Characterization of attenuation and reliability of PCB integrated optical waveguides

Ever-increasing bandwidth demands are generally understood to be the incentive for increasing clock rates. Optical interconnects offer distinct advantages for transmission of data rates higher than 10 Gbit/s. Consequently, future printed circuit boards will be hybrid devices comprising electrical functions and optical waveguides. This thesis surveys existing technologies and materials for fabrication of optical waveguides and evaluates them with respect to their capability for printed circuit board integration. Of these approaches the waveguide-in-copper technology receives particular attention, as most tests within this thesis have been performed on samples of this in-house technology. This technology has been developed as collaboration between the Electronics Packaging Laboratory from TU Dresden and the Fraunhofer Institute for Reliability and Microintegration (Institut für Zuverlässigkeit und ikrointergration - IZM, Berlin). The optical attenuation of these highly multimode waveguides is an important quality characteristic, while its repeatable determination proves to be a challenge. The doctoral thesis at hand is a contribution to the improved repeatability of attenuation measurements of PCB integrated waveguides, by introducing an imaging measurement technique. A dedicated set-up for automated attenuation measurement has been developed and a specific dichromic laser source for single-mode and multimode launching has been designed. On the basis of this state-of-the-art experimental set-up for the characterization of integrated (highly) multimode waveguides detailed investigations on coupling conditions, dependence on immersion and launching with different sources have been realized. Two large scale reliability tests have been performed for the waveguide-in-copper technology. The high temperature storage at 125◦C, which is below thermal curing onset, led to a deterioration of the attenuation, but the waveguides remained functional beyond one month duration. For the 85/85 test on the other hand one observed an increase after 120 h and after 300 h already all waveguides failed. The results of this thesis are well suited to concretize future standardization attempts for the characterization of integrated waveguides.