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Poling study of electro-optic polymers in silicon slot waveguides

Silicon slot waveguide based Mach Zender interferometric modulators were built with electro-optic (EO) polymers in the slot as the modulated media. In order to enhance the macroscopic electro-optic effect in the polymers the molecules that provide the large polarizability need to be aligned prior to operation to match the direction of the applied modulating field. This aligning process, also called as poling process, is difficult in the slot waveguide modulators due to the unique structure and small dimensionality of the slots in the waveguides. While hybrid silicon-EO polymer modulators have been demonstrated with ultra low drive voltage, the polymer EO activity was low compared to thin film performances. We compared alternatives to enhance the poling field over the electro optic polymer and concluded that the well known surface states in silicon affect the conductivity of silicon significantly when thin silicon is used as poling electrode. A solution to this negative effect was attempted by passivating the surface with a 5 nm thin TiO2 conforming atomic layer deposition over the silicon prior to spin casting and poling the EO polymers. We achieved a factor of 2 enhancement in the polymer's electro optic activity after poling as a result and achieved a low 0.52 V*cm voltage length product in the MZ modulator we built with this technique.