Subwavelength metallic coaxial waveguides in the optical range: Role of the plasmonic modes

Abstract

A theoretical investigation is presented of the mode propagation and attenuation in a nanometric coaxial waveguide in real metal. By a rapid comparison with other structures, it is established that a coaxial waveguide has propagative modes with very interesting properties: the cutoff wavelengths are very large, they become larger when a perfectly electric conductor is replaced by gold or silver (real metal), and they can be increased when the outer and inner radii are very close one to other. By studying dispersion curves and field structures, it is shown that surface plasmon modes are responsible for these properties. By simply changing the geometrical parameters of the structure, a very large effective index and very low group velocities could be obtained. We also establish that, in spite of the metal losses, a reasonable large propagation length could be obtained (50μm) which should allow applications for guiding light in nano-optics

Optical transmission of periodic annular apertures in metal film on high-refractive index substrate: The role of the nanopillar shape

“…There have been studies considering AAA with glass as a substrate, in the near-infrared, and the visible regime. [1][2][3][4][5][6] Recently, it was experimentally demonstrated an enhanced transmission around 90%. 9 When glass is used a substrate, it is possible to take advantage of the resonance associated with the cutoff of the TE 11 mode of individual annular apertures.…”

“…[1][2][3][4][5][6] Such nanostructures provide additional functionalities compared to simple circular apertures in terms of very high absolute transmission related to specific waveguided modes in annular apertures, absent in simple circular holes. Coupled to surface plasmon polariton modes on metal film interfaces, these modes provide a possibility to achieve high transmission, field enhancement as well as high extraction efficiency of light trapped in the substrates.…”

Discretely guided electromagnetic effective medium

“…At higher frequencies, the dimensions of the coaxial waveguides must be reduced to accommodate the subwavelength limit, and so in the optical range, nanoscopically small coaxial waveguides (nanocoax) must be used. Such nanocoaxes have been recently fabricated [19], and shown [19][20][21] to propagate plasmon polaritons which, for frequencies sufficiently below the constituent metal plasma frequency(ies), closely resemble conventional TEM waveguide modes. Coupling of radiation to the nanocoax arrays is envisioned via antenna couplers.…”

Enhanced backscattering by multiple nanocylinders illuminated by TE plane wave

“…21. Metallic waveguide structures were also studied in the role of the plasmonic modes theoretically, 22 and nanosilicon waveguide is analyzed in Ref. 23 47 and focusing surface plasmons by changing the incident angle are shown in Ref.…”