ultra-wide field-of-view, in accordance with one or more embodiments. The DCA  300  includes a light generator  305 , an imaging device  310 , and a controller  315  coupled to both the light generator  305  and the imaging device  310 . The DCA  300  may be configured to be a component of the NED  100  in  FIG. 1A  and/or a component of the HMD  200  in  FIG. 2A . Thus, the DCA  300  may be an embodiment of the DCA  150  in  FIG. 1B  and/or an embodiment of the DCA  265  in  FIG. 2B ; the light generator  305  may be an embodiment of the illumination source  155  in  FIG. 1B  and/or an embodiment of the light generator  275  in  FIG. 2B ; and the imaging device  310  may be an embodiment of the imaging device  160  in  FIG. 1B  and/or an embodiment of the imaging device  280  in  FIG. 2B . 
     The light generator  305  is configured to illuminate and scan a local area  320  with structured light in accordance with emission instructions from the controller  315 . The light generator  305  includes an illumination source  325  (e.g., laser diode) configured to emit one or more optical beams  330 . The illumination source  325  may directly generate the one or more optical beams  330  as polarized light. The one or more optical beams  330  can be circularly polarized (right handed or in other embodiments left handed). In alternate embodiments, the one or more optical beams  330  can be linearly polarized (vertical and horizontal), or elliptically polarized (right or left). Alternatively, the illumination source  325  may emit unpolarized light, and a polarizing element (not shown in  FIG. 3A ) separate from the illumination source  325  may generate the one or more optical beams  330  as polarized light, based in part on the emission instructions from the controller  315 . The polarizing element may be integrated into the illumination source  325  or placed in front of the illumination source  325 . In some embodiments, for depth sensing based on time-of-flight, the one or more optical beams  330  are temporally modulated for generating temporally modulated illumination of the local area  320 . 
     A beam conditioning assembly  335  collects light emitted from the illumination source  325  and directs the collected light toward a portion of an AOD  340 . The beam conditioning assembly  335  may be composed of one or more optical elements, e.g., lenses having specific optical powers. 
     The AOD  340  diffracts light into one or more dimensions. The AOD  340  is composed of one or more acousto-optic devices or plates that generate diffracted scanning beams  345  in one or two dimensions by diffracting the one or more optical beams  330 . In some embodiments, the diffracted scanning beams  345  represent structured light of a defined pattern, e.g., a pattern of light having parallel stripes, a dot pattern, etc. In some embodiments, the AOD  340  is configured to function as at least one dynamic diffraction grating that diffracts the one or more optical beams  330  to form the diffracted scanning beams  345  based in part on emission instructions from the controller  315 . Each acousto-optic device in the AOD  340  may include a transducer or an array of transducers and one or more diffraction areas (not shown in  FIG. 3A ). Responsive to at least one radio frequency in the emission instructions, the transducer or the array of transducers of the acousto-optic device in the AOD  340  may be configured to generate at least one sound wave in the one or more diffraction areas of the acousto-optic device to form the at least one dynamic diffraction grating. 
     The AOD  340  can be configured to actively scan a plurality of diffraction angles at which the one or more optical beams  330  are diffracted and interfered to form the diffracted scanning beams  345 . The AOD  340  is configured to scan the plurality of diffraction angles between, e.g., −5 degrees and +5 degrees. In this way, the diffracted scanning beams  345  formed by the AOD  340  covers a scanning zone with a field-of-view of, e.g., 10 degrees, along one or two dimensions. In some embodiments, the AOD  340  is configured to scan the plurality of diffraction angles with the scanning resolution of 0.1 degree, thus supporting a fine-grained scanning. Due to a relatively narrow scanning zone, the AOD  340  can support fast scanning with scanning speeds, e.g., in the order of MHz. 
     The AOD  340  can be used to scan the local area  320  at discrete angles or a continuum of angles, depending on a radio frequency signal that drives the AOD  340 , controlled by, e.g., the controller  315 . In some embodiments, to achieve scanning of discrete angles (e.g., 0, +x, and −x degrees along x dimension, and 0, +y, −y degrees along y dimension), each acousto-optic device in the AOD  340  is driven by a specific radio frequency signal having a frequency of, e.g., f c , f c +f m , f c −f m , for scanning of discrete angles along a corresponding dimension. In one or more embodiments, an angle of light incident to each acousto-optic device in the AOD  340  satisfies a Bragg matching condition. Note that f c  is a frequency of a carrier signal and f m  is a frequency of a modulation signal that modulates the carrier signal for generating the radio frequency signal that drives an acousto-optic device within the AOD  340 . The frequency of carrier signal, f c , can be set to be around a center of a frequency bandwidth of the AOD  340  in order to maximize the diffraction efficiency of the diffracted scanning beams  345 . In addition, the value of 2f m  should be smaller than an acoustic resonant 3 dB frequency bandwidth of each acousto-optic device within the AOD  340 . Note also that the frequency bandwidth of the AOD  340  is relatively narrow, providing a relatively narrow angular spread (band) in the Bragg regime for the diffracted scanning beams  345 . In alternate embodiments, to achieve fast scanning of a continuum of angles (e.g., with resolution smaller than 0.1 degrees, along both x and y dimensions), each acousto-optic device of the AOD  340  is driven by a frequency sweep signal (e.g., controlled by the controller  315 ) that performs frequency sweep during a short time duration. For example, the frequency sweep signal may cover frequencies from f c −f m  to f c +f m  with a defined frequency resolution of Δ f m  that is related to a time bandwidth product of an acousto-optic device of the AOD  340 . 
     In some embodiments, a radio frequency driving power of the AOD  340  controlled by the controller  315  can be up to 500 mW, and a driving radio frequency controlled by the controller  315  can be in the range of a few MHz up to GHz. In one embodiment, the AOD  340  is configured as a diffraction grating device having an array of transducers. In an alternate embodiment, the AOD  340  is configured as a diffraction grating device having a single transducer. The AOD  340  represents a dynamic phase grating suitable for achieving both dynamic and high speed scanning, based on a sound wave traveling through a crystal that diffracts the one or more optical beams  330  and creates the diffracted scanning beams  345  as real-time configurable structured light. In some embodiments, the AOD  340  can accept the one or more optical beams  330  having visible to infrared wavelengths. In some embodiments, efficiency of the AOD  340  depends on a bandwidth of each transducer in the AOD  340 , which can be designed to maintain efficiency between, e.g., 80% and 90%. 
     In some embodiments, the one or more optical beams  330  are incident on the AOD  340  at an angle that satisfies the Bragg matching condition. The AOD  340  may directly generate the diffracted scanning beams  345  as polarized light (e.g., circularly polarized light) by orienting the one or more optical beams  330  to a crystal in the AOD  340  in a geometry satisfying the Bragg matching condition. Note that the diffracted scanning beams  345  can be either right handed circularly polarized or left handed circularly polarized based on the crystal in the AOD  340 . In some embodiments, a state of polarization (SOP) of the one or more optical beams  330  incident to the AOD  340  matches an eigenstate of polarization at the Bragg angle for achieving maximum diffraction efficiency of the AOD  340 . A polarization element can be included in front of the AOD  340  (not shown in  FIG. 3A ) to maximize the diffraction efficiency of the AOD  340 , if the SOP of the one or more optical beams  330  does not match the eigenstate of polarization at the Bragg angle for phase matching condition. 
     The AOD  340  provides ultrafast scanning speed to dynamically scan arbitrary patterns that can be projected to one or more objects in the local area  320 . The AOD  340  operates based on one or more different crystal types, each crystal type having a wide spectral bandwidth and being transparent for light from visible to infrared wavelengths. Hence, the AOD  340  can diffract the one or more optical beams  330  in a wide wavelength range. Depending on a configuration of the NED  100  and/or the HMD  200 , the AOD  340  can be implemented as a different type of device. In one embodiment, the AOD  340  is implemented as a bulk device. In another embodiment, the AOD  340  is implemented as a plate device, i.e., a compact version of a bulk device. In yet another embodiment, the AOD  340  is implemented as a thin film device based on a surface propagating acoustic wave deflector. Depending on a type of scanning, the AOD  340  may include a different number of acousto-optic devices or elements. In one embodiment, the AOD  340  includes a single acousto-optic device or element for generating the diffracted scanning beams  345  as one-dimensional scanning beams for one-dimensional random scanning. In an alternate embodiment, the AOD  340  includes at least one pair of acousto-optic devices whose axes of orientation are orthogonal to each other. Accordingly, one acousto-optic device in a pair of acousto-optic devices diffracts light in one dimension (e.g., x) and the second acousto-optic device in the pair diffracts the x-diffracted light along an orthogonal dimension (e.g., y), thereby generating the diffracted scanning beams  345  as two-dimensional scanning beams for two-dimensional random scanning. Each acousto-optic device or element in the AOD  340  can be configured to function as a dynamic diffraction grating that diffracts incident light by a specific diffraction angle based in part on the emission instructions from the controller  315 . Additional details regarding structure and operation of an acousto-optic device is described with regard to U.S. application Ser. No. 15/599,353, filed on May 18, 2017, and U.S. application Ser. No. 15/643,912, filed on Jul. 7, 2017, which are incorporated by reference in their entireties. 
     A liquid crystal device (LCD)  350  is positioned in front of the AOD  340 . The LCD  350  is configured to further diffract light received from the AOD  340 , based in part on the emission instructions from the controller  315 . The LCD  350  diffracts the diffracted scanning beams  345  to generate structured light  355  having an ultra-wide field-of-view for scanning the local area  320 . It should be understood that the structured light  355  with the ultra-wide field-of-view can be generated by the DCA  300  having a reverse order of the AOD  340  and the LCD  350  where the AOD  340  is positioned in front of the LCD  350  (the embodiment not shown in  FIG. 3A ). 
     The LCD  350  includes a plurality of active liquid crystal gratings (LCGs) in an optical series. Note that an active LCG is in optical series with another active LCG when light diffracted by the active LCG is incident to the other active LCG. Each active LCG in the LCD  350  is configured to further diffract the diffracted scanning beams  345  by a specific diffraction angle, which can be controlled based in part on the emission instructions from the controller  315 . In some embodiments, each active LCG can be made based on, e.g., photo-alignment with liquid crystal polymers and a polarization holography setup. In some embodiments, the LCD  350  includes three active LCGs, thus forming with the AOD  340  a series of four active diffraction layers. At any time instant, two diffraction layers out of four diffraction layers may be in an active state (e.g., controlled by the controller  315 ) and generate the structured light  355  covering an ultra-wide scanning field of the local area  320 . In some embodiments, at most two of LCGs in the LCD  350  are in active states providing diffraction of corresponding incident light. 
     In some embodiments, based on modulation of optical axis, the LCGs in the LCD  350  can be Pancharatnam-Berry phase gratings, polarization volume gratings, or conventional LCGs. In some other embodiments, based on refractive index modulation, the LCGs in the LCD  350  can be conventional LCGs with patterned indium tin oxide (ITO) films or hidden dielectric pattern to generate in-homogenous electric field across a substrate for producing grating effect. In some other embodiments, based on modulation of thickness, the LCGs in the LCD  350  can be implemented using liquid crystal cells with in-homogenous cell gap across a substrate for generating grating effect. In some other embodiments, the LCGs in the LCD  350  can be implemented by filling liquid crystals into substrates having a grating structure on one or both sides of the substrates. In some other embodiments, the LCGs in the LCD  350  can be polarization sensitive or polarization non-sensitive depending on a configuration and polarization state of the illumination source  325 . 
     The LCD  350  may utilize switchable or non-switchable liquid crystal cells, depending on the working principle of LCGs within the LCD  350 . In one or more embodiments, the switchable liquid crystal cells function as a switchable half-wave plate. In some embodiments, the light generator  305  of the DCA  300  may include polarization correction elements, depending on the working principle of LCGs in the LCD  350 , layer stack configuration of the AOD  340  and/or the LCD  350 , and a polarization state of the illumination source  325 . A polarization correction element integrated into the DCA  300  may be a linear polarizer, a circular polarizer, a quarter waveplate, a c-plate, or combination thereof. 
     A projection assembly  360  is positioned in front of the combination of the AOD  340  and the LCD  350 . The projection assembly  360  includes one or more optical elements (lenses). Optionally, the projection assembly  360  includes a polarizing element for polarization of the structured light  355 . The structured light  355  may be selected from a group consisting of linearly polarized light (vertical and horizontal), right handed circularly polarized light, left handed circularly polarized light, and elliptically polarized light. The projection assembly  360  projects the structured light  355  into the local area  320  over an ultra-wide field-of-view, e.g., of 160 degrees along x dimension and/or y dimension. The structured light  355  illuminates portions of the local area  320 , including one or more objects in the local area  320 . A reflected structured light  365  is generated based on reflection of the structured light  355  from the one or more objects in the local area  320 . 
     The imaging device  310  captures one or more images of the one or more objects in the local area  320  by capturing the portions of the reflected structured light  365 . In one embodiment, the imaging device  310  is an infrared camera configured to capture images in an infrared spectrum. In another embodiment, the imaging device  310  is configured to capture an image light of a visible spectrum. The imaging device  310  can be configured to operate with a frame rate in the range of kHz to MHz for fast detection of objects in the local area  320 . In an embodiment, the imaging device  310  includes a polarizing element placed in front of a camera for receiving and propagating the reflected structured light  365  of a particular polarization. The reflected structured light  365  may be selected from a group consisting of linearly polarized light (vertical and horizontal), right handed circularly polarized light, left handed circularly polarized light, and elliptically polarized light. It should be noted that polarization of the reflected structured light  365  can be different than polarization of the structured light  355  that illuminates the local area  320 . In some embodiments, the imaging device  310  includes more than one camera. 
     In some embodiments, the DCA  300  includes a light shutter (not shown in  FIG. 3A ) coupled to the imaging device  310 . The light shutter can operate such that the NED  100  or the HMD  200  switches between an AR mode and a VR mode. In one embodiment, the light shutter is implemented as a mechanical component. In the AR mode, the mechanical light shutter may be open and portions of the reflected structured light  365  propagates to a detector of the imaging device  310 . In the VR mode, the mechanical light shutter may be closed to block one or more portions of the reflected structured light  365  from reaching the detector of the imaging device  310 . In another embodiment, the light shutter is implemented as a polarizer configured to propagate light of specific polarization, e.g., based on polarization instructions from the controller  315 . In the AR mode, the light shutter implemented as a polarizer may be configured to propagate light having the same polarization as one or more portions of the reflected structured light  365 . In the VR mode, the light shutter implemented as a polarizer may be configured to block propagation of light having the same polarization as one or more portions of the reflected structured light  365 . 
     The controller  315  is configured to control operations of various components of the DCA  300  in  FIG. 3A . In some embodiments, the controller  315  provides emission instructions to the illumination source  325  to control intensity of the one or more optical beams  330 , modulation of the one or more optical beams  330 , a time duration during which the illumination source  325  is activated, etc. The controller  315  may further create the emission instructions which include a radio frequency at which the AOD  340  is driven. The controller  315  may generate the emission instructions based on, e.g., a predetermined list of values for the radio frequency stored in a look-up table of the controller  315 . In an embodiment, the predetermined radio frequencies are stored as waveforms in an electronic chip, e.g., in a direct digital synthesizer (not shown in  FIG. 3A ) coupled to the controller  315 . In another embodiment, the emission instructions are created by a voice control integrated into the controller  315 . Upon a verbal request, the voice control of the controller  315  computes a radio frequency for driving the AOD  340  to generate the diffracted scanning beams  345  and the structured light  355  of a specific spatial frequency suitable for detection of stationary object(s) and/or tracking of moving object(s) in the local area  320  at a certain distance from the imaging device  310 . 
     The controller  315  can modify the radio frequency at which the AOD  340  is driven to adjust a diffraction angle at which the one or more optical beams  330  are diffracted. In this way, the controller  315  can instruct the AOD  340  to scan a plurality of diffraction angles at which the one or more optical beams  330  are diffracted and interfered to form the diffracted scanning beams  345  and the structured light  355 . A radio frequency at which the AOD  340  is driven may control a separation of the optical beams  330  diffracted by the AOD  340 . Hence, a spatial frequency of the resulting diffracted scanning beams  345  (and of the structured light  355 ) directly depends on the radio frequency at which the AOD  340  is driven. 
     As shown in  FIG. 3A , the controller  315  is further coupled to the imaging device  310  and can be configured to determine depth information for the one or more objects in the local area  320 . The controller  315  is configured to determine depth information for the one or more objects based at least in part on the captured one or more images of portions of the reflected structured light  365 . In some embodiments, the controller  315  can be configured to determine the depth information based on polarization information of the reflected structured light  365  and polarization information of the structured light  355 . For a depth sensing method based on structured light illumination, the controller  315  is configured to determine the depth information based on phase-shifted patterns of the portions of the reflected structured light  365  distorted by shapes of the one or more objects in the local area  320 , and to use triangulation calculation to obtain a depth map of the local area  320 . 
       FIG. 3B  illustrates a scanning field  370 , which may be covered by the structured light  355  generated by the DCA  300  in  FIG. 3A , in accordance with one or more embodiments. As shown in  FIG. 3B , the scanning field  370  includes a plurality of sub-zones  375 . In the illustrative embodiment shown in  FIG. 3B , the scanning field  370  covers a field-of-view of 160 degrees along both x and y axes, whereas each sub-zone  375  covers 10 degrees along y axis. As discussed above in conjunction with  FIG. 3A , the controller  315  configures, via the emission instructions, the AOD  340  to scan a plurality of diffraction angles at which the one or more optical beams  330  are diffracted and interfered to form the diffracted scanning beams  345 . In the embodiment illustrated in  FIG. 3B , the AOD  340  scans diffraction angles between −5 degrees and +5 degrees, e.g., with scanning resolution of 0.1 degrees and scanning speed in the order of MHz. In this way, the AOD  340  is configured to achieve fast and fine-grained scanning within each subzone  375  of the scanning field  370 . 
     As also discussed above in conjunction with  FIG. 3A , the controller  315  further configures, via the emission instructions, each active LCG within the LCD  350  to further diffract the diffracted scanning beams  345  by a specific diffraction angle at a particular time instant. In some embodiments, diffraction angles achieved by each active LCG within the LCD  350  are larger than one or more diffraction angles achieved by the AOD  340 . In this way, the LCD  350  is configured to generate the structured light  355  that scans the local area  320  from one sub-zone  375  to another (not necessarily adjacent) sub-zone  375  of the scanning field  370 , with a scanning speed, e.g., in the order of kHz. Thus, the LCD  350  with the plurality of active LCGs enables scanning with an ultra-wide field-of-view and a large diffraction angle. In some embodiments, a size of the AOD  340  and a size of the LCD  350  are of sub-millimeter order. Power consumption of the AOD  340  and the LCD  350  is, e.g., between 10 mW and 100 mW. An active LCG within the LCD  350  having a large diffraction angle (e.g., of 75 degrees) can achieve high efficiency by using highly birefringent and dual twist or multiple twisted structures. 
       FIG. 3C  illustrates a table  380  with different diffraction settings of the AOD  340  and the active LCGs within the LCD  350  for covering the scanning field  370  in  FIG. 3B  having a field-of-view between −80 degrees and +80 degrees, in accordance with one or more embodiments. Note that columns in the table  380  in  FIG. 3C  correspond to different time instants, e.g., time instants t −80 , t −70 , . . . , t 0 , . . . , t 60 , t 70 , t 80 , not necessarily in chronological order. In the illustrative embodiment of  FIG. 3C , the AOD  340  is configured to diffract the one or more optical beams  330  by a diffraction angle between −5 degrees and +5 degrees, with the resolution of, e.g., 0.1 degree to form the diffracted scanning beams  345  (and the structured light  355 ) for fast and fine-grained scanning within any sub-zone  375  of the scanning field  370  in  FIG. 3B . In the illustrative embodiment of  FIG. 3C , the LCD  350  includes three active LCGs, e.g., LCG 1 , LCG 2 , LCG 3 , in optical series; LCG 1  provides a fixed diffraction angle of either −15 degrees or +15 degrees; LCG 2  provides a fixed diffraction angle of either −35 degrees or +35 degrees; and LCG 3  provides a fixed diffraction angle of either −75 degrees or +75 degrees. In this way, the combination of the AOD  340  and the LCD  350  generates the structured light  355  that scans the local area  320  from one sub-zone  375  to another (not necessarily adjacent) sub-zone  375  of the scanning field  370 , with a fast scanning speed within each sub-zone  375  and a moderate speed of switching between sub-zones  375 . 
     In some embodiments, the controller  315  of the DCA  300  in  FIG. 3A  adjusts, based in part on the emission instructions over a plurality of time instants, settings of the AOD  340  and of each active LCG in the LCD  350  to generate the structured light  355  for covering the scanning field  370  in  FIG. 3B  in the plurality of time instants. As shown, e.g., in the first column of the table  380  in  FIG. 3C  corresponding to a time instant t −80 , the controller  315  adjusts the settings of the AOD  340  and of the LCD  350  so that a diffraction angle of the AOD  340  is −5 degrees, LCG 1  and LCG 2  are in an inactive state, and a diffraction angle of LCG 3  is −75 degrees. Thus, at the time instant t −80 , a total diffraction angle generated by the combination of the AOD  340  and the LCD  350  is −80 degrees. Then, the controller  315  adjusts the settings of the AOD  340  to change, during a plurality of time instants, e.g., with MHz speed and resolution of 0.1 degree, a diffraction angle between −5 degrees and +5 degrees. In the same time, the controller  315  does not adjust the settings of the active LCGs within the LCD  350 , i.e., LCG 1  and LCG 2  are still in the inactive state and a diffraction angle of LCG 3  is still −75 degrees. In this way, the structured light  355  generated by the combination of the AOD  340  and the LCD  350  scans one sub-zone  375  of the scanning field  370  in  FIG. 3B . 
     The scanning process can continue by switching from one sub-zone  375  to another (not necessarily adjacent) sub-zone  375  in  FIG. 3B  in accordance with the settings shown in the table  380  in  FIG. 3C  until the entire scanning field  370  in  FIG. 3B  is covered by the structured light  355 . At each time instant shown in  FIG. 3C , a different sub-zone  375  of the scanning field  370  in  FIG. 3B  is covered. As shown in  FIG. 3C , at each time instant, at most two diffraction layers out of three active LCGs in the LCD  350  are in active states. Because the AOD  340  and the LCGs in the LCD  350  are active components, the AOD  340  and each active LCG in the LCD  350  can be configured to be in active state or in inactive state based on an electrical field, controlled by, e.g., the controller  315 . 
     In the illustrative embodiment of  FIG. 3C , the AOD  340  is in active state for scanning small angles and achieving fast and fine-grained scanning within any sub-zone  375  of the scanning field  370  in  FIG. 3B . The AOD  340  may be configured to scan continuously over a range from −5 degrees to +5 degrees within the sub-zone  375 . Thus, to achieve fast and continuous subzone scanning, the AOD  340  is in active state. In some embodiments, the AOD  340  and the LCD  350  are configured to operate in a discrete scanning mode, where the sub-zone  375  is not scanned by the AOD  340  and at least one LCG in the LCD  350  is in active state. In the discrete scanning mode, the LCD  350  can scan discretely one or more beams of the structured light  355  in large angles (e.g., from −50 degrees to −60 degrees) without scanning within the sub-zone  375 . In the discrete scanning mode, the AOD  340  can be deactivated to save power. In the power save mode when the AOD  340  is in inactive state, the zeroth order un-diffracted beam  345  from the AOD  340  is scanned by at least one active LCG of the LCD  350 . 
       FIG. 4  is a flow chart illustrating a process  400  of determining depth information of objects in a local area based on ultra-wide field-of-view scanning, which may be implemented at the NED  100  shown in  FIG. 1A  and/or the HMD  200  shown in  FIG. 2A , in accordance with one or more embodiments. The process  400  of  FIG. 4  may be performed by the components of a DCA (e.g., the DCA  300 ). Other entities (e.g., a NED, a HMD, and/or console) may perform some or all of the steps of the process in other embodiments. Likewise, embodiments may include different and/or additional steps, or perform the steps in different orders. 
     The DCA generates  410  (e.g., via a controller) emission instructions. The DCA may provide the emission instructions to an illumination source within the DCA. Based on the emission instructions, the illumination source may emit one or more optical beams. In some embodiments, the DCA generates the emission instructions which include information about at least one radio frequency. 
     The DCA provides  420  (e.g., via the controller) the emission instructions to an AOD to generate diffracted scanning beams from one or more optical beams by diffracting the one or more optical beams by at least one diffraction angle using the AOD to form the diffracted scanning beams based in part on the emission instructions. Responsive to the at least one radio frequency in the emission instructions, the DCA generates at least one sound wave within the AOD to form at least one dynamic diffraction grating. In some embodiments, the DCA modifies the at least one radio frequency in the emission instructions to adjust a diffraction angle of the at least one diffraction angle at which the one or more optical beams are diffracted in each dimension and interfered to form the diffracted scanning beams. 
     The DCA provides  430  (e.g., via the controller) the emission instructions to a LCD comprising a plurality of LCGs, each LCG having an active state in which the LCG diffracts the diffracted scanning beams by another diffraction angle larger than the at least one diffraction angle based in part on the emission instructions to generate the structured light. Each LCG is configured to diffract the diffracted scanning beams by a fixed diffraction angle larger than the at least one diffraction angle based in part on the emission instructions to generate the structured light. 
     The DCA may project (e.g., via a projection assembly) the structured light into a local area. In some embodiments, the DCA projects the structured light to illuminate an ultra-wide field-of-view of the local area for accurate depth scanning. The DCA may also control (e.g., via the controller) a scanning sub-zone of the ultra-wide field-of-view of the local area by controlling dynamic diffraction gratings of the AOD and LCGs within the DCA. 
     The DCA captures  440  (e.g., via an imaging device) one or more images of portions of the structured light reflected from one or more objects in the local area. In some embodiments, the imaging device of the DCA includes a polarizing element and a camera, wherein the polarizing element is positioned in front of the camera. The polarizing element is configured to receive the portions of the reflected structured light having a specific polarization and to propagate the received portions of reflected polarized light pattern to the camera. 
     The DCA determines  450  (e.g., via the controller) depth information for the one or more objects based at least in part on the captured one or more images. In some embodiments, the DCA determines  450  the depth information for the one or more objects based in part on polarization information of the captured portions of the reflected structured light. 
     In some embodiments, the DCA is configured as part of a NED, e.g., the NED  100  in  FIG. 1A . In some other embodiments, the DCA is configured as part of a HMD, e.g., the HMD  200  in  FIG. 2A . In one or more embodiments, the DCA provides the determined depth information to a console coupled to the NED or the HMD. The console is then configured to generate content for presentation on an electronic display of the NED or the HMD, based on the depth information. In another embodiment, the DCA provides the determined depth information to a module of the NED or the HMD that generates content for presentation on the electronic display of the NED or the HMD, based on the depth information. In an alternate embodiment, the DCA is integrated into a HMD as part of an artificial reality system. In this case, the DCA may be configured to sense and display objects behind a head of a user wearing the HMD or display objects recorded previously. 
     System Environment 
       FIG. 5  is a block diagram of one embodiment of an artificial reality system  500  in which a console  510  operates. The artificial reality system  500  may be a NED system or a HMD system. The artificial reality system  500  may operate in an artificial reality system environment. In some embodiments, the artificial reality system  500  shown by  FIG. 5  comprises a HMD  505  and an input/output (I/O) interface  515  that is coupled to the console  510 . In some other embodiments (not shown in  FIG. 5 ), the artificial reality system  500  includes a NED coupled to the console  510 . While  FIG. 5  shows an example HMD system  500  including one HMD  505  and on I/O interface  515 , in other embodiments any number of these components may be included in the artificial reality system  500 . For example, there may be multiple HMDs  505  each having an associated I/O interface  515 , with each HMD  505  and I/O interface  515  communicating with the console  510 . In alternative configurations, different and/or additional components may be included in the artificial reality system  500 . Additionally, functionality described in conjunction with one or more of the components shown in  FIG. 5  may be distributed among the components in a different manner than described in conjunction with  FIG. 5  in some embodiments. For example, some or all of the functionality of the console  510  is provided by the HMD  505 . 
     The HMD  505  is a head-mounted display that presents content to a user comprising virtual and/or augmented views of a physical, real-world environment with computer-generated elements (e.g., two-dimensional (2D) or three-dimensional (3D) images, 2D or 3D video, sound, etc.). In some embodiments, the presented content includes audio that is presented via an external device (e.g., speakers and/or headphones) that receives audio information from the HMD  505 , the console  510 , or both, and presents audio data based on the audio information. The HMD  505  may comprise one or more rigid bodies, which may be rigidly or non-rigidly coupled together. A rigid coupling between rigid bodies causes the coupled rigid bodies to act as a single rigid entity. In contrast, a non-rigid coupling between rigid bodies allows the rigid bodies to move relative to each other. An embodiment of the HMD  505  is the HMD  200  described above in conjunction with  FIG. 2A . 
     The HMD  505  includes a DCA  520 , an electronic display  525 , an optical assembly  530 , one or more position sensors  535 , an IMU  540 , an optional eye tracking system  545 , and an optional varifocal module  550 . Some embodiments of the HMD  505  have different components than those described in conjunction with  FIG. 5 . Additionally, the functionality provided by various components described in conjunction with  FIG. 5  may be differently distributed among the components of the HMD  505  in other embodiments. 
     The DCA  520  captures data describing depth information of an area surrounding some or all of the HMD  505 . The DCA  520  can compute the depth information using the data (e.g., based on captured portions of structured light), or the DCA  520  can send this information to another device such as the console  510  that can determine the depth information using the data from the DCA  520 . 
     The DCA  520  includes a light generator, an imaging device and a controller that may be coupled to both the light generator and the imaging device. The light generator of the DCA  520  is configured to illuminate a local area with structured light in accordance with emission instructions from the controller. The light generator comprises an illumination source, an AOD, an LCD, and a projection assembly. The illumination source is configured to emit one or more optical beams. The AOD generates diffracted scanning beams from the one or more beams emitted from the illumination source. The AOD is configured to function as a dynamic diffraction grating that diffracts the one or more optical beams to form the diffracted scanning beams based in part on the emission instructions. The LCD includes a plurality of active LCGs. Each LCG is configured to diffract the diffracted scanning beams based in part on the emission instructions to generate the structured light. The projection assembly is configured to project the structured light into the local area. The imaging device of the DCA  520  is configured to capture one or more images of portions of the structured light reflected from one or more objects in the local area. The controller of the DCA  520  generates the emission instructions and provides the emission instructions to the light generator of the DCA  520 . The controller of the DCA  520  is also configured to determine depth information for the one or more objects based at least in part on the captured one or more images of portions of the reflected structured light. The DCA  520  may be an embodiment of the DCA  300  in  FIG. 3A . 
     The electronic display  525  displays 2D or 3D images to the user in accordance with data received from the console  510 . In various embodiments, the electronic display  525  comprises a single electronic display or multiple electronic displays (e.g., a display for each eye of a user). Examples of the electronic display  525  include: a liquid crystal display, an OLED display, an ILED display, an AMOLED display, a TOLED display, some other display, or some combination thereof. The electronic display  525  may be an embodiment of the electronic display  245  in  FIG. 2B . 
     The optical assembly  530  magnifies image light received from the electronic display  525 , corrects optical errors associated with the image light, and presents the corrected image light to a user of the HMD  505 . The optical assembly  530  includes a plurality of optical elements. Example optical elements included in the optical assembly  530  include: an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, a reflecting surface, or any other suitable optical element that affects image light. Moreover, the optical assembly  530  may include combinations of different optical elements. In some embodiments, one or more of the optical elements in the optical assembly  530  may have one or more coatings, such as partially reflective or anti-reflective coatings. 
     Magnification and focusing of the image light by the optical assembly  530  allows the electronic display  525  to be physically smaller, weigh less and consume less power than larger displays. Additionally, magnification may increase the field-of-view of the content presented by the electronic display  525 . For example, the field-of-view of the displayed content is such that the displayed content is presented using almost all (e.g., approximately 110 degrees diagonal), and in some cases all, of the user&#39;s field-of-view. Additionally in some embodiments, the amount of magnification may be adjusted by adding or removing optical elements. 
     In some embodiments, the optical assembly  530  may be designed to correct one or more types of optical error. Examples of optical error include barrel or pincushion distortions, longitudinal chromatic aberrations, or transverse chromatic aberrations. Other types of optical errors may further include spherical aberrations, chromatic aberrations or errors due to the lens field curvature, astigmatisms, or any other type of optical error. In some embodiments, content provided to the electronic display  525  for display is pre-distorted, and the optical assembly  530  corrects the distortion when it receives image light from the electronic display  525  generated based on the content. The optical assembly  530  may be an embodiment of the optical assembly  250  in  FIG. 2B . 
     The IMU  540  is an electronic device that generates data indicating a position of the HMD  505  based on measurement signals received from one or more of the position sensors  535  and from depth information received from the DCA  520 . A position sensor  535  generates one or more measurement signals in response to motion of the HMD  505 . Examples of position sensors  535  include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU  540 , or some combination thereof. The position sensors  535  may be located external to the IMU  540 , internal to the IMU  540 , or some combination thereof. 
     Based on the one or more measurement signals from one or more position sensors  535 , the IMU  540  generates data indicating an estimated current position of the HMD  505  relative to an initial position of the HMD  505 . For example, the position sensors  535  include multiple accelerometers to measure translational motion (forward/back, up/down, left/right) and multiple gyroscopes to measure rotational motion (e.g., pitch, yaw, roll). In some embodiments, the IMU  540  rapidly samples the measurement signals and calculates the estimated current position of the HMD  505  from the sampled data. For example, the IMU  540  integrates the measurement signals received from the accelerometers over time to estimate a velocity vector and integrates the velocity vector over time to determine an estimated current position of a reference point on the HMD  505 . Alternatively, the IMU  540  provides the sampled measurement signals to the console  510 , which interprets the data to reduce error. The reference point is a point that may be used to describe the position of the HMD  505 . The reference point may generally be defined as a point in space or a position related to the HMD&#39;s  505  orientation and position. 
     The IMU  540  receives one or more parameters from the console  510 . The one or more parameters are used to maintain tracking of the HMD  505 . Based on a received parameter, the IMU  540  may adjust one or more IMU parameters (e.g., sample rate). In some embodiments, certain parameters cause the IMU  540  to update an initial position of the reference point so it corresponds to a next position of the reference point. Updating the initial position of the reference point as the next calibrated position of the reference point helps reduce accumulated error associated with the current position estimated the IMU  540 . The accumulated error, also referred to as drift error, causes the estimated position of the reference point to “drift” away from the actual position of the reference point over time. In some embodiments of the HMD  505 , the IMU  540  may be a dedicated hardware component. In other embodiments, the IMU  540  may be a software component implemented in one or more processors. The IMU  540  may be an embodiment of the IMU  230  in  FIG. 2A . 
     In some embodiments, the eye tracking system  545  is integrated into the HMD  505 . The eye tracking system  545  determines eye tracking information associated with an eye of a user wearing the HMD  505 . The eye tracking information determined by the eye tracking system  545  may comprise information about an orientation of the user&#39;s eye, i.e., information about an angle of an eye-gaze. In some embodiments, the eye tracking system  545  is integrated into the optical assembly  530 . An embodiment of the eye-tracking system  545  may comprise an illumination source and an imaging device (camera). 
     In some embodiments, the varifocal module  550  is further integrated into the HMD  505 . The varifocal module  550  may be coupled to the eye tracking system  545  to obtain eye tracking information determined by the eye tracking system  545 . The varifocal module  550  may be configured to adjust focus of one or more images displayed on the electronic display  525 , based on the determined eye tracking information obtained from the eye tracking system  545 . In this way, the varifocal module  550  can mitigate vergence-accommodation conflict in relation to image light. The varifocal module  550  can be interfaced (e.g., either mechanically or electrically) with at least one of the electronic display  525  and at least one optical element of the optical assembly  530 . Then, the varifocal module  550  may be configured to adjust focus of the one or more images displayed on the electronic display  525  by adjusting position of at least one of the electronic display  525  and the at least one optical element of the optical assembly  530 , based on the determined eye tracking information obtained from the eye tracking system  545 . By adjusting the position, the varifocal module  550  varies focus of image light output from the electronic display  525  towards the user&#39;s eye. The varifocal module  550  may be also configured to adjust resolution of the images displayed on the electronic display  525  by performing foveated rendering of the displayed images, based at least in part on the determined eye tracking information obtained from the eye tracking system  545 . In this case, the varifocal module  550  provides appropriate image signals to the electronic display  525 . The varifocal module  550  provides image signals with a maximum pixel density for the electronic display  525  only in a foveal region of the user&#39;s eye-gaze, while providing image signals with lower pixel densities in other regions of the electronic display  525 . In one embodiment, the varifocal module  550  may utilize the depth information obtained by the DCA  520  to, e.g., generate content for presentation on the electronic display  525 . 
     The I/O interface  515  is a device that allows a user to send action requests and receive responses from the console  510 . An action request is a request to perform a particular action. For example, an action request may be an instruction to start or end capture of image or video data or an instruction to perform a particular action within an application. The I/O interface  515  may include one or more input devices. Example input devices include: a keyboard, a mouse, a game controller, or any other suitable device for receiving action requests and communicating the action requests to the console  510 . An action request received by the I/O interface  515  is communicated to the console  510 , which performs an action corresponding to the action request. In some embodiments, the I/O interface  515  includes an IMU  540  that captures calibration data indicating an estimated position of the I/O interface  515  relative to an initial position of the I/O interface  515 . In some embodiments, the I/O interface  515  may provide haptic feedback to the user in accordance with instructions received from the console  510 . For example, haptic feedback is provided when an action request is received, or the console  510  communicates instructions to the I/O interface  515  causing the I/O interface  515  to generate haptic feedback when the console  510  performs an action. 
     The console  510  provides content to the HMD  505  for processing in accordance with information received from one or more of: the DCA  520 , the HMD  505 , and the I/O interface  515 . In the example shown in  FIG. 5 , the console  510  includes an application store  555 , a tracking module  560 , and an engine  565 . Some embodiments of the console  510  have different modules or components than those described in conjunction with  FIG. 5 . Similarly, the functions further described below may be distributed among components of the console  510  in a different manner than described in conjunction with  FIG. 5 . 
     The application store  555  stores one or more applications for execution by the console  510 . An application is a group of instructions, that when executed by a processor, generates content for presentation to the user. Content generated by an application may be in response to inputs received from the user via movement of the HMD  505  or the I/O interface  515 . Examples of applications include: gaming applications, conferencing applications, video playback applications, or other suitable applications. 
     The tracking module  560  calibrates the HMD system  500  using one or more calibration parameters and may adjust one or more calibration parameters to reduce error in determination of the position of the HMD  505  or of the I/O interface  515 . For example, the tracking module  560  communicates a calibration parameter to the DCA  520  to adjust the focus of the DCA  520  to more accurately determine positions of structured light elements captured by the DCA  520 . Calibration performed by the tracking module  560  also accounts for information received from the IMU  540  in the HMD  505  and/or an IMU  540  included in the I/O interface  515 . Additionally, if tracking of the HMD  505  is lost (e.g., the DCA  520  loses line of sight of at least a threshold number of structured light elements), the tracking module  560  may re-calibrate some or all of the HMD system  500 . 
     The tracking module  560  tracks movements of the HMD  505  or of the I/O interface  515  using information from the DCA  520 , the one or more position sensors  535 , the IMU  540  or some combination thereof. For example, the tracking module  550  determines a position of a reference point of the HMD  505  in a mapping of a local area based on information from the HMD  505 . The tracking module  560  may also determine positions of the reference point of the HMD  505  or a reference point of the I/O interface  515  using data indicating a position of the HMD  505  from the IMU  540  or using data indicating a position of the I/O interface  515  from an IMU  540  included in the I/O interface  515 , respectively. Additionally, in some embodiments, the tracking module  560  may use portions of data indicating a position or the HMD  505  from the IMU  540  as well as representations of the local area from the DCA  520  to predict a future location of the HMD  505 . The tracking module  560  provides the estimated or predicted future position of the HMD  505  or the I/O interface  515  to the engine  555 . 
     The engine  565  generates a 3D mapping of the area surrounding some or all of the HMD  505  (i.e., the “local area”) based on information received from the HMD  505 . In some embodiments, the engine  565  determines depth information for the 3D mapping of the local area based on information received from the DCA  520  that is relevant for techniques used in computing depth. The engine  565  may calculate depth information using one or more techniques in computing depth from one or more polarized structured light patterns. In various embodiments, the engine  565  uses the depth information to, e.g., update a model of the local area, and generate content based in part on the updated model. 
     The engine  565  also executes applications within the HMD system  500  and receives position information, acceleration information, velocity information, predicted future positions, or some combination thereof, of the HMD  505  from the tracking module  560 . Based on the received information, the engine  565  determines content to provide to the HMD  505  for presentation to the user. For example, if the received information indicates that the user has looked to the left, the engine  565  generates content for the HMD  505  that mirrors the user&#39;s movement in a virtual environment or in an environment augmenting the local area with additional content. Additionally, the engine  565  performs an action within an application executing on the console  510  in response to an action request received from the I/O interface  515  and provides feedback to the user that the action was performed. The provided feedback may be visual or audible feedback via the HMD  505  or haptic feedback via the I/O interface  515 . 
     In some embodiments, based on the eye tracking information (e.g., orientation of the user&#39;s eye) received from the eye tracking system  545 , the engine  565  determines resolution of the content provided to the HMD  505  for presentation to the user on the electronic display  525 . The engine  565  provides the content to the HMD  605  having a maximum pixel resolution on the electronic display  525  in a foveal region of the user&#39;s gaze, whereas the engine  565  provides a lower pixel resolution in other regions of the electronic display  525 , thus achieving less power consumption at the HMD  505  and saving computing cycles of the console  510  without compromising a visual experience of the user. In some embodiments, the engine  565  can further use the eye tracking information to adjust where objects are displayed on the electronic display  525  to prevent vergence-accommodation conflict. 
     ADDITIONAL CONFIGURATION INFORMATION 
     The foregoing description of the embodiments of the disclosure has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. 
     Some portions of this description describe the embodiments of the disclosure in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, computationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. Furthermore, it has also proven convenient at times, to refer to these arrangements of operations as modules, without loss of generality. The described operations and their associated modules may be embodied in software, firmware, hardware, or any combinations thereof. 
     Any of the steps, operations, or processes described herein may be performed or implemented with one or more hardware or software modules, alone or in combination with other devices. In one embodiment, a software module is implemented with a computer program product comprising a computer-readable medium containing computer program code, which can be executed by a computer processor for performing any or all of the steps, operations, or processes described. 
     Embodiments of the disclosure may also relate to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, and/or it may comprise a general-purpose computing device selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a non-transitory, tangible computer readable storage medium, or any type of media suitable for storing electronic instructions, which may be coupled to a computer system bus. Furthermore, any computing systems referred to in the specification may include a single processor or may be architectures employing multiple processor designs for increased computing capability. 
     Embodiments of the disclosure may also relate to a product that is produced by a computing process described herein. Such a product may comprise information resulting from a computing process, where the information is stored on a non-transitory, tangible computer readable storage medium and may include any embodiment of a computer program product or other data combination described herein. 
     Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments is intended to be illustrative, but not limiting, of the scope of the disclosure, which is set forth in the following claims.