The Bionic Lense: Inspired by the Human Eye

Our eyes enable us to see in all kinds of situations – near or far, by day or by night. A bionic eye that is every bit as adaptable is currently under development at the Faculty of Engineering of the University of Freiburg: A team of engineers led by Prof. Dr. Hans Zappe from the Department of Microsystems Engineering (IMTEK) is working on a system with a flexible lens and an iris made out of controllable liquids that functions according to the same principle as the human eye.

_{Photo: Universität Freiburg/Gisela-und-Erwin-Sick-Professur für Mikrooptik}

Lenses and apertures are the tools of photographers. Mounted onto the front of the camera, they are responsible for adjusting the focus and the brightness of the photos. Most professional photographic objectives consist of a variety of fixed lenses and apertures. Mother nature, on the other hand, can boast a far more compact and flexible system: the human eye. This optical system enables us to create a sharp image of our environment on the retina. All it needs to accomplish this is one lens and one iris: The lens provides a sharp image and the iris regulates the amount of light allowed to pass through. Prof. Dr. Hans Zappe, holder of the Gisela and Erwin Sick Chair of Micro-Optics at the University of Freiburg, wants to copy this principle. He and his team are using microtechnology and new materials to develop a lens and an iris that work together in a bionic imaging system. The team hopes to have a system for demonstration purposes ready by the end of the year 2014. The demonstration model will then serve as a basis for improving the novel components. The challenge is to find a technology that enables the lens and the iris to move in a similar way to the eye.

A flexible lens

The lens in the human eye focuses the image generated on the retina. This is made possible by a muscle, the ciliary muscle, which changes the shape of the flexible lens. The refraction of the lens changes, causing a different area of the image to appear in focus on the retina. This process is called accommodation. Zappe’s bionic eye is capable of changing its shape too. To accomplish this, the researchers fixed tiny anchors to the lens. Micromotors pull on the lens to flatten it. This reduces the curvature and refraction of the lens, allowing it to focus on objects that are farther away. The photographer can achieve the same effect by rotating the photographic objective on his camera. However, this involves several lenses being moved closer together instead of a single lens being deformed as in the human eye. In the video, the flexible lens is adjusted as the anchors pull on it.

Synthetic muscle fibers

In order to come even closer to nature’s model, the researchers are now working with synthetic muscle fibers for adjusting the lens. Instead of micromotors, they are using so-called liquid crystal elastomers that contract when heated.

A controllable liquid iris

The iris serves as the eye’s aperture: It regulates the amount of light allowed to reach the retina by opening and closing. A ring muscle in the iris reduces the diameter of the pupils in high light conditions. This pupillary reflex inspired the researchers to build an iris-like structure that reduces the size of the aperture by means of moving liquids. Black liquid is fixed in a chamber on electrical contacts. It is surrounded by a clear oil. To change the diameter of the ink ring, the researchers apply an electrical voltage, as shown in the video: The ring becomes wider and allows less light through the middle.

Portrait of the researcher

Prof. Dr. Hans Zappe

hat am Massachusetts Institute of Technology/USA ein Elektroingenieurstudium abgeschlossen und erhielt 1989 die Doktorwürde an der University of California, Berkeley/USA. Anschließend forschte er zu Elektronik, integrierter Optik und Halbleiterlasern beim Technologiekonzern IBM/USA, später am Fraunhofer-Institut für Angewandte Festkörperphysik in Freiburg und am Centre Suisse d’Electronique et de Microtechnique in Zürich/Schweiz. 2000 übernahm er den Lehrstuhl für Mikrooptik am Institut für Mikrosystemtechnik der Universität Freiburg, seit 2012 hat er die Gisela-und-Erwin-Sick-Professur für Mikrooptik inne. Er gründete und betreut das Schwerpunktprogramm „Aktive Mikrooptik“ der Deutschen Forschungsgemeinschaft und, mit Kollegen der Universität Hannover, den Sonderforschungsbereich „Planare optronische Systeme“.

Gallery

The tunable iris and the flexible lens

Photos: Gisela-und-Erwin-Sick-Professur für Mikrooptik


^{The iris}


^{The lense}

Pictures from the lab of Prof. Dr. Hans Zappe

Photos: Mathilde Bessert-Nettelbeck



^{Researchers try different inks to optimize the iris.}	^{They test the lens in an optical lab.}	^{Researchers work on the inks and microelectronic devices to optimize the iris}

More infromations on the "active microoptics" projects of the German Science Foundation can be found here.

In DFG Science TV you will hear and the Freiburg researchers talk about their project.

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