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Self-organized filamentation of photoresponsive polymers during UV curing

: Streppel, U.; Michaelis, D.; Bräuer, A.


Grote, J.G. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Organic photonic materials and devices V : 27 - 30 January 2003, San Jose, California, USA
Bellingham/Wash.: SPIE, 2003 (SPIE Proceedings Series 4991)
ISBN: 0-8194-4791-9
Photonics West <2003, San Jose/Calif.>
Conference Paper
Fraunhofer IOF ()
filamentation; UV curing; self-organization; modulational instability; refractive index change

The exposure of thick UV sensitive polymer layers leads to the formation of self -organized refractive index filaments, which appear after a certain layer thickn ess, typically in the range of 50 gm. This effect has strong influence on the fa brication of, e.g., high precision micro-optical elements. In particular, diffra ction limited micro-lenses with high sag or high aspect ratio on-chip collimator s require a perfect index homogeneity. We show that the saturable and irreversib le change of the polymer refractive index causes a modulational instability (MI) , which finally leads to the creation of filaments. It will be presented that a maximum growth rate for a certain spatial frequency of an initial perturbation e xists. This MI gain determines the dynamics of the filament formation. The impac t of the exposure conditions, e.g., chemical process parameters, on the homogene ity of the UV cured polymer is discussed for ORMOCER TM type polymers.