Functional flexible organic–inorganic hybrid polymer for two photon patterning of optical waveguides

The lately in literature described use of two photon based photo processes for producing optical interconnections arises the need of suitable optical functional materials. The present work concerns the development, investigation and processing of a flexible siloxane based organic–inorganic hybrid (OIH) material for the fabrication of optical waveguides for data transmission on printed circuit boards (PCBs). In the developed system the waveguide core is formed by two photon induced photopolymerization (TPIP) of selected monomers, which are dissolved in a polysiloxane matrix. Through the photo induced polymerization an interpenetrating network is generated, resulting in a refractive index change between the non-illuminated waveguide cladding and the illuminated core material. Due to the optical transparency, flexibility and chemical and thermal stability, polysiloxanes were chosen as optical matrix material. Different types of methacrylates with a high refractive index were used as monomers. In order to obtain a high contrast in refractive index, the monomers were removed from non-illuminated regions in a vacuum process after laser exposure. The written optical waveguides were evidenced by phase contrast microscopy, revealing an excellent structuring behavior of the developed material. Optical techniques e.g. cut-back measurements and light extraction tests were applied to characterize the inscribed waveguide structures and to detect the resulting optical loss. Conversion rate of the monomers, which occurred through structuring, was verified by FTIR. To determine the refractive index change upon UV irradiation spectroscopic ellipsometry was applied. As a result of the polymerization, a difference of Δn=0.02 between the non-illuminated cladding and the illuminated core material was detected. Additionally, prototypes of optical interconnects on PCBs were fabricated by inscription of a waveguide bundle between a mounted laser and photo diode, resulting in the desired increase of the transmitted photocurrent after TPA structuring. In conclusion, the obtained results demonstrate that fully flexible optical interconnects are accessible by the developed process.