Influence and utilization of UV-induced refractive index changes of photopolymers for the fabrication of 3D micro-optical elements

The exposure of UV-sensitive polymers leads to a saturable and irreversible chan ge of the refractive index up to 0.1 due to the polymerization generated changin g material density. This non-linear phenomenon has a strong impact on the struct ure formation in the UV-assisted fabrication of thick micro-optical elements. E. g., appearing self-focusing effects and time-dependent absorption influence the sidewall geometry, while self-guiding effects have impact on the internal index distribution. Based on a material model, which describes the index change as a f unction of a set of process parameters, a modified iterative beam propagation al gorithm is developed to simulate the structure formation. It is shown theoretica lly as well as experimentally that the variation of process parameters, e.g. the photo initiator concentration or the initial complex exposure field distribution, offer possibilities to control the structure formation and to make use of the self-organizing tendency. The developed patteming method is optimized for stand ard contact lithography processes, e.g., in a mask aligner, requiring only low e xposure intensities below 10 mW/cm2. This enables for performing integral wafer- scale patteming processes, e.g., on optoelectronical substrates. The realization of arrayed on-chip conic light concentrators are presented as an exemplary appl ication.