You can see better with facets
A synthetic plastic eye, which looks confusingly like a real insect eye even under the microscope, promises a full all-round view. And it is relatively easy to manufacture - the most difficult processes are carried out by the material itself.
He who is on the menu of many enemies should have his eyes everywhere. In accordance with this maxim, insects have developed an optical apparatus with which they can look ahead and behind at the same time and can recognize flowers, prey and nearby movements at lightning speed: the compound eye. It is composed of hundreds or thousands of individual units - so-called ommatidia - which together provide a picture of the environment. A true marvel of nature that, with its tiny dimensions, makes the technical optics of humans look like coarse glassware.
But humans are ambitious and sometimes clever. For a long time it was believed that it was practically impossible to build an artificial compound eye, but this has now become reality. The bionicists Ki-Hun Jeong, Jaeyoun Kim and Luke Lee from the University of California at Berkeley have developed astonishingly precise compound eyes that closely resemble the natural models - even under the microscope.
Perhaps the most surprising thing about the work of the three scientists is how easy it is to manufacture the filigree product – once you know how. After all, the task is to produce lenses with a diameter of around 25 micrometers – thousandths of a millimeter – which are connected to a light guide of up to 300 micrometers in length. The relative arrangement to each other must be so precise that as little light as possible is lost. If you have several thousand of these artificial ommatidia together, they have to be aligned in such a way that they direct their light to a detector in an orderly manner. Anyone who has ever taken the trouble to load a cheese hedgehog evenly for a party can imagine the difficulties this causes on a scale of 1:10,000.
Lee's team therefore chose a slightly different approach. They began by constructing the overall eye and then had the light drill its own circuit paths. To do this, they used existing microtechnology tools to create a honeycomb layer of tiny lenses, which they covered with an elastic polymer. The lenses pressed into the plastic, which was then drawn into the desired semicircular shape using a vacuum. This was the form in which any number of resin casts could be made.
The decisive trick in further production was the way the resin hardened. Ultraviolet light, which was directed onto the blank with a conventional large lens, served as the initiator of the process. The light refracted at each of its elevations like a microlens and focused itself in the resin. The material polymerized as a result of the irradiation, changed its refractive index and formed a kind of light guide that exactly matched the geometry of the respective microlens. The researchers then only had to thermally crosslink the non-exposed resin in a different way and thus fix the state achieved.
The result is a complex eye made of 8370 individual lenses, each with a diameter of 25 micrometers and an individually adapted light guide of 150 to 300 micrometers in length - technical data that correspond almost exactly to a bee's eye, which, however, only comprises up to 4900 ommatidia.
What the artificial eyes still lack is the receptor at the end of the light guide. Here the scientists are thinking of electronic CCD sensors, such as those used in digital cameras. Or spectroscopes, which break down the incident light into its wavelength components and can analyze them in this way.
The most difficult part of a micro complex camera is the optics. Once the whole device is complete, it will provide new insights in a variety of areas. In medicine, for example, it could provide images of areas inside the body that are simply too narrow for ordinary endoscopes. With its all-round view, it is ideal for surveillance tasks, and of course the military has their own ideas of where they would like to look. Compound eyes do their job in peaceful mayflies as well as in predatory wasps. In an emergency, the only thing that helps is a targeted blow with the rolled-up newspaper – then privacy is restored.
