ECE PhD Thesis Defense: Tornike Shubitidze

ECE PhD Thesis Defense: Tornike Shubitidze

Title: Developing Optical Materials and Devices for Nonlinear Nanophotonics on the Si Platform

Presenter: Tornike Shubitidze

Advisor: Professor Luca Dal Negro

Chair: Professor David Lake

Committee: Professor Luca Dal Negro, Professor Anna Swan, Professor Enrico Bellotti, Professor Sahar Sharifzadeh.

Google Scholar: https://scholar.google.com/citations?user=ljgmMZkAAAAJ&hl=en&oi=ao

Abstract: Nonlinear optical devices represent a frontier in modern photonics, enabling transformative capabilities in frequency conversion, signal processing, and quantum information. This dissertation investigates the use of epsilon-near-zero (ENZ) materials nanostructures to bypass the efficiency limitations of traditional dielectric systems. Central to this work is the nonlinear response of Indium Tin Oxide (ITO) at its ENZ point, where the vanishing permittivity leads to an intrinsic enhancement of the longitudinal electric field (Ez). We first demonstrate the integration of ITO nanolayers within 1D Silicon Dioxide/Silicon Nitride (SiO2/SiN) Tamm Plasmon-Polariton (TPP) structures. In these resonant systems, we report a record-high refractive index modulation of ∆n ≈ 2 and a > 100× enhancement in harmonic generation efficiency at exceptionally low pump intensities. To further manipulate these interactions, we explore hybrid TPP-microcavity systems using non-hermitian coupled mode theory approach. By tuning the spacer layer thickness, we achieve a transition from weak to strong coupling, resulting in hybridized polaritonic states with characteristic anti-crossing behavior. Furthermore, utilizing Rigorous Coupled-Wave Analysis (RCWA), we design hybrid TPP microcavity nanostructures with multiple ultra-high q resonances along with photonic crystal lattices in both square and triangular geometries with embedded ITO nanolayers. These structures support Bound States in the Continuum (BICs), enabling extreme light localization robust across both s- and p-polarizations. By embedding ITO nanolayers within these high-localization environments, we achieve significantly enhanced second-harmonic (SHG) and third-harmonic generation (THG). A key contribution of this work is the momentum-resolved characterization of these signals via k-space imaging allowing for the direct visualization of nonlinear emission channels and confirms that the enhancement stems from the combination of BIC-mediated confinement and the field enhancement at the ENZ transition. This research provides a scalable platform for high-efficiency nonlinear frequency converters and ultra-sensitive integrated photonic sensors. Finally, we demonstrate light emission enhancement in aperiodic photonic membranes with multifractal and hyperuniform isotropic pinwheel structures and explored their impact for enhanced harmonic generation and wave localization phenomena.