Bio-inspired metalens extracts depth from defocus

November 08, 2019 //By Julien Happich
metalens
Getting their inspiration from the peculiar optics found in jumping spiders’ eyes, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have devised a metalens that could be used to design a novel type of fast and power-efficient depth sensors.


Top-view SEM image of the right portion of a fabricated
metalens. (Scale bar: 2µm) (C) Enlarged view of the
highlighted region in B, with nanopillars corresponding
to the 2 lens-phase profiles marked with red and blue.
(Scale bar: 500 nm.) (D) Side-view SEM image of the
edge of the metalens. (Scale bar: 200 nm.)

In each of their two principal eyes, jumping spiders sport a multi-tiered retina that simultaneously receives multiple images of a prey with different amounts of defocus, from which they can accurately decode the prey’s distance even with little brain power. Trying to emulate the multi-tiered retina optics, the researchers designed special metalens optics that split the light passing through an aperture, forming two differently defocused images at distinct regions of a single planar photosensor. Using fewer than 700 floating point operations per output pixel, they are then able to interpret the two images and build a depth map to represent object distance.

This depth extraction technique also known as “depth from defocus” is traditionally implemented with large cameras featuring motorized internal components that can capture differently focused images over time. But this cumbersome approach has speed limitations and is compute intensive.


The metalens depth sensor estimates depth by mimicking the jumping spider. It uses a metalens to simultaneously capture 2 images with different defocus, and it uses efficient calculations to produce depth from these images. The images depicted on the photosensor were taken from experiments and show 2 fruit flies located at different distances. The corresponding depth map computed by the sensor is shown on the right (red is closer, blue is farther).


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