PATENT DOCUMENT

Publication Number: US-12158546-B2
Application Number: US-202117214960-A
Country: US
Kind Code: B2

Title: Emitters behind display

Abstract:
An optoelectronic device includes a display, including a first substrate, which is transparent to optical radiation at a given wavelength, and a first array of display cells including pixel circuit elements disposed on the first substrate at a first pitch, with gaps of a predefined size between the pixel circuit elements. An emitter array includes a second substrate, parallel and in proximity to the first substrate, and a second array of emitters, which are disposed on the second substrate at a second pitch that is different from the first pitch, and which are configured to emit optical radiation at the given wavelength toward the first substrate. Control circuitry is configured to identify the emitters that are aligned with the gaps between the pixel circuit elements and to selectively drive the identified emitters to emit the optical radiation through the gaps.

Claims:
The invention claimed is: 
     
       1. An optoelectronic device, comprising:
 a display, comprising:
 a first substrate, which is transparent to optical radiation at a given wavelength; and 
 a first array of display cells comprising pixel circuit elements disposed on the first substrate at a first pitch, with gaps of a predefined size between the pixel circuit elements; 
 
 an emitter array, comprising:
 a second substrate, parallel to the first substrate; and 
 a second array of emitters, which are disposed on the second substrate at a second pitch that is different from the first pitch, and which are configured to emit optical radiation at the given wavelength toward the first substrate; and 
 
 control circuitry, which is configured to identify the emitters that are aligned with the gaps between the pixel circuit elements and to selectively drive the identified emitters to emit the optical radiation through the gaps, while the remaining emitters in the second array are not actuated. 
 
     
     
       2. The optoelectronic device according to  claim 1 , wherein the second pitch is smaller than the predefined size of the gaps. 
     
     
       3. The optoelectronic device according to  claim 1 , and comprising a plurality of sensors of the optical radiation configured to detect the optical radiation emitted by the emitters and reflected from the pixel circuit elements,
 wherein the control circuitry is configured to identify the emitters responsively to the reflected radiation detected by the sensors. 
 
     
     
       4. The optoelectronic device according to  claim 3 , wherein the sensors are disposed on the second substrate. 
     
     
       5. The optoelectronic device according to  claim 3 , wherein the sensors are configured to detect a time of flight of the reflected radiation, and the control circuitry is configured to distinguish the radiation reflected from the pixel circuit elements responsively to the detected time of flight. 
     
     
       6. The optoelectronic device according to  claim 5 , wherein the sensors comprise single-photon avalanche diodes (SPADs). 
     
     
       7. The optoelectronic device according to  claim 3 , wherein the sensors are configured to detect an intensity of the reflected radiation, and the control circuitry is configured to distinguish the radiation reflected from the pixel circuit elements responsively to the detected intensity. 
     
     
       8. The optoelectronic device according to  claim 7 , wherein the sensors comprise photodiodes. 
     
     
       9. The optoelectronic device according to  claim 3 , wherein the control circuitry is configured to identify the emitters that minimize the radiation that is reflected from the pixel circuit elements and to selectively drive the identified emitters. 
     
     
       10. The optoelectronic device according to  claim 1 , wherein the emitters comprise microlenses, which are configured to focus the optical radiation from each of the emitters to converge to a waist at the first substrate. 
     
     
       11. The optoelectronic device according to  claim 10 , wherein the second substrate comprises first and second faces, wherein the emitters are formed on the first face of the second substrate and are configured to emit respective beams of radiation through the second substrate, and wherein the microlenses are formed on the second face of the second substrate in respective alignment with the emitters. 
     
     
       12. The optoelectronic device according to  claim 1 , wherein the emitters comprise vertical-cavity surface-emitting lasers (VCSELs). 
     
     
       13. An optoelectronic device, comprising:
 a display, comprising:
 a first substrate, which is transparent to optical radiation at a given wavelength; and 
 a first array of display cells comprising pixel circuit elements disposed on the first substrate at a first pitch, with gaps of a predefined size between the pixel circuit elements; 
 
 an emitter array, comprising:
 a second substrate, parallel to the first substrate; and 
 a second array of emitters, which are disposed on the second substrate at a second pitch that is different from the first pitch, and which are configured to emit optical radiation at the given wavelength toward the first substrate; 
 
 a plurality of sensors of the optical radiation configured to detect the optical radiation emitted by the emitters and reflected from the pixel circuit elements; and 
 control circuitry, which is configured to identify the emitters that are aligned with the gaps between the pixel circuit elements and to selectively drive the identified emitters to emit the optical radiation through the gaps, 
 wherein the control circuitry is configured to identify the emitters that minimize the radiation that is reflected from the pixel circuit elements and to selectively drive the identified emitters, and 
 wherein the control circuitry is configured to actuate multiple sets of the emitters to emit the optical radiation in succession, to measure the radiation that is reflected from the display due to each of the sets, and to identify one of the sets of the emitters that is to be selectively driven responsively to the measured radiation. 
 
     
     
       14. A method for display, comprising:
 providing a display, comprising a first substrate, which is transparent to optical radiation at a given wavelength, and a first array of display cells comprising pixel circuit elements disposed on the first substrate at a first pitch, with gaps of a predefined size between the pixel circuit elements; 
 placing an emitter array, comprising a second substrate and a second array of emitters, which are disposed on the second substrate at a second pitch that is different from the first pitch and are configured to emit optical radiation at the given wavelength, such that the second substrate is parallel to the first substrate and the emitters emit the optical radiation toward the first substrate; 
 identifying the emitters that are aligned with the gaps between the pixel circuit elements; and 
 selectively driving the identified emitters to emit the optical radiation through the gaps, while the remaining emitters in the second array are not actuated. 
 
     
     
       15. The method according to  claim 14 , wherein the second pitch is smaller than the predefined size of the gaps. 
     
     
       16. The method according to  claim 14 , wherein identifying the emitters comprises detecting the optical radiation that is emitted by the emitters and reflected from the pixel circuit elements, and identifying the emitters responsively to the reflected radiation. 
     
     
       17. The method according to  claim 16 , wherein detecting the optical radiation comprises detecting a time of flight of the reflected radiation, and distinguishing the radiation reflected from the pixel circuit elements responsively to the detected time of flight. 
     
     
       18. The method according to  claim 16 , wherein detecting the optical radiation comprises detecting an intensity of the reflected radiation, and distinguishing the radiation reflected from the pixel circuit elements responsively to the detected intensity. 
     
     
       19. The method according to  claim 16 , wherein detecting the optical radiation comprises identifying the emitters that minimize the radiation that is reflected from the pixel circuit elements. 
     
     
       20. The method according to  claim 14 , wherein the emitters comprise microlenses, which are configured to focus the optical radiation from each of the emitters to converge to a waist at the first substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application 63/008,852, filed Apr. 13, 2020, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to optoelectronic devices, and particularly to illuminators and displays. 
     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 of optical radiation. 
     SUMMARY 
     Embodiments of the present invention that are described hereinbelow provide improved designs and methods for integrating illuminators with displays. 
     There is therefore provided, in accordance with an embodiment of the invention, an optoelectronic device, which includes a display, including a first substrate, which is transparent to optical radiation at a given wavelength, and a first array of display cells including pixel circuit elements disposed on the first substrate at a first pitch, with gaps of a predefined size between the pixel circuit elements. An emitter array includes a second substrate, parallel and in proximity to the first substrate, and a second array of emitters, which are disposed on the second substrate at a second pitch that is different from the first pitch, and which are configured to emit optical radiation at the given wavelength toward the first substrate. Control circuitry is configured to identify the emitters that are aligned with the gaps between the pixel circuit elements and to selectively drive the identified emitters to emit the optical radiation through the gaps. 
     In a disclosed embodiment, the second pitch is smaller than the predefined size of the gaps. 
     In some embodiments, the device includes a plurality of sensors of the optical radiation configured to detect the optical radiation emitted by the emitters and reflected from the pixel circuit elements, wherein the control circuitry is configured to identify the emitters responsively to the reflected radiation detected by the sensors. Typically, the sensors are disposed on the second substrate. In one embodiment, the sensors are configured to detect a time of flight of the reflected radiation, and the control circuitry is configured to distinguish the radiation reflected from the pixel circuit elements responsively to the detected time of flight. In this case, the sensors may include single-photon avalanche diodes (SPADs). 
     Alternative or additionally, the sensors are configured to detect an intensity of the reflected radiation, and the control circuitry is configured to distinguish the radiation reflected from the pixel circuit elements responsively to the detected intensity. In a disclosed embodiment, the sensors include photodiodes. 
     Further additionally or alternatively, the control circuitry is configured to identify the emitters that minimize the radiation that is reflected from the pixel circuit elements and to selectively drive the identified emitters. In a disclosed embodiment, the control circuitry is configured to actuate multiple sets of the emitters to emit the optical radiation in succession, to measure the radiation that is reflected from the display due to each of the sets, and to identify one of the sets of the emitters that is to be selectively driven responsively to the measured radiation. 
     In some embodiments, the emitters include microlenses, which are configured to focus the optical radiation from each of the emitters to converge to a waist at the first substrate. In one embodiment, the second substrate includes first and second faces, wherein the emitters are formed on the first face of the second substrate and are configured to emit respective beams of radiation through the second substrate, and wherein the microlenses are formed on the second face of the second substrate in respective alignment with the emitters. 
     In a disclosed embodiment, the emitters include vertical-cavity surface-emitting lasers (VCSELs). 
     There is also provided, in accordance with an embodiment of the invention, a method for display, which includes providing a display, including a first substrate, which is transparent to optical radiation at a given wavelength, and a first array of display cells including pixel circuit elements disposed on the first substrate at a first pitch, with gaps of a predefined size between the pixel circuit elements. An emitter array, including a second substrate and a second array of emitters, which are disposed on the second substrate at a second pitch that is different from the first pitch and are configured to emit optical radiation at the given wavelength, is placed such that the second substrate is parallel and in proximity to the first substrate and the emitters emit the optical radiation toward the first substrate. The emitters that are aligned with the gaps between the pixel circuit element are identified and are selectively driven to emit the optical radiation through the gaps. 
     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, in accordance with an embodiment of the invention; 
         FIG.  2    is a schematic front detail view of a display, in accordance with an embodiment of the invention; 
         FIG.  3    is a schematic front detail view of the display of  FIG.  2    superimposed over a VCSEL chip, in accordance with an embodiment of the invention; 
         FIG.  4    is a schematic frontal view of the VCSEL chip of  FIG.  3   , in accordance with an embodiment of the invention; 
         FIG.  5    is a schematic sectional view of a part of an array of emitters and sensors and a display, in accordance with an embodiment of the invention; 
         FIG.  6    is a schematic representation of a calibration method for selecting VCSELs for actuation, in accordance with an embodiment of the invention; and 
         FIG.  7    is a schematic sectional view of a VCSEL with an integral microlens under a display, in accordance with another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Various sorts of portable computing devices (referred to collectively as “portable devices” in the description), such as smartphones, augmented reality (AR) devices, virtual reality (VR) devices, smart watches, and smart glasses, comprise both optical displays and sources of 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.) For example, the front side of a smartphone may include a display screen, a camera for capturing images of the user&#39;s face, and an illumination source for illuminating the face during image capture. The ongoing increase in the size, resolution, and brightness of the displays of these portable devices imposes strict limitations on the space available for apertures of various emitter and sensor modules within the front sides these devices. 
     Display layouts can be designed with a transparent window in a gap between the pixel circuit elements within each pixel of the display. An emitter, such as a VCSEL (vertical-cavity surface-emitting laser), placed behind this window and aligned with it will emit an optical beam through the window. Consequently, an array of emitters behind an array of windows can provide illumination for applications of the portable device, such as 3D mapping or face recognition. Efficient transmission of the radiation through the windows, however, requires aligning the emitters with the respective windows to an accuracy of a few microns. Mechanical alignment to this degree of accuracy between an array of emitters and a display is very difficult, if not impossible, using currently available fabrication methods. 
     The embodiments of the present invention that are described herein address these problems by providing an optoelectronic device comprising a display with a given pixel pitch and an emitter array, mounted behind the display, with an emitter pitch that is different from the pixel pitch. As a result of the difference in the pitches, most of the emitters will not be aligned with the transparent windows defined by the gaps between the pixel circuit elements, but some of the emitters will be aligned with respective gaps. Control circuitry identifies the emitters that are aligned with the gaps between the pixel circuit elements and selectively drives these emitters to emit their optical radiation through the gaps. The remaining emitters are typically not actuated (except possibly during a test and calibration phase). Thus, the need for precise manufacturing alignment of the emitter array behind the display is obviated. 
     In the disclosed embodiments, the display comprises an array of display cells formed on a first substrate, such as a glass substrate, which is transparent to optical radiation at the wavelength emitted by the emitter array. Each display cell comprises one or more gaps between the pixel circuit elements, providing windows at the emitter wavelength. The emitter array in formed on a second substrate, such as a semiconductor substrate, which is mounted parallel and in proximity to the first substrate, and oriented so that the emitters emit optical radiation toward the first substrate. 
     The pitch of the emitter array can advantageously be made smaller than either of the lateral dimensions of the transparent windows in the display cells. In this case, even with only coarse lateral mechanical alignment, some emitters are always aligned with respective windows. 
     Various calibration procedures can be used to identify the emitters that are to be actuated, and possibly to change the selection in the field. (Such changes may be necessitated, for example, due to shifts in alignment over time, particularly if the device undergoes some mechanical shock.) For this purpose, in some embodiments, the emitter array also comprises sensors, which may be either interspersed with the emitters or arrayed in some other location on the second substrate, or may be disposed on a separate substrate. The control circuitry uses the sensors to measure the radiation from each emitter that is reflected back from the pixel circuit elements toward the second substrate. Emitters that are aligned with respective gaps have low back-reflection and are identified for actuation on this basis. In one embodiment, which is described in detail hereinbelow, the control circuitry measures the time between emission of pulses from the emitters and detection of photons at the sensors in order to identify the short-range reflections that are characteristic of back-reflection from the pixel circuit elements. 
       FIG.  1    is a schematic frontal view of a portable device  20 , in accordance with an embodiment of the invention. Portable device  20  comprises a display  22 , covering most of the front of the portable device. Portable device  20  further comprises an optical radiation source  24 , which may be utilized for applications such as, for example, 3D mapping or face recognition. The embodiments of the invention enable the placement of source  24  behind an active part of display  22 , as indicated by a dotted-line frame  26 . Such a placement of source  24  saves display area, as otherwise the source would have to be placed in a notch area  28  (utilized for other devices, for example cameras and other radiation sensors), thus enlarging the notch and consequently reducing the useful area of display  22 . 
       FIG.  2    is a schematic frontal view of a detail  29  of display  22 , in accordance with an embodiment of the invention. Display  22  comprises a substrate  45 , such as glass, which is transparent to optical radiation at wavelengths in the visible and near infrared ranges. An array of display cells  30  is formed on substrate  45  by methods of display fabrication that are known in the art. Each display cell  30  comprises pixel circuit elements disposed on substrate  45 , such as an OLED (organic light-emitting diode)  32  and a TFT (thin-film transistor)  34  for switching the OLED, as well as conductors  38  connecting the pixel circuits to electronics external to display  22 . 
     Display cells  30  are spaced on substrate  45  at a certain pixel pitch, with gaps  36  of a predefined size, defining transparent windows, between the pixel circuit elements. In the pictured example, cells  30  have a pitch in the x-direction of W C,x =80 μm and a pitch in the y-direction of W C,y =60 μm. The dimensions of gap  36  are an x-width of W W,x =20 μm and a y-width of W W,y =50 μm. The x- and y-directions are indicated by Cartesian coordinate axes  39 . 
     Detail  29  is presented only as an example of display cells  30  with gaps  36  of typical dimensions. Other kinds of display cells, with other layouts and dimensions and other kinds of pixel circuit elements, may be used, as long as they include a sufficient gap to serve as a transparent window in each cell  30 . 
       FIG.  3    is a schematic view of detail  29  of display  22  superimposed over an emitter array, such as a VCSEL chip  40 , in accordance with an embodiment of the invention. VCSELs  42   a ,  42   b ,  42   c , and  42   d  on chip  40  are visible through respective gaps  36   a ,  36   b ,  36   c , and  36   d  and are selectively driven to emit optical radiation through the respective gaps. The arrangement of a 2×2 matrix of VCSELs  42   a ,  42   b ,  42   c , and  42   d  in this manner may be used, for example, for providing illumination for a proximity sensor. In alternative embodiments, different arrangements and numbers of VCSELs  42  may be used. 
       FIG.  4    is a schematic frontal view of VCSEL chip  40  of  FIG.  3   , in accordance with an embodiment of the invention. VCSEL chip  40  comprises a matrix  43  of VCSELs  42 , disposed on a substrate  51 , such as a semiconductor substrate. VCSELs  42   a ,  42   b ,  42   c , and  42   d  in matrix  43  are the specific VCSELs that are aligned with gaps  36   a ,  36   b ,  36   c , and  36   d  in  FIG.  3   . These VCSELs are identified and are driven selectively to emit optical radiation through the respective gaps  36 , while the remaining VCSELs in matrix  43  are not actuated. 
     Matrix  43  is laid out in this example at an equal pitch P in both x- and y-dimensions, although other arrangements of the emitters are also possible. Pitch P is different from the dimensions W W,x  or W W,y  of gap  36  and is advantageously smaller than the gap dimensions, in order to ensure that there will be at least one VCSEL  42  aligned with each gap. For example, for the dimensions given in  FIG.  2   , pitch P may be chosen to be on the order of 10 μm or less. Choosing a pitch P that is much smaller than either of the two dimensions of gap  36  ensures that even coarse lateral alignment tolerance between VCSEL chip  40  and display  22  will yield an alignment of a VCSEL  42  with each desired gap  36 . (“Lateral alignment” refers to alignment in the plane of VCSEL chip  40 .) In an alternative embodiment, VCSELs  42  may be arranged in a matrix with unequal pitches P x  and P y  in the x- and y-dimensions, respectively, with the requirement that P x &lt;W W,x  and P y &lt;W W,y , wherein x and y again refer to the Cartesian coordinate axes  39  of  FIG.  2   . 
       FIG.  5    is a schematic sectional view of a part of an array  44  of emitters and sensors and of display  22 , in accordance with an embodiment of the invention. Array  44  is positioned under display  22  in proximity and parallel to it. Array  44  comprises pairs of emitters—in this embodiment VCSELs  42 —and sensors—in this embodiment SPADs (single-photon avalanche diodes)  48 —on substrate  51 . Only two emitter/sensor pairs, VCSELs  42   e  and  42   f  and SPADs  48   e  and  48   f , are shown for the sake of simplicity. Substrate  51  may comprise, for example, a silicon substrate with CMOS (complementary metal-oxide semiconductor) circuitry for forming SPADs  48  and for driving both the SPADs and VCSELs  42 . Alternatively, other types of emitters and sensors may be used, and a given sensor may be shared among multiple emitters. 
     Control circuitry  50  is coupled to VCSELs  42  and SPADs  48 . Array  44  in the pictured example is positioned under display  22  so that the pair comprising VCSEL  42   e  and SPAD  48   e  is aligned with gap  36 , whereas the pair comprising VCSEL  42   f  and SPAD  48   f  is not aligned with a gap. SPADs detect the optical radiation emitted by the corresponding VCSELs  42  and reflected from the pixel circuit elements, such as OLEDs  32 , TFTs  34 , and conductors  38 . Control circuitry  50  identifies the emitters that are aligned with gaps  36  based on the reflected radiation detected by the SPADs. Specifically, control circuitry  50  identifies the VCSELs that minimize the radiation that is reflected from the pixel circuit elements and selectively drives these identified emitters. The remaining VCSELs  42  in array  44  are not driven and remain inactive. Circuitry that can be used for this sort of selective actuation of VCSELs is described, for example, in U.S. Patent Application Publication 2019/0363520, whose disclosure is incorporated herein by reference. This selective actuation scheme is useful in reducing the power consumed by the VCSEL chip, as well as reducing the amount of stray light that is reflected into device  20 . 
     As shown in  FIG.  5   , VCSELs  42   e  and  42   f  emit respective beams  52   e  and  52   f  of optical radiation. Beam  52   e  is transmitted through gap  36  (above VCSEL  42   e ) into the space above display  22 . Only a small portion of the beam is reflected to SPAD  48   e  due to residual surface reflections from substrate  45  (typically a few percent), indicated by an arrow  58 . Beam  52   f , however, is blocked by the pixel circuit elements, and consequently a large fraction of beam  52   f  (with the possible exception of a small portion absorbed by the pixel circuit elements) is reflected toward SPAD  48   f , as shown by an arrow  60 . Thus, on the basis of the signals from SPADs  48   e  and  48   f , control circuitry  50  can identify and will subsequently drive VCSEL  42   e , but will not drive VCSEL  42   f.    
     Although various types of sensors can be used in detecting the reflections from display, SPADs  48  are advantageous in providing an output that is indicative of the time of flight of photons emitted by VCSELs  42  and reflected back to the corresponding SPADs. Control circuitry  50  estimates the time of flight based on the time difference between each pulse applied to drive a VCSEL and the detection pulse output by the corresponding SPAD. Reflections from the pixel circuit elements will be characterized by very short times of flight, and thus can be distinguished from reflections that may reach the SPADs from more distant objects in front of device  20 . 
     In an alternative embodiment, the sensors of optical radiation comprise analog photodiodes, rather than SPADs  48 . Control circuitry  50  receives from the photodiodes, via an analog-to-digital converter, for example, a signal representing the integrated intensity of the reflected radiation. In this case, control circuitry  50  will select the VCSELs for which the reflected signals were weak, indicating that are probably located behind gaps  36 . 
     To make use of this phenomenon in identifying the VCSELs  42  that are aligned with gaps  36 , control circuitry  50  actuates in succession multiple VCSELs or sets of VCSEL  42  to emit optical radiation as trains of short pulses. Control circuitry  50  further receives and measures signals from SPADs  48 , and calculates the times of flight and numbers of the received pulses. As the return pulses, indicated by arrows  58  and  60 , return from display cells  30 , the calculated times of flight are equal, representing the round-trip distance from VCSEL  42  to the display and then to SPAD  48 . However, due to the much smaller reflectance from substrate  45  at gap  36  than from the pixel circuit elements, such as OLEDs  32  and TFTs  34 , the number of the pulses received by SPAD  48   e  with short time of flight will be much smaller than the number received by SPAD  48   f . This difference in the pulse counts provides control circuitry  50  with the means to identify those VCSELs  42  that are aligned with gaps  36  based on minimized reflected radiation. 
       FIG.  6    is a schematic representation of a calibration method for identifying those VCSELs  42  that are aligned with gaps  36 , in accordance with an embodiment of the invention. The disclosed method comprises N successive steps, which are detailed below.  FIG.  6    shows steps  1 ,  2 ,  3 , and N, and the details of the method are shown in step  1 . 
     A set of VCSELs  42  in matrix  43  of VCSEL chip  40  is defined by a unit cell  62  of four VCSELs  42   g ,  42   h ,  42   i , and  42   j , forming a 2×2 matrix. (The four VCSELs forming the unit cell are marked by clear centers.) Unit cell  62  also comprises four SPADs  48 , each associated with one of the four VCSELs  42  of the unit cell (as shown in  FIG.  5   , but omitted from  FIG.  6    for the sake of simplicity). The transverse (x,y) dimensions of the 2×2 matrix are selected to be an integer multiple of the pitches W C,x , and W C,y  of display cells  30  ( FIG.  2   ). Since the pitch P of matrix  43  is much smaller than either of the dimensions W W,x  or W W,y  of gap  36 , at least one of unit cells  62  will have its four VCSELs aligned with respective gaps in four corresponding display cells  30 . (Even if the lateral dimensions of the 2×2 matrix of unit cell  62  are not an exact multiple of the pitches W C,x  and W C,y , a selection for alignment is possible due the small pitch P.) 
     The objective of the method of  FIG.  6    is to identify one of unit cells  62  in VCSEL matrix  43  that is aligned with gaps  36 . The number of steps N is a function of the size of unit cell  62  and the number of VCSELs  42  in matrix  43 . Although the present example uses a unit cell comprising a 2×2 matrix of VCSELs  42 , unit cells comprising other numbers and arrangements of VCSELs may alternatively be used. 
     In each of the N steps of the method, control circuitry  50  defines a different position for unit cell  62 , i.e., the control circuitry shifts the unit cell across matrix  43  in successive discrete steps of length P. At each step, control circuitry  50  drives the four VCSELs of unit cell  62  to emit a train of short pulses of optical radiation, and receives pulses reflected from display cells  30  from the four SPADs  48  that are associated with the four VCSELs of the unit cell. Control circuitry  50  calculates the total number of pulses from the four SPADs  48  of unit cell  62  as a function of time, as shown in a histogram plot  64 . The pulses due to reflection from display cells  30  can be identified based on the short round-trip-time between VCSELs  42  and SPADS, as marked by a dotted line frame  66 . 
     Step  1  shows unit cell  62  in the top-left corner of matrix  43 . In plot  64 , a large number of pulses are seen within frame  66  (with a few stray pulses outside the frame), indicating a strong reflection back to the four SPADs  48  associated with the current position of unit cell  62 . The strong reflection indicates that the four VCSELs in the current location of unit cell  62  are not aligned with gaps  36 , but rather the radiation they emit impinges on pixel circuit elements in the corresponding display cells. This situation corresponds to the one shown in  FIG.  5    by arrow  60 . 
     In step  2 , control circuitry  50  has shifted unit cell  62  by one pitch interval P to the right. Similarly to step  1 , a large number of pulses are seen within frame  66 , again indicating a misalignment of VCSELs  42  of unit cell  62  vis-à-vis gaps  36 . 
     In step  3 , control circuitry  50  has shifted unit cell  62  by a further pitch interval P to the right. Now the number of pulses within frame  66  is considerably lower than in steps  1  and  2 , indicating that the SPADs of unit cell  62  in the location of step  3  have received optical radiation reflected from gaps  36 . In this location, the four VCSELs of the unit cell are aligned with gaps  36 . This situation corresponds to the one shown in  FIG.  5    by arrow  58 . 
     In subsequent steps  4 ,  5 , . . . , N, the number of return pulses may be further monitored in order to identify an optimal location of unit cell  62 , with a minimal number of pulse counts within frame  66 . Control circuitry  50  selects the VCSELs in this unit cell to be driven during the operation of device  20 . 
     Although  FIG.  6    shows a certain simple strategy for identification of the optimal choice of VCSELs to be driven, other, more efficient search strategies may alternatively be used and are considered to be within the scope of the present invention. 
       FIG.  7    is a schematic sectional view of a VCSEL  70  with an integral microlens  80  under display  22 , in accordance with another embodiment of the invention. Microlens  80  focuses the optical radiation from VCSEL  70  to converge to a waist  84  at substrate  45  of display  22 , and thus to pass cleanly through gap  36 . A similar microlens is formed in the beam path of each of the VCSELs in the emitter array, for example the VCSELs in matrix  33 . 
     In the pictured example, VCSEL  70  is formed on a bottom face  72  of substrate  51 , and emits optical radiation into the substrate as a beam  76 . Substrate  51  may comprise, for example, GaAs (gallium arsenide). Microlens  80  is formed on a top face  78  of substrate  51 . This sort of arrangement of a VCSEL with integrated microlens is described, for example, in U.S. patent application Ser. No. 16/779,609, filed Feb. 2, 2020, whose disclosure is incorporated herein by reference. Alternatively, other arrangements of microlenses may be used, as are known in the art. 
     Microlens  80  transmits and refocuses beam  76  into a beam  82  and projects it towards gap  36  in display  22 . Microlens  80 , together with VCSEL  70  and substrate  51 , is designed and positioned so that waist  84  of beam  82  is located at substrate  45 . This design minimizes the cross-section of beam  82  at gap  36  so that the beam may pass through the gap without losses from impinging on pixel circuit elements at the edges of the gap. An anti-reflective coating  86  may be deposited on top face  78  for reduction of reflection losses from the top face. 
     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: 20210329
Publication Date: 20241203
Grant Date: 20241203
Priority Date: 20200413
Inventors: LAFLAQUIERE, ARNAUD
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B3/0056", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4861", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B3/0056", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4861", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4865", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0693", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/023", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0426", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3225", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4865", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3225", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/006", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B3/0056", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4861", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4865", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 75581653