Magic stairs, a staircase loop, is a kind of optical illusion. Such cognitive paradox is an inherent defect when two-dimensional (2D) images represent high-dimensional information. For this demand, we demonstrate an intelligent depth-sensing system prototype applicable for diverse scenes, a switchable stereo vision system that adopts a 60 × 60 achromatic meta-lens array to measure depth over a 30-cm range with the support of deep learning. This system combines a light field camera and a structured light system to adapt to all light levels. The design, application, and experimental verification of the intelligent depth-sensing meta-device are reported in this talk.

We present the main results from the Horizon 2020 project Smart-Flex focusing on the development of variable emissivity optical solar reflector foils for radiative cooling in the space environment. The OSR coating is made of two functional blocks, namely a variable emitter topped by a low emissivity solar reflector. The variable emitter is a Perfect Metamaterial Absorber designed for strong and broadband plasmonic resonance absorption in the thermal IR. It consists of a metal back-reflector, a dielectric spacer, and an array of doped Vanadium Dioxide (W:VO2) EM micro-antennas that are switched-off through metal-to-insulator transition when the temperature drops below 10°C. The solar reflector is a wideband dielectric filter of about 30 layers made of materials that are transparent across the entire spectrum from the VIS to the thermal IR. All the layers of the two blocks are deposited by standard vacuum techniques, while the array is patterned by Nano Imprint Lithography (NIL). Our experimental demonstration is fabricated onto a flexible Kapton foil with active metasurface area of 100x100 mm2, which achieves the initial requirements. The devices show a mechanically and thermally robust response which passed some critical ageing tests ageing tests including bending, thermal cycling and charged particle at doses equivalent to 2 years GEO. The presentation focuses on the various developments in materials, fabrication techniques and durability testing.

Here we extend dispersion engineering in metasurfaces to time-domain applications and demonstrate nanocoatings that temporally reshape ultrashort laser pulses. The only 600 nm thin devices provide previously unavailable transmissive anomalous group delay dispersion in the visible to near-infrared spectral region and compensate for the dispersion of up to 2 mm thick fused silica. We show how they can straightforwardly compress light pulses down to the few-cycle limit or be coated onto most conventional optics to allow their direct application in ultrafast lasers. Combining this capability with nanoscopic spatial control opens pathways to create space- and time-varying beams.

There have been intense efforts in fullwave inverse design of large-scale metasurface with potentially broad-bandwidth / multi-frequency and multi-functional performance. However, conventional simulation tools used in the design process show poor scalability in accuracy and efficiency with size (thickness and diameter). Fast direct solvers based on volume integral equation (VIE) can reach linear scalability but are very difficult to implement, especially beyond two-dimensional settings. Here, we use the Duan-Rokhlin method, a convenient VIE solver, to simulate large structures with near-optimal time complexity O(NlogN). We demonstrate its high efficiency and accuracy in large-scale simulation and inverse design process.

Alloys of sulphur, selenium and tellurium, often referred to as chalcogenide semiconductors offer a highly versatile, compositionally-controllable material platform for reconfigurable metamaterial applications. They present various high- and low-index dielectric, low-epsilon and plasmonic properties across ultra-violet (UV), visible and infrared frequencies, in addition to an ultra-fast, non-volatile, electrically-/optically-induced switching capability between phase states with markedly different electromagnetic properties. We show that by integrating chalcogenide metasurfaces on the tip and side of optical fibers as well as silicon photonic waveguide platforms a range of wavelength-tunable modulators for telecommunication networks and synaptic weights for emerging neuromorphic computing applications can be realized.

The COVID-19 pandemic has brought to light a critical need of point-of-care testing. Here, we demonstrate two metasurface-based multi-signal biosensing platforms. The first is based on the extraordinary optical transmission phenomenon of plasmonic nanohole arrays, which provides both optical and electrochemical signals. The second is based on all-dielectric TiO2 metasurfaces, which enables simultaneous triple optical signals: spectral, spatial (geometric parameter of gradient metasurfaces), and colorimetric readouts. The multi-signal readouts are cross-validated and experimentally demonstrated by refractive index sensing and biomolecular detection. Working in the visible spectrum, metasurface-based biosensors point towards ultra-compact and cost-effective solutions suitable for point-of-care testing.

This conference presentation was prepared for the Metamaterials, Metadevices, and Metasystems 2022 conference at SPIE Optics + Photonics 2022.

We address the question whether technological mishaps (inaccurate meta-atoms dimensions, shapes or positions) do really influence the response of a metasurface? Using both simulations and experiments on purposely miss-fabricated samples, we analyze the robustness of phase gradient metasurfaces. Surprisingly, we observe that a "perfect" structure, without any defects, is not the one that exhibits the best performance in terms of efficiency and angular response. Actually, we demonstrate that specific, well-controlled, defects can significantly enhance the performance of such a metasurface and explain this behavior using the resonance and near-field properties of the corresponding nanostructures.

Mechanical displacement is one of the mechanisms that can be utilized for realizing tunable optical metasurfaces. We propose nano-electromechanically tunable metasurfaces based on slot mode resonances at telecom wavelength. Utilizing high aspect ratio silicon slabs that can bend towards each other on a substrate, we achieve a robust device that can cover large areas. Upon applying 40 V, the device can achieve 4 nm spectral shift which gives rise to a 70% amplitude modulation. At the cost of a higher power consumption, the proposed device is mechanically robust and can be used in beam steering, modulation and wavefront shaping.

This conference presentation was prepared for the Metamaterials, Metadevices, and Metasystems 2022 conference at SPIE Optics + Photonics 2022.

Here we directly emulate a two-dimensional Dirac equation with a position-dependent mass term in a photonic crystal and present a new type of photonic resonators with light confinement originating in relativistic Dirac physics. Some of the modes of such resonators represent eigenmodes of a supersymmetric Hamiltonian. To test our concept, we designed, fabricated, and studied a resonator operating in the mid-IR region. Direct imaging of the structure in both real and Fourier spaces confirmed existence of the modes. The demonstrated approach offers a new route for designing photonic devices and probing supersymmetric quantum physics by using a classical photonic platform.

In the infrared nanophotonics requires the compression of the wavelength of light to length scales below the diffraction limit. This can be achieved through the formation of polaritons, with two predominant forms being the plasmon and phonon polariton. Here we will discuss how leveraging polaritonic strong coupling and extreme forms of material anisotropy, such as the low symmetry of monoclinic or triclinic crystals can be used dictate the polaritonic dispersion relation, giving rise to novel optical phenomena such as hyperbolicity and shear polaritons. The talk will highlight ultra-strong polariton coupling in the context of IR emitters, to control light propagation and in modifying thermal dissipation at ultrafast time scales.

Molecular vibrations can couple to optical cavities to create new hybrid states called polaritons. The magnitude of this coupling, measured as the vacuum Rabi splitting (Ω), correlates with modified materials processes such as photon emission, molecular energy transfer, and chemical reaction rates. In this talk, I will first discuss active control of cavity coupling strength. We demonstrate active tuning of excitonic strong coupling in a system where organic dyes strongly couple to propagating surface plasmon polaritons (SPPs) and modulation of vibrational strong coupling in a Fabry-Perot cavity coupled to an organic charge shuttling molecule. Next, I will discuss results indicating modified chemical reaction rates for an alcoholysis addition reaction forming urethane monomers. Cavity tuning was used to selectively couple to reactant, solvent, and product vibrational modes resulting in a chemical response that is cavity tuning dependent. Lastly, and in light of the search for an understanding of the mechanisms leading to modified chemical and physical properties, I will present a theoretical description of the density of polariton states relative to molecular dark states. This work will also discuss the differences between polariton states generated in microcavities, slabs, and in the bulk.

Surface polaritons are fundamentally interesting for different technological applications, but their coupling to light is generally weak due to their momentum mismatch. In this work, we show that coupling plane-waves into polaritons is a fundamentally inefficient process. We show nevertheless that a small scatterer placed at a suitable distance from a given surface can couple light completely into the surface modes supported by the surface, under illumination by an adequately modulated field. We corroborate the analytical results by performing fully-numerical simulations using realistic setups, which exhibit a very strong enhancement of the absorption into surface plasmons under the prescribed optimal conditions.

The perfect absorption of light has been traditionally achieved by layered structures whose thickness is at least λ/4n. To achieve electromagnetically thin perfect absorbers, research has focused on metallic metasurfaces which require complex nanofabrication. MoS2 is a promising material for ultra-thin perfect absorbers due to the high oscillator strength of its excitonic transitions and layered nature. However previous efforts to increase MoS2 absorption involve intricate fabrication. Our work shows enhanced absorption in monolayers, perfect absorption and exciton-polaritons in MoS2 slabs. This work simultaneously presents a simple approach to achieve perfect absorption in ultra-thin non-metallic structures and to observe cavity-free exciton-polaritons.

Layered van der Waals materials possess intriguing optical and electronic properties [1-3]. In particular, TMDCs near their excitonic resonance exhibit high index in the visible and near-infrared bands [4-6]. Moreover, hBN shows very large positive real material permittivity in the mid-infrared bands due to sharp phonon polaritonic resonance [7,8]. In this work, we explore the high refractive index photonics enabled by these materials. We examine light guiding performance in structures made of TMDCs and hBN at different wavelength ranges and find that due to their high index, it is possible to achieve efficient optical confinement within atomically thin channels. [1] Manzeli, S., Ovchinnikov, D., Pasquier, D., Yazyev, O.V. and Kis, A., 2017. 2D transition metal dichalcogenides. Nature Reviews Materials, 2(8), pp.1-15. [2] Wang, Q.H., Kalantar-Zadeh, K., Kis, A., Coleman, J.N. and Strano, M.S., 2012. Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nature nanotechnology, 7(11), pp.699-712. [3] Mak, K.F. and Shan, J., 2016. Photonics and optoelectronics of 2D semiconductor transition metal dichalcogenides. Nature Photonics, 10(4), pp.216-226. [4] Morozov, Y. V.; Kuno, M. Optical Constants and Dynamic Conductivities of Single Layer MoS2, MoSe2, and WSe2. Appl. Phys. Lett. 2015, 107, 083103. [5] A.; Hughes, H. Kramers-Kronig Analysis of the Reflectivity Spectra of 2H-MoS2, 2H-MoSe2 and 2H-MoTe2. J. Phys. C: Solid State Phys. 1979, 12, 881. [6] R.; Baranov, D. G.; Munkhbat, B.; Cuadra, J.; Käll, M.; Shegai, T. Transition Metal Dichalcogenide Nanodisks as High-Index Dielectric Mie Nanoresonators. Nat. Nanotechnol. 2019, 14, 679-683. [7] Tamagnone M, Ambrosio A, Chaudhary K, et al. Ultra-confined mid-infrared resonant phonon polaritons in van der Waals nanostructures[J]. Science advances, 2018, 4(6): eaat7189. [8] A J, Dai S, Vurgaftman I, et al. Ultralow-loss polaritons in isotopically pure boron nitride[J]. Nature materials, 2018, 17(2): 134-139.

In this summary, we report an experimental demonstration of plasma frequency tuning of a multilayer-based ENZ metafilm. The demonstrated ENZ metafilm consists of alternating layers of ITO and SiO2. The optical properties, such as the effective plasma frequency and damping coefficients, of the demonstrated metafilm were controlled by changing the volume fraction of the metal layer. The measured effective permittivity values from an ellipsometry analysis show good agreement with the calculated results using a simple Maxwell-Garnett effective medium theory.

Dynamic THz modulations with adaptive metamaterials have been demonstrated. By utilizing the significant volume shrinkage during the phase-transition of phase-transition materials, a specially designed chiral structure performs drastically structural deformation. The rapid geometrical change modulating the polarization of the incident THz wave is fully designable, continuously tunable, and reversible. Large azimuth rotation angle and ellipticity angle changes have been observed. The metamaterials are actuated by either global heating or Joule heating, providing an efficient way to modulate THz waves with high modulation depth. This brings us a prosperous future of broader THz applications such as radar, communications, and imaging systems.

Tunable metasurfaces have been steadily investigated to miniaturize optical devices by altering active module that is equipped with mechanical actuators. However, almost all of recent tunable metasurfaces focused on switching functionality between two distinct states or more. Here, we proposed spin-selective metasurfaces, which perfectly absorb certain circularly polarized light, while reflecting counter circularly polarized light with desired phases. The metasurfaces consist of split ring resonators on metal-dielectric metal structures to enlarge their plasmonic responses, approaching near-zero reflection of LCP, and 14% reflection of RCP at the wavelength of 635 nm. With the metasurface, we implanted it on electrically tunable liquid crystals for intensity tuning of encoded holograms. 23-steps of hologram intensities are experimentally demonstrated with liquid crystal integrated split ring resonators. Considering that previous spin-selective metasurfaces are designed with a complex fabrication process, our liquid crystal integrated split ring resonators will be a dominant option for altering active and bulky optical components.

We present a metasurface design that works as a helicity preserving mirror. To engineer the metasurface, we employed an inversion scheme based on approximation theory, combining a forward solver with a heuristic optimization method. The design was tested through numerical simulations and, employing a Mueller matrix formalism, we show that at the design wavelength the proposed structure reflects both left and right circular polarizations without changing their helicity.

In contrast to the conventional Gaussian beams or plane waves, the interaction of structured lights with matter and meta-matter can pave the way toward novel optical effects such as exciting higher order multipolar moments or enabling nonradiating anapole states. In this work, Laguerre-Gaussian (LG) beams with various orbital angular momentum are used to excite and control the spectral location of the magnetic quadrupole modes within the all-dielectric meta-atoms. To experimentally validate this phenomenon, silicon-based meta-atoms are fabricated and illuminated by various LG beams. The experimental results are in good agreement with the theoretical predictions.

Monolayer transition metal dichalcogenides (TMDs) with an atomically thin nature are promising materials for electronics and photonics, especially at highly scaled lateral dimensions. However, the characteristically low total absorption of photons in the monolayer TMD has become a challenge in the access to and realization of monolayer TMD-based high-performance optoelectronic functionalities and devices. Here, we report gate-tunable plasmonic phototransistors (photoFETs) that consist of monolayer molybdenum disulfide (MoS2) photoFETs integrated with the two-dimensional plasmonic crystals. The plasmonic photoFET has an ultrahigh photoresponsivity achieving a 7.2-fold enhancement in the photocurrent compared to pristine 2D material-based photoFETs. The achievement is based on the breakthrough of the realization and characterization of a gate-tunable atomistically-thin phototransistor device consisting of a monolayer MoS2 photoFET integrated with a two-dimensional (2D) plasmonic crystal to enhance the light absorption rate, photo-carrier generation rate, photo-gating, and hot-carrier transfer rate. Moreover, this talk will describe different design of plasmonic phototransistors that is extensible to other types of 2D materials for ultrathin high-performance optoelectronic devices at highly scaled dimensions. Finally, we will discuss prospects for next-generation ultra-compact optoelectronic devices in the trans-Moore era.

We present the first demonstration of coherent random lasing in optically thin quasi-2D lead-halide perovskite. The intensity fluctuations of laser emission exhibited a large-tailed Lévy distribution, establishing random lasing nature of the observed stimulated emissions. Operation in the diffusive regime was indicated by the relatively large observed photon mean free path (4.5 μm) compared to the lasing wavelength (~550 nm). The coherent spectral modes were found to extend through the entire pump-laser volume. Such lasing modes are sensitive to the local position of the pump spot, suggesting the potential application in sensing subtle variation of local environment. The simple solution processing of quasi-2D perovskites makes them practical for augmenting a variety of meta-devices with non-Hermitian properties to make advanced nanolaser designs with controllable figures of merit.

We show that the recombination rate from excitons in Lead Halide Perovskite (LHP) polycrystalline thin films is suppressed, rather than enhanced, when they are placed on hyperbolic metamaterials and a plasmonic substrate by 30% and 50%, respectively. We reveal that these LHP films enjoy a dominant in-plane transition dipole, which is responsible for the decrease in the recombination rate. In triple cation LHPs we observe a 10-fold decrease in the recombination rate, comparable to recombination rate suppression obtained by Photonic Crystal cavities. By controlling the recombination rate of LHPs, we demonstrate a 250% increase in photoresponsivity of LHP-based photodetectors.

We analyze the impact of angular selectivity on the radiative cooling performance of thermal emitters. We show that combining angular and spectral selectivity enables realizing deep subfreezing temperatures. While angularly selective thermal emitters are robust to environmental effects, they require management of non-radiative heat transfer processes. We introduce a general scheme to realize angularly and spectrally selective absorption/emission using a thin film stack consisting with a total thickness of ~ 9 μm; an order of magnitude less than previously proposed angular selective thermal emitters. We finally discuss the prospects of angular selectivity based on conic mirrors.

In this work, we study the enhanced nonlinear light-matter interaction in hybrid Weyl-semimetal-plasmonic structure by depositing silver nanocubes on a TaAs surface with a silicon nitride spacer thus leveraging the unique ability of plasmonics to squeeze electromagnetic field within a small volume far below the diffraction limit. Pumping the fabricated hybrid structure utilizing a 800-nm fundamental wavelength pulse at 100 fs we achieve second harmonic generation (SHG) at 400 nm with a 300 percent enhancement of SHG signal while the estimated actual plasmonic SHG enhancement is 90-fold.

We discuss traditional second and third harmonic generation from metallic mirrors, gratings, and novel nonlinear optical properties of metal/vacuum interfaces. The boundary is a spillout region composed of free electrons having exponentially decreasing density that vanishes within an atomic diameter. Classical electrodynamics cannot discern field variations either between atoms or over the distance of a decaying wave function. The boundary consists of a single spatial discretization step, a function of unknown average density. This layer acts like an epsilon-near-zero material that enhances the local field by more than three orders of magnitude, alongside a dramatic decrease of nonlinear thresholds.

We study the nonlinear optical up-conversion of doubly resonant GaP metasurfaces based on bound state in the continuum (BIC) resonances driven by leaky-waveguide modes. The fabricated metasurface is simultaneously illuminated by two excitation beams, pump and signals beams, exciting transverse-electric and -magnetic waveguide modes. The nonlinear mixing of these modes results in generation of strong sum-frequency emission in the visible spectrum. We observe a non-trivial dependence of the sum-frequency emission with the polarization of the pump beam, explained by the excitation of multipoles at the SFG wavelength. A normalized conversion efficiency of 3.5 × 10-5 [W-1] is measured in the forward direction.

We experimentally demonstrate near-infrared to ultraviolet (UV) wavelength conversion in an As2S3-based metasurface that is strongly enhanced by the excitation of a quasi-bound states in the continuum resonance near 1064 nm. We report the all-optical, ultrafast tunability of the QBIC resonance and the third harmonic induced by Kerr effects. These results give rise to a range of novel applications for UV sensors and lasers.

Circularly polarized optical excitation of plasmonic nanostructures causes coherent circulating motion of their electrons, which in turn, gives rise to strong optically induced magnetization— a phenomenon known as the inverse Faraday effect (IFE). In this study we report how the IFE also significantly decreases plasmon damping. By modulating the optical polarization state incident on achiral plasmonic nanostructures from linear to circular, we observe reversible increases of reflectance by 78% as well as simultaneous increases of optical field concentration by 35.7% under 10^9 W/m2 continuous wave (CW) optical excitation. Our results outline strategies for actively modulating intrinsic losses in the metal, and thereby, the optical mode quality and field concentration via opto-magnetic effects encoded in the polarization state of incident light.

we exploit the resonance inside the slab to boost the second-harmonic generation from the lithium niobate half-etching-slab metasurface system, which hosts two kinds of BIC states formed by TE and TM odd modes. We reveal the mechanisms of the formation of the two BIC states and three main processes that influence the conversion efficiency from the pump light into the SH radiation. This approach of constructing boosted second-harmonic generation can be applied in any low-index nonlinear materials, which can expand a range of the applications, such as nonlinear imaging, quantum light source, and high-resolution sensing.

We introduce a radically different approach to material engineering relying on the self-interaction that electrons in a two-dimensional material experience when an electrically neutral structure is placed in its vicinity. Based on rigorous theoretical methods, we predict strong modifications in the optical, electrical, and thermal properties of a monolayer semiconductor as a disruptive approach to tailor the properties of atomic layers for application in nanodevices, which can also be applied to other types of materials to control their properties with great flexibility.

Machine learning is widely used for optimization or classification tasks. Unfortunately, extensive labeled datasets are often required for training machine learning models. In this work we demonstrate that incorporating physics-driven constraints into machine learning algorithms can dramatically improve both accuracy and extendibility of resulting models, simultaneously reducing the size of the required training set and enabling training on unlabeled data. Physics-informed machine learning is illustrated on example of predicting optical modes supported by periodic layered composites. The approach can be readily utilized for analysis of electromagnetic modes in composites with 2D periodic geometry or in complex waveguiding structures.

We demonstrate a new methodology of modelling phenomena and devices of quantum photonics on a quantum computer by replicating the evolution of a single-photon state on a transmon, superconducting charge device of IBM quantum computer.

Waveguides with extremely anisotropic metamaterial cores support propagating modes even when their cross section is deeply subwavelength. A funnel-shaped structure with microscale base, nanoscale tip, and hyperbolic core can therefore act as an efficient optical link between the diffraction-limited and subwavelength domains. In this work we analyze the potential applications of this platform for mid-IR near-field scanning optical microscopy. We present the relationship between the shape and composition of the funnels and the resulting compression of light, characterized by both the intensity and the spread of electromagnetic field in the vicinity of the funnel tip.

The ability to tailor an ultrafast pulse at will has far-reaching impacts on numerous fields in modern science and technology. Here, we demonstrate simultaneous and independent control of the temporal and spatial degrees of freedom of an ultrabroad bandwidth, near-infrared femtosecond pulse using a single-layer dielectric metasurface. Exotic femtosecond pulses exhibiting a rich set of time-evolving instantaneous polarization states and structured wavefronts are both theoretically and experimentally demonstrated. Such an approach opens new possibilities in studying fundamental light-matter interactions at the femtosecond timescale and has the potential to enable applications in chiral spectroscopy, coherent control, and nonlinear optics.

In this talk we discuss our theoretical and experimental studies of a family of null solutions to Helmholtz equation in 3D free space - optical vortices, or zero lines of complex amplitude in a propagating light field. When multiple light beams overlap in three-dimensional space, their interference produces tangled lines of complete darkness – optical vortices that can form closed loops – links or knots. We design all-dielectric optical metasurfaces – nanostructures enabling unprecedented control over the amplitude, polarization and phase of optical fields, for generation of optical knots, and study their stability, evolution, and third-harmonic generation using knots as a fundamental wave. Knotted electromagnetic fields may find applications in three-dimensional optical manipulations or as potential candidates for new information carriers in classical and quantum communication systems.

We introduce conformal grayscale metamaterials as a new class of volumetric electromagnetic media capable of supporting highly multiplexed responses and arbitrary, curvilinear form factors. The grayscale dielectric landscape is advantageous because it offers an expanded design space that supports many exceptionally high performing device designs, many which are accessible using adjoint variables optimization. We experimentally fabricate microwave metamaterials using additive manufacturing and demonstrate structures with extreme dispersion profiles, an airfoil-shaped beam steering device, and a conformal carpet cloak. We anticipate that conformal volumetric metasurfaces will lead to new classes of compact and multi-functional imaging, sensing, and communications systems.

Present day space exploration is hindered by the limitation of propulsion systems. Light sailing has a potential to offer fast and low cost travel across the solar system and beyond. Here we discuss principles of extreme solar and laser sailing. We show that with the availability of proper materials and systems change in space exploration paradigm is possible. We then show that metamaterials are particularly studied for the design of solar and laser sails. We discuss several promising photonic designs and detail our ongoing experimental effort. Finally, we provide an outlook for future of lightsailing for space exploration.

Laser-driven light sails need to withstand very high intensities of incident light, and therefore must comprise low-loss materials that remain low loss with increasing temperatures. We will describe our measurements of temperature-dependent optical properties of materials (oxides, nitrides, semiconductors) for the development of metasurfaces for laser-driven light sails. We use oscillator-based models to fit ellipsometry data at different temperatures in the wavelength region where a precise measurement can be made, and revise these models with datapoints in the low-absorption region measured using photo-thermal common-path interferometry. We also demonstrate how metasurface performance is affected by the temperature-dependent properties of constituent materials.

Rectification is a nonlinear optical effect that arises using metal–insulator–metal (MIM) rectifying diodes. These devices can be tuned to exhibit a memory (hysteresis) of a previous state in the electrical behavior like a memristor that conduct through energy barriers. Voltage- or field-reconfigurable MIM rectifiers, ‘memrectifiers’, are combined with magnetic materials to enable rectifiers to ‘remember’ their state with a low-energy abrupt switch to change conduction state. We demonstrate early stage devices where minimal power will be needed to magnetically reconfigure the electrical behavior of the rectifier, and the permanent magnetic moment in the Co layer will preserve the memrectifier’s state without power draw. The MIM diode is comprised of Nb-(NbOx)–Co, building on Nb-NbOx-Au MIM diodes. The niobium oxide dielectric layer has a high dielectric constant; we are investigating the stoichiometry. NbOx was deposited with thicknesses 5–50 nm. Diode electrical characteristics were investigated using current density vs. voltage (J-V) measurements, and x-ray spectroscopy, FTIR, and ellipsometry probed composition of the layers. The top Co–Au layer was micro-patterned in a range of square sizes. J–V curves characteristics determined barrier heights. Al bottom metal layers were also deposited.

Significant miniaturization of high-Q supercavity systems with planar technology requires novel coupling structures that excite the desired set of resonant modes. We review the physics of bound states in the continuum (BICs) of open, high-index dielectric resonators, excited by new complex sources that enable a controlled interference in the system. We show that, in avoided-crossing regimes associated with quasi-BICs, the controlled retardation of inducing currents can bring up the Q-factors beyond the state-of-the-art levels in optimized, fully-symmetric systems. We illustrate our theory with proof-of-concept experiments in microwaves, comparing high-index dielectric resonators excited by microstrip structures with different mode complexity.

Photonic Time Crystals (PTCs) are dielectric media whose refractive index is modulated periodically in time at time scales of an optical cycle. These systems conserve momentum but not energy, and are characterized by momentum bands and bandgaps, where the amplitudes of their eigenmodes can increase (or decrease) exponentially. But more interesting than all the rest - I will discuss the classical and quantum features of light emission in PTCs from various radiation sources, such as free electrons, classical dipoles, quantum fluctuations, and the emission by atoms. The latter opens new avenues for making widely tunable lasers that extract energy from the temporal modulation of the medium.

We report the experimental observation of second-order corner skin modes in a two-dimensional non-Hermitian electric circuit network describable with the Su-Schrieffer-Heeger model in one spatial direction and the Hatano-Nelson model in the orthogonal direction. A circuit Laplacian is reconstructed by a series of current-voltage measurements, from which complex admittance spectra and corresponding voltage distributions are obtained. In a L×L square lattice, the number of corner skin modes is found to be 2L, implying that the observed corner skin modes originate from a non-Hermitian topology.

Nonlocal metasurfaces—metasurfaces with an engineered momentum-dependent (spatially-dispersive) response—represent an emerging direction in the field of flat optics, with applications ranging from optical computing to ultra-compact imaging systems. In this talk, we present our recent efforts on this exciting topic at the frontier of the field of metasurfaces. We broadly discuss how nonlocal designs afford new degrees of freedom that enable functionalities and performance metrics unattainable using local metasurfaces and conventional optics. As a relevant example, we present our recent work on nonlocal metasurfaces for space compression ("spaceplates"), with a focus on their bandwidth performance, physical bounds, and optimal designs.

Tunable nanostructures and nanocavities can be used to manipulate dynamically an incoming wavefront at sub-wavelength scales. Realizing such systems is, however, challenging both from the design aspects, particularly if one looks for practical configurations with single-pixel control. In this talk, we will show how interfacing liquid crystals with different nanocavities can be used for this means. In particular, we will present configurations employing dielectric nanoantennas for dynamic beam steering with single-pixel control and extended field of view, as well as the potential of Fabry-Perot nanocavities to extend these devices to multi-chromatic (RGB) operation.

Surface patterning of azobenzene-containing thin films using digital holography microscopy with built-in laser interference setup leads a way to rapid fabrication of diffractive optical elements. The light-induced mass-migration of photochromic materials enables the formation of topographies in a one-step photolithographic process, which is a challenge to existing microfabrication methods. A method for in-situ metrology of surface modifications enables the study and control of the inscribed patterns. As example, we present high-resolution and large-area optical elements that were produced by forming the topographies pixel by pixel according to a digital twin.

Previous approaches for achieving asymmetric transmission (AT) of light rely on nonreciprocal systems, which are limited to having external bias or high input powers. We show AT from a metasurface comprising dielectric nanogratings on two sides of a silicon nitride membrane. The proposed metagrating provides wideband AT over multiple operational windows, and we demonstrate that such metasurfaces can be realized using both noble plasmonic metals and chalcogenide phase change materials to achieve reconfigurable AT. The proposed structure has various applications, from enhancing efficiencies in photovoltaic systems to tunable isolators and electromagnetic shielding.

This conference presentation was prepared for the Metamaterials, Metadevices, and Metasystems 2022 conference at SPIE Optics + Photonics 2022.

Electro optic modulators being key for many signal processing systems must adhere to requirements given by both electrical and optical constrains. Distinguishing between charge driven (CD) and field driven (FD) designs, we ask whether fundamental performance benefits can be claimed of modulators based on emerging electro-optic materials. Following primary metrics, we compare the performance of emerging electro-optic and electro-absorption modulators such as graphene, transparent conductive oxides, and Si, based on charge injection with that of the ‘legacy’ FD modulators, such as those based on lithium niobate and quantum confined Stark effect. We show that for rather fundamental reasons, FD modulators always outperform CD ones in the conventional wavelength scale waveguides. However, for waveguide featuring a sub-wavelength optical mode, such as those assisted by plasmonics, the emerging CD devices are indeed highly competitive.

Experimental and theoretical studies of broadband metamaterial absorbers and their application for infrared spectroscopic gas molecules sensing are presented. We design a metamaterial absorber consisting of an array of conical helix gold structures and fabricated it by the use of electron beam lithography and dry etching techniques. Broadband absorptive properties of the proposed metamaterial absorber was confirmed both numerically and experimentally. In order to realize higher sensitivity on IR spectroscopy, three-dimensional vertical-oriented metal-insulator-metal (v-MIM) metamaterial absorber is also proposed. By using v-MIM metamaterial absorber, we successfully detected 20 ppm concentration of carbon dioxide and butane molecules with negligible background noise.

Halide perovskites are an excellent platform for the realization of dielectric metasurfaces thanks to their high refractive index, large area solution processability, and compositional tunability of bandgap, luminescence and transport parameters [1]. Following the first demonstration of an all-dielectric perovskite metamaterial [2], there have been several demonstrations of passive [3] and light-emitting [4,5] metasurfaces with complex functionalities. In addition, halide perovskites offer opportunities for the realization of optoelectronic devices, including photovoltaic cells, photodetectors, light-emitting diodes and transistors, opening the way for direct integration of functional metasurfaces into electrically driven metadevices. Here we will present the recent realization of perovskite light-emitting metatransistors with unprecedented control of electroluminescence parameters at the subwavelength regime: spectrum, polarization, luminosity, wavefront and directionality. We will also show that exciton-polariton electroluminescence is achievable in this platform, enabling the development of electrically driven polariton metadevices operating in the strong coupling regime. References: 1. G. Adamo, J. Tian, H.N.S. Krishnamoorthy, D. Cortecchia, G. Long, C. Soci, C., “Perovskite metamaterials and metasurfaces,” in Halide Perovskites for Photonics, edited by A. Vinattieri and G. Giorgi (AIP Publishing, Melville, New York, 2021), pp. 10-1–10-28. 2. B. Gholipour, G. Adamo, D. Cortecchia, H.N.S. Krishnamoorthy, M. D. Birowosuto, N. I. Zheludev, C. Soci, “Organometallic perovskite metasurfaces,” Adv. Mater. 29, 1604268 (2017). 3. G. Long, G. Adamo, J. Tian, M. Klein, H.N.S. Krishnamoorthy, E. Feltri, H. Wang, C. Soci, “Perovskite metasurfaces with large superstructural chirality”, Nature Communications 13, 1551 (2022). 4. J. Tian, G. Adamo, H. Liu, M. Klein, S. Han, H. Liu, C. Soci, “Optical Rashba effect in a light‐emitting perovskite metasurface,” Adv. Mater., 2109157 (2022). 5. J. Tian, G. Adamo, H. Liu, M. Wu, M. Klein, J. Deng, N. S. S. Ang, R. Paniagua-Domínguez, H. Liu, A. I. Kuznetsov, C. Soci, “Phase-change perovskite tunable microlaser,” arXiv:2107.05239, (2021).

We present an ultra-broadband, high-performance and fabrication-tolerant Y–junction enhanced with subwavelength grating metamaterials. Exhaustive measurements over a 1420–1680 nm bandwidth show fundamental mode excess loss under 0.3 dB considering a minimum-feature-size of 50 nm and below 0.5 dB for a 100 nm resolution scenario. Subwavelength Y–junctions with artificially induced errors of ±10 nm further demonstrate the fabrication-tolerant response of our design. Moreover, our proposed splitter exhibits first-order transverse electric mode excess loss lower than 1.5 dB within a 170 nm bandwidth (1420–1590 nm) in both 50 nm and 100 nm resolution scenarios.

In this presentation, a new concept of an achromatic metafiber that focuses light coming out from the fiber facet over wavelengths of interest will be introduced. The achromatic metafiber consists of achromatic metalens microprinted on a telecommunication single-mode fiber. The 3D meta-atoms of which height is a geometric degree of freedom provide large variation of group delay, capable of realizing large time-bandwidth product. As a demonstration, direct scanning confocal imaging using the metafiber is facilitated over entire telecommunication wavelengths. Our compact achromatic metafiber may envisage many photonics applications such as hyperspectral imaging, in vivo deep-tissue imaging, and wavelength-multiplexed fiber communications.

Optical metasurfaces offer unique opportunities for tailoring the interaction of light with nanoscale matter. Due to their flat nature, their integration with two-dimensional materials consisting of only a single molecular layer is particularly interesting. This talk reviews our recent and ongoing activities in hybridizing optical metasurfaces composed of designed nanoresonators nanoscale waveguides with different types of two-dimensional materials.

Tunable optical devices powered by metasurfaces provide a new path for functional planar optics. Lenses with tunable focal lengths could play a key role in various fields with applications in imaging, displays, and augmented and virtual reality devices. Here, we present a method for computationally designing an RGB-achromatic bifocal metalens and experimentally realize it through a scalable one-step nanoimprinting technique using a TiO2 nanoparticle embedded resin combined with an electrically tunable liquid crystal cell.

We theoretically and experimentally demonstrate a novel design of broadband double-layer achromatic metalens working for wavelengths ranging from 400-700 nm. By exploiting a dielectric staircase layer, we significantly extended the range of attainable group delay with a library of nanoantennas with moderate shape complexity. Our experiment results show that our metalens has a Strehl ratio of >80%, and the focal length variation is less than 3% over the entire visible band, exhibiting excellent broadband achromatic focusing. Our work could shed light on overcoming the size and bandwidth limits of achromatic metalenses and facilitate applications such as microscopy and spectral imaging.

While topological properties of electromagnetic waves are commonly associated with photonic (i.e. periodic) structures, it has been recently demonstrated that even continuous media such as magnetized plasmas can support topologically protected one-way edge states. We demonstrate that, under some circumstances, such waves can be damped even without any dissipation, i.e. for a purely Hermitian permittivity tensor. Such damping is attributed to localized resonances in the inhomogeneous transition region between topologically trivial and nontrivial domains. Despite such damping, backscattering remains suppressed owing to topological protection. More complex magnetic field geometries, such as helically-winding field lines, will also be discussed.

We report applications of monolayer and multilayer Van der Waals (vdW) materials, transition metal dichalcogenides (TMDCs) and hexagonal boron nitride (hBN), for enhanced and enriched light-matter interactions in topological metasurfaces. First, we show that one can selectively couple spin-polarized edge modes to the valley-polarized excitons in monolayer TMDCs. The resultant exciton-polaritons allow a directional transfer of the valley degree of freedom and spin of excitons. Second, we demonstrate that a similar approach can be applied to phonons in mid-infrared domain, and the transverse vibrations in an hBN film are directionally guided in a resilient manner, avoiding backscattering due to defects.

Many emerging technologies in adaptive optics, energy conversion, and storage demand powerful design tools for nanophotonics. Phase, symmetry, and topology arising from quantum many-body effects are such powerful tools that bring a paradigm shift to nanophotonics. Here, we present two classes of nanophotonic devices based on quantum many-body systems. In the first case, non-Hermitian nanophotonic devices with non-trivial topology enable efficient solid-state energy conversion and thermal imaging. In the latter, light-matter interaction in a quantum material enables ultra-low power nonlinear optical devices. These approaches demonstrate how the new powerful design tools break many inherent trade-offs and pave the way for extreme nanophotonics.

We demonstrate the emergence of a new class of guided modes in photonic metasurfaces with a gradient change of mass term across boundary between topological and trivial domains. These modes possess spin degeneracy and exhibit splitting in their quality factors due to spin-dependent radiative losses. In experiment we probe our spin-full guided modes by selectively exciting them with circularly polarized light of opposite handedness and we confirm significant difference in the radiative losses for selected k-vectors. Metasurfaces supporting these modes can be used for spin-full waveguiding and can find applications in integrated photonics due to the possibility of spin multiplexing.

In this work we propose a method to achieve improved topological edge sates by engineering an optimal profile of the transition at the boundary between topological and trivial domains. From experiment and simulation results we confirmed that the quality factor of edge state for smooth transition profile can be increased by more than an order compared to the edge state of a conventional step profile. At the same time the modes retained their topological resilience, which, when combined with the reduced radiative leakage, enables robust photonic transport over long distances even above the light line.

In nanophotonics, small mode volume and high-quality factor (Q-factor) resonances fundamentally scales with high refractive index values. Topological insulators (TI) are a new class of materials possessing narrow bulk bandgap and gapless Dirac surface states, and exhibit ultra high permittivity values. In this work, I will discuss our latest results on Bi2Te3 and Bi2Se3 TI meta-optics. Using polarized far-field and near field Nanospectroscopy we reveal that Bi2Se3 nanobeams exhibit mid-infrared resonant modes with 2pi phase shifts across the resonance. We further demonstrate that Bi2Te3 metasurfaces exhibit deep subwavelength resonant modes utilizing their record high index value peaking at n~11.

We present a new class of structured optical media - composite materials that support guided modes which originate from the recently discovered electromagnetic "ghost" waves. Such "ghost crystals" show a broad range of novel optical phenomena - from the exceptional points to the linear-optical equivalent of the exchange interaction in correlated fermionic systems. In particular, the formation of the propagating waves in optical "ghost crystals" is related to the spin interaction in the Ising model, offering full control on the exchange dynamics and leading to a realization of the ferromagnetic – antiferromagnetic phase transition in a linear-optical system.

In this work we implement theoretical proposal of Smolyaninov and Narimanov (Phys. Rev. Lett. 105, 067402 (2010)) who demonstrated that extraordinary light waves in hyperbolic metamaterials may exhibit “two times” physics behavior. This behavior is observed via experimental study of nonlinear optics of iron/cobalt ferrofluid-based hyperbolic metamaterials, which shows considerable similarities with gravitation theory. We will present high-resolution images of self-focusing effect in this metamaterial, which were obtained as a function of light intensity and varying incidence angle with respect to the optical axis of the metamaterial.

This conference presentation was prepared for the Metamaterials, Metadevices, and Metasystems 2022 conference at SPIE Optics + Photonics 2022.

This conference presentation was prepared for the Metamaterials, Metadevices, and Metasystems 2022 conference at SPIE Optics + Photonics 2022.

This conference presentation was prepared for the Metamaterials, Metadevices, and Metasystems 2022 conference at SPIE Optics + Photonics 2022.

This conference presentation was prepared for the Metamaterials, Metadevices, and Metasystems 2022 conference at SPIE Optics + Photonics 2022.

This conference presentation was prepared for the Metamaterials, Metadevices, and Metasystems 2022 conference at SPIE Optics + Photonics 2022.

This conference presentation was prepared for the Metamaterials, Metadevices, and Metasystems 2022 conference at SPIE Optics + Photonics 2022.