Modal analysis and coupling in metal-insulator-metal waveguides

Şükrü Ekin Kocabaş, Georgios Veronis, David A. B. Miller, and Shanhui Fan
Phys. Rev. B 79, 035120 – Published 26 January 2009

Abstract

This paper shows how to analyze plasmonic metal-insulator-metal waveguides using the full modal structure of these guides. The analysis applies to all frequencies, particularly including the near infrared and visible spectrum, and to a wide range of sizes, including nanometallic structures. We use the approach here specifically to analyze waveguide junctions. We show that the full modal structure of the metal-insulator-metal (MIM) waveguides—which consists of real and complex discrete eigenvalue spectra, as well as the continuous spectrum—forms a complete basis set. We provide the derivation of these modes using the techniques developed for Sturm-Liouville and generalized eigenvalue equations. We demonstrate the need to include all parts of the spectrum to have a complete set of basis vectors to describe scattering within MIM waveguides with the mode-matching technique. We numerically compare the mode-matching formulation with finite-difference frequency-domain analysis and find very good agreement between the two for modal scattering at symmetric MIM waveguide junctions. We touch upon the similarities between the underlying mathematical structure of the MIM waveguide and the PT symmetric quantum-mechanical pseudo-Hermitian Hamiltonians. The rich set of modes that the MIM waveguide supports forms a canonical example against which other more complicated geometries can be compared. Our work here encompasses the microwave results but extends also to waveguides with real metals even at infrared and optical frequencies.

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  • Received 16 September 2008

DOI:https://doi.org/10.1103/PhysRevB.79.035120

©2009 American Physical Society

Authors & Affiliations

Şükrü Ekin Kocabaş1,*, Georgios Veronis2,†, David A. B. Miller1,‡, and Shanhui Fan1,§

  • 1Ginzton Laboratory, Stanford University, Stanford, California 94305, USA
  • 2Department of Electrical and Computer Engineering and Center for Computation and Technology, Louisiana State University, Baton Rouge, Louisiana 70803, USA

  • *kocabas@ieee.org
  • gveronis@lsu.edu
  • dabm@ee.stanford.edu
  • §shanhui@stanford.edu

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Issue

Vol. 79, Iss. 3 — 15 January 2009

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