As their paper “Xenos peckii vision inspires an ultrathin digital camera” suggests, the researchers got their inspiration from paper wasps’ endoparasite Xenos peckii, whose compound eyes are unlike those of most insects and crustaceans. Distributed at the periphery of its compound eyes, each of the endoparasite’s eyelets (or optical units) consists of a relatively large convex facet lens backed with over a hundred photoreceptor cells. Through their 3D spatial distribution and orientation, each such optical unit detects part of the overall field-of-view FOV, but with improved spatial resolution and sensitivity compared to other compound eyes only sporting one or few photoreceptor cells per eyelet.
Now, in order to translate these attributes into a compact physical design, the researchers sandwiched multiple concave microprisms and microlenses combined with pinhole arrays on a flat image sensor. In this setup, the light path for each microprism playing the role of an eyelet is focused across multiple pixels playing the role of the photoreceptors).
Rather than being restricted by a lithography-friendly planar configuration with a limited field-of-view, the authors opted for an inverted spherically-shaped artificial compound eye design which they report could easily be manufactured through only a few imprinting and lithography steps.
The artificial eyelet demonstrated in the paper features a single concave microprism (designed through ball lens imprinting and backside lithography) to tilt the optical axis, a single microlens to focus light from the microprism, an aperture to block light from adjacent channels, and black polymer surrounding each channel to reduce optical crosstalk.
Multiple design parameters such as the inter-eyelet spacing and viewing angle overlap, the microprism’s radius of curvature, the microlens’ focal lens and the diameter of the bottom aperture can be tuned to optimize the camera’s specification, notably its field of view and the overlap viewing angle between neighbouring channels. All these parameters can also be used to improve image resolution during the image reconstruction process. In the proof-of-concept implementation, each microprism channel was about 100μm in diameter, backed by a large number of 1.75×1.75μm pixels on a 2Mpixel sensor.
The honeycomb-packed concave hexagonal microprism and microlens plates were fabricated separately and stacked over a conventional CMOS image sensor, yielding a tiny camera only 3.4mm in diameter, 1.4mm high and capable of high-resolution imaging with a 68º field-of-view.
Unlike other large field-of-view cameras which leverage multiple and often bulky lenses along their optical axis to compensate for optical aberrations, the bio-inspired camera operates as is. The authors expect such ultrathin digital cameras to find their way in compact imaging systems for surveillance and reconnaissance instruments, medical imaging apparatuses, mobile devices, and other optical sensors.
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