Attenuation of slow Metal-Insulator-Metal plasmonic waveguides, from Joule absorption to roughness-induced backscattering

TL;DR

This paper combines analytical and numerical methods to study how fabrication imperfections, especially roughness, affect the attenuation of slow metal-insulator-metal plasmonic waveguides, highlighting the significance of backscattering.

Contribution

It provides a quantitative analysis of absorption and backscattering losses in realistic waveguides, revealing the importance of roughness-induced backscattering at low group velocities.

Findings

Backscattering becomes significant at small group velocities.

Attenuation scales with group velocity.

Fabrication quality influences loss mechanisms.

Abstract

By combining analytical and numerical approaches, we theoretically investigate the effect of fabrication imperfections, e.g. roughness at metal interfaces, on nanometer metal-insulator-metal waveguides supporting slow gap-plasmon modes. Realistic devices with vapor deposition- and chemically-grown metal films are considered. We obtain quantitative predictions for the attenuations induced by absorption and by backscattering, and analytically derive how both attenuations scale with respect to the group velocity. Depending on the material parameters and fabrication quality, roughness-induced backscattering is find to be a significant additional source of attenuation for small group velocities, which is often neglected in the literature.