Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Milos A. Popovic

Second Advisor

Juliet T. Gopinath

Third Advisor

Wounjhang Park

Fourth Advisor

Kelvin H. Wagner

Fifth Advisor

Anatoly Khilo

Abstract

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.

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