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

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International audienceAbstract We theoretically demonstrate the possibility of obtaining nanosources through an original schema based on the generation of the radially polarized surface plasmon mode of a cylindrical metallic tip. This mode has no cutoff radius and can propagate along the tip walls until its nanometric-sized apex. Instead of radiating from the tip end, the guided mode will give rise to a nanospotlight via the well-known antenna effect. 3D calculations demonstrate that both surface plasmon-guided mode and antenna effect are directly involved in the light confinement. Near-field optical microscopy can benefit significantly from this kind of probe because the sample does not need to be directly illuminated