This PDF file contains the front matter associated with SPIE Proceedings Volume 11795, including the Title Page, Copyright information, and Table of Contents

State-of-the-art microscopes use intense lasers that can severely disturb biological processes, function and viability. This introduces hard limits on performance that only quantum photon correlations can overcome. In this talk I will report recent work from my laboratory which demonstrates this absolute quantum advantage [1]. We show, specifically, that quantum correlations enable signal-to-noise beyond the photodamage-free capacity of conventional microscopy. Broadly, this represents the first demonstration that quantum correlations can allow sensing beyond the limits introduced by optical intrusion upon the measurement process. We achieve this in a coherent Raman microscope, which we use to image molecular bonds within a cell with both quantum-enhanced contrast and sub-wavelength resolution. This allows the observation of nanoscale biological structures that would otherwise not be resolved. Coherent Raman microscopes allow highly selective biomolecular finger-printing in unlabelled specimens, but photodamage is a major roadblock for many applications. By showing that this roadblock can be overcome, our work provides a path towards order-of-magnitude improvements in both sensitivity and imaging speed.

Supervised neural networks are rising as an algorithm of choice for surrogate models in photonics, because they are versatile, fast to evaluate, easily differentiable, and perform well in high-dimensional problems. However, the drawback of this black box approach is that it requires a lot of data. Unfortunately in the context of photonics, data is generated through expensive full solves of Maxwell’s equations. This talk will present ways to open the black box for better data efficiency and performance of deep surrogate models. The first part of this talk will present how active learning can reduce the need for data by at least an order of magnitude by adapting the data generation to the model learning. The second part will present how information about the physics can be incorporated into the neural network for more efficiency.

Deep neural networks are empirically derived systems that have transformed research methods and are driving scientific discovery. Artificial electromagnetic materials, such as electromagnetic metamaterials, photonic crystals, and plasmonics, are research fields where deep neural network results evince the data driven approach; especially in cases where conventional computational and optimization methods have failed. We propose and demonstrate a deep learning method capable of finding accurate solutions to ill-posed inverse problems, where the conditions of existence and uniqueness are violated. A specific example of finding the metasurface geometry which yields a radiant exitance matching the external quantum efficiency of gallium antimonide is demonstrated.

A new deep-learning approach based on dimensionality reduction techniques for the design and knowledge discovery in nanophotonic structures will be presented. It is shown that reducing the dimensionality of the response and design spaces in a class of nanophotonic structures can provide new insight into the physics of light-matter interaction in such nanostructures while facilitating their inverse design. These unique features are achieved while considerably reducing the computation complexity through dimensionality reduction. It is also shown that this approach can enable an evolutionary design method in which the initial design can be evolved intelligently into an alternative with favorable specification like less complexity, more robustness, less power consumption, etc. In addition to providing the details about the fundamental aspects of the latent learning approach, its application to design of reconfigurable metasurfaces will be demonstrated.

Discovering novel, unconventional optical designs in combination with advanced machine-learning assisted data analysis techniques can uniquely enable new phenomena and breakthrough advances in many areas including imaging, sensing, energy, and quantum information technology. It demonstrated that compared to other inverse-design approaches that require extreme computation power to undertake a comprehensive search within a large parameter space, machine learning assisted topology optimization can expand the design space while improving the computational efficiency. This talk will highlight our most recent findings on 1) merging topology optimization with artificial-intelligence-assisted algorithms and 2) integrating machine-learning based analysis with photonic design and quantum optical measurements.

Nonlinearity provides a key functionality for a plurality of devices, effects, and systems. In this talk I show that both all-optical and electro-optical nonlinearity can be strongly enhanced at the slow-light effect epsilon-near-zero (ENZ). I share our recent experimental demonstrations including (a) temporally tailoring ENZ nonlinearity (Optics Letters 2020), (b) spectrally 400nm broadband ENZ enhancement, (b) GHz-fast yet micrometer-compact electro-optic modulator within a MZI-Silicon-ITO hybrid platform (OPTICA 2020, Scientific Reports 2021), and (c) Kramers-Kronig-enhanced electro-absorption modulator (NANOPHOTONICS 2019). Together, these technologies show that monolithic integration of TCO into PICs provides functionality beyond Silicon photonics with application in datacom, sensing, and neuromorphic computing.

This Conference Presentation, “Tunable ultranarrow band thermal emitter rapid designed by Monte Carlo tree search,” was recorded for the Optics + Photonics 2021 held in San Diego, California, United States.

Deep learning has recently become an important part of nanophotonic device design, with many researchers leveraging the power of neural networks to aid in inverse-design analysis. Acting as surrogate models for full-wave solvers, neural networks are now employed to develop new metasurface elements and gain insight into the underlying physics which dictate their behavior. A new avenue of discovery, which has been facilitated by the recent developments in deep learning, lies in the domain of metasurface robustness, a subject that presents many challenges to traditional solvers. Characterizing even relatively simple designs with a full-wave solver may be computationally expensive enough to make optimization challenging or even intractable. On the other hand, robustness must be measured by introducing some form of tolerance analysis into an optimization. Structures must be perturbed many times over, perhaps even in an exhaustive fashion. When the process is further complicated by considering complex design parameterizations (with many degrees of freedom), these full-wave optimizations are no longer tractable. However, deep neural networks can help to counter these challenges owing to their GPU speedup and powerful learning characteristics. By evaluating many full-wave metasurface designs ahead-oftime and investing them into neural network training, the network can then be used in tolerance analysis for substantial speedups down the road. This work showcases how we designed a suitable neural network for this purpose, as well as several studies conducted using this deep learning platform in this important area of metasurface robustness.

We present a few novel deep learning techniques for applications in photonics. Of particular interest are few-shot techniques which minimize the amount of needed training data.

Over the past decades, we have witnessed tremendous progress and success of photonic metamaterials. By tailoring the geometry of the building blocks of metamaterials and engineering their spatial distribution, we can control the amplitude, polarization state, phase and trajectory of light in an almost arbitrary manner. However, the conventional physics- or rule-based approaches are insufficient for designing multi-functional and multi-dimensional metamaterials, since the degrees of freedom in the design space become extremely large. Deep learning, a subset of machine learning that learns multilevel abstraction of data using hierarchically structured layers, could potentially accelerate the development of complex metamaterials and other photonic structures with high efficiency, accuracy and fidelity. In this talk, I will present our recent works that employ advanced deep learning techniques to design and evaluate distinct photonic metamaterials.

Optical metadevices are commonly simulated using ideal structures. These perfect geometries are useful for finding significant features of their optical response. In practice, fabrication of such metadevices often results in non-ideal rough structures. Surface roughness is relatively difficult to implement for non-parametrically generated metadevice geometries. We present a method of simulating the effects of surface roughness on the optical response of metastructures using open source Python packages to generate rough importable meshes. The optical response is then simulated using a FEM solver. By simulating many structures with identical roughness statistics, we demonstrate inhomogeneous broadening in the average response.

A central challenge in the development of nanophotonic structures and metamaterials is identifying the optimal design for a target functionality and understanding the physical mechanisms that enable the optimized device’s capabilities. In this talk, we will describe deep learning-driven strategies to both design complex nanophotonic structures, including across multiple device categories, as well as understand their behavior. We will highlight potential pathways to making deep learning a tool for global inverse design across multiple device categories, while also opening up the 'black box' of the machine learning algorithm to understand why a particular optimized design works well.

I will discuss the role of network architecture in the GLOnet inverse optimization platform, in which the global optimization process is reframed as the training of a generative neural network. I will show how a properly selected network architecture can smoothen the design space and how the architecture can be tailored based on the type and dimensionality of the design problem. I will also discuss new methods in which neural networks can serve as high speed surrogate Maxwell solvers capable of aiding the inverse design process. These hybrid physics- and data-driven concepts can apply to a broad range of nanophotonics systems.

Classical and quantum photonics with superior properties can be implemented in a variety of old (silicon, silicon nitride) and new (silicon carbide, diamond) photonic materials by combining state of the art optimization and machine learning techniques (photonics inverse design) with new fabrication approaches. In addition to making photonics more robust to errors in fabrication and temperature, more compact, and more efficient, this approach is also crucial for enabling new photonics applications, such as on chip laser driven particle accelerators, and semiconductor quantum simulators.

The realization of integrated quantum photonic circuits is crucial for scalable quantum computing and information processing applications. One of the milestones is the realization of highly-efficient coupling of pre-determined single-photon sources into the on-chip environment. Along with solid-state quantum sources, like quantum dots and defects in solids, quantum defects in 2D materials have attracted significant interest due to their quantum emission properties and stability. We have developed an adjoint-topology optimization framework to improve the coupling efficiency of color centers in hBN to the silicon nitride platform. We have demonstrated more than 75% coupling efficiency with a topology optimized coupler.

We reports on recent advances in applications of deep learning and topologically structured light to far-field non-destructive imaging with deep subwalength resolution and picometric metrology

Vibrational polaritons are hybrid light-matter states arising from the collective strong-coupling of ensembles of localized molecular vibrations and IR modes in a microcavities. Ground-state chemical reactions have been experimentally shown to be modified by vibrational polaritons. Currently available theories seem to be unable to explain these observations. We will describe our most recent progress in the understanding of this puzzle. In particular, we will highlight how cavity versions of transition-state and Marcus theories for chemical kinetics are limited in explaining the experiments. We argue that the underlying problem is the large number of molecules N that partake in the collective strong coupling, yielding an enormous ratio of dark states per polariton mode. We conclude with a potential solution to this problem, which relies on recognizing the conditions under which the many dark states can yield nontrivial chemical dynamics.

While spatially coherent emission has been experimentally observed for several photoluminescent devices composed of metallic nanostructures, no model is currently able to compute the spatial coherence function of the emitted fields, and thus to explain its origin. We introduce a model of light emission by thermalized ensembles of emitters which connects the coherence of the fields at two positions to the power absorbed by the system when illuminated by two sources. We can apply it to the study of the spatial coherence properties of the light emitted by a layer of molecular dyes deposited on top of a silver layer.

Nonlinear optical (NLO) materials have attracted considerable attention due to their potential applications for wavelength converters and electro-optical modulators. One way to fabricate SHG materials is to align asymmetric organic dyes with high second-order hyperpolarizability constants. Here, we demonstrate one-dimensional alignment of asymmetric organic dyes in pores of metal-organic framework (MOF). MOF with Kagome-type lattice was synthesized to encapsulate the organic dyes in its one-dimensional pores. The organic dyes were oriented along with the onedimensional pores, which was confirmed by fluorescence under linearly-polarized excitation light.

Materials with adaptable properties could impact optoelectronics (tunable sensors or filters) and chemical reactivity (triggered reactivity). It is widely known that strong material absorptions resonant with an optical cavity can lead to the formation of new hybrid light-matter states called polaritons. Strikingly, cavity-modified material properties (e.g., electrical conductivity, optical emission/absorption, chemical reaction rates and branching ratios) have been demonstrated and, the degree to which they are modified, shown to depend on the energy positions of these new hybrid states. Our work shows real-time tuning of these states through electrochemical cycling and optical excitation of the coupled species.

In the last decade a host of seminal experimental results have demonstrated that properties and dynamics of molecules and solids can be modified and controlled by coupling strongly to the electromagentic field of a photonic environment, e.g. an optical cavity. For a detailed understanding of such changes it becomes necessary to use first-principles approaches to strong light-matter interactions. In this talk I will discuss the fundamental setting for such ab-initio methods, the Pauli-Fierz quantum field theory in Coulomb gauge, introduce quantum-electrodynamical density-functional theory as an efficient and accurate simulation technique and highlight novel effects that become accessible. Among others I demonstrate how conduction and absorption properties are modified, how collective strong coupling can induce strong local modifications and how bound states in the continuum appear.

Thin films of semiconducting single-walled carbon nanotubes (SWCNTs) are ideal for strong light-matter coupling. We demonstrate optically and electrically pumped near-infrared exciton-polaritons at room temperature and the possibility to tune between weak, strong and ultrastrong coupling in field-effect transistors [Nat. Mater. 2017, 16, 911] and electrochromic devices [ACS Photonics 2018, 5, 2074]. While these polaritons are observed in simple metal-clad microcavities, coherent coupling of carbon nanotube excitons with hybrid plasmon-photonic modes results in plasmon-exciton polaritons (‘plexcitons’) [Nano Lett. 2018, 18, 4927]. Furthermore, covalent functionalization of SWCNTs creates luminescent defects with red-shifted emission. Without changing the polariton branch structure, radiative pumping through these emissive defects leads to an up to 10-fold increase of the polariton population in microcavities with detunings for large photon fractions [ACS Photonics 2021, 8, 182].

We present a microscopic model describing the transition to strong coupling regime for an emitter resonantly coupled to a surface plasmon in a metal-dielectric structure. We demonstrate that the shape of scattering spectra is determined by an interplay of two distinct mechanisms. First is the near-field coupling between the emitter and the plasmon mode which underpins energy exchange between the system components and gives rise to exciton-induced transparency minimum in scattering spectra prior the transition to strong coupling regime. The second mechanism is Fano interference between the plasmon dipole and the plasmon-induced emitter’s dipole as the system interacts with the radiation field. We show that the Fano interference can strongly affect the overall shape of scattering spectra, leading to the inversion of spectral asymmetry that was recently reported in the experiment.

In this talk, I will discuss strong light-matter interactions achieved by using transition metal dichalcogenides (TMDs) 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 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.

Molecular ensembles in confined infrared (IR) fields have emerged as a promising platform for condensed-phase cavity QED at room temperature, for the development of scalable architectures for IR quantum optics also at the nanoscale. We develop a Markovian open quantum system approach to study the dynamics of molecular vibrations in infrared nanocavities under femtosecond pulse driving, as implemented in recent nanoprobe spectroscopy experiments with polymer-coated IR gold antennas. We describe the time-domain signatures of the crossover from weak to strong coupling regimes in these nanocavities, provide mechanistic insights on the conditions for implementing coherent phase-space rotations of the nanocavity field using a tip nanoprobe, and discuss the tunable role of molecular anharmonicity as a function of pump power. Our work offers microscopic design strategies for quantum state preparation and control with emitter-nanocavity hybrids using infrared quantum optics.

Structured light carrying spin and orbital angular momentum brings about new light-matter interactions in optical nanostructures. We demonstrate the possibility of using structured light beams carrying orbital angular momentum (OAM) to access resonant modes of all-dielectric meta-atoms that cannot be excited by the conventional Gaussian beam or by a plane wave. We use multipole decomposition approach to match extinction resonances with high-order multipole excitation. These results can find applications in sensing, spectroscopy, and enable new regimes of nonlinear optical interactions.

We present phonic funnels, a novel material platform, that enables a smooth optical link between the diffraction-limited and deep subwavelength areas. Photonic funnels comprise conical structures with hyperbolic cores that enable highly confined propagation of light and perfectly conducting walls that isolate the core of the funnel from the surroundings. We demonstrate realization of the funnels with semiconductor metamaterial platform, with minimum diameter of the opening of the order of 1/30-th of free space wavelength and characterize propagation of light through the funnels experimentally and theoretically. We also analyze funnel-induced modulation of emission.

In this talk, I discuss our recent research activity in nano-optics, polaritonics and electromagnetics, showing how suitably tailored metamaterials open exciting venues to realize new light phenomena and devices. I discuss in particular the role of broken symmetries in tailoring nano-optical phenomena, including tunable diffraction-free wave propagation and topological phenomena based on tailored lattice symmetries, time-reversal symmetry breaking in optical metamaterials, and parity-time symmetric phenomena.

Photonic funnels, conical structures with hyperbolic cores, that have been recently demonstrated at mid-IR frequencies, provide a platform to avoid the diffraction limit and enable a smooth optical link between the nanoscale and microscale. Orbital angular momentum (OAM) of beams play important role in optical manipulation, microscopy, and potentially optical communications.. In this work we analyze theoretically the interaction structured light (light that has non-zero OAM) with photonic funnels. In particular, we study the effect of light confinement, facilitated through the geometric profile of the funnel, on spatial structure of the mode, and its local intensity.

This Conference Presentation, “Transition metal dichalcogenide nanophotonic metaplatforms,” was recorded at SPIE Optics + Photonics 2021 held in San Diego, California, United States.

Chalcogenide based materials are excellent candidates for implementing static and dynamic meta-optics as they possess very high permittivities and support large modulation of optical constants through various mechanisms such as, phase-change, photon-darkening, laser writing and anomalous thermo-optic effects. We present a study of various chalcogenide compositions used for static and active metasurfaces. We start with large area CVD grown amorphous Selenium nanoparticles on various substrates and show that their Mie-resonant response spans the entire mid-infrared range. By coupling Se Mie-resonators to ENZ substrates we demonstrate an order of magnitude increase in quality factor. Next, we investigate topological insulators Bi2Te3 metasurfaces and demonstrate that these high permittivity metasurfaces can yield very large absorption resonances that are tunable in the infrared range. Finally, we demonstrate ultra-wide dynamic tuning of PbTe metasurface resonators.

Efficient light manipulation at subwavelength scales in the mid-infrared (MIR) region is essential for various applications and can be harnessed from intrinsic low-loss dielectric resonators. Here, we demonstrate the fabrication of truncated spherical selenium (Se) resonators with tunable high-quality (Q) factor Mie resonances. Large area amorphous Se subwavelength resonators of varying sizes were grown on different substrates, using a novel CVD process. We demonstrate size-tunable Mie resonances spanning the 2-16 µm range, for single isolated resonators and large area ensembles, respectively. We show strong tunable absorption resonances (90%) in ensembles of resonators in a significantly broad MIR range. Moreover, by coupling resonators to epsilon-near-zero (ENZ) substrates, we engineer high-Q resonances as high as Q=40. These findings open up new possibilities in meta-atom paints, anti-reflective coatings, detection technology, and large area metasurface fabrications.

Great efforts have been made to explore the Fano resonances in two-dimensional transition metal dichalcogenides (TMDs) coupled with plasmonic nanostructures in the visible region. However, the intrinsic losses of metallic materials and the TMD exciton linewidths of at least tens of meV at room temperature (RT) inevitably limit the achievable Q factor of the Fano resonance. Herein, we integrate a monolayer WS2 with single hydrogenated amorphous silicon nanospheres (SiNSs) in water. Pronounced asymmetric Fano resonances with a Q factor up to 104 at the A exciton frequency (2.0 eV) are observed at RT. Fano fitting and modified coupled-mode theory both suggest a decreased A exciton linewidth of ~10 meV as compared to the reported value (~60 meV). This is attributed to the enhanced decay of trion in WS2. Moreover, directional Fano coupling can be achieved by exciting the hybrid from the SiNS or WS2 side, providing more possibilities in device implementation.

Direct experimental elucidation of steady-state energy distributions of hot-carriers in plasmonic nanostructures is key for systematically advancing and evaluating competing theoretical frameworks as well as for rationally engineering hot-carrier technologies. In this study, we present a novel scanning probe-based approach and show that quantum transport measurements from single molecule junctions, created by trapping suitably chosen single molecules between an ultra-thin gold film supporting surface plasmon polaritons and a scanning tunneling microscope probe tip, can enable quantification of plasmonic hot-carrier energy distributions. Several key physical insights on the nature of hot-carrier distributions, obtained from these measurements, will be discussed.

Recent years have seen growing interest to the applications of hot carriers generated in plasmonic structures for photodetection and photocatalysis. Many questions, however, still remain waiting for answer, starting from exactly what is the physical mechanism enabling these applications and culminating in what is the ultimate efficiency of hot carrier plasmonic processes. In my talk I will attempt to answer at least some of these questions.

Energy can be added to electromagnetic waves in several different fashions. We identify a mechanism, distinct from conventional ones, in which compression of lines of force is the active ingredient. There are instances of this in other contexts: a superconductor repels magnets because the magnetic lines of forces are compressed as they are rejected by the superconductor. We show that in some circumstances the number of lines of force, electric and magnetic, in a time dependent system is conserved and amplification occurs when these lines of force are squeezed closer together.

We report the first known example of a subwavelength plasmonic upconverting nanolaser with a low threshold. This perovskite-based plasmonic upconverting nanolaser features a record-small mode volume and an ultralow lasing threshold. Besides, we observed temporal coherence of the emission, which is an important feature of lasing. To co-optimize the pump photon absorption and the upconverted photon emission rate, the lasing result was made possible based on plasmonic titanium nitride. Moreover, we also demonstrated a new concept of lasing from a quantum emitter utilizing an intense localized electromagnetic field. A continuous-wave lasing was observed from single perovskite (CsPbBr3) quantum dot in a gap-plasmon nanocavity with an ultralow threshold of 1.9 Wcm-2 at 120 K. In the end, we will discuss the outlook for perovskite plasmonic nanolasers as on-chip light sources for bio-imaging, optical communication applications.

Metasurfaces are a promising platform to exceed their traditional counterparts not only in compactness but also for functionality. However, current designs are limited when trying to implement multiple, non-paraxial functions with a single metasurface as they are bound to either a small angular range or to low efficiencies. Here, we present a new non-local metasurface design that enables the implementation of multiple, independent functions with a large difference in deflection angle. We further demonstrate the capabilities of this approach for advanced control of light emission systems by creating a wavelength-tunable external cavity laser with holographic output based on such metasurface.

In this summary, we report an experimental demonstration of a low-loss multilayer-based ENZ metafilm. The demonstrated ENZ metafilm consists of alternating layers of Ag and SiN. 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.

We present a theoretical study of the collective quasiparticle excitations responsible for the electromagnetic response of ultrathin plane-parallel homogeneous periodic single-wall carbon nanotube arrays and weakly inhomogeneous single-wall carbon nanotube films. We show that in addition to varying film composition, the collective response can be controlled by varying the film thickness. For single-type nanotube arrays, the real part of the dielectric response shows a broad negative refraction band near a quantum interband transition of the constituent nanotube, whereby the system behaves as a hyperbolic metamaterial at higher frequencies than those classical plasma oscillations have to offer. By decreasing nanotube diameters it is possible to push this negative refraction into the visible region, and using weakly inhomogeneous multi-type nanotube films broadens its bandwidth.

In this study, we obtained epsilon-near-zero metamaterial at visible range by designing and fabricating a metal-dielectric multilayer anisotropic hyperbolic metamaterial. To do this, we experimentally characterize and extract the permittivity. We have used the epsilon-near-zero (ENZ) feature of hyperbolic metamaterial as a substrate to manipulate the resonance of plasmonic nanoantennas. We demonstrate that the vanishing index of the substrate slows down the resonance shift of the antenna, known as pinning effect. Moreover, we have controlled the pinning effect. Later, we show by optically pumping with fs pulses at a proper wavelength the ENZ point of the structure alters, in comparison to the linear case. The change in the effective permittivity happens in the order of unity, leading to ultrafast light-induced refractive index change. The localized surface plasmon resonance of metal nanoantenna is significantly influenced by the size, shape, and environment but also its substrate.

Ballistic metamaterials that are metal-dielectric composites with the unit cell size smaller than electron mean free path, represent a new class of composite media with many unique properties, such as hyperbolic response above the plasma frequency. In these materials the electromagnetic response of the composite is controlled by the surface scattering of the free electrons at the metal-dielectric interface.

Time-varying metasurfaces have recently emerged as a new topic of interest for control of light at the nanoscale and exploration of fundamental physics. We demonstrate time diffraction from a time slit in an unstructured metasurface. In a pump-probe experiment, excitation of the Berreman mode of a thin film of Indium-Tin-Oxide over gold leads to strong, efficient all-optical modulation of the film, and to time diffraction of the probe. In comparison to previous works in unstructured epsilon-near-zero films, we obtain a 6 nm frequency shift and a 23 nm broadening using lower intensities and a significantly lower thickness of 40 nm, which demonstrates the minimal footprint of the structure. The deeply subwavelength nature of the sample makes a time-varying interpretation simple and efficient, paving the way for time-dependent architectures for ultrafast optical experiments.

Incorporating planar optics such as metalenses or metacorrectors into optical designs can drastically improve the performance of imaging systems with additional benefits such as cost, size and weight improvements. However, modeling of such hybrid lenses is challenging because of the multi-scale nature of the simulation. We demonstrate that one can combine ray optic simulations with full wave electromagnetic simulations and Fourier optics approaches to model a whole compound/hybrid lens considering all metasurface unit cell interactions and to study the effect of possible fabrication errors.

I will discuss how the ideas from topological photonics can be used for complete reimagining of the architectures of photonic devices such as add/drop filters, logical gates, and topology-controlled cavities. Both first- and second-order photonic topological insulators will be utilized for creating novel photonic cavities. Time permitting, I will discuss the new physics brought into topological photonics by including non-Hermitian (gain/loss) effects.

We review recent advances in the physics and technology of plasmonic and dielectric nanomechanical metamaterials, wherein optical and mechanical resonances can be coupled to provide a plethora of dynamic photonic functionalities. External electric, magnetic, thermal, acoustic and optical stimuli drive pico/nanometric displacements of the metamaterial building blocks, modulating optical properties at MHz frequencies.

We provide proof of concept demonstrations of halide perovskite light emitting metadevices, like a phase-change tunable vortex laser with optical bistability and a chiral light emitting metasurface with high degree of circular polarization.

Meta-surfaces are composed of an array of artificial nanostructures. The electromagnetic wave can be manipulated with its phase, polarization, and amplitude at will. Nowadays, the demand for photonics is extended from classical to quantum optics. With the advent of the post-Moore era, the fabrication technology of the semiconductor industry has faced the problem of the physical limitation approach. They have urgently needed to find out new methods and new physics to break through this dilemma. Quantum optics technology is the most suitable solution for this situation. Here, the design, fabrication, and application of the novel optical meta-devices are reported from classical to quantum optics in this talk. The meta-lens array with achromatism is used to demonstrate a light field system for imaging and sensing. The integrated meta-lens array is used to demonstrate a high dimensional quantum light source chip with excellent performance of quantum fidelity.

Metamaterials offer an ideal platform to test quantum interactions with free electrons, and in addition, they can be designed to mould the quantum wave function of electron beams. In this talk, we discuss recent advances in our understanding of quantum effects associated with the interaction between free electrons and optical modes in nanomaterials. We then focus on optical modes in metamaterial and their interaction with free electrons, based on which we present optimum structures for free-electron shaping with the purpose of performing electron microscopy with improved spectral/spatial/temporal resolution in the sub-meV/sub-nm/sub-fs range.

We review the physics of photonic bound states in the continuum (BICs) and their applications to metadevices, including enhancement of nonlinear response, light-matter interaction, and development of active nanophotonic devices. In particular, we discuss how BIC-empowered dielectric metastructures can be used to generate efficiently high-order optical harmonics from bulk and to boost the intrinsic nonlinearity of transition metal dichalcogenide (TMD) flakes. We explore TMD resonators composed of structured dielectric arrays and individual nanoparticles for strong light-matter coupling phenomena. We discuss the extension of metasurface functionalities for biosensing applications in biomarker detection and quantum information processing with entangled photons. Finally, we demonstrate how tunability of BICs in the momentum space can be used to realize a novel type of efficient lasing based on a finite-size cavity with a small footprint.

Toroidal light pulses are few-cycle pulses with doughnut-like electromagnetic field configuration and non-separable, “entangled”-like spatiotemporal structure. Toroidal light pulses exhibit self-similar and skyrmionic topological features and exotic propagation dynamics including isodiffracting and non-diffracting effects. Following the recent observation of such pulses, this talk will report on metamaterial-based schemes for their generation and detection and introduce tomography approaches for characterizing their “entangled” spatiotemporal profile. Implications for light-matter interactions, in particular in the context of toroidal electrodynamics, non-radiating configurations, and Lorentz non-reciprocity, will also be discussed.

I will give an overview of our recent experiments of the coupling of an atomic emitter with surface plasmons of a metamaterial.

Flat lenses based on metasurfaces promise to shrink imaging systems. While volume of a flat lens is negligible, the light field must propagate through a sizeable volume of image space behind the lens to finally form an image. This constrains the opportunity to shrink imaging systems. We introduce a general metric the Volumetric Imaging Efficiency (VIE) and show it’s an effective tool to compare disparate lenses and technologies. We use the VIE to illustrate the trade space where flat lenses excel – short focal length, wide angle lenses. We quantify their performance against conventional bulk lenses and discuss challenges for scaling to longer focal lengths.

Stacking of Mie-resonant all-dielectric metasurfaces and other functional layers such as mirrors, spacers or two-dimensional materials offers interesting new opportunities for tailoring the response of the metasurface system. This talk will discuss several examples of such stacked systems, which we have experimentally realized. In particular, chiral bilayer dielectric metasurfaces achieving a record-high chiro-optical response and a resonant dielectric metasurface, which is separated from a metallic mirror by a dielectric spacer layer with a gradually varying thickness will be discussed. Altogether, our results show that the considered stacked photonic systems allow for obtaining important new optical response features and functionalities with respect to single-layer dielectric metasurfaces.

We demonstrate the strong coupling between excitons in organic molecules and all-dielectric metasurfaces supporting Mie surface lattice resonances (MSLRs). MSLRs have extended mode volumes and large quality factors, which enables to achieve collective strong coupling with large coupling strengths and Rabi energies. Moreover, due to the electric and magnetic character of the MSLR given by the Mie resonance, we show that the hybridization of the exciton with the MSLR results in exciton-polaritons that inherit this character as well. Our results demonstrate the potential of all-dielectric metasurfaces as novel platform to investigate and manipulate exciton-polaritons in low-loss polaritonic devices.

We present an alternative approach to dielectric meta-surfaces and demonstrate its scalability, mechanical durability and laser damage resilience. 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 nano-particles mask. We will present new approaches developed to “boost” the attainable optical response based on new underlying physics of the laser printed Au nanoparticle mask.

Crossbar architectures are a highly popular platform in the electronics industry for enabling high-component density at the nanoscale, in today’s constantly shrinking electronic devices. These structures are akin to metal-insulator-metal (MIM) architectures widely used in nanophotonics and are key to the realization of a range of reconfigurable and addressable metasurfaces. Therefore, the application of nanophotonic design principles to such electronic platforms provides an unexplored path towards the integration of nanophotonic technologies into telecommunication and computing platforms. We show here that these crossbar-architectures can be engineered to act as addressable metasurfaces exhibiting, multispectral optical resonances forming the basis for next-generation optical computing systems, while still preserving their electronic functionality.

Compact Optical components sensitive to incident wave-vector direction are essential in image-processing, wavefront-manipulation, and metrology such as LIDAR. Here we demonstrate a new class of metasurfaces which exhibit optical spectral features strongly correlated with incident illumination angle. The spectra of such metasurfaces feature sharp transmission dips centred around 800 nm when illuminated at oblique incidence, where the strength of the dip increases as incident angle increases remaining tightly confined within a 100 nm band. The metasurfaces are capable of accepting large incident angles (>30°) without the appearance of higher-order diffraction modes, while displaying dramatic transmission decreases (~80% reduction).

This Conference Presentation, “Angle-dependent resonance modes in terahertz photonic crystals and metasurfaces,” was recorded at SPIE Optics + Photonics 2021 held in San Diego, California, United States.

Thermal radiation is nominally broadband, incoherent, and isotropic, so controlling the spectral, temporal, and directional characteristics of thermal emission is an important frontier in imaging and chemical fingerprinting. The use of thermal metasurfaces, whose emission properties can be finely tailored, has recently become of great interest. Here we theoretically demonstrate the thermal emission of a metasurface arising from the coupled emission from a plasmonic mode in graphene nanoribbons and the guided mode resonance of a 1D photonic crystal. We also discuss the utility of a computationally cheap approach based on coupled-mode theory to model the device scattering characteristics.

We propose and theoretically demonstrate the existence of Spoof surface waves in the terahertz spectral range (0.1-1 THz). Those surface waves supported by a corrugated surface with subwavelength patterning, in opposition of the Spoof Plasmons, are made of non-conductive lossless materials with positive permittivity. Particularly, we focus on the theoretical study and engineering of an infinite corrugated surface with 1D array of grooves made of lossless high permittivity material able to support Spoof Surface waves in the terahertz spectral range. An analytic derivation of the dispersion relation is presented in the case of deeply subwavelength period of a corrugated structure using impedance boundary conditions at the interfaces and are verified numerically. In addition, various optical properties such as the modal size and the propagation distances of those surface waves are studied, where we theoretically show that the studied ideal metamaterial can be engineered to support well defined surface waves with subwavelength modal size in the spectral range 0.1-1 THz, thus could lead to new revolution in multiple domains such as terahertz sensing. Finally, the possibility of an ideal amplitude-bases sensor made of the corrugated surface made of high positive permittivity material such as TiO2 ceramic utilizing Spoof surface waves to interrogate various analytes is discussed.

Optoelectronic devices, including terahertz (THz) photoconductive detectors and emitters, require efficient optical absorption and ultrafast photoconductivity switching. To overcome material limitations of standard photoconductors, here we demonstrate perfectly absorbing all-dielectric photoconductive metasurfaces made of interconnecting nanoscale GaAs channels. The metasurface supports two degenerate Mie modes - the electric and magnetic dipoles - which are critically coupled to the incident 800 nm excitation to achieve full absorption. The combination of perfect absorption, photoconductivity and wavelength tunability makes the metasurfaces ideal for terahertz photoconductive detectors that use pump beams in the near-infrared spectral range. In this application, the metasurface replaces the bulk, sub-optimal active region in the gap of a THz antenna with an ultra-thin (160 nm), highly absorbing photoconductive layer.

Optomechanical interactions allow coherent conversion of signals between optical and mechanical domains. Self-assembled metallic nanocavities containing single molecular layers act as mechanical springs/oscillators. Interaction of light and matter in these sub-nm mode volumes allows extreme optomechanical coupling and single mid-infrared (MIR) photon sensitivity. Here we achieve frequency upconversion of MIR incoming photons to visible photons via surface-enhanced Raman spectroscopy in doubly-resonant metasurfaces. Our results on efficient frequency upconversion of infrared radiation in visible regime via molecular optomechanics open new potential in plasmon-based low-cost infrared spectroscopic techniques.

Nanoscale photothermal effects induce substantial changes in the optical response experienced by probing light. We take advantage of the strong temperature modulation of the graphene conductivity to propose an all-optical technique of excitation and manipulation of plasmons in graphene and thin metallic films. We demonstrate the ability of graphene and thin metal films to undergo ultrafast photothermal optical modulation under pump-probe conditions, with depths as large as >70% over a wide spectral range.

In this talk we theoretically and experimentally investigate an interesting family of null solutions to Helmholtz equation in 3D free space - optical vortices, or zero lines of complex amplitude in a propagating light field, that are knotted or linked in a certain way. 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 and evolution in engineered colloidal suspensions with saturable Kerr-like nonlinearity. These studies are further generalized to characterization of knot evolution in turbid linear and nonlinear media, such as clouds, fog, biological media, and undersea environments. Knotted electromagnetic fields may find applications in three-dimensional optical manipulations or could be considered as candidates for new information carriers in classical and quantum communication systems.

We present a design and detailed fabrication of periodic and quasi-periodic plasmonic arrays including infrared scattering, patterning stripe, particle, and hole arrays with large periodicities for longwave IR scattering, and experimental reflectivity and backwards scattering from these metamaterials. We experimentally verify LWIR and other infrared diffraction from sparser arrays and arrays of holes in plasmonic metals. We simulate, using critical coupling analytical models and numerical algorithms, the reflectivity, scattering, etc. of these metamaterial arrays, and compare to the laser-based measurements. We also investigate a hole array in a plasmonic material (Ag).We find plasmonic resonances at both the air-Ag and Ag-substrate interfaces to be present, increasing transmission via the Extraordinary Optical Transmission effect, which may be tuned by an electromagnetic field to shift the resonance position, and in the future may enable novel tunable rectification.

Efforts to examine large optical nonlinear response in structured and novel electromagnetic materials are ongoing. This work is partly motivated by the promise of leveraging structural resonances or regions of exotic materials response, such as the epsilon near zero or ENZ regime, to amplify the underlying nonlinear response of component materials. We explore the photo-induced change in optical properties under photoexcitation using pump-probe spectroscopy. The response shows characteristics wavelength and polarization dependent features that support the emergence of hyperbolic dispersion.

We present the theory of parametrically resonant surface plasmon polaritons. We show that a temporal modulation of the dielectric properties of the medium adjacent to a metallic surface can lead to efficient energy injection into the surface plasmon polariton modes supported at the interface. When the permittivity modulation is induced by a pump field exceeding a certain threshold intensity, such field undergoes a reverse saturable absorption process. We introduce a time-domain formalism to account for pump saturation and depletion effects. Finally, we discuss the viability of these effects for optical limiting applications. the abstract two lines below author names and addresses.

Specular optical activity manifests itself as the rotation of light polarization when reflecting from chiral materials and diffusive scattering from chiral liquids. The effect is generally extremely weak, especially in the visible domain. Here we demonstrate strong specular optical activity at the wavelength of 660nm in achiral non-magnetic metasurfaces featuring nano-scale periodic slit patterns milled into a gold film. We reveal through experiment and simulations that the metasurfaces with reduced structural symmetry are able to induce directionally dependent polarization rotation with magnitude of ~1°, which mimics longitudinal MOKE in magnetized films.

In this work, we investigate the focusing efficiency and focal length dependence of a near infrared (NIR) metalens on the longitudinal and transverse modes of a Gaussian beam. We then propose a spatial multiplexing approach to design the metalens singlet optimized for mixed spectral and spatial modes. We have also made some metalens that can produce donut beam and Bessel beam.The finite difference time domain (FDTD) method is employed to simulate the designed metalens,and use photolithography to make metalens

Strongly coupled material excitations to optical modes has shown potential to modify the material’s chemistry. The optical modes are usually given by an external cavity, such as Fabry-Pérot cavities, which may limit the scope of applications. Here we highlight the possibility of self-coupling electronic or vibrational resonances to optical modes sustained by the materials themselves. We show electronic and vibrational cavity-free polaritons in concrete examples, such as a slab of excitonic material and a spherical water droplet in vacuum. The abundance of cavity-free polaritons in simple structures points at their practical importance for polaritonic chemistry, exciton transport, and modified material properties.

The paper reports the second harmonic generation (SHG) behaviors of dolmen-type Au nanorod (AuNR) trimer structure, in which two of the AuNR’s are arrayed in parallel and the third is arrayed perpendicular to them. Our experimental results demonstrated that the SHG signal from the trimer was 25 times higher than that from the referential isolated AuNR monomer and dimer. The geometry of the AuNR was centro-symmetric, and it was forbidden in the second-order nonlinear susceptibility under the electric dipole approximations. The coupled plasmon mode in noncentrosymmetrically arranged trimer provided the nanometric optical fields suitable for the 2nd-order nonlinear optics.

Design and performance analysis of a high efficiency, nanohole based, polarization-insensitive, all-dielectric, immersion metalens is presented, which is to be monolithically integrated into a backside illuminated HgCdTe based photodetector with CdZnTe (4%) as the substrate material for MWIR (3-5 μm) applications. Although HgCdTe based IR imaging dominate the high-performance end of the market, enhancing the signal-to-noise ratio (SNR) performance is still one of the challenges. This is typically dealt with either by improving the quantum efficiency (QE) with the employment of AR surfaces and photon trapping schemes or by decreasing the noise level with a reduction in detector volume. Decreasing either the thickness or the area of the detector, which comes with a performance degradation in QE in return, does the volume reduction. Nevertheless, the reduced QE can be recovered through light concentration with the employment of microlenses in the case of reduced area, which is typically realized with curved lenses presenting curve formation and packaging related issues. These issues can be overcome with the utilization of lithography-compatible metalenses carved into the substrate material. Thus, in this study, a nanohole based array of 40×40 is optimized to be monolithically integrated into CdZnTe (4%) substrate with a placement period of 1.0μm, a depth of around 4.9μm in order to construct a metalens structure with a numerical aperture of 0.63, and operation wavelength of 4.0μm. The nanohole width changes within a range of 0.35μm to 0.83μm in order to provide 2π phase coverage. Single layer of SiO₂ based antireflective surface is introduced to the design in order to enhance the focusing efficiency, which is determined to be around 91%.

Realizing full-dimensional arbitrary manipulation of optical waves, which is known to be important for the implementation of optical devices with ondemand functionalities, still remains a challenge. Recently, Metasurfaces have shown unprecedented capabilities for the manipulation of optical waves at the subwavelength scale. Here, we demonstrated the use of chiral mirrors for the implementation of spin-selective multidimensional manipulation of optical waves. we validated that the three dimensions (amplitude, phase and operation wavelength) of optical waves is directly related to the three main structure variables of the designed chiral mirror. By simply and orderly changing the three structural variables of the designed chiral mirror, the spin-selective full and near independent manipulation of amplitude and phase of optical waves with a large and continuous wavelength agility can be implemented

Aluminum-doped zinc oxide metamaterial emerged as a promising plasmonic material due to its low optical loss and high conductivity. The Hong-Ou-Mandel effect is a result of two photons interfering on a beam-splitter. The coincidence rate of the detectors will drop to zero when the identical input photons overlap perfectly in time which results in the Hong-Ou-Mandel dip. If the time delay is scanned, the position of the HOM dip can be measured with femtosecond precision. Therefore, this two-photon interference effect has the potential for applications in precision measurement of time delays. Here, we experimentally observed Hong-Ou-Mandel interference for multilayered AZO/ZnO metamaterial. The Hong-Ou-Mandel effect was observed using a biphoton source with a periodically-poled Potassium Titanyl Phosphate crystal and two single photon counting modules monitoring the output from a beam splitter at 810 nm wavelength. The coincidence probability for separable photons, as a function of time delay τ, was fitted using least square method. The multilayered AZO/ZnO sample (carrier concentration 10²⁰ -10²¹cm^-3) on quartz substrate was used for delay. Our measurements show that the extracted time delay τ=25 µm for multilayered AZO/ZnO was about two orders of magnitude larger than expected from the thickness of the sample.

Recently reconfigurable phase change chalcogenide based metamaterials/metasurfaces have shown great promise in the realization of high speed large contrast all-optical switching and beam-steering devices with built-in memory functionality at a fraction of a wavelength in size across the ultraviolet to infrared frequency range. To incorporate these devices into current telecommunication platforms, integration with photonic waveguide architectures is a must as they present the most mature, widely used commercial photonic device platform today. Here, we present a new class of waveguide-integrated reconfigurable all-dielectric metasurfaces utilizing high refractive index phase change chalcogenides and discuss the unique considerations, design, and physical principles that are essential for integrating such nanostructures into waveguides where illumination is provided through controlled evanescent coupling of guided modes into the metamaterial structure.

We spin coated thin films of PMMA polymer doped with HITC laser dye onto microscope cover slides under applied flexural stress and found the patterns of scattering (milkiness) to correlate with the spatial variation of the pressure pattern. We further deposited thin gold films on top of the HITC:PMMA films and measured highly unusual transmission spectra of Au collected from strongly deformed (stressed) local areas of the sample. These spectra, which strongly deferred from those of plain Au films deposited onto unstressed glass, could not be described by simple, e.g. Maxwell Garnett, effective media models, calling for a thorough theoretical study.

Systems with coupling between magnetic and plasmonic effects can bring new developments in fields of plasmonics and magnetics. In our work we fabricate and study permalloy surfaces with one-dimensional profile modulation and various modulation parameters. Using optical characterization, ferromagnetic resonance, Brillouin light scattering and numerical methods we show that such metasurfaces demonstrate in-plane magnetic anisotropy determined by the structural geometry, and support both spin-wave and surface plasmon polariton resonances determined by the modulation parameters and sample orientation. The combination of plasmonic and magnetic properties makes these structures potential candidates for applications in magnetically controlled plasmonics and optically controlled magnetics

In this work, an electromechanical metasurface is designed for wave controlling of multi-mode guided waves in plate, including shear horizontal wave, symmetrical mode and anti-symmetrical mode of Lamb waves. The metasurface is constructed by staggered arrangement of in-plane polarized and out-of-plane polarized piezoelectric patches, which are connected with shunting circuits. The transmitted phase of different guided wave modes can be changed individually in 0~2π range by adjusting the negative capacitances of the shunting circuits without changing the structure geometry. By coding transmitted phase along the metasurface, multi-function including tunable focusing and tunable anomalous refraction of guided waves can be achieved by wave front control. Furthermore, by modulating each mode wave simultaneously, the incident mixed guided wave can be separated after transmitting through the metasurface and specific wave mode can be further extracted.

Sub-wavelength periodic nanostructures have unique properties that can lead to various applications in the field of photonics including cloaking, perfect absorption, perfect reflection and negative refractive index. Dielectric structures, unlike their metal counterparts, have low losses thus providing an alternative in various applications. In this work, we study the light-matter interaction in high refractive index dielectric periodic metasurfaces made of Tellurium cubes in air. In our earlier investigations in this direction with smaller periodicities, we observed a novel non-radiative state (anapole) immediately following a highly transparent state at higher frequencies and a reflection band at lower frequencies. In the current paper, we investigate the effect of periodicity of the metasurface on the response spectrum and most importantly on the observed transparent state. By studying the spatial distribution of the electric and magnetic fields and detailed multipole analysis, we see that the response spectrum is significantly affected by the periodicity of the metasurface. As the periodicity is increased, the band-like structure diminishes and a suppression of the electric dipole resonance is observed while the magnetic dipole resonance remains unaffected except for a shift towards lower frequencies. The highly transparent state which is a hybrid mode of electric dipole and quadrupole, however, is found to be independent of the periodicity of the structure, which has not been reported earlier in detail as per our knowledge.

The unidirectional scattering of high index metasurfaces is explored at Kerker condition using numerical simulations. We obtained the generalized first Kerker condition for an array of Silicon disks on a dielectric substrate that shows complete forward scattering using the multipole expansion method. We observe a significant Purcell enhancement for the quantum emitter embedded in the disk with emission wavelength overlapping with Kerker condition with a directional emission pattern. We also observed that this enhancement largely depends on the emitter's location and can be further engineered with the refractive index of disks.