Digital cameras with designs inspired by the arthropod eye

In today's (May 2) issue of Nature, we report a recent achievement in applying mechanics principles of stretchable electronics and optics to create biologically inspired artificial compound eye cameras. It was also highlighted in the Nature News & Views, "Optical devices: Seeing the world through an insect's eyes".

In arthropods, evolution has created a remarkably sophisticated class of imaging systems, with a wide-angle field of view, low aberrations, high acuity to motion and an infinite depth of field. A challenge in building digital cameras with the hemispherical, compound apposition layouts of arthropod eyes is that essential design requirements cannot be met with existing planar sensor technologies or conventional optics. Here we present materials, mechanics and integration schemes that afford scalable pathways to working, arthropod-inspired cameras with nearly full hemispherical shapes (about 160 degrees). Their surfaces are densely populated by imaging elements (artificial ommatidia), which are comparable in number (180) to those of the eyes of fire ants (Solenopsis fugax) and bark beetles (Hylastes nigrinus). The devices combine elastomeric compound optical elements with deformable arrays of thin silicon photodetectors into integrated sheets that can be elastically transformed from the planar geometries in which they are fabricated to hemispherical shapes for integration into apposition cameras. Our imaging results and quantitative ray-tracing-based simulations illustrate key features of operation. These general strategies seem to be applicable to other compound eye devices, such as those inspired by moths and lacewings (refracting superposition eyes), lobster and shrimp (reflecting superposition eyes), and houseflies (neural superposition eyes).

Mechanics has been critically important for this development. Since both the elastomeric optical element and silicon photodetector arrays were fabricated at planar geoetries and transformed to hemispherical shapes, very large strains are introduced into these arrays. Mechanics was the key to ensure that strains introduced don't affect the optics and electronics of the optical elements and silicon photodetectors, respectively. Here, we used strain isolation design to make the optics system stretchable. Each microlens element was sitting on top of an elastomeric pedestal, and then integrated onto a continuous elastomeric sheet. In such a design, the strains introduced in the elastomeric sheet cannot be effectively transferred into the microlenses, and the pedestals served as "strain isolation" layer. For the silicon photodetector array, a mesh layout design of isolated photodetectors interconnected by serpentine metal bridges was used to ensure maximal stretchability in the electronic system.