PATENT DOCUMENT

Publication Number: US-12147038-B2
Application Number: US-201916539818-A
Country: US
Kind Code: B2

Title: Optical systems with interleaved light redirectors

Abstract:
An electronic device may include a display that produce images. The display may generate light for an optical system that redirects the light towards an eye box. The optical system may include a waveguide that propagates the light in a first direction towards the output coupler. The output coupler may couple the light out of the waveguide towards the eye box while inverting a parity of the light about the first direction. The coupler may include a first element such as a set of partial mirrors or diffractive gratings that redirects a first portion of the light in a second direction. The coupler may include a second element that redirects a second portion of the light in a third direction opposite the second direction. The first element may redirect the second portion and the second element may redirect the first portion towards the eye box.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 a projector; and 
 an optical system configured to receive light from the projector and configured to redirect the light in a first direction, wherein the optical system includes an input coupler, an output coupler, and a waveguide that propagates the light along a second direction, the output coupler comprising:
 a grating medium having a first surface and a second surface opposite the first surface, 
 a first light-redirecting element configured to redirect the light in a third direction and in the first direction, the first light-redirecting element extending from the first surface to the second surface of the grating medium and comprising a first set of diffractive gratings having a first set of grating vectors extending from a first k-space region to a second k-space region and having second set of grating vectors extending parallel to the first set of grating vectors and from a third k-space region to a fourth k-space region, and 
 a second light-redirecting element that overlaps the first light-redirecting element and that is configured to redirect the light in a fourth direction opposite the third direction and in the first direction, wherein the waveguide has a first exterior surface and a second exterior surface opposite the first exterior surface, the first and second light-redirecting elements are superimposed in a same volume of the grating medium that is located within an interior of the waveguide between the first exterior surface and the second exterior surface, the output coupler is configured to couple the light out of the waveguide through the first surface of the grating medium, the second light-redirecting element extends from the first surface to the second surface of the grating medium, and the second set of light-redirecting elements comprises a second set of diffractive gratings having a third set of grating vectors extending from the first k-space region to the third k-space region and having a fourth set of grating vectors extending parallel to the third set of grating vectors and from the second k-space region to the fourth k-space region. 
 
 
     
     
       2. The electronic device of  claim 1 , wherein the first light-redirecting element is configured to redirect, in the first direction, the light that was redirected by the second light-redirecting element in the fourth direction. 
     
     
       3. The electronic device of  claim 2 , wherein the second light-redirecting element is configured to redirect, in the first direction, the light that was redirected by the first light-redirecting element in the third direction. 
     
     
       4. The electronic device of  claim 3 , wherein the first light-redirecting element comprises a first set of partially-reflective mirrors at a first orientation and wherein the second light-redirecting element comprises a second set of partially-reflective mirrors at a second orientation that are interleaved among the first set of partially-reflective mirrors. 
     
     
       5. The electronic device of  claim 3 , wherein the first light-redirecting element comprises a first set of volume holograms. 
     
     
       6. The electronic device of  claim 5 , wherein the second light-redirecting element comprises a second set of volume holograms. 
     
     
       7. The electronic device of  claim 6 , wherein each of the volume holograms in the first set comprises index of refraction variations oriented in a first direction and wherein each of the volume holograms in the second set comprises index of refraction variations oriented in a second direction that is different from the first direction. 
     
     
       8. The electronic device of  claim 6 , wherein the first and second sets of volume holograms comprise reflection holograms. 
     
     
       9. The electronic device of  claim 6 , wherein the first and second sets of volume holograms comprise transmission holograms. 
     
     
       10. The electronic device of  claim 1 , wherein the first and second light-redirecting elements are configured to invert a parity of an image in the light about the second direction. 
     
     
       11. The electronic device of  claim 10 , wherein the projector is configured to emit an inverted version of the image in the light received by the optical system. 
     
     
       12. The electronic device of  claim 1 , wherein the first light-redirecting element comprises a first volume hologram having a first line of constant refractive index and a second line of constant refractive index parallel to the first line of constant refractive index, the second light-redirecting element comprises a second volume hologram having a third line of constant refractive index, and the third line of constant refractive index of the second volume hologram contacts and intersects both the first line of constant refractive index and the second line of constant refractive index of the first volume hologram. 
     
     
       13. An electronic device comprising:
 a display unit; and 
 an optical system that receives light from the display unit and that redirects the light for view, wherein the optical system includes a waveguide that propagates the light along a first axis and an output coupler that redirects the light out of the waveguide, the output coupler receives the light with a first parity about the first axis, the output coupler is configured to redirect the light out of the waveguide with a second parity about the first axis that is opposite to the first parity, the output coupler comprises a first set of diffraction gratings and a second set of diffraction gratings that are in direct contact with each other and superimposed in a same volume of a grating medium, the grating medium has a first surface and a second surface opposite the first surface, the diffraction gratings in the first and second sets extend from the first surface to the second surface, the first and second diffraction gratings diffract the light out of the waveguide through the first surface, the first set of diffraction gratings have a first set of grating vectors extending from a first k-space region to a second k-space region and have a second set of grating vectors extending parallel to the first set of grating vectors and from a third k-space region to a fourth k-space region, and the second set of diffraction gratings have a third set of grating vectors extending from the first k-space region to the third k-space region and have a fourth set of grating vectors extending parallel to the third set of grating vectors and from the second k-space region to the fourth k-space region. 
 
     
     
       14. The electronic device of  claim 13 , wherein the display unit is configured to emit the light with an image that is inverted about the first axis. 
     
     
       15. The electronic device of  claim 13 , wherein the first set of diffraction gratings is configured to diffract the light in a first direction along a second axis, the second set of diffraction gratings is configured to diffract the light diffracted in the first direction by the first set of diffraction gratings in a second direction along a third axis, the second set of diffraction gratings is configured to diffract the light in a third direction along the second axis that is opposite to the first direction, and the first set of diffraction gratings is configured to diffract the light diffracted by the second set of diffraction gratings in the third direction in the second direction along the third axis. 
     
     
       16. An electronic device comprising:
 a projector that emits light; 
 a waveguide configured to propagate the light in a first direction; and 
 an optical coupler that couples the light out of the waveguide in a second direction, the optical coupler comprising:
 a first set of diffraction gratings configured to diffract a first portion of the light in a third direction, and 
 a second set of diffraction gratings overlapping the first set of diffraction gratings and configured to diffract a second portion of the light in a fourth direction opposite the third direction, wherein:
 the first set of diffraction gratings is configured to diffract the second portion of the light diffracted by the second set of diffraction gratings in the second direction, 
 the second set of diffraction gratings is configured to diffract the first portion of the light diffracted by the first set of diffraction gratings in the second direction, 
 the first set of diffraction gratings have a first set of grating vectors extending from a first k-space region to a second k-space region and a second set of grating vectors extending parallel to the first set of grating vectors and from a third k-space region to a fourth k-space region, and 
 the second set of diffraction gratings have a third set of grating vectors extending from the first k-space region to the third k-space region and a fourth set of grating vectors extending parallel to the third set of grating vectors and from the second k-space region to the fourth k-space region. 
 
 
 
     
     
       17. The electronic device of  claim 16 , wherein the first set of diffraction gratings and the second set of diffraction gratings are superimposed in a same volume of a grating medium.

Description:
This application claims the benefit of provisional patent application No. 62/735,560, filed Sep. 24, 2018, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to optical systems and, more particularly, to optical systems for displays. 
     Electronic devices may include displays that present images close to a user&#39;s eyes. For example, devices such as virtual reality and augmented reality headsets may include displays with optical elements that allow users to view the displays. 
     It can be challenging to design devices such as these. If care is not taken, the components used in displaying content may be unsightly and bulky and may not exhibit desired levels of optical performance. 
     SUMMARY 
     An electronic device such as a head-mounted device may have one or more near-eye displays that produce images for a user. The head-mounted device may be a pair of virtual reality glasses or may be an augmented reality headset that allows a viewer to view both computer-generated images and real-world objects in the viewer&#39;s surrounding environment. 
     The near-eye display may include a display unit that generates light and an optical system that redirects the light from the display unit towards an eye box. The optical system may include an input coupler and an output coupler formed on a waveguide. The input coupler may redirect light from the display unit so that it propagates in the waveguide in a first direction towards the output coupler. The output coupler may couple the light out of the waveguide and in a second direction towards the eye box while inverting a parity of the light about the first direction. 
     The output coupler may include a first light redirecting element that redirects a first portion of the light in a third direction and may include a second light redirecting element that redirects a second portion of the light in a fourth direction opposite the third direction. The first light redirecting element may redirect the second portion of the light redirected by the second light redirecting element towards the eye box in the second direction. The second light redirecting element may redirect the first portion of the light redirected by the first light redirecting element towards the eye box in the second direction. The first and second light redirecting elements may be co-located (e.g., interleaved or overlapping) in the output coupler. The first and second light redirecting elements may include respective sets of diffractive gratings such volume holograms. In another suitable arrangement, the light redirecting elements may include partially reflective mirrors. The output coupler may fill a large eye box with uniform intensity light over a wild field of view while reducing or minimizing the optical path for the light through the output coupler. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram of an illustrative system having a display in accordance with some embodiments. 
         FIG.  2 A  is a top view of an illustrative display system having an optical system including an input coupler and an output coupler at least partially embedded in a waveguide substrate in accordance with some embodiments. 
         FIG.  2 B  is a top view of an illustrative display system having an optical system including an input coupler and an output coupler formed on a waveguide substrate in accordance with some embodiments. 
         FIG.  3    is a front view of an illustrative output coupler having interleaved (co-located) light redirecting elements that invert vertical-axis parity of an incoming image in accordance with some embodiments. 
         FIG.  4    is a perspective view of an illustrative output coupler having interleaved light redirecting elements in accordance with some embodiments. 
         FIG.  5    is a ray diagram showing how illustrative interleaved first and second light redirecting elements in an output coupler may redirect light in different directions in accordance with some embodiments. 
         FIG.  6    is a top view showing how illustrative interleaved first and second light redirecting elements may be formed from different sets of diffractive gratings in accordance with some embodiments. 
         FIGS.  7 A and  7 B  are bottom views showing how illustrative light redirecting elements may be formed using reflection-type or transmission-type diffractive gratings in accordance with some embodiments. 
         FIG.  8    is a perspective view of an illustrative light redirecting element formed from a partially-reflective mirror in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative system having a device with one or more near-eye display systems is shown in  FIG.  1   . System  10  may be a head-mounted device having one or more displays such as near-eye displays  20  mounted within support structure (housing)  8 . Support structure  8  may have the shape of a pair of eyeglasses (e.g., supporting frames), may form a housing having a helmet shape, or may have other configurations to help in mounting and securing the components of near-eye displays  20  on the head or near the eye of a user. Near-eye displays  20  may include one or more display modules such as display modules  20 A and one or more optical systems such as optical systems  20 B. Display modules  20 A may be mounted in a support structure such as support structure  8 . Each display module  20 A may emit light  38  (image light) that is redirected towards a user&#39;s eyes at eye box  24  using an associated one of optical systems  20 B. 
     The operation of system  10  may be controlled using control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for controlling the operation of system  10 . Circuitry  16  may include storage such as hard disk drive storage, nonvolatile memory (e.g., electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  16  may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, graphics processing units, application specific integrated circuits, and other integrated circuits. Software code may be stored on storage in circuitry  16  and run on processing circuitry in circuitry  16  to implement operations for system  10  (e.g., data gathering operations, operations involving the adjustment of components using control signals, image rendering operations to produce image content to be displayed for a user, etc.). 
     System  10  may include input-output circuitry such as input-output devices  12 . Input-output devices  12  may be used to allow data to be received by system  10  from external equipment (e.g., a tethered computer, a portable device such as a handheld device or laptop computer, or other electrical equipment) and to allow a user to provide head-mounted device  10  with user input. Input-output devices  12  may also be used to gather information on the environment in which system  10  (e.g., head-mounted device  10 ) is operating. Output components in devices  12  may allow system  10  to provide a user with output and may be used to communicate with external electrical equipment. Input-output devices  12  may include sensors and other components  18  (e.g., image sensors for gathering images of real-world object that are digitally merged with virtual objects on a display in system  10 , accelerometers, depth sensors, light sensors, haptic output devices, speakers, batteries, wireless communications circuits for communicating between system  10  and external electronic equipment, etc.). 
     Display modules  20 A may be liquid crystal displays, organic light-emitting diode displays, laser-based displays, or displays of other types. Optical systems  20 B may form lenses that allow a viewer (see, e.g., a viewer&#39;s eyes at eye box  24 ) to view images on display(s)  20 . There may be two optical systems  20 B (e.g., for forming left and right lenses) associated with respective left and right eyes of the user. A single display  20  may produce images for both eyes or a pair of displays  20  may be used to display images. In configurations with multiple displays (e.g., left and right eye displays), the focal length and positions of the lenses formed by components  20 B may be selected so that any gap present between the displays will not be visible to a user (e.g., so that the images of the left and right displays overlap or merge seamlessly). 
     If desired, optical system  20 B may contain components (e.g., an optical combiner, etc.) to allow real-world image light from real-world images or objects  28  to be combined optically with virtual (computer-generated) images such as virtual images in image light  38 . In this type of system, which is sometimes referred to as an augmented reality system, a user of system  10  may view both real-world content and computer-generated content that is overlaid on top of the real-world content. Camera-based augmented reality systems may also be used in device  10  (e.g., in an arrangement which a camera captures real-world images of object  28  and this content is digitally merged with virtual content at optical system  20 B). 
     System  10  may, if desired, include wireless circuitry and/or other circuitry to support communications with a computer or other external equipment (e.g., a computer that supplies display  20  with image content). During operation, control circuitry  16  may supply image content to display  20 . The content may be remotely received (e.g., from a computer or other content source coupled to system  10 ) and/or may be generated by control circuitry  16  (e.g., text, other computer-generated content, etc.). The content that is supplied to display  20  by control circuitry  16  may be viewed by a viewer at eye box  24 . 
       FIG.  2 A  is a top view of an illustrative display  20  that may be used in system  10  of  FIG.  1   . As shown in  FIG.  2 A , near-eye display  20  may include one or more display modules such as display module  20 A and an optical system such as optical system  20 B. Optical system  20 B may include optical elements such as waveguide  28 , input coupler  30 , and output coupler  32 . Display module  20 A may include a display unit  36  and a collimating lens  34 . If desired, display module  20 A may be mounted within support structure  8  of  FIG.  1    while optical system  20 B may be mounted between portions of support structure  8  (e.g., to form a lens that aligns with eye box  24 ). Other mounting arrangements may be used, if desired. 
     Display unit  36  may be a display unit based on a liquid crystal display, organic light-emitting diode display, cathode ray tube, plasma display, projector display (e.g., a projector based on an array of micromirrors), liquid crystal on silicon display, or other suitable type of display. Display  36  may generate light  38  associated with image content to be displayed to eye box  24 . Light  38  may be collimated using a lens such as collimating lens  34 . Optical system  20 B may be used to present light  38  output from display unit  36  to eye box  24 . 
     Optical system  20 B may include one or more couplers such as input coupler  30  and output coupler  32 . In the example of  FIG.  2 A , input coupler  30  and output coupler  32  are at least partially embedded in a waveguide structure such as waveguide  28  (e.g., a polymer, glass, or other transparent substrate capable of guiding light via total internal reflection). In the example of  FIG.  2 B , input coupler  30  and output coupler  32  are formed on an outer surface of waveguide  28 . 
     Input coupler  30  may be configured to couple light  38  from display unit  36  into waveguide  28 , whereas output coupler  32  may be configured to couple light  38  from within waveguide  28  to the exterior of waveguide  28  towards eye box  24 . For example, display  36  may emit light  38  in direction −Z towards optical system  20 B. When light  38  strikes input coupler  30 , input coupler  30  may redirect light  38  so that it propagates within waveguide  28  via total internal reflection towards output coupler  32  (e.g., in direction X). When light  38  strikes output coupler  32 , output coupler  32  may redirect light  38  out of waveguide  28  towards eye box  24  (e.g., back along the Z-axis). 
     Input coupler  30  and output coupler  32  may be based on reflective and refractive optics or may be based on holographic (e.g., diffractive) optics. In arrangements where couplers  30  and  32  are formed from reflective and refractive optics, couplers  30  and  32  may include one or more reflectors (e.g., an array of micromirrors, partial mirrors, or other reflectors). In arrangements where couplers  30  and  32  are based on holographic optics, couplers  30  and  32  may include volume holographic media such as photopolymers, gelatin such as dichromated gelatin, silver halides, holographic polymer dispersed liquid crystal, or other suitable volume holographic media. 
     A holographic recording may be stored as an optical interference pattern (e.g., alternating regions of different indices of refraction) within the photosensitive optical material. The optical interference pattern may create a holographic grating that, when illuminated with a given light source, diffracts light to create a three-dimensional reconstruction of the holographic recording. The diffractive grating may be a non-switchable diffractive grating that is encoded with a permanent interference pattern or may be a switchable diffractive grating in which the diffracted light can be modulated by controlling an electric field applied to the holographic recording medium. 
     If desired, couplers  30  and  32  may have thickness T 1 . Waveguide  28  may have thickness T 2 . Thicknesses T 1  and T 2  may be any desired values. If desired, couplers  32  and  30  may be sandwiched between different substrate layers in the waveguide. In another suitable arrangement, couplers  30  and  32  may be formed on the surface of waveguide  28 , as shown in  FIG.  2 B  (e.g., as opposed to being embedded in waveguide  28  as shown in  FIG.  2 A ). 
     Using thick films for couplers  30  and  32  may help increase uniformity in the output image and may provide more material in which to record different optical functions. One optical function recorded in coupler  30 , for example, may redirect light having a given input angle to a first output angle (e.g., 45°), whereas another optical function recorded in coupler  30  may redirect light having a given input angle to a second output angle (e.g., 60°). Couplers  30  and  32  may, if desired, be multiplex holograms (e.g., three-color holograms such as red-green-blue holograms) for forming color images. The diffraction efficiency in each coupler  30  and  32  may be modulated (e.g., may vary across the width of couplers  30  and  32 ) so that light exits each coupler in a smooth, uniform manner. 
     In practice, it may be desirable for output coupler  32  to fill as large of an eye box  24  with uniform intensity light  38  as possible. If desired, light redirecting elements in output coupler  32  may be configured to expand light  38  in one or more dimensions while also coupling light  38  out of waveguide  28 . The light redirecting elements may be formed from mirrors (e.g., partially reflective mirrors) or diffractive gratings (e.g., volume holograms) as two examples. 
     In some scenarios, different light redirecting elements are arranged in a sequential manner in the output coupler for redirecting the light in different directions. However, arranging light redirecting elements in a sequential manner may consume an excessive amount of space within system  10 , where space is often at a premium. Space within system  10  may be more efficiently utilized by co-locating multiple light redirecting elements for redirecting (expanding) light  38  in different directions (e.g., in an overlapping or interleaved arrangement in or on waveguide  28 ). In scenarios where the light redirecting elements are formed using partial mirrors oriented at different angles, the mirrors may be co-located by interleaving different mirrors at different orientations throughout coupler  32 . In scenarios where the light redirecting elements are formed using diffractive gratings such as volume holograms, the diffractive gratings may be written to the same volume holographic medium (e.g., each volume hologram may be formed from different interference patterns of refractive index modulations that are superimposed on the same volume of medium). Despite being located in the same volume, the gratings in each light redirecting element may diffract incoming light in different respective directions. 
       FIG.  3    is a front view of output coupler  32  having first and second light redirecting elements for redirecting image light  38  in different directions and to thereby expand the image light output from the waveguide to eye box  24  in two dimensions. As shown in  FIG.  3   , output coupler  32  in or on waveguide  28  may include a first light redirecting element  50  that is co-located (interleaved) with a second light redirecting element  48 . In one suitable arrangement, first light redirecting element  50  may include a set of mirrors (e.g., partially reflective mirrors) arranged in a first orientation whereas second light redirecting element  50  includes a set of mirrors arranged in a second orientation. In another suitable arrangement, first light redirecting element  50  may include a first set of one or more diffraction gratings (volume holograms) arranged in a first orientation (e.g., where the alternating indices of refraction associated with element  50  are arranged parallel to a first direction) whereas second light redirecting element  48  may include a second set of one or more diffraction gratings (volume holograms) arranged in a second orientation (e.g., where the alternating indices of refraction associated with element  48  are arranged parallel to a second direction that is different from the first direction). Each set of diffraction gratings may extend across the entire volume of coupler  32 , for example. 
     Light  38  may be conveyed to coupler  32  through waveguide  28 . First light redirecting element  50  may be configured to reflect light  38  about a first reflective axis whereas second light redirecting element  48  is configured to reflect light  38  about a second reflective axis that is different from the first reflective axis. Each light redirecting element may be configured to perform dual functions on light  38 . For example, each light redirecting element may be configured to redirect light  38  both in a vertical direction (parallel to the Y-axis) and may be configured to redirect light  38  out of coupler  32  (e.g., parallel to the Z-axis). 
     As shown in the example of  FIG.  3   , first light redirecting element  50  may redirect light  38  traveling in the +Y and +X directions downwards (e.g., in the −Y direction) and outwards (e.g., in the +Z direction), as shown by arrows  42  and  40 . At the same time, second light redirecting element  48  may redirect light  38  traveling in the −Y and +X directions upwards (e.g., in the +Y direction) and outwards (e.g., in the +Z direction), as shown by arrows  44  and  40 . In other words, light that has been +Y expanded by redirecting element  48  may be output coupled by the other light redirecting element  50  and the light that has been −Y expanded by redirecting element  50  may be output coupled by the other light redirecting element  48 . In this way, each light redirecting element may perform two different redirection operations (e.g., four total redirection operations such as +Y expansion, output coupling of +Y expanded light, −Y expansion, and output coupling of −Y expanded light) so that only two redirecting elements need be formed in coupler  32  (rather than requiring four separate light redirecting components to respectively perform +Y expansion, output coupling of +Y expanded light, −Y expansion, and output coupling of −Y expanded light). This may serve to reduce the manufacturing cost and complexity of system  10 , to reduce optical travel distance, to increase throughput, and to optimize space use without sacrificing field of view. In addition, this may serve to reduce the number of interactions with the light redirecting elements necessary for each of the light rays to reach the eye, thereby increasing efficiency of the output coupler. 
     Light redirecting elements  48  and  52  may vertically invert images in light  38  about the X-axis (e.g., the Y-axis parity of the images in light  38  may be reversed by coupler  32 ). In order to counteract the parity inversion of coupler  32 , images in incoming light  38  may be vertically inverted (e.g., about the X-axis) prior to being provided to coupler  32 . As shown in the example of  FIG.  3   , incoming light  22  may be provided with a vertically inverted image  46 ′ prior to being conveyed to coupler  32  (e.g., inverted image  46 ′ may be emitted by display  36  of  FIG.  2 A  as an inverted image or display  36  may emit an un-inverted image that is inverted by optical components such as lenses and/or mirrors between display  36  and output coupler  32 ). As shown in  FIG.  3   , light redirecting components  50  and  48  serve to vertically invert inverted image  46 ′ to recover un-inverted image  46  that is coupled out of the waveguide and provided to eye box  24  ( FIG.  1   ). 
       FIG.  4    is a perspective view of output coupler  32 . As shown in  FIG.  4   , light  38  provided to output coupler  32  may include inverted image  46 ′. Output coupler  32  may redirect light  38  in the +Y direction (as shown by arrow  44 ) and the +Z direction (as shown by arrow  40 ) using light redirecting element  48 . At the same time, output coupler  32  may redirect light  38  in the −Y direction (as shown by arrow  42 ) and the +Z direction (as shown by arrow  40 ) using light redirecting element  50 . This may serve to vertically invert the inverted image  46 ′ to recover un-inverted image  46  that is provided to eye box  24 . By performing light expansion operations in this way using coupler  32 , a relatively large eye box  24  may be filled with uniform intensity image light for a wide field of view. 
     The examples of  FIGS.  3  and  4    only show one or two light redirection operations performed by coupler  32  for the sake of clarity. In practice, these light redirections are performed throughout coupler  32  as light  38  propagates down the length of coupler  32 . Light  38  may be continuously expanded in the +Y and −Y directions while propagating in the +X direction and being output coupled in the +Z direction.  FIG.  5    is a ray diagram showing how light  38  may be redirected by the redirecting elements  50  and  48  in coupler  32  during propagation. 
     As shown in  FIG.  5   , incoming light  38  may be redirected in the +Y direction and in the +Z direction by redirecting elements  48  (as shown by arrows  44  and  40 ) and may be redirected in the −Y direction and in the +Z direction by redirecting elements  50  (as shown by arrows  42  and  40 ). Light redirecting elements  48  and  50  may only be partially reflective (or transmissive) and may not redirect all of the incoming light at any given point. In other words, some of light  38  continues to propagate down the length of coupler  32 , as shown by arrows  60 . This light is further reflected (as shown by arrows  40 ,  44 , and  42 ) as it propagates down coupler  32 . Arrows (rays)  44  and  40  of  FIG.  5    may, for example, be produced by light redirecting element  48  of  FIG.  3    whereas arrows  42  and  40  are produced by light redirecting element  50 . 
     Light redirecting elements  48  and  50  may be formed using partially reflective mirrors, diffractive gratings (e.g., volume holograms, surface holograms, etc.), or other components.  FIG.  6    is a top view of coupler  32  showing an example of how light redirecting elements  48  and  50  may be formed from diffractive gratings. As shown in  FIG.  6   , coupler  32  may include a first set of diffractive gratings  72  used to form first light redirecting element  50  and a second set of diffractive gratings  74  used to form second light redirecting element  48 . The first set of gratings  72  and the second set of gratings  74  may both be written to the same volume holographic medium  73  (sometimes referred to as grating medium  73  or writing medium  73 ). The first set of gratings  72  may, for example, be written to medium  73  before or after writing the second set of gratings  74  to medium  73 . In another suitable arrangement, the first and seconds sets of gratings may be written to different media and/or may be formed on different substrates (e.g., the sets of gratings may be overlapping either within the same volume of medium or within or on different overlapping media). 
     The first set of gratings  72  may be formed from variations in index of refraction that are provided with the same orientation in medium  73 . The variations in index of refraction may be modulated to form one or more different diffractive gratings (holograms) within set  72 . Different modulations/grating pitches may be used to form the different respective gratings (holograms) within set  72 . The different respective gratings may allow light redirecting element  50  to operate on a range of input angles and/or colors by redirecting light from the range of input angles and/or colors in the same output direction. 
     Similarly, the second set of gratings  74  may be formed from variations in index of refraction that are provided with the same orientation in medium  73  (e.g., an orientation that is different from the orientation of the first set of gratings  72 ). The variations in index of refraction may be modulated to form one or more different diffractive gratings (holograms) within set  74 . Different modulations/grating pitches may be used to form the different respective gratings (holograms) within set  74 . The different respective gratings may allow light redirecting element  48  to operate on a range of input angles and/or colors by redirecting light from the range of input angles and/or colors in the same output direction. 
     In momentum space (e.g., three dimensional k-space), the first set of gratings  72  of first light redirecting element  50  may exhibit a first grating vector from a first k-space region to a second k-space region and may exhibit a second grating vector from a third k-space region to a fourth k-space region. The second set of gratings  74  of second light redirecting element  48  may exhibit a third grating vector from the first region to the third region and may exhibit a fourth grating vector from the second region to the fourth region. The third and fourth grating vectors may extend parallel to each other in k-space, for example. Similarly, the first and second grating vectors may extend parallel to each other in k-space. 
     The first grating vector may be associated with diffraction of incoming light in the −Y direction of  FIG.  3    by the first set of gratings  72  (light redirecting element  50 ). The third grating vector may be associated with diffraction of incoming light in the +Y direction of  FIG.  3    by the second set of gratings  74  (light redirection element  48 ). The second grating vector may be associated with the diffraction of the light diffracted in the +Y direction by second set of gratings  74  in the +Z direction (towards eye box  24 ) by the first set of gratings  72  (light redirection element  50 ). Similarly, the fourth grating vector may be associated with the diffraction of the light diffracted in the −Y direction by first set of gratings  72  in the +Z direction (towards eye box  24 ) by the second set of gratings  74 . 
     In other words, the second set of diffraction gratings  74  may out couple the light that is diffracted in the −Y direction by the first set of gratings  72  and the first set of diffraction gratings  72  may out couple the light that is diffracted in the +Y direction by the second set of gratings  74 . In this way, all of the incoming light may be out coupled towards eye box  24 , regardless of whether the light was diffracted in the +Y or −Y directions (e.g., regardless of the k-space path followed so that a single coherent image  46  is produced at eye box  24  rather than double images). 
     The first set of gratings  72  and the second set of gratings  74  each include multiple different diffractive gratings (holograms) having grating vectors extending between different points within the first, second, third, and fourth k-space regions. In this way, each set of gratings may actually include different individual gratings for operating on input light over a range of angles. For example, the second set of gratings  74  may include an individual grating having a grating vector extending between any pair of points in the first and third k-space regions and a grating vector extending between any pair of points in the second and fourth k-space regions. Similarly, the first set of gratings  72  may include individual gratings having grating vectors extending from any desired points in the first k-space region to corresponding points in the second k-space region and extending from any desired points in the third k-space region to corresponding points in the fourth k-space regions. The k-space regions may be three-dimensional volumes if desired so that each set of gratings operates on a range of colors in addition to a range of input angles, for example. 
     The diffractive gratings in first set  72  and second set  74  may be reflection-type (mirror-type) diffraction gratings or transmission-type diffraction gratings.  FIG.  7 A  is a bottom view of a reflection-type grating  100  that may be used to form the gratings in sets  72  and  74 . As shown in  FIG.  7 A , reflective grating  100  operates by diffracting light  38  with the opposite z-direction of the incident light  38 .  FIG.  8 B  is a bottom view of a transmission grating-type diffraction grating  102  that may be used to form the gratings in sets  72  and  74 . As shown in  FIG.  7 B , transmission grating  102  operates by diffracting light  38  with the same z-direction of the incident light  38 . Either of the reflection-type gratings  100  of  FIG.  7 A  or the transmission-type gratings  102  of  FIG.  7 B  may be used to implement the diffractive gratings in light redirecting elements  48  and  50 . 
     In another suitable arrangement, light redirecting elements  48  and  50  may be formed using partial mirrors.  FIG.  8    is a perspective view of an illustrative partial mirror  110  that may be used to form light redirecting elements  48  and  50 . As shown in  FIG.  8   , partial mirror  110  may reflect a first portion of incoming light  38  and may transmit a second portion  38 ′ of the incoming light. Mirror  110  may have a normal axis  112  that is oriented at non-zero angles with respect to each of the X, Y, and Z axes. This may allow mirror  110  to reflect light  38  in both the +Y and +Z directions (e.g., when used to implement light redirecting element  48  of  FIG.  3   ) or to reflect light  38  in both the −Y and +Z directions (e.g., when used to implement light redirecting element  50  of  FIG.  3   ). Mirrors such as mirrors  110  that are oriented in different directions (e.g., for elements  48  and  50 ) may be distributed in an interleaved pattern throughout output coupler  32 . These examples are merely illustrative and, in general, any desired diffractive and/or reflective structures may be used to form light redirection elements  48  and  50 . 
     When configured using the structures of  FIGS.  1 - 8   , display  20  may exhibit a relatively wide field of view and may fill a relatively wide eye box  24  with light of uniform intensity. Co-locating light redirection elements  48  and  50  may reduce the optical travel distance for light  38  to reduce haze and scattering in the system while occupying a reduced or minimal amount of space within system  10 . 
     A physical environment refers to a physical world that people can sense and/or interact with without aid of electronic systems. Physical environments, such as a physical park, include physical articles, such as physical trees, physical buildings, and physical people. People can directly sense and/or interact with the physical environment, such as through sight, touch, hearing, taste, and smell. 
     In contrast, a computer-generated reality (CGR) environment refers to a wholly or partially simulated environment that people sense and/or interact with via an electronic system (e.g., an electronic system including the display systems described herein). In CGR, a subset of a person&#39;s physical motions, or representations thereof, are tracked, and, in response, one or more characteristics of one or more virtual objects simulated in the CGR environment are adjusted in a manner that comports with at least one law of physics. For example, a CGR system may detect a person&#39;s head turning and, in response, adjust graphical content and an acoustic field presented to the person in a manner similar to how such views and sounds would change in a physical environment. In some situations (e.g., for accessibility reasons), adjustments to characteristic(s) of virtual object(s) in a CGR environment may be made in response to representations of physical motions (e.g., vocal commands). 
     A person may sense and/or interact with a CGR object using any one of their senses, including sight, sound, touch, taste, and smell. For example, a person may sense and/or interact with audio objects that create 3D or spatial audio environment that provides the perception of point audio sources in 3D space. In another example, audio objects may enable audio transparency, which selectively incorporates ambient sounds from the physical environment with or without computer-generated audio. In some CGR environments, a person may sense and/or interact only with audio objects. Examples of CGR include virtual reality and mixed reality. 
     A virtual reality (VR) environment refers to a simulated environment that is designed to be based entirely on computer-generated sensory inputs for one or more senses. A VR environment comprises a plurality&#39; of virtual objects with which a person may sense and interact. For example, computer-generated imagery of trees, buildings, and avatars representing people are examples of virtual objects. A person may sense and/or interact with virtual objects in the VR environment through a simulation of the person&#39;s presence within the computer-generated environment, and/or through a simulation of a subset of the person&#39;s physical movements within the computer-generated environment. 
     In contrast to a VR environment, which is designed to be based entirely on computer-generated sensory inputs, a mixed reality (MR) environment refers to a simulated environment that is designed to incorporate sensory inputs from the physical environment, or a representation thereof, in addition to including computer-generated sensory inputs (e.g., virtual objects). On a virtuality continuum, a mixed reality environment is anywhere between, but not including, a wholly physical environment at one end and virtual reality environment at the other end. 
     In some MR environments, computer-generated sensory inputs may respond to changes in sensory inputs from the physical environment. Also, some electronic systems for presenting an MR environment may track location and/or orientation with respect to the physical environment to enable virtual objects to interact with real objects (that is, physical articles from the physical environment or representations thereof). For example, a system may account for movements so that a virtual tree appears stationery with respect to the physical ground. Examples of mixed realities include augmented reality and augmented virtuality. 
     An augmented reality (AR) environment refers to a simulated environment in which one or more virtual objects are superimposed over a physical environment, or a representation thereof. For example, an electronic system for presenting an AR environment may have a transparent or translucent display through which a person may directly view the physical environment. The system may be configured to present virtual objects on the transparent or translucent display, so that a person, using the system, perceives the virtual objects superimposed over the physical environment. Alternatively, a system may have an opaque display and one or more imaging sensors that capture images or video of the physical environment, which are representations of the physical environment. The system composites the images or video with virtual objects, and presents the composition on the opaque display. A person, using the system, indirectly views the physical environment by way of the images or video of the physical environment, and perceives the virtual objects superimposed over the physical environment. As used herein, a video of the physical environment shown on an opaque display is called “pass-through video,” meaning a system uses one or more image sensor(s) to capture images of the physical environment, and uses those images in presenting the AR environment on the opaque display. Further alternatively, a system may have a projection system that projects virtual objects into the physical environment, for example, as a hologram or on a physical surface, so that a person, using the system, perceives the virtual objects superimposed over the physical environment. 
     An augmented reality environment also refers to a simulated environment in which a representation of a physical environment is transformed by computer-generated sensory information. For example, in providing pass-through video, a system may transform one or more sensor images to impose a select perspective (e.g., viewpoint) different than the perspective captured by the imaging sensors. As another example, a representation of a physical environment may be transformed by graphically modifying (e.g., enlarging) portions thereof, such that the modified portion may be representative but not photorealistic versions of the originally captured images. As a further example, a representation of a physical environment may be transformed by graphically eliminating or obfuscating portions thereof. 
     An augmented virtuality (AV) environment refers to a simulated environment in which a virtual or computer generated environment incorporates one or more sensory inputs from the physical environment. The sensory inputs may be representations of one or more characteristics of the physical environment. For example, an AV park may have virtual trees and virtual buildings, but people with faces photorealistically reproduced from images taken of physical people. As another example, a virtual object may adopt a shape or color of a physical article imaged by one or more imaging sensors. As a further example, a virtual object may adopt shadows consistent with the position of the sun in the physical environment. 
     There are many different types of electronic systems that enable a person to sense and/or interact with various CGR environments. Examples include head mounted systems, projection-based systems, heads-up displays (HUDs), vehicle windshields having integrated display capability, windows having integrated display capability, displays formed as lenses designed to be placed on a person&#39;s eyes (e.g., similar to contact lenses), headphones/earphones, speaker arrays, input systems (e.g., wearable or handheld controllers with or without haptic feedback), smartphones, tablets, and desktop/laptop computers. A head mounted system may have one or more speaker(s) and an integrated opaque display. Alternatively, a head mounted system may be configured to accept an external opaque display (e.g., a smartphone). The head mounted system may incorporate one or more imaging sensors to capture images or video of the physical environment, and/or one or more microphones to capture audio of the physical environment. Rather than an opaque display, a head mounted system may have a transparent or translucent display. The transparent or translucent display may have a medium through which light representative of images is directed to a person&#39;s eyes. The display may utilize digital light projection, OLEDs, LEDs, uLEDs, liquid crystal on silicon, laser scanning light source, or any combination of these technologies. The medium may be an optical waveguide, a hologram medium, an optical combiner, an optical reflector, or any combination thereof. In one embodiment, the transparent or translucent display may be configured to become opaque selectively. Projection-based systems may employ retinal projection technology that projects graphical images onto a person&#39;s retina. Projection systems also may be configured to project virtual objects into the physical environment, for example, as a hologram or on a physical surface. The display systems described herein may be used for these types of systems and for any other desired display arrangements. The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20190813
Publication Date: 20241119
Grant Date: 20241119
Priority Date: 20180924
Inventors: OH, SE BAEK
STEELE, BRADLEY C.
COCILOVO, BYRON R.
AIETA, Francesco
MYHRE, GRAHAM B.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B5/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/0187", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B5/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/0178", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B5/1814", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0944", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/0174", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/4272", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/1086", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0081", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/0187", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B2027/0178", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0944", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/1814", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/0174", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0103", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B2027/0187", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B2027/0178", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0944", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/1814", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 69884217