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uni'wissen 01-2014_ENG

An imaging system that works like an eye: That is the goal the team at Prof. Dr. Hans Zappe’s lab has set itself. Sebastian Petsch is working on a lens, Stefan Schuladen on an aperture. The researchers are experimenting with liquids and plastics in order to develop a technology that comes closer to functioning like the human eye than was previously possible. The eye reproduces the environment in various light intensities and colors. The essential structures for this are the lens and the iris, which create an image on the retina. The cells of the retina read this image and pass the information on to the brain. People also try to capture images on photos or videos – and their quality is getting better all the time. With technologies like 3D film or Ultra HD tele- vision, the entertain- ment industry is getting closer and closer to a genuine visual experience. The cameras that produce these images also need a lens to focus light and a system to produce a sharp image. As the eye is the visual system we are most familiar with, engineers take it as a model when designing lenses and objectives. “But until now we did not have materials that imitate the movement of the human lens and iris to replicate the physiology of the eye,” explains Zappe, holder of the Gisela and Erwin Sick Chair of Micro-Optics at the Department of Microsystems Engineering (IMTEK) of the University of Freiburg. His team is using the latest microtechnology and flexible materials to develop an imaging system that works like an eye and adapts to different light conditions. In June 2013 Zappa and his PhD students Schuh- laden and Petsch succeeded in constructing an initial prototype of an imaging system of this kind. Rubber Lenses and Liquid Aperture The lens system of the eye consists of the cornea, the lens, and the iris. The lens and the iris adapt to light conditions: Muscles deform the flexible lens and change the focal length, allowing a sharp image to appear on the retina. The iris opens and closes to regulate the amount of light that can pass through the lens. In contrast to this flexible mechanism, cameras and microscopes use hard lenses that slide up and down to set the focus. The aperture assumes the task of the iris. It regulates the intensity of the light allowed to pass through and the depth of field. These com- ponents take up a lot of space. In comparison to professional camera lenses, some of which barely fit into a suitcase, the eye is a remarkably compact structure. The Freiburg researchers have now succeed- ed in imitating the adaptability of the eye in com- pact form with flexible lenses and apertures. The “It was possible to set the sharpness and lighting according to the same principle at work in the eye.” Micromotors change the curvature of the lens by pulling on tiny anchors. This can be used to focus an image. 29