| The strong light localization and long photon lifetimes in two-dimensional silicon photonic crystal nanocavities with high quality factor (Q ) and subwavelength modal volume (V) significantly enhance the light-matter interactions, presenting many opportunities to explore new functionalities in silicon nanophotonic integrated circuits for on-chip all-optical information processing, optical computation and optical communications. This thesis will focus on the design, nanofabrication, and experimental characterization of both passive and active silicon nanophotonic devices based on two-dimensional high-Q silicon photonic crystal nanocavities. Three topics of controlling light with these high-Q nanocavities will be presented, including (1) photon confinement mechanism and cavity resonance tuning, (2) enhancement of optical nonlinearities, and (3) all-optical analogue to coherent interferences.;The first topic is photon confinement in two-dimensional high- Q silicon photonic crystal nanocavities. In Chapter 2, the role of Q/V as the figure of merit for the enhanced light-matter interaction in optical microcavities and nanocavities is explained and different types of high-Q optical microcavities and nanocavities are reviewed with an emphasis on two-dimensional photonic crystal nanocavities. Then the nanofabrication process and the Q characterization are illustrated for the two-dimensional silicon photonic crystal nanocavities. In Chapter 3, the post-fabrication digital resonance tuning of high-Q silicon photonic crystal nanocavities using atomic layer deposition is proposed and demonstrated, with wide tuning range and precise control of cavity resonances while preserving high quality factors.;The second topic is the enhancement of optical nonlinearities in two-dimensional high-Q silicon photonic crystal nanocavities, including stimulated Raman scattering and thermo-optical nonlinearities. In Chapter 4, the enhanced stimulated Raman scattering for low threshold Raman lasing in the designed high-Q silicon photonic crystal nanocavities are proposed and numerically analyzed through the derived coupled-mode equations, with various contributions on Raman gain, optical losses, and dispersion effects. In Chapter 5, the observation of enhanced optical nonlinearities and optical bistabilities due to the two-photon-absorption induced thermo-optic effect in high-Q silicon photonic crystal nanocavities with both Lorentzian resonances and Fano resonances is presented. The experimental results highlight the ultra-low switching energy, high switching contrast, and the low threshold wavelength detuning for Fano resonances, benefiting from the sharp and asymmetric Fano lineshapes.;The third topic is all-optical analogue to coherent interference phenomena in atomic systems including Fano interference and electromagnetically induced transparency (EIT). In Chapter 5, the optical analogue to Fano interference is studied in an optical system consisting of a photonic crystal nanocavity side-coupled to a waveguide with two partially reflecting elements, where the coherent interference between the discrete energy state and the continuum will give sharp and asymmetric Fano lineshapes, which can be used for low-threshold optical bistable switching with a high switching contrast. In Chapter 6, another coherent interference phenomenon called electromagnetically induced transparency (EIT) is introduced. The deterministic tuning of all-optical analogue to EIT in coherently-coupled silicon photonic crystal nanocavities is demonstrated experimentally. Through thermo-optic tuning of wavelength detuning and phase difference between these coupled nanocavities, the stepwise control of the EIT-like coherent interference is realized. The designed EIT-like optical system is analyzed well through the coupled-mode equations. These results can be used for realization of all-optical stopping of light. |
