Effect of structural asymmetry on three layer plasmonic waveguide properties

In this work, we study the effects of structural asymmetry of the plasmonic waveguide on its properties. In contrast to the symmetric waveguides, odd and even mode dispersion of the asymmetric structure is characterized by a double-peak behavior of the real part and a step-like behavior of the imaginary part. In between low-loss spectral windows of these modes, we introduce the phenomenon of plasmonic quasi-bandgap and numerically confirm its existence. The nature of the observed quasi-bandgap opening is explained in terms of the near-zero value of an effective permittivity for plasmonic modes in the waveguide. The adjustment of the plasmonic quasi-bandgap spectrum is demonstrated with the structural modification of the plasmonic waveguide. As a prospective application example, we illustrate a new concept of coupling control between surface plasmons and propagating waves by employing a tapered nonadiabatic insulator-metal-insulator waveguide.