Inhibition and enhancement of electromagnetic radiation using optical waveguides and Bragg microcavities

Thesis (Ph. D.)--University of Rochester. College of Engineering and Applied Science. Insitute of Optics, 1994.This thesis investigates aspects of the dipole-surface problem to examine radiative effects occurring due to the coupling of a radiating system to its environment. Lifetime variations and resonance frequency shifts for a dipole in the presence of multilayered structures are investigated classically. Structures examined include dielectric and metal-clad planar waveguides, planar waveguides with embedded gratings, and planar and spherical Bragg structures. The research is of fundamental interest for furthering the understanding of dipole-surface interactions. The experimental results and theoretical techniques detailed should also prove useful for applications, including fluorescence assays and photonic bandgap devices. A vector theory is developed describing wave coupling in planarly and spherically stratified structures. This theory is the basis for formulating a large class of problems where electromagnetic wave coupling is a primary consideration. For linearly and radially periodic structures, a coupled-amplitude theory is detailed that directly models the processes of contra-directional coupling and distributed feedback. This coupled-amplitude formalism evolves from a scalar Green' s function technique and a characterization of electromagnetic fields by decoupled components. The classical problem of a radiating source in the presence of planarly layered media is considered. Using a dyadic Green' s function method, the degree of inhibition or enhancement of radiation is related to an effective amplitude reflection coefficient associated with the structure. An enhanced molecular fluorescence system is analyzed using this theory. Experimental results are presented for two waveguide systems that provide a significant enhancement. The experiments emphasize the applicability of the enhanced fluorescent technique to certain diagnostic systems, while the theory relates the observed enhancement to concepts of energy transfer and mode coupling. A calculation of radiative effects in a finite-size, spherical Bragg structure is detailed. It is determined that relatively small structures can produce measurable changes in the radiative damping rate, provided the refractive index modulation is sufficiently large. This work is of potential practical interest in gauging finite-size effects in proposed photonic bandgap structures of similar size, and stresses the connection with earlier investigations of dipole-mirror interactions from which this thesis evolves