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J. Stampfl, R. Inführ, K. Stadlmann, N.U Pucher, H. Lichtenegger, V. Schmidt, R. Liska:
"Materials for the fabrication of optical waveguides with two photon photopolymerization";
Talk: Fifth International WLT Conference on Lasers in Manufacturing, München (invited); 06-15-2009 - 06-18-2009; in: "Lasers in Manufacturing 2009", A. Ostendorf (ed.); AT Fachverlag GmbH, Stuttgart (2009), P1 - P4.

Two photon photopolymerization (2PP) is an innovative method for 3D-structuring structural and functional materials. 2PP allows the fabrication of sub-micron structures from a photopolymerizable resin. By the use of near-infrared (NIR) lasers it is possible to produce 3D structures with a spatial feature resolution as good as 200 nm. This technique can be used in polymer-based photonic and micro-electromechanical systems (MEMS), for 3D optical data storage or for the inscription of optical waveguides into materials based on a local refractive index change upon laser exposure. Since the 2PP only takes place inside the focus of the laser beam, complex 3D-structures can be inscribed into a suitable matrix material.

In the presented work, 2PP is used to write optical waveguides into a prefabricated mechanically flexible polydimethylsiloxane matrix. The waveguides were structured by selectively irradiating a polymer network, which was swollen by a monomer mixture. The monomer was polymerized by two photon photopolymerization and the uncured monomer was removed by evaporation at elevated temperatures. This treatment led to a local change in refractive index in the order of Δn = 0.02, which was significantly above the industrial requirement of Δn = 0.003. The measured optical losses were around 2.3dB/cm. Since all unreacted monomers were removed by evaporation, the final waveguide was stable up to temperatures of more than 200°C.

Since commercially available one-photon-photoinitiators are only of limited use for 2PP, a new class of photoinitiators (PIs) has been developed. These PIs exhibit a large 2PP-crossection and therefore contribute to a process with higher throughput. The PIs were evaluated using UV-Vis and fluorescence measurements. The TPA-cross-section was determined by the use an open aperture Z-scan technique. In 2PP structuring tests the ideal building parameters for each PI were determined, indicating that the presented PIs can be used at very low concentrations (0.05 wt%).

http://publik.tuwien.ac.at/files/PubDat_175855.pdf

Project Head Jürgen Stampfl:
Herstellung planarer Wellenleiter mit Zweiphotonenpolymerisation