Nanophotonic Devices for Modulation and Enhanced Raman Spectroscopy

Nanophotonic devices, which typically rely on metal nanostructures that support surface plasmon polaritons, have been demonstrated to provide sub-wavelength confinement of light down to the nanoscale and thus achieve superior enhancement of local electromagnetic (EM) fields. A wide range of applications that can benefit from nanophotonics have been proposed. In this thesis, we investigate the use of several representative nanophotonic structures to design devices that can improve performance in two specific applications: (1) modulators based on the phase change material vanadium dioxide (VO2) and (2) enhanced Raman spectroscopy. As well, conventional dielectric based photonic devices are designed to provide proof-of-concept experimental demonstrations for: (A) all-optical VO2 modulator with planar integration of both control and signal beams, and (B) broadband orthogonal coupler bend to interface between dielectric wire and slot-type waveguides. These dielectric devices serve as bases for future implementations using more advanced nanophotonic structures as presented in this thesis. First, a unique hybrid plasmonic waveguide functionalized with VO2 to form a modulator, in which the electric-field distribution within the waveguide cross-section can be engineered precisely, is shown to exhibit enhanced performance compared to implementation using the silicon wire waveguide. It is also one of the smallest modulator designs proposed to date that features amongst the highest extinction ratio and optical bandwidth. For the application to enhanced Raman spectroscopy, first an artificial hyperbolic material, which consists of a multilayer stack of ultra sub-wavelength alternating metal and dielectric layers, to construct nano-dimers for surface-enhanced Raman spectroscopy is investigated. Although the novel nanophotonic device provides much enhanced local EM fields and photonic density of states in comparison to pure metal nanoresonators, the increased absorption leads to overall reduced Raman enhancement factors for molecules located within their near-fields. Finally, pure metal, hybrid, and hyperbolic material plasmonic slot waveguides are studied for enhancing Raman scattering in a regime where both strategies of EM field enhancement and increase in light-matter interaction volume (as well as improved delivery of excitation light and collection of Raman scattered signal) are employed. The nanoscale plasmonic slot waveguides attain much higher Raman enhancement compared to optofluidic photonic crystal fibers, and thus they are suitable when ultra-low analyte volume is required in a portable instrument.Ph.D