Bridging the Gap between Dielectric Nanophotonics and the Visible Regime with Effectively Lossless Gallium Phosphide Antennas

Enhanced spontaneous radiation of quantum dots based on modulated anapole states in dielectric metamaterial

Dielectric nanostructures exhibit low-loss electrical and magnetic resonance, making them ideal for quantum information processing. In this study, the periodic double-groove silicon nanodisk (DGSND) is used to support the anapole state. Based on the distribution properties of the electromagnetic field in anapole states, the anapoles are manipulated by cutting the dielectric metamaterial. Quantum dots (QDs) are used to stimulate the anapole and control the amplification of the photoluminescence signal within the QDs. By opening symmetrical holes in the long axis of the nanodisk in the dielectric metamaterial, the current distribution of Mie resonance can be adjusted. As a result, the toroidal dipole moment is altered, leading to an enhanced electric field (E-field) and Purcell factor. When the dielectric metamaterial is deposited on the Ag substrate separated by the silicon dioxide (SiO2) layer, the structure exhibits ultra-narrow perfect absorption with even higher E-field and Purcell factor enhancement compared to silicon (Si) nanodisks.

Spatial photoluminescence and lifetime mappings of quasi-2D perovskites coupled with a dielectric metasurface

Light-matter interaction between quantum emitters and optical cavities plays a vital role in fundamental quantum photonics and the development of optoelectronics. Resonant metasurfaces are proven to be an efficient platform for tailoring the spontaneous emission (SE) of the emitters. In this work, we study the interplay between quasi-2D perovskites and dielectric TiO2 metasurfaces. The metasurface, functioning as an open cavity, enhances electric fields near its plane, thereby influencing the emissions of the perovskite. This is verified through angle-resolved photoluminescence (PL) studies. We also conducted reflectivity measurements and numerical simulations to validate the coupling between the quasi-2D perovskites and photonic modes. Notably, our work introduces a spatial mapping approach to study Purcell enhancement. Using fluorescence lifetime imaging microscopy (FLIM), we directly link the PL and lifetimes of the quasi-2D perovskites in spatial distribution when positioned on the metasurface. This correlation provides unprecedented insights into emitter distribution and emitter-resonator interactions. The methodology opens a new (to the best of our knowledge) approach for studies in quantum optics, optoelectronics, and medical imaging by enabling spatial mapping of both PL intensity and lifetime, differentiating between uncoupled quantum emitters and those coupled with different types of resonators.

Fluorescence Enhancement in Topologically Optimized Gallium Phosphide All-Dielectric Nanoantennas

Nanoantennas capable of large fluorescence enhancement with minimal absorption are crucial for future optical technologies from single-photon sources to biosensing. Efficient dielectric nanoantennas have been designed, however, evaluating their performance at the individual emitter level is challenging due to the complexity of combining high-resolution nanofabrication, spectroscopy and nanoscale positioning of the emitter. Here, we study the fluorescence enhancement in infinity-shaped gallium phosphide (GaP) nanoantennas based on a topologically optimized design. Using fluorescence correlation spectroscopy (FCS), we probe the nanoantennas enhancement factor and observe an average of 63-fold fluorescence brightness enhancement with a maximum of 93-fold for dye molecules in nanogaps between 20 and 50 nm. The experimentally determined fluorescence enhancement of the nanoantennas is confirmed by numerical simulations of the local density of optical states (LDOS). Furthermore, we show that beyond design optimization of dielectric nanoantennas, increased performances can be achieved via tailoring of nanoantenna fabrication.

High-directivity far-field radiation of quantum dot-based single-photon emitter coupled to polymeric circular waveguide resonant grating

Solid-state single-photon emitters (SPEs) commonly encounter the limitation of quasi-omnidirectional radiation patterns, which poses challenges in utilizing their emission with conventional optical instruments. In this study, we demonstrate the tailoring of the far-field radiation patterns of SPEs based on colloidal quantum dots (QDs), both theoretically and experimentally, by employing a polymer-based dielectric antenna. We introduce a simple and cost-effective technique, namely low one-photon absorption direct laser writing, to achieve precise coupling of a QD into an all-polymer circular waveguide resonance grating. By optimizing the geometry parameters of the structure using 3D finite-difference time-domain simulations, resonance at the emission wavelength of QDs is achieved in the direction perpendicular to the substrate, resulting in photon streams with remarkably high directivity on both sides of the grating. Theoretical calculations predict beam divergence values below 2°, while experimental measurements using back focal plane imaging yield divergence angles of approximately 8°. Our study contributes to the evaluation of concentric circular grating structures employing low refractive index polymer materials, thereby expanding the possibilities for their application.

Single-emitter super-resolved imaging of radiative decay rate enhancement in dielectric gap nanoantennas

High refractive index dielectric nanoantennas strongly modify the decay rate via the Purcell effect through the design of radiative channels. Due to their dielectric nature, the field is mainly confined inside the nanostructure and in the gap, which is hard to probe with scanning probe techniques. Here we use single-molecule fluorescence lifetime imaging microscopy (smFLIM) to map the decay rate enhancement in dielectric GaP nanoantenna dimers with a median localization precision of 14 nm. We measure, in the gap of the nanoantenna, decay rates that are almost 30 times larger than on a glass substrate. By comparing experimental results with numerical simulations we show that this large enhancement is essentially radiative, contrary to the case of plasmonic nanoantennas, and therefore has great potential for applications such as quantum optics and biosensing.

High-aspect-ratio dielectric pillar with nanocavity backed by metal substrate in the infrared range

We investigated absorption and field enhancements of shallow nanocavities on top of high-aspect-ratio dielectric pillars in the infrared range. The structure includes a high-aspect-ratio nanopillar array of high refractive index, with nano-cavities on top of the pillars, and a metal plane at the bottom. The enhancement factor of electric field intensity reaches 3180 in the nanocavities and peak absorption reaches 99%. We also investigated the finite-size effect of the presented structure to simulate real experiments. Due to its narrow absorption bandwidth 3.5 nm, it can work as a refractive index sensor with sensitivity 297.5 nm/RIU and figure of merit 85. This paves the way to directly control light field at the nanoscales in the infrared light range. The investigated nanostructure will find applications in multifunctional photonics devices such as chips for culturing cells, refractive index sensors, biosensors of single molecule detection and nonlinear sensors.

Multi-wavelength unidirectional forward scattering properties of the arrow-shaped gallium phosphide nanoantenna

An arrow-shaped gallium phosphide nanoantenna exhibits both near-field electric field enhancement and far-field unidirectional scattering, and the interference conditions involve electric and magnetic quadrupoles as well as toroidal dipoles. By using long-wavelength approximation and exact multipole decomposition, the interference conditions required for far-field unidirectional transverse light scattering and backward near-zero scattering at multiple wavelengths are determined. The near-field properties are excellent, as exemplified by large Purcell factors of 4.5×109 for electric dipole source excitation, 464.68 for magnetic dipole source excitation, and 700 V/m for the field enhancement factor. The degree of enhancement of unidirectional scattering is affected by structural parameters such as the angle and thickness of the nanoantenna. The arrow-shaped nanoantenna is an efficient platform to enhance the electric field and achieve high directionality of light scattering. Moreover, the nanostructure enables flexible manipulation of light waves and materials, giving rise to superior near-field and far-field performances, which are of great importance pertaining to the practicability and application potential of optical antennas in applications such as spectroscopy, sensing, displays, and optoelectronic devices.

Precisely constructing hybrid nanogap arrays via wet-transfer of dielectric metasurfaces onto a plasmonic mirror

We propose a new method for fabricating hybrid metasurfaces by combining Mie and plasmonic resonances. Our approach involves obtaining an ultrasmooth gold film and separately structuring monocrystalline silicon (c-Si) nanoantenna arrays, which are then wet-transferred and finally immobilized onto the gold film. The experimental and simulation analysis reveals the importance of the native oxide layer of Si and demonstrates fascinating dispersion curves with nanogap resonances and bound states in the continuum. The localized field enhancements in the nanogap cavities result from the coupling between multipolar Mie resonances and their mirror images in the gold film. This effective method improves our understanding of hybrid modes and offers opportunities for developing active metasurfaces, such as depositing c-Si nanoantenna arrays onto stretchable polydimethylsiloxane substrates or electro-optic and piezoelectric sensitive lithium niobate films for potential applications in MEMS, LiDAR, and beyond.

Radiative suppression of exciton-exciton annihilation in a two-dimensional semiconductor

Two-dimensional (2D) semiconductors possess strongly bound excitons, opening novel opportunities for engineering light-matter interaction at the nanoscale. However, their in-plane confinement leads to large non-radiative exciton-exciton annihilation (EEA) processes, setting a fundamental limit for their photonic applications. In this work, we demonstrate suppression of EEA via enhancement of light-matter interaction in hybrid 2D semiconductor-dielectric nanophotonic platforms, by coupling excitons in WS2 monolayers with optical Mie resonances in dielectric nanoantennas. The hybrid system reaches an intermediate light-matter coupling regime, with photoluminescence enhancement factors up to 102. Probing the exciton ultrafast dynamics reveal suppressed EEA for coupled excitons, even under high exciton densities >1012 cm-2. We extract EEA coefficients in the order of 10-3, compared to 10-2 for uncoupled monolayers, as well as a Purcell factor of 4.5. Our results highlight engineering the photonic environment as a route to achieve higher quantum efficiencies, for low-power hybrid devices, and larger exciton densities, towards strongly correlated excitonic phases in 2D semiconductors.

Wafer-scale inverted gallium phosphide-on-insulator rib waveguides for nonlinear photonics

We report a gallium phosphide-on-insulator (GaP-OI) photonic platform fabricated by an intermediate-layer bonding process aiming to increase the manufacture scalability in a low-cost manner. This is enabled by the "etch-n-transfer" sequence, which results in inverted rib waveguide structures. The shallow-etched 1.8 µm-wide waveguide has a propagation loss of 23.5 dB/cm at 1550 nm wavelength. Supercontinuum generation based on the self-phase modulation effect is observed when the waveguides are pumped by femtosecond pulses. The nonlinear refractive index of GaP, n₂, is extracted to be 1.9 × 10^-17 m²/W, demonstrating the great promise of the GaP-OI platform in third-order nonlinear applications.

Sub-picosecond collapse of molecular polaritons to pure molecular transition in plasmonic photoswitch-nanoantennas

Molecular polaritons are hybrid light-matter states that emerge when a molecular transition strongly interacts with photons in a resonator. At optical frequencies, this interaction unlocks a way to explore and control new chemical phenomena at the nanoscale. Achieving such control at ultrafast timescales, however, is an outstanding challenge, as it requires a deep understanding of the dynamics of the collectively coupled molecular excitation and the light modes. Here, we investigate the dynamics of collective polariton states, realized by coupling molecular photoswitches to optically anisotropic plasmonic nanoantennas. Pump-probe experiments reveal an ultrafast collapse of polaritons to pure molecular transition triggered by femtosecond-pulse excitation at room temperature. Through a synergistic combination of experiments and quantum mechanical modelling, we show that the response of the system is governed by intramolecular dynamics, occurring one order of magnitude faster with respect to the uncoupled excited molecule relaxation to the ground state.

Recent Advances in Metaphotonic Biosensors

Metaphotonic devices, which enable light manipulation at a subwavelength scale and enhance light-matter interactions, have been emerging as a critical pillar in biosensing. Researchers have been attracted to metaphotonic biosensors, as they solve the limitations of the existing bioanalytical techniques, including the sensitivity, selectivity, and detection limit. Here, we briefly introduce types of metasurfaces utilized in various metaphotonic biomolecular sensing domains such as refractometry, surface-enhanced fluorescence, vibrational spectroscopy, and chiral sensing. Further, we list the prevalent working mechanisms of those metaphotonic bio-detection schemes. Furthermore, we summarize the recent progress in chip integration for metaphotonic biosensing to enable innovative point-of-care devices in healthcare. Finally, we discuss the impediments in metaphotonic biosensing, such as its cost effectiveness and treatment for intricate biospecimens, and present a prospect for potential directions for materializing these device strategies, significantly influencing clinical diagnostics in health and safety.

Fluorophore-Decorated Mie Resonant Silicon Nanosphere for Scattering/Fluorescence Dual-Mode Imaging

Inorganic nanoparticles with multiple functions have been attracting attention as multimodal nanoprobes in bioimaging, biomolecule detection, and medical diagnosis and treatment. A drawback of conventional metallic nanoparticle-based nanoprobes is the Ohmic losses that lead to fluorescence quenching of attached molecules and local heating under light irradiation. Here, metal-free nanoprobes capable of scattering/fluorescence dual-mode imaging are developed. The nanoprobes are composed of a silicon nanosphere core having efficient Mie scattering in the visible to near infrared range and a fluorophore doped silica shell. The dark-field scattering and photoluminescence images/spectra for nanoprobes made from different size silicon nanospheres and different kinds of fluorophores are studied by single particle spectroscopy. The fluorescence spectra are strongly modified by the Mie modes of a silicon nanosphere core. By comparing scattering and fluorescence spectra and calculated Purcell factors, the fluorescence enhancement factor is quantitatively discussed. In vitro scattering/fluorescence imaging studies on human cancer cells demonstrate that the developed nanoparticles work as scattering/fluorescence dual-mode imaging nanoprobes.

Lifetime visualization of femtosecond laser-induced plasma on GaP crystal

Gallium phosphide (GaP) is a widely used and promising semiconductor material for photonics devices and we suppose the ultrafast laser can be a competitive tool for GaP processing. We used an 800 nm centered femtosecond (fs) laser with a pulse duration of 50 fs to irradiate the GaP crystal. The ablation threshold was first determined, and then the ultrafast dynamics including plasma expansion, shockwave formation and propagation, and spectral evolution were acquired and analyzed. The evolution of ejected plasma in the initial stage changed from cylindrical to planar propagation with the augment of laser fluence. The study on the propagation properties of shockwaves showed that the energy of propelling shockwaves accounted for 12% to 18% of the laser pulse energy at all fluences above the ablation threshold. A prominent plasma splitting was observed at a fluence slightly higher than the threshold, and a phenomenon that the plasma protruded out of the shockwaves was also found. Finally, the transient temperature and density of electron at different fluences were calculated. The temperature difference between the plasma and the shockwave proved the heating effect of the plasma during ablation.

Mode Hybridization in Silicon Core-Gold Shell Nanosphere

A dielectric core-metal shell nanosphere has attracted scientific and technological interests due to the unique optical resonances arising from the hybridization of surface plasmon modes and cavity modes. The previous studies focus on a low-index dielectric core without its own optical resonances. Here, optical resonances of a core-shell nanosphere with a high refractive index (n ≈ 4) core with the lowest order Mie resonances in the visible range are investigated theoretically and experimentally. Scattering and absorption spectra of a core-shell nanosphere for different values of the core refractive index are first analyzed, and there is a transition of the hybridization scheme around n ≈ 2. Above the value, a characteristic hybridized mode with strong absorption and weak scattering emerges in the near-infrared range. A core-shell nanosphere composed of a silicon core and a gold shell is prepared, and the resonance modes are studied by single particle scattering spectroscopy and electron energy loss spectroscopy (EELS) in a transmission electron microscope. The core-shell nanospheres exhibit the hybridized modes depending on the core diameter. The hybridized mode as well as the higher order one that is not observable in the scattering spectroscopy is observed in the EELS.

Surface Functionalization and Texturing of Optical Metasurfaces for Sensing Applications

Optical metasurfaces are planar metamaterials that can mediate highly precise light-matter interactions. Because of their unique optical properties, both plasmonic and dielectric metasurfaces have found common use in sensing applications, enabling label-free, nondestructive, and miniaturized sensors with ultralow limits of detection. However, because bare metasurfaces inherently lack target specificity, their applications have driven the development of surface modification techniques that provide selectivity. Both chemical functionalization and physical texturing methodologies can modify and enhance metasurface properties by selectively capturing analytes at the surface and altering the transduction of light-matter interactions into optical signals. This review summarizes recent advances in material-specific surface functionalization and texturing as applied to representative optical metasurfaces. We also present an overview of the underlying chemistry driving functionalization and texturing processes, including detailed directions for their broad implementation. Overall, this review provides a concise and centralized guide for the modification of metasurfaces with a focus toward sensing applications.

Overcoming the Diffraction Limit on the Size of Dielectric Resonators Using an Amplifying Medium

Existing methods for the creation of subwavelength resonators use either structures with negative permittivity, by exploiting subwavelength plasmonic resonances, or dielectric structures with a high refractive index, which reduce the wavelength. Here, we provide an alternative to these two methods based on a modification of the modes of dielectric resonators by means of an active medium. On the example of the dielectric active layer of size substantially smaller than a half-wavelength of light, we demonstrate that there is a gain at exceeding of which the change in phase due to the reflection at the layer boundaries compensates the change in phase due to propagation over the layer. Above this value of the gain, an unconventional mode forms, in which the phase shift after a round-trip of the light is zero. We show that this mode can be exploited to create a laser, the size of which is much smaller than the wavelength of the generated light and scales inversely with the square of absolute value of the refractive index in the active medium. Our results pave the way to creation of dielectric lasers of subwavelength size.

Sum-Frequency Generation in High-Q GaP Metasurfaces Driven by Leaky-Wave Guided Modes

Resonant metasurfaces provide a unique platform for enhancing multiwave nonlinear interactions. However, the difficulties over mode matching and material transparency place significant challenges in the enhancement of these multiwave processes. Here we demonstrate efficient nonlinear sum-frequency generation (SFG) in multiresonant GaP metasurfaces based on guided-wave bound-state in the continuum resonances. The excitation of the metasurface by two near-infrared input beams generates strong SFG in the visible spectrum with a conversion efficiency of 2.5 × 10^-4 W^-1, 2 orders of magnitude higher than the one reported in Mie-type resonant metasurfaces. In addition, we demonstrate the nontrivial polarization dependence on the SFG process. In contrast to harmonic generation, the SFG process is enhanced when using nonparallel polarized input-beams. Importantly, by varying the input pump beam polarization it is possible to direct the SFG emission to different diffraction orders, thereby opening up new opportunities for nonlinear light sources and infrared to visible light conversion.

Nonlinear and ultrafast all-dielectric metasurfaces at the center for integrated nanotechnologies

Metasurfaces control optical wavefronts via arrays of nanoscale resonators laid out across a surface. When combined with III-V semiconductors with strong optical nonlinearities, a variety of nonlinear effects such as harmonic generation and all-optical modulation can be enabled and enhanced at the nanoscale. This review presents our research on engineering and boosting nonlinear effects in ultrafast and nonlinear semiconductor metasurfaces fabricated at the Center for Integrated Nanotechnologies. We cover our recent works on parametric generation of harmonic light via direct and cascaded processes in GaAs-metasurfaces using Mie-like optical resonances or symmetric-protected bound state in the continuum, and then describe the recent advances on harmonic generation in all-dielectric metasurfaces coupled to intersubband transitions in III-V semiconductor heterostructures. The review concludes on the potential of metasurfaces to serve as the next platform for on-chip quantum light generation.

Third- and Second-Harmonic Generation in All-Dielectric Nanostructures: A Mini Review

Frequency conversion such as harmonic generation is a fundamental physical process in nonlinear optics. The conventional nonlinear optical systems suffer from bulky size and cumbersome phase-matching conditions due to the inherently weak nonlinear response of natural materials. Aiming at the manipulation of nonlinear frequency conversion at the nanoscale with favorable conversion efficiencies, recent research has shifted toward the integration of nonlinear functionality into nanophotonics. Compared with plasmonic nanostructures showing high dissipative losses and thermal heating, all-dielectric nanostructures have demonstrated many excellent properties, including low loss, high damage threshold, and controllable resonant electric and magnetic optical nonlinearity. In this review, we cover the recent advances in nonlinear nanophotonics, with special emphasis on third- and second-harmonic generation from all-dielectric nanoantennas and metasurfaces. We discuss the main theoretical concepts, the design principles, and the functionalities of third- and second-harmonic generation processes from dielectric nanostructures and provide an outlook on the future directions and developments of this research field.

Multifunctional and Transformative Metaphotonics with Emerging Materials

Future technologies underpinning multifunctional physical and chemical systems and compact biological sensors will rely on densely packed transformative and tunable circuitry employing nanophotonics. For many years, plasmonics was considered as the only available platform for subwavelength optics, but the recently emerged field of resonant metaphotonics may provide a versatile practical platform for nanoscale science by employing resonances in high-index dielectric nanoparticles and metasurfaces. Here, we discuss the recently emerged field of metaphotonics and describe its connection to material science and chemistry. For tunabilty, metaphotonics employs a variety of the recently highlighted materials such as polymers, perovskites, transition metal dichalcogenides, and phase change materials. This allows to achieve diverse functionalities of metasystems and metasurfaces for efficient spatial and temporal control of light by employing multipolar resonances and the physics of bound states in the continuum. We anticipate expanding applications of these concepts in nanolasers, tunable metadevices, metachemistry, as well as a design of a new generation of chemical and biological ultracompact sensing devices.

Transition Metal Dichalcogenide Dimer Nanoantennas for Tailored Light-Matter Interactions

Transition metal dichalcogenides have emerged as promising materials for nanophotonic resonators because of their large refractive index, low absorption within a large portion of the visible spectrum, and compatibility with a wide range of substrates. Herein, we use these properties to fabricate WS₂ double-pillar nanoantennas in a variety of geometries enabled by the anisotropy in the crystal structure. Using dark-field spectroscopy, we reveal multiple Mie resonances, to which we couple WSe₂ monolayer photoluminescence and achieve Purcell enhancement and an increased fluorescence by factors up to 240 for dimer gaps of 150 nm. We introduce postfabrication atomic force microscope repositioning and rotation of dimer nanoantennas, achieving gaps as small as 10 ± 5 nm, which enables a host of potential applications, including strong Purcell enhancement of single-photon emitters and optical trapping, which we study in simulations. Our findings highlight the advantages of using transition metal dichalcogenides for nanophotonics by exploring applications enabled by their properties.

Vacuum ultraviolet nonlinear metalens

Vacuum ultraviolet (VUV) light plays an essential role across science and technology, from molecular spectroscopy to nanolithography and biomedical procedures. Realizing nanoscale devices for VUV light generation and control is critical for next-generation VUV sources and systems, but the scarcity of low-loss VUV materials creates a substantial challenge. We demonstrate a metalens that both generates-by second-harmonic generation-and simultaneously focuses the generated VUV light. The metalens consists of 150-nm-thick zinc oxide (ZnO) nanoresonators that convert 394 nm (~3.15 eV) light into focused 197-nm (~6.29 eV) radiation, producing a spot 1.7 μm in diameter with a 21-fold power density enhancement as compared to the wavefront at the metalens surface. The reported metalens is ultracompact and phase-matching free, allowing substantial streamlining of VUV system design and facilitating more advanced applications. This work provides a useful platform for developing low-loss VUV components and increasing the accessibility of the VUV regime.

Design and Optimization of All-Dielectric Fluorescence Enhancing Metasurfaces: Towards Advanced Metasurface-Assisted Optrodes

The need for miniaturized biological sensors which can be easily integrated into medical needles and catheters for in vivo liquid biopsies with ever-increasing performances has stimulated the interest of researchers in lab-on-fiber (LOF) technology. LOF devices arise from the integration of functional materials at the nanoscale on the tip of optical fibers, thus endowing a simple optical fiber with advanced functionalities and enabling the realization of high-performance LOF biological sensors. Consequently, in 2017, we demonstrated the first optical fiber meta-tip (OFMT), consisting of the integration of plasmonic metasurfaces (MSs) on the optical fiber end-face which represented a major breakthrough along the LOF technology roadmap. Successively, we demonstrated that label-free biological sensors based on the plasmonic OFMT are able to largely overwhelm the performance of a standard plasmonic LOF sensor, in view of the extraordinary light manipulation capabilities of plasmonic array exploiting phase gradients. To further improve the overall sensitivity, a labelled sensing strategy is here suggested. To this end, we envision the possibility to realize a novel class of labelled LOF optrodes based on OFMT, where an all-dielectric MS, designed to enhance the fluorescence emission by a labelled target molecule, is integrated on the end-face of a multimode fiber (MMF). We present a numerical environment to compute the fluorescence enhancement factor collected by the MMF, when on its tip a Silicon MS is laid, consisting of an array of cylindrical nanoantennas, or of dimers or trimers of cylindrical nanoantennas. According to the numerical results, a suitable design of the dielectric MS allows for a fluorescence enhancement up to three orders of magnitudes. Moreover, a feasibility study is carried out to verify the possibility to fabricate the designed MSs on the termination of multimode optical fibers using electron beam lithography followed by reactive ion etching. Finally, we analyze a real application scenario in the field of biosensing and evaluate the degradation in the fluorescence enhancement performances, taking into account the experimental conditions. The present work, thus, provides the main guidelines for the design and development of advanced LOF devices based on the fluorescence enhancement for labelled biosensing applications.

Thermo-optical reshaping of second-harmonic emission from dimer all-dielectric nanoresonators

All-dielectric nanophotonics offers a wide range of possibilities for thermally induced light manipulation at the nanoscale. High quality resonances allow for efficient light-to-heat conversion supported by various temperature detection approaches based on thermally sensitive intrinsic optical responses. In this work, we study theoretically a phenomenon of the photothermal reshaping of the radiation pattern of second-harmonic generation (SHG) that occurs in resonant all-dielectric systems. In the suggested geometry, a near-IR pulsed laser is used for SHG while a continuous wave visible laser simultaneously heats the structure. The thermo-optical switching of the resonant optical states in the nanostructures governs the reconfiguration of the emission pattern, without significant loss in the magnitude of the SHG. We believe, that our findings will pave the way for subwavelength-size near-IR thermally switchable nonlinear optical devices.

Manipulation of Exciton Dynamics in Single-Layer WSe2 Using a Toroidal Dielectric Metasurface

Recent advances in emerging atomically thin transition metal dichalcogenide semiconductors with strong light-matter interactions and tunable optical properties provide novel approaches for realizing new material functionalities. Coupling two-dimensional semiconductors with all-dielectric resonant nanostructures represents an especially attractive opportunity for manipulating optical properties in both the near-field and far-field regimes. Here, by integrating single-layer WSe₂ and titanium oxide (TiO₂) dielectric metasurfaces with toroidal resonances, we realized robust exciton emission enhancement over 1 order of magnitude at both room and low temperatures. Furthermore, we could control exciton dynamics and annihilation by using temperature to tailor the spectral overlap of excitonic and toroidal resonances, allowing us to selectively enhance the Purcell effect. Our results provide rich physical insight into the strong light-matter interactions in single-layer TMDs coupled with toroidal dielectric metasurfaces, with important implications for optoelectronics and photonics applications.

Bright single photon emitters with enhanced quantum efficiency in a two-dimensional semiconductor coupled with dielectric nano-antennas

Single photon emitters in atomically-thin semiconductors can be deterministically positioned using strain induced by underlying nano-structures. Here, we couple monolayer WSe₂ to high-refractive-index gallium phosphide dielectric nano-antennas providing both optical enhancement and monolayer deformation. For single photon emitters formed on such nano-antennas, we find very low (femto-Joule) saturation pulse energies and up to 10⁴ times brighter photoluminescence than in WSe₂ placed on low-refractive-index SiO₂ pillars. We show that the key to these observations is the increase on average by a factor of 5 of the quantum efficiency of the emitters coupled to the nano-antennas. This further allows us to gain new insights into their photoluminescence dynamics, revealing the roles of the dark exciton reservoir and Auger processes. We also find that the coherence time of such emitters is limited by intrinsic dephasing processes. Our work establishes dielectric nano-antennas as a platform for high-efficiency quantum light generation in monolayer semiconductors.

Single photon emitters (SPEs) in 2D semiconductors can be deterministically positioned using localized strain induced by underlying nanostructures. Here, the authors show SPE coupling in WSe₂ to GaP dielectric nanoantennas, substantially increasing quantum efficiency and photoluminescence brightness.

Light-induced symmetry breaking for enhancing second-harmonic generation from an ultrathin plasmonic nanocavity

Efficient frequency up-conversion of coherent light at the nanoscale is highly demanded for a variety of modern photonic applications, but it remains challenging in nanophotonics. Surface second-order nonlinearity of noble metals can be significantly boosted up by plasmon-induced field enhancement, however the related far-field second-harmonic generation (SHG) may also be quenched in highly symmetric plasmonic nanostructures despite huge near-field amplification. Here, we demonstrate that the SHG from a single gold nanosphere is significantly enhanced when tightly coupled to a metal film, even in the absence of a plasmon resonance at the SH frequency. The light-induced electromagnetic asymmetry in the nanogap junction efficiently suppresses the cancelling of locally generated SHG fields and the SH emission is further amplified through preferential coupling to the bright, bonding dipolar resonance mode of the nanocavity. The far-field SHG conversion efficiency of up to [Formula: see text] W-1 is demonstrated from a single gold nanosphere of 100 nm diameter, two orders of magnitude higher than for complex double-resonant plasmonic nanostructures. Such highly efficient SHG from a metal nanocavity also constitutes an ultrasensitive nonlinear nanoprobe to map the distribution of longitudinal vectorial light fields in nanophotonic systems.

Semiconductor Bow-Tie Nanoantenna from Coupled Colloidal Quantum Dot Molecules

Top-down fabricated nanoantenna architectures of both metallic and dielectric materials show powerful functionalities for Raman and fluorescence enhancement with relevance to single molecule sensing while inducing directionality of chromophore emission with implications for single photon sources. We synthesize the smallest bow-tie nanoantenna by selective tip-to-tip fusion of two tetrahedral colloidal quantum dots (CQDs) forming a dimer. While the tetrahedral monomers emit non-polarized light, the bow-tie architecture manifests nanoantenna functionality of enhanced emission polarization along the bow-tie axis, as predicted theoretically and revealed by single-particle spectroscopy. Theory also predicts the formation of an electric-field hotspot at the bow-tie epicenter. This is utilized for selective light-induced photocatalytic metal growth at that location, unlike growth on the free tips in dark conditions, thus demonstrating bow-tie dimer functionality as a photochemical reaction center.

Dielectric optical nanoantennas

Nanophotonics allows the manipulation of light on the subwavelength scale. Optical nanoantennas are nanoscale elements that enable increased resolution in bioimaging, novel photon sources, solar cells with higher absorption, and the detection of fluorescence from a single molecule. While plasmonic nanoantennas have been extensively explored in the literature, dielectric nanoantennas have several advantages over their plasmonic counterparts, including low dissipative losses and near-field enhancement of both electric and magnetic fields. Nanoantennas increase the optical density of states, which increase the rate of spontaneous emission due to the Purcell effect. The increase is quantified by the Purcell factor, which depends on the mode volume and the quality factor. It is one of the main performance parameters for nanoantennas. One particularly interesting feature of dielectric nanoantennas is the possibility of integrating them into optical resonators with a high quality-factor, further improving the performance of the nanoantennas and giving very high Purcell factors. This review introduces the properties and parameters of dielectric optical nanoantennas, and gives a classification of the nanoantennas based on the number and shape of the nanoantenna elements. An overview of recent progress in the field is provided, and a simulation is included as an example. The simulated nanoantenna, a dimer consisting of two silicon nanospheres separated by a gap, is shown to have a very small mode volume, but a low quality-factor. Some recent works on photonic crystal resonators are reviewed, including one that includes a nanoantenna in the bowtie unit-cell. This results in an enormous increase in the calculated Purcell factor, from 200 for the example dimer, to 8 × 10⁶ for the photonic crystal resonator. Some applications of dielectric nanoantennas are described. With current progress in the field, it is expected that the number of applications will grow and that nanoantennas will be incorporated into new commercial products. A list of relevant materials with high refractive indexes and low losses is presented and discussed. Finally, prospects and major challenges for dielectric nanoantennas are addressed.

Electrically Actuated Varifocal Lens Based on Liquid-Crystal-Embedded Dielectric Metasurfaces

Compact varifocal lenses are essential to various imaging and vision technologies. However, existing varifocal elements typically rely on mechanically actuated systems with limited tuning speeds and scalability. Here, an ultrathin electrically controlled varifocal lens based on a liquid crystal (LC) encapsulated dielectric metasurface is demonstrated. Enabled by the field-dependent LC anisotropy, applying a voltage bias across the LC cell modifies the local phase response of the silicon meta-atoms, in turn modifying the metalens focal length. In a numerical implementation, a voltage-actuated metalens with continuous zoom and up to 20% total focal shift is demonstrated. The LC-based metalens concept is experimentally verified through the design and fabrication of a bifocal metalens that facilitates high-contrast switching between two discrete focal lengths upon application of a 9.8 V_pp voltage bias. Owing to their ultrathin thickness and adaptable design, LC-driven dielectric metasurfaces open new opportunities for compact varifocal lensing in a diversity of modern imaging applications.

An Efficient Deep-Subwavelength Second Harmonic Nanoantenna Based on Surface Plasmon-Coupled Dilute Nitride GaNP Nanowires

High-index semiconductor nanoantennae represent a powerful platform for nonlinear photon generation. Devices with reduced footprints are pivotal for higher integration capacity and energy efficiency in photonic integrated circuitry (PIC). Here, we report on a deep subwavelength nonlinear antenna based on dilute nitride GaNP nanowires (NWs), whose second harmonic generation (SHG) shows a 5-fold increase by incorporating ∼0.45% of nitrogen (N), in comparison with GaP counterpart. Further integrating with a gold (Au) thin film-based hybrid cavity achieves a significantly boosted SHG output by a factor of ∼380, with a nonlinear conversion efficiency up to 9.4 × 10^-6 W^-1. In addition, high-density zinc blende (ZB) twin phases were found to tailor the nonlinear radiation profile via dipolar interference, resulting in a highly symmetric polarimetric pattern well-suited for coupling with polarization nano-optics. Our results manifest dilute nitride nanoantenna as promising building blocks for future chip-based nonlinear photonic technology.

Large-area all-dielectric metasurface fabricated by an anodized aluminum oxide template

Transmissive metasurfaces formed by high-index dielectric materials have received great attention due to its potential in holograms, deflectors, beam converters, and flat lenses. However, a key challenge of all-dielectric metasurfaces is the limited scale and high cost in fabrication, such as electron beam lithography (EBL) and focused ion beam (FIB) lithography. In this paper, for the first time to our knowledge, an anodized aluminum oxide (AAO) template is combined with titanium dioxide (TiO₂) metasurface fabrication with advantages of large area (>2cm²) and low cost. Using the ordered anodized aluminum oxide (AAO) as an evaporation mask, a TiO₂ nanocylinder array is deposited through the AAO mask onto the SiO₂ substrate. Electric and magnetic dipole resonances of TiO₂ metasurface appear in the visible spectrum. Furthermore, we demonstrate the interaction of the CsPbBr_1.5I_1.5 quantum dot (QD) emission with magnetic dipole (MD) resonance of TiO₂ metasurface. Our results reveal that the metasurface exhibits remarkable photoluminescence (PL) enhancement of 25%. Up to now, a TiO₂ metasurface with 2.25-cm²-large area using AAO template method has never been attempted. Different from the metasurfaces fabricated by FIB and EBL, our method offers great ease for large-area metasurface fabrication, which is convenient for metasurface researchers and avoids costly facilities.

Second harmonic generation in gallium phosphide nano-waveguides

We designed, fabricated and tested gallium phosphide (GaP) nano-waveguides for second harmonic generation (SHG). We demonstrate SHG in the visible range around 655 nm using modal phase matching. We observe phase matched SHG for different combinations of interacting modes by varying the widths of the waveguides and tuning the wavelength of the pump. We achieved a normalized internal SHG conversion efficiency of 0.4% W^-1cm^-2 for a continuous-wave pump at wavelength of 1283.5 nm, the highest reported in the literature for a GaP waveguide. We also demonstrated temperature tuning of the SHG wavelength with a slope of 0.17 nm/^°C. The presented results contribute to the development of integrated photonic platforms with efficient nonlinear wave-mixing processes for classical and quantum applications.

Steering and Encoding the Polarization of the Second Harmonic in the Visible with a Monolithic LiNbO3 Metasurface

Nonlinear metasurfaces constitute a key asset in meta-optics, given their ability to scale down nonlinear optics to sub-micrometer thicknesses. To date, nonlinear metasurfaces have been mainly realized using narrow band gap semiconductors, with operation limited to the near-infrared range. Nonlinear meta-optics in the visible range can be realized using transparent materials with high refractive index, such as lithium niobate (LiNbO3). Yet, efficient operation in this strategic spectral window has been so far prevented by the nanofabrication challenges associated with LiNbO3, which considerably limit the aspect ratio and minimum size of the nanostructures (i.e., meta-atoms). Here we demonstrate the first monolithic nonlinear periodic metasurface based on LiNbO3 and operating in the visible range. Realized through ion beam milling, our metasurface features a second-harmonic (SH) conversion efficiency of 2.40 × 10-8 at a pump intensity as low as 0.5 GW/cm2. By tuning the pump polarization, we demonstrate efficient steering and polarization encoding into narrow SH diffraction orders, opening novel opportunities for polarization-encoded nonlinear meta-optics.

Optical Tuning of Resistance Switching in Polycrystalline Gallium Phosphide Thin Films

The nanoscale resistive switching characteristics of gallium phosphide (GaP) thin films directly grown on Si are investigated as a function of incident light. The formation of conductive channels along the grain boundaries is attributed to the presence of point defects and structural disorder, which provide the ideal environment to enable the filamentary switching process. Both first-principles calculations and UV-vis and photoluminescence spectroscopy strongly point to the possibility of mid-gap electronic states in the polycrystalline GaP film due to such defects. To study the photonic excitation, photoconductive atomic force microscopy (phAFM) measurement is conducted. We observe photocurrents even for incident photon energies lower than the band gap, consistent with the presence of mid-gap electronic states; the photocurrents increase in direct proportion to the incident photon energy with a concomitant decrease in the filament resistance. This demonstrates GaP directly integrated on Si can be a promising photonic resistive switching materials system.

Few-Mode Field Quantization of Arbitrary Electromagnetic Spectral Densities

We develop a framework that provides a few-mode master equation description of the interaction between a single quantum emitter and an arbitrary electromagnetic environment. The field quantization requires only the fitting of the spectral density, obtained through classical electromagnetic simulations, to a model system involving a small number of lossy and interacting modes. We illustrate the power and validity of our approach by describing the population and electric field spatial dynamics in the spontaneous decay of an emitter placed in a complex hybrid plasmonic-photonic structure.

Recent advances in plasmonic nanocavities for single-molecule spectroscopy

Plasmonic nanocavities are able to engineer and confine electromagnetic fields to subwavelength volumes. In the past decade, they have enabled a large set of applications, in particular for sensing, optical trapping, and the investigation of physical and chemical phenomena at a few or single-molecule levels. This extreme sensitivity is possible thanks to the highly confined local field intensity enhancement, which depends on the geometry of plasmonic nanocavities. Indeed, suitably designed structures providing engineered local optical fields lead to enhanced optical sensing based on different phenomena such as surface enhanced Raman scattering, fluorescence, and Förster resonance energy transfer. In this mini-review, we illustrate the most recent results on plasmonic nanocavities, with specific emphasis on the detection of single molecules.

Entangled photons from subwavelength nonlinear films

Miniaturized entangled photon sources, in particular based on subwavelength metasurfaces, are highly demanded for the development of integrated quantum photonics. Here, as a first step towards the development of quantum optical metasurfaces (QOMs), we demonstrate generation of entangled photons via spontaneous parametric down-conversion (SPDC) from subwavelength films. We achieve photon pair generation with a high coincidence-to-accidental ratio in lithium niobate and gallium phosphide nanofilms. By implementing the fiber spectroscopy of SPDC in nanofilms, we measure a spectrum with a bandwidth of 500 nm, limited only by the overall detection efficiency. The spectrum reveals vacuum field enhancement due to a Fabry-Perot resonance inside the nonlinear films. It also suggests a strategy for observing SPDC from QOM. Our experiments lay the groundwork for future development of flat SPDC sources, including QOM.

Coupling of Germanium Quantum Dots with Collective Sub-radiant Modes of Silicon Nanopillar Arrays

In this paper, we demonstrate the infrared photoluminescence emission from Ge(Si) quantum dots coupled with collective Mie modes of silicon nanopillars. We show that the excitation of band edge dipolar modes of a linear nanopillar array results in strong reshaping of the photoluminescence spectra. Among other collective modes, the magnetic dipolar mode with the polarization along the array axis contributes the most to the emission spectrum, exhibiting an experimentally measured Q-factor of around 500 for an array of 11 pillars. The results belong to the first experimental evidence of light emission enhancement of quantum emitters applying collective Mie resonances in finite nanoresonators and therefore represent an important contribution to the new field of active all-dielectric meta-optics.

Raman and optical characteristics of van der Waals heterostructures of single layers of GaP and GaSe: a first-principles study

Inorganic single layers of GaP and GaSe can form novel ultra-thin heterostructures displaying unique Raman and optical properties.

Template Dissolution Interfacial Patterning of Single Colloids for Nanoelectrochemistry and Nanosensing

Deterministic positioning and assembly of colloidal nanoparticles (NPs) onto substrates is a core requirement and a promising alternative to top-down lithography to create functional nanostructures and nanodevices with intriguing optical, electrical, and catalytic features. Capillary-assisted particle assembly (CAPA) has emerged as an attractive technique to this end, as it allows controlled and selective assembly of a wide variety of NPs onto predefined topographical templates using capillary forces. One critical issue with CAPA, however, lies in its final printing step, where high printing yields are possible only with the use of an adhesive polymer film. To address this problem, we have developed a template dissolution interfacial patterning (TDIP) technique to assemble and print single colloidal AuNP arrays onto various dielectric and conductive substrates in the absence of any adhesion layer, with printing yields higher than 98%. The TDIP approach grants direct access to the interface between the AuNP and the target surface, enabling the use of colloidal AuNPs as building blocks for practical applications. The versatile applicability of TDIP is demonstrated by the creation of direct electrical junctions for electro- and photoelectrochemistry and nanoparticle-on-mirror geometries for single-particle molecular sensing.

Continuous Wave Second Harmonic Generation Enabled by Quasi-Bound-States in the Continuum on Gallium Phosphide Metasurfaces

Resonant metasurfaces are an attractive platform for enhancing the nonlinear optical processes, such as second harmonic generation (SHG), since they can generate large local electromagnetic fields while relaxing the phase-matching requirements. Here, we demonstrate visible range, continuous wave (CW) SHG by combining the attractive material properties of gallium phosphide with high quality-factor photonic modes enabled by bound states in the continuum. We obtain efficiencies around 5e-5% W^-1 when the system is pumped at 1200 nm wavelength with CW intensities of 1 kW/cm². Moreover, we measure external efficiencies of 0.1% W^-1 with pump intensities of only 10 MW/cm² for pulsed irradiation. This efficiency is higher than the values previously reported for dielectric metasurfaces, but achieved here with pump intensities that are two orders of magnitude lower. These results take metasurface-based SHG a step closer to practical applications.

Gallium phosphide optical metasurfaces for visible light applications

There are few materials that are broadly used for fabricating optical metasurfaces for visible light applications. Gallium phosphide (GaP) is a material that, due to its optical properties, has the potential to become a primary choice but due to the difficulties in fabrication, GaP thin films deposited on transparent substrates have never been exploited. In this article we report the design, fabrication, and characterization of three different amorphous GaP metasurfaces obtained through sputtering. Although the material properties can be further optimized, our results show the potential of this material for visible applications making it a viable alternative in the material selection for optical metasurfaces.

Highly efficient unidirectional forward scattering induced by resonant interference in a metal-dielectric heterodimer

We demonstrate that a metal-dielectric heterodimer structure can satisfy a nearly ideal first Kerker condition at a wavelength close to the resonance peak of the dimer, yielding efficient unidirectional forward scattering with a high forward-to-backward scattering ratio (≈48 dB) and remarkable enhancement of the forward scattering intensity (∼2.68 times compared to a single dielectric nanoparticle). Using a rigorous analytical dipole-dipole interaction model, the underlying mechanism is revealed, in which the originally weak electric dipole moment of the dimer is significantly enhanced owing to the strong resonant interference between the localized surface plasmon resonance of the metal and the Mie resonances of the dielectric material, which could up-match the magnetic dipole moment of the dimer at a wavelength close to the resonance peak, boosting the forward scattering efficiency. To achieve the optimal conditions, the sizes of the metal and dielectric constituents as well as the gap distance of the dimer have to be physically and delicately tuned to ensure a perfect match in both the amplitudes and phases of the electric and magnetic dipole moments of the dimer. On top of that, the loss of the heterodimer can be effectively suppressed to a level well below that of a pure metal nanoparticle, which further benefits the forward scattering efficiency. The flexibility in designing the dimer geometry and choosing metal-dielectric material combinations enables efficient unidirectional forward scattering in a broadband spectrum (UV to visible) with an intermediate gap distance (10-20 nm), greatly expanding the application scope. The proposed hybrid dimer could serve as a powerful and versatile building block in many emergent fields such as metasurfaces, nanoantennae, etc.

Nanostructured amorphous gallium phosphide on silica for nonlinear and ultrafast nanophotonics

Nanophotonics based on high refractive index dielectrics relies on appreciable contrast between the indices of designed nanostructures and their immediate surrounding, which can be achieved by the growth of thin films on low-index substrates. Here we propose the use of high index amorphous gallium phosphide (a-GaP), fabricated by radio-frequency sputter deposition, on top of a low refractive index glass substrate and thoroughly examine its nanophotonic properties. Spectral ellipsometry of the amorphous material demonstrates the optical properties to be considerably close to crystalline gallium phosphide (c-GaP), with low-loss transparency for wavelengths longer than 650 nm. When nanostructured into nanopatches, the second harmonic (SH) response of an individual a-GaP patch is characterized to be more than two orders of magnitude larger than the as-deposited unstructured film, with an anapole-like resonant behavior. Numerical simulations are in good agreement with the experimental results over a large spectral and geometrical range. Furthermore, by studying individual a-GaP nanopatches through non-degenerate pump-probe spectroscopy with sub-10 fs pulses, we find a more than 5% ultrafast modulation of the reflectivity that is accompanied by a slower decaying free carrier contribution, caused by absorption. Our investigations reveal a potential for a-GaP as an adequate inexpensive and CMOS-compatible material for nonlinear nanophotonic applications as well as for photocatalysis.

Direct visualization of phase-matched efficient second harmonic and broadband sum frequency generation in hybrid plasmonic nanostructures

Second harmonic generation and sum frequency generation (SHG and SFG) provide effective means to realize coherent light at desired frequencies when lasing is not easily achievable. They have found applications from sensing to quantum optics and are of particular interest for integrated photonics at communication wavelengths. Decreasing the footprints of nonlinear components while maintaining their high up-conversion efficiency remains a challenge in the miniaturization of integrated photonics. Here we explore lithographically defined AlGaInP nano(micro)structures/Al₂O₃/Ag as a versatile platform to achieve efficient SHG/SFG in both waveguide and resonant cavity configurations in both narrow- and broadband infrared (IR) wavelength regimes (1300-1600 nm). The effective excitation of highly confined hybrid plasmonic modes at fundamental wavelengths allows efficient SHG/SFG to be achieved in a waveguide of a cross-section of 113 nm × 250 nm, with a mode area on the deep subwavelength scale (λ ²/135) at fundamental wavelengths. Remarkably, we demonstrate direct visualization of SHG/SFG phase-matching evolution in the waveguides. This together with mode analysis highlights the origin of the improved SHG/SFG efficiency. We also demonstrate strongly enhanced SFG with a broadband IR source by exploiting multiple coherent SFG processes on 1 µm diameter AlGaInP disks/Al₂O₃/Ag with a conversion efficiency of 14.8% MW^-1 which is five times the SHG value using the narrowband IR source. In both configurations, the hybrid plasmonic structures exhibit >1000 enhancement in the nonlinear conversion efficiency compared to their photonic counterparts. Our results manifest the potential of developing such nanoscale hybrid plasmonic devices for state-of-the-art on-chip nonlinear optics applications.

Nanogap-Rich TiO2 Film for 2000-Fold Field Enhancement with High Reproducibility

Titanium dioxide (TiO₂) is a crucial semiconductor for photocatalysts, solar cells, hydrogen evolution reactions, and antivirus agents. The properties and performances of these applications can improve significantly if the integrated TiO₂ acts as a light harvester through a large field enhancement. This study investigates the electromagnetic field enhancement of a nanogap-rich TiO₂ film with a large area, prepared by a facile dry process at room temperature. Herein, the loading pressure is applied to the TiO₂ particles for closely packing them in the film. The field enhancement, as a function of the loading pressure, is explored from the fluorescence intensity enhancement of a dye molecule. An average enhancement factor >2000 is achieved, which is a remarkable record for semiconductors. Furthermore, the reproducibility is significant; the relative standard deviation value is small (∼4%). Calculations were performed using the finite-difference-time-domain method. A nanogap of 5 nm yields the highest EF for triangular-prism TiO₂ particles.

Gallium Phosphide Nanowires in a Free-Standing, Flexible, and Semitransparent Membrane for Large-Scale Infrared-to-Visible Light Conversion

Engineering of nonlinear optical response in nanostructures is one of the key topics in nanophotonics, as it allows for broad frequency conversion at the nanoscale. Nevertheless, the application of the developed designs is limited by either high cost of their manufacturing or low conversion efficiencies. This paper reports on the efficient second-harmonic generation in a free-standing GaP nanowire array encapsulated in a polymer membrane. Light coupling with optical resonances and field confinement in the nanowires together with high nonlinearity of GaP material yield a strong second-harmonic signal and efficient near-infrared (800-1200 nm) to visible upconversion. The fabricated nanowire-based membranes demonstrate high flexibility and semitransparency for the incident infrared radiation, allowing utilizing them for infrared imaging, which can be easily integrated into different optical schemes without disturbing the visualized beam.