Optimal light harvesting structures at optical and infrared frequencies

One-dimensional light harvesting structures with a realistic geometry nano-patterned on an opaque metallic film are optimized to render high transmission efficiencies at optical and infrared frequencies. Simple design rules are developed for the particular case of a slit-groove array with a given number of grooves that are symmetrically distributed with respect to a central slit. These rules take advantage of the hybridization of Fabry-Perot modes in the slit and surface modes of the corrugated metal surface. Same design rules apply for optical and infrared frequencies. The parameter space of the groove array is also examined with a conjugate gradient optimization algorithm that used as a seed the geometries optimized following physical intuition. Both uniform and nonuniform groove arrays are considered. The largest transmission enhancement, with respect to a uniform array, is obtained for a chirped groove profile. Such enhancement is a function of the wavelength. It decreases from 39% in the optical part of the spectrum to 15% at the long wavelength infrared.Comment: 13 pages, 5 figure

Scattering of surface plasmons by one-dimensional periodic nanoindented surfaces

In this work, the scattering of surface plasmons by a finite periodic array of one-dimensional grooves is theoretically analyzed by means of a modal expansion technique. We have found that the geometrical parameters of the array can be properly tuned to achieve optimal performance of the structure either as a Bragg reflector or as a converter of surface plasmons into light. In this last case, the emitted light is collimated within a few degrees cone. Importantly, we also show that a small number of indentations in the array are sufficient to fully achieve its functional capabilities.Comment: 5 pages, 5 figures; changed sign convention in some definition

Una aproximación teórica a las propiedades fotónicas de los ópalos artificiales

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica de la Materia Condensada. Fecha de lectura 20-02-2004Bibliografí

Metallo-dielectric core-shell nanospheres as building blocks for optical three-dimensional isotropic negative-index metamaterials

Materials showing electromagnetic properties that are not attainable in naturally occurring media, so-called metamaterials, have been lately, and still are, among the most active topics in optical and materials physics and engineering. Among these properties, one of the most attractive ones is the subdiffraction resolving capability predicted for media having an index of refraction of -1. Here, we propose a fully three-dimensional, isotropic metamaterial with strong electric and magnetic responses in the optical regime, based on spherical metallo-dielectric core-shell nanospheres. The magnetic response stems from the lowest, magnetic-dipole resonance of the dielectric shell with a high refractive index, and can be tuned to coincide with the plasmon resonance of the metal core, responsible for the electric response. Since the response does not originate from coupling between structures, no particular periodic arrangement needs to be imposed. Moreover, due to the geometry of the constituents, the metamaterial is intrinsically isotropic and polarization independent. It could be realized with current fabrication techniques with materials such as silver (core) and silicon or germanium (shell). For these particular realistic designs, the metamaterials present a negative index in the range of 1.2-1.55οm. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.The authors acknowledge support from the Spain Ministerio de Ciencia e Innovacion´ through the Consolider-Ingenio project EMET (CSD2008-00066) and NANOPLAS (FIS2009- 11264) and from the Comunidad de Madrid (grant MICROSERES P2009/TIC-1476). RP-D acknowledges support from CSIC through a JAE-Pre grantPeer Reviewe

Fano-like interference of plasmon resonances at a single rod-shaped nanoantenna

Single metallic nanorods acting as half-wave antennas in the optical range exhibit an asymmetric, multi-resonant scattering spectrum that strongly depends on both their length and dielectric properties. Here we show that such spectral features can be easily understood in terms of Fano-like interference between adjacent plasmon resonances. On the basis of analytical and numerical results for different geometries, we demonstrate that Fano resonances may appear for such single-particle nanoantennas provided that interacting resonances overlap in both spatial and frequency domains.Comment: 18 pages, 9 figure

Scattering of surface plasmon polaritons by one-dimensional inhomogeneities

The scattering of surface plasmons polaritons by a one-dimensional defect of the surface is theoretically studied, by means of both Rayleigh and modal expansions. The considered defects are either relief perturbations or variations in the permittivity of the metal. The dependence of transmission, reflection and out-of-plane scattering on parameters defining the defect is presented. We find that the radiated energy is forwardly directed (with respect to the surface plasmon propagation) in the case of an impedance defect. However, for relief defects, the radiated energy may be directed into backward or forward (or both) directions, depending on the defect width.Comment: 10 pages, 5 figures, corrected typos, some minor modifications in figures. Accepted in Phys. Rev.

Metallo-dielectric core-shell nanospheres as building blocks for optical three-dimensional isotropic negative-index metamaterials

Materials showing electromagnetic properties that are not attainable in naturally occurring media, so-called metamaterials, have been lately, and still are, among the most active topics in optical and materials physics and engineering. Among these properties, one of the most attractive ones is the subdiffraction resolving capability predicted for media having an index of refraction of -1. Here, we propose a fully three-dimensional, isotropic metamaterial with strong electric and magnetic responses in the optical regime, based on spherical metallo-dielectric core-shell nanospheres. The magnetic response stems from the lowest, magnetic-dipole resonance of the dielectric shell with a high refractive index, and can be tuned to coincide with the plasmon resonance of the metal core, responsible for the electric response. Since the response does not originate from coupling between structures, no particular periodic arrangement needs to be imposed. Moreover, due to the geometry of the constituents, the metamaterial is intrinsically isotropic and polarization independent. It could be realized with current fabrication techniques with materials such as silver (core) and silicon or germanium (shell). For these particular realistic designs, the metamaterials present a negative index in the range of 1.2-1.55 μm.Ministerio de Ciencia e Innovación CSD2008-00066, FIS2009- 11264Comunidad de Madrid MICROSERES P2009/TIC-147

Efficient unidirectional nanoslit couplers for surface plasmons

Plasmonics is based on surface plasmon polariton (SPP) modes which can be laterally confined below the diffraction limit, thereby enabling ultracompact optical components. In order to exploit this potential, the fundamental bottleneck of poor light-SPP coupling must be overcome. In established SPP sources (using prism, grating} or nanodefect coupling) incident light is a source of noise for the SPP, unless the illumination occurs away from the region of interest, increasing the system size and weakening the SPP intensity. Back-side illumination of subwavelength apertures in optically thick metal films eliminates this problem but does not ensure a unique propagation direction for the SPP. We propose a novel back-side slit-illumination method based on drilling a periodic array of indentations at one side of the slit. We demonstrate that the SPP running in the array direction can be suppressed, and the one propagating in the opposite direction enhanced, providing localized unidirectional SPP launching.Comment: 13 pages, 4 figure

Modulation of surface plasmon coupling-in by one-dimensional surface corrugation

Surface plasmon-polaritons have recently attracted renewed interest in the scientific community for their potential in sub-wavelength optics, light generation and non-destructive sensing. Given that they cannot be directly excited by freely propagating light due to their intrinsical binding to the metal surface, the light-plasmon coupling efficiency becomes of crucial importance for the success of any plasmonic device. Here we present a comprehensive study on the modulation (enhancement or suppression) of such coupling efficiency by means of one-dimensional surface corrugation. Our approach is based on simple wave interference and enables us to make quantitative predictions which have been experimentally confirmed at both the near infra-red and telecom ranges.Comment: 20 pages, 13 figures, submitted to New Journal of Physics, revised tex