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We study how nanophotonic structures can be used for determining the position of a nearby nanoscale object with subwavelength accuracy. Through perturbing the near-field environment of a metasurface transducer consisting of nano-apertures in a metallic film, the location of the nanoscale object is transduced into the transducer’s far-field optical response. By monitoring the scattering pattern of the nanophotonic near-field transducer and comparing it to measured reference data, we demonstrate the two-dimensional localization of the object accurate to 24 nm across an area of 2 × 2 μm. We find that adding complexity to the nanophotonic transducer allows localization over a larger area while maintaining resolution, as it enables encoding more information on the position of the object in the transducer’s far-field response.

A modified set-up for Raman spectroscopy is proposed to utilize an AFM probe in a regime beyond the dependence on near field optics. Possible mechanisms for the observed enhancement have been explored through comparisons to spectra from other enhanced Raman techniques, including surface enhanced Raman, interference enhanced Raman and polarized Raman spectroscopies. The effects of polarization, focusing and interference are heightened when near field effects are diminished, giving rise to spectral enhancement. This technique allows for the characterization of a sub-20 nm monolayer of polystyrene-block-poly(2 vinyl pyridine) reverse micelles and paves the way for a promising method of non-destructive analysis of large self-assembled arrays of colloids.

The electromagnetic properties of ordered hole nanostructures in very thin metal films are characterized using CdSe/CdS nanocrystals (NCs) as nanoprobes. The characterization of the local density of optical states (LDOS) on the nanostructure is possible by the measurement of their photoluminescence decay rate. Statistical measurements are performed in the far field to show the average increase of optical modes. A determinist approach using an active single NC nanoprobe in the near field gives access to a more precise characterization of the LDOS. The optical properties of the structure come from the coupling between localized surface plasmons created by the holes and surface plasmon polaritons. A strong concentration of optical modes is observed around the holes thanks to the active near-field nanoprobe. With different NC orientations, the strong influence of the component perpendicular to the surface in the very near field of the LDOS is observed. Finite differential time domain simulations of the different components of the electric field in the very near field of the structure confirm that the localization of the electric field around the holes is only due to the normal component as observed with the nanoprobe.

The optical-based super-resolution, non-invasive method is preferred for the inspection of surfaces with massive microstructures widely applied in functional surfaces. The Structured Illumination Microscopy (SIM) uses standing-wave illumination to reach optical super-resolution. Recently, coherent SIM is being studied. It can obtain both the super-resolved intensity distribution and the phase and amplitude distribution from the sample surface. By analysis of the phase-depth dependency, the depth measurement for microgroove structures with coherent SIM is expected. FDTD analysis is applied for observing the near-field response of microgroove narrower than the diffraction limit under the standing-wave illumination. The near-field phase shows depth dependency in this analysis.

Photonic spin-orbit interaction has attracted much attention in recent years. This talk first reports the efficient generation of ultra-compact optical vortex (OV) in achiral nanostructures, which has a radius of only 1 μm and possesses a signal-to-noise ratio larger than 6 dB. A spin-selective and phase-resolved scanning near-field optical microscope (SNOM) is employed to probe and visualize the OV generation process in the spin basis. Furthermore, a SNOM system is developed for probing and analyzing nonlinear optical signals in nanostructures with subwavelength resolution, which images the near-field third-harmonic generation from an anapole dark-mode state in a silicon nanodisk.

We study the modification of fluorescence emission and decay rate of single fluorescent molecules in the near field of a periodic plasmonic nanostructure formed by a square lattice of Au hollow conical pillars with a periodicity of 250 nm. We perform nanometer-resolved imaging of the LDOS by simultaneously mapping the position and the decay rate of photoactivatable single-molecules with a novel super-resolved microscopy approach which enables multiplexed and super-resolved fluorescence lifetime imaging at the single-molecule level (smFLIM) with a field of view of ~10 µm2. We observe the LDOS modification of such optically rich material at different illumination conditions and we measure a large Purcell factor enhancement which increases for oblique illumination of the nanostructure.

Topologically tailored photonic crystals offer robust transport of optical states in quantum and classical systems. However, quantifying the robustness of edge states in topologically protected PhCs has remained elusive. In our recent work, we report a rigorous quantitative evaluation of topological photonic edge eigenstates, emulating the quantum valley Hall effect (VPC), and analyze their transport properties in the telecom wavelength range using a phase-resolved near-field optical microscope. Our results demonstrate that the backscattering energy ratio for the VPC is two orders of magnitude smaller compared to that in a conventional W1 waveguide. Such an evaluation opens a pathway for creating quantum photonic networks that can achieve secure and robust communications.

Optical superoscillation refers to an intriguing phenomenon of a wave packet that can oscillate locally faster than its highest Fourier component, which potentially produces an extremely localized wave in the far field. It provides an alternative way to overcome the diffraction limit, hence improving the resolution of an optical microscopy system. However, the optical superoscillatory waves are inevitably accompanied by strong side lobes, which limits their fields of view and, hence, potential applications. Here, we report both experimentally and theoretically a new superoscillatory wave form, which not only produces significant feature size down to deep subwavelength, but also completely eliminates side lobes in a particular dimension. We demonstrate a new mechanism for achieving such a wave form based on a pair of moonlike sharp-edge apertures. The resultant superoscillatory wave exhibits Bessel-like forms, hence allowing long-distance propagation of subwavelength structures. The result facilitates the study of optical superoscillation and on a fundamental level eliminates the compromise between the superoscillatory feature size and the field of view.

A review of recent progress in optical recording of surface relief structures in the films of two classes of photoresponsive non-crystalline materials (azobenzene-containing polymers and amorphous chalcogenides) is presented. Various aspects related to light-driven macroscopic effects for these materials where stimulated surface patterning through selective mass transport process due to the interaction of matter with polarized light are discussed. Self-assembling processes initiated by polarized light illumination resulting in the formation of multiscale periodic reliefs on the photosensitive material surface are analyzed. Extensive experimental data describing different aspects of photomanipulated surface relief patterning using vectorial optical fields and structured light beams are summarized. Anisotropic nanoscale motion in amorphous azopolymer and chalcogenide films induced by a tightly focused polarized laser beam is considered. Similarities and differences in the manifestation of competition and cooperation between polarization-driven and intensity-driven mechanisms responsible for material displacement in chalcogenide glasses and amorphous azopolymers are analyzed. Possibilities for optimization and speeding up the process of holographic recording of periodic relief gratings in amorphous azopolymer and chalcogenide films at various configurations for combination of optical beams to produce 2D and 3D relief architecture on the film surface are discussed.

Overcoming the classical diffraction limit in optical microscopy is known to be achievable by a variety of far-field and near-field microscopy techniques. More recently, so-called micro-object-based optical super-resolution microscopy techniques have emerged. In this review, we provide an overview of the state-of-the-art of optical super-resolution imaging techniques. In the first section, far-field techniques are discussed, which can be considered as advanced classical optical microscopy methods that mostly operate with fluorescent samples. In the second section, near-field techniques are presented that achieve super-resolution by maintaining a close distance between a nanometric detection unit and the sample, such that evanescent waves can be captured and processed. Near-field methods typically involve some scanning procedure to be able to map a reasonably large area of the sample. In the third section, dielectricmicro-object-based techniques are discussed. These provide amore recent, practical and affordable alternative to the other super-resolution microscopies. Finally, we provide a comparison of the presented techniques in terms of performance and cost, pointing out the application-specific strength of each imaging method. (c) 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Chiral optical fields (typified by circularly polarized light) localized on the nanoscale enhance the chiral light–matter interaction, which may provide novel potential applications. This property enables the development of an ultrasensitive method for characterization of chiral molecules and nanoscale magnetic control realized by an all-optical method to interconnect spintronic nano-optical devices. A local chiral light source with switchable handedness or controllable chirality is indispensable for building such applications for practical use. In the current major method used for local chiral light generation, the handedness of the light is controlled by the handedness of the nanomaterial, which is not convenient when we need to change the handedness of the light. We experimentally achieve here generation and active control of a highly chiral local optical field by using a combination of an achiral gold nanorod and achiral linearly polarized optical field. By tilting the azimuth angle for the incident l...

This special section presents recent results in the field of infrared (IR) and terahertz (THz) optoelectronics, which have been developing rapidly over the past decades. The progress of IR and THz technologies affects a variety of fundamental problems in material science, astrophysics, chemistry and biology, medical diagnosis, and high-resolution and multispectral imaging modalities.

Cylindrical vector beams (CVBs), which possesses polarization distribution of rotational symmetry on the transverse plane, can be developed in many optical technologies. Conventional methods to generate CVBs contain redundant interferometers or need to switch among diverse elements, thus being inconvenient in applications containing multiple CVBs. Here we provide a passive polarization-selective device to substitute interferometers and simplify generation setup. It is accomplished by reversing topological charges of orbital angular momentum based on polarization-selective Gouy phase. In the process, tunable input light is the only condition to generate CVB with arbitrary topological charges. To cover both azimuthal and radial parameters of CVBs, we express the mapping between scalar Laguerre-Gaussian light on basic Poincar\'e sphere and CVB on high-order Poincar\'e sphere. The proposed device simplifies the generation of CVBs enormously, and thus has potentials in integrated devices for both quantum and classic optical experiments., Comment: 9 pages, 4 figures

Visible light can interact efficiently with the vibronic and electronic systems of a sample and fetch rich information about the intrinsic features, such as the chemical, physical and biological properties of the sample. Optical techniques have therefore been convenient tools for a long time to analyze and image various materials. However, the spatial resolution in optical microscopy is restricted by the diffraction limit of light, making it impossible to study samples much smaller than the wavelength of the probing light. This restriction can be overcome if a conventional optical microscopy, such as Raman microscopy, is combined with near-field techniques. Tip-enhanced Raman spectroscopy (TERS) is such a technique. It utilizes a sharp metallic nano-tip to intensely enhance and strongly confine light within a tiny volume near the tip-apex and enables characterization of samples at the nanoscale. In this Chapter, we discuss the details of this technique and explain how light can be tightly confined into a nanometric volume for true nanoscale exploration of samples. TERS is still a young technique and has been going through a rapid development in the past two decades, which has not only made it more reliable and sturdier over the period, but has also brought this apparently complicated technique out from the laboratories of the veterans to the market for researchers who are experts in different fields. This has obviously happened with improved adaptability, flexibility and robustness with possibilities of a wide range of applications. We will discuss some interesting applications and related instrumentations for TERS.

The work was partially supported by Sweden's innovation agency Vinnova (Large area CVD graphene-based sensors/IR-photodetectors 2020-00797) and EU CAMART2 project (European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No.739508). TY acknowledges European Regional Development Fund Project No. 1.1.1.2/VIAA/4/20/740., Infrared radiation reflection and transmission of a single layer of gold micropatch two-dimensional arrays, of patch length ∼1.0 µm and width ∼0.2 µm, have been carefully studied by a finite-difference time-domain (FDTD) method, and Fourier-transform infrared spectroscopy (FTIR). Through precision design of the micropatch array structure geometry, we achieve a significantly enhanced reflectance (85%), a substantial diffraction (10%), and a much reduced transmittance (5%) for an array of only 15% surface metal coverage. This results in an efficient far-field optical coupling with promising practical implications for efficient mid-infrared photodetectors. Most importantly we find that the propagating electromagnetic fields are transiently concentrated around the gold micropatch array in a time duration of tens of ns, providing us with a novel efficient near-field optical coupling. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Published under the CC BY 4.0 license., Vinnova 2020-00797; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2; ERDF 1.1.1.2/VIAA/4/20/740.

To reduce the effects of global warming, visible and near-infrared light must be used more efficiently. Deep ultraviolet light (8 eV) is required for the direct dissociation of CO2 by light; however, the introduction of a metal complex has made it possible to realize CO2 reduction with visible light. We demonstrate that the optical near field (ONF) can increase the CO2 reduction rate. For this, we used gold clusters, because they can be a suitable source for ONFs, as their size and density can be controlled by the number of gold atoms. By attaching a metal complex near gold clusters with diameters of 1.0 to 1.3 nm, we confirm that the reduction rate of CO2 to CO increased by 1.5 to 2.1 times. The gold clusters were sufficiently small; therefore, there was no plasmonic resonant peak or heat generation. Because the near-field effect is based on a photochemical reaction, it can be applied to other metal complexes used in CO2 reduction, and it has other applications such as water splitting and water purification.

We investigate the optical properties of nanostructures of antimony sulfide (Sb2S3), a direct-bandgapsemiconductor material that has recently sparked considerable interest as a thin film solar cell absorber.Fabrication from a nanoparticle ink solution and two- and three-dimensional nanostructuring with patternsizes down to 50 nm have recently been demonstrated. Insight into the yet unknown nanoscopic opticalproperties of these nanostructures is highly desired for their future applications in nanophotonics. Weimplement a spectrally broadband scattering-type near-field optical spectroscopy technique to study individualSb2S3nanodots with a 20-nm spatial resolution, covering the range from 700 to 900 nm. We show that inthis below-bandgap range, the Sb2S3nanostructures act as high-refractive-index, low-loss waveguideswith mode profiles close to those of idealized cylindrical waveguides, despite a considerable structuraldisorder. In combination with their high above-bandgap absorption, this makes them promising candidatesfor applications as dielectric metamaterials, specifically for ultrafast photoswitching. published

With the development of integrated circuits, MEMS devices and biotechnology, people are demanding more and more for the detection of complex micro-structures. The diffraction limit of light restricts the resolution of traditional optical microscopes. Near-field optical microscopes can avoid Rayleigh criterion and break through the diffraction limit by detecting the details of objects with evanescent waves to achieve super resolution measurement. The minimum resolution of 60nm can be achieved by balancing the light throughout and aperture size of the aperture SNOM. While, the resolution of the scattering SNOM depends on the curvature radius of the tip of the probe. The resolution below 20nm can be obtained, but the signal can be extracted by a composite interference optical system and phase-locked technology. People have continued to pursue the development of near-field optical microscope with more convenient, more reliable and smaller resolution. In this paper, a surface plasmon probe with the combination of aperture and scattering is presented. The structure is shown in the attached drawings. On the basis of a commercial AFM probe, a composite probe based on the combination of surface plasmon enhancement and scattering probe focusing was formed by coating SiO 2 probe and etching a single ring. The structure of the probe was optimized, in order to achieve larger enhancement of the light field. Furthermore, the combination of aperture SNOM illumination can greatly suppress background noise and achieve higher signal-to-noise ratio. By these two technologies, interference optical system and phase-locked technology can be avoided, thus simplifying the design of SNOM instruments. The finite-difference time-domain method is utilized to simulate and calculate the field distribution of the focusing spot and optimize the microstructure of the excited surface plasmon, which provides a strong theoretical support for the probe fabrication.

We study the local density of optical states (LDOS) for lossy dielectric substrates whose electric permittivity has a vanishing real part, approaching zero from the positive side of the real axis. A criterion for evaluating the threshold height above (below) which radiative (non-radiative) processes dominate for a dipole emitter is established. We focus on the case of a vertical dipole above the ϵ -near-zero (ENZ) substrate and show that, in the lossless case, complete LDOS cancellation originates from radiative modes in its near field. We evaluate the performance of commercially available ENZ materials and quantify the limits of such cancellation effects with the intrinsic losses of the substrate.

CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior FINEP - Financiadora de Estudos e Projetos, Financiadora de Estudos e Projetos Tip-enhanced Raman spectroscopy (TERS) has reached nanometer spatial resolution for measurements performed at ambient conditions and subnanometer resolution at ultrahigh vacuum. Super-resolution (beyond the tip apex diameter) TERS has been obtained mostly in the gap mode configuration, where a conductive substrate localizes the electric fields. Here we present experimental and theoretical TERS to explore the field distribution responsible for spectral enhancement. We use gold tips of 40 ± 10 nm apex diameter to measure TERS on graphene, a spatially delocalized two-dimensional sample, sitting on different substrates: (i) glass, (ii) a thin layer of gold and (iii) a surface covered with 12 nm diameter gold spheres, for which 6 nm resolution is achieved at ambient conditions. The super-resolution is due to the field configuration resulting from the coupled tip-sample-substrate system, exhibiting a nontrivial spatial surface distribution. The field distribution and the symmetry selection rules are different for nongap versus gap mode configurations. This influences the overall enhancement which depends on the Raman mode symmetry and substrate structure.

We theoretically and experimentally present hybridly polarized vector optical fields (HP-VOFs) with elliptic symmetry in an elliptic coordinate system. Compared with the traditional cylindrical HP-VOFs, there is an additional degree of freedom for this new kind of vector optical field, which is the interval between the two foci in the elliptic coordinate system. Except for discussing the singularities of the HP-VOFs, we concentrate on studying the energy transfer of the tightly focused HP-VOFs with elliptic symmetry in free space. We summarize the rules of the energy transfer and introduce a reference optical field to explain them. We hope these results can provide a new way to flexibly modulate tightly focused fields, which may be applied in realms such as optical machining, optical trapping, and information transmission.

We theoretically investigate the bistable spontaneous emission behavior of a single emitter in the vicinity of a hybrid V O 2 –Au nanoshell. The hybrid nanoshell is illuminated by a continuous wave pump laser. The incident beam generates heat through light absorption and causes the V O 2 to undergo a phase change from semiconductor to metallic mode. Our calculation shows that for certain values, over a range of incident laser intensity [ 0.25 ( G W / m 2 ) < I < 0.84 ( G W / m 2 )], at the resonance wavelength of the V O 2 (semiconductor)–Au nanoshell ( λ = 630 n m ), there is a reasonable bistable contrast for the two spontaneous emission rate values: the radiative and nonradiative decay rates. Our results provide important general guidelines for enabling platforms for optical switching sources and tunable sensors.

At the planar interface between a material and vacuum, the complex surface response S(omega)=[eps(omega) 1]/[eps(omega)+1], with eps(omega) the relative complex dielectric permittivity of the material, exhibit resonances, typical of the surface polariton modes, when eps(omega) ~ 1. We show that for a moderately sharp resonance, S(omega) is satisfactorily described with a mere (complex) Lorentzian, independently of the details affecting the various bulk resonances describing ) eps(omega). Remarkably, this implies a quantitative correlation between the resonant behaviors of Re[S(omega)] and Im[S(omega)], respectively associated to dispersive and dissipative effects in the surface near-field. We show that this "strong resonance" approximation easily applies, and discuss its limits, based upon published data for sapphire, CaF2 and BaF2. Extension to interfaces between two media or to a non planar interface is briefly considered., Comment: accepted for publication in Optics Letters

Subwavelength optical resonators and scatterers are dramatically expanding the toolset of the optical sciences and photonics engineering. By offering the opportunity to control and shape light waves in nanoscale volumes, recent developments using high-refractive-index dielectric scatterers gave rise to efficient flat-optical components such as lenses, polarizers, phase plates, color routers, and nonlinear elements with a subwavelength thickness. In this work, we take a deeper look into the unique interaction of light with rod-shaped amorphous silicon scatterers by tapping into their resonant modes with a localized subwavelength light source-an aperture scanning near-field probe. Our experimental configuration essentially constitutes a dielectric antenna that is locally driven by the aperture probe. We show how leaky transverse electric and magnetic modes can selectively be excited and form specific near-field distribution depending on wavelength and antenna dimensions. The probe's transmittance is furthermore enhanced upon coupling to the Fabry-Perot cavity modes, revealing all-dielectric nanorods as efficient transmitter antennas for the radiation of subwavelength emitters, in addition to constituting an elementary building block for all-dielectric metasurfaces and flat optics.

Resonant waveguide gratings (RWGs) are subwavelength structures of great interest for biosensors, optical filters and optical security applications. We demonstrate and characterize a beam steering device, where the in-coupling and out-coupling processes make use of different RWGs that share the same ultrathin dielectric waveguide. This device enables selective color-filtering and redirection of a white light source (such as a white LED). Furthermore, this structure is compatible with up-scalable fabrication processes such as roll-to-roll replication, and is relevant for high-volume production. Because of its color selectivity and its use in low coherence illumination conditions, such a beam steering device could be implemented in a variety of optical applications such as optical security, multifocal or monochromatic lenses, biosensors, and see-through optical combiners for near-eye displays.

We demonstrate a fiber-integrated quantum optical circulator that is operated by a single atom and that relies on the chiral interaction between emitters and transversally confined light. Like its counterparts in classical optics, our circulator exhibits an inherent asymmetry between light propagation in the forward and the backward direction. However, rather than a magnetic field or a temporal modulation, it is the internal quantum state of the atom that controls the operation direction of the circulator. This working principle is compatible with preparing the circulator in a coherent superposition of its operational states. Such a quantum circulator may thus become a key element for routing and processing quantum information in scalable integrated optical circuits. Moreover, it features a strongly nonlinear response at the single-photon level, thereby enabling, e.g., photon number-dependent routing and novel quantum simulation protocols., 22 pages, 5 figures

With the rapid development of microelectronic industry of data processing, data storage/reading, and various optoelectronic devices, the demand for small-sized optical components and optical systems is increasing. Diffractive optics has a potential to improve optical systems by increasing their reliability, robustness, and functional integration, while reducing their sizes. The present work investigated diffractive optical elements with subwavelength features for near-field focusing and laser cavity. Fresnel zone plates (FZPs) in the visible wavelengths were studied for near-field focusing. In addition, for laser cavity reflectors, 2-dimensional grating based on high-index-contrast materials was investigated. Near-field focusing properties of FZPs were investigated in the visible regime by a 3-dimensional finite-difference time-domain (FDTD) method. It was proposed to use phase zone plate structured on a glass to improve the diffraction efficiency of subwavelength focusing. Furthermore, a simple analytical model was used to show that high numerical aperture phase FZP under the linearly polarized illumination produces a rotationally asymmetric focal spot. With a radially polarized illumination, rotationally symmetric focal spot with a minimum beamwidth of 0.39l is obtained. Focusing behavior of phase FZPs fabricated using Focused ion beam (FIB) was characterized by near-field scanning optical microscope (NSOM) and shown to be in agreement with the simulation results. The use of a 2-dimensional high-index-contrast grating (HCG) with a square periodic lattice is proposed to realize surface-emitting lasers. With a suitable design of the 2-dimensional HCGs, Q factor as high as 1032 was achieved. DOCTOR OF PHILOSOPHY (MAE)

The single-beam gradient force optical tweezers have transformed various fields of scientific research by enabling manipulation and characterization of single molecules. Conventional optical tweezers pose limitations in trapping particles in the sub-Rayleigh regime. These limitations have been overcome with the help of plasmonic nanoapertures like the double-nanohole aperture. A modified colloidal lithography technique has been used in fabrication of double-nanohole apertures achieving dimensions appropriate for trapping single molecules in this regime. This paper demonstrates optical trapping of a single 10 nm enzyme, rubisco, using double-nanohole apertures fabricated using the modified colloidal lithography technique as well as presents the results from transmission characterization of different double-nanohole apertures carried out using the finite-difference time-domain (FDTD) simulations.

Light–matter interaction in two-dimensional photonic or phononic materials allows for the confinement and manipulation of free-space radiation at sub-wavelength scales. Most notably, the van der Waals heterostructure composed of graphene (G) and hexagonal boron nitride (hBN) provides for gate-tunable hybrid hyperbolic plasmon phonon-polaritons (HP3). Here, we present the anisotropic flow control and gate-voltage modulation of HP3 modes in G-hBN on an air–Au microstructured substrate. Using broadband infrared synchrotron radiation coupled to a scattering-type near-field optical microscope, we launch HP3 waves in both hBN Reststrahlen bands and observe directional propagation across in-plane heterointerfaces created at the air–Au junction. The HP3 hybridization is modulated by varying the gate voltage between graphene and Au. This modifies the coupling of continuum graphene plasmons with the discrete hBN hyperbolic phonon polaritons, which is described by an extended Fano model. This work represents the fir...

A key concept underlying the specific functionalities of metasurfaces, i.e. arrays of subwavelength nanoparticles, is the use of constituent components to shape the wavefront of the light, on-demand. Metasurfaces are versatile and novel platforms to manipulate the scattering, colour, phase or the intensity of the light. Currently, one of the typical approaches for designing a metasurface is to optimize one or two variables, among a vast number of fixed parameters, such as various materials' properties and coupling effects, as well as the geometrical parameters. Ideally, it would require a multi-dimensional space optimization through direct numerical simulations. Recently, an alternative approach became quite popular allowing to reduce the computational cost significantly based on a deep-learning-assisted method. In this paper, we utilize a deep-learning approach for obtaining high-quality factor (high-Q) resonances with desired characteristics, such as linewidth, amplitude and spectral position. We exploit such high-Q resonances for the enhanced light-matter interaction in nonlinear optical metasurfaces and optomechanical vibrations, simultaneously. We demonstrate that optimized metasurfaces lead up to 400+ folds enhancement of the third harmonic generation (THG); at the same time, they also contribute to 100+ folds enhancement in optomechanical vibrations. This approach can be further used to realize structures with unconventional scattering responses., Comment: 29 pages, 7 figures

We simulate the image generated by a microsphere residing in contact on top of an exposed Blu-ray disk surface, when observed by a conventional microscope objective. While microsphere lenses have been used to focus light beyond the diffraction limit and to produce super-resolution images, the nature of the light-sample interaction is still under debate. Simulations in related articles predict the characteristics of the photonic nanojet (PNJ) formed by the microsphere, but so far, no data has been published on the image formation in the far-field. For our simulations, we use the open source package Angora and the commercial software RSoft FullWave. Both packages implement the Finite Difference Time Domain (FDTD) approach. Angora permits us to accurately simulate microscope imaging at the diffraction limit. The RSoft FullWave is able to record the steady-state complex electrical and magnetic fields for multiple wavelengths inside the simulation domain. A microsphere is simulated residing on top of a dielectric substrate featuring sub-wavelength surface features. The scattered light is recorded at the edges of the simulation domain and is then used in the near-field to far-field transformation. The light in the far field is then refocused using an idealized objective model, to give us the simulated microscope image. Comparisons between the simulated image and experimentally acquired microscope images verify the accuracy of our model, whereas the simulation data predicts the interaction between the PNJ and the imaged sample. This allows us to isolate and quantify the near-field patterns of light that enable super-resolution imaging, which is important when developing new micro-optical focusing structures.

An investigation of the influence of an evanescent wave on the dynamics of motion of erythrocytes in blood plasma is presented. Computer simulation of erythrocytes moving in an evanescent field and experimental demonstration of the forecasted motion substantiate the possibility for control of position of red blood cells in a solution. The range of velocities of transversal motion of erythrocytes due to the action of the optical force of the generated evanescent field is determined as a function of the angle of illumination of a cell by a linearly polarized wave with the azimuth of polarization 45 deg.

The effective optical constants of fishnet metamaterial are affected by the surrounding dielectric material or layers Analytical formulas were derived to retrieve the effective optical constants of fishnet metamaterial surrounded by different bulk materials, from reflection and transmission coefficients, and the effective optical constants of the fishnet embedded in thin film layers stack were retrieved numerically. With increase of the refractive index of the surrounding dielectric material as well as of the thickness of the nearby dielectric layers, the plasmonic resonance spectral position undergoes redshift while the absolute maximum value of negative refractive index of fishnet decreases.

Plasmonic systems have attracted remarkable interest due to their application to the subwavelength confinement of light and the associated enhancement of light-matter interactions. However, this requires light to dwell at a given spatial location over timescales longer than the coupling rate to any relevant loss mechanism. Here we develop a general strategy for the design of stopped-light plasmonic metasurfaces, by taking advantage of the conformal symmetry which underpins near-field optics. By means of the analytical technique of transformation optics, we propose a class of plasmonic gratings which is able to achieve ultra-slow group velocities, effectively freezing surface plasmon polaritons in space over their whole lifetime. Our method can be universally applied to the localization of polaritons in metallic systems, as well as in highly doped semiconductors and even two-dimensional conductive and polar materials, and may find potential applications in nano-focusing, nano-imaging, spectroscopy and light-harvesting., Comment: 7 pages, 5 figures

Unique optical and chemical properties of gold nanoparticles (NPs), besides their compatibility with biological entities, have led to the emergence of gold NPs as ideal candidates for biomedical applications if their size can be controlled with nanometer resolution. Taking advantage of (i) enhanced and confined dual wavelength counterpropagating leaky surface plasmons, (ii) different chemical potential dependencies of graphene’s optical transitions for different incident wavelengths, and (iii) different and intensive size dependencies of the extinction efficiency of plasmonic gold NPs for different incident wavelengths, (i) efficient, (ii) tunable, and (iii) bidirectional tweezers with nanometer precision have been proposed. At low laser intensities, but at the cost of speed, the proposed setup can be relatively compact due to the realized bidirectional feature that cannot be achieved in conventional unidirectional tweezers. Finite-difference time-domain calculations show that the proposed setup benefits from a dynamical fast tuning of the screening radius ( ∼ 1.73 µ s / m m 2 ), high bidirectional sorting sensitivity ( ∼ 14 n m / m e V ), and low tuning voltage ( ∼ 0.35 V ). The ability to integrate miniaturized parallel systems with individual operation on a single chip is another potential capability of the proposed system, which makes it a promising candidate for future lab-on-a-chip devices.

Optical metamaterials offer precise control over the properties and interactions of light at the nanoscale, attracting interest in many new fields of research including chemical and molecular sensing, magnetic antennas, and photovoltaic elements. By utilizing the phenomenon of extraordinary optical transmission (EOT) plasmonic devices enable the detection of minute changes in the local, near-surface, dielectric properties of materials, opening up a wide range of different applications. Characterization of the optoelectronic properties of ultra-thin films is of paramount importance for a wide range of electronic applications including integrated circuit production. However, it is often extremely difficult to achieve using conventional imaging techniques. Here, it is demonstrated that plasmonic color filters can be used for the direct optical imaging and characterization of ion implantation in thin films. A model system consisting of variable doses of gallium ions implanted within titanium oxide thin films is used. It is observed that the ion implantation dose leads to a variation in the measured plasmon resonance spectra, which can be further enhanced through the use of bimodal nanopixel arrays. Using Monte Carlo simulations and the Maxwell-Garnett relation, the observed plasmon resonance spectra in terms of the gallium ion implantation dose is quantitatively interpreted.

Coupled localized surface plasmon resonances (LSPRs) in periodic arrays of metallic nanowires are attractive for use in sensing applications due to their light enhancement and their sensitivity to the surrounding environment. Due to the interwire coupling, they behave as plasmonic waveguides with high wavevector modes that require bulky methods for efficient excitation. In this contribution, we demonstrate the excitation of coupled LSPRs in gold nanowires with photonic modes supported by an optical waveguide made with ion exchange technology. Currently, although weakly-coupled LSPRs are experimentally demonstrated, strongly-coupled LSPRs are only demonstrated numerically due to the challenge represented by the fabrication of a high density nanowire array with current electron beam lithography. Due to their operation across the visible spectrum and its low-loss coupling to standard optical fibers, integrated nanowires on glass waveguides open new perspectives for the development of hybrid photonic-plasmonic integrated optical devices.

We present a novel multi-hole core photonic crystal fiber for guiding and confining light in subwavelength-diameter low-refractive-index air holes of core, even when light is guided based on total internal reflection. The low-loss, broadband and single-mode guiding properties of the fiber are studied. The propagation mechanism in subwavelength and low-refractive-index holes is analyzed by evanescent wave coupling. Light confinement and enhancement are caused by large discontinuity of the electric field at dielectric interfaces. Multiple subwavelength air holes in the core can guide light together, coupling and coherent with each other. Arrays of air holes in the core can be used as a means of patterning light on a submicrometer regime. The high light intensity in multiple long holes enables a variety of applications in nonlinear light management, optical modulation, and gas sensing.

A tip-enhanced near-field optical microscope, based on a shear-force atomic force microscope with plasmonic tip coupled to an inverted, confocal optical microscope, has been constructed for nanoscale chemical (Raman) imaging of surfaces. The design and validation of the instrument, along with its application to near-field Raman mapping of patterned organic thin films (coumarin-6 and Cu(II) phthalocyanine), are described. Lateral resolution of the instrument is estimated at 50 nm (better than λ/10), which is roughly dictated by the size of the plasmonic tip apex. Additional observations, such as the distance scaling of Raman enhancement and the inelastic scattering background generated by the plasmonic tip, are presented. Copyright © 2016 John Wiley & Sons, Ltd.

Protein-based multi-mode interference optical micro-splitters (P-MMIs) were customized from bovine serum albumin aqueous ink by maskless and noncontact femtosecond laser direct writing. Good bio-/eco-compatibility could be achieved using protein-based biopolymers. As a premise of protein waveguide-based devices like P-MMIs, protein-based optical micro-waveguides were tested with $\sim 0.059$ -dB/ $\mu \text{m}$ transmission loss for more bio-transparent 633-nm light. With satisfactory implementation of micro/nano-scale structure details, prototyping P-MMIs (two device geometries designed for 532 nm and 633 nm respectively) were fabricated and operated well as fundamental integrated optical devices for light splitting for the first time to our knowledge.

Efficient, broadband, and polarization-independent optical input/output (I/O) coupling of silicon photonics chips is significant for its practical application, and single-mode vertical optical I/O coupling will be necessary for high-density optical I/O connections required in future high-performance computing systems. We demonstrated such optical coupling using a 45° mirror, which was integrated by a cost-effective dicing technique with a polishing process. The 45° mirrors were integrated into Si-rich silica (SiOx) waveguides on a Si substrate. To evaluate the light beam profile, which was important factor for the single-mode optical coupling, we measured near field patterns and far field patterns of light beams reflected by the 45° mirror. Owing to the polishing process, high-quality single-mode beams were successfully obtained as the vertical optical output. Using the fabricated 45° mirrors, the efficient single-mode vertical optical coupling with loss penalty of around 0.3 dB was demonstrated. The wavelength-dependent loss was less than 0.6 and 0.2 dB for TE and TM polarization, respectively. The polarization-dependent loss was also very small and it was less than 0.2 dB in 1500–1600 nm.

The recent progress in laser processing reaches a level where a precise fabrication that overcomes the diffraction limit of the far-field optics can be achieved. Laser processing mediated by enhanced near field is one of the attractive methods to provide highly precise structuring with a simple apparatus. In this review, we describe the fundamentals of the electromagnetic near field in the vicinity of small structures and the application of its specific properties for nanomodification. Theoretical and experimental results on nanoablation based on electromagnetic field enhancement due to plasmon polariton excitation and Mie scattering are discussed. High-throughput nanohole fabrication mediated by arrayed nanospheres is discussed, as the coupling effect of near field is also considered. In addition, recent fabrication techniques and their potential applications in nanopatterning, nanoscale deformation, and biophotonics are discussed.

The relatively low energy of the terahertz light (THz, 1 THz = 4.14 meV) promises the non-invasive optical imaging of the biomedical objects. However, the THz light inherently suffers the optical diffraction limit and the subwavelength microstructures cannot be resolved. We propose the planar hybrid-lens comprising the multiple slits and the two-dimensional rod array for the subwavelength focusing of the THz light beyond the diffraction limit. The hybrid-lens is investigated by the finite difference time domain simulation (FDTD). The spectra of the rod array obtained by FDTD are compared with the spectra calculated by the analytical model. The subwavelength focal spot about 20 µm (λ/7.5) at the frequency 2 THz is demonstrated by FDTD. The array of the subwavelength focal spots on the opposite side of the multiple slits are generated by the interferences of the Floquet-Bloch waves which can be guided through the rod array. The hybrid-lens can function as the subwavelength focusing and the substrate simultaneously which may serve as the new tool in the high-speed imaging and sensing of the subwavelength biomedical objects by using the THz light.

The thin microcavity theory for near-field optics is proposed in this study. By applying the power flow theorem and the variable theorem,the bi-harmonic differential governing equation for electromagnetic field of a three-dimensional thin microcavity is derived for the first time. Then by using the Hankel transform, this governing equation is solved exactly and all the electromagnetic components inside and outside the microcavity can be obtained accurately. According to the above theory, the near-field optical diffraction from a subwavelength aperture embedded in a thin conducting film is investigated, and numerical computations are performed to illustrate the edge effect by an enhancement factor of 1.8 and the depolarization phenomenon of the near-field transmission in terms of the distance from the film surface. This thin microcavity theory is verified by the good agreement between our results and those in the previous literatures. The thin microcavity theory presented in the study should be useful in the possible applications of the thin microcavities in near-field optics and thin-film optics.

Exploiting the uniquely tunable optical response and the strong optical Kerr nonlinearity of a graphene sheet conjugated by the propagating leaky surface plasmons (SPs) excited on top of gold (Au) stripes, an efficient and high-speed electrically reconfigurable plasmonic tweezer is presented. It is demonstrated that using a number of electrically and optically isolated Au stripes and topped graphene, metallic, and dielectric nanoparticles (NPs) can be trapped, sensed, guided, and sorted in a controllable manner. Also, numerical simulations show that at high enough SP fields, the fundamental SP mode is laterally self-focused by an induced laterally graded refractive index and consequently experiences weaker edge effects. It is shown that a more confined and enhanced SP mode in the nonlinear regime is beneficial to trapping and sensing applications. The proposed stacked structure of a nonpatterned graphene sheet and Au stripes offers an efficient and powerful method for developing reconfigurable plasmofluidic channels in controlling the trajectory of label-free NPs.

A metallic microcones array-based plasmonic strcture is presented as an example for the purpose of experimentally exploring the dependence of ambient temperature and incident angle on resonance and absorption properties. The microcones array is fabricated using the technique of heavy ion tracking. The technique has advantages of large-area patterning, high-aspect ratio of unit dimension, controllable length, and multichoice of materials. Fabrication steps, mathematical fitting, and experimental measurements of optical absorption spectra are presented. To analyze the experimental data regarding thetemperature-dependence effect, a theoretical formula, a quasi-Gauss model, is applied to describe the relationship between temperature (T) and plasmonic wavelength (λSP). Our experimental results demonstrate that the variation of temperature and incident angle strongly affect the sensitivity of λSP and its absorption properties. Our experimental results indicate that this structure is capbale of acting as an optical sensor for detection of temperature and angular denpendence.