1,720,997 research outputs found
On the Polarization Properties of Metamaterial Lenses
No full textIn this letter, the polarization properties of composite planar dielectric structures fed by point sources are investigated. With an appropriate choice of substrate heights and dielectric constants, the structure is a leaky wave antenna (LWA), based on a (Fabry-Perot)-like effect, which enhances the directivity of isotropic sources (e.g., dipoles or slots). These antennas have been deeply investigated in the past, especially from the antenna gain point of view. Nevertheless, the aspect concerning with the polarization has not been well explored yet. In our analysis, we show that this high-gain antenna is very well polarized when the excitation is provided by a perfectly polarized feeding source. This concept is important in the design of overlapped apertures in multifeed aperture systems
Numerical Analysis of Propagating and Radiating Properties of Hollow Core Photonic Band Gap Fibres for THz Applications
No full textHollow core photonic bandgap fibres (HC-PBGFs) are numerically investigated in order to obtain low loss wave-guiding and good aperture field distribution in the terahertz region (0.1-10 THz) of the electromagnetic spectrum. The purity of the aperture field distribution at the HC-PBGF section combined with low loss propagation and high coupling efficiency with free-space propagating Gaussian beams suggest a possible employment of such a structure as aperture antennas, for possible feed systems in THz applications and in THz wireless sensing
PLASMONIC NANOANTENNA FOR POSSIBLE CMOS INTEGRATION
No full textPlasmonic nanoantennas have gained interest in several environments like integrated
photonics, biosensing, microscopy and solar cells, due to their capability
in collecting and conveying the electromagnetic radiation in the visible and in
the near visible regions. However, examples of antennas applied to integrated
circuits are conspicuously rare even if they are able to provide a solution to the
bandwidth shortage problem. In this work I have developed a new plasmonic
nanoantenna configuration able to be easily coupled with a transmission line in
order to enable the direct connection with plasmonic modulators and demodulators.
Furthermore, the antenna shows a tunable double resonance that allows
for bidirectional communications without the use of complex TDD techniques.
The size of the antenna and the materials employed are all suitable for future
CMOS integration
Transmission line equivalent circuit model applied to a plasmonic grating nanosurface for light trapping
Full text linkIn this paper, we show how light absorption in a plasmonic grating nanosurface can be calculated by means of a simple, analytical model based on a transmission line equivalent circuit. The nanosurface is a one-dimensional grating etched into a silver metal film covered by a silicon slab. The transmission line model is specified for both transverse electric and transverse magnetic polarizations of the incident light, and it incorporates the effect of the plasmonic modes diffracted by the ridges of the grating. Under the assumption that the adjacent ridges are weakly interacting in terms of diffracted waves, we show that the approximate, closed form expression for the reflection coefficient at the air-silicon interface can be used to evaluate light absorption of the solar cell. The weak-coupling assumption is valid if the grating structure is not closely packed and the excitation direction is close to normal incidence. Also, we show the utility of the circuit theory for understanding how the peaks in the absorption coefficient are related to the resonances of the equivalent transmission model and how this can help in designing more efficient structures
Effect of a dielectric coating on quenching in a molecule-nanosphere system
No full textWe investigate the effect a dielectric coating has on the energy transfer between a molecule and a silver nanosphere. For a fixed wavelength excitation resonant with the bare nanoparticle, increasing the shell thickness increases the non-radiative decay rate and decreases the radiative decay rate, which decreases the total efficiency of the emission process. The excitation wavelength can be tuned to improve the efficiency for coated nanoparticles, leading to values that are comparable to bare nanoparticles. As such, dielectric coatings are able to effectively limit quenching without sacrificing efficiency
Sensing Properties of a Fabry-Perot Dielectric Structure and Dimer Nanoparticles
Full text linkWe investigate the use of a Fabry-Perot dielectric structure combined with differently shaped nanoparticles for Surface Enhanced Raman Scattering. In particular, we show how an ideal two-layer Fabry-Perot configuration enhances the local surface field of silver nanoparticles positioned on the surface of the structure. We develop the concept using disc dimers and then extend the discussion to bowtie nanoparticles. The structure is excited by a single emitter, which couples to the nanoparticles through the dielectric layers, producing a wide aperture field that can be used to excite multiple dimers. We show how an array of nanoparticles can be properly arranged in order to increase the total scattering signal generated from the structure. The layered geometry produces robust field properties in between nanoparticles, making the overall sensing characteristics less sensitive to the interparticle seperation distance and incident polarization
Distance dependent quenching effect in nanoparticle dimers
No full textIn this paper, we investigate the emission characteristics of a molecule placed in the gap of a nanoparticle dimer configuration. The emission process is described in terms of a local field enhancement factor and the overall quantum yield of the system. The molecule is represented as a dipolar source, with fixed length and fed by a constant current. We first describe the coupled dimer-molecule system and compare these results to a single sphere-molecule system. Next, the effect of dimer size is investigated by changing the radius of the nanoparticles. We find that when the radius increases, a saturation effect occurs that trends towards the case of a radiating dipole between two flat interfaces, which we refer to as a parallel plate waveguide geometry. An analytical solution for the parallel plate waveguide geometry is presented and compared to the results for the spherical dimer configuration. We use this approximation as a reference solution, and also, it provides useful guidelines to understand the physical mechanism behind the energy transfer between the molecule and the dimer. We find that the emission intensity undergoes a quenching effect only when the inter-nanoparticle gap distance of the dimer is very small, meaning that strong coupling prevails over energy engaged in the heating process unless the molecule is extremely close to the metal surface
Propagating and radiating properties of Broadband Hollow Core fibers in Terahertz spectral region
No full textIn this paper Hollow Core Microstructured Fibers consisting of a regular arrangement of dielectric tubes of Teflon are numerically investigated in order to obtain efficient and highly directive aperture antennas for Terahertz applications. The good aperture field distribution allow to obtain high power coupling coefficient with freely propagationg gaussian beams, narrow beamwidth and low side lobe level over a wide range of frequencies as wide as 1.5THz centered at 2.25 THz. Antenna performances are not affected by fiber dimension allowing a more flexible design in order to better meet the requirements of a particular application. An array configuration of fibers arranged in a hexagonal lattice have been also investigated
Fibre microstrutturate a nucleo cavo per applicazioni nella gamma dei Terahertz
No full textPropagation characteristics of a hollow core microstructured fibre in the THz regime are numerically investigated. The fibre cladding consists of a triangular lattice formed by a periodic arrangement of Teflon dielectric tubes. Low loss and low dispersion frequencyranges can be tuned out just by changing the tubes thickness, irrespectively of their diameter
Fibre a nucleo cavo per applicazioni nella gamma dei THz
No full textIn this paper a hollow core photonic band gap fiber is numerically investigated in order to obtain low loss waveguiding in the terahertz region (0.1-10 THz) of the electromagnetic spectrum. Waveguide design in this spectral region is a major challenge due to the high conductivity losses of metals and high absorption of thedielectrics. Numerical results show the eventuality to reach propagation loss two decades lower than the bulk absorption losses of the material used to make the fiber, over a wide range of wavelength
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