
369. S. E. Kocabas, G. Veronis, D. A. B. Miller, and S. H. Fan, “Modal Analysis and Coupling in MetalInsulatorMetal Waveguides,” Phys. Rev. B 79, 035120 (2009)
This paper shows how to analyze plasmonic metalinsulatormetal 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 metalinsulatormetal (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 SturmLiouville 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 modematching technique. We numerically compare the modematching formulation with finitedifference frequencydomain 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 quantummechanical pseudoHermitian 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.
Full text available for
download 