Abstract:
The present disclosure describes structured light projection in which a structured light projector includes a light emitter and a compound patterned mask. The mask includes a spacer substrate that is transparent to a wavelength of light emitted by the light emitter. On a first side of the spacer substrate is a first reflective surface having apertures therein to allow light to pass through. Lenses are arranged to focus light, produced by the light emitter, toward the apertures in the first reflective surface. A second reflective surface on a second side of the spacer substrate opposite the first side has apertures therein to allow light passing through the spacer substrate to exit the compound patterned mask.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    The present application claims the benefit of priority of U.S. Provisional Patent Application No. 62/143,392, filed on Apr. 6, 2015, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates to structured light projection. 
       BACKGROUND 
       [0003]    Various imaging applications use compact optoelectronic modules that can be integrated, for example, within personal computing devices such as smart phones, tablets, laptops or personal computers. In some applications, the module can include a light source to project a structured light pattern onto a scene that includes one or more objects of interest. Light from the projected pattern is reflected by the objects in the scene and is sensed by one or more imagers for use, for example, in stereo matching to generate a three-dimensional image. The structured light can provide additional texture for matching pixels in the stereo images. 
         [0004]    One challenge, however, in designing a light projector to project a pattern onto the scene is how to replicate, in an effective manner, a particular pattern in the far field (i.e., on the objects in the scene). 
       SUMMARY 
       [0005]    The present disclosure describes structured light projection using a compound patterned mask. 
         [0006]    For example, in one aspect, a structured light projector includes a light emitter and a compound patterned mask. The mask includes a spacer substrate that is transparent to a wavelength of light emitted by the light emitter. On a first side of the spacer substrate is a first reflective surface having apertures therein to allow light to pass through. Lenses are arranged to focus light, produced by the light emitter, toward the apertures in the first reflective surface. A second reflective surface on a second side of the spacer substrate opposite the first side has apertures therein to allow light passing through the spacer substrate to exit the compound patterned mask. 
         [0007]    Some implementations include one or more of the following features. For example, in some cases, each of the first and second reflective surfaces comprises a metal or some other reflective coating. In some instances, each of the first and second reflective surfaces comprises at least one of gold, aluminum, chromium or a dichroic material. 
         [0008]    The lenses can include an array of micro lenses each of which is arranged to focus light to a respective one of the apertures in the first reflective surface. In some implementations, the structured light projector includes an optical collimator disposed between the light emitter and the compound patterned mask. The optical collimator can be arranged to uniformly illuminate the compound patterned mask with light produced by the light emitter. 
         [0009]    An arrangement of the apertures in the first reflective surface can match an arrangement of the lenses. Further, the arrangement of apertures in the first reflective surface can differ from an arrangement of the apertures in the second reflective surface. 
         [0010]    In some cases, the light emitter includes multiple vertical cavity surface emitting lasers. The light projector produces, in some implementations, a structured pattern of light in the IR or near-IR region of the spectrum. 
         [0011]    In another aspect, the disclosure describes an optoelectronic apparatus that includes a light projector operable to project a structured light pattern onto an object, and an image sensor arranged to receive light reflected by the object. 
         [0012]    In accordance with another aspect, the disclosure describes a method of producing structured light. The method includes causing light of a particular wavelength to be emitted toward a plurality of lenses and causing the light received by the lenses to be focused toward apertures in a first reflective surface. Some of the light is allowed to pass through apertures in a second reflective surface spaced apart from the first reflective surface, whereas some of the light is reflected from the second reflective surface back toward the first reflective surface. Subsequently, some of the reflected light is reflected, by the first reflective surface, back toward the second reflective surface such that at least some of the previously reflected light passes through the apertures in the second reflective surface. 
         [0013]    The compound patterned mask can, in some cases, help increase the optical throughput of the mask so as to replicate more effectively the projected optical pattern in the far field. The light projectors described here can be used, for example, in encoded light and active stereo applications. 
         [0014]    Other aspects, features and advantages will be readily apparent from the following detailed description, the accompanying drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  illustrates an example of optoelectronic system that includes a light projector. 
           [0016]      FIG. 2  illustrates an example of the light projector. 
           [0017]      FIG. 3  illustrates an example of an arrangement of vertical cavity surface emitting lasers (VCSELs) for the light projector. 
           [0018]      FIG. 4  illustrates further details of the light projector in some implementations. 
           [0019]      FIGS. 5A and 5B  illustrate further details of the light projector in some implementations. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    As illustrated in  FIG. 1 , an optoelectronic system includes a light projector  20  to project a structured light pattern  28  onto one or more objects in a scene  26  of interest. In some implementations, the projected pattern consists of light in the IR or near-IR region of the spectrum. Light from the projected pattern  28  can be reflected by the object(s) in the scene  26  and sensed by an image sensor  22  that includes spatially distributed light sensitive components (e.g., pixels) that are sensitive to a wavelength of light emitted by the light projector  20 . The detected signals can be read-out and used, for example, by processing circuitry for stereo matching to generate a 3D image. In some cases, one or more optical elements such as lenses  28  help direct the light reflected from the scene  26  toward the image sensor  22 . Using structured light can be advantageous, for example, in providing additional texture for matching pixels in the stereo images. 
         [0021]    In some implementations, the light projector  20 , the lenses  28  and the image sensor  22  are integrated within a mobile host computing device such as a cellular phone, smartphone, tablet, personal data assistant, or notebook computer with networking capability. In such cases, the light projector  20 , the lenses  28  and the image sensor  22  can be disposed below a front side cover glass of the host device. The structured light emitted by the light projector  20  can result in a pattern  28  of discrete features (i.e., texture or encoded light) being projected onto objects in the scene  26  external to the host device. In some instances, the light projector  20 , the lenses  28  and the image sensor  22  are components of the same optoelectronic module. In other implementations, the light projector  20  can be a discrete component that is not integrated into the same module as the image sensor  22  and/or lens  28 . Further, the light projector  20  can be used in other types of applications (e.g., proximity sensing, distance determinations using triangulation) as well and is not limited to the imaging applications referred to above. 
         [0022]    As illustrated in  FIG. 2 , the light projector  20  can include, for example, a high-power light emitting element  30  such as a laser diode, VCSEL or array of VCSELs operable to emit a predetermined narrow range of wavelengths, e.g., in the IR or near-IR part of the spectrum. An example of a suitable VCSEL array layout is illustrated in  FIG. 3 . In the illustrated example, the overall dimensions of the array are X×Y, where the width X=198 μm, and the length Y=342 μm. In the illustrated example, the vertical distance d 1  between adjacent rows of VCSELs is 22 μm, and the vertical pitch d 2  of the arrangement is 44 μm. Also in the illustrated example, the horizontal distance d 3  between adjacent columns of VCSELs is 38 μm, and the horizontal pitch d 4  of the arrangement is 76 μm. Different dimensions may be appropriate for some implementations. 
         [0023]    The light projector  20 , in some cases, is operable to emit light in the range of about 850 nm+10 nm, or in the range of about 830 nm+10 nm, or in the range of about 940 nm+10 nm. Different wavelengths and ranges may be appropriate for other implementations. In some instances, the optical output of the light projector  20  in the range of 20-500 mW. For example, in a particular implementation, the individual VCSELs have a circular emitting profile with a numerical aperture (NA) of 0.15 and a peak power of 5 mW. The total output power of the VCSEL array in some cases is about 250 mW. 
         [0024]    As further shown in  FIG. 2 , the light projector  20  includes an optical collimator  32  arranged to uniformly illuminate a compound patterned mask  34  with light from the emitter  30 . The collimator  32  can include, for example, one or more collimating lenses disposed between the light emitter  30  and the compound patterned mask  34 . Further, in some cases, the compound projection mask  34  can be illuminated uniformly by a diffractive optical element disposed between the VCSEL array and the mask  34 . In some implementations (e.g., where the distance between the VCSEL array of other light emitter  30  is sufficiently large), the collimator  32  can be omitted. 
         [0025]    The compound patterned mask  34  can cover a relatively large area compared to the area of the VCSEL array or other light source  30 . Light beams passing through the mask  34  then pass through a projection lens  36  to project light beams  38  that produce the structured light pattern  28 . 
         [0026]    Details of the compound patterned mask  34  according to some implementations are illustrated in  FIG. 4 . The mask  34  is composed of a spacer substrate  46  that is substantially transparent to the wavelength(s) of light emitted by the VCSEL array or other light emitter  30 . The spacer substrate  46  separates a first reflective surface  44  from a second reflective surface  48 . The first reflective surface  44  is disposed on the surface of the substrate  46  closer to the light emitter  30 , whereas the second reflective surface  48  is disposed on the surface of the substrate  46  further from the light emitter  30 . Further, a micro lens array  41  including micro lenses  42  is disposed on the first reflective surface  44  such that the first reflective surface  44  is disposed between the micro lens array  41  and the transparent substrate  46 . The reflective surfaces  44 ,  48  are composed of a material that is reflective for wavelength(s) of light emitted by the VCSEL array or other light emitter  30 . 
         [0027]    As further illustrated in  FIGS. 5A and 5B , each of the reflective surfaces  44 ,  48  can be formed, for example, as a reflective coating composed, for example, of gold (Au), aluminum (Al), chromium (Cr) or a dichroic material. The coatings  44 ,  48  can be made of the same reflective material as one another or of different reflective materials. Each of the reflective coatings  44 ,  48  has respective transparent apertures  50 ,  52  through which light beams can pass. The arrangement of apertures  50  in the first reflective coating  44  should substantially match and be aligned with the arrangement of micro lenses  41 . The arrangement of apertures  52  in the second reflective coating  48  are used to generate the light beams  38  for the projected light pattern  28 . Thus, the arrangement of apertures  52  in the second reflective coating  48  can appear to be random, though they may be designed to project a predetermined or specified pattern onto one or more objects. 
         [0028]    In operation, light from the VCSEL array or other emitter  30  is collimated (if necessary) and the light beams exiting the collimator  32  are incident on the micro lenses  42  of array  41 . Each micro lens  42  focuses all or most of the incident light through a respective corresponding one of the apertures  50  in the first reflective surface  44  of the mask  34 . Some of the light passing through the transparent spacer substrate  46  passes through the apertures  52  in the second reflective surface  48  of the mask  34 . On the other hand, some of the light (e.g., beam  54  in  FIG. 4 ) that passes through the spacer substrate  46  initially may not pass through one of the apertures  52  in the second reflective surface  48 , but instead may be incident on the reflective surface  48  itself. In that case, second reflective surface  48  reflects the light (e.g., beam  56 ) back through the spacer substrate  46  toward the first reflective surface  44 . While some of the light reflected back toward the first reflective surface  44  may be lost if it passes back though one of the apertures  50 , in many cases the light  56  will be incident on the first reflective surface  44 , which will reflect the light (e.g., beam  58 ) back toward the second reflective surface  48 . At least in some cases, the reflected beam  58  will pass through one of the apertures  52  in the second reflective surface  48 , thereby increasing the amount of light  38  that contributes to the pattern projected onto the scene  26 . Some of the light beams may be reflected back in forth multiple times between the first and second reflective surfaces  44 ,  48  before passing through one of the apertures  52 . The compound patterned mask  34  thus can help increase the optical throughput of the mask  34  and more effectively replicating the projected optical pattern in the far field. 
         [0029]    Various modifications can be made within the spirit of the disclosure. Thus, other implementations are within the scope of the claims.