Diffractive optical surfaces with spatially variable structures angle

• Applicants: Professor Dr. Ralf Bernhard Bergmann; Professor Dr.-Ing. Ekkard Brinksmeier
• Subject Area: Microsystems
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257419907

For the fabrication of compact and highly functional optical systems, technical surfaces with a complex structure are required. The degree of attainable complexity is given by the degrees of freedom offered by the fabrication process. For the fabrication of diffractive optics, the available degrees of freedom mostly concern the height of the optical element within a limited surface area, often referred to as pixel. The surface angle within that surface area is termed structure angle and is determined by the fabrication process. The structure angle determines the optical functionality of the element to a high degree. Current Methods for a modulation of the structure angle are either restricted to simple geometries or result in a significant increase of fabrication effort and approximation related errors. There is currently no approach that facilitates the exploitation of a direct modulation of the structure angle for the fabrication of complex diffractive optics.Such an approach could yield a new class of optical elements, that modulate both the phase and the phase gradient of wave fields and thereby combine the advantages of diffractive and freeform optics. Because of the unique properties of these optics, systems could be developed that allow beam shaping independent of the temporal coherence of the light source. These structures could e.g. be used as anti-counterfeiting tags that can be verified using the camera of a mobile phone. For laser material processing, they could be used as beam shaping optics, that yield a high reconstruction quality independent of the utilized light source.The goal of the project is the development of the scientific foundations for the realization and utilization of a spatially varying structure angle in a diamond turning process. On the one hand, a fabrication process shall be developed, that allows for the dynamic adjustment of the structure angle in the fabrication process. On the other hand a physical model and design approach shall be developed, that displays the principal and practical boundaries for beam shaping with this new degree of freedom. For the demonstration of the developed methods and models, an optical surface shall be fabricated, that facilitates the formation of predefined intensity distributions at different reconstruction distances. Thereby, a foundation is developed for the realization of an anti-counterfeiting system that allows verification of authenticity with common mobile phones.

• DFG Programme: Research Grants
• Participating Person: Dr.-Ing. Oltmann Riemer