Today the US Patent & Trademark Office published a patent application from Apple that relates to Apple's TrueDepth camera. The invention filed in April 2018 would suggest that the patent advances the TrueDepth camera. Apple notes that an optoelectronic device includes a semiconductor substrate and a monolithic array of light-emitting elements, including first and second sets of the light-emitting elements arranged on the substrate in respective first and second two-dimensional patterns, which are interleaved on the substrate. The two groups of VCSEL diodes introduced in this invention may be used in conjunction with a high-resolution image sensor in imaging module to implement a zoom function in depth mapping system.
Overall, compact optical projectors are used in a variety of applications. For example, such projectors may be used to cast a pattern of coded or structured light onto an object for purposes of three-dimensional (3D) mapping (also known as depth mapping). This kind of projector is used in the iPhone X TrueDepth camera noted in the photo below as the "Dot Projector." In our cover graphic, we see Apple's Phil Schiller pointing out various elements that make up the iPhone X TrueDepth Camera.
Apple's patent figure 1 FIG. 1 is a schematic side view of a 3D mapping system. It's the same patent figure used in Apple's 2015 patent that we covered earlier; The other figures presented below is what's new to this invention. In patent FIG. 2 we see a projection assembly with its patterning element.
Apple's patent FIG. 8 is a schematic top view of a semiconductor die on which a patterned emitter array has been formed; FIG. 11 is a schematic top view of a semiconductor die on which a patterned emitter array has been formed.
Introducing Two Groups of VCSEL Diodes
More specifically, Apple's patent FIG. 11 illustrates the introduction of two-groups of VCSEL Diodes which is new to the invention. FIG. 11 is a schematic top view of a semiconductor die on which a monolithic VCSEL array has been formed. This array is similar to the array of FIG. 8, except that in the embodiment of FIG. 11 there are two groups of VCSEL diodes #182 and #184, which are driven by separate conductors #186 and #188.
The two groups of VCSEL diodes that are shown in figure 11 may be used in conjunction with a high-resolution image sensor in imaging module #32 (of FIG. 1 above), to implement a zoom function in depth mapping system #20 (FIG. 1).
The separate power lines feeding the two groups may be implemented either by providing separate power traces to the two groups within a single metal layer of the VCSEL die, or by adding a metal layer, so that each group is fed by a different layer.
The two groups may contain the same or different numbers of diodes, depending on the desired performance characteristics of the system. The image sensor is assumed to support binning of neighboring detector elements (which provides enhanced sensitivity and speed at the cost of reduced resolution), cropping of the sensing area, and adjustable clock rate. These features are offered by various commercially-available image sensors.
In wide-angle mode, one of the two groups of VCSEL diodes (for example, diodes 182) receives power, while the other group is shut off. As a result, the group that is powered on may be driven at high power, to increase the brightness of the individual spots in the pattern, without exceeding the overall power rating of the VCSEL die. (Higher power per emitter is possible because of the increased distance between the active neighboring emitters in this mode, which reduces the associated heating effect.).
Meanwhile, image sensor #42 (FIG. 1) operates in binning mode, and thus forms a low-resolution image of the entire field of view of the system. Because the detector elements of the image sensor are binned, the image sensor can capture and output the image at high speed. The processor measures the transverse shifts of the pattern in this image in order to generate an initial low-resolution depth map.
The processor may segment and analyze the low-resolution depth map in order to recognize objects of potential interest, such as a human body, within the field of view.
The embodiment described above makes optimal use of both the power resources of the VCSEL-based pattern projector and the detection resources of the image sensor. In both, the wide-angle and zoom modes, the scanning speed and sensitivity of the of the image sensor can be adjusted (by binning, cropping, and clock rate adjustment) to provide depth maps of the appropriate resolution, typically at a constant frame rate, such as 30 frames/sec.
Apple's patent application 20180231373 was filed back in Q2 2018.
The patent report that we covered in 2015 showed that Benny Pesach was the sole inventor of this particular invention. In the updated patent, we see that Zafrir Mor was listed as the second inventor who is still listed on LinkedIn as the CSO at Prime Sense in Israel with no reference to Apple. Apple acquired PrimeSense in 2013.
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