We theoretically show that coaxial waveguides composed of a metallic core, surrounded by a dielectric cylinder and clad by a metal outer layer exhibit negative refractive index modes over a broad spectral range in the visible. For narrow dielectric gaps (10 nm GaP embedded in Ag) a figure-of-merit of 18 can be achieved at λ0 = 460 nm. For larger dielectric gaps the negative index spectral range extends well below the surface plasmon resonance frequency. By fine-tuning the coaxial geometry the special case of n = −1 at a figure-of-merit of 5, or n = 0 for a decay length of 500 nm can be achieved.

Opt. Express
Photonic Materials

de Waele, R, Burgos, S.P, Atwater, H.A, & Polman, A. (2010). Negative refractive index in coaxial plasmon waveguides. Opt. Express, 18(12), 12770–12778. doi:10.1364/OE.18.012770