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New wafer-scale fabrication method for stacked optical waveguide interconnects and 3D microoptic structures using photo-responsive (inorganic-organic hybrid-) polymers

: Streppel, U.; Dannberg, P.; Wächter, C.; Bräuer, A.; Fröhlich, L.; Houbertz, R.; Popall, M.


Optical materials 21 (2003), No.1-3, pp.475-483
ISSN: 0925-3467
Journal Article
Fraunhofer IOF ()
stacked polymer waveguide; multilayer polymer waveguide; inorganic-organic hybrid polymer; UV pattering; photosensitivity; vertical integration; non-linear index change; light stability

Integrated optical circuits are one of the key building blocks of present and future telecom and datacom network components. In contrast to the rapid growing demands on an increased number of data transport channels, the integration density of the currently used planar waveguide chips is limited by their lateral dimension. A general approach to overcome this problem is the transition from planar integration schemes towards the third dimension. This requires a suitable technology, which is closely linked to an adapted material system. Considering the various requirements of integrated optical components, a technology for the stacking of optical waveguides is developed using hybrid inorganic-organic polymers (ORMOCERâs). The investigation of the optical and light stability properties of this material system is presented as the essential step for the new stacking technology. In general, ORMOCERâs offer easy access to standard processing methods known from microelectronics and enables, e.g ., a precise definition of the waveguide structures by UV photolithography. A detailed theoretical and experimental investigation of the UV patterning process concerning the non-linear response of the material to the exposure light is done. This is the necessary basis for the fabrication of reliable working waveguide stacks with perfect structure and refractive index homogeneity, substantially reverting to standard processes. The applicability of the newly developed wafer-scale fabrication method is presented by the exemplary realization of a stack composed of four layers of single mode waveguides with a total stack height of 90 µm. Based on the experiences with UV induced local curing of polymers, the potential of a controlled photopolymerization for the realization of complex integrated optical and photonic structures is discussed.