Integrated Silicon-Based Photonic, Acoustic and Optomechanical Devices

Integration of photonic and other types of micro- and nanoscale devices in silicon and silicon- based material platforms allows one to leverage existing large-scale wafer-based manufacturing infrastructure and tools developed for the integrated circuit (IC) industry. This thesis explores chip- scale silicon photonic structures that include physical contacts that are intimate with the optical field, evanescent confinement of acoustic waves using slowness contrast silicon-based materials, and the implementation of optomechanical devices in monolithic CMOS microelectronics platforms. The unifying objective of this work was to make progress toward photonic and optomechanical devices that are densely integrable on chip, and potentially also monolithically with state-of-the- art transistors, in optical and optomechanical circuits.Loss avoidance in photonic structures with contacts is designed and explained using a novel mechanism, imaginary coupling of modes. Periodic contacts are treated as an index perturbation and designed to radiatively couple two eigenmodes of the unperturbed structure, so as to construct a low-loss supermode with a field distribution pattern that “avoids” the contacts. Using this concept, a linear waveguide crossing array and a circular “wiggler” resonator are designed and experimentally demonstrated. The “wiggler” resonator is further suspended while sustaining a high quality factor above 100,000.Evanescent confinement and guiding of elastic waves on chip based on material contrast is investigated theoretically in the context of silicon-based materials, as an alternative to confining acoustic waves using air-solid interfaces in suspended structures. Calculations of material intrinsic and radiation losses suggest that compact wavelength-scale acoustic/phononic devices can be built on chip to form complex circuitries.Combining optics and acoustics, optical forces and integration of suspended optomechanical devices in CMOS microelectronics processes are explored. Waveguide design to maximize static radiation pressure in a vertically coupled dual ring structure, and the initial design of an optome- chanical “wiggler” resonator are discussed. Post processing steps to suspend devices fabricated in an unmodified CMOS microelectronics process are proposed with current experimental progress presented

On-chip nano-optomechanical whispering gallery resonators

This thesis work focuses on the design, fabrication and measurement of Gallium Arsenide (GaAs) nano-optomechanical disk resonators. These disks are both GHz frequency mechanical resonators, and high Q (>10^5) optical whispering gallery mode resonators. By confining optical and mechanical energy on a sub-µm^3 volume, they enable extremely large optomechanical coupling strengths (g0>1 MHz). We present the technological developments which enabled the integration of these resonators with optical coupling waveguides directly on a semiconductor chip, while maintaining state of the art performance. We discuss the different optomechanical coupling mechanisms (radiation pressure, photoelasticity) in GaAs disks, as well as the sources of optical and mechanical dissipation in these resonators. We present as well optomechanical experiments in air and in a cryostat at low temperature, which go from the measurement of Brownian motion and the observation of dynamical back-action, to the first attempts to approach the quantum regime of mechanical displacement. Finally, we present an additional nano-optomechanical development carried out on the silicon nitride (SiN) platform, which lead to the fabrication of high Q on-chip whispering gallery mode resonators. After the study of the optical instability and self-pulsing dynamics of these resonators, we present the first signatures of dissipative optomechanical coupling in these systems

Entropy Generation and Thermoelastic Damping in the In-plane Vibration of Microring Resonators

Thermoelastic damping is a critical issue for designing very high quality factor microresonators. This paper derives the entropy generation, associated with the irreversibility in heat conduction, that is used for ring resonators in in-plane vibration and presents an analytical model of thermoelastic damping according to heat increments calculated by entropy theory. We consider the heat flow only in radial thickness of the ring and obtain a complex temperature field that is out of phase with the mechanical stress. The thermoelastic dissipation is calculated in the perspective of heat increments that appear due to entropy generation. The analytical model is validated by comparing with an LR (Lifshitz and Roukes) model, finite-element method and measurement. The accuracy of the present model is found to be very high for different ambient temperatures and structures. The effects of structure dimensions and vibration frequencies on entropy generation and thermoelastic damping is investigated for ring resonators under in-plane vibration