PATENT DOCUMENT

Publication Number: US-11815677-B1
Application Number: US-202016871069-A
Country: US
Kind Code: B1

Title: Display using scanning-based sequential pupil expansion

Abstract:
Image projection apparatus includes an image generating assembly, which is configured to project a sequence of line images extending in a first direction. A scanning mirror is positioned to receive and to reflect the line images while rotating about a mirror axis parallel to the first direction. A pupil expander has an edge positioned to receive the line images reflected by the scanning mirror and a face extending in a second direction non-parallel to the first direction and to the edge, and which is configured to direct simultaneously through the face multiple, parallel replicas of the expanded line images arrayed along the second direction.

Claims:
The invention claimed is: 
     
         1 . Image projection apparatus, comprising:
 an image generating assembly, which is configured to project a sequence of line images extending in a first direction;   a scanning mirror positioned to receive and to reflect the line images while rotating about a mirror axis parallel to the first direction; and   a pupil expander, which has an edge positioned to receive the line images reflected by the scanning mirror and a face extending in a second direction non-parallel to the first direction and to the edge, and which is configured to direct simultaneously through the face multiple, parallel replicas of the line images arrayed along the second direction.   
     
     
         2 . The apparatus according to  claim 1 , and comprising a controller, which is configured to drive the image generating assembly in synchronization with the scanning mirror so that the sequence of line images form successive raster lines in a two-dimensional image projected through the face of the pupil expander. 
     
     
         3 . The apparatus according to  claim 1 , wherein the scanning mirror that is positioned to receive and to reflect the line images is a first scanning mirror, and wherein the image generating assembly comprises:
 at least one source of optical radiation;   collimation optics configured to receive, collimate, and project the optical radiation;   a second scanning mirror positioned to receive and to reflect the collimated optical radiation while rotating about a mirror axis parallel to the second direction;   a beam expander configured to receive the radiation reflected by the second scanning mirror and to expand the received radiation into a pupil that is expanded in the first direction; and   a controller, which is configured to drive and modulate the at least one source in synchronization with the second scanning mirror so as to form the line images.   
     
     
         4 . The apparatus according to  claim 3 , wherein the at least one source of optical radiation comprises a photonic integrated circuit comprising:
 a substrate;   multiple emitters on or in proximity to the substrate; and   a plurality of waveguides, which are disposed on the substrate and comprise respective input ends coupled to respective ones of the emitters and output ends arranged in an array having a predefined pitch.   
     
     
         5 . The apparatus according to  claim 4 , wherein the multiple emitters comprise at least three emitters configured to emit optical radiation at blue, green, and red wavelengths. 
     
     
         6 . The apparatus according to  claim 4 , wherein the pitch is between 5 and 50 microns. 
     
     
         7 . The apparatus according to  claim 4 , wherein the beam expander comprises an optically transparent prism configured to propagate the radiation received from the second scanning mirror by total internal reflection, and wherein the prism comprises an internal beam splitting coating configured to split the radiation propagated by the total internal reflection into multiple parts, which propagate in the prism by total internal reflection. 
     
     
         8 . The apparatus according to  claim 1 , wherein the pupil expander is at least partially transparent to optical radiation. 
     
     
         9 . The apparatus according to  claim 1 , and comprising an eyeglass frame, wherein the pupil expander is mounted in the frame so as to be positioned in front of an eye of a user of the apparatus who is wearing the frame. 
     
     
         10 . The apparatus according to  claim 9 , wherein the first direction is parallel to a longitudinal axis of a body of the user who is wearing the frame. 
     
     
         11 . The apparatus according to  claim 9 , wherein in the first direction is perpendicular to a longitudinal axis of a body of the user who is wearing the frame. 
     
     
         12 . Image projection apparatus, comprising:
 an image generating assembly, which is configured to project a sequence of line images extending in a first direction and comprises: 
 multiple emitters of optical radiation, arranged in a linear array extending in the first direction; 
 collimation optics configured to receive, collimate, and project the optical radiation; and 
 a beam expander configured to receive and expand the collimated radiation in the first direction so as to expand a pupil of the apparatus in the first direction; 
   a scanning mirror positioned to receive and to reflect the line images while rotating about a mirror axis parallel to the first direction; and   a pupil expander, which has an edge positioned to receive the line images reflected by the scanning mirror and a face extending in a second direction non-parallel to the first direction and to the edge, and which is configured to direct simultaneously through the face multiple, parallel replicas of the line images arrayed along the second direction.   
     
     
         13 . The apparatus according to  claim 12 , wherein the emitters are configured to emit the optical radiation at multiple different wavelengths, and the apparatus comprises a controller, which is configured to modulate the emitters so as to generate respective pixels of the line images. 
     
     
         14 . The apparatus according to  claim 12 , wherein the beam expander comprises an array of parallelepipedal, optically transparent prisms, which are disposed along the first direction. 
     
     
         15 . The apparatus according to  claim 14 , wherein an interface between adjacent parallelepipedal prisms in the array comprises an optical coating, which is configured to partially reflect and partially transmit the optical radiation impinging on the interface. 
     
     
         16 . A method for image projection, comprising:
 projecting a sequence of line images extending in a first direction toward a scanning mirror positioned to receive and to reflect the line images;   driving the scanning mirror to rotate about a mirror axis parallel to the first direction; and   receiving the line images reflected by the scanning mirror through an edge of a pupil expander, which has a face extending in a second direction non-parallel to the first direction and to the edge, and which directs simultaneously through the face multiple, parallel replicas of the line images arrayed along the second direction.   
     
     
         17 . The method according to  claim 16 , wherein projecting the sequence of line images comprises generating the line images in synchronization with the scanning mirror so that the sequence of line images form successive raster lines in a two-dimensional image projected through the face of the pupil expander. 
     
     
         18 . The method according to  claim 16 , wherein the line images are generated by an image generating assembly, which comprises:
 multiple emitters of optical radiation, arranged in a linear array extending in the first direction;   collimation optics configured to receive, collimate, and project the optical radiation; and   a beam expander configured to receive and expand the collimated radiation in the first direction so as to expand a pupil of the method in the first direction.   
     
     
         19 . The method according to  claim 16 , wherein the scanning mirror that is positioned to receive and to reflect the line images is a first scanning mirror, and wherein the line images are generated by an image generating assembly, which comprises:
 at least one source of optical radiation;   collimation optics configured to receive, collimate, and project the optical radiation;   a second scanning mirror positioned to receive and to reflect the collimated optical radiation while rotating about a mirror axis parallel to the second direction; and   a beam expander configured to receive the radiation reflected by the second scanning mirror and to expand the received radiation into a pupil that is expanded in the first direction,   wherein generating the line images comprises driving and modulating the at least one source in synchronization with the second scanning mirror so as to form the line images.   
     
     
         20 . The method according to  claim 19 , wherein the beam expander comprises an optically transparent prism configured to propagate the radiation received from the second scanning mirror by total internal reflection, and wherein the prism comprises an internal beam splitting coating configured to split the radiation propagated by the total internal reflection into multiple parts, which propagate in the prism by total internal reflection.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Pat. Application 62/847,970, filed May 15, 2019, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to optoelectronic systems, and particularly to methods and devices for image projection. 
     BACKGROUND 
     Image projection devices are used to project electronically generated images either onto a screen or directly into the eye of an observer. For example, virtual reality (VR) systems project an image to be viewed by an observer in, for example, game and educational applications. Augmented reality (AR) systems combine the image generated by a VR system with the scene observed passively through the AR system in applications such as, for example, surgery and complicated mechanical assembly. 
     Image projection devices may emit light of different wavelengths from multiple sources, which may appear as different colors. (The terms “optical radiation” and “light” as used in the present description and in the claims refer generally to any and all of visible, infrared, and ultraviolet radiation.) In visual display applications it is customary to refer to the three wavelength ranges of red, green, and blue as RGB, wherein the central wavelengths of the ranges are, for example, 640 nm for red, 532 nm for green, and 450 nm for blue. Depending on the types of sources that are used, the RGB wavelengths may also comprise spectral bands around the central wavelengths, with widths of 10 nm, 20 nm, or more. 
     SUMMARY 
     Embodiments of the present invention that are described herein provide improved apparatus and methods for optical scanning, delivery and projection. 
     There is therefore provided, in accordance with an embodiment of the invention, image projection apparatus, including an image generating assembly, which is configured to project a sequence of line images extending in a first direction. A scanning mirror is positioned to receive and to reflect the line images while rotating about a mirror axis parallel to the first direction. A pupil expander has an edge positioned to receive the line images reflected by the scanning mirror and a face extending in a second direction non-parallel to the first direction and to the edge, and which is configured to direct simultaneously through the face multiple, parallel replicas of the expanded line images arrayed along the second direction. 
     In a disclosed embodiment, the apparatus includes a controller, which is configured to drive the image generating assembly in synchronization with the scanning mirror so that the sequence of line images form successive raster lines in a two-dimensional image projected through the face of the pupil expander. 
     In some embodiments, the image generating assembly includes multiple emitters of optical radiation, arranged in a linear array extending in the first direction and collimation optics configured to receive, collimate, and project the optical radiation. A beam expander is configured to receive and expand the collimated radiation in the first direction so as to expand a pupil of the apparatus in the first direction. In a disclosed embodiment, the emitters are configured to emit the optical radiation at multiple different wavelengths, and the apparatus includes a controller, which is configured to modulate the emitters so as to generate respective pixels of the line images. 
     Additionally or alternatively, the beam expander includes an array of parallelepipedal, optically transparent prisms, which are disposed along the first direction. Typically, an interface between adjacent parallelepipedal prisms in the array includes an optical coating, which is configured to partially reflect and partially transmit the optical radiation impinging on the interface. 
     In alternative embodiments, the scanning mirror that is positioned to receive and to reflect the line images is a first scanning mirror, and the image generating assembly includes at least one source of optical radiation and collimation optics configured to receive, collimate, and project the optical radiation. A second scanning mirror is positioned to receive and to reflect the collimated optical radiation while rotating about a mirror axis parallel to the second direction. A beam expander is configured to receive the radiation reflected by the second scanning mirror and to expand the received radiation into a pupil that is expanded in the first direction. A controller is configured to drive and modulate the at least one source in synchronization with the second scanning mirror so as to form the line images. 
     In a disclosed embodiment, the at least one source of optical radiation includes a photonic integrated circuit including a substrate, multiple emitters on or in proximity to the substrate, and a plurality of waveguides, which are disposed on the substrate and include respective input ends coupled to respective ones of the emitters and output ends arranged in an array having a predefined pitch. Additionally or alternatively, the multiple emitters include at least three emitters configured to emit optical radiation at blue, green, and red wavelengths. Typically, the pitch is between 5 and 50 microns. 
     Further additionally or alternatively, the beam expander includes an optically transparent prism configured to propagate the radiation received from the second scanning mirror by total internal reflection, and the prism includes an internal partially reflective coating that splits the beam according to its dielctric design. The coating is configured to split the radiation propagated by the total internal reflection into multiple parts, which propagate in the prism by total internal reflection. 
     In a disclosed embodiment, the pupil expander is at least partially transparent to optical radiation. 
     In some embodiments, the apparatus includes an eyeglass frame, wherein the pupil expander is mounted in the frame so as to be positioned in front of an eye of a user of the apparatus who is wearing the frame. 
     There is also provided, in accordance with an embodiment of the invention, a method for image projection, which includes projecting a sequence of line images extending in a first direction toward a scanning mirror positioned to receive and to reflect the line images, and driving the scanning mirror to rotate about a mirror axis parallel to the first direction. The line images reflected by the scanning mirror are received through an edge of a pupil expander, which has a face extending in a second direction non-parallel to the first direction and to the edge, and which directs simultaneously through the face multiple, parallel replicas of the expanded line images arrayed along the second direction. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1  and  2    are schematic pictorial illustrations, in front and rear views, respectively, of an image projection apparatus, in accordance with an embodiment of the invention; 
         FIG.  3    is a schematic top view of the apparatus of  FIGS.  1  and  2   , in accordance with an embodiment of the invention; 
         FIG.  4    is a schematic sectional view of an image projection apparatus, showing details of an image generating assembly and a scanning mirror assembly, in accordance with an embodiment of the invention; 
         FIG.  5    is a schematic detail view of an image generating assembly, showing details of optical operation of a beam expander, in accordance with an embodiment of the invention; 
         FIG.  6    is a flowchart that schematically shows a flow of optical signals in an image projection apparatus, in accordance with an embodiment of the invention; 
         FIGS.  7   a  and  7   b    are schematic side and top views, respectively, of an image projection apparatus, in accordance with another embodiment of the invention; 
         FIG.  8    is a flowchart that schematically shows a flow of optical signals in the apparatus of  FIGS.  7   a  and  7   b   , in accordance with an embodiment of the invention; and 
         FIG.  9    is a schematic frontal view of an image projection apparatus, in accordance with an alternative embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     A number of current applications, for example VR and AR systems, require an image projector to project a two-dimensional (2D) image collimated and distributed in angle space toward an area with a diagonal dimension of at least a few centimeters. This area may be termed the “eye box.” An observer will locate the entrance pupil of the observer’s eye in the eye box, which should be sufficiently large to accommodate the natural eye motions of the observer. There is a need for image projectors that are both compact and light-weight, with high optical resolution, high efficiency, and low power consumption. 
     The embodiments of the present invention that are described herein address the above needs so as to provide a compact and efficient image projector. The image projector is based on combining a one-dimensional (1D) image generating assembly with a scanning mirror and a pupil expander. The embodiments may also incorporate emitters, additional scanners, optical components, and photonic integrated circuits (PICs) to form the 1D image generating assembly. 
     In the disclosed embodiments, the image projector comprises an image generating assembly, which projects a sequence of line images extending in a first direction, for example the vertical direction in AR eyeglasses. A scanning mirror is positioned to receive and to reflect the line images while rotating about a mirror axis parallel to the first direction (a vertical axis in the above example). The scanning mirror reflects the line images in through the edge of a pupil expander, for example a pupil expander extending across the field of view of the eye in the AR eyeglasses. The face of the pupil expander, in other words, extends in a second direction non-parallel to the axis direction of the mirror and to the edge of the pupil expander. The pupil expander will thus direct simultaneously through the face (toward the eye of the person wearing the eyeglasses) multiple, parallel replicas of the expanded line images, with the replicas arrayed along the second direction. These light fields are arranged in the eye box, where the observer’s eye will be located. 
     In display applications, such as in AR eyeglasses, the line image corresponds to a single raster line (along a vertical direction in the above example) within a two-dimensional (2D) image that is to be projected through the face of the pupil expander. The pixels of the line image are modulated in synchronization with the rotation of the mirror to generate successive lines of the 2D image, which are then projected by the beam expander at different, respective angles. In some embodiments, a controller is configured to drive the image generating assembly in synchronization with the scanning mirror based on the image content that is to be displayed, with each scan of the mirror corresponding to a successive image frame. Various types of pupil expanders may be used in conjunction with the image generating assembly for this purpose. 
     Embodiments of the present invention that are described hereinbelow provide a number of different types of 1D image generating assemblies. In some embodiments, the 1D image generating assembly comprises multiple emitters emitting optical radiation at several wavelengths. The outputs of the emitters are combined by a photonic integrated circuit (PIC) into a single multi-color output or an array of outputs, whose intensities and colors are modulated by fast modulation of the emitters. A fast scanning mirror, rotating about an axis perpendicular to the (slower) scanning mirror mentioned above, expands the output of the PIC to produce the 1D line image. 
     In alternative embodiments, the 1D image generating assembly comprises a linear array of optical emitters, which are modulated to generate a line image, along with optics to collimate and expand this line image to produce the 1D line image that is scanned by the scanning mirror. These embodiments obviate the need for a fast scanning mirror, though at the cost of a larger, and possibly more cumbersome, array of emitters. 
     Image Projection Apparatus Using an Emitter Array 
     Reference is now made to  FIGS.  1  and  2   , which are schematic pictorial illustrations, in front and rear views, respectively, of an image projection apparatus  20 , in accordance with an embodiment of the invention. Apparatus  20  may be used, for example, as part of an AR system, as well as in other image projection applications. 
     Apparatus  20  is based on a typical format of eyeglasses. For the sake of simplicity, only the left side of apparatus  20  (as referenced to an observer wearing the system) is shown. The right side is a mirror image of the left side. Alternatively, the right side may comprise only a lens with or without optical power, but without a display. 
     Apparatus  20  comprises a suitably modified eyeglass frame  22 , a 1D image generating assembly  24 , a scanning mirror assembly  26 , and a 1D pupil expander  28 . A controller  30  is coupled to image generating assembly  24  and to scanning mirror assembly  26 . Pupil expander  28  is mounted in frame  22  so as to be positioned, in place of (or in parallel with) an eyeglass lens, in front of an eye of a user of apparatus  20  who is wearing the frame. Image generating assembly  24  and a scanning mirror assembly  26  are likewise mounted on frame  22 , either internally (as shown in the figures) or externally. 
     Image generating assembly  24  comprises an emitter array  34 , collimation optics  36 , and a 1D beam expander  38 . Collimation optics  36  are rotationally symmetrical, but have their apertures shaped to form rectangles so as to minimize the form factor of the design. This is accomplished due to the narrow horizontal dimension of emitter array  34 . Emitter array  34  comprises a mostly linear array of vertical-cavity surface-emitting lasers (VCSELs) or micro-light-emitting diodes (micro-LEDs), with a large number of emitters, for example one thousand or several thousands, in the vertical direction, and a few emitters, for example three or four, in the horizontal direction. Alternatively, array  34  may comprise larger or smaller numbers of rows and/or columns of emitters. In the following, beam and pupil are used interchangeably. An image comprises multiple beams distributed in the angular domain. 
     Scanning mirror assembly  26  comprises an elongated rectangular first scanning mirror  40  and a mirror actuator  42 , such as a galvanometer, with an axis of rotation of the scanning mirror assembly parallel to the Y-axis of a Cartesian coordinate system  32 . In the pictured embodiment, the Y-axis is parallel to the vertical axis of the eyeglasses, as well as to the longitudinal axis of the body of a user of apparatus  20 . (Cartesian coordinate system  32  is used for the sake of clarity and convenience only. Other coordinate systems may be alternatively used.) The dimensions of scanning mirror  40  are, for example, 20 mm × 5 mm, wherein the long dimension, along the axis of rotation, is determined by the dimension of pupil expander  28  in Y-direction. Minimizing the short dimension, perpendicular to the axis of rotation, enables high-speed scanning and makes it possible to integrate assembly  26  unobtrusively into the eyeglass frame of apparatus  20 . The typical range of scan frequencies of scanning mirror assembly  26  is 30 Hz or higher, so that the image (as explained below with reference to  FIG.  3   ) produced by a full angular scan is seen by an observer as one image. Alternatively, scanning mirror assembly  26  may comprise a long rotating polygon with an electric motor drive. 
     Pupil expander  28  comprises, for example, a waveguide, a surface grating, or a holographic element. Pupil expanders of these sorts are known in the art of AR displays, for example, and their details are beyond the scope of the present description. 
       FIG.  3    is a schematic top view of apparatus  20 , in accordance with an embodiment of the invention.  FIGS.  2  and  3    show the flow of optical signals from emitter array  34  to their exit from pupil expander  28 . Emitter array  34  emits a 1D image comprising many beams, which are collimated by collimation optics  36  and are nominally projected in the Z-direction towards beam expander  38 , as indicated by an arrow  50 . Beam expander  38 , in turn, expands the beams in the Y-direction. The angular range of the image (in the Y-direction) is determined by the length of emitter array  34  and the focal length of collimation optics  36 . The spatial extent of the beam is determined by beam expander  38 . 
     The expanded 1D image produced by beam expander  38  is reflected by mirror  40  over a range of angles toward the X-direction, entering pupil expander  28  through an edge  29 , as indicated by arrows  52 . This range of reflected angles defines the observed field-of-view in the X direction of the apparatus. Pupil expander  28  expands the received beams into multiple, parallel replicas arrayed across the X-direction and projects them through a face  31  (oriented in the X-Y-plane) toward the negative Z-direction, as shown by arrows  54 . 
     As illustrated in  FIG.  2   , scanning mirror  40  receives the 1D image from emitter array  34  and collimation optics  36  through beam expander  38 . Scanning mirror  40  is shown in  FIG.  3    in two angular orientations labelled by  40   a  and  40   b , wherein orientation  40   a  is shown by a solid line and orientation  40   b  is shown by a dotted line. 
     When scanning mirror  40  is in orientation  40   a  and receives the collimated and expanded beams that make up the 1D image, it reflects and projects the image as shown by an arrow  52   a  (solid arrow) into pupil expander  28  through its edge  29 . Pupil expander  28 , in turn, expands the image in the X-direction and emits this 2D image out of the pupil expander through face  31  into the (negative) Z-direction, as shown by solid arrows  54   a . A solid line  60   a , parallel to arrows  54   a , indicates the direction where an eye  62 , placed behind pupil expander  28  in system  20 , would form an image corresponding to the line image reflected by scanning mirror  40  in orientation  40   a . Thus, a given angular orientation of scanning mirror  40  corresponds to a given apparent direction of a 1D line image, where the observer can see a distant and resolvable object. 
     Similar considerations may be applied, when scanning mirror  40  is oriented in orientation  40   b : The collimated, expanded, and reflected beams of the 1D image are now projected into pupil expander  28  along a dotted-line arrow  52   b , which are converted into beams emitted along dotted-line arrows  54   b . In this way the beams are expanded along the X-direction to fill a 2D eye box. A dotted line  60   b  indicates now the direction in which an image would be seen by eye  62 . 
     Thus, driving both emitter array  34  and mirror actuator  42  by controller  30  in a synchronized manner, a full 2D image is displayed by apparatus  20 . The term “full 2D image” refers to an image with a 2D extent in the angular domain. The 1D line image contained in the collimated beams reflected by scanning mirror  40  at all the different angular orientations form the raster lines of this 2D image. A typical spatial extent of the eye box containing the beams near the observer’s eye is approximately 20 mm × 20 mm, and a typical angular extent of the image is ±10° × ±10°, although other spatial and angular extents of the eye box and the image, respectively, are possible. The scanning frequency of scanning mirror assembly  26  is sufficiently high so that the full angular extent in X-direction is observed as a single image by the human observer. 
       FIG.  4    is a schematic sectional view of apparatus  20 , showing details of image generating assembly  24  and scanning mirror assembly  26 , in accordance with an embodiment of the invention. 
     As explained above with reference to  FIG.  2   , emitter array  34  emits a 1D section of the 2D image, which is collimated by collimation optics  36  and projected in the Z-direction towards beam expander  38 , as indicated by arrow  50 . Emitter array  34 , collimation optics  36 , and beam expander  38  together form a 1D image generating assembly  24 . Beam expander  38  comprises multiple optically transparent parallelepipedal prisms  70 , with partially reflecting coatings  72  between adjacent prisms. The 1D image represented by arrow  50  is repeatedly partially reflected and partially transmitted by parallelepipedal prisms  70 , resulting in a 1D image expanded in the Y-direction, as shown by arrows  74 . The expanded 1D image is projected onto scanning mirror  26 , and from there towards pupil expander  28 , as shown in  FIG.  2   . 
       FIG.  5    is a schematic detail view of image generating assembly  24 , showing details of optical operation of beam expander  38 , in accordance with an embodiment of the invention. 
     Beam expander  38  comprises parallelepipedal prisms  84 , which are sufficiently thick in the Z-direction so that the collimated 1D image, represented by arrow  50 , experiences several reflections within each prism, as represented, for example, by an arrow  86 . 
       FIG.  6    is a flowchart  90  that schematically shows the flow of optical signals in apparatus  20 , in accordance with an embodiment of the invention. In flowchart  90 , rectangles indicate a component or action of apparatus  20 , and ellipses indicate an image and/or pupil produced by the preceding components or actions. The angular extent of the image and the spatial extent of the pupil are indicated within each ellipse by a table, such as Table 1 shown below as an example. 
     
       
         
          TABLE 1
           
               
               
               
             
               
                 Example of angular extent of an image and spatial extent of a pupil in X- and Y-directions (ang = angular, spat = spatial, S = small, L = large) 
               
               
                   
                 ang 
                 spat 
               
             
            
               
                 X 
                 S 
                 S 
               
               
                 Y 
                 L 
                 S 
               
            
           
         
       
     
     For the sake of brevity, we refer herein to angular extent as pertaining to the image and to spatial extent as pertaining to the pupil. Table 1 indicates an image and a pupil, wherein in the X-direction both angular and spatial extents are small, and wherein in the Y-direction the angular extent is large but spatial extent is small. A small angular extent indicates that only a narrow angular subset, such as 1°, of the final image is included, whereas a large angular extent indicates that a full angular view, such as ±10°, of the final image is included. A small spatial extent indicates a small pupil width, such as 1 mm, whereas a large spatial extent indicates a full width of the final pupil, which is the eye box, and can be 20 mm. 
     In an emission step  92 , emitter array  34  emits an image with a full angular extent in the Y-direction (the direction of the emitter array), but with only a small angular extent in X-direction. In a collimation step  94 , the image is collimated by collimation optics  36 , producing, as indicated in a first image step  96 , a collimated 1D image with a small beam diameter (small extent in both X- and Y-directions). The image from first image step  96  is expanded in the Y-direction by beam expander  38  in a beam expansion step  98 , producing, as shown in a second image step  100 , a 1D image where the image is large in the Y-direction but remains small in the X-direction. 
     The image from second image step  100  is received and scanned in a scan step  102  by scanning mirror  40  and projected into pupil expander  28 , which in turn expands the pupil in a pupil expansion step  104 . This produces a pupil with a large extent in both X- and Y-directions, but still only a small angular extent in the X-direction, as indicated in a third image step  106 . A feedback step  108  takes the process back to emission step  92 , where a 1D image corresponding to the next angular orientation of scanning mirror  40  is emitted, as illustrated in  FIG.  3   . Finally, when emitter array  34  and scanning mirror  40  have looped through the full angular extent of the image in X-direction, an image with full angular extent emitted from a pupil of full spatial extent is produced, as indicated in a fourth image step  110 . 
     Image Projection Apparatus Using Dual Scanning Mirrors 
       FIGS.  7   a  and  7   b    are schematic side and top views, respectively, of an image projection apparatus  200 , in accordance with another embodiment of the invention. 
     Apparatus  200  comprises emitters  202 , for example edge-emitting lasers, driven by drivers  204  and emitting light at different wavelengths, such as at RGB wavelengths, into a photonic integrated circuit (PIC)  206 . PIC  206  comprises strip waveguides  208  formed on a substrate  210 . (The term “strip waveguide” refers to a waveguide that is formed on a substrate and typically has a lateral dimension that does not exceed a few hundreds of nanometers or a few microns, such as 500 nm or 2 microns.) Waveguides  208  may be formed by a photolithographic process of, for example, silicon nitride (Si 3 N 4 ) on a quartz (SiO 2 ) substrate  210 . Emitters  202  can be coupled to input ends  211  of the respective waveguides  208  by edge coupling or by free-space beam-waist imaging optics. The paths of waveguides  208  are formed in such a way that at their exit ends  212  the neighboring waveguides are separated by small distances, for example, about 10 microns, or more generally, between 5 and 50 microns. 
     In one embodiment, emitters  202  comprise multiple groups of RGB emitters, and PIC  206  comprises one strip waveguide  208  for each emitter. In this case, multiple lines of pixels of the final 2D image may be generated simultaneously by suitable modulation of emitters  202 . Thus, for example, with three groups of emitters  202 , three lines with RGB wavelengths are generated simultaneously. 
     Apparatus  200  further comprises collimation optics  214 , an optically transparent prism  216 , and a fast-axis scanning mirror  218 . Collimation optics  214  receive the light emitted by PIC  206 , collimate it and project it through prism  216  onto fast-axis scanning mirror  218 . Referring to  FIG.  7   a    and to a Cartesian coordinate system  220 , fast-axis scanning mirror  218  rotates around an axis parallel to the Z-axis. (For the sake of simplicity, fast-axis scanning mirror  218  is not shown in  FIG.  7   b   . Cartesian coordinate system  220  is used for the sake of clarity and convenience only. Other coordinate systems may be alternatively used.) 
     As further detailed in  FIG.  8   , the scan of fast-axis scanning mirror  218 , together with the temporal modulation of emitters  202 , produces a 1D image oriented in the Y-direction. The scan frequency of fast-axis scanning mirror  218  is sufficiently high so that the fast-axis scanning mirror performs a full scan (produces a full 1D image in the Y-direction) for each scan position of a scanning mirror  240  scanning in the X-direction. The frequency of the fast-axis scan is typically in excess of 23 kHz, while the frequency of the slow-axis scan is between 90 and 120 Hz. Due to the requirement of a high scan frequency, fast-axis scanning mirror  218  typically comprises a lightweight mirror rotating in a resonant scanning mode. Alternatively, fast-axis scanning mirror  218  may comprise a high-speed rotating polygon, driven by an electric motor. 
     The directions of rays  222  from collimation optics  214  to prism  216  are arranged in such a way that, with a prism angle a, these rays pass through the prism onto fast-axis scanning mirror  218 . Choosing the range of rotation angles of fast-axis scanning mirror  218  appropriately, rays  224  reflected from the fast-axis scanning mirror enter prism  216  and are then “trapped” in the prism due to total internal reflection (TIR) from long faces  225  of the prism. A folding mirror  230  may be used for beam folding for a compact design of apparatus  200 . Prism  216  comprises an internal 50/50 beam splitting coating  226 , parallel to long faces  225 , which, in conjunction with the bouncing of trapped rays  227  within the prism, produces multiple copies of the rays. Modulating emitters  202  temporally in synchronization with the rotation of fast-axis scanning mirror  218 , together with the ray multiplication within prism  216 , produces a 1D image in the Y-direction at an exit face  228  of prism  216 . 
     PIC  206  with emitters  202  and drivers  204 , together with collimation optics  214 , prism  216 , and fast-axis scanning mirror  218  form a 1D image generating assembly  232 , which generates a 1D image that extends in the Y-direction, similar to the 1-D image produced by image generating assembly  24 , as shown in the preceding figures. 
     The 1D image exiting from exit face  228  is projected onto scanning mirror  240 , and from there into a pupil expander  242 . Scanning mirror  240  and pupil expander  242  are either identical with or similar to scanning mirror  40  and pupil expander  28  of  FIGS.  1 - 4   . 
       FIG.  8    is a flowchart  250  that schematically shows the flow of optical signals in apparatus  200 , in accordance with an embodiment of the invention. In flowchart  250  (similarly to flowchart  90 ), rectangles indicate a component or action of apparatus  200 , and ellipses indicate an image and/or pupil produced by the preceding components or actions. Tables within the ellipses indicate the image extents. 
     In an emission step  252 , RGB emitters  202  emit respective optical signals into PIC  206 , which, in waveguiding step  254 , projects the optical signals into collimation optics  214 . In collimation step  256 , collimation optics  214  collimate and project the optical signals onto fast-axis scanning mirror  218 , which produces 1D image in a first scanning step  258 . Through a next-Y step  260 , RGB emitters  202  emit a new optical signal for each respective new rotation angle of fast-axis scanning mirror  218 . 
     The resulting image is indicated in a first image step  262  (corresponding to first image step  96  in flowchart  90 .) In a prism step  264 , the combination of a small-diameter pupil and a small-angle image passes through prism  216 , and is expanded into a 1D nominal pupil with a large spatial extent in the Y-direction, as shown in a second image step  266  (corresponding to second image step  100  in flowchart  90 ). Similarly to flowchart  90 , the image from second image step  266  is received and scanned in a scan step  268  by scanning mirror  240  and projected into pupil expander  242 , which in turn expands the pupil in a pupil expansion step  270 . This produces, in a third image step  272 , an image emitted from a pupil of a large spatial extent in both X- and Y-directions and a large angular extent in the Y-direction, but still a small angular extent in the X-direction. A feedback step  274  takes the process back to the next orientation of scanning mirror  240  and to the loop comprising steps  252 - 260 , where a 1D image corresponding to the next angular orientation of scanning mirror  240  is emitted. Finally, with repeated loops through feedback step  274 , an image emitted from a pupil with a full spatial extent with the desired angular extents of the final image is produced, as indicated in a fourth image step  276 . 
       FIG.  9    is a schematic frontal view of an image projection apparatus  320 , in accordance with an alternative embodiment of the invention. The principles of this embodiment are similar to those of the preceding embodiments, with an image generating assembly  324 , a scanning mirror  326 , and a pupil expander  328  mounted in an eyeglass frame  322 . In the present embodiment, however, the line images output by image generating assembly  324 , as well as the rotational axis of mirror  326 , extend in the X-direction, meaning that they will be perpendicular to the longitudinal axis of the body of a user who is wearing frame  322 . 
     As in the embodiment of  FIGS.  7   a / b   , collimation optics  332  collect the light output by emitters  330  and direct the resulting beams toward a fast-axis scanning mirror  334 , which rotates about the Z-axis. Scanning mirror  334  directs the scanned beam into a 1D beam expander  336 , which produces line images extending across the X-direction. Scanning mirror  326  serves as the slow-axis scanning mirror and reflects the line images in the Y-direction, into pupil expander  328 . The pupil expander thus directs two-dimensional images in the -Z direction, toward the eye of the user. 
     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Metadata:
Filing Date: 20200511
Publication Date: 20231114
Grant Date: 20231114
Priority Date: 20190515
Inventors: HAJATI, ARMAN
SHPUNT, ALEXANDER
UPTON, Robert S.
GERSON, YUVAL
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B27/0081", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B26/105", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0081", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B26/105", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B26/105", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0081", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2027/0178", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 88700750