Kocabas S.E. Nano-Metallic Optics for Waveguides and Photodetectors

ProQuest, 2009. — 191 p.A Dissertation Submitted to the Department of Electrical Engineering and the Committee on Graduate Studies of Stanford University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy.This dissertation focuses on the use of nano-metallic structures in optical systems, specifically in waveguide geometries and photodetectors. The use of metals makes it possible to design optical components that are smaller than the wavelength of light. The optical properties of metals at infrared and visible wavelengths enable such designs.
The first part of the dissertation focuses on waveguides and investigates the metal-insulator-metal (MIM) geometry. We begin by deriving the full set of modes that the MIM geometry supports. We show the necessity of taking into consideration all supported modes through the use of mode-matching calculations. Following our analysis of the modal structure of the MIM waveguides, we then illustrate how to analyze junctions of MIM waveguides by designing a mode converter which converts the mode of a large waveguide into that of a smaller waveguide. Our analysis uses scattering matrices and is much faster than full-field simulations. We conclude the first part of the dissertation by providing an exact circuit model for waveguide junctions.
The second part of the dissertation is about scattering of light off of nano-metallic volumes. We review various techniques of scattering analysis, and then illustrate a photodetector design which integrates an antenna for near-infrared wavelengths with a sub-wavelength volume of Ge. The use of the antenna makes it possible to focus light into a sub-wavelength volume. We then describe the experimental work we did with Si photodetectors of different geometries and provide our measurement results. Finally, we present our conclusions.