Engineering Aperiodic Spiral Order for Photonic-Plasmonic Device Applications
Committee Members: Advisor: Luca Dal Negro, MSE/ECE; Anna Swan, MSE/ME; Siddharth Ramachandran, IMSE/ECE; Enrico Bellotti, MSE/ECE; Appointed Chair: JC Bird, MSE/ME
Abstract: Deterministic arrays of metal (i.e., Au) nano-particles and dielectric (i.e., Si and SiN) nano-pillars arranged in aperiodic spiral geometries (Vogel’s spirals) have been introduced as a novel platform for engineering enhanced photonic-plasmonic coupling and increased light-matter interaction over broad frequency and angular spectra for planar optical devices. Vogel’s spirals lack both translational and orientational symmetry in real space, while displaying continuous circular symmetry (i.e., rotational symmetry of infinite order) in reciprocal Fourier space. The novel regime of “circular multiple light scattering” in finite-size deterministic structures has been investigated. The distinctive geometrical structure of Vogel spirals has been studied by a multifractal analysis, Fourier-Bessel decomposition, and Delaunay tessellation methods, leading to spiral structure optimization for novel localized optical states with broadband fluctuations in their photonic mode density. Experimentally, a number of designed passive and active spiral structures have been fabricated and characterized using dark-field optical spectroscopy, ellipsometry, and Fourier space imaging. Polarization-insensitive planar omnidirectional diffraction has been demonstrated and engineered over a large and controllable range of frequencies. Device applications to enhanced LEDs, novel lasers, and thin-film solar cells with enhanced absorption have been specifically targeted. Additionally, using Vogel spirals we have investigated the direct (i.e. free space) generation of optical vortices, with well-defined and controllable values of orbital angular momentum, paving the way to the engineering and control of novel types of phase discontinuities (i.e., phase dislocation loops) in compact, chip-scale optical devices. Finally, we report on the design, modeling, and experimental demonstration of array-enhanced nanoantennas for polarization-controlled multispectral nanofocusing, nanoantennas for resonant near- field optical concentration of radiation to individual nanowires, and aperiodic double resonance surface enhanced Raman scattering substrates.