Resonantly Enhanced Sagnac Interferometry Using Surface Plasmon Polaritons

Abstract

We present a theoretical model and experimental results for a Sagnac ring interferometer resonantly enhanced via surface plasmon resonance (SPR). One defining characteristic of a resonance is the π change in phase that occurs across the resonance. For a narrow resonance, this results in a steep phase profile which proves advantageous when utilized within a phase-based detection scheme, providing a resonant enhancement that has the potential to greatly improve the sensitivity of Sagnac interferometers. Furthermore, surface plasmon resonance serves as the mechanism underlying surface plasmon sensing, one of the more commonly used techniques for detection and characterization of a variety of interfacial events. This method relies on the excitation of surface bound electromagnetic waves, known as surface plasmon polaritons (SPPs), which propagate along the interface of a metal and dielectric and exhibit a field profile that decays exponentially into both media. Excitation of SPPs within an interferometric environment provides an avenue for investigation into the potential benefits of this resonant enhancement. In addition, it carries the capacity for insight into applications of SPR sensors using interferometric techniques, some of which may be inaccessible to intensity based detection schemes.

We begin this dissertation by providing necessary background information, such as the interference equations describing the interferometer outputs and the SPP dispersion relation. We then detail the features of SPR and explore modifications to the resonance shape by variation of the system parameters. We fabricate and characterize thin silver films, suitable for supporting SPPs, to be used in sensing experiments. We design a theoretical model to compute the response of the resonantly enhanced interferometer to various perturbations and calculate the corresponding sensitivities. Finally, we construct a resonantly enhanced interferometer in the laboratory, analyze the optical data collected from both interferometer output ports, and comment on the promise of this and similar devices moving forward.