Control of the diffracted response of a metallic wire array with double period: experimental demonstration.

In recent papers, it has been theoretically shown that by using dual-period wire gratings, it is possible to control the relative efficiencies of the diffracted orders, regardless of the wires' material, incident polarization and wavelength. In this Letter, we experimentally demonstrate, for the first time, that by appropriately choosing the geometrical parameters of a nanometric periodic structure, it is possible to control the optical response in the visible range. We show examples of nanostructures designed to cancel out or to intensify a particular diffraction order. Such nanostructures allow a broad control over the directionality and the intensity of the diffracted light, which makes them useful for applications such as highly directional optical nanoantennas and photonic multiplexers.

Resonant effects in periodic gratings comprising a finite number of grooves in each period.

We give numerical evidence of a kind of resonance that appears in infinite perfectly conducting gratings comprising a finite number of grooves in each period when illuminated by a normally incident p-polarized plane wave. This phenomenon is intimately connected with the particular distribution of the phase of the electromagnetic field inside the cavities, which is automatically generated by waves of certain resonant wavelengths. The resonances appear as sharp peaks in the specularly reflected efficiency and are accompanied by a significant intensification of the interior field. We study the particular case of rectangular cavities and consider configurations with different numbers of grooves per period. The diffraction problem is solved for s and p polarization by using the modal method, which proves to be especially suitable for this profile.

Surface shape resonances and surface plasmon polariton excitations in bottle-shaped metallic gratings.

We study surface plasmon polariton excitations and surface shape resonances in a lossy metallic grating with bivalued cavities. The modal formalism is used to solve the diffraction problem for the infinite grating and the homogeneous problem for a single cavity in a plane surface. Both polarization modes are considered. We provide curves of reflected efficiency versus wavelength as well as near-field plots. The resonances are identified as dips in the reflected efficiency, which imply significant power absorptions. Results for various depths of the cavities and for several angles of incidence are shown, where the different types of resonant behavior can be appreciated. Particular attention is paid to the changes introduced by the finite conductivity of the metal in relation to the results obtained for a perfect conductor.