The weak optical nonlinearities of natural materials restrict device sizes in photonic integrated circuits to dimensions far larger than conventional electronics. By exploiting the strong coupling between photons and collective electron oscillations in metals, plasmonics can confine light far below the Abbe diffraction limit. This increased confinement leads to enhanced nonlinear interactions that can be used for a wide range of applications. This thesis examines the integration of plasmonic components into semiconductor photonic architectures in order to utilize the strong light-matter interactions inherent in plasmonics to improve the performance of photonic integrated circuits.

In order to study integrated plasmonic devices, free-space laser light must first be coupled into the optical devices. To this end, a directional plasmonic-photonic coupler was designed to efficiently couple ultrashort pulses on-chip. Then, silicon hybrid gap plasmon waveguides (HGPWs) were studied for their waveguiding properties which includes the transition from photonic-like to plasmonic-like properties depending on gap width. Three-photon absorption photoluminescence in selectively deposited quantum dots showed the viability of these waveguides for extreme nanofocusing, which can be used to enhance light-matter interactions.

With the capability for high light intensities comes the possibility of nonlinear applications such as frequency mixing in the HGPWs. Four-wave mixing (FWM) in these waveguides was thus first explored theoretically and found to be promising, with conversion efficiencies comparable to photonic devices, and with no reliance upon phase-matching or dispersion considerations. The Z-scan measurement technique was utilized to explore organic polymers for the high nonlinearity and low refractive index necessary for plasmonics. Solution processing of such films is also advantageous for integrating the nonlinear material within nanoscopic gaps. Finally, once a suitable nonlinear polymer was found, FWM in the HGPWs was explored experimentally. These findings give further evidence of the capabilities of plasmonics to enable strong light-matter interactions in extremely small volumes.