The theoretical background of microcavities for photonic applications has been extensively investigated in theory over the past two decades. These structures provide the ability to filter wavelength, support high-Q modes and enhance intensity within the cavities while maintaining a small device footprint. Such characteristics make these structures good candidates to optimize performance and shrink the size of devices for both linear and nonlinear optics. However, recent advancements in silicon-based fabrication technology provide access to dopants for active control, material layers such as germanium and silicon nitride, and 3D-integration technologies that were previously exclusive to electronics development, leading to tremendous progress in cavity-based integrated photonic circuits.
Using the silicon photonic platform developed by our group, high-performance microcavity-based structures have been demonstrated for optical signal routing, detection, and lasing applications. We first introduce partial-drop filters and present results using them to achieve a highly uniform wavelength-division-multiplexing (WDM) compatible optical multicast system. We then implement a waveguide-coupled resonant detector using a germanium layer grown on top of the silicon. In addition to having low dark current and high-speed performance, the resonant detector extends the wavelength detection range beyond 1620nm while maintaining a device radius only 4.5µm. Furthermore, an easy-to-fabricate waveguide-coupled trench-based Al2O3 microcavity is presented, achieving a Q-factor on the order of 106 with a bend radius on the scale of 100µm. Compact on-chip rare-earth-ion (ytterbium, erbium, thulium) doped Al2O3 lasers were then demonstrated with sub-milliwatt lasing thresholds, showing the suitability of trench-based cavity platform for achieving optically pumped on-chip lasers.
Prof. Erich P. Ippen
Prof. Qing Hu
Prof. Michael R. Watts (Thesis Supervisor)