Development of a new fabrication method for stacked optical waveguides using inorganic-organic copolymers

We present a recently developed technology for the stacking of optical waveguides using hybrid inorganic-organic polymers (ORMOCER(R)s). Among advantages with respect to the use of low-cost conventional processing methods (e.g. photopatterning, spin coating), this material system offers high thermal stability and low optical attenuation at telecom wavelengths. The stacking process faces several fundamental problems, such as broadening of the structures during UV patterning or the appearance of index inhomogeneities generated by diffusion effects. In addition, the nonlinear index change of the polymer materials during polymerization has to be considered carefully to ensure defined index distributions in all layers. A solution meeting these requirements, substantially reverting to standard processes, is presented. The key points, an UV absorber method and a combined UV and thermal curing, are investigated in detail. As an example, the realization and test of an optical fanout element composed of four waveguide layers, each with 8 channels of equal path lengths, is shown.