Beschreibung
Printing of optical waveguides is an approach to large-volume implementation of optical data transmission in
conventional electronic systems. Flexographic printing can be used to apply optical waveguides with circular-segment cross-sections to planar substrates. In this work, a concept for integrating printed optical waveguides into printed circuit boards (PCBs) is investigated, taking the requirements of industrial processing into account. A planar waveguide structure model is defined that is applicable to lamination processes used in PCB manufacturing. Due to thermal stress on the substrate during this process, polymer waveguides are printed on polyimide (PI) substrate. To ensure optical functionality, matching refractive indices in the form of printed cladding structures are required. Manufacturing multilayer waveguide structures requires new processes for generating the end facets of the waveguide core. To reduce the attenuation caused by optical coupling, one primary requirement is low facet roughness. In this paper, we present a way to flexographic print fully cladded waveguides on PI substrates. Different waveguide layer compositions are characterized with respect to their geometry by confocal measurements. Milling with monocrystalline diamond cutters is presented as a method for preparing the end facets. Finally, the attenuation of the prepared waveguides is measured and discussed as a function of the waveguide and end facet properties. By this, flexographic printed and ready-to-integrate waveguides are achieved, approaching the target of optical PCBs.
