Integrated Hollow-Core Microcavity Arrays - Building Blocks for Optical Sensing and Quantum Information

• Author / Creator

  Bitarafan, Mohammadhossein

• This thesis describes an experimental and theoretical study of a novel class of air-core microcavities on chips, monolithically fabricated by the controlled formation of delamination buckles within a-Si/SiO2-based multilayer thin film stacks. First, arrays of dome-shaped microcavities were fabricated via buckling over circularly patterned low-adhesion films. The stress-driven self-assembly process produces cavities with highly predictable geometries matching with elastic buckling theory. Optical experiments revealed reflectance-limited finesse of >10^3, implying low roughness and minimal defects. These devices were aimed at operating in a fundamental mode regime; thus, mode volumes as low as ~1.3λ^3 and potential for single-atom cooperativity of ~50 were achieved, making this type of cavities an interesting candidate for quantum-optics applications. Next, the viability of providing open-access to the core of the buckled-dome microcavities was explored by fabricating dome-shaped microcavities intersecting with hollow waveguide channels. Optical studies showed that connection to channels had minimal adverse effects on the morphological symmetry of the aforementioned devices, especially at the center where the optical modes reside. This monolithic approach, accordingly, holds promise to enable the introduction of liquid or gaseous analytes into the core of this class of microcavities. The possibility for open-access to the cavity volume, along with good optical properties, makes these cavities good candidates for applications in sensing and cavity quantum electrodynamics (CQED). The buckled upper mirror in the dome-shaped microcavities is inherently a flexible plate, which thus allows interesting options for tuning the resonance wavelength. Hence, comprehensive studies were carried out to analytically and experimentally examine the temperature dependence of the resonance wavelength of the buckled microcavities. Aiming to explore their potential for optomechanical studies, the effective spring constant and mechanical mode frequencies of the buckled domes were also experimentally and theoretically studied. Related to their thermal tunability, absorption by the mirror layers of light circulating inside the core of dome-shaped cavities at or near resonance gives rise to nonlinear effects. For optical input powers in the W range, we observed bistability in the output transmission spectra of the above-mentioned resonators. This behavior, which we showed to arise mainly due to photothermal effects, was studied analytically using first-order approximations, and the predictions were shown to be in good agreement with experimental results. Finally, the buckling process was employed to fabricate a novel class of three-dimensional (3D) microcavities, in which the lateral confinement is provided by Bragg mirrors while axial (in-plane) confinement is provided by mode cutoff sections in the hollow waveguides. The cutoff sections were implemented as back-to-back dual tapers, which can be realized easily using the buckling-based fabrication processes. Optical experiments on numerous dual-tapers confirmed high reflection in wavelength ranges subject to cutoff, and high transmission at shorter wavelengths. Thus, the dual tapers can be used as a novel type of waveguide-based short-pass filter. Additionally, 3D microcavities were fabricated by cascading two dual-taper waveguides. Optical experiments revealed Q > 10^4 along with mode volume ~100λ^3 , which promises a cooperativity of C > 1, making them of great interest in quantum information studies. Furthermore, this approach to forming axially varying hollow waveguides on chips is expected to provide new strategies for controlling the dispersion and confinement of light within optofluidic and CQED systems.

• Subjects / Keywords

  • Integrated Optics, Microcavity

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3416TD01

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.