This PDF file contains the front matter associated with SPIE Proceedings Volume 11344, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Optical enantioselectivity of chiral molecules could be enhanced by depositing them on suitable nanostructured substrates. Different kind of chiral substrates can be developed, but chiral features are in general difficult to fabricate or costly. Self-assembled approach allows realizing plasmonic metasurfaces with a low cost reliable procedure. In this case asymmetric fabrication parameters can induce chiral optical response of the realised substrate. Self-organized polystyrene spheres deposited on glass substrate, are utilised to produce asymmetric hole array on a metal thin film. In our case the spheres (518 nm in diameter) where reduced by selective reactive ion etching and then covered by gold (and other metals), that is evaporated at a glancing angle. After the removing of the spheres an elliptical-hole array is produced forming a circular-dichroic substrate. The circular dichroic response of light interacting with the substrate can be tuned by choosing proper incidence angle and excitation wavelength, while the flat nature of the metasurface is very useful for easy molecular deposition processes. Two new enantiomers (right-handed and left-handed molecules) have been synthesized in order to present a good circular dichroism in the visible range and to be tested on the realized metasurfaces. Different tests were carried out on the samples, investigating the spectral optical properties of the structures with and without chiral molecules on top of them. The results are very promising due to the possibility of easily tuning and optimizing the optical response.

This presentation was first delivered at Optics + Photonics on 12 August 2019 and has been included as part of this Digital Forum to enable scholarly dialogue. Please use the original citation when citing: Proceedings Volume 11080, Metamaterials, Metadevices, and Metasystems 2019; 110800S (2019) https://doi.org/10.1117/12.2530087

The sensing of chiral molecules is important for chemical, pharmaceutical, and medical applications. The determination of the relative concentration of the two molecular mirror versions (enantiomers) in a given mixture is of particular importance for several reasons, in particular because the two enantiomers can have very different biological effects. This task can be achieved by circular dichroism (CD), the normalized difference between the absorption of incident left- and right-handed circularly polarized light. The molecular CD signal is typically weak, and many different kinds of nanostructures have been proposed for enhancing it. Most of them provide local enhancements only in electromagnetically small near-field regions attached to the material structures, resulting in vanishing total enhancements when experimentally meaningful analyte volumes are considered. In this talk, I will present the design of a cavity composed of two parallel arrays of silicon disks that allows to enhance the total CD signal by more than two orders of magnitude for a given molecule concentration and given thickness of the cell containing the molecules. I will show that the underlying principle is helicity-preserving first-order diffraction into helicity-preserving modes with large transverse momentum and long lifetimes. In sharp contrast, in a conventional Fabry-Perot cavity, each reflection flips the handedness of light, leading to large intensity enhancements inside the cavity, yet to smaller CD signals than without the cavity.

Nanoscale optical integration is nowadays a strategic technological challenge and the ability of generating and manipulating nonlinear optical processes in sub-wavelength volumes is pivotal to realize efficient sensing probes and photonic sources for the next-generation communication technologies. Yet, confining nonlinear processes below the diffraction limit remains a challenging task because phase-matching is not a viable approach at the nanoscale. The localized fields associated to the resonant modes of plasmonic and dielectric nanoantennas offer a route to enhance and control nonlinear processes in highly confined volumes. In my talk I will discuss two nonlinear platforms based on plasmonic and dielectric nanostructures. The first relies on a broken symmetry antenna design, which brings about an efficient second harmonic generation (SHG). We recently applied this concept to an extended array of non-centrosymmetric nanoantennas for sensing applications. I will also show the evidence of a cascaded second-order process in Third Harmonic Generation (THG) in these nanoantennas. Recently, dielectric nanoantennas emerged as an alternative to plasmonic nanostructures for nanophotonics applications, thanks to their sharp magnetic and electric Mie resonances along with the low ohmic losses in the visible/near-infrared region of the spectrum. I will present our most recent studies on the nonlinear properties of AlGaAs dielectric nanopillars. The strong localized modes along with the broken symmetry in the crystal structure of AlGaAs allow obtaining more than two orders of magnitude higher SHG efficiency with respect to plasmonic nanoantennas with similar spatial footprint and using the same pump power. I will also discuss a few key strategies we recently adopted to optically switch the SHG in these antennas even on the ultrafast time scale. Finally, I will show how to effectively engineer the sum frequency generation via the Mie resonances in these nanoantennas. These results draw a viable blueprint towards room-temperature all optical logic operation at the nanoscale.

Single-photon sources constitute one of the crucial enabling technologies for quantum communications, quantum computation, and quantum-enhanced metrology. Typical quantum emitters (QEs) used for realizing single-photon sources feature low emission rates, non-directional emission, and poorly defined polarization properties, characteristics that prevent QEs from being directly used in quantum technologies. By using properly nanostructured environment, i.e., by coupling QEs with nanocavities or nanoantennas, the QE emission characteristics can be improved drastically due to the Purcell effect and properly engineered near-field interactions that determine the far-field radiation properties. Single photons carrying spin angular momentum (SAM), i.e., circularly polarized single photons generated typically by subjecting QEs to a strong magnetic field at low temperatures, are at the core of chiral quantum optics [1] enabling non-reciprocal single-photon configurations and deterministic spin-photon interfaces. In this talk, I present a conceptually new approach to the room-temperature generation of SAM-coded single photons (SSPs) entailing QE non-radiative coupling to surface plasmons that are transformed, by interacting with an optical metasurface [2], into a collimated stream of SSPs with the designed handedness. The results of detailed simulations as well as the first experimental results are presented, and their implications for experiments in chiral quantum optics are discussed. References: 1. P. Lodahl, S. Mahmoodian, S. Stobbe, A. Rauschenbeutel, P. Schneeweiss, J. Voltz, H. Pichler, and P. Zoller, “Chiral quantum optics,” Nature 541, 473–480 (2017). 2. F. Ding, A. Pors, and S. I. Bozhevolnyi, “Gradient metasurfaces: a review of fundamentals and applications,” Rep. Prog. Phys. 81, 026401(2017).

The interaction of circularly polarized light with matter is the basis for molecular circular dichroism spectroscopy, optical spin manipulation, and optical torques. However, chiroptical effects are usually hampered by weak chiral light-matter interaction. Nanophotonic structures can enhance optical intensity to boost interactions, but magnifying chiral effects requires that the near field remains chiral in the process. Here, we propose the conditions, limits and guidelines for enhancing different chiroptical effects near achiral metasurfaces with maximum chirality of the evanescent fields. We illustrate these conditions with arrays of metal and dielectric nanodisks and decompose their distinct electromagnetic metrics into propagating and evanescent Fourier orders. We prove that chirality metrics like circular dichroism and the degree of circular polarization, which go hand-in-hand in the far field for propagating plane waves, are incompatible in the evanescent near field. As a result, a nanostructure cannot be universally optimal for different chirality metrics and therefore applications. For example, arrays tailored for enhanced spin excitation with spatially uniform circular polarization destroy circular dichroism. Conversely, we predict a limit of maximum attainable circular dichroism in highly evanescent Fourier orders through a simple relation with the evanescent wavevector and polarization. We demonstrate that silicon nanodisk arrays can enhance chiral effects within these constraints. Our results define the limits on the ability of nanophotonic platforms to enhance different chiral light-matter interactions simultaneously. Our work provides design rules for diverse chiroptical applications such as molecular spectroscopy, information technology and optical nanomanipulation.

Geometry, associated with three dimensions: width, length and height, is an important concept for electromagnetic and optical engineers. We have been successful to manipulate the light and the electromagnetic radiation by changing the geometry of for example antennas, scatterers, and etc. However, time is the fourth dimension which must be also employed in electromagnetic and optical engineering to control over radiation and realize novel devices. In this talk, we will present the recent results in our group on this research area. First, we will show that nonreciprocal metasurfaces can be engineered as tunable and multifunctional devices. Our idea is to exert nonharmonic spatiotemporal modulation functions on the meta-atoms. Non-harmonic modulation provides additional freedoms for the control of nonreciprocity in metasurfaces. It is demonstrated that a variety of nonreciprocal devices like isolators, gyrators and circulators could be incorporated into a uniform hardware platform by changing only the modulation functions. Then, we will show that spatial modulation is not an essential requirement for achieving nonreciprocity in time-modulated metasurfaces. If the metasurfaces are bianisotropic, modulating such structures only in time can also induce strong nonreciprocity.

In this talk, I will present a multilayer all-dielectric metasurface architecture with the goal of increasing the design landscape of metaoptics. The layers are fabricated separately and then combined allowing for various combinations of unit cell geometries. This ultimately allows for independent control over any two properties; amplitude, phase, and polarization. The approach can also allow any of these properties to be independently designed at two wavelengths. This freedom is used to realize metaoptics with a wide range of functionalities including multiwavelength holograms and lenses as well as 3D holograms. I will also discuss how this design freedom can be used for realizing metaoptics for optical computing.

Chiral photonic metasurfaces were extensively studied because of their ability to act as ultrathin circular polarizers and their potential in chiral sensing [1, 2]. Chiral nanostructures are structures that lack inversion symmetry, i.e., they cannot be mapped onto their mirror image. In nanophotonics, this property allows for a selective interaction with circularly polarized light. The dependence of the optical response of some material on the circular polarization state of the impinging light is called circular dichroism. While huge progress was made in the last decade in creating optical metasurfaces with tailored circular dichroism, the designs realized so far were, with very few exceptions [3, 4], based on plasmonic implementations [5]. However, the large absorption losses in plasmonic devices at optical frequencies often limit their applicability. Here, we study the properties of chiral nanostructures based on high refractive index dielectric materials. In addition to exhibiting low losses, they offer additional opportunities based on multipolar Mie-type response of their building blocks [6]. We experimentally and numerically investigated the zeroth-order transmission spectra of chiral nanostructures consisting of twisted silicon-nanocuboids when illuminated by right and left circularly polarized (RCP and LCP) light. Our experimental and simulated zeroth-order transmission spectra show pronounced difference in the transmission spectra for RCP and LCP light. In conclusion, we have successfully demonstrated an all-dielectric metasurface exhibiting a pronounced chiral optical response. Our results offer important opportunities for high-efficiency circular polarizing elements. [1] Gansel, J. K. et al., M. Science 2009, 325,1513−1515. [2] Zhao, Y. et al., Nat. Commun. 2016, 8, 1−8. [3]Zhu. A. et al., Light: Science & Applications 2018, 7, 17158. [4]Ma. Z. et al., Opt. Express 2018, 26, 6067-6078. [5] Decker, M. et al., Opt. Lett. 2009, 34, 2501−2503. [6] Staude, I. and Schilling, J., Nature Photonics, 2017, 11, 274-284.

The talk highlights our recent efforts in modelling the nonlinear optical processes integrated with nanophotonic devices with a particular emphasis on lasing with feedback from topologically exotic metasurfaces. We have developed a computational multiphysics framework that provides a comprehensive understanding of the nonlinear light-matter interaction dynamics in nanophotonic devices. Our technique relies on a semi-classical approach that utilises carrier kinetics to model the nonlinear media in the time domain, where the rate equations are coupled to the Maxwell equations to provide a full-wave multiphysics framework for modelling nonlinear nanophotonic structures. The framework has been applied to a large number of nonlinear processes, including the enhancement of optical limiting in a plasmonic metasurface, spacing from a nanohole array, two-photon absorption, random lasing, and many others. The talk presents a computational effort in modeling nanophotonics devices coupled to two-photon absorbing media. A six-level system is used to model the kinetics of two-photon absorption with organic dyes. This model is successfully used to match the spectral response of the organic 4,4’-bis(diphenylamino) stilbene (BDPAS) at low and high excitation energies and can be employed for accurate full-wave analysis of structured nanophotonic devices with multi-photon absorption media. Then, the numerical analysis of a dielectric metasurface-based nanolaser and the experimental validation of the numerical results is chosen as the central theme, considering nanolasers with feedback from exotic all-dielectric metasurfaces with bound states in the continuum (BICs). Metasurfaces find a wide variety of applications due to their versatile functionalities and more straightforward fabrication vs bulk metamaterials. However, their spectral response is generally broad, hindering their applicability to devices requiring sharp spectral features. We utilise the exotic phenomenon of BICs to realise high Q-factor resonances in all-dielectric metasurfaces. The designed BIC-based metasurfaces exhibit operation independent of polarisation with resonances in the visible.

In this study, we investigate AlGaN metasurface increasing the light-extraction efficiency (LEE) of AlGaN-based deepultraviolet light-emitting diodes (DUV-LEDs) by utilizing the finite-difference time-domain (FDTD) method. As a first step, a unit cell of metasurface structure adopting the AlGaN cylindrical resonator, which highly increases the transmittance near 280 nm wavelength before the critical angle, was searched numerically. A selected unit cell structure with the resonator was lattice constant a =110 nm with square lattice, the height of cylinder h = 45 nm, and radius r = 40 nm. Transmittance map was constructed for the optimized unit cell as functions of wavelength and incidence angle of plane waves for TE and TM polarized sources, respectively. The map showed perfect transmittance near 280 nm wavelength with normal incidence. Angle-dependent transmittance slowly decreases as the incidence angle increases, but as the incidence angle positions near the critical angle, the decrease of transmittance is gradually accelerated. As a next step, the extracted AlGaN metasurface structure is uniformly deployed to a flip chip LED, and light-extraction efficiencies are calculated as a function of p-GaN thickness for TE and TM mode sources, respectively. The dimension of LED considered in this study was about 2μm× 2μm×1μm. Calculated LEE values clearly showed that by adopting the designed AlGaN metasurface, LEE always increases regardless of p-GaN thickness based on the fundamental increment of transmittance.

Optical metasurfaces consisting of designed nanoresonators arranged in a planar fashion were successfully demonstrated to allow for the realization of a large variety of flat optical components [1]. While most metasurfaces realized so far focused on the isolated scattering properties of the metasurface itself, the opportunities offered by tailoring the substrate properties are often neglected. Here we consider a silicon nanocylinder metasurface exhibiting electric and magnetic dipolar Mie-type resonances at near-infrared frequencies, which is situated on a gold mirror. The metasurface and the mirror are separated by a dielectric spacer layer with a gradually varying thickness. We analytically, numerically and experimentally investigate how systematic changes in the spacer layer thickness influence the optical reflection spectra of the metasurface. For experimental realization, we covered the pre-fabricated silicon nanocylinder metasurface with a wedge-shaped dielectric layer. Afterwards, the dielectric layer was coated with a gold layer, which acted as the mirror. For optical characterization, we measured the reflection spectra of the sample from the metasurface side at different positions on the sample, where each position corresponds to a different spacer thickness. Our measurements show that a transition from perfect reflection to perfect absorption occurs when the spacer thickness changes by only few tens of nanometers. To understand the physical origin of the observed features, we numerically calculated the metasurface reflection spectra as a function of the spacer layer thickness and furthermore employed a semi-analytical S-matrix based theory to our system [2], revealing that the observed feature originates from an interference effect of different types of modes supported by the structure. Our results offer interesting new opportunities for tunable and switchable functional flat optical devices. [1] N. Yu et al., Nat. Mater. 13, 139–150 (2014) [2] C. Menzel et al., Phys. Rev. A 93, 063832 (2016)

Metamaterials---artificial electromagnetic media that are structured on the subwavelength scale---were initially suggested for the realisation of negative-index media, and later they became a paradigm for engineering electromagnetic space and control¬ling propagation of waves. However, applications of metamaterials in optics are limited due to inherent losses in metals employed for the realisation of artificial optical magnetism. Recently, we observe the emergence of a new field of all-dielectric resonant meta-optics aiming at the manipulation of strong optically-induced electric and magnetic Mie-type resonances in dielectric and semiconductor nanostructures with relatively high refractive index. Unique advantages of dielectric resonant nanostructures over their metallic counterparts are low dissipative losses and the enhancement of both electric and magnetic fields that provide competitive alternatives for plasmonic structures including optical nanoantennas, efficient biosensors, passive and active metasurfaces, and functional metadevices. This talk will highlight some recent advances in all-dielectric Mie-resonant meta-optics including active nanophotonics as well as the recently emerged fields of topological photonics and nonlinear metasurfaces.

Nonlinear optics is present in our daily life with many applications, e.g. light sources for microsurgery or green laser pointer. All of them use bulk materials such as glass fibres or crystals. Generating nonlinear effects from materials at the nanoscale can expand the applications to biology as imaging markers or sensors, and to optoelectronic integrated devices. However, the nonlinear emission efficiency of nanostructures is low due to their small volumes. In our work, we show strategies to enhance the second harmonic generation (SHG) at the nanoscale with the goal of developing nonlinear photonics devices for a broad spectral range. So far, the SHG from metallic and semiconductor nanostructures as gold or gallium arsenide has been successfully shown. However, the application range of these materials is generally limited to the visible-near-infrared range by their high absorption. We use metal oxides such as barium titanate (BTO) and lithium niobate (LNO) as an alternative platform for nanoscale nonlinear photonics in a broad spectral range. Both BTO and LNO are noncentrosymmetric materials with high refractive index and high energy band gaps, transparent down to the near-ultraviolet range. We demonstrate linear Mie resonances in BTO and LNO nanostructures, such as nanospheres or nanocubes. Further, we show that these resonances enhance the SHG emission from the nanostructures. We also perform simulations to understand the underlying mechanism of this enhancement. Finally, we explore fabrication methods for BTO and LNO nanostructures that will allow the controlled integration of BTO and LNO nanostructures for nonlinear metasurfaces.

The optical manipulation of small particles has many important applications in nanotechnologies. In particular, fluctuation-induced optical Casimir-Polder forces are relevant in a variety of situations. Typically, when a particle stands nearby a perfectly smooth material surface the lateral force vanishes in equilibrium situations due to the translational invariance of the system. Recently, it was shown that graphene biased with a drift-current can be a very promising platform for nonreciprocal plasmonics in the infrared range. The drift current enables the propagation of unidirectional surface plasmons as the wave can be dragged by the moving electrons. Here, we investigate how the drift-current bias affects the light-matter interactions and demonstrate that it gives rise to an anomalous lateral drag force

There is growing interest and technological opportunity in nanomechanics and the fundamentals of nano- to pico-scale dynamics, which derive from the fact that electromagnetic and quantum forces become stronger as the dimensions of objects decrease, competing with elastic forces at sub-micron scales; while movements become faster as mass decreases, achieving Gigahertz bandwidth at the nanoscale. We report on a novel approach to the visualization of such movements that is based on the detection of secondary electrons and photons emerging from the interaction of a focused electron beam with moving components of nano-objects. The technique extends the static (zero-frequency) imaging capabilities of a conventional scanning electron microscope to enable hyperspectral spatial mapping of fast (MHz-GHz) thermal and externally-driven nano- to pico-scale motion in nanostructures.

This presentation was first delivered at Photonics West 2020 on 4 February 2020 and has been included as part of this Digital Forum to enable scholarly dialogue. Please use the original citation when citing: Proceedings Volume 11284, Smart Photonic and Optoelectronic Integrated Circuits XXII; 112840W (2020) https://doi.org/10.1117/12.2545127

Searching for natural materials exhibiting larger electron-electron interactions constitutes a traditional approach to high temperature superconductivity research. Very recently we pointed out that the newly developed field of electromagnetic metamaterials deals with the somewhat related task of dielectric response engineering on a sub-100 nm scale. Considerable enhancement of the electron-electron interaction may be expected in such metamaterial scenarios as in epsilon near zero (ENZ) and hyperbolic metamaterials. In both cases dielectric function may become small and negative in substantial portions of the relevant four-momentum space, leading to enhancement of the electron pairing interaction. This approach has been verified in experiments with aluminium-based metamaterials. Metamaterial superconductor with Tc = 3.9 K have been fabricated, that is three times that of pure aluminium (Tc = 1.2 K), which opens up new possibilities to considerably improve Tc of other simple superconductors. A theoretical model based on the Maxwell-Garnett approximation provides a microscopic explanation of this effect in terms of electron-electron pairing mediated by a hybrid plasmon-phonon excitation. We report the observations of this excitation in Al-Al2O3 core-shell metamaterials using inelastic neutron scattering. This result provides support for this novel mechanism of superconductivity in metamaterials.

The possibility of efficiently using metamaterials in acousto-optics has been demonstrated. Diffraction of light in heterogeneous medium with non-uniform spatial distribution of dielectric nanoparticles taking into account absorption of light is investigated. It is shown that by changing the concentration of dielectric nanoparticles in the medium, complete elimination of side oscillations and suppression of the “tails” of the diffraction reflection curve can be achieved. The possibility of controlling the hardware function of acousto-optic devices by changing the material, concentration, size, shape and spatial orientation of the inclusions, as well as the polarization of the incident radiation is shown. It is shown, that extremely large electric field enhancement can be observed in an anisotropic crystal in the presence of spatial apodization of the amplitude or abrupt change in the phase of acoustic wave.

Topologically protected plasmonic states with wide topological band gaps provide unprecedented robustness against disorder-induced backscattering. In this study, we design a graphene bi-layer metasurface that possesses valley-Hall topological plasmonic modes in a nontrivial bandgap. In particular, the breaking of mirror symmetry of two graphene layers is achieved via a horizontal shift of the hole lattice of the top layer, which leads to topologically protected edge modes in the nontrivial bandgap. The corresponding band dispersion of the topological edge modes shows unidirectional propagation features. Moreover, we have designed a sensitive molecular sensor based on such graphene bi-layer metasurfaces, using the fact that the chemical potential of graphene varies upon adsorption of gas molecules. This effect leads to a marked variation of the transmission of the topological mode, and thus a sensing device with large sensitivity can be realized.

We use a genetic algorithm to optimize 2-D periodic arrays of truncated square-based pyramids made of successive stacks of metal/dielectric layers. The objective is to achieve a quasi-perfect broadband absorption of normally incident radiations with wavelengths comprised between 420 and 1600 nm. We compare the results one can obtain by considering (i) Ni, Ti, Al or Cr for the metal, and (ii) poly(methyl methacrylate) (PMMA) or TiO₂ for the dielectric. The structures considered consist of only one, two or three stacks of each metal/dielectric combination. The absorption spectrum of these structures is calculated by a Rigorous Coupled Waves Analysis method. A genetic algorithm is then used to determine optimal values for the period of the system, the lateral dimensions of each stack of metal/dielectric and the width of each dielectric. The results show that Ni/PMMA represents the best metal/dielectric combination. With an optimized structure made of only three stacks of Ni/PMMA, it is possible indeed to absorb 99.8% of the considered incident radiations. An integrated absorptance of 99.4% is achieved with three stacks of Ti/PMMA or Cr/PMMA. Aluminium is not to recommend for this application. The solutions obtained with this metal are indeed too sensitive on the geometrical parameters of the system.

Artificially engineered light-matter interactions provide a unique degree of freedom to tailor wavefront of the incident waves, through pixelated engineering of its phase, amplitude, and polarization. Such dynamic control introduces various intriguing functionalities. Here, we propose a highly efficient metamirror with circular dichroism, which enables selective reflection with preserved handedness and complete absorption of other polarization. The building block of circular dichroism metamirror working on the principle of Jones calculus. For such a phenomenon, it is necessary to break the nfold rotational (n < 2) symmetry and mirror symmetry simultaneously. The proposed highly efficient metamirror with circular dichroism designed in the microwave regime for wavefront engineering. The demonstrated methodology exhibits full reflection for left circularly polarized EM waves without reversing its handedness and completely absorbing the other handedness. Multifunctionality and fabrication simplicity makes the proposed light-matter interaction a promising route for detection and manipulation of circularly polarized light, encryption, and chiral imaging.

The solution to the electromagnetic scattering of a sphere was published by Gustav Mie more than hundred years ago and is well-known as the Mie theory. In Mie theory, the ratio between the scattered and the incident field coefficients in the spherical basis is expressed in terms of the Mie coefficient. These Mie coefficients depend in an intricate manner on the spheres’ radius and the involved material properties of both the sphere and the ambient. To enable a systematic analysis of the accessible optical properties from spheres, these explicit expressions are not useful because they are too complicated. These Mie coefficients simply contain too many degrees of freedom. For fundamental research, it is of utmost importance to have easy expressions at hand that express all values of Mie coefficients that are accessible in general. The precise geometrical and material properties of a sphere that offer these coefficients can be identified in a secondary step. But if these accessible coefficients depend on the least number of degrees of freedom, they would allow for a systematic analysis of all observable effects using spherical scatterers. These desired simple expressions have been previously identified only for non-absorbing materials. However, a model for absorbing particles has never been reported. Here, while using the optical theorem we derive the generic equations to express any possible Mie coefficient of an absorbing sphere. Our model for absorbing particles can facilitate the study of absorbing systems such as perfect absorbers, optical torque calculations, cooling, thermal emitters etc. Using the proposed model, one can systematically analyse through all the possible space and search for specific functionality as it will be demonstrated at selected applications at the talk.

Structuring of a medium on the wavelength and subwavelength scales significantly enriches its interaction with light leading to new optical effects. As a result, it fuels the interest in planar artificial structures like photonic crystals, metasurfaces and plasmonic crystals, which have found tremendous success in light manipulation and applications in sensing, routing, light localization, enhancement of the nonlinear effects. The deep insight into optical phenomena in artificial structures requires necessarily numerical simulations. For periodic structures such as photonic crystals and diffraction gratings, numerical methods like finite-difference time-domain method (FDTD) and rigorous coupled-wave analysis (RCWA) are widely used. These methods have definite drawbacks, as the FDTD requires large computer memory to store the field values in the nodes of a 3D mesh, and high computational effort for the time simulation; the RCWA demands extra labor for the accurate treatment of a grating made of metal or anisotropic materials. Because the optical effects in highly anisotropic metal-based artificial structures like hypercrystals are of practical interest, we have proposed hybrid finite-difference frequency-domain (FDFD) approach for the calculation of light diffraction in such periodic structures. The improvement is achieved by handling the direct values instead of Fourier series, which is the core of the RCWA. Using this approach, we predict the excitation of the Dyakonov plasmons in hypercrystal formed by trenches in hyperbolic metamaterials.

We experimentally characterized the electrical conductivity and the IR emissivity (in the 3.5-5.1 micron spectral) range of samples consisting of carbon nanotubes (CNTs) dispersed into poly(ethylene terephthalate) (PET) matrix. The experimental results show a percolation effect in the electrical conductance along with an emissivity increase with the amount of dispersed CNTs. Maxwell Garnett effective medium approximation was then employed in order to reconstruct the obtained results in the infrared, while morphological investigation (SEM micrographies and White light interferometry) highlighted the effect of surface roughness introduced by CNTs inclusions.

In this work we discuss the design, fabrication, and characterization of hyperbolic metamaterials (HMMs) based on plasmonic metals and solution processable perovskites. The optical properties of the HMMs are characterized using spectroscopic anisotropic ellipsometry, angle resolved reflectometry and compared with the theoretical/simulated results derived from the effective medium approximation (EMA) approach. Furthermore, the impact of replacing the outer layer on the homogenization of the composite is studied by monitoring the evolution of ψ and Δ of the HMMs in each fabrication step. The HMMs presented here exhibite epsilon near zero (ENZ) and epsilon near pole (ENP) near 550 nm. Finally, we show how this material can be used for effective light concentration in the field of perovskite solar cells exploiting the unusual optical constants near the ENZ/ENP regions.

It was recently demonstrated in the experiments [1,2] that the internal photoemission efficiency can reach several tens of percents because of “coherent” or, “surface” photoemission. In present work we provide theoretical description of this effect assuming the surface photoemissionin the structureconsisting ofthe Schottky-barrier metal-semiconductor interface with the Quantum Well (QW) inside. We take into account the difference of dielectric permittivities for the metal and the semiconductor which strongly affects the photoemission efficiency. We show that QW inside the Schottky-barrier can lead to (a) lowering the threshold energy of the photoemission due to resonance tunneling of electrons through the intermediate quasi-level of energy in QW; (b) the photoemission efficiency can be increased by several orders of magnitude.

In this paper, we report demonstration of sub-wavelength high-index contrast gratings which exhibit guided mode resonances for enhancing nonlinear optical effects from 2D materials transferred on top of the structures. Twodimensional hexagonal arrays of c-Si nanodisks on a silicon-on-insulator wafer have been designed to have normal incidence resonance in the 1550-1650 nm wavelength region. Numerical simulations were performed to show resonance variations with structural parameters and corresponding field enhancements outside the structure to aid nonlinear optical response from materials placed on top of the structures. The fabricated structures were characterized for linear reflection using an external cavity tunable laser as the incident light source at close to normal incidence and compared with simulated reflection. As a proof-of-concept, we transferred few-layer Gallium Selenide (GaSe) flake on to the grating using a dry transfer method to examine second harmonic generation response of GaSe in presence of the grating. Second harmonic generation measurements showed strong SHG signal from the GaSe on top of the grating structure, with enhancement of ~ 15x observed at 1645 nm close to fundamental resonance wavelength. No SHG emission was observed from the silicon nanodisks withput the GaSe overlayer. Spectral and power of the SHG were also characterized. This work shows that the potential of heterogeneous integration of high nonlinearity 2D materials on to silicon based resonant optical structures to realize high efficiency nonlinear metasurfaces.

Dense integration of photonic components in photonic integrated circuits presents an important challenge. To reduce the cross talk between the components and thus enable denser integration, sub-wavelength all-dielectric metamaterial claddings have been investigated. Such structures can be realized by patterning subwavelength ridges around the core of the integrated waveguide. In this contribution we present the results of analytical calculations and numerical simulations of optical systems with slab and strip waveguides with all-dielectric metamaterial cladding and investigate the effects on evanescent field in the cladding. We show that a high refractive index contrast between the core and surrounding material is vital for the performance of all-dielectric metamaterial claddings. In particular we include silicon, silicon oxide and silicon nitride materials in our investigation.

Optical properties (reflection, refractive index, real and imaginary part of permittivity function) of rough titanium surfaces fabricated by anodizing method at different anodic voltage have been studied. It is shown that a negative region in the visible wavelength range is observed on a rough titanium surface in the refractive index spectrum; its minimum appeared to be red-shifted shifted with surface roughness increase. These optical-nonlinear effects are studied by means s- and p-polarized light reflection coefficients spectra and permittivity spectra registration. It is also shown that the generation of surface plasmon oscillations in the visible spectral region on the rough titanium surface is possible. Excitation of surface plasmons is found to be accompanied by redistribution of the incident electromagnetic energy on the surface and leads to various nonlinear effects including negative values of the refractive index.

In this work, we study chiral effects in well-known 2D plasmonic nanohole arrays with a triangular unit cell. The chirality can be induced by moving from circular to elliptical nanohole shape and tilting the ellipse away from the array symmetry. This symmetry breaking induces a different absorption of the circularly polarized light of opposite handedness, i.e. circular dichroism. We numerically study circular dichroism at normal incidence in elliptic nanoholes in Au in the spectral range 400-1000 nm. CD arises in transmission and absorption spectra in the same wavelength region of extraordinary optical transmission, indicating highly resonant light-metasurface coupling mechanisms. We focus on its dependence on the elliptic nanohole tilt and further proceed with the ellipse radii optimization. The optimized CD is on the order of 80%, and it is robust with respect to the radii and rotation angle variations. Moreover, such samples could be produced by means of low-cost nanosphere lithography, which makes them interesting for applications in enhanced sensing of chiral biomolecules.

Many resonant structures in the microwave region need damping of parasitic or higher order modes in order to optimise their performance. In cavities or other systems operating in accelerating structures, for example, the mitigation of spurious resonance effects is indispensable to achieve high quality particle beams. We present here a parametric study on the absorption properties of a multilayered metamaterial having the shape of a truncated pyramid to be used as light, small volume damper in a microwave cavity. Full wave simulations have been performed for a single absorber varying its size and number of layers and for a linear array changing the distance between the single elements. A case study is proposed, where a single pyramid is inserted in a real pillbox cavity. Measurements of the cavity response without and with the metamaterial absorber are presented and compared with numerical results.