PATENT DOCUMENT

Publication Number: US-10866426-B2
Application Number: US-201916277875-A
Country: US
Kind Code: B2

Title: Scanning mirror display devices

Abstract:
An electronic device may have a light source such as a laser light source. The light source may emit light into a waveguide. A phase grating may diffract the light that is emitted into the waveguide to produce diffracted light. The diffracted light may be oriented parallel to a surface normal of an angled edge of the waveguide and parallel to a surface normal of a microelectromechanical systems mirror element in a two-dimensional scanning microelectromechanical systems mirror that is coupled to the edge of the waveguide. A wave plate may be interposed between the mirror and the edge of the waveguide to change the polarization state of light reflected from the mirror element relative to incoming diffracted light from the phase grating. The phase grating may be configured so that the reflected light is not diffracted by the phase grating.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a waveguide having opposing first and second surfaces and an edge extending from the first surface to the second surface at a non-parallel angle with respect to the first surface; 
 a light source configured to provide p-polarized light; 
 an output coupler; 
 an overmodulated transmission phase grating configured to diffract the p-polarized light from the light source to produce diffracted light having a first polarization that is transmitted through the first surface of the waveguide; 
 a scanning mirror configured to receive the diffracted light through the edge of the waveguide and configured to reflect the diffracted light to produce reflected light, wherein the waveguide is configured to provide the reflected light to the output coupler, and wherein the output coupler is configured to direct light from the waveguide towards an eye box; and 
 a wave plate, wherein the diffracted light passes through the wave plate to the scanning mirror, wherein the reflected light from the scanning mirror has a second polarization after passing through the wave plate to the waveguide. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the overmodulated transmission phase grating has an index of refraction modulation and thickness configured to exhibit 0% s-polarization diffraction efficiency and 100% p-polarization diffraction efficiency. 
     
     
       3. The electronic device defined in  claim 1  further comprising:
 control circuitry configured to generate an image in the eye box by controlling the scanning mirror and the light source. 
 
     
     
       4. The electronic device defined in  claim 1  wherein the light source comprises a laser light source and wherein the wave plate is between the scanning mirror and the edge of the waveguide. 
     
     
       5. The electronic device defined in  claim 1  wherein the output coupler is configured to overlay, at the eye box, light from real-world objects with the light from the waveguide. 
     
     
       6. The electronic device defined in  claim 1 , wherein the output coupler comprises a phase grating. 
     
     
       7. The electronic device defined in  claim 6 , further comprising:
 a transparent cover layer; and 
 a photopolymer layer interposed between the waveguide and the transparent cover layer, wherein the output coupler and the overmodulated transmission phase grating are formed within the photopolymer layer. 
 
     
     
       8. An electronic device, comprising:
 a waveguide having a surface and an edge that extends at a non-parallel angle with respect to the surface; 
 a light source configured to provide light having a first polarization to the surface of the waveguide; 
 an output coupler on the waveguide; 
 a transmission phase grating configured to diffract the light from the light source to produce diffracted light having the first polarization; 
 a scanning mirror that is configured to receive the diffracted light through the edge of the waveguide and that is configured to reflect the diffracted light to produce reflected light, wherein the waveguide is configured to provide the reflected light to the output coupler via total internal reflection and wherein the output coupler is configured to direct the reflected light towards an eye box; and 
 a wave plate, wherein the diffracted light passes through the wave plate to the scanning mirror and wherein the reflected light from the scanning mirror has a second polarization after passing through the wave plate to the waveguide. 
 
     
     
       9. The electronic device defined in  claim 8 , wherein the transmission phase grating does not diffract light of the second polarization. 
     
     
       10. The electronic device defined in  claim 8 , wherein the first polarization comprises P-polarization. 
     
     
       11. The electronic device defined in  claim 10 , wherein the second polarization comprises S-polarization. 
     
     
       12. The electronic device defined in  claim 8  further comprising:
 control circuitry configured to generate an image in the eye box by controlling the scanning mirror and the light source. 
 
     
     
       13. The electronic device defined in  claim 12  wherein the light source comprises a laser light source and wherein the wave plate is between the scanning mirror and the edge of the waveguide. 
     
     
       14. The electronic device defined in  claim 8   
       further comprising:
 a transparent cover layer; and 
 a photopolymer layer interposed between the waveguide and the transparent cover layer, wherein the transmission phase grating and the output coupler are in the photopolymer layer. 
 
     
     
       15. An optical system comprising:
 a waveguide having opposing first and second surfaces and an edge extending from the first surface to the second surface; 
 a light source configured to produce light; 
 a transmissive diffraction grating at the first surface and configured to diffract the light produced by the light source to produce diffracted light, the second surface of the waveguide being configured to reflect the diffracted light towards the edge; 
 an output coupler on the waveguide; and 
 a scanning mirror at the edge, wherein the scanning mirror is configured to reflect the diffracted light back into the waveguide as reflected light, wherein the waveguide is configured to propagate the reflected light towards the output coupler via total internal reflection, and wherein the output coupler is configured to direct the reflected light towards an eye box. 
 
     
     
       16. The optical system defined in  claim 15 , wherein the transmissive diffraction grating is configured to diffract light of a first polarization with greater diffraction efficiency than light of a second polarization and wherein the light produced by the light source has the first polarization. 
     
     
       17. The optical system defined in  claim 16 , wherein the reflected light has the second polarization. 
     
     
       18. The optical system defined in  claim 17 , further comprising a waveplate interposed between the edge and the scanning mirror. 
     
     
       19. The optical system defined in  claim 17 , wherein the edge extends at a non-perpendicular angle with respect to the first and second surfaces. 
     
     
       20. The optical system defined in  claim 15 , wherein the edge extends at a non-perpendicular angle with respect to the first and second surfaces.

Description:
This application claims priority to U.S. provisional patent application No. 62/636,530 filed Feb. 28, 2018, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and, more particular, to electronic devices that display images. 
     Electronic devices such as head-mounted devices contain displays. The displays may be used in displaying computer-generated virtual reality and mixed reality content. If care is not taken, however, such systems may be overly complex, bulky, and uncomfortable to wear. 
     SUMMARY 
     An electronic device may have a light source such as a laser light source. The light source may emit light into a waveguide. A phase grating may diffract the light. Diffracted light may pass through an angled edge of the waveguide to a mirror element in a scanning mirror system that is coupled to the edge of the waveguide. 
     A wave plate may be used to change the polarization state of light reflected from the mirror element relative to incoming diffracted light from the phase grating. The phase grating may be configured to be polarization sensitive so that reflected light of a particular polarization is not diffracted by the phase grating. Alternatively, a reflective polarizer may be interposed between the phase grating and the waveguide. 
     The phase grating may be a Bragg polarization grating, an overmodulated transmission grating, a reflection or transmission volume hologram, or other suitable phase grating. 
     During operation, control circuitry may dynamically adjust the intensity and color of light emitted by the light source while controlling the two-dimensional scanning of the mirror element. The reflected light from the mirror is guided along the waveguide to an output coupler. The output coupler directs the reflected light to an eye box, so that a user&#39;s eye in the eye box receives an image corresponding to the output produced by the scanning mirror and light source. The output coupler and light guide may be transparent, which allows the user to view real-world objects while viewing the images overlaid on top of the real-world objects. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device in accordance with an embodiment. 
         FIGS. 2, 3, 4, 5A, and 5B  are diagrams of illustrative display systems for electronic devices in accordance with embodiments. 
         FIG. 6  is a diagram of an illustrative display system that may use a pair of single dimensional mirrors in accordance with an embodiment. 
         FIG. 7  is a diagram of an illustrative metasurface polarization grating coupler in accordance with an embodiment. 
         FIG. 8  is a diagram of an illustrative display system with couplers for different wavelengths in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with a display system is shown in  FIG. 1 . Electronic device  10  may be configured to be worn by a user (e.g., device  10  may be a head-mounted device) or other suitable electronic equipment (e.g., a cellular telephone or other portable equipment). As shown in  FIG. 1 , electronic device  10  may have control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other 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 used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  22  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  22  may include sensors  18  and other components for gathering input and/or providing a user with output. Sensors  18  in input-output devices  22  may include strain gauge sensors, proximity sensors, ambient light sensors, touch sensors, force sensors, temperature sensors, pressure sensors, image sensors, gaze tracking sensors, three-dimensional sensors, gesture sensors, magnetic sensors, accelerometers, gyroscopes and other sensors for measuring orientation (e.g., position sensors, orientation sensors), microelectromechanical systems sensors, and other sensors. Sensors  18  may be light-based sensors (e.g., proximity sensors or other sensors that emit and/or detect light), capacitive sensors (e.g., sensors that measure force and/or touch events using capacitance measurements). Strain gauges, piezoelectric elements, capacitive sensors, and other sensors may be used in measuring applied force and can therefore be used to gather input from a user&#39;s fingers or other external source of pressure. Sensors  18  and other input-output devices  22  may gather user gesture input, user touch input, user force input, button press input from a user, or other user input. If desired, sensors  18  may include microphones to gather audio signals (e.g., user voice commands). Devices  22  may also include other components for providing a user with output and for gathering input from a user and/or the environment surrounding device  10 . For example, devices  22  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators (e.g., piezoelectric vibrating components, etc.), cameras, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  22  and may receive status information and other output from device  10  using the output resources of input-output devices  22 . In some configurations, a remote control or other accessor that is linked to device  10  via a wired or wireless communications path may be used in providing input to device  10 . 
     Input-output devices  22  may include one or more display systems such as display system (display)  14 . Display system  14  may be based on any suitable display technology. With one suitable arrangement, which is sometimes described herein as an example, display system  14  includes a scanning mirror. The scanning mirror may be a microelectromechanical systems mirror having a microelectromechanical systems mirror element that can be deflected or may be a galvanometer mirror (e.g., an electromagnetically controlled mirror). The scanning mirror may be a two-dimensional mirror with a mirror element that can be deflected about two orthogonal axes or may include a pair of one-dimensional scanning mirror devices (as examples). 
     A light source such as a laser or other source of light may produce light that is deflected by the mirror. An optical system based on a waveguide may be used to direct light from the light source to the scanning mirror and from the scanning mirror to an eye box associated with the eye(s) of a viewer. Display system  14  may be mounted in head-mountable support structures  20  (e.g., helmets, hats, goggles, eye glasses, or other structures that are mounted on a head of a user). 
       FIGS. 2, 3, 4, 5A, and 5B  are top views of illustrative display systems for use in an electronic device such as device  10  of  FIG. 1 . 
     As shown in  FIG. 2 , display system  14  may include a light source such as light source  24 . System  14  may also have a waveguide such as waveguide  36  that has a transparent waveguide substrate layer such as layer  50  (e.g., a layer of clear glass or polymer). Light source  24  may include one or more components such as light-emitting diodes or lasers that produce light  26  and associated optical components (e.g., lenses, fibers, etc.) for producing a collimated beam of light  26 . With one illustrative configuration, light source  24  includes lasers of different colors such as red, green, and blue lasers that produce a collimated output beam of light  26 . Light  26  is directed onto mirror element  30  (e.g., a microelectromechanical systems mirror element) of two-dimensional scanning mirror  32  (e.g., a two-dimensional scanning microelectromechanical systems mirror) by phase grating  34 . Light  26  then reflects from mirror element  32  and is confined within waveguide  36  by total internal reflection until being coupled towards viewer eye  38  in eye box  40  by output coupler  42 . Output coupler  42  and waveguide  36  are transparent, which allows a user (viewer eye  38 ) to view real-world objects such as real-world object  12  while simultaneously viewing images from output coupler  42  that are overlaid on portion of the real-world objects (e.g., mixed reality content can be provided to the user). 
     During operation, mirror element  32  may be tilted dynamically about the X and Y axes of  FIG. 2  in response to control signals from control circuitry  16  at input  44 . At the same time, the color (and intensity) of beam  26  can be adjusted dynamically by control circuitry  16  by varying the relative contribution of the output light from each of the differently colored lasers in light source  24 . This allows an image made up of individually colored pixels (e.g., a computer-generated image to be overlaid on real-world images) to be presented to eye box  40  and viewer&#39;s eye  38  in eye box  40 . Device  10  may include two display systems  14 —one for the user&#39;s left eye and one for the user&#39;s right eye. The system components associated with a single eye are shown in  FIG. 2 . 
     In the illustrative configuration of  FIG. 2 , phase grating  34  is a thick phase grating such as a Bragg polarization grating (e.g., a thick polarization grating with a thickness d much larger than its pitch A and/or with a value of Q that is greater than 10 or other suitable value, where Q is given by equation 1).
 
 Q= 2πλ d/nΛ   (1)
 
     In equation 1, λ represents the wavelength of light  26  and n is the refractive index. 
     In this type of configuration, light  26  from source  24  is diffracted towards scanning mirror  32  at an angle A with respect to surface normal n of grating  34 . The value of A may be at least 40°, at least 50°, 50-70°, or other suitable value. A wave plate such as wave plate  46  may be interposed between scanning mirror  32  and angled surface  48  of waveguide  36  or a wave plate such as wave plate  46  may be located at other suitable locations between grating  34  and mirror  32 . Surface  48  may be characterized by a surface normal that is oriented at a non-zero angle with respect to the longitudinal axis of waveguide  36  and a non-zero angle with respect to surface normal n (e.g., the edge of waveguide  36  may have a surface normal that is oriented at a non-zero angle such as an angle of between 10° and 80° with respect to the surface normal n associated with the Bragg polarization grating). 
     Angled surface  48  may have a surface normal parallel to incoming light  70 . The angular orientation of surface  48  may be selected to help direct reflected light  72  with a desired angular orientation. The angular orientation of reflected light  72  may be chosen to support a wide range of angles of reflected light while ensuring this light is refractively coupled into waveguide  36  from mirror  32  and is guided within waveguide  36 . In particular, the angle of surface  48  may be chosen to allow light with a maximum range of reflected angles to be refractively coupled through the edge of element  50  and guided along the length of waveguide  36  in accordance with the principle of total internal reflection. In an illustrative arrangement, the surface of mirror  32  may be parallel to surface  48  when mirror  32  is at the center of its nominal scan range and the incoming light from grating  34  is normally incident on surface  48 . This type of arrangement allows for a relatively large amount of reflected beam area when mirror  32  is at the nominal center of its scan range. Other arrangements may be used, if desired. 
     In some configurations, grating  34  may be formed in photopolymer layer  52  (e.g., a polymer layer such as a liquid crystal polymer layer whose index of refraction can be locally changed by light exposure during a laser grating writing operation). Output coupler  42  may be a phase grating formed in photopolymer layer  54 . 
     If desired, photopolymer layer  54  may be covered by a cover layer such as cover layer  60  to help protect layer  54 . Layer  60  may be formed from glass or polymer. A cover layer (e.g., a cover layer such as layer  60  formed of glass or polymer) may also be used to cover and protect layer  52 . The thickness of the cover layer(s) such as layer  60  may be about 0.3 mm, at least 0.05 mm, less than 0.7 mm, or other suitable thickness. The thickness of photopolymer layer  54  (and layer  52 ) may be 5-500 microns, at least 2 microns, at least 5 microns, at least 10 microns, less than 1000 microns, or other suitable thickness. The thickness of waveguide layer  50  may be 0.5 to 1.5 mm, at least 0.2 mm, at least 0.4 mm, less than 2 mm, or other suitable thickness. 
     In configurations for system  14  in which grating  34  is a polarization grating, grating  34  exhibits polarization-sensitive diffraction properties (i.e., grating  34  preferentially diffracts light of a particular polarization). Grating  34  is preferably configured to diffract most of the light that is incident on grating  34  in a single order (in addition to the zero-order mode where there is no diffraction), thereby enhancing efficiency (e.g., at least 80% of incident energy may be diffracted into a single order, at least 90%, etc.). Furthermore, the diffracted light will often be in a different polarization state than that which was incident on the grating. Light source  24  may include optical fibers, lenses, wave plates, and/or other optical elements to help control beam size and polarization for light  26  as light  26  is emitted from light source  24 . 
     In the example of  FIG. 2 , light  26  is initially right-hand circularly polarized and grating  34  is configured to efficiently diffract incoming right-hand circularly polarized light towards mirror  32  in direction  70  at angle A with respect to surface normal n of grating  34  as left-hand circularly polarized light. This diffracted light  26  then reaches mirror  32  (e.g., at a nominally 90° angle relative to the surface of element  30 ). Light  26  reflects from mirror  32  in direction  72  (e.g., as right-hand circularly polarized light), which is not diffracted by grating  34  upon return and therefore is guided along the interior of waveguide  36  in accordance with the principle of total internal reflection. Upon reaching output coupler  42 , light  26  is coupled out of waveguide  36  towards eye box  40 . Optional wave plate  46  may be configured to adjust the polarization state of the light reflected from mirror  32  to ensure that diffraction losses of light  26  upon reaching grating  34  are minimized. In the example of  FIG. 2 , grating  34  is a reflective Bragg polarization grating, but grating  34  may also be configured as a transmissive Bragg polarization grating. The light diffracted from grating  34  may not necessarily be in the orthogonal polarization state to that which is incident (as in this example with incident right-hand circularly polarized light and diffracted left-hand circularly polarized light). For example, after diffracting or reflecting from an optical element, linearly polarized or circularly polarized light may become elliptically polarized. In general, the wave plate  46  on surface  48  or other suitable location between grating  34  and mirror  32  is configured such that the polarization sate of the returned light, having passed through the wave plate multiple times, is such that it is minimally diffracted by the grating over a desired range of angles and thus propagates along waveguide  36  in accordance with the principle of total internal reflection. In some arrangements, wave plate  46  may be omitted or may be configured to perform only a relatively weak “cleanup” function (e.g., adjusting elliptically polarized light that has reflected from mirror  32  back to a desired circular or linear polarization state). 
     In the illustrative configuration of  FIG. 3 , phase grating  34  is a transmission polarization grating such as an overmodulated volume phase transmission grating in which the index of refraction modulation and thickness of the grating are configured so that the grating is overmodulated and s-polarization diffraction efficiency is 0% while p-polarization diffraction efficiency is 100%. Light  26  is emitted from light source  24  with a polarization state that is efficiently diffracted by grating  34 . For example, light  26  may be emitted from light source  24  with a p polarization. Grating  34  may be configured to diffract a large amount (e.g., at least 80%, at least 90%, or other suitable amount) of incident p-polarized light  26  into a single diffraction order (e.g., at angle A with respect to surface normal n of grating  32 ). The value of angle A may be at least 40°, 50-70°, or other suitable value. The diffracted p-polarized light at angle A reflects from the interior of waveguide  36  and passes through wave plate  46  to mirror  32  (or, if desired, passes directly to mirror  32  through wave plate  46 ). Light  26  then reflects from mirror  32 . Wave plate  46  may be a quarter wave plate, so that light  26  is rotated in polarization from a first polarization state (e.g., p-polarization) to a second polarization state (e.g., s-polarization) after passing through quarter wave plate  46  to mirror  32  and back. Grating  34  is tuned to diffract p-polarized light and not s-polarized light, so the s-polarized light that is reflected in direction  72  is not diffracted by grating  34  and is reflected internally in waveguide  36  in accordance with the principle of total internal reflection. Output coupler  42  couples light  26  out of waveguide  36  towards eye box  40 . 
     In the illustrative configuration of  FIG. 4 , light source  24  emits light  26  at an angle A 1  with respect to surface normal n of grating  34  (e.g., a volume grating). Incident angle A 1  is chosen so that incident angle A 2  plus the diffracted angle B is 90° (Brewster&#39;s condition is satisfied). In this arrangement, only s-polarized light is diffracted and thus the grating acts as a polarization grating to selectively diffract s-polarization and not p-polarization. 
     Initially, light  26  is s-polarized and is efficiently diffracted by grating  34  in direction  70  at an angle B with respect to surface normal n. Light  26  reflects from mirror  32  in direction  72 . Wave plate  46  may be a quarter wave plate. As light  26  passes through wave plate  46  and back, the polarization state of light  26  rotates by 90° (becoming orthogonal to the original polarization state of light  26  from light source  24 ), so that light  26  that is traveling in direction  72  is p polarized and is not diffracted by grating  34 . As a result, light  26  is confined within waveguide  36  by total internal reflection until reaching coupler  42 . This Brewster&#39;s condition arrangement may use either a reflection grating (as shown in  FIG. 4 ) or a transmission grating, as long as the sum of the incident and diffracted angles is 90° (Brewster&#39;s condition is satisfied). 
     If desired, system  14  may incorporate a reflective polarizer that overlaps grating  34  (e.g., a transmissive or reflective volume phase grating). This type of arrangement is shown in  FIGS. 5A and 5B . 
     In the example of  FIG. 5A , grating  34  is a transmission grating (e.g., a transmission volume hologram) that is configured to efficiently diffract light  26  in a single order (e.g., with an efficiency of at least 80%, at least 90%, etc.). Light  26  that is emitted by light source  24  may be s-polarized or p-polarized and is efficiently diffracted in direction  70  by grating  34  in the same polarization state. Reflective polarizer  90  is interposed between grating  34  and waveguide  36  and exhibits high reflection for a given polarization state (p-polarized or s-polarized) and high transmission for the opposite polarization state (respectively, s-polarized or p-polarized). Polarizer  90  and light source  24  are configured so that linearly polarized light (s-polarized or p-polarized) from light source  24  is passed towards mirror  32  by grating  34  and is transmitted through polarizer  90 . After passing through quarter wave plate  46  and back (after reflecting from mirror  32 ), light  26  is rotated in polarization and is reflected by reflective polarizer  90 . Light  26  is rotated to the orthogonal polarization from that originally incident on grating  34  and reflective polarization  90 . The light reflected from mirror  32  does not reach grating  34  and therefore is not diffracted by grating  34 . After reflecting from polarizer  90 , light  26  is confined within waveguide  36  by total internal reflection until reaching coupler  42 . 
     In the example of  FIG. 5B , grating  34  is a reflective grating (e.g., a reflection volume hologram) that is configured to efficiently diffract light  26  of a first polarization state in a single order (e.g., with an efficiency of at least 80%, at least 90%, etc.) while not diffracting light  26  of a second (e.g., opposite) polarization state. The first polarization state may be, for example, s-polarization, p-polarization, right-hand circular polarization, etc. Quarter wave plate  46  may be used to convert light  26  from the first to second polarization state. With this arrangement, reflective polarizer  90 , is configured to pass light of the first polarization state and reflect light of the second polarization state. Light from light source  24  has the first polarization state and passes through reflective polarizer  90  and is diffracted in direction  70  by grating  34 . Reflected light  26  traveling in direction  72  has the second polarization state and is reflected from reflective polarizer  90  (and is not diffracted by grating  34 ). As a result, light  26  is confined within waveguide  36  by total internal reflection until reaching coupler  42 . 
     The gratings  34  of  FIGS. 5A and 5B  may be any suitable gratings (Bragg polarization gratings, reflective or transmissive gratings, reflective or transmissive volume holograms, etc.). 
     As shown in  FIG. 6 , scanning mirror  32  may be formed from two one-dimensional scanning mirrors  34 A and  34 B rather than a single two-dimensional scanning mirror. Light from light source  24  may be directed to first one-dimensional scanning mirror  32 B (e.g., by mirror  80 ). Mirror  32 B may perform one dimension of beam scanning on the light emitted by light source  24 . A second dimension of beam scanning may be performed after the scanned beam from first mirror  32 B reflects off of second one-dimensional scanning mirror  32 A. If desired, light source  24 , mirror  80 , and mirror  32 B may be replaced by a one-dimensional array of light emitters (e.g., light-emitting diodes or lasers). Moreover, mirror system  14  may also be formed from pairs of one-dimensional scanning mirrors that are located at different positions relative to waveguide  36 . The arrangements of  FIG. 6  is illustrative. 
     If desired, grating  34  may be a polarization grating formed from metasurface structures. Polarization grating  34  serves as a polarization grating coupler that decouples light input (transmission) and light output (reflection). In this system, polarization grating  34  performs double duty. In particular, grating  34  couples light into waveguide  36  with a specific angle in its transmission mode (blaze of first order), while also reflecting light back inside the waveguide over a wide range of angles in two dimensions (Δθ˜±20° &amp; Δφ˜±20°) in its reflection mode. 
     Metasurfaces for grating  34  may be formed from an array of nanostructures such as silicon pillars or other structures. Metasurface polarization grating couplers formed in this way may be used to form grating  34  on waveguide  36  of system  14  or maybe used in other systems that involve coupling and reflecting light (e.g., different systems where a grating operates in transmission mode and reflection mode). 
     Metasurface polarization grating couplers may be configured to work independently under different polarizations (e.g., different linear polarization or different circular polarizations). Multiwavelength operation may be supported, if desired. For example, grating  14  may be configured to work independently for different linear polarizations for red, green, and blue light or may be configured to work independently for different circular polarizations for red, green, and blue light. Metasurface gratings may receive light  26  from light source  24  using an arrangement of type shown in  FIG. 3 or 5A  (e.g., an arrangement in which light  26  directly illuminates grating  34  from outside of waveguide  36 ) or using an arrangement of the type shown in  FIG. 4 or 5B  (e.g., an arrangement in which light  26  is coupled into the material forming waveguide  36  before illuminating the inner surface of grating  34 ). 
       FIG. 7  is a top view of grating  34  formed from a metasurface structure (sometimes referred to as a metasurface grating). As shown in  FIG. 7 , metasurface grating  34  may have nanostructures  34 ″ that extend in a two-dimensional array across the surface of waveguide  36  (e.g., in lateral dimensions a and b). Nanostructures  34 ″ may be nanoposts (nanopillars) such as rectangular nanoposts or nanoposts of other shapes. The height H of nanostructures  34 ″ (e.g., the size of nanostructures  34 ″ measured along dimension h, which is oriented out of the page in  FIG. 7 ) may be at least 200 nm, at least 400 nm, less than 800 nm, less than 500 nm, or other suitable size. Nanostructures  34 ″ may be formed from any suitable material (e.g., semiconductors, organic and/or inorganic dielectrics, metals, other materials, and/or combinations of materials). As an example, nanostructures  34 ″ may be formed from crystalline silicon, which has a high refractive index and is sufficiently transparent at visible wavelengths. 
     Nanostructures  34 ″ may include different types of nanostructures that are organized in a random pattern without repeating elements or other irregular and non-periodic pattern or that are organized in a repeating pattern to form an array of nanostructures  34 ″ for grating  34 . In the example of  FIG. 7 , nanostructures  34 ″ include four different types of nanostructures. The first type has dimensions a 1  and b 1  along lateral dimensions a and b, respectively. The second, third, and fourth types of nanostructures  34 ″ have, respectively, dimensions (a 2 , b 2 ), (a 3 , b 3 ), and (a 4 , b 4 ). In an illustrative configuration, a 1  is about 45 nm, b 1  is about 70 nm, a 2  is about 80 nm, b 2  is about 50 nm, a 3  is about 100 nm, b 3  is about 44 nm, a 4  is about 125 nm, and b 4  is about 42 nm, the value of h is about 360 nm, and grating  34  handles linearly polarized green light at 532 nm and a 30° illumination angle in transmission mode (as an example). Illustrative phase shifts associated with these four different types of nanostructures  34 ″ in this example are shown by the traces in the two graphs of  FIG. 7 . Nanostructures  34 ″ are configured so that, in a first polarization (e.g., TM), nanostructures  34 ″ exhibit high (e.g., 100%) transmission and, as shown in  FIG. 7 , the different types of nanostructures  34 ″ exhibit respective phase shifts of 0, π/2, π, and 3π/2 (blaze first order). Nanostructures  34 ″ are also configured so that in a second polarization (e.g., TE), nanostructures  34 ″ exhibit high (e.g., 100%) reflection and, as shown in  FIG. 7 , exhibit phase shifts of 0 (blaze zeroth order). In general, grating  34  may be configured to have any suitable number of different nanostructures  34 ″ and nanostructures  34 ″ of any suitable dimensions, may be configured to handle, any desired wavelength(s) of light, may be configured to support any desired angles of operation, any desired polarizations, etc. The example of  FIG. 7  is merely illustrative. In some configurations, nanostructures  34 ″ may form a metagrating that induces a polarization conversion to incident light, i.e., from right-hand circularly polarized (or TM polarized) light the diffraction orders can be left-hand circularly polarized (or TE) and vice versa. 
       FIG. 8  shows how multiple wavelengths of light  26  may be handled using multiple different gratings  34  (e.g., metasurface gratings, sometimes referred to as nanostructure gratings, or other suitable gratings). System  14  may have, for example, a blue grating  34 B, a green grating  34 G, and a red grating  34 R that are formed at multiple different locations along the length of waveguide  36 . In a first illustrative configuration, blue light B, green light G, and red light R are respectively applied to gratings  34 B,  34 G, and  34 R from outside of layer  50  (e.g., using an arrangement of the type shown in  FIG. 3  or  FIG. 5A ). In a second illustrative configuration, blue light B′, green light G′, and red light R′ are respectively applied to gratings  34 B,  34 G, and  34 R from inside of layer  50  (e.g., using an arrangement of the type shown in  FIG. 2  or  FIG. 5B ). 
     In general, the metasurface of grating  34  may be configured to handle transmission or reflection modes of operation. For input, each metasurface may blaze the first order of the designed wavelength and blaze the zeroth order for the longer wavelength(s). For output, each metasurface may blaze the zeroth order for all the distinct wavelengths (red, green, and blue here). 
     Metasurfaces for grating  34  may be designed using nanostructure of any suitable sizes. Other optical elements such as collimators may be also be added using metasurface layers. 
     The foregoing is merely illustrative and various modifications can be to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20190215
Publication Date: 20201215
Grant Date: 20201215
Priority Date: 20180228
Inventors: HANSOTTE, Eric J.
COCILOVO, BYRON R.
OH, SE BAEK
KAMALI, Seyedeh Mahsa
AIETA, Francesco
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B5/1871", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/1861", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0031", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0056", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/1861", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/34", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B26/101", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/015", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0176", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B26/101", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/0112", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B5/1871", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0011", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0031", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B26/101", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/1871", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0056", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0031", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0176", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B2027/0112", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B5/1861", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/015", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 67685780