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Self-organized filamentation of photoresponsive polymers during UV curing
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.