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 $\left(50\mu \mathrm{m}\right)$ which should allow applications for guiding light in nano-optics.

Light transmission through arranged nanostructures can be increased comparing to what was observed three years ago by Ebbesen et al. [Nature, 391, 667 (1998)]. The results obtained recently by Krishnan et al. [Opt. Commun. 200, 1 (2001)] with gold hole grating are confirmed, but a new design is suggested in order to enhance the light transmission. A three-dimensional finite difference time domain simulation was performed in order to obtain the spectral response of metallic periodic structures in the visible domain. The grating structure is modified by filling the central region of each hole with a concentric cylinder of smaller diameter. The grating now consists of a periodic array of annular apertures. Theoretical simulations were performed with such a subwavelength silver grating. It is shown that the transmission efficiency can reach 80% in the visible spectral range.

The authors demonstrate how slow group velocities that are easily attainable at the band edge of photonic crystals can drastically enhance the electro-optical effect on tunable photonic crystal components. This property opens up the possibility of microsized nonlinear devices with low power requirement. In this letter we show how these possibilities for enhancement of nonlinear effects have been used to fabricate a 13×13μm2 sized lithium niobate photonic crystal intensity modulator that shows an enhanced electro-optic effect 312 times bigger than the one predicted by the classical Pockels effect for an equivalent device in bulk material.

Excitation and propagation of surface plasmons in silver films structured with narrow straight grooves were visualized in unprecedented detail by means of near-field optical techniques. Reflectivity, transmissivity, and scattering loss of the grooves are demonstrated. Their values are determined semiquantitatively. The surface plasmon attenuation are found to be dominated by material and surface/interface imperfections.