A biologically inspired artificial eye

Peters’ elephantnose fish inhabits muddy, vegetation-covered rivers in west and central Africa. Although the fish relies on electrolocation to navigate and to find food, its weak eyes have evolved a distinctive sensitivity-enhancing mechanism. Between the eye’s transparent inner retina, which receives light focused by the lens, and the photoreceptors, which convert light into neural impulses, lies a closely packed array of crystalline microcups. Because of their reflective inner surfaces, the microcups concentrate light onto the photoreceptors, thereby boosting sensitivity. Hewei Liu, Yinggang Huang, and Hongrui Jiang of the University of Wisconsin–Madison have designed and built a marble-sized artificial eye that uses a similar mechanism. The eye’s 6-mm-diameter ball lens focuses light onto a 48 × 48 array of glass microcups that lines a retina made from a transparent polymer and coupled to a CMOS imager. The light enters a microcup through the 77-μm-diameter front aperture and continues to the 20 μm rear aperture either by passing straight down the 120 μm length of the microcup or by reflecting off the aluminum-coated parabolic sides. To make the microcups, Liu, Huang, and Jiang used a computer-controlled laser to cut the entire array from a single piece of glass. After sputter coating the array with aluminum, the researchers etched away the back of the substrate until it was thin enough to flex and conform to the eye’s spherical retina. Compared with an otherwise identical eye that lacks the array, the fish-inspired eye boosts the photosensitivity by a factor of about three across a waveband that extends from 400 nm (violet) to 900 nm (near-IR). (H. Liu, Y. Huang, H. Jiang, Proc. Natl. Acad. Sci. USA, in press, doi:10.1073/pnas.1517953113 .)