On Tuesday, the U.S. Patent and Trademark Office officially granted Apple a patent that relates to a possible next generation technology for applications such as Face ID. Apple’s current form of Face ID uses diffractive optical element (DOE) technology whereas in the future, Apple may use “metasurface optical elements” (MOEs).

MOE-based Illumination Projector

Apple’s Face ID uses  project patterned radiation (spot illumination) so as to illuminate the target region with a pattern of spots for three-dimensional (3D) mapping of the region. Apple’s granted patent suggests that the company could adopt a more advanced methodology for Face ID in the future based on a MOE-based illumination projector.

Structured light projectors that are used to project patterns of spots in portable devices typically comprise at least two separate optical elements: a diffractive optical element (DOE), which splits each of the beams emitted by an array of light sources into multiple sub-beams, and a collimating lens, which projects the beams to form a corresponding pattern of spots on a target. (The order of the elements may be reversed, with the collimator before the splitter.) Although projectors of this sort have been made compact enough to fit into a smartphone, there is a need for still more compact designs.

The patent address using “metasurface optical elements” (MOEs) which combines both beam splitting and collimation capabilities in a single, flat element.

The patent provide Figures of optoelectronic apparatus comprising a pattern projector, which comprises an array of emitters, which emit beams of optical radiation, and an MOE mounted over the array.

The MOE comprises an optical substrate with an optical metasurface, which both collimates and splits each of the emitted beams into a respective group of collimated sub-beams, and directs the collimated sub-beams toward a target to form a pattern of spots on the target. Combining the projector optics into a single MOE not only reduces the size and cost of the pattern projector, but also simplifies assembly and reduces the sensitivity of the design to fabrication errors, relative to designs using multiple optical elements.

In some embodiments, that apparatus also comprises a camera, which captures images of the part of the target that falls within its field of view (FOV). As the axis of the pattern projector is typically offset transversely relative to the camera, it is desirable that the direction of the projected pattern be tilted toward the camera axis to increase the overlap between the area of the pattern and the FOV of the camera. In this way, the same MOE simultaneously applies an angular tilt to the projection axis relative to the camera axis (in addition to its collimation and beam splitting functions), so that the pattern of spots extends across the FOV.

A controller actuates the two arrays of emitters separately, so the FOV of the camera may be alternately illuminated by spot illumination and by flood illumination.

(Click on image to Enlarge)

Apple’s patent FIG. 1 above is a schematic side view of an optoelectronic apparatus #100 that comprises of a camera #102, a projection module (source of optical radiation) #104, and a controller #106. The camera captures an image of a target #108 over a field of view (FOV #110). Under the control of the controller, the projection module emits either multiple beams #112 of optical radiation, illuminating FOV #110 with a pattern of spots #114, or a homogeneous beam #116 of flood illumination projected toward the FOV. Both beams and homogeneous beam are tilted toward FOV in order to provide full coverage of illumination to the FOV.

FIG. 2 is a schematic side view of an optoelectronic apparatus #150 comprises a camera #152, a projection module #154, and a controller #156. The apparatus is similar to apparatus in FIG. 1, with the exception that a tilt is applied to the imaging optics of the camera, for example by incorporation of a suitable MOE in the imaging optics, rather than in the projection module.   

FIG. 6 is a schematic frontal view #502 of a portion of spot MOE #208.

For full details, review Apple’s granted patent 12313812.