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Stronger light confinement can be enabled by nanoantennas in the nanostructure and result in efficient control of the directionality of the scattering. We report on an observation of the well-pronounced multipolar resonances from nickel nanoantennas originating from collective effects. We show that the collective coupling of multipolar modes from weak scatterers can substantially enhance the electric dipole and quadrupole resonances. We also demonstrate the generalized lattice Kerker effect in this nanoantenna array. Resonant multipolar excitations within nickel nanoantenna arrays can significantly enhance phenomena such as magneto-optical effects, indicating promising potential for advanced applications in the field of nanophotonics and sensing. [ABSTRACT FROM AUTHOR]

Plasmonic nanoantennas have attracted much attention lately, among other reasons because of the directionality of light emitted by fluorophores coupled to their localized surface plasmon resonances. Plasmonic picocavities, i.e., cavities with mode volumes below 1 nm3, could act as enhanced antennas due to their extreme field confinement, but the directionality on their emission is difficult to control. In this work, we show that the plasmonic picocavity formed between the tip of a scanning tunneling microscope and a metal surface with a monoatomic step shows directional emission profiles and, thus, can be considered as a realization of a picoantenna. Electromagnetic calculations demonstrate that the observed directionality arises from the reshaping and tilting of the surface charges induced at the scanning tip due to the atomic step. Our results pave the way to exploiting picoantennas as an efficient way for the far-field probing and control of light-matter interactions below the nanoscale. [ABSTRACT FROM AUTHOR]

This work presents a novel approach to achieve directional and normal thermal emission from epsilon‐near–zero (ENZ) materials. ENZ materials exhibit near–zero permittivity at the ENZ point, resulting in some unique properties compared to conventional optical materials including infinite wavelength, constant phase distribution, and decoupling of spatial and temporal fields inside the ENZ material. These properties are used to engineer the far‐field thermal emission from optical antennas fabricated on ENZ film in the mid‐infrared. By coupling the antenna resonance mode with the Berreman mode of the ENZ material, highly directional and normal emission is demonstrated. This approach could have significant implications for thermal management, energy conversion, and sensing applications. [ABSTRACT FROM AUTHOR]

Self-assembling of plasmonic nanoparticles into an oligomer can produce optical nanoantennas with resonant magnetic responses, which constitutes a promising platform to study magnetic light-matter interactions at the nanoscale. However, these self-assembled magnetic nanostructures typically feature a flat-lying geometric configuration, giving rise to out-of-plane magnetic dipole (MD) moments that cannot couple to the far-field light efficiently. Herein, we propose a new geometric configuration of plasmonic nanoantennas to realize in-plane MD responses. This is achieved by elegantly coupling a plasmonic nanoparticle oligomer to one or more adjacent metal mirrors, virtually forming a vertically standing nanoparticle tetramer or trimer, yet with in-plane MD moments. We verified this design strategy by numerically simulating the resonance responses of three typical mirror-coupled nanostructures, all exhibiting pronounced resonant MD characters. Furthermore, optical magnetic emitters can be readily coupled to these plasmonic nanoantennas and gain an emission enhancement of two orders of magnitude while simultaneously featuring a high emission directionality (collection efficiency up to ∼ 70 % evaluated with common microscopy optics). We believe these mirror-enabled magnetic nanoantennas could lead to novel nanophotonic devices fully exploiting the magnetic nature of light. [ABSTRACT FROM AUTHOR]

As screen sizes are becoming larger and larger, exceeding human physical limitations for direct interaction via touching, remote control is inevitable. However, among the current solutions, inertial gyroscopes are susceptible to positional inaccuracies, and gesture recognition is limited by cameras' focus depths and viewing angles. Provided that the issue of ghost points can be effectively addressed, grating antenna light-trapping technology is an ideal candidate for multipoint inputs. Therefore, we propose a differential amplitude modulation scheme for grating antenna-based multi-beam optical touch, which can recognize different incidence points. The amplitude of the incident beams was first coded with different pulse widths. Then, following the capture of incident beams by the grating antenna and their conversion into electrical currents by the aligned detector arrays, the incident points of the individual beams were recognized and differentiated. The scheme was successfully verified on an 18-inch screen, where two-point optical touch with a position accuracy error of under 3 mm and a response time of less than 7 ms under a modulation frequency of 10 kHz on both incident beams was achieved. This work demonstrates a practical method to achieve remote multi-point touch, which can make digital mice more accurately represent the users' pointing directions by obeying the natural three-point one-line aiming rule instantaneously. [ABSTRACT FROM AUTHOR]

Nanoscale metal–organic frameworks (NMOFs) exhibit unique properties for drug delivery, including ultrahigh storage capabilities, biocompatibility, biodegradability, and sustained release of encapsulated cargo. However, due to their localized electronic states, MOFs are nonresponsive to external stimuli such as light or magnetic fields. This study investigates the integration of light‐responsive nanoantennas into NMOFs to enhance their application as smart drug delivery nanosystems. By integrating gold bipyramid nanoantennas within ZIF‐8 and NU‐1000 NMOFs, core@shell nanosystems are created with photothermal capabilities. Utilizing cresyl violet as a model drug, the loading and release dynamics of these nanosystems are analyzed, demonstrating controlled drug release under near‐infrared (NIR) light stimulation. Photothermal release studies conducted in living cells reveal the potential of these nanocomposites for spatiotemporal targeted, light‐activated drug delivery. Further evaluation of the NU‐1000 nanocomposite loaded with chemotherapeutics—doxorubicin, carboplatin, and oxaliplatin—in both 2D and 3D cell cultures shows the nanosystem effectiveness in cell internalization and therapeutic NIR activation. The findings demonstrate that the incorporation of stimuli‐responsive elements into NMOFs offers a promising approach for developing advanced drug delivery platforms. [ABSTRACT FROM AUTHOR]

The objective of this article is to examine potential techniques for suppressing solar heat flow on the optical antenna of a laser communication sensor. Firstly, the characteristics of the geosynchronous Earth orbit's (GEO) space radiation environment are analysed, and a combined passive and active thermal control solution is proposed. Secondly, the temperature distribution of the lasercom sensor under extreme operating conditions is simulated utilising IDEAS-TMG (6.8 NX Series) software, which employs Monte Carlo and radiative heat transfer numerical calculation methods. Finally, a strategy for avoiding direct sunlight around midnight is proposed. The simulation results demonstrated that the thermal control solution and solar avoidance strategy proposed in this paper achieved long-term fine-stable control of the temperature field of the optical antenna, which met the thermal permissible communication hours per daily orbit cycle in excess of 14 h per day. [ABSTRACT FROM AUTHOR]

To keep pace with the expanding data capacity in modern communications and increasing on‐chip integration density, it is highly desirable to have electro‐optic modulators featured with compact footprint, large modulation bandwidth, low energy consumption, and full complementary metal‐oxide‐semiconductor (CMOS) compatibility. Here, this work experimentally demonstrates a high‐speed electro‐optic modulator in the telecommunication wavelength range made of a 1D chain resonator of Mie‐resonant silicon nanoparticles. The modulator exploits the plasma dispersion effect and works in the carrier depletion configuration. The resulting large modulation bandwidth over 40 GHz and low energy consumption of 23 fJ bit−1 are attributed to its ultra‐compact footprint of 10 µm2. The open eye diagrams are measured up to 40 Gbits s−1. The modulators are fabricated at wafer level by a silicon photonic foundry using CMOS‐compatible process. This modulator shows promise for achieving higher integration density and larger modulation bandwidth. It can be added to the existing on‐chip device building blocks library and used for a wide range of applications, including data communication, quantum photonics, and non‐reciprocal optics. [ABSTRACT FROM AUTHOR]

Interference between the electric and magnetic dipole-induced in Mie nanostructures has been widely demonstrated to tailor the scattering field, which was commonly used in optical nano-antennas, filters, and routers. The dynamic control of scattering fields based on dielectric nanostructures is interesting for fundamental research and important for practical applications. Here, it is shown theoretically that the amplitude of the electric and magnetic dipoles induced in a vanadium dioxide nanosphere can be manipulated by using laser-induced metal-insulator transitions, and it is experimentally demonstrated that the directional scattering can be controlled by simply varying the irradiances of the excitation laser. As a straightforward application, we demonstrate a high-performance optical modulator in the visible band with high modulation depth, fast modulation speed, and high reproducibility arising from a backscattering setup with the quasi-first Kerker condition. Our method indicates the potential applications in developing nanoscale optical antennas and optical modulation devices. [ABSTRACT FROM AUTHOR]

Reciprocal scatterers necessarily extinguish the same amount of incoming power when excited from opposite directions. This property implies that it is not possible to realize scatterers that are transparent when excited from one direction but that scatter and absorb light for the opposite excitation, limiting opportunities in the context of asymmetric imaging and nanophotonic circuits. This reciprocity constraint may be overcome with an external bias that breaks time-reversal symmetry, posing however challenges in terms of practical implementations and integration. Here, we explore the use of tailored nonlinearities combined with geometric asymmetries in suitably tailored resonant nanoantennas. We demonstrate that, under suitable design conditions, a nonlinear scatterer can be cloaked for one excitation direction, yet strongly scatters when excited at the same frequency and intensity from the opposite direction. This nonreciprocal scattering phenomenon opens opportunities for nonlinear nanophotonics, asymmetric imaging and visibility, all-optical signal processing and directional sensing. [ABSTRACT FROM AUTHOR]

We study numerically and experimentally the second-harmonic generation (SHG) from rectangular metagratings of V-shaped gold nanoantennas. We show that by carefully engineering the array pitch to steer the diffraction orders toward the single antenna emission, the extracted signal is maximized. This enhancement is attributed to the angular overlap between the radiation pattern and array factor and is comparable to the improvement yielded by the coupling of surface lattice resonances (SLRs) with local modes. Moreover, we demonstrate a simple technique to experimentally reconstruct the emission diagram of an antenna from measurements of the collective grating response as a function of the excitation angle. Excellent agreement is obtained with simulations when the sample is immersed either in air or in water, which is crucial in view of future sensing application. Thanks to the high signal-to-noise ratio and low dependence on the statistical particle dispersity, this method constitutes an effective alternative to back-focal plane imaging when very weak signals such as SHG are involved. [ABSTRACT FROM AUTHOR]

An array of metallic nanoparticles can diffract or concentrate the incident electromagnetic wave and behave as an antenna. In this paper, the effects of the inner sub-wavelength structure of nanoparticles are studied on the directivity of the plasmonic nanoantenna, which is coated on the output of a waveguide. Three 5*5 element configurations are analyzed: nanocubes, nanoshells, and nanoframes array. Numerical results are obtained using the 3D FDTD technique. The results show that structured nanoantennas can improve the antenna's directivity due to the plasmonic properties and hybridization mechanism. Between the three configurations investigated in the 250–800 nm wavelength range, the nanoshell array exhibits maximum and minimum amounts of its directivity at 321.5 nm and 591 nm, respectively. At 558 nm, nanoframes and nanoshells' arrays show the same amount of directivity, and from the wavelength greater than 558 nm, the nanoframe array has the best performance. The results may help design and fabricate directive optical fiber endcaps. [ABSTRACT FROM AUTHOR]

Optical antenna resonators enable control of light‐matter interactions on the nano‐scale via electron–photon hybrid states in strong coupling. Specifically, mid‐infrared (MIR) nano‐antennas coupled to saturable intersubband transitions in multi‐quantum‐well (MQW) semiconductor heterostructures allow for the coupling strength to be tuned through antenna resonance and field intensity. Here, tip‐enhanced nano‐scale variation of antenna‐MQW coupling across the antenna is demonstrated, with a spatially‐dependent coupling strength gaq$g_{\rm aq}$ varying from 73 (strong coupling) to 24 cm−1$\rm {cm}^{-1}$ (weak coupling). This behavior is modeled based on the spatially dependent local constructive and destructive interference between tip and antenna fields. Using a quantum‐mechanical density‐matrix model of the MQW system with its designed values of transition dipole moment, doping density, and population decay time, the picosecond IR pulse coupling to intersubband transitions and the associated tip induced strong‐field saturation effects are described. These results present a new regime of nonlinear IR light‐matter control based on the dynamic manipulation of quantum hybrid states on the nanoscale and in the infrared, with a perspective regarding extension to molecular vibrations. [ABSTRACT FROM AUTHOR]

Thermoelectric nanoantennas have been extensively investigated due to their ability to directly convert infrared (IR) radiation into direct current without an additional rectification device. In this study, we introduce a thermoelectric nanoantenna geometry for maximum output voltage (Voc) and propose an optimal series array configuration with a finite number of antennas to enhance the Voc. A finite and open-ended SiO2 substrate, with a thickness of a quarter-effective wavelength at a frequency of 28.3 THz, is used to generate standing waves within the substrate. An array of antennas is then positioned optimally on the substrate to maximize the temperature difference ( ∆ T ) between hot and cold areas, thereby increasing the average Voc per antenna element. In numerical simulations, a linearly polarized incident wave with a power density of 1.42 W/cm2 is applied to the structure. The results show that a single antenna with the optimum geometry on a substrate measuring 35 µm × 35 µm generates a ∆ T of 64.89 mK, corresponding to a Voc of 1.75 µV. Finally, a series array of 5 × 6 thermoelectric nanoantennas on a 150 µm × 75 µm substrate including measurement pads achieves an average ∆ T of 49.60 mK with a total Voc of 40.18 µV, resulting in an average Voc of 1.34 µV per antenna element and a voltage responsivity (βv) of 0.77 V/W. This value, achieved solely by optimizing the antenna geometry and open-ended substrate, matches or exceeds the Voc and βv of approximately 1 µV and 0.66 V/W, respectively, from suspended thermoelectric antenna arrays over air cavities. Therefore, the proposed thermoelectric nanoantenna array device, characterized by high stability and ease of fabrication, is suitable for manufacturing massive nanoantenna arrays for high-output IR-DC energy harvesters. [ABSTRACT FROM AUTHOR]

The utilization of optical antennas for active control of far-field radiation at the subwavelength scale is crucial in various scientific and technological applications. We propose a thermally tunable disk design of indium tin oxide (ITO) and aluminum gallium nitride ( Al 0.18 Ga 0.82 As ), enabling a switch between absorption and scattering. Furthermore, the control of far-field radiation pattern can be easily realized by combining ITO and Al 0.18 Ga 0.82 As to enhance or suppress emission. Our results demonstrate that hybrid structures can be dynamically tuned with temperature variations. In the proposed design, a frequency is achieved at the wavelength of 1240 nm. The thermal tunability of hybrid structures introduces new multifunctional possibilities for light manipulation, thereby enhancing the potential applications of new devices in the near-infrared range. [ABSTRACT FROM AUTHOR]

We demonstrate a quantum ratchet detector, which is a high-resistance photovoltaic mid-infrared detector based on an engineered spatial arrangement of subbands. In photovoltaic quantum-well photodetectors, in which unidirectional photocurrent is generated by asymmetric quantum-well structures, maximization of device resistance by suppressing undesired electron transports is crucial for minimizing noise. A semi-quantitative guideline suggests the significance of spatial separation between wavefunctions for reducing the conductance from the ground state. Here, we employ a step quantum well made of a shallow floor and a deep well. Photoexcited electrons are quickly transferred to a separated location from the ground state through fast resonant tunneling and phonon scattering, and then they are allowed to flow in only one direction. This architecture is made possible by the use of a GaAs/AlGaAs material system, and it achieves a resistance as high as 6.0 × 104 Ωcm2 with a single-period structure. Combined with optical patch antennas for responsivity enhancement, we demonstrate a maximum background-limited specific detectivity of 6.8 × 1010 cmHz1/2/W at 6.4 μm, 77 K for normal incidence, and a background-limited-infrared-photodetector temperature of 98 K. [ABSTRACT FROM AUTHOR]

There is a growing interest in the development of transportable optical ground station (TOGS) as an important component of laser communication network. The object of this paper is a TOGS designed for optical LEO satellite downlink as well as for long-distance aircraft downlink. A composite gravity compensation mount is proposed to simplify and efficiently suppress the low-order aberrations of an 800 mm aperture primary mirror with variable orientation of the optical antenna of a TOGS as it changes pointing. In this study, first we describe the composition of the TOGS and the utility of each part. Second, taking the minimization of the primary mirror deformation as the optimization objective, we employ the particle swarm optimization algorithm to find the optima of several key structural parameters by Isight software. Next, the annular Zernike polynomials are adopted to fit the wavefront error over the entire surface of the primary mirror for describing low-order aberrations, proving that the composite mount effectively suppresses the wavefront error to smaller than ⋋ /27, as the elevation angle changes from the horizontal to the vertical one. Finally, the ZYGO interferometer wavefront detections show that, after eliminating fabrication imperfections, the RMS of the wavefront error over the entire surface of the mirrors for horizontal and vertical axes, due to deformation, are 0.04⋋ and 0.035⋋, respectively. Compared to the results of the fitted wavefront error, the relative errors are 9.5% and 8.1%. The results show the validity and feasibility of the optimized composite mount and the wavefront fitting method, which can prove its reference significance for the budget and allocation of the systematic wavefront error in meter-scale optical antenna of the TOGS for satellite downlink. [ABSTRACT FROM AUTHOR]

Nanophotonics can enhance the inherent weak signal exhibited by chiral molecules in circular dichroism (CD) spectroscopy experiments. One mechanism to achieve this CD enhancement is based on increasing the optical chirality produced by nanophotonics antennas in their near‐field, where chiral molecules are placed. However, ascertaining whether this CD enhancement is reached presents significant experimental challenges due to the complexity of measuring near‐field optical chirality. Here, it is demonstrated that a local and single measurement of the degree of circular polarization in the far‐field enables quantifying near‐field CD enhancements. Thereby, based on this far‐field measurement, the optimal response of the antenna is predicted for enhanced chiral sensing. Experimental validation of this near‐to‐far‐field relation is provided for silicon spherical nanoantennas. The experimental results, supported by analytical theory and exact numerical simulations, can be interesting for the experimental characterization of devices capable of enhancing CD from a single far‐field Stokes measurement. [ABSTRACT FROM AUTHOR]

Fast modulation of optical signals that carry multidimensional information in the form of wavelength, phase or polarization has fueled an explosion of interest in integrated photonics. This interest however masks a significant challenge which is that independent modulation of multi-wavelength carrier signals in a single waveguide is not trivial. Such challenge is attributed to the longitudinal direction of guided-mode propagation, limiting the spatial separation and modulation of electric-field. Here, we overcome this using a single photonic element that utilizes active coherent (near) perfect absorption. We make use of standing wave patterns to exploit the spatial-degrees-of-freedom of in-plane modes and individually address elements according to their mode number. By combining the concept of coherent absorption in spatio-spectral domain with active phase-change nanoantennas, we engineer and test an integrated, reconfigurable and multi-spectral modulator operating within a single element. Our approach demonstrates for the first time, a non-volatile, wavelength-addressable element, providing a pathway for exploring the tunable capabilities in both spatial and spectral domains of coherent nanophotonics. [ABSTRACT FROM AUTHOR]

We report on the experimental investigation, by means of spatially-resolved cathodoluminescence spectroscopy, of rectangular all-dielectric Ge nanoantennas sustaining Fabry-Perot resonances. The combination of spatial and spectral resolution allows us to directly image the standing-wave pattern of the local density of optical states inside the nanoantennas, which is the fingerprint of the resonant Purcell contribution to the overall emission enhancement previously reported in the literature for the same structures. Our results confirm that the emission properties of Ge nanostructures can be effectively tuned by engineering the local density of optical states and that cathodoluminescence provides valuable information to experimentally address such modulation in their emission properties. [ABSTRACT FROM AUTHOR]

This study showcases an experimental demonstration of near‐field optical trapping and dynamic manipulation of an individual extracellular vesicle. This is accomplished through the utilization of a plasmonic dielectric nanoantenna designed to support an optical anapole state—a non‐radiating optical state resulting from the destructive interference between electric and toroidal dipoles in the far‐field, leading to robust near‐field enhancement. To further enhance the field intensity associated with the optical anapole state, a plasmonic mirror is incorporated, thereby boosting trapping capabilities. In addition to demonstrating near‐field optical trapping, the study achieves dynamic manipulation of extracellular vesicles by harnessing the thermoelectric effect. This effect is induced in the presence of an ionic surfactant, cetyltrimethylammonium chloride, combined with plasmonic heating. Furthermore, the thermoelectric effect improves trapping stability by a deep trapping potential. In summary, the hybrid plasmonic‐dielectric trapping platform offers a versatile approach for actively transporting, stably trapping, and dynamically manipulating individual extracellular vesicles. [ABSTRACT FROM AUTHOR]

This work investigates a metasurface design to achieve remarkable second harmonic generation (SHG) conversion efficiency and enhance effective nonlinear susceptibility using the finite element method. The elements of the designed structure are composed of a rectangular split-ring resonator Ag film, a bowtie-shaped Ag nanoantenna, and a pair of Bi bars that induce nonlinear optical phenomena due to the nonuniform distribution of the electric and magnetic fields within the device surface. The simulation results agree perfectly with the theory and demonstrate outstanding achievements in terms of SHG conversion efficiency (η) and effective nonlinear susceptibility ( χ e f f (2) ). Specifically, the metasurface reaches a peak η value of 4.544 × 10 − 8 and an effective nonlinear susceptibility of 3.4 × 10 4 pm/V. This work presents a novel and versatile design to achieve high η and χ e f f (2)   in an SHG metasurface. [ABSTRACT FROM AUTHOR]

High‐index Mie‐resonant dielectric nanostructures provide a new framework to manipulate light at the nanoscale. In particular their local field confinement together with their inherently low losses at frequencies below their bandgap energy allows to efficiently boost and control linear and nonlinear optical processes. Here, nanoantennas composed of a thin indium‐tin oxide (ITO) layer in the center of a dielectric gallium phosphide (GaP) nanodisc are investigated. While the linear response is similar to that of a pure GaP nanodisc, it is shown that second harmonic generation is enhanced across a broadband wavelength range. On the other hand, third harmonic generation is only marginally enhanced around the epsilon‐near‐zero wavelength of ITO. Linear and nonlinear finite‐difference time‐domain simulations show that despite the high refractive index contrast leading to strong field confinement inside the antenna's ITO layer, the nanogap enhancement effect is mitigated by the low nonlinear volume of the nanogap layer and the antenna's behavior at the harmonic wavelength. Measurement of ITO and GaP nonlinear susceptibilities additionally show a comparative advantage for harmonic generation in GaP. These investigations deliver insights on the mechanisms at play in nonlinear nanogap antennas and their potential applications as nanoscale devices. [ABSTRACT FROM AUTHOR]

Favorable growth of asymmetric hetero‐nanostructures consisting of plasmonic metals and semiconductors or topological nanomaterials is highly desired because the performance of nonlinear optical antennas is closely related to their composition and morphology symmetry. In this work, two methods are proposed to overgrow PtSe2, a semiconductor or topological semimetal material, onto Au nanorods (AuNRs) to form Au/AuPt/PtSe2 and Au/AgPtSe2 heterorods via wet chemical technique. Both Au/AuPt/PtSe2 and Au/AgPtSe2 heterorods show asymmetric morphologies: the Au/AuPt/PtSe2 heterorods show a partially hollow morphology with an etched AuNR coated by AuPt and PtSe2 shells; the Au/AgPtSe2 heterorods prepared by Ag‐mediated overgrowth method have a toothbrush shape with AgPtSe2 attached on the side surface near one end of AuNRs. The two asymmetric heterorods show significantly enhanced nonlinear radiations of second harmonic generation with the excitation laser wavelength tuning from 1220 to 1315 nm, and a maximal nonlinear enhancement factor of 16 is achieved, which is attributed to the interaction of gold core with platinum selenide shell and the broken symmetry of heterostructures. The findings provide a strategy to prepare metal‐topological heterostructures as optical antennas with optimized performance in the application of nonlinear photonic nanodevices. [ABSTRACT FROM AUTHOR]

This paper proposes a broadband optical transparent antenna using a transparent conductor film on a transparent polyethylene terephthalate (PET) substrate. The planar wide‐slot antenna coupling fed by microstrip has a wide impedance bandwidth, so it is selected to design the transparent antenna. The upper surface of the PET substrate is a microstrip line with a fork‐shaped tuning branch, and the lower surface is a wide slot. They were made of transparent conductor film. Finally, a new capacitive coupling method is used to feed the transparent antenna. The transparent conductor film used in the antenna is metal mesh, which was developed by 3M company. The metal mesh with an open area greater than 80% to achieve high transmittance. The measured results show that the impedance bandwidth is 177% (0.30–5.0 GHz), and the gain of the antenna varies from 5.06 to 7.8 dBi over the entire frequency band. Therefore, it can be well applied to the current indoor mobile communication system. [ABSTRACT FROM AUTHOR]

We report the fabrication and characterization of a plasmonic metasurface comprising electrically-contacted sub-wavelength gold dipole nanoantennas, conformally coated by a thin hafnia film, an indium tin oxide layer and a backside mirror, forming metal–oxide–semiconductor (MOS) capacitors, for use as an electrically-tunable reflectarray or metasurface. By voltage biasing the nanoantennas through metallic connectors and leveraging the carrier refraction effect in the MOS capacitors, our measurements demonstrate phase control in reflection over a range of about 30°, with a constant magnitude of reflection coefficient of 0.5, and the absence of secondary lobes. Comprehensive electromagnetic and quantum carrier models of the structure are developed and are in excellent agreement with the measurements. The metasurface holds promise for use as an optical phased array. [ABSTRACT FROM AUTHOR]

Optical antennas are nanostructures that introduce unprecedented possibilities for light–matter interaction at the nanoscale. An appropriately tailored plasmonic antenna can enhance the total radiative decay rate and modify the angular radiation pattern of a single‐quantum emitter through controlled near‐field coupling. Despite their ability to surpass the fundamental diffraction limit and confine the electromagnetic field to a tiny mode volume, fabricating 3D sharp scanning nanoscale plasmonic structures with desired aspect ratio is yet an ambitious goal. The fabrication of nanocones by gold evaporation on commercial atomic force microscopy probes followed by a focused ion beam milling technique is presented. The method is versatile and allows the fabrication of nanocones with desired dimensions around 100 nm along with an aspect ratio of ≈1. Their optical properties are studied and it is shown how the variation in the refractive index of the dielectric substrate affects the localized surface plasmon resonance of the nanocones, the decay rate enhancement, and the quantum yield of an emitter relevant for fluorescence/Raman scanning experiments. Theoretical studies using finite‐difference time‐domain calculations have guided the fabrication process and are consistent with experimental results. [ABSTRACT FROM AUTHOR]

The highly localized field of the plasmonic nanostructures can amplify the chiroptical effects. While most efforts have been focused on spectral responses in real space for chiroptical effects of the plasmonic nanostructures, we present alternative extrinsic chiroptical effects with respect to angular emission patterns in momentum space based on the designed directional nanoantennas. First, the chiroptical effects with respect to spectral responses for the antenna are investigated and decomposed based on the multipolar expansion method. Through the traditional spectral responses, there seems to be no chirality. However, when we turn to the angular emission patterns in the momentum space for the nanoantenna, large local angular chiroptical effects are observed. The chiroptical effects assessed by the difference of azimuth angle emission lobes under left- and right-circularly polarized light illumination can reach 180°. The multipolar analysis combined with Green's function method in a stratified medium is constructed to explain the unidirectional emission and chiral phenomenon, which agrees well with the simulation results. Moreover, the local angular chiroptical effects are also highly tunable by changing the refractive index of the surrounding medium. Our study on local angular chiroptical effects provides a new perspective to understand the chirality, and the large extrinsic chirality for the nanoantenna sheds a new light for biosensing and chiral photon detection. [ABSTRACT FROM AUTHOR]

The pursuit for enhanced light‐matter interactions using ever more suitable plasmonic materials has led to the development of novel bulk materials, such as ϵ‐near‐zero (ENZ) media. The ability to control the free carrier density gives semiconductors a significant advantage over traditionally used noble metals and phonon‐based materials as ENZ media for infrared applications. A metal‐ENZ‐metal structure is designed of epitaxially‐grown III‐V semiconductors and patterned into nanoantennas by electron‐beam lithography (from 200 up to 1800 nm) and demonstrates plasmonic resonances tuned from the terahertz up to the near‐infrared, according to the ENZ doping level (1 × 1016, 1 × 1019, and 2 × 1019 cm‐3). Experimental results, corroborated by numerical simulations, show that the designed metal‐ENZ‐metal structure is a promising vehicle to provide additional insights regarding ENZ‐based phenomena including the resonance pinning, the near‐constant phase, and the dispersive nature of ENZ materials. It is believed that III‐V semiconductors within a metal‐ENZ‐metal structure address the problem of weak light‐matter interactions and shall greatly benefit infrared applications, e.g., sensing and communication, as they can be engineered to take advantage of both plasmon and ENZ effects and integrated onto modern photonics devices. [ABSTRACT FROM AUTHOR]

Optical nanoantennas demonstrate the ability to confine and enhance electromagnetic fields. This ability makes nanoantennas essential tools for highresolution microscopy. The nanoantenna resonance and response can be tuned by changing their size, shape, and material as well as adjusting the probing conditions, e.g. excitation wavelength. In this paper we simulated the propagation and interaction of visible light with computer generated models of butterfly nanoantenna arrays using the finite-difference time-domain (FDTD) method. The simulations were used to understand and predict the experimental results obtained with scanning nearfield microscopy (SNOM) on commercially available samples. Simulation parameters are chosen carefully to reflect the measurement conditions. [ABSTRACT FROM AUTHOR]

Resonant optical antennas (ROAs) are nanodevices that can enhance the electromagnetic field in their vicinity and scatter the light in the far field. The enhanced field is localized in subdiffraction-limited volume. Their ability to exhibit strong field enhancement in the gap makes them suitable for coupling with quantum emitters. This paper introduced two novel bimodal and triple-modal asymmetric cross-shaped optical nanoantenna designs. The performance of the reported nanoantennas is numerically studied via the finite element method (FEM). The electric field enhancements and optical cross-sections are calculated to characterize the performance of the designs. These nanoantennas are low-symmetry and polarization-sensitive devices. Furthermore, the reported plasmonic nanostructures exhibit two or three tunable resonances in the optical and near-infrared wavelength regions with ultra-high field enhancement. The reported coupled cross-shaped exhibits a field enhancement of 45.9 for the high-energy resonance and 149.4 for the low-energy resonance, respectively, on E TOT / E IN scale. [ABSTRACT FROM AUTHOR]

In this article, a novel MoS2 based wideband absorber is proposed that covers the whole visible spectrum. The structure is composed of a single MoS2 layer on top of a Si/SiO2 distributed Bragg reflector. Coupled Au Nanospheres are utilized on top of the MoS2 layer that broaden the absorption spectrum as a result of the coupling between the plasmonic modes of individual particles. By optimizing the geometrical features of the plasmonic Nano-antennas, a high absorption value reaching more than 80% in the range of 400–600 nm is obtained which decreases to 50% at 700 nm. The application of the proposed structure in designing a wideband visible light photodetector is discussed either. [ABSTRACT FROM AUTHOR]

Dielectric nanostructures exhibit intriguing optical properties and outstanding advantages in designing optical nanoantennas and metasurfaces compared to plasmonic nanostructures. This study employs classical electrodynamic methods to comprehensively explore the scattering characteristics of silicon triangular nanoprisms in monomer and oligomer forms. For monomeric nanoprisms, the scattering spectra reveal two distinct and prominent resonance peaks attributed to magnetic dipole (MD) and electric dipole (ED) modes. Reducing interparticle gaps within dimeric structures leads to noticeable blueshifts in MD resonance peaks with stable intensities, in contrast to the nearly constant position and significantly reduced intensities of the ED resonance peaks. A pronounced Fano-like resonance was observed upon transitioning to tetrameric and hexameric configurations, resulting from the coupling between MD and ED modes. A broad resonance peak also emerges in the long-wavelength region due to MD-to-MD coupling. The simulations conducted herein hold significant theoretical implications, advancing our comprehension of the scattering properties of dielectric nanoparticles and contributing valuable insights into fundamental nanophotonics. [ABSTRACT FROM AUTHOR]

An optically transparent antenna fed by a coplanar L-probe is proposed in this paper. Indium-doped tin oxide (ITO) with a sheet resistance of 3.5 Ω/sq etched on a soda-lime glass substrate is used as radiation array and ground to achieve high optical transmittance. TM $ _{10} $ 10 and TM $ _{20} $ 20 modes are excited simultaneously to expand work bandwidth. The fabricated antenna achieves a –10 dB reflection bandwidth of 27.5% from 4.7 to 6.2 GHz with the overall size of 42 mm × 42 mm × 3.3 mm. Different from many antennas composed of ITO, the proposed antenna exhibits directional radiation patterns with the maximum realized gain of 4.6 dBi and the maximum efficiency of 61%. Meanwhile, the optical transmittance of the antenna can reach above 58%. [ABSTRACT FROM AUTHOR]

Low efficiency of Terahertz (THz) radiation and radiation power have limited the development of THz Science and Technology. Thus, with the aims of achieving greater photoconductive current and improving radiation characteristics of THz photoconductive antenna (PCA), this study utilized Extraordinary Optical Transmission (EOT) of light passing through various subwavelength metal structures to control and restrain the light wave in subwavelength scale. Furthermore, by grooving the grating electrode structure, the influence of metal grating's EOT on the transmission field of PCA were investigated and analyzed. Simulation results show that the effect of local electric field enhancement is significant. When the incident power is 0.1 W, the peak value of the local electric field reaches 7. 0 4 × 1 0 7 V/m. In addition, comparing to the grating electrode with no groove structure in which the field intensity was less than 4. 2 8 × 1 0 6 V/m, the local electric field increased by 16.4 times, respectively. Correspondingly, the photocurrent intensity of the improved photoconductive plasmonic structure is increased by 72.3 times. In conclusion, the improved plasma photoconductive structure was shown to obviously enhance the transmission field strength of semiconductor materials and the current of the PCA, and accordingly, to improve the THz radiation capability. [ABSTRACT FROM AUTHOR]

Multidimensional spin-selective manipulation of optical waves is crucial for various intriguing applications in modern nanophotonics, such as quantum-information processing and chiral sensing and imaging. In this work, we observed giant broadband asymmetric transmission of circularly polarized waves and spin-preserving reflection, together with near-unity transmission circular dichroism, in a planar chiral metasurface composed of high-index transition-metal-dichalcogenide nanoantennas with large material anisotropy. The perpendicular and parallel electric and magnetic dipole moments excited in the nanoantennas under circularly polarized waves are explored to account for the asymmetric transmission and optical chirality. Combined with the Pancharatnam–Berry phase, we achieved the wavefront manipulation for transmitted circularly polarized waves with an efficiency approaching 91.5% and spin-selective focusing of an incident light via a metasurface metalens. Our work will pave the way for studying the multidimensional manipulation of optical spins through engineering transition-metal-dichalcogenide-based metasurfaces. [ABSTRACT FROM AUTHOR]

The antennas that share radiators with solar cells are applicable to collect energy and integrate radio frequency functions. In this paper, a solar cell integrated multiband antenna is proposed on the basis of Vivaldi antenna structure. Unlike prior research, it has the capacity to reconfigure working frequencies and radiation performance of the antenna through optical control of the solar cell. The purpose of reconfiguration is achieved by means of two switching diodes placed between the differential Vivaldi radiator and conducted via biasing from the solar cell. The integrated solar cell functions both as part of the radiator and as the biasing source for switching diodes. According to the simulation and measurement results, the antenna performs consistently at around 5 GHz, while the radiation performance can be reconfigured at 1.16 and 3 GHz under illumination. In this way, the proposed antenna can fulfill various functions such as green energy collection, wireless communication, and light detection, which makes it applicable in the Internet of Things for low‐power wireless sensor terminal. [ABSTRACT FROM AUTHOR]

The strong coupling between electronic transitions and resonant cavity modes, facilitated by coherent energy transfer, presents unprecedented opportunities for tailoring the photoelectronic properties of constituent components. Here, the concept of Kerker effect is leveraged to demonstrate the dynamic control of scattering directionality in dielectric nanostructures by tuning the exciton‐photon coupling. First, theoretical evidence for a significant modification of the scattering directionality of a dielectric metastructure engineered by excitonic polaritons is provided. As a proof of concept, self‐coupled metasurfaces composed of bulk MoS2, which exhibit a forward/backward scattering ratio up to 20, are constructed. Importantly, tunable directionality is achieved by thermally controlling the excitonic coupling to the Mie modes. The simulated results are in good agreement with the experimental measurements, and the subsequent multipole decompositions effectively elucidate the underlying mechanism, attributed to the interplay between electric and magnetic dipole modes that are modified by excitons. The findings shed light on the control of light flow in the far field through coherent light–matter interactions, thereby opening up numerous possibilities for active optical antennas and quantum emitters on a nanoscale. [ABSTRACT FROM AUTHOR]

Antennas are important components in optical phased arrays. However, their far-field performance deteriorates when random phase noise is introduced because of fabricating errors. For the first time, we use a finite-difference time-domain solution to quantitatively analyze the far-field characteristics of Si and Si3N4 antennas considering process errors. Under rough surface conditions based on a fishbone structure, we find that the quality of the main lobe of the Si antenna deteriorates badly, with −0.87 dB and −0.51 dB decreases in the sidelobe level and 5.78% and 3.74% deteriorations in the main peak power in the φ (phase-controlled) and θ (wavelength-controlled) directions, respectively. However, the Si3N4 antenna is only slightly impacted, with mere 0.39% and 0.71% deteriorations in the main peak power in the φ and θ directions, respectively, which is statistically about 1/15 of the Si antenna in the φ direction and 1/5 in the θ direction. The decreases in the sidelobe level are also slight, at about −0.08 dB and −0.01 dB, respectively. Furthermore, the advantages of the Si3N4 antenna become more remarkable with the introduction of random errors into the waveguide width and thickness. This work is of great significance for the design and optimization of OPA chips. [ABSTRACT FROM AUTHOR]

The achievement of significant photoluminescence (PL) in lanthanide ions (Ln3+) has primarily relied on host sensitization, where energy is transferred from the excited host material to the Ln3+ ions. However, this luminous mechanism involves only one optical antenna, namely the host material, which limits the accessibility of excitation wavelength‐dependent (Ex‐De) PL. Consequently, the wider application of Ln3+ ions in light‐emitting devices is hindered. In this study, we present an organic–inorganic compound, (DMA)4LnCl7 (DMA+=[CH3NH2CH3]+, Ln3+=Ce3+, Tb3+), which serves as an independent host lattice material for efficient Ex‐De emission by doping it with trivalent antimony (Sb3+). The pristine (DMA)4LnCl7 compounds exhibit high luminescence, maintaining the characteristic sharp emission bands of Ln3+ and demonstrating a high PL quantum yield of 90–100 %. Upon Sb3+ doping, the compound exhibits noticeable Ex‐De emission with switchable colors. Through a detailed spectral study, we observe that the prominent energy transfer process observed in traditional host‐sensitized systems is absent in these materials. Instead, they exhibit two independent emission centers from Ln3+ and Sb3+, each displaying distinct features in luminous color and radiative lifetime. These findings open up new possibilities for designing Ex‐De emitters based on Ln3+ ions. [ABSTRACT FROM AUTHOR]

In this article challenges and potential solutions in the field of signal exchange between layers of a 3D integrated circuit (IC) using through silicon vias (TSVs) are discussed. The current technology uses copper channels, but it has limitations such as stress along the TSV joint and oxidation of copper during operation, which can affect the transmission characteristics and service life of the product. We propose a solution by replacing copper channels with nanophotonics technology, specifically optical antennas capable of wireless signal transmission. This technology has shown potential for high-speed data transmission with frequencies reaching hundreds of THz. A series of simulations was conducted in order to evaluate abilities of nanoantennas transmitter-receiver system to send data to a distance of 50 microns. Calculated results show, that wireless optical antennas communication system is able to send signal to such interval, but further studies are necessary to explore potential capabilities of dielectric and metal antennas in this area. [ABSTRACT FROM AUTHOR]

Increasing technological progress in space technology is accompanied by an increased demand for accuracy. The alignment of optical instruments or antennas on the satellite platform requires structural stability that can no longer be achieved with traditional, passive methods, such as the use of materials with high stiffness or low coefficient of thermal expansion. Within the Infrared Astronomy Satellite Swarm Interferometry (IRASSI) project, an approach to actively stabilizing structures against low-frequency periodic heat induced deformations has been developed and simulated. In this study, the basic functionality of that thermomechanical FEM model is demonstrated by means of the thermal transfer functions between the changes in the applied heat and the resulting temperature changes, as well as a closed loop filter and controller approach consisting of a Linear Quadratic Regulator (LQR) and a Kalman filter. For this purpose, an experimental setup consisting of an aluminum plate with 14 temperature sensors, four heating elements for controlling the structure and one heating element for simulating the perturbation is used. The evaluation of the thermal transfer functions in the model compared to the experimental setup shows a deviation of the phase shift of less than 0.6% and an amplitude shift of less than 3.5% on average. A Kalman filter processes the temperature measurement in order to obtain an optimal estimate for the LQR controller, which then calculates the necessary change in the heating power of the four control heating elements to minimize the displacements at the desired two positions in x- and y-direction. The verification is performed by a camera system as an external validation tool, which is able to resolve micron-scale displacements by measuring the spatial displacement of a speckle pattern applied to the structure using sub-pixel accurate image correlation algorithms. While the range of values of the amplitudes of the displacements is 8.93 μ in the uncontrolled case, an improvement of more than 4.6 dB could be achieved by applying the filter and controller system. Thus, it is demonstrated that this method has the potential to further improve already highly stable structures or to make lighter and cheaper materials with poorer passive stability values usable through active structural stabilization. • The stabilization of structures has so far been done only with passive methods. • Novel approach of active stabilization significantly increases dimensional stability. • Heating elements as actuators specifically influence the displacement field. • Smart structures can be quickly and easily adapted for applications in space. [ABSTRACT FROM AUTHOR]

Optical antennas are nanostructures that introduce unprecedented possibilities for light–matter interaction at the nanoscale. An appropriately tailored plasmonic antenna can enhance the total radiative decay rate and modify the angular radiation pattern of a single‐quantum emitter through controlled near‐field coupling. Despite their ability to surpass the fundamental diffraction limit and confine the electromagnetic field to a tiny mode volume, fabricating 3D sharp scanning nanoscale plasmonic structures with desired aspect ratio is yet an ambitious goal. The fabrication of nanocones by gold evaporation on commercial atomic force microscopy probes followed by a focused ion beam milling technique is presented. The method is versatile and allows the fabrication of nanocones with desired dimensions around 100 nm along with an aspect ratio of ≈1. Their optical properties are studied and it is shown how the variation in the refractive index of the dielectric substrate affects the localized surface plasmon resonance of the nanocones, the decay rate enhancement, and the quantum yield of an emitter relevant for fluorescence/Raman scanning experiments. Theoretical studies using finite‐difference time‐domain calculations have guided the fabrication process and are consistent with experimental results.

In this paper, the switched-beam nanoantenna (NA) concept is introduced with a theoretical design of an inhomogeneous dielectric flat lens modelled with different materials to steer and enhance the radiation in a particular direction based on shifting the illuminator element. Firstly, the design of hybrid plasmonic NA is introduced and analyzed considering different silicon patch shapes such as rectangular, circular, hexagonal, and elliptical shapes. The elliptical patch NA achieves a gain of up to 10.7 dBi and a return loss of − 14.41 dB. Then the design of a gradient-index dielectric flat lens with the NA is introduced to improve the antenna performance by increasing the directivity and consequently decreasing the beam-width. Furthermore, the beam-steering capabilities by displacement of the NA according to different feeding points along the X and Y-direction. By using the gradient-index dielectric flat lens, the gain is increased to 18.4 dBi with an improvement in the return loss reach to − 19.15 dB compared with traditional NA. In addition, the beam-steering capabilities were achieved with a range ± 60° × ± 55° with acceptable average antenna gain, side-lobe levels, and half power beam-width of 16.5 dBi, − 12.3 dB and 13.6° respectively. [ABSTRACT FROM AUTHOR]

Optical transparent antennas (OTAs) are a relatively new technology that allows for high-speed wireless communication using a transparent antenna placed on the surface of a mobile device. However, scheduling OTA transmissions can be challenging due to several factors that must be considered. One critical consideration when developing a scheduling plan for OTAs is bandwidth. OTA-based mobile terminals require a significant amount of bandwidth to transmit and receive data, which means it's essential to ensure that enough bandwidth is available for OTA transmissions. This can be achieved by monitoring network traffic patterns and allocating sufficient bandwidth for OTA transmissions. Another important factor to consider is the signal strength of OTA transmissions. The strength of these signals can be affected by factors such as weather conditions, interference from other sources, and the location of the mobile terminal. Scheduling of OTAs can be planned successfully when the signal strength is optimal to ensure that transmissions can take place without any hurdles. Developing a scheduling plan for OTAs in mobile terminals is a complicated process, requiring consideration of several factors. These include ensuring sufficient bandwidth for OTA transmissions due to their high bandwidth requirements, signal strength should be optimal and OTA usage should be minimal when battery levels are low to conserve power. Additionally, network congestion and user preferences should also be considered when scheduling the OTAs. The smart scheduling mechanisms are required to handle the mobile applications while handling OTAs on mobile terminals. This study is proposing a modified traffic load clustering (MTLC) scheduling mechanism for scheduling OTAs on mobile terminals. The proposed MTLC method offers better spectrum efficiency above 90%, time-slot utilization between 88 and 95%, and channel utilization between 80 and 90% during scheduling of optical antennas. It also optimizes the latency time, throughput, and outperforms other algorithms. [ABSTRACT FROM AUTHOR]

A mathematical model of a new optical (1550 nm) antenna with an electrically controlled radiation pattern is presented. The working principle is considered, and the main parameters are calculated. As distinct from existing solutions, the antenna does not require convergence of beams at a distance of one half of wavelength. In the framework of the model, an electro-optical switch based on lithium niobate is calculated. Such antenna elements as a phase shifter and deflector are presented and calculated. [ABSTRACT FROM AUTHOR]