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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]

Active metasurfaces have recently emerged as compact, lightweight, and efficient platforms for dynamic control of electromagnetic fields and optical responses. However, the complexities associated with their post-fabrication tunability significantly hinder their widespread applications, especially for the mid-infrared range due to material scarcity and design intricacy. Here, we experimentally demonstrate highly dynamic, pixelated modulations of coherent mid-infrared emission based on an electrically programmable plasmonic metasurface integrated with graphene field-effect transistors (Gr-FETs). The ultrabroad infrared transparency of graphene allows for customized control over plasmonic meta-atoms, thus achieving coherent mid-infrared states across a broad range of wavelengths, directions, and polarizations. The spatial temperature modulation generated by Gr-FETs is effectively synergized with the emissivity control by the localized surface plasmon polaritons and quasi-bound states in the continuum from gold nanoantennas. This integrated temperature-emissivity modulation of metasurfaces is systematically extended to form a pixelated 2D array with low crosstalk, envisioning advanced approaches toward scalable 2D electrical wiring for densely packed, independently addressable pixels. The realization of active metasurfaces operating in the infrared range remains challenging due to design complexities and scarcity of suitable materials. Here, the authors report the realization of electrically programmable plasmonic metasurfaces integrated with graphene transistors, enabling pixelated thermal emission with low cross-talk and enhanced coherence. [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]

The coupling of nanostructures with emerging 2D semiconductors is gaining significant interest thanks to the unique features of these hybrids systems, which make them key platforms for next‐generation applications in electronics, optoelectronics, and sensing. Top‐down lithographic approaches uniquely enable the fully deterministic high‐resolution fabrication of nanostructures, but some of them, like electron‐beam lithography and focused ion‐beam lithography, employ energetic particles that may damage 2D materials causing an unwanted loss of functionality. Herein thermal scanning probe lithography is applied for the realization of metallic nanoantennas directly on top of exfoliated 2D MoS2 flakes, showing it can avoid the degradation of this delicate substrate. It is shown that the morphologic and optical features of MoS2 are fully preserved after the lithography. [ABSTRACT FROM AUTHOR]

In the realm of nanotechnology, the integration of quantum emitters with plasmonic nanostructures has emerged as an innovative pathway for applications in quantum technologies, sensing, and imaging. This research paper provides a comprehensive exploration of the photoluminescence enhancement induced by the interaction between quantum emitters and tailored nanostructure configurations. Four canonical nanoantennas (spheres, rods, disks, and crescents) are systematically investigated theoretically in three distinct configurations (single, gap, and nanoparticle-on-mirror nanoantennas), as a representative selection of the most fundamental and commonly studied structures and arrangements. A detailed analysis reveals that the rod gap nanoantenna configuration achieves the largest photoluminescence enhancement factor, of up to three orders of magnitude. The study presented here provides insights for the strategic design of plasmonic nanoantennas in the visible and near-IR spectral range, offering a roadmap for these structures to meet specific requirements in plasmon-enhanced fluorescence. Key properties such as the excitation rate, the quantum yield, the enhanced emitted power, or the directionality of the emission are thoroughly reviewed. The results of this overview contribute not only to the fundamental understanding of plasmon-enhanced emission of quantum emitters but also set the basis for the development of advanced nanophotonic devices with enhanced functionalities. [ABSTRACT FROM AUTHOR]

Chiral plasmonic nanoantennas exhibit unique chiroptical properties in both the near‐field and far‐field, offering exciting opportunities for applications in chiroptical sensing, circularly polarized luminescence, and quantum communication. Recent advances in chiral plasmonics have facilitated the creation of nanoparticles with intrinsic chirality at the single‐particle level. However, the far‐field directionality of these chiral nanoantennas is not well understood. In this work, A numerical study is conducted on a single plasmonic nanoantenna that undergoes a size‐preserving compression, transitioning from a straight nanorod to left‐ or right‐handed helices with varying pitches. These nanostructures showcase distinct mode‐dependent chiroptical far‐field properties, encompassing positive or negative dissymmetry factors, 3D power radiation patterns, and angular distribution of circular polarization, under both plane‐wave and point‐source excitations. The findings provide new insights into angle‐resolved spectroscopies of intrinsically chiral plasmonic nanoparticles and the applications of chiral plasmonic nanoantennas for controlling circularly polarized light emission in nanophotonics. [ABSTRACT FROM AUTHOR]

By combining ErIII and YbIII ions with 3,6-dithiophene-anilate (Th2An) and scorpionate hydrotris(pyrazol-1-yl)borate (HBpz3−) ligands new luminescent dinuclear complexes are obtained. The two materials formulated as [((HB(pz)3)2Yb)2(μ-th2An)]·4DCM·1.3H2O 1Yb and [((HB(pz)3)2Er)2(μ-th2An)]·4DCM·1.8H2O 1Er, respectively, have been structurally characterized by SC-XRD and PXRD studies. This study presents a comprehensive investigation of the photophysical properties of the Th2An ligand for the first time. Our findings reveal the crucial role of the thiophene anilate as an effective optical antenna, which sensitizes near-infrared (NIR)-emitting lanthanide ions, specifically ErIII and YbIII. The significant impact of vibrational quenching on the LnIII NIR emission efficiency has been also highlighted. [ABSTRACT FROM AUTHOR]

Many technical approaches were implemented in the antenna manufacturing process to maintain the desired miniaturization of the size of the antenna model which can be employed in various applied systems such as medical communication systems. Furthermore, over the past several years, nanotechnology science has rapidly grown in a wide variety of applications, which has given rise to novel ideas in the design of antennas based on nanoscale merits, leading to the use of antennae as an essential linkage between the human body and the different apparatus of the medical communication system. Some medical applications dealt with different antenna configurations, such as microstrip patch antenna or optical nanoantenna in conjugate with sensing elements, controlling units, and monitoring instruments to maintain a specified healthcare system. This study summarizes and presents a brief review of the recent applications of antennas in different medical communication systems involving highlights, and drawbacks with explores recommended issues related to using antennas in medical treatment. [ABSTRACT FROM AUTHOR]

Optical nanoantennas concentrate light into their local fields. The field concentration property is governed by the plasmonic resonances and their interference. Here, we present a method for controllable local-field interferences in the hot spot of nanorods and experimentally demonstrate that the field enhancement can be tuned in a wide range. For this, we design nanoparticles with given phase relations between their plasmonic eigenmodes and at the same time tune the phase between the components of the external field by changing its polarization state to achieve in-phase excitation of the plasmon modes. Strong-field photoemission is applied to probe the field enhancement property of the nanorods employing femtosecond pulses of different polarization states. Our findings provide a new degree of freedom in plasmonic resonance tuning and may inspire diverse designs of local-field responses and expand the applications in nanoscale sensing, spectroscopy, and dynamically tunable devices. [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. [ABSTRACT FROM AUTHOR]

This paper proposes an asymmetric inset-fed mesh antenna with optical transparency using a mesh structure. It was investigated for its effects on the antenna characteristics by varying the length and width of the patch as well as the width and number of the lines in the mesh structure. Based on the results, a mesh antenna operating in the S-band at 2.4 GHz was designed using an FR-4 dielectric substrate with a thickness of 1 mm and a dielectric constant of 4.3. Two types of antennas with transparency levels of 76% and 85% were fabricated, and the return loss, axial ratio, gain and radiation pattern characteristics of the antennas were measured, and the results were very similar to the simulation results. It is expected that the antenna proposed in this paper, which combines circular polarization and optical properties, could be utilized in Micro-satellite applications. [ABSTRACT FROM AUTHOR]

Attosecond science has demonstrated that electrons can be controlled on the sub-cycle time scale of an optical waveform, paving the way towards optical frequency electronics. However, these experiments historically relied on high-energy laser pulses and detection not suitable for microelectronic integration. For practical optical frequency electronics, a system suitable for integration and capable of generating detectable signals with low pulse energies is needed. While current from plasmonic nanoantenna emitters can be driven at optical frequencies, low charge yields have been a significant limitation. In this work we demonstrate that large-scale electrically connected plasmonic nanoantenna networks, when driven in concert, enable charge yields sufficient for single-shot carrier-envelope phase detection at repetition rates exceeding tens of kilohertz. We not only show that limitations in single-shot CEP detection techniques can be overcome, but also demonstrate a flexible approach to optical frequency electronics in general, enabling future applications such as high sensitivity petahertz-bandwidth electric field sampling or logic-circuits. Characterisation of optical frequency electric fields and its integration within ultrafast currents in nanostructures is a crucial step for the development of petahertz electronics devices. Here the authors demonstrate singleshot measurement of the phase of a laser pulse with on-chip arrays of hundreds of metallic nanoantennas. [ABSTRACT FROM AUTHOR]

The emission rate of atom-like photon sources can be significantly improved by coupling them to plasmonic resonant nanostructures. These arrangements function as nanoantennas, serving the dual purpose of enhancing light–matter interactions and decoupling the emitted photons. However, there is a contradiction between the requirements for these two tasks. A small resonator volume is necessary for maximizing interaction efficiency, while a large antenna mode volume is essential to achieve high emission directivity. In this work, we analyze a hybrid structure composed of a noble metal plasmonic resonant nanoparticle coupled to the atom-like emitter, which is designed to enhance the emission rate, alongside a corner reflector aimed at optimizing the angular distribution of the emitted photons. A comprehensive numerical study of silver and gold corner reflector nanoantennas, employing the finite difference time domain method, is presented. The results demonstrate that a well-designed corner reflector can significantly enhance photon emission directivity while also substantially boosting the emission rate. [ABSTRACT FROM AUTHOR]

Controlling and channeling light emissions from unpolarized quantum dots into specific directions with chiral polarization remains a key challenge in modern photonics. Stacked metasurface designs offer a potential compact solution for chirality and directionality engineering. However, experimental observations of directional chiral radiation from resonant metasurfaces with quantum emitters remain obscure. In this paper, we present experimental observations of unidirectional chiral emission from a twisted bi-layer metasurface via multi-dimensional control, including twist angle, interlayer distance, and lateral displacement between the top and bottom layers, as enabled by doublet alignment lithography (DAL). First, maintaining alignment, the metasurface demonstrates a resonant intrinsic optical chirality with near-unity circular dichroism of 0.94 and reflectance difference of 74%, where a high circular dichroism greater than 0.9 persists across a wide range of angles from −11 to 11 degrees. Second, engineered lateral displacement induces a unidirectional chiral resonance, resulting in unidirectional chiral emission from the quantum dots deposited onto the metasurface. Our bi-layer metasurfaces offer a universal compact platform for efficient radiation manipulation over a wide angular range, promising potential applications in miniaturized lasers, grating couplers, and chiral nanoantennas. Simultaneous control of the direction and polarization of quantum emission using photonic nanostructures is a long-standing challenge in photonics. Here, the authors experimentally demonstrate unidirectional chiral emission from a twisted bilayer metasurface with multi-dimensional control. [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]

This article provides an overview of plasmonic nano-antennas for photonic applications. This paper delves into the theoretical analysis of nano/optical antennas, including optical antenna impedance, near and far field characteristics, and directivity. The materials used for manufacturing optical antennas are discussed in the context of terahertz communication. The comparative analysis of different types of fabrication techniques on the nanoscale is presented as a requirement for the implementation of nano-antennas. The testing mechanism of the nano-antenna using microscopy techniques is also presented. A detailed review of the different shapes of the nano-antennas that are used for applications in the field of photonics is discussed. According to this review article, graphene, gold, and silver are the most promising materials. It is also noticed that pen-dip and direct growth are fast and inexpensive techniques for nano-antenna fabrication. [ABSTRACT FROM AUTHOR]

In September 2018, NASA launched the ICESat-2 satellite into a 500 km high Earth orbit. It carried a truly unique lidar system, i.e., the Advanced Topographic Laser Altimeter System or ATLAS. The ATLAS lidar is capable of detecting single photons reflected from a wide variety of terrain (land, ice, tree leaves, and underlying terrain) and even performing bathymetric measurements due to its green wavelength. The system uses a single 5-watt, Q-switched laser producing a 10 kHz train of sub-nanosecond pulses, each containing 500 microjoules of energy. The beam is then split into three "strong" and three "weak" beamlets, with the "strong" beamlets containing four times the power of the "weak" beamlets in order to satisfy a wide range of Earth science goals. Thus, ATLAS is capable of making up to 60,000 surface measurements per second compared to the 40 measurements per second made by its predecessor multiphoton instrument, the Geoscience Laser Altimeter System (GLAS) on ICESat-1, which was terminated after several years of operation in 2009. Low deadtime timing electronics are combined with highly effective noise filtering algorithms to extract the spatially correlated surface photons from the solar and/or electronic background noise. The present paper describes how the ATLAS system evolved from a series of unique and seemingly unconnected personal experiences of the author in the fields of satellite laser ranging, optical antennas and space communications, Q-switched laser theory, and airborne single photon lidars. [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]

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 purpose of this work is to study, using automated modeling methods, the possibility of scanning in frequency and beamforming of plasmonic graphene strip nanoantennas, which are electrically tunable by varying the chemical potential of graphene in the terahertz (THz), far-, and mid-infrared (IR) ranges. Graphene, which has exceptional electromagnetic, mechanical, electrical, and thermal properties, is promising for reconfigurable THz antennas due to its high conductivity and tunability in the THz range. Modeling of the performances of THz plasmonic graphene strip nanoantennas for various values of chemical potential was carried out using the CST Microwave Studio 2023 software package. The results of modeling the controllability of the reflection coefficients at the input of the nanoantenna and the radiation pattern (RP) at the resonance frequencies of the fundamental mode of surface plasmon-polaritons (SPPs) and the second-order SPP mode were obtained when changing the values of the chemical potential (0.3–0.7 eV) in the THz, far-, mid-IR ranges. It follows from the modeling results that it is possible to tune operating frequencies (frequency scanning) from THz to the far- and mid-IR ranges and form a multibeam RP of reconfigurable graphene strip nanoantennas by changing the chemical potential of graphene (applying an external electric field) without changing their geometry and dimensions. [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]

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]

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]

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]

Optically resonant nano-antennas represent relatively new and promising functionalities for expanding the uses of optical frequencies in communication and sensing. These nano-scale devices built of metal or dielectric materials, take action through effectively modulating light at the nano-scale, thus avoiding limitations of conventional optical devices, including the diffraction limit. Nano-antennas are pencils of light that have the capacity to focus electromagnetic light energy into highly confined spaces due to their small size; they give precise control of electromagnetic energy which is fundamental for improving the speed, and encoding capacity of optical communication networks. Nanoantennas have higher responsivity to changes in the environment; thus, they can be used in biosensing and environmental sensing with improved capability in detecting small changes in molecular or chemical concentrations. Besides integrating them into photonic circuits may enable the shrinking of the size of optical devices as well as improving the performance of the devices. This paper discuss the application of nano-antennas and studies the design, material and fabrication method with high efficiency, low loss and preferable radiation characteristics for use in different application. Further research in the development of nano-antennas will expand High-speed data transmission, real time sensing, optical system miniaturization that will enhance telecommunication, medical diagnostics, and nanotechnology innovations. [ABSTRACT FROM AUTHOR]

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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]

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]

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]

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]

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]

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]

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]

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]

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]