This PDF file contains the front matter associated with SPIE Proceedings Volume 10719, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Metasurfaces provide a new basis for recasting optical components into thin planar elements, easy to optically align and control aberrations, leading to a major reduction in footprint, system complexity and cost as well as the introduction of new optical functions.1, 2, 3. Their planarity allows for fabrication routes directly in line with conventional processes of the mature integrated circuit (IC) industry.1 I foresee great technological and scientific penetration of CMOS compatible metasurface-based optical components, ranging from metalenses4-6 to novel polarization optics7, 8. Camera modules for high volume applications, such as cell phones, will be the greatest beneficiaries. The technology required to mass produce metasurfaces dates back to the early 1990s, when the feature sizes of semiconductor manufacturing became smaller than the wavelength of light, advancing in stride with Moore’s law. This provides the possibility of unifying two industries: semiconductor manufacturing and lens-making, whereby the same technology used to make computer chips is used to make metalenses and other optical components, based on metasurfaces. A major obstacle for this to happen had to be overcome. With metasurfaces, the data describing large designs are faced with the challenge of enormous file sizes due to having millions or billions of individual microscopic metaelements (necessitated by the subwavelength size criterion) described over macroscopically large device areas. This extremely high data density over large areas generates unmanageably large total file sizes, limiting the fabrication of optical components such as metalenses to sizes no larger than a few millimeters. Using our new scalable metasurface layout compression algorithm (METAC) that exponentially reduces design file sizes (by 3 orders of magnitude for a centimeter diameter lens) and stepper photolithography, we have recently shown the design and fabrication of metalenses with extremely large areas, up to centimeters in diameter and beyond.9 Finally I envision a future of digital optics based on metasurfaces with increased density of optical components and functionalities per metasurface; it is tempting to speculate that an empirical law might govern its growth, akin to Moore’s Law for digital electronics. References: 1. F. Capasso, Nanophotonics DOI: 10.1515/nanoph-2018-0004 (2018) 2. N. Yu et al. Science 334, 333 (2011) 3. N. Yu and F. Capasso Nature Materials 13, 139 (2014) 4. M. Khorasaninejad et al. Science 352, 1190 (2016) 5. M. Khorasaninejad and F. Capasso, Science 358, 8100 (2017) 6. W-T. Chen et al. Nature Nanotechnology (2018) doi:10.1038/s41565-017-0034-6 7. J. P. B. Mueller et al. Physical Review Letters 118, 113901 (2017) 8. J. P. B. Mueller et al. Optica 3, 42 (2016) 9. A. She et al. Optics Express 26, 1573 (2018)

Energy conversion in a physical system requires time-translation invariance breaking according to Noether's theorem. Closely associated with this symmetry-conservation relation, the frequencies of electromagnetic waves are found to be converted as the waves propagate through a temporally varying medium. Thus, effective temporal control of the medium, be it artificial or natural, through which the waves are propagating, lies at the heart of linear frequency conversion. Here, we explain the basic principle of linear frequency conversion in a rapidly time-variant metadevice and show various interesting properties and future prospects of rapidly time-variant metadevices.

Because time and space play a similar role in wave propagation, wave propagation is affected by spatial modulation or by time modulation of the refractive index. Here we emphasize the role of time modulation. We show that sudden changes of the medium properties generate instant wave sources that emerge instantaneously from the entire wavefield and can be used to control wavefield and to revisit the way to create time-reversed waves. Experimental demonstrations of this approach will be presented. More sophisticated time manipulations can also be studied and extension of these concepts in the field of plasmonics will be presented.

In this work, we combine the plasmonic material with high index dielectric to design a metasurface. With the dyadic Green function and coupled-dipole approach, a Huygens’ metasurface is obtained by two dimensional array of subwavelength Ag core-Si shell nanoparticles, the transmission efficiency is close to unity in a broadband spectrum, and the reflection is completely eliminated by spectrally overlapping the magnetic dipole resonance with the electric dipole resonance. The designed high transmitted Huygens’ metasurface can be applied to wavefront shaping and beam forming.

Plasmonic gold nanoantennas are highly efficient nanoscale nonlinear light converters. The nanoantennas provide large resonant light interaction cross sections as well as strongly enhanced local fields. The actual frequency conversion, however, takes places inside the gold volume and is thus ultimately determined by the microscopic gold nonlinearity which has been found to significantly surpass common bulk nonlinear materials. While the influence of the nanoantenna geometry and hence the plasmonic resonance has been studied in great detail, only little attention has been paid to the microscopic material nonlinearity. Here we show that the microscopic third-order nonlinearity of gold is in fact a resonant one by virtue of interband transitions between the d- and sp-bands. Utilizing a large set of resonant nanoantennas and a fiber-feedback optical parametric oscillator as broadband tunable light source, we show that the radiated third-harmonic signals significantly increase at the onset of interband transitions, namely, as soon as the third harmonic becomes resonant with allowed interband transitions. With the help of an anharmonic oscillator model and independent reference measurements on a gold film we can unambiguously demonstrate that the observed third-harmonic increase is related to a strongly wavelength-dependent microscopic third-order gold nonlinearity, which is additionally underlined by quantitative agreement between simulation and measurement. This additional tuning parameter allows further manipulation and optimization of nonlinear nanoscale systems and thus renders the investigation of other plasmonic materials, especially with interband transitions located in the ultra-violet range, highly intriguing.

The time-bandwidth limit refers to the trade-off between the time delay that can be applied to a signal as it travels through a device and its bandwidth. Recently, there have been several studies showing that this bound can be broken in nonreciprocal nano-structures, including nonreciprocal cavities and terminated unidirectional waveguides. Here, we explore the physical mechanisms involved in these structures, and explore the opportunities offered by non-reciprocal elements to control the delay applied to an impinging signal.

We have studied the effects of metallic substrates, lamellar metal-dielectric stacks and Fabry-Perot cavities on spontaneous emission and concentration quenching of luminescence of the HITC laser dye. Among the most intriguing results of this research are: (1) The long-range (~50 nm) inhibition of the concentration quenching (Förster energy transfer to quenching centers) by metallic and lamellar metal-dielectric substrates and (2) Enhancement of the spontaneous emission quantum yield with reduction of the cavity size below 100 nm.

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.

We have recently developed a computational approach to inverse-design photonics based on desired performance, with fabrication constraints and structure robustness incorporated in design process. Our approach performs physics guided search through the full parameter space until the optimal solution is reached. Resulting device designs are non-intuitive, but are fabricable using standard techniques, resistant to temperature variations of hundreds of degrees, typical fabrication errors, and they outperform state of the art counterparts by orders of magnitide in footprint, efficiency and stability. This is completely different from conventional approach to design photonics, which is almost always performed by brute-force or intuition-guided tuning of a few parameters of known structures, until satisfactory performance is achieved, and which almost always leads to sub-optimal designs. Apart from integrated photonics, our approach is also applicable to any other optical and quantum optical devices and systems.  

A filter which its bandpass frequency can be reconfigured is presented. Its central frequency ranges from 316 MHz to 392 MHz (22% tuning). The filter is based on a miniaturized compose right/left-handed ring resonator. The reconfiguration of its resonant frequency is implemented by shifting a short location, thus changing its effective lefthanded inductance. This is opposed to the conventional capacitance change of other reconfigurable filters. The relation short location versus central frequency is quasi-linear. The short location could be controlled by a servomotor configuration.

Tunable and reconfigurable metadevices constructed by metamaterials and metasurfaces will bring optics and photonics the highly desired on-demand property control. In this talk, I will introduce our recent work on three types of tunable and reconfigurable metadevices based on different principles for different applications. We demonstrated a continuous orbital angular momentum (OAM) transmitter comprising bilaterally symmetric gratings with an aperture to create arbitrary rational-order optical vortex beams without a theoretical limit. The vortex beam has a distinguished spiniform wavefront with phase singularities located equidistant along a line and tunes its average OAM by changing the number of singularities the beam accommodates. The approach realizes both non-integer and arbitrary rational-order generation of OAM and enables the exploration of quantum entanglement using such continuous OAMs. Phase change material GST is known for its huge optical property difference between amorphous and crystalline states. We used fs laser pulse trains to create high resolution multi-level phase changes in GST films and demonstrated reconfigurable optical devices like lens in various types, iteratively modifiable grayscale photomasks and waveguides for bidirectional transport of nanoparticles. Si based photonics with CMOS compatibility is of great interest for the potential integrations with electronics and the benefits from the scalable Si process. We used a CMOS compatible process to create an electrically and thermally tunable Si metasurface for broadband terahertz antireflection application. Perfect antireflection condition can be precisely achieved. The methodology suggests a possibility of using all-silicon platform for making atomically smooth and tunable metadevices in THz and other frequency range.

Nanoplasmonic (meta-)materials and nanophotonics have the unique ability to confine light in extremely sub-wavelength volumes and thereby strongly enhance the effective strength of electromagnetic fields. Fundamentally, such high-field enhancement can alter the local density of states experienced by a photoactive molecule to unprecedented degrees and control its exchange of energy with light. For a sufficiently strong field enhancement, one enters the strong-coupling regime, where the energy exchange between the excited states of molecules/materials and plasmons is faster than the de-coherence processes of the system. As a result, the excitonic state of the molecule becomes entangled with the photonic mode, forming hybrid excitonic-photonic states. These hybrid-states are part light, part matter and allow for characteristic Rabi oscillations of atomic excitations to be observed. Until recently, the conditions for achieving strong-coupling were most commonly met at low temperatures, where de-coherence processes are suppressed. As a major step forward, we have recently demonstrated room-temperature strong coupling of single molecules in a plasmonic nano-cavity [1] which was achieved using a host-guest chemistry technique, controlling matter at the molecular level. Concurrently, linking nano-spectroscopy of quantum dots with strong coupling allows to lithographically realise a strong-coupling set-up that couples dark plasmonic modes and quantum dots [2]. Remarkably, through strong coupling we obtain spectroscopic access to otherwise veiled states (such as the charged trion state) enabled through a strong-coupling induced speed up of the radiative dynamics of the quantum dot states [3]. Considering the key importance of strong coupling in quantum optics our findings pave the road for a wide range of ultrafast quantum optics experiments and quantum technologies at ambient conditions. Moreover, the pronounced position-dependent spectral changes may lead to new types of quantum sensors and near-field quantum imaging modalities. Finally we shall consider strong coupling in hyperbolic metamaterials. References [1] R. Chikkaraddy, B. de Nijs, F. Benz, S. J. Barrow, O. A. Sherman, E. Rosta, A. Demetriadou, P. Fox, O. Hess and J. J. Baumberg, Nature 535, 127 (2016). [2] N Kongsuwan, A Demetriadou, R. Chikkaraddy, F. Benz, V. A. Turek, U. F. Keyser, J. J. Baumberg and O. Hess, ACS Photonics 5, 186 (2017) [3] H. Gross, J. M. Hamm, T. Tuffarelli, O. Hess and B. Hecht, Science Advances 4, eaar4906 (2018).

We develop a theory for spontaneous decay of a quantum emitter (QE) situated near metal-dielectric structure supporting localized surface plasmons. If plasmon resonance is tuned close to the QE emission frequency, the emission is enhanced due to energy transfer from QE to localized plasmon mode followed by photon emission by plasmonic antenna. The emission rate is determined by intimate interplay between the plasmon coupling to radiation field and the Ohmic losses in metal. Here we develop plasmon Green function approach that includes plasmon’s interaction with radiation to obtain explicit expressions for radiative decay rate and optical polarizability of a localized plasmon mode in arbitrary plasmonic nanostructure. Within this approach, we provide consistent definition of plasmon mode volume by relating it to plasmon mode density, which characterizes the plasmon field confinement, and recover the standard cavity form of the Purcell factor, but now for plasmonic systems. We show that, for QE placed at ”hot spot” near sharp tip of a small metal nanostructure, the plasmon mode volume scales with the metal volume while being very sensitive to the proximity to the tip. Finally, we derive the enhancement factor for radiated power spectrum for any nanoplasmonic system and relate it to the Purcell factor for spontaneous decay rate. We illustrate our results by numerical example of a QE situated near gold nanorod tip.

Three-dimensional (3D) metafilms composed of periodic arrays containing single and multiple micrometer-scale vertical split ring resonators per unit cell were fabricated using membrane projection lithography. In contrast to planar and stacked planar structures such as cut wire pairs and fishnet structures, these 3D metafilms have a thickness t ~λ_d/4, allowing for classical thin film effects in the long wavelength limit. The infrared specular far-field scattering response was measured for metafilms containing one and two resonators per unit cell, and compared to numerical simulations. Excellent agreement in the frequency region below the onset of diffractive scattering was obtained. The metafilms demonstrate strong bi-anisotropic polarization dependence. Further, we show that for 3D metafilms, just as in solids, complex unit cells with multiple atoms (inclusions) per unit cell possess a richer set of excitation mechanisms. The highlight of these new coupling mechanisms is the excitation of the 3D analog to the 2D cut-wire-pair magnetic response.

We analyze and design the reflection phase characteristics in metasurface based asymmetric Fabry-Perot cavities, consisting of a metallic metasurface backed by a ground metal plane. The metamaterial cavity is modeled using transmission line theory and effective surface admittance approach, where the free space and substrate are described by equivalent transmission lines. The individual metasurface is modeled by an equivalent surface admittance connected at the junction of the transmission lines. Analysis using the above model reveals that the effective metasurface susceptence and cavity thickness govern the resonance frequency of the cavity structure. While, the effective metasurface conductance at that frequency determines whether the overall cavity resonator is in under coupled, critically coupled or over coupled regimes. Therefore by appropriately controlling the metasurface effective conductance and the cavity thickness, the metasurface cavity can be designed to have desired resonant regime. In under and critically coupled regimes, the cavity resonator exhibits a reflection phase variation limited between 90° and 270°. While in over coupled regime, reflection phase variation from 0° to 360° is exhibited. We demonstrate and verify the above results using full wave EM simulations. Using an example metasurface consisting of cross shaped resonators, we demonstrate controlling effective metasurface conductance to realize any desired reflection amplitude and phase. The presented results provide important guidelines for realizing phase control devices such as lenses or beam deflectors. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science, ICT and Future Planning) (No. 2017R1A2B3004049).

Plasmons in atomic-scale structures exhibit intrinsic quantum phenomena related to both the finite confinement that they undergo and the small number of electrons on which they are supported. Their interaction with two-level emitters is also evidencing strong quantum effects. In this talk I will discuss several salient features of plasmons in graphene and other atomic-scale materials with particular emphasis on their application to obtain unprecedented meta material properties, such as ultrafast heat transfer, strong nonlinear response, and optical quantum behavior.

The success of metal-based plasmonics for manipulating light at the nanoscale has been empowered by imaginative designs and advanced nano-fabrication. However, the fundamental optical and electronic properties of elemental metals, the prevailing plasmonic media, are difficult to alter using external stimuli. This limitation is particularly restrictive in applications that require modification of the plasmonic response at subpicosecond timescales. This handicap has prompted the search for alternative plasmonic media, with graphene emerging as one of the most capable candidates for infrared wavelengths. We visualized and elucidated the properties of non-equilibrium photo-induced plasmons in a high-mobility graphene monolayer. We activated plasmons with femtosecond optical pulses in a specimen of graphene that otherwise lacks infrared plasmonic response at equilibrium. In combination with static nano-imaging results on plasmon propagation, our infrared pump–probe nano-spectroscopy investigation reveals new aspects of carrier relaxation in heterostructures based on high-purity graphene [Ni et al. Nature Photonics 10, 244 (2016)]. We performed similar experiments for both III-V and II-VI semiconductors. I will discuss merits of graphene and of conventional semiconductors for ultra-fast plasmonic applications.

In this paper, we review our recent research efforts on “open” topological photonic structures in the presence of radiation loss or material loss/gain. We focus on three main topics: (a) The topological nature of embedded eigenstates, or bound states in the continuum, in suitably engineered dielectric metasurfaces; (b) Open topological wave-guiding structures with radiation loss, which support topologically-protected one-way leaky modes that may act as a bridge between freespace radiation and unidirectional guided waves; (c) Non-Hermitian topological waveguides with gain and loss, which exhibit exceptional points of degeneracy accompanied by anomalous topologically-protected propagation properties.

Topological photonics enable us to design novel devices that exploit counter-intuitive propagation of electromagnetic waves. The key ingredient of topological photonics is a photonic topological insulator (PTI): a periodic structure that, in its bulk form, exhibits a propagation bandgap for a range of frequencies, yet supports localized edge states when interfaced with a different photonic structure exhibiting a bandgap for the same frequency range. Several types of PTIs emulating their respective condensed matter counterparts have already been proposed and experimentally demonstrated. One of the simplest PTIs exploits the valley degree of freedom in photonic crystals with a C_3 spatial symmetry. I will describe two examples of such structures: one designed and experimentally demonstrated at microwave frequencies and another designed for the mid-IR spectral range. We show that the microwave PTI structure, which is based on a metallic waveguide with an embedded array of specially designed metal rods, exhibits the previously unknown phenomenon of valley-protected “perfect” refraction: when interfaced with another waveguide, the edge states refract from the PTI metamaterial into the waveguide without any reflection. For the nanoscale topological metamaterial, we utilize graphene surface plasmons (GSPs) that propagate through a sheet of graphene with nano-patterned landscape of chemical potential. The chemical potential landscaping is achieved using an electrically biased metagate placed in close proximity of the graphene sheet. The advantage of this scheme is that the topological properties of the GSPs can be rapidly turned on and off, thus heralding the new era of active topological photonics on a nanoscale

Advancements in micro-and nano-fabrication techniques are enabling the realization of high-performance metasurfaces which exploit the generalized Snell’s law of refraction to achieve disruptive optical functionalities. Moreover, metasurfaces can be used in conjunction with conventional optical elements to achieve massive size, weight, and power (SWaP) reduction. However, no commercial tools exist which can efficiently model optical systems whose geometrical features span many orders-of-magnitude in spatial scale. Therefore, new forward solvers must be developed in order to make such multiscale problems tractable. Furthermore, optimization of multiscale optical systems is crucially-important in order to maximize system performance and minimize SWaP. While how one achieves a specific set of desired performances with conventional optical elements is generally well understood and thoroughly presented in design textbooks, it is not always clear how to design a nanoscale optical device to best achieve a desired set of performances. Therefore, a small subset of well-understood and/or canonical structures such as split-ring resonators are typically employed to achieve the targeted functionality. However, relaxing the device’s topological constraints may lead to improved performance albeit at the expense of a larger solution space to explore. To mitigate this issue, we employ custom state-of-the art multi-objective and surrogate-assisted optimization algorithms to explore the solution space afforded by emerging manufacturing techniques in order to design metasurface topologies that achieve an arbitrary number of user-specified performance criteria.

Metasurfaces are thin-film optical devices that use nanoscale geometric designs to shape the wavefront of electromagnetic waves. In this talk, we discuss how adjoint-based inverse design can be used to produce high efficiency metasurfaces that can efficiently respond to a broad range of incident wave inputs. We discuss two classes of devices. First, we demonstrate periodic dielectric metasurfaces that can support ultra-high efficiency (>90%) anomalous refraction for nearly arbitrary combinations of incident and outgoing angles. Both polarization dependent and independent device configurations can be realized, and the achieved metrics exceed the capabilities of conventional metasurfaces and diffraction gratings based on Littrow mounting by a large margin. Second, we discuss a route towards aperiodic devices. Our general design strategy is to sub-divide the desired phase profile into wavelength-scale sections and use topology optimization to design each of these sections individually. Compared to design schemes that focus on optimizing the entire device at once, our method has clear advantages in scalability and computational efficiency. We show that with our design approach, we can theoretically and experimentally produce high efficiency, high numerical aperture lenses. All of the devices presented here utilize dielectric nanostructures that support strong near-field optical interactions with neighboring structures and non-trivial optical mode dynamics, thereby extending their functionality beyond that of discrete phase shifters.

Topological insulators are materials that behave as insulators in their interior but support boundary conducting states due the non-trivial topological order. These edge states are robust to defects and imperfections, allowing lossless energy transport along the surface. Topological insulators were first discovered in field of electronics, but recently photonic analogues of these systems were realized. Most of experimentally demonstrated photonic topological insulators to date are bulky, incompatible with current semiconductor fabrication process or operate in microwave frequency range. In this work, we show silicon photonic-crystal-based Valley-Hall topological insulator operating at telecommunication wavelengths. Light propagation along the trapezoidally-shaped path with four 120 degrees turns is demonstrated and compared with propagation along the straight line. Nearly the same transmittance values for both cases confirm robust light transport in such Valley-Hall topological photonic crystal. In the second part of this talk, we discuss the possibility of dynamic tuning of the proposed topological insulator by modulation of the refractive index of silicon. The modulation is facilitated by shining focused ultraviolet pulsed light onto silicon photonic crystal slab. Ultraviolet light illumination causes formation of electron-hole pairs, excitation of free-carriers and results into decrease of refractive index with estimated modulation on the order of 0.1. Due to the index change, spectral position of the bandgap and the edge states shift allowing their dynamic control. Proposed concept can find applications in communication field for fast all-optical switching and control over light propagation.

The unlimited control of the amplitude and phase of a light wave has been a primary goal of optics since its inception. Recently, the advent of nanostructures materials, metamaterials, and metasurfaces have led to new approaches for manipulating the flow of light. However these devices are not as agile as desired because their functionality is generally defined at the time of fabrication. To extend the capabilities of such materials, tunability and dynamic control has been explored with many successes, and one promising candidate for control is nonlinear optics. Traditionally, nonlinear approaches have been difficult to achieve due to the small induced changes to the constituent material, but recent advances in materials have identified several potential platforms which can make photons talk more efficiently. Here we will discuss and review the recent advances in nonlinear optical processes in near-zero-index materials as well as in emerging alternative plasmonic materials which are opening the door to engineer extreme nonlinear light matter interactions for dynamic metamaterials and integrated photonics.

Efficient injection of light into strongly scattering medium is the foremost condition for a wide range of sensing and imaging applications. However, turbidity leads to strong suppression of light intensity at distances greater than transport mean free path away from the source. Tailoring the incident fields via wavefront shaping technique offers an exciting approach to enhance light injection by exploiting the so-called open eigenchannels that penetrate to depths much greater than transport mean free path. The drawback of this approach is that it requires a feedback either from within or at the opposite side of the sample. Tailoring incident wavefront based either on optimization or characterization of transmission matrix of the medium is an imperfect and a time-consuming process that limits efficacy and range of applications of this approach. Recently, a much simpler strategy for enhanced light injection was proposed and experimentally demonstrated. It is based on exploiting pore imperfections in the surface of turbid medium that can readily exist in many natural and artificial materials. This technique turned out to be highly efficient in enhancing light-matter interactions, because upon injection, the light is unlikely to escape through the same pore. In this talk, we will introduce the physical mechanisms for the enhanced injection in different regimes of system parameters such as the size of the pore, transport mean free path, and absorption length. We will also discuss a possibility of combining this microstructure-based approach with wavefront shaping.

Flat optical devices based on metasurfaces composed of sub-wavelength high index dielectric structures, promise to revolutionize the field of free-space optics. I discuss our work on optical systems composed of several metasurfaces like camera lenses, tunable lens systems actuated via micro-electro-mechanics, and on-chip spectrometers.

Materials where the real part of the permittivity is near zero are known to have interesting nonlinear optical properties such as enhanced harmonic generation and large nonlinear refraction (NLR). In particular, the NLR of highly doped semiconductors such as Indium Tin Oxide and Aluminum doped Zinc Oxide is enhanced in the near-infrared spectral regions, where the real part of the permittivity crosses zero, the precise wavelength of which can be tuned by controlling the doping level.. This is also known as the epsilon near zero (ENZ) regime, although the imaginary part of the permittivity is not necessarily small at this wavelength. In order to characterize these nonlinearities, we use the Beam-Deflection (BD) method to directly characterize the temporal dynamics and polarization dependence of the nondegenerate NLR and nonlinear absorption of doped semiconductors at ENZ. BD has sensitivity to induced optical path length as small as 1/20,000 of a wavelength, which enables us to resolve NLR in the presence of large nonlinear absorption backgrounds. The BD technique also allows separation of instantaneous bound electronic nonlinearities from non-instantaneous mechanisms such as the carrier redistribution effects that dominate in ENZ materials,. We can also study the dependence on relative polarization and incidence angle of excitation and probe waves. Our method also reveals the effect of tuning the wavelength of excitation or probe waves through ENZ separately and we find that that the strong wavelength dependence of nonlinearities around the ENZ point is quite different for pump and probe waves.

The dramatic optical property change of optical phase change materials (O-PCMs) between their amorphous and crystalline states potentially allows the realization of reconfigurable photonic devices with enhanced optical functionalities and low power consumption, such as reconfigurable optical components, optical switches and routers, and photonic memories. Conventional O-PCMs exhibit considerable optical losses, limiting their optical performance as well as application space. In this talk, we present the development of a new group of O-PCMs and their implementations in novel meta-optic devices. Ge-Sb-Se-Te (GSST), obtained by partially substituting Te with Se in traditional GST alloys, feature unprecedented broadband optical transparency covering the telecommunication bands to the LWIR. A drastic refractive index change between the amorphous and crystalline states of GSST is realized and the transition is non-volatile and reversible. Optical metasurfaces consist of optically-thin, subwavelength meta-atom arrays which allow arbitrary manipulation of the wavefront of light. Capitalizing on the dramatically-enhanced optical performance of GSST, transparent and ultra-thin reconfigurable meta-optics in mid-infrared are demonstrated. In one example, GSST-based all-dielectric nano-antennae are used as the fundamental building blocks for meta-optic components. Tunable and switchable metasurface devices are developed, taking advantage of the materials phase changing properties.

Dielectric nanoantennas and metasurfaces have recently become a new trend in nanophotonics thanks to their low-loss resonant behaviour based on both electric and magnetic resonant modes [1]. Most of the recent developments in this field are related to silicon nanostructures, which demonstrate excellent resonances in the visible and near-IR parts of the spectrum. Other material platforms such as titanium dioxide (TiO2), gallium nitride (GaN), gallium arsenide (GaAs) and gallium phosphide (GaP) have also been explored to generate low-loss resonances at visible frequencies and explore linear and nonlinear optical effects. Though some of these materials (e.g. GaAs, GaN and GaP) are well-known active semiconductors famous for their emission properties, so far, only passive nanoantenna-based device functionalities have been realized. In this presentation, I will first review the recent progress of our team in the field of dielectric nanoantennas and metasurfaces demonstrating some unique passive device functionalities related to high-angle light bending and focusing. Then I will discuss active light-emitting devices based on the nanoantenna concepts. In particular, I will demonstrate the first optically-pumped laser based on semiconductor nanoantenna structures. Finally I will present active tuning of nanoantenna characteristics using external electrical signals. References: 1) A. I. Kuznetsov et al., “Optically resonant dielectric nanostructures”, Science 354, aag2472 (2016).

Metasurfaces composed of designed Mie-resonant semicondcutor nanoparticles offer unique opportunities for controlling the properties of light fields [1]. Most prominently, they can impose a spatially variant phase shift onto an incident light field, thereby providing control over its wave front with high transmittance efficiency [2]. Furthermore, due to their resonant optical response, they can enhance and manipulate light emission processes, including spontaneous emission and nonlinear frequency generation. This talk will provide an overview of our recent advances in light-emitting Mie-resonant semiconductor metasurfaces. In particular, we have studied spontaneous emission from metasurfaces integrated with various types of emitters, including semiconductor quantum dots, monolayers of transition metal dichalcogenides, and fluorescent centers in the substrate [3]. We have also investigated nonlinear frequency generation in metasurfaces composed of materials with high second-order nonlinear susceptibility, such as gallium arsenide [4]. By combining spatial mapping, spectroscopy, and Fourier imaging of the metasurfaces’ emission, we show that the directional and spectral properties of both the spontaneously emitted and the nonlinear generated light can be tailored by the metasurface design. Our results demonstrate that Mie-resonant semiconductor metasurfaces offer an interesting route towards ultra-flat sources of tailored light fields. [1] I. Staude and J. Schilling, Nature Photon. 11, 274–284 (2017). [2] K. E. Chong et al., Nano Lett. 15, 5369–5374 (2015). [3] A. Vaskin et al., ACS Photonics, Just Accepted Manuscript, DOI: 10.1021/acsphotonics.7b01375 (2018). [4] S. Liu et al., Nano Lett. 16, 5426–5432 (2016).

With recent advances in nanophotonics, metasurfaces based on nano-resonators have facilitated novel types of optical devices. In particular, the interplay between different degrees of freedom, involving polarization and spatial modes, boosted classical polarization measurements and imaging applications. However, the use of metasurfaces for measuring the quantum states of light remains largely unexplored. Conventionally, the task of quantum state tomography is realized with several bulk optical elements, which need to be reconfigured multiple times. Such setups can suffer from decoherence, and there is a fundamental and practical interest in developing integrated solutions for measurement of multi-photon quantum states. We present a new concept and the first experimental realization of all-dielectric metasurfaces with no tuneable elements for imaging-based reconstruction of the full quantum state of entangled photons. Most prominently, we implement multi-photon interferometric measurements on a sub-wavelength thin optical element, which delivers ultimate miniaturization and extremely high robustness. Specifically, we realize a highly transparent all-dielectric metasurface, which spatially splits different components of quantum-polarization states. Then, a simple one-shot measurement of correlations with polarization-insensitive on-off click detectors enables complete reconstruction of multi-photon density matrices with high precision. In our experiment, we prepare sets of polarization states and reconstruct their density matrices with a high fidelity of over 99% for single photon states and above 95% for two-photon states. Our work provides a fundamental advance in the imaging of quantum states, where multi-photon quantum interference takes place at sub-wavelength scale.

Focal plane arrays (FPAs) as a two-dimensional detector pixel matrix positioned in the focal plane of an optical system have been developed continuously for obtaining higher resolution. On the other hand, for developing highresolution, compact-size FPAs, used methods such as the miniaturization of pixel size leads to serious problems such as increased optical crosstalk. In this study, we proposed highly efficient all-dielectric metasurface lens arraybased FPA at mid-wave infrared spectrum. All-dielectric metasurface lens arrays were numerically demonstrated to achieve high optical efficiency above 85%. Moreover, our design compared with conventional and earlier metasurface-based studies has exhibited much superior optical crosstalk performance. While standing the high efficiency, optical crosstalk is decreased to low level of ≤ 2.8%. A figure-of-merit (FoM) is also defined for the device performance, which is designated as the focusing efficiency per optical crosstalk times the f-number. The results show that a FOM of approximately 90 is achieved. These proposed all-dielectric metasurface lens arrays demonstrate great potential for increasing the signal to noise ratio and sensitivity thus paving the way for compactsize and high-resolution FPAs to be deployed in various applications including thermal cameras, imaging devices and bolometers.

Spin polarized light is commonly used to sense chiral structures, which are very recurrent in biological materials and organic compounds. Therefore, manipulating optical spin has many applications in bio-sensing, stereochemistry, and DNA structural analysis. Devices that demonstrate spin dependent optical response typically require multi-layer bianaisotropic structures or biaxial crystals. Dielectric metasurfaces can provide lighter, simpler and more efficient approach. We design and implement a silicon based metasurface that transmit only one optical spin and reflect the other. Utilizing an array of highly anisotropic rectangular silicon nano-antennas with high aspect ratio. These nano-antenna induce two kinds of optical phase-shifts which are independently controlled. One of them is the phase-shift induced by electric and magnetic Mie resonances excited inside the Silicon nano-antennas which is controlled by antennas' dimensions, while the other one is the Pancharatnam-Berry phase-shift controlled by the geometric orientations of the nano-antennas. A planar array of Si nano-antennas with different dimensions (i.e, different Mie Scattering phases), and different orientations (i.e, different geometric phases) are judiciously designed to achieve the spin based performance. The Mie phase and geometric phase coherently interact to interfere constructively for one optical spin and destructively for the other, leading to the differential optical response between opposite spins. The effect is experimentally demonstrated in the visible and NIR spectral range.

The multiscale optimization of metafilm-based photonic systems may still remain computationally expensive, especially if the individual unit cell evaluations are not efficient. To circumvent this, we propose the use of effective bianisotropic tiles. In the simplest case, the homogenized metafilm can be obtained using a standard technique that approximates each cell by a tile with effective permittivity and permeability producing the same far-field response. This approach fails in the cases of symmetry breaking inside the cell - the cases common in metafilms with anisotropic unit cells fabricated on substrates. To overcome this problem, we are using bianisotropic homogenization (BAH), where a BA tensor accounts for spatial asymmetries. Here, we introduce new approaches to BAH of metafilms capable to interpolate their angular-dependent and frequency dispersive behavior. Our proposed approach is most general - by taking advantage of the fundamental theorems of linear algebra, we compare the retrieved eigenvalues with known theoretical cases. We verified our approaches with the conventional BAH techniques using normal incidence or tangential surface polarizations. The use of the optical dispersion, based on the generalized dispersive material model imposed by a set of Padé approximants allows for a flexible time-domain operation. Furthermore, accounting for the illumination intensity implies an innovative development of the BAH for non-linear metafilms. We demonstrate that, even with existing limitations, the proposed BAH technique offers extraordinary means for multiscale design of functional metadevices in frequency and time domains with useful expansions to the most general problems of non-linear optics, quantum computing, and imaging.

Metasurface optics have offered a fresh perspective into light-matter interactions, providing an unsurpassed means to engineer the wavefront of light transiting a subwavelength interface. However, strictly planar surface architectures using conventional antenna elements have performed quite inefficiently, as they contain purely electric modes and thus do not possess the magnetic modes necessary to generate the optimal Huygens-like scattering profile. And while multi-layer stacks of these 2D sheet admittances have been consistently demonstrated as the only feasible solution to-date for plasmonic-based Huygens-like metastructures, their experimental performance is often degraded by non-analytical behavior or fabrication limitations, leaving dielectric architectures as the best hope for real-world metasurface optical applications. In this work, we propose a new alternative for highly-efficient plasmonic metasurfaces: a 3D architecture which produces a Huygens-like total field and exhibits transmittances of approximately 80% at any targeted phase retardation across the full 2π phase space. The 3D unit cell consists of a cubic silicon cavity, with the interior walls of the cavity modeled as grids of voxels. The grids are initially represented in a binary fashion as a random assortment of either a metal (gold) or a dielectric (air), then iterated through a genetic algorithm routine, flipping the value of individual voxels until a maximum transmittance was reached at the desired total field phase retardation. Optimized designs for eight phase values were chosen to construct a metasurface lens. Simulation, fabrication and experimental results of both the individual element and the lens are presented.

INVITED talk

Metamaterials are artificial structures, having extraordinary abilities to manipulate electromagnetic waves far beyond the limits of natural materials. Due to the technology of fabrication, planer metamaterials are greatly restricted by pure magnetic resonant modes induced by in-plane EM waves. In this work, we numerically demonstrate vertical double-split ring resonators by finite-element method software (CST). Our samples were fabricated by metal stress-driven self-folding method, which is so called 4D printing. In the beginning, we define our patterns in two-dimensional with by electron beam lithography and deposit Ni/Au bilayer metal on silicon substrate. After etching out underlying substrate by ICP-RIE, released stress in metal will deform our 2D metal patterns into 3D metamaterials. Comparing with single-split ring resonators, DSRRs are considered with more freedom to tailor resonance frequency by changing the length of arms and the distance between them. Here we investigated the effects of symmetry breaking and resonance mode hybridization at mid-infrared wavelength using coupled DSRRs. The proposed 3D metamaterials indicate some potential applications like modulators and filters in compact optical metadevices.

Localized surface phonon-polariton (SPhP) resonances in polar semiconductor nanostructures can provide highly sub-diffractional electromagnetic fields. Furthermore, SPhP resonances offer enhanced resonant quality factors when compared to plasmon-polariton based systems. The various material platforms and nanostructure geometries achievable in polar semiconductors suggest they would be ideal platforms for tunable, long-wavelength photonics applications. Moreover, the constituent atomic basis defines the operating frequency regime for SPhP resonances; tunable from the mid-infrared to THz. Here, we investigate Raman active aspects of SPhP modes in GaN nanowire arrays that are grown via selective area molecular beam epitaxy. We detect strong Raman peaks within the Reststrahlen band of GaN that are not found in the bulk GaN Raman spectrum. These SPhP modes occur around 700 cm^-1 (~ 14.3 microns), offering a spectral region for device applications which is currently not accessible by plasmonic based systems or other SPhP enabled materials. Utilizing selective area epitaxy, we created GaN nanowire arrays with various diameters and pitches, from which the Raman spectra showed tuning of the apparent SPhP resonances. Infrared reflectance measurements were also performed with an FTIR microscope to further establish the physical properties of the resonances. Finally, computational studies of the structures’ reflectance were used to solidify our understanding of the geometry/SPhP-resonance-tuning relationship.

Integrated circuits revolutionized electronics long time ago and paved the way towards minimized microprocessors today. In analogy, plasmonics aims at the creation of highly integrated optical networks on a small chip that enable the implementation of ultra-small sensors or optical processors. In the terahertz frequency regime, we investigate the propagation of tightly bound pure surface waves on specifically designed meta-surfaces. While most presented metasurfaces on a thin film in the literature support waveguide mode propagation in the thin film substrate, whose evanescent electromagnetic fields form the surface waves at the waveguide boundaries, we observed pure surface waves that are not coupled to a waveguide mode in the thin film. Such meta-surfaces are particularly advantageous for use as surface sensors, since the surface waves carry most of their energy in the space between the surface and air and almost no energy in the thin film substrate. This is in strict contrast to most of the presented meta-surfaces in literature so far, which guide a significant part of unusable energy in the inaccessible region of the substrate. Furthermore, we study structures of Goubau lines and meta-surfaces that combine excellent spectrally broadband terahertz surface wave guiding with frequency-selective meta-surface areas and meta-surface sub-wavelength resonators on a chip. In detail, we investigate the coupling efficiency between Goubau lines and meta-surfaces.

Metamaterial based electromagnetically induced transparency (EIT) analogue have attracted as an alternative way to realize exotic EIT applications such as slow light devices and biosensors. Researches on metamaterial EIT analogues have recently focused on the realization of active system to control the EIT-like spectral properties via various external stimuli, including optical, mechanical, and thermal methods. Graphene based EIT metamaterials have been also reported through the numerical analysis as an electrically controlled active system, but there are no experimental reports in terahertz regime due to insufficient electrical mobility and conductance variation range of practical graphene sheets to realize active EIT analogues. In our previous study, we had reported a new concept of metamaterial analogue to achieve EIT-like phenomena, in which cut-wire (CW) pair and pseudo complementary cut-wire (CCW) were orthogonally combined with each other, generating EIT-like properties by funneling terahertz waves through the pseudo-CCW hole in broad reflection resonance of CW pair. Since this extraordinary transmission could be easily suppressed with resistive conductors along the pseudo-CCW structure, we designed the ion-gel gated graphene lines on the center of meta-atom structures to control the funneling of terahertz waves. Controlling the electromagnetic funneling provided switchable EIT-like spectral properties of the proposed metamaterials and we numerically confirmed that the graphene lines successfully acted as switching materials, even if the lines were formed with practically achievable graphene films. Finally, we verified that the fabricated EIT metamaterials experimentally showed 54.9% of modulation depth and 1ps of group delay change at the transmission peak in terahertz range.

Recent decades metamaterials in terahertz frequencies become very popular in the scientific society. Metamaterials is an arrangement of artificial structural elements (unit cell) that gives properties which cannot be found in nature. The effective properties of metamaterials depend on their design. This fact provides a big variety in applications of metamaterials as filters, absorbers, polarizers, etc. In this work we have studied the influence of the chiral metasurface resonator conductivity on polarizing properties of the metasurface. The unit cell of the metasurface consists of metallic gammadion crosses on both sides of the dielectric substrate. The petals of the upper resonators were partly made of different metals. Each combination of metals in design of the resonator leads to a difference in transmission of the metasurface. Due to chirality, transmission coefficients for left- and right-handed polarized waves are different. This phenomenon causes changes in the polarization ellipse of transmitted wave. The metasurface was numerically simulated using CST Microwave Studio by finite-elements method in frequency domain. The virtual experiment shows a difference in ellipticity and azimuth polarization rotation angle spectra of resonators with different conductivity. These results provide usage of materials with changeable conductivity, for example, graphene, in development of tunable polarization converter. The investigated metasurface might be used in terahertz polarimetry of cancer, teeth and skin deceases. These measurements can be performed by terahertz time-domain spectroscopy.

We recently introduced laminate metamaterials composed of a dielectric ABC layer sequence made by atomic-layer deposition. The ABC sequence breaks inversion symmetry, allowing for second-harmonic generation. Here, we discuss 3D polymeric woodpile photonic crystals conformally coated with such ABC laminate metamaterials (unpublished). In our experiments on such meta-crystals with 24 layers and 600 nm rod spacing at around 800-900 nm fundamental wavelength, we find up to 1000-fold enhancement of the second-harmonic conversion efficiency as compared to the same ABC laminate on a planar glass substrate (for 45 degrees angle of incidence with respect to the substrate and p-polarization). To clarify the underlying mechanism, we have performed extensive numerical calculations based on solving the full-wave problem for the fundamental wave, computing the second-harmonic 3D source-term distribution assuming tensor elements for the ABC laminate as found previously, and numerically computing the resulting emitted second-harmonic wave. This analysis indicates that the enhancement is consistent with guided-mode resonant excitations at the fundamental wavelength inside of the 3D meta-crystal slab, leading to a standing-wave behavior providing beneficial local-field enhancements.

Nonlinear plasmonic metasurfaces, as a subset of metamaterials, allow for active functionality not found in natural optical materials; including switching, wavelength conversion, routing, adaptive focusing. Metasurfaces in particular are compact, cascadable and easy to fabricate with established planar technologies, and therefore deserve particular attention. Here we focus on nonlinear plasmonic metasurfaces, where the nonlinear response of the metal is considered in nanostructured plasmonic metasurfaces. Past works have demonstrated that the Lorentz contribution to nonlinear plasmonic metasurfaces is typically negligible. In this work, we discuss the physical reasons why this is true and show experimental results of designs where the Lorentz contribution is maximized, with some surprising results. Finally, the prospects of these demonstrations for future metasurface applications, including high efficiency wavelength conversion, are discussed.

Optical second harmonic generation in plasmonic metasurfaces is gaining significant interest to exploit simultaneously the strong near-field enhancement in meta-atoms and the radiation control inherent to metamaterials. Here, we propose a new approach to enhance and control the second harmonic generation beyond the standard nonlinear reflection law. A localized and a propagating plasmon modes are combined in a reflective phase-gradient metasurface composed of silver nanorods on the top of a silver mirror. Due to the phase evolution over the metasurface, the reflected second harmonic beam angle differs from that of the incident beam, contrary to the second harmonic generation from standard interfaces. The second harmonic generation from the metasurface is observed using a nonlinear Fourier microscope and the underlying mechanisms are revealed using full-wave 3D simulations. Interestingly, the second harmonic light is mainly generated by the silver plate and corresponds to anomalous nonlinear reflection following a generalized nonlinear reflection law. These results reveal a new paradigm for the control of nonlinear light conversion at interfaces.

Recent advances in material science have led to the development of materials that exhibit remarkably strong light-matter coupling. We will discuss two examples. The first is related to the new wave of discoveries based on materials that have zero (real) permittivity and a low imaginary part, so that the real part of the refractive index is also close to zero. These “epsilon near zero” (ENZ) materials have been used to show nonlinear Kerr (i.e. transient and nearly instantaneous light-induced) refractive variations of the order of unity and thus several orders of magnitude higher than in any other materials. These effects have been demonstrated in very thin, submicron-scale films of transparent oxide materials such as ITO and AZO and could therefore lead to very compact devices. We have also studied four-wave-mixing processes, uncovering even larger enhancements due to the low refractive index, with the first observation of a net internal gain n the generation of a negatively refracted beam from a subwavelength film. This allows to implement, for example, the ideal conditions required for a time-reversing and perfect imaging film as originally described by Pendry. The second topic will focus on the opposite intensity regime, i.e. single photon and quantum optics with metasurfaces. We have shown that polarisation sensitive metasurfaces can be used in combination with entangled photon pairs to nonlocally control the image generated by the metasurface. We will discuss ongoing work aimed at using metasurfaces to fully characterise quantum states of light and quantify the degree of entanglement.

Second harmonic generation is one of the fundamental nonlinear optical processes that is at the heart of communication and sensing applications. Due to the underlying crystal symmetry, second harmonic generation in noble metal-nanostructures is dominated by metal/dielectric interfaces with only weak (magneto-dipole and quadrupolar) contributions coming from the bulk of the metal inclusions. Here we demonstrate that, in metamaterials, nonlinear contributions from individual plasmonic inclusions can add up together, resulting in the bulk nonlinear polarization. The resulting nonlinear response can be described in terms of volumetric second harmonic polarizability that relates unit-cell averaged nonlinear polarization to a product of unit-cell averaged fundamental fields. The amplitude of this effective nonlinear polarizability is comparable to that of common nonlinear crystals. In order to analyze nonlinear response of the plasmonic nanowire arrays we compare experimental results to numerical solutions of Maxwell equations where second harmonic response is calculated using nonlinear hydrodynamic model. Numerical solutions of Maxwell equations are also used to analyze the spatial and spectral distributions of fundamental and nonlinear fields across the composites and, in the end, to guide and validate the development of analytical description of effective second harmonic polarizability. The developed analytical description of the second harmonic generation in plasmonic composites opens new avenues for engineering of nonlinear response.

Electron tunnelling is a quantum-mechanical effect which allows the transport of electrons across a nanoscale junction between two conducting electrodes. During the tunnelling process, the broadband fluctuation in the tunnelling current can excite surface plasmons－the collective oscillations of free electron gas－in metallic nanostructures, providing an alternative way for the excitation of plasmons with advantages such as high compactness, fast response, and free of background. While the relatively low electron-to-plasmon conversion efficiency in single tunnel junctions can be improved by the design of nanostructure, high-density and large-scale tunnel junctions are highly required for the convenience of signal detection in practical applications. Here, by taking advantage of the high-density Au nanorod array, we demonstrated facile and large-scale electrical launching of surface plasmons in plasmonic nanorod metamaterials based on inelastic electron tunneling. Moreover, by harvesting the simultaneously generated hot electrons, we show that the light emission (radiative decay of plasmons) can be dynamically modulated due to the hot-electron-activated chemical reactions in the junctions.

Transparent conductive oxides (TCOs) have attracted a great deal of interest in the past few years as alternative materials for plasmonics in the near-infrared region. In contradistinction to noble metals, TCOs such as Indium Tin Oxide (ITO) display a vast tunability of their optical and electronic properties via doping and electric bias. The possibility of actively switching between a low-loss dielectric regime and a high-absorption plasmonic regime has been exploited for the design and realization of ultra-compact electro-absorption modulators, as well as for the proposal of novel multimode modulator architectures. At the heart of the applications outlined before is the electron accumulation layer that is created at the interface between a TCO layer and an insulator under appropriate electric bias. Here a rigorous study of the electromagnetic characteristics of these electron accumulation layers is presented. The unique modal properties of these systems that emerge as a consequence of the graded nature of their permittivity profiles are highlighted. The concept of Accumulation-layer Surface Plasmons is introduced and the conditions for the existence or for the suppression of surface-wave eigenmodes are analyzed.

Optical degrees of freedom shape the nature of light-matter interaction. In photonic structures, optical degrees of freedom are commonly described by electromagnetic modes. However, because modes only describe the free-oscillations of light in a structure, they properly account for light-matter interaction only if the physics in question stems solely from the structure rather than be driven by a source. This condition is often violated in nanophotonic systems, envisaged to combine nanoscale geometries and compact light sources into unified functional platforms. Therefore, in such nanostructures the source necessarily induces a tangible forced response not described by electromagnetic modes. Here we experimentally and theoretically explore a new class of optical degrees of freedom that drives the forced response of nanostructures in the presence of sources: Brewster plasmons. We experimentally observe and theoretically prove their existence in a variety of nanostructures, ranging from thin gold films to complex stratified media. We demonstrate with both far-field and near-field measurements that Brewster plasmons exhibit unique nontrivial topological properties compared to standard photonic modes and surface plasmons. These include far-field observable complex fields, exceptional points in which several Brewster plasmons coalesce, and polarization-independent flat-dispersion responses. Moreover, we show that some well-known plasmonic phenomena commonly attributed to surface plasmons actually stem from Brewster plasmon excitations, most notably the Kretschmann reflectance dip and the superlensing effect. Finally, we discuss the future role Brewster plasmons can play in propelling nanophotonics applications, such as in the field of biosensing.

In this work, a novel design of dielectric zero-index metamaterial (ZIM) filled photonic crystal defect waveguides have been proposed. The ZIM used here is basically a photonic crystal having Dirac cone at gamma point of the band structure. Existence of Dirac cone implies the linear dispersion in the vicinity of the Dirac point which is the main reason behind the zero-index behaviour. It has been shown in this article, that when such metamaterial is inserted inside a photonic crystal defect waveguide it reduces the effect of bending on transmission coefficient as compared to the conventional designs. The proposed design comprises of square arrays of Si rods in air, in which, the periodicity to wavelength ratio (a/λ) for ZIM and the surrounding photonic bandgap (PBG) structure are 0.541 and 0.35 respectively. Wavelength of operation is 1550 nm. Furthermore, as the ZIM is made up dielectric only, its free from ohmic losses.

All-optical operation holds promise as the future of computing technology, and key components will include miniaturized waveguides (WGs) and optical switches that control narrow bandwidths. Nanowires (NWs) offer an ideal platform for nanoscale WGs, but their utility has been limited by the lack of comprehensive coupling scheme and of band selectivity. Here, we introduce a NW geometric superlattice (GSL) that allows controlled, narrow-band guiding in Si NWs through direct coupling of a Mie resonance with a bound guided state (BGS). Periodic diameter modulation in a GSL creates a Mie-BGS coupled-excitation that manifests as a scattering dark state with a pronounced scattering dip in the Mie resonance envelope. The frequency of the coupled mode, tunable from the visible to near-infrared, is determined by the pitch of the GSL and exhibits a Fourier-transform limited bandwidth. Using a combined GSL-WG system, we demonstrate spectrally-selective guiding and optical switching at telecommunication wavelengths, highlighting the potential to use NW GSLs for the design of on-chip optical components.

Optical beams with a phase term proportional to the azimuthal angle possess a singularity at the beam center and carry an orbital angular momentum (OAM). The OAM beams find important applications including the trapping and rotation of microscopic objects, atom-light interactions and optical communications. The OAM beams can be generated by spiral phase plates or spatial light modulators which are bulky. Recently, planar optical components including q-plates, arrays of nano-antennas and all-dielectric metasurfaces, have attracted significant attention. However, they lack reconfigurability, which means that once the components are fabricated, their functionality cannot be changed. In this work, we experimentally demonstrate a nonlinear metasurface-based beam converter which is designed to transform a Hermite-Gaussian beam to a vortex beam with an OAM in a transmission mode. The proposed converter is built of an array of nano-cubes made of chalcogenide(As2S3) glass. Chalcogenides offer several advantages for designing all-dielectric, nonlinear metasurfaces, including high linear refractive index at near-infrared wavelengths, low losses, and relatively high third-order nonlinear coefficient. In particular, reconfigurability is enabled by the intensity-dependent refractive index or Kerr nonlinearity. Input Hermite-Gaussian beam at low intensity transmitting through the metasurface acquired an OAM, while at high intensity, remained its original intensity and phase profile. The parameters of the reconfigurable metasurface were optimized and its functionality was verified using numerical simulation and in laboratory experiments. Compared to conventional metasurfaces, their nonlinear counterparts are likely to enable a number of novel devices for all-optical switching and integrated circuits applications.

Inspired by the long carrier lifetimes (electron-electron and electron-phonon) in graphene and other 2D materials we have designed and developed computational strategies to integrate designer 2D metals, starting with Argentene and Cuphene. Cuphene and Argentene are new 2D materials that consist of a single atomic layer of silver/copper. These 2D metals have the potential to exhibit 10 times the conductance of optimally-doped graphene, and 50 times that of conventional 3D copper lines scaled to 1 nm dimensions. Achieving high carrier density and mobility in a 2D material like Cuphene or Argentene, will be transformative for atomic-scale photonics (extremely relevant in next generation architectures) and optical elements such as monolayer waveguides, sensors, and emission control layers. Realizing the potential of 2D metals, truly monolayer metals, requires an understanding of single-crystalline atomic layers of metals. Further, we identify suitable combinations of substrates and metals, with computational screening of thermodynamic stability. In addition to 3D crystalline substrates, we also investigate the feasibility of metal monolayers on existing 2D materials in order to facilitate their incorporation into van der Waals stacks. This is an example of carrier lifetime-driven approach to quantum materials where we expect time-domain properties of a monolayer to be distinct from few-layer and bulk. Taking this work further, we will discuss lifetimes and scattering in new classes of quantum materials including Weyl semimetals (WSMs). The field of topological materials with strong electron-electron interactions is well established and has been the subject of intense research over the past few decades. In parallel, the field of photonics has made tremendous progress in connecting spatio-temporal measurements of new quantum materials, including 2D plasmonics and Moir\'{e} structure localized potentials, to theoretical predictions. The study of the interplay between topological properties, quantum optics and plasmonic interactions in these materials has only very recently started to receive attention. Experimental demonstrations in Type II Dirac/Weyl semimetals, materials where electrons effectively interact as massless relativistic particles (Weyl fermions) and in 3D the conduction and valence bands touch at isolated points, have shown evidence of a viscous electronic transport regime similar to hydrodynamic electron flow observed at charge neutrality in graphene. In this regime, electron-electron scattering dominates over impurity scattering and other momentum-relaxing processes so that momentum is quasi-conserved and electron flow can be described using the formalism of hydrodynamics. This leads to a variety of surprising behaviors such as breakdown of the Wiedemann-Franz law, appearance of electron vortices, and tunable viscosity via magnetic field in a Weyl semimetal. Understanding these physical processes in materials is of both fundamental and practical importance, yet these problems pose unique theoretical and computational challenges. The simultaneous contribution of processes that occur on many time and length scales, not only make direct computational approaches very difficult, they also make comparisons with experimental observations challenging. Here we report a new microscopic model of this behavior using a combination of ab initio scattering methods and fluid dynamics techniques. Our work establishes a connection between the observed hydrodynamic phenomena in Weyl semi metals, crystal structure and symmetry and their optical properties.

Understanding the temperature evolution of optical properties in thin metals is critical for rational design of practical metal based nanophotonic components operating at high temperatures in a variety of research areas, including plasmonics and near-field radiative heat transfer. In this talk, we will present our recent experimental findings on the temperature induced deviations in the optical responses of single- and poly-crystalline metal films – gold, silver and titanium nitride thin films - at elevated temperatures upto 900 0C, in the wavelength range from 370 to 2000 nm. Our findings show that while the real part of the dielectric function changes marginally with temperature, the imaginary part varies drastically. Furthermore, the temperature dependencies were found to be strongly dependent on the film thickness and microstructure/crystallinity. We attribute the observed changes in the optical properties to predominantly three physical processes: 1) increasing electron-phonon interactions, 2) reducing free electron densities and, 3) changes in the electron effective mass. Using extensive numerical simulations we demonstrate the importance of incorporating the temperature induced deviations into numerical models for accurate multiphysics modeling of practical high temperature plasmonic components. We also provide experiment-fitted models to describe the temperature-dependent metal dielectric functions as a sum of Drude and critical point/Lorentz oscillators. These causal analytical models could enable accurate multiphysics modeling of nanophotonic and plasmonic components operating at high temperatures in both frequency and time domains.

Metamaterials have revolutionized the ways we control light and design optical materials. Researchers have been highly successful in designing sub-wavelength “meta-atoms” to achieve new optical functionalities. On the other hand, “meta-atoms” have to be made of natural materials, therefore one can further tune the responses of metamaterials by varying the constituent natural materials and achieve even broader range of optical properties. In my research lab, we conduct extensive exploration of optical materials beyond the widely used noble metals to achieve novel capabilities of metaphotonic systems. Here I would like to share some of our recent progresses on implementing new material platforms in metaphotonics: First I will present an all-solid, rewritable metacanvas using phase change materials, on which arbitrary photonic devices can be rapidly and repeatedly written and erased for real-time manipulation of light waves. Different patterns can be written and erased on the same metacanvas with a low-power laser. Dynamic manipulation of optical waves is demonstrated with the metacanvas, specifically light propagation, polarization, and reconstruction. This dynamic optical system without moving parts opens possibilities where photonic elements can be field-programmed to deliver complex, system-level functionalities. We have also demonstrated a simple bottom-up approach to create self-assembled, nanostructured metamaterials with controllable structural geometry and temperature-tunable optical response from spinodally-decomposed VO2-TiO2 epitaxial thin films. As-grown solid solution films are driven to phase separate upon post-annealing and we demonstrate the ability to deterministically create horizontally- or vertically-aligned lamellae consisting of Ti- and V-rich phases. The optical iso-frequency surface of the self-assembled nanostructures can be made to exhibit a temperature-tunable transition from elliptic to hyperbolic dispersion in the near-infrared range and thus the formation of hyperbolic metamaterial response. Lastly, I will talk about our recent efforts in achieving functional metasurfaces in the UV range by introducing new material platforms and new light-manipulation mechanisms.

The epsilon-near-zero (ENZ) spectral region in metamaterials has shown unique opportunities for enhancing light-matter interactions, particularly due to the large variation of dielectric permittivity over a small frequency range. In this work, ultrashort pulse propagation at the ENZ point is investigated using both the split-step method approach to solving Nonlinear Schrödinger’s equation (NLSE) and the one-dimensional finite-difference time-domain (FDTD) method. We use an estimation for chromatic dispersion at the ENZ for the NLSE, and low input powers for the initial pulse to minimize nonlinearities for both methods. The permittivity for the AZO/ZnO structure was varied only in the AZO layer, which we estimated using Drude model. We found that the damping frequency, γ, in the Drude model has the most influence on pulse shaping during propagation as it relates to losses within the material. Results from our 1D FDTD simulations have shown soliton-like behavior for incoming ultrashort pulses with duration 100 fs in the ENZ region up to 300 nm lengths for γ = 1x10¹¹ and 1x10¹² Hz.

Electrochromic materials demonstrating reversible color upon application of a small voltage are of interest for various optoelectronic applications. Polyaniline (PANI) is a promising material due to its high conductivity, high contrast in coloration change, low operation voltages, and long-term stability without degradation as compared to other conducting polymers. However, very slow color switching limits its use in modern applications. In this work, we explore opportunities to enhance PANI performance with effects of the modified local environment in vicinity of plasmonic metasurfaces. We study the changes in coloration as a response to applied potential in the circular voltammetry setup, simultaneously recording both electric current and changes in reflectivity, and compare the effects observed in thin PANI films deposited on gold nanomesh structures with those in films deposited on flat gold. The films deposited onto gold metasurfaces demonstrate much sharper response and faster saturation in color with the increase in voltage than those on the flat gold. Additional features are seen at small voltages (0.1 V). Based on our experimental results, the enhanced switching is likely associated with the accelerated charge transport in vicinity of the metasurface and not related to charging or hot electrons.

Epsilon-near-zero (ENZ) material possesses the dielectric permittivity near-zero in a range of optical spectrum. Real part of Drude-type dielectric permittivity goes through zero at the plasma frequency of noble metals, doped semiconductor, and conducting oxide. Another example is hyperbolic metamaterial, where transverse negative and transverse positive hyperbolic dispersions are distinguished at ENZ spectral position. In organic molecular aggregates a van der Waals coupling between ground and excited states of neighboring molecular excitons leads to resonance Davydov splitting, resulting in a coherent super dipole moment. A collection of Lorentzian oscillators in a narrow spectral range is associated with a negative real part dielectric permittivity from Kramers-Kronig dispersion relation, permitting the existence of ENZ spectral range. We study a series of optical films of donor-acceptor-donor organic pi-conjugated molecules to relate the strength of donor group with ENZ property. In order to characterize ENZ spectral response, spectroscopic ellipsometry (SE), attenuated total internal reflection (ATR) spectra, GIWAXS and NEXAFS measurements as well as linear optical spectra of reflection and absorption are employed. Also to relate linear optical spectra with ATR spectra, FDTD simulation is carried out by use of dielectric permittivity spectra obtained from SE measurement. Preliminary data show that both strength of donor group of individual organic molecules and the orientation of molecular planes as well as degree of aggregates of molecular aggregates in film are associated with ENZ response. Advantages of organic ENZ materials are found to be the simple sample preparation by spin-coating or thermal evaporation and the tunability of ENZ spectral range covering visible and near IR spectrum.

Metasurfaces with broadband optical absorption and engineered thermal emissivity have gained significant interest for applications that require precise control over optical and thermal energy pathways, for example, as selective absorbers in solar heating schemes, or as thermal emitters in thermophotovoltaics. Our laboratory has also recently explored the use of such metasurface absorbers in thermionic power convertor applications. In contrast with traditional methods of photothermalization, plasmonic metasurfaces can also resonantly promote a large population of photo-excited non-thermal ‘hot’ electrons, so that the photo-induced effective temperature of absorbers is a complex combination of separate phononic and electronic contributions, even under steady-state solar excitation. Here we show how systematic analysis of the photo-induced surface temperature of metasurface absorbers using anti-stokes raman thermometry can be used to separately analyze the extent of vibrational (phononic) heating versus the effective temperature of the electron gas, as well as provide more detailed insight into the non-equilibrium electron distribution under steady-state CW illumination. The spectral dependence of the luminescent up-conversion of anti-stokes scattered photons reflects contributions from both phonon interactions as well as direct electron scattering, and these contributions can be decoupled by analyzing the dependence on excitation wavelength, intensity, substrate temperature, and other systematic variations of structural features of the metasurface.

Nitrogen-vacancy (NV) color centers in diamond possess electronic spins that one can manipulate coherently at room temperature using RF signals. The optical spin readout plays a key role in their performance for nanoscale magnetometry and quantum information processing. We demonstrate that plasmonic nanostructures can simultaneously guide optical, microwave and low-frequency signals ensuring spin manipulation and readout in an ultracompact setting. They can also enhance detected photon rates through efficient photon collection and shortening of the fluorescence lifetime. We show that in the case of dense NV ensembles the design of the optical readout interface must emphasize photon collection efficiency over Purcell enhancement. However, in the case of single NV centers, large Purcell enhancement may significantly improve the spin readout sensitivity. Enhancement for high-fidelity readout can be provided by nanoparticle-on-metal antennas featuring ultraconfined plasmonic modes.

In this work we present a generalized coupled mode formulation dedicated to waveguides based on double-negative (DNG) as well as single-negative (SNG) metamaterials. Our approach is derived from generalized reciprocity relation, instead of polarization perturbation, which extends its applicability to lossy reciprocal media, including SNG materials. The coupled mode equations are established for various SNG/DNG multi-waveguide configurations and illustrated for two coupled systems based on SNG medium.

One of only few possibilities how to impose nonreciprocity in guiding subwavelength structures is to apply an external magnetic field (mainly in the Voigt configuration). In such a case, one-way (nonreciprocal) propagation of SP is not only possible but may bring many interesting phenomena in connection with magnetoplasmons (MSP). We have developed an efficient 2D numerical technique based on MO aperiodic rigorous coupled wave analysis – MOaRCWA. In our in-house tool, the artificial periodicity is imposed within a periodic 1D RCWA method, in the form of the complex transformation and / or uniaxial perfectly matched layers. We have combined the MOaRCWA simulations with (quasi)analytical predictions in order to study MSP performance of plasmonic nanostructures with highly-dispersive polaritonic InSb material, in the presence of external magnetic field. Here, Voigt MO effect can be used to impose nonreciprocity (one-way propagation) bringing new interesting phenomena in connection with MSP. As an example of interesting structures studied, InSb-based THz waveguides were analyzed. We have shown that the one-way bandwidth can be controlled by an external magnetic field and by the permittivity and thickness of the dielectric guiding layer. Based on such analysis of simple guiding structures, we have proceeded with modeling of several more complex magnetooptical InSb microstructures in THz range. Finally, recently, we have worked on the extension of our MOaRCWA numerical tool to fully 3D case.

The field of nanophotonics consists of interesting phenomena such as polaritons; quasi-particles that arise from lightmatter coupling. Some of the well-studied kinds of polaritons include surface plasmon polaritons (SPPs) and surface phonon polaritons (SPhPs). Surface enhanced infrared absorption (SEIRA) technique is a popular application of SPPs where the limitation of low molecular absorption cross section in IR-spectroscopy can be overcome by the introduction of SPPs in this technique. Especially in sensing applications, resonant SEIRA uses resonant metal nanoantennas in order to increase the EM near-fields on the nanometer scale, increasing light-matter interaction and thus amplifying the measured signature of very small particles. Mode coupling between metallic resonant structures and phonon polaritons supported by polar dielectric materials (e.g., h-BN, AlN, and SiC) in the IR regime with resulting field enhancement and transparency windows exhibiting Fano-like line shape will be presented. Finite element analysis is implemented to characterize the individual modes, validated against theory, in order to identify and fully characterize the resulting coupled modes in the integrated structure. Coupled-mode theory analysis reveals the anti-crossing modal coupling behavior via extinction cross-section.

Low-loss planar transmission lines are required for integrated optical or plasmonic nanocircuits. Full characterization of these lines is necessary for designing nanocircuits. This paper shows a method to calculate the attenuation and propagation constants of a patch-antenna-coupled microstrip transmission line (MTL) at 28.3THz that is suitable for measurement implementation via near-field microscopy techniques. After illumination with a Gaussian beam, a standing wave is formed by the electric near field along the MTL observed at the metal-air interface. By fitting an analytical standing wave expression to the near-field standing wave, the attenuation and propagation constants are determined. With the MTL characterized, a similar technique can be applied to determine the input impedance of an unknown load fed by the MTL. The quantification of antenna impedance and transmission line parameters provide requisite information for improving impedance matching and collection efficiency. Ansys High Frequency Structure Simulator (HFSS) is implemented to predict the computational results.

Metasurfaces are expected to realize the miniaturization of conventional refractive optics into planar structures; however, they suffer from large chromatic aberration due to the high phase dispersion of their subwavelength building blocks, limiting their real applications in imaging and displaying systems. In this paper, a high-efficient broadband achromatic metasurface (HBAM) is designed and numerically demonstrated to suppress the chromatic aberration in the continuous visible spectrum. The HBAM consists of TiO2 nanofins as the metasurface building blocks (MBBs) on a layer of glass as the substrate, providing a broadband response and high polarization conversion efficiency for circularly polarized incidences in the desired bandwidth. The phase profile of the metasurface can be separated into two parts: the wavelength -independent basic phase distribution represented by the Pancharatnam-Berry (PB) phase, depending only on the orientations of the MBBs, and the wavelength-dependent phase dispersion part. The HBAM applies resonance tuning for compensating the phase dispersion, and further eliminates the chromatic aberration by integrating the phase compensation into the PB phase manipulation. The parameters of the HBAM structures are optimized in finite difference time domain (FDTD) simulation for enhancing the efficiency and achromatic focusing performance. Using this approach, this HBAM is capable of focusing light of wavelengths covering the entire visible spectrum (from 400 nm to 700 nm) at the same focal plane with the spot sizes close to the diffraction limit. The minimum polarization conversion efficiency of most designed MBBS in such spectrum is above 20%. This design could be viable for various practical applications such as cameras and wearable optics.

The concept of supersymmetry originated in the fields of particle physics and enabled treatment for bosons and fermions on equal footing. Supersymmetry has rapidly expanded to other fields such as quantum mechanics, where it provided a way of generating pairs and families of potentials with similar properties, e.g. different reflection-less potentials; and optics where it can be used to design (de)multiplexing arrays of waveguides. In the first part of the talk, we show that for parity-time symmetric structures supersymmetric transformation is isospectral only locally (at a specific amplitude of gain and loss). Moreover we show that depending on whether a passive mode (with real propagation constant) or an active mode (with gain or loss) is removed, the parity-time symmetry of the system is preserved or broken as a function of gain/loss amplitude. In the second part of the talk we investigate the influence of supersymmetric transformation on the scattering spectrum of reflection-less structures and systems with epsilon-near-zero materials. We show that the transmission/reflection properties of a structure containing an epsilon-near-zero material can be mimicked using materials with refractive index values above unity, which are more easily accessible and introduce smaller losses to the system. The relation between these two systems is governed by supersymmetry. We conduct a quantitative performance analysis of realistic structure in which the continuous variation of the refractive index is replaced by the step-wise profile corresponding to a realistic layered structure. Our studies pave the way towards achieving remarkable properties of the epsilon-near-zero materials with the use of much more accessible materials compatible with the state-of-the-art integrated optics fabrication.

Hyperbolic metamaterials (HMMs) consisting of alternating dielectric and metal layers are playing a key role in the field of nanophotonics due to their wide range of potential applications including thermal emission engineering, photonic density states engineering, super resolution imaging and sensing. Gold is a practical plasmonic material to fabricate HMMs in the visible to near- infrared range due to its high chemical stability. As a noble metal, Au needs an adhesion promoter and recently amino-propyl-trimethoxy-silane (APTMS) was used instead of metallic adhesion layers. We showed that these latter ones, classically Ti or Cr, increase the losses of the propagating plasmons as compared with APTMS. In this work, we have successfully fabricated and characterized HMMs with various number of periods . The gold layer was 10 nm and the dielectric 12 nm thick, thus allowing for hyperbolic dispersion in the near-infrared range. We have used APTMS adhesion layer on each interface between Au and alumina to provide a better adhesion and also to obtain high quality smooth layers. The Au and alumina layers were fabricated using sputtering and atomic layer deposition techniques, respectively. The use of these techniques helps to obtain a high HMM quality, having a final roughness of 0.80 nm RMS, even after the tenth period. Using these structures, we show that the effective medium approach (EMA) may be used even for a structures with as little as 3 periods. The optical characterization shows very good agreement with the theoretically predicted ones, both rigorous approach, as well as EMA ones.

Purcell enhancement can be realized using hyperbolic metamaterials (HMMs) composed of alternating metal/dielectric multilayers of subwavelength thickness. By adjusting the filling fraction of the metal layer, this structure possesses an effective hyperbolic dispersion and can access to epsilon-near-zero (ENZ) with one of the principal components of the permittivity tensor passes through zero. The unique property theoretically yields a large local density of state (LDOS) enabling to support a high Purcell factor and enhanced spontaneous emission rate of a quantum emitter in the vicinity. However, the property of the fabricated HMM deviates from the ideal characteristics estimated by effective medium theory (EMT) due to the finite thickness of the unit cell. Therefore, the actual LDOS and Purcell factor reduce significantly. Additionally, the outcoupling of the high-k waves from HMM remains challenging. It relies on small-area nanostructure due to the incapability of large-area nanofabrication. In this paper, we experimentally and theoretically study the effect of the unit cell thickness in Ag/ITO HMMs on the enhancement of QD emission. The study on 320 nm thick HMM formed by three different unit cell thicknesses ranging from 80 to 20 nm suggested that the Purcell factor increases as the unit cell thickness decreases. We also demonstrate a large-area outcoupling method using self-assembled nanoparticle monolayer to promote the detectable QD emission in the far field. A maximum enhancement factor of ~40 was observed by incorporating the nanoparticle monolayer. This enhancement technique and large-area outcoupling will find applications in display and biosensing.

We present an extended approach towards analysis of controlled mode coupling in multi-waveguide systems based on tunable hyperbolic metamaterials (THMMs), derived from generalized reciprocity relation, suitable for lossy reciprocal anisotropic media. The expressions for overlap integrals and coupling coefficients for various waveguide systems with Type I and Type II HMM media are provided as functions of an external bias. For the first time, the application of coupled mode theory is illustrated for HMMs by example of a perturbed waveguide as well as a directional coupler, where coupling between modes and waveguides is controlled with an external voltage.

Optical elements that couple the spin/orbital angular momentum (SAM/OAM) of light have found a range of applications in classical and quantum optics. The J-plate, which refers to the variable denoting the photon’s total angular momentum (TAM), is a metasurface device that allows converting arbitrary, orthogonal input SAM states into two unique OAM states. Using independent phase control of any orthogonal basis of polarization states, the J-plate permits the conversion of arbitrary polarizations into states with arbitrary OAM. Here, we present a further development: Cascaded J-plates provide for versatile combinations of OAM states on any orthogonal basis of spin states. J-plates operating on different polarization bases and imparting independent values of OAM are designed and experimentally demonstrated to generate multiple OAM channels with different polarization states. The generated OAM states are determined by the superposition of the OAM states of the individual J-plates while the generated SAM states are determined by the polarization basis of the last J-plate. Theoretically, there are maximum of 2^n channels of OAM and n×2^n channels of TAM that can be generated by n such cascaded J-plates. It is also demonstrated that cascaded J-plates may produce complex structured light. Cascading J-plates provides a new way to control the TAM of a laser beam. These results may find application in quantum and classical communication.

Refractive and conventional optical elements such as prisms and lenses are heavy, large-sized and have limited performance in light-material interactions. Due to these severe constraints, new types of structures called metasurfaces, which are composed of subwavelength structural elements with subwavelength thicknesses, are used instead of conventional and refractive based optical elements. Metasurfaces enable unprecedented control of phase, polarization, amplitude and impedance of incident light. Thanks to these very effective features, metasurfaces have gathered remarkable attention in wavefront manipulation of photons for various applications. Earlier attempts have deployed plasmonic metasurfaces in the designs. However, the light coupled to plasmons suffers from great optical loss, which restricts high transmission efficiency, at visible wavelengths due to intrinsic heat dissipation. This problem can be overcome using all dielectric structures operating mainly in the transmission mode. Here, we numerically demonstrate vortex beam generation having donut-like intensity profile and 60% transmission efficiency. In this study, we use all dielectric metasurface that is composed of thick glass substrate and crystalline silicon which is shaped as trapezoid structure at 532 nm visible wavelength. The refractive indices of glass substrate and crystalline silicon are 1.46 and 4.15 with height of 220 nm, respectively at the designed wavelength. We have achieved 0-2π phase distribution by scaling trapezoid shaped silicon at fixed height. The interface of metasurface segmented 8 regions is filled with trapezoid shaped silicon with a π/4 phase increment in an azimuthal pattern. The obtained vortex beam can be used in various applications such as light trapping, optical tweezers, and laser beam forming.

Mechanical metamaterials represent a novel interesting class or structural composites that manifest behaviors beyond the scope of traditional materials mechanics. Those include negative elastic moduli and basic symmetries breaking, such as reciprocity of mechanical deformation. The ongoing research aims to understand relationships between a desired property, which often corresponds to an exotic domain in the overall design space, and the material’s internal structure. Some of the recent studies use multistabilities at the unit cell level to deploy a load-induced polymorphic phase transformation in an entire material sample. When properly designed, this phase transformation can lead to a contraction of the material sample in the direction of an increasing load, a manifest of the negative extensibility phenomenon. Other studies suggest that properly designed highly nonlocal periodic lattices can provide metamaterials with anomalous spectral properties leading to reversal of the Saint-Venant edge effect. In this presentation, we overview recent developments in the analysis and design of these interesting material systems, and outline their opportunities for nonlinear acoustics and structural health monitoring.

We present a numerical methods that allows to compute the field scattered by a collection of resonant elements. It is a hybrid scheme based on one part on a variant of the DDA to deal with a single scatterer, associated with a multiple scattering theory based on Calder`on projectors and the method of fictitious sources. This allows to deal efficiency with aperiodic set of scatterers not disposed arbitrary in space.

This paper is devoted to simulation of speckle field dynamics during coherent light scattering by cement surface in the process of hydration. Accent is made on cement which includes carbon nanotubes. Such inclusion promises significant increase of concrete mechanical properties qualities. Cement particles are represented by the spheres whose sizes and reflection indices are changing during the hydration process. Carbon nanotubes affect speed of hydration process for surrounding particles. It is shown that intensity fluctuations of scattered coherent radiation is suitable technique for the analysis both fast and slow processes of mineral binders hydration and forming polycrystalline structures in the process of hardening. The results of simulation are in good agreement with the experimental data.

A reconfigurable dual-passband to single-passband filter, which is based on miniaturized ring resonators, is presented. The filter is designed for 448 MHz and 668 MHz as the central passband frequencies. Simulations are used for enhancing the design. The lower passband can be eliminated by just changing the location of a short. The filter is implemented using microstrip technology on a RO3010 substrate with thickness of 1.28 mm. Measurements for the optional eliminated band are in good agreement with the expected values. The transmission is -3 dB at the central frequency for dual-passband configuration and -26 dB for single-passband configuration.

In this article, we analyze the propagation response of Fibonacci based hypercrystals composed by metallic dielectric multilayered metamaterials. The estructure can be engineered to behave as mirrors or stop band filters and absorbers for visible and infrared radiation. The propagation properties of the proposed hypercrystal can be easily tunned and drastically changed by adjusting their geometrical and optical parameters.

Enhancing electrical conductance in organic semiconductors has been a focus of intense research over last few decades. The improvement can be made by optimizing either the material or the device architecture. As it has been shown in [Orgiu et al., Nature Materials, 2015], strong coupling of organic molecules with a nanostructured plasmonic substrate can significantly improve the molecules’ electrical conductivity. In the present study, we searched for the effect of strong coupling with a Fabry-Perot cavity on the conductivity of the semiconducting Poly (3- hexylthiophene) (P3HT) polymer. Despite the observation of the strong coupling evidenced by a very large Rabi splitting of 1.0 eV, the increase of electrical conductivity with increase of the P3HT film thickness was primarily affected by an increase of the polymer’s order in thick P3HT films.

The objective of this study was to control the transmission, dispersion and, eventually, the nonlinearity of an optical fiber by intercepting and manipulating the evanescent field extending from the core to the cladding with a variety of plasmonic and metamaterial nanostructures. The access to evanescent waves is enabled by placing the core close to the flat surface of the cladding in the so-called D-shaped fiber design. In the first phase of the project, reported here, the numerical simulations of D-shaped fibers with deposited metal (Au) have been performed. We, furthermore, demonstrated that the fiber transmission can be controlled by highly concentrated rhodamine 6G molecules deposited onto the fiber’s flat surface.

In this work, we study infrared optical pump-induced changes in terahertz conductivity of multi-layer graphene on a silicon substrate using terahertz time-domain spectroscopy. Results indicate that the conductivity and optical parameters of investigated material strongly depend on a pumping intensity and the presence of FeCl₃ molecules intercalation. The findings are helpful for determining the most optically tunable material towards designing of optically controllable terahertz devices based on new two-dimensional material beyond graphene monolayer.

The work is dedicated to design of epsilon-near-zero metamaterials (ENZ) in terahertz frequency range. Two materials were investigated: the first material is the one-layered single-wire medium (SWM) and the second material consists of the planar parallel metal stripes on the layer of polyethylene terephthalate (PET). The wired medium was designed using analytical approximation of thin wire structures and verified by numerical simulations. The striped metamaterial was designed using numerical simulations software and its performance was experimentally verified by terahertz timedomain spectroscopy.

Modulating the fractal dimension of nanoporous gold is possible to tune the effective dielectric response over a wide spectral range of infrared wavelengths. The plasma edge and effective plasma frequency depend on the fractal dimension, which can be controlled by varying the preparation condition. The fractal porous metal has superior plasmonic properties compared to bulk gold. The long skin depth of porous metal on the order of 100-200 nm, enables the penetration of optical energy deep into the nanopores where molecules can be loaded, thus achieving more effective light-matter coupling. These findings may open new pathways to engineering the optical response of fractal-like or selfsimilar metamaterials.