This PDF file contains the front matter associated with SPIE Proceedings Volume 10671, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

This paper derives the macroscopic electric and magnetic fields and the surface susceptibilities for a metasurface, starting from the microscopic scatterer distribution. It is assumed that these scatterers behave as electric and magnetic dipoles under the influence of the incident radiation. Interestingly not only the retarded electromagnetic fields from oscillating dipoles are relevant to pass from the microscopic to the macroscopic representation, but the advanced fields must be considered too. It is found that the macroscopic fields are the sum of the incident fields plus the radiation-reaction fields acting on a single scatterer. Both the local fields and the radiation-reaction fields are necessary to fix the electric and magnetic surface susceptibilities.

Achieving nonreciprocal light propagation is of fundamental importance in photonic devices and systems. Nonreciprocal effects are typically obtained using bulky magneto-optical materials externally biased by a static magnetic field. Notably, it was recently demonstrated that some of these magnetically-biased systems with a broken-time reversal symmetry have nontrivial topological properties and support unidirectional backscattering immune chiral edge modes. Nevertheless, the required external magnetic bias, together with the relatively weak gyrotropic responses achievable at optical frequencies, makes the integration of such elements in nanophotonic systems extremely difficult. Because of this, there has been recently a great effort in the development of magnetic-free solutions that give nonreciprocal responses and are fully compatible with modern highly-integrated photonic systems. Here we propose a novel route to achieve magnetic-free nonreciprocal subwavelength light propagation. We theoretically demonstrate that by biasing a graphene sheet with a direct electric current it is possible to break the Lorentz reciprocity and have a broadband regime of unidirectional propagation of surface plasmons. Remarkably, we prove that the drift-current biasing also enables enhancing the propagation length of the graphene plasmons. Furthermore, it is shown that the surface plasmons supported by the graphene sheet with a drift current are protected against backscattering from obstacles and imperfections, similar to the “one-way” topologically protected chiral edge modes supported by topological photonic systems. We believe that these findings may open a new and exciting opportunity towards the full integration of nonreciprocal components in nanophotonic systems.

We study the polarisation and geometry dependence of four-wave mixing (FWM) on nanocross arrays. The arrays are composed of gold meta-atoms fabricated via EBL and lift-off on a glass substrate coated with a 15 nm ITO film. The individual nanocrosses are C4-symmetric, 360 nm by 360 nm, with 80 nm wide arms. The array period is 550 nm. FWM is generated by two-colour illumination. The two input wavelengths are 1028 nm (wavelength 1) and 1310 nm (wavelength 2), and we look for the degenerate FWM signal at 846 nm (2*frequency 1 - frequency 2). Using all combinations of handedness for circularly polarised inputs, we verify the theoretical selection rules for FWM on systems of this type. They are LLL-L, RRR-R, LRR-L, and RLL-R, where the first letter is the handedness of beam 2, the following two are the handedness of beam 1, and the last letter is the handedness of the output FWM. We measure several metasurfaces. In each, the two nanocrosses in a unit cell are rotated towards each other by an angle theta, which is varied 0 to 45 degrees in 7.5 degree increments. With co-polarised inputs (LLL and RRR) the FWM signal is the same from all metasurfaces. With cross-polarised inputs (LRR and RLL) it follows cos^2(4*theta). This behaviour, which is predicted theoretically, is due to the nonlinear Pancharatnam-Berry geometric phase of the FWM from the rotated nanocrosses. We further support our results with numerical simulations, which match the experimental behaviour for all metasurfaces and show the angle-dependent phase of the nonlinear polarisations on the meta-atoms.

All-dielectric nanoparticles clusters have been attracted the attention recently due to their ability to sustain the specific collective modes excitation leading to new interesting effects such as Fano resonances. However, it is difficult to recognize such modes in the linear optical response of the structure without detecting the near field profile directly. In this work we propose a new method for detection of the oligomer eigenmodes excitation and numerically proof it for the nanoparticles cluster in the form of a trimer. These modes are indistinguishable in the linear optical response of the structure, but manifest themselves in the nonlinear response such as third- harmonic generation dependence on the pump polarization orientation. We belief that our method can be used for experimental identification of the eigenmodes of the complex all-dielectric structures such as oligomers of all-dielectric nanoparticles.

The manipulation of light-frequency upconversion on the nanoscale at the optical regime can benefit a wide variety of existing applications,[1] enhancing (bio)imaging resolution,[2] increasing optical sensing sensitivity,[3,4] improving solar light harvesting,[5,6] and bettering control of optically triggered intracellular drug delivery mechanisms.[7,8] Benefiting from large intrinsic nonlinearities, low absorption, and high field enhancement abilities, all-dielectric nanoantennas are considered essential for efficient nonlinear processes at subwavelength volumes.[9-11] We present an all-dielectric germanium nanosystem exhibiting a strong third order nonlinear response and efficient third harmonic generation in the optical regime. A thin germanium nanodisk shows a pronounced valley in its scattering cross section at the dark anapole mode, while the electric field energy inside the disk is maximized due to high confinement within the dielectric. We investigate the dependence of the third harmonic signal on disk size and pump wavelength to reveal the nature of the anapole mode. Each germanium nanodisk generates a high effective third order susceptibility of χ(3) = 4.3 × 10−9 esu, corresponding to an associated third harmonic conversion efficiency of 0.0001% at an excitation wavelength of 1650 nm, which is 4 orders of magnitude greater than the case of an unstructured germanium reference film.[12] Furthermore, we demonstrate a higher-order anapole mode in a 200 nm thick germanium nanodisk that delivers the highest THG efficiency on the nanoscale at optical frequencies. We observe a highly improved electric field confinement effect within the dielectric disk at this higher-order mode, leading to THG conversion efficiencies as large as 0.001% at a third harmonic wavelength of 550 nm.[13] In addition, by mapping the THG emission across the nanodisk, we are able to unveil the anapole near-field intensity distributions, which show excellent agreement with numerical simulations. A similar nonlinear optical response is observed in the case of degenerate FWM where two different pump wavelengths are coupled to a single high-order resonant mode. However, when the two pump wavelengths are coupled to different high-order modes, the FWM process is partially suppressed due to a diminished near-field spatial overlap of the mixed wavelengths within the disk.[14] These findings not only open new possibilities for the optimization of upconversion processes through the appropriate engineering of suitable dielectric materials, but also remarkably expand contemporary knowledge on localized modes in dielectric nanosystems.

One of the central goals of the field of nonlinear optics is to bring the control of light to ultrafast time scales using structures that are easily integrated into nano-optic devices. The ability to design the polarization state of a signal light pulse, with a second control light pulse, at THz rates, will allow new techniques to be developed such as ultrafast polarimetry and quantum state manipulation. Here we all-optically control, with a femtosecond pulse, the anisotropy of a metamaterial to change the polarization state of signal light at a switching rate of 0.3THz, which is found to be closely linked to the electron temperature distribution within the structure and so can be tuned with the control light wavelength. We experimentally measure more than 60° rotation of the polarization orientation of the signal light. This effect is due to an induced phase shift of the extraordinary wave compared to the ordinary wave of the signal light. Polarization control is observed in both transmission and reflection and shown to be general to any anisotropic metamaterial. Considering only the signal light, its leading edge can alter the polarization state of the pulse allowing the pulse’s incident intensity to be encoded in its transmitted polarization state.

Metasurfaces composed of designed Mie-resonant semiconductor nanoparticles offer unique opportunities for controlling the properties of light fields transmitted through them or reflected from them [1]. Such metasurfaces can e.g. impose a spatially variant phase shift onto an incident light field, thereby providing control over its wave front with high transmittance efficiency [2]. However, most semiconductor metasurfaces realized so far were passive and linear, and their optical response was permanently encoded into the structure during fabrication. Recently, a growing amount of research is concentrated on the integration of emitters and optical nonlinearities into semiconductor metasurfaces and on obtaining dynamic control of their optical response. This talk will provide an overview of our recent advances in active, nonlinear, and tunable Mie-resonant semiconductor metasurfaces. In particular, we have studied spontaneous emission from metasurfaces incorporating various types of emitters, including semiconductor quantum dots, monolayers of transition metal dichalcogenides, and fluorescent centers in the substrate. For emission frequencies below or near the fundamental electronic bandgap of the respective semiconductor material, the individual Mie-resonant metasurface building blocks can provide the functionality of dielectric nanoantennas, and exhibit high directivity, Purcell enhancement, and near-unity radiation efficiencies [3,4]. Consequently, we may understand an active metasurface as a two-dimensional array of resonant dielectric nanoantennas, which are excited by localized emitters that are located in their vicinity. In order to characterize the emission properties of our active metasurfaces, we perform micro-photoluminescence imaging, spectroscopy, and Fourier imaging for a variety of different active metasurface architectures. Our results show that the directional and spectral properties of the emitted light can be tailored by the metasurface design. Using nonlinear Fourier imaging, we have also investigated second harmonic generation in metasurfaces composed of III-V semiconductors. We show that the generated second harmonic signal depends sensitively on the polarization of the pump field. For dynamic tuning of the metasurface response, we make use of the strong spectral dispersion associated with the resonant optical response of the metasurfaces in combination with the sensitivity of the resonance properties on the dielectric environment of the individual nanoresonators. Specifically, by integrating a silicon metasurface into a nematic-liquid-crystal cell, we have demonstrated dynamic tuning of the metasurface linear-optical response using an applied voltage as control parameter [5]. Finally, by combining resonance tuning based on liquid crystals with spontaneous emission enhancement by Mie-type resonances, we have achieved dynamic control of the emission from an active metasurface consisting of silicon nanoresonators coupled to a fluorescent substrate. [1] I. Staude & J. Schilling, Nature Photon. 11, 274–284 (2017). [2] K. E. Chong et al., Nano Lett. 15, 5369–5374 (2015). [3] A. E. Krasnok et al., Opt. Exp. 20, 20599 (2012). [4] X. Zambrana-Puyalto & N. Bonod, Phys. Rev. B 91, 195422 (2015). [5] A. Komar et al., Appl. Phys. Lett. 110, 071109 (2017).

Metasurfaces have been strongly investigated to realize a paradigm shift from classical optics. Unlikely the classical optics dealing with light rays in accordance with geometric-optic principles, metasurfaces allow the control of wavefront in subwavelength thickness on flat surfaces [1,2]. As conventional convex lenses, metalenses on flat surface without any macroscopic surface curvature have tremendous capability in future flat optics. They can also be used to replace the expensive compound lens systems in a number of consumer electronic products such as optical storages, digital cameras, microscopes, etc. Providing a flat, form factor, metalenses have a large degree of freedom in designing miniaturized sensors as well. Typically, metasurfaces are composed of an array of planar nanostructures that locally provide the change of amplitude or phase of light in reflection or transmission. The phase modulation on each nanostructure leads to the change of wavefront for a new class of flat optical elements [3-5]. For example, high-contrast transmit arrays (HCTAs) have been reported to demonstrate subwavelength-thick lenses with high-numerical aperture and large focal efficiency [6,7]. This is a promising approach to make metasurfaces consisting of an array of subwavelength dielectric nanoposts on flat surface; however, a full coverage of phase from 0 to 2 pi is not readily achievable due to phase defects, when the post diameter is chosen to be varied. The phase defects are originated from resonances at the wavelength of interest, hindering a gradual increase of phase with respect to the variation of post diameters. Such defects deteriorate optical performance compared with conventional curved lenses, particularly in focal spot sizes and focusing efficiencies. Here we propose a novel method to repair phase defects and achieve a full, 2 pi phase coverage with free of defects, which provides complete phase matches with theoretical calculations. We apply this method to demonstrate the convex-lens-like metalens with high numerical aperture (NA), small focal spot size, and high focusing efficiency in near-infrared region (1.55 microns). Together with the theoretical design and simulation, we prepare metalenses using silicon photolithography and nanofabrication and analyze experimental observations. The measured full width at half maximum (FWHM) of the focal spot and focusing efficiency show a high performance for numerical apertures of 0.3 ~0.7. This achievement offers considerable opportunities for various applications using metasurfaces based on controlled wavefront with free of defects. References [1] D. Fattal, J. Li, Z. Peng, M. Fiorentino, and R. G. Beausoleil, Nature Photon. 4, 466 (2010). [2] F. Aieta, M. A. Kats, P. Genevet, and F. Cappaso, Science 347, 1342 (2015). [3] N. Yu and F. Cappaso, Nature Mater. 13, 139 (2014). [4] M. Khorasaninejad, W. T. Chen, R. C. Devlin, J. Oh, A. Y. Zhu, F. Cappaso, Science 352, 1190 (2016). [5] A. Arbabi, Y. Horie, M. Bagheri, and A. Faraon, Nature Nanotech. 10, 937 (2015). [6] A. Arbabi, Y. Horie, A. J. Ball, M. Bagheri, and A. Faraon, Nature Commun. 6, 7069 (2015). [7] A. Arbabi, R. M. Briggs, Y. Horie, M. Bagheri, and A. Faraon, Opt. Express 23, 248830 (2015).

Resonant high-index dielectric nanostructures have recently emerged as a new direction in nanophotonics, which might compliment and/or substitute conventional plasmonics in multiple application areas [1]. Major advantages of dielectric nanoantenna approach are low losses at optical frequencies and wide range of appropriate materials such silicon, germanium, gallium arsenide, titanium dioxide, and other semiconductors, which are well known and widely accepted by existing semiconductor industries. Apart from that, high-index dielectric nanostructures naturally possess strong optical magnetic and electric resonances, which open opportunities to observe novel effects related to optical magnetism as well as to interference of coherent electric and magnetic responses. Some of such new effects related to directional light scattering (also known as Kerker conditions), Huygens’ dielectric metasurfaces and generalized Brewster effect have already been demonstrated over the last few years [1]. In this talk, I will focus on application of resonant effects in dielectric nanoantennas and metasurfaces to design devices with unique functionalities. In particular I will show how resonance interference in dielectric metasurfaces can be applied to efficiently bend visible light at extremely high angles (>80 degrees). Based on this effect I will demonstrate flat lenses with free-space numerical aperture of ~0.99, which significantly exceed all flat and bulk optics analogues. I will also show how metasurfaces can be designed to operate simultaneously at all RGB wavelengths in the visible spectrum. References: 1) A. I. Kuznetsov et al., “Optically resonant dielectric nanostructures”, Science 354, aag2472 (2016). 2) R. Paniagua-Domínguez et al., “A metalens with near-unity numerical aperture”, arXiv:1705.00895 (2017). 3) E. Khaidarov et al., “Asymmetric nanoantennas for ultra-high angle broadband visible light bending”. Nano Letters (2017), DOI: 10.1021/acs.nanolett.7b02952.

As transformation optics matures and evolves into technology, one may reasonably ask whether any significant new insights are to be had at the conceptual level. In this talk I will focus upon two such issues: 1) Reflectionless media: Using transformation optics we can design, quite trivially, a medium that has zero reflection for all incidence angles and all polarizations. While it is clear how to interpret this result in terms of ‘impedance matching’ (wherein only the components parallel to the interface contribute to the impedance), it is less clear how a continuously varying medium produced via transformation optics (e.g. the standard cloaking transformation) can be interpreted as being ‘impedance matched’, since there is then no interface. This leads us on to some general considerations for the design of zero-reflection media. 2) Curvature: The relationship between transformation optics and curvature has been re-examined, and has yielded a surprise. It is now well established that transformation optics does not induce curvature, since any deformation of the electromagnetic field is accompanied by a deformation of the metric, ensuring that parallel rays remain parallel. But there is a striking, and as far as I am aware, unexplored similarity between the constitutive map of macroscopic electromagnetics, and Riemannian curvature. Even in flat vacuum, where the ‘constitutive map’ is simply the Hodge dual, it is possible to define a Riemann tensor purely in terms of the vacuum permittivity, ε_0 and the vacuum permeability, μ_0. This ‘hidden’ curvature is not curvature with respect to physical space, but is an abstract curvature that is constant throughout physical space, even for flat vacuum. Transformation Optics can then distort this latent curvature yielding a structure that is both locally non-trivial, and inhomogeneous. Curvature has been present all the time!

Causality and passivity constraints appear in constitutive equations of any material or meta-material and characterise the interaction electromagnetic radiation with matter. These constraints result in the well-known physical limitations which affect the design of a cloak. However, there are items in the realm of partial differential equations, namely transmission eigenvalue problems in electromagnetics, which have ignored such physical limitations and are nonetheless believed to play a role in cloaking theory. Herewith, some properties of elliptic partial differential equations are recalled; the main properties of Maxwell-Herglotz pairs are listed; transmission eigenvalue problems are stated, their connections with the properties of the “far-field scattering” operator and to “nearly non-scattering” solutions are discussed. Finally, results coming from transmission eigenvalue problems of electromagnetics, where material models ignore causality and passivity, are shown to be of limited application to cloaking.

Non-Hermitian potentials, as known since a decade, can favor unidirectionality of the flows in one and two-dimensional systems. Inspired by such counterintuitive property of non-Hermitian potential, we propose a novel concept of PT-vector fields to manipulate the field flows in two- (or higher) dimensional systems. The idea is based on designing complex potentials favoring arbitrary vector fields of directionality 𝑝⃗(𝑟⃗) with desired shapes and topologies. To achieve this, we derive a new mathematical tool referred as local Hilbert transform. We study interesting cases of such vector fields in the form of sink, vortex, and circular channel, constructed from different background patterns using local Hilbert transform. This new concept provides a precise control over the dynamics of the probe fields, which may have potential applications in technological systems.

The investigation of hyperbolic metamaterials, shows that metal layers that are part of graphene structures, and also types I and II layered systems, are readily controlled. Since graphene is a nicely conducting sheet it can be easily managed. The literature only reveals a, limited, systematic, approach to the onset of nonlinearity, especially for the methodology based around the famous nonlinear Schrödinger equation [NLSE]. This presentation reveals nonlinear outcomes involving solitons sustained by the popular, and more straightforward to fabricate, type II hyperbolic metamaterials. The NLSE for type II metatamaterials is developed and nonlinear, non-stationary diffraction and dispersion in such important, and active, planar hyperbolic metamaterials is developed. For rogue waves in metamaterials only a few recent numerical studies exist. The basic model assumes a uniform background to which is added a time-evolving perturbation in order to witness the growth of nonlinear waves out of nowhere. This is discussed here using a new NLSE appropriate to hyperbolic metamaterials that would normally produce temporal solitons. The main conclusion is that new pathways for rogue waves can emerge in the form of Peregrine solitons (and near-Peregrines) within a nonlinear hyperbolic metamaterial, based upon double negative guidelines, and where, potentially, magnetooptic control could be practically exerted.

The research of new plasmonic materials [1], alternative to standard noble metals, for the realization of photonic devices in the THz-to-visible range is continuously increasing. In this regard, new classes of materials such as transparent conductors and phase change materials (PCMs) have been proposed as promising plasmonic and/or hyperbolic metamaterials in the visible and infrared (IR) range. From one hand, transparent conductors (TCs) are electrical conductive materials with a low absorption of light in the visible range. The unique combination of metallicity and transparency makes them appealing for a variety of applications, including photovoltaic cells, flat displays, invisible electronics and waveguides. TCs are obtained by doping wide band-gap semiconductors with metal ions. Yet, the remarkable combination of conductivity in an albeit wide-gap (transparent) material is not fully understood, along with the effect of dopants and defects on charge transport and reflectivity. On the other hand, PCMs can undergo electronic and structural transitions, upon thermal, electrical, chemical or mechanical excitations. Materials that undergo metal-insulator transitions are particularly appealing as they radically modify their electrical and optical properties. This unique property is largely used to realized multi-switchable photonic devices such as plasmonic nanoantennas, ultrafast light emission modulators and near-field thermal transfer device. Here, by using first principles approaches based on DFT for the characterization of single materials and effective medium theory (EMT) for the characterization of composites, we present the optoelectronic and plasmonic properties of two different classes of metal-oxide materials: transparent conducting oxides (Al-ZnO and Ta-TiO2) and metal-oxides PCM (VO2). In the first case, we investigate the microscopic effects of metal doping (e.g. Al, Cu, Ta) [2] and defects (e.g. vacancies) [3-4] on the optical and electronic properties of TCOs and how this reflects on the plasmonic response of surface-plasmon polaritons or layered hyperbolic metamaterials, in connection with other dielectric media (e.g. ZnO, ZnS, etc). In the second case, we focus on disordered mixtures and planar homostructures resulting from the coexistence of metallic and semiconducting phases of VO2. This joint-phase combination, which has been experimentally realized, gives rise to an optical metamaterial without the introduction of other different media. This homojunction exhibits tunable optoelectronic properties, with highly anisotropic permittivity, and type-II hyperbolic behaviour in the mid-IR [5]. The possibility of generate volume-plasmon polariton waves in VO2 metamaterial is eventually discussed. [1] G.V. Naik, et al., Adv. Mater., 25, 3264–3294, (2013). [2] A. Calzolari, et al., ACS Photonics, 1, 703-709, (2014). [3] A. Catellani, et al., J. Mater Chem. C, 3, 8419-8424, (2015). [4] S. Benedetti et al., PCCP. Phys (2017), in press. [5] M. Eaton et al., (2017) submitted.

Optical metamaterials have been shown to offer a number of useful properties, including enhancement and control of spontaneous emission, chemical and biosensing and nonlinear optical control and manipulation. To date, however, the vast majority of research has been conducted into the properties of visible (or longer) wavelength systems. The materials typically chosen for this work, such as the coinage metals (Ag, Au, Cu) for visible wavelength applications become unsuitable for use in the ultraviolet due to inter- and intraband driven absorption. In order to develop metamaterials in the ultraviolet different materials need to be considered. Ultraviolet metamaterials are proposed to have additional benefits and functionalities in addition to those present in previously considered systems. For instance, the autofluorescence of biological materials typically lies in the UV range (DNA fluoresces at around 260 nm) and this can be coupled to the optical response of UV metamaterials to allow label-free fluorescence (allowing the studying of biological materials and cells in a near-native state, without the use of potentially bio-perturbing dyes) as well as detection at lower concentrations. UV-range substrates are also of interest for SERS applications due to the fact that the enhancement scales as ν^4, dramatically increasing the efficiency of the process. Here we demonstrate the development and characterisation of a large area, self assembled metamaterial for use in the ultraviolet wavelength range. Anodised aluminium oxide (AAO) provides a template for the growth of nanorods of deep-UV suitable metals, Aluminium and Gallium. These metamaterials consist of nanorods with geometric parameters smaller than the free-space wavelength of UV light (diameter around 25 nm, inter-rod separation around 60 nm) grown vertically from a UV-suitable substrate. The precise geometric parameters are controlled by the anodisation conditions, allowing tunability of the spectral response of the metamaterial. Aluminium is well documented to be the best choice of material for UV plasmonic and metamaterial use, due to its large, negative real permittivity and low imaginary permittivity in the UV range, and gallium presents interesting behaviour due to its relatively low melting point (30°C), with the liquid and solid state showing significant differences in their optical properties. Both systems have been optically characterised across the UV and visible wavelength ranges and compared with numerical modelling in order to analyse and describe their behaviour.

The control of spontaneous emission via the design of composite materials with engineered electromagnetic properties is important for the development of new faster and brighter sources of illumination with applications ranging from biophysics to quantum optical technologies. In particular, the fabrication of nanostructures leading to broadband enhancement of emission is of great interest. Hyperbolic plasmonic metamaterials have recently emerged as a very flexible platform for this purpose as they provide a high local density of electromagnetic states available for the radiative relaxation of emitters. This is due to their peculiar mode structure governed by both the structural nonlocal response and the dispersion properties. Here, we investigate the modification of the spontaneous emission rate and intensity enhancement of emitters located inside a nanorod-based hyperbolic metamaterial. We experimentally show the coupling of the radiated emission to the waveguided mode of a planar hyperbolic metamaterial with finite thickness. The emitters located inside this planar hyperbolic metamaterial waveguide exhibit an almost 50-fold reduction of the decay rate and 3-fold intensity enhancement of the fluorescence coupled to the mode. We also discuss the effect of nanostructuring the nanorod-based metamaterial on the spontaneous emission properties of emitters located inside it, where suitable designs can lead to further enhancement of the radiative rate and improved light extraction of the emission coupled to the high-wavevector modes of the metamaterial to the far-field, useful for the development of efficient and fast free-space light-emitting devices.

Publisher’s Note: This video, originally published on 23 May 2018, was withdrawn per author request.

We discuss the use of non-linear effects in metamaterials to break time-reversal symmetry, allowing signal transmission from one direction to another, but not the other way around. Compared to other approaches for breaking reciprocity, non-linear metamaterials have the significant advantage of not relying on any form of external bias, and they can be used for the protection of sources or other sensitive equipment from strong external signals. We also discuss their implications in the context of self-induced topological protection.

A theoretical framework for the quasi-monochromatic electromagnetic (EM) processes such as excitation and propagation of long wave packets in dispersive, dissipative, bianisotropic media with weak and slow nonlinearity is developed. The time-dependent EM fields associated with such processes are expressed as products of two functions: the slowly varying complex amplitude (SVCA) and the quickly oscillating carrier. The material parameters are treated as operators acting on time-dependent EM fields. By expanding these operators in the Maxwell equations in a series with respect to a small time scale parameter a system of equations for the SVCAs of the EM fields in such media is formulated. In the linear case, the dynamic equations for the SVCAs that correspond to the transverse components of the electric and magnetic fields resemble the vector transmission line equations. The obtained system of equations is used to derive the dyadic Green functions for the SVCAs of the EM fields in bianisotropic media. This framework is applied for modeling propagation of partially coherent EM radiation in a material whose parameters may depend on the amount of the EM energy that has passed through it. The same framework can be used in studying propagation of modulated EM waves through a waveguiding system that includes bianisotropic metamaterial components. Applications of the developed formalism for the important special case of uniaxial bianisotropic media are outlined, with a few characteristic examples of beam and wave-packet propagation considered in detail.

Dynamic plasmonic metasurface holograms Jianxiong Li1, and Na Liu1,2* 1Max-Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany 2Kirchhoff Institute for Physics, University of Heidelberg, Im Neuenheimer Feld 227, 69120 Heidelberg, Germany. E-mail: laura.liu@is.mpg.de Plasmonic metasurfaces represent a new class of quasi two-dimensional metamaterials that provide fascinating capabilities for manipulating light with an ultrathin platform. Such metasurfaces allow for generating a wide range of position-dependent discontinuous interfacial phase profiles. By simply engineering the metasurface-induced phase profile, a nearly arbitrary wavefront can be achieved. This unique approach promises interesting device applications beyond the scope of conventional components that rely on gradual phase accumulation for wavefront shaping. Several exotic phenomena have been demonstrated using metasurfaces including anomalous reflection and refraction,[1] the spin Hall effect of light, plasmonic metalens, optical polarization conversion, among others. Recently, metasurfaces have been also used to achieve computer-generated holograms (CGH) with high efficiency and high image quality in the visible and near-infrared regions.[2] The dispersionless nature of metasurfaces enables broadband operation without sacrificing the image quality. Thus, metasurface holograms feature a great advantage over other conventional methods such as CGH with spatial light modulators or diffraction optical elements. In this work, we demonstrate dynamic plasmonic holography based on catalytic magnesium (Mg) metasurfaces in the visible range. Through the unique hydrogenation and dehydrogenation between Mg and magnesium hydride (MgH2), different information components on the plasmonic holograms become fully addressable in space and can be individually switched on/off. This results in dynamic plasmonic holograms with designated multiple states, giving rise to high-level information control with unprecedented dynamic performance. Our work outlines the inevitable transformation from metasurfaces to metadevices, opening the door to a futuristic research horizon. Such dynamic plasmonic holograms will allow for a wealth of applications for high-resolution displays,[3] advanced security labels, high-density data storage and information processing. References [1] Yu, N. et al. Light Propagation with phase discontinuities: generalized laws of reflection and refraction. Science 334, 333–337 (2011). [2] Zheng, G. et al. Metasurface holograms reaching 80% efficiency. Nat. Nano. 10, 308–312 (2015). [3] Duan, X. et al. Dynamic plasmonic colour display. Nat. Commun. 8, 14606 (2017).

The propagation of electromagnetic waves can be manipulated at the nanoscale by surface plasmons supported by ultra thin metal layers. An adhesion layer, with thickness in the order of few nanometerss is used for depositing ultra thin metal gold layers. Cr and Ti are the most popular metallic adhesion layers. Apart from them, a non metallic silane based wetting layer like (3-Aminopropyl)trimethoxysilane (APTMS) can be used. The behaviour of the propagating surface plasmons due to the influence of these adhesion layers has not been thoroughly investigated. To study the influence of the adhesion layers on propagating plasmons for use in plasmonic and metamaterial applications,we experimentally compared the performances of the ultra-thin gold layers using Cr and APTMS adhesion layers and without any adhesion layer. We show that the gold layers using APTMS adhesion exhibit short range surface plasmon polaritons (SR-SPPs) with characteristics close to the theoretical calculations, considering an ideal gold film.

Metamaterials concept has been under extensive development over the past two decades and has been proven to be beneficial for a wide range of practical applications in both microwave and optical spectral ranges. In particular, it is commonly used for tailoring light-matter interactions on nanoscale. While many different approaches towards metamaterials fabrication exist, most of them are limited to “top-down” concept, including but not limited to lithographic methods, like photolithography, e-beam and nanoimprint lithography. On the other hand, the “bottom-up” chemical self-assembly techniques offer several distinctive advantages like throughput and cost-effectiveness, allowing large-scale production of composites. Here a novel metamaterial platform, based on mesoporous vaterite particles (further referred to as cargoes) is proposed and demonstrated. Controllable doping of micron and sub-micron scale dielectric hosts with metal nanoparticles enables tuning effective plasma frequency of new composites and, as the result, allows tailoring properties of collective localized plasmon resonances that they support. Furthermore, newly developed fabrication protocols enable introducing active materials (e.g. dyes and colloidal quantum dots) within vaterite cargoes and tailor their emission properties. Introduction of high concentration of active materials into compound particles allows compensating material losses in the medium with gain. Moreover, by coating the surface of the particles with passivating agents, it is possible to achieve long-term stability of such compound cargos in different types of solvents. Both unrestricted three-dimensional motion (compared to two-dimensional trapping of metallic particles) and rotation by circularly polarized trapping beams were demonstrated. Theoretical, numerical and experimental studies of those novel composites with beforehand mentioned properties will be presented. The vaterite-based metamaterial platform paves a way to new fundamental investigations and enables to introduce concepts of ultra-bright controllably floating imaging agents for relevant bio-medical applications.

Based on their ability to provide control over wavefront, polarization and spectrum of light fields while having just nanoscale thickness, optical metasurfaces are promising candidates for flat optical components. Typically, metasurfaces consist of designed metallic or dielectric scatterers, which are arranged in a planar fashion on a subwavelength scale. Notably, most metasurfaces realized so far were based on periodic arrangements of the individual building blocks. Disorder, for example in the positioning, shape, or orientation of its building blocks, was usually associated with a deterioration of the optical properties due to an increase of incoherent scattering. Consequently, disorder related research in metasurfaces mainly concentrated on the development of designs which are robust against deviations from a perfect ordered geometry [1,2]. However, more recently, researchers started recognizing the introduction of controlled disorder as a handle to engineer metasurfaces exhibiting specific optical properties not accessible with periodic arrangements. For example, the introduction of disorder can decrease unwanted anisotropy in the optical response [3] and it can enhance the channel capacity of wavefront shaping metasurfaces [4]. Here we investigate two different types of disordered metasurfaces. In a first study, we consider a chiral plasmonic metasurface consisting of twisted gold-nanorod dimers. Chiral metasurfaces and metamaterials were intensively studied in the past. Most prominently, they can exhibit huge optical activity [5] and were suggested for applications as polarizing elements [6,7] or nanophotonic sensors. Using polarization spectroscopy and interferometric white-light spectroscopy, we demonstrate that the introduction of rotational disorder at the unit-cell level enables the realization of chiral plasmonic metasurfaces supporting pure circular dichroism, i.e., which is not accompanied by linear birefringence. Importantly, we show experimentally that the polarization eigenstates of these metasurfaces, which coincide with the fundamental right- and left-handed circular polarizations, do not depend on the wavelength in the spectral range of interest. Thereby, our metasurfaces closely mimic the behaviour of natural chiral media, while providing a much stronger circular dichroism. In a second study, we concentrate on disordered silicon metasurfaces exhibiting electric and magnetic dipolar Mie-type resonances [8]. Silicon metasurfaces exhibit very low absorption losses in the near-infrared spectral range, thereby opening the door to long-range in-plane interactions between the individual nanoresonators. We systematically investigate how the introduction of different types of positional disorder influences the complex transmittance spectra of these metasurfaces, showing that disorder provides an independent degree of freedom for engineering their spatial and spectral dispersion. [1] C. Helgert et al., Phys. Rev. B 79, 233107 (2009). [2] N. Papasimakis et al., Phys. Rev. B 80, 041102(R) (2009). [3] S. S. Kruk et al., Phys. Rev. B 88, 201404(R) (2013). [4] D. Veksler et al., ACS Photonics 2, 661 (2015). [5] M. Decker et al., Opt. Lett. 35, 1593 (2010). [6] J. K. Gansel et al., Science 325, 1513 (2009). [7] Y. Zhao et al., Nat. Commun. 3, 870 (2012). [8] M. Decker et al., Adv. Opt. Mater. 3, 813 (2015).

In order to model the heat transfer dynamics in metamaterials (MMs), we develop a self-consistent theoretical formalism that combines the photonic mechanism, which involves the effects of the radiative heat transfer, with the phononic one, which comprises the effects of heat generation, heat storage, and heat conduction. The thermal conductivity tensor of the materials and the latent heat associated with material phase transitions are also considered in the formalism. As the first attempt in the construction of such a theory, here we study the propagation of fluctuating electromagnetic fields with slowly varying amplitudes (FEFSVA) through a dispersive and dissipative medium described by uniaxial effective permittivity and permeability tensors. Using the Poynting theorem for FEFSVA, we calculate the corresponding heat generation, accumulation, and release terms in a generalized heat transport equation. The dynamics of FEFSVA and its relation to the fluctuating source currents is described by constructing the matrix of dynamic dyadic Green’s functions. In the framework of the fluctuation- dissipation theorem, we obtain correlation between the 6-vector fluctuating current densities with SVA through relating the power spectral density of these currents to the local temperature and the frequency-dependent constitutive parameters in a narrow band around the carrier frequency. With a motivation in the study of how the slowed down FEFSVA impacts on the heat conduction, we employ our formalism in order to obtain the group velocity of the FEFSVA propagating through a layered hyperbolic MM with the Drude type dispersion.

The development of plasmonic and metamaterial devices requires the research of high-performance materials alternative to standard noble metals. Recently refractory Titanium Nitride has been proposed as a valid alternative to gold, [1] even for application in harsh and high-temperature environments. Indeed, being refractory this compound exhibits extraordinary mechanical stability over a large range of temperatures (∼2000 ◦ C) and pressures (∼3.5 Mbar), well above the melting point of standard noble metals (∼800 ◦ C). This material is furthermore resistant to corrosion and compatible with silicon technology. TiN has optical and plasmonic properties (color, electron density, plasmon frequency) very similar to gold and has been exploited for the realization of waveguides, broadband absorbers, local heaters, and hyperbolic metamaterials in connection with selected dielectric media (e.g., MgO, AlN, sapphire, etc.). Even though the fundamental mechanical and optoelectronic properties of TiN have been largely studied so far from experimental and theoretical points of view, very little is know about its plasmonic behavior. Here, we present a fully-first-principles investigation, based on time-dependent density functional theory (TDDFT), of the plasmon properties of stoichiometric titanium nitride.[2] The microscopic origin of plasmonic excitations are analyzed in terms of the fundamental collective and/or radiative exctations of TiN electronic structure. From the simulation of energy-loss spectra at different momentum transfer, we derive the TiN plasmon dispersion relations that are directly accessible by experimental measurements. We furthermore analyze different interfaces between TiN and conventional semiconductors in order to describe TiN surface-plasmon polaritons for the realization of hyperbolic metamaterials and waveguides. We also investigated the optoelectronic charcateristics of the compound in relation to the crystal phase transition, experimentally observed at very high pressure. The microscopic origin of the plasmon resonances and their dispersions have been discussed on the basis of the analysis of the electronic structure and of the interplay between collective and single-particle excitations, which determine the screening and dissipation effects of the electronic system. The similarities and the differences with other noble metals, in particular with gold, are thoroughly discussed all along the paper. Our ab initio results confirm that at standard conditions TiN exhibits plasmonic properties in the visible and near-IR regime, very close to gold, in agreement with experimental data. In contrast with malleable noble metals, the hardness of refractory ceramics allows for the exploitation of plasmonic properties also at high temperature and under pressure, conditions where standard plasmonic materials cannot be used. [1] G. V. Naik, V. M. Shalaev, and A. Boltasseva, Science 344, 263 (2014). [2] A. Catellani and A. Calzolari, Phys. Rev. B 95, 115145 (2017)

The possibility to control the infrared (IR) absorption and thermal emission on subwavelength scales has attracted large interest in the recent years thanks to the opportunities granted by nanostructured metamaterials. For example highly frequency selective and directional thermal emitters/absorbers have been proposed for a large variety of applications ranging from sensing and security to cooling and energy harvesting [1]. In order to introduce a control of the emissivity as a function of the temperature thermochromic and phase change materials have been considered. In particular Vanadium dioxide (VO2) has become a widely-studied material for applications such as metamaterials, smart windows and supercapacitors, thanks to its strong optical transmittance changes at the IR and THz regions and huge resistance jump [2]. The control mechanism is achieved by taking advantage of the metal-insulator phase transition of VO2 at its critical temperature (~68 °C). We numerically show the control of spatial and spectral features of the far field thermal emission pattern of nanoantenna arrays, composed of alternating Gold and VO2 rods, as a function of the temperature. In this work we performed a numerical study by modifying a previously developed model [3] based on the fluctuational electrodynamics approach and on the discretization of the resulting volume integral equation to calculate relative emissivity and spatial emission pattern of nanoparticle ensembles smaller than the thermal wavelength lam=hc/kBT [4]. The drastic changes of the VO2 refractive index across its metal-insulator phase transition produce strong differences in the behavior of the overall system by creating or destroying evanescent wave coupling between different elements of the nanoantenna. The study of IR thermal nano-emitters is crucial for the realization of coherent thermal nano-sources in the mid and far IR for sensing applications and thermal management as well as thermal logic gates on the nanoscale. References: [1] I. E. Khodasevych, L. Wang, A. Mitchell, and G. Rosengarten, Micro- and nano- structured surfaces for selective solar absorption, Adv. Opt. Mat. 3, 852 (2015). [2] Liu, M. et al. Phase transition in bulk single crystals and thin films of VO2 by nanoscale infrared spectroscopy and imaging. Phys. Rev. B 91, 245155 (2015). [3] M. Centini, A. Benedetti, M. C. Larciprete, A. Belardini, R. Li Voti, M. Bertolotti, C. Sibila, “Midinfrared thermal emission properties of finite arrays of gold dipole nanoantennas” Phys. Rev. B 92(20) 205411 (2015) [4] C. Wuttke and A. Rauschenbeutel, “Thermalization via Heat Radiation of an Individual Object Thinner than the Thermal Wavelength”, Phys. Rev. Lett. 111, 024301 (2013)

We investigated a metamaterial composed by silicon carbide (SiC) subwavelength oriented wires, onto silicon substrate in the mid- to long- infrared range. A simple but versatile method was developed and implemented, combining homogenization techniques with the transfer matrix method for birefringent layered materials to model an effective medium layer where different inclusions content (filling factor) as well as different shape and orientation of inclusions (depolarization factors) are taken into account. The typical spectral features associated to oriented inclusions are thus exploited to design a selective emissivity feature, pertaining sharp resonances at infrared wavelengths. Taming and tuning the strength and the position of the phonon resonance of polar materials allows the design of versatile optical elements and infrared filters, in order to design an effective medium with specifically tuned emissive properties.

One of the most important problems of metamaterials and metasurfaces research is the derivation and the analysis of the effective parameters. They allow to examine the structure without singling out each element and it is the significant advantage for practical use. Recently, it has been shown that in virtue of a subwavelength thickness metasurfaces can be described within an effective conductivity approach. Such an effective surface conductivity describes the properties of a metasurface in the far-field as well as in the near-field. We derive and analyze the effective surface conductivity of a plasmonic resonant anisotropic metasurface theoretically and numerically. With the help of obtained effective conductivity we study the near-field properties of this metasurface, in particular, the equal frequency contours of surface waves. We show the topological transition from elliptical to hyperbolic-like dispersion regime for the surface waves on a hyperbolic metasurface. Finally, we study the influence of spatial dispersion on the eigenmodes spectrum and analyze the hyperbolic regime of a metasurface with strong spatial dispersion.

Photonic metasurfaces can be used to locally control the phase, polarization, and amplitude of electromagnetic waves by scattering the wave at the sub-wavelength building blocks of the metasurface. By structuring the metasurface in a suitable way, a large variety of applications with ultrathin components become possible. For instance, metasurfaces can be used for imaging, sensing, and microscopy. Phase plates introducing a helical and radial phase profile are of interest for information technologies, as they can extend the information volume of data transfer by, e.g., encoding information in the azimuthal and radial indices of Laguerre-Gaussian modes. We demonstrate metasurfaces based on off-resonant optical scatterers that generate Laguerre-Gaussian modes from a Gaussian input beam. We show how the geometrical Pancharatnam-Berry phase can be used to design a metasurface with spatially variant phase shifting property. The according phase plates are characterized not only by the continuous phase shift in azimuthal direction around the beam axis, but also by phase discontinuities in radial direction. The metasurfaces are fabricated using electron beam lithography. We employ gold rods with a length of 220 nm to modify the properties of a circular polarized wave. More specifically, the locally induced phase of light with the opposite helicity can be controlled by rotating each rod by a certain angle relative to a reference axis. This arises from the geometrical Pancharatnam-Berry phase: The phase shift introduced by a rod is proportional to the inclination angle of the antenna with the reference axis. To achieve an azimuthal phase gradient, necessary to generate a helical phase profile, the orientation of the rods placed on a circle around the metasurface center rotates by multiples of π per turn. To design radial discontinuities, neighboring rods are shifted by π/2. Since the rods are not necessarily driven in resonance, this metasurface allows for broadband operation in the visible and near-infrared regime. Interferometric measurements reveal a spiral phase distribution resulting from the introduced helical phase profile. By the method of digital holography and the use of a holographic microscope, the phase introduced by the metasurface can be reconstructed. An achromatic grating allows the control of coherence in this apparatus [1]. Therefore, high resolution phase maps can be measured. In addition to the Laguerre-Gaussian metasurfaces, we also present a multifunctional metasurface that coalesces the functionality of two conventional optical elements. In particular, it combines the property of generating a doughnut shaped intensity pattern with the focusing property of a lens. Three dimensional phase measurements of this metasurface were performed. Our experimental results are in good agreement with numerical calculations using Fourier optics and Fresnel approximation. [1] Slabý, Tomáš, et al. "Off-axis setup taking full advantage of incoherent illumination in coherence-controlled holographic microscope." Optics Express 21.12 (2013): 14747-14762.

Nonequilibrium hot carriers formed near the interfaces of semiconductors or metals play a crucial role in chemical catalysis and optoelectronic processes. In addition to excitation by optical illumination, such hot carriers can also be generated due to electron tunnelling, a quantum-mechanical effect which allows the transport of electrons across a nanoscale junction between two conducting electrodes. Here we study electron tunnelling effects in electrically-driven plasmonic nanorod metamaterials containing up to 10^11 tunnel junctions per square centimeters and show that the generation of hot electrons makes the tunnel junctions highly reactive, facilitating strongly confined chemical reactions which can in turn modulate the tunnelling processes. To form nanometer scale gaps for electron tunneling, an overgrown plasmonic nanorod metamaterial (Au nanorod assembly electrochemically grown in a substrate-supported, thin-film porous aluminum oxide template) was first ion-milled at an oblique angle (75º with respect to the normal to the sample surface) to make the embedded Au nanorods ~1 nm shorter than surrounding aluminum oxide. Then, a droplet of eutectic gallium and indium (EGaIn) was added onto the sample surface working as an upper electrode, forming millions of ~1-nm air gaps between the Au nanorod tips and the EGaIn. When a low voltage (2.5 V) was applied between the Au nanorods and the EGaIn, a strong light emission was observed from the substrate side (~ 4 mm2 in size) due to the radiative decay of plasmonic modes excited in the nanorod metamaterial by inelastic tunnelling electrons. With an increasing applied bias, the intensity of emission increases gradually, and is accompanied by a blue-shift of the cutoff wavelength (the energies of the emitted photons are always less than the energy of tunnelling electrons). Apart from the excitation of plasmons and photons by the inelastic tunnelling electrons, hot electrons are generated simultaneously in the tips of Au nanorods by the elastic tunnelling electrons while leaving hot holes in the EGaIn. The large flux of energetic hot electrons makes the otherwise inert tunnel junctions highly reactive, facilitating the oxidation and reduction reactions in the junctions involving O2 and H2 molecules, respectively. These reactions are monitored either optically by changes in the intensity of light emission (~50%) resulting from the radiative decay of tunnelling-generated surface plasmons, or electrically via tunnelling current variations (~10%). Electrically-driven plasmonic nanorod metamaterial with reactive tunnel junctions comprises a fertile platform merging photonics, electronics and chemistry at the nanoscale, opening up opportunities for developing electron tunnelling-based devices, such as sensors, light sources, nanoreactors, modulators and photodetectors.

Digital imaging has been steadily improving over the past decades and we are moving towards a wide use of multi- and hyperspectral cameras. A key component of such imaging systems are color filter arrays, which define the spectrum of light detected by each camera pixel. Hence, it is essential to develop a variable, robust and scalable way for controlling the transmission of light. Nanostructured surfaces, also known as metasurfaces, offer a promising solution as their transmission spectra can be controlled by shaping the wavelength-dependent scattering properties of their constituting elements. Here we present, metasurfaces based on silicon nanodisks, which provide filter functions with amplitudes reaching 70-90% of transmission, and well suitable for RGB and CMY color filter arrays, the initial stage towards the further development of hyperspectral filters. We suggest and discuss possible ways to expand the color gamut and improve the color values of such optical filters.

This paper shows a detailed analysis of the semiconductor-to-metal transition (SMT) in a vanadium dioxide (VO₂) film deposited on silicon wafer. The vanadium dioxide phase transition is studied in the wide mid-infrared range 2-12 μm, by analyzing the transmittance and the reflectance measurements, and the calculated emissivity from the sample. The temperature behavior of the emissivity during the SMT put into evidence the phenomenon of the anomalous absorption in vanadium dioxide which has been explained by applying the Maxwell Garnett effective medium approximation theory. A strong hysteresis phenomenon of about 8°C has also been found for transmittance, reflectance and emissivity. Experimental results show how the use of these techniques represent a good tool for a quantitative measurement of the infrared properties in the MIR range.

A key recent advance in nanophotonics field has been the emergence of tunable, switchable and reconfigurable metasurfaces offering “optical properties on demand”. With these devices, light propagation does not have to be static, as traditionally assumed, but may be changed at will at any point in space and/or moment in time. Various approaches have been developed to realize optical components made from metadevices reconfigurable by mechanical, electrical, or optical means. In general, however, most of the existing reconfigurable metasurfaces tune the properties over the entire device homogeneously when stimulated. The ability to tailor the optical properties of individual meta-molecules in planar metasurfaces promises to open up unprecedented opportunities in applications such as high capacity communications, dynamic beam shaping and adaptive optics. In this work, we pioneered the novel single-meta-molecule addressable digitally reconfigurable metadevices using the emerging paradigms of tunable metasurfaces - functional matter structured on the sub-wavelength scale, and by engaging new ideas of phase-change material integrated with nanostructures for dynamic light control. In our design, low loss dielectric nanostructures (amorphous Si nanorods) are patterned on top of phase-change foundation structures to form the hybrid meta-molecule. As for the phase-change medium, we use the chalcogenide glasses (e.g. germanium-antimony-telluride), which is widely exploited in rewritable optical disk storage technology and non-volatile electronic memories due to its good thermal stability, high switching speed, large number of achievable rewriting cycles and pronounced contrast of dielectric properties observed between two phases. The phase-change process in chalcogenide glasses is a material reaction to the photothermal effects. Using tightly-focused low-energy fs laser pulses to excite the phase transition results in a sharp border between the amorphous background and crystallized spots, allowing individual single meta-molecules to be addressed. The reconfiguration of meta-molecules will be accomplished by re-amorphization of the phase-change material with a high-energy single optical pulse. The preliminary simulation results demonstrated the reconfigurable metasurfaces for phase and resonance frequency modulation of light based on the innovative platform of digitally and individually reconfigurable meta-molecules for applications in active beam shape and hologram display. This development will progress photonic technology enabling increased information flow, while reducing power consumption and achieving new levels of miniaturization for photonic devices.

New healthcare initiatives including personalized medicine, global health, point-of-care diagnostics require breakthrough developments in biosensing technologies. Unfortunately, current biosensors are time consuming, costly, bulky, require infrastructure and trained laboratory professional, making them unsuitable for disease control and patient care in the field. To address these challenges we employ novel physics and engineering toolkits, such as nanophotonics, nanofabrication, microfluidics. Nanostructured optical metasurfaces based on plasmonics, all-dielectrics or low-dimensional materials are of great interest for biosensor development [1]. They can confine the light below the fundamental diffraction limit and create extremely intense electromagnetic fields in volumes much smaller than the wavelength of light. These features are especially promising for device applications. In this talk I will cover nanoengineered metasurfaces interfaced with biology and chemistry for realization of ultra-sensitive, real-time, label-free and high-throughput biosensors. We exploit metasurfaces for detection of infectious pathogens, disease biomarkers and live cells. For infectious disease applications, we are developing multiplexed nanoplasmonic biosensor arrays for one-step simultaneous detection of bacteria directly from body fluids towards point-of-care devices for efficient population screening and rapid control [2]. With disease biomarkers we are introducing new sensing methodologies for in-vivo protein and lipid analysis under biological conditions [3]. Significantly, our sensor based on surface enhanced infrared spectroscopy is even sensitive to the conformational changes of diseases proteins [4]. Most recently, we presented a new microfluidic-integrated nanoplasmonic biosensor for the study of cell signaling in a label-free and real-time manner. We demonstrated the applicability of our nanobiosensor for long-term monitoring of cytokine secretion from live cancer cells [5]. In parallel, we explore novel two materials for biosensing due to their exceptional opto-electronic properties [6]. In particular by exploiting the unique tunabality of graphene plasmonics with electrostatic gating, we recently demonstrated a dynamically tunable plasmonic Mid-IR biosensor that can extract complete optical refractive index of proteins over a broad spectrum. This talk will cover some of these recent developments. [1] Altug et al. “Nano-optics get practical” Nature Nanotechnology, Vol 10, p. 11-15 (2015). [2] Soler et al. “Multiplexed Nanoplasmonic Biosensor for One-step Detection of Major STD Bacteria in Urine” Biosensors & Bioelectronics, Vol. 94, p. 560-567 (2017). [3] Limaj et al. “Infrared Plasmonic Biosensor for Real-Time and Label-Free Monitoring of Lipid Membranes” Nano Letters, Vol 16, p. 1502–1508 (2016). [4] Etezadi et al. “Nanoplasmonic mid-infrared biosensor for in vitro protein secondary structure detection” Light: Science & Applications, Vol. 6, p. e17029 (2017). [5] Li et al. “Plasmonic nanohole array biosensor for label-free and real-time analysis of live cell secretion” Lab on a Chip, Vol. 17, p. 2208-2217 (2017). [6] D. Rodrigo et al. “Mid-infrared Plasmonic Biosensing with Graphene”, Science, Vol 349, p. 165-168 (2015).

Nanoplasmonic sensing is a very active and diverse field with a wide variety of applications in chemistry, biomolecular and materials science [1]. Optically resonant molecular systems often display what is called a strong coupling to the nanophotonic systems. This is primarily explored for the nanophotonics active control and in the studies of quantum optics [2]. At the same time, the strong coupling of the molecular resonances to the nanoplasmonic antennas has not been addressed to follow the light-induced molecular processes. Here we combine an exemplary molecular photo-switch, from the spiropyran photochromic family, with anisotropic nanoplasmonic antennas to earn the monitoring tool for the light-activated processes using molecular and nanoplasmonic resonances strong coupling regime. We follow the reversible photo-isomerization of the spiropyran photoswitch from the spiro form to the merocyanine form by tuning in the nanoplasmon antenna to the excitonic state of the merocyanine form (at 570 nm), prompting the formation of a hybrid excitonic-plasmonic state. Our anisotropic nanoantenna provides two polarization-dependent spectrally separated resonances in the visible region, allowing for separate monitoring of the plasmon-exciton strong coupling and the conventional enhanced optical near-field refractive index sensing. This system uncovers a new modality in polaritonic chemistry and optical label-free monitoring of the photo-activated processes and can find applications in photocatalysis, biosensing and in hybrid molecular-nanoantenna actively modulated systems. [1] M. I. Stockman, Science 348, 287 (2015); A. Dmitriev (Ed.), Nanoplasmonic Sensors, Springer NY (2012). [2] Yoshie, T. et al. Nature 432, 200 (2004) ; Kasprzak, J. et al. Nature Mater. 9, 304 (2010); Reinhard, A. et al. Nature Photon. 6, 93 (2012). 

Assembly of nanoscale building blocks into hierarchical superstructure by self-assembly is one of the most pursued topics in nanoparticles chemistry. The possibilities obtainable when individual components arrange themselves into an ordered structure are limitless and of great interest. Spherical colloidal clusters have been proposed to possess remarkable collective supermodes with large local field enhancements, and a spectral response extending from the near-infrared to deep into the mid-infrared region. As such, these superstructures hold great promise as a sensing platform that is capable of addressing the whole spectral domain of vibrational molecular fingerprints, while simultaneously exploiting the advantages of their plasmonic constituents [1], [2]. By exploiting these properties of the self-assembled metamaterials supercluster, we report the experimental measurement of near and mid- IR plasmonic collective modes by monitoring the Raman scattering of 4-Mercaptobenzoic acid with a confocal microscope. The strongly enhanced Raman signal allows measurement of the plasmonic mode with a lateral resolution lower than 300 nm and a vertical one of 300 nm. As the supercluster structure possesses tunable optical modes, different plasmonic responses are mapped according to the cluster size and the excitation wavelength. Moreover, as SERS allows sensitive detection of molecules, the remarkable and tunable modes excitable inside the spherical colloidal clusters can provide an efficient platform for ultra-sensitive molecular spectroscopy. To this end proof-of-principle implementation of the superclusters as an efficient platform for pH sensing of the surrounding medium is reported [2]. REFERENCES [1] V. A. Turek, L. N. Elliott, A. I. I. Tyler, A. Demetriadou, J. Paget, M. P. Cecchini, A. R. Kucernak, A. A. Kornyshev, and J. B. Edel, “Self-assembly and applications of ultraconcentrated nanoparticle solutions,” ACS Nano, vol. 7, no. 10, pp. 8753–8759, 2013. [2] A. Lauri, L. Velleman, X. Xiao, E. Cortes, J. B. Edel, V. Giannini, A. Rakovich, and S. A. Maier, “3D Confocal Raman Tomography to Probe Field Enhancements inside Supercluster Metamaterials,” ACS Photonics, vol. 8, no. 4, p. pp 2070-2077, 2017.

In this talk, we will present metamaterial based nanobiosensors, nanophotodetectors and perfect absorbers. Our results show that a plasmonic structure can be successfully applied to bio-sensing applications and extended to the detection of specific bacteria species. A highly tunable design for obtaining double resonance substrates to be used in Surface Enhanced Raman Spectroscopy will also be presented. Surface Enhanced Raman Scattering experiments are conducted to compare the enhancements obtained from double resonance substrates to those obtained from single resonance gold truncated nano-cones. We will present a UV plasmonic antenna integrated metal semiconductor metal (MSM) photodetector based on GaN. We designed and fabricated Al grating structures. Well defined plasmonic resonances are measured in the reflectance spectra. Optimized grating structure integrated photodetectors exhibit more than eight-fold photocurrent enhancement. We also demonstrate a facile, lithography free, and large scale compatible fabrication route to fabricate ultra-broadband wide angle perfect absorber based on metal-insulator-metal-insulator (MIMI) stack design. 600 nm band-width (400 nm – 1000 nm) is attained utilizing this planar design. This design is later improved by introduction of non-uniform texturing and employing disordered nano hole plasmonic patterns where the overall process is large scale compatible and lithography free. Our findings show that the optimized design can retain light absorption above 90% over a wide range wavelength of 400 nm – 1490 nm. To the best of our knowledge, this bandwidth is the highest among other reported studies that employ such multilayer architectures.

A major challenge facing plasmon nanophotonics is the poor dynamic tunability. A functional nanophotonic element would feature the real-time sizeable tunability of transmission, reflection of light’s intensity or polarization over a broad range of wavelengths, and would be robust and easy to integrate. Here we devise an ultra-thin chiroptical surface, built on 2D nanoantennas, where the chiral light transmission is controlled by the externally applied magnetic field. We produced a class of highly tunable by the magnetic field macroscale bottom-up plasmonic chiroptical surfaces. The tuned parameter is the chiroptical transmission, enabled by the nanoantenna design that accommodates ferromagnetic plasmonic elements. The already significant chiroptical response of this system is further tuned up to 150% by the external magnetic field. The presented compact 2D design promises the easy integration and potentially fast operation in the broad spectral range, enabling this type of functional plasmonic surfaces entering the realm of practical optical devices. The magnetic field-induced modulation of the far-field chiroptical response with this surface exceeds 100% in the visible and near-infrared spectral ranges, opening the route for nanometer-thin magnetoplasmonic light-modulating surfaces tuned in real time and featuring a broad spectral response. For this we design a 2D composite trimer nanoantennas comprising three near-field-coupled nanosized disks of diameters close to 100 nm and identical height of 30 nm, of which one is made of a ferromagnetic material and the other two are made of a noble metal. The use of two materials breaks the 2D rotational symmetry, endowing the handedness to the trimer that results in a chiroptical response in otherwise structurally symmetric nanoantenna. We leverage on the presence of the plasmon resonances in metallic nanoferromagnets to add the magnetoplasmonic functionality to the system.

The concept of the rapidly developing area of high-index resonant meta-optics is extended to the field of mag- netically active materials. We numerically analyze magneto-optical response of hybrid nickel-silicon (Ni/Si) nanoantennas in comparison with an all-dielectric analog based on the bismuth substituted iron yttrium garnet- silicon (Bi:YIG/Si) nanoantennas. The results demonstrate the multifold enhancement of the magneto-optical effects due to the Mie-type resonances excitation in the structure. To further optimize the magneto-optical re- sponse and achieve a significant enhancement of the effect, the metasurfaces composed of Ni/Si nanoantennas of the different shape and configuration are numerically simulated. The magneto-optical effects can be significantly enhanced by means of the specific design of these hybrid metasurfaces.

Chipless radiofrequency identification (chipless-RFID) has emerged as an alternative to RFID systems with tags equipped with chips. The main advantage of chipless-RFID over chipped-RFID is the lower cost of the tags, since the silicon integrated circuits (IC) of chipped tags are replaced with planar passive encoders in chipless tags. The main limitations of chipless-RFID tags are the data storage capability and tag size. In this paper, we propose an approach for the implementation of chipless-RFID systems, based on near-field coupling and sequential bit reading, which alleviates the previous limitations. The tags are implemented by chains of split ring resonators (SRRs) printed on a substrate (including plastic and paper substrates), and the logic state ’1’ or ‘0’ is dictated by the presence or absence of these resonant elements at predefined positions (alternatively, programmable tags can be implemented by detuning certain resonant elements). Tag reading is achieved by means of a transmission line fed by a harmonic signal conveniently tuned, so that such signal is amplitude modulated by tag motion above the line (in proximity to it) due to inductive coupling. Such chipless-RFID system is especially suited for security and authentication applications, by directly printing the planar passive encoders on the items of interest (e.g., corporate and official documents, ballots, exams, etc.). It is demonstrated that the number of achievable bits is only limited by tag size; therefore, the proposed system is compatible with chipped-RFID system in terms of data capacity.

Dielectric and metallic nanostructures can be tailored to provide unusual interaction with light waves. For example, they support localized resonances highly sensitive to the surroundings, complex scattering patterns and ultrafast nonlinearities. When arranged in 2D or 3D lattices, they form metasurfaces and metamaterials that enable to manipulate free-space light beams at will. However, the properties of such nanostructures also manifest when isolated, which could be used to advance in the miniaturization of photonic integrated circuits beyond the diffraction limit as well as to achieve new functionalities not attainable in conventional integrated optics. This could lead to the paradigm of hybrid plasmonicphotonic circuits consisting of subwavelength processing units linked by lossless dielectric waveguides. Here, I will show efficient ways to integrate dielectric and metallic nanostructures with silicon waveguides. The resulting structures could be useful in biosensing, Raman spectroscopy or ultrafast all-optical switching. In addition, I will show that when the nanostructure is placed asymmetrically with respect to the waveguide axis, it gives rise to spin-orbit interaction. This effect enables new functionalities such as polarization synthesis or Stokes nanopolarimetry, which can be implemented on a silicon chip in ultra-small foot-prints.

Silicon photonics is considered an enabling technology for next generation datacom applications, providing ultra-compact and high-bandwidth transceivers that are cost-effectively fabricated at the existing CMOS facilities. Among photonic devices developed in silicon, Bragg gratings are routinely used for the realization of key functionalities including wavelength filtering, dispersion engineering and sensing. However, the realization of Bragg filters that simultaneously provides narrowband operation and high rejection remains a challenge in the Si platform. Indeed, the small core size of Si wires, together with the high index contrast between the silicon and the oxide cladding results in a strong interaction of the optical mode with the Bragg structure. Several approaches have been proposed to implement narrowband Bragg filters in Si wires including ultra-small corrugations (a few nanometres), periodic claddings, sub-wavelength engineering or inter-mode coupling. Nevertheless, these filters typically have comparatively weak light rejection performance due to fabrication errors limiting the accurate control of the grating geometry over few millimeter-long waveguide structures. In this work, we present a novel waveguide Bragg grating geometry that leverages the large index contrast between Si and air in membrane waveguides to overcome these limitations, yielding both narrow bandwidth and high rejection ratio. We use a novel waveguide corrugation geometry that radiates out the higher order modes, allowing effective single-mode operation for micrometric fully etched membrane waveguides. The high mode confinement of these waveguides results in weak interaction with the sidewall corrugation, thus narrowband operation is achieved. On the other hand, the high rejection ratio is achieved by combining reflection and radiation effects within the Bragg resonance. Based on this concept, we designed and experimentally demonstrated notch filters in single-etch suspended Si waveguides with cross-sections as large as 0.5 µm (height) by 1.1 µm (width). We show a narrow bandwidth of 4 nm for a 500 nm wide corrugation, with a high rejection ratio exceeding 50 dB for a filter length of only 700 µm

Recently, organic perovskite solar cell has achieved remarkable increase in its efficiency, and reached over 22% in 2017. However, its efficiency could be increased further using nanophotonic techniques for guiding incident light to perovskite active layer. Metasurface cross grating nanostructure would control light reflection and transmission over wide range of wavelength. Using metasurface with perovskite solar cell, will increase generated photocurrent and enhance overall efficiency. Our results show that light absorption enhancement and light reflection reduction are highly depending on dimensions, periodicity and coated material used of metasurface cross grating nanostructures. Controlling electric and magnetic dipoles in gold metasurface and Mie resonance dipoles in dielectric coating material would enhance generated photocurrent over planar perovskite structure. Comparison between plasmonic and all dielectric metasurface performance would give us more understanding for light reflection reduction mechanism. Using three-dimensional optical modeling based on finite element method simulation tool for all our results would enhance its accuracy. For verifying our results, we made comparison between our results and previously reported work for planar perovskite solar and good matching achieved in light absorption and generated current. Adding suggested plasmonic and dielectric metasurface cross grating nanostructures inside perovskite solar cells, will enhance its overall efficiency.

Energy-efficient ultrafast all-optical signal processing may contribute to solving growing bandwidth and energy challenges in optical telecommunications. However, conventional solutions for all-optical data processing rely on nonlinear optical materials with inherent minimum power requirements and trade-offs between bandwidth and speed. In contrast, the coherent interaction of light-with-light in an absorber of nanoscale thickness can facilitate high-contrast modulation of one optical signal with another, ultimately with few-femtosecond response times and at arbitrarily low (even single photon) intensities. We report here on the first demonstration of a fiberized metamaterial device for all-optical signal processing based upon coherent modulation of absorption. The integrated metadevice is based on a plasmonic metamaterial of nanoscale thickness fabricated on the core area of a single-mode optical fibre, and designed to operate over the 1530 – 1565 nm telecoms wavelength range. We demonstrate signal processing operations analogous to logical NOT, XOR and AND functions at effective rates from tens of kbit/s up to 40 Gbit/s with energy consumption as low as 2.5 fJ/bit, as well as selective absorption and transmission of picosecond pulses and the generation of 1 ps ‘dark pulses’. We anticipate that such metadevices, with THz bandwidth, may provide solutions for quantum information networks as well as orders-of-magnitude improvements in speed and energy consumption over existing nonlinear approaches to all-optical signal processing in coherent information networks.

In this contribution, we present the application of an optical metasurface polarization rotator in an Atomic Force Microscopy (AFM) setup. In AFM, the laser beam used to measure the cantilever deflection is not entirely intercepted by the cantilever surface. Consequently, the remainder of the beam illuminates part of the surface under measurement. Part of the light scattered by the surface is intercepted by the Position Sensitive Detector (PSD), interfering with the measurement of the light that is directly reflected by the cantilever. This reduces the measurement Signal-to-Noise Ratio (SNR), decreasing the AFM accuracy and generating artefacts. To enhance the SNR we propose a metasurface reflective polarization rotator, directly integrated on the cantilever. The metasurface elliptical resonators, oriented at a certain angle with respect to the incoming polarization state, will induce different phase shifts on the two components parallel to the orthogonal axes of the ellipse. By properly tuning the dimensions of the resonators, a 90° rotation of the reflected light polarization with respect to the incident polarization is realized. We arrive at three designs with cross-polar reflectivities of 0.82, 0.86 and 0.66 and total reflectivities of 0.83, 0.87 and 0.68 correspondingly. The metasurface allows to discriminate the desired light, reflected by the cantilever, from stray light from the sample surface, which maintains mostly the original polarization. In this paper, performance of the different configurations will be presented and discussed together with other considerations relative to the mechanical performances of the enhanced cantilever.

Miniaturized devices with multiple functionalities are exceedingly required in integrated optical systems. Flat nanostructures, named metasurfaces, provide fascinating boulevard for complex structuring and manipulation of light such as optical vortex generation, lensing, imaging, harmonic generation etc. at micron scale. Since, the performance of metal-based plasmonic metasurfaces is significantly limited by their optical absorption and losses, lossless dielectric materials (in the operational spectrum) provide decent alternative to attain higher efficiency. Here, a novel, polarization insensitive and highly efficient method for light structuring is demonstrated based on amorphous silicon (with subwavelength thickness of 400 nm) at an operational wavelength of 633 nm. The proposed phase gradient metasurface is based on circular cylindrical nanopillars of amorphous silicon exhibits two optical properties, the lensing and orbital angular momentum generation. The cylindrical nature of the pillar plays a pivotal role to make the overall structure as polarization insensitive. The proposed innovative methodology will provide an interesting road towards the development and realization of multi-functional ultrathin nanodevices which will find numerous applications in integrated photonics.

We use a genetic algorithm to optimize broadband absorption by 2-D periodic arrays of pyramidal structures made of one, two or three stacks of nickel/poly(methyl methacrylate) (Ni/PMMA) layers. The objective was to achieve perfect absorption of normally incident radiations with wavelengths comprised between 420 and 1600 nm. The absorption spectrum of these pyramidal 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 Ni/PMMA and the width of each layer of PMMA. The idea consists in working with a population of individuals that represent possible solutions to the problem. The best individuals are selected. They generate new individuals for the next generation. Random mutations in the coding of parameters are introduced. A local optimization procedure that works on the data collected by the algorithm is used to accelerate convergence. This strategy is repeated from generation to generation in order to determine a globally optimal set of parameters. The optimal three-stacks structure determined by this approach turns out to absorb 99.8% of the incident radiations over the considered 420-1600 nm wavelength range. A value of 99.4% is achieved with pyramids made of only two stacks of Ni/PMMA layers while a one-stack pyramidal structure absorbs 95.0% over the same wavelength range. These results are surprisingly competitive considering the small number of layers involved in the design. They prove the interest of an evolutionary approach to optical engineering problems.

Metasurface studies have demonstrated vast applications to control optical properties of light based on the ability to design unit cells with desired phase and reflectivity in 2D subwavelength periodic arrays. The simplified design strategy is only an approximation since the unit cells can be subject to near-field coupling effects due to influence from neighbor unit cells. In this work, we try to investigate this effect by numerically and experimentally studying the near-field response from gold nanobricks of varied length, fabricated in both quasi-periodic and periodic configuration on top of dielectric-coated (SiO2) layer and gold layer at telecommunication wavelength (1500 nm), which is the commonly used gap plasmon configuration for efficient metasurfaces. The experimental near-field investigation is performed using a phase-resolved scattering-type scanning near-field optical microscopy (s-SNOM) in the transmission mode. We demonstrate that near-field coupling becomes significant when edge-to-edge separation between GSP elements goes below ~200-250 nm. We also show that the reflection phase of any GSP element is approximately equal to its doubled near-field phase. Thus, our studies provide a direct explanation of a reduced performance of a densely-packed GSP metasurfaces. This technique can accurately predict the performance of different types of metasurfaces by observing their near-field response in different periodic configurations by considering factors ignored in the design stage, which include fabrication uncertainties, wrong design considerations along with near-field coupling effects.

Metasurfaces – artificial 2D sheet structures with sub-wavelength periodicity and dimensions of elements – are paving the way to improve traditional optical components by integrating multiple functionalities into one optically flat device. With the progress in nano-fabrication methods, different applications of metasurfaces were demonstrated experimentally, ranging from artificial plasmonic colouring to flat optical components. In this work, we demonstrate implementation of a bifunctional gap-surface-plasmon-based metasurface which, in reflection mode, splits orthogonal linear light polarizations and focuses into different focal spots. The fabricated configuration consists of 50 nm thick gold nanobricks with different lateral dimensions, organized in an array of 240 nm x 240 nm unit cells on the top of a 50 nm thick silicon dioxide layer, which is deposited on an optically thick reflecting gold substrate. Structure is fabricated using standard electron beam lithography and lift-off techniques. Characterization is performed using scanning electron microscopy and optical measurements, including investigation of wavelength dependence of efficiency, focal length and polarization extinction ratio. Our device features high efficiency (up to ~65%) and polarization extinction ratio (up to ~30 dB), exhibiting broadband response in the near-infrared band (750 950 nm wavelength) with the focal length and numerical aperture dependent on the wavelength of incident light. The proposed optical component can be straightforwardly integrated into photonic circuits or fiber optic devices which employ polarization multiplexing.

We show that a planar metal-dielectric-metal structure has a resonant characteristic that can be used to filter specific colors of the visible spectrum depending of the choice of the material used in the dielectric layer. The resonance occurs when the reflection phase is canceled out with the phase of the propagation. We numerically demonstrate a structure that can be used as an RGB optical filter with three different dielectric materials, with transmission of above 60%. The planar structure exhibits wide-angle transmission for angles of incidence up to 50° for the red and blue colors and up to 30° for the green color.

Plasmonic groove structures, which are widely known for its absorbent properties of light, are numerically investigated. Genetic algorithms have been successfully used to aid in the design of two-dimensional high efficiency wide-angle plasmonic groove absorbers for visible wavelengths. The novel periodic groove structure exhibits absorption above 90% for ultra-broadband wavelengths ranging from 300 to 700nm. The resonant modes induce localized zero wavevector plasmon polaritons in the metallic material which favors absorption and may also enhance non-linear optical processes.

In this work we analytically and numerically study the impact of dye infiltration in multilayer hyperbolic meta- materials. The dyes we use in our model are four-level dyes with an absorption and an emission line. Starting from the Maxwell-Bloch equations we derive a semi-analytical model for the coupling of an oscillator in a one- dimensional periodic structure. We compare our model with exact results obtained using the transfer-matrix method. In the weak coupling regime, both absorption and emission lines perturb the optical mode (in a finite multilayer) or the band (in an infinite multilayer) in similar ways, introducing positive and negative imaginary parts to the dispersion of Bloch vector within the bands without altering their shapes. In contrast, in the strong-coupling regime, the two lines are responsible for different phenomena: while coupling to the absorption line causes a severe distortion of the band due to classical Rabi splitting, coupling to the emission line causes fork-shaped bifurcations reminiscent of PT-symmetry breaking scenarios, with apparition of exceptional points at the loss-gain compensation frequencies.

Efficiency of CZTS (Cu₂ZnSnS₄) based thin film solar cell has witnessed rapid increase from nearly 5.7% in 2005 to more than 9% in 2016. These enhancements made CZTS solar cell a good candidate for low cost solar cells. However, low efficiency limit this choice, therefore, enhancing generated photocurrent would enhance overall efficiency. Metasurface has attracted great interest in last decade because of its ability for reducing light reflection and increasing light transmission over wide range of electromagnetic waves spectrum. Plasmonic metasurface has many advantages for antireflective surface with minor light losses disadvantages. All dielectric metasurface is promising because light losses would minimize and give better performance over plasmonic metasurface. Our results indicate that, light coupling to CZTS solar cells could be enhanced much more than planar structure after using suggested optimum dimension, pitch, coated dielectric thickness. Role of electric and magnetic diploes excited in gold wires and Mie resonance dipoles in dielectric play important role in guiding light to CZTS substrate, through our result, we suggest method for controlling them. Using three-dimensional optical modelling based on finite element method simulation tool for all our proposed structures. For verifying our results, we compared our simulated planar CZTS solar cells with fabricated one in previous work and good matching achieved for light absorption. Integrating suggested wire grating plasmonic and dielectric wire grating metasurface with planar CZTS solar cells would enhance its overall efficiency furthermore more.

Intensive researches in the area of metasurfaces have provided a new insight to obtain flat and compact optical systems. In this letter, we numerically show that, highly efficient tunable beam steering effect in transmission mode is achieved at wavelength λ = 550 nm using nematic liquid crystals (LCs) infiltrated into double sided metasurfaces. Using the electrooptical feature of LCs, the phase profile of the metasurfaces is controlled and thus, the transmitted beam is deflected within the range from -15° to 15° steering angles. Transparent dielectric materials are used in the designed structure that provides highly efficient beam-steering; the corresponding transmission efficiency is above 83% in the visible spectrum, which is another superiority of the proposed hybrid tunable structure over present plasmonic/metamaterial approaches. The designed metasurface still preserves its beam deflection property covering the visible spectrum and hence, such hybrid structure can be implemented for broadband electro-optically controllable beam steering applications.