Optomechanical Coupling in Suspended Photonic Crystal Edge Defect Devices
Abstract
Silicon photonics, despite its rapid advancement and competitive edge in various high-performance applications, faces inherent challenges for integrating nonlinear components caused by two-photon absorption (TPA) and inefficient phase modulation mechanisms. These limitations restrict its broader application in large scale systems like quantum computing, optical switching, and phased arrays, where high-speed, efficient, and small components are needed. This thesis explores the use of photonic crystal edge defects to help address this using optomechanical coupling. It focuses on two primary applications: the generation of an optical frequency comb and the demonstration of a scalable phase tuner. Optomechanical coupling (OMC) offers a promising avenue to overcome the challenges mentioned above. In the strong coupling regime, OMC can facilitate the generation of optical frequency combs with MHz line spacing, a phenomenon that holds significant potential for applications in high-resolution spectroscopy, precision metrology, and RF photonics. However, demonstrating these combs has been challenging due to stringent low-loss requirements. Photonic crystal edge defects are a promising platform offering strong OMC and the potential to harness other nonlinear effects. This thesis demonstrates an optomechanical frequency comb with 33 MHz spacing. The comb was observed for a photon-phonon cooperativity, the ratio of coupling strength over system loss, of 0.088 which is to the author's knowledge the lowest reported to date. In the weak coupling regime, optomechanical phase tuners present an opportunity by providing compact, low-power alternatives to existing the phase tuning methods of thermo-optic and free-carrier dispersion. These approaches are often limited by speed, power consumption, or scalability. A novel, compact optomechanical phase tuner enhanced by a slow light edge defect waveguide was developed in this work. Measurements demonstrated a $V_{\pi}$ phase shift down to 0.75 V while maintaining a large, 200 nm feature size. In addition to the above two applications, this thesis addresses the practical challenges of designing and fabricating optomechanical silicon photonic devices. Particularly, fabrication challenges when integrating electrical components into optomechanical devices and the modelling challenges of fluid damping in dynamically driven devices with nanoscale features. The research results demonstrate the viability of photonic crystal edge defects for both optomechanical frequency comb generation and phase tuning, marking a significant step forward in the commercial scalability of silicon photonics for advanced applications.