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Multipolarized nanoantennae are promising for terahertz applications due to their ability to support multiple resonance and polarization sensitivity. This study investigates the behavior of multipolarized gold nanoantennae placed on a Si-SiO2 substrate and compares their performance with antennae in air. The results show that the resonance frequency shifts from 27 THz in the air to 26 THz on the SiSiO2 substrate. SEM and FTIR analysis confirmed the antenna dimensions and optical response, with experimental reflectance spectra revealing resonance at 21 THz and 26 THz. The multi-polarized antenna demonstrated stable performance across different polarization angles compared to traditional dipole antennae, making it suitable for various terahertz applications. These findings provide insights into optimizing nanoantenna design for advanced sensors and communication systems. [ABSTRACT FROM AUTHOR]

In this study, we present optical and numerical analysis methods to enhance the absorbed power of metallic nanoantenna arrays on a glass substrate under solar irradiance. A comprehensive exploration of various materials (Au, Pt, core-shell Ag-Pt, and Al-Al 2 O 3 ), morphologies (rectangular prism, cylindrical, triangular prism, and hexagram prism with the same volume of metal), and arrangements (periodic, disorder, and amorphous) was conducted to optimize absorbed power and heat production for maximizing the photothermal effect. In periodic arrangements, the absorbed power increased 1.5 to 3 times (minimum to maximum) by optimizing the period across different nanoantenna configurations. Morphologies characterized by sharp angles (triangular, hexagram) exhibited 1.3 to 1.7 times higher absorbed power. Despite Pt's shorter absorption decay length, it demonstrated broader absorption across the solar spectrum, resulting in 1.15 to 1.3 times more absorbed power than Au. Incorporating an Ag core with a Pt shell enhanced the absorbed power by 1.2 to 1.35 times compared to Au. The hexagram Ag-Pt nanoantenna displayed the highest absorbed power in periodic and disordered arrangements, while the triangular Pt excelled in amorphous configurations. The triangular Al-Al 2 O 3 nanoantenna exhibited 1.14 times higher absorbed power compared to the rectangular Au, presenting a cost-effective manufacturing option. The behavior of plasmon fields and destructive interference was investigated for the nanoantenna array. Three absorption regions were observed: near-distance with minimum absorption due to plasma turbulence, middle-distance (resonance period) with maximum absorption due to plasmon fields enhanced each other, and far-distance with constant absorption due to interference happening between the nanoantenna and incident light without other effects. [ABSTRACT FROM AUTHOR]

Electrically tunable graphene‐metal metasurfaces with controllable optical properties have attracted interest for straightforward manipulation of free space light. Their resonance tuning range depends on graphene's electrical transport characteristics, which are affected by its quality, operating conditions, and the device design. An important example of the latter is the direct contact of metallic antennas with the graphene layer that limits the extent to which a bias voltage can tune the metasurface's permittivity. In this work, this issue is resolved in a straightforward and fabrication‐efficient way for graphene‐metal hybrid metasurfaces with multiple plasmonic resonances. It is demonstrated that the incorporation of a 10 nm Al2O3 barrier layer enhances the tuning range of mid‐infrared resonances compared to metasurfaces without barrier layer, i.e., from 300 to 700 nm for a 7.3 µm resonance and from 110 to 140 nm for a 4.7 µm resonance. The improved tunability of the metal/dielectric/graphene metasurface can be attributed to the reduced electrical coupling between metal and graphene, as confirmed by an equivalent circuit model. These results bring closer the use of active metasurfaces based on two‐dimensional materials under ambient conditions, with possible applications as optical filters, modulators, and information processing devices that require dynamic control of light. [ABSTRACT FROM AUTHOR]

Multipolarized nanoantennae are promising for terahertz applications due to their ability to support multiple resonance and polarization sensitivity. This study investigates the behavior of multipolarized gold nanoantennae placed on a Si-SiO2 substrate and compares their performance with antennae in air. The results show that the resonance frequency shifts from 27 THz in the air to 26 THz on the SiSiO2 substrate. SEM and FTIR analysis confirmed the antenna dimensions and optical response, with experimental reflectance spectra revealing resonance at 21 THz and 26 THz. The multi-polarized antenna demonstrated stable performance across different polarization angles compared to traditional dipole antennae, making it suitable for various terahertz applications. These findings provide insights into optimizing nanoantenna design for advanced sensors and communication systems.

Nanoparticle-on-mirror systems have shown promise in nanophotonics for enhancing light emission from quantum sources. In this study, we introduce a new subclass of hybrid systems called nanoparticle-in-pit. We conducted simulations to analyze the scattering properties and near-field enhancement of emission for a silicon nanoparticle near a gold surface and in a nanopit. Our focus was on investigating the impact of different geometric parameters of a nanoantenna on the optical resonances. The proposed nanoantenna exhibited Fano-like resonances, achieving a high Q-factor of up to 100 and subwavelength near-field confinement. Additionally, for silicon nanoparticles in the visible spectrum, we demonstrated the presence of various resonances that can enhance both the absorption and emission of quantum emitters by adjusting the geometric parameters of the nanoantenna. For real applications, we suggest the core-shell configuration of a silicon nanoparticle with a dielectric shell as a more suitable one. The properties of silicon nanoparticle-based nanoantennas presented in this study surpass those of a silicon nanoparticle on a gold surface, opening up possibilities for nanophotonic applications using high-index dielectric nanoparticles. [ABSTRACT FROM AUTHOR]

Liquid crystal (LC) based spatial light modulators (SLMs) are a type of versatile device capable of arbitrarily reconfiguring the wavefront of light. For current commercial LC-SLM devices, the large pixel size limits their application to diffractive optics and 3D holographic displays. Pixel miniaturization of these devices is challenging due to emerging inter-pixel crosstalk, ultimately linked to the thick LC layer necessary for full phase (or amplitude) control. Integration of metasurfaces, i.e., 2D arrangements of resonant nanoantennas, with thin LC has emerged as a promising platform to boost light modulation, enabling realization of sub-wavelength pixel size SLMs with full phase (or amplitude) control. In most devices realized so far, however, the presence of an alignment layer, necessary to induce a preferential initial LC orientation, increases the voltage requirement for resonance tuning and reduces the efficiency of light modulation, something that accentuates for an ultra-thin (e.g., submicron) metasurface-LC cell. Here, we present an alternative strategy by which the LC molecular alignment is purely controlled by the periodicity and geometry of the nanoantenna without any additional alignment layer. The nanoantennas are specifically designed for the double purpose of sustaining optical resonances that are used for light modulation and to, simultaneously, induce the required LC pre-alignment. The proposed device structure allows lower voltage and reduced switching times (sub-millisecond) compared to devices including the alignment layer. This novel strategy thus helps to improve the performance of these miniaturized-pixel devices, which have emerged as one of the potential candidates for the next generation of products in a wide range of applications, from virtual/augmented reality (VR/AR) and solid-state light detection and ranging (LiDAR), to 3D holographic displays and beyond. [ABSTRACT FROM AUTHOR]

Nanofabrication technologies significantly influence the development of modern optical science. One of such technologies is laser‐induced transfer, which allows the creation of single Mie‐resonant spherical particles on a wide range of substrates. This study shows that this method can provide asymmetric dimers at the output: a single femtosecond pulse being focused on a silicon‐on‐insulator wafer results in appearing two nearly spherical particles of different sizes. The resulting dimers are characterized by scanning electron microscopy, elastic light scattering and Raman spectroscopy to gain insight into their structural properties. Back focal plane imaging and variable‐color evanescent‐wave illumination are then employed to measure the light scattering patterns from isolated dimers. Due to the interference of the excited resonances, the observed patterns are strongly asymmetric in a range of visible wavelengths, which is consistent with theoretical predictions. The results demonstrate the potential of asymmetric silicon dimers made by single‐shot laser‐induced transfer for color routing at visible light. [ABSTRACT FROM AUTHOR]

Terahertz (THz) technology is the utilization of electromagnetic waves with frequencies in the range of 0.1 to 10 terahertz. This frequency range is also known as the submillimeter range, lying between the microwave and infrared regions of the electromagnetic spectrum. Terahertz technology has numerous applications in various fields, such as communications, spectroscopy, imaging, and sensing. In communications, terahertz waves can transmit large amounts of data over short distances and potentially revolutionize wireless communication networks. Recently, scientists and researchers have been concentrating on terahertz technology as it continues to evolve. In this paper, we design and simulate a rectangular-shaped patch nanoantenna with a line-feeding technique; the proposed antenna is based on three layers: a perfect electric conductor (PEC) patch, a silicon substrate layer, and a fully PEC ground plane layer. The main aim is to study the impact of altering the nanoantenna's parameters, including shape, size, ground plane, feed line, and patch nanostructures, on its behavior. The simulated antenna operates in triple-bands of frequrncywhich are 571.85, 715.66, and 905.05 THz. As a result, the applications of this terahertz frequency band are within the visible range. [ABSTRACT FROM AUTHOR]

Active metasurfaces provide unique advantages for on-demand light manipulation at a subwavelength scale for emerging visual applications of displays, holographic projectors, optical sensors, light detection and ranging (LiDAR). These applications put stringent requirements on switching speed, cycling duration, electro-optical controllability, modulation contrast, optical efficiency and operation voltages. However, previous demonstrations focus only on particular subsets of these key performance requirements for device implementation, while the other performance metrics have remained too low for any practical use. Here, we demonstrate an active Huygens’ metasurface based on conductive polyaniline (PANI), which can be in-situ grown and optimized on the metasurface. We have achieved simultaneously on the active metasurface switching speed of 60 frame per second (fps), switching duration of more than 2000 switching cycles without noticeable degradation, hysteresis-free controllability over intermediate states, modulation contrast of over 1400 %, optical efficiency of 28 % and operation voltage range within 1 V. Such PANI-powered active metasurface design can be readily incorporated into other metasurface concepts to deliver high-reliability electrical control over its optical response, paving the way for compact and robust electro-optic metadevices.

Herein, the radiation patterns of single-split ring resonators (SSRRs) and double-split ring resonators (DSRRs) in the vertical direction are tailored by reconfiguring the resonator geometries. To design unequal arm lengths for controlling the floating split angle of the resonators and changing their electromagnetic multipole compositions, vertical metamaterials were fabricated using the metal-stress-driven self-folding method. The simulation results well agree with the experimental transmittance and reflectance results and demonstrate the geometry-dependent angle variation of the far-field radiation. Symmetric SSRRs and DSRRs radiate in the vertical and horizontal directions, respectively. With increasing pad shift, the radiation angle of the asymmetric SSRR completely rotates toward the horizontal direction along the ring plane, but the DSRRs can rotate only from 0° to 45° to the horizontal plane. Furthermore, by decomposing the multipoles into their constituents, we show that the directional scattering performance can be verified by manipulating the horizontal and vertical components of the electric dipoles. This novel combination of SSRRs and DSRRs can effectively and efficiently reconfigure the radiation direction in the infrared (IR) region, paving the way for color routers, metasurfaces, and directive IR emitters in compact optical metadevices.

Liquid crystal (LC) based spatial light modulators (SLMs) are a type of versatile device capable of arbitrarily reconfiguring the wavefront of light. For current commercial LC-SLM devices, the large pixel size limits their application to diffractive optics and 3D holographic displays. Pixel miniaturization of these devices is challenging due to emerging inter-pixel crosstalk, ultimately linked to the thick LC layer necessary for full phase (or amplitude) control. Integration of metasurfaces, i.e., 2D arrangements of resonant nanoantennas, with thin LC has emerged as a promising platform to boost light modulation, enabling realization of sub-wavelength pixel size SLMs with full phase (or amplitude) control. In most devices realized so far, however, the presence of an alignment layer, necessary to induce a preferential initial LC orientation, increases the voltage requirement for resonance tuning and reduces the efficiency of light modulation, something that accentuates for an ultra-thin (e.g., submicron) metasurface-LC cell. Here, we present an alternative strategy by which the LC molecular alignment is purely controlled by the periodicity and geometry of the nanoantenna without any additional alignment layer. The nanoantennas are specifically designed for the double purpose of sustaining optical resonances that are used for light modulation and to, simultaneously, induce the required LC pre-alignment. The proposed device structure allows lower voltage and reduced switching times (sub-millisecond) compared to devices including the alignment layer. This novel strategy thus helps to improve the performance of these miniaturized-pixel devices, which have emerged as one of the potential candidates for the next generation of products in a wide range of applications, from virtual/augmented reality (VR/AR) and solid-state light detection and ranging (LiDAR), to 3D holographic displays and beyond.

An effective performance enhancement model for the thin film solar cell conjointly based on extraordinary transmission and nanoantenna is proposed and investigated. The absorber layer of the extraordinary transmission based solar cell contains a metallic thin film with periodic holes. Maximum extraordinary transmission is accomplished as the metallic film has the same refractive index on both sides. Increased light transmission causes the absorber layer to absorb more light, which increases short circuit current density and subsequently the efficiency of the thin film solar cell. The presented analysis demonstrates that adding a square nano patch on the top surface of the absorber layer can further boost the extraordinary transmission. The extraordinary transmission is increased because of the formation of cavity nanoantenna. Cavity nanoantenna increases the coupling of light into the hole due to the excitation of surface plasmons polaritons. The proposed design of solar cell exhibits around 98% absorption and the short circuit current density is increased by a factor of 3.23. The study has been carried out using finite difference time domain (FDTD) method.

A dielectric nanosphere with orthogonal electric dipole (ED) and magnetic dipole (MD) Mie resonances can be a nanoantenna radiating circularly polarized light in specific directions if the amplitudes and the phase relations are properly designed. First, theoretical calculations show that a silicon nanosphere illuminated with a linearly polarized plane wave radiates circularly polarized light at the wavelength in between the ED and MD resonances if the refractive index of a surrounding medium (nm) is ≈1.3; the ellipticity of the scattered light can be >0.99 when nm is in a 1.19–1.35 range. Size‐purified silicon nanospheres suspended in water (nm = 1.33) are then prepared, and the angle‐ and circular‐polarization‐resolved scattering spectra are studied. It is experimentally demonstrated that circularly polarized light is radiated in specific directions under linearly polarized plane wave illumination. The results also show that the wavelength of the radiation of circularly polarized light can be controlled in the whole visible range by controlling the silicon nanosphere diameter in 100–200 nm range. [ABSTRACT FROM AUTHOR]

Light‐harvesting is a fundamental process in nature, which inspires researchers to develop artificial systems for photocatalysis, photovoltaics, and biosensing. A previously introduced light‐harvesting nanoantenna, based on polymeric nanoparticles (NPs) loaded with rhodamine dyes and bulky hydrophobic counterions, provides a record‐breaking antenna effect ≈1000. However, the high dye cooperativity of its thousands of encapsulated dyes causes energy losses by traces of self‐quenched dye aggregates. Here, it is found that these imperfections can be suppressed by blank hydrophobic salts (BHS) formed by the same bulky counterion (fluorinated tetraphenylborate) with an optically inactive cation, analogs of ionic liquids. The presence of BHS increases twofold the fluorescence quantum yields and fluorescence lifetimes of NPs and suppresses their fluorescence blinking. This study assumes that BHS provides an excess of bulky counterions that excludes traces of dye aggregates. As a result, an efficient Forster resonance energy transfer (FRET) is achieved from 40 000 dye donors to a single acceptor within a 70 nm particle, leading to the antenna effect of 4800, which is by far the highest value reported to date. Using this nanoantenna, a single‐molecule detection of the FRET acceptor is realized at low excitation power using an RGB camera of a smartphone. [ABSTRACT FROM AUTHOR]

Active metasurfaces provide unique advantages for on-demand light manipulation at a subwavelength scale for emerging visual applications of displays, holographic projectors, optical sensors, light detection and ranging (LiDAR). These applications put stringent requirements on switching speed, cycling duration, electro-optical controllability, modulation contrast, optical efficiency and operation voltages. However, previous demonstrations focus only on particular subsets of these key performance requirements for device implementation, while the other performance metrics have remained too low for any practical use. Here, we demonstrate an active Huygens' metasurface based on conductive polyaniline (PANI), which can be in-situ grown and optimized on the metasurface. We have achieved simultaneously on the active metasurface switching speed of 60 frame per second (fps), switching duration of more than 2000 switching cycles without noticeable degradation, hysteresis-free controllability over intermediate states, modulation contrast of over 1400 %, optical efficiency of 28 % and operation voltage range within 1 V. Such PANI-powered active metasurface design can be readily incorporated into other metasurface concepts to deliver high-reliability electrical control over its optical response, paving the way for compact and robust electro-optic metadevices. [ABSTRACT FROM AUTHOR]

An efficient structure of thin film solar cell (TFSC) is designed and investigated using a plasmonic nanoantenna for improving the performance of the solar cell. The proposed design is formed as a shape of "Swastika," an ancient geometrical figure, designed by bending the conventional dipole antenna up to optimal lengths. The designed antenna is positioned on the top of the absorber layer which is made up with amorphous silicon and is topped with an anti-reflection layer of Indium Tin Oxide. Due to Swastika shape, the structure equally responds to the different polarized waves and becomes polarization-insensitive and thus can significantly enhance the performance of the thin-film solar cells. The new design confines the electric field in a larger area. This confinement is due to the presence of additional feed gaps produced by bending the conventional dipole antenna, increasing the absorption. The simulation results show that the design provides an absorption enhancement of 99.2% in the absorber layer. [ABSTRACT FROM AUTHOR]

This review article outlines research on nanoantennas in infrared bands and visible bands over the last one and half decades. The objective of this survey is to highlight basic insights and state-of-the-art developments based on applications. Besides, characterization and fabrication methods are also presented. The authors also proposed a dipole nanoantenna of multi-layer geometry which provides better efficiency and wider bandwidth. It offers an impedance bandwidth of 312 THz with maximum radiation efficiency and peak realized gain of 82.1% and 2.95 dBi, respectively. This proposed antenna provides an omnidirectional radiation pattern, which is a suitable candidate for energy harvesting and other photonic applications. [ABSTRACT FROM AUTHOR]

Electrons injected into one-dimensional (1D) metals are efficiently converted into infrared plasmons because the unique property of the Luttinger liquid, a strongly correlated electronic matter in one-dimensional (1D) metals, prohibits excitations of other quasiparticles. Using the Luttinger liquid behavior, the electrically driven 1D metals can be used as a feed for optical nanoantennas. Nanoantennas can couple the 1D Luttinger liquid plasmons in the feed to the radiating photons in free space. In this work, we suggest design principles for the 1D metallic Luttinger liquid feed and the nanoantennas to obtain high injection and radiation efficiencies, respectively. We expect that our work can promote experimental efforts to realize electrically driven Luttinger liquid-fed nanoantennas and efficient infrared light sources.

The results of a theoretical study of the behavior of a system of nanophotonic devices, consisting of receiving and transmitting plasmonic metal antennas, are presented. Based on the finite element method, the main parameters of antennas located in the TSV channel and receiving a signal in the terahertz frequency range are calculated. The limiting range of signal transmission and the coefficient of its amplification are determined. Conclusions are drawn on the suitability of the presented configuration as a system for wireless data transmission and reception in three-dimensional integrated circuits. [ABSTRACT FROM AUTHOR]

Surface-enhanced spectroscopies, such as surface-enhanced Raman scattering (SERS), fluorescence (SEF), circular dichroism, etc., are powerful tools for investigating nano-entities with high sensitivities. Owing to the giant local electric field confined in a plasmonic nanogap, nanogap-enhanced spectroscopies could detect samples with ultralow concentrations, even down to the single-molecule level for SERS and SEF. This great ability to detect analytes with ultralow concentrations provides opportunities for early diagnosis and monitoring in modern biomedicine. However, local laser excitations would inevitably bring about unwanted disruptive background perturbations, local heating, and the consequent geometry reshaping and biological analyte damages. Remote spectroscopies avoiding direct laser exposure to the samples can be treated as remarkable solutions. Here, we combined the nanoparticle-on-mirror (NPoM) family with the philosophy of remote spectroscopy to construct so-called “NPoM pairs” structures. They consist of two identical NPoMs with matched resonances yet separate functions either as receiving or transmitting antennas. A figure of merit for evaluating the remote spectroscopies was put forward, which accounts for the efficiencies in three processes, i.e., receiving, transporting, and transmitting. In addition, we experimentally demonstrated the performances of these NPoM pairs by proof-of-principle applications on the remote SERS and SEF. The optical access of the spectral information in these NPoM pairs both locally and remotely manifests themselves as fundamental building blocks for remote spectroscopies.

Integration of multiple diversified functionalities into an ultracompact platform is crucial for the development of on-chip photonic devices. Recently, a promising all-dielectric two-dimensional platform based on Bloch surface waves (BSWs) sustained by dielectric multilayer has been proposed to enable various functionalities and provide novel approach to photonic devices. Here, we design and fabricate a multifunctional directional coupler to achieve both spectral and polarimetric routing by employing asymmetric nanoslits in a dielectric multilayer platform. Due to the dispersion property of BSWs, the directional coupling behavior is sensitive to wavelength and polarization. We demonstrate numerically and experimentally the wavelength selective directional coupling of TE BSW mode with an intensity ratio of the BSW excitation in opposite directions reaching 10 dB. Polarization selective directional coupling is also achieved at specific operating wavelength due to different response to a nanoantenna for TE and TM BSWs. The proposed two-dimensional photonic device opens new pathway for a wide range of practical applications such as molecular sensing, imaging with different polarization, and spectral requirements.

Graphene (G)-plasmonic nanoparticles (NPs) systems have found immense nanoscale applications via utilizing the sensitive optical response of graphene to the photo-induced electrons transferred from attached NPs. These electrons are emitted from the plasmonic metal NPs under the influence of a Localized Surface Plasmon Resonance (LSPR). Here, we first present theoretical investigations of the photoemission electrons in the G-plasmonic NPs system influenced by the LSPR of NPs. A rigorous theoretical approach is used to determine the level of photo-exited electrons and the optimal parameters for achieving a highest photoemission yield. The photoemission of electrons is mainly driven by the surface photoelectric effect in which an electron near the particle surface absorbs photon energy and overcomes the potential barrier at the metal–graphene boundary. For a thorough investigation, we study the effects of the material and geometry of NPs and the intensity of the LSPR field on the rate of photoemission. It is shown that silver nanoparticles combined with graphene are more effective in enhancing light–matter interaction in graphene owing to the lower interfacial energy barrier and higher field enhancement. Finally, we verify that the photo-induced electron density predicted by our calculations is matched with that obtained by combining theoretical and Raman-based experimental results. [ABSTRACT FROM AUTHOR]

This paper investigates a nano-scaled patch antenna in optical frequency range. The proposed nanoantenna consists of a circular patch of dimension 130 × 130 nm2, placed on a glass substrate with thickness 112 nm. To protect the antenna against environmental jeopardies, a superstrate layer of dimensions 40 × 2.5 × 110.4 nm3 has been added. To enhance the performance of the antenna in terms of bandwidth and efficiency and to obtain circular polarization, multiple slots are added into the patch and ground plane of the proposed nanoantenna. The suggested antenna resonates at 182 THz with an impedance bandwidth of about 47 THz (160–207 THz) and a minimum radiation efficiency of 96.54% throughout the entire operating band. The operating bandwidth of the designed nano antenna corresponds to a wavelength range of 1449–1875 nm which covers the entire wavelength of the third optical communication window centered at 1550 nm. Besides, the proposed antenna is circularly polarized which make it very interesting in wireless communication system because it has the advantage to emit the electromagnetic radiation in a corkscrew fashion which allows efficient transmission to the receiver. The proposed antenna covers the telecom optical communication wavelength bands, S-band (1460–1530 nm), C-band (1530–1565 nm), and L-band (1565-1625 nm) in the operating range of 160 THz–207 THz. The proposed nanoantenna with circular polarization might be useful for various integrated components and variety of applications such as optical communication, nano photonics, biosensing, and spectroscopy and could play an essential role in progress of plasmonic sensors. [ABSTRACT FROM AUTHOR]

In this work, a PIT-like transparency is realized via the strong coupling of plasmonic dipole and epsilon-near-zero (ENZ) mode. Numerical simulations with the finite difference time-domain method (FDTD) demonstrate that triple transparent windows are achieved. The tunability of PIT resonant frequency and transmission amplitude can be achieved by changing the length or gap of the gold nanorods and the carrier concentration of ITO. Finally, it is found that the sensitivity of the model with the change of refractive index of background materials has reached 330.57 THz/RIU, and the figure of merit (FOM) has reached 27.54/RIU. This provides a theoretical reference for the application of the model in optical storage, filtering, and ultra-sensitive infrared band sensor design. [ABSTRACT FROM AUTHOR]

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All-dielectric nanoantennas, consisting of high refractive index semiconductor material, are drawing a great deal of attention in nanophotonics. Owing to their ability to manipulate efficiently the flow of light within sub-wavelength volumes, they have become the building blocks of a wide range of new photonic metamaterials and devices. The interaction of the antenna with light is largely governed by its size, geometry, and the symmetry of the multitude of optical cavity modes it supports. Already for simple antenna shapes, unraveling the full modal spectrum using conventional far-field techniques is nearly impossible due to the spatial and spectral overlap of the modes and their symmetry mismatch with incident radiation fields. This limitation can be circumvented by using localized excitation of the antenna. Here, we report on the experimental near-field probing of optical higher order cavity modes (CMs) and whispering gallery modes (WGMs) in amorphous silicon nanoantennas with simple, but fundamental, geometrical shapes of decreasing rotational symmetry: a disk, square, and triangle. Tapping into the near-field using an aperture type scanning near-field optical microscope (SNOM) opens a window on a rich variety of optical patterns resulting from the local excitation of antenna modes of different order with even and odd parity. Numerical analysis of the antenna and SNOM probe interaction shows how the near-field patterns reveal the node positions of – and allows us to distinguish between – cavity and whispering gallery modes. As such, this study contributes to a richer and deeper characterization of the structure of light in confined nanosystems, and their impact on the structuring of the light fields they generate.

Nanoantenna fusion photonics and nanotechnology can manipulate light through the ultra-thin structure composed of sub-wavelength antennas, and meet the important requirements for miniaturized optical components, completely changing the field of optics. However, the device design process is still time-consuming and consumes computing resources. Besides, the professional knowledge requirements of engineers are also high. Relying on the algorithm’s inference ability and excellent computing ability, artificial intelligence has great potential in the fields of material design, material screening, and device performance prediction. However, the deep learning (DL) requires a mass of data. Therefore, this article proposes a method for the forward and inverse design of nanoantenna based on DL. Compared with the previous work, the network uses a two-dimensional matrix as input, which has a simple structure and is more suitable for the advantages of deep netural network. Simultaneously, the small datasets can be used to achieve higher accuracy. In the forward prediction, 100% of the data error is less than 0.007; in the inverse prediction, the data with error less than 0.05 accounted for 90%, 99.8% and 100% of the length, height, and width’s datasets. It demonstrates that the method can improve the automation of the design process and reduce the consumption of computer resources. [ABSTRACT FROM AUTHOR]

Scattering patterns of nanoantennas consisting of closely spaced parallel gold and silver nanoplatelets are numerically calculated. It is demonstrated that such a system scatters light in different directions depending on its wavelength. It is found that variations of nanoplatelet widths and lengths makes it possible to widely vary the wavelength at which the dominating light scattering direction reverses. A convenient way to select nanoplatelet sizes to design a nanoantenna with a specified switch wavelength is proposed. [ABSTRACT FROM AUTHOR]

Abstract Detecting and quantifying intracellular microRNAs (miRNAs) are a critical step in resolving a cancer diagnostic and resolving the ensemble of gene products that orchestrate the living state of cells. However, the nanoprobe for detecting low abundance miRNAs in cell cytosol is restricted by either the “one-to-one” signal-trigger model or difficulty for cytosol delivery. To address these challenges, we designed a light-harvesting nanoantenna-based nanoprobe, which directs excitation energy to a single molecule to sensitively detect cytosolic miRNA. With light irradiation, the light-harvesting nanoantenna effectively disrupted lysosomal structures by generation of reactive oxygen species, substantially achieved cytosol delivery. The nanoantenna containing > 4000 donor dyes can efficiently transfer excitation energy to one or two acceptors with 99% efficiency, leading to unprecedented signal amplification and biosensing sensitivity. The designed nanoantenna can quantify cytosolic miR-210 at zeptomolar level. The fluorescence lifetime of the donor exhibited good relationship with miR-210 concentration in the range of 0.032 to 2.97 amol/ngRNA. The zeptomole sensitivity of nanoantenna provides accurate bioimaging of miR-210 both in multiple cell lines and in vivo assay, which creates a pathway for the creation of miRNA toolbox for quantitative epigenetics and personalized medicine.

Here we theoretically investigate the cooperative effects between plasmonic nanoantennas mediated by whispering gallery modes (WGMs) of wavelength-scale dielectric resonators. Strong constructive cooperative effects can be obtained which lead to significantly enhanced optical responses of the antennas. This is represented by the enhanced absorption peaks or the broadened spectra of the antennas. An important feature in producing the strong cooperative effects is that the energies transfer constructively or destructively from different antennas to a WGM first. This requires the simultaneous excitation of the plasmonic modes of the antennas by a source. Otherwise, the cooperative effect between the antennas becomes much weaker. The spectral behaviors related to the cooperative effects are also highly dependent on the relative spectral overlapping between the antennas and WGM, the antenna-WGM coupling strength and the number of antennas. Specifically, the integrated absorption of each antenna in a four-antenna case can be about 4 times larger than that of the one-antenna case. The enhanced optical responses of the plasmonic antennas are important for enhancing light-matter interactions.

We designed and prepared a novel anemone-like array substrate (ALAS) integrated pump-free microfluidic sensor based on surface-enhanced Raman spectroscopy (SERS). ALAS substrate forms ordered nanoantenna arrays on polystyrene (PS) nanospheres, which can improve the light-capturing efficiency of the substrate and induce surface plasmon resonance. It successfully achieved multi-dimensional enhancement of electric field coupling and further enhanced the Raman scattering signals of the Raman reporter molecules. Driven by a capillary pump, the seawater containing Hg2+ can be loaded in 100 s without the need for cumbersome syringe pumps. Our results demonstrated that the integrated sensor exhibits excellent responsiveness in detecting Hg2+ within the concentration range of 10−7 to 10−12 mol L−1. The detection limit can reach 1 pmol L−1. Therefore, we believe that this ALAS integrated microfluidic sensor provides a promising solution for the rapid and sensitive detection of Hg2+. [Display omitted] • The newly anemone-like array substrate (ALAS) showed multi-dimensional synergistically coupled SERS enhancement. • The ALAS contained nanospheres and nanoantennas to provide large surface area and improved the ssDNA modification. • The capillary force from comb-like structural channels and hydrophilic inner surface eliminates the need of syringe pump. [ABSTRACT FROM AUTHOR]

Nanoantenna based on surface plasma polariton (SPR) resonance effect has been integrated respectively with pyroelectric and thermopile infrared detectors. This on-chip integration has enabled narrowband infrared detector for miniaturization of Non-Dispersive Infrared (NDIR) gas sensors as well as multi-component gas sensing. Herein, we propose and construct nanoantenna integrated quantum dot photodetector to further overcome the limitations of thermal detectors such as relatively slow response and low detectivity. We focus on PbS colloidal quantum dots (CQDs) owing to their strong absorption toward near infrared light and convenient integration with silicon substrates. The PECVD grown SiO 2 and EBE grown Au nanodisks were subsequently deposited on PbS CQD layer to form a metal-insulator-semiconductor (MIS) architecture. Typically, the nanoantenna integrated photodetector exhibited a narrowband photoresponse at peak wavelength around 1300 nm, with a 24 % improvement in the responsivity compared to conventional devices. NDIR gas-sensing studies based on the nanoantenna integrated narrowband photodetector show that the selectivity for specific gases (CH 4 and NH 3 in this study) is obtained without the need for additional narrowband filters, and lower detection limits are also achieved because of the higher photoresponse at specific wavelength. Our proof-of-concept work demonstrates the advantages of nanoantenna integrated narrowband photodetector for infrared gas sensing. • Combination of surface plasmons and photoelectric effects. • PbS(QD) detector with micro-nano optical antenna applied to gas sensing. • The theoretical detection limits of ammonia and methane are 481 ppm and 170 ppm. [ABSTRACT FROM AUTHOR]

Controlling directionality of optical emitters is of utmost importance for their application in communication and biosensing devices. Metallic nanoantennas have been proven to affect both excitation and emission properties of nearby emitters, including the directionality of their emission. In this regard, optical directional nanoantennas based on a Yagi–Uda design have been demonstrated in the visible range. Despite this impressive proof of concept, their overall size (~λ2/4) and considerable number of elements represent obstacles for the exploitation of these antennas in nanophotonic applications and for their incorporation onto photonic chips. In order to address these challenges, we investigate an alternative design. In particular, we numerically study the performance of a recently demonstrated "ultracompact" optical antenna based on two parallel gold nanorods arranged as a side-to-side dimer. Our results confirm that the excitation of the antiphase mode of the antenna by a nanoemitter placed in its near-field can lead to directional emission. Furthermore, in order to verify the feasibility of this design and maximize the functionality, we study the effect on the directionality of several parameters, such as the shape of the nanorods, possible defects in the dimer assembly, and different positions and orientations of the nanoemitter. We conclude that this design is robust to structural variations, making it suitable for experimental upscaling. [ABSTRACT FROM AUTHOR]

Coherent perfect absorption (CPA) describes the absence of all outgoing modes from a lossy resonator, driven by lossless incoming modes. Here, we show that for nanoresonators that also exhibit radiative losses, e.g., plasmonic nanoantennas, a generalized version of CPA (gCPA) can be applied. In gCPA outgoing modes are suppressed only for a subset of (guided plasmonic) modes while other (radiative) modes are treated as additional loss channels - a situation typically referred to as perfect impedance matching. Here we make use of gCPA to show how to achieve perfect impedance matching between a single nanowire plasmonic waveguide and a plasmonic nanoantenna. Antennas with both radiant and subradiant characteristics are considered. We further demonstrate potential applications in background-free sensing.

Nanoscale devices, also called nanomachines, form communication networks and cooperate with each other so that they can be used to perform complicated tasks. Such networks of nanodevices, named nanonetworks, envisioned to serve the functionality and performance of today’s Internet. This paper presents a comparative review of the state-of-the-art electromagnetic (EM) nanonetworks highlighting their potentials and challenges in a comprehensive manner. We first introduce the promising areas of applications of nanonetworks; therein, we explain how it can be useful in biomedical fields, environmental domains, consumer products, military systems, and on-chip wireless communications. Then, the survey focuses on the basic principles of fundamental physical layer issues enabling nanonetworks; the discussion includes frequency bands, modulation and demodulation, and EM properties of nanoparticles. Subsequently, the study provides an overview of transmission characteristics including channels, channel coding, and energy constraint nature of nanonetworks. Furthermore, we provide an in-depth discussion on nanoantenna highlighting its variants and their characteristics; give an overview of network layer issues; and discuss the security issues in EM nanonetworks. The study argues that despite the significant recent development of EM communication as one of the most desired modes of nano communications, the limited capabilities of nanomachines introduce a new set of challenges and unique requirements and pose unseen characteristics that need to be deliberately addressed. On that, the review finally provides a critical discussion on the applicability of EM mode for nano communication networks highlighting the future challenges with a set of perspectives of possible solutions.

We report on single-photon emitters for the telecommunication O-band (1260–1360 nm), which comprise an InAs/(In)GaAs quantum dot with asymmetric barriers, placed inside a semiconductor tapered nanocolumn acting as a photonic nanoantenna. The implemented design of the barriers provides a shift in the quantum dot radiation wavelength towards the O-band, while the nanoantenna collects the radiation and ensures its effective output. With non-resonant optical pumping, the average count rate of emitted single photons exceeds 10 MHz with the second-order correlation function g (2) (0) = 0.18 at 8 K. [ABSTRACT FROM AUTHOR]

The strong coupling between single quantum emitters and resonant optical micro/nanocavities is beneficial for understanding light and matter interactions. Here, we propose a plasmonic nanoantenna placed on a metal film to achieve an ultra-high electric field enhancement in the nanogap and an ultra-small optical mode volume. The strong coupling between a single quantum dot (QD) and the designed structure is investigated in detail by both numerical simulations and theoretical calculations. When a single QD is inserted into the nanogap of the silver nanoantenna, the scattering spectra show a remarkably large splitting and anticrossing behavior of the vacuum Rabi splitting, which can be achieved in the scattering spectra by optimizing the nanoantenna thickness. Our work shows another way to enhance the light/matter interaction at a single quantum emitter limit, which can be useful for many nanophotonic and quantum applications. [ABSTRACT FROM AUTHOR]

A solution‐based bottom‐up process to produce one‐ and two‐dimensional arrays of densely packed spherical nanoparticles (NPs) of crystalline silicon (Si), having the lowest order Mie resonance in the visible range, is developed. First, an agglomeration‐free solution of Si NPs with a narrow size distribution is prepared. By using grooves fabricated on the surface of a polymer as a template, arrays of Si NPs with different shapes are formed by a template‐assisted self‐assembly method, and then they are transferred to an arbitrary substrate. To demonstrate proper formation of Si NP arrays, polarization‐resolved scattering spectra are measured for different size linear arrays, i.e., a monomer to a pentamer, of Si NPs placed on a silica substrate. The observed spectra are well‐reproduced by the numerical simulations. When the polarization direction of incident light is parallel to the array axis, the scattering spectra are strongly modified from that of a Si NP monomer due to near‐field coupling of the electric dipole (ED) modes. In a Si NP tetramer, the peak of the ED mode overlaps with that of the magnetic dipole (MD) mode and strong forward scattering is observed at the MD peak wavelength due to the Kerker effect. [ABSTRACT FROM AUTHOR]

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The coupling of gold nanoantennas (AuNAs) in the arrangement of monomers in bidimensional gratings is investigated both experimentally and numerically. The influence of edge diffraction, corresponding to the grazing propagation of specific diffracted orders, and the dependence of grating parameters on lattice plasmon modes are studied. It is shown that the grating pitch influences the spectral position of the Rayleigh wavelength related to the grazing diffraction in air and/or in glass. In order to investigate the effect of diffraction and its interplay with the Rayleigh wavelength, extinction measurements with different incidence angles are carried out. For incidence angles above θ = 20 ∘ , along with the excitation of quadrupolar and vertical modes, very narrow dips or sharp excitations are observed in the spectra. These ones strongly depend on the respective spectral position of Rayleigh anomaly and specific dipolar mode, on the propagation direction of the grazing diffraction, and on the considered plasmon mode. These features are explained in the light of numerical calculations obtained with Green's tensor method. All the above different characteristics and couplings are of great practical interest, especially for a possible implementation in biosensor devices and for other technological applications spanning from precision medicine and life science to telecommunications and energy systems. [ABSTRACT FROM AUTHOR]

Thermally induced particle hopping in the nanoscale double-well potential is fundamental in material design and device operation. After the proposal of the basic hopping theory, several experimental studies, including some using the optical trapping method, have validated the theoretical approach over various friction ranges of the surrounding medium. However, only external parameters, such as viscosity, temperature, and pressures, have been varied in practical circumstances, and other tools capable of adjusting the potential profile itself to modulate the hopping rate are needed. By using metallic nanoantenna with various gap sizes and different optical pump power, we engineered a double-well potential landscape and directly observed the hopping of a single nanoparticle with a diameter of 4 nm. The distance between the two potential wells was 0.6–5 nm, and the maximum well depth and maximum height of the central potential barrier were approximately 69 and 4 kBT, respectively. The hopping rate was governed by the Arrhenius law and showed a vertex when the barrier height was approximately 2 kBT, which was in good agreement with the computational expectations.