Refractive index change and thermo-optic effect in polydimethylsiloxane nanocomposites with oxide nanoparticles induced by proton beam writing

We studied polydimethylsiloxane nanocomposites with oxides such as TiO₂, SiO₂, and Al₂O₃ aiming at proton beam writing (PBW) of buried optical waveguides. Relatively high transmission was achieved for 1.0 wt% TiO₂/PDMS composite without aggregation. The refractive index can be tunable by varied TiO₂ concentration in nanocomposites. We evaluated refractive index changes by 1.0 MeV proton irradiation. Refractive index of TiO₂/PDMS nanocomposite increased at low fluence of less than 100 nC/mm² and then decreased at higher fluence. On the other hand, we observed monotonic increase of the refractive index as a function of fluence for PDMS and PDMS nanocomposites with SiO₂ and Al₂O₃. We also compared thermo optic effect of PDMS nanocomposites. We evaluated buried optical waveguides in TiO₂/PDMS nanocomposite written by PBW for near field patterns with single mode waveguide.