Abstract:
The use of one or more angled or curved and diverging light pipes or reflectors placed in a light source&#39;s, e.g. diode&#39;s, emission path at appropriate distances, angles and divergence, such that a diode&#39;s emission spot size is modified and or redirected from the diode&#39;s natural emission path to alternative planes at angle to the diode&#39;s natural emission path so that a diode emission safe spot size can be achieved on any plane at angle to the original diode natural emission path at minimum distances from the diode&#39;s point of emission.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention claims priority from U.S. Patent Application No. 61/594,856 filed Feb. 3, 2012, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a depth camera for a time flight system, and in particular to a depth camera with a low profile for use in small form factor applications. 
     BACKGROUND OF THE INVENTION 
     In a Time of Flight (ToF) based depth detecting camera or other diode emission based depth detection device, laser safety is a critical issue as is camera or device form factor. Various applications of such technology require varying light source power levels. The higher the power level required, the larger the diode&#39;s emission spot size must be to be considered Class 1 laser safe. A conventional depth camera  1 , illustrated in  FIG. 1 , includes a laser light source  2  with a diffusing optic  3 , and a light detector  4  with a receiving optic and filter  5 . Laser safety is normally achieved by placing the diffusing optic  3  perpendicular to the emission path to increase the effective emission spot size  6  as seen by the viewer. The greater the distance D, i.e. the optic  3  is from the emission point of the light source  2 , the larger the spot size  6  becomes. The higher the light source power, the larger the spot  6  needs to be and the further the diffusion optic  4  must be from the emission source to maintain Class 1 laser safety. 
     Unfortunately, in today&#39;s world of miniaturized electronic devices, having to increase the camera or diode emission based device&#39;s size in the direction D of a diode&#39;s natural emission path may not meet a particular application or device&#39;s form factor requirements. 
     In the camera  1 , the depth D has to be minimized so that the camera  1  can be fit into very tight spaces in the bezels of various displays, e.g. TVs, Laptops, Tablets, Computer Monitors, and Cell Phones. Unfortunately, the dimension D is limited by the sensor receive optic  5  and the placement of the diffuser  3  based on a given optical power level to maintain Class 1 laser safety. 
     An object of the present invention is to overcome the shortcomings of the prior art by providing a low profile, small form factor depth camera that is capable of fitting into the bezels of a plurality of display devices. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention relates to a depth camera device comprising:
         a light source for launching a beam of light along a natural emission path at a natural divergence angle;   an angled reflector for redirecting the beam of light from the natural emission path to a required direction of emission, while expanding the beam of light to a divergence angle greater than the natural divergence angle;   a detector array for receiving and detecting returning portions of the beam of light reflected off of objects within the field of view; and   receiver optics for receiving and focusing the returning portions of the beam of light onto the detector array.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein: 
         FIG. 1  is a schematic diagram of a conventional depth camera device; 
         FIG. 2  is a schematic diagram of a depth camera in accordance with the present invention; 
         FIG. 3  is a schematic diagram of an alternative embodiment of the angled light pipe of the depth camera of  FIG. 2 ; 
         FIG. 4  is a schematic diagram of an alternative embodiment of the angled light pipe of the depth camera of  FIG. 2 ; 
         FIG. 5  is an isometric view of a depth camera system in accordance with the present invention; 
         FIG. 6  is a schematic diagram of a receiver optic of the depth camera system of  FIG. 5 ; 
         FIG. 7  is a schematic diagram of an alternative embodiment of a receiver optic of the depth camera system of  FIG. 5 ; and 
         FIG. 8  is a schematic diagram of an alternative embodiment of a receiver optic of the depth camera system of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , a depth camera  11  in accordance with the present invention includes a light source  12 , e.g. laser diode, with a diffuser optic  13 , if necessary, for launching a beam of light into a field of view, and a light detector array  14  with a receiver optic  15  for receiving and detecting portions of the beam of light reflected off of objects in the field of view. Typically the receiver optic  15  can include at least one lens and an optical filter for filtering out background light not of the same wavelength as the light source  12 . 
     In accordance with the present invention, the light source  12  is disposed to emit the beam of light along a natural emission path, which is substantially different, e.g. perpendicular, to the required direction of emission for the field of view of the camera  11 . An angled or curved diverging light pipe or reflector  17  is placed in the natural emission path of the light source  12  to increase the emission spot size at an exit point, e.g. at the diffuser optic  13  if additional diffusion is necessary. A reflective surface  18  is disposed at an acute angle to the natural direction of emission to redirect the beam of light to the required direction of emission. Ideally, the angle of the reflective surface  18  to the direction of emission provides total internal reflection and may additionally expand the beam of light. The light source  12  and the light pipe and/or reflector  17  are positioned and sized so that the natural emission divergence angle β of the light source  12  is contained within the light pipe  17 , which has a larger divergence angle α than the divergence angle β of the light source  12 , i.e. resulting in a spot size at the exit of the light pipe  17  larger than the emission entrance spot size and larger than would normally occur traversing distances d 1  and d 2  in air. Ideally, the spot size on the reflective surface  18 , at the exit of the light pipe  17  or at the diffuser  13  would be at or near a Class 1 laser safe size. Additionally, in the preferred embodiment, the light pipe or reflector  17  and the light source  12  are positioned so that the distance needed between the emission point of the light source  12  and the reflective surface  18  to achieve a Class 1 laser safe spot size on the reflective surface  18  or exit spot size of the light pipe  17  is managed in a direction d 1  where the device&#39;s form factor requirement may be less challenging, and at an angle, e.g. perpendicular, to the required direction of emission, d 2 . A device&#39;s length rather than width or depth for example, may be less restrictive. The secondary diffusion optic, i.e. the diffuser  13 , may or may not be necessary depending on whether or not the desired level of diffusion has occurred or if a diffusion pattern is applied to the exit surface of the light pipe or reflector  17 . In some embodiments, the reflector  17  comprises the convex reflective surface  18  provided on a separate support structure without requiring the light pipe. 
     Ideally, the light pipe  17  is comprised of a material with a higher index of refraction than air, e.g. silica, germanium etc. 
     In an alternate embodiment illustrated in  FIG. 3 , a light pipe and/or reflector  27  is provided in which the planar reflective surface  18  is replaced by an arcuate or convex reflective surface  28  providing even greater divergence of the beam of light. The other characteristics of the light pipe and/or reflector  27  are substantially the same as those of the light pipe or reflector  17 , e.g. the natural emission divergence angle β of the light source  12  is contained within the light pipe or fully on the reflective surface  18 , which has a larger divergence angle α than the light source&#39;s divergence angle β. In some embodiments, the reflector  27  includes the convex reflective surface  28  provided on a separate support structure without requiring the light pipe. 
     In an alternate embodiment illustrated in  FIG. 4 , a light pipe and/or reflector  37  is provided in which the planar reflective surface  18  is replaced by an arcuate or concave reflective surface  38  providing collimation of the beam of light. The other characteristics of the light pipe and/or reflector  37  are substantially the same as those of the light pipe and/or reflector  17  and  27 , e.g. the natural emission divergence angle β of the light source  12  is contained within the light pipe  37  or fully on the reflective surface  38 , which has a divergence angle α near or equal to zero after light pipe or reflector collimation. In some embodiments, the reflector  37  comprises the concave reflective surface  38  provided on a separate support structure without requiring the light pipe. 
     A concave reflective surface  38  is used rather than convex surface  28 , so that the light beam is collimated rather than diverged. The diffuser  13  works better with a collimated input beam than a divergent beam. Accordingly, the beam is expanded along the form factor friendly axis d 1 , collimated just prior to the diffuser  13  and then further expanded, if necessary, by the diffuser  13 . Ideally, the expansion of the beam of light is conducted in the form factor friendly direction d 1  so that the spot on the reflective surface  38  or at the exit of the light pipe  37  is Class 1 laser safe. Alternatively, when full class 1 beam expansion cannot be completed in the form factor friendly direction and further expansion is necessary, the diffuser  13  is provided at the exit of the light pipe and/or reflector  37  to further modify the light beam. The diffuser  13  is an optical element whose output beam characteristics are different (reshaped, usually wider and more diffuse) from the input beam characteristics. 
     With reference to  FIG. 5 , a complete depth camera assembly  30  includes a pair of light sources  12 , each with their own diffuser optic  13 , if required, and light pipe and/or reflector optics  17 ,  27  or  37 , illustrated as a self-supported reflector with a reflective surface  18 / 28 / 38 , mounted on printed circuit board  31 . The natural direction of emission is illustrated as vertically, defined by the height of the PCB  31 ; however, the light source  12  could also be directed laterally so that the natural direction of emission is along the longitudinal axis of the PCB  31 , if more distance d 1  is required. In the illustrated embodiment the height of the PCB  31  is 7 mm, while the width of the depth cameral assembly  30  (d 2 ) is 13 mm and the length is 110 mm; however, other measurements are within the scope of the invention depending upon the requirements of the host device. A color (RGB) camera  32  is also provided in the depth camera assembly  30  to provide conventional color pictures and video, as is well known in the art. A data and power connector  33  is provided for connecting the camera assembly  32  to a host device. 
     A 3D imager produces phase measurements that are processed either on sensor or in a remote coprocessor to produce actual range data. Such a camera can be used in “Z-only” mode for applications, which require the use of range data only. The camera could also be used in “RGB+Z”, i.e. full 3D depth and 2 dimensional colors, modes for applications which utilize both traditional color as well as depth images. Depth and color processing can be done in the camera or with a pass-through mode in which unprocessed data can be passed to the host for processing. 
     To ensure the reception side of the depth camera  11  fits into the low profile form factor, a single or multiple lens element receiver optic  35  is designed with a combination of one or more light pipes and/or angled reflectors placed behind one or more lens elements in the natural reception path to redirect the light&#39;s natural path to new paths, e.g. substantially perpendicular to the natural reception path. The lens elements, angled reflectors and light pipes are positioned relative to one another so that the length of the objective lens&#39; natural reception path can be optimally distributed within a given form factor volume. More specifically, the positioning of light pipes and lens elements is done so that overall objective lens length or diameter are managed in directions where the device&#39;s form factor requirement may be less challenging. A device&#39;s length rather than width or depth for example, may be less restrictive. 
     The basic idea is to change the direction of lens light after entry into the first lens element so that the length of the compound lens can be distributed in a direction more friendly to the host device&#39;s lateral or perpendicular directions, which is critical for small form factor depth cameras for embedding in various host devices. 
     With reference to  FIG. 6 , the receiver optic  35 ′ includes the entry optic  15 , e.g. suitable lensing and optical filters, as herein before described, and a first angled reflector  41  for redirecting the returning light from the natural reception path to the new paths in the d 1  direction substantially perpendicular to the natural reception path, i.e. parallel to the PCB  31 . The first angled reflector  41  includes a reflective surface at an acute angle to the incoming light and the PCB  31 , e.g. 45°. A straight light pipe  42  is included for guiding the returning light to a second angled reflector  43 , which redirects the returning light to the detector array  14 . The straight light pipe  42  can also provide additional focusing, if the distance d 1  provided is insufficient to provide the required size and shape of spot size for the detector array  14 . The second angled reflector  43  includes a reflective surface at an acute angle to the incoming light and the PCB  31 , e.g. 45°. 
     With reference to  FIG. 7 , the receiver optic  35 ″ includes the entry optic  15 , e.g. suitable lensing and optical filters, as herein before described, and the first angled reflector comprises a first curved light pipe  51  for redirecting the returning light from the natural reception path to the new paths in the d 1  direction substantially perpendicular to the natural reception path, i.e. parallel to the PCB  31 . The first curved light pipe  51  includes one or more reflective surfaces at an acute angle to the incoming light and the PCB  31 , e.g. 45°. The straight light pipe  42  is included for guiding the returning light to the second angled reflector in the form of a second angled light pipe  53 , which redirects the returning light to the detector array  14 . The straight light pipe  42  can also provide additional focusing, if the distance d 1  provided is insufficient to provide the required size and shape of spot size for the detector array  14 . The second curved light pipe  53  includes one or more reflective surfaces at an acute angle to the incoming light and the PCB  31 , e.g. 45°. 
     With reference to  FIG. 8 , the receiver optic  35 ″′ includes the entry optic  15 , e.g. suitable lensing and optical filters, as herein before described, and the first curved light pipe  51  for redirecting the returning light from the natural reception path to the new paths in the d 1  direction substantially perpendicular to the natural reception path, i.e. parallel to the PCB  31 . The first curved light pipe  51  includes one or more reflective surfaces at an acute angle to the incoming light and the PCB  31 , e.g. 45°. The straight light pipe  42  is included for guiding the returning light to the detector array  14 , which is disposed perpendicular to the PCB  31 , by suitable supports. The straight light pipe  42  can also provide additional focusing, if the distance d 1  provided is insufficient to provide the required size and shape of spot size for the detector array  14 . 
     Since the light detector array  14  is non-circular, one, some or all lens elements in the receiving optics  35 , including the straight light pipe  42 , are cropped on top, or top &amp; bottom, or top, bottom &amp; sides, etc. such that the objective lens image circle is reformatted to more closely match the non-circular light sensing array format and thereby further reducing or optimizing camera or device form factor.