PATENT DOCUMENT

Publication Number: US-11237332-B1
Application Number: US-202016871068-A
Country: US
Kind Code: B1

Title: Direct optical coupling of scanning light engines to a waveguide

Abstract:
An optical apparatus includes an optically transparent slab waveguide including first and second, mutually-parallel planar faces and an edge non-parallel to the planar faces. A radiation source directs a beam of optical radiation to enter the waveguide through the first planar face at an entrance location and entrance angle selected so that the beam subsequently exits the waveguide at an exit location in a surface selected from among the second planar face and the edge. A scanning mirror is positioned to receive the beam that has exited through the surface and to reflect the beam back through the surface into the waveguide while the scanning mirror rotates about an axis parallel to the surface over a range of angles selected so as to cause the beam, after reflection back into the waveguide through the surface, to propagate within the waveguide by total internal reflection (TIR).

Claims:
The invention claimed is: 
     
       1. An optical apparatus, comprising:
 an optically transparent slab waveguide comprising first and second, mutually-parallel planar faces and a planar wedge-shaped edge, having a surface that is non-parallel and non-normal to the planar faces; 
 a radiation source configured to direct a beam of optical radiation to enter the waveguide through the first planar face at an entrance location and entrance angle selected so that the beam subsequently exits the waveguide at an exit location in the surface of the wedge-shaped edge that is non-parallel and non-normal to the planar faces; and 
 a scanning mirror positioned to receive the beam that has exited through the surface and to reflect the beam back through the surface into the waveguide while the scanning mirror rotates about an axis parallel to the surface over a range of angles selected so as to cause the beam, after reflection back into the waveguide through the surface, to propagate within the waveguide by total internal reflection (TIR) between the first and second planar faces. 
 
     
     
       2. The optical apparatus according to  claim 1 , wherein the beam exits the surface at a selected exit angle relative to the surface, and wherein the range of angles over which the scanning mirror rotates is selected so as to cause the beam reflected back from the scanning mirror to enter the surface and impinge on the first planar face at angles exceeding a critical angle for TIR within the waveguide. 
     
     
       3. The optical apparatus according to  claim 1 , and comprising an optically transparent prism comprising first and second, mutually non-parallel planar prism faces and positioned between the radiation source and the slab waveguide so that the beam from the radiation source enters the prism through the second prism face and exits from the prism through the first prism face so as to enter the waveguide through the first planar face at the entrance location and entrance angle such that the beam subsequently exits the waveguide at the exit location. 
     
     
       4. The optical apparatus according to  claim 1 , wherein the waveguide comprises an out-coupler configured to intercept the beam that propagates within the waveguide by total internal reflection and to couple the beam out of the waveguide. 
     
     
       5. The optical apparatus according to  claim 4 , wherein the scanning mirror rotates over a range of angles exceeding 50°. 
     
     
       6. The optical apparatus according to  claim 1 , wherein the scanning mirror is positioned in proximity to and parallel to the planar edge. 
     
     
       7. The optical apparatus according to  claim 1 ,
 wherein the apparatus comprises an optically transparent prism, which comprises first and second, mutually non-parallel planar prism faces and is positioned with the first prism face in proximity to the second planar face of the waveguide and the second prism face, which defines the surface of the wedge-shaped edge through which the beam exits and enters the waveguide, in proximity to the scanning mirror. 
 
     
     
       8. The optical apparatus according to  claim 7 , wherein the prism is positioned so that the beam exiting the waveguide at the exit location enters the prism through the first prism face and exits the prism through the second prism face to impinge on the scanning mirror, which reflects the beam back through the second prism face so that the reflected beam exits the prism through the first prism face and reenters the waveguide through the second planar face at an angle exceeding a critical angle for TIR within the waveguide. 
     
     
       9. The optical apparatus according to  claim 1 , wherein the radiation source comprises an array of emitters and projection optics configured to collect the optical radiation from the emitters and to direct the optical radiation toward the entrance location. 
     
     
       10. A method for optical scanning, comprising:
 directing a beam of optical radiation to enter an optically transparent slab waveguide, which comprises first and second, mutually-parallel planar faces and a planar wedge-shaped edge, having a surface that is non-parallel and non-normal to the planar faces, through the first planar face at an entrance location and entrance angle selected so that the beam subsequently exits the waveguide at an exit location in the surface of the wedge-shaped edge that is non-parallel and non-normal to the planar faces; 
 positioning a scanning mirror to receive the beam that has exited through the surface and to reflect the beam back through the surface into the waveguide; and 
 rotating the scanning mirror about an axis parallel to the surface over a range of angles selected so as to cause the beam, after reflection back into the waveguide through the surface, to propagate within the waveguide by total internal reflection (TIR) between the first and second planar faces. 
 
     
     
       11. The method according to  claim 10 , wherein the beam exits the surface at a selected exit angle relative to the surface, and wherein the range of angles over which the scanning mirror rotates is selected so as to cause the beam reflected back from the scanning mirror to enter the surface and impinge on the first planar face at angles exceeding a critical angle for TIR within the waveguide. 
     
     
       12. The method according to  claim 10 , and comprising positioning an optically transparent prism, which comprises first and second, mutually non-parallel planar prism faces, between the radiation source and the slab waveguide so that the beam from the radiation source enters the prism through the second prism face and exits from the prism through the first prism face so as to enter the waveguide through the first planar face at the entrance location and entrance angle such that the beam subsequently exits the waveguide at the exit location. 
     
     
       13. The method according to  claim 10 , wherein the waveguide comprises an out-coupler configured to intercept the beam that propagates within the waveguide by total internal reflection and to couple the beam out of the waveguide. 
     
     
       14. The method according to  claim 13 , wherein the scanning mirror rotates over a range of angles exceeding 50°. 
     
     
       15. The method according to  claim 10 , wherein the scanning mirror is positioned in proximity to and parallel to the planar edge. 
     
     
       16. The method according to  claim 10 ,
 wherein the method comprises positioning an optically transparent prism, which comprises first and second, mutually non-parallel planar prism faces, with the first prism face in proximity to the second planar face of the waveguide and the second prism face, which defines the surface of the wedge-shaped edge through which the beam exits and enters the waveguide, in proximity to the scanning mirror. 
 
     
     
       17. The method according to  claim 16 , wherein the prism is positioned so that the beam exiting the waveguide at the exit location enters the prism through the first prism face and exits the prism through the second prism face to impinge on the scanning mirror, which reflects the beam back through the second prism face so that the reflected beam exits the prism through the first prism face and reenters the waveguide through the second planar face at an angle exceeding a critical angle for TIR within the waveguide. 
     
     
       18. The method according to  claim 10 , wherein directing the beam comprises collecting the optical radiation from an array of emitters and directing the optical radiation from the array toward the entrance location.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application 62/847,974, filed May 15, 2019, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to methods and devices for projection of optical radiation, and particularly to compact optical scanners. 
     BACKGROUND 
     Scanning light engines are used for generating images in various display apparatuses, which project electronically generated images either onto a screen or directly into the eye of an observer. Waveguides are used as one alternative for conveying the generated images from the light engine to a display or directly into the eye of an observer in augmented reality (AR) and virtual reality (VR) systems. 
     SUMMARY 
     Embodiments of the present invention that are described herein provide improved apparatus and methods for optical scanning and projection. 
     There is therefore provided, in accordance with an embodiment of the invention, an optical apparatus, including an optically transparent slab waveguide including first and second, mutually-parallel planar faces and an edge non-parallel to the planar faces. A radiation source is configured to direct a beam of optical radiation to enter the waveguide through the first planar face at an entrance location and entrance angle selected so that the beam subsequently exits the waveguide at an exit location in a surface selected from among a group of surfaces consisting of the second planar face and the edge. A scanning mirror is positioned to receive the beam that has exited through the surface and to reflect the beam back through the surface into the waveguide while the scanning mirror rotates about an axis parallel to the surface over a range of angles selected so as to cause the beam, after reflection back into the waveguide through the surface, to propagate within the waveguide by total internal reflection (TIR) between the first and second planar faces. 
     In the disclosed embodiments, the beam exits the surface at a selected exit angle relative to the surface, and the range of angles over which the scanning mirror rotates is selected so as to cause the beam reflected back from the scanning mirror to enter the surface and impinge on the first planar face at angles exceeding a critical angle for TIR within the waveguide. 
     In some embodiments, the apparatus includes an optically transparent prism including first and second, mutually non-parallel planar prism faces and positioned between the radiation source and the slab waveguide so that the beam from the radiation source enters the prism through the second prism face and exits from the prism through the first prism face so as to enter the waveguide through the first planar face at the entrance location and entrance angle such that the beam subsequently exits the waveguide at the exit location. Additionally or alternatively, the waveguide includes an out-coupler configured to intercept the beam that propagates within the waveguide by total internal reflection and to couple the beam out of the waveguide. In a disclosed embodiment, the scanning mirror rotates over a range of angles exceeding 50°. 
     In some embodiments, the surface through which the beam exits the waveguide at the exit location is the edge of the waveguide, and wherein the edge is planar and non-normal to the planar faces of the waveguide. In these embodiments, the scanning mirror is typically positioned in proximity to and parallel to the planar edge. 
     Alternatively, the surface through which the beam exits the waveguide at the exit location is the second planar face of the waveguide, and the apparatus includes an optically transparent prism, which includes first and second, mutually non-parallel planar prism faces and is positioned with the first prism face in proximity to the exit location in the second planar face of the waveguide and the second prism face in proximity to the scanning mirror. In a disclosed embodiment, the prism is positioned so that the beam exiting the waveguide at the exit location enters the prism through the first prism face and exits the prism through the second prism face to impinge on the scanning mirror, which reflects the beam back through the second prism face so that the reflected beam exits the prism through the first prism face and reenters the waveguide through the second planar face at an angle exceeding a critical angle for TIR within the waveguide. 
     In some embodiments, the radiation source includes an array of emitters and projection optics configured to collect the optical radiation from the emitters and to direct the optical radiation toward the entrance location. 
     There is also provided, in accordance with an embodiment of the invention, a method for optical scanning, which includes directing a beam of optical radiation to enter an optically transparent slab waveguide, which includes first and second, mutually-parallel planar faces and an edge non-parallel to the planar faces, through the first planar face at an entrance location and entrance angle selected so that the beam subsequently exits the waveguide at an exit location in a surface selected from among a group of surfaces consisting of the second planar face and the edge. A scanning mirror is positioned to receive the beam that has exited through the surface and to reflect the beam back through the surface into the waveguide. The scanning mirror rotates about an axis parallel to the surface over a range of angles selected so as to cause the beam, after reflection back into the waveguide through the surface, to propagate within the waveguide by total internal reflection (TIR) between the first and second planar faces. 
     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 
         FIG. 1  is a schematic sectional view of an optical apparatus, in accordance with an embodiment of the invention; 
         FIG. 2  is a schematic sectional view of an optical apparatus, in accordance with another embodiment of the invention; 
         FIG. 3  is schematic sectional view of an optical apparatus, in accordance with yet another embodiment of the invention; 
         FIG. 4  is a schematic pictorial illustration of an optical apparatus, in accordance with a further embodiment of the invention; and 
         FIG. 5  is a schematic sectional view of an optical 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 coupling light from a scanning light engine into a waveguide. There is a need for compact coupling solutions that provide efficient optical coupling over a wide angular field. The embodiments of the present invention that are described herein address this need by means of a wedge-shaped edge of the waveguide, with a small scanning mirror in close proximity to the wedge-shaped edge. 
     In the disclosed embodiments, optical apparatus comprises an optically transparent slab waveguide with mutually-parallel planar faces that define first and second planes. These faces can be used to provide a light containment volume that allows light to propagate down the waveguide. In some embodiments, a planar edge of the slab waveguide, which is contained between the first and second planes, is shaped to form a wedge between these planes. In other words, the planar edge is not normal to the planar faces, meaning that one angle between the edge and one of the planes is acute, and the other angle between the edge and the other plane is obtuse. For purposes of the present description, the “first plane” and “second plane” are designated such that the angle between the edge and the first plane is acute, and the angle between the edge and the second plane is obtuse. The acute angle can conveniently be 45°, but other angles may alternatively be used, based on optimal light coupling efficiency. In an alternative embodiment, the wedge is provided by an additional prism in proximity to the second planar face of the waveguide. 
     A source of radiation directs a beam of optical radiation so that it enters the waveguide through the first planar face at an entrance location, which is typically near the edge. (The terms “optical radiation,” “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.) The angle of incidence and the location of the beam on the first plane are chosen so that, after refraction within the waveguide, the beam exits the waveguide through an exit location in another surface of the waveguide, which may be either the edge or the second planar face. 
     The scanning mirror is positioned adjacent to and facing this other surface, so that it receives the beam that exits the waveguide. The scanning mirror rotates about an axis that is parallel to the surface (either the edge or the second planar face), with sufficient space between the scanning mirror and the surface to prevent the scanning mirror from striking the edge during its rotation. The range of the rotational angles of the scanning mirror is determined so that the reflected beam re-enters the waveguide through the surface, and then impinges on the first planar face at angles exceeding a critical angle for total internal reflection (TIR) within the waveguide. The range of angles of incidence is chosen so that once the beam has re-entered the waveguide, it is “trapped” between the first and second planar faces due to TIR. The light will then propagate inside the waveguide by repeated TIRs, until it encounters a structure in the waveguide that modifies its propagation vector. This modification can be enabled by an out-coupling structure. 
     The range of the rotational angles of the scanning mirror is used to enable different propagation angles for the beam inside the waveguide, and thus enable different angular directions for the beam after it is, for example, coupled out of the waveguide. 
     Scanning Via the Edge of the Waveguide 
       FIG. 1  is a schematic sectional view of an optical apparatus  20 , in accordance with an embodiment of the invention. 
     Optical apparatus  20  comprises a source of radiation  22 , a slab waveguide  24 , and a scanning mirror  26 . Slab waveguide  24  comprises an optically transparent material, such as glass, with a refractive index n, having a first planar face  28  and a second planar face  30 . First and second planar faces  28  and  30  define respective first and second planes  29  and  31 . A planar edge  32  is contained between first plane  29  and second plane  31 , and it is shaped to form a wedge between these planes, i.e., the planar edge is not normal to the first and second planes. Edge  32  forms an acute wedge angle α with first plane  29 . In the pictured example, α=45°, although other values for a may alternatively be used. 
     Scanning mirror  26  rotates about an axis  34 , which is parallel to edge  32 , with rotational motion as shown by an arrow  33 . The angle of rotation of scanning mirror  26  is denoted by β, wherein angle β is measured from a fixed (but arbitrarily chosen) reference line  35 . Although axis  34  is shown in the figure to be contained within scanning mirror  26 , the axis may alternatively be positioned outside the mirror. Scanning mirror  26  is positioned at a distance from edge  32  that enables the mirror, on the one hand, to receive beams of radiation exiting from the edge, and, on the other hand, to rotate freely over a required angular range of rotation without striking the waveguide. This feature is detailed below. 
     Source  22  emits one or more beams of radiation, shown by rays  40 . In one embodiment, for example, source  22  is part of a light engine, which emits an array of visible light beams that are modulated temporally, spatially and possibly spectrally to create an image, which is projected through waveguide  24 . (Various sorts of light engines may be used for this purpose; and details of the light engine are beyond the scope of the present description.) Rays  40  impinge on first planar face  28  at an angle of incidence θ 1 , and refract into waveguide  24  into rays  42  at an angle θ 2 . Angle θ 2  is determined by Snell&#39;s law: n×sin(θ 2 )=sin(θ 1 ), wherein n is the refractive index of waveguide  24 , and the refractive index of the incident medium (air) is taken to be 1. 
     Rays  42  impinge on edge  32  and exit from waveguide  24  as rays  44  after refraction at the edge. It is advantageous to select wedge angle α so as to minimize the refraction (change in the direction) at edge  32 . Rays  44  are reflected by scanning mirror  26  into rays  46 , which impinge on edge  32 , re-enter waveguide  24  as rays  48 , and impinge on first planar face  28  at an angle incidence of θ 3 . For simplicity of illustration, the angles of incidence and the refraction of rays  42  and  46  at edge  32  are not shown in the figure. 
     Angle of incidence θ 1 , wedge angle α, and the range of rotation angles β are chosen so that the angle of incidence θ 3  exceeds the critical angle θ c , given by sin(θ c )=1/n, over the entire range β. The critical angle gives the limiting angle of incidence for TIR, i.e., any ray incident from inside waveguide  24  on first or second planar face  28  or  30  at an angle of incidence exceeding the critical angle θ c  is totally internally reflected back into the waveguide. Specifically, the requirement for rotation angles β is such that the respective entrance angles of rays  46  (angles of incidence of rays  46  at edge  32 ) exceed the respective exit angles of rays  44  (angles of incidence of rays  44  at edge  32 ) by a sufficient amount so that angle θ 3  exceeds the critical angle θ c . When source  22  emits a non-collimated beam, i.e., rays  40  are not mutually parallel, each ray  40  will impinge first on planar face  28  at a different angle of incidence θ 1 , and the condition for all angles θ 1 , wedge angle α, and rotation angles β is that all resulting angles of incidence θ 3  exceed the critical angle θ c . Thus a non-collimated beam emitted by source  22  will limit the range of rotation angles β to a smaller range than that for a collimated beam. 
     The beam defined by rays  48  continues to propagate within waveguide  24  by TIR between first and second planar faces  28  and  30 , as indicated by dotted lines  50 , until it encounters a structure (not shown in this figure) in the waveguide that modifies its propagation, such as, for example, an out-coupler. 
     It is desirable for some applications of optical apparatus  20 , for example in a VR system, to maximize the angular range of rays  48 . As the critical angle θ c  decreases with increasing refractive index n, it is advantageous for waveguide  24  to comprise glass or another suitable transparent material with a high refractive index, for example 1.6, 1.7, or 1.8. Similarly, it is advantageous to choose angle θ 1  so that angle θ 2  is as close as practical to the critical angle θ c , as this will enable scanning mirror  26  to scan from a near-normal incidence to rays  44 . Using the above design guidelines, waveguide  24  is capable of supporting a wide angular range, even in excess of 50°, for rays extracted by an out-coupler from waveguide  24 , meaning that mirror  26  may similarly be made to scan over a range of angles exceeding 50°. 
       FIG. 2  is a schematic sectional view of an optical apparatus  52 , in accordance with another embodiment of the invention. Optical apparatus  52  is similar to optical apparatus  20 , with the addition of an out-coupler  54 . Out-coupler  54  is configured to couple out of waveguide  24  a portion of rays  48  that reach the out-coupler. Out-coupler comprises, for example, a thick volume hologram. Alternatively, out-coupler  54  may comprise a thin volume hologram, a surface grating, or partially-reflective surfaces. 
     Rays  40  emitted by source  22  propagate, as in  FIG. 1 , through first planar face  28  and edge  32  to scanning mirror  26  and back into waveguide  24  into rays  48 . Rays  48  propagate inside waveguide  24  by TIR until they reach out-coupler  54 , and are then coupled out of waveguide  24  as rays  56 . The coupling may take place gradually along the length of out-coupler  54 , as shown in  FIG. 2 . This sort of extended out-coupling is useful, for example, in expanding the pupil of an image formed by modulation of light source  22  and scanning of mirror  26 , as explained above. Alternatively, rays  56  may be coupled out of waveguide  24  through face  30 . Further alternatively, rays  48  may be coupled out of the waveguide as a narrow beam through either or both of faces  28  and  30  or through the far edge of the waveguide, opposite edge  32 . 
       FIG. 3  is schematic sectional view of optical apparatus  60 , in accordance with yet another embodiment of the invention. 
     Optical apparatus  60  is similar to optical apparatus  20 , except that it comprises a prism  62 , comprising an optically transparent material, with a first prism face  70  and a second prism face  72 , wherein the first and second prism faces are not mutually parallel. Prism face  70  is in contact with or adjacent to first planar face  28 , in proximity to edge  32 . It is advantageous to have prism  62  comprise the same material (i.e., have the same refractive index n) as waveguide  24 , as this minimizes losses due to Fresnel-reflections from the interface between first prism face  70  and first planar face  28 . Alternatively, a difference Δn in the refractive indices of waveguide  24  and prism  62  may be, for example, Δn=0.1, yielding a low reflectance at the interface, typically 0.1%. 
     Rays  40  emitted by source  22  impinge on prism face  72 , and are refracted into rays  68 , thus effectively turning rays  40  toward edge  32 . When waveguide  24  and prism  62  comprise the same optical material, rays  68  continue through first prism face  70  unrefracted into rays  42 . Alternatively, when the refractive indices differ by, for example Δn=0.1, the change in direction from rays  68  to rays  42  is typically less than 5°. Rays  42  continue, as in  FIG. 1 , to scanning mirror  26  and from there back into waveguide  24 , propagating inside the waveguide by TIR as rays  48 . 
     The use of prism  62  to turn rays  40  relaxes the requirements for positioning and orientation of source  22 , thus relaxing the overall design constraints of optical apparatus  60 . 
       FIG. 4  is a schematic pictorial illustration of an optical apparatus  80 , in accordance with another embodiment of the invention. 
     Optical apparatus  80  is similar to optical apparatus  60 , except that it comprises a wide-angle source of radiation  82 . Wide-angle source  82  comprises an extended emitter  84 , comprising, for example, an array of vertical-cavity surface-emitting lasers (VCSELs) or light-emitting diodes (LEDs). Wide-angle source  82  further comprises projection optics  86 , which collect the light emitted by extended emitter  84  and project it toward waveguide  24  as rays  88  over a wide angular range, for example over ±45°. 
     Similarly to rays  40  in optical apparatus  60 , rays  88  impinge on prism  62 , and propagate further through first planar face  28  and edge  32  to scanning mirror  26  and back into waveguide  24 , where the rays propagate by TIR as rays  90 , corresponding to rays  48  in optical apparatus  60 . Rays spread angularly in the plane of waveguide  24 , corresponding to the angular spread of rays  88 . Rays  90  may, for a sufficiently long distances of propagation (not shown in  FIG. 4 ), impinge on a right and a left side-wall  92  and  94 , respectively, of waveguide  24 . As long as the angles of incidence of rays  90  on sidewalls  92  and  94  exceeds the critical angle, rays  90  are totally internally reflected back into waveguide  24 . Otherwise rays  90  will partially refract out of waveguide  24  and partially reflect back into it. 
     Scanning Via the Planar Face of the Waveguide 
       FIG. 5  is a schematic sectional view of an optical apparatus  100 , in accordance with an alternative embodiment of the invention. Optical apparatus  100  comprises a radiation source  102  and a slab waveguide  108 , which are largely similar in operation to the radiation sources and waveguides in the embodiments described above, except that the exit location through which the beam exits waveguide  108  toward scanning mirror  26  is in second planar face  30  of waveguide  108 , rather than the edge. 
     Radiation source  102  comprises an extended emitter  104 , comprising, for example, an array of VCSELs or LEDs, along with projection optics  106 , which collect the light emitted by extended emitter  104  and project it toward waveguide  108 . As in the embodiment of  FIG. 3 , a prism  110  is positioned between radiation source  102  and slab waveguide  108 . Rays  40  of the beam from radiation source  102  enter prism  110  through an entrance face and exit from the prism through an exit face. Refraction by prism  110  causes the beam to enter waveguide  108  through first planar face  28  at an entrance location and entrance angle chosen so that the beam subsequently exits waveguide  108  at the desired exit location in face  30 . Alternatively, radiation source  102  may itself be angled relative to waveguide  108  (as in the embodiments of  FIGS. 1 and 2 , for example), in which case prism  110  may not be required. 
     Apparatus  100  comprises an additional optically transparent prism  112 , which comprises mutually non-parallel planar prism faces. Prism  112  is positioned with one of these faces in proximity to the exit location of the beam from second planar face  30  of waveguide  108  and the other face in proximity to scanning mirror  26 . The beam exiting waveguide  108  at the exit location enters prism  112  through one face and exits the prism through the other face to impinge on scanning mirror  26 . The scanning mirror reflects the beam back through prism  112 , while rotating over a range of angles, so that the reflected, scanned beam exits prism  112  through the prism face that is in proximity to second planar face  30 . This scanned beam reenters waveguide  108  through second planar face  30  at an angle exceeding the critical angle for TIR within the waveguide. Hence, rays  48  will propagate through waveguide  108  by TIR, as in the preceding embodiments, and will then be coupled out into rays  56  by out-coupler  54 . 
     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: 20220201
Grant Date: 20220201
Priority Date: 20190515
Inventors: HAJATI, ARMAN
UPTON, Robert S.
GERSON, YUVAL
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B27/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B26/105", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/4214", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/4259", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2006/0098", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/26", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/4259", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B2006/0098", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/26", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 80034576