Patent Publication Number: US-2023154424-A1

Title: Integrated electronic and photonic backplane architecture for display panels

Description:
BACKGROUND 
     Field of the Various Embodiments 
     Embodiments of the present disclosure relates generally to video displays, head-mounted displays and, more specifically, to an integrated electronics and photonic backplane architecture for display panels. 
     Description of the Related Art 
     A display assembly, included in optical assemblies such as head-mounted displays, mobile displays, and so forth, operates by using pixels to control light wavelengths that propagate to a lens. The lens concentrates light wavelengths provided by the display assembly to reach the eye of the user as an image. For example, a virtual reality display assembly includes a thin-film transistor (TFT) liquid crystal display (LCD) panel disposed on a backlight unit (BLU) that acts as a light source for the TFT LCD panel. 
     In some examples, each of the LCD panel and the backlight unit is packaged with a cover glass. When the LCD panel is disposed on the cover glass of the backlight unit, the cover glass over the backlight unit creates a large distance between the backlight unit and the LCD panel. At least one drawback of conventional display assemblies is that, when the light source, such as a laser source or a light-emitting diode (LED) array, is randomly scattered by the backlight unit, the directionality of the light scattered by the backlight unit becomes large and uncontrollable. This leads to a low photon efficiency and limited fill factor for the amount of light that the display panel provides. Further, the large distances between layers result in bulky designs that limit how such display assemblies can be included in compact optical assemblies. 
     Some display assemblies include a photonic integrated circuit (PIC)-based backlight unit in order to precisely control the emission cone of a given light source on a pixel-by-pixel basis, improving the photon efficiency of the backlight unit. However, such display assemblies require post-fabrication alignment at a high precision, which is costly and time-consuming. These PIC-based backlight units also include cover glass over the LCD panel and backlight unit, which similarly cause the assembly to be bulky. Moreover, the distance between the PIC-based backlight unit and the LCD panel causes a large amount of crosstalk between neighboring pixels. 
     SUMMARY 
     In various embodiments, an apparatus comprises a composite backplane that modulates light from a light source, the composite backplane comprising an electronics layer disposed on a substrate, a photonics integrated circuit (IC) layer disposed on the electronics layer that causes light from the light source to propagate in a first direction, and an active light modulation (ALM) interface layer disposed on the photonics IC layer controls an active medium layer in order to control the light propagating in the first direction. 
     Other embodiments include a display system comprising a display panel comprising a composite backplane, including an electronics layer disposed on a substrate, a photonics integrated circuit (IC) layer disposed on the electronics layer that directs light from a light source to propagate in a first direction, and an active light modulation (ALM) interface layer disposed the photonics IC layer, an active medium layer disposed on the ALM interface layer comprising sets of pixels including sets of an active media, and a top cover layer, and a controller causing the display panel to modify the light controlled via the active medium layer or the photonic IC layer. 
     At least one technical advantage of the disclosed embodiments relative to the prior art is that that composite backplane comprising a photonic integrated circuit layer disposed between an electronic IC and a liquid crystal interface layer enables the composite backplane to possess a compact composition that support various types of light sources (e.g., lasers, light-emitting diodes, etc.) and provides high efficiency and high pixel density. Further, the composite backplane can be fabricated using various lithographic fabrication processes and can be included in a wide range of display assemblies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the various embodiments can be understood in detail, a more particular description of the inventive concepts, briefly summarized above, may be had by reference to various embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of the inventive concepts and are therefore not to be considered limiting of scope in any way, and that there are other equally effective embodiments. 
         FIG.  1    illustrates a die fabrication system configured to implement one or more aspects of the present disclosure. 
         FIG.  2    illustrates a view of a composite backplane processed by the device fabrication system of  FIG.  1   , according to various embodiments of the present disclosure. 
         FIG.  3    illustrates views of various configurations for a liquid crystal interface layer included in a composite backplane of  FIG.  2   , according to various embodiments of the present disclosure 
         FIGS.  4 A- 4 B  illustrates views of various configurations for a photonic integrated circuit layer included in the composite backplane of  FIG.  2   , according to various embodiments of the present disclosure. 
         FIGS.  5 A- 5 B  illustrates views of various configurations for an electronics integrated circuit layer included in the composite backplane of  FIG.  2   , according to various embodiments of the present disclosure. 
         FIGS.  6 A- 6 C  illustrates views of various configurations for a liquid crystal cell  600  including the composite backplane of  FIG.  2   , according to various embodiments of the present disclosure. 
         FIG.  7    sets forth a flow diagram of method steps for fabricating a composite backplane for a display panel, according to the various embodiments of the present disclosure. 
         FIG.  8    is a block diagram of an embodiment of a near-eye display (NED) system in which a console operates, according to various embodiments. 
         FIG.  9 A  is a diagram of an NED, according to various embodiments. 
         FIG.  9 B  is another diagram of an NED, according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth to provide a more thorough understanding of the various embodiments. However, it will be apparent to one skilled in the art that the inventive concepts may be practiced without one or more of these specific details. 
     Overview 
     As described above, one problem with conventional approaches for display panels is that the composition of layers needed to provide a quality image causes various wavelengths of light to be blocked or propagate in directions other than towards the lens of a display assembly, resulting in large losses in efficiency associated with providing light, such as low pixel efficiency and a low fill factor. Further, various techniques to raise the efficiency of the display panel cause the fabrication process to become more complex. For example, the process may require specialized fabrication and calibration equipment in order to properly align pixels in a given display panel, significantly increasing the cost and complexity associated with including the display panel as a component in display assemblies. 
     Accordingly, in various embodiments disclosed herein, a die fabrication system produces a composite backplane that includes a specific set of layers to control light provided from a light source. The die fabrication system disposes a set of layers in sequence to produce a composite backplane for a liquid crystal unit in order to drive a display panel that is compact, highly-efficient, and possesses a high pixel density. The composite backplane includes an electronic IC layer, a photonic integrated circuit (PIC) layer, and an active light modulation (ALM) interface layer over a substrate that directs light to a set of pixels in a separate active medium layer. 
     The composite backplane can be included in both front-lit display panels and back-lit display panels and can support various light sources (e.g., lasers, light-emitting diodes, etc.) and provides a high color gamut. Further, the composite backplane can be fabricated using various lithographic fabrication processes to produce a compact composition that can be included in a wide range of display assemblies. Such assemblies can be used in systems that control the light provided via amplitude modulation (e.g., two-dimensional display panels) or via phase modulation (e.g., coherent holographic display panels). 
     System Overview 
       FIG.  1    illustrates a die fabrication system  100  configured to implement one or more aspects of the present disclosure. As shown, die fabrication system  100  includes a wafer  102 , a fabrication system  110 , and etched backplanes  120 . The fabrication system  110  includes a projection lens  112 , a photomask  114 , and a wafer loader  116 . The etched backplane  120  includes composite backplane  121  that includes an active light modulation (ALM) interface layer  122 , a photonic integrated circuit (IC) layer  124 , an electronic IC layer  126 , and a substrate  128 . 
     In operation, the fabrication system  110  causes the wafer loader  116  to manipulate the wafer  102  via moving, rotating, slicing, etc. The fabrication system  110  also causes the projection lens  112  and photomask  114  to pattern portions of the wafer  102  to generate the etched backplane  120 . In various embodiments, the fabrication system  110  uses various lithography-based nano-manufacturing processes associated with fabricating electronic components and/or photonic components in order to pattern the etched backplanes  120  on the wafer  102 . In some embodiments, the fabrication system  110  separates the etched backplanes  120  into separate die packages, where each die package includes a composite backplane  121 . In such instances, the respective composite backplanes may be combined with other layers and/or components to fabricate display assemblies, such as a display panel, a device containing a display panel (e.g., a mobile phone, tablet, wearable near-eye display, etc.), and so forth. 
     Upon fabrication, a display panel including the composite backplane  121  may be thinner than other display panels due to reduced gaps between respective layers of the composite backplane  121 . For example, a gap between the ALM interface layer  122  and the photonic IC layer  124  may be reduced compared to other techniques, as the composite backplane  121  does not include a cover glass over the photonics IC layer  124 . Further, the thickness of the composite backplane  121  could be reduced by including electronic modules for controlling the respective ALM interface layer  122  and the photonics IC layer  124  in the electronic IC  126 . In such instances, a composite backplane  121  having a composition that includes the ALM interface layer  122 , the photonics IC layer  124  and the electronic IC  126  in this manner enables the composite backplane  121  to provide a better fill factor, defined as a ratio of the light emitting area of each pixel to the surface area occupied by the pixel, for the display panel. 
     The wafer  102  may be a semiconducting material, such as silicon, that is used to fabricate an IC die package. In various embodiments, the fabrication system  110  may perform various techniques on the wafer  102  in order to generate the etched backplanes  120 . For example, the fabrication system  110  could perform wafer-level packaging (WLP) techniques to pattern and dice the wafer  102  in order to produce the IC die packages. In some embodiments, the fabrication system  110  could perform panel-level packaging techniques to generate a panel-sized composite backplane  121  to drive a display panel of a specified size. Additionally or alternatively, in some embodiments, the fabrication system  110  may perform other techniques (e.g., flip chip packaging, quilt packaging, etc.) to prepare the etched backplanes  120 . 
     The fabrication system  110  includes one or more devices that pattern and/or slice portions of the wafer  102  in order to generate the etched backplanes  120 . For example, the fabrication system  110  could include one or more devices, such as one or more wafer loaders  116  (e.g.,  116   a ,  116   b , etc.), photomasks  114  (e.g.,  114   a ,  114   b , etc.), projection lenses  112  (e.g.,  112   a ,  112   b , etc.) and/or other devices (e.g., grinders, coaters, developers, etchers, strippers, etc.) that perform various processes to pattern the surface of the wafer  102 . For example, the fabrication system  110  could use the projection lens  112  and the photomask  114  in conjunction to form a given layer of the etched backplanes  120 . In such instances, the fabrication system  110  could use different projection lenses  112  and/or photomasks  114  to form the different layers included in the composite backplane  121 . In some embodiments, the fabrication system  110  could also include devices that perform various functions to form layers on the wafer  102 . In such instances, the fabrication system  110  could perform a technique, such as chemical mechanical planarization (CMP), that adds layers that form a given substrate and/or layer on the surface of the wafer  102 . In some embodiments, one or more devices included in the fabrication system  110  may perform other processes in the fabrication process. For example, the wafer loader  116  could grind and polish a surface of the wafer  102  before proceeding to add a given layer onto the wafer  102 . 
     The processing unit  108  includes one or more processors that control the operation of the fabrication system  110 . In various embodiments, the processing unit  108  may be one or more central processing units (CPUs), multi-core processors, microprocessors, microcontrollers, digital signal processors, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and/or the like. In some embodiments, the processing unit  108  may be included as part of an operator workstation and/or operated separately from, but in coordination with, the operator workstation. The memory  104  may be used to store software executed by the processing unit  108 . The memory  104  may also store one or more data structures used during the operation of the fabrication system  110 . The memory  104  may include one or more types of machine-readable media. Some common forms of machine-readable media may include 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, and/or any other medium from which a processor or computer is adapted to read. 
     The processing unit  108  executes the fabrication application  106  to produce etched backplanes  120  via control of one or more devices in the fabrication system  110  (e.g., the projection lens  112 , the photomask  114 , the wafer loader  116 , etc.). In various embodiments, the fabrication application  106  may receive inputs specifying configurations for each of the layers  122 - 126  included in the composite backplane  121 . The fabrication application  106  may cause the one or more devices in the fabrication system  110  to pattern layers onto the wafer  102  in order to produce the etched backplanes  120 . For example, the fabrication application  106  could receive a device design as an input that specifies the configuration of components in each of the layers  122 - 126 . In such instances, the processing unit  108  could execute the fabrication application  106  to control the fabrication system  110  when patterning successive layers of the etched backplanes  120 . 
     In some embodiments, the fabrication application  106  may optimize the configuration of one or more layers  122 - 126  based on a target configuration. For example, an operator could identify one or more separate characteristics (e.g., light source type, light source position, modulation type, etc.) of a device that will include the composite backplane  121 . In such instances, the fabrication application  106  could determine the components to include in each respective layer  122 - 126  and position components within each layer  122 - 126  in an arrangement that enables the composite backplane  121  to possess the characteristics specified in the target configuration. 
     The etched backplanes  120  include one or more portions of a composite backplane  121  that are used to drive the operation of a display panel. In some embodiments, the etched backplanes  121  are a patterned and etched version of the wafer  102  and include backplanes for multiple packages (e.g., multiple display panels). In some embodiments, the fabrication system  110  may slice the wafer into separate panels, where the etched backplanes  120  include a set of separate composite backplanes  121 . 
     A composite backplane  121  is a version of a display device backplane that provides structural support for a display panel. As shown, the composite backplane  121  includes a composition of layers that combine to drive and control light provided by a light source and modulated by a set of liquid crystals in a separate layer. For example, a display panel including a layer of liquid crystals (not shown) and the composite backplane  121  may use one or more electrodes included in the ALM interface layer  122  to control the orientation of subsets of liquid crystals in order to control the polarity of light rays passing through the liquid crystal layer. 
     For example, the composite backplane  121  could compose three layers that are fabricated in sequence using standard lithographic manufacturing processes. In this example, the layers include the ALM interface layer  122  that includes a set of pixelated conducting pads (e.g., electrodes) for liquid crystal cells; the ALM interface layer  122  could also include a black matrix layer, a reflection control coating (e.g., anti-reflection coating, partial-reflection coating, high-reflection coating, etc.). The layers also include the photonic IC layer  124  that includes light-guiding waveguides and out-coupling components in single-layer or multi-layer configurations. The layers can also include the electronic IC layer  126  that includes electronic bus lines for power, control &amp; data, as well as integrated electronic circuitry for components in the ALM interface layer  122  and the photonic IC layer  124 . In some embodiments, one or more vertical metallic via paths (“vias”) are used to connect the electronic IC layer  126  with the ALM interface layer  122  and the photonic IC layer  124 , respectively. 
       FIG.  2    illustrates a view of a composite backplane  200  processed by the device fabrication system  100  of  FIG.  1   , according to various embodiments of the present disclosure. As shown, the composite backplane  200  includes the ALM interface layer  122 , the photonic IC layer  124 , the electronic IC layer  126 , and the substrate  128 . The ALM interface layer  122  includes pixelated electrodes  220 , a black matrix layer  217 , and an alignment layer  218 . The photonic IC layer includes light-guiding waveguides  214  and output couplers  215 . The electronic IC layer  126  includes electronic ICs  212 , metallic vias  210 , and electronic bus lines  208 . 
     As shown, the composite backplane  200  controls the light generated by a light source. In particular, the composite backplane  200  controls both an active media, such as liquid crystals (not shown), via the pixelated electrodes  220  included in the ALM interface layer  122  and the light-guiding waveguides (“photonic circuits”)  214 , output couplers  215 , and other light modulating and out-coupling components. In particular, the light-guiding waveguides  214  control the light  206  provided by a light source, such as a side light source or other light source (e.g., front-lit light source, back-light lit source) that provides the light to the photonic IC layer. In addition, the pixelated electrodes in the ALM interface layer  122  control sets of active media in a separate active medium layer that modify the polarization of the light provided by the light source. 
     Controlling the light propagating from the light source through multiple components increases the light efficiency (e.g., photon efficiency, pixel density, etc.) due to reductions in optical crosstalk between neighboring pixels and greater control of emission cones for the light. The composite backplane  200  provides benefits associated with both reflective designs that modulate front-lit light sources and transmissive designs that modulate back-lit light sources. Further, the configuration of the composite backplane  121  increases the fill factor due to reductions in components between layers, such as moving most electronic components to a separate electronic IC  126  and connecting the electronic components with other components using metallic via paths  210 . 
     In some embodiments, the composite backplane  200  may operate in conjunction with a front-lit light source, such as a liquid crystal on silicon (LCOS) layer disposed on the composite backplane  120 . In such instances, a display panel including the LCOS layer and the composite backplane may act as a spatial light modulator and may include additional components in the layers  122 - 126  in order to separate the incident and reflected light paths of light generated by the light source in the LCOS layer. In other embodiments, the composite backplane  200  may operate in conjunction with a back-lit light source and act as a spatial light modulator for a transmissive liquid crystal layer. 
     In various embodiments, the composite backplane  200  may be integrated with other devices or components. For example, the composite backplane  200  could be integrated with one or more on-chip light sources, such as laser sources, superluminescent light-emitting diode (SLED) sources and/or light-emitting diode (LED) arrays. In such cases, the device may act as a stand-alone display module that modulates light produced by the on-chip light sources. In various embodiments, the light source can be any type of LED (e.g., LED, pLED, organic light-emitting diode (OLED), quantum-dot light-emitting diode (QDLED), perovskite light-emitting diode (PeLED), etc.). In some embodiments, the light source can be one or more lasers, such as diode lasers, vertical cavity surface emission lasers, heterogeneously-integrated lasers, hybrid lasers, fiber lasers, and so forth. In some embodiments, the light source may be a nonlinear light source from one or more other light sources, such as a pump laser field, a sum-frequency generation source, second-harmonic generation source, a four-wave-mixing source, a difference-frequency generation source, a parametric down-conversion source, and so forth. 
     Additionally or alternatively, the composite backplane  200  may be integrated with additional integrated circuit modules in order to enable more power-efficient data processing and transferring of data between the processor and the light modulating components in the layers  122 - 124 . 
     Variations for the Composite Backplane Architecture 
       FIG.  3    illustrates views of various configurations for a liquid crystal interface layer included in a composite backplane  200  of  FIG.  2   , according to various embodiments of the present disclosure. As shown, a set of candidate ALM interface layers  300  include candidate ALM interface layer configurations  310 - 330 . 
     As shown, each configuration  310 - 330  of the ALM interface layer  122  can be combined independently with other configurations for the respective photonics IC layer  124  and/or the electronic IC  126 . In various embodiments, each of the candidate ALM interface layers  300  may act as an active pixel interface layer that includes components to control one or more ALM pixel cells for a given active medium (e.g., a set of liquid crystals in an active media layer that control light for one pixel). The ALM interface layer  300  may also include different types of optical coating (e.g., AR or PR coating  216 ), alignment layers to position the electrodes, and/or black matrix layers that block extraneous light between pixels. 
     For example, configuration  310  could include a set of pixelated electrodes  220  to control separate active media pixel cells (not shown). In such instances, the pixelated electrodes can provide individual electronic control signals to separate pixel cells. The configuration  310  may include an anti-reflective (AR) coating  216  for single-pass operation of the pixel cells, or partial-reflective (PR) coating  216  for resonance-mode operation of the pixel cells. 
     In various embodiments, the candidate ALM interface layers  300  may include an alignment layer  218 . In some embodiments, the structure of the alignment layer  218  may be based on a micro-structured surface that can be lithographically fabricated, or the structure may be based on materials that can be spun on top of the device. In some embodiments, the alignment layer  218  fills gaps between components in the layer. For example, configuration  310  illustrates the alignment layer occupying spaces between the pixelated electrodes  220 . 
     In some embodiments, the candidate ALM interface layers  300  may include black matrix layers  217 . The black matrix layer  217  may be located at various vertical positions within the ALM interface layer  122  and/or the photonics IC layer  124 . For example, the black matrix layer  217  could be positioned in spaces between the pixelated electrodes  220  and may be made of a reflective metallic material. When the black matrix layer  217  is fabricated with the other components in the ALM interface layer  300 , the black matrix layer  217  is positioned correctly and no post-fabrication alignment is necessary. In some embodiments, the black matrix layer may reduce crosstalk between pixel cells by blocking or reflecting light that would otherwise propagate through the ALM interface layer  300 . In such instances, the black matrix layer  217  reduces the amount of light seen in order to restrict further refraction. In some embodiments, the configuration of the black matrix layer  217  may differ. For example, configuration  320  includes a black matrix layer  217  that includes a thin black matrix film below each electrode  220  and thicker sections between each electrode  220 . In configuration  330 , the black matrix layer  217  is also included in the optical coating layer  216 . 
     In various embodiments, a particular configuration  310 - 330  may be selected based on a set of design, fabrication, and/or operating characteristics. For example, a designer could select specific materials and fabrication processes for the ALM interface layer  300  in order to be compatible with the fabrication of the photonic IC layer  124  and/or the electronic IC layer  126  (e.g., maximum processing temperature, material compatibility, etc.). In another example, a designer may specify the configuration of the electrodes and/or the black matrix layer in order to control a greater number of pixels or to suppress optical inefficiencies like scattering and crosstalk. 
       FIGS.  4 A- 4 B  illustrate views of various configurations for a photonic integrated circuit layer included in the composite backplane  200  of  FIG.  2   , according to various embodiments of the present disclosure. As shown in  FIG.  4 A , a set of candidate photonic IC layers  400  include candidate photonic IC layer configurations  410 - 430 ; as shown in  FIG.  4 B , a second set of candidate photonic IC layers  440  include multi-layer photonic IC layer configurations  450 - 470 . 
     In various embodiments, each of the candidate photonic IC layers  400 ,  440  may include a single layer or multiple layers of photonic integrated circuits (PICs)  214  embedded in a substrate. In operation, the PICs  214  may include color multiplexers (MUX), color demultiplexers (DEMUX), waveguides, couplers, splitters, active light modulating components, and/or out-coupling components. The active PIC components can include amplitude modulators, phase modulators, polarization modulators, etc. that provide active control in the property of the emitted light. Each of the active PIC components can be driven by electronic circuitry built in the electronic IC layer and connected with vertical metallic vias. Each active PIC component  214  can perform various operations on incoming light, such as focusing, splitting, isolation, polarization modulation, coupling, amplitude modulation and/or phase modulation. 
     In various embodiments, some of the PIC components may be light-coupling components that connect the PICs  214  to the light source. For example, the light-coupling components may be optical fibers, light guides, waveguides, nanowires, microwires, lenses, waveguide-grating couplers, waveguide mode converter, lensed fibers, metalenses, plasmonics-based couplers, and so forth. In various embodiments, some of the PIC components may be out-coupling components, such as output couplers  215  that couple light from the PICs  214  and turn the wavelengths of light  206  into free space in a specific direction (e.g., direct the light vertically towards the active medium layer). Additionally or alternatively, the out-coupling components may include waveguide grating couplers, ring resonators, side-coupled scatterers, top-coupled scatterers, etc. The gratings can contain multi-material-layers, multi-etch-depth, straight or slanted, or any combination. 
     In some embodiments, a given configuration  420 ,  430  may include an additional layer, such as a dielectric high-reflective (HR) coating  422  or a metallic film  432  beneath the PICs  214  in order to improve the out-coupling efficiency of the output couplers  215  by reflecting some of the light towards the pixel cells. Additionally or alternatively, a particular configuration  410 - 430 ,  450 - 470  may be selected based on a set of design, fabrication, and/or operating characteristics. For example, a designer could select specific materials and fabrication processes for the photonics IC layer  400 ,  440  in order to be compatible with the fabrication of the ALM interface layer  122  and/or the electronic IC layer  126  (e.g., maximum processing temperature, material compatibility, etc.). 
     In various embodiments, as shown in  FIG.  4 B , some configurations  450 - 470  may include multiple layers of PICs  214  (e.g.,  214   a ,  214   b ,  214   c , etc.). In such instances, the light  206   a  from the light source may be coupled (as illustrated by  206   b ) between a first layer of waveguides  214   a  and a second layer of waveguides  214   b . In some embodiments, the configuration  460  may include an active intensity modulator  452  that dynamically controls properties of the light  206 . In some embodiments, the photonic IC layer  440  may include various PIC layers  214  (e.g., 1-6 layers) of varying lengths. For example, configurations  450 ,  460  include two PIC layers  214  and configuration  470  includes three PIC layers  214  and multiple active intensity modulators  452 . 
       FIGS.  5 A- 5 B  illustrate views of various configurations for an electronics integrated circuit (IC) layer included in the composite backplane of  FIG.  2   , according to various embodiments of the present disclosure. As shown, a set of candidate electronics IC layers  500  include candidate electronic IC layer configurations  510 - 540 . 
     In various embodiments, each of the configurations  510 - 540  may incorporate complementary metal-oxide-semiconductor (CMOS) technology or other semiconductor IC technology (e.g., PMOS and NMOS). The electronic modules included in the electronics IC layer  500  may be based on Silicon wafers (similar to LCOS technology), or using TFT technology (α-Si, low-temperature polycrystalline silicon (LTPS), Organic-TFT, oxide-TFT, LTPS+oxide-TFT, etc.) on transparent substrates. 
     In various embodiments, the electronic IC layer  500  may contain power, data, and other electronic bus lines, as well as circuitry for each active pixel cell to drive a set of active media included in the pixel cell. For example, configuration  530  includes a set of electronic IC modules  212   a ,  212   b ,  212   c  that drive separate pixelated electrodes  220 . Each electronic module  212  is connected to the component in using metallic via paths  210  that may be positioned between components, such as metallic vias being positioned between the PIC components  214  in the photonic IC layer  124  in order to connect to the pixelated electrodes  220  in the ALM interface layer  122 . In another example, the configuration  540  includes one or more electronic modules  212   d  for the PIC components (e.g., active PIC components) in the photonic IC layer  124 . The electronic module  212   d  is connected to the active PIC component through metallic vias that connect to the active PIC component in the photonic IC layer  124 . 
     In some embodiments, the electronics IC layer  500  may contain additional circuitry (e.g., metallic vias  210 , electronic bus lines  208 ) and/or additional electronic modules  212   e . For example, the configuration  540  includes additional electronic modules (e.g., modules  212   e  for the ALM interface layer  122 , modules  212   f  for the photonics IC layer  124 ) in order to provide on-chip processing of data for a display panel. The additional electronic modules  212   e ,  212   f  could improve the power consumption, data processing, transfer speed by transmitting commands to other electronic ICs  212  that control the components in the other layers  122 - 124 . 
       FIGS.  6 A- 6 C  illustrate views of various configurations for a cell  600  including the composite backplane  200  of  FIG.  2   , according to various embodiments of the present disclosure. As shown in  FIG.  6 A , the cell  600  includes the substrate  128 , the electronics IC layer  126 , the photonics IC layer  124 , the ALM interface layer  122 , an active medium layer  620 , and top layer  610 . In some embodiments, the top layer  610  may include an optical coating  602  (e.g., an AR coating), a polarizer layer  604 , an electrostatic shielding layer  606 , a top substrate  608 , an electrode layer  614  and/or an alignment layer  614 . Although cell  600  is shown with liquid crystals as the active media, the cell  600  can include other active media in lieu of liquid crystals in the active media layer  620 . 
     In operation, the pixelated electrodes  220  control separate sets of active media, such as liquid crystals  622  included in the active medium layer  620 , in order to control the light output from the cell  600 . For example, the pixelated electrodes  220  could separately modulate the amplitude of separate subsets of liquid crystals  622  in order to modify the amplitude of light output from the cell  600 . In other embodiments, the pixelated electrodes  220  may control other types of active media. 
     As shown in  FIG.  6 B , the pixelated electrodes  220  could separately modulate the phase of separate subsets of liquid crystals  622  in order to modify the light output from the cell  640 . In such instances, the top layer  610  may not include the polarizer layer  604 . The respective portions  644 ,  646  of the light  206  output by the cell  622  may have different polarizations based on the polarization of the different subsets of the liquid crystals  622 . 
     As shown in  FIG.  6 C , the portion of a pixel cell illustrates a top view  660  and an isometric view  680  of portions of the composite backplane  200  included in the cells  600 ,  640 . As shown in the respective top and isometric views  660 ,  680 , the metallic vias  210  and electronic buses  208  are positioned in locations to provide connections to other components in other layers (e.g., the output couplers  215 , the pixelated electrodes  220 ) and minimize obstruction of wavelengths of light  206  as the light propagates through the composite backplane  200 . 
       FIG.  7    sets forth a flow diagram of method steps  700  for fabricating a composite backplane for a display panel, according to the various embodiments of the present disclosure. Although the method steps are described in conjunction with  FIGS.  1 - 6 C , persons of ordinary skill in the art will understand that any system configured to perform this method and/or methods described herein, in any order, and in any combination not logically contradicted, is within the scope of the present disclosure. 
     As shown, the method  700  begins at step  702 , where the fabrication system  110  determines a configuration for the electronics IC layer  126 . In various embodiments, the fabrication application  106  included in the fabrication system  110  may receive indications of a specific configuration of components (e.g., electrodes  220 ) used to control sets of active media in a separate active media layer  620 . In some embodiments, the configuration may include additional characteristics and/or components, such as the location of the black matrix layer  217 , optical coating layer  216 , and/or the alignment layer  218 . 
     In some embodiments, the fabrication application  106  may optimize the configuration of one or more layers  122 - 126  based on a target configuration. For example, an operator could identify one or more separate characteristics (e.g., light source type, light source position, modulation type, etc.) of a device that will include the composite backplane  121 . In such instances, the fabrication application  106  could determine the components to include in each respective layer  122 - 126  and position components within each layer  122 - 126  in an arrangement that enables the composite backplane  121  to possess the characteristics specified in the target configuration. 
     At step  704 , the fabrication system  110  determines a configuration for the photonics IC layer  124 . In various embodiments, the fabrication application  106  may receive indications of a specific configuration of components, such as specific photonic circuits  214 , output couplers  215 , and/or additional layers  422 ,  432  to include in the photonic IC layer  124 . The photonic layer  124  uses the specified components to control the wavelengths of light  206  from the light source. In some embodiments, the photonic IC layer  124  includes active PIC components (e.g., amplitude, phase, and/or polarization modulators) that actively control the light  206 . 
     At step  706 , the fabrication system  110  determines a configuration for the electronics IC layer  126 . In various embodiments, the fabrication application  106  may receive indications of a specific configuration of components to include in the electronics IC layer  126 . In some embodiments, the components include specific integrated circuit modules used to control the operation of components in other layers, such as the electrodes  220  in the ALM interface layer  122  and/or the active PIC components in the photonic IC layer  124 . In some embodiments, the electronics IC layer  126  may include additional components, such as additional bus lines  208  for power, metallic via paths  210  for communication, and/or additional electronic IC modules  212  for data processing. 
     At step  708 , the fabrication system  110  forms a composite backplane  200  based on the determined layers. In various embodiments, the fabrication application  106  may produce a composite backplane  121  that includes each of the determined layers  122 - 126 . Upon determining the design for the composite backplane  121 , the fabrication system  110  causes the wafer loader  116  to manipulate the wafer  102  and uses the projection lens  112  and photomask  114  to pattern portions of the wafer  102  to generate etched backplane  120  that includes multiple panels of the composite backplane  121 . In various embodiments, the fabrication system may use various lithography-based nano-manufacturing processes associated with fabricating electronic components and/or photonic components in order to pattern various the etched backplanes  120  on the wafer  102 . 
     At step  710 , the fabrication system  110  fabricates a display panel that includes the composite backplane  200 . In various embodiments, the fabrication system  100  combines the composite backplane  121  with other layers, such as the active medium layer  620 , top layer  610 , and/or components to fabricate display assemblies, such as a display panel, a device containing a display panel (e.g., a mobile phone, tablet, wearable near-eye display, etc.), and so forth. In various embodiments, the fabricated display panel does not require post-fabrication alignment of the components included in the composite backplane  121 . 
     The Artificial Reality System 
     Embodiments of the 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) or near-eye display (NED) connected to a host computer system, a standalone HMD or NED, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers. 
       FIG.  8    is a block diagram of an embodiment of a near-eye display (NED) system  800  in which a console operates, according to various embodiments. The NED system  800  may operate in a virtual reality (VR) system environment, an augmented reality (AR) system environment, a mixed reality (MR) system environment, or some combination thereof. The NED system  800  shown in  FIG.  8    comprises a NED  805  and an input/output (I/O) interface  875  that is coupled to the console  870 . In various embodiments, the composite display system  800  is included in or operates in conjunction with the NED system  800 . For example, the composite display system  800  may be included within NED  805  or may be coupled to the console  870  and/or the NED 
     While  FIG.  8    shows an example NED system  800  including one NED  805  and one I/O interface  875 , in other embodiments any number of these components may be included in the NED system  800 . For example, there may be multiple NEDs  805 , and each NED  805  has an associated I/O interface  875 . Each NED  805  and I/O interface  875  communicates with the console  870 . In alternative configurations, different and/or additional components may be included in the NED system  800 . Additionally, various components included within the NED  805 , the console  870 , and the I/O interface  875  may be distributed in a different manner than is described in conjunction with  FIGS.  1 - 3 B  in some embodiments. For example, some or all of the functionality of the console  870  may be provided by the NED  805  and vice versa. 
     The NED  805  may be a head-mounted display that presents content to a user. The content may include virtual and/or augmented views of a physical, real-world environment including computer-generated elements (e.g., two-dimensional or three-dimensional images, two-dimensional or three-dimensional video, sound, etc.). In some embodiments, the NED  805  may also present audio content to a user. The NED  805  and/or the console  870  may transmit the audio content to an external device via the I/O interface  875 . The external device may include various forms of speaker systems and/or headphones. In various embodiments, the audio content is synchronized with visual content being displayed by the NED  805 . 
     The NED  805  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. 
     As shown in  FIG.  8   , the NED  805  may include a depth camera assembly (DCA)  855 , one or more locators  820 , a display  825 , an optical assembly  830 , one or more position sensors  835 , an inertial measurement unit (IMU)  840 , an eye tracking system  845 , and a varifocal module  850 . In some embodiments, the display  825  and the optical assembly  830  can be integrated together into a projection assembly. Various embodiments of the NED  805  may have additional, fewer, or different components than those listed above. Additionally, the functionality of each component may be partially or completely encompassed by the functionality of one or more other components in various embodiments. 
     The DCA  855  captures sensor data describing depth information of an area surrounding the NED  805 . The sensor data may be generated by one or a combination of depth imaging techniques, such as triangulation, structured light imaging, time-of-flight imaging, stereo imaging, laser scan, and so forth. The DCA  855  can compute various depth properties of the area surrounding the NED  805  using the sensor data. Additionally or alternatively, the DCA  855  may transmit the sensor data to the console  870  for processing. Further, in various embodiments, the DCA  855  captures or samples sensor data at different times. For example, the DCA  855  could sample sensor data at different times within a time window to obtain sensor data along a time dimension. 
     The DCA  855  includes an illumination source, an imaging device, and a controller. The illumination source emits light onto an area surrounding the NED  805 . In an embodiment, the emitted light is structured light. The illumination source includes 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 (such as edge emitters), inorganic or organic light-emitting diodes (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 illumination source can emit light having a structured light pattern. The imaging device captures ambient light in the environment surrounding NED  805 , in addition to light reflected off of objects in the environment that is generated by the plurality of emitters. In various embodiments, the imaging device may be an infrared camera or a camera configured to operate in a visible spectrum. The controller coordinates how the illumination source emits light and how the imaging device captures light. For example, the controller may determine a brightness of the emitted light. In some embodiments, the controller also analyzes detected light to detect objects in the environment and position information related to those objects. 
     The locators  820  are objects located in specific positions on the NED  805  relative to one another and relative to a specific reference point on the NED  805 . A locator  820  may be a light emitting diode (LED), a corner cube reflector, a reflective marker, a type of light source that contrasts with an environment in which the NED  805  operates, or some combination thereof. In embodiments where the locators  820  are active (i.e., an LED or other type of light emitting device), the locators  820  may emit light in the visible band (˜380 nm to 950 nm), in the infrared (IR) band (˜950 nm to 9700 nm), in the ultraviolet band (70 nm to 380 nm), some other portion of the electromagnetic spectrum, or some combination thereof. 
     In some embodiments, the locators  820  are located beneath an outer surface of the NED  805 , which is transparent to the wavelengths of light emitted or reflected by the locators  820  or is thin enough not to substantially attenuate the wavelengths of light emitted or reflected by the locators  820 . Additionally, in some embodiments, the outer surface or other portions of the NED  805  are opaque in the visible band of wavelengths of light. Thus, the locators  820  may emit light in the IR band under an outer surface that is transparent in the IR band but opaque in the visible band. 
     The display  825  displays two-dimensional or three-dimensional images to the user in accordance with pixel data received from the console  870  and/or one or more other sources. In various embodiments, the display  825  comprises a single display or multiple displays (e.g., separate displays for each eye of a user). In some embodiments, the display  825  comprises a single or multiple waveguide displays. Light can be coupled into the single or multiple waveguide displays via, e.g., a liquid crystal display (LCD), 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, a laser-based display, one or more waveguides, other types of displays, a scanner, a one-dimensional array, and so forth. In addition, combinations of the display types may be incorporated in display  825  and used separately, in parallel, and/or in combination. 
     The optical assembly  830  magnifies image light received from the display  825 , corrects optical errors associated with the image light, and presents the corrected image light to a user of the NED  805 . The optical assembly  830  includes a plurality of optical elements. For example, one or more of the following optical elements may be included in the optical assembly  830 : an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, a reflecting surface, or any other suitable optical element that deflects, reflects, refracts, and/or in some way alters image light. Moreover, the optical assembly  830  may include combinations of different optical elements. In some embodiments, one or more of the optical elements in the optical assembly  830  may have one or more coatings, such as partially reflective or antireflective coatings. 
     In some embodiments, the optical assembly  830  may be designed to correct one or more types of optical errors. Examples of optical errors 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, in addition to other types of optical errors. In some embodiments, visual content transmitted to the display  825  is pre-distorted, and the optical assembly  830  corrects the distortion as image light from the display  825  passes through various optical elements of the optical assembly  830 . In some embodiments, optical elements of the optical assembly  830  are integrated into the display  825  as a projection assembly that includes at least one waveguide coupled with one or more optical elements. 
     The IMU  840  is an electronic device that generates data indicating a position of the NED  805  based on measurement signals received from one or more of the position sensors  835  and from depth information received from the DCA  855 . In some embodiments of the NED  805 , the IMU  840  may be a dedicated hardware component. In other embodiments, the IMU  840  may be a software component implemented in one or more processors. 
     In operation, a position sensor  835  generates one or more measurement signals in response to a motion of the NED  805 . Examples of position sensors  835  include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, one or more altimeters, one or more inclinometers, and/or various types of sensors for motion detection, drift detection, and/or error detection. The position sensors  835  may be located external to the IMU  840 , internal to the IMU  840 , or some combination thereof. 
     Based on the one or more measurement signals from one or more position sensors  835 , the IMU  840  generates data indicating an estimated current position of the NED  805  relative to an initial position of the NED  805 . For example, the position sensors  835  include multiple accelerometers to measure translational motion (forward/back, up/down, left/right) and multiple gyroscopes to measure rotational motion (e.g., pitch, yaw, and roll). In some embodiments, the IMU  840  rapidly samples the measurement signals and calculates the estimated current position of the NED  805  from the sampled data. For example, the IMU  840  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 NED  805 . Alternatively, the IMU  840  provides the sampled measurement signals to the console  870 , which analyzes the sample data to determine one or more measurement errors. The console  870  may further transmit one or more of control signals and/or measurement errors to the IMU  840  to configure the IMU  840  to correct and/or reduce one or more measurement errors (e.g., drift errors). The reference point is a point that may be used to describe the position of the NED  805 . The reference point may generally be defined as a point in space or a position related to a position and/or orientation of the NED  805 . 
     In various embodiments, the IMU  840  receives one or more parameters from the console  870 . The one or more parameters are used to maintain tracking of the NED  805 . Based on a received parameter, the IMU  840  may adjust one or more IMU parameters (e.g., a sample rate). In some embodiments, certain parameters cause the IMU  840  to update an initial position of the reference point so that 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 drift errors in detecting a current position estimate of the IMU  840 . 
     In various embodiments, the eye tracking system  845  is integrated into the NED  805 . The eye-tracking system  845  may comprise one or more illumination sources (e.g., infrared illumination source, visible light illumination source) and one or more imaging devices (e.g., one or more cameras). In operation, the eye tracking system  845  generates and analyzes tracking data related to a user&#39;s eyes as the user wears the NED  805 . In various embodiments, the eye tracking system  845  estimates the angular orientation of the user&#39;s eye. The orientation of the eye corresponds to the direction of the user&#39;s gaze within the NED  805 . The orientation of the user&#39;s eye is defined herein as the direction of the foveal axis, which is the axis between the fovea (an area on the retina of the eye with the highest concentration of photoreceptors) and the center of the eye&#39;s pupil. In general, when a user&#39;s eyes are fixed on a point, the foveal axes of the user&#39;s eyes intersect that point. The pupillary axis is another axis of the eye that is defined as the axis passing through the center of the pupil and that is perpendicular to the corneal surface. The pupillary axis does not, in general, directly align with the foveal axis. Both axes intersect at the center of the pupil, but the orientation of the foveal axis is offset from the pupillary axis by approximately −1° to 8° laterally and ±4° vertically. Because the foveal axis is defined according to the fovea, which is located in the back of the eye, the foveal axis can be difficult or impossible to detect directly in some eye tracking embodiments. Accordingly, in some embodiments, the orientation of the pupillary axis is detected and the foveal axis is estimated based on the detected pupillary axis. 
     In general, movement of an eye corresponds not only to an angular rotation of the eye, but also to a translation of the eye, a change in the torsion of the eye, and/or a change in shape of the eye. The eye tracking system  845  may also detect translation of the eye, i.e., a change in the position of the eye relative to the eye socket. In some embodiments, the translation of the eye is not detected directly, but is approximated based on a mapping from a detected angular orientation. Translation of the eye corresponding to a change in the eye&#39;s position relative to the detection components of the eye tracking unit may also be detected. Translation of this type may occur, for example, due to a shift in the position of the NED  805  on a user&#39;s head. The eye tracking system  845  may also detect the torsion of the eye, i.e., rotation of the eye about the pupillary axis. The eye tracking system  845  may use the detected torsion of the eye to estimate the orientation of the foveal axis from the pupillary axis. The eye tracking system  845  may also track a change in the shape of the eye, which may be approximated as a skew or scaling linear transform or a twisting distortion (e.g., due to torsional deformation). The eye tracking system  845  may estimate the foveal axis based on some combination of the angular orientation of the pupillary axis, the translation of the eye, the torsion of the eye, and the current shape of the eye. 
     As the orientation may be determined for both eyes of the user, the eye tracking system  845  is able to determine where the user is looking. The NED  805  can use the orientation of the eye to, e.g., determine an inter-pupillary distance (IPD) of the user, determine gaze direction, introduce depth cues (e.g., blur image outside of the user&#39;s main line of sight), collect heuristics on the user interaction in the VR media (e.g., time spent on any particular subject, object, or frame as a function of exposed stimuli), some other function that is based in part on the orientation of at least one of the user&#39;s eyes, or some combination thereof. Determining a direction of a user&#39;s gaze may include determining a point of convergence based on the determined orientations of the user&#39;s left and right eyes. A point of convergence may be the point that the two foveal axes of the user&#39;s eyes intersect (or the nearest point between the two axes). The direction of the user&#39;s gaze may be the direction of a line through the point of convergence and through the point halfway between the pupils of the user&#39;s eyes. 
     In some embodiments, the varifocal module  850  is integrated into the NED  805 . The varifocal module  850  may be communicatively coupled to the eye tracking system  845  in order to enable the varifocal module  850  to receive eye tracking information from the eye tracking system  845 . The varifocal module  850  may further modify the focus of image light emitted from the display  825  based on the eye tracking information received from the eye tracking system  845 . Accordingly, the varifocal module  850  can reduce vergence-accommodation conflict that may be produced as the user&#39;s eyes resolve the image light. In various embodiments, the varifocal module  850  can be interfaced (e.g., either mechanically or electrically) with at least one optical element of the optical assembly  830 . 
     In operation, the varifocal module  850  may adjust the position and/or orientation of one or more optical elements in the optical assembly  830  in order to adjust the focus of image light propagating through the optical assembly  830 . In various embodiments, the varifocal module  850  may use eye tracking information obtained from the eye tracking system  845  to determine how to adjust one or more optical elements in the optical assembly  830 . In some embodiments, the varifocal module  850  may perform foveated rendering of the image light based on the eye tracking information obtained from the eye tracking system  845  in order to adjust the resolution of the image light emitted by the display  825 . In this case, the varifocal module  850  configures the display  825  to display a high pixel density in a foveal region of the user&#39;s eye-gaze and a low pixel density in other regions of the user&#39;s eye-gaze. 
     The I/O interface  875  facilitates the transfer of action requests from a user to the console  870 . In addition, the I/O interface  875  facilitates the transfer of device feedback from the console  870  to the user. 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, such as pausing video playback, increasing or decreasing the volume of audio playback, and so forth. In various embodiments, the I/O interface  875  may include one or more input devices. Example input devices include: a keyboard, a mouse, a game controller, a joystick, and/or any other suitable device for receiving action requests and communicating the action requests to the console  870 . In some embodiments, the I/O interface  875  includes an IMU  840  that captures calibration data indicating an estimated current position of the I/O interface  875  relative to an initial position of the I/O interface  875 . 
     In operation, the I/O interface  875  receives action requests from the user and transmits those action requests to the console  870 . Responsive to receiving the action request, the console  870  performs a corresponding action. For example, responsive to receiving an action request, console  870  may configure I/O interface  875  to emit haptic feedback onto an arm of the user. For example, console  870  may configure I/O interface  875  to deliver haptic feedback to a user when an action request is received. Additionally or alternatively, the console  870  may configure the I/O interface  875  to generate haptic feedback when the console  870  performs an action, responsive to receiving an action request. 
     The console  870  provides content to the NED  805  for processing in accordance with information received from one or more of: the DCA  855 , the eye tracking system  845 , one or more other components of the NED  805 , and the I/O interface  875 . In the embodiment shown in  FIG.  8   , the console  870  includes an application store  860  and an engine  865 . In some embodiments, the console  870  may have additional, fewer, or different modules and/or components than those described in conjunction with  FIG.  8   . Similarly, the functions further described below may be distributed among components of the console  870  in a different manner than described in conjunction with  FIG.  8   . 
     The application store  860  stores one or more applications for execution by the console  870 . An application is a group of instructions that, when executed by a processor, performs a particular set of functions, such as generating content for presentation to the user. For example, an application may generate content in response to receiving inputs from a user (e.g., via movement of the NED  805  as the user moves his/her head, via the I/O interface  875 , etc.). Examples of applications include: gaming applications, conferencing applications, video playback applications, or other suitable applications. 
     In some embodiments, the engine  865  generates a three-dimensional mapping of the area surrounding the NED  805  (i.e., the “local area”) based on information received from the NED  805 . In some embodiments, the engine  865  determines depth information for the three-dimensional mapping of the local area based on depth data received from the NED  805 . In various embodiments, the engine  865  uses depth data received from the NED  805  to update a model of the local area and to generate and/or modify media content based in part on the updated model of the local area. 
     The engine  865  also executes applications within the NED system  800  and receives position information, acceleration information, velocity information, predicted future positions, or some combination thereof, of the NED  805 . Based on the received information, the engine  865  determines various forms of media content to transmit to the NED  805  for presentation to the user. For example, if the received information indicates that the user has looked to the left, the engine  865  generates media content for the NED  805  that mirrors the user&#39;s movement in a virtual environment or in an environment augmenting the local area with additional media content. Accordingly, the engine  865  may generate and/or modify media content (e.g., visual and/or audio content) for presentation to the user. The engine  865  may further transmit the media content to the NED  805 . Additionally, in response to receiving an action request from the I/O interface  875 , the engine  865  may perform an action within an application executing on the console  870 . The engine  865  may further provide feedback when the action is performed. For example, the engine  865  may configure the NED  805  to generate visual and/or audio feedback and/or the I/O interface  875  to generate haptic feedback to the user. 
     In some embodiments, based on the eye tracking information (e.g., orientation of the user&#39;s eye) received from the eye tracking system  845 , the engine  865  determines a resolution of the media content provided to the NED  805  for presentation to the user on the display  825 . The engine  865  may adjust a resolution of the visual content provided to the NED  805  by configuring the display  825  to perform foveated rendering of the visual content, based at least in part on a direction of the user&#39;s gaze received from the eye tracking system  845 . The engine  865  provides the content to the NED  805  having a high resolution on the display  825  in a foveal region of the user&#39;s gaze and a low resolution in other regions, thereby reducing the power consumption of the NED  805 . In addition, using foveated rendering reduces a number of computing cycles used in rendering visual content without compromising the quality of the user&#39;s visual experience. In some embodiments, the engine  865  can further use the eye tracking information to adjust a focus of the image light emitted from the display  825  in order to reduce vergence-accommodation conflicts. 
       FIG.  9 A  is a diagram of an NED  900 , according to various embodiments. In various embodiments, NED  900  presents media to a user. The media may include visual, auditory, and haptic content. In some embodiments, NED  900  provides artificial reality (e.g., virtual reality) content by providing a real-world environment and/or computer-generated content. In some embodiments, the computer-generated content may include visual, auditory, and haptic information. The NED  900  is an embodiment of the NED  805  and includes a front rigid body  905  and a band  910 . The front rigid body  905  includes an electronic display element of the electronic display  825  (not shown in  FIG.  9 A ), the optics assembly  830  (not shown in  FIG.  9 A ), the IMU  840 , the one or more position sensors  935 , the eye tracking system  945 , and the locators  922 . In the embodiment shown by  FIG.  9 A , the position sensors  935  are located within the IMU  840 , and neither the IMU  840  nor the position sensors  935  are visible to the user. 
     The locators  922  are located in fixed positions on the front rigid body  905  relative to one another and relative to a reference point  915 . In the example of  FIG.  9 A , the reference point  915  is located at the center of the IMU  840 . Each of the locators  922  emits light that is detectable by the imaging device in the DCA  855 . The locators  922 , or portions of the locators  922 , are located on a front side  920 A, a top side  920 B, a bottom side  920 C, a right side  920 D, and a left side  920 E of the front rigid body  905  in the example of  FIG.  9 A . 
     The NED  900  includes the eye tracking system  945 . As discussed above, the eye tracking system  945  may include a structured light generator that projects an interferometric structured light pattern onto the user&#39;s eye and a camera to detect the illuminated portion of the eye. The structured light generator and the camera may be located off the axis of the user&#39;s gaze. In various embodiments, the eye tracking system  945  may include, additionally or alternatively, one or more time-of-flight sensors and/or one or more stereo depth sensors. In  FIG.  9 A , the eye tracking system  945  is located below the axis of the user&#39;s gaze, although the eye tracking system  945  can alternately be placed elsewhere. Also, in some embodiments, there is at least one eye tracking unit for the left eye of the user and at least one tracking unit for the right eye of the user. 
     In various embodiments, the eye tracking system  945  includes one or more cameras on the inside of the NED  900 . The camera(s) of the eye tracking system  945  may be directed inwards, toward one or both eyes of the user while the user is wearing the NED  900 , so that the camera(s) may image the eye(s) and eye region(s) of the user wearing the NED  900 . The camera(s) may be located off the axis of the user&#39;s gaze. In some embodiments, the eye tracking system  945  includes separate cameras for the left eye and the right eye (e.g., one or more cameras directed toward the left eye of the user and, separately, one or more cameras directed toward the right eye of the user). 
       FIG.  9 B  is a diagram of an NED  950 , according to various embodiments. In various embodiments, NED  950  presents media to a user. The media may include visual, auditory, and haptic content. In some embodiments, NED  950  provides artificial reality (e.g., augmented reality) content by providing a real-world environment and/or computer-generated content. In some embodiments, the computer-generated content may include visual, auditory, and haptic information. The NED  950  is an embodiment of the NED  805 . 
     NED  950  includes frame  952  and display  954 . In various embodiments, the NED  950  may include one or more additional elements. Display  954  may be positioned at different locations on the NED  950  than the locations illustrated in  FIG.  9 B . Display  954  is configured to provide content to the user, including audiovisual content. In some embodiments, one or more displays  954  may be located within frame  952 . 
     NED  950  further includes eye tracking system  945  and one or more corresponding modules  956 . The modules  956  may include emitters (e.g., light emitters) and/or sensors (e.g., image sensors, cameras). In various embodiments, the modules  956  are arranged at various positions along the inner surface of the frame  952 , so that the modules  956  are facing the eyes of a user wearing the NED  950 . For example, the modules  956  could include emitters that emit structured light patterns onto the eyes and image sensors to capture images of the structured light pattern on the eyes. As another example, the modules  956  could include multiple time-of-flight sensors for directing light at the eyes and measuring the time of travel of the light at each pixel of the sensors. As a further example, the modules  956  could include multiple stereo depth sensors for capturing images of the eyes from different vantage points. In various embodiments, the modules  956  also include image sensors for capturing 2D images of the eyes. 
     In sum, a die fabrication system integrates a active light modulation interface layer, a photonic integrated circuit layer, and an electronic integrated circuit layer on a substrate to form a composite backplane. The composite backplane is added to an active medium layer and a top layer to form a composite display panel, such as a liquid crystal display (LCD) panel. The composite backplane  121  includes at least three layers that are fabricated in sequence using a standard lithographic manufacturing process. The layers include an active light modulation interface layer  122  that includes a set of pixelated electrodes for controlling groups of active media that modify the amplitude or phase of wavelengths of light propagating through the active media. The composite backplane also includes a photonic integrated circuit layer that includes light-guiding waveguides and coupling components to control the modulation and direction of wavelengths of light generated by a light source. The composite backplane also includes an electronic integrated circuit layer that includes electronic bus lines and integrated electronic circuitry for components in the active light modulation interface layer and the photonic integrated circuit layer. 
     At least one technical advantage of the disclosed embodiments relative to the prior art is that the composite backplane provides an overall compact size, small weight, and reduced system complexity. In particular, the composite backplane does not require post-fabrication alignment between a photonic integrated circuit layer and an active light modulation interface, or alignment between bottom and top substrates of a liquid crystal cell. Further, a distance between the photonic integrated circuit layer and an active medium layer is greatly reduced, which improves performance of the display panel by increasing the light efficiency, reducing optical crosstalk, and providing greater control on the emission cones generated by the light source. In addition, the composition of the composite backplane improves the fill factor of a display panel due to the arrangement of the photonic integrated circuit layer over the electronic integrated circuit layer. 
     1. In various embodiments, an apparatus comprises a composite backplane that modulates light from a light source, comprising an electronics layer disposed on a substrate, a photonics integrated circuit (IC) layer disposed on the electronics layer that causes light from the light source to propagate in a first direction, and an active light modulation (ALM) interface layer disposed on the photonics IC layer controls an active medium layer in order to control the light propagating in the first direction. 
     2. The apparatus of clause 1, where the ALM interface layer comprises a set of electrodes that modulate one or more pixels, an alignment layer between the set of electrodes, and at least one of an anti-reflection (AR) or a partial-reflection (PR) coating, where the set of electrodes modulate the light propagating in the first direction by controlling corresponding pixels. 
     3. The apparatus of clause 1 or 2, where the ALM interface layer further comprises a black matrix layer interspersed between the set of electrodes, the active medium layer comprises a layer of liquid crystals as an active light modulation medium, and the alignment layer is disposed on the black matrix layer and the set of electrodes. 
     4. The apparatus of any of clauses 1-2, where the photonics IC layer comprises one or more light-guiding waveguides that receive the light produced by the light source and perform a set of optical operations, and a set of output couplers that direct the light from the one or more light-guiding waveguides to propagate in the first direction. 
     5. The apparatus of any of clauses 1-4, where the light source comprises at least one of a light-emitting diode or a laser. 
     6. The apparatus of any of clauses 1-5, where the photonics IC layer further comprises a light-coupling component that connects the light source with the one or more light-guiding waveguides. 
     7. The apparatus of any of clauses 1-6, where the photonics IC layer further comprises a set of optical couplers and a set of intensity modulators, wherein the set of optical couplers and the set of intensity modulators direct at least a portion of the light included in a first light-guiding waveguide to a second light-guiding waveguide. 
     8. The apparatus of any of clauses 1-7, where the electronics layer comprises a first electronic circuit that controls a device included in the ALM interface layer, a first metallic via path through the electronics layer and the photonics IC layer that couples first electronic circuit to the device included in the ALM interface layer, a second electronic circuit that controls a device included in the photonics IC layer, and a second metallic via path through the electronics layer that couples the second electronic circuit to the device included in the photonics IC layer. 
     9. The apparatus of any of clauses 1-8, where the electronics layer further comprises at least a set of electronic circuits that are connected to the first electronic circuit or the second electronic circuit via additional via paths, and the set of electronic circuits process input data and generates a set of one or more control signals for the ALM interface layer or the photonics IC layer. 
     10. The apparatus of any of clauses 1-9, further comprising an active medium layer disposed on the ALM interface layer comprising sets of active media included in a set of pixels, and a top cover layer disposed on the active medium layer, where the sets of active media modify at least one property of the light propagating in the first direction; and each pixel in a set of pixels independently modulates a portion of the light propagating in the first direction. 
     11. In various embodiments, a display system comprises a display panel comprising a composite backplane, including an electronics layer disposed on a substrate, a photonics integrated circuit (IC) layer disposed on the electronics layer that directs light from a light source to propagate in a first direction, and an active light modulation (ALM) interface layer disposed the photonics IC layer, an active medium layer disposed on the ALM interface layer comprising sets of pixels including sets of an active media, and a top cover layer, and a controller causing the display panel to modify the light controlled via the active medium layer or the photonic IC layer. 
     12. The system of clause 11, where the top cover layer comprises at least one of a photoalignment layer, an electrode layer, or a mechanical supporting layer. 
     13. The system of clause 11 or 12, where the light source comprises at least one of a light-emitting diode (LED), a laser, a superluminescent LED, or a nonlinear optical source, and the photonics IC layer further comprises a light-coupling component that connects the light source with the one or more light-guiding waveguides. 
     14. The system of any of clauses 11-13, where each pixel in the set of pixels independently modulates at least one property of the light propagating in the first direction. 
     15. The system of any of clauses 11-14, where the ALM interface layer includes a set of electrodes that modulate the light propagating in the first direction by controlling the sets of the active media, and the controller causes the display panel to modify the light by sending control signals to the set of electrodes. 
     16. The system of any of clauses 11-15, where the photonics IC layer comprises one or more light-guiding waveguides that receive the light produced by the light source and perform a set of optical operations, and a set of output couplers that direct the light from the one or more light-guiding waveguides to propagate in the first direction, where the controller causes the display panel to modify the light by sending control signals to at least one of the one or more light-guiding waveguides or the set of output couplers. 
     17. The system of any of clauses 11-16, where the display panel performs amplitude modulation on the light provided by the light source. 
     18. The system of any of clauses 11-17, where the display panel comprises a holographic display that performs phase modulation on the light provided by the light source. 
     19. The system of any of clauses 11-18, wherein the display panel includes the light source. 
     20. The system of any of clauses 11-19, where the electronics layer comprises a first electronic circuit that controls a device included in the ALM interface layer, a first metallic via path through the electronics layer and the photonics IC layer that couples first electronic circuit to the device included in the ALM interface layer, a second electronic circuit that controls a device included in the photonics IC layer, and a second metallic via path through the electronics layer that couples the second electronic circuit to the device included in the photonics IC layer. 
     Any and all combinations of any of the claim elements recited in any of the claims and/or any elements described in this application, in any fashion, fall within the contemplated scope of the present invention and protection. 
     The descriptions of the various embodiments have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. 
     Aspects of the present embodiments may be embodied as a system, method or computer program product. Accordingly, aspects of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “module,” a “system,” or a “computer.” In addition, any hardware and/or software technique, process, function, component, engine, module, or system described in the present disclosure may be implemented as a circuit or set of circuits. Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
     Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
     Aspects of the present disclosure are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine. The instructions, when executed via the processor of the computer or other programmable data processing apparatus, enable the implementation of the functions/acts specified in the flowchart and/or block diagram block or blocks. Such processors may be, without limitation, general purpose processors, special-purpose processors, application-specific processors, or field-programmable gate arrays. 
     The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     While the preceding is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.