Enhancement of plasmonic photovoltaics with pyramidal nanoparticles.

Light trapping as a result of embedding plasmonic nanoparticles (NPs) into photovoltaics (PVs) has been recently used to achieve better optical performance compared to conventional PVs. This light trapping technique enhances the efficiency of PVs by confining incident light into hot-spot field regions around NPs, which have higher absorption, and thus more enhancement of the photocurrent. This research aims to study the impact of embedding metallic pyramidal-shaped NPs inside the PV's active region to enhance the efficiency of plasmonic silicon PVs. The optical properties of pyramidal-shaped NPs in visible and near-infrared spectra have been investigated. The light absorption into silicon PV is significantly enhanced by embedding periodic arrays of pyramidal NPs in the cell compared to the case of bare silicon PV. Furthermore, the effects of varying the pyramidal-shaped NP dimensions on the absorption enhancement are studied. In addition, a sensitivity analysis has been performed, which helps in identifying the allowed fabrication tolerance for each geometrical dimension. The performance of the proposed pyramidal NP is compared with other frequently used shapes, such as cylinders, cones, and hemispheres. Poisson's and Carrier's continuity equations are formulated and solved for the current density-voltage characteristics associated with embedded pyramidal NPs with different dimensions. The optimized array of pyramidal NPs provides an enhancement of 41% in the generated current density when compared to the bare silicon cell.

Dual-polarized nanocrescent antenna designed using efficient optimization techniques.

A novel nanocrescent antenna with polarization diversity is introduced. It is formed from a crescent-shaped patch fed with a coupled strip transmission line. The antenna is located on top of a SiO2 thin film with a shielding ground layer underneath. The structure is supported by an arbitrary substrate. Polarization of the radiated field can be adjusted to be along either one of the two orthogonal polarizations based on which one of the two crescent patch modes is going to be excited. The excitation of either one of these two modes of the patch is achieved by switching between the two propagating modes of the feeding coupled strip transmission line. Using a dual-polarized antenna allows doubling the optical communication system's capacity via frequency reuse. The new crescent antenna dimensions are optimized to satisfy several goals, such as minimizing the losses, the deviation of the main beam direction away from broadside, and maximizing the radiation efficiency and axial ratio. Through the optimization process, simple surrogate kriging models replace the detailed electromagnetic simulation. The optimal response is achieved by applying two different optimizers. The first optimizer employs the design-centering technique using normed distances. The multiobjective particle swarm with the preference ranking organization method for enrichment evaluations is used by the second optimizer. In order to identify the critical dimensions to which the nanoantenna is most sensitive, a sensitivity analysis is used. The optimized antenna is capable of switching its radiation between two orthogonal pure linear polarizations with maximum radiation along the broadside direction. The size of the proposed antenna is about 500nm×500nm. Its impedance-matching bandwidth is higher than 30 THz centered around 193 THz (1550 nm). Its gain and radiation efficiency are higher than 5.2 dBi and 85%, respectively, all over the working frequency band.

Enhanced plasmonic photovoltaic using embedded novel gear-shaped nanoparticles.

In this paper, novel gear-shaped nanoparticles are introduced for the first time to enhance the photovoltaic (PV) efficiency. This has been achieved via increasing the overall power absorption by the PV semiconductor material in both visible and near-infrared ranges. The modes of the new gear-shaped nanoparticles are investigated. A parametric study has been performed which demonstrates how the design parameters of the proposed nanoparticles can be engineered for best overall power absorption within a Si surrounding medium. A figure of merit (FoM) is defined that takes into account all objectives. An optimization technique is applied to obtain the optimum set of the gear's dimensions, penetration depth, and periodicity for the maximum possible FoM. The optimum gear-shaped nanoparticles design offers 48% enhancement in the FoM if compared with a bare Si block with no nanoparticles and 7% enhancement over the conventional disk-shaped nanoparticles. The enhancement gained by the embedded gear-shaped nanoparticles on the J-V characteristics of the PV is also studied, and the effects of changing the dimensions and the position of nanoparticles on the J-V characteristics enhancement are investigated.

Dendritic optical antennas: scattering properties and fluorescence enhancement.

With the development of nanotechnologies, researchers have brought the concept of antenna to the optical regime for manipulation of nano-scaled light matter interactions. Most optical nanoantennas optimize optical function, but are not electrically connected. In order to realize functions that require electrical addressing, optical nanoantennas that are electrically continuous are desirable. In this article, we study the optical response of a type of electrically connected nanoantennas, which we propose to call "dendritic" antennas. While they are connected, they follow similar antenna hybridization trends to unconnected plasmon phased array antennas. The optical resonances supported by this type of nanoantennas are mapped both experimentally and theoretically to unravel their optical response. Photoluminescence measurements indicate a potential Purcell enhancement of more than a factor of 58.

Artificial neural network modeling of plasmonic transmission lines.

In this paper, new models based on an artificial neural network (ANN) are developed to predict the propagation characteristics of plasmonic nanostrip and coupled nanostrips transmission lines. The trained ANNs are capable of providing the required propagation characteristics with good accuracy and almost instantaneously. The nonlinear mapping performed by the trained ANNs is written as closed-form expressions, which facilitate the direct use of the results obtained in this research. The propagation characteristics of the investigated transmission lines include the effective refractive index and the characteristic impedance. The time needed to simulate 1000 different versions of the transmission line structure is about 48 h, using a full-wave electromagnetic solver compared to 3 s using the developed ANN model.

Integral equations formulation of plasmonic transmission lines.

In this paper, a comprehensive integral equation formulation of plasmonic transmission lines is presented for the first time. Such lines are made up of a number of metallic strips with arbitrary shapes and dimensions immersed within a stack of planar dielectric or metallic layers. These lines support a number of propagating modes. Each mode has its own phase constant, attenuation constant, and field distribution. The presented integral equation formulation is solved using the Method of Moments (MoM). It provides all the propagation characteristics of the modes. The new formulation is applied to a number of plasmonic transmission lines, such as: single rectangular strip, horizontally coupled strips, vertically coupled strips, triangular strip, and circular strip. The numerical study is performed in the frequency (wavelength) range of 150-450 THz (0.66-2.0 µm). The results of the proposed technique are compared with those obtained using Lumerical mode solution, and CST. Very good agreement has been observed. The main advantage of the MoM is its intrinsic speed for this type of problem compared to general purpose solvers.