Transmission line equivalent circuit model applied to a plasmonic grating nanosurface for light trapping

In 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

Spectral Filtering of the Spatial Green\u2019s Function

N/

PLASMONIC NANOANTENNA FOR POSSIBLE CMOS INTEGRATION

Plasmonic 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

Hollow core fibre for THz applications

This work is focused on the analysis of hollow core photonic band gap fibres (HC-PBGFs) for THz applications. Waveguide design in this spectral region is a major challenge due to the high conductivity losses of metals and high absorption of the dielectrics. HC-PBGFs are dielectric waveguides in which the power fraction propagating in the dielectric is very low, and losses due to material absorption are dramatically reduced. HC-PBGFs have been proposed and developed from the end of 90's for applications in visible and near infrared (NIR) spectrum, and in few years propagation losses have been dramatically reduced from tens of dB/m to few dB/Km

Numerical Analysis of Propagating and Radiating Properties of Hollow Core Photonic Band Gap Fibres for THz Applications

Hollow 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

On the Polarization Properties of Metamaterial Lenses

In 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

Distance dependent quenching effect in nanoparticle dimers

In 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

Nanocircuit Loading of Plasmonic Waveguides

We apply the optical nanocircuit concepts to model and design optical nanofilters in realistic plasmonic waveguides of different nature, including strips and groove waveguides. The nanocircuit elements are designed to fit the waveguide geometry, and its equivalent impedance is analytically calculated by substituting the role of the conduction current with displacement current. The effect of plasmonic waveguide walls is rigorously modeled in terms of an extra nanocircuit loading that is included in our model.We show via numerical results that the nanocircuit approachmay be effectively applied to the design of nanofilters, analogous to familiar concepts at radio-frequencies

Two-dimensional plasmonic nanosurface for photovoltaics

In this paper, we investigate a two-dimensional corrugated plasmonic nanosurface for efficient light trapping in a photovoltaic cell. Inspired by a well-known one-dimensional grating nanosurface, the present configuration is composed of two perpendicular gratings in the metal film that intersect to yield cross-shaped nanoelements. The surface corrugation is then covered by a silicon film. An additional degree of freedom can be introduced into the design by interrupting the grid in both directions. We show that this extra spacing between the array elements can be used to tune the absorption properties of the nanosurface. By including the effect of the solar spectrum, we demonstrate how this two-dimensional configuration is more efficient than its one-dimensional counterpart in terms of the actual short circuit photocurrent density. Finally, we propose possible extensions of this structure design, which can further enhance the solar cell performance