Impedance for Wave Guiding Devices from the Microwave Frequency Regime to Optics and Plasmonics

Abstract

We have derived expressions that generalized the impedance concept for wave guiding devices from the microwave frequency regime to optics and plasmonics. Our  expressions were based on electromagnetic eigen modes that are excited at the  interface of a structure. Impedance in electromagnetic wave theory is the ratio of the  electric and magnetic field strength. The ratio between the electric and magnetic field  is not constant over the cross section in most devices. This caused several suggestions  using averaged or integrated fields which were heuristically proposed for a manifold  of photonic structures not only waveguides. The area of photonic crystals were  several such heuristic approaches excited until it was proven that the so called Bloch  impedance, the ratio of the surface averaged fields was analytically correct solution,  provided that the photonic crystal operates only in its fundamental modes.  Electromagnetic response closely resembles the solution in the quasistatic limit.  Plasmonic metal-insulator-metal waveguide and a waveguide at microwave  frequencies facilitated the use of traditional impedance for this kind of structure in  plasmonics. For this we required lumped circuit parameters to the radio frequency  domain. Impedance definition must correctly describe the reflection that occurs at the  boundary between two different structures. We analysed the reflection at an interface  of impedance discontinuity i.e. between two different structures. A plasmonic  insulator-metal-insulator waveguide characterized by referential impedance;  illustrates another photonic structure. We have used Bragg reflector, i.e periodic  corrugations in a metal film which intended to describe impedance. In case of circuit  theory; we considered as part of a photonic network. Our approach was based on a  decomposition of the electromagnetic fields into eigenmodes. We have chosen it  because the relatively strong loss in the metal that prevented the use of many radio  frequency derivations and the open boundary condition that made it possible to find  suitable analogies to voltage and current. We observed that the impedance for the  reciprocity based overlap of eigen modes. We found that applicability of simple  circuit parameters ends and how the impedance can be interpreted beyond any  particular point. The unconjugated reciprocity framework set up to solve for the