This PDF file contains the front matter associated with SPIE Proceedings Volume 11460 including the Title Page, Copyright information, and Table of Contents.

A fully stabilized optical frequency comb provides equally spaced frequencies for a precise ruler in optical frequency metrology. This talk will review recent progress in single and dual comb generation from diode pumped solid-state and vertical emitting semiconductor lasers. A modelocked integrated external-cavity surface-emitting laser (MIXSEL) integrates both the gain and the saturable absorber layer within the same semiconductor wafer which simplifies the laser geometry to a linear straight cavity with excellent noise performance. In dual-comb operation, the initially unpolarized beam is split with an intracavity birefringent crystal. A dual-comb MIXSEL has been used for molecular spectroscopy without the need of any additional stabilization. Novel concepts solved the Q-switching problem for gigahertz femtosecond solid-state lasers and enabled stable dual-comb generation as well.

The concept of an optical metasurface, an engineered array of plasmonic or dielectric antennas/resonators, is best known for its applications to making ultra-thin lenses and other far-field optical devices. When combined with active materials, such as liquid crystals, thermo-refractive, and electrically tunable 2D materials, a new class of time-varying metasurfaces is emerging, and being explored for practical applications such as rapidly dynamic-focus lenses and ultra-fast polarimeters, and ellipsometers. Nonlinear semiconductors are explored as an exciting material platform for low-loss metasurfaces capable of generating harmonics of light with high conversion efficiency. Finally, the emerging concepts for combining rapid tunability and high effective nonlinearity of metasurfaces will be discussed, with the goal of simultaneous enhancement of the bandwidth and photon conversion efficiency in structured materials.

The differentiator consists of carefully designed 2D photonic crystal (PhC) slab that can transform an image into its second-order derivative. Based on interference between the direct transmission and low quality factor quasi-guided modes, the PhC slab exhibits angular-dependent transmission for P polarization but remains reflective for S polarization, which avoids polarization mixing in the transmission matrix. Fourier imaging was carried out showing a quadratic transfer function for an NA up to 0.315, which allows one to resolve features on the scale of 1.94λ. To showcase practical applications, the nanophotonic differentiator was directly integrated into an optical microscope and onto a camera sensor demonstrating the ease at which it can be vertically integrated into existing imaging systems. Furthermore, we demonstrate a compound bilayer flat optical by integrating the differentiator with a metalens for realizing a compact and monolithic image processing system. In all cases, the use of the nanophotonic differentiator allows for a significant reduction in size compared to traditional systems as one does not need to pass through the Fourier plane for performing complex image processing. This freedom should open new doors for optical analog image processing in applications involving machine vision.

Using superoscillations from a nanostructured Pancharatnam-Berry-phase metasurface serving as a marker, and four different polarization states of an incident laser, a recent paper (Science 364, 771 (2019)) reported 1nm localization errors at 800nm vacuum wavelength. Here, we show experimentally (unpublished) that digital optical-image cross-correlation analysis can achieve localization errors of 0.09nm with 12.5ms time resolution for similar marker footprints. Our approach uses incoherent unpolarized white light rather than a laser for illumination and works even for bare sample surfaces. Using time-harmonic modulation and synchronized stroboscopic illumination, we have taken nanometric movies at frequencies around 100kHz (Nature Commun. 10, 3384 (2019)).

In this talk, we provide an overview of our recent efforts on deriving and elucidating bandwidth limits for two important classes of metamaterial devices: (i) metalenses and (ii) invisibility cloaks. (i) Recent works have demonstrated broadband metalenses with minimized chromatic aberrations, potentially paving the way for ultrathin achromatic optics. Within this context, here we derive fundamental bandwidth limits to achromatic metalenses, regardless of their implementation, and we show that all metalenses designed thus far obey these bounds. (ii) In the second part of the talk, we focus on the problem of broadband invisibility and address some relevant issues that have been the subject of debate in the recent literature. Specifically, we clarify that “active” invisibility cloaks suffer from fundamental bandwidth and size limitations that arise due to causality and stability.

We develop photonic funnels, structures that provide efficient optical coupling between nano- and micro-worlds. The funnels represent conical waveguides with highly anisotropic cores and highly conductive cladding that have one opening with crossection of the order of free space wavelength and the second opening with deep subwavelength crossection. We fabricate all-semiconductor photonic funnels at mid-infrared frequency range and demonstrate, theoretically and experimentally, efficient confinement of mid-infrared light to wavelength/30 areas. Theoretically, we predict efficient out-coupling of light from ultra-small areas to diffraction-limited domain.

we demonstrate 2D photonic HOTI (PHOTI) with topological states two dimensions lower than the one of the host system. We consider a photonic metacrystal of distorted Kagome lattice geometry that exhibits topological bulk polarization, leading to the emergence of 1D topological edge states and of higher order 0D states confined to the corners of the structure. Interestingly, in addition to corner states due to the nearest neighbour interactions and protected by generalized chiral symmetry 1, we discover and take advantage of a new class of topological corner states sustained by long-range interactions, available in wave-based systems, such as in photonics. Our findings demonstrate that photonic HOTIs possess richer physics compared to their condensed matter counterparts, offering opportunities for engineering novel designer electromagnetic states with unique topological robustness.

We demonstrate, theoretically and experimentally, that a traveling electric charge passing from one photonic crystal into another generates edge waves—electromagnetic modes with frequencies inside the common photonic band gap localized at the interface—via a process of transition edge-wave radiation (TER). A simple and intuitive expression for the TER spectral density is derived and then applied to a specific structure: two interfacing photonic topological insulators with opposite spin-Chern indices. We show that TER breaks the time-reversal symmetry and enables valley- and spin-polarized generation of topologically protected edge waves propagating in one or both directions along the interface. Experimental measurements at the Argonne Wakefield Accelerator Facility are consistent with the excitation and localization of the edge waves. The concept of TER paves the way [1] for novel particle accelerators and detectors.

In this work, we extend the scope of the metallic and dielectric states by treating a pure metal or dielectric as the limiting case of a metal-dielectric layered metamaterial. The metamaterial with metal filling ratio larger than one-half shares the same topological invariant as a pure metal and thus exhibits some metallic behaviors. In contrast, the dielectric-rich metamaterial and a pure dielectric are topologically equivalent and display dielectric properties. This new understanding gives surface plasmon polariton (SPP) at a metal/dielectric interface a new physical meaning: the limiting case of a topological edge state. Finally, a complex structure also supports hidden topological effects if it is transformed from a layered metamaterial possessing an edge state.

Despite being very weak, the chiral optical response of natural media plays a fundamental role in several areas of photonics, medicine, pharmacology, and quantum optics. Topological insulators are a class of materials in which spin-momentum locking induces a preferential response of surface electrons to circularly polarized light. However, the resulting spin-polarized photocurrents are often hindered by the strong contribution of bulk electrons. Here we show that the intrinsic circular photogalvanic effect in topological insulator BSTS (Bi_1.5Sb_0.5Te_1.8Se^1.2), probed by helicity dependent photocurrent, can be enhanced by one order of magnitude when a non-chiral metamaterial design is patterned on the crystal surface. This method can be adopted to control the polarization properties of Dirac materials beyond topological insulators by metamaterial design, opening up new opportunities for the detection of quantum light, molecular sensing, and the realization of opto-spintronic devices.

Optical resonators confine light for a long but yet finite time due to unavoidable radiation. The concept of bound states in the continuum allows to reduce dramatically radiation from optical resonators due to interference and strong coupling akin exotic electronic waves introduced in quantum mechanics a century ago. This talk will summarize the recent progress in the physics and applications of bound states in the continuum (BICs) in metaphotonics. In particular, we aim to present the experimental observation of the quasi-BIC modes (also termed “supercavity modes”) in subwavelength high-index dielectric resonators in both radiofrequency and optics ranges. The supercavity mode manifests itself clearly via characteristic peculiarities of the Fano resonance and radiation patterns. We will also review the properties of other types of quasi-BIC modes such as those in extended structures and discuss their applications in nonlinear optics and ultrafast optical switching.

Multilayered Al:ZnO/ZnO metamaterial, a material that exhibits unique optical properties such as hyperbolic dispersion, attracted a high research interest due to its low optical loss and high conductivity. Combination of the optical gain and strong anisotropy for the Al:ZnO/ZnO metamaterial provide novel opportunities to control spontaneous emission. High doping concentrations (10²⁰- 10²¹ cm^-3 ) for Al:ZnO/ZnO require the inclusion the effect of the band filling. While ZnO has a large bandgap of ~3.3 eV, it has been suggested that in Al:ZnO the Burstein-Moss effect results in an increase in bandgap and thus a decrease in emitted wavelength, which may partially explain the suppression of visible photoluminescence and increase in ultraviolet photoluminescence observed in highly doped Al:ZnO. Here, we investigated the interplay between bandgap renormalization and band filling (Burstein-Moss effect). The results of our calculations show that the energy shift due to the Burstein-Moss effect (blue-shift) and bandgap renormalization (redshift) strongly depends on carrier concentration in multilayered Al:ZnO/ZnO. We found that the energy blue-shift due to BursteinMoss compensates the red-shift from the bandgap renormalization when a carrier concentration reaches 10²⁰ cm^-3 .

Optical antennas have become ubiquitous tools to enhance the spontaneous emission of atoms, molecules and quantum dots. In this presentation, we report a series of experimental results investigating the emission of light by ensembles of interacting emitters coupled to resonators. First, we report the observation of a strong plasmon−exciton coupling regime in a system consisting of a layer of nanoplatelets on top of a gold planar surface. Reflectometry measurements and mode analysis lead to the non-ambiguous derivation of a Rabi splitting between two polaritonic branches. Secondly, we investigate the polarized and directional emission of light by a patterned layer of nanoplatelets optically pumped. Models based on the paradigm of the Purcell effect mediated radiation fail to fully explain spectral and spatial features observed in such experiments, such as the emergence of spatial coherence or the suppression of quenching. We discuss and highlight the differences between emission by a single emitter and by a thermalized assembly of quantum emitters to show that a statistical framework is required to understand their interactions with optical antennas. Based on these considerations, we introduce a model of light emission by thermalized ensembles of emitters, and find good agreement between our model and experimental data.

We present our latest progress in the study of different tunable and active mechanisms in various materials that exhibit large modulation of optical constants and are used to implement active resonators and metasurfaces. We first discuss tuning of infrared Mie-resonant Si and Ge metasurfaces by modulating their free carrier density. We then move to discuss thermo-optic (TO) effects in Si, Ge and InSb and demonstrate tuning of Mie resonances by more than the resonance linewidth. Exploiting the peak TO coefficient of Si near its bandgap, we realize reconfigurable metasurfaces and tunable metafilters. We also show that phase transition materials such as VO₂ can be used to implement active devices. We demonstrate electrically tunable Ge on VO₂ resonators acting both as amplitude and phase modulators. Finally, we demonstrate ultra-wide dynamic tuning of PbTe meta-atoms. Taking advantage of the anomalously large TO coefficient and high refractive index of PbTe, we demonstrate high-quality factor resonances that are tuned by several linewidths with temperature modulation as small as ΔT~10K. We reveal that the origin for this exceptional tunability is due to an increased TO coefficient of PbTe at low temperatures. When combined into metasurface arrays these effects can be exploited in ultra-narrow active notch filers and metasurface phase shifters that require only few-kelvin modulation. We also study photoluminescence properties of lead chalcogenides from single antenna resonators and metasurface arrays towards the implementation of infrared emitting metasurfaces.

We have realized a new platform for multiplexing different spectral functionalities in a single meta-surface device using metal oxide plasmonics for infrared applications with very low cross-talk in the UV-Visible. Here we demonstrate the use of oxygen plasma patterning as a technique to selectively and locally modulate the carrier density in planar Al-doped ZnO (AZO) metasurfaces without any resulting surface topography. Using this approach, embedded metal oxide plasmonic metasurfaces are demonstrated for infrared applications with high transparency in the visible spectrum. By combining the embedded planar AZO metasurfaces with gold antenna metasurfaces, we realize a multiband visible-IR metasurface. We also demonstrate its performance as a metasurface optical solar reflector (OSR) for use in thermal control of spacecraft.

We present an alternative approach to dielectric meta-surfaces based on resonant elements which has far less limitations on scalability and durability. The process is based on laser raster-scan of a thin metal film on a glass, followed by dry-etching and removal of the metal mask. Since the air-glass volumetric ratio mixing approach is limited by the depth of the layer, we have developed approaches to “boost” the attainable phase response, to be discussed here.

Optical meta-devices using meta-surfaces which composed of artificial nanostructures are able to manipulate the electromagnetic phase and amplitude at will. The great advantages of meta-devices are their new properties, lighter weight, small size, high efficiency, better performance, broadband operation, lower energy consumption, and CMOS compatibility for mass production. Given the demand for photonics, many optical meta-devices for the application and control of incident light are being quickly developed for beam deflection and reflection, polarization control and analysis, holography, second-harmonic generation, laser, tunability, imaging, absorption, focusing of light, multiplex color routing and light-field sensing. The design, fabrication and application of the novel optical meta-devices are reported in this talk.

A surface wave antenna operating in the 2.4GHz band and efficient for launching surface electromagnetic waves at metal/dielectric interfaces is presented. The antenna operation is based on the strong field enhancement at the antenna tip, which results in efficient excitation of surface waves propagating along nearby metal surfaces. Since surface electromagnetic waves may efficiently tunnel through deep subwavelength channels from inner to outer metal/dielectric interface of a metal enclosure, this antenna is useful for broadband radio communication through various conductive enclosures, such as typical commercial Faraday cages.

Metasurfaces having deep sub-wavelength infrared periodicities have been explored in the past for perfect absorbers [1], active photonic systems, etc. Typically, these metasurfaces exhibit absorption and scattering resonances when the polarization is perpendicular to the stripes, while when the polarization is parallel to the stripes, a broadband high reflectivity is achieved. Metamaterial Longwave Infrared (LWIR) stripe arrays are challenging to fabricate in large (~1” or large) formats, needed for advanced nano-manufacturing, because their sub-wavelength periodicities are too small for standard photolithography in some cases. We employ photolithography to pattern stripe arrays with large periodicities (>7 μm), in order to experimentally verify LWIR diffraction, which has not been generally explored as much as shorter wavelengths, due to challenges in measuring LWIR diffraction in the laboratory. We employ tunable LWIR and Short-wave Infrared SWIR lasers to verify the diffraction from sparser arrays. We pattern metamaterial LWIR arrays using advanced (non-standard) next-generation lithography equipment, and present experimental reflectivity and backwards scattering from these metamaterial LWIR arrays. We simulate, using critical coupling analytical models and the Finite Difference Time Domain (FDTD) numerical algorithm, the reflectivity, scattering, absorption, and transmission of these metamaterial (Aluminum) arrays, and compare to the laser-based measurements. We also measure characteristics of single- and arrayed polymer (polyethylene) fibers, and contrast the results to those of Al stripes in the metasurface. Finally, we compare these measurements to those of a rectangular array of ~ 200 nm Al dots on glass, which showed that forward scattering cuts off for wavelength larger than periodicity, as expected from diffraction theory. Stripe-based metasurface arrays such as these may enable new active metasurfaces in the future, since electrical functionality is easily incorporated in the wire-like high-conductivity stripes extending across the metasurface. Analogous polymer fiber arrays may enable a new generation of smart textiles, if they are integrated with conductive metal fibers or themselves contain conductive additive particles (e.g., metal or carbon nanoparticles). In both cases, being LWIR metamaterials, these metal and polymer stripe and fiber arrays will allow unusual control of thermal functionality – another route, besides electrical, to ‘smart’ active metasurfaces and metamaterials.

Dielectric metasurfaces, which consist of spatially distributed sub-wavelength structures that impart controlled local phase shifts to the exiting light, allow access to modifying the wavefront and achieve desired function of the output beam. By adjusting the sub-wavelength structures’ shape, size, and choice of material, one can locally control the effective refractive index that affects the output light’s phase, amplitude, and dispersion, allowing various degrees of freedom in design parameters. The first generation of metasurfaces consisted of individual lab prototypes that in crucial parts relied on electron beam lithography, which severely restricted scalability. Meanwhile, mask-based methods such as deep UV lithography have been successfully adopted. While such methods open the door to high-throughput fabrication of metasurfaces, they are still limited in their achievable sample dimensions due to size restrictions imposed by wafer-based methods. By using roll-to-roll (R2R) methods, we were able to make large area metasurfaces that could find their use in displays and AR/VR applications, for example. In addition, R2R creates a lower cost method of manufacture for large volumes. In order to utilize R2R methods, there are two important challenges to overcome. First, the pattern must be extended over the large area of a film surface. Second, standard metasurface designs need to be adapted to the material and process constraints of R2R manufacturing. The R2R fabrication route is an extension of large-scale industrial processes that can produce wide format rolls of film.

We present a model for exciton-plasmon coupling based on energy exchange mechanism between quantum emitters (QE) and localized surface plasmons in metal-dielectric structures. Plasmonic correlations between QEs give rise to a collective state exchanging its energy cooperatively with a resonant plasmon mode. By defining carefully the plasmon mode volume for a QE ensemble, we obtain a relation between the QE-plasmon coupling and the cooperative energy transfer rate that is expressed in terms of local fields. For a single QE near a sharp metal tip, we find analytically the enhancement factor for the QE-plasmon coupling relative to the QE coupling to a cavity mode. For QEs distributed in an extended region enclosing a plasmonic structure, we find that the ensemble QE-plasmon coupling saturates to a universal value independent on system size and shape, consistent with the experiment.

In this talk I will discuss strong light-matter interactions achieved by using transition metal dichalcogenides (TMDCs) as the resonant material in both plasmonic nanocavities and Mie resonance sustained by the high-refractive index of the material itself. As a result of this interaction, one typically observes the emergence of new polaritonic eigenstates. These states are of hybrid nature and possess both light and matter characteristics, which is reflected in vacuum Rabi splitting, observed in the absorption or transmission spectra. Because of the hybrid nature of these states, the excited state temporal dynamics can be significantly altered in comparison to the uncoupled system dynamics. This, in turn, can have profound effects on the emission and photochemical processes. I will show that TMDCs are a particularly interesting polaritonic system in this sense."

The mid-infrared spectra of many polar materials are dominated by highly reflective reststrahlen bands that occur between the transverse and longitudinal optical phonons. Within the reststrahlen bands, light can couple with optical phonons to support phonon-polariton modes. These modes enhance light-matter interactions through the concentration of light to nanoscale dimensions, and therefore, are particularly promising for mid-infrared nanophotonic applications. Here, we discuss our work on expanding the spectral range over which phonon-polaritons are supported by using new material systems, as well as active tuning of the modes via carrier photoinjection. In particular, we report on the confinement of hyperbolic phonon-polaritons in calcite, a ubiquitous polar material. We also report the use of the LO-phonon-plasmon-coupling (LOPC) effect to actively tune the Berreman mode of a GaN thin film.

Electromagnetic (EM) metamaterials represent an important class of artificial materials composed of arrays of subwavelength unit-cell structures, which are also known as meta-atoms, with engineered effective optical properties, such as effective permittivity and permeability. Metamaterials provide a powerful platform to implement dynamic and nonlinear electromagnetic materials. Specifically, the effective permittivity and permeability can be tailored and reconfigured to construct metamaterial devices by modulating or actuating the constituent meta-atoms. By leveraging microelectromechanical system (MEMS) technology, active metamaterial devices, such as modulators, absorbers, and tunable waveplates, may be implemented. We developed myriad functional terahertz (THz) metamaterial devices based on MEMS actuators and optical excitation to manipulate the THz waves towards practical applications. In addition to far-field radiation, metamaterials exhibit extraordinary near-field properties yielding the capacity to tailor electric and magnetic field distributions. We studied the electron emission and nonlinear resonance response in THz metamaterials due to the electric-field enhancement effect. Furthermore, intelligent magnetic metamaterials for boosting the signal to noise ratio (SNR) of magnetic resonance imaging (MRI) have been developed. We employed the nonlinear response in metamaterials consisting sub-wavelength helical resonators and varactor-loaded split ring resonators to selectively enhance the magnetic field, thereby improving the SNR of MRI. Future practical applications of metamaterials will be explored and discussed.

We discuss a new class of nonlinear absorbers termed Plasmonic Parametric Absorbers (PPA) relying on the recently introduced concept of Plasmonic Parametric Resonance (PPR). In contrast with conventional localized plasmonic resonances, whereby modes are excited directly by an external field of frequency and spatial profile matching those of a given mode of the plasmonic particle, PPR is a form of amplification in which a pump field transfers energy to a mode in an indirect fashion. In PPR in fact the modes of a plasmonic structure are amplified by means of a temporal permittivity modulation of the background medium interacting with an appropriate pump field. Such permittivity variation translates into a modulation of the modal resonant frequency, and under specific conditions amplification can occur. Among the unique characteristics of PPR is the possibility of accessing modes of arbitrarily high order with a simple spatially uniform pump, provided that such pump exceeds a certain intensity threshold. It is such threshold behavior that can lead to PPAs, a type of nonlinear metamaterial absorber with rather unique properties. PPAs exhibit a reverse saturable absorption behavior whereby an incident field that is parametrically resonant with one or more of the modes of a plasmonic particle experiences a strongly enhanced absorption whenever its intensity exceeds the relevant PPR threshold. Such effect makes PPAs very promising candidates for optical limiting applications, in addition of being of fundamental interest in the emerging field of nonlinear plasmonics.

The nanomechanical metamaterials offer the possibilities of manipulating exotic electromagnetic properties on demand. Such metamaterial exhibit profound electro-optical, magneto-optical and acousto-optical switching and modulation, optical nonlinearity for modulating light with light, asymmetric transmission, and tunable chirality. The electromagnetic properties of nanomechanical metamaterial structure strongly depend on the spatial arrangement of its building blocks. By constructing metamaterials on elastically deformable scaffolds we can dynamically control the nanoscale spacing among constituent elements across the entire metamaterial array with external stimuli. Based on this approach, we use electrostatic, Lorentz, near field optical forces and sound to drive high-contrast, high-speed active tuning, modulation and switching of photonic metamaterial properties and to deliver exotic electromagnetic properties. We also report a novel approach to the visualization of nanoscale movements of picometre scale Brownian and stimulation movements of the individual building blocks of these functional metamaterials.

Materials with vanishing real part of permittivity, also known as epsilon-near-zero (ENZ), have emerged as a new paradigm to obtain large optical nonlinearities. Transparent conducting oxides such as indium tin oxide (ITO) naturally exhibit an ENZ condition in the near-infrared and close to their plasma frequency. The peculiarity of ENZ materials is their highly dispersive nature explained by Drude model, allowing to obtain reduced group velocity at frequencies where the phase velocity is enhanced. This condition can dramatically increase the phase sensitivity caused by any given changes in material permittivity. To accurately address the NLO mechanism in such materials, we present a generalized formalism for the nonlinear phase shift for a dispersive material, where it includes contributions from both group velocity and phase velocity. We experimentally demonstrate that the nonlinear phase can reach to the values close to π/2 when the probe beam is at ENZ, while the index change in the conventional definition is not enhanced necessarily. In this work, we present nonlinear optical measurements using the nondegenerate Beam Deflection (BD) methodology at normal incident together with cross-phase modulation experiments. BD is a pump-probe method that directly characterizes the ultrafast response of the nonlinear phase-shift, hence nonlinear refraction. We see no polarization dependence proving that bound electronic third-order nonlinearities are negligible compared to the sub-picosecond fast carrier effects. We also present that frequency shift is highly sensitive to the temporal dynamics of the nonlinear phase shift suggesting that short pulses may help to improve the magnitude of frequency shift.

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 exhibit “two times” physics behavior. This behavior is observed via experimental study of gravity-like nonlinear optics of iron/cobalt-based ferrofluid hyperbolic metamaterials. In addition to conventional temporal coordinate, the spatial coordinate oriented along the optical axis of the metamaterial also exhibits timelike character, which leads to very unusual “two times” physics behavior in these systems.

There is a growing interest in engineering of thermal emitters using metamaterials concepts for applications in energy harvesting, radiative cooling, and thermal camouflage. This talk will describe our efforts to achieve ultrafast control of thermal emission via engineered free-carrier dynamics in semiconductors, resulting in the generation of thermal pulses on nanosecond and picosecond scales. Then, this talk will introduce a metrology method that can remotely measure the three-dimensional temperature distributions of target objects, based on careful analysis of light thermally emitted from that object.

Bound states in the continuum (BIC) attracted great attention in the photonics community. The existence of such states has led to numerous applications, including optical sensors and filters. Here we report on the approach to externally tune a magnitude and spectral position of high-Q resonances, associated with not symmetry-protected BIC state in silicon nitride (Si3N4) photonic crystals. We show that BIC properties can be controlled by the external thermal impact. These results can be used to construct compact and thermally stable optical sensors immune to harsh environmental conditions.

Photonic metamaterials have driven the development of innovative devices with novel functionalities. Research in this field has relied upon noble plasmonic metals that suffer from optical loss, low-melting-points, cost and incompatibility with CMOS technology. Alternative material platforms such as chalcogenide semiconductors, oxides, and nitrides have been explored to overcome these challenges. Refractory metal oxides are highly versatile and are often overlooked in the realization of metamaterials and metadevices. Metal-oxide bilayers grown by vapor deposition, followed by annealing, enable a class of metamaterial coatings (meta-coatings) that offer tuneable resonant behaviour across visible frequencies. These meta-coatings are fabricated without nanopatterning allowing for large-scale fabrication.

To fully unlock the capacity of engineered optical media, metadevices and metasystems are exploited with progressively greater complexity, including those with arbitrarily complicated topology, spatially variant building blocks, and multi-layered configurations. The astronomical degrees of freedom associated with such structures have obstructed effective design of them based on the conventional wisdom. Here we present a series of machine learning frameworks, consolidating deep neural networks, evolutionary strategy, and advanced patter generation methods for the inverse design of meta-structures in response to on-demand optical properties, with extensive case studies for multiplexed wavefront control, holography, and optical computing.

Within this work, we will discuss our recent and promising advances in the development of machine learning assisted optimization schemes for plasmonic/photonic meta-structures design development. We will showcase that by coupling adversarial autoencoding network with topology optimization, it is possible to expand conventional meta-device design methodology to a global optimization space. In the second part of the talk, we will cover our recent effort on coupling machine learning classification/regression algorithms with quantum measurements. Particularly, we will show that the synergy between advanced machine learning assisted data analysis with quantum optical measurements dramatically reduces data collection time as well as increases the accuracy of the measurements.

We develop an approach that enables characterization of wavelength-scale objects with deep subwavelength resolution. The technique combines diffractive imaging that out-couples the information about the subwavelength features of the object into the far-field zone with machine learning that analyzes the resulting patterns. Recovery of complex objects with 120-nm resolution with ~530-nm light is demonstrated experimentally. Our theoretical analysis suggests that the same objects can be recovered with up to 2-micron-wavelength light. Our work opens the door for new characterization tools that combine high spatial resolution, fast data acquisition, and artificial intelligence

We introduce a non-intrusive far-field optical microscopy, which reveals the fine structure of an object through its far-field scattering pattern under illumination with topologically structured light containing deeply subwavelength singularity features. The object is reconstructed by a neural network trained on a large number of scattering events. We demonstrate resolving powers two orders of magnitude beyond the conventional “diffraction limit” of λ/2.

Modern image sensors consist of systems of cascaded and bulky spherical optics for imaging with minimal aberrations. While these systems provide high quality images, their improved functionality comes at the cost of increased size and weight. One route to reduce a system’s complexity is via computational imaging, in which much of the aberration correction and functionality of the optics is shifted to post-processing in software. Alternatively, a designer could miniaturize the optics by replacing them with diffractive optical elements, which mimic the functionality of refractive systems in a more compact form factor. Metasurfaces are an extreme example of such diffractive elements, in which quasiperiodic arrays of resonant subwavelength optical antennas impart spatially varying changes on a wavefront. While separately both computational imaging and metasurfaces are promising avenues toward simplifying optical systems, a synergistic combination of these fields can further enhance system performance and facilitate advanced capabilities. In this talk, I will present a method to combine these two techniques to enable ultrathin optics for performing full-color and varifocal imaging across the whole visible spectrum as well as high precision depth sensing. I will also discuss the use of computational techniques for designing metasurfaces with exotic behaviors lacking any intuition-informed design, as well as for performing computation on incident light, with applications in optical information processing, sensing, and computing.

Inverse design using topology optimization has proven to be highly effective to design metasurfaces with high performance. In particular, adjoint-based gradient computations can iteratively dielectric distributions to perform local optimization of freeform devices, and these computations can be incorporated into global topology optimizers such as GLOnets. A major challenge is incorporating fabricability constraints, such as the enforcement of the minimum feature size of the pattern, such that the final design is compatible with experimental lithography and etching steps. We introduce a conceptually new method that allows us to accurately impose constraints through reparametrization. The pixelated device pattern is reparametrized by a new set of parameters where design constraints are naturally and robustly incorporated. Updates to this new reparametrized latent space during the optimization are achieved using backpropagation. We demonstrate the effectiveness of this scheme by design

In this paper the response of light propagation in hypercrystals (I.E, structures composed by metamaterial) have been numerically analyzed. The heterojunctions were considered to demonstrate that the optical properties change the behavior of the structure at visible and optical frequencies. The structure is composed by periodic layers to combine properties of photonic crystals and hyperbolic metamaterials that present different physical properties not found in nature. In most of cases have been composed by metal and semiconductor in alternate layers. To design a structure the Fibonacci's sequence was used to define the sequence order of layers. The materials used in simulations are Gold and Aluminum for as metals and Silicon for the as semiconductor. To compose a heterojunction photo detector part it was considered the low work-function metal Aluminum, for the intrinsic crystal Silicon, and high work-function metal Gold in this sequential layers.

Nanoparticles of high-refractive-index materials like semiconductors enable strong confinement of light at the subwavelength scale because of the strong reflection from material boundaries and excitation of Mie resonances within the nanoscale-size particle. Recently, transition metal dichalcogenides (TMDCs) from the family of van der Waals layered materials have been shown to exhibit tailorable optical properties along with strong nonlinearity, high refractive index, and anisotropy originating from layered structure of the material. We envision that TMDCs are a promising material platform for designing metasurfaces and ultra-thin optical elements: these van der Waals materials show a strong spectral response on light excitations in visible and near-infrared ranges, and nanostructure characteristics can be controlled by nanoantenna dimensions and their arrangement [1]. Here, we investigate a periodic array of disk-shaped nanoantennas made of a TMDC material, tungsten disulfide, placed on top of a thin intermediate layer of high-index material such as silicon and low-index oxide substrate. Planar photonics with efficient subwavelength light control can be designed based on transdimensional lattices that operate in the translational regime between 2D and 3D [2]. Such transdimensional lattices include 3D-engineered nanoantennas supporting multipole Mie resonances and arranged in the 2D arrays with collective effects. The periodic arrangement of the nanoantenna array facilitates the strong coupling of light into the thin high-index layer. We show that the nanostructure resonances and coupling between nanoantennas and substrate in TMDC disk-shaped nanoantenna array can be controlled by the variation in silicon layer thickness and have a dependence on the presence of index-match superstrate cover.

Plasmon drag effect (PLDE), i.e. giant enhancement of photocurrents in plasmonic metasurfaces, provides opportunities for compact electric monitoring of plasmon excitations. In the experiment, we test the sensitivity of PLDE to local environment in 1 D profile modulated silver surfaces. Photoinduced voltages observed in at plasmon resonance conditions show extreme sensitivity to presence of monolayers deposited using Langmuir Blodgett (LB) technique. Excited under the certain angle the photocurrents switch their polarity to the opposite upon addition of a single monolayer of stearic acid. The effect presents interest for application in nanoscale sensing.

In this work, we present a colloidal Mie resonators consisting of highly crystalline Si nanospheres [1-4]. Such colloidal Mie resonators acting as nanoantennas and building blocks for colloidal metamaterials have advantages in solution-based fabrication of thin film optical devices.

In this work, we utilize metasurface lenses (metalenses) as optical concentrators for photodetectors. In particular, we design and fabricate metalenses for the wavelength range 3.5 -4.5 μm and integrate them with infrared photodetectors. Infrared photodetector technologies, especially in the mid- to long wavelength IR, need to be cooled to achieve optimal performance. Reducing the amount of required cooling will ease their use in space applications where small size, weight and power consumption (SWaP) is of high importance. In this work we address this issue by monolithically integrating metalenses with gallium antimonide (GaSb)-based infrared photodetectors. The metalenses are fabricated on the back side of a GaSb substrate and the detectors are then fabricated on the front side. The metalenses consist of nanopillars and the fabrication is performed by e-beam lithography and ICP plasma etching, leaving metalenses etched into the back side of the GaSb. The nanopillar diameters range from 200 nm to 1.4 μm and the nanopillars all have a height of 2 μm. By back side illuminating the photodetectors (i.e., through the metalenses) we obtain an enhanced optical collection area of the photodetectors and thereby an enhanced detectivity when operated at a specific temperature. Alternatively, this enhanced detectivity can be traded in for an increased operating temperature of the detectors. By being suitable for array-scale fabrication, our work paves the way for future high-operating temperature GaSb-based focal plane arrays.

Optical components based on Pancharatman-Berry phase feature a polarization-dependent diffraction that can be used to fabricate lenses and gratings with unique properties. In recent years, the great progress made in the fabrication of the metasurfaces required for these optical components has lowered their cost and has made them widely available. One of the often overlooked properties of optical components based on geometrical phases is that, contrary to dynamical phases, their phase can be measured using a polarimetric technique without need to resorting to interferometry methods. This is possible because the Pancharatnam-Berry phase is not controlled by an optical path difference; it results from a space variant polarization manipulation. In this work we apply Mueller matrix microscopy to measure the geometrical phase of GP lenses and polarization gratings. We show that a single space resolved Mueller matrix measurement with micrometric resolution is enough to obtain a full characterization phase-profile of these GP-based optical components and evaluate their performance.The analysis can be extended to multiple wavelengths to study the chromatic dependence of the optical parameters of the lens or the grating.

Metamaterials and, more recently, metasurfaces have been the focus of extensive research activities, as they play an ever-increasing role in the design of integrated photonics platform. Stacked metasurfaces are also currently investigated as an alternative route to design devices with enhanced optical properties or to propose exotic effects that cannot be achieved in single-layered metasurfaces. In this study, we theoretically show and experimentally demonstrate that stacked Metallic Wire-Grid Metasurfaces (MWGMs) can exhibit polarisation-induced Fano resonances owing to the basic polarisation properties of MWGM. We first present an original model based on an extended Jones formalism together with a circulating field approach, which reveals the underlying principle of polarisation-induced Fano resonances. Then, an experimental proof of concept was realised in the THz region to support the theoretical investigations using commercially available MWGMs, which shows good agreement with the model’s numerical results.

In this abstract, I will discuss our efforts in realizing multifunctional metaholograms that can encode multiple pieces of information in a monolayer device for anticounterfeiting applications. First, I will present a spin-multiplexed visible metahologram [1]. A straightforward method for encoding multiple pieces of information in a single metahologram device is using polarization. To obtain significant birefringence for the control and reversal of photon spin, two sets of nanorods are designed, and depending on their orientation, they imprint inversed spin photons along their corresponding geometrical phase. As a result, this allows switching between two different images by simply flipping the handedness of the circularly polarized light on the transmission-type metahologram with 61% diffraction efficiency. Second, I will introduce a direction-multiplexed visible metahologram [2]. This approach is to multiplex two distinct pieces of information onto a monolayer metahologram operating in the forward and backward directions depending on the direction of light incident on the device. Particularly, in this part we will reveal underlying physics of high transmission efficiency (around 75%), which is the antiferromagnetic resonances in the a-Si:H nanorod. Finally, I will propose a wavelength-multiplexed visible/NIR switchable metahologram. The device consists of a-Si:H and gold (Au) metasurfaces in a monolayer device, which is fabricated by the electron beam lithography overlay process [3]. The a-Si:H metasurfaces generate a visible hologram and the Au metasurfaces produce a invisible(NIR) hologram simultaneously with low crosstalk. I believe our efforts for making a multiplexed metahologram will lead to pragmatic anticounterfeiting applications.

Here we report a novel approach to create tunable and reconfigurable microwave metamaterials using metal ink printing on a paper. Our approach enables easy-to-fabricate but still highly functional and tunable elements. An array of asymmetric split ring resonators was printed on a photopaper to induce Fano resonances in the microwave region (~ 10 GHz). Then, the printed paper was cut line by line and folded, so that a step height between neighboring unit cells can be created and tuned. With the varying step height between neighboring cells, our sample demonstrates significant spectral shifts and resonance tuning despite its simple geometry. Depending on the cutting direction, we observe either spectral redshift or blueshift. We explain our experimental observations based on the interactions between electric/magnetic dipoles in the neighboring unit cell. Moreover, we observe phase singularity at the zero amplitude position of the Fano resonance spectrum. The spectral phase exhibits a drastic change at this singularity point, and the phase spectrum can be also largely tuned with the geometry change in our sample. The drastic changes in phase could be very useful for various applications, such as optical sensing and beam steering.

Metamaterials have emerged as the basis of a novel optoelectronic platform operating in the terahertz (THz) range, due to their versatility and strong light-matter interaction. The necessary design of efficient modulators and detectors requires a detailed investigation of metamaterial resonances and their interplay with an active medium, e.g. graphene. An aperture-SNOM (a-SNOM) system based on picosecond THz pulses was used to investigate the spectral characteristics of a set of lithographically tuned metamaterial coupled resonators. This approach allowed the mapping of the supported E-field of each resonator a few microns from the device plane, yielding bonding and antibonding modes reminiscent of electromagnetic induced transparency.

Polarization characterizes the orientational property of an electromagnetic field. It plays an important role in scientific applications ranging from remote sensing to medical diagnostics. In this paper, we propose a novel design of an ultracompact polarimeter, consisting of two ordinary metalenses and a bifocal metalens. Based on the intensities of incident light at four individual points collected by the metasurface, we reconstruct the Stokes parameters via a transformation matrix. Simulation results show that, the root mean square error of each element of the Stokes parameters is less than 0.0064 at the wave band of 1010-1120nm. Therefore, the proposed polarimeter guarantees a high performance in real-time SOP measurements.

Due to the intrinsically weak chirality of biomolecules, discriminating between enantiomers, i.e., chiral molecules of opposite handedness, in low-concentrated solutions by an optical means is one of the unsolved problems in nano-optics. It is even more challenging to separate chiral objects at the nanoscale by optical forces. The key to alleviating the fundamental difficulty of these tasks is to construct an optical field, preferentially in the ultraviolet (UV) region, that carries intense optical chirality with comparable contributions from its electric and magnetic components. However, this requirement has not been met in nanophotonic structures, predominantly because of the lack of magnetic responses in plasmonic materials and the insufficient field enhancement by dielectrics. Innovative designs are highly desired to overcome the limitations from materials. In this work, we systematically investigate the resonance modes in a dielectric metasurface as well as their evolution and interplay as the design variables are engineered. We show that, based on two different mechanisms, 100-fold enhancement of optical chirality can be achieved at near-UV wavelengths with different linewidths. The first one arises from the sharp Fano interference between two distinct magnetic resonances of the unit cell of the metasurface, both of which are enhanced by the coupling across the lattice. The second one originates solely from the magnetic dipole resonance, whereas the chiral hotspots spatially overlap the electric counterparts, forming ideal sites to exert helicity-dependent optical forces on chiral objects at the nanoscale. Our findings pave the way towards practical solutions to the ultimate challenges of chiral optics.

In this work, we present a narrow-band (sub-100 cm^-1 ) and multi-band metamaterial perfect absorber operating in the mid-IR frequency regime for analysis of biomolecules with vibrational spectroscopy. The presented perfect absorber is based on multi-layer metamaterial plasmonic nanoantennas. We used numerical and experimental work to fine tune the parameters of the PA and control its spectral response. The suggested PA system provides high absorbance values (100%) in the mid-IR region and near-field enhancement factor of 10³ at the corresponding resonance values. The experimental results are well agreeing the numerical results. The working principle of the presented perfect absorption can be both explained by impedance matching and critical coupling phenomenon. The fabricated PA shows strong narrow band resonance and all the resonance energy could be transferred to thin films (10 nm) for higher sensitivity. In addition, PA shows multi-band resonances within the mid-IR region, thus it can be effectively used for simultaneously detecting the different biomolecular fingerprints. In this sense, we experimentally observed absorption of carbonyl (C=O) and asymmetric methyl (-CH₃) stretching bands of thin polymethyl methacrylate (PMMA) film on the narrow band resonance of PA.

Our work combines the extreme nonlinear properties in MQWs with the implementation of metasurface. We introduce the quantum multilayer composed of TiN/Al₂O₃ as a tunable metamaterial, which couples with the localized plasmonic resonances (gap plasmon) of an array of gold nano-antennas forming a meta-device. When the metasurface sample is illuminated by a collimated low-intensity laser with a linear polarization, the reflected beam is being diffracted as the left- and right-handed circularly polarized (LCP and RCP) components into 1 order, respectively. While for the case of a high-intensity laser illumination, the metasurface will act as a mirror, i.e. the linear polarization remains unchanged with both RCP and LCP components reflected to its zero-order. Furthermore, a tunable hologram is demonstrated based on our proposed design. A clear image is observed when the metasurface is illuminated by a low-intensity laser, while for the high-intensity case, the image will disappears Our finding paves the way for nonlinear optical modulators25, high speed all-optical switchs26 and reflective tunable displays.

Optical analog signal processing technology has been widely studied and applied in a variety of science and engineering fields. It overcomes the low-speed and high-power consumption disadvantages compared with its digital counterparts. One kind of the optical analog signal processing, optical edge detection, is a useful method for characterizing boundaries. In another context, metasurface as a recently developed technology has been introduced to optical imaging and processing and attracted much attentions. Here, we propose a new mechanism to implement an optical spatial differentiator consisting of a designed Pancharatnam-Berry (PB) phase metasurface inserted between two orthogonally aligned linear polarizers. Unlike other spatial differentiator approaches, our method does not depend on complex layered structures or critical plasmonic coupling condition, but instead based on spin-to-orbit interactions. Experiment confirms that broadband optical analog computing enables the edge detection of an object and achieves tunable resolution at the resultant edges. Furthermore, metasurface orientation dependent edge detection is also demonstrated experimentally.

Over the last decade, much research has been directed towards making conventional optical devices such as lenses and waveguides using flat surfaces. Using planar optics provides compact on-chip platforms that are easily integrated. In addition, it allows for new degrees of freedom for controlling the flow of light as well as avoids the accumulation of amplitude and phase changes that occur to the wave in conventional optical systems when propagating over distances from one component to the other. In this paper, we present a metasurface design made of c-shaped metallic elements that supports confined surface wave propagation. The c-shaped design provides high self-collimation which is advantageous for use in surface waveguiding. Another advantage of using the c-shaped design is that by carefully choosing its dimensions, one can engineer its equifrequency contour to split the linearly polarized wave into two circularly polarized waves of different helicities propagating with different k-vectors along the surface. This makes the c-shaped metasurface efficient for use as a polarization-based beam splitter. Additionally, we show that by slowly rotating the c-shaped cells and varying its size along the surface, we were able to steer the circularly polarized surface wave with only one helicity along a specified curved path while completely blocking the other helicity. This work highlights the high degree of freedom achieved from using homogenous metasurface designs for manipulating the spin-orbit interaction of electromagnetic waves and providing a great control on their polarization and propagation properties on the surface.

We report on the optical properties of nanoporous gold leaf (NPGL) metamaterials consisting of single and multiple-fold layers, and having different pore and ligament sizes. Due to their complex structure, such metamaterials have a unique optical property, which distinguishes them from homogeneous gold films. Thus, the transmission spectra of NPGLs feature two characteristic peaks positioned at ~ 490 nm and ~560 nm to 605 nm. The most notable result of this study is that the optical properties of NPGLs can be tuned by changing the dielectric environment and by applying voltage in an electrochemical cell.

We investigated amplified scattering of low-index Mie-resonators using guided-mode resonance from lattice. The diffracted light into first order is coupled to the lattice, thereby boosting the scattering of gallium nitride (GaN) nanopillars. This momentum matching condition is bounded by refractive index of substrate and effective refractive index of the GaN pillars. The effective refractive index is determined by the filling ratio of the GaN pillar inside a specific periodicity of unit cell. By changing the filling ratio, we were able to control cut-off frequency of coupling and the amplification of scattering. We designed spectral filters composed of array of GaN nanopillars, and amplitude of filtered light is decreased as the filling ratio is decreased. This special features enable to produce full and gradient structural colors; we successfully demonstrate micropirnts colored by red, green and blue in gradient.

Meta-particles are electromagnetically small scattering particles employed in the design of metasurfaces and metamaterial antennas. The process of designing meta-particles is conventionally iterative, where full-wave simulations of the meta-particle are performed while systematically changing the geometric parameters, and sometimes the material properties, of the particle. Such iterative approaches are generally resource intensive and time consuming, hence a surrogate model based approach may potentially save significant resources and time during the meta-particle design phase. In this work, we demonstrate employing two different surrogate models to estimate the scattering behavior of a “dogbone” meta-particle, namely Kriging and inverse distance. Results show that the Kriging model outperforms the inverse distance model and is capable of achieving very good approximation compared to full-wave simulation, even with a small number of design space sample points.

We implement an efficient artificial neural network (ANN), for the analysis and rapid inverse design of dielectric and planar hyperbolic metamaterial based waveguides operating in the infrared wavelength (λ) telecommunication spectrum (1200nm to 1700nm), where long propagation length and high confinement of the fields are desirables. We consider waveguides made of alternate metal-dielectric layers anisotropic claddings, surrounding a homogeneous core. The main device propagation properties to be computed by the proposed ANN are the length propagation (L) and the penetration depth (dp) associated to every design (outputs of the ANN). They are function of the λ excitation, metal (nm), dielectric (nd) refractive indexes of the layers and core refractive index (nc) as physical parameters. Our approach demonstrates high behavior prediction, design accuracy and minimal modeling parameters.

High-Q resonance are universal resources across different branches of physics, e.g., in acoustics, electronics, and electromagnetics, etc. Recently, quasibound states in the continuum (quasi-BICs) has become an enabling platform for realizing high-Q resonance. Therefore, it is highly attractive to employ the quasi-BICs for exploring the nonlinear optical process in nanoscale with light coupling from space. In this work, we’ve achieved the high-Q quasi-BIC resonance in all-dielectric metasurfaces by introducing asymmetry in the unit cells. We’ve achieved quasi-BIC resonance in telecom band under the normal excitation condition. By tuning pico-second pulsed into the quasi-BIC resonance, third harmonic generation with a normalized conversion efficiency of 1.4x10^−8/W^2 and even pronounced second harmonic generation which is in absence in silicon are simultaneously achieved.

The interlayer exciton of van der Waals heterostructure has become a promising platform for realizing Bose-Einstein condensation and demonstrating novel excitonic devices. For increasing the critical temperature of bosonic condensation or long-range transport, the short lifetime of the interlayer excitons has to be improved by suppressing both the radiative and non-radiative recombination processes[1,2]. However, due to its out-of-plane electric dipole nature, the radiative recombination of the interlayer exciton has not yet been able to be suppressed with conventional optical approaches[3,4]. Here, we present a theoretical study on the reflective metasurface that can suppress the density of optical states for the out-of-plane dipole moment. The metasurface consists of Au nanodisks arranged in a square lattice on the Au substrate. We examined the out-of-plane dipole emitter inside the 20-nm-thick hexagonal-BN layer, which is placed on the flat surface of the 140-nm-thick SiO₂ layer covering the Au disk array. We targeted the WSe2/MoSe₂ interlayer exciton of which the radiation wavelength is 900 nm. Blocking the radiative decay channels of the dipole emitter to the horizontal directions as well as the vertical directions, the proposed metasurface strongly suppresses the Purcell factor down to ~0.011 at maximum (~0.018 on average), which corresponds to the enhancement of the radiative decay time as amount as ~91 times (~56 times).

There are significant recent interests in using nanophotonic structures to perform computations in the optical domain. Specifically in optical image processing, there have been a number of demonstrations using nanophotonic structures to perform edge detection and spatial filtering operations on images without the bulky 4f systems. These structures have the advantage of being compact, fast and low power. However, all previous works using nanophotonic structures, can only operate with coherent light. Here we introduce a hybrid optoelectronic approach that enables one to use nanophotonic structures to perform differentiation operation with spatially incoherent light. As a demonstration we consider a photonic crystal slab structure, and show that differentiation operation with incoherent light can be achieved by subtracting the two output images at two different frequencies, after passing through the designed structure. Both second order and first order differentiation are demonstrated with corresponding structure design. Our method is robust to noise compared to exact differentiation computation, and directly integrable into existing image sensors. This approach points to a new avenue for improving image sensors using nanophotonic structures, and has potential applications in real scene image processing and object recognition.

The orbital angular momentum (OAM) of light has been applied to a variety of areas such as optical tweezers, interferometry, and high-resolution microscopy.^{1, 2} Metasurfaces, two-dimensional engineered structures with subwavelength features, give access to tailored functionalities through highly efficient phase shifting and polarization conversion. However, conventional designs with a single metasurface element produce vortex beams with fixed OAM of ℓ~ which limits the potential application areas. In this study, we propose and design a metasurface doublet lens structure having the property of generating variable modes controlled by the rotation angle. Inspired by Moir´e-lenses, the proposed structure consists of two all-dielectric metasurfaces where the second lens has the reverse phase profile compared to the first one. This causes the cancellation of the total phase shift at the nominal position. In our design, we rotate the second element with a discrete set of angles from 0 to 5.6 degrees with respect to the optical axis and obtain a set of the modes from ℓ = 0 to 4. We demonstrate that the structure converts the input plane wave to the vortex beams with OAM modes as a function of the rotation angle. We model the unit cell structure working at wavelength 532 nm a with circular cross-section, fixed height and variable radius titanium dioxide nanopillar on a fused-silica substrate. Nanopillar locations are distributed in a square lattice form with subwavelength periodicity which is suitable for conventional microelectronics fabrication methods. We believe our design can be used in optical trapping to detect different sizes of micro-particles and to create reconfigurable microoptomechanical pumps.

Water is a promising dielectric material for broadband absorption of great interest for microwave applications due to their dispersive characteristics and imaginary permittivity part. In this work, several broadband absorbers operating in the microwave between 5.0 Ghz to 30.0 Ghz will be analyzed. Higher absorption for TE and TM polarized electromagnetic waves with efficiency above 90% has been observed for microwave frequencies while optical transparence can occur simultaneously. The analyzed water-based metamaterial absorbers exhibit a wide-angle absorption. These kind of structures can be applied to stealth and electromagnetic compatibility technology.

Hyperbolic metamaterials composed of horizontally stacked metal and dielectric multilayer have recently attracted scientific interest as a platform to enhance and observe optical spin Hall effect. However, the large optical spin Hall effect in the horizontal hyperbolic metamaterials always accompanies extremely low efficiency, which obstructs its implementation on practical usage. Reducing the sample thickness to augment the transmission causes diminishment of the optical spin Hall effect. Here, we demonstrate that a vertical hyperbolic metamaterial can enhance the optical spin Hall effect by several orders of magnitude in comparison to that of its horizontal counterpart. Under the same conditions of material combinations and total thickness, the enhancement, which is incident angle-dependent, can be higher than 800-fold when the incident angle is 5°, and 5000-fold when the incident angle is 1°. As a proof of concept, we fabricate a large-scale gold nano-grating by nanoimprint lithography and observe the enhancement of optical spin Hall effect experimentally, which agree well with the simulated result. The gigantic optical spin Hall effect in a vertical hyperbolic metamaterial will offers a venue for helicity-dependent control of optical devices such as filters, sensors, switches and beam splitters.

Experimental investigations of the effects of limiting of a beam traversing a different light-scattering medium based on liquid crystals are presented. It is shown that the result of limiting of the beam at the output of the medium depends on the magnitudes of the phase delays of the singly forward scattered partial signals. Investigations of the effects of limiting has been carried out using nematic liquid crystals MBBA with carbon nanotubes (CNT) in comparison wihs a solution of the same liquid crystals doped by carbon nanodots. Liquid crystals dopped by carbon nanotubes or nanodots, located between crossed polarizers, delays external optical radiation as its power increases to a certain critical level. This can be explained by the phase changes in the LC dopped by the nanoparticles under the action of heating aimed by radiation or an applying external electromagnetic field. Observed phenomena strongly influenced by shape, size and concentration of CNT, as well as the sensitivity of the liquid crystal to the illuminating beam power rate has increased.

Recent progresses on passive radiative cooling methods have achieved cooling to a temperature below ambient surface [1, 2]. Here, we propose one-dimensional photonic crystals for high performance radiative cooling [3]. For high performance radiative cooling, high solar reflectance at solar region is essential as well as strong thermal emission in the atmospheric window between 8 and 13 micrometers. We demonstrate simultaneous structural optimization of one-dimensional photonic crystals for both wavelength region of solar and mid-IR. For photonic structural design, an evolutionary optimization of genetic algorithm is used to optimize both types of materials and structure parameters of the multilayer structures. The designed photonic structures strongly reflect light at solar region while strongly emit light in the atmospheric window. The designed photonic structures show very high radiative cooling performance because it is optimized in both regions at the same time. We believe the research finding will provide a possibility to solve energy problems.

In this paper the response of electromagnetic waves propagation in plasmonic structures composed by metals and dielectrics has been numerically analyzed. Thermal-optical coefficient was considered to demonstrate that the optical properties change the behavior of the structure at visible and infrared frequencies. The structure is composed by alternated thin layers of metal and semiconductor. The materials used in simulations are Silver for metal, Silica and Silicon for the semiconductors. Under temperature variations, these materials change their properties, like refractive index and can affect optical properties like absorbance, transmittance and reflectance. Besides, the incident angle was considerate as a variable. The Finite Element Method has been used to carry the simulations.

To meet the demand for ever-increasing data transfer rates in fiber optic communications, there is great interest in space-division multiplexing of light. Mode-division multiplexing, a subset of space-division multiplexing, increases the channel capacity of a system by spatial conversion and coupling of optical signals into the orthogonal modes of a multimode fiber channel. Current mode multiplexers, which rely on directional couplers, photonic lanterns, and free-space optics, can be challenging to fabricate, align, and scale to a large number of modes with low loss and crosstalk. As a result, more resources have to be spent on amplifiers and digital signal processing which increases the cost of the communications system. Metasurfaces offer a solution to this problem and have shown wide success in realizing various optics. Being lithographically patterned with subwavelength-scale dielectric structures, metasurfaces allow full control of the wavefront. We adopt a folded metasurface configuration by coating the dielectric structures with cladding and depositing metal on both sides of a glass substrate. Inside the substrate, light interacts with the metasurface multiple times to yield unprecedented abilities in shaping light. Based on this platform, we demonstrate a metasurface mode multiplexer design with low loss and crosstalk in the telecom. It directly aligns to an array of input fibers and an output fiber and converts each input mode into the orthogonal modes of the latter fiber. Short-distance and long-haul communication systems such as data centers and submarine links, respectively, can benefit from this mode multiplexer.

In this talk, a novel method to model finite metaclusters that can steer the energy of an incident wave preferentially toward a given direction will be presented. This design is realized by solving an inverse multiple scattering problem for selecting a desired energy distribution of scattered waves. The incident wave energy can be redirected toward a desired direction using a 2D metacluster configuration with a finite number of fluid cylinders embedded in a homogeneous fluid medium. For a faster implementation of the method, we consider a small cylindrical particle limit which corresponds to low frequency scattering. The required mechanical properties of fluid scatterers are defined by T-matrix components obtained by solving a linear system of equations. A major challenge in implementing and applying our computational model to the design of metacluster devices is to ensure that the scatterers remain manufacturable using available conventional materials. These metaclusters are designed by minimizing the relative error between given and computed scattering patterns and by using advanced optimization algorithms and deep learning. Steering the incident acoustic wave energy is realized by designing simple physically implementable configurations consisting of only three or more scatterers.

Sensors based on different types of guiding modes have been used for sensor applications for a long time. Those technologies were commercialized and actively used in different sensing applications. However, new challenges in biomedical research are requiring even better sensors. One of those new perspective technologies is plasmonic hyperbolic metamaterials. It was shown that those structures have a big potential for sensing. In order to compare these new guiding structures with traditional ones, we performed the analysis of sensitivity for different guiding structures: optical dielectric waveguide, surface-plasmon polaritons, long-range surface plasmon polaritons (LRSPP), plasmonic hyperbolic materials with a combination of metal and dielectric layers. All structures were placed on the BK7 glass substrate and we set wavelength at 1550 nm. We used the Si₃N₄ layer a waveguiding medium for the dielectric waveguide, we used gold for all plasmonic structures. The water layer on the top of all structures was used as a sensing area. For guiding modes coupling we used diffraction gratings for a few reasons. Firstly, there are no materials with a refractive index capable to couple guiding modes. Secondly, diffraction gratings provide compact, a planar design which is easier to keep the structure in the thermostatic condition And last but not least, we used coupling gratings with the same grating profile (sinusoidal) and the same corrugation depth so all guiding modes will be coupled the same way. Our results showed that plasmonic hyperbolic structures indeed have much higher sensitivity comparing with the traditional guided wave sensors based on dielectric waveguides and surface plasmon-polaritons.

Meta-optics based on optically resonant all-dielectric structures is a rapidly developing research area driven by its potential applications for low-loss efficient metadevices. Halide perovskite metasurfaces are of particular interest for meta-optics, as they offer unique opportunities for the light control at subwavelength scale in real optoelectronic devices. In this report, we demonstrate suppression of reflection from MAPbBr3 perovskite layer from 25% down to a few percent level by it nanostructuring and, thus, optimization of its optical response. To achieve the strongest reflectivity suppression, we employ the so-called Kerker regime when electric and magnetic Mie resonances in each meta-atom are matched properly in a broad spectral range. Our results have a high potential for application in thin-film photovoltaics where reflection reduction plays a key role in device performance.

Photonic Bandgap Crystals (PBGs) have begun to see use in optical communication networks and photonic device coupling due to their high, selective transmission bandgaps and novel optical filtering properties. Understanding how PBGs can be designed for varying purposes is crucial in continuing to find practical applications of these crystals. PBGs are typically periodic as the math is well understood and the transmission or reflection of periodic optical structures is generally well-known, even in closed form. Crystal lattices in position space can be shown to correlate to an “inverse lattice” in momentum space through Fourier analysis. With further description, we can express any form of crystal as a sum of its fundamental, periodic lattices. For simplicity, we analyze only 1-dimensional structures but generate the groundwork for descriptions in higher dimensions. This description of aperiodic lattices allows us to extract information about effective lattice periods and effective lattice wave numbers supported by the crystal lattice. Using the Transfer Matrix Method (TMM) we further examine the optical properties of aperiodic structures by generating dispersion diagrams of general structures. By comparing the results of the TMM and the results of the effective lattice parameters, we seek to determine the efficacy of the claim that disordered structures are sums of ordered structures. To do so, we will apply novel disordered functions such as the logistic map to generate layer thicknesses of an aperiodic crystal and compare results from both the TMM and Lumerical FDTD simulations.

Optical microscopy provides unparalleled tools for understanding and characterization of small-scale objects. We have recently developed an approach that combines diffractive imaging and machine learning to characterize wavelength-scale objects with subwavelength resolution based on few (or, often, single) measurement. The technique relies on the diffraction interaction between finite-sized diffraction grating and an object to outcouple information about both sub-wavelength and wavelength-scale features of the object into the far field and on machine learning to characterize the object based on its diffractive signature. In this work we aim to understand the flow of information through the image recognition process. We parameterize the diffractive signatures in Bessel and Fourier representations and analyze the performance of the recovery routines dependent on the choice of the harmonics in these expansions. Separately, we analyze the subset of the harmonics that are used by the machine learning algorithms in identifying the objects. Performance of the recovery routines as a function of noise is also analyzed. Our study provides an insight into the dynamics of machine learning and it helps identify the information channels that are crucial for optimal recovery of complex objects with high resolution, fidelity, and speed.

We analyze the mid-infrared emission resulting from the interplay between a type-II superlattice (T2SL) material and semiconductor-based plasmonic “designer metals”. We demonstrate an order of magnitude emission enhancement, accompanied by spectral reshaping, relative to all-dielectric T2SL counterparts and provide a theoretical description of the underlying physics. The all-semiconductor LWIR emitters with integrated plasmonic components, developed in this work, represent novel approach to broadband room-temperature mid-IR sources.

Bulk optics have been used for various optical instruments such as microscope or camera, but it has limitations in size and thickness because of accumulation of various lenses. Metalenses are an emerging field as one of the next-generation optical technology for miniaturization of optical system. Subwavelength thick nanostructures on metalens control the amplitude, phase, absorption, emission, and transmittance of incident light. Focal length can be control by adjusting phase shift from 0 to 2π according to the change of shape, size, and period of nanostructures. Many kinds of metalens such as GaN nanopillar, Si nanodisk, or TiO₂ nanofin have been studied recently, but chromatic aberration correction problem remains as the limitation in metalenses. Some researches such as group delay dispersion have been conducted to correct chromatic aberration, low focusing efficiency ( ~ 10 %) is unresolved limitation. In this work, we suggested a new method to design achromatic metalens for 400, 600 and 800 nm wavelengths focusing. Spatial multiplexing method can correct chromatic aberration very simply. First, three metalenses are designed for each wavelengths. In the next step, meta-atoms of each metalenses are interleaved in one metalens. The coupling between three kinds of meta-atoms is small, therefore we can expect three wavelength focusing in one metalens. We used finite-difference time-domain (FDTD) simulation to investigate field distribution and focusing efficiency of each metalenses. By using this method, we demonstrated achromatic metalens with numerical aperture of 0.89, which focus light at 400, 600, and 800 nm to same focal spot. Focusing efficiency of achromatic metalens for 400, 600 and 800 nm are 38, 44 and 54%, respectively. This design method can attend significant role to demonstrate desired achromatic metalens.

A multifocal metasurface lens is designed for a K-band patch antenna array consisting of 4 × 4 elements. The lens is constructed using a two-layer “dogbone” meta-particle structure and is placed 0.5 mm away from the array. The choice of this particular design emphasizes simplicity and cost-effectiveness, without much sacrifice in performance. Full-wave simulations are performed to catalog the scattering behavior of the dogbone metaparticle along with its geometric parameters. Two methods of fabrication were investigated to fabricate the design, namely, mechanical etching and chemical etching. Experimental results show that chemical etching produced a meta-lens with higher gain compared to mechanical etching. However, the gain enhancement in both lenses is observed at a higher frequency than originally intended in the design.

Chalcogenide glasses offer a unique platform for the realization of reconfigurable and tunable metasurfaces, as evidenced through the emergence of reconfigurable phase change metamaterials. Reconfiguration in these devices involves a thermally intensive melt/quench phase transition process which can reduce device lifetimes and degrade performance. Notably, metal doped chalcogenide semiconductors also exhibit photo-induced long-range movement of their constituent metal ions in their amorphous phase, resulting in non-volatile changes to refractive index and conductivity, removing the need for a phase transition. We utilize this photo-ionic movement in amorphous nanostructured silver-doped germanium selenide metasurfaces to demonstrate reversible non-volatile switching over optical frequencies.

A forced-mode composite resonator is used on a moisture sensor to characterize humidity percent of honey at the microwave regime. Sensors of two different shapes, one rectangular and one circular, are designed and fabricated using commercial phenolic sheets. The resulting resonant frequency of the sensor changes as a function of the humidity contained in the sample. Honey samples are placed inside small glass bottles and this foreign material is taken into consideration. Measurement results are as expected and when the effective permittivity value of the samples is too high the modes will interchange.

High damage threshold mirrors are necessary in high power laser systems. Different factors influence the rate of laser damage of these types of mirrors. In this research, the first thing that we tried was to simulate mirrors that are suitable for the reflectance spectra and are also in possession of high theoretically laser damage threshold at 10600 nm. After the task of simulation, the fabrication and coating process was performed by physical evaporation and in order to check the reflectance of the samples, their reflectance spectra were taken by uv-visible spectroscopy and their reflectance at 10600 nm is more than 99.5%. Finally, by measuring the thresholds of laser damage of mirrors made with continuous CO₂ lasers, we came to the conclusion that the all-dielectric mirror with ZnS substrate has the highest laser induced damage threshold.

In recent decades, research in the field of optoelectronics has attracted great interest. Modulators are one of the most usable optical components in the optical communication systems. The most important parameters for a modulator are high modulation speed, small footprint, and large optical bandwidth. In this paper we design and fabricate an all-optical intensity modulator based on optical microfiber in which graphene oxide replaces the clad of microfiber. We chemically etched the clad of multimode optical fiber. Then we coated aqueous solution of graphene oxide with concentration 5 mg/ml on the microfiber that has 90° curvature. The graphene oxide was irradiated directly by the pump laser (power=500 mW) at wavelength 405 nm from outside the microfiber. We were able to achieve a maximum modulation depth of 27.3% by graphene oxide. The modulator has been built has many advantages such as compatibility with optical communications, easy fabrication, and low cost.

We study nonlinear wave phenomena in hyperbolic and plasma-like dielectric isotropic metamaterials, dielectric-graphene (DG), dielectric-semiconductor (DS) and dielectric-metal (DM) plasma-like media (PM) (DGPM, DSPM, DMPM, respectively). When a THz beam passes through a layered DGPM in the presence of external magnetic field, we show the ability to effectively control the resonant complex nonlinear conductivity of graphene and modulation of the beam amplitude. In the hyperbolic nonlinear active IR field concentrator, the possibilities of (i) forming three types of focused nonlinear wave structures and (ii) the quasi-chaotic behaviour of the field amplitude inside the region of focusing in the above-threshold regime are demonstrated. Non-stationary regime for incident beam is included into consideration. When pulses in the IR range impinge a layer of a planar hyperbolic metamaterial with gain-active inclusions providing resonant nonlinear dissipation, the formed wave beam demonstrates pronounced synergistic behaviour with both “absorption” and “survival” phenomena. In a multilayer DMPM operating in the THz range, the transmission of a wave beam happens with the nonlinear medium transparency, whereas the medium nonlinearity is manifested via the nonlinear conductivity/nonlinear losses. In this case, quantum effects in thin metal layers were taken into account. They led, in particular, to nonlocality of the medium response. These and other theoretically revealed effects are experimentally realizable, provided with estimates for the parameters of structures and materials, and can be useful in creating effectively controllable nonlinear modulators, limiters, concentrators, sensors, devices with harmonic generation and frequency mixing, and other devices.