Silicon photonics is a subject of growing interest with the potential of delivering planar electro-optical devices with chip scale integration. The past ten years have provided new developments in this area including novel devices utilizing the linear, nonlinear, and semiconductor behaviors of silicon. This thesis is dedicated to the investigation of nonlinear properties of silicon relevant to chip scale planar optical devices. In particular, this thesis is focused on utilizing silicon nonlinearities to demonstrate ultrafast pulse generation, ultrafast pulse characterization, and wavelength conversion suitable for long wavelength applications.

One of the impediments of silicon photonics is the presence of nonlinear losses. Indeed, nonlinear losses mitigate the development of silicon based laser and amplifiers. The first part of this research investigates the transient behavior of these nonlinear losses, two photon absorption (TPA) and free-carrier effects, and utilizes them for ultrafast pulse generation and mode-locking. Particular achievements include identification of the dominant nonlinear losses and demonstration of mode-locked lasers. As an extension of this research, a dual-wavelength laser is demonstrated using Raman scattering in silicon.

In the second part of this work, a chip-scale pulse characterization method utilizing Kerr nonlinearity in silicon is established and a pulse retrieval algorithm is optimized for chip-scale devices. This is the first frequency resolved optical gating (FROG) system demonstrated in silicon, which shows the ability to measure ultrafast pulses without the phase matching requirement. With the short interaction length and the low dispersion, dispersion engineered waveguides can improve the resolution over a wide bandwidth.

In the last part of this thesis, wavelength conversion capability via four-wave-mixing at mid-infrared (2μm-6μm) is investigated since TPA is negligible for wavelengths beyond 2ìm. In particular, Kerr effect and waveguide design are studied to accomplish wavelength conversions in mid-infrared. Since conventional cladding material, silica, is opaque in mid-infrared, the needs for new waveguide designs and new materials are highlighted and the potential candidate materials are studied. The study shows that silicon-based wavelength conversion can increase the capabilities of mid-infrared application by converting the mature detection and source at communication wavelengths to mid-infrared wavelengths.