Complex micro optical systems out of the 3D printer
Using the additive manufacturing method developed by the Stuttgart research team, optical free form surfaces can be created with sub-micrometer accuracy. The precision of the 3D laser writing allows not only for construction of conventional spherical lenses, but also the more ideal surfaces such as paraboloids or aspheres of higher order are possible. In particular, this method allows implementing optical lens systems with two or more lenses, opening the door to aberration correction and micro-optical imaging systems with unprecedented quality.
PhD student Timo Gissibl in the group of professor Harald Giessen at the University of Stuttgart printed micro-objectives with a diameter and height of only 125 µm, even on optical fibers. This permits the construction of novel and extremely small endoscopes for medical and industrial applications – such endoscopes are suited for smallest body openings or machine parts that can be inspected. The optical design was realized in the Stuttgart Research Center for Photonics Engineering by Ph.D. student Simon Thiele from the group of professor Alois Herkommer at the Institute of Technical Optics in Stuttgart.
Timo Gissibl also succeeded in printing optical free form surfaces and miniature objectives directly onto CMOS image chips, which thus create an extremely compact sensor. Using such optics, smallest cameras from drones, not larger than a bee, are possible. Also, extremely small sensors for autonomous cars and robots are conceivable. Even smallest body sensors and surround-cameras for cellphones could be created with this method.
The researchers were also able to combine their optics with illumination systems. Optics on an LED, which concentrates light in a certain direction, can thus be extremely small. Additionally, illumination of ring-shaped areas, triangles, or elongated rectangles can be realized with such miniature free-form optics.
The femtosecond laser used to print the microscopic lenses features pulse durations smaller than 100 femtoseconds. It is being focused in a microscope into liquid photoresist which rests on a glass substrate or an optical fiber. Two photons of the 785 nm laser beam (red) are being absorbed simultaneously in the focus and expose the photoresist, causing the polymer to crosslinks and harden. The laser beam is directed with a scanner or by moving the substrate over the substrate. After exposure, the unexposed photoresist is washed away with a solvent. Only the hardened transparent polymer remains and forms the optical element.
3D printing of optics is going to open an entire new ear of optics manufacturing, the researchers believe. “The time from the idea, the optics design, a CAD model, to the finished, 3D printed micro-objectives is going to be less than a day”, says Giessen. “We are going to open potentials just like computer-aided design and computer-integrated manufacturing did in mechanical engineering a few years ago”.
The project was supported by Baden-Württemberg Stiftung foundation. Karlsruhe-based startup Nanoscribe designed the highly precise femtosecond 3D printer.
For more information, contact Prof. Dr. Harald Giessen (giessen@physik.uni-stuttgart.de ).
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Sub-micron features out of the 3D printer
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