Nanoantennas Research Articles

Optimization of the plasmonic nano-rods-based absorption coefficient using TLBO algorithm

We have used the teaching–learning-based optimization (TLBO) algorithm to design the plasmonic nano-rods in order to achieve the maximum absorption coefficient spectrum. In TLBO, a group of learners controls the nano-rod radius, the nano-rods distance, and the number of nano-rods in two dimensions. This approach is useful in optical applications such as solar cell and plasmonic nano antenna.

Nanoscale plasmonic antenna difference formation implementation effect on field enhancement

In this article, different implementation of plasmonic nano-antenna for optical range is presented. Nano antennas are designed based on I, U, dual I and dual U metamaterial structures. Different models of nano-antenna are studied for E field density, transmission coefficient, ACS (absorption cross section) parameter and E2 enhancement for different wavelengths when linear polarization wave incident to nano antenna as a source field. Also, field enhancement and its relation with dual structure and comparison with single model are noticed. As shown here, single arrangement gives better field enhancement in comparison to dual structures but here we try to modify the result of dual U shape structure and enhancement of E field. On the other hand, benefits of U shape structure in nano-antenna design such as dual band characteristic and higher field enhancement are shown. At last different metamaterial formations to improve filed enhancement in this nano antenna is noticed here. The nano structures are based on deposition of silver layers on silicon-nitride substrate.

Plasmonic enhancement of blue fluorescence in ZnO nanoparticles

Silver nanoparticles (Ag NP) can behave like optical nano antennas by confining and enhancing the incident electromagnetic field (EM) around them due to localized surface Plasmon resonance (LSPR). Such augmented near field of plasmonic nano antennas has been harnessed to enhance blue fluorescence emission from ZnO nanoparticles optimally conjugated with Ag NPs. Overlapping of LSPR band with excitation range of ZnO and near field calculated through Finite difference time domain simulations of exact Ag NP correlates with fluorescence enhancement results. Plasmon coupled visible fluorescence enhancement from semiconductor emitters opens up fresh possibilities in light harvesting.

Optical nano antennas: state of the art, scope and challenges as a biosensor along with human exposure to nano-toxicology.

The concept of optical antennas in physical optics is still evolving. Like the antennas used in the radio frequency (RF) regime, the aspiration of optical antennas is to localize the free propagating radiation energy, and vice versa. For this purpose, optical antennas utilize the distinctive properties of metal nanostructures, which are strong plasmonic coupling elements at the optical regime. The concept of optical antennas is being advanced technologically and they are projected to be substitute devices for detection in the millimeter, infrared, and visible regimes. At present, their potential benefits in light detection, which include polarization dependency, tunability, and quick response times have been successfully demonstrated. Optical antennas also can be seen as directionally responsive elements for point detectors. This review provides an overview of the historical background of the topic, along with the basic concepts and parameters of optical antennas. One of the major parts of this review covers the use of optical antennas in biosensing, presenting biosensing applications with a broad description using different types of data. We have also mentioned the basic challenges in the path of the universal use of optical biosensors, where we have also discussed some legal matters.

Tailoring local density of optical states to control emission intensity and anisotropy of quantum dots in hybrid photonic-plasmonic templates

We report results of controlled tuning of the local density of states (LDOS) in versatile, flexible, and hierarchical self assembled plasmonic templates. Using 5 nm diameter gold (Au) spherical nanoantenna within a polymer template randomly dispersed with quantum dots, we show how the photoluminescence intensity and lifetime anisotropy of these dots can be significantly enhanced through LDOS tuning. Finite difference time domain simulations corroborate the experimental observations and extend the regime of enhancement to a wider range of geometric and spectral parameters bringing out the versatility of these functional plasmonic templates. It is also demonstrated how the templates act as plasmonic resonators for effectively engineer giant enhancement of the scattering efficiency of these nano antenna embedded in the templates. Our work provides an alternative method to achieve spontaneous emission intensity and anisotropy enhancement with true nanoscale plasmon resonators.

High-intensity directional surface plasmonic excitation based on the multi metallic slits with nano-antenna

Micro-nano structure optical device based on surface plasmon polariton such as super lens, micro-nano resonators and waveguides, etc. owns great applications in different research fields, especially in integrated optics and nanophotonics, for it has extremely small size and can be integrated into a micro-nano optical system. Comparatively, the directional wave exciter attracts much attention since it breaks the symmetries of wave propagation and excitation and can be applied to a micro-nano optical logic modulation system in the future. In order to realize the high-efficiency directional excitation in ultra-small structure based on surface plasmon polariton, a newly designed metal insulator metal waveguide based surface plasmon directional exciter with multiple channels and nano antenna is presented in this paper. The basic structure of the surface plasmon directional exciter is a two-slit metal plate, and the directional propagation surface plasmon wave is generated according to wave interference. To obtain a single surface plasmon wave in the specific orientation, a phase difference of π/2 between the surface waves generated by slits is necessary. To achieve the different phase differences, both heights and widths of the channels are calculated according to the waveguide mode function. It is worth noting that the directional wave exciter with dual channels is able to generate unsymmetrical wave propagation, however, the excitation efficiency is rather low, which restricts its potential applications in micro-nano optical system. In the paper, in order to further raise the coupling efficiency of the excited surface plasmon wave, and increase its propagation, other additional channels are designed in the directional wave exciter structure. Compared with the traditional dual channel system, the additional channels with similar parameters, and the same interference features are introduced in the surface plasmon directional exciter to increase the light transmission and surface wave energy. In addition, a nano antenna structure based on resonance is presented on the structure surface to enhance the surface plasmon excitation as well. The design tactics of the directional surface plasmon wave exciter are analytically explained in the paper. With numerical calculation based on the finite difference time domain method, the simulation result proves that the proposed surface plasmon wave directional exciter is able to generate single orientation surface wave with extremely high coupling ratio. Moreover, with additional multiple channels and nano antenna, the energy of the directional coupled surface plasmon wave is improved obviously, which indicates that the propagation distance of the surface plasmon wave is increased. In the simulation, both the additional channels and nano antenna are able to increase the energy and propagation distance of the surface plasmon wave obviously: the energies of directional propagated surface plasmon waves of four and six channel directional wave exciters with nano antenna are 6.74 times and 9.30 times that of the traditional dual slit directional wave exciter without nano antenna, respectively. Moreover, it is worth noting that the newly designed nano antenna based multi-channel enhanced surface plasmon wave directional exciter owns compact structure and can be easily fabricated at low cost. It is believed that this work can be an important reference for designing micro and nano photonic and plasmonic elements in integrated optics.

Plasmonic coupling with most of the transition metals: a new family of broad band and near infrared nanoantennas.

In this article, we show for the first time, both theoretically and empirically, that plasmonic coupling can be used to generate Localized Surface Plasmon Resonances (LSPRs) in transition metal dimeric nano-antennas (NAs) over a broad spectral range (from the visible to the near infrared) and that the spectral position of the resonance can be controlled through morphological variation of the NAs (size, shape, interparticle distance). First, accurate calculations using the generalized Mie theory on spherical dimers demonstrate that we can take advantage of the plasmonic coupling to enhance LSPRs over a broad spectral range for many transition metals (Pt, Pd, Cr, Ni etc.). The LSPR remains broad for low interparticle distances and masks the various hybridized modes within the overall resonance. However, an analysis of the charge distribution on the surface of the nanoparticles reveals these modes and their respective contributions to the observed LSPR. In the case of spherical dimers, the transfer of the oscillator strengths from the "dipolar" mode to higher orders involves a maximum extinction cross-section for intermediate interparticle distances of a few nanometers. The emergence of the LSPR has been then experimentally illustrated with parallelepipedal NAs (monomers and dimers) made of various transition metals (Pt, Pd and Cr) and elaborated by nanolithography. Absolute extinction cross-sections have been measured with the spatial modulation spectroscopy technique over a broad spectral range (300-900 nm) for individual NAs, the morphology of which has been independently characterized by electron microscopy imaging. A clear enhancement of the LSPR has been revealed for a longitudinal excitation and plasmonic coupling has been clearly evidenced in dimers by an induced redshift and broadening of the LSPR compared to monomers. Furthermore, the LSPR has been shown to be highly sensitive to slight modifications of the interparticle distance. All the experimental results are well in agreement with finite element method (FEM) calculations in which the main geometrical parameters characterizing the NAs have been derived from electron microscopy imaging analysis. The main advantage of dimers as compared to monomers lies in the generation of a well-defined and highly enhanced electromagnetic field (the so-called "hot spots") within the interparticle gap that can be exploited in photo-catalysis, magneto-plasmonics or nano-sensing.

Optimisation of the Detection Sensitivity of Plasmonic Nanoantenna Based Sensors for Mid-infrared Spectroscopy

In this paper we report on the optimisation of the optical characteristics of 2D-arrays of plasmonic gold nanoantennas (NA) that can be used as high sensitivity mid-infrared spectroscopic sensor for the detection of chemical/biological substances by using the Surface Enhanced Infrared Absorption (SEIRA) technique. This approach allows to detect the presence of a substance adsorbed on the NA by measuring its optical absorption under the conditions for which the maximum of the reflectivity response of the 2D-array occurs at the same wavelength of the substance maximum absorption peak. In particular, by acting on the 2D-array periodicity, NA shape, size and thickness, numerical simulations of the 2D-array detection response, based on Finite Element Method (FEM), demonstrate that is possible to obtain an increase in the detection sensitivity of more than three orders of magnitude with respect to that one achievable if the same substance is deposited on an unstructured planar metal surface, independently from the wavelength at which the substance absorption occurs. Moreover, we present the results of an analysis of the dependence of the 2D-array maximum reflectivity and peak wavelength on the geometrical parameters characterising the NA and the 2D-array.

Limitations of Extreme Nonlinear Ultrafast Nanophotonics

AbstractHigh-harmonic generation (HHG) has been established as an indispensable tool in optical spectroscopy. This effect arises for instance upon illumination of a noble gas with sub-picosecond laser pulses at focussed intensities significantly greater than 1012W/cm2. HHG provides a coherent light source in the extreme ultraviolet (XUV) spectral region, which is of importance in inner shell photo ionization of many atoms and molecules. Additionally, it intrinsically features light fields with unique temporal properties. Even in its simplest realization, XUV bursts of sub-femtosecond pulse lengths are released. More sophisticated schemes open the path to attosecond physics by offering single pulses of less than 100 attoseconds duration.Resonant optical antennas are important tools for coupling and enhancing electromagnetic fields on scales below their free-space wavelength. In a special application, placing field-enhancing plasmonic nano antennas at the interaction site of an HHG experiment has been claimed to boost local laser field strengths, from insufficient initial intensities to sufficient values. This was achieved with the use of arrays of bow-tie-shaped antennas of ∼ 100nm in length. However, the feasibility of this concept depends on the vulnerability of these nano-antennas to the still intense driving laser light.We show, by looking at a set of exemplary metallic structures, that the threshold fluence Fth of laser-induced damage (LID) is a greatly limiting factor for the proposed and tested schemes along these lines.We present our findings in the context of work done by other groups, giving an assessment of the feasibility and effectiveness of the proposed scheme.

A Novel Design of Circular Edge Bow-Tie Nano Antenna for Energy Harvesting

AbstractIn this study, a novel nano antenna is designed in order to convert the high frequency solar energy, thermal energy or earth re-emitted sun’s energy into electricity. The proposed antenna is gold printed on a SiO

Limitations of Extreme Nonlinear Ultrafast Nanophotonics

Abstract High-harmonic generation (HHG) has been established as an indispensable tool in optical spectroscopy. This effect arises for instance upon illumination of a noble gas with sub-picosecond laser pulses at focussed intensities significantly greater than 1012W/cm2. HHG provides a coherent light source in the extreme ultraviolet (XUV) spectral region, which is of importance in inner shell photo ionization of many atoms and molecules. Additionally, it intrinsically features light fields with unique temporal properties. Even in its simplest realization, XUV bursts of sub-femtosecond pulse lengths are released. More sophisticated schemes open the path to attosecond physics by offering single pulses of less than 100 attoseconds duration. Resonant optical antennas are important tools for coupling and enhancing electromagnetic fields on scales below their free-space wavelength. In a special application, placing field-enhancing plasmonic nano antennas at the interaction site of an HHG experiment has been claimed to boost local laser field strengths, from insufficient initial intensities to sufficient values. This was achieved with the use of arrays of bow-tie-shaped antennas of ∼ 100nm in length. However, the feasibility of this concept depends on the vulnerability of these nano-antennas to the still intense driving laser light.We show, by looking at a set of exemplary metallic structures, that the threshold fluence Fth of laser-induced damage (LID) is a greatly limiting factor for the proposed and tested schemes along these lines.We present our findings in the context of work done by other groups, giving an assessment of the feasibility and effectiveness of the proposed scheme.

Broadband diodelike asymmetric transmission of linearly polarized light in ultrathin hybrid metamaterial

We present the underlying theory, the design specifications, and the experimental demonstration of the broadband diodelike asymmetric transmission of linearly polarized light in the near-infrared regime. This result is achieved through the use of a two-layer hybrid metamaterial, composed of an L-shaped metallic particle and a double nano antenna. The experimental results are shown to agree well with the theoretical predictions and the simulated transmission spectra. The realization of the diodelike asymmetric transmission can be attributed to the combination of two independently functioning metallic structures, which are shown to perform their respective function even when shifted away from perfect alignment. This work offers a further step in developing broadband diodelike asymmetric transmission for use in electromagnetic devices.

A silicon nanowire photodetector using Au plasmonic nanoantennas

Abstract We suggest a silicon nanowire (SiNW) photodetector side-contacted with hemispherical Au nanoantennas (NAs) that can remarkably amplify the intensity of the near-infrared optical field. The plasmonic NA suppresses visible-range guided mode excitation in SiNW, which enables our photodetector to possess a near-infrared-selective response and overcome the inherent poor optical absorption of Si. The NA can form Schottky contacts with SiNWs for enhancing carrier collection. The vertical NW array also has the geometrically beneficial effects of wide tolerance in light polarization with reduced material consumption.

Location effect on gold nano bi-domes based absorption coefficient

Binary particle swarm optimization (BPSO) algorithm was used to generate the binary gold nano bi-domes for getting higher absorption coefficient spectrum. The simulation results show that absorption coefficient strongly depends on the localized position of nano particles and non-periodic structures have more appropriate response in term of absorption coefficient. This approach can be useful in optical applications such as solar cell and plasmonic nano antenna.

Binary TLBO algorithm assisted for designing plasmonic nano bi-pyramids-based absorption coefficient

A new efficient binary optimization method based on Teaching–Learning-Based Optimization (TLBO) algorithm is proposed to design an array of plasmonic nano bi-pyramids in order to achieve maximum absorption coefficient spectrum. In binary TLBO, a group of learners consisting of a matrix with binary entries controls the presence (‘1’) or the absence (‘0’) of nanoparticles in the array. Simulation results show that absorption coefficient strongly depends on the localized position of plasmonic nanoparticles. Non-periodic structures have more appropriate response in term of absorption coefficient. This approach is useful in optical applications such as solar cells and plasmonic nano antenna.

Underpinning Hybridization Intuition for Complex Nanoantennas by Magnetoelectric Quadrupolar Polarizability Retrieval

A central idea in plasmonics and metamaterials is to interpret scattering resonances as resulting from hybridization of electric dipoles. Recent developments in metamaterials as well as in plasmonic Fano systems have further included magnetic dipoles and electric quadrupoles in this reasoning. We derive a method to retrieve dipole and quadrupole polarizability tensors of nano scatterers from full-wave simulations, which allows us to underpin this intuitive reasoning by quantifying the existent modes and their strengths in complex nano antennas. By application to a dolmen plasmon structure, we show how the retrieval sheds new light on plasmon induced transparency. Further, we show how to implement radiative corrections to a dipole–quadrupole model applicable when scatterers are placed near a surface, sphere, or stratified medium, similar to the known correction of dipole polarizabilities by the local density of optical states. We demonstrate how this model allows us to interpret near field excitation data ...

Invited Presentation: Optical Properties of Carbon Nanotube/Chromophores Assemblies

The delocalized π-electronic system of carbon nanotubes allows them to link non-covalently to a lot of different organic molecules. In contrast to covalent functionalization, this weak interaction preserves most of the nanotubes intrinsic properties (photoluminescence or mobility for instance) but still leads to a strong enough coupling so as to give stable compounds and to induce new and efficient functionalities [1, 2]. We focus on nanotubes / chromophores compounds where the latter acts as an optical nano antenna that absorbs light and transfers its energy to the nanotube, allowing a uniform excitation of all the chiral species in the sample [3, 4, 5, 6, 7].In this presentation, we will focus on the latest developments of our research in this topic.

Nanoantennas for ultrabright single photon sources

We propose to use nanoantennas (NAs) coupled to incoherently pumped quantum dots for ultrabright single photon emission. Besides fully quantum calculations, we analyze an analytical expression for the emitted photon rate. From these analytical considerations, it turns out that the Purcell factor and the pumping rate are the main quantities of interest. We also disclose a trade-off between the emitted photon rate and the nonclassical nature of the emitted light. This trade-off has to be considered while designing suitable NAs, which we also discuss in depth.

Tuning the Scattering Response of the Optical Nano Antennas Using Graphene

In this paper, we propose the tuning of the optical nano antenna in the visible spectrum using graphene. A dipole structure for the nano antenna is considered with the resonating wavelength at the VIS-NIR spectrum range. Resonance is determined using the scattering characteristics of the dipole antenna. Placing monolayer and bilayers of graphene sheets on top of the optical nano antenna will result in a change in the resonating wavelength. The input impedance of the resultant structures is calculated. The FDTD simulation results for resonance characteristics were verified with the experiment results. Such architecture of graphene on top of the dipole nano antennas can be used for different biological and chemical gas sensors.

Large enhancement of nonlinear terahertz absorption in intrinsic GaAs by plasmonic nano antennas

We demonstrate remarkably strong nonlinear terahertz (THz) effects in an intrinsic GaAs wafer patterned with a nanometer-width slot antenna array. The antenna near-field reaches 20 MV/cm due to the huge field enhancement in the plasmonic nano-structure (field enhancement factor, α ≅ 50). The THz fields are strong enough to generate high density free carriers (Ne > 1017 cm−3) via interband excitations associated with impact ionizations and thus to induce large absorption of the THz radiation (>35%). The nonlinear THz interactions take place in the confined region of nanometer-scale layer adjacent to the antenna.