PATENT DOCUMENT

Publication Number: US-11754767-B1
Application Number: US-202117151170-A
Country: US
Kind Code: B1

Title: Display with overlaid waveguide

Abstract:
An optoelectronic device includes a display configured to emit first optical radiation in a first wavelength band through a front surface of the display. A planar optical waveguide, which is transparent in the first wavelength band, is overlaid on the display and is configured to guide second optical radiation in a second wavelength band along a direction transverse to the front surface. One or more diffractive structures are formed in the planar optical waveguide so as to couple the guided second optical radiation between the planar optical waveguide and a region in front of or behind the display.

Claims:
The invention claimed is: 
     
       1. An optoelectronic device, comprising:
 a display comprising:
 a display base; and 
 groups of pixels, which are disposed on the display base and configured to emit first optical radiation in a first wavelength band through a front surface of the display; 
 
 a planar optical waveguide, which is transparent in the first wavelength band and is overlaid across the display base, and which is configured to guide second optical radiation in a second wavelength band along a direction transverse to the front surface; 
 at least one emitter, which is configured to emit a beam of the second optical radiation into the planar optical waveguide; 
 a first diffractive structure formed in a first area of the planar optical waveguide so as to couple the beam of the second optical radiation that is guided through the planar optical waveguide out of the planar optical waveguide into a region in front of the display; 
 a second diffractive structure formed in a second area of the planar optical waveguide so as to couple incoming second optical radiation from the region in front of the display into the planar optical waveguide, whereby the incoming second optical radiation is guided through the planar optical waveguide; and 
 at least one sensor, which is coupled to receive and sense the incoming second optical radiation that has been guided through the planar optical waveguide. 
 
     
     
       2. The optoelectronic device according to  claim 1 , wherein the first wavelength band is a visible band, while the second wavelength band is an infrared band. 
     
     
       3. The optoelectronic device according to  claim 1 , wherein the planar optical waveguide has a bottom surface in contact with the display and a top surface opposite the bottom surface, and wherein at least one of the one or more diffractive structures is formed in the top surface of the planar optical waveguide. 
     
     
       4. The optoelectronic device according to  claim 1 , wherein the planar optical waveguide has a bottom surface in contact with the display and a top surface opposite the bottom surface, and wherein at least one of the one or more diffractive structures is formed in the bottom surface of the planar optical waveguide. 
     
     
       5. The optoelectronic device according to  claim 1 , wherein the one or more diffractive structures have heights that are smaller than a shortest wavelength in the first wavelength band. 
     
     
       6. The optoelectronic device according to  claim 1 , wherein the one or more diffractive structures are spectrally selective, so as to preferentially diffract the second optical radiation in the second wavelength band. 
     
     
       7. The optoelectronic device according to  claim 6 , wherein the one or more diffractive structures are configured to diffract the second optical radiation at different first and second wavelengths in the second wavelength band so as to propagate in the planar optical waveguide at different, respective first and second angles of propagation. 
     
     
       8. The optoelectronic device according to  claim 7 , and wherein the at least one sensor comprises first and second sensors, which are coupled to detect the second optical radiation propagating through the planar optical waveguide at the first and second wavelengths, respectively. 
     
     
       9. The optoelectronic device according to  claim 1 , wherein the one or more diffractive structures are angularly selective, so as to preferentially diffract the second optical radiation that is incident on the one or more diffractive structures in a selected angular range. 
     
     
       10. The optoelectronic device according to  claim 9 , wherein the one or more diffractive structures are configured to diffract the second optical radiation propagating in different first and second directions in the region in front of or behind the display so as to propagate in the planar optical waveguide at one or more respective angles of propagation. 
     
     
       11. The optoelectronic device according to  claim 10 , wherein the at least one sensor is coupled to detect the second optical radiation propagating through the planar optical waveguide at the one or more respective angles of propagation. 
     
     
       12. The optoelectronic device according to  claim 1 , wherein the at least one emitter is located at an edge of the planar optical waveguide, outside an area of the display. 
     
     
       13. The optoelectronic device according to  claim 1 , wherein the at least one sensor is located at an edge of the planar optical waveguide, outside an area of the display. 
     
     
       14. A method for guiding radiation, comprising:
 providing a display comprising a display base and groups of pixels comprising emitters, which are disposed on the display base and configured to emit first optical radiation in a first wavelength band through a front surface of the display; 
 overlaying on the display a planar optical waveguide, which is transparent in the first wavelength band and is configured to guide second optical radiation in a second wavelength band along a direction transverse to the front surface; 
 coupling at least one emitter to emit a beam of the second optical radiation into the planar optical waveguide; 
 forming a first diffractive structure in a first area of the planar optical waveguide so as to couple the beam of the second optical radiation that is guided through the planar optical waveguide out of the planar optical waveguide into a region in front of the display; 
 forming a second diffractive structure in a second area of the planar optical waveguide so as to couple incoming second optical radiation from the region in front of the display into the planar optical waveguide, whereby the incoming second optical radiation is guided through the planar optical waveguide; and 
 coupling at least one sensor to receive and sense the incoming second optical radiation that has been guided through the planar optical waveguide. 
 
     
     
       15. The method according to  claim 14 , wherein the one or more diffractive structures are spectrally selective, so as to preferentially diffract the second optical radiation in the second wavelength band. 
     
     
       16. The method according to  claim 14 , wherein the one or more diffractive structures are angularly selective, so as to preferentially diffract the second optical radiation that is incident on the one or more diffractive structures in a selected angular range.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application 62/985,354, filed Mar. 5, 2020, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to optoelectronic devices, and particularly to displays with associated sources and sensors of optical radiation. 
     BACKGROUND 
     Wearable and/or portable consumer devices, such as smartphones, augmented reality (AR) devices, virtual reality (VR) devices, and smart glasses, comprise optical displays, as well as sources and sensors of optical radiation. 
     SUMMARY 
     Embodiments of the present invention that are described hereinbelow provide improved display devices and associated methods. 
     There is therefore provided, in accordance with an embodiment of the invention, an optoelectronic device, including a display configured to emit first optical radiation in a first wavelength band through a front surface of the display. A planar optical waveguide, which is transparent in the first wavelength band, is overlaid on the display and is configured to guide second optical radiation in a second wavelength band along a direction transverse to the front surface. One or more diffractive structures are formed in the planar optical waveguide so as to couple the guided second optical radiation between the planar optical waveguide and a region in front of or behind the display. 
     In a disclosed embodiment, the first wavelength band is a visible band, while the second wavelength band is an infrared band. 
     In one embodiment, the planar optical waveguide has a bottom surface in contact with the display and a top surface opposite the bottom surface, and at least one of the one or more diffractive structures is formed in the top surface of the planar optical waveguide. Alternatively or additionally, at least one of the one or more diffractive structures is formed in the bottom surface of the planar optical waveguide. 
     In some embodiments, the one or more diffractive structures have heights that are smaller than a shortest wavelength in the first wavelength band. 
     Additionally or alternatively, the one or more diffractive structures are spectrally selective, so as to preferentially diffract the second optical radiation in the second wavelength band. In some embodiments, the one or more diffractive structures are configured to diffract the second optical radiation at different first and second wavelengths in the second wavelength band so as to propagate in the planar optical waveguide at different, respective first and second angles of propagation. In one embodiment, the device includes first and second sensors, which are coupled to detect the second optical radiation propagating through the planar optical waveguide at the first and second wavelengths, respectively. 
     Further additionally or alternatively, the one or more diffractive structures are angularly selective, so as to preferentially diffract the second optical radiation that is incident on the one or more diffractive structures in a selected angular range. In some embodiments, the one or more diffractive structures are configured to diffract the second optical radiation propagating in different first and second directions in the region in front of or behind the display so as to propagate in the planar optical waveguide at one or more respective angles of propagation. In a disclosed embodiment, the device includes one or more sensors, which are coupled to detect the second optical radiation propagating through the planar optical waveguide at the one or more respective angles of propagation. 
     In further embodiments, the device includes at least one emitter, which is coupled to emit the second optical radiation into the planar optical waveguide so that the radiation propagates in the waveguide as a guided wave and exits through at least one of the diffractive structures into the region in front of or behind the display. In a disclosed embodiment, the at least one emitter is located at an edge of the planar optical waveguide, outside an area of the display. 
     Additionally or alternatively, the device includes at least one sensor, which is coupled to receive the second optical radiation that has entered the planar optical waveguide from the region in front of or behind the display and propagated through the planar optical waveguide to the at least one sensor as a guided wave. In a disclosed embodiment, the at least one sensor is located at an edge of the planar optical waveguide, outside an area of the display. 
     There is also provided, in accordance with an embodiment of the invention, a method for guiding radiation, which includes providing a display configured to emit first optical radiation in a first wavelength band through a front surface of the display. A planar optical waveguide, which is transparent in the first wavelength band and is configured to guide second optical radiation in a second wavelength band along a direction transverse to the front surface, is overlaid on the display. One or more diffractive structures are formed in the planar optical waveguide so as to couple the guided second optical radiation between the planar optical waveguide and a region in front of or behind the display. 
     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 frontal view of a portable device with a display, in accordance with embodiments of the invention; 
         FIGS.  2  and  3    are schematic pictorial illustrations showing functions of the device of  FIG.  1   , in accordance with embodiments of the invention; 
         FIG.  4    is a schematic sectional view of an illumination module overlaid on a display, in accordance with an embodiment of the invention; 
         FIG.  5    is a schematic sectional view of an illumination module overlaid on a display, in accordance with another embodiment of the invention; 
         FIG.  6    is a schematic sectional view of a waveguide comprising an angularly-selective diffractive-transmissive grating, in accordance with an embodiment of the invention; 
         FIG.  7    is a schematic sectional view of a waveguide comprising an angularly-selective diffractive-reflective grating, in accordance with another embodiment of the invention; 
         FIG.  8    is a schematic sectional view of a waveguide comprising a spectrally-selective diffractive-transmissive grating, in accordance with yet another embodiment of the invention; 
         FIG.  9    is a schematic sectional view of a waveguide with a spectrally and angularly selective diffractive-reflective grating, in accordance with an embodiment of the invention; 
         FIG.  10    is a plot of a calculated spectral transmittance of the grating of  FIG.  9   , in accordance with an embodiment of the invention; 
         FIG.  11    is a schematic sectional view of a receiving sensing module configured to sense ambient light (ALS), in accordance with an embodiment of the invention; 
         FIG.  12    is a schematic sectional view of a receiving sensing module configured for multi-band spectral sensing of ambient light, in accordance with an embodiment of the invention; and 
         FIGS.  13   a  and  13   b    are a schematic top view and a schematic sectional view, respectively, of a three-band receiving spectral sensing module, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     Wearable and other sorts of portable consumer devices (referred to collectively as “portable devices” in the description), such as smartphones, augmented reality (AR) devices, virtual reality (VR) devices, and smart glasses comprise optical displays, and may also comprise sensor modules for sensing optical radiation. (The terms “optical rays,” “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.) The ongoing increase in the size of the display of these portable devices imposes strict limitations on the space available for various emitter and sensor modules within these devices. 
     Traditional sensing systems in portable devices comprise modules performing functions such as illumination, ambient light sensing, image capture, gesture recognition, and proximity sensing. Each type of module typically contains a lens assembly, as well as illumination and/or sensing devices that emit or receive optical radiation within different spectral regions through a variety of physical apertures located within the portable devices. These modules compete for space with the display (or displays) of the portable device, and may increase, for example, the physical size of a smartphone or the frame thickness of AR glasses. 
     The embodiments of the present invention that are described herein address these problems by providing a planar optical waveguide that is overlaid on the display of a portable device, which guides radiation across the surface of the display without interfering with the display functionality. The waveguide can be coupled to a functional module, such as an emission source, comprising one or more emitters, or a photodetection module, comprising one or more sensors (or both), which is typically located outside the display area, in order to guide radiation to or from the module. 
     In the disclosed embodiments, the display presents images by emitting optical radiation in a first wavelength band, typically in the visible range. The optical waveguide is transparent in this first wavelength band and permits the optical radiation emitted by the display to be transmitted through the waveguide, while guiding optical radiation in a second wavelength band by total internal reflection within the waveguide to and/or from the functional module. Diffractive structures in the waveguide couple the guided optical radiation in the second wavelength band between the waveguide and the region in front of or behind the display, for example by out-coupling or in-coupling certain fractions of the guided optical radiation in different directions. Thus, the waveguide couples the radiation in the second wavelength band between this region (either toward or away from the user) and the functional module, without significantly reducing the available display area and without interfering with the ability of a user of the device to view the images presented by the display. 
     In some embodiments, the first and second wavelength bands are disjoint. For example, the display may emit light in the visible spectrum (400-700 nm), while the waveguide operates in the infrared (IR) range (above 700 nm). Alternatively, the first and second wavelength bands may partially overlap, with the second wavelength band comprising at least some wavelengths within the visible spectrum. In either case, because the waveguide, including the diffractive structures, is transparent to the optical radiation emitted by the display, they can share the display area without any interference with the user&#39;s ability to observe the display. 
     In some embodiments, optical emitters and sensors, operating in the second wavelength band, are coupled to the waveguide, and are configured to emit optical radiation into the waveguide or to receive optical radiation from the waveguide. A functional module comprising the planar waveguide, diffractive structures, emitters, and/or sensors can perform one or more functions of the portable device, such as emitting flood and/or structured illumination, ambient light sensing (ALS), image sensing, three-dimensional (3D) mapping, motion sensing, and gesture recognition. 
     The diffractive structures in the waveguide may comprise, for example, surface-relief features, features with localized index gradients, features surrounded by media with dissimilar refractive indices, or form-birefringent Pancharatnam-Berry (geometric phase) liquid crystal molecules. 
     The diffractive structures may comprise any sorts of diffractive patterns that are known in the art, including one-dimensional or two-dimensional patterns of straight or curved lines, line segments with various lengths and angular orientations, and sub-wavelength circular or elliptically-shaped pillars, holes and tubes, as well as arbitrarily-shaped geometries. The diffractive structures may comprise localized regions with dissimilar patterns. The regions can be made contiguous, or can be separated from each other, in which case the unpatterned surface regions connecting the localized patterns reflect the guided light by total internal reflection without coupling the light out. The heights of the diffractive structures are in general smaller than the wavelengths of light from the display, so as to minimize their impact on the appearance of the display as seen by an observer. By adjusting the parameters of the diffractive structures, such as the size, shape, height, material, the fractional amount of light coupled out of the waveguide and/or into the waveguide, as well as the propagation direction, can be altered. In the present description and in the claims, the term “grating” is used interchangeably with the term “diffractive structure.” 
     The structures may be formed using a variety of fabrication techniques, such as techniques based on material removal (optical or e-beam lithography followed by a surface etch), material modification (laser writing), or additive manufacturing (two-photon polymerization, nano-imprint). 
     Several waveguide layers may be integrated into a monolithic multi-layer assembly. 
     Embodiments of the present invention are described hereinbelow specifically with reference to the integration of waveguides and associated components with the display of a portable device, such as a smartphone. The principles of the present invention, however, may similarly be applied to enable emission and/or collection of optical radiation in conjunction with other sorts of displays, for illumination, sensing and other purposes. 
     System Description 
       FIG.  1    is a schematic frontal view of a portable device  20 , in accordance with an embodiment of the invention. Device  20  comprises a display  22 , with a planar waveguide  24  overlaid on a front surface  26  of the display. Diffractive structures  28 ,  30 , and  32  are formed in waveguide  24  in front of display  22 . Optical radiation emitters  34  and  36  are formed in device  20  at the edge of waveguide  24 , outside the area of display  22 . An array of optical sensors  38  is formed in contact with waveguide  24 , similarly outside the area of display  22 . A controller  40  is coupled to display  22 , to emitters  34  and  36 , and to sensors  38 . (For the sake of simplicity, the connections to and from the controller are not shown in  FIG.  1   .) 
     Display  22  emits optical radiation in a display wavelength band between wavelengths λ 1  and λ 2  through front surface  26  toward a region in front of the display. The display wavelength band typically comprises visible light, with λ 1 =400 nm and λ 2 =700 nm, but alternatively, the display may emit radiation over a narrower visible band, or even in the infrared or ultraviolet range in some applications. 
     Waveguide  24  is transparent in the display wavelength band, and is configured to guide second optical radiation in a guided wavelength band between wavelengths λ 3  and λ 4  along a direction transverse to front surface  26 . In order to reduce interference by diffractive structures  28 ,  30 , and  32  with the optical radiation emitted by display  22  (i.e., optical radiation in the display wavelength band (λ 1  . . . λ 2 )), the optical path difference introduced by the diffractive structures should be significantly smaller than the wavelengths within the band emitted by the display. In order to make the guided optical radiation invisible to an observer, the guided wavelength band may be limited to infrared or ultraviolet regions. Alternatively, the guided wavelength band may include visible wavelengths, for example wavelengths falling between the emission wavelengths of the pixels of display  22 . 
     Optical radiation emitters  34  and  36 , such as light-emitting diodes (LEDs) or laser diodes, emit radiation in the guided wavelength band (λ 3  . . . λ 4 ) into waveguide  24 , from whence the radiation is coupled out by respective diffractive structures  32  and  28 . Optical radiation impinging from the region in front of device  20  onto diffractive structure  30 , is coupled by the diffractive structure into waveguide  24 , which in turn conveys the radiation to sensors  38 . 
       FIGS.  2  and  3    are schematic pictorial illustrations showing functions of device  20 , in accordance with embodiments of the invention. Items that are identical to those in  FIG.  1    are labelled with the same numerical labels. 
     In  FIG.  2   , device  20  takes a picture of a subject  50 . Radiation emitted by emitter  36  ( FIG.  1   ) is radiated out of waveguide  24  by diffractive structure  28  as flood illumination  52 , illuminating subject  50 . Illumination  52  is reflected and scattered by subject  50  back toward device  20  as rays  54 , and impinges on diffractive structure  30 . (For the sake of clarity, rays  54  are shown as emanating only from a single point  56 , whereas in reality all illuminated points on subject  50  radiate similar rays.) Diffractive structure  30  couples rays  54  into waveguide  24 , which conveys the rays to sensors  38  ( FIG.  1   ). Controller  40  receives signals from sensors  38  responsively to rays  54 , and by computational imaging reconstructs an image of subject  50 . 
     In  FIG.  3   , device  20  captures a 3D map of subject  50 . Radiation emitted by emitter  34  ( FIG.  1   ) is radiated out of waveguide  24  by diffractive structure  30  as structured light, for example as discrete beams  60 , projecting spots  62  onto subject  50 . Beams  60  are reflected and scattered from spots  62  back toward device  20 , as shown by rays  64  reflected and scattered from a spot  62   a . As in  FIG.  2   , diffractive structure  30  couples rays  64  into waveguide  24 , which conveys the rays to sensors  38 . Controller  40  receives signals from sensors  38  responsively to rays  64 , and by computational imaging reconstructs an image of each one of spots  62  on subject  50 . Controller  40  finds the distance of each spot  62  from device  20  by triangulation, and thus constructs a 3D map of subject  50 . By 3D mapping of, for example, a hand of subject  50  over several consecutive image frames, the movements of the hand in 3D space may be recorded for gesture recognition. 
     Alternatively, emitter  34  may emit beams  60  in the form of short pulses, and sensors  38 , comprising single-photon avalanche diodes (SPADs), for example, may measure the time-of-flight (TOF) of the pulses for purposes of 3D mapping and gesture recognition. 
     In the present description, the surface of the display on which the waveguide is disposed is referred to for the sake of convenience as the front surface. The embodiments shown in  FIGS.  1 - 3    relate to portable products such as smartphones, in which the display and the diffractive structures of the waveguide emit light through and receive light from the same side of the device, to and from the region in front of the display. In other devices, however, such as AR devices, the display may emit light toward the user, while the diffractive structures of the waveguide emit radiation to and receive radiation from the region behind the display, away from the user. In such embodiments of the present invention, the waveguide and the associated diffractive structures may thus be overlaid on the back surface of the display. 
     Illumination Modules 
       FIG.  4    is a schematic sectional view of an illumination module  100  overlaid on the front surface of a display  102 , in accordance with an embodiment of the invention. Illumination module  100  comprises a waveguide  104 , an emitter  106 , an in-coupling grating  108 , and out-coupling gratings  110 . Display  102  comprises a display base  112  and groups of polychromatic (multi-wavelength) pixels  114 . 
     Emitter  106  comprises an array of vertical-cavity surface-emitting lasers (VCSELs), emitting IR optical radiation, which is invisible to an observer viewing display  102 . In-coupling grating  108  comprises, for example, alternating periodic parallel lines with varying refractive index. In-coupling grating  108  couples the IR radiation emitted by emitter  106  into waveguide  104  over a range of angles such that the coupled radiation propagates in the waveguide by total internal reflection (TIR) from top and bottom planar surfaces  116  and  118  of the waveguide, as shown by arrows  120 . 
     Out-coupling gratings  110  are formed in top planar surface  116 , and they interact with the radiation propagating in waveguide  104  by coupling a fraction of the radiation out of the waveguide through frustrated total internal reflection (FTIR), as shown by arrows  122 . The directions of the IR radiation exiting waveguide  104  are based on local spacings and angular orientations of the sub-wavelength patterns of out-coupling gratings  110 , as well as the directions of the guided waves, according to the laws of diffraction. While out-coupling gratings  110  are shown in  FIG.  4    as localized regions along top surface  116 , they can be expanded to cover the entire patterned area of the waveguide. 
     Each group of pixels  114  comprises emitters emitting optical radiation at different visible wavelengths. For example, a group  114  may comprise a red-emitting pixel, a green-emitting pixel, and a blue-emitting pixel, wherein the emission spectra of the pixels are respectively centered at 650 nm, 550 nm, and 450 nm. Alternatively, a group  114  may comprise different numbers of pixels emitting at different wavelengths. The radiation emitted by the pixels of each group  114 , shown by arrows  124 , traverses waveguide  104  substantially without interference by the waveguide, which is transparent to the visible radiation. Due to their low topography, even out-coupling gratings  110  have only an insignificant impact on the radiation emitted by pixels in groups  114 . 
       FIG.  5    is a schematic sectional view of an illumination module  200  overlaid on a display  202 , in accordance with another embodiment of the invention. Illumination module  200  comprises a waveguide  204 , an emitter  206 , an in-coupling face  208 , and out-coupling gratings  210 . Display  202  comprises a display base  212  and groups of polychromatic pixels  214 . 
     Emitter  206  comprises an edge-emitting laser, emitting IR optical radiation. In-coupling face  208  is a planar surface, which is angled in order to couple the IR radiation emitted by emitter  206  into waveguide  204  over a range of angles such that the coupled radiation propagates in the waveguide by TIR from top and bottom planar surfaces  216  and  218  of the waveguide, as shown by arrows  220 . The radiation emitted by emitter  206  may be shaped by micro-optics (not shown), prior to coupling into waveguide  204 , into a beam that is narrow in the direction perpendicular to surfaces  216  and  218 , but wide along in a transverse direction. 
     Similarly to module  100  ( FIG.  4   ), the IR radiation propagating in waveguide  204  through TIR is coupled out by out-coupling gratings  210 , as shown by arrows  222 . Display  202  emits, similarly to display  102  ( FIG.  4   ) visible radiation, which is transmitted through module  200 , as shown by arrows  224 , without significant interference. 
     In order to minimize the impact of out-coupling gratings  110  ( FIG.  4   ) and  210  ( FIG.  5   ) on the visible light emitted by displays  102  and  202 , the heights of the out-coupling gratings are chosen to be substantially smaller than the shortest wavelength of the visible light (400 nm). For example, out-coupling gratings that are between 50 and 100 nm high with appropriate spacing between the grating lines will couple out a sufficient portion of the guided IR radiation from the waveguide, while transmitting between 85% and 97% of the visible light emitted by the display, depending on the wavelength and the polarization of the visible light. 
     The grating heights may be tailored for different display pixels in order to further minimize the influence of the gratings onto the transmitted visible light. For example, as visible light at the blue end of the spectrum exhibits a lower transmittance (higher diffraction) through the gratings than light at longer wavelengths, the heights of the gratings above the pixels emitting blue light may be further reduced, or the gratings above these pixels may be completely eliminated. 
     Sensing Modules 
       FIG.  6    is a schematic sectional view of a waveguide  300  comprising an angularly-selective diffractive-transmissive grating  302 , in accordance with an embodiment of the invention. The grating is “angularly selective” in the sense that it preferentially diffracts radiation in a particular angular range, while having insignificant effect on angles outside this range. Waveguide  300 , together with grating  302 , comprise a part of a receiving sensing module, which is overlaid on a display (not shown in this figure) in a similar manner to the overlay of illumination module  100  on display  102  ( FIG.  4   ). 
     Monochromatic light at a wavelength A impinges on grating  302  at several angles of incidence, as shown by arrows  304 ,  306 ,  308 ,  310 , and  312 . While the light from most of the incident directions will propagate through grating  302  (as shown by arrows  304   a ,  306   a ,  310   a , and  312   a ) without being substantially affected, a significant fraction of light from a direction designated by arrow  308  (or a small cone of angles around that direction) will be strongly diffracted, as shown by an arrow  314 . The spatial frequency of grating  302  is chosen so that the diffracted light impinges on a bottom surface  316  of waveguide  300  at an angle of incidence  8  that exceeds the critical angle of the waveguide. Thus, the diffracted light propagates by TIR as a guided wave between the bottom surface and a top surface  318  of waveguide  300 . The undiffracted part of the light from the direction indicated by arrow  308  propagates through waveguide  300  at reduced power, as indicated by a dotted arrow  308   a.    
     The guided wave propagating in waveguide  300  may impinge on a sensor or array of sensors (such as sensors  38  in  FIG.  1   ), for example for sensing and mapping objects, as illustrated in  FIGS.  2 - 3   , or for sensing ambient light, as detailed in  FIGS.  11 ,  12  and  13     a - 13   b , below. This sort of angularly-selective grating and waveguide is particularly suited for directionally-selective sensing applications. Multiple gratings, with different respective acceptance angles, may be formed on the same waveguide or on different waveguides in order to collect light from different angular ranges and to direct the light in each range to a different, respective sensor. Controller  40  ( FIG.  1   ) may then combine the directional sensor signals in order to reconstruct a 2D image or 3D map of the region from which the light is received. 
       FIG.  7    is a schematic sectional view of a waveguide  400  comprising an angularly-selective diffractive-reflective grating  402 , in accordance with another embodiment of the invention. With the exception of diffractive-reflective grating  402 , which replaces the function of diffractive-transmissive grating  302  of  FIG.  6   , the same labels are used in  FIG.  7    as in  FIG.  6   . The light entering from the direction denoted by arrow  308  is diffracted by grating  402  into waveguide  400 , but now by reflection rather than by transmission. Thus, a part of light impinging on waveguide  400  is coupled into the waveguide. As in the embodiment of  FIG.  6   , the in-coupling may be angularly selective. 
       FIG.  8    is a schematic sectional view of a waveguide  500  comprising a spectrally-selective diffractive-transmissive grating  502 , in accordance with yet another embodiment of the invention. The grating is “spectrally selective” in the sense that it preferentially diffracts radiation in a particular wavelength band, while having insignificant effect on wavelengths outside this band. Polychromatic light impinges on grating  502  with an angle of incidence a for all wavelengths. Arrows  504 ,  506 , and  508  represent light at three different wavelengths. For example, arrow  504  may denote blue light, arrow  506  may denote green light, and arrow  508  may denote red light. (Here the terms “blue,” “green,” and “red” are used to denote specific wavelengths, for example 450 nm, 550 nm, and 650 nm, respectively. Alternatively, these terms may denote spectral bands around certain center wavelengths.) 
     Grating  502  in this embodiment is configured so that only green light is diffracted by the grating, whereas the other wavelengths are transmitted through the grating without hindrance, as represented by arrows  504   a  and  508   a . The green light that is diffracted by grating  502 , shown by an arrow  510 , impinges on a bottom planar surface  512  of waveguide  500  at an angle θ, which exceeds the critical angle inside the waveguide. Thus, as in the embodiments of  FIGS.  6 - 7   , the light diffracted into waveguide  500  will propagate between bottom surface  512  and a top surface  514  as a guided wave by TIR, and may be subsequently intercepted by a sensor, such as sensors  38  in  FIG.  1   . A small fraction of the green light (arrow  506 ) is transmitted by grating  502 , exiting waveguide  500  as an arrow  506   a.    
     Rather than spectrally-selective diffractive-transmissive grating  502 , a spectrally-selective diffractive-reflective grating may be employed, similarly to the embodiment shown in  FIG.  7   , for coupling light into waveguide  500 . 
     This sort of spectrally-selective grating can be used in spectrally-selective sensing applications. Multiple gratings, with different spectral bands, may be formed on the same waveguide or on different waveguides in order to collect light in different wavelength ranges and to direct the light in each range to a different, respective sensor. Controller  40  ( FIG.  1   ) may then combine the directional sensor signals in order to extract spectral information with respect to the region from which the light is received. An array of gratings that are both angularly and spectrally selective can be used in capturing and reconstructing a color image. 
       FIG.  9    is a schematic sectional view of a waveguide  600  with a spectrally and angularly selective diffractive-reflective grating  602 , in accordance with an embodiment of the invention. Grating  602  may be used in implementing the functionality of grating  402  ( FIG.  7   ), or grating  904  ( FIG.  12   , below). 
     Grating  602  comprises a uniform layer  604  and a patterned layer  606 . Only the area of waveguide  600  facing grating  602  is shown in  FIG.  9   . The dimensions and the refractive indices of waveguide  600  and grating  602  are given in Table 1, below. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 DIMENSIONS AND REFRACTIVE INDICES 
               
               
                 OF WAVEGUIDE 600 AND GRATING 602 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 refractive 
                   
                   
                 mesa 
               
               
                   
                   
                 index at 
                 thickness 
                 period 
                 width 
               
               
                   
                 material 
                 940 nm 
                 (μm) 
                 P (nm) 
                 W (nm) 
               
               
                   
               
               
                 waveguide 
                 fused 
                 1.45 
                 10-1000 
                 — 
                 — 
               
               
                 600 
                 silica 
                   
                   
                   
                   
               
               
                 uniform 
                 Si 3 N 4   
                 2.15 
                 0.131 
                 — 
                 — 
               
               
                 layer 604 
                   
                   
                   
                   
                   
               
               
                 patterned 
                 SiO 2   
                 1.45 
                 0.098 
                 341 
                 289 
               
               
                 layer 606 
               
               
                   
               
            
           
         
       
     
     The inventors have calculated that grating  602  diffracts 53.3% of light at the wavelength of 500 nm into the −1 st  diffractive order in reflection, when the angle of incidence into uniform layer  604  is 10°. The −1 st  order is diffracted at an angle of −56.1°, which exceeds the critical angle of 43.6° of waveguide  600 , resulting in propagation of the diffracted and reflected light as a guided wave within the waveguide. 
       FIG.  10    is a plot  700  of a calculated spectral transmittance of grating  602  ( FIG.  9   ), in accordance with an embodiment of the invention. A curve  702  shows the transmittance T (vertical axis) of grating  602  as a function of wavelength A from 400 nm to 700 nm (horizontal axis) at an angle of incidence of 10°. The transmittance exceeds 0.9 (90%) across the entire spectral range of the plot, with the exception of two narrow notches  704  and  706 . Notch  704  at a wavelength of 500 nm represents reflections into the −1 st  diffraction order (53.9%) and into the 0 th  order (26.3%, specular reflection), and notch  706  at 635 nm represents reflections into the 0 th  order (93.5%, specular reflection.) Due to their narrow spectral width, the impact of notches  704  and  706  on the light received by an observer from a display under grating  602  is minimal. 
     Varying the angle of incidence onto grating  602  will change the locations of notches  704  and  706  with respect to the horizontal (wavelength) axis, but the notches remain narrow, and will not impact the visual perception of an underlying display. 
       FIG.  11    is a schematic sectional view of a sensing module  800  configured to sense ambient light (ALS), in accordance with an embodiment of the invention. Sensing module  800  comprises a waveguide  802 , in-coupling gratings  804 ,  806 , and  808 , an out-coupling grating  810 , and a sensor  812 . 
     In-coupling gratings  804 ,  806 , and  808  are similar to grating  502  ( FIG.  8   ), in that each of them couples light into waveguide  802  from a specific direction at a specific wavelength. Each grating couples light in from a different angle. For example, grating  804  couples light in from an angle  81 , grating  806  couples light in from an angle normal to the plane of waveguide  802 , and grating  808  couples light in from an angle  82 . Configuring gratings  804 ,  806 , and  808  to couple light in from different angles extends the angular range of the sensed ambient light. Alternatively, different numbers of gratings, such as two, four, five, or more, may be used to receive light from different numbers of angles and different spectral ranges. 
     The light coupled into waveguide  802  by gratings  804 ,  806 , and  808  is guided within the waveguide to out-coupling grating  810 , which diffracts the guided light into sensor  812 . Sensor  812  comprises a photodetector, such as a photodiode or a single-photon avalanche diode (SPAD), which emits a signal in response to the light received through grating  810 . Sensor  812  may be located outside the area of a display  814  on which waveguide is overlaid, so as not to interfere with the display. 
       FIG.  12    is a schematic sectional view of a sensing module  900  configured for multi-band spectral sensing of ambient light (ALS), in accordance with another embodiment of the invention. 
     Sensing module  900  comprises a waveguide  902 , a spectrally and angularly sensitive diffractive-reflective grating  904 , and sensors  906 ,  908 , and  910 . Grating  904  is both angularly and spectrally selective in that it reflects a given wavelength impinging only from a specific direction. For example, blue light arriving from a direction  912  is diffracted and reflected into waveguide  902  as guided light shown by an arrow  914 . Similarly, green light arriving from a direction  916  is coupled into guided light shown by an arrow  918 , and red light arriving from a direction  920  is coupled into guided light shown by an arrow  922 . The different angles of propagation within waveguide  902  cause the different wavelengths to be further spatially separated. Sensors  906 ,  908 , and  910  are positioned so that each sensor receives a different wavelength: Sensor  906  receives blue light (arrow  914 ), sensor  908  receives green light (arrow  918 ), and sensor  910  receives red light ( 922 ). As in  FIG.  11   , sensors  906 ,  908 , and  910  may be located outside the display area. 
     Thus a single grating  904  separates the spectral bands and redirects them onto different photosensitive areas through a waveguiding process, thus enabling characterization of the spectral distribution of the received ambient light. 
       FIGS.  13   a  and  13   b    are a schematic top view and a schematic sectional view, respectively, of a three-band spectral sensing module  950 , in accordance with an embodiment of the invention. Sensing module  950  comprises a waveguide  952 , in-coupling transmission gratings  954 ,  956 , and  958 , out-coupling transmission gratings  960 ,  962 , and  964 , sensors  966 ,  968 ,  970 , and optional spectral filters  972 ,  974 , and  976 . 
     Gratings  954 ,  956 , and  958  are sub-wavelength transmission gratings, which diffract light impinging at a high angle of incidence into the −1 st  diffracted order with an almost 100% diffraction efficiency. The diffraction is schematically shown in  FIG.  13   b   , wherein arrows  978  denote the impinging light and arrows  980  denote the −1 st  order diffraction. The diffraction angle is sufficiently high so that the diffracted light propagates as a guided wave in waveguide  952 . As projected into the plane of waveguide  952 , the direction of propagation of the diffracted light (arrows  980 ) is opposite to the direction of the impinging light (arrows  978 ). (For simplicity, the back-and-forth reflections in waveguide  952  have been omitted in  FIG.  13   b   .) Each of gratings  954 ,  956 , and  958  further exhibits a wavelength-dependent diffraction efficiency, so that discrete spectral bands are coupled in by each grating. For example, grating  954  has peak coupling in blue light, grating  956  has peak coupling in green light, and grating  958  has peak coupling in red light. The three wavelengths of the in-coupled light propagate within waveguide  952  to out-coupling gratings  960 ,  962 , and  964 , which couple the light into respective sensors  966 ,  968 , and  970 . Optional spectral filters  972 ,  974 , and  976  may be overlaid on the sensors for additional spectral separation. 
     In the present example, gratings  954 ,  956 , and  958  are etched into a fused silica substrate. The dimensions and calculated performance at the design wavelength of each grating are given for their specific wavelengths in Table 2, below. Each grating has a grating period P, step height h, and mesa width W (mesas denoting the protruding areas of a grating). The gratings are designed for an angle of incidence of 66°, and for TE-polarized light. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 PROPERTIES OF GRATINGS 954, 956, AND 958 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Design 
                   
                   
                   
                 Diffraction 
                   
               
               
                   
                 wave- 
                   
                   
                 Width 
                 efficiency 
                 Reflec- 
               
               
                   
                 length 
                 Period 
                 Height 
                 W 
                 to −1 st   
                 tivity 
               
               
                 Grating 
                 (nm) 
                 P (nm) 
                 h (nm) 
                 (nm) 
                 order (%) 
                 (%) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 954 
                 420 
                 216 
                 311 
                 95 
                 99.89 
                 0.09 
               
               
                 956 
                 500 
                 257 
                 369 
                 113 
                 99.89 
                 0.06 
               
               
                 958 
                 600 
                 308 
                 446 
                 134 
                 99.88 
                 0.07 
               
               
                   
               
            
           
         
       
     
     The transmittance of the gratings for low angles of incidence does not exhibit diffraction, i.e. light propagates same as though a planar interface, and exceeds 95% transmission across the entire visible spectrum. Diffraction effects emerge at larger angles (about 30 deg. incident angle for 500 nm wavelength), and will gradually increase, reaching its peak efficiency of 99.89% at 66 deg. The gratings have a high coupling efficiency into the waveguide at large angles of incidence, and a low impact on the radiation emitted by a display underneath the waveguide at the typical viewing angles. Thus, the impact of the gratings on the displayed image is minimal. 
     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: 20210117
Publication Date: 20230912
Grant Date: 20230912
Priority Date: 20200305
Inventors: SOSKIND, YAKOV G.
SHPUNT, ALEXANDER
TOWNSEND, GRAHAM C.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/0016", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0093", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N13/332", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04N2213/001", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0093", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0038", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0016", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0093", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N13/332", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04N2213/001", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 87933234